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Glucocorticoid

Glucocorticoids (or, less commonly, glucocorticosteroids) are a class of corticosteroids, which are a class of steroid hormones. Glucocorticoids are corticosteroids that bind to the glucocorticoid receptor[1] that is present in almost every vertebrate animal cell. The name "glucocorticoid" is a portmanteau (glucose + cortex + steroid) and is composed from its role in regulation of glucose metabolism, synthesis in the adrenal cortex, and its steroidal structure (see structure below).

Glucocorticoids are part of the feedback mechanism in the immune system, which reduces certain aspects of immune function, such as inflammation. They are therefore used in medicine to treat diseases caused by an overactive immune system, such as allergies, asthma, autoimmune diseases, and sepsis. Glucocorticoids have many diverse effects such as pleiotropy, including potentially harmful side effects.[2] They also interfere with some of the abnormal mechanisms in cancer cells, so they are used in high doses to treat cancer. This includes inhibitory effects on lymphocyte proliferation, as in the treatment of lymphomas and leukemias, and the mitigation of side effects of anticancer drugs.

Glucocorticoids affect cells by binding to the glucocorticoid receptor. The activated glucocorticoid receptor-glucocorticoid complex up-regulates the expression of anti-inflammatory proteins in the nucleus (a process known as transactivation) and represses the expression of proinflammatory proteins in the cytosol by preventing the translocation of other transcription factors from the cytosol into the nucleus (transrepression).[2]

Glucocorticoids are distinguished from mineralocorticoids and sex steroids by their specific receptors, target cells, and effects. In technical terms, "corticosteroid" refers to both glucocorticoids and mineralocorticoids (as both are mimics of hormones produced by the adrenal cortex), but is often used as a synonym for "glucocorticoid". Glucocorticoids are chiefly produced in the zona fasciculata of the adrenal cortex, whereas mineralocorticoids are synthesized in the zona glomerulosa.

Cortisol (or hydrocortisone) is the most important human glucocorticoid. It is essential for life, and it regulates or supports a variety of important cardiovascular, metabolic, immunologic, and homeostatic functions. Various synthetic glucocorticoids are available; these are widely utilized in general medical practice and numerous specialties, either as replacement therapy in glucocorticoid deficiency or to suppress the body's immune system.

Effects Edit

 
Steroidogenesis showing glucocorticoids in green ellipse at right with the primary example being cortisol[3] It is not a strictly bounded group, but a continuum of structures with increasing glucocorticoid effect.

Glucocorticoid effects may be broadly classified into two major categories: immunological and metabolic. In addition, glucocorticoids play important roles in fetal development and body fluid homeostasis.

Immune Edit

Glucocorticoids function via interaction with the glucocorticoid receptor (see details below):

  • Upregulate the expression of anti-inflammatory proteins.
  • Downregulate the expression of proinflammatory proteins.

Glucocorticoids are also shown to play a role in the development and homeostasis of T lymphocytes. This has been shown in transgenic mice with either increased or decreased sensitivity of T cell lineage to glucocorticoids.[4]

Metabolic Edit

The name "glucocorticoid" derives from early observations that these hormones were involved in glucose metabolism. In the fasted state, cortisol stimulates several processes that collectively serve to increase and maintain normal concentrations of glucose in the blood.

Metabolic effects:

  • Stimulation of gluconeogenesis, in particular, in the liver: This pathway results in the synthesis of glucose from non-hexose substrates, such as amino acids and glycerol from triglyceride breakdown, and is particularly important in carnivores and certain herbivores. Enhancing the expression of enzymes involved in gluconeogenesis is probably the best-known metabolic function of glucocorticoids.
  • Mobilization of amino acids from extrahepatic tissues: These serve as substrates for gluconeogenesis.
  • Inhibition of glucose uptake in muscle and adipose tissue: A mechanism to conserve glucose
  • Stimulation of fat breakdown in adipose tissue: The fatty acids released by lipolysis are used for production of energy in tissues like muscle, and the released glycerol provide another substrate for gluconeogenesis.
  • Increase in sodium retention and potassium excretion leads to hypernatremia and hypokalemia[5]
  • Increase in hemoglobin concentration, likely due to hindrance of the ingestion of red blood cell by macrophage or other phagocyte.[1]
  • Increased urinary uric acid[6]
  • Increased urinary calcium and hypocalcemia[7]
  • Alkalosis[8]
  • Leukocytosis[9]

Excessive glucocorticoid levels resulting from administration as a drug or hyperadrenocorticism have effects on many systems. Some examples include inhibition of bone formation, suppression of calcium absorption (both of which can lead to osteoporosis), delayed wound healing, muscle weakness, and increased risk of infection. These observations suggest a multitude of less-dramatic physiologic roles for glucocorticoids.[4]

Developmental Edit

Glucocorticoids have multiple effects on fetal development. An important example is their role in promoting maturation of the lung and production of the surfactant necessary for extrauterine lung function. Mice with homozygous disruptions in the corticotropin-releasing hormone gene (see below) die at birth due to pulmonary immaturity. In addition, glucocorticoids are necessary for normal brain development, by initiating terminal maturation, remodeling axons and dendrites, and affecting cell survival[8] and may also play a role in hippocampal development. Glucocorticoids stimulate the maturation of the Na+/K+/ATPase, nutrient transporters, and digestion enzymes, promoting the development of a functioning gastro-intestinal system. Glucocorticoids also support the development of the neonate's renal system by increasing glomerular filtration.

Arousal and cognition Edit

 
A graphical representation of the Yerkes-Dodson curve

Glucocorticoids act on the hippocampus, amygdala, and frontal lobes. Along with adrenaline, these enhance the formation of flashbulb memories of events associated with strong emotions, both positive and negative.[9] This has been confirmed in studies, whereby blockade of either glucocorticoids or noradrenaline activity impaired the recall of emotionally relevant information. Additional sources have shown subjects whose fear learning was accompanied by high cortisol levels had better consolidation of this memory (this effect was more important in men).[better source needed] The effect that glucocorticoids have on memory may be due to damage specifically to the CA1 area of the hippocampal formation.

In multiple animal studies, prolonged stress (causing prolonged increases in glucocorticoid levels) have shown destruction of the neurons in the hippocampus area of the brain, which has been connected to lower memory performance.[5][10][6]

Glucocorticoids have also been shown to have a significant impact on vigilance (attention deficit disorder) and cognition (memory). This appears to follow the Yerkes-Dodson curve, as studies have shown circulating levels of glucocorticoids vs. memory performance follow an upside-down U pattern, much like the Yerkes-Dodson curve. For example, long-term potentiation (LTP; the process of forming long-term memories) is optimal when glucocorticoid levels are mildly elevated, whereas significant decreases of LTP are observed after adrenalectomy (low-glucocorticoid state) or after exogenous glucocorticoid administration (high-glucocorticoid state). Elevated levels of glucocorticoids enhance memory for emotionally arousing events, but lead more often than not to poor memory for material unrelated to the source of stress/emotional arousal.[11] In contrast to the dose-dependent enhancing effects of glucocorticoids on memory consolidation, these stress hormones have been shown to inhibit the retrieval of already stored information.[7] Long-term exposure to glucocorticoid medications, such as asthma and anti-inflammatory medication, has been shown to create deficits in memory and attention both during and, to a lesser extent, after treatment,[12][13] a condition known as "steroid dementia".[14]

Body fluid homeostasis Edit

Glucocorticoids could act centrally, as well as peripherally, to assist in the normalization of extracellular fluid volume by regulating body's action to atrial natriuretic peptide (ANP). Centrally, glucocorticoids could inhibit dehydration induce water intake;[15] peripherally, glucocorticoids could induce a potent diuresis.[16]

Mechanism of action Edit

Transactivation Edit

Glucocorticoids bind to the cytosolic glucocorticoid receptor, a type of nuclear receptor that is activated by ligand binding. After a hormone binds to the corresponding receptor, the newly formed complex translocates itself into the cell nucleus, where it binds to glucocorticoid response elements in the promoter region of the target genes resulting in the regulation of gene expression. This process is commonly referred to as transcriptional activation, or transactivation.[17][18]

The proteins encoded by these up-regulated genes have a wide range of effects, including, for example:[18]

Transrepression Edit

The opposite mechanism is called transcriptional repression, or transrepression. The classical understanding of this mechanism is that activated glucocorticoid receptor binds to DNA in the same site where another transcription factor would bind, which prevents the transcription of genes that are transcribed via the activity of that factor.[17][18] While this does occur, the results are not consistent for all cell types and conditions; there is no generally accepted, general mechanism for transrepression.[18]

New mechanisms are being discovered where transcription is repressed, but the activated glucocorticoid receptor is not interacting with DNA, but rather with another transcription factor directly, thus interfering with it, or with other proteins that interfere with the function of other transcription factors. This latter mechanism appears to be the most likely way that activated glucocorticoid receptor interferes with NF-κB - namely by recruiting histone deacetylase, which deacetylate the DNA in the promoter region leading to closing of the chromatin structure where NF-κB needs to bind.[17][18]

Nongenomic effects Edit

Activated glucocorticoid receptor has effects that have been experimentally shown to be independent of any effects on transcription and can only be due to direct binding of activated glucocorticoid receptor with other proteins or with mRNA.[17][18]

For example, Src kinase which binds to inactive glucocorticoid receptor, is released when a glucocorticoid binds to glucocorticoid receptor, and phosphorylates a protein that in turn displaces an adaptor protein from a receptor important in inflammation, epidermal growth factor, reducing its activity, which in turn results in reduced creation of arachidonic acid - a key proinflammatory molecule. This is one mechanism by which glucocorticoids have an anti-inflammatory effect.[17]

Pharmacology Edit

 
Dexamethasone – a synthetic glucocorticoid binds more powerfully to the glucocorticoid receptor than cortisol does. Dexamethasone is based on the cortisol structure but differs at three positions (extra double bond in the A-ring between carbons 1 and 2 and addition of a 9-α-fluoro group and a 16-α-methyl substituent).

A variety of synthetic glucocorticoids, some far more potent than cortisol, have been created for therapeutic use. They differ in both pharmacokinetics (absorption factor, half-life, volume of distribution, clearance) and pharmacodynamics (for example the capacity of mineralocorticoid activity: retention of sodium (Na+) and water; renal physiology). Because they permeate the intestines easily, they are administered primarily per os (by mouth), but also by other methods, such as topically on skin. More than 90% of them bind different plasma proteins, though with a different binding specificity. Endogenous glucocorticoids and some synthetic corticoids have high affinity to the protein transcortin (also called corticosteroid-binding globulin), whereas all of them bind albumin. In the liver, they quickly metabolize by conjugation with a sulfate or glucuronic acid, and are secreted in the urine.

Glucocorticoid potency, duration of effect, and the overlapping mineralocorticoid potency vary. Cortisol is the standard of comparison for glucocorticoid potency. Hydrocortisone is the name used for pharmaceutical preparations of cortisol.

The data below refer to oral administration. Oral potency may be less than parenteral potency because significant amounts (up to 50% in some cases) may not reach the circulation. Fludrocortisone acetate and deoxycorticosterone acetate are, by definition, mineralocorticoids rather than glucocorticoids, but they do have minor glucocorticoid potency and are included in this table to provide perspective on mineralocorticoid potency.

Comparative oral corticosteroid potencies[19][20][21][22]
Name Glucocorticoid potency Mineralocorticoid potency Terminal half-life (hours)
Cortisol (hydrocortisone) 1 1 8
Cortisone 0.8 0.8 8
Prednisone 3.5–5 0.8 16–36
Prednisolone 4 0.8 16–36
Methylprednisolone 5–7.5 0.5 18–40
Dexamethasone 25–80 0 36–54
Betamethasone 25–30 0 36–54
Triamcinolone 5 0 12–36
Deflazacort 6.5 1.3
Fludrocortisone acetate 15 200 24
Deoxycorticosterone acetate 0 20
Aldosterone 0.3 200–1000
Beclometasone 8 sprays 4 times every day equivalent to orally 14 mg prednisone once a day

Therapeutic use Edit

Glucocorticoids may be used in low doses in adrenal insufficiency. In much higher doses, oral or inhaled glucocorticoids are used to suppress various allergic, inflammatory, and autoimmune disorders. Inhaled glucocorticoids are the second-line treatment for asthma. They are also administered as post-transplantory immunosuppressants to prevent the acute transplant rejection and the graft-versus-host disease. Nevertheless, they do not prevent an infection and also inhibit later reparative processes. Newly emerging evidence showed that glucocorticoids could be used in the treatment of heart failure to increase the renal responsiveness to diuretics and natriuretic peptides. Glucocorticoids are historically used for pain relief in inflammatory conditions.[23][24][25] However, corticosteroids show limited efficacy in pain relief and potential adverse events for their use in tendinopathies.[26]

Replacement Edit

Any glucocorticoid can be given in a dose that provides approximately the same glucocorticoid effects as normal cortisol production; this is referred to as physiologic, replacement, or maintenance dosing. This is approximately 6–12 mg/m2/day of hydrocortisone (m2 refers to body surface area (BSA), and is a measure of body size; an average man's BSA is 1.9 m2).

Therapeutic immunosuppression Edit

Glucocorticoids cause immunosuppression, and the therapeutic component of this effect is mainly the decreases in the function and numbers of lymphocytes, including both B cells and T cells.

The major mechanism for this immunosuppression is through inhibition of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). NF-κB is a critical transcription factor involved in the synthesis of many mediators (i.e., cytokines) and proteins (i.e., adhesion proteins) that promote the immune response. Inhibition of this transcription factor, therefore, blunts the capacity of the immune system to mount a response.[2]

Glucocorticoids suppress cell-mediated immunity by inhibiting genes that code for the cytokines IL-1, IL-2, IL-3, IL-4, IL-5, IL-6, IL-8 and IFN-γ, the most important of which is IL-2. Smaller cytokine production reduces the T cell proliferation.[27]

Glucocorticoids, however, not only reduce T cell proliferation, but also lead to another well known effect - glucocorticoid-induced apoptosis. The effect is more prominent in immature T cells still inside in the thymus, but peripheral T cells are also affected. The exact mechanism regulating this glucocorticoid sensitivity lies in the Bcl-2 gene.[28]

Glucocorticoids also suppress the humoral immunity, thereby causing a humoral immune deficiency. Glucocorticoids cause B cells to express smaller amounts of IL-2 and of IL-2 receptors. This diminishes both B cell clone expansion and antibody synthesis. The diminished amounts of IL-2 also cause fewer T lymphocyte cells to be activated.

The effect of glucocorticoids on Fc receptor expression in immune cells is complicated. Dexamethasone decreases IFN-gamma stimulated Fc gamma RI expression in neutrophils while conversely causing an increase in monocytes.[29] Glucocorticoids may also decrease the expression of Fc receptors in macrophages,[30] but the evidence supporting this regulation in earlier studies has been questioned.[31] The effect of Fc receptor expression in macrophages is important since it is necessary for the phagocytosis of opsonised cells. This is because Fc receptors bind antibodies attached to cells targeted for destruction by macrophages.

Anti-inflammatory Edit

Glucocorticoids are potent anti-inflammatories, regardless of the inflammation's cause; their primary anti-inflammatory mechanism is lipocortin-1 (annexin-1) synthesis. Lipocortin-1 both suppresses phospholipase A2, thereby blocking eicosanoid production, and inhibits various leukocyte inflammatory events (epithelial adhesion, emigration, chemotaxis, phagocytosis, respiratory burst, etc.). In other words, glucocorticoids not only suppress immune response, but also inhibit the two main products of inflammation, prostaglandins and leukotrienes. They inhibit prostaglandin synthesis at the level of phospholipase A2 as well as at the level of cyclooxygenase/PGE isomerase (COX-1 and COX-2),[32] the latter effect being much like that of NSAIDs, thus potentiating the anti-inflammatory effect.

In addition, glucocorticoids also suppress cyclooxygenase expression.[33]

Glucocorticoids marketed as anti-inflammatories are often topical formulations, such as nasal sprays for rhinitis or inhalers for asthma. These preparations have the advantage of only affecting the targeted area, thereby reducing side effects or potential interactions. In this case, the main compounds used are beclometasone, budesonide, fluticasone, mometasone and ciclesonide. In rhinitis, sprays are used. For asthma, glucocorticoids are administered as inhalants with a metered-dose or dry powder inhaler.[34] In rare cases, symptoms of radiation induced thyroiditis has been treated with oral glucocorticoids.[35]

Hyperaldosteronism Edit

Glucocorticoids can be used in the management of familial hyperaldosteronism type 1. They are not effective, however, for use in the type 2 condition.

Heart failure Edit

Glucocorticoids could be used in the treatment of decompensated heart failure to potentiate renal responsiveness to diuretics, especially in heart failure patients with refractory diuretic resistance with large doses of loop diuretics.[36][37][38][39][40][41][42]

Resistance Edit

 
Corticosteroid resistance mechanisms

Resistance to the therapeutic uses of glucocorticoids can present difficulty; for instance, 25% of cases of severe asthma may be unresponsive to steroids. This may be the result of genetic predisposition, ongoing exposure to the cause of the inflammation (such as allergens), immunological phenomena that bypass glucocorticoids, pharmacokinetic disturbances (incomplete absorption or accelerated excretion or metabolism) and viral and/or bacterial respiratory infections.[27][43]

Side effects Edit

Glucocorticoid drugs currently being used act nonselectively, so in the long run they may impair many healthy anabolic processes. To prevent this, much research has been focused recently on the elaboration of selectively acting glucocorticoid drugs. Side effects include:

In high doses, hydrocortisone (cortisol) and those glucocorticoids with appreciable mineralocorticoid potency can exert a mineralocorticoid effect as well, although in physiologic doses this is prevented by rapid degradation of cortisol by 11β-hydroxysteroid dehydrogenase isoenzyme 2 (11β-HSD2) in mineralocorticoid target tissues. Mineralocorticoid effects can include salt and water retention, extracellular fluid volume expansion, hypertension, potassium depletion, and metabolic alkalosis.

Immunodeficiency Edit

Glucocorticoids cause immunosuppression, decreasing the function and/or numbers of neutrophils, lymphocytes (including both B cells and T cells), monocytes, macrophages, and the anatomical barrier function of the skin.[48] This suppression, if large enough, can cause manifestations of immunodeficiency, including T cell deficiency, humoral immune deficiency and neutropenia.

Withdrawal Edit

In addition to the effects listed above, use of high-dose glucocorticoids for only a few days begins to produce suppression of the patient's adrenal glands suppressing hypothalamic corticotropin-releasing hormone (CRH) leading to suppressed production of adrenocorticotropic hormone (ACTH) by the anterior pituitary.[19] With prolonged suppression, the adrenal glands atrophy (physically shrink), and can take months to recover full function after discontinuation of the exogenous glucocorticoid.

During this recovery time, the patient is vulnerable to adrenal insufficiency during times of stress, such as illness. While suppressive dose and time for adrenal recovery vary widely, clinical guidelines have been devised to estimate potential adrenal suppression and recovery, to reduce risk to the patient. The following is one example:

  • If patients have been receiving daily high doses for five days or less, they can be abruptly stopped (or reduced to physiologic replacement if patients are adrenal-deficient). Full adrenal recovery can be assumed to occur by a week afterward.
  • If high doses were used for six to 10 days, reduce to replacement dose immediately and taper over four more days. Adrenal recovery can be assumed to occur within two to four weeks of completion of steroids.
  • If high doses were used for 11–30 days, cut immediately to twice replacement, and then by 25% every four days. Stop entirely when dose is less than half of replacement. Full adrenal recovery should occur within one to three months of completion of withdrawal.
  • If high doses were used more than 30 days, cut dose immediately to twice replacement, and reduce by 25% each week until replacement is reached. Then change to oral hydrocortisone or cortisone as a single morning dose, and gradually decrease by 2.5 mg each week. When the morning dose is less than replacement, the return of normal basal adrenal function may be documented by checking 0800 cortisol levels prior to the morning dose; stop drugs when 0800 cortisol is 10 μg/dl. Predicting the time to full adrenal recovery after prolonged suppressive exogenous steroids is difficult; some people may take nearly a year.
  • Flare-up of the underlying condition for which steroids are given may require a more gradual taper than outlined above.

See also Edit

References Edit

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Further reading Edit

  • Wolkowitz OM, Burke H, Epel ES, Reus VI (Oct 2009). "Glucocorticoids. Mood, memory, and mechanisms". Annals of the New York Academy of Sciences. 1179: 19–40. doi:10.1111/j.1749-6632.2009.04980.x. PMID 19906230. S2CID 222085554.

External links Edit

glucocorticoid, less, commonly, glucocorticosteroids, class, corticosteroids, which, class, steroid, hormones, corticosteroids, that, bind, glucocorticoid, receptor, that, present, almost, every, vertebrate, animal, cell, name, glucocorticoid, portmanteau, glu. Glucocorticoids or less commonly glucocorticosteroids are a class of corticosteroids which are a class of steroid hormones Glucocorticoids are corticosteroids that bind to the glucocorticoid receptor 1 that is present in almost every vertebrate animal cell The name glucocorticoid is a portmanteau glucose cortex steroid and is composed from its role in regulation of glucose metabolism synthesis in the adrenal cortex and its steroidal structure see structure below GlucocorticoidDrug classChemical structure of cortisol hydrocortisone an endogenous glucocorticoid as well as medication Class identifiersSynonymsCorticosteroid GlucocorticosteroidUseAdrenal insufficiency allergic inflammatory and autoimmune disorders asthma organ transplantATC codeH02ABBiological targetGlucocorticoid receptorChemical classSteroidsIn WikidataGlucocorticoids are part of the feedback mechanism in the immune system which reduces certain aspects of immune function such as inflammation They are therefore used in medicine to treat diseases caused by an overactive immune system such as allergies asthma autoimmune diseases and sepsis Glucocorticoids have many diverse effects such as pleiotropy including potentially harmful side effects 2 They also interfere with some of the abnormal mechanisms in cancer cells so they are used in high doses to treat cancer This includes inhibitory effects on lymphocyte proliferation as in the treatment of lymphomas and leukemias and the mitigation of side effects of anticancer drugs Glucocorticoids affect cells by binding to the glucocorticoid receptor The activated glucocorticoid receptor glucocorticoid complex up regulates the expression of anti inflammatory proteins in the nucleus a process known as transactivation and represses the expression of proinflammatory proteins in the cytosol by preventing the translocation of other transcription factors from the cytosol into the nucleus transrepression 2 Glucocorticoids are distinguished from mineralocorticoids and sex steroids by their specific receptors target cells and effects In technical terms corticosteroid refers to both glucocorticoids and mineralocorticoids as both are mimics of hormones produced by the adrenal cortex but is often used as a synonym for glucocorticoid Glucocorticoids are chiefly produced in the zona fasciculata of the adrenal cortex whereas mineralocorticoids are synthesized in the zona glomerulosa Cortisol or hydrocortisone is the most important human glucocorticoid It is essential for life and it regulates or supports a variety of important cardiovascular metabolic immunologic and homeostatic functions Various synthetic glucocorticoids are available these are widely utilized in general medical practice and numerous specialties either as replacement therapy in glucocorticoid deficiency or to suppress the body s immune system Contents 1 Effects 1 1 Immune 1 2 Metabolic 1 3 Developmental 1 4 Arousal and cognition 1 5 Body fluid homeostasis 2 Mechanism of action 2 1 Transactivation 2 2 Transrepression 2 3 Nongenomic effects 3 Pharmacology 4 Therapeutic use 4 1 Replacement 4 2 Therapeutic immunosuppression 4 3 Anti inflammatory 4 4 Hyperaldosteronism 4 5 Heart failure 5 Resistance 6 Side effects 6 1 Immunodeficiency 6 2 Withdrawal 7 See also 8 References 9 Further reading 10 External linksEffects Edit Steroidogenesis showing glucocorticoids in green ellipse at right with the primary example being cortisol 3 It is not a strictly bounded group but a continuum of structures with increasing glucocorticoid effect Glucocorticoid effects may be broadly classified into two major categories immunological and metabolic In addition glucocorticoids play important roles in fetal development and body fluid homeostasis Immune Edit Glucocorticoids function via interaction with the glucocorticoid receptor see details below Upregulate the expression of anti inflammatory proteins Downregulate the expression of proinflammatory proteins Glucocorticoids are also shown to play a role in the development and homeostasis of T lymphocytes This has been shown in transgenic mice with either increased or decreased sensitivity of T cell lineage to glucocorticoids 4 Metabolic Edit The name glucocorticoid derives from early observations that these hormones were involved in glucose metabolism In the fasted state cortisol stimulates several processes that collectively serve to increase and maintain normal concentrations of glucose in the blood Metabolic effects Stimulation of gluconeogenesis in particular in the liver This pathway results in the synthesis of glucose from non hexose substrates such as amino acids and glycerol from triglyceride breakdown and is particularly important in carnivores and certain herbivores Enhancing the expression of enzymes involved in gluconeogenesis is probably the best known metabolic function of glucocorticoids Mobilization of amino acids from extrahepatic tissues These serve as substrates for gluconeogenesis Inhibition of glucose uptake in muscle and adipose tissue A mechanism to conserve glucose Stimulation of fat breakdown in adipose tissue The fatty acids released by lipolysis are used for production of energy in tissues like muscle and the released glycerol provide another substrate for gluconeogenesis Increase in sodium retention and potassium excretion leads to hypernatremia and hypokalemia 5 Increase in hemoglobin concentration likely due to hindrance of the ingestion of red blood cell by macrophage or other phagocyte 1 Increased urinary uric acid 6 Increased urinary calcium and hypocalcemia 7 Alkalosis 8 Leukocytosis 9 Excessive glucocorticoid levels resulting from administration as a drug or hyperadrenocorticism have effects on many systems Some examples include inhibition of bone formation suppression of calcium absorption both of which can lead to osteoporosis delayed wound healing muscle weakness and increased risk of infection These observations suggest a multitude of less dramatic physiologic roles for glucocorticoids 4 Developmental Edit Glucocorticoids have multiple effects on fetal development An important example is their role in promoting maturation of the lung and production of the surfactant necessary for extrauterine lung function Mice with homozygous disruptions in the corticotropin releasing hormone gene see below die at birth due to pulmonary immaturity In addition glucocorticoids are necessary for normal brain development by initiating terminal maturation remodeling axons and dendrites and affecting cell survival 8 and may also play a role in hippocampal development Glucocorticoids stimulate the maturation of the Na K ATPase nutrient transporters and digestion enzymes promoting the development of a functioning gastro intestinal system Glucocorticoids also support the development of the neonate s renal system by increasing glomerular filtration Arousal and cognition Edit A graphical representation of the Yerkes Dodson curveGlucocorticoids act on the hippocampus amygdala and frontal lobes Along with adrenaline these enhance the formation of flashbulb memories of events associated with strong emotions both positive and negative 9 This has been confirmed in studies whereby blockade of either glucocorticoids or noradrenaline activity impaired the recall of emotionally relevant information Additional sources have shown subjects whose fear learning was accompanied by high cortisol levels had better consolidation of this memory this effect was more important in men better source needed The effect that glucocorticoids have on memory may be due to damage specifically to the CA1 area of the hippocampal formation In multiple animal studies prolonged stress causing prolonged increases in glucocorticoid levels have shown destruction of the neurons in the hippocampus area of the brain which has been connected to lower memory performance 5 10 6 Glucocorticoids have also been shown to have a significant impact on vigilance attention deficit disorder and cognition memory This appears to follow the Yerkes Dodson curve as studies have shown circulating levels of glucocorticoids vs memory performance follow an upside down U pattern much like the Yerkes Dodson curve For example long term potentiation LTP the process of forming long term memories is optimal when glucocorticoid levels are mildly elevated whereas significant decreases of LTP are observed after adrenalectomy low glucocorticoid state or after exogenous glucocorticoid administration high glucocorticoid state Elevated levels of glucocorticoids enhance memory for emotionally arousing events but lead more often than not to poor memory for material unrelated to the source of stress emotional arousal 11 In contrast to the dose dependent enhancing effects of glucocorticoids on memory consolidation these stress hormones have been shown to inhibit the retrieval of already stored information 7 Long term exposure to glucocorticoid medications such as asthma and anti inflammatory medication has been shown to create deficits in memory and attention both during and to a lesser extent after treatment 12 13 a condition known as steroid dementia 14 Body fluid homeostasis Edit Glucocorticoids could act centrally as well as peripherally to assist in the normalization of extracellular fluid volume by regulating body s action to atrial natriuretic peptide ANP Centrally glucocorticoids could inhibit dehydration induce water intake 15 peripherally glucocorticoids could induce a potent diuresis 16 Mechanism of action EditTransactivation Edit Glucocorticoids bind to the cytosolic glucocorticoid receptor a type of nuclear receptor that is activated by ligand binding After a hormone binds to the corresponding receptor the newly formed complex translocates itself into the cell nucleus where it binds to glucocorticoid response elements in the promoter region of the target genes resulting in the regulation of gene expression This process is commonly referred to as transcriptional activation or transactivation 17 18 The proteins encoded by these up regulated genes have a wide range of effects including for example 18 Anti inflammatory lipocortin I p11 calpactin binding protein secretory leukocyte protease inhibitor 1 SLPI and Mitogen activated protein kinase phosphatase MAPK phosphatase Increased gluconeogenesis glucose 6 phosphatase and tyrosine aminotransferaseTransrepression Edit The opposite mechanism is called transcriptional repression or transrepression The classical understanding of this mechanism is that activated glucocorticoid receptor binds to DNA in the same site where another transcription factor would bind which prevents the transcription of genes that are transcribed via the activity of that factor 17 18 While this does occur the results are not consistent for all cell types and conditions there is no generally accepted general mechanism for transrepression 18 New mechanisms are being discovered where transcription is repressed but the activated glucocorticoid receptor is not interacting with DNA but rather with another transcription factor directly thus interfering with it or with other proteins that interfere with the function of other transcription factors This latter mechanism appears to be the most likely way that activated glucocorticoid receptor interferes with NF kB namely by recruiting histone deacetylase which deacetylate the DNA in the promoter region leading to closing of the chromatin structure where NF kB needs to bind 17 18 Nongenomic effects Edit Activated glucocorticoid receptor has effects that have been experimentally shown to be independent of any effects on transcription and can only be due to direct binding of activated glucocorticoid receptor with other proteins or with mRNA 17 18 For example Src kinase which binds to inactive glucocorticoid receptor is released when a glucocorticoid binds to glucocorticoid receptor and phosphorylates a protein that in turn displaces an adaptor protein from a receptor important in inflammation epidermal growth factor reducing its activity which in turn results in reduced creation of arachidonic acid a key proinflammatory molecule This is one mechanism by which glucocorticoids have an anti inflammatory effect 17 Pharmacology Edit Dexamethasone a synthetic glucocorticoid binds more powerfully to the glucocorticoid receptor than cortisol does Dexamethasone is based on the cortisol structure but differs at three positions extra double bond in the A ring between carbons 1 and 2 and addition of a 9 a fluoro group and a 16 a methyl substituent A variety of synthetic glucocorticoids some far more potent than cortisol have been created for therapeutic use They differ in both pharmacokinetics absorption factor half life volume of distribution clearance and pharmacodynamics for example the capacity of mineralocorticoid activity retention of sodium Na and water renal physiology Because they permeate the intestines easily they are administered primarily per os by mouth but also by other methods such as topically on skin More than 90 of them bind different plasma proteins though with a different binding specificity Endogenous glucocorticoids and some synthetic corticoids have high affinity to the protein transcortin also called corticosteroid binding globulin whereas all of them bind albumin In the liver they quickly metabolize by conjugation with a sulfate or glucuronic acid and are secreted in the urine Glucocorticoid potency duration of effect and the overlapping mineralocorticoid potency vary Cortisol is the standard of comparison for glucocorticoid potency Hydrocortisone is the name used for pharmaceutical preparations of cortisol The data below refer to oral administration Oral potency may be less than parenteral potency because significant amounts up to 50 in some cases may not reach the circulation Fludrocortisone acetate and deoxycorticosterone acetate are by definition mineralocorticoids rather than glucocorticoids but they do have minor glucocorticoid potency and are included in this table to provide perspective on mineralocorticoid potency Comparative oral corticosteroid potencies 19 20 21 22 Name Glucocorticoid potency Mineralocorticoid potency Terminal half life hours Cortisol hydrocortisone 1 1 8Cortisone 0 8 0 8 8Prednisone 3 5 5 0 8 16 36Prednisolone 4 0 8 16 36Methylprednisolone 5 7 5 0 5 18 40Dexamethasone 25 80 0 36 54Betamethasone 25 30 0 36 54Triamcinolone 5 0 12 36Deflazacort 6 5 1 3Fludrocortisone acetate 15 200 24Deoxycorticosterone acetate 0 20 Aldosterone 0 3 200 1000 Beclometasone 8 sprays 4 times every day equivalent to orally 14 mg prednisone once a day Therapeutic use EditGlucocorticoids may be used in low doses in adrenal insufficiency In much higher doses oral or inhaled glucocorticoids are used to suppress various allergic inflammatory and autoimmune disorders Inhaled glucocorticoids are the second line treatment for asthma They are also administered as post transplantory immunosuppressants to prevent the acute transplant rejection and the graft versus host disease Nevertheless they do not prevent an infection and also inhibit later reparative processes Newly emerging evidence showed that glucocorticoids could be used in the treatment of heart failure to increase the renal responsiveness to diuretics and natriuretic peptides Glucocorticoids are historically used for pain relief in inflammatory conditions 23 24 25 However corticosteroids show limited efficacy in pain relief and potential adverse events for their use in tendinopathies 26 Replacement Edit Any glucocorticoid can be given in a dose that provides approximately the same glucocorticoid effects as normal cortisol production this is referred to as physiologic replacement or maintenance dosing This is approximately 6 12 mg m2 day of hydrocortisone m2 refers to body surface area BSA and is a measure of body size an average man s BSA is 1 9 m2 Therapeutic immunosuppression Edit See section on Immunodeficiency below for adverse effects Glucocorticoids cause immunosuppression and the therapeutic component of this effect is mainly the decreases in the function and numbers of lymphocytes including both B cells and T cells The major mechanism for this immunosuppression is through inhibition of nuclear factor kappa light chain enhancer of activated B cells NF kB NF kB is a critical transcription factor involved in the synthesis of many mediators i e cytokines and proteins i e adhesion proteins that promote the immune response Inhibition of this transcription factor therefore blunts the capacity of the immune system to mount a response 2 Glucocorticoids suppress cell mediated immunity by inhibiting genes that code for the cytokines IL 1 IL 2 IL 3 IL 4 IL 5 IL 6 IL 8 and IFN g the most important of which is IL 2 Smaller cytokine production reduces the T cell proliferation 27 Glucocorticoids however not only reduce T cell proliferation but also lead to another well known effect glucocorticoid induced apoptosis The effect is more prominent in immature T cells still inside in the thymus but peripheral T cells are also affected The exact mechanism regulating this glucocorticoid sensitivity lies in the Bcl 2 gene 28 Glucocorticoids also suppress the humoral immunity thereby causing a humoral immune deficiency Glucocorticoids cause B cells to express smaller amounts of IL 2 and of IL 2 receptors This diminishes both B cell clone expansion and antibody synthesis The diminished amounts of IL 2 also cause fewer T lymphocyte cells to be activated The effect of glucocorticoids on Fc receptor expression in immune cells is complicated Dexamethasone decreases IFN gamma stimulated Fc gamma RI expression in neutrophils while conversely causing an increase in monocytes 29 Glucocorticoids may also decrease the expression of Fc receptors in macrophages 30 but the evidence supporting this regulation in earlier studies has been questioned 31 The effect of Fc receptor expression in macrophages is important since it is necessary for the phagocytosis of opsonised cells This is because Fc receptors bind antibodies attached to cells targeted for destruction by macrophages Anti inflammatory Edit Glucocorticoids are potent anti inflammatories regardless of the inflammation s cause their primary anti inflammatory mechanism is lipocortin 1 annexin 1 synthesis Lipocortin 1 both suppresses phospholipase A2 thereby blocking eicosanoid production and inhibits various leukocyte inflammatory events epithelial adhesion emigration chemotaxis phagocytosis respiratory burst etc In other words glucocorticoids not only suppress immune response but also inhibit the two main products of inflammation prostaglandins and leukotrienes They inhibit prostaglandin synthesis at the level of phospholipase A2 as well as at the level of cyclooxygenase PGE isomerase COX 1 and COX 2 32 the latter effect being much like that of NSAIDs thus potentiating the anti inflammatory effect In addition glucocorticoids also suppress cyclooxygenase expression 33 Glucocorticoids marketed as anti inflammatories are often topical formulations such as nasal sprays for rhinitis or inhalers for asthma These preparations have the advantage of only affecting the targeted area thereby reducing side effects or potential interactions In this case the main compounds used are beclometasone budesonide fluticasone mometasone and ciclesonide In rhinitis sprays are used For asthma glucocorticoids are administered as inhalants with a metered dose or dry powder inhaler 34 In rare cases symptoms of radiation induced thyroiditis has been treated with oral glucocorticoids 35 Hyperaldosteronism Edit Glucocorticoids can be used in the management of familial hyperaldosteronism type 1 They are not effective however for use in the type 2 condition Heart failure Edit Glucocorticoids could be used in the treatment of decompensated heart failure to potentiate renal responsiveness to diuretics especially in heart failure patients with refractory diuretic resistance with large doses of loop diuretics 36 37 38 39 40 41 42 Resistance Edit Corticosteroid resistance mechanismsResistance to the therapeutic uses of glucocorticoids can present difficulty for instance 25 of cases of severe asthma may be unresponsive to steroids This may be the result of genetic predisposition ongoing exposure to the cause of the inflammation such as allergens immunological phenomena that bypass glucocorticoids pharmacokinetic disturbances incomplete absorption or accelerated excretion or metabolism and viral and or bacterial respiratory infections 27 43 Side effects EditGlucocorticoid drugs currently being used act nonselectively so in the long run they may impair many healthy anabolic processes To prevent this much research has been focused recently on the elaboration of selectively acting glucocorticoid drugs Side effects include Immunodeficiency see section below Hyperglycemia due to increased gluconeogenesis insulin resistance and impaired glucose tolerance steroid diabetes caution in those with diabetes mellitus Increased skin fragility easy bruising Negative calcium balance due to reduced intestinal calcium absorption 44 Steroid induced osteoporosis reduced bone density osteoporosis osteonecrosis higher fracture risk slower fracture repair Weight gain due to increased visceral and truncal fat deposition central obesity and appetite stimulation see corticosteroid induced lipodystrophy Hypercortisolemia with prolonged or excessive use also known as exogenous Cushing s syndrome Impaired memory and attention deficits 45 See steroid dementia syndrome Adrenal insufficiency if used for long time and stopped suddenly without a taper Muscle and tendon breakdown proteolysis weakness reduced muscle mass and repair 46 26 Expansion of malar fat pads and dilation of small blood vessels in skin Lipomatosis within the epidural space 47 Excitatory effect on central nervous system euphoria psychosis Anovulation irregularity of menstrual periods Growth failure delayed puberty Increased plasma amino acids increased urea formation negative nitrogen balance Glaucoma due to increased ocular pressure Cataracts Topical steroid withdrawalIn high doses hydrocortisone cortisol and those glucocorticoids with appreciable mineralocorticoid potency can exert a mineralocorticoid effect as well although in physiologic doses this is prevented by rapid degradation of cortisol by 11b hydroxysteroid dehydrogenase isoenzyme 2 11b HSD2 in mineralocorticoid target tissues Mineralocorticoid effects can include salt and water retention extracellular fluid volume expansion hypertension potassium depletion and metabolic alkalosis Immunodeficiency Edit Glucocorticoids cause immunosuppression decreasing the function and or numbers of neutrophils lymphocytes including both B cells and T cells monocytes macrophages and the anatomical barrier function of the skin 48 This suppression if large enough can cause manifestations of immunodeficiency including T cell deficiency humoral immune deficiency and neutropenia Main pathogens of concern in glucocorticoid induced immunodeficiency 48 Bacteria Enterobacteriaceae including Salmonella species Legionella micdadei Listeria monocytogenes Mycobacterium tuberculosis Nontuberculous mycobacteria Nocardia asteroides Rhodococcus equi Staphylococcus aureus StreptococciFungi Aspergillus Blastomyces Candida species including Candida albicans Coccidioides immitis Cryptococcus neoformans Fusarium species Histoplasma capsulatum Talaromyces marneffei Pneumocystis jirovecii Pseudallescheria boydii ZygomycosisViruses Adenovirus Cytomegalovirus Herpes simplex virus Human papillomavirus Influenza parainfluenza Respiratory syncytial virus Varicella zosterOther Cryptosporidiosis Isospora belli Strongyloides stercoralis Toxoplasma gondiiWithdrawal Edit This article needs more reliable medical references for verification or relies too heavily on primary sources Please review the contents of the article and add the appropriate references if you can Unsourced or poorly sourced material may be challenged and removed Find sources Glucocorticoid news newspapers books scholar JSTOR May 2018 In addition to the effects listed above use of high dose glucocorticoids for only a few days begins to produce suppression of the patient s adrenal glands suppressing hypothalamic corticotropin releasing hormone CRH leading to suppressed production of adrenocorticotropic hormone ACTH by the anterior pituitary 19 With prolonged suppression the adrenal glands atrophy physically shrink and can take months to recover full function after discontinuation of the exogenous glucocorticoid During this recovery time the patient is vulnerable to adrenal insufficiency during times of stress such as illness While suppressive dose and time for adrenal recovery vary widely clinical guidelines have been devised to estimate potential adrenal suppression and recovery to reduce risk to the patient The following is one example If patients have been receiving daily high doses for five days or less they can be abruptly stopped or reduced to physiologic replacement if patients are adrenal deficient Full adrenal recovery can be assumed to occur by a week afterward If high doses were used for six to 10 days reduce to replacement dose immediately and taper over four more days Adrenal recovery can be assumed to occur within two to four weeks of completion of steroids If high doses were used for 11 30 days cut immediately to twice replacement and then by 25 every four days Stop entirely when dose is less than half of replacement Full adrenal recovery should occur within one to three months of completion of withdrawal If high doses were used more than 30 days cut dose immediately to twice replacement and reduce by 25 each week until replacement is reached Then change to oral hydrocortisone or cortisone as a single morning dose and gradually decrease by 2 5 mg each week When the morning dose is less than replacement the return of normal basal adrenal function may be documented by checking 0800 cortisol levels prior to the morning dose stop drugs when 0800 cortisol is 10 mg dl Predicting the time to full adrenal recovery after prolonged suppressive exogenous steroids is difficult some people may take nearly a year Flare up of the underlying condition for which steroids are given may require a more gradual taper than outlined above See also EditList of corticosteroids List of corticosteroid cyclic ketals List of corticosteroid esters Aminoglutethimide blocks glucocorticoid secretion GITR glucocorticoid induced TNF receptor Glucocorticoid receptor Immunosuppressive drug Membrane glucocorticoid receptor Metyrapone blocks glucocorticoid secretion Selective glucocorticoid receptor agonist Topical glucocorticoids Topical steroid Steroid atrophy Topical steroid withdrawal Non steroidal anti inflammatory drug NSAID References Edit a b Pelt AC 2011 Glucocorticoids effects 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Medicine 30 3 517 e5 10 doi 10 1016 j ajem 2011 01 023 PMID 21406321 Henderson Ishbel Caiazzo Elisabetta McSharry Charles Guzik Tomasz J Maffia Pasquale 2020 10 01 Why do some asthma patients respond poorly to glucocorticoid therapy Pharmacological Research 160 105189 doi 10 1016 j phrs 2020 105189 ISSN 1043 6618 Gennari C May 1993 Differential effect of glucocorticoids on calcium absorption and bone mass British Journal of Rheumatology 32 Suppl 2 11 4 doi 10 1093 rheumatology 32 suppl 2 11 PMID 8495275 Keenan PA Jacobson MW Soleymani RM Mayes MD Stress ME Yaldoo DT Dec 1996 The effect on memory of chronic prednisone treatment in patients with systemic disease Neurology 47 6 1396 402 doi 10 1212 WNL 47 6 1396 PMID 8960717 S2CID 20430943 Gelber JD January 2017 CORR Insights Corticosteroid Injections Give Small and Transient Pain Relief in Rotator Cuff Tendinosis A Meta analysis Clinical Orthopaedics and Related Research 475 1 244 246 doi 10 1007 s11999 016 5044 4 PMC 5174046 PMID 27572298 Koch CA Doppman JL Patronas NJ Nieman LK Chrousos GP Apr 2000 Do glucocorticoids cause spinal epidural lipomatosis When endocrinology and spinal surgery meet Trends in Endocrinology and Metabolism 11 3 86 90 doi 10 1016 S1043 2760 00 00236 8 PMID 10707048 S2CID 31233438 a b Klein NC Go CH Cunha BA Jun 2001 Infections associated with steroid use Infectious Disease Clinics of North America 15 2 423 32 viii doi 10 1016 s0891 5520 05 70154 9 PMID 11447704 Further reading EditWolkowitz OM Burke H Epel ES Reus VI Oct 2009 Glucocorticoids Mood memory and mechanisms Annals of the New York Academy of Sciences 1179 19 40 doi 10 1111 j 1749 6632 2009 04980 x PMID 19906230 S2CID 222085554 External links EditGlucocorticoids at the U S National Library of Medicine Medical Subject Headings MeSH Retrieved from https en wikipedia org w index php title Glucocorticoid amp oldid 1171931047, wikipedia, wiki, book, books, library,

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