Chronic Dexamethasone Treatment Research Articles

Supplementation with Vitamin D3 Protects against Mitochondrial Dysfunction and Loss of BDNF-Mediated Akt Activity in the Hippocampus during Long-Term Dexamethasone Treatment in Rats.

Dexamethasone (DEXA) is a commonly used steroid drug with immunosuppressive and analgesic properties. Unfortunately, long-term exposure to DEXA severely impairs brain function. This study aimed to investigate the effects of vitamin D3 supplementation during chronic DEXA treatment on neurogenesis, mitochondrial energy metabolism, protein levels involved in the BDNF-mediated Akt activity, and specific receptors in the hippocampus. We found reduced serum concentrations of 25-hydroxyvitamin D3 (25(OH)D3), downregulated proBDNF and pAkt, dysregulated glucocorticosteroid and mineralocorticoid receptors, impaired mitochondrial biogenesis, and dysfunctional mitochondria energy metabolism in the DEXA-treated group. In contrast, supplementation with vitamin D3 restored the 25(OH)D3 concentration to a value close to that of the control group. There was an elevation in neurotrophic factor protein level, along with augmented activity of pAkt and increased citrate synthase activity in the hippocampus after vitamin D3 administration in long-term DEXA-treated rats. Our findings demonstrate that vitamin D3 supplementation plays a protective role in the hippocampus and partially mitigates the deleterious effects of long-term DEXA administration. The association between serum 25(OH)D3 concentration and BDNF level in the hippocampus indicates the importance of applying vitamin D3 supplementation to prevent and treat pathological conditions.

Chronic Dexamethasone Treatment Leads to Less Weight Gain and Ameliorated Glucose Tolerance in Mice; Role of the Cytoprotective Nrf2 Pathway

Introduction: Chronic glucocorticoid administration is necessary in a variety of conditions including but not limited to autoimmune, inflammatory and cancer-related diseases in order to relieve symptoms and sustain disease progression. However, there are adverse effects that include increase in glucose levels and others whose severity depends on the dose and duration of glucocorticoid exposure. It has been described that dexamethasone induces oxidative stress in cells by increasing reactive oxygen species (ROS) and this is one of the causes of insulin resistance at the cellular level. Nrf2 is a transcription factor which co-ordinates the antioxidant response and its activation has been shown to ameliorate insulin resistance in murine models. Hypothesis: We hypothesized that deletion of Nrf2 will lead to a more glucose intolerant insulin resistant phenotype in mice chronically treated with dexamethasone as cells would be exposed to higher ROS levels. Methods: To this end, 3-months old wild-type (WT) and Nrf2 knockout (KO) C57BL6J mice were treated intraperitoneally with 2 mg/kg dexamethasone or saline 3 times per week for 3 months. 5-10 mice were included per genotype per treatment and both male and female mice were used. Weekly measurements of body weights were performed and intraperitoneal glucose tolerance tests were done on the second and third month of treatment. Mice were sacrificed 24 hours after the last dose of dexamethasone and blood, white adipose tissue, soleus muscle and liver were collected for RNA preparation and quantitative RT-PCR analysis. Quantitative analysis of trabecular bone parameters was performed by micro-CT. Results: Both male and female mice treated with dexamethasone gained less weight over time and surprisingly were more glucose tolerant than the control group. Absence of Nrf2 did not seem to considerably affect the body weight but KO mice tended to have lower body weights after dexamethasone treatment in both genders with the effect on male mice being statistically significant (25% lower, p<0.05). Surprisingly, both WT and KO mice of both genders showed lower fasting blood glucose levels after 3 months of treatment and better glucose tolerance. Livers of KO mice showed lower levels (~50%) of the cytoprotective genes Nqo1 and Gclc as expected but no difference was observed after dexamethasone treatment. Sarcopenia muscle markers Mafbx1 and Murf1 showed no significant changes. Male mice showed increased expression of Pnpla3 in white adipose tissue indicating increased lipolysis upon dexamethasone exposure. Micro-CT showed minor changes in the bone parameters without difference between male WT and Nrf2KO mice. Conclusions: Dexamethasone unexpectedly led to better glucose tolerance and lower body weight which is uncommon in humans but it has been described previously in mouse models. More analyses are in progress to fully elucidate this phenotype.

Neuroimmune Response Mediated by Cytokines in Natural Scrapie after Chronic Dexamethasone Treatment.

The actual role of prion protein-induced glial activation and subsequent cytokine secretion during prion diseases is still incompletely understood. The overall aim of this study is to assess the effect of an anti-inflammatory treatment with dexamethasone on different cytokines released by neuroglial cells that are potentially related to neuroinflammation in natural scrapie. This study emphasizes the complex interactions existent among several pleiotropic neuromodulator peptides and provides a global approach to clarify neuroinflammatory processes in prion diseases. Additionally, an impairment of communication between microglial and astroglial populations mediated by cytokines, mainly IL-1, is suggested. The main novelty of this study is that it is the first one assessing in situ neuroinflammatory activity in relation to chronic anti-inflammatory therapy, gaining relevance because it is based on a natural model. The cytokine profile data would suggest the activation of some neurotoxicity-associated route. Consequently, targeting such a pathway might be a new approach to modify the damaging effects of neuroinflammation.

Эффективность α-липоевой кислоты в компенсации расстройств сократительной функции скелетной мышцы, вызванных длительным введением дексаметазона, в модельных экспериментах на животных

The aim of the study was to evaluate the efficacy of a-lipoic acid (a-LA) in correcting disorders of the contractile function of a mixed type skeletal muscle (m. tibial anterior) induced by chronic dexamethasone (DM) treatment in an animal model.Methods. Experiments were performed on sexually mature female rats (190-200 g) divided into four groups: control (intact rats, C group, n=10), experimental group 1 (30-day dexamethasone treatment, DM group, n=10), experimental group 2 (30-day dexamethasone plus a-lipoic acid treatment, DM+a-LA group, n=10), and experimental group 3 (30-day a-lipoic acid treatment, a-LA group, n=10). Dexamethasone (KRKA, Slovenia) was administered every two days, i.p., at a dose of 0.25 mg/kg, which was equivalent to the clinical therapeutic dose. a-Lipoic acid (Berlition-600, BERLIN-CHEMIE, Germany) was administered daily at a dose of 35 mg/kg, s.c. Stimulation electromyography and myography were performed in an acute experiment, under sodium thiopental (100 mg/kg) anesthesia, on day 30. Electrophysiological and contractile parameters of the anterior tibial muscle were recorded during stimulation with suprathreshold electrical current via the fibular nerve.Results. a-LA in combination with DM prevented decreases in the number of activated muscular motor units (MMU) and muscle mass, the degree of the muscle post-tetanic potentiation, and disorders of contractile and temporal parameters of single and tetanic contractions, which were typical for animals of the DM group. The a-LA plus DM treatment even significantly increased the relaxation rate of a single contraction (by 34%) and the rate of tetanic contraction development (by 80%) compared to the control group (p<0.05), which were also typical for the a-LA group. These facts indirectly evidence the absence of pronounced dystrophic changes in muscle fibers in animals of the DM+a-LA group. At the same time, although the shortened period of maximum muscle work capacity, which was typical for the DM group, was not observed in the DM+a-LA group, this period was no longer than in the control either, as distinct from the a-LA group. This fact suggests the absence of positive effects of a-LA on the muscle work capacity when a-LA is administered in combination with DM. The a-LA+DM treatment reversed the increased fatigue and the reduced ability to recover of the muscle after fatigable work (FW) observed in the DM group. Moreover, the a-LA+DM treatment even increased the rate of muscle recovery after FW, which was also characteristic for the a-LA group. This was confirmed by the absence of decreased rates of muscle shortening after FW, which was typical for the DM group, and by the absence of significant decreases in the single contraction amplitude and the number of activated MMU after FW, which was typical not only for the DM group, but also for the control.Conclusion. The changes in muscle functional parameters in the DM and DM+a-LA groups evidence pronounced contractile disorders and impaired ability of the muscle to recover after FW in the DM group. In the DM+a-LA group, the muscle contractile function was not significantly impaired. Moreover, the muscle ability to recover after FW was not reduced in the DM+a-LA-group. In this group, the ability to recover was even increased compared to the control, which was also characteristic for the a-LA-group. These facts allow considering a-LA as a possible therapy for correction of steroid myopathy.

Neuroimmune Response in Natural Preclinical Scrapie after Dexamethasone Treatment.

A recently published report on chronic dexamethasone treatment for natural scrapie supported the hypothesis of the potential failure of astroglia in the advanced stage of disease. Herein, we aimed to extend the aforementioned study on the effect of this anti-inflammatory therapy to the initial phase of scrapie, with the aim of elucidating the natural neuroinflammatory process occurring in this neurodegenerative disorder. The administration of this glucocorticoid resulted in an outstanding reduction in vacuolation and aberrant protein deposition (nearly null), and an increase in glial activation. Furthermore, evident suppression of IL-1R and IL-6 and the exacerbation of IL-1α, IL-2R, IL-10R and IFNγR were also demonstrated. Consequently, the early stage of the disease is characterized by an intact neuroglial response similar to that of healthy individuals attempting to re-establish homeostasis. A complex network of neuroinflammatory markers is involved from the very early stages of this prion disease, which probably becomes impaired in the more advanced stages. The in vivo animal model used herein provides essential observations on the pathogenesis of natural scrapie, as well as the possibility of establishing neuroglia as potential target cells for anti-inflammatory therapy.

Metabolic and behavioral changes induced by chronic treatment with dexamethasone in mice: differential effects in males and females

Stress is characterized as one of the main factors that contribute to the development of psychiatric and metabolic diseases. Through excessive activation of the hypothalamic-pituitary-adrenal (HPA) axis, and the resulting release of cortisol (in humans) or corticosterone (in rodents), the chronic increase in these hormones has been shown to contribute significantly to the development of depression and type 2 diabetes. Given the increase in mental disorders and metabolic pathologies in recent years, a better understanding of the factors contributing to the development of these conditions has become an important object of study. Here, we evaluated the behavioral and metabolic effects of chronic administration of dexamethasone, at a dose of 4 mg/kg, for 21 days, in male and female mice. The results indicate that dexamethasone treatment resulted in anxious like-behavior and passive stress-coping behavior in male and female mice. Moreover, we uncover sex-specific outcomes of chronic dexamethasone treatment on metabolic phenotypes in mice. Treatment with dexamethasone specifically resulted in a significant weight loss and increased plasma concentration of total proteins in male mice. Also, dexamethasone-induces hypercholesterolemia was observed in both male and female mice, although it did not impact glucose levels and glucose tolerance after glucose loading. The present study reproduced some metabolic and behavioral effects observed in humans exposed to excess glucocorticoids, providing preclinical evidence for future studies.

Assessment of Glial Activation Response in the Progress of Natural Scrapie after Chronic Dexamethasone Treatment.

Neuroinflammation has been correlated with the progress of neurodegeneration in many neuropathologies. Although glial cells have traditionally been considered to be protective, the concept of them as neurotoxic cells has recently emerged. Thus, a major unsolved question is the exact role of astroglia and microglia in neurodegenerative disorders. On the other hand, it is well known that glucocorticoids are the first choice to regulate inflammation and, consequently, neuroglial inflammatory activity. The objective of this study was to determine how chronic dexamethasone treatment influences the host immune response and to characterize the beneficial or detrimental role of glial cells. To date, this has not been examined using a natural neurodegenerative model of scrapie. With this aim, immunohistochemical expression of glial markers, prion protein accumulation, histopathological lesions and clinical evolution were compared with those in a control group. The results demonstrated how the complex interaction between glial populations failed to compensate for brain damage in natural conditions, emphasizing the need for using natural models. Additionally, the data showed that modulation of neuroinflammation by anti-inflammatory drugs might become a research focus as a potential therapeutic target for prion diseases, similar to that considered previously for other neurodegenerative disorders classified as prion-like diseases.

Maternal betaine protects rat offspring from glucocorticoid-induced activation of lipolytic genes in adipose tissue through modification of DNA methylation.

Excessive exposure of glucocorticoids activates adipose lipolysis, increases circulating free fatty acids, and contributes to ectopic lipid deposition in liver and skeletal muscle. Our previous study demonstrated that maternal betaine supplementation attenuates glucocorticoid-induced hepatic lipid accumulation in rat offspring. However, it is unclear whether maternal betaine supplementation is effective in preventing glucocorticoid-induced lipolysis in the adipose tissue of offspring. In this study, 20 pregnant rats were fed with basal or betaine-supplemented (10g/kg) diets throughout gestation and lactation, and the offspring rats were raised on the basal diet from weaning till 3months of age followed by daily intraperitoneal injection of saline or 0.1mg/kg dexamethasone (DEX) for 3weeks. Chronic DEX treatment significantly (P < 0.05) decreased serum corticosterone level and increased proinflammatory cytokines, such as TNFα, IL-1β, and IL-6. Meanwhile, GR protein content in adipose tissue was increased in response to DEX treatment, which was associated with a significant (P < 0.05) up-regulation of ATGL and HSL expression at both mRNA and protein levels. All these DEX-induced changes were significantly (P < 0.05) attenuated in progeny rats derived from betaine-supplemented dams. Furthermore, DEX-induced hypomethylation of ATGL and HSL gene promoters was reversed by maternal betaine supplementation. Taken together, these results suggest that maternal betaine supplementation is effective in alleviating glucocorticoid-induced lipolysis in adipose tissue with modification of DNA methylation on the promoter of lipolytic genes.

An ANGPTL4–ceramide–protein kinase Cζ axis mediates chronic glucocorticoid exposure–induced hepatic steatosis and hypertriglyceridemia in mice

Chronic or excess glucocorticoid exposure causes lipid disorders such as hypertriglyceridemia and hepatic steatosis. Angptl4 (angiopoietin-like 4), a primary target gene of the glucocorticoid receptor in hepatocytes and adipocytes, is required for hypertriglyceridemia and hepatic steatosis induced by the synthetic glucocorticoid dexamethasone. Angptl4 has also been shown to be required for dexamethasone-induced hepatic ceramide production. Here, we further examined the role of ceramide-mediated signaling in hepatic dyslipidemia caused by chronic glucocorticoid exposure. Using a stable isotope-labeling technique, we found that dexamethasone treatment induced the rate of hepatic de novo lipogenesis and triglyceride synthesis. These dexamethasone responses were compromised in Angptl4-null mice (Angptl4-/-). Treating mice with myriocin, an inhibitor of the rate-controlling enzyme of de novo ceramide synthesis, serine palmitoyltransferase long-chain base subunit 1 (SPTLC1)/SPTLC2, decreased dexamethasone-induced plasma and liver triglyceride levels in WT but not Angptl4-/- mice. We noted similar results in mice infected with adeno-associated virus-expressing small hairpin RNAs targeting Sptlc2. Protein phosphatase 2 phosphatase activator (PP2A) and protein kinase Cζ (PKCζ) are two known downstream effectors of ceramides. We found here that mice treated with an inhibitor of PKCζ, 2-acetyl-1,3-cyclopentanedione (ACPD), had lower levels of dexamethasone-induced triglyceride accumulation in plasma and liver. However, small hairpin RNA-mediated targeting of the catalytic PP2A subunit (Ppp2ca) had no effect on dexamethasone responses on plasma and liver triglyceride levels. Overall, our results indicate that chronic dexamethasone treatment induces an ANGPTL4-ceramide-PKCζ axis that activates hepatic de novo lipogenesis and triglyceride synthesis, resulting in lipid disorders.

Dexamethasone-induced Krüppel-like factor 9 expression promotes hepatic gluconeogenesis and hyperglycemia.

Chronic glucocorticoid therapy has serious side effects, including diabetes and fatty liver. However, the molecular mechanisms responsible for steroid-induced diabetes remain largely enigmatic. Here, we show that hepatic Krüppel-like factor 9 (Klf9) gene expression is induced by dexamethasone and fasting. The overexpression of Klf9 in primary hepatocytes strongly stimulated Pgc1a gene expression through direct binding to its promoter, thereby activating the gluconeogenic program. However, Klf9 mutation abolished the stimulatory effect of dexamethasone on cellular glucose output. Adenovirus-mediated overexpression of KLF9 in the mouse liver markedly increased blood glucose levels and impaired glucose tolerance. Conversely, both global Klf9-mutant mice and liver-specific Klf9-deleted mice displayed fasting hypoglycemia. Moreover, the knockdown of Klf9 in the liver in diabetic mouse models, including ob/ob and db/db mice, markedly lowered fasting blood glucose levels. Notably, hepatic Klf9 deficiency in mice alleviated hyperglycemia induced by chronic dexamethasone treatment. These results suggest a critical role for KLF9 in the regulation of hepatic glucose metabolism and identify hepatic induction of KLF9 as a mechanism underlying glucocorticoid therapy-induced diabetes.

SGK1/FOXO3 Signaling in Hypothalamic POMC Neurons Mediates Glucocorticoid-Increased Adiposity.

Although the central nervous system has been implicated in glucocorticoid-induced gain of fat mass, the underlying mechanisms are poorly understood. The aim of this study was to investigate the possible involvement of hypothalamic serum- and glucocorticoid-regulated kinase 1 (SGK1) in glucocorticoid-increased adiposity. It is well known that SGK1 expression is induced by acute glucocorticoid treatment, but it is interesting that we found its expression to be decreased in the arcuate nucleus of the hypothalamus, including proopiomelanocortin (POMC) neurons, following chronic dexamethasone (Dex) treatment. To study the role of SGK1 in POMC neurons, we produced mice that developed or experienced adult-onset SGK1 deletion in POMC neurons (PSKO). As observed in Dex-treated mice, PSKO mice exhibited increased adiposity and decreased energy expenditure. Mice overexpressing constitutively active SGK1 in POMC neurons consistently had the opposite phenotype and did not experience Dex-increased adiposity. Finally, Dex decreased hypothalamic α-melanocyte-stimulating hormone (α-MSH) content and its precursor Pomc expression via SGK1/FOXO3 signaling, and intracerebroventricular injection of α-MSH or adenovirus-mediated FOXO3 knockdown in the arcuate nucleus largely reversed the metabolic alterations in PSKO mice. These results demonstrate that POMC SGK1/FOXO3 signaling mediates glucocorticoid-increased adiposity, providing new insights into the mechanistic link between glucocorticoids and fat accumulation and important hints for possible treatment targets for obesity.

Ginsenoside Rg1 protects against neuronal degeneration induced by chronic dexamethasone treatment by inhibiting NLRP-1 inflammasomes in mice.

Glucocorticoids (GCs) are known to alter neuronal plasticity, impair learning and memory and play important roles in the generation and progression of Alzheimer's disease. There are no effective drug options for preventing neuronal injury induced by chronic GC exposure. Ginsenoside Rg1 (Rg1) is a steroidal saponin found in ginseng. The present study investigated the neuroprotective effect of Rg1 on neuroinflammation damage induced by chronic dexamethasone (5 mg/kg for 28 days) exposure in male mice. Our results showed that Rg1 (2 and 4 mg/kg) treatment increased spontaneous motor activity and exploratory behavior in an open field test, and increased the number of entries into the new object zone in a novel object recognition test. Moreover, Rg1 (2 and 4 mg/kg) treatment significantly alleviated neuronal degeneration and increased MAP2 expression in the frontal cortex and hippocampus. Additionally, inhibition of NLRP-1 inflammasomes was also involved in the mechanisms underlying the effect of Rg1 on GC-induced neuronal injury. We found that Rg1 (2 and 4 mg/kg) treatment increased the expression of glucocorticosteroid receptor and decreased the expression of NLRP-1, ASC, caspase-1, caspase-5, IL-1β and IL-18 in the hippocampus in male mice. The present study indicates that Rg1 may have protective effects on neuroinflammation and neuronal injury induced by chronic GC exposure.

Chronic dexamethasone treatment results in hippocampal neurons injury due to activate NLRP1 inflammasome in vitro

Neuroinflammation mediated by NLRP-1 inflammasome plays an important role in the pathogenesis of neurodegeneration diseases such as Alzheimer's disease (AD). Chronic glucocorticoids (GCs) exposure has deleterious effect on the structure and function of neurons and was found to be correlated with development and progression of AD. We hypothesize that chronic glucocorticoids may down-regulate the expression of glucocorticoids receptor (GR) and activate NLRP-1 inflammasome in hippocampal neurons, which may promote neuroinflammation and induce neuronal injury. The present results showed that chronic DEX exposure significantly increased LDH release and apoptosis, decreased MAP2 and GR expression in hippocampal neurons. DEX (5μΜ) exposure for 3d significantly increased the expression of NLRP-1, ASC, caspase-1 and IL-1β in the hippocampal neurons and the release of IL-1β and IL-18 in the supernatants. Moreover, DEX (1, 5μΜ) treatment for 3d significantly increased the expression of NF-κB in hippocampal neurons. The GR antagonist, mifepristone (RU486), had protective effects on chronic DEX induced hippocampal neurons injury and NLRP1 inflammasome activation. The results suggest that chronic GCs exposure can decrease GR expression and increase neuroinflammation via NLRP1 inflammasome and promote hippocampal neurons degeneration, which may play an important role in the progression and development of AD.

A Novel Model of Dexamethasone-Induced Hypertension: Use in Investigating the Role of Tyrosine Hydroxylase.

Our objective was to study hypertension induced by chronic administration of synthetic glucocorticoid, dexamethasone (DEX), under nonstressful conditions and examine the role of catecholamine biosynthesis. To achieve this, we did the following: 1) used radiotelemetry to record mean arterial pressure (MAP) and heart rate (HR) in freely moving rats, and 2) administered different doses of DEX in drinking water. To evaluate the involvement of tyrosine hydroxylase (TH), the rate-limiting step in catecholamine biosynthesis, we treated rats with the TH inhibitor, α-methyl-para-tyrosine (α-MPT), for 3 days prior to administration of DEX and assessed TH mRNA and protein expression by quantitative real-time polymerase chain reaction and Western blot in the adrenal medulla. We observed a dose-dependent elevation in blood pressure with a DEX dose of 0.3 mg/kg administered for 10 days, significantly increasing MAP by +15.0 ± 1.1 mm Hg, while concomitantly reducing HR. Although this DEX treatment also significantly decreased body weight, pair-fed animals that showed similar decreases in body weight due to lowered food intake were not hypertensive, suggesting that body weight changes may not account for DEX-induced hypertension. Chronic DEX treatment significantly increased the TH mRNA and protein levels in the adrenal medulla, and α-MPT administration not only reduced DEX pressor effects, but also inhibited TH (serine(40)) phosphorylation. Our study thus validates a novel model to study hypertension induced by chronic intake of DEX in freely moving rats not subject to the confounding factors of previous models and establishes its dependence on concomitant activation of peripheral catecholamine biosynthesis.

Chronic glucocorticoids exposure enhances neurodegeneration in the frontal cortex and hippocampus via NLRP-1 inflammasome activation in male mice

Neuroinflammation plays an important role in the pathogenesis of neurodegenerative diseases, such as Alzheimer’s disease (AD) and depression. Chronic glucocorticoids (GCs) exposure has deleterious effects on the structure and function of neurons and is associated with development and progression of AD. However, little is known about the proinflammatory effects of chronic GCs exposure on neurodegeneration in brain. Therefore, the aim of this study was to evaluate the effects of chronic dexamethasone (DEX) treatment (5mg/kg, s.c. for 7, 14, 21 and 28days) on behavior, neurodegeneration and neuroinflammatory parameters of nucleotide-binding oligomerization domain-like receptor pyrin domain-containing 1 (NLRP-1) inflammasome in male mice. The results showed that DEX treatment for 21 and 28days significantly reduced the spontaneous motor activity and exploratory behavior of the mice. In addition, these mice showed significant neurodegeneration and a decrease of microtubule-associated protein 2 (MAP2) in the frontal cortex and hippocampus CA3. DEX treatment for 7, 14, 21 and 28days significantly decreased the mRNA and protein expression of glucocorticoid receptor (GR). Moreover, DEX treatment for 21 and 28days significantly increased the proteins expression of NLRP-1, Caspase-1, Caspase-5, apoptosis associated speck-like protein (ASC), nuclear factor-κB (NF-κB), p-NF-κB, interleukin-1β (IL-1β), IL-18 and IL-6 in the frontal cortex and hippocampus brain tissue. DEX treatment for 28days also significantly increased the mRNA expression levels of NLRP-1, Caspase-1, ASC and IL-1β. These results suggest that chronic GCs exposure may increase brain inflammation via NLRP-1 inflammasome activation and induce neurodegeneration.

Anterior and posterior segment changes in rat eyes with chronic steroid administration and their responsiveness to antiglaucoma drugs

Steroid-induced ocular hypertension (SIOH) is associated with topical and systemic use of steroids. However, SIOH-associated anterior and posterior segment morphological changes in rats have not been described widely. Here we describe the pattern of intraocular pressure (IOP) changes, quantitative assessment of trabecular meshwork (TM) and retinal morphological changes and changes in retinal redox status in response to chronic dexamethasone treatment in rats. We also evaluated the responsiveness of steroid-pretreated rat eyes to 5 different classes of antiglaucoma drugs that act by different mechanisms. Up to 80% of dexamethasone treated animals achieved significant and sustained IOP elevation. TM thickness was significantly increased and number of TM cells was significantly reduced in SIOH rats compared to the vehicle-treated rats. Quantitative assessment of retinal morphology showed significantly reduced thickness of ganglion cell layer (GCL) and inner retina (IR) in SIOH rats compared to vehicle-treated rats. Estimation of retinal antioxidants including catalase, superoxide dismutase and glutathione showed significantly increased retinal oxidative stress in SIOH animals. Furthermore, steroid-treated eyes showed significant IOP lowering in response to treatment with 5 different drug classes. This indicated the ability of SIOH eyes to respond to drugs acting by different mechanisms. In conclusion, SIOH was associated with significant morphological changes in TM and retina and retinal redox status. Additionally, SIOH eyes also showed IOP lowering in response to drugs that act by different mechanisms of action. Hence, SIOH rats appear to be an inexpensive and noninvasive model for studying the experimental antiglaucoma drugs for IOP lowering and neuroprotective effects.

Melatonin pretreatment prevented the effect of dexamethasone negative alterations on behavior and hippocampal neurogenesis in the mouse brain

Glucocorticoids play various physiological functions via the glucocorticoid receptor (GR). Glucocorticoid is associated with the pathophysiology of depression. Dexamethasone (DEX), a synthetic GR agonist, has a greater affinity for GR than the mineralocorticoid receptor (MR) in the hippocampus of pigs and may mimic the effects of GR possession. DEX decreases neurogenesis and induces damage to hippocampal neurons that is associated with depressive-like behavior. Melatonin, a hormone mainly synthesized in the pineal gland, is a potent free radical scavenger and antioxidant. Melatonin alters noradrenergic transmission in depressed patients. It may be interesting to further explore the mechanism of melatonin that is associated with the role of stress as a key factor to precipitate depression and as a factor altering neurogenesis. In this study, we assessed the capability of melatonin to protect the hippocampus of mouse brains to counteract the effects of chronic DEX treatment for 21 days on depressive-like behavior and neurogenesis. Our results revealed that chronic administration of DEX induced depressive-like behavior and that this could be reversed by pretreatment with melatonin. Moreover, the number of 5-bromo-2-deoxyuridine (BrdU)-immunopositive cells and doublecortin (DCX; the neuronal-specific marker) protein levels were significantly reduced in the DEX-treated mice. Pretreatment with melatonin was found to renew BrdU and DCX expression in the dentate gyrus. Furthermore, pretreatment with melatonin prevented DEX-induced reductions in GR and an extracellular-signal-regulated kinase (ERK1/2) in the hippocampal area. Melatonin may protect hippocampal neurons from damage and reverse neurogenesis after chronic DEX by activating brain-derived neurotrophic (BDNF) and ERK1/2 cascades. These results revealed that melatonin pretreatment prevented the reduction of cell proliferation, immature neuron precursor cells, and GR and ERK1/2 expression. This finding indicates that melatonin attenuates the DEX-induced depressive-like behavior, supporting the notion that melatonin possesses anti-stress and neurogenic actions.

Glucocorticoids have a role in renal cortical expression of the SNAT3 glutamine transporter during chronic metabolic acidosis

Glucocorticoids are involved in many aspects of regulation of acid-base homeostasis, including the stimulation of renal ammoniagenesis during chronic metabolic acidosis. Plasma glutamine is the principal substrate for ammoniagenesis under these conditions. Expression of the System N glutamine transporter SNAT3 is increased in the renal proximal tubules during acidosis. In vivo studies in rats using 1) sham and adrenalectomized rats, 2) the glucocorticoid receptor antagonist RU486, and 3) dexamethasone treatment demonstrated involvement of glucocorticoids in regulation of SNAT3 expression. Adrenalectomy attenuated the acidosis-induced increase in renal cortical SNAT3 mRNA approximately 40%, and treatment with dexamethasone (1 mg x kg(-1) x day(-1) sc) partially reversed this effect. RU486 also blunted the acidosis-induced increase in SNAT3 expression approximately 50%. Chronic dexamethasone treatment (0.1 mg x kg(-1) x day(-1) sc, 6 days) of normal rats slightly increased SNAT3 expression. In all cases, renal glutamine arteriovenous difference mirrored SNAT3 expression and activity in the proximal tubules, suggesting that SNAT3 regulates glutamine uptake during acidosis. These studies indicate that glucocorticoids regulate acid-base homeostasis during metabolic acidosis in part by regulating expression of the System N transporter SNAT3.

Glucocorticoid-induced insulin resistance in skeletal muscles: defects in insulin signalling and the effects of a selective glycogen synthase kinase-3 inhibitor

Treatment with glucocorticoids, especially at high doses, induces insulin resistance. The aims of the present study were to identify the potential defects in insulin signalling that contribute to dexamethasone-induced insulin resistance in skeletal muscles, and to investigate whether the glycogen synthase-3 (GSK-3) inhibitor CHIR-637 could restore insulin-stimulated glucose metabolism. Skeletal muscles were made insulin-resistant by treating male Wistar rats with dexamethasone, a glucocorticoid analogue, for 12 days. Insulin-stimulated glucose uptake, glycogen synthesis and insulin signalling were studied in skeletal muscles in vitro. Dexamethasone treatment decreased the ability of insulin to stimulate glucose uptake, glycogen synthesis and glycogen synthase fractional activity. In addition, the dephosphorylation of glycogen synthase by insulin was blocked. These defects were paralleled by reduced insulin-stimulated protein kinase B (PKB) and GSK-3 phosphorylation. While expression of PKB, GSK-3 and glycogen synthase was not reduced by dexamethasone treatment, expression of the p85alpha subunit of phosphatidylinositol 3-kinase (PI 3-kinase) was increased. Inhibition of GSK-3 by CHIR-637 increased glycogen synthase fractional activity in soleus muscle from normal and dexamethasone-treated rats, although the effect was more pronounced in control rats. CHIR-637 did not improve insulin-stimulated glucose uptake in muscles from dexamethasone-treated rats. We demonstrated that chronic dexamethasone treatment impairs insulin-stimulated PKB and GSK-3 phosphorylation, which may contribute to insulin resistance in skeletal muscles. Acute pharmacological inhibition of GSK-3 activated glycogen synthase in muscles from dexamethasone-treated rats, but GSK-3 inhibition did not restore insulin-stimulated glucose uptake.

Contraction activates glucose uptake and glycogen synthase normally in muscles from dexamethasone-treated rats

Glucocorticoids cause insulin resistance in skeletal muscle. The aims of the present study were to investigate the effects of contraction on glucose uptake, insulin signaling, and regulation of glycogen synthesis in skeletal muscles from rats treated with the glucocorticoid analog dexamethasone (1 mg x kg(-1) x day(-1) ip for 12 days). Insulin resistance in dexamethasone-treated rats was confirmed by reduced insulin-stimulated glucose uptake (approximately 35%), glycogen synthesis (approximately 70%), glycogen synthase activation (approximately 80%), and PKB Ser(473) phosphorylation (approximately 40%). Chronic dexamethasone treatment did not impair glucose uptake during contraction in soleus or epitrochlearis muscles. In epitrochlearis (but not in soleus), the presence of insulin during contraction enhanced glucose uptake to similar levels in control and dexamethasone-treated rats. Contraction also increased glycogen synthase fractional activity and dephosphorylated glycogen synthase at Ser(645), Ser(649), Ser(653), and Ser(657) normally in muscles from dexamethasone-treated rats. After contraction, insulin-stimulated glycogen synthesis was completely restored in epitrochlearis and improved in soleus from dexamethasone-treated rats. Contraction did not increase insulin-stimulated PKB Ser(473) or glycogen synthase kinase-3 (GSK-3) phosphorylation. Instead, contraction increased GSK-3beta Ser(9) phosphorylation in epitrochlearis (but not in soleus) in muscles from control and dexamethasone-treated rats. In conclusion, contraction stimulates glucose uptake normally in dexamethasone-induced insulin resistant muscles. After contraction, insulin's ability to stimulate glycogen synthesis was completely restored in epitrochlearis and improved in soleus from dexamethasone-treated rats.