Serum glucose, insulin and C-peptide response to oral glucose after intravenous administration of hydrocortisone and methylprednisolone in man

Molecular Mechanisms of Glucocorticoid-Induced Insulin Resistance

Glucocorticoids (GCs) are steroids secreted by the adrenal cortex under the hypothalamic-pituitary-adrenal axis control, one of the major neuro-endocrine systems of the organism. These hormones are involved in tissue repair, immune stability, and metabolic processes, such as the regulation of carbohydrate, lipid, and protein metabolism. Globally, GCs are presented as ‘flight and fight’ hormones and, in that purpose, they are catabolic hormones required to mobilize storage to provide energy for the organism. If acute GC secretion allows fast metabolic adaptations to respond to danger, stress, or metabolic imbalance, long-term GC exposure arising from treatment or Cushing’s syndrome, progressively leads to insulin resistance and, in fine, cardiometabolic disorders. In this review, we briefly summarize the pharmacological actions of GC and metabolic dysregulations observed in patients exposed to an excess of GCs. Next, we describe in detail the molecular mechanisms underlying GC-induced insulin resistance in adipose tissue, liver, muscle, and to a lesser extent in gut, bone, and brain, mainly identified by numerous studies performed in animal models. Finally, we present the paradoxical effects of GCs on beta cell mass and insulin secretion by the pancreas with a specific focus on the direct and indirect (through insulin-sensitive organs) effects of GCs. Overall, a better knowledge of the specific action of GCs on several organs and their molecular targets may help foster the understanding of GCs’ side effects and design new drugs that possess therapeutic benefits without metabolic adverse effects.

Twenty-four-hour profiles of plasma glucose, insulin, C-peptide and free fatty acid in subjects with varying degrees of glucose tolerance following short-term, medium-dose prednisone (20 mg/day) treatment: evidence for differing effects on insulin secretion and action

OBJECTIVE

To determine the time course and prandial effects of short-term, medium-dose prednisone on 24-h metabolic patterns under standardized conditions.

CONTEXT

Glucocorticoids (GCs) adversely affect glucose homoeostasis but 24-h profiles of glucose, insulin, C-peptide and free fatty acids (FFAs) following short-term, medium-dose prednisone treatment in persons with varying degrees of glucose tolerance are not well defined.

DESIGN

An open-label cross-sectional interventional study.

SUBJECTS

Three groups were prospectively studied: persons with type 2 diabetes (T2DM; n = 7), persons 'at risk' for T2DM (AR; n = 8) and persons with normal glucose tolerance (NGT; n = 5).

METHODS

Before and after 3-day treatment with prednisone 20 mg each morning, subjects underwent 24-h frequent blood sampling. Eucaloric mixed meals were provided at 08:00, 12:00 and 18:00 h. Insulin/glucose ratio provided an estimate of β-cell response to meal stimuli.

MEASUREMENTS

Plasma glucose, insulin, C-peptide, haemoglobin A1c and FFA.

RESULTS

Prednisone induced greater increases in glucose levels from midday (P = 0·001) to midnight (P = 0·02) in the T2DM than the AR and NGT groups. In contrast, insulin (P = 0·03) and C-peptide (P = 0·04) levels decreased postbreakfast in the T2DM group, whereas no changes in the morning but higher C-peptide levels (P = 0·03) from midday to midnight were observed in the AR group. In the T2DM group, insulin/glucose ratio decreased postbreakfast (P = 0·04) and increased postdinner (P = 0·03). Fasting glucose, insulin and C-peptide levels were unchanged in all groups, and FFA levels modestly increased postdinner (P = 0·03) in the NGT group.

CONCLUSION

Short-term, medium-dose prednisone treatment induces postprandial hyperglycaemia in T2DM and AR predominantly from midday to midnight because of suppression of insulin secretion followed by decreased insulin action that dissipates overnight. Effective treatment of prednisone-induced hyperglycaemia should target both rapid onset relative insulin deficiency and a less than 24-h total duration of effect.

Corticoadrenal activity in rat regulates betaine-homocysteine S-methyltransferase expression with opposite effects in liver and kidney

Betaine-homocysteine S-methyltransferase (BHMT) is an enzyme that converts homocysteine (Hcy) to methionine using betaine as a methyl donor. Betaine also acts as osmolyte in kidney medulla, protecting cells from high extracellular osmolarity. Hepatic BHMT expression is regulated by salt intake. Hormones, particularly corticosteroids, also regulate BHMT expression in rat liver. We investigated to know whether the corticoadrenal activity plays a role in kidney BHMT expression. BHMT activity in rat kidneys is several orders of magnitude lower than in rat livers and only restricted to the renal cortex. This study confirms that corticosteroids stimulate BHMT activity in the liver and, for the first time in an animal model, also up-regulate the BHMT gene expression. Besides, unlike the liver, corticosteroids in rat kidney down-regulate BHMT expression and activity. Given that the classical effect of adrenocortical activity on the kidney is associated with sodium and water re-absorption by the distal tubule leading to volume expansion, by promoting lesser use of betaine as a methyl donor, corticosteroids would preserve betaine for its other role as osmoprotectant against changes in the extracellular osmotic conditions. We conclude that corticosteroids are, at least in part, responsible for the inhibition of BHMT expression and activity in rat kidneys.

Effects of antenatal steroids on ischemic brain injury in near-term ovine fetuses

BACKGROUND

Hypoxia/ischemia in utero can result in brain damage to the fetus and newborn. Antenatal steroids are a routine part of the management of women who develop premature labor. Pretreatment of young postnatal rats with dexamethasone before hypoxic/ischemic insults has been reported to attenuate brain injury. However, the effects of antenatal steroids on ischemic brain injury in fetuses have not been investigated.

OBJECTIVE

We examined the effects of maternally administered antenatal corticosteroids on ischemic brain injury in near-term ovine fetuses.

METHODS

Chronically instrumented fetuses at 122 days of gestation were studied 12 h after the last of four 4 mg dexamethasone, or placebo injections were given over 48 h to the ewes. Groups were dexamethasone/ischemic, placebo/ischemic and sham-treated control. Fetuses were exposed to 30 min of carotid occlusion (ischemia) or no occlusion (control) and 72 h of reperfusion. Whole brain coronal sections stained with Luxol fast blue-hematoxylin-eosin were scored for white matter and cerebral cortical lesions. Both areas received pathological scores of 0 to 5 reflecting the degree of injury (0=0%, 1=1-10%, 2=11-50%, 3=51-90%, 4=91-99% and 5=100%). Bilateral carotid blood flow also was measured before, during and after brain ischemia in the dexamethasone/ischemic and placebo/ischemic groups.

RESULTS

White matter (WM) and cerebral cortical scores did not differ between the dexamethasone/ischemic and placebo/ischemic (WM: 3.0+/-1.9 and 2.9+/-1.7; cortex: 3.1+/-1.7 and 2.6+/-1.8, mean+/-S.D.) groups. White matter and cerebral cortical scores were higher in the dexamethasone/ischemic (WM: 3.0+/-1.9, P<0.02; cortex: 3.1+/-1.7, P<0.005) and placebo/ischemic (WM: 2.9+/-1.7, P<0.006; cortex: 2.6+/-1.8, P<0.007) than control (WM: 0.2+/-0.4; cortex: 0.2+/-0.4) group. Carotid blood flow was relatively higher (P<0.05) after 24, 48 and 72 h of reperfusion in the dexamethasone/ischemic than placebo/ischemic group.

CONCLUSIONS

We conclude that maternal pretreatment with antenatal dexamethasone did not attenuate ischemic brain injury in the fetus, and that carotid blood flow was higher during reperfusion in fetuses of dexamethasone than placebo-treated ewes, most likely secondary to decreases in arterial oxygen tension.

Effects of postnatal dexamethasone on blood-brain barrier permeability and brain water content in newborn lambs

We showed that antenatal corticosteroids reduced blood-brain barrier permeability in fetuses at 60 and 80%, but not 90% of gestation, and decreased brain water content in fetuses. Our objective was to examine the effects of postnatal corticosteroids on regional blood-brain barrier permeability and brain water content in newborn lambs. Three dexamethasone treatment groups were studied in 3- to 5-day-old lambs. A 0.01 mg/kg dose was selected to estimate the amount of dexamethasone that might have reached fetuses via antenatal treatment of ewes in our previous studies. The other doses (0.25 and 0.5 mg/kg) were chosen to approximate those used clinically to treat infants with bronchopulmonary dysplasia. Lambs were randomly assigned to receive four intramuscular injections of dexamethasone or placebo given 12 h apart on days 3 and 4 of age. Blood-brain barrier function was measured with the blood-to-brain transfer constant (K(i)) to alpha-aminoisobutyric acid, brain plasma volume was measured with polyethylene glycol for the calculation of K(i,) and brain water was measured by wet-to-dry tissue weights. Postnatal treatment with corticosteroids did not reduce barrier permeability in newborn lambs. Brain blood volume was higher in the 0.25 and 0.5 mg/kg dose dexamethasone groups than in the placebo group. Brain water content did not differ among the groups. We conclude that postnatal treatment with corticosteroids did not reduce regional blood-brain barrier permeability or brain water content but increased the brain plasma volume in newborn lambs. These findings are consistent with our previous work indicating that barrier permeability is responsive to corticosteroids at 60 and 80% of gestation and brain water regulation at 60% of gestation, but not in near-term fetuses or newborn lambs.

Exogenous and endogenous corticosteroids modulate blood-brain barrier development in the ovine fetus

We previously reported decreases in blood-brain barrier permeability in the ovine fetus at 80% of gestation after antenatal corticosteroids and shown that permeability is not reduced in newborn lambs after postnatal corticosteroids. We now test the hypotheses that exogenous antenatal corticosteroids decrease blood-brain barrier permeability at 60% but not 90% of gestation in ovine fetuses and that endogenous increases in plasma cortisol concentrations are associated with ontogenic decreases in barrier permeability during gestation. Chronically instrumented ovine fetuses were studied 12 h after the last of four 6-mg dexamethasone or placebo injections were given 12 h apart over 48 h to ewes. Fetuses at 80% of gestation from placebo-treated ewes studied under the same protocol were also included. Blood-brain barrier function was quantified with the blood-to-brain transfer constant (K(i)) to alpha-aminoisobutyric acid. K(i) values were lower in cerebral cortex, caudate nucleus, hippocampus, superior colliculus, thalamus, medulla, and cervical spinal cord in fetuses of dexamethasone- than placebo-treated ewes at 60% but not 90% of gestation. Regional brain K(i) values demonstrated inverse correlations with increases in gestation and plasma cortisol concentrations in most brain regions. We conclude that maternal treatment with exogenous corticosteroids was associated with decreases in blood-brain barrier permeability at 60% but not 90% of gestation and that increases in gestation and endogenous cortisol concentrations were associated with ontogenic decreases in barrier permeability during fetal development.

Acute methylprednisolone administration induces a transient alteration of glucose tolerance and pyruvate dehydrogenase in humans

BACKGROUND

Glucocorticoid administration induces alteration of glucose tolerance, and impairment of glucose oxidation may contribute to glucocorticoid-induced derangement of glucose metabolism. We investigated glucose tolerance following methylprednisolone administration in humans. In the same model, we evaluated pyruvate dehydrogenase (PDH), the rate limiting enzyme of glucose oxidation, in peripheral blood mononuclear cells.

MATERIALS AND METHODS

Methylprednisolone (2 x 40 mg, iv, one dose every 12 h) was administered to six healthy volunteers. Glucose tolerance was evaluated through an oral glucose tolerance test (oGTT, 75 g glucose) at least a week before and after drug administration (2 and 24 h post-drug). To assess modifications of lipid metabolism circulating free fatty acids (FFA) and glycerol were measured, during fasting and oGTT. The active form of PDH (PDHa) was evaluated in peripheral blood mononuclear cells, both as ex vivo activity and as in vitro response to insulin (30 pmol l-1).

RESULTS

Methylprednisolone induced an alteration of glucose tolerance 2 h after its administration. Such alteration was completely reversed at 24 h. Alteration of glucose tolerance was accompanied by decreased ex vivo PDHa activity. PDH responsiveness to insulin in vitro was also impaired. Circulating FFA were unmodified, but decreased glycerol levels suggested a slight inhibition of lipolysis.

CONCLUSIONS

Acute methylprednisolone administration in humans induced a transient decrease of glucose tolerance 2 h after drug administration, accompanied by hyperinsulinaemia, inhibition of ex vivo PDH activity and its response to insulin in vitro. These alterations were completely abolished at 24 h, suggesting that methylprednisolone can be safely administered acutely. Furthermore, methylprednisolone induced only minor modifications of circulating FFA and glycerol, indicating minimal impact on lipid metabolism.

Antenatal steroids decrease blood-brain barrier permeability in the ovine fetus

Antenatal corticosteroid therapy reduces the incidence of intraventricular hemorrhage in premature infants. Enhanced microvascular integrity might provide protection against intraventricular hemorrhage. In the adult, there is evidence to suggest that the blood-brain barrier may be under hormonal control. We hypothesized that antenatal corticosteroids decrease blood-brain barrier permeability in the preterm ovine fetus. Chronically instrumented 120-day-gestation fetuses were studied 12 h after the last of four 6-mg dexamethasone (n = 5) or placebo (n = 6) injections had been given over 48 h to the ewes. Blood-brain barrier function was quantified with the blood-to-brain transfer constant (Ki) for alpha-aminoisobutyric acid (AIB). Ki was significantly lower across brain regions in the fetuses of ewes that received antenatal dexamethasone compared with placebo (ANOVA; interaction, F = 2.54, P < 0.004). In fetuses of dexamethasone- and placebo-treated ewes, Ki (microliter . g brain wt-1. min-1, mean +/- SD) was, respectively, 2.43 +/- 0.27 vs. 3.41 +/- 0.74 in the cortex, 4.46 +/- 0.49 vs. 5.29 +/- 0.85 in the cerebellum, and 3.70 +/- 0.49 vs. 5.11 +/- 0.70 in the medulla. We conclude that antenatal treatment with corticosteroids reduces blood-brain permeability in the ovine fetus.

Kinetics of dexamethasone-induced alterations of glucose metabolism in healthy humans

Six healthy human subjects were studied during three 75-g oral, [13C]glucose tolerance tests to assess the kinetics of dexamethasone-induced impairment of glucose tolerance. On one occasion, they received dexamethasone (4 x 0.5 mg/day) during the previous 2 days. On another occasion, they received a single dose (0. 5 mg) of dexamethasone 150 min before ingestion of the glucose load. On the third occasion, they received a placebo. Postload plasma glucose was significantly increased after both 2 days dexamethasone and single dose dexamethasone compared with control (P < 0.05). This corresponded to a 20-23% decrease in the metabolic clearance rate of glucose, whereas total glucose turnover ([6,6-2H]glucose), total (indirect calorimetry) and exogenous glucose oxidation (13CO2 production), and suppression of endogenous glucose production were unaffected by dexamethasone. Plasma insulin concentrations were increased after 2 days of dexamethasone but not after a single dose of dexamethasone. In a second set of experiments, the effect of a single dose of dexamethasone on insulin sensitivity was assessed in six healthy humans during a 2-h euglycemic hyperinsulinemic clamp. Dexamethasone did not significantly alter insulin sensitivity. It is concluded that acute administration of dexamethasone impairs oral glucose tolerance without significantly decreasing insulin sensitivity.