Olanzapine's effects on hypothalamic transcriptomics and kinase activity.

Olanzapine is a second-generation antipsychotic that disrupts metabolism and is associated with an increased risk of type 2 diabetes. The hypothalamus is a key region in the control of whole-body metabolic homeostasis. The objective of the current study was to determine how acute peripheral olanzapine administration affects transcription and serine/threonine kinase activity in the hypothalamus. Hypothalamus samples from rats were collected following the pancreatic euglycemic clamp, thereby allowing us to study endpoints under steady state conditions for plasma glucose and insulin. Olanzapine stimulated pathways associated with inflammation, but diminished pathways associated with the capacity to combat endoplasmic reticulum stress and G protein-coupled receptor activity. These pathways represent potential targets to reduce the incidence of type 2 diabetes in patients taking antipsychotics.

Effects of acute olanzapine exposure on central insulin-mediated regulation of whole body fuel selection and feeding.

The use of antipsychotics is associated with severe disruptions in whole body glucose and lipid metabolism which may in part occur through the central nervous system and impaired insulin action at the brain. Here we investigated whether olanzapine treatment might also affect the ability of central insulin treatment to regulate food intake and fuel preference in the light and dark cycle. Male Sprague-Dawley rats were treated with olanzapine (or vehicle solution; 3 mg/kg, subcutaneous) and a simultaneous acute intracerebral ventricular (ICV) infusion of insulin (or vehicle; 3 µL at 10mU; ICV) at the beginning of the 12-h light and dark cycles. Olanzapine treatment reduced RER in the dark and light phases (most consistently in the 4-hours post-treatment), while ICV insulin reduced average RER predominantly in the dark phase, but also at the end of the light cycle. The RER lowering effect of ICV-insulin during the light cycle was absent in the group co-administered olanzapine. The reduction in RER during the dark phase was mirrored by decreased food intake with ICV insulin, but not olanzapine treated rats. The reduction in food intake by ICV-insulin was abolished in rats co-administered olanzapine suggesting rapid induction of central insulin resistance. A combination of ICV-insulin and olanzapine similarly reduced RER in the dark phase, independent of changes in food intake. Olanzapine treatment, alone or in combination with ICV-insulin, significantly reduced VCO2 at regular intervals in the dark phase (specifically 3 h post-treatment), while VO2 was not significantly altered by either treatment. Finally, heat production was increased by olanzapine treatment in the light phase, though this effect was not consistent. The findings confirm that acute olanzapine treatment directly reduces RER and suggest that treatment with this drug may also override central insulin-mediated reductions in food intake at the hypothalamus (while still independently favoring fatty acid oxidation). Acute central insulin similarly reduces RER, but in contrast to olanzapine, this may represent a physiologically appropriate response to reduction in food intake.

Resveratrol prevents insulin resistance caused by short-term elevation of free fatty acids in vivo.

Elevated levels of plasma free fatty acids (FFA), which are commonly found in obesity, induce insulin resistance. FFA activate protein kinases including the proinflammatory IκBα kinase ß (IKKß), leading to serine phosphorylation of insulin receptor substrate 1 (IRS-1) and impaired insulin signaling. To test whether resveratrol, a polyphenol found in red wine, prevents FFA-induced insulin resistance, we used a hyperinsulinemic-euglycemic clamp with a tracer to assess hepatic and peripheral insulin sensitivity in overnight-fasted Wistar rats infused for 7 h with saline, Intralipid plus 20 U·mL(-1) heparin (IH; triglyceride emulsion that elevates FFA levels in vivo; 5.5 µL·min(-1)) with or without resveratrol (3 mg·kg(-1)·h(-1)), or resveratrol alone. Infusion of IH significantly decreased glucose infusion rate (GIR; P < 0.05) and peripheral glucose utilization (P < 0.05) and increased endogenous glucose production (EGP; P < 0.05) during the clamp compared with saline infusion. Resveratrol co-infusion, however, completely prevented the effects induced by IH infusion: it prevented the decreases in GIR (P < 0.05 vs. IH), peripheral glucose utilization (P < 0.05 vs. IH), and insulin-induced suppression of EGP (P < 0.05 vs. IH). Resveratrol alone had no effect. Furthermore, IH infusion increased serine (307) phosphorylation of IRS-1 in soleus muscle (∼30-fold, P < 0.001), decreased total IRS-1 levels, and decreased IκBα content, consistent with activation of IKKß. Importantly, all of these effects were abolished by resveratrol (P < 0.05 vs. IH). These results suggest that resveratrol prevents FFA-induced hepatic and peripheral insulin resistance and, therefore, may help mitigate the health consequences of obesity.

Effect of N-acetyl-l-cysteine on insulin resistance caused by prolonged free fatty acid elevation.

Circulating free fatty acids (FFAs) are elevated in obesity and cause insulin resistance. The objective of the current study was to determine whether the antioxidant N-acetyl-l-cysteine (NAC) prevented hepatic and peripheral insulin resistance caused by prolonged elevation of plasma FFAs. Chronically cannulated Wistar rats received saline (SAL), Intralipid plus heparin (IH), IH plus NAC, or NAC i.v. infusion for 48 h. Insulin sensitivity was determined using the hyperinsulinemic-euglycemic clamp with tritiated glucose tracer. IH induced hepatic and peripheral insulin resistance (P<0.05). NAC co-infusion did not prevent insulin resistance in the liver, although it was able to prevent peripheral insulin resistance. Prolonged IH infusion did not appear to induce oxidative stress in the liver because hepatic content of protein carbonyl, malondialdehyde, and reduced to oxidized glutathione ratio did not differ across treatment groups. In alignment with our insulin sensitivity results, IH augmented skeletal muscle protein carbonyl content and this was prevented by NAC co-infusion. Taken together, our results indicate that oxidative stress mediates peripheral, but not hepatic, insulin resistance resulting from prolonged plasma FFA elevation. Thus, in states of chronic plasma FFA elevation, such as obesity, antioxidants may protect against peripheral but not hepatic insulin resistance.

In vivo effects of polyunsaturated, monounsaturated, and saturated fatty acids on hepatic and peripheral insulin sensitivity.

OBJECTIVE: Free fatty acids (FFAs) cause insulin resistance and are often elevated in obesity. Chronic ingestion of diets rich in saturated fat induces more insulin resistance than diets rich in unsaturated fat, however, it remains unclear whether different FFAs cause distinct levels of insulin resistance in the short-term, which is relevant to the feeding and fasting cycle. Protein kinase C (PKC)-δ is implicated in hepatic insulin resistance. Therefore, we investigated the effects of short-term elevation of fatty acids with different degrees of unsaturation on hepatic insulin action and liver PKC-δ membrane translocation, a marker of activation. MATERIALS/METHODS: Triglyceride emulsions of Soybean Oil+Heparin (polyunsaturated (POLY)), Olive Oil+Heparin (monounsaturated (MONO)), Lard Oil+Heparin (saturated (SATU)), or saline (SAL) were infused intravenously for 7h to elevate plasma FFA concentrations ~3-4 fold in rats. During the last 2h of infusion, a hyperinsulinemic-euglycemic clamp with tritiated glucose methodology was performed to examine hepatic and peripheral insulin sensitivity. RESULTS: Surprisingly, SATU, MONO, and POLY impaired peripheral insulin sensitivity (glucose utilization divided by insulin) to a similar extent. Furthermore, all lipids induced a similar degree of hepatic insulin resistance compared to SAL. Although there were changes in hepatic content of lipid metabolites, there were no significant differences in liver PKC-δ membrane translocation across fat groups. CONCLUSIONS: In summary, in the short-term, FFAs with different degrees of unsaturation impair peripheral insulin sensitivity and induce hepatic insulin resistance as well as hepatic PKC-δ translocation to the same extent.

Maternal taurine supplementation in rats partially prevents the adverse effects of early-life protein deprivation on ß-cell function and insulin sensitivity.

Dietary protein restriction during pregnancy and lactation in rats impairs ß-cell function and mass in neonates and leads to glucose intolerance in adult offspring. Maternal taurine (Tau) supplementation during pregnancy in rats restores ß-cell function and mass in neonates, but its long-term effects are unclear. The prevention of postnatal catch-up growth has been suggested to improve glucose tolerance in adult offspring of low-protein (LP)-fed mothers. The objective of this study was to examine the relative contribution of ß-cell dysfunction and insulin resistance to impaired glucose tolerance in 130-day-old rat offspring of LP-fed mothers and the effects of maternal Tau supplementation on ß-cell function and insulin resistance in these offspring. Pregnant rats were fed i) control, ii) LP, and iii) LP+Tau diets during gestation and lactation. Offspring were given a control diet following weaning. A fourth group consisting of offspring of LP-fed mothers, maintained on a LP diet following weaning, was also studied (LP-all life). Insulin sensitivity in the offspring of LP-fed mothers was reduced in females but not in males. In both genders, LP exposure decreased ß-cell function. Tau supplementation improved insulin sensitivity in females and ß-cell function in males. The LP-all life diet improved ß-cell function in males. We conclude that i) maternal Tau supplementation has persistent effects on improving glucose metabolism (ß-cell function and insulin sensitivity) in adult rat offspring of LP-fed mothers and ii) increasing the amount of protein in the diet of offspring adapted to a LP diet after weaning may impair glucose metabolism (ß-cell function) in a gender-specific manner.

Duration of rise in free fatty acids determines salicylate's effect on hepatic insulin sensitivity.

We have shown in rats that sodium salicylate (SS), which inhibits IkBa kinase B (IKKB), prevents hepatic and peripheral insulin resistance caused by short-term (7  h) i.v. administration of Intralipid and heparin (IH). We wished to further determine whether this beneficial effect of SS persisted after prolonged (48  h) IH infusion, which better mimics the chronic free fatty acid (FFA) elevation of obesity. Hence, we performed hyperinsulinemic euglycemic clamps with tritiated glucose methodology to determine hepatic and peripheral insulin sensitivity in rats infused with saline, IH, IH and SS, or SS alone. SS prevented peripheral insulin resistance (P<0.05) caused by prolonged plasma FFA elevation; however, it did not prevent hepatic insulin resistance. In skeletal muscle, protein levels of phospho-IkBa were augmented by prolonged IH administration and this was prevented by SS, suggesting that IH activates while SS prevents the activation of IKKB. Markers of IKKB activation, namely protein levels of phospho-IkBa and IkBa, indicated that IKKB is not activated in the liver after prolonged FFA elevation. Phosphorylation of serine 307 at insulin receptor substrate (IRS)-1, which is a marker of proximal insulin resistance, was not altered by IH administration in the liver, suggesting that this is not a site of hepatic insulin resistance in the prolonged lipid infusion model. Our results suggest that the role of IKKB in fat-induced insulin resistance is time and tissue dependent and that hepatic insulin resistance induced by prolonged lipid elevation is not due to an IRS-1 serine 307 kinase.

Susceptibility to fatty acid-induced ß-cell dysfunction is enhanced in prediabetic diabetes-prone biobreeding rats: a potential link between ß-cell lipotoxicity and islet inflammation.

ß-Cell lipotoxicity is thought to play an important role in the development of type 2 diabetes. However, no study has examined its role in type 1 diabetes, which could be clinically relevant for slow-onset type 1 diabetes. Reports of enhanced cytokine toxicity in fat-laden islets are consistent with the hypothesis that lipid and cytokine toxicity may be synergistic. Thus, ß-cell lipotoxicity could be enhanced in models of autoimmune diabetes. To determine this, we examined the effects of prolonged free fatty acids elevation on ß-cell secretory function in the prediabetic diabetes-prone BioBreeding (dp-BB) rat, its diabetes-resistant BioBreeding (dr-BB) control, and normal Wistar-Furth (WF) rats. Rats received a 48-h iv infusion of saline or Intralipid plus heparin (IH) (to elevate free fatty acid levels ~2-fold) followed by hyperglycemic clamp or islet secretion studies ex vivo. IH significantly decreased ß-cell function, assessed both by the disposition index (insulin secretion corrected for IH-induced insulin resistance) and in isolated islets, in dp-BB, but not in dr-BB or WF, rats, and the effect of IH was inhibited by the antioxidant N-acetylcysteine. Furthermore, IH significantly increased islet cytokine mRNA and plasma cytokine levels (monocyte chemoattractant protein-1 and IL-10) in dp-BB, but not in dr-BB or WF, rats. All dp-BB rats had mononuclear infiltration of islets, which was absent in dr-BB and WF rats. In conclusion, the presence of insulitis was permissive for IH-induced ß-cell dysfunction in the BB rat, which suggests a link between ß-cell lipotoxicity and islet inflammation.

Short-term oral α-lipoic acid does not prevent lipid-induced dysregulation of glucose homeostasis in obese and overweight nondiabetic men.

Prolonged elevation of plasma free fatty acids (FFAs) induces insulin resistance and impairs pancreatic ß-cell adaptation to insulin resistance. The mechanisms whereby lipid induces these impairments are not fully defined but may involve oxidative stress, inflammation, and endoplasmic reticulum stress. α-Lipoic acid (ALA), a commonly used health supplement with antioxidant, anti-inflammatory, and AMPK-activating properties, has been shown to have therapeutic value in type 2 diabetes and its complications. Here we examined the effects of ALA on insulin sensitivity and secretion in humans under the conditions of 24-h iv lipid infusion to elevate plasma FFAs. Eight overweight and obese male subjects underwent four randomized studies each, 4-6 wk apart: 1) SAL, 2-wk oral placebo followed by 24-h iv infusion of saline; 2) IH, 2-wk placebo followed by 24-h iv infusion of intralipid plus heparin to raise plasma FFAs approximately twofold; 3) IH + ALA, 2-wk ALA (1,800 mg/day) followed by 24-h infusion of intralipid plus heparin; and 4) ALA, 2-wk ALA followed by 24-h infusion of saline. Insulin secretion rates (ISR) and insulin sensitivity were assessed with a 2-h, 20-mmol/l hyperglycemic clamp and a hyperinsulinemic euglycemic clamp, respectively. ISR was not significantly different between treatments. Lipid infusion impaired insulin sensitivity with and without ALA pretreatment. These results indicate that ALA, administered orally at this dose for 2 wk, does not protect against lipid-induced insulin resistance in overweight and obese humans.

The effect of high-dose sodium salicylate on chronically elevated plasma nonesterified fatty acid-induced insulin resistance and ß-cell dysfunction in overweight and obese nondiabetic men.

Prolonged elevation of plasma nonesterified fatty acids (NEFA) induces insulin resistance and impairs pancreatic ß-cell adaptation to insulin resistance. Studies in rodents suggest that inflammation may play a role in this "lipotoxicity." We studied the effects of sodium salicylate, an anti-inflammatory agent, on lipid-induced alterations in ß-cell function and insulin sensitivity in six overweight and obese nondiabetic men. Each subject underwent four separate studies, 4-6 wk apart, in random order: 1) SAL, 1-wk placebo followed by intravenous (iv) infusion of saline for 48 h; 2) IH, 1-wk placebo followed by iv infusion of intralipid plus heparin for 48 h to raise plasma NEFA approximately twofold; 3) IH + SS, 1-wk sodium salicylate (4.5 g/day) followed by 48-h IH infusion; and 4) SS, 1-wk oral sodium salicylate followed by 48-h saline infusion. After 48-h saline or lipid infusion, insulin secretion and sensitivity were assessed by hyperglycemic clamp and euglycemic hyperinsulinemic clamp, respectively, in sequential order. Insulin sensitivity was reduced by lipid infusion (IH = 67% of SAL) and was not improved by salicylate (IH + SS = 56% of SAL). Lipid infusion also reduced the disposition index (P < 0.05), which was not prevented by sodium salicylate. Salicylate reduced insulin clearance. These data suggest that oral sodium salicylate at this dose impairs insulin clearance but does not ameliorate lipid-induced insulin resistance and ß-cell dysfunction in overweight and obese nondiabetic men.

High multivitamin intake by Wistar rats during pregnancy results in increased food intake and components of the metabolic syndrome in male offspring.

The effect of high multivitamin intake during pregnancy on the metabolic phenotype of rat offspring was investigated. Pregnant Wistar rats (n=10 per group) were fed the AIN-93G diet with the recommended vitamin (RV) content or a 10-fold increase [high vitamin (HV) content]. In experiment 1, male and female offspring were followed for 12 wk after weaning; in experiment 2, only males were followed for 28 wk. Body weight (BW) was measured weekly. Every 4 wk, after an overnight fast, food intake over 1 h was measured 30 min after a gavage of glucose or water. An oral glucose tolerance test was performed every 3-5 wk. Postweaning fasting glucose, insulin, ghrelin, glucagon-like peptide-1, and systolic blood pressure were measured. No difference in BW at birth or litter size was observed. Food intake was greater in males born to HV dams (P<0.05), and at 28 wk after weaning, BW was 8% higher (P<0.05) and fat pad mass was 27% higher (P<0.05). Food intake reduction after the glucose preload was nearly twofold less in males born to HV dams at 12 wk after weaning (P<0.05). Fasting glucose, insulin, and ghrelin were 11%, 62%, and 41% higher in males from HV dams at 14 wk after weaning (P<0.05). Blood glucose response was 46% higher at 23 wk after weaning (P<0.01), and systolic blood pressure was 16% higher at 28 wk after weaning (P<0.05). In conclusion, high multivitamin intake during pregnancy programmed the male offspring for the development of the components of metabolic syndrome in adulthood, possibly by its effects on central mechanisms of food intake control.

Vasopeptidase inhibitor omapatrilat induces profound insulin sensitization and increases myocardial glucose uptake in Zucker fatty rats: Studies comparing a vasopeptidase inhibitor, angiotensin-converting enzyme inhibitor, and angiotensin II type I receptor blocker.

BACKGROUND: ACE inhibitors (ACEIs) improve insulin resistance and prevent type 2 diabetes, possibly mediated by inhibition of bradykinin (BK) degradation. The vasopeptidase inhibitor omapatrilat (OMA) raises BK to a greater extent than ACEIs by dual enzyme inhibition, whereas its insulin-sensitizing effects and mechanisms have not been investigated. METHODS AND RESULTS: We compared the insulin-sensitizing effects of OMA, ramipril (an ACEI), losartan (an angiotensin II type 1 receptor blocker), and placebo by 2-step euglycemic hyperinsulinemic clamp in insulin-resistant Zucker fatty rats (n=6 to 7 in each group). OMA resulted in a lower rate of endogenous glucose production than placebo at baseline (35+/-5 versus 54+/-4 mmol x kg(-1) x min(-1), P<0.01), greater suppression of endogenous glucose production by low-dose insulin (73+/-11% versus 27+/-18%, P<0.05), and greater glucose disposal at high-dose insulin (135+/-5 versus 92+/-4 mmol x kg(-1) x min(-1), P<0.01). Ramipril tended to improve insulin sensitivity, but losartan did not. OMA significantly increased 2-deoxyglucose uptake by myocardium, fat, and skeletal muscle. Ramipril increased 2-deoxyglucose uptake only by some skeletal muscles, but losartan did not. The insulin-sensitizing effects of OMA were blocked significantly by HOE-140 (a BK, B2 receptor antagonist) and NG-nitro-L-arginine methyl ester (a nitric oxide synthase inhibitor) in all tissues except myocardium. CONCLUSIONS: OMA induces profound insulin sensitization and increases myocardial glucose uptake in Zucker fatty rats. This effect is greater than that of ramipril and probably occurs at least in part via stimulation of the B2 receptor. OMA has the potential for greater type 2 diabetes prevention than ACEI.

The composition of dietary fat directly influences glucose-stimulated insulin secretion in rats.

Acute elevations of plasma free fatty acid (FFA) levels augment glucose-stimulated insulin secretion (GSIS). Prolonged elevations of FFA levels reportedly impair GSIS, but no one has previously compared GSIS after prolonged exposure to saturated or unsaturated fat. Rats received a low-fat diet (Low-Fat) or one enriched with either saturated (Lard) or unsaturated fat (Soy) for 4 weeks. Insulin responses during hyperglycemic clamps were augmented by saturated but not unsaturated fat (580 +/- 25, 325 +/- 30, and 380 +/- 50 pmol x l(-1) x min(-1) in Lard, Soy, and Low-Fat groups, respectively). Despite hyperinsulinemia, the amount of glucose infused was lower in the Lard compared with the Low-Fat group. Separate studies measured GSIS from the perfused pancreas. Without fatty acids in the perfusate, insulin output in the Lard group (135 +/- 22 ng/30 min) matched that of Low-Fat rats (115 +/- 13 ng/30 min), but exceeded that of Soy rats (80 +/- 7 ng/30 min). When FFAs in the perfusate mimicked the quantity and composition of plasma FFAs in intact animals, in vivo insulin secretory patterns were restored. Because the GSIS of rats consuming Lard diets consistently exceeded that of the Soy group, we also assessed responses after 48-h infusions of lard or soy oil. Again, lard oil exhibited greater insulinotropic potency. These data indicate that prolonged exposure to saturated fat enhances GSIS (but this does not entirely compensate for insulin resistance), whereas unsaturated fat, given in the diet or by infusion, impairs GSIS. Inferences regarding the impact of fatty acids on GSIS that are based on models using unsaturated fat may not reflect the effects of saturated fat.