Increased incidence of hepatic insulin-sensitizing substance (HISS)-dependent insulin resistance in female rats prenatally exposed to ethanol

Hepatalin: the missing link in prediabetes, obesity, and type 2 diabetes

Hepatalin is a hormone secreted by the liver in response to pulses of insulin after a mixed nutrient meal, but only if the liver receives two permissive synergistic feeding signals from the stomach. Hepatalin stimulates glucose uptake and storage as glycogen in skeletal muscle, heart, and kidney but not liver, intestines, or adipocytes. Insulin acts primarily on liver and fat. Reduced hepatalin action results in postprandial hyperglycemia, compensatory elevation of insulin secretion, and a resultant shift in partitioning of nutrient energy storage from glycogen in muscle, to fat. Chronic hepatalin suppression leads to a predictable chronology of dysfunctions, first diagnosable as Absence of Meal-induced Insulin Sensitization (AMIS) which progresses to prediabetes, adiposity, and type 2 diabetes. The focus on nutrient partitioning and the role of hepatalin allows AMIS to be diagnosed, prevented, and treated, including through the use of lifestyle interventions.

A synergistic, balanced antioxidant cocktail, protects aging rats from insulin resistance and absence of meal-induced insulin sensitization (AMIS) syndrome

A series of in vivo and in vitro studies using animal and human models in the past 15 years have demonstrated that approximately 55% (~66% in humans) of the glucose disposal effect of an i.v. injection of insulin in the fed state is dependent on the action of a second hormone, hepatic insulin sensitizing substance (HISS), which is released from the liver and stimulates glucose uptake in muscle, heart and kidneys. Sensitization of the insulin response by a meal through release of HISS is called meal-induced insulin sensitization (MIS). Absence of HISS action results in postprandial hyperglycemia, hyperinsulinemia, hyperlipidemia, adiposity, increased free radical stress and a cluster of progressive metabolic and cardiovascular dysfunctions referred to as the AMIS (absence of meal-induced insulin sensitization) syndrome. Reduced HISS release accounts for the insulin resistance that occurs with aging and is made worse by physical inactivity and diets high in sucrose or fat. This brief review provides an update of major metabolic disturbances associated with aging due to reduction of HISS release, and the protection against these pathological changes in aging animals using a balanced synergistic antioxidant cocktail SAMEC (S-adenosylmethionine, vitamins E and C). The synergy amongst the components is consistent with the known benefits of antioxidants supplied by a mixed diet and acting through diverse mechanisms. Using only three constituents, SAMEC appears suitable as an antioxidant specifically targeting the AMIS syndrome.

Electroacupuncture improves glucose tolerance through cholinergic nerve and nitric oxide synthase effects in rats

The purpose of this investigation was to evaluate the effect and mechanisms of electroacupuncture (EA) at the bilateral Zusanli acupoints (ST-36) on glucose tolerance in normal rats. Intravenous glucose tolerance test (IVGTT) was performed to examine the effects of electroacupuncture (EA) on glucose tolerance in rats. The EA group underwent EA at the ST-36, with settings of 15 Hz, 10 mA, and 60 min; the control group underwent the same treatments, but without EA. Atropine, hemicholinium-3 (HC-3) or NG-nitro-L-arginine methyl ester (L-NAME) were injected into the rats alone or simultaneously and EA was performed to investigate differences in plasma glucose levels compared to the control group. Plasma samples were obtained for assaying plasma glucose and free fatty acid (FFA) levels. Western blot was done to determine the insulin signal protein and nNOS to exam the correlation between EA and improvement in glucose tolerance. The EA group had significantly lower plasma glucose levels compared to the control group. Plasma glucose levels differed significantly between the EA and control groups after the administration of L-NAME, atropine, or HC-3 treatments alone, but there were no significant differences in plasma glucose with combined treatment of L-NAME and atropine or L-NAME and HC-3. EA decreased FFA levels and enhanced insulin signal protein (IRS1) and nNOS activities in skeletal muscle during IVGTT. In summary, EA stimulated cholinergic nerves and nitric oxide synthase for lowering plasma FFA levels to improve glucose tolerance.

Electroacupuncture stimulation using different frequencies (10 and 100 Hz) changes the energy metabolism in induced hyperglycemic rats

PURPOSE: To investigate the effect of 10 and 100 Hz peripheral electro-estimulation (electroacupuncture, EAc) at Zusanli (ST-36) and Zhongwan (CV-12) acupoints on blood glucose and lactate levels and tissue (liver and kidney) concentrations of lactate in hyperglycemic induced anesthetized rats. METHODS: Thirty-six rats were randomly assigned to 3 groups (n=12): G1: basal (anesthesia: ketamine (90mg kg-1 body weight)+ xylazine (10mg/kg-1 body weight, i.p.); G2: anesthesia+EA10Hz EAc and G3: anesthesia+EA100Hz EAc). EAc stimulation was delivered for 30 min at 10 mA at selected acupoints. Blood and tissue (kidney, liver) samples were collected at the end of the EAc application (n=6, T30) and 30 minutes later (n=6, T60) for biochemical analysis. G1 samples were collected at the same timepoints. ANOVA followed by Tukey's Multiple Comparison Test was used for statistical analyses. RESULTS: Glycemia decreased significantly (p<0.001) in G2/G3 rats in all timepoints. Kidney and liver lactate concentrations decreased significantly (p>0.001) in G2/G3 rats at T-60 and at T30 timepoints in G2 compared with G1 rats. Lactacedemia decreased significantly at T30 timepoint in G2 compared with G1 rats. G1/G3 tissue lactate levels were not different. CONCLUSIONS: Electroacupuncture (10 Hz) applied to St-36 and CV-12 acupoints decreases glycemia and lactacedemia and liver and kidney lactate concentrations. We hypothesize that the decrease in lactate levels may be related to greater energy production due to enhanced lactate to pyruvate conversion. Higher frequency (100 Hz) failed to promote the same effect.

The liver-brain axis of alcohol-mediated neurodegeneration: role of toxic lipids

Alcohol abuse causes progressive toxicity and degeneration in liver and brain due to insulin resistance, which exacerbates oxidative stress and pro-inflammatory cytokine activation. Alcohol-induced steatohepatitis promotes synthesis and accumulation of ceramides and other toxic lipids that cause insulin resistance. Ceramides can readily cross the blood-brain barrier, and ceramide exposure causes neurodegeneration with insulin resistance and oxidative stress, similar to the effects of alcohol. Therefore, in addition to its direct neurotoxic effects, alcohol misuse establishes a liver-brain axis of neurodegeneration mediated by toxic lipid trafficking across the blood-brain barrier, leading to progressive white matter degeneration and cognitive impairment.

Insulin resistance in experimental alcohol-induced liver disease

BACKGROUND AND AIM

Chronic ethanol consumption impairs liver regeneration due, in part, to inhibition of insulin signaling. This study characterizes the mechanisms and consequences of ethanol-impaired insulin signaling in relation to oxidative injury and altered gene expression.

METHODS

Long-Evans rats were fed for 8 weeks with isocaloric liquid diets containing 0% (control) or 37% ethanol (caloric content). Livers were used to examine histopathology, indices of oxidative stress, gene expression required for insulin and insulin-like growth factor (IGF) signaling, insulin-responsive gene expression, i.e. glyceraldehydes-3-phosphate dehydrogenase (GAPDH) and aspartyl-asparaginyl-beta-hydroxylase (AAH), and competitive equilibrium binding to the insulin, IGF-I, and IGF-II receptors.

RESULTS

Chronic ethanol exposure caused liver injury with increased hepatocellular steatosis, inflammation, apoptosis, and increased immunoreactivity for activated caspase-3, 8-hydroxy-2'-deoxyguanosine, and 4-hydroxy-2,3-nonenol. These effects were associated with increased expression of IGF-I receptor, IGF-II, and IGF-II receptor, and expression of IGF-I, AAH, and GAPDH, which mediate energy metabolism and cell motility/remodeling, and reduced binding to the insulin receptor.

CONCLUSIONS

Chronic ethanol-induced liver injury causes insulin resistance with inhibition of insulin-responsive genes needed for metabolism, remodeling, and regeneration. In contrast, the IGF-I and IGF-II signaling mechanisms remain relatively preserved, suggesting that insulin-regulated hepatic functions may be selectively vulnerable to the toxic effects of ethanol.

Alcohol-induced disruption of endocrine signaling

This article contains the proceedings of a symposium at the 2006 ISBRA meeting in Sydney Australia, organized and cochaired by Martin J. Ronis and Thomas M. Badger. The presentations were (1) Effect of long-term ethanol consumption on liver injury and repair, by Jack R. Wands; (2) Alcohol-induced insulin resistance in liver: potential roles in regulation of ADH expression, ethanol clearance, and alcoholic liver disease, by Thomas M. Badger; (3) Chronic gestational exposure to ethanol causes brain insulin and insulin-like growth factor resistance, by Suzanne M de la Monte; (4) Disruption of IGF-1 signaling in muscle: a mechanism underlying alcoholic myopathy, by Charles H. Lang; (5) The role of reduced plasma estradiol and impaired estrogen signaling in alcohol-induced bone loss, by Martin J. Ronis; and (6) Short-term influence of alcohol on appetite-regulating hormones in man, by Jan Calissendorff.

Abnormal glucose homeostasis in adult female rat offspring after intrauterine ethanol exposure

Adverse events during pregnancy, including prenatal ethanol (EtOH) exposure, are associated with insulin-resistant diabetes in male rat offspring, but it is unclear whether this is true for female offspring. We investigated whether prenatal EtOH exposure alters glucose metabolism in adult female rat offspring and whether this is associated with reduced in vivo insulin signaling in skeletal muscle. Female Sprague-Dawley rats were given EtOH, 4 g.kg(-1).day(-1) by gavage throughout pregnancy. Glucose tolerance test and hyperinsulinemic euglycemic clamp were performed, and insulin signaling was investigated in skeletal muscle, in adult female offspring. We gave insulin intravenously to these rats and determined the association of glucose transporter-4 with plasma membranes, as well as the phosphorylation of phosphoinositide-dependent protein kinase-1 (PDK1), Akt, and PKCzeta. Although EtOH offspring had normal birth weight, they were overweight as adults and had fasting hyperglycemia, hyperinsulinemia, and reduced insulin-stimulated glucose uptake. After insulin treatment, EtOH-exposed rats had decreased membrane glucose transporter-4, PDK1, Akt, and PKCzeta in the gastrocnemius muscle, compared with control rats. Insulin stimulation of PDK1, Akt, and PKCzeta phosphorylation was also reduced. In addition, the expression of the protein tribbles-3 and the phosphatase enzyme activity of phosphatase and tensin homolog deleted on chromosome 10 (PTEN), which prevent Akt activation, were increased in muscle from EtOH-exposed rats. Female rat offspring exposed to EtOH in utero develop insulin-resistant diabetes in association with excessive PTEN and tribbles-3 signaling downstream of the phosphatidylinositol 3-kinase pathway in skeletal muscle, which may be a mechanism for the abnormal glucose tolerance.

The effect of acute, chronic, and prenatal ethanol exposure on insulin sensitivity

Ethanol has been considered as a lifestyle factor that may influence the risk of type 2 diabetes mellitus. In healthy adults, acute ethanol consumption results in insulin resistance. Acute ethanol consumption causes insulin resistance selectively in skeletal muscle by an indirect mechanism. Possible mediators include triglycerides (TGs), catecholamines, acetaldehyde, alterations in insulin binding, and hepatic insulin sensitizing substance (HISS). Recent studies in rats showed that acute administration of ethanol causes insulin resistance in a dose-dependent manner that is secondary to the blockade of insulin-induced HISS release. Chronic ethanol consumption may improve insulin sensitivity, but the results from the randomized controlled trials are mixed. Differences in ethanol dose, consumption period, and abstention period may account for the discrepant results. Epidemiological studies have suggested that the relationship between ethanol and insulin sensitivity is either an inverted U-shape or a positive linear relationship. Future randomized controlled trials should consider the dose of ethanol and the duration of ethanol consumption and abstention in the experimental design. Chronic prenatal and postnatal (nursing) ethanol exposure results in insulin resistance that is secondary to the absence of HISS release/action with the HISS-independent insulin action and insulin-like growth factor-1 (IGF-1)-mediated glucose disposal action remaining unimpaired. The impaired HISS release may be related to a reduction in hepatic glutathione (GSH) levels. The effect of chronic ethanol consumption on HISS has not been evaluated.

Enhanced insulin sensitivity using electroacupuncture on bilateral Zusanli acupoints (ST 36) in rats

In this study, intravenous glucose tolerance test (ivGTT) and insulin challenge test (ICT) were applied to evaluate the influence of electroacupuncture (EA) on insulin sensitivity in rats. Firstly, hypoglycemic activity was confirmed on normal Wistar rats (36+/-12%) and streptozotocin (STZ)-induced diabetic rats (13+/-8%) after 60 min of 15 Hz EA on bilateral Zusanli acupoints. The rats were divided into the experiment group (EG) and control group (CG) randomly. After fasting, plasma glucose and insulin levels were assayed in the normal Wistar rats undergoing ivGTT. Plasma glucose levels and hypoglycemic activity were also evaluated in the normal Wistar rats and STZ diabetic rats during ICT. As the data showed, EA improved the glucose tolerance from 15 to 90 min (p<0.005 compared with the plasma glucose levels of the CG) during ivGTT. In addition, significant improvement in the Homeostasis Model Assessment (HOMA) index was found in the EG from 15 to 90 min (p<0.005 compared with the CG). More hypoglycemic activity was achieved in normal Wistar and STZ diabetic rats in the EG than in the CG (from 30 to 60 min) during ICT. In conclusion, the results suggest that 15 Hz EA at bilateral Zusanli acupoints improved glucose tolerance. Thus, EA should be considered as an alternative method for improving insulin sensitivity and/or increase insulin-hypoglycemic activity in rats.