Alcohol Suppresses Meal-Induced Insulin Sensitization

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.

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.

Synergistic protection by S-adenosylmethionine with vitamins C and E on liver injury induced by thioacetamide in rats

Free radicals are involved in the pathogenesis of acute liver injury induced by thioacetamide (TAA). We investigated the effects of S-adenosylmethionine (SAMe) combined with/without vitamins C and E on TAA-induced acute liver injury in rats. TAA was given intraperitoneally (200 mg kg-1). Antioxidant treatments (SAMe, 25 mg kg-1; vitamin C, 100 mg kg-1; vitamin E, 200 mg kg-1, intraperitoneal) were given 1 h later. Liver histology, enzymology, and ability to release hepatic insulin-sensitizing substance (HISS) were assessed. TAA caused liver tissue injury, increased liver enzymes, and decreased insulin sensitivity (p<0.01). Blockade of HISS release by atropine did not further decrease insulin sensitivity in rats with TAA insult, indicating that the decrease in insulin sensitivity was HISS dependent. Treatment with SAMe alone or vitamins C+E slightly improved liver histology but not the changes in liver enzymes and insulin sensitivity. Combined treatment with SAMe plus vitamins C+E greatly protected the liver from tissue injury, the increase in liver enzymes, and the decrease in insulin sensitivity. In conclusion, acute liver injury causes HISS-dependent insulin resistance (HDIR). There are synergistic antioxidative effects among the antioxidants, SAMe and vitamins C and E, that protect the liver from TAA-induced HDIR, suggesting that antioxidant treatment may best be done using a balanced "cocktail."