Hyperinsulinemia and VLDL kinetics

The association of lipid metabolism and non-alcoholic fatty liver disease in children with obesity

Aim:

Obesity, insulin resistance, and hyperlipidemia have been shown as risk factors for non-alcoholic fatty liver disease. In this study, the association between lipid and lipoprotein metabolism abnormalities and the presence of non-alcoholic fatty liver disease was investigated in patients with obesity.

Material and Methods:

In this study, the clinical, laboratory and imaging findings of 357 children and adolescent patients (199 girls and 158 boys) aged 2–18 years who were diagnosed as having obesity between 2013 and 2018 were retrospectively analyzed. The clinical and laboratory features of the patients who were diagnosed as having non-alcoholic fatty liver disease using ultrasonography were compared with patients who did not have non-alcoholic fatty liver disease. All lipid and lipoprotein levels were defined as hypo-, normo- and hyperlipidemic in comparison with the reference values according to age and sex.

Results:

The frequency of non-alcoholic fatty liver disease was 44.5% in the entire study group and was higher in males (p<0.05). The body weight, body mass index, alanine aminotransferase, glucose, insulin, non-high-density lipoprotein-cholesterol, and HOMA-IR scores were found to be higher in the patients with non-alcoholic fatty liver disease, whereas the high-density lipoprotein-cholesterol level was lower (p<0.05). There was no difference in the frequency of non-alcoholic fatty liver disease among the patients with low, normal, and high total cholesterol, triglyceride and low-density lipoprotein-cholesterol levels (p>0.05). The frequency of lipid metabolism disorder (hypolipidemia and/or hyperlipidemia) was found as 77.5% in all patients.

Conclusion:

Non-alcoholic liver disease and lipid metabolism disorders are common in children and adolescents with obesity. The frequency of non-alcoholic fatty liver disease in hypolipidemic, normolipidemic, and hyperlipidemic patients was not different. This finding indicated that the increase in the amount of body fatty tissue and insulin resistance were more important risk factors in the development of non-alcoholic fatty liver disease.

The effect of chronic insulin delivery via the intraperitoneal versus the subcutaneous route on hepatic triglyceride secretion rate in streptozotocin diabetic rats

Chronic intraperitoneal or subcutaneous insulin administration increases triglyceride secretion rate (TGSR) in normal rats. We wished to determine the effect of this treatment on TGSR and the hepatic lipogenic enzymes acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS) in diabetic rats. Streptozotocin-diabetic rats, untreated (D), diabetic rats treated with insulin (3 U/day for 21 days) intraperitoneally (IP) or subcutaneously (SC) and non-diabetic rats (N) were studied. TGSR was determined using Triton WR-1339. Fasting glucose and triglyceride levels, high in D, were normalized by insulin treatment regardless of route. Peripheral insulin levels were lowest in D and highest in SC, portal insulin levels were lowest in D and highest in IP. Non-esterified fatty acid levels were not elevated in D, presumably due to adipose tissue depletion. TGSR was reduced in D (P<0.05) and was normalized following insulin administration, regardless of route. ACC activity was normal, but FAS was decreased in D (P<0.05). ACC and FAS were normal in both IP and SC. Thus, in streptozotocin-diabetic rats, chronic intraperitoneal or subcutaneous insulin treatment increases TGSR and FAS activity from their low levels in insulin-deficient rats to levels equal to but not higher than those in normal rats.

Contributions of de novo synthesis of fatty acids to total VLDL-triglyceride secretion during prolonged hyperglycemia/hyperinsulinemia in normal man

Triglycerides (TG) are synthesized in the liver principally from two sources of fatty acids (FA): FA synthesized de novo in the liver and preformed FA. We have measured the rate of secretion of de novo synthesized FA and total secretion of FA bound to VLDL-TG in healthy men (n = 5) in the basal state, and after 1 (day 1) and 4 d (day 4) of a hypercaloric carbohydrate diet (approximately 2.5 times energy expenditure) that generated a moderate endogenous hyperinsulinemia (plasma insulin approximately 60 microU/ml). Prolonged carbohydrate hyperalimentation/hyperinsulinemia increased plasma VLDL-TG approximately 10-fold in part due to a 3.4-fold increase in total VLDL-TG secretion rate (basal state = 72+/-23, day 4 = 242+/-78 micromol TG/kg/d). Although the secretion of de novo synthesized FA increased throughout the study (basal state = 1.1+/-0.4, day 1 = 15.9+/-7.9, day 4 = 50.0+/-18.8 micromol TG/ kg/d), the 2.7-fold increase in secretion rate of preformed FA (basal state = 70+/-23, day 4 = 191+/-57 micromol TG/kg/d) quantitatively contributed the most to total VLDL-TG secretion rate. Decreased catabolism of VLDL-TG also contributed to the hypertriglyceridemia as reflected by an approximately fourfold decrease in both fractional turnover rate (basal state = 9.2+/-3.8, day 1 = 2.1+/-0.2, day 4 = 2.1+/-0.3 pools/d) and rate of clearance (basal state = 0.35+/-0.08, day 1 = 0.11+/-0.01, day 4 = 0.09+/-0.01 liter/kg/d) of VLDL-TG. Thus, the primary difference between 1 and 4 d of hyperinsulinemia in conjunction with carbohydrate hyperalimentation is the increase in hepatic secretion of preformed FA into VLDL-TG.