Rat Plasma VLDL Composition and Concentration and Hepatic Lipase and Lipoprotein Lipase Activities Are Impaired during Two Types of Protein Malnutrition and Unaffected by Balanced Refeeding1

Abstract

The relationships between VLDL concentrations and composition and changes in hepatic lipase and lipoprotein lipase activities were determined in rats, during the consumption of two low protein diets (2% casein or 5% gluten) (protein malnutrition) for 28 d, followed by the refeeding of a balanced diet for 14 d (15% casein) (refeeding). A control group was fed 15% casein for 42 d. In the control group, total lipolytic activity increased with age (r = 0.83, P < 0.001), whereas in both depleted groups, this activity remained low and stable throughout the period of protein malnutrition. At d 28 of protein malnutrition, plasma total lipolytic activities were significantly reduced in both depleted groups, (P < 0.05); hepatic lipase values represented 23% of the control value and lipoprotein lipase activity was about 11% of the control value. Moreover, lipid supply was even more dramatically diminished by the strong reduction in plasma VLDL concentration in both depleted groups. At d 14 of refeeding, lipoprotein lipase activities remained low in both depleted groups. Hepatic lipase activity was similar in the control and casein groups, but significantly higher in the gluten group. The VLDL composition varied significantly with each type of protein malnutrition and could be attributable to the different low levels of plasma VLDL-apolipoprotein C of rats fed both depleted protein diets, which involve an inhibiting or activating effect on lipoprotein lipase activity. Therefore, our results indicated that both protein-deficient diets investigated may diminish fatty acid supply in the various tissues involved.

Insulin injection restored increased insulin receptor substrate (IRS)-2 protein during short-term protein restriction but did not affect reduced insulin-like growth factor (IGF)-I mRNA or increased triglyceride accumulation in the liver of rats

“…Since decreased VLDL-triglyceride secretion is generally observed in protein-deprived animals, decreased VLDL synthesis and triglyceride transport from the liver, which accompany decreased apolipoprotein B (apoB) levels, have been proposed as the primary mechanism of fatty liver generation. 3,4,[33][34][35] In accord with these observations, we found significant decreases in plasma triglyceride concentrations in the 5C animals, and this occurred independently of insulin administration. Furthermore, although its role in protein malnutrition remains largely unknown, endoplasmic reticulum stress, which promotes steatosis, has recently been found to inhibit apoB secretion.…”

Low-protein diet prevents tissue lipoprotein lipase activity increase in growing rats

“…Moreover, in protein-depleted rats, Agbedana (1980) showed that LPL activity is significantly reduced in adipose tissue, whereas there are no significant changes in heart and liver lipolytic activities. In a previous study, we have shown that total plasma lipolytic activity, which represents HL and LPL activities, remains low and stable in rats throughout the period of protein malnutrition (Lamri et al 1995). We have also observed that VLDL composition varies significantly with the type of protein malnutrition (50 g wheat gluten or 20 g casein/kg).…”

Low protein diets produce divergent effects on energy balance

“…In addition to modulating energy intake and expenditure, moderate protein restriction in rats and mice has been consistently associated with alterations in body composition including reduction in lean mass, increased body fat content and development of fatty liver 6 8 9 14 17 32 33 . Protein restricted rats attempt to catch-up on body weight and adipose reserves following refeeding on a standard protein diet 34 35 36 37 38 . However, less is known of the temporal changes in body composition, energy intake and energy expenditure following realimentation of protein restricted animals to standard protein diets.…”