Effect of Drugs on Plasma Triglyceride Metabolism

Physical inactivity amplifies the sensitivity of skeletal muscle to the lipid-induced downregulation of lipoprotein lipase activity

Physical inactivity is a risk factor for lipoprotein disorders and the metabolic syndrome. Physical inactivity has a powerful effect on suppressing lipoprotein lipase (LPL) activity in skeletal muscle, the rate-limiting enzyme for hydrolysis of triglyceride (TG)-rich lipoproteins. We tested the ability of several compounds to prevent the decrease in LPL. The present study minimized standing and ordinary light nonexercise movements in rats to compare the effects of inactivity and nonexercise activity thermogenesis (NEAT) on LPL activity. The key new insight was that the typically quick decrease in LPL activity of oxidative muscle caused by physical inactivity was prevented by nicotinic acid (NA), whereas inhibitors of TNF-alpha, inducible nitric oxide synthase, and NF-kappaB had no such effect. NA was administered at a dose known to acutely impede the appearance of plasma TG from the liver and free fatty acids from adipose tissue, and it was effective at intentionally lowering plasma lipid concentrations to the same level in active and inactive groups. As measured from heparin-releasable LPL activity, LPL in the microvasculature of the most oxidative muscles was approximately 90% lower in the inactive group compared with controls, and this suppression was completely blocked by NA. In contrast to inactivity, NA did not raise muscle LPL in ambulatory controls, whereas a large exogenous fat delivery did decrease LPL activity. In vitro control studies revealed that NA did not have a direct effect on skeletal muscle LPL activity. In conclusion, physical inactivity amplifies the ability of plasma lipids to suppress muscle LPL activity. The light ambulatory contractions responsible for NEAT are sufficient for mitigating these deleterious effects.

The effects of nicotinic acid and xanthinol nicotinate on human memory in different categories of age. A double blind study

The treatment effect of nicotinic acid and xanthinol nicotinate on human memory was compared with placebo in 96 healthy subjects. Forty-three subjects were young (35-45 years), 30 subjects middle aged (55-65 years) and 23 subjects were old aged (75-85 years). Pre- and post-treatment scores were measured on a battery of memory tasks, covering sensory register, short-term memory and long-term memory. The treatment regime was 1 dragee t.i.d. for 8 weeks. The administration of xanthinol nicotinate (500 mg, containing 141.7 mg nicotinic acid), nicotinic acid (141.7 mg) and placebo (lactose) was double-blind. Pre- and post-treatment scores were analysed by means of a multivariate covariance technique, the pre-treatment score serving as covariate. Nicotinic acid treatment resulted in improvement of sensory register and short-term memory, while xanthinol nicotinate improved sensory register, short-term memory and long-term memory. In comparison with placebo, both active compounds yielded improvements of 10-40%, depending on type of task. Treatment effects of nicotinic acid were predominantly found in the young and middle-aged, whereas treatment effects of xanthinol nicotinate were predominantly found in the old. These results are interpreted by the supposed activity of nicotinic acid at the cell membrane, improving neuronal transmission, and of xanthinol nicotinate inside the cell, enhancing cell metabolism and oxygen supply in the brain.

Effects of colestipol, clofibrate, and placebo on plasma lipoproteins of patients with hypercholesterolemia

To evaluate the effectiveness of colestipol and clofibrate in patients with hypercholesterolemia and normal concentrations of triglycerides, 27 patients were randomized into three groups, and colestipol, clofibrate, and avicel powder placebo were compared for effects on concentration of total plasma lipid and lipoprotein cholesterol and triglyceride in a single blind protocol over 8 mo. Mean pretreatment values for low density lipoprotein (LDL)-cholesterol and very low density lipoprotein (VLDL) triglyceride were 250 mg/dl and 68 mg/dl, respectively. Colestipol (30 g/day) lowered total- and LDL-cholesterol by 25% and 31%k, respectively, while VLDL-triglyceride rose. Overall clofibrate lowered total- and LDL-cholesterol by 13% and 12% while lowering VLDL-triglyceride 21% and VLDL cholesterol by 50%. For clofibrate, certain patients showed a more pronounced effect than others: in seven of nine patients clofibrate lowered both mean total- and LDL-cholesterol by 17% (range 8% to 31%) and 19% (range 10%--44%) respectively, whereas two patients did not respond to clofibrate. High density lipoproteins were not affected by either colestipol or clofibrate in these patients. Thus, while colestipol was more consistently effective, certain hypercholesterolemic patients responded equally well to clofibrate with substantial lowering of total-, LDL-, and VLDL-cholesterol.