Till Örebro universitet

Plasma cholesterol and triglyceride levels are twice as high in hibernating brown bears (Ursus arctos) than healthy humans. Yet, bears display no signs of early-stage atherosclerosis development when adult. To explore this apparent paradox, we analysed plasma lipoproteins from the same ten bears in winter (hibernation) and in summer using size exclusion chromatography, ultracentrifugation and electrophoresis. LDL cholesterol binding to arterial proteoglycans, and plasma cholesterol efflux capacity were also evaluated. The data collected and analysed from bears were also compared with those from healthy humans. In bears the cholesterol esters, unesterified cholesterol, triglyceride and phospholipid content of VLDL and LDL were higher in winter than in summer. The percentage lipid composition of LDL differed between bears and humans, but did not change seasonally in bears. Bear LDL was larger, richer in triglycerides, showed pre-beta electrophoretic mobility and had 5-10 times lower binding to arterial proteoglycans than human LDL. Finally, plasma cholesterol efflux capacity was higher in bears than in humans, especially the HDL fraction when mediated by ABCA1. These results suggest that in brown bears the absence of early atherogenesis is likely associated with a lower affinity of LDL cholesterol for arterial proteoglycans and an elevated cholesterol efflux capacity of bear plasma.