Hibernating brown bears are protected against atherogenic dyslipidemia

Area of Science:

• Physiology
• Biochemistry
• Comparative Biology

Background:

• Hibernators must manage significant metabolic shifts during dormancy.
• Atherogenic hyperlipidemia is a concern in humans but not observed in hibernating bears.

Purpose of the Study:

• To investigate the mechanisms brown bears use to avoid atherogenic hyperlipidemia during hibernation.
• To analyze lipoprotein and cholesterol metabolism in hibernating vs. non-hibernating bears.

Main Methods:

• Assessed lipoprotein sizes and sub-classes, plasma enzyme activities, and muscle lipid composition.
• Measured plasma antioxidant capacities and inflammatory markers in winter- and summer-captured bears.

Main Results:

• Hibernating bears showed increased lipid levels but stabilized high-density lipoprotein (HDL) composition via higher cholesteryl-ester transfer-protein activity.
• Inflammatory metabolites decreased, correlating inversely with increased cardioprotective HDL proportions and sizes.
• Lower muscle cholesterol and lecithin-cholesterol acyltransferase activity suggested controlled peripheral cholesterol metabolism.
• Enhanced plasma antioxidant capacities prevented lipid oxidative damage.

Conclusions:

• Brown bears effectively manage large lipid fluxes during hibernation without adverse atherogenic effects.
• Mechanisms include stabilized HDL, reduced inflammation, controlled cholesterol synthesis, and robust antioxidant defenses.