Acetyl-L-carnitine influences the fluidity of brain microsomes and of liposomes made of rat brain microsomal lipid extracts.

The fluorescence anisotropy (r) of diphenylhexatriene (DPH) was measured in different preparations (bovine spinal cord phosphatidylserine liposomes, rat brain microsomes, liposomes made with rat brain microsomal lipid having different phospholipid:cholesterol ratios) at temperatures ranging from 10 degrees to 55 degrees C. Phosphatidylserine liposomes exhibited an exponential relationship of r versus temperature, whereas the relationship shown by microsomes and liposomes prepared with microsomal lipid extracts was a linear one. The removal of protein and high phospholipid:cholesterol ratios decreased the slope of the lines (fluidity increased), although the intercept was unaffected. This means that differences were better appreciated at high temperatures and were well evident at 37 degrees C. Acetyl-L-carnitine decreased r in rat brain microsomes and in liposomes made with microsomal lipids with different phospholipid:cholesterol ratios. The fluidifying effect of acetyl-L-carnitine was mild but statistically significant and could explain, at least in part, the data reported in the literature of acetyl-L-carnitine acting on some parameters affected by ageing. Besides, acetyl-L-carnitine seemed to oppose the changes of viscosity due to lipid peroxidation, which has been reported to increase in ageing and dementia. L-carnitine shares the properties of its acetyl ester, but only in part.