Seasonal variation in copper-mediated low-density lipoprotein oxidation in vitro is related to varying plasma concentration of oxidised lipids in summer and winter

The seasonal variation of CuCl 2 -mediated low density lipoprotein (LDL) oxidation (10 muM Cu2+ , lag phase, rate of oxidation and maximum absorbance at 234 nm) were measured in 43 men and women on 4-6 occasions (mean 5.7+/-0.5 ) over a 12-month period. The lag phase averaged 52.7+/-0.6 min and did not differ by gender. Lag phase and rate of the rapid propagation phase of LDL oxidation showed a sinusoidal pattern over the year (increased and reduced oxidative susceptibility during January and June-July, respectively; both p <0.001 ). Changes in plasma alpha-tocopherol, ascorbic acid, lycopene or beta-carotene concentrations did not explain seasonal differences in oxidative susceptibility of LDL in vitro . Nor did plasma lipid content of linoleic acid, the main substrate of lipid peroxidation, vary. However, the amount of hydroperoxy- plus hydroxy-fatty acids in plasma lipids varied according to season ( p <0.024) and was related to the lag phase ( r =-0.26, p <0.001). Seasonal variation in oxidative susceptibility was not significant after adjusting for hydroperoxy- plus hydroxy-fatty acids ( p =0.506). Isolated LDL is more vulnerable to Cu2+-induced lipid peroxidation during the winter and this may be due to the higher amount of oxidised lipids during that period.