Distinct cholesterol and phospholipid incorporation at the platelet plasma membrane of hyperlipidemic subjects: structural order and function

Abstract

Plasma lipid composition, platelet aggregation, cholesterol (Ch)/glycoprotein IIb-IIIa (GP) and phospholipid (Ph)/GP molar ratios, fatty acid composition and structural order (1, 6-diphenyl-1, 3, 5-hexatriene (DPH) fluorescence anisotropy at 35 C (r) of human platelet plasma membranes (HPPM) were measured in four DPH,35 groups of hyperlipidemic patients (II: plasma Ch < 250 mg/dl and TG (triglycerides) <220 mg/dl, n = 21; III: Ch > 250 mg/dl and TG < 220 mg/dl, n = 23; IV: Ch < 250 mg/dl and TG > 220 mg/dl, n = 18; and V: Ch > 250 mg/dl and TG > 220 mg/dl, n = 12) and compared with those of the control group (I). Our results were: (i) in groups III, IV and V the HPPM (Ch + Ph)/GP molar ratio increased 7.0 7.7% (mean SD); (ii) the Ph/GP molar ratio increased significantly in groups III, IV and V, but most in IV and V, while the Ch/GP molar ratio increased only in groups III and V; (iii) the mean relative increase of Ch with respect to Ph in the HPPM of groups III, IV and V was 140% 21% and 54%, respectively; (iv) the Ch/GP molar ratio was correlated with LDL-Ch (0.41 0.16, P < 0.002, n = 55, for all the subjects and 0.60 0.11, P < 2.10-4, n = 33, for subjects with TG < 220 mg/dl), however, it was totally uncorrelated with HDL-Ch; (v) the HPPM Ch/Ph molar ratio was positively correlated with plasma Ch (r = 0.51 0.08, P < 1.10-6, n = 83) and with (LDL + HDL) Ch (r = 0.64 0.07, P < 1.10-6, n = 73), the former correlation increased significantly ( r = 0.67 0.07, P < 1.10-6, n = 53) when done only for subjects with TG < 220 mg/dl; (vi) the Ch/Ph molar ratio was only increased in group III (0.70 0.03, P < 3.10-5, n = 23) and decreased in group IV (0.62 0.02, P < 0.001, n = 18); (vii) the fatty acid/GP molar ratio was significantly increased in groups IV and V, however, a significant absolute and relative increase of C16:0 and C18:1 was observed only in severe hypertriglyceridemia (> 500 mg/dl), together with a relative decrease of C18:0 and C20:4 ( n - 6); (viii) the HPPM structural order, as probed by r , was negatively correlated with DPH,35 plasma TG (r =- 0.61 0.10, P < 4.10-5, n = 39), the Ph/GP molar ratio (r =-0.58 0.10, P < 2.10-4, n = 39) and the the (C18:1 + C18:2))/GP molar ratio (r =- 0.80 0.05, P < 1.10-6, n = 39), however, it was independent of plasma and HPPM Ch; (ix) the higher HPPM Ch/Ph molar ratio in group III was associated (r = 0.58 0.12, P < 0.005, n = 22) with a moderately higher platelet reactivity to collagen. We conclude that Ch and Ph were distinctly incorporated to HPPM in the different groups of hyperlipidemia and, therefore, that the absolute increase of Ch and Ph was more informative to understand the structural and functional modifications of the HPPM in hyperlipidemias, than the Ch/Ph molar ratio. On the other hand, the r was sensitive to the DPH,35 increase in the content of HPPM Ph and C18:1 + C18:2 and it was insensitive to the increase in the Ch content.