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Biomedical subjects

J S Bennett

Publications and source records attributed to J S Bennett.

At least 91 records · Page 5Linked to original sources
PubMed1977

Abnormalities of cholesterol-phospholipid composition in platelets and low-density lipoproteins of human hyperbetalipoproteinemia.

Platelets from most patients with type IIa hyperlipoproteinemia (IIa) aggregate in the presence of lower concentrations of epinephrine and adenosine diphosphate (ADP) than are necessary to aggregate normal platelets. We have observed a comparable functional alteration in human platelets made cholesterol-rich in vitro by incubation in a milieu artificially rich in free cholesterol relative to phospholipid. We therefore examined platelet aggregation and lipid composition of platelets and of plasma low-density lipoprotein (LDL) in 19 individuals with IIa (including three homozygotes), seven normolipidemic individuals with symptomatic, angiographically-documented coronary atherosclerosis (atherosclerosis group), and 23 asymptomatic, normolipidemic subjects (control group). More than 99 percent of platelet cholesterol was unesterified. There was a 7 percent increase in the cholesterol content of whole platelets per mole of platelet phospholipid (C/PL) in IIa as compared to normal controls. This resulted from a 22 percent increase in the C/PL of IIa platelet membranes with no change in the C/PL of the soluble or granule fraction. The C/PL of IIa platelets was 6 percent greater than that of platelets from patients with atherosclerosis. As compared to those of normal controls, IIa platelets aggregated in response to a ninefold lower concentration of epinephrine (p less than 0.001) and a twofold lower concentration of ADP (p less than 0.02). The response of atherosclerosis platelets to these agents was comparable to that of controls. In all groups, there was a negative correlation between the log concentration of epinephrine required to produce complete platelet aggregation and the platelet C/PL (r = -0.06; p less than 0.002). The composition of LDL isolated from the plasma of patients with IIa was characterized by a 39 percent increase in the amount of free cholesterol relative to protein and a 35 percent increase in C/PL, as compared with control LDL. These values were increased 23 and 19 percent, respecitvely, when IIa was compared with the atherosclerosis group. In all groups the C/PL of LDL correlated well with the C/PL of platelets (r = =0.61; p less than 0.001). However, a simple cause-and-effect relationship did not appear to exist since (1) erythrocyte membrane C/PL was not affected and (2) normal platelets or erythrocytes underwent no change in C/PL during 18 hours' incubation in IIa plasma. These studies demonstrate that LDL and platelets in IIa contain an increased amount of free cholesterol relative to its principal solubilizer, phospholipid. In platelets this correlates with an increased sensitivity to aggregating agents. Moreover, the similarity between the functional abnormality in IIa platelets and that previously observed in normal platelets made cholesterol-rich in vitro suggests that the lipid composition of platelet membranes may have a direct effect on the function of platelets in man.

Adolescent↗
PubMed1976

Halofenate: a potent inhibitor of normal and hypersensitive platelets.

Platelet hypersensitivity has been documented in diabetes and angina pectoris and can be partially reversed in hyperbetalipoproteinemia by clofibrate. We therefore examined the effects of incubating another lipid-lowering agent, halofenate, with both normal platelets and platelets made hypersensitive in vitro by incorporation of 55 per cent excess cholesterol into their membranes. At therapeutic concentrations, halofenate caused a time- and dose-dependent inhibition of the aggregation of normal platelets by epinephrine. After 30 minutes' incubation at 37 degrees C., halofenate significantly inhibited the extent of aggregation by 88 per cent (p less than 0.01), whereas clofibrate inhibited aggregation by 44 per cent (p less than 0.01). Halofenate was a more potent inhibitor of platelets than clofibrate (p less than 0.01). The mean threshold concentration of epinephrine necessary for aggregation of normal platelets (4.2 muM) was not significatnly increased with clofibrate (10 muM) but was markedly elevated with halofenate (245 muM; p less than 0.001). Significant but less dramatic increases in threshold concentration of ADP and collagen were found with halofenate but no clofibrate. Cholesterol-rich platelets were 114-fold more sensitive to epinephrine and twofold more sensitive to ADP than normal platelets but after incubation with halofenate became even less sensitive than normal. Clofibrate inhibited the extent of aggregation of hypersensitive platelets but did not alter the threshold concentration of epinephrine necessary for aggregation. Thus, halofenate is more potent than clofibrate in reducing the sensitivity of normal platelets to aggregating agents in vitro and can completely reverse experimentally produced platelet hypersensitivity. These data suggest that halofenate might be useful in reversing increased platelet sensitivity in cardiovascular diseases.

Adenosine Diphosphate↗