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Biomedical subjects

S J Shattil

Publications and source records attributed to S J Shattil.

At least 127 records · Page 7Linked to original sources
PubMed1978

Platelet function in essential thrombocythemia. Decreased epinephrine responsiveness associated with a deficiency of platelet alpha-adrenergic receptors.

Platelets from two patients with essential thrombocythemia failed to aggregate or release serotonin in response to concentrations of epinephrine that aggregated platelets from normal controls. Therefore, we studied their alpha-adrenergic receptors, using 3H-dihydroergocryptine (3H-DHE), an alpha-adrenergic antagonist. These platelets contained an average (mean +/- S.E.) of 210 +/- 18 and 227 +/- 27 3H-DHE binding sites per platelet--less than half that found on control platelets, 464 +/- 37 (P less than 0.01). In contrast, platelets from two other patients with essential thrombocythemia responded to epinephrine and contained a normal number of 3H-DHE sites. Platelets in essential thrombocythemia demonstrated normal kinetics of 3H-DHE binding and normal affinities for 3H-DHE and for epinephrine. When control platelets were preincubated with a half-saturating concentration of 3H-DHE, there was a diminution of epinephrine-induced platelet function comparable to that seen in essential thrombocythemia. Thus, a deficiency of alpha-adrenergic receptors may account for diminished functional responsiveness of platelets to epinephrine in some patients with essential thrombocythemia.

Aged↗
PubMed1978

Increased fluidity of human platelet membranes during complement-mediated immune platelet injury.

Complement appears to be involved in the destruction of platelets in certain clinical disorders, such as quinidine purpura and post-transfusion purpura. In both disorders, the classical complement sequence is activated by antigen-antibody complexes. It has been suggested that the terminal components of the complement sequence insert into the hydrophobic core of cell surface membranes and that this process leads to cell lysis. Fluidity is a fundamental property of lipids within the membrane's hydrophobic core. To examine the interaction of complement with membranes, we investigated the effect of complement activation on the fluidity of human platelet membranes. Complement was fixed to platelets using a post-transfusion purpura antibody, and membrane lipid fluidity was assessed in terms of fluorescence anisotropy using two fluorescent probes, 1,6-diphenyl-1,3,5-hexatriene and 9-(12-anthroyl) stearic acid. Microviscosity, expressed in poise, was derived from the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene.Post-transfusion purpura antibody plus complement made platelet membranes more fluid as evidenced by a 21% decrease in anisotropy and a 35% decrease in microviscosity of platelets at 37 degrees C, and this was associated with platelet lysis ((51)Cr release). Complement damage to platelets was accompanied by a 10-15% increase in DeltaE, the fusion activation energy for microviscosity, indicating that complement not only decreased membrane microviscosity but also made membrane lipids less ordered. These changes were consistent and rapid, with platelet lysis and the reduction in microviscosity being half-maximal by 6 min. They were prevented by inactivation of complement with heat or with EDTA, and they were not observed when C5-deficient plasma was used as the complement source. Qualitatively similar changes in platelet membrane fluidity were observed when complement was fixed to platelets by a quinidine-dependent anti-platelet antibody rather than by post-transfusion purpura antibody. Post-transfusion purpura antibody plus complement also decreased the microviscosity of isolated platelet membranes. Moreover, the lipids extracted from platelets lysed by complement had a 22% decrease in microviscosity (P < 0.01), with no associated changes in the amount of cholesterol relative to phospholipid or in the amounts of the various phospholipids. These studies demonstrate that lipids within the hydrophobic core of platelet membranes damaged by complement become more fluid, and this is associated with platelet lysis. These findings are consistent with the concept that the insertion of the terminal complement components into the platelet membrane bilayer perturbs lipid-lipid interactions within the membrane's hydrophobic core.

Antibodies↗
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

Membrane microviscosity and human platelet function.

An increased sensitivity to epinephrine-induced aggregation has been observed both in platelets obtained from patients with type IIa hyperlipoproteinemia and in normal platelets following incubation with cholesterol-rich lecithin dispersions. We have reported previously that the membrane fraction of platelets is enriched with cholesterol relative to phospholipid under each of these conditions. To further explore the effect of cholesterol on platelet membranes, we have examined the fluidity (microviscosity) of whole platelets and platelet subcellular fractions using a hydrophobic fluorescent probe, 1,6-diphenyl-1,3,5-hexatriene (DPH), under conditions in which the cholesterol-to-phospholipid mole ratio (C/PL) of platelets was varied by incubation with various cholesterol-lecithin sonicated dispersions. The C/PL of platelets directly influenced the rotational diffusion of DPH, as indicated by changes in fluorescence polarization. This was reflected in an increase in microviscosity at 37 degrees C (ETA37) from 2.84 P in normal platelets to 4.06 P in platelets with a 118% increase in C/PL. Conversely, platelets with a 43% decrease in C/PL had a 13% decrease in eta37. A strong correlation (r = 0.94) existed between C/PL and eta37 throughout this entire range. However, C/PL had no effect on the excited-state fluorescence lifetime of DPH. Both C/PL and eta37 were lower in isolated platelet membranes than in the platelet granule fraction. When platelets were incubated for 20 h with cholesterol-rich dispersions, there was an increase in C/PL and eta37 in both the membrane and granule fractions. However, this occurred more rapidly in membranes so that, at 5 h (a time when an increased sensitivity of whole platelets to epinephrine is evident), membrane C/PL had increased 55% and eta37 had increased 42%, whereas granule C/PL and eta37 had changed minimally. Cholesterol-rich platelets and subcellular fractions had a lower fusion (or flow) activation energy for viscosity (deltaE), reflecting a higher degree of order, and the converse was true in cholesterol-poor platelets. Moreover, a strong negative correlation existed between the percent change in deltaE and the percent change in eta37 induced either by cholesterol incorporation or depletion. These data demonstrate that cholesterol influences the fluidity and the degree of order within the hydrophobic core of platelet membranes. Changes induced in these physical properties by an excess of cholesterol relative to phospholipid may underlie the abnormal reception or transmission of the aggregation stimulus in cholesterol-rich platelets.

Binding Sites↗
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↗
PubMed1975

Modification of red cell membrane structure by cholesterol-rich lipid dispersions. A model for the primary spur cell defect.

Cholesterol-rich membranes are the hallmark of "spur" red cells. Spur cells accumulate cholesterol from cholesterol-rich serum lipoproteins. Previous studies suggested that this added cholesterol is responsible for both the altered morphology and the destruction of spur cells. To examine this process in the absence of other serum factors, cholesterol-lecithin dispersions with varying amounts of unesterified cholesterol (C) relative to phospholipid (P) were prepared, and their influence on normal human red cells was studied. Cholesterol-rich lipid dispersions (C/P mole ration greater 1.0) transferred cholesterol to both red cell membranes and serum lipoproteins, and cholesterol-poor dispersions (C/P mole ration less 1.0) depleted red cells of cholesterol. Changes in membrane cholesterol paralleled changes in membrane surface area, as calculated from osmotic fragility, with a 0.22 percent variation in surface area per 1.0 percent variation in cholesterol content. Cold-induced compression of membrane surface area was increased in cholesterol-poor red cells (C/P equals 0.4), whereas the surface area of cholesterol-rich membranes (C/P equals 1.80) underwent no compression. Although the Na and K permeability of red cells severely depleted of cholesterol was increased, lesser degrees of depletion had no effect, and the permeability of cholesterol-rich cells was normal. However, increasing membrane cholesterol caused a progressive decrease in red cell deformability, as measured by filtration. Cholesterol-poor red cells were spherocytic in appearance and cholesterol-rich cells were broad and flat, indicative of their surface areas. In addition, cholesterol-rich cells had an irregular contour due to folding of the periphery of the cell. This shape abnormality was identical to that of both spur cells after splenectomy and normal red cells incubated in spur serum. Normalization of the C/P of spur serum by added phospholipid prevented the increase in membrane cholesterol and surface area and the transformation of cell shape. These studies establish that the cholesterol content of red cells is dependent on the C/P of their milieu, either lipoproteins or cholesterol-lecithin dispersions. Moreover, the surface area, deformability, and contour of cholesterol-rich red cells are a direct function of their increased membrane C/P. Although cholesterol-rich spur cells are further modified in the circulation of patients with spleens, this abnormality of the membrane lipid bilayer, induced by cholesterol-rich cholesterol-lecithin dispersions, represents the primary spur cell defect.

Anemia, Hemolytic↗
PubMed1975

Platelet hypersensitivity induced by cholesterol incorporation.

Platelets from individuals with familial hypercholesterolemia show increased sensitivity to the aggregating atents, epinephrine and ADP. Since the mechanism of this abnormal sensitivity is unknown, we examined, in vitro, the influence of the plasma lipid environment on the function of platelets. The composition of plasma lipids was altered by the addition of sonicated cholesterol-dipalmitoyl lecithin liposomes which were "cholesterol normal" (cholesterol-phospholipid mole ratio [C/P] equals 1.0, "cholesterol rich" (C/P eauals 2.2), or "cholesterol poor" (C/P equals 0). Cholesterol-normal liposomes had no influence on platelet lipids or platelet function. In contrast, after incubation for 5 h at 37 degrees C with cholesterol-rich liposomes, normal platelets acquired 39.2% excess cholesterol with no change in phospholipids or protein. The percent increase in platelet membrane cholesterol was three-fold that of the granule fraction. The acquisition of cholesterol by platelets was associated with a 35-fold increase in sensitivity to epinephrine-induced aggregation (P less than 0.001) and 15-fold increase to ADP aggregation (P less than 0.001), as determined both by aggregometry and by [13C]serotonin release. Response to thrombin or collagen was unchanged. Platelets incubated with cholesterol-poor liposomes underwent a selective loss of 21.4% cholesterol and this was associated with an 18-fold reduction in their sensitivity to epinephrine. These studies demonstrate that the cholesterol content of platelets is dependent on the lipid composition of the milier. Cholesterol acquired by platelets may exert its effect on platelet function by a modification of the platelet membrane.

Adenosine Diphosphate↗
PubMed1973

M-components.

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Adult↗