Membrane bilayer balance and platelet shape: morphological and biochemical responses to amphipathic compounds

Bile Salt- and Lysophosphatidylcholine-induced Membrane Damage in Human Erythrocytes

The interaction of bile salts and lysophosphatidylcholine (LPC) with membranes has implications both in understanding the aetiology of a number of gastrointestinal disorders, including gastritis, gastric ulcers and colonic cancer, and in enhancing drug absorption by various epithelia. The membrane toxicity of nine bile salts (the sodium (S) salts of chenodeoxycholate (CDC), deoxycholate (DC) and cholate (C) and their glycine (G) and taurine (T) conjugates) and LPC was determined using erythrocyte haemolysis as a model parameter. Washed human erythrocytes were incubated for 15–60 min at 20°C with media buffered at pH 8, 7 and 6. Bile salt toxicity was shown to be a function of type, concentration, pH and contact time with the membrane. At pH 7 toxicity decreased in the order LPC > unconjugated dihydroxy salts (SDC and SCDC) > conjugated deoxycholates (SGDC and STDC) > conjugated chenodeoxycholates (SGCDC and STCDC) > unconjugated trihydroxy salt (SC) > conjugated trihydroxy salts (SGC and STC). Incubation with equimolar combinations of bile salts (SDC + SCDC; STCDC + SGDC; SDC + STDC) indicated that the resultant damage was an additive function of the damage induced by the individual bile salts.

Perioperative complications of hypothermia

Perioperative hypothermia is a common and serious complication of anesthesia and surgery and is associated with many adverse perioperative outcomes. It prolongs the duration of action of inhaled and intravenous anesthetics as well as the duration of action of neuromuscular drugs. Mild core hypothermia increases thermal discomfort, and is associated with delayed post anaesthetic recovery. Mild hypothermia significantly increases perioperative blood loss and augments allogeneic transfusion requirement. Only 1.9 degrees C core hypothermia triples the incidence of surgical wound infection following colon resection and increases the duration of hospitalization by 20%. Hypothermia adversely affects antibody- and cell-mediated immune defences, as well as the oxygen availability in the peripheral wound tissues. Furthermore mild hypothermia triples the incidence of postoperative adverse myocardial events. Thus, even mild hypothermia contributes significantly to patient care costs and needs to be avoided.

Determination of lipid bilayer/water partition coefficient of new phenothiazines using the second derivative of absorption spectra method

The partition coefficients (K(p)) between lipid bilayer of phosphatidylcholine (PC) vesicles and buffer for five new phenothiazines were determined using the second derivatives of ultraviolet absorption spectra. The lambda(max) of absorption band for each of the investigated phenothiazine derivatives (PDs) was shifted to the longer wavelengths in the presence of PC vesicles with increasing of lipid concentration. As a result of light scattering in liposome suspension no isosbestic point could be observed in absorption spectra. However, the background signal could be eliminated using the method of second derivative of absorption spectra. In the second derivative of absorption spectra two isosbestic points were observed. Changes of intensity (Delta D) of second derivative of absorption spectra at the lambda(max) (wavelength of absorption maximum for drug in buffer) caused by the increase in lipid concentration were measured for set of phenothiazine derivatives. K(p) for these drugs were calculated from the relationship between Delta D and lipid concentration. The K(p) values for all studied phenothiazine derivatives are in the order of magnitude of 10(5) and they increase about 1.7-fold when length of the alkyl phenothiazine chain was enhanced by addition of the each next one (-CH(2)) group. Substitution of -H atom by -CF(3) group at position 2 of phenothiazine ring results in 3.5-fold increase in K(p) values.

Identification and purification of aminophospholipid flippases

Transbilayer phospholipid asymmetry is a common structural feature of most biological membranes. This organization of lipids is generated and maintained by a number of phospholipid transporters that vary in lipid specificity, energy requirements and direction of transport. These transporters can be divided into three classes: (1) bidirectional, non-energy dependent 'scramblases', and energy-dependent transporters that move lipids (2) toward ('flippases') or (3) away from ('floppases') the cytofacial surface of the membrane. One of the more elusive members of this family is the plasma membrane aminophospholipid flippase, which selectively transports phosphatidylserine from the external to the cytofacial monolayer of the plasma membrane. This review summarizes the characteristics of aminophospholipid flippase activity in intact cells and describes current strategies to identify and isolate this protein. The biochemical characteristics of candidate flippases are critically compared and their potential role in flippase activity is evaluated.

Phosphoinositide metabolism and shape control in sheep red blood cells

Metabolic depletion of sheep red blood cells leads to decreased intracellular concentrations of ATP and reduced glutathione as well as degradation of phosphoinositides. In sheep red blood cells, depletion of ATP induced two types of shape transformation: one early phase involving formation of protrusions on the cell surface similar to those observed upon depletion of human red blood cells; and one late phase, in which the sheep red blood cells develop long, rod-shaped projections. During the initial stages of shape changes, degradation of the phosphoinositides parallels the discocyte-echinocyte transformation, thus giving further support to a shape-controlling mechanism based on the bilayer-couple hypothesis. However, formation of the long projections does not coincide with turnover of the phosphoinositides but rather with the level of reduced glutathione. This indicates that development of these rod-like extensions on the cell surface is induced by oxidative processes that may well involve cross-linking of membrane skeleton proteins.

Vesiculation induced by amphiphiles and ionophore A23187 in porcine platelets: a transmission electron microscopic study

Amphiphiles, known to induce exo- and endovesiculation in human erythrocytes, were studied by means of transmission electron microscopy (TEM) for their ability to induce shedding of vesicles (microparticles) from the porcine platelet plasma membrane. While echinocytogenic amphiphiles induced shedding of vesicles to the extracellular medium (exovesiculation), stomatocytogenic amphiphiles did not induce endovesiculation. The rapid (< 1 min) formation of many thin spicules in platelets upon treatment with echinocytogenic amphiphiles, indicates that spicule-formation is caused by a primary interaction of the amphiphile with the plasma membrane. Agonist- (Ca(2+)-ionophore A23187, thrombin and collagen) induced shape changes, however, seem to involve contractile cytoskeletal processes since treated cells attained heavily irregular shapes with broad pseudopods. Our study indicates that the mechanisms involved in amphiphile- and agonist-induced exovesiculation differ. Amphiphile-induced exovesicles are mainly electron-dense spherical structures (phi 150-200 nm) which originate from the formed spicules. Ionophore A23187-induced exovesicles are large (phi 200-800 nm) predominantly electron-lucent structures which are mainly shed from the cell body and seem to originate from extrusions of the canalicular system. Our study shows that there are several similarities but also obvious differences in the response of platelets and erythrocytes to amphiphile-treatment.

Platelet lysis and functional perturbation by 13-methyl myristate. The major fatty acid in Flavobacterium ranacida

Flavobacterium ranacida consisted of 75% of 13-methyl myristate in total fatty acids. The acid at > 60 microM caused the lysis of gel-filtered platelets (GFP) in both time- and concentration-dependent manners. Scanning electron microscopy showed that: 1). GFP in 40 microM of the acid changed the morphology to speculate discoid shape at 15 sec, and to ellipsoids after 30 sec; and 2), the cells gradually swelled to spherical forms as the concentration of the acid increased. At nonlytic concentration, the acid inhibited platelet responses to various agonists with differential concentrations. The order of inhibitory potency was U46619 > low dose collagen > ADP-fibrinogen > phorbol ester > high dose collagen. The results demonstrated that 13-methyl myristate exhibited both cell lytic activity and perturbation on membrane function.

Effects of exogenous phospholipids on platelet activation

Intercalation of amphipaths into the plasma membrane of platelets has a marked effect on their morphology. Incubation of platelets with phosphatidylcholines (PC) results in rounding of the platelet body and speculation, while incubation with aminophospholipids such as dilauroylphosphatidylserine (DLPS) results in a biphasic shape change consistent with the bilayer couple model (Sheetz, M.P. and Singer, S.J. (1982) Proc. Natl. Acad. Sci. USA 71, 4457-4461) and with the activity of an aminophospholipid translocator facilitating transverse bilayer diffusion (Daleke, D.L. and Huestis, W.H. (1985) Biochemistry 24, 5406-5416). The present study extends this work to investigate the effects of PC and PS on platelet responses to a natural agonist, thrombin. PC incorporation produces a concentration-dependent progression of shape changes, beginning with surface ruffling and development of fine spicules, followed by sphering of the cell body, and ending with the apparent loss of spicules. PC reduces platelet responses to thrombin only under conditions that promote membrane vesiculation, seen morphologically as a loss of spicules and biochemically as a loss of 14C-PC labeled membrane. PS homologues of varying acyl chain composition induce concentration- and time-dependent platelet sphering. Incorporation of PS inhibits thrombin-induced platelet shape change, granule secretion, and protein phosphorylation. Inhibition of these responses requires transit of the exogenous PS to the cytofacial leaflet of the membrane bilayer.

Translocation of spin-labeled phospholipids through plasma membrane during thrombin- and ionophore A23187-induced platelet activation

After incorporation of spin-labeled phosphatidylcholine, phosphatidylserine, and phosphatidylethanolamine analogues in the outer leaflet of the plasma membrane in resting platelets, more than 90% amino-head analogues accumulated within 30 min in the inner leaflet by aminophospholipid translocase activity, while choline analogues mostly remained on the outer leaflet. Platelets were then activated by thrombin or Ca2+ ionophore A23187. No outward movement of internally located spin-labeled aminophospholipids was observed during thrombin-induced activation, whereas the influx of externally located probes increased slightly. During A23187-mediated activation, similar slightly increased influx was observed, while 40-50% of the initially internally located aminophospholipids could then be extracted from the outer leaflet. This sudden exposure on the outer face was dependent on an increase in intracellular Ca2+ and achieved in less than 2 min at 37 degrees C. Inhibition of translocase activity by N-ethylmaleimide did not induce any aminophospholipid outflux. When probes were incorporated on the outer face of the plasma membrane in resting platelets, they were still fully accessible from the extracellular medium after A23187-induced activation. Moreover, they were distributed between the vesicles and remnant platelets in proportion to the external membrane phospholipidic content in each structure. This suggested that no scrambling of plasma membrane leaflets occurred during the vesicle blebbing. Moreover, the spin-labeled aminophospholipids exposure rate and amplitude were unchanged when vesicle formation was inhibited by the calpain inhibitor calpeptin. These results indicate that loss of asymmetry thus inducing generation of a catalytic surface is not the consequence of vesicle formation. Conversely, we propose that vesicle shedding is an effect of PL transverse redistribution and calpain-mediated proteolysis during activation.

Chlorpromazine increases the turnover of metabolically active phosphoinositides and elevates the steady-state level of phosphatidylinositol-4-phosphate in human platelets

Non-permeabilizing concentrations (< 40 microM) of chlorpromazine (CPZ) increase the radioactivity of phosphatidylinositol-4-phosphate (PIP) in platelets pre-labelled with [32P]Pi, but the biochemical mechanisms underlying this increase are poorly understood. Incubation of [32P]Pi-labelled, gel-filtered platelets with 25 microM CPZ for 10 min increased: (1) the mass of PIP from 315 to 476 nmol/10(11) platelets but not the total inositol phospholipid mass, (2) the specific phosphodiester radioactivities in phosphatidylinositol (PI), PIP and phosphatidylinositol-4,5-bisphosphate (PIP2) by 34, 63 and 37%, respectively, and (3) the specific phosphomonoester radioactivities in PIP and PIP2 by 53 and 10%, respectively. In control platelets (no CPZ) the specific radioactivity of the phosphodiester was the same in PI, PIP and PIP2, and the specific radioactivity in the phosphomonoester in PIP and PIP2 was 55% of that of the gamma-phosphoryl in ATP, measured as metabolically active, actin-bound ADP. These results suggest that 55% of each of PI, PIP and PIP2 constitutes a metabolic pool which is labelled by 32P in the platelets, while the remainder is in a metabolically inactive pool and not labelled. CPZ has two major effects: (1) CPZ interferes with the kinase and phosphohydrolase reactions that maintain the steady-state level of PIP in the metabolic phosphoinositide pool, resulting in a 92% increase in the PIP level of this pool, and (2) CPZ causes synthesis (45% in 10 min) of new phosphodiester in the metabolically active phosphoinositides by tentative stimulation of the turnover of the phosphoinositide cycle, de novo phosphoinositide synthesis and/or diacylglycerol formation through phospholipases C and D. The marked alteration by CPZ of phosphoinositide metabolism may be part of the mechanism by which this drug effects its psychotropic action.

The inhibition of human platelet function by ganodermic acids

Human gel-filtered platelets aggregate at greater than 20 microM-ganodermic acid S [lanosta-7,9(11),24-triene-3 beta, 15 alpha-diacetoxy-26-oic acid] [Wang, Chen, Shiao & Wang (1989) Biochim. Biophys. Acta 986, 151-160]. This study showed that platelets at less than 20 microM-ganodermic acid S displayed both concentration- and time-dependent inhibition of function, in which the agent potency in response to inducers was ADP-fibrinogen greater than collagen greater than thrombin. The agent caused a biphasic time-dependent effect on platelet phosphoinositide metabolism. The first phase involved the decrease in the pool size of phosphoinositide by 10-20%. The second phase, in which both the resynthesis of phosphatidylinositol 4,5-bisphosphate (PIP2) and the decrease of [32P]phosphatidic acid occurred, took place after 30 min. Scanning electron microscopy also revealed a time-dependent morphological change in platelets in the presence of the agent. The cells initially became spiculate discs, then swelled to a 'potato-like' morphology at 60 min. Further studies on the time-dependent inhibition of thrombin response revealed that: (1) the percentage inhibition of cell aggregation was comparable with that occurring with an increase of cytosolic free Ca2+ concentration [( Ca2+]i) or the phosphorylation of marker proteins; (2) [32P]Pi-labelled platelets showed the time-dependent inhibition of thrombin-stimulated PIP2 resynthesis as indicated by first-2-min time-course studies of phosphoinositide interconversion; (3) scanning electron microscopy revealed that the aged platelet population showed an increase in the percentage of non-responding cells on prolonged incubation. The results, taken together, enabled one to discuss a possible mechanism for the time-dependent inhibition by ganodermic acid S of platelet response to thrombin.

Inhibition of thrombus formation in vivo by novel antiplatelet agent

The antithrombotic and antihemostatic effects of the novel antiplatelet compound, alpha, alpha'-bis[3-(N,N-diethylcarbamoyl)piperidino]-p-xylene dihydrobromide (GT-12), were investigated in a baboon model of platelet-dependent thrombosis under high flow conditions. In this model, segments of collagen-coated tubing and Dacron vascular graft were placed as thrombus-inducing extension devices in exteriorized femoral arteriovenous shunts. The deposition of 111In-labeled platelets was measured for each thrombogenic segment throughout 1 hour by using gamma camera imaging. In addition, the 125I-fibrin retained in the forming thrombus was measured. Intravenous infusion of GT-12 (100 mumol/kg, 63.3 mg/kg) over a 15-minute period before the insertion of the test segments prolonged the bleeding time from a baseline value of 4.4 +/- 0.4 min to 7.6 +/- 1.0 min (p = 0.036) and inhibited platelet aggregation ex vivo induced by adenosine diphosphate (ED50 4.7 +/- 0.9 to 10.3 +/- 2.2 microM; p less than 0.02) and collagen (ED50 2.0 +/- 0.4 to 8.0 +/- 2.4 micrograms/ml; p less than 0.05). Deposition of platelets and fibrin was decreased in concert by 30% (p less than 0.05) for vascular grafts and possibly collagen segments at the end of the 60-minute observation period. We conclude that GT-12 is antithrombotic for Dacron graft-induced thrombus formation in vivo.

The effect of ganodermic acid S on human platelets

Incubation of gel-filtered human platelets in ganodermic acid S (lanosta-7,9(11), 24-trien-3 beta, 15 alpha-diacetoxy-26-oic acid) showed that uptake of the agent by platelets was a simple diffusion process. The agent caused platelet aggregation at concentrations above 20 microM. Above the threshold, the extent of cell aggregation was in a linear relationship to the agent concentration. Below the aggregation threshold, platelets showed neither the resynthesis of [32P] phosphatidylinositol 4,5-bisphosphate ([32P]PIP2) and [32P] phosphatidylinositol 4-phosphate ([32P]PIP) nor the accumulation of [32P] phosphatidic acid ([32P]PA). The results suggested that ganodermic acid S caused the activation of PIP2 hydrolysis. Scanning electron microscopy revealed that the morphology of platelets below the aggregation threshold appeared to be spiculate discoid shape. Above the threshold, the cells rounded up to spiculate irregular forms.

The aggregation of human platelet induced by ganodermic acid S

Incubation of gel-filtered human platelets in ganodermic acid S (lanosta-7,9(11),24-trien-3 beta,15 alpha-diacetoxy-26-oic acid) showed that within a min 80% of the agent was taken up by the cells. The process of uptake was a simple diffusion, and the partition coefficient was about 10(5). The agent caused platelet aggregation at a concentration above 20 microM. Above the threshold, the extent of cell aggregation was in a linear relationship to the agent concentration. Also, the % of cell aggregation was comparable to the elevation of: (1) cytosolic free Ca2+ concentration [( Ca2+]i); (2) protein phosphorylation; and (3) serotonin release. Also, it was correlated with the change in the interconversion of phosphoinositides. Moreover, platelets in various concentrations of ganodermic acid S appeared to show different time-course profiles in the changes of [32P]phosphoinositides and [32P]phosphatidic acid (PA). Upon addition of the agent, platelets showed an initial increase in all of the [32P]phosphoinositides, and then the level of each kind of phosphoinositide decreased sequentially in phosphatidylinositol 4,5-bisphosphate (PIP2), phosphatidylinositol 4-phosphate (PIP) and phosphatidylinositol (PI). Below the aggregation threshold, platelets showed neither the resynthesis of [32P]PIP2 and [32P]PIP nor the accumulation of [32P]PA. However, at 25 and 50 microM, platelets showed not only the resynthesis of [32P]PIP2 and [32P]PIP but also the accumulation of [32P]PA. Interestingly, at 100 microM ganodermic acid S, platelets did not show the resynthesis of [32P]PIP2 and [32P]PIP. In this case, the level of [32P]PA accumulation and that of [32P]PI decrease were less than those found in platelets at 50 microM ganodermic acid S. The results suggested that ganodermic acid S caused the activation of PIP2 hydrolysis. Scanning electron microscopy (scanning EM) revealed that the morphology of platelets below the aggregation threshold appeared to be spiculate discoid shape. Above the threshold, the cells rounded up to spiculate irregular forms, which showed an elongation of filopodia after prolonged 30-s incubation. In addition, platelets at greater than or equal to 50 microM ganodermic acid S showed the occurrence of membrane vesiculation. Hence, the incorporation of ganodermic acid S into platelet membrane resulted in the change of membrane morphology.

Relationships between chemical structure and inhibition of epinephrine-induced human blood platelet aggregation

The effect of structural features in a series of carbamoylpiperidine and nipecotoylpiperazine congeners on epinephrine-induced aggregation of human blood platelets is examined. Epinephrine-induced primary aggregation is effectively inhibited by the nipecotoylpiperazine derivatives (culminating at an IPA50 of 11.9 microM). While among nipecotoylpiperazine as well as carbamoylpiperidine congeners there are potent inhibitors of ADP-stimulated platelet function (cresting at an IA50 of 12.4 and 11.4 microM, respectively), the carbamoylpiperidine analogs are much less active (e.g., IPA50 of 298.1), or practically inactive, in impeding epinephrine-induced primary aggregation (PA).

The solubilization and morphological change of human platelets in various detergents

The solubilization of human gel-filtered platelets by octyl glucoside, Triton X-100, dodecylsulfate, and deoxycholate was compared from the analysis of (1) cell lysis, (2) marker leakiness, and (3) component solubility. These analyses all revealed that the effect of detergent concentration on the solubilization of platelets by these detergents was exerted in three stages, i.e., the prelytic, lytic, and complete platelet-lysis stages. These analyses also indicated several differences among platelets in these detergents. (i) The ratio of the platelet-saturation concentration (PSC) to critical micellar concentration (CMC) was about 1/2 for octyl glucoside. Triton X-100 and dodecylsulfate, while it was close to 1 for deoxycholate. (ii) Platelets in octyl glucoside. Triton X-100, and dodecylsulfate all showed parallel curves in cell lysis, protein solubilization and marker leakiness, while the platelet lysis in deoxycholate was identical to the phospholipid solubilization. (iii) The solubility curves of various components in Triton X-100 and deoxycholate were parallel. However, the solubility of cholesterol in octyl glucoside was lower than that of protein and phospholipid. In dodecylsulfate, the solubility of phospholipid and cholesterol was very low in comparison with that of protein. In addition, morphological studies using scanning electron microscopy (scanning EM) revealed that the solubilization by octyl glucoside or Triton X-100 might occur via membrane area expansion. On the other hand, the solubilization by dodecylsulfate or deoxycholate showed membrane vesiculation prior to cell lysis. Moreover, in the prelytic stage, the morphological change in platelets in octyl glucoside showed only concentration dependence by swelling to an ellipsoid and then to a sphere. However, the morphological change in platelets in the other three detergents was dependent not only on the detergent concentration but also on prolonged incubation. Specifically, in Triton X-100, the cells initially changed to spiculate discs and then reached their final shape as swollen discs with surface invagination. In dodecylsulfate and deoxycholate the morphological changes were almost the same. The cell initially deformed in shape to a spiculate disc and finally to a stretched-out flat form. The results are discussed according to the bilayer couple hypothesis. Also, in the prelytic stage, these detergents caused inhibition of the response of platelets to collagen and ADP-fibrinogen.