Platelet function (third of three parts)

The levels of TGFβ1, VEGF, PDGF-BB, and PF4 in platelet-rich plasma of professional soccer players: a cross-sectional pilot study

Background

Regenerative therapy using platelet-rich plasma (PRP), a rich source of growth factors, has become popular in orthopedic sports medicine. Elite athletes prefer PRP therapy for their injured muscles and tendons primarily to avoid the possible risks of surgical treatment. However, the clinical effectiveness of PRP therapy in elite athletes compared to that in non-athletes remains unknown. Therefore, to investigate the effectiveness of PRP therapy in professional athletes (pro-athletes), we focused on the quality of PRP preparations and compared the levels of bioactive molecules between pro-athletes and non-athletes.

Methods

PRP was prepared from healthy, non-smoking male professional soccer players (pro-athletes) (n = 22) and non-athletes (VEGF: n = 34, others: n = 38). The levels of TGFβ1, PDGF-BB, VEGF, and PF4 were determined using ELISA kits. Polyphosphate was probed with 4’,6-diamidino-2-phenylindole and monitored using a fluorometer. The body composition of the donors was determined using a bathroom weighing scale.

Results

The levels of TGFβ1 and VEGF were significantly lower in pro-athletes than in non-athletes, whereas PF4 levels were significantly higher in pro-athletes. No significant difference was found in PDGF-BB levels between these groups. Biomolecule levels were not correlated with polyphosphate levels.

Conclusion

TGFβ1, VEGF, and PDGF-BB levels in pro-athletes were not higher than those in non-athletes. These findings suggest that growth factor levels in PRP may not be a predominant determinant of the clinical effectiveness of PRP therapy in pro-athletes. Increased PF4 levels in pro-athletes suggest an immunological function of PRP that may positively influence tissue regeneration.

Platelets in defense against bacterial pathogens

Platelets interact with bacterial pathogens through a wide array of cellular and molecular mechanisms. The consequences of this interaction may significantly influence the balance between infection and immunity. On the one hand, recent data indicate that certain bacteria may be capable of exploiting these interactions to gain a virulence advantage. Indeed, certain bacterial pathogens appear to have evolved specific ways in which to subvert activated platelets. Hence, it is conceivable that some bacterial pathogens exploit platelet responses. On the other hand, platelets are now known to possess unambiguous structures and functions of host defense effector cells. Recent discoveries emphasize critical features enabling such functions, including expression of toll-like receptors that detect hallmark signals of bacterial infection, an array of microbicidal peptides, as well as other host defense molecules and functions. These concepts are consistent with increased risk and severity of bacterial infection as correlates of clinical abnormalities in platelet quantity and quality. In these respects, the molecular and cellular roles of platelets in host defense against bacterial pathogens are explored with attention on advances in platelet immunobiology.

Evaluation of platelet number and function and fibrinogen level in patients bitten by snakes of the Bothrops genus

Platelet function and plasma fibrinogen levels were evaluated in 14 patients, 10 males and 4 females, aged 13-59 years bitten by Bothrops genus snakes. There was a statistical difference (p < 0.05) among plasma fibrinogen levels evaluated 24 and 48 hours after envenomation. There was a tendency towards normalization after 48 hours of treatment. The low platelet number was clear in 24-48 hour evaluations with a tendency towards normalization after 48 hours of treatment (p < 0.05). When platelet function was stimulated by collagen and epinephrine, it appeared to be within normal values. On the other hand, when it was stimulated by adenosine diphosphate (ADP), platelet function was hypoaggregated by a single micromol concentration until 48 hours after treatment. At a 3 micromol concentration, there were alterations only before specific treatment (p < 0.05). Fibrinogen levels and fibrin degradation product (FDP) levels appeared to be altered in 83.33% of patients evaluated. The authors suggest that platelet hypoaggregation is related to decreased fibrinogen and increased FDP levels.

Mechanisms of tumor necrosis induced by photodynamic therapy

Despite great progress and promising results achieved in cancer treatment by photodynamic therapy (PDT), the exact mechanism of tumor photosensitization in vivo by porphyrins and related phototherapeutic agents has not been fully explored and understood. This review is an attempt to gather available data on various processes occurring in neoplastic cells, microvasculature, non-vascular stroma and circulating blood within PDT-treated tumors. This information is necessary to understand the mechanisms governing the very complex processes which eventually lead to tumor necrosis.

Dietary fats and platelet function among Finnish men

The aim of this study was to elucidate the role of platelet aggregation as a risk factor for ischemic heart disease (IHD) and the relationship between fatty acids and platelet function. Platelet aggregation upon adenosine diphosphate (ADP), adrenaline and thrombin were measured in middle aged men in east and west, two regions of Finland with a nearly twofold difference in IHD mortality. Platelet aggregation results were correlated with the fatty acid compositions of plasma lipid fractions, adipose tissue triglycerides and platelet phospholipids. There was no significant east-west difference in platelet reactivity to ADP, adrenaline and thrombin. ADP-induced platelet aggregation showed significant negative correlations with all the platelet C20-C22 n-3 polyunsaturated fatty acids (PUFA), but significant positive correlations with the percentage of 18:2n-6 in adipose tissue and plasma cholesterol esters (CE) and triglycerides (TG). Adrenaline-induced aggregation correlated negatively with the percentage of 20:5n-3 in plasma CE and TG, and positively with the total percentage of saturated fatty acids in platelets. Aggregation upon thrombin had a negative correlation with the 20:3n-6/20: 4n-6 ratio in plasma CE and a positive correlation with 18:2n-6 in adipose tissue. The percentages of the major PUFA in platelets correlated significantly with the same fatty acids in plasma CE and phospholipids PL. Platelet 20: 5n-3 had a highly significant negative correlation with the percentage of 18: 2n-6 in plasma and adipose tissue lipids. Platelet 20: 4n-6 was unrelated to its precursors in plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Toxicological assessment of the hemostatic system, regulatory requirements, and industry practice

Disturbances of the hemostatic system which may be caused by chemicals include hemorrhagic diathesis, caused by inhibition of blood clotting, impairment of platelet function, and hyperactivity of fibrinolysis. Activation of the plasmatic clotting system, platelet aggregation, and inhibition of fibrinolysis may lead to thromboembolic complications. Although much is known about the functions of the hemostatic system a rational and cost-effective approach for its assessment in industrial toxicology is lacking. In this review the physiology of hemostasis and the available laboratory tests are discussed, current regulatory requirements are described, and industry practice is analyzed based on experience accumulated over the last 23 years. Proposals for a more flexible and scientific approach to testing of hemostatic mechanisms in toxicology are made.

Platelet activation studied by fluorescence polarization

Platelet activation was elevated by changes in the fluorescence anisotropy of the sulfhydryl-reactive fluorescent probe, (5-[2-(iodoacetyl) aminacetyl]aminonaphthalene-1-sulfonic acid. The membrane-permeable fluorophore was shown to bind to a multitude of cytoplasmic and membrane proteins. Platelets were stimulated by addition of thrombin, arachidonic acid or ADP under conditions that did not induce aggregation. A sudden increase in the fluorescence anisotropy, r of moderate degree (25-33%) occurred during the first 60 s after exposure of platelets to the aggregating agents and was sustained during the entire period of observation (15-18 min). Phenylmethylsulfonyl thrombin was unable to produce these changes in fluorescence anisotropy. Preincubation of platelets with colchicine reduced r within 30-60 s after platelets were exposed to thrombin. These findings are interpreted as an indication of a general decrease in the 'motional freedom' of the fluorophores and indirectly their ligand molecules.

The effects of cigarette smoke and nicotine on platelet thrombus formation in stenosed dog coronary arteries: inhibition with phentolamine

This study was undertaken to examine in vivo the effects of cigarette smoke on cyclic reductions in coronary flow due to platelet thrombus formation in the stenosed coronary arteries of anesthetized dogs. The circumflex coronary artery of 21 mongrel dogs was stenosed 60 - 80%, with blood flow measured with an electromagnetic flow probe. After the administration of cigarette smoke, plasma epinephrine was elevated nine times the control level (p less than 0.001) and peak mean blood pressure was elevated one and one-half times control (p less than 0.01). The hematocrit increased several percent (p less than 0.01) with cigarette smoke, although blood gases and pH remained unchanged. In all 21 dogs, spontaneous reductions in coronary blood flow were greatly exacerbated in the stenosed circumflex artery as evidenced by the number of flow reductions, the increased size of the reductions and the rate of flow reduction. Nicotine administered intravenously in doses comparable to those achieved through absorption of cigarette smoke by the lungs provoked similar responses of alpha-adrenergic stimulation and potentiation of the platelet thrombus formation. An alpha-adrenergic antagonist, phentolamine, was given (3 mg/kg) intravenously to inhibit the exacerbated platelet thrombus formation due to cigarette smoke or infused nicotine. In 18 of 21 dogs, an acute occlusive platelet thrombus was prevented 15 minutes after phentolamine and after phentolamine and after a cigarette smoke or nicotine challenge. This study confirms a link between cigarette smoking, platelet formation, and the potential for humans to develop an acute occlusive platelet thrombus in a diseased and stenotic coronary artery.

Platelet aggregation in partially obstructed vessels and its elimination with aspirin

In 35 open chest anesthetized dogs coronary and aortic blood flow were measured with electromagnetic flowmeters while aortic and distal coronary blood pressure and an epicardial ECG were recorded. A fixed amount of stenosis (60-80%) was produced in the coronary artery by an externally applied plastic cylinder. In 24 of the 35 dogs the coronary blood flow showed cyclical reductions to near zero, with a sudden spontaneous return to near control levels. During reduced flow the epicardial ECG showed ST-segment depression suggestive of ischemia, and ventricular premature beats were often noted. Six animals died acutely during episodes of reduced flow. After 35 mg/kg of aspirin were given intravenously the cyclical reductions in coronary blood flow were abolished and the in vitro platelet aggregations were reduced from a control of 62.1 +/- 15 units (Born technique) to an average of 23.7 +/- 12 units. Histologic sections of the narrowed coronary artery obtained when coronary flow was reduced show an amorphous mass in the lumen which was thought to be a platelet aggregate. Perhaps a similar process of platelet aggregation occurs in the stenosed coronary arteries in man, producing acute coronary obstruction, ischemia, and sudden death.

Platelet lipoproteins. A comparative study with serum lipoproteins

The nature of human platelet lipoproteins was studied in two series of experiments. In the first series, whole platelets were utilized for extraction of lipoproteins by three different methods: chloroform/methanol/phenol; saline; or sucrose-gradient ultracentrifugation of platelet homogenates. By polyacrylamide gel electrophoresis we were able to demonstrate the existence of lipoprotein in the extracts obtained by the last two methods. These lipoproteins were found not to share antigenic determinants with alpha and beta serum lipoproteins. The second series of experiments utilized platelets solubilized either in sodium deoxycholate or sodium dodecyl sulfate. The solubilized product was characterized by double immunodiffusion and polyacrylamide gel electrophoresis. The nonidentity between plasma and platelet lipoproteins previously demonstrated in the first series of experiments was confirmed. This nonidentity was also supported by a comparison between the apoproteins of purified serum lipoproteins and platelet proteins released after solubilization with sodium dodecyl sulfate. No identical protein fractions were found. Our results suggest that, unlike erythrocyte membrane lipoproteins, the platelet lipoproteins are structurally different from plasma lipoproteins.

Evidence for a single class of thrombin-binding sites of human platelets

We previously demonstrated that human platelets bind a small number of thrombin molecules with high affinity and a larger number with relatively lower affinity (Tollefsen, D. M., Feagler, J. R., and Majerus, P. W. (1974), J. Biol. Chem. 249, 2646). In the present report, equilibrium binding studies using [125I]DIP-thrombin (diisopropylphosphoryl-thrombin) over the range of 0.0002-10 U/ml yield a Hill coefficient of 0.775. Measurements of the rate of dissociation of [125I]DIP-thrombin bound to platelets at relatively high affinity (0.04 U/ml added) indicate a much faster dissociation in the presence of 14 U/ml unlabeled DIP-thrombin (T 1/2 = 1.0 min) than in its absence (T 1/2 - 140 min). [125I]DIP-thrombin bound at low affinity (1.0U/ml added) dissociates from platelets with a T 1/2 = 1.7 min in the absence of unlabeled DIP-thrombin. These results suggest a negative cooperative interaction among receptor sites for thrombin; i.e., as thrombin binds to unoccupied sites, high-affinity receptors are apparently converted to low-affinity receptors. In an attempt to detect whether there is heterogeneity of thrombin receptors, [125I]DIP-thrombin was covalently cross-linked to intact platelets using 1 mM glutaraldehyde. A single complex (apparent molecular weight, 200 000) containing [125I]DIP-thrombin was formed throughout a range of thrombin concentrations in which both high- and low-affinity binding was observed. Since incorporation of [125I]DIP-thrombin into this complex did not occur in the absence of platelets and was inhibited by unlabeled thrombin, the complex may represent thrombin cross-linked to its receptor. We conclude that a single class of receptor sites can account for both high- and low-affinity binding of thrombin to platelets, although interaction between nonidentical sites cannot be excluded.

Distribution of free sulfhydryl and disulfide groups among platelet membrane proteins

Reactive sulfhydryl and disulfide groups were identified in platelet membrane proteins resolved by sodium dodecyl sulfate-polycrylamide gel electrophoresis. Platelet membranes treated with N-ethyl(1-14C)maleimide, phenyl(203Hg)mercuric acetate and p-chloro(203Hg)mercuribenzoate showed similar patterns of distribution of sulfhydryl groups among the sodium dodecyl sulfate-solubilized membrane proteins. Four major and two minor polypeptides ranging in molecular weight from greater than 200 000 to 20 000 were found to have reactive SH groups. Reduction of membrane proteins by sulfite coupled with subsequent mercaptide formation of the resultant monothiols led to the identification of four polypeptides with disulfide bonds. Reaction of platelet membranes with 14C-labeled 5,5'-dithio-bis(2-nitrobenzoic acid) resulted changes in the distribution profile of the solubilized membrane proteins suggestive of a polymerization process dependent upon, 5,5'-dithio-bis(2-nitrobenzoic acid)-induced intermolecular disulfide interchange.

Regulation of platelet phosphorylase

A sensitive fluorimetric enzyme assay was developed for study of activation of glycogen phosphorylase (EC 2.4.1.1) in intact platelets and in platelet extracts. Activity was calculated as AMP independent (activity in the absence of AMP), total (activity in the presence of 1 mM AMP), and AMP dependent (difference between AMP independent and total). The following observations were made with intact rat platelets. (1) Stimulation of platelets with thrombin caused a 7-fold increase in total activity, with increases in both AMP-dependent and AMP-independent activities. Maximum activation was obtained within 10 s after addition of thrombin. (2) The divalent cation ionophore A23187 caused a similar, though less pronounced, activation of phosphorylase. (3) Acceleration of glycogenolysis by inhibition of respiration with cyanide caused similar changes in phosphorylase activity but with the maximum effect observed only after 45 s. (4) Dibutyryl cyclic AMP had two effects; it partially activated phosphorylase and blocked further activation by thrombin, but not A23187. Similar effects were observed with human platelets, but low resting levels of phosphorylase activity could not be maintained so that changes were not as large as with rat platelets. Experiments with extracts of rat platelets gave the following results. (1) Phosphorylase activity in many extracts of non-stimulated platelets could be increased by incubation with Mg2+-ATP and Ca2+; ethyleneglycol-bis-(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA) partially inhibited. (2) In some extracts there was essentially no activation by incubation with Mg2+-ATP and Ca2+, but addition of cyclic AMP GAVE PARTIAL ACTIVATIon while addition of rabbit muscle phosphorylase kinase gave full activation. (3) Incubation of extracts of thrombin-stimulated platelets caused conversion of AMP-dependent to AMP-indeptndent activity. It is concluded that platelet phosphorylase exists in an inactive and two active forms. Conversion of the inactive to the active forms and of the AMP-dependent to the AMP-independent form is catalyzed by a kinase(s) that requires Ca2+ for full activity and is activated through a cyclic AMP-mediated process. The major change following physiological stimulation is an increase in both active forms, with little change in their ratio.

Platelet survival in patients with homograft and prosthetic heart valves. Correlation with incidence of thromboembolism

Manohitharajah, S. M., Rahman, A. N., Donnelly, R. J., Deverall, P. B., and Watson, D. A. (1974).Thorax, 29, 639-642. Platelet survival in patients with homograft and prosthetic heart valves. Investigations in the past have demonstrated shortened platelet survival time in patients with prosthetic heart valves. This suggested that platelets contribute to thromboembolism in this group. Homograft valves and the newer models of the Starr-Edwards prosthesis have proved less thrombogenic than those previously employed, but platelet survival studies in patients with these valves are lacking. In this study platelet function, survival, and its relation to haemolysis were determined in 28 patients following mitral valve replacement and in two patients following mitral valvotomy: 14 patients had a frame-mounted homograft aortic valve; 13 patients had a Starr-Edwards prosthesis model 6310 or 6320, and one had a Starr-Edwards prosthesis model 6000. Normal platelet function and survival was found in both the homograft and the Starr valve groups. The patient with the earlier model of the Starr valve (model 6000) had a shortened platelet survival time. The two patients following mitral valvotomy had normal platelet survival. The fact that platelet abnormalities were not demonstrable in our patients with homograft valves and newer Starr-Edwards prostheses may explain the low incidence of thromboembolism in this group. Platelet survival studies are a useful parameter to determine the potential thrombogenic nature of prosthetic valves. Platelet survival time was not influenced by the presence or severity of haemolysis.

The tumor-promoter phorbol ester (12-O-tetradecanoyl-phorbol-13-acetate), a potent aggregating agent for blood platelets

The phorbol ester 12-0-tetradecanoyl-phorbol-13-acetate, a potent tumor-promoting agent, caused irreversible platelet aggregation when more than 0.02 microM was stirred with human citrated or heparinized platelet-rich plasma (PRP). With washed platelets, 1 nM was effective. The alcohol phorbol, which has little tumor-promoting activity, failed to cause platelet aggregation. With all but low concentrations of phorbol ester, aggregation was succeeded by a rapid phase. The latter was prevented or reduced by enzymes which destroy ADP and by aspirin, was associated with a change in platelet shape, and was presumably due to released ADP. At higher concentrations, only a rapid phase was seen, and these inhibitors were not effective. Low concentrations did not aggregate platelets in PRP containing sufficient EDTA or EGTA to chelate ionized calcium or in PRP from thrombasthenic patients; higher concentrations caused slight aggregation. Both the primary, non-ADP-dependent aggregation and the rapid ADP-dependent aggregation were markedly inhibited by substances which increase cyclic AMP, metabolic inhibitors, and the sulfhydryl inhibitor N-ethylmaleimide. Phorbol ester reduced platelet cyclic AMP only when it had been previously elevated by prostaglandin E(1). 1 microM did not release beta-glucuronidase, lactic dehydrogenase, or inflammatory material from platelets in 4-5 min despite marked aggregation, but liberated all three in 30 min. The possibility is discussed that low phorbol ester concentrations cause primary aggregation by a direct action on platelet actomyosin.

Studies on human platelet gangliosides

Gangliosides, glycosphingolipids which contain sialic acid, were studied in human platelets. They represented 0.5% of the platelet lipids and accounted for 6% of the total neuraminic acid content of platelets. Three major ganglioside fractions were identified and characterized. Ganglioside I was hematoside (G(6)) and comprised 92% of the platelet gangliosides. It contained glucose, galactose, and sialic acid in molar ratios of 1:1:1 and no hexosamine. The major fatty acid was behenate (22:0). Ganglioside I was also identified in isolated platelet granules and membranes. Ganglioside II (5%) contained glucose, galactose, sialic acid, and hexosamines (molar ratios 1:2:1:1). The hexosamines were glucosamine (72%) and galactosamine (28%). It was therefore designated as ganglioside lacto-N-neotetraose. Ganglioside III (2%) contained disialosyllactosyl ceramide (G(3A)) as well as two other gangliosides which could not be precisely characterized. Gangliosides I, II, and III were susceptible to the action of Clostridium perfringens neuraminidase as evidenced by full recovery of sialic acid in its free form after incubation. Neutral platelet glycolipids were qualitatively examined by thin-layer chromatography. The major component was lactosyl ceramide. Interactions of gangliosides I and III and serotonin-(14)C were examined in an equilibrium dialysis system at 4 degrees C. The gangliosides bound serotonin-(14)C in relatively small quantities, whereas control lipids were negative. The binding was essentially unchanged by reverse dialysis, ultracentrifugation and subsequent thin-layer chromatography. The results are comparable to the previously observed nonmetabolic interactions between whole platelets and serotonin in the cold. It is suggested that the orientation and specific distribution of platelet membrane glycolipids may be important determinants of the unique surface properties of platelets.

Studies on the interaction between collagen and a plasma kallikrein-like activity. Evidence for a surface-active enzyme system

This study has demonstrated that collagen particles, after exposure to platelet-poor human plasma and subsequent washing, generate a kinin-like agent when incubated with prekinin substrate. The binding of kinin-generating activity to collagen in the plasma collagen incubation mixture occurs rapidly, whereas the loss of this activity in the incubation mixture occurs relatively slowly. The Hageman factor appeared to be necessary for the surface-bound kinin-generating activity, as this activity was absent in collagen exposed to Hageman factor-deficient plasma. These studies have partially characterized the plasma-derived enzymatic activity bound to collagen. Incubation of collagen with plasma caused a concentration-dependent reduction in the kinin-producing activity which was generated by the addition of ellagic acid, a known activator of plasma kallikrein. The kinin-inducing activity bound to collagen is inhibited by soybean trypsin inhibitor, Trasylol, serum C1 inactivator and the plasma alpha(2)-macroglobulin, but not by lima bean trypsin inhibitor. An eluate prepared from plasma-treated collagen, when compared with purified plasma kallikrein, shared a similar inhibitor profile. Selective chemical blockage of the free carboxyl groups on the collagen molecule, or heat denaturation, inactivated the ability of the collagen to generate kinin-like activity after incubation with plasma. Removal of the collagen telopeptides or blockage of the free amino groups failed to affect the collagen-plasma interaction. The binding of partially purified plasma kallikrein to collagen was found to have similar structural and chemical requirements. These data indicate that there is a structural and chemical specificity for the activation and binding of plasma kallikrein-like activity by collagen. These studies suggest that a plasma kallikrein may function as a surface-bound enzyme system.

A thrombin-sensitive protein of human platelet membranes

The action of thrombin on intact human platelets has been studied with the aid of polyacrylamide gel electrophoresis in sodium dodecylsulfate. A single major membrane protein band with a molecular weight of 190,000 disappears after thrombin treatment, while a new membrane protein with a molecular weight of 107,000 appears. This may represent hydrolysis of the thrombin-sensitive protein. When platelets are disrupted or when the thrombin-sensitive protein is solubilized from membranes prior to thrombin treatment, no hydrolysis occurs. The effect of thrombin on the platelet membrane protein is complete within 2 min which suggests that hydrolysis of this membrane protein may trigger the physiological effects of thrombin on platelets.