Reevaluation of sex differences in platelet aggregation in a physiologic system

Sex-Related Differences in Platelet Aggregation: A Literature Review Supplemented with Local Data from a Group of Generally Healthy Individuals

The process of platelet aggregation is often influenced by several factors including sex and age. A literature review confirmed the existence of sex-related differences in platelet aggregation. Although 68 out of 78 papers found such differences, there are still some controversies regarding these differences, which can be due to multiple factors (age, trigger, concomitant disease, sample handling, etc.). These outcomes are discussed in line with novel results obtained from a local study, in which blood samples from a total of 53 overall healthy women and men with ages ranging from 20 to 66 years were collected. Aggregation was induced with seven different triggers (ristocetin, thrombin receptor activating peptide 6 [TRAP-6], arachidonic acid [AA], platelet-activating factor 16 [PAF-16], ADP, collagen, or thromboxane A₂ analog U-46619) ex vivo. In addition, three FDA-approved antiplatelet drugs (vorapaxar, ticagrelor, or acetylsalicylic acid [ASA]) were also tested. In general, women had higher aggregation responses to some agonists (ADP, TRAP), as well as lower benefit from inhibitors (ASA, vorapaxar). The aggregatory responses to AA and TRAP decreased with age in both sexes, while responses to ADP, U-46619, and PAF were affected by age only in women. In conclusion, more studies are needed to decipher the biological importance of sex-related differences in platelet aggregation in part to enable personalized antiplatelet treatment.

The effect of the menstrual cycle and of decompression stress on arachidonic acid-induced platelet aggregation and on intrinsic platelet thromboxane production in women compared with men

Menstrual cycle variations in platelet aggregation and thromboxane production in association with sex steroids have been reported. External stimuli such as decompression sickness have been associated with clotting activity changes, specifically, increased platelet aggregation. Differences in response of platelets from women and men, when subjected to such a stress, have been observed. This study evaluated the ability of washed platelets from women in the proliferative and secretory phases of the menstrual cycle to aggregate in response to arachidonic acid and the aggregation difference between washed platelets from women and men in response to decompression stress and arachidonic acid. Additionally, platelet thromboxane production differences between the assessed platelet populations were compared. Our results indicate no difference in platelet aggregability between phases of the menstrual cycle. A significant aggregation difference between platelets from women and men was noted. Platelets from women were more sensitive to arachidonic acid aggregation. These differences were not affected by decompression stress. No difference in thromboxane B2 production was noted between the platelet populations evaluated.

Extracellular-free Ca++ accounts for the sex difference in the aggregation of human platelets in citrated platelet-rich plasma

It has been shown in Poiseuille flow, that the ADP-induced aggregation of human platelets in citrated plasma from female donors is significantly greater than from male donors over a range of mean tube shear rate, G, from 41.9 s-1 to 1920 s-1 and mean transit time, t, from 0.2 to 86 s. The present work verifies the sex difference at G = 335 s-1 and t = 43 s and deals with the effect of free Ca2+ on it. An inverse correlation between the extent of single platelet aggregation and donor hematocrit, and between hematocrit and the plasma ionized calcium concentration, [Ca2+], as well as a positive correlation between the extent of single platelet aggregation and [Ca2+] was found. This indicated that the sex difference is due to hematocrit-dependent differences in the [Ca2+] that result when a fixed volume of the chelating agent citrate is used to anticoagulate blood. When the initial citrate concentration was adjusted to compensate for the variable volume dilution of citrate in plasma among donors and the [Ca2+] of males raised above that of females, the sex difference was reversed. Again, aggregation correlated with [Ca2+]. At the physiological [Ca2+] in both heparinized PRP and hirudinized PRP, the rate of aggregation and aggregate size were much greater than in citrated plasma but no sex difference was detected.

Metabolism of arachidonic acid by macaque platelets. Implications for studies on atherosclerosis

The metabolism of [1-14C]arachidonic acid [( 1-14C]AA) by washed platelets from macaques and human subjects was investigated. The results were as follows: At substrate levels of 1 microM, similar amounts of prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2 alpha), prostaglandin D2 (PGD2), and thromboxane A2 (TXA2), measured as thromboxane B2 (TXB2), were produced from [1-14C]AA by platelets from rhesus, Celebes black, and cynomolgus macaques and humans. An increase in the AA concentration from 1 microM to 20 microM decreased the TXB2: PGD2 ratio (aggregator: antiaggregator) from greater than 5 to less than 2 in all series. In the human series, the ratio decrease was due to an increase in PGD2 production; in the macaque series, PGD2 production increased and TXB2 production decreased. Under basal conditions and at 1 microM AA concentrations, the amounts of prostaglandins and thromboxanes produced by platelets from male and female rhesus macaques were the same. An increase in substrate concentration from 1 microM to 20 microM AA decreased TXB2 production and increased PGD2 production to the same extent in platelets from male and female rhesus macaques. Imidazole increased prostaglandin production and decreased TXB2 production by platelets from both male and female rhesus macaques. The TXB2: PGD2 ratios were reduced below 1.5; there was no difference between the ratios in the two series. In the presence of 1 mM imidazole, greater amounts of prostaglandins and thromboxanes were produced in the male than in the female series. These data indicate that macaque's platelets are a suitable model for the study of AA metabolism in human platelets.