SummaryThe tail bleeding time (BT) in rats definitely varies according to the method applied. Of the various variables that may influence BT, we have evaluated the position (horizontal or vertical) of the tail, the environment (air or saline), the temperature (4°, 23° or 37° C) and the type of anaesthesia. Transection of the tail tip cannot be used to screen drugs active on platelet function since it is sensitive to coagulation defects. Template BT in contrast is not modified by heparin and is sensitive to defects of platelet number and function (“storage pool disease”, dipyridamole-like drugs, exogenous prostacyclin). In contrast the test fails to detect aspirin-induced platelet dysfunction. The evidence reported indicates that thromboxane A2-prostacyclin balance is not a factor regulating BT. Aspirin treatment however may be a precipitating factor when associated with other abnormalities of platelet function.Template BT is a valid screening test for platelet disorders and for antiplatelet drugs.

SummaryThrombin-activated human platelets release substance(s) of a prote-ic nature which induce an increase in the intracellular calcium concentration in polymorphonuclear leukocytes (PMN). Aim of this study was to characterize the platelet released product(s) responsible for PMN stimulation.PMN-stimulating activity was isolated from platelet supernatant by FPLC and HPLC. The N-terminal sequence analysis revealed that the purified fractions consisted in 90% of a peptide of 73 amino acids and in 10% of a peptide of 74 amino acids; both are truncated forms of the connective tissue-activating peptide III (CTAP-III), a platelet a-granule product, and have 3 and 4 additional amino acids at the N-terminus compared with the neutrophil-activating peptide 2 (NAP-2): Asp-Leu-Tyr and Ser-Asp-Leu-Tyr, respectively. Treatment of platelet supernatant (previously depleted of PMN-activating nucleotides) with Affi-gel heparin resulted in the disappearance of PMN-stimulating effects, suggesting that NAP-2 variants, which are heparin-binding proteins, account for ATP-independent PMN-stimulating activity of the supernatant. Cross-desensitization between rNAP-2 and the platelet supernatant and inhibition by the anti-NAP-2 antibody are in agreement with this conclusion. Although NAP-2 and its variants are reportedly generated from the inactive precursors, CTAP-III and platelet basic protein, through a proteolytic cleavage, NAP-2 variants were not generated in our system by proteases deriving from platelets or contaminating leukocytes. Indeed, treatment of intact platelet suspensions with different protease inhibitors failed to modify the calcium stimulating activity of the resulting supernatants. In conclusion, thrombin-activated platelets release NAP-2 variants which are not generated outside the platelets by proteolytic processing but are released in an active form. This finding enhances our understanding of platelet-PMN interaction in thrombosis and inflammation.

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Background: Hydroxychloroquine (HCQ) was proposed as potential treatment for COVID-19, but its association with mortality is not well characterized. We conducted two meta-analyses to evaluate the association between HCQ (with or without azithromycin (AZM)) and total mortality in COVID-19 patients. Methods: Articles were retrieved until October 20th, 2020 by searching in seven databases. Data were combined using the general variance-based method on relative risk estimates. Results: A total of 26 articles were found (N=‬44,521 ‬COVID-19 patients, including N=7,324 from 4 randomized clinical trials (RCTs)); 10 studies were valuable for analysing the association of HCQ+AZM. Overall, the use of HCQ was associated with 21% lower mortality risk (pooled risk ratio: 0.79, 95%CI: 0.67 to 0.93; high level of heterogeneity: I2=82%, random effects). This association vanished (1.10, 95%CI: 0.99 to 1.23 and 1.10, 95%CI: 0.99 to 1.23) when daily dose >400 mg or total dose >4,400 mg were used, respectively). HCQ+AZM was also associated with 25% lower mortality risk, but uncertainty was large (95%CI: 0.50 to 1.13; P=0.17). No association was apparent when only pooling the 4 RCTs (13.8% of the overall weight; pooled risk ratio: 1.11, 95%CI: 0.99 to 1.24). Conclusions: HCQ use was not associated with either increased or decreased mortality in COVID-19 patients when 4 RCTs only were evaluated, while a 7% to 33% reduced mortality was observed when observational studies were also included. The association was mainly apparent when pooling studies using lower doses of HCQ. These findings can help disentangling the debate on HCQ use in COVID-19.

SummaryPlasma fibrinolytic activity and tissue-type plasminogen activator (t-PA) were defective in response to venous stasis in five out of ten patients with peripheral occlusive artery disease. Discontinuous infusions of iloprost, a stable synthetic analogue of prostacyclin, restored a normal fibrinolytic response in all five patients but did not induce a parallel increase of plasma t-PA. These findings suggest that in addition to the possible benefits due to its vasodilatory and antiplatelet activity, iloprost may improve the fibrinolytic activity in patients with atherosclerotic disease, providing them with further antithrombotic protection. The profibrinolytic effect of iloprost seems not to depend on its ability to induce vascular t-PA release. Rather, it might be related to its inhibitory effect on PAI release from platelets, endothelial cells and/or hepatocytes. Venous occlusion test represents an easy diagnostic approach to fibrinolytic defects, even if related to arterial disease, and may help select patients who need therapeutic intervention.