AIM To examine the effect of high doses of vitamin C(VitC) on ex vivo human platelets(PLTs).METHODS Platelet concentrates collected for therapeutic or prophylactic transfusions were exposed to:(1) normal saline(control);(2) 0.3 mmol/L VitC(Lo VitC); or(3) 3 mmol/L VitC(Hi VitC, final concentrations) and stored appropriately. The Vit C additive was preservative-free buffered ascorbic acid in water, pH 5.5 to 7.0, adjusted with sodium bicarbonate and sodium hydroxide. The doses of Vit C used here correspond to plasma Vit C levels reported in recently completed clinical trials. Prior to supplementation, a baseline sample was collected for analysis. PLTs were sampled again on days 2, 5 and 8 and assayed for changes in PLT function by: Thromboelastography(TEG), for changes in viscoelastic properties; aggregometry, for PLT aggregation and adenosine triphosphate(ATP) secretion in response to collagen or adenosine diphosphate(ADP); and flow cytometry, for changes in expression of CD-31, CD41 a, CD62 p and CD63. In addition, PLT intracellular Vit C content was measured using a fluorimetric assay for ascorbic acid and PLT poor plasma was used for plasma coagulation tests [prothrombin time(PT), partial thrombplastin time(PTT), functional fibrinogen] and Lipidomics analysis(UPLC ESI-MS/MS).RESULTS VitC supplementation significantly increased PLTs intracellular ascorbic acid levels from 1.2 mmol/L at baseline to 3.2 mmol/L(Lo VitC) and 15.7 mmol/L(Hi VitC, P < 0.05). VitC supplementation did not significantly change PT and PTT values, or functional fibrinogen levels over the 8 d exposure period(P > 0.05). PLT function assayed by TEG, aggregometry and flow cytometry was not significantly altered by Lo or Hi VitC for up to 5 d. However, PLTs exposed to 3 mmol/L VitC for 8 d demonstrated significantly increased R and K times by TEG and a decrease in the α-angle(P < 0.05). There was also a fall of 20 mm in maximum amplitude associated with the Hi VitC compared to both baseline and day 8 saline controls. Platelet aggregation studies, showed uniform declines in collagen and ADP-induced platelet aggregations over the 8-d study period in all three groups(P > 0.05). Collagen and ADP-induced ATP secretion was also not different between the three groups(P > 0.05). Finally, VitC at the higher dose(3 mmol/L) also induced the release of several eicosanoids including thromboxane B2 and prostaglandin E2, as well as products of arachidonic acid metabolism via the lipoxygenases pathway such as 11-/12-/15-hydroxyicosatetraenoic acid(P < 0.05).CONCLUSION Alterations in PLT function by exposure to 3 mmol/L VitC for 8 d suggest that caution should be exerted with prolonged use of intravenous high dose VitC. AIM To examine the effect of high doses of vitamin C (VitC) on ex vivo human platelets (PLTs). METHODS Platelet concentrates collected for therapeutic or prophylactic transfusions were exposed to: (1) normal saline (control); / L VitC (Lo VitC); or (3) 3 mmol / L VitC (Hi VitC, final concentrations) and stored appropriately. The Vit C additive was preserved in free buffered ascorbic acid in water, pH 5.5 to 7.0, adjusted with sodium bicarbonate and sodium hydroxide. The doses of Vit C used here correspond to plasma Vit C levels reported in recently completed clinical trials. Prior to supplementation, a baseline sample was collected for analysis. PLTs were sampled again on days 2, 5 and 8 and assayed for changes in PLT function by: Thromboelastography (TEG), for changes in viscoelastic properties; aggregometry, for PLT aggregation and adenosine triphosphate (ATP) secretion in response to collagen or adenosine diphosphate (ADP); and flow cytometry, for changes in expression of CD-31, CD41 a PLT intracellular Vit C content was measured using a fluorimetric assay for ascorbic acid and PLT poor plasma was used for plasma coagulation tests [prothrombin time (PT), partial thrombplastin time (PTT), functional fibrinogen] (VLC) and Lipidomics analysis (UPLC ESI-MS / MS) .RESULTS VitC supplementation significantly increased PLTs intracellular ascorbic acid levels from 1.2 mmol / L at baseline to 3.2 mmol / L (Lo VitC) and 15.7 mmol / ). PTT PTT values, or functional fibrinogen levels over the 8 d exposure period (P> 0.05). PLT function assayed by TEG, aggregometry and flow cytometry was not significantly altered by Lo or Hi VitC for up to 5 d. However, PLTs exposed to 3 mmol / L VitC for 8-d showed an increased R and K times by TEG and a decrease in α-angle (P <0.05). There was also a fall of 20 mm in maximum amplitude associated with the Hi VitC compared to both baseline and day 8 saline controls. Platelet aggregation studies, showed uniform declines in collagen and ADP-induced platelet aggregations over the 8-d study period in all three groups (P> 0.05). Collagen and ADP-induced ATP secretion was also not different between the Three groups (P> 0.05). Finally, VitC at the higher dose (3 mmol / L) also induced the release of several eicosanoids including thromboxane B2 and prostaglandin E2, as well as products of arachidonic acid metabolism via the lipoxygenases pathway such as 11 - / 12- / 15-hydroxyicosatetraenoic acid (P <0.05) .CONCLUSION Alterations in PLT function by exposure to 3 mmol / L VitC for 8 d suggest that caution should be exerted with prolonged use of intravenous high dose VitC.