Background and purpose

Some clinical studies have reported increased myocardial infarction in people living with HIV taking the antiretroviral abacavir sulphate (ABC). Given that clinical studies contain confounding variables (e.g. HIV status), we investigated the pharmacological impact of antiretrovirals on platelet function in HIV‐negative volunteers in order to identify mechanisms of increased cardiovascular risk.
Experimental approach

Platelets were isolated from healthy volunteers and HIV‐negative subjects enrolled on a Phase I clinical trial and platelet function evaluated using aggregometry and flow cytometry. In vivo platelet thromboembolism was monitored in anaesthetised mice.
Key results

Human platelet aggregation was unaffected by all antiretrovirals tested but ABC treatment led uniquely to increased platelet granule release. ABC also interrupted nitric oxide (NO)‐mediated inhibition of platelet aggregation and increased in vivo aggregation in mice. An alternative antiretroviral, tenofovir, did not affect platelet function. Furthermore, aggregation and activation of platelets isolated from twenty subjects taking clinically‐relevant doses of tenofovir were comparable to baseline samples.
Conclusions and implications

ABC can enhance platelet activation, independently of HIV status suggesting a potential pharmacological effect that is absent with tenofovir. Mechanistically, we propose that ABC enhances platelet degranulation and interrupts NO‐mediated platelet inhibition. The interaction of ABC with NO signalling is supported by data demonstrating ABC‐mediated enhancement of aggregation in vivo and in vitro responses that persist in the presence of NO. Although an association between ABC and platelet activation has not been confirmed in patients, these findings provide evidence of a mechanistic link between platelet activation and antiretroviral therapy.