Upadacitinib enhances platelet procoagulant responses in a subset of healthy individuals and patients with SLE: a pilot study.

BACKGROUND

Janus kinase inhibitors (JAKis) are emerging therapies for SLE, but concerns regarding thromboembolic risk persist. Clinical trials in SLE have not consistently demonstrated an increased risk of thrombotic events and the effects of JAK inhibition on platelet function remain incompletely understood.

OBJECTIVES

To investigate whether the JAK1 inhibitor upadacitinib modulates platelet procoagulant membrane dynamics (PMD) in vitro and to explore the associated cytokine signatures.

METHODS

Whole blood from patients with SLE (n=10) and healthy controls (n=10) was preincubated with upadacitinib (0, 60 and 300 ng/mL). Platelet-rich plasma was analysed using confocal microscopy and Volocity software (Quorum Technology) to quantify PMD markers. We used Alexa Fluor 488 CD62p to detect degranulation, Alexa Fluor 568 Annexin-V to detect phosphatidylserine exposure and Alexa Fluor 647 PAC-1 to detect integrin αIIbβ3 activation. Participants were stratified as JAKi-activated or JAKi-null depending on whether PMD markers were amplified on JAK inhibition or remained unaffected. We then used Luminex xMAP technology to quantify 96 human plasma cytokines, chemokines and growth factors.

RESULTS

Platelet responses were heterogeneous. Approximately 30% of both groups exhibited increased platelet activation and procoagulant responses ('JAKi-activated'), whereas the remainder remained unaffected. Platelets of patients with SLE demonstrated elevated baseline activation, characterised as preactivation or autoactivation. JAKi-activated phenotypes were associated with increased plasma levels of interleukin (IL)-4 and tumour necrosis factor-beta (TNF-β) after JAK inhibition. In vitro, we showed that recombinant IL-4 and TNF-β directly activated platelets or primed platelet responses to procoagulant agonists, supporting a potential indirect mechanism for the enhanced procoagulation observed in our JAKi-activated subpopulations.

CONCLUSIONS

Upadacitinib was associated with enhanced platelet activation and procoagulant responses in vitro in a subset of individuals with SLE and healthy controls. These findings are preliminary and hypothesis-generating. Further studies are required to determine clinical relevance and validate stratification approaches.