# Multifaceted Effects of Thymoquinone on Platelet Calcium Homeostasis

## TL;DR

Thymoquinone strongly inhibits platelet activation and aggregation, with unique effects on calcium levels, suggesting potential as a therapeutic agent.

## Contribution

First demonstration of TQ's acute inhibitory effects on platelet activation via GPCRs and ITAM-containing receptors.

## Key findings

- TQ inhibits ADP- and Trap-6-induced aggregation without reducing [Ca2+]i levels.
- TQ inhibits CRP-induced aggregation and [Ca2+]i mobilization.
- DTT prevents TQ effects, suggesting involvement of protein disulfide isomerases.

## Abstract

What are the main findings?
Thymoquinone (TQ) strongly and acutely inhibited agonist-induced platelet activation and aggregation. TQ differentially regulates GPCR and GPVI receptor activation by enhancing [Ca2+]i mobilization by GPCR-induced activation and inhibition of GPVI-induced [Ca2+]i mobi-lization.Presented data are the first example in which complete inhibition of ADP- and Trap-6-, but not CRP-induced, aggregation is accompanied by high [Ca2+]i levels.

Thymoquinone (TQ) strongly and acutely inhibited agonist-induced platelet activation and aggregation. TQ differentially regulates GPCR and GPVI receptor activation by enhancing [Ca2+]i mobilization by GPCR-induced activation and inhibition of GPVI-induced [Ca2+]i mobi-lization.

Presented data are the first example in which complete inhibition of ADP- and Trap-6-, but not CRP-induced, aggregation is accompanied by high [Ca2+]i levels.

What is the implication of the main finding?
TQ could be a valuable molecule for the analysis of calcium homeostasis in platelets and other cells.TQ is now considered a promising therapeutic agent against cancer, and our results, that TQ is a potent inhibitor of platelets, should be taken into account, especially in pathological situations with possible bleeding complications.

TQ could be a valuable molecule for the analysis of calcium homeostasis in platelets and other cells.

TQ is now considered a promising therapeutic agent against cancer, and our results, that TQ is a potent inhibitor of platelets, should be taken into account, especially in pathological situations with possible bleeding complications.

Thymoquinone (TQ), the main bioactive ingredient of Nigella sativa, exhibits numerous pharmacological activities and is used for the prevention of many diseases including hypertension and cancer. However, information concerning the effects of TQ on platelets is limited. In this study, we used the upgraded laser microparticle analyzer LaSca-TMF for simultaneous analysis of platelet shape change, aggregation, and changes in [Ca2+]i. We showed that TQ acutely inhibited platelet aggregation induced by ADP, Trap-6, and CRP; however, the rise of [Ca2+]i was inhibited only in CRP-stimulated platelets, but not in ADP- or Trap-6-stimulated ones. DTT, a thiol-reducing agent, prevented TQ-induced effects in platelets, indicating that protein disulfide isomerases could be involved in the regulation of TQ effects on platelets. Our results, for the first time, demonstrated acute inhibitory effects of TQ on platelet activation induced by GPCRs and ITAM-containing receptors, which were independent of PKA and caspase-3 activation. To the best of our knowledge, this is the first example in which complete inhibition of ADP- and Trap-6-, but not CRP-induced, aggregation is accompanied by high [Ca2+]i levels. Additional experimental approaches are required to explain some effects of TQ on calcium homeostasis and TQ could be a valuable molecule for the analysis of calcium homeostasis in platelets and other cells.