# Effect of phosphodiesterase inhibitors on platelet function

## TL;DR

This study explores how inhibitors of phosphodiesterase enzymes affect platelet function, showing that different inhibitors impact platelet activation and aggregation depending on the pathway involved.

## Contribution

The study reveals that PDE inhibitors' effects on platelets depend on their specific targets and the activation pathways involved.

## Key findings

- Inhibition of all platelet PDEs by IBMX reduced platelet activation and aggregation across multiple agonists.
- Ibudilast preferentially inhibits PDE-3 and reduces activation by ADP and TRAP, but not CRP-A.
- Combining Sildenafil and Ibudilast had an additive effect on platelet activation.

## Abstract

Phosphodiesterase enzymes (PDEs) play a pivotal role in regulating platelet activity by modulating intracellular levels of cAMP and cGMP. Modulation of PDE-2, -3 and -5 activity by suitable inhibitors has been found to reduce platelet activity, and thus thrombus formation.

Our aim was to study Ibudilast effects on platelet activation, degranulation and aggregation. Therefore, we used the nonspecific PDE inhibitors IBMX as well as the PDE-5 inhibitor Sildenafil as controls. Platelet agonists collagen-related peptide (CRP-A), adenosine diphosphate (ADP) and thrombin receptor activator peptide (TRAP6) were used to induce distinct activation pathways. PDE inhibition was quantified by western blot analysis. Platelet activity was assessed using flow cytometry, light transmission aggregometry and in vitro thrombus formation.

Inhibition of all platelet PDEs by IBMX substantially reduced platelet activation and aggregation in response to all tested platelet agonists. Ibudilast preferentially inhibits PDE-3 in platelets. Ibudilast decreased platelet activation and aggregation induced by ADP and TRAP, but not CRP-A. Sildenafil alone induced no reduction in PDE activity, platelet activation or aggregation. However, the combination of Sildenafil and Ibudilast had an additive effect on platelet activation. Interestingly, all tested PDE inhibitors demonstrated a significant effect on platelet-dependent thrombus formation.

In conclusion, the effect of PDE inhibitors on platelet function is influenced by two primary factors: the pharmacological target of the inhibitor and the cAMP/cGMP interaction with the activation pathways induced. Platelet activation by ADP via P2Y12 and TRAP via PAR1 showed a greater response to PDE inhibitors than platelet activation by CRP via GPVI.

Graphical illustration of the PDE isoenzymes in platelets and their role in cAMP/cGMP metabolism (left side). Influence of PDE activity on platelet activation (right side). (ATP, AMP, cAMP: adenosine triphosphate, adenosine monophosphate, cyclic adenosine monophosphate; GTP, GMP, cGMP: guanosine triphosphate, guanosine monophosphate, cyclic guanosine monophosphate; AC: adenylate cyclase; sGC: soluble guanylate cyclase; PKA, PKG: protein kinase A, protein kinase G; NO: nitric oxide; VASP: vasodilator-stimulated phosphoprotein; VASP-P: phosphorylated VASP.Image 1

•All three PDE isoforms expressed in platelets are involved in regulating platelet function.•The effect of PDEs on platelet function depends on distinct activation pathways.•The influence of PDE inhibitors on platelet function is depending on their inhibitory profile.

All three PDE isoforms expressed in platelets are involved in regulating platelet function.

The effect of PDEs on platelet function depends on distinct activation pathways.

The influence of PDE inhibitors on platelet function is depending on their inhibitory profile.