Profibrinolytic Activity of Nattokinase (Subtilisin NAT): Cleavage of Plasminogen Activator Inhibitor Type 1

This basic science study characterized a key molecular mechanism by which nattokinase (subtilisin NAT, purified from Bacillus subtilis, the organism in natto) exerts profibrinolytic activity: by cleaving and inactivating plasminogen activator inhibitor type 1 (PAI-1), the principal physiological inhibitor of the body’s own fibrinolytic system.

In biochemical assays, nattokinase was found to degrade PAI-1 at specific cleavage sites, inactivating its inhibitory function. This leaves tissue plasminogen activator (tPA) and urokinase (uPA) free to convert plasminogen to plasmin, the active fibrinolytic protease that dissolves fibrin clots. Nattokinase thus promotes fibrinolysis through both direct fibrinolytic activity (cleaving fibrin) and indirect enhancement (removing PAI-1 inhibition of endogenous tPA/uPA).

The mechanistic elegance of this dual pathway — direct fibrin dissolution plus PAI-1 inactivation — explains nattokinase’s potent fibrinolytic activity in vitro. The clinical question that remains unresolved is whether nattokinase survives intact through gastric and intestinal digestion to reach systemic circulation at biologically active concentrations. Evidence for meaningful oral bioavailability of enzymatically active nattokinase in humans is limited.

There are no randomized clinical trials demonstrating that oral nattokinase supplementation reduces cardiovascular events, thrombotic events, or cardiovascular mortality. The mechanistic pathway is scientifically interesting but has not translated into clinical outcome evidence.

We rate the evidence moderate for basic science. A carefully executed biochemical study establishing nattokinase’s PAI-1 cleavage mechanism — providing mechanistic understanding of nattokinase’s profibrinolytic action but insufficient to support clinical application without human pharmacokinetic and outcome data.