Selective Anti-Giardial Action of Indirubin: Biochemical and Functional Evidence for Inhibition of Triosephosphate Isomerase and Aldose Reductase in Giardia lamblia.

The emergence of clinical resistance to conventional antigiardials underscores the need for compounds with novel mechanisms of action. This study demonstrates that indirubin exerts antigiardial activity by targeting important metabolic enzymes in Giardia lamblia. Indirubin induced a concentration-dependent decrease in trophozoite proliferation and viability, correlating with reduced activity of native triosephosphate isomerase and aldose reductase. Using recombinant enzymes, indirubin directly inhibited triosephosphate isomerase and aldose reductase, with the parasite enzymes showing greater susceptibility than their human orthologs. Structural and computational analyses suggest preferential binding of indirubin at the dimer interface of triosephosphate isomerase and within the NADP(H)-binding pocket of aldose reductase. The dual enzymatic inhibition was concordant with methylglyoxal accumulation, extensive protein carbonylation, and the formation of advanced glycation end products. These effects culminated in apoptotic-like death and severe ultrastructural damage, including alteration of the adhesive disc and microtubule networks. By targeting vulnerabilities in the metabolic and redox pathways of G. lamblia through a multifactorial mechanism distinct from current therapies, our findings support indirubin as a promising candidate for the treatment of giardiasis.