In vitro amoebicidal activity of S-nitrosoglutathione and S-nitroso-N-acetylcysteine against trophozoites of Acanthamoeba castellanii

Sir, Acanthamoeba spp. are free-living protozoa that are widely spread in the environment and can infect the human eye, causing a sight-threatening keratitis. Acanthamoeba keratitis is a potentially devastating ocular infection with an increasing number of cases, where the use of soft contact lenses, especially under inappropriate care conditions, and corneal abrasion are considered the two most important risk factors.1 The current treatment of Acanthamoeba keratitis involves a combination of an amoebicidal drug, such as hexamidine (Desomedine®) or propamidine isethionate (Brolene®), with chlorhexidine gluconate or biguanides possessing cysticidal properties.2 In spite of adequate treatment, the final visual acuity is severely compromised2 and secondary ocular complications can occur, worsening the prognosis. Drug resistance has also been reported.3 The severity of this pathology makes research for new effective drugs necessary. Nitric oxide (NO) plays a key role in a myriad of physiological systems and S-nitrosothiols (RSNOs) are NO donor molecules possibly involved in NO-dependent biological signalling processes.4S-nitrosoglutathione (GSNO) is an endogenous RSNO that displays antimicrobial activity in vitro5 and S-nitroso-N-acetylcysteine (SNAC) is a non-endogenous RSNO that has biochemical properties similar to GSNO,6 including in vitro antimicrobial properties against Leishmania.5 Sodium nitroprusside (SNP) is an inorganic NO donor complex where NO is coordinated as a nitrosonium ligand (NO+) to the iron (Fe2+) centre,7 and has been clinically used for decades to reduce blood pressure in hypertensive emergencies and during surgery.