In Vitro Efficacy of Nikkomycin Z against the Human Isolate of the Microsporidian Species Encephalitozoon hellem

Abstract

Since 1985 microsporidia have been recognized as a cause of emerging infections in humans, mainly in immunocompromised human immunodeficiency virus-positive subjects. As chitin is a basic component of the microsporidian infective stage, the spore, we evaluated in vitro the susceptibility of a human-derived strain of Encephalitozoon hellem to nikkomycin Z, a peptide-nucleoside antibiotic known as a competitive inhibitor of chitin synthase enzymes. Transmission electron microscopy showed that this drug, at 25 g/ml, reduced the number of parasitic foci by about 35% ؎ standard deviation after 7 days of culture (P < 0.0001) and induced cell damage of both mature and immature spores and also other sporogonic and merogonic stages. In particular, an irregular outline of the cell shape and an abnormally condensed cytoplasm in meronts and sporonts were documented. Also, the polar tubule and the polaroplast membranes appeared disarrayed in the sporoblast stage. The spore wall showed an enlarged endospore and delaminated exospore. Mature spores had a complete cytoplasmic disorganization and a swollen and delaminated cell wall. No ultrastructural cell damage was observed in uninfected control cultures treated with the drug.Microsporidia are widespread, obligate intracellular parasites of most vertebrates and invertebrates. In addition to their causing infections in animals (19), there is great interest in studying these microorganisms because some genera and species have been recognized as a cause of opportunistic infections in immunocompromised humans, chiefly human immunodeficiency virus-positive subjects (9). Although albendazole, a benzimidazole derivative, has been found to be effective in vitro and in a series of patients infected by Encephalitozoon spp. to date there are no other drugs that are proved consistently efficacious against microsporidia infecting humans.The microsporidian spore is the stage of the parasite that contains chitin in the cell wall (2, 3, 4). Chitin provides high resistance to the environment and confers structural rigidity to the infective stage. Chitin is a carbohydrate polymer not present in mammalian cells, and chitin synthesis inhibition should be a target for microsporidian-specific therapy.Nikkomycin Z (NIK-Z) is a peptide-nucleoside antibiotic that was recovered as a potent competitive inhibitor of chitin synthase enzymes of fungi and insects and has structural similarity to UDP-N-acetylglucosamine (6, 7). In particular NIK-Z has been found to be effective in vitro and in vivo against some extracellular and intracellular fungal pathogens (5, 12, 13, 16). Moreover, this drug is well tolerated and easily degradable (11, 12) and therefore also might be considered as a potential candidate for therapeutic use against microsporidia. We present the results of a preliminary in vitro study on the sensitivity of NIK-Z on a human isolate of Encephalitozoon hellem. MATERIALS AND METHODSCulture system. The study was performed on a E. hellem isolate (PV-5-95) from a subject with asymptomatic microspo...

Therapeutic targets for the treatment of microsporidiosis in humans

“…cuniculi and Enc. hellem in vitro and could induce cell damage in both mature and immature spores (Figure 1C) 178, 179 . Polyoxin exhibits an even higher inhibition than Nikkomycin in controlling Enc.…”

Zoonotic Potential of the Microsporidia

“…Although microsporidiosis in general can be successfully treated with albendazole and fumagillin, therapy for the most prevalent species, E. bieneusi, is difficult (129,204). Indeed, a few studies have demonstrated that inhibitors of chitin synthase enzymes are effective against microsporidia (19,270).…”

Current Therapy and Therapeutic Targets for Microsporidiosis

“…Nikkomycin Z (12) inhibited the growth of Enc. hellem in fetal bovine lung fibroblast cells and the infectivity of any spores that developed in drug-treated cultures ( Bigliardi et al, 2000 ). Polyoxin D (13) and nikkomycin Z were shown to reduce the number of parasitic foci in Enc.…”