Human Salivary Histatins: Promising Anti-Fungal Therapeutic Agents

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Abstract
Histatins constitute a group of small, cationic multifunctional proteins present in the saliva of human and some nonhuman primates. The most significant function of histatins may be their anti-fungal activity against Candida albicans and Cryptococcus neoformans. Histatins have been extensively studied at both the protein and gene levels. The structure-function relationship of histatins with respect to their candidacidal activity has also been studied by means of recombinant histatin variants, as well as by chemically synthesized histatin fragments. The mechanism of histatins' action on Candida albicans is not clear, but it appears to be different from that of azole-based anti-fungal drugs which interrupt ergosterol synthesis. During the past 20 years, fungal infections have become more prevalent as a result of the emergence of AIDS, as well as, paradoxically, modern medical advances. The toxicity of current anti-fungal medicine, the emergence of drug-resistant strains, and the availability of only a few types of anti-fungal agents are the major disadvantages of current anti-fungal therapy. Therefore, the importance of the search for new, broad-spectrum anti-fungals with little or no toxicity cannot be overemphasized. The following properties make histatins promising anti-fungal therapeutic agents: (1) They have little or no toxicity; (2) they possess high cidal activities against azole-resistant fungal species and most of the fungal species tested; and (3) their candidacidal activity is similar to that of azole-based antifungals. Current research efforts focus on the development of improved histatins with enhanced cidal activity and stability, and of suitable and effective histatin delivery systems. These and other approaches may help to outpace the growing list of drug-resistant and opportunistic fungi causing life-threatening, disseminating diseases. The histatins with improved protective properties may also be used as components of artificial saliva for patients with salivary dysfunction.