Neopterin as an Endogenous Antioxidant.

Abstract

Neopterin is an α-amino-hydroxypteridine derivative, and a precursor of biopterin, which is derived from guanosine triphosphate. As for biological roles of pteridines, 5, 6, 7, 8-tetrahydrobiopterin serves as a cofactor for mammalian aromatic amino acid monooxygenases, and thus regulate the biosynthesis of neurotransmitters including dopamine, norepinephrine and serotonin. Although the exact physiological functions of pteridines are still obscure, it has been suggested that neopterin might act as an endogenous inhibitor of folate synthesis in view of the major role of interferon-γ in the induction of antibacterial, anti-protozoal, and antifungal states in parasitized cells. In a clinical field, a significant elevation of urinary or serum pteridine levels has been found in patients with various malignant disorders, as well as in patients with viral diseases such as acquired immunodeficiency syndrome (AIDS). Active oxygen species such as superoxide anion radicals are thought to be potent pathogenic factors in various viral diseases, and the pathogenesis may involve not direct viral cytotoxicity and/or reactivity of active oxygen species. That is, an excess amount of active oxygen species following overreaction of immunodefense response against the virus-infected organs, may participate in the mechanism of tissue injuries observed in various types of viral diseases. Based on these reports, functional roles of neopetrin relating to the active oxygen species has easily been anticipated. In this review, neopterin as an endogenous antioxidant is described.