ascorbic-acid and 5-hydroxydopa

The present study was conducted to clarify the mechanism responsible for enhancement of the anti-melanoma activity of levodopa methylester by supplemental ascorbate in vivo. 5-Hydroxydopa, a known cytotoxic agent and the major metabolite formed from levodopa in the presence of ascorbate and mushroom tyrosinase in vitro, was assessed for its antitumor activity against i.p. and s.c. inoculated B16 melanoma, P388 leukemia, and L1210 leukemia in mice with and without supplemental ascorbate. Treatment with 5-hydroxydopa failed to significantly increase survival of mice bearing i.p. or s.c. pigmented and non-pigmented B16 melanomas even though it inhibited local tumor growth. Treatment increased survival of both P388 and L1210 leukemias, and this increase was more pronounced in mice bearing i.p. tumors than in mice bearing s.c. tumors. This treatment significantly decreased final tumor weight of both leukemias implanted s.c., and inhibited ascites formation in mice inoculated with i.p. tumors. Ascorbate supplementation decreased or abrogated the effect of 5-hydroxydopa on survival in mice bearing i.p. or s.c. leukemia tumors and decreased survival relative to control mice bearing i.p. or s.c. pigmented and s.c. non-pigmented tumors. It did not affect survival of treated mice bearing i.p. non-pigmented melanoma tumors. Ascorbate supplementation did not modify the effect of 5-hydroxydopa treatment on primary s.c. tumor growth in mice bearing melanoma or leukemia tumors nor did it affect ascites formation in treated mice bearing i.p. leukemia tumors. The lack of correlation between the observed inhibition of primary tumor growth and the absence of an effect on survival in 5-hydroxydopa treated mice bearing i.p. melanoma may relate to an inability of this drug to interfere with tumor metastasis. These data argue against a role for 5-hydroxydopa as a metabolically derived cytotoxic formed in situ during concurrent treatment with levodopa methylester and supplemental ascorbate.

Topics: Animals; Ascorbic Acid; Dihydroxyphenylalanine; Drug Interactions; Female; Leukemia L1210; Leukemia P388; Male; Melanoma; Mice; Mice, Inbred C57BL; Mice, Inbred DBA

When tyrosine was incubated with tyrosinase in the presence of ascorbic acid, dopa and 5-hydroxydopa were formed and the enzyme was inactivated. In the presence of catalase, more dopa and 5-hydroxydopa were formed because enzyme inactivation was prevented. Incubation of dopa and cysteine with small amounts of mushroom tyrosinase led to rapid inactivation of the enzyme. This inactivation was accelerated in the presence of catalase. New systems developed have been useful in demonstrating the role of hydrogen peroxide in tyrosinase inactivation by several compounds of importance in melanin biochemistry. Cysteine and glutathione inactivated tyrosinase. Addition of catalase increased the inactivation at high thiol concentrations, but decreased the inactivation at low concentrations. Ascorbic acid and 5-hydroxydopamine also inactivated tyrosinase, but with these compounds inactivation was completely prevented by addition of catalase. The inactivation by dopamine was negligible under the experimental conditions. Inactivation of tyrosinase by ascorbic acid and by 5-OH-dopamine was found dependent on oxygen, whereas inactivation by cysteine and glutathione was independent of oxygen. Large amounts of serum albumin protected tyrosinase from inactivation by ascorbic acid and 5-OH-dopamine, but did not prevent inactivation by cysteine and glutathione. The presence of substrate had a protective effect on the inactivation of tyrosinase by cysteine.

Topics: Ascorbic Acid; Basidiomycota; Catalase; Catechol Oxidase; Cysteine; Dihydroxyphenylalanine; Glutathione; Monophenol Monooxygenase

The recently discovered intermediate product in melanin formation, 5-OH-dopa, is formed in large amounts when dopa is oxidized by tyrosinase in the presence of ascorbic acid.

Topics: Ascorbic Acid; Catechol Oxidase; Cysteine; Cysteinyldopa; Dihydroxyphenylalanine; Melanins; Monophenol Monooxygenase; Oxidation-Reduction