Sulfonation of curcuminoids: Characterization and contribution of individual SULT enzymes

Scope: Poor oral bioavailability of curcuminoids limited their various applications, and one of the main reasons is their rapid metabolism in vivo. Sulfonation via sulfotransferases (SULTs) is an important metabolic pathway for such compounds. The objective of this study is to determine the SULT-isoform-specific metabolic fingerprint, tissue-specific rate, and reaction kinetic profiles to describe the characterization and contribution of curcuminoids sulfonation. Methods and results: Sulfonation of curcuminoids was investigated by using nine expressed SULT isoforms and four pooled human tissue S9 fractions. The results showed that human small intestine is the predominant tissue responsible for sulfonation of curcuminoids. SULT1A3 is a major isoform catalyzing sulfonation of curcumin and demethoxycurcumin, but not for bisdemethoxycurcumin. SULT1B1 is only responsible for sulfonation of curcumin. Although SULT1C4 and 1E1 could highly catalyze the sulfate conjugations toward all the three compounds, the correlativities with human small intestine S9 fractions were much weaker (R-2 = 0.100-0.482). Almost all the kinetic profiles of the SULT isoforms for curcuminoids exhibited substrate inhibition kinetics. Conclusion: This investigation contributed to elucidate the SULT-mediated metabolism and detoxication of curcuminoids at molecular levels and in different organs.