Discovery of the curcumin metabolic pathway involving a unique enzyme in an intestinal microorganism

Abstract

Polyphenol curcumin, a yellow pigment, derived from the rhizomes of a plant (Curcuma longa Linn) is a natural antioxidant exhibiting a variety of pharmacological activities and therapeutic properties. It has long been used as a traditional medicine and as a preservative and coloring agent in foods. Here, curcumin-converting microorganisms were isolated from human feces, the one exhibiting the highest activity being identified as Escherichia coli. We are thus unique in discovering that E. coli was able to act on curcumin. The curcumin-converting enzyme was purified from E. coli and characterized. The native enzyme had a molecular mass of about 82 kDa and consisted of two identical subunits. The enzyme has a narrow substrate spectrum, preferentially acting on curcumin. The microbial metabolism of curcumin by the purified enzyme was found to comprise a two-step reduction, curcumin being converted NADPHdependently into an intermediate product, dihydrocurcumin, and then the end product, tetrahydrocurcumin. We named this enzyme "NADPH-dependent curcumin/dihydrocurcumin reductase" (CurA). The gene (curA) encoding this enzyme was also identified. A homology search with the BLAST program revealed that a unique enzyme involved in curcumin metabolism belongs to the mediumchain dehydrogenase/reductase superfamily. microbial screening | bioconversion S ince the dawn of civilization, natural compounds have been used as a source of medicine and foods based on their tremendous biological activities. One of the natural compounds that has been documented as having been used as a spice and a pigment since 1900 B.C. is curcumin (1). Curcumin, defined as a bis-α, β-unsaturated β-diketone (Fig. S1), has been found exclusively in the roots of Curcuma longa Linn (Zingiberaceae) (2). Curcumin has many different applications because it has a surprisingly wide variety of beneficial uses, including food coloration, cosmetics utility, and fabric dying. In addition, curcumin has a wide range of medical properties, including antitumor, antiinflammatory, antioxidant, anticancer, and analgesic uses (3). Recently, curcumin has been used in the treatment of Alzheimer's disease (4) and malaria (5), and improvement of wound healing (6). Curcumin in the diet is partially absorbed in the intestine (7). A considerable portion of the ingested curcumin reaches the cecum and colon, where a large population of indigenous bacteria exists. Although analysis of curcumin metabolism and biosynthesis would lead to the discovery of other unknown advantages of this compound, there has neither been purification of enzymes involved in the metabolic pathway for curcumin nor identification of their genes in living organisms. In addition, no information is available regarding the effect of the intestinal bacteria on curcumin metabolism.Studies on such curcumin-converting microorganisms and functional analyses of the curcumin-converting enzymes and genes would facilitate clarification of the metabolism of curcumin. In the present article, we report the isolation of cur...

Application of ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry to identify curcumin metabolites produced by human intestinal bacteria

“…The intestinal tract is thought to play an important role in the metabolic disposition of curcumin [22,23]. Curcumin-metabolizing microorganisms were isolated from human feces, and the purification and characterization of a curcumin-converting enzyme was reported in previous study [23]. However, these previous studies did not provide detailed information about the metabolic pathways affecting curcumin in intestinal bacteria, although curcumin has been taken orally as a food agent or medicine since ancient times.…”

“…The intestinal bacteria model is a useful in vitro tool to predict drug-metabolism pathways in vivo. The intestinal tract is thought to play an important role in the metabolic disposition of curcumin [22,23]. Curcumin-metabolizing microorganisms were isolated from human feces, and the purification and characterization of a curcumin-converting enzyme was reported in previous study [23].…”

“…In addition, the fragment ion m/z 203 could further lose CH 3 to form the fragment ion at m/z 188. Thus, M21 were identified as hydroxylated and acetylated curcumin.The metabolite M22 had a retention time of 3.64 min and exhibited a protonated ion at m/z 441, indicating that the molecular formula was C23 H 22 O 9 . The high energy mass spectrum of M22 showed fragment ions at m/z 383, 367, 291, 203, 191, 175, 159, and 151.…”

Drug Metabolism by the Host and Gut Microbiota: A Partnership or Rivalry?

“…The pharmacologic activity of curcumin is thought to be due to the formation of its metabolite tetrahydrocurcumin by the gut microbiota. Analyses of microorganisms isolated from human feces revealed that Escherichia coli exhibited among the highest curcumin-metabolizing activities (Hassaninasab et al, 2011). The responsible enzyme was identified as CurA, NADPH-dependent curcumin/dihydrocurcumin reductase, which bears similarities to members of the medium-chain dehydrogenase/ reductase superfamily.…”

Discovery of a sesamin-metabolizing microorganism and a new enzyme

“…sesamin | metabolism | lignan | tetrahydrofolate W e have been involved in studies of not only microbial metabolism of man-made compounds (1-3) but also biologically active natural compounds, such as curcumin (4). In this study, we characterize the microbial metabolism of the lignan sesamin.…”