Natural Curcuminoids Research Articles

Metabolic engineering of Escherichia coli for the biosynthesis of various phenylpropanoid derivatives

Plants produce a variety of natural products with promising biological activities, such as the phenylpropanoids resveratrol and curcumin. While these molecules are naturally assembled through dedicated plant metabolic pathways, combinatorial biosynthesis has become an attractive tool to generate desired molecules. In this work, we demonstrated that biosynthetic enzymes from different sources can be recombined like legos to make various molecules. Seven biosynthetic genes from plants and bacteria were used to establish a variety of complete biosynthetic pathways in Escherichia coli to make valuable compounds. Different combinations of these biosynthetic bricks were made to design rationally various natural product pathways, yielding four phenylpropanoid acids (cinnamic acid, p-coumaric acid, caffeic acid, and ferulic acid), three bioactive natural stilbenoids (resveratrol, piceatannol and pinosylvin), and three natural curcuminoids (curcumin, bisdemethoxycurcumin and dicinnamoylmethane). A curcumin analog dicaffeoylmethane was synthesized by removing a methyltransferase from the curcumin biosynthetic pathway. Furthermore, introduction of a fungal flavin-dependent halogenase into the resveratrol biosynthetic pathway yielded a novel chlorinated molecule 2-chloro-resveratrol. This work thus provides a novel and efficient biosynthetic approach to creating various bioactive molecules. Further expansion of the library of the biosynthetic bricks will provide a resource for rational design of various phenylpropanoids via the combinatorial biosynthesis approach.

Production of curcuminoids from tyrosine by a metabolically engineered Escherichia coli using caffeic acid as an intermediate.

Curcuminoids are phenylpropanoids with high pharmaceutical potential. Herein, we report an engineered artificial pathway in Escherichia coli to produce natural curcuminoids through caffeic acid. Arabidopsis thaliana 4-coumaroyl-CoA ligase and Curcuma longa diketide-CoA synthase (DCS) and curcumin synthase (CURS1) were used to produce curcuminoids and 70 mg/L of curcumin was obtained from ferulic acid. Bisdemethoxycurcumin and demethoxycurcumin were also produced, but in lower concentrations, by feeding p-coumaric acid or a mixture of p-coumaric acid and ferulic acid, respectively. Additionally, curcuminoids were produced from tyrosine through the caffeic acid pathway. To produce caffeic acid, tyrosine ammonia lyase from Rhodotorula glutinis and 4-coumarate 3-hydroxylase from Saccharothrix espanaensis were used. Caffeoyl-CoA 3-O-methyltransferase from Medicago sativa was used to convert caffeoyl-CoA to feruloyl-CoA. Using caffeic acid, p-coumaric acid or tyrosine as a substrate, 3.9, 0.3, and 0.2 mg/L of curcumin were produced, respectively. This is the first time DCS and CURS1 were used in vivo to produce curcuminoids and that curcumin was produced by feeding tyrosine. We have shown that curcumin can be produced using a pathway involvoing caffeic acid. This alternative pathway represents a step forward in the heterologous production of curcumin using E. coli.

Heterologous production of curcuminoids.

Curcuminoids, components of the rhizome of turmeric, show several beneficial biological activities, including anticarcinogenic, antioxidant, anti-inflammatory, and antitumor activities. Despite their numerous pharmaceutically important properties, the low natural abundance of curcuminoids represents a major drawback for their use as therapeutic agents. Therefore, they represent attractive targets for heterologous production and metabolic engineering. The understanding of biosynthesis of curcuminoids in turmeric made remarkable advances in the last decade, and as a result, several efforts to produce them in heterologous organisms have been reported. The artificial biosynthetic pathway (e.g., in Escherichia coli) can start with the supplementation of the amino acid tyrosine or phenylalanine or of carboxylic acids and lead to the production of several natural curcuminoids. Unnatural carboxylic acids can also be supplemented as precursors and lead to the production of unnatural compounds with possibly novel therapeutic properties. In this paper, we review the natural conversion of curcuminoids in turmeric and their production by E. coli using an artificial biosynthetic pathway. We also explore the potential of other enzymes discovered recently or already used in other similar biosynthetic pathways, such as flavonoids and stilbenoids, to increase curcuminoid yield and activity.

Curcumin analogues inhibit phosphodiesterase-5 and dilate rat pulmonary arteries.

Phosphodiesterase (PDE)-5 inhibitors are useful as vasodilators for the treatment of pulmonary arterial hypertension. We aimed to study curcumin analogues for PDE5 inhibitory activity and vasorelaxation of rat pulmonary arteries. Three natural curcuminoids (1-3) and six synthetic analogues (4-9) were tested for PDE5 and PDE6 inhibitory activities using enzymatic radioassay. Their vasorelaxation was measured using freshly isolated segments of rat pulmonary artery and aorta. Curcuminoids (1-3) mildly inhibited PDE5 (half maximal inhibitory concentration (IC50 ) = 18 µm): the metamethoxyl of curcumin was important for PDE5 inhibition. But hydroxyl rearrangements, removing both methoxyls and one ketomethylene, yielded the potent 7 and 9 (IC50 = 4 µm) (compared with sildenafil, IC50 = 0.03 µm). Only 1, 3 and 4 were PDE5 selective over PDE6. Triazole-carboxylic addition provided water-solubility while preserving potency. All analogues possessed concentration-dependent vasorelaxant activity on pulmonary arteries (40% of maximal effective concentration (EC40 ) = 29-90 µm, maximum response = 60-90% at 300 µm), while compounds (1-8) were weakly acting in aorta (maximum response <40%). Only demethoxycurcumin (2) and analogues 5, 8, 9 had endothelium-dependent actions. Sildenafil was highly potent (EC40 = 0.04 µm) and highly endothelium dependent in pulmonary artery but weak on intact aorta (EC40 = 1.8 µm). Activity profiles suggest actions through additional cell pathways for promoting vasorelaxation. Curcumin analogues are potential leads for developing efficacious and selective PDE5 inhibitors and other pathologies of pulmonary hypertension.

Synthesis and biological evaluation of glucosyl curcuminoids.

Medicinal plants proved to be a rich source in exploring a variety of lead structures in the development of new drugs. The natural curcuminoids have gained considerable attention in recent years for their multiple beneficial pharmacological and biological activities. Clinical application of these curcuminoids is often impaired due to their poor water solubility, resulting in low in vivo bioavailability of the active compound in humans. The objective of the present study is to synthesize glucosyl conjugates of curcumin 1 and tetrahydrocurcumin 4 and to evaluate their biological activities. The study highlights the synthesis of curcumin-β-di-glucoside 3 (yield 71%) and tetrahydrocurcumin-β-di-glucoside 6 (yield 64%) in good yields in a biphasic reaction medium using a phase transfer catalyst under simple and ecofriendly conditions. Both the glucosyl curcuminoids showed enhanced antioxidant, tyrosinase enzyme inhibitory, antimicrobial and potent cytotoxic activity. The improved biological activity may be due to the increased solubility of the glucosyl conjugated compounds compared to the native curcuminoids; this was further confirmed by partition coefficient studies. Thus, the synthesized glucosyl curcumin may serve as promising future therapeutic molecule in the management of cancer, whereas glucosyl tetrahydrocurcumin can be a useful ingredient in achromatic food and in cosmetic applications.

Efficient stabilization of natural curcuminoids mediated by oil body encapsulation

Curcumin is a natural hydrophobic polyphenol found in the powdered rhizomes of Curcuma longa. Due to its capacity to interfere with many signalling pathways, it has been shown that curcumin has potential beneficial pharmacological effects including antioxidant, anti-inflammatory, anticarcinogenic properties. However, the use of curcumin is fairly restricted because of its poor water solubility, low bioavailability, inadequate tissue absorption and degradation at alkaline pH. In the present contribution, we first verified the anti-proliferative effects of natural curcuminoids towards two different cell lines derived from an ovarian and a breast adenocarcinoma cancer. Later, curcuminoids were successfully encapsulated into reconstituted oil bodies. Once encapsulated into the triacylglycerol cores of the reconstituted oil bodies, curcumin, the most hydrophobic and active of the three curcuminoids, was better stabilized in comparison with albumin stabilization. Oil body encapsulated curcuminoids showed the same effects on cancer cell viability as the free drug, confirming the great potential of natural oil bodies as micro/nano-capsules in drug delivery applications.

Inhibitory effects of di-O-demethylcurcumin on interleukin-1β-induced interleukin-6 production from human gingival fibroblasts

Background/purposeCurcumin is a polyphenolic phytochemical isolated from the medicinal plant Curcuma longa L. This phytochemical exhibits anti-inflammatory and antioxidant properties. The aim of this study was to find a curcuminoid compound that has a better effect on the suppression of interleukin-1β (IL-1β)-induced IL-6 production than curcumin in human gingival fibroblasts (HGFs). Materials and methodsThe parent curcuminoids 1–3 were isolated from the rhizomes of C. longa and 17 curcuminoid analogs 4–20 were synthesized from the parent curcuminoids. The condition for IL-6 production by HGFs after inducing the cells with IL-1β was optimized. HGFs were incubated with curcuminoids (0.016–20 μg/mL) for 30 minutes before adding IL-1β (2 ng/mL). After 24 hours of incubation, the culture media were harvested and determined for IL-6 contents using an enzyme-linked immunosorbent assay method. Prednisolone, an immunosuppressive drug, was used as a positive control. Half maximal effective concentration (EC50) is measured and reported as the concentration required for 50% inhibition of the levels found in the control medium. ResultsThe maximum IL-6 production was achieved when the HGFs were exposed to an IL-1β concentration of 2 ng/mL for 24 hours; however, addition of the immunosuppressant prednisolone inhibited the production of IL-6. Among the analogs, di-O-demethylcurcumin (5) exhibited the most potent anti-IL-6 activity with an EC50 of 2.18 ± 0.07 μg/mL, which was approximately eightfold more active than the natural curcuminoids 1–3. Cell viability was not significantly affected when the concentration of di-O-demethylcurcumin was less than 20 μg/mL. ConclusionDi-O-demethylcurcumin exhibited an inhibitory effect on the production of IL-6 by IL-1β-induced HGFs and can thus serve as a lead compound with its inhibiting property for IL-6 production.

P-gp upregulation may be blocked by natural curcuminoids, a novel class of chemoresistance-preventing agent

Once multidrug resistance (MDR) occurs in cancer cells, it is very difficult to reverse since overexpression of P-glycoprotein (P-gp) is accompanied by altered expression of numerous other activated target genes. Previously, we reported that curcumin pretreatment would be an ideal method to prevent acquired drug resistance induced by adriamycin, administered prior to the development of MDR. To further confirm the previous results, we examined the potency of 3forms of curcuminoids present in turmeric as potent preventers of acquired drug resistance. K562 cells were pretreated with or without curcuminoids for 24h and co-incubated with adriamycin. P-gp and mdr1 mRNA levels were analyzed separately by flow cytometry and quantitative real-time RT-PCR. In addition, we performed an MTT assay to determine the adriamycin-induced cytotoxicity with or without pretreatment with curcuminoids. Short- and long-term exposure of native K562 cells to adriamycin led to upregulation of P-gp and formation of acquired drug resistance. However, after pretreatment with curcuminoids, the above processes were significantly inhibited. The MTT assay examined the enhanced effect of curcuminoids on adriamycin‑induced cytotoxicity. Results from western blotting showed that curcuminoids could inhibit the adriamycin-induced increase of NF-κB nuclear translocation and activation. Finally, under the long-term exposure model, we proved that curcumin was capable of blocking the occurrence of MDR in the cell line throughout the 56-day culture period. This study reveals that curcuminoids have the potency to block the upregulation of P-gp and its mRNA induced by short- and long-term exposure to adriamycin. Curcuminoids may be a novel class of potent chemoresistance-preventing agent with high safety and the potential for widespread clinical use.

Anti‐inflammatory Activity of Natural and Synthetic Curcuminoids

The anti-inflammatory activity of three natural curcuminoids and eight synthetic curcuminoids was studied using the mouse paw oedema method. Among the natural curcuminoids, curcumin III was the most effective anti-inflammatory agent. Curcumin III produced an inhibition of 86·8% of the mice paw oedema at a concentration of 50 mg kg−1 body weight whereas curcumin I and curcumin II produced an inhibition of 72·4% and 65·1%, respectively at the same concentration. Among the synthetic curcuminoids, salicyl (63·0% inhibition), veratryl (62·6%) and piperonal (61·1%) curcuminoids were found to be potent anti-inflammatory agents, followed by p-anisyl curcuminoid (58·6%). There was a correlation between the anti-inflammatory activities of the curcuminoids and their observed antioxidant activities, reported earlier.

In vitro inhibitory effect of tetrahydrocurcuminoids on Fusarium proliferatum growth and fumonisin B1 biosynthesis

Many plant pathogens produce toxic metabolites when growing on food and feed. Some antioxidative components seem to prevent fungal growth and mycotoxin formation. Recently, we synthesized a new class of powerful antioxidative compounds, i.e. tetrahydrocurcuminoids, and its structure/antioxidant activity relationships have been established. The South West of France produces large amounts of corn, which can be infected by Fusarium species, particularly F. proliferatum. In this context, the efficiency of tetrahydrocurcuminoids, which can be obtained from natural curcuminoids, was investigated to control in vitro the growth of F. proliferatum and the production of its associated mycotoxin, fumonisin B1. The relation between structure and antifungal activity was studied. Tetrahydrocurcumin (THC1), with two guaiacyl phenolic subunits, showed the highest inhibitory activity (measured as radial growth on agar medium) against the F. proliferatum development (67% inhibition at a concentration of 13.6 µmol ml−1). The efficiencies of THC2 (36% at a concentration of 11.5 µmol ml−1), which contains syringyl phenolic units, and THC3 (30% at a concentration of 13.6 µmol ml−1), which does not have any substituent on the aromatic rings, were relatively close. These results indicate that the simultaneous presence of guaiacyl phenols and the enolic function of the β-diketone moiety play an important role in the inhibition mechanisms. The importance of this combination was confirmed using n-propylguaiacol and acetylacetone as molecular models. Under the same conditions, ferulic acid and eugenol, other natural phenolic antioxidants, were less efficient in inhibiting fungal growth. THC1 also reduced fumonisin B1 production in liquid medium by approximately 35, 50 and 75% at concentrations of 0.8, 1.3, and 1.9 µmol ml−1, respectively. These very low inhibitory concentrations show that tetrahydrocurcuminoids could be one of the most promising biobased molecules for the control of mycotoxinogen fungal strains.

ChemInform Abstract: Isoxazole Analogues of Curcuminoids with Highly Potent Multidrug‐Resistant Antimicrobacterial Activity.

AbstractThe natural curcuminoids (I), obtained from the medical plant Curcuma longa L., are structurally modified by alkylation, dealkylation, heterocyclization as well as reduction/oxidation reactions.

Curcuminoid analogs with potent activity against Trypanosoma and Leishmania species

The natural curcuminoids curcumin ( 1), demethoxycurcumin ( 2) and bisdemethoxycurcumin ( 3) have been chemically modified to give 46 analogs and 8 pairs of 1:1 mixture of curcuminoid analogs and these parent curcuminoids and their analogs were assessed against protozoa of the Trypanosoma and Leishmania species. The parent curcuminoids exhibited low antitrypanosomal activity (EC 50 for our drug-sensitive Trypanosoma brucei brucei line (WT) of compounds 1, 2 and 3 are 2.5, 4.6 and 7.7 μM, respectively). Among 43 curcuminoid analogs and 8 pairs of 1:1 mixture of curcuminoid analogs tested, 8 pure analogs and 5 isomeric mixtures of analogs exhibited high antitrypanosomal activity in submicromolar order of magnitude. Among these highly active analogs, 1,7-bis(4-hydroxy-3-methoxyphenyl)hept-4-en-3-one ( 40) was the most active compound, with an EC 50 value of 0.053 ± 0.007 μM; it was about 2-fold more active than the standard veterinary drug diminazene aceturate (EC 50 0.12 ± 0.01 μM). Using a previously characterized diminazene-resistant T. b. brucei (TbAT1-KO) and a derived multi-drug resistant line (B48), no cross-resistance of curcuminoids was observed to the diamidine and melaminophenyl arsenical drugs that are the current treatments. Indeed, curcuminoids carrying a conjugated keto (enone) motif, including 40, were significantly more active against T. b. brucei B48. This enone motif was found to contribute to particularly high trypanocidal activity against all Trypanosoma species and strains tested. The parent curcuminoids showed low antileishmanial activity (EC 50 values of compounds 1 and 2 for Leishmania mexicana amastigotes are 16 ± 3 and 37 ± 6 μM, respectively) while the control drug, pentamidine, displayed an EC 50 of 16 ± 2 μM. Among the active curcuminoid analogs, four compounds exhibited EC 50 values of less than 5 μM against Leishmania major promastigotes and four against L. mexicana amastigotes. No significant difference in sensitivity to curcuminoids between L. major promastigotes and L. mexicana amastigotes was observed. The parent curcuminoids and most of their analogs were also tested for their toxicity against human embryonic kidney (HEK) cells. All the curcuminoids exhibited lower toxicity to HEK cells than to T. b. brucei bloodstream forms and only one of the tested compounds showed significantly higher activity against HEK cells than curcumin ( 1). The selectivity index for T. b. brucei ranged from 3-fold to 1500-fold. The selectivity index for the most active analog, the enone 40, was 453-fold.

Macrophage Migration Inhibitory Factor (MIF) Tautomerase Inhibitors as Potential Novel Anti-Inflammatory Agents: Current Developments

Macrophage migration inhibitory factor (MIF), the pro-inflammatory cytokine, first described in 1966, plays an essential role in both, innate and adaptive immune response. It has been implicated in tumour growth and angiogenesis and it exerts an antagonistic action against glucocorticoid immunosuppressive effect. Its perplexing enzymatic tautomerase activity has attracted considerable interest in the last decade. It has been suggested, that a multitude of autoimmune/inflammatory/neoplastic disease states might benefit from therapeutic measures, targeting MIF. Hence, small molecule inhibitors of MIF are relentlessly sought as potential anti-inflammatory (antitumour) agents, while a true in vivo substrate for MIF still remains unidentified. One of the first studied MIF inhibitor group was the D-dopachrome family, and its carboxyderivatives have shown good inhibitory effect, as well as the fluorosubstituted phenylpyruvic acid class. The substance ISO-1 of isoxazoline skeleton was the first small molecular inhibitor of MIF, not related to its known substrates. N-acetyl-p-benzoquinone, an acetaminophen metabolite and its synthetic derivatives exerted submicromolar IC(50) values. An acetylenic compound, the 2-oxo-4-phenyl-3-butynoate is a potent active-site-directed irreversible inhibitor of the phenyl pyruvate tautomerase activity of MIF. Some oxygen heterocycles, coumarines and chromenes, have also drawn attention as MIF inhibitors. The alpha,beta-unsaturated carbonyl compounds constitute a large novel class of MIF inhibitors. Several potent inhibitors were found among the cinnamic acid derivatives, thealpha,beta-unsaturated cyclic ketones, and the natural curcuminoids. Some other plant derived compounds were also studied. One of the latest developments in the field is the synthesis of AVP-13546, an exceptionally potent inhibitor. The structural pattern of MIF enzyme inhibitors exhibits wide variety; compounds having quite different molecular backbones belong to the MIF inhibitor family. In this paper, the separate classes of MIF inhibitors are discussed.

Recent advances in the investigation of curcuminoids

More than 30 Curcuma species (Zingiberaceae) are found in Asia, where the rhizomes of these plants are used as both food and medicine, such as in traditional Chinese medicine. The plants are usually aromatic and carminative, and are used to treat indigestion, hepatitis, jaundice, diabetes, atherosclerosis and bacterial infections. Among the Curcuma species, C. longa, C. aromatica and C. xanthorrhiza are popular. The main constituents of Curcuma species are curcuminoids and bisabolane-type sesquiterpenes. Curcumin is the most important constituent among natural curcuminoids found in these plants. Published research has described the biological effects and chemistry of curcumin. Curcumin derivatives have been evaluated for bioactivity and structure-activity relationships (SAR). In this article, we review the literature between 1976 and mid-2008 on the anti-inflammatory, anti-oxidant, anti-HIV, chemopreventive and anti-prostate cancer effects of curcuminoids. Recent studies on curcuminoids, particularly on curcumin, have discovered not only much on the therapeutic activities, but also on mechanisms of molecular biological action and major genomic effects.

Glucuronidation of curcuminoids by human microsomal and recombinant UDP‐glucuronosyltransferases

Glucuronidation is an important pathway in the metabolism of curcumin, but the isoforms of uridine-5'-diphosphoglucuronosyltransferase (UGT) involved are not known. Here, we report on the glucuronidation of the three natural curcuminoids and their major phase I metabolites with microsomes from human liver and intestine as well as with human recombinant UGTs. Microsomes from human liver generated predominantly the phenolic and small amounts of the alcoholic glucuronide of each curcuminoid, whereas intestinal microsomes formed only the phenolic conjugates but with higher activities. The phenolic glucuronidation of the curcuminoids was predominantly catalyzed by hepatic UGT1A1 and intestinal UGT1A8 and 1A10, whereas UGT1A9, 2B7, and 1A8 exhibited high activities for hexahydro-curcuminoids. UGT1A9 was able to form the alcoholic glucuronide of each curcuminoid in addition to the phenolic conjugate. These data suggest that the gastrointestinal tract contributes substantially to the glucuronidation of curcuminoids in humans, which may have important implications for their pharmacokinetic fate in vivo.

α-Glucosidase inhibition of natural curcuminoids and curcumin analogs

Natural curcumin ( 1), demethoxycurcumin ( 2) and bisdemethoxycurcumin ( 3) isolated from Curcuma longa (turmeric), and synthetic curcumin analogs ( A 1–7 , B 1–7 , C 1–6 and D 1–7 ) were evaluated in vitro for the α-glucosidase inhibitory activity via UV and circular dichroism (CD) spectroscopy. The results indicated that natural curcuminoid compound 3 showed a remarkable inhibitory effect with IC 50 of 23.0 μM, and the synthetic compounds A 2 , B 2 , C 2 and D 2 showed potent inhibitory effects with IC 50 of 2.8, 2.6, 1.6 and 8.2 μM, respectively. Kinetic study exhibited that the mechanism of α-glucosidase inhibition of both 3 and C 2 was non-competitive. The structure activity relationship revealed that the ortho dihydroxyl groups could form a more tight interaction with α-glucosidase to exert more potential inhibitory activities.

Modulation of human multidrug-resistance MDR-1 gene by natural curcuminoids.

Multidrug resistance (MDR) is a phenomenon that is often associated with decreased intracellular drug accumulation in patient's tumor cells resulting from enhanced drug efflux. It is related to the overexpression of a membrane protein, P-glycoprotein (Pgp-170), thereby reducing drug cytotoxicity. A variety of studies have tried to find MDR modulators which increase drug accumulation in cancer cells. In this study, natural curcuminoids, pure curcumin, demethoxycurcumin and bisdemethoxycurcumin, isolated from turmeric (Curcuma longa Linn), were compared for their potential ability to modulate the human MDR-1 gene expression in multidrug resistant human cervical carcinoma cell line, KB-V1 by Western blot analysis and RT-PCR. Western blot analysis and RT-PCR showed that all the three curcuminoids inhibited MDR-1 gene expression, and bisdemethoxycurcumin produced maximum effect. In additional studies we found that commercial grade curcuminoid (approximately 77% curcumin, 17% demethoxycurcumin and 3% bisdemthoxycurcumin) decreased MDR-1 gene expression in a dose dependent manner and had about the same potent inhibitory effect on MDR-1 gene expression as our natural curcuminoid mixtures. These results indicate that bisdemethoxycurcumin is the most active of the curcuminoids present in turmeric for modulation of MDR-1 gene. Treatment of drug resistant KB-V1 cells with curcumin increased their sensitivity to vinblastine, which was consistent with a decreased MDR-1 gene product, a P-glycoprotein, on the cell plasma membrane. Although many drugs that prevent the P-glycoprotein function have been reported, this report describes the inhibition of MDR-1 expression by a phytochemical. The modulation of MDR-1 expression may be an attractive target for new chemosensitizing agents.

Synthesis of (+/-)-cassumunins A and B, new curcuminoid antioxidants having protective activity of the living cell against oxidative damage.

A chemical synthesis of cassumunins A (1) and B (2), natural curcuminoid antioxidants, was developed. The synthesis was started from o-vanillin and after nine reaction steps resulted in 20% and 26% overall yields of 1 and 2, respectively. The synthetic cassumunins showed stronger protective activity than curcumin against oxidative cell death induced by hydrogen peroxide in a rat thymocyte system.

Antimutagenic and anticarcinogenic activity of natural and synthetic curcuminoids

Five synthetic curcuminoids and three natural curcuminoids were investigated for their antimutagenic and anti-promotional activity. The natural curcuminoids, curcumin I (diferuloylmethane), curcumin II (feruloyl- p-hydroxycin-namoylmethane) and curcumin III (bis-( p-hydroxycinnamoyl)methane) isolated from Curcuma longa were found to be potent inhibitors of mutagenesis and crotean oil-induced tumour promotion. Curcumin III produced 87.6% inhibition to 2-acetamidofluorene (2-AAF) induced mutagenesis, at a concentration of 100 μg/plate, curcumin II and curcumin I produced 70.5% and 68.3% inhibition at the same concentration. All the synthetic curcuminoids were found to inhibit 2-AAF-induced mutagenicity among which salicyl-and anisylcurcuminoids were the most active. Curcumin III was the most effective anti-promotor among natural curcuminoids. While 90% of the control animals were having papillomas on the 10th week of tumour initiation, only 10% of the curcumin III-treated animals, 20% of the curcumin II-treated animals, and 40% of the curcumin I-treated animals were having papillomas. Salicylcurcuminoid, which was causing no papillomas by the 10th week, was the most potent anti-carcinogen among the synthetic curcuminoids. Piperonal curcuminoid also exhibited anti-promotional activity.

Anti-tumour and antioxidant activity of natural curcuminoids.

Matural curcuminoids, curcumin, I, II and III isolated from turmeric (Curcuma longa) were compared for their cytotoxic, tumour reducing and antioxidant activities. Curcumin III was found to be more active than the other two as a cytotoxic agent and in the inhibition of Ehrlich ascites tumour in mice (ILS 74.1%). These compounds were also checked for their antioxidant activity which possibly indicates their potential use as anti-promoters. The amount of curcuminoids (I, II and III) needed for 50% inhibition of lipid peroxidation was 20, 14 and 11 g/m. Concentrations needed for 50% inhibition of superoxides were 6.25, 4.25 and 1.9 micrograms/ml and those for hydroxyl radical were 2.3, 1.8 and 1.8 micrograms/ml, respectively. The ability of these compounds to suppress the superoxide production by macrophages activated with phorbol-12-myristate-13-acetate (PMA) indicated that all the three curcuminoids inhibited superoxide production and curcumin III produced maximum effect. These results indicate that curcumin III is the most active of the curcuminoids present in turmeric. Synthetic curcumin I and III had similar activity to natural curcumins.