Biochemical Pharmacology, Copyright 0 1996 Elsevier Vol. 52, pp. 519-525, Science Inc. ISSN 1996. 0006-2952/96/$15.00 + 0.00 PII SOOOS-2952(96)00302-4 ELSEVIER Involvement Antioxidative of the P-Diketone Moiety in the Mechanism of Tetrahydrocurcumin Yasunori Sugiyamu, Shunro Kawakishi and Toshihiko Osawa” DEPARTMENT OF APPLIED BIOLOGICAL SCIENCES, NAGOYA UNIVERSITY, NAGOYA 464-01, ABSTRACT. major We examined metabolites butylhydroperoxide. investigate the inhibitory of curcumin, effects The results demonstrated the mechanism of curcumin on the lipid peroxidation that THC of antioxidative activity, and tetrahydrocurcumin of erythrocyte membrane showed a greater inhibitory we examined the effects JAPAN (THC), ghosts one of the induced by tert- effect than curcumin. of several inhibitors, To such as enzymes, hydroxyl radical scavengers, IO, quencher, and chelating agents for metal ions. Given that all inhibitors failed to inhibit membrane peroxidation, THC must scavenge radicals such as tert-butoxyl radical and peroxyl radical. To clarify the antioxidative mechanism of THC, in particular the role of the P-diketone moiety, dimethylated THC was incubated with peroxyl radicals generated by thermolysis of 2,2’-azobis(2,4antioxidant dimethylvaleronitrile). Four dimethoxybenzoic acid, fourth oxidation product oxidation products seems to be an unstable mined. These results suggest that the B-diketone of the C--C THC bond at the active logical properties KEY The rhizome widely methylene is one of the major metabolites WORDS. moiety of THC coloring between agent (turmeric) has and spice three of which and its detailed were must exhibit two carbonyls it may also exhibit structure identified been antioxidative activity by cleavage moiety. the same physiological Because and pharmaco- moiety as well as phenolic B-diketone; antioxidant; radical scavenger Holder et al.  did not find any free or conjugated curcumin in the bile after intravenous administration of the treatment of inflammatory and other diseases [l]. Curcumin (diferuloylmethane, Fig. 1) has been identified as the [3H]curcumin; according to them, one of the major metabolites in the bile is the glucuronide conjugate of THCt (Fig. 1). THC, a colorless compound less polar than curcumin, major pigment in turmeric and has been reported to possess both antioxidative and antiinflammatory activities [2-61. Recent studies indicate that curcumin inhibits the micro- absorption from the intestines. THC the physiological and pharmacological some-mediated min. foods, and it has also been used in indigenous medicine for The 1996. tetrahydrocurcumin; in many as 3,4acid. has not been deter- in the B-diketone in viva by means of the B-diketone PHARMACOL 52;4:519-525, longa Linn of Curcuma used as a yellow intermediate, of curcumin, Curcuma longa Linn; curcumin; detected, and 3-(3,4-dimethoxyphenyl)-propionic carbon as the active form of curcumin hydroxy groups. BEHEM were 3’,4’-dimethoxyacetophenone, mutagenicity of benzo[u]pyrene and 7,12- seems to be the transformed product of curcumin during may be involved in properties of curcu- dimethylbenz[a]anthracene , and that it also acts as a strong inhibitor of tumor promotion in mouse skin by 12- In the course of our investigation to find novel types of antioxidative substances in plant materials, two B- O-tetradecanoylphorbol-13-acetate . Several studies on the absorption and metabolism diketone-type antioxidants, TTAD and 4-hydroxytritriacontan-16,18-dione, were isolated and identified as of cur- cumin have been reported. Ravindranath and Chandrasekhara have reported on the absorption and tissue distribution of curcumin in rats [9, lo] and its in viva absorption after oral administration using [3H]curcumin [ll]. Their results show that curcumin is transformed during absorption from the intestines and that the transformed product, which is a less polar and colorless compound than curcumin, enters the serosal side. On the other hand, *Corresponding author: Dr. Toshihiko Osawa, Laboratory of Food and Biodynamics, Department of Applied Biological Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-01, Japan. Tel. 01 l-81-52-7894126; FAX 011-81-52-789-4120. Received 19 June 1995; accepted 26 February 1996. novel natural antioxidants from Eucalyptus leaf wax [13, 141. Because curcumin also has a B-diketone moiety, this moiety must play an important role in the antioxidative activity of curcumin in uiuo. However, the antioxidative mechanism of B-diketone-type antioxidants is not clear. t Abbreuinnons: THC, tetrahydrocurcumin; TTAD, n-tritriacontan-16,18dione; CLA, conjugated dienoic derivatives of linoleic acid; t-BuOOH, rert-buoilhydroperoxide; PtO,, platinum oxide; AMVN, 2,2’-azobis(2,4dimethylvaleronitrile); AAPH, 2,2’-azobis(2-amidinopropane)dihydrochioride; DTPA, diethylenetriamine-N,N,N’,N”,N”-pentaacetic acid; DABCO, 1,4-diazabicyclo-[2,2,2] oc t ane; TBA, 2-thiobarbituric acid; SOD, superoxide dismutase; DMTHC, dimethoxytetrahydrocurcumin; and TBARS, TBA-reacting substance. 520 Y. Sugiyama et al. 0 0 OCH, Hydrogenation Pt02 OH Curcumin Tetrahydrocurcumin FIG. 1. Preparation Recently, inhibits of tetrahydrocurcumin Hirose et al.  reported that TTAD hepatic and pancreatic carcinogenesis. (THC) from curcumin by hydrogenation strongly Moreover, Pariza and Ha  reported that CLA are effective in inhibiting benzo[a]pyrene-induced forestomach neoplasia in mice and also in suppressing the process of tumor promotion in the mouse forestomach . One of the possible (THC) with PtO,. Uehara et nl. . After hydrogenation, THC was purified by preparative TLC (5% MeOH in CHCl,, R, = 0.86) with a yield of 42.5%. The identity and purity of THC were confirmed by using MS, IR, UV, and NMR spectra. THC: FAB-MS m/s 395 (M + Na)‘; IR (KBr) v,,, 3430 (OH), 3060-2840 (CH), 1603 (C=O), 1033 (OCH,,)cm-‘; mechanisms for the anticarcinogenicity of CLA is thought to be that an oxidized derivative of CLA must be the actual ultimate antioxidant form rather than CLA itself, although UV(EtOH) Xm,,(log E) 225(4.16), 282(4.24) nm; ‘H NMR (CDCl,) 6 2.54 (4H, t,J = 8.1 Hz, 1, 7), 2.74-2.88 (4H, m, the structure of the active form has not been determined. (lH(enol), s, 4), 5.65 (2H, broad, OH), 6.65 (2H, d,J = 7.8 Hz, 6’, 6”), 6.67 (2H, s, 2’,2”), 6.81 (2H, d, J = 7.8 Hz, 5’,5”). However, it has been suggested that the introduction P-diketone moiety into the CLA molecule of the is the most likely candidate as the active form of CLA [ 171. Therefore, it is very important to investigate the antioxidative mechanism of B-diketone-type antioxidants. In this study, we examined the inhibitory effects of cur- cumin and THC on t-BuOOH-induced lipid peroxidation. To investigate the mechanism of antioxidative activity, we examined the contribution of oxidizing species in the per- oxidation system. This paper also gives details on the antioxidative mechanism at the B-diketone moiety of THC and reports on an investigation of the metabolic THC in reaction with peroxyl radicals. MATERIALS pathway of was obtained after purification by preparative silica gel TLC (5% MeOH in CHCl,, Merck Art. 13895) from turmeric, which was a gift from the Daiwa Kasei Co., Ltd., Saitama, Japan. The yield of curcumin was 76.0%. PtOz, AMVN, AAPH, mannitol, DABCO, 3,4_dimethoxybenzaldehyde, DMSO, DTPA, and acetyl acetone were purchased from Wako Pure Chemical Industries Ltd., Osaka, Japan. TBA was purchased from Merck (Darmstadt, F.R.G.). Egg yolk phosphatidylcholine, SOD (from bovine erythrocytes), and catalase (from bovine liver) were purchased from the Sigma Chemical Co. (St. Louis, MO, U.S.A.). Commercially available rabbit blood was obtained from Japan Biotest Laboratories Inc. (Kokubunji, Tokyo, Japan). t-BuOOH was purchased from the Tokyo Kasei Kogyo Co., Ltd., Tokyo, Japan. Preparation of Curcuminoid THC. Curcumin tion with PtO, s, 4), 3.83 to THC as the catalyst according (6H, s, OCH,), 5.42 DMTHC. DMTHC was prepared synthetically by condensation of 3,4-dimethoxybenzaldehyde and acetyl acetone by the method of Pabon . The identity of the synthetic compound was established by using MS, IR, UV, and NMR spectra. Dimethoxycurcumin was reduced to DMTHC by hydrogenation with PtO, as described above. DMTHC was purified by preparative TLC (n-hexane:ethyl acetate = 1: 1, R, = 0.53) with a yield of 52.0%. The identity and purity were confirmed by using MS, IR, UV, and NMR spectra. DMTHC: EI-MS m/z 400 (M’); IR (KBr) v,,, 2937 (CH), 1592 (C=O), 1029 (OCH,) cm’; UV (EtOH) &_(log E) 228(4.23), 280(4.26) nm; ‘H NMR (CDCl,) 6 2.57 (4H, t, (4H, m, 2,6), 3.53 (2H(keto), 4), 3.866-3.871 (12H, m, OCH,), 6.72-6.82 (6H, m, 2’,5’,6’,2”,5”,6”). 5.46 (lH(enol), s, s, 4), Antioxidatiwe Assay Commercially available rabbit blood (100 mL) was diluted with 300 mL of isotonic buffer solution (10 mM phosphate buffer, pH 7.4/152 mM NaCl). After centrifugation (1500 g, 20 mm), the blood was lysed in 300 mL of 10 mM phosphate buffer, pH 7.4. Erythrocyte membrane ghosts were pelleted by centrifugation (20,000 g, 40 min), and the precipitate was diluted to give a suspension (1 .O mg protein/ mL). Peroxidation of the erythrocyte membrane ghosts induced by t-BuOOH was carried out by a method described previously . After incubation at 37” for 20 min, the formation of TBARS was determined at 532 nm. Preparation of Liposotnes Derivatives was converted (2H(keto), _I = 7.8 Hz, 1,7), 2.82-2.91 AND METHODS Materials Curcumin 2, 6), 3.49 by hydrogena- to the method of Liposomes were prepared from egg yolk phosphatidylcholine. Egg yolk phosphatidylcholine was suspended in 10 Antioxidative Mechanism of Tetrahydrocurcumin 521 mM phosphate buffer (pH 7.4) and vortexed. Liposomes were always handled in an atmosphere of nitrogen, to prevent auto-oxidation. OGdation of DMTHC DMTHC ( 100 kmol) and AMVN (3 mmol) were dissolved in oxygen-saturated acetonitrile and incubated in a screwcap test tube at 37” according to the method of Liebler et al. . AMVN was used in order to replicate the method of Liebler et al.  on a larger scale. DMTHC (4 kmol) incorporated in the liposomes (10 mg/mL phosphate buffer) and AAPH (200 p_mol) were incubated in a screw-cap test tube at 37”. AAPH was used instead of AMVN in the liposome experiment because AMVN is insoluble in phosphate buffer. Oxidation OJ 0 products were analyzed by reverse- 50 phase HPLC on a Develosil ODS-5 column (4.6 x 150 mm) (Nomura Chemical Co., Ltd.). An aliquot of the reaction mixture was eluted with a linear gradient of a two-solvent system at a flow rate of 1.0 mL/min. Solvent trifluoroacetic acid:methanol 82) and solvent A (0.1% B (100% methanol) were used for the gradient. The gradient employed was as follows: 100 to 0% A in 30 min, isocratic at 0% A for 10 min, 0 to 100% A in 10 min. The elution was monitored by absorbance at 280 nm. The peak area was determined by use of a Shimadzu C-R3A Chromatopac. 200 150 250 Concentration (PM) FIG. 2. Inhibitory effects of curcumin and THC on the Lipid peroxidation of erythrocyte membrane ghosts induced by t-BuOOH. After erythrocyte membrane ghosts at a concentration of 1.0 mg protein/ml were incubated with 2.0 mM t-BuOOH for 20 min in the presence or absence of each curcuminoid, TBARS formation was determined at 532 nm. A control containing no added curcuminoids represented 100% lipid peroxidation (1.66 pM MDA equivalents). Results are the means * SD from four separate experiments. information RESULTS 100 on the role of the B-diketone moiety of THC, the antioxidative effect of the phenolic hydroxyl groups was blocked by methylation of the groups. The dimethylated THC was prepared by hydrogenation of curcumin with PtO, as the catalyst (Fig. 1). All olefinic protons in the ‘H THC, NMR spectra of curcumin were found to disappear in the ‘H NMR spectrum of THC. All spectroscopic data of THC thetic compound with PtO,, after dimethoxycurcumin was prepared as shown in Materials and Methods. The identity were identical with those described in a previous paper on this compound . We examined the inhibitory effects of curcumin and and purity of the synthesized DMTHC THC, AMVN at 37” in oxygen-saturated acetonitrile. dependent reaction of DMTHC with AMVN which is one of the major metabolites of curcumin, on the lipid peroxidation of erythrocyte membrane ghosts induced by t-BuOOH. Concentration-dependent inhibition was observed, and THC exhibited a greater inhibitory effect than curcumin, especially at 150 p,M (Fig. 2). To investigate the mechanism of antioxidative activity, we examined what kind of oxidizing species are involved in the lipid peroxidation. We investigated the effects of inhibitors of active oxygen species, such as antioxidant enzymes, hydroxyl radical scavengers (mannitol and DMSO), ‘0, quencher (DABCO), and chelating agents for metal ions (DTPA), on the lipid peroxidation of erythrocyte membrane ghosts by determining TBARS formation. As shown in Fig. 3, all inhibitors failed to inhibit membrane peroxidation. This result supported the previously reported result that tert-butoxyl radical may be the oxidizing species in lipid peroxidation . THC must scavenge radicals, such as alkoxyl radical or peroxyl radical, and these effects are superior to curcumin. The antioxidative mechanism of THC, especially at the @-diketone moiety, was also investigated. To obtain more DMTHC, was obtained by hydrogenation of the syn were confirmed by using MS, IR, UV, and NMR spectra. DMTHC was incubated with peroxyl radicals, generated by the thermolysis of The timewas exam- ined by reverse-phase HPLC on a Develosil ODS-5 column. Four oxidation products were detected as shown in Fig. 4A. Peaks 1, 2, and 3 were found to increase with incubation time. On the other hand, peak 4 decreased gradually after 33 hr of incubation (Fig. 5). This result suggests that peak 4 must be an unstable intermediate in the reaction of DMTHC with AMVN. The reaction mixture was rapidly chilled by immersion in ice at 33 hr, and the reaction was stopped to determine the structure of peak 4. These four products were isolated and characterized. The proposed structures of the isolated peaks l-3 are shown in Table 1; identification was performed by ‘H NMR and EI-MS. Isolated peak 4 was also investigated. The ‘H NMR spectrum of the product suggested the possibility of the presence of hydroperoxide, although the detailed structure has not been determined. We also used the liposome model in order to mimic the erythrocyte membranes. DMTHC incorporated in the liposomes was incubated with AAPH, which generates peroxyl radicals similarly to AMVN. As a result 522 Y. Sugiyama et al. lase, mannitol, DMSO, DABCO, and DTPA) failed to inhibit membrane peroxidation, tert-butoxyl radical may be the oxidizing species in lipid peroxidation as reported previously , and THC must scavenge radicals such as alkoxyl radical and peroxyl radical. Even though the concentration used was high (10 mM), the approximately 40% inhibition of lipid peroxidation by DABCO suggests that either singlet oxygen has a minor role in the t-BuOOHinduced lipid peroxidation process or, more likely, DABCO is also a poor scavenger of alkoxyl or peroxyl radicals. We have found two novel B-diketone-type antioxidants, TTAD and 4-hydroxy-tritriacontan-16,18-dione [13, 141. Recently, Hirose et al.  reported that TTAD inhibits hepatic and pancreatic carcinogenesis. simple B-diketones strongly Several such as 1,l ,l-trifluoroacetylacetone, DMTHC 4 FIG. 3. Effects of inhibitors on the lipid peroxidation of erythrocyte membrane ghosts induced by t-BuOOH. After erythrocyte membrane ghosts at a concentration of 1.0 mg protein/mL were incubated with 2.0 mM t-BuOOH for 20 min in the presence or absence of various active oxygen scavengers, the formation of TBARS was determined at 532 nm. A control containing no added scavengers represented 100% lipid peroxidation (2.26 PM MDA equivalents). Res suits are the means * SD from four separate experiments. L/ of the reaction, three oxidation products (peaks l-3) have been identified based on similar retention times as the peaks l-3 detected obtained with AMVN; (Fig. 4B). DMTHC ucts in both oxidation DMTHC however, peak 4 was not gave the same reaction 1, prod- model systems. DISCUSSION Given that THC must be the transformed product of cur- cumin during absorption from the intestines [9-121, the transformed THC must be transported in blood and distributed in some tissues such as liver or kidney. We examined the inhibitory effects of curcumin and THC on the lipid peroxidation of erythrocyte membrane ghosts induced by t-BuOOH. The result demonstrated that THC showed a greater inhibitory effect that curcumin, especially at 150 p,M (Fig. 2). Curcumin has been reported to act as a strong inhibitor of mutagenicity  and tumor promotion in mouse skin by 120-tetradecanoylphorbol-13-acetate . Therefore, THC may have more effective antimutagenicity or antitumor activity than curcumin. We examined oxidizing species in the lipid peroxidation of erythrocyte membrane ghosts to investigate the mechanism of antioxidative activity. We investigated the effects of several inhibitors on lipid peroxidation by determining TBARS formation. Because all inhibitors used (SOD, cata- 10 Retention Time (min) FIG. 4. HPLC profile of DMTHC oxidized with AMVN (A) and AAPH (B). DMTHC (100 pmol) was incubated with 3 mmol AMVN for 33 hr (A), and DMTHC (4 pmol) incor# porated into the liposomes (10 mg/mL phosphate buffer) was incubated with 200 pmol AAPH for 94 hr (B). An aliquot of the solution was submitted for reverse-phase HPLC on a Develosil ODS-5 column (4.6 x 150 mm) as described in Materials and Methods. Antioxidative 523 Mechanism of Tetrahydrocurcumin dative effect of the phenolic blocked by methylation the p-diketone hydroxy groups of THC moiety alone on the antioxidative nism was investigated. Dimethylated prepared as described in Materials exhibited was of the groups, and then the role of approximately THC, and Methods. 36% inhibition mecha- DMTHC, (64.15 was DMTHC & 0.006% lipid peroxidation) at 150 FM on the lipid peroxidation erythrocyte membrane ghosts induced by t-BuOOH. Peroxyl radicals are known to be the chain-carrying cals in lipid peroxidation, and their reactions erol, one of the phenolic-type antioxidants, -0 20 40 60 100 80 Reaction Time (hr) FIG. 5. Time-dependent changes of oxidation products of DMTHC during incubation with AMVN. DMTHC at a concentration of 100 pmol was incubated with 3 mmol AMVN. An aliquot of the solution was submitted for reverse-phase HPLC on a Develosil ODS-5 column (4.6 x 150 mm), and the peak area was determined by use of a Shimadzu C-R3A Chromatopac as described in Materials and Methods. peroxyl radicals carboxyl)-propane] generated reactions with peroxyl Given this background, oxyl radicals, AMVN which were generated mechanism by thermolysis acetonitrile, found to increase with incubation time and were identified detailed structure e suggesting that it must be an unstable intermediate reaction of DMTHC acid the of isolated peak 4 has yet to be deter- ‘H NMR EI-MS 8 (ppm) (m/z) 3.95 3.96 6.92 7.59 7.77 (3H, (3H, (lH, (lH, (IH, s) s) d, _I = 8.4) d, J = 1.9) dd, I = 8.4, 1.9) 182 (M’) 167 2.58 3.95 3.94 6.90 7.53 7.59 (3H, (3H, (3H, (lH, (lH, (lH, s) s) s) d, J = 8.3) d, J = 2.0) dd, I = 8.3, 2.0) 180 (M’) 165 137 77 t, ] = 7.7) t, I = 7.7) s) s) (3H, m) 210 (M’) 151 121 91 77 0 3-(3,4-Dimethoxyphenylj-propionic in the with peroxyl radicals. Although mined, the ‘H NMR spectrum suggests the possibility of the presence of hydroperoxide. From these data, an antioxidative mechanism of DMTHC (P-diketone moiety of THC) is proposed, as shown in Fig. 6. Both enol and keto forms of product C acid, respec- tively. Peak 4 decreased gradually after 33 hr of incubation, TABLE 1. Structures and analytical data for oxidation products of DMTHC H&O antioxi- acid, 3’,4’-dimethoxyacetophe- of P-diketone-type antioxidants. Because THC, one of the major metabolites of curcumin, also has a p-diketone moiety, which may play an important role in antioxidative OH of to confirm of P-diketone-type none, and 3-(3,4-dimethoxyphenyl)-propionic H&O the dants. Four oxidation products were detected by reversephase HPLC as shown in Fig. 4A. Peaks 1, 2, and 3 were acetylacetone, benzoylacetone and dibenzoylmethane were reported to inhibit mutagenicity induced by 2-nitrofluorene using the Salmonella typhimurium strain . Therefore, it is very important to investigate the antioxidative mechanism Oxidation Yamauchi radicals generated from AMVN. DMTHC was incubated with per- as 3,4-dimethoxybenzoic activity, we examined the antioxidative mechanism of the P-diketone-type antioxidants by using THC. The antioxi- azobis[(n-butyl-  also have reported at 37” in oxygen-saturated the antioxidative For example, of tocopherol and azobis(isobutyronitrile).  and Matsuo et al. et al. from radi- with tocoph- have been stud- ied by numerous investigators [21, 25-271. Winterle et al.  reported the reactions with of 2.67 (2H, 2.92 (2H, 3.86 (3H, 3.87 (3H, 6.74-6.82 524 Y. Sugiyama et al. 0 0 H&O OCH, H&O OCH, ROO . HQ \ 0 0 0 H&O OCH, H&O OCY H&O OCY H&O OCH3 ;;IdOH ,““;- ;z&f+J;;; 3 3 3 H 3-(3,4-Dimethoxyphenyl)-propionic 02 acid ROO1 b 1 co2 L 0 (ROO l co2 0 : Peroxyl radicals) H&O H,CO 3’,4’-Dimethoxyacetophenone FIG. 6. Proposed antioxidative mechanism DMTHC must scavenge free radicals, and the C-C bond at the active methylene carbon between two carbonyls in the p-diketone moiety is cleaved. As a result, 3-(3,4dimethoxyphenyl)-propionic acid was formed, and 3,4dimethoxybenzoic acid and 3’,4’-dimethoxyacetophenone were produced as secondary oxidation products. This mechanism has been confirmed by the reaction of DMTHC incorporated in the liposomes with AAPH, because the 3,4-Dimethoxybenzoic acid of DMTHC. same three oxidation products have been identified (Fig. 4B). These results strongly support the conclusion that the P-diketone moiety must play an important role in the antioxidative mechanism of THC. Although many workers [21, 25-271 have reported on phenolic-type natural antioxidants including tocopherol, this is the first report to show the involvement of the P-diketone moiety in antioxidative mechanisms. Antioxidative This Mechanism study on the antioxidative ketone-type antioxidants indicates moiety may play an important antimutagenesis type antioxidants inhibit addition, of curcumin expected such as TTAD because THC the of P-diP-diketone of 13. because P-diketonehave been reported and carcinogenesis to [7, 8, 151. In is the rapidly metabolized during absorption that THC mechanism that role in the elucidation or anticarcinogenesis, tumor promotion 525 of Tetrahydrocurcumin product from the intestines, may have the same important 15. it is physi- ological and pharmacological properties as the active form of curcumin in vioo by means of the P-diketone moiety as well as phenolic hydroxy groups. A detailed testing this conclusion is underway. 14. 16. experiment 17. References 1. Nadkarni Nadkarni KM, Curcuma longa. In: Indian Mat&a Medica (Ed. KM), pp. 414-417. Popular Prakashan, Bombay, 18. 1976. 2. Sharma OP, Antioxidant activity of curcumin and related compounds. Biochem PharmacoI 25: 1811-1812, 1976. of diferuloyl 3. Srimal RC and Dhawan BN, Pharmacology methane (curcumin), a nonsteroidal anti-inflammatory agent. J Phurm Phannucol25: 447452, 1973. activ4. Rao TS, Basu N and Siddiqui HH, Anti-inflammatory ity of curcumin analogues. Indian J Med Res 75: 574-578, 1982. 5. Mukhopadhyay A, Basu N, Ghatak N and Gujral PK, Antiinflammatory and irritant activities of curcumin analogues in rats. Agents Actions 12: 508-515, 1982. R, Saraf AP and Balwani JH, Comparison of 6. Yegnanarayan anti-inflammatory activity of various extracts of Curcuma longa (Linn). Indian J Med Res 64: 601-608, 1976. 7. Nagabhushan M, Amonkar AJ and Bhide SV, In vitro antimutagenicity of curcumin against environmental mutagens. Food Chem Toxicol25: 545-547, 1987. 8. Huang M-T, Smart RC, Wong C-Q and Conney AH, Inhibitory effect of curcumin, chlorogenic acid, caffeic acid, and ferulic acid on tumor promotion in mouse skin by 12-Otetradecanoylphorbol-13-acetate. Cancer Res 48: 5941-5946, 1988. 9. Ravindranath V and Chandrasekhara N, Absorption and tissue distribution of curcumin in rats. Toxicology 16: 259-265, 1980. 10. Ravindranath V and Chandrasekhara N, In vitro studies on the intestinal absorption of curcumin in rats. Toxicology 20: 251-257, 1981. 11. Ravindranath V and Chandrasekhara N, Metabolism of curcumin-Studies with [3H]curcumin. Toxicology 22: 337-344, 1982. 12. Holder GM, Plummer JL and Ryan AJ, The metabolism and excretion of curcumin (1,7-bis-(4-hydroxy-3-methoxy- 19. 20. 21. 22. 23. 24. 25. 26. 27. phenyl)-1,6-heptadiene-3,5-dione) in the rat. Xenobiotica 8: 761-768, 1978. Osawa T and Namiki M, A novel type of antioxidant isolated from leaf wax of Eucalyptus leaves. Agric Biol Chem 45: 735739, 1981. Osawa T and Namiki M, Natural antioxidants isolated from Eucalyptus leaf waxes. J Agric Food Chem 33: 777-780, 1985. Hirose M, Ozaki K, Takaba K, Fukushima S, Shirai T and Ito N, Modifying effects of the naturally occurring antioxidants y-oryzanol, phytic acid, tannic acid and n-tritriacontane16,18-dione in a rat wide-spectrum organ carcinogenesis model. Carcinogenesis 12: 1917-1921, 1991. Pariza MW and Ha YL, Conjugated dienoic derivatives of linoleic acid: Mechanism of anticarcinogenic effect. In: Mutagens and Carcinogens in the Diet (Eds. Pariza MW, Aeschbather HU, Felton JS and Sato S), pp. 217-221. Wiley-Liss, New York, 1990. Ha YL, Storkson J and Pariza MW, Inhibition of benzo(n)pyrene-induced mouse forestomach neoplasia by conjugated dienoic derivatives of linoleic acid. Cancer Res 50: 1097-I 101, 1990. Uehara S, Yasuda I, Akiyama K, Morita H, Takeya K and Itokawa H, Diaryl-heptanoids from the rhizomes of Curcuma xanthorrhiza and [email protected] officinarum. Chem Pharm Bull (Tokyo) 35: 3298-3304, 1987. Pabon HJJ, A synthesis of curcumin and related compounds. Ret True, Chim Pays Bas 83: 379-386, 1964. Osawa T, Ide A, Su J-D and Namiki M, Inhibition of lipid peroxidation by ellagic acid. J Agric Food Chem 35: 808-812, 1987. Liebler DC, Baker PF and Kaysen KL, Oxidation of vitamin E: Evidence for competing autoxidation and peroxyl radical trapping reactions of the tocopheroxyl radical. J Am Chem Sot 112: 6995-7000, 1990. Roughley PJ and Whiting DA, Experiments in the biosynthesis of curcumin. J Chem Sot Perkin Trans I 2379-2388, 1973. Cadenas E and Sies H, Low level chemiluminescence of liver microsomal fractions initiated by tert-butyl hydroperoxide. Eur J Biochem 124: 349-356, 1982. Wang CY, Lee M-S, Nagase H and Zukowski K, Inhibition by diacylmethane derivatives of mutagenicity and nucleic acid binding of 2-aminofluorene derivatives. J Nat1 Cancer lnst 81: 1743-1747, 1989. Winterle J, Dulin D and Mill T, Products and stoichiometry of reaction of vitamin E with alkylperoxy radicals. J Or-g Chem 49: 491-495, 1984. Yamauchi R, Matsui T, Satake Y, Kato K and Ueno Y, Reaction products of cy-tocopherol with a free radical initiator, 2,2’-azobis(2,4-dimethylvaleronitrile). Lipids 24: 204-209, 1989. Matsuo M, Matsumoto S, Iitaka Y and Niki E, Radicalscavenging reactions of vitamin E and its model compound, 2,2,5,7,8-pentamethylchroman-6-01, in a tert-butylperoxyl radical-generating system. J Am Chem Sot 11 I: 7179-7185, 1989.
© Copyright 2018 ExploreDoc