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PubMed2002

Cellular protection with proanthocyanidins derived from grape seeds.

Grape seed proanthocyanidins have been reported to possess a broad spectrum of pharmacological and medicinal properties against oxidative stress. We have demonstrated that IH636 proanthocyanidin extract (GSPE) provides excellent protection against free radicals in both in vitro and in vivo models. GSPE had significantly better free radical scavenging ability than vitamins C, E and beta-carotene and demonstrated significant cytotoxicity towards human breast, lung and gastric adenocarcinoma cells, while enhancing the growth and viability of normal cells. GSPE protected against tobacco-induced apoptotic cell death in human oral keratinocytes and provided protection against cancer chemotherapeutic drug-induced cytotoxicity in human liver cells by modulating cell cycle/apoptosis regulatory genes such as bcl2, p53 and c-myc. Recently, the bioavailability and mechanistic pathways of cytoprotection by GSPE were examined on acetaminophen-induced hepatotoxicity and nephrotoxicity, amiodarone-induced pulmonary toxicity, doxorubicin-induced cardiotoxicity, DMN-induced immunotoxicity and MOCAP-induced neurotoxicity in mice. Serum chemistry changes, integrity of genomic DNA and histopathology were assessed. GSPE pre-exposure provided near complete protection in terms of serum chemistry changes and DNA damage, as well as abolished apoptotic and necrotic cell death in all tissues. Histopathological examination reconfirmed these findings. GSPE demonstrated concentration-/dose-dependent inhibitory effects on the drug metabolizing enzyme cytochrome P450 2E1, and this may be a major pathway for the anti-toxic potential exerted by GSPE. Furthermore, GSPE treatment significantly decreased TNFalpha-induced adherence of T-cells to HUVEC by inhibiting VCAM-1 expression. These results demonstrate that GSPE is highly bioavailable and may serve as a potential therapeutic tool in protecting multiple target organs from structurally diverse drug- and chemical-induced toxicity.

Animals↗
PubMed2004

Synergistic effect of Scutellaria baicalensis and grape seed proanthocyanidins on scavenging reactive oxygen species in vitro.

Scutellaria baicalensis (SbE) is a commonly used Chinese herb medicine and grape seed proanthocyanidins is a popular herbal supplement in the United States. Both herbs have been shown to possess potent antioxidant effects. Using an in vitro model to produce the reactive oxygen species (ROS) generation (H2O2/FeSO4 for hydroxyl radicals, xanthine/xanthine oxidase for suproxide), we observed that Scutellaria baicalensis and grape seed proanthocyanidins acted synergistically to scavenge ROS. Our data suggest that a combination of these two herbs can potentially enhance their antioxidant efficacy, allowing lower dosages of each drug to be used. This has the advantage of avoiding possible side effects that may arise when higher doses of a single herb are used in an attempt to achieve a maximum degree of antioxidant activity.

Drug Synergism↗
PubMed2005

Antinociceptive effect of proanthocyanidins from Croton celtidifolius bark.

The chemical composition of the chromatography 63 subfraction (63SF) from the ethyl acetate soluble fraction of the crude extract of Croton celtidifolius bark presented a high content of total proanthocyanidins (75.0+/-2.3%). HPLC analysis of 63SF revealed a dimeric profile (e.g.catechin-(4alpha-->8)-catechin and gallocatechin-(4alpha-->8)-catechin) and polymeric proanthocyanidins. In pharmacological investigations, 63SF administered intraperitoneally exhibited dose-dependent antinociceptive activity against several chemical stimuli, including the intraperitoneal injection of acetic acid (ID50 (the dose of 63SF which was able to reduce the nociceptive response by 50% relative to the control value)=0.9 (0.5-1.6)) and the intraplantar injection of capsaicin (ID50=13.0 (10.0-17.0)), glutamate (ID50=4.0 (2.0-7.0)) and formalin (ID50 first phase=36.0 (24.0-53.0) and late phase=11.0 (8.0-14.0)). 63SF administered orally exhibited an antinociceptive effect in the formalin test (ID50 first phase=125.0 (89.0-177.0) and late phase=65.0 (33.0-95.0)). In the same test, 63SF was effective when given soon after the first phase, as well as exhibiting therapeutic activity. Furthermore, 63SF was effective in models of thermal nociception including tail-flick and hot-plate tests. When the mice were treated in the neonatal period with capsaicin, the antinociceptive effect of 63SF in the first phase of the formalin test was abolished, but pretreatment with naltrexone did not change the antinociceptive effect of 63SF. Together, these results provide evidence that 63SF exerted a pronounced systemic antinociception against chemical (acetic acid, formalin, glutamate and capsaicin tests) and thermal (hot-plate and tail-flick tests) nociceptive models of pain in mice at a dose that did not interfere with the locomotor activity. The mechanism by which this sub-fraction produced antinociception remains unclear, but it is unlikely to involve the activation of the opioid system. However, unmyelinated C-fibres sensitive to treatment with capsaicin are likely to participate in antinociception caused by 63SF.

Administration, Oral↗
PubMed1998

Proanthocyanidins from barley bran potentiate retinoic acid-induced granulocytic and sodium butyrate-induced monocytic differentiation of HL60 cells.

Polyphenol extract from barley bran (BPE) induced nitro blue tetrazolium (NBT) reducing activity and alpha-naphthyl butyrate esterase activity in HL60 human myeloid leukemia cells. Because BPE induced the biochemical markers of HL60 cell differentiation, we investigated the effects of proanthocyanidins isolated from BPE on the HL60 cell differentiation of HL60 cells. Prodelphinidin B-3, T1, T2, and T3 induced 26-40% NBT-positive cells and 22-32% alpha-naphthyl butyrate esterase-positive cells. Proanthocyanidins potentiated retinoic acid (all-trans-retinoic acid)-induced granulocytic and sodium butyrate-induced monocytic differentiation in HL60 cells.

Anthocyanins↗
PubMed2001

The cellular and molecular basis of health benefits of grape seed proanthocyanidin extract.

Red grape seed extract containing proanthocyanidins and other antioxidants are being used as nutritional supplements by many health conscious individuals. The beneficial effects of grape seed proanthocyanidins (GSPE) have been reported, however, little is known about their mechanism(s) of action. One of the beneficial effects of GSPE is chemoprevention of cellular damage. The precise mechanism by which GSPE mediates, chemoprevention is not yet understood. This report addresses this issue. We investigated the mechanisms of actions of GSPE, which ameliorates chemotherapy-induced toxic effects of Idarubicin (Ida) and 4,-hydroxyperoxycyclophosphamide (4-HC) in normal human Chang liver cells. Exposure to GSPE resulted in a significant reduction in apoptosis in response to the cytotoxicity of chemotherapeutic agents. RT-PCR analysis showed a significant increase in the anti-apoptotic gene Bcl-2 and a decrease in the cell cycle associated and proapoptotic genes, c-myc and p53 in cells treated with GSPE. These results suggest that some of the chemopreventive effects of GSPE are mediated by upregulating Bcl-2 and down regulating c-myc and p53 genes.

Animals↗
PubMed1993

Localization of proanthocyanidins using in situ-hydrolysis with sulfuric acid.

A valuable method for specific localization of proanthocyanidins in plant tissues is given. The specificity is based on the acid hydrolysis of condensed tannins in situ via hot sulfuric acid, yielding bright red anthocyanidins. This treatment did not cause noticeable damage of tissue embedded in glycol methacrylate prior to sectioning. Further proof of specificity was achieved by control staining with the flavan-3-ol-selective p-dimethylaminocinnamaldehyde (DMACA) reagent. In addition, comparison of adjacent sections stained with the DMACA reagent may give coarse information about the degree of polymerization of the proanthocyanidins.

Anthocyanins↗
PubMed2004

Mechanical evaluation of effect of grape seed proanthocyanidins extract on debilitated mandibles in rats.

Grape seed proanthocyanidins extract (GSPE), whose principal ingredient is proanthocyanidins, shows many activities such as cholesterol lowering effects, antioxidant effects, anti-tumor effects, cardioprotective effects, and protection against ultraviolet rays. However, reports of the effects of GSPE on bone are rare. We performed a mechanical analysis of the effect of GSPE on the interior structure of rat mandibular bone in the growth period, using three-dimensional peripheral quantitative computed tomography (pQCT). A low-calcium/high-calcium diet with supplementary GSPE was compared to a low-calcium/high-calcium diet in rats with debilitated mandibular bones. The group who received added GSPE showed a significant increase in cortical bone density, cross-sectional area, and trabecular bone mineral content (p<0.05). A significant increase was also seen in the results of a non-invasive stress strain index (SSI) (p<0.01) in the added GSPE. Our findings suggest that GSPE can increase bone quality and bone strength of rat mandibles in the growth period.

Alveolar Bone Loss↗
PubMed1999

The cytotoxic effects of a novel IH636 grape seed proanthocyanidin extract on cultured human cancer cells.

Grape seed proanthocyanidins are natural antioxidants which possess a broad spectrum of chemoprotective properties against free radicals and oxidative stress. In this study, we have assessed the cytotoxicity of a novel IH636 grape seed proanthocyanidin extract (GSPE) against MCF-7 human breast cancer cells, A-427 human lung cancer cells, CRL-1739 human gastric adenocarcinoma cells and K562 chronic myelogenous leukemic cells at 25 and 50 mg/lit concentrations for 0-72 h using cytomorphology and MTT cytotoxicity assay. In addition, we compared the effects on normal human gastric mucosal cells and normal J774A.1 murine macrophage cells with the effects on the cancer cell lines. Concentration- and time-dependent cytotoxic effects of GSPE were observed on the MCF-7 breast cancer, A-427 lung cancer and gastric adenocarcinoma cells. Following incubation of the MCF-7 cells with 25 mg/lit of the GSPE approximately 6.5, 30 and 43% inhibitions in cell growth were observed at 24, 48 and 72 h of incubation, respectively, while incubation of the MCF-7 cells with 50 mg/lit of the GSPE resulted in 11, 35 and 47% inhibition in cell growth at these same points, respectively. Similar results were observed in the A-427 and gastric adenocarcinoma cells. GSPE exhibited no cytotoxicity toward the neoplastic K562 myelogenous leukemic cells. However, GSPE enhanced the growth and viability of the normal human gastric mucosal cells and J774A.1 murine macrophage cells. These data demonstrate that GSPE exhibited cytotoxicity towards some cancer cells, while enhancing the growth and viability of the normal cells which were examined.

Adenocarcinoma↗
PubMed2001

Protection against drug- and chemical-induced multiorgan toxicity by a novel IH636 grape seed proanthocyanidin extract.

Grape seed proanthocyanidins have been demonstrated to exhibit a broad spectrum of pharmacological, therapeutic and chemoprotective properties. In our previous studies, IH636 grape seed proanthocyanidin extract (GSPE, commercially known as ActiVin) demonstrated excellent concentration- and dose-dependent free radical scavenging abilities in both in vitro and in vivo models and provided significantly better protection than vitamins C, E and beta-carotene. GSPE demonstrated significant cytotoxicity towards human breast, lung and gastric adenocarcinoma cells, while enhancing the growth and viability of normal human gastric mucosal cells and macrophage J774A.1 cells. In this study, the bioavailability and protective ability of GSPE were examined against acetaminophen-induced hepatoxicity, amiodarone-induced pulmonary toxicity, doxorubicin-induced cardiotoxicity, cadmium chloride-induced nephrotoxicity, dimethylnitrosamine-induced spleenotoxicity and O-ethyl-S,S-dipropyl phosphorodithioate (MOCAP)-induced neurotoxicity in mice. In each experiment, half of the test animals were orally fed GSPE for 7-10 days prior to drug/chemical exposure, while the other half received no GSPE. Parameters of analysis included changes in serum chemistry [alanine amino-transferase (ALT), blood urea nitrogen and creatine kinase], histopathology and integrity of genomic DNA. The results indicated that GSPE preexposure prior to the drugs/chemicals such as acetaminophen, amiodarone, doxorubicin, cadmium chloride or dimethylnitrosamine treatment, provided near complete protection in terms of serum chemistry changes (ALT, blood urea nitrogen and creatine kinase) and inhibition of both forms of cell death, e.g., apoptosis and necrosis. DNA damage in various tissues triggered by these agents was significantly reduced. Histopathological examination of the organs evaluated reflected similar patterns to those of the serum chemistry and DNA results. MOCAP exposure showed symptoms of severe neurotoxicity coupled with serum chemistry changes in the absence of any significant genomic change or brain pathology. GSPE afforded only partial protection in the brain tissue. These results suggest that GSPE exposure is bioavailable and provides significant multiorgan protection against drug- and chemical-induced toxic assaults.

Alanine Transaminase↗
PubMed2000

Unique organoprotective properties of a novel IH636 grape seed proanthocyanidin extract on cadmium chloride-induced nephrotoxicity, dimethylnitrosamine (DMN)-induced splenotoxicity and mocap-induced neurotoxicity in mice.

Several observations, both in humans and laboratory animals, have suggested that proanthocyanidins exhibit a broad spectrum of pharmacological, therapeutic and chemoprotective properties. Specifically, some of our earlier studies have shown that IH636 grape seed proanthocyanidin extract (GSPE, commercially known as ActiVin) provides excellent concentration- and dose-dependent protection against toxicities induced by diverse agents, such as acetaminophen, hydrogen peroxide, 12-O-tetradecanoylphorbol-13-acetate (TPA), smokeless-tobacco extract, idarubicin and 4-hydroxyperoxycyclophosphamide in both in vitro and in vivo models. In some models, GSPE proved to be a better cytoprotectant than vitamins C, E and beta-carotene. The purpose of this investigation was three fold: (i) to indirectly assess the bioavailability of GSPE in multiple target organs, (ii) quantify GSPE's capacity to avert cadmium chloride (CdCl2)-induced nephrotoxicity, dimethylnitrosamine (DMN)-induced splenotoxicity and O-ethyl-S,S-dipropyl phosphorodithioate (MOCAP)-induced neurotoxicity, and lastly (iii) to evaluate possible mechanisms of protection in mice. In order to determine all these, three separate experiments were designed and each experiment consisted of four groups, such as vehicle control, GSPE alone, toxicant alone and GSPE + toxicant. GSPE was administered orally (100 mg/Kg) for 7-8 days prior to the toxicant exposure. Parameters of the analyses included evaluation of serum chemistry changes (ALT, BUN and CK), histopathology and integrity of genomic DNA, both quantitatively and qualitatively. Results indicate that GSPE preexposure prior to cadmium chloride and DMN provided near complete protection in terms of serum chemistry changes (ALT, BUN and CK) and inhibition of both forms of cell death. e.g., apoptosis and necrosis. DNA damage, a common denominator usually associated with both apoptosis and necrosis was significantly reduced by GSPE treatment. Histopathological examination of organs correlated strongly with the changes in serum chemistry and the DNA modification data. Surprisingly, MOCAP exposure showed symptoms of neurotoxicity coupled with serum chemistry changes in the absence of any significant genomic DNA damage or brain pathology. Although, GSPE appeared to partially protect the neural tissue, it powerfully antagonized MOCAP-induced mortality. Taken together, this study suggests that in vivo GSPE-preexposure may protect multiple target organs from a variety of toxic assaults induced by diverse chemical entities.

Activins↗
PubMed2000

In vivo protection of dna damage associated apoptotic and necrotic cell deaths during acetaminophen-induced nephrotoxicity, amiodarone-induced lung toxicity and doxorubicin-induced cardiotoxicity by a novel IH636 grape seed proanthocyanidin extract.

Grape seed extract, primarily a mixture of proanthocyanidins, has been shown to modulate a wide-range of biological, pharmacological and toxicological effects which are mainly cytoprotective. This study assessed the ability of IH636 grape seed proanthocyanidin extract (GSPE) to prevent acetaminophen (AAP)-induced nephrotoxicity, amiodarone (AMI)-induced lung toxicity, and doxorubicin (DOX)-induced cardiotoxicity in mice. Experimental design consisted of four groups: control (vehicle alone), GSPE alone, drug alone and GSPE+drug. For the cytoprotection study, animals were orally gavaged 100 mg/Kg GSPE for 7-10 days followed by i.p. injections of organ specific three drugs (AAP: 500 mg/Kg for 24 h; AMI: 50 mg/Kg/day for four days; DOX: 20 mg/Kg for 48 h). Parameters of study included analysis of serum chemistry (ALT, BUN and CPK), and orderly fragmentation of genomic DNA (both endonuclease-dependent and independent) in addition to microscopic evaluation of damage and/or protection in corresponding PAS stained tissues. Results indicate that GSPE preexposure prior to AAP, AMI and DOX, provided near complete protection in terms of serum chemistry changes (ALT, BUN and CPK), and significantly reduced DNA fragmentation. Histopathological examination of kidney, heart and lung sections revealed moderate to massive tissue damage with a variety of morphological aberrations by all the three drugs in the absence of GSPE preexposure than in its presence. GSPE+drug exposed tissues exhibited minor residual damage or near total recovery. Additionally, histopathological alterations mirrored both serum chemistry changes and the pattern of DNA fragmentation. Interestingly, all the drugs, such as, AAP, AMI and DOX induced apoptotic death in addition to necrosis in the respective organs which was very effectively blocked by GSPE. Since AAP, AMI and DOX undergo biotransformation and are known to produce damaging radicals in vivo, the protection by GSPE may be linked to both inhibition of metabolism and/or detoxification of cytotoxic radicals. In addition, its' presumed contribution to DNA repair may be another important attribute, which played a role in the chemoprevention process. Additionally, this may have been the first report on AMI-induced apoptotic death in the lung tissue. Taken together, these events undoubtedly establish GSPE's abundant bioavailability, and the power to defend multiple target organs from toxic assaults induced by structurally diverse and functionally different entities in vivo.

Acetaminophen↗
PubMed2003

Prodelphinidin trimers and characterization of a proanthocyanidin oligomer from Cistus albidus.

Two new natural prodelphinidin trimers have been isolated from the air-dried herb of Cistus albidus, epigallocatechin-(4beta --> 8)-gallocatechin-(4alpha --> 8)-catechin and epigallocatechin-(4beta --> 8)-gallocatechin-(4alpha --> 8)-gallocatechin in addition to catechin, gallocatechin and thirteen known proanthocyanidins. The structures were determined on the basis of 1D- and reverse 2D-NMR (HSQC, HMBC) experiments of their peracetylated derivatives, MALDI-TOF-MS and by acid-catalysed degradation with phloroglucinol. A more abundant higher oligomeric proanthocyanidins fraction was also isolated and its chemical constitution studied by 13C-NMR. The mean molecular weight of the higher oligomeric fraction was estimated to be 6-7 flavan-3-ol-units.

Anthocyanins↗
PubMed2006

Grape seed proanthocyanidin extract (GSPE) and antioxidant defense in the brain of adult rats.

BACKGROUND: Proanthocyanidin (PA) is a naturally occurring antioxidant from grape seed extract. The present study aims at assessing the neuroprotective effects of grape seed proanthocyanidin (GSPE) on the cerebral cortex (CC), cerebellum (CB), and hippocampus (HC) in the adult rat brain. MATERIAL/METHODS: GSPE was orally administered at 25, 50, and 75 mg per kg body weight daily and for a total period of 9 weeks. Antioxidant enzymes (AOEs), superoxide dismutase (SOD), and catalase (CAT) were analyzed along with malondialdehyde (MDA) and protein carbonyl content (PCC) as markers of lipid peroxidation (LPO) and protein oxidation (PO). The cholinergic system was studied by analyzing choline acetyl tranferase (ChAT) and acetylcholine esterase (AChE) activites along with acetylcholine content (ACh). RESULTS: The results obtained revealed an increased SOD activity in the 75-mg PA-supplemented animals, with a substantial decrease in MDA and PCC. The cholinergic neurotransmittary system analysis showed increased ChAT activity indicative of increased Ach content in the supplemented animals and the increase was more in the 75-mg PA group with a concomitant and moderate decrease in AChE activity. Regional changes were more with reference to HC. CONCLUSIONS: Our study shows that PA intake in moderately low quantity is effective in up-regulating the antioxidant defense mechanism by attenuating LPO and PO. Changes in the cholinergic system, however, indicate an increase in the ACh concentration with a moderate reduction in AChE activity, suggesting further that PA may have a potent role in enhancing cognition in older rats.

Acetylcholine↗
PubMedDate not supplied

[Effect of catechins and proanthocyanidins on the initial stage of protein biosynthesis].

Catechins and proanthocyanidins have been studied for their effect on initial stage of the protein biosynthesis. It has been found that (+)-catechin in all concentrations studied does not influence the intensity of t-RNA aminoacylation by 14C-glycine and 14C-arginine. Proanthocyanidins, namely, dimers B-3, B-6 and trimer C2 in the concentration of 10(-3) M completely inhibit the initial stage of the protein biosynthesis.

Animals↗
PubMed1997

Oxygen free radical scavenging abilities of vitamins C and E, and a grape seed proanthocyanidin extract in vitro.

Proanthocyanidins, a group of polyphenolic bioflavonoids, have been reported to exhibit a wide range of biological, pharmacological and chemoprotective properties against oxygen free radicals. We have assessed the concentration-dependent oxygen free radical scavenging abilities of a grape seed proanthocyanidin extract (GSPE), vitamin C and vitamin E succinate (VES) as well as superoxide dismutase, catalase and mannitol against biochemically generated superoxide anion and hydroxyl radical using a chemiluminescence assay and cytochrome c reduction. A concentration-dependent inhibition was demonstrated by GSPE. At a 100 mg/l concentration, GSPE exhibited 78-81% inhibition of superoxide anion and hydroxyl radical. Under similar conditions, vitamin C inhibited these two oxygen free radicals by approximately 12-19%, while VES inhibited the two radicals by 36-44%. The combination of superoxide dismutase and catalase inhibited superoxide anion by approximately 83%, while mannitol resulted in an 87% inhibition of hydroxyl radical. The results demonstrate that GSPE is a more potent scavenger of oxygen free radicals as compared to vitamin C and VES.

Anthocyanins↗
PubMed2005

Antioxidant properties of proanthocyanidins of Uncaria tomentosa bark decoction: a mechanism for anti-inflammatory activity.

Decoctions prepared from the bark of Uncaria tomentosa (cat's claw) are widely used in the traditional Peruvian medicine for the treatment of several diseases, in particular as a potent anti-inflammatory agent. Therefore, the main purpose of this study was to determine if the well-known anti-inflammatory activity of cat's claw decoction was related with its reactivity with the oxidant species generated in the inflammatory process and to establish a relationship between such antioxidant ability and its phenolic composition. We observed that the decoction prepared according to the traditional Peruvian medicine presented a potent radical scavenger activity, as suggested by its high capacity to reduce the free radical diphenylpicrylhydrazyl, and by its reaction with superoxide anion, peroxyl and hydroxyl radicals as well as with the oxidant species, hydrogen peroxide and hypochlorous acid. It also protected membrane lipids against peroxidation induced by the iron/ascorbate system, as evaluated by the formation of thiobarbituric acid-reactive substances (TBARs). The decoction phenolic profile was established by chromatographic analysis (HPLC/DAD and TLC) revealing essentially the presence of proanthocyanidins (oligomeric procyanidins) and phenolic acids, mainly caffeic acid. Thus, our results provide evidence for an antioxidant mechanism underlying the anti-inflammatory activity of cat's claw and support some of the biological effects of proanthocyanidins, more exactly its antioxidant and radical scavenging activities.

Animals↗
PubMed1989

Proanthocyanidins from Krameria triandra root.

Oligomeric proanthocyanidins were isolated from rhatany root (Krameria triandra) and characterised by acid hydrolysis, thiolytic degradation, and spectroscopic methods. They consisted of 2-14 flavanol units with mainly 2,3-cis configuration and with a propelagonidin:procyanidin ratio of 65:35. The predominant interflavan linkage was [4,8]. [4,6]-Bonds were present in the higher oligomers, presumably forming branched chain units. The astringency of the drug was mainly due to proanthocyanidins with degrees of polymerization from 5-10, and these were also the astringent compounds of rhatany tea and tincture. A pharmacological screening of the extract revealed a significant antimicrobial effect.

Animals↗
PubMed2004

Suppression of the biosynthesis of proanthocyanidin in Arabidopsis by a chimeric PAP1 repressor.

Flavonoids are secondary metabolites that are specific to higher plants. PAP1, a member of the family of MYB domain transcription factors in Arabidopsis, is a positive regulator of the biosynthesis of anthocyanin. We show here that a chimeric PAP1 repressor, in which the EAR-motif repression domain from SUPERMAN was fused to PAP1, suppressed the expression of four flavonoid biosynthetic genes, namely CHS, DFR, LDOX, and BAN, in siliques, and inhibited the accumulation of proanthocyanidin, even in the presence of an endogenous positive regulator, such as TT2. This suppression resulted in the formation of light yellow seeds in 35S::PAP1SRDX transgenic plants. Our results indicate that PAP1 has the potential ability to regulate the biosynthesis not only of anthocyanin but also of proanthocyanidin. Our gene silencing system, using chimeric repressors, appears to be a useful tool for the manipulation of the biosynthesis of secondary metabolites in plants.

Journal Article↗