Herbs with potent antioxidant activity generally have anticancer activity as well. Whether to use antioxidants concurrently with chemotherapy or radiotherapy has been questioned. Chemotherapy and radiotherapy cause DNA damage to both normal cells and cancer cells by causing free radical damage; one concern is that antioxidants will reduce the efficacy of treatment. On the other hand, antioxidants protect healthy tissue from damage, and after and between conventional treatment, antioxidants continue to offer benefit as anticancer agents themselves. Anecdotal evidence provided by veterinary herbalists indicates that herbal antioxidants can continue to be used alongside conventional treatment without adversely affecting the outcome.
Green tea (Camellia sinensis): Green tea polyphenols in mice increased antioxidant levels and glutathione peroxidase, catalase, and quinine reductase in skin, small bowel, liver, and lungs. These combined activities make green tea an effective chemopreventive agent against the initiation, promotion, and progression of multistage carcinogenesis. Human clinical trials suggest that the concentrated extract EGCG (epigallocatechin gallate), dosed at approximately 200mg daily, is most efficient at improving blood antioxidant levels.
Redgrape (Vltis Vinifera): Resveratrol, a phytoalexin found in red wine, inhibits the metabolic activation of carcinogens, has antioxidant and anti-inflammatory properties, decreases cell proliferation, and induces apoptosis. Oligomeric proanthocyanidins (OPCs) increased NK cell cytotoxicity, modulated levels of interleukins from immune compromised mice (including those infected with retrovirus), and demonstrated antimutagenic activity in vitro.
Hawthorn (Crataegus Spp): Crataegus contains OPCs, and much of what is known about grape seed extract applies to Crataegus.
Milk Thistle (Silybum Marianum): Silymarin and silibinin (silybin) are antioxidants that react with free radicals, transforming them into more stable, less reactive compounds. The cancer chemoprevention and anticarcinogenic effects of silymarin have been shown to be caused by its major constituent, silibinin. Its antitumor effect occurs primarily at stage I tumor promotion; silymarin may act by inhibiting COX-2 and IL-loc. Such effects may involve inhibition of promoter-induced edema, hyperplasia, the proliferation index, and the oxidant state. Silibinin may also have anti-angiogenic effects.
Turmeric (Curcuma longa): The abilities of turmeric to scavenge radicals, reduce iron complex, and inhibit peroxidation may explain the possible mechanisms by which turmeric exhibits its beneficial effects in medicine. The anticancer properties of curcumin have been demonstrated in cultured cells and animal studies. Curcumin inhibits lipoxygenase activity and is a specific inhibitor of COX-2 expression. It halts carcinogenesis by inhibiting cytochrome P450 enzyme activity and increasing levels of glutathione-S-transferase.
Dan Shen (Salvia Miltiorrhiza): Dan shen is a potent antioxidant that demonstrates free radical scavenging activity. Recent studies showed that one of its tanshinone constituents possesses cytotoxic activity against many kinds of human carcinoma cell lines, induces differentiation and apoptosis, and inhibits invasion and metastasis of cancer cells. Its mechanisms are believed to be inhibition of DNA synthesis and proliferation of cancer cells; regulation of the expression of genes related to proliferation, differentiation, and apoptosis; inhibition of the telomerase activity of cancer cells; and change in the expression of cellular surface antigen.
Bilberry (Vaccinium myrtillus): The anthocyanosides in bilberry inhibit protein and lipid oxidation. Components of bilberry have been reported to exhibit potential anticarcinogenic activity in vitro, as demonstrated by inhibition of the induction of ornithine decarboxylase (ODC) by the tumor promoter phorbol 12-myristate 13-acetate (TPA).
Schisandra (Schisandra Chinensis): Schisandra lignans act as free radical scavengers and inhibit iron-induced lipid peroxidation and superoxide anion production. Geranylgeranoic acid, a constituent of Schisandra, has been shown to induce apoptosis in a human hepatoma-derived cell line.
Ginkgo (Glnkgo Biloba): This leaf extract has significant antioxidant activity because of its flavonoid and terpenoid components. Recent studies with various models show that the anticancer properties of Ginkgo are related to antioxidant, antiangiogenic, and gene-regulatory actions. Antiangiogenic activity may involve antioxidant activity and the ability to inhibit both inducible and endothelial forms of nitric oxide synthase. Exposure of human breast cancer cells to a Ginkgo extract altered expression of the genes involved in the regulation of cell proliferation, cell differentiation, or apoptosis. Exposure of human bladder cancer cells to a Ginkgo extract produces an adaptive transcriptional response that augments antioxidant status and inhibits DNA damage. Flavonoid and terpenoid constituents of Ginkgo extracts may act in a complementary manner to inhibit several carcinogenesis-related processes; therefore, the total extracts may be required for optimal effects.
Ginger (Zingiber Officinale): Some pungent constituents in ginger and other zingiberaceous plants such as gingerol have potent antioxidant and anti-inflammatory effects, and some of them exhibit antitumor promotional activity in experimental carcinogenesis. The chemopreventive effects are probably associated with antioxidative and anti-inflammatory activities.
Rosemary (Rosmarinus officinalis): Several extracts and constituents of rosemary have exhibited antioxidant activity. The volatile oil was reported to be toxic to leukemia cells. Topical administration of a methanol extract 5 minutes before application of carcinogens to the dorsal surface of mice reduced the irritation and promotion of tumors. Application of rosemary extract before carcinogen application reduced the formation of metabolite-DNA adducts by 30% and 54%, respectively. In rats, dietary supplementation with 1% rosemary extract for 21 weeks reduced the development of induced mammary carcinoma in the treated group, compared with the control group (40% vs 75%, respectively).