Antioxidant and anticancer activities of Moringa Oleifera
Published in the Journal of Medicinal Plant Research, by Suphachai Charoensin, University of Phayoa, Thailand
(This research paper was edited and condensed for easier reading)
Cancer is the leading cause of mortality worldwide. According to the cancer reports published by the World Health Organization (WHO) and the World Cancer Research Fund, the incidence of cancer is still increasing especially due to diet, environment and carcinogenic virus infections. In hospitals, conventional drugs are commonly prescribed to cancer patients. However, due to less toxic and adverse effects of phytochemicals, the research on medicinal plants and cancer has been intensified.
Moringa oleifera or ´drumstick´ is a member of Moringaceae, and it is grown extensively in many Southeast Asian countries particularly in Thailand, India, Philippines and Pakistan. It has long been known as a food plant in Thai cuisine and as an ingredient of Indian traditional medicine. The leaves contain nutrients especially essential amino acids, vitamins, minerals and β-carotene. For this reason, it is used as an alternative source for
nutritional supplements and growth promoters in some countries. Apart from nutritional
benefits, M. oleifera is reported to be used for the treatment of rheumatism, ascites, infection, hiccough influenza and internal abscess. Many recent reports on disease prevention by M. oleifera have been reported. The leaf extract is capable of reducing hyperglycemia and dyslipidemia. The ethanol extract of the leaves prevented
cyclophosphamide-induced micronucleus formation and DNA damage in mice. The
aqueous extract enhanced hepatic glutathione restoration. Recently, it was reported that tender pods decreased the formation of erythrocyte micronucleus in mice injected with 7,12-dimethylbenz(a)anthracene. It also demonstrated inhibitory potential against azoxymethane-induced colon carcinogenesis. Moreover, it has been reported that the leaf extract had potent antiproliferative activity and apoptosis inducing capacity on tumor (KB) cell line, and it also increased the cytotoxicity of chemotherapy on pancreatic
To date, a variety of biological activities of parts of M. oleifera have been reported. Nevertheless, there are limited evidences for M. oleifera leaf in terms of cancer therapy and prevention. Therefore, the aim of the present study was to investigate the in vitro antiproliferative activity of M. oleifera leaf extract on three types of human
cancer cell lines (HepG2, Caco-2 and MCF-7). Furthermore, the in vitro cancer chemoprevention was carried out using the established method, quinone reductase
Although M. oleifera has been reported for its benefits and biological activities, little is known scientifically about its antioxidant property and cancer prevention ability. Herein, M. oleifera extracts were evaluated for their in vitro antioxidant, antiproliferative and chemopreventive activities.
In the etiology of cancer, free radicals are one of the major factors necessary to cause DNA mutation, which in turn triggers the initiation stage of carcinogenesis. Exogenous antioxidants from natural sources can improve the function of the endogenous antioxidant system which is responsible for preventing free radicals in the body. Polyphenol is recognized as a potent antioxidant, and is found in M. oleifera extracts. Recently, Charoensin and Wongpoomchai (2012) reported that the aqueous extract of M. oleifera leaves contained polyphenols and had DPPH radical scavenging activity. Furthermore, there are some reports which claim that M. oleifera leaves are rich in polyphenols and flavonoids and have antioxidant activity. In accordance with the previous works, M. oleifera leaves extracted with methanol and dichloromethane also showed antioxidant activity. The chemical analysis of M. oleifera extracted with methanol had shown that the major polyphenols comprised of gallic acid, quercetin and kaempferol.
Accumulating reports have suggested that many naturally-occurring substances exhibit cancer chemotherapeutic effects. The main advantage of using phytochemicals as anticancer agents is that they seem to have low adverse effects, and are more cost-effective than commercial drugs. Therefore, it is worth searching for new biologically-active phytochemicals.
The present study is the first report of M. oleifera extract regarding antiproliferations of HepG2, Caco-2 and MCF-7 cancer cells, which are not reported elsewhere. Moreover, it confirms the previous studies of cytotoxicity of M. oleifera extracts on human cancer cells such as pancreatic cancer cell, colon cancer cells and KB tumor cell. It was found that DE had more potent cytotoxicity than ME on all cancer cell lines. According to the present work, each extract differently inhibited cell proliferation. This might be partly due to the differences in genotype and phenotype of cancerous cells and the active compounds in each extract. Different types of cancers have different mutational signatures. The certain genes responsible for cell cycle and cell death are mutated in cancer cells, whereas all genes in normal cells still remain original. The mechanism underlying inhibition of cancer and normal cell proliferation is therefore determined by genetic differences which cause in both types of cells specificity and sensitivity to M. oleifera extract. However, the molecular mechanism by which the extract modulates cancer cell proliferation (cell cycle) and death (apoptosis) remains elusive and needs further investigation.
Although M. oleifera has variously biological activities, most of them rely on pod, seed and flower. As a result, it is needed to investigate more biological functions of its leaves. Since there are limited reports regarding cancer prevention, the present study aimed to evaluate chemo-preventive properties. In cancer research, there are many standard methods to evaluate whether a test sample is chemopreventive. QR or NADPH:quinone oxidoreductase 1 (NQO1) is a phase II detoxifying enzyme and catalyzes the 2-electron reduc-tion of a broad range of chemicals especially quinones. The 2-electron reduction of quinones to hydroquinones by QR is believed to be primarily a detoxifying reaction since it bypasses the formation of the carcinogenic semiquinone and other chemicals. It also protects cells against reactive oxygen species generated by quinones and related compounds. Elevated QR levels correlate with prevention of in vivo chemical-induced carcino-genesis in the stage of initiation and promotion. Furthermore, with advantages in terms of reliability, high throughput and less-time consumption, the in vitro assay, particularly cell-based testing system relevant for prevention of in vivo carcinogenesis, has been established and used in laboratories extensively. For these reasons, QR is widely used as the anticarcinogenic phase II marker enzyme for evaluating cancer chemopreventive agents rather than other enzymes. In the present work, M. oleifera extracts were assayed for their ability to induce QR activity on Hepa1c1c7 cells. It was seen that DE could induce QR activity, whereas ME had no inductive effect (Figure 3). In recent reports, it was shown that the hot water extract of M. oleifera leaves had high polyphenols and antioxidant activity. It also showed potent QR induction (CD value = 99.70±10.44 μg/ml) and antimutagenicity against 2-(2-furyl)-3-(5-nitro-2-furyl)-acrylamide induced mutagenesis. The theory of QR induction in the context of structure-activity relationship is described. The flavonoids with 2 or 3 double bonds in the C ring are crucially essential for QR induction, while the hydroxylation of the B ring is not essential. The mechanism by which polyphenols and flavonoids induce QR gene expression is well understood. The induction of QR gene is regulated on the transcriptional level mediated by antioxidant response element (ARE), controlled by the nuclear factor E2-related factor 2 (Nrf2). Activation of the Nrf2/ARE pathway by polyphenols with antioxidant activity (quercetin and kaempferol), or by non-flavonoid com-pounds (glucosinolate and sulforaphane) is the key step of QR gene up-regulation. This molecular mechanism leads to the increased level of QR. From the present result, it was seen that M. oleifera extracted with dichloromethane induced a QR activity with higher potential than that extracted with methanol. Regarding polyphenols and flavonoids, both compounds were determined in DE, with relative amounts of that of ME. This could be the major factor for increased QR activity and cancer cell antiproliferation. Apart from flavonoids, M. oleifera leaves have been reported to release glucosinolate compounds, when extracted with less polar solvent. 4-(alpha-l-rhamnopyranosyloxy)-benzylglucosinolate and three monoacetyl isomers were isolated from the leaves. In addition, the glycosides including niaziminin A and B, and isothiocyanates were reported. This is the significant reason regarding the potent QR induction as well as the cancer cell antiproliferation of DE. Hence, both effects of M. oleifera might arise from the flavonoids alone, or from the synergy with other compounds.
Conclusively, the M. oleifera dichloromethane extract shows high antioxidant activity, potent cancer cell anti-proliferation, and induction of quinone reductase. These findings indicate the medicinal value of M. oleifera.