Evaluation of chemopreventive potential of eugenol on N-methyl-N'-nitro-N-nitroso-guanidine-induced gastric carcinogenesis in Wistar rats.
Cancer of the stomach, the second most common malignancy world-wide, is a major cause of mortality in Chennai, India. Chemoprevention has received growing attention as a means to reduce stomach cancer incidence and mortality. The present study was carried out on male Wistar rats to evaluate the chemopreventive effects of eugenol (4-allyl-methoxyphenol), a natural phenolic constituent of clove oil, cinnamon, basil, and nutmeg, used primarily as a food flavouring agent, on NF-kB signaling, apoptosis, invasion, and angiogenesis during N-methyl-N-nitro-N-nitrosoguanidine (MNNG)--induced gastric carcinogenesis. Animals in group 1 and 2 were given MNNG (150 mg./kg, bw) by intragastric intubation three times with a gap of two weeks for 26 weeks. Animals in group 2 received in addition, intragastric administration of eugenol at 100 mg/kg bw, three times per week starting on the day following the first exposure to MNNG and continued until the end of the experimental period. Animals is group 3 were administered eugenol alone at a concentration of 100 mg/kg bw. Group 4 animals served as control.
MNNG-induced gastric tumours were characterized by NF-kB activation that correlated with upregulation of IKK[beta], and phosphorylation and degradation of IkB[alpha]. Furthermore, upregulation of cyclins and PCNA with down regulation of p21, p53, and Gadd45 suggested that the proliferative advantage in gastric carcinomas is dependent on elevated constitutive NF-kB activity. In addition, animals administered MNNG developed gastric carcinomas that displayed apoptosis avoidance coupled with upregulation of proinvasive and angiogenic factors. Administration of eugenol significantly reduced the incidence of MNNG-induced gastric tumours by suppressing NF-kB activation and modulating the expression of NF-kB target genes that regulate cell proliferation and cell survival. Eugenol induced apoptosis via the mitochondrial pathway by modulating the Bcl-2 family proteins, Apaf-1, cytochrome C, and caspases and inhibited invasion, and angiogenesis as evidenced by changes in the activities of MMPs and the expression of MMP-2 and -9, VEGF, VEGF, VEGFR1, TIMP-2 and RECK.
It was concluded that phytochemicals such as eugenol that are capable of targeting NF-kB signaling pathway, by manipulating the equilibrium between pro- and anti-apoptotic proteins as well as the delicate balance between stimulators and inhibitors of invasion and angiogenesis are attractive candidate for preventing tumour progression.
Dr. S. Nagini
Department of Biochemistry and Biotechnology