Inhibition by curcumin of diethylnitrosamine-induced hepatic hyperplasia, inflammation, cellular gene products and cell-cycle-related proteins in rats.

Curcumin (CCM), a major yellow pigment of turmeric obtained from powdered rhizomes of the plant Curcuma longa Linn, is commonly used as coloring agent in foods, drugs and cosmetics. In this study we report that gavage administration of 200 mg/kg or 600 mg/kg CCM effectively suppressed diethylnitrosamine (DEN)-induced liver inflammation and hyperplasia in rats, as evidenced by histopathological examination. Immunoblotting analysis showed that CCM strongly inhibited DEN-mediated the increased expression of oncogenic p21(ras) and p53 proteins in liver tissues of rats. In cell-cycle-related proteins, CCM selectively reduced the expression of proliferating cell nuclear antigen (PCNA), cyclin E and p34(cdc2), but not Cdk2 or cyclin D1. Moreover, CCM also inhibited the DEN-induced increase of transcriptional factor NF-kappa B. However, CCM failed to affect DEN-induced c-Jun and c-Fos expression. It has become widely recognized that the development of human hepatocellular carcinoma (HCC) is predominantly due to the chronic inflammation by virus, bacteria or chemical. Our results suggest a potential role for CCM in the prevention of HCC.

Curcumin-containing diet inhibits diethylnitrosamine-induced murine hepatocarcinogenesis.

Curcumin has been widely used as a spice and coloring agent in foods. Recently, curcumin was found to possess chemopreventive effects against skin cancer, forestomach cancer, colon cancer and oral cancer in mice. Clinical trials of curcumin for prevention of human cancers are currently ongoing. In this study, we examine the chemopreventive effect of curcumin on murine hepatocarcinogenesis. C3H/HeN mice were injected i.p. with N-diethylnitrosamine (DEN) at the age of 5 weeks. The curcumin group started eating 0.2% curcumin-containing diet 4 days before DEN injection until death. The mice were then serially killed at the scheduled times to examine the development of hepatocellular carcinoma (HCC) and changes in intermediate biological markers. At the age of 42 weeks, the curcumin group, as compared with the control group (DEN alone), had an 81% reduction in multiplicity (0.5 versus 2.57) and a 62% reduction in incidence (38 versus 100%) of development of HCC. A series of intermediate biological markers were examined by western blot. While hepatic tissues obtained from the DEN-treated mice showed a remarkable increase in the levels of p21(ras), PCNA and CDC2 proteins, eating a curcumin-containing diet reversed the levels to normal values. These results indicate that curcumin effectively inhibits DEN-induced hepatocarcinogenesis in the mouse. The underlying mechanisms of the phenomenon and the feasibility of using curcumin in the chemoprevention of human HCC should be further explored.

Inhibition of the membrane translocation and activation of protein kinase C, and potentiation of doxorubicin-induced apoptosis of hepatocellular carcinoma cells by tamoxifen.

Hepatocellular carcinoma (HCC) is characterized by high drug resistance to currently available chemotherapeutic agents. In a prospective clinical study, we have demonstrated that high-dose tamoxifen significantly enhanced the therapeutic efficacy of doxorubicin in patients with far-advanced HCC. In a search for a possible mechanism, we found that tamoxifen at a clinically achievable concentration (2.5 microM) significantly enhanced doxorubicin-induced cytotoxicity and apoptosis of Hep-3B cells, a multidrug resistance (MDR)-1 expressing HCC cell line. This synergistic cytotoxic effect of tamoxifen, at this concentration, however, was not mediated by MDR inhibition. Instead, as evidenced by both western blot and immunofluorescence studies, tamoxifen inhibited the cytoplasmic-membrane translocation of protein kinase C (PKC)-alpha. 12-O-Tetradecanoylphorbol-13-acetate (TPA) restored the membrane translocation of PKC-alpha and abrogated the synergistic cytotoxicity of tamoxifen. We also showed that tamoxifen, at this concentration, did not directly affect the enzyme activity of PKC. Further, membrane translocation of other membrane-bound proteins, such as Ras protein, was similarly inhibited by tamoxifen, but could not be restored by the addition of TPA. Together, these data suggested that tamoxifen may act on the cytoplasmic membrane, and thereby inhibit PKC-alpha translocation to the membrane where it is activated. We hypothesize that high-dose tamoxifen may be an effective modulator of doxorubicin in the treatment of HCC, and suggest that biochemical modulation of PKC as a measure to improve systemic chemotherapy for HCC deserves further investigation.