The prevention of cancer
We are interested in understanding mechanisms involved in the prevention of cancer (chemoprevention). The role of diet and lifestyle in the development of various types of cancer including colorectal, breast, prostate etc is currently under debate by numerous workers.
Curcumin (turmeric spice) is derived from the rhizome of Curcuma longa and is used to impart colour and flavour to food. Turmeric spice contains, in addition to curcumin, desmethoxycurcumin, bisdesmethoxycurcumin and numerous volatile oils. Epidemiological evidence, laboratory and animal studies indicate a cancer preventive role for curcumin. The cancer preventive action of curcumin may be mediated by a number of mechanisms, including an ability to influence drug metabolising enzymes, specifically enzymes that activate procarcinogens. Curcumin may also interfere with cell signalling pathways involved in cancer cell growth.
Investigations of Curcumin Metabolism Using Human Hepatocytes
In preparation for a forthcoming clinical trial in collaboration with workers at the MRC toxicology unit, Leicester University, and the oncology unit in Leicester, we wish to determine the metabolic profile for curcumin in humans.
Hepatocytes, parenchymal cells, make up more than 80% of the liver by weight and about 93% by volume. High levels of phase I enzymes, including cytochrome P450s, phase II conjugation enzymes and cofactors, responsible for such reactions, are found within the hepatocytes. We have shown that hepatocyte suspensions, prepared by our two step method, usually display greater than 80% viability.
These primary hepatocytes in suspension are a useful tool for our metabolic studies and characteristically maintain viability for up to 6 hours. Hepatocytes are prepared from resected liver tissue, multi-organ donors and non-heart beating donors. Freshly isolated human hepatocytes (4 x 106 cells/ml) were incubated, in suspension, with curcumin (10M, 100 M) in a shaking incubator at 37°C. At various time points, up to 12 hours, samples were collected and immediately frozen at -80°C until required for HPLC analysis. Cell viability (trypan blue exclusion) and cytochrome P450 function (ROD assay) were determined. Curcumin protected isolated human hepatocytes from loss of CYP3A4 and CYP1A activity (determined using ROD activity) over time in culture.
Isolated human hepatocytes convert curcumin to two major metabolites. Curcumin may be a useful natural adjunct to hepatocyte cultures. The tissue protective effect of curcumin may be related to its hepatic metabolism.