DNA damage in horticultural farmers: a pilot study showing an association with organophosphate pesticide exposure.

A study of horticultural farmers exposed to organophosphate pesticides (OPs) and controls investigated the relationships between OP exposure, DNA damage and oxidative stress. Blood acetylcholinesterase (AChE) and urinary dialkylphosphate (DAP) levels determined exposure and 8-hydroxy-29- deoxyguanosine (8OHdG) indicated oxidative stress status. The farmers had approximately 30% lower AChE activity and increased DAP levels compared with the controls, reflecting moderate OP exposure. They had higher DNA damage than the controls and there was a significant positive relationship between DAP and DNA damage with greater than 95% power. The farmers also had a significant positive relationship between urinary DAP and 8OHdG levels.

Glucuronidation of the soyabean isoflavones genistein and daidzein by human liver is related to levels of UGT1A1 and UGT1A9 activity and alters isoflavone response in the MCF-7 human breast cancer cell line.

The soyabean isoflavones genistein and daidzein, which may protect against some cancers, cardiovascular disease and bone mineral loss, undergo substantial Phase 2 metabolism, predominantly glucuronidation. We observed a correlation between rates of metabolism of marker substrates of specific UGTs and rates of glucuronidation of genistein and daidzein in vitro by a panel of human liver microsomes, demonstrating that UGT1A1 and UGT1A9, but not UGT1A4, make a major contribution to the metabolism of these isoflavones by human liver. These findings were substantiated by observations that recombinant human UGT1A1 and UGT1A9, but not UGT1A4, catalysed the production of the major glucuronides of both genistein and daidzein in vitro. Recombinant human UGT1A8 also metabolised both genistein and daidzein, whereas UGT1A6 was specific to genistein and UGTs 2B7 and 2B15 were inactive, or only marginally active, with either isoflavone as substrate. The intestinal isoform UGT1A10 metabolised either both isoflavones or genistein only, depending on the commercial supplier of the recombinant enzyme, possibly as a result of a difference in amino acid sequence, which we were unable to confirm. Daidzein (16 microM) increased cell death in the MCF-7 human breast cancer cell line and this effect was reversed by glucuronidation. In view of a well-characterised functional polymorphism in UGT1A1, these observations may have implications for inter-individual variability in the potential health-beneficial effects of isoflavone consumption.

Metabolism of the soyabean isoflavone daidzein by CYP1A2 and the extra-hepatic CYPs 1A1 and 1B1 affects biological activity.

Metabolism of the isoflavones daidzein and genistein, which may protect against some cancers, was studied using human liver microsomes and recombinant CYP isoforms. The detection of three, more polar metabolites of each isoflavone by RP-HPLC required NADPH, consistent with CYP-mediated metabolism. For different liver preparations, metabolite generation from daidzein showed a significant linear correlation with metabolite generation from genistein, indicating metabolism by the same CYP(s). The lowest rate of metabolism of both isoflavones was by the preparation with the lowest CYP1A2 activity. Metabolite peak areas were substantially and significantly reduced by the CYP1A2 inhibitor furafylline and to a lesser extent by the CYP2E1 inhibitor 4-methylpyrazole. Recombinant CYP1A2, but not CYP2E1, generated the metabolites of daidzein and genistein and recombinant CYP1A1 and CYP1B1, expressed at sites including the breast and prostate, were also active. The effects of two CYP-derived metabolites of daidzein, 6,7,4'-trihydroxyisoflavone and 7,3',4'-trihydroxyisoflavone, were studied in the MCF-7 human breast cancer cell line at a concentration (50 microM) at which daidzein induces an antiproliferative response. 7,3',4'-Trihydroxyisoflavone reduced total cell numbers to a greater extent than 6,7,4'-trihydroxyisoflavone or daidzein and increased cell death. Together, these data demonstrate proof of principle that CYP-mediated metabolism of daidzein can be an activation pathway. We conclude that CYP1A2 makes the major contribution to the hepatic metabolism of both daidzein and genistein and along with metabolism at sites of hormone-dependent tumours may enhance a cancer-protective effect of daidzein if sufficiently high concentrations are reached in target tissues.