Poor metabolisers of debrisoquine reveal their true colours

Genetic variants in the metabolism of omega-6 and omega-3 fatty acids: their role in the determination of nutritional requirements and chronic disease risk

The tissue composition of polyunsaturated fatty acids is important to health and depends on both dietary intake and metabolism controlled by genetic polymorphisms that should be taken into consideration in the determination of nutritional requirements. Therefore at the same dietary intake of linoleic acid (LA) and alpha-linolenic acid (ALA), their respective health effects may differ due to genetic differences in metabolism. Delta-5 and delta-6 desaturases, FADS1 and FADS2, respectively, influence the serum, plasma and membrane phospholipid levels of LA, ALA and long-chain polyunsaturated fatty acids during pregnancy, lactation, and may influence an infant's IQ, atopy and coronary heart disease (CHD) risk. At low intakes of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), polymorphisms at the 5-lipoxygenase (5-LO) level increase the risk for CHD whereas polymorphisms at cyclooxgenase-2 increase the risk for prostate cancer. At high intakes of LA the risk for breast cancer increases. EPA and DHA influence gene expression. In future, intervention studies on the biological effects of LA, ALA and LC-PUFAs, and the effects of genetic variants in FADS1 and FADS2, 5-LO and cyclooxygenase-2 should be taken into consideration both in the determination of nutritional requirements and chronic disease risk. Furthermore, genome-wide association studies need to include environmental exposures and include diet in the interaction between genetic variation and disease association.

CYP2D6 status of extensive metabolizers after multiple-dose fluoxetine, fluvoxamine, paroxetine, or sertraline

The aim of this study was to evaluate the CYP2D6 inhibitory effects of four selective rerotonin re-uptake inhibitors (SSRIs). Thirty-one healthy subjects were phenotyped as extensive metabolizers using the dextromethorphan/dextrorphan (DM/DX) urinary ratio as a marker for CYP2D6 activity before and after 8 days of administration of fluoxetine 60 mg (loading dose strategy), fluvoxamine 100 mg, paroxetine 20 mg, or sertraline 100 mg in a parallel-group design. Statistical analysis was performed on log-transformed DM/DX ratios because of variability within and between treatment groups. DM/DX ratios before (DM/DX(BL)) and after (DM/DX(SSRI)) were compared within and between the four SSRI groups. DM/DX(BL) ratios were not significantly different between the four SSRI treatment groups. Comparing within groups, significant differences between DM/DX(BL) and DM/DX(SSRI) were found for the fluoxetine (p < 0.001; ratio values, 0.020 vs. 0.364) and paroxetine (p = 0.0005, ratio values 0.029 vs. 1.085) but not for the fluvoxamine or sertraline groups. Comparing between groups, significant differences in DM/DX(SSRI) ratios were found for fluoxetine versus sertraline (p = 0.0019, DM/DX = 0.364 vs. 0.057), fluoxetine versus fluvoxamine (p < 0.0001, DM/DX = 0.364 vs. 0.019), paroxetine versus sertraline (p = 0.0026, DM/DX = 1.085 vs. 0.057), and paroxetine versus fluvoxamine (p < 0.0001, DM/DX = 1.085 vs. 0.019). No significant differences were noted between the two potent CYP2D6 inhibitors, fluoxetine and paroxetine, or the two weakest inhibitors, fluvoxamine and sertraline. Five subjects in the fluoxetine and four subjects in the paroxetine groups changed to poor metabolizer phenotype (DM/DX > or = 0.3) after treatment. Although CYP2D6 inhibitory effects of fluvoxamine and sertraline did not yield significant differences from baseline, some subjects exhibited DM/DX ratio increases of 150 to 200%. One paroxetine-treated subject did not exhibit any CYP2D6 inhibition. SSRI dose and plasma concentration may be correlated with the extent of CYP2D6 inhibition and should be further investigated.

Changes in debrisoquine hydroxylation capacity following liver surgery

Liver transplantation or the surgical construction of portacaval shunts may radically alter an individual's debrisoquine hydroxylation capacity. Good clinical management should encompass a full awareness of such changing needs and problems in patients who undergo hepatic surgery.

Debrisoquine metabolism in Chinese patients with Alzheimer's and Parkinson's diseases

We determined the oxidative phenotype and metabolic ratio of debrisoquine in 96 Chinese patients with Alzheimer's disease (n = 12), Parkinson's disease (n = 55), and using patients with stroke and cervical spondylosis as controls (n = 29). We did not find any difference in debrisoquine metabolic phenotype among Parkinson's disease, Alzheimer's disease, and control patients as judged by chi-square analysis. In addition, the metabolic ratio of all our patients was less than 12.6. The result suggested that Chinese patients with Parkinson's disease and Alzheimer's disease metabolize debrisoquine at a velocity not different from that of their Western counterparts even though the frequency distribution of debrisoquine metabolism phenotyping in these two populations is quite different.

Oxidative polymorphism of debrisoquine is not related to human colo-rectal cancer

The oxidative polymorphism of debrisoquine (DBQ) has been determined in 89 patients with colo-rectal cancer and in 556 normal control subjects. Four patients and 34 controls, with a metabolic ratio greater than 12.6, were classified as poor metabolisers of DBQ (n.s.). No difference was found in the distribution of the frequencies of the MR of DBQ between patients and controls. It is concluded that polymorphic oxidation of DBQ is not related to the risk of developing colo-rectal cancer in human beings.

Polymorphic oxidation of debrisoquine in lung cancer patients

Oxidative polymorphism of debrisoquine (DBQ) was assessed in 84 patients (81 male) with histologically proven bronchogenic carcinoma and in 143 healthy male smokers. 80 (95%) patients and 133 (93%) controls, with a metabolic ratio (MR) below 12.6, were classified as extensive metabolisers of DBQ (no significant difference between patients and controls). Only 1 of the 73 patients with epidermoid or microcytic carcinomas was classified as a poor metaboliser (PM) (P = 0.031 compared with controls). 63 patients (75%) and 110 controls (77%) showed a very fast oxidative rate, with MR values under 1 (not significant). The EM phenotype of DBQ might be a secondary genetic risk factor for developing bronchogenic carcinoma in male smokers.