Determination of debrisoquine and 4-hydroxydebrisoquine by high-performance liquid chromatography: application to the evaluation of CYP2D6 genotype and debrisoquine metabolic ratio relationship

The drug-metabolizing cytochrome P450 (CYP) enzyme CYP2D6 is involved in the metabolism of several clinically important drugs. So far more than 50 different

CYP2D6 phenotypes among Malays in Malaysia

BACKGROUND

Although they originated from China, Malays have undergone a lot of intermarriages. A study suggested that CYP2D6 poor metabolism (PM) phenotype was more common in Malays compared to Chinese. CYP2D6 is highly polymorphic and is involved in the metabolism of many drugs and has been implicated in some environmentally-induced diseases. It is therefore useful to further study this polymorphism in Malays.

OBJECTIVE

To study debrisoquine metabolism phenotypes in healthy Malay volunteers.

METHOD

We administered debrisoquine to 51 Malays and used HPLC to measure urinary debrisoquine and 4-hydroxy debrisoquine to calculate debrisoquine metabolic ratios (MR).

RESULTS

Debrisoquine MR varied widely and with probit analysis we were able to identify population subsets. Although the frequency distribution for the MR showed a right shift, the shift was less than that reported for the Chinese population. We also found 2 poor metabolizers and one ultra rapid metaboliser in the population.

CONCLUSION

The genetic polymorphism of debrisoquine in Malays differs from that in the Chinese. Both their PM prevalence and their MR distribution suggest that they are intermediate between Europeans and Chinese in relation to this polymorphism. Studies to compare CYP2D6 genotypes between them and related races would be useful to further define these differences.

Adverse drug reactions and debrisoquine/sparteine (P450IID6) polymorphism in patients with fibromyalgia

OBJECTIVE

To assess the frequency of adverse drug reaction in patients with fibromyalgia in relation to medications prescribed for this condition. To evaluate the potential role of the P450IID6 phenotype in the pathogenesis of these adverse drug reactions.

METHODS

Thirty-five patients with fibromyalgia were assessed using a structured questionnaire with demographic and clinical data and perceived adverse drug reactions. A sample of 60 patients with rheumatoid arthritis and 62 patients with localized back pain served as controls. The P450IID6 phenotype was determined for each of the fibromyalgia patients.

RESULTS

Overall, 141 patients had used NSAID and 79 (56%) of them reported adverse effects. Antidepressant drugs were used by 68 patients and 35 (51%) patients had adverse effects. Muscle relaxant drugs were used by 48 patients and 15 (31%) of them reported side effects. Analgesics were used by 122 patients and 22 (18%) had experienced adverse effects. Statistical differences in the frequency of adverse effects were found with antidepressant drugs in the fibromyalgia group, compared with rheumatoid arthritis (p=0.01) and back pain (p=0.02). Four of the 35 patients (11.4%) had a metabolic ratio (M.R.) greater than 0.30 (log M.R.= -0.52) indicative of the poor metabolizers (PM) phenotype. M.R. varied from 0.005 (log M.R. = -2.30) to 4.99 (log M.R. = 0.70).

CONCLUSIONS

The problem of adverse drug reactions in fibromyalgia patients does not appear to correlate with the PM phenotype of the P450IID6 oxidative enzyme. It also is unlikely that altered xenobiotic detoxification attributable to this PM phenotype would have a significant role in the development of fibromyalgia.

Use of biomarkers in epidemiology. The example of metabolic susceptibility to cancer

This paper examines the methodological problems faced in epidemiological studies which use a particular class of biomarkers, those of genetic susceptibility to cancer. Their use in epidemiology is increasing, they raise special methodological questions and entail particular ethical consequences. A list of questions concerning the validity of the studies is discussed. (1) Is the test used to measure the genotype valid, i.e. sensitive and specific? (2) Is there a discrepancy between the genotype and its phenotypic expression? (3) If so, what conditions are deemed to be responsible for such discrepancy (for example, metabolic impairment due to cancer)? (4) Is there clear evidence that one phenotype is associated with an increased risk of cancer? (5) Is a specific chemical exposure known to be a cause of the cancer at issue and metabolized by the polymorphic enzyme? (6) Can any confounding exposure, i.e. some exposure which is associated with the phenotypic expression (for example by inducing the enzyme activity) and also with cancer risk, be identified? (7) Can any kind of selection bias, i.e. selective inclusion of subjects in the study, conditional to their metabolic status, be identified? (8) Are the results of the studies consistent and internally coherent? For example, does the association appear with all histologic types of cancer at a certain site? If not, is there any convincing explanation for the discrepancies?

Spectrophotometric analysis of some guanidino drugs by acid-dye and charge-transfer complexation methods

Two spectrophotometric methods are described for the determination of guanethidine sulphate (I), guanfacine hydrochloride (II), guanoclor sulphate (III), guanoxan sulphate (IV) and debrisoquine sulphate (V). The first method involves ion-pair formation of the selected compounds (I-V) with bromocresol purple at pH 3.8. The yellow ion pair is extracted with chloroform and the absorbance is measured at about 415 nm. The second method is based on the reaction of the basic guanidino compounds (I, III-V) with iodine in chloroform to give molecular charge-transfer complexes with maximum absorbance at 292 and 345 nm. Beer's law was obeyed for both methods and the relative standard deviations were found to be less than 2%. The apparent molar absorptivities were found to be 2.1 x 10(4) to 6.9 x 10(4) l mol-1 cm-1 using bromocresol purple and 0.7 x 10(4) to 2.4 x 10(4) l mol-1 cm-1 using iodine. The investigated drugs were assayed in tablets. The mean percentage recoveries were found to be 99.8-100.8% by the acid-dye method and around 100.4% by the charge-transfer complexation method.

Gas chromatography/mass spectrometry assays for the determination of debrisoquine and sparteine metabolites in microsomal fractions of rat liver

Debrisoquine and sparteine are prototype substrates of a genetic deficiency in cytochrome P450-dependent drug metabolism. Sensitive assays of in vitro oxidation of sparteine and debrisoquine are required for evaluation of this polymorphism. The activities were measured by quantitative analysis of 2-dehydrosparteine and 4-hydroxydebrisoquine production, respectively, using capillary column gas chromatography coupled with mass selective ion detection. With a single extraction, separation of parent drug, metabolite, and a suitable internal standard was readily achievable. Time-dependent production of both metabolites could be detected from as little as 40 micrograms of microsomal protein. Both activities showed a maximal activity with a 240-min incubation period. The ability to simultaneously quantify the parent drug and its metabolite suggests it would also be useful for evaluation of in vivo metabolism.

Oxidation phenotyping with debrisoquine in Germany (East)

An hplc method is described which determines debrisoquine and its metabolite, 4-hydroxydebrisoquine, quantitatively after conversion of the guanidine moieties into the corresponding pyrimidines. Sensitivity, precision, and accuracy have been sufficient enough for the reliable hydroxylation phenotyping of 145 non-related healthy volunteers (64 males, 81 females, 31-80 years). 17 (11%) were poor metabolizers of debrisoquine (gene frequency: 34.2%).

Comparison of gas chromatographic and high-performance liquid chromatographic assays for the determination of debrisoquine and its 4-hydroxy metabolite in human fluids

A comparison of an established gas chromatographic assay for 4-hydroxydebrisoquine and debrisoquine and a modified high-performance liquid chromatographic assay was made. Both assays used guanoxan as the internal standard and required derivatization of all three compounds with acetylacetone at 96 degrees C for 2.5 h and subsequent ethereal extraction and cleaning steps before chromatographic analysis. For detailed pharmacokinetic studies the gas chromatographic assay was more sensitive in the measurement of low concentrations in plasma, but the liquid chromatographic assay was adequate for phenotyping the 4-hydroxylation of debrisoquine in a population. In the latter assay a mobile phase consisting of 70% methanol in water at pH 3.5 (adjusted with orthophosphoric acid containing 10 mM 1-pentanesulphonic acid was employed (flow-rate 1.5 ml/min) with a pre-column (C8) linked to a reversed-phase muBondapak C18 cartridge in a Z-module. The eluate was detected at 248 nm. With this assay it was observed that the buccal absorption of debrisoquine and 4-hydroxy-debrisoquine was affected by the pH of the buccal medium. This indicates that urinary pH may influence the excretion of both substances at high pH. The debrisoquine-to-4-hydroxydebrisoquine ratio may be dose-dependent.