Acetylator phenotype and congenital malformations

Phenylalanine 4-monooxygenase: the "sulfoxidation polymorphism"

1. Consistent differences in the proportion of an orally administered dose of S-carboxymethyl-l-cysteine subsequently excreted in the urine as S-oxide metabolites were reported 40 years ago. This observation suggested the existence of inter-individual variation in the ability to undertake the enzymatic S-oxygenation of this compound. Pedigree studies and investigations employing twin pairs indicated a genetically controlled phenomenon overlaid with environmental influences. It was reproducible and not related to gender or age.2. Studies undertaken in several healthy volunteer cohorts always provided similar results that were not significantly different when statistically analysed. However, when compared to these healthy populations, a preponderance of subjects exhibiting the characteristic of poor sulfoxidation of S-carboxymethyl-l-cysteine was found within groups of patients suffering from various disease conditions. The most striking of these associations were witnessed amongst subjects diagnosed with neurodegenerative disorders; although, underlying mechanisms were unknown.3. Exhaustive investigation has identified the enzyme responsible for this S-oxygenation reaction as the tetrahydrobiopterin-dependent aromatic amino acid hydroxylase, phenylalanine 4-monooxygenase classically assigned the sole function of converting phenylalanine to tyrosine. The underlying principle is discussed that enzymes traditionally associated solely with intermediary metabolism may have as yet unrecognised alternative roles in protecting the organism from potential toxic assault.

Isoniazid acetylation phenotyping in Saudi Arabs

AIMS

The present study is designed to investigate the acetylator status in Saudi Arabs.

METHODS

Isoniazid (INH) acetylation phenotyping was studied in 136 Saudi Arabs in Riyadh, Saudi Arabia, using a single plasma sample taken 3 h post-INH oral dose of 200 mg. Metabolic ratio (MR) of plasma acetyl-INH (Ac-INH) to INH was used to determine the acetylation phenotype.

RESULTS

The MR had a bimodal distribution with an antimode of 1.0. The frequency distribution of slow acetylators (MR < 1.0) was 94.9% (n = 129). Using Hardy-Weinberg Law, the gene frequency (q) of the recessive allele determining slow acetylator phenotype was found to be 0.97.

CONCLUSION

INH phenotyping suggests a high frequency of slow acetylators among Saudi Arabs. There was no association between the MR of plasma Ac-INH/INH and age or gender.

N-acetylation phenotyping using dapsone in a Jordanian population

1. The N-acetylation of dapsone (DDS) was studied in 160 unrelated healthy Jordanian volunteers. 2. The frequency of slow acetylators determined using the plasma monoacetyldapsone (MADDS) to DDS ratio (MADDS/DDS), was 67.5% with a 95% confidence interval of 59 to 76%. Slow acetylators had an acetylation ratio of less than 0.42. 3. Applying the Hardy-Weinberg Law, the frequency of the recessive allele controlling slow acetylation was found to be 0.82 +/- 0.02. 4. The frequency distribution histogram of the plasma MADDS/DDS ratio showed an apparent trimodal pattern. The number of homozygous (n = 16) and heterozygous (n = 36) rapid acetylators derived from the observed data did not agree with those predicted for the respective rapid acetylators (n = 5 and n = 47) according to the Hardy-Weinberg Law. The suggested antimode used to discriminate the two groups was 0.82. 5. The mean plasma concentration of MADDS and the mean plasma acetylation ratio were about three times lower in slow than in rapid acetylators. However, there was no difference in mean plasma DDS concentration between slow and rapid acetylators. 6. There was a significant correlation (r = 0.853, P less than 0.001) between plasma MADDS concentration and the acetylation ratio. For DDS such a correlation was absent (r = 0.059, P = 0.23).

Syntheses of metabolites of S-carboxymethyl-L-cysteine and S-methyl-L-cysteine and of some isotopically labelled (2H, 13C) analogues

The chemical syntheses of human metabolites of S-carboxymethyl-L-cysteine (3) and S-methyl-L-cysteine (12) are described. The additional preparation of some 2H- and 13C-labelled isotopomers enabled the direct evaluation of the stabilities of 3 and 12 under physiological conditions and also facilitated the unambiguous assignments of the signals in the 13C-NMR spectra of all compounds mentioned.