No abstract

No abstract

A subgroup of 10-15% of Caucasians are termed phenotypical 'intermediate metabolizers' of drug substrates of CYP2D6 because they have severely impaired yet residual in-vivo function of this cytochrome P450. Genotyping based on the currently known CYP2D6 alleles does not predict this phenotype satisfactorily. A systematic sequencing strategy through 1.6 kb of the CYP2D6 5'-flanking sequence revealed six mutations of which three were exclusively associated with the functional CYP2D6*2 allele (-1496 C to G; -652 C to T; and -590 G to A), two were associated with the nonfunctional *4 and with the functional *10-alleles (-1338 C to T and -912 G to A) and one (-1147 A to G) was seen in all *2, *4 and *10-alleles investigated. The -1496 C to G mutation was found to be polymorphic within CYP2D6*2 alleles. In a family study, the wild-type CYP2D6 *2[-1496 C] and the novel variant [-1496 G] allele co-segregated with lower and higher CYP2D6 in-vivo function, respectively, as shown by phenotyping using sparteine as probe drug. In a representative population sample selected for genotypes comprising one CYP2D6*2 and one non-functional allele, the median urinary metabolic ratio (MRs) for sparteine oxidation was 4.4-fold reduced in individuals with the variant allele (*2[-1496 G], MRs = 0.53, n = 27) compared with individuals lacking the mutation (*2[-1496 C], MRs = 2.33, n = 12; P < 0.0001). The mutation -1496 C to G has an estimated frequency of approximately 20% in the general population and allows establishment of a genotype for the identification of over 60% of intermediate metabolizers in Caucasian populations.

This study aimed to characterize the intestinal and hepatic expression and function of CYP2C enzymes in the same set of subjects. CYP2C isoform-specific quantitative reverse transcription-polymerase chain reaction assays, Western immunoblotting and marker reactions of CYP2C8, CYP2C9 and CYP2C19 activities were employed to investigate expression and activity of the CYP2C isoforms in samples of small intestine and liver obtained from 15 patients undergoing gastrectomy or pancreatoduodenectomy. The rank order for CYP2C mRNA expression in the intestine was CYP2C9 = CYP2C18 > CYP2C19 > CYP2C8, whereas that in the liver was CYP2C9 > CYP2C8 > CYP2C18 > CYP2C19. The rank order for expression of CYP2C protein in the intestine was CYP2C9 > CYP2C19 > CYP2C8 (content below limit of quantification) > CYP2C18 (not detected) and that in the liver was CYP2C9 > CYP2C8 > CYP2C19 > CYP2C18 (not detected). The CYP2C9 protein content was approximately 10-fold higher in the liver than in the intestine (P < 0.001). The CLint for the formation of D-703 from verapamil (marker of CYP2C8 activity) was 7.6-fold higher (P < 0.001) and that for the diclofenac 4'-hydroxylation (marker of CYP2C9 activity) was 6.1-fold higher (P < 0.001) in the liver than in the intestine. Apart from a borderline positive correlation (r = 0.58, P = 0.0504) between the intestinal and hepatic CLint for the diclofenac 4'-hydroxylation, no intra-individual relationships between these tissues with respect to expression or activity of different CYP2C isoforms were found. Collectively, these results show that CYP2C8, CYP2C9 and CYP2C19 are expressed as functional enzymes in the human small intestine, and further suggest that CYP2C genes are independently regulated in human intestine and liver. Although, overall, the expression and activity of CYP2C enzymes is lower in the gut than in the liver, the surface area of the proximal small intestine is large and intestinal CYP2C9 and CYP2C19 may well contribute to the first-pass metabolism of their substrate drugs.

No abstract

Progressive telomere shortening occurs in somatic cells, and with increasing donor age a significant decline in telomere length has been shown in various postnatal tissues. In contrast, little is known about changes in telomere length during human fetal development. Therefore, we measured telomere length in the leukocyte fraction of umbilical cord blood samples from 15 preterm (Ͻ37 wk of gestation) and 11 full-term (Ͼ37 wk of gestation) neonates using the telomere restriction fragment assay. Whereas no differences in mean (Ϯ SD) telomere restriction fragment between the groups of preterm neonates (8512 Ϯ 523 bp) and full-term newborns (8323 Ϯ 503 bp) could be found, significantly longer telomeres (p ϭ 0.002) were found in very low birth weight preterm neonates when compared with low birth weight preterm neonates. In addition, a rapid and significant decline in mean telomere restriction fragment was observed between 27 and 32 wk of gestation (p ϭ 0.02, r ϭ 0.79) followed by a period of no significant loss of telomere repeats between 33 and 42 wk of gestation. These results are consistent with the known almost maximal proliferation rate of hematopoietic progenitor cells before 32 wk of gestation. The initial decrease in telomere restriction fragment could be caused by ontogenyrelated functional alterations of hematopoietic cells or differences in stem cell turnover or the rate of telomere loss per cell division. Telomeres play a major role in chromosome structure and function by protecting their degradation and apparently contributing to the attachment of chromosome ends to the nuclear envelope. Telomeres lose a portion of their noncoding repetitive DNA sequences with each cell division, and the ribonucleoprotein enzyme telomerase can compensate for this by synthesis of telomere repeats onto chromosomes (1-3). Despite the observation that some immortalized cell lines manifest stable telomeres without evidence of telomerase activity (4), telomerase-dependent telomere elongation seems to be the most important mechanism for maintaining telomere length in vitro and in vivo.In man telomerase is expressed during embryogenesis. Ulaner and Giudice (5) examined telomerase activity in various fetal tissues from 8 to 21 wk of gestation. They found that all tissues expressed telomerase at the earliest ages analyzed, followed by tissue-specific suppression during embryogenic development. After birth this enzyme is repressed in most somatic tissues (6), and high activity persists only in germline cells.Whereas in most postnatal somatic tissues telomerase is not expressed, low levels of this enzyme are detected in hematopoietic progenitor cells, activated lymphocytes (7), intestinal crypt cells (8), the basal layer of the skin (9), and during the proliferative phase in the premenopausal endometrium (10, 11). It is assumed that the low telomerase activity compensates the increased loss of telomere repeats associated with the high rate of cell turnover in these tissues. However, in contrast to germline and tumor cells, these low l...

Dihydrocodeine O-demethylation to dihydromorphine is impaired in poor metabolizers of sparteine. The main urinary metabolites after administration of dihydrocodeine are the parent compound and its conjugates in extensive and poor metabolizers.

The majority of shed human enterocytes collected with a multilumen perfusion catheter were still functionally active and not apoptotic. Harvesting of spontaneously shed enterocytes provides a new tool for studies on expression and function of intestinal proteins.