Salim M. A. Bastaki

Polymorphic N-acetyltransferase (NAT2) genotyping of Emiratis.

Polymorphic N-acetyltransferase (NAT2) genotypes were determined in 106 unrelated Emiratis by PCR-RFLP analysis to obtain estimates of allele frequencies. Thirteen different genotypes were found, four associated with the rapid acetylator phenotype and nine with the slow acetylator phenotype. Among 67 phenotypically slow acetylators, there was 100% concordance between phenotype and genotype. Among 39 phenotypically rapid acetylators, 37 possessed at least one wild type allele; a 95% concordance with genotype. Seven different NAT2 alleles associated with slow acetylation were found. The commonest was a NAT2*5 type (C481T) allele which occurred with a frequency of 0.53, a significantly higher frequency than has been reported for other ethnic groups. A second slow allele, a NAT2*6 type (G590A), occurred with a frequency of 0.21. The most common genotypes found were NAT2*5/*5 homozygotes, NAT2*5/*6 heterozygotes and NAT2*4/*5 heterozygotes with frequencies of 0.25, 0.25 and 0.22 respectively. The high overall prevalence of alleles associated with slow acetylation (173/212; 81.6%) among Emiratis is consistent with previously reported high frequency of the slow acetylator phenotype in Arabs. Two apparently new slow alleles were identified but have not yet been fully characterized. One appears to be a NAT2*5 variant allele. The other uncharacterized allele appears likely to contain an entirely new mutation associated with slow acetylation.

Diversity in expression of glucose‐6‐phosphate dehydrogenase deficiency in females

The aims of this study were to determine the prevalence of glucose‐6‐phosphate dehydrogenase (G6PD) deficiency in the United Arab Emirates (UAE), to describe the different mutations in the population, to determine its prevalence, and to study inheritance patterns in families of G6PD‐deficient individuals. All infants born at Tawam Hospital, Al‐Ain, UAE from January 1994 to September 1996 were screened at birth for their G6PD status. In addition, those attending well‐baby clinics during the period were also screened for the disorder. Families of 40 known G6PD‐deficient individuals, selected randomly from the records of three hospitals in the country, were assessed for G6PD deficiency. Where appropriate, this was followed by definition of G6PD mutations. Of 8198 infants, 746 (9.1%), comprising 15% of males and 5% of females tested, were found to be G6PD deficient. A total of 27 families were further assessed: of these, all but one family had the nt563 Mediterranean mutation. In one family, two individuals had the nt202 African mutation. The high manifestation of G6PD deficiency in women may be due to the preferential expression of the G6PD‐deficient gene and X‐inactivation of the normal gene, and/or to the presence of an ‘enhancer’ gene that makes the expression of the G6PD deficiency more likely. The high level of consanguinity which, theoretically, should result in a high proportion of homozygotes and consequently a higher proportion of females with the deficiency, was not found to be a significant factor.

Comparison of five antisecretory agents acting via gastric H+/K+-ATPase.

Lansoprazole(L), pantoprazole (P), rabeprazole and RO-18-5364 (RO) are new benzimidazole derivatives which rival omeprazole (O) as proton pump inhibitors (PPIs) for treatment of ulcer disease. In this study, we compared the effects of these compounds on acid secretion and determined their relative potencies in relation to their effect on [14C]-aminopyrine (AP) accumulation in isolated gastric glands. Inhibition of AP (1.2 microCi x mL(-1)) accumulation was measured in rabbit isolated gastric glands. dbcAMP (1 mmol; stimulant of acid secretion) and Ro 20-1724 (0.1 mmol; a phosphodiasterase inhibitor) were added to the Eppendorf tubes containing the PPIs and AP and dose-response curves were done for each drug after incubating for 5, 10 and 20 min at 37 degrees C and AP accumulation was determined using a scintillation counter. All the PPIs significantly (P < 0.001) inhibited acid secretion as demonstrated by the inhibition of AP accumulation in the isolated gastric glands. Minimum inhibition occurred at a concentration of 0.001 micromol for lansoprazole and omeprazole, 0.01 micromol for rabeprazole and RO 18-5364 and 0.02 micromol for pantoprazole. No differences were observed between PPIs with regards to the maximum inhibition they produce. When expressed as a percentage inhibition of control at 10-min incubation and at concentrations of 1 micromol, L showed 85.6 +/- 0.5, O 87 +/- 0.5, P 83.2 +/- 1.1, R 86.4 +/- 1.1 and RO 87.8 +/- 1.9 inhibition respectively. When comparing the IC50 values, their relative potencies were different. Maximum potency was shown by L (0.007 micromol) > O (0.012 micromol) > R (0.018 micromol) > RO (0.034 micromol) > P (0.050 micromol). All the new PPIs showed different potencies as inhibitors of acid secretion as evident from their IC50s. Extensive ulcer healing trials demonstrated comparable efficacy with a number of studies indicating that symptoms relief are more rapid with P and L, while in this study L appeared to be the most potent in inhibiting AP accumulation in the isolated gastric glands.

Identification of New Alleles and the Determination of Alleles and Genotypes Frequencies at the CYP2D6 Gene in Emiratis

CYP2D6 belongs to the cytochrome P450 superfamily of enzymes and plays an important role in the metabolism of 20–25% of clinically used drugs including antidepressants. It displays inter-individual and inter-ethnic variability in activity ranging from complete absence to excessive activity which causes adverse drug reactions and toxicity or therapy failure even at normal drug doses. This variability is due to genetic polymorphisms which form poor, intermediate, extensive or ultrarapid metaboliser phenotypes. This study aimed to determine CYP2D6 alleles and their frequencies in the United Arab Emirates (UAE) local population. CYP2D6 alleles and genotypes were determined by direct DNA sequencing in 151 Emiratis with the majority being psychiatric patients on antidepressants. Several new alleles have been identified and in total we identified seventeen alleles and 49 genotypes. CYP2D6*1 (wild type) and CYP2D6*2 alleles (extensive metaboliser phenotype) were found with frequencies of 39.1% and 12.2%, respectively. CYP2D6*41 (intermediate metaboliser) occurred in 15.2%. Homozygous CYP2D6*4 allele (poor metaboliser) was found with a frequency of 2% while homozygous and heterozygous CYP2D6*4 occurred with a frequency of 9%. CYP2D6*2xn, caused by gene duplication (ultrarapid metaboliser) had a frequency of 4.3%. CYP2D6 gene duplication/multiduplication occurred in 16% but only 11.2% who carried more than 2 active functional alleles were considered ultrarapid metabolisers. CYP2D6 gene deletion in one copy occurred in 7.5% of the study group. In conclusion, CYP2D6 gene locus is heterogeneous in the UAE national population and no significant differences have been identified between the psychiatric patients and controls.

Comparison of the antisecretory and antiulcer activity of epidermal growth factor, urogastrone and transforming growth factor alpha and its derivative in rodents in vivo

This study investigates the effects of epidermal growth factor (EGF), urogastrone (UG) and transforming growth factor-alpha (TGFα) and its derivative on dimaprit- and pentagastrin-induced gastric acid secretion and on acidified ethanol (AE)-evoked ulcer formation in anaesthetized rats. EGF, TGFα and UG administered subcutaneously (s.c.) 30 min before dimaprit inhibited gastric acid secretion. Against pentagastrin-stimulated secretion, TGFα inhibited, while EGF and UG potentiated, acid secretion dose-dependently. Intraduodenal (i.d.) administration of TGFα and UG had no effect, while EGF potentiated, both secretagogue-induced acid secretion in the same dosage schedule. Administration of either EGF, UG or TGFα i.v. bolus, in response to continuous infusion of dimaprit resulted in a significant (p < 0.05–p < 0.001) inhibition of acid secretion which was transient and returned to normal within 30–45 min for UG while it slowly returned to normal for EGF and TGFα. The truncated form of TGFα (amino acids 34–43) did not show any antisecretory effect when administered parenterally. Acidified ethanol produced gastric haemorrhagic lesions in the rat 1 h after oral administration. The gastric mucosal protective effects of TGFα, EGF and UG administered either orally or s.c. 30 min before the administration of AE were dose-dependent against this model of ulcer induction. Indomethacin (Indo), administered 15 min before AE to inhibit prostanoids biosynthesis, significantly (p < 0.001) reduced the cytoprotective effects of TGFα, EGF and UG and aggravated the ulcer index when administered s.c. The results show that PGs may be involved in mediating the protective effects of the three growth factors. Administration of NG-nitro-L argininemethylester (L-NAME) 15 min prior to TGFα, EGF and UG s.c. or orally, significantly (p < 0.001) decreased the degree of ulcer indices and was able to reduce the protective effects of TGFα, EGF and UG, thus including the role of NO in mediating the protective effects of these growth factors. In conclusion, these results have demonstrated that EGF, UG and TGFα have a short and reversible inhibitory effect on dimaprit-stimulated gastric acid secretion and each is effective parenterally but not orally. UG and EGF potentiated, while, TGFα inhibited pentagastrin-stimulated acid secretion. In addition, TGFα seems to lose its activity when it is truncated from the C terminus. The present study also suggests that EGF, UG and TGFα are equally effective against AE-induced gastric ulcer and bring about their cytoprotective action through their reduction of acid secretion and through PG and NO pathways.

Effects of anaesthetic agents on basal and histamine-stimulated acid secretion in the fistula rat

Objectives: Anaesthetized rats or surgically modified preparations such as the Shay rat are widely used to study upper gastrointestinal function in the laboratory. Despite the existence of reports demonstrating that agents such as barbiturates can influence acid output, a systematic study of the effects of anaesthetics on gastric secretion has not been undertaken. Methods: Basal and histamine-stimulated acid output were measured in chronic fistula rats after administration of injectable and volatile anaesthetics frequently used in studies of gastric secretion in anaesthetized animals. With the exception of ether, for which recovery is very rapid, sedating rather than full anaesthetic doses were used. Results: Chloralose (40mg/kg) had no significant effect on gastric secretion. Pentobarbitone (25 mg/kg) inhibited basal and histamine-stimulated acid output, but the effect was relatively short-lived and secretion returned to control levels after 2h. Urethane (750 mg/kg) markedly inhibited basal acid output and abolished the secretory response to histamine given 15 to 60 min later. The effects of urethane on acid secretion persisted for the entire 3h duration of experiments, during which time basal acid output declined to levels observed in fully anaesthetized rats given 1.5 g/kg. Full anaesthesia with ether for 60 min also caused profound inhibition of basal secretion and, like urethane, abolished the effect of histamine despite the fact that the animals recovered consciousness within 5 min. Conclusions: The differential activity of anaesthetics and profound antisecretory activity of ether and urethane should be taken into account when studying gastrointestinal function and mucosal ulceration in anaesthetized animals. European Journal of Gastroenterology & Hepatology 1995, 7:1199–1202

Effect of alpha-tocopherol supplementation on the ultrastructural abnormalities of peripheral nerves in experimental diabetes.

Abstract  Ultrastructural observations were made on myelinated fibers in the tibial nerves in order to investigate the beneficial effects of α‐tocopherol administration in streptozotocin‐diabetic rats. Male Wistar rats, aged 12 weeks and weighing between 250 g to 300 g were studied. Six onset control rats were used to obtain the baseline parameters for this strain and age. Further 3 groups—untreated diabetic animals, diabetic animals treated with α‐tocopherol, and age‐matched controls—were studied over a 3‐month period. In the diabetic animal, administration of α‐tocopherol resulted in a significant increase (p < 0.05) in total plasma vitamin E levels when compared with other groups. Myelinated fiber cross‐sectional area (p < 0.05), axonal area (p < 0.01) and myelin sheath area (p < 0.05) were significantly less in the tibial nerve of diabetic animals than in age‐matched controls, but not different from those of onset controls. In the α‐tocopherol treated diabetic animals, the values for these parameters were intermediate without showing significant difference when compared with age‐matched controls and untreated diabetics. The “g” ratio (axon to fiber area) did not differ between any experimental groups. The number of large myelinated fibers were less in the untreated diabetic animals, but in the α‐tocopherol‐treated diabetics, the values were significantly higher (p < 0.05) than with untreated diabetics and were similar to those of age‐matched controls. In conclusion, this ultrastructural study reiterated the fact that structural abnormalities of myelinated fibers occur in experimental diabetes and that α‐tocopherol administration may be useful in preventing the development of these abnormalities.

Intrauterine growth restriction and skeletal variations in mouse fetuses induced by vigabatrin administered at preimplantation stages of development

ABSTRACT  Epileptic women do not withdraw antiepileptic drug (AED) therapy during pregnancy, therefore, exposure to AED during preimplantation stages might result in considerable embryonic concentrations endangering development. Neither clinical nor experimental research has addressed this important issue adequately. Vigabatrin (VGB), a second generation AED, is both effective and well tolerated as an add‐on therapy in epilepsy with partial seizures. However, there is little data on the possible reproductive toxicity of this widely used drug. The objective of the present study was to evaluate the effects of VGB on pregnancy and pregnancy outcome in an experimental model. VGB was administered in single doses of 450 mg/kg intraperitoneally (IP) to groups of mice on one of gestation days (GD) 1, 3, or 5. The treated animals consumed moderately reduced amounts of food and water on the day of treatment, so the controls were saline‐injected and food and water‐restricted to match the amounts consumed by the experimental animals. All animals were killed on GD 18. VGB treatment did not interfere with implantation, nor did it cause significant embryo resorption. However, it caused significant reduction in fetal bodyweight and increased frequency of growth restricted fetuses which weighed two standard deviations (SD) less than the mean of the controls. The VGB group fetuses also had retarded development of the skeletal system in terms of delay in maturity of the suproccipital bone development, cervical and coccygeal vertebral hypoplasia, and poor ossification of the bones of the fore and hind paws. Another major finding was the increased incidence of minor malformations, such as the presence of cervical ribs and sternal anomalies. The results of this study show that VGB administered at preimplantation stages of development causes intrauterine growth restriction (IUGR) and augments minor malformation rates in mice. Future studies must address the mechanisms of VGB‐induced IUGR and minor malformations.

Valproic acid-induced congenital malformations : Clinical and experimental observations

ABSTRACT With a large number of epileptic women being in the childbearing age group, complications of pregnancy in epileptic patients are of concern. Epileptic women are treated with antiepileptic drugs (AED) whether they are pregnant or not. Contrary to prevailing opinion, recent data suggest that epilepsy per se contributes significantly to birth defects possibly because of the same genetic susceptibility that predisposes to epilepsy. Many of these defects closely resemble those attributed to exposure to AED. The syndromes attributed to various AED also considerably overlap with each other. Valproic acid (VPA) induces several minor and major malformations. The relative risk for spina bifida in VPA exposed pregnancies is nearly 20 times higher than that for the general population and about 10 times higher than that attributed to other anticonvulsants. Fetuses of experimental animals treated with VPA during pregnancy exhibit exencephaly unlike the human offspring in whom VPA induces spina bifida. The cranial and spinal malformations observed in humans and laboratory animals indicate that VPA has a preferentially deleterious effect on the neural crest. Several AEDs including VPA tend to lower maternal plasma folate levels. In view of the beneficial effects of periconceptional folate supplementation in prevention of neural tube defects (NTD), future research should be directed at the role of folate in the possible alleviation of VPA‐induced NTD. It is also necessary to continue prospective studies to monitor the old and new AED prescribed and to evaluate the role of interactions between drugs used in combinations.

PD-136,450: A CCK2 (gastrin) receptor antagonist with antisecretory, anxiolytic and antiulcer activity

This study investigated the effects of PD-136,450 (PD), a highly selective ligand for the CCK2 receptor, on gastric acid and pancreatic secretions, gastric cytoprotection and anxious behaviour in the rat and rabbit. PD inhibited gastrin (but not dimaprit) stimulated acid secretion in anaesthetized and conscious rats (IC50 of 1 mg kg−1 sc) and inhibited 14C-aminopyrine uptake in isolated gastric glands from rabbits. In addition, PD decreased dose-dependently gastric haemorrhagic lesions in rats treated orally with acidified ethanol. Both, the antisecretory effects on gastric acid secretion and the gastric cytoprotective effects were less potent compared with the proton pump inhibitor omeprazole. PD strongly increased pancreatic secretion, which was substantially inhibited by the CCK1 antagonist L-364,718 (but not by the CCK2 antagonist L-365,260). PD also showed significant anxiolytic activity as assessed by a black and white box two-compartment activity assay. Both, time spent in the dark compartment and latency for movement from the light to the dark compartment was increased by PD (similarly with 5 mg kg−1 diazepam). In conclusion, PD inhibited gastrin-stimulated gastric acid secretion, decreased ethanol-induced damage to the gastric mucosa, stimulated pancreatic secretion (via CCK1 receptors) and displayed anxiolytic activity. Thus, PD may have utility as an adjunct therapy in peptic ulcer disease by countering the actions of gastrin and increasing acid neutralization and mucosal protection.