Para-aminosalicylic acid significantly reduced tenofovir exposure in human subjects: Mismatched findings from in vitro to in vivo translational research.

AIMS: Tenofovir and para-aminosalicylic acid (PAS) may be coprescribed to treat patients with concomitant infections of human immunodeficiency virus and Mycobacterium tuberculosis bacteria. Both drugs are known to have remarkable renal uptake transporter-mediated clearance. Owing to the lack of clinical studies on drug-drug interaction between the 2 drugs, we conducted a translational clinical study to investigate the effect of PAS on tenofovir pharmacokinetics (PK). METHODS: Initially, we studied in vitro renal uptake transporter-mediated drug-drug interactions using stably transfected cells with human organic anion transporters (OAT1 and OAT3). Later, we estimated clinical drug interactions using static and physiologically based PK modelling. Finally, we investigated the effects of PAS-calcium formulation (PAS-Ca) on tenofovir disoproxil fumarate PK in healthy male Korean subjects. RESULTS: PAS inhibited OAT1- and OAT3-mediated tenofovir uptake in vitro. The physiologically based PK drug-drug interaction model suggested a 1.26-fold increase in tenofovir peak plasma concentration when coadministered with PAS. By contrast, an open-label, randomized, crossover clinical trial evaluating the effects of PAS-Ca on tenofovir PK showed significantly altered geometric mean ratio (90% confidence intervals) of maximum plasma concentration (Cmax ) and area under the curve (AUC0-inf ) by 0.33 (0.28-0.38) and 0.29 (0.26-0.33), respectively. CONCLUSION: Our study findings suggest that the PAS-Ca formulation significantly reduced systemic exposure to tenofovir through an unexplained mechanism, which was contrary to the initial prediction. Caution should be exercised while predicting in vivo PK profiles from in vitro data, particularly when there are potential confounders such as pharmaceutical interactions.

Relation of the Allelic Variants of Multidrug Resistance Gene to Agranulocytosis Associated With Clozapine.

Clozapine use is associated with leukopenia and more rarely agranulocytosis, which may be lethal. The drug and its metabolites are proposed to interact with the multidrug resistance transporter (ABCB1/MDR1) gene product, P-glycoprotein (P-gp). Among various P-glycoprotein genetic polymorphisms, nucleotide changes in exons 26 (C3435T), 21 (G2677T), and 12 (C1236T) have been implicated for changes in pharmacokinetics and pharmacodynamics of many substrate drugs. In this study, we aimed to investigate the association between these specific ABCB1 polymorphisms and clozapine-associated agranulocytosis (CAA). Ten patients with a history of CAA and 91 control patients without a history of CAA, despite 10 years of continuous clozapine use, were included. Patient recruitment and blood sample collection were conducted at the Hacettepe University Faculty of Medicine, Department of Psychiatry, in collaboration with the members of the Schizophrenia and Other Psychotic Disorders Section of the Psychiatric Association of Turkey, working in various psychiatry clinics. After DNA extraction from peripheral blood lymphocytes, genotyping was performed using polymerase chain reaction and endonuclease digestion. Patients with CAA had shorter duration of clozapine use but did not show any significant difference in other clinical, sociodemographic characteristics and in genotypic or allelic distributions of ABCB1 variants and haplotypes compared with control patients. Among the 10 patients with CAA, none carried the ABCB1 all-variant haplotype (TT-TT-TT), whereas the frequency of this haplotype was approximately 12% among the controls. Larger sample size studies and thorough genetic analyses may reveal both genetic risk and protective factors for this serious adverse event.

Lower CYP2C9 activity in Turkish patients with Behçet's disease compared to healthy subjects: a down-regulation due to inflammation?

BACKGROUND: We previously reported on a Swedish patient with Behçet's disease (BD) who was an ultra-rapid metaboliser of drugs catalysed by CYP2C9. Was this extreme metabolism caused by the disease? AIM: This study aims to compare the genotype/phenotype of CYP2C9 in patients with BD and healthy subjects. As the occurrence of BD is high in Turkey, all subjects were recruited from this country. METHODS: Genotyping of CYP2C9 was performed using standard PCR-RFLP and allele-specific PCR methods. Phenotyping of CYP2C9 was performed by administration of a 50-mg single oral dose of losartan and by calculating the urinary metabolic ratio (MR) of probe drug to its metabolite E-3174. Quantitation was performed by HPLC. RESULTS: The frequency of CYP2C9*2 and *3 was not significantly different between the Behçet's disease patients (12.5 and 8.7%) and the healthy subjects (8.9 and 8.2%). The geometric mean losartan MR was higher in the 52 patients (1.75) than in the 96 healthy subjects (1.02) (p = 0.002; t-test). Within the genotypes *1/*1, there was a significant difference of MR between patients and healthy subjects (P = 0.006). All but three of the Behçet's disease patients were treated with colchicine. In nine subsequent patients, we found no significant effect of 2 weeks of treatment with colchicine on the CYP2C9 MR. CONCLUSION: Contrary to expectation, the CYP2C9 activity was lower in Turkish BD patients compared to healthy subjects. As this seems not to be due to colchicine treatment, our hypothesis is that inflammation related to BD might have caused the down-regulation of the CYP2C9 activity due to immune cytokine reactions. The ultra-rapid metabolism of CYP2C9 substrate drugs in the Swedish patient was not due to her BD.

Effects of genetic polymorphisms of CYP2J2, CYP2C9, CYP2C19, CYP4F2, CYP4F3 and CYP4A11 enzymes in preeclampsia and gestational hypertension.

INTRODUCTION: The aim of this study was to investigate the effects of cytochrome P450 (CYP) 2J2, CYP2C9, CYP2C19 and CYP4F2, CYP4F3 and CYP4A11 genetic polymorphisms in preeclampsia and gestational hypertension (GHT) patients in a sample of Turkish population. MATERIALS-METHODS: Patients (n = 168; 110 GHT and 58 preeclampsia) and healthy pregnant women (n = 155, controls) participated in the study. For genotyping, polymerase chain reaction (PCR) and restriction analysis (RFLP) were used. Substance levels were measured using LC-MS. RESULTS: Plasma DHET levels in GHT and preeclampsia patients were significantly lower than those in the control group (62.7%, 66.3% vs.100.0%, respectively, p < 0.0001). An increase in CYP2J2*7 allele frequency was observed in the preeclampsia group, as compared to GHT group (12.1% vs. 4.5%; odds ratio, O.R. = 2.88, p < 0.01). The frequencies of CYP2C19*2 and*17 alleles were higher in GHT group as compared to the control group (17.7% vs. 11.6%, O.R. = 1.99, p < 0.01; and 28.6% vs.18.4%, O.R. = 2.03, p < 0.01, respectively). An increased frequency of CYP4F3 rs3794987 G allele was found in GHT group as compared to the control group (48.0% vs. 38.0%; O.R. = 1.53, p < 0.01). DISCUSSION: DHET plasma levels were significantly reduced in hypertensive pregnant groups as compared to the control group. The allele frequency distributions for CYP2J2*7, CYP2C19 *2, *17 and CYP4F3 rs3794987 were significantly different in hypertensive pregnant patients as compared to the healthy control subjects. Our results may suggest that investigated genetic polymorphisms may be useful in diagnosis and clinical management of GHT and preeclampsia patients.

Evaluation of lansoprazole as a probe for assessing cytochrome P450 2C19 activity and genotype-phenotype correlation in childhood.

PURPOSE: Lansoprazole, a cytochrome P450 2C19 (CYP2C19) substrate, has been widely used in children to manage acid-related diseases. CYP2C19 exhibits marked genetic polymorphisms, and distribution of these polymorphisms varies among different ethnic groups. There is limited data regarding the use of probe drugs for determining CYP2C19 activity in children. The aim of this study was to evaluate lansoprazole as an in vivo phenotyping probe for assessing CYP2C19 activity in children. METHODS: The CYP2C19*2, *3, and *17 variants were determined in 244 children. Three hours after a single oral dose of lansoprazole (n = 94) or omeprazole (n = 19), plasma lansoprazole and 5-hydroxy lansoprazole or omeprazole and 5-hydroxy omeprazole concentrations were analyzed by high-performance liquid chromatography. RESULTS: The CYP2C19*17 was the most frequent variant allele (24.4%). The group of patients with CYP2C19*17*17 genotype had a 70% lower (p < 0.05) mean lansoprazole plasma concentration compared with the CYP2C19*1*1 genotype group, whereas the CYP2C19*2*2 group had 6.9-fold higher (p < 0.01) mean lansoprazole plasma concentration. Lansoprazole metabolic ratios (lansoprazole/5-hydroxy-lansoprazole) were found to be significantly lower in the *17*17 [mean ± standard deviation (SD); 2.8 ± 2.1] group and higher in the *2*2 group (63.5 ± 12.2) compared with that of the *1*1 genotype group (6.1 ± 4.5). CONCLUSION: According to our results from a Turkish pediatric population, lansoprazole is a suitable probe drug for phenotyping CYP2C19. The CYP2C19*2 and *17 variants should be taken into consideration in predicting the clinical outcome of therapy with lansoprazole in the pediatric population.

Comparative Assessment of Outcomes in Drug Treatment for Smoking Cessation and Role of Genetic Polymorphisms of Human Nicotinic Acetylcholine Receptor Subunits.

Objective: To investigate the effects of genetic polymorphisms of human nicotinic acetylcholine receptor subunits α3, α4 and α5, which are encoded by CHRNA3, CHRNA4 CHRNA5 genes, respectively, on nicotine addiction and outcomes of pharmacological treatments for smoking cessation. Methods: A total of 143 smokers and 130 non-smokers were included. Genotyping for CHRNA3 rs578776, CHRNA4 rs1044396-rs1044397, CNRNA5 rs16969968 polymorphisms was performed by PCR, flowed by RFLP. Clinical outcomes and success rates of pharmacological treatments for smoking cessation with nicotine replacement therapy (NRT), bupropion or varenicline were determined at the 12th week of the treatment. Results: Overall, 52 out of 143 (36.4%) smokers who received pharmacotherapy were able to quit smoking. Success rates for smoking cessation were similar for female (30.3%) and male (41.6%) subjects (p = 0.16). The success rate for smoking cessation treatment with varenicline (58.5%) was significantly higher as compared to other treatments with NRT (20.0%), bupropion (32.3%) or bupropion + NRT (40.0%) (chi-square test, p = 0.001). Smoker vs. non-smoker status and the clinical outcomes of drugs used for smoking cessation were found similar in subjects carrying wild-type and variant alleles of human nicotinic acetylcholine receptor α subunits. Conclusion: In this study, smoking cessation treatment with varenicline was significantly more effective than treatments with nicotine replacement or bupropion in a cohort of Turkish subjects. Smoker/non-smoker status and the clinical outcomes of treatment with pharmacological agents were similar in subjects with wild-type or variant alleles for human nicotinic acetylcholine receptor subunits α3 (CHRNA3), α4 (CHRNA4) and α5 (CHRNA5).

Effects of Genetic Polymorphisms of Drug Transporter ABCB1 (MDR1) and Cytochrome P450 Enzymes CYP2A6, CYP2B6 on Nicotine Addiction and Smoking Cessation.

OBJECTIVES: To determine the effects of genetic polymorphisms of ABCB1 (MDR1), CYP2A6, CYP2B6 on smoking status, and clinical outcomes of smoking cessation therapies in a Turkish population. METHODS: 130 smokers and 130 non-smokers were recruited. Individuals who never smoked were described as non-smokers. 130 smokers were treated with nicotine replacement therapy (NRT) (n = 40), bupropion (n = 47), bupropion + NRT (n = 15), and varenicline (n = 28). Smokers were checked by phone after 12 weeks of treatment whether they were able to quit smoking or not. Genotyping and phenotyping were performed. RESULTS: Cessation rates were as follows; 20.0% for NRT, 29.8% for bupropion, 40.0% for bupropion + NRT, 57.1% for varenicline (p = 0.013). The frequency of ABCB1 1236TT-2677TT-3435TT haplotype was significantly higher in non-smokers as compared to smokers (21.5% vs. 10.8, respectively; p = 0.018). Neither smoking status nor smoking cessation rates were associated with genetic variants of CYP2A6 (p = 0.652, p = 0.328, respectively), or variants of CYP2B6 (p = 0.514, p = 0.779, respectively). CONCLUSION: Genetic variants of the drug transporter ABCB1 and the 1236TT-2677TT-3435TT haplotype was significantly associated with non-smoking status. Neither ABCB1 nor CYP2A6, CYP2B6 genetic variants were associated with smoking cessation rates at the 12th week of drug treatment.

Multidrug resistance in patients undergoing resective epilepsy surgery is not associated with C3435T polymorphism in the ABCB1 (MDR1) gene.

PURPOSE: The C3435T polymorphism in the gene coding for P-glycoprotein (ABCB1) has been correlated with drug resistance in patients with epilepsy. However, replication studies have revealed conflicting results and the reason for this is not clear. We investigated the frequency of C3435T polymorphism in epileptic Turkish patients who underwent resective epilepsy surgery and compared our results with healthy controls. METHODS: DNA samples were obtained from 100 healthy controls and 89 consecutive adult patients who underwent resective brain surgery due to refractory seizures at our epilepsy center. Genotypes for the C3435T polymorphism were determined by PCR and restriction analysis. RESULTS: Comparison of drug-resistant patients and healthy controls revealed no significant difference in allele frequency (C vs. T; chi(2)=0.015, p=0.90) and genotype frequency (chi(2)=2.05, p=0.36). The findings in the pure hippocampal sclerosis (HS) group (n=73) were not significantly different from control subjects, either (allele frequency: chi(2)=0.29, p=0.59; genotype frequency: chi(2)=2.14, p=0.34). CONCLUSIONS: Our findings failed to prove an association between C3435T polymorphism and drug resistance in a sample of Turkish patients with refractory epilepsy who underwent resective brain surgery.

Inhibitory effect of valproic acid on cytochrome P450 2C9 activity in epilepsy patients.

Drug interactions constitute a major problem in the treatment of epilepsy because drug combinations are so common. Valproic acid is a widely used anticonvulsant drug with a broad therapeutic spectrum. Case reports suggest interaction between valproic acid and other drugs metabolized mainly by cytochrome P450 isoforms. The aim of this study was to evaluate the inhibitory effect of valproic acid on cytochrome P450 2C9 (CYP2C9) activity by using losartan oxidation as a probe in epilepsy patients. Patients were prescribed sodium valproate (mean 200 mg/day for the first week and 400 mg/day in the following period) according to their clinical need. A single oral dose of 25 mg losartan was given to patients before and after the first dose, first week and 4 weeks of valproic acid treatment. Losartan and E3174, the CYP2C9-derived carboxylic acid metabolite of losartan in 8 hr urine were assayed by using high pressure liquid chromatography. Urinary losartan/E3174 ratio did not change significantly on the first day (0.9, 0.3-3.5; median, range), and first week (0.6, 0.2-3.8; median, range), while a significant increase was observed after 4 weeks of valproic acid treatment (1.1, 0.3-5.7; median, range) as compared to that of measured before valproic acid administration (0.6, 0.1-2.1; median, range) (P = 0.039). The degree of inhibition was correlated with the steady-state plasma concentrations of valproic acid (r(2) = 0.70, P = 0.04). The results suggest an inhibitory effect of valproic acid on CYP2C9 enzyme activity in epilepsy patients at steady state. The risk of pharmacokinetic drug-drug interactions should be taken into account during concomitant use of valproic acid and CYP2C9 substrates.

Decreased Activity and Genetic Polymorphisms of CYP2C19 in Behçet's Disease.

Behçet's disease (BD) is a systemic autoimmune disorder. Cytochrome P450 enzymes (CYPs) are responsible for various drug metabolism reactions as well as those of endogenous substances which may be associated with autoimmune disease susceptibility. Recently, we reported that in patients with BD, CYP2C9 seems to be down-regulated due to inflammation. In the same Turkish patients with BD, we investigated whether also CYP2C19 activity is decreased. Lansoprazole (30 mg) was given as a probe drug to evaluate CYP2C19 activity in 59 patients with BD and 27 healthy control volunteers. An HPLC method was used to determine plasma lansoprazole and its metabolite, 5-hydroxy lansoprazole, concentrations. The genotyping for CYP2C19 *2, *3 and *17 polymorphisms was made using PCR-RFLP. The median lansoprazole/5-hydroxy lansoprazole metabolic ratio (MR) in patients with BD was 2.6-fold higher as compared to the healthy control group (p = 0.001, 22.6 (1.3-26) and 8.8 (0.5-140) as median and range, respectively). The CYP2C19*17*17 genotype frequency was found to be significantly less in the BD group as compared to the healthy controls (1.7% versus 14.8% in controls, p = 0.01). Additionally, colchicine treatment did not affect the CYP2C19 enzyme activity in six patients (p = 0.43). In conclusion, the patients with BD had lower CYP2C19 enzyme activity and lower frequency of the CYP2C19*17 allele as compared to those of the healthy controls. Further studies are warranted on the mechanisms underlying this relation. This study should also be applied to other autoimmune diseases similarly characterized by local or systemic inflammation.

Effects of Genetic Polymorphisms of Cytochrome P450 Enzymes and MDR1 Transporter on Pantoprazole Metabolism and Helicobacter pylori Eradication.

Pantoprazole is a proton pump inhibitor that is commonly used in the treatment of peptic ulcer disease (PUD) and metabolized by cytochrome P450 (CYP) enzymes CYP2C19 and CYP3A4. Pantoprazole is a substrate for multi-drug resistance protein 1 (MDR1). Single nucleotide polymorphisms (SNPs) in CYP2C19, CYP3A4 and MDR1 affect enzyme activity or gene expression of proteins and may alter plasma pantoprazole concentrations and treatment success in PUD. In this study, we aimed to investigate the association between genetic polymorphisms in CYP2C19, CYP3A4 and MDR1 and pharmacokinetics of pantoprazole and therapeutic outcome in patients with either Helicobacter pylori-associated [H.P.(+)]-PUD or [H.P.(+)]-gastritis. The plasma pantoprazole concentrations were determined by using an HPLC method at the third hour after a 40-mg tablet of pantoprazole administration in 194 newly diagnosed patients with either [H.P.(+)]-PUD or [H.P.(+)]-gastritis. Genotyping was performed by using PCR-RFLP and DNA sequencing. Among patients appearing for follow-up examination (n = 105), the eradication rate for H. pylori was 82.8% (n = 87). The median pantoprazole plasma concentrations in poor metabolizers (PM), rapid metabolizers (RM) and ultrarapid metabolizers (URM) were 2.07, 1.69 and 1.28 µg/ml, respectively (p = 0.04). CYP3A4*1G and *22 polymorphisms did not affect plasma pantoprazole concentrations and H. pylori eradication rate. The MDR1 genetic polymorphisms did not affect plasma pantoprazole concentrations. MDR1 3435CC-2677GG-1236CC haplotype carriers had lower H. pylori eradication rate (60%) than the remaining subjects (84.9%) while the difference was not statistically significant (p = 0.07). In conclusion, while CYP2C19 genetic polymorphisms significantly affected plasma pantoprazole concentrations, polymorphisms of CYP2C19, CYP3A4 and MDR1 did not affect H. pylori eradication rates.

Neonatal jaundice and bilirubin UDP-glucuronosyl transferase 1A1 gene polymorphism in Turkish patients.

Bilirubin uridine diphosphate-glucuronosyltransferase (B-UGT) is the rate-limiting enzyme for the conjugation of bilirubin with glucuronic acid in its excretion process into the bile. Variations in B-UGT gene (UGT-1A1) have been related to disorders characterised by hyperbilirubinaemia. The aim of this study was to investigate whether the number of thymine-adenine repeats in the promoter region of UGT-1A1 was related to non-physiologic hyperbilirubinemia of unexplained aetiology in Turkish newborns. These patients (n=106) were genotyped for their thymine-adenine repeat number in the promoter region of UGT-1A1, and were divided into two groups according to their bilirubin level. Forty-nine newborns with bilirubin levels higher than 17 mg/dl within the first ten days of life comprised the hyperbilirubinaemia group and 25 newborns with bilirubin levels higher than 10 mg/dl after fifteen days of life formed the prolonged jaundice group. Thirty-two newborns were included as healthy controls. The observed frequencies for the wild-type six repeat allele thymine-adenine (TA(6)) within each subject group were similar (P>0.05; 75.5%, 78.0% and 73.4%, respectively). Likewise, the distribution of TA(6/6), TA(6/7) and TA(7/7) genotypes among three groups were similar. These results imply that the TA(7) repeat allele of UGT1A1 (UGT1A1*28) is a common variant in the Turkish population. Our results do not suggest an association between thymine-adenine repeat polymorphism of UGT1A1 and hyperbilirubinaemia of unexplained aetiology or prolonged jaundice in Turkish neonates.

Inhibitory effect of 5-fluorouracil on cytochrome P450 2C9 activity in cancer patients.

Drug interactions have been reported between 5-fluorouracil and cytochrome P450 2C9 (CYP2C9) substrates, S-warfarin and phenytoin. This study was performed to determine the influence of 5-fluorouracil on cytochrome P450 2C9 (CYP2C9) activity in colorectal cancer patients (n=17) receiving 5-fluorouracil. Losartan was used as a marker to assess CYP2C9 activity. Losartan and its CYP2C9 dependent metabolite, E-3174, were determined in urine. The ratios of urinary losartan/E-3174 before and after the 5-fluorouracil treatment were compared for each patient. Genotyping was performed to detect the CYP2C9*2 and CYP2C9*3. At the end of the first cycle of 5-fluorouracil, losartan/E-3174 ratio was increased by 28.0% compared to the pre-treatment values (P=0.15). In five patients recruited for phenotyping after three 5-fluorouracil cycles, the metabolic ratio was increased significantly by 5.3 times (P=0.03). The results suggest that in most patients 5-fluorouracil inhibited CYP2C9 activity. This inhibition was more pronounced when the total administered dose increased. This finding may help explain the mechanism of interaction between 5-fluorouracil and CYP2C9 substrates.

Association of the ABCB1 3435C>T polymorphism with antiemetic efficacy of 5-hydroxytryptamine type 3 antagonists.

BACKGROUND: Resistance to antiemetic treatment with 5-hydroxytryptamine type 3 (5-HT(3)) receptor antagonists is still a major problem resulting in patient discomfort and poor compliance to chemotherapy. We hypothesized that clinical resistance to 5-HT(3) antagonists is associated with the single-nucleotide polymorphism (3435C>T) in the gene that codes for the drug efflux transporter adenosine triphosphate-binding cassette subfamily B member 1 (ABCB1). METHODS: Patients with cancer (N = 216) treated with chemotherapeutic regimens composed of highly or moderately emetogenic agents were examined for their antiemetic responses to tropisetron, ondansetron, or granisetron. The efficacy of antiemetic treatment was documented by self-report charts for 5 days after chemotherapy. ABCB1 3435C>T genotype was determined to analyze its association with the antiemetic efficacy of 5-HT(3) antagonists. RESULTS: Within the first 24 hours of chemotherapy, the complete control rate of nausea and vomiting was higher in subjects with the ABCB1 TT genotype (n = 49) as compared with those with the CC (n = 60) or CT (n = 107) genotype (P = .044). The type of 5-HT(3) antagonists influenced the effect of genotype on antiemetic responses. The complete control rates were 92.9% in TT subjects (n = 14) in comparison to homozygote (47.6%, n = 21, P = .009) or heterozygote (56.1%, n = 41, P = .02) carriers of the 3435 C allele in granisetron-treated patients. However, during the delayed phase of chemotherapy, the complete control rates did not differ across genotypes. CONCLUSION: These results suggest that ABCB1 3435C>T polymorphism is associated with antiemetic treatment efficacy in patients with cancer treated with 5-HT(3) antagonists, particularly in granisetron-treated patients, during the short-term phase of chemotherapy.

Propranolol-induced relaxation in the rat basilar artery.

Propranolol is a non-selective beta-adrenergic receptor blocker used in the treatment of cardiovascular diseases and migraine prophylaxis. Although it has been shown that propranolol dilates the peripheral arteries of rat, its action in the central nervous system vasculature has not been investigated. In this study, the effects of propranolol in rat basilar artery were investigated. Basilar arteries from male Wistar rats were examined in a myograph system. The relaxant effects of propranolol, pindolol, atenolol, pizotifen and methysergide were examined in basilar arteries precontracted by serotonin or PGF2α. Only propranolol and pizotifen induced vasorelaxations; the pD2 values were 5.23±0.13 and 5.94±0.03; respectively. The vasorelaxation induced by propranolol and pizotifen was not affected by endothelium or the presence of l-NOARG and/or indomethacin. The calcium channel blocking activity of propranolol and pizotifen was compared with that of nifedipine in a calcium free solution with high K(+) (60mM) concentration. These drugs shifted the concentration-response curves of calcium induced contractions with pA2 values of 5.45±0.04; 7.14±0.09; and 9.22±0.06 respectively. The P2Y receptor agonist UTP was used to induce sustained and stable contractions in basilar artery segments. Nifedipine caused a marked, but an incomplete relaxation. Cyclopiazonic acid, an inhibitor of sarcoplasmic reticulum calcium channels, but not propranolol or pizotifen abolished the remaining tonus after partial relaxations obtained with nifedipine. These results suggest that propranolol causes vasorelaxation by blocking the L-type voltage-gated calcium channels in the rat basilar artery.

Functional effects of endothelial nitric oxide synthase genetic polymorphisms on haemorheological parameters in healthy human individuals.

The constitutive endothelial nitric oxide synthase (eNOS) plays a major role in circulatory homoeostasis and shows genetic polymorphism. eNOS is expressed and functional in blood cells, including erythrocytes. There is limited knowledge about the consequences of eNOS genetic variability in haemorheological parameters and erythrocyte functioning. The purpose of this study was to investigate the effects of three eNOS genetic polymorphisms, namely exonic G894T (Glu298Asp), intronic VNTR (27-bp repeat) and 5'-flanking T(-786)C polymorphisms on haemorheological variables, such as erythrocyte deformability and erythrocyte aggregation (rouleaux formation) in healthy non-smoking volunteers. Sixty subjects (19 women, 41 men) were examined for genotypes and haemorheological variables. Genotypes were determined by polymerase chain reaction and restriction analysis. Haemorheological variables were measured by means of a laser-assisted optical rotational cell analyser (LORCA). Erythrocyte aggregation was significantly decreased in individuals with 894TT genotype when compared to subjects with the (G) allele. Aggregation indices (AI) were 54.7±3.2% versus 61.0±0.9% (p=0.026), and the half-lives (t(1/2) ) for aggregation formation were 3.43±0.43 versus 2.55±0.12 sec. (p=0.024), respectively. Similarly, VNTR-bb genotype significantly altered erythrocyte aggregability. AI values were 58.7±1.1% in subjects with VNTR-a allele versus 63.7±1.2% in subjects with bb genotype (p=0.011); t(1/2) values were 2.86±0.16 versus 2.20±0.13 sec., respectively (p=0.016). T(-786)C polymorphism did not change any haemorheological parameters. These findings suggest that eNOS 894TT genotype is associated with decreased erythrocyte aggregation, while VNTR-bb genotype increases aggregability in healthy human individuals. eNOS genetic variants may contribute in the pathogenesis of microvascular disorders by altering erythrocyte functions in human beings.

Aqueous humour penetration of moxifloxocin and gatifloxacin eye drops in different dosing regimens before phacoemulsification surgery.

AIM: To compare the aqueous humour penetration of moxifloxacin 0.5% and gatifloxacin 0.3% eye drops administered in two different dosing regimens during phacoemulsification surgery. METHODS: This prospective, randomised study included 97 patients. The patients were randomly divided into two treatment groups to receive either moxifloxacin or gatifloxacin. All patients received the topical antibiotics four times per day for 2 days prior to surgery. Patients in each group were further subdivided to receive additional doses of antibiotic drops as two drops 30 min apart (subgroup 1) versus four drops 10 min apart (subgroup 2) 1 h prior to the surgery. At the beginning of surgery, 0.1 ml of aqueous humour was aspirated, and the concentrations of moxifloxacin and gatifloxacin were analysed by high-performance liquid chromatography. RESULTS: The mean concentrations of moxifloxacin and gatifloxacin in the aqueous humour were 0.72 ± 0.40 µg/ml and 0.47 ± 0.29 µg/ml, respectively, in the first subgroup, and 1.95 ± 1.05 µg/ml and 0.77 ± 0.52 µg/ml, respectively, in the second subgroup. Both the inter-group (p=0.006 and p=0.000, respectively) and the intra-group (p=0.000 and p=0.035, respectively) differences between the aqueous humour concentrations of moxifloxacin and gatifloxacin subgroups were statistically significant. CONCLUSION: Moxifloxacin, given in the same dosage, penetrated the aqueous humour better then gatifloxacin during cataract surgery. The penetration of both antibiotics increased significantly when the dosage of the agent was doubled.