Oral epigallocatechin gallate reduces intestinal nadolol absorption via modulation of Oatp1a5 and Oct1 transcriptional levels in spontaneously hypertensive rats.

BACKGROUND: Concurrent use of epigallocatechin-3-gallate (EGCG) and medication may lead to botanical-drug interactions, subsequently therapeutic failure or drug toxicity. It has been reported that EGCG reduces plasma nadolol bioavailability in normotensive models. Nevertheless, evidence on the effects of EGCG on hypertensive model, and the possible underlying mechanism have not been elucidated. OBJECTIVES: This study aims (i) to investigate the effects of EGCG on nadolol pharmacokinetics (maximum plasma concentration, time to achieve maximum concentration, area under the time-plasma concentration curve, plasma half-life and total clearance) and subsequently its impact on blood pressure control; and (ii) to identify transcriptional regulatory roles of EGCG on the nadolol intestinal and hepatic drug-transporters in SHR. METHODS: Male SHR were pre-treated with a daily dose of EGCG (10 mg/kg body weight, i.g.) for 13 days. On day-14, a single dose of nadolol (10 mg/kg body weight) was given to the rats 30 min after the last dose of EGCG administration. Systolic blood pressure (SBP) was measured at 6-h and 22-h post-nadolol administration. Plasma and urinary nadolol concentrations were quantified using high-performance liquid chromatography, and pharmacokinetic parameters were analyzed by using non-compartmental analysis. Hepatic and ileal Oatp1a5, P-gp, and Oct1 mRNA expressions were determined by real-time PCR. RESULTS: SBP of SHR pre-treated with EGCG and received nadolol was significantly higher than those which were not pre-treated with EGCG but received nadolol. Pre-treatment of EGCG resulted in a marked reduction of plasma nadolol maximum concentration (Cmax) and area under the time-plasma concentration curve (AUC) by 53% and 51% compared to its control. The 14-day treatment with oral EGCG led to a significant downregulation of mRNA levels of ileal Oatp1a5, P-gp, and Oct1 genes by 4.03-, 8.01- and 4.03-fold; and hepatic P-gp, and Oct1 genes by 2.61- and 2.66-fold. CONCLUSION: These data concluded that exposure to EGCG could lead to reduced nadolol bioavailability and therefore, uncontrolled raised blood pressure and higher risks of cardiovascular events. Our data suggest that the reduced nadolol bioavailability is associated with the downregulation of ileal Oatp1a5 and Oct1 mRNA levels that subsequently lead to poor absorption of nadolol to the systemic circulation.

ß-Blocker Use and Risk of Mortality in Heart Failure Patients Initiating Maintenance Dialysis.

RATIONAL & OBJECTIVE: Beta-blockers are recommended for patients with heart failure (HF) but their benefit in the dialysis population is uncertain. Beta-blockers are heterogeneous, including with respect to their removal by hemodialysis. We sought to evaluate whether ß-blocker use and their dialyzability characteristics were associated with early mortality among patients with chronic kidney disease with HF who transitioned to dialysis. STUDY DESIGN: Retrospective cohort study. SETTING & PARTICIPANTS: Adults patients with chronic kidney disease (aged≥18 years) and HF who initiated either hemodialysis or peritoneal dialysis during January 1, 2007, to June 30, 2016, within an integrated health system were included. EXPOSURES: Patients were considered treated with ß-blockers if they had a quantity of drug dispensed covering the dialysis transition date. OUTCOMES: All-cause mortality within 6 months and 1 year or hospitalization within 6 months after transition to maintenance dialysis. ANALYTICAL APPROACH: Inverse probability of treatment weights using propensity scores was used to balance covariates between treatment groups. Cox proportional hazard analysis and logistic regression were used to investigate the association between ß-blocker use and study outcomes. RESULTS: 3,503 patients were included in the study. There were 2,115 (60.4%) patients using ß-blockers at transition. Compared with nonusers, the HR for all-cause mortality within 6 months was 0.79 (95% CI, 0.65-0.94) among users of any ß-blocker and 0.68 (95% CI, 0.53-0.88) among users of metoprolol at transition. There were no observed differences in all-cause or cardiovascular-related hospitalization. LIMITATIONS: The observational nature of our study could not fully account for residual confounding. CONCLUSIONS: Beta-blockers were associated with a lower rate of mortality among incident hemodialysis patients with HF. Similar associations were not observed for hospitalizations within the first 6 months following transition to dialysis.

Drug Distribution to Retinal Pigment Epithelium: Studies on Melanin Binding, Cellular Kinetics, and Single Photon Emission Computed Tomography/Computed Tomography Imaging.

Melanin binding is known to affect the distribution and elimination of ocular drugs. The purpose of this study was to evaluate if the extent of drug uptake to primary retinal pigment epithelial (RPE) cells could be estimated based on in vitro binding studies with isolated melanin and evaluate the suitability of single photon emission computed tomography/computed tomography (SPECT/CT) in studying pigment binding in vivo with pigmented and albino rats. Binding of five compounds, basic molecules timolol, chloroquine, and nadolol and acidic molecules methotrexate and 5(6)-carboxy-2',7'-dichlorofluorescein (CDCF), was studied using isolated melanin from porcine choroid-RPE at pH 5.0 and 7.4. The uptake to primary porcine RPE cells was studied with timolol, chloroquine, methotrexate, and CDCF. The cell study setting was modeled using parameters from the in vitro binding study. In vivo kinetics of 3-[I-123]-iodochloroquine was studied by the SPECT/CT method in albino and pigmented rats. All basic compounds bound to melanin at both pH values, whereas the acidic compounds bound more at pH 5.0 than at pH 7.4. The basic compounds (chloroquine, timolol) showed significant cellular uptake, unlike the acidic compounds (methotrexate, CDCF). On the basis of the modeling, melanin binding was a major factor governing the overall drug distribution to the RPE cells. Likewise, melanin binding explained distribution of 3-[I-123]-iodochloroquine in the pigmented RPE, whereas drug accumulation was not seen in the albino rat. This study demonstrates the suitability of noninvasive SPECT/CT imaging in monitoring ocular melanin binding in vivo. These studies are a useful step toward understanding the pharmacokinetic impact of melanin binding.

The Nonmetabolized ß-Blocker Nadolol Is a Substrate of OCT1, OCT2, MATE1, MATE2-K, and P-Glycoprotein, but Not of OATP1B1 and OATP1B3.

Nadolol is a nonmetabolized ß-adrenoceptor antagonist and is a substrate of OATP1A2, but not of OATP2B1. However, other drug transporters involved in translocation of nadolol have not been characterized in detail. We therefore investigated nadolol as a potential substrate of the hepatic uptake transporters OATP1B1, OATP1B3, and OCT1 and of the renal transporters OCT2, MATE1, and MATE2-K expressed in HEK cells. Moreover, the importance of P-glycoprotein (P-gp) for nadolol transport was studied using double transfected MDCK-OCT1-P-gp cells. Nadolol was not transported by OATP1B1 and OATP1B3. In contrast, a significantly higher nadolol accumulation (at 1 and 10 µM) was found in OCT1, OCT2, MATE1, and MATE2-K cells compared to control cells (P < 0.01). Km values for OCT2-, MATE1-, and MATE2-K-mediated nadolol uptake were 122, 531, and 372 µM, respectively. Cimetidine (100 µM, P < 0.01) and trimethoprim (100 µM, P < 0.001) significantly inhibited OCT1-, OCT2-, MATE1-, and MATE2-K-mediated nadolol transport. The P-gp inhibitor zosuquidar significantly reduced basal to apical nadolol transport in monolayers of MDCK-OCT1-P-gp cells. In summary, nadolol is a substrate of the cation transporters OCT1, OCT2, MATE1, MATE2-K, and of P-gp. These data will aid future in vivo studies on potential transporter-mediated drug-drug or drug-food interactions with involvement of nadolol.

Do beta 3-adrenoceptors mediate metabolic responses to isoprenaline.

We investigated whether the putative beta 3-adrenoceptors mediated metabolic responses to isoprenaline. Seven normal volunteers received infusions of isoprenaline, a (beta 1, beta 2 and beta 3-agonist), at 0.5-3.0 micrograms/min. They were pretreated with either placebo, 25 mg atenolol (a selective beta 1 antagonist), or 5, 20 and 80 mg nadolol (which blocks beta 1 and beta 2 but not beta 3-adrenoceptors). Isoprenaline markedly (30.6%) increased basal metabolic rate (BMR): this increase was significantly reduced by 25 mg atenolol but not by 5 mg nadolol. Significant beta 2-blockade (from tremor data) occurred with 5 mg nadolol but not with 25 mg atenolol. This suggests that beta 1 but not beta 2-adrenoceptors are involved in the mediating thermogenic effects of isoprenaline. However, the rise in BMR was not totally blocked even by 80 mg nadolol (9.5%), which produced complete beta 1/beta 2 blockade, as evidenced by the elimination of the chronotropic effect of isoprenaline. This implies that the thermogenic response has a non-beta 1/beta 2-mediated component. There were also significant increases in plasma free fatty acids, glycerol, glucose, insulin and lactate, but these were completely abolished by beta 1/beta 2 blockade. Overall, isoprenaline produced an increase in BMR which is only partly due to stimulation of beta 1-adrenoceptors, and which is not associated with beta 1/beta 2-mediated effects on carbohydrate and fat metabolism. This suggests the possibility of thermogenic beta 3-adrenoceptors in man, although their location and role remain unknown.

Formation of the N-nitroso derivatives of six beta-adrenergic-blocking agents and their genotoxic effects in rat and human hepatocytes.

Six beta-adrenergic-blocking drugs, atenolol, metoprolol, nadolol, oxprenolol, propranolol and sotalol, were found to react with sodium nitrite in HCl solution, yielding the corresponding N-nitrosamines. The genotoxic activity of the six nitrosamines was evaluated in primary cultures of both rat and human hepatocytes; DNA fragmentation was measured by the alkaline elution technique, and DNA repair synthesis by quantitative autoradiography. Positive dose-related responses were produced in cells of both species after 20 h of exposure to the following subtoxic concentrations: NO-propranolol, 0.01-0.1 mM; NO-oxprenolol, 0.03-1 mM; NO-atenolol and NO-metoprolol, 0.1-1 mM; and NO-nadolol and NO-sotalol, 0.3-3 mM. Modest but statistically significant differences between the DNA-damaging potencies for the two species were observed with NO-atenolol and NO-oxprenolol, which were both more active against rat hepatocytes, and with NO-propranolol, which was more active against human hepatocytes. At equal or higher concentrations, the six N-nitrosamines did not produce DNA fragmentation in Chinese hamster lung V79 cells; this indicates that they behave as indirectly acting compounds, which need to be transformed into reactive metabolites in order to exert a genotoxic effect.