Extra-Renal Elimination of Uric Acid via Intestinal Efflux Transporter BCRP/ABCG2

Urinary excretion accounts for two-thirds of total elimination of uric acid and the remainder is excreted in feces. However, the mechanism of extra-renal elimination is poorly understood. In the present study, we aimed to clarify the mechanism and the extent of elimination of uric acid through liver and intestine using oxonate-treated rats and Caco-2 cells as a model of human intestinal epithelium. In oxonate-treated rats, significant amounts of externally administered and endogenous uric acid were recovered in the intestinal lumen, while biliary excretion was minimal. Accordingly, direct intestinal secretion was thought to be a substantial contributor to extra-renal elimination of uric acid. Since human efflux transporter BCRP/ABCG2 accepts uric acid as a substrate and genetic polymorphism causing a decrease of BCRP activity is known to be associated with hyperuricemia and gout, the contribution of rBcrp to intestinal secretion was examined. rBcrp was confirmed to transport uric acid in a membrane vesicle study, and intestinal regional differences of expression of rBcrp mRNA were well correlated with uric acid secretory activity into the intestinal lumen. Bcrp1 knockout mice exhibited significantly decreased intestinal secretion and an increased plasma concentration of uric acid. Furthermore, a Bcrp inhibitor, elacridar, caused a decrease of intestinal secretion of uric acid. In Caco-2 cells, uric acid showed a polarized flux from the basolateral to apical side, and this flux was almost abolished in the presence of elacridar. These results demonstrate that BCRP contributes at least in part to the intestinal excretion of uric acid as extra-renal elimination pathway in humans and rats

Individualising the dose of allopurinol in patients with gout

Aims: The aims of the study were to: 1) determine if a plasma oxypurinol concentration-response relationship or an allopurinol dose-response relationship best predicts the dose requirements of allopurinol in the treatment of gout; and 2) to construct a nomogram for calculating the optimum maintenance dose of allopurinol to achieve target serum urate (SU) concentrations. Methods: A nonlinear regression analysis was used to examine the plasma oxypurinol concentration- and allopurinol dose-response relationships with serum urate. In 81 patients (205 samples), creatinine clearance (CLCR), concomitant diuretic use and SU concentrations before (UP) and during (UT) treatment were monitored across a range of allopurinol doses (D, 50-700 mg daily). Plasma concentrations of oxypurinol (C) were measured in 47 patients (98 samples). Models (n = 47 patients) and predictions from each relationship were compared using F-tests, r2 values and paired t-tests. The best model was used to construct a nomogram. Results: The final plasma oxypurinol concentration-response relationship (UT=UP-C*(UP-UR)/(ID50+C), r2 = 0.64) and allopurinol dose-response relationship (UT=UP-D*(UP-UR)/(ID50+D), r2 = 0.60) did not include CLCR or diuretic use as covariates. There was no difference (P = 0.87) between the predicted SU concentrations derived from the oxypurinol concentration- and allopurinol dose-response relationships. The nomogram constructed using the allopurinol dose-response relationship for all recruited patients (n = 81 patients) required pretreatment SU as the predictor of allopurinol maintenance dose. Conclusions: Plasma oxypurinol concentrations, CLCR and diuretic status are not required to predict the maintenance dose of allopurinol. Using the nomogram, the maintenance dose of allopurinol estimated to reach target concentrations can be predicted from UP

Developing Potent Human Uric Acid Transporter 1 (hURAT1) Inhibitors

The kidneys are a vital organ in the human body. They serve several purposes including homeostatic functions such as regulating extracellular fluid volume and maintaining acid-base and electrolyte balance and are essential regarding the excretion of metabolic waste. Furthermore, the kidneys play an important role in uric acid secretion/reabsorption. Abnormalities associated with kidney transporters have been associated with various diseases, such as gout. The current study utilized Xenopus oocytes expressing human uric acid transporter 1 (hURAT1; SLC22A12) as an in vitro method to investigate novel compounds and their ability to inhibit 14C-uric acid uptake via hURAT1. We have prepared and tested a series of 2-ethyl-benzofuran compounds and probed the hURAT1 in vitro inhibitor structure-activity relationship. As compared to dimethoxy analogues, monophenols formed on the C ring showed the best in vitro inhibitory potential. Compounds with submicromolar (i.e., IC 50 \u3c 1000 nM) inhibitors were prepared by brominating the corresponding phenols to produce compounds with potent uricosuric activity

Acute gastrointestinal bleeding: proposed study outcomes for new randomised controlled trials

BackgroundAcute gastrointestinal bleeding (GIB) remains a common cause of hospitalisation. However, interpretation and comparisons of published studies in GIB have been hampered by disparate study methodology.AimsTo make recommendations about outcome measures to be used in future randomised controlled trials (RCTs) of patients with acute bleeding from any GI source (nonvariceal UGI, variceal, small bowel, or colon) and suggest new RCTs in acute GIB for future peer-reviewed funding.MethodsAs part of a National Institutes of Health conference entitled "Hemostatic Outcomes in Clinical Trials", a group of GIB experts performed targeted critical reviews of available evidence with the goal of proposing a bleeding outcome that could potentially be applied to different disciplines. In addition, the panel sought to develop a clinically meaningful primary endpoint specifically for acute GIB, potentially allowing a more contemporary regrouping of clinically relevant outcomes.ResultsThe primary endpoint proposed was a composite outcome of further bleeding within 30 days after randomisation leading to red blood cell transfusion, urgent intervention (repeat endoscopy; interventional radiology or surgery), or death. Secondary outcomes may include the individual components of the primary outcome, length of hospitalisation, serious adverse events, and health care resource utilisation.ConclusionThe proposed endpoint may help move the GIB field forward by focusing on the most clinically relevant outcomes for patients with acute GIB of all types and informing study design and importance of sample size determination for future RCTs in GIB

Developing Potent Human Uric Acid Transporter 1 (hURAT1) Inhibitors

The kidneys are a vital organ in the human body. They serve several purposes including homeostatic functions such as regulating extracellular fluid volume, maintaining acid-base and electrolyte balance, and are essential regarding the excretion of metabolic waste. Furthermore, the kidneys play an important role in uric acid secretion/re-absorption. Abnormalities associated with kidney transporters have been associated with various diseases, such as gout. The current study utilized Xenopus oocytes expressing human uric acid transporter 1 (hURAT1; SLC22A12) as an in vitro method to investigate novel compounds and their ability to inhibit (14)C-uric acid uptake via hURAT1. We have prepared and tested a series of 2-ethyl-benzofuran compounds and probed the hURAT1 in vitro inhibitor structure-activity relationship (SAR). Compared to di-methoxy analogs, mono-phenols formed on the C-Ring showed the best in vitro inhibitory potential. Compounds with sub-micromolar (i.e. IC(50) < 1000 nM) inhibitors were prepared by brominating the corresponding phenols to produce compounds with potent uricosuric activity