Hypouricemic and uricosuric actions of AA-193 in a hyperuricemic rat model

Uricosuric agents decrease the plasma urate level in rats by concomitant treatment with topiroxostat, a novel xanthine oxidoreductase inhibitor

OBJECTIVES

The aim of this study was to establish the rat model for evaluating hypouricemic effects by some uricosuric agents.

METHODS

Rats were made hyperuricemic by subcutaneous administration of potassium oxonate, a uricase inhibitor, or made hypouricemic by oral administration of topiroxostat, a xanthine oxidoreductase inhibitor. Furthermore, rats were co-treated with topiroxostat and inosine, a urate precursor. In each condition, hypouricemic effects by uricosuric agents were examined.

KEY FINDINGS

In potassium oxonate-treated rats, treatment with uricosuric agents such as FYU-981, F12859 and probenecid showed no hypouricemic effect. On the other hand, in topiroxostat-treated rats, uricosuric agents remarkably lowered plasma urate level compared with topiroxostat treatment alone, with a dose dependency of 30 and 100 mg/kg for FYU-981 and F12859 each. The decrease in the plasma urate level observed in the topiroxostat-treated rats disappeared by further co-treatment with inosine.

CONCLUSIONS

Effects of uricosuric agents on the plasma urate level in rats were sensitive to the rate of urate formation. Induction of slower urate formation by topiroxostat provides valuable model for evaluation of hypouricemic effects by uricosuric agents in rats.

Mechanisms of antihyperuricemic effect of Phyllanthus niruri and its lignan constituents

ETHNOPHARMACOLOGICAL RELEVANCE

Phyllanthus niruri Linn. (Euphorbiaceae) is used as folk medicine in South America to treat excess uric acid. Our initial study showed that the methanol extract of Phyllanthus niruri and its lignans were able to reverse the plasma uric acid of hyperuricemic animals.

AIM OF THE STUDY

The study was undertaken to investigate the mechanisms of antihyperuricemic effect of Phyllanthus niruri and its lignan constituents.

MATERIAL AND METHODS

The mechanisms were investigated using xanthine oxidase assay and uricosuric studies in potassium oxonate- and uric acid-induced hyperuricemic rats.

RESULTS

Phyllanthus niruri methanol extract exhibited in vitro xanthine oxidase inhibition with an IC50 of 39.39 microg/mL and a moderate in vivo xanthine oxidase inhibitory activity. However, the lignans display poor xanthine oxidase inhibition in vitro and a relatively weak in vivo inhibitory activity at 10mg/kg. On the other hand, intraperitoneal treatment with Phyllanthus niruri methanol extract showed 1.69 folds increase in urinary uric acid excretion when compared to the hyperuricemic control animals. Likewise, the lignans, phyllanthin, hypophyllanthin and phyltetralin exhibited up to 2.51 and 11.0 folds higher in urinary uric acid excretion and clearance, respectively. The co-administration of pyrazinamide with phyllanthin exhibited a significant suppression of phyllanthin's uricosuric activity resembling that of pyrazinamide with benzbromarone.

CONCLUSIONS

The present study showed that the antihyperuricemic effect of Phyllanthus niruri methanol extract may be mainly due to its uricosuric action and partly through xanthine oxidase inhibition, whereas the antihyperuricemic effect of the lignans was attributed to their uricosuric action.

The Dual Actions of Morin (3,5,7,2′,4′-Pentahydroxyflavone) as a Hypouricemic Agent: Uricosuric Effect and Xanthine Oxidase Inhibitory Activity

Hyperuricemia is associated with a number of pathological conditions such as gout. Lowering of elevated uric acid level in the blood could be achieved by xanthine oxidase inhibitors and inhibitors of renal urate reabsorption. Some natural compounds isolated from herbs used in traditional Chinese medicine have been previously demonstrated to possess xanthine oxidase inhibitory activities. In the present investigation, morin (3,5,7,2',4'-pentahydroxyflavone), which occurs in the twigs of Morus alba L. documented in traditional Chinese medicinal literature to treat conditions akin to gout, was demonstrated to exert potent inhibitory action on urate uptake in rat renal brush-border membrane vesicles, indicating that this compound acts on the kidney to inhibit urate reabsorption. Lineweaver-Burk transformation of the inhibition kinetics data demonstrated that the inhibition of urate uptake was of a competitive type, with a K(i) value of 17.4 microM. In addition, morin was also demonstrated to be an inhibitor of xanthine oxidase. Lineweaver-Burk analysis of the enzyme kinetics indicated that the mode of inhibition was of a mixed type, with K(i) and K(ies) values being 7.9 and 35.1 microM, respectively. Using an oxonate-induced hyperuricemic rat model, morin was indeed shown to exhibit an in vivo uricosuric action, which could explain, in part at least, the observed hypouricemic effect of morin in these rats. The potential application of this compound in the treatment of conditions associated with hyperuricemia was discussed.

Mechanism of the uricosuric action of E3040, a drug used to treat inflammatory bowel disease II: study using DBA/2N mice

In the initial phase of clinical studies, it was shown that E3040, a new type of anti-inflammatory drug, reduced plasma uric acid levels. The present study describes a comparison of the excretion of uric acid in the proximal tubules of the kidney after administration of E3040 and its conjugates, sulphate and glucuronide, with that of other general uricosuric agents in DBA/2N mice. The aim of this investigation was to elucidate the mechanism for the uricosuric action of E3040. It was found that E3040 increased the excretion rate of uric acid in a dose-dependent manner, and the excretion rates following 10 and 50 mg/kg doses were significantly greater than that of the control group. The paradoxical effect observed with probenecid was not seen in the E3040 dose-response curve for the uric acid excretion rate. Neither E3040-sulphate nor E3040-glucuronide increased the excretion rate of uric acid significantly, even at a high dose, such as 200 mg/kg. In the pyrazinoic acid suppression test, the uric acid excretion rate after concomitant administration of E3040 and pyrazinoic acid was significantly higher than that after administration of pyrazinoic acid alone, and the rate after concomitant administration was 30% of the level after administration of E3040 alone. The change in the excretion rate of uric acid after concomitant administration of E3040 and pyrazinoic acid was similar to that of AA193, a selective inhibitor of the presecretory reabsorption of uric acid. From these results, it appears that E3040 may exert its uricosuric action by reducing the presecretory reabsorption of uric acid rather than increasing its secretion.

Mechanism of the uricosuric action of the anti-inflammatory drug E3040 used to treat inflammatory bowel disease I: study using a rat model of hyperuricemia

E3040, a new class of anti-inflammatory drug, was found to reduce the plasma uric acid level in the first phase of clinical studies. In the present study, the mechanism of the uricosuric action of E3040 was investigated using the hyperuricemia model rat. The fractional excretion of uric acid (FEurate), an indicator of the excretion of uric acid in the renal tubules, at 30, 60 and 90 min after administration of E3040 (50 mg kg(-1)) was significantly elevated as compared with that in the control. This elevation of the FEurate by E3040 was dose-dependent. Although the FEurate was elevated spontaneously 30 min after administration of E3040-sulfate (E-Sul) and glucuronide (E-Glu) (100 mg kg(-1), respectively), the value was not significantly different from the control. Based on these results, it was suggested that E3040 has a uricosuric action, probably in the proximal tubules, and the uricosuric action after administration of E3040 may be mainly due to the parent drug. Concerning the tissue distribution, the kidney concentration of E-Sul after i.v. administration of the E3040 (50 mg kg(-1)) was higher than that of the parent drug (kidney/plasma ratio approximately 2).