Xanthine Oxidoreductase Inhibitors Suppress the Onset of Exercise-Induced AKI in High HPRT Activity Urat1-Uox Double Knockout Mice.

BACKGROUND: Hereditary renal hypouricemia type 1 (RHUC1) is caused by URAT1/SLC22A12 dysfunction, resulting in urolithiasis and exercise-induced AKI (EIAKI). However, because there is no useful experimental RHUC1 animal model, the precise pathophysiologic mechanisms underlying EIAKI have yet to be elucidated. We established a high HPRT activity Urat1-Uox double knockout (DKO) mouse as a novel RHUC1 animal model for investigating the cause of EIAKI and the potential therapeutic effect of xanthine oxidoreductase inhibitors (XOIs). METHODS: The novel Urat1-Uox DKO mice were used in a forced swimming test as loading exercise to explore the onset mechanism of EIAKI and evaluate related purine metabolism and renal injury parameters. RESULTS: Urat1-Uox DKO mice had uricosuric effects and elevated levels of plasma creatinine and BUN as renal injury markers, and decreased creatinine clearance observed in a forced swimming test. In addition, Urat1-Uox DKO mice had increased NLRP3 inflammasome activity and downregulated levels of Na+-K+-ATPase protein in the kidney, as Western blot analysis showed. Finally, we demonstrated that topiroxostat and allopurinol, XOIs, improved renal injury and functional parameters of EIAKI. CONCLUSIONS: Urat1-Uox DKO mice are a useful experimental animal model for human RHUC1. The pathogenic mechanism of EIAKI was found to be due to increased levels of IL-1ß via NLRP3 inflammasome signaling and Na+-K+-ATPase dysfunction associated with excessive urinary urate excretion. In addition, XOIs appear to be a promising therapeutic agent for the treatment of EIAKI.

Perfecting a high hypoxanthine phosphoribosyltransferase activity-uricase KO mice to test the effects of purine- and non-purine-type xanthine dehydrogenase (XDH) inhibitors.

BACKGROUND AND PURPOSE: Purine metabolism in mice and human differ in terms of uricase (Uox) activity as well as hypoxanthine phosphoribosyltransferase (HPRT) activity. The aim of this study was the establishment of high HPRT activity-Uox knockout (KO) mice as a novel hyperuricaemic model. Then to investigate the effects of purine-type xanthine dehydrogenase (XDH) inhibitor, allopurinol, and non-purine-type XDH inhibitor, topiroxostat, on purine metabolism. EXPERIMENTAL APPROACH: A novel hyperuricaemic mouse model was established by mating B6-ChrXCMSM mice with uricase KO mice. The pharmacological effects of allopurinol and topiroxostat were explored by evaluating urate, hypoxanthine, xanthine and creatinine in the plasma and urine of these model mice. Furthermore, we analysed the effect of both drugs on erythrocyte hypoxanthine phosphoribosyltransferase activity. KEY RESULTS: Plasma urate level and urinary urate/creatinine ratio significantly decreased after administration of allopurinol 30 mg·kg-1 or topiroxostat 1 mg·kg-1 for 7 days. The urate-lowering effect was equivalent for allopurinol and topiroxostat. However, the urinary hypoxanthine/creatinine ratio and xanthine/creatinine ratio after treatment with topiroxostat were significantly lower than for allopurinol. In addition, the urinary oxypurine/creatinine ratio was significantly lowered after treatment with topiroxostat, but allopurinol elicited no such effect. Furthermore, allopurinol inhibited mouse erythrocyte hypoxanthine phosphoribosyltransferase, while topiroxostat did not. CONCLUSIONS AND IMPLICATIONS: High hypoxanthine phosphoribosyltransferase activity- uricase KO mice were established as a novel hyperuricaemic animal model. In addition, topiroxostat, a non-purine-type xanthine dehydrogenase inhibitor, elicited a potent plasma urate-lowering effect. However, unlike allopurinol, topiroxostat did not perturb the salvage pathway, resulting in lowered total oxypurine excretion.

Distribution of transient receptor potential cation channel subfamily V member 1-expressing nerve fibers in mouse esophagus.

Transient receptor potential cation channel subfamily V member 1 (TRPV1) plays a role in esophageal function. However, the distribution of TRPV1 nerve fibers in the esophagus is currently not well understood. In the present study, we investigated the distribution of TRPV1 and neurotransmitters released from TRPV1 nerve fibers in the mouse lower esophagus. Furthermore, we investigated changes in the presence of TRPV1 in the mouse model of esophagitis. Numerous TRPV1-immunoreactive nerve fibers were seen in both the submucosal layer and myenteric plexus of the lower esophagus and colocalized with calcitonin gene-related peptide (CGRP). TRPV1 colocalized with substance P in axons in the submucosal layer and myenteric plexus. TRPV1 colocalized with neuronal nitric oxide synthase in the myenteric plexus. We observed some colocalization of CGRP with the vesicular acetylcholine (ACh) transporter, packaging of ACh into synaptic vesicles after its synthesis in terminal cytoplasm, in the submucosal layer and myenteric plexus. In the esophagitis model, the number of the TRPV1 nerve fibers did not change, but their immunoreactive intensity increased compared with sham-operated mice. Inhibitory effect of exogenous capsaicin on electrically stimulated twitch contraction significantly increased in esophagitis model compared with the effect in sham-operated mice. Overall, these results suggest that TRPV1 nerve fibers projecting to both the submucosal and muscle layer of the esophagus are extrinsic spinal and vagal afferent neurons. Furthermore, TRPV1 nerve fibers contain CGRP, substance P, nitric oxide, and ACh. Therefore, acid influx-mediated TRPV1 activation may play a role in regulating esophageal relaxation.

Experimental colitis alters expression of 5-HT receptors and transient receptor potential vanilloid 1 leading to visceral hypersensitivity in mice.

Abnormalities of primary afferent nerve fibers are strongly associated with the visceral hypersensitivity state in inflammatory bowel disease. Hypersensitivity of afferent fibers occurs during inflammation. Therefore, to gain an insight into the alterations to receptors and channels expressed in primary afferent neurons, the current study aimed to investigate the time-dependent dynamic changes in levels of 5-hydroxytryptamine (5-HT)(3) receptors, 5-HT(4) receptors, transient receptor potential vanilloid type 1 (TRPV1) channels, and 5-HT regulatory factors in dextran sulfate sodium (DSS)-induced colitis model mice. 5-HT signaling molecules were detected by indirect staining with specific antibodies. TRPV1-immunoreactivity was detected by staining with fluorescein-conjugated tyramide amplification. To assess nociception, visceromotor responses (VMRs) to colorectal distension were measured by electromyography of abdominal muscles. Immunohistochemical analysis and VMRs to colorectal distention were measured during induction of DSS colitis (days 4 and 7). Inflammation led to downregulation of serotonin transporter immunoreactivities with concomitant increases in 5-HT and tryptophan hydroxylase-1-positive cell numbers. TRPV1-expressing nerve fibers gradually increased during DSS treatment. Abundant nonneuronal TRPV1-immunopositive cell-like structures were observed on day 7 of DSS treatment but not on day 4. The number of 5-HT(3) receptor-expressing nerve fibers in the mucosa was increased on day 7. On the other hand, the number of 5-HT(4) receptor-expressing nerve fibers in the mucosa decreased on day 7. We made the novel observation of increased expression of neuronal/nonneuronal TRPV1 channels and 5-HT(3) receptors, and decreased expression of 5-HT(4) receptors in the mucosa in a DSS-induced colitis model. Visceral hyperalgesia was observed on day 7 but not on day 4. A TRPV1 antagonist and a 5-HT(3) receptor antagonist attenuated the visceral hyperalgesia to the control level. The alterations of 5-HT signaling via 5-HT(3) receptors and of TRPV1 channels in mucosa may contribute to the visceral hypersensitivity in colitis model mice.

Localization of TRPV1 and contractile effect of capsaicin in mouse large intestine: high abundance and sensitivity in rectum and distal colon.

We investigated immunohistochemical differences in the distribution of TRPV1 channels and the contractile effects of capsaicin on smooth muscle in the mouse rectum and distal, transverse, and proximal colon. In the immunohistochemical study, TRPV1 immunoreactivity was found in the mucosa, submucosal, and muscle layers and myenteric plexus. Large numbers of TRPV1-immunoreactive axons were observed in the rectum and distal colon. In contrast, TRPV1-positive axons were sparsely distributed in the transverse and proximal colon. The density of TRPV1-immunoreactive axons in the rectum and distal colon was much higher than those in the transverse and proximal colon. Axons double labeled with TRPV1 and protein gene product (PGP) 9.5 were detected in the myenteric plexus, but PGP 9.5-immunoreactive cell bodies did not colocalize with TRPV1. In motor function studies, capsaicin induced a fast transient contraction, followed by a large long-lasting contraction in the rectum and distal colon, whereas in the transverse and proximal colon only the transient contraction was observed. The capsaicin-induced transient contraction from the proximal colon to the rectum was moderately inhibited by an NK1 or NK2 receptor antagonist. The capsaicin-induced long-lasting contraction in the rectum and distal colon was markedly inhibited by an NK2 antagonist, but not by an NK1 antagonist. The present results suggest that TRPV1 channels located on the rectum and distal colon play a major role in the motor function in the large intestine.