Nocturnal polyuria is a condition that significantly impairs quality of life and increased mortality. Its pathogenesis is not well understood and existing therapies have limited efficacy. We have reported a nocturnal polyuria mouse model to combine nitric oxide (NO) deficiency and salt loading, in which overactivation of the intrarenal SPAK(STE20/SPS1-related proline–alaninerich protein kinase)–NCC(sodium chloride co-transporter) pathway in the distal renal tubule suppresses sodium excretion during the day and causes nocturnal polyuria. We focused on the fact that the SPAK-NCC pathway is, in part, regulated by oxidative stress1, and we hypothesized that oxidative stress may cause nocturnal polyuria. We have recently developed a novel hydrogen-producing Si-based agent, which is orally ingestible and features sustained hydrogen generation by reacting with water in the intestine. Hydrogen is well known for its antioxidant properties and the efficacy of silicon-based agents has been reported in rat remnant kidney models, rat ischemia-reperfusion injury model and rat varicocele model2, all of which showed a reduction in oxidative stress. In this study, we aimed to show the effect of oxidative stress on nocturnal polyuria and to evaluate the efficacy of a novel antioxidant, Si-based agents, on nocturnal polyuria

19-week-old C57BL6/J male mice were fed L-NAME (NO synthase inhibitor) and a 1% high-salt diet for 2 weeks to create a nocturnal polyuria model. Oxidative stress in kidney was assessed by immunohistochemical staining for 4-hydroxynonenal (4-HNE) and real-time PCR of NADPH oxidase subunit, which regulates the production of ROS. Si-based agent was used as antioxidant stress agents: The Si-based agent we co-developed is orally ingestible and features sustained hydrogen generation to inhibit oxidative stress production. Urine volume was measured by the aVSOP method3 after two weeks of treatment with the silicone-containing diet or silicone-free diet. Briefly, a roll of laminated filter paper, pretreated to turn urine dark purple, was rolled up under a water-repellent wire grid at a speed of 10 cm per h. Mice were housed for 4 days in cages with dimensions of 110 mm × 160 mm × 75 mm (H × D × W). Urination was counted, tracked, and converted to volume using software The diurnal polyuria index (inactive urine volume /daily urine volume) was calculated for the index corresponding to nocturnal polyuria in humans. Intrarenal NCC activation was assessed by phosphorylation of NCC using Western blotting.

First, renal oxidative stress was significantly increased in nocturnal polyuria mice compared to control mice (7.7±1.4 vs 11.6±2.1, p<0.05). Treatment with the silicon component significantly reduced oxidative stress in nocturnal polyuria mice group (11.6±2.1 vs 4.4±1.1, p<0.01). The mRNA expression of the subunit of NADPH oxidase, which regulates one of the pathways controlling the production of oxidative stress, was significantly up-regulated in the nocturnal polyuria mice group compared to the control mice group.
Second, treatment of the control mice with the Si-based agent did not significantly change DPi (0.12 vs 0.07, n.s.) or the daily urine volume (2220 µl vs 1991 µl, n.s.). On the other hand, administration of Si-based agent to the nocturnal polyuria mice group decreased the DPi (0.28 vs 0.17, p<0.01) and did not change the daily urine volume (2489 µl vs 2607 µl).
Finally, treatment of the nocturnal polyuria mice with silicone component decreased phosphorylated NCC (0.99 vs 0.77, p<0.05).

4-HNE-positive cells in the distal renal tubules and subunit of NADPH oxidase were significantly increased in nocturnal polyuria group compared with control (P<0.05), indicating the association between oxidative stress and nocturnal polyuria. Si-based agent decreased oxidative stresse and inhibited phosphorylation of NCC, finally improving nocturnal polyuria.

Oxidative stress causes nocturnal polyuria via intrarenal SPAK-NCC pathway .A newly co-developed antioxidant, Si-based agent, is a promising treatment for nocturnal polyuria by reducing oxidative stress.

Wang, C. et al. Low-dose L-NAME induces salt sensitivity associated with sustained increased blood volume and sodium-chloride cotransporter activity in rodents. Kidney Int 98, 1242–1252 (2020)
Inagaki, Y. et al. Novel hydrogen-producing Si-based agent reduces oxidative stress, and improves sperm motility and in vitro fertilization rate in varicocoele. Andrology 9, 376–383 (2021)
Takezawa, K. et al. Authentic role of ATP signaling in micturition reflex. Sci Rep 6, 19585 (2016)

Continence 2S2 (2022) 100328
DOI: 10.1016/j.cont.2022.100328