Succinate and its receptor, the G protein-coupled receptor 91 (GPR91), have pathological implications in metabolic syndrome (MetS) and its associated bladder dysfunction, particularly in decreasing bladder cAMP levels and promoting proinflammation. Using fructose-fed rats (FFRs), a rat model of MetS, we investigate the effects of vinpocetine (a phosphodiesterase-1 inhibitor) and celecoxib (a selective cyclooxygenase-2 inhibitor) on MetS-associated bladder overactivity. Phenotypes of the overactive bladder, including increased micturition frequency and a shortened intercontractile interval in cystometry, were observed in FFRs, together with elevated succinate levels in the liver and serum and the downregulation of GPR91 in the liver and urinary bladder. Treatments with vinpocetine and celecoxib improved tissue fibrosis and ameliorated the overexpression of the inflammatory cytokines, such as IL-1β, in the liver and bladder. In bladder organ bath studies, vinpocetine, but not celecoxib, treatment restored the contraction and relaxation responses of the detrusor muscle strip in response to KCl, carbachol, and forskolin stimulation. At a molecular level, vinpocetine and celecoxib treatments modulated the downstream messengers of GPR91 (i.e., ERK1/2 and JNK), suppressed NF-κB and IL-1β expressions in the bladder, and prevented the fibrogenesis observed in FFRs. The exogenous application of succinate to a bladder organ bath significantly reduced the forskolin-induced cAMP production by the detrusor muscle, which was notably restored in the presence of vinpocetine. Together, these results suggest that vinpocetine may alleviate the MetS-associated bladder overactivity by restoring the succinate-modulated detrusor cAMP production and exerting the anti-inflammatory effects in the bladder detrusor muscle.
Keywords: fructose; metabolic syndrome; overactive bladder; succinate; vinpocetine.