Succinate, increased in metabolic syndrome, activates GPR91 receptor signaling in urothelial cells

Succinate Regulates Exercise-Induced Muscle Remodelling by Boosting Satellite Cell Differentiation Through Succinate Receptor 1

BACKGROUND

Skeletal muscle remodelling can cause clinically important changes in muscle phenotypes. Satellite cells (SCs) myogenic potential underlies the maintenance of muscle plasticity. Accumulating evidence shows the importance of succinate in muscle metabolism and function. However, whether succinate can affect SC function and subsequently coordinate muscle remodelling to exercise remains unexplored.

METHODS

A mouse model of high-intensity interval training (HIIT) was used to investigate the effects of succinate on muscle remodelling and SC function by exercise capacity test and biochemical methods. Mice with succinate receptor 1 (SUCNR1)-specific knockout in SCs were generated as an in vivo model to explore the underlying mechanisms. RNA sequencing of isolated SCs was performed to identify molecular changes responding to succinate-SUCNR1 signalling. The effects of identified key molecules on the myogenic capacity of SCs were investigated using gain- and loss-of-function assays in vitro. To support the translational application, the clinical efficacy of succinate was explored in muscle-wasting mice.

RESULTS

After 21 days of HIIT, mice supplemented with 1.5% succinate exhibited striking gains in grip strength (+0.38 ± 0.04 vs. 0.26 ± 0.03 N, p < 0.001) and endurance (+276.70 ± 55.80 vs. 201.70 ± 45.31 s, p < 0.05), accompanied by enhanced muscle hypertrophy and neuromuscular junction regeneration (p < 0.001). The myogenic capacity of SCs was significantly increased in gastrocnemius muscle of mice supplemented with 1% and 1.5% succinate (+16.48% vs. control, p = 0.008; +47.25% vs. control, p < 0.001, respectively). SUCNR1-specific deletion in SCs abolished the modulatory influence of succinate on muscle adaptation in response to exercise, revealing that SCs respond to succinate-SUCNR1 signalling, thereby facilitating muscle remodelling. SUCNR1 signalling markedly upregulated genes associated with stem cell differentiation and phosphorylation pathways within SCs, of which p38α mitogen-activated protein kinase (MAPK; fold change = 6.7, p < 0.001) and protein kinase C eta (PKCη; fold change = 12.5, p < 0.001) expressions were the most enriched, respectively. Mechanistically, succinate enhanced the myogenic capacity of isolated SCs by activating the SUCNR1-PKCη-p38α MAPK pathway. Finally, succinate promoted SC differentiation (1.5-fold, p < 0.001), ameliorating dexamethasone-induced muscle atrophy in mice (p < 0.001).

CONCLUSIONS

Our findings reveal a novel function of succinate in enhancing SC myogenic capacity via SUCNR1, leading to enhanced muscle adaptation in response to exercise. These findings provide new insights for developing pharmacological strategies to overcome muscle atrophy-related diseases.

Association between novel anthropometric indices and overactive bladder: a population-based study

Background

Abdominal obesity is recognized as a key risk factor for developing OAB. However, traditional measures of obesity, such as the waist-to-height ratio (WHtR), waist circumference, and body mass index (BMI), may not sufficiently capture fat distribution in the body. This study aims to evaluate the relationship between novel anthropometric indices and OAB, providing a more accurate assessment of obesity-related risk factors.

Methods

The National Health and Nutrition Examination Survey (NHANES) data from 2007 to 2018 were utilized, comprising 27,560 participants. To assess the association and discriminative ability of novel anthropometric indices, including the Body Roundness Index (BRI), A Body Shape Index (ABSI), Waist-to-Weight Index (WWI), and Relative Fat Mass (RFM), with OAB, we employed multivariable logistic regression, restricted cubic spline (RCS) analysis, subgroup analysis, and receiver operating characteristic (ROC) curve methods.

Results

Multivariable logistic regression analysis indicated that higher levels of novel anthropometric indices were positively associated with OAB prevalence. One z-score increase in WWI, BRI, RFM, and ABSI was associated with a 16, 31, 57, and 5% higher likelihood of OAB, respectively. RCS analysis revealed a non-linear relationship between RFM and OAB. ROC analysis indicated that WWI (AUC = 0.680) and RFM (AUC = 0.661) provided better diagnostic accuracy than traditional measures such as BMI (AUC = 0.599). Subgroup analyses supported the robustness of these findings.

Conclusion

Novel anthropometric indices were positively associated with OAB prevalence. WWI and RFM demonstrated significantly better diagnostic value for OAB than BMI and WHtR. Future studies should investigate the potential of combining multiple anthropometric indices to improve predictive accuracy and conduct prospective studies to determine causality.

A Dataset for Constructing the Network Pharmacology of Overactive Bladder and Its Application to Reveal the Potential Therapeutic Targets of Rhynchophylline

Objectives: Network pharmacology is essential for understanding the multi-target and multi-pathway therapeutic mechanisms of traditional Chinese medicine. This study aims to evaluate the influence of database quality on target identification and to explore the therapeutic potential of rhynchophylline (Rhy) in treating overactive bladder (OAB). Methods: An OAB dataset was constructed through extensive literature screening. Using this dataset, we applied network pharmacology to predict potential targets for Rhy, which is known for its therapeutic effects but lacks a well-defined target profile. Predicted targets were validated through in vitro experiments, including DARTS and CETSA. Results: Our analysis identified Rhy as a potential modulator of the M3 receptor and TRPM8 channel in the treatment of OAB. Validation experiments confirmed the interaction between Rhy and these targets. Additionally, the GeneCards database predicted other targets that are not directly linked to OAB, corroborated by the literature. Conclusions: We established a more accurate and comprehensive dataset of OAB targets, enhancing the reliability of target identification for drug treatments. This study underscores the importance of database quality in network pharmacology and contributes to the potential therapeutic strategies for OAB.

Discovery of a SUCNR1 antagonist for potential treatment of diabetic nephropathy: In silico and in vitro studies

Diabetic nephropathy (DN) is one of the most severe complications of diabetes mellitus. Succinate Receptor 1 (SUCNR1), a member of the G-protein-coupled receptor (GPCR) family, represents a potential target for treatment of DN. Here, utilizing multi-strategy in silico virtual screening methods containing AlphaFold2 modelling, molecular dynamics (MD) simulation, ligand-based pharmacophore screening, molecular docking and machine learning-based similarity clustering, we successfully identified a novel antagonist of SUCNR1, AK-968/12117473 (Cpd3). Through extensive in vitro experiments, including dual-luciferase reporter assay, cellular thermal shift assay, immunofluorescence, and western blotting, we substantiated that Cpd3 could specifically target SUCNR1, inhibit the activation of NF-κB pathway, and ameliorate epithelial-mesenchymal transition (EMT) and extracellular matrix (ECM) deposition in renal tubular epithelial cells (NRK-52E) under high glucose conditions. Further in silico simulations revealed the molecular basis of the SUCNR1-Cpd3 interaction, and the in vitro metabolic stability assay indicated favorable drug-like pharmacokinetic properties of Cpd3. This work not only successfully pinpointed Cpd3 as a specific antagonist of SUCNR1 to serve as a promising candidate in the realm of therapeutic interventions for DN, but also provides a paradigm of dry-wet combined discovery strategies for GPCR-based therapeutics.

Unmasking the Metabolite Signature of Bladder Cancer: A Systematic Review

Bladder cancer (BCa) research relying on Omics approaches has increased over the last few decades, improving the understanding of BCa pathology and contributing to a better molecular classification of BCa subtypes. To gain further insight into the molecular profile underlying the development of BCa, a systematic literature search was performed in PubMed until November 2023, following the PRISMA guidelines. This search enabled the identification of 25 experimental studies using mass spectrometry or nuclear magnetic resonance-based approaches to characterize the metabolite signature associated with BCa. A total of 1562 metabolites were identified to be altered by BCa in different types of samples. Urine samples displayed a higher likelihood of containing metabolites that are also present in bladder tumor tissue and cell line cultures. The data from these comparisons suggest that increased concentrations of L-isoleucine, L-carnitine, oleamide, palmitamide, arachidonic acid and glycoursodeoxycholic acid and decreased content of deoxycytidine, 5-aminolevulinic acid and pantothenic acid should be considered components of a BCa metabolome signature. Overall, molecular profiling of biological samples by metabolomics is a promising approach to identifying potential biomarkers for early diagnosis of different BCa subtypes. However, future studies are needed to understand its biological significance in the context of BCa and to validate its clinical application.

Synthesis and secretion of Nerve Growth Factor is regulated by Nitric Oxide in bladder cells in vitro under a hyperglycemic environment

Urine samples of female patients with overactive bladder (OAB) are characterized by low levels of nerve growth factor (NGF) and elevated concentrations of nitric oxide (NO) compared to healthy controls. We therefore examined how NO might regulate NGF synthesis using rat bladder smooth muscle (SMCs) and urothelial (UROs) cells in culture. In UROs, incubation in hyperglycemic conditions to mimic insulin insensitivity present in the OAB cohort increased secretion of NO and concomitantly decreased NGF, except when the NO synthase inhibitor, l-NAME (1 mM) was present. Sodium nitroprusside (SNP) (300 μM, 24 h), a NO generator, decreased NGF levels and decreased cyclic GMP (cGMP) content, a process validated by the cGMP synthase inhibitor ODQ (100 μM). Alternatively, SNP increased mRNA of both NGF and matrix metalloproteinase-9 (MMP-9). MMP-9 knockout of UROs by Crispr-Cas9 potently decreased the effect of SNP on NGF, implying a dependent role of NO on MMP-9. On the other hand, matrix metalloproteinase-7 (MMP-7) activity was increased by SNP, which taken together with increase in NGF mRNA, suggests a compensatory mechanism. In SMCs, hyperglycemic conditions had the same effect on extracellular content of NO and NGF than in UROs. SNP also decreased NGF secretion but increased cGMP content. Stable permeable analogs of cGMP 8-(4-Chlorophenylthio)-cGMP (1 mM) and N2,2'-O-Dibutyryl-cGMP (3 mM) inhibited NGF release. NGF and MMP-9 mRNA expression was unchanged by SNP. Deletion of MMP-9 in SMCs by Crispr-Cas9 did not alter the effect of SNP. Finally, SNP decreased MMP-7 activity, diminishing the conversion of proNGF to NGF. These results demonstrate that enhanced NO secretion triggered by high glucose decreases NGF secretion through pathways unique for each cell type that involve cGMP and proteases MMP-7 and MMP-9. These results might help to explain our observations from the urine from patients with OAB associated with metabolic syndrome.

G protein-coupled receptor 55 activated by palmitoylethanolamide is associated with the development of nocturia associated with circadian rhythm disorders

AIMS

Bladder function is regulated by clock genes and dysregulation of circadian bladder function can cause nocturia. The blood concentration of palmitoylethanolamide (PEA), a fatty acid metabolite, changes with circadian rhythm. Clock gene abnormalities demonstrate the highest PEA levels during the sleep phase. PEA is a GPR55 agonist that influences urination; therefore, increased PEA during the sleep phase may cause nocturia. Herein, we investigated the function of GPR55 to evaluate the relationship between GPR55 and nocturia that evoked higher PEA during the sleep phase in patients with circadian rhythm disorders.

MAIN METHODS

Male C57BL/6 mice were used. GPR55 localization was evaluated by immunofluorescence staining, qRT-PCR, and western blotting. Variations in PEA-induced intracellular Ca2+ concentrations were measured in primary cultured mouse urothelial cells (UCs) using Ca2+ imaging. PEA-induced NGF and PGI2 release in UCs was measured by ELISA. The micturition reflex pathway after PEA administration was evaluated using immunofluorescence staining.

KEY FINDINGS

GPR55 was predominant in the UC layer. PEA induced release of Ca2+ from the endoplasmic reticulum into the UC cytoplasm. ELISA and immunofluorescence staining revealed that NGF and PGI2 were released from bladder UCs, stimulated the pontine micturition center in mice, and induced nocturia.

SIGNIFICANCE

The loss of regular circadian metabolizing rhythm in fatty acids causes higher blood PEA levels during the sleep phase. Binding of PEA to GPR55 in UC may activate the downstream processes of the micturition reflex, leading to nocturia. These findings suggest a new mechanism for nocturia and its potential as a therapeutic target.

An evolving view of complex II-noncanonical complexes, megacomplexes, respiration, signaling, and beyond

Mitochondrial complex II is traditionally studied for its participation in two key respiratory processes: the electron transport chain and the Krebs cycle. There is now a rich body of literature explaining how complex II contributes to respiration. However, more recent research shows that not all of the pathologies associated with altered complex II activity clearly correlate with this respiratory role. Complex II activity has now been shown to be necessary for a range of biological processes peripherally related to respiration, including metabolic control, inflammation, and cell fate. Integration of findings from multiple types of studies suggests that complex II both participates in respiration and controls multiple succinate-dependent signal transduction pathways. Thus, the emerging view is that the true biological function of complex II is well beyond respiration. This review uses a semichronological approach to highlight major paradigm shifts that occurred over time. Special emphasis is given to the more recently identified functions of complex II and its subunits because these findings have infused new directions into an established field.

Comprehensive analysis of the prognosis, tumor microenvironment, and immunotherapy response of SDHs in colon adenocarcinoma

Background

Succinate dehydrogenase (SDH), one of the key enzymes in the tricarboxylic acid cycle, is mainly found in the mitochondria. SDH consists of four subunits encoding SDHA, SDHB, SDHC, and SDHD. The biological function of SDH is significantly related to cancer progression. Colorectal cancer (CRC) is one of the most common malignant tumors globally, whose most common histological subtype is colon adenocarcinoma (COAD). However, the correlation between SDH factors and COAD remains unclear.

Methods

The data on pan-cancer was obtained from The Cancer Genome Atlas (TCGA) database. Kaplan-Meier survival analysis showed the prognostic ability of SDHs. The cBioPortal database reflected genetic variations of SDHs. The correlation analysis was conducted between SDHs and mitochondrial energy metabolism genes (MMGs) and the protein-protein interaction (PPI) network was built. Consequently, Univariate and Multivariate Cox Regression Analysis on SDHs and other clinical characteristics were conducted. A nomogram was established. The ssGSEA analysis visualized the association between SDHs and immune infiltration. Immunophenoscore (IPS) explored the correlation between SDHs and immunotherapy, and the correlation between SDHs and targeted therapy was investigated through Genomics of Drug Sensitivity in Cancer. Finally, qPCR and immunohistochemistry detected SDHs' expression.

Results

After assessing SDHs differential expression in pan-cancer, we found that SDHB, SDHC, and SDHD benefit COAD patients. The cBioPortal database demonstrated that SDHA was the top gene in mutation frequency rank. Correlation analysis mirrored a strong link between SDHs and MMGs. We formulated a nomogram and found that SDHB, SDHC, SDHD, and clinical characteristics correlated with COAD patients' survival. For T helper cells, Th2 cells, and Tem, SDHA, SDHB, SDHC, and SDHD were significantly enriched in the high expression group. Moreover, COAD patients with high SDHA expression were more suitable for immunotherapy. And COAD patients with different SDHs' expression have different sensitivity to targeted drugs. Further verifying the gene and protein expression levels of SDHs, we found that the tissues were consistent with the bioinformatics analysis.

Conclusions

Our study analyzed the expression and prognostic value of SDHs in COAD, explored the pathway mechanisms involved, and the immune cell correlations, indicating that SDHs might be biomarkers for COAD patients.

Urinary ATP Levels Are Controlled by Nucleotidases Released from the Urothelium in a Regulated Manner

Adenosine 5′-triphosphate (ATP) is released in the bladder lumen during filling. Urothelial ATP is presumed to regulate bladder excitability. Urinary ATP is suggested as a urinary biomarker of bladder dysfunctions since ATP is increased in the urine of patients with overactive bladder, interstitial cystitis or bladder pain syndrome. Altered urinary ATP might also be associated with voiding dysfunctions linked to disease states associated with metabolic syndrome. Extracellular ATP levels are determined by ATP release and ATP hydrolysis by membrane-bound and soluble nucleotidases (s-NTDs). It is currently unknown whether s-NTDs regulate urinary ATP. Using etheno-ATP substrate and HPLC-FLD detection techniques, we found that s-NTDs are released in the lumen of ex vivo mouse detrusor-free bladders. Capillary immunoelectrophoresis by ProteinSimple Wes determined that intraluminal solutions (ILS) collected at the end of filling contain ENTPD3 > ENPP1 > ENPP3 ≥ ENTPD2 = NT5E = ALPL/TNAP. Activation of adenylyl cyclase with forskolin increased luminal s-NTDs release whereas the AC inhibitor SQ22536 had no effect. In contrast, forskolin reduced and SQ22536 increased s-NTDs release in the lamina propria. Adenosine enhanced s-NTDs release and accelerated ATP hydrolysis in ILS and lamina propria. Therefore, there is a regulated release of s-NTDs in the bladder lumen during filling. Aberrant release or functions of urothelial s-NTDs might cause elevated urinary ATP in conditions with abnormal bladder excitability.

Vinpocetine Ameliorates Metabolic-Syndrome-Associated Bladder Overactivity in Fructose-Fed Rats by Restoring Succinate-Modulated cAMP Levels and Exerting Anti-Inflammatory Effects in the Bladder Detrusor Muscle

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.

Circulating pyruvate is a potent prognostic marker for critical COVID-19 outcomes

Background

Coronavirus-19 (COVID-19) disease is driven by an unchecked immune response to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus which alters host mitochondrial-associated mechanisms. Compromised mitochondrial health results in abnormal reprogramming of glucose metabolism, which can disrupt extracellular signalling. We hypothesized that examining mitochondrial energy-related signalling metabolites implicated in host immune response to SARS-CoV-2 infection would provide potential biomarkers for predicting the risk of severe COVID-19 illness.

Methods

We used a semi-targeted serum metabolomics approach in 273 patients with different severity grades of COVID-19 recruited at the acute phase of the infection to determine the relative abundance of tricarboxylic acid (Krebs) cycle-related metabolites with known extracellular signaling properties (pyruvate, lactate, succinate and α-ketoglutarate). Abundance levels of energy-related metabolites were evaluated in a validation cohort (n=398) using quantitative fluorimetric assays.

Results

Increased levels of four energy-related metabolites (pyruvate, lactate, a-ketoglutarate and succinate) were found in critically ill COVID-19 patients using semi-targeted and targeted approaches (p<0.05). The combined strategy proposed herein enabled us to establish that circulating pyruvate levels (p<0.001) together with body mass index (p=0.025), C-reactive protein (p=0.039), D-Dimer (p<0.001) and creatinine (p=0.043) levels, are independent predictors of critical COVID-19. Furthermore, classification and regression tree (CART) analysis provided a cut-off value of pyruvate in serum (24.54 µM; p<0.001) as an early criterion to accurately classify patients with critical outcomes.

Conclusion

Our findings support the link between COVID-19 pathogenesis and immunometabolic dysregulation, and show that fluorometric quantification of circulating pyruvate is a cost-effective clinical decision support tool to improve patient stratification and prognosis prediction.

Metabolic Syndrome and Overactive Bladder Syndrome May Share Common Pathophysiologies

Metabolic syndrome (MetS) is defined by a group of cardiovascular risk factors, including impaired glucose tolerance, central obesity, hypertension, and dyslipidemia. Overactive bladder (OAB) syndrome consists of symptoms such as urinary urgency, frequency, and nocturia with or without urge incontinence. The high prevalences of metabolic syndrome (MetS) and overactive bladder (OAB) worldwide affect quality of life and cause profound negative impacts on the social economy. Accumulated evidence suggests that MetS might contribute to the underlying mechanisms for developing OAB, and MetS-associated OAB could be a subtype of OAB. However, how could these two syndromes interact with each other? Based on results of animal studies and observations in epidemiological studies, we summarized the common pathophysiologies existing between MetS and OAB, including autonomic and peripheral neuropathies, chronic ischemia, proinflammatory status, dysregulation of nutrient-sensing pathways (e.g., insulin resistance at the bladder mucosa and excessive succinate intake), and the probable role of dysbiosis. Since the MetS-associated OAB is a subtype of OAB with distinctive pathophysiologies, the regular and non-specific medications, such as antimuscarinics, beta-3 agonist, and botulinum toxin injection, might lead to unsatisfying results. Understanding the pathophysiologies of MetS-associated OAB might benefit future studies exploring novel biomarkers for diagnosis and therapeutic targets on both MetS and OAB.

Effects of fatty acid metabolites on nocturia

Dysregulation of circadian rhythm can cause nocturia. Levels of fatty acid metabolites, such as palmitoylethanolamide (PEA), 9-hydroxy-10E,12Z-octadecadienoic acid (9-HODE), and 4-hydroxy-5E,7Z,10Z,13Z,16Z,19Z-docosahexaenoic acid (4-HDoHE), are higher in the serum of patients with nocturia; however, the reason remains unknown. Here, we investigated the circadian rhythm of fatty acid metabolites and their effect on voiding in mice. WT and Clock mutant (ClockΔ19/Δ19) mice, a model for nocturia with circadian rhythm disorder, were used. Levels of serum PEA, 9-HODE, and 4-HDoHEl were measured every 8 h using LC/MS. Voiding pattern was recorded using metabolic cages after administration of PEA, 9-HODE, and 4-HDoHE to WT mice. Levels of serum PEA and 9-HODE fluctuated with circadian rhythm in WT mice, which were lower during the light phase. In contrast, circadian PEA and 9-HODE level deteriorated or retreated in ClockΔ19/Δ19 mice. Levels of serum PEA, 9-HODE, and 4-HDoHE were higher in ClockΔ19/Δ19 than in WT mice. Voiding frequency increased in PEA- and 4-HDoHE-administered mice. Bladder capacity decreased in PEA-administered mice. The changes of these bladder functions in mice were similar to those in elderly humans with nocturia. These findings highlighted the novel effect of lipids on the pathology of nocturia. These may be used for development of biomarkers and better therapies for nocturia.

Priming, Triggering, Adaptation and Senescence (PTAS): A Hypothesis for a Common Damage Mechanism of Steatohepatitis

Understanding the pathomechanism of steatohepatitis (SH) is hampered by the difficulty of distinguishing between causes and consequences, by the broad spectrum of aetiologies that can produce the phenotype, and by the long time-span during which SH develops, often without clinical symptoms. We propose that SH develops in four phases with transitions: (i) priming lowers stress defence; (ii) triggering leads to acute damage; (iii) adaptation, possibly associated with cellular senescence, mitigates tissue damage, leads to the phenotype, and preserves liver function at a lower level; (iv) finally, senescence prevents neoplastic transformation but favours fibrosis (cirrhosis) and inflammation and further reduction in liver function. Escape from senescence eventually leads to hepatocellular carcinoma. This hypothesis for a pathomechanism of SH is supported by clinical and experimental observations. It allows organizing the various findings to uncover remaining gaps in our knowledge and, finally, to provide possible diagnostic and intervention strategies for each stage of SH development.

Deleterious impact of nerve growth factor precursor (proNGF) on bladder urothelial and smooth muscle cells

The nerve growth factor precursor (proNGF) activates p75^NTR receptor and promotes cell death in different tissues, yet this pathophysiological effect is not fully described in the bladder. The aim of this study was to identify the biological effect of proNGF/p75^NTR activation on urothelial and smooth muscle (SM) cells of rodents' bladder. Cell viability was assessed by MTT assay which showed a significant reduction in urothelial viability after 24 h of incubation with proNGF in culture medium [5 or 10 nM], an effect not seen in SM cells. Western blot analysis on cellular protein extracts showed increased expression of the transmembrane TNF-α and activation of RhoA in urothelial cells exposed to proNGF with no evidence of a nuclear translocation of NF-κB assessed by western blotting on nuclear extracts and immunofluorescence. The activation of p75^NTR-death domain related pathways in urothelial cells such as TNF-α or RhoA had a downstream effect on NO release and the junctional protein occludin, as estimated respectively by colorimetric and western blotting. On the other hand, proNGF did not induce TNF-α or RhoA expression in SM cells, but induced a significant NF-κB nuclear translocation. ProNGF had a different impact on SM as evidenced by a significant dose- and time-dependent increase in SM proliferation and migration examined by MTT test and cell migration assay. Together, our results indicate that activation of proNGF/p75^NTR axis induces degenerative changes to the urothelial layer impacting its barrier and signaling integrity, while promoting adaptive proliferative changes in detrusor SM cells that can interfere with the contractile phenotype essential for proper bladder function.

Receptor GPR91 contributes to voiding function and detrusor relaxation mediated by succinate

AIM

Succinate activates the receptor GPR91 identified in the bladder. The present study aims to unravel the mechanisms of bladder relaxation by succinate and how the receptor is involved in structural and functional changes of the bladder.

METHODS

Physiological recordings of bladder function were carried out by cystometry and organ bath from C57BL/6 mice, homozygous GPR91^-/- mice, and Sprague-Dawley (SD) rats. GPR91 expression was confirmed by polymerase chain reaction and tissue morphology was examined by light (Masson trichrome) and fluorescence microscopy. Nitric oxide (NO) and ATP secretion were measured.

RESULTS

Bladders of GPR91 KO mice had a greater mass to body weight ratio with a thicker bladder wall compared to C57BL/6 mice. They also displayed increased basal and maximal bladder pressures, and decreased intercontraction intervals, bladder capacity, micturition volume, and compliance. During cystometry, bladders of SD rats and C57BL/6 mice instilled with succinate (10 mM) showed signs of relaxation while bladders of GPR91 KO mice were unresponsive. Similarly, in organ bath, succinate relaxed bladder strips preincubated with carbachol, except GPR91 KO ones. Relaxation was stronger in the presence of urothelium and independent of NO synthesis. Bladder strips from all mice groups showed similar responses to KCl, carbachol, and electrical stimulation. In vitro, succinate increased NO secretion in urothelial cell culture of both C57BL6 and GPR91 KO mice while ATP secretion was potently decreased by succinate in C57BL6 culture only.

CONCLUSION

Succinate through GPR91 is essential to bladder structure and contraction. GPR91 relaxes the detrusor partially by decreasing urothelial ATP secretion.

Biomarkers for the toxicity of sublethal concentrations of triclosan to the early life stages of carps

Accumulation, contents of protein, non-enzymatic antioxidant glutathione (GSH and GSSG), lipid peroxidation product (melondialdehyde-MDA) and organic acids (fumarate, succinate, malate and citrate), and activities of neurological (acetylcholinesterase-AChE), detoxification (glutathione S-transferase-GST) and metabolic (lactate dehydrogenase-LDH, aspartate transaminase-AST and alanine transaminase-ALT) enzymes were recorded in the hatchlings of Cyprinus carpio, Ctenopharyngodon idella, Labeo rohita and Cirrhinus mrigala after 7 and 14 days exposure and 10 days post exposure (recovery period) to sublethal concentrations (0.005, 0.01, 0.02 and 0.05 mg/L) of triclosan, a highly toxic and persistent biocide used in personal care products. Accumulation was maximum between 7-14 days at 0.01 mg/L for C. carpio and L. rohita but at 0.005 mg/L for C. idella and C. mrigala. No triclosan was observed at 0.005 mg/L in C. carpio and C. mrigala after recovery. Significant decline in protein, glutathione and acetylcholinesterase but increase in glutathione S-transferase, lactate dehydrogenase, aspartate transaminase, alanine transaminase, melondialdehyde and organic acids over control during exposure continued till the end of recovery period. Integrated biomarker response (IBR) analysis depicted higher star plot area for glutathione and glutathione S-transferase during initial 7 days of exposure, thereafter, during 7-14 days of exposure and the recovery period, higher star plot area was observed for acetylcholinesterase, aspartate transaminase, alanine transaminase and organic acids. Higher star plot area was observed for protein in all the species throughout the study. The study shows that L. rohita is most sensitive and glutathione, acetylcholinesterase, aspartate transaminase and alanine transaminase are the biomarkers for the toxicity of sublethal concentrations of TCS.

Biochemical markers for prolongation of the acute stress of triclosan in the early life stages of four food fishes

In the present study, embryos of four food fishes viz. Cyprinus carpio, Ctenopharyngodon idella, Labeo rohita and Cirrhinus mrigala were given acute (96 h) exposure to their respective LC₀, LC₁₀ and LC₃₀ (causing 0, 10 and 30% mortality, respectively) concentrations of triclosan [TCS, 5-chloro-2-(2,4-dichlorophenoxy) phenol], a broad spectrum biocide. Bioaccumulation, contents of protein, non-enzymatic antioxidants (GSH and GSSG), MDA (lipid peroxidation product) and organic acids (fumarate, succinate, malate and citrate) along with the activities of AChE (neurological enzyme), GST (detoxification enzyme) and three metabolic enzymes (LDH, AST and ALT) were estimated after 48 and 96 h exposure and 10 days post exposure. Around 1/10 of the TCS in water got accumulated in the hatchlings after 96 h, increase over 48 h values was maximum at LC₀ (+195.30, +143.23 and + 140.75%) but minimum at LC₃₀ (+89.62, +84.26 and + 126.72%) for C. idella, L. rohita and C. mrigala, respectively. In C. carpio, TCS got accumulated only at LC₃₀ after 48 h but at all the concentrations after 96 h exposure. Contents of protein, GSH, GSSG and activity of AChE decreased but activities of GSH, LDH, AST and ALT and contents of MDA and organic acids increased concentration dependently in all the fishes. TCS declined by 85-90% but its toxic effects on biomolecules prolonged till the end of the recovery period. Such acute exposures are accidental but there is a need to evaluate biomarkers for prolongation of the stress of small concentrations especially LC₀ and LC₁₀ (causing negligible mortality) of lipophilic pollutants like TCS.

Urinary metabolomics predict the severity of overactive bladder syndrome in an aging female population

INTRODUCTION AND HYPOTHESIS

To identify urinary metabolites that can facilitate the diagnosis and the characterization of the underlying pathophysiology of the association between the overactive bladder syndrome (OAB) and metabolic syndrome.

METHODS

We used gas chromatography-mass spectrometry to compare the urinary metabolome of 20 females of 50-80 years of age with OAB to that of 20 controls of the same age group. We performed urinary metabolomic analysis and obtained serum markers of metabolic syndrome for each subject. Participants completed a clinical evaluation and validated self-reported questionnaires of lower urinary tract symptoms as well as a one-day voiding diary.

RESULTS

In the OAB subjects, we identified increased urinary levels of markers of mitochondrial dysfunction (itaconate, malate and fumarate), oxidative stress (L-pyroglutamate and α-hydroxyglutarate) and ketosis (α-hydroxybutyrate and α-hydroxyisobutyrate). The increased levels of these markers correlated significantly with the OAB symptoms score on questionnaires. We found, using a multiple linear regression model, that age, blood glucose and urine metabolites (malate, fumarate and α-hydroxyisobutyrate) were significant predictive factors of OAB severity. Fumarate had high sensitivity as a biomarker of OAB due to metabolic syndrome, based on a statistically significant receiver-operating characteristic (ROC) curve, indicating its potential as a diagnostic tool.

CONCLUSIONS

Altogether, these findings establish that urinary metabolites of mitochondrial dysfunction, ketosis and oxidative stress can be potential biomarkers of OAB severity and diagnosis.

Regulation of succinate dehydrogenase and role of succinate in cancer

Succinate dehydrogenase (SDH) has been classically considered a mitochondrial enzyme with the unique property to participate in both the citric acid cycle and the electron transport chain. However, in recent years, several studies have highlighted the role of the SDH substrate, i.e. succinate, in biological processes other than metabolism, tumorigenesis being the most remarkable. For this reason, SDH has now been defined a tumor suppressor and succinate an oncometabolite. In this review, we discuss recent findings regarding alterations in SDH activity leading to succinate accumulation, which include SDH mutations, regulation of mRNA expression, post-translational modifications and endogenous SDH inhibitors. Further, we report an extensive examination of the role of succinate in cancer development through the induction of epigenetic and metabolic alterations and the effects on epithelial to mesenchymal transition, cell migration and invasion, and angiogenesis. Finally, we have focused on succinate and SDH as diagnostic markers for cancers having altered SDH expression/activity.

Beta-3 Adrenoceptor Signaling Pathways in Urothelial and Smooth Muscle Cells in the Presence of Succinate

Succinate, an intermediate metabolite of the Krebs cycle, can alter the metabolomics response to certain drugs and controls an array of molecular responses in the urothelium through activation of its receptor, G-protein coupled receptor 91 (GPR91). Mirabegron, a β3-adrenergic receptor (β3-AR) agonist used to treat overactive bladder syndrome (OAB), increases intracellular cAMP in the detrusor smooth muscle cells (SMC), leading to relaxation. We have previously shown that succinate inhibits forskolin-stimulated cAMP production in urothelium. To determine whether succinate interferes with mirabegron-mediated bladder relaxation, we examined their individual and synergistic effect in urothelial-cell and SMC signaling. We first confirmed β3-AR involvement in the mirabegron response by quantifying receptor abundance by immunoblotting in cultured urothelial cells and SMC and cellular localization by immunohistochemistry in rat bladder tissue. Mirabegron increased cAMP levels in SMC but not in urothelial cells, an increase that was inhibited by succinate, suggesting that it impairs cAMP-mediated bladder relaxation by mirabegron. Succinate and mirabegron increased inducible nitric oxide synthesis and nitric oxide secretion only in urothelial cells, suggesting that its release can indirectly induces SMC relaxation. Succinate exposure decreased the expression of β3-AR protein in whole bladder in vivo and in SMC in vitro, indicating that this metabolite may lead to impaired pharmacodynamics of the bladder. Together, our results demonstrate that increased levels of succinate in settings of metabolic stress (e.g., the metabolic syndrome) may lead to impaired mirabegron and β3-AR interaction, inhibition of cAMP production, and ultimately requiring mirabegron dose adjustment for its treatment of OAB related to these conditions.