Longitudinal studies of time-dependent changes in both bladder and erectile function after streptozotocin-induced diabetes in Fischer 344 male rats

Methylglyoxal and Advanced Glycation End Products (AGEs): Targets for the Prevention and Treatment of Diabetes-Associated Bladder Dysfunction?

Methylglyoxal (MGO) is a highly reactive α-dicarbonyl compound formed endogenously from 3-carbon glycolytic intermediates. Methylglyoxal accumulated in plasma and urine of hyperglycemic and diabetic individuals acts as a potent peptide glycation molecule, giving rise to advanced glycation end products (AGEs) like arginine-derived hydroimidazolone (MG-H1) and carboxyethyl-lysine (CEL). Methylglyoxal-derived AGEs exert their effects mostly via activation of RAGE, a cell surface receptor that initiates multiple intracellular signaling pathways, favoring a pro-oxidant environment through NADPH oxidase activation and generation of high levels of reactive oxygen species (ROS). Diabetic bladder dysfunction is a bothersome urological complication in patients with poorly controlled diabetes mellitus and may comprise overactive bladder, urge incontinence, poor emptying, dribbling, incomplete emptying of the bladder, and urinary retention. Preclinical models of type 1 and type 2 diabetes have further confirmed the relationship between diabetes and voiding dysfunction. Interestingly, healthy mice supplemented with MGO for prolonged periods exhibit in vivo and in vitro bladder dysfunction, which is accompanied by increased AGE formation and RAGE expression, as well as by ROS overproduction in bladder tissues. Drugs reported to scavenge MGO and to inactivate AGEs like metformin, polyphenols, and alagebrium (ALT-711) have shown favorable outcomes on bladder dysfunction in diabetic obese leptin-deficient and MGO-exposed mice. Therefore, MGO, AGEs, and RAGE levels may be critically involved in the pathogenesis of bladder dysfunction in diabetic individuals. However, there are no clinical trials designed to test drugs that selectively inhibit the MGO-AGEs-RAGE signaling, aiming to reduce the manifestations of diabetes-associated bladder dysfunction. This review summarizes the current literature on the role of MGO-AGEs-RAGE-ROS axis in diabetes-associated bladder dysfunction. Drugs that directly inactivate MGO and ameliorate bladder dysfunction are also reviewed here.

Potential role of oxidative stress in the pathogenesis of diabetic bladder dysfunction

Diabetes mellitus is a chronic metabolic disease, posing a considerable threat to global public health. Treating systemic comorbidities has been one of the greatest clinical challenges in the management of diabetes. Diabetic bladder dysfunction, characterized by detrusor overactivity during the early stage of the disease and detrusor underactivity during the late stage, is a common urological complication of diabetes. Oxidative stress is thought to trigger hyperglycaemia-dependent tissue damage in multiple organs; thus, a growing body of literature has suggested a possible link between functional changes in urothelium, muscle and the corresponding innervations. Improved understanding of the mechanisms of oxidative stress could lead to the development of novel therapeutics to restore the redox equilibrium and scavenge excessive free radicals to normalize bladder function in patients with diabetes.

Established and emerging treatments for diabetes-associated lower urinary tract dysfunction

Dysfunction of the lower urinary tract (LUT) including urinary bladder and urethra (and prostate in men) is one of the most frequent complications of diabetes and can manifest as overactive bladder, underactive bladder, urinary incontinence, and as aggravated symptoms of benign prostate hyperplasia. We have performed a selective literature search to review existing evidence on efficacy of classic medications for the treatment of LUT dysfunction in diabetic patients and animals, i.e., α1-adrenoceptor and muscarinic receptor antagonists, β3-adrenoceptor agonists, and phosphodiesterase type 5 inhibitors. Generally, these agents appear to have comparable efficacy in patients and/or animals with and without diabetes. We also review effects of antidiabetic medications on LUT function. Such studies have largely been performed in animal models. In the streptozotocin-induced models of type 1 diabetes, insulin can prevent and reverse alterations of morphology, function, and gene expression patterns in bladder and prostate. Typical medications for the treatment of type 2 diabetes have been studied less often, and the reported findings are not yet sufficient to derive robust conclusions. Thereafter, we review animal studies with emerging medications perhaps targeting diabetes-associated LUT dysfunction. Data with myoinositol, daidzein, and with compounds that target oxidative stress, inflammation, Rac1, nerve growth factor, angiotensin II receptor, serotonin receptor, adenosine receptor, and soluble guanylyl cyclase are not conclusive yet, but some hold promise as potential treatments. Finally, we review nonpharmacological interventions in diabetic bladder dysfunction. These approaches are relatively new and give promising results in preclinical studies. In conclusion, the insulin data in rodent models of type 1 diabetes suggest that diabetes-associated LUT function can be mostly or partially reversed. However, we propose that considerable additional experimental and clinical studies are needed to target diabetes itself or pathophysiological changes induced by chronic hyperglycemia for the treatment of diabetic uropathy.

Daidzein attenuates urinary bladder dysfunction in streptozotocin-induced diabetes in rats by NOX-4 and RAC-1 inhibition

Reactive oxygen species via NADPH oxidase (NOX) activation are involved in the pathogenesis of many disease conditions such as diabetes and its complications. In the present study, we have examined the effect of daidzein in the management of diabetic cystopathy. Diabetes was induced in male Sprague Dawley rats via intraperitoneal injection of streptozotocin (STZ) at a dose of 55 mg/kg. After 6 weeks of diabetes induction, animals were treated with daidzein orally at a dose of 25, 50, and 100 mg/kg for 4 weeks. Diabetic animals showed increase (p < 0.001) in bladder capacity (4.32 ± 0.43 mL) and residual volume (2.53 ± 0.19 mL) when compared with normal control animals (2.10 ± 0.40 mL and 0.51 ± 0.12 mL res). Treatment with daidzein at dose of 50 and 100 mg/kg significantly reduced the elevated bladder capacity (2.91 ± 0.11 mL, p < 0.01 and 2.65 ± 1.13 mL, p < 0.001) and residual volume (1.40 ± 0.15 mL, p < 0.001 and 1.15 ± 0.05 mL, p < 0.001). Daidzein-treated animals also showed improvement in voiding efficiency. Elevated threshold and baseline pressure were also found to be reduced in diabetic animals after 4 weeks of daidzein treatment. Daidzein treatment also prevented the loss of antioxidant enzymes in the urinary bladder and also reduced the expression of NOX-4 and RAC-1 in the bladder. From the results, it can be concluded that daidzein showed a beneficial effect on urinary bladder dysfunction in diabetic animals.

Hyperglycemic memory in the rat bladder detrusor is associated with a persistent hypomethylated state

Hyperglycemic memory is associated with several complications of diabetes. Although there is some physiological evidence that this phenomenon occurs with diabetic bladder dysfunction (DBD), there have been no studies in bladder that provide evidence of hyperglycemic memory at the molecular/biochemical level. In the present studies, we determined the effects of long-term diabetes on the metabolome of bladder detrusor in a rat model of streptozotocin-induced type-1-diabetes and the ability of insulin treatment to normalize metabolic changes. These studies demonstrated that although insulin reversed a majority of the metabolic changes caused by diabetes, with long-term diabetes there was a persistent decrease in the methylation index (indicated by a reduced ratio of S-adenosylmethionine to S-adenosyl homocysteine) after insulin treatment. We confirmed a "hypomethylated environment" develops in diabetic detrusor by demonstrating an overall reduction in methylated detrusor DNA that is only partially reversed with glycemic control. Furthermore, we confirmed that this hypomethylated environment is associated with epigenetic changes in the detrusor genome, which are again mostly, but not completely, reversed with glycemic control. Overall our studies provide strong molecular evidence for a mechanism by which diabetes alters methylation status and gene expression in the detrusor genome, and that these epigenetic modifications contribute to hyperglycemic memory. Our work suggests novel treatment strategies for diabetic patients who have attained glycemic control but continue to experience DBD. For example, epigenomic data can be used to identify "actionable gene targets" for its treatment and would also support a rationale for approaches that target the hypomethylation index.

Alterations in the phosphodiesterase type 5 pathway and oxidative stress correlate with erectile function in spontaneously hypertensive rats

To explore how alterations in the phosphodiesterase type 5 (PDE5) signalling pathway and oxidative stress correlate with changes in the expression of relaxation and contraction molecules and erectile dysfunction (ED) in the corpus cavernosum smooth muscle (CCSM) of spontaneously hypertensive rats (SHR). In this study, SHR and Wistar‐Kyoto (WKY) rats were used. Erectile function was determined by apomorphine test and electrical stimulation (ES) of cavernous nerve. Masson's trichrome staining and confocal microscopy were performed. Nitric oxide synthase (NOS), PDE5, phosphorylated‐PDE5 and α1‐adrenergic receptor (α1AR) were determined by RT‐PCR and Western blotting while oxidative stress in CC was determined by colorimetric analysis. SHR exhibited obvious ED. CC of SHR showed less SM but more collagen fibres. The expression of NOS isoforms in SHR was significantly decreased while all α1AR isoforms were increased. In addition, PDE5 and phosphorylated‐PDE5 were down‐regulated and its activity attenuated in the hypertensive rats. Meanwhile, the SHR group suffered oxidative stress, which may be modulated by endoplasmic reticulum stress and NADPH oxidase up‐regulation. Dysregulation of NOS and α1AR, histological changes and oxidative stress in CC may be associated with the pathophysiology of hypertension‐induced ED. In addition, PDE5 down‐regulation may lead to the decreased efficacy of PDE5 inhibitors in some hypertensive ED patients and treatment of oxidative stress could be used as a new therapeutic target for this type of ED.

miR-363 Alleviates Detrusor Fibrosis via the TGF-β1/Smad Signaling Pathway by Targeting Col1a2 in Rat Models of STZ-Induced T2DM

Dysregulated expression of microRNAs (miRNAs or miRs) has been implicated in the pathophysiology of type 2 diabetes mellitus (T2DM). However, their underlying role in the complication of detrusor fibrosis remains poorly understood. Therefore, this study aimed to examine the potential functional relevance of miR-363 in detrusor fibrosis of rats with streptozotocin (STZ)-induced T2DM through the predicted target gene collagen type I alpha 2 (Col1a2). Immunohistochemical analysis found an increase in the positive expression of collagen type III alpha 1 (Col3a1) and Col1a2 in detrusor tissues, where miR-363 expression was decreased. Next, gain- and loss-of-function experiments were performed to clarify the effects of miR-363 and Col1a2 on the activities of bladder detrusor cells. Of note, binding affinity between miR-363 and Col1a2 was verified by a dual-luciferase reporter gene assay and RNA immunoprecipitation (RIP) assay. Upregulated miR-363 inhibited Col1a2 expression, which led to increased expression of B-cell lymphoma 2 (Bcl-2) and Smad7 and accelerated cell viability, along with decreases in cell apoptosis and Col3a1, Bcl-2-associated X protein (Bax), transforming growth factor (TGF)-β1, and Smad4 expressions. In conclusion, miR-363 upregulation reduces detrusor fibrosis in rats with STZ-induced T2DM through suppression of the TGF-β1/Smad signaling pathway by targeting Col1a2. Therefore, our study provided further insights for the development of new therapeutic targets for T2DM.

Erectile dysfunction attenuation by naringenin in streptozotocin-induced diabetic rats

Diabetes mellitus is associated with sexual dysfunction, which leads to infertility in animal models. The aim of this study was to evaluate sexual behavior in diabetic rats administered with naringenin. Rats were classified into five groups including healthy controls, those with STZ-induced diabetes, and those with STZ-induced diabetes then treated with 25, 50, or 100 mg kg^-1  day^-1 of naringenin. Male rats were introduced to sexually receptive females, and data were collected regarding sexual behavior and erectile activity. Blood samples were taken and histopathological analyses were carried out. ANOVA and the Student-Newman-Keuls t test were used for statistical comparisons. Sexual behavioral, mount latency, intromission latency, ejaculation latency, and postejaculatory interval were significantly increased in diabetic rates compared with controls (p < 0.001). The NG-treated rats showed a significant improvement in testosterone and cyclic guanosine monophosphate levels, and testicular oxidative stress and inflammatory biomarkers were corrected in a dose-dependent manner compared with controls. The treatment protocol used in this study led to the elimination of sexual impairment resulting from DM, and naringenin showed significant antiinflammatory and antioxidant effects in testicular cells. PRACTICAL APPLICATIONS: Erectile dysfunction occurs in more than 50% of men who are diagnosed with diabetes mellitus. The prevalence of ED is 25% in patients younger than 50 years and 75% in those older than 50 years. Chronic DM leads to oxidative stress, which has significant effects on sexual behavior, spermatogenesis, and sperm biology. Phenolic compounds have been reported to reduce streptozotocin-induced oxidative stress in experimental animal models. In addition, they have significant effects on the generation of sperm (spermatogenesis), which is involved in the pathogenesis of chronic DM. Our study was designed to examine the effect of naringenin, a flavone flavonoid, on oxidative stress, the inflammatory process, sexual behavior, erectile activity through spermatogenesis, and cavernous cyclic guanosine monophosphate in streptozotocin-induced diabetic rats.

Urothelial MaxiK-activity regulates mucosal and detrusor metabolism

There is increasing evidence for a role of MaxiK potassium channel-activity in regulating the metabolism and intracellular signaling of non-contractile bladder mucosal tissues. At present however no studies have determined the impact of urothelial MaxiK-activity on overall bladder metabolism. To address this we have investigated the effect of bladder lumen instillation of the MaxiK inhibitor, iberiotoxin (IBTX), on mucosal and detrusor metabolism using metabolomics. Since IBTX does not cross plasma membranes, when instilled into the bladder lumen it would only effect urothelially expressed MaxiK-activity. Surprisingly IBTX treatment caused more effect on the metabolome of the detrusor than mucosa (the levels of 17% of detected detrusor metabolites were changed in comparison to 6% of metabolites in mucosal tissue following IBTX treatment). In mucosal tissues, the major effects can be linked to mitochondrial-associated metabolism whereas in detrusor there were additional changes in energy generating pathways (such as glycolysis and the TCA cycle). In the detrusor, changes in metabolism are potentially a result of IBTX effecting MaxiK-linked signaling pathways between the mucosa and detrusor, secondary to changes in physiological activity or a combination of both. Overall we demonstrate that urothelial MaxiK-activity plays a significant role in determining mitochondrially-associated metabolism in mucosal tissues, which effects the metabolism of detrusor tissue. Our work adds further evidence that the urothelium plays a major role in determining overall bladder physiology. Since decreased MaxiK-activity is associated with several bladder pathophysiology's, the changes in mucosal metabolism reported here may represent novel downstream targets for therapeutic interventions.

Altered blood flow in cerebral perforating arteries of rat models of diabetes: A synchrotron radiation microangiographic study toward clinical evaluation of white matter hyperintensities

AIM

As altered blood flow in the cerebral perforating arteries (PA) might be related to development of cerebral white matter hyperintensities, we examined whether the hemodynamic relationship of the PA and middle cerebral artery (MCA) is altered in rat models of diabetes, compared with normal rats and a rat model of sinoatrial denervation (blood pressure fluctuation model).

METHODS

We used microangiography with monochromatic synchrotron radiation to measure the diameters of the PA and MCA at 4.5 μm resolution in five groups of rats: (i) Long-Evans Tokushima Otsuka (LETO); (ii) Otsuka Long-Evans Tokushima Fatty (a model of type 2 diabetes with obesity); (iii) LETO with sinoaortic denervation (LETO + SAD); (iv) F344; and (v) F344 + streptozotocin (a model of type 1 diabetes).

RESULTS

Compared with LETO, Otsuka Long-Evans Tokushima Fatty rats showed a significant reduction in the diameter of both PA and MCA, though the PA/MCA diameter ratio was unchanged. In contrast, compared with LETO, LETO + SAD rats showed an increased MCA diameter, and the PA/MCA diameter ratio was decreased. Compared with F344 rats, the MCA diameter was increased in F344 + streptozotocin rats, and the PA/MCA diameter ratio was decreased. Scatter diagrams showed that the diameters of the PA and MCA were essentially independent of each other in the two types of diabetic models.

CONCLUSION

PA were consistently visualized at high resolution by means of microangiography using synchrotron radiation. The present results show that rat diabetic models exhibit changes in PA diameter and PA/MCA diameter ratio, which might be related to the development of diabetes-associated cerebral white matter hyperintensities.

Novel insights into development of diabetic bladder disorder provided by metabolomic analysis of the rat nondiabetic and diabetic detrusor and urothelial layer

There are at present no published studies providing a global overview of changes in bladder metabolism resulting from diabetes. Such studies have the potential to provide mechanistic insight into the development of diabetic bladder disorder (DBD). In the present study, we compared the metabolome of detrusor and urothelial layer in a 1-mo streptozotocin-induced rat model of type 1 diabetes with nondiabetic controls. Our studies revealed that diabetes caused both common and differential changes in the detrusor and urothelial layer's metabolome. Diabetes resulted in similar changes in the levels of previously described diabetic markers in both tissues, such as glucose, lactate, 2-hydroxybutyrate, branched-chain amino acid degradation products, bile acids, and 1,5-anhydroglucitol, as well as markers of oxidative stress. In the detrusor (but not the urothelial layer), diabetes caused activation of the pentose-phosphate and polyol pathways, concomitant with a reduction in the TCA cycle and β-oxidation. Changes in detrusor energy-generating pathways resulted in an accumulation of sorbitol that, through generation of advanced glycation end products, is likely to play a central role in the development of DBD. In the diabetic urothelial layer there was decreased flux of glucose via glycolysis and changes in lipid metabolism, particularly prostaglandin synthesis, which also potentially contributes to detrusor dysfunction.

Diabetes attenuates urothelial modulation of detrusor contractility and spontaneous activity

OBJECTIVES

To investigate the effect of diabetes on urothelial modulation of bladder contractility.

METHODS

Bladder strips (urothelium intact or denuded) were prepared from 8-week-old streptozotocin-induced diabetic (n = 19) and non-diabetic control rats (n = 10). The effect of modulators of MaxiK (iberiotoxin and tetraethylammonium) and Kv7 (XE991 and retigabine) potassium channel activity were investigated for their effects on both carbachol-induced force generation and spontaneous contractile activity.

RESULTS

In bladder strips from non-diabetic animals, the presence of the urothelium resulted in marked sensitivity to carbachol-induced force generation by modulators of MaxiK and Kv7 channel activity, whereas in the diabetic animal urothelial sensitivity to these agents was significantly diminished. Urothelial-intact bladder strips from non-diabetic animals were more sensitive to modulators of Kv7 activity in reducing the amplitude of spontaneous phasic contractions than urothelial-denuded bladder strips, whereas in diabetic animals the presence or absence of the urothelium did not alter the sensitivity to modulators of Kv7 activity. Spontaneous activity in the presence of tetraethylammonium was not affected by the urothelium in bladder strips from either diabetic or non-diabetic animals.

CONCLUSIONS

The presence of the urothelium in bladders from non-diabetic animals modulates the activity of potassium blockers to affect bladder contractility, whereas in the diabetic bladder this effect is attenuated. These findings could help to explain the lack of success of pharmaceutical treatments targeting potassium channels to treat bladder pathology in patients with diseases imparing urothelial function.

The effect of methamphetamine on an animal model of erectile function

In the US methamphetamine is considered a first-line treatment for attention-deficit hyperactivity disorder. It is also a common drug of abuse. Reports in patients and abusers suggest its use results in impotence. The efficacy of phosphodiesterase-5 inhibitors (PDE5i) to restore erectile function in these patient groups also has not been determined. In these studies, we determined if the rat is a suitable animal model for the physiological effects of methamphetamine on erectile function, and if a PDE5i (tadalafil) has an effect on erectile function following methamphetamine treatment. In acute phase studies, erectile function was measured in male Sprague-Dawley rats, before and after administration of 10 mg/kg methamphetamine i.p. Chronically treated animals received escalating doses of methamphetamine [2.5 mg/kg (1st week), 5 mg/kg (2nd week), and 10 mg/kg (3rd week)] i.p. daily for 3 weeks and erectile function compared with untreated controls. The effect of co-administration of tadalafil was also investigated in rats acutely and chronically treated with methamphetamine. Erectile function was determined by measuring the intracorporal pressure/blood pressure ratio (ICP/BP) following cavernous nerve stimulation. In both acute and chronic phase studies, we observed a significant increase in the rates of spontaneous erections after methamphetamine administration. In addition, following stimulation of the cavernous nerve at 4 and 6 mA, there was a significant decrease in the ICP/BP ratio (approximately 50%), indicative of impaired erectile function. Tadalafil treatment reversed this effect. In chronically treated animals, the ICP/BP ratio following 4 and 6 mA stimulation decreased by approximately 50% compared with untreated animals and erectile dysfunction (ED) was also reversed by tadalafil. Overall, our data suggest that the rat is a suitable animal model to study the physiological effect of methamphetamine on erectile function. Our work also provides a rationale for treating patients that report ED associated with therapeutics-containing methamphetamine or amphetamine with PDE5i.

Autonomic neuropathy in experimental models of diabetes mellitus

Autonomic neuropathy complicates diabetes by increasing patient morbidity and mortality. Surprisingly, considering its importance, development and exploitation of animal models has lagged behind the wealth of information collected for somatic symmetrical sensory neuropathy. Nonetheless, animal studies have resulted in a variety of insights into the pathogenesis, neuropathology, and pathophysiology of diabetic autonomic neuropathy (DAN) with significant and, in some cases, remarkable correspondence between rodent models and human disease. Particularly in the study of alimentary dysfunction, findings in intrinsic intramural ganglia, interstitial cells of Cajal and the extrinsic parasympathetic and sympathetic ganglia serving the bowel vie for recognition as the chief mechanism. A body of work focused on neuropathologic findings in experimental animals and human subjects has demonstrated that axonal and dendritic pathology in sympathetic ganglia with relative neuron preservation represents one of the neuropathologic hallmarks of DAN but it is unlikely to represent the entire story. There is a surprising selectivity of the diabetic process for subpopulations of neurons and nerve terminals within intramural, parasympathetic, and sympathetic ganglia and innervation of end organs, afflicting some while sparing others, and differing between vascular and other targets within individual end organs. Rather than resulting from a simple deficit in one limb of an effector pathway, autonomic dysfunction may proceed from the inability to integrate portions of several complex pathways. The selectivity of the diabetic process appears to confound a simple global explanation (e.g., ischemia) of DAN. Although the search for a single unifying pathogenetic hypothesis continues, it is possible that autonomic neuropathy will have multiple pathogenetic mechanisms whose interplay may require therapies consisting of a cocktail of drugs. The role of multiple neurotrophic substances, antioxidants (general or pathway specific), inhibitors of formation of advanced glycosylation end products and drugs affecting the polyol pathway may be complex and therapeutic elements may have both salutary and untoward effects. This review has attempted to present the background and current findings and hypotheses, focusing on autonomic elements including and beyond the typical parasympathetic and sympathetic nervous systems to include visceral sensory and enteric nervous systems.

Time-dependent changes of erectile function in diabetic rats: role of systemic endothelial dysfunction

PURPOSE

To understand the potential contribution of systemic endothelial dysfunction to diabetic erectile dysfunction, and the time course of erectile dysfunction in a streptozotocin (STZ)-induced diabetic rat model.

MATERIALS AND METHODS

Among 84, 12-week-old Sprague-Dawley rats, 48 rats received intraperitoneal STZ and were classified into six groups of diabetes by the period of observation (n=8). The remaining 36 rats were also grouped, similar to the diabetic groups, and served as normal controls. After 4, 6, 8, 10, 12, and 14 weeks of diabetes (serum glucose >250 mg%), all rats underwent cavernous nerve electrostimulation (3 V, 0.2 ms, 30 sec) with varying frequency (2.5~20 Hz). At the end of the study, 8 ml of blood was taken to measure the plasma markers of endothelial function and glycosylated hemoglobin.

RESULTS

Compared to the control, significant reduction of erectile response was not observed until eight weeks after diabetes induction. The diabetic rats had elevation of all plasma markers except for l-selectin. However, the correlation analysis revealed that no systemic marker of endothelial dysfunction was associated with change in erectile function. Only the level of hemoglobin A1c (HbA1c) showed a modest but significant correlation with the peak intracavernosal pressure, corrected by mean arterial pressure (ρ=-0.183), and the area under the curve of the cavernosometry (ρ=-0.207).

CONCLUSIONS

Significant reduction of erectile function was not observed until eight weeks after the induction of diabetes. Except for HbA1c, there was no systemic marker associated with endothelial activation and erectile function in the diabetic rats.

Smooth muscle myosin expression, isoform composition, and functional activities in rat corpus cavernosum altered by the streptozotocin-induced type 1 diabetes

Diabetes mellitus (DM) is a quite common chronic disease, and the prevalence of erectile dysfunction (ED) is three times higher in this large population. Although diabetes-related ED has been studied extensively, the actin-myosin contractile apparatus was not examined. The mRNAs encoding smooth muscle myosin (SMM) heavy chains (MHC) and essential light chains (LC(17)) exist as several different alternatively spliced isoforms with distinct contractile properties. Recently, we provided novel data that blebbistatin (BLEB), a specific myosin II inhibitor, potently relaxed corpus cavernosum smooth muscle (CCSM). In this study, we examine whether diabetes alters SMM expression, alternative splicing, and/or functional activities, including sensitivity to BLEB. By using streptozotocin (STZ)-induced 2-mo diabetic rats, functional activities were tested in vivo by intracavernous pressure (ICP) recording during cavernous nerve stimulation and in vitro via organ bath contractility studies. SMM isoform composition was analyzed by competitive RT-PCR and total SMM, myocardin, and embryonic SMM (SMemb) expression by real-time RT-PCR. Results revealed that the blood glucose level of STZ rats was 407.0 vs. 129.5 mg/dl (control). STZ rats exhibited ED confirmed by significantly increased CCSM contractile response to phenylephrine and decreased ICP response. For STZ rats, SM-B, LC(17a) and SM2 isoforms, total SMM, and myocardin expression increased, whereas SM-A, LC(17b), and SM1 isoforms were decreased, with SMemb unchanged. BLEB was significantly more effective in relaxing STZ CCSM both in vitro and in vivo. Thus we demonstrated a novel diabetes-specific effect on alternative splicing of the SMM heavy chain and essential light chain genes to a SMM isoform composition favoring a heightened contractility and ED. A switch to a more contractile phenotype was supported further by total SMM expression increase. Moreover, the change in CCSM phenotype was associated with an increased sensitivity to BLEB, which may serve as a novel pharmacotherapy for ED.

Functional, morphological and molecular characterization of bladder dysfunction in streptozotocin-induced diabetic mice: evidence of a role for L-type voltage-operated Ca2+ channels

BACKGROUND AND PURPOSE

Diabetic cystopathy is one of the most common and incapacitating complications of diabetes mellitus. This study aimed to evaluate the functional, structural and molecular alterations of detrusor smooth muscle (DSM) in streptozotocin-induced diabetic mice, focusing on the contribution of Ca(2+) influx through L-type voltage-operated Ca(2+) channels (L-VOCC).

EXPERIMENTAL APPROACH

Male C57BL/6 mice were injected with streptozotocin (125 mg·kg(-1) ). Four weeks later, contractile responses to carbachol, α,β-methylene ATP, KCl, extracellular Ca(2+) and electrical-field stimulation were measured in urothelium-intact DSM strips. Cystometry and histomorphometry were performed, and mRNA expression for muscarinic M(2) /M(3) receptors, purine P2X1 receptors and L-VOCC in the bladder was determined.

KEY RESULTS

Diabetic mice exhibited higher bladder capacity, frequency, non-void contractions and post-void pressure. Increased bladder weight, wall thickness, bladder volume and neural tissue were observed in diabetic bladders. Carbachol, α,β-methylene ATP, KCl, extracellular Ca(2+) and electrical-field stimulation all produced greater DSM contractions in diabetic mice. The L-VOCC blocker nifedipine almost completely reversed the enhanced DSM contractions in bladders from diabetic animals. The Rho-kinase inhibitor Y27632 had no effect on the enhanced carbachol contractions in the diabetic group. Expression of mRNA for muscarinic M(3) receptors and L-VOCC were greater in the bladders of diabetic mice, whereas levels of M(2) and P2X1 receptors remained unchanged.

CONCLUSIONS AND IMPLICATIONS

Diabetic mice exhibit features of urinary bladder dysfunction, as characterized by overactive DSM and decreased voiding efficiency. Functional and molecular data suggest that overactive DSM in diabetes is the result of enhanced extracellular Ca(2+) influx through L-VOCC.

In vitro and in vivo relaxation of urinary bladder smooth muscle by the selective myosin II inhibitor, blebbistatin

OBJECTIVE To investigate the in vitro and in vivo effects of blebbistatin (a small cell-permeable molecule with high affinity and selectivity toward the myosin II contractile molecule) on bladder smooth muscle (SM) contractility, as antimuscarinic therapy is only 65-75% effective in treating overactive bladder (OAB) and is associated with considerable side-effects, with a < 25% continuation rate at 1 year. MATERIALS AND METHODS Bladder and aortic strips from adult male rats, and human bladder strips obtained from open prostatectomy, were used for organ-bath studies of blebbistatin. Awake cystometry was also used in rats in both the presence and absence of intravesically delivered blebbistatin. RESULTS Blebbistatin dose-dependently and completely relaxed both KCl- and carbachol-induced rat detrusor and endothelin-1-induced human bladder contraction. Pre-incubation with 10 µm blebbistatin attenuated carbachol responsiveness by ≈ 65% while blocking electrical field stimulation-induced bladder contraction reaching 50% inhibition at 32 Hz. The basal tone and amplitude of spontaneous contraction were also significantly diminished. Urodynamic variables were obviously altered by intravesical infusion with blebbistatin. CONCLUSION Our novel data show that blebbistatin strongly relaxes both rat and human bladder contraction induced by various physiological stimuli. Coupled with our in vivo data showing that nanomole doses of blebbistatin significantly alter urodynamic variables to produce a less active bladder, our results suggest the possibility of intravesically administered blebbistatin binding at myosin II being developed as a therapeutic treatment for OAB via a novel targeting of the SM contractile apparatus.

Change of erectile function and responsiveness to phosphodiesterase type 5 inhibitors at different stages of streptozotocin-induced diabetes in rats

INTRODUCTION

It has been suggested that risk of erectile dysfunction (ED) increases with duration of diabetes and phosphodiesterase type 5 inhibitors (PDE5I) are not as effective in treatment of diabetes-associated ED. However, few studies have investigated time-dependent change in erectile function during the course of diabetes.

AIM

To investigate time-dependent change in erectile function and responsiveness to PDE5I in streptozotocin-induced diabetic rats and to understand the pathophysiology of diabetic ED.

MAIN OUTCOME MEASURES

At 6, 8, 10, 12, and 14 weeks after diabetic induction, erectile function was assessed by cavernous nerve stimulation before and after administration of DA-8159, a novel PDE5I. Penile tissue was assessed for apoptosis with immunohistochemistry. Protein expression of Rho-kinase 2 (ROCK2), myosin phosphatase targeting subunit 1 (MYPT1), and endothelial nitric oxide synthase (eNOS) was evaluated by Western blot.

METHODS

Streptozotocin was injected into 50 8-week-old male Sprague-Dawley rats, which were then classified into five diabetic groups according to the observation period.

RESULTS

Diabetic rats maintained normal erectile responses until 6 weeks of diabetes. Following 8 weeks, the rats showed lower erectile responses at higher frequencies of nerve stimulation, which were normalized to control by administration of DA-8159. In contrast, erectile responses were significantly decreased in 10-week diabetic rats, and administration of DA-8159 resulted in partial recovery of normal responses. At more than 12 weeks, rats demonstrated severe deterioration of erectile function, which did not fully respond to PDE5I. Corporal apoptosis was significantly increased after 10 weeks. Upregulation of ROCK2 was found at 6 weeks, and was followed by an increase of MYPT1 phosphorylation. Phosphorylation of eNOS showed marked suppression at 6 weeks and remained lower during the experimental period.

CONCLUSIONS

Impairment of erectile function was followed by decreased responsiveness to PDE5I during the course of diabetes. The RhoA/ROCK pathway played an important role in diabetes-associated ED.

Oxidative stress status accompanying diabetic bladder cystopathy results in the activation of protein degradation pathways

OBJECTIVE

• To investigate the role that oxidative stress plays in the development of diabetic cystopathy.

MATERIALS AND METHODS

• Comparative gene expression in the bladder of non-diabetic and streptozotocin (STZ)-induced 2-month- old diabetic rats was carried out using microarray analysis. • Evidence of oxidative stress was investigated in the bladder by analyzing glutathione S-transferase activity, lipid peroxidation, and carbonylation and nitrosylation of proteins. • The activity of protein degradation pathways was assessed using Western blot analysis.

RESULTS

• Analysis of global gene expression showed that detrusor smooth muscle tissue of STZ-induced diabetes undergoes significant enrichment in targets involved in the production or regulation of reactive oxygen species (P = 1.27 × 10(-10)). The microarray analysis was confirmed by showing that markers of oxidative stress were all significantly increased in the diabetic bladder. • It was hypothesized that the sequelae to oxidative stress would be increased protein damage and apoptosis. • This was confirmed by showing that two key proteins involved in protein degradation (Nedd4 and LC3B) were greatly up-regulated in diabetic bladders compared to controls by 12.2 ± 0.76 and 4.4 ± 1.0-fold, respectively, and the apoptosis inducing protein, BAX, was up-regulated by 6.76 ± 0.76-fold.

CONCLUSION

• Overall, the findings obtained in the present study add to the growing body of evidence showing that diabetic cystopathy is associated with oxidative damage of smooth muscle cells, and results in protein damage and activation of apoptotic pathways that may contribute to a deterioration in bladder function.