Kanchan Chitaley

Anatomy, Physiology, and Pathophysiology of Erectile Dysfunction

INTRODUCTION Significant scientific advances during the past 3 decades have deepened our understanding of the physiology and pathophysiology of penile erection. A critical evaluation of the current state of knowledge is essential to provide perspective for future research and development of new therapies. AIM To develop an evidence-based, state-of-the-art consensus report on the anatomy, physiology, and pathophysiology of erectile dysfunction (ED). METHODS Consensus process over a period of 16 months, representing the opinions of 12 experts from seven countries. MAIN OUTCOME MEASURE Expert opinion was based on the grading of scientific and evidence-based medical literature, internal committee discussion, public presentation, and debate. RESULTS ED occurs from multifaceted, complex mechanisms that can involve disruptions in neural, vascular, and hormonal signaling. Research on central neural regulation of penile erection is progressing rapidly with the identification of key neurotransmitters and the association of neural structures with both spinal and supraspinal pathways that regulate sexual function. In parallel to advances in cardiovascular physiology, the most extensive efforts in the physiology of penile erection have focused on elucidating mechanisms that regulate the functions of the endothelium and vascular smooth muscle of the corpus cavernosum. Major health concerns such as atherosclerosis, hyperlipidemia, hypertension, diabetes, and metabolic syndrome (MetS) have become well integrated into the investigation of ED. CONCLUSIONS Despite the efficacy of current therapies, they remain insufficient to address growing patient populations, such as those with diabetes and MetS. In addition, increasing awareness of the adverse side effects of commonly prescribed medications on sexual function provides a rationale for developing new treatment strategies that minimize the likelihood of causing sexual dysfunction. Many basic questions with regard to erectile function remain unanswered and further laboratory and clinical studies are necessary.

Vasodilator-Stimulated Phosphoprotein Regulates Proliferation and Growth Inhibition by Nitric Oxide in Vascular Smooth Muscle Cells

Objective—Vasodilator-stimulated phosphoprotein (VASP) was identified as a substrate for cGMP-dependent protein kinase (PKG) and cAMP-dependent protein kinase (PKA). It is preferentially phosphorylated at serine239 by PKG, whereas serine157 is a preferred phosphorylation site for PKA. In addition, serine157 is phosphorylated by PKC in response to serum. We have investigated the effects of VASP and VASP phosphorylation at serine157 and serine239 on smooth muscle cell (SMC) proliferation and nitric oxide (NO)-mediated growth inhibition. Methods and Results—Aortic SMCs derived from VASP-deficient mice were transduced with retroviral vectors encoding either wild-type VASP or VASP mutants (S157A-VASP and S239A-VASP), in which serine157 and serine239, respectively, were replaced by a nonphosphorylatable amino acid, alanine. Expression of wt-VASP and S239A-VASP significantly increased proliferation, whereas expression of S157A-VASP was inhibitory. Expression of S239A-VASP rendered SMCs less sensitive to growth inhibition by the NO donor, S-nitroso-n-acetylpenicillamine, when compared with cells expressing wt-VASP. Similar effects were observed in cultured rat SMCs in which wt-VASP, S157A-VASP, and S239A-VASP were expressed. Conclusions—Our data suggest that VASP phosphorylation at serine157 is required for the growth-stimulatory effect of VASP in SMCs, whereas VASP phosphorylation at serine239 is involved in the growth inhibitory effects of NO on SMCs.

Adeno-associated viral gene transfer of dominant negative RhoA enhances erectile function in rats.

We previously reported the inhibition of Rho-kinase to result in increased intracavernosal pressure (ICP) in an in vivo rat model of erection. Expression of an upstream activator of Rho-kinase, RhoA, has been demonstrated in the penile vasculature; however, the functional role of RhoA in the regulation of erection remains unknown. We used adeno-associated viral gene transfer of a dominant negative RhoA mutant (T19NRhoA) into rat cavernosum to test the hypothesis that RhoA activation is physiologically important for maintenance of the non-erect state and inhibition of this pathway leads to erection. Anesthetized, male, Sprague-Dawley rats transfected with the T19NRhoA mutant exhibited an elevated baseline ICP/mean arterial pressure (MAP) and nerve stimulation-induced ICP/MAP as compared with beta-galactosidase-transfected controls. The novel findings of this study demonstrate a functional role of RhoA in maintaining the flaccid penis and provide support for the inhibition of RhoA as a potential therapy for the enhancement of erectile function.

Type 2 Diabetes Mellitus and Erectile Dysfunction

INTRODUCTION Diabetes mellitus (DM) is a major risk factor for the development of erectile dysfunction (ED). Although most diabetic ED cases are in patients with type 2 diabetes (T2DM), the majority of basic science studies examining mechanisms of diabetic ED have been conducted in animal models of type 1 diabetes. AIM Recently, however, clinical and laboratory-based studies have uncovered some key underlying factors of T2DM-associated ED, which we have compiled in this review of T2DM ED. MAIN OUTCOME MEASURES The outcomes discussed in this review include major mechanisms underlying T2DM, discussing both clinical and basic science studies. METHODS We conducted an extensive search of pertinent clinical and basic science literature using PUBMED. RESULTS Mechanisms causing ED in T2DM are multifactorial and often lead to resistance to current therapy. Systemic effects of hyperglycemia and hypogonadism contribute to the development of impaired vasodilatory signaling, smooth muscle cell hypercontractility, and veno-occlusive disorder in T2DM ED. CONCLUSIONS Understanding the different causes for ED in T2DM patients may allow targeted therapy for improved erectile function.

Vasodilator-stimulated phosphoprotein is a substrate for protein kinase C

Vasodilator‐stimulated phosphoprotein (VASP), an actin binding protein localized to areas of focal contacts, is a substrate for the cyclic adenosine monophosphate/cyclic guanosine monophosphate (cAMP/cGMP)‐dependent protein kinases (PKA, PKG). In this study, we show that serum stimulation of vascular smooth muscle cells (SMCs) induces VASP phosphorylation on Ser157, in a mechanism not dependent on PKA or PKG. We tested the possibility that protein kinase C (PKC), a regulator of cytoskeletal function, is involved. PKC inhibition or down‐regulation prevented serum‐induced phosphorylation of VASP at Ser157 in rat vascular SMCs. Additionally, recombinant PKCα directly phosphorylated Ser157 on VASP. In summary, our data support the hypothesis that PKC phosphorylates VASP and mediates serum‐induced VASP regulation.

Diabetes, Obesity and Erectile Dysfunction: Field Overview and Research Priorities

PURPOSE We provide an overview of basic, clinical and epidemiological research in the field of erectile dysfunction and important research priorities presented at the 2009 National Institute of Diabetes and Digestive and Kidney Diseases symposium on Urological Complications of Diabetes and Obesity. MATERIALS AND METHODS Experts in molecular biology, physiology, pharmacology, clinical trials, epidemiology and urological surgery highlighted current knowledge on erectile dysfunction associated with diabetes mellitus and obesity. RESULTS Predictable associations between erectile dysfunction, and poor diabetic control and modifiable risk factors, including body mass index, have not yet been translated into randomized trials in the United States. The relationship between erectile dysfunction and metabolic syndrome, and surrogate markers for erectile dysfunction requires further investigation. Basic research aimed at discovering disease mechanisms and therapeutic targets has focused on autonomic neuropathy, vascular dysfunction, smooth muscle contractile function and matrix. However, significant gaps exist in regard to the integration of molecular, cellular and functional data. Animal models of type 2 diabetes and obesity associated erectile dysfunction require investigation because most basic science studies have used rodent models of type 1 diabetes. CONCLUSIONS Studies are needed to synthesize a systems biology understanding of erectile function/dysfunction, and characterize and disseminate rodent models of erectile dysfunction associated with type 2 diabetes and obesity. Clinical studies are needed of promising intervention and prevention strategies. Leveraging existing and future cohort phenotypes, and biological samples is needed for risk factor analysis, biomarker discovery and genome wide association studies.

Erectile dysfunction in the type II diabetic db/db mouse: impaired venoocclusion with altered cavernosal vasoreactivity and matrix

The number of men with type II diabetes-associated erectile dysfunction (ED) continues to grow rapidly; however, the majority of basic science studies has examined mechanisms of ED in animal models of type I diabetes. In this study, we first establish an in vivo mouse model of type II diabetic ED using the leptin receptor mutated db/db and wild-type control BKS mouse. Furthermore, we hypothesized that dual mechanistic impairments contribute to the impaired erectile function in the type II diabetic mouse, altered vasoreactivity, and venoocclusive disorder. In vivo erectile function was measured as intracavernosal pressure (ICP) normalized to mean arterial pressure (MAP) following electrical stimulation of the cavernosal nerve. Venoocclusion was assessed by the maintenance of elevated in vivo ICP following intracorporal saline infusion. Vasoreactivity of isolated cavernosum in response to contractile and dilatory stimulation was examined in vitro by myography. Collagen and elastin content were evaluated by quantification of hydroxyproline and desmosine, respectively, as well as by quantitative PCR and histological analysis of isolated cavernosum. Erectile function was significantly decreased in db/db vs. BKS mice in a manner consistent with impairments in venoocclusive ability and decreased inflow. Heightened vasoconstriction and attenuated dilation in cavernosum of db/db vs. BKS mice suggest an overall lowered relaxation ability and thus impaired filling of the cavernosal spaces. A decrease in desmosine and hydroxyproline as well as lowered mRNA levels for tropoelastin, fibrillin-1, and alpha1(I) collagen were detected. These vasoreactive and sinusoidal matrix alterations may alter tissue compliance dispensability, preventing the normal expansion necessary for erection.

Type 1 and Type 2 Diabetic-Erectile Dysfunction: Same Diagnosis (ICD-9), Different Disease?

INTRODUCTION Although hyperglycemia is a common defining feature of both type 1 and type 2 diabetes, many unique characteristics distinguish these diseases, including insulin and lipid levels, obesity status, and inflammatory agent profiles. In the laboratory, the presence of erectile dysfunction (ED) has been established in animal models of both type 1 and type 2 diabetes. AIM The purpose of this study was to determine whether unique mechanisms underlie ED in type 1 vs. type 2 diabetic animal models. MAIN OUTCOME MEASURES Many mechanisms can underlie ED, including impaired dilatory signaling, heightened contractile sensitivity, and veno-occlusive disorder. METHODS Using PubMed, the literature was mined to evaluate what is known about which mechanism underlie ED in type 1 vs. type 2 diabetic animal models. RESULTS Impaired cavernosal vasodilation has been established in type 1 diabetic rodents. This dysfunction appears to be mediated by a severe defect in non-adrenergic-non-cholinergic nerve signaling, as well as impairment in penile endothelial function. In contrast, type 2 diabetic animals appear to have minimal impairment in parasympathetic-mediated dilatory function, but do have evidence of endothelial dysfunction. Type 2 diabetic models also exhibit a significant and striking increase in cavernosal contractile sensitivity, and a significant veno-occlusive disorder, neither of which is consistently reported in type 1 diabetic animals. CONCLUSIONS With the distinct mechanisms underlying the ED phenotype in animal models of type 1 and type 2 diabetes, tailoring therapeutic treatments for diabetic-ED to the specific mechanisms underlying this disease complication may be warranted. Further examination of mechanisms underlying ED in diabetic human patients may thus lead to significant changes in the way urologists diagnose, code, and treat diabetic-ED.

Proceedings of the 2008 American Urological Association Foundation Summer Research Conference on Sexual Medicine, August 2008, Linthicum, Maryland, USA Sponsored by the AUA Foundation, NIDDK and SBURType 1 and Type 2 Diabetic‐Erectile Dysfunction: Same Diagnosis (ICD‐9), Different Disease?

INTRODUCTION Although hyperglycemia is a common defining feature of both type 1 and type 2 diabetes, many unique characteristics distinguish these diseases, including insulin and lipid levels, obesity status, and inflammatory agent profiles. In the laboratory, the presence of erectile dysfunction (ED) has been established in animal models of both type 1 and type 2 diabetes. AIM The purpose of this study was to determine whether unique mechanisms underlie ED in type 1 vs. type 2 diabetic animal models. MAIN OUTCOME MEASURES Many mechanisms can underlie ED, including impaired dilatory signaling, heightened contractile sensitivity, and veno-occlusive disorder. METHODS Using PubMed, the literature was mined to evaluate what is known about which mechanism underlie ED in type 1 vs. type 2 diabetic animal models. RESULTS Impaired cavernosal vasodilation has been established in type 1 diabetic rodents. This dysfunction appears to be mediated by a severe defect in non-adrenergic-non-cholinergic nerve signaling, as well as impairment in penile endothelial function. In contrast, type 2 diabetic animals appear to have minimal impairment in parasympathetic-mediated dilatory function, but do have evidence of endothelial dysfunction. Type 2 diabetic models also exhibit a significant and striking increase in cavernosal contractile sensitivity, and a significant veno-occlusive disorder, neither of which is consistently reported in type 1 diabetic animals. CONCLUSIONS With the distinct mechanisms underlying the ED phenotype in animal models of type 1 and type 2 diabetes, tailoring therapeutic treatments for diabetic-ED to the specific mechanisms underlying this disease complication may be warranted. Further examination of mechanisms underlying ED in diabetic human patients may thus lead to significant changes in the way urologists diagnose, code, and treat diabetic-ED.

Strain Differences in Susceptibility to In Vivo Erectile Dysfunction Following 6 weeks of Induced Hyperglycemia in the Mouse

INTRODUCTION With the large-scale availability of transgenic and knockout mouse models, the use of mice may greatly facilitate the examination of the mechanisms underlying diabetic erectile dysfunction (ED). Although in vitro studies of the mouse cavernosum show impairment of vasoreactivity, to date, no studies have demonstrated the in vivo impairment of erectile function in diabetic mice. AIM To establish whether mouse models of type I diabetes exhibit in vivo ED. METHODS Hyperglycemia was induced by injection with streptozotocin (STZ, 125 mg/kg x 2 days) in two mouse strains, C57BLKS (BKS) and BALB/c. Six weeks after injection, the cavernosum was removed from some mice for the in vitro assessment of the endothelium and nerve-mediated dilatory responses of the cavernosal strips. The in vivo assessment of intracorporal pressure normalized to mean arterial pressure, in response to the electrical stimulation of the cavernosal nerve, was performed in the remaining mice. MAIN OUTCOME MEASURES The main outcome measure of this study was the in vivo assessment of erectile function following diabetic induction in mice. RESULTS Despite similar levels of sustained hyperglycemia following STZ injection, the phenotype of diabetic ED was observed only in BKS and not BALB/c mice. The cavernosum from diabetic BKS mice showed decreased endothelium-dependent dilation in response to acetylcholine (ACh), as well as impaired parasympathetic nerve-mediated relaxation. There was no change in ACh or nerve-mediated relaxation in the cavernousum from diabetic vs. control BALB/c mice. Further, in vivo physiologic assessment of erectile activity revealed a significant decrease in erectile function in diabetic BKS but not in BALB/c mice. CONCLUSION Together these data first established in vivo ED in a mouse model of type I diabetes (BKS mouse) and importantly demonstrated that certain inbred strains may be protected from hyperglycemia-induced erectile impairment. Further study of the strain-dependent effects may offer important clues into the mechanisms of ED as it relates to type I diabetes.