Tadalafil reduces visceral adipose tissue accumulation by promoting preadipocytes differentiation towards a metabolically healthy phenotype: Studies in rabbits

Dapagliflozin improves erectile dysfunction in patients with type 2 diabetes mellitus: An open-label, non-randomized pilot study

INTRODUCTION

The role of dapagliflozin on erectile dysfunction (ED), a condition widely affecting patients with type 2 diabetes mellitus (T2DM), has not yet been studied.

AIM

The aim of the study was to evaluate the effects of dapagliflozin alone or in combination with tadalafil on ED in patients with T2DM.

METHODS

This was an open-label, non-randomized pilot study involving 30 Caucasian male patients with T2DM and severe ED. They were equally divided into three groups, assigned to treatment with tadalafil 5 mg/day (Group 1), tadalafil 5 mg/day plus dapagliflozin 10 mg/day (Group 2) and dapagliflozin 10 mg/day (Group 3) for 3 months. The presence and the severity of ED were evaluated at enrolment and after treatment, by the International Index of Erectile Function 5-item (IIEF-5) questionnaire and the dynamic penile echo colour Doppler ultrasound (PCDU) examination.

RESULTS

At the end of treatment, the three groups showed a significant improvement in IIEF-5 score, by 294%, 375% and 197%, in Groups 1, 2 and 3, respectively. PCDU evaluation showed a significant increase in peak systolic velocity by 178.9%, 339% and 153%; acceleration time was significantly shortened in Group 2 (-26.2%) and was significantly lower than in Group 1 and 3 (-7.2% and -6.6%), while no significant difference was found in end-diastolic velocity after treatment. The greatest rates of improvement were observed in Group 2 for all the end points.

CONCLUSIONS

Dapagliflozin improves ED in patients with T2DM and enhances the efficacy of tadalafil. Further studies are needed to confirm our results explain the mechanism(s) by which dapagliflozin exerts its effects on ED.

Inhibition of phosphodiesterase 5A by tadalafil improves SIRT1 expression and activity in insulin-resistant podocytes

A decrease in intracellular levels of 3',5'-cyclic guanosine monophosphate (cGMP) has been implicated in the progression of diabetic nephropathy. Hyperglycemia significantly inhibits cGMP-dependent pathway activity in the kidney, leading to glomerular damage and proteinuria. The enhancement of activity of this pathway that is associated with an elevation of cGMP levels may be achieved by inhibition of the cGMP specific phosphodiesterase 5A (PDE5A) using selective inhibitors, such as tadalafil. Hyperglycemia decreased the insulin responsiveness of podocytes and impaired podocyte function. These effects were associated with lower protein amounts and activity of the protein deacetylase sirtuin 1 (SIRT1) and a decrease in the phosphorylation of adenosine monophosphate-dependent protein kinase (AMPK). We found that PDE5A protein levels increased in hyperglycemia, and PDE5A downregulation improved the insulin responsiveness of podocytes with reestablished SIRT1 expression and activity. PDE5A inhibitors potentiate nitric oxide (NO)/cGMP signaling, and NO modulates the activity and expression of SIRT1. Therefore, we investigated the effects of tadalafil on SIRT1 and AMPK in the context of improving the insulin sensitivity in podocytes and podocyte function in hyperglycemia. Our study revealed that tadalafil restored SIRT1 expression and activity and activated AMPK by increasing its phosphorylation. Tadalafil also restored stimulating effect of insulin on glucose transport in podocytes with high glucose-induced insulin resistance. Additionally, tadalafil improved the function of podocytes that were exposed to high glucose concentrations. Our results display novel mechanisms involved in the pathogenesis of glomerulopathies in diabetes, which may contribute to the development of more effective treatment strategies for diabetic nephropathy.

Beyond Erectile Dysfunction: cGMP-Specific Phosphodiesterase 5 Inhibitors for Other Clinical Disorders

Cyclic guanosine monophosphate (cGMP), an important intracellular second messenger, mediates cellular functional responses in all vital organs. Phosphodiesterase 5 (PDE5) is one of the 11 members of the cyclic nucleotide phosphodiesterase (PDE) family that specifically targets cGMP generated by nitric oxide-driven activation of the soluble guanylyl cyclase. PDE5 inhibitors, including sildenafil and tadalafil, are widely used for the treatment of erectile dysfunction, pulmonary arterial hypertension, and certain urological disorders. Preclinical studies have shown promising effects of PDE5 inhibitors in the treatment of myocardial infarction, cardiac hypertrophy, heart failure, cancer and anticancer-drug-associated cardiotoxicity, diabetes, Duchenne muscular dystrophy, Alzheimer's disease, and other aging-related conditions. Many clinical trials with PDE5 inhibitors have focused on the potential cardiovascular, anticancer, and neurological benefits. In this review, we provide an overview of the current state of knowledge on PDE5 inhibitors and their potential therapeutic indications for various clinical disorders beyond erectile dysfunction.

The metabolic role of prolactin: systematic review, meta-analysis and preclinical considerations

INTRODUCTION

Hyperprolactinemia has been proven to induce hypogonadism and metabolic derangements in both genders, while the consequences of prolactin (PRL) deficiency have been poorly investigated.

AREAS COVERED

To systematically review and analyze data from clinical studies focusing on the metabolic consequences of abnormally high prolactin levels (HPRL) and low prolactin levels (LPRL). In addition, data from preclinical studies about underlying pathophysiological mechanisms were summarized and discussed.

EXPERT OPINION

PRL contributes to providing the correct amount of energy to support the mother and the fetus/offspring during pregnancy and lactation, but it also has a homeostatic role. Pathological PRL elevation beyond these physiological conditions, but also its reduction, impairs metabolism and body composition in both genders, increasing the risk of diabetes and cardiovascular events. Hence, hypoprolactinemia should be avoided as much as possible during treatment with dopamine agonists for prolactinomas. Patients with hypoprolactinemia, because of endogenous or iatrogenic conditions, deserve, as those with hyperprolactinemia, careful metabolic assessment.

Tadalafil and Steroid Hormones Interactions in Adipose, Bone and Prostate Tissues: Focus on Translational Perspectives

Tadalafil is a selective phosphodiesterase type-5 (PDE5) inhibitor that is approved for the treatment of men with erectile dysfunction (ED) and/or benign prostate hyperplasia (BPH) -associated symptoms. Besides its classical actions on PDE5 within the genitourinary tract, where the specific enzyme expression is maximal, it may exert different systemic effects. This is mainly due to the pleiotropic distribution of PDE5 enzyme throughout the human (and animal) body, where it can exert protective effects in different clinical conditions. Recently, it has been demonstrated that tadalafil may display novel actions on androgen receptor (AR) expression and activity and cytochrome P19a1 (Cyp19a1) and estrogen receptor β (ERβ) expression in different in vitro systems, such as adipose, bone and prostate cancer cells, where it can act as a selective modulator of steroid hormone production. This may determine novel potential mechanism(s) of control in pathophysiologic pathways. In this review, we summarize basic research and translational results applicable to the use of tadalafil in the treatment of obesity, bone loss and prostate cancer.

Treatment potential of LPCN 1144 on liver health and metabolic regulation in a non-genomic, high fat diet induced NASH rabbit model

PURPOSE

Low free testosterone (T) level in men is independently associated with presence and severity of Non-Alcoholic Steatohepatitis (NASH). The histological and molecular effects of oral testosterone prodrug LPCN 1144 treatment on hepatic fibrosis and NASH features are unknown. A metabolic syndrome-induced NASH model in rabbits consuming high fat diet (HFD) has been previously used to assess treatment effects of injectable T on hepatic fibrosis and NASH features. Here we present results on LPCN 1144 in this HFD-induced, NASH preclinical model.

METHODS

Male rabbits were randomly assigned to five groups: regular diet (RD), HFD, HFD + 1144 vehicle (HFD + Veh), HFD + 1144 (1144), and HFD + 1144 + α-tocopherol (1144 + ALPHA). Rabbits were sacrificed after 12 weeks for liver histological, biochemical and genetic analyses. Histological scores were obtained through Giemsa (inflammation), Masson's trichrome (steatosis and ballooning), and Picrosirius Red (fibrosis) staining.

RESULTS

Compared to RD, HFD and HFD + Veh significantly worsened NASH features and hepatic fibrosis. Considering HFD and HFD + Veh arms, histological and biomarker features were not significantly different. Both 1144 and 1144 + ALPHA arms improved mean histological scores of NASH as compared to HFD arm. Importantly, percentage of fibrosis was improved in both 1144 (p < 0.05) and 1144 + ALPHA (p = 0.05) treatment arms vs. HFD. Both treatment arms also reduced HFD-induced inflammation and fibrosis mRNA markers. Furthermore, 1144 treatments significantly improved HFD-induced metabolic dysfunctions.

CONCLUSIONS

Histological and biomarker analyses demonstrate that LPCN 1144 improved HFD-induced hepatic fibrosis and NASH biochemical, biomolecular and histochemical features. These preclinical findings support a therapeutic potential of LPCN 1144 in the treatment of NASH and of hepatic fibrosis.

Priming metabolism with the type 5 phosphodiesterase: the role of cGMP-hydrolyzing enzymes

The cyclic guanosine monophosphate (cGMP) signaling system is one of the most prominent regulators of many physiopathological processes in humans and rodents. It has been strongly established as an accomplished cellular signal involved in the regulation of energy homeostasis and cell metabolism, and pharmacological enhancement of cGMP has shown beneficial effects in metabolic disorders models. cGMP intracellular levels are finely regulated by phosphodiesterases (PDEs). The main enzyme responsible for the degradation of cGMP is PDE5. Preclinical and clinical studies have shown that PDE5 inhibitors (PDE5i) have beneficial effects on improving insulin resistance and glucose metabolism representing a promising therapeutic strategy for the treatment of metabolic disorders. This review aims to describe the molecular basis underlying the use of PDE5i to prompt cell metabolism and summarize current clinical trials assessing the effects of PDE5i on glucose metabolism.

The PDE5 inhibitor udenafil ameliorates nonalcoholic fatty liver disease by improving mitochondrial function

Nonalcoholic fatty liver disease (NAFLD) refers to a series of diseases, including simple steatosis, caused by the excessive accumulation of fat in hepatocytes, nonalcoholic steatohepatitis with inflammation and fibrosis, and more advanced forms of cirrhosis. The pathogenic mechanisms underlying fatty liver and the progression from simple fatty liver to hepatitis and cirrhosis remain unclear. One potentially unifying mechanism may be a dysregulation of free fatty acid oxidation. The oversupply of fatty acids to the liver can result in mitochondrial dysfunction leading to the accumulation of lipids in the liver. Interestingly, there have been several reports showing that inhibitors of phosphodiesterase 5 (PDE5) can increase mitochondrial biogenesis, preserve mitochondrial function in vitro. And, we have recently demonstrated that the phosphodiesterase type 5 inhibitor udenafil improves insulin sensitivity by increasing mitochondrial function in adipocytes. In this study, we aimed to examine the effects of the PDE5 inhibitor udenafil on NAFLD in the ob/ob mouse model. Treatment of ob/ob mice for 6 weeks with udenafil reduced fat mass and fasting glucose. Importantly, udenafil caused a reduction in lipid accumulation in the liver of these mice, including hepatic triglyceride (TG) and cholesterol levels. Mechanistically, udenafil decreased the proinflammatory cytokines in the liver. Also, udenafil increased the levels in the liver of the important lipolytic enzymes and the levels of several mitochondrial β-oxidation related genes. Similar effects were seen in udenafil treated primary hepatocytes. We believe that our study makes a significant contribution to the literature because the results from our study suggest that udenafil may be an effective treatment for NAFLD by improving mitochondrial function.

Testosterone treatment is associated with reduced adipose tissue dysfunction and nonalcoholic fatty liver disease in obese hypogonadal men

PURPOSE

In both preclinical and clinical settings, testosterone treatment (TTh) of hypogonadism has shown beneficial effects on insulin sensitivity and visceral and liver fat accumulation. This prospective, observational study was aimed at assessing the change in markers of fat and liver functioning in obese men scheduled for bariatric surgery.

METHODS

Hypogonadal patients with consistent symptoms (n = 15) undergoing 27.63 ± 3.64 weeks of TTh were compared to untreated eugonadal (n = 17) or asymptomatic hypogonadal (n = 46) men. A cross-sectional analysis among the different groups was also performed, especially for data derived from liver and fat biopsies. Preadipocytes isolated from adipose tissue biopsies were used to evaluate insulin sensitivity, adipogenic potential and mitochondrial function. NAFLD was evaluated by triglyceride assay and by calculating NAFLD activity score in liver biopsies.

RESULTS

In TTh-hypogonadal men, histopathological NAFLD activity and steatosis scores, as well as liver triglyceride content were lower than in untreated-hypogonadal men and comparable to eugonadal ones. TTh was also associated with a favorable hepatic expression of lipid handling-related genes. In visceral adipose tissue and preadipocytes, TTh was associated with an increased expression of lipid catabolism and mitochondrial bio-functionality markers. Preadipocytes from TTh men also exhibited a healthier morpho-functional phenotype of mitochondria and higher insulin-sensitivity compared to untreated-hypogonadal ones.

CONCLUSIONS

The present data suggest that TTh in severely obese, hypogonadal individuals induces metabolically healthier preadipocytes, improving insulin sensitivity, mitochondrial functioning and lipid handling. A potentially protective role for testosterone on the progression of NAFLD, improving hepatic steatosis and reducing intrahepatic triglyceride content, was also envisaged.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02248467, September 25th 2014.

Correcting imbalance of sex hormones by a phosphodiesterase 5 inhibitor improves copulatory dysfunction in male rats with type 2 diabetes

INTRODUCTION

Sexual dysfunction is a common complication in men with type 2 diabetes and is often refractory to treatment. This study investigated the long-term influence of the phosphodiesterase 5 inhibitor (PDE5I) tadalafil on the level of sex hormones and sexual function in male Otsuka Long-Evans Tokushima Fatty (OLETF) rats as an animal model of spontaneous type 2 diabetes.

RESEARCH DESIGN AND METHODS

We treated 36-week-old male OLETF and non-diabetic Long-Evans Tokushima Otsuka (LETO) rats with oral tadalafil (100 µg/kg/day) for 12 weeks; sham groups received vehicle for 12 weeks. Before and after tadalafil treatment, serum levels of total and free testosterone, estradiol, luteinizing hormone (LH), follicle-stimulating hormone and proinflammatory cytokines were compared among four treatment groups. Copulatory function was examined by matching each rat to an estrous female. After completion of the experiment, total fat mass in the abdomen was measured.

RESULTS

Testosterone levels were significantly lower in OLETF versus LETO rats at 36 weeks. After 12 weeks of tadalafil treatment, levels of testosterone were significantly increased both in OLETF-tadalafil and LETO-tadalafil groups versus vehicle groups. Tadalafil decreased estradiol levels both in OLETF and LETO rats. Furthermore, tadalafil increased serum LH levels with a reduction of proinflammatory cytokines. Total fat mass was significantly lower in the OLETF-tadalafil group versus the OLETF-vehicle group. A significant suppression of copulatory behavior, that is, elongation of intromission latency was found in OLETF rats. However, tadalafil treatment for 12 weeks shortened the intromission latency.

CONCLUSION

Our results indicate that tadalafil treatment might improve copulatory disorder in the type 2 diabetic model via improvement of an imbalance in sex hormones and an increase in LH levels.

Diet-Induced Rabbit Models for the Study of Metabolic Syndrome

Obesity and metabolic syndrome (MetS) have become a growing problem for public health and clinical practice, given their increased prevalence due to the rise of sedentary lifestyles and excessive caloric intake from processed food rich in fat and sugar. There are several definitions of MetS, but most of them describe it as a cluster of cardiovascular and metabolic alterations such as abdominal obesity, reduced high-density lipoprotein (HDL) and elevated low-density lipoprotein (LDL) cholesterol, elevated triglycerides, glucose intolerance, and hypertension. Diagnosis requires three out of these five criteria to be present. Despite the increasing prevalence of MetS, the understanding of its pathophysiology and relationship with disease is still limited. Indeed, the pathological consequences of MetS components have been reported individually, but investigations that have studied the effect of the combination of MeS components on organ pathological remodeling are almost nonexistent. On the other hand, animal models are a powerful tool in understanding the mechanisms that underlie pathological processes such as MetS. In the first part of the review, we will briefly overview the advantages, disadvantages and pathological manifestations of MetS in porcine, canine, rodent, and rabbit diet-induced experimental models. Then, we will focus on the different dietary regimes that have been used in rabbits to induce MetS by means of high-fat, cholesterol, sucrose or fructose-enriched diets and their effects on physiological systems and organ remodeling. Finally, we will discuss the use of dietary regimes in different transgenic strains and special rabbit breeds.

Brown and Brite: The Fat Soldiers in the Anti-obesity Fight

Brown adipose tissue (BAT) is proposed to maintain thermal homeostasis through dissipation of chemical energy as heat by the uncoupling proteins (UCPs) present in their mitochondria. The recent demonstration of the presence of BAT in humans has invigorated research in this area. The research has provided many new insights into the biology and functioning of this tissue and the biological implications of its altered activities. Another finding of interest is browning of white adipose tissue (WAT) resulting in what is known as beige/brite cells, which have increased mitochondrial proteins and UCPs. In general, it has been observed that the activation of BAT is associated with various physiological improvements such as a reduction in blood glucose levels increased resting energy expenditure and reduced weight. Given the similar physiological functions of BAT and beige/ brite cells and the higher mass of WAT compared to BAT, it is likely that increasing the brite/beige cells in WATs may also lead to greater metabolic benefits. However, development of treatments targeting brown fat or WAT browning would require not only a substantial understanding of the biology of these tissues but also the effect of altering their activity levels on whole body metabolism and physiology. In this review, we present evidence from recent literature on the substrates utilized by BAT, regulation of BAT activity and browning by circulating molecules. We also present dietary and pharmacological activators of brown and beige/brite adipose tissue and the effect of physical exercise on BAT activity and browning.

INT-767 prevents NASH and promotes visceral fat brown adipogenesis and mitochondrial function

The bile acid receptors, farnesoid X receptor (FXR) and Takeda G-protein-coupled receptor 5 (TGR5), regulate multiple pathways, including glucose and lipid metabolism. In a rabbit model of high-fat diet (HFD)-induced metabolic syndrome, long-term treatment with the dual FXR/TGR5 agonist INT-767 reduces visceral adipose tissue accumulation, hypercholesterolemia and nonalcoholic steatohepatitis. INT-767 significantly improves the hallmarks of insulin resistance in visceral adipose tissue (VAT) and induces mitochondrial and brown fat-specific markers. VAT preadipocytes isolated from INT-767-treated rabbits, compared to preadipocytes from HFD, show increased mRNA expression of brown adipogenesis markers. In addition, INT-767 induces improved mitochondrial ultrastructure and dynamic, reduced superoxide production and improved insulin signaling and lipid handling in preadipocytes. Both in vivo and in vitro treatments with INT-767 counteract, in preadipocytes, the HFD-induced alterations by upregulating genes related to mitochondrial biogenesis and function. In preadipocytes, INT-767 behaves mainly as a TGR5 agonist, directly activating dose dependently the cAMP/PKA pathway. However, in vitro experiments also suggest that FXR activation by INT-767 contributes to the insulin signaling improvement. INT-767 treatment counteracts HFD-induced liver histological alterations and normalizes the increased pro-inflammatory genes. INT-767 also induces a significant reduction of fatty acid synthesis and fibrosis markers, while increasing lipid handling, insulin signaling and mitochondrial markers. In conclusion, INT-767 significantly counteracts HFD-induced liver and fat alterations, restoring insulin sensitivity and prompting preadipocytes differentiation toward a metabolically healthy phenotype.

Biochemical and Ultrastructural Cardiac Changes Induced by High-Fat Diet in Female and Male Prepubertal Rabbits

Early weight gain induced by high-fat diet has been identified as a predictor for cardiac disease, one of the most serious public health problems. Our goal is to study the influence of a HFD on biochemical, oxidant stress parameters, and the cardiac ultrastructure in both male and female prepubertal models. Experiments were carried on 24 prepubertal New Zealand white rabbits, randomly assigned to male and female control (MC and FC, resp.) or HFD (MHFD and FHFD, resp.) groups (n = 6) for 3 months. Body and heart weights and some biochemical and oxidative stress parameters such as lipids, calcium, CKMB, MDA, uric acid, ascorbic acid, and AOA are evaluated in plasma and the left ventricle. Under HFD effect, plasma parameters, such as lipids (TL, PL, and LDL-C), MDA, and CK-MB, increase more significantly in male than in female groups, when AA decreases. Some cardiac parameters such as TG and UA increase, when AA and AOA decrease; these variations are more significant in FHFD. In both male and female rabbits, HFD caused changes in heart ultrastructure, junctional complexes, mitochondria size and form, and so on. Early HFD feeding induced overweight, oxidative stress, and metabolic alterations in plasma and the heart of prepubertal rabbits, whereas lipotoxicity has especially a negative impact on male plasma but affects more the female heart ultrastructure.

Molecular mechanisms underlying metabolic syndrome: the expanding role of the adipocyte

The metabolic syndrome (MetS) is defined as a cluster of 3 or more metabolic and cardiovascular risk factors and represents a serious problem for public health. Altered function of adipose tissue has a significant impact on whole-body metabolism and represents a key driver for the development of these metabolic derangements, collectively referred as to MetS. In particular, increased visceral and ectopic fat deposition play a major role in the development of insulin resistance and MetS. A large body of evidence demonstrates that aging and MetS share several metabolic alterations. Of importance, molecular pathways that regulate lifespan affect key processes of adipose tissue physiology, and transgenic mouse models with adipose-specific alterations in these pathways show derangements of adipose tissue and other metabolic features of MetS, which highlights a causal link between dysfunctional adipose tissue and deleterious effects on whole-body homeostasis. This review analyzes adipose tissue-specific dysfunctions, including metabolic alterations that are related to aging, that have a significant impact on the development of MetS.-Armani, A., Berry, A., Cirulli, F., Caprio, M. Molecular mechanisms underlying metabolic syndrome: the expanding role of the adipocyte.

Tadalafil improves lean mass and endothelial function in nonobese men with mild ED/LUTS: in vivo and in vitro characterization

PURPOSE

Phosphodiesterase type-5 inhibitor administration in diabetic men with erectile dysfunction (ED) is associated with reduced waist circumference. We evaluated potential effects of daily tadalafil administration on body composition and investigated its possible mechanism(s) of action in C₂C₁₂ skeletal muscle cells in vitro.

METHODS

Forty-three men on stable caloric intake (mean age 48.5 ± 7; BMI 25.5 ± 0.9 kg/m²) complaining mild ED and/or low urinary tract symptoms (LUTS) were randomly assigned to receive tadalafil (TAD) 5 mg/daily (once-a-day=OAD-TAD; n = 23) or 20 mg on-demand (on-demand=OD-TAD; n = 20) for 2 months. Primary outcomes were variations of body composition measured by Dual-energy X-ray absorptiometry; secondary outcomes were ED/LUTS questionnaire scores along with hormone (testosterone, estradiol, insulin) and endothelial function (Endopat2000) variations.

RESULTS

OAD-TAD increased abdominal lean mass (p < 0.01) that returned to baseline after 2 months withdrawal. LUTS scores improved (p<0.01) in OD-TAD while ED scores improved (p < 0.01) in both groups. We found significant improvements in endothelial function (p < 0.05) that directly correlated with serum insulin (p < 0.01; r = 0.3641) and inversely correlated with estradiol levels (p < 0.01; r = 0.3655) even when corrected for potential confounders. Exposure of C₂C₁₂ cells upon increasing tadalafil concentrations (10^-7 to 10^-6 M) increased total androgen receptor mRNA and protein expression as well as myogenin protein expression after 24 and 72 h (2.8 ± 0.4-fold and 1.4 ± 0.02-fold vs. control, respectively, p < 0.05).

CONCLUSIONS

Daily tadalafil improved lean mass content in non-obese men probably via enhanced insulin secretion, estradiol reduction, and improvement of endothelial function in vivo. The in vitro increased myogenin and androgen receptor protein expression in skeletal muscle cells suggests a translational action of phosphodiesterase type-5 on this receptor.

Influence of the PDE5 inhibitor tadalafil on redox status and antioxidant defense system in C2C12 skeletal muscle cells

Phosphodiesterase type 5 inhibitors (PDE5Is), widely known for their beneficial effects onto male erectile dysfunction, seem to exert favorable effects onto metabolism as well. Tadalafil exposure increases oxidative metabolism of C2C12 skeletal muscle cells. A rise in fatty acid (FA) metabolism, requiring more oxygen, could induce a larger reactive oxygen species (ROS) release as a byproduct thus leading to a redox imbalance. The aim of this study was to determine how PDE5I tadalafil influences redox status in skeletal muscle cells to match the increasing oxidative metabolism. To this purpose, differentiated C2C12 skeletal muscle cells were treated with tadalafil and analyzed for total antioxidant capacity (TAC) and glutathione levels as marker of redox status; enzyme activity of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) engaged in antioxidant defense; and lipid peroxidation (TBARS) and protein carbonyls (PrCar) as markers of oxidative damage. Tadalafil increased total intracellular glutathione (tGSH), CAT, SOD, and GPx enzymatic activities while no changes were found in TAC. A perturbation of redox status, as showed by the decrease in the ratio between reduced/oxidized glutathione (GSH/GSSG), was observed. Nevertheless, it did not cause any change in TBARS and PrCar levels probably due to the enhancement in the antioxidant enzymatic network. Taken together, these data indicate that tadalafil, besides improving oxidative metabolism, may be beneficial to skeletal muscle cells by enhancing the enzymatic antioxidant system capacity.