Melatonin and tadalafil treatment improves erectile dysfunction after spinal cord injury in rats

Revealing Melatonin's Mysteries: Receptors, Signaling Pathways, and Therapeutics Applications

Melatonin (5-methoxy-acetyl tryptamine) is a sleep-inducing hormone, and the pineal gland produces it in response to the circadian clock of darkness. In the body, MT1 and MT2 receptors are mostly found, having an orthosteric pocket and ligand binding determinants. Melatonin acts by binding on melatonin receptors, intracellular proteins, and orphan nuclear receptors. It inhibits adenyl cyclase and activates phospholipase C, resulting in gene expression and an intracellular alteration environment. Melatonin signaling pathways are also associated with other intracellular signaling pathways, i. e., cAMP/PKA and MAPK/ERK pathways. Relative expression of different proteins depends on the coupling profile of G protein, accounting pharmacology of the melatonin receptor bias system, and mediates action in a Gi-dependent manner. It shows antioxidant, antitumor, antiproliferative, and neuroprotective activity. Different types of melatonin agonists have been synthesized for the treatment of sleeping disorders. Researchers have developed therapeutics that target melatonin signaling, which could benefit a wide range of medical conditions. This review focuses on melatonin receptors, pharmacology, and signaling cascades; it aims to provide basic mechanical aspects of the receptor's pharmacology, melatonin's functions in cancer and neurodegenerative diseases, and any treatments and drugs designed for these diseases. This will allow a basic comparison between the receptors in question, highlighting any parallels and differences that may exist and providing fundamental knowledge about these receptors to future researchers.

Melatonin, a natural antioxidant therapy in spinal cord injury

Spinal cord injury (SCI) is a sudden onset of disruption to the spinal neural tissue, leading to loss of motor control and sensory function of the body. Oxidative stress is considered a hallmark in SCI followed by a series of events, including inflammation and cellular apoptosis. Melatonin was originally discovered as a hormone produced by the pineal gland. The subcellular localization of melatonin has been identified in mitochondria, exhibiting specific onsite protection to excess mitochondrial reactive oxygen species and working as an antioxidant in diseases. The recent discovery regarding the molecular basis of ligand selectivity for melatonin receptors and the constant efforts on finding synthetic melatonin alternatives have drawn researchers' attention back to melatonin. This review outlines the application of melatonin in SCI, including 1) the relationship between the melatonin rhythm and SCI in clinic; 2) the neuroprotective role of melatonin in experimental traumatic and ischemia/reperfusion SCI, i.e., exhibiting anti-oxidative, anti-inflammatory, and anti-apoptosis effects, facilitating the integrity of the blood-spinal cord barrier, ameliorating edema, preventing neural death, reducing scar formation, and promoting axon regeneration and neuroplasticity; 3) protecting gut microbiota and peripheral organs; 4) synergizing with drugs, rehabilitation training, stem cell therapy, and biomedical material engineering; and 5) the potential side effects. This comprehensive review provides new insights on melatonin as a natural antioxidant therapy in facilitating rehabilitation in SCI.

Proniosomal Gel-Loaded Phosphodiesterase Inhibitors (Sildenafil, Vardenafil, and Tadalafil): Prospects for Topical Penile Therapy of Tadalafil for Treatment of Erectile Dysfunction

Oral phosphodiesterase inhibitors have emerged as a game changer for the treatment of erectile dysfunction (ED) since attaining FDA approval for its first member, sildenafil, in 1998. Topical penile therapy could be a viable replacement for oral medication that would transform the treatment of ED for many decades to come. This innovative idea could offer a safer topical alternative with less vision and cardiovascular side effects than the oral route. This work aims at developing proniosomal gels for three selected members (sildenafil, vardenafil, and tadalafil) and investigating the proniosomal gels on a rodent model. Niosomes derived from the parent proniosomal gels were characterized for entrapment efficiency (EE%), size, polydispersity index (PDI), zeta potential, and morphology. Proniosomal gels were evaluated for skin permeation, in vivo mating behaviors, and biochemical assays of nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) post penile topical administrations. The optimized proniosomes loaded with tadalafil (F1-T) were compared with oral tablets (Cialis®). Proniosomal gels demonstrated significant enhancement of skin penetration by up to 5.5-fold, compared to control topical suspension. Tadalafil-loaded proniosomes showed superior skin permeability over sildenafil- and vardenafil-loaded proniosomes. In addition, significant improvement was noticed regarding intromission number, intromission ratio, NO, and cGMP for the proniosomal gel F1-T, compared to the untreated control. No statistically significant (p > 0.05) differences in sexual performance or biochemical parameters (NO and cGMP levels) were recorded among orally and topically (tadalafil proniosomal gel) administered groups. These findings support tadalafil topical penile therapy as a promising alternative to the oral route.

Therapeutic and Prophylactic Role of Vitamin D and Curcumin in Acetic Acid-Induced Acute Ulcerative Colitis Model

Ulcerative Colitis (UC) is a disease that negatively affects quality of life and is associated with sustained oxidative stress, inflammation and intestinal permeability. Vitamin D and Curcumin; It has pharmacological properties beneficial to health, including antioxidant and anti-inflammatory properties. Our study investigates the role of Vitamin D and Curcumin in acetic acid-induced acute colitis model. To investigate the effect of Vitamin D and Curcumin, Wistar-albino rats were given 0.4 mcg/kg Vitamin D (Post-Vit D, Pre-Vit D) and 200 mg/kg Curcumin (Post-Cur, Pre-Cur) for 7 days and acetic acid was injected into all rats except the control group. Our results; colon tissue TNF-α, IL-1β, IL-6, IFN-γ and MPO levels were found significantly higher and Occludin levels were found significantly lower in the colitis group compared to the control group (p < 0.05). TNF-α and IFN-γ levels decreased and Occludin levels increased in colon tissue of Post-Vit D group compared to colitis group (p < 0.05). IL-1β, IL-6 and IFN-γ levels were decreased in colon tissue of Post-Cur and Pre-Cur groups (p < 0.05). MPO levels in colon tissue decreased in all treatment groups (p < 0.05). Vitamin D and Curcumin treatment significantly reduced inflammation and restored the normal histoarchitecture of the colon. From the present study findings, we can conclude that Vitamin D and Curcumin protect the colon from acetic acid toxicity with their antioxidant and anti-inflammatory potential.

Erectile Dysfunction: Pharmacological Pathways with Understudied Potentials

Erectile dysfunction (ED) is a public health concern worldwide. In the past, it was perceived as a phenomenon attributed to age advancement. However, more individuals are affected every year that do not fall under that age criterion. Epidemiological research revealed that this abnormality has an association with endothelial dysfunction connected to several cardiovascular (CV) risk factors. Currently, ED is interpreted as a clinical marker for future adverse events and not only as a present health issue that negatively affects the quality of life. The management of ED involves lifestyle modifications, therapeutic optimization for comorbid conditions, and pharmacological and psychosexual therapy. Phosphodiesterase type 5 (PDE5) inhibitors are the first-line pharmacological agents to be prescribed for such a condition. Nonetheless, other pharmacological pathways and agents remain underinvestigated or were investigated at some stage. This review aimed to present to future researchers interested in this field with some pharmacological agents that showed favorable effects on a limited number of studies on human subjects or experimental models.

Evidence for the Benefits of Melatonin in Cardiovascular Disease

The pineal gland is a neuroendocrine gland which produces melatonin, a neuroendocrine hormone with critical physiological roles in the circadian rhythm and sleep-wake cycle. Melatonin has been shown to possess anti-oxidant activity and neuroprotective properties. Numerous studies have shown that melatonin has significant functions in cardiovascular disease, and may have anti-aging properties. The ability of melatonin to decrease primary hypertension needs to be more extensively evaluated. Melatonin has shown significant benefits in reducing cardiac pathology, and preventing the death of cardiac muscle in response to ischemia-reperfusion in rodent species. Moreover, melatonin may also prevent the hypertrophy of the heart muscle under some circumstances, which in turn would lessen the development of heart failure. Several currently used conventional drugs show cardiotoxicity as an adverse effect. Recent rodent studies have shown that melatonin acts as an anti-oxidant and is effective in suppressing heart damage mediated by pharmacologic drugs. Therefore, melatonin has been shown to have cardioprotective activity in multiple animal and human studies. Herein, we summarize the most established benefits of melatonin in the cardiovascular system with a focus on the molecular mechanisms of action.

Dynamic erectile responses of a novel penile organ model utilizing TPEM†

Male penis is required to become erect during copulation. In the upper (dorsal) part of penis, the erectile tissue termed corpus cavernosum (CC) plays fundamental roles for erection by regulating the inner blood flow. When blood flows into the CC, the microvascular complex termed sinusoidal space is reported to expand during erection. A novel in vitro explant system to analyze the dynamic erectile responses during contraction/relaxation is established. The current data show regulatory contraction/relaxation processes induced by phenylephrine (PE) and nitric oxide (NO) donor mimicking dynamic erectile responses by in vitro CC explants. Two-photon excitation microscopy (TPEM) observation shows the synchronous movement of sinusoidal space and the entire CC. By taking advantages of the CC explant system, tadalafil (Cialis) was shown to increase sinusoidal relaxation. Histopathological changes have been generally reported associating with erection in several pathological conditions. Various stressed statuses have been suggested to occur in the erectile responses by previous studies. The current CC explant model enables to analyze such conditions through directly manipulating CC in the repeated contraction/relaxation processes. Expression of oxidative stress marker and contraction-related genes, Hypoxia-inducible factor 1-alpha (Hif1a), glutathione peroxidase 1 (Gpx1), Ras homolog family member A (RhoA), and Rho-associated protein kinase (Rock), was significantly increased in such repeated contraction/relaxation. Altogether, it is suggested that the system is valuable for analyzing structural changes and physiological responses to several regulators in the field of penile medicine.

Melatonin Treatment Ameliorates Hyperhomocysteinemia-Induced Impairment of Erectile Function in a Rat Model

BACKGROUND

Hyperhomocysteinemia (HHcy) has been reported to be strongly correlated with the occurrence of erectile dysfunction (ED), but the mechanisms are not fully understood. Moreover, whether melatonin could be a potential treatment of HHcy-induced ED needs to be elucidated.

AIM

The aim of this study was to investigate the effects of melatonin on HHcy-induced ED and the potential mechanisms via modulating oxidative stress and apoptosis.

METHODS

The Sprague-Dawley (SD) rat model of HHcy was induced by 7% methionine (Met)-rich diets. 36 male SD rats were randomly distributed into 3 groups (n = 12 per group): control group, 7% Met group, and 7% Met + melatonin (Mel; 10 mg/kg, intraperitoneal injection) treatment group. After 4 weeks, the erectile function of all rats was evaluated by electrical stimulation of the cavernous nerve. Histologic and molecular alterations of the corpus cavernosum were also analyzed by immunofluorescence, immunohistochemistry, enzyme-linked immunosorbent assay, Western blotting, and polymerase chain reaction.

OUTCOMES

HHcy-induced ED rat models were successfully established, and Mel could preserve erectile function mainly through inhibiting oxidative stress via the Erk1/2/Nrf2/HO-1 signaling pathway and suppression of apoptosis.

RESULTS

Erectile function was significantly reduced in the rats with HHcy compared with that in the control group and was ameliorated in the HHcy rats treated with Mel. Compared with the control group, the rats in the HHcy group showed the following: (1) higher levels of total plasma homocysteine; (2) fewer neuronal nitric oxide synthase-positive cells in the corpus cavernous; (3) higher levels of reactive oxygen species and malondialdehyde, higher expression levels of nicotinamide adenine dinucleotide phosphate oxidase, and lower activities of superoxide dismutase, indicating an overactivated oxidative stress; (4) lower expression levels of Erk1/2/Nrf2/HO-1 signaling pathway components; and (5) higher levels of apoptosis, as determined by the expression levels of Bax, Bcl-2, and caspase 3. Mel treatment improved the erectile response, as well as histologic and molecular alterations.

CLINICAL TRANSLATION

Our study on a rodent model of HHcy provided evidence that Mel could be a potential therapeutic method for HHcy-related ED.

CONCLUSIONS

Mel treatment improves erectile function in rats with HHcy probably by potential antioxidative stress activity. This finding provides evidence for a potential new therapy for HHcy-induced ED. Tang Z, Song J, Yu, Z, et al. Melatonin Treatment Ameliorates Hyperhomocysteinemia-Induced Impairment of Erectile Function in a Rat Model. J Sex Med 2019;16:1506-1517.

Neuroprotective effects of melatonin on erectile dysfunction in streptozotocin-induced diabetic rats

PURPOSE

To explore the neuroprotective effects and its possible mechanisms of melatonin (MT) on erectile dysfunction in streptozotocin-induced diabetic rats.

METHODS

Twenty-eight Sprague-Dawley rats received intraperitoneal injection of streptozotocin and 8 weeks later, the determined diabetic rats randomly got intraperitoneal injection of phosphate buffer solution (PBS) or MT. Another 12 normal rats received PBS treatment. Four weeks later, intracavernous pressure, mean arterial pressure, pathological changes in penis, and major pelvic ganglion (MPG) were measured. Malondialdehyde, superoxide dismutase, p38 and p-p38 levels in penis were detected.

RESULTS

Diabetic rats showed significant decreases of erectile function accompanied with serious neuropathy in dorsal penile nerve (DPN) and MPG, meanwhile collagen deposition, oxidative stress, and p-p38 levels in penis were elevated. Melatonin treatment partially but significantly improved the erectile function, ameliorated neuropathy in DPN and MPG, and decreased collagen deposition, oxidative stress, and p-p38 levels in diabetic rats.

CONCLUSIONS

Melatonin treatment helps improve erectile function and ameliorate neuropathy and fibrosis in diabetic rats. These may be associated with reductions in oxidative stress, p38MAPK signaling pathway, and neuropathy.

Low serum melatonin levels are associated with erectile dysfunction

OBJECTIVE

Melatonin is a hormone secreted from the pineal gland and has anti-oxidative and anti-inflammatory effects. Oxidative stress is considered as an important factor in the etiology of erectile dysfunction (ED), and in many experimental models, positive results have been obtained with melatonin treatment. This study aimed to measure serum melatonin levels in ED patients and to investigate the possible relationship between ED and melatonin levels.

MATERIALS AND METHODS

Sixty-two patients diagnosed with mild, moderate or severe ED according to the five-item International Erectile Function Index (IIEF-5) and 22 healthy individuals were included in the study. The serum melatonin levels, anthropometric data, and other biochemical and hormonal parameters of all the subjects were recorded. Detailed anamnesis was also obtained in terms of diabetes, hypertension, cardiovascular diseases, smoking status, and alcohol use.

RESULTS

The serum melatonin level was found 34.2±13.3 ng/dL in the mild ED group, 33.3±14.7 ng/dL in the moderate ED group, 34.8±17.2 ng/dL in the severe ED group, and 44.6±16.5 ng/dL in the control group. The serum melatonin levels were significantly lower in all ED groups compared to the control group (p=0.019). There was no significant difference in the serum melatonin levels between the three ED groups. Diabetes, hypertension, cardiovascular diseases, smoking and alcohol use were not significantly different between the ED groups (p>0.05).

CONCLUSION

We consider that if our findings are supported by further studies with larger populations, the measurement of the serum melatonin level may have a future role in the diagnosis and treatment of ED.

Resveratrol treatment may preserve the erectile function after radiotherapy by restoring antioxidant defence mechanisms, SIRT1 and NOS protein expressions

Radiotherapy (RT) for prostate cancer (PC) can cause erectile dysfunction (ED) by damaging neurovascular structures with oxidative stress. In this study, we evaluated the effects of resveratrol, an antioxidant, on post-RT ED. Fifty rats in five groups were evaluated; control (C), prostate-confined radiotherapy with short- and long-term vehicle or resveratrol treatment. Cavernosal tissues were obtained to analyze glutathione (GSH), nitric oxide (NO), cyclic guanosine monophosphate (cGMP), 8-hydroxy-2'-deoxy-guanosine (8-OHdG) levels and superoxide dismutase (SOD), caspase-3 activities, sirtuin-1, Foxo-3, nNOS, and eNOS protein expressions. Intracavernosal pressures (ICP) were measured for the long-term treatment group. In the RT + long-term vehicle treatment group, tissue GSH, NO, cGMP, and SOD activity were decreased while 8-OHdg levels and caspase-3 activities were increased. Radiotherapy caused a decrease in sirtuin-1, nNOS, and eNOS protein expressions. These parameters were reversed by resveratrol treatment. Foxo-3 protein expressions were unaltered in the RT + short-term vehicle treatment group and started to increase as a defense mechanism in the RT + long-term vehicle group; however, resveratrol treatment caused a significant increase in Foxo-3 expressions. Resveratrol preserved the metabolic pathways involved in erectile function and provided functional protection. Resveratrol can be used as a supplementary agent in patients undergoing radiotherapy to preserve erectile function.

Biomaterial strategies for limiting the impact of secondary events following spinal cord injury

The nature of traumatic spinal cord injury (SCI) often involves limited recovery and long-term quality of life complications. The initial injury sets off a variety of secondary cascades, which result in an expanded lesion area. Ultimately, the native tissue fails to regenerate. As treatments are developed in the laboratory, the management of this secondary cascade is an important first step in achieving recovery of normal function. Current literature identifies four broad targets for intervention: inflammation, oxidative stress, disruption of the blood-spinal cord barrier, and formation of an inhibitory glial scar. Because of the complex and interconnected nature of these events, strategies that combine multiple therapies together show much promise. Specifically, approaches that rely on biomaterials to perform a variety of functions are generating intense research interest. In this review, we examine each target and discuss how biomaterials are currently used to address them. Overall, we show that there are an impressive amount of biomaterials and combinatorial treatments which show good promise for slowing secondary events and improving outcomes. If more emphasis is placed on growing our understanding of how materials can manage secondary events, treatments for SCI can be designed in an increasingly rational manner, ultimately improving their potential for translation to the clinic.

Melatonin for the treatment of spinal cord injury

Spinal cord injury (SCI) from trauma or disease severely impairs sensory and motor function. Neurorehabilitation after SCI is a complex medical process that focuses on improving neurologic function and repairing damaged connections in the central nervous system. An increasing number of preclinical studies suggest that melatonin may be useful for the treatment of SCI. Melatonin is an indolamine that is primarily secreted by the pineal gland and known to be regulated by photoperiodicity. However, it is also a versatile hormone with antioxidative, antiapoptotic, neuroprotective, and anti-inflammatory properties. Here, we review the neuroprotective properties of melatonin and the potential mechanisms by which it might be beneficial in the treatment of SCI. We also describe therapies that combine melatonin with exercise, oxytetracycline, and dexamethasone to attenuate the secondary injury after SCI and limit potential side effects. Finally, we discuss how injury at different spinal levels may differentially affect the secretion of melatonin.

Melatonin protects diabetic heart against ischemia-reperfusion injury, role of membrane receptor-dependent cGMP-PKG activation

It has been demonstrated that the anti-oxidative and cardioprotective effects of melatonin are, at least in part, mediated by its membrane receptors. However, the direct downstream signaling remains unknown. We previously found that melatonin ameliorated myocardial ischemia-reperfusion (MI/R) injury in diabetic animals, although the underlying mechanisms are also incompletely understood. This study was designed to determine the role of melatonin membrane receptors in melatonin's cardioprotective actions against diabetic MI/R injury with a focus on cGMP and its downstream effector PKG. Streptozotocin-induced diabetic Sprague-Dawley rats and high-glucose medium-incubated H9c2 cardiomyoblasts were utilized to determine the effects of melatonin against MI/R injury. Melatonin treatment preserved cardiac function and reduced oxidative damage and apoptosis. Additionally, melatonin increased intracellular cGMP level, PKGIα expression, p-VASP/VASP ratio and further modulated myocardial Nrf-2-HO-1 and MAPK signaling. However, these effects were blunted by KT5823 (a selective inhibitor of PKG) or PKGIα siRNA except that intracellular cGMP level did not changed significantly. Additionally, our in vitro study showed that luzindole (a nonselective melatonin membrane receptor antagonist) or 4P-PDOT (a selective MT₂ receptor antagonist) not only blocked the cytoprotective effect of melatonin, but also attenuated the stimulatory effect of melatonin on cGMP-PKGIα signaling and its modulatory effect on Nrf-2-HO-1 and MAPK signaling. This study showed that melatonin ameliorated diabetic MI/R injury by modulating Nrf-2-HO-1 and MAPK signaling, thus reducing myocardial apoptosis and oxidative stress and preserving cardiac function. Importantly, melatonin membrane receptors (especially MT₂ receptor)-dependent cGMP-PKGIα signaling played a critical role in this process.

Wogonin prevents rat dorsal root ganglion neurons death via inhibiting tunicamycin-induced ER stress in vitro

Wogonin is a natural flavonoid isolated from the root of Scutellaria baicalensis Georgi, which has been widely used in various research areas for its anti-oxidant, anti-inflammatory, and anti-cancer activities. It also presents a neuroprotective effect in the brain while encounters stress conditions, but the mechanisms controlling the neuroprotective effect of wogonin are not clear. In this study, we investigated the biomechanism underlying the neuroprotective effect of wogonin on rat dorsal root ganglion (DRG) neurons. Wogonin pre-treatment at 75 μM significantly increased the cell viability of DRG neurons and decreased the number of the propidium iodide-positive DRG neurons before the endoplasmic reticulum (ER) stress is being induced by tunicamycin (TUN) (0.75 μg/mL). In addition, Wogonin also inhibited the release of LDH and up-regulated the level of GSH. Furthermore, wogonin decreased the activation of ER stress-related molecules, including glucose-regulated protein 78 (GRP78), GRP94, C/EBP-homologous protein, active caspase12 and active caspase3, phosphorylation of pancreatic ER stress kinase, and eukaryotic initiation factor 2 alpha (eIF2α). In summary, our results indicated that wogonin could protect DRG neurons against TUN-induced ER stress.

Penile erectile dysfunction after brachial plexus root avulsion injury in rats

Our previous studies have demonstrated that some male patients suffering from brachial plexus injury, particularly brachial plexus root avulsion, show erectile dysfunction to varying degrees. However, the underlying mechanism remains poorly understood. In this study, we evaluated the erectile function after establishing brachial plexus root avulsion models with or without spinal cord injury in rats. After these models were established, we administered apomorphine (via a subcutaneous injection in the neck) to observe changes in erectile function. Rats subjected to simple brachial plexus root avulsion or those subjected to brachial plexus root avulsion combined with spinal cord injury had significantly fewer erections than those subjected to the sham operation. Expression of neuronal nitric oxide synthase did not change in brachial plexus root avulsion rats. However, neuronal nitric oxide synthase expression was significantly decreased in brachial plexus root avulsion + spinal cord injury rats. These findings suggest that a decrease in neuronal nitric oxide synthase expression in the penis may play a role in erectile dysfunction caused by the combination of brachial plexus root avulsion and spinal cord injury.