Control of rat bladder neck relaxation with NORD-1, a red light-reactive nitric oxide releaser: In vitro study

Efficacy of a Red-Light Controllable Nitric Oxide Releaser for Neurogenic Erectile Dysfunction: A Study Using a Rat Model of Cavernous Nerve Injury

PURPOSE

Neurogenic erectile dysfunction (ED) is a common side effect of radical prostatectomy (RP) because of cavernous nerve damage. In these patients, the production of nitric oxide (NO), which is important for erection, is decreased in the corpus cavernosum. Therefore, NO donors are useful for post-RP ED. However, short half-life and systemic side effects are problems of NO application in ED therapy. To avert these problems, we developed a red-light controllable NO releaser, NORD-1. This study aimed to investigate the effect of NORD-1 and red-light irradiation on neurogenic ED using a rat model of bilateral cavernous nerve injury (BCNI).

MATERIALS AND METHODS

BCNI and sham operations were conducted on 8-week-old rats. After 4 weeks, erectile function was evaluated using changes in intracavernous pressure (ICP) during electrostimulation of the cavernous nerve. ICP was measured under three conditions; without NORD-1 and red-light irradiation, with NORD-1 and without red-light irradiation, and with NORD-1 and red-light irradiation. SiR650 which absorbs red-light but does not release NO was used for the negative control. After the experiment, localization of NORD-1 was observed using a microscope.

RESULTS

Erectile function in a BCNI rat model was significantly decreased compared to sham-operated rats (p<0.05). After injecting NORD-1 into the penis, erectile function did not change without red-light irradiation. However, the combination of NORD-1 and red-light irradiation significantly improved erectile function (p<0.05) without affecting systemic arterial pressure. In contrast, when SiR650 was used, erectile function did not change in all three conditions. NORD-1 was detected only in the corpus cavernosum and not in the urethra and dorsal vein.

CONCLUSIONS

NORD-1 combined with red-light irradiation is effective for ED induced by cavernous nerve injury. This treatment may have low risks of hypotension and urinary incontinence, and it can replace the current treatment for post-RP ED.

The Evolution of Nitric Oxide Function: From Reactivity in the Prebiotic Earth to Examples of Biological Roles and Therapeutic Applications

Nitric oxide was once considered to be of marginal interest to the biological sciences and medicine; however, there is now wide recognition, but not yet a comprehensive understanding, of its functions and effects. NO is a reactive, toxic free radical with numerous biological targets, especially metal ions. However, NO and its reaction products also play key roles as reductant and oxidant in biological redox processes, in signal transduction, immunity and infection, as well as other roles. Consequently, it can be sensed, metabolized and modified in biological systems. Here, we present a brief overview of the chemistry and biology of NO—in particular, its origins in geological time and in contemporary biology, its toxic consequences and its critical biological functions. Given that NO, with its intrinsic reactivity, appeared in the early Earth’s atmosphere before the evolution of complex lifeforms, we speculate that the potential for toxicity preceded biological function. To examine this hypothesis, we consider the nature of non-biological and biological targets of NO, the evolution of biological mechanisms for NO detoxification, and how living organisms generate this multifunctional gas.

[A novel approach to treating erectile dysfunction with a light-controlled nitric oxide donor]

It has long been known that nitric oxide (NO) is involved in the initiation and maintenance of erection. For this reason, NO supplementation has been considered a useful target for the treatment of erectile dysfunction (ED), and many studies have been conducted. However, to date, no compounds have been launched for a variety of reasons. One of the reasons is the systemic adverse reactions. In order to solve this problem, we focused on light-controlled NO donors and investigate their potential application in ED treatment. Light-controlled NO donors have three main characteristics: first, they release NO only at the site of light irradiation, second, they release NO only during the time of light irradiation, and third, the amount of NO released can be controlled according to the light intensity. These features suggest that light-responsive NO donors may be useful for ED therapy. Our group has been working on the development of light-controlled NO donors, and has so far developed the blue light-controlled NO donor "NOBL-1", the yellowish-green light-controlled NO donor "NO-Rosa", and the red light-controlled NO donor "NORD-1". Our recent studies have shown that NORD-1 and red light can enhance the erectile response in rats at the in vivo level. Next, we examined the effects of NORD-1 and red light using a neurogenic ED model, which is believed to be less effective than existing ED drugs. The results showed that red light irradiation after NORD-1 administration enhanced the erectile response and improved ED in the neurogenic ED model. These results suggest that NORD-1, a light-controlled NO donor, and red light can enhance the erectile response in rats and may have potential as an ED drug. Although optimization of the compound is essential, it is expected that a new therapeutic approach called photobiotherapy for ED will be developed in the future.