Visible light induces nitric oxide (NO) formation in sperm and endothelial cells.

BACKGROUND: Visible light-based stimulation using low-intensity lasers, LEDs, and broadband visible light devices has been recently introduced for therapy of human tissues in the absence of exogenous photosensitizers. Nitric oxide (NO) formation might be a potential mechanism for photobiomodulation because it is synthesized in cells by nitric oxide synthase (NOS), which contains both flavin and heme groups that absorb visible light. NO synthesis may also result from increased reactive oxygen species (ROS), which are found in various cell cultures following visible light illumination. NO is mainly known for inducing blood vessel dilation by endothelial cells, and in sperm cells NO is considered as an important agent in acrosome reaction and capacitation process, which are essential for successful fertilization. PURPOSE: To study NO formation in endothelial and sperm cells following visible light irradiation. MATERIALS AND METHODS: Sperm and endothelial cells were illuminated with broadband visible light, 400-800 nm, 130 mW/cm(2), for 5 minutes. During illumination, the endothelial cells were incubated in PBS free of Ca(+2) and Mg(+2), and the sperm cells were incubated in NKM buffer, to induce "stress conditions." NO production was quantified by using the Griess reagent which reacts with nitrite in the medium to yield an Azo compound which has an absorption band at 540 nm. RESULTS: Visible light illumination increased NO concentration both in sperm and endothelial cells. Blue light was more effective than red. Light-induced NO occurred only when endothelial cells were incubated in PBS free of Ca(+2) and Mg(+2), and in sperm cells, only when incubated in NKM. CONCLUSION: Light induces NO formation in endothelial and sperm cells. In endothelial cells, NO formation may explain previous results demonstrating enhanced wound healing and pain relief following illumination. In illuminated sperm cells, NO formation may account for the enhanced fertilization rate.

Low-energy laser irradiation promotes cellular redox activity.

Low-energy visible light (LEVL) has been shown to stimulate cell functions. This is called "photobiostimulation" and has been used successfully over the last three decades for treating a range of conditions, including soft tissue injuries, severe wounds, chronic pain, and more. Nevertheless, the mechanism of photobiostimulative processes is still being debated. It is obvious that, in order to interact with the living cell, light has to be absorbed by intracellular chromophores. In a search for chromophores responsible for photobiostimulation, endogenous porphyrins, mitochondrial and membranal cytochromes, and flavoproteins were found to be suitable candidates. The above-mentioned chromophores are photosensitizers that generate reactive oxygen species (ROS) following irradiation. As the cellular redox state has a key role in maintaining the viability of the cell, changes in ROS may play a significant role in cell activation. In the present review, we summarize evidence demonstrating that various ROS and antioxidants are produced following LEVL illumination. We found that very little evidence for NO formation in illuminated non-vascular smooth muscle cells exists in the literature. We suggest that the change in the cellular redox state which plays a pivotal role in maintaining cellular activities leads to photobiostimulative processes.