ORIGINAL ARTICLE Increase in the nitric oxide release without changes in cell viability of macrophages after laser therapy with 660 and 808 nm lasers Igor Henrique Morais Silva 1 & Samantha Cardoso de Andrade 1 & Andreza Barkokebas Santos de Faria 1 & Deborah Daniela Diniz Fonsêca 1 & Luiz Alcino Monteiro Gueiros 1 & Alessandra Albuquerque Tavares Carvalho 1 & Wylla Tatiana Ferreira da Silva 2 & Raul Manhães de Castro 2 & Jair Carneiro Leão 1 Received: 29 March 2016 /Accepted: 22 August 2016 # Springer-Verlag London 2016 Abstract The aim of this study was to evaluate the influence of low-level laser therapy (LLLT) with different parameters and wavelengths on nitric oxide (NO) release and cell viabil- ity. Irradiation was performed with Ga-Al-As laser, continu- ous mode and wavelengths of 660 and 808 nm at different energy and power densities. For each wavelength, powers of 30, 50, and 100 mW and times of 10, 30, and 60 s were used. NO release was measured using Griess reaction, and cell via- bility was evaluated by mitochondrial reduction of bromide 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bro- mide (MTT) to formazan. LLLT promoted statistically signif- icant changes in NO release and MTT value only at the wave- length of 660 nm (p < 0.05). LLLT also promoted an increase in the NO release and cell viability when the energy densities 64 (p = 0.04) and 214 J/cm 2 (p = 0.012), respectively, were used. LLLT has a significant impact on NO release without affecting cell viability, but the significance of these findings in the inflammatory response needs to be further studied. Keywords Inflammation . Laser therapy . Macrophages . MTT . Nitric oxide . NO Introduction Low-level laser therapy (LLLT) consists of the use of low light irradiances capable of influencing cell behavior by means of photobiomodulation, either stimulating or inhibiting cell be- havior [1]. Within the medical-dental therapeutic arsenal, LLLT has been shown to be effective in the treatment of dif- ferent diseases through its anti-inflammatory, analgesic, and tissue biostimulatory effects [2]. LLLT accelerates the healing process, as it promotes an increase in collagen fiber synthesis and fibroblast proliferation [3–5] by stimulating the secretion of growth factors for these cells [6, 7]. In addition, the following are effects promoted by LLLT, enabling faster, efficient repair to occur with fewer painful symptoms due to the modulation of inflammation: the release of an endogenous opioids [8], reduction in prostaglandins (PGE-2) [9], reduction in cycloxygenase 2 (COX-2) expres- sion [9] and edema by the action on microcirculation and activation of the lymphatic system [10]. LLLT produces an anti-inflammatory effect by inhibiting leukocyte differentia- tion, cell and plasma exudation, as well as a reduction in the secretion of substances such as IL-6, MCP-1, IL-10, TNF-α, IL-1β, IL-6, and nitric oxide (NO) [11–13]. In the reduction of NO, LLLT changes the functioning of enzyme NO synthase (NOS) [14] in addition to stimulating the production of other factors involved in the cure process, such as PDGF and TGF-β [15]. NO is a soluble gas permeable to membrane, which per- forms different biologic functions in numerous physiological processes, including vasodilatation, neurotransmission, and inflammation [16, 17]. NO production is associated with NOS enzyme activity, which may be found in three isoforms: induced NOS (iNOS), endothelial NOS (eNOS), and neuronal NOS [18]. In inflammation, NO is an inflammatory modulator produced from the amino acid L-arginine by iNOS enzyme * Igor Henrique Morais Silva igorrecife@hotmail.com 1 Department of Clinic and Preventive Dentistry, Pernambuco Federal University, Av. Prof. Moraes Rego, 1235, Recife, PE, Brazil 50670-901 2 Department of Nutrition, Pernambuco Federal University, Recife, PE, Brazil Lasers Med Sci DOI 10.1007/s10103-016-2061-1