To evaluate the effects of L-Arginine on mitochondrial function, nitric oxide (NO) synthesis and presence of nitrative stress.

L-Arginine has been proposed as a treatment of stroke-like episodes in MELAS (Mitochondrial Encephalomyopathy Lactic Acidosis and Stroke-like syndrome). It is hypothesized that as an NO precursor, Arginine restores NO levels in blood vessels, improving cerebral blood flow. However, the exact mechanism of action is still not clear. Furthermore, NO is also involved in the regulation of the respiratory chain, mitochondrial biogenesis, oxidative stress and redox signaling.

The experiments were performed with cybrid cells derived from osteosarcoma, harboring wild type mtDNA (143B) and m.3243A>G, the main cause of MELAS. Cells were treated with L-Arginine followed by evaluation of mitochondrial function (respiratory chain enzyme activity), mitochondrial content (expression of SDHA, Western blotting), NO content (intracellular NO indicator, DAF-FM diacetate), and nitrative stress (immunostaining, anti-nitrotyrosine antibody).

Mitochondrial function and content were not affected by L-Arginine. Intracellular NO was increased in m.3243A>G cells (1.98 ± 0.29 a.u.) at basal conditions compared to 143B cells (1.01 ± 0.03 a.u.). After treatment with L-Arginine we observed a reduction in intracellular NO in m.3243A>G cells (1.98 ± 0.29 vs 0.93 ± 0.0.9 a.u.) and no significant change in 143B cells (1.01±0.03 vs 0.98±0.04 a.u.). Basal levels of nitrated proteins were increased in m.3243A>G cells. After treatment nitrated proteins  were reduced in m.3243A>G (55 ± 2.8%) and increased in 143B cells (120 ± 3%).