Plasma concentrations of arginine and related amino acids following traumatic brain injury: Proline as a promising biomarker of brain damage severity

The aim of this study was to find a plasma biomarker, in relation with nitric oxide (NO), as a sign of brain damage severity following traumatic brain injury (TBI). We first investigated the post-traumatic evolution of the plasma concentrations of NO via the level of NO end-products metabolites (nitrite plus nitrate, NOx), that of l-arginine (Arg) and amino acids involved in its metabolism as well as the time course of neurological score in a rat model of lateral fluid percussion brain injury. First, the level of NOx was increased in plasma at 24 and 48 h post-TBI with a marked increase at 72 h. In contrast, this elevation was neither accompanied by a modification of plasma concentrations of Arg, nor of amino acids involved in NO and Arg metabolism, l-ornithine (Orn), l-glutamate (Glu), and l-glutamine (Gln). Second, TBI induced a fall of plasma l-proline (Pro) concentrations. The time course of post-TBI neurological deficit showed also a decrease of neurological score at 24, 48, and 72 h. Furthermore, there is a weak negative correlation between the neurological score and the plasma level of NOx (r = −0.305; P < 0.05), while a marked positive correlation has been found between the neurological score and the plasma level of Pro (r = 0.563; P < 0.001). In conclusion, the plasma concentrations of Pro could be a promising marker of post-traumatic neurological deficit.