Physiology and metabolism in closed head injury

Association of sub-acute changes in plasma amino acid levels with long-term brain pathologies in a rat model of moderate-severe traumatic brain injury

Introduction

Traumatic brain injury (TBI) induces a cascade of cellular alterations that are responsible for evolving secondary brain injuries. Changes in brain structure and function after TBI may occur in concert with dysbiosis and altered amino acid fermentation in the gut. Therefore, we hypothesized that subacute plasma amino acid levels could predict long-term microstructural outcomes as quantified using neurite orientation dispersion and density imaging (NODDI).

Methods

Fourteen 8-10-week-old male rats were randomly assigned either to sham (n = 6) or a single moderate-severe TBI (n = 8) procedure targeting the primary somatosensory cortex. Venous blood samples were collected at days one, three, seven, and 60 post-procedure and NODDI imaging were carried out at day 60. Principal Component Regression analysis was used to identify time dependent plasma amino acid concentrations after in the subacute phase post-injury that predicted NODDI metric outcomes at day 60.

Results

The TBI group had significantly increased plasma levels of glutamine, arginine, alanine, proline, tyrosine, valine, isoleucine, leucine, and phenylalanine at days three-seven post-injury. Higher levels of several neuroprotective amino acids, especially the branched-chain amino acids (valine, isoleucine, leucine) and phenylalanine, as well as serine, arginine, and asparagine at days three-seven post-injury were also associated with lower isotropic diffusion volume fraction measures in the ventricles and thus lesser ventricular dilation at day 60.

Discussion

In the first such study, we examined the relationship between the long-term post-TBI microstructural outcomes across whole brain and the subacute changes in plasma amino acid concentrations. At days three to seven post-injury, we observed that increased plasma levels of several amino acids, particularly the branched-chain amino acids and phenylalanine, were associated with lesser degrees of ventriculomegaly and hydrocephalus TBI neuropathology at day 60 post-injury. The results imply that altered amino acid fermentation in the gut may mediate neuroprotection in the aftermath of TBI.

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, NO(x)), 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 NO(x) 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 NO(x) (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.

[Is the metabolic response self-limited in head trauma? Analysis of acute phase proteins and glycemia]

There are many reports supporting a self-limitation mechanism involved with hypermetabolic response after severe cranial injury. It was proposed a study with severe head injury patients, in three stages of the evolution. The first 7 days after admission (moment 1-M1), the second three days latter (M2) and the last 7 days after the first (M3). Among male patients with severe head injury, attended between January 1992 and December 1993 in University Hospital of Botucatu, UNESP, were selected 28 male patients, with Glasgow severity scale between 4 and 6, with pO2 < 70 mm Hg, weighting 60 kg or more. Among these patients, 6 finished the study, including analysis of the excretion of N, acute phase proteins, glycemia, triglycerides and amine nitrogen. During the study there were no changes in nitrogen balance and there was a decrease in protein C-reative. Glycemia tends to fall within two weeks after injury. The authors make some considerations about possible mechanisms involved in brain modulation associated with the period of dependence of hypermetabolism and hypercatabolism after closed brain injury. There are some evidences that the brain responds to head trauma with a gobal non specific way, which tends to be reorganized beyond the first two weeks after lesion. The study does not show any influence of the type and severity of head trauma.

Intensive management of severe head injury

Intensive management of patients with severe head injury offers the best hope of minimizing death and functional disability in a young, working population. Secondary neurologic insult can be decreased by cardiorespiratory support and ICP control from the outset. Rapid neurologic assessment, airway management, and support of circulation are the basis of emergency management for head injury. Patients with severe head injury require intensive care management for two major reasons: management of ICP and management of organ system dysfunction. Care should not be withheld because of initially grim (and inaccurate) prognostic assessment. Newer techniques for assessing the adequacy of cerebral circulation may allow refinement of management strategies in the future.

Traumatic brain injury creates biphasic systemic hemodynamic and organ blood flow responses in rats

Traumatic brain injury affects systemic circulation as well as directly damages the brain. The present study examined the effects of fluid percussion brain injury on systemic hemodynamics and organ arterial blood flow in rats. Rats were prepared for fluid percussion injury under anesthesia. Twenty-four hours later, rats were anesthetized (1.0% halothane in N2O:O2) and prepared for radioactive microsphere measurement of cardiac output and organ blood flow. After baseline blood flow and physiological measurements were established, the rats were injured (2.47 +/- 0.02 atm, n = 17) or not injured (n = 20). Additional blood flow determinations were made at two of the following four time (T) points: 5, 15, 30, and 60 min after the injury or sham injury. Fluid percussion brain injury produced an immediate systemic hypertension followed by a hypotension and low cardiac output. Organ blood flows remained constant or increased for 30 min and then declined. Decreased blood flow was most pronounced in the kidneys and the spleen and was less severe in the liver. The reduced cardiac output was redistributed to favor blood flow through the heart and pancreas. These data suggest that traumatic brain injury creates a hyperdynamic period followed by a hypodynamic state with a heterogeneous hypoperfusion among organs.

Comparison of creatinine and inulin clearances in multiple trauma

Creatinine clearance (Ccr) is a good predictor of renal dysfunction. However, numerous analytical interferences have been observed with the classical measurement of creatinine by Jaffé's procedure. This prospective study was conducted to compare 4 methods for determining creatinine; and also endogenous creatinine clearance with inulin clearance (Cin) to estimate the glomerular filtration rate. The 4 different techniques for measuring creatinine were: 1) 2 techniques using Jaffé's colorimetric reaction: one with rapid and the other with slow kinetics: 2) 2 more selective methods: enzymatic procedure and high performance liquid chromatography (HPLC). Measurements were performed in 13 multiple trauma patients after stabilization and in 5 comatose patients (control group) over a 3-day period, with strict 24-h urine collection. On the second day, inulin clearance and para-aminohippuric acid clearance (Cpah) were measured. Measurement of creatinine by Jaffé's procedure yields significantly higher levels than those obtained by the other methods. Higher levels of both plasma and urinary creatinine were observed in the multiple trauma patients with all the methods used. There were no significant differences in Ccr, Cin, Cpah between the multiple trauma patients and the control patients. The best correlations between inulin clearance and creatinine clearance were observed for Jaffé's rapid kinetics (r = 0.90) in the control group and for the enzymatic procedure in the multiple trauma group (r = 0.55). Plasma creatinine is not a useful indicator in multiple trauma. The correlation between creatinine clearance and inulin clearance is not very strong in multiple trauma, indicating that the relative evolution (not the absolute values) of creatinine clearance is of interest.