The role of L-arginine metabolism in neurocritical care patients

Quantifying acute changes in neurometabolism following blast-induced traumatic brain injury

Brain health is largely dependent on the metabolic regulation of amino acids. Brain injuries, diseases, and disorders can be detected through alterations in free amino acid (FAA) concentrations; and thus, mapping the changes has high diagnostic potential. Common methods focus on optimizing neurotransmitter quantification; however, recent focus has expanded to investigate the roles of molecular precursors in brain metabolism. An isocratic method using high performance liquid chromatography with electrochemical cell detection was developed to quantify a wide range of molecular precursors and neurotransmitters: alanine, arginine, aspartate, serine, taurine, threonine, tyrosine, glycine, glutamate, glutamine, and γ-Aminobutyric acid (GABA) following traumatic brain injury. First, baseline concentrations were determined in the serum, cerebrospinal fluid, hippocampus, cortex, and cerebellum of naïve male Sprague Dawley rats. A subsequent study was performed investigating acute changes in FAA concentrations following blast-induced traumatic brain injury (bTBI). Molecular precursor associated FAAs decreased in concentration at 4 h after injury in both the cortex and hippocampus while those serving as neurotransmitters remained unchanged. In particular, the influence of oxidative stress on the observed changes within alanine and arginine pathways following bTBI should be further investigated to elucidate the full therapeutic potential of these molecular precursors at acute time points.

Are We Ready for Clinical Therapy based on Cerebral Autoregulation? A Pro-con Debate

Cerebral autoregulation (CA) is a physiological mechanism that maintains constant cerebral blood flow regardless of changes in cerebral perfusion pressure and prevents brain damage caused by hypoperfusion or hyperperfusion. In recent decades, researchers have investigated the range of systemic blood pressures and clinical management strategies over which cerebral vasculature modifies intracranial hemodynamics to maintain cerebral perfusion. However, proposed clinical interventions to optimize autoregulation status have not demonstrated clear clinical benefit. As future trials are designed, it is crucial to comprehend the underlying cause of our inability to produce robust clinical evidence supporting the concept of CA-targeted management. This article examines the technological advances in monitoring techniques and the accuracy of continuous assessment of autoregulation techniques used in intraoperative and intensive care settings today. It also examines how increasing knowledge of CA from recent clinical trials contributes to a greater understanding of secondary brain injury in many disease processes, despite the fact that the lack of robust evidence influencing outcomes has prevented the translation of CA-guided algorithms into clinical practice.

Multi-Mechanistic Approaches to the Treatment of Traumatic Brain Injury: A Review

Traumatic brain injury (TBI) is a leading cause of death and disability worldwide. Despite extensive research efforts, the majority of trialed monotherapies to date have failed to demonstrate significant benefit. It has been suggested that this is due to the complex pathophysiology of TBI, which may possibly be addressed by a combination of therapeutic interventions. In this article, we have reviewed combinations of different pharmacologic treatments, combinations of non-pharmacologic interventions, and combined pharmacologic and non-pharmacologic interventions for TBI. Both preclinical and clinical studies have been included. While promising results have been found in animal models, clinical trials of combination therapies have not yet shown clear benefit. This may possibly be due to their application without consideration of the evolving pathophysiology of TBI. Improvements of this paradigm may come from novel interventions guided by multimodal neuromonitoring and multimodal imaging techniques, as well as the application of multi-targeted non-pharmacologic and endogenous therapies. There also needs to be a greater representation of female subjects in preclinical and clinical studies.

Potential preventive markers in the intracerebral hemorrhage process are revealed by serum untargeted metabolomics in mice using hypertensive cerebral microbleeds

Hypertensive cerebral microbleeds (HCMB) may be the early stage of hypertensive intracerebral hemorrhage (HICH), which is a serious threat to health due to its high mortality and disability rates. The early clinical symptoms of HCMB may not be significant. Moreover, it is difficult to achieve early diagnosis and intervention for targeted prevention of HICH. Although hypertension (HTN) is a predisposition for HCMB, it remains unclear whether there is any difference between hypertensive patients with or without HCMB. Therefore, we carried out liquid chromatography-mass spectrometry (LC-MS) to analyze early biomarkers for HCMB in mice with hypertension and to lay the foundation for early prevention of HICH in hypertensive patients. In total, 18 C57 male mice were randomly divided into the HCMB (n = 6), HTN (n = 6), and control groups (CON, n = 6). Hematoxylin-eosin and diaminobenzidine staining were used to assess the reliability of the model. The metabolite expression level and sample category stability were tested using the displacement test of orthogonal partial least squares discriminant analysis (OPLS-DA). Significant differences in metabolites were screened out using variable importance in the projection (VIP > 1), which were determined using the OPLS-DA model and the P-value of the t-test (P < 0.05) combined with the nonparametric rank-sum test. With an area under the curve (AUC) > 0.85 and a P-value of 0.05, the receiver operating characteristic curve (ROC) was used to further screen the distinct metabolites of HCMB. Compared with the HTN and CON groups, the HCMB group had significantly higher blood pressure and lower average body weight (P < 0.05). Through untargeted LC-MS analysis, 93 distinct metabolites were identified in the HCMB (P < 0.05, VIP > 1) group. Among these potential biomarkers, six significantly decreased and eight significantly increased differential metabolites were found. Meanwhile, we found that the HCMB group had statistically distinct arginine and purine metabolism pathways (P < 0.05), and citrulline may be the most significant possible biomarker of HCMB (AUC > 0.85, P < 0.05). All of these potential biomarkers may serve as early biomarkers for HICH in hypertension.

Hydrogen sulfide prevents the vascular dysfunction induced by severe traumatic brain injury in rats by reducing reactive oxygen species and modulating eNOS and H2S-synthesizing enzyme expression

AIM

To assess the effects of subchronic administration with NaHS, an exogenous H₂S donor, on TBI-induced hypertension and vascular impairments.

MAIN METHODS

Animals underweministration does not prevent the body weight loss but slightly imnt a lateral fluid percussion injury, and the hemodynamic variables were measured in vivo by plethysmograph method. The vascular function in vitro, the ROS levels by the DCFH-DA method and the expression of H₂S-synthesizing enzymes and eNOS by Western blot were measured in isolated thoracic aortas at day 7 post-TBI. The effect of L-NAME on NaHS-induced effects in vascular function was evaluated. Brain water content was determined 7 days after trauma induction. Body weight was recorded throughout the experimental protocol, whereas the sensorimotor function was evaluated using the neuroscore test at days -1 (basal), 2, and 7 after the TBI induction.

KEY FINDINGS

TBI animals showed: 1) an increase in hemodynamic variables and ROS levels in aortas; 2) vascular dysfunction; 3) sensorimotor dysfunction; and 4) a decrease in body weight, the expression of H₂S-synthesizing enzymes, and eNOS phosphorylation. Interestingly, NaHS subchronic administration (3.1 mg/kg; i.p.; every 24 h for six days) prevented the development of hypertension, vascular dysfunction, and oxidative stress. L-NAME abolished NaHS-induced effects. Furthermore, NaHS treatment restored H₂S-synthesizing enzymes and eNOS phosphorylation with no effect on body weight, sensorimotor impairments, or brain water content.

SIGNIFICANCE

Taken together, these results demonstrate that H₂S prevents TBI-induced hypertension by restoring vascular function and modulating ROS levels, H₂S-synthesizing enzymes expression, and eNOS phosphorylation.

Construction of N-CDs and Calcein-Based Ratiometric Fluorescent Sensor for Rapid Detection of Arginine and Acetaminophen

In our study, a unique ratiometric fluorescent sensor for the rapid detection of arginine (Arg) and acetaminophen (AP) was constructed by the integration of blue fluorescent N-CDs and yellowish-green fluorescent calcein. The N-CD/calcein ratiometric fluorescent sensor exhibited dual emission at 435 and 519 nm under the same excitation wavelength of 370 nm, and caused potential Förster resonance energy transfer (FRET) from N-CDs to calcein. When detecting Arg, the blue fluorescence from the N-CDs of the N-CD/calcein sensor was quenched by the interaction of N-CDs and Arg. Then, the fluorescence of our sensor was recovered with the addition of AP, possibly due to the stronger association between AP and Arg, leading to the dissociation of Arg from N-CDs. Meanwhile, we observed an obvious fluorescence change from blue to green, then back to blue, when Arg and AP were added, exhibiting the “on–off–on” pattern. Next, we determined the detection limits of the N-CD/calcein sensor to Arg and AP, which were as low as 0.08 μM and 0.02 μM, respectively. Furthermore, we discovered that the fluorescence changes of the N-CD/calcein sensor were only responsible for Arg and AP. These results suggested its high sensitivity and specificity for Arg and AP detection. In addition, we have successfully achieved its application in bovine serum samples, indicating its practicality. Lastly, the logic gate was generated by the N-CD/calcein sensor and presented its good reversibility. Overall, we have demonstrated that our N-CD/calcein sensor is a powerful sensor to detect Arg and AP and that it has potential applications in biological analysis and imaging.