L-citrulline, classified as a nonessential amino acid, is synthesized predominantly via Delta-1-pyrroline carboxylate synthase in the endothelial cells of the small intestine. In mammals, small quantities of citrulline are also produced in nitric oxide synthase-expressing cells. Considering the fact that the enzymes involved in the endogenous synthesis of L-citrulline are all located in the mitochondria and the fact that citrulline is a component of the citrulline-nitric oxide (NO) cycle, we hypothesized that the distinct clinical, biochemical, and morphological characteristics of MELAS, a maternally inherited mitochondrial disorder, might be due to alterations in nitric oxide homeostasis. Analysis of serum from MELAS patients showed that levels of plasma arginine were similar in both patients and in controls. However, levels of citrulline in MELAS patients were significantly lower than in controls, and there was a clear inverse correlation between arginine and citrulline levels in these patients. We found no correlation between the level of heteroplasmy and the plasma levels of either arginine or citrulline. We discuss the depressed citrulline levels in MELAS patients, who have an unusual and paradoxical pattern of vascular respiratory chain expression, in the context of NO homeostasis.
Background And Objectives: Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) syndrome is a maternally inherited mitochondrial disorder that mostly affects the central nervous system and skeletal muscle. This study provides a comprehensive summary of the clinical symptoms, multisystemic pathogenesis, and genetic characteristics of MELAS syndrome. The aim was to improve comprehension of clinical practice and gain a deeper understanding of the latest pathophysiological theories.
Mitochondrial tRNA (mt-tRNA) modifications play pivotal roles in decoding and sustaining tRNA stability, thereby enabling synthesis of essential respiratory complex proteins in mitochondria. Consequently, loss of human mt-tRNA modifications caused by mutations in the mitochondrial or nuclear genome can cause life-threatening mitochondrial diseases such as encephalopathy and cardiomyopathy. In this article, we first provide a comprehensive overview of the functions of mt-tRNA modifications, the responsible modification enzymes, and the diseases caused by loss of mt-tRNA modifications.
Background: MELAS (Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like episodes) is a common subtype of mitochondrial encephalomyopathy. However, few studies have explored the relationship between biochemical markers and prognosis. This study aimed to explore the relationship between clinical and biochemical markers and prognosis of patients with MELAS.
Mitochondrial DNA (mtDNA) encodes genes essential for oxidative phosphorylation. The m.3243A>G mutation causes severe disease, including myopathy, lactic acidosis and stroke-like episodes (MELAS) and is the most common pathogenic mtDNA mutation in humans.
Primary mitochondrial disorders (PMDs) are rare and complex conditions resulting from faults in the mitochondrial respiratory chain, leading to significant clinical variability among patients.
Studying these disorders is challenging due to low statistical power in single-center studies and the wide range of symptoms even among individuals with identical genotypes.
Recent years have seen significant progress through multicenter research efforts and the establishment of national and international registries for mitochondrial patients, enhancing our understanding of PMDs and paving the way for future developments.
