The Relationship between Mitochondrial Respiratory Chain Activities in Muscle and Metabolites in Plasma and Urine: A Retrospective Study

Characterization of metabolic alterations in the lean metabolically unhealthy alpha defensin transgenic mice

Inflammation is consistently linked to dysmetabolism. In transgenic mice (Def+/+) model the neutrophilic peptide, alpha defensin, proved atherogenic. This phenotype occurred despite favorable cholesterol and glucose levels, and lower body weight and blood pressure. In this study, integration of metabolic&behavioral phenotyping system, endocrine, biochemical and mitochondrial assessment, pathological and immunohistochemical tests, and multiple challenge tests was established to explore the metabolic impact of alpha defensin. Compared to the control group, Def+/+ mice exhibited lower total energy expenditure and carbohydrate utilization, and higher fat oxidation. Their ACTH-cortisol and thyroid profiles were intact. Intriguingly, they had low levels of glucagon, with high ammonia, uric acid, triglyceride, and lactate. Mitochondrial evaluations were normal. Overall, defensin-induced hypoglucagonemia is associated with lipolysis, restricted glucose oxidation, and enhanced wasting. Def+/+ mice may be a useful model for studying the category of lean, apparently metabolically healthy, and atherosclerotic phenotype, with insight into a potential inflammatory-metabolic link.

A systematic review of metabolomic findings in adult and pediatric renal disease

Chronic kidney disease (CKD) affects over 0.5 billion people worldwide across their lifetimes. Despite a growingly ageing world population, an increase in all-age prevalence of kidney disease persists. Adult-onset forms of kidney disease often result from lifestyle-modifiable metabolic illnesses such as type 2 diabetes. Pediatric and adolescent forms of renal disease are primarily caused by morphological abnormalities of the kidney, as well as immunological, infectious and inherited metabolic disorders. Alterations in energy metabolism are observed in CKD of varying causes, albeit the molecular mechanisms underlying pathology are unclear. A systematic indexing of metabolites identified in plasma and urine of patients with kidney disease alongside disease enrichment analysis uncovered inborn errors of metabolism as a framework that links features of adult and pediatric kidney disease. The relationship of genetics and metabolism in kidney disease could be classified into three distinct landscapes: (i) Normal genotypes that develop renal damage because of lifestyle and / or comorbidities; (ii) Heterozygous genetic variants and polymorphisms that result in unique metabotypes that may predispose to the development of kidney disease via synergistic heterozygosity, and (iii) Homozygous genetic variants that cause renal impairment by perturbing metabolism, as found in children with monogenic inborn errors of metabolism. Interest in the identification of early biomarkers of onset and progression of CKD has grown steadily in the last years, though it has not translated into clinical routine yet. This systematic review indexes findings of differential concentration of metabolites and energy pathway dysregulation in kidney disease and appraises their potential use as biomarkers.

Potential Biomarkers of Mitochondrial Dysfunction Associated with COVID-19 Infection

Mitochondria play crucial roles in modulating immune responses, and viruses can in turn moderate mitochondrial functioning. Therefore, it is not judicious to assume that clinical outcome experienced in patients with COVID-19 or long COVID may be influenced by mitochondrial dysfunction in this infection. Also, patients who are predisposed to mitochondrial respiratory chain (MRC) disorders may be more susceptible to worsened clinical outcome associated with COVID-19 infection and long COVID. MRC disorders and dysfunction require a multidisciplinary approach for their diagnosis of which blood and urinary metabolite analysis may be utilized, including the measurement of lactate, organic acid and amino acid levels. More recently, hormone-like cytokines including fibroblast growth factor-21 (FGF-21) have also been used to assess possible evidence of MRC dysfunction. In view of their association with MRC dysfunction, assessing evidence of oxidative stress parameters including GSH and coenzyme Q10 (CoQ10) status may also provide useful biomarkers for diagnosis of MRC dysfunction. To date, the most reliable biomarker available for assessing MRC dysfunction is the spectrophotometric determination of MRC enzyme activities in skeletal muscle or tissue from the disease-presenting organ. Moreover, the combined use of these biomarkers in a multiplexed targeted metabolic profiling strategy may further improve the diagnostic yield of the individual tests for assessing evidence of mitochondrial dysfunction in patients pre- and post-COVID-19 infection.

The Biochemical Assessment of Mitochondrial Respiratory Chain Disorders

Mitochondrial respiratory chain (MRC) disorders are a complex group of diseases whose diagnosis requires a multidisciplinary approach in which the biochemical investigations play an important role. Initial investigations include metabolite analysis in both blood and urine and the measurement of lactate, pyruvate and amino acid levels, as well as urine organic acids. Recently, hormone-like cytokines, such as fibroblast growth factor-21 (FGF-21), have also been used as a means of assessing evidence of MRC dysfunction, although work is still required to confirm their diagnostic utility and reliability. The assessment of evidence of oxidative stress may also be an important parameter to consider in the diagnosis of MRC function in view of its association with mitochondrial dysfunction. At present, due to the lack of reliable biomarkers available for assessing evidence of MRC dysfunction, the spectrophotometric determination of MRC enzyme activities in skeletal muscle or tissue from the disease-presenting organ is considered the ‘Gold Standard’ biochemical method to provide evidence of MRC dysfunction. The purpose of this review is to outline a number of biochemical methods that may provide diagnostic evidence of MRC dysfunction in patients.

Blood biomarkers for assessment of mitochondrial dysfunction: An expert review

Although mitochondrial dysfunction is the known cause of primary mitochondrial disease, mitochondrial dysfunction is often difficult to measure and prove, especially when biopsies of affected tissue are not available. In order to identify blood biomarkers of mitochondrial dysfunction, we reviewed studies that measured blood biomarkers in genetically, clinically or biochemically confirmed primary mitochondrial disease patients. In this way, we were certain that there was an underlying mitochondrial dysfunction which could validate the biomarker. We found biomarkers of three classes: 1) functional markers measured in blood cells, 2) biochemical markers of serum/plasma and 3) DNA markers. While none of the reviewed single biomarkers may perfectly reveal all underlying mitochondrial dysfunction, combining biomarkers that cover different aspects of mitochondrial impairment probably is a good strategy. This biomarker panel may assist in the diagnosis of primary mitochondrial disease patients. As mitochondrial dysfunction may also play a significant role in the pathophysiology of multifactorial disorders such as Alzheimer's disease and glaucoma, the panel may serve to assess mitochondrial dysfunction in complex multifactorial diseases as well and enable selection of patients who could benefit from therapies targeting mitochondria.

Elevated levels of urine isocitrate, hydroxymethylglutarate, and formiminoglutamate are associated with arterial stiffness in Korean adults

Recent evidence suggests that cellular perturbations play an important role in the pathogenesis of cardiovascular diseases. Therefore, we analyzed the association between the levels of urinary metabolites and arterial stiffness. Our cross-sectional study included 330 Korean men and women. The brachial-ankle pulse wave velocity was measured as a marker of arterial stiffness. Urinary metabolites were evaluated using a high-performance liquid chromatograph-mass spectrometer. The brachial-ankle pulse wave velocity was found to be positively correlated with l-lactate, citrate, isocitrate, succinate, malate, hydroxymethylglutarate, α-ketoisovalerate, α-keto-β-methylvalerate, methylmalonate, and formiminoglutamate among men. Whereas, among women, the brachial-ankle pulse wave velocity was positively correlated with cis-aconitate, isocitrate, hydroxymethylglutarate, and formiminoglutamate. In the multivariable regression models adjusted for conventional cardiovascular risk factors, three metabolite concentrations (urine isocitrate, hydroxymethylglutarate, and formiminoglutamate) were independently and positively associated with brachial-ankle pulse wave velocity. Increased urine isocitrate, hydroxymethylglutarate, and formiminoglutamate concentrations were associated with brachial-ankle pulse wave velocity and independent of conventional cardiovascular risk factors. Our findings suggest that metabolic disturbances in cells may be related to arterial stiffness.

Biomarkers for mitochondrial energy metabolism diseases

Biomarkers are an indicator of biologic or pathogenic processes, whose function is indicating the presence/absence of disease or monitoring disease course and its response to treatment. Since mitochondrial disorders (MDs) can represent a diagnostic challenge for clinicians, due to their clinical and genetic heterogeneity, the identification of easily measurable biomarkers becomes a high priority. Given the complexity of MD, in particular the primary mitochondrial respiratory chain (MRC) diseases due to oxidative phosphorylation (OXPHOS) dysfunction, a reliable single biomarker, relevant for the whole disease group, could be extremely difficult to find, most of times leading the physicians to better consider a 'biosignature' for the diagnosis, rather than a single biochemical marker. Serum biomarkers like lactate and pyruvate are largely determined in the diagnostic algorithm of MD, but they are not specific to this group of disorders. The concomitant determination of creatine (Cr), plasma amino acids, and urine organic acids might be helpful to reinforce the biosignature in some cases. In recent studies, serum fibroblast growth factor 21 (sFGF21) and serum growth differentiation factor 15 (sGDF15) appear to be promising molecules in identifying MD. Moreover, new different approaches have been developed to discover new MD biomarkers. This work discusses the most important biomarkers currently used in the diagnosis of MRC diseases, and some approaches under evaluation, discussing both their utility and weaknesses.

Mutation in the COX4I1 gene is associated with short stature, poor weight gain and increased chromosomal breaks, simulating Fanconi anemia

We describe a novel autosomal recessive form of mitochondrial disease in a child with short stature, poor weight gain, and mild dysmorphic features with highly suspected Fanconi anemia due to a mutation in COX4I1 gene. Whole Exome Sequencing was performed then followed by Sanger confirmation, identified a K101N mutation in COX4I1, segregating with the disease. This nuclear gene encodes the common isoform of cytochrome c oxidase (COX) subunit 4 (COX 4-1), an integral regulatory part of COX (respiratory chain complex IV) the terminal electron acceptor of the mitochondrial respiratory chain. The patient's fibroblasts disclosed decreased COX activity, impaired ATP production, elevated ROS production, decreased expression of COX4I1 mRNA and undetectable (COX4) protein. COX activity and ATP production were restored by lentiviral transfection with the wild-type gene. Our results demonstrate the first human mutation in the COX4I1 gene linked to diseases and confirm its role in the pathogenesis. Thus COX4I1 mutations should be considered in any patient with features suggestive of this diagnosis.