The multiple roles of coenzyme Q in cellular homeostasis and their relevance for the pathogenesis of coenzyme Q deficiency

Coenzyme Q (CoQ) is a redox active lipid that plays a central role in cellular homeostasis. It was discovered more than 60 years ago because of its role as electron transporter in the mitochondrial respiratory chain. Since then it has become evident that CoQ has many other functions, not directly related to bioenergetics. It is a cofactor of several mitochondrial dehydrogenases involved in the metabolism of lipids, amino acids, and nucleotides, and in sulfide detoxification. It is a powerful antioxidant and it is involved in the control of programmed cell death by modulating both apoptosis and ferroptosis. CoQ deficiency is a clinically and genetically heterogeneous group of disorders characterized by the impairment of CoQ biosynthesis. CoQ deficient patients display defects in cellular bioenergetics, but also in the other pathways in which CoQ is involved. In this review we will focus on the functions of CoQ not directly related to the respiratory chain, and on how their impairment is relevant for the pathophysiology of CoQ deficiency. A better understanding of the complex set of events triggered by CoQ deficiency will allow to design novel approaches for the treatment of this condition.

New pathogenic variants in COQ4 cause ataxia and neurodevelopmental disorder without detectable CoQ10 deficiency in muscle or skin fibroblasts

COQ4 is a component of an enzyme complex involved in the biosynthesis of coenzyme Q₁₀ (CoQ₁₀), a molecule with primary importance in cell metabolism. Mutations in the COQ4 gene are responsible for mitochondrial diseases showing heterogeneous age at onset, clinical presentations and association with CoQ₁₀ deficiency. We herein expand the phenotypic and genetic spectrum of COQ4-related diseases, by reporting two patients harboring bi-allelic variants but not showing CoQ₁₀ deficiency. One patient was found to harbor compound heterozygous mutations (specifically, c.577C>T/p.Pro193Ser and the previously reported c.718C>T/p.Arg240Cys) associated with progressive spasticity, while the other harbored two novel missense (c.284G>A/p.Gly95Asp and c.305G>A/p.Arg102His) associated with a neurodevelopmental disorder. Both patients presented motor impairment and ataxia. To further understand the role of COQ4, we performed functional studies in patient-derived fibroblasts, yeast and "crispant" zebrafish larvae. Micro-oxygraphy showed impaired oxygen consumption rates in one patient, while yeast complementation assays showed that all the mutations were presumably disease related. Moreover, characterization of the coq4 F0 CRISPR zebrafish line showed motor defects and cell reduction in a specific area of the hindbrain, a region reminiscent of the human cerebellum. Our expanded phenotype associated with COQ4 mutations allowed us to investigate, for the first time, the role of COQ4 in brain development in vivo.

Mutations in COQ8B (ADCK4) found in patients with steroid-resistant nephrotic syndrome alter COQ8B function

Mutations in COQ8B cause steroid-resistant nephrotic syndrome with variable neurological involvement. In yeast, COQ8 encodes a protein required for coenzyme Q (CoQ) biosynthesis, whose precise role is not clear. Humans harbor two paralog genes: COQ8A and COQ8B (previously termed ADCK3 and ADCK4). We have found that COQ8B is a mitochondrial matrix protein peripherally associated with the inner membrane. COQ8B can complement a ΔCOQ8 yeast strain when its mitochondrial targeting sequence (MTS) is replaced by a yeast MTS. This model was employed to validate COQ8B mutations, and to establish genotype-phenotype correlations. All mutations affected respiratory growth, but there was no correlation between mutation type and the severity of the phenotype. In fact, contrary to the case of COQ2, where residual CoQ biosynthesis correlates with clinical severity, patients harboring hypomorphic COQ8B alleles did not display a different phenotype compared with those with null mutations. These data also suggest that the system is redundant, and that other proteins (probably COQ8A) may partially compensate for the absence of COQ8B. Finally, a COQ8B polymorphism, present in 50% of the European population (NM_024876.3:c.521A > G, p.His174Arg), affects stability of the protein and could represent a risk factor for secondary CoQ deficiencies or for other complex traits.

Infective and non-infective endocarditis in critically ill patients: a clinical-pathological study

The aims of this study are to estimate the incidence, the outcome and the associated risk factors of infective and non-infective endocarditis (IE and NIE, respectively) in intensive care unit (ICU) patients. We studied the post-mortem findings and the clinical data of the patients who died in our ICU between 1996 and 2010. Of the 765 reviewed autopsies, 21 patients (2.7%) presented cardiac vegetations. These cases consisted of 12 IEs and 9 NIEs. Three patients with IE had a mechanical prosthetic valve, and in 11 cases invasive devices had been used. Multiple peripheral embolisms were discovered at autopsy. In particular, the brain appeared to be more affected in patients with IE, while pulmonary embolisms were commonly associated with NIE. Blood cultures were positive in nine patients with IE. The imaging diagnostics (transthoracic and transesophageal echocardiography) which were seldom performed in both groups, proved to be of little help. As a consequence, an IE was correctly diagnosed before death in three patients (25%) and suspected in two other cases (17%), while a NIE was diagnosed before death in one patient alone. In conclusions, critically ill patients admitted to general ICUs, multiple factors related both to the underlying conditions and to performed procedures can facilitate the occurrence of IE and NIE making, at the same time, their diagnosis challenging. Many cases, in fact, are diagnosed only at autopsy. Yet again, post-mortem examination proves to be an invaluable tool for the evaluation of diagnostic accuracy in critical care.

Pulmonary embolism in critically ill patients receiving antithrombotic prophylaxis: a clinical-pathologic study

PURPOSE

The true incidence of pulmonary embolism (PE) in critically ill adult patients receiving antithrombotic prophylaxis is unknown, as well as the impact on the outcome. The aim of this study was to assess the incidence of PE in a surgical and medical intensive care unit and to evaluate the presence of risk factors that could be helpful in identifying patients at higher risk of missed diagnosis.

MATERIALS AND METHODS

We retrospectively reviewed the autopsies and clinical data of all patients who died in our intensive care unit from 1996 to 2007. All patients received prophylaxis with subcutaneous low-molecular weight heparin.

RESULTS

Among the 600 autopsies, the clinical diagnosis of PE was confirmed in 13 patients (true positives) and not confirmed in 20 patients; in 73 patients, the PE was discovered only at the autopsy (false negatives [FNs]). The overall incidence of PE in our patients was 14.3%. Pulmonary embolism was considered the cause of death in 45% of FNs and 77% of true positives. Among all comorbidities, only a recent abdominal surgery and the presence of acute renal failure were associated with a higher risk of missed diagnosis. In the FN group, there was a significantly higher frequency of cases of septic shock.

CONCLUSIONS

Despite thromboprophylaxis, critically ill patients remain at risk for PE; and because of the difficulty in diagnosing it clinically, the death certificate diagnosis of PE underestimates the problem.

Acute myocardial infarction in non-cardiac critically ill patients: a clinical-pathological study

BACKGROUND

In patients admitted to the Intensive Care Unit (ICU) for non cardiac disease, the diagnosis of acute coronary syndromes can be challenging. The aim of the study was to define the rate of discrepancies concerning the diagnosis of acute myocardial infarction and to evaluate the presence of risk factors that could be helpful in identifying patients at higher risk of missed diagnosis.

METHODS

We compared clinical and autopsy records of 600 critically ill patients who died in our ICU in a 10-years period. We identified patients in whom acute myocardial infarction was reported as the cause of death on the clinical records or was discovered only at post-mortem examination. These subjects were subsequently divided into two Groups: patients in Group 1 underwent diagnostic evaluation for acute myocardial infarction whereas those in Group 2 were not investigated for.

RESULTS

In Group 1, a definite clinical diagnosis was reached in 11 patients (14,7%) but remained undetermined in 37 patients (48%). The diagnosis was totally missed in 8 patients in Group 1 (10,6%) and in 20 patients of Group 2 (26,6%). The diagnostic discrepancy was higher in septic patients, in whom the correct diagnosis of acute myocardial infarction was established at a rate lower than 50% in respect to non-septic patients.

CONCLUSIONS

Our experience strengthens the role of post-mortem examination as a source of feed-back of the overall diagnostic and therapeutic approach especially in septic patients, where the diagnostic error is more frequent.

B-type natriuretic peptide as a predictor of outcome in a general intensive care unit

BACKGROUND

B-type natriuretic peptide is a hormone secreted by the heart in response to ventricular wall stress. Increased B-type natriuretic peptide plasma levels are also found as a consequence of noncardiac conditions including sepsis, surgery-induced systemic inflammatory response syndrome and kidney failure. Since these conditions are common in general intensive care unit patients, we hypothesized that B-type natriuretic peptide could be a helpful marker in predicting outcome in this setting.

METHODS

We measured plasma B-type natriuretic peptide concentrations in 228 patients at admission to our general intensive care unit. The primary aim of the study was to investigate the relationship between B-type natriuretic peptide and hospital mortality. The secondary aim of the study was to investigate the association between B-type natriuretic peptide and severity of disease, quantified by the Simplified Acute Physiology Score II.

RESULTS

Logistic regression revealed a positive association between B-type natriuretic peptide level and in-hospital death (OR= 1.59; 95% CI 1.30 to 1.95; p<0.0001) and a Cox proportional hazards regression model showed that B-type natriuretic peptide was significantly associated with the risk of death (HR=1.27; 95% CI 1.11 to 1.46; p=0.0005). B-type natriuretic peptide was higher in patients who died in the hospital than in those who survived (371.20 pg/ml vs. 127.10 pg/ml; p<0.0001). There was a positive correlation between B-type natriuretic peptide and Simplified Acute Physiology Score II (r=0.50; 95% CI 0.40 to 0.59; p<0.0001).

DISCUSSION

B-type natriuretic peptide on admission is an independent prognostic marker of outcome in an unselected cohort of critically ill patients.

Early and prolonged ECG alterations resembling a myocardial injury after severe amitriptyline poisoning

Evidence of cardiovascular toxicity is present in the majority of tricyclic antidepressant overdoses. We report the case of a 63-year-old woman admitted to our department with a severe amitriptyline poisoning. The ECG at admission showed a pattern mimicking an acute anteroseptal subepicardial infarction. This pattern persisted for 11 days. Myocardial enzymes and echocardiographic findings never confirmed an ischemic event. At discharge, the ECG returned normal without cardiac or neurologic sequelae. Our experience suggest that after severe tricyclic antidepressant ingestion, ECG alterations resembling myocardial injury may occur early and last for a longer period than previously reported.