Modeling the mitochondrial cardiomyopathy of Barth syndrome with iPSC and heart-on-chip technologies

Studying monogenic mitochondrial cardiomyopathies may yield insights into mitochondrial roles in cardiac development and disease. Here, we combine patient-derived and genetically engineered iPSCs with tissue engineering to elucidate the pathophysiology underlying the cardiomyopathy of Barth syndrome (BTHS), a mitochondrial disorder caused by mutation of the gene Tafazzin (TAZ). Using BTHS iPSC-derived cardiomyocytes (iPSC-CMs), we defined metabolic, structural, and functional abnormalities associated with TAZ mutation. BTHS iPSC-CMs assembled sparse and irregular sarcomeres, and engineered BTHS “heart on chip” tissues contracted weakly. Gene replacement and genome editing demonstrated that TAZ mutation is necessary and sufficient for these phenotypes. Sarcomere assembly and myocardial contraction abnormalities occurred in the context of normal whole cell ATP levels. Excess levels of reactive oxygen species mechanistically linked TAZ mutation to impaired cardiomyocyte function. Our study provides new insights into the pathogenesis of Barth syndrome, suggests new treatment strategies, and advances iPSC-based in vitro modeling of cardiomyopathy

No Relevant Relationship between Glucose Variability and Oxidative Stress in Well-Regulated Type 2 Diabetes Patients

A strong relationship between glycemic variability and oxidative stress in poorly regulated type 2 diabetes (T2DM) on oral medication has been reported. However, this relationship was not seen in type 1 diabetes. The purpose of this study is to reexamine the relation between glycemic variability and oxidative stress in a cohort of T2DM patients on oral medication. Twenty-four patients with T2DM on oral glucose lowering treatment underwent 48 hours of continuous glucose monitoring (CGMS® System GoldTM, Medtronic MiniMed) and simultaneous collection of two consecutive 24-hour urine samples for determination of 15(S)-8-iso-prostaglandin F2α (PGF2α) using high-performance liquid chromatography tandem mass spectrometry. Standard deviation (SD) and mean amplitude of glycemic excursions (MAGE) were calculated as markers of glycemic variability. Included in the study were 66.7% males with a mean age (range) of 59 (36-76) years and a mean (SD) HbA1c of 6.9% (0.7). Median [interquartile range (IQR)] urinary 15(S)-8-iso-PGF2α excretion was 176.1 (113.6-235.8) pg/mg creatinine. Median (IQR) SD was 31 (23-40) mg/dl and MAGE 85 (56-106) mg/dl. Spearman correlation did not show a significant relation for SD (ρ = 0.15, p = .49) or MAGE (ρ = 0.23, p = .29) with 15(S)-8-iso-PGF2α excretion. Multivariate regression analysis adjusted for age, sex, HbA1c, and exercise did not alter this observation. We did not find a relevant relationship between glucose variability and 15(S)-8-iso-PGF2α excretions in T2DM patients well-regulated with oral medication that would support an interaction between hyperglycemia and glucose variability with respect to the formation of reactive oxygen specie

Introduction of a Fluorine Atom at C3 of 3-Deazauridine Shifts Its Antimetabolic Activity from Inhibition of CTP Synthetase to Inhibition of Orotidylate Decarboxylase, an Early Event in the de Novo Pyrimidine Nucleotide Biosynthesis Pathway

The antimetabolite prodrug 3-deazauridine (3DUrd) inhibits CTP synthetase upon intracellular conversion to its triphosphate, which selectively depletes the intracellular CTP pools. Introduction of a fluorine atom at C3 of 3DUrd shifts its antimetabolic action to inhibition of the orotidylate decarboxylase (ODC) activity of the UMP synthase enzyme complex that catalyzes an early event in pyrimidine nucleotide biosynthesis. This results in concomitant depletion of the intracellular UTP and CTP pools. The new prodrug (designated 3F-3DUrd) exerts its inhibitory activity because its monophosphate is not further converted intracellularly to its triphosphate derivative to a detectable extent. Combinations with hypoxanthine and adenine markedly potentiate the cytostatic activity of 3F-3DUrd. This is likely because of depletion of 5-phosphoribosyl-1-pyrophosphate (consumed in the hypoxanthine phosphoribosyl transferase/adenine phosphoribosyl transferase reaction) and subsequent slowing of the 5-phosphoribosyl-1-pyrophosphate-dependent orotate phosphoribosyl transferase reaction, which depletes orotidylate, the substrate for ODC. Further efficient anabolism by nucleotide kinases is compromised apparently because of the decrease in pK(a) brought about by the fluorine atom, which affects the ionization state of the new prodrug. The 3F-3DUrd monophosphate exhibits new inhibitory properties against a different enzyme of the pyrimidine nucleotide metabolism, namely the ODC activity of UMP synthase.status: publishe

An UPLC-MS/MS assay to measure glutathione as marker for oxidative stress in cultured cells

Oxidative stress plays a role in the onset and progression of a number of diseases, such as Alzheimer’s disease, diabetes and cancer, as well as ageing. Oxidative stress is caused by an increased production of reactive oxygen species and reduced antioxidant activity, resulting in the oxidation of glutathione. The ratio of reduced to oxidised glutathione is often used as a marker of the redox state in the cell. Whereas a variety of methods have been developed to measure glutathione in blood samples, methods to measure glutathione in cultured cells are scarce. Here we present a protocol to measure glutathione levels in cultured human and yeast cells using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC–MS/MS)

A novel UPLC-MS/MS based method to determine the activity of N-acetylglutamate synthase in liver tissue.

N-acetylglutamate synthase (NAGS) plays a key role in the removal of ammonia via the urea cycle by catalyzing the synthesis of N-acetylglutamate (NAG), the obligatory cofactor in the carbamyl phosphate synthetase 1 reaction. Enzymatic analysis of NAGS in liver homogenates has remained insensitive and inaccurate, which prompted the development of a novel method. UPLC-MS/MS was used in conjunction with stable isotope (N-acetylglutamic-2,3,3,4,4-d5 acid) dilution for the quantitative detection of NAG produced by the NAGS enzyme. The assay conditions were optimized using purified human NAGS and the optimized enzyme conditions were used to measure the activity in mouse liver homogenates. A low signal-to-noise ratio in liver tissue samples was observed due to non-enzymatic formation of N-acetylglutamate and low specific activity, which interfered with quantitative analysis. Quenching of acetyl-CoA immediately after the incubation circumvented this analytical difficulty and allowed accurate and sensitive determination of mammalian NAGS activity. The specificity of the assay was validated by demonstrating a complete deficiency of NAGS in liver homogenates from Nags -/- mice. The novel NAGS enzyme assay reported herein can be used for the diagnosis of inherited NAGS deficiency and may also be of value in the study of secondary hyperammonemia present in various inborn errors of metabolism as well as drug treatmen

Is there an effect of obstructive sleep apnea syndrome on oxidative stress and inflammatory parameters in patients with craniofacial anomalies?

The aim of this study was to test the hypothesis that obstructive sleep apnea syndrome (OSAS) exhibits oxidative stress and inflammation in patients who have a congenital, craniofacial anomaly.This prospective, cross-sectional cohort study included ambulant sleep study data to asses OSAS in patients with syndromic craniosynostosis and Treacher Collins syndrome. Laboratory analyses were performed including malondialdehyde, tumor necrosis factor α (TNF-α), interleukin 6, and high-sensitivity C-reactive protein.Forty-eight patients were included; 11 were adults; 37 were children. The patients' body mass indexes were normal, with a median (SD) of 0.7 (-1.82 to 2.48) in children and 20.5 (15.2-29.4) in adults. Obstructive sleep apnea syndrome was diagnosed in 23 of 48 patients. It was mild (median obstructive apnea-hypopnea index [oAHI], 2.3; oxygenation-desaturation index [ODI], 0.9) in 16 patients and moderate/severe in 7 patients (median oAHI, 10.8; ODI, 5.0). Neither oxidative stress nor inflammation had a correlation with the oAHI and ODI. Only TNF-α was found significantly higher in both the OSAS and non-OSAS groups compared with the reference values (median, 15.1 pg/mL and 12.3 pg/mL versus 4.05 [0.0-8.1 pg/mL], P < 0.001 and P < 0.001, respectively).Based on our findings we conclude that (mainly mild) OSAS, oxidative stress, as well as high-sensitivity C-reactive protein and interleukin 6 levels are not abnormal in the day time in a population of nonobese patients with a craniofacial anomaly. The increased level of TNF-α cannot be explained by OSAS. Future research should focus on mapping chronobiologic changes for further interpretation of the result

RodZ and PgsA Play Intertwined Roles in Membrane Homeostasis of Bacillus subtilis and Resistance to Weak Organic Acid Stress

Weak organic acids like sorbic and acetic acid are widely used to prevent growth of spoilage organisms such as Bacilli. To identify genes involved in weak acid stress tolerance we screened a transposon mutant library of Bacillus subtilis for sorbic acid sensitivity. Mutants of the rodZ (ymfM) gene were found to be hypersensitive to the lipophilic weak organic acid. RodZ is involved in determining the cell's rod-shape and believed to interact with the bacterial actin-like MreB cytoskeleton. Since rodZ lies upstream in the genome of the essential gene pgsA (phosphatidylglycerol phosphate synthase) we hypothesized that expression of the latter might also be affected in rodZ mutants and hence contribute to the phenotype observed. We show that both genes are co-transcribed and that both the rodZ::mini-Tn10 mutant and a conditional pgsA mutant, under conditions of minimal pgsA expression, were sensitive to sorbic and acetic acid. Both strains displayed a severely altered membrane composition. Compared to the wild-type strain, phosphatidylglycerol and cardiolipin levels were lowered and the average acyl chain length was elongated. Induction of rodZ expression from a plasmid in our transposon mutant led to no recovery of weak acid susceptibility comparable to wild-type levels. However, pgsA overexpression in the same mutant partly restored sorbic acid susceptibility and fully restored acetic acid sensitivity. A construct containing both rodZ and pgsA as on the genome led to some restored growth as well. We propose that RodZ and PgsA play intertwined roles in membrane homeostasis and tolerance to weak organic acid stres

Genistein in Sanfilippo disease: A randomized controlled crossover trial

Objective: Sanfilippo disease (mucopolysaccharidosis type III [MPS III]) is a rare neurodegenerative metabolic disease caused by a deficiency of 1 of the 4 enzymes involved in the degradation of heparan sulfate (HS), a glycosaminoglycan (GAG). Genistein has been proposed as potential therapy but its efficacy remains uncertain. We aimed to determine the efficacy of genistein in MPS III. Methods: Thirty patients were enrolled. Effects of genistein were determined in a randomized, crossover, placebocontrolled intervention with a genistein-rich soy isoflavone extract (10mg/kg/day of genistein) followed by an openlabel extension study for patients who were on genistein during the last part of the crossover. Results: Genistein resulted in a significant decrease in urinary excretion of total GAGs (p 0.02, slope = 0.68mg GAGs/mmol creatinine/mo) and in plasma concentrations of HS (p 0.01, slope = 15.85ng HS/ml/mo). No effects on total behavior scores or on hair morphology were observed. Parents or caregivers could not predict correctly during which period of the crossover a patient was on genistein. Interpretation: Genistein at 10mg/kg/day effectively reduces urinary excretion of GAGs and plasma HS concentration in patients with MPS III. However, the absolute reduction in GAGs and in HS is small and values after 12 months of treatment remain within the range as observed in untreated patients. No clinical efficacy was detected. Substantially higher doses of genistein might be more effective as suggested by recent studies in animal models. ANN NEUROL 2012; 71: 110-12