Inspiratory flow-resistive breathing, respiratory muscle-induced systemic oxidative stress, and diaphragm fatigue in healthy humans.

We questioned whether the respiratory muscles of humans contribute to systemic oxidative stress following inspiratory flow-resistive breathing, whether the amount of oxidative stress is influenced by the level of resistive load, and whether the amount of oxidative stress is related to the degree of diaphragm fatigue incurred. Eight young and healthy participants attended the laboratory for four visits on separate days. During the first visit, height, body mass, lung function, and maximal inspiratory mouth and transdiaphragmatic pressure (Pdimax) were assessed. During visits 2-4, participants undertook inspiratory flow-resistive breathing with either no resistance (control) or resistive loads equivalent to 50 and 70% of their Pdimax (Pdimax50% and Pdimax70%) for 30 min. Participants undertook one resistive load per visit, and the order in which they undertook the loads was randomized. Inspiratory muscle pressures were higher (P < 0.05) during the 5th and Final min of Pdimax50% and Pdimax70% compared with control. Plasma F2-isoprostanes increased (P < 0.05) following inspiratory flow-resistive breathing at Pdimax70%. There were no increases in plasma protein carbonyls or total antioxidant capacity. Furthermore, although we evidenced small reductions in transdiapragmaic twitch pressures (PdiTW) after inspiratory flow-resistive breathing at Pdimax50% and Pdimax70%, this was not related to the increase in plasma F2-isoprostanes. Our novel data suggest that it is only when sufficiently strenuous that inspiratory flow-resistive breathing in humans elicits systemic oxidative stress evidenced by elevated plasma F2-isoprostanes, and based on our data, this is not related to a reduction in PdiTW.NEW & NOTEWORTHY We examined whether the respiratory muscles of humans contribute to systemic oxidative stress following inspiratory flow-resistive breathing, whether the amount of oxidative stress is influenced by the level of resistive load, and whether the amount of oxidative stress is related to the degree of diaphragm fatigue incurred. It is only when sufficiently strenuous that inspiratory flow-resistive breathing elevates plasma F2-isoprostanes, and our novel data show that this is not related to a reduction in transdiaphragmatic twitch pressure.

Targeted mitochondrial therapy using MitoQ shows equivalent renoprotection to angiotensin converting enzyme inhibition but no combined synergy in diabetes.

Mitochondrial dysfunction is a pathological mediator of diabetic kidney disease (DKD). Our objective was to test the mitochondrially targeted agent, MitoQ, alone and in combination with first line therapy for DKD. Intervention therapies (i) vehicle (D); (ii) MitoQ (DMitoQ;0.6 mg/kg/day); (iii) Ramipril (DRam;3 mg/kg/day) or (iv) combination (DCoAd) were administered to male diabetic db/db mice for 12 weeks (n = 11-13/group). Non-diabetic (C) db/m mice were followed concurrently. No therapy altered glycaemic control or body weight. By the study end, both monotherapies improved renal function, decreasing glomerular hyperfiltration and albuminuria. All therapies prevented tubulointerstitial collagen deposition, but glomerular mesangial expansion was unaffected. Renal cortical concentrations of ATP, ADP, AMP, cAMP, creatinine phosphate and ATP:AMP ratio were increased by diabetes and mostly decreased with therapy. A higher creatine phosphate:ATP ratio in diabetic kidney cortices, suggested a decrease in ATP consumption. Diabetes elevated glucose 6-phosphate, fructose 6-phosphate and oxidised (NAD+ and NADP+) and reduced (NADH) nicotinamide dinucleotides, which therapy decreased generally. Diabetes increased mitochondrial oxygen consumption (OCR) at complex II-IV. MitoQ further increased OCR but decreased ATP, suggesting mitochondrial uncoupling as its mechanism of action. MitoQ showed renoprotection equivalent to ramipril but no synergistic benefits of combining these agents were shown.

Effects of exercise and lifestyle intervention on oxidative stress in chronic kidney disease.

OBJECTIVES: Determine the effects of a 12-month exercise and lifestyle intervention program on changes in plasma biomarkers of oxidative stress in pre-dialysis chronic kidney disease (CKD) patients. METHODS: A total of 136 stage 3-4 CKD patients were randomized to receive standard nephrological care with (N = 72) or without (N = 64) a lifestyle and exercise intervention for 12 months. Plasma total F2-isoprostanes (IsoP), glutathione peroxidase (GPX) activity, total antioxidant capacity (TAC), anthropometric and biochemical data were collected at baseline and at 12 months. RESULTS: There were no significant differences between groups at baseline. There were no significant differences in changes for standard care and lifestyle intervention, respectively, in IsoP (p = 0.88), GPX (p = 0.87), or TAC (p = 0.56). Patients identified as having high IsoP at baseline (>250 pg/mL) had a greater decrease in IsoP with lifestyle intervention compared to standard care; however, the difference was not statistically significant (p = 0.06). There was no difference in the change in kidney function (eGFR) between standard care and lifestyle intervention (p = 0.33). DISCUSSION: Exercise and lifestyle modification in stage 3-4 CKD did not produce changes in systemic biomarkers of oxidative stress over a 12-month period, but patients with high IsoP may benefit most from the addition of intervention to standard care.

High intensity interval training favourably affects antioxidant and inflammation mRNA expression in early-stage chronic kidney disease.

Increased levels of oxidative stress and inflammation have been linked to the progression of chronic kidney disease. To reduce oxidative stress and inflammation related to chronic kidney disease, chronic aerobic exercise is often recommended. Data suggests high intensity interval training may be more beneficial than traditional aerobic exercise. However, appraisals of differing modes of exercise, along with explanations of mechanisms responsible for observed effects, are lacking. This study assessed effects of eight weeks of high intensity interval training (85% VO2max), versus low intensity exercise (45-50% VO2max) and sedentary behaviour, in an animal model of early-stage chronic kidney disease. We examined kidney-specific mRNA expression of genes related to endogenous antioxidant enzyme activity (glutathione peroxidase 1; Gpx1, superoxide dismutase 1; Sod1, and catalase; Cat) and inflammation (kidney injury molecule 1; Kim1 and tumour necrosis factor receptor super family 1b; Tnfrsf1b), as well as plasma F2-isoprostanes, a marker of lipid peroxidation. Compared to sedentary behaviour, high intensity interval training resulted in increased mRNA expression of Sod1 (p=0.01) and Cat (p<0.001). Compared to low intensity exercise, high intensity interval training resulted in increased mRNA expression of Cat (p<0.001) and Tnfrsf1b (p=0.047). In this study, high intensity interval training was superior to sedentary behaviour and low intensity exercise as high intensity interval training beneficially influenced expression of genes related to endogenous antioxidant enzyme activity and inflammation.

Oxidative stress contributes to muscle atrophy in chronic kidney disease patients.

OBJECTIVES: Patients with chronic kidney disease have impaired muscle metabolism, resulting in muscle atrophy. Oxidative stress has previously been identified as a significant contributor to muscle atrophy in other populations, but the contribution in chronic kidney disease is unknown. The aim of this study was to investigate the association between oxidative stress, grip strength, and lean mass in patients with chronic kidney disease. METHODS: This is a cross-sectional study of 152 participants with stage 3 or 4 chronic kidney disease. Outcome measures include grip strength, lean mass, plasma total F2-isoprostanes, inflammation, peak oxygen uptake, and standard clinical measures. RESULTS: Thirty four (22.4%) chronic kidney disease patients had elevated oxidative stress levels (plasma F2-isoprostanes >250 pg/ml), with 82% of patients below age-predicted grip strength normative values. There was a significant negative association between plasma F2-isoprostanes and grip strength (r = -0.251) and lean mass (r = -0.243). There were no associations with inflammation markers. Multiple linear regression identified plasma F2-isoprostanes as a significant predictor of grip strength independent of other predictors: sex, diabetes status, body mass index, body fat percent, and phosphate (adjusted r(2) = 69.5, P < 0.001). DISCUSSION: Plasma F2-isoprostanes were independently associated with reduced strength in chronic kidney disease patients.

Optimized method for quantification of total F(2)-isoprostanes using gas chromatography-tandem mass spectrometry.

F2-isoprostanes are produced from the oxidative degradation of arachidonic acid and are considered the gold standard marker of lipid peroxidation in biological samples. We developed a liquid-liquid extraction method for the determination of total isoprostanes using negative chemical ionization gas chromatography-tandem mass spectrometry in plasma and tissue homogenates. Incorporating liquid-liquid extraction allows for greater sample through-put than current approaches. Here we describe the protocol and include numerous trouble-shooting suggestions. The method found healthy individuals with 150-250 pg of isoprostanes per ml of plasma and end stage kidney disease patients to have the highest measured values of up to 1100 pg/ml. This assay has an accurate working linear range of 40-1000 pg of isoprostanes (100-2500 pg/ml) and an average coefficient of variance of 7%. Tissue values for healthy mice liver were 50-70 pg/µg protein. This method provides increased ion selectivity and detection capabilities with economical sample through-put.

Variability in oxidative stress biomarkers following a maximal exercise test.

The oxidative stress response to maximal exercise may provide useful clinical biomarkers for assessing redox homeostasis. The aim was to determine the between-individual variability in the exercise-induced change in oxidative stress measures and investigate predictors of these responses. Plasma F2-isoprostanes (Isop), protein carbonyls (PCs), glutathione peroxidase (GPX) activity and total antioxidant capacity (TAC) were measured before and after a maximal treadmill exercise test. Exercise produced significant increases in Isop (27.0%), PC (6.2%) and GPX (7.8%). There were large between-individual coefficients of variation: Isop (152%), PC, (240%), GPX (130%) and TAC (243%).