Regulation of ATR-dependent DNA damage response by nitric oxide.

We have shown that nitric oxide limits ataxia-telangiectasia mutated signaling by inhibiting mitochondrial oxidative metabolism in a ß-cell selective manner. In this study, we examined the actions of nitric oxide on a second DNA damage response transducer kinase, ataxia-telangiectasia and Rad3-related protein (ATR). In ß-cells and non-ß-cells, nitric oxide activates ATR signaling by inhibiting ribonucleotide reductase; however, when produced at inducible nitric oxide synthase-derived (low micromolar) levels, nitric oxide impairs ATR signaling in a ß-cell selective manner. The inhibitory actions of nitric oxide are associated with impaired mitochondrial oxidative metabolism and lack of glycolytic compensation that result in a decrease in ß-cell ATP. Like nitric oxide, inhibitors of mitochondrial respiration reduce ATP levels and limit ATR signaling in a ß-cell selective manner. When non-ß-cells are forced to utilize mitochondrial oxidative metabolism for ATP generation, their response is more like ß-cells, as nitric oxide and inhibitors of mitochondrial respiration attenuate ATR signaling. These studies support a dual role for nitric oxide in regulating ATR signaling. Nitric oxide activates ATR in all cell types examined by inhibiting ribonucleotide reductase, and in a ß-cell selective manner, inducible nitric oxide synthase-derived levels of nitric oxide limit ATR signaling by attenuating mitochondrial oxidative metabolism and depleting ATP.

Decision-Making in Pleural Drainage Following Lung Resection in Children: A Western Pediatric Surgery Research Consortium Survey.

INTRODUCTION: Studies of adults undergoing lung resection indicated that selective omission of pleural drains is safe and advantageous. Significant practice variation exists for pleural drainage practices for children undergoing lung resection. We surveyed pediatric surgeons in a 10-hospital research consortium to understand decision-making for placement of pleural drains following lung resection in children. METHODS: Faculty surgeons at the 10 member institutions of the Western Pediatric Surgery Research Consortium completed questionnaires using a REDCap survey platform. Descriptive statistics and bivariate analyses were used to characterize responses regarding indications and management of pleural drains following lung resection in pediatric patients. RESULTS: We received 96 responses from 109 surgeons (88 %). Most surgeons agreed that use of a pleural drain after lung resection contributes to post-operative pain, increases narcotic use, and prolongs hospitalization. Opinions varied around the immediate use of suction compared to water seal, and half routinely completed a water seal trial prior to drain removal. Surgeons who completed fellowship within the past 10 years left a pleural drain after wedge resection in 45 % of cases versus 78 % in those who completed fellowship more than 10 years ago (p = 0.001). The mean acceptable rate of unplanned post-operative pleural drain placement when pleural drainage was omitted at index operation was 6.3 % (±4.6 %). CONCLUSIONS: Most pediatric surgeons use pleural drainage following lung resection, with recent fellowship graduates more often omitting it. Future studies of pleural drain omission demonstrating low rates of unplanned postoperative pleural drain placement may motivate practice changes for children undergoing lung resection. LEVEL OF EVIDENCE: V.

Chest Tube Management following Lung Resection in Pediatric Patients: A Retrospective Analysis.

BACKGROUND: Pleural drainage following lung resection is almost universally practiced in pediatric surgery, but its necessity has been questioned in adult literature. We performed a cross-sectional study of pediatric patients undergoing lung resection to characterize chest tube (CT) practices and clarify their utility. METHOD: Retrospective chart review of patients <21 years of age undergoing pulmonary lobectomy or wedge resection at an academic children's hospital from 2013 to 2022. Variables regarding demographics and post-operative CT management were recorded. RESULTS: 130 procedures meet inclusion criteria: 59 lobectomies (group 1), 19 diagnostic wedges (group 2), and 52 excisional wedges (group 3). 74.6% of group 1 patients had no air leak, and median CT duration was 2 days. In group 2, 89.5% had no air leak and median CT duration was 1 day. In Group 3, 80.8% had no air leak and median CT duration was 1 day. Overall, 43.1% patients had their CT removed on post-operative day 1 and 21.5% on post-operative day 2. CONCLUSION: CT duration following lung resection in pediatric patients is typically brief, with most patients having no air leak and CT removal within 2 days of surgery. Obligatory CT drainage may not be necessary in select patients undergoing lung resection. LEVEL OF EVIDENCE: Level IV. TYPE OF STUDY: Retrospective Study.

BCAA Metabolism and Insulin Sensitivity - Dysregulated by Metabolic Status?

Branched-chain amino acids (BCAAs) appear to influence several synthetic and catabolic cellular signaling cascades leading to altered phenotypes in mammals. BCAAs are most notably known to increase protein synthesis through modulating protein translation, explaining their appeal to resistance and endurance athletes for muscle hypertrophy, expedited recovery, and preservation of lean body mass. In addition to anabolic effects, BCAAs may increase mitochondrial content in skeletal muscle and adipocytes, possibly enhancing oxidative capacity. However, elevated circulating BCAA levels have been correlated with severity of insulin resistance. It is hypothesized that elevated circulating BCAAs observed in insulin resistance may result from dysregulated BCAA degradation. This review summarizes original reports that investigated the ability of BCAAs to alter glucose uptake in consequential cell types and experimental models. The review also discusses the interplay of BCAAs with other metabolic factors, and the role of excess lipid (and possibly energy excess) in the dysregulation of BCAA catabolism. Lastly, this article provides a working hypothesis of the mechanism(s) by which lipids may contribute to altered BCAA catabolism, which often accompanies metabolic disease.

Leucine, Palmitate, or Leucine/Palmitate Cotreatment Enhances Myotube Lipid Content and Oxidative Preference.

Branched-chain amino acids (BCAA) such as leucine stimulate favorable metabolic processes involved in lean tissue preservation and skeletal muscle metabolism. However, higher levels of circulating BCAA correlate with severity of metabolic disease (including diabetes/insulin resistance), and may result from dysregulated BCAA catabolism. Past observations have demonstrated potential interaction between BCAA and dietary fat; however, much of this relationship remains underexplored. This study investigated the effect of leucine both with and without palmitate on oxidative and glycolytic metabolism, as well as indicators of BCAA catabolism using cultured skeletal muscle cells. Specifically, C2C12 myotubes were treated with or without varying concentrations of leucine both with and without palmitate for 24 h. Leucine treatment significantly elevated mRNA expression of metabolic regulators including peroxisome proliferator-activated receptor-gamma coactivator 1-alpha versus leucine with concurrent palmitate treatment. Interestingly, leucine-only, palmitate-only, and leucine with palmitate all significantly increased cellular lipid content, which translated into significantly increased oxidative capacity under substrate-limited conditions. However, upon the addition of excess substrate and carnitine, discrepancies in peak metabolic capacities between various treatments were no longer observed, suggesting leucine, palmitate, or the combination thereof causes a shift in metabolic preference from glycolytic to oxidative. These data also suggest leucine's effect on mitochondrial metabolism may result in part from increased lipid stores in addition to other previously documented pathways.

Metabolic effects of physiological levels of caffeine in myotubes.

Caffeine has been shown to stimulate multiple major regulators of cell energetics including AMP-activated protein kinase (AMPK) and Ca2+/calmodulin-dependent protein kinase II (CaMKII). Additionally, caffeine induces peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) and mitochondrial biogenesis. While caffeine enhances oxidative metabolism, experimental concentrations often exceed physiologically attainable concentrations through diet. This work measured the effects of low-level caffeine on cellular metabolism and gene expression in myotubes, as well as the dependence of caffeine's effects on the nuclear receptor peroxisome proliferator-activated receptor beta/delta (PPARß/δ). C2C12 myotubes were treated with various doses of caffeine for up to 24 h. Gene and protein expression were measured via qRT-PCR and Western blot, respectively. Cellular metabolism was determined via oxygen consumption and extracellular acidification rate. Caffeine significantly induced regulators of mitochondrial biogenesis and oxidative metabolism. Mitochondrial staining was suppressed in PPARß/δ-inhibited cells which was rescued by concurrent caffeine treatment. Caffeine-treated cells also displayed elevated peak oxidative metabolism which was partially abolished following PPARß/δ inhibition. Similar to past observations, glucose uptake and GLUT4 content were elevated in caffeine-treated cells, however, glycolytic metabolism was unaltered following caffeine treatment. Physiological levels of caffeine appear to enhance cell metabolism through mechanisms partially dependent on PPARß/δ.

Characterization of the metabolic effect of ß-alanine on markers of oxidative metabolism and mitochondrial biogenesis in skeletal muscle.

PURPOSE: ß-alanine is a common component of numerous sports supplements purported to improve athletic performance through enhanced carnosine biosynthesis and related intracellular buffering. To date, the effects of ß-alanine on oxidative metabolism remain largely unexplored. This work investigated the effects of ß-alanine on the expression of proteins which regulate cellular energetics. METHODS: C2C12 myocytes were cultured and differentiated under standard conditions followed by treatment with either ß-alanine or isonitrogenous non-metabolizable control D-alanine at 800µM for 24 hours. Metabolic gene and protein expression were quantified by qRT-PCR and immunoblotting, respectively. Glucose uptake and oxygen consumption were measured via fluorescence using commercially available kits. RESULTS: ß-alanine-treated myotubes displayed significantly elevated markers of improved oxidative metabolism including elevated peroxisome proliferator-activated receptor ß/δ (PPARß/δ) and mitochondrial transcription factor a (TFAM) which led to increased mitochondrial content (evidenced by concurrent increases in cytochrome c content). Additionally, ß-alanine-treated cells exhibited significantly increased oxygen consumption compared to control in a PPARß/δ-dependent manner. ß-alanine significantly enhanced expression of myocyte enhancer factor 2 (MEF-2) leading to increased glucose transporter 4 (GLUT4) content. CONCLUSION: ß-alanine appears to increase cellular oxygen consumption as well as the expression of several cellular proteins associated with improved oxidative metabolism, suggesting ß-alanine supplementation may provide additional metabolic benefit (although these observations require in vivo experimental verification).

Acute ß-Hydroxy-ß-Methyl Butyrate Suppresses Regulators of Mitochondrial Biogenesis and Lipid Oxidation While Increasing Lipid Content in Myotubes.

Leucine modulates synthetic and degradative pathways in muscle, possibly providing metabolic benefits for both athletes and diseased populations. Leucine has become popular among athletes for improving performance and body composition, however little is known about the metabolic effects of the commonly consumed leucine-derived metabolite ß-hydroxy-ß-methyl butyrate (HMB). Our work measured the effects of HMB on metabolic protein expression, mitochondrial content and metabolism, as well as lipid content in skeletal muscle cells. Specifically, cultured C2C12 myotubes were treated with either a control or HMB ranging from 6.25 to 25 µM for 24 h and mRNA and/or protein expression, oxygen consumption, glucose uptake, and lipid content were measured. Contrary to leucine's stimulatory effect on metabolism, HMB-treated cells exhibited significantly reduced regulators of lipid oxidation including peroxisome proliferator-activated receptor alpha (PPARα) and PPARß/δ, as well as downstream target carnitine palmitoyl transferase, without alterations in glucose or palmitate oxidation. Furthermore, HMB significantly inhibited activation of the master regulator of energetics, AMP-activated protein kinase. As a result, HMB-treated cells also displayed reduced total mitochondrial content compared with true control or cells equivocally treated with leucine. Additionally, HMB treatment amplified markers of lipid biosynthesis (PPARγ and fatty acid synthase) as well as consistently promoted elevated total lipid content versus control cells. Collectively, our results demonstrate that HMB did not improve mitochondrial metabolism or content, and may promote elevated cellular lipid content possibly through heightened PPARγ expression. These observations suggest that HMB may be most beneficial for populations interested in stimulating anabolic cellular processes.

Leucine stimulates PPARß/δ-dependent mitochondrial biogenesis and oxidative metabolism with enhanced GLUT4 content and glucose uptake in myotubes.

Leucine stimulates anabolic and catabolic processes in skeletal muscle, however little is known about the effects of leucine on peroxisome proliferator-activated receptor (PPAR) activity. This work characterized the effects of 24-h leucine treatment on metabolic parameters and protein expression in cultured myotubes. Leucine significantly increased PPARß/δ expression as well as markers of mitochondrial biogenesis, leading to significantly increased mitochondrial content and oxidative metabolism in a PPARß/δ-dependent manner. However, leucine-treated cells did not display significant alterations in uncoupling protein expression or oxygen consumed per relative mitochondrial content suggesting leucine-mediated increases in oxidative metabolism are a function of increased mitochondrial content and not altered mitochondrial efficiency. Leucine treatment also increased GLUT4 content and glucose uptake as well as PPARγ and FAS expression leading to increased total lipid content. Leucine appears to activate PPAR activity leading to increased mitochondrial biogenesis and elevated substrate oxidation, while simultaneously promoting substrate/lipid storage and protein synthesis.

trans-Cinnamaldehyde stimulates mitochondrial biogenesis through PGC-1α and PPARß/δ leading to enhanced GLUT4 expression.

Type 2 diabetes is characterized by insulin resistance and chronic hyperglycemia, and is increasing in incidence and severity. This work explored the effects of trans-cinnamaldehyde (CA) on carbohydrate metabolism, mitochondrial content, and related metabolic gene and protein expression in cultured myotubes treated with various concentrations of CA for up to 24 h. CA treatment increased myotube myocyte enhancer factor 2 (MEF2) along with glucose transporter 4 (GLUT4) content. CA treatment also significantly increased expression of markers of improved oxidative metabolism including 5' adenosine monophosphate-activated protein kinase (AMPK), peroxisome proliferator-activated receptor γ coactivator 1 α (PGC-1α), cytochrome c (CytC), as well as peroxisome proliferator-activated receptor α (PPARα) and PPARß/δ. Despite increased expression of proteins associated with improved oxidative metabolism and glucose uptake, CA-treated myotubes exhibited significantly reduced oxidative metabolism compared with controlled cells. Additionally, CA treatment increased markers of glucose-mediated lipid biosynthesis without elevated PPARγ and sterol receptor element binding protein 1c (SREBP-1c) expression. The ability of CA to stimulate mitochondrial biogenesis and GLUT4 expression suggests CA may offer possible benefits for metabolic disease. However, increases in markers of fatty acid synthesis with simultaneously reduced oxidative metabolism suggest CA may have counterproductive effects for metabolic disease, warranting a need for further investigation.