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We aimed to investigate how assimilation of nutrients affects the postprandial responses of glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) and to evaluate the effect of pancreatic enzyme substitution (PES) on insulin secretion in patients with chronic pancreatitis (CP) and pancreatic exocrine insufficiency (PEI). Eight male patients with CP and PEI were studied. Blood was sampled frequently on two separate days after ingestion of a liquid meal with and without PES, respectively. Eight healthy male subjects served as a control group. [beta]-Cell responsiveness was estimated as changes in insulin secretion rates in response to changes in postprandial plasma glucose (PG). There was no difference in the PG incremental area under curve (AUC) for patients with and without PES [406 [+ or -] 100 vs. 425 [+ or -] 80 mM * 4 h (mean [+ or -] SE), P = 0.8]. The response of total GLP-1 was higher after PES (AUC: 7.8 [+ or -] 1.2 vs. 5.3 [+ or -] 0.6 nM * 4 h, P = 0.01), as was the response of total GIP (AUC: 32.7 [+ or -] 7.5 vs. 21.1 [+ or -] 8.3 nM * 4 h, P = 0.01). Concurrently, both plasma insulin, plasma C-peptide, and total insulin secretion increased after PES (AUC: 17.7 [+ or -] 4.2 vs. 13.6 [+ or -] 2.9 nM * 4 h, P = 0.02; 237 [+ or -] 31.4 vs. 200 [+ or -] 27.4 nM * 4 h, P = 0.005; and 595 [+ or -] 82 vs. 497 [+ or -] 80 pmol * [kg.sup.-1] * 4 h, P = 0.01, respectively). [beta]-Cell responsiveness to glucose was not significantly different on the two study days for patients with CP. These results suggest that the secretion of GLP-1 and GIP is under influence of the digestion and absorption of nutrients in the small intestine and that PES increases insulin secretion. pancreatic exocrine insufficiency; glucagon-like peptide-1; glucose-dependent insulinotropic polypeptide

Nicotinamide adenine dinucleotide (NAD+) can be synthesized by nicotinamide phosphoribosyltransferase (NAMPT). We aimed to determine the role of NAMPT in maintaining NAD+ levels, mitochondrial function, and metabolic homeostasis in skeletal muscle cells. We generated stable Nampt knockdown (shNampt KD) C2C12 cells using a shRNA lentiviral approach. Moreover, we applied gene electrotransfer to express Cre recombinase in tibialis anterior muscle of floxed Nampt mice. In shNampt KD C2C12 myoblasts, Nampt and NAD+ levels were reduced by 70% and 50%, respectively, and maximal respiratory capacity was reduced by 25%. Moreover, anaerobic glycolytic flux increased by 55%, and 2-deoxyglucose uptake increased by 25% in shNampt KD cells. Treatment with the NAD+ precursor nicotinamide riboside restored NAD+ levels in shNampt cells and increased maximal respiratory capacity by 18% and 32% in control and shNampt KD cells, respectively. Expression of Cre recombinase in muscle of floxed Nampt mice reduced NAMPT and NAD+ levels by 38% and 43%, respectively. Glucose uptake increased by 40%, and mitochondrial complex IV respiration was compromised by 20%. Hypoxiainducible factor (HIF)-1α-regulated genes and histone H3 lysine 9 (H3K9) acetylation, a known sirtuin 6 (SIRT6) target, were increased in shNampt KD cells. Thus, we propose that the shift toward glycolytic metabolism observed, at least in part, is mediated by the SIRT6/HIF1α axis. Our findings suggest that NAMPT plays a key role for maintaining NAD+ levels in skeletal muscle and that NAMPT deficiency compromises oxidative phosphorylation capacity and alters energy homeostasis in this tissue. [ABSTRACT FROM AUTHOR]

We aimed to investigate how assimilation of nutrients affects the postprandial responses of glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) and to evaluate the effect of pancreatic enzyme substitution (PES) on insulin secretion in patients with chronic pancreatitis (CP) and pancreatic exocrine insufficiency (PET). Eight male patients with CP and PEI were studied. Blood was sampled frequently on two separate days after ingestion of a liquid meal with and without PES, respectively. Eight healthy male subjects served as a control group. β-Cell responsiveness was estimated as changes in insulin secretion rates in response to changes in postprandial plasma glucose (PG). There was no difference in the PG incremental area under curve (AUC) for patients with and without PES [406 ± 100 vs. 425 ± 80 mM·4 h (mean ± SE), P = 0.8]. The response of total GLP-1 was higher after PES (AUC: 7.8 ± 1.2 vs. 5.3 ± 0.6 nM·4 h, P = 0.01), as was the response of total GIP (AUC: 32.7 ± 7.5 vs. 21.1 ± 8.3 nM·4 h, P = 0.01). Concurrently, both plasma insulin, plasma C-peptide, and total insulin secretion increased after PES (AUC: 17.7 ± 4.2 vs. 13.6 ± 2.9 nM·4 h, P = 0.02; 237 ± 31.4 vs. 200 ± 27.4 nM·4 h, P = 0.005; and 595 ± 82 vs. 497 ± 80 pmol·kg-1·4 h, P = 0.01, respectively). β-Cell responsiveness to glucose was not significantly different on the two study days for patients with CP. These results suggest that the secretion of GLP-1 and GIP is under influence of the digestion and absorption of nutrients in the small intestine and that PES increases insulin secretion. [ABSTRACT FROM AUTHOR]

Nicotinamide adenine dinucleotide (NAD + ) can be synthesized by nicotinamide phosphoribosyltransferase (NAMPT). We aimed to determine the role of NAMPT in maintaining NAD + levels, mitochondrial function, and metabolic homeostasis in skeletal muscle cells. We generated stable Nampt knockdown (sh Nampt KD) C2C12 cells using a shRNA lentiviral approach. Moreover, we applied gene electrotransfer to express Cre recombinase in tibialis anterior muscle of floxed Nampt mice. In sh Nampt KD C2C12 myoblasts, Nampt and NAD + levels were reduced by 70% and 50%, respectively, and maximal respiratory capacity was reduced by 25%. Moreover, anaerobic glycolytic flux increased by 55%, and 2-deoxyglucose uptake increased by 25% in sh Nampt KD cells. Treatment with the NAD + precursor nicotinamide riboside restored NAD + levels in sh Nampt cells and increased maximal respiratory capacity by 18% and 32% in control and sh Nampt KD cells, respectively. Expression of Cre recombinase in muscle of floxed Nampt mice reduced NAMPT and NAD + levels by 38% and 43%, respectively. Glucose uptake increased by 40%, and mitochondrial complex IV respiration was compromised by 20%. Hypoxia-inducible factor (HIF)-1α-regulated genes and histone H3 lysine 9 (H3K9) acetylation, a known sirtuin 6 (SIRT6) target, were increased in shNampt KD cells. Thus, we propose that the shift toward glycolytic metabolism observed, at least in part, is mediated by the SIRT6/HIF1α axis. Our findings suggest that NAMPT plays a key role for maintaining NAD + levels in skeletal muscle and that NAMPT deficiency compromises oxidative phosphorylation capacity and alters energy homeostasis in this tissue.

Unlike cardiac and skeletal muscle, little is known about vascular smooth muscle mitochondrial respiration. Therefore, the present study examined mitochondrial respiratory rates in smooth muscle of healthy human feed arteries and compared with that of healthy cardiac and skeletal muscles. Cardiac, skeletal, and smooth muscles were harvested from a total of 22 subjects (53 ± 6 yr), and mitochondrial respiration was assessed in permeabilized fibers. Complex I + II, state 3 respiration, an index of oxidative phosphorylation capacity, fell progressively from cardiac to skeletal to smooth muscles (54 ± 1, 39 ± 4, and 15 ± 1 pmol·s(-1)·mg(-1), P < 0.05, respectively). Citrate synthase (CS) activity, an index of mitochondrial density, also fell progressively from cardiac to skeletal to smooth muscles (222 ± 13, 115 ± 2, and 48 ± 2 μmol·g(-1)·min(-1), P < 0.05, respectively). Thus, when respiration rates were normalized by CS (respiration per mitochondrial content), oxidative phosphorylation capacity was no longer different between the three muscle types. Interestingly, complex I state 2 normalized for CS activity, an index of nonphosphorylating respiration per mitochondrial content, increased progressively from cardiac to skeletal to smooth muscles, such that the respiratory control ratio, state 3/state 2 respiration, fell progressively from cardiac to skeletal to smooth muscles (5.3 ± 0.7, 3.2 ± 0.4, and 1.6 ± 0.3 pmol·s(-1)·mg(-1), P < 0.05, respectively). Thus, although oxidative phosphorylation capacity per mitochondrial content in cardiac, skeletal, and smooth muscles suggest all mitochondria are created equal, the contrasting respiratory control ratio and nonphosphorylating respiration highlight the existence of intrinsic functional differences between these muscle mitochondria. This likely influences the efficiency of oxidative phosphorylation and could potentially alter ROS production.

Chronic ischemic heart disease is associated with myocardial hypoperfusion. The resulting hypoxia potentially inflicts damage upon the mitochondria, leading to a compromised energetic state. Furthermore, ischemic damage may cause excessive production of reactive oxygen species (ROS), producing mitochondrial damage, hereby reinforcing a vicious circle. Ischemic preconditioning has been proven protective in acute ischemia, but the subject of chronic ischemic preconditioning has not been explored in humans. We hypothesized that mitochondrial respiratory capacity would be diminished in chronic ischemic regions of human myocardium but that these mitochondria would be more resistant to ex vivo ischemia and, second, that ROS generation would be higher in ischemic myocardium. The aim of this study was to test mitochondrial respiratory capacity during hyperoxia and hypoxia, to investigate ROS production, and finally to assess myocardial antioxidant levels. Mitochondrial respiration in biopsies from ischemic and nonischemic regions from the left ventricle of the same heart was compared in nine human subjects. Maximal oxidative phosphorylation capacity in fresh muscle fibers was lower in ischemic compared with nonischemic myocardium (P < 0.05), but the degree of coupling (respiratory control ratio) did not differ (P > 0.05). The presence of ex vivo hypoxia did not reveal any chronic ischemic preconditioning of the ischemic myocardial regions (P > 0.05). ROS production was higher in ischemic myocardium (P < 0.05), and the levels of antioxidant protein expression was lower. Diminished mitochondrial respiration capacity and excessive ROS production demonstrate an impaired mitochondrial function in ischemic human heart muscle. No chronic ischemic preconditioning effect was found.