Carbohydrate ingestion reduces skeletal muscle acetylcarnitine availability but has no effect on substrate phosphorylation at the onset of exercise in man

This study investigated the effect of reduced acetylcarnitine availability on oxidative metabolism during the transition from rest to steady-state exercise. Eight male subjects completed two randomised exercise trials at 68 % of the peak rate of O2 uptake (V̇O2,peak). On one occasion subjects ingested 1 g (kg body mass)−1 glucose 75 min prior to exercise (CHO), whereas the other trial acted as a control (CON). Muscle samples were obtained pre- and 75 min post-ingestion, and following 1 and 10 min of exercise. Plasma glucose and insulin were elevated (P < 0.05), and plasma free fatty acids (FFA) were lower at the onset of exercise in CHO. Acetylcarnitine (CON, 4.8 ± 1.8; CHO, 1.5 ± 0.9 mmol (kg dry mass (d.m.))−1, P < 0.05) and acetyl CoA (CON, 13.2 ± 2.3; CHO, 6.3 ± 0.6 μmol (kg d.m.)−1, P < 0.05) were lower at rest, whereas pyruvate dehydrogenase activation (PDHa) was greater in CHO compared with CON (CON, 0.78 ± 0.07; CHO, 1.44 ± 0.19 mmol min−1 (kg wet mass (w.m.))−1). Respiratory exchange ratio (RER) was significantly elevated during exercise in CHO. The acetyl groups increased at similar rates at the onset of exercise (1 min) and there was no difference in substrate phosphorylation as determined from lactate accumulation and phosphocreatine degradation between trials. Subsequently, oxidative metabolism during the transition from rest to steady-state exercise was not affected by prior carbohydrate ingestion. Although exercise resulted in the rapid activation of PDH in both trials, PDHa was greater at 1 min in CHO (CON, 2.36 ± 0.22; CHO, 2.91 ± 0.18 mmol min−1 (kg w.m.)−1). No differences in muscle metabolite levels and PDHa were observed after 10 min of moderate exercise between trials. In summary, at rest, carbohydrate ingestion induced multiple metabolic changes which included decreased acetylcarnitine availability and small increases in PDHa. The prior changes in PDHa and acetylcarnitine availability had no effect on substrate phosphorylation and oxidative metabolism at the onset of exercise. These data suggest that acetylcarnitine availability is unlikely to be the site of metabolic inertia during the transition from rest to steady-state moderate intensity exercise.

Long-term effects of a reduced fat diet intervention on cardiovascular disease risk factors in individuals with glucose intolerance

The long-term effects on cardiovascular disease risk factors of a reduced fat (RF), ad libitum diet were compared with usual diet (control, CD) in glucose intolerance individuals.

Participants were 136 adults aged ≥40 years with ‘glucose intolerance’ (2 h blood glucose 7–11.0 mmol/l) detected at a Diabetes Survey who completed at 1 year intervention study of reduced fat, ad libitum diet versus usual diet. They were re-assessed at 2, 3 and 5 years. Main outcome measures were blood pressure, serum concentrations of total cholesterol, HDL and LDL cholesterol, total cholesterol:HDL ratio, triglycerides and body weight.

The reduced fat diet lowered total cholesterol (P<0.01), LDL cholesterol (P≤0.05), total cholesterol:HDL ratio (P≤0.05), body weight (P<0.01) and systolic blood pressure (P≤0.05) initially and diastolic blood pressure (P<0.01) long-term. No significant changes occurred in HDL cholesterol or triglycerides. In the more compliant 50% of the intervention group, systolic and diastolic blood pressure levels and body weight were lower at 1, 2 and 3 years (P<0.05).

It was concluded that a reduced fat ad libitum diet has short-term benefits for cholesterol, body weight and systolic blood pressure and long-term benefits for diastolic blood pressure without significantly effecting HDL cholesterol and triglycerides despite participants regaining their lost weight.

Pyruvate dehydrogenase activation and kinase expression in human skeletal muscle during fasting

Fasting forces adaptive changes in whole body and skeletal muscle metabolism that increase fat oxidation and decrease the oxidation of carbohydrate. We tested the hypothesis that 40 h of fasting would decrease pyruvate dehydrogenase (PDH) activity and increase PDH kinase (PDK) isoform mRNA expression in human skeletal muscle. The putative transcriptional activators of PDK isozymes, peroxisome proliferator-activated receptor-α (PPAR-α) protein, and forkhead homolog in rhabdomyosarcoma (FKHR) mRNA were also measured. Eleven healthy adults fasted after a standard meal (25% fat, 60% carbohydrate, 15% protein) with blood and skeletal muscle samples taken at 3, 15, and 40 h postprandial. Fasting increased plasma free fatty acid, glycerol, and β-hydroxybutyrate concentrations and decreased glucose and insulin concentrations. PDH activity decreased from 0.88 ± 0.11 mmol acetyl-CoA · min^-1 · kg wet muscle wt^-1 at 3 h to 0.62 ± 0.10 (P = not significant) and 0.39 ± 0.06 (P < 0.05) mmol · min^-1 · kg wet mass^-1 after 15 and 40 h of fasting. Although all four PDK isoforms were expressed in human skeletal muscle, PDK^-2 and -4 mRNA were the most abundant. PDK^-1 and ^-3 mRNA abundance was ~1 and 15% of the PDK^-2 and 4^- levels, respectively. The 40-h fast had no effect on PDK^-1, ^-2, and ^-3 mRNA expression. PDK-4 mRNA was significantly increased ~3-fold after 15 h and ~14-fold after 40 h of fasting. Skeletal muscle PPAR-α protein and FKHR mRNA abundance were unaffected by the fast. The results suggest that decreased PDH activation after 40 h of fasting may have been a function of the large increase in PDK-4 mRNA expression and possible subsequent increase in PDK protein and activity. The changes in PDK-4 expression and PDH activity did not coincide with increases in the transcriptional activators PPAR-α and FKHR.

Effects of aerobic training on pyruvate dehydrogenase and pyruvate dehydrogenase kinase in human skeletal muscle

This study examined the effects of short- and long-term aerobic training on the stable up-regulation of pyruvate dehydrogenase (PDH) and PDH kinase (PDK) in human skeletal muscle. We hypothesized that 8 weeks, but not 1 week, of aerobic training would increase total PDH (PDHt) and PDK activities compared to pretraining, and this would be detectable at the level of gene transcription (mRNA) and/or gene translation (protein). Resting muscle biopsies were taken before and after 1 and 8 weeks of aerobic cycle exercise training. PDHt and PDK activities, and their respective protein and mRNA expression, did not differ after 1 week of aerobic training. PDHt activity increased 31% after 8 weeks and this may be partially due to a 1.3-fold increase in PDH-E₁α protein expression. PDK activity approximately doubled after 8 weeks of aerobic training and this was attributed to a 1.3-fold increase in PDK2 isoform protein expression. Similar to 1 week, no changes were observed at the mRNA level after 8 weeks of training. These findings  suggest that aerobically trained human skeletal muscle has an increased maximal capacity to utilize carbohydrates, evident by increased PDHt, but increased metabolic control sensitivity to pyruvate through increased contribution of PDK2 to total PDK activity.

A mechanistic study on reduced toxicity of irontecan by coadministered thalidomide, a tumor necrosis factor-a inhibitor

Dose-limiting diarrhea and myelosuppression compromise the success of irinotecan (7-ethyl-10-[4-[1-piperidino]-1-piperidino] carbonyloxycamptothecin) (CPT-11)-based chemotherapy. A recent pilot study indicates that thalidomide attenuates the toxicity of CPT-11 in cancer patients. This study aimed to investigate whether coadministered thalidomide modulated the toxicities of CPT-11 and the underlying mechanisms using several in vivo and in vitro models. Diarrhea, intestinal lesions, cytokine expression, and intestinal epithelial apoptosis were
monitored. Coadministered thalidomide (100 mg/kg i.p. for 8 days) significantly attenuated body weight loss, myelosuppression, diarrhea, and intestinal histological lesions caused by CPT-11 (60 mg/kg i.v. for 4 days). This was accompanied by inhibition of tumor necrosis factor-, interleukins 1 and 6 and interferon-, and intestinal epithelial apoptosis. Coadministered
thalidomide also significantly increased the systemic exposure of CPT-11 but decreased that of SN-38 (7-ethyl-10-hydroxycampothecin). It significantly reduced the biliary excretion and cecal exposure of CPT-11, SN-38, and SN-38 glucuronide. Thalidomide hydrolytic products inhibited hydrolysis of CPT-11 in rat liver microsomes but not in primary rat hepatocytes. In addition, thalidomide and its major hydrolytic products, such as phthaloyl glutamic acid (PGA), increased the intracellular accumulation of CPT-11 and SN-38 in primary rat hepatocytes. They also significantly decreased the transport of CPT-11 and SN-38 in Caco-2 and parental MDCKII cells. Thalidomide and PGA also significantly inhibited P-glycoprotein (PgP/MDR1), multidrug resistance-associated protein (MRP1)- and MRP2-mediated CPT-11 and SN-38 transport in MDCKII cells. These results provide insights into the pharmacodynamic and  pharmacokinetic mechanisms for the protective effects of thalidomide against CPT-11-induced intestinal toxicity.

Pharmacokinetic mechanisms for reduced toxicity of irinotecan by coadministered Thalidomide

The clinical use of irinotecan (CPT-11) is hindered by dose-limiting diarrhea and myelosuppression. Recent clinical studies indicate that thalidomide, a known tumor necrosis factor-alpha inhibitor, ameliorated the toxicities induced by CPT-11. However, the mechanisms for this are unknown. This study aimed to investigate whether combination of thalidomide modulated the toxicities of CPT-11 using a rat model and the possible role of the altered pharmacokinetic component in the toxicity modulation using in vitro models. The toxicity model was constructed by treatment of healthy rats with CPT-11 at 60 mg/kg per day by intravenous (i.v.) injection. Body weight, acute and delayed-onset diarrhea, blood cell counts, and macroscopic and microscopic intestinal damages were monitored in rats treated with CPT-11 alone or combined therapy with thalidomide at 100 mg/kg administered by intraperitoneal (i.p.) injection. Single dose and 5-day multiple-dose studies were conducted in rats to examine the effects of concomitant thalidomide on the plasma pharmacokinetics of CPT-11 and its major metabolites SN-38 and SN-38 glucuronide (SN-38G). The effect of CPT-11 on thalidomide's pharmacokinetics was also checked. Rat liver microsomes and a rat hepatoma cell line, H4-II-E cells, were used to study the in vitro metabolic interactions between these two drugs. H4-II-E cells were also used to investigate the effect of thalidomide and its hydrolytic products on the transport of CPT-11 and SN-38. In addition, the effect of thalidomide and its hydrolytic products on rat plasma protein binding of CPT-11 and SN-38 was examined. Administration of CPT-11 by i.v. for 4 consecutive days to rats induced significant body weight loss, decrease in neutrophil and lymphocyte counts, severe acute- and delayed-onset diarrhea, and intestinal damages. These toxicities were alleviated when CPT-11 was combined with thalidomide. In both single-dose and 5-day multiple-dose pharmacokinetic study, coadministered thalidomide significantly increased the area under the plasma concentration-time curve (AUC) of CPT-11, but the AUC and elimination half-life (t(1/2)) of SN-38 were significantly decreased. However, CPT-11 did not significantly alter the pharmacokinetics of thalidomide. Thalidomide at 25 and 250 microM and its hydrolytic products at a total concentration of 10 microM had no significant effect on the plasma protein binding of CPT-11 and SN-38, except for that thalidomide at 250 microM caused a significant increase in the unbound fraction (f(u)) of CPT-11 by 6.7% (P < 0.05). The hydrolytic products of thalidomide (total concentration of 10 microM), but not thalidomide, significantly decreased CPT-11 hydrolysis by 16% in rat liver microsomes (P < 0.01). The formation of both SN-38 and SN-38G from CPT-11, SN-38 glucuronidation, or intracellular accumulation of both CPT-11 and SN-38 in H4-II-E cells followed Michaelis-Menten kinetics with the one-binding site model being the best fit for the kinetic data. Coincubation or 2-hr preincubation of thalidomide at 25 microM and 250 microM and its hydrolytic products at 10 microM did not show any significant effects on CPT-11 hydrolysis and SN-38 glucuronidation. However, preincubation of H4-II-E cells with thalidomide (250 microM), its hydrolytic products (total concentration of 10 microM), or phthaloyl glutamic acid (one major thalidomide hydrolytic product, 10 microM) significantly increased the intracellular accumulation of SN-38, but not CPT-11 (P < 0.01). The dose-limiting toxicities of CPT-11 were alleviated by combination with thalidomide in rats and the pharmacokinetic modulation by thalidomide may partially explain its antagonizing effects on the toxicities of CPT-11. The hydrolytic products of thalidomide, instead of the parental drug, modulated the hepatic hydrolysis of CPT-11 and intracellular accumulation of SN-38, probably contributing to the altered plasma pharmacokinetics of CPT-11 and SN-38. Further studies are needed to explore the role of both pharmacokinetics and pharmacodynamic components in the protective effect of thalidomide against the toxicities of CPT-11.

Reduced ankle dorsiflexion range may increase the risk of patellar tendon injury among volleyball players

Patellar tendon injury, a chronic overuse injury characterised by pain during tendon loading, is common in volleyball players and may profoundly restrict their ability to compete. This cross-sectional study investigated the association between performance factors and the presence of patellar tendon injury. These performance factors (sit and reach flexibility, ankle dorsiflexion range, jump height, ankle plantarflexor strength, years of volleyball competition and activity level) were measured in 113 male and female volleyball players. Patellar tendon health was determined by measures of pain and ultrasound imaging. The association between these performance factors and patellar tendon health (normal tendon, abnormal imaging without pain, abnormal imaging with pain) was investigated using analysis of variance. Only reduced ankle dorsiflexion range was associated with patellar tendinopathy (p < 0.05). As coupling between ankle dorsiflexion and eccentric contraction of the calf muscle is important in absorbing lower limb force when landing from a jump, reduced ankle dorsiflexion range may increase the risk of patellar tendinopathy.

Reduced Skeletal Muscle Uncoupling Protein-3 Content in Prediabetic Subjects and Type 2 Diabetic Patients: Restoration by Rosiglitazone Treatment

Context: The mitochondrial uncoupling protein-3 (UCP3) has been implicated in the protection of the mitochondrial matrix against lipid-induced mitochondrial damage. Recent evidence points toward mitochondrial aberrations as a major contributor to the development of insulin resistance and diabetes, and UCP3 is reduced in diabetes.
Objective: We compared skeletal muscle UCP3 protein levels in prediabetic subjects [i.e. impaired glucose tolerance (IGT)], diabetic patients, and healthy controls and examined whether rosiglitazone treatment was able to restore UCP3.
Patients, Design, Intervention: Ten middle-aged obese men with type 2 diabetes mellitus [age, 61.4 ± 3.1 yr; body mass index (BMI), 29.8 ± 2.9 kg/m2], nine IGT subjects (age, 59.0 ± 6.6 yr; BMI, 29.7 ± 3.0 kg/m2), and 10 age- and BMI-matched healthy controls (age, 57.3 ± 7.4 yr; BMI, 30.1 ± 3.9 kg/m2) participated in this study. After baseline comparisons, diabetic patients received rosiglitazone (2 x 4 mg/d) for 8 wk.
Main Outcome Measures: Muscle biopsies were sampled to determine UCP3 and mitochondrial protein (complex I–V) content.
Results: UCP3 protein content was significantly lower in prediabetic IGT subjects and in diabetic patients compared with healthy controls (39.0 ± 28.5, 47.2 ± 24.7, and 72.0 ± 23.7 arbitrary units, respectively; P < 0.05), whereas the levels of the mitochondrial protein complex I–V were similar between groups. Rosiglitazone treatment for 8 wk significantly increased insulin sensitivity and muscle UCP3 content (from 53.2 ± 29.9 to 66.3 ± 30.9 arbitrary units; P < 0.05).
Conclusion: We show that UCP3 protein content is reduced in prediabetic subjects and type 2 diabetic patients. Eight weeks of rosiglitazone treatment restores skeletal muscle UCP3 protein in diabetic patients.

Design of reduced-order state/unknown input observers: a descriptor system approach

This paper addresses the problem of estimating simultaneously a linear function of both the state and unknown input of linear system with unknown inputs. By adopting the descriptor system approach, the problem can be conveniently solved. Observers proposed in this paper are of low-order and do not include the derivatives of the outputs. New conditions for the existence of reduced-order observers are derived. A design procedure for the determination of the observer parameters can also be easily derived based on the derived existence conditions

Design of reduced-order observers for neutral time-delay systems

This paper presents a method for the design of reduced-order observers for a class of linear time-delay systems of the neutral-type. Conditions for the existence of reduced-order observers that are capable of asymptotically estimating any given function of the state vector are derived. A step-by-step design procedure is given for the determination of the observer parameters. A numerical example is given to illustrate the design procedure.