Increasing skeletal muscle carnitine content in older individuals increases whole-body fat oxidation during moderate-intensity exercise

Intramyocellular lipid (IMCL) utilization is impaired in older individuals, and IMCL accumulation is associated with insulin resistance. We hypothesized that increasing muscle total carnitine content in older men would increase fat oxidation and IMCL utilization during exercise, and improve insulin sensitivity. Fourteen healthy older men (69 ± 1 year, BMI 26.5 ± 0.8 kg/m² ) performed 1 h of cycling at 50% VO₂ max and, on a separate occasion, underwent a 60 mU/m² /min euglycaemic hyperinsulinaemic clamp before and after 25 weeks of daily ingestion of a 220 ml insulinogenic beverage (44.4 g carbohydrate, 13.8 g protein) containing 4.5 g placebo (n = 7) or L-carnitine L-tartrate (n = 7). During supplementation, participants performed twice-weekly cycling for 1 h at 50% VO₂ max. Placebo ingestion had no effect on muscle carnitine content or total fat oxidation during exercise at 50% VO₂ max. L-carnitine supplementation resulted in a 20% increase in muscle total carnitine content (20.1 ± 1.2 to 23.9 ± 1.7 mmol/kg/dm; p < 0.01) and a 20% increase in total fat oxidation (181.1 ± 15.0 to 220.4 ± 19.6 J/kg lbm/min; p < 0.01), predominantly due to increased IMCL utilization. These changes were associated with increased expression of genes involved in fat metabolism (ACAT1, DGKD & PLIN2; p < 0.05). There was no change in resting insulin-stimulated whole-body or skeletal muscle glucose disposal after supplementation. This is the first study to demonstrate that a carnitine-mediated increase in fat oxidation is achievable in older individuals. This warrants further investigation given reduced lipid turnover is associated with poor metabolic health in older adults.

Enriching a protein drink with leucine augments muscle protein synthesis after resistance exercise in young and older men

Maximizing anabolic responses to feeding and exercise is crucial for muscle maintenance and adaptation to exercise training. We hypothesized that enriching a protein drink with leucine would improve anabolic responses to resistance exercise (RE: 6 × 8 knee-extension repetitions at 75% of 1-RM) in both young and older adults. Groups (n = 9) of young (24 ± 6 y, BMI 23 ± 2 kg m^-2) and older men (70 ± 5 y, BMI 25 ± 2 kg m^-2) were randomized to either: (i) RE followed by Slim-Fast Optima (SFO 10 g PRO; 24 g CHO) with 4.2 g of leucine (LEU) or, (ii) RE + SFO with 4.2 g of alanine (ALA; isonitrogenous control). Muscle biopsies were taken before, immediately after, and 1, 2 and 4 h after RE and feeding. Muscle protein synthesis (MPS) was measured by incorporation of [1, 2-¹³C₂] leucine into myofibrillar proteins and the phosphorylation of p70S6K1 by immunoblotting. In young men, both area under the curve (AUC; FSR 0-4 h P < 0.05) and peak FSR (0.11 vs. 0.08%.h.^-1; P < 0.05) were greater in the SFO + LEU than in the SFO + ALA group, after RE. Similarly, in older men, AUC analysis revealed that post-exercise anabolic responses were greater in the SFO + LEU than SFO + ALA group, after RE (AUC; FSR 0-4 h P < 0.05). Irrespective of age, increases in p70S6K1 phosphorylation were evident in response to both SFO + LEU and SFO + ALA, although greater with leucine supplementation than alanine (fold-change 2.2 vs. 3.2; P < 0.05), specifically in the older men. We conclude that addition of Leucine to a sub-maximal PRO bolus improves anabolic responses to RE in young and older men.

Relative Contribution of Intramyocellular Lipid to Whole-Body Fat Oxidation Is Reduced With Age but Subsarcolemmal Lipid Accumulation and Insulin Resistance Are Only Associated With Overweight Individuals

Insulin resistance is closely related to intramyocellular lipid (IMCL) accumulation, and both are associated with increasing age. It remains to be determined to what extent perturbations in IMCL metabolism are related to the aging process per se. On two separate occasions, whole-body and muscle insulin sensitivity (euglycemic-hyperinsulinemic clamp with 2-deoxyglucose) and fat utilization during 1 h of exercise at 50% VO2max ([U-(13)C]palmitate infusion combined with electron microscopy of IMCL) were determined in young lean (YL), old lean (OL), and old overweight (OO) males. OL displayed IMCL content and insulin sensitivity comparable with those in YL, whereas OO were markedly insulin resistant and had more than twofold greater IMCL in the subsarcolemmal (SSL) region. Indeed, whereas the plasma free fatty acid Ra and Rd were twice those of YL in both OL and OO, SSL area only increased during exercise in OO. Thus, skeletal muscle insulin resistance and lipid accumulation often observed in older individuals are likely due to lifestyle factors rather than inherent aging of skeletal muscle as usually reported. However, age per se appears to cause exacerbated adipose tissue lipolysis, suggesting that strategies to reduce muscle lipid delivery and improve adipose tissue function may be warranted in older overweight individuals.

Obesity Appears to Be Associated With Altered Muscle Protein Synthetic and Breakdown Responses to Increased Nutrient Delivery in Older Men, but Not Reduced Muscle Mass or Contractile Function

Obesity is increasing, yet despite the necessity of maintaining muscle mass and function with age, the effect of obesity on muscle protein turnover in older adults remains unknown. Eleven obese (BMI 31.9 ± 1.1 kg · m(-2)) and 15 healthy-weight (BMI 23.4 ± 0.3 kg · m(-2)) older men (55-75 years old) participated in a study that determined muscle protein synthesis (MPS) and leg protein breakdown (LPB) under postabsorptive (hypoinsulinemic-euglycemic clamp) and postprandial (hyperinsulinemic hyperaminoacidemic-euglycemic clamp) conditions. Obesity was associated with systemic inflammation, greater leg fat mass, and patterns of mRNA expression consistent with muscle deconditioning, whereas leg lean mass, strength, and work done during maximal exercise were no different. Under postabsorptive conditions, MPS and LPB were equivalent between groups, whereas insulin and amino acid administration increased MPS in only healthy-weight subjects and was associated with lower leg glucose disposal (LGD) (63%) in obese men. Blunting of MPS in the obese men was offset by an apparent decline in LPB, which was absent in healthy-weight subjects. Lower postprandial LGD in obese subjects and blunting of MPS responses to amino acids suggest that obesity in older adults is associated with diminished muscle metabolic quality. This does not, however, appear to be associated with lower leg lean mass or strength.

Pharmacological enhancement of leg and muscle microvascular blood flow does not augment anabolic responses in skeletal muscle of young men under fed conditions

Skeletal muscle anabolism associated with postprandial plasma aminoacidemia and insulinemia is contingent upon amino acids (AA) and insulin crossing the microcirculation-myocyte interface. In this study, we hypothesized that increasing muscle microvascular blood volume (flow) would enhance fed-state anabolic responses in muscle protein turnover. We studied 10 young men (23.2 ± 2.1 yr) under postabsorptive and fed [iv Glamin (∼10 g AA), glucose ∼7.5 mmol/l] conditions. Methacholine was infused into the femoral artery of one leg to determine, via bilateral comparison, the effects of feeding alone vs. feeding plus pharmacological vasodilation. We measured leg blood flow (LBF; femoral artery) by Doppler ultrasound, muscle microvascular blood volume (MBV) by contrast-enhanced ultrasound (CEUS), muscle protein synthesis (MPS) and breakdown (MPB; a-v balance modeling), and net protein balance (NPB) using [1,2-(13)C2]leucine and [(2)H5]phenylalanine tracers via gas chromatography-mass spectrometry (GC-MS). Indexes of anabolic signaling/endothelial activation (e.g., Akt/mTORC1/NOS) were assessed using immunoblotting techniques. Under fed conditions, LBF (+12 ± 5%, P < 0.05), MBV (+25 ± 10%, P < 0.05), and MPS (+129 ± 33%, P < 0.05) increased. Infusion of methacholine further enhanced LBF (+126 ± 12%, P < 0.05) and MBV (+79 ± 30%, P < 0.05). Despite these radically different blood flow conditions, neither increases in MPS in response to feeding (0.04 ± 0.004 vs. 0.08 ± 0.01%/h, P < 0.05) nor improvements in NPB (-4.4 ± 2.4 vs. 16.4 ± 5.7 nmol Phe·100 ml leg(-1)·min(-1), P < 0.05) were affected by methacholine infusion (MPS 0.07 ± 0.01%/h; NPB 24.0 ± 7.7 nmol Phe·100 ml leg(-1)·min(-1)), whereas MPB was unaltered by either feeding or infusion of methacholine. Thus, enhancing LBF/MBV above that occurring naturally with feeding alone does not improve muscle anabolism.

Effect of tumor burden and subsequent surgical resection on skeletal muscle mass and protein turnover in colorectal cancer patients

BACKGROUND

Cachexia is a consequence of tumor burden caused by ill-defined catabolic alterations in muscle protein turnover.

OBJECTIVE

We aimed to explore the effect of tumor burden and resection on muscle protein turnover in patients with nonmetastatic colorectal cancer (CRC), which is a surgically curable tumor that induces cachexia.

DESIGN

We recruited the following 2 groups: patients with CRC [n = 13; mean ± SEM age: 66 ± 3 y; BMI (in kg/m(2)): 27.6 ± 1.1] and matched healthy controls (n = 8; age: 71 ± 2 y; BMI: 26.2 ± 1). Control subjects underwent a single study, whereas CRC patients were studied twice before and ~6 wk after surgical resection to assess muscle protein synthesis (MPS), muscle protein breakdown (MPB), and muscle mass by using dual-energy X-ray absorptiometry.

RESULTS

Leg muscle mass was lower in CRC patients than in control subjects (6290 ± 456 compared with 7839 ± 617 g; P < 0.05) and had an additional decline after surgery (5840 ± 456 g; P < 0.001). Although postabsorptive MPS was unaffected, catabolic changes with tumor burden included the complete blunting of postprandial MPS (0.038 ± 0.004%/h in the CRC group compared with 0.065 ± 0.006%/h in the control group; P < 0.01) and a trend toward increased MPB under postabsorptive conditions (P = 0.09). Although surgical resection exacerbated muscle atrophy (-7.2%), catabolic changes in protein metabolism had normalized 6 wk after surgery. The recovery in postprandial MPS after surgery was inversely related to the degree of muscle atrophy (r = 0.65, P < 0.01).

CONCLUSIONS

CRC patients display reduced postprandial MPS and a trend toward increased MPB, and tumor resection reverses these derangements. With no effective treatment of cancer cachexia, future therapies directed at preserving muscle mass should concentrate on alleviating proteolysis and enhancing anabolic responses to nutrition before surgery while augmenting muscle anabolism after resection.

Poor tolerability of thalidomide in end-stage oesophageal cancer

Oesophageal cancer cachexia is a significant clinical problem, resulting in excessive morbidity and mortality. In a pilot study, 10 patients with cachexia due to advanced cancer of the oesophagus gained weight, including lean tissue, after 14-day treatment with thalidomide. Here, we present randomised placebo controlled trial data over a 6-week period to test the hypothesis that thalidomide is superior to placebo in terms of weight gain in patients with cachexia caused by oesophageal cancer. Thalidomide, 200 mg daily, or an identical placebo was given to patients with advanced oesophageal cancer. Total body weight and lean body mass were assessed in addition to drug tolerability and performance indices. Thirty-four patients were recruited. Of these, six given thalidomide and 16 given placebo completed the protocol; all withdrawals were due to adverse drug reactions or complications of disease. Thalidomide showed no benefit over placebo in participants who completed the protocol. These data suggest that thalidomide is poorly tolerated in patients with advanced cancer of the oesophagus and may not ameliorate the progression of cachexia. In the absence of hard supportive evidence, off-licence treatment with thalidomide should be used with great caution as an adjunct to nutritional support in patients with advanced cancer.

Blunting of insulin inhibition of proteolysis in legs of older subjects may contribute to age-related sarcopenia

BACKGROUND

Reduced postprandial muscle proteolysis is mainly due to increased insulin availability. Whether rates of proteolysis in response to low physiologic doses of insulin are affected by aging is unknown.

OBJECTIVES

We tested the hypothesis that suppression of leg protein breakdown (LPB) by insulin is blunted in older subjects, together with blunted activation of Akt-protein kinase B (PKB).

DESIGN

Groups of 8 young [mean (+/-SD) age: 24.5 +/- 1.8 y] and older (65.0 +/- 1.3 y) participants were studied during euglycemic (5 mmol/L), isoaminoacidemic (blood leucine approximately 120 micromol/L) clamp procedures at plasma insulin concentrations of approximately 5 and approximately 15 microIU/mL for 1.5 h. Leg amino acid balance, whole-leg protein turnover (as dilution of amino acid tracers), and muscle protein synthesis were measured with D(5)-phenylalanine and [1,2-(13)C(2)]leucine. The kinase activity of muscle Akt-PKB and the extent of phosphorylation of signaling proteins associated with the mTOR (mammalian target of rapamycin) pathway were measured before and after the clamp procedures.

RESULTS

Basal LPB rates were not different between groups (66 +/- 11 compared with 51 +/- 10 nmol leucine x 100 mL leg(-1) x min(-1) and 30 +/- 5 compared with 24 +/- 4 nmol phenylalanine x 100 mL leg(-1) x min(-1) in young and older groups, respectively). However, although insulin at approximately 15 microIU/mL lowered LPB by 47% in the young subjects (P < 0.05) and abolished the negative leg amino acid balance, this caused only a 12% fall (P > 0.05) in the older group. Akt-PKB activity mirrored decreases in LPB. No differences were seen in muscle protein synthesis or associated anabolic signaling phosphoproteins.

CONCLUSIONS

At moderate availability, the effect of insulin on LPB is diminished in older human beings, and this effect may be mediated through blunted Akt-PKB activation.

Reduction and Mutagenic Activation of Nitroaromatic Compounds by a Mycobacterium sp

Volume 60, no. 12, p. 4264: Figure 1B should appear as shown below. [This corrects the article on p. 4263 in vol. 60.].

Reduction and mutagenic activation of nitroaromatic compounds by a Mycobacterium sp

Mycobacterium sp. strain Pyr-1 cells, which were grown to the stationary phase in media with and without pyrene, were centrifuged and resuspended in a medium containing 1-nitropyrene. Cells that had been grown with pyrene oxidized up to 20% of the added 1-nitropyrene to 1-nitropyrene-cis-9,10- and 4,5-dihydrodiols. However, cells that had been grown without pyrene reduced up to 70% of the 1-nitropyrene to 1-aminopyrene but did not produce dihydrodiols. The nitroreductase activity was oxygen insensitive, intracellular, and inducible by nitro compounds. Nitroreductase activity was inhibited by p-chlorobenzoic acid, o-iodosobenzoic acid, menadione, dicumarol, and antimycin A. Extracts from cells that had been grown without pyrene activated 1-nitropyrene, 1-amino-7-nitrofluorene, 2,7-dinitro-9-fluorenone, 1,3-dinitropyrene, 1,6-dinitropyrene, and 6-nitrochrysene to DNA-damaging products, as shown in Salmonella typhimurium tester strains by the reversion assay and by induction of the umuC gene. Activation of nitro compounds, as shown by the umu test, was enhanced by NADPH. This study shows that Mycobacterium sp. strain Pyr-1 metabolizes nitroaromatic compounds by both oxidative and reductive pathways. During reduction, it generates products that are mutagenic.

Metabolism of phenanthrene by Phanerochaete chrysosporium

The white rot fungus Phanerochaete chrysosporium metabolized phenanthrene when it was grown for 7 days at 37 degrees C in a medium containing malt extract, D-glucose, D-maltose, yeast extract, and Tween 80. After cultures were grown with [9-14C]phenanthrene, radioactive metabolites were extracted from the medium with ethyl acetate, separated by high-performance liquid chromatography, and detected by liquid scintillation counting. Metabolites from cultures grown with unlabeled phenanthrene were identified as phenanthrene trans-9,10-dihydrodiol, phenanthrene trans-3,4-dihydrodiol, 9-phenanthrol, 3-phenanthrol, 4-phenanthrol, and the novel conjugate 9-phenanthryl beta-D-glucopyranoside. Identification of the compounds was based on their UV absorption, mass, and nuclear magnetic resonance spectra. Since lignin peroxidase was not detected in the culture medium, these results suggest the involvement of monooxygenase and epoxide hydrolase activity in the initial oxidation and hydration of phenanthrene by P. chrysosporium.

Stereoselective formation of a K-region dihydrodiol from phenanthrene by Streptomyces flavovirens

The metabolism of phenanthrene, a polycyclic aromatic hydrocarbon (PAH), by Streptomyces flavovirens was investigated. When grown for 72 h in tryptone yeast extract broth saturated with phenanthrene, the actinomycete oxidized 21.3% of the hydrocarbon at the K-region to form trans-9,10-dihydroxy-9,10-dihydrophenanthrene (phenanthrene trans-9,10-dihydrodiol). A trace of 9-phenanthrol was also detected. Metabolites isolated by thin-layer and high performance liquid chromatography were identified by comparing chromatographic, mass spectral, and nuclear magnetic resonance properties with those of authentic compounds. Experiments using [9-14C]phenanthrene showed that the trans-9,10-dihydrodiol had 62.8% of the radioactivity found in the metabolites. Circular dichroism spectra of the phenanthrene trans-9,10-dihydrodiol indicated that the absolute configuration of the predominant enantiomer was (-)-9S,10S, the same as that of the principal enantiomer produced by mammalian enzymes. Incubation of S. flavovirens with phenanthrene is an atmosphere of 18O2, followed by gas chromatographic/mass spectral analysis of the metabolites, indicated that one atom from molecular oxygen was incorporated into each molecule of the phenanthrene trans-9,10-dihydrodiol. Cytochrome P-450 was detected in 105,000 x g supernatants prepared from cell extracts of S. flavovirens. The results show that the oxidation of phenanthrene by S. flavovirens was both regio- and stereospecific.