Biomedical subjects

C H Fang

Publications and source records attributed to C H Fang.

41 records · Page 3Linked to original sources

PubMedDate not supplied

Burn injuries in rats upregulate the gene expression of the ubiquitin-conjugating enzyme E2(14k) in skeletal muscle.

Burn injuries are associated with muscle cachexia, which mainly reflects protein breakdown in the ubiquitin-proteasome pathway. Ubiquitination of proteins degraded by this mechanism is regulated by multiple enzymes, including the 14-kd ubiquitin-conjugating enzyme, E2(14k). In this study, burn injuries in rats resulted in increased levels of the 1.2 kilobase E2(14k) transcript in the white, fast-twitch extensor digitorum longus muscle with no changes or only minor changes in the red, slow-twitch soleus muscle, liver, and kidney. The results provide the first evidence that burn injuries upregulate the gene expression of E2(14k) in skeletal muscle and suggest that ubiquitin-proteasome-dependent muscle protein breakdown after thermal injuries may, at least in part, be regulated by E2(14k).

Animals↗

PubMedDate not supplied

Enteral feeding in burn hypermetabolism: nutritional and metabolic effects of different levels of calorie and protein intake.

Enteral nutrition was provided by continuous pump-controlled gastrostomy tube feeding for 14 days in 97 guinea pigs bearing a 30% full thickness burn. Seven defined combinations of caloric and protein intake were studied. With a caloric intake of 175 kcal/kg/day, equaling the measured energy expenditure, the animals receiving 10% of calories as protein had a significantly greater postburn weight loss (p less than 0.05) and muscle mass depletion (p less than 0.05), and a significantly lower muscle nitrogen concentration (p less than 0.05), serum albumin level (p less than 0.01) and liver nitrogen content (p less than 0.01). With the same caloric intake but with more than 20% of calories as protein, the weight loss and the muscle wasting were reduced, but not abolished, and the serum albumin level and liver nitrogen content were normalized. Also with the diets containing 200 kcal/kg/day the muscle tissue depletion could not be abolished. However, with this caloric intake, the animals given 20% of calories as protein had a lower weight loss and a higher serum albumin level (p less than 0.01), but also a greater fat infiltration of the liver (p less than 0.01). At both levels of caloric intake, the nitrogen balance correlated significantly with the level of nitrogen intake but did not correlate with the changes of body weight. The incidence of diarrhea was lowest in animals fed 20% protein calories at a caloric intake of 175 kcal/kg/day. All things considered, the best metabolic and nutritional results were obtained with diets containing 20 to 30% of calories as protein and providing a caloric intake that paralleled the measured energy expenditure.

Abdominal Muscles↗

PubMedDate not supplied

Is muscle protein turnover regulated by intracellular glutamine during sepsis?

BACKGROUND: Low muscle glutamine levels during sepsis are associated with reduced protein synthesis and elevated protein breakdown, in particular myofibrillar protein breakdown. It is not known if this is a causal or coincidental relationship. We tested the hypothesis that muscle protein turnover rates are directly regulated by glutamine. METHODS: Paired extensor digitorum longus muscles from nonseptic (sham-operated) and septic rats (16 hours after cecal ligation and puncture) were incubated in the absence or presence of 15 mmol glutamine/L. The effect of glutamine was tested in unsupplemented medium or in medium containing 1 mU/mL of insulin or a mixture of amino acids at normal plasma concentrations. Protein synthesis was measured as incorporation of 14C-phenylalanine into protein; total and myofibrillar protein breakdown was determined by measuring tyrosine and 3-methylhistidine, respectively. RESULTS: Muscles accumulated intracellular glutamine well above normal concentrations in the presence of 15 mmol glutamine/L. In spite of this, protein synthesis was not affected by glutamine, neither when muscles were incubated in unsupplemented medium nor in medium containing insulin or amino acid mixture. Total protein breakdown was not influenced by glutamine when muscles were incubated in unsupplemented medium or with insulin but was reduced by glutamine in the presence of an amino acid mixture. Myofibrillar protein breakdown was unaffected by glutamine in unsupplemented medium and in medium containing insulin but was increased by glutamine in the presence of amino acid mixture. CONCLUSION: Reduced muscle protein synthesis and increased myofibrillar protein breakdown during sepsis are probably not caused by the low intracellular glutamine levels noticed in this condition.

Amino Acids↗

PubMedDate not supplied

Insulin-like growth factor 1 stimulates protein synthesis and inhibits protein breakdown in muscle from burned rats.

BACKGROUND: Burn injury is associated with substantial whole-body protein loss, reflecting mainly a catabolic response in skeletal muscle. Recent studies suggest that treatment with insulin-like growth factor 1 (IGF-1) may reverse the catabolic response to burn injury, but the effects of IGF-1 on muscle protein synthesis and breakdown rates after burn injury are not known. We tested the hypothesis that IGF-1 blunts the catabolic response in skeletal muscle after burn injury by stimulating protein synthesis and inhibiting protein breakdown and that this effect of IGF-1 is caused by a direct effect on muscle tissue. METHODS: Intact extensor digitorum longus muscles from burned, sham-burned, and untreated rats were incubated in the absence or presence of different concentrations of IGF-1. Total and myofibrillar protein breakdown rates were measured as net release of tyrosine and 3-methylhistidine, respectively. Protein synthesis rates were determined by measuring the incorporation of (U-14C)-phenylalanine into protein. RESULTS: IGF-1 stimulated protein synthesis and inhibited protein breakdown in a dose-dependent fashion in muscles from burned and unburned rats. The maximal effect of IGF-1 on protein synthesis was seen at a hormone concentration of 100 ng/mL, whereas protein breakdown was further inhibited when the hormone concentration was increased to 1 microgram/mL. Ubiquitin messenger RNA (mRNA) levels were reduced by IGF-1 in incubated muscles, suggesting that IGF-1 may inhibit ubiquitin-dependent protein breakdown. CONCLUSIONS: These results suggest that the anabolic effects of IGF-1 after burn may reflect inhibited protein breakdown and stimulated protein synthesis in skeletal muscle and that this response may be caused by a direct effect of IGF-1 on muscle tissue.

Animals↗

PubMedDate not supplied

The anabolic effects of IGF-1 in skeletal muscle after burn injury are not caused by increased cell volume.

BACKGROUND: In a recent report, insulin-like growth factor 1 (IGF-1) stimulated protein synthesis and inhibited protein breakdown in skeletal muscle after bum injury. The mechanism of the anabolic effects of IGF-1 in skeletal muscle is not known. We tested the hypotheses that IGF-1 stimulates protein synthesis and inhibits protein breakdown in skeletal muscle secondary to cell swelling and that cell swelling in itself induces an anabolic response in muscle tissue. METHODS: Extensor digitorum longus muscles from control and burned rats were incubated in the absence or presence of 1 microg/mL of IGF-1. Protein synthesis and breakdown rates were determined by measuring incorporation of 14C-phenylalanine into protein and net release of tyrosine, respectively. Cell volume was measured by determining wet and dry weight and by using 3H-mannitol as an extracellular marker. RESULTS: IGF-1 stimulated protein synthesis and inhibited protein breakdown in muscles from nonburned and burned rats without influencing cell volume. Incubating muscles in hypo-osmotic medium increased cell volume by 17% and inhibited protein breakdown by 14% but did not influence protein synthesis. CONCLUSIONS: The anabolic effects of IGF-1 in skeletal muscle are not caused by increased cell volume. The results differ from those reported previously in liver cells in which the anabolic effects of IGF-1 were associated with cell swelling. The role of changes in cell volume in the regulation of protein metabolism may be different in skeletal muscle than in other tissues.

Animals↗