2000

Am J Physiol Endocrinol Metab. 2005 May 3.
Three weeks of caloric restriction alters protein metabolism in normal weight, young men.
Friedlander AL, Braun B, Pollack M, Macdonald JR, Fulco CS, Muza SR, Rock PB, Henderson GC, Horning MA, Brooks GA, Hoffman AR, Cymerman A.
VA Palo Alto Health Care System, Palo Alto, CA, USA; University of Massachusetts, Amherst, MA, USA.

The effects of prolonged caloric restriction on protein kinetics in lean subjects has not been previously investigated. PURPOSE: To test the hypotheses that 21 days of caloric restriction (CR) in lean subjects would a) result in significant losses of lean mass despite a suppression in leucine turnover and oxidation, and b) negatively impact exercise performance. METHODS: Nine young, normal weight men (23+/-5 y, 78.6+/-5.7 kg, VO2peak: 45.2+/-7.3 ml(.)kg(-1)(.)min(-1),mean+/-SD) were underfed by 40% of the calories required to maintain body weight (BW) for 21 days and lost 3.8+/-0.3 kg BW and 2.0+/-0.4 kg lean mass. Protein intake was kept at 1.2 g(.)kg(-1)(.)day(-1). Leucine kinetics were measured using KIC reciprocal pool model in the post-absorptive state during rest and 50 minutes of exercise (EX) at 50% of VO2peak. Body composition, basal metabolic rate (BMR) and exercise performance were measured throughout the intervention. RESULTS: At rest, leucine flux (~131 micromol(.)kg(-1)(.)hr(-1)) and oxidation (Rox; ~19 micromol(.)kg(-1)(.)hr(-1)) did not differ pre- and post- CR. During EX, leucine flux (129+/-6 vs. 121+/-6) and Rox (54+/-6 vs. 46+/-8)were lower following CR than pre-CR. Nitrogen balance was negative throughout the intervention (~3.0gN(.)d(-1)) and BMR declined from 1898+/-262 kcal(.)d(-1) to 1670+/-203. Aerobic performance (VO2peak, endurance cycling) was not impacted by CR, but arm flexion endurance decreased by 20%. CONCLUSIONS: Three weeks of caloric restriction reduced leucine flux and oxidation during exercise in normal weight young men. However, despite negative nitrogen balance and loss of lean mass, whole body exercise performance was well maintained in response to CR.

Arch Biochem Biophys. 2005 Apr 15;436(2):276-84.
Calorie restriction improves whole-body glucose disposal and insulin resistance in association with the increased adipocyte-specific GLUT4 expression in Otsuka Long-Evans Tokushima fatty rats.
Park SY, Choi GH, Choi HI, Ryu J, Jung CY, Lee W.
Department of Biochemistry, College of Medicine, Dongguk University, Kyungju, Kyungpook 780-714, Korea.

Calorie restriction (CR) has been shown to improve peripheral insulin resistance and type 2 diabetes in animal models. However, the exact mechanism of CR on GLUT4 expression and translocation in insulin-sensitive tissues has not been well elucidated. In the present study, we examine the effect of CR on the expression of glucose transporter 4 (GLUT4), GLUT4 translocation, and glucose transport activity in adipose tissue from Otsuka Long-Evans Tokushima Fatty (OLETF) rat and control (LETO) rats. CR (70% of satiated group) ameliorated hyperglycemia and improved impaired glucose tolerance (IGT) in OLETF rats. In skeletal muscle, the expression levels of GLUT4 and GLUT1 were not significantly different between LETO and OLETF rats, and were not affected by CR. By contrast, the expression level of GLUT4 was markedly decreased in the adipose tissue of OLETF rats, but was dramatically increased by CR. The GLUT4 recruitment stimulated by insulin was also improved in OLETF rat adipocytes by CR. The insulin-stimulated 2-deoxyglucose (2DG) uptake was significantly increased in adipocytes from the CR OLETF rats, as compared with the satiated OLETF rats. Taken together, these results suggest that CR improves whole body glucose disposal and insulin resistance in OLETF rats, and that these effects may associate with the increased adipocyte-specific GLUT4 expression.

2000

J Gerontol A Biol Sci Med Sci 2000 Nov;55(11):B522-9
Reversible effects of long-term caloric restriction on protein oxidative damage.
Forster MJ, Sohal BH, Sohal RS.
Department of Pharmacology, University of North Texas Health Science Center at Fort Worth, 76107, USA.

The age-associated increase in oxidative damage in ad libitum-fed mice is attenuated in mice fed calorically restricted (CR) diets. The objective of this study was to determine if this effect results from a slowing of age-related accumulation of oxidative damage, or from a reversible decrease of oxidative damage by caloric restriction. To address these possibilities, crossover studies were conducted in C57BL/6 mice aged 15 to 22 months that had been maintained, after 4 months of age, on ad libitum (AL) or a 60% of AL caloric regimen. One half of the mice in these groups were switched to the opposite regimen of caloric intake for periods up to 6 weeks, and protein oxidative damage (measured as carbonyl concentration and loss of sulfhydryl content) was measured in homogenates of brain and heart. In AL-fed mice, the protein carbonyl content increased with age, whereas the sulfhydryl content decreased. Old mice maintained continuously under CR had reduced levels of protein oxidative damage when compared with the old mice fed AL. The effects of chronic CR on the carbonyl content of the whole brain and the sulfhydryl content of the heart were fully reversible within 3-6 weeks following reinstatement of AL feeding. The effect of chronic CR on the sulfhydryl content of the brain cortex was only partially reversible. The introduction of CR for 6 weeks in the old mice resulted in a reduction of protein oxidative damage (as indicated by whole brain carbonyl content and cortex sulfhydryl), although this effect was not equivalent to that of CR from 4 months of age. The introduction of CR did not affect the sulfhydryl content of the heart. Overall, the current findings indicate that changes in the level of caloric intake may reversibly affect the concentration of oxidized proteins and sufhydryl content. In addition, chronic restriction of caloric intake also retards the age-associated accumulation of oxidative damage. The magnitude of the reversible and chronic effects appears to be dependent upon the tissue examined and the nature of the oxidative alteration.

1999

Eur J Cell Biol 1999 Aug;78(8):573-9
Fasting-induced apoptosis in rat liver is blocked by cycloheximide.
Tessitore L; Tomasi C; Greco M.
Dipartimento di Scienze Mediche, Universita del Piemonte Orientale, Novara, Italy.

The effect of cycloheximide (CH) on the fasting-induced changes of rat liver cell and protein turnover has been investigated. Late starvation phase (3-4-day-fasting period) was characterised by a decrease in liver weight and protein and DNA content. The loss of DNA was not related to liver cell necrosis but due not only to depression of cell proliferation as shown by the drop in the labelling index but also induction of apoptosis. This type of apoptosis was documented by the increase in the apoptotic index (cells labelled by TUNEL) and transglutaminase activity as well as by DNA fragmentation. The liver cells of fasted rats appeared smaller as shown by the higher cell density and DNA/protein ratio than in controls. Females were more resistant to fasting-induced apoptosis than males. A single dose of CH, a drug primary known as inhibitor of protein synthesis, induced or enhanced apoptosis in fed and 2-days fasted male rats, respectively, without any sign of cell necrosis. On the contrary, the administration of repeated doses of CH blocked apoptosis induced by fasting. CH "froze" protein and DNA content as well as apoptotic process at the level of 2 days-fasted rats. While fasting-induced liver protein loss resulted from a marked reduction in protein synthesis with a slight decrease in degradation, repeated treatment with CH virtually blocked protein loss by abolishing protein catabolism. These data suggest a direct relationship between the catabolic side of protein turnover and the apoptotic process.

Obes Res 1999 Jan;7(1):97-105
Human uncoupling proteins and obesity.
Schrauwen P; Walder K; Ravussin E.
Clinical Diabetes and Nutrition Section, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Phoenix AZ 85016, USA.

Uncoupling protein (UCP) 2 and UCP3 are newly discovered proteins that can uncouple ATP production from mitochondrial respiration, thereby dissipating energy as heat and affecting energy metabolism efficiency. In contrast to UCP1, which is only present in brown adipose tissue, UCP2 has a wide tissue distribution, whereas UCP3 is expressed predominantly in skeletal muscle. Some evidence of a role for UCPs in modulating metabolic rate was provided by linkage and association studies. Furthermore, UCP3 gene _expression was found to correlate negatively with body mass index and positively with sleeping metabolic rate in Pima Indians. Treatment with thyroid hormone increases _expression of the UCP2 and UCP3 genes. Other regulators of UCP2 and UCP3 gene _expression are beta3-adrenergic agonists and glucocorticoids. Surprisingly, fasting has a stimulatory effect on UCP2 and UCP3 mRNA levels, possibly explained by the effects of free fatty acid on UCP2 and UCP3 gene _expression.

1998

J Clin Endocrinol Metab 1998 Jul;83(7):2450-3
Uncoupling protein-2 messenger ribonucleic acid _expression during very-low-calorie diet in obese premenopausal women.
Barbe P; Millet L; Larrouy D; Galitzky J; Berlan M; Louvet JP; Langin D.
INSERM Unit 317, Louis Bugnard Institute, Rangueil Hospital, Paul Sabatier University, Toulouse, France.

Uncoupling protein-2 (UCP2) is a mitochondrial protein expressed in a wide range of human tissues. By uncoupling respiration from ATP synthesis, UCP2 might be involved in the control of energy expenditure. We have investigated UCP2 gene _expression in human adipose tissue. In eight subjects, we found a positive correlation (r = 0.91, P < 0.002) between subcutaneous and visceral fat depots UCP2 messenger RNA (mRNA) levels, suggesting that UCP2 mRNA level in subcutaneous adipose tissue is a good index of UCP2 gene _expression in whole body adipose tissues. The effect of a 25-day very-low-calorie diet un UCP2 mRNA level and resting metabolic rate was investigated in eight obese premenopausal women. There was no difference in UCP2 mRNA levels before and during the diet. After 25 days of hypocaloric diet, a positive correlation was found between adipose tissue UCP2 mRNA level and resting metabolic rate adjusted for lean body mass (r = 0.82, P < 0.01). These results show that very-low-calorie diet, unlike short-term fasting, is not associated with an induction in UCP2 mRNA _expression, and that adipose tissue UCP2 mRNA levels may be related to variations in resting energy expenditure in humans.

1997

J Clin Invest 1997 Dec 1;100(11):2665-70
Increased uncoupling protein-2 and -3 mRNA _expression during fasting in obese and lean humans.
Millet L; Vidal H; Andreelli F; Larrouy D; Riou JP; Ricquier D; Laville M; Langin D.
Institut National de la Sante et de la Recherche Medicale Unite 317, Institut Louis Bugnard, Universite Paul Sabatier, Batiment L3, Hopital Rangueil, 31403 Toulouse Cedex 4, France.

Uncoupling protein-2 and -3 (UCP2 and UCP3) are mitochondrial proteins that show high sequence homology with the brown adipocyte-specific UCP1. UCP1 induces heat production by uncoupling respiration from ATP synthesis. UCP2 is widely expressed in human tissues, whereas UCP3 _expression seems restricted to skeletal muscle, an important site of thermogenesis in humans. We have investigated the regulation of UCP2 and UCP3 gene _expression in skeletal muscle and adipose tissue from lean and obese humans. UCP2 and -3 mRNA levels were not correlated with body mass index (BMI) in skeletal muscle, but a positive correlation (r = 0.55, P < 0.01, n = 22) was found between UCP2 mRNA level in adipose tissue and BMI. The effect of fasting was investigated in eight lean and six obese subjects maintained on a hypocaloric diet (1,045 kJ/d) for 5 d. Calorie restriction induced a similar 2-2.5-fold increase in UCP2 and -3 mRNA levels in lean and obese subjects. To study the effect of insulin on UCP gene _expression, six lean and five obese subjects underwent a 3-h euglycemic hyperinsulinemic clamp. Insulin infusion did not modify UCP2 and -3 mRNA levels. In conclusion, the similar induction of gene _expression observed during fasting in lean and obese subjects shows that there is no major alteration of UCP2 and -3 gene regulation in adipose tissue and skeletal muscle of obese subjects. The increase in UCP2 and -3 mRNA levels suggests a role for these proteins in the metabolic adaptation to fasting.

1994

Int J Obes Relat Metab Disord 1994 May;18(5):351-3
Protein sparing on very low calorie diets: ground squirrels succeed where obese people fail.
Karmann H; Mrosovsky N; Heitz A; Le Maho Y.
Centre d'Ecologie et Physiologie Energetiques, Centre National de la Recherche Scientifique, Strasburg, France.

During seasonal cycles in ground squirrels, as in many other species, there are periods of spontaneous loss of appetite, very low calorie intake and a 30% loss in body mass. Measurements of nitrogen balance during early and later stages of the mass loss phase of the cycle (-1.2 +/- 6.7 and +13.1 +/- 8.8 mg/24 h, respectively) showed a total sparing of protein, indicating a selective use of fat. However, when no food at all was available, nitrogen balance was negative (-45 +/- 5 mg/24 h). Provided that they have access to some food, ground squirrels are therefore able to compensate for any protein utilization, while at the same time selectively losing large amounts of fat. It appears that a factor related to spontaneous reduction in food intake enables these animals to achieve the total sparing of protein that eludes dieting humans on comparably low caloric intakes.