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Abstract
The principal objective of this study was to determine the effects of leucine on body weight reduction in high fat diet-induced overweight rats. To induce overweight, six-month-old male Sprague-Dawley rats (n = 80) were divided into 8 groups; one group of 10 rats was fed on a normal fat diet and the remaining 70 rats were fed on a high-fat diet (40% of energy as fat) for 14 weeks. Then, 10 rats fed on the normal fat diet and another 10 rats fed on the high fat diet were sacrificed to identify overweight induction. The remaining 60 rats were divided randomly into 6 groups according to body weight and fed on one of the diets with different dietary fat levels (9.6% or 40% of energy as fat) and leucine levels (0, 0.6 or 1.2 g/kg BW) for the following 5 weeks of experiments. The body weight loss in the Leu-administered groups (0.6 g, 1.2 g/kg BW) was significantly higher than those of Leu non-administered groups. The perirenal fat pad weights in the Leu-administered groups were significantly lower than those of the Leu non-administered groups. Of the hepatic enzymes, glucose-6-phosphate dehydrogenase (G6PDH) activities were reduced significantly in the Leu-administered groups than in the Leu non-administered groups. With the oral glucose tolerance test (OGTT), the incremental areas under the curve of the glucose response (IAUC) of the Leu-administered groups were significantly lower than those of the Leu non-administered groups. The fasting glucose concentration and HOMA-IR of the Leu-administered groups were significantly lower than those of the Leu non-administered groups. In conclusion, the results of this study suggest that one of the possible mechanisms of leucine in the observed body weight reduction might involve the inhibition of lipogenic enzyme activities such as glucose-6-phosphate dehydrogenase, rather than the activation of lipolysis enzymes. Additionally, leucine adminstration resulted in improved glucose metabolism.
Figures and Tables
 | Fig. 1Perirenal fat pad (A) and epididymal fat pad (B) in rats fed diets with different levels of dietary fat and/or leucine (see Table 1 for group description). The high fat induced animals were orally administered Leucine as separate feeding for 5 weeks with control diet or continuous high fat diet. Values are expressed as mean ± SE shown by vertical bars. Values with different letters are significantly different at α = 0.05 level by one-way ANOVA.
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 | Fig. 2Activities of carnitine palmitoyl transferase (A), glucose-6-phosphate dehydrogenase (B), and malic enzyme (C) in rats fed diets with different levels of fat and/or leucine. Values are expressed as mean ± SE shown by vertical bars. Values with different letters are significantly different at α = 0.05 level by oneway ANOVA.
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 | Fig. 3Blood glucose concentrations during oral glucose tolerance test in rats fed diets with different levels of fat and/or leucine. The animals received orally administered glucose (1 g/kg bw) with or without leucin after overnight fasting for 12 h. Blood glucose levels were determined from tail blood samples at 0, 30, 60, 90, and 120 min and incremental blood glucose concentrations were integrated over a period of 2h (A: control diet with different leucine levels, B: high fat diet, C: incremental area under the curve of the glucose response). Values are expressed as mean ± SE shown by vertical bars. Values with different letters are significantly different at α = 0.05 level by one-way ANOVA.
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 | Fig. 4Effect of leucine with or without high fat diet for 5 weeks on biochemical parameters of blood glucose. Values are expressed as mean ± SE shown by vertical bars. Values with different letters are significantly different at α = 0.05 level by oneway ANOVA. A: Fasting blood glucose (A), B: plasma insulin, C: glucagon concentrations, D: insulin/glucagon ratio, E: HOMA-IR (Fasting plasma insulin (µU/mL) × fasting blood glucose (mmol/l)/22.5).
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Table 1
Composition of experimental diets (g/kg diet)
1) Control: AIN-93M diet (9.6% of energy as fat), High fat: AIN-93M diet (40% of energy as fat), CLO: AIN-93M diet (9.6% of energy as fat), CLL: AIN-93M diet (9.6% of energy as fat) + 0.6 g/kg BW Leu, CLH: AIN-93M diet (9.6% of energy as fat) + 1.2 g/kg BW Leu, HLO: AIN-93M diet (40% of energy as fat), HLL: AIN-93M diet (40% of energy as fat) + 0.6 g/kg BW Leu, HLH: AIN-93M diet (40% of energy as fat) + 1.2 g/kg BW Leu
2) Mineral mix (AIN-93M-MIX)(g/kg mixture): calcium carbonate 357.00, potassium phosphate monobasic 250.00, potassium citrate H2O 28.00, sodium chloride 74.00, potassium sulfate 46.60, magnesium oxide 24.00, ferric citrate U.S.P. 6.06, zinc carbonate 1.65, manganous carbonate 0.63, cupric carbonate 0.30, potassium iodate 0.01, sodium selenate 0.01025, ammonium paramolybdate 4H2O 0.00795, sodium metasilicate 9H2O 1.45, chromium potassium sulfate 12H2O 0.275, lithium chloride 0.0174, boric acid, 0.0815 sodium fluoride 0.0635, nickel carbonate 0.0318, ammonium vanadate 0.0066 and sucrose finely powered 209.806.
3) Vitamin mix (AIN-93-VX)(g/kg mixture): niacin 3.00, calcium pantothenate 1.60, pyridoxine HCl 0.70, thiamine HCl 0.60, riboflavin 0.60, folic acid 0.20, biotin 0.02, vitamin E acetate (500 IU/g) 15.00, vitamin B12 (0.1%) 2.50, vitamin A palmitate (500,000 IU/g) 0.80, Vitamin D3 (400,000 IU/g) 0.25, Vitamin K1/Dextrose Mix (10 mg/g) 7.50 and sucrose 967.23
Table 2
Food intake and body weight in rats fed diets with different levels of dietary fat during and after overweight induction period
1) See Table 1
2) Mean ± standard error (S.E)
3) Values within a column with different letters are significantly different at α = 0.05 level by Student's t test
4) Values within a column are not significant at α = 0.05 level by Student's t test
Table 3
Food intake, calorie intake and body weight in rats fed diets with different levels of fat and/or leucine
1) See Table 1
2) Mean ± standard error (S.E)
3) Values within a column with different letters are significantly different at α = 0.05 level by Duncan's multiple range test
4) Values within a column are not significant at α = 0.05 level by Duncan's multiple range test
5) Statistical significance of experimental factors was calculated using two-way ANOVA. A: Effect of dietary fat level was significant at α = 0.05, B: Effect of leucine level was significant at α = 0.05, AB: Interaction of dietary fat and leucine level was significant at α = 0.05
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