Long-term Different Amounts Of Protein Feeding Normal Rat Islet ¦Â-cell Function And Insulin Sensitivity

English Abstract[Objective] To observe the effect of long-term protein diet with normal total calorie intake on islet β cell function in normal rats in order to probe the association of dietary protein with type 2 diabetes mellitus(T2DM).[Methods] 70 healthy male Wistar rats(8 weeks old) were selected and divided into four groups including routine diet(NC,n=16), high protein diet(HP,n=19), low protein diet(LP,n=16) and high fat diet(HF,n=19).The total calorie ingestion of each rat per day was similar and feeding duration was 24 weeks. Body weight, fasting blood glucose(FBG) and fasting plasma insulin(FINS) were monitored during feeding. The insulin secretary function of β cells, especially acute insulin response(AIR),was assessed by intravenous glucose tolerance test(IVGTT) in 32-week-old rats.[Results] l.Body weight and visceral fat mass: Compared with NC , there were no differences in body weight and visceral fat mass of HP or LP group(P<0.05),but rats taking HF had significantly higher body weight[(559.3±58.8)g vs (503.1 ± 36.2)g,p<0.005]and developed severe visceral obesity [visceral fat rate (9.3 ±2.5)% vs (4.8 ± 1.2)%,P<0.01]. 2.FBG and FINS: There were no differences in FBG levels of the four groups. But FINS levels were significantly higher in HF than in NC[(1.6± 0.5)ng/ml vs (1.0 ± 0.3)ng/ml,P<0.005].3.IVGTT (1) Blood glucose: There were nodifferences in blood glucose levels among HP,LP and NC. The blood glucose levels by IVGTT at 5min,10min,30min were statistically higher in HF than in NC[(17.2± 0.9)mmol/L vs (16.2 + 1.5)mmol/L,P<0.05;(14.8 ± l.l)mmol/L vs (12.7 ± 0.9)mmol/L,P<0.001;(9.5±1.4)mmol/L vs (7.1 ± 1.3)mmol/L,P<0.001].(2) Plasma insulin: 5min and lOmin plasma insulin levels were markedly higher in HP than in NC [(6.5±0.8)ng/ml vs (4.9±0.7)ng/ml,P<0.001;(3.9±0.6)ng/ml vs (3.1 ±0.5)ng/ml,P<0.001],importantly lower in HF than in NC[(1.9 + 0.7)ng/ml vs (4.9 + 0.7)ng/ml,P<0.001;(2.5±0.5)ng/ml vs (3.1 ± 0.5)ng/ml,P<0.005]. There were no differences in plasma insulin levels between LP and NC .The insulin levels at 30min,60min,120min were differently higher in HF than in NC[30min:(2.4 ± 0.4)ng/ml vs (1.1 + 0.2)ng/ml,P<0.001;60min:(1.8 + 0.4)ng/ml vs (1.0 + 0.2)ng/ml,P<0.001;120min:(1.4 + 0.4)ng/ml vs (0.9 + 0.2)ng/ml,P<0.005]. 4.The area under the curve (AUC) (1) AUC of blood glucose (AUC-BG) There were no differences in AUC-BG among HP,LP and NC(P>0.05). But the AUC-BG was significantly higher in HF than in NC[0-30min:(39.0+1.9)mmol/L vs (34.5 + 1.6)mmol/L, PO.001;0-120min:(54.7 + 2.9)mmol/L vs (48.0±2.1 )mmol/L,P<0.001 ]. (2) AUC of Insulin(AUC-Ins) The AUC-Ins was significantly higher in HP than in NC[0-30min:(11.5 + 0.8)ng/ml vs (9.1 ±0.8)ng/ml,P<0.001;0-120min:(13.8 + l.l)ng/ml vs (11.2 + 0.9)ng/ml,P<0.001]and lower in HF than in NC[(6.5± l.l)ng/ml vs (9.1 ±0.8)ng/ml,P<0.001;( 10.2+ 1.3)ng/ml vs (9.1 +0.8)ng/ml,P<0.05].There were no differences in AUC-Ins between LP and NC group.[Conclusion] Unlike high fat feeding,the long-term high protein ingestion with total calorie may significantly enhance acute insulin response by IVGTT in rats. The effect of low protein intake on insulin secretion of rats is not obvious. It suggests that long-term high protein diet isn't closely associated with islet P cell function injury and onset of T2DM in normal individuals.English Abstract[Objective] To explore the effect of long- term protein intake with normal total calorie on the apoptosis and bax,bcl-2 expression of apoptosis-related genes of islet cells in normal rats.(Methods] 70 normal male Wistar rats(8 weeks old) were fed on a normal chow (NC,n=16),or a high protein diet(HP ,44% of calories as protein, n=19), or a low protein diet (LP,13% of calories as protein,n=16), or a high fat diet(HF,47% of calories as fat ,n=19) for 24 weeks.The rats were killed after intravenous glucose tolerance test (IVGTT) and evaluated the expression of the bax and bcl-2 of islet Pcells with image analysis of immunohistochemistry. The apoptotic P cells in pancreas were detected and quantified by the TUNEL technology (labeling of DNA strand breaks).[Results] l.The observation under microscope after HE dye There were no significant differences in the pancreatic pathology among four groups.2.The image analysis (l)The bax expression (D bax positive area of p cells There were no differences in p cell bax positive area among HP,LP and NC(p>0.05) while it was significantly higher in HF than in NC[(0.16± 0.03)% vs (0.07±0.02) %, p<0.01]. (2) Grey level There were no differences in grey level among HP,LP and NC(p>0.05).But it was significantly lower in HF than in NC[(159.22±3.72) vs(190.42 ±4.00) ,p<0.01]. (2)The bcl-2 expression ?bcl-2 positive area of pcells There were no differences in P cell bcl-2 positive area among HP,LP and NC(p>0.05) while it was significantly lower in HF than in NC[(0.05±0.02)% vs (0.17± 0.03)%,p<0.01]. (2) Grey level There were no differences in grey level among HP,LP and NC(p>0.05).But it was significantly higher in HF than in NC [ ( 214.79± 3.53) vs (195.82 ± 5.66), p<0.01]. (3)The apoptosis rate of islet pcells There were no differences in the apoptosis rate of islet pcells among HP,LP and NC(p>0.05)while it was significantly higher in HF than in NC[( 12.26 ±2.09)% vs (2.88± 0.19) %, pO.Ol].[Conclusion] Unlike the high fat diet,the long-term protein feeding with normal total calorie might not induce the apoptosis of isletpcells in normal rats.English abstract[Objective] Abundant evidences support that high-fat diet can cause insulin resistance(IR), but few study is performed to verify the effect of long-term protein diet on insulin sensitivity.lt is helpful to identify the effect for prevention and treatment of diabetes. In this study ,HOMA-IR and adiponectin are used as two markers to reflect the insulin sensitivity .To observe the effect of long-term protein diet on the two markers in normal rats in order to probe the effect of long-term protein diet with normal total calorie on the insulin sensitivity.[Methods] 70 healthy male Wistar rats (8 weeks old) were selected and divided into four groups including: normal chow(NC,n=16)> high-protein diet(HP, 44% calories for protein, mainly casein, n=19)> low-protein diet(LP,13% calories for protein,n=16^ high -fat diet (HF,47% calories for fat, mainly pig oil,n=19).They were cleanly feeded for 24 weeks by a special staff, the calorie of daily food was controlled at 70kcal for one rat. Body weight,fasting blood glucose(FBG) and fasting plasma insulin(FINS) were monitored during feeding. The levels of plasma adiponectin were tested by radioimmunity and HOMA - IR was calculated by the method: HOMR - IR = FBGXFINS/ 22. 5 in 32-week-old rats.[Results] 1.H0MA-IR: HOMA-IR of HP and LP had no differences from NC group(p>0.05) .while HOMA-IR was significantly increased in HF group comparedwith NC group[(0.32±0.13)v5 (0.17 + 0.06),P<0.001].2.plasma adiponetin levels: The levels of plasma adiponectin were significantly increased in HP group compared with NC group[(23.7±4.4) y g/ml vs (20.2 + 3.6) y g/ml,P<0.05], while significantly decreased in HF group[(14.3 + 4.0) y g/ml vs (20.2 + 3.6) u g/ml,P<0.001].There were no differences in plasma adiponectin between LP and NC group.[Conclusion] Long-term feeding with different amount of protein can result in different effect on insulin sensitivity in normal rats. Long-term high-protein diet may enhance the insulin sensitivity of target tissues, while the low-protein diet has no effect on insulin action in normal rats.