Effects of High Protein Diets on Brush Border Membrane Enzymes and Carbohydrate Metabolism in Rat Intestine and Liver

Background and Objective:We are what we eat.Adequate balanced nutrition is important to maintain health.However, sugar, fat and protein-rich diets, fried and processed foods and so called popular or TV diets such as Atkins diet cause negative effects on human health.Primarily, they affect structure and functions of the intestine, liver and kidney.In the present study, effects of high protein diets were assessed on various serum parameters and on enzymes of brush border membrane and energy yielding metabolic pathways such as glycolysis, TCA cycle, gluconeogenesis HMP shunt in small intestine and liver of rats.Materials and Methods: Rats were fed with high protein diets for 28 d.At the end of the experiment, rats were sacrificed under light ether anaesthesia and blood samples were collected and small intestines and livers were extracted and processed for the preparation of homogenates and brush border membrane vesicles (BBMV).The present study was carried out to investigate the effects of HPD on body weights, serum parameters and enzymes of carbohydrate metabolism in BBM of the rats' intestines and livers.Results: Results showed that high protein diets increased serum glucose and decreased inorganic phosphate; however, serum cholesterol and phospholipids were unchanged.High protein diets significantly increased the activity of alkaline phosphatase (ALkPase) and -glutamyl transferase (GGTase) in mucosal brush border membranes but decreased the sucrase activity.The activity of metabolic enzymes of lactate dehydrogenase (LDH) involved in glycolysis and malate (MDH), succinate (SDH) and isocitrate (ICDH) dehydrogenase involved in TCA cycle significantly decreased by high protein diets in the intestine.The activity of glucose-6-phosphate dehydrogenase (G6PDH, HMP shunt) and NADP-malic enzyme (ME) significantly decreased; however, gluconeogenesis enzymes of glucose-6-phosphatase (G6Pase) and fructose-6-bisphosphatase (FBPase) increased in intestine by high protein diets.High protein diets decreased the activity of LDH and MDH whereas increased the activity of FBPase, G6Pase, G6PDH and ME in the liver. Conclusion:In conclusion, consumption of high protein diets caused extensive alterations in the intestinal brush-border membrane enzymes.The activity of enzymes of glycolysis and TCA cycle decreased but those of glucose production and HMP shunt increased by high protein diets in the intestine.The metabolic activity was differentially affected by high protein diets in the liver as shown by the changes in associated enzymes.The enzymes of glycolysis and TCA cycle decreased but those of gluconeogenesis and HMP shunt as well as ME significantly increased by high protein diets in the liver.