Effect Of Whey Protein On Diabetes Mellitus Control In Mice

【Objective】Diabetes is a common chronic disease with multi-factors such as genetic, environmental, dietary, behavioral and other factors. Milk is one of the staple foods, which contains many nutrients. Whey protein is accounted for 20% of total milk protein. Recently, whey protein has attracted increasing attention for its beneficial effect on diabetes. In the present study, the mechanism by which whey protein control diabetes was investigated using streptozotocin (STZ)-induced diabetes in mice.【Methods】SPF grade male ICR mice were used to induce non-insulin-dependent diabetes mellitus and insulin-dependent diabetes mellitus models by intraperitoneal injection of 100mg/kg and 160mg/kg of STZ, respectively. Mice were assigned at random to four groups, each intragastrically administering with 0%, 10%, 20% and 40% of the whey protein every other day and lasted for 4 weeks. Body weight, food and water intakes were recorded once a week. Fasting blood glucose and plasma insulin were measured before whey protein gavage, at the middle of experiment and at the end of experiment. At the end of the experiment, plasma lipids, malondialdehyde and leptin were also measured. Pancreatic morphology was observed through electron microscope. In addition, the composition of amino acid in whey protein and plasma level of amino acids were analyzed by high performance liquid chromatography (HPLC) equipped with amino acid column.【Results】The model mice showed obvious polydipsia, polyphagia, particularly in mice administered 160mg/kg STZ. The body weight also decreased in 160mg/kg STZ administering mice. Pancreatic morphology indicated that islets shrank in 100mg/kg STZ administering mice, and decreased number of islets and nuclear fusion and necrosis ofβcells in 160mg/kg STZ administering mice.There was no significant difference in fasting blood glucose among groups. In normal mice and 100mg/kg STZ administering mice, plasma insulin levels were significantly lower in 40% whey protein group than 0% whey protein group (control group). 160mg/kg STZ administering mice showed very low level of plasma insulin, suggesting the loss of insulin secretion. The ratio of insulin to glucose reflected insulin sensitivity. Comparing with control group, this ratio in normal mice was significantly lower in 40% whey protein group at the middle of experiment, and in all whey protein groups at the end of experiemt. This ratio in 100mg/kg STZ administering mice was also significantly lower in 40% whey protein group than other three groups at the end of the experiment.In normal mice, the plasma levels of triglycerides and low-density lipoprotein cholesterol (LDL-C) were significantly lower in 40% whey protein group than in control group. With the increase of whey protein, their levels decreased in a dose-response pattern. In modeling mouse, the plasma levels of triglycerides, total cholesterol, high density lipoprotein cholesterol (HDL-C) and LDL-C had no significant differences among four whey protein groups.At the end of the experiment, plasma leptin levels of 100mg/kg STZ administering mice increased with whey protein gavage without statistical significance. Its level closed to 0 in 160mg/kg STZ administering mice. Plasma malondialdehyde levels in different concentrations of whey protein found no significant differences in three kinds of mice.According to the HPLC measurement, branched-chain amino acids are accounted for 25.65% of amino acids in whey protein used in this study, which is consistent with previous studies. The plasma levels of branched-chain amino acids increased after whey protein gavage with dose-response pattern.【Conclusion】In the present study, STZ successfully induced non-insulin-dependent diabetes mellitus and insulin-dependent diabetes mellitus models. Whey protein increased insulin sensitivity of the normal mice and 100mg/kg STZ administering mice, improved lipid profile of normal mice. The mechanism is likely to increase plasma branched-chain amino acids after intake of whey protein.