The effects of separate and concurrent Lactobacillus plantarum and inulin supplementation on intestinal levels of serotonin and BDNF, cardiac expression of serotonin and BDNF receptors, and apoptotic markers in male rats with type 2 diabetes

Abstract

Background and aims: Type 2 diabetes mellitus (T2DM), as a metabolic disorder, leads to diabetic cardiomyopathy, characterized by cardiomyocyte apoptosis and myocardial fibrosis. Serotonin and brain-derived neurotrophic factor (BDNF) are two neurotransmitters with the ability to regulate cardiomyocyte apoptosis and myocardial fibrosis via their cardiac receptors. In the present experimental study, we assessed the effects of Lactobacillus plantarum (L. plantarum) and/or inulin administration on the protein expression of cardiac apoptotic markers by regulating intestinal, serum, and cardiac levels of serotonin and BDNF as well as their cardiac receptors. Methods: Sixty male Wistar rats were randomly divided into six groups: Healthy Control (HC); Diabetic Control (DC); Diabetic Sham group (DSh); Diabetic + L. plantarum (DL); Diabetic + inulin (DI) and Diabetic + L. plantarum + inulin (DLI). High-fat diet and streptozotocin (35mg/kg intraperitoneally) were used to induce diabetes. Then, they were administrated with L. plantarum (107 CFU/mL), inulin, or their combination for eight weeks. The inulin content was ascertained based on 5% of the rats’ daily food weight and dissolved in the rats' drinking water. At the endpoint, the animals were anesthetized and blood samples obtained from the cardiac puncture of the rats. Furthermore, ileum and ventricle segments were homogenized and stored at −80°C, until biochemical and Western blot analysis. The concentrations of serotonin and BDNF were measured using ELISA assay. Besides, the Western blot analysis was used to determine the protein expression of 5-HT2B and TrkB receptors as well as the cardiac apoptotic and anti-apoptotic markers. Results: Concurrent use of L. plantarum and inulin resulted in reduced levels of intestinal and serum serotonin (P=0.01 and P=0.001, respectively). In addition, it could significantly increase serum BDNF concentration (P<0.001). However, no significant changes were observed in the intestinal BDNF of the treatment groups after supplementation. Moreover, simultaneous administration of L. plantarum and inulin showed a remarkable rise in cardiac concentrations of serotonin and BDNF (P<0.001 and P=0.001, respectively). Also, it caused a significant enhancement in the expression of cardiac serotonin and BDNF receptors (P<0.001, both) as well as a remarkable fall in the cardiac interstitial and perivascular fibrosis (P<0.001, both) and cardiomyocyte apoptosis (P=0.01). Moreover, concurrent use of L. plantarum and inulin significantly increased the ratio of p-Akt to Akt (P<0.001) along with the remarkable reduction of caspase-3 expression and Bax to Bcl-2 ratio in the heart tissue (P<0.001, both). Besides, there was a strong correlation of cardiac 5-HT2B and TrkB receptors with interstitial/ perivascular fibrosis and cardiomyocyte apoptosis (P<0.001, both). Conclusion: Overall, the results revealed beneficial impacts of L. plantarum and supplementation on intestinal serotonin and BDNF as well as their cardiac receptors and decreased levels of cardiac apoptotic markers in diabetic rats. It seems that L. plantarum and inulin administration could be considered as a novel adjunct therapy to reduce cardiac complications of T2DM.