Rice bran extract attenuates cognitive impairment by enhancing pancreatic β-cell insulin secretion in STZ-induced diabetic rats targeting the PPARγ/PDX1 pathway

Abstract

Type I diabetes (T1D), also known as juvenile diabetes, is an autoimmune disease that causes gradual destruction of pancreatic cells and leads to intellectual disability, neuropathy, cognitive impairment, and impaired learning ability in children. Despite standard treatment with synthetic human insulin, T1D patients can maintain up to 40% of their insulin-producing islets. PPARγ receptor activation research that aims to restore β-cell biology could help reverse the loss of pancreatic mass that comes with getting older and improve β-cell function. Egyptian RB ethanol extract (RBE), previously reported with PPARγ agonist activity, showed an increase in insulin secretion both in vivo and in INS-1 cells. The exact antidiabetic RBE mechanism is still unclear. The present study aims to investigate the molecular RBE mechanism in glucose-stimulating insulin secretion and restoration of β cell function. A diabetic rat streptozotocin (STZ) model was used; five groups were designed. The STZ-diabetic rats were treated with RBE daily for 21 days compared to an insulin-treated group. Biochemical parameters and quantitative RT-PCR of β-cell genes related to the PPAR/PDX1 signaling pathway were performed, and the influence on cognitive ability was confirmed by behavioral testing (Y-maze and NOR) and histological examination. The RBE-treated group reversed blood glucose, Glut2, Ca2 +, and insulin levels in diabetic rats, with pancreatic insulin levels significantly increasing compared to the insulin group. With the exception of PDX1, RBE boosted PPARγ, SERCA, and PrKC gene expression. RBE also restored cognitive functions. This study suggests that RBE may enhance memory and cognition by increasing peripheral insulin secretion through PPARγ regulator activity.

Keywords: Cognition; Diabetes; Insulin; PPARγ; Rice bran extract.

Fig. 1

Effect of oral treatment with RB (100 mg/kg/day) and Ins. (5 IU/200 g/day) on blood glucose level: Effect of treatment with RB (100 mg/kg/day, P.O), and Ins. (5 IU/200 g/day, S.C)on blood glucose level a) after induction b) after week 1 c) after week 2 d) after week 3 e) Along weeks of the experiment in STZ diabetic rats. Rats were injected with multiple low doses of STZ on the first four days For every single week, Statistical analysis was done using One-way ANOVA followed by a Tukey post-test Along the weeks, Statistical analysis was done using two-way ANOVA followed by a Bonferroni post-test Values are presented as mean ± SEM (n=12)

Fig. 2

Effect of oral treatment with RB (100 mg/kg/day) and Ins. (5 IU/200 g/day) on blood insulin level: Effect of treatment with RB (100 mg/kg/day, P.O.), and Ins. (5 IU/200 g/day, S.C)on blood insulin level a) after induction b) after week 1 c) after week 2 d) after week 3 e) Along weeks of the experiment in STZ diabetic rats. Rats were injected with multiple low doses of STZ on the first four days For every single week, Statistical analysis was done using One-way ANOVA followed by a Tukey post-test Along the weeks, Statistical analysis was done using two-way ANOVA followed by a Bonferroni post-test Values are presented as mean ± SEM (n=6)

Fig. 3

Effect of daily oral treatment with RB (100 mg/kg/day) and Ins. (5 IU/200 g/day) on HOMA-β and pancreatic biochemical parameters: Effect of treatment with RB (100 mg/kg/day, P.O.), and Ins. (5 IU/200 g/day, S.C)on HOMA-β (a, b) along weeks of the experiment and on pancreatic tissue levels for c) insulin d) GLUT2 e) calcium at the end of the experiment in STZ diabetic rats. Rats were injected with multiple low doses of STZ on the first four days HOMA-beta values calculated as:] blood insulin concentration (μU/ml) ×20[/] blood glucose (mmol/L) -3.5[ (a): Statistical analysis was done using two-way ANOVA followed by a Bonferroni post-test (b): Pearson correlation map for HOMA-beta values. The correlation coefficient is shown by the color bar: dark blue indicates strongly positive correlations, light blue indicates week positive correlation, white denotes negative correlations, and red denotes strongly negative correlations (c), (d), (e): Statistical analysis was done using One-way ANOVA followed by a Tukey post-test. Values are presented as mean ± SEM (n=6)

Fig. 4

Effect of oral treatment with RB (100 mg/kg/day), and Ins. (5 IU/200 g/day) on pancreatic gene Expression: Effect of treatment with RB (100 mg/kg/day, P.O), and Ins. (5 IU/200 g/day, S.C)on pancreatic gene Expression Levels for a) PPARℽ b) SERCA c) Prkc d) Pdx1 at the end of the experiment in in STZ diabetic rats. Rats were injected with multiple low doses of STZ on the first four days Statistical analysis was done using One-way ANOVA followed by a Tukey post-test Values are presented as mean ± SEM (n=6)

Fig. 5

Effect of oral treatment with RB (100 mg/kg/day), and Ins. (5 IU/200 g/day) on pancreas histopathology: Effect of treatment with RB (100 mg/kg/day, P.O.), and Ins. (5 IU/200 g/day, S.C.) on pancreas histopathology in STZ- diabetic rats Photomicrographs of rat pancreas sections stained with H&E (X100), a) control rats b) RB- control treated rats, c) Diabetic rats d) RB-treated Diabetic rats e) INS- treated diabetic rats As shown, the control groups, the pancreas exhibited a normal histopathological structure. The pancreas in STZ-diabetic rats showed exocrine acini (EX) cell atrophy, vacuolation (arrow), necrosis, and a significant decline in the number of beta cells leading to the islets of Langerhans (IL), dilated (double head arrow), congested (*) blood arteries and mononuclear cells (ICI) infiltrated. RB-treated diabetic rats had apparently mild vacuolation (arrow), congested (*) blood arteries and mononuclear cells (ICI) infiltrated. As well as a moderate increase in Islets of Langerhans (IL). The pancreas of INS-treated diabetic rats displayed moderate vacuolation (arrow), congested (*) blood arteries and mononuclear cells (ICI) infiltrated. As well as a moderate increase in Islets of Langerhans (IL). Statistical analysis was done using the Kruskal-Wallis test followed by a Dunn’s post-test. Values are presented as mean ± SEM

Fig. 6

Effect of treatment with RB (100 mg/kg/day) and Ins. (5 IU/200 g/day) on Amyloid plaque formation: Photomicrographs of rat brain sections stained with Congo red (X25), a) control rats, b) RB-control-treated rats, c) Diabetic rats, d) RB-treated Diabetic rats, e) INS-treated diabetic rats Control groups showed normal staining with Congo red. Diabetic group presented numerous dark red-stained plaques (arrows). INS-treated diabetic rats revealed sporadic red-stained plaque (arrow). RB-treated diabetic rats had few red-stained plaques (arrows)

Fig. 7

Effect of oral treatment with RB (100 mg/kg/day) and Ins. (5 IU/200 g/day) on behavioral tests: Effect of treatment with RB (100 mg/kg/day, P.O.) and Ins. (5 IU/200 g/day, S.C.)on (a) percentage alteration in the Y-maze test and (b) discrimination index in the Novel Object Recognition (NOR) test at the end of the experiment in STZ diabetic rats. Rats were injected with multiple low doses of STZ on the first four days For NOR test statistical analysis was done using one-way ANOVA followed by a Tukey post-test. For Y-maze test statistical analysis was done using Kruskal-Wallis followed by a Dunn’s post-test. Values are presented as mean ± SEM (n = 6)