Functional modulation of gut microbiota in diabetic rats following dietary intervention with pistachio nuts (Pistacia vera L.)

Abstract

Background: Gut microbiota holds a key-role in numerous biological functions and has emerged as a driving force for the development of diabetes. Diet contributes to gut microbiota diversity and functionality providing a tool for the prevention and management of the disease. The study aimed to investigate the effect of a dietary intervention with pistachio nuts, a rich source of monounsaturated fatty acids, dietary fibers and phytochemicals on gut microbiota composition in the rat model of Type 1 Diabetes.

Methods: Male Wistar rats were randomly assigned into four groups: healthy animals which received control diet (CD) or pistachio diet (PD), and diabetic animals which received control diet (DCD) or pistachio diet (DPD) for 4 weeks. Plasma biochemical parameters were determined and histological examination of liver and pancreas was performed at the end of the dietary intervention. Adherent intestinal microbiota populations in jejunum, ileum, caecum and colon were analyzed. Fecal microbiota populations at the beginning and the end of the study were determined by microbiological analysis and 16S rRNA sequencing.

Results: Diabetic animals of both groups exhibited high plasma glucose and low insulin concentrations, as well as characteristic pancreatic lesions. Pistachio supplementation significantly increased lactobacilli and bifidobacteria populations in jejunum, ileum and caecum (p < 0.05) and normalized microbial flora in all examined intestinal regions of diabetic animals. After 4 weeks of supplementation, populations of bifidobacteria and lactobacilli were increased in feces of both healthy and diabetic animals, while enterococci levels were decreased (p < 0.05). Next Generation Sequencing of fecal samples revealed increased and decreased counts of Firmicutes and Bacteroidetes, respectively, in healthy animals that received the pistachio diet. Actinobacteria OTUs were higher in diabetic animals and increased over time in the pistachio treated groups, along with increased abundance of Bifidobacterium. Lactobacillus, Turicibacter and Romboutsia populations were elevated in healthy animals administered the pistachio nuts. Of note, relative abundance of Bacteroides was higher in healthy than in diabetic rats (p < 0.05).

Conclusion: Dietary pistachio restored normal flora and enhanced the presence of beneficial microbes in the rat model of streptozotocin-induced diabetes.

Keywords: Bifidobacteria; Gut microbiota; Lactobacilli; Pistachio nuts; Streptozotocin-induced diabetes; Type 1 diabetes.

Fig. 1

Effect of pistachio diet on fecal microbiota population in healthy and diabetic animals at 0 and 4th week of pistachio supplementation. Data are expressed as mean ± SEM. Data with different superscript letters are significantly different p < 0.05, according to the post hoc ANOVA statistical analysis. TAC: total aerobic counts, CD: healthy animals that received the control diet, PD: healthy animals that received the pistachio diet, DCD: diabetic animals that received the control diet, DPD: diabetic animals that received the pistachio diet. ^ap < 0.05 vs timepoint 0 of the same sample, ^bp < 0.05 PD vs CD, ^cp < 0.05 DPD vs DCD, ^dp < 0.05 CD vs DCD.

Fig. 2

Effect of pistachio diet on gut microbiota population of healthy and diabetic animals in: (a) jejunum, (b) ileum, (c) caecum, (d) colon. Data are expressed as mean ± SEM. Data with different superscript letters are significantly different p < 0.05, according to the post hoc ANOVA statistical analysis. TAC: total aerobic counts, CD: healthy animals that received the control diet, PD: healthy animals that received the pistachio diet, DCD: diabetic animals that received the control diet, DPD: diabetic animals that received the pistachio diet. ^ap < 0.05 vs CD, ^bp < 0.05 vs PD, ^cp < 0.05 vs DCD, ^dp < 0.05 vs DPD.

Fig. 2

Effect of pistachio diet on gut microbiota population of healthy and diabetic animals in: (a) jejunum, (b) ileum, (c) caecum, (d) colon. Data are expressed as mean ± SEM. Data with different superscript letters are significantly different p < 0.05, according to the post hoc ANOVA statistical analysis. TAC: total aerobic counts, CD: healthy animals that received the control diet, PD: healthy animals that received the pistachio diet, DCD: diabetic animals that received the control diet, DPD: diabetic animals that received the pistachio diet. ^ap < 0.05 vs CD, ^bp < 0.05 vs PD, ^cp < 0.05 vs DCD, ^dp < 0.05 vs DPD.

Fig. 3

Taxonomic-binning in phyla level with normalized relative abundances, CD: healthy animals that received the control diet, PD: healthy animals that received the pistachio diet, DCD: diabetic animals that received the control diet, DPD: diabetic animals that received the pistachio diet. Parenthesis indicating the timepoint of the diet, 0: baseline week and 4: after 4 weeks of dietary intervention with pistachio nuts.

Fig. 4

(a) Phylogenetic tree of representative OTUs, which are represented with different colors, from 16S rRNA analysis constructed using Maximum-Likelihood algorithm in MEGAX-program, different colors represent the variant genera, (b) Taxonomic-binning in genus level with normalized relative abundances, CD: healthy animals that received the control diet, PD: healthy animals that received the pistachio diet, DCD: diabetic animals that received the control diet, DPD: diabetic animals that received the pistachio diet, parenthesis indicating the timepoint of the diet, 0:baseline week and 4: after 4 weeks of dietary intervention with pistachio nuts. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 5

Diversity indices (a) Simpson’s and (b) Shannon’s expressed as mean ± SEM. Data with different superscript letters are significantly different p < 0.05, according to the post hoc ANOVA statistical analysis. ^ap < 0.05 vs timepoint 0 of the same sample, ^bp < 0.05 PD vs CD, ^cp < 0.05 DPD vs PD, ^dp < 0.05 DCD vs CD.

Fig. 6

Representative sections from pancreas and liver of healthy and STZ-induced diabetic rats. Eosin-hematoxylin stain, 200x. A. Pancreatic section of healthy animal shows a well-preserved cellular architecture. The islets of Langerhans exert a homogenous morphology of β-cells (arrow). B. Pancreatic section of STZ-induced diabetic rat shows degranulation and vacuolation of β-cells (arrow). C, D. Liver sections from healthy (C) and diabetic (D) animals demonstrate normal architecture of the liver parenchyma without evidence of portal inflammation or necrosis.