Induction of Beneficial Changes in Glucose Homeostasis, Lipid Profile, Inflammation, Retinopathy, Bile Acids and Gut Microbiota in Streptozotocin-Induced Type 1 Diabetes Mellitus by Essential Fatty Acids

Abstract

Background: Essential fatty acids (EFAs) n3 alpha-linolenic acid (ALA) and n6 linoleic acid (LA) have been shown to improve lipid metabolism, promote nervous system development, suppress inflammation, and are of benefit in diabetes mellitus and cancer. But the exact mechanism of their action(s) is not clear. In the present study, we evaluated the effects of ALA and LA on glucose homeostasis, circulating lipid profile, inflammatory markers, gut microbiome, and bile acids in streptozotocin (STZ)-induced type 1 diabetes with retinopathy in rats. We also measured vitreal LXA4 levels in patients with diabetic retinopathy since arachidonic acid (AA), the precursor of LXA4, is derived from LA. Methods: The study was performed in male Sprague Dawley rats. Type 1 DM was induced by intraperitoneal injection of STZ. The type 1 DM animals received LA or ALA 100 ug/day via intraperitoneal route on alternate days till the end of the study (21 days after the DM onset). In these animals, glucose homeostasis and lipid profile were evaluated. Plasma and retinal fatty acid profile by gas chromatography (GC), retinal histology by H&E staining, activities of desaturases in the retina and liver tissues and inflammatory markers by qRT-PCR, and composition of the gut microbiota by 16S rDNA sequencing technology of the fecal samples were performed. In addition, short-chain fatty acids (SCFAs) and bile acids (BAs) in the feces and liver of rats were assayed by GC and liquid chromatography coupled with tandem mass spectrometry (UHPLC–MS/MS), respectively. Human vitreal samples obtained from patients with proliferative diabetic retinopathy (PDR) were analyzed for their fatty acids profile and LXA4 levels and compared with those with macular hole (control). Findings: LA and ALA-treated STZ-induced type 1 DM animals showed significant reduction in their plasma glucose levels, pro-inflammatory cytokines (IL-6 and TNF-α), changes in the composition of gut microbiome in the form of an increase in the abundance of Ruminococcaceae (ALA-treated group), Alloprevotella, Prevotellaceae_Ga6A1_group, Ruminococcaceae_UCG_010 and Ruminococcus_1 (in LA-treated group) , an increase in acetic acid and butyric acid, and an increase in the fecal concentrations of CA, CDCA and TUDCA and a decrease in GCA. Concentrations of hepatic CDCA, TCDCA, and TUDCA were significantly increased in ALA treated animals while CDCA were elevated in those with LA treatment. STZ-treated animals showed significant decrease in plasma LA, GLA, and AA and ALA levels with no significant changes in retinal fatty acid composition. All these changes reverted to normal in LA and ALA treated group. The changes in the plasma fatty acid composition were accompanied by significant alterations in the expression of desaturases, COX-2 and 5-LOX and 12-LOX enzymes and pro- and anti-inflammatory cytokines. In addition, retinal LXA4 levels were found to be decreased in patients with PDR. Interpretation: The results of the present study suggest that ALA and LA administration can improve plasma glucose levels, suppress inflammation, and produce significant beneficial alterations in the gut microbiota, plasma lipid profile and EFAs metabolism. Decrease in retinal LXA4 levels in those with PDR agree with the suggestion that EFAs metabolism is altered in T1DM and DR. These results imply a significant role for EFAs and their metabolites in the pathobiology of type 1 DM and diabetic retinopathy. Funding Information: The project was funded by the National Natural Science Foundation of China (No. 82000886), and Natural Science Foundation of Zhejiang Province (No.LQ20H120011). Declaration of Interests: Authors have no conflicts of interest to declare. Ethics Approval Statement: This study was approved by the animal ethics committee of the Second Affiliated Hospital of Zhejiang University school of medicine. All experimental procedures using animals were performed in accordance with the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research. This study was approved by the Clinical Ethical Research Committee of the Second Affiliated Hospital of Zhejiang University school of medicine. The study was performed as per the tenets of Helsinki declaration. Informed consent obtained from all the participating patients.