Estudo do efeito de proteínas e peptídeos naturais bioativos no tratamento de diabetes mellitus

Abstract

Diabetes mellitus (DM) is a public health issue, characterised by hyperglycaemia. The aim of the present study was to evaluate the effect of natural bioactive proteins and peptides in the treatment of DM. Accordingly, this thesis is divided into three chapters. The first chapter outlines the protocol for the systematic review (SR) as registered in the International Register of Prospective Systematic Reviews (PROSPERO, number: CRD42022355540), which guided the construction of the SR presented in the second chapter. In the second chapter, the SR was conducted with the aim of answering the starting question: which peptides or proteins have been studied in silico for the treatment of diabetes mellitus? The articles were selected based on PECOs (Population, Exposure, and Context) from databases such as PubMed, ScienceDirect, Scopus, Web of Science, Virtual Health Library, and EMBASE. Based on the eligibility criteria, five articles were included, and risk of bias was assessed using the adapted Strengthening the Reporting of Empirical Simulation Studies (STRESS) tool. The results showed that proteins and/or peptides extracted from natural sources interacted in silico with therapeutic targets involved in DM management, such as α-amylase, dipeptidyl peptidase IV (DPP-IV), α-glucosidase, insulin receptor (IR), glucose transporter type 2 (GLUT-2), and sodium-glucose co-transporter 1 (SGLT1), and when re-evaluated in vivo, they promoted a reduction in fasting blood glucose, improvement in pancreatic morphology, positive regulation of insulin secretion and expression, reduction or maintenance of plasma insulin, decreased HOMA-IR, increased HOMA-β, and maintenance of GLP-1. It was demonstrated that in silico studies provided crucial insights into therapeutic strategies for DM. In the third chapter, a preclinical study was conducted to evaluate the effect of trypsin inhibitor isolated from tamarind seed (ITT) in zebrafish, with increased fasting blood glucose triggered by overfeeding with Artemia sp. Protein glycation (in vitro and in vivo), biochemical parameters, relative expression of the IR gene, and morphological changes in organs and tissues relevant to T2D were evaluated. DM2 diagnosis was made using Accu-Chek® to assess fasting capillary glucose in the fish before the start of treatments. The animals (N = 140), of both sexes, were distributed into four groups (n = 35): 1) healthy animals without treatment and fed a normal diet; 2) animals with DM2 without treatment and overfed; 3) animals with DM2 treated with ITT (25 mg/L) and overfed; 4) animals with DM2 treated with ITT (25 mg/L) and fed a normal diet for 10 days. Fasting blood glucose was 62.33 mg/dL (2.52) for normo-fed animals and 104.70 mg/dL (4.16) for overfed animals pre-treatment (p = 0.008). No significant change (p > 0.05) was observed in the in vitro glycation of bovine serum albumin for ITT concentrations of 1.4 and 5 mg/mL; however, the concentration of 25 mg/mL ITT significantly increased glycation (p < 0.01). This finding was not maintained when checking the formation of advanced glycation end-products (AGEs) in vivo (p > 0.05) between the groups analysed, using 25 mg/L. After treatment, a significant reduction (p < 0.01) in fasting blood glucose, HOMA-IR, and QUICKI index, and a significant increase (p < 0.01) in HOMA-β were observed in animals treated with ITT and overfeeding compared to the untreated DM2 group, but these values did not show significant differences (p > 0.05) compared to healthy animals, except for the QUICKI index. Significant increases (p < 0.01) in insulin were observed for all groups in relation to the healthy control. Furthermore, ITT promoted negative regulation of the relative expression of IR in adipose and skeletal muscle tissue. Additionally, histopathological findings revealed lower visceral adiposity, pancreatic and hepatic steatosis, and renal degeneration in animals treated with ITT and overfed. However, further studies are needed to elucidate the mechanisms underlying the reduction in fasting blood glucose.