Relationship of the glycation gap to diabetes and its complications, and the potential role of adipokines

Abstract

Background: Diabetes mellitus has become a global health menace and the management cost to both developed and developing countries is biting hard on the economy. Diabetes mellitus is primarily caused by hyperglycaemia and research has confirmed the strong link of obesity as a precursor of type 2 diabetes. Hyperglycaemia is a major and an independent risk factor of cardiovascular disease (CVD) and atherosclerosis in diabetes. Obesity is also associated with cardiovascular disease which is one of the diabetic complications. Stress which is one the predisposing factor of obesity generates a vicious cycle leading to the release of high level of inflammatory adipokines and this is the link between obesity and CVD. Adipokines are believed to have a role in diabetic complications. This research intends to understand the role some specified adipokines plays in insulin secretions and beta cell failure. Glycation is a common and spontaneous reaction of proteins or lipids becoming glycated after exposure to sugars, occurring in vivo without the controlling action of an enzyme. Deglycation is an enzyme-mediated pathway and fructoseamine-3-kinase (FN3K) is believed to be one of the major enzymes. FN3K is known to play a protective role in the development of vascular complications in diabetes patients. In the absence of deglycation or deglycating enzymes, advanced glycation endproducts (AGEs) are formed. This research work employed 1-deoxy-1-morpholino fructose (DMF) a major enzyme which can prevent deglycation to show the importance of deglycation in beta cell and FN3K role in insulin secretion. Method: This research work analysed glycoprotein acetylation (GlycA) a known inflammatory marker that tracks systemic inflammation and cardiovascular risk. The investigation of the potential role of inflammation in the GGap using a novel (and putatively better than existing measures such as CRP) marker of inflammation, GlycA was carried out. A total of 54 diabetic patients were used for this research work and divided into 2 groups. GGap negative (G0) = 34 and GGap positive (G1) = 20. 1H- Nuclear Magnetic Resonance (NMR) was used to analyse the samples and measuring the different peaks. Glycoscale was used for glycoproteins while liposcale was used for lipoproteins. Laboratory analyses were carried out to ascertain the pathophysiological role of adipokines in inducing insulin secretion. The laboratory analysis includes assessment of insulin secretion from MIN6 and BRIN-BD11 cells, effects of WISP1 on beta cells viability, effects of some adipokines (WISP1, eNAMPT/Visfatin, sFRP4) on insulin secretions/release from pancreatic beta cell. To this end, MIN6 cells were cultured in low and high glucose media, treated with different concentrations of adipokines, and tested for insulin secretion, beta cell failure and cell viability. Using insulin ELISA assay, the concentrations of insulin release/secretions was measured while cell viability was determined by using prestoleblue. Results: Visfatin/eNAMPT exhibited a dose dependant insulin response at high concentrations. WISP1 acute effects (incubating cells for 48hours) shows a dose-dependent outcome on insulin secretions and a reduced effects at high concentrations. Chronic effects of WISP1 (incubation of cells for over 72 hours) shows increase acute GSIS over 72hr period independent of glucose or WISP1 concentrations (P-value = 0.0025). With low glucose, MIN6 cell viability decreases over 72 hours while at high glucose, cells didn’t appear to have proliferated much over 72 hours. sFRP4 had an increased effect at higher glucose levels. The introduction of FN3K inhibitor in the presence of high glucose led to a drastic fall in insulin release with P value = 0.005. GlycA and GlycB but not GlycF concentrations were elevated in the Positive GGap group (p<0.001). BMI was higher in positive GGap indicating its link to diabetes and its complications. VLDL was higher in cholesterol and triglyceride in positive GGap patients while HDL was lower in cholesterol and triglyceride in positive GGap patients (p<0.001). Conclusion: This research has been able to show that the selected adipokines are able to induce insulin secretion. GGap positive patients are more susceptible to diabetes complications. GlycA and GlycB but not GlycF shows to be potent biomarker of inflammation. Lipoproteins particles of GGap positive patients are more exposed to diabetes complications. Lipoprotein particle measurement may be useful in patients at risk of CVD.