Plasma Insulin/Erythrocytic Aldose Reductase Ratio as a Predictor for Hepatocellular Carcinoma among Type II Diabetics and Hepatitis C Virus-infected Patients

Insights from the fructose-derived product glucoselysine: Revisiting the polyol pathway in diabetic complications

Advanced glycation end-products (AGEs) have been extensively studied because of their close association with the onset and progression of diabetic complications. However, owing to their formation through diverse metabolic pathways, AGEs often reflect a wide range of pathological conditions rather than being specific to diabetic complications. Consequently, identifying an AGE that directly correlates only with diabetic complications remains a challenge. Chronic hyperglycemia not only saturates the glycolytic pathway but also upregulates the polyol pathway, leading to the excessive production of fructose, a highly reactive reducing sugar. Although it has long been understood that fructose-derived AGEs contribute to diabetic complications, their chemical structures remain unidentified. Recent breakthroughs have revealed that glucoselysine (GL) is a primary fructose-specific AGE. Unlike other AGEs, GL is exclusively formed from fructose and not from other reducing sugars, such as glucose or galactose. This specificity provides GL with a distinct advantage in that its production pathway can be traced, making it a reliable indicator of polyol pathway activity. Furthermore, emerging evidence suggests that GL levels correlate with the progression of diabetic complications, including both micro- and macrovascular complications, making it a promising biomarker. GL's potential extends beyond diagnostics, as it may serve as a therapeutic target for managing complications associated with prolonged hyperglycemia and enhanced of polyol pathway. This review focuses on the enhanced polyol pathway and the formation of GL and discusses its biochemical characteristics, clinical significance, and potential as a novel diagnostic marker and therapeutic target in diabetic care.

Glucoselysine, a unique advanced glycation end-product of the polyol pathway and its association with vascular complications in type 2 diabetes

Glucoselysine (GL) is an unique advanced glycation end-product derived from fructose. The main source of fructose in vivo is the polyol pathway, and an increase in its activity leads to diabetic complications. Here, we aimed to demonstrate that GL can serve as an indicator of the polyol pathway activity. Additionally, we propose a novel approach for detecting GL in peripheral blood samples using liquid chromatography-tandem mass spectrometry and evaluate its clinical usefulness. We successfully circumvent interference from fructoselysine, which shares the same molecular weight as GL, by performing ultrafiltration and hydrolysis without reduction, successfully generating adequate peaks for quantification in serum. Furthermore, using immortalized aldose reductase KO mouse Schwann cells, we demonstrate that GL reflects the downstream activity of the polyol pathway and that GL produced intracellularly is released into the extracellular space. Clinical studies reveal that GL levels in patients with type 2 diabetes are significantly higher than those in healthy participants, while Nδ-(5-hydro-5-methyl-4-imidazolon-2-yl)ornithine (MG-H1) levels are significantly lower. Both GL and MG-H1 show higher values among patients with vascular complications; however, GL varies more markedly than MG-H1 as well as hemoglobin A1c, fasting plasma glucose, and estimated glomerular filtration rate. Furthermore, GL remains consistently stable under various existing drug treatments for type 2 diabetes, whereas MG-H1 is impacted. To the best of our knowledge, we provide important insights in predicting diabetic complications caused by enhanced polyol pathway activity via assessment of GL levels in peripheral blood samples from patients.