Naila Rabbani

Metabolic dysfunction–associated steatotic liver disease (MASLD) is a major non-communicable disease with global prevalence of 38% and no early-stage treatment. It has risk factors of insulin resistance, impaired glucose tolerance, type 2 diabetes, and diets rich in glucose and fructose. In this review, we explore evidence of abnormal increased early-stage glycolytic intermediates, glycolytic overload, in the initiation of MASLD and propose a new strategy for improved therapy. Glucose is mainly metabolized to glucose-6-phosphate by glucokinase (GCK) in the human liver. This is slowed by the competitive inhibitor, glucokinase regulatory protein (GKRP), with inhibition potentiated by fructose-6-phosphate and lifted by fructose-1-phosphate. The in situ activity of GCK is predicted to increase up to 3-fold by dietary glucose and over 4-fold with concurrent fructose. Related increased glycolytic intermediates activate carbohydrate response element binding protein (ChREBP), hexosamine pathway, and methylglyoxal-stimulated unfolded protein response (UPR). Activation of ChREBP contributes to enhanced lipogenesis and impaired suppression of hepatic glucose production by down-regulation of insulin receptor substrate-2 (IRS-2). IRS-1 signaling is maintained, contributing to enhanced lipogenesis through activation of sterol response element binding protein-1c and down-regulation of IRS-2. Hexosamine pathway activity stabilizes GCK and ChREBP to proteolysis, and the UPR stimulates inflammation and fibrosis. Hepatocytes then export glucose excessively, increasing fasting plasma glucose and risk of peripheral insulin resistance, type 2 diabetes, and vascular complications. Activators of nuclear factor erythroid 2-related factor 2 (Nrf2) provide a novel strategy for therapy. They divert excess glucose metabolism to the pentosephosphate pathway, decreasing activation of ChREBP and hexosamine pathway and formation of methylglyoxal, and decrease lipogenic gene expression. Nrf2 activator, trans-resveratrol and hesperetin combination, corrected glycolytic overload and insulin resistance clinically and now merits evaluation for early-stage treatment of MASLD.

The diagnosis of early-stage osteoarthritis (eOA) is important in disease management and outcomes. Herein we report the clinical validation of a blood test for the diagnosis of eOA in a large patient cohort using trace-level glycated and oxidized amino acid analytes. Subjects were recruited and enrolled in two study groups: subjects with eOA of the hip (n = 110) and asymptomatic controls (n = 120). Their plasma was analyzed for glycated and oxidized amino acids by quantitative liquid chromatography–tandem mass spectrometry. Algorithms were developed using plasma hydroxyproline and 12 glycated and oxidized amino acid analyte features to classify the subjects with eOA and asymptomatic controls. The accuracy was defined as the percentage of the subjects correctly classified in the test set validation. The minimum number of analyte features required for the optimum accuracy was five glycated amino acid analytes: N_ω-carboxymethyl-arginine, hydroimidazolones derived from glyoxal, methylglyoxal and 3-deoxyglucosone, and glucosepane. The classification performance metrics included an accuracy of 95%, sensitivity of 96%, specificity of 94%, area under the curve of the receiver operating characteristic curve of 99%, and positive and negative predictive values of 94% and 97%. We concluded that an assay of five trace-level glycated amino acids present in plasma can provide a simple blood test for the screening of eOA. This is predicted to improve the case identification for expert referral 9-fold.

Hyperglycemia in early-stage embryogenesis is linked to diabetic embryopathy. High-glucose-concentration-induced accumulation of hexokinase-2 (HK2) may initiate metabolic dysfunction that contributes to diabetic embryopathy, including increased formation of methylglyoxal (MG). In this study, we evaluated changes in HK2 protein levels and embryo dysmorphogenesis in an experimental model of diabetic embryopathy. Rat embryos were cultured with high glucose concentrations, and the effects of glyoxalase 1 (Glo1) inducer, trans-resveratrol and hesperetin (tRES + HESP) were evaluated. Rat embryos, on gestational day 9, were cultured for 48 h in low and high glucose concentrations with or without tRES + HESP. Embryo crown–rump length, somite number, malformation score, concentrations of HK2 and Glo1 protein, rates of glucose consumption, and MG formation were assessed. Under low-glucose conditions, embryos exhibited normal morphogenesis. In contrast, high-glucose conditions led to reduced crown–rump length and somite number, and an increased malformation score. The addition of 10 μM tRES + HESP reversed these high glucose-induced changes by 60%, 49%, and 47%, respectively. Embryos cultured in high glucose showed increases in HK2 concentration (42%), glucose consumption (75%), and MG formation (27%), normalized to embryo volume. These elevated HK2 levels were normalized by treatment with 10 μM tRES + HESP. Thus, high-glucose-induced metabolic dysfunction and embryopathy may both be initiated by HK2 accumulation and may be preventable with tRES + HESP treatment.

A dietary supplement, trans-resveratrol and hesperetin (tRES+HESP)—also known as GlucoRegulate—induces increased expression of glyoxalase 1 (Glo1) by activation of transcription factor Nrf2, countering accumulation of the reactive dicarbonyl glycating agent, methylglyoxal. tRES+HESP corrected insulin resistance and decreased fasting and postprandial plasma glucose and low-grade inflammation in overweight and obese subjects in a clinical trial. The aim of this study was to explore, for the first time, health-beneficial gene expression other than Glo1 induced by tRES+HESP in human endothelial cells and fibroblasts in primary culture and HepG2 hepatoma cell line and activity of cis-resveratrol (cRES) as a Glo1 inducer. We measured antioxidant response element-linked gene expression in these cells in response to 5 µM tRES+HESP by the NanoString method. tRES+HESP increases gene expression linked to the prevention of dicarbonyl stress, lipid peroxidation, oxidative stress, proteotoxicity and hyperglycemia-linked glycolytic overload. Downstream benefits were improved regulation of glucose and lipid metabolism and decreased inflammation, extracellular matrix remodeling and senescence markers. The median effective concentration of tRES was ninefold lower than cRES in the Glo1 inducer luciferase reporter assay. The GlucoRegulate supplement provides a new treatment option for the prevention of type 2 diabetes and metabolic dysfunction–associated steatotic liver disease and supports healthy aging.

Hyperglycemia is a risk factor for the development of insulin resistance, beta-cell glucotoxicity, and vascular complications of diabetes. We propose the hypothesis, hexokinase-linked glycolytic overload and unscheduled glycolysis, in explanation. Hexokinases (HKs) catalyze the first step of glucose metabolism. Increased flux of glucose metabolism through glycolysis gated by HKs, when occurring without concomitant increased activity of glycolytic enzymes—unscheduled glycolysis—produces increased levels of glycolytic intermediates with overspill into effector pathways of cell dysfunction and pathogenesis. HK1 is saturated with glucose in euglycemia and, where it is the major HK, provides for basal glycolytic flux without glycolytic overload. HK2 has similar saturation characteristics, except that, in persistent hyperglycemia, it is stabilized to proteolysis by high intracellular glucose concentration, increasing HK activity and initiating glycolytic overload and unscheduled glycolysis. This drives the development of vascular complications of diabetes. Similar HK2-linked unscheduled glycolysis in skeletal muscle and adipose tissue in impaired fasting glucose drives the development of peripheral insulin resistance. Glucokinase (GCK or HK4)-linked glycolytic overload and unscheduled glycolysis occurs in persistent hyperglycemia in hepatocytes and beta-cells, contributing to hepatic insulin resistance and beta-cell glucotoxicity, leading to the development of type 2 diabetes. Downstream effector pathways of HK-linked unscheduled glycolysis are mitochondrial dysfunction and increased reactive oxygen species (ROS) formation; activation of hexosamine, protein kinase c, and dicarbonyl stress pathways; and increased Mlx/Mondo A signaling. Mitochondrial dysfunction and increased ROS was proposed as the initiator of metabolic dysfunction in hyperglycemia, but it is rather one of the multiple downstream effector pathways. Correction of HK2 dysregulation is proposed as a novel therapeutic target. Pharmacotherapy addressing it corrected insulin resistance in overweight and obese subjects in clinical trial. Overall, the damaging effects of hyperglycemia are a consequence of HK-gated increased flux of glucose metabolism without increased glycolytic enzyme activities to accommodate it.

Autism Spectrum Disorder (ASD) is a common neurodevelopmental disorder in children. It is currently diagnosed by behaviour-based assessments made by observation and interview. In 2018 we reported a discovery study of a blood biomarker diagnostic test for ASD based on a combination of four plasma protein glycation and oxidation adducts. The test had 88% accuracy in children 5–12 years old. Herein, we present an international multicenter clinical validation study (N = 478) with application of similar biomarkers to a wider age range of 1.5–12 years old children. Three hundred and eleven children with ASD (247 male, 64 female; age 5.2 ± 3.0 years) and 167 children with typical development (94 male, 73 female; 4.9 ± 2.4 years) were recruited for this study at Sidra Medicine and Hamad Medical Corporation hospitals, Qatar, and Hospital Regional Universitario de Málaga, Spain. For subjects 5–12 years old, the diagnostic algorithm with features, advanced glycation endproducts (AGEs)—N^ε-carboxymethyl-lysine (CML), N^ω-carboxymethylarginine (CMA) and 3-deoxyglucosone-derived hydroimidazolone (3DG-H), and oxidative damage marker, o,o’-dityrosine (DT), age and gender had accuracy 83% (CI 79 – 89%), sensitivity 94% (CI 90–98%), specificity 67% (CI 57–76%) and area-under-the-curve of receiver operating characteristic plot (AUROC) 0.87 (CI 0.84–0.90). Inclusion of additional plasma protein glycation and oxidation adducts increased the specificity to 74%. An algorithm with 12 plasma protein glycation and oxidation adduct features was optimum for children of 1.5–12 years old: accuracy 74% (CI 70–79%), sensitivity 75% (CI 63–87%), specificity 74% (CI 58–90%) and AUROC 0.79 (CI 0.74–0.84). We conclude that ASD diagnosis may be supported using an algorithm with features of plasma protein CML, CMA, 3DG-H and DT in 5–12 years-old children, and an algorithm with additional features applicable for ASD screening in younger children. ASD severity, as assessed by ADOS-2 score, correlated positively with plasma protein glycation adducts derived from methylglyoxal, hydroimidazolone MG-H1 and N^ε(1-carboxyethyl)lysine (CEL). The successful validation herein may indicate that the algorithm modifiable features are mechanistic risk markers linking ASD to increased lipid peroxidation, neuronal plasticity and proteotoxic stress.

Accumulation of advanced glycation endproducts (AGEs) is linked to decline in renal function, particularly in patients with diabetes. Major forms of AGEs in serum are protein-bound AGEs and AGE free adducts. In this study, we assessed levels of AGEs in subjects with and without diabetes, with normal renal function and stages 2 to 4 chronic kidney disease (CKD), to identify which AGE has the greatest progressive change with decline in renal function and change in diabetes. We performed a cross-sectional study of patients with stages 2–4 CKD, with and without diabetes, and healthy controls (n = 135). Nine protein-bound and free adduct AGEs were quantified in serum. Most protein-bound AGEs increased moderately through stages 2–4 CKD whereas AGE free adducts increased markedly. Methylglyoxal-derived hydroimidazolone MG-H1 free adduct was the AGE most responsive to CKD status, increasing 8-fold and 30-fold in stage 4 CKD in patients without and with diabetes, respectively. MG-H1 Glomerular filtration flux was increased 5-fold in diabetes, likely reflecting increased methylglyoxal glycation status. We conclude that serum MG-H1 free adduct concentration was strongly related to stage of CKD and increased in diabetes status. Serum MG-H1 free adduct is a candidate AGE risk marker of non-diabetic and diabetic CKD.

On 20–24 September 2021, leading researchers in the field of glycation met online at the 14th International Symposium on the Maillard Reaction (IMARS-14), hosted by the authors of this introductory editorial, who are from Doha, Qatar

The study of the glyoxalase system by Thornalley and co-workers in clinical diabetes mellitus and correlation with diabetic complications revealed increased exposure of patients with diabetes to the reactive, dicarbonyl metabolite methylglyoxal (MG). Twenty-eight years later, extended and built on by Thornalley and co-workers and others, the glyoxalase system is an important pathway contributing to the development of insulin resistance and vascular complications of diabetes. Other related advances have been: characterization of a new kind of metabolic stress—‘dicarbonyl stress’; identification of the major physiological advanced glycation endproduct (AGE), MG-H1; physiological substrates of the unfolded protein response (UPR); new therapeutic agents—‘glyoxalase 1 (Glo1) inducers’; and a refined mechanism underlying the link of dysglycemia to the development of insulin resistance and vascular complications of diabetes.