Glycation of LDL and HDL by methylglyoxal and link to increased risk of atherosclerosis

Cardiovascular disease (CVD) is the major cause of premature death in diabetes and is mainly driven by increased arterial atherosclerosis. Increased risk of atherosclerosis is associated with high levels of LDL and more particularly with high levels of small, dense LDL (sdLDL). The risk of CVD is increased 2 – 3 fold in diabetes where typical increase of sdLDL is 2 – 3 fold. Plasma levels of sdLDL correlate with carotid intima-media thickness and are linked to risk of CVD. The processes associated with transformation of LDL to sdLDL are not fully understood. Increased atherogenicity of sdLDL may be linked, in part, to non-oxidative modifications of its major lipoprotein, apolipoprotein B100 (ApoB100) – such as modification by methylglyoxal.

Methylglyoxal is a potent dicarbonyl glycating agent increased 2 – 5 fold in patients with diabetes. Glycation of LDL by methylglyoxal is directed to arginine residues in ApoB100, forming mainly the hydroimidazolone MG-H1 – a major advanced glycation endproduct (AGE) in physiological systems. MG-H1 is a major AGE of LDL in healthy people and is increased up to 5 fold in LDL of patients with type 2 diabetes. Diabetic patients receiving treatment with metformin had decreased plasma methylglyoxal concentration and decreased MG-H1-modified LDL. We studied the effect on atherogenicity of human LDL modified by methylglyoxal to minimal physiological extent (MGmin-LDL).

MGmin-LDL had decreased particle size, increased binding to proteoglycans and increased aggregation in vitro. MGmin-LDL was bound by the LDL receptor but not by the scavenger receptor and had increased binding affinity for cell surface heparin sulfate-containing proteoglycan with increased partitioning onto the aortal wall. A computed structural model predicted that methylglyoxal modification of apolipoprotein B100 induces distortion, increasing exposure of the N-terminal proteoglycan binding domain on the surface of LDL – likely mediating particle re-modelling and increased proteoglycan binding. Methylglyoxal modification of LDL forms small, dense LDL with increased atherogenicity, providing a new route to atherogenic LDL – “super sticky” MGmin-LDL.

Summary scheme

Glycation of low density lipoprotein by methylglyoxal and link to risk of atherosclerosis a. Reaction of methylglyoxal with arginine residues to from hydroimidazolone MG-H1. b. and c. Structural basis of functional change in LDL by methylglyoxal modification. Molecular model of human ApoB100 residues 1 – 300. Schematic representation: red cylinders, α-helix, cyan arrows – β-sheets (arrows point to C-terminus), PG binding domain (residues 84 – 94) – green space-fill and R18 or MG-H1-18 – space-fill atom color-coded. Unmodified ApoB100 (b.) and methylglyoxal-modified ApoB100 (c.).

Principal publications

Rabbani, N., Chittari, M.V., Zehnder, D., Ceriello, A. and Thornalley, P.J. (2009) High dose metformin therapy reduces glycation and oxidative damage to apolipoprotein B100 and may decelerate atherosclerosis in patients with type 2 diabetes. Diabetologia 52, 1293.

Rabbani, N., Godfrey, L., Xue, M., Shaheen, F., Geoffrion, M., Milne, R. and Thornalley, P.J. (2011) Glycation of LDL by Methylglyoxal Increases Arterial Atherogenicity. A Possible Contributor to Increased Risk of Cardiovascular Disease in Diabetes. Diabetes 60, 1973-1980

Glycation of high density lipoprotein by methylglyoxal and link to increased risk of atherosclerosis

The risk of cardiovascular disease (CVD) increases with age, diabetes and renal failure. Residual high risk of CVD in the general population suggests development of CVD is linked to risk factors unaddressed by current therapy. CVD mediated by arterial atherosclerosis has decreased plasma high density lipoprotein cholesterol (HDL-C) as risk factor. The major lipoprotein component of plasma HDL, apolipoprotein A-1 (ApoA1), correlates strongly with HDL-C and is more closely associated with anti-atherogenic protection. Impaired anti-atherogenic function of HDL independent of HDL-C is an emerging concept in the etiology of CVD.

Large prospective studies suggest the risk of coronary heart disease is linked to ApoA1 and impaired glycemic control – with hyperglycemia-increased reactive metabolite, methylglyoxal, as a potential mediator of HDL dysfunction. Plasma concentrations of methylglyoxal are increased by short-term and persistent hyperglycemia. Protein modification by methylglyoxal is relatively rapid and increases in aging, with further marked increases in diabetes and renal failure. Glycation of proteins by methylglyoxal is directed toward arginine residues, forming mainly the hydroimidazolone MG-H1 – a quantitatively and functionally important advanced glycation endproduct (AGE) in physiological systems. We quantified the modification of HDL by methylglyoxal and related dicarbonyls in healthy people and patients with type 2 diabetes (T2DM), characterized structural, functional and physiological consequences of the modification and predicted the importance in high CVD risk groups. HDL is modified by methylglyoxal and related dicarbonyl metabolites accounted for 2.6% HDL and increased to 4.5% in patients with T2DM.  HDL2 and HDL3 were modified by methylglyoxal to similar extents in vitro. Methylglyoxal modification induced re-structuring of the HDL particles, decreasing stability and plasma half-life in vivo. It occurred at sites of apolipoprotein A-1 in HDL linked to membrane fusion, intramolecular bonding and ligand binding.  Kinetic modelling of methylglyoxal modification of HDL predicted a negative correlation of plasma HDL-C with methylglyoxal-modified HDL. This was validated clinically. It also predicted dicarbonyl modification produces 2 – 6% decrease in total plasma HDL and 5 – 13% decrease in functional HDL clinically. We conclude that methylglyoxal modification of HDL accelerates its degradation and impairs its functionality in vivo, likely contributing to increased risk of CVD – particularly in high CVD risk groups. In the Healthy aging through Functional Food (HATFF or Hats-off) study, plasma HDL levels correlated negatively to plasma protein MG-H1 and plasma D-lactate – a surrogate marker to flux of methylglyoxal formation, suggesting increased methylglyoxal exposure decreases HDL.

Summary scheme

Glycation of high density lipoprotein by methylglyoxal and link to risk of atherosclerosis A. Structural basis of functional change of methylglyoxal modified HDL. Molecular model of human ApoA1 residues 40 – 243. Schematic representation: trefoil structure of trimeric ApoA1 with color-coded peptide chains and hotspot methylglyoxal, glycation sites on each chain: R123 (cyan) in helix 5 and R149 (dark blue) in helix 6 either side of hinge at residue 133. B. and C. R27 and MG-H1-27, respectively, in the N-terminal domain 1 – 43.26 D. and E. R123 and MG-H1-123 in helix 5.  F. and G. R149 and MG-H1-149 in helix 6. H. One compartment modelling of the effect of dicarbonyl glycation on plasma HDL. Panels I.K. show relaxation from the steady-state of healthy subjects (time zero) to new steady-states of 2, 3 and 4-fold increased dicarbonyl concentration – I. decreasing concentration series of total HDL, J. increasing concentration series of dicarbonyl-modified HDL (DC-HDL), and K. decreasing concentration series of functional HDL.  L. Negative association of plasma HDL-C to MG-H1content of HDL.

Principal publications

Godfrey, L., Yamada-Fowler, N., Thornalley, P.J. and Rabbani, N. (2014) Arginine-directed glycation and decreased HDL plasma concentration and functionality. Nutrition and Diabetes 4, e134.

Rabbani, N., Xue, M., Weickert, M.O. and Thornalley, P.J. (2021) Reversal of insulin resistance in overweight and obese subjects by trans-resveratrol and hesperetin combination – link to dysglycemia, blood pressure, dyslipidemia and low-grade inflammation.  Nutrients 13, 237.