Carboxymethyllysine Concentration Research Articles

Plasma levels of advanced glycation end products in children with renal disease.

In adults, advanced glycation end products (AGEs) rise slowly in tissues and circulation during aging, and accumulate at an accelerated rate both in diabetes and chronic renal insufficiency (CRI). We aimed to investigate the pattern of AGE accumulation in children/adolescents with CRI and on renal replacement therapy by dialysis and transplantation. Concentrations of fluorescent AGEs, carboxymethyllysine (CML) and lipofuscin-like substance (LFLS, a marker of lipid peroxidation) were followed. Data were obtained from 11 CRI patients on conservative treatment (age 12.6+/-1.7 years, serum creatinine: 205.7+/-17.5 micromol/l), ten patients on renal replacement therapy with dialysis (13.6+/-1.7 years, 698.2+/-48.9 micromol/l) and nine patients after kidney transplantation (15.9+/-1.1 years, 115.9+/-12.0 micromol/l) and comparison made with the data from 28 healthy controls (11.8+/-8.2 years, 44.1+/-8.2 micromol/l). In controls, an age-dependent rise of fluorescent AGE and CML levels was observed. In the CRI group, fluorescent AGEs [0.38+/-0.03x105 arbitrary units (AU)] and CML (369+/-26 ng/ml) concentrations were doubled compared with controls (0.16+/-0.03x105 AU and 189+/-42 ng/ml, respectively) and even higher levels were revealed in dialyzed patients (0.80+/-0.05x105 AU; 650+/-94 ng/ml). Successful kidney transplantation significantly reduced but did not normalize fluorescent AGE levels (0.39+/-0.03 x105 AU), while the decline in CML levels (550+/-47 ng/ml) was insignificant. Plasma LFLS was elevated in CRI (19.6+/- 1.7 AU) and was even higher in dialyzed children (32.0+/-5.3 AU) compared with healthy controls (7.1+/- 1.4 AU). Kidney transplantation did not normalize LFLS levels (20.3+/-5.3 AU), pointing to persistently enhanced lipid peroxidation. Our study provides the first data on enhanced fluorescent AGEs and CML levels in children/adolescents with CRI and on dialysis. Successful renal transplantation decreased but did not normalize AGE levels, probably because of still-impaired renal function with enhanced oxidative stress, as well as the influence of immunosuppressive therapy.

Fortification of milk with iron-ascorbate promotes lysine glycation and tryptophan oxidation

Abstract Infant formulas are supplemented with iron and ascorbate for nutritional purposes, but activation of the advanced Maillard reaction by iron and production of hydroxyl radicals by the iron-ascorbate system may damage the proteins with possible nutritional loss. In this study, we evaluate the deleterious actions of iron and ascorbate, namely lysine damage and tryptophan oxidation on whey-lactose samples incubated at 60 °C. Iron-catalysed ascorbate oxidation enhanced lysine blockage mainly by ascorbylation, whereas lactosylation was little influenced. A three-fold increase in the accumulation rate of fluorescent advanced Maillard products (AMP) was observed in the presence of iron/ascorbate and AMP fluorescence was well correlated to carboxymethyllysine concentration in the samples. The tryptophan degradation rate was 2.5-fold higher in the presence of iron-ascorbate and the loss of this amino-acid was exponentially correlated with AMP fluorescence, similarly whatever iron-ascorbate was present or not. Application of milder heat treatments to infant formulas would allow to decrease the extent of these undesirable reactions.

Increased levels of vascular endothelial growth factor and advanced glycation end products in aqueous humor of patients with diabetic retinopathy.

Clinical studies have shown a relationship between diabetic retinopathy and vascular endothelial growth factor (VEGF) levels in ocular fluid. Advanced glycation end products (AGEs) have been implicated in diabetes complications, including diabetic retinopathy. Nepsilon-(carboxymethyl) lysine (CML) is a glycoxidation product that may be a marker of oxidative stress. In this study, we used enzyme-linked immunosorbent assays to determine the levels of VEGF, non-CML AGE and CML in the aqueous humor and serum of 82 Japanese patients with type 2 diabetes and 60 non-diabetic subjects. VEGF, non-CML AGE, and CML concentrations in aqueous humor and serum were then compared with the severity of diabetic retinopathy. Immunohistochemical detection analysis of non-CML AGE and CML was also performed using retinal tissues from patients with progressive diabetic retinopathy. Aqueous levels of VEGF, non-CML AGE and CML increased along with the progression of diabetic retinopathy compared to age-matched controls. After coagulation therapy, the VEGF, non-CML AGE, and CML levels were significantly reduced. Immunostaining showed diffuse co-localization of non-CML AGE and CML around microvessels and in the glial cells of proliferative membranes from patients with progressive diabetic retinopathy. These findings suggest that glycation and glycoxidation reactions (or oxidation, as revealed by CML) may contribute to both the onset and progression of diabetic retinopathy.

Circulating advanced glycation end product levels in rats rapidly increase with acute renal failure

Advanced glycation end products (AGEs) are formed on proteins and peptides slowly during aging, and they accumulate in circulation and tissues in diabetes and chronic renal failure. Except for nonenzymatic glycation, enhanced oxidative/carbonyl stress is supposed to participate in their formation. The kidney plays a key role in disposal of AGEs, particularly AGE-peptides. We assumed that even a short time combination of enhanced oxidative/carbonyl stress and a lack of renal function should result in elevation of circulating AGE levels. To verify this hypothesis, two models of acute renal failure in rats, bilateral nephrectomy and bilateral ureteral ligation, were employed, and the data were compared with those of sham-operated animals. AGE levels determined fluorimetrically or as carboxymethyllysine concentration rose by a factor of three within 48 hours. Enhanced levels of malondialdehyde and lipofuscin pointed to an enhanced oxidative/carbonyl stress. Activity of antioxidant enzymes such as superoxide dismutase and glutathione peroxidase were not compromised, or were even elevated, respectively. Total antioxidant status increased, probably as a consequence of an accumulation of indols and benzoic acid derivatives, uremic toxins with scavenging capacities, as shown for hippurate. Evidence was given that circulating AGEs in the model of acute renal failure in rats undergo a substantial rise within a short time period. A source of increased AGEs is not clear, since except for the lack of the kidney function, accelerated synthesis of AGEs under enhanced oxidative/carbonyl stress as well as liberation of AGEs from tissues due to protein catabolism might be anticipated. If AGEs accumulate in acute renal failure in humans, their contribution to acute toxicity, or of the development of the complications later, might be of importance.

Caloric Restriction Decreases Age-Dependent Accumulation of the Glycoxidation Products, Nisin-(Carboxymethyl)lysine and Pentosidine, in Rat Skin Collagen

Nonenzymatic glycation of body proteins and subsequent advanced glycation reactions have been implicated in the aging process, while caloric restriction (CR) in rodents results in an increase in both mean and maximum life span. We have evaluated the effect of chronic (25 months) CR on glycation of blood proteins and accumulation of advanced glycation and oxidation (glycoxidation) products, N epsilon-(carboxymethyl)lysine (CML), and pentosidine, in skin collagen. Brown-Norway rats, fed ad libitum (AL) from birth, were divided into two equal groups at 4 months of age and placed on AL or CR diets (CR = 60% of AL diet). Cohorts of animals were sacrificed at 7, 13, and 25 months after the initiation of CR. At necropsy glycated hemoglobin was measured by affinity HPLC and glycated plasma protein by the fructosamine assay; extracts of skin collagen were analyzed by gas chromatography-mass spectrometry for CML and by reversed-phase HPLC for pentosidine. Glycation of hemoglobin, plasma proteins, and skin collagen was decreased significantly (18-33%) by CR. Concentrations of CML and pentosidine increased significantly with age in skin collagen in both AL and CR animals; however, CR significantly reduced levels of CML (25%), pentosidine (50%), and fluorescence (15%) in collagen in the oldest rats. We conclude that CR reduces the extent of glycation of blood and tissue proteins and the age-related accumulation of glycoxidation products in skin collagen.

L-arginine reduces glomerular basement membrane collagen N epsilon-carboxymethyllysine in the diabetic db/db mouse.

The present study was carried out to examine the effect of L-arginine on advanced stage nonenzymatic glycosylation end products in glomerular basement membrane (GBM) as represented by carboxymethyllysine (CML). Twelve db/db mice were given a solution containing a daily dosage of L-arginine of 50 mg/kg body weight orally. Twelve db/db mice served as controls. At the end of the 4-months study period treated animals had significantly lower concentrations of CML (0.084 +/- 0.008, 0.071-0.098 nmol/mumol OH-proline; mean +/- SD, range, p less than 0.01) compared to untreated controls (0.11 +/- 0.018, 0.095-0.152 nmol/mumol OH-proline). In addition, there was a significant positive correlation between GBM thickness and concentrations of CML (r = 0.86, p less than 0.001). We conclude that reduction of CML concentrations in treated db/db mice possibly reflects a beneficial effect of L-arginine on advanced stage nonenzymatic glycosylation end-products in GBM. In addition, measuring CML concentrations might have future clinical implications as a noninvasive parameter for basement membrane thickening.

Effect of Diabetes and Aging on Carboxymethyllysine Levels in Human Urine

Carboxymethyllysine (CML) has been identified as a modified amino acid that accumulates with age in human lens proteins and collagen. CML may be formed by oxidation of fructoselysine (FL), the Amadori adduct formed on nonenzymatic glycosylation of lysine residues in protein, or by reaction of ascorbate with protein under autoxidizing conditions. We proposed that measurements of tissue and urinary CML may be useful as indices of oxidative stress or damage to proteins in vivo. To determine the extent to which oxidation of nonenzymatically glycosylated proteins contributes to urinary CML, we measured the urinary concentrations of FL and CML in diabetic (n = 26) and control (n = 28) patients. The urinary concentration of FL correlated strongly with HbA1 measurements and was significantly higher in diabetic compared with control samples (9.2 +/- 6.5 and 4.0 +/- 2.8 micrograms/mg creatinine, respectively; P less than 0.0001). There was also a strong correlation between the concentrations of CML and FL in both diabetic and control urine (r = 0.67, P less than 0.0001) but only a weakly significant increase in the CML concentration in diabetic compared with control urine (1.2 +/- 0.5 and 1.0 +/- 0.3 micrograms/mg creatinine, respectively; P = 0.05). The molar ratio of CML to FL was significantly lower in diabetic compared with control patients (0.25 +/- 0.12 and 0.43 +/- 0.16, respectively; P less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)