Glycation Of Low-density Lipoprotein Research Articles

Glycated LDL generates reactive species that damage cell components, oxidize hemoglobin and alter surface morphology in human erythrocytes

Low-density lipoprotein (LDL) transports cholesterol to various tissues via the blood. Glycation of LDL occurs during hyperglycemic condition which is characterised by persistently high blood glucose level. Circulating erythrocytes can come in direct contact with glycated LDL (G-LDL). The objective of this study was to investigate the effect of G-LDL on human erythrocytes, specifically on hemoglobin, intracellular generation of reactive species and the antioxidant defence system. Isolated erythrocytes were incubated with G-LDL (3 and 6 mg/ml) and native LDL (6 mg/ml) at 37 °C for 24 h. Native LDL and G-LDL untreated erythrocytes were similarly incubated at 37 °C and served as control. G-LDL treatment increased hemolysis compared to control and native LDL-treated erythrocytes. Incubation of erythrocytes with G-LDL led to an increase in protein oxidation and lipid peroxidation while greatly decreasing the total sulfhydryl content. It also significantly enhanced hemoglobin oxidation, heme degradation, and the release of free iron moiety. Treatment with G-LDL led to an appreciable increase in the production of reactive oxygen and nitrogen species. The antioxidant power and activities of major antioxidant enzymes were drastically reduced, while critical membrane-bound enzymes were inhibited. The surface morphology of G-LDL-treated erythrocytes was altered leading to the formation of echinocytes. Importantly, treatment of erythrocytes with native LDL did not significantly affect the above-mentioned parameters and values were similar to the corresponding controls. Thus, G-LDL is cytotoxic to human erythrocytes and causes oxidative damage to cell components. This can reduce the oxygen-transporting ability of blood and also result in red cell senescence and anemia.

Identification of Glycoxidative Lesion in Isolated Low-Density Lipoproteins from Diabetes Mellitus Subjects.

Methylglyoxal (MG) is a precursor for advanced glycation end-products (AGEs), which have a significant role in diabetes. The present study is designed to probe the immunological response of native and glycated low-density lipoprotein (LDL) in experimental animals. The second part of this study is to probe glycoxidative lesion detection in low-density lipoproteins (LDL) in diabetes subjects with varying disease duration. The neo-epitopes attributed to glycation-induced glycoxidative lesion of LDL in DM patients' plasma were, analyzed by binding of native and MG-modified LDL immunized animal sera antibodies using an immunochemical assay. The plasma purified human LDL glycation with MG, which instigated modification in LDL. Further, the NewZealand-White rabbits were infused with unmodified natural LDL (N-LDL) and MG-glycatedLDL to probe its immunogenicity. The glycoxidative lesion detection in LDL of DM with disease duration (D.D.) of 5-15 years and D.D. > 15 years was found to be significantly higher as compared to normal healthy subjects (NHS) LDL. The findings support the notion that prolonged duration of diabetes can cause structural alteration in LDL protein molecules, rendering them highly immunogenic in nature. The presence of LDL lesions specific to MG-associated glycoxidation would further help in assessing the progression of diabetes mellitus.

Glycation of LDL: AGEs, impact on lipoprotein function, and involvement in atherosclerosis.

Atherosclerosis is a complex disease, and there are many factors that influence its development and the course of the disease. A deep understanding of the pathological mechanisms underlying atherogenesis is needed to develop optimal therapeutic strategies and treatments. In this review, we have focused on low density lipoproteins. According to multiple studies, their atherogenic properties are associated with multiple modifications of lipid particles. One of these modifications is Glycation. We considered aspects related to the formation of modified particles, as well as the influence of modification on their functioning. We paid special attention to atherogenicity and the role of glycated low-density lipoprotein (LDL) in atherosclerosis.

Effect of crocin on glycated human low-density lipoprotein: A protective and mechanistic approach

Human low-density lipoprotein (LDL) is known to have a role in coronary artery diseases when it undergoes modification due to hyperglycaemic conditions. Plant products like crocin play an essential role in protecting against oxidative stress and in the production of advanced glycation end-products (A.G.E.s). In this study, the anti-glycating effect of crocin was analyzed using various biochemical, spectroscopic, and in silico approaches. Glycation-mediated oxidative stress was confirmed by nitroblue tetrazolium, carbonyl content, and lipid peroxidation assays, and it was efficiently protected by crocin in a concentration-dependent manner. A.N.S. fluorescence, thioflavin T (ThT) assay, and electron microscopy confirmed that the structural changes in LDL during glycation lead to the formation of fibrillar aggregates, which can be minimized by crocin treatment. Moreover, secondary structural perturbations in LDL were observed using circular dichroism (CD) and Fourier transform infrared spectroscopy (FTIR), where crocin was found to prevent the loss of secondary structure in glycated LDL. Spectroscopic studies like U.V. absorbance, fluorescence spectroscopy, CD, FTIR, and fluorescence resonance energy transfer (FRET) provided insights into the interaction mechanism between LDL and crocin. Molecular docking supports these results with a highly negative binding energy of −10.3 kcal/mol, suggesting the formation of a stable ldl-crocin complex. Our study indicates that crocin may be a potent protective agent against coronary artery diseases by limiting the glycation of LDL in people with such disorders.

Preventive Effect of Eucalyptol on the Formation of Aorta Lesions in the Diabetic-Atherosclerotic Rat.

Background:Glycation, inflammation, and oxidative stress are the cardinal motivators of diabetes vascular complications. Here, we studied the effect of eucalyptol (EUC) on the formation of atheromatous lesions, glycation, oxidative stress, and inflammatory markers as well as insulin resistance, lipid profile, and activity of glyoxalase-1 (GLO-I) in the atherosclerotic rat model.Methods:Diabetic-atherosclerosis induced in rats with a combination of streptozotocin and atherogenic diet. Two groups of rats, normal and diabetic-atherosclerotic, were treated intragastrically with EUC (200 mg/kg) once daily for 3 months. Fasting blood sugar (FBS), insulin, insulin resistance index, lipid profile, the activity of GLO-I, low-density lipoprotein (LDL) glycation and oxidation markers, inflammatory markers, creatinine in the serum, and proteinuria in the urine of all rats were determined.Results:EUC inhibited the formation of any atheromatous lesions in atherosclerotic rats. Further, EUC displayed the lowering effect on glycemia, insulin resistance, LDL glycation, and oxidation products, and tumor necrosis factor (TNF)-α as well as it exhibited the improving effect on lipid profile, the activity of GLO-I, and renal function in the diabetic rat (P < 0.001).Conclusions:EUC prevented the formation of the atheromatous lesions and improved renal function in the atherosclerotic rat model due to a reduction of glycation, oxidative stress, and inflammatory mediators.

Binding to heparin triggers deleterious structural and biochemical changes in human low-density lipoprotein, which are amplified in hyperglycemia

Low-density lipoprotein (LDL) binding to arterial proteoglycans initiates LDL retention and modification in the arterial wall, triggering atherosclerosis. The details of this binding, its effectors, and its ramifications are incompletely understood. We combined heparin affinity chromatography with biochemical, spectroscopic and electron microscopic techniques to show that brief binding to heparin initiates irreversible pro-atherogenic remodeling of human LDL. This involved decreased structural stability of LDL and increased susceptibility to hydrolysis, oxidation and fusion. Furthermore, phospholipid hydrolysis, mild oxidation and/or glycation of LDL in vitro increase the proteolytic susceptibility of apoB and its heparin binding affinity, perhaps by unmasking additional heparin-binding sites. For LDL from hyperglycemic type-2 diabetic patients, heparin binding was particularly destabilizing and caused apoB fragmentation and LDL fusion. However, for similar patients whose glycemic control was restored upon therapy, LDL-heparin binding affinity was rectified and LDL structural stability was partially restored. These results complement previous studies of LDL binding to arterial proteoglycans and suggest that such interactions may produce a particularly pro-atherogenic subclass of electronegative LDL. In summary, binding to heparin alters apoB conformation, perhaps by partially peeling it off the lipid, and triggers pro-atherogenic LDL modifications including hydrolysis, oxidation, and destabilization. Furthermore, phospholipid lipolysis, mild oxidation and glycation of LDL in vitro strengthen its binding to heparin, which helps explain stronger binding observed in hyperglycemic LDL. Combined effects of hyperglycemia and heparin binding are especially deleterious but are largely rectified upon diabetes therapy. These findings help establish a mechanistic link between diabetes and atherosclerosis.

Inhibitory effects of compounds isolated from roots of Cynanchum wilfordii on oxidation and glycation of human low-density lipoprotein (LDL)

Abstract Low-density lipoprotein (LDL) modification such as oxidation and glycation has been known to play a significant role in the initiation and progression of atherosclerosis. The inhibitors on LDL modification have been emerged as a new strategy to be a supplement for prevention of atherosclerosis. In an effort to discover inhibitors on LDL modification from natural products, phytochemical investigation on Cynanchum wilfordii roots were performed, leading to isolation of acetophenones (1–6) including a new one (1) and nine pregnane-type steroids (7–15). The structure of the compound 1 was determined by analysis of 1D and 2D NMR spectral data analysis. All the isolated compounds were evaluated for their inhibitory activities against LDL modification. Among them, compounds 2 and 5 strongly inhibited LDL oxidation and glycation. These results suggest that compounds 2 and 5 from C. wilfordii may provide potential protective effects against atherosclerosis via inhibition of LDL oxidation and glycation.

Increased retention of LDL from type 1 diabetic patients in atherosclerosis-prone areas of the murine arterial wall

Background and aimsType 1 diabetes accelerates the development of atherosclerotic cardiovascular diseases. Retention of low-density lipoprotein (LDL) in the arterial wall is a causal step in atherogenesis, but it is unknown whether diabetes alters the propensity of LDL for retention. The present study investigated whether LDL from type 1 diabetic and healthy non-diabetic subjects differed in their ability to bind to the arterial wall in a type 1 diabetic mouse model. MethodsFluorescently-labeled LDL obtained from type 1 diabetic patients or healthy controls was injected into mice with type 1 diabetes. The amount of retained LDL in the atherosclerosis-prone inner curvature of the aortic arch was quantified by fluorescence microscopy. Healthy control LDL was in vitro glycated, analyzed for protein glycation by LC-MS/MS, and tested for retention propensity. ResultsRetention of LDL from type 1 diabetic patients was 4.35-fold higher compared to LDL from nondiabetic subjects. Nuclear magnetic resonance (NMR) spectroscopy analysis of LDL revealed no differences in the concentration of the atherogenic small dense LDL between type 1 diabetic and non-diabetic subjects. In vitro glycation of LDL from a non-diabetic subject increased retention compared to non-glycated LDL. LC-MS/MS revealed four new glycated spots in the protein sequence of ApoB of in vitro glycated LDL. ConclusionsLDL from type 1 diabetic patients showed increased retention at atherosclerosis-prone sites in the arterial wall of diabetic mice. Glycation of LDL is one modification that may increase retention, but other, yet unknown, mechanisms are also likely to contribute.

Immunochemical studies on native and glycated LDL – An approach to uncover the structural perturbations

Glycation initiates with the non-enzymatic reaction of amino group of proteins and lipoproteins by carbonyl group of sugar moiety and intermediates of glycative stress such as methylglyoxal (MG). The initial glycation leads to the formation of early glycation products (Amadori products) which undergo rearrangement, cyclization and dehydration to form advanced glycation end products (AGEs). The main objective of the present study is to investigate the non-enzymatic glycation of low density lipoprotein (LDL) by MG at different concentration and at increasing incubation time period in vitro. This modification may increase the formation of Amadori products and AGEs which are physico-chemically characterized with respect to the extent of LDL modification. Additionally, immunogenicity of native and MG modified LDL (MG-LDL) was probed in female rabbits in vivo. Immunogenicity of MG-LDL was found to be highly immunogenic, eliciting high titer immunogen-specific antibodies while native form of LDL is less immunogenic. Furthermore, the histopathology and immune-fluorescence studies suggest that the kidney section of immunized rabbits exhibit the presence of immune complex (MG-LDL-IgG) deposition in the glomerular basement membrane (GBM).

Chlorogenic acid inhibits non-enzymatic glycation and oxidation of low density lipoprotein

: To investigate the effect of chlorogenic acid (CGA) on non-enzymatic glycation and oxidation of low density lipoprotein (LDL). : The non-enzymatic glycation incubation system of LDL-glucose was established. The contents of early glycation products (Amodori product) and intermediate products (dicarbonyl compound) were determined by ultraviolet-visible spectrophotometry, and the content of advanced glycation end products (AGEs) was determined by fluorescence spectrophotometry. The LDL oxidation incubation system was established. The contents of thiobarbituric acid reactive substances(TBARS) and conjugated diene were determined by ultraviolet-visible spectrophotometry. The tryptophan fluorescence quenching, and the content of lipofuscin, total fluorescence products, active aldehydes and malondialdehyde were determined by fluorescence spectrophotometry, and further verified by three-dimensional fluorescence spectroscopy. : In the LDL glycation experiment, 150 μg/mL and 300 μg/mL CGA inhibited the formation of Amadori product, dicarbonyl compounds and AGEs. In the LDL oxidation experiment, 15 μg/mL and 25 μg/mL CGA inhibited the formation of TBARS effectively; 5 μg/mL and 10 μg/mL CGA inhibited tryptophan fluorescence quenching, and the formation of active aldehydes, malondialdehyde, total fluorescence products, lipofuscin and conjugated diolefine. And the three-dimensional fluorescence spectroscopy showed the same results. : CGA can inhibit non-enzymatic glycation and oxidation of LDL.

Effect of carnosine supplementation on the plasma lipidome in overweight and obese adults: a pilot randomised controlled trial

Carnosine has been shown to reduce oxidation and glycation of low density lipoprotein hence improving dyslipidaemia in rodents. The effect of carnosine on human plasma lipidome has thus far not been investigated. We aimed to determine whether carnosine supplementation improves the plasma lipidome in overweight and obese individuals. Lipid analysis was performed by liquid chromatography mass spectrometry in 24 overweight and obese adults: 13 were randomly assigned to 2 g carnosine daily and 11 to placebo, and treated for 12 weeks. Carnosine supplementation maintained trihexosylceramide (0.01 ± 0.19 vs −0.28 ± 0.34 nmol/ml, p = 0.04), phosphatidylcholine (77 ± 167 vs −81 ± 196 nmol/ml, p = 0.01) and free cholesterol (20 ± 80 vs −69 ± 80 nmol/ml, p = 0.006) levels compared to placebo. Trihexosylceramide was inversely related with fasting insulin (r = −0.6, p = 0.002), insulin resistance (r = −0.6, p = 0.003), insulin secretion (r = −0.4, p = 0.05) and serum carnosinase 1 activity (r = −0.3, p = 0.05). Both phosphatidylcholine and free cholesterol did not correlate with any cardiometabolic parameters. Our data suggest that carnosine may have beneficial effects on the plasma lipidome. Future larger clinical trials are needed to confirm this.

Syzygium cumini leaf extract inhibits LDL oxidation, but does not protect the liproprotein from glycation

Etnopharmacological relevanceSyzygium cumini (L.) Skeels is a plant widely used in folk medicine to treat diabetes mellitus (DM). The tea from its leaves is frequently used by diabetics for lowering hyperglycemia. There is a close relationship between DM and atherosclerosis, a chronic immuno-inflammatory disease, were the early stages encompass oxidative and glycative modifications in the structure of low density lipoprotein (LDL). Aim of this studyTo investigate the potential protective effects of aqueous-leaf extract from Syzygium cumini (S.cExt) against CuSO4-induced oxidation and methylglyoxal (MG)-induced glycation of human LDL in vitro. Materials and methodsLDL oxidative changes were evaluated by measuring conjugated dienes (CD) formation, thiobarbituric acid reactive substances (TBARS) levels, quenching of tryptophan (Trp) fluorescence and structural modifications in LDL particle. In LDL glycated by MG (glyLDL), we determined the levels of fluorescent advanced glycation end products (AGEs) and mobility by agarose gel electrophoresis. ResultsS.cExt blocked oxidative events induced by CuSO4 in human LDL, plasma and serum. Fourier transform infrared spectroscopy (FT-IR) revealed that specific regions of apoB100 were oxidized by CuSO4 in human LDL and that S.cExt reduced these oxidations. Unlike, the increased AGEs levels and eletrophoretic mobility observed in LDL MG-glycated were not modified by S.cExt. ConclusionThe findings herein indicate that S.cExt could be tested in atherogenesis models as potential protective agent against LDL oxidation.

Abstract 591: Increased Retention of LDL From Type 1 Diabetic Patients in an Atherosclerosis-prone Area of the Murine Arterial Wall

Background: Individuals with type 1 diabetes mellitus (T1DM) are at high risk of developing atherosclerotic cardiovascular disease but the exact mechanisms by which T1DM accelerates atherosclerosis remain unknown. In the present study, we investigated whether modifications of low density lipoprotein (LDL) in T1DM patients causes an increased retention of LDL in the vessel wall. Methods and Results: Fluorescently-labeled human LDL from either T1DM patients (n=10) or healthy non-diabetic subjects (control) (n=7) was injected into mice with T1DM. After 24 hours, when LDL was completely cleared from the circulation, cryosections of the inner curvature of the aortic arch (i.e. atherosclerosis prone area) was analyzed for retained LDL by fluorescence microscopy (Red in figure A). We found significantly more retained T1DM LDL (n=10) compared to LDL from non-diabetic subjects (n=7) with a fold change of 4.35 (p &lt; 0.05). Nuclear magnetic resonance (NMR) spectroscopy analysis of LDL revealed no differences in the level of the atherogenic small dense LDL between T1DM LDL (274.4±47.8 nmol/L) and non-diabetic LDL (263.8±55.3 nmol/L). Using LiCor Odyssey infrared imaging scanning of the whole aorta en face, we found that in vitro glycation of LDL from a non-diabetic subject significantly increased retention (n=8) compared to LDL prepared similarly but without glucose (n=8), with a fold change of 8.87 (p &lt; 0.001) (Figure B). Conclusion: LDL from patients with T1DM as well as ex vivo glycated LDL showed increased retention at atherosclerosis-prone sites in the arterial wall of mice. This may contribute to the accelerated development of atherosclerosis in T1DM.

English

The modified low-density lipoprotein (LDL; glycated and oxidized) is more atherogenic and are poorly recognized by LDL receptor. In the present study, an attempt has been made to evaluate the effects of Triphala on LDL modification in experimentally treated rats and in human LDL. The effect of ethanolic extract of Triphala on LDL oxidation susceptibility in high fat diet fed and STZ induced rats was evaluated. The inhibitory effect of Triphala on LDL oxidation and glycation was investigated using copper and glucose induced human LDL, respectively in vitro. The co-presence of Triphala extract significantly increased lag phase and minimized the conjugated dienes formation in dose dependent manner. Copper mediated LDL oxidation was characterized by elevated indices of thiobarbituric acid reactive substance (TBARS), whereas co-presence of Triphala extract significantly minimized the production of TBARS. The results of this investigation shows that Triphala probably with their antioxidant properties inhibited LDL glycation and oxidation and provide scientific reasons regarding the possible medical benefits of using Triphala to prevent diabetic and cardiovascular complications. &nbsp; Key words: Triphala, low-density lipoprotein (LDL) oxidation, LDL glycation, high fat diet, streptozotocin (STZ).

Studies on glycation of human low density lipoprotein: A functional insight into physico-chemical analysis

Glycation of biomolecules leads to the establishment of advanced glycation end products (AGEs), which have significant role in the pathophysiology of diabetes leading to disorders, such as atherosclerosis. Ribose appears to be the most reactive among the naturally occurring sugars and contribute significantly to the glycation reactions in vivo, however, no report has been published to discuss d-ribose induced glycation of low density lipoprotein (LDL). The present study initially focuses on the glycation of commercially available LDL using different concentrations of d-ribose for varied incubation time intervals. The structural perturbations induced in LDL were analyzed by UV–vis, fluorescence & circular dichroism spectroscopy, and thermal denaturation studies. The ketoamine moieties, carbonyl content and HMF content were also quantitated in native and glycated LDL. We report structural perturbations, increased carbonyl content, ketoamine moieties and HMF content in d-ribose induced glycated LDL (LDL-AGEs) as compared to native analogue. These results provide evidence that LDL-AGEs could interfere in normal physiological functions and might contribute in the initiation of diabetes induced atherosclerosis and other secondary cardiovascular problems in diabetic patients. Though ours is a preliminary study, we are sure it would open the topic for further studies.

High-density lipoprotein impedes glycation of low-density lipoprotein

Glycation of low-density lipoprotein (LDL) increases its atherogenicity, but whether high-density lipoprotein (HDL) can protect LDL against glycation is not known. LDL and HDL were isolated from 32 volunteers with serum HDL cholesterol concentrations ranging from 0.76 to 2.01 (mean = 1.36) mmol/L. Glycation of LDL was induced by incubation with 0-80 mmol/L glucose for 7 days at 37°C under nitrogen in the presence of and absence of human HDL. Glycation of LDL apolipoprotein B (apoB) doubled at glucose 50 and 80 mmol/L (both p < 0.001), and this increase was ameliorated by HDL. In the absence of glucose, 0.11 (0.01) [mean (standard error, SE)] mg apoB/mg LDL protein was glycated increasing to 0.22 (0.02) mg/mg at glucose 80 mmol/L in the absence of HDL, but remaining at 0.13 (0.01) mg/mg when autologous HDL was present. Heterologous HDL from a further study of 12 healthy participants was similarly effective in impeding LDL apoB glycation. HDL impeded not only glycation but also the lipid peroxidation, free amino group consumption and increased electrophoretic mobility of LDL which accompanied glycation. HDL from participants with higher serum paraoxonase1 (PON1) was more effective in impeding glycation and the related processes. In conclusion, HDL can impede the glucose-induced glycoxidation of LDL. PON1 may be important for this function of HDL.

Levels of MDA-LDL in Circulating Immune Complexes Predict Myocardial Infarction in the Veterans Affairs Diabetes Trial (VADT) Cohort

Synopsis: In previous studies, authors have demonstrated a relationship between modified low-density lipoprotein (LDL) and cardiovascular disease (CVD); however, few have examined the relationship between the content of modified LDL in circulating immune complexes (ICs) and CVD, even though the majority of modified LDL in plasma circulates as part of immune complexes. Purpose: To determine whether high levels of oxidized LDL (oxLDL), malondialdehyde-LDL (MDA-LDL), and advanced glycation end products-LDL (AGE-LDL) in circulating IC are associated with incident cardiovascular events in the VADT cohort of type 2 diabetes (T2DM). Methods: We performed prospective analyses to determine associations between modified LDL-IC and vascular end points among 907 VADT subjects (mean age 59.8 years; 96.8% male; 40.9% minority). Modified LDL-IC were measured a median of 2 years after entry into the VADT study, and participants were subsequently followed an average of 3.7 years for outcomes. Cox proportional hazard models were used to calculate hazard ratios (HRs) for macrovascular end points in relation to modified LDL-IC quartile. The primary composite end point included documented myocardial infarction (MI); stroke; death from cardiovascular causes; new or worsening congestive heart failure; surgical intervention for cardiac, cerebrovascular, or peripheral vascular disease; inoperable coronary artery disease; and amputation for ischemic gangrene. Results: During follow-up, 16.8%, 4.7% and 6.4% of participants had a primary composite end point, MI or death, respectively. After wed adjusted for age, minority status, treatment arm, whether an individual had an event before the VADT, as well as systolic blood pressure (SBP) level, LDL-C level and statin use at the time of IC measurement, individuals in the highest quartile of MDALDL IC as compared with individuals in the lowest quartile of MDA-LDL IC were at greater risk of MI (hazard ratio [HR] 2.44; 95% confidence interval [95% CI] 1.0325.77) and the composite end point (HR 1.71; 95% CI 1.0422.80) but similar risk of all-cause mortality (HR 1.15; 95% CI 0.5222.52). In contrast, oxLDL-IC and AGE-LDL-IC were not associated with cardiovascular events. Moreover, subsequent analysis found that individuals with high MDA-LDL IC and low oxLDL-LDL IC were at particularly high risk of MI relative to individuals with low MDA-LDL IC and low oxLDL-IC (HR 3.46; 95% CI 1.5227.87). Results were similar when AGELDL IC was substituted for oxLDL-IC (HR 2.56; 95% CI 1.0626.20). Conclusions: Our study indicates that high levels of MDALDL in isolated IC predict future MI and cardiovascular events in patients with T2DM and supports distinct roles of different modified forms of LDL in the occurrence of macrovascular events.

High levels of oxidized LDL in circulating immune complexes are associated with increased odds of developing abnormal albuminuria in Type 1 diabetes

Modified low-density lipoprotein (LDL) immune complexes (IC) have proinflammatory properties and play a role in albuminuria development. We measured oxidized LDL (oxLDL) and advanced glycation end-product (AGE)-LDL in IC isolated from sera of Type 1 diabetic subjects followed for 14-20 years and studied their association with abnormal albuminuria. Patients with albumin excretion rates (AER)<40 mg/24 h at baseline and follow-up (n=302) were deemed resistant to developing abnormal albuminuria. Patients with AER<40 mg/24 h at baseline whose AER levels progressed to >40 mg/24 h were considered prone to abnormal albuminuria (n=185), those who progress to AER>299 mg/24 h were considered as having macroalbuminuria (n=57). The odds of developing abnormal albuminuria were estimated by logistic regression based on natural log-transformed levels of oxLDL and AGE-LDL in IC and stratified by baseline AER decile. OxLDL and AGE-LDL were significantly higher in IC isolated from patients progressing to abnormal albuminuria. In unadjusted conditional logistic analysis, an increase of 1 SD in oxLDL and AGE-LDL levels in IC significantly increased the odds ratio (OR) for development of macroalbuminuria, respectively, by a factor of 2.5 and 1.8 (P<0.001, P=0.008). The increased odds of developing macroalbuminuria remained significant when adjusted for treatment group, diabetes duration, retinopathy, baseline hemoglobin A1c and LDL (OR=2.5 and 1.8, respectively, P<0.01). Higher levels of oxLDL and AGE-LDL in circulating IC were associated with increased odds to develop abnormal albuminuria.

Epigallocatechin gallate (EGCG) binds to low-density lipoproteins (LDL) and protects them from oxidation and glycation under high-glucose conditions mimicking diabetes

Abstract The aim of this study was to determine whether low-density lipoprotein (LDL)-bound epigallocatechin gallate (EGCG) attenuates LDL oxidation and glycation under high-glucose (HG) conditions mimicking diabetes. Pooled plasma was preincubated with EGCG for three hours, followed by sequential ultracentrifugation and extensive dialysis to isolate LDL. The kinetics of α-tocopherol and EGCG consumption in LDL were measured by a solid-phase extraction system with HPLC-diode array detection (HPLC-DAD) upon oxidation. EGCG enrichment effectively increased the resistance of LDL to oxidation caused by HG/Cu 2+ . A dose-dependent inhibition of HG-mediated long-term glycation of LDL was also observed by LDL-bound EGCG. Data from HPLC-DAD demonstrated that EGCG was able to bind lipoproteins and to facilitate the antioxidant and antiglycation properties of LDL. This study suggests that loading plasma with EGCG is an efficient way to increase the content of this phytochemical in LDL, which may imply favourable in vivo activity of EGCG in diabetes.

The polyphenolics in the aqueous extract of Psidium guajava kinetically reveal an inhibition model on LDL glycation

Guava [Psidium guajava L. (Myrtaceae)] budding leaf extract (PE) has shown tremendous bioactivities. Previously, we found seven major compounds in PE, i.e., gallic acid, catechin, epicatechin, rutin, quercetin, naringenin, and kaempferol. PE showed a potentially active antiglycative effect in an LDL (low density lipoprotein) mimic biomodel, which can be attributed to its large content of polyphenolics. The glycation and antiglycative reactions showed characteristic distinct four-phase kinetic patterns. In the presence of PE, the kinetic coefficients were 0.000438, 0.000060, 0.000, and −0.0001354 ABS-mL/mg-min, respectively, for phases 1 to 4. Computer simulation evidenced the dose-dependent inhibition model. Conclusively, PE contains a large amount of polyphenolics, whose antiglycative bioactivity fits the inhibition model.