Association between plasma oxidized low-density lipoprotein and diabetic nephropathy

Febuxostat Protects Human Aortic Valve Endothelial Cells From Oxidized Low-density Lipoprotein-Induced Injury and Monocyte Attachment

ABSTRACT

Atherosclerosis (AS) is a common cardiovascular disease with high morbidity and mortality. The pathogenesis of AS is closely related to endothelial dysfunction, which is mainly induced by oxidative stress, inflammation, and enhanced adhesion of monocytes to endothelial cells on the vessel wall. Febuxostat is a novel antigout agent recently reported to exert protective effects on endothelial dysfunction. This study aims to investigate the protective capacity of febuxostat against oxidized low-density lipoprotein (ox-LDL)-induced injury and monocyte attachment to endothelial cells. Human aortic valve endothelial cells (HAVECs) were stimulated with ox-LDL in the presence or absence of febuxostat (5 and 10 μM) for 6 hours. Mitochondrial reactive oxygen species were measured using MitoSox red staining, and the level of protein carbonyl was detected using enzyme-linked immunosorbent assay (ELISA). The expressions of IL-6, TNF-α, tissue factor (TF), VCAM-1, and ICAM-1 were evaluated with qRT-PCR assay and ELISA. Calcein-AM staining was used to determine the attachment of U937 monocytes to HAVECs. quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR) and Western blot were used to measure the expression level of early growth response 1 (Egr-1) in HAVECs. First, the elevated expression of LOX-1, activated oxidative stress, excessive secreted inflammatory factors, and promoted expression of TF induced by stimulation with ox-LDL were significantly reversed by febuxostat, indicating a protective effect of febuxostat against endothelial dysfunction. Second, the upregulated VCAM-1 and ICAM-1, as well as the increased proportion of adhered monocytes to HAVECs induced by ox-LDL, were significantly alleviated by febuxostat. Finally, the promoted expression level of Egr-1 induced by ox-LDL was pronouncedly suppressed by febuxostat. We conclude that febuxostat protected HAVECs from ox-LDL-induced injury and monocyte attachment.

Oxidized LDL Is Associated with eGFR Decline in Proteinuric Diabetic Kidney Disease: A Cohort Study

Diabetic kidney disease (DKD) is a highly heterogenous disease, including the proteinuric and the nonproteinuric pattern. Oxidized low-density lipoprotein (ox-LDL) is progressively increased in DKD and causes direct damage to kidney tubular epithelial cells through a mechanism similar to that underlying the deleterious effect of lipid peroxides in the vascular endothelium. We aimed to examine the association between plasma ox-LDL cholesterol and clinical endpoints in DKD patients. Ninety-one patients with established proteinuric DKD and diabetic retinopathy were enrolled and prospectively followed for 10 years or the occurrence of death, or at least 30% decline in eGFR, or progression to end-stage kidney disease (ESKD) requiring renal replacement therapy (primary outcome). At the end of the study, both eGFR and proteinuria were reassessed. Secondary outcomes of the study were the percentage change in eGFR and proteinuria over time for each patient. At baseline, patients were divided into 2 groups according to the median ox-LDL value (i.e., below or equal and above 66.22 U/L). Both Kaplan-Meier curves (p = 0.001, log-rank test) and univariate Cox regression analysis showed that high ox-LDL was associated with the primary outcome (HR = 3.42, 95%CI = 1.55 − 7.56, p = 0.002). After adjustment for various well-known cofounders, multivariate Cox analysis showed that the association between increased circulating ox-LDL levels and the composite kidney endpoint remained significant (HR = 2.87, 95%CI = 1.14–7.20, p = 0.025). Regarding the secondary outcome of eGFR decline, the assessment of areas under the curves (AUC) showed that ox-LDL outperformed several cofounding factors (AUC 71%, 95%CI = 0.59 − 0.83, p = 0.001) and had better accuracy to predict deterioration of eGFR over time than baseline proteinuria (AUC 67%, 95%CI = 0.54 − 0.79, p = 0.014). Increased ox-LDL might be associated with disease progression in proteinuric DKD.

Oxidized LDL Modifies the Association between Proteinuria and Deterioration of Kidney Function in Proteinuric Diabetic Kidney Disease

Proteinuria is characterized by low accuracy for predicting onset and development of diabetic kidney disease (DKD) because it is not directly associated with molecular changes that promote DKD, but is a result of kidney damage. Oxidized low-density lipoprotein (ox-LDL) reflects oxidative stress and endothelial dysfunction, both underlying the development of proteinuria and loss of kidney function in DKD. We aimed to investigate whether ox-LDL modifies the association between proteinuria and progression of DKD in a cohort of 91 patients with proteinuric DKD and diabetic retinopathy, followed for 10 years. The primary endpoint was a combined kidney outcome of eGFR decline ≥30% or progression to end-stage kidney disease. After the end of the study, we considered the percentage change of eGFR over time as our secondary outcome. Proteinuria was associated with both outcomes, and ox-LDL amplified the magnitude of this link (p < 0.0001 for primary and p < 0.0001 for secondary outcome, respectively). After adjustment for duration of diabetes, history of cardiovascular disease and serum albumin, ox-LDL remained a significant effect modifier of the association between proteinuria and eGFR decline over time (p = 0.04). Our study shows that in proteinuric DKD, circulating ox-LDL levels amplified the magnitude of the association between proteinuria and progression of DKD.

The Association of dp-ucMGP with Cardiovascular Morbidity and Decreased Renal Function in Diabetic Chronic Kidney Disease

We aimed to investigate the possible association of the inactive, dephosphorylated, uncarboxylated matrix Gla protein (dp-ucMGP) with oxidized low-density lipoprotein (ox-LDL) and all-cause/cardiovascular (CV) mortality and renal function in diabetic chronic kidney disease (CKD). Ox-LDL and dp-ucMGP were determined in 66 diabetic CKD patients. All patients were prospectively followed for seven years, or until the occurrence of death, or a composite renal outcome of 30% estimated glomerular filtration rate (eGFR) reduction or progression to end-stage renal disease (ESRD) requiring dialysis occurred. Secondary outcomes were the occurrence of CV events. Kaplan-Meier curves showed that patients with plasma dp-ucMGP levels above the median (≥656 pM) had a significantly higher risk for all study endpoints. After adjustment for several well-known cofounders, multivariate Cox analysis showed that high plasma dp-ucMGP levels were associated with all-cause mortality (Hazard ratio-HR = 2.63, 95% Confidence Interval-CI = 1.17-5.94, p = 0.02), CV mortality (HR = 2.82, 95% CI = 1.07-7.49, p = 0.037) and progression of CKD (HR = 4.02, 95% CI = 1.20-13.46, p = 0.024). Circulating dp-ucMGP is associated with mortality and decreased renal function in diabetic CKD.

Malondialdehyde-modified LDL-related variables are associated with diabetic kidney disease in type 2 diabetes

BACKGROUND AND AIMS

Oxidized low-density lipoprotein (oxLDL) causes the development of atherosclerosis and kidney injury. Although circulating oxLDL levels were reportedly increased in type 2 diabetic patients with macroalbuminuria, it remains unclear whether albuminuria or the reduced glomerular filtration rate (GFR) is independently associated with the circulating oxLDL level. This study aimed to elucidate the association between the stage of diabetic nephropathy and serum malondialdehyde-modified LDL (MDA-LDL) and the ratio of MDA-LDL to LDL-cholesterol (MDA-LDL/LDL).

METHODS AND RESULTS

This retroactive cross-sectional study used data from 402 patients with type 2 diabetes. Patients undergoing hemodialysis were excluded. Serum MDA-LDL levels were significantly increased with increases in severity of albuminuria (103 ± 44 U/L, 109 ± 54 U/L, and 135 ± 72 U/L for normoalbuminuria, microalbuminuria, and macroalbuminuria, respectively; P for trend = 0.020) but not according to the estimated GFR (eGFR). An increased MDA-LDL/LDL ratio was significantly associated with both increased albuminuria (35 ± 13, 37 ± 14, and 40 ± 15 for normoalbuminuria, microalbuminuria, and macroalbuminuria, respectively; P for trend = 0.003) and reduced eGFR (34 ± 13, 36 ± 13, 38 ± 12, and 51 ± 28 for grade 1, 2, 3 and 4, respectively; P for trend = 0.002). Multiple linear regression analysis showed that neither the albumin excretion rate nor eGFR but ln-transformed triglycerides and LDL-C levels were independent determinants of both serum MDA-LDL levels and MDA-LDL/LDL ratios.

CONCLUSION

Serum MDA-LDL levels and MDA-LDL/LDL ratios were increased in those with dyslipidemia associated with diabetic kidney disease.

Diabetes adversely affects phospholipid profiles in human carotid artery endarterectomy plaques

Patients with diabetes are at higher risk of developing carotid artery stenosis and resultant stroke. Arachidonoyl phospholipids affect plaque inflammation and vulnerability, but whether diabetic patients have unique carotid artery phospholipidomic profiles is unknown. We performed a comprehensive paired analysis of phospholipids in extracranial carotid endarterectomy (CEA) plaques of matched diabetic and nondiabetic patients and analyzed mass spectrometry-derived profiles of three phospholipids, plasmenyl-phosphatidylethanolamine (pPE), phosphatidylserine (PS), and phosphatidylinositol (PI), in maximally (MAX) and minimally (MIN) diseased CEA segments. We also measured levels of arachidonic acid (AA), produced by pPE hydrolysis, and choline-ethanolamine phosphotransferase 1 (CEPT1), responsible for most pPE de novo biosynthesis. In paired analysis, MIN CEA segments had higher levels than MAX segments of pPE (P < 0.001), PS (P < 0.001), and PI (P < 0.03). MIN diabetic plaques contained higher levels than MAX diabetic plaques of arachidonoyl pPE38:4 and pPE38:5 and CEPT1 was upregulated in diabetic versus nondiabetic plaques. AA levels were relatively greater in MIN versus MAX segments of all CEA segments, and were higher in diabetic than nondiabetic plaques. Our findings suggest that arachidonoyl phospholipids are more likely to be abundant in the extracranial carotid artery plaque of diabetic rather than nondiabetic patients.

Low-density lipoprotein oxidation biomarkers in human health and disease and effects of bioactive compounds

Based on the significance of oxidized low-density lipoprotein (LDL) in health and disease, this review focuses on human studies addressing oxidation of LDL, including three lines of biomarkers, (i) ex vivo LDL resistance to oxidation, a "challenge test" model, (ii) circulating oxidized LDL, indicating the "current in vivo status", and (iii) autoantibodies against oxidized LDL as fingerprints of an immune response to oxidized LDL, along with circulating oxysterols and 4-hydroxynonenal as biomarkers of lipid peroxidation. Lipid peroxidation and oxidized LDL are hallmarks in the development of various metabolic, cardiovascular and other diseases. Changes further occur across life stages from infancy to older age as well as in athletes and smokers. Given their responsiveness to targeted nutritional interventions, markers of LDL oxidation have been employed in a rapidly growing number of human studies for more than 2 decades. There is growing interest in foods, which, besides providing energy and nutrients, exert beneficial effects on human health, such as protection of DNA, proteins and lipids from oxidative damage. Any health claim, however, needs to be substantiated by supportive evidence derived from human studies, using reliable biomarkers to demonstrate such beneficial effects. A large body of evidence has accumulated, demonstrating protection of LDL from oxidation by bioactive food compounds, including vitamins, other micronutrients and secondary plant ingredients, which will facilitate the selection of oxidation biomarkers for future human intervention studies and health claim support.

Serum Ceruloplasmin Level as a Predictor for the Progression of Diabetic Nephropathy in Korean Men with Type 2 Diabetes Mellitus

BACKGROUND

Oxidative stress is known to be associated with progression of diabetic kidney disease. Ceruloplasmin acts as a pro-oxidant under conditions of severe oxidative stress. Thus, we conducted a longitudinal observational study to evaluate whether the serum ceruloplasmin level is a predictive biomarker for progression of diabetic nephropathy.

METHODS

A total of 643 Korean men with type 2 diabetes mellitus were enrolled. Serum ceruloplasmin was measured using a nephelometric method. Progression of diabetic nephropathy was defined as transition in albuminuria class (i.e., normoalbuminuria to microalbuminuria, microalbuminuria to macroalbuminuria, or normoalbuminuria to macroalbuminuria) and/or a greater than 2-fold increase of serum creatinine at follow-up compared with the baseline value.

RESULTS

During the follow-up period (median, 2.7 years; range, 0.3 to 4.4 years), 49 of 643 patients (7.6%) showed the progression of diabetic nephropathy and three patients (0.5%) developed end-stage renal disease. Baseline ceruloplasmin levels were higher in the progressors than in the nonprogressors (262.6±40.9 mg/L vs. 233.3±37.8 mg/L, P<0.001). Kaplan-Meier analysis showed a significantly higher incidence of nephropathy progression according to ceruloplasmin tertile (log-rank test, P<0.001). The hazard ratio (HR) for progression of diabetic nephropathy was significantly higher in the highest ceruloplasmin tertile category compared with the lowest ceruloplasmin tertile category, even after adjusting for confounding variables (HR, 3.32; 95% confidence interval, 1.28 to 8.61; P=0.003).

CONCLUSION

Baseline serum ceruloplasmin is an independent predictive factor for the progression of diabetic nephropathy in patients with type 2 diabetes mellitus.

Association of Plasma Adiponectin and Oxidized Low-Density Lipoprotein with Carotid Intima-Media Thickness in Diabetic Nephropathy

AIMS

We sought to determine the association between levels of adiponectin and oxidized low-density lipoprotein (ox-LDL) in patients with diabetic nephropathy as well as their effect on carotid intima-media thickness (cIMT).

METHODS

Adiponectin and ox-LDL were determined in 25 diabetic patients without nephropathy and 94 patients at different stages of diabetic nephropathy including subjects on hemodialysis. cIMT was measured using real-time B-mode ultrasonography.

RESULTS

Plasma adiponectin levels increased significantly with severity of diabetic nephropathy (P = 0.002), on the contrary to ox-LDL which decreased with disease severity (P < 0.001). cIMT was significantly higher at late stages of diabetic nephropathy compared with early stages (P = 0.022). Adiponectin was a significant negative predictor of ox-LDL levels (β = -5.45, P = 0.023), independently of confounding factors. There was no significant correlation between cIMT and adiponectin or ox-LDL either in the total sample population or according to disease staging. Cluster analysis showed that patients with the highest cIMT values, highest levels of adiponectin, and lowest levels of ox-LDL were included in one cluster and all assigned to stage 5 of diabetic nephropathy.

CONCLUSIONS

There was no significant association between adiponectin or ox-LDL and cIMT and, therefore, other factors affecting this surrogate marker of cardiovascular disease in diabetic nephropathy should be sought.

Determining the Relationship Between Homocysteinemia and Biomarkers of Inflammation, Oxidative Stress and Functional Kidney Status in Patients with Diabetic Nephropathy

Background: One of the leading causes of terminal renal failure is diabetic nephropathy. The aim of this study was to determine the relationship between homocysteine levels and the biomarkers of renal function, inflammation and oxidative stress, as well as the incidence of macrovascular complications in patients with diabetic nephropathy.

Methods: Sixty-four patients with diabetic nephropathy were included in this study. They were divided according to their homocysteine levels into two groups: hyperhomocysteinemic (HHcy, n=47) and normohomocysteinemic patients (NHCy, n=17). The re sults were compared to a control group (n=20) with normal renal function and without diabetes. Besides homocysteine, cystatine C, creatinine, urea, albuminuria, creatinine clearance, lipid status parameters, apolipoprotein A-I and B, lipo protein (a), CRP, fibrinogen, oxidative LDL were determined using appropriate methods. The incidence of macro vascular diabetic complications was also determined.

Results: The results indicate that the level of renal dysfunction is greater in HHcy than in NHcy patients (p<0.05). In HHcy patients levels of oxLDL were also higher compared to NHcy patients (119.3±140.4 vs. 71.4±50.8 ng/mL, disp< 0.05) as well as fibrinogen levels (4.3±1.3 vs. 3.7±0.8 g/L, p<0.05). The in cidence of macrovascular complications is more frequent in HHcy than in NHcy patients (55.3. vs. 35.3 %, p>0.05), and in patients with macroalbuminuria compared to patients with microalbuminuria (65% vs. 39%, p<0.05).

Conclusions: It can be concluded that HHcy is significantly present in patients with diabetic nephropathy, especially if there is greater reduction of renal function. Besides that, significantly higher concentrations of inflammatory (fibrinogen) and oxidative stress (oxLDL) markers were present in HHcy patients with diabetic nephropathy compared to NHcy patients.Therefore in diabetic nephropathy patients it is useful to regularly monitor the levels of homocysteine, as well as inflammatory and markers of oxidative stress.

Comparison of ox-LDL Levels in Diabetic Patients with Normo-, Micro-, and Macroalbuminuria with Their First Degree Relatives and the Healthy Control Group

Oxidized low density lipoprotein (ox-LDL) is a product of oxidative stress. In this cross-sectional study, we compared the ox-LDL concentrations in diabetic patients with normoalbuminuria (n = 28), microalbuminuria (n = 28), and macroalbuminuria (n = 28) with their first degree relatives (n = 28) and healthy control people (n = 31). They were selected by consecutive patient selection method. The ox-LDL level was assayed using ELISA. We measured blood pressure, lipid profile, fasting plasma glucose (FPG), and HbA1c in all groups. There was no significant difference in ox-LDL concentrations among normoalbuminuric, microalbuminuric, and macroalbuminuric diabetic groups. In diabetic patients with micro- and macroalbuminuria, ox-LDL concentration was higher than their first degree relatives (P = 0.04 and P = 0.03) and control group (P = 0.001 and P = 0.03, resp.). In normoalbuminuric diabetic persons, ox-LDL concentration was just higher than that of healthy people (P = 0.02). There was no statistically significant difference in ox-LDL levels between normoalbuminuric diabetic patients and their first degree relatives. In conclusion, the presence and progression of albuminuria in diabetic patients are not related to ox-LDL concentration and genetic predisposition influences the plasma OX-LDL level. Larger sample size is needed to confirm this conclusion in future studies.

Aqueous Extract from Hibiscus sabdariffa Linnaeus Ameliorate Diabetic Nephropathy via Regulating Oxidative Status and Akt/Bad/14-3-3γ in an Experimental Animal Model

Several studies point out that oxidative stress maybe a major culprit in diabetic nephropathy. Aqueous extract of Hibiscus sabdariffa L. (HSE) has been demonstrated as having beneficial effects on anti-oxidation and lipid-lowering in experimental studies. This study aimed at investigating the effects of Hibiscus sabdariffa L. on diabetic nephropathy in streptozotocin induced type 1 diabetic rats. Our results show that HSE is capable of reducing lipid peroxidation, increasing catalase and glutathione activities significantly in diabetic kidney, and decreasing the plasma levels of triglyceride, low-density lipoprotein (LDL) and increasing high-density lipoprotein (HDL) value. In histological examination, HSE improves hyperglycemia-caused osmotic diuresis in renal proximal convoluted tubules (defined as hydropic change) in diabetic rats. The study also reveals that up-regulation of Akt/Bad/14-3-3γ and NF-κB-mediated transcription might be involved. In conclusion, our results show that HSE possesses the potential effects to ameliorate diabetic nephropathy via improving oxidative status and regulating Akt/Bad/14-3-3γ signaling.

Should we measure routinely oxidised and atherogenic dense low-density lipoproteins in subjects with type 2 diabetes?

Beyond low-density lipoprotein (LDL)-cholesterol concentrations, in recent years, several clinical studies have shown that both oxidised and small, dense LDL have a strong predictive role for the presence of vascular atherosclerosis. These two lipid parameters seem to have a synergistic impact on cardiovascular risk, with a greater importance in patients at higher-risk, such as those with type-2 diabetes. Increased levels of oxidised and small, dense LDL levels are a feature of diabetic dyslipidaemia, and small, dense LDL have been shown to be a good predictor of future cardiovascular events, at both univariate and multivariate analyses. On the other hand, although the association of oxidised LDL with surrogate markers of atherosclerosis is consistent, the correlation with hard clinical end points seems to be smaller. Yet, measurement of these two lipid parameters has not been widely used in daily practice because of the limited availability of clinical data and methodological problems: lack of availability of easy, cheap and reproducible essays for measurement of oxidised and, particularly, small, dense LDL has reduced their assessment in large clinical end-points trials. However, on the basis of available data, the therapeutic modulation of small, dense LDL is significantly associated with reduced cardiovascular risk, even after adjustment for confounding factors. In conclusion, the routine measurement of oxidised and small, dense LDL in patients with type-2 diabetes cannot be recommended in daily clinical practice so far; yet, their measurement is strongly encouraged to better understand their role on the cardiovascular risk of patients with type-2 diabetes.

Role of triglyceride-rich lipoproteins in diabetic nephropathy

Diabetic nephropathy is an increasingly important cause of morbidity and mortality worldwide. A large body of evidence suggests that dyslipidemia has an important role in the progression of kidney disease in patients with diabetes. Lipids may induce renal injury by stimulating TGF-beta, thereby inducing the production of reactive oxygen species and causing damage to the glomeruli and glomerular glycocalyx. Findings from basic and clinical studies strongly suggest that excess amounts of a variety of lipoproteins and lipids worsens diabetes-associated microvascular and macrovascular disease, increases glomerular injury, increases tubulointerstitial fibrosis, and accelerates the progression of diabetic nephropathy. The increasing prevalence of obesity, type 2 diabetes mellitus, and diabetic nephropathy means that interventions that can interrupt the pathophysiological cascade of events induced by lipoproteins and lipids could enable major life and cost savings. This Review discusses the structural, cellular, and microscopic findings associated with diabetic nephropathy and the influence of lipoproteins, specifically triglyceride-rich lipoproteins (TGRLs), on the development and perpetuation of diabetic nephropathy. Some of the accepted and hypothesized mechanisms of renal injury relating to TGRLs are also described.

Circulating oxidized LDL: a biomarker and a pathogenic factor

PURPOSE OF REVIEW

Oxidized LDL (oxLDL) contributes to many atherogenic steps in the vascular wall, but the significance of oxLDL in circulating blood remains unclear. Recent progress in procedures for measuring both human and murine oxLDL has provided growing evidence of the importance of circulating oxLDL.

RECENT FINDINGS

Circulating oxLDL is elevated in patients with advanced atherosclerosis, such as coronary heart disease and ischemic stroke, and also reflects early atherosclerotic changes and metabolic disorders including diabetes and obesity. In-vitro exposure to oxLDL increased mononuclear cell nuclear factor-kappaB activity, suggesting a pathogenic role of circulating oxLDL in exacerbation of oxidative stress. In addition, adenoviral administration of secreted scavenger receptor-A1, which functions as a decoy, suppresses foam cell formation in LDL receptor-deficient mice via a blockade of modified LDL incorporation into macrophages. Furthermore, when lectin-like oxLDL receptor-1 was ectopically expressed in the liver, circulating oxLDL was reduced, resulting in complete prevention of atherosclerotic progression in apolipoprotein E-deficient mice. Thus, circulating oxLDL impacts atherogenic formation.

SUMMARY

The roles of circulating oxLDL in atherosclerotic pathogenesis are now attracting considerable attention. OxLDL removal from circulating blood is a promising therapeutic strategy against atherosclerosis.

Association of macroalbuminuria with oxidized LDL and TGF-beta in type 2 diabetic patients: a case-control study

The pathogenesis of diabetic nephropathy, mainly characterized by macroalbuminuria, is still poorly understood, but it is reported that transforming growth factor-beta (TGF-beta) plays a key role. In vitro evidence suggests that administration of oxidized LDL (ox-LDL) can lead to upregulation of TGF-beta by human glomerular mesangial cells. This study aimed to evaluate the association between macroalbuminuria, ox-LDL, and TGF-beta in diabetic patients. A total of 77 type 2 diabetic patients with macroalbuminuria (albumin excretion rate: AER > or = 300 mg/24 h) and 66 patients with normoalbuminuria (AER < or = 30 mg/24 h) were recruited. Fasting blood samples were obtained and serum levels of ox-LDL and TGF-beta were determined. Ox-LDL and TGF-beta were significantly higher in patients with macroalbuminuria than in those with normoalbuminuria (98.93 + or - 3.99 vs. 72.45 + or - 2.48 U/l; P < 0.001 and 6.46 + or - 0.74 vs. 2.49 + or - 0.39 ng/ml; P < 0.001, respectively). In patients with macroalbuminuria, there was a significant correlation between Ox-LDL and TGF-beta (r = 0.376; P < 0.01). AER was significantly correlated to ox-LDL (r = 0.302; P < 0.05) and TGF-beta (r = 0.306; P < 0.05) in macroalbuminuric patients. This association remained significant after adjustment for potential confounders. Adjustment for TGF-beta (ox-LDL), attenuated the association of ox-LDL (TGF-beta) with AER. In conclusion, this study demonstrated the association of TGF-beta and ox-LDL with albuminuria in macroalbuminuric type 2 diabetic patients, and suggested that this relationship is highly mediated through the correlation between TGF-beta and ox-LDL.

CXCL16 and oxLDL are induced in the onset of diabetic nephropathy

Diabetic nephropathy (DN) is a major cause of end-stage renal failure worldwide. Oxidative stress has been reported to be a major culprit of the disease and increased oxidized low density lipoprotein (oxLDL) immune complexes were found in patients with DN. In this study we present evidence, that CXCL16 is the main receptor in human podocytes mediating the uptake of oxLDL. In contrast, in primary tubular cells CD36 was mainly involved in the uptake of oxLDL. We further demonstrate that oxLDL down-regulated alpha(3)-integrin expression and increased the production of fibronectin in human podocytes. In addition, oxLDL uptake induced the production of reactive oxygen species (ROS) in human podocytes. Inhibition of oxLDL uptake by CXCL16 blocking antibodies abrogated the fibronectin and ROS production and restored alpha(3) integrin expression in human podocytes. Furthermore we present evidence that hyperglycaemic conditions increased CXCL16 and reduced ADAM10 expression in podocytes. Importantly, in streptozotocin-induced diabetic mice an early induction of CXCL16 was accompanied by higher levels of oxLDL. Finally immunofluorescence analysis in biopsies of patients with DN revealed increased glomerular CXCL16 expression, which was paralleled by high levels of oxLDL. In summary, regulation of CXCL16, ADAM10 and oxLDL expression may be an early event in the onset of DN and therefore all three proteins may represent potential new targets for diagnosis and therapeutic intervention in DN.

Polyphenol extracts from Hibiscus sabdariffa Linnaeus attenuate nephropathy in experimental type 1 diabetes

Diabetic nephropathy progressed to end-stage renal disease (ESRD) is found in type 1 or type 2 diabetes. Oxidative stress is one of the precipitation factors in diabetic nephropathy. Previously, Hibiscus sabdariffa Linnaeus and its polyphenol extracts were found to possess antioxidative effects. This study is aimed to investigate the effect of Hibiscus sabdariffa L. polyphenol extract (HPE) in streptozotocin (STZ) induced diabetic nephropathy. The results show that HPE reduced kidney mass induced by STZ significantly, as well as improving hydropic change of renal proximal convoluted tubules in the rats. HPE also significantly reduced serum triglyceride, total cholesterol and LDL in STZ induced rats. Treatment with HPE significantly increased the activity of catalase and glutathione and reduced lipid peroxidation (thiobarbituric acid-reactive substances, TBARS). The findings of this research show the beneficial effects of HPE on STZ induced diabetic nephropathy including pathology, serum lipid profile and oxidative marker in kidney.

Association of oxidized low-density lipoprotein and transforming growth factor-beta in type 2 diabetic patients: a cross-sectional study

Recent in vitro evidence suggests that oxidized low-density lipoprotein (ox-LDL) stimulates the expression of transforming growth factor-beta (TGF-beta) by human glomerular epithelial cells. An elevated level of TGF-beta, which is a multifunctional growth cytokine, is also reported in diabetic patients. This study aimed to determine the association between ox-LDL and TGF-beta in healthy and type 2 diabetic participants. A total of 80 type 2 diabetic patients, who were referred to the outpatient diabetes clinic of a university general hospital, and 80 healthy controls matched for sex, age, and body mass index (BMI) were recruited. Fasting blood samples were obtained, and fasting plasma glucose, cholesterol, high-density lipoprotein-cholesterol (HDL-c), LDL-cholesterol, triglycerides, creatinine, HbA1C, ox-LDL, and TGF-beta were measured. Ox-LDL and TGF-beta were significantly greater in diabetic patients than healthy controls (72.66 +/- 3.11, 46.02 +/- 1.64, P < 0.001 and 4.75 +/- 0.43, 2.06 +/- 0.31, P < 0.001, respectively). Ox-LDL was significantly correlated to TGF-beta in diabetic patients (r = 0.318, P = 0.004). This significant association was not observed in healthy controls (r = 0.148, P = 0.191). In multivariate linear regression analysis after adjustment for age, sex, BMI, and creatinine, ox-LDL was a significant independent predictor of TGF-beta (beta = 0.308, P = 0.007). In conclusion, this study demonstrated that ox-LDL is significantly correlated to TGF-beta in type 2 diabetic patients.

Measurement of plasma oxidized low-density lipoprotein and its clinical implications

Oxidized low-density lipoprotein (OxLDL) has been shown to exist in human circulating plasma. Several groups including ours have developed methods for immunologically measuring OxLDL, which have been applied to several clinical, both cross-sectional and prospective, studies. These data clearly show that OxLDL levels correlate well with the severity of cardiovascular diseases. In particular, recent observations suggest that plasma OxLDL levels could be a useful marker for predicting future cardiovascular events; however, substantial differences exist among the different methods of OxLDL measurement. To evaluate the clinical data on circulating OxLDL, a proper understanding of the similarity, differences, and limitation of the methods is needed. This paper summarizes the characteristics of the methods used and recent clinical findings.

Clinical significance of the physicochemical properties of LDL in type 2 diabetes

Atherosclerosis is the leading cause of death in type 2 diabetes. LDL cholesterol and atherosclerosis are related, both in healthy people and those with diabetes; however, people with diabetes are more prone to atheroma, even though their LDL cholesterol levels are similar to those in their non-diabetic peers. This is because LDL particles are modified in the presence of diabetes to become more atherogenic. These modifications include glycation in response to high plasma glucose levels; oxidative reactions mediated by increased oxidative stress; and transfer of cholesterol ester, which makes the particles smaller and denser. The latter modification is strongly associated with hypertriglyceridaemia. Oxidatively and non-oxidatively modified LDL is involved in plaque formation, and may thus contribute to the accelerated atherosclerosis. This review discusses the techniques currently used to determine the physicochemical properties of LDL, and examines the evidence that modification of these properties plays a role in the accelerated atherosclerosis associated with type 2 diabetes.

Role of lipid control in diabetic nephropathy

Patients with diabetic nephropathy are known to be associated with many lipoprotein abnormalities, including higher plasma levels of very low-density lipoprotein, low-density lipoprotein and triglycerides, and lower levels of high-density lipoprotein. Many studies have reported that lipids may induce both glomerular and tubulointerstitial injury through mediators such as cytokines, reactive oxygen species, chemokines, and through hemodynamic changes. Clinical studies in patients with diabetic nephropathy showed that lipid control can be associated with an additional effect of reduction in proteinuria. Experimental studies demonstrated that lipid-lowering agents exerted a certain degree of renoprotection, through both indirect effects from lipid lowering and a direct effect on cell protection. Therefore, lipid control appears to be important in the prevention and treatment of diabetic nephropathy. Diabetic nephropathy has become the leading cause of end-stage renal failure in many countries, including Taiwan. One of the major risk factors for the development and progression of diabetic nephropathy is dyslipidemia. In this paper we will review the role of lipid in mediating renal injury and the beneficial effects of lipid control in diabetic nephropathy.

9HODE stimulates cell proliferation and extracellular matrix synthesis in human mesangial cells via PPARgamma

Plasma oxidized low-density lipoprotein (OX-LDL) levels are elevated in patients with renal diseases, including diabetic nephropathy. We examined effects of OX-LDL on cell proliferation and extracellular matrix (ECM) production by using normal human mesangial cells. Furthermore, we examined possible involvement of peroxisome proliferator-activated receptor gamma (PPARgamma). Mesangial cell proliferation with OX-LDL, 9-hydroxy-10,12-octadecadienoic acid (9HODE), and 13-hydroxy-9,11-octadecadienoic acid (13HODE), the major components of OX-LDL, were determined by 5-bromo-2'-deoxyuridine (BrdU) or 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT) incorporation. The effect of OX-LDL on mesangial cell proliferation with PD98059 pretreatment was determined by BrdU incorporation. Type IV collagen, fibronectin, and PPARgamma expression with OX-LDL or 9HODE or 13HODE was determined by Western blotting. Type IV collagen expression with antisense oligonucleotide against PPARgamma pretreatment was also determined by Western blotting. The effect of PD98059 pretreatment on PPARgamma expression was determined by Western blotting. In mesangial cells exposed to isolated OX-LDL from human plasma, BrdU incorporation was increased, and this increase was deleted by PD98059. Type IV collagen expression was significantly increased by OX-LDL. 9HODE and 13HODE increased BrdU and MTT incorporation into mesangial cells and also increased expressions of Type IV collagen and fibronection, the major components of ECM. PPARgamma expression in mesangial cells was stimulated by 9HODE. The reduction of PPARgamma synthesis by pretreatment of antisense oligonucleotide against PPARgamma remarkably attenuated Type IV collagen synthesis induced by 9HODE. PPARgamma expression induced by 9HODE was also reduced by PD98059 pretreatment. These findings demonstrate that 9HODE, the major component of OX-LDL, stimulates cell proliferation and ECM production of human mesangial cells. In addition, the stimulatory effects are, at least in part, mediated by PPARgamma, which may exist in downstream of ERK1/2 pathway.

Clinical Significance of Serum Oxidized Low-Density Lipoprotein/β2-Glycoprotein I Complexes in Patients with Chronic Renal Diseases

BACKGROUND

Peroxidation of low-density lipoprotein (LDL) plays an important role in the development of dyslipidemias associated with the progression of chronic renal disorders. We recently reported [J Lipid Res 2001;42:697, 2002;43:1486, 2003;44:716] that oxidized LDL (oxLDL) interacts with an endogenous plasma protein, beta2-glycoprotein I (beta2GPI), via specific ligands. In the present study, the prevalence and clinical significance of oxLDL/beta2GPI complexes were evaluated in patients with chronic renal disorders.

METHODS

Serum levels of oxLDL/beta(2)GPI complexes were measured by ELISA in patients with chronic renal disease and their association with clinical manifestations was assessed.

RESULTS

The serum levels of oxLDL/beta2GPI complexes were significantly higher in patients with chronic renal failure (CRF), chronic nephritis (CN) and diabetes mellitus than those in healthy individuals. The presence of complexes in patients with CN was significantly associated with high dietary protein and sodium chloride intake, but not with lipid metabolic parameters. Malondialdehyde-modified LDL was significantly associated with total cholesterol and LDL cholesterol in all patient groups, but did not correlate with renal function parameters.

CONCLUSIONS

Serum oxLDL/beta2GPI complexes, generated by oxidative stress and associated with high dietary protein and salt intake, might be a novel risk factor and a diagnostic marker for the development of chronic renal diseases, especially IgA nephropathy.

The antioxidant effects of statins

Oxidative stress contributes to the initiation and the development of atherosclerotic plaques and adversely influences myocardial integrity. Statins interfere with oxidation in several ways that may contribute to reducing the atherogenic process. In addition to direct antioxidant effects, statins reduce circulating oxidized low-density lipoproteins (oxLDL) and inhibit their uptake by macrophages. They also reduce circulating markers of oxidation such as F2-isoprostane and nitrotyrosine. Statins inhibit oxidant enzymes activity such as that of reduced nicotinamide adenine dinucleotide phosphate (NAD[P]H) oxidase and myeloperoxidase and up-regulate the activity of antioxidant enzymes such as catalase and paraoxonase. They reduce endothelial dysfunction mainly by their ability to enhance endothelial nitric oxide bioavailability, which is achieved by several mechanisms. The antioxidant properties of statins extend to organ protection especially the myocardium and the lungs.

Association of dyslipidemia and effects of statins on nonmacrovascular diseases

BACKGROUND

Statins have mechanisms of action that expand their effects beyond cholesterol lowering and atherosclerotic medical conditions.

OBJECTIVE

This review summarizes clinical evidence for the association of dyslipidemia and the effects of statin use on aortic stenosis, Alzheimer's dementia (AD), osteoporosis, prevention of diabetes mellitus (DM), diabetic retinopathy, age-related macular degeneration, and diabetic/nondiabetic nephropathy.

METHODS

An English-language literature search was conducted using MEDLINE (1966-June 2003). Bibliographies of retrieved articles were reviewed. Search terms included statin, HMG-CoA reductase inhibitors, aortic stenosis, Alzheimer's dementia, osteoporosis, prevention of diabetis, diabetic retinopathy, age-related macular degeneration, diabetic nephropathy, and nondiabetic nephropathy.

RESULTS

Three retrospective cohort trials have shown an association between statin use and the progression of aortic stenosis; one of these trials observed a 45% decrease in aortic valve area in 1 year. In AD, one cross-sectional analysis found 60% to 73% lower AD rates in lovastatin or pravastatin recipients ( P<0.001 ). Of the multiple observational studies on the effect of statins on fracture risk, some have shown a decreased risk, with an odds ratio as low as 0.50 (95% CI, 0.33-0.76); others have demonstrated no association. A post hoc analysis of the West of Scotland Coronary Prevention Study found a 30% reduction in the development of DM ( P=0.042 ), but this was not duplicated in the Anglo-Scandinavian Cardiac Outcomes Trial-Lipid Lowering Arm. A small clinical trial of 6 patients (11 eyes) demonstrated improved retinal hard exudates with pravastatin treatment in patients with diabetic retinopathy. In a cross-sectional analysis, age-related macular degeneration was found to be less common among statin users than nonusers (4% [ 1/27 ] vs 22% [ 76/352 ]; P=0.02. Multiple small clinical trials of 19 to 56 patients with diabetic and nondiabetic nephropathy at various stages generated inconsistent results for an association between statin use and decreased albumin excretion rate and decreased rate of decline in glomerular filtration.

CONCLUSION

Data of variable quantity and quality support the use of statins as adjuncts in the treatment of nonmacrovascular diseases.