Development of capture assays for different modifications of human low-density lipoprotein

ASSOCIATIONS BETWEEN ACCELERATED ATHEROSCLEROSIS, OXIDIZED LDL IMMUNE COMPLEXES, AND IN VITRO ENDOTHELIAL DYSFUNCTION IN SYSTEMIC LUPUS ERYTHEMATOSUS

Systemic lupus erythematosus (SLE) is an independent risk factor for atherosclerosis. This study was designed to determine the association between atherosclerosis, oxidized LDL immune complexes (oxLDL-IC), and endothelial dysfunction in SLE. SLE patients were recruited, and carotid atherosclerotic total plaque area (TPA) was determined by ultrasound. Levels of oxLDL-IC were measured. In vitro endothelial function was measured by aortic endothelial nitric oxide (NO) production after culture of human aortic endothelial cells (HAEC) with SLE serum. Levels of oxLDL-IC are associated significantly with TPA. In vitro HAEC NO production after culture with SLE serum was positively correlated with serum complement. HAEC NO production was increased with sepiapterin to couple eNOS. To our knowledge, this is the first study to demonstrate an association between subclinical accelerated atherosclerosis and oxLDL-IC in SLE. This is also the first study to demonstrate the effect of sepiapterin on improving in vitro aortic endothelial cell function in SLE.

Immune Complexes and the Risk of CVD in Type 1 Diabetes

We investigated whether the composition of modified forms of LDL in circulating immune complexes (LDL-ICs) was associated with cardiovascular disease (CVD) outcomes, including any CVD, major adverse cardiac and cerebrovascular events (MACCE), myocardial infarction (MI), and coronary artery disease, in type 1 diabetes (T1D). Our results demonstrate that the baseline levels of oxidized LDL (oxLDL), MDA-modified LDL (MDA-LDL), and advanced glycosylation-modified LDL (AGE-LDL) in circulating ICs were associated with the four CVD outcomes in unadjusted models, and adjustment by age and mean HbA_1c only resulted in minimal reduction of these associations. After adjustments were made for other cardiovascular risk factors, particularly LDL cholesterol, oxLDL-IC and MDA-LDL-IC remained independently associated with the risk of CVD, and oxLDL-IC was independently associated with the risk of MACCE and MI. In the majority of cases, the baseline levels of modified LDL-IC (measured many years before the occurrence of any CVD event) were associated with the risk of CVD over a 25-year period even after adjustment for other risk factors (including LDL cholesterol). Therefore, modified LDL biomarkers may help identify patients with T1D at high risk for MACCE and CVD events very early in the evolution of the disease, before other signals of disease are apparent.

Modification of HDL by reactive aldehydes alters select cardioprotective functions of HDL in macrophages

While increased levels of high-density lipoprotein (HDL)-cholesterol correlate with protection against cardiovascular disease, recent findings demonstrate that HDL function, rather than HDL-cholesterol levels, may be a better indicator of cardiovascular risk. One mechanism by which HDL function can be compromised is through modification by reactive aldehydes such as acrolein (Acro), 4-hydroxynonenal, and malondialdehyde (MDA). In this study, we tested the hypothesis that modification of HDL with reactive aldehydes would impair HDL's athero-protective functions in macrophages. Compared to native HDL, Acro- and MDA-modified HDL have impaired abilities to promote migration of primary peritoneal macrophages isolated from C57BL6/J mice. Incubation of macrophages with MDA-HDL also led to an increased ability to generate reactive oxygen species. Our studies revealed that the changes in HDL function following aldehyde modification are likely not through activation of canonical nuclear factor-kappa B signaling pathways. Consistent with this finding, treatment of either noncholesterol-loaded macrophages or foam cells with modified forms of HDL does not lead to significant changes in expression levels of inflammatory markers. Importantly, our data also demonstrate that changes in HDL function are dependent on the type of modification present on the HDL particle. Our findings suggest that modification of HDL with reactive aldehydes can impair some, but not all, of HDL's athero-protective functions in macrophages.

Cholesterol in Pancreatic β-Cell Death and Dysfunction: Underlying Mechanisms and Pathological Implications

The mechanisms or causes of pancreatic β-cell death as well as impaired insulin secretion, which are the principal events of diabetic etiopathology, are largely unknown. Diabetic complications are known to be associated with abnormal plasma lipid profile, mainly elevated level of cholesterol and free fatty acids. However, in recent years, elevated plasma cholesterol has been implicated as a primary modulator of pancreatic β-cell functions as well as death. High-cholesterol diet in animal models or excess cholesterol in pancreatic β-cell causes transporter desensitization and results in morphometric changes in insulin granules. Moreover, cholesterol is also held responsible to cause oxidative stress, mitochondrial dysfunction, and activation of proapoptotic markers leading to β-cell death. The present review focuses on the pathways and molecularevents that occur in the β-cell under the influence of excess cholesterol that hampers the basal physiology of the cell leading to the progression of diabetes.

Gold nanoparticle-antibody conjugates for specific extraction and subsequent analysis by liquid chromatography-tandem mass spectrometry of malondialdehyde-modified low density lipoprotein as biomarker for cardiovascular risk

Oxidized low-density lipoproteins (OxLDLs) like malondialdehyde-modified low-density lipoprotein (MDA-LDL) play a major role in atherosclerosis and have been proposed as useful biomarkers for oxidative stress. In this study, gold-nanoparticles (GNPs) were functionalized via distinct chemistries with anti-MDA-LDL antibodies (Abs) for selective recognition and capture of MDA-LDL from biological matrices. The study focused on optimization of binding affinities and saturation capacities of the antiMDA-LDL-Ab-GNP bioconjugate by exploring distinct random and oriented immobilization approaches, such as (i) direct adsorptive attachment of Abs on the GNP surface, (ii) covalent bonding by amide coupling of Abs to carboxy-terminated-pegylated GNPs, (iii) oriented immobilization via oxidized carbohydrate moiety of the Ab on hydrazide-derivatized GNPs and (iv) cysteine-tagged protein A (cProtA)-bonded GNPs. Depending on immobilization chemistry, up to 3 antibodies per GNP could be immobilized as determined by ELISA. The highest binding capacity was achieved with the GNP-cProtA-Ab bioconjugate which yielded a saturation capacity of 2.24±0.04μgmL(-1) GNP suspension for MDA-LDL with an affinity Kd of 5.25±0.11×10(-10)M. The GNP-cProtA-antiMDA-LDL bioconjugate revealed high specificity for MDA-LDL over copper(II)-oxidized LDL as well as native human LDL. This clearly demonstrates the usefulness of the new GNP-Ab bioconjugates for specific extraction of MDA-LDL from plasma samples as biomarkers of oxidative stress. Their combination as specific immunoextraction nanomaterials with analysis by LC-MS/MS allows sensitive and selective detection of MDA-LDL in complex samples.

Oxidized LDL and AGE-LDL in circulating immune complexes strongly predict progression of carotid artery IMT in type 1 diabetes

OBJECTIVE

Over 90% of modified LDL in circulation is associated to specific antibodies circulating as part of immune complexes (IC); however, few studies have examined their relationship with cardiovascular disease.

METHODS

We report the relationship between circulating concentrations of IC of oxidized LDL (oxLDL-IC), malondialdehyde-LDL (MDA-LDL-IC) and advanced glycation end products-LDL (AGE-LDL-IC) and progression of atherosclerosis over a 12 year period in 467 individuals with type 1 diabetes who participated in the Diabetes Control and Complications Trial (DCCT) and the Epidemiology of Diabetes Interventions and Complications (EDIC) study. OxLDL-IC, AGE-LDL-IC and MDA-LDL-IC levels were measured at DCCT closeout. Internal carotid intima-medial thickness (IMT) was measured at EDIC follow-up years 1, 6 and 12.

RESULTS

OxLDL-IC, AGE-LDL-IC and MDA-LDL-IC levels were significantly correlated with age, lipid levels, blood pressure levels and albumin excretion rates. Levels of oxLDL, AGE-LDL and MDA-LDL in isolated LDL-IC were highly inter-correlated (r = 0.66-0.84, P < 0.0001). After adjusting for cardiovascular risk factors individuals in the upper quartile of oxLDL-IC had a 2.98-fold increased odds (CI: 1.34, 6.62) of having IMT ≥ 1.00 mm and had a 5.13-fold increased odds (CI: 1.98, 13.3) of having significant IMT progression, relative to those in the lowest quartile. Parallel odds ratios for AGE-LDL-IC were 2.95 (CI: 1.37, 6.34) and 3.50 (CI: 1.38, 8.86), while results for MDA-LDL-IC were 1.76 (0.87, 3.56) and 2.86 (1.20, 6.81).

CONCLUSION

Our study indicates that high levels of oxLDL-IC and AGE-LDL-IC are important predictors of carotid intima-medial thickening in patients with type 1 diabetes.

Pathogenic role of modified LDL antibodies and immune complexes in atherosclerosis

There is strong evidence supporting a key role of the adaptive immune response in atherosclerosis, given that both activated Th cells producing predominantly interferon-γ and oxidized LDL (oxLDL) and the corresponding antibodies have been isolated from atheromatous plaques. Studies carried out using immune complexes (IC) prepared with human LDL and rabbit antibodies have demonstrated proatherogenic and pro-inflammatory properties, mostly dependent on the engagement of Fcγ receptors Ⅰ and Ⅱ in macrophages and macrophage-like cell lines. Following the development of a methodology for isolating modified LDL (mLDL) antibodies from serum and isolated IC, it was confirmed that antibodies reacting with oxLDL and advanced glycation end product-modified LDL are predominantly IgG of subtypes 1 and 3 and that mLDL IC prepared with human reagents possesses pro-inflammatory and proatherogenic properties. In previous studies, LDL separated from isolated IC has been analyzed for its modifications, and the reactivity of antibodies isolated from the same IC with different LDL modifications has been tested. Recently, we obtained strong evidence suggesting that the effects of mLDL IC on phagocytic cells are modulated by the composition of the mLDL. Clinical studies have shown that the level of mLDL in circulating IC is a strong predictor of cardiovascular disease (CVD) and, in diabetic patients, other significant complications, such as nephropathy and retinopathy. In conclusion, there is convincing ex vivo and clinical data supporting the hypothesis that, in humans, the humoral immune response to mLDL is pathogenic rather than protective.

Immunoassay of modified forms of human low density lipoprotein in isolated circulating immune complexes

Modified lipoproteins are able to induce inflammatory reactions through innate immunity pathways and are immunogenic, leading to an autoimmune response that results in the formation of proinflammatory immune complexes. The measurement of circulating oxidized lipoproteins and corresponding antibodies has, therefore, been proposed as an approach to assess the risk for complications in patients with diabetes and for the risk of cardiovascular disease in the general population. However, the majority of modified low density lipoprotein (LDL) in the peripheral circulation exists in the form of immune complexes, and this is a significant obstacle for the measurement of modified LDL and the corresponding antibodies. In this manuscript, we describe in detail the methodology developed by our group for isolation and fractionation of circulating immune complexes (IC), allowing the accurate assay of different LDL modifications. This approach has resulted in several studies showing that the levels of modified LDL are risk factors with a stronger association to diabetic retinopathy, nephropathy, and macrovascular disease. Ongoing research is focused on evaluating the predictive power of modified LDL levels for the development or progression of atherosclerotic cardiovascular disease in other patient populations and on the simplification of the assay to make it more applicable to diagnostic laboratories.

The levels of MDA-LDL in circulating immune complexes predict myocardial infarction in the VADT study

OBJECTIVE

Circulating immune complexes (IC) containing modified forms of LDL (mLDL) are strongly pro-inflammatory and strong predictors of cardiovascular disease (CVD) progression in type 1 diabetes. The present study was undertaken to determine whether the levels of oxidized LDL (oxLDL), malondialdehyde-LDL (MDA-LDL) and advanced glycation end products-LDL (AGE-LDL) in IC predict incident CVD events in type 2 diabetes (VADT cohort).

METHODS AND RESULTS

Levels of mLDL in IC were measured in 907 patients of the VADT cohort, a median of two years after entry into the study. Participants were followed for an average of 3.7 years for vascular outcomes. Hazard ratios (HRs) for CV endpoints in relation to mLDL-IC quartiles were calculated by Cox proportional hazard models. The primary composite CVD endpoint included documented myocardial infarction (MI); stroke; death from CVD; congestive heart failure; cardiac, cerebrovascular, or peripheral VD surgical intervention; inoperable CVD; and amputation for ischemic gangrene. During follow-up, 4.7% and 16.8% of participants had an MI or a composite endpoint, respectively. After adjustments by conventional risk factors, individuals in the highest quartile of MDA-LDL-IC were at higher risk of MI [HR = 2.44 (95% CI: 1.03, 5.77)] and composite endpoint [HR = 1.71 (95% CI: 1.04, 2.80)], relative to individuals in the lowest quartile. Similar comparisons for oxLDL and AGE-LDL levels yielded HR values of 1.08 and 1.31 for MI and 0.91 and 1.34 for composite endpoint.

CONCLUSIONS

Our study indicates that high levels of MDA-LDL in isolated IC predict future MI and acute CV events in patients with type 2 diabetes.

High concentrations of AGE-LDL and oxidized LDL in circulating immune complexes are associated with progression of retinopathy in type 1 diabetes

OBJECTIVE

To determine whether immunocomplexes (ICs) containing advanced glycation end product (AGE)-LDL (AGE-LDL) and oxidized LDL (oxLDL) contribute to the development of retinopathy over a 16-year period in subjects with type 1 diabetes.

RESEARCH DESIGN AND METHODS

Levels of AGE-LDL and oxLDL in ICs were measured in 517 patients of the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC) cohort. Retinopathy was assessed by stereoscopic fundus photography. Cox proportional hazards models were used to assess the effect of AGE-LDL-ICs and oxLDL-ICs on retinopathy progression.

RESULTS

In unadjusted models, higher baseline levels of AGE-LDL-ICs and oxLDL-ICs significantly predicted progression of diabetic retinopathy outcomes. After adjustment by study-design variables (treatment group, retinopathy cohort, duration of type 1 diabetes, and baseline albumin excretion rate [AER], hemoglobin A(1c) (HbA(1c)), and Early Treatment Diabetic Retinopathy Study [ETDRS] score), one SD increase in IC levels was associated with 47% (hazard ratio [HR] 1.47 [95% CI 1.19-1.81]; AGE-LDL-IC) and 45% (1.45 [1.17-1.80]; oxLDL-IC) increased risk of developing proliferative diabetic retinopathy (PDR) and 37% (1.37 [1.12-1.66]; to both ICs) increased risk of progressing to severe nonproliferative retinopathy. Analyses were stratified by retinopathy cohort because results differed between primary and secondary cohorts. For AGE-LDL-ICs, HR for progression to PDR was 2.38 (95% CI 1.30-4.34) in the primary cohort and attenuated in the secondary cohort (1.29 [1.03-1.62]). Similar results were observed for oxLDL-ICs.

CONCLUSIONS

Increased levels of AGE-LDL and oxLDL in ICs are associated with increased risk for progression to advanced retinopathy in patients with type 1 diabetes, indicating that the antibody response to modified LDL plays a significant role in retinopathy progression.

The Pathogenic Role of the Adaptive Immune Response to Modified LDL in Diabetes

The main causes of morbidity and mortality in diabetes are macro and microvascular complications, including atherosclerosis, nephropathy, and retinopathy. As the definition of atherosclerosis as a chronic inflammatory disease became widely accepted, it became important to define the triggers of vascular inflammation. Oxidative and other modifications of lipids and lipoproteins emerged as major pathogenic factors in atherosclerosis. Modified forms of LDL (mLDL) are pro-inflammatory by themselves, but, in addition, mLDLs including oxidized, malondialdehyde (MDA)-modified, and advanced glycation end (AGE)-product-modified LDL induce autoimmune responses in humans. The autoimmune response involves T cells in the arterial wall and synthesis of IgG antibodies. The IgG auto-antibodies that react with mLDLs generate immune complexes (IC) both intra and extravascularly, and those IC activate the complement system as well as phagocytic cells via the ligation of Fcγ receptors. In vitro studies proved that the pro-inflammatory activity of IC containing mLDL (mLDL-IC) is several-fold higher than that of the modified LDL molecules. Clinical studies support the pathogenic role of mLDL-IC in the development of macrovascular disease patients with diabetes. In type 1 diabetes, high levels of oxidized and AGE-LDL in IC were associated with internal carotid intima-media thickening and coronary calcification. In type 2 diabetes, high levels of MDA-LDL in IC predicted the occurrence of myocardial infarction. There is also evidence that mLDL-IC are involved in the pathogenesis of diabetic nephropathy and retinopathy. The pathogenic role of mLDL-IC is not unique to diabetic patients, because those IC are also detected in non-diabetic individuals. But mLDL-IC are likely to reach higher concentrations and have a more prominent pathogenic role in diabetes due to increased antigenic load secondary to high oxidative stress and to enhanced autoimmune responses in type 1 diabetes.

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

BACKGROUND

Modified low-density lipoprotein (LDL) immune complexes (IC) have proinflammatory properties and play a role in albuminuria development.

METHODS

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.

RESULTS

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).

CONCLUSION

Higher levels of oxLDL and AGE-LDL in circulating IC were associated with increased odds to develop abnormal albuminuria.

Spermatogenic and sperm quality differences in an experimental model of metabolic syndrome and hypogonadal hypogonadism

The synergistic effect of the co-morbidities that comprise metabolic syndrome (MetS) is increasingly being recognised as an important contributor in the pathology of a broad spectrum of seemingly disparate conditions. However, in terms of male reproductive function, beyond erectile dysfunction, little is known about the influence of this cohort (collectively or separately) on spermatogenesis and sperm quality. The aims of this study were to assess the reproductive tract of a MetS animal model for detrimental changes, to determine whether a group of compounds (advanced glycation end products and their receptor) known to cause cell dysfunction and DNA damage was present and assess whether hypogonadotropic hypogonadism was the main contributing factor for the changes seen. Animals fed a high-fat diet were found to have significantly increased cholesterol, triglycerides, blood glucose, mean arterial pressure and visceral fat levels. Although serum testosterone was decreased, no changes were seen in either testicular or epididymal histology. Immunolocalisation ofNϵ-carboxymethyl-lysine and the receptor for advanced glycation end products was found in the testes, epididymides and sperm of the two treated groups of animals; however, ELISA did not show any difference in protein levels. Similarly, assessment of sperm nuclear DNA (nDNA) fragmentation by acridine orange test did not find significant differences in nDNA integrity. We conclude that the minimal effect on spermatogenesis and sperm quality seen in our model is probably due to the moderate increase of blood glucose rather than the hypogonadism.

LDL-containing immune complexes in the DCCT/EDIC cohort: associations with lipoprotein subclasses

Immune complexes containing modified LDL (LDL-IC) and NMR-determined Total LDL particle concentrations are significantly associated with intima-media thickness (IMT). We analyzed the associations between concentrations of NMR-determined lipoprotein subclasses and LDL-IC in the DCCT/EDIC cohort. LDL-IC concentrations in women and men of the DCCT/EDIC cohort did not differ significantly and were positively associated with Total LDL particle concentrations in men and women (r=0.34, r=0.32, respectively; P<.01) and with Small LDL concentration (r=0.22, r=0.13, respectively; P<.01). In women, Large LDL concentrations were also associated with LDL-IC (r=0.20, P<.01) while in men, the association was more modest (r=0.11, P<.05). Thus, both Small and Large LDL are associated with LDL-IC formation. Based on the results from statistical mediation analyses, we concluded that plasma concentrations of LDL-IC may provide a physiological link between the statistically significant association of Total LDL particle concentration with carotid artery IMT in subjects with Type 1 diabetes. Furthermore, after adjusting for conventional risk factors, there was a decrease in LDL-IC concentration even in the presence of high Total LDL particle concentrations in those women with high concentrations of Large HDL, but the association was not evident in men. This suggests that the associations between Large HDL and Total LDL particle concentrations, and their associations with LDL-IC levels, differ by gender and suggest that LDL-IC partially mediate the contribution of Total LDL particle concentration to increased carotid IMT in diabetic men.

Levels of oxidized LDL and advanced glycation end products-modified LDL in circulating immune complexes are strongly associated with increased levels of carotid intima-media thickness and its progression in type 1 diabetes

OBJECTIVE

High cholesterol levels in circulating immune complexes (IC), surrogate markers of modified LDL, are associated with increased carotid intima-media thickness (IMT) and cardiovascular events in type 1 diabetes. Different modifications of LDL are involved in IC formation, but which of these are predictive of vascular events is not known. Therefore, we measured oxidized LDL (oxLDL), advanced glycation end products-modified LDL (AGE-LDL), and malondialdehyde-modified LDL (MDA-LDL) in IC and determined their relationship with increased carotid IMT and compared the strength of the association with that observed with conventional risk factors.

RESEARCH DESIGN AND METHODS

Levels of oxLDL, AGE-LDL, and MDA-LDL were measured in circulating IC isolated from sera of 479 patients of the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC) cohort, collected at baseline. Internal and common carotid IMT were measured 8 and 14 years later by DCCT/EDIC.

RESULTS

OxLDL, AGE-LDL, and MDA-LDL levels in circulating IC were significantly correlated with diabetes duration, BMI, and lipid and blood pressure, but not with age. Multivariate logistic regression models indicated that individuals in the highest versus lowest quartile of oxLDL and AGE-LDL in IC had a 6.11-fold [confidence interval (CI) 2.51-14.8] and a 6.4-fold (CI 2.53-16.2) increase in the odds of having high carotid IMT, respectively, after adjusting for conventional risk factors. Parallel analyses resulted in odds ratios of 2.62 (CI 1.24, 5.55) for LDL-C, 1.45 (CI 0.69, 3.03) for diastolic blood pressure, and 2.33 (CI 1.09, 4.99) for A1C.

CONCLUSIONS

OxLDL and AGE-LDL in circulating IC were significantly associated with progression and increased levels of carotid IMT in type 1 diabetes.

Oxidized LDL immune complexes and coronary artery calcification in type 1 diabetes

OBJECTIVE

Oxidized LDL (oxLDL) and oxLDL antibodies form immune complexes (IC) that reflect essential components in the development of atherosclerosis: dyslipidemia, oxidative stress and induction of a pro-inflammatory humoral immune response. We measured oxLDL in IC (oxLDL-IC) isolated from patients with type 1 diabetes to assess the relationship between oxLDL-IC and coronary artery calcification (CAC).

METHODS

OxLDL was measured in IC isolated from baseline samples from a subgroup of 476 patients of the Diabetes Control and Complications Trial (DCCT). CAC was determined by computed tomography (CT) 11-20 years later. Multivariable log-binomial regression models were used to estimate the risk ratios associated with having a high CAC score with an increase of 1 standard deviation (SD) of the natural logarithm of oxLDL-IC.

RESULTS

Multivariable regression models indicate that a 1 SD increase in the levels of oxLDL-IC was associated with a 37% increase in the risk of having high CAC score (RR=1.36; 95% CI: 1.12-1.67) at follow-up after adjustment for DCCT treatment group, retinopathy/AER groups, gender and CT scanning site as well as baseline age, diabetes duration and HbA1C %. Further adjustment for smoking status, blood pressure and LDL resulted in a risk ratio of 1.23 (95% CI: 1.01-1.50) which remained statistically significant indicating that baseline oxLDL-IC is independently associated with the development of CAC.

DISCUSSION

Increased levels of oxLDL-IC are associated with the development of coronary calcification. This observation reinforces previously published clinical and experimental data demonstrating that oxLD-IC has pro-inflammatory and proatherogenic properties.

The level of malondialdehyde-modified LDL and LDL immune complexes in patients with rheumatoid arthritis

OBJECTIVES

To explore possible associations of malondialdehyde-modified low-density lipoprotein (MDA-LDL) and LDL-immune complexes (LDL-IC) with atherosclerosis in rheumatoid arthritis (RA).

DESIGN AND METHODS

Plasma MDA-LDL, LDL-IC levels and mechanisms of the changes were investigated in RA patients with or without coronary artery disease (CAD), simple CAD patients and control.

RESULTS

MDA-LDL and LDL-IC levels were found increased in all the studied patients, the RA patients with CAD exhibited the most significant changes. MDA-LDL levels were higher in the RA patients with CAD than those both in the simple RA and CAD patients. Multiple linear regression analysis showed that CAD, LDL-IC and erythrocyte sedimentation rate accounted for 36.5% of the variation in MDA-LDL levels; and age, activity, MDA-LDL and rheumatoid factors accounted for 34.5% of the variation in LDL-IC.

CONCLUSIONS

High levels of MDA-LDL and LDL-IC are risk factors for increased risk of atherosclerosis in RA patients and are associated with inflammation.

Clinical significance of the humoral immune response to modified LDL

Human low density lipoprotein (LDL) undergoes oxidation and glycation in vivo. By themselves, oxidized LDL (oxLDL) and AGE-LDL have proinflammatory properties and are considered atherogenic. But the atherogenicity of these lipoproteins are significantly increased as a consequence of the formation of immune complexes (IC) involving specific autoantibodies. OxLDL and AGE antibodies have been shown to be predominantly of the IgG1 and IgG3 isotypes. OxLDL antibodies are able to activate the complement system by the classical pathway and to induce FcR-mediated phagocytosis. In vitro and ex vivo studies performed with modified LDL-IC have proven their pro-inflammatory and atherogenic properties. Clinical studies have demonstrated that the levels of circulating modified LDL-IC correlate with parameters indicative of cardiovascular and renal disease in diabetic patients and other patient populations. The possibility that spontaneously formed or induced modified LDL antibodies (particularly IgM oxLDL antibodies) may have a protective effect has been suggested, but the data is unclear and needs to be further investigated.

Biomarcadores de peroxidação lipídica na aterosclerose

A aterosclerose é caracterizada por uma resposta inflamatória crônica da parede arterial, iniciada por uma lesão do endotélio, cuja etiologia está relacionada à modificação oxidativa da lipoproteína de baixa densidade. O objetivo deste trabalho é apresentar os principais metabólitos envolvidos nos processos bioquímicos de peroxidação lipídica, discutindo as vantagens e desvantagens dos métodos empregados para a mensuração dos biomarcadores de peroxidação lipídica relacionados com a aterosclerose. A avaliação da oxidação das lipoproteínas pode ser realizada pela determinação dos produtos gerados durante a peroxidação lipídica, como os isoprostanos, hidroperóxidos lipídicos, aldeídos, fosfolípides oxidados e os produtos da oxidação do colesterol. A suscetibilidade das partículas de lipoproteína de baixa densidade à oxidação pode ser avaliada in vitro, após a indução da peroxidação lipídica por azoiniciadores radicalares lipossolúveis, hidrossolúveis, ou mais comumente, pelos íons cobre. Por outro lado, as modificações da lipoproteína de baixa densidade, pela ação das lipoxigenases e peroxidases, ou oxidação não-enzimática, resultam no aumento da carga negativa destas partículas e podem contribuir para a geração in vivo de uma subfração de lipoproteína de baixa densidade minimamente oxidada, denominada lipoproteína de baixa densidade eletronegativa (lipoproteína de baixa densidade). A determinação das concentrações desta partícula pode ser realizada em plasma por cromatografia líquida ou por imunoensaios..Diversos métodos podem ser utilizados para a avaliação dos biomarcadores de peroxidação lipídica in vivo e in vitro, porém, a definição do marcador mais adequado, depende de uma avaliação criteriosa das vantagens, desvantagens e particularidades de cada análise, levando-se em consideração os objetivos do estudo que será conduzido.