Carbamylation of LDL and its relationship with myeloperoxidase in type 2 diabetes mellitus

High-density lipoprotein in diabetes: Structural and functional relevance

Low levels of high-density lipoprotein-cholesterol (HDL-C) is considered a major cardiovascular risk factor. However, recent studies have suggested a more U-shaped association between HDL-C and cardiovascular disease. It has been shown that the cardioprotective effect of HDL is related to the functions of HDL particles rather than their cholesterol content. HDL particles are highly heterogeneous and have multiple functions relevant to cardiometabolic conditions including cholesterol efflux capacity, anti-oxidative, anti-inflammatory, and vasoactive properties. There are quantitative and qualitative changes in HDL as well as functional abnormalities in both type 1 and type 2 diabetes. Non-enzymatic glycation, carbamylation, oxidative stress, and systemic inflammation can modify the HDL composition and therefore the functions, especially in situations of poor glycemic control. Studies of HDL proteomics and lipidomics have provided further insights into the structure-function relationship of HDL in diabetes. Interestingly, HDL also has a pleiotropic anti-diabetic effect, improving glycemic control through improvement in insulin sensitivity and β-cell function. Given the important role of HDL in cardiometabolic health, HDL-based therapeutics are being developed to enhance HDL functions rather than to increase HDL-C levels. Among these, recombinant HDL and small synthetic apolipoprotein A-I mimetic peptides may hold promise for preventing and treating diabetes and cardiovascular disease.

Carbamylated lipoproteins in diabetes

Diabetic dyslipidemia is characterized by quantitative and qualitative abnor-malities in lipoproteins. In addition to glycation and oxidation, carbamylation is also a post-translational modification affecting lipoproteins in diabetes. Patients with type 2 diabetes (T2D) exhibit higher levels of carbamylated low-density lipoproteins (cLDL) and high-density lipoproteins (cHDL). Accumulating evidence suggests that cLDL plays a role in atherosclerosis in diabetes. cLDL levels have been shown to predict cardiovascular events and all-cause mortality. cLDL facilitates immune cell recruitment in the vascular wall, promotes accumulation of lipids in macrophages, and contributes to endothelial dysf-unction, endothelial nitric oxide-synthase (eNOS) inactivation and endothelial repair defects. Lastly, cLDL induces thrombus formation and platelet aggregation. On the other hand, recent data have demonstrated that cHDL serum level is independently associated with all-cause and cardiovascular-related mortality in T2D patients. This relationship may be causative since the atheroprotective properties of HDL are altered after carbamylation. Thus, cHDL loses the ability to remove cholesterol from macrophages, to inhibit monocyte adhesion and recruitment, to induce eNOS activation and to inhibit apoptosis. Taken together, it seems very likely that the abnormalities in the biological functions of LDL and HDL after carbamylation contribute to atherosclerosis and to the elevated cardiovascular risk in diabetes.

High-Density Lipoprotein Alterations in Type 2 Diabetes and Obesity

Alterations affecting high-density lipoproteins (HDLs) are one of the various abnormalities observed in dyslipidemia in type 2 diabetes mellitus (T2DM) and obesity. Kinetic studies have demonstrated that the catabolism of HDL particles is accelerated. Both the size and the lipidome and proteome of HDL particles are significantly modified, which likely contributes to some of the functional defects of HDLs. Studies on cholesterol efflux capacity have yielded heterogeneous results, ranging from a defect to an improvement. Several studies indicate that HDLs are less able to inhibit the nuclear factor kappa-B (NF-κB) proinflammatory pathway, and subsequently, the adhesion of monocytes on endothelium and their recruitment into the subendothelial space. In addition, the antioxidative function of HDL particles is diminished, thus facilitating the deleterious effects of oxidized low-density lipoproteins on vasculature. Lastly, the HDL-induced activation of endothelial nitric oxide synthase is less effective in T2DM and metabolic syndrome, contributing to several HDL functional defects, such as an impaired capacity to promote vasodilatation and endothelium repair, and difficulty counteracting the production of reactive oxygen species and inflammation.

Exploring the mechanism of the antithrombotic effects of Pueraria lobata and Pueraria lobata var. thomsonii based on network pharmacology

ETHNOPHARMACOLOGICAL RELEVANCE

Pueraria lobata (Willd.) Ohwi and Pueraria lobata var. thomsonii (Benth.) Maesen are nutritious medicine food homology plants that are widely used in the food and health products industry and are excellent natural materials for the development of new health foods, with great potential for domestic and foreign markets. Clinically, P. lobata and P. thomsonii are used to treat coronary heart disease, atherosclerosis, cerebral infarction and other cardiovascular diseases, and antithrombotic actions may be their core effect in the treatment of thrombotic diseases. However, the underlying mechanisms of the antithrombotic properties of P. lobata and P. thomsonii have not been clarified.

METHODS

First, P. lobata and P. thomsonii were identified by high-performance liquid chromatography (HPLC). An arteriovenous bypass thrombosis rat model was established. Thrombus dry‒wet weight, platelet accumulation rate and the four coagulation indices, including activated partial thromboplastin time (APTT), prothrombin time (PT), thrombin time (TT) and fibrinogen (FIB), were detected in plasma to manifest the P. lobata and P. thomsonii antithrombotic function. Network pharmacology and molecular docking methods were used to obtain key targets and verify reliability. David 6.8 was used for GO and KEGG analyses to explore pathways and potential targets for P. lobata and P. thomsonii antithrombotic functions. Prostaglandin I2 (PGI2), thromboxane A2 (TXA2), cyclooxygenase 2 (COX-2), myeloperoxidase (MPO) and endothelial nitric oxide synthase (eNOS) were tested by enzyme-linked immunosorbent assay (ELISA).

RESULTS

The results indicated that P. lobata and P. thomsonii can reduce thrombus dry‒wet weight and platelet accumulation in rats and inhibit TT, APTT, FIB, and PT. A comprehensive network pharmacology approach successfully identified 9 active ingredients in P. lobata and P. thomsonii. The main active ingredients include polyphenols, amino acids and flavonoids. A total of 15 antithrombotic function targets were obtained, including 3 key targets (PTGS2, NOS3, MPO). Pathway analysis showed 10 significant related pathways and 29 biological processes. P. lobata and P. thomsonii inhibited platelet aggregation by upregulating PGI2 and downregulating TXA2, inhibited PTGS2 to reduce inflammation, and increased the level of eNOS to promote vasodilation. In addition, P. lobata and P. thomsonii alleviated oxidative stress by increasing SOD levels and significantly decreasing MDA contents.

CONCLUSION

The results of the study further clarify the antithrombotic mechanism of action of P. lobata and P. thomsonii, which provides a scientific basis for the development of new drugs for thrombogenic diseases and lays the foundation for the development of P. lobata and P. thomsonii herbal resources and P. lobata and P. thomsonii health products.

Modified Lipoproteins Induce Arterial Wall Inflammation During Atherogenesis

Circulating apolipoprotein B-containing lipoproteins, notably the low-density lipoproteins, enter the inner layer of the arterial wall, the intima, where a fraction of them is retained and modified by proteases, lipases, and oxidizing agents and enzymes. The modified lipoproteins and various modification products, such as fatty acids, ceramides, lysophospholipids, and oxidized lipids induce inflammatory reactions in the macrophages and the covering endothelial cells, initiating an increased leukocyte diapedesis. Lipolysis of the lipoproteins also induces the formation of cholesterol crystals with strong proinflammatory properties. Modified and aggregated lipoproteins, cholesterol crystals, and lipoproteins isolated from human atherosclerotic lesions, all can activate macrophages and thereby induce the secretion of proinflammatory cytokines, chemokines, and enzymes. The extent of lipoprotein retention, modification, and aggregation have been shown to depend largely on differences in the composition of the circulating lipoprotein particles. These properties can be modified by pharmacological means, and thereby provide opportunities for clinical interventions regarding the prevention and treatment of atherosclerotic vascular diseases.

Dysfunctional High-density Lipoprotein: The Role of Myeloperoxidase and Paraoxonase-1

Low circulating high-density lipoproteins (HDL) are not only defining criteria for metabolic syndrome, but are more generally associated with atherosclerotic cardiovascular disease (ASCVD) and other chronic diseases. Oxidative stress, a hallmark of cardio-metabolic disease, further influences HDL activity by suppressing their function. Especially the leukocyte- derived enzyme myeloperoxidase (MPO) has recently attracted great interest as it catalyzes the formation of oxidizing reactive species that modify the structure and function of HDL, ultimately increasing cardiovascular risk. Contrariwise, paraoxonase-1 (PON1) is an HDL-associated enzyme that protects HDL from lipid oxidation and then acts as a protective factor against ASCVD. It is noteworthy that recent studies have demonstrated how MPO, PON1 and HDL form a functional complex in which PON1 partially inhibits the MPO activity, while MPO in turn partially inactivates PON1.In line with that, a high MPO/PON1 ratio characterizes patients with ASCVD and metabolic syndrome and has been suggested as a potential marker of dysfunctional HDL as well as a predictor of ASCVD. In this review, we summarize the evidence on the interactions between MPO and PON1 with regard to their structure, function and interaction with HDL activity. We also provide an overview of in vitro and experimental animal models, finally focusing on clinical evidence from a cohort of patients with ASCVD and metabolic syndrome.

Carbamylated HDL and Mortality Outcomes in Type 2 Diabetes

OBJECTIVE

Carbamylation is part of the aging process and causes adverse changes in the structure and function of proteins. Lipoproteins are subjected to carbamylation. We investigated the usefulness of carbamylated HDL as a prognostic indicator of survival in patients with type 2 diabetes and the association with mortality outcomes.

RESEARCH DESIGN AND METHODS

Baseline plasma carbamylated HDL was measured by ELISA in a cohort of 1,517 patients with type 2 diabetes. The primary outcome was all-cause mortality, and the secondary outcomes were cause-specific deaths, including cardiovascular, renal, infection, and cancer related.

RESULTS

Over a median follow-up of 14 years, 292 patients died, and the mortality rate was 14.5 per 1,000 person-years. Plasma carbamylated HDL level was higher in those with a fatal outcome (46.1 ± 17.8 µg/mL vs. 32.9 ± 10.7; P < 0.01). Patients in the third (hazard ratio [HR] 2.11; 95% CI 1.40-3.17; P < 0.001) and fourth quartiles (HR 6.55; 95% CI 4.67-9.77; P < 0.001) of carbamylated HDL had increased mortality risk. After adjustment for conventional risk factors, elevated carbamylated HDL was independently associated with all-cause mortality (HR 1.39; 95% CI 1.28-1.52; P < 0.001) as well as with all the cause-specific mortalities. Adding plasma carbamylated HDL level improved the power of the multivariable models for predicting all-cause mortality, with significant increments in C index (from 0.78 to 0.80; P < 0.001), net reclassification index, and integrated discrimination improvement.

CONCLUSIONS

Carbamylation of HDL renders HDL dysfunctional, and carbamylated HDL is independently associated with mortality outcomes in patients with type 2 diabetes.

Association of carbamylated high-density lipoprotein with coronary artery disease in type 2 diabetes mellitus: carbamylated high-density lipoprotein of patients promotes monocyte adhesion

BACKGROUND

Increasing evidence showed that carbamylated lipoprotein accelerated atherosclerosis. However, whether such modification of high-density lipoprotein (HDL) particles alters in type 2 diabetes mellitus (T2DM) patients and facilitates vascular complications remains unclear. We aimed to investigate the alteration of the carbamylation in HDL among T2DM patients and clarify its potential role in atherogenesis.

METHODS

A total of 148 consecutive T2DM patients undergoning angiography and 40 age- and gender-matched control subjects were included. HDL was isolated from plasma samples, and the concentration of HDL carbamyl-lysine (HDL-CBL) was measured. Furthermore, the HDL from subjects and in-vitro carbamylated HDL (C-HDL) was incubated with endothelial cells and monocyte to endothelial cell adhesion. Adhesion molecule expression and signaling pathway were detected.

RESULTS

Compared with the control group, the HDL-CBL level was remarkably increased in T2DM patients (6.13 ± 1.94 vs 12.00 ± 4.06 (ng/mg), P < 0.001). Of note, HDL-CBL demonstrated a more significant increase in T2DM patients with coronary artery disease (CAD) (n = 102) than those without CAD (n = 46) (12.75 ± 3.82 vs. 10.35 ± 4.11(ng/mg), P = 0.001). Multivariate logistic regression analysis demonstrated that higher HDL-CBL level was independently associated with a higher prevalence of CAD in diabetic patients after adjusting for established cofounders (adjusted odds ratio 1.174, 95% confidence Interval 1.045-1.319, p = 0.017). HDL from diabetic patients with CAD enhanced greater monocyte adhesion than that from the non-CAD or the control group (P < 0.001). Such pro-atherogenic capacity of diabetic HDL positively correlated with HDL-CBL level. Furthermore, in-vitro incubation of carbamylated HDL (C-HDL) with endothelial promoted monocyte to endothelial cell adhesion, induced upregulation of cell adhesion molecules expression, and activated NF-κB/p65 signaling in endothelial cells. Inhibiting carbamylation of HDL or NF-κB activation attenuated the monocyte to endothelial cell adhesion and cell surface adhesion molecules expression.

CONCLUSIONS

Our study identified elevated carbamylation modification of HDL from T2DM patients, especially in those with concomitant CAD. We also evidenced that C-HDL enhanced monocyte to endothelial cell adhesion, indicating a potential pro-atherogenic role of C-HDL in atherosclerosis among T2DM patients. Trial registration https://register.clinicaltrials.gov , NCT04390711 Registered on 14 May 2020; Retrospectively registered.

Novel biomarkers for the evaluation of aging-induced proteinopathies

Proteinopathies are characterized by aging related accumulation of misfolded protein aggregates. Irreversible covalent modifications of aging proteins may significantly affect the native three dimentional conformation of proteins, alter their function and lead to accumulation of misfolded protein as dysfunctional aggregates. Protein misfolding and accumulation of aberrant proteins are known to be associated with aging-induced proteinopathies such as amyloid ß and tau proteins in Alzheimer's disease, α-synuclein in Parkinson's disease and islet amyloid polypeptides in Type 2 diabetes mellitus. Protein oxidation processes such as S-nitrosylation, dityrosine formation and some of the newly elucidated processes such as carbamylation and citrullination recently drew the attention of researchers in the field of Gerontology. Studying over these processes and illuminating their relations between proteinopathies may help to diagnose early and even to treat age related disorders. Therefore, we have chosen to concentrate on aging-induced proteinopathic nature of these novel protein modifications in this review.

Carbamylated Lipoproteins and Progression of Diabetic Kidney Disease

BACKGROUND AND OBJECTIVES

Protein carbamylation is a consequence of uremia and carbamylated lipoproteins contribute to atherogenesis in CKD. Proteins can also be carbamylated by a urea-independent mechanism, and whether carbamylated lipoproteins contribute to the progression of CKD has not been investigated.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A case-control study was performed to determine whether there were changes in plasma levels of carbamylated lipoproteins in individuals with type 2 diabetes with eGFR >60 ml/min per 1.73 m² compared with a group of age- and sex-matched healthy controls. A cohort of 1320 patients with type 2 diabetes with baseline eGFR ≥30 ml/min per 1.73 m² was longitudinally followed up to evaluate the association between carbamylated lipoproteins and progression of CKD. The primary kidney outcome was defined as doubling of serum creatinine and/or initiation of KRT during follow-up. Plasma carbamylated LDLs and HDLs was measured by ELISA.

RESULTS

In individuals with diabetes with eGFR >60 ml/min per 1.73 m², both plasma carbamylated LDL and HDL levels were higher compared with healthy controls (P<0.001). After a mean follow-up of 9 years of the diabetic cohort, individuals in the top quartile of carbamylated LDL (hazard ratio, 2.21; 95% confidence interval, 1.42 to 3.46; P<0.001) and carbamylated HDL (hazard ratio, 4.53; 95% confidence interval, 2.87 to 7.13; P<0.001) had higher risk of deterioration of kidney function compared with those in the lowest quartile. On multivariable Cox regression analysis, plasma carbamylated LDL was no longer associated with kidney outcome after adjusting for baseline eGFR and potential confounding factors. However, the association between plasma carbamylated HDL and kidney outcome remained significant and was independent of HDL cholesterol.

CONCLUSIONS

Plasma carbamylated HDL but not carbamylated LDL was independently associated with progression of CKD in patients with type 2 diabetes.

Proatherogenic Importance of Carbamylation-induced Protein Damage and Type 2 Diabetes Mellitus: A Systematic Review

INTRODUCTION & BACKGROUND

Protein carbamylation is a non-enzymatic and irreversible posttranslational process. It affects functions of numerous enzymes, hormones and receptors playing several roles in diabetes pathogenesis by changing their native structures. Detrimental consequences of oxidative protein damage comprise, but are not limited to glyoxidation, lipoxidation and carbonylation reactions. Since the carbamylated plasma proteins are strongly related to the glycemic control parameters of diabetes, they may have an additive value and emerge as potential biomarkers for the follow up, prognosis and treatment of diabetes mellitus.

METHODS & RESULTS

To conduct our systematic review, we used PubMed and Semantic Scholar, and used 'Protein carbamylation and diabetes' and 'Protein carbamylation and atherosclerosis' as keywords and looked into about five hundred manuscripts. Manuscripts that are not in English were excluded as well as manuscripts that did not mention carbamylation to maintain the focus of the present article. Similar to glycation, carbamylation is able to alter functions of plasma proteins and their interactions with endothelial cells and has been shown to be involved in the development of atherosclerosis.

CONCLUSION

At this stage, it seems clear that protein carbamylation leads to worse clinical outcomes. To improve patient care, but maybe more importantly to improve healthcare-prevention, we believe the next stage involves understanding how exactly protein carbamylation leads to worse outcomes and when and in what group of people anti-carbamylation therapies must be employed.

Serum Levels of Carbamylated LDL and Soluble Lectin-Like Oxidized Low-Density Lipoprotein Receptor-1 Are Associated with Coronary Artery Disease in Patients with Metabolic Syndrome

Background and objectives: Lectin-like oxidized low density lipoprotein receptor-1 (LOX-1) has been recognized as the primary receptor for carbamylated low-density lipoproteins (cLDL) and is increasingly being viewed as a critical mediator of vascular inflammation and atherosclerosis. The aim of the current study was to evaluate the possible role of circulating cLDL and soluble LOX-1 (sLOX-1) as potential biomarkers of metabolic syndrome (MetS) as well as of coronary artery disease (CAD) among MetS patients. Materials and Methods: The serum levels of cLDL and sLOX-1 were measured by ELISA in 30 MetS patients without CAD, 30 MetS patients with CAD, and 30 healthy controls. Results: Patients with MetS had significantly higher serum levels of both cLDL and sLOX-1 than the healthy controls but lower in comparison to MetS + CAD subjects. Serum sLOX-1 concentration correlated significantly with fasting glucose (rs = 0.414, p = 0.001) and high-density lipoprotein (HDL)-cholesterol (rs = -0.273, p = 0.035) in the whole MetS cohort, whereas it correlated with cLDL only in the MetS + CAD subgroup (rs = 0.396, p = 0.030). The receiver-operating characteristic (ROC) curves of cLDL and sLOX-1 for MetS diagnosis had area under the curve (AUC) values of 0.761 and 0.692, respectively. AUC values of cLDL and sLOX-1 for CAD diagnosis among MetS patients were 0.811 and 0.739. Elevated serum levels of cLDL and sLOX-1 were associated with a higher risk of MetS development [odds ratio (OR) 24.28, 95% confidence interval (CI): 5.86-104.61, p < 0.001 and OR 4.75; 95% CI: 1.58-14.25, p = 0.009] as well as with presence of CAD among MetS subjects (OR 11.23; 95% CI: 3.10-40.71, p < 0.001 and OR 4.03; 95% CI: 1.73-11.84, p = 0.019, respectively). Conclusions: The present study underscores the potential of cLDL and sLOX-1 as promising biomarkers for diagnosis and risk assessment of MetS and CAD among the MetS population.

PON-1 carbamylation is enhanced in HDL of uremia patients

High-density lipoprotein (HDL) carbamylation has been known in uremia patients. Paraoxonase-1 (PON-1) is an important HDL protein responsible for HDL anti-oxidant, arylesterase and lactonase activities. PON-1 carbamylation in uremic HDL has never been explored. We isolated HDL from uremia patients and control healthy subjects for study. Sandwich ELISA was used to estimate carbamylated PON-1 protein expression in HDL, and nanoflow liquid chromatography-tandem mass spectrometry (nanoLC-MS/MS) was applied to identify the amino acid in PON-1 carbamylated. PON-1 enzyme activities were estimated by substrates conversion method. HDL anti-oxidant activity was gauged by fluorescence changes of indicator dye in the presence of H₂O₂. Our study results proved that the degree of PON-1 carbamylation was higher in uremic HDL than in control HDL. Sandwich ELISA study showed that carbamylated PON-1 concentration in uremic HDL was 1.49 ± 0.08 fold higher than that in HDL from controls (p < 0.05). The nanoLC-MS/MS showed that the carbamylation of lysine 290 (K290) of PON-1, a residue adjacent to PON-1 activity determining site, was detected in uremic HDL but not detected in control HDL. K290 carbamylation leads to local conformation changes that reduce accessible solvent accessibility. The HDL paraoxonase, arylesterase, and lactonase activities were all significantly lower in uremia patients than in control subjects. Additionally, HDL anti-antioxidant ability was also lower in uremia patients. Carbamylation of PON-1 in uremia patients could be one of the factors in impairing PON-1 enzyme activities and HDL anti-oxidation function.

A review of the molecular mechanisms of hyperglycemia-induced free radical generation leading to oxidative stress

The prevalence of diabetes is growing worldwide with an increasing morbidity and mortality associated with the development of diabetes complications. Free radical production is a normal biological process that is strictly controlled and has been shown to be important in normal cellular homeostasis, and in the bodies response to pathogens. However, there are several mechanisms leading to excessive free radical production that overcome the normal protective quenching mechanisms. Studies have shown that many of the diabetes complications result from excessive free radical generation and oxidative stress, and it has been shown that chronic hyperglycemia is a potent inducer for free radical production, generated through several pathways and triggering multiple molecular mechanisms. An understanding of these processes may help us to improving our preventive or therapeutic strategies. In this review, the major molecular pathways involved in free radical generation induced by hyperglycemia are described.

Chronic Kidney Disease and Disproportionally Increased Cardiovascular Damage: Does Oxidative Stress Explain the Burden?

Chronic kidney disease (CKD) patients are among the groups at the highest risk for cardiovascular disease and significantly shortened remaining lifespan. CKD enhances oxidative stress in the organism with ensuing cardiovascular damage. Oxidative stress in uremia is the consequence of higher reactive oxygen species (ROS) production, whereas attenuated clearance of pro-oxidant substances and impaired antioxidant defenses play a complementary role. The pathophysiological mechanism underlying the increased ROS production in CKD is at least partly mediated by upregulation of the intrarenal angiotensin system. Enhanced oxidative stress in the setting of the uremic milieu promotes enzymatic modification of circulating lipids and lipoproteins, protein carbamylation, endothelial dysfunction via disruption of nitric oxide (NO) pathways, and activation of inflammation, thus accelerating atherosclerosis. Left ventricular hypertrophy (LVH) and heart failure are hallmarks of CKD. NADPH oxidase activation, xanthine oxidase, mitochondrial dysfunction, and NO-ROS are the main oxidative pathways leading to LVH and the cardiorenal syndrome. Finally, a subset of antioxidant enzymes, the paraoxonases (PON), deserves special attention due to abundant clinical evidence accumulated regarding reduced serum PON1 activity in CKD as a contributor to the increased burden of cardiovascular disease. Future, meticulously designed studies are needed to assess the effects of antioxidant therapy on patients with CKD.

Mechanisms and consequences of carbamoylation

Protein carbamoylation is a non-enzymatic post-translational modification that binds isocyanic acid, which can be derived from the dissociation of urea or from the myeloperoxidase-mediated catabolism of thiocyanate, to the free amino groups of a multitude of proteins. Although the term 'carbamoylation' is usually replaced by the term "carbamylation" in the literature, carbamylation refers to a different chemical reaction (the reversible interaction of CO₂ with α and ε-amino groups of proteins). Depending on the altered molecule (for example, collagen, erythropoietin, haemoglobin, low-density lipoprotein or high-density lipoprotein), carbamoylation can have different pathophysiological effects. Carbamoylated proteins have been linked to atherosclerosis, lipid metabolism, immune system dysfunction (such as inhibition of the classical complement pathway, inhibition of complement-dependent rituximab cytotoxicity, reduced oxidative neutrophil burst, and the formation of anti-carbamoylated protein antibodies) and renal fibrosis. In this Review, we discuss the carbamoylation process and evaluate the available biomarkers of carbamoylation (for example, homocitrulline, the percentage of carbamoylated albumin, carbamoylated haemoglobin, and carbamoylated low-density lipoprotein). We also discuss the relationship between carbamoylation and the occurrence of cardiovascular events and mortality in patients with chronic kidney disease and assess the effects of strategies to lower the carbamoylation load.

Modified Lipids and Lipoproteins in Chronic Kidney Disease: A New Class of Uremic Toxins

Chronic kidney disease (CKD) is associated with an enhanced oxidative stress and deep modifications in lipid and lipoprotein metabolism. First, many oxidized lipids accumulate in CKD and were shown to exert toxic effects on cells and tissues. These lipids are known to interfere with many cell functions and to be pro-apoptotic and pro-inflammatory, especially in the cardiovascular system. Some, like F2-isoprostanes, are directly correlated with CKD progression. Their accumulation, added to their noxious effects, rendered their nomination as uremic toxins credible. Similarly, lipoproteins are deeply altered by CKD modifications, either in their metabolism or composition. These impairments lead to impaired effects of HDL on their normal effectors and may strongly participate in accelerated atherosclerosis and failure of statins in end-stage renal disease patients. This review describes the impact of oxidized lipids and other modifications in the natural history of CKD and its complications. Moreover, this review focuses on the modifications of lipoproteins and their impact on the emergence of cardiovascular diseases in CKD as well as the appropriateness of considering them as actual mediators of uremic toxicity.

Cyanate-Impaired Angiogenesis: Association With Poor Coronary Collateral Growth in Patients With Stable Angina and Chronic Total Occlusion

Background

Cyanate has recently gained attention for its role in the pathogenesis of vascular injury. Nonetheless, the effect of cyanate on angiogenesis remains unclear.

Methods and Results

In this study, we demonstrated that oral administration of cyanate impaired blood perfusion recovery in a mouse hind‐limb ischemia model. A reduction in blood perfusion recovery at day 21 was observed in the ischemic tissue of cyanate‐treated mice. Likewise, there were fewer capillaries in the ischemic hind‐limb tissue of cyanate‐exposed mice. Our in vitro study showed that cyanate, together with its carbamylated products, inhibited the migration, proliferation, and tube‐formation abilities of endothelial cells. Further research revealed that cyanate regulated angiogenesis partly by interrupting the vascular endothelial growth factor receptor 2/phosphatidylinositol 3‐kinase/Akt pathway. The serum concentrations of homocitrulline, a marker of cyanate exposure, were determined in 117 patients with stable angina and chronic total occlusion. Consistent with the antiangiogenic role of cyanate, homocitrulline levels were increased in patients with poor coronary collateralization (n=58) compared with those with high collateralization (n=59; 21.09±13.08 versus 15.54±9.02 ng/mL, P=0.009). In addition, elevated homocitrulline concentration was a strong predictor of poor coronary collateral growth.

Conclusions

Impaired angiogenesis induced by cyanate might contribute to poor coronary collateral growth.

Carbamylated Low-Density Lipoprotein (cLDL)-Mediated Induction of Autophagy and Its Role in Endothelial Cell Injury

Patients with chronic kidney disease (CKD) have high risk of cardiovascular complications. Plasma levels of carbamylated proteins produced by urea-derived isocyanate or thiocyanate are elevated in CKD patients and that they are significant predictors of cardiovascular events and all-cause mortality. Carbamylated LDL (cLDL) has pro-atherogenic properties and is known to affect major biological processes relevant to atherosclerosis including endothelial cell injury. The underlying mechanisms of cLDL-induced endothelial cell injury are not well understood. Although autophagy has been implicated in atherosclerosis, cLDL-mediated induction of autophagy and its role in endothelial cell injury is unknown. Our studies demonstrate that human coronary artery endothelial cells (HCAECs) respond to cLDL by specific induction of key autophagy proteins including LC3-I, beclin-1, Atg5, formation of lipid-conjugated LC3-II protein, and formation of punctate dots of autophagosome-associated LC3-II. We demonstrated that autophagy induction is an immediate response to cLDL and occurred in a dose and time-dependent manner. Inhibition of cLDL-induced autophagy by a specific siRNA to LC3 as well as by an autophagy inhibitor provided protection from cLDL-induced cell death and DNA fragmentation. Our studies demonstrate that autophagy plays an important role in cLDL-mediated endothelial cell injury and may provide one of the underlying mechanisms for the pathogenesis of cLDL-induced atherosclerosis in CKD patients.

Protein carbamylation is a hallmark of aging

Aging is a progressive process determined by genetic and acquired factors. Among the latter are the chemical reactions referred to as nonenzymatic posttranslational modifications (NEPTMs), such as glycoxidation, which are responsible for protein molecular aging. Carbamylation is a more recently described NEPTM that is caused by the nonenzymatic binding of isocyanate derived from urea dissociation or myeloperoxidase-mediated catabolism of thiocyanate to free amino groups of proteins. This modification is considered an adverse reaction, because it induces alterations of protein and cell properties. It has been shown that carbamylated proteins increase in plasma and tissues during chronic kidney disease and are associated with deleterious clinical outcomes, but nothing is known to date about tissue protein carbamylation during aging. To address this issue, we evaluated homocitrulline rate, the most characteristic carbamylation-derived product (CDP), over time in skin of mammalian species with different life expectancies. Our results show that carbamylation occurs throughout the whole lifespan and leads to tissue accumulation of carbamylated proteins. Because of their remarkably long half-life, matrix proteins, like type I collagen and elastin, are preferential targets. Interestingly, the accumulation rate of CDPs is inversely correlated with longevity, suggesting the occurrence of still unidentified protective mechanisms. In addition, homocitrulline accumulates more intensely than carboxymethyl-lysine, one of the major advanced glycation end products, suggesting the prominent role of carbamylation over glycoxidation reactions in age-related tissue alterations. Thus, protein carbamylation may be considered a hallmark of aging in mammalian species that may significantly contribute in the structural and functional tissue damages encountered during aging.

Association of Plasma Myeloperoxidase Level with Risk of Coronary Artery Disease in Patients with Type 2 Diabetes

Aims. This study aimed to investigate whether the change of plasma myeloperoxidase (MPO) level would be associated with the incidence of coronary artery disease (CAD) among diabetic patients. Methods. 339 patients with type 2 diabetes mellitus (DM) underwent coronary angiography. Of them, 204 cases had CAD and were assigned to CAD group and 135 cases without CAD were assigned to non-CAD group. Results. Compared to non-CAD group, CAD group had higher level of plasma MPO (p < 0.01). Multiple linear regression analysis showed that plasma MPO level was correlated with Gensini score. Multiple logistic analysis showed that the odds ratios for CAD across increasing tertiles of MPO level were 1.191 (0.971–1.547) and 1.488 (1.115–2.228) (p = 0.048, p = 0.009 versus 1st tertile of MPO level, resp.) by adjusting for age, sex, and other conventional risk factors for CAD. The subjects were stratified into nine groups according to tertiles of MPO and HbA1c. The odds ratio for CAD was significantly higher in group with highest levels of MPO and HbA1c (OR = 4.08, p < 0.01). Conclusion. Plasma MPO level was positively correlated with the degree of coronary artery stenosis in type 2 diabetic patients, and increasing blood glucose might amplify the association between MPO and CAD.

Protein carbamylation is associated with heart failure and mortality in diabetic patients with end-stage renal disease

Serum carbamylated albumin (C-Alb) levels are associated with excess mortality in patients with diabetic end stage renal disease. To gain insight into the pathophysiology of carbamylation, we determined associations between C-Alb and causes of death in patients on chronic hemodialysis. The Die Deutsche Diabetes Dialyse Studie (4D study) was a randomized controlled trial testing the effects of atorvastatin on survival in diabetic patients on dialysis during a median follow-up of 4 years. We stratified 1,161 patients by C-Alb to see if differences in carbamylation altered the effects of atorvastatin on survival. Baseline C-Alb significantly correlated with serum cardiac stress markers troponin T and N-terminal pro-B-type-natriuretic peptide, and was associated with history of heart failure and arrhythmia. C-Alb was strongly associated with 1-year adjusted risk of CV mortality, sudden cardiac death and the 4-year risk of death from congestive heart failure (Hazard Ratios of 3.06, 3.78 and 4.64, respectively), but not with myocardial infarction or stroke. Patients with low C-Alb, treated with atorvastatin, experienced a significant improvement in their 4-year survival (Hazard Ratio 0.692). High C-Alb levels are associated with ongoing cardiac damage, risk of congestive heart failure and sudden cardiac death. Thus, carbamylation and uremic cardiomyopathy are associated in patients with diabetes mellitus and kidney disease. Additionally, statins were specifically beneficial to hemodialysis patients with low C-Alb.

Modified low density lipoprotein and lipoprotein-containing circulating immune complexes as diagnostic and prognostic biomarkers of atherosclerosis and type 1 diabetes macrovascular disease

In atherosclerosis; blood low-density lipoproteins (LDL) are subjected to multiple enzymatic and non-enzymatic modifications that increase their atherogenicity and induce immunogenicity. Modified LDL are capable of inducing vascular inflammation through activation of innate immunity; thus, contributing to the progression of atherogenesis. The immunogenicity of modified LDL results in induction of self-antibodies specific to a certain type of modified LDL. The antibodies react with modified LDL forming circulating immune complexes. Circulating immune complexes exhibit prominent immunomodulatory properties that influence atherosclerotic inflammation. Compared to freely circulating modified LDL; modified LDL associated with the immune complexes have a more robust atherogenic and proinflammatory potential. Various lipid components of the immune complexes may serve not only as diagnostic but also as essential predictive markers of cardiovascular events in atherosclerosis. Accumulating evidence indicates that LDL-containing immune complexes can also serve as biomarker for macrovascular disease in type 1 diabetes.