Acrolein inactivates paraoxonase 1: changes in free acrolein levels after hemodialysis correlate with increases in paraoxonase 1 activity in chronic renal failure patients

Sexual dimorphism association of combined exposure to volatile organic compounds (VOC) with kidney damage

BACKGROUND

Epidemiological evidence emphasizes air pollutants' role in chronic kidney disease (CKD). Volatile organic compounds (VOCs) contribute to air pollution, yet research on VOCs and kidney damage, especially gender disparities, is limited.

METHODS

This study analyzed NHANES data to explore associations between urinary VOC metabolite mixtures (VOCMs) and key kidney-related parameters: estimated glomerular filtration rate (eGFR), albumin-to-creatinine ratio (ACR), chronic kidney disease (CKD), and albuminuria. Mediation analyses assessed the potential mediating roles of biological aging (BA) and serum albumin in VOCM mixtures' effects on kidney damage. Sensitivity analyses were also conducted.

RESULTS

The mixture analysis unveiled a noteworthy positive association between VOCM mixtures and the risk of developing CKD, coupled with a significant negative correlation with eGFR within the overall participant cohort. These findings remained consistent when examining the female subgroup. However, among male participants, no significant link emerged between VOCM mixtures and CKD or eGFR. Furthermore, in both the overall and female participant groups, there was an absence of a significant correlation between VOCM mixtures and either ACR or albuminuria. On the other hand, in male participants, while no significant correlation was detected with albuminuria, a significant positive correlation was observed with ACR. Pollutant analysis identified potential links between kidney damage and 1,3-butadiene, toluene, ethylbenzene, styrene, xylene, acrolein, crotonaldehyde and propylene oxide. Mediation analyses suggested that BA might partially mediate the relationship between VOCM mixtures and kidney damage.

CONCLUSION

The current findings highlight the widespread exposure to VOCs among the general U.S. adult population and indicate a potential correlation between exposure to VOC mixtures and compromised renal function parameters, with notable gender disparities. Females appear to exhibit greater sensitivity to impaired renal function resulting from VOCs exposure. Anti-aging treatments may offer some mitigation against kidney damage due to VOCs exposure.

Acrolein produced during acute kidney injury promotes tubular cell death

Acute kidney injury is an important global health concern as it is associated with high morbidity and mortality. Polyamines, essential for cell growth and proliferation, are known to inhibit cardiovascular disease. However, under conditions of cellular damage, toxic acrolein is produced from polyamines by the enzyme spermine oxidase (SMOX). We used a mouse renal ischemia-reperfusion model and human proximal tubule cells (HK-2) to investigate whether acrolein exacerbates acute kidney injury by renal tubular cell death. Acrolein visualized by acroleinRED was increased in ischemia-reperfusion kidneys, particularly in tubular cells. When HK-2 cells were cultured under 1% oxygen for 24 h, then switched to 21% oxygen for 24 h (hypoxia-reoxygenation), acrolein accumulated and SMOX mRNA and protein levels were increased. Acrolein induced cell death and fibrosis-related TGFB1 mRNA in HK-2 cells. Administration of the acrolein scavenger cysteamine suppressed the acrolein-induced upregulation of TGFB1 mRNA. Cysteamine also inhibited a decrease in the mitochondrial membrane potential observed by MitoTrackerCMXRos, and cell death induced by hypoxia-reoxygenation. The siRNA-mediated knockdown of SMOX also suppressed hypoxia-reoxygenation-induced acrolein accumulation and cell death. Our study suggests that acrolein exacerbates acute kidney injury by promoting tubular cell death during ischemia-reperfusion injury. Treatment to control the accumulation of acrolein might be an effective therapeutic option for renal ischemia-reperfusion injury.

Strategies for optimizing urea removal to enable portable kidney dialysis: A reappraisal

BACKGROUND

Portable hemodialysis has the potential to improve health outcomes and quality of life for patients with kidney failure at reduced costs. Urea removal, required for dialysate regeneration, is a central function of any existing/potential portable dialysis device. Urea in the spent dialysate coexists with non-urea uremic toxins, nutrients, and electrolytes, all of which will interfere with the urea removal efficiency, regardless of whether the underlying urea removal mechanism is based on urease conversion, direct urea adsorption, or oxidation. The aim of the current review is to identify the amount of the most prevalent chemicals being removed during a single dialysis session and evaluate the potential benefits of an urea-selective membrane for portable dialysis.

METHODS

We have performed a literature search using Web of Science and PubMed databases to find available articles reporting (or be able to calculate from blood plasma concentration) > 5 mg of individually quantified solutes removed during thrice-weekly hemodialysis sessions. If multiple reports of the same solute were available, the reported values were averaged, and the geometric mean of standard deviations was taken. Further critical literature analysis of reported dialysate regeneration methods was performed using Web of Science and PubMed databases.

RESULTS

On average, 46.0 g uremic retention solutes are removed in a single conventional dialysis session, out of which urea is only 23.6 g. For both urease- and sorbent-based urea removal mechanisms, amino acids, with 7.7 g removal per session, could potentially interfere with urea removal efficiency. Additionally for the oxidation-based urea removal system, plentiful nutrients such as glucose (24.0 g) will interfere with urea removal by competition. Using a nanofiltration membrane between dialysate and oxidation unit with a molecular weight cutoff (MWCO) of ~200 Da, 67.6 g of non-electrolyte species will be removed in a single dialysis session, out of which 44.0 g are non-urea molecules. If the membrane MWCO is further decreased to 120 Da, the mass of non-electrolyte non-urea species will drop to 9.3 g. Reverse osmosis membranes have been shown to be both effective at blocking the transport of non-urea species (creatinine for example with ~90% rejection ratio), and permissive for urea transport (~20% rejection ratio), making them a promising urea selective membrane to increase the efficiency of the oxidative urea removal system.

CONCLUSIONS

Compiled are quantified solute removal amounts greater than 5 mg per session during conventional hemodialysis treatments, to act as a guide for portable dialysis system design. Analysis shows that multiple chemical species in the dialysate interfere with all proposed portable urea removal systems. This suggests the need for an additional protective dialysate loop coupled to urea removal system and an urea-selective membrane.

Reduction of protein-bound uraemic toxins in plasma of chronic renal failure patients: A systematic review

BACKGROUND

Protein-bound uraemic toxins (PBUTs) accumulate in patients with chronic kidney disease and impose detrimental effects on the vascular system. However, a unanimous consensus on the most optimum approach for the reduction of plasma PBUTs is still lacking.

METHODS

In this systematic review, we aimed to identify the most efficient clinically available plasma PBUT reduction method reported in the literature between 1980 and 2020. The literature was screened for clinical studies describing approaches to reduce the plasma concentration of known uraemic toxins. There were no limits on the number of patients studied or on the duration or design of the studies.

RESULTS

Out of 1274 identified publications, 101 studies describing therapeutic options aiming at the reduction of PBUTs in CKD patients were included in this review. We stratified the studies by the PBUTs and the duration of the analysis into acute (data from a single procedure) and longitudinal (several treatment interventions) trials. Reduction ratio (RR) was used as the measure of plasma PBUTs lowering efficiency. For indoxyl sulphate and p-cresyl sulphate, the highest RR in the acute studies was demonstrated for fractionated plasma separation, adsorption and dialysis system. In the longitudinal trials, supplementation of haemodialysis patients with AST-120 (Kremezin®) adsorbent showed the highest RR. However, no superior method for the reduction of all types of PBUTs was identified based on the published studies.

CONCLUSIONS

Our study shows that there is presently no technique universally suitable for optimum reduction of all PBUTs. There is a clear need for further research in this field.

Uremic Toxins and Their Relation with Oxidative Stress Induced in Patients with CKD

The presence of toxins is believed to be a major factor in the development of uremia in patients with chronic kidney disease (CKD) and end-stage renal disease (ESRD). Uremic toxins have been divided into 3 groups: small substances dissolved in water, medium molecules: peptides and low molecular weight proteins, and protein-bound toxins. One of the earliest known toxins is urea, the concentration of which was considered negligible in CKD patients. However, subsequent studies have shown that it can lead to increased production of reactive oxygen species (ROS), and induce insulin resistance in vitro and in vivo, as well as cause carbamylation of proteins, peptides, and amino acids. Other uremic toxins and their participation in the damage caused by oxidative stress to biological material are also presented. Macromolecules and molecules modified as a result of carbamylation, oxidative stress, and their adducts with uremic toxins, may lead to cardiovascular diseases, and increased risk of mortality in patients with CKD.

Paraoxonase 1 concerning dyslipidaemia, cardiovascular diseases, and mortality in haemodialysis patients

Paraoxonase 1 (PON1) is known for preventing atherosclerosis through lipid-modifying features, antioxidant activity, anti-inflammatory, anti-apoptosis, anti-thrombosis, and anti-adhesion properties. Uremic patients requiring haemodialysis (HD) are especially prone to atherosclerosis and its complications. We analysed the PON1 gene (PON1) polymorphisms and serum PON1 (paraoxonase) activity concerning dyslipidaemia and related cardiovascular diseases and mortality to show how they associate under uremic conditions modified by maintenance HD treatment. The rs662 AA + AG (OR 1.76, 95%CI 1.10-2.80, P = 0.018), rs854560 TT (OR 1.48, 95%CI 1.04-2.11, P = 0.031), and rs854560 AT + TT (OR 1.28, 95%CI 1.01-1.63, P = 0.040) contributed to the prevalence of atherogenic dyslipidaemia diagnosed by the triglyceride (TG)/HDL-cholesterol ratio ≥ 3.8. The normalized serum PON1 activity positively correlated with atherogenic dyslipidaemia (ẞ 0.67 ± 0.25, P = 0.008). The PON1 rs854560 allele T was involved in the higher prevalence of ischemic cerebral stroke (OR 1.38, 1.02-1.85, P = 0.034). The PON1 rs705379 TT genotype contributed to cardiovascular (HR 1.27, 95% CI 1.03-1.57, P = 0.025) and cardiac (HR 1.34, 95% CI 1.05-1.71, P = 0.018) mortality. All P-values were obtained in multiple regression analyses, including clinical variables. Multifaceted associations of PON1 with dyslipidaemia, ischemic cerebral stroke, and cardiovascular mortality in HD patients provide arguments for the consideration of PON1 and its protein product as therapeutic targets in the prevention of atherosclerosis and its complications in uremic patients.

Association of Serum Paraoxonase/Arylesterase Activity With All-Cause Mortality in Maintenance Hemodialysis Patients

CONTEXT

In end-stage renal disease (ESRD), serum high-density lipoprotein cholesterol (HDL-C) level is not an accurate predictor of mortality, partly because it does not necessarily correlate with indices of HDL function. Paraoxonase (PON) is a major enzyme constituent of HDL and a key component of HDL antioxidant activity. Apolipoprotein A-I (Apo A-1) is the core HDL structural protein that plays a major role in various aspects of HDL function.

OBJECTIVE

We sought to examine PON activity and Apo A-I levels in patients with ESRD vs healthy controls.

DESIGN AND SETTING

PON/arylesterase activity was measured in 499 patients with maintenance hemodialysis (MHD) and 24 healthy controls with similar distributions of age, sex, and race/ethnicity. Serum acrolein-modified Apo A-I was measured in 30 patients with MHD and 10 healthy controls.

MAIN OUTCOME MEASURES

Multilevel Cox models were used to assess associations among PON activity, Apo A-I, and HDL-C levels with 12-month all-cause mortality.

RESULTS

PON activity was significantly lower in patients with MHD vs controls. Furthermore, acrolein-modified Apo A-I levels were higher in patients with MHD vs controls. In fully adjusted models, high PON activity was associated with lower 12-month mortality, whereas no difference of mortality risk was observed across HDL-C levels. The combination of high PON and low Apo A-I compared with low PON and low Apo A-I was associated with lower mortality risk.

CONCLUSIONS

In patients with MHD, PON activity had a stronger association with 12-month mortality than HDL-C. Future studies are needed to examine the role of these markers as potential diagnostic and therapeutic tools in ESRD.

Circulating Lactonase Activity but Not Protein Level of PON-1 Predicts Adverse Outcomes in Subjects with Chronic Kidney Disease

The burden of cardiovascular disease and death in chronic kidney disease (CKD) outpaces that of the other diseases and is not adequately described by traditional risk factors alone. Diminished activity of paraoxonase (PON)-1 is associated with increased oxidant stress, a common feature underlying the pathogenesis of CKD. We aimed to assess the prognostic value of circulating PON-1 protein and PON lactonase activity on adverse clinical outcomes across various stages and etiologies of CKD. Circulating PON-1 protein levels and PON lactonase activity were measured simultaneously in patients with CKD as well as a cohort of apparently healthy non-CKD subjects. Both circulating PON-1 protein levels and PON lactonase activity were significantly lower in CKD patients compared to the non-CKD subjects. Similarly, across all stages of CKD, circulating PON-1 protein and PON lactonase activity were significantly lower in patients with CKD compared to the non-CKD controls. Circulating PON lactonase activity, but not protein levels, predicted future adverse clinical outcomes, even after adjustment for traditional risk factors. The combination of lower circulating protein levels and higher activity within the CKD subjects were associated with the best survival outcomes. These findings demonstrate that diminished circulating PON lactonase activity, but not protein levels, predicts higher risk of future adverse clinical outcomes in patients with CKD.

Uremic toxins: some thoughts on acrolein and spermine

Chronic kidney disease (CKD) is characterized by the progressive reduction of glomerular filtration rate and subsequent retention of organic waste compounds called uremic toxins. While patients with CKD are at a higher risk of premature death due to cardiovascular complications, this increased risk cannot be completely explained by classical cardiovascular risk factors such as hypertension, diabetes mellitus, and obesity. Instead, recent research suggests that uremic toxins may play a key role in explaining this marked increase in cardiovascular mortality in patients with CKD. While spermine, a tetra-amine, has previously been hypothesized to act as an uremic toxin, the following review presents a summary of recent literature that casts doubt on this assertion. Instead, acrolein, an oxidative product of spermine and the triamine spermidine, is likely responsible for the toxic effects previously attributed to spermine.

Acrolein increases macrophage atherogenicity in association with gut microbiota remodeling in atherosclerotic mice: protective role for the polyphenol-rich pomegranate juice

The unsaturated aldehyde acrolein is pro-atherogenic, and the polyphenol-rich pomegranate juice (PJ), known for its anti-oxidative/anti-atherogenic properties, inhibits macrophage foam cell formation, the hallmark feature of early atherosclerosis. This study aimed to investigate two unexplored areas of acrolein atherogenicity: macrophage lipid metabolism and the gut microbiota composition. The protective effects of PJ against acrolein atherogenicity were also evaluated. Atherosclerotic apolipoprotein E-deficient (apoE^-/-) mice that were fed acrolein (3 mg/kg/day) for 1 month showed significant increases in serum and aortic cholesterol, triglycerides, and lipid peroxides. In peritoneal macrophages isolated from the mice and in J774A.1 cultured macrophages, acrolein exposure increased intracellular oxidative stress and stimulated cholesterol and triglyceride accumulation via enhanced rates of their biosynthesis and over-expression of key regulators of cellular lipid biosynthesis: sterol regulatory element-binding proteins (SREBPs), 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGCR), and diacylglycerol acyltransferase1 (DGAT1). Acrolein-fed mice demonstrated a major shift in the gut microbiota composition, including a significant phylum-level change in increased Firmicutes and decreased Bacteroidetes. At the family level, acrolein significantly increased the prevalence of Ruminococcaceae and Lachnospiraceae of which the Coprococcus genus was significantly and positively correlated with serum, aortic and macrophage lipid levels and peroxidation. The pro-atherogenic effects of acrolein on serum, aortas, macrophages, and the gut microbiota were substantially abolished by PJ. In conclusion, these findings provide novel mechanisms by which acrolein increases macrophage lipid accumulation and alters the gut microbiota composition in association with enhanced atherogenesis. Moreover, PJ was found as an effective strategy against acrolein atherogenicity.

Homocysteine in Chronic Kidney Disease

Hyperhomocysteinemia occurs in chronic- and end-stage kidney disease at the time when dialysis or transplant becomes indispensable for survival. Excessive accumulation of homocysteine (Hcy) aggravates conditions associated with imbalanced homeostasis and cellular redox thereby resulting in severe oxidative stress leading to oxidation of reduced free and protein-bound thiols. Thiol modifications such as N-homocysteinylation, sulfination, cysteinylation, glutathionylation, and sulfhydration control cellular responses that direct complex metabolic pathways. Although cysteinyl modifications are kept low, under Hcy-induced stress, thiol modifications persist thus surpassing cellular proteostasis. Here, we review mechanisms of redox regulation and show how cysteinyl modifications triggered by excess Hcy contribute development and progression of chronic kidney disease. We discuss different signaling events resulting from aberrant cysteinyl modification with a focus on transsulfuration.

Acrolein impairs the cholesterol transport functions of high density lipoproteins

High density lipoproteins (HDL) are considered athero-protective, primarily due to their role in reverse cholesterol transport, where they transport cholesterol from peripheral tissues to the liver for excretion. The current study was designed to determine the impact of HDL modification by acrolein, a highly reactive aldehyde found in high abundance in cigarette smoke, on the cholesterol transport functions of HDL. HDL was chemically-modified with acrolein and immunoblot and mass spectrometry analyses confirmed apolipoprotein crosslinking, as well as acrolein adducts on apolipoproteins A-I and A-II. The ability of acrolein-modified HDL (acro-HDL) to serve as an acceptor of free cholesterol (FC) from COS-7 cells transiently expressing SR-BI was significantly decreased. Further, in contrast to native HDL, acro-HDL promotes higher neutral lipid accumulation in murine macrophages as judged by Oil Red O staining. The ability of acro-HDL to mediate efficient selective uptake of HDL-cholesteryl esters (CE) into SR-BI-expressing cells was reduced compared to native HDL. Together, the findings from our studies suggest that acrolein modification of HDL produces a dysfunctional particle that may ultimately promote atherogenesis by impairing functions that are critical in the reverse cholesterol transport pathway.

Activation of paraoxonase 1 after hemodialysis is associated with HDL remodeling and its increase in the HDL2 fraction and VLDL

BACKGROUND

Paraoxonase 1 (PON1) activity is lower in renal failure patients. We hypothesize that part of the salutatory effect of hemodialysis on PON1 activity that we have previously found is due to HDL remodeling and shift of PON1 among HDL particles.

METHODS

A total of 42 patients (18 females and 24 males, 63 ± 12 yr) on long-term HD, with a mean dialysis course of 6.4 yr (range 1-19 yr), were recruited. PON1 arylesterase and lactonase activities, PON1 and apolipoprotein distribution in HDL subclasses were measured by gel gradient electrophoresis and western blotting.

RESULTS

The 3 different activities of PON1 we measured were significantly lower in patients as compared to control subjects; lactonase by 11%, triesterase by 19% and arylesterase by 20%, p<0.01. HDL increased slightly by 4.6%. LDL increased by 13% and VLDL decreased by 30%. These data are compatible with enhanced lipolysis of VLDL that is transformed into LDL. VLDL-PON1 activity increases significantly by 60%. PON1 activity increases by 16% in HDL2 whereas by this approach we could determine a 10% increase in the total area under the curve corresponding to total HDL. Changes in total lactonase activity were associated with changes in VLDL-PON1 and HDL2. In parallel with PON1 activation and shifts among particles, there are significant changes in apoE which increases notably in HDL2, paralleling the changes in PON1. No significant changes in apoAI or apoA-II the main structural HDL apolipoproteins were apparent after dialysis.

CONCLUSIONS

HD produces an activation of PON1 that can be predicted in part (30%) by efficiency of dialysis and in part (25%) by PON1 shifts to HDL2or VLDL (p<0.01). The removal of inhibitors and the change in the environment of PON1 in the micro-heterogeneity of HDL subclasses optimizes PON1 activity.

Diminished antioxidant activity of high-density lipoprotein-associated proteins in chronic kidney disease

Background

Decreased serum arylesterase activity, catalyzed by the high‐density lipoprotein–associated paraoxonase (PON)‐1, is associated with increased oxidant stress and atherosclerosis risk. We sought to determine the prognostic value of serum PON‐1 activity, as monitored by PON or arylesterase activities, in subjects with chronic kidney disease (CKD), particularly in relation to established cardiac biomarkers.

Methods and Results

Serum arylesterase and PON activities were measured in sequential subjects with CKD (n=630; estimated glomerular filtration rate [eGFR] <60 mL/min per 1.73 m²) and an age‐ and sex‐matched control group of non‐CKD subjects (n=315) presenting for cardiac evaluations and prospectively followed for incident (3‐year) major adverse cardiac events (composite of death, nonfatal myocardial infarction, and stroke). Serum arylesterase activity in CKD subjects was lower compared with that in non‐CKD control subjects [median (interquartile range) 94 (77 to 112) versus 103 (85 to 121) μmol(L·min) per mL, P<0.001]; similarly, PON activity in CKD subjects was lower compared with that in non‐CKD control subjects [median (interquartile range) 474 (275 to 936) versus 586 (301 to 1118) nmol(L·min) per mL, P<0.001]. Lower serum arylesterase (hazard ratio 1.8, 95% CI 1.26 to 2.57, P<0.01) was a predictor of poorer outcomes. After adjusting for traditional risk factors and medication use, lower serum arylesterase (hazard ratio 1.55, 95% CI 1.08 to 2.23, P<0.05) still conferred an increased risk of major adverse cardiac events at 3 years.

Conclusions

In patients with CKD, decreased serum arylesterase activity, a measure of diminished antioxidant properties of PON‐1, predicts higher risk of incident long‐term adverse cardiovascular events (heart attack, stroke, or death) in multivariable models adjusting for established clinical and biochemical risk factors.

A nonradioisotope chemiluminescent assay for evaluation of 2-deoxyglucose uptake in 3T3-L1 adipocytes. Effect of various carbonyls species on insulin action

We have developed a rapid nonradioisotope chemiluminescent assay adapted to high-throughput screening experiments, to evaluate glucose uptake activity in cultured cells. For chemiluminescence quantification of 2-deoxyglucose, we used a luminol oxidation reaction after an enzymatic dephosphorylation of 2-deoxyglucose-6-phosphate. All reactions were performed at 37 °C by consecutive addition of reagents, and the assay is able to quantify 2DG in picomole per well. To confirm the reliability of this method, we have evaluated the dose-effect of insulin, GLUT4 inhibitors and insulin-sensitizing agent on 2DG uptake into 3T3-L1 cells. The results obtained with the assay for 2DG uptake in vitro in the absence or presence of insulin stimulation, were similar to those obtained by the previous radioisotopic and enzymatic methods. We have also used this assay to evaluate the effect of various reactive carbonyl and oxygen species on insulin-stimulated 2DG-uptake into adipocytes. All reactive carbonyl species tested decreased insulin-stimulated glucose uptake in a time- and dose-dependent manner without affecting basal glucose uptake in 3T3-L1 cells. 4-hydroxynonenal was found to be the most potent in the impairment of glucose uptake. This new enzymatic chemiluminescent assay is rapid and useful for measurement of 2DG uptake in insulin-responsive in cultured cells.

The human paraoxonase gene cluster as a target in the treatment of atherosclerosis

The paraoxonase (PON) gene cluster contains three adjacent gene members, PON1, PON2, and PON3. Originating from the same fungus lactonase precursor, all of the three PON genes share high sequence identity and a similar β propeller protein structure. PON1 and PON3 are primarily expressed in the liver and secreted into the serum upon expression, whereas PON2 is ubiquitously expressed and remains inside the cell. Each PON member has high catalytic activity toward corresponding artificial organophosphate, and all exhibit activities to lactones. Therefore, all three members of the family are regarded as lactonases. Under physiological conditions, they act to degrade metabolites of polyunsaturated fatty acids and homocysteine (Hcy) thiolactone, among other compounds. By detoxifying both oxidized low-density lipoprotein and Hcy thiolactone, PONs protect against atherosclerosis and coronary artery diseases, as has been illustrated by many types of in vitro and in vivo experimental evidence. Clinical observations focusing on gene polymorphisms also indicate that PON1, PON2, and PON3 are protective against coronary artery disease. Many other conditions, such as diabetes, metabolic syndrome, and aging, have been shown to relate to PONs. The abundance and/or activity of PONs can be regulated by lipoproteins and their metabolites, biological macromolecules, pharmacological treatments, dietary factors, and lifestyle. In conclusion, both previous results and ongoing studies provide evidence, making the PON cluster a prospective target for the treatment of atherosclerosis.

Paraoxonase 1 in chronic kidney failure

In this review we summarize the findings from the literature and our own laboratory on the decreased PON1 activity in renal failure, the mechanisms proposed and the effect of interventions. In addition to profound alterations in lipoproteins, reduced serum PON1 activity has been clearly established in the past decade and could contribute to accelerated development of atherosclerosis in ESRD and in HD. PON1 lactonase activity is lower in ESRD patients. Hemodialysis partially restores PON1 lactonase and the other activities. PON1 activity recovery after dialysis suggests that uremic toxins may play a mechanistic role in PON1 inactivation. Lower PON1 activity in CRF patients is associated with low thiol concentration, high CRP, and is beneficially enhanced with vitamin C and flavonoids. Changes in HDL subclasses, namely lower HDL₃ in these patients may also play a role in PON1 lower activity. Future research should focus on: (1) mechanistic studies on causes for low PON1 activity and mass; (2) prospective studies focusing on whether there is an added predictive value in measuring PON1 activity (and PON1 activity in HDL₃) in this patient population; (3) intervention studies attempting to increase PON1 activity.

Protein oxidation markers in women with and without gestational diabetes mellitus: a possible relation with paraoxonase activity

AIMS

To clarify the levels of protein oxidation markers such as protein carbonyl (PCO), protein hydroperoxides (P-OOH), advanced oxidation protein products (AOPP) and nitrotyrosine (NT), as well as antioxidative enzymes such as paraoxonase (PON-1) in women with and without gestational diabetes mellitus (GDM).

METHODS

The study was conducted on 23 women with GDM and 22 women without GDM. The levels of the P-OOH, AOPP, and PON-1 were determined by colorimetric methods; whereas NT and PCO levels were measured by ELISA.

RESULTS

The concentrations of protein oxidation markers were significantly increased and PON1 activity was significantly decreased in GDM group compared to those of normal pregnant women. The control group showed a significant negative correlation between PON-1 and PCO (r=-0.451, p=0.027); whereas in GDM group, there was a significant positive correlation between P-OOH and HbA1c (r=0.89, p=0.001). There was no significant correlation between AOPP, PON-1, P-OOH, PCO, and HbA1c in either group.

CONCLUSIONS

There is evidence of a possible association between protein oxidation and decreased PON1 activity in GDM. The increase in protein oxidation parameters in the GDM group leading to decreased PON1 activity might, we think, create a predisposition for clinical complications in GDM group.

Protein modification by acrolein: relevance to pathological conditions and inhibition by aldehyde sequestering agents

Acrolein (ACR) is a toxic and highly reactive α,β-unsaturated aldehyde widely distributed in the environment as a common pollutant and generated endogenously mainly by lipoxidation reactions. Its biological effects are due to its ability to react with the nucleophilic sites of proteins, to form covalently modified biomolecules which are thought to be involved as pathogenic factors in the onset and progression of many pathological conditions such as cardiovascular and neurodegenerative diseases. Functional impairment of structural proteins and enzymes by covalent modification (crosslinking) and triggering of key cell signalling systems are now well-recognized signs of cell and tissue damage induced by reactive carbonyl species (RCS). In this review, we mainly focus on the in vitro and in vivo evidence demonstrating the ability of ACR to covalently modify protein structures, in order to gain a deeper insight into the dysregulation of cellular and metabolic pathways caused by such modifications. In addition, by considering RCS and RCS-modified proteins as drug targets, this survey will provide an overview on the newly developed molecules specifically tested for direct or indirect ACR scavenging, and the more significant studies performed in the last years attesting the efficacy of compounds already recognized as promising aldehyde-sequestering agents.

Formaldehyde induces neurotoxicity to PC12 cells involving inhibition of paraoxonase-1 expression and activity

1. Formaldehyde (FA) has been found to cause toxicity to neurons. However, its neurotoxic mechanisms have not yet been clarified. Increasing evidence has shown that oxidative damage is one of the most critical effects of formaldehyde exposure. Paraoxonase-1 (PON-1) is a pivotal endogenous anti-oxidant. Thus, we hypothesized that FA-mediated downregulation of PON1 is associated with its neurotoxicity. 2. In the present work, we used PC12 cells to study the neurotoxicity of FA and explore whether PON-1 is implicated in FA-induced neurotoxicity. 3. We found that FA has potent cytotoxic and apoptotic effects on PC12 cells. FA induces an accumulation of intracellular reactive oxygen species along with downregulation of Bcl-2 expression, as well as increased cytochrome c release. FA significantly suppressed the expression and activity of PON-1 in PC12 cells. Furthermore, H(2)S, an endogenous anti-oxidant gas, antagonizes FA-induced cytotoxicity as well as 2-hydroxyquinoline, a specific inhibitor of PON-1, which also induces cytotoxicity to PC12 cells. 4. The results of the present study provide, for the first time, evidence that the inhibitory effect on PON-1 expression and activity is involved in the neurotoxicity of FA, and suggest a promising role of PON-1 as a novel therapeutic strategy for FA-mediated toxicity.

Acrolein scavengers: reactivity, mechanism and impact on health

Acrolein (ACR) is an α,β-unsaturated aldehyde that exists extensively in the environment and (thermally processed) foods. It can also be generated through endogenous metabolism. Its high electrophilicity makes this aldehyde notorious for its facile reaction with biological nucleophiles, leading to the modification of proteins/DNA and depletion of glutathione. Recent studies also have revealed its roles in disturbing various cell signing pathways in biological systems. With growing evidences of ACR's implication in human diseases, strategies to eliminate its hazardous impacts are of great importance. One of the intervention strategies is the application of reactive scavengers to directly trap ACR. Some known ACR scavengers include sulfur (thiol)-containing and nitrogen (amino)-containing compounds as well as the newly emerging natural polyphenols. In this review, the interactions between ACR and its scavengers are highlighted. The discussion about ACR scavengers is mainly focused on their chemical reactivity, trapping mechanisms as well as their roles extended to biological relevance. In addition to their direct trapping effect on ACR, these scavengers might possess multiple functions and offer additional benefits against ACR-induced toxicity. A comprehensive understanding of the mechanism involved may help to establish ACR scavenging as a novel therapeutic intervention against human diseases that are associated with ACR and/or oxidative stress.

Paraoxonase-1 and ischemia-modified albumin in patients with end-stage renal disease

End-stage renal disease (ESRD) with and/or without treatment by hemodialysis (HD) is associated with accelerated atherosclerosis, leading to cardiovascular disease (CVD) including acute coronary syndromes. Therefore, the regulation of CVD is a crucial issue for ESRD patients. Given the recent reports that paraoxonase-1 (PON-1) and ischemia-modified albumin (IMA) could predict CVD-related mortality in ESRD, the two recent biomarkers may be useful for preventive strategies for CVD. This review paper presents current data on the relationships between PON-1, IMA, and ESRD. Many studies have shown that circulating PON-1 activity is lower in ESRD patients, and we have shown that its levels increase after HD. Although circulating IMA levels can increase before HD in ESRD patients, there remains to be little data. Our pilot study has shown a significant inverse correlation between PON-1 and IMA in ESRD patients. Although the pathogenic link between PON-1 and IMA remains speculative, considering both biomarkers may provide new insights into the prevention of CVD in ESRD patients.

Effect of reactive oxygen and carbonyl species on crucial cellular antioxidant enzymes

Numerous reactive oxygen species (ROS) and reactive carbonyl species (RCS) issuing from lipid and sugar oxidation are known to damage a large number of proteins leading to enzyme inhibition and alteration of cellular functions. Whereas studies in literature only focus on the reactivity of one or two of these compounds, we aimed at comparing in the same conditions of incubations (4 and 24h at 37°C) the effects of both various RCS (4-hydroxynonenal, 4-hydroxyhexenal, acrolein, methylglyoxal, glyoxal, malondialdehyde) and ROS (H₂O₂, AAPH) on the activity of key enzymes involved in cellular oxidative stress: superoxide dismutase (Cu,Zn-SOD), glutathione peroxidase (GPx), glutathione S-transferase (GST) and glucose-6-phosphate dehydrogenase (G6PDH). This was realized both in vitro on purified proteins and MIAPaCa-2 cells. Incubation of these enzymes with RCS resulted in a significant time- and concentration-dependent inhibition for both pure enzymes and in cell lysates. Among all RCS and ROS, hydroxynonenal (HNE) was observed as the most toxic for all studied enzymes except for SOD and is followed by hydrogen peroxide. At 100μM, HNE resulted in a 50% reduction of GPx, 56% of GST, 65% of G6PDH, and only 10% of Cu,Zn-SOD. Meanwhile it seems that concentrations used in our study are closer to biological conditions for ROS than for RCS. H₂O₂ and AAPH-induced peroxyl radicals may be probably more toxic towards the studied enzymes in vivo.

Atherosclerosis in chronic kidney disease: the role of macrophages

Patients with chronic kidney disease (CKD) are at increased risk of atherosclerotic cardiovascular disease and loss of renal parenchyma accelerates atherosclerosis in animal models. Macrophages are central to atherogenesis because they regulate cholesterol traffic and inflammation in the arterial wall. CKD influences macrophage behavior at multiple levels, rendering them proatherogenic. Even at normal creatinine levels, macrophages from uninephrectomized Apoe(-/-) mice are enriched in cholesterol owing to downregulation of cholesterol transporter ATP-binding cassette subfamily A member 1 levels and activation of nuclear factor κB, which leads to impaired cholesterol efflux. Interestingly, treatment with an angiotensin-II-receptor blocker (ARB) improves these effects. Moreover, atherosclerotic aortas from Apoe(-/-) mice transplanted into renal-ablated normocholesterolemic recipients show plaque progression and increased macrophage content instead of the substantial regression seen in recipient mice with intact kidneys. ARBs reduce atherosclerosis development in mice with partial renal ablation. These results, combined with the clinical benefits of angiotensin-converting-enzyme (ACE) inhibitors and ARBs in patients with CKD, suggest an important role for the angiotensin system in the enhanced susceptibility to atherosclerosis seen across the spectrum of CKD. The role of macrophages could explain why these therapies may be effective in end-stage renal disease, one of the few conditions in which statins show no clinical benefit.

Trifluoroethanol increases albumin's susceptibility to chemical modification

Acrolein-dependent chemical modification is implicated in the etiology of postoperative cognitive dysfunction (POCD). We examined this process further using human serum albumin (HSA), which is a target of acrolein modification and contains anesthetic binding sites. We tested whether trifluoroethanol (TFE), which mimics inhaled anesthetics, affects the susceptibility of HSA to modification by acrolein. We observed that acrolein promoted the formation of fluorescent adducts. TFE (10%) increased the amount of acrolein-HSA adducts. TFE (40%) caused a 5-fold increase in adduct formation. Acrolein also increased tryptophan anisotropy of HSA, which was further increased by TFE (10%). Acrolein-induced protein cross-linking was also increased in the presence of TFE (40%). These observations suggest that TFE promotes acrolein-induced modification of HSA, supporting a putative mechanism for POCD.

Antithrombin activity is inhibited by acrolein and homocysteine thiolactone: Protection by cysteine

Conditions in which serum or tissue acrolein levels are high (e.g.: renal failure, heavy smoking, oxidative stress) are also associated with increased thrombogenicity. Another emerging cardiovascular risk factor is homocysteine, and its derivative, homocysteine thiolactone. Antithrombin is one of the most important inhibitors of blood coagulation Since its activation by heparin binding requires critical interactions involving 3 Lys residues; we hypothesized that acrolein or homocysteine thiolactone impair antithrombin activity. When we incubated human antithrombin with increasing concentrations of acrolein (0-2 mmol/L) over a short period of time (0-4 h), a time and concentration dependent loss of activity was apparent (IC(50)=0.25 mmol/L). At 2 mmol/L, maximum inhibition (60%) is achieved at 1 h. This loss of activity was mirrored by changes in the electrophoretic pattern (homogeneity of the native antithrombin band as well as polymerization). In the same conditions, homocysteine thiolactone produces a significant, yet far less pronounced effect; acrolein being 3 times more potent than homocysteine thiolactone. When antithrombin was co-incubated with acrolein and cysteine, only less than 10% of antithrombin activity was lost. Aminoguanidine or carnosine displayed a significant yet, minor protective effect. The results suggest that in conditions where circulating or local acrolein concentrations are increased (atheroma plaque, thrombosis, sites of lipoperoxidation, smokers), acrolein-mediated loss of antithrombin activity could be a plausible phenomenon. This could contribute to explain increased thrombogenicity in smokers and in other conditions, as well as pointing at dietary intervention or the use of thiol-conserving reducing compounds as putative coadjuvant therapeutic measures.

Lipid peroxidation in hemodialysis patients: effect of vitamin C supplementation

OBJECTIVES

Renal failure is associated with several metabolic disturbances and increasing evidences support a role of oxidative stress and impaired antioxidant defence in the pathologic mechanisms that may contribute to accelerated atherogenesis in these patients. Aim of the study was to further investigate the relationship between oxidative stress and chronic renal failure.

DESIGN AND METHODS

We compared the paraoxonase (PON1) activity, the levels of lipid hydroperoxides and AGE adducts in plasma of hemodialysis patients before and after intravenous administration of vitamin C.

RESULTS

An increase in lipid hydroperoxides, AGE adducts and a decrease in the activity of PON1 were observed in patients with respect to controls. The comparison before and after supplementation with vitamin C showed an increase of PON1 activity and a decrease of AGE and lipid hydroperoxides levels.

CONCLUSIONS

The results provide further evidence that lipid peroxidation and impairment of antioxidant system in plasma of patients may play a role in renal disease and suggest that evaluation of PON1 activity could represents an useful approach to monitor antioxidant treatment and new dialysis therapies.