Kinetic assay for the determination of the oxidative stress biomarker, advanced oxidation protein products (AOPP) in the human blood plasma

A number of human diseases and pathological conditions were found to be associated with increased oxidative stress. In the literature several techniques are available for the assessment of oxidative stress, but most of them are not applicable for a routine medical laboratory due to the complex methodology and/or financial reasons. We report here on a simple, inexpensive, kinetic assay for the determination of the oxidative stress biomarker, advanced oxidation protein products (AOPP) in the human blood plasma. METHODS: This study involved 70 patients (47M/23F; mean age: 64.6 y; range: 16-85) admitted to our Department with a wide range of cardiovascular and peripheral vascular diseases. Three critically ill patients were assigned for monitoring purposes. Plasma AOPP were simultaneously determined using an end-point assay as reference method and by a kinetic method developed in our laboratory. Plasma fibrinogen concentration was measured according to the Clauss method. RESULTS: There was a highly significant correlation (r2 = 0.588; p < 0.0001) between AOPP concentration (reference method) and AOPP reactivity (kinetic method). Both AOPP concentration and AOPP reactivity also significantly correlated with plasma fibrinogen concentration (r2 = 0.780; p < 0.0001; r2 = 0.564; p < 0.0001). The three representative cases presented appear to support the relevance of our novel method in the monitoring of critically ill patients. CONCLUSIONS: This simple and inexpensive kinetic assay can be widely used in any routine laboratory interested in oxidative stress research. It is especially recommended for monitoring critically ill or other patients.     

Human blood plasma advanced oxidation protein products (AOPP) correlates with fibrinogen levels

In 1996 a novel oxidative stress biomarker, referred to as advanced oxidation protein products (AOPP) was detected in the plasma of chronic uremic patients. The aim of the present studies was to find out that which plasma fraction(s) is responsible for AOPP reactivity. Thermal treatment of pooled samples of human citrate-plasma or EDTA-plasma at 50 degrees C resulted in a rapid and parallel loss of fibrinogen concentration and AOPP reactivity. On the basis of time course and t1/2 values following thermal treatment, AOPP was indistinguishable from fibrinogen. There was a statistically significant (p < 0.0001) correlation between levels of blood plasma fibrinogen and AOPP in patients (n = 61) with various peripheral vascular or cardiovascular diseases. There was also a significant (p < 0.0001) relationship between plasma levels of fibrinogen and molar AOPP/fibrinogen ratio indicating that higher fibrinogen concentrations were associated with more oxidatively transformed groups on the molecule. Results of the present studies suggest that post-translationally modified fibrinogen is a key molecule responsible for human plasma AOPP reactivity. It remains to be elucidated what is the pathophysiological significance of the post-translationally modified fibrinogen in the inflammation-associated events of atherosclerosis, in platelet aggregation, and as a cardiovascular risk biomarker.     

Human blood plasma advanced oxidation protein products (AOPP) correlates with fibrinogen levels

In 1996 a novel oxidative stress biomarker, referred to as advanced oxidation protein products (AOPP) was detected in the plasma of chronic uremic patients. The aim of the present studies was to find out that which plasma fraction(s) is responsible for AOPP reactivity. Thermal treatment of pooled samples of human citrate-plasma or EDTA-plasma at 50°C resulted in a rapid and parallel loss of fibrinogen concentration and AOPP reactivity. On the basis of time course and t_1/2 values following thermal treatment, AOPP was indistinguishable from fibrinogen. There was a statistically significant (p < 0.0001) correlation between levels of blood plasma fibrinogen and AOPP in patients (n = 61) with various peripheral vascular or cardiovascular diseases. There was also a significant (p < 0.0001) relationship between plasma levels of fibrinogen and molar AOPP/fibrinogen ratio indicating that higher fibrinogen concentrations were associated with more oxidatively transformed groups on the molecule. Results of the present studies suggest that post-translationally modified fibrinogen is a key molecule responsible for human plasma AOPP reactivity. It remains to be elucidated what is the pathophysiological significance of the post-translationally modified fibrinogen in the inflammation-associated events of atherosclerosis, in platelet aggregation, and as a cardiovascular risk biomarker.     

Oxidized proteins as a marker of oxidative stress during coronary heart surgery

The measurement of the degree of oxidative stress in patients often causes problems because of the lack of useful parameters. Therefore, we used an ELISA technique to evaluate serum protein carbonyls as a parameter of oxidative stress in patients during coronary heart surgery. Protein carbonyls were detected in serum samples of 14 patients undergoing coronary surgery and cardiopulmonary artery bypass grafting. A clear 2- to 3-fold increase in protein carbonyls in serum samples taken from human venous coronary sinus could be detected in the reperfusion period of the heart. We compared these data with markers of oxidative stress previously used, such as the glutathione status and the lipid peroxidation product malondialdehyde (MDA). Strong correlations of the protein carbonyl formation with MDA (r2 = 0.86) and oxidized glutathione (r2 = 0.81) were found in the early reperfusion stage. Increased levels of oxidized glutathione and MDA were detected only in the early reperfusion period. In contrast, the serum protein carbonyl content remained elevated for several hours, indicating a considerably slower serum clearance of oxidized proteins compared with that of lipid peroxidation products and the normalization of the glutathione status. We therefore concluded that the measurement of serum carbonyls by this ELISA technique is suitable to detect oxidative stress in serum samples of patients. The relative stability of the parameter makes the protein carbonyl detection even more valuable for clinical purposes.     

Determination of salicylate hydroxylation products as an in vivo oxidative stress marker

The in vivo measurement of highly reactive free radicals, such as the z.rad OH radical, is very difficult. New specific markers, which are based on the ability of z.rad OH to attack the benzene rings of aromatic molecules, are currently under investigation. The produced hydroxylated compounds can be measured directly. In vivo, radical metabolism of salicylic acid produces two main hydroxylated derivatives (2,3- and 2,5-dihydroxybenzoic acids). The latter acid can be also produced by enzymatic pathways through the cytochrome P-450 system, while the former acid is reported to be solely formed by direct hydroxyl radical attack. Therefore, measurement of 2, 3-DHBA, following oral administration of the drug acetyl salicylate, could be proposed for assessment of oxidative stress in vivo. In this paper, a sensitive method for the identification and quantification of hydroxylation products from the reaction of z. rad OH with salicylate in vivo is presented. It employs a high performance liquid chromatography and electrochemical detection system. A detection limit of < 1 pmol for the hydroxylation products has been achieved with linear response over at least five orders of magnitude. Using this technique, we measured plasma levels of 2,3- and 2,5-DHBA dihydroxylated derivatives and salicylic acid and determined the ratios following administration of 1 g acetyl salicylate in 20 healthy subjects.     

Plasma phosphatidylcholine hydroperoxide as a new marker of oxidative stress in alcoholic patients

Quantitative analysis of plasma phosphatidylcholine hydroperoxide (PCOOH) is an important step in evaluating the biochemical processes leading to oxidative injury. However, secondary products of lipid peroxidation are now used as indices. One hundred nine alcoholic patients, aged 22-81 years (mean +/- SEM, 52.0 +/- 1.3 years), and 21 healthy volunteers, aged 41-79 years (51.2 +/- 2.2 years), participated in this study. Plasma PCOOH was measured by HPLC with chemiluminescence detection. Plasma PCOOH concentration was significantly higher in alcoholic patients (46.1 +/- 4.1 pmol/ml) than in controls (15.6 +/- 1.8 pmol/ml). It was significantly higher in patients with blood alcohol (88.0 +/- 10.5 pmol/ml) than in those without alcohol (32.6 +/- 3.1 pmol/ml). The patients with high levels of aspartate aminotransferase, alanine aminotransferase, gamma-glutamyl transpeptidase (gamma-GTP), and triglyceride (TG) showed significantly higher PCOOH concentrations than did patients with normal levels. The PCOOH level was positively correlated with levels of gamma-GTP, HDL, blood alcohol concentration, and TG. Plasma PCOOH levels in 29 alcoholic patients after a 6 week abstinence were decreased significantly (22.8 +/- 11.1 pmol/ml), which was associated with improvement on liver function tests. This is the first measurement of plasma PCOOH in alcoholic patients. These results suggest the involvement of lipid peroxidation in alcohol-induced liver damage and confirm that the PCOOH plasma concentration is a new marker of alcohol consumption as well as oxidative stress in alcoholic patients.     

Elevated homocysteine level and prognosis in patients with acute coronary syndrome: a meta-analysis

Objective: Controversial results exist with respect to the association between elevated homocysteine level and adverse prognosis in acute coronary syndrome (ACS) patients. We performed a meta-analysis to evaluate the prognostic value of homocysteine level on ACS patients.

Materials and methods: A comprehensive literature search of PubMed and Embase databases was conducted prior to August 2018. Prospective observational studies reporting the association of baseline homocysteine level with major adverse cardiovascular events (MACE), cardiovascular or all-cause mortality in ACS patients were selected. Pooled risk ratio (RR) and corresponding 95% confidence intervals (CI) were calculated for the highest versus the lowest homocysteine level.

Results: Ten studies including 4120 ACS patients were identified. ACS patients with the highest homocysteine level had an increased risk of MACE (RR 2.01; 95% CI 1.53–2.64) and all-cause mortality (RR 2.05; 95% CI 1.50–2.79) after controlling confounding factors. However, the association between elevated homocysteine level and cardiovascular mortality (RR 1.08; 95% CI 0.83–1.39) was not statistically significant.

Conclusions: Elevated homocysteine level was associated with an increased risk of MACE and all-cause mortality among ACS patients. However, the association of elevated homocysteine level with cardiovascular mortality in ACS patients should be further confirmed in future studies.     

Plasma apolipoprotein O level increased in the patients with acute coronary syndrome

Apolipoprotein (apo) O is a novel apolipoprotein that is present predominantly in high density lipoprotein (HDL). However, overexpression of apoO does not impact on plasma HDL levels or functionality in human apoA-I transgenic mice. Thus, the physiological function of apoO is not yet known. In the present study, we investigated relationships between plasma apoO levels and high-sensitive C-reactive protein (hs-CRP) levels, as well as other lipid parameters in healthy subjects (n = 111) and patients with established acute coronary syndrome (ACS) (n = 50). ApoO was measured by the sandwich dot-blot technique with recombinant apoO as a protein standard. Mean apoO level in healthy subjects was 2.21 ± 0.83 μg/ml whereas it was 4.94 ± 1.59 μg/ml in ACS patients. There were significant differences in plasma level of apoO between two groups (P < 0.001). In univariate analysis, apoO correlated significantly with lg(hsCRP) (r = 0.48, P < 0.001) in ACS patients. Notably, no significant correlation between apoO and other lipid parameters was observed. Logistic regression analysis showed that plasma apoO level was an independent predictor of ACS (OR = 5.61, 95% CI 2.16-14.60, P < 0.001). In conclusion, apoO increased in ACS patients, and may be regarded as an independent inflammatory predictor of ACS patients.     

Quantification of noncyclooxygenase derived prostanoids as a marker of oxidative stress

Recently, we discovered there is a unique class of prostaglandin F2-like compounds that are formed in vitro from arachidonoyl-containing lipids in plasma by a free radical-catalyzed mechanism. More recent studies have elucidated that these prostanoids are also produced in vivo in humans by a similar noncyclooxygenase mechanism. Levels of these PGF2 compounds detected by a mass spectrometric assay in normal human plasma and urine range from approximately 5-50 pg/mL and 500-3000 pg/mg creatinine, respectively. Circulating levels of the compounds were shown to increase by as much as 200-fold in animal models of free radical-induced lipid peroxidation. These results suggest that quantification of these prostanoids may provide a new approach to assess oxidative stress in vivo in humans. Potential advantages of this approach are that the mass spectrometric assay has a high degree of sensitivity, accuracy, and specificity and the assay can be used to quantitate these compounds in a variety of biological fluids. In addition, quantification of these compounds is of interest because these compounds possess biological activity. Disadvantages of the assay are the potential of ex vivo formation of these compounds in biological fluids containing lipids and, further, these compounds must be differentiated from PGF2 compounds that are formed via the cyclooxygenase enzyme. In addition, because the levels of these compounds in normal human plasma and urine are relatively high, assaying these compounds in circulating plasma and urine may be somewhat insensitive for the detection of increased production at isolated sites of oxidant injury within the body, in which case sampling near localized sites of their formation may be required.(ABSTRACT TRUNCATED AT 250 WORDS)     

Breath alkanes as a marker of oxidative stress in different clinical conditions

We assessed oxidative stress in three different clinical conditions: smoking, human immunodeficiency virus (HIV) infection, and inflammatory bowel disease, using breath alkane output and other lipid peroxidation parameters such as plasma lipid peroxides (LPO) and malondialdehyde (MDA). Antioxidant micronutrients such as selenium, vitamin E, C, beta-carotene and carotenoids were also measured. Lipid peroxidation was significantly higher and antioxidant vitamins significantly lower in smokers compared to nonsmokers. Beta-carotene or vitamin E supplementation significantly reduced lipid peroxidation in that population. However, vitamin C supplementation had no effect. In HIV-infected subjects, lipid peroxidation parameters were also elevated and antioxidant vitamins reduced compared to seronegative controls. Vitamin E and C supplementation resulted in a significant decrease in lipid peroxidation with a trend toward a reduction in viral load. In patients with inflammatory bowel disease, breath alkane output was also significantly elevated when compared to healthy controls. A trial with vitamin E and C is underway. In conclusion, breath alkane output, plasma LPO and MDA are elevated in certain clinical conditions such as smoking, HIV infection, and inflammatory bowel disease. This is associated with lower levels of antioxidant micronutrients. Supplementation with antioxidant vitamins significantly reduced these lipid peroxidation parameters. The results suggest that these measures are good markers for lipid peroxidation.     

Increased oxidative stress is correlated with mitochondrial dysfunction in chagasic patients

Previously, we have shown in an experimental model of Trypanosoma cruzi infection that increased oxidative stress and antioxidant insufficiency are associated with myocardial (cellular and mitochondrial) oxidative damage and mitochondrial functional decline and might be of pathological significance in Chagas disease. In the present study, we investigated whether enhanced oxidative stress and mitochondrial functional decline are found in human chagasic patients. Our data show substantially higher plasma (two-four-fold) and mitochondrial (67%) malonylaldehyde (MDA) levels in chagasic (n = 80, group 2) compared to healthy (n = 50, group 1) subjects. Moreover, antioxidant defense was compromised in chagasic patients. Hence, we noted a 50% decline in glutathione content and losses of 31, 60, and 68% in glutathione peroxidase, superoxide dismutase (SOD), and MnSOD activities, respectively, relative to the findings in healthy controls. Further, chagasic subjects exhibited decreased mitochondrial respiratory complex (CI: 72%; CIII: 71%) activities. Nonchagasic cardiomyopathy subjects (n = 20, group 3) exhibited marginally higher plasma MDA levels compared to gp1 subjects and were not compromised in plasma antioxidant defense capacity. These data suggest that human chagasic patients sustain an antioxidant/oxidant imbalance and a mitochondrial decline of respiratory complex activities in the circulatory system. A positive correlation between increased MDA levels, MnSOD decline, and inhibition of respiratory complexes suggests that oxidative stress may contribute to mitochondrial dysfunction in chagasic patients.     

Increased susceptibility to oxidative stress as a proximate cost of reproduction

In iteroparous species high investment in current reproduction is usually paid in terms of reduced future reproduction and increased mortality. However, the proximal mechanisms of these costs remain poorly understood. Free radicals arising as by‐products of normal metabolic activities have deleterious effects on cellular proteins, lipids and DNA, and this phenomenon is known as oxidative stress. Since reproduction is an energetically demanding activity, which increases both basal and field metabolic rates, one could expect that breeding effort generates an oxidative stress whose strength depends on the availability and efficiency of antioxidant defences. In agreement with this prediction, we show here for the first time that reproduction decreases antioxidant defences, illustrating that oxidative stress represents a cost of reproduction. We suggest that increased susceptibility to oxidative stress might be a general proximal connection between reproduction and survival underlying other mechanistic links previously acknowledged.     

Ophthalmic acid is a marker of oxidative stress in plants as in animals

Background

Ophthalmic acid (OPH), γ-glutamyl-L-2-aminobutyryl-glycine, a tripeptide analogue of glutathione (GSH), has recently captured considerable attention as a biomarker of oxidative stress in animals. The OPH and GSH biosynthesis, as well as some biochemical behaviors, are very similar. Here, we sought to investigate the presence of OPH in plants and its possible relationship with GSH, known to possess multiple functions in the plant development, growth and response to environmental changes.

Salicylate hydroxylation as an early marker of in vivo oxidative stress in diabetic patients.

In vivo metabolism of salicylic acid produces two main hydroxylated derivatives (2,5- and 2,3-dihydroxybenzoic acid). The former can be produced by enzymatic pathways through the cytochrome P-450 system, while the latter is reported to be solely formed by direct hydroxyl radical attack. Therefore, measurement of 2,3-dihydroxybenzoate, following oral administration of salicylate in its acetylated form (aspirin), has been proposed for assessment of oxidative stress. In this article we report plasma levels of 2,3- and 2,5-dihydroxybenzoates following the administration of 1 g aspirin and plasma levels of thiobarbituric acid-reactive material (TBARM) in well-controlled diabetic patients and in healthy subjects. 2,3-Dihydroxybenzoate levels were significantly higher (23%) in diabetic patients than in controls (63.4 +/- 20.1 versus 49.0 +/- 6.8 nM; p < .05). On the other hand, TBARM values were not significantly different between groups. These results suggest that the method is useful to reveal in vivo oxidative stress independently from the peroxidation of lipids, and they support the hypothesis that oxygen radicals are involved in the pathogenesis of chronic complications of diabetes.     

Procalcitonin as a prognostic marker in patients with acute myocardial infarction

Background: Procalcitonin is involved in the inflammatory response and is associated with adverse prognosis in certain conditions.

Aims: To investigate the association between procalcitonin and major adverse cardiac events (MACE), left ventricular (LV) function and remodelling following acute myocardial infarction (AMI).

Methods: Plasma procalcitonin was measured in 977 patients with AMI. Subjects were followed for MACE (median 671 days). A subgroup underwent echocardiography at discharge and follow-up LV function and volume assessment.

Results: Procalcitonin was associated with MACE on uni- and multivariable analysis. Kaplan–Meier assessment revealed an adverse outcome in subjects with procalcitonin above the median. Procalcitonin was related to markers of LV dysfunction and remodelling.

Conclusion: Procalcitonin is associated with MACE, LV dysfunction and remodelling post-AMI.