Advanced oxidation protein products (AOPP): novel uremic toxins, or components of the non-enzymatic antioxidant system of the plasma proteome?

Black currant anthocyanins normalized abnormal levels of serum concentrations of endothelin-1 in patients with glaucoma

PURPOSE

Our recent study, which involved a randomized, placebo-controlled, double-masked 24-month trial (Ophthalmologica 2012;228:26-35), revealed that oral administration of black currant anthocyanins (BCACs) slowed down the visual field deterioration and elevation of ocular blood flow of open-angle glaucoma (OAG). To elucidate the underlying mechanisms of these BCAC-induced effects, as possible factors affecting glaucomatous optic neuropathy, changes of serum endothelin-1 (ET-1), nitric oxide (NO), and antioxidative activities were examined in the present study.

METHODS

From among patients with OAG who participated in the randomized, placebo-controlled, double-masked trial, serum specimens were obtained from BCAC-treated (n=19) or placebo-treated (n=19) patients at baseline and every 6 months. Healthy volunteers (n=20) with age and gender matching the patients were used as a control. Serum ET-1 concentration, [NO2(-)] and [NO2(-) + NO3(-)] levels, advanced oxidation protein products (AOPP), and antioxidant activities were measured by using commercially available kits.

RESULTS

At the trial baseline, serum ET-1 concentrations were significantly lower in patients with OAG (BCACs, 3.18±1.06 pg/mL; placebo, 3.44±0.84 pg/mL) than those in healthy volunteers (4.38±1.03 pg/mL) (one-way analysis of variance and a Tukey's multiple comparison post hoc test, P<0.05). Upon administration of BCACs, serum ET-1 concentrations increased to the levels of those in healthy volunteers during the 24-month period. In contrast, those of placebo-treated patients remained at lower levels (3.82±1.14 pg/mL). While [NO2(-)] and [NO2(-)+NO3(-)] levels, AOPP, and antioxidative activities of patients from both the BCACs and placebo groups showed comparable levels to those of healthy subjects at baseline, no significant changes were observed during the observational period in either the BCAC or placebo groups.

CONCLUSIONS

Among the possible beneficial effects of BCACs toward visual field progression in patients with OAG, our present results suggest that BCACs caused normalization of serum ET-1 levels, and this may modulate ET-1-dependent regulation of the ocular blood hemodynamics.

Redox albuminomics: oxidized albumin in human diseases

SIGNIFICANCE

Albumin is the major contributor to colloid oncotic pressure and also serves as an important carrier protein of many endogenous and exogenous molecules throughout the body. In blood and extravascular fluids, albumin is susceptible to different oxidative modifications, especially thiol oxidation and carbonylation. Because of its metal-binding properties and the redox properties of its Cys34 thiol, albumin displays an important antioxidant activity. As albumin is the predominant protein in most body fluids, its Cys34 represents the largest fraction of free thiols within body fluids.

RECENT ADVANCES

Evidence that albumin oxidation takes place in vivo has been reported only recently. Different redox proteomic, mass spectrometric, and chromatographic techniques have shown albumin redox modifications in various human pathophysiological conditions. As a whole, most data here presented demonstrate that massive albumin oxidation occurs in vivo in different biological fluids and, to some extent, that this process is correlated to organ dysfunction.

CRITICAL ISSUES

Recent reports suggest that the albumin redox state may serve as a global biomarker for the redox state in the body in various human diseases. However, further study is required to elucidate the exact relationship between albumin oxidation and pathology. In addition, it is unknown if some albumin oxidized forms may also have diagnostic uses.

FUTURE DIRECTIONS

Application of specific redox proteomics techniques for the characterization of oxidized albumin forms in screening studies is required. A further challenge will be to analyze how these oxidative albumin modifications are related to real impact to the body.

Redox proteomics in study of kidney-associated hypertension: new insights to old diseases

SIGNIFICANCE

The kidney helps to maintain low blood pressure in the human body, and impaired kidney function is a common attribute of aging that is often associated with high blood pressure (hypertension). Kidney-related pathologies are important contributors (either directly or indirectly) to overall human mortality. In comparison with other organs, kidney has an unusually wide range of oxidative status, ranging from the well-perfused cortex to near-anoxic medulla.

RECENT ADVANCES

Oxidative stress has been implicated in many kidney pathologies, especially chronic kidney disease, and there is considerable research interest in oxidative stress biomarkers for earlier prediction of disease onset. Proteomics approaches have been taken to study of human kidney tissue, serum/plasma, urine, and animal models of hypertension.

CRITICAL ISSUES

Redox proteomics, in which oxidative post-translational modifications can be identified in protein targets of oxidative or nitrosative stress, has not been very extensively pursued in this set of pathologies.

FUTURE DIRECTIONS

Proteomics studies of kidney and related tissues have relevance to chronic kidney disease, and redox proteomics, in particular, represents an under-exploited toolkit for identification of novel biomarkers in this commonly occurring pathology.

Salivary markers of oxidative stress are related to age and oral health in adult non-smokers

BACKGROUND

Salivary concentrations of thiobarbituric acid-reacting substances (TBARS) are associated with the periodontal status assessed as papillary bleeding index (PBI). Whether this association is age independent is currently unclear. Salivary concentrations of advanced oxidation protein products (AOPPs) and advanced glycation end products (AGEs) have not been assessed in relation to age or oral health yet. The aim of our study was to analyse salivary markers of oxidative stress in dental patients in relation to age, gender and oral health.

METHODS

Consecutive adult non-smoking dental patients were enrolled (n = 204; aged 19-83 years). PBI and the caries index (CI) were assessed. Markers of oxidative stress, such as TBARS, AOPPs and AGEs, and the total antioxidant capacity (TAC) were measured in saliva samples taken before clinical examination.

RESULTS

Linear regression showed that salivary TBARS, AGEs and TAC significantly increase with age (r squared = 5.3%, 2.1% and 5%, respectively). PBI is an independent predictor of salivary TBARS (r squared = 5.5%), and the CI negatively affected AOPPs (r = 3.2%) and positively affected TBARS (r = 2.5%). Gender did not affect any of the analysed parameters.

CONCLUSIONS

Age as a significant contributor to the variance should be taken into account in studies focusing on salivary markers of oxidative stress. The relationship between PBI and salivary TBARS confirms results from previous studies. In addition, our results show that the association is age independent. Negative association between the CI and AOPPs might be related to recent findings that AOPP might be actually a marker of non-enzymatic antioxidant status.

Relationship of advanced oxidative protein products in human saliva and plasma: age- and gender-related changes and stability during storage

The blood levels of advanced oxidative protein products (AOPP) elevate in aging and age-related diseases. However, saliva AOPP in healthy humans have been unexplored. Thus, we investigated 143 Chinese healthy adults to assay age- and gender-related changes in saliva and plasma AOPP levels and the stability of saliva AOPP stored both at - 20°C and - 80°C. We found the mean AOPP levels in saliva and plasma of 119 subjects were 7.51 ± 3.20 and 28.31 ± 5.53 μmol/L (μM). An age-dependent increase was observed in both saliva and plasma AOPP levels. This increase was particularly significant in the elderly subjects compared with that in the young and middle-aged ones. A significant positive correlation among age, saliva and plasma AOPP levels was observed. No gender-dependent difference was observed in either saliva or plasma AOPP levels during the aging process. Furthermore, AOPP levels in the 24 saliva samples showed no significant change at every successive determination during 4 weeks at - 80°C, whereas those levels significantly increased after 7 days of storage at - 20°C. These results indicate the feasibility to screen aging biochemical indicators using saliva AOPP as an alternative to blood AOPP. Saliva AOPP samples are suitable to be stored at - 80°C.