Ufuk Çakatay

Oxidative protein damage in early stage Type 1 diabetic patients

To examine the influence of oxidative stress on oxidative protein damage, we studied 51 young Type 1 diabetic patients clinically free of complications and 48 healthy normolipidaemic age-matched controls. We determined: (1) plasma carbonyl (PCO), plasma total thiol (T-SH), and nitrotyrosine (NT) levels as markers of oxidative protein damage; (2) plasma lipid hydroperoxide (LHP), and nitric oxide (NO) levels as markers of oxidative stress; (3) plasma total antioxidant capacity (TAO), ceruloplasmin (Cp), transferrin (TRF), unsaturated iron binding capacity (UIBC), erythrocyte glutathione (GSH), and erythrocyte superoxide dismutase (SOD) as markers of free radical scavengers. There were no significant differences in the levels of these markers between prepubertal diabetic patients and the controls. The levels of both of PCO and LHP were increased in adolescent and young adult Type 1 diabetic patients with respect to their controls. In the adolescent group, patient versus control values for PCO were 1.04+/-0.067 versus 0.67+/-0.0274 nmol/mg and for LHP they were 2. 10+/-1.09 versus 1.00+/-0.4 nmol/mg. In the young adult group, patient versus control values for PCO were 0.99+/-0.054 versus 0. 66+/-0.02 nmol/mg and for LHP they were 1.96+/-0.78 versus 1.15+/-0. 4 nmol/mg. TAO levels were significantly decreased in adolescent diabetic patients compared to their controls (0.92+/-0.27 vs. 1. 86+/-0.37) and in young adult diabetic patients compared to their controls (0.80+/-0.27 vs. 2.11+/-0.54 nmol/mg). T-SH was not different between diabetic patients and the controls. Serum NT, NO, and erythrocyte SOD levels were not different either between three groups of diabetic patients or between the patients and their controls. We attribute this lack of difference to limited disease duration. Changes in markers of oxidative stress other than NT, NO, and SOD observed in adolescent and young adult early stage Type 1 diabetic patients contribute to the imbalance in the redox status of the plasma. We attribute this imbalance to metal-catalyzed protein oxidation in both groups of Type 1 diabetic patients clinically free from complications.

Relation of oxidative protein damage and nitrotyrosine levels in the aging rat brain.

An increase in oxidative stress may contribute to the development of oxidative protein damage in the aging rat brain. In the present study, we investigated the relation between nitrotyrosine levels and other oxidative protein damage parameters such as protein carbonyl and protein thiol, as well as oxidative stress parameters such as total thiol, nonprotein thiol, and lipid hydroperoxides in the brain tissue of young, adult, and old Wistar rats. Brain nitrotyrosine levels of old rats were significantly decreased compared with those of young rats. Young and adult rats were not significantly different as far as these parameters were concerned, however, brain protein carbonyl and lipid hydroperoxide levels of old rats were significantly increased compared with those of young and adult rats. On the other hand, brain tissue total thiol, nonprotein thiol, and protein thiol levels of old rats were significantly decreased compared with those of young and adult rats. The strong correlation we found between protein carbonyl and lipid hydroperoxide levels indicates a striking relation between protein oxidation and lipid peroxidation in the aging brain tissue. The results of this study suggest that protein carbonyl formation is both a sensitive and a specific marker of brain aging. However, decreased nitrotyrosine levels in old rats, in contradiction to the expected, may be due to mechanisms other than oxidative protein damage in the aging rat brain.

Relation of aging with oxidative protein damage parameters in the rat skeletal muscle

OBJECTIVES An increase in oxidative stress may contribute to the development of oxidative protein damage in the aging rat skeletal muscle. Our aim was to reveal protein carbonyl (PCO), advanced oxidation protein products (AOPP), a novel marker of oxidative stress, and protein thiol (P-SH) levels as markers of protein oxidation, as well as lipid hydroperoxide (LHP) levels as a marker of lipid peroxidation, and relation of nitrotyrosine (NT) levels with these markers in skeletal muscle tissue of young, adult, and old male Wistar rats. DESIGN AND METHODS In the present study, we investigated the relation between aging and oxidative protein damage parameters such as PCO, NT, AOPP, and P-SH, as well as oxidative stress parameters such as total thiol, nonprotein thiol, and LHP in the skeletal muscle tissue of young, adult, and old Wistar rats. RESULTS PCO and NT levels of old rats were significantly increased compared with those of young and adult rats. Skeletal muscle AOPP levels were significantly increased in old rats compared with those of adult rats. P-SH levels were significantly decreased in old rats compared with those of young rats. CONCLUSIONS The finding that the increase in PCO levels of young vs. old group was more significant than that of adult vs. old group may suggest that PCO formation is an early specific marker of aging process in skeletal muscle. In addition, increased levels of nitrotyrosine in the skeletal muscle of the old rat group may be a novel specific marker of oxidative protein damage in the aging muscle. The absence of correlation between oxidative protein damage markers mentioned above and LHP levels may indicate that protein oxidation and lipid peroxidation in the aging rat skeletal tissue are two distinct mechanisms.

Relation of plasma protein oxidation parameters and paraoxonase activity in the ageing population

The incidence of atherosclerosis increases with age. Oxidative changes in proteins and lipids are considered to be among the molecular mechanisms leading to endothelial dysfunction. Paraoxonase (PON1) is exclusively associated with high-density lipoprotein (HDL) and protects both HDL and low-density lipoprotein (LDL) from oxidation. PON1 has two cysteine residues for its antioxidant function. We investigated the relation between PON1 activity and protein oxidation parameters such as protein hydroperoxides (P-OOH), protein carbonyl (PCO), total thiol (T-SH) and advanced oxidation protein products (AOPP). Our study also covered other oxidative stress parameters such as oxidised LDL (oxLDL) and superoxide dismutase activity in the plasma of young, middle-aged and elderly individuals. PON1 activity of elderly and middle-aged individuals was decreased significantly compared with that in the young group. oxLDL levels of elderly individuals were increased significantly compared with those of both the young and middle-aged individuals. P-OOH, PCO and AOPP levels of the elderly and middle aged individuals were higher compared with those of the young. On the other hand, T-SH levels of the elderly and middle-aged individuals were lower compared with those of the young. Side by side with the decrease in the T-SH levels in the middle-aged and elderly groups as compared to the young, the increase we have observed in other protein oxidation parameters in the groups leading to decreasing PON1 activity might, we think, create a predisposition to atherosclerosis.

Effect Of α‐Lipoic Acid On Lipid Peroxidation And Anti‐Oxidant Enzyme Activities In Diabetic Rats

1. Oxidative damage has been suggested to be a contributory factor in the development and complications of diabetes. Recently, α‐lipoic acid (ALA) has gained considerable interest as an anti‐oxidant. Various studies have indicated the anti‐ oxidant effects of ALA and its reduced form dihydrolipoic acid. Therefore, it appears that these compounds have important therapeutic potential in conditions where oxidative stress is involved. The aim of the present study was to investigate the effect of ALA supplementation on lipid peroxidation and anti‐oxidant enzyme activities in various tissues in diabetic rats.

Relation between bladder cancer and protein oxidation.

DNA, protein oxidation and lipid peroxidation possess a major impact in carcinogenesis. Also, inflammatory and oxidative events have remarkable importance in bladder cancer. Thus, in this study total protein, protein carbonyl, nitrotyrosine, thiol residues, non-protein thiols, lipid peroxidation, and also, because of their relations to the above parameters, iron and iron binding levels have been investigated in patients with bladder cancer and in control group. Statistical evaluation of the results demonstrated significantly lower plasma protein levels in the patients with bladder cancer, as compared to the healthy control group. Serumiron levels in patients with invasive bladdercancer were found to be significantly lowerwhen compared with non-invasive group. Proteincarbonyl groups were remarkably higher inbladder cancer patients than in healthycontrols. Patients with bladder cancer weredemonstrated to have significantly lower levelsof total thiol groups and protein-bound thiolgroups as compared to healthy controls.Protein-bound thiol groups in patients withinvasive bladder cancer revealed a moresignificant decline, than in non-invasivegroup.

Male rats exhibit higher oxidative protein damage than females of the same chronological age

The basis of the difference in life expectancy between males and females is still unknown. Previous studies have provided compelling evidence for the presence of oxidized proteins, and lipids in advanced human atherosclerotic lesions. The gender factor responsible for such protein oxidation is unknown and controversial. Our aim was to reveal the difference between protein oxidation parameters of male and female rats of the same chronological age to understand the protein oxidation mechanisms enabling females live longer than males. In the current study, we investigated the relation between protein hydroperoxide levels (P-OOH) and other protein oxidation parameters such as protein carbonyl (PCO), total thiol (T-SH), advanced oxidation protein products (AOPP), and nitrotyrosine (NT). Our study also covered other oxidative stress parameters such as lipid hydroperoxides (L-OOH), and superoxide dismutase (SOD) activity in the plasma of male and female aged rats. Plasma P-OOH and AOPP levels of male rats were significantly higher compared with those of the female rats. T-SH levels were significantly lower in the aged male rats compared with those of the female rats. On the other hand, PCO, NT, and L-OOH levels, and SOD activity were all found to be not different. These data support the hypothesis that elevated levels of P-OOH and AOPP contribute to the extent of protein, but not lipid, oxidation in plasma of aged male rats. Furthermore, the results presented here may also rationalize studies, which have shown that protein oxidation is modulated on the basis of gender dependency.

Oxidative Protein Damage in Type I Diabetic Patients With and Without Complications

To examine the influence of oxidative stress on oxidative protein damage, we studied 47 Type I diabetic patients with and without complications. We determined plasma protein carbonyl, plasma protein thiol and nitrotyrosine levels as markers of oxidative protein damage, plasma lipid hydroperoxide levels as markers of oxidative stress, and plasma total thiol, plasma nonprotein thiol, erythrocyte glutathione, plasma ceruloplasmin, transferrin and total iron binding capacity as markers of free radical scavenging. There were no significant differences in nitrotyrosine, total plasma thiol, protein thiol, and erythrocyte glutathione levels between diabetic patients with complications and without complications. However, plasma protein carbonyl, lipid hydroperoxide, and nonprotein thiol levels were significantly increased in diabetic patients with complications compared with diabetic patients without complications. Although redox status of plasma is impaired in diabetic patients, we suppose these significantly different markers reflect enhanced oxidative protein damage in diabetic patients with complications.

Postmenopausal Hormone Replacement Therapy Use Decreases Oxidative Protein Damage

Objectives: The aim of this study is to evaluate oxidative protein damage (OPD) by investigating protein carbonyl (PCO) and nitrotyrosine (NT) levels, oxidative stress by total thiol (T-SH), erythrocyte glutathione (GSH) and nitric oxide (NO) levels in women receiving hormone replacement therapy (HRT). Materials and Methods: To examine the influence of oxidative stress on OPD, we studied 12 postmenopausal women who had received HRT for 6 months, and 13 postmenopausal women who did not receive HRT, as the control group. All subjects were non-smokers. Blood samples were drawn in the fasting state and processed within 1 h of collection. For NT and NO, serum samples were stored at –70°C until analysis; all other parameters were determined on the same day of collection. Results: After 6 months, plasma PCO and T-SH levels were decreased, GSH and NO levels were increased, and NT levels were not changed in 12 postmenopausal women receiving HRT. Except the NT levels, the rest of the parameters did not significantly change in the control group. Interestingly, mean NT levels in the control group increased significantly. Conclusions: A crucial part of the protective effect of HRT on the cardiovascular system arises secondary to the interaction between estrogen and vessel wall. Our results suggest that an important component of the mechanism underlying this interaction may depend on estrogen’s antioxidant effect and its preventive role in OPD.

EFFECTS OF HORMONE REPLACEMENT THERAPY ON LIPID PEROXIDES AND OXIDATION SYSTEM IN POSTMENOPAUSAL WOMEN

A short-term evaluation of 6 months of estrogen therapy on oxidant status in 38 postmenopausal women was conducted. The levels of serum lipid peroxidation products, glutathione (GSH) status, and glutathione-related enzymes were evaluated before and after 6 months of hormone replacement therapy. After 6 months of estrogen treatment there was a significantly increased concentration of thiobarbituric acid-reactive substances (TBARS), which are an end product of lipid peroxidation. This was accompanied by a significant increase in the activity of glutathione peroxidase (GSH-Px). However, the activities of glutathione reductase (GSSG-R) and superoxide dismutase (SOD) were significantly decreased and total protein thiols were reduced. Data suggest that hormone replacement therapy in postmenopausal women is associated with oxidant mechanisms.