Responses of thiols to an oxidant challenge: differences between blood and tissues in the rat

Research progress of using micro/nanomotors in the detection and therapy of diseases related to the blood environment

Micro/nanomotors bring new possibilities for the detection and therapy of diseases related to the blood environment with their unique motion effect. This work reviews the research progress of using micro/nanomotors in the detection and therapy of diseases related to the blood environment. First, we outline the advantages of using micro/nanomotors in blood-related disease detection. To be specific, the motion capability of micro/nanomotors can increase plasma or blood fluid convection and accelerate the interaction between the sample and the capture probe. This allows the effective reduction of the amount of reagents and treatment steps. Therefore, the application of micro/nanomotors significantly improves the analytical performance. Second, we discuss the key challenges and future prospects of micro/nanomotors in the treatment of blood-environment related diseases. It is very important to design a unique treatment plan according to the etiology and specific microenvironment of the disease. The next generation of micro/nanomotors is expected to bring exciting progress to the detection and therapy of blood-environment related diseases.

Keap1 redox-dependent regulation of doxorubicin-induced oxidative stress response in cardiac myoblasts

Doxorubicin (DOX) is a widely prescribed treatment for a broad scope of cancers, but clinical utility is limited by the cumulative, dose-dependent cardiomyopathy that occurs with repeated administration. DOX-induced cardiotoxicity is associated with the production of reactive oxygen species (ROS) and oxidation of lipids, DNA and proteins. A major cellular defense mechanism against such oxidative stress is activation of the Keap1/Nrf2-antioxidant response element (ARE) signaling pathway, which transcriptionally regulates expression of antioxidant genes such as Nqo1 and Gstp1. In the present study, we address the hypothesis that an initial event associated with DOX-induced oxidative stress is activation of the Keap1/Nrf2-dependent expression of antioxidant genes and that this is regulated through drug-induced changes in redox status of the Keap1 protein. Incubation of H9c2 rat cardiac myoblasts with DOX resulted in a time- and dose-dependent decrease in non-protein sulfhydryl groups. Associated with this was a near 2-fold increase in Nrf2 protein content and enhanced transcription of several of the Nrf2-regulated down-stream genes, including Gstp1, Ugt1a1, and Nqo1; the expression of Nfe2l2 (Nrf2) itself was unaltered. Furthermore, both the redox status and the total amount of Keap1 protein were significantly decreased by DOX, with the loss of Keap1 being due to both inhibited gene expression and increased autophagic, but not proteasomal, degradation. These findings identify the Keap1/Nrf2 pathway as a potentially important initial response to acute DOX-induced oxidative injury, with the primary regulatory events being the oxidation and autophagic degradation of the redox sensor Keap1 protein.

N7-glycidamide-guanine DNA adduct formation by orally ingested acrylamide in rats: a dose-response study encompassing human diet-related exposure levels

Acrylamide (AA) is formed during the heating of food and is classified as a genotoxic carcinogen. The margin of exposure (MOE), representing the distance between the bench mark dose associated with 10% tumor incidence in rats and the estimated average human exposure, is considered to be of concern. After ingestion, AA is converted by P450 into the genotoxic epoxide glycidamide (GA). GA forms DNA adducts, primarily at N7 of guanine (N7-GA-Gua). We performed a dose-response study with AA in female Sprague-Dawley (SD) rats. AA was given orally in a single dosage of 0.1-10 000 μg/kg bw. The formation of urinary mercapturic acids and of N7-GA-Gua DNA adducts in liver, kidney, and lung was measured 16 h after application. A mean of 37.0 ± 11.5% of a given AA dose was found as mercapturic acids (MAs) in urine. MA excretion in urine of untreated controls indicated some background exposure from endogenous AA. N7-GA-Gua adduct formation was not detectable in any organ tested at 0.1 μg AA/kg bw. At a dose of 1 μg/kg bw, adducts were found in kidney (around 1 adduct/10(8) nucleotides) and lung (below 1 adduct/10(8) nucleotides) but not in liver. At 10, respectively, 100 μg/kg bw, adducts were found in all three organs, at levels close to those found at 1 μg AA/kg, covering a range of about 1-2 adducts/10(8) nucleotides. As compared to DNA adduct levels from electrophilic genotoxic agents of various origin found in human tissues, N7-GA-Gua adduct levels within the dose range of 0.1-100 μg AA/kg bw were at the low end of this human background. We propose to take the background level of DNA lesions in humans more into consideration when doing risk assessment of food-borne genotoxic carcinogens.

Low molecular mass thiols, disulfides and protein mixed disulfides in rat tissues: influence of sample manipulation, oxidative stress and ageing

Most of the data in studies investigating the contribution of oxidative stress to some human diseases and to ageing derive from measurements carried out in blood, on the basis of the assumption that any alteration of the hematic thiol/disulfide balance should reflect a corresponding alteration in other less accessible tissues. But it is evident that the information that can be gleaned from a direct analysis in specific tissues is largely greater. Nevertheless, the accurate measurement of disulfides is frequently hampered by the artifactual oxidation occurring during sample manipulation as a consequence of the presence of heme-proteins. Therefore, the levels of disulfide forms of low molecular mass thiols in tissues are still poorly investigated, even if their measurements could represent a powerful index of the oxidative status. Here we have used an artifact-free procedure to measure low molecular mass thiols and their disulfides in different rat tissues. Our findings suggest that disulfides are a reliable biomarker of even slight oxidative damage. In tissues of aged rats we observed that either oxidative stress or glutathione depletion alone can occur in different tissues during ageing. Interestingly, among the investigated thiols, only homocysteine showed a tendency to increase in some organs with ageing.

Cellular redox potential and hemoglobin S-glutathionylation in human and rat erythrocytes: A comparative study

The rat is commonly used to evaluate responses of red blood cells (RBCs) to oxidative stress. How closely the rat RBC model predicts the human RBC human response has not been well characterized. The objective of this study was to compare human and rat RBC responses to the thiol-specific oxidant tert-butylhydroperoxide by monitoring the intraerythrocyte glutathione redox potential and its correlation with hemoglobin S-glutathionylation. Changes in redox potential did not differ significantly between rat and human RBCs under the considered conditions, and both human and rat hemoglobins were apparently S-glutathionylated by a thiol-disulfide exchange mechanism with glutathione disulfide, though the extent of S-glutathionylation in rat erythrocytes was more than 10-fold higher than in human ones. On the contrary, human and rat hemoglobin S-glutathionylation differently correlated with redox potential for the glutathione redox couple, suggesting that the formation of S-glutathionylated hemoglobin was not simply a function of glutathione disulfide concentration or glutathione/glutathione disulfide ratio and that the content of reactive cysteines in hemoglobin beta globin can strongly influence intraerythrocyte glutathione metabolism and distribution between free and hemoglobin-bound forms. This study reveals fundamental physiological differences in rat and human RBCs because of differences in rat and human beta globin cysteine and reactivity, which can have important implications for the study of rat biology as a whole and for the use of rats as models for human beings under physiological and pathological circumstances and, therefore, highlights the need for caution when extrapolating rat responses to humans.

Oxidative stress induces a reversible flux of cysteine from tissues to blood in vivo in the rat

Glutathione (GSH) plays a key role in defense against oxidative stress. The availability of GSH is ensured in tissues by systems devoted to its maintenance in the reduced state and by the flux of GSH and cysteine between sites of biosynthesis and sites of utilization. Little is known about the effect of oxidative stress on the distribution of low-molecular-mass thiols and their exchange rate between tissues. In this study, we found that a slow infusion of diamide (a specific thiol-oxidizing compound) evoked a dramatic increase in blood cysteine in rats. Our data suggest that inter-organ exchange of cysteine occurs, that cysteine derives from both glutathione via gamma-glutamyl transpeptidase and methionine via homocysteine and the trans-sulfuration pathway, and that these pathways are considerably influenced by oxidative stress.

Pyruvate kinase is protected by glutathione-dependent redox balance in human red blood cells exposed to reactive oxygen species

To determine the antioxidant role of glutathione (GSH) in human red blood cells (RBCs), we investigated the effect of disrupting GSH homeostasis on the oxidative modification of thiol-dependent enzymes by exposure to tert-butyl hydroperoxide (BHP). When hemolysate was incubated with BHP, significant decreases in enzyme activity were observed. However, the inactivation did not occur in intact RBC suspensions that were exposed to BHP. In this study, we used two independent treatments aimed at decreasing the level of reduced form of GSH, pre-incubation with a glutathione reductase inhibitor or glucose-free medium to examine the influences of preventing GSH-dependent antioxidant and reactivation activity on thiol-dependent enzyme. Pyruvate kinase (PK) activity clearly decreased along with depletion of GSH compared to other glycolytic enzyme activities by BHP exposure in RBCs. The addition of GSH, but not glucose, before BHP exposure completely prevented the inactivation of PK in hemolysate; however, partial reactivation of inactivated PK was observed by post-addition of both GSH and glutaredoxin at an early stage during BHP exposure. Moreover, hydroxyl radicals but not hydrogen peroxide inactivated PK. These results suggest that PK is highly susceptible to radicals and that GSH is essential to protect PK activity by not only directly scavenging radicals but also by systematically reactivating oxidized enzyme in human RBCs.

Paraoxonase 1 (PON1) attenuates diabetes development in mice through its antioxidative properties

Paraoxonase 1 (PON1) is a lipo-lactonase which is associated with HDL and possesses antioxidative properties. Diabetes is characterized by increased oxidative stress and by decreased PON1 activity. We aimed to analyze whether oxidative status and PON1 levels in mouse sera and macrophages could affect streptozotocin (STZ)-induced diabetes development. We have used two models of mice under low oxidative stress: STZ-injected apolipoprotein E-deficient mice supplemented with the antioxidant vitamin E, and P47(phox) knockout mice. In both mice models the decreased serum basal oxidative stress, was associated with a decreased rate of diabetes development, compared with control STZ-injected apolipoprotein E-deficient mice or with C57BL mice respectively. These data suggest that oxidative stress accelerates diabetes development. Next, we analyzed the effect of PON1 on macrophage oxidative stress and on diabetes development in STZ-injected C57BL mice, PON1 knockout mice, and PON1 transgenic mice. PON1 overexpression was associated with decreased diabetes-induced macrophage oxidative stress, decreased diabetes development, and decreased mortality, in comparison to C57BL mice, and even more so when compared to PON1KO mice. We thus concluded that on increasing PON1 expression in mice, diabetes development is attenuated, a phenomenon which could be attributed to the antioxidative properties of PON1, as decrement of oxidative stress significantly attenuated STZ-induced diabetes development.

Distribution, adaptation and physiological meaning of thiols from vertebrate hemoglobins

In the present review, the sequences of hemoglobins (Hb) of 267 adult vertebrate species belonging to eight major vertebrate taxa are examined for the presence and location of cysteinyl residues in an attempt at correlation with their ecophysiology. Essentially, all vertebrates have surface cysteinyl residues in Hb molecules whereby their thiol groups may become highly reactive. Thiol-rich Hbs may display eight or more thiols per tetramer. In vertebrates so far examined, the cysteinyl residues occur in 44 different sequence positions in alpha chains and 41 positions in beta chains. Most of them are conservatively located and occur in only a few positions in Teleostei, Aves and Mammalia, whereas they are dispersed in Amphibia. The internal cysteinyl residue alpha104 is ubiquitous in vertebrates. Residue beta93 is highly conserved in reptiles, birds and mammals. The number of cysteine residues per tetramer with solvent access varies in vertebrates, mammalians and bony fish having the lowest number of external residues, whereas nearly all external cysteine residues in Aves and Lepidosauria are of the surface crevice type. In cartilaginous fish, amphibians, Crocodylidae and fresh water turtles, a substantial portion of the solvent accessible thiols are of the totally external type. Recent evidence shows that some Hb thiol groups are highly reactive and undergo extensive and reversible S-thiolation, and that they may be implicated in interorgan redox equilibrium processes. Participation of thiol groups in nitric oxide ((*)NO) metabolism has also been proved. The evidence argues for a new physiologically relevant role for Hb via involvement in free radical and antioxidant metabolism.

Involvement of vertebrate hemoglobin in antioxidant protection: chicken blood as a model

Redox balance can be described as the equilibrium between oxidative and reductive forces within the cell. These forces control several cellular events, including the modulation of redox-sensitive receptors and signaling pathways. In cells, glutathione is the major non-protein thiol and is considered the main redox buffer. The ratio between the oxidized (GSSG) and reduced (GSH) forms reflects the cellular redox balance. Reactive protein thiols, including vertebrate hemoglobin (Hb), have been proposed as effective antioxidants that can contribute to the redox balance. To further explore this possibility, chicken ( Gallus gallus (L., 1758)) blood was used as a model system. The use of known oxidants (hydroperoxides, diamide, and a system generating reactive oxygen species) originated a pattern of glutathiolation in chicken erythrocytes that was fully reversed after removal of the oxidant, this being consistent with a physiological response. The glutathiolation sequence correlates to kinetic data on chicken Hb cysteine reactivity. The major chicken hemoglobin (Hb A) is responsible for most of the glutathiolated protein where the presence of externally positioned and fast-reacting cysteines is a contributing factor. The antioxidant potential of fast-reacting Hb cysteines is in line with the conservation of cysteine residues in Hb stereochemical positions in more than 95% of the available avian Hb sequences. This may represent an evolutionary trend for the antioxidant function of externally positioned and reactive cysteines in abundant proteins.

S-Glutathionylation regulates HDL-associated paraoxonase 1 (PON1) activity

HDL-associated paraoxonase 1 (PON1) undergoes inactivation under oxidative stress and is preserved by dietary antioxidants. PON1 cysteines can affect PON1 enzymatic activities. S-Glutathionylation, a redox regulatory mechanism characterized by the formation of a mixed disulfide between a protein thiol and oxidized glutathione (GSSG), was shown to preserve some enzymes from irreversible inactivation under pathological conditions. We questioned whether PON1 activity is regulated by S-glutathionylation. Incubation of PON1 or HDL with GSSG indeed resulted in a dose-dependent inactivation of PON1 activities, including its physiological activity to increase HDL-mediated macrophage cholesterol efflux. This PON1 inactivation was associated with the formation of a mixed disulfide bond between GSSG and PON1's cysteine residue(s), as detected by immunoblotting with anti-glutathione IgG. PON1 activity was recovered following the addition of a reducing agent, DL-Dithiothreitol (DTT), to the PON1-SSG complex. We thus conclude that HDL-associated serum PON1 can undergo S-glutathionylation under oxidative stress with a consequent reversible inactivation.

Low-carbohydrate diet and oxidative stress in diabetic and nondiabetic rats

Hyperglycemia of diabetes has been implicated in increased tissue oxidative stress, with consequent development of secondary complications. Thus, stabilizing glucose levels near normal levels is of utmost importance. Because diet influences glycemic control, this study investigated whether a low-carbohydrate (5.5%) diet confers beneficial effects on the oxidative status of the heart, kidney, and liver in diabetes. Male and female normal and diabetic rats were fed standard chow (63% carbohydrates) or low-carbohydrate diet for 30 days. Elevated glucose, HbA(1c), and alanine and aspartate aminotransferases in diabetic animals were reduced or normalized by the low-carbohydrate diet. While diabetes increased cardiac activities of glutathione peroxidase and catalase, low-carbohydrate diet normalized cardiac glutathione peroxidase activity in diabetic animals, and reduced catalase activity in females. Diabetic rats fed low-carbohydrate diet had altered activities of renal glutathione reductase and superoxide dismutase, but increased renal glutathione peroxidase activity in diabetic animals was not corrected by the test diet. In the liver, diabetes was associated with a decrease in catalase activity and glutathione levels and an increase in glutathione peroxidase and gamma-glutamyltranspeptidase activities. Decreased hepatic glutathione peroxidase activity and lipid peroxidation were noted in diet-treated diabetic rats. Overall, the low-carbohydrate diet helped stabilize hyperglycemia and did not produce overtly negative effects in tissues of normal or diabetic rats.