The protective effect of alpha-tocopherol against dichromate-induced renal tight junction damage is mediated via ERK1/2

The effect of cereal type and α-tocopherol supplementation on selective quality and processability parameters of milk from late lactation grazing dairy cows

This research communication addressed the hypothesis that late lactation cows offered an oat-grain-based supplement or a high level of α-TOC supplementation at pasture would have improved milk composition and processability. Over a grazing period of 49 d, 48 Holstein Friesian dairy cows were randomly assigned to one of four dietary treatments. The dietary treatments were: control, pasture only (CTRL), pasture + 2.65 kg DM barley-based concentrate + 350 IU α-TOC/kg (BARLO), pasture + 2.65 kg DM oat-based concentrate + 350 IU α-TOC/kg (OATLO) and pasture + 2.65 kg DM oat-based concentrate + 1050 IU α-TOC/kg (OATHI). Within this randomised complete block design experiment cows were blocked on days in milk (DIM) and balanced for parity, milk yield and composition. Rennet coagulation time (RCT) was reduced in milk from cows offered OATHI compared to CTRL cows and OATLO. Concentration of conjugated linoleic acid (CLA) was increased by OATHI compared to OATLO and in OATLO compared to CTRL. Supplementation with OATHI reduced individual saturated fatty acids (SFAs) in milk compared to OATLO. In conclusion, supplementing grazing dairy cows with an oat-based supplement improved total milk CLA concentration compared to pasture only. Offering a high level of α-TOC (2931 IU/d) to dairy cows reduced RCT, individual SFA and increased total CLA concentration of milk compared to a lower α-TOC level (738 IU α-TOC/d).

The effects of cereal type and α-tocopherol level on milk production, milk composition, rumen fermentation, and nitrogen excretion of spring-calving dairy cows in late lactation

Grass-based production systems use concentrate supplementation primarily when pasture quality and availability have declined. Barley is a common concentrate ingredient; however, oat grain grows well in Ireland, is a source of lipids and fiber, and may provide an alternative to barley. The antioxidant α-tocopherol (α-TOC) plays a role in cell membrane structure, and it has the potential to improve tight junction structures of the mammary gland that deteriorate in late lactation. The objective of this research was to investigate the effect of cereal type and α-TOC level on milk yield, milk composition, rumen fermentation, and N excretion in late-lactation dairy cows at pasture and when housed indoors on grass silage. Forty-eight Holstein Friesian dairy cows were blocked on days in milk (+185 d in milk) and balanced for parity, pre-experimental milk yield, milk composition, and body condition score and assigned to 1 of 4 dietary treatments in a randomized complete block design (n = 12). The dietary treatments were control (C) base diet; base diet + barley-based concentrate + low α-TOC (350 IU/kg) (B); base diet + oat-based concentrate + low α-TOC (350 IU/kg) (O); and base diet + oat-based concentrate + high α-TOC (1,050 IU/kg) (O+T). Following a 14-d acclimation period, diets were offered for a 49-d experimental period at pasture (P1) and a 21-d experimental period indoors (P2). The base diet was grazed grass in P1 and grass silage in P2. In P2, cows on C also received 2.65 kg (dry matter) of a standard concentrate. In P1, supplementation increased milk and milk solids yield (B: 20.7 kg/d, 1.74 kg/d; O: 20.6 kg/d, 1.81 kg/d; O+T: 20.5 kg/d, 1.77 kg/d, respectively) compared with C (17.8 kg/d, 1.60 kg/d). Cows offered B had a lower milk fat (4.60%) concentration than C (5.00%) and O (4.90%). In P2, cereal type and α-TOC level did not alter milk production. In conclusion, concentrate supplementation increased milk and milk solids yield and cows offered O had a higher milk fat concentration than cows offered B. Increasing the level of α-TOC had no major effect on production parameters measured in P1 or in P2.

Phytochemical analysis and nephroprotective effect of cactus (Opuntia ficus-indica) cladodes on sodium dichromate-induced kidney injury in rats

Environmental and occupational exposure to chromium compounds, especially hexavalent chromium, is widely recognized as potentially nephrotoxic in humans and animals. The present study aimed to assess the efficacy of cactus (Opuntia ficus-indica) against sodium dichromate-induced nephrotoxicity, oxidative stress, and genotoxicity. Cactus cladodes extract (CCE) was phytochemically studied and tested in vitro for its potential antioxidant activities. Additionally, the preventive effect of CCE against sodium dichromate-induced renal dysfunction in a Wistar rat model (24 rats) was evaluated. For this purpose, CCE at a dose of 100 mg/kg was orally administered, followed by 10 mg/kg sodium dichromate (intraperitoneal injection). After 40 days of treatment, the rats were sacrificed, and the kidneys were excised for histological, lipid peroxidation, and antioxidant enzyme analyses. The phenol, flavonoid, tannin, ascorbic acid, and carotenoid contents of CCE were considered to be important. Our analyses showed that 1 mL of CCE was equivalent to 982.5 ± 1.79 μg of gallic acid, 294.37 ± 0.84 μg of rutin, 234.78 ± 0.24 μg of catechin, 204.34 ± 1.53 μg of ascorbic acid, and 3.14 ± 0.51 μg of β-carotene. In vivo, pretreatment with CCE was found to provide significant protection against sodium dichromate-induced nephrotoxicity by inhibiting lipid peroxidation, preserving normal antioxidant activities, and protecting renal tissues from lesions and DNA damage. The nephroprotective potential of CCE against sodium dichromate toxicity might be due to its antioxidant properties.

Sulforaphane prevents maleic acid-induced nephropathy by modulating renal hemodynamics, mitochondrial bioenergetics and oxidative stress

Maleic acid (MA)-induced nephropathy that is characterized by proteinuria, glycosuria, phosphaturia and a deficient urinary acidification and concentration. Sulforaphane (SF) is an indirect antioxidant that shows nephroprotective effects. The aim of the present work was to test the pre-treatment with SF against the MA-induced nephropathy. Wistar rats (230-260 g) were separated in the following groups: control, MA (which received 400 mg/kg of MA), SF + MA (which received MA and 1 mg/kg of SF each day for four days) and SF (which only received SF). MA induced proteinuria, an increase in urinary excretion of N-acetyl-β-d-glucosaminidase, and a decrease in plasma glutathione peroxidase activity, renal blood flow, and oxygenation and perfusion of renal cortex. All these impairments correlated with higher levels of oxidative damage markers and exacerbated superoxide anion production on renal cortex. Moreover, MA impaired mitochondrial bioenergetics associated to complex I, mitochondrial membrane potential and respiratory control index and increased the mitochondrial production of hydrogen peroxide. Further it disrupted mitochondrial morphology. SF prevented all the above-described alterations. In conclusion, the protective effect of SF against MA-induced nephropathy is associated with preservation of mitochondrial bioenergetics, amelioration of oxidative stress and improvement of renal hemodynamics and renal cortex oxygenation.

Aldosterone signaling regulates the over-expression of claudin-4 and -8 at the distal nephron from type 1 diabetic rats

Hyperglycemia in diabetes alters tight junction (TJ) proteins in the kidney. We evaluated the participation of aldosterone (ALD), and the effect of spironolactone (SPL), a mineralocorticoid receptor antagonist, on the expressions of claudin-2, -4, -5 and -8, and occludin in glomeruli, proximal and distal tubules isolated from diabetic rats. Type 1 diabetes was induced in female Wistar rats by a single tail vein injection of streptozotocin (STZ), and SPL was administrated daily by gavage, from days 3–21. Twenty-one days after STZ injection the rats were sacrificed. In diabetic rats, the serum ALD levels were increased, and SPL-treatment did not have effect on these levels or in hyperglycemia, however, proteinuria decreased in SPL-treated diabetic rats. Glomerular damage, evaluated by nephrin and Wilm’s tumor 1 (WT1) protein expressions, and proximal tubular damage, evaluated by kidney injury molecule 1 (Kim-1) and heat shock protein 72 kDa (Hsp72) expressions, were ameliorated by SPL. Also, SPL prevented decrement in claudin-5 in glomeruli, and claudin-2 and occludin in proximal tubules by decreasing oxidative stress, evaluated by superoxide anion (O₂^●―) production, and oxidative stress markers. In distal tubules, SPL ameliorated increase in mRNA, protein expression, and phosphorylation in threonine residues of claudin-4 and -8, through a serum and glucocorticoid-induced kinase 1 (SGK1), and with-no-lysine kinase 4 (WNK4) signaling pathway. In conclusion, this is the first study that demonstrates that ALD modulates the expression of renal TJ proteins in diabetes, and that the blockade of its actions with SPL, may be a promising therapeutic strategy to prevent alterations of TJ proteins in diabetic nephropathy.

Protective effects of boron and vitamin E on ethylene glycol-induced renal crystal calcium deposition in rat

Objectives. Kidney stone disease is a common form of renal disease. Antioxidants, such as vitamin E (Vit E) and boron, are substances that reduce the damage caused by oxidation.

Methods. Adult male rats were divided into 5 groups (n=6). In group 1, rats received standard food and water for 28 days (control group); in group 2, standard rodent food and water with 0.75% ethylene glycol/d (dissolved in drinking water) (EG Group); in group 3, similar to group 2, with 3 mg of boron/d (dissolved in water) (EG+B Group); in group 4, similar to group 2, with 200 IU of vitamin E injected intraperitoneally on the first day and the 14th day, (EG+Vit E Group); in group 5, mix of groups 3 and 4, respectively (EG+B+Vit E Group).

Results. Kidney sections showed that crystals in the EG group increased significantly in comparison with the control group. Crystal calcium deposition score in groups of EG+B (160), EG+Vit E, and EG+B+Vit E showed a significant decrease compared to EG group. Measurement of the renal tubules area and renal tubular epithelial histological score showed the highest significant dilation in the EG group. Tubular dilation in the EG+B+Vit E group decreased compared to the EG+B and EG+Vit E groups.

Conclusions. Efficient effect of boron and Vit E supplements, separately and in combination, has a complimentary effect in protection against the formation of kidney stones, probably by decreasing oxidative stress.

The nephroprotection exerted by curcumin in maleate-induced renal damage is associated with decreased mitochondrial fission and autophagy

We have previously reported that the antioxidant curcumin exerts nephroprotection in maleate-induced renal damage, a model associated with oxidative stress. However, the mechanisms involved in curcumin protective effect were not explored, to assess this issue, curcumin was administered daily by gavage (150 mg/kg) five days before a single maleate (400 mg/kg)-injection. Curcumin prevented maleate-induced proteinuria, increased heat shock protein of 72 KDa (Hsp72) expression, and decreased plasma glutathione peroxidase activity. Maleate-induced oxidative stress by increasing the nicotinamide-adenine dinucleotide phosphate oxidase 4 (NOX4) and mitochondrial complex I-dependent superoxide anion (O₂ •^- ) production, formation of malondialdehyde (MDA)- and 3-nitrotyrosine (3-NT)-protein adducts and protein carbonylation and decreased GSH/GSSG ratio. Curcumin treatment ameliorated all the above-described changes. The maleate-induced epithelial damage, evaluated by claudin-2 and occludin expressions, was ameliorated by curcumin. It was found that maleate-induced oxidative stress promoted mitochondrial fission, evaluated by dynamin-related protein (Drp) 1 and fission (Fis) 1 expressions and by electron-microscopy, and autophagy, evaluated by phospho-threonine 389 from p70 ribosomal protein S6 kinase (p-Thr 389 p70S6K), beclin 1, microtubule-associated protein 1A/1B-light chain 3 phosphatidylethanolamine conjugate (LC3-II), autophagy-related gene 5 and 12 (Atg5-Atg12) complex, p62, and lysosomal-associated membrane protein (LAMP)-2 expressions in isolated proximal tubules and by electron-microscopy and LC-3 immunolabelling. Curcumin treatment ameliorated these changes. Moreover, curcumin alone induced autophagy in proximal tubules. These data suggest that the nephroprotective effect exerted by curcumin in maleate-induced renal damage is associated with decreased mitochondrial fission and autophagy. © 2016 BioFactors, 42(6):686-702, 2016.

Curcumin prevents cisplatin-induced decrease in the tight and adherens junctions: relation to oxidative stress

Curcumin is a polyphenol and cisplatin is an antineoplastic agent that induces nephrotoxicity associated with oxidative stress, apoptosis, fibrosis and decrease in renal tight junction (TJ) proteins. The potential effect of curcumin against alterations in TJ structure and function has not been evaluated in cisplatin-induced nephrotoxicity. The present study explored whether curcumin is able to prevent the cisplatin-induced fibrosis and decreased expression of the TJ and adherens junction (AJ) proteins occludin, claudin-2 and E-cadherin in cisplatin-induced nephrotoxicity. Curcumin (200 mg kg(-1)) was administered in three doses, and rats were sacrificed 72 h after cisplatin administration. Curcumin was able to scavenge, in a concentration-dependent way, superoxide anion, hydroxyl radical, peroxyl radical, singlet oxygen, peroxynitrite anion, hypochlorous acid and hydrogen peroxide. Cisplatin-induced renal damage was associated with alterations in plasma creatinine, expression of neutrophil gelatinase-associated lipocalin and of kidney injury molecule-1, histological damage, increase in apoptosis, fibrosis (evaluated by transforming growth factor β1, collagen I and IV and α-smooth muscle actin expressions), increase in oxidative/nitrosative stress (evaluated by Hsp70/72 expression, protein tyrosine nitration, superoxide anion production in isolated glomeruli and proximal tubules, and protein levels of NADPH oxidase subunits p47(phox) and gp91(phox), protein kinase C β2, and Nrf2) as well as by decreased expression of occludin, claudin-2, β-catenin and E-cadherin. Curcumin treatment prevented all the above-described alterations. The protective effect of curcumin against cisplatin-induced fibrosis and decreased proteins of the TJ and AJ was associated with the prevention of glomerular and proximal tubular superoxide anion production induced by NADPH oxidase activity.

Simvastatin attenuates chromium-induced nephrotoxicity in rats

Background

Hexavalent Chromium (Cr (VI)) compounds are extremely toxic and have been demonstrated to induce nephrotoxicity associated with oxidative stress in humans and animals. The wide environmental distribution of these agents lead to an increase interest of preventive effects of its adverse effects.

Objectives

The propose of the present study was to determine the potential protective effects of simvastatin (SIMV) on Cr (VI)-induced nephrotoxicity in rat.

Materials and Methods

Forty-eight adult male Wistar rats (180-220 g BW) were randomly assigned to eight groups (n = 6). Group one received SIMV 20 mg/kg/day. Group two was given vehicle only. Groups three, five and seven received intraperitoneally (i.p) sodium dichromate (Cr (VI)) at doses of 8, 12 and 16 mg/kg body weight. Groups four, six and eight pretreated with the 20 mg/kg SIMV 30 minutes to prior administration of Cr (VI) at doses of 8, 12 and 16 mg/kg, respectively. The experiment repeated for eight consecutive days. Twenty-four hours after the last administration, animals were killed with overdose of sodium pentobarbital. Kidney tissues were excised for measuring malondialdehyde (MDA), glutathione (GSH) and histopathological examination.

Results

Chromium induced a dose dependent elevation of MDA and reduction of GSH levels. Histopathological manifestations were observed in Cr (VI)-treated rats. SIMV administration restored Cr (VI) produced biochemical and morphological changes in rat kidney. SIMV decreased MDA values and increased GSH levels in Cr (VI)-treated rats. SIMV clearly reversed the microscopic damage, demonstrating its protective effects against Cr (VI)-induced kidney injury.

Conclusions

This observation suggests that SIMV may have a protective effect against Cr (VI)-induced oxidative stress in rat kidney.

Curcumin prevents maleate-induced nephrotoxicity: relation to hemodynamic alterations, oxidative stress, mitochondrial oxygen consumption and activity of respiratory complex I

The potential protective effect of the dietary antioxidant curcumin (120 mg/Kg/day for 6 days) against the renal injury induced by maleate was evaluated. Tubular proteinuria and oxidative stress were induced by a single injection of maleate (400 mg/kg) in rats. Maleate-induced renal injury included increase in renal vascular resistance and in the urinary excretion of total protein, glucose, sodium, neutrophil gelatinase-associated lipocalin (NGAL) and N-acetyl β-D-glucosaminidase (NAG), upregulation of kidney injury molecule (KIM)-1, decrease in renal blood flow and claudin-2 expression besides of necrosis and apoptosis of tubular cells on 24 h. Oxidative stress was determined by measuring the oxidation of lipids and proteins and diminution in renal Nrf2 levels. Studies were also conducted in renal epithelial LLC-PK1 cells and in mitochondria isolated from kidneys of all the experimental groups. Maleate induced cell damage and reactive oxygen species (ROS) production in LLC-PK1 cells in culture. In addition, maleate treatment reduced oxygen consumption in ADP-stimulated mitochondria and diminished respiratory control index when using malate/glutamate as substrate. The activities of both complex I and aconitase were also diminished. All the above-described alterations were prevented by curcumin. It is concluded that curcumin is able to attenuate in vivo maleate-induced nephropathy and in vitro cell damage. The in vivo protection was associated to the prevention of oxidative stress and preservation of mitochondrial oxygen consumption and activity of respiratory complex I, and the in vitro protection was associated to the prevention of ROS production.

Renal tight junction proteins are decreased in cisplatin-induced nephrotoxicity in rats

Cisplatin (CP) is an antineoplastic agent that induces nephrotoxicity and oxidative stress. It is unknown whether renal tight junction (TJ) proteins expression and localization are modified in CP-induced nephrotoxicity.

OBJECTIVE

To study if the expression of the TJ proteins occludin, claudin-2, claudin-5 and zonula occludens-1 (ZO-1) is modified in rats with CP-induced nephrotoxicity.

MATERIALS AND METHODS

Male Wistar rats (n = 5/group) were injected with saline solution (V group), and the other group (CP group) was injected with a single dose of saline solution and CP (7.5 mg/kg i.p.). Rats were sacrificed 72 h after CP injection and blood, and 24-h urine samples were collected. Several plasma and urinary injury biomarkers as well as renal histopathology lesions, oxidative and nitrosative stress markers were evaluated, and protein levels of ocludin, claudin-2, claudin-5, ZO-1 were measured by Western blot. Statistically significant changes noted with different p < 0.05 versus V.

RESULTS

Nephrotoxicity was evident by histological alterations, glycosuria, decrease in creatinine clearance, increase in fractional excretion of sodium, serum creatinine and kidney injury molecule-1. These changes were associated with oxidative/nitrosative stress (increased renal abundance of 3-nitrotyrosine and protein kinase Cβ2 and decreased renal expression of nuclear factor-erythroid-2-related factor 2) and decreased activity of antioxidant enzymes. Finally, it was found that CP-induced renal damage was associated with decreased renal expression of occludin and claudin-2.

DISCUSSION AND CONCLUSION

CP altered the TJ proteins expression and localization in the proximal tubule that was associated with oxidative/nitrosative stress.

Oxidative stress induces claudin-2 nitration in experimental type 1 diabetic nephropathy

Renal complications in diabetes are severe and may lead to renal insufficiency. Early alterations in tight junction (TJ) proteins in diabetic nephropathy (DN) have not been explored and the role of oxidative stress in their disassembly has been poorly characterized. We investigated the expression and distribution of TJ proteins: claudin-5 in glomeruli (GL), occludin and claudin-2 in proximal tubules (PTs), and ZO-1 and claudin-1, -4, and -8 in distal tubules (DTs) of rats 21 days after streptozotocin injection. Redox status along the nephron segments was evaluated. Diabetes increased kidney injury molecule-1 expression. Expression of sodium glucose cotransporters (SGLT1 and SGLT2) and facilitative glucose transporter (GLUT2) was induced. Increased oxidative stress was present in GL and PTs and to a lesser extent in DTs (measured by superoxide production and PKCβ2 expression), owing to NADPH oxidase activation and uncoupling of the endothelial nitric oxide synthase-dependent pathway. Claudin-5, occludin, and claudin-2 expression was decreased, whereas claudin-4 and -8 expression increased. ZO-1 was redistributed from membrane to cytosol. Increased nitration of tyrosine residues in claudin-2 was found, which might contribute to decrement of this protein in proximal tubule. In contrast, occludin was not nitrated. We suggest that loss of claudin-2 is associated with increased natriuresis and that loss of glomerular claudin-5 might explain early presence of proteinuria. These findings suggest that oxidative stress is related to alterations in TJ proteins in the kidney that are relevant to the pathogenesis and progression of DN and for altered sodium regulation in diabetes.

S-allylcysteine prevents cisplatin-induced nephrotoxicity and oxidative stress

Objectives

Cisplatin (CP) is an antineoplastic agent that induces nephrotoxicity and oxidative stress. S-allylcysteine (SAC) is a garlic-derived antioxidant. This study aims to explore whether SAC protects against CP-induced nephrotoxicity in rats.

Methods

In the first stage, the SAC protective dose was determined by measuring renal damage and the oxidative stress markers malondialdehyde, oxidized proteins and glutathione in rats injected with CP. In the second stage, the effect of a single dose of SAC on the expression of nuclear factor-erythroid 2-related factor-2 (Nrf2), protein kinase C beta 2 (PKCβ2) and nicotinamide adenine dinucleotide phosphate oxidase subunits (p47phox and gp91phox) was studied. In addition, the effect of SAC on oxidative stress markers and on the activity of catalase (CAT), glutathione peroxidase (GPx) and glutathione reductase (GR) in isolated proximal and distal tubules were evaluated.

Key findings

SAC (25 mg/kg) prevented the CP-induced renal damage and attenuated CP-induced decrease in Nrf2 levels and increase in PKCβ2, p47phox and gp91phox expression in renal cortex and oxidative stress and decrease in the activity of CAT, GPx and GR in proximal and distal tubules.

Conclusions

These data suggest that SAC provides renoprotection by attenuating CP-induced oxidative stress and decrease in the activity of CAT, GPx and GR.

Evaluation of protective action of α-tocopherol in chromium-induced oxidative stress in female reproductive system of rats

The present study was aimed to investigate whether α-tocopherol could protect the chromium (Cr) VI-induced oxidative stress in female reproductive system of rats and to explore the underlying mechanisms of the same. A total of 24 Wistar adult female rats were equally divided into four groups. Group 1 served as control, while groups 2 and 3 were administered K2Cr2O7 (10 mg/kg b.wt. s.c. single dose). In addition to Cr, group 3 also received α-tocopherol @ 125 mg/kg daily by oral gavage for 14 days. Group 4 was maintained as α-tocopherol control (dose as above). Body weights were recorded at the beginning and at the end of experiment. Further, the rats were observed for occurrence of estrus cycle. At the end of 14 days, blood samples were drawn for sero-biochemical analysis. Subsequently, all the rats were sacrificed to collect uterus along with ovaries for assay of tissue peroxidation, anti-oxidant and functional markers, and histopathology. Administration of chromium (Cr) VI to rats revealed a significant (P < 0.05) accumulation of cholesterol and a prolonged diestrus phase leading to impaired fertility in rats. Administration of chromium (Cr) VI significantly (P < 0.05) reduced the antioxidant markers such as superoxide dismutase (SOD) and reduced glutathione (GSH), along with significant (P < 0.05) increase in peroxidation markers such as malondialdehyde and protein carbonyls in ovaries. The functional marker in serum such as total protein was decreased, whereas other functional markers viz alanine transaminase (ALT), blood urea nitrogen (BUN) and creatinine were increased. Prominent pathological changes were observed in the uterus and ovaries of Cr-treated group. Co-treatment with α-tocopherol significantly (P < 0.05) reversed the (Cr) VI induced changes.

Tight junction proteins and oxidative stress in heavy metals-induced nephrotoxicity

Kidney is a target organ for heavy metals. They accumulate in several segments of the nephron and cause profound alterations in morphology and function. Acute intoxication frequently causes acute renal failure. The effects of chronic exposure have not been fully disclosed. In recent years increasing awareness of the consequences of their presence in the kidney has evolved. In this review we focus on the alterations induced by heavy metals on the intercellular junctions of the kidney. We describe that in addition to the proximal tubule, which has been recognized as the main site of accumulation and injury, other segments of the nephron, such as glomeruli, vessels, and distal nephron, show also deleterious effects. We also emphasize the participation of oxidative stress as a relevant component of the renal damage induced by heavy metals and the beneficial effect that some antioxidant drugs, such as vitamin A (all-trans-retinoic acid) and vitamin E (α-tocopherol), depict on the morphological and functional alterations induced by heavy metals.

The effects of chromium(VI) on the thioredoxin system: implications for redox regulation

Hexavalent chromium [Cr(VI)] compounds are highly redox active and have long been recognized as potent cytotoxins and carcinogens. The intracellular reduction of Cr(VI) generates reactive Cr intermediates, which are themselves strong oxidants, as well as superoxide, hydrogen peroxide, and hydroxyl radical. These probably contribute to the oxidative damage and effects on redox-sensitive transcription factors that have been reported. However, the identification of events that initiate these signaling changes has been elusive. More recent studies show that Cr(VI) causes irreversible inhibition of thioredoxin reductase (TrxR) and oxidation of thioredoxin (Trx) and peroxiredoxin (Prx). Mitochondrial Trx2/Prx3 are more sensitive to Cr(VI) treatment than cytosolic Trx1/Prx1, although both compartments show thiol oxidation with higher doses or longer treatments. Thiol redox proteomics demonstrate that Trx2, Prx3, and Trx1 are among the most sensitive proteins in cells to Cr(VI) treatment. Their oxidation could therefore represent initiating events that have widespread implications for protein thiol redox control and for multiple aspects of redox signaling. This review summarizes the effects of Cr(VI) on the TrxR/Trx system and how these events could influence a number of downstream redox signaling systems that are influenced by Cr(VI) exposure. Some of the signaling events discussed include the activation of apoptosis signal regulating kinase and MAP kinases (p38 and JNK) and the modulation of a number of redox-sensitive transcription factors including AP-1, NF-κB, p53, and Nrf2.

Occludin protein family: oxidative stress and reducing conditions

The occludin-like proteins belong to a family of tetraspan transmembrane proteins carrying a marvel domain. The intrinsic function of the occludin family is not yet clear. Occludin is a unique marker of any tight junction and is found in polarized endothelial and epithelial tissue barriers, at least in the adult vertebrate organism. Occludin is able to oligomerize and to form tight junction strands by homologous and heterologous interactions, but has no direct tightening function. Its oligomerization is affected by pro- and antioxidative agents or processes. Phosphorylation of occludin has been described at multiple sites and is proposed to play a regulatory role in tight junction assembly and maintenance and, hence, to influence tissue barrier characteristics. Redox-dependent signal transduction mechanisms are among the pathways modulating occludin phosphorylation and function. This review discusses the novel concept that occludin plays a key role in the redox regulation of tight junctions, which has a major impact in pathologies related to oxidative stress and corresponding pharmacologic interventions.

Eryptosis and oxidative damage in type 2 diabetic mellitus patients with chronic kidney disease

It has been suggested that oxidative stress may participate in the progression of diabetes and its complications. Long-term complications of type 2 diabetes mellitus (T2DM) include retinopathy, atherosclerosis, shortened life span of erythrocytes, nephropathy, and chronic kidney disease (CKD). Oxidative damage has been associated with erythrocyte apoptosis induction in other pathological conditions. Our aim was to study the presence of eryptosis and its possible relationship with oxidative damage in patients with T2DM without CKD (T2DM/CKD(-)) and in patients with T2DM and CKD (T2DM/CKD(+)).Oxidative damage of lipids erythrocytes were increased in diabetic patients. The highest lipoperoxidation was found in T2DM/CKD(+). Likewise, the lower plasma total antioxidant capacity, GSH/GSSG ratio, and GSH in erythrocytes were found in T2DM/CKD(+) patients. A negative correlation was found between plasma total antioxidant capacity and oxidative damage. Phosphatidylserine (PS) externalization was measured in erythrocytes to evaluate eryptosis. Annexin binding in erythrocytes of T2DM/CKD(+) patients was higher than in healthy subjects and T2DM/CKD(-) patients. A positive correlation between lipoperoxidation and PS externalization in erythrocytes was found. This work showed that the erythrocytes of diabetic patients have increased oxidative damage, a reduction of antioxidant systems and more erythrocyte PS externalization. The duration of diabetes and the presence of CKD increase both oxidative damage and eryptosis. It is possible that a longer time of evolution induces an increase in erythrocyte oxidative damage and the consumption of blood antioxidant systems, adding to the osmotic stress in CKD and so contributes to an increase in PS externalization in diabetic patients.

A dystroglycan/plectin scaffold mediates mechanical pathway bifurcation in lung epithelial cells

In alveolar epithelial cells (AECs), the membrane-anchored proteoglycan dystroglycan (DG) is a mechanoreceptor that transmits mechanical stretch forces to activate independently the ERK1/2 and the adenosine 5'-monophosphate-activated protein kinase (AMPK) signaling cascades in a process called pathway bifurcation. We tested the hypothesis that the cytoskeleton cross-linker plectin, known to bind both DG and AMPK in muscle cells, acts as a scaffold to regulate DG-mediated mechanical stimulation and pathway bifurcation. We demonstrate that plectin and DG form a complex in AECs and that this complex interacts with ERK1/2 and AMPK. Plectin knockdown reduces DG interaction with AMPK but not with ERK1/2. Despite this, mechanoactivation of both signaling pathways is significantly attenuated in AECs deficient in plectin. Thus, DG has the dual role of mechanical receptor and scaffold for ERK1/2, whereas plectin acts as a scaffold for AMPK signaling but is also required for DG-mediated ERK1/2 activation. We conclude that the DG-plectin complex plays a central role in transmitting mechanical stress from the extracellular matrix to the cytoplasm.