High glucose-induced oxidative stress causes apoptosis in proximal tubular epithelial cells and is mediated by multiple caspases

Treatment of the post-ischaemic inflammatory syndrome of diabetic nephropathy

BACKGROUND

Diabetes mellitus and its complications are a public health problem of epidemic proportions. Both diabetes and chronic kidney disease (CKD) increase the risk of acute kidney injury (AKI). Months after a single episode of acute ischaemia to the diabetic kidney, we have found an accelerated progression of nephropathy, with impaired function, severe renal inflammation, microvascular dysfunction, fibrosis and apoptotic cell death. We termed this entity the post-ischaemic inflammatory syndrome. We now test the hypothesis that blocking inflammation ameliorates the post-ischaemic inflammatory syndrome.

METHODS

Obese-diabetic ZS rats (F(1) hybrids of spontaneously hypertensive heart failure and Zucker fatty diabetic rats) were treated with mycophenolate mofetil (MMF), subjected to renal ischaemia or sham surgery, and monitored via the powerful technique of intravital microscopy.

RESULTS

Amelioration of post-ischaemia inflammation with MMF therapy improved long-term renal function, microvascular dysfunction, fibrosis and apoptosis.

CONCLUSION

These data support the hypothesis that the post-ischaemic inflammatory syndrome accelerates diabetic CKD, is a critical determinant of injury, and can be successfully treated.

Clinical benefits of tight glycaemic control: effect on the kidney

Acute kidney injury is a frequent and life-threatening complication of critical illness. Prevention of this condition is crucial. Two randomized single center trials in critically ill patients have shown a decrease in acute kidney injury by tight glycaemic control, an effect that appears most pronounced in surgical patients. Subsequent randomized trials did not confirm this renoprotective effect. This apparent contradiction is likely explained by methodological differences between studies, including different patient populations, insufficient patient numbers, comparison with a different control group, use of inaccurate blood glucose analyzers, and differences in the degree of reaching the target blood glucose level. The optimal glycaemic target for renoprotection in critical illness remains to be defined. Possible mechanisms underlying the renoprotective effect of tight glycaemic control are prevention of glucose overload and toxicity and the associated mitochondrial damage, an anti-inflammatory or anti-apoptotic effect, prevention of endothelial dysfunction, and an improvement of the lipid profile.

The role of reactive oxygen species in apoptosis of the diabetic kidney

Increased levels of reactive oxygen species (ROS) by hyperglycemia can induce apoptosis of renal cells and diabetic nephropathy. The redox balance in the renal cell seems, therefore, of the utmost importance. ROS-mediated apoptosis may be further aggravated by an inadequate cytoprotective response against ROS. When there are insufficient cytoprotective and ROS scavenging molecules, ROS lead to considerable cellular damage and to a point of no return in apoptosis. Induction of cytoprotective proteins may prevent or attenuate apoptosis, renal cell injury, and finally diabetic nephropathy. Here, we discuss some mechanisms of apoptosis and several strategies that have been probed to ameliorate, or to prevent apoptosis in the diabetic kidney.

Oral hydrogen water prevents chronic allograft nephropathy in rats

Reactive oxygen species (ROS) contribute to the development of interstitial fibrosis and tubular atrophy seen in chronic allograft nephropathy (CAN). As molecular hydrogen gas can act as a scavenger of ROS, we tested the effect of treatment with hydrogen water (HW) in a model of kidney transplantation, in which allografts from Lewis rats were orthotopically transplanted into Brown Norway recipients that had undergone bilateral nephrectomy. Molecular hydrogen was dissolved in water and recipients were given HW from day 0 until day 150. Rats that were treated with regular water (RW) gradually developed proteinuria and their creatinine clearance declined, ultimately leading to graft failure secondary to CAN. In contrast, treatment with HW improved allograft function, slowed the progression of CAN, reduced oxidant injury and inflammatory mediator production, and improved overall survival. Inflammatory signaling pathways, such as mitogen-activated protein kinases, were less activated in renal allografts from HW-treated rats as compared with RW-treated rats. Hence, oral HW is an effective antioxidant and antiinflammatory agent that prevented CAN, improved survival of rat renal allografts, and may be of therapeutic value in the setting of transplantation.

Dexamethasone ameliorates renal ischemia-reperfusion injury

In the setting of renal ischemia-reperfusion injury (IRI), the effect and mechanism of action of glucocorticoids are not well understood. In rat renal IRI, a single dose of dexamethasone administered before ischemia, or at the onset of reperfusion, ameliorated biochemical and histologic acute kidney injury after 24 h. Dexamethasone upregulated Bcl-xL, downregulated ischemia-induced Bax, inhibited caspase-9 and caspase-3 activation, and reduced apoptosis and necrosis of proximal tubular cells. In addition, dexamethasone decreased the number of infiltrating neutrophils and ICAM-1. We observed the protective effect of dexamethasone in neutrophil-depleted mice, suggesting a neutrophil-independent mechanism. In vitro, dexamethasone protected human kidney proximal tubular (HK-2) cells during serum starvation and IRI-induced apoptosis, but inhibition of MEK 1/2 abolished its anti-apoptotic effects in these conditions. Dexamethasone stimulated rapid and transient phosphorylation of ERK 1/2, which required the presence of the glucocorticoid receptor and was independent of transcriptional activity. In summary, in the setting of renal ischemia-reperfusion injury, dexamethasone directly protects against kidney injury by a receptor-dependent, nongenomic mechanism.

Interplay between Akt and p38 MAPK pathways in the regulation of renal tubular cell apoptosis associated with diabetic nephropathy

Hyperglycemia induces p38 MAPK-mediated renal proximal tubular cell (RPTC) apoptosis. The current study hypothesized that alteration of the Akt signaling pathway by hyperglycemia may contribute to p38 MAPK activation and development of diabetic nephropathy. Immunoblot analysis demonstrated a hyperglycemia-induced increase in Akt phosphorylation in diabetic kidneys at 1 mo, peaking at 3 mo, and dropping back to baseline by 6 mo. Immunohistochemical staining with anti-pAkt antisera localized Akt phosphorylation to renal tubules. Maximal p38 MAPK phosphorylation was detected concomitant with increase in terminal uridine deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells and caspase-3 activity in 6-mo diabetic kidneys. Exposure of cultured RPTCs to high glucose (HG; 22.5 mM) significantly increased Akt phosphorylation at 3, 6, and 9 h, and decreased thereafter. In contrast, p38 MAPK phosphorylation was detected between 9 and 48 h of HG treatment. Increased p38 MAPK activation at 24 and 48 h coincided with increased apoptosis, demonstrated by increased caspase-3 activity at 24 h and increased TUNEL-positive cells at 48 h of HG exposure. Blockade of p38 cascade with SB203850 inhibited HG-induced caspase-3 activation and TUNEL-positive cells. Overexpression of constitutively active Akt abrogated HG-induced p38 MAPK phosphorylation and RPTC apoptosis. In addition, blockade of the phosphatidylinositol-3 kinase/Akt pathway with LY294002 and silencing of Akt expression with Akt small interfering RNA induced p38 MAPK phosphorylation in the absence of HG. These results collectively suggest that downregulation of Akt activation during long-term hyperglycemia contributes to enhanced p38 MAPK activation and RPTC apoptosis. Mechanism of downregulation of Akt activation in 6-mo streptozotocin diabetic kidneys was attributed to decreased Akt-heat shock protein (Hsp) 25, Akt-p38 interaction, and decreased PTEN activity. Thus PTEN or Hsp25 could serve as potential therapeutic targets to modulate Akt activation and control p38 MAPK-mediated diabetic complications.

Acute kidney injury in the elderly population

The elderly population is more prone to acute kidney injury (AKI) than younger populations. Older patients have less renal reserve because of reduced glomerular filtration rates due to anatomic/functional changes, and concomitant diseases such as hypertension, diabetes, atherosclerosis, heart failure, ischemic renal disease, and obstructive uropathy. The risk of AKI may also increase as a result of aggressive diagnostic and therapeutic procedures, which include medical agents, radiology, and surgical intervention. AKI in the elderly has a multifactorial physiopathology due to different etiologies. Studies that have specifically compared prognosis of AKI in elderly versus young over the recent years suggest that age is a predictor of long-term outcome. In most cases, the treatment of AKI is similar for all age groups. The majority of critically ill patients with AKI will eventually need renal replacement therapy (RRT). The influence of RRT on renal outcome remains a subject of intense investigation and debate. Avoiding situations that could damage the kidney is an important strategy to prevent AKI development in the elderly, besides medical and interventional therapeutics.

Postischemic inflammatory syndrome: a critical mechanism of progression in diabetic nephropathy

Diabetes is a major epidemic, and diabetic nephropathy is the most common cause of end-stage renal disease. Two critical components of diabetic nephropathy are persistent inflammation and chronic renal ischemia from widespread vasculopathy. Moreover, acute ischemic renal injury is common in diabetes, potentially causing chronic kidney disease or end-stage renal disease. Accordingly, we tested the hypothesis that acute renal ischemia accelerates nephropathy in diabetes by activating proinflammatory pathways. Lean and obese-diabetic ZS rats (F(1) hybrids of spontaneously hypertensive heart failure and Zucker fatty diabetic rats) were subjected to bilateral renal ischemia or sham surgery before the onset of proteinuria. The postischemic state in rats with obesity-diabetes was characterized by progressive chronic renal failure, increased proteinuria, and renal expression of proinflammatory mediators. Leukocyte number in obese-diabetic rat kidney was markedly increased for months after ischemia. Intrarenal blood flow velocity was decreased after ischemia in lean control and obese-diabetic rats, although it recovered in lean rats. At 2 mo after ischemia, blood flow velocity decreased further in sham-surgery and postischemia obese-diabetic rats, so that RBC flow velocity was only 39% of control in the obese-diabetic rats after ischemia. In addition, microvascular density remained depressed at 2 mo in kidneys of obese-diabetic rats after ischemia. Abnormal microvascular permeability and increases in interstitial fibrosis and apoptotic renal cell death were also more pronounced after ischemia in obese-diabetic rats. These data support the hypothesis that acute renal ischemia in obesity-diabetes severely aggravates chronic inflammation and vasculopathy, creating a self-perpetuating postischemia inflammatory syndrome, which accelerates renal failure.

Attenuation of renoinflammatory cascade in experimental model of diabetic nephropathy by sesamol

Diabetes has become the most common single cause of end-stage renal disease (ESRD) in the United States and Europe. Approximately 30-40% of patients with type I and 15% with type II diabetes mellitus develop end ESRD. The study was designed to evaluate the impact of sesamol on renal function and renoinflammatory cascade in streptozotocin (STZ)-induced diabetes. STZ-induced diabetic rats were treated with sesamol (2, 4, and 8 mg/kg/day; po) or with vehicle from the fifth to eighth weeks. After 8 weeks, urine albumin excretion, urine output, serum creatinine, blood urea nitrogen, creatinine, and urea clearance were measured. Cytoplasmic and nuclear fractions of kidney were prepared for the quantification of oxidative-nitrosative stress (lipid peroxidation, superoxide dismutase, catalase, nonprotein thiols, total nitric oxide), tumor necrosis factor-alpha (TNF-alpha), tissue growth factor-1 beta (TGF-beta1), p65 subunit of NFkappabeta, and caspase-3. After 8 weeks of STZ injection, the rats produced significant alteration in renal function, increased oxidative-nitrosative stress, TNF-alpha, TGF-beta1, caspase-3 activity in cytoplasmic lysate, and active p65 subunit of NFkappabeta in nuclear lysate of kidney of diabetic rats. Interestingly, co-administration of sesamol significantly and dose-dependently prevented biochemical and molecular changes associated with diabetes. Moreover, diabetic rats treated with insulin-sesamol combination produced more pronounced effect on molecular parameters as compared to their respective groups. The data reveal that sesamol modulates the release of profibrotic cytokines, oxidative stress, ongoing chronic inflammation, and apoptosis and thus exerts a marked renoprotective effect.

The role of nitric-oxide synthase in the regulation of UVB light-induced phosphorylation of the alpha subunit of eukaryotic initiation factor 2

UV light induces phosphorylation of the alpha subunit of the eukaryotic initiation factor 2 (eIF2alpha) and inhibits global protein synthesis. Both eIF2 kinases, protein kinase-like endoplasmic reticulum kinase (PERK) and general control of nonderepressible protein kinase 2 (GCN2), have been shown to phosphorylate eIF2alpha in response to UV irradiation. However, the roles of PERK and GCN2 in UV-induced eIF2alpha phosphorylation are controversial. The one or more upstream signaling pathways that lead to the activation of PERK or GCN2 remain unknown. In this report we provide data showing that both PERK and GCN2 contribute to UV-induced eIF2alpha phosphorylation in human keratinocyte (HaCaT) and mouse embryonic fibroblast cells. Reduction of expression of PERK or GCN2 by small interfering RNA decreases phosphorylation of eIF2alpha after UV irradiation. These data also show that nitric-oxide synthase (NOS)-mediated oxidative stress plays a role in regulation of eIF2alpha phosphorylation upon UV irradiation. Treating the cells with the broad NOS inhibitor N(G)-methyl-l-arginine, the free radical scavenger N-acetyl-l-cysteine, or the NOS substrate l-arginine partially inhibits UV-induced eIF2alpha phosphorylation. The results presented above led us to propose that NOS mediates UV-induced eIF2alpha phosphorylation by activation of both PERK and GCN2 via oxidative stress and l-arginine starvation signaling pathways.

High glucose concentration in cell culture medium does not acutely affect human mesenchymal stem cell growth factor production or proliferation

Optimizing the function and proliferative capacity of stem cells is essential to maximize their therapeutic benefits. High glucose concentrations are known to have detrimental effects on many cell types. We hypothesized that human mesenchymal stem cells (hMSCs) cultured in high glucose-containing media would exhibit diminished proliferation and attenuated production of VEGF, hepatocyte growth factor (HGF), and FGF2 in response to treatment with TNF-alpha, LPS, or hypoxia. hMSCs were plated in medium containing low (5.5 mM) and high (20 mM or 30 mM) glucose concentrations and treated with TNF-alpha, LPS, or hypoxia. Supernatants were collected at 24 and 48 h and assayed via ELISA for VEGF, HGF, and FGF2. In addition, hMSCs were cultured on 96-well plates at the above glucose concentrations, and proliferation at 48 h was determined via bromo-2'-deoxy-uridine (BrdU) incorporation. At 24 and 48 h, TNF-alpha, LPS, and hypoxia-treated hMSCs produced significantly higher VEGF, HGF, and FGF2 compared with control. Hypoxia-induced VEGF production by hMSCs was the most pronounced change over baseline. At both 24 and 48 h, glucose concentration did not affect production of VEGF, HGF, or FGF2 by untreated hMSCs and those treated with TNF-alpha, LPS, or hypoxia. Proliferation of hMSCs as determined via BrdU incorporation was unaffected by glucose concentration of the media. Contrary to what has been observed with other cells, hMSCs may be resistant to the short-term effects of high glucose. Ongoing efforts to characterize and optimize ex vivo and in vivo conditions are critical if the therapeutic benefits of MSCs are to be maximized.

Mitochondrial superoxide plays a crucial role in the development of mitochondrial dysfunction during high glucose exposure in rat renal proximal tubular cells

Diabetic nephropathy is the leading cause of end-stage renal disease in the United States. Despite several studies indicating a role for mitochondrial oxidative stress and mitochondrial dysfunction in the development of diabetic complications, the precise mechanisms underlying renal mitochondrial dysfunction and renal cell injury remain unclear. The hypothesis of the current study was that high-glucose-mediated generation of mitochondrial superoxide is a key early event that leads to mitochondrial injury in renal proximal tubular cells. To ascertain the role of mitochondrial superoxide we have tested whether overexpression of the primary mitochondrial antioxidant, manganese superoxide dismutase (MnSOD), protects against hyperglycemia-induced renal injury using normal rat renal proximal tubular cells (NRK). NRK cells were exposed to high glucose (25 mM) and the changes in the mitochondrial membrane potential, ATP levels, and superoxide generation and the loss of cell viability were measured at 24 and 48 h after high glucose exposure. Our results indicate that high glucose first induced superoxide generation and hyperpolarization in the mitochondria, followed by a secondary event, which involved a decline in ATP levels, partial Complex III inactivation, and loss of cell viability. These high-glucose-induced changes were completely prevented by overexpression of MnSOD in NRK cells. However, MnSOD activity was not changed after high glucose exposure in vitro or during the early stages of diabetes using the streptozotocin rat model. These findings show for the first time that hyperglycemic induction of superoxide production within the mitochondria initiates specific mitochondrial injury (i.e., Complex III) via a mechanism independent of MnSOD inactivation.

Hyperglycemia alters renal cell responsiveness to pressure in a model of malignant hypertension

OBJECTIVE

Poor glycemic control contributes to development of diabetic nephropathy. However, for a majority of clinical situations, the mechanisms responsible for high glucose-induced aggravation of renal tissue injury are not fully elucidated. We investigated responsiveness to pressure of various renal cell subsets subjected to hyperglycemic environment in an in-vitro model of malignant hypertension.

METHODS

Rat renal mesangium, epithelium and endothelium were exposed to high glucose-containing medium for 10 days and then subjected to high hydrostatic pressure for 1 h to simulate the incidence of malignant hypertension. In some cultures, renin-angiotensin system was experimentally suppressed prior to pressure application. Proliferation, apoptosis, intrarenal p53, H2O2 and angiotensin-II synthesis were subsequently assessed.

RESULTS

By contrast to cultures not exposed to high glucose, in all hyperglycemic cells p53 expression, angiotensin-II synthesis and apoptosis were increased, whereas proliferation depressed, irrespective of pressure enforcement. H2O2 release was enhanced by high pressure per se, and increased further following exposure to high glucose. In all diabetic cultures, inhibition of p53 by a specific inhibitor pifithrin concomitantly significantly decreased apoptosis.

CONCLUSION

Hyperglycemic environment alters responsiveness of renal cells to in-vitro simulation of malignant hypertension. The main consequence of either malignant hypertension or hyperglycemia is exaggerated apoptosis. However, the operating mechanisms differ: Malignant hypertension stimulates renal cell apoptosis via increased angiotensin-II, whereas hyperglycemia elicits apoptosis via augmented p53. By contrast to pressure-induced excessive proliferation of normoglycemic cells, hyperglycemia prohibits elevated proliferation in response to pressure. Angiotensin-II production is maximally augmented by hyperglycemic environment and is not stimulated further by pressure application.

Metformin suppresses high glucose-induced poly(adenosine diphosphate-ribose) polymerase overactivation in aortic endothelial cells

Overactivation of poly(adenosine diphosphate-ribose) polymerase (PARP), an enzyme involved in cellular response to DNA injury resulting from oxidative and nitrosative stress, is considered to play a key role in the pathogenesis of diabetes complications by promoting numerous vascular dysfunctions. In this study, we examined the ability of metformin, which was reported to possess intrinsic vasculoprotective properties independently of its antihyperglycemic effects, to inhibit PARP activation induced by high glucose concentrations in bovine aortic endothelial cells; and we investigated the potential mechanisms involved in this inhibition. The PARP activity was measured by cellular enzyme-linked immuno-specific assay (CELISA) method; cell poly(ribosyl)ated protein polymer accumulation was evaluated by immunofluorescence. Peroxynitrite anion productions were determined using dihydrorhodamine 123 fluoroprobe; and expression of p47phox subunit of nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase was analyzed by Western blot in the absence and presence of protein kinase C and NAD(P)H oxidase inhibitors (calphostin and diphenyleneiodonium chloride, respectively). Our data showed that a therapeutically relevant concentration of metformin (5.10(-5) mol/L) was able to abolish PARP activation, to reduce poly(ribosyl)ated protein polymer accumulation, to decrease intracellular peroxynitrite anion level, and to reverse the overexpression of p47phox in bovine aortic endothelial cells stimulated by 25 mmol/L glucose in a similar manner to that of calphostin or diphenyleneiodonium chloride. Taken together, these results suggest that metformin could inhibit glucose-induced PARP activation through blockade of a protein kinase C-dependent NAD(P)H oxidase activation pathway. We propose that some of the beneficial effects of metformin on vascular endothelial cell functions in diabetes may be related to its inhibitory effect on PARP overactivation and its deleterious consequences.

Erythropoietic stress and anemia in diabetes mellitus

Anemia is one of the world's most common preventable conditions, yet it is often overlooked, especially in people with diabetes mellitus. Diabetes-related chronic hyperglycemia can lead to a hypoxic environment in the renal interstitium, which results in impaired production of erythropoietin by the peritubular fibroblasts and subsequent anemia. Anemia in patients with diabetes mellitus might contribute to the pathogenesis and progression of cardiovascular disease and aggravate diabetic nephropathy and retinopathy. Anemia occurs earlier in patients with diabetic renal disease than in nondiabetic individuals with chronic kidney disease. Although erythropoietin has been used to treat renal anemia for nearly two decades, debate persists over the optimal target hemoglobin level. Most guidelines recommend that hemoglobin levels be maintained between 105g/l and 125g/l. The suggested role of anemia correction--to prevent the progression of left ventricular hypertrophy in patients with diabetes mellitus--is yet to be established. However, an emphasis on regular screening for anemia, alongside that for other diabetes-related complications, might help to delay the progression of vascular complications in these patients.

Moderate exercise attenuates caspase-3 activity, oxidative stress, and inhibits progression of diabetic renal disease in db/db mice

Diabetic nephropathy, the leading cause of end-stage renal disease, is characterized by a proapoptotic and prooxidative environment. The mechanisms by which lifestyle interventions, such as exercise, benefit diabetic nephropathy are unknown. We hypothesized that exercise inhibits early diabetic nephropathy via attenuation of the mitochondrial apoptotic pathway and oxidative damage. Type 2 diabetic db/db and normoglycemic wild-type mice were exercised for an hour everyday at a moderate intensity for 7 wk, following which renal function, morphology, apoptotic signaling, and oxidative stress were evaluated. Exercise reduced body weight, albuminuria, and pathological glomerular expansion in db/db mice independent of hyperglycemic status. Changes in renal morphology were also related to reduced caspase-3 (main effector caspase in renal apoptosis), caspase-8 (main initiator caspase of the "extrinsic" pathway) activities, and TNF-alpha expression. A role for the mitochondrial apoptotic pathway was unlikely as both caspase-9 activity (initiator caspase of this pathway) and expression of regulatory proteins such as Bax and Bcl-2 were unchanged. Kidneys from db/db mice also produced higher levels of superoxides and had greater oxidative damage concurrent with downregulation of superoxide dismutase (SOD) 1 and 3. Interestingly, although exercise also increased superoxides, there was also upregulation of multiple SODs that likely inhibited lipid (hydroperoxides) and protein (carbonyls and nitrotyrosine) oxidation in db/db kidneys. In conclusion, exercise can inhibit progression of early diabetic nephropathy independent of hyperglycemia. Reductions in caspase-3 and caspase-8 activities, with parallel improvements in SOD expression and reduced oxidative damage, could underlie the beneficial effects of exercise in diabetic kidney disease.

N-acetylcysteine prevents glucose/glucose oxidase-induced oxidative stress, mitochondrial damage and apoptosis in H9c2 cells

AIMS

High blood glucose may auto-oxidize and generate free radicals, which are proposed to induce apoptosis in cardiac cells. The aim of the present study was to investigate the cell damage induced by glucose/glucose oxidase-dependent oxidative stress and the protective effect of N-acetylcysteine (NAC) on H9c2 cardiac muscle cells.

MAIN METHODS

H9c2 cells were exposed to 33 mM glucose (G)+1.6 milliunits (mU) of glucose oxidase (GO) and termed G/GO. Cell apoptosis, generation of reactive oxygen species (ROS-super oxide anion and hydrogen peroxide) and reactive nitrogen species (RNS-peroxinitrite), and the change in mitochondrial membrane potential (DeltaPsim) was studied using flow cytometry and confocal microscopy, and cytochrome c release was measured using confocal microscopy. The expression of Bcl-2, Bax and the activation of procaspase-9 was studied by western blot.

KEY FINDINGS

Exposure of H9c2 cells to G/GO resulted in a significant increase in cellular apoptosis (P<0.05) and the generation of ROS and RNS (P<0.001). Further, G/GO treatment led to a decrease in DeltaPsim, release of cytochrome c, decrease in Bcl-2, increase in Bax expression and the activation of procaspase-9. Treatment with NAC significantly decreased apoptosis (P<0.05) and reduced the levels of ROS and RNS (P<0.001). NAC was also able to normalize DeltaPsim, inhibit cytochrome c release, increase Bcl-2 and decrease Bax expression and procaspase-9 activation.

SIGNIFICANCE

Our studies suggest that NAC has antioxidative and antiapoptotic activity against G/GO-induced oxidative stress through the inhibition of mitochondrial damage in H9c2 cells.

Attenuation of diabetic nephropathy by tocotrienol: involvement of NFkB signaling pathway

AIM

Diabetic nephropathy is a serious complication for patients with diabetes mellitus. Approximately 30-40% of patients with type I and 15% with type II diabetes mellitus develop end stage renal disease. The study was designed to evaluate the impact of tocotrienol on renal function and reno-inflammatory cascade in streptozotocin-induced diabetes.

MAIN METHODS

Streptozotocin (STZ)-induced diabetic rats were treated with tocotrienol (25, 50 and 100 mg/kg), alpha-tocopherol (100 mg/kg) or with vehicle form 5th to 8th weeks. After 8 weeks, urine albumin excretion, urine output, serum creatinine, blood urea nitrogen, creatinine and urea clearance were measured. Cytoplasmic and nuclear fractions of kidney was prepared for the quantification of oxidative-nitrosative stress (lipid peroxidation, superoxide dismutase, catalase, non protein thiols, total nitric oxide), tumor necrosis factor-alpha (TNF-alpha), tissue growth factor-1beta (TGF-beta1), p65 subunit of NFkappabeta and caspase-3.

KEY FINDINGS

After 8 weeks of STZ injection, the rats produced significant alteration in renal function, increased oxidative-nitrosative stress, TNF-alpha, TGF-beta1, caspase-3 activity in cytoplasmic lysate and active p65 subunit of NFkappabeta in nuclear lysate of kidney of diabetic rats. Interestingly, co-administration of tocotrienol significantly and dose-dependently prevented biochemical and molecular changes associated with diabetes. Tocotrienol (100 mg/kg) was demonstrated to be more effective than alpha-tocopherol (100 mg/kg). Moreover, diabetic rats treated with insulin-tocotrienol combination produced more pronounced effect on molecular parameters as compared to their respective groups.

SIGNIFICANCE

Taken together, the data reveal that tocotrienol modulates the release of profibrotic cytokines, oxidative stress, ongoing chronic inflammation and apoptosis and thus exerts a marked renoprotective effect.

Serofendic acid protects from iodinated contrast medium and high glucose probably against superoxide production in LLC-PK1 cells

BACKGROUND

It is well known that patients with chronic kidney disease, including diabetic nephropathy, often develop cardiovascular diseases. In case of radiographic procedures, reduced renal function may be deteriorated by the use of iodinated contrast medium (CM). This is known as CM-induced nephropathy. In this study, we have focused on the mechanisms of this type of injury in diabetic nephropathy and the preventive effects of serofendic acid.

METHODS

We evaluated the cytotoxicity of CM and high glucose on tubular epithelial cells using an LLC-PK1 cell line, and measured cell viability with an alamarBlue assay. We further evaluated superoxide production levels measured by dihydroethidium. We also examined the protective effects of serofendic acid on cytotoxicity with superoxide production of CM and high glucose.

RESULTS

CM reduced cell numbers in a dose-dependent and time-dependent manner in LLC-PK1 cells. Furthermore, cytotoxicity of CM in diluted concentration was additively influenced by high glucose. CM and high glucose increased superoxide production, which was evaluated by the response to dihydroethidium, and was suppressed by serofendic acid. Cytotoxicity of CM, high glucose, and H(2)O(2) was suppressed by serofendic acid, as well as the suppression by N-acetylcysteine on CM toxicity. Interestingly, the recovery by serofendic acid in H(2)O(2)- and high glucose-induced cellular injury was to the basal level, in contrast with the partial recovery from CM-induced injury. Finally, serofendic acid suppressed CM-induced injury and high glucose-induced apoptosis.

CONCLUSIONS

These results suggest that CM and high glucose induce cytotoxicity and oxidative stress in LLC-PK1 cells and that serofendic acid protects the injury probably from superoxide generation.

Oxidative stress as a common mediator for apoptosis induced-cardiac damage in diabetic rats

AIM

To investigate the possible role of oxidative stress as a common mediator of apoptosis and cardiac damage in diabetes.

MATERIALS AND METHODS

This experimental work was conducted on 5 groups of Wistar rats. Group I was the control group. Diabetes type 1 was induced in other groups (by streptozotocin) and animals received insulin or vitamin E (300 mg /kg body weight), both insulin and vitamin E, or no treatment for 4 weeks according to their group. At the end of the study, serum and cardiac tissues were examined for biochemical parameters of cardiac function, oxidative stress and apoptosis. Electron microscopy pictures of cardiac tissue were also evaluated for signs of cardiac damage

RESULTS

Markers of oxidative stress, apoptosis, inflammation as well as manifestations of cardiac damage as assessed by electron microscopy were significantly decreased in rats treated with both insulin and vitamin E when compared with untreated diabetic rats or rats treated with either insulin or vitamin E alone

CONCLUSION

Administration of both vitamin E and insulin was effective in reducing markers of oxidative stress and apoptosis and improving parameters of cardiac function in experiments animals. Antioxidants might prove beneficial as an adjuvant treatment in addition to insulin in type 1 diabetes associated with manifestations of cardiac complications.

Mitochondrial fission mediates high glucose-induced cell death through elevated production of reactive oxygen species

AIMS

One of the main causes of cardiovascular complications in diabetes is the hyperglycaemia-induced cell injury, and mitochondrial fission has been implicated in the apoptotic process. We investigated the role of mitochondrial fission in high glucose-induced cardiovascular cell injury.

METHODS AND RESULTS

We used several types of cultured mouse, rat, and bovine cells from the cardiovascular system, and evaluated mitochondrial morphology, reactive oxygen species (ROS) levels, and apoptotic parameters in sustained high glucose incubation. Adenoviral infection was used for the inhibition of the fission protein DLP1. We found that mitochondria were short and fragmented in cells incubated in sustained high glucose conditions. Under the same conditions, cellular ROS levels were high and cell death was increased. We demonstrated that the increased level of ROS causes mitochondrial permeability transition (MPT), phosphatidylserine exposure, cytochrome c release, and caspase activation in prolonged high glucose conditions. Importantly, maintaining tubular mitochondria by inhibiting mitochondrial fission in sustained high glucose conditions normalized cellular ROS levels and prevented the MPT and subsequent cell death. These results demonstrate that mitochondrial fragmentation is an upstream factor for ROS overproduction and cell death in prolonged high glucose conditions.

CONCLUSION

These findings indicate that the fission-mediated fragmentation of mitochondrial tubules is causally associated with enhanced production of mitochondrial ROS and cardiovascular cell injury in hyperglycaemic conditions.

Renal mitochondrial damage and protein modification in type-2 diabetes

Although mitochondrial reduction-oxidation (redox) stress and increase in membrane permeability play an important role in diabetic-associated renal microvasculopathies, it is unclear whether the intra-renal mitochondrial oxidative stress induces mitochondrial protein modifications, leading to increase mitochondrial membrane permeability. The hypothesis is that mitochondrial oxidative stress induces mitochondrial protein modification and leakage in the mitochondrial membrane in type-2 diabetes. The present study was conducted to determine the involvement of intra-renal mitochondrial oxidative stress in mitochondrial protein modifications and modulation of membrane permeability in the setting of type-2 diabetes. Diabetes was induced by 6-week regimen of a high calorie and fat diet in C57BL/6J mice (Am J Physiol 291:F694-F701, 2006). Subcellular fractionation was carried out in kidney tissue from wild type and diabetic mice. All fractions were highly enriched in their corresponding marker enzyme. Subcellular protein modifications were determined by Western blot and 2-D proteomics. The results suggest that diabetes-induced oxidative stress parallels an increase in NADPH oxidase-4 (NOX-4) and decrease in superoxide dismutase-1, 2 (SOD-1, 2) expression, in mitochondrial compartment. We observed loss of mitochondrial membrane permeability as evidenced by leakage of mitochondrial cytochrome c and prohibitin to the cytosol. However, there was no loss in control tissue. The 2-D Western blots for mitochondrial post-translational modification showed an increase in nitrotyrosine generation in diabetes. We conclude that diabetes-induced intra-renal mitochondrial oxidative stress is reflected by an increase in mitochondrial membrane permeability and protein modifications by nitrotyrosine generation.

Blockade of chronic high glucose-induced endothelial apoptosis by Sasa borealis bamboo extract

Hyperglycemia is a causal factor in the development of diabetic vascular complications including impaired vascular smooth muscle contractility and increased cell proliferation. The present study was designed to investigate the effects of Sasa borealis water-extract (SBwE) on chronic hyperglycemia-induced oxidative stress and apoptosis in human umbilical endothelial cells (HUVEC). HUVEC were cultured in 5.5 mM low glucose, 5.5 mM glucose plus 27.5 mM mannitol as an osmotic control, or 33 mM high glucose for 5 days in the absence and presence of 1-30 microg/ ml SBwE. Caspase-3 activation and Annexin V staining revealed chronic high glucose-induced endothelial apoptotic toxicity with a generation of oxidants detected by DCF-fluorescence, and these effects were reversed by SBwE at > or =1 microg/ml in a dose-dependent manner. Cytoprotective SBwE substantially reduced the sustained high glucose-induced expression of endothelial nitric oxide synthase and attenuated the formation of peroxynitrite radicals. The suppressive effects of SBwE were most likely mediated through blunting activation of PKC beta 2 and NADPH oxidase promoted by high glucose. In addition, this bamboo extract modulated the high glucose-triggered mitogen-activated protein kinase-dependent upregulation of heat-shock proteins. Our results suggest that SBwE suppressed these detrimental effects caused by PKC-dependent peroxynitrite formation via activation of NADPH oxidase and induction of nitric oxide synthase and heat-shock protein family that may be essential mechanisms responsible for increased apoptotic oxidative stress in diabetic vascular complications. Moreover, the blockade of high glucose-elicited heat-shock protein induction appeared to be responsible for SBwE-alleviated endothelial apoptosis. Therefore, SBwE may be a therapeutic agent for the prevention and treatment of diabetic endothelial dysfunction and related complications.

Epigallocatechin gallate, a constituent of green tea, regulates high glucose-induced apoptosis

A high concentration of glucose has been implicated as a causal factor in initiation and progression of diabetic complications, and there is evidence to suggest that hyperglycemia increases the production of free radicals and oxidative stress. Therefore, compounds that scavenge reactive oxygen species may confer regulatory effects on high glucose-induced apoptosis. Epigallocatechin gallate (EGCG), the major polyphenolic of green tea, is reported to have an antioxidant activity. We investigated the effect of EGCG on high glucose-induced apoptosis in U937 cells. Upon exposure to 35 mM glucose for 2 days, there was a distinct difference between untreated cells and cells pre-treated with 1 microM EGCG for 2 h in regard to cellular redox status and oxidative DNA damage to cells. EGCG pre-treated cells showed significant suppression of apoptotic features such as DNA fragmentation, damage to mitochondrial function, and modulation of apoptotic marker proteins upon exposure to high glucose. This study indicates that EGCG may play an important role in regulating the apoptosis induced by high glucose presumably through scavenging of reactive oxygen species.

Mechanisms of disease: the hypoxic tubular hypothesis of diabetic nephropathy

Diabetic nephropathy is traditionally considered to be a primarily glomerular disease, although this contention has recently been challenged. Early tubular injury has been reported in patients with diabetes mellitus whose glomerular function is intact. Chronic hypoxia of the tubulointerstitium has been recognized as a mechanism of progression that is common to many renal diseases. The hypoxic milieu in early-stage diabetic nephropathy is aggravated by manifestations of chronic hyperglycemia-abnormalities of red blood cells, oxidative stress, sympathetic denervation of the kidney due to autonomic neuropathy, and diabetes-mellitus-induced tubular apoptosis; as such, tubulointerstitial hypoxia in diabetes mellitus might be an important early event. Chronic hypoxia could have a dominant pathogenic role in diabetic nephropathy, not only in promoting progression but also during initiation of the condition. Early loss of tubular and peritubular cells reduces production of 1,25-dihydroxyvitamin D3 and erythropoietin, which, together with dysfunction of their receptors caused by the diabetic state, diminishes the local trophic effects of the hormones. This diminution could further compromise the functional and structural integrity of the parenchyma and contribute to the gradual decline of renal function.

Attenuation of interstitial fibrosis and tubular apoptosis in db/db transgenic mice overexpressing catalase in renal proximal tubular cells

OBJECTIVE

The present study investigated the relationships between reactive oxygen species (ROS), interstitial fibrosis, and renal proximal tubular cell (RPTC) apoptosis in type 2 diabetic db/db mice and in db/db transgenic (Tg) mice overexpressing rat catalase (rCAT) in their RPTCs (db/db rCAT-Tg).

RESEARCH DESIGN AND METHODS

Blood pressure, blood glucose, and albuminuria were monitored for up to 5 months. Kidneys were processed for histology and apoptosis studies (terminal transferase-mediated dUTP nick-end labeling or immunostaining for active caspase-3 and Bax). Real-time quantitative PCR assays were used to quantify angiotensinogen (ANG), p53, and Bax mRNA levels.

RESULTS

db/db mice developed obesity, hyperglycemia, hypertension, and albuminuria. In contrast, db/db rCAT-Tg mice became obese and hyperglycemic but had normal blood pressure and attenuated albuminuria compared with db/db mice. Kidneys from db/db mice displayed progressive glomerular hypertrophy, glomerulosclerosis, interstitial fibrosis, and tubular apoptosis and increased expression of collagen type IV, Bax, and active caspase-3, as well as increased ROS production. These changes, except glomerular hypertrophy, were markedly attenuated in kidneys of db/db rCAT-Tg mice. Furthermore, ANG, p53, and Bax mRNA expression was increased in renal proximal tubules of db/db mice but not of db/db rCAT-Tg mice.

CONCLUSIONS

Our results indicate a crucial role for intra-renal ROS in the progression of hypertension, albuminuria, interstitial fibrosis, and tubular apoptosis in type 2 diabetes and demonstrate the beneficial effects of suppressing ROS formation.

Potential interventions in sepsis-related acute kidney injury

Sepsis is an important cause of morbidity and mortality. Acute kidney injury often complicates sepsis, leading to greater complexity, cost of care, and worsening prognosis. In recent years, a consensus definition of acute kidney injury has been developed, facilitating research into the pathophysiology and epidemiology of this disorder. New and emerging biomarkers to recognize kidney injury before functional abnormalities are manifest may allow early recognition and facilitate prevention or treatment. Furthermore, advances in the clinical management of sepsis may have secondary benefits with respect to renal outcomes. Existing and hybrid extracorporeal therapies are being investigated not only as means to replace lost kidney function but also to modulate the immune response to sepsis. For those who have more advanced forms of kidney injury, strategies to promote renal recovery are being sought to minimize the long-term consequences of impaired kidney function. This review provides an update on the current state of the science and a glimpse toward the future of intervention in sepsis-related acute kidney injury.

Change in post-translational modifications of histone H3, heat-shock protein-27 and MAP kinase p38 expression by curcumin in streptozotocin-induced type I diabetic nephropathy

BACKGROUND AND PURPOSE

Curcumin has been used to treat cancer, diabetes and other pathologies. However, little is known regarding its role in altering post-translational modifications of histone H3. A recent report suggests that acute hyperglycaemia induces a global down-regulation of gene expression in human tissues and epigenetic regulation of gene expression could be a novel mechanism underlying the pathological processes of hyperglycaemia. The present study was undertaken to examine changes in histone modification by curcumin treatment which prevents development of type I diabetic nephropathy.

EXPERIMENTAL APPROACH

Male Sprague-Dawley rats were rendered diabetic using a single dose of streptozotocin (55 mg kg(-1), i.p.). Diabetic nephropathy was assessed by measurements of blood urea nitrogen, albumin and creatinine levels. Post-translational modifications of histone H3, heat shock protein-27 (HSP-27) and mitogen-activated protein (MAP) kinase p38 expression were examined by western blotting.

KEY RESULTS

Treatment of diabetic rats with curcumin significantly decreased blood urea nitrogen and creatinine and increased albumin; variables associated with the development of diabetic nephropathy. There were also increased levels of HSP-27 and MAP kinase (p38) in diabetic kidney. However, curcumin treatment prevented this increase in HSP-27 and p38 expression. Moreover, at nuclear level curcumin prevented the decrease in dephosphorylation and increases acetylation of histone H3.

CONCLUSIONS AND IMPLICATIONS

Our results suggested that protection against development of diabetic nephropathy by curcumin treatment involved changes in post-translational modifications of histone H3, expression of HSP-27 and MAP kinase p38 in diabetic kidney.

Apoptosis in the kidneys of patients with type II diabetic nephropathy

The occurrence and extent of apoptosis in the kidneys of patients with diabetic nephropathy is largely unknown. We evaluated apoptosis in renal biopsies obtained from patients with early or advanced type II diabetic nephropathy. Apoptosis was about 6- and 3-fold higher, respectively, in glomeruli and tubules in kidneys of patients with early nephropathy than in the normal kidney and this was not further increased in advanced diabetic nephropathy. Glomerular apoptosis was related directly to hemoglobin A1(c) and systolic blood pressure, whereas tubular cell apoptosis correlated to diabetes duration and low-density lipoprotein-cholesterol. Fas, Fas ligand, and p38 mitogen-activated protein kinase expressions were enhanced in glomeruli and tubules; however, this did not correlate with apoptosis. In patients with proteinuria, apoptosis was associated with the subsequent loss of kidney function. When these parameters were subjected to multivariate analysis, only glomerular apoptosis retained a significant independent predictive value. Our findings suggest that apoptosis might be a clinically relevant mechanism of glomerular and tubular cell loss in proteinuric type II diabetic patients.

Blockade of oxidative stress by vitamin C ameliorates albuminuria and renal sclerosis in experimental diabetic rats

PURPOSE

Oxidative stress has been suggested to play a role as a common mediator of apoptosis and kidney damage in diabetes. However, it is uncertain whether the apoptosis occurs in the kidney during the course of diabetes. We investigated the occurrence of apoptosis in the diabetic rat kidney, the role of oxidative stress and the effect of an antioxidant on apoptosis in the diabetic rat kidney.

MATERIALS AND METHODS

Otsuka-Long-Evans-Tokushima-Fatty rats, an animal model for type 2 diabetes, were randomized into a non-treated diabetic (n=8) and a vitamin C-treated group (n=8). Long-Evans Tokushima Otsuka rats (n=8) were used as a control.

RESULTS

Apoptosis was present in the epithelial cells of the proximal tubules in diabetic rats. The number of apoptotic cells, albuminuria, proteinuria, glomerular and tubulointerstitial sclerosis, and renal malondialdehyde were significantly decreased in vitamin C-treated diabetic rats when compared to the untreated diabetic rats. The decreased slit pore density (number of slit pores per underlying glomerular basement membrane length) as assessed by electron microscopy was also significantly restored by treatment with vitamin C without significantly affecting plasma glucose in diabetic rats.

CONCLUSION

By blocking these pathophysiologic processes, a blockade of oxidative stress by vitamin C might become a useful adjunct to albuminuria and renal sclerosis in diabetic nephropathy.

Protective effect of persimmon peel polyphenol against high glucose-induced oxidative stress in LLC-PK1 cells

The effect of persimmon peel polyphenol (PPP) on high glucose-induced oxidative stress was investigated using LLC-PK(1) cells, which is susceptible to oxidative stress. High-concentration glucose (30 mM) treatment induced LLC-PK(1) cell death, but high molecular-PPP (HMPPP) and low molecular-PPP (LMPPP), at concentrations of 5 or 10 microg/ml, significantly inhibited the high glucose-induced cytotoxicity. Furthermore, treatment with HMPPP or LMPPP dose-dependently reduced the intracellular reactive oxygen species level increased by 30 mM glucose. In addition, nitric oxide, superoxide and peroxynitrite levels were increased by 30 mM glucose treatment, but they were concentration-dependently inhibited by HMPPP or LMPPP treatment. High glucose levels induced the overexpressions of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) proteins, but HMPPP or LMPPP treatment reduced the overexpressions of these proteins. HMPPP or LMPPP also inhibited the nuclear translocation of nuclear factor-kappa B (NF-kappaB) induced by 30 mM glucose in LLC-PK(1) cells. In particular, LMPPP exhibited stronger inhibitory activities on high glucose induced oxidative stress than HMPPP. These findings indicate the potential benefits of persimmon peel as a valuable source of antioxidants in the diabetic condition which will reduce the oxidative stress induced by hyperglycemia.

Diabetes increases apoptosis and necrosis in both ischemic and nonischemic human myocardium: Role of caspases and poly–adenosine diphosphate–ribose polymerase

OBJECTIVES

Diabetes is an important predictor of morbidity and mortality after cardiac surgery, but the reason is unclear. The aims of these studies, therefore, were to elucidate whether cell death is greater in ischemic and nonischemic diabetic human myocardium than in nondiabetic myocardium and to investigate the underlying mechanism.

METHODS

The right atrial appendages (n = 8 per group) of patients without diabetes and patients with type 1 and 2 diabetes were subjected to 90 minutes of simulated ischemia and 120 minutes reoxygenation. Tissue injury was measured by the release of creatine kinase into the media, and cellular apoptosis and necrosis were assessed in tissue by the terminal transferase deoxyuridine triphosphate nick-end labeling assay and propidium iodide staining. Initiator and effector caspases activations were also measured.

RESULTS

Apoptosis and necrosis were greater in the type 2 and type 1 diabetes groups than in the nondiabetes group both in fresh tissue and after simulated ischemia-reoxygenation. Activation of effector caspases was also higher in the diabetes groups than in the nondiabetes group after simulated ischemia-reoxygenation. Caspase-3 inhibition reduced apoptosis in all study groups without influencing necrosis; however, poly-adenosine diphosphate-ribose polymerase inhibition resulted in a similar reduction in apoptosis and in necrosis in all groups, whereas caspase-2 inhibition did not.

CONCLUSIONS

Diabetes increases both apoptosis and necrosis in human myocardium, both fresh and after being subjected to ischemia-reoxygenation, an effect that is mediated, at least in part, by caspase-3 and poly-adenosine diphosphate-ribose polymerase activation. These results may explain the increased cardiac-related morbidity and mortality associated with cardiac surgery in patients with diabetes.

Ursolic acid regulates high glucose-induced apoptosis

A high concentration of glucose has been implicated as a causal factor in initiation and progression of diabetic complications and there is evidence to suggest that hyperglycemia increases the production of free radicals and oxidative stress. Therefore, compounds that scavenge reactive oxygen species (ROS) may confer regulatory effects on high glucose-induced apoptosis. Ursolic acid (UA), a pentacyclic triterpene, is reported to have an antioxidant activity. We investigated the effect of UA on high glucose-induced apoptosis in U937 cells. Upon exposure to 35 mM glucose for two days, there was a distinct difference between untreated cells and cells pre-treated with 50 nM UA for 2 h in regard to cellular redox status and oxidative DNA damage to cells. UA pre-treated cells showed significant suppression of apoptotic features such as DNA fragmentation, damage to mitochondrial function and modulation of apoptotic marker proteins upon exposure to high glucose. This study indicates that UA may play an important role in regulating the apoptosis induced by high glucose presumably through scavenging of ROS.

Oxidative stress as a common pathway to chronic tubulointerstitial injury in kidney allografts

A major challenge for kidney transplantation is to dissect out the identifiable causes of chronic allograft tubulointerstitial fibrosis and to develop cause-specific treatment strategies. There has been a recent interest in the role of oxidative stress (OS) as a mediator of injury in chronic allograft tubular atrophy (TA) and interstitial fibrosis (IF). A review of the literature and data from my laboratory studying chronic allograft TA/IF in rat, rhesus monkey, and human kidneys suggests that OS is increased in graft-infiltrating macrophages, activated myofibroblasts, interstitium, and areas of tubular injury. Chronic allograft OS may be induced by inflammation, abnormal tissue oxygenation, immunosuppressant drugs, and comorbid clinical conditions including diabetes, hypertension, proteinuria, anemia, and dyslipidemia. Moreover, OS-induced chronic TA/IF is associated with signaling pathways including inflammation, apoptosis, hypoxia, and epithelial-to-mesenchymal transition. Most of these injury pathways participate in a self-perpetuating cycle with OS. In conclusion, evidence suggests that OS is a common mechanism of injury in chronic allograft TA/IF. However, most available data demonstrate a correlation and no causal relationship. Furthermore, the extent to which TA/IF is dependent on OS is unknown. These questions may be answered by prospective randomized placebo-control trials examining the role of select antioxidants in the prevention of chronic allograft TA/IF.

Mitochondria are the major targets in albumin-induced apoptosis in proximal tubule cells

Nephrotic-range proteinuria is considered a poor prognostic factor. A correlation between tubulointerstitial injury and the degree of proteinuria is well established. In an attempt to explain the tubular atrophy that is observed in advanced glomerulonephritides, this study investigated apoptotic mechanisms in cultured human proximal tubule cells (HKC-8) that were exposed to endotoxin-free albumin (5, 10, and 20 mg/ml). Apoptosis was detected by Hoechst 33342; annexin staining; and assays for caspases 3, 8, and 9. The apoptotic effect of albumin was maximal at 10 mg/ml albumin, and necrosis prevailed in cells that were incubated with 20 mg/ml. Increase in caspase-9 and -3 activity was observed starting at 6 and maximally at 16 to 24 h. The proapoptotic Bcl-2 protein Bax was upregulated at 6 h, associated with translocation of cytochrome-c from mitochondria to cytosol and alteration in the mitochondrial membrane potential. Production of reactive oxygen species (ROS) was significant at 6 h but declined at 16 and 24 h. Treatment with ROS scavenger dimethylthiourea or antioxidant N-acetylcysteine did not alleviate caspase-3 production. Pan protein kinase C inhibitor bisindolylmaleimide-1 protected the cells from apoptosis. It is concluded that albumin induces apoptosis in human proximal tubule cells by stimulating mitochondrial apoptotic pathway independent of ROS production.

Catalase overexpression attenuates angiotensinogen expression and apoptosis in diabetic mice

Increased generation of reactive oxygen species (ROS) leads to oxidative stress in diabetes. Catalase is a highly conserved heme-containing protein that reduces hydrogen peroxide to water and oxygen and is an important factor decreasing cellular injury owing to oxidative stress. Hyperglycemic conditions increase oxidative stress and angiotensinogen gene expression. Angiotensinogen conversion to angiotensin II leads to a furtherance in oxidative stress through increased generation of reactive oxygen species. In this study, we utilized mice transgenically overexpressing rat catalase in a kidney-specific manner to determine the impact on ROS, angiotensinogen and apoptotic gene expression in proximal tubule cells of diabetic animals. Proximal tubules isolated from wild-type and transgenic animals without or with streptozotocin-induced diabetes were incubated in low glucose media in the absence or presence of angiotensin II or in a high-glucose media. Our results show that the overexpression of catalase prevents the stimulation of ROS and angiotensinogen mRNA in tubules owing to elevated glucose or angiotensin II in vitro. Additionally, overexpression of catalase attenuated ROS generation, angiotensinogen and proapoptotic gene expression and apoptosis in the kidneys of diabetic mice in vivo. Our studies point to an important role of ROS in the pathophysiology of diabetic nephropathy.

Melatonin is more effective than taurine and 5-hydroxytryptophan against hyperglycemia-induced kidney-cortex tubules injury

The antioxidative effects of melatonin (Mel), 5-hydroxytryptophan (5-HTP) and taurine (TAU) on hyperglycemia-induced oxidative stress was investigated in primary cultures of kidney-cortex tubule cells grown in metabolically and hormonally defined medium. In the presence of 30 mm glucose (hyperglycemic conditions), cell viability was decreased by about 35% in comparison with that estimated in the glucose-depleted medium probably as a result of induction of apoptosis, as concluded from: (i) chromatin condensation and DNA fragmentation assays, (ii) a significant enhancement of reactive oxygen species (ROS) production, (iii) 8-hydroxydeoxyguanosine (8-OHdG) generation, (iv) an increased protein peroxidation and (v) a decline of reduced glutathione (GSH) levels leading to a disturbed glutathione redox state. The addition of 100 microm Mel to the hyperglycemic medium resulted in a twofold decrease in both 8-OHdG accumulation and protein peroxidation as well as restoration of the control intracellular ROS levels accompanied by a substantial increase in GSH/oxidized glutathione (GSSG) ratio due to a decline in GSSG content. ROS elimination was also achieved in the presence of 1 mm TAU which diminished protein and DNA injuries by about 25% and 30%, respectively. On the contrary, the action of 100 microm 5-HTP on ROS level, 8-OHdG generation, protein peroxidation and GSH/GSSG ratio was negligible. Thus, in contrast to 5-HTP and TAU, Mel might be considered as beneficial for diabetes therapy, particularly in terms of reduction of hyperglycemia-induced kidney injury.