Inhibition of oxidant-induced lipid peroxidation in cultured renal tubular epithelial cells (LLC-PK1) by quercetin

Herbal antioxidants in dialysis patients: a review of potential mechanisms and medical implications

The consumption of exogenous antioxidants isolated from herbal extracts has shown beneficial effects on ameliorating dialysis-related complications through debilitating oxidative stress and inflammatory process. Many clinical studies available in public databases have reported the improved consequences of dialysis in patients supplemented with herbal antioxidants. Exploration of such data offers great possibilities for gaining insights into the potential mechanisms and medical implications of herbal antioxidants. In this work, the mechanisms and implications of some famous bioactive substances including silymarin, curcumin, resveratrol, emodin, and quercetin on the consequences of dialysis in chronic kidney disease (CKD) patients were explored. The protective features of silymarin are due to the flavonoid complex silybin. Curcumin is an active element from the root of curcuma longa with extensive beneficial properties, including antioxidant, anti-inflammatory activity, and inhibitory effects on cell apoptosis. Resveratrol can reduce the oxidative stress by neutralization of free radicals. Emodin is known as a natural anthraquinone derivative isolated from Chinese herbs. Finally, quercetin has been reported to exhibit several properties including antioxidant, anti-diabetic, analgesic, antihistaminic, antiviral, cholesterol reducer, and renal hemodynamic modulator. However, potential mechanisms and medical implications of the aforementioned herbal antioxidants seem to be more complicated, that is, more studies are required in this field.

Quercetin, a Promising Clinical Candidate for The Prevention of Contrast-Induced Nephropathy

Iodinated contrast media (CM) are the leading cause of acute renal failure of toxic origin. Between 21% and 50% of patients that receive them develop contrast-induced nephropathy (CIN). All prophylactic measures used so far have failed to provide effective prevention. Since oxidative stress is involved in the damage, a possible preventive strategy could be the administration of antioxidant substances, such as quercetin. This compound has shown renoprotective effects in experimental studies. The aim of this study was to evaluate whether quercetin may be helpful in preventing CIN in patients undergoing coronary catheterization. A clinical phase II study was conducted. Patients were distributed in two groups, namely, CM (patients who only received contrast media) and CM+Q (patients who were pretreated with quercetin orally for 3-5 days). Results showed less incidence of CIN in the CM+Q group, possibly due to glomerular protection, evidenced by a lower increase in serum creatinine and albuminuria; and a lower decrease in the glomerular filtration rate (GFR). Furthermore, in this group, the relative risk of developing CIN observed in patients that received a high dose of contrast media was inferior. In conclusion, this is the first study that demonstrates that quercetin is a promising safe candidate in preventing CIN.

Onion bulb extract reduces colitis severity in mice via modulation of colonic inflammatory pathways and the apoptotic machinery

ETHNOPHARMACOLOGICAL RELEVANCE

The use of nutraceutical-based products has increased in recent years due to their demonstrated efficacy and their good safety profile. Onion is one of the most commonly used plants in the traditional medicine for the management of various conditions including inflammatory and gastrointestinal diseases. However, little is known regarding the molecular mechanism of the anti-inflammatory effects of onion particularly in inflammatory bowel disease (IBD).

AIM OF THE STUDY

To test the anti-inflammatory effects of onion bulb extract (OBE) in an IBD mouse model and the molecular mechanisms responsible for these effects such as modulation of the expression and/or the activity profile of various pro-inflammatory molecules.

MATERIALS AND METHODS

Colitis was induced in mice by dextran sulfate sodium (DSS) daily administration for 5 days. Animals were sacrificed, colons were removed and the severity of the inflammation was determined by the gross and histological assessments. The colonic level/activity of various cytokines and chemokines were measured using proteome profiling-based assay, western blotting, and immunofluorescence techniques.

RESULTS

DSS-induced colitis was significantly reduced by the daily OBE treatment and 5-aminosalicylic acid (5-ASA, positive control), particularly at 100-200 mg/kg doses, at both the gross and histological levels. OBE was also shown to reduce colonic expression and activity of several pro-inflammatory molecules and signaling pathways, such as mitogen activated protein kinase family, mammalian target of rapamycin, cyclooxygenase-2, and tissue inhibitors of metalloproteinases. In addition, OBE reduced the expression of interferon-γ, various C-C and C-X-C chemokines, and molecules involved in the apoptotic machinery such as cytochrome c, caspase-3 and -8, B-cell lymphoma-extra-large and -2.

CONCLUSIONS

OBE showed anti-inflammatory actions in IBD mouse model, which is attributed, in part, to the modulation of the expression and the activity of important pro-inflammatory molecules and signaling pathways involved in the inflammatory response. These data suggest that OBE may be a promising lead in the therapeutic management of IBD.

Does silybin protect against toxicity induced by polymyxin E in rat kidney?

AIMS

Although once a common antibiotic, polymyxin E fell out of favor after reports of its nephrotoxicity. However, recent concerns with gram-negative bacteria, which are resistant to multiple antibiotics, have resulted in increased interest in polymyxin E. Silybin is a known antihepatotoxic drug and may have potential for protecting the kidney from polymyxin E. Therefore, the aim of the current study was to evaluate whether silybin affected the damages produced by polymyxin E on the rat kidney.

METHODS

Four groups of rats with 10 rats per group were included in the study: control (no treatment, group I), vehicle (control vehicle treatment, group II), polymyxin E treatment (group III), and polymyxin E and silybin treatment (group IV). Groups II-IV received intravenous treatment twice a day for 7 days. All rats were euthanized after 7 days. Histological, ultrastructural, and morphometric analyses were performed on the rats' kidney tissues.

RESULTS

Analysis of tissues from group III showed differences from groups I and II, such as glomerular and tubular affection and changes in morphometric measures. Results for group IV were more similar to those of groups I and II than those of group III.

CONCLUSIONS

Our results suggested that administering silybin with polymyxin E alleviated polymyxin E-induced nephrotoxicity in the rat kidney. Future biochemical studies should investigate whether silybin could ameliorate the nephrotoxicity caused by polymyxin E in rats and whether concomitant administration of silybin could be an effective clinical pharmacological strategy to protect against polymyxin E-induced insult in human kidneys.

Beneficial effect of the bioflavonoid quercetin on cholecystokinin-induced mitochondrial dysfunction in isolated rat pancreatic acinar cells

The pathogenesis of acute pancreatitis (AP) is still poorly understood. Thus, a reliable pharmacological therapy is currently lacking. In recent years, an impairment of the energy metabolism of pancreatic acinar cells, caused by Ca(2+)-mediated depolarization of the inner mitochondrial membrane and a decreased ATP supply, has been implicated as an important pathological event. In this study, we investigated whether quercetin exerts protection against mitochondrial dysfunction. Following treatment with or without quercetin, rat pancreatic acinar cells were stimulated with supramaximal cholecystokinin-8 (CCK). CCK caused a decrease in the mitochondrial membrane potential (MMP) and ATP concentration, whereas the mitochondrial dehydrogenase activity was significantly increased. Quercetin treatment before CCK application exerted no protection on MMP but increased ATP to a normal level, leading to a continuous decrease in the dehydrogenase activity. The protective effect of quercetin on mitochondrial function was accompanied by a reduction in CCK-induced changes to the cell membrane. Concerning the molecular mechanism underlying the protective effect of quercetin, an increased AMP/ATP ratio suggests that the AMP-activated protein kinase system may be activated. In addition, quercetin strongly inhibited CCK-induced trypsin activity. The results indicate that the use of quercetin may be a therapeutic strategy for reducing the severity of AP.

Toxic effects of microbial phenolic acids on the functions of mitochondria

Low-molecular-weight phenolic acids (PhAs) phenylacetate, phenyllactate, phenylpropionate, p-hydroxyphenyllactate, and p-hydroxyphenylacetate are essentially the products of the degradation of aromatic amino acids and polyphenols by the intestinal microflora. In sepsis, the concentrations of some of these acids in the blood increase tens of times. Assuming that these compounds can cause the mitochondrial dysfunction in sepsis, we examined their effects on respiration, the induction of pore opening, and the production of reactive oxygen species (ROS) in mitochondria. It was found that phenylpropionate and phenylacetate produce a more toxic effect on mitochondria than the other phenolic acids. At concentrations 0.01-0.1 mM they decreased the rate of oxidation of NAD-dependent substrates and activated the Ca2+- and menadione-induced opening of the cyclosporin A-sensitive pore and the production of ROS. The disturbances caused by these PhAs are similar to those observed in mitochondria in sepsis, and hence the rise in their level may be one of the causes of mitochondrial dysfunctions. Phenyllactate, p-hydroxyphenyllactate, and p-hydroxyphenylacetate inhibited the production of ROS and pore opening, acting as antioxidants. Thus, the ability of PhAs to affect the mitochondrial functions, as well as an increase in their concentrations in sepsis (the total concentration of these PhAs in the blood is close to 0.1 mM), suggests that PhAs can be directly involved in the development of mitochondrial failure.

Antioxidants in the Prevention of Renal Disease

Reactive oxygen species (ROS) play a key role in the pathophysiological processes of renal diseases. The cellular damage is mediated by an alteration in the antioxidant status, which increases the concentration of ROS in the stationary state (oxidative stress). Oxidative stress mediates a wide range of renal impairments, from acute renal failure, rhabdomyolysis, obstructive nephropathy, hyperlipidemia, and glomerular damage to chronic renal failure and hemodialysis. Therefore, interventions favoring the scavenging and/or depuration of ROS (dietary and pharmacological antioxidants) should attenuate or prevent the oxidative stress, thereby mitigating against the subsequent renal damage.

Improved Cold Preservation of Kidney Tubular Cells by Means of Adding Bioflavonoids to Organ Preservation Solutions

BACKGROUND

Cold ischemia and reperfusion during renal transplantation result in release of reactive oxygen species. The aim of this study is to examine whether cold storage induced cell injury can be ameliorated by adding flavonoids directly to preservation solutions.

METHODS

Cultured renal tubular epithelial cells (LLC-PK1) were stored in University of Wisconsin (UW) or Euro-Collins (EC) solution at 4 degrees C for 20 hours. Preservation solutions were supplemented with various flavonoids. After rewarming, structural and metabolic cell integrity was measured by lactate dehydrogenase (LDH) release and MTT-test, and lipid peroxidation was assessed from generation of thiobarbituric acid-reactive substances (TBARS).

RESULTS

Twenty hours of cold storage resulted in a substantial loss of cell viability in both preservation solutions (in EC: LDH release 92.4+/-2.7%; MTT-test 0.5+/-0.7%). Addition of luteolin, quercetin, kempferol, fisetin, myricetin, morin, catechin, and silibinin significantly reduced cell injury (for luteolin in EC: LDH release 2.4+/-1.6%; MTT-test 110.3+/-10.4%, P<0.01; TBARS-production (related to cold stored control cells) 8.9+/-2.6%). No cytoprotection was found for apigenin, naringenin, and rutin. Protective potency of flavonoids depends on number of hydroxyl-substituents and lipophilicity of the diphenylpyran compounds.

CONCLUSION

Cold storage induced injury of renal tubular cells was substantially ameliorated by adding selected flavonoids directly to preservation solutions.

Quercetin, a bioflavonoid, attenuates ferric nitrilotriacetate-induced oxidative renal injury in rats

An iron chelate, ferric nitrilotriacetate (Fe-NTA), induces acute proximal tubular necrosis as a consequence of lipid peroxidation and oxidative tissue damage, that eventually leads to high incidence of renal adenocarcinomas in rodents. This study was designed to investigate the effect of quercetin, a bioflavonoid with antioxidant potential, on Fe-NTA-induced nephrotoxicity in rats. One hour after a single intraperitoneal (i.p.) injection of Fe-NTA (8 mg iron/kg), a marked deterioration of renal architecture and renal function was observed. Fe-NTA induced a significant renal oxidative stress demonstrated by elevated thiobarbituric acid reacting substances (TBARS) and reduction in activities of renal catalase, superoxide dismutase and glutathione reductase. Pretreatment of animals with quercetin (2 mg/kg, i.p.) 30 minutes before Fe-NTA administration markedly attenuated renal dysfunction, morphological alterations, reduced elevated TBARS and restored the depleted renal antioxidant enzymes. These results clearly demonstrate the role of oxidative stress and its relation to renal dysfunction, and suggest a protective effect of quercetin on Fe-NTA-induced nephrotoxicity in rats.

Reversal of Experimental Myoglobinuric Acute Renal Failure in Rats by Quercetin, a Bioflavonoid

The occurrence of acute renal failure (ARF) following rhabdomyolysis has been put at between 10 and 40% of cases, and accounts for between 3 and 15% of all cases of ARF. Reactive oxygen intermediates have been demonstrated to play an etiological role in myoglobinuric renal failure. This study was performed to explore the protective effect of quercetin, a bioflavonoid, in an experimental model of myoglobinuric ARF in rats. Four groups of rats were employed in this study: group 1 served as control, group 2 was given 50% glycerol (8 ml/kg, i.m.), group 3 was given glycerol + quercetin (2 mg/kg, i.p.), and group 4 was given glycerol + DMSO (the solvent for quercetin, 5 ml/kg, i.p.). Renal injury was assessed by measuring serum creatinine, blood urea nitrogen, creatinine and urea clearance. The oxidative stress was measured by renal malondialdehyde levels, reduced glutathione levels and by enzymatic activity of catalase, glutathione reductase, and superoxide dismutase. Glycerol administration resulted in a marked renal oxidative stress, significantly deranged the renal functions as well as renal cytoarchitecture. All these factors were significantly improved by quercetin treatment. Because of its radical-scavenging and iron-chelating properties, quercetin protected the kidney against the glycerol-induced oxidative stress and resultant renal dysfunction. Based on these results, this study confirms the role of oxidative stress and demonstrates the renoprotective potential of quercetin in this rhabdomyolysis-mimicking model.

Bioflavonoids attenuate renal proximal tubular cell injury during cold preservation in Euro-Collins and University of Wisconsin solutions

BACKGROUND

Cold ischemia and reperfusion during kidney transplantation are associated with release of free oxygen radicals and damage of renal tubular cells. Bioflavonoids may diminish cold storage-induced injury due to antioxidant and iron chelating activities. This study was designed to delineate the renoprotective mechanisms of bioflavonoids and to define the structural features conferring cytoprotection from cold injury.

METHODS

LLC-PK1 cells were preincubated for three hours with bioflavonoids and cold stored in University of Wisconsin (UW)- or Euro-Collins (EC)-solution for 20 hours. After rewarming, cell viability was assessed by the lactate dehydrogenase (LDH) release, MTT-test, and amino acid transport activity. Lipid peroxidation was assessed from the generation of thiobarbituric acid-reactive substances.

RESULTS

Twenty-hours of cold storage of LLC-PK1 cells resulted in a substantial loss of cell integrity that was more pronounced in the EC (LDH release, 93.6 +/- 1.6%) than the UW solution (67.2 +/- 6.9%; P < 0.0001). Pretreatment with quercetin significantly enhanced cell survival (LDH release, 5.4 +/- 2.7% for UW and 8.4 +/- 4.2% for EC) in a concentration dependent manner. Structure-activity studies revealed similar renoprotection for kaempferol, luteolin and fisetin, unlike myricetin, morin, apigenin, naringenin, catechin, silibinin and rutin. Lipid peroxidation was reduced (UW alone, 2.7 +/- 1.2 vs. UW+quercetin 0.5 +/- 0.2 nmol/mg protein, P < 0.01), and l-threonine uptake completely sustained by pretreatment with quercetin, kaempferol, luteolin, and fisetin. However, renoprotection by fisetin was rapidly lost during rewarming. Protective properties of bioflavonoids were governed by the number and arrangement of hydroxyl substitutes, electron-delocalization, sterical planarity, and lipophilicity of the basic diphenylpyran skeleton.

CONCLUSION

Cold storage-induced renal tubular cell injury is ameliorated by bioflavonoids. Renoprotective effects of bioflavonoids are defined by structure, suggesting that flavonoids are incorporated into membrane lipid bilayers and interfere with membrane lipid peroxidation.

Cytoprotective effect of curcumin in human proximal tubule epithelial cells exposed to shiga toxin

We conducted the following experiments to determine whether curcumin, an antioxidant compound extracted from the spice tumeric, inhibits cell death induced by Shiga toxin (Stx) 1 and 2 in HK-2 cells, a human proximal tubule cell line. Cells were incubated for 24-48 h with Stx1 or Stx2, 0-100 ng/ml. Test media contained either no further additives or 10-50 microM curcumin. Exposure to Stx1 and Stx2, 100 ng/ml, reduced cell viability to approximately 25% of control values after 24 h and 20 microM curcumin restored viability to nearly 75% of control. Cell staining confirmed that Stx1 and Stx2-induced damage in HK-2 cells involved a combination of apoptosis and necrosis. Thus, Stx1 caused apoptosis and necrosis in 12.2 +/- 2.2 and 12.7 +/- 0.9% of HK-2 cells, respectively. Similarly, Stx2 caused apoptosis and necrosis in 13.4 +/- 2.1 and 9.0 +/- 0.5% of HK-2 cells, respectively. Addition of 20 microM curcumin decreased the extent of apoptosis and necrosis to 2.9 +/- 2.0 and 3.8 +/- 0.2%, respectively in the presence of Stx1 and to 3.0 +/- 2.1 and 3.9 +/- 0.3%, respectively, for Stx2 (P < 0.01). Stx-induced apoptosis and its inhibition by curcumin were confirmed by DNA gel electrophoresis and by an assay for fragmentation. The protective effect of curcumin against Stx1 and Stx2-induced injury to HK-2 was not related to its antioxidant properties. Instead, curcumin enhanced expression of heat shock protein 70 (HSP70) in HK-2 cells under control conditions and after exposure to Stx1 or Stx2. No injury was detectable after incubation of LLC-PK(1) or OK cells, non-human proximal tubule cell lines, with Stx1 or Stx2. Thus, curcumin inhibits Stx-induced apoptosis and necrosis in HK-2 cells in vitro. The cytoprotective effect of curcumin against Stx-induced injury in cultured human proximal tubule epithelial cells may be a consequence of increased expression of HSP70.

Pharmacological interventions of cyanide-induced cytotoxicity and DNA damage in isolated rat thymocytes and their protective efficacy in vivo

Cyanide inhibits the mitochondrial respiratory chain enzyme cytochrome oxidase causing histotoxic hypoxia. It is primarily considered as a neurotoxin but its other toxic manifestations are also well documented. Cyanide-induced apoptosis in neuronal cells has also been demonstrated recently. At the same time we also reported that potassium cyanide (KCN) produces extensive cytotoxicity and DNA fragmentation in rat thymocytes. The DNA damage was sensitive to elevated levels of extracellular Ca2+ and was attenuated by Zn2+ (modulator of Ca2+ dependent endonuclease), N-acetylcysteine (free radical scavenger) and diltiazem (Ca2+ channel blocker). In a continuation of this work, in the present study we have shown that the cytotoxicity and DNA fragmentation induced by 5 mM KCN was preceded by loss of mitochondrial integrity (MTT assay and rhodamine-123 staining) and nuclear viability (propidium iodide uptake) which were mediated by generation of reactive oxygen species (DCHF-DA staining). The DNA damage was also accompanied by nuclear fragmentation (Hoechst 33342 staining), a phenomenon that characterises the 'apoptotic' type of cell death. The in vitro toxic insult of KCN was challenged by pre-treatment (0.5 h), simultaneous treatment or post-treatment (0.5-3 h) of various pharmacological agents viz., Trolox (antioxidant), EGTA (Ca2+ modulator) and aurintricarboxylic acid (ATA; Ca2+/Mg2+ dependent endonuclease inhibitor). In addition, Quercetin (antioxidant) was tested as simultaneous treatment alone and was found to be ineffective. On the basis of various biochemical indices and DNA fragmentation (quantitative and qualitative), simultaneous treatment of Trolox was found to be the most effective in attenuating cyanide toxicity in vitro. This protection can be attributed to interventions in oxidative stress-mediated cell injury which is an early event preceding DNA damage. Both EGTA and ATA could not prevent this damage. Trolox also increased the LD(50) of KCN in mice 2.5-fold as compared to 1.8- and 1.6-fold for EGTA and ATA, respectively.

Anti-apoptotic effect of quercetin: intervention in the JNK- and ERK-mediated apoptotic pathways

BACKGROUND

Bioflavonoid quercetin inhibits hydrogen peroxide (H2O2)-induced apoptosis via intervention in the activator protein 1 (AP-1)-mediated apoptotic pathway. In this report, we investigated molecular events involved in the anti-apoptotic effect of quercetin, focusing especially on its effects on the family of mitogen-activated protein (MAP) kinases.

METHODS

Cultured mesangial cells were exposed to H2O2, and activation of c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinases (ERKs), and p38 MAP kinase was evaluated in the presence or absence of quercetin. Using pharmacological and genetic inhibitors, the roles for individual MAP kinases in H2O2-induced apoptosis were examined. Involvement of ERKs in the induction and activation of AP-1 was also investigated using Northern blot analysis and a reporter assay.

RESULTS

Mesangial cells exposed to H2O2 exhibited rapid phosphorylation of JNK, ERKs, and p38 MAP kinase. Quercetin abrogated the activation of all three MAP kinases in response to H2O2. Pretreatment with MAP kinase kinase inhibitor PD098059 or JNK-c-Jun/AP-1 inhibitor curcumin attenuated the H2O2-induced apoptosis. In contrast, the p38 MAP kinase inhibitor SB203580 did not improve the cell survival. Consistently, transfection with dominant-negative mutants of ERK1 and ERK2 or a dominant-negative mutant of JNK inhibited H2O2-induced apoptosis. Transfection with a dominant-negative p38 MAP kinase did not attenuate the apoptotic process. Inhibition of ERKs by PD098059 suppressed induction of c-fos without affecting early induction of c-jun, leading to attenuated activation of AP-1 in response to H2O2.

CONCLUSIONS

These results suggested that (1) activation of JNK and ERKs, but not p38 kinase, is required for the H2O2-induced apoptosis; and (2) suppression of the JNK-c-Jun/AP-1 pathway and the ERK-c-Fos/AP-1 pathway is involved in the anti-apoptotic effect of quercetin.