Effect of aminoguanidine on ischemia/reperfusion injury in rat small intestine

Protective effect of aminoguanidine against lipopolysaccharide-induced hepatotoxicity and liver dysfunction in rat

Lipopolysaccharide (LPS) as the major component of the outer membrane of Gram-negative bacteria activates macrophages to produce a high level of pro-inflammatory cytokines which is considered as a cause of liver dysfunction. Overproduction of nitric oxide (NO) has been suggested to have a role in hepatic injury. The aim of the present study was to explore the protective effects of aminoguanidine (AG) as inducible nitric oxide synthase (iNOS) inhibitor against LPS -induced liver dysfunction in rat. The animals were divided into five groups: (1) control (2) LPS (3) LPS-AG50, (4) LPS-AG100 and (5) LPS-AG150. LPS (1 mg/kg) was injected for 5 weeks and AG (50, 100 and 150 mg/kg) was administered 30 min before LPS. Drugs were injected intraperitoneally. LPS induced liver dysfunction presented by increasing the serum level of alkaline phosphatase (ALK-P), alanine aminotransferase (ALT), aspartate aminotransferase (AST). Pretreatment with AG restored harmful effects of LPS on liver function. In addition, LPS resulted in hepatotoxicity, accompanied by enhancing the level of interleukin (IL)-6, malondialdehyde (MDA) and nitric oxide (NO) metabolites and decreasing the content of total thiol groups and superoxide dismutase (SOD) and catalase (CAT) activity. Injection of AG before LPS attenuated LPS-induced hepatotoxicity through decreasing the level of IL-6, MDA and NO metabolites and increasing total thiols and SOD and CAT activity. Considering the protective effect of AG which was seen in the present study, it seems that increased levels of NO due to activation of iNOS has a role in LPS-induced hepatic injury.

Protective effect of glutamine on the main and adjacent organs damaged by ischemia-reperfusion in rats

Intestinal ischemia and reperfusion (I/R) causes cellular and tissue damage to the intestine and remote organs such as the liver. Increased production of ROS and nitric oxide and dysregulation of cytoprotective enzymes may be involved in intestinal I/R. The aim was to evaluate the protective effects of glutamine on the intestine and liver of rats with intestinal I/R injury. Twenty male Wistar rats (300 g) were divided into four groups: sham-operated (SO), glutamine + SO (G + SO), I/R, and glutamine + I/R (G + I/R). Occlusion of the SMA for 30 min was followed by 15-min reperfusion. Glutamine (25 mg/kg/day) was administered once daily 24 and 48 h before I/R induction. Blood and tissue of were collected for aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels, histopathological analysis, immunohistochemistry of IL-1β and TNF-α, thiobarbituric acid reactive substance (TBARS) and nitric oxide, Nrf2/keap1, superoxide dismutase (SOD), NADPH quinone oxidoreductase1 (NQO1), inducible nitric oxide synthase (iNOS), heat shock protein (HSP70), glucose-regulated protein 78 (GRP78), and activating transcription factor 6 (ATF-6) by western blot. Statistic analysis by ANOVA-Student-Newman-Keuls test (mean ± SE) significantly was p < 0.05. Tissue damage, AST, ALT, IL-1β, TNF-α, TBARS, NO, Keap1, iNOS, GRP78, and ATF-6 expression were significantly lower in the G + I/R group as compared to the I/R group. Expression of Nrf2, SOD, NQO1, and HSP70, was significantly higher in the G + I/R group as compared to I/R group. Pre-treatment with glutamine provided protection against oxidative damage in the intestine and liver in an experimental model of intestinal I/R.

Potential protective effect of etanercept and aminoguanidine in methotrexate-induced hepatotoxicity and nephrotoxicity in rats

Methotrexate (MTX), a chemotherapeutic and immunosuppressant drug, is generally well-tolerated by most patients. However, its cytotoxic nature contributes to life-threatening side effects including hepatotoxicity and nephrotoxicity. The present study investigated the possible role of tumor necrosis factor-alpha (TNF-α) inhibitor, etanercept and inducible nitric oxide synthase (iNOS) inhibitor, aminoguanidine, on MTX-induced hepatotoxicity and nephrotoxicity in rats. Rats were divided into 7 groups: control group, etanercept group, aminoguanidine group, MTX group, MTX+etanercept group, MTX+aminoguanidine group, and MTX+etanercept+aminoguanidine group. MTX caused hepatotoxicity and nephrotoxicity as evidenced biochemically by significant increase in serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), urea and creatinine, respectively as well as by histopathological changes. Such effects were associated with significant changes in oxidative stress markers (malondialdehyde (MDA), nitric oxide (NO), superoxide dismutase (SOD), catalase, and glutathione (GSH)) as well as by upregulation of TNF-α, iNOS and caspase-3 expressions in hepatic and renal tissues. Etanercept and aminoguanidine significantly attenuated MTX-hepatotoxicity and nephrotoxicity. The protective effect of either agent was associated with significant improvement in oxidative stress parameters as well as by downregulation of TNF-α, iNOS and caspase-3 expressions in hepatic and renal tissues. The study suggested that inhibitors of either TNF-α and/or iNOS have protective effect in MTX-induced hepatotoxicity and nephrotoxicity. The protective effect of either agent relies, at least partially, on their antioxidant effects and decreased TNF-α, iNOS, and caspase-3 expressions.

Treatment with Recombinant Trichinella spiralis Cathepsin B-like Protein Ameliorates Intestinal Ischemia/Reperfusion Injury in Mice by Promoting a Switch from M1 to M2 Macrophages

Intestinal ischemia/reperfusion (I/R) injury, in which macrophages play a key role, can cause high morbidity and mortality. The switch from classically (M1) to alternatively (M2) activated macrophages, which is dependent on the activation of STAT6 signaling, has been shown to protect organs from I/R injuries. In the current study, the effects of recombinant Trichinella spiralis cathepsin B-like protein (rTsCPB) on intestinal I/R injury and the potential mechanism related to macrophage phenotypes switch were investigated. In a mouse I/R model undergoing 60-min intestinal ischemia followed by 2-h or 7-d reperfusion, we demonstrated that intestinal I/R caused significant intestinal injury and induced a switch from M2 to M1 macrophages, evidenced by a decrease in levels of M2 markers (arginase-1 and found in inflammatory zone protein), an increase in levels of M1 markers (inducible NO synthase and CCR7), and a decrease in the ratio of M2/M1 macrophages. RTsCPB reversed intestinal I/R-induced M2-M1 transition and promoted M1-M2 phenotype switch evidenced by a significant decrease in M1 markers, an increase in M2 markers, and the ratio of M2/M1 macrophages. Meanwhile, rTsCPB significantly ameliorated intestinal injury and improved intestinal function and survival rate of animals, accompanied by a decrease in neutrophil infiltration and an increase in cell proliferation in the intestine. However, a selective STAT6 inhibitor, AS1517499, reversed the protective effects of rTsCPB by inhibiting M1 to M2 transition. These findings suggest that intestinal I/R injury causes a switch from M2 to M1 macrophages and that rTsCPB ameliorates intestinal injury by promoting STAT6-dependent M1 to M2 transition.

Nitric oxide decreases the permselectivity of the paracellular pathway in thick ascending limbs

Thick ascending limbs reabsorb 25% to 30% of the filtered NaCl. About 50% to 70% is reabsorbed via the transcellular pathway and 30% to 50% is reabsorbed through the Na-selective paracellular pathway. Nitric oxide (NO) inhibits transepithelial Na reabsorption, but its effects on the paracellular pathway are unknown. We hypothesized that NO decreases the selectivity of the paracellular pathway in thick ascending limbs via cGMP-dependent protein kinase. To assess relative Na/Cl permeability ratios (PNa/PCl), we perfused rat thick ascending limbs and measured the effect of reducing bath NaCl on transepithelial voltage, creating dilution potentials, with vehicle, NO donors, and endogenous NO. PNa/PCl was calculated using the Goldman-Hodgkin-Katz equation. Reducing bath Na/Cl to 16/8, 32/24, and 64/56 mmol/L created dilution potentials of -13.6±2.2, -10.8±3.0, and -6.1±0.9 mV, respectively. Calculated PNa/PCls were 2.0±0.2, 2.2±0.5, and 1.9±0.2. The NO donor spermine NONOate (200 µmol/L) blunted the dilution potential caused by 32/24 mmol/L Na/Cl from -11.1±2.1 to -6.5±1.6 mV (P<0.004) and PNa/PCl from 2.2±0.4 to 1.5±0.2. Nitroglycerin (200 µmol/L), another NO donor, also reduced PNa/PCl. Controls showed no significant changes. Dibutyryl-cGMP decreased dilution potentials from -13.4±2.9 to -7.5±1.8 mV (n=6; P<0.01). cGMP-dependent protein kinase inhibition with KT5823 (4 µmol/L) blocked the effect of spermine NONOate, whereas phosphodiesterase 2 inhibition did not. Endogenously produced NO mimicked the effect of the NO donors. In conclusion, NO reduces the selectivity of the paracellular pathway in thick ascending limbs via cGMP and cGMP-dependent protein kinase.

Effect of aminoguanidine on sciatic functional index, oxidative stress, and rate of apoptosis in an experimental rat model of ischemia-reperfusion injury

This study was conducted to investigate the potential protective effects of aminoguanidine (AG) on sciatic functional index (SFI), oxidative stress status, and apoptosis index using a rat model of experimental sciatic nerve ischemia-reperfusion injury (I/R). Treatment groups received 150 mg AG/kg body mass, 24 h after the induction of ischemia. After reperfusion for 2, 4, 7, 14, and 28 days, we evaluated measured SFI, plasma antioxidant enzymes, total antioxidant capacity (TAC), malondialdehyde (MDA), and index of apoptosis. SFI was significantly improved on the 7th and 14th day of reperfusion in the AG-treated groups. AG treatment resulted in the significant reduction of MDA levels on the 7th and 14th day of reperfusion. TAC was only increased after 7 days of reperfusion compared with the untreated group. SOD activity was decreased in both the untreated and AG-treated groups by comparison with the control, but did not show a significant change. GPx activity decreased only after 7 days of reperfusion. The maximal rate of apoptosis occurred on the 7th day of reperfusion. Treatment with AG significantly reduced this enhancement. AG exhibits positive effects against sciatic nerve I/R injury, possibly in part because of the protective effects of AG against apoptosis and I/R-induced oxidative stress.

Pretreatment with mineralocorticoid receptor blocker reduces intestinal injury induced by ischemia and reperfusion: involvement of inhibition of inflammatory response, oxidative stress, nuclear factor κB, and inducible nitric oxide synthase

BACKGROUND

Spironolactone (Sp), a mineralocorticoid receptor antagonist, protects against the ischemia reperfusion (IR) injury of retina, kidney, heart, and brain. We aimed to investigate the effects of Sp on intestinal IR injury.

METHODS

Male Wistar rats were randomly divided into: (1) a sham control group; (2) an IR control group, subjected to 30 min ischemia and 3 h reperfusion; (3) a group treated with Sp (20 mg/kg) for 3 d before the IR; and (4) a sham-operated control group treated with Sp (20 mg/kg). After the reperfusion, blood and intestinal tissue samples were collected to evaluate histopathologic state, neutrophil infiltration (by measuring myeloperoxidase activity), levels of the cytokines (tumor necrosis factor α, interleukin 1α [IL-1α], interferon γ, monocyte chemotactic protein-1, granulocyte macrophage-colony stimulating factor, and IL-4), malondialdehyde (MDA) and reduced glutathione contents, and immunohistochemical expressions of nuclear factor κB, inducible nitric oxide synthase (iNOS), and caspase-3.

RESULTS

MDA content, myeloperoxidase activity, and plasma levels of tumor necrosis factor α, IL-1α, and monocyte chemotactic protein-1 were all elevated in IR, indicating the oxidative stress and local and systemic inflammatory response. Sp administration markedly reduced the MDA content and the cytokine levels. The pretreatment alleviated intestinal injury, neutrophil infiltration, and the expressions of caspase-3, iNOS, and NFκB.

CONCLUSIONS

The results implicate that Sp may have a strong protective effect against the intestinal IR injury. The effect can be mediated via suppression of both systemic inflammatory response and apoptosis through amelioration of oxidative stress and generation of proinflammatory cytokines, iNOS, caspase-3, and nuclear factor κB. Therefore, mineralocorticoid receptor antagonism might be of potential therapeutic benefit in cases of intestinal IR damage.

Mesenteric lymph reperfusion exacerbates spleen injury caused by superior mesenteric artery occlusion shock

The intestinal lymph pathway plays an important role in the pathogenesis of organ injury following superior mesenteric artery occlusion (SMAO) shock. We hypothesized that mesenteric lymph reperfusion (MLR) is a major cause of spleen injury after SMAO shock. To test this hypothesis, SMAO shock was induced in Wistar rats by clamping the superior mesenteric artery (SMA) for 1 h, followed by reperfusion for 2 h. Similarly, MLR was performed by clamping the mesenteric lymph duct (MLD) for 1 h, followed by reperfusion for 2 h. In the MLR+SMAO group rats, both the SMA and MLD were clamped and then released for reperfusion for 2 h. SMAO shock alone elicited: 1) splenic structure injury, 2) increased levels of malondialdehyde, nitric oxide (NO), intercellular adhesion molecule-1, endotoxin, lipopolysaccharide receptor (CD14), lipopolysaccharide-binding protein, and tumor necrosis factor-α, 3) enhanced activities of NO synthase and myeloperoxidase, and 4) decreased activities of superoxide dismutase and ATPase. MLR following SMAO shock further aggravated these deleterious effects. We conclude that MLR exacerbates spleen injury caused by SMAO shock, which itself is associated with oxidative stress, excessive release of NO, recruitment of polymorphonuclear neutrophils, endotoxin translocation, and enhanced inflammatory responses.