The effects of NMDA receptor antagonists over intestinal ischemia/reperfusion injury in rats

Antinociceptive and adverse effects of morphine:ketamine mixtures in rats

Prescription opioids are the gold standard for treating moderate to severe pain despite their well-documented adverse effects. Of all prescription medications, opioids are abused most widely, and fatal overdoses have reached epidemic levels. One strategy for improving the margin of safety of opioids is combining them with non-opioid drugs to decrease the opioid dose needed for pain relief, thereby reducing adverse effects that occur with larger doses. The N-methyl-D-aspartate receptor antagonist ketamine has been used safely as an analgesic but only under a very limited range of conditions. The current studies characterized the antinociceptive, behavioral suppressant, and gastrointestinal effects of morphine and ketamine alone and in mixtures to determine their interaction in 24 adult male Sprague-Dawley rats (n = 8 per assay). Given alone, both morphine and ketamine produced antinociception, decreased responding for food, and reduced gastrointestinal transit (i.e. produced constipation). The effects of morphine:ketamine mixtures generally were additive, except for the antinociceptive effects of 1:1 mixtures for which the difference in slope (i.e. non-parallel shift) between the observed and predicted effects suggested synergy at smaller doses and additivity at larger doses. The potency of morphine to produce constipation was not enhanced by administration of morphine:ketamine mixtures with antinociceptive effects. The nature of the interaction between morphine and ketamine for adverse effects such as dependence, withdrawal, abuse, or respiratory depression remains unknown but also might be related to the ratio of each drug in mixtures. It will be important to identify conditions that produce the largest potential therapeutic window in humans.

Beneficial effects of memantine on ischemia/reperfusion injury following torsion/detorsion induced testicular damage in rats: Improvement in histological and biochemical parameters

INTRODUCTION

Testicular torsion is a common urologic emergency and one of the causes of infertility in males. Hence, prompt diagnosis and treatment are important to prevent testicular damages. It has been reported that memantine, a drug for Alzheimer's disease has anti-oxidative role against cerebral ischemic stroke and cardiac ischemia reperfusion.

OBJECTIVE

In this experimental study, the effects of memantine on a testicular torsion injury in adolescent rat testis after ischemia/reperfusion (I/R) were evaluated.

STUDY DESIGN

Thirty-six adolescent rats were divided into three groups with 12 rats per group including sham-operated, T/D (torsion/detorsion) + vehicle, and T/D + memantine (10 mg/kg). Testicular torsion was induced for 2 h by rotating right testis 720⁰ in the clockwise direction. In treated group 30 min before detorsion, a single intraperitoneal dose of memantine was administered. After 4 h of reperfusion, orchiectomy was conducted and Histopathological and biochemical evaluations of testicular tissue samples were performed.

RESULTS

The malondialdehyde level in the T/D group was significantly greater than in the sham operated group. Moreover, the testicular malondialdehyde values in the T/D + memantine group were significantly lower than in the T/D group. Also, significant decreases occurred in catalase and superoxide dismutase activities in the T/D group compared with sham operated group. These values were significantly greater in the memantine group than in the T/D group. Furthermore, after induction of T/D, histopathological evaluations also revealed severe testicular damages which were improved by memantine administration.

DISCUSSION

Memantine prevented increases in oxidative stress markers and reductions of antioxidants during I/R injury in the current study. Subsequently the histologic injury was reduced in rats treated with memantine. The antioxidant characteristics of memantine and its protective effects have been shown in our study.

CONCLUSION

These results suggest that administration of memantine before detorsion prevents I/R cellular damage in testicular torsion. This drug probably acts through reduction of reactive oxygen species and support antioxidant enzyme systems.

Pathophysiological Changes During Ischemia-reperfusion Injury in Rodent Hepatic Steatosis

BACKGROUND/AIM

Ischemia and reperfusion injuries may produce deleterious effects on hepatic tissue after liver surgery and transplantation. The impact of ischemia-reperfusion injury (IRI) on the liver depends on its substrate, the percentage of liver ischemic tissue subjected to IRI and the ischemia time. The consequences of IRI are more evident in pathologic liver substrates, such as steatotic livers. This review is the result of an extended bibliographic PubMed search focused on the last 20 years. It highlights basic differences encountered during IRI in lean and steatotic livers based on studies using rodent experimental models.

CONCLUSION

The main difference in cell death between lean and steatotic livers is the prevalence of apoptosis in the former and necrosis in the latter. There are also major changes in the effect of intracellular mediators, such as TNFα and IL-1β. Further experimental studies are needed in order to increase current knowledge of IRI effects and relevant mechanisms in both lean and steatotic livers, so that new preventive and therapeutic strategies maybe developed.

The effects of amantadine on lung tissue in lower limb ischemia/reperfusion injury model in rats

Background

This study aims to evaluate the effect of amantadine on lung tissue of after lower limb ischemia/reperfusion injury in rats.

Methods

A total of 24 Wistar rats were divided into four equal groups including six rats in each: sham group (Group S), amantadine group (Group A), ischemia/reperfusion group (Group I/R), and ischemia/reperfusion + amantadine group (Group I/R-A). All groups underwent a midline abdominal incision. In Groups I/R and I/R-A, the infrarenal abdominal aorta was clamped for 120 min and, then, reperfused for 120 min after removal of the clamp. Amantadine hydrochloride 45 mg/kg was administered intraperitoneally to the rats of Groups A and Group I/R-A 15 min before surgery. At the end of reperfusion period (240 min), all rats were sacrificed, and their lung tissues were obtained. Lung tissue catalase and superoxide dismutase activities and glutathione S-transferase and malondialdehyde levels were analyzed. Lung tissues were examined histopathologically.

Results

Catalase activity was lower in Groups A, I/R, and I/R-A compared to Group S. Superoxide dismutase activity was higher in Group I/R than Group S. Superoxide dismutase activity in Groups I/R-A and A decreased, compared to Groups S and I/R. Glutathione S-transferase levels decreased in Groups I/R and A, compared to Group S. Glutathione S-transferase levels in Group I/R-A were higher than Groups I/R and A. The highest level of malondialdehyde was found in Group I/R and the lowest level was found in Group I/R-A. According to histopathological examination, infiltration scores were significantly lower in Group S than Groups I/R and I/R-A (p=0.009 and p=0.011, respectively). The alveolar wall thickening scores in Group I/R were also significantly higher than Groups S and Group A (p=0.001 and p=0.001, respectively).

Conclusion

Lung tissue can be affected histopathologically by ischemia/ reperfusion injury and this injury can be reversed by amantadine administration.

Estradiol prevented intestinal ischemia and reperfusion-induced changes in intestinal permeability and motility in male rats

OBJECTIVES

Ischemia and reperfusion (I/R) in the intestine could lead to severe endothelial injury, compromising intestinal motility. Reportedly, estradiol can control local and systemic inflammation induced by I/R injury. Thus, we investigated the effects of estradiol treatment on local repercussions in an intestinal I/R model.

METHODS

Rats were subjected to ischemia via the occlusion of the superior mesenteric artery (45 min) followed by reperfusion (2h). Thirty minutes after ischemia induction (E30), 17β-estradiol (E2) was administered as a single dose (280 μg/kg, intravenous). Sham-operated animals were used as controls.

RESULTS

I/R injury decreased intestinal motility and increased intestinal permeability, accompanied by reduced mesenteric endothelial nitric oxide synthase (eNOS) and endothelin (ET) protein expression. Additionally, the levels of serum injury markers and inflammatory mediators were elevated. Estradiol treatment improved intestinal motility, reduced intestinal permeability, and increased eNOS and ET expression. Levels of injury markers and inflammatory mediators were also reduced following estradiol treatment.

CONCLUSION

Collectively, our findings indicate that estradiol treatment can modulate the deleterious intestinal effects of I/R injury. Thus, estradiol mediates the improvement in gut barrier functions and prevents intestinal dysfunction, which may reduce the systemic inflammatory response.

NDRG2 is expressed on enteric glia and altered in conditions of inflammation and oxygen glucose deprivation/reoxygenation

Enteric glial cells are more abundant than neurons in the enteric nervous system. Accumulating evidence has demonstrated that enteric glial cells share many properties with astrocytes and play pivotal roles in intestinal diseases. NDRG2 is specifically expressed in astrocytes and is involved in various diseases in the central nervous system. However, no studies have demonstrated the expression of NDRG2 in enteric glial cells. We performed immunostaining of adult mouse tissue, human colon sections, and primary enteric glial cells and the results showed that NDRG2 was widely expressed in enteric glial cells. Meanwhile, our results showed that NDRG2 was upregulated after treatment with pro-inflammatory cytokines and exposure to oxygen glucose deprivation/reoxygenation, indicating that NDRG2 might be involved in these conditions. Moreover, we determined that NDRG2 translocated to the nucleus after treatment with pro-inflammatory cytokines but not after exposure to oxygen glucose deprivation/reoxygenation. This study is the first to show the expression and distribution of NDRG2 in the enteric glia. Our results indicate that NDRG2 might be involved in the pathogenesis of enteric inflammation and ischemia/reperfusion injury. This study shows that NDRG2 might be a molecular target for enteric nervous system diseases.

Effect of atenolol pre-treatment in heart damage in a model of intestinal ischemia-reperfusion

PURPOSE

To investigate the effects of atenolol in inflammatory mediator and oxidative stress in a myocardial injury by intestinal ischemia/reperfusion in rat model.

METHODS

Adult Wistar male rats were randomly (n=8), anesthetized and divided in: Sham: submitted to operation only; group SS+IR: intravenous saline infusion following superior mesenteric artery occlusion during 60 minutes (ischemia) and open for 120 minutes (reperfusion); group AT+IR: intravenous atenolol infusion (2 mg/kg) following superior mesenteric artery occlusion during 60 minutes (ischemia) and open for 120 minutes (reperfusion); and group AT+I+AT+R: intravenous atenolol infusion following superior mesenteric artery occlusion during 60 minutes (ischemia) and in the time 45 minutes other atenolol doses were administrated and the artery was open for 120 minutes (reperfusion), all animals were submitted to muscular relaxation for mechanical ventilation. In the end of experiment the animals were euthanized and the hearts tissue were morphology analyzed by histology and malondialdehyde by ELISA, and the plasma were analyzed for tumor necrosis factor-alpha by ELISA.

RESULTS

The group SS+IR demonstrated the higher malondialdehyde levels when compared with the atenolol treated-groups (p=0.001) in the heart tissue. The tumor necrosis factor-alpha level in plasma decrease in the treated groups when compared with SS+IR group (p=0.001). Histology analyses demonstrate pyknosis, edema, cellular vacuolization, presence of inflammatory infiltrate and band contraction in the heart tissue of the rats.

CONCLUSION

Atenolol significantly reduce the degree of cardiac damage after intestinal ischemia-reperfusion.

Antagonism of ionotropic glutamate receptors attenuates chemical ischemia-induced injury in rat primary cultured myenteric ganglia

Alterations of the enteric glutamatergic transmission may underlay changes in the function of myenteric neurons following intestinal ischemia and reperfusion (I/R) contributing to impairment of gastrointestinal motility occurring in these pathological conditions. The aim of the present study was to evaluate whether glutamate receptors of the NMDA and AMPA/kainate type are involved in myenteric neuron cell damage induced by I/R. Primary cultured rat myenteric ganglia were exposed to sodium azide and glucose deprivation (in vitro chemical ischemia). After 6 days of culture, immunoreactivity for NMDA, AMPA and kainate receptors subunits, GluN₁ and GluA_1–4, GluK_1–3 respectively, was found in myenteric neurons. In myenteric cultured ganglia, in normal metabolic conditions, -AP5, an NMDA antagonist, decreased myenteric neuron number and viability, determined by calcein AM/ethidium homodimer-1 assay, and increased reactive oxygen species (ROS) levels, measured with hydroxyphenyl fluorescein. CNQX, an AMPA/kainate antagonist exerted an opposite action on the same parameters. The total number and viability of myenteric neurons significantly decreased after I/R. In these conditions, the number of neurons staining for GluN₁ and GluA_1–4 subunits remained unchanged, while, the number of GluK_1–3-immunopositive neurons increased. After I/R, -AP5 and CNQX, concentration-dependently increased myenteric neuron number and significantly increased the number of living neurons. Both -AP5 and CNQX (100–500 µM) decreased I/R-induced increase of ROS levels in myenteric ganglia. On the whole, the present data provide evidence that, under normal metabolic conditions, the enteric glutamatergic system exerts a dualistic effect on cultured myenteric ganglia, either by improving or reducing neuron survival via NMDA or AMPA/kainate receptor activation, respectively. However, blockade of both receptor pathways may exert a protective role on myenteric neurons following and I/R damage. The neuroprotective effect may depend, at least in part, on the ability of both receptors to increase intraneuronal ROS production.

Carvacrol alleviates ischemia reperfusion injury by regulating the PI3K-Akt pathway in rats

Background

Liver ischemia reperfusion (I/R) injury is a common pathophysiological process in many clinical settings. Carvacrol, a food additive commonly used in essential oils, has displayed antimicrobials, antitumor and antidepressant-like activities. In the present study, we investigated the protective effects of carvacrol on I/R injury in the Wistar rat livers and an in vitro hypoxia/restoration (H/R) model.

Methods

The hepatoportal vein, hepatic arterial and hepatic duct of Wistar rats were isolated and clamped for 30 min, followed by a 2 h reperfusion. Buffalo rat liver (BRL) cells were incubated under hypoxia for 4 h, followed normoxic conditions for 10 h to establish the H/R model in vitro. Liver injury was evaluated by measuring serum levels of alanine aminotransferase (ALT) and aspatate aminotransferase (AST), and hepatic levels of superoxide dismutase (SOD), catalase (CAT), glutathione (GSH) and malondiadehyde (MDA), and hepatic histology and TUNEL staining. MTT assay, flow cytometric analysis and Hoechst 33258 staining were used to evaluate the proliferation and apoptosis of BRL cells in vitro. Protein expression was examined by Western Blot analysis.

Results

Carvacrol protected against I/R-induced liver damage, evidenced by significantly reducing the serum levels of ALT and AST, histological alterations and apoptosis of liver cells in I/R rats. Carvacrol exhibited anti-oxidative activity in the I/R rats, reflected by significantly reducing the activity of SOD and the content of MDA, and restoring the activity of CAT and the content of GSH, in I/R rats. In the in vitro assays, carvacrol restored the viability and inhibited the apoptosis of BRL cells, which were subjected to a mimic I/R injury induced by hypoxia. In the investigation on molecular mechanisms, carvacrol downregulated the expression of Bax and upregulated the expression of Bcl-2, thus inhibited the activation of caspase-3. Carvacrol was also shown to enhance the phosphorylation of Akt.

Conclusion

The results suggest that carvacrol could alleviate I/R-induced liver injury by its anti-oxidative and anti-apoptotic activities, and warrant a further investigation for using carvacrol to protect I/R injury in clinic.

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.

The protective effects of different-time-ischemic preconditioning on the reperfusion injury in fatty livers in rats

BACKGROUND

The present study was aimed to investigate the protective effects of different-time-ischemic preconditioning on the reperfusion injury in fatty livers in rats, and to elucidate the mechanisms underlying the protective effects and the optimal safe ischemic preconditioning time on the hepatic IR injury in steatotic livers.

METHODOLOGY/PRINCIPAL FINDINGS

A rat fatty liver model was established by high-fat diet feeding. We investigated the changes in the concentration of AST, ALT, LDH and NO in the serum, and of MDA, SOD, and MPO in the liver samples in response to different ischemic preconditioning times and ischemia-reperfusion injury. Histological analysis was performed to evaluate the results of the hepatic fatty infiltration. 1) At 24 h after 15 min ischemic preconditioning with 10 min reperfusion (15 min +10 min IP), the extent and area of the necrosis was markedly higher in the fatty liver samples with respect to IR, compared to the normal liver samples. 2) In response to the treatment of 5/8 min +10 min IP, the fatty liver group showed lower levels of serological indicators and liver MDA and MPO compared to the other groups, while the SOD activity of the fatty liver group was significantly higher than the other groups (p<0.05). Compared to the corresponding IR group, all IP groups showed a significantly higher serum NO concentration (p<0.05). Among the fatty liver groups, the 5/8 min+10 min IP group showed the highest NO concentration (p<0.05).

CONCLUSIONS/SIGNIFICANCE

Fat infiltration could aggravate the ischemia-reperfusion injury in the rat liver. Furthermore, ischemic preconditioning could increase the tolerance of the fatty liver, which was induced by the high-fat diet, to hepatic ischemia-reperfusion injury in rats. The protocol of 5/8 min +10 min IP was the optimal regimen for the treatment of moderate and severe fatty livers.

N(1)-(quinolin-2-ylmethyl)butane-1,4-diamine, a polyamine analogue, attenuated injury in in vitro and in vivo models of cerebral ischemia

It has been widely recognized that glutamate (Glu)-induced cytotoxicity, intracellular calcium overload and excessive free radical production are the key players in the development and progression of ischemic brain injury. Since MK-801, an antagonist of N-methyl-d-aspartate (NMDA) receptor, showed many adverse reactions that hampered its clinical applications, development of safe and effective agent for the treatment of cerebral ischemia is eagerly required. This study was to investigate the effects of N(1)-(quinolin-2-ylmethyl)butane-1,4-diamine (QMA), a polyamine analogue, on the in vitro and in vivo models of cerebral ischemic damage. The results revealed that pretreatment with QMA could attenuate Glu, putrescine (Put) and oxygen-glucose deprivation (OGD)-induced cell death, lipid peroxidation as well as the elevation of reactive oxygen species (ROS) and intracellular [Ca(2+)](i) in pheochromocytoma (PC12) cells and in rat primary cortical neurons. The results also demonstrated that QMA could inhibit NMDA-mediated intracellular [Ca(2+)](i) accumulation in rat primary cortical neurons and reduce brain infarct volume in middle cerebral artery occlusion (MCAO) rats. The present report suggested that polyamines played a crucial role in the pathological processes of cerebral ischemic damage and that QMA or other novel polyamine analogues could be promising therapeutic candidates for stroke by virtue of their anti-hypoxia and antioxidation property.

Neuroprotective effects of racemic ketamine and (S)-ketamine on spinal cord injury in rat

BACKGROUND

The aim of this study was to investigate and to compare the potential neuroprotective effects of racemic ketamine, (S)-ketamine and methylprednisolone after an experimental spinal cord injury model in rats.

METHODS

Fifty-nine Wistar albino rats were divided into three main groups as acute stage (A), subacute stage (SA) and sham groups and then acute and subacute stage groups were divided into four groups regarding the used drug as control (CONT), racemic ketamine (RK), (S)-ketamine (SK) and methylprednisolone (MP) groups. A dorsal laminectomy was performed; and spinal cord injury was induced by using a temporary aneurysm clip. Four hours later from the clip compression, except those of the sham and control groups, the drugs (60 mg/kg racemic ketamine, 60 mg/kg (S)-ketamine or 30 mg/kg methylprednisolone) were administered intraperitoneally. At 72th h and 7th days of the study, the spinal cords of rats were removed from T8 level to the conus medullaris level. The specimens were and evaluated histopathologically, tissue lipid peroxidation (LPO) and myeloperoxidation (MPO) levels were measured and biochemically.

RESULTS

The histopathological results were similar both in the acute and in the subacute stage groups. There was a statistically significant difference among all groups regarding the tissue LPO levels (p<0.001). There was a statistically significant difference between the CONT-A group and the MP-A, RK-A and SK-A groups (p=0.004, p<0.001 and p=0.007, respectively) in acute stage and between the CONT-SA group and SK-SA group (p=0.002) in subacute stage. There was a statistically significant difference among all groups regarding the tissue MPO levels (p=0.001). The median MPO levels were similar among acute stage groups (p=0.057), but there was a statistical difference among subacute stage groups (p=0.046).

CONCLUSION

(S)-ketamine is more effective than methylprednisolone and racemic ketamine to reduce the LPO levels in subacute stage of spinal cord injury in rats. And, it is as effective as methylprednisolone in preventing secondary spinal cord injury histopathologically.

Intestinal and liver changes after chronic ketamine and ketamine plus alcohol treatment

The effects of long-term chronic ketamine treatment on the intestine and the liver were studied in the ICR mice which had daily intraperitoneal injection of ketamine at 30 mg/kg per day for 7 months. The intestine showed no significant pathology after treatment but had a decrease of the positive sites of proliferative cell nuclear antigen in the mucosae of the intestines after ketamine and ketamine plus alcohol (added in the last month) treatment. No significant apoptosis (via TUNEL) nor necrosis (via lactic acid dehydrogenase) was detected in the intestines of all control and ketamine-treated groups, with the exception of an increase of lactic acid dehydrogenase in the mucosae of the intestines of the ketamine plus alcohol group. In the liver, loss of glycogen was observed in animals after ketamine and ketamine plus alcohol treatment, in addition to the pathology reported in a previous work. The decrease in quantity of glycogen in the liver reflected either a failure of glycogen synthesis from glucose or an increase of glycogenolysis in the liver.

Comparative effects of triflusal, S-adenosylmethionine, and dextromethorphan over intestinal ischemia/reperfusion injury

Ischemia/reperfusion (I/R) is a condition that stimulates an intense inflammatory response. No ideal treatment exists. Triflusal is an antiplatelet salicylate derivative with anti-inflammatory effects. S-adenosylmethionine is a metabolic precursor for glutathione, an endogenous antioxidant. Dextromethorphan is a low-affinity N-methyl-D-aspartate receptor inhibitor. There is evidence that these agents modulate some of the pathways involved in I/R physiopathology. Intestinal I/R was induced in rats by clamping the superior mesenteric artery for 60 minutes, followed by 60 minutes of reperfusion. Rats either received saline or the drugs studied. At the end of the procedure, serum concentrations of tumor necrosis factor-alpha (TNF-alpha), malonaldehyde (MDA), and total antioxidant capacity (TAC) were determined and intestinal morphology analyzed. I/R resulted in tissue damage, serum TNF-alpha and MDA elevations, and depletion of TAC. All drugs showed tissue protection. Only triflusal reduced TNF-alpha levels. All drugs lowered MDA levels, but only triflusal and S-adenosylmethionine maintained the serum TAC.

The effects of sirolimus on target organs during mesenteric ischemia and reperfusion damage in an experimental rat model

BACKGROUND

Mesenteric ischemia and reperfusion (I/R) syndrome (MIRS) has been considered a clinicopathologic entity associated with a variety of clinically severe conditions with decreased intestinal blood flow and has been known to induce I/R damage in various organs. Sirolimus (SRL), a macrolide antibiotic isolated from a strain of Streptomyces hygroscopicus, is a potent and nonnephrotoxic immunosuppressant.

OBJECTIVE

This study was designed to investigate the potential impact of sirolimus on MIRS-induced I/R damage in renal, intestinal, pulmonary, and hepatic tissues in an experimental rat model.

METHODS

Twenty-four male Sprague-Dawley rats, aged 6 to 8 weeks and weighing 280 (±20 g), were studied. Using computer-generated random numbers, rats were assigned to 1 of the following 3 groups: group 1 (I/R group, n = 8), group 2 (I/R + sirolimus group, n = 8), and group 3 (control group, n = 8). Sirolimus, in a 1 mg/mL (60 mL) solution, was administered intraperitoneally in a dose of 1.5 mg/kg/d to the rats assigned to group 2 starting from 3 days before the surgical procedure. In surgery, a laparotomy was performed to clamp the superior mesenteric artery and, thus, induce bowel ischemia in groups 1 and 2. After 60 minutes of ischemia, the microvascular clamp on the superior mesenteric artery was removed for 3 hours of reperfusion. Soon after experimental induction of MIRS, bowel, lung, kidney, and liver specimens from each animal were harvested for both biochemical and histopathologic analysis.

RESULTS

There were statistically significant differences between groups 1 and 3 with regard to degrees of intestinal (P < 0.001), hepatic (P = 0.001), renal (P < 0.001), and pulmonary (P = 0.01) I/R damage. The lung specimens from group 2 had less inflammation and perivascular edema formation compared with specimens from group 1, but no statistical significance was observed between the groups (P < 0.33). There were statistically significant differences between groups 1 and 2 with regard to degrees of intestinal, hepatic, and renal I/R damage (P = 0.001 for all).

CONCLUSION

The findings of the present study demonstrate the attenuating effects of sirolimus on I/R damage in the intestine and remote organs, including the liver and kidney in the setting of MIRS in an experimental rat model. As a therapeutic implication, the utility of sirolimus may be of clinical value in procedures associated with a high likelihood of I/R damage, including major abdominal operations and renal transplantation. However, whether these results apply to humans is unclear. Additional experimental and clinical studies are warranted to confirm the clinical utility of sirolimus in conditions potentially associated with I/R damage.

Protein kinase C modulates NMDA receptors in the myenteric plexus of the guinea pig ileum during in vitro ischemia and reperfusion

BACKGROUND

Ischemic episodes lead to profound functional and structural alterations of the gastrointestinal tract which may contribute to disorders of intestinal motility. Enhancement of glutamate overflow and the consequent activation of NMDA (N-methyl-D-aspartate) receptors may participate to such changes by modulating different enteric neurotransmitter systems, including cholinergic motor pathways.

METHODS

The molecular mechanism/s underlying activation of NMDA receptors in the guinea pig ileum were investigated after glucose/oxygen deprivation (in vitro ischemia) and during reperfusion.

KEY RESULTS

The number of ileal myenteric neurons positive for NR1, the functional subunit of NMDA receptors, and its mRNA levels were unchanged after in vitro ischemia/reperfusion. In these conditions, the protein levels of NR1, and of its phosphorylated form by protein kinase C (PKC), significantly increased in myenteric neurons, whereas, the levels of NR1 phosphorylated by protein kinase A (PKA) did not change, with respect to control values. Spontaneous glutamate overflow increased during in vitro ischemia/reperfusion. In these conditions, the NMDA receptor antagonists, D(-)-2-amino-5-phosphonopentanoic acid [(D)-AP5] (10 μmol L(-1)) and 5,7-dichlorokynurenic acid (5,7-diClKyn acid) (10 μmol L(-1)) and the PKC antagonist, chelerythrine (1 μmol L(-1)), but not the PKA antagonist, H-89 (1 μmol L(-1)), were able to significantly depress the increased glutamate efflux.

CONCLUSIONS & INFERENCES

The present data suggest that in the guinea pig ileum during in vitro ischemia/reperfusion, NR1 protein levels increase. Such event may rely upon posttranscriptional events involving NR1 phosphorylation by PKC. Increased NR1 levels may, at least in part, explain the ability of NMDA receptors to modulate a positive feedback on ischemia/reperfusion-induced glutamate overflow.

Neuroprotective effects of magnesium-sulfate on ischemic injury mediated by modulating the release of glutamate and reduced of hyperreperfusion

This study examined the neuroprotective effects of magnesium-sulfate (MgSO(4)) on the cerebral blood flow (CBF) and extracellular glutamate concentration in an eleven vessel occlusion (11VO) rat model. Twenty-one male Sprague-Dawley rats (250-350g) were used for the 11VO ischemic model, which was induced by a 10-min transient occlusion. The animals were divided into 3 groups, including ischemic-induced animals (ischemia group), ischemic-induced and MgSO(4) treated animals (MgSO(4) group), and sham animals for comparison. The real-time extracellular glutamate concentration was measured using a microdialysis biosensor, and the CBF was monitored by laser Doppler flowmetry. Neuronal cell death in the hippocampal region was observed 72h after ischemia by several stains (Nissl, DAPI, NeuN, and cleaved caspase3). A significant decrease in %CBF was observed in both the ischemia and MgSO(4) groups, such as ~10% during the ischemic period. However, the MgSO(4) group showed a significant decrease in the initial reperfusion %CBF compared to the ischemia group. A significantly lower level of glutamate release was observed in the MgSO(4) group than in the ischemia group during the ischemic and reperfusion episode. Our staining results revealed a significant decrease in neuronal cell death in the hippocampus in the MgSO(4) group compared to the ischemia group. These results suggest that MgSO(4) is responsible for the protection of neuronal cells by suppressing the release of extracellular glutamate under ischemic conditions and the CBF response during the initial reperfusion period.

Ischemic post-conditioning to counteract intestinal ischemia/reperfusion injury

Intestinal ischemia is a severe disorder with a variety of causes. Reperfusion is a common occurrence during treatment of acute intestinal ischemia but the injury resulting from ischemia/reperfusion (IR) may lead to even more serious complications from intestinal atrophy to multiple organ failure and death. The susceptibility of the intestine to IR-induced injury (IRI) appears from various experimental studies and clinical settings such as cardiac and major vascular surgery and organ transplantation. Whereas oxygen free radicals, activation of leukocytes, failure of microvascular perfusion, cellular acidosis and disturbance of intracellular homeostasis have been implicated as important factors in the pathogenesis of intestinal IRI, the mechanisms underlying this disorder are not well known. To date, increasing attention is being paid in animal studies to potential pre- and post-ischemia treatments that protect against intestinal IRI such as drug interference with IR-induced apoptosis and inflammation processes and ischemic pre-conditioning. However, better insight is needed into the molecular and cellular events associated with reperfusion-induced damage to develop effective clinical protection protocols to combat this disorder. In this respect, the use of ischemic post-conditioning in combination with experimentally prolonged acidosis blocking deleterious reperfusion actions may turn out to have particular clinical relevance.