Influence of ezetimibe on ADMA-DDAH-NO pathway in rat liver subjected to partial ischemia followed by global reperfusion

Exploring the role of dimethylarginine dimethylaminohydrolase-mediated reduction in tissue asymmetrical dimethylarginine levels in cardio-protective mechanism of ischaemic postconditioning in rats

Objectives

Reperfusion of ischaemic myocardium results in reduced nitric oxide (NO) biosynthesis by endothelial nitric oxide synthase (eNOS) leading to endothelial dysfunction and subsequent tissue damage. Impaired NO biosynthesis may be partly due to increased levels of asymmetrical dimethylarginine (ADMA), an endogenous inhibitor of eNOS. As dimethylarginine dimethylaminohydrolase (DDAH) is a key enzyme responsible for degradation of ADMA, the present study was designed to explore the role of DDAH/ADMA/NO pathway in cardio-protective mechanism of ischaemic postconditioning.

Materials and Methods

Isolated rat hearts were subjected to myocardial ischaemia for 30 min followed by reperfusion for 2 hours in control group. Myocardial injury was assessed by measurement of infarct size, left ventricular developed pressure (LVDP), lactate dehydrogenase (LDH) and creatine kinase (CK) enzymes in coronary effluents. The reperfused hearts were homogenised and tissue concentration of nitrite, ADMA level and DDAH enzyme activity was determined.

Results

A significant increase in infarct size, LDH, CK release in coronary effluents and ADMA level in myocardial tissue was observed in control group. The increase in tissue ADMA coincided with reductions of NO tissue concentrations and DDAH activity. Ischaemic postconditioning significantly attenuated ischaemia-reperfusion induced myocardial injury manifested in the terms of decreased infarct size, LDH, CK, tissue ADMA along with increase in NO levels and DDAH enzyme activity. Pretreatment with L-Homocysteine (300 µM), a competitive inhibitor of DDAH, and L-NG-nitroarginine methyl ester (L-NAME; 100 µM), an inhibitor of eNOS, completely abolished ischaemic postconditioning-induced myocardial protection.

Conclusion

Enhancing DDAH activity by postconditioning may be a novel target to reduce ADMA level and increase NO bioavailability to prevent myocardial ischaemia-reperfusion injury.

Ezetimibe Attenuates Oxidative Stress and Neuroinflammation via the AMPK/Nrf2/TXNIP Pathway after MCAO in Rats

Oxidative stress and neuroinflammation play essential roles in ischemic stroke-induced brain injury. Previous studies have reported that Ezetimibe (Eze) exerts antioxidative stress and anti-inflammatory properties in hepatocytes. In the present study, we investigated the effects of Eze on oxidative stress and neuroinflammation in a rat middle cerebral artery occlusion (MCAO) model. One hundred and ninety-eight male Sprague-Dawley rats were used. Animals assigned to MCAO were given either Eze or its control. To explore the downstream signaling of Eze, the following interventions were given: AMPK inhibitor dorsomorphin and nuclear factor erythroid 2-related factor 2 (Nrf2) siRNA. Intranasal administration of Eze, 1 h post-MCAO, further increased the endogenous p-AMPK expression, reducing brain infarction, neurologic deficits, neutrophil infiltration, microglia/macrophage activation, number of dihydroethidium- (DHE-) positive cells, and malonaldehyde (MDA) levels. Specifically, treatment with Eze increased the expression of p-AMPK, Nrf2, and HO-1; Romo-1, thioredoxin-interacting protein (TXNIP), NOD-like receptor protein 3 (NLRP3), Cleaved Caspase-1, and IL-1β were reduced. Dorsomorphin and Nrf2 siRNA reversed the protective effects of Eze. In summary, Eze decreases oxidative stress and subsequent neuroinflammation via activation of the AMPK/Nrf2/TXNIP pathway after MCAO in rats. Therefore, Eze may be a potential therapeutic approach for ischemic stroke patients.

Ezetimibe, a NPC1L1 inhibitor, attenuates neuronal apoptosis through AMPK dependent autophagy activation after MCAO in rats

Autophagy activation exerts neuroprotective effects in the ischemic stroke model. Ezetimibe (Eze), a Niemann-Pick disease type C1-Like 1 (NPC1L1) pharmacological inhibitor, has been reported to protect hepatocytes from apoptosis via autophagy activation. In this study, we explored whether Eze could attenuate neuronal apoptosis in the rat model of middle cerebral artery occlusion (MCAO), specifically via activation of the AMPK/ULK1/autophagy pathway. Two hundred and one male Sprague-Dawley rats were subjected to transient MCAO followed by reperfusion. Eze was administered 1 h after MCAO. To elucidate the underlying molecular mechanism, Dorsomorphin, a selective AMPK inhibitor, and 3-methyladenine (3-MA), an autophagy inhibitor, were injected intracerebroventricularly before MCAO. Infarct volume, neurological score, brain cholesterol levels, immunofluorescence staining, Western blot, and Fluoro-Jade C (FJC) staining were used to evaluate the effects of Eze. The endogenous NPC1L1 expression increased and mainly expressed in neurons after MCAO. Intranasal administration of Eze reduced brain infarct volume at 24 and 72 h after MCAO, with improved short and long-term neurological functions after MCAO. Eze reduced brain cholesterol levels (total cholesterol, free cholesterol and cholesteryl esters) and the number of FJC-positive neurons. The expression of phosphorylated AMPK (p-AMPK) and downstream ULK1, Beclin1, LC3BII, Bcl-2, and Bcl-xl increased, while P62 and proapoptotic Bax decreased after treatment with Eze. Pretreatment with Dorsomorphin and 3-MA reversed the beneficial effects of Eze. These findings suggest that intranasal administration of Eze plays neuroprotective role through autophagy activation after MCAO in rats. Lowered cholesterol levels and AMPK activation may act in conjunction to induce autophagy after treatment with Eze. Eze merits further investigation as a potential therapeutic agent in ischemic stroke patients.

Changes in Biliary Levels of Arginine and its Methylated Derivatives after Hepatic Ischaemia/Reperfusion

Arginine (Arg) can be methylated to form symmetrical dimethylarginine (SDMA) and asymmetrical dimethylarginine (ADMA), the latter an endogenous inhibitor of nitric oxide synthase (NOS). SDMA is excreted in the urine, while ADMA is mainly subjected to degradation in the liver. Arg competes with ADMA and SDMA for cellular transport across cationic amino-acid transporters (CATs). We evaluated the changes in serum, tissue and biliary levels of Arg, citrulline (Cit), ADMA and SDMA and the modifications in CATs after ischaemia-reperfusion (I/R). Male Wistar rats were subjected to 30-min. partial-hepatic ischaemia or sham-operated. After 60-min. reperfusion, the concentrations of ADMA, SDMA, Arg and Cit in serum, tissue and bile were measured. Serum levels of AST, ALT and alkaline phosphatase (AP) levels were determined. mRNA of cationic transporter 2A (CAT-2A) and 2B (CAT-2B) were also quantified. An increase in ADMA and a decrease in SDMA were observed in bile at the end of reperfusion. On the contrary, lower tissue ADMA levels and higher SDMA levels were quantified. No serum changes in ADMA and SDMA were found. A decrease in Arg and an increase of Cit were detected in serum, bile and tissue after I/R. A marked increase in AST, ALT and AP levels in serum confirmed I/R injury. A decrease in mRNA transporter CAT-2A but not in CAT-2B was detected. This study supported a biliary CAT-2B-dependent transport of ADMA and demonstrated, for the first time, that the liver is also responsible for the biliary excretion of SDMA into the bile.

Changes in ADMA/DDAH pathway after hepatic ischemia/reperfusion injury in rats: the role of bile

We investigated the effects of hepatic ischemia/reperfusion (I/R) injury on asymmetric dimethylarginine (ADMA, a nitric oxide synthase inhibitor), protein methyltransferase (PRMT) and dimethylarginine dimethylaminohydrolase (DDAH) (involved, resp., in ADMA synthesis and degradation), and the cationic transporter (CAT). Male Wistar rats were subjected to 30 or 60 min hepatic ischemia followed by 60 min reperfusion. ADMA levels in serum and bile were determined. Tissue ADMA, DDAH activity, DDAH-1 and CAT-2 protein, DDAH-1 and PRMT-1 mRNA expression, GSH/GSSG, ROS production, and lipid peroxidation were detected. ADMA was found in bile. I/R increased serum and bile ADMA levels while an intracellular decrease was detected after 60 min ischemia. Decreased DDAH activity, mRNA, and protein expression were observed at the end of reperfusion. No significant difference was observed in GSH/GSSG, ROS, lipid peroxidation, and CAT-2; a decrease in PRMT-1 mRNA expression was found after I/R. Liver is responsible for the biliary excretion of ADMA, as documented here for the first time, and I/R injury is associated with an oxidative stress-independent alteration in DDAH activity. These data are a step forward in the understanding of the pathways that regulate serum, tissue, and biliary levels of ADMA in which DDAH enzyme plays a crucial role.

Adalimumab ameliorates abdominal aorta cross clamping which induced liver injury in rats

The aim of this study was to investigate the possible protective effects of adalimumab (ADA) on cell damage in rat liver tissue during ischemia/reperfusion (I/R) injury of infrarenal abdominal aorta. Thirty male Wistar-albino rats were divided into three groups: control, I/R, and I/R+ADA, each group containing 10 animals. Laparotomy without I/R injury was performed in the control group animals. Laparotomy in the I/R group was followed by two hours of infrarenal abdominal aortic cross ligation and then two hours of reperfusion. ADA (50 mg/kg) was administered intraperitoneally as a single dose, to the I/R+ADA group, five days before I/R. The tumor necrosis factor-alpha (TNF-α) (pg/mg protein) and nitric oxide (NO) (µmol/g protein) levels in the I/R group (430.8 ± 70.1, 8.0 ± 1.1, resp.) were significantly higher than those in the I/R+ADA group (338.0 ± 71.6, P = 0.006; 6.3 ± 1.2, P = 0.008) and the control group (345.5 ± 53.3, P = 0.008; 6.5 ± 1.5, P = 0.010, resp.). I/R causes severe histopathological injury to the liver tissue, but ADA leads to much less histopathological changes. ADA treatment significantly decreased the severity of liver I/R injury. ADA pretreatment may have protective effects on experimental liver injury.

Adalimumab ameliorates abdominal aorta cross clamping which induced liver injury in rats

The aim of this study was to investigate the possible protective effects of adalimumab (ADA) on cell damage in rat liver tissue during ischemia/reperfusion (I/R) injury of infrarenal abdominal aorta. Thirty male Wistar-albino rats were divided into three groups: control, I/R, and I/R+ADA, each group containing 10 animals. Laparotomy without I/R injury was performed in the control group animals. Laparotomy in the I/R group was followed by two hours of infrarenal abdominal aortic cross ligation and then two hours of reperfusion. ADA (50 mg/kg) was administered intraperitoneally as a single dose, to the I/R+ADA group, five days before I/R. The tumor necrosis factor-alpha (TNF-α) (pg/mg protein) and nitric oxide (NO) (µmol/g protein) levels in the I/R group (430.8 ± 70.1, 8.0 ± 1.1, resp.) were significantly higher than those in the I/R+ADA group (338.0 ± 71.6, P = 0.006; 6.3 ± 1.2, P = 0.008) and the control group (345.5 ± 53.3, P = 0.008; 6.5 ± 1.5, P = 0.010, resp.). I/R causes severe histopathological injury to the liver tissue, but ADA leads to much less histopathological changes. ADA treatment significantly decreased the severity of liver I/R injury. ADA pretreatment may have protective effects on experimental liver injury.

Age-related changes in ADMA-DDAH-NO pathway in rat liver subjected to partial ischemia followed by global reperfusion

BACKGROUND

Liver function is affected during ischemia/reperfusion (IR). We evaluated the effect of the aging process on selected parameters determining the NO level in rat liver subjected to IR.

METHODS

The animals were divided into the C-2 and the IR-2 group of young rats (2-4 months old) and the C-12 and the IR-12 group of older rats (12-14 months old). Livers belonging to the IR-2 and the IR-12 group were subjected to partial ischemia (60 min) and reperfusion (4 h). Blood samples were obtained after surgeries to estimate the activity of aminotransferases, as well as just before ischemia and during reperfusion (15, 120, and 240 min) to estimate concentration of arginine (Arg) and its derivatives: asymmetric and symmetric dimethylarginine (ADMA, SDMA). After IR, dimethylarginine dimethylaminohydrolase (DDAH) activity and protein concentration of inducible nitric oxide synthase (iNOS) were measured in liver homogenates.

RESULTS

In the IR-2 group ADMA level increased the most between 15 and 120 min of reperfusion and was the highest of all the groups (0.72±0.2 μmol/l). In the IR-12 group ADMA level decreased significantly and was lower compared to all the other groups at 15 min (0.42±0.2 μmol/l) and to IR-2 at 120 (0.52±0.1 μmol/l) and 240 min (0.38±0.1 μmol/l) of reperfusion. Only the IR-2 group SDMA level increased significantly between 15 (0.75±0.9 μmol/l) and 240 min (1.0±1.2 μmol/l) of reperfusion. At the beginning of the surgery the Arg level was significantly higher in young rats (C-2: 102.1±35.7 μmol/l; IR-2: 114.63±28.9 μmol/l) than in older ones (C-12: 41.88±44.7 μmol/l; IR-12: 28.64±30.6 μmol/l). In the C-2 group the Arg level (77.41±37.5 μmol/l) and Arg/ADMA (A/A) ratio (138.03±62.8 μmol/l) were significantly higher compared to the ischemic groups at 15 min and to all the other groups at 120 (Arg: 47.17±31.7 μmol/l; A/A: 88.28±66.2 μmol/l) and 240 min (Arg: 43.87±21.9 μmol/l; A/A: 118.02±106.3 μmol/l). In the IR-2 group Arg level (11.4±12.0 μmol/l) and A/A ratio (16.11±16.2 μmol/l) decreased significantly at 15 min and during the next phase of reperfusion the levels of those parameters were low, comparably to those in IR-12. As a result of IR, a decrease in DDAH activity and an increase in iNOS protein concentration were observed only in the young rats.

CONCLUSIONS

We found that in the non-ischemic groups the Arg level may be affected by the aging process. Under IR conditions, important changes in DDAH-ADMA-NO pathway were observed only in young livers.