Chronic inhibition of central Angiotensin-converting enzyme ameliorates colchicine-induced memory impairment in mice

Captopril is more effective than Perindopril against aluminium chloride induced amyloidogenesis and AD like pathology

Alzheimer's disease (AD) is a common neurodegenerative disorder. Aluminium chloride induces AD like pathology in rats. Renin angiotensin system plays a significant role in the pathogenesis and occurrence of Alzheimer's disease. In the present study we evaluated and compared the effect of Captopril and Perindopril against aluminium chloride induced amyloidogenesis and cognitive dysfunction in rats. Wistar rats of both sex were divided randomly into four groups i.e. Group I was served as normal control and treated with normal saline, Group II was administered with AlCl3 (100 mg/kg, p. o.) and Group III and IV received Captopril (30 mg/kg, p. o.) and Perindopril (5 mg/kg, p. o.) respectively 1hr prior to administration of AlCl3. All the doses were given once daily for 42 days. The evaluation of memory function was carried out in Y-maze (spontaneous alternation), radial arm maze (number of correct responses) and elevated plus maze (transfer latency). After behavioral studies, estimation of antioxidant status (brain and serum), amyloid-β content (brain) and histopathology of brain hippocampus region was done. Administration of AlCl3 for 42 days impaired cognitive dysfunction. Captopril and Perindopril prevented AlCl3 induced cognitive dysfunction by improving spontaneous alternation behavior, number of correct responses and reducing transfer latency. They also increase the antioxidant status, reduce the Aβ42 content in the brain and reverse the histopathological changes caused by AlCl3 in hippocampal region. Both Captopril and Perindopril protects against aluminium chloride induced amyloidogenesis and AD like pathology. Captopril is found to be more effective than Perindopril.

Animal models of chemotherapy-induced cognitive decline in preclinical drug development

RATIONALE

Chemotherapy-induced cognitive impairment (CICI), chemobrain, and chemofog are the common terms for mental dysfunction in a cancer patient/survivor under the influence of chemotherapeutics. CICI is manifested as short/long term memory problems and delayed mental processing, which interferes with a person's day-to-day activities. Understanding CICI mechanisms help in developing therapeutic interventions that may alleviate the disease condition. Animal models facilitate critical evaluation to elucidate the underlying mechanisms and form an integral part of verifying different treatment hypotheses and strategies.

OBJECTIVES

A methodical evaluation of scientific literature is required to understand cognitive changes associated with the use of chemotherapeutic agents in different preclinical studies. This review mainly emphasizes animal models developed with various chemotherapeutic agents individually and in combination, with their proposed mechanisms contributing to the cognitive dysfunction. This review also points toward the analysis of chemobrain in healthy animals to understand the mechanism of interventions in absence of tumor and in tumor-bearing animals to mimic human cancer conditions to screen potential drug candidates against chemobrain.

RESULTS

Substantial memory deficit as a result of commonly used chemotherapeutic agents was evidenced in healthy and tumor-bearing animals. Spatial and episodic cognitive impairments, alterations in neurotrophins, oxidative and inflammatory markers, and changes in long-term potentiation were commonly observed changes in different animal models irrespective of the chemotherapeutic agent.

CONCLUSION

Dyscognition exists as one of the serious side effects of cancer chemotherapy. Due to differing mechanisms of chemotherapeutic agents with differing tendencies to alter behavioral and biochemical parameters, chemotherapy may present a significant risk in resulting memory impairments in healthy as well as tumor-bearing animals.

Sattar MA, Kamel FO, Ramadan WS, Alzahrani YA. Possible combined effect of perindopril and Azilsartan in an experimental model of dementia in rats

Renin-angiotensin system exerted deleterious effects on learning and cognitive functions through different mechanisms. The present study has been designed to evaluate the protective effect of perindopril and azilsartan as monotherapy or in combination on aluminum chloride (AlCl3) induced neurobehavioral and pathological changes in Alzheimeric rats. Male Wistar rats were divided into nine groups (n = 6); negative control, AlCl3 treated, vehicle, AlCl3 and Azilsartan (3.5 mg/kg, 7 mg/kg) co-treated, AlCl3 and perindopril (0.5 mg/kg, 1 mg/kg) co-treated, AlCl3 and (Azilsartan 3.5 mg/kg + perindopril 0.5 mg/kg), and AlCl3 and (Azilsartan 7 mg/kg + perindopril 1 mg/kg), all groups were treated for consecutive 60 days. Then, memory function was evaluated by the Y- maze test. Amyloid Peptide - 42 (Aβ-42), Acetylcholinesterase (AChE), Malondialdehyde (MDA), Tumor necrosis factor (TNF-α) and Nitric Oxide (NO) levels in the hippocampus were assessed with (ELISA) kits. The histopathological studies of the hippocampal dentate gyrus (DG) and Cornu Ammonis-3 (CA3) were also performed. Oral administration of either azilsartan and perindopril alone or in combined for 60 days have shown; improvement of cognitive function, significant reduction in the hippocampal levels of Aβ-42, Acetylcholinesterase, Malondialdehyde (MDA), Tumor necrosis factor (TNF-α) and reserved most of histopathological changes in dentate gyrus (DG) and Cornu Ammonis-3 (CA3) that mediated by Alcl3. Our behavioral, biochemical, and histopathological studies indicate that perindopril and azilsartan have neuroprotective effects on the AD model of rats induced by AlCl3, suggesting that perindopril and azilsartan may be a candidate drugs for the treatment of AD.

Aliskiren and captopril improve cognitive deficits in poorly controlled STZ-induced diabetic rats via amelioration of the hippocampal P-ERK, GSK3β, P-GSK3β pathway

Learning and memory deficits are obvious symptoms that develop over time in patients with poorly controlled diabetes. Hyperactivity of the renin-angiotensin system (RAS) is directly associated with β-cell dysfunction and diabetic complications, including cognitive impairment. Here, we investigated the protective and molecular effects of two RAS modifiers, aliskiren; renin inhibitor and captopril; angiotensin converting enzyme inhibitor, on cognitive deficits in the rat hippocampus. Injection of low dose streptozotocin for 4 days resulted in type 1 diabetes. Then, poorly controlled diabetes was mimicked with ineffective daily doses of insulin for 4 weeks. The hyperglycaemia and pancreatic atrophy caused memory disturbance that were identifiable in behavioural tests, hippocampal neurodegeneration, and the following significant changes in the hippocampus, increases in the inflammatory marker interleukin 1β, cholinesterase, the oxidative stress marker malondialdehyde and protein expression of phosphorylated extracellular-signal-regulated kinase and glycogen synthase kinase-3 beta versus decrease in the antioxidant reduced glutathione and protein expression of phosphorylated glycogen synthase kinase-3 beta. Blocking RAS with either drugs along with insulin amended all previously mentioned parameters. Aliskiren stabilized the blood glucose level and restored normal pancreatic integrity and hippocampal malondialdehyde level. Aliskiren showed superior protection against the hippocampal degeneration displayed in the earlier behavioural modification in the passive avoidance test, and the aliskiren group outperformed the control group in the novel object recognition test. We therefore conclude that aliskiren and captopril reversed the diabetic state and cognitive deficits in rats with poorly controlled STZ-induced diabetes through reducing oxidative stress and inflammation and modulating protein expression.

Captopril and Valsartan May Improve Cognitive Function Through Potentiation of the Brain Antioxidant Defense System and Attenuation of Oxidative/Nitrosative Damage in STZ-Induced Dementia in Rat

Purpose: Previous findings have shown the crucial roles of brain renin-angiotensin system (RAS) in pathogenesis of Alzheimer's disease (AD). Since RAS inhibitors may have beneficial effects on dementia and cognitive function in elderly people, the aim of present study was to examine the neuroprotective actions of captopril and valsartan on memory function and neuronal damage in experimental model of AD. Methods: Adult forty male Wistar rats (220-280g) were randomly divided into 5 groups; Control, Vehicle, Alzheimer and treatment groups. AD was induced by the injections of streptozotocin (3mg/kg, bilateral intracerebroventricular) at days 1&3. Treated rats received orally captopril (50mg/kg/day) and valsartan (30mg/kg/day). Memory function and histological assessments were done at termination of experiment. Finally, superoxide dismutase (SOD) and catalase (CAT) activities as well as malondialdehyde (MDA) and NOx contents were determined. Results: There was a significant increase in the mean value of latency in Alzheimer group (66%). Captopril and valsartan considerably decreased this value in both treatment groups (45% and 72%, respectively). In Alzheimer group the activities of brain's SOD and CAT reduced (40% and 47%, respectively) in accompany with an increase in MDA and NOx contents (49% and 50%, respectively). Captopril and valsartan significantly increased the activities of brain's SOD and CAT concomitant reduction in MDA and NOx contents. Also, histopathological damages noticeably decreased in both treatment groups. Conclusion: Our findings indicate that RAS inhibition by using captopril and valsartan potentiates the antioxidant defense system of brain and reduces oxidative/nitrosative stress in accompany with neuronal damage during AD.

MEMRI detects neuronal activity and connectivity in hypothalamic neural circuit responding to leptin

Hypothalamus plays the central role in regulating energy homeostasis. To understand the hypothalamic neurocircuit in responding to leptin, Manganese-Enhanced MRI (MEMRI) was applied. Highly elevated signal could be mapped in major nuclei of the leptin signaling pathway, including the arcuate nucleus (ARC), paraventricular nucleus (PVN), ventromedial hypothalamus (VMH) and dorsomedial hypothalamus (DMH) in fasted mice and the enhancement was reduced by leptin administration. However, whether changes in MEMRI signal reflect Ca²⁺ channel activity, neuronal activation or connectivity in the leptin signaling pathway are not clear. By blocking L-type Ca²⁺ channels, the signal enhancement in the ARC, PVN and DMH, but not VMH, was reduced. By disrupting microtubule with colchicine, signal enhancement of the secondary neural areas like DMH and PVN was delayed which is consistent with the known projection density from ARC into these regions. Finally, strong correlation between c-fos expression and MEMRI signal increase rate was observed in the ARC, VMH and DMH. Together, we provide experimental evidence that MEMRI signal could represent activity and connectivity in certain hypothalamic nuclei and hence may be used for mapping activated neuronal pathway in vivo. This understanding would facilitate the application of MEMRI for evaluation of hypothalamic dysfunction in metabolic diseases.

Overproduction of nitric oxide intensifies brain infarction and cerebrovascular damage through reduction of claudin-5 and ZO-1 expression in striatum of ischemic brain

Nitric oxide (NO) overproduction has been demonstrated from different NO-synthase overexpression or hyperactivity after brain ischemia. Here, we examined the effects of inhibition of NO overproduction on brain infarction, cerebrovascular damage and expression of claudin-5 and zonula occludens-1 (ZO-1) in striatum of ischemic brain. The experiment was performed in three groups of rats; sham, control ischemia and ischemic treatment. Brain ischemia was induced by 60min of middle cerebral artery occlusion (MCAO) followed by 24h of reperfusion. Treated rats received L-NAME 30min before induction of ischemia (1mg/kg, i.p.). Infarct volume and histopathological changes of ischemic striatum were assessed by TTC and LFB staining methods, respectively. Ultimately, quantitative RT-PCR was used for assessment of claudins-5 and ZO-1 expression. MCAO in the control group induced infarction (135±25mm³) at large areas of striatum in accompany with neuronal damages, whereas L-NAME significantly reduced infarction (87±16mm³) and neuronal injuries. The mRNA of ZO-1 and claudin-5 decreased in ischemic striatum, whereas inhibition of NO overproduction by L-NAME attenuated this reduction for these genes. Our findings indicated that NO overproduction after brain ischemia plays a crucial role in neuronal damage especially at striatal regions. Hence, inhibition of excessive NO production may save striatal cerebrovascular integrity of ischemic brain.

Acetylcholinesterase Inhibition Attenuates the Development of Hypertension and Inflammation in Spontaneously Hypertensive Rats

BACKGROUND

It is hypothesized that chronic increase of availability of acetylcholine, resulting from the effect of antiacetylcholinesterases, may prevent autonomic imbalance and reduce inflammation yielding benefic effects for cardiovascular disorders in hypertension. The effect of long-term administration of antiacetylcholinesterase agents with central and/or peripheral action, i.e., donepezil and pyridostigmine, were investigated on arterial pressure (AP), sympathovagal balance, plasma cytokine levels, and cardiac remodeling in spontaneously hypertensive rats (SHR).

METHODS

Chronic treatment with donepezil or pyridostigmine started before the onset of hypertension. AP was measured by plethysmography every 4 weeks. At the end of 16 weeks of treatment, methylatropine was used to evaluate the cardiac vagal tone; AP and pulse interval (PI) variability were also evaluated followed by plasma and heart collection for analysis.

RESULTS

Pyridostigmine, which does not cross the blood-brain barrier, increased cardiac vagal tone, and reduced cardiomyocyte diameter and collagen density, but did not affect the AP and plasma cytokine levels. Donepezil, which crosses the blood-brain barrier, attenuated the development of hypertension, increased cardiac vagal tone, and improved AP and PI variability. Likewise, donepezil reduced the plasma levels of tumor necrosis factor-α, interleukin 6, and interferon γ, besides reducing cardiomyocyte diameter and collagen density.

CONCLUSIONS

Donepezil attenuated the development of hypertension in SHR probably involving antiinflammatory effects, indicating that acetylcholinesterase inhibition yields benefic effects for antihypertensive therapy.

Interactions between levetiracetam and cardiovascular drugs against electroconvulsions in mice

BACKGROUND

Hypertension and heart failure belong to common comorbid conditions with epilepsy so drug interactions between antiepileptics and cardiovascular drugs are possible in clinical practice. The aim of this study was to evaluate the effects of angiotensin AT1 receptor antagonists (losartan potassium and candesartan cilexetil), angiotensin-converting enzyme (ACE) inhibitors (captopril and perindopril arginine) and diuretics (hydrochlorothiazide and ethacrynic acid) on the anticonvulsant activity of levetiracetam (LEV) in mice.

METHODS

The protective action of LEV was examined in the maximal electroshock seizure threshold test. Drugs were administered intraperitoneally (ip). Additionally, combinations of cardiovascular drugs with LEV were tested for adverse effects in the passive avoidance task and the chimney test.

RESULTS

Losartan potassium (50mg/kg), candesartan cilexetil (8mg/kg), captopril (50mg/kg), hydrochlorothiazide (100mg/kg) and ethacrynic acid (100mg/kg) did not affect the anticonvulsant activity of LEV. Perindopril arginine (10mg/kg) raised the convulsive threshold for LEV administered at doses of 100, 300 and 500mg/kg. This interaction could be pharmacodynamic in nature because the brain concentration of LEV remained unchanged by perindopril. The adverse effects of the combined treatment with LEV and cardiovascular drugs were not observed in the passive avoidance task or the chimney test.

CONCLUSIONS

Although experimental data can be hardly extrapolated to clinical practice, it is suggested that perindopril arginine may positively influence the anticonvulsant action of LEV in epileptic patients. The use of losartan potassium, candesartan cilexetil, captopril, hydrochlorothiazide or ethacrynic acid in patients treated with LEV seems neutral regarding its anticonvulsant activity.

Potential of protease inhibitor in 3-nitropropionic acid induced Huntington's disease like symptoms: mitochondrial dysfunction and neurodegeneration

Huntington's disease (HD) is a genetic, neurodegenerative disorder mainly characterized by motor dysfunction, cognitive decline and psychiatric disturbances. 3-Nitropropionic acid (3-NP) is an inhibitor of succinate dehydrogenase (Complex II) of the mitochondrial respiratory chain, which thereby reduces production of ATP. It induces neurotoxicity by causing striatal degeneration, energy deficit and oxidative stress. Angiotensin converting enzyme (ACE) is an important protease in the renin angiotensin system (RAS) responsible for the conversion of Angiotensin I to Angiotensin II. Angiotensin-II stimulates mitochondrial oxidant release leading to depression of energy metabolism. ACE inhibitors have shown promise in disorders like stress, anxiety, and depression in addition to showing beneficial effects in cognitive disorders like Alzheimer's. Angiotensin-II inhibition enhances energy production by lowering mitochondrial oxidant production, and hence protects mitochondrial structure. Trandolapril is a centrally active ACE inhibitor. 3-NP administered systematically (20mg/kg, i.p) for 4 days consecutively induced HD like symptoms - loss of body weight, neurobehavioral alterations like memory dysfunction (elevated plus maze, Morris water maze performance), Hind-limb impairment (Narrow beam test), motor incoordination (locomotor activity). Biochemical studies on brain tissue showed increased lipid peroxidation, nitrite levels and acetylcholinesterase activity along with decreased levels of reduced glutathione, catalase activity. Mitochondrial enzyme complex activities (I, II, IV and MTT assay) were found to be significantly lowered in brain mitochondria. Administration of Trandolapril (4 and 6 mg/kg, p.o) daily for 12 days showed significant improvement in body weight, neurobehavioral parameters, oxidative stress and mitochondrial enzyme activities in rat brain. These findings were further confirmed by histopathological studies which showed improvement in 3-NP induced brain lesions. This study indicates that Trandolapril could be an effective treatment option for the management of HD.