Intranasal Administration Of Nerve Growth Factor (NGF) Prevents Behavioral And Histological Deficits In Aluminum-exposure Rats

ObjectiveAlzheimer's disease, the most common neurodegenerative disorder and the most frequent cause of dementia, becomes increasingly common with advancing age. Progressive impairment of recent memory is typically clinical findings of Alzheimer's disease. In the late stages psychiatric symptoms and behavioral disturbances may be prominent.The characteristic histopathology is the presence of large numbers of neurofibrillary tangles, senile plaques, and cholinergic neurons granulovascuolar in the brain, especially in the neocortex and hippocampus of patients with Alzheimer's disease. Intra-neurofibrillary tangles consists of hyperphosphorylated, twisted filaments of the cytoskeletal protein tau, whereas extra-senile plaques are the depositions of amyloidp, a 39-43-amino-acid-long peptide derived from the proteolitic processing of amyloid precursor protein.Although Alzheimer's disease is a disease of unknown etiology, but the neurotoxicity of amyloidp has been commonly accepted as the pivotal factor in the generation and progress of AD.Degeneration of cholinergic neuronal pathways and depletion of the choline acetyltransferase have been found in the brains of patients dying of Alzheimer's disease, these changes may contribute to its clinical expression. Therefor, cholinergic replacement therapy has been used in an effort at symptomatic treatment of memonic and cognitive deficits. The drugs tried have included acetylcholine precursors, drugs that stimulate acetylcholine release, acetylcholinesterase inhibitors, muscarinic cholinergic receptor agonists. Several other pharmacologic treatments have been proposed for cognitive dysfunction in Alzheimer's disease, including cerebral vasodilators, central nervous system stimulants, opioid antagonists and neuropeptides. But of these, none has been proved unequivocally to reverse existing deficits or arrest the disease's progression.Recent research advances in neuroscience show that nerve growth factor (NGF) plays an important role in the growth, development, differenciation, maintenance and regeneration of various type neurons in the CNS.It is also the important trophic factor for cholinergic neurons. NGF increases the synthesis of choline acetyltransferase and prevents cholinergic neurons degeneration caused by experimental injury or associated with physiological and pathological situation, such as aging and Alzheimer's disease. Although the results lay the groundwork to propose a therapeutic use of NGF in AD, the blood-brain barrier represents a major problem in developing a NGF-based treatment for Alzheimer's disease because it prevents this large molecule from reaching the brain. Intracere-broventricular administration NGF, directly infusing NGF into parenchyma, and delivering NGF ex vivo gene are used respectively in order to bypass the blood-brain barrier. However, these approaches not only require the use of risky surgical procedures, high cost but also may lead severe complications such as infections, extra damage and so on. Until 1995, Frey and coworkers showed that NGF and other trophic factors, such as IGF-â… , can be delivered to the brain via the olfactory and/or trigeminal pathways by intranasal administration, which provided a noninvasive delivery NGF to the brain. After that CapsoniS' work demonstrated that the intranasal NGF delivery was effective in rescuing AD-like neurodegeneration in transgenic mice. But the cause of AD is complicated. Most cases of AD are sporadic, only approximately 10% of AD cases are genetic basis. So it is very important to study the efficacy of intranasal NGF delivery in preventing AD-like changes in non transgenic model of AD. No currently available related data have been reported.In the present study, we injected AlCl₃ into rat lateral cerebral ventricle to establish non transgenic model of AD, and examined the spatial memorry and immunohistochemical and histological changes after injection, and the effects of intranasal administration of NGF on the changes. This study aims at elucidating the role of intranasal administration of NGF in preventing rats in Al exposure from Alzheimer-like changes and may provide new method for treatment of non genetic AD by noninvasive route of administration for delivery of NGF.MethodsAlCl₃ was injected into rat lateral cerebral ventricle to establish non transgenic model of AD. Spatial learning and memory changes in aluminum (Al) exposure rats, and the effect on the changes induced by intranasal administration of NGF were measured by using Morris water maze. Immunohistochemical staining was used to detect the effect of intranasal administration of NGF onP-amyloid depositions in frontal cortex and hippocampus of Al exposure rats, and HE staining was used to detect neuronal changes, and the expression level of APP and ADAM 10 were determined by using Western blot.Results1. Morris water maze taskThe escape latency in the experimental group rats did not differ significantly from those in the control group rats (P＞0.05), and there was no significant difference between the experimental group and the control group in terms of the number of annulus crossings (the number of times the previous platform location was crossed over) (P＞0.05). However, the escape latency in the model group rats prolonged significantly compared with those of control group rats, and there was a significant difference between the model group and the control group in terms of the number of annulus crossings, the difference was statistically significant (P＜0.05). 2. HE analysisNerve cells arrange intensive, eumorphism, cell membrane and nuclear membrane integrated in the control group experimental group rats of hippocampus. Nerve cells obvious depletion, arrange rarefaction and lightly dying, paramorphia, cell membrane and nuclear membrane pyknosis and rupture, vacuolus.3. Western blot analysisCompared with control group (integrated density value cortex: 0.22±0.04, hippocamp: 0.31±0.05), the expression of APP in the rat brain of model group (integrated density value cortex: 1.28±0.13, hippocamp: 1.41±0.26) and experimental group (cortex: 1.16±0.15, hippocamp: 1.32±0.23) increased remarkably, and the integrated density values of APP were statistically significant (P＜0.05).A significant increase of integrated density value ratio of ADAM 10 in experimental group rat brain (integrated density value cortex: 0.93±0.16 hippocamp: 0.98±0.20) was noted, Comparing with control group (cortex: 0.19±0.07 hippocamp: 0.21±0.06) (P＜0.05). Compared with control group, the integrated density value ratio of AD AM10 in model group rat brain (cortex: 0.16±0.04, hippocamp: 0.19±0.05) was not increase (P＞0.05).4. Immunohistochemical stainingThe Aβ_1-40 antibody revealedβ-amyloid depositions in the frontal cortex and hippocampus of model group animals. No labeling is seen in sections from control and experimental group rats.Conclusion1. Intranasal administration of nerve growth factor (NGF) can resist the nerve poisonous function of aluminum, can prevent availably from Alzheimer-like behavioral and histological deficits in aluminum-exposure rats, and have the nerve protection function.2. Resisting the nerve toxicity of aluminum by up-regulation the ADAM 10 expression level, making over expressionβ-APP pass theα-Secretase degradation path, increasing theα-APPs of the dissolubility, and obstructing formation of Aβthat do not dissolve, may be one of the nerve protection mechanism of NGF.3. Up-regulation the expression level of gene in the hippocampus of rats may be one of mechanism of molecular toxicology of IBA that damaged neurons in hippocampus.