H.S. Sharma, D.F. Muresanu, J.V. Lafuente, R. Patnaik, Z.R. Tian, A. Ozikzilcik, H. Mössler, A. Sharma
Keywords: neprilysin, cerebrolsyin, TiO2 nanowired delivery, Alzheimer's Disease, amyloid beta peptide, gliosis, blood-brain barrier
Summary:Neprilysin (NPL) is an endogenous enzyme that functions as rate-limiting step in amyloid-beta peptide (AβP) degradation. There are reasons to believe that an imbalance between production and clearance of AβP results in its accumulation leading to development of Alzheimer’s Disease (AD). In several cases of AD the metalloprotease NPL brain concentration is decreased. Also NPL knocked out mice exhibited AD like brain pathology and behavioural dysfunctions. This suggests that enhancing the NPL concentartions by therapeutic means may reduce brain pathology in AD. Recently some evidences suggest that focal brain injury or traumatic head injury could also induce alterations in NPL activity in the brain and in the CSF. Although brain injury alone could results in deposition of AβP in the brain indicating that AD may result following brain trauma. Thus, it is interesting to find out whether traumatic brain injury (TBI) could further exacerbate AβP infusion induced brain pathology. Furthermore, in such situation whether NPL has any protective role if administered exogenously either alone or with other neuroprotective gents e.g., cerebrolysin. AD like brain pathology was induced by AβP (1-40) administration intraventricularly (i.c.v.) in the left lateral ventricle 250 ng/10 µl once daily for 4 weeks in control or TBI rats. The TBI was produced by a longitudinal lesion over the right parietal cerebral cortex (2 mm deep and 4 mm long) after opening of the skull under anesthesia. After 30 days of the 1st AP infusion, the rats exhibited breakdown of the blood-brain barrier (BBB) extravasation of endogenous/exogenous protein tracers, brain edema formation, and AP deposits in several parts of the brain. The brain pathology showed neuronal, glial and axonal changes. In separate group of rats, TiO2 nanowired Cerebrolysin (25 µl, NWCBL) and/or TiO2 nanowired NPL (1 µg in 10 µl) was infused into the left cerebral ventricles daily starting from 1 week after the onset of AP infusion and terminated 1 week before the last infusion. Our results show that AβP infusion in TBI cases exacerbated brain pathology in various regions e.g., cerebral cortex, hippocampus, thalamus, hypothalamus and cerebellum. TiO2 NWCBL was able to thwarts brain pathology in AD cases in both healthy and TBI rats. However, NPL alone was able to reduce some of the brain pathology in healthy animals after AβP infusion. On the other hand a combination of NWCBL and NW-NPL resulted in profound neuroprotection in TBI following AβP infusion. Our results are the first to show that a combination of nanodelivered NPL and CBL has additive effects on neuroprotection in AD, not reported earlier.