TiO2-cerebrolysin attenuates SiO2 and hyperthermia induced neuropathic pain pathology

Our military personals are the most prone to neuropathic pain that are engaged in combat operation across the World. Also, blast injuries leading to arm or leg amputation are another source of neuropathic pain that is still difficult to treat with suitable therapeutic agents. However, whether a combination of silica dust (SiO2 nanoparticles, NPs) and high environmental heat could act synergistically to enhance the pathophysiology of neuropathic pain in our soldiers is still unclear. We have previously shown that exposure of engineered nanoparticles from metals Ag, Cu and Al enhances the breakdown of the blood-spinal cord barrier (BSCB), astrocytic activation and cord pathology in a rat model of neuropathic pain produced by peripheral L-4 and L-5 nerve lesion. In present investigation we investigated whether chronic exposure of SiO2 NPs in heat could exacerbate the pathology of neuropathic pain in a rat model. In addition, nanodelivery of cerebrolysin was also examined in this model. Male adult rats (20-25 weeks of age) subjected to L4-L5 nerve lesion and allowed to survive 10 weeks that induces leakage of the BSCB to proteins, activation of astrocytes, myelin damage and neuronal injuries in the cord. In separate groups, identical nerve lesion was produced in animals that are exposed to SiO2 NPs (50-60 nm, 50 mg/kg, i.p. daily for 1 week) at room temperature or in rats reared at high ambient temperature (34° C) for 8 days. In all three groups of rats BSCB breakdown to albumin, glial fibrillary acidic protein (GFAP) and myelin basic protein (MBP) immunoreactivity along with neuronal injury using Nissl staining were performed after 10 weeks of nerve lesion. Our results showed that the magnitude of BSCB leakage (+250 to 300 %), astrocytic activation (+100 to 240 %) and myelin (+80 to 140 % degradation) or nerve injuries (+250 to 380 % increase) were most exacerbated after nerve lesion in animals that were reared at high ambient temperature with sSiO2 NPs as compared to nerve lesion in saline treated rats at room temperature. SiO2 NPs alone also enhanced nerve lesion induced cord pathology as compared to saline treated group after nerve lesion significantly. Administration of cerebrolysin (5 ml/kg, i.v. daily, Ever NeuroPharma, Austria) in these animals for 1 week from the day of nerve lesion significantly attenuated cord pathology in SiO2 exposed animals at room temperature but not in animals that were reared at high ambient temperature. Interestingly TiO2 nanowired cerebrolysin when administered in animals reared at 34°C and exposed to SiO2 NPs significantly reduced cord pathology when the drug was given after 2 to 3 weeks (but not after 4 weeks) of nerve lesion.  These observations are the first to suggests that a combination of heat and SiO2 NPs aggravate neuropathic pain induced cord pathology and nanowired cerebrolysin if administered within early periods after the nerve insult (within 2 to 3 weeks) most of the symptoms of cord pathology could be prevented indicating a promising potential of nanowired delivery of cerebrolysin.