Crotoxin Conjugated to SBA-15 Nanostructured Mesoporous Silica Induces Long-Last Analgesic Effect in the Neuropathic Pain Model in Mice

Abstract

Neuropathic pain is a disease caused by structural and functional plasticity in central and peripheral sensory pathways that produce alterations in nociceptive processing. Currently, pharmacological treatment for this condition remains a challenge. Crotoxin (CTX), the main neurotoxin of Crotalus durissus terrificus rattlesnake venom, has well described prolonged anti-inflammatory and antinociceptive activities. In spite of its potential benefits, the toxicity of CTX remains a limiting factor for its use. SBA-15 is an inert nanostructured mesoporous silica that, when used as a vehicle, may reduce toxicity and potentiate the activity of different compounds. Based on this, we propose to conjugate crotoxin with SBA-15 (CTX:SBA-15) in order to investigate if when adsorbed to silica, CTX would have its toxicity reduced and its analgesic effect enhanced in neuropathic pain induced by the partial sciatic nerve ligation (PSNL) model. SBA-15 enabled an increase of 35% of CTX dosage. Treatment with CTX:SBA-15 induced a long-lasting reduction of mechanical hypernociception, without modifying the previously known pathways involved in antinociception. Moreover, CTX:SBA-15 reduced IL-6 and increased IL-10 levels in the spinal cord. Surprisingly, the antinociceptive effect of CTX:SBA-15 was also observed after oral administration. These data indicate the potential use of the CTX:SBA-15 complex for neuropathic pain control and corroborates the protective potential of SBA-15.

The Crotoxin:SBA-15 Complex Down-Regulates the Incidence and Intensity of Experimental Autoimmune Encephalomyelitis Through Peripheral and Central Actions

“…Although the mechanisms by which SBA-15 decreases the toxicity of compounds is not clear, the controlled release of them may contribute to that. In accordance, previous studies from our group have demonstrated that SBA-15 allows an increase of CTX dose with non-toxic effects (37).…”

“…In the in vivo assays, the following compounds were used: 40 mg/kg of CTX (22,44) or 54 mg/kg of CTX:SBA-15 administered by subcutaneous (s.c., 200 ml) route, since SBA-15 conjugation enabled an increase of 35% of CTX non-toxic dosage, as previously demonstrated by our group (37). The animals were treated with 5 doses (1 administration/day for 5 consecutive days) or with a single administration, starting from the 5 th day post-immunization, based on previous results from our group which considered the onset of the first symptom of the disease to start the treatment (pain threshold alteration that occurred in the 4 th day after immunization) (45).…”

“…We previously described that the repetitive administration of CTX (40 mg/kg), starting from the 5 th day post-immunization (5 consecutive doses 40 mg/kg) was effective in reducing EAEinduced clinical signs (45). Since SBA-15 conjugation enables an increase of 35% in CTX non-toxic dosage, a dose of 54 mg/kg was used in the present study (37). CTX:SBA-15 induced analgesic effect during the observed period when compared to the EAE group (Figure 1A).…”

“…However, CTX is a neurotoxin, and its use, especially in high doses or in chronic schedules, is limited by its toxic effect, mainly for debilitating conditions. Hence, taking advantage of the silica SBA-15 beneficial effects as a carrier agent (37,57), we previously demonstrated that SBA-15 attenuates CTX-induced toxic effects by increasing in 35% the CTX lethal dose 50% (LD 50 ) (37). Thus, this work aimed to improve the immunomodulatory effect of CTX through its adsorbing to SBA-15 in the EAE model.…”

“…The properties of nanostructured silica in to carry, to protect, and to deliver the entrapped antigens or compounds are attributed to its hexagonal nanostructured pores, which protect compounds against proteolysis, organic solvents, high shear stresses, and low pH (57,76,77). Previous data from our group demonstrated that silica does not alter some of the mediators known to be responsible for the antinociceptive effect of CTX (37). Considering that, the fact that once encapsulated and kept entrapped in the silica, the compound may have its release controlled (34,78) could be a possible explanation for the SBA-induced CTX effect potentiation in EAE animals.…”