Title

 

Authors

C. Giordano¹,D. Siniscalco¹, D. Melisi², L. Luongo¹, A. Curcio², E. Palazzo¹, I. Marabese¹, M. De Chiaro¹, M.G. Rimoli², S. Maione¹, V. de Novellis^1
 
1Dept of Experimental Medicine, Section of Pharmacology “L. Donatelli”, Faculty of Medicine and Surgery, Second University of Naples, Via Costantinopoli, 16 80138 Naples, Italy
²Dept of Pharmaceutical and Toxicological Chemistry, Faculty of Pharmacy, University of Naples Federico II, Via Pansini, 8 Naples, Italy

 

Abstract

This study has investigated whether the galactosyl ester prodrug of N^ω-nitro-L-arginine (NAGAL), shows enhanced analgesic efficacy in healthy mice and in models of visceral and neuropathic pain: the writhing test and the spared nerve injury (SNI), respectively. NAGAL was compared to methyl ester pro-drug of N^ω-nitro-L-arginine (L-NAME), a widely exploited non-specific nitric oxide synthase (NOS) inhibitor, for analgesic potential. The writhing test revealed that the ED₅₀ value, along with the 95% confidence limit (CL) was 3.82 (1.77–6.04) mg/kg for NAGAL and, 36.75 (20.07–68.37) mg/kg for L-NAME. Notably, NAGAL elicited a greater anti-allodynic effect than L-NAME did in neuropathic mice. Biomolecular and morphological studies revealed that spared nerve injury increased the expressions of pro-inflammatory enzymes (caspase-1) and two glial cell biomarkers: integrin alpha M (ITGAM) and glial fibrillary acidic protein (GFAP) in the spinal cord. Finally, GLUT-3, an isoform of the hexose transporters capable to bind NAGAL and inducible NOS (iNOS), were found to be over-expressed in the activated astrocytes of the spinal cord of neuropathic mice. NAGAL administration normalized expression levels of these biomarkers. NAGAL showed a greater efficacy in inhibiting visceral pain and allodynia than L-NAME possibly by a greater cell permeation through the hexose transporter which is highly over-expressed by activated glia.