Initial characterization of the transplant of immortalized chromaffin cells for the attenuation of chronic neuropathic pain

Cultures of embryonic day 17 (E17) rat adrenal and neonatal bovine adrenal cells were conditionally immortalized with the temperature-sensitive allele of SV40 large T antigen (tsTag) and chromaffin cell lines established. ind icative of the adrenal chromaffin phenotype, these cells expressed immunore activity (ir) for tyrosine hydroxylase (TH), the first enzyme in the synthe tic pathway for catecholamines. At permissive temperature in vitro (33 degr eesC), these chromaffin cells are proliferative, have a typical rounded chr omaffin-like morphology, and contain detectable TH-ir. At nonpermissive tem perature in vitro (39 degreesC), these cells stop proliferating and express increased TH-ir. When these immortalized chromaffin cells were transplante d in the lumbar subarachnoid space of the spinal cord 1 week after a unilat eral chronic constriction injury (CCI) of the rat sciatic nerve, they survi ved longer than 7 weeks on the pia mater around the spinal cord and continu ed to express TH-ir. Conversely, grafted chromaffin cells lost Tag-ir after transplant and Tag-ir was undetectible in the grafts after 7 weeks in the subarachnoid space. At no time did the grafts form tumors after transplant into the host animals. These grafted chromaffin cells also expressed immuno reactivities for the other catecholamine-synthesizing enzymes 7 weeks after grafting, including: dopamine-P-hydroxylase (DPH) and phenylethanolamine-N -methyltransferase (PNMT). The grafted cells also expressed detectable immu noreactivities for the opioid met-enkephalin (ENK), the peptide galanin (GA L), and the neurotransmitters gamma -aminobutyric acid (GABA) and serotonin (5-HT). Furthermore, after transplantation, tactile and cold allodynia and tactile and thermal hyperalgesia induced by CCI were significantly reduced during a 2-8-week period, related to the chromaffin cell transplants. The maximal antinociceptive effect occurred 1-3 weeks after grafting. Control a drenal fibroblasts, similarly immortalized and similarly transplanted after CCI, did not express any of the chromaffin antigenic markers, and fibrobla st grafts had no effect on the allodynia and hyperalgesia induced by CCI. T hese data suggest that embryonic and neonatal chromaffin cells can be condi tionally immortalized and will continue to express the phenotype of primary chromaffin cells in vitro and in vivo; grafted cells will ameliorate neuro pathic pain after nerve injury and can be used as a homogeneous source to e xamine the mechanisms by which chromaffin transplants reverse chronic pain. The use of such chromaffin cell lines that are able to deliver antinocicep tive molecules in models of chronic pain after nerve and spinal cord injury (SCI) offers a novel approach to pain management.