No detectable analgesic effects in the formalin test even with one million bovine adrenal chromaffin cells

Viability and Functionality of Bovine Chromaffin Cells Encapsulated into Alginate-PLL Microcapsules with a Liquefied Inner Core

Implantation of adrenal medullary bovine chromaffin cells (BCC), which synthesize and secrete a combination of pain-reducing neuroactive compounds including catecholamines and opioid peptides, has been proposed for the treatment of intractable cancer pain. Macro- or microencapsulation of such cells within semi-permeable membranes is expected to protect the transplant from the host's immune system. In the present study, we report the viability and functionality of BCC encapsulated into microcapsules of alginate-poly-L-lysine (PLL) with a liquefied inner core. The experiment was carried out during 44 days. Empty microcapsules were characterized in terms of morphology, permeability, and mechanical resistance. At the same time, the viability and functionality of both encapsulated and nonencapsulated BCC were evaluated in vitro. We obtained viable BCC with excellent functionality: immunocytochemical analysis revealed robust survival of chromaffin cells 30 days after isolation and microencapsulation. HPLC assay showed that encapsulated BCC released catecholamines basally during the time course study. Taken together, these results demonstrate that viable BCC can be successfully encapsulated into alginate-PLL microcapsules with a liquefied inner core.

Antinociceptive effect of intrathecal microencapsulated human pheochromocytoma cell in a rat model of bone cancer pain

Human pheochromocytoma cells, which are demonstrated to contain and release met-enkephalin and norepinephrine, may be a promising resource for cell therapy in cancer-induced intractable pain. Intrathecal injection of alginate-poly (l) lysine-alginate (APA) microencapsulated human pheochromocytoma cells leads to antinociceptive effect in a rat model of bone cancer pain, and this effect was blocked by opioid antagonist naloxone and alpha 2-adrenergic antagonist rauwolscine. Neurochemical changes of cerebrospinal fluid are in accordance with the analgesic responses. Taken together, these data support that human pheochromocytoma cell implant-induced antinociception was mediated by met-enkephalin and norepinephrine secreted from the cell implants and acting at spinal receptors. Spinal implantation of microencapsulated human pheochromocytoma cells may provide an alternative approach for the therapy of chronic intractable pain.

Noradrenergic pain modulation

Norepinephrine is involved in intrinsic control of pain. Main sources of norepinephrine are sympathetic nerves peripherally and noradrenergic brainstem nuclei A1-A7 centrally. Peripheral norepinephrine has little influence on pain in healthy tissues, whereas in injured tissues it has variable effects, including aggravation of pain. Its peripheral pronociceptive effect has been associated with injury-induced expression of novel noradrenergic receptors, sprouting of sympathetic nerve fibers, and pronociceptive changes in the ionic channel properties of primary afferent nociceptors, while an interaction with the immune system may contribute in part to peripheral antinociception induced by norepinephrine. In the spinal cord, norepinephrine released from descending pathways suppresses pain by inhibitory action on alpha-2A-adrenoceptors on central terminals of primary afferent nociceptors (presynaptic inhibition), by direct alpha-2-adrenergic action on pain-relay neurons (postsynaptic inhibition), and by alpha-1-adrenoceptor-mediated activation of inhibitory interneurons. Additionally, alpha-2C-adrenoceptors on axon terminals of excitatory interneurons of the spinal dorsal horn possibly contribute to spinal control of pain. At supraspinal levels, the pain modulatory effect by norepinephrine and noradrenergic receptors has varied depending on many factors such as the supraspinal site, the type of the adrenoceptor, the duration of the pain and pathophysiological condition. While in baseline conditions the noradrenergic system may have little effect, sustained pain induces noradrenergic feedback inhibition of pain. Noradrenergic systems may also contribute to top-down control of pain, such as induced by a change in the behavioral state. Following injury or inflammation, the central as well as peripheral noradrenergic system is subject to various plastic changes that influence its antinociceptive efficacy.

Involvement of protein kinase C in 5-HT-evoked thermal hyperalgesia and spinal fos protein expression in the rat

The present study was designed to characterize nociceptive response induced by 5-hydroxytryptamine (5-HT) and to investigate effects of inhibition of protein kinase C (PKC) in the periphery on noxious stimulus-evoked activity of the secondary neurons in the spinal cord. Subcutaneous injection of 5-HT (50 microg) and alpha-methylserotonin (alpha-m-5-HT, 5-HT2A receptor agonist, 50 microg) into the unilateral hindpaw evoked significant decreases in paw withdrawal latency (PWL). The 5-HT-induced hyperalgesia was abolished by ketanserin (5-HT2A antagonist, 10 microg, intraplantarly or i.pl.), but not by WAY100635 (5-HT1A antagonist, 100 microg, i.pl.). 5-HT and alpha-m-5-HT also evoked numerous expressions of c-Fos-like immunoreactivity (c-fos-LI) in the ipsilateral dorsal horn (predominantly laminae I-II) of the lumbar spinal cord. However, treatment with 8-OH-DPAT (5-HT1A receptor agonist, 100 microg, i.pl.) elicited only moderate thermal hyperalgesia and very limited expression of spinal c-fos-LI. Intraplantar chelerythrine (2, 6 or 10 microg), a PKC inhibitor, dose-dependently attenuated the hyperalgesia evoked by alpha-m-5-HT. Chelerythrine (10 microg, i.pl.) also completely prevented the development of hyperalgesia evoked by 5-HT but not by 8-OH-DPAT. Furthermore, pretreatment with chelerythrine significantly inhibited the expressions of c-fos-LI evoked by alpha-m-5-HT in laminae I-VI and by 5-HT in laminae I-II. These results demonstrate that PKC activation was involved in the development of nociceptive responses elicited by 5-HT and activation of peripheral 5-HT2A, but not 5-HT1A, receptors. The study also provides evidence at a cellular level that inhibition of PKC in the periphery suppresses the 5-HT-evoked neuronal activity in the central nervous system.

Intrathecal grafting of porcine chromaffin cells reduces formalin-evoked c-Fos expression in the rat spinal cord

Chromaffin cells from the adrenal gland secrete a combination of neuroactive compounds including catecholamines, opioid peptides, and growth factors that have strong analgesic effects, especially when administered intrathecally. Preclinical studies of intrathecal implantation with xenogeneic bovine chromaffin cells in rats have provided conflicting data with regard to analgesic effects, and recent concern over risk of prion transmission has precluded their use in human clinical trials. We previously developed a new, safer source of adult adrenal chromaffin cells of porcine origin and demonstrated an in vivo antinociceptive effect in the formalin test, a rodent model of tonic pain. The goal of the present study was to confirm porcine chromaffin cell analgesic effects at the molecular level by evaluating neural activity as reflected by spinal cord c-Fos protein expression. To this end, the expression of c-Fos in response to intraplantar formalin injection was evaluated in animals following intrathecal grafting of 10(6) porcine or bovine chromaffin cells. For the two species, adrenal chromaffin cells significantly reduced the tonic phases of the formalin response. Similarly, c-Fos-like immunoreactive neurons were markedly reduced in the dorsal horns of animals that had received injections of xenogeneic chromaffin cells. This reduction was observed in both the superficial (I-II) and deep (V-VI) lamina of the dorsal horn. The present study demonstrates that both xenogeneic porcine and bovine chromaffin cells transplanted into the spinal subarachnoid space of the rat can suppress formalin-evoked c-Fos expression equally, in parallel with suppression of nociceptive behaviors in the tonic phase of the test. These findings confirm previous reports that adrenal chromaffin cells may produce antinociception by inhibiting activation of nociceptive neurons in the spinal dorsal horn. Taken together these results support the concept that porcine chromaffin cells may offer an alternative xenogeneic cell source for transplants delivering pain-reducing neuroactive substances.

Intrathecal xenogeneic chromaffin cell grafts reduce nociceptive behavior in a rodent tonic pain model

Adrenal medullary chromaffin cells synthetize and secrete a combination of pain-reducing neuroactive compounds including catecholamines and opioid peptides. Previous reports have shown that implantation of chromaffin cells into the spinal subarachnoid space can reduce both acute and chronic pain in several animal models. We recently demonstrated that human chromaffin cell grafts in the cerebrospinal fluid (CSF) could alleviate intractable cancer pain after failure of systemic opiates. However, wider application of this approach was limited by the limited availability of allogeneic donor material. Alternatively, chromaffin cells from xenogeneic sources such as bovine adrenal medulla were successful in the experimental treatment of pain, but recent concern over risk of prion transmission precluded use of bovine grafts in human clinical trials. The objective of the present study was to investigate the possibility of developing a new xenogeneic porcine source of therapeutic chromaffin cells because this strategy is currently considered the safest for transplantation in man. In the present study, we report the isolation and the characterization of primary porcine chromaffin cells (PCC) compared to bovine cells. We show, for the first time, that these cells grafted in the rat subarachnoid space can attenuate pain-related behaviors as assessed by the formalin test, a model of tonic pain. Moreover, in addition to behavioral studies, immunohistochemical analysis revealed robust survival of chromaffin cells 35 days after transplantation. Taken together, these results support the concept that porcine chromaffin cells may offer an alternative xenogeneic cell source for transplants delivering pain-reducing neuroactive substances.

Endogenous opiates and behavior: 2002

This paper is the twenty-fifth consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2002 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).