Antinociceptive and anti-inflammatory properties of an adenosine kinase inhibitor and an adenosine deaminase inhibitor

Abstract

Spinal administration of an adenosine kinase inhibitor, alone or in combination with an adenosine deaminase inhibitor, produces antinociception in inflammatory pain tests. In the present study, we examined the antinociceptive and anti-inflammatory effects produced by the peripheral (intraplantar) administration of 5′-amino-5′-deoxyadenosine (an adenosine kinase inhibitor), 2′-deoxycoformycin (an adenosine deaminase inhibitor), and combinations of both agents in the carrageenan-induced thermal hyperalgesia and paw oedema model in the rat. When injected in the ipsilateral paw immediately prior to carrageenan injection, both agents produced antinociception only at the highest dose (1 μmol), whereas a reduction in paw swelling was evident at a lower dose (300 nmol). Significant augmentation in both the antinociceptive and anti-inflammatory effects was seen when 5′-amino-5′-deoxyadenosine and 2′-deoxycoformycin were co-administered in equimolar doses at all dose levels. Both effects were mediated via activation of adenosine receptors, as indicated by blockade by an adenosine receptor antagonist. When administered into the contralateral paw, 1 μmol 5′-amino-5′-deoxyadenosine+1 μmol 2′-deoxycoformycin produced prominent antinociception, indicating a systemic drug activity. There was only a modest reduction in paw oedema in the carrageenan-injected (ipsilateral) paw, suggesting that much of this activity was locally mediated. Reversal of systemic effects on thermal thresholds by an intrathecal adenosine receptor antagonist implicates a spinal site of action in this instance. An ipsilateral administration of 1 μmol 5′-amino-5′-deoxyadenosine, but not 1 μmol 2′-deoxycoformycin, reduced carrageenan-induced c-Fos expression in the spinal dorsal horn, and this was further reduced by the peripheral co-injection of the two agents. These results provide evidence for a predominantly spinal antinociceptive effect and a predominantly peripheral anti-inflammatory effect produced by inhibitors of adenosine kinase and adenosine deaminase.