Copper complexes of non-steroidal antiinflammatory agents: analgesic activity and possible opioid receptor activation

Cu(II)2(acetylsalicylate)4, Cu(II)(anthranilate)2, Cu(II)2[1-(p-chlorobenzoyl)-5-methoxy-2-methyl-3-indolylacetate]4, Cu(II)(3,5-diisopropylsalicylate)2, Cu(II)(salicylate)2, Cu(II)2(2-[3-(trifluoromethyl)-phenyl]aminonicotinate)4, Cu(II)(L-alaninate)2, Cu(II)(L-cystinate)2, and Cu(II)(glycinate)2 were generally found to be more effective analgesics than their parent ligands, Cu(II)(chloride)2, and Cu(II)2(acetate)4 in the Writhing Mouse and Adjuvant Arthritic Rat pain models following subcutaneous and oral administration. Comparison of the time course of analgesia for salicylic acid and Cu(II)(salicylate)2 in the adjuvant arthritis pain model revealed that this complex had more sustained activity in addition to being more potent than salicylic acid. Cu(II)2(indomethacin)4 was also found to be as effective as morphine in both pain models. These data and pertinent literature are discussed in support of the hypothesis that copper complexes activate copper-dependent opioid receptors.