Abstract:
Background: Curcumin and piperine are major bioactive compounds of Curcuma longa and Piper nigrum, widely
consumed as spices and fock medicine. The combinational use of these plants is a common practice in Southeast
Asia. Synergism between curcumin and piperine has been found in several animal models but not in periodontal
disease and diabetes, and the antinociceptive interaction is still unknown. Hence, the present study aimed to assess
the interaction between curcumin and piperine in pain and its potential CNS side efect profle.
Methods: Formalin test and in vitro LPS-stimulated RAW 264.7 macrophage cells were used to assess the synergis tic interaction of curcumin and piperine in a mouse model of infammatory pain. Tail-fick and cold plate tests were
applied to determine the antinociceptive synergism between piperine and curcumin. The interaction was determined
by applying isobolographic analysis. The potential CNS-side efects of the curcumin and piperine combination were
also assessed using LABORAS automated home-cage behavioral analysis.
Results: Curcumin alone dose-dependently improved pain-like behaviors in the formalin, tail-fick, and cold plate
tests with the ED50 of 71.4, 34.4, and 31.9 mg/kg, respectively. Additionally, piperine exhibited efcacy in the formalin,
tail-fick, and cold plate tests with the ED50 of 18.4, 8.1, and 28.1 mg/kg, respectively. The combination of curcumin
and piperine (1:1 ED50 ratio) produced synergistic interaction in the formalin, tail-fick, and cold plate tests as assessed
signifcantly lower experimental ED50 values (5.9, 5.2, and 5.5 mg/kg) compared to theoretical ED50 values (44.9, 21.3,
and 30.0 mg/kg), isobologram analysis, and interaction index values of 0.13, 0.24 and 0.18, respectively. The synergis tic interaction of curcumin and piperine was further confrmed by the efcacy of the combination in LPS-stimulated
RAW 264.7 macrophage cells. Curcumin and piperine interacted synergistically, reducing proinfammatory mediators.
The combination also demonstrated better compatibility profles with neuronal cells. Furthermore, the curcumin piperine combination had no efects on mouse spontaneous locomotor behaviors in LABORAS automated home
cage monitoring.
Conclusion: Overall, the present study demonstrates strong antinociceptive synergism between curcumin and pip erine in mouse models with no potential CNS side efects, suggesting its possible use in clinical trials
