Acute Immunomodulatory Effects of Fentanyl and its Three New Analogues in Swiss Albino Mice

Abstract

Fentanyl is a potent synthetic opioid analgesic. However, due to its several limitations, new analogues are being synthesised for better pain management. We have earlier reported the synthesis and bio-efficacy of fentanyl and its eight new analogues (1-8) in mice. Among eight analogues tested, N-(1-(2-phenoxyethyl)-4-piperidinyl)propionanilide (2), N-isopropyl-3-(4-(N-phenylpropionamido)piperidin-1-yl)propanamide (5), and N-t-butyl-3-(4-(N-phenylpropionamido)piperidin-1-yl)propanamide (6) were found to be more effective and less toxic compared to fentanyl. Therapeutic efficacy of fentanyl and its analogues are known to be compromised due to many adverse effects, including alterations in the immune system. Therefore, the present study was undertaken to assess the acute effect of fentanyl and its three analogues (2, 5, and 6) on plasma levels of different pro-inflammatory cytokines such as interleukin-1β (IL-1β), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α), and anti-inflammatory cytokines such as interleukin-10 (IL-10) at different time points. Mice were intraperitoneally treated with 0.50 LD50 of the compounds and cytokines were measured 1 h, 2 h, 4 h, and 24 h post-exposure. Compared to control, none of the treatments produced any change in TNF-α and IL-1β levels. However, IL-6 levels were significantly elevated between 1 h to 2 h post-exposure in fentanyl and analogue 2 treated groups. Further, IL-10 levels were found to be significantly increased in fentanyl, analogue 2, and 6 treated groups at 1 h and 2 h post-exposure. Pre-treatment of naltrexone (opioid receptor antagonist) blocked the effects of fentanyl, confirming that its effects were opioid receptor- dependent. However, effect of naltrexone on analogue 2 and 6 was not conclusively evidenced, indicating that immunomodulatory changes caused by the analogues could have some additional implications as well. The present study reveals undesirable effects of fentanyl and its new analogues on cytokines homeostasis, thereby limiting their use in pain management.