Specific Features of Analgesic Effect of Docosahexaenoic Acid in Rats with Neuropathic Pain Syndrome

Bioactive compounds for neuropathic pain: An update on preclinical studies and future perspectives

Among different types of chronic pain, neuropathic pain (NP), arising from damage to the nervous system, including peripheral fibers and central neurons, is notoriously difficult to treat and affects 7-10% of the general population. Currently available treatment options for NP are limited and opioid analgesics have severe side effects and can result in opioid use disorder. Recent studies have exhibited the role of dietary bioactive compounds in the mitigation of NP. Here, we assessed the effects of commonly consumed bioactive compounds (ginger, curcumin, omega-3 polyunsaturated fatty acids, epigallocatechin gallate, resveratrol, soy isoflavones, lycopene, and naringin) on NP and NP-related neuroinflammation. Cellular studies demonstrated that these bioactive compounds reduce inflammation via suppression of NF-κB and MAPK signaling pathways that regulate apoptosis/cell survival, antioxidant, and anti-inflammatory responses. Animal studies strongly suggest that these regularly consumed bioactive compounds have a pronounced anti-NP effect as shown by decreased mechanical allodynia, mechanical hyperalgesia, thermal hyperalgesia, and cold hyperalgesia. The proposed molecular mechanisms include (1) the enhancement of neuron survival, (2) the reduction of neuronal hyperexcitability by activation of antinociceptive cannabinoid 1 receptors and opioid receptors, (3) the suppression of sodium channel current, and (4) enhancing a potassium outward current in NP-affected animals, triggering a cascade of chemical changes within, and between neurons for pain relief. Human studies administered in this area have been limited. Future randomized controlled trials are warranted to confirm the findings of preclinical efficacies using bioactive compounds in patients with NP.

The search for translational pain outcomes to refine analgesic development: Where did we come from and where are we going?

Pain measures traditionally used in rodents record mere reflexes evoked by sensory stimuli; the results thus may not fully reflect the human pain phenotype. Alterations in physical and emotional functioning, pain-depressed behaviors and facial pain expressions were recently proposed as additional pain outcomes to provide a more accurate measure of clinical pain in rodents, and hence to potentially enhance analgesic drug development. We aimed to review how preclinical pain assessment has evolved since the development of the tail flick test in 1941, with a particular focus on a critical analysis of some nonstandard pain outcomes, and a consideration of how sex differences may affect the performance of these pain surrogates. We tracked original research articles in Medline for the following periods: 1973-1977, 1983-1987, 1993-1997, 2003-2007, and 2014-2018. We identified 606 research articles about alternative surrogate pain measures, 473 of which were published between 2014 and 2018. This indicates that preclinical pain assessment is moving toward the use of these measures, which may soon become standard procedures in preclinical pain laboratories.

Beneficial effects of fish oil enriched in omega-3 fatty acids on the development and maintenance of neuropathic pain

OBJECTIVE

The aim of this work was to assess the preventive effect of an eicosapentaenoic acid/docosahexaenoic acid-concentrate fish oil on neuropathic pain development and regenerative features of sciatic nerve in rats.

METHODS

In the present study, rats with chronic constriction injury (CCI) of the sciatic nerve and sham-operated ones received fish oil enriched in omega-3 fatty acids (0.36 or 0.72 g/kg per day, oral) or saline solution for 21 days, with thermal hyperalgesia and mechanical allodynia being assessed before and 3, 7, 14 and 21 days after injury.

KEY FINDINGS

Fish oil enriched in omega-3 fatty acids (0.72 g/kg) reversed thermal hyperalgesia and significantly reduced mechanical allodynia. In addition, ω-3 treatment (0.72 g/kg) promoted the recovery of the Sciatic Functional Index as well as restored axonal density and morphology, without the formation of neuroma in the injured sciatic nerves after 21 days.

CONCLUSION

We conclude that the fish oil enriched in omega-3 fatty acids administration relieves thermal hyperalgesia and mechanical allodynia effectively and also enhances the recovery process in rats with CCI of the sciatic nerve. These findings might contribute to new therapeutic approaches including omega-3 fatty acids in neuropathic pain treatment.