Autophagy: An Emerging Target for Developing Effective Analgesics

Abstract

Inadequate treatment of acute and chronic pain causes depression, anxiety, sleep disturbances, and increased mortality. Abuse and overdose of opioids and the side effects associated with chronic use of NSAID illustrate the need for development of safer and effective pain medication. Working toward this end, an in silico tool based on an emergent intelligence analytical platform that examines interactions between protein networks was used to identify molecular mechanisms involved in regulating the body's response to painful stimuli and drug treatments. Examining interactions between protein networks associated with the expression of over 20 different pain types suggests that the regulation of autophagy plays a central role in modulation of pain symptoms (see Materials and Methods). Using the topology of this regulatory scheme as an in silico screening tool, we identified that combinations of functions targeted by cannabidiol, myo-inositol, and fish oils with varying ratios of eicosapentaenoic and docosahexaenoic acids are projected to produce superior analgesia. For validating this prediction, we administered combinations of cannabidiol, myo-inositol, and fish oils to rats that received formalin injections in hind paws, prior to substance administration, and showed that analgesic effects produced by these combinations were comparable or superior to known NSAID analgesics, which suggests that these combinations have potential in treatment of pain.

Figure 1

Protein interaction networks of biological processes regulated in pain perceptions. Edges show physical interactions between proteins. Biological processes overlapping with this network fragment regulating pain show that autophagy-related proteins play an essential role and they interact with pain-related pathways such as opioid, cytokine, DNA metabolism, and steroid signaling.

Figure 2

Protein interaction networks of pain perception and 31,000 pharmacological active substances. Overlapping studies of 15 proteins identified (Figure 1) with protein networks of 32,000 pharmacologically active molecules identified that endocannabinoids, opioids, and dopamine interact with proteins involved in autophagy and PI3K serves a pivotal role in regulating pain by these molecules.

Figure 3

Effect of formalin on inducing pain in rat models. Total events, licking plus flinches, were counted every three minutes, and means ± SE of six different experiments were used to draw the graph.

Figure 4

Effect of Anacin, Paracetamol, and Ibuprofen (IBU) on formalin-induced phase 2 pain in rats. All the drug doses are HED. Anacin 800 is a combination of aspirin 800 mg and caffeine 65 mg, Anacin 500 has only 500 mg of aspirin with 65 mg caffeine. Para1000: Paracetamol 1000 mg, Para 500: Paracetamol 500 mg, IBU-400: Ibuprofen 400 mg, and IBU-200: Ibuprofen 200 mg.

Figure 5

Effect of omega-3 (krill oil), CBD, and myo-inositol on formalin-induced pain in rats. All the doses are human equivalent dose. Krill 3200: krill oil 3200 mg, CBD50: CBD 50 mg, and In500: myo-inositol 500 mg.

Figure 6

Effect of different doses of omega-3 (krill oil), CBD, and myo-inositol on formalin-induced phase 2 pain in rats. The doses are human equivalent dose (HED) and ranged from 100 to 3200 mg for krill oil, 3.125 to 50 mg for CBD, and 31.25 to 500 mg for myo-inositol.

Figure 7

Effect of combinations of cannabinoids and autophagy inducers on formalin-induced pain in rats. The doses are human equivalent dose (HED). 7a, KC: krill oil 800 mg + CBD 12.5 mg; 7b, KI: krill oil 400 mg + inositol 250 mg; 7c, CI: CBD 6.25 mg + inositol 125 or 250 mg; 7d, KC: krill oil 800 mg + caffeine 65 mg; 7e, CBD 3.125 mg + caffeine 65 mg.