Background & Aims

Neuropathic pain is primarily associated with nerve lesion, and characterized by microglial reactivity and central sensitization, pointing out the evident nerve-immune system interactions. P2X4 is an ion channel, which expression is strongly increased in reactive microglia in the ipsilateral dorsal horn of the spinal cord following injury. Their activation by ATP contributes to spinal inflammatory responses, like release of brain-derived neurotrophic factor (BDNF). Although this phenomenon is quite well described, it is not well known in which pain models P2X4 antagonism would lead to significant pain relief. In the present study, we used a novel, potent and selective P2X4 antagonist, ORM-43089, to study possible pain alleviation in three different rat models: chronic constriction injury (CCI), streptozotocin (STZ)-induced diabetic neuropathy and Complete Freund’s Adjuvant (CFA)-induced joint pain model.

Methods

Drug effects were assessed up to 3-4 days after once daily oral treatment in various pain models and readouts in Wistar rats. The last assessment was followed by collection of plasma and brain for the determination of compound concentrations.

CCI was induced by making four loose ligations with chromic gut around the sciatic nerve. Diabetic neuropathy was induced by i.p. injection of STZ (55 mg/kg). Increase in mechanical hypersensitivity in both models was assessed with von Frey monofilaments using the up & down method. Joint pain was induced by intra-articular ankle injection of CFA (50 µg), and pain in walking was used as an endpoint.

Efficacy data was analysed by the Kruskal-Wallis test followed by Dunn’s multiple comparison test. All efficacy studies were randomised and blinded, and principles from the Arrive guidelines were applied.

Results

In both CCI and STZ-induced diabetic neuropathy model mechanical hypersensitivity was robustly increased 2-3 weeks post-intervention allowing the drug testing within that time window. ORM-43089 was orally administered once daily at doses of 10 and 100 m/kg for 3-4 days. In CCI rats dose-dependent reduction in mechanical hypersensitivity was observed after acute and repeated administrations. The effect was enhanced after repeated dosing.
In STZ rats, the reduction in mechanical hypersensitivity was observed, but only after four days of dosing. In contrary, ORM-43089 treatment could not alleviate pain in walking in the CFA joint pain model. Naproxen 7.6 mg/kg (p.o.) on the other hand significantly improved limping of the paw.

Brain and plasma concentrations were well in line in all three studies; unbound concentration in the brain at the lower dose was reaching rat IC50, whereas the higher dose was resulting in five times higher concentrations

Conclusions

The results presented here support the involvement of central P2X4 receptors in various chronic pain conditions. It also suggests that P2X4 antagonism is an attractive approach to treat neuropathic but possibly not joint pain.

References

G. Burnstock, Nat. Rev. Drug Discovery 2008, 7, 575-590

Presenting Author

Johanna Kela

Poster Authors

Johanna Kela

MSc

Orion Pharma

Lead Author

E-mail

Lauri Louhivuori

Ph.D.

Orion Pharma

Lead Author

E-mail

Katja Kuokkanen

Ph.D.

Orion Pharma

Lead Author

E-mail

Janne Kaskinoro

M.Sc.

Orion Pharma

Lead Author

E-mail

Olli Törmäkangas

Ph.D.

Orion Pharma

Lead Author

E-mail

Josef Messinger

Ph.D.

Orion Pharma

Lead Author

E-mail

Carina Stenfors

Orion Corporation

Lead Author

E-mail

Aliaa Abdelrahman

Ph.D.

University of Bonn

Lead Author

E-mail

Ali El-Tayeb

University of Bonn

Lead Author

E-mail

Christa E. Müller

University of Bonn

Lead Author

E-mail

Topics

  • Treatment/Management: Pharmacology: Novel Targets