Background & Aims

Chronic neuropathic pain affects up to 10% of the general population, and shows higher prevalence in women than men. Importantly, most existing treatments provide unsatisfactory relief to these patients.

The intrathecal administration of the neuropeptide galanin (Gal) exerts significant antiallodynic effects, acting through the GalR1 receptor. In contrast, systemic administration of Gal has been poorly exercised due to the general assumption of insufficient blood-brain barrier (BBB) ​​crossing plus sensitivity to circulating endopeptidases. A novel BBB-penetrating peptide (CVG) fusion with the active fragment of Gal (Gal(1-16)), named Galancy (CVG/Gal(1-16)) was developed to increase the central nervous system (CNS) bioavailability of galanin and its biological effect.

The aim of this study is to demonstrate whether systemic administration of Galancy will result in anti-allodynic effects, compared to the administration of Gal(1-16) alone. Brain homing of the compound and sexual dimorphism are included in the analysis.

Methods

In male and female, 8 weeks old Sprague Dawley rats, neuropathic pain was induced by spared nerve injury (SNI) of the right sciatic nerve. A week after injury, rats received two intravenous doses (75µM peak blood concentration, each dose) of either Galancy, Gal(1-16), CVG, or vehicle, at 0 and 3 h after initiation of pharmacological experiments. Pain-like behavioral analysis was conducted by means of the von Frey test (mechanical allodynia), the Choi test (cold allodynia) and guarding pain score (ongoing pain), 1 day before injury, days 0 and 7 after injury, and 30 min, 1, 2, 4, 6 and 12 h, and 1, 3 and 5 days after initiation of treatment with each compound. Rats that did not develop mechanical allodynia 7 days after injury were not included in the study. Finally, an experiment using a T7 phage displaying the BBP-g was performed to establish brain homing of the compound.

Results

Compared to vehicle, Galancy significantly reduced mechanical allodynia for at least 24 h in both sexes. Interestingly, Gal(1-16)-treated male or female rats also exhibited reduced mechanical allodynia when compared to vehicle-treated rats, but limited to 2-6 h after administration. CVG alone did not revert signs of mechanical allodynia. Area under the curve analysis confirmed the greater biological effect of Galancy against CVG (male: 141.1±20vs 79.4±13; P=0.0452; female:138.6±16.43 vs76.95±14.86; P=0.02) or vehicle (male:141.1±20 vs 65.01±10.28;P=0.007; female: 138.6±16.43 vs 60.74±9.211; P=0.002). In addition, Galancy resulted in reduced ongoing pain, particularly at 2 or 4 h after administration, in males and females, respectively. Conversely, no significant effects were detected for any compound and between sexes on cold allodynia. Finally, homing analysis revealed considerable presence of Galancy in various areas of the CNS, compared to animals receiving Gal(1-16) alone.

Conclusions

Our study reveals a number of relevant findings:
The BBB-penetrating peptide conjugate Galancy exerts a 24 h antiallodynic effect when administered systemically in rats with neuropathic pain. These effects appear not to be affected by sex differences.

Unexpectedly, we show that the biologically active fragment of Gal, Gal(1-16), is also capable of inducing significant anti-allodynic effects, although shorter-lasting (up to 6 h) than observed with Galancy.

Altogether, these results suggest a potential therapeutic use of fusing a BBB-penetrating peptides with a neuroactive agent for the relief of chronic pain.

References

  • Ghazisaeidi S et al, Neuropathic Pain: Mechanisms, Sex Differences, and Potential Therapies for a Global Problem. Annu Rev PharmacolToxicol. 2023 Jan 20; 63:565-583.
  • Liu, H.X., et al., Receptor subtype-specific pronociceptive and analgesic actions of galanin in the spinal cord: selective actions via GalR1 and GalR2 receptors. Proc Natl Acad Sci U S A, 2001. 98(17): p. 9960-4.
  • Wiesenfeld-Hallin, Z., et al., The effect of intrathecal galanin on the flexor reflex in rat: increased depression after sciatic nerve section. Neurosci Lett, 1989. 105(1-2): p. 149-154.
  • Pardridge, W.M., Blood-brain barrier delivery. Drug Discov Today, 2007. 12(1-2): p. 54-61.
  • Weiss, N., et al., The blood-brain barrier in brain homeostasis and neurological diseases. Biochem Biophys Acta, 2009. 1788(4): p. 842-57.

Presenting Author

Bernardo Miguel

Poster Authors

Bernardo Miguel

Dr. med.

Instituto de Investigaciones en Medicina Traslacional (IIMT) CONICET-Universidad Austral, Facultad de Ciencias Biomédicas, Universidad Austral, Pilar, Buenos Aires, Argentina

Lead Author

Maarja Haugas PhD

Laboratory of Precision and Nanomedicine, Institute of Biomedicine and Translational Medicine, University of Tartu, Tartu, Estonia.

Lead Author

Marcelo Villar

Instituto de Investigaciones en Medicina Traslacional (IIMT) CONICET-Universidad Austral, Facultad de Ciencias Biomédicas, Universidad Austral, Pilar, Buenos Aires, Argentina

Lead Author

Tomas Hökfelt PhD

Professor

Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden

Lead Author

Tambet Teesalu PhD

Professor

Laboratory of Precision and Nanomedicine, Institute of Biomedicine and Translational Medicine, University of Tartu, Tartu, Estonia

Lead Author

Pablo Brumovsky

Instituto de Investigaciones en Medicina Traslacional (IIMT) CONICET-Universidad Austral, Facultad de Ciencias Biomédicas, Universidad Austral, Pilar, Buenos Aires, Argentina

Lead Author

Topics

  • Treatment/Management: Pharmacology: Novel Targets