title: Kynurenic acid and zaprinast induce analgesia by modulating HCN channels through GPR35 activation.
abstract: Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels have a key role in the control of cellular excitability. HCN2, a subgroup of the HCN family channels, are heavily expressed in small dorsal root ganglia (DRG) neurons and their activation seems to be important in the determination of pain intensity. Intracellular elevation of cAMP levels activates HCN-mediated current (Ih) and small DRG neurons excitability. GPR35, a Gi/o coupled receptor, is highly expressed in small DRG neurons, and we hypothesized that its activation, mediated by endogenous or exogenous ligands, could lead to pain control trough a reduction of Ih current. Patch clamp recordings were carried out in primary cultures of rat DRG neurons and the effects of GPR35 activation on Ih current and neuronal excitability were studied in control conditions and after adenylate cyclase activation with either forskolin or prostaglandin E2 (PGE2). We found that both kynurenic acid (KYNA) and zaprinast, the endogenous and synthetic GPR35 agonist respectively, were able to antagonize the forskolin-induced depolarization of resting membrane potential by reducing Ih-mediated depolarization. Similar results were obtained when PGE2 was used to activate adenylate cyclase and to increase Ih current and the overall neuronal excitability. Finally, we tested the analgesic effect of both GPR35 agonists in an in vivo model of PGE2-induced thermal hyperalgesia. In accord with the hypothesis, both KYNA and zaprinast showed a dose dependent analgesic effect. In conclusion, GPR35 activation leads to a reduced excitability of small DRG neurons in vitro and causes a dose-dependent analgesia in vivo. GPR35 agonists, by reducing adenylate cyclase activity and inhibiting Ih in DRG neurons may represent a promising new group of analgesic drugs.
authors.affiliation: Department of Neurosciences, Psychology, Drug Research and Child Health, University of Florence, Viale Pieraccini 6, 50139 Florence, Italy. Electronic address: francesco.resta@unifi.it.
authors.forename: Francesco
authors.initials: F
authors.lastname: Resta
authors.affiliation: Department of Neurosciences, Psychology, Drug Research and Child Health, University of Florence, Viale Pieraccini 6, 50139 Florence, Italy; Azienda Ospedaliero-Universitaria Careggi, Toxicology Unit, Largo Brambilla 1, 50139, Florence, Italy. Electronic address: alessio.masi@unifi.it.
authors.forename: Alessio
authors.initials: A
authors.lastname: Masi
authors.affiliation: Department of Neurosciences, Psychology, Drug Research and Child Health, University of Florence, Viale Pieraccini 6, 50139 Florence, Italy. Electronic address: maria.sili@unifi.it.
authors.forename: Maria
authors.initials: M
authors.lastname: Sili
authors.affiliation: Department of Neurosciences, Psychology, Drug Research and Child Health, University of Florence, Viale Pieraccini 6, 50139 Florence, Italy. Electronic address: annunziatina.laurino@unifi.it.
authors.forename: Annunziatina
authors.initials: A
authors.lastname: Laurino
authors.affiliation: Department of Neurosciences, Psychology, Drug Research and Child Health, University of Florence, Viale Pieraccini 6, 50139 Florence, Italy. Electronic address: flavio.moroni@unifi.it.
authors.forename: Flavio
authors.initials: F
authors.lastname: Moroni
authors.affiliation: Department of Neurosciences, Psychology, Drug Research and Child Health, University of Florence, Viale Pieraccini 6, 50139 Florence, Italy; Azienda Ospedaliero-Universitaria Careggi, Toxicology Unit, Largo Brambilla 1, 50139, Florence, Italy. Electronic address: guido.mannaioni@unifi.it.
authors.forename: Guido
authors.initials: G
authors.lastname: Mannaioni
mesh_terms: D000698:Analgesia / Q000379:methods*; D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005727:Ganglia, Spinal / Q000187:drug effects / Q000378:metabolism; D006930:Hyperalgesia / Q000188:drug therapy / Q000378:metabolism; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels / Q000819:agonists / Q000502:physiology*; D007736:Kynurenic Acid / Q000494:pharmacology / Q000627:therapeutic use*; D011688:Purinones / Q000494:pharmacology / Q000627:therapeutic use*; D051381:Rats; D017208:Rats, Wistar; D043562:Receptors, G-Protein-Coupled / Q000819:agonists* / Q000378:metabolism*
chemical_list: C513985:GPR35 protein, rat; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D011688:Purinones; D043562:Receptors, G-Protein-Coupled; C011145:zaprinast; D007736:Kynurenic Acid
keywords: 123983); 2745687); 3845); 5722); CID 2745687 (Pubchem CID; DRG; GPR35; HCN; Kynurenic acid; Kynurenic acid (Pubchem CID; Pain; ZD7288 (Pubchem CID; Zaprinast; Zaprinast (Pubchem CID