title: Altered serum levels of kynurenine metabolites in patients affected by cluster headache.
abstract: BACKGROUND
  The reported efficacy of memantine in the treatment of patients with cluster headache (CH) suggests that NMDA receptors are involved in mechanisms of nociceptive sensitization within the trigeminal system associated with CH. NMDA receptors are activated or inhibited by neuroactive compounds generated by tryptophan metabolism through the kynurenine pathway. In the accompanying manuscript, we have found that serum levels of all kynurenine metabolites are altered in patients with chronic migraine. Here, we have extended the study to patients affected by episodic or chronic CH as compared to healthy controls.
  
  
  METHODS
  We assessed serum levels of kynurenine (KYN), kynurenic Acid (KYNA), anthranilic acid (ANA), 3-hydroxy-anthranilic acid (3-HANA), 3-hydroxykynurenine (3-HK), xanthurenic acid (XA), quinolinic acid (QUINA), tryptophan (Trp) and 5-hydroxyindolacetic acid (5-HIAA) by means of a liquid chromatography/tandem mass spectrometry (LC/MS-MS) method in 21 patients affected by CH (15 with episodic and 6 with chronic CH), and 35 age-matched healthy subjects. Patients with psychiatric co-morbidities, systemic inflammatory, endocrine or neurological disorders, and mental retardation were excluded.
  
  
  RESULTS
  LC/MS-MS analysis of kynurenine metabolites showed significant reductions in the levels of KYN (-36 %), KYNA (-34 %), 3-HK (-51 %), 3-HANA (-54 %), XA (-25 %), 5-HIAA (-39 %) and QUINA (-43 %) in the serum of the overall population of patients affected by CH, as compared to healthy controls. Serum levels of Trp and ANA were instead significantly increased in CH patients (+18 % and +54 %, respectively). There was no difference in levels of any metabolite between patients affected by episodic and chronic CH, with the exception of KYN levels, which were higher in patients with chronic CH.
  
  
  CONCLUSIONS
  The reduced levels of KYNA (an NMDA receptor antagonist) support the hypothesis that NMDA receptors are overactive in CH. A similar reduction in KYNA levels was shown in the accompanying manuscript in patients affected by chronic migraine. The reduced levels of XA, a putative analgesic compound, may contribute to explain the severity of pain attacks in CH. These data, associated with the data reported in the accompanying manuscript, supports a role for the kynurenine pathway in the pathophysiology of chronic headache disorders.
authors.affiliation: Department of Psychiatry, Harvard Medical School, Boston, MA, USA. martina.curto@uniroma1.it.|Department of Molecular Medicine, Sant'Andrea Medical Center, Sapienza University of Rome, Via di Grottarossa 1035-1039, Rome, 00189, Italy. martina.curto@uniroma1.it.|Regional referral headache center, Sant'Andrea Hospital, Rome, Italy. martina.curto@uniroma1.it.
authors.forename: Martina
authors.initials: M
authors.lastname: Curto
authors.affiliation: Advanced Molecular Diagnostics, IDI-IRCCS, Rome, Italy.
authors.forename: Luana
authors.initials: L
authors.lastname: Lionetto
authors.affiliation: Department of Molecular Medicine, Sant'Andrea Medical Center, Sapienza University of Rome, Via di Grottarossa 1035-1039, Rome, 00189, Italy.|Advanced Molecular Diagnostics, IDI-IRCCS, Rome, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Negro
authors.affiliation: Advanced Molecular Diagnostics, IDI-IRCCS, Rome, Italy.
authors.forename: Matilde
authors.initials: M
authors.lastname: Capi
authors.affiliation: Department of Molecular Medicine, Sant'Andrea Medical Center, Sapienza University of Rome, Via di Grottarossa 1035-1039, Rome, 00189, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Perugino
authors.affiliation: IRCCS Neuromed, Pozzilli, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Fazio
authors.affiliation: Headache Center and Geriatrics Clinic, Department of Medicine and Science of Aging, "G. D'Annunzio" University, Chieti, Italy.
authors.forename: Maria Adele
authors.initials: MA
authors.lastname: Giamberardino
authors.affiliation: Advanced Molecular Diagnostics, IDI-IRCCS, Rome, Italy.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Simmaco
authors.affiliation: IRCCS Neuromed, Pozzilli, Italy.|Department of Physiology and Pharmacology, Sapienza University of Rome, Rome, Italy.
authors.forename: Ferdinando
authors.initials: F
authors.lastname: Nicoletti
authors.affiliation: Department of Molecular Medicine, Sant'Andrea Medical Center, Sapienza University of Rome, Via di Grottarossa 1035-1039, Rome, 00189, Italy.|Regional referral headache center, Sant'Andrea Hospital, Rome, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Martelletti
mesh_terms: D000328:Adult; D003027:Cluster Headache / Q000097:blood / Q000378:metabolism*; D005260:Female; D006801:Humans; D006897:Hydroxyindoleacetic Acid / Q000097:blood; D007736:Kynurenic Acid / Q000097:blood; D007737:Kynurenine / Q000031:analogs & derivatives / Q000097:blood / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D017378:Quinolinic Acid / Q000097:blood; D014364:Tryptophan / Q000097:blood; D014977:Xanthurenates / Q000097:blood; D062367:ortho-Aminobenzoates / Q000097:blood
chemical_list: D014977:Xanthurenates; D062367:ortho-Aminobenzoates; C031385:anthranilic acid; C005045:3-hydroxykynurenine; D007737:Kynurenine; D006897:Hydroxyindoleacetic Acid; C028330:xanthurenic acid; D014364:Tryptophan; D017378:Quinolinic Acid; D007736:Kynurenic Acid
keywords: Cluster headache; Glutamate; Kynurenine; NMDA receptors; Pain