Gamma-aminobutyric acid concentrations in benign parotid tumours and unstimulated parotid saliva E JEZEWSKA 1,2 , A SCINSKA 1,2 , W KUKWA 1 , A SOBOLEWSKA 3 , D TURZYNSKA 3 , J SAMOCHOWIEC 4 , P BIENKOWSKI 5 1 Department of Otolaryngology, Czerniakowski Hospital, Warsaw Medical University, 2 Consultant Otolaryngologist Unit and Departments of 3 Neurochemistry and 5 Pharmacology, Institute of Psychiatry and Neurology, Warsaw, and 4 Department of Psychiatry, Pomeranian Medical Academy, Szczecin, Poland Abstract Objective: Apart from its role as an inhibitory neurotransmitter, γ-aminobutyric acid is also thought to regulate various stages of cell proliferation and differentiation in the brain and periphery. The present study aimed to assess the levels of γ-aminobutyric acid and its biochemical precursor glutamic acid (glutamate) in benign parotid tumours and in unstimulated parotid saliva. Method: Unstimulated parotid saliva was collected bilaterally, using the swab method, in 20 patients with unilateral pleomorphic adenoma or Warthin’s tumour. Samples of tumour and adjacent salivary tissue were collected during tumour resection. Results: Concentrations of γ-aminobutyric acid and glutamate, but not aspartate, were significantly higher in the tumour tissue than in the non-tumour tissue. There was no significant difference in salivary concentrations of γ- aminobutyric acid, glutamate or aspartate, comparing the involved and non-involved side. Conclusion: The present results provide preliminary evidence that γ-aminobutyric acid may be involved in the growth of benign parotid tumours. Key words: Parotid Neoplasms; Saliva; Gamma-Aminobutyric acid Introduction Gamma-aminobutyric acid (GABA) is a non-proteo- genic amino acid present in bacteria, plants and animals. 1 In mammalian cells, GABA is synthesised from glutamic acid (glutamate) by glutamic acid decar- boxylase and from polyamines with the aid of diamine oxidase. 1,2 Gamma-aminobutyric acid is a major inhibitory neurotransmitter in the adult mammalian brain, acting at either ionotropic (GABA A and GABA C ) or metabotropic (GABA B ) receptors. 1,3,4 Apart from its role as an inhibitory neurotransmitter, GABA is also thought to regulate different stages of brain neurogenesis, including proliferation, migration, differentiation and synaptic integration of newborn neurons. 4,5 Glutamic acid decarboxylase, diamine oxidase, GABA and GABA receptors can also be present in non-neuronal tissues, including heart, liver, gut, pan- creas, salivary glands, ovary and testis. 1,4,6 Although the exact role of GABA in peripheral tissues remains to be established, it is accepted that GABA and GABA receptors are involved in cell proliferation and differentiation. 1,4 Recently, it has been found that GABA negatively regulates proliferation of pluripotent stem cells in peripheral embryonic and adult tissues. 7,8 In line with the involvement of GABA in neuronal and non-neuronal cell proliferation, 4,5,7,8 it has been reported that GABA levels are significantly higher in malignant tissue of the thyroid, 9 colon 10,11 and mammary glands, 12 compared with normal tissue. Higher GABA levels have also been found in benign colonic adenomas, compared with healthy control tissue. 11 Tatsuta and colleagues 13,14 were the first group to suggest a functional link between GABA and oncogenesis, by showing that GABA and the clini- cally utilised GABA B agonist baclofen suppressed gastric carcinogenesis in the rat. More recently, it has been suggested that GABA acts as a near-universal signal which can inhibit the mitotic activity and migration of tumour cells. 6,8 When considering the possible clinical applications of GABA concentration measurement, it is worthy of note that elevated Accepted for publication 15 July 2010 First published online 17 December 2010 The Journal of Laryngology & Otology (2011), 125, 492–496. MAIN ARTICLE © JLO (1984) Limited, 2010 doi:10.1017/S0022215110002574