Baran Halina, Kronsteiner Carina, Kepplinger Berthold
Karl Landsteiner Research Institute for Neurochemistry, Neuropharmacology, Neurorehabilitation and Pain Treatment Mauer-Amstetten, Low Austria, Austria,
Karl Landsteiner Research Institute for Neurochemistry, Neuropharmacology, Neurorehabilitation and Pain Treatment Mauer-Amstetten, Low Austria, Austria.
Neurosignals. 2020 Mar 11;28(1):1-13. doi: 10.33594/000000217.
BACKGROUND/AIMS: Fluids of the human body such as serum, cerebrospinal fluid and saliva contain a wide variety of proteins. Because kynurenic acid (KYNA) has been detected in human saliva, we wondered if KYNA could be produced in saliva by KYNA-synthesising enzymes, namely the kynurenine aminotransferases KAT I, KAT II and KAT III.
Thirty samples of human saliva from control volunteers were investigated. KAT activity was measured in the presence of 1 mM pyruvate and 2 µM or 100 µM L-kynurenine and KYNA production was assessed by high-performance liquid chromatography.
Saliva dose- and time-dependently produced KYNA. KAT activity ranged between 900 and 1050 pmol/mg protein/h: 900 for KAT I, 950 for KAT III and 1050 for KAT II. KYNA was synthesised in saliva at a physiological concentration of 2 µM L-kynurenine and at a higher concentration of 100 µM. Investigation of the distributions of the enzymes in saliva revealed that KAT I, KAT II and KAT III activity in a centrifuge-obtained pellet ranged from ~100% to 120%; in the supernatant, the percentage was between 0% and 20%. We observed a nonsignificant tendency for lower KAT activity in women's saliva than in men's. KATs present in saliva were sensitive to the GABA-transaminase inhibitor γ-acetylenic GABA, with a concentration of 100 µM γ-acetylenic GABA significantly blocking the formation of KYNA (50% of control, p < 0.05). Furthermore, KATs in saliva were sensitive to anti-dementia drugs, such as D-cycloserine and cerebrolysin, in an in vitro study.
Our data revealed for the first time the presence of KAT I, KAT II and KAT III proteins in human saliva. KAT activity was found mostly in pelleted cells, suggesting their presence in salivary gland cells. KAT proteins in saliva are sensitive to drugs blocking KYNA formation. Our data indicate the presence of cells in saliva involved in the biochemical machinery of the kynurenine pathway. Their role in the digestive process remains to be clarified. We speculate that modulation of KYNA formation in the mouth by food and/or drugs might affect glutamate neurotransmission and cholinergic activity in the CNS and/or periphery and play a role under physiological as well as pathological conditions.
背景/目的：人体的体液如血清、脑脊液和唾液中含有多种蛋白质。由于在人类唾液中检测到了犬尿喹啉酸（KYNA），我们想知道KYNA是否可由犬尿喹啉酸合成酶，即犬尿氨酸转氨酶KAT I、KAT II和KAT III在唾液中产生。
对30份来自对照志愿者的人类唾液样本进行了研究。在存在1 mM丙酮酸和2 μM或100 μM L-犬尿氨酸的情况下测量KAT活性，并通过高效液相色谱法评估KYNA的产生。
唾液中KYNA的产生呈剂量和时间依赖性。KAT活性在900至1050 pmol/mg蛋白质/小时之间：KAT I为900，KAT III为950，KAT II为1050。在2 μM L-犬尿氨酸的生理浓度和100 μM的较高浓度下，唾液中均可合成KYNA。对唾液中这些酶分布的研究表明，离心获得的沉淀中KAT I、KAT II和KAT III的活性范围为~100%至120%；在上清液中，该百分比在0%至20%之间。我们观察到女性唾液中KAT活性低于男性，但差异无统计学意义。唾液中存在的KAT对GABA转氨酶抑制剂γ-乙炔基GABA敏感，100 μM的γ-乙炔基GABA浓度可显著阻断KYNA的形成（为对照的50%，p < 0.05）。此外，在体外研究中，唾液中的KAT对抗痴呆药物如D-环丝氨酸和脑蛋白水解物敏感。
我们的数据首次揭示了人类唾液中存在KAT I、KAT II和KAT III蛋白。KAT活性主要存在于沉淀细胞中，表明它们存在于唾液腺细胞中。唾液中的KAT蛋白对阻断KYNA形成的药物敏感。我们的数据表明唾液中存在参与犬尿氨酸途径生化机制的细胞。它们在消化过程中的作用仍有待阐明。我们推测食物和/或药物对口腔中KYNA形成的调节可能会影响中枢神经系统和/或外周的谷氨酸神经传递和胆碱能活性，并在生理和病理条件下起作用。
