Effects of pyrroloquinoline quinone and imidazole pyrroloquinoline on biological activities and neural functions.

Pyrroloquinoline quinone (PQQ) is contained in fruits and vegetables and in human breast milk. It has been reported that PQQ has high reactivity and changes to an imidazole structure (imidazole pyrroloquinoline) by a reaction with an amino acid at a high ratio in nature. A comparative study was conducted to clarify physiological effects including neuroprotective effects, growth-promoting effect, antioxidative effects and a stimulatory effect on mitochondriogensis of PQQ and imidazole pyrroloquinoline (IPQ) using a human neuroblastoma cell line and a hepatocellular carcinoma cell line. We also compared the expression levels of human cytochrome c oxidase subunit IV isoform Ⅰ (COX4/1), which is an index of the amount of mitochondria in the cells that had been exposed to PQQ, PQQH2 and IPQ. The results of the comparison showed that IPQ had almost the same biological activities as those of PQQ except for anti-oxidative activity. It was also shown that PQQ and IPQ improve the memory learning ability of aged mice and that BioPQQ® improves brain function in the language field in humans.

Direct activation of GABAA receptors by substances in the organic acid fraction of Japanese sake.

We investigated the effect of substances present in Japanese sake on the response of ionotropic γ-aminobutyric acid (GABA)A receptors expressed in Xenopus oocytes. Sake was fractionated by ion-exchange chromatography. The fraction containing organic acids (OA fraction) showed agonist activities on the GABAA receptor. OA fractions from sake were analyzed by capillary electrophoresis time-of-flight mass spectrometry (CE-TOFMS). Of the 64 compounds identified, 13 compounds showed GABAA receptor agonist activities. Especially, l-lactic acid showed high agonist activity and its EC50 value was 37µM. Intraperitoneal injections of l-lactic acid, gluconic acid, and pyruvic acid (10, 10, and 5mg/kg BW, respectively), which showed agonistic activity on the GABAA receptor, led to significant anxiolytic effects during an elevated plus-maze test in mice.

Comparison of the neurotoxicities between volatile organic compounds and fragrant organic compounds on human neuroblastoma SK-N-SH cells and primary cultured rat neurons.

These are many volatile organic compounds (VOCs) that are synthesized, produced from petroleum or derived from natural compounds, mostly plants. Fragrant and volatile organic compounds from plants have been used as food additives, medicines and aromatherapy. Several clinical and pathological studies have shown that chronic abuse of VOCs, mainly toluene, causes several neuropsychiatric disorders. Little is known about the mechanisms of neurotoxicity of the solvents. n-Octanal, nonanal, and 2-ethyl-1-hexanol, which are used catalyzers or intermediates of chemical reactions, are released into the environment. Essential oils have the functions of self-defense, sterilization, and antibiosis in plants. When volatile organic compounds enter the body, there is the possibility that they will pass through the blood-brain barrier (BBB) and affect the central nervous system (CNS). However, the direct effects of volatile organic compounds on neural function and their toxicities are still unclear. We compared the toxicities of n-octanal, nonanal and 2-ethyl-1-hexanol with those of five naturally derived fragrant organic compounds (FOCs), linalool, cis-3-hexen-1-ol, isoamyl alcohol, n-propyl alcohol and n-phenethyl alcohol. MTT assay of human neuroblastoma SK-N-SH cells showed that the IC50 values of linalool, cis-3-hexen-1-ol, isoamyl alcohol, n-propyl alcohol and phenethyl alcohol were 1.33, 2.3, >5, >5, and 2.39 mM, respectively, and the IC50 values of toluene, n-octanal, nonanal and 2-ethyl-1-hexanol were 850, 37.2, 8.31 and 15.1 µM, respectively. FOCs showed lower toxicities than those of VOCs. These results indicate that FOCs are safer than other compounds.

Differential modulation of NR1-NR2A and NR1-NR2B subtypes of NMDA receptor by PDZ domain-containing proteins.

The PSD-95/Dlg/ZO-1 (PDZ) domain-containing proteins MALS and PSD-95 localize to post-synaptic densities and bind the COOH-termini of NR2 subunits of the NMDA receptor. The effects of MALS-2 and PSD-95 on the channel activity of NMDA receptors were compared using the Xenopus oocyte expression system. Both MALS-2 and PSD-95 increased the current response of the NR1-NR2B receptor to l-glutamate. In contrast, the current response of the NR1-NR2A receptor was increased by PSD-95 but not by MALS-2. MALS-2 had no effect either on the potentiation of NR1-NR2A or NR1-NR2B channel activity by protein kinase C, or on Src-mediated potentiation of NR1-NR2A activity, whereas PSD-95 almost completely inhibited the effects of these protein kinases. Construction of chimeras of MALS-2 and PSD-95 revealed that the first two PDZ domains and two NH(2)-terminal cysteine residues are essential for the inhibitory effects of PSD-95 on protein kinase C-mediated potentiation of NR1-NR2A and NR1-NR2B channel activity, respectively. The second of the three PDZ domains of PSD-95 was required for its inhibition of Src-mediated potentiation of NR1-NR2A activity. These results indicate that the NR1-NR2A and NR1-NR2B receptors are modulated differentially by MALS-2 and PSD-95, and that similar regulatory effects of PSD-95 on these receptors are achieved by distinct mechanisms.

PSD-95 eliminates Src-induced potentiation of NR1/NR2A-subtype NMDA receptor channels and reduces high-affinity zinc inhibition.

The channel activity of NMDA receptors is regulated by phosphorylation by protein kinases and by interaction with other proteins. Recombinant NR1/NR2A subtype NMDA receptor channels are potentiated by the protein tyrosine kinase Src, an effect which is mediated by a reduction in the high-affinity, voltage-independent Zn(2+) inhibition. However, it has been reported that Src-induced potentiation of NMDA receptor currents in hippocampus neurons is not mediated by a reduction in Zn(2+) inhibition. The post-synaptic density protein PSD-95 interacts with the C-terminus of NR2 subunits of the NMDA receptor. Here we demonstrate that PSD-95 eliminates the Src-induced potentiation of NR1/NR2A channels expressed in oocytes and reduces the sensitivity of the channels to Zn(2+). Our results reveal that the absence of Src-induced potentiation of PSD-95-coupled NR1/NR2A channels is not to due to the reduced sensitivity of these channels to Zn(2+). These results indicate that PSD-95 functionally modulates NR1/NR2A channels and explain why Src-induced potentiation of NMDA receptor currents in hippocampus neurons is not mediated by a reduction in Zn(2+) inhibition.