Insulin-releasing effect of quinaldic acid and its relatives on isolated Langerhans islets

Electrochemical γ-Selective Deuteration of Pyridines

Herein, we first report a γ-selective deuteration reaction of pyridines via H/D exchange without the need for preinstalled directing groups and transformable functional groups. The electrochemical process offers an attractive approach to producing γ-deuterated pyridines under gentle conditions. The broad substrate scope, excellent deuterium incorporation, and remarkable selectivity of the electrochemical method make it applicable for the late-stage modification of pharmaceutical molecules.

Quinaldic acid in synovial fluid of patients with rheumatoid arthritis and osteoarthritis and its effect on synoviocytes in vitro

BACKGROUND

Previously, we have demonstrated that kynurenic acid (KYNA), an endogenous metabolite of tryptophan formed along kynurenine pathway, is present in synovial fluid of rheumatoid arthritis (RA) and osteoarthritis (OA) patients. In this study, the goal was to investigate the presence of quinaldic acid (QUDA), a putative metabolite of KYNA, in synovial fluid of RA and OA patients.

METHODS

The effect of QUDA on proliferation and motility of synovial fibroblasts and its interaction with KYNA were determined in vitro. The study was conducted on synovial fluid obtained from 38 patients with RA and 15 patients with OA. QUDA was identified and quantified using the gas chromatography-mass spectrometry (GC-MS) method. In vitro experiments were conducted on rabbit synoviocyte cell line HIG-82.

RESULTS

Presence of QUDA was detected in all 53 samples of synovial fluid. The concentration of QUDA in synovial fluid obtained from patients with RA was 28.6 ± 14.9 pmol/ml, which was lower in comparison with OA 42.3 ± 10.0 pmol/ml. QUDA content positively correlated with the number of tender joints and negatively with the total cell counts determined in synovial fluid of RA patients. It did not correlate with KYNA content. QUDA reduced both proliferation and motility of synoviocytes in a dose-dependent manner. The enhancement of antiproliferative action of QUDA by KYNA was evidenced.

CONCLUSIONS

Data show a local deficit of QUDA in RA patients and suggest its potential role as an endogenous substance controlling synoviocyte viability.

Quinaldic acid inhibits proliferation of colon cancer ht-29 cells in vitro: effects on signaling pathways

Quinaldic acid is presumed to be a derivative of kynurenic acid, a tryptophan metabolite with proven antiproliferative activity towards cancer cells in vitro. The aim of present study was to evaluate the activity of quinaldic acid in colon cancer cells. The antiproliferative potential of quinaldic acid was assessed in HT-29, LS180 and Caco-2 cells. Suppression of metabolic activity (IC50 of 0.5mM for HT-29 and LS180 cells, 0.9mM for Caco-2 cells) and DNA synthesis (IC50 of 2.7, 4.3, 2mM for HT-29, LS180 and Caco-2 cells, respectively) were observed in all tested cell lines. It is noteworthy that quinaldic acid in antiproliferative concentrations was non-toxic to normal colon epithelium CCD 841 CoTr cells. Concomitantly, alterations in several signaling pathways in HT-29 cells were observed. Quinaldic acid led to changes in the phosphorylation level of extracellular-signal-regulated kinase (ERK) 1/2, p38, cAMP response element-binding protein (CREB) and Akt (protein kinase B) kinases. Moreover, changes in the CREB transcription factor were also found at the gene expression level. Antiproliferative activity and signaling pathways modulatory potential of quinaldic acid in colon cancer cells in vitro has been stated.

Purification, characterization and identification of rat liver mitochondrial kynurenine aminotransferase with alpha-aminoadipate aminotransferase

Kynurenine aminotransferase (L-kynurenine:2-oxoglutarate aminotransferase (cyclizing), EC 2.6.1.7) was purified 378-fold from rat liver mitochondria by digitonin solubilization, heat treatment, DEAE-Sepharose CL-6B chromatography, Sephadex G-100 gel filtration, hydroxyapatite chromatography and chromatofocusing. Elution patterns of alpha-aminoadipate aminotransferase (EC 2.6.1.39) activity were identical with those of kynurenine aminotransferase activity on all column chromatographies. The ratios of the two specific activities were constant throughout the purification. On polyacrylamide gel electrophoresis both activities were detected at the same position. Both enzymatic activities showed the same inactivation curves upon heat inactivation at various temperatures. alpha-Aminoadipate showed competitive inhibiton against kynurenine or 3-hydroxykynurenine. alpha-Ketoadipate was utilized in the kynurenine aminotransferase reaction as an amino acceptor in place of alpha-ketoglutarate. The Km value for alpha-ketoadipate was 10 microM, lower than for alpha-ketoglutarate. These observations indicate that kynurenine aminotransferase is identical with alpha-aminoadipate aminotransferase. The Km values of purified kynurenine aminotransferase were determined at pH 6.5 as: kynurenine, 4.3 mM; pyridoxal 5'-phosphate, 4.2 microM; alpha-ketoglutarate, 20 microM (kynurenine substrate), and 3-hydroxykynurenine, 5.7 mM; pyridoxal 5'-phosphate, 1.7 microM; alpha-ketoglutarate, 13 microM (3-hydroxy-kynurenine substrate). The enzyme was strongly inhibited by Hg2+ and p-chloromercuribenzoate.

Inhibition by kynurenine metabolites of proinsulin synthesis in isolated pancreatic islets

The effect of kynurenine metabolites on insulin biosynthesis was investigated in isolated pancreatic islets of the rat. Both quinaldic acid and 8-hydroxyquinaldic acid were found to produce significant inhibition of the proinsulin synthesis. However, the conversion process of proinsulin to insulin in the islet was not affected by these kynurenine metabolites. Furthermore, the inhibitory effect of these end-metabolites of dynurenine was characterized by preferential inhibition of proinsulin synthesis as distinct from non-insulin protein synthesis in the islet. In contrast to the significant inhibitory effect of quinaldic acid and 8-hydroxyquinaldic acid on proinsulin synthesis, xanthurenic acid and kynurenic acid were far less effective, and L-tryptophan, L-kynurenine, 3-hydroxyanthranilic acid and quinolinic acid showed little ability to inhibit proinsulin synthesis in islets.

Transplantation of preserved pancreatic islets into the portal vein of rats

Langerhans islets were isolated from the exocrine pancreata of Wistar rats by the improved collagenase-digestion method. The isolated islets were preserved in a tissue culture medium for seven days. Transplantation of these preserved islets into the portal vein of streptozotocin-induced diabetic rats resulted in a significant reduction of hyperglycemia, polyuria and glucosuria, and a restoration of weight gain. It was found that these effects could be maintained for 16 weeks. In order to normalize the K-values and plasma insulin levels, at least 600 islets had to be transplanted into each diabetic rat.