Dynamics of D-amino acid oxidase in kidney epithelial cells under amino acid starvation

D-amino acid oxidase (DAO) is a flavoenzyme catalyzing the oxidation of D-amino acid (AA)s. In the kidney, its expression is detected in proximal tubules, and DAO is considered to play a role in the conversion of D-form AAs to α-keto acids. LLC-PK1 cells, a pig renal proximal tubule cell line, were used to elucidate the regulation of DAO protein synthesis and degradation. In this study, we showed that trypsinization of LLC-PK1 cells in culture system rapidly reduced the intracellular DAO protein level to approximately 33.9% of that before treatment, even within 30 min. Furthermore, we observed that the DAO protein level was decreased when LLC-PK1 cells were subjected to AA starvation. To determine the degradation pathway, we treated the cells with chloroquine and MG132. DAO degradation was found to be inhibited by chloroquine, but not by MG132 treatment. We next examined whether or not DAO was degraded by autophagy. We found that AA starvation led to an increased accumulation of LC3-II, suggesting that DAO protein is degraded by autophagy due to AA starvation conditions. Furthermore, treatment with cycloheximide inhibited DAO protein degradation. Taken together, DAO protein is degraded by autophagy under starvation. The present study revealed the potential dynamics of DAO correlated with renal pathophysiology.

P219L substitution in human D-amino acid oxidase impacts the ligand binding and catalytic efficiency

Human D-amino acid oxidase (DAO) is a flavoenzyme that is implicated in neurodegenerative diseases. We investigated the impact of replacement of proline with leucine at Position 219 (P219L) in the active site lid of human DAO on the structural and enzymatic properties, because porcine DAO contains leucine at the corresponding position. The turnover numbers (kcat) of P219L were unchanged, but its Km values decreased compared with wild-type, leading to an increase in the catalytic efficiency (kcat/Km). Moreover, benzoate inhibits P219L with lower Ki value (0.7-0.9 µM) compared with wild-type (1.2-2.0 µM). Crystal structure of P219L in complex with flavin adenine dinucleotide (FAD) and benzoate at 2.25 Å resolution displayed conformational changes of the active site and lid. The distances between the H-bond-forming atoms of arginine 283 and benzoate and the relative position between the aromatic rings of tyrosine 224 and benzoate were changed in the P219L complex. Taken together, the P219L substitution leads to an increase in the catalytic efficiency and binding affinity for substrates/inhibitors due to these structural changes. Furthermore, an acetic acid was located near the adenine ring of FAD in the P219L complex. This study provides new insights into the structure-function relationship of human DAO.

Age- and gender-dependent D-amino acid oxidase activity in mouse brain and peripheral tissues: implication for aging and neurodegeneration

D-amino acid oxidase (DAO) is a flavoenzyme, catalysing oxidative deamination of D-amino acids to produce corresponding α-keto acids, ammonia and hydrogen peroxide. In our search for DAO activity among various tissues, we developed a sensitive assay based on hydrogen peroxide production involving enzyme-coupled colorimetric assay with peroxidase. We first optimized buffer components to extract DAO protein from mouse tissues. Here we show that DAO activity was detected in kidney, cerebellum, medulla oblongata, midbrain and spinal cord, but not in liver. In addition, we observed that DAO activity and expression were decreased in thoracic and lumbar regions of spinal cord in aged mice when compared with young mice, indicating that decreased DAO is involved in motoneuron degeneration during senescence. We also found gender difference in DAO activity in the kidney, suggesting that DAO activity is influenced by sexual dimorphism. We newly detected DAO activity in the epididymis, although undetected in testis. Furthermore, DAO activity was significantly higher in the caput region than corpus and cauda regions of epididymis, indicating that D-amino acids present in the testis are eliminated in epididymis. Taken together, age- and gender-dependent DAO activity in each organ may underlie the human pathophysiology regulated by D-amino acid metabolism.

A GIS methodology for the real-time assessment of micro-pollutant concentration in river: application to the Lake Biwa basin in Japan

For integrated water management in the future, the real-time assessment of toxic micro-pollutant concentrations in rivers is required, since these pollutants cause various irreversible and adverse effects in the environment. In this research, a GIS (Geographical Information System) methodology using EMC (Event Mean Concentration) was established for estimating the SS (Suspended Solids) concentration that strongly sorbs organic micro-pollutants. The GIS was applied to the Lake Biwa basin in Japan. On non-point sources, it was found that in some rivers the upstream SS concentrations could become greater than those in downstream, which suggested thatthe environmental improvement measures in downstream waters arenot always appropriate. For effective use of this GIS methodology, the improvement of the GIS model is necessary and up-to-date data should be kept in constant readiness, which leads to an ideal integrated water quantity and quality management in the future.

Increased susceptibility of decay-accelerating factor deficient mice to anti-glomerular basement membrane glomerulonephritis

To prevent complement-mediated autologous tissue damage, host cells express a number of membrane-bound complement inhibitors. Decay-accelerating factor (DAF, CD55) is a GPI-linked membrane complement regulator that is widely expressed in mammalian tissues including the kidney. DAF inhibits the C3 convertase of both the classical and alternative pathways. Although DAF deficiency contributes to the human hematological syndrome paroxysmal nocturnal hemoglobinuria, the relevance of DAF in autoimmune tissue damage such as immune glomerulonephritis remains to be determined. In this study, we have investigated the susceptibility of knockout mice that are deficient in GPI-anchored DAF to nephrotoxic serum nephritis. Injection of a subnephritogenic dose of rabbit anti-mouse glomerular basement membrane serum induced glomerular disease in DAF knockout mice but not in wild-type controls. When examined at 8 days after anti-glomerular basement membrane treatment, DAF knockout mice had a much higher percentage of diseased glomeruli than wild-type mice (68.8 +/- 25.0 vs 10.0 +/- 3.5%; p < 0.01). Morphologically, DAF knockout mice displayed increased glomerular volume (516 +/- 68 vs 325 +/- 18 x 10(3) microm(3) per glomerulus; p < 0.0001) and cellularity (47.1 +/- 8.9 vs 32.0 +/- 3.1 cells per glomerulus; p < 0.01). Although the blood urea nitrogen level showed no difference between the two groups, proteinuria was observed in the knockout mice but not in the wild-type mice (1.4 +/- 0.7 vs 0.02 +/- 0.01 mg/24 h albumin excretion). The morphological and functional abnormalities in the knockout mouse kidney were associated with evidence of increased complement activation in the glomeruli. These results support the conclusion that membrane C3 convertase inhibitors like DAF play a protective role in complement-mediated immune glomerular damage in vivo.

Dual CCK-A and CCK-B receptor antagonists (II). Preparation and structure activity relationships of 5-alkyl-9-methyl-1,4-benzodiazepines and discovery of FR208419

In our continuing research for dual CCK-A and -B antagonists, according to our hypothesis that dual CCK-A and -B antagonists should be more efficacious than selective CCK-A antagonists for the treatment of pancreatitis, we have prepared various 5-alkyl-9-methyl-1,4-benzodiazepines. From the compounds prepared, 1-cyclohexyl-carbonylmethyl-5-ethyl-9-methyl-3- (m-tolylureido)-2-oxo-1,4-benzodiazepine, (40) was selected as a candidate for development due to its well-balanced high affinity for both receptors. The R-enantiomer of 40, (R)-40 (FR 208419), had 27-fold higher affinity for the CCK-A receptor and 8-fold more potent CCK-B receptor binding activity than (S)-40. The biological activity after p.o. administration of (R)-40, estimated from the ID50 value (0.23 mg/kg p.o.) obtained by preliminary evaluation by gastric emptying effects, is considered to be high enough for further development. This compound is now undergoing further biological evaluations with a view to clinical development.

Effect of FK480, a CCK-A receptor antagonist, on spontaneously developed chronic pancreatitis in WBN/Kob rats

The effect of FK480, a cholecystokinin-A (CCK-A) selective receptor antagonist, on spontaneously developed chronic pancreatitis was examined in WBN/Kob rats. Animals at age 18 weeks (18w-Control) already had the histologic appearance of chronic pancreatitis as indicated by inflammatory cell infiltration and fibrotic degeneration with interstitial edema. Rats treated with vehicle from 18 to 26 weeks of age (26w-Control) showed further development of pancreatitis as characterized by more extensive appearance of inflammatory cell infiltration and fibrotic changes, with the pancreatic weight significantly decreased. Serum amylase levels of 26w-Control animals were slightly decreased compared with those of 18w-Control animals, although the difference was not statistically significant. When rats were treated orally with 1, 10, and 100 microg/kg FK480 from 18 to 26 weeks of age, the decrease in serum amylase levels recovered dose dependently compared with 26w-Control, and the level in animals treated with 100 microg/kg FK480 was almost the same as that in 18w-Control rats. Histologic examinations revealed that the appearance of the pancreas of animals treated with FK480 was slightly improved with respect to inflammatory cell infiltration and edematous changes at the highest dose examined, although the difference was not statistically significant. Although blockade of the CCK-A receptor could be considered to exacerbate chronic pancreatitis due to possible inhibition of the trophic action of CCK, our results suggest that CCK-A receptor antagonists may not be detrimental to chronic pancreatitis.

Augmentation of the inhibitory effect of FK480, a CCK-A receptor antagonist, on pancreatic exocrine secretion by achlorhydria

The effect of intraluminal acid and cholecystokinin (CCK) receptor blockade on the pancreatic secretory response was examined in rats. Blockade of gastric acid secretion by YM022 (CCK-B receptor antagonist) or famotidine (histamine-2 receptor antagonist) resulted in a significant suppression of casein-stimulated pancreatic exocrine secretion as determined by juice volume and amylase secretion. Ligation of the gastric pylorus, which leads to complete prevention of gastric acid from entering the duodenum, also suppressed pancreatic exocrine secretion. FK480 (CCK-A receptor antagonist) inhibited pancreatic exocrine secretion dose dependently at doses of 0.01-1.0 mg/kg. When submaximal doses of FK480 and YM022 were treated concomitantly, pancreatic exocrine secretion was inhibited more profoundly than when treated solely. Hydrochloric acid (HCl; 0.05 N), injected into the duodenum, stimulated pancreatic exocrine secretion to a level comparable to that exhibited by intraduodenal casein. This effect of HCl was inhibited by FK480 (1.0 mg/kg) but not by YM022 (1.0 mg/kg). These findings suggest that inhibition of gastric acid secretion leads to the suppression of pancreatic exocrine secretion through mechanisms mediated by CCK-A receptors.

[Chronic left ventricular epicardial pacing by the perforated endocardial electrode through the cardiac vein]

We report a rare complication of endocardial pacing electrode implantation. A 64-year-old man, who was implanted transvenous pacemaker system by the other hospital one month ago, visited our outpatient clinic with the complaint of diaphragmatic twitching. Left ventricular pacing was highly suspected because of right bandle branch block pattern by 12 leads ECG. Pericardial effusion was observed by echocardiography, and angiography revealed the pacing electrode coursing through the coronary sinus and perforated the cardiac vein towards the posterior wall of the left ventricle. A new generator and a pacing electrode were implanted on the other side. Pericardial drainage was not performed because hemodynamics was stable. The patient discharged hospital on 18th postoperative day without any complication.

Studies on a novel, potent and orally effective cholecystokinin A antagonist, FK-480. Synthesis and structure-activity relationships of FK-480 and related compounds

We prepared various novel tricyclic 1,4-benzodiazepine derivatives as cholecystokinin (CCK) A antagonists, which were evaluated preliminarily for inhibition of 125I-CCK-8 binding to rat pancreatic membranes in vitro and inhibiting effect on CCK-8-induced inhibition of charcoal meal gastric emptying in mice. On the basis of structure-activity relationship (SAR) studies, as well as the stability and availability of the starting materials of those compounds, (S)-N-[1-(2-fluorophenyl)-3,4,6,7-tetrahydro-4-oxo- pyrrolo[3,2,1-jk][1,4]benzodiazepin-3-yl]- 1H-indole-2-carboxamide (9f, FK-480) was selected as a candidate compound for further evaluation. The absolute configuration of the precursor of FK-480, (3S)-amino-1,4-benzodiazepine derivative ((S)-8a, R1 = F) was determined by an X-ray crystallographic study of its ureido derivative with (S)-alpha-methylbenzyl isocyanate. FK-480 is now undergoing clinical studies for the treatment of chronic pancreatitis.

Pharmacological profile of FK480, a novel cholecystokinin type-A receptor antagonist: comparison to loxiglumide

The pharmacological profile of FK480[(S)-(+)-N-<1-(2)-fluorophenyl)-3,4,6,7-tetra hydro-4-oxo-pyrrolo(3,2,1-jk) (1,4)benzodiaze-pine-3-yl>-1H-indole-2- carboxamide], a novel cholecystokinin type-A (CCK-A) receptor antagonist, was compared with that of the CCK-A receptor antagonist, loxiglumide. Both FK480 and loxiglumide inhibited 125I-labeled CCK-8 (125I-CCK-8) binding to rat pancreatic and guinea-pig gallbladder membranes with IC50 values of 0.40 +/- 0.04 and 0.06 +/- 0.02 nM for FK480 and 330 +/- 66 and 66 +/- 10 nM for loxiglumide, respectively. These two agents also inhibited 125I-CCK-8 binding to guinea-pig brain (cerebral cortex) receptors with respective IC50 values of 72 +/- 11 nM and > 10 microM, indicating less affinity to central receptors. Intravenous administration of FK480 (ED50 = 18 micrograms/kg) was 2800 times more potent than that of loxiglumide (ED50 = 50 mg/kg) in inhibiting CCK-8-induced pancreatic amylase secretion in rats. Furthermore, FK480 had ED50 values of 10 and 8.4 micrograms/kg, respectively, in antagonizing CCK-8-induced inhibition of charcoal meal gastric emptying in mice when administered orally 1 or 5 hr before the CCK-8. Loxiglumide (ED50 = 23.5 mg/kg, when administered orally 1 hr before the CCK-8) also antagonized it, but its activity was 2400 times less than that of FK480. We conclude that FK480 is a potent, orally effective CCK-A receptor antagonist with long duration of action.

Effect of immobilization stress on pipecolic acid transport in mouse brain areas and peripheral tissues

Transport activity of d-pipecolic acid and of l-pipecolic acid in mouse brain and peripheral tissues were tested, and the effect of immobilization stress was described, along with the method for preparative, enantiomeric resolution and purification of d,l-pipecolic acid using high performance liquid chromatography equipped with a chiral column. It was found that l-isomer, an endogenous substance, was more rapidly transported to brain and liver than the d-isomer, non-endogenous one, which was more rapidly eliminated into the kidney. Immobilization stress caused acceleration of transport of l-pipecolic acid into the brain region, liver and heart, but not that of d-pipecolic acid. From these results it was suggested that the elevation of pipecolic acid concentration caused by stress might be exerted through its stimulatory effect on the transport of l-pipecolic acid into the tissues.