A mutation of the Wilson disease protein, ATP7B, is degraded in the proteasomes and forms protein aggregates

BACKGROUND & AIMS

Wilson disease is a genetic disorder characterized by the accumulation of copper in the body as a result of a defect of copper excretion from hepatocytes. The intracellular localization of the Wilson disease gene product, ATP7B, was recently identified as the late endosomes. Various mutations have been documented in patients with Wilson disease. The clinical manifestations vary greatly among the patients; however, there is little information on the genotype-phenotype correlation.

METHODS

We investigated the distribution of a common ATP7B mutant His1069Gln and a mutant Asp1270Ser by expressing the mutants tagged with green fluorescent protein in Huh7 and HEK293 cells. Intracellular organelles were visualized by fluorescence microscopy.

RESULTS

Although the wild-type ATP7B and Asp1270Ser mutant localized in the late endosomes, His1069Gln mutant did not locate in the late endosomes and was degraded by the proteasomes in the cytoplasm. Furthermore, His1069Gln formed aggresomes composed of the degradates and intermediate filaments at the microtubule-organizing center. These aggresomes were similar to Mallory bodies on electron microscopy.

CONCLUSIONS

The different protein properties of ATP7B mutants may explain the variety of clinical spectrums in patients with Wilson disease.

Sequential-replenishment mechanism of exocytosis in pancreatic acini

Here we report exocytosis of zymogen granules, as examined by multiphoton excitation imaging in intact pancreatic acini. Cholecystokinin induces Ca 2+ oscillations that trigger exocytosis when the cytosolic Ca 2+ concentration exceeds 1 microM. Zymogen granules fused with the plasma membrane maintain their Omega-shaped profile for an average of 220 s and serve as targets for sequential fusion of granules that are located within deeper layers of the cell. This secondary exocytosis occurs as rapidly as the primary exocytosis and accounts for most exocytotic events. Granule-granule fusion does not seem to precede primary exocytosis, indicating that secondary fusion events may require a plasma-membrane factor. This sequential-replenishment mechanism of exocytosis allows the cell to take advantage of a large supply of fusion-ready granules without needing to transport them to the plasma membrane.

Comparative report on transplantation and relevant ethical problems in five European countries, and some reflections on Japan

Comparison of transplantation medicine in Sweden, Denmark, Germany, Spain and Portugal reveals many and important differences with respect to frequency of transplantations, frequency of life donations, legal regulations and influence of the family on organ donation. The differences observed are at least partly related to cultural and value differences between the various countries, but many questions need to be studied systematically and in more detail before useful conclusions can be drawn. One study would have to address the problem of how differences in the family influence on organ donation can be explained. Another question needing further clarification concerns the exact meaning of "medical decision" and "medical criteria" because these terms, on which access to- and selection from the waiting list largely depends, are equivocally defined and seem to differ according to different traditions. Open questions also arise with respect to the influence of "closeness or distance" on medical decision making. The findings indicate that it would be premature to propose common guidelines to be observed within Europe as long as the above mentioned and some further questions have not been systematically studied and thoroughly analyzed.

Relation of type II transforming growth factor-beta receptor to hepatic fibrosis and hepatocellular carcinoma

Hepatocarcinogenesis is closely related to hepatic fibrosis. In this study, we investigated the relationship of type II transforming growth factor-beta receptor (T beta RII) to hepatic fibrosis and hepatocellular carcinoma (HCC). In vivo: liver tissues were obtained from 30 patients (10 chronic hepatitis, 7 cirrhosis, 13 HCC). Protein expression and immunolocalization of T beta RII were examined by Western blot analysis and immunohistochemistry. In vitro: T beta RII protein expression in hepatoma cell lines (HepG2, Hep3B, HLE, HLF and Huh7) was examined by Western blot analysis. Next, we transfected T beta RII cDNA to Huh7, and compared the change of cell number and observed the induction of apoptosis after TGF-beta1 treatment using a FACScan flow cytometer. In vivo: T beta RII immunolocalization in liver tissues was significantly decreased in patients with HCC compared with that of patients with chronic hepatitis or liver cirrhosis. In Western blot analysis, T beta RII expression in tissues attenuated in comparison with that in non-tumor tissues in some patients with HCC. In vitro: T beta RII protein expression in HLE, HLF and Huh7 cells was weaker than that in HepG2 and Hep3B cells. In Huh7 cells transfected T beta RII cDNA, cell arrest and apoptosis were obviously induced. These results indicated that human HCC has a reduced expression of T beta RII for TGF-beta1. This may provide a selective growth advantage to HCC to escape the inhibitory growth signals of TGF-beta1, and may be linked with critical steps in the growth of hepatoma cells.

In vivo demonstration of alpha(1A)-adrenoceptor subtype selectivity of KMD-3213 in rat tissues

The present study was undertaken to characterize the in vivo alpha(1)-adrenoceptor binding of KMD-3213, a novel selective antagonist of alpha(1A)-adrenoceptors, in rat tissues by using a tritiated ligand with high specific activity, in comparison with that of [(3)H]prazosin. A significant degree of in vivo specific binding of [(3)H]KMD-3213 after i.v. injection of the radioligand (1. 4 nmol/kg) was seen in most rat tissues, except the cerebral cortex, spleen, and liver, which showed a little or no specific binding. There was a notable difference among tissues in the time course of specific [(3)H]KMD-3213 binding after i.v. injection of the ligand. The specific binding in the lung, kidney, and spleen was greatest at 10 min and declined rapidly with the disappearance of the ligand from the plasma. On the other hand, [(3)H]KMD-3213 binding in the submaxillary gland, vas deferens, and prostate attained peak levels at 60 min, and a considerable degree of binding was present even at 240 min. After i.v. injection of a similar dose (1.2 nmol/kg) of [(3)H]prazosin in rats, the in vivo specific binding in the submaxillary gland was greatest at 10 min and then it fell rapidly, whereas [(3)H]prazosin binding in the spleen attained a peak level at 60 min, and this was maintained even at 120 min. The AUC(0-120) values of the specific binding for [(3)H]KMD-3213, compared with those of [(3)H]prazosin, were markedly lower in the rat aorta, spleen, and liver, whereas the prostate, submaxillary gland, and lung showed significantly higher AUC(0-120) values of [(3)H]KMD-3213 compared with [(3)H]prazosin. Furthermore, the in vivo specific binding of [(3)H]KMD-3213 at dose ranges of 1.4 to 13.6 nmol/kg increased linearly in the prostate and submaxillary gland, but did not increase in a dose-dependent manner in the spleen. On the other hand, there was a dose-dependent increase in the in vivo specific binding of [(3)H]prazosin at doses of 1.2 to 10.6 nmol/kg in all tissues. The in vivo specific binding of [(3)H]KMD-3213 in rat tissues was reduced by concomitant i.v. injection of low doses of prazosin in a dose-dependent manner, but not by even a relatively high dose of yohimbine. In conclusion, the present study shows that KMD-3213 binds to the alpha(1A)-adrenoceptor subtype with a higher affinity than to the alpha(1B)- and alpha(1D)- subtypes under in vivo condition, thus leading to prostate selectivity.

Disposition and alpha(1)-adrenoceptor binding characteristics of JTH-601 and its metabolites in rat tissues

The present study was performed to characterize the disposition and alpha(1)-adrenoceptor binding of JTH-601, a novel alpha(1L)-adrenoceptor antagonist, and its metabolites (beta-D-glucopyranosyl uronic acid, JTH-601-G1; hydrogen sulfate, JTH-601-S1) in the rat prostate and other tissues. JTH-601, JTH-601-G1, and JTH-601-S1 inhibited competitively specific [(3)H]tamsulosin binding in the prostate, submaxillary gland, and spleen of rats in vitro, and the inhibitory effect of JTH-601 was 2. 5 to 6.4 times more potent than that of its metabolites. JTH-601 and its metabolites inhibited dose dependently in vivo specific [(3)H]tamsulosin binding in the particulate fraction of the prostate, aorta, submaxillary gland, and spleen of rats. Compared with that of JTH-601, the in vivo inhibitory effect of JTH-601-G1 was 1.9 to 2. 9 times more potent, and the effect of JTH-601-S1 was 1.3 to 3.2 times less potent. Based on the ratios of ID(50) values, JTH-601 and JTH-601-G1 appeared to be 4.0 to 6.9 times more selective than prazosin as far as the alpha(1)-adrenoceptors in the prostate and submaxillary gland versus the spleen or aorta were concerned. The total radioactivity in rat tissues after i.v. injection of [(3)H]JTH-601-G1 was considerably lower than that of [(3)H]JTH-601. The plasma concentration of [(3)H]JTH-601-G1 at 10 min after i.v. injection in rats was 3 times higher than that of [(3)H]JTH-601, and conversely, the concentration in the prostate was 3 times lower. Although in vivo [(3)H]JTH-601-G1 binding at 10 min was significantly lower than that of [(3)H]JTH-601 in most rat tissues, there was comparable binding between these radioligands in the prostate and vas deferens. Specific binding of [(3)H]JTH-601, at 60 min after i.v. injection compared with that at 10 min, was considerably reduced in rat tissues except the prostate and vas deferens, both of which showed relatively sustained binding. In conclusion, the present study has shown that JTH-601 and its metabolites bind to alpha(1)-adrenoceptors in rat tissues in vivo and that JTH-601-G1 retains the prostatic alpha(1)-adrenoceptor subtype selectivity of its parent compound.

Identification of novel first exons in Ad4BP/SF-1 (NR5A1) gene and their tissue- and species-specific usage

It has been demonstrated that the mammalian Ad4BP/SF-1 (NR5A1) gene is regulated precisely in sex, tissue, and developmental stage specific manners. To clarify the complex transcriptional regulation, we investigated in the present study whether the gene transcription is regulated by multiple promoters accompanied by noncoding first exons. Novel first exons (Io and Ig) were identified downstream of the already identified exon Ia. Nucleotide sequences revealed that Ia and Ig exons were well conserved, whereas Io exon was less conserved among the mouse, rat, and human genes. Interestingly, the splice donor of the mouse and human Io and human Ig exons do not satisfy the consensus sequence. Transcripts containing Ia, Io, and Ig were detected in all rat tissues examined, while the transcript containing Io was undetectable in the corresponding tissues of mice. The lack of exon Io usage in the mouse was confirmed by transient transfection assays with cultured cells. Quantitative RT-PCR analysis revealed that the transcript containing Ig exon was the main product in the pituitary but significantly less in the spleen, suggesting that the regulation of Ad4BP/SF-1 gene transcription in the pituitary and spleen is distinct from that of other tissues. The above findings, together with the structural abnormality at the splice donor site, suggest that acquisition of the multiple first exons enables the Ad4BP/SF-1 gene to be regulated differentially in different animal species and in different tissues in the same animal.

Ameliorating effects of amlodipine on plasma and myocardial catecholamines in BIO 53.58 Syrian hamsters, a model of dilated cardiomyopathy

Our previous study has shown that the concentrations of norepinephrine, epinephrine and dopamine in the plasma of BIO 53.58 hamsters (a model of dilated cardiomyopathy: DCM) at 18 weeks of age (severe cardiomyopathic stage) were twice those of age-matched F1B control and conversely the myocardial norepinephrine level was decreased. The present study was undertaken to examine the effect of amlodipine on catecholamine concentration, myocardial receptors and histopathological changes in BIO 53.58 hamsters. Oral administration of amlodipine (10 mg/kg/day) for 7 weeks in 11 week-old-BIO 53.58 hamsters brought about marked decreases in the concentrations of norepinephrine, epinephrine and dopamine in the plasma, compared with those in vehicle-treated BIO 53.58 hamsters. This was accompanied by a concomitant increase in the concentration of myocardial catecholamine concentration. In other words, the concentrations of catecholamines in plasma and myocardium of amlodipine administered BIO 53.58 hamsters approximated to the control level in age-matched F1B. In addition, amlodipine administration caused a significant reduction of calcium deposition with a tendency toward a decrease in the myocardial necrosis, and it had little effect on the affinity and number of specific binding for (+)-[3H]PN 200-110, (-)-[125I]iodocyanopindolol (CYP) and [3H]prazosin in the myocardium. In conclusion, the present study shows that administration of amlodipine in BIO 53.58 hamsters may exhibit ameliorating effect on plasma and myocardial catecholamines with a significant reduction of calcium deposition. These data may offer further support for the use of amlodipine in patients with DCM.

Coexistence of chronic myelogenous leukemia and multiple myeloma. Case report and review of the literature

A case report of simultaneous presentation of chronic myelogenous leukemia (CML) and multiple myeloma (MM) in a 72-year-old female is described. Our case was typical of Ph1-positive and chimeric bcr-abl messenger RNA-positive CML. Furthermore, a marked IgG (kappa-type) paraproteinemia was present. Fluorescence in situ hybridization showed that 97% of marrow nucleated cells were positive for bcr-abl fusion signal, when myeloma cells in the bone marrow amounted to 19.0%. In the literature survey, 4 similar cases with coexistence of CML and MM have been identified.

Improvement in the histopathology of hearts from cardiomyopathic BIO TO-2 hamsters following long-term administration of amlodipine and cilnidipine

The effect of long-term administration of amlodipine and cilnidipine was examined on the histopathology and 1,4-dihydropyridine (DHP) calcium channel antagonist receptors in the left ventricle of BIO TO-2 hamsters, a model of dilated cardiomyopathy (DCM). Oral administration of amlodipine (3 and 10 mg/kg/d, 19 weeks) in 7 week-old BIO TO-2 hamsters produced a significant reduction in calcium deposition and necrosis with little change in the cavity area and fibrosis. A reduction of calcium deposition and necrosis in the myocardium of BIO TO-2 hamsters was also seen following similar administration of cilnidipine (10 mg/kg/d). The long-term administration of amlodipine (3 and 10 mg/kg/d) caused a significant increase (36.6 and 21.7%, respectively) in the Bmax for specific (+)-[3H]PN 200-110 binding in the myocardium from BIO TO-2 hamsters, compared with that in control hamsters. In conclusion, the present study has shown that long-term administration of amlodipine and cilnidipine improves calcium deposition and necrosis in the myocardium from BIO TO-2 hamsters. Thus, these data suggest that both agents may be effective pharmacological treatments of DCM.

Copper does not alter the intracellular distribution of ATP7B, a copper-transporting ATPase

Wilson's disease is a genetic disorder characterized by the accumulation of copper in the body due to a defect of biliary copper excretion. However, the mechanism of biliary copper excretion has not been fully clarified. We examined the effect of copper on the intracellular localization of the Wilson disease gene product (ATP7B) and green fluorescent protein (GFP)-tagged ATP7B in a human hepatoma cell line (Huh7). The intracellular organelles were visualized by fluorescence microscopy. GFP-ATP7B colocalized with late endosome markers, but not with endoplasmic reticulum, Golgi, or lysosome markers in both the steady and copper-loaded states. ATP7B mainly localized at the perinuclear regions in both states. These results suggest that the main localization of ATP7B is in the late endosomes in both the steady and copper-loaded states. ATP7B seems to translocate copper from the cytosol to the late endosomal lumen, thus participating in biliary copper excretion via lysosomes.

In vivo specific binding characteristics and pharmacokinetics of a 1,4-dihydropyridine calcium channel antagonist in the senescent mouse brain

PURPOSE

To characterize the in vivo specific binding and pharmacokinetics of a 1,4-dihydropyridine (DHP) calcium channel antagonist, PN 200-110, in the senescent brain, using senescence-accelerated prone mice (SAMP8) and senescence-resistant mice (SAMR1).

METHODS

Blood, brain, and heart samples were taken periodically from SAMR1 and SAMP8 following intravenous injection of (+)-[3H]PN 200-110, and the concentration of (+)-[3H]PN 200-110 in the plasma and tissues was determined. In addition, the in vivo specific binding of (+)-[3H]PN 200-110 in the brains of SAMRI and SAMP8 was measured periodically after intravenous injection of the radioligand.

RESULTS

There was very little significant difference between SAMR1 and SAMP8 in terms of the half-life (t(1/2)), total body clearance (CL(tot)), steady-state volume of distribution (Vd(ss)). and AUC for the plasma concentration of (+)-[3H]PN 200-110 after intravenous injection of the radioligand. The brain concentration (AUCbrain) for (+)-[3H]PN 200-110 and the brain/plasma AUC ratio (AUCbrain/AUCplasma) were significantly lower in SAMP8 than in SAMR1, and the heart concentration (AUCheart) and the heart/plasma AUC ratio (AUCheart/AUCplasma) were similar in both strains. Also, the brain/plasma unbound AUC ratio (AUCbrain/AUCplasma-free) for (+)-[3H]PN 200-110 was significantly lower in SAMP8 than in SAMRI. The in vivo specific binding (AUCspecific binding, maximal number of binding sites: Bmax) of (+)-[3H]PN 200-110 was significantly lower in brain particulate fractions of SAMP8 than SAMR1.

CONCLUSIONS

The concentration and in vivo specific binding of (+)-[3H]PN 200-110 was significantly reduced in the senescent brain. The simultaneous analysis of the concentrations of centrally acting drugs and the in vivo specific binding in the brain in relation to their pharmacokinetics may be valuable in evaluating their CNS effects.

Restriction-site-specific PCR as a rapid test to detect enterohemorrhagic Escherichia coli O157:H7 strains in environmental samples

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is an important food-borne pathogen in industrialized countries. We developed a rapid and simple test for detecting E. coli O157:H7 using a method based on restriction site polymorphisms. Restriction-site-specific PCR (RSS-PCR) involves the amplification of DNA fragments using primers based on specific restriction enzyme recognition sequences, without the use of endonucleases, to generate a set of amplicons that yield "fingerprint" patterns when resolved electrophoretically on an agarose gel. The method was evaluated in a blinded study of E. coli isolates obtained from environmental samples collected at beef cattle feedyards. The 54 isolates were all initially identified by a commonly used polyclonal antibody test as belonging to O157:H7 serotype. They were retested by anti-O157 and anti-H7 monoclonal antibody enzyme-linked immunosorbent assay (ELISA). The RSS-PCR method identified all 28 isolates that were shown to be E. coli O157:H7 by the monoclonal antibody ELISA as belonging to the O157:H7 serotype. Of the remaining 26 ELISA-confirmed non-O157:H7 strains, the method classified 25 strains as non-O157:H7. The specificity of the RSS-PCR results correlated better with the monoclonal antibody ELISA than with the polyclonal antibody latex agglutination tests. The RSS-PCR method may be a useful test to distinguish E. coli O157:H7 from a large number of E. coli isolates from environmental samples.

Cholestasis with altered structure and function of hepatocyte tight junction and decreased expression of canalicular multispecific organic anion transporter in a rat model of colitis

Cholestasis is frequently associated with inflammatory bowel disease. Because some cholestasis is resulted from altered hepatocyte tight junctions (TJs) or the canalicular multispecific organic anion transporter, we have investigated the following topics in a rat model of inflammatory bowel disease: (1) alterations in hepatocyte TJs and in the canalicular multispecific organic anion transporter, (2) etiologic factors for cholestasis, and (3) effects of antibiotics on cholestasis. Rats with trinitrobenzene sulfonic acid-induced colitis were studied 24 hours after treatment. Hepatocyte TJs and the canalicular multispecific organic anion transporter were evaluated by immunostaining for TJ-associated proteins, 7H6 and ZO-1, and multidrug resistance protein 2 (mrp2). To investigate etiologic factors causing cholestasis, portal endotoxin and proinflammatory cytokines were examined. The effects of polymyxin B, penicillin G, or metronidazole on immunostaining for 7H6, ZO-1, mrp2, and cholestasis were investigated. (1) Immunostaining for 7H6 and ZO-1 colocalized outlining the bile canaliculi and immunostaining for mrp2 localized on the canalicular membrane in controls. Treatment with trinitrobenzene sulfonic acid induced significant cholestasis and caused translocation of immunostaining for 7H6, but not that for ZO-1, to the cytoplasm and diminished immunostaining for mrp2 on the canaliculus membrane. (2) The levels of portal endotoxin, but not proinflammatory cytokines, was increased. (3) Polymyxin B, but not the other antibiotics, prevented alterations in immunostaining for both 7H6 and mrp2, and cholestasis. We described that both hepatocyte TJs and the canalicular multispecific organic anion transporter were altered and that gut-derived endotoxin levels in the portal blood were increased in this rat colitis model.

Brain distribution of 6-mercaptopurine is regulated by the efflux transport system in the blood-brain barrier

6-mercaptopurine (6-MP) has been used clinically for 40 years to maintain remission in patients with acute lymphoblastic leukemia (ALL). However, central nervous system (CNS) relapses frequently occur in patients with ALL who continuously receive anticancer drugs, including 6-MP, during remission maintenance therapy. The cause of such CNS relapse is not well understood. One possible reason may involve the restricted distribution of 6-MP in the brain. This study, therefore, investigates the blood-brain barrier (BBB) transport which largely regulates 6-MP distribution in the brain using a quantitative microdialysis technique and centers on the efflux transport of 6-MP across the BBB. The brain tissue, cerebrospinal fluid (CSF), or hippocampal interstitial fluid (ISF) concentration of 6-MP was very low compared with the unbound plasma concentration, suggesting that 6-MP distribution in the brain is highly restricted. Kinetic analyses of this BBB transport showed that the efflux clearance from brain ISF to plasma across the BBB (CLout) is approximately 20-times greater than the influx clearance from plasma to brain (CLin). The CLout was significantly reduced by 1mM N-ethylmaleimide (NEM), a sulfhydryl-modifying agent, suggesting the participation of transport protein in the efflux of 6-MP across the BBB. In addition, efflux transport was inhibited by an intracerebral infusion of probenecid (1.5 mM), p-aminohippuric acid (PAH, 3.0 mM), benzoate (3.6 mM), or salicylate (3.7 mM) administered through a microdialysis probe, but neither choline (0.8 mM) nor tetraethylammonium (TEA, 0.7 mM) had any effect. These data suggest that the restricted 6-MP brain distribution may be ascribed to efficient efflux from the brain, possibly via both the organic anion transport system, shared with probenecid and PAH, and the monocarboxylic acid transport system, shared with benzoate and salicylate.

Reduction of serum thyroxine concentrations by methylsulfonyl metabolites of tetra-, penta- and hexachlorinated biphenyls in male Sprague-Dawley rats

Male Sprague-Dawley rats received four consecutive intraperitoneal doses of nine methylsulfonyl (MeSO2) metabolites of tetra-, penta- and hexachlorinated biphenyls (tetra-, penta- and hexaCBs) to determine their effects on thyroid hormone levels. Nine MeSO2 metabolites, major MeSO2-PCBs detected in human milk, liver and adipose tissue, were 3-MeSO2-2,2',4',5-tetraCB (3-MeSO2-CB49), 3-MeSO2-2,3',4',5-tetraCB (3-MeSO2-CB70), 3-MeSO2-2,2',3',4',5-pentaCB (3-MeSO2-CB87), 3-MeSO2-2,2',4',5,5'-pentaCB (3-MeSO2-CB101), 4-MeSO2-2,2',4',5,5'-pentaCB (4-MeSO2-CB101), 3-MeSO2-2,2',3',4',5,6-hexaCB (3-MeSO2-CB132), 3-MeSO2-2,2',3',4',5,5'-hexaCB (3-MeSO2-CB141), 3-MeSO2-2,2',4',5,5',6-hexaCB (3-MeSO2-CB149) and 4-MeSO2-2,2',4',5,5',6-hexaCB (4-MeSO2-CB149). All nine MeSO2 metabolites (20 micromol/kg once daily for four days) reduced serum total thyroxine levels (16-44%) at a much lower dose than phenobarbital (431 micromol/kg once daily for four days) on days 2, 3, 4 and 7 after the last dosage. Total triiodothyronine level was reduced 37% by treatments with 3-MeSO2-CB49 and 3-MeSO2-CB149 at day 7, but increased 35% and 38% by 3-MeSO2-CB70 and 4-MeSO2-CB101 at days 3 and 4, respectively. The reductions in thyroxine levels led to an increase in thyroid-stimulating hormone levels by 3-MeSO2-CB49, 3-MeSO2-CB87, 3-MeSO2-CB101, 3-MeSO2-CB132, 3-MeSO2-CB141, 3-MeSO2-CB149 and 4-MeSO2-CB149. A 30% increase in thyroid weight was produced by 3-MeSO2-CB101 and 3-MeSO2-CB141 treatments. Total cytochrome P450 content and the activity of 7-pentoxyrosorufin O-dealkylase were increased by all seven 3-MeSO2-PCBs. 3-MeSO2-CB49, 3-MeSO2-CB87, 3-MeSO2-CB101 and 3-MeSO2-CB132 also increased the activity of 7-ethoxyresorufin O-dealkylase. Thus, it is likely that all nine tested MeSO2 metabolites could influence thyroid hormone metabolism. The results show that tested 3- and 4-MeSO2 metabolites of tetra-, penta- and hexaCBs reduce thyroid hormone levels in rats, suggesting that the metabolites may act as endocrine-disrupters.

Role of ATP7B in biliary copper excretion in a human hepatoma cell line and normal rat hepatocytes

BACKGROUND & AIMS

Wilson's disease is a genetic disorder characterized by the accumulation of copper in the body caused by a defect of biliary copper excretion. The Wilson's disease gene has been cloned; however, the precise localization of the gene product (ATP7B) and its role in biliary copper excretion have not been clarified.

METHODS

We constructed a chimeric protein between green fluorescent protein (GFP) and ATP7B (GFP-ATP7B) and expressed it in a human hepatoma cell line (Huh7) and isolated rat hepatocytes. The Golgi apparatus, late endosomes, lysosomes, and bile canaliculus were visualized by fluorescence microscopy. Brefeldin A and nocodazole were used to redistribute the Golgi proteins. Bafilomycin A1 was used to analyze the association between GFP-ATP7B and the late endosomes.

RESULTS

GFP-ATP7B colocalized with rhodamine-dextran and late endosome markers but not with the Golgi markers, lysosome markers, or a tight junction protein. Brefeldin A and nocodazole redistributed the Golgi proteins, but they did not affect the distribution of ATP7B.

CONCLUSIONS

Although it is widely believed that ATP7B is located at the Golgi apparatus, its main localization is in late endosomes. ATP7B seems to translocate copper from the cytosol to the late endosomal lumen, thus participating in biliary copper excretion via lysosomes.

Alteration in membrane fluidity of rat liver microsomes and of liposomes by protoporphyrin and its anti-lipidperoxidative effect

The effect of protoporphyrin (PP) on membrane fluidity was investigated by electron paramagnetic resonance spectroscopy using doxyl stearate spin probes in relation to the anti-lipidperoxidative effect of PP. PP decreased the membrane fluidity in rat liver microsomes at concentrations above 1 mM and also in phosphatidylcholine (PC)-cholesterol (Cho) (100:8, a molar basis) liposomes. The lipid peroxidation stimulated by Fe2+ and L-ascorbic acid in those membrane preparations was attenuated along with the decrease in membrane fluidity by PP. Similar results were also found in Cho-rich PC (100:30 to 100) liposomes having less fluidity. These results suggest that the decrease in the membrane fluidity caused by PP may be involved in the antioxidative action of PP.

The induction of hepatic microsomal UDP-glucuronosyltransferase by the methylsulfonyl metabolites of polychlorinated biphenyl congeners in rats

The effects of nine methylsulfonyl (MeSO(2)) metabolites of tetra-, penta- and hexachlorinated biphenyls (tetra-, penta- and hexaCBs; 20 micromol/kg once daily for 4 days) on the hepatic microsomal UDP-glucuronosyltransferase (UDP-GT) were investigated in male Sprague-Dawley rats. Each of the seven 3-MeSO(2)-PCBs, 3-MeSO(2)-2, 2',4',5-tetraCB (3-MeSO(2)-CB49), 3-MeSO(2)-2,3',4',5-tetraCB (3-MeSO(2)-CB70), 3-MeSO(2)-2,2',3',4',5-pentaCB (3-MeSO(2)-CB87), 3-MeSO(2)-2,2',4',5,5'-pentaCB (3-MeSO(2)-CB101), 3-MeSO(2)-2,2',3', 4',5,6-hexaCB (3-MeSO(2)-CB132), 3-MeSO(2)-2,2',3',4',5,5'-hexaCB (3-MeSO(2)-CB141), 3-MeSO(2)-2,2',4',5,5',6-hexaCB (3-MeSO(2)-CB149) and 4-MeSO(2)-2,2',4',5,5'-pentaCB (4-MeSO(2)-CB101) increased the activities of UDP-GT toward chloramphenicol, 4-nitrophenol and 4-methylumbelliferone. 4-MeSO(2)-2,2',4',5,5',6-hexaCB (4-MeSO(2)-CB149) increased the activity of UDP-GT toward chloramphenicol (UGT2B1) but not toward 4-nitrophenol (UGT1A6) and 4-methylumbelliferone (UGT1A6). The activity of UDP-GT toward thyroxine (T(4)) significantly increased after the administration of each of the seven 3-MeSO(2)-PCBs and 4-MeSO(2)-CB101. Significant correlation was found between the activity of UDP-GT toward T(4) and serum total T(4) concentration after the administration of each of the MeSO(2) derivatives except 4-MeSO(2)-CB149. In conclusion, seven 3-MeSO(2)-PCBs and 4-MeSO(2)-CB101 induce both UGT2B1 and UGT1A6, and 4-MeSO(2)-CB149 induces UGT 2B1. The results from the present study indicate that increase in the hepatic T(4) glucuronidation after the administration of the seven 3-MeSO(2)-PCBs and 4-MeSO(2)-CB101 possibly because of the induction of both UGT1A1 and UGT1A6 caused the reduction of serum T(4) levels.

Increase in receptor binding affinity for nimodipine in the rat brain with permanent occlusion of bilateral carotid arteries

The permanent occlusion of bilateral common carotid arteries (2VO) in rats has been shown to cause progressive and long-lasting cognitive deficits which may be due to impairment of memory retention and/or memory recall process. To clarify the function of voltage dependent calcium channels and the receptor binding of nimodipine by chronic cerebral ischemia, we examined specific (+)-[3H]PN 200-110 binding and the effect of oral administration of nimodipine in brain regions and hearts of rats, at 2 weeks to 4 months after permanent 2VO. There was no significant difference in either dissociation constant (Kd) or maximal number of binding sites (Bmax) for (+)-[3H]PN 200-110 in the cerebral cortex, hippocampus, corpus striatum and thalamus between 2VO and sham rats. In addition, in vitro inhibitory effect of nimodipine on cerebral cortical (+)-[3H]PN 200-110 binding in 2VO rats was similar to that in sham rats. Compared to control rats, oral administration of nimodipine to both 2VO and sham rats at 2 months after permanent 2VO brought about a significant increase in Kd values of specific (+)-[3H]PN 200-110 binding in the cerebral cortex, hippocampus, thalamus and myocardium, and the increase in Kd values was much larger in brain regions of 2VO rats than sham rats. However, the increase in Kd values in the myocardium did not differ between 2VO and sham rats. This observation suggests an increased in vivo binding affinity for nimodipine in chronic ischemic brain. In conclusion, the present study has shown that oral administration of nimodipine may cause a greater occupation in vivo of 1,4-dihydropyridine (DHP) calcium channel antagonist receptors in brains of permanent 2VO rats than in sham rats. Thus, nimodipine may be pharmacologically effective in preventing brain dysfunction due to cerebral ischemia in vivo.

Negative chronotropic and inotropic effects of class I antiarrhythmic drugs assessed in isolated canine blood-perfused sinoatrial node and papillary muscle preparations

The present study was designed to assess the negative chronotropic and inotropic effects of 10 class I antiarrhythmic drugs, using isolated canine blood-perfused sinoatrial node and papillary muscle preparations. Each drug showed negative chronotropic and inotropic effects in a dose-related manner. The potency of the suppressive effect on the sinoatrial automaticity was in the order of aprindine, quinidine, flecainide, lidocaine, mexiletine, cibenzoline, disopyramide, procainamide, tocainide, and phenytoin, while the effect on the ventricular contraction was in the order of aprindine, flecainide, cibenzoline, lidocaine, mexiletine, disopyramide, tocainide, phenytoin, quinidine, and procainamide. The differences in the suppressive effects could not necessarily be explained by their subclassification, based either on action potential duration or kinetic properties of dissociation or association with sodium channels. On the other hand, we found a good correlation between the negative inotropic effects of class I drugs in this study and the canine antiarrhythmic plasma concentrations for the digitalis- and coronary ligation-induced ventricular arrhythmia models in our previous studies. However, the negative chronotropic effects of the drugs showed a poor correlation with the antiarrhythmic plasma drug concentrations. The data shown in this paper may provide a convenient guideline for predicting acute cardiosuppressive effects of antiarrhythmic drugs, especially in patients with reduced cardiac function.

Blood-brain barrier transport of 125I-labeled basic fibroblast growth factor

PURPOSE

This study was carried out to examine the blood-brain barrier (BBB) transport of human basic fibroblast growth factor (bFGF) and investigate its mechanism.

METHODS

The BBB transport of 125I-bFGF was measured by several in vivo methods including intravenous administration, in situ internal carotid artery perfusion, and intracerebral microinjection. The in vitro binding of 125I-bFGF was characterized using freshly prepared bovine brain capillaries.

RESULTS

The distribution volume of 125I-bFGF in the postvascular supernatant increased with the perfusion time, and exceeded the space occupied by the brain microvasculature and its trichloroacetic acid (TCA) precipitability was more than 90%. 125I-bFGF avidly bound to isolated bovine brain capillaries with a Bmax of 206 +/- 48 pmol/mg protein, and a Kd of 36.5 +/- 15.7 nM. This binding was significantly inhibited by unlabeled bFGF and heparin in a concentration-dependent manner. The cationic peptides, protamine and poly-L-lysine (each 300 microM), produced over 85% inhibition of 125I-bFGF binding to brain capillaries. Furthermore, glycosaminoglycans with a sulfate residue, chondroitin sulfate B and C (each 10 microg/mL) also inhibited the binding of 125I-bFGF The in vivo transcytosis of 125I-bFGF from the luminal side to the brain was also inhibited by the presence of heparin (10 microg/mL) and poly-L-lysine (300 microM), whereas neither hyaruronic acid (10 microg/mL) nor insulin (10 microM) had any effect. In addition to these results, the brain efflux index method was used to confirm that the transcytosis of 125I-bFGF from brain to blood across the BBB was negligible.

CONCLUSIONS

These results suggest that 125I-bFGF is transported across the BBB, possibly by an adsorptive-mediated transcytosis mechanism that is triggered by binding to negatively charged species on the luminal membrane surface of the brain microvasculature, such as heparan sulfate proteoglycans.

Effect of heavy metals on the growth of a methanogen in pure culture and coculture with a sulfate-reducing bacterium

The sensitivity of a methanogen and sulfate-reducing bacterium isolated from a sea-based landfill site to Cd2+ and Cu2+ was studied. Methanogens and sulfate-reducing bacteria in leachates of the waste disposal site were enumerated using the MPN method. Methanobacterium thermoautotrophicum KHT-2, isolated from the leachate, could not grow at 0.5 mM Cd2+ or 1.0 mM Cu2+. Desulfotomaculum sp. RHT-3, isolated from the same leachate, was able to insolubilize 3.0 mM Cd2+ or 2.0 mM Cu2+ by production of hydrogen sulfide. When strains KHT-2 and RHT-3 were cultured together in the presence of the heavy metals, strain KHT-2 could grow at high heavy metal concentrations after insolubilization of the metals by strain RHT-3.

Brain receptor binding characteristics and pharmacokinetics of JTP-2942, a novel thyrotropin-releasing hormone (TRH) analogue

JTP-2942 competed with [3H]-Me-TRH for the binding sites in rat brain in vitro, and its inhibitory effect was approximately 17 times less potent than TRH, as shown by Ki values of 673 and 39.7 nM, respectively. Both JTP-2942 and TRH significantly increased apparent dissociation constant (Kd values) for brain [3H]-Me-TRH binding. Intravenous injection of JTP-2942 (0.3-3 mg/kg) and TRH (3 and 10 mg/kg) produced a significant reduction of [3H]-Me-TRH binding sites (Bmax values) in rat brain. Although the decrease by TRH was maximal 10 min after the injection and declined rapidly with time, the decrease by JTP-2942 (1 and 3 mg/kg) tended to be maximal at 30 min later and it lasted until 120 min. The intravenous injection of JTP-2942 was at least 3 times more potent than that of TRH in decreasing Bmax values for brain [3H]-Me-TRH binding. Plasma concentration of JTP-2942 (0.3-3 mg/kg) after intravenous injection in rats rose with the increase of dose, and it peaked immediately after the injection, thereafter decreasing with t1/2 of 19.3-29.9 min. It is concluded that JTP-2942, compared to TRH, may exert fairly potent and sustained occupation of brain TRH receptors under in vivo condition. Thus, JTP-2942 could be clinically useful for the treatment of CNS disorders.