Human L-type amino acid transporter 1 (LAT1): characterization of function and expression in tumor cell lines

System L is a major nutrient transport system responsible for the transport of large neutral amino acids including several essential amino acids. We previously identified a transporter (L-type amino acid transporter 1: LAT1) subserving system L in C6 rat glioma cells and demonstrated that LAT1 requires 4F2 heavy chain (4F2hc) for its functional expression. Since its oncofetal expression was suggested in the rat liver, it has been proposed that LAT1 plays a critical role in cell growth and proliferation. In the present study, we have examined the function of human LAT1 (hLAT1) and its expression in human tissues and tumor cell lines. When expressed in Xenopus oocytes with human 4F2hc (h4F2hc), hLAT1 transports large neutral amino acids with high affinity (K(m)= approximately 15- approximately 50 microM) and L-glutamine and L-asparagine with low affinity (K(m)= approximately 1.5- approximately 2 mM). hLAT1 also transports D-amino acids such as D-leucine and D-phenylalanine. In addition, we show that hLAT1 accepts an amino acid-related anti-cancer agent melphalan. When loaded intracellularly, L-leucine and L-glutamine but not L-alanine are effluxed by extracellular substrates, confirming that hLAT1 mediates an amino acid exchange. hLAT1 mRNA is highly expressed in the human fetal liver, bone marrow, placenta, testis and brain. We have found that, while all the tumor cell lines examined express hLAT1 messages, the expression of h4F2hc is varied particularly in leukemia cell lines. In Western blot analysis, hLAT1 and h4F2hc have been confirmed to be linked to each other via a disulfide bond in T24 human bladder carcinoma cells. Finally, in in vitro translation, we show that hLAT1 is not a glycosylated protein even though an N-glycosylation site has been predicted in its extracellular loop, consistent with the property of the classical 4F2 light chain. The properties of the hLAT1/h4F2hc complex would support the roles of this transporter in providing cells with essential amino acids for cell growth and cellular responses, and in distributing amino acid-related compounds.

Vitamin D3 up-regulated protein 1 mediates oxidative stress via suppressing the thioredoxin function

As a result of identifying the regulatory proteins of thioredoxin (TRX), a murine homologue for human vitamin D3 up-regulated protein 1 (VDUP1) was identified from a yeast two-hybrid screen. Cotransfection into 293 cells and precipitation assays confirmed that mouse VDUP1 (mVDUP1) bound to TRX, but it failed to bind to a Cys32 and Cys35 mutant TRX, suggesting the redox-active site is critical for binding. mVDUP1 was ubiquitously expressed in various tissues and located in the cytoplasm. Biochemical analysis showed that mVDUP1 inhibited the insulin-reducing activity of TRX. When cells were treated with various stress stimuli such as H2O2 and heat shock, mVDUP1 was significantly induced. TRX is known to interact with other proteins such as proliferation-associated gene and apoptosis signal-regulating kinase 1. Coexpression of mVDUP1 interfered with the interaction between TRX and proliferation-associated gene or TRX and ASK-1, suggesting its roles in cell proliferation and oxidative stress. To investigate the roles of mVDUP1 in oxidative stress, mVDUP1 was overexpressed in NIH 3T3 cells. When cells were exposed to stress, cell proliferation was declined with elevated apoptotic cell death compared with control cells. In addition, c-Jun N-terminal kinase activation and IL-6 expression were elevated. Taken together, these results demonstrate that mVDUP1 functions as an oxidative stress mediator by inhibiting TRX activity.

Molecular cloning and characterization of multispecific organic anion transporter 4 expressed in the placenta

A cDNA encoding a novel multispecific organic anion transporter, OAT4, was isolated from a human kidney cDNA library. The OAT4 cDNA consisted of 2210 base pairs that encoded a 550-amino acid residue protein with 12 putative membrane-spanning domains. The amino acid sequence of OAT4 showed 38 to 44% identity to those of other members of the OAT family. Northern blot analysis revealed that OAT4 mRNA is abundantly expressed in the placenta as well as in the kidney. When expressed in Xenopus oocytes, OAT4 mediated the high affinity transport of estrone sulfate (K(m) = 1.01 microM) and dehydroepiandrosterone sulfate (K(m) = 0.63 microM) in a sodium-independent manner. OAT4 also mediated the transport of ochratoxin A. OAT4-mediated transport of estrone sulfate was inhibited by several sulfate conjugates, such as p-nitrophenyl sulfate, alpha-naphthyl sulfate, beta-estradiol sulfate, and 4-methylumbelliferyl sulfate. By contrast, glucuronide conjugates showed little or no inhibitory effect on the OAT4-mediated transport of estrone sulfate. OAT4 interacted with chemically heterogeneous anionic compounds, such as nonsteroidal anti-inflammatory drugs, diuretics, sulfobromophthalein, penicillin G, and bile salts, whereas tetraethylammonium, an organic cation, did not. OAT4 is the first member of the multispecific organic anion transporter family, which is expressed abundantly in the placenta. OAT4 might be responsible for the elimination and detoxification of harmful anionic substances from the fetus.

Serotonin transporter gene polymorphism and antidepressant response

We examined allelic polymorphisms of the serotonin transporter (5-HTT) gene and antidepressant response to 6 weeks' treatment with the selective serotonin reuptake inhibitor (SSRI) drugs fluoxetine or paroxetine. We genotyped 120 patients and 252 normal controls, using polymerase chain reaction of genomic DNA with primers flanking the second intron and promoter regions of the 5-HTT gene. Diagnosis of depression was not associated with 5-HTT polymorphisms. Patients homozygous l/l in intron 2 or homozygous s/s in the promoter region showed better responses than all others (p < 0.0001, p = 0.0074, respectively). Lack of the l/l allele form in intron 2 most powerfully predicted non-response (83.3%). Response to SSRI drugs is related to allelic variation in the 5-HTT gene in depressed Korean patients.

Isoform-specific interaction of the alpha1A subunits of brain Ca2+ channels with the presynaptic proteins syntaxin and SNAP-25

Presynaptic Ca2+ channels are crucial elements in neuronal excitation-secretion coupling. In addition to mediating Ca2+ entry to initiate transmitter release, they are thought to interact directly with proteins of the synaptic vesicle docking/fusion machinery. Here we report isoform-specific, stoichiometric interaction of the BI and rbA isoforms of the alpha1A subunit of P/Q-type Ca2+ channels with the presynaptic membrane proteins syntaxin and SNAP-25 in vitro and in rat brain membranes. The BI isoform binds to both proteins, while only interaction with SNAP-25 can be detected in vitro for the rbA isoform. The synaptic protein interaction ("synprint") site involves two adjacent segments of the intracellular loop connecting domains II and III between amino acid residues 722 and 1036 of the BI sequence. This interaction is competitively blocked by the corresponding region of the N-type Ca2+ channel, indicating that these two channels bind to overlapping regions of syntaxin and SNAP-25. Our results provide a molecular basis for a physical link between Ca2+ influx into nerve terminals and subsequent exocytosis of neurotransmitters at synapses that have presynaptic Ca2+ channels containing alpha1A subunits.

Diverse roles of the tumor necrosis factor family member TRANCE in skeletal physiology revealed by TRANCE deficiency and partial rescue by a lymphocyte-expressed TRANCE transgene

Tumor necrosis factor-related, activation-induced cytokine (TRANCE), a tumor necrosis factor family member, mediates survival of dendritic cells in the immune system and is required for osteoclast differentiation and activation in the skeleton. We report the skeletal phenotype of TRANCE-deficient mice and its rescue by the TRANCE transgene specifically expressed in lymphocytes. TRANCE-deficient mice showed severe osteopetrosis, with no osteoclasts, marrow spaces, or tooth eruption, and exhibited profound growth retardation at several skeletal sites, including the limbs, skull, and vertebrae. These mice had marked chondrodysplasia, with thick, irregular growth plates and a relative increase in hypertrophic chondrocytes. Transgenic overexpression of TRANCE in lymphocytes of TRANCE-deficient mice rescued osteoclast development in two locations in growing long bones: excavation of marrow cavities permitting hematopoiesis in the marrow spaces, and remodeling of osteopetrotic woven bone in the shafts of long bones into histologically normal lamellar bone. However, osteoclasts in these mice failed to appear at the chondroosseous junction and the metaphyseal periosteum of long bones, nor were they present in tooth eruption pathways. These defects resulted in sclerotic metaphyses with persistence of club-shaped long bones and unerupted teeth, and the growth plate defects were largely unimproved by the TRANCE transgene. Thus, TRANCE-mediated regulation of the skeleton is complex, and impacts chondrocyte differentiation and osteoclast formation in a manner that likely requires local delivery of TRANCE.

Identification and characterization of a Na(+)-independent neutral amino acid transporter that associates with the 4F2 heavy chain and exhibits substrate selectivity for small neutral D- and L-amino acids

A cDNA was isolated from the mouse brain that encodes a novel Na(+)-independent neutral amino acid transporter. The encoded protein, designated as Asc-1 (asc-type amino acid transporter 1), was found to be structurally related to recently identified mammalian amino acid transporters for the transport systems L, y(+)L, x(C)(-), and b(0,+), which are linked, via a disulfide bond, to the type II membrane glycoproteins, 4F2 heavy chain (4F2hc), or rBAT (related to b(0,+) amino acid transporter). Asc-1 required 4F2hc for its functional expression. In Western blot analysis in the nonreducing condition, a 118-kDa band, which seems to correspond to the heterodimeric complex of Asc-1 and 4F2hc, was detected in the mouse brain. The band shifted to 33 kDa in the reducing condition, confirming that Asc-1 and 4F2hc are linked via a disulfide bond. Asc-1-mediated transport was not dependent on the presence of Na(+) or Cl(-). Although Asc-1 showed a high sequence homology (66% identity at the amino acid level) to the Na(+)-independent broad scope neutral amino acid transporter LAT2 (Segawa, H., Fukasawa, Y., Miyamoto, K., Takeda, E., Endou, H., and Kanai, Y. (1999) J. Biol. Chem. 274, 19745-19751), Asc-1 also exhibited distinctive substrate selectivity and transport properties. Asc-1 preferred small neutral amino acids such as Gly, L-Ala, L-Ser, L-Thr, and L-Cys, and alpha-aminoisobutyric acid as substrates. Asc-1 also transported D-isomers of the small neutral amino acids, in particular D-Ser, a putative endogenous modulator of N-methyl-D-aspartate-type glutamate receptors, with high affinity. Asc-1 operated preferentially, although not exclusively, in an exchange mode. Asc-1 mRNA was detected in the brain, lung, small intestine, and placenta. The functional properties of Asc-1 seem to be consistent with those of a transporter subserving the Na(+)-independent small neutral amino acid transport system asc.

Novel compound 2-methyl-2H-pyrazole-3-carboxylic acid (2-methyl-4-o-tolylazo-phenyl)-amide (CH-223191) prevents 2,3,7,8-TCDD-induced toxicity by antagonizing the aryl hydrocarbon receptor

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a widespread environmental pollutant with many toxic effects, including endocrine disruption, reproductive dysfunction, immunotoxicity, liver damage, and cancer. These are mediated by TCDD binding to and activating the aryl hydrocarbon receptor (AhR), a basic helix-loop-helix transcription factor. In this regard, targeting the AhR using novel small molecule inhibitors is an attractive strategy for the development of potential preventive agents. In this study, by screening a chemical library composed of approximately 10,000 compounds, we identified a novel compound, 2-methyl-2H-pyrazole-3-carboxylic acid (2-methyl-4-o-tolylazo-phenyl)-amide (CH-223191), that potently inhibits TCDD-induced AhR-dependent transcription. In addition, CH-223191 blocked the binding of TCDD to AhR and inhibited TCDD-mediated nuclear translocation and DNA binding of AhR. These inhibitory effects of CH-223191 prevented the expression of cytochrome P450 enzymes, target genes of the AhR. Unlike many known antagonists of AhR, CH-223191 did not have detectable AhR agonist-like activity or estrogenic potency, suggesting that CH-223191 is a specific antagonist of AhR. It is noteworthy that CH-223191 potently prevented TCDD-elicited cytochrome P450 induction, liver toxicity, and wasting syndrome in mice. Taken together, these results demonstrate that this novel compound, CH-223191, may be a useful agent for the study of AhR-mediated signal transduction and the prevention of TCDD-associated pathology.

Major hepatic resection using vascular isolation and hypothermic perfusion

The technique and results of 29 major hepatic resections using the method of complete vascular isolation and hypothermic perfusion of the liver are reported. The method enables the surgeon to perform otherwise difficult or impossible resections through chilled bloodless hepatic parenchyma. Major intrahepatic vascular structures can thus be recognized and controlled readily under clear vision. Direct neoplastic involvement of, or tumor thrombi in the portal vein, hepatic vein or vena cava, can be successfully dealt with by appropriate surgical measures. The operative mortality was 10.3% for this series which included many tumors previously deemed unresectable. The technical detail and intraoperative physiologic monitoring crucial to success in the use of the method are described. It is hoped that with the widened scope of resectability afforded by this technique, and the use of adjuvant chemotherapy, the currently experienced low cure rates for hepatic cancer can be improved.

Expression cloning of a Na+-independent aromatic amino acid transporter with structural similarity to H+/monocarboxylate transporters

A cDNA was isolated from rat small intestine by expression cloning which encodes a novel Na+-independent transporter for aromatic amino acids. When expressed in Xenopus oocytes, the encoded protein designated as TAT1 (T-type amino acid transporter 1) exhibited Na+-independent and low-affinity transport of aromatic amino acids such as tryptophan, tyrosine, and phenylalanine (Km values: approximately 5 mm), consistent with the properties of classical amino acid transport system T. TAT1 accepted some variations of aromatic side chains because it interacted with amino acid-related compounds such as l-DOPA and 3-O-methyl-DOPA. Because TAT1 accepted N-methyl- and N-acetyl-derivatives of aromatic amino acids but did not accept their methylesters, it is proposed that TAT1 recognizes amino acid substrates as anions. Consistent with this, TAT1 exhibited sequence similarity (approximately 30% identity at the amino acid level) to H+/monocarboxylate transporters. Distinct from H+/monocarboxylate transporters, however, TAT1 was not coupled with the H+ transport but it mediated an electroneutral facilitated diffusion. TAT1 mRNA was strongly expressed in intestine, placenta, and liver. In rat small intestine TAT1 immunoreactivity was detected in the basolateral membrane of the epithelial cells suggesting its role in the transepithelial transport of aromatic amino acids. The identification of the amino acid transporter with distinct structural and functional characteristics will not only facilitate the expansion of amino acid transporter families but also provide new insights into the mechanisms of substrate recognition of organic solute transporters.

Development of the Korean versions of WHO Quality of Life scale and WHOQOL-BREF

The purpose of this study was to develop the Korean version of World Health Organization Quality of Life study assessment instrument (WHOQOL) and WHOQOL-BREF, an abbreviated version of WHOQOL and to identify contributing factors in the quality of life of Koreans. The WHOQOL and WHOQOL-BREF were translated into colloquial Korean according to instructions of the WHOQOL study group. Then the Korean questionnaire was applied to 538 subjects, composed of 171 medical patients and 367 healthy subjects who volunteered to rate the scale. Finally, 486 subjects completed the rating. Collected data were analyzed statistically. The Korean version of WHOQOL and WHOQOL-BREF domain scores demonstrated good test-retest reliability, internal consistency, criterion validity, content validity and discriminant validity. The physical, psychological, social and environmental domains made a significant contribution to explaining the variance in the quality of life while the independence and spiritual domains made a lesser contribution. The domain scores produced by the WHOQOL-BREF correlated highly with the WHOQOL. The physical health domain contributed most in overall quality of life, while the social domain made the least contribution. These results suggest that the Korean version of WHOQOL and WHOQOL-BREF are valid and reliable in the assessment of quality of life and that physical domain is contributing most and social and spiritual factors are contributing least to the quality of life in Koreans.

Induction of angiotensin converting enzyme in the neointima after vascular injury. Possible role in restenosis

Angiotensin II (Ang II) promotes growth of vascular smooth muscle cells in vitro. Consistent with this, Ang II enhances neointimal proliferation in vivo after vascular injury, while angiotensin converting enzyme (ACE) inhibitors attenuate this process. Since tissue ACE plays a key role in the control of local Ang II production, we examined whether vascular injury resulted in an increase in vascular ACE expression that may result in increased Ang II production. Abdominal aorta of Sprague-Dawley rats were injured with a 2 French balloon catheter. Morphometrical changes, ACE enzymatic activity, and localization of ACE by immunohistochemistry in injured and uninjured aorta were analyzed. Vascular ACE activity in the injured aorta was significantly higher than in the uninjured aorta, while serum and lung ACE levels were not different between the two groups. The cellular distribution of the ACE protein in the neointima was similar to that of alpha smooth muscle actin but differed from those of endothelial (von Willebrand factor) or monocytes/macrophages (ED-1) markers, demonstrating that ACE was expressed in neointimal smooth muscle cells. These data demonstrate that vascular injury results in the induction of vascular ACE and suggest that the inhibition of vascular ACE may be important in the prevention of restenosis after balloon injury.

Clinical and angiographic follow-up of spontaneous isolated superior mesenteric artery dissection

OBJECTIVES

To observe the clinical features and angiographic findings in patients with a spontaneous isolated superior mesenteric artery dissection (SISMAD) and to identify any correlation between them.

METHODS

From a single institution, 32 patients (22 symptomatic patients at presentation; mean age 54years; men 97%) with SISMAD were retrospectively reviewed. All patients were available for clinical follow-up after treatment (conservative, n=28, 88%, open or endovascular superior mesenteric artery (SMA) reconstruction, n=4, 12%), and follow-up CT scans were available in 28 patients (mean 22months, range 1-80months).

RESULTS

We found a positive correlation between pain severity and dissection length (p=0.03, rho=0.50, Spearman's partial correlation analysis). After conservative treatment, only one patient (3%) required bowel resection, and there was no difference in outcome between patients who were treated with anticoagulation or anti-platelet therapy and those who were not (p=1.00, Fisher's exact test). No patients had progression of their lesion on the follow-up CT angiography.

CONCLUSIONS

In SISMAD patients, dissection length is positively associated with more severe clinical symptoms. After conservative treatment, we observed a benign clinical course and no CT progression of the dissection, even without anticoagulation or anti-platelet therapy. Based on our observation, patients with SISMAD can be treated conservatively without anticoagulation therapy.

Coevolution of the spexin/galanin/kisspeptin family: Spexin activates galanin receptor type II and III

The novel neuropeptide spexin (SPX) was discovered using bioinformatics. The function of this peptide is currently under investigation. Here, we identified SPX along with a second SPX gene (SPX2) in vertebrate genomes. Syntenic analysis and relocating SPXs and their neighbor genes on reconstructed vertebrate ancestral chromosomes revealed that SPXs reside in the near vicinity of the kisspeptin (KISS) and galanin (GAL) family genes on the chromosomes. Alignment of mature peptide sequences showed some extent of sequence similarity among the 3 peptide groups. Gene structure analysis indicated that SPX is more closely related to GAL than KISS. These results suggest that the SPX, GAL, and KISS genes arose through local duplications before 2 rounds (2R) of whole-genome duplication. Receptors of KISS and GAL (GAL receptor [GALR]) are phylogenetically closest among rhodopsin-like G protein-coupled receptors, and synteny revealed the presence of 3 distinct receptor families KISS receptor, GALR1, and GALR2/3 before 2R. A ligand-receptor interaction study showed that SPXs activate human, Xenopus, and zebrafish GALR2/3 family receptors but not GALR1, suggesting that SPXs are natural ligands for GALR2/3. Particularly, SPXs exhibited much higher potency toward GALR3 than GAL. Together, these results identify the coevolution of SPX/GAL/KISS ligand genes with their receptor genes. This study demonstrates the advantage of evolutionary genomics to explore the evolutionary relationship of a peptide gene family that arose before 2R by local duplications.

Effects of direct-fed microbials on growth performance, gut morphometry, and immune characteristics in broiler chickens

This study was conducted to compare growth performance, gut morphometry, and parameters of local and systemic immunity in broiler chickens fed for 22 consecutive days with a diet supplemented with Bacillus spp. as direct-fed microbials (DFM), a commercial product incorporating 3 DFM, or a nonsupplemented diet. Direct-fed microbials did not significantly modify BW gain and most failed to affect serum antibody levels in response to immunization with a recombinant Eimeria protein. However, altered intestinal morphometric measurements were readily apparent in DFM-fed chickens as revealed by increased villus height and crypt depth compared with non-DFM-fed controls. In addition, serum levels of alpha-1-acid glycoprotein as an inflammatory marker were reduced in DFM-fed birds, whereas splenic lymphocyte proliferation, intestine intraepithelial lymphocyte subpopulations, and cytokine mRNA levels in intraepithelial lymphocytes were increased, decreased, or unchanged compared with controls depending on the DFM used. These results provide a rational scientific basis for future studies to investigate DFM as immunomodulating agents to enhance host protective immunity against enteric pathogens in broiler chickens.

Major hepatic resection for neoplasia: personal experience in 108 patients

One hundred eight patients have undergone major hepatic resection by the senior author during the eight year period April 1970 to April 1978. Primary liver cancer was present in 36; metastatic colorectal cancer in 25, miscellaneous metastatic cancers in 15, hepatoblastoma in 5, gallbladder cancer in 4, and bile duct cancer in 3. Benign tumors, principally giant hemangioma, were resected in 20 additional patients. The 30 day operative mortality rate was 9% overall. Prior to 1975, 41 of the resections were done using the vascular isolation perfusion technique. The operative mortality rate of 17% for this technique is a reflection of early experience and the advanced stage of disease of many patients. The operative mortality for the standard resection has been only 4%. Subphrenic abscess has developed in only 13% of patients during the past three years. Postoperative hospitalization has been shortened, being a median of 13 days. The resectability rate for malignant disease was 33%. Forty-six percent of the resections were performed with curative intent. Fifty-four per cent were palliative, performed in individuals with regional spread or distant metastasis. After curative surgery, three year survival was 88% for individuals with primary liver cancer and 72% with metastatic colorectal cancer. After palliative resection, the rates were 31 and 0%, respectively. The three year survival rate is 46% overall, being 81% for the curative resection group and 18% for the palliative group. Tumor markers proved useful in monitoring patients after hepatic resection.

Podocyte biology in diabetic nephropathy

Glomerular visceral epithelial cells, namely podocytes, are highly specialized cells and give rise to primary processes, secondary processes, and finally foot processes. The foot processes of neighboring podocytes interdigitate, leaving between them filtration slits. These are bridged by an extracellular substance, known as the slit diaphragm, which plays a major role in establishing size-selective barrier to protein loss. Furthermore, podocytes are known to synthesize matrix molecules to the glomerular basement membrane (GBM), including type IV collagen, laminin, entactin, and agrin. Because diabetic nephropathy is clinically characterized by proteinuria and pathologically by glomerular hypertrophy and GBM thickening with foot process effacement, podocytes have been the focus in the field of research on diabetic nephropathy. As a result, many investigations have demonstrated that the diabetic milieu per se, hemodynamic changes, and local growth factors such as transforming growth factor-beta and angiotensin II, which are considered mediators in the pathogenesis of diabetic nephropathy, induce directly and/or indirectly hypertrophy, apoptosis, and structural changes, and increase type IV collagen synthesis in podocytes. This review explores some of the structural and functional changes of podocytes under diabetic conditions and their role in the development and progression of diabetic nephropathy.

Regional pancreatectomy: en bloc pancreatic, portal vein and lymph node resection

Eighteen patients are reported who have had a regional pancreatectomy. The pancreatic segment of portal vein was excised with en bloc total pancreatectomy and regional lymph node dissection in all 18. Venous repair was by end-to-end anastomosis without a graft. Five of the 18 also had various arterial resections and reconstructions. Sixteen of the 18 had been explored and deemed nonresectable elsewhere. This operation has doubled the resectability rate in this institution. The 30-day operative mortality rate was 16.6%. Acurarial survival is 62% at one year compared with 36% one year survival rate for patients undergoing pancreaticoduodenectomy for less advanced cancer in previous years. A more valid comparison would be between those who had a palliative procedure since most patients in the present series were initially considered unresectable. One year survival for these patients was 22%. The quality of life was good for most patients.

Altered nociceptive response in mice deficient in the alpha(1B) subunit of the voltage-dependent calcium channel

Calcium influx through N-type calcium channels mediates synaptic transmission at numerous central synapses and transduces nociceptive information in the spinal dorsal horn. However, the precise role of N-type calcium channels in pain perception is not fully elucidated. To address this issue, we generated and analyzed knockout mice for alpha(1B,) the pore-forming subunit of the N-type calcium channel. Homozygous mutants are viable, fertile, and show normal motor coordination. In small-diameter dorsal root ganglion neurons from mutants the density of calcium channel currents is significantly reduced, which can be accounted for by the abolition of N-type currents. We performed several pain-related behavioral tests using the mutant mice. alpha(1B)-Deficient mice show reduced response to mechanical stimuli in the von Frey test and increased tail flick latency in response to radiant heat, indicating altered spinal reflexes. However, pain response in the hot plate test is normal. In the formalin paw test, the mutant mice exhibit significantly attenuated response in Phase 2, but normal pain behaviors in Phase 1. The response to visceral inflammatory pain caused by acetic acid is also reduced in alpha(1B) knockout mice. These results suggest that the alpha(1B) subunit of N-type calcium channel plays a major role in pain perception by acting at the spinal level, but not at the supraspinal level.

Altered serotonin synthesis, turnover and dynamic regulation in multiple brain regions of mice lacking the serotonin transporter

To evaluate the consequences of inactivation of the serotonin transporter (SERT) gene on 5-HT homeostasis and function, 5-HT synthesis and turnover rates were measured using the decarboxylase inhibition method in multiple brain regions (frontal cortex, striatum, brainstem, hippocampus and hypothalamus) from mice with a genetic disruption of SERT. 5-HT synthesis rates were increased 30-60% in the different brain regions of SERT -/- mice compared to littermate +/+ control mice despite 55-70% reductions in tissue 5-HT concentrations. Brain regions that possessed a greater capacity to increase synthesis and turnover (frontal cortex, striatum) demonstrated lesser reductions in tissue 5-HT. Female SERT -/- mice had greater increases (79%) in brain 5-HT synthesis than male -/- mice did (25%), a finding associated with higher brain tryptophan concentrations in females. Despite increased 5-HT synthesis, there was no change in either TPH2 or TPH1 mRNA levels or in maximal in vitro TPH activity in the brainstem of SERT -/- mice. Catecholamine homeostasis as reflected in brain tissue concentrations and in synthesis and turnover of dopamine and norepinephrine was unchanged in SERT -/- mice. Taken together, the results demonstrate a markedly altered homeostatic situation in SERT -/- mice that lack 5-HT reuptake, resulting in markedly depleted tissue stores that are inadequately compensated for by increased 5-HT synthesis, with brain region and gender specificity observed.

Human cystine/glutamate transporter: cDNA cloning and upregulation by oxidative stress in glioma cells

A human cDNA for amino acid transport system x(C)(-) was isolated from diethyl maleate-treated human glioma U87 cells. U87 cells expressed two variants of system x(C)(-) transporters hxCTa and hxCTb with altered C-terminus regions probably generated by the alternative splicing at 3'-ends. Both hxCTa and hxCTb messages were also detected in spinal cord, brain and pancreas, although the level of hxCTb expression appears to be lower than that of hxCTa in these tissues. When expressed in Xenopus oocytes, hxCTb required the heavy chain of 4F2 cell surface antigen (4F2hc) and exhibited the Na(+)-independent transport of L-cystine and L-glutamate, consistent with the properties of system x(C)(-). In agreement with this, 137 kDa band was detected by either anti-xCT or anti-4F2hc antibodies in the non-reducing condition in western blots, whereas it shifted to 50 kDa or 90 kDa bands in the reducing condition, indicating the association of two proteins via disulfide bands. We found that the expression of xCT was rapidly induced in U87 cells upon oxidative stress by diethyl maleate treatment, which was accompanied by the increase in the L-cystine uptake by U87 cells. Because of this highly regulated nature, xCT in glial cells would fulfill the task to protect neurons against oxidative stress by providing suitable amount of cystine to produce glutathione.

Analysis of water-macromolecule proton magnetization transfer in articular cartilage

These studies were designed to establish which structural elements of cartilage are responsible for proton magnetization transfer between water (Hf) and macromolecules (Hr) observed in MRI studies on articular cartilage. Saturation transfer techniques were used to monitor magnetization transfer in vitro on samples of the two major constituents of cartilage: collagen and proteoglycan. Articular cartilage samples were also evaluated in vitro before and after the removal of the proteoglycan fraction. Isolated hydrated collagen exhibited a significant proton magnetization transfer rate with water. In contrast, proteoglycans exhibited no proton magnetization transfer. Articular cartilage, in vitro, exhibited a high degree of magnetization transfer with water protons consistent with previous MRI studies in vivo. Enzymatic removal of proteoglycan from the cartilage did not alter the magnetization transfer rate between Hr and Hf. These data demonstrate that the structure and concentration of the collagen matrix are the predominant determinants of the magnetization transfer process in articular cartilage with little or no contribution from proteoglycans. This specificity of the magnetization transfer effect may prove useful in the noninvasive evaluation of cartilage composition and structure in vivo.

Takayasu's arteritis: assessment of disease activity with contrast-enhanced MR imaging

OBJECTIVE

The purpose of this study was to evaluate the role of contrast-enhanced MR imaging in the determination of disease activity in patients with Takayasu's arteritis.

SUBJECTS AND METHODS

High-resolution contrast-enhanced T1-weighted spinecho MR imaging using small fields of view (14-20 cm) and thin slices (4-5 mm) was performed in 26 patients with Takayasu's arteritis and 16 healthy subjects. The degree of aortic mural enhancement was assessed by measuring signal intensity and by visually estimating it in comparison with that of the myocardium.

RESULTS

Contrast-enhanced MR imaging showed more enhancement of thickened aortic wall compared with myocardium, thus suggesting active Takayasu's arteritis on MR imaging in 16 patients. Determination of disease activity using contrast-enhanced MR imaging was concordant with clinical findings in 23 patients (88.5%). Contrast-enhanced MR findings were concordant with laboratory findings in most patients (erythrocyte sedimentation rate in 92.3% [24/26] and C-reactive protein in 84.6% [22/26]). The measured signal intensity of the aortic wall relative to that of myocardium during the early phase of contrast-enhanced MR imaging correlated well with the erythrocyte sedimentation rate (r = 0.78, p < 0.005) and with the C-reactive protein level (r = 0.63, p < 0.005).

CONCLUSION

Contrast-enhanced MR imaging provides information about disease activity of Takayasu's arteritis, which may be useful in the diagnosis and treatment of Takayasu's arteritis.

Expression of a system L neutral amino acid transporter at the blood-brain barrier

Amino acid transport system L has been proposed to be one of the major nutrient transport systems at the blood-brain barrier. Using immunohistochemical analyses, a system L transporter LAT1 was shown to be expressed in the brain capillary endothelial cells in rats. Because LAT1 was coexpressed with 4F2 heavy chain which brings LAT1 to the plasma membrane, LAT1 is proposed to be functional in the plasma membrane of brain capillary endothelial cells. Both LAT1 and 4F2hc immunoreactivities were detected in a double line appearance surrounding endothelial cell nuclei, suggesting both proteins are present in the luminal and abluminal membranes. LAT1 is, thus, a blood-brain barrier system L transporter responsible for the permeation of aromatic or branched-chain amino acids and amino acid-related drugs such as L-DOPA.