Search PubMed⌕ Search

Biomedical subjects

R Kannan

Publications and source records attributed to R Kannan.

At least 37 records · Page 2Linked to original sources
PubMed1999

Protection from oxidant injury by sodium-dependent GSH uptake in retinal Müller cells.

Glutathione (GSH) is known to play an important role in regulating oxidative damage to cells. The present study was initiated to examine the effect of exogenous GSH on oxidative injury in a retinal Müller cell line and to characterize GSH transport in these cells. Rat Müller cells (rMC-1) were incubated with varying concentrations of t-butylhydroperoxide (t-BHP) to induce oxidative stress, and cell viability was measured after addition of GSH. In other studies, kinetics of GSH uptake and Na+-dependency were examined by incubating cells with35S-GSH in Na+-containing and Na+-free buffers. GSH uptake was studied with GSH at concentrations varying from 0. 05-10 m m in NaCl buffer. In the presence of sodium, extracellular GSH provided protection against t-BHP-induced oxidant injury to rMC-1 cells; in contrast, the amino acid precursors of GSH did not have any effect on cell viability. GSH was taken up by rMC-1 cells in a concentration- and sodium-dependent manner. Kinetic studies revealed both a high affinity (Km approximately 0.31 m m) and low affinity Km( approximately 4.2 m m) component. Furthermore, GSH depletion had no significant effect on the rate of GSH uptake. The results show that physiological concentrations of GSH can protect Müller cells from oxidative injury. Both Na+-dependent and Na+-independent transport systems for GSH exist in Müller cells, and the Na+-dependent GSH transporter may be involved in the protective role of GSH.

Animals↗
PubMed1999

Purification of active matrix metalloproteinase catalytic domains and its use for screening of specific stromelysin-3 inhibitors.

The matrix metalloproteinase (MMP) stromelysin-3 (ST3) has been shown to be involved in malignant tumor progression and therefore represents an attractive therapeutical target. In order to screen for ST3 synthetic inhibitors, we have produced and purified the catalytic domain of ST3, matrilysin, stromelysin-2, and membrane type-1 MMP from inclusion bodies in a bacterial system. Our strategy allowed the purification of MMPs directly in the active form, thereby avoiding in vitro activation. A total of 140,000 synthetic compounds from the Bristol-Myers Pharmaceutical Research Institute chemical deck were tested, using a substrate-based colorimetric enzymatic assay, in which ST3 activity was evaluated through its ability to cleave and inactivate alpha-1 proteinase inhibitor. One ST3 inhibitor belonging to the cephalosporin family of antibiotics was thereby identified.

Animals↗
PubMed1999

GSH transport in immortalized mouse brain endothelial cells: evidence for apical localization of a sodium-dependent GSH transporter.

We have previously shown GSH transport across the blood-brain barrier in vivo and expression of transport in Xenopus laevis oocytes injected with bovine brain capillary mRNA. In the present study, we have used MBEC-4, an immortalized mouse brain endothelial cell line, to establish the presence of Na+-dependent and Na+-independent GSH transport and have localized the Na+-dependent transporter using domain-enriched plasma membrane vesicles. In cells depleted of GSH with buthionine sulfoximine, a significant increase of intracellular GSH could be demonstrated only in the presence of Na+. Partial but significant Na+ dependency of [35S]GSH uptake was observed for two GSH concentrations in MBEC-4 cells in which gamma-glutamyltranspeptidase and gamma-glutamylcysteine synthetase were inhibited to ensure absence of breakdown and resynthesis of GSH. Uniqueness of Na+-dependent uptake in MBEC-4 cells was confirmed with parallel uptake studies with Cos-7 cells that did not show this activity. Molecular form of uptake was verified as predominantly GSH, and very little conversion of [35S]cysteine to GSH occurred under the same incubation conditions. Poly(A)+ RNA from MBEC expressed GSH uptake with significant (approximately 40-70%) Na+ dependency, whereas uptake expressed by poly(A)+ RNA from HepG2 and Cos-1 cells was Na+ independent. Plasma membrane vesicles from MBEC were separated into three fractions (30, 34, and 38% sucrose, by wt) by density gradient centrifugation. Na+-dependent glucose transport, reported to be localized to the abluminal membrane, was found to be associated with the 38% fraction (abluminal). Na+-dependent GSH transport was present in the 30% fraction, which was identified as the apical (luminal) membrane by localization of P-glycoprotein 170 by western blot analysis. Localization of Na+-dependent GSH transport to the luminal membrane and its ability to drive up intracellular GSH may find application in the delivery of supplemented GSH to the brain in vivo.

Animals↗
PubMed1999

Corneal transport of circulating glutathione in normal and galactosemic guinea pigs.

PURPOSE: To study synthesis and transport of glutathione (GSH) in guinea-pig cornea and to determine the effect of galactose feeding and growth on transport. METHODS: Steady-state level and maximal rate of synthesis of GSH (GSH-SR) were determined in guinea pigs fed 50% galactose diet for 10 days and in controls. By using a model of in situ eye perfusion, corneal transport of [35S]GSH (4 nM) and [14C]sucrose was measured as a function of time (1-10 min) in normal guinea pigs under gamma-glutamyltranspeptidase (GGT)-inhibited and uninhibited conditions. The unidirectional constant of GSH uptake was determined as a function of GSH concentration in the perfusate. The effect of galactose feeding on corneal uptake of tracer GSH was determined in control and 10-day galactose-fed guinea pigs. Levels of GSH and uptake of GSH also were measured in corneas from three different age groups: 10 days, 4 weeks, and 9 months. RESULTS: The mean GSH level (nmol/ mg protein) in corneas of control guinea pigs was 47.6, which decreased to 36.4 (p<0.05) in 10-day galactose-fed animals. The GSH-SR was not significantly different in the two groups (1.98 vs. 2.27 nmol/min/mg protein, respectively; p = NS). Corneal uptake of tracer [35S]GSH (4 nM) was linear up to 10 min and was several-fold higher than that of the impermeable marker [14C]sucrose. The unidirectional rate constant (corrected for sucrose) for GSH was 4.03+/-0.21x10(-3)/min. GSH uptake in normal guinea pigs occurred by a saturable process with a Km of 24+/-4 microM and Vmax of 92+/-14 pmol/min/g and was significantly inhibited by GSH and GSH monoethyl ester at 60 microM concentrations. Corneal uptake of tracer GSH in galactose-fed guinea pigs showed a dramatic decrease (almost to that of sucrose) as compared with control guinea pigs. GSH uptake was similar in corneas of 10-day and 4-week-old guinea pigs, whereas that in 9-month-old guinea pigs showed a significant (approximately 80%) decrease in uptake. CONCLUSION: Cellular uptake of GSH by the cornea in the young, adult guinea pigs is carrier mediated via mechanism(s) that can be dissociated from the transpeptidation pathway. The reduced availability of circulating GSH may be an important factor in the development of corneal pathology associated with aging and corneal hydration due to relative GSH deficiency.

Aging↗
PubMed1999

Regulation of gamma-glutamylcysteine synthetase subunit gene expression in retinal Müller cells by oxidative stress.

PURPOSE: To study regulation of gamma-glutamylcysteine synthetase (GCS) heavy and light subunit gene expression in Müller cells under conditions of oxidative stress. METHODS: Experiments were carried out with an SV40 transformed cell line (rMC-1) that exhibits the phenotype of rat retinal Müller cells. Endogenous glutathione levels were modified by treating cells with diethyl maleate (DEM), D,L-buthionine sulfoximine (BSO), or tert-butylhydroquinone (TBH). In other experiments, cells were grown in either high (28 mM) or normal (5.5 mM) glucose medium for 1 week to examine the effects of hyperglycemia. Cells were processed for reduced glutathione (GSH) measurement, RNA extraction, cell count, and, in some cases, lactate dehydrogenase activity. The steady state mRNA levels of GCS heavy and light subunits were measured by northern blot analysis using specific cDNA probes. Changes in mRNA levels were normalized to beta-actin or 18S rRNA. RESULTS: Treatment with DEM for 30 minutes depleted cell GSH to 20% to 30% of the normal value. GSH content recovered completely 6 hours after returning to normal medium. BSO treatment for 12 hours followed by a medium change for 6 hours resulted in a cell GSH level that was 26% that of untreated cells. If cells were left in BSO for 18 hours, however, GSH levels were reduced to < 1%. Treatment with TBH for 12 hours led to a 77% increase in cellular GSH level. Treatment with DEM, TBH, or BSO for 18 hours led to a significant induction of the mRNA level of the GCS subunits, regardless of glucose concentration in the medium. Shorter BSO treatment exerted no effect. Prolonged hyperglycemia resulted in 30% lower GSH level, 55% lower GCS heavy subunit, and 30% lower GCS light subunit mRNA levels. CONCLUSIONS: Oxidative stress induced the gene expression of GCS heavy and light subunits in Müller cells. The effect of BSO on mRNA levels correlated with the degree of GSH depletion. Prolonged hyperglycemia lowered GCS subunit mRNA and GSH levels.

Animals↗
PubMed1999

Hyperthyroidism due to papillary carcinoma of the thyroid--a case report.

A rare case of papillary carcinoma of the thyroid producing hyperthyroidism is presented. A young patients presented seven years after a thyroid operation with metastatic disease in the cervical lymph nodes and a history of deteriorating vision in the left eye. He also had a lesion in the base of the skull which could not be established to be metastasis from the thyroid cancer. There was clinical and biochemical evidence of hyperthyroidism. Radionuclide scan revealed uptake in the residual thyroid tissue and patchy uptake by the cervical lymph nodes. The patient underwent a complete thyroidectomy and radical neck dissection of the left side and 'berry-picking' of the lymph nodes on the right side. Although the patient became euthyroid post-operatively, his general condition deteriorated and he rapidly lost vision in both eyes before any ablative therapy could be instituted for the tumour in the base of the skull. The patient was lost to follow-up.

Adult↗
PubMed1998

Membrane type-1 matrix metalloprotease and stromelysin-3 cleave more efficiently synthetic substrates containing unusual amino acids in their P1' positions.

The influence of the substrate P1' position on the specificity of two zinc matrix metalloproteases, membrane type-1 matrix metalloprotease (MT1-MMP) and stromelysin-3 (ST3), was evaluated by synthesizing a series of fluorogenic substrates of general formula dansyl-Pro-Leu-Ala-Xaa-Trp-Ala-Arg-NH2, where Xaa in the P1' position represents unusual amino acids containing either long arylalkyl or alkyl side chains. Our data demonstrate that both MT1-MMP and ST3 cleave substrates containing in their P1' position unusual amino acids with extremely long side chains more efficiently than the corresponding substrates with natural phenylalanine or leucine amino acids. In this series of substrates, the replacement of leucine by S-para-methoxybenzyl cysteine increased the kcat/Km ratio by a factor of 37 for MT1-MMP and 9 for ST3. The substrate with a S-para-methoxybenzyl cysteine residue in the P1' position displayed a kcat/Km value of 1.59 10(6) M-1 s-1 and 1.67 10(4) M-1 s-1, when assayed with MT1-MMP and ST3, respectively. This substrate is thus one of the most rapidly hydrolyzed substrates so far reported for matrixins, and is the first synthetic peptide efficiently cleaved by ST3. These unexpected results for these two matrixins suggest that extracellular proteins may be cleaved by matrixins at sites containing amino acids with unusual long side chains, like those generated in vivo by some post-translational modifications.

Amino Acids↗
PubMed1998

Amebic liver abscess with jaundice.

A case of an amebic liver abscess with unusual clinical manifestations is presented. A middle-aged male with an abscess in both lobes of the liver presented with obstructive jaundice due to pressure on the porta hepatis with stasis of the bile in the intrahepatic biliary radicals. The patient did not respond to repeated needle aspirations and thus required open drainage. Subsequently, the patient developed a biliary leak through the drainage sites, and an injection of contrast dye into the cavity revealed a communication between the abscess cavities and the biliary tree. The biliary leak stopped spontaneously, and the large cavities also closed completely during the followup period.

Biliary Tract↗
PubMed1998

Glutathione transport in immortalized HLE cells and expression of transport in HLE cell poly(A)+ RNA-injected Xenopus laevis oocytes.

PURPOSE: To determine reduced glutathione (GSH) transport in cultured human lens epithelial cells (HLE-B3) and plasma membrane vesicles and to study the expression of GSH transport in Xenopus laevis oocytes injected with poly(A)+ RNA from HLE-B3 cells. METHODS: Confluent HLE-B3 cells pretreated with 10 mM DL-buthionine sulfoximine and 0.5 mM acivicin were used in GSH uptake studies. The uptake of 35S-GSH was performed for 30 minutes in either NaCl medium (Na+-containing) or choline chloride medium (Na+-free) at 37 degrees C and 4 degrees C. The molecular form of 35S uptake was determined by high-performance liquid chromatography. GSH uptake kinetics were studied in acivicin and buthionine sulfoximine-treated HLE-B3 cells in NaCl medium in the concentration range 0.01 microM to 50 mM. The transport of GSH and the effect of Na+ on uptake also were determined in mixed plasma membrane vesicles from HLE-B3 cells. In oocyte expression studies, HLE-B3 poly(A)+ RNA was injected into X. laevis oocytes and GSH uptake experiments were performed 3 days after injection. The uptake of 35S-GSH and GSH efflux rates were determined in HLE-B3 poly(A)+ RNA-injected oocytes. RESULTS: No significant difference was found in the uptake of 1 mM GSH+/-acivicin (17.7+/-4.3 versus 15.7+/-1.4 picomoles/min(-1) per 10(6) cells). However, GSH uptake was significantly lower in Na+-free medium compared with Na+-containing medium (10.3+/-0.7 versus 16.8+/-0.9 picomoles/min(-1) per 10(6) cells; P < 0.01). GSH uptake in NaCl medium was carrier mediated. GSH uptake showed partial sodium dependency from 5 microM to 5 mM GSH in mixed plasma membrane vesicles from HLE-B3 cells. Oocytes injected with HLE-B3 poly(A) RNA expressed uptake and efflux of GSH. Uptake showed partial Na+ dependency at various GSH concentrations. The efflux rates were approximately 30-fold higher than those in water-injected oocytes (0.48+/-0.03 versus 0.016+/-0.005 (nanomoles per hour(-1) per oocyte, respectively). The molecular form of uptake in cultured cells and in oocyte studies was predominantly as intact GSH. CONCLUSIONS: HLE-B3 cells and plasma membrane vesicles transported GSH by a carrier-mediated process. HLE-B3 poly(A)+ RNA injected X laevis oocytes expressed GSH transport. GSH uptake was partially Na+ dependent in all systems. HLE-B3 cells offer a useful model for characterizing GSH transport and for studying its regulatory role in the etiology of cataracts.

Animals↗
PubMed1997

Low de novo glutathione synthesis from circulating sulfur amino acids in the lens epithelium.

Transport of circulating sulfur amino acids (SAA) into the lens epithelium and de novo glutathione (GSH) synthesis were studied in the perfused guinea-pig eye. Plasma-to-aqueous transfer of SAA was in their intact form (> or = 98%) and comparable with sucrose (an extracellular marker) within 30 min. The unidirectional transport rates (ml min-1 g-1) of 35S-labeled cystine, cystine and methionine into the epithelium were: 0.0057, 0.0003 and 0.0073 from plasma, and 1.41, 0.005 and 1.69 from aqueous, respectively. The unidirectional epithelial uptake was limited to 1 min for all three [35S]SAA, and the isotopic steady-state ratio was achieved between 1 and 30 min. Cortical uptake was time-dependent and progressive between 1 and 30 min, but undetectable within 1 min. The high performance liquid chromatography (HPLC) analysis of the epithelium revealed that following 1 min of unidirectional [35S]cysteine transport, 3% of the label was incorporated into GSH and > or = 95% was as cysteine. An average incorporation of [35S]cysteine into GSH within the 30 min period was 0.83% min-1 and 1%/min for the epithelium and cortex, respectively. Infusions of [35S]cystine and methionine failed to demonstrate incorporation into GSH. Maximal rates of de novo GSH epithelial synthesis were approximately 3 and 12 pmol g-1 from plasma and aqueous cysteine, respectively. A t1/2 of 5480 hr was estimated if epithelial GSH had to be replaced exclusively by synthesis from aqueous cysteine. Given the limited aqueous and epithelial cysteine pools, and low (from cysteine) or undetectable (from cystine and methionine) incorporation of the label into GSH, we conclude that de novo GSH synthesis from circulating and aqueous SAA can be only a minor source of the millimolar concentration of GSH in the epithelium.

Amino Acids, Sulfur↗
PubMed1997

High-level expression of the prohormones proenkephalin, pro-neuropeptide Y, proopiomelanocortin, and beta-protachykinin for in vitro prohormone processing.

Prohormone substrates are required for investigation of the proteolytic processing of prohormones and proproteins into active peptide hormones and neurotransmitters. However, the lack of prohormone proteins has been a limiting factor in elucidating proteolytic mechanisms for conversion of prohormones into active peptides. Therefore, in this study, cloned cDNAs encoding the prohormones proenkephalin (PE), pro-neuropeptide Y (pro-NPY), pro-opiomelanocortin (POMC), and beta-protachykinin (beta-PT) were utilized to express recombinant prohormones in Escherichia coli. High-level expression of milligrams of prohormones was achieved with the pET3c expression vector utilizing the T7 promoter for production of PE, pro-NPY, and POMC, as demonstrated by SDS-PAGE gel electrophoresis, Western blots, and 35S-methionine labeling. In addition, beta-PT was expressed at high levels as fusion proteins with the maltose-binding protein and glutathione S-transferase by the pMAL-c and pGEX-2T expression vectors, respectively. Relative rates of processing by the established processing proteases "prohormone thiol protease" (PTP), 70-kDa aspartyl protease, and PC1/ 3 and PC2 (PC, prohormone convertase) were examined with purified PE, pro-NPY, and POMC. Distinct preferences of processing enzymes for different prohormones was demonstrated. PTP preferred PE and pro-NPY substrates, whereas little processing of POMC was detected. In contrast, the 70-kDa aspartyl protease cleaved POMC more readily than pro-NPY or PE. However, PC1/3 and PC2 prefer POMC as substrate. Demonstration of selectivity of processing enzymes for prohormone substrates illustrates the importance of expressing recombinant prohormones for in vitro processing studies.

Animals↗
PubMed1997

Matrix metalloproteinases as stromal effectors of human carcinoma progression: therapeutic implications.

The matrix metalloproteinases (MMPs) are extracellular zinc-enzymes implicated in a number of physiological and pathological tissue remodeling processes, including cancer progression. For a long time they have been thought to be produced by malignant cells and to specifically contribute to tumor invasion, through their ability to degrade extracellular matrix components. However, studies performed over the last few years have demonstrated that extracellular proteinases implicated in the progression of human carcinomas, including most MMPs, are in fact predominantly expressed by stromal and not by cancer cells. Furthermore, membrane receptors, activators and/or binding sites for some of these proteinases are also predominantly found to be associated with stromal cells. These findings, together with the observation that MMPs can cleave some molecules implicated in controlling growth factor activities, suggest that the role of MMPs during cancer progression is not limited to facilitating malignant cell invasion alone but is also likely to participate in other aspects of the malignant phenotype. MMPs should in fact be regarded as pan-regulators of tissue neoformation characteristic of malignant tumors, which includes both epithelial cell expansion and stroma formation. In this context, synthetic MMP inhibitors which are presently designed should lead to the development of a new generation of anticancer agents with additional beneficial properties compared to the existing cytotoxic agents used in the treatment of human malignancies.

Extracellular Matrix↗
PubMed1997

Liver and lens glutathione and cysteine regulation in galactose-fed guinea pigs.

PURPOSE: To study the mechanism of lenticular glutathione (GSH) depletion in galactose-fed guinea pigs, with particular reference to correlations between liver and lens GSH, precursor (cysteine) status and GSH synthetic capacities. METHODS: Guinea pigs in the ad libitum-fed state were fed powdered guinea pig chow containing 50% galactose for 3 and 14-16 days. Plasma GSH and GSH levels in lens, liver and freshly isolated hepatocytes were determined. Maximal rates of GSH synthesis in liver and lens as well as steady state levels of precursor cysteine were also determined. In separate experiments, linear rate of 35S-cysteine uptake was studied in isolated hepatocytes from control and galactose-fed animals. Lens and liver GSH decreased significantly with galactose feeding. Hepatic GSH showed a dramatic decrease (approximately 83%) as early as day 3 whereas approximately 43% decrease was observed in lens. The maximal GSH synthetic rates (GSH-SR) in the whole lens and liver on days 3 and 14-16 were not different from those of controls. Steady-state levels of cysteine also decreased in both tissues with galactose feeding, and the magnitude of decrease was higher in the liver as compared to the lens. The rate of cysteine uptake in hepatocytes isolated from galactose-fed guinea pigs was significantly lower for the cysteine concentrations studied (10 microM to 1 mM) as compared to control uptake. The decreased steady-state liver GSH and cysteine levels in galactose-fed guinea pigs caused a significant decrease in plasma (and aqueous) GSH concentrations. CONCLUSIONS: We concluded that the decrease in lens GSH due to galactose occurs without alterations in the capacity of GSH synthesis, in either lens or liver. It is suggested that decreased hepatic GSH, resulting in reduced plasma GSH levels due to decreased GSH efflux into plasma, may contribute to impairment in plasma to lens GSH transport with galactose. Thus, the functional role of recently identified lens GSH transporters, particularly that of Na(+)-dependent GSH transporter, in galactose-induced cataract formation will be worthy of investigation.

Animals↗
PubMed1996

SNAP-25 is differentially expressed by noradrenergic and adrenergic chromaffin cells.

This study examines chromaffin cell expression of the synaptosomal-associated protein SNAP-25 in the adrenal medulla by immunoblotting, immunocytochemistry and PCR. Both mRNAs coding for the SNAP-25 isoforms a and b were detected and SNAP-25 was found to be present in all chromaffin cells in adult rat adrenal gland sections. It was essentially restricted to a zone close to the cytoplasmic face of the plasma membrane in the majority of cells, but located extensively throughout the cytoplasm in a chromaffin cell sub-population, identified by double immunofluorescence labelling to have a noradrenergic phenotype. This differential SNAP-25 expression may reflect different stages in the phenotypic development of the sympathoadrenal lineage and be related to an additional functional role in noradrenergic chromaffin cells not associated with secretion.

Adrenal Medulla↗
PubMed1996

Evidence for the existence of a sodium-dependent glutathione (GSH) transporter. Expression of bovine brain capillary mRNA and size fractions in Xenopus laevis oocytes and dissociation from gamma-glutamyltranspeptidase and facilitative GSH transporters.

Our laboratory previously has shown apparent carrier-mediated glutathione (GSH) uptake across the blood-brain barrier (BBB) in two animal models. In the present study, when Xenopus oocytes were injected with bovine brain capillary mRNA expression of intact GSH, uptake was observed after 3 days. When total mRNA was converted to cDNA and subfractionated with subsequent cRNA injection into oocytes, three distinct fractions (5, 7-8, and 11-12) expressed carrier-mediated intact GSH transport. Northern blot analysis established the presence of RcGshT, the previously cloned sodium-independent hepatic canalicular transporter, only in fraction 5. GSH transport activity in fraction 7 was significantly inhibited by replacement of NaCl with choline chloride and by sulfobromophthalein-GSH, neither of which affects RcGshT. The Na(+)-dependent GSH uptake kinetics exhibited high affinity (approximately 400 micron) and low affinity (approximately 10 mM) components. Fraction 11 expressed Na(+)-independent transport of intact GSH and also contained the GGT transcript. In conclusion, we have identified three distinct sized transcripts from bovine brain capillary mRNA which express GSH transport: one fraction expresses a novel Na(+)-dependent GSH uptake which can be dissociated unequivocally from both GGT and RcGshT for the first time and which may account for uptake of GSH against its electrochemical gradient at the BBB.

Animals↗
PubMed1996

Transport of circulating reduced glutathione at the basolateral side of the anterior lens epithelium: physiologic importance and manipulations.

Transport of circulating reduced glutathione (GSH) was studied at the basolateral side of the lens epithelium by using an in situ vascular eye perfusion technique in guinea-pigs with rapid sampling to ensure detecting initial uptakes. The unidirectional transport rates of [35S]-GSH (4 nM) from plasma and aqueous into the epithelial cytosol were 0.046 +/- 0.003 and 6.88 +/- 0.39 min-1, respectively. HPLC analysis indicated that over 94% of [35S]-GSH remained intact in the epithelium and cortex in the presence or absence of gamma-glutamyl transpeptidase inhibitor, serine borate. Simultaneous infusion of [35S-cysteine]-GSH and [3H-glycine]-GSH confirmed the non-involvement of gamma-glutamyl transpeptidase in GSH transport across the lenticular membranes by showing that 35S/3H ratio in the epithelium and cortex was the same as in the aqueous and plasma. GSH epithelial influx was reduced by 53% (P < 0.01) by 0.3 mM sulphobromophtalein-GSH, a GSH conjugate that does not inhibit the facilitative GSH transporter, RcGshT, recently found in the lens. At physiologic concentration of circulating GSH at 30 microM, GSH epithelial influx was 0.77 nmol min-1 g-1; a t1/2 of 85.4 hr was estimated if endogenous epithelial GSH had to be replaced exclusively by plasma-derived GSH. The level of GSH in the epithelium was increased by 38% (P < 0.05) by 1 hr arterial infusion of GSH at 20 mM. The aqueous concentration of GSH under these conditions was 1.2 mM so that accumulation in the epithelium occurred a greater than six-fold concentration gradient. It is concluded that: (a) transport of GSH at the basolateral side of the epithelium is mediated by a concentrative mechanism distinct from RcGshT: (b) circulating GSH may represent a major source for epithelial GSH under physiologic conditions; and (c) the level of GSH in the epithelium can be manipulated by exogenous GSH.

Animals↗
PubMed1996

Ectomesenchymal chondromyxoid tumor of the anterior tongue: a report of three cases.

Ectomesenchymal chondromyxoid tumor is a newly described benign neoplasm that presents clinically as a firm, painless, slow-growing mass that typically involves the anterior dorsal tongue. It has been reported to occur over a wide age range (9 to 78 years) and has no apparent sex predilection. Histologically, the tumor is composed of a well-circumscribed, unencapsulated lobular proliferation of fusiform and polygonal cells in a chondromyxoid matrix. Features such as multilobulated nuclei, foci of cellular atypia, and infiltration may be present. Though disturbing, these do not appear to indicate malignant behavior. We report three cases of ectomesenchymal chondromyxoid tumors that confirm the previously described clinical, histologic, and immunohistochemical features. In addition, we describe the ultrastructural features of one of the cases.

Actins↗