Totally laparoscopic feeding jejunostomy

BACKGROUND

A feeding jejunostomy should be used for nutritional support in a small subset of patients. Minimal-access approaches for the placement of jejunal tubes have been described, but they often require special equipment not common to all operating theaters. We describe a technique of totally laparoscopic jejunostomy tube (LJT) placement using equipment found in most operating theaters.

METHODS

Thirty-five patients underwent LJT over a 12-month period. Indications included gastroparesis, anorexia nervosa, oral cancer, cerebral palsy, and Huntington's chorea. The technique involved three incisions for trocars (one for a 10-mm camera and two for 5-mm working ports) and one small incision for the tube. A 16-Fr T-tube was passed transabdominally under direct vision, and a jejunotomy was made approximately 20 cm distal to the ligament of Trietz. Each limb of the T-tube was passed into the lumen of the bowel, and a purse-string suture was placed around the enterotomy and tied intracorporeally. After insertion, the serosa surrounding the insertion site is tacked to the anterior abdominal wall in four places with a reusable stainless steel suture passer. To test whether the tube was watertight, we injected methylene blue solution into the tube.

RESULTS

All of the patients tolerated the procedure well. There were no operative deaths. Five LJTs were electively removed in the office. One patient was reoperated on 10 days postoperatively because of intractable pain, but the source of pain was not found and the LJT was intact.

CONCLUSIONS

LJT may be placed safely using the described technique. No significant morbidity or mortality occurred in our series. The results of this study have prompted us to consider LJT for any patient requiring access to the jejunum for feeding.

Bulk band gaps in divalent hexaborides

Complementary angle-resolved photoemission and bulk-sensitive k-resolved resonant inelastic x-ray scattering of divalent hexaborides reveal a >1 eV X-point gap between the valence and conduction bands, in contradiction to the band overlap assumed in several models of their novel ferromagnetism. This semiconducting gap implies that carriers detected in transport measurements arise from defects, and the measured location of the bulk Fermi level at the bottom of the conduction band implicates boron vacancies as the origin of the excess electrons. The measured band structure and X-point gap in CaB6 additionally provide a stringent test case for many-body quasiparticle band calculations.

The poor quality of information about laparoscopy on the World Wide Web as indexed by popular search engines

BACKGROUND

This study was undertaken to determine the quality of information on the Internet regarding laparoscopy.

METHODS

Four popular World Wide Web search engines were used with the key word "laparoscopy." Advertisements, patient- or physician-directed information, and controversial material were noted.

RESULTS

A total of 14,030 Web pages were found, but only 104 were unique Web sites. The majority of the sites were duplicate pages, subpages within a main Web page, or dead links. Twenty-eight of the 104 pages had a medical product for sale, 26 were patient-directed, 23 were written by a physician or group of physicians, and six represented corporations. The remaining 21 were "miscellaneous." The 46 pages containing educational material were critically reviewed. At least one of the senior authors found that 32 of the pages contained controversial or misleading statements. All of the three senior authors (LKN, NAO, GAF) independently agreed that 17 of the 46 pages contained controversial information.

CONCLUSION

The World Wide Web is not a reliable source for patient or physician information about laparoscopy. Authenticating medical information on the World Wide Web is a difficult task, and no government or surgical society has taken the lead in regulating what is presented as fact on the World Wide Web.

Effects of heat shock protein 70 (Hsp70) on arsenite-induced genotoxicity

Arsenic, a human carcinogen, is genotoxic, although its mechanism(s) of action for tumorigenesis is not well understood. Among the toxicity-related properties of this chemical are its clastogenic and aneugenic activities, as well as its capacity for inducing stress-response in the form of elevated heat shock protein (HSP) expression. In the present study, we evaluated the effects of Hsp70 expression on arsenite (As)-induced structural and numerical chromosome anomalies in human cells. Human MCF-7 Tet-off cells stably transfected with a pTRE/Hsp70-1 transgene construct were used to regulate Hsp70 levels prior to in vitro As exposures. Separate cultures of relatively high vs. low Hsp70-expressing cells were established. A cytokinesis block micronucleus assay with kinetochore immunostaining was used to detect micronuclei (MN) derived from chromosome breakage (K-MN) or loss (K+MN). These studies demonstrated significant increases in micronucleus frequencies in response to As following either a long exposure (5 or 10 microM for 46 hr), or short exposure (10 or 40 microM for 8 hr) protocol. Overall, the long protocol was more efficient in producing K+MN and cells with multiple MN. Overexpressing Hsp70 resulted in significant reductions in the percent of cells positive for MN for both the long and short As exposure protocols. Both K+ and K- types of As-induced MN were lower in cells with elevated Hsp70 as compared to cells without overexpression of Hsp70. We conclude that the dose and duration of As exposure influence the type as well as amount of chromosomal alteration produced and that inducible Hsp70 protects against both the clastogenic and aneugenic effects of this chemical.

The glyoxylate cycle in an arbuscular mycorrhizal fungus. Carbon flux and gene expression

The arbuscular mycorrhizal (AM) symbiosis is responsible for huge fluxes of photosynthetically fixed carbon from plants to the soil. Lipid, which is the dominant form of stored carbon in the fungal partner and which fuels spore germination, is made by the fungus within the root and is exported to the extraradical mycelium. We tested the hypothesis that the glyoxylate cycle is central to the flow of carbon in the AM symbiosis. The results of (13)C labeling of germinating spores and extraradical mycelium with (13)C(2)-acetate and (13)C(2)-glycerol and analysis by nuclear magnetic resonance spectroscopy indicate that there are very substantial fluxes through the glyoxylate cycle in the fungal partner. Full-length sequences obtained by polymerase chain reaction from a cDNA library from germinating spores of the AM fungus Glomus intraradices showed strong homology to gene sequences for isocitrate lyase and malate synthase from plants and other fungal species. Quantitative real-time polymerase chain reaction measurements show that these genes are expressed at significant levels during the symbiosis. Glyoxysome-like bodies were observed by electron microscopy in fungal structures where the glyoxylate cycle is expected to be active, which is consistent with the presence in both enzyme sequences of motifs associated with glyoxysomal targeting. We also identified among several hundred expressed sequence tags several enzymes of primary metabolism whose expression during spore germination is consistent with previous labeling studies and with fluxes into and out of the glyoxylate cycle.

The glyoxylate cycle in an arbuscular mycorrhizal fungus. Carbon flux and gene expression

The arbuscular mycorrhizal (AM) symbiosis is responsible for huge fluxes of photosynthetically fixed carbon from plants to the soil. Lipid, which is the dominant form of stored carbon in the fungal partner and which fuels spore germination, is made by the fungus within the root and is exported to the extraradical mycelium. We tested the hypothesis that the glyoxylate cycle is central to the flow of carbon in the AM symbiosis. The results of (13)C labeling of germinating spores and extraradical mycelium with (13)C(2)-acetate and (13)C(2)-glycerol and analysis by nuclear magnetic resonance spectroscopy indicate that there are very substantial fluxes through the glyoxylate cycle in the fungal partner. Full-length sequences obtained by polymerase chain reaction from a cDNA library from germinating spores of the AM fungus Glomus intraradices showed strong homology to gene sequences for isocitrate lyase and malate synthase from plants and other fungal species. Quantitative real-time polymerase chain reaction measurements show that these genes are expressed at significant levels during the symbiosis. Glyoxysome-like bodies were observed by electron microscopy in fungal structures where the glyoxylate cycle is expected to be active, which is consistent with the presence in both enzyme sequences of motifs associated with glyoxysomal targeting. We also identified among several hundred expressed sequence tags several enzymes of primary metabolism whose expression during spore germination is consistent with previous labeling studies and with fluxes into and out of the glyoxylate cycle.

Expression of inducible Hsp70 enhances the proliferation of MCF-7 breast cancer cells and protects against the cytotoxic effects of hyperthermia

Heat shock proteins (Hsps) are ubiquitous proteins that are induced following exposure to sublethal heat shock, are highly conserved during evolution, and protect cells from damage through their function as molecular chaperones. Some cancers demonstrate elevated levels of Hsp70, and their expression has been associated with cell proliferation, disease prognosis, and resistance to chemotherapy. In this study, we developed a tetracycline-regulated gene expression system to determine the specific effects of inducible Hsp70 on cell growth and protection against hyperthermia in MCF-7 breast cancer cells. MCF-7 cells expressing high levels of Hsp70 demonstrated a significantly faster doubling time (39 hours) compared with nonoverexpressing control cells (54 hours). The effect of elevated Hsp70 on cell proliferation was characterized further by 5-bromo-2'deoxyuridine labeling, which demonstrated a higher number of second and third division metaphases in cells at 42 and 69 hours, respectively. Estimates based on cell cycle analysis and mean doubling time indicated that Hsp70 may be exerting its growth-stimulating effect on MCF-7 cells primarily by shortening of the G0/G1 and S phases of the cell cycle. In addition to the effects on cell growth, we found that elevated levels of Hsp70 were sufficient to confer a significant level of protection against heat in MCF-7 cells. The results of this study support existing evidence linking Hsp70 expression with cell growth and cytoprotection in human cancer cells.

Aspartate and glutamate transport in acutely and chronically ethanol exposed neonatal rat primary astrocyte cultures

Maintenance of the ionic and osmotic composition of the extracellular fluid (ECF) is essential for the optimal functioning of the central nervous system (CNS). Changes in ion and neurotransmitter levels in the cerebrospinal fluid (CSF) can have profound effects on the processing and transmission of neuronal signals. Cell swelling during correction of isotonic imbalances can produce a series of events leading to inappropriate release of excitatory amino acids (EAA). Given the osmoregulatory demands of the CNS, it is not surprising that it possesses well-developed osmoregulatory mechanisms capable of maintaining both extracellular and intracellular ionic composition and volume within narrow limits, despite large fluctuations in the ionic composition and osmolarity of the plasma. We have undertaken a series of studies to test the hypothesis that ethanol (EtOH) acts as an osmotic stressor and stimulates osmoregulatory processes in astrocytes. In the course of these studies, we have investigated the effects of acute and chronic exposure to EtOH on cell volume, as well as uptake and release of amino acids in neonatal rat primary astrocyte cultures.

Methylmercury inhibits cysteine uptake in cultured primary astrocytes, but not in neurons

The maintenance of adequate intracellular glutathione (GSH) concentrations is dependent on the availability and transport of the rate-limiting substrate, cysteine. A suggested mechanism of methylmercury (MeHg) neurotoxicity in brain involves the formation of oxygen radicals, and a decrease in intracellular levels of GSH. Recently, we have characterized various cysteine transport systems (both Na(+)-dependent and -independent) in cerebrocortical astrocytes and hippocampal neurons. The present study was carried out to investigate the effect of MeHg on cysteine uptake in both astrocytes and neurons, and to determine whether cysteine transport is differentially affected in the two cell types by MeHg treatment. Sixty-minute pretreatment with MeHg caused significant concentration-dependent inhibition in cysteine uptake in astrocytes, but not in neurons. As most of the cysteine transport is Na(+)-dependent (80-90% of total), additional studies focused on MeHg's effect on the Na(+)-dependent cysteine transporters X(AG(-)) and ASC. An additive inhibitory effect on cysteine uptake was observed in astrocytes treated with MeHg (5 microM) plus sub-maximal inhibitory concentrations (0.1 and 0.5 mM) of threo-beta-hydroxy-aspartate (THA), a specific inhibitor of the Na(+)-dependent transporter, X(AG(-)), compared to astrocytes treated with MeHg (P<0.001) or THA alone (P<0.05). There was no additive effect of MeHg and maximal inhibitory concentrations of THA (1.0 and 5.0 mM) on astrocytic cysteine uptake inhibition. Additional studies examined the sensitivity of the Na(+)-dependent ASC transport system to MeHg treatment. Maximal inhibitory concentration of L-serine (10 mM) alone had a rather modest inhibitory effect on cysteine uptake, and when applied in the presence of MeHg there was no additive effect. These results suggest that the inhibition of cysteine uptake by MeHg in astrocytes occurs through specific inhibition of both the X(AG(-)) as well as the ASC transport system.

Primary skeletal muscle lymphoma presenting as refractory cellulitis

The right torso of a 55-year-old woman showed diffuse skin and soft-tissue changes suggestive of cellulitis. However, several clinical and radiologic features, including the subacute and non-toxic nature of the illness and the patient's lack of response to antibiotic therapy, indicated a noninfectious etiology. Malignancy was suggested by striking changes seen on computed tomographic scanning--including extensive infiltration and enlargement of the musculature of the right shoulder girdle, the intercostal musculature, the latissimus dorsi, and the rhomboids; focal enlargement of the right paraspinal muscles; and enlargement of the psoas and the iliacus muscles and of the musculature around the hip joint. The mediastinal, hilar, and paraaortic regions showed no adenopathy. A large hypodense lesion of approximately 4.5 cm, which was seen in the caudate lobe of the liver, raised the concern of a metastatic focus of malignancy. Because of these findings, an immediate muscle biopsy was performed. Results showed a non-Hodgkin's lymphoma with a B-cell phenotype. Although primary skeletal muscle lymphoma is very uncommon in patients without human immunodeficiency virus infection, clinical presentation of refractory cellulitis, as seen in the current case, is extremely rare.

Detection of early gene expression changes by differential display in the livers of mice exposed to dichloroacetic acid

Dichloroacetic acid (DCA) is a major by-product of water disinfection by chlorination. Several studies have demonstrated the hepatocarcinogenicity of DCA in mice when administered in drinking water. The mechanism of DCA carcinogenicity is not clear and we speculate that changes in gene expression may be important. In order to analyze early changes in gene expression induced by DCA treatment we used the differential display method. Mice were treated with 2 g/l DCA in drinking water for 4 weeks. Total RNAs were obtained from livers of both control and treated mice for analysis. Of approximately 48 000 bands on the differential display gels representing an estimated 96% of RNA species, 381 showed differences in intensity. After cloning and confirmation by both reverse-northern and northern analyses, six differentially expressed genes were found. The expression of five of these genes was suppressed in the DCA-treated mice while one was induced. After sequencing, four genes were identified and two were matched to expressed sequence tags through the BLAST program. These genes are alpha-1 protease inhibitor, cytochrome b5, stearoyl-CoA desaturase and carboxylesterase. Stearoyl-CoA desaturase was induced approximately 3-fold in the livers of DCA-treated mice and the other three genes were suppressed approximately 3-fold. Stearoyl-CoA desaturase, cytochrome b5 and carboxylesterase are endoplasmic reticulum membrane-bound enzymes involved in fatty acid metabolism. The expression pattern of four of these genes was similar in DCA-induced hepatocellular carcinomas and the 4 week DCA-treated mouse livers. The expression of stearoyl-CoA desaturase and one of the unidentified genes returned to control levels in the carcinomas. Understanding the roles and interactions between these genes may shed light on the mechanism of DCA carcinogenesis.

Methylmercury has a selective effect on mitochondria in cultured astrocytes in the presence of [U-(13)C]glutamate

The effect of methylmercury on glutamate metabolism was studied by (13)C magnetic resonance spectroscopy. Cerebral cortical astrocytes were pretreated with methylmercury, either 1 microM for 24 h, or 10 microM for 30 min, and subsequently with 0.5 mM [U-(13)C]glutamate for 2 h. Labeled glutamate, glutamine, aspartate and glutathione were present in cell extracts, and glutamine, aspartate and lactate in the medium of all groups. HPLC analysis of these amino acids showed no changes in concentrations between groups. Surprisingly, the amounts of [U-(13)C]glutamate and unlabeled glucose taken up by the astrocytes were unchanged. Furthermore, the amounts of most metabolites synthesized from [U-(13)C]glutamate were also unchanged in all groups. However, formation of [U-(13)C]lactate was decreased in the 10 microM methylmercury group. This was not observed for labeled aspartate. It is noteworthy that both [U-(13)C]lactate and [U-(13)C]aspartate can only be derived from [U-(13)C]glutamate via mitochondrial metabolism. [U-(13)C]glutamate enters the tricarboxylic acid cycle (located in mitochondria) after conversion to 2-[U-13C]oxoglutarate and [U-(13)C]aspartate is formed from [U-(13)C]oxaloacetate, as is [U-(13)C]lactate. [U-(13)C]lactate can also be formed from [U-(13)C]malate. This differential effect on labeled aspartate and lactate indicates cellular compartmentation and thus selective vulnerability of mitochondria within the astrocytes to the effects of methylmercury. The decreased lactate production from glutamate might be detrimental to surrounding cells since lactate has been shown to be an important substrate for neurons.

Exacerbation of neuronal cell death by activation of group I metabotropic glutamate receptors: role of NMDA receptors and arachidonic acid release

Both ionotropic and metabotropic glutamate receptors have been implicated in the pathogenesis of neuronal injury. Activation of group I metabotropic glutamate receptors (mGluR) exacerbates neuronal cell death, whereas inhibition is neuroprotective. However, the mechanisms involved remain unknown. Activation of group I mGluR modulates multiple signal transduction pathways including stimulation of phosphoinositide hydrolysis, potentiation of NMDA receptor activity, and release of arachidonic acid. Here we demonstrate that whereas activation of group I mGluR by (S)-3,5-dihydroxyphenylglycine (DHPG) potentiates NMDA-induced currents and intracellular calcium increases in rat cortical neuronal cultures, partial effects of group I mGluR activation or inhibition on neuronal injury induced by oxygen-glucose deprivation remain despite NMDA receptor blockade. DHPG stimulation also increases basal arachidonic acid release from rat neuronal-glial cultures and potentiates injury-induced arachidonic acid release in these cultures. Thus, activation of group I mGluR may exacerbate neuronal injury through multiple mechanisms, which include positive modulation of NMDA receptors and enhanced release of arachidonic acid.

Multiple caspases are involved in beta-amyloid-induced neuronal apoptosis

beta-amyloid peptide (Abeta) has been implicated in the pathogenesis of Alzheimer disease and has been reported to induce apoptotic death in cell culture. Cysteine proteases, a family of enzymes known as caspases, mediate cell death in many models of apoptosis. Multiple caspases have been implicated in Abeta toxicity; these reports are conflicting. We show that treatment of cerebellar granule cells (CGC) with Abeta25-35 causes apoptosis associated with increased activity of caspases-2, -3 and -6. Selective inhibition of each of these three caspases provides significant protection against Abeta-mediated apoptosis. In contrast, no change in caspase-1 activity was seen after Abeta25-35 application, nor was inhibition of caspase-1 neuroprotective. Similar to CGC, cortical neuronal cultures treated with Abeta25-35 demonstrate increased caspase-3 activity but not caspase-1 activity. Furthermore, significant neuroprotection is elicited by selective inhibition of caspase-3 in cortical neurons administered Abeta25-35, whereas selective caspase-1 inhibition has no effect. Taken together, these findings indicate that multiple executioner caspases may be involved in neuronal apoptosis induced by Abeta.

Lessons learned from laparoscopic gastric banding for morbid obesity

BACKGROUND

Laparoscopic gastric banding is a minimally invasive bariatric operation that is increasing in popularity at many centers worldwide. Although this procedure is not yet approved in the United States, clinical trials are ongoing.

METHODS

We report our results of a 3-year follow-up on 60 patients who underwent the laparoscopic gastric band procedure for the treatment of morbid obesity. The procedure was performed at the Wesley Obesity Clinic in Brisbane, Australia.

RESULTS

At follow-up, 51 of the 60 patients (85%) still had the laparoscopic gastric band in place. All of the patients had a lower body weight after undergoing the procedure. The average weight loss was 39 kg (range 2 to 98 kg), representing a loss of 65% of average excess body weight. Twenty-five of 51 patients (49%) regained some weight after their initial loss, but the average amount was only 5 kg. The remaining 26 patients have remained at their lowest body weight recorded after the procedure or are continuing to lose weight. There was no operative mortality. Complications predominantly were caused by band slippage (21%), which has been nearly eliminated in recent practice (1 slip in the last 225 cases). Subsequent modifications in the technique to prevent band slippage included placing the band near the level of the esophagus, with minimal disruption of the posterior gastric attachments and diligent suturing of the band in place.

CONCLUSIONS

We conclude that the laparoscopic gastric band is effective in short- and long-term weight loss. The high rate of reoperation for repositioning has been avoided in current practice.

The uptake of cysteine in cultured primary astrocytes and neurons

One of the vitally important functions of glutathione (GSH) is to adequately protect cells against toxic chemicals, reactive oxygen metabolites and free radical species. The amino acid, cysteine, is the key rate-limiting substrate for the biosynthesis of GSH, and the maintenance of adequate intracellular GSH levels is dependent upon the extracellular availability and transport of cysteine into cells. In the present study, primary cultures of astrocytes and neurons were employed to characterize cysteine transport systems. Both astrocytes and neurons used Na(+)-dependent systems as the major route for cysteine uptake (80-90% of total), while Na(+)-independent uptake represented a minor component of total transport (10-20% of total). Among the Na(+)-dependent systems, X(AG(-)) was the major contributor (approx. 80-90%) for cysteine uptake in both neurons and astrocytes, with a minor contribution from the ASC transport system (Na(+)-dependent neutral amino acid transport system for alanine, serine, and cysteine). In the Na(+)-independent transport systems (10-20% of total cysteine transport), multifunctional ectoenzyme/amino acid transporter gamma-glutamyltranspeptidase (GGT), and the neutral amino acid L-system contributed approximately equally towards cysteine uptake, in both neurons and astrocytes. The present studies demonstrate that astrocytes and neurons accumulate cysteine by both Na(+)-dependent and Na(+)-independent uptake systems, with major uptake occurring through the X(AG(-)) system and minor uptake via the ASC, GGT and L-systems.

Ethanol-induced swelling in neonatal rat primary astrocyte cultures

We tested the hypothesis that astrocytes swell in response to ethanol (EtOH) exposure. The experimental approach consisted of an electrical impedance method designed to measure cell volume. In chronic experiments, EtOH (100 mM) was added to the culture media for 1, 3, or 7 days. The cells were subsequently exposed for 15 min to isotonic buffer (122 mM NaCl) also containing 100 mM EtOH. Subsequently, the cells were washed and exposed to hypotonic buffer (112 mM NaCl) containing 100 mM mannitol. Chronic exposure to EtOH led to a marked increase in cell volume compared with control cells. Specific anion cotransport blockers, such as SITS, DIDS, furosemide, or bumetanide, when simultaneously added with EtOH to hyponatremic buffer, failed to reverse the EtOH-induced effect on swelling. In acute experiments, confluent neonatal rat primary astrocyte cultures were exposed to isotonic media (122 mM NaCl) for 15 min, followed by 45-min exposure to hypotonic media (112 mM NaCl, mimicking in vivo hyponatremic conditions associated with EtOH withdrawal) in the presence of 0-100 mM EtOH. This exposure led to a concentration-dependent increase in cell volume. Combined, these studies suggest that astrocytes exposed to EtOH accumulate compensatory organic solutes to maintain cell volume, and that in response to hyponatremia and EtOH withdrawal their volume increases to a greater extent than in cells exposed to hyponatremia alone. Furthermore, the changes associated with EtOH are osmotic in nature, and they are not reversed by anion cotransport blockers.

Methylmercury-mediated inhibition of 3H-d-aspartate transport in cultured astrocytes is reversed by the antioxidant catalase

Astrocytes are essential for removal of glutamate from the extracellular space in the central nervous system. The neurotoxic heavy metal methylmercury potently and specifically inhibits the transport of glutamate in cultured astrocytes by an unknown mechanism. Glutamate transport in astrocytes is also inhibited by reactive oxygen species. A glutamate-induced transporter current is inhibited both by reactive oxygen species and thiol oxidizing agents. These observations suggest that oxidation of the transporter might mediate methylmercury-induced inhibition of glutamate transport. In the present study, we examined the ability of thiol reducing or oxidizing agents to inhibit transport of 3H-D-aspartate, a glutamate analog, in primary cultures of neonatal rat astrocytes. To assess if methylmercury-mediated inhibition of 3H-aspartate transport was due to overproduction of reactive oxygen species, we tested the ability of Trolox, alpha-phenyl-tert-butyl nitrone (PBN), or catalase to attenuate the methylmercury-induced inhibition of aspartate uptake. Neither the thiol reducing agent dithiothreitol (DTT), nor the thiol oxidizing agent 5,5'-dithio-bis(2-nitrobenzoic) acid (DTNB) had any effect on 3H-aspartate transport suggesting that the thiol redox state does not alter transporter function. In contrast, the antioxidant catalase (1000 U/ml) significantly attenuated methylmercury-induced inhibition of 3H-aspartate uptake, suggesting that excess reactive oxygen species, specifically H2O2, inhibit the function of an astrocytic excitatory amino acid transporter (EAAT1). Prolonged exposure (6 h) to inhibitors of glutamate transport significantly decreased EAAT1 mRNA levels suggesting that transporter expression is related to function. This study suggests that methylmercury-induced overproduction of H2O2 is a mechanism for inhibition of glutamate transport and transporter expression in cultured astrocytes.

Methylmercury inhibits the in vitro uptake of the glutathione precursor, cystine, in astrocytes, but not in neurons

Maintenance of adequate intracellular glutathione (GSH) levels is vital for intracellular defense against oxidative damage. The toxic effects of methylmercury (MeHg) are attributable, at least in part, to elevated levels of reactive oxygen species, and thus decreases in GSH synthesis may increase methylmercury toxicity. Astrocytes have recently been proposed to play an essential role in providing GSH precursors to neurons. Therefore, cystine transport, a prerequisite to GSH production, was characterized in cultured astrocytes and neurons, and the effects of methylmercury on this transport were assessed. Astrocytes and neurons both possessed temperature dependent transport systems for cystine. Astrocytes accumulated cystine by Na+-independent (X(C)-) and -dependent (X(AG)-) systems while neurons used exclusively Na+-independent systems. Inhibition of the X(AG)- transport system decreased cystine transport in astrocytes to levels equivalent to those in sodium-depleted conditions, suggesting that cystine is carried by a glutamate/aspartate transporter in astrocytes. Inhibition of the multifunction ectoenzyme/amino acid transporter gamma-glutamyltranspeptidase (GGT) decreased cystine transport in both neurons and astrocytes. Inhibition of System X(C)- with quisqualate also decreased cystine uptake in both astrocytes and neurons. These data demonstrate that cultured astrocytes accumulate cystine via three independent mechanisms, System X(AG)-, System X(C)-, and GGT, while cultured hippocampal neurons use System X(C)- and GGT exclusively. Inhibition of cystine uptake in astrocytes by methylmercury appears to be due to actions on the System X(AG)- transporter.

The application of a compact multispectral imaging system with integrated excitation source to in vivo monitoring of fluorescence during topical photodynamic therapy of superficial skin cancers

A novel, compact and low-cost multispectral fluorescence imaging system with an integrated excitation light source is described. Data are presented demonstrating the application of this method to in vivo monitoring of fluorescence before, during and after topical 5-aminolevulinic acid photodynamic therapy of superficial skin cancers. The excitation source comprised a fluorescent tube with the phosphor selected to emit broadband violet light centered at 394 nm. The camera system simultaneously captured spectrally specific images of the fluorescence of the photosensitizer, protoporphyrin IX, the illumination profile and the skin autofluorescence. Real-time processing enabled images to be manipulated to create a composite image of high contrast. The application and validation of this method will allow further detailed studies of the characteristics and time-course of protoporphyrin IX fluorescence, during topical photodynamic therapy in human skin in vivo.

Mercuric chloride, but not methylmercury, inhibits glutamine synthetase activity in primary cultures of cortical astrocytes

Methylmercury (MeHg) is highly neurotoxic with an apparent dose-related latency period between time of exposure and the appearance of symptoms. Astrocytes are known targets for MeHg toxicity and a site of mercury localization within the central nervous system (CNS). Glutamine synthetase (GS) is an enzyme localized predominately within astrocytes. GS converts two potentially toxic molecules, glutamate and ammonia, to the relatively non-toxic amino acid, glutamine. During prolonged exposure to MeHg, inorganic mercury (I-Hg) accumulates within the brain, suggesting in situ demethylation of MeHg to I-Hg. To determine if speciation of mercurials would differentially alter GS activity and expression, neonatal rat primary astrocyte cultures were exposed to MeHg or mercuric chloride (HgCl2) for 1 or 6 h. MeHg produced no changes in GS activity, protein, or mRNA at any time or dose tested. In contrast, HgCl2 produced a dose dependent decrease in astrocytic GS activity at both 1 and 6 h. There were no changes in GS protein or mRNA levels following HgCl2 exposure. Additional studies were carried out to determine GS activity in cell lysates incubated with HgCl2 or MeHg. In cell lysates, HgCl2 was three-times more potent than MeHg in inhibiting GS activity. The inhibition of GS activity in cell lysates by HgCl2 was reversed by the addition of dithiothreitol (DTT), while DTT did not restore GS activity following MeHg. These data suggest that astrocytic GS activity is not inhibited by physiologically relevant concentrations of MeHg, but is inhibited by I-Hg, which is present in CNS following chronic MeHg exposure.

A novel conformer of oxidized Paracoccus pantotrophus cytochrome cd(1) observed by freeze-quench NIR-MCD spectroscopy

Paracoccus pantotrophus cytochrome cd(1) is a physiological nitrite reductase and an in vitro hydroxylamine reductase. The oxidised "as isolated" form of the enzyme has bis-histidinyl coordinated c-heme and upon reduction its coordination changes to histidine/methionine. Following treatment of reduced enzyme with hydroxylamine, a novel, oxidised, conformer of the enzyme is obtained. We have devised protocols for freeze-quench near-ir-MCD spectroscopy that have allowed us to establish unequivocally the c-heme coordination of this species as His/Met. Thus it is shown that the catalytically competent, hydroxylamine reoxidised, form of P. pantotrophus cytochrome cd(1) has different axial ligands to the c-heme than "as isolated" enzyme.

Time-resolved infrared spectroscopy reveals a stable ferric heme-NO intermediate in the reaction of Paracoccus pantotrophus cytochrome cd1 nitrite reductase with nitrite

Cytochrome cd(1) is a respiratory enzyme that catalyzes the physiological one-electron reduction of nitrite to nitric oxide. The enzyme is a dimer, each monomer containing one c-type cytochrome center and one active site d(1) heme. We present stopped-flow Fourier transform infrared data showing the formation of a stable ferric heme d(1)-NO complex (formally d(1)Fe(II)-NO(+)) as a product of the reaction between fully reduced Paracoccus pantotrophus cytochrome cd(1) and nitrite, in the absence of excess reductant. The Fe-(14)NO nu(NO) stretching mode is observed at 1913 cm(-1) with the corresponding Fe-(15)NO band at 1876 cm(-1). This d(1) heme-NO complex is still readily observed after 15 min. EPR and visible absorption spectroscopic data show that within 4 ms of the initiation of the reaction, nitrite is reduced at the d(1) heme, and a cFe(III) d(1)Fe(II)-NO complex is formed. Over the next 100 ms there is an electron redistribution within the enzyme to give a mixed species, 55% cFe(III) d(1)Fe(II)-NO and 45% cFe(II) d(1)Fe(II)-NO(+). No kinetically competent release of NO could be detected, indicating that at least one additional factor is required for product release by the enzyme. Implications for the mechanism of P. pantotrophus cytochrome cd(1) are discussed.

Effects of endotoxemia and sepsis on bilirubin oxidation by rat brain mitochondrial membranes

Sepsis is believed to increase the risk of bilirubin brain toxicity, but the mechanism is not known. Adult male Sprague-Dawley rats were injected intraperitoneally with either 20 mg/kg Escherichia coli lipopolysaccharide, approximately 5 x 10(9)/kg CFU Listeria monocytogenes or vehicle 48 h prior to sacrifice. Rats were killed with an intraperitoneal injection of pentobarbital. Mitochondrial membrane fractions were produced by homogenization of the brains and differential centrifugation in 0.32 M sucrose. The mitochondrial pellet was resuspended in distilled water and sonicated to rupture the mitochondria. The protein concentration of the suspension was standardized to 2.5 mg/ml. Bilirubin oxidation was assayed in a pH 8.2, 0.1 M barbital buffer containing 10 microM bilirubin, 5 mM EDTA, and 500 U/ml catalase. Optical density was measured at 440 nm before and after a 60-min incubation at 37.5 degrees C. There were no differences between the control, endotoxemic, and septic groups as far as the ability of brain mitochondrial membranes to oxidize bilirubin (bilirubin oxidation rate: 289 +/- 11 vs. 295 +/- 9 vs. 296 +/- 12 pmol/min/mg protein, mean +/- SD). We conclude that endotoxemia or sepsis do not change the ability of brain mitochondrial membranes to oxidize bilirubin. If sepsis truly increases the risk of bilirubin encephalopathy in neonatal jaundice, this is likely to involve other mechanisms.