Studies on the in situ physiology of Thiothrix spp. present in activated sludge

The in situ physiology of the filamentous sulphur bacterium Thiothrix spp. was investigated in an industrial wastewater treatment plant with severe bulking problems as a result of overgrowth of Thiothrix. Identification and enumeration using fluorescence in situ hybridization (FISH) with species-specific 16S and 23S rRNA probes revealed that 5-10% of the bacteria in the activated sludge were Thiothrix spp. By using a combination of FISH and microautoradiography it was possible to study the in situ physiology of probe-defined Thiothrix filaments under different environmental conditions. The Thiothrix filaments were very versatile and showed incorporation of radiolabelled acetate and/or bicarbonate under heterotrophic, mixotrophic and chemolithoautotrophic conditions. The Thiothrix filaments were active under anaerobic conditions (with or without nitrate) in which intracellular sulphur globules were formed from thiosulphate and acetate was taken up. Thiothrix-specific substrate uptake rates and growth rates in activated sludge samples were determined under different conditions. Doubling times of 6-9 h under mixotrophic conditions and 15-30 h under autotrophic conditions were estimated. The key properties that Thiothrix might be employing to outcompete other microorganisms in activated sludge were probably related to the mixotrophic growth potential with strong stimulation of acetate uptake by thiosulphate, as well as stimulation of bicarbonate incorporation by acetate in the presence of thiosulphate.

No involvement of nicotinic receptors in the facilitation of acetylcholine outflow in mouse cortex in the presence of neostigmine and atropine

The role of nicotinic and muscarinic receptors in the modulation of acetylcholine release was studied using field stimulated mouse cortex slices incubated with [(3)H]-choline. Both acetylcholine (100 microM) and the cholinesterase inhibitor neostigmine (100 microM) inhibited the stimulation-induced (S-I) outflow of radioactivity but in the presence of atropine (0.3 microM) an enhancement was seen, which may be indicative of facilitatory nicotinic receptors. Mecamylamine (100 microM) was unable to antagonize the enhancement seen in the presence of acetylcholine and atropine. The nicotinic agonist dimethylphenylpiperazinium (30 microM) did not facilitate S-I outflow of radioactivity. A range of nicotinic blockers had no effect on the enhancement seen in the presence of neostigmine and atropine, nor did indomethacin, the 5HT(3) antagonist MDL 7222 nor the NMDA antagonist MK-801. The inability to block this effect suggests that nicotinic receptors are not involved. We postulate, at least for neostigmine, that the facilitation is an artefact because of the use of [(3)H]-choline as a radiotracer whereby the efflux of radioactivity is enhanced because the radiolabelled acetylcholine is not metabolized to choline and therefore flows out of the tissue more readily.

Dexamethasone increases the incorporation of [3H]serine into phosphatidylserine and the activity of serine base exchange enzyme in mouse thymocytes: a possible relation between serine base exchange enzyme and apoptosis

The exposure of phosphatidylserine toward the external surface of the membrane is a well-established event of programmed cell death. The possibility that an apoptotic stimulus influences the metabolism of this phospholipid could be relevant not only in relation to the previously mentioned event but also in relation to the capability of membrane phosphatidylserine to influence PKC activity. The present investigation demonstrates that treatment of mouse thymocytes with the apoptotic stimulus dexamethasone, enhances the incorporation of [3H]serine into phosphatidylserine. Cell treatment with dexamethasone also enhanced the activity of serine base exchange enzyme, assayed in thymocyte lysate. Both the effects were observed at periods of treatment preceding DNA fragmentation. The addition of unlabelled ethanolamine, together with [3H]serine to the medium containing dexamethasone-treated thymocytes lowered the radioactivity into phosphatidylserine. Serine base exchange enzyme activity was influenced by the procedure used to prepare thymocyte lysate and was lowered by the addition of fluoroaluminate, that is widely used as a G-protein activator. The increase of serine base exchange enzyme activity induced by dexamethasone treatment was observed independently by the procedure used to prepare cell lysate and by the presence or absence of fluoroaluminate.

Meal fatty acid uptake in human adipose tissue: technical and experimental design issues

The adipose tissue uptake of dietary fat has been studied using fatty acid radiotracers incorporated into a meal, followed by adipose tissue biopsies. A number of experimental design issues, including the use of isotopic tracers to measure meal fatty acid oxidation and plasma appearance of tracer, as well as the heterogeneity of adipose tissue fatty acid uptake, have been addressed. We examined these questions in a study of 24 volunteers (12 men and 12 women) who consumed a meal containing [(3)H]triolein and [(14)C]triolein. Slight differences in the purity of [(3)H]triolein vs. [(14)C]triolein were found, which could affect the apparent adipose tissue uptake of meal fatty acids. The adipose tissue triglyceride specific activity from bilateral biopsy sites agreed well, implying that a unilateral biopsy is satisfactory for measuring tracer uptake. Meal fatty acid oxidation measured using [(3)H]triolein and [(14)C]triolein was well correlated (r = 0.79, P < 0.0001). The peak tracer appearance in plasma chylomicrons occurred 1 h after the ingestion of a second, unlabeled meal. Our findings have implications for the experimental design of future meal fatty acid tracer/adipose tissue biopsy studies.

Tritiated thymidine ([3H]-TdR) and immunocytochemical tracing of cellular fate within the asexually dividing cestode Mesocestoides vogae (syn. M. corti)

This report documents the presence of an active thymidine kinase (TK) system within Mesocestoides vogae tetrathyridia as quantified by tritiated thymidine ([3H]-TdR) incorporation using liquid scintillation counting. A 100-fold increase in [3H]-TdR incorporation was observed at 37 degrees C when compared with its incorporation at 0 degrees C. Thymidine's competitive analogue, BrdU, competed for sites within newly replicated DNA. Immunohistochemical trials performed here using antibodies against BrdU identified cells that have entered and passed through S-phase. Positively stained nuclei were most numerous at the anterior tip of tetrathyridia especially within the ganglia, lesser numbers of these cells occurred along the growing commissure and amongst surface tegumental cytons suggesting that stem cells do not exist in one region but are found throughout the entire body. As M. vogae has no internal organ systems the major sites for cell proliferation are those exhibiting maximal cell recruitment and undergoing tissue repair. These results show that it is possible to monitor changes in the cell recruitment pattern within this cestode. Thus use of BrdU and immunohistochemistry demonstrates how spatial arrangement and cellular reorganization can be successfully traced within M. vogae.

Pharmacological properties of naturally occurring variants of the human norepinephrine transporter

The human norepinephrine transporter (hNET) gene has five sequence polymorphisms that predict amino acid substitutions in the transporter protein: Val69Ile, Thr99Ile, Val245Ile, Val449Ile, and Gly478Ser. In order to functionally characterize the naturally occurring transporter variants, we used site-directed mutagenesis to establish the hNET variants and compared some basic pharmacological properties (uptake of norepinephrine and its inhibition by the tricyclic antidepressant desipramine) in COS-7 cells transiently expressing variant hNETs and wild-type hNET. None of the hNET variants displayed changes in the potency (Ki) of desipramine for inhibition of norepinephrine uptake. Furthermore, variants Val69Ile, Thr99Ile, ValZ45Ile, and Val449Ile did not affect kinetic constants (Km, Vmax) of norepinephrine uptake. However, COS-7 cells expressing the hNET variant Gly478Ser displayed an approximately four-fold increase in the Km for norepinephrine, while the Vmax was unaffected. The increase in the Km, which is equivalent to a four-fold reduction in the affinity of the variant hNET for its natural substrate norepinephrine, indicates that the glycine in position 478 is part of a substrate recognition domain. The reduced clearance of released norepinephrine by reuptake through the Gly478Ser variant might cause an increase in the synaptic and the circulating concentration of norepinephrine. Elevated norepinephrine concentrations have been associated with human diseases and it will be interesting to explore a possible contribution by the Gly478Ser variant to certain disease states.

Effect of benzylpenicillin on murein biosynthesis, turnover and structure in Listeria monocytogenes cells

The action of beta-lactam antibiotics such as ampicillin and benzylpenicillin on cells of Listeria monocytogenes appears to be bacteriostatic. However, after approximately two hours in the presence of 10 x MIC of benzylpenicillin the cells begin to rapidly lose viability without undergoing lysis. In this report we present the results of studies on the biosynthesis of murein in L. monocytogenes cells during the first 120 min of their exposure to benzylpenicillin as measured by the continuous and pulse incorporation of the precursor N-acetyl-D-[1-3H]glucosamine. The turnover of the murein sacculus in the presence of penicillin as well as the lack of discernible changes in the molecular structure of the murein synthesised in the presence of benzylpenicillin is also discussed.

Glycosylphosphatidylinositol (GPI) hydrolysis by transforming growth factor-beta1 (TGF-beta1) as a potential early step in the inhibition of epithelial cell proliferation

Glycosylphosphatidylinositol (GPI) was previously identified in rabbit articular chondrocytes as being a precursor of inositolphosphate glycan (IPG), released upon (Transforming Growth Factor-beta) (TGF-beta) exposure, and capable of mimicking the proliferative effects of the growth factor. Here, using mink lung epithelial cells (CCL 64), which are known to be growth-inhibited by TGF-beta, we studied the potential role of GPI-derived molecules in the antiproliferative effect of TGF-beta1. We first identified an endogenous pool of GPI material and three different anionic forms of IPG in epithelial cells pre-labeled with [3H]glucosamine. Shortly (8 min) after TGF-beta1 addition, the cells responded by a rapid and transient hydrolysis of GPI, accompanied by the release of the most anionic form of IPG. This TGF-beta-released IPG, after partial purification, was shown to decrease the proliferation of CCL 64 cells. Moreover, anti-IPG antibodies reduced the effects of TGF-beta and blocked the effects of partially purified IPG. These data strongly suggest that GPI hydrolysis may be an early step of the TGF-beta signalling pathway involved in growth inhibition of epithelial cells.

An antibody for macrophage migration inhibitory factor suppresses tumour growth and inhibits tumour-associated angiogenesis

To verify the role of macrophage migration inhibitory factor (MIF) in tumourigenesis, we examined the effect of an anti-MIF antibody on tumour growth and angiogenesis. We inoculated murine colon adenocarcinoma cell line colon 26 cells subcutaneously into the flank in BALB/c mice. After nine days, we treated tumour-bearing mice with an anti-rat MIF antibody by intraperitoneal injection on days 9, 11, 13, 15, 17, 19 and 21. We found significant inhibition of tumour growth by this treatment from day 15 to day 22. Next, we implanted a chamber filled with colon 26 cells, which only passes soluble factors, in the subcutaneous fascia of the flank, and treated mice with the anti-rat MIF antibody at days 1, 3 and 5. By histological examination at day 6, angiogenesis within the subcutaneous fascia in contact with the chamber was markedly suppressed. In vitro, we added an anti-human MIF antibody to human umbilical vein endothelial cells (HUVEC) to evaluate its effect on cell growth by measurement of [3H]thymidine incorporation. We observed that the anti-MIF antibody significantly suppressed [3H]thymidine uptake by HUVEC. These results suggest the possibility that MIF is involved in tumourigenesis via promotion of angiogenesis.

Kinetics of peptide uptake and tissue distribution following a single intranasal dose of peptide

We have previously used intranasal (i.n.) peptide application to induce mucosal tolerance in experimental autoimmune encephalomyelitis (EAE). This strategy, however, appeared to give rise to similar phenomena of tolerance observed as a result of systemic administration of soluble antigenic peptide. We were interested, therefore, in the uptake and tissue distribution of peptide following i.n. treatment. In the H-2u mouse model of EAE, the highly tolerogenic peptide analogue Ac1-9[4Y] of myelin basic protein (MBP) displays high affinity binding to Au MHC class II. For the purpose of the present study this peptide was synthesised to contain a tritiated acetyl group and a protocol was developed to recover radioactivity in solubilised tissues taken at various times after [3H]Ac1-9[4Y] i.n.. Radiolabel loads of the lung and gastro-intestinal tract were initially high but declined rapidly. Radiolabel uptake by blood and lymphoid tissues followed similar kinetics with peak levels around 2.5-4 hours after i.n. administration. Concentrations were high in the draining cervical lymph nodes (CLN) but also reached significant levels in the spleen and 'nondraining' inguinal lymph nodes. The presence of intact antigenic peptide was demonstrated in spleens and CLN from Ac1-9[4Y] i.n. treated mice. Cell suspensions prepared from these tissues at selected time points after peptide i.n. were able to stimulate peptide-specific T cell lines up to at least one day after peptide i.n., suggesting long lasting formation of stable Au-Ac1-9[4Y] complexes in vivo.

Human herpesvirus 8 open reading frame 21 is a thymidine and thymidylate kinase of narrow substrate specificity that efficiently phosphorylates zidovudine but not ganciclovir

Human herpesvirus 8 (HHV8) open reading frame (ORF) 21 is predicted to encode a protein similar to the thymidine kinase (TK) enzyme of other herpesviruses. Expressed in mammalian cells, ORF 21 was found to have low TK activity, based on poor growth in media containing hypoxanthine-aminopterin-thymidine (HAT) and low incorporation of [(3)H]thymidine into high-molecular-weight DNA. Kinetic analysis using HHV8 TK as a purified glutathione S-transferase (GST) fusion protein showed that the enzyme has a comparatively high K(m) for thymidine (dThd) of approximately 33.2 microM. Nearly 50% of the phosphorylated product of the reaction with dThd was thymidylate. This monophosphate kinase activity was more pronounced with 3'-azido-3'-deoxythymidine (AZT), in which 78% of the reaction product was AZT diphosphate. Thymidine analogs competitively inhibited dThd phosphorylation by HHV8 TK, while 2'-deoxyguanosine, 2'-deoxyadenosine, 2'-deoxycytidine, and corresponding analogs did not. Further competition experiments revealed that the nucleoside analog ganciclovir (GCV), at up to 1,000-fold molar excess, could not significantly inhibit dThd phosphorylation by the enzyme. In support of these data, 143B TK(-) cells expressing HHV8 TK phosphorylated GCV very poorly and were not susceptible to GCV toxicity compared to parental cells. Phosphorylation of [(3)H]GCV by a purified GST-HHV8 TK fusion protein was not detected by high-pressure liquid chromatography analysis. Structural features of HHV8 TK substrate recognition were investigated. Therapeutic implications of these findings are discussed.

Dose contribution from metabolized organically bound tritium after chronic tritiated water intakes in humans

Our earlier study of acute tritiated water intakes in humans has demonstrated that the dose contribution from metabolized organically bound tritium is less than 10% of the body water dose. To further demonstrate that the dose contribution from the organically bound tritium per unit intake of tritiated water is the same, regardless of whether the intake is acute (all at once) or chronic (spread over time), urine samples from six male radiation workers with chronic tritiated water intakes were collected and analyzed for tritium. These workers have a well-documented dose history and a well-controlled tritium bioassay database, providing assurance that their tritium intakes were in the form of tritiated water. Each month for a full calendar year, urine samples were collected from each exposed worker. The monthly concentration of tritiumin-urine for each exposed worker was no lower than 10(4) Bq L(-1) but no higher than 10(5) Bq L(-1). These urine samples were analyzed for tritiated water and organically bound tritium to determine the ratio of these tritiated species in urine. The average ratio of tritiated water to organically bound tritium in urine for each exposed worker was 330 +/- 129 (range, 297-589). In calculating the dose to these workers, we assumed that, under steady-state conditions, the ratio of the specific activity of tritium (3H activity per gH) in the organic matter and water fractions of urine is representative of the ratio of the specific activity of tritium in the organic matter and water fractions of soft tissue. A mathematical model was developed and used to estimate the dose increase from the metabolized organically bound tritium based on the ratio of tritiated water to organically bound tritium in urine. The resulting average dose from the organically bound tritium was 6.9 +/- 3.1% (range, 4.7-9.9%) of the body water dose for the six male workers, and agrees well with the value obtained from our acute tritiated water intakes study in humans. The observed dose contribution from organically bound tritium, relative to body water dose, is in agreement with current recommendations of assigning 10% of total body water dose for organically bound tritium in soft tissues after tritiated water intakes.

Effect of heparin and related glycosaminoglycan on PDGF-induced lung fibroblast proliferation, chemotactic response and matrix metalloproteinases activity

Fibroblast migration, proliferation, extracellular matrix protein synthesis and degradation are the key events in various biological and pathological processes in pulmonary fibrosis. In addition, biopsy specimens from the lungs of patients with pulmonary fibrosis show increased numbers of mast cells which have metachromatic granules containing heparin, histamine and proteases. Little is known about how these products influence pulmonary fibrosis. In the present study, we investigated the effect of heparin and related glycosaminoglycans on PDGF-induced lung fibroblast proliferation and chemotactic response in vitro. In addition, we examined the effect of heparin on both the induction of matrix metalloproteinases (MMPs) and MMPs activity in lung fibroblasts in vitro. Heparin, de-N-sulphated heparin but not heparan sulphate inhibited PDGF-induced lung fibroblast proliferation. In contrast, only heparin inhibited PDGF-stimulated human lung fibroblast chemotaxis. Negatively charged poly-L-glutamic acid had no effect on either fibroblast proliferation or chemotaxis. Thus the negative charge alone cannot account for the ant-proliferative and anti-chemotactic effects of heparin. Furthermore, heparin and heparan sulphate also had no inhibitory effect on induction of MMPS, including MMP-1 (interstitial collagenase), MMP-2 (gelatinase A) and MMP-9 (gelatinase B). Only heparin inhibited both MMP-1 and MMP-2/MMP-9 activity. Additionally, tissue inhibitor of metalloproteinase type 1 (TIMP-1) and type 2 (TIMP-2) inhibited PDGF-stimulated human lung fibroblast chemotaxis. The ability of heparin to inhibit fibroblast chemotaxis may account for the inhibitory effect of heparin on MMP activity. The above results suggested that heparin and related glycosaminoglycans differentially regulate PDGF-induced lung fibroblast proliferation, chemotaxis and MMPs activity and further that these effects may have a key role in extracellular matrix remodeling in inflammatory lung disease.

The reactions of articular cartilage to experimental wounding: role of apoptosis

OBJECTIVE

To determine the cellular and matrix responses to experimental wounding of articular cartilage.

METHODS

Immature and mature bovine articular cartilage was used as an in vitro model system to study the cellular responses to cartilage wounding. Explant cultures were wounded centrally with a trephine and maintained for up to 10 days. TUNEL labeling together with ultrastructural analyses were used to assess the nature of the observed cell death. In vitro labeling with 3H-thymidine was used to detect cell proliferation, and 2 antibodies (COL2-3/4M and BC-13) were used to detect changes in matrix turnover.

RESULTS

Cell death was observed as a response to wounding and was considered to be a combination of necrosis and apoptosis. In immature tissue, cell death was more pronounced, particularly in the articular surface region. Within the area of cell death, many cells that did not die subsequently underwent proliferation. The collagenous network showed evidence of denaturation in the area of the wound, but "aggrecanase" activity was not detected.

CONCLUSION

There are 2 contrasting, but related, responses to cartilage wounding--apoptosis and proliferation. In order to improve cartilage repair, future studies need to elucidate the regulatory mechanisms that determine these responses.

Isotope dilution spaces of mice injected simultaneously with deuterium, tritium and oxygen-18

The isotope dilution technique for measuring total body water (TBW), and the doubly labelled water (DLW) method for measuring energy expenditure, are both sensitive to small variations in the ratio of the hydrogen to oxygen-18 dilution space. Since the dilution space ratio varies between individuals, there has been much recent debate over what causes this variability (i.e. physiological differences between individuals or analytical error in the isotope determinations), and thus which values (individual or a population mean dilution space ratio) should be employed for TBW and DLW calculations. To distinguish between physiological and analytical variability, we injected 15 non-reproductive and 12 lactating mice (Mus musculus, outbred MF1) simultaneously with deuterium, tritium and oxygen-18. The two hydrogen labels were administered and analysed independently, therefore we expected a strong correlation between dilution space ratios based on deuterium and tritium if most of the variation in dilution spaces was physiological, but only a weak correlation if most of the variation was analytical. Dilution spaces were significantly influenced by reproductive status. Dilution spaces expressed as a percentage of body mass averaged 15.7 % greater in lactating mice than in non-reproductive mice. In addition, the hydrogen tracer employed had a significant effect (deuterium spaces were 2.0 % larger than tritium spaces). Deuterium and tritium dilution spaces, expressed as a percentage of body mass, were highly correlated. Dilution space ratios ranged from 0.952 to 1. 146 when using deuterium, and from 0.930 to 1.103 when using tritium. Dilution space ratios based on deuterium and tritium were also highly correlated. Comparison of standard deviations of the dilution space ratio based on deuterium in vivo and in vitro indicated that only 4.5 % of the variation in the dilution space ratios observed in the mice could be accounted for by analytical variation in the deuterium and oxygen-18 analyses. Although our results include data which were outside the limits previously regarded as biologically possible, the correlations that we detected strongly suggest that variation in the observed dilution space ratio was mostly physiological rather than analytical.

T cell lines specific for polyomavirus T-antigen recognize T-antigen complexed with nucleosomes: a molecular basis for anti-DNA antibody production

We have previously demonstrated that in vivo expression of the polyomavirus DNA-binding T-antigen initiated production of IgG antibodies to T-antigen and to DNA, but not to a panel of autoantigens not related to nucleosomes, indicating an antigen-selective T cell-dependent B cell response. In this study, we demonstrate that CD4-positive T cells from both normal and systemic lupus erythematosus (SLE) patients readily proliferate in response to pure T-antigen, and also to T-antigen in complex with nucleosomes. T-antigen-specific T cell lines from both normal individuals and SLE patients proliferate in response to nucleosome-T-antigen complexes, but not to nucleosomes or histones. B cells co-cultured with T-antigen-specific T cells and stimulated with nucleosome-T-antigen complexes produce anti-T-antigen and anti-DNA antibodies, indicating that such CD4-positive T cells have the potential to interact with B cells specific for individual components of nucleosome-T-antigen complexes. Thus, a non-self DNA-binding protein like polyomavirus T-antigen may initiate and maintain an antibody response to DNA when T-antigen is actively expressed.

Chronic liver injury alters basal and stimulated nitric oxide production and 3H-thymidine incorporation in cultured sinusoidal endothelial cells from rats

BACKGROUND/AIM

Under pathological conditions the nitric oxide synthase (NOS)-mediated nitric oxide production of sinusoidal endothelial cells might be altered. Therefore, studies were performed to evaluate the nitrite formation by cultured sinusoidal endothelial cells from rat livers chronically injured by thioacetamide and the effect of endogenously or exogenously generated nitric oxide on their proliferative activity.

METHODS

Basal and stimulated nitrite formation, expression of NOS and DNA synthesis were examined in sinusoidal endothelial cells isolated and cultivated from livers with incipient or advanced chemically-induced cirrhosis.

RESULTS

Cultured sinusoidal endothelial cells from injured livers exhibited a reduced basal and an increased lipopolysaccharide-stimulated nitrite production when compared with controls. Western blot analysis revealed a markedly reduced protein expression of endothelial NOS (eNOS) and inducible NOS (iNOS) in sinusoidal endothelial cells from both experimental groups when compared with controls. Lipopolysaccharide stimulated iNOS expression in sinusoidal endothelial cells from control livers only marginally, and from those with cirrhosis more strongly. There was no clear correlation between the amount of enzyme and nitrite formation. Cultured sinusoidal endothelial cells from livers with incipient cirrhosis showed a higher proliferative activity than controls. Endogenously-produced nitric oxide inhibited DNA synthesis in all groups in a cGMP-independent way. Exogenously-generated nitric oxide affected DNA synthesis differently in sinusoidal endothelial cells from controls and injured livers.

CONCLUSION

The results provide evidence that cultured sinusoidal endothelial cells from controls and livers with incipient or advanced cirrhosis differ with respect to basal and lipopolysaccharide-stimulated nitrite production. The data can be taken as evidence that in sinusoidal endothelial cells from livers chronically injured by thioacetamide, eNOS and iNOS are aberrantly expressed and differently regulated.

Growth hormone receptor expression and function in meningiomas: effect of a specific receptor antagonist

OBJECT

This study was undertaken to explore the effects of growth hormone (GH) and the GH-stimulated peptide insulin-like growth factor-1 (IGF-1) on the growth rate of meningiomas.

METHODS

Polymerase chain reaction and ribonuclease protection assays were used to demonstrate that GH receptor messenger RNA was present in all 14 meningioma specimens studied, regardless of tumor grade. Both wild type (GHRwt) and a previously described exon 3 deletion isoform (GHRd3) of the GH receptor were identified in individual tumor specimens. The importance of the GH receptor was assessed using a GH receptor antagonist (B2036). Blockade of the GH receptor with B2036 reduced serum-induced DNA synthesis, as measured by thymidine incorporation, by 8 to 33% (mean 20%) in primary meningioma cultures. Tumors that expressed the GHRwt and GHRd3 isoforms, or a combination of the two, were all responsive to antagonist treatment. The importance of IGF- in stimulating meningioma cell growth was also assessed. It was found that IGF-1 increased thymidine incorporation in primary meningioma cultures in a dose-dependent manner: 1 ng/ml, 5 ng/ml, and 10 ng/ml resulted in increases in thymidine incorporation of 21%, 43%, and 176%, respectively, over baseline values.

CONCLUSIONS

In these studies the authors demonstrate that activation of the GH/IGF-1 axis significantly increases the growth rate of meningiomas. Blockade of the GH receptor on tumor cells inhibited tumor growth. If these findings are confirmed in animal studies, agents that downregulate the GH/IGF-1 axis might represent a potential adjuvant therapy in the management of patients with meningioma.

Evaluation of 3-azidiamantane as photoaffinity probe of cytochrome P450

3-azidiamantane (DIA-N2) has been shown to be a photolabile carbene-generating probe interacting specifically with cytochrome P450 (P450) active centre. To evaluate the modification of P450 by the probe, radiolabelled [9-3H]-3-azidiamantane was prepared by reductive dehalogenation of its precursor, 3-oxo-9-bromodiamantane ethylene ketal. The synthesis was optimized as the proper precursor and reaction conditions were concerned to produce 96% pure product (overall yield 59%). An incorporation efficacy of the probe photoactivated at 366 nm was examined with two different proteins, BSA and rat phenobarbital-inducible P450 2B1, both having hydrophobic binding sites. Under photolysis the photoaffinity probe generated short-lived (> 90%) intermediates binding immediately to the protein. The yield of photoactivated DIA-N2 incorporation was 12% and 11% for BSA and P450, respectively. The presence of reduced glutathione, a scavenger of reactive intermediates, did not affect the probe incorporation markedly. On the other hand, scavengers entering the P450 active centre, methanol and dithiothreitol, reduced the protein labelling by 36% and 42%, respectively. Similarly, at DIA-N2, aminopyrine (substrates), and metyrapone (inhibitor) 50 times molar excess over the probe, prevented its binding by about 40%. In addition, when photoaffinity labelling was carried out with microsomal preparation, the substrate with a high affinity for the P450 2B1, diamantane, (at 20 times molar excess to the probe) caused 47% inhibition of the P450 covalent labelling. These results, suggesting a high specificity of the probe binding, show that it can be applied as a photoaffinity probe for cytochrome P450 2B1 active centre studies.

Modulation of spontaneous and stimulation-evoked transmitter release from rat sympathetic neurons by the cognition enhancer linopirdine: insights into its mechanisms of action

The mechanisms by which the cognition enhancer linopirdine may affect transmitter release were investigated in cultures of rat superior cervical ganglion neurons. Overflow of previously incorporated [3H]noradrenaline evoked by 10 microM UTP or 0.1 microM bradykinin was enhanced by linopirdine at > or =3 microM, overflow evoked by 25 mM K(-), 100 microM nicotine, or 300 microM ATP was enhanced by linopirdine at > or =10 microM, and overflow due to 40 mM K+ or electrical field stimulation was not altered by linopirdine. Ba2+ (0.3 mM) augmented the same types of stimulation-evoked overflow to a similar extent as linopirdine. K+ (25 mM), nicotine (100 microM), and ATP (300 microM) triggered transmitter release in a partially tetrodotoxin-resistant manner, and the release-enhancing action of linopirdine was lost in the presence of tetrodotoxin (1 microM). Linopirdine (10 microM) raised spontaneous tritium outflow and reduced currents through muscarinic K+ (K(M)) channels with a similar time course. The secretagogue action of linopirdine was concentration- and Ca2(+)-dependent and abolished by tetrodotoxin (1 microM) or Cd2+ (100 microM). Linopirdine (10 microM) added to the partial inhibition of K(M) channels by 1 or 3 mM Ba2(+) but not to the complete inhibition by 10 mM Ba2(+). Likewise, the secretagogue action of 1 and 3 mM, but not that of 10 mM, Ba2+ was enhanced by linopirdine. These results indicate that linopirdine facilitates and triggers transmitter release via blockade of K(M) channels and suggest that these K+ channels are located at neuronal somata rather than at presynaptic sites.

Role of peroxisomal oxidation in the conversion of arachidonic acid to eicosatrienoic acid in human skin fibroblasts

Human skin fibroblasts converted [5,6,8,9,11,12,14,15-3H]arachidonic acid ([3H]20:4) to eicosatrienoic acid (20:3), but appreciable amounts of radiolabeled 20:3 were not detected in corresponding incubations with [1-(14)C]20:4. This indicates that the main pathway for synthesizing 20:3 from arachidonic acid in the fibroblast involves oxidative removal of the carboxyl group of arachidonic acid. Fibroblasts deficient in long-chain acyl coenzyme A dehydrogenase (LCAD) converted [3H]20:4 to [3H]20:3. However, Zellweger fibroblasts that are deficient in peroxisomal fatty acid oxidation did not, indicating that the oxidative removal of the carboxyl group occurs in the peroxisomes. [3H]Hexadecatrienoic acid (16:3) was the main product that accumulated when [3H]20:4 was incubated with normal, LCAD deficient, and very long-chain acyl coenzyme A dehydrogenase (VLCAD) deficient fibroblasts, but Zellweger fibroblasts did not form this product. Normal fibroblasts converted [3H]16:3 to radiolabeled 20:3 and arachidonic acid. These findings suggest that some of the 16:3 produced from arachidonic acid by peroxisomal beta-oxidation can be recycled and that this recycling process constitutes a novel pathway for the conversion of arachidonic acid to 20:3 in human fibroblasts.

Involvement of PKR in the regulation of myogenesis

The involvement of the double-stranded RNA-activated protein kinase PKR in the regulation of the myogenic process was investigated. For this purpose, the murine myogenic cell line C2C12 was used. The cells were first cultivated in either growth medium or differentiation medium (DM), and the activation of PKR during differentiation was determined by monitoring its enzymatic activity and by immunoblot analysis. A significant increase in both parameters was detected already at 24 h in DM, whereas in cells grown in growth medium, the increase was evident only after 96 h, when spontaneous differentiation was observed in highly crowded cultures. Consequently, we established the direct effect of PKR activation on the myogenic process. C2C12 cells were transfected with an expression vector harboring a cDNA molecule encoding human PKR fused to the inducible metallothionein promoter. One of the clones (clone 8) expressing high levels of PKR was selected and further analyzed. In the presence of ZnCl2, which activates the promoter, the rate of cell growth of the transfected cells was clearly reduced compared to that of wild-type C2C12 cells transfected with only the neomycin-resistant gene (C2-NEO). In addition, altered morphology with partial fusion was observed. Biochemically, an increase in creatine kinase activity accompanied by an increased rate of expression of the myogenic protein troponin T and the myogenic transcription factors myoD and myogenin was detected in clone 8 cells exposed to ZnCl2. Most importantly, an induction in the level of cyclin-dependent kinase inhibitor p21WAF1 and an increase in the level of the underphosphorylated active form of the tumor suppressor protein pRb concomitant with the down-regulation of cyclin D1 and c-myc were also evident in the transfected clones. These changes were similar to those observed in normal C2C12 cells cultivated in DM. We conclude that PKR is an important regulatory protein participating in the myogenic process.

Histamine H3 receptor-mediated inhibition of noradrenaline release in the human brain

Stimulation-evoked 3H-noradrenaline release in human cerebrocortical slices was inhibited by histamine (in a manner sensitive to clobenpropit) and by imetit, suggesting H3 receptor-mediated inhibition of noradrenaline release in human brain.

Expression and function of lymphocyte function associated antigen-3 (LFA-3) at the blood-brain barrier

Lymphocyte function associated antigen-3 (LFA-3) is a cell surface glycoprotein involved in antigen independent T-cell activation and proliferation. The expression and function of LFA-3 at the blood-brain barrier were studied in an in vitro model consisting of primary cultures of human brain microvessel endothelial cells (HBMEC). Surface expression of LFA-3 was detected by immunogold silver staining and the presence of RNA by reverse transcriptase-polymerase chain reaction (RT-PCR). Unstimulated HBMEC in primary culture constitutively express LFA-3 on their surface. Expression is only marginally upregulated following stimulation with tumor necrosis factor-alpha (TNF-alpha) or interferon-gamma (IFN-gamma). Similarly, LFA-3 RNA is present constitutively in unstimulated HBMEC with minimal increase after co-incubation with TNF-alpha and IFN-gamma. The function of LFA-3 as a costimulatory molecule on HBMEC was investigated by incubating purified CD4+ T-lymphocytes with resting or IFN-gamma treated HBMEC monolayers. Proliferation of alpha-CD3 activated CD4+ T-cells was significantly increased upon incubation with resting or activated endothelial cells. Monoclonal antibodies to LFA-3 consistently blocked the proliferative response by 64-76%. The ability of the cerebral endothelium to express LFA-3 and provide secondary signals for T-cell proliferation suggests that cerebral EC may be important in the initiation of inflammatory responses in the human central nervous system.

Metabolic processing of newly synthesized link protein in bovine articular cartilage explant cultures

In explant cultures of articular cartilage from cattle of different ages radiolabeled leucine was shown to be incorporated into link proteins 1, 2 and 3. The newly synthesized link proteins were incorporated into and lost from the cartilage extracellular matrix with time. The levels of radiolabeled link proteins 1 and 2 remaining in the matrix declined over the culture period, but there was an initial increase in the amount of radiolabeled link protein 3, before its level declined. The turnover time of the radiolabeled link proteins 1 and 2 were similar, indicating that neither link protein was preferentially processed to generate link protein 3, nor lost from the extracellular matrix. The majority of the radiolabeled link protein lost from the cartilage matrix could not be recovered from the culture medium, suggesting that turnover of the radiolabeled aggrecan complexes involves the newly synthesized link protein being internalized by the chondrocytes. Inclusion of cytotoxic proteinase inhibitors to the culture medium resulted in a marked decrease in the rate of loss of link protein from the cartilage, suggesting that the catabolism of link protein is cell-mediated and dependent on metabolically active cells.