Distribution of chloride channel-2-immunoreactive neuronal and astrocytic processes in the hippocampus

The chloride homeostasis of neurons and non-neuronal cells is maintained in part by a voltage-sensitive inwardly rectifying chloride conductance through the chloride channel-2. This channel is activated by hyperpolarization and extracellular hypotonicity. In the present study, hippocampal sections were immunostained for chloride channel-2, and somata and dendrites of both pyramidal and non-pyramidal cells were found to be immunoreactive. In addition, glial processes in the vicinity of small blood vessels were also immunostained, whereas the neuropil of strata pyramidale and lacunosum-moleculare contained chloride channel-2-positive punctate structures. Electron microscopy and double immunostaining using antibodies against chloride channel-2 and glial fibrillary acidic protein confirmed that the dense network of chloride channel-2-positive processes corresponds to the end feet of astrocytes. The distribution of chloride channel-2-immunoreactive astrocytes was inhomogeneous throughout the hippocampus: strata oriens, pyramidale and lacunosum-moleculare of CA1-CA3 and the outer molecular layer of the dentate gyrus contained the majority of immunoreactive end feet, whereas the other layers showed sparse labeling. Subcellular studies demonstrated that, in addition to astrocytes, chloride channel-2 was localized in the membrane of dendrites, dendritic spines, cell bodies and axon initial segments of neurons, frequently close to, or within active zones of, symmetrical synapses.Thus, chloride channel-2 appears to be involved in transmembrane chloride movements associated with GABAergic synaptic transmission. The specific laminar distribution of chloride channel-2-positive astroglial processes coinciding with that of GABAergic axon terminals suggests that the network of astrocytes may be able to siphon and deliver Cl(-) ions to layers with intense GABAergic transmission, thereby increasing the efficacy of GABA(A) receptor-mediated inhibition.

Inducible cyclic AMP early repressor produces reactivation of latent herpes simplex virus type 1 in neurons in vitro

Herpes simplex virus type 1 (HSV-1) establishes a latent infection in neurons of the peripheral nervous system. During latent HSV-1 infection, viral gene expression is limited to latency-associated transcripts (LAT). HSV-1 remains latent until an unknown mechanism induces reactivation. The ability of the latent virus to periodically reactivate and be shed is essential to the transmission of disease. In vivo, the stimuli that induce reactivation of latent HSV-1 include stress, fever, and UV damage to the skin at the site of initial infection. In vitro, in primary neurons harboring latent HSV-1, nerve growth factor (NGF) deprivation or forskolin treatment induces reactivation. However, the mechanism involved in the induction of reactivation remains poorly understood. An in vitro neuronal model of HSV-1 latency was used to investigate potential mechanisms involved in the induction of reactivation of latent HSV-1. In situ hybridization analysis of neuronal cultures harboring latent HSV-1 showed a marked, rapid decrease in the percentage of LAT-positive neurons following induction of reactivation by NGF deprivation or forskolin treatment. Western blot analysis showed a corresponding increase in expression of the cellular transcription factor inducible cyclic AMP early repressor (ICER) during reactivation. In transient-transfection assays, ICER downregulated LAT promoter activity. Expression of ICER from a recombinant adenoviral vector induced reactivation and decreased the percentage of LAT-positive neurons in neuronal cultures harboring latent HSV-1. These results indicate that ICER represses LAT expression and induces reactivation of latent HSV-1.

ClC-2 chloride channels contribute to HTC cell volume homeostasis

Membrane Cl(-) channels play an important role in cell volume homeostasis and regulation of volume-sensitive cell transport and metabolism. Heterologous expression of ClC-2 channel cDNA leads to the appearance of swelling-activated Cl(-) currents, consistent with a role in cell volume regulation. Since channel properties in heterologous models are potentially modified by cellular background, we evaluated whether endogenous ClC-2 proteins are functionally important in cell volume regulation. As shown by whole cell patch clamp techniques in rat HTC hepatoma cells, cell volume increases stimulated inwardly rectifying Cl(-) currents when non-ClC-2 currents were blocked by DIDS (100 microM). A cDNA closely homologous with rat brain ClC-2 was isolated from HTC cells; identical sequence was demonstrated for ClC-2 cDNAs in primary rat hepatocytes and cholangiocytes. ClC-2 mRNA and membrane protein expression was demonstrated by in situ hybridization, immunocytochemistry, and Western blot. Intracellular delivery of antibodies to an essential regulatory domain of ClC-2 decreased ClC-2-dependent currents expressed in HEK-293 cells. In HTC cells, the same antibodies prevented activation of endogenous Cl(-) currents by cell volume increases or exposure to the purinergic receptor agonist ATP and delayed HTC cell volume recovery from swelling. These studies provide further evidence that mammalian ClC-2 channel proteins are functional and suggest that in HTC cells they contribute to physiological changes in membrane Cl(-) permeability and cell volume homeostasis.

In vitro reaction to orthopaedic biomaterials by macrophages and lymphocytes isolated from patients undergoing revision surgery

Periprosthetic tissues observed at sites of loose total joint implants exhibit abundant macrophages, lymphocytes, fibroblasts and particulate debris. Macrophages phagocytose orthopaedic debris and release proinflammatory cytokines, chemokines, matrix metalloproteinases and other substances. In addition, other cell types present in tissues harvested from the bone-implant interface are thought to influence periprosthetic bone resorption. The present study examined the effects of polymethylmethacrylate (PMMA), cobalt chrome molybdenum alloy (CoCr), and titanium-alloy particle challenge on macrophages co-cultured with lymphocytes in vitro. Potential synergistic effects of lymphocytes on macrophage activation were determined by measuring interleukin-6 and tumor necrosis factor-alpha release following exposure to orthopaedic biomaterial particles. Exposure of macrophages or macrophages co-cultured with lymphocytes to all three types of particles resulted in increased release of interleukin-6 and tumor necrosis factor-alpha at 48 h, when compared to macrophages or macrophages co-cultured with lymphocytes, respectively, cultured in the absence of particles. Lymphocytes isolated from periprosthetic tissues secreted increased basal levels of cytokines relative to peripheral blood lymphocytes. Higher doses of PMMA and titanium-alloy particles stimulated increased levels of cytokine release in the macrophage and macrophage/lymphocyte groups. In contrast, a higher dose of CoCr particles (0.075% v/v) was not as effective as the 0.015% v/v dose, indicating probable CoCr toxicity. The macrophage/lymphocyte co-culture did not show synergism between the two types of cells with respect to cytokine release. T-cells at the bone-implant interface may alter the biological response to particulate debris.

Urinary thiocyanate levels as a biomarker for the generation of inorganic cyanide from benzyl cyanide in the rat

A colorimetric procedure was developed and validated for the determination of thiocyanate in rat urine over the concentration range of 7-7000 microg/ml. It was applied to the determination of thiocyanate following its oral administration to male and female rats. The mean percentage urinary recoveries of sodium thiocyanate given by oral gavage at 10 and 100 mg/kg were 60 and 39%, respectively, for male rats and 89 and 73% for females over a period of 3 days. Most of the elimination occurred in the 0-48-h period post-dosing but significant amounts were still being excreted in the 48-72-h period. It was concluded from these results that the recoveries of urinary thiocyanate were such that this anion was suitable for use as a biomarker for the release of cyanide from organonitriles such as benzyl cyanide. Benzyl cyanide (150 mg/kg) administered orally to rats led to markedly increased urinary thiocyanate levels; for male rats this was equivalent to 54% of the dose and for females this was 65% over a period of 3 days. When adjusted for incomplete recoveries of the marker, thiocyanate, these values equated to 61 and 89%, respectively. It was concluded that this validated assay could be used to assess cyanide release from topically applied fragrance organonitriles (Potter, J., Smith, R.L., Api, A.M., 2000. An assessment of the release of inorganic cyanide from the fragrance materials, benzyl cyanide, geranyl nitrile and citronellyl nitrile applied dermally to the rat. Food and Chemical Toxicology 39, 147-151).

An assessment of the release of inorganic cyanide from the fragrance materials benzyl cyanide, geranyl nitrile and citronellyl nitrile applied dermally to the rat

Organonitriles are widely used as components of fragrances that are incorporated into consumer products, many of which are for human topical use. Some organontriles are readily broken down metabolically to potentially toxic inorganic cyanide. Studies were therefore undertaken to assess whether this occurs with three representative fragrance nitriles, namely, benzyl cyanide, geranyl nitrile and citronellyl nitrile when applied dermally to the rat. The nitriles (benzyl cyanide, 150 mg/kg; geranyl and citronellyl nitriles, 400 mg/kg) were applied to the shaved backs of rats and maintained under occlusion for 24 h. Urine samples were collected for 0-24 h, 24-48 h and 48-72 h from the time of first application. These samples were analysed for thiocyanate, a biomarker for cyanide formation in vivo, as described previously (Potter, J., Smith, R.L., Api, A.M., 2000. Urinary thiocyanate levels as a biomarker for the generation of inorganic cyanide from benzyl cyanide in the rat. Food and Chemical Toxicology 39, 141-146). In the case of benzyl cyanide, there was a marked increase in urinary thiocyanate levels attributable to the release of cyanide in vivo. The amount of thiocyanate recovered was equivalent to 37% of the dose for males and 32% for females. For geranyl nitrile there was no significant increase in urinary thiocyanate excretion and there was only a marginal increase in the case of citronellyl nitrile that was equivalent to 0.40% of the applied dose for males and 0.29% for females.

In situ stimulation of groundwater denitrification with formate to remediate nitrate contamination

In situ stimulation of denitrification has been proposed as a mechanism to remediate groundwater nitrate contamination. In this study, sodium formate was added to a sand and gravel aquifer on Cape Cod, MA, to test whether formate could serve as a potential electron donor for subsurface denitrification. During 16- and 10-day trials, groundwater from an anoxic nitrate-containing zone (0.5-1.5 mM) was continuously withdrawn, amended with formate and bromide, and pumped back into the aquifer. Concentrations of groundwater constituents were monitored in multilevel samplers after up to 15 m of transport by natural gradient flow. Nitrate and formate concentrations were decreased 80-100% and 60-70%, respectively, with time and subsequent travel distance, while nitrite concentrations inversely increased. The field experiment breakthrough curves were simulated with a two-dimensional site-specific model that included transport, denitrification, and microbial growth. Initial values for model parameters were obtained from laboratory incubations with aquifer core material and then refined to fit field breakthrough curves. The model and the lab results indicated that formate-enhanced nitrite reduction was nearly 4-fold slower than nitrate reduction, but in the lab, nitrite was completely consumed with sufficient exposure time. Results of this study suggest that a long-term injection of formate is necessary to test the remediation potential of this approach for nitrate contamination and that adaptation to nitrite accumulation will be a key determinative factor.

Ethylamine in human urine

The urinary excretion of ethylamine has been measured in 200 unrelated healthy volunteers (100 male, 100 female) who maintained their normal diet. The average daily output was 7.82+/-7.03 mg (mean+/-S.D.) (8.01+/-7.40 male; 7.64+/-6.67 female) with a range of values spreading from 0.22 to 35.27 mg. Dietary studies investigating 41 food substances did not highlight any major sources of this amine, except that drinking tea increased subsequent urinary ethylamine levels.

Compound heterozygosity for missense mutations in the flavin-containing monooxygenase 3 (FM03) gene in patients with fish-odour syndrome

Fish-odour syndrome is a highly unpleasant disorder of hepatic trimethylamine (TMA) metabolism characterized by a body odour reminiscent of rotting fish, due to excessive excretion of the malodorous free amine. Although fish-odour syndrome may exhibit as sequelae with other conditions (e.g. liver dysfunction), many patients exhibit an inherited, more persistent form of the disease. Ordinarily, dietary-derived TMA is oxidized to the nonodorous N-oxide by hepatic flavin-containing monooxygenase 3 (FMO3). Our previous demonstration that a mutation, P153L (C to T), in the FMO3 gene segregated with the disorder and inactivated the enzyme confirmed that defects in FMO3 underlie the inherited form of fish-odour syndrome. We have investigated the genetic basis of the disorder in two further affected pedigrees and report that the three propositi are all compound heterozygotes for causative mutations of FMO3. Two of these individuals possess the P153L (C to T) mutation and a novel mutation, N61S (A to G). The third is heterozygous for novel, M4341 (G to A), and previously reported, R492W (C to T), mutations. Functional characterization of the S61, 1434 and W492 variants, via baculovirus-mediated expression in insect cells, confirmed that all three mutations either abolished, or severely attenuated, the capacity of the enzyme to catalyse TMA N-oxidation. Although 1434 and W492 were also incapable of catalysing the S-oxidation of methimazole, S61 was fully active with this sulphur-containing substrate. Since an asparagine is conserved at the equivalent position to N61 of FMO3 in mammalian, yeast and Caenorhabditis elegans FMOs, the characterization of the naturally occurring N61S (A to G) mutation may have identified this asparagine as playing a critical role specifically in FMO-catalysed N-oxidation.

Characterization of promoter function and cell-type-specific expression from viral vectors in the nervous system

Viral vectors have become important tools to effectively transfer genes into terminally differentiated cells, including neurons. However, the rational for selection of the promoter for use in viral vectors remains poorly understood. Comparison of promoters has been complicated by the use of different viral backgrounds, transgenes, and target tissues. Adenoviral vectors were constructed in the same vector background to directly compare three viral promoters, the human cytomegalovirus (CMV) immediate-early promoter, the Rous sarcoma virus (RSV) long terminal repeat, and the adenoviral E1A promoter, driving expression of the Escherichia coli lacZ gene or the gene for the enhanced green fluorescent protein. The temporal patterns, levels of expression, and cytotoxicity from the vectors were analyzed. In sensory neuronal cultures, the CMV promoter produced the highest levels of expression, the RSV promoter produced lower levels, and the E1A promoter produced limited expression. There was no evidence of cytotoxicity produced by the viral vectors. In vivo analyses following stereotaxic injection of the vector into the rat hippocampus demonstrated differences in the cell-type-specific expression from the CMV promoter versus the RSV promoter. In acutely prepared hippocampal brain slices, marked differences in the cell type specificity of expression from the promoters were confirmed. The CMV promoter produced expression in hilar regions and pyramidal neurons, with minimal expression in the dentate gyrus. The RSV promoter produced expression in dentate gyrus neurons. These results demonstrate that the selection of the promoter is critical for the success of the viral vector to express a transgene in specific cell types.

Echocardiographic predictors of survival in low gradient aortic stenosis

Echocardiographic predictors of long-term survival for patients with low gradient aortic stenosis who undergo aortic valve replacement have not been previously reported. This study shows that patients with larger pre- and postoperative left ventricular volumes, a lower mean preoperative aortic pressure gradient, and failure of volumes to decrease and ejection fraction to increase postoperatively may have a poor prognosis.

The interaction of MRI contrast agents with phospholipids

The molecular interactions of three clinically used MRI contrast agents with lipid vesicles, consisting of egg phosphatidylcholine (EPC), have been studied using high-field NMR techniques. At a molar ratio of one contrast agent molecule to five phospholipid molecules, a significant increase in the proton resonance line width occurred for certain lipid head group moieties. A large decrease in the T1 relaxation times for the head group moieties was also observed. These two effects occurred regardless of the ionic status and the chelate structure of the three contrast agents. The structure of the contrast agents did, however, affect the magnitude of the two NMR parameter changes. These NMR effects also differed in magnitude amongst the various head group entities. The NMR effects were greatest for the head group moieties at or near the vesicle-water interface. The results are discussed in terms of the structure of the phospholipid-water interface. Since the use of contrast agents has become routine in clinical MRI, our results are of importance in terms of the interaction of the agents with physiological surfaces, many of which contain phospholipids. The understanding of such interactions should be of value not only for improved diagnostics, but also in the development of new contrast agents.

G-protein activity requirement for polymethylmethacrylate and titanium particle-induced fibroblast interleukin-6 and monocyte chemoattractant protein-1 release in vitro

Periprosthetic granulomatous membranes consisting of fibroblasts, macrophages, lymphocytes, foreign body giant cells, and abundant particulate debris occur at sites of implant loosening. Previous studies demonstrate that fibroblasts respond to particulate debris through the release of interleukin-6 (IL-6), prostaglandin E(2), and matrix metalloproteinases in vitro. C-C chemokines are observed in granulomatous tissue surrounding loosened prosthetic implants and are released by macrophages and fibroblasts in response to particle challenge in vitro. This study tested the hypothesis that G protein activity is required for fibroblast activation by titanium and polymethylmethacrylate (PMMA) particles, and that inhibition of G protein activity would alter IL-6 and and monocyte chemoattractant protein-1 (MCP-1) release from activated fibroblasts. The specific inhibitor of G protein activity, pertussis toxin, was added to the fibroblasts to examine the effects of G protein activity with respect to the production of IL-6 and MCP-1 by orthopedic biomaterial-challenged fibroblasts in vitro. Interleukin-1beta (IL-1beta), a proven activator of MCP-1 and interleukin-6, was used as a positive control. Exposure of fibroblasts to titanium and polymethylmethacrylate (PMMA) particles resulted in a dose-dependent release of MCP-1 and IL-6. Challenge with PMMA particles at doses of 0.150%, 0.300%, and 0.600% vol/vol increased the release of interleukin-6 by 7-, 19-, and 22-fold, respectively, compared to fibroblasts exposed to serum-free culture medium alone at 24 h. Challenge with PMMA particles at doses of 0.075%, 0.150%, 0.300%, and 0.600% vol/vol increased the release of MCP-1-6 by 2.5-, 3.6-, 4. 3-, and 4.5-fold, respectively, compared to fibroblasts exposed to serum-free culture medium alone. Challenge with titanium particles at concentrations of 0.075%, 0.150%, 0.300%, and 0.600% vol/vol increased the release of interleukin-6 by 2.6-, 6.4-, 9.6-, and 10. 0-fold, respectively, compared to fibroblasts exposed to serum-free culture medium alone at 24 h. Challenge with titanium particles at concentrations of 0.038%, 0.075%, 0.150%, 0.300%, and 0.600% vol/vol increased the release of MCP-1 by 2.9-, 3.1-, 5.8-, 5.4-, and 5. 8-fold, respectively, compared to fibroblasts exposed to serum-free culture medium alone. Pretreatment of fibroblasts with pertussis toxin inhibited the release of interleukin-6 and MCP-1 from PMMA and titanium particle challenged fibroblasts in a dose-dependent manner. PMMA particle induced fibroblast IL-6 release was inhibited by 23.6% and 35.3% with 20- and 200-ng/mL doses of pertussis toxin, respectively. Titanium particle induced fibroblast IL-6 release was inhibited by 48.2% and 56.3% with 20- and 200-ng/mL doses of pertussis toxin, respectively. PMMA particle-induced fibroblast MCP-1 release was inhibited by 36.0%, 50.4%, and 60.1% with 2-, 20- and 200-ng/mL doses of pertussis toxin, respectively. Titanium particle-induced fibroblast MCP-1 release was inhibited by 15.5%, 53.2%, and 64.6% with 2-, 20-, and 200-ng/mL doses of pertussis toxin, respectively. This study suggests that fibroblasts localized in periprosthetic membranes are a source of macrophage chemoattractant factors and proinflammatory mediators that may influence granuloma formation and lead to periprosthetic bone resorption. Furthermore, this study shows that G proteins are involved in particle-induced fibroblast activation, as evidenced by decrease levels of particle induced IL-6 and MCP-1 release following pertussis toxin treatment. (c) 2000 John Wiley & Sons, Inc.

Effects of local infusion of TGFbeta on bone ingrowth in rabbit chambers

The local delivery of exogenous growth factors may help achieve a stable, long-lasting prosthetic interface around primary and revision joint replacements. This study examines the effects of local infusion of transforming growth factor beta (TGFbeta) in an in vivo model of tissue differentiation within bone. The Drug Test Chamber was implanted in the proximal medial tibial metaphysis of 8 mature rabbits unilaterally. The chamber contained a 1 x 1 x 5 mm canal for tissue ingrowth. The chamber was connected to an osmotic diffusion pump via polyvinyl tubing. 3.5 microg of recombinant TGFbeta1 was infused for 1 day or 1 week with subsequent harvesting of the ingrown tissue after 3 weeks. Each TGFbeta treatment was followed by two, 3-week infusions of carrier alone and harvesting of the ingrown tissue. TGFbeta for 1 day increased, and TGFbeta for 1 week decreased the percentage of bone in the chamber, compared to the initial control harvest after carrier alone. These changes, however, did not reach statistical significance. The number of vitronectin receptor positive cells in total, adjacent to bone and away from bone was higher after treatment with TGFbeta for 1 day, compared to 1 week. In an "unperturbed" bone ingrowth system (i.e., if bone ingrowth is not initially suppressed by other stimuli), this dose of TGFbeta did not enhance bone ingrowth using the DTC model.

On a likelihood-based goodness-of-fit test of the beta-binomial model

When faced with proportion data that exhibit extra-binomial variation, data analysts often consider the beta-binomial distribution as an alternative model to the more common binomial distribution. A typical example occurs in toxicological experiments with laboratory animals, where binary observations on fetuses within a litter are often correlated with each other. In such instances, it may be of interest to test for the goodness of fit of the beta-binomial model; this effort is complicated, however, when there is large variability among the litter sizes. We investigate a recent goodness-of-fit test proposed by Brooks et al. (1997, Biometrics 53, 1097-1115) but find that it lacks the ability to distinguish between the beta-binomial model and some severely non-beta-binomial models. Other tests and models developed in their article are quite useful and interesting but are not examined herein.

Induction of interleukin-6 release in human osteoblast-like cells exposed to titanium particles in vitro

Orthopaedic wear debris induces release of bone-resorbing factors from macrophages and fibroblasts. However, the extent to which elemental metallic particles induce bone cells to express factors contributing to implant loosening remains unclear. This study showed that exposure of MG-63 osteoblast-like cells to titanium particles at a concentration of 0.30% v/v resulted in a 15-fold increase in IL-6 release into the culture medium after 24 hours, when compared with cells without particles. Northern blots revealed that exposure of MG-63 cells to titanium particles at a concentration of 0.30% v/v for 24 hours increased IL-6 mRNA signal levels by 9.6-fold, when compared with control cultures. Pretreatment of MG-63 cells with cytochalasin B prevented the particle-induced increase of IL-6 expression but did not alter the basal level of IL-6 release from cells cultured in the absence of particles. The protein kinase C inhibitor, H7, and the serine/threonine kinase inhibitor, genistein, abolished the particle-induced increase in IL-6 release at a concentration of 100 microM for each compound. In contrast, an inhibitor of protein kinase A, HA1004, had no effect on the particle-induced increase in IL-6 release. The transcription factors, nuclear factor IL-6 and nuclear factor kappa B, translocated into the nucleus within 1 hour of particle exposure. This study showed that osteoblast-like cells respond to titanium particles through increased expression of the proinflammatory cytokine, IL-6, in a process requiring phagocytosis and intracellular signaling pathways. These results suggest that osteoblasts play a direct role in implant loosening because of localized release of soluble mediators such as interleukin-6.

Ultrastructural identification of dentate granule cell death from pilocarpine-induced seizures

Cell loss in the hippocampal formation is a common event in patients with temporal lobe epilepsy. The belief that dentate granule neurons are relatively resistant to excitotoxic injury has recently been challenged both, in epileptic patients and in animal models of temporal lobe epilepsy. The nature of dentate granule cell damage in epilepsy has been reported as either apoptotic, necrotic or both. The lack of a consensus on this topic stems from use of different animal models and different experimental techniques for characterizing the apoptotic/necrotic process. Using electron microscopy for defining the, nature of cell loss and one of the main animal models of status epilepticus (SE) we have focussed on the nature of the degenerative process in dentate granule cells. Ultrastructural morphological changes of these cells were evaluated 2.5-48 h after pilocarpine-induced status epilepticus. A variety of morphologies ranging from apoptosis to necrosis, could be seen at 2.5 h after SE onset and continued at least over the following 48 h. Some cells displayed coalescence of chromatin against nuclear membranes. In such cases however, chromatin did not have well-defined edges (as it should, if it were apoptosis). Condensation of cytoplasm. present in both processes was also frequently found. Neither obvious apoptotic budding-off of cytoplasm nor typical membrane-bound apoptotic bodies were found. Our results indicate that in the dentate granule cell layer pilocarpine-induced SE promotes a degenerative process in which apoptotic and necrotic features overlap.

Threshold dependence of mortality effects for fine and coarse particles in Phoenix, Arizona

Daily data for fine (< 2.5 microns) and coarse (2.5-10 microns) particles are available for 1995-1997 from the U.S. Environmental Protection Agency (EPA) research monitor in Phoenix, AZ. Mortality effects on the 65 and over population were studied for both the city of Phoenix and for a region of about 50 mi around Phoenix. Coarse particles in Phoenix are believed to be natural in origin and spatially homogeneous, whereas fine particles are primarily vehicular in origin and concentrated in the city itself. For this reason, it is natural to focus on city mortality data when considering fine particles, and on region mortality data when considering coarse particles, and most of the results reported here correspond to those assignments. After allowing for seasonality and long-term trend through a nonlinear (B-spline) trend curve, and also for meteorological effects based on temperature and specific humidity, a regression of mortality was performed on PM using several different measures for PM. Based on a linear PM effect, we found a statistically significant coefficient for coarse particles, but not for fine particles, contrary to what is widely believed about the effects of coarse and fine particles. An analysis of nonlinear pollution-mortality relationships, however, suggests that the true picture is more complicated than that. For coarse particles, the evidence for any nonlinear or threshold-based effect is slight. For fine particles, we found evidence of a threshold, most likely with values in the range of 20-25 micrograms/m3. We also found some evidence of interactions of the PM effects with season and year. The main effect here is an apparent seasonal interaction in the coarse PM effect. An attempt was made to explain this in terms of seasonal variation in the chemical composition of PM, but this led to another counterintuitive result: the PM effect is highest in spring and summer, when the anthropogenic concentration of coarse PM is lowest as determined by a principal components analysis. There was no evidence of confounding between the fine and coarse PM effects. Although these results are based on one city and should be considered tentative until replicated in other studies, they suggest that the prevailing focus on fine rather than coarse particles may be an oversimplification. The study also shows that consideration of nonlinear effects can lead to real changes of interpretation and raises the possibility of seasonal effects associated with the chemical composition of PM.

Turning genes off by Ssn6-Tup1: a conserved system of transcriptional repression in eukaryotes

The Ssn6-Tup1 repressor forms one of the largest and most important gene-regulatory circuits in budding yeast. This circuit, which appears conserved in flies, worms and mammals, exemplifies how a 'global' repressor (i.e. a repressor that regulates many genes in the cell) can be highly selective in the genes it represses. It also explains how, given the appropriate signal, specific subsets of these genes can be derepressed. Ssn6-Tup1 seems especially robust, bringing about a high level of repression irrespective of its precise placement on DNA or of specific features of the DNA control regions of its target genes. This high degree of repression probably results from several distinct mechanisms acting together.

Monocyte migration inhibitory factor synthesis and gene expression in particle-activated macrophages

This study analysed MIF mRNA and protein expression in human macrophages exposed in vitro to polymethylmethacryate and titanium alloy particles. MIF levels released from macrophages without exposure to particles were in the range of 2-4 ng/ml. Exposure of macrophages to particles as demonstrated increased MIF release at 0. 075%-0.225% v/v particle concentration, which was maximal at 12-24 h. MIF mRNA signal levels in cells with and without particles at a concentration of 0.075% showed no significant differences in a time course experiment. The profile of MIF release in response to increasing particle concentration coincided with increased release of lactate dehydrogenase. The viability of the cells was unchanged by the addition of particles as determined by 3H-thymidine uptake. These data suggest that MIF expression may represent an independent macrophage response to locally high particle concentrations.

Effects of polyethylene particles on tissue surrounding knee arthroplasties in rabbits

Clinical studies suggest a role for polyethylene (PE) wear debris in the pathogenesis of osteolysis and loosening of total joint replacements. In this study, submicron particles of ultrahigh molecular weight PE (UHMWPE) were placed around pressfit tibial hemiarthroplasties in rabbits to determine the biological reaction. After 6 months the periprosthetic tissue was harvested and characterized biochemically by measuring the extracellular matrix macromolecules, collagen, and glycosaminoglycan (GAG) and quantifying the expression of inflammatory/osteolytic mediators [prostaglandin E2 (PGE2), hexosaminidase, transforming growth factor beta (TGF beta), and interleukins-6 and -1 (IL-6, IL-1)]. Particle exposure resulted in a decrease in levels of total extracellular matrix molecules including a 53% decrease in total GAG (p < 0.05) and a 74% decrease in total collagen (p < 0.005). Collagen content remained significantly decreased when normalized for cellularity (DNA content). Total TGF beta release exhibited a downward trend (p = 0.06) in the particle exposed group. Hexosaminidase and PGE2 levels did not show a difference between groups; however, when normalized for cellularity, PGE2 values exhibited an upward trend in the particle exposed group (p = 0.1). IL-6 was undetected by bioassay and ELISA. Previous studies emphasized that PE debris enhances the degradation of bone. The data from this in vivo model suggest that submicron UHMWPE particles may also act to inhibit biosynthetic pathways of bone and mesenchymal tissue. Decreased levels of collagen, GAG, and TGF beta expression may indicate suppression of bone formation, possibly through a downregulation of osteoblast activity.

A sequence resembling a peroxisomal targeting sequence directs the interaction between the tetratricopeptide repeats of Ssn6 and the homeodomain of alpha 2

The tetratricopeptide repeat (TPR) is a 34-aa sequence motif, typically found in tandem clusters, that occurs in proteins of bacteria, archea, and eukaryotes. TPRs interact with other proteins, although few details on TPR-protein interactions are known. In this paper we show that a portion of a loop in the homeodomain of the DNA-binding protein alpha2 is required for its recognition by the TPRs of the corepressor Ssn6. The amino acid sequence of this loop is similar to the sequences recognized by the TPRs of an entirely different protein, Pex5, which directs peroxisomal import. We further show that alpha2 can be made to bind specifically in vitro to the TPRs of Pex5 and that a point mutation that disrupts the alpha2-Ssn6 interaction also disrupts the alpha2-Pex5 interaction. These results demonstrate that two different TPR proteins recognize their target by a similar mechanism, raising the possibility that other TPR-target interactions could occur through the same means.