Assembly of protein tertiary structures from fragments with similar local sequences using simulated annealing and Bayesian scoring functions

We explore the ability of a simple simulated annealing procedure to assemble native-like structures from fragments of unrelated protein structures with similar local sequences using Bayesian scoring functions. Environment and residue pair specific contributions to the scoring functions appear as the first two terms in a series expansion for the residue probability distributions in the protein database; the decoupling of the distance and environment dependencies of the distributions resolves the major problems with current database-derived scoring functions noted by Thomas and Dill. The simulated annealing procedure rapidly and frequently generates native-like structures for small helical proteins and better than random structures for small beta sheet containing proteins. Most of the simulated structures have native-like solvent accessibility and secondary structure patterns, and thus ensembles of these structures provide a particularly challenging set of decoys for evaluating scoring functions. We investigate the effects of multiple sequence information and different types of conformational constraints on the overall performance of the method, and the ability of a variety of recently developed scoring functions to recognize the native-like conformations in the ensembles of simulated structures.

The axis-inducing activity, stability, and subcellular distribution of beta-catenin is regulated in Xenopus embryos by glycogen synthase kinase 3

The serine/threonine kinase Xgsk-3 and the intracellular protein beta-catenin are necessary for the establishment of the dorsal-ventral axis in Xenopus. Although genetic evidence from Drosophila indicates that Xgsk-3 is upstream of beta-catenin, direct interactions between these proteins have not been demonstrated. We demonstrate that phosphorylation of beta-catenin in vivo requires an in vitro amino-terminal Xgsk-3 phosphorylation site, which is conserved in the Drosophila protein armadillo. beta-catenin mutants lacking this site are more active in inducing an ectopic axis in Xenopus embryos and are more stable than wild-type beta-catenin in the presence of Xgsk-3 activity, supporting the hypothesis that Xgsk-3 is a negative regulator of beta-catenin that acts through the amino-terminal site. Inhibition of endogenous Xgsk-3 function with a dominant-negative mutant leads to an increase in the steady-state levels of ectopic beta-catenin, indicating that Xgsk-3 functions to destabilize beta-catenin and thus decrease the amount of beta-catenin available for signaling. The levels of endogenous beta-catenin in the nucleus increases in the presence of the dominant-negative Xgsk-3 mutant, suggesting that a role of Xgsk-3 is to regulate the steady-state levels of beta-catenin within specific subcellular compartments. These studies provide a basis for understanding the interaction between Xgsk-3 and beta-catenin in the establishment of the dorsal-ventral axis in early Xenopus embryos.

The hematopoietic growth factor KL is encoded by the Sl locus and is the ligand of the c-kit receptor, the gene product of the W locus

Mutations at the steel locus (Sl) of the mouse affect the same cellular targets as mutations at the white spotting locus (W), which is allelic with the c-kit proto-oncogene. We show that KL, a hematopoietic growth factor obtained from conditioned medium of BALB/c 3T3 fibroblasts that stimulates the proliferation of mast cells and early erythroid progenitors, specifically binds to the c-kit receptor. The predicted amino acid sequence of isolated KL-specific cDNA clones suggests that KL is synthesized as an integral transmembrane protein. Linkage analysis maps the KL gene to the Sl locus on mouse chromosome 10, and KL sequences are deleted in the genome of the Sl mouse. These results indicate that the Sl locus encodes the ligand of the c-kit receptor, KL.

Predicting the clinical status of human breast cancer by using gene expression profiles

Prognostic and predictive factors are indispensable tools in the treatment of patients with neoplastic disease. For the most part, such factors rely on a few specific cell surface, histological, or gross pathologic features. Gene expression assays have the potential to supplement what were previously a few distinct features with many thousands of features. We have developed Bayesian regression models that provide predictive capability based on gene expression data derived from DNA microarray analysis of a series of primary breast cancer samples. These patterns have the capacity to discriminate breast tumors on the basis of estrogen receptor status and also on the categorized lymph node status. Importantly, we assess the utility and validity of such models in predicting the status of tumors in crossvalidation determinations. The practical value of such approaches relies on the ability not only to assess relative probabilities of clinical outcomes for future samples but also to provide an honest assessment of the uncertainties associated with such predictive classifications on the basis of the selection of gene subsets for each validation analysis. This latter point is of critical importance in the ability to apply these methodologies to clinical assessment of tumor phenotype.

Role for E2F in control of both DNA replication and mitotic functions as revealed from DNA microarray analysis

We have used high-density DNA microarrays to provide an analysis of gene regulation during the mammalian cell cycle and the role of E2F in this process. Cell cycle analysis was facilitated by a combined examination of gene control in serum-stimulated fibroblasts and cells synchronized at G(1)/S by hydroxyurea block that were then released to proceed through the cell cycle. The latter approach (G(1)/S synchronization) is critical for rigorously maintaining cell synchrony for unambiguous analysis of gene regulation in later stages of the cell cycle. Analysis of these samples identified seven distinct clusters of genes that exhibit unique patterns of expression. Genes tend to cluster within these groups based on common function and the time during the cell cycle that the activity is required. Placed in this context, the analysis of genes induced by E2F proteins identified genes or expressed sequence tags not previously described as regulated by E2F proteins; surprisingly, many of these encode proteins known to function during mitosis. A comparison of the E2F-induced genes with the patterns of cell growth-regulated gene expression revealed that virtually all of the E2F-induced genes are found in only two of the cell cycle clusters; one group was regulated at G(1)/S, and the second group, which included the mitotic activities, was regulated at G(2). The activation of the G(2) genes suggests a broader role for E2F in the control of both DNA replication and mitotic activities.

Sequence and analysis of chromosome 4 of the plant Arabidopsis thaliana

The higher plant Arabidopsis thaliana (Arabidopsis) is an important model for identifying plant genes and determining their function. To assist biological investigations and to define chromosome structure, a coordinated effort to sequence the Arabidopsis genome was initiated in late 1996. Here we report one of the first milestones of this project, the sequence of chromosome 4. Analysis of 17.38 megabases of unique sequence, representing about 17% of the genome, reveals 3,744 protein coding genes, 81 transfer RNAs and numerous repeat elements. Heterochromatic regions surrounding the putative centromere, which has not yet been completely sequenced, are characterized by an increased frequency of a variety of repeats, new repeats, reduced recombination, lowered gene density and lowered gene expression. Roughly 60% of the predicted protein-coding genes have been functionally characterized on the basis of their homology to known genes. Many genes encode predicted proteins that are homologous to human and Caenorhabditis elegans proteins.

Myc requires distinct E2F activities to induce S phase and apoptosis

Previous work has shown that the Myc transcription factor induces transcription of the E2F1, E2F2, and E2F3 genes. Using primary mouse embryo fibroblasts deleted for individual E2F genes, we now show that Myc-induced S phase and apoptosis requires distinct E2F activities. The ability of Myc to induce S phase is impaired in the absence of either E2F2 or E2F3 but not E2F1 or E2F4. In contrast, the ability of Myc to induce apoptosis is markedly reduced in cells deleted for E2F1 but not E2F2 or E2F3. From this data, we propose that the induction of specific E2F activities is an essential component in the Myc pathways that control cell proliferation and cell fate decisions.

Protein folding: the endgame

The last stage of protein folding, the "endgame," involves the ordering of amino acid side-chains into a well defined and closely packed configuration. We review a number of topics related to this process. We first describe how the observed packing in protein crystal structures is measured. Such measurements show that the protein interior is packed exceptionally tightly, more so than the protein surface or surrounding solvent and even more efficiently than crystals of simple organic molecules. In vitro protein folding experiments also show that the protein is close-packed in solution and that the tight packing and intercalation of side-chains is a final and essential step in the folding pathway. These experimental observations, in turn, suggest that a folded protein structure can be described as a kind of three-dimensional jigsaw puzzle and that predicting side-chain packing is possible in the sense of solving this puzzle. The major difficulty that must be overcome in predicting side-chain packing is a combinatorial "explosion" in the number of possible configurations. There has been much recent progress towards overcoming this problem, and we survey a variety of the approaches. These approaches differ principally in whether they use ab initio (physical) or more knowledge-based methods, how they divide up and search conformational space, and how they evaluate candidate configurations (using scoring functions). The accuracy of side-chain prediction depends crucially on the (assumed) positioning of the main-chain. Methods for predicting main-chain conformation are, in a sense, not as developed as that for side-chains. We conclude by surveying these methods. As with side-chain prediction, there are a great variety of approaches, which differ in how they divide up and search space and in how they score candidate conformations.

Photoinduced doping in heterostructures of graphene and boron nitride

The design of stacks of layered materials in which adjacent layers interact by van der Waals forces has enabled the combination of various two-dimensional crystals with different electrical, optical and mechanical properties as well as the emergence of novel physical phenomena and device functionality. Here, we report photoinduced doping in van der Waals heterostructures consisting of graphene and boron nitride layers. It enables flexible and repeatable writing and erasing of charge doping in graphene with visible light. We demonstrate that this photoinduced doping maintains the high carrier mobility of the graphene/boron nitride heterostructure, thus resembling the modulation doping technique used in semiconductor heterojunctions, and can be used to generate spatially varying doping profiles such as p-n junctions. We show that this photoinduced doping arises from microscopically coupled optical and electrical responses of graphene/boron nitride heterostructures, including optical excitation of defect transitions in boron nitride, electrical transport in graphene, and charge transfer between boron nitride and graphene.

Role of envelope glycoprotein carbohydrate in human immunodeficiency virus (HIV) infectivity and virus-induced cell fusion

Human immunodeficiency virus (HIV) envelope glycoprotein interactions with cell surface CD4 are involved in both virion infectivity and virally mediated cell fusion. D-mannose-specific lectins such as Con A specifically blocked virion infectivity and cell fusion. Studies with a recombinant vaccinia virus containing the HIV envelope gene demonstrated that Con A-mediated inhibition of HIV-induced fusion involved lectin binding to the viral envelope glycoprotein. These results indicate the importance of envelope glycosylation in the pathobiology of HIV infection, and suggest potential mechanisms for interfering with HIV infectivity and cytopathology.

A point mutation inactivating the sulfonylurea receptor causes the severe form of persistent hyperinsulinemic hypoglycemia of infancy in Finland

Mutations in genes encoding the ATP-regulated potassium (K(ATP)) channels of the pancreatic beta-cell (SUR1 and Kir6.2) are the major known cause of persistent hyperinsulinemic hypoglycemia of infancy (PHHI). We collected all cases of PHHI diagnosed in Finland between 1983 and 1997 (n = 24). The overall incidence was 1:40,400, but in one area of Central Finland it was as high as 1:3,200. Haplotype analysis using polymorphic markers spanning the SUR1/Kir6.2 gene cluster confirmed linkage to the 11p region. Sequence analysis revealed a novel point mutation in exon 4 of SUR1, predicting a valine to aspartic acid change at amino acid 187 (V187D). Of the total cases, 15 affected individuals harbored this mutation in heterozygous or homozygous form, and all of these had severe hyperinsulinemia that responded poorly to medical treatment and required subtotal pancreatectomy. No K(ATP) channel activity was observed in beta-cells isolated from a homozygous patient or after coexpression of recombinant Kir6.2 and SUR1 carrying the V187D mutation. Thus, the mutation produces a nonfunctional channel and, thereby, continuous insulin secretion. This unique SUR1 mutation explains the majority of PHHI cases in Finland and is strongly associated with a severe form of the disease. These findings provide diagnostic and prognostic utility for suspected PHHI patients.

Sequence and analysis of chromosome 5 of the plant Arabidopsis thaliana

The genome of the model plant Arabidopsis thaliana has been sequenced by an international collaboration, The Arabidopsis Genome Initiative. Here we report the complete sequence of chromosome 5. This chromosome is 26 megabases long; it is the second largest Arabidopsis chromosome and represents 21% of the sequenced regions of the genome. The sequence of chromosomes 2 and 4 have been reported previously and that of chromosomes 1 and 3, together with an analysis of the complete genome sequence, are reported in this issue. Analysis of the sequence of chromosome 5 yields further insights into centromere structure and the sequence determinants of heterochromatin condensation. The 5,874 genes encoded on chromosome 5 reveal several new functions in plants, and the patterns of gene organization provide insights into the mechanisms and extent of genome evolution in plants.

Characterization of N-linked oligosaccharides by electrospray and tandem mass spectrometry

Electrospray and tandem mass spectrometry are used to characterize underivatized oligosaccharides that have been digested from asparagine side chains of glycoproteins. Oligosaccharides that contain sialic acids were detected with the best sensitivity in the negative-ion detection mode whereas those that do not contain sialic acid were detected with the best sensitivity in the positive-ion detection mode. The positive-ion abundances of oligosaccharides were greatly enhanced in electrospray mass spectra by adding 10 mM sodium acetate or ammonium acetate to the sample solvent. Tandem mass spectrometry was used to determine primary structural features of the oligosaccharides. Methodology that has been developed on branched high-mannose, hybrid, and complex carbohydrate standards was applied to a mixture of oligosaccharides that were digested with N-glycanase from the glycoprotein, ovalbumin. The composition and relative abundances of individual oligosaccharides obtained from the electrospray mass spectrum compare favorably to those obtained by anion-exchange chromatography/pulsed amperometric detection and by gel permeation chromatography of the oligosaccharides after radiolabelling the reducing end of the carbohydrates. The oligosaccharide content of ovalbumin was independently determined from the heterogeneity observed in the electrospray mass spectrum of the intact 44-kDa glycoprotein. Comparison of the oligosaccharide compositions determined before and after enzymatic digestion shows a selective digestion of high-mannose and low molecular weight oligosaccharides by N-glycanase.

Satisfaction with continuous glucose monitoring in adults and youths with Type 1 diabetes

AIMS

To describe satisfaction with continuous glucose monitoring in Type 1 diabetes; to correlate continuous glucose monitoring satisfaction scores with usage; and to identify common themes in perceived benefits and barriers of monitoring reported by adults, youths and the parents of youths in the Juvenile Diabetes Research Foundation continuous glucose monitoring trials.

METHODS

The Continuous Glucose Monitoring Satisfaction Scale questionnaire was completed after 6 months of monitoring. Participants also answered open-ended queries of positive and negative attributes of continuous glucose monitoring.

RESULTS

More frequent monitoring was associated with higher satisfaction for adults (n = 224), youths (n = 208) and parents of youths (n = 192) (all P < 0.001) in both the 'benefits' and 'hassles' sub-scales of the Continuous Glucose Monitoring Satisfaction Scale, but the greatest differences between the two groups involved scores on hassle items. Common barriers to monitoring use included insertion pain, system alarms and body issues; while common benefits included glucose trend data, opportunities to self-correct out-of-range glucose levels and to detect hypoglycaemia.

CONCLUSIONS

As frequent use of continuous glucose monitoring is associated with improved glycaemic control without increased hypoglycaemia it is important to overcome barriers, reinforce benefits and set realistic expectations for this technology in order to promote its more consistent and frequent use in individuals with Type 1 diabetes.

Mechanism of the Body-Centered Cubic—Hexagonal Close-Packed Phase Transition in Iron

The transition from body-centered cubic to hexagonal close-packed phase in iron has been studied in a diamond anvil cell with synchrotron radiation. The hexagonal close-packed phase, when it first appears, has a ratio of lattice parameters that is significantly larger than normal. This is attributed to a displacive mechanism that causes a distortion of the hexagonal close-packed structure in a body-centered cubic matrix. The hexagonal close-packed phase adjacent to a boundary with the body-centered cubic phase is stretched in the c direction and compressed in the a direction when it first forms.

Treatment with anti-vascular cell adhesion molecule 1 monoclonal antibody induces long-term murine cardiac allograft acceptance

Daily in vivo treatment of murine H-2d --> H-2b cardiac allograft recipients with 400 micrograms/day i.p. of M/K-2, a mAb to the endothelial adhesion molecule VCAM-1, resulted in prolongation of graft survival. The surviving allografts showed little of the histologic changes observed in acutely rejecting control allografts. When antibody treatment was discontinued after 20 days, grafts continued to function for at least 40 more days. This was approximately 30 days after mAb was no longer detectable by ELISA in the circulation, or by immunoperoxidase staining at the graft site. The most notable feature of grafts that survived 60 days was the presence of mild interstitial fibrosis. Endothelial reactivity was minimal with the mAbs MECA-32 and M/K-2, which have been used in previous studies to visualize the extensive endothelial inflammation that develops during untreated acute rejection. There was a mild cellular infiltrate containing T cells, but few macrophages. However, infiltrating T cells appeared to be inactive in that IL-2R+ cells were immunohistologically undetectable and mRNA for IL-2, IL-4, or IFN-gamma was undetectable by polymerase chain reaction. In general, the immunologic conditions in these long-term grafts differed from those seen in normal cardiac tissue, cardiac isografts, or cardiac allografts. These data demonstrate that M/K-2 mAb can suppress cardiac allograft rejection and induce long-term graft acceptance. This graft survival appears to be associated with the development of a unique state of immunity at the graft site.

Radiocarbon constraints on the glacial ocean circulation and its impact on atmospheric CO2

While the ocean’s large-scale overturning circulation is thought to have been significantly different under the climatic conditions of the Last Glacial Maximum (LGM), the exact nature of the glacial circulation and its implications for global carbon cycling continue to be debated. Here we use a global array of ocean–atmosphere radiocarbon disequilibrium estimates to demonstrate a ∼689±53 ¹⁴C-yr increase in the average residence time of carbon in the deep ocean at the LGM. A predominantly southern-sourced abyssal overturning limb that was more isolated from its shallower northern counterparts is interpreted to have extended from the Southern Ocean, producing a widespread radiocarbon age maximum at mid-depths and depriving the deep ocean of a fast escape route for accumulating respired carbon. While the exact magnitude of the resulting carbon cycle impacts remains to be confirmed, the radiocarbon data suggest an increase in the efficiency of the biological carbon pump that could have accounted for as much as half of the glacial–interglacial CO₂ change.

Establishing the efficiency of the biological carbon pump is needed to constrain the impact of ocean circulation on the carbon cycle. Here, the authors compile a global array of ocean–atmosphere radiocarbon disequilibrium estimates and evaluate the strength of the carbon pump over the last glacial maximum.

Dexamethasone pharmacokinetics in the inner ear: comparison of route of administration and use of facilitating agents

There is growing otologic interest in treating inner ear disorders, such as sudden sensorineural hearing loss and acute or unremitting Meniere's disease, with intratympanic dexamethasone (IT-DEX). Although anecdotally reported, there are no scientific clinical papers and few prior laboratory research publications on the subject. This study compares perilymph dexamethasone concentrations after systemic and intratympanic administration and assesses the role of 3 potential transport facilitators of IT-DEX into perilymph. Forty guinea pigs (79 ears) were randomly separated into 5 groups. Dexamethasone levels were measured by radioimmunoassay. IT-DEX resulted in higher perilymph steroid levels than intravenous dexamethasone (P < 0.05). Histamine facilitator resulted in significantly higher perilymph steroid levels than IT-DEX alone (P < 0.05). Neither hyaluronic acid nor dimethylsulfoxide was a potent facilitator. This study demonstrates that IT-DEX administration results in superior perilymph levels within 1 hour of administration and does not result in systemic absorption. Histamine is a potent facilitating agent. The clinical implications are considerable.

Prophylactic use of antibiotics for nonlaboring patients undergoing cesarean delivery with intact membranes: a meta-analysis

OBJECTIVE

We performed a meta-analysis to examine the role of antibiotic prophylaxis in preventing postoperative infections among nonlaboring women undergoing cesarean delivery with intact membranes.

STUDY DESIGN

A computerized literature search was performed with MEDLINE. Studies were included if they contained data on patients undergoing cesarean delivery in the absence of labor and ruptured membranes. Only randomized trials with a placebo control group were included.

RESULTS

Seven studies were found. Use of antibiotics decreased the risk of all infectious outcomes reported. When the results of 4 studies were pooled, prophylactic antibiotic use was associated with a significant reduction in postoperative fever (relative risk, 0.25; 95% confidence interval, 0.14-0.44). A similar reduction was noted for endometritis in 4 studies (relative risk, 0.05; 95% confidence interval, 0.01-0.38). Two studies reported on wound infection and showed a trend toward a protective effect (relative risk, 0.59; 95% confidence interval, 0.24-1.45).

CONCLUSION

The prophylactic use of antibiotics reduces the risk of postoperative infectious complications after cesarean delivery even in the population at lowest risk.

Immunostimulatory DNA pre-priming: a novel approach for prolonged Th1-biased immunity

Immunostimulatory DNA sequences (ISS) have been shown to promote CTL and Th1 immune responses to coinjected antigens. This phenomenon can be attributed to the capacity of ISS to induce the secretion of type-1 cytokines and to up regulate costimulatory ligands on antigen-presenting cells. We hypothesized that ISS administration prior to antigen administration (prepriming), via the mechanisms stated above, would Th1 bias immune responses to subsequently injected antigens for an extended period of time. The data presented show that ISS provide in vivo adjuvant activity for up to 2 weeks after intradermal or intranasal delivery. Furthermore, the results demonstrate that ISS prepriming can induce immune responses that are significantly stronger than with ISS/antigen covaccination. ISS prepriming offers an alternative approach to the traditional use of adjuvants (i.e., antigen/adjuvant coinjection) and expands the potential clinical applications for ISS.

Indomethacin promotes germinal matrix microvessel maturation in the newborn beagle pup

BACKGROUND AND PURPOSE

Although indomethacin has been demonstrated to prevent germinal matrix and intraventricular hemorrhage in clinical and animal studies, the mechanism of action of this agent to prevent hemorrhage remains unclear. Previous studies have demonstrated both that the microvessels in the germinal matrix of newborn beagle pups undergo basement membrane maturation during the first 4 postnatal days and that indomethacin may promote laminin deposition in tumor cell culture systems.

METHODS

We employed the newborn beagle pup model to test the hypothesis that indomethacin may stimulate laminin deposition in germinal matrix microvessels. Newborn pups were randomized to receive either 0.1 mg/kg/dose i.p. indomethacin or an equal volume of saline diluent. Pups received doses of study medication once a day for 1, 2, or 3 days and were studied on postnatal days 1, 2, 3, or 4. Pups were anesthetized and systemically perfused with buffered formalin; the brains were removed and prepared for immunohistochemical study.

RESULTS

Sections stained with Bandeiraea lectin demonstrated that there was no difference in germinal matrix vessel density among the postnatal ages studied; similarly, there were no differences in vessel density between saline- and indomethacin-treated animals at any postnatal age. Quantification of germinal matrix stained intensity by confocal microscopy demonstrated significant increases in indomethacin-treated pups for both laminin staining at postnatal days 2 (p = 0.05) and 3 (p = 0.0009) and type V collagen staining at postnatal day 2 (p = 0.011). Although staining for beta 1 integrins increased across postnatal ages, there were no differences between saline- and indomethacin-treated animals.

CONCLUSIONS

These data suggest that indomethacin may stimulate basement membrane deposition in the germinal matrix microvessels of newborn beagle pups to prevent germinal matrix and/or intraventricular hemorrhage.

Distribution of divalent metal transporter-1 in the monkey basal ganglia

An accumulation of iron occurs in the brain with age, and it is thought that this may contribute to the pathology of certain neurodegenerative diseases, including Parkinson's disease. In this study, we elucidated the distribution of divalent metal transporter-1 (DMT1) in the monkey basal ganglia by immunocytochemistry, and compared it with the distribution of ferrous iron in these nuclei by Turnbull's Blue histochemical staining. We observed a general correlation between levels of DMT1, and iron staining. Thus, regions such as the caudate nucleus, putamen, and substantia nigra pars reticulata contained dense staining of DMT1 in astrocytic processes, and were also observed to contain large numbers of ferrous iron granules. The exceptions were the globus pallidus externa and interna, which contained light DMT1 staining, but large numbers of ferrous iron granules. The thalamus, subthalamic nucleus, and substantia nigra pars compacta contained neurons that were lightly stained for DMT1, but few or no iron granules. The high levels of DMT1 expression in some of the nuclei of the basal ganglia, particularly the caudate nucleus, putamen, and substantia nigra pars reticulata, may account for the high levels of iron in these regions.

The cost-effectiveness and budget impact of competing therapies in hepatic encephalopathy - a decision analysis

BACKGROUND

Treatment options for hepatic encephalopathy have disparate risks and benefits. Non-absorbable disaccharides and neomycin are limited by uncertain efficacy and common dose-limiting side effects. In contrast, rifaximin is safe and effective in hepatic encephalopathy, but is more expensive.

METHODS

We conducted a decision analysis to calculate the cost-effectiveness of six strategies in hepatic encephalopathy: (i) no hepatic encephalopathy treatment, (ii) lactulose monotherapy, (iii) lactitol monotherapy, (iv) neomycin monotherapy, (v) rifaximin monotherapy and (vi) up-front lactulose with crossover to rifaximin if poor response or intolerance of lactulose ('rifaximin salvage'). The primary outcome was cost per quality-adjusted life-year gained.

RESULTS

Under base-case conditions, 'do nothing' was least effective and rifaximin salvage was most effective. Lactulose monotherapy was least expensive, and rifaximin monotherapy was most expensive. When balancing cost and effectiveness, lactulose monotherapy and rifaximin salvage dominated alternative strategies. Compared to lactulose monotherapy, rifaximin salvage cost an incremental US$2315 per quality-adjusted life-year-gained. The cost of rifaximin had to fall below US$1.03/tab in order for rifaximin monotherapy to dominate lactulose monotherapy.

CONCLUSIONS

Rifaximin monotherapy is not cost-effective in the treatment of chronic hepatic encephalopathy at current average wholesale prices. However, a hybrid salvage strategy, reserving rifaximin for lactulose-refractory patients, may be highly cost-effective.

Adhesion of uric acid crystals to the surface of renal epithelial cells

Adhesion of microcrystals that nucleate in tubular fluid to the apical surface of renal tubular cells could be a critical step in the formation of kidney stones, 12% of which contain uric acid (UA) either alone or admixed with calcium oxalates or calcium phosphates. UA crystals bind rapidly to monolayer cultures of monkey kidney epithelial cells (BSC-1 line), used to model the surface of the nephron, in a concentration-dependent manner. The urinary glycoproteins osteopontin, nephrocalcin, and Tamm-Horsfall glycoprotein had no effect on binding of UA crystals to the cell surface, whereas other polyanions including specific glycosaminoglycans blocked UA crystal adhesion. Specific polycations also inhibited adhesion of UA crystals and appeared to exert their inhibitory effect by coating cells. However, removal of anionic cell surface molecules with neuraminidase, heparitinase I, or chondroitinase ABC each increased UA crystal binding, and sialic acid-binding lectins had no effect. These observations suggest that hydrogen bonding and hydrophobic interactions play a major role in adhesion of electrostatically neutral UA crystals to renal cells, unlike the interaction of calcium-containing crystals with negatively charged molecules on the apical cell surface via ionic forces. After adhesion to the plasma membrane, subsequent cellular events could contribute to UA crystal retention in the kidney and the development of UA or mixed calcium and UA calculi.