Exposure to inhaled THM: comparison of continuous and event-specific exposure assessment for epidemiologic purposes

Trihalomethanes (THMs) (chloroform, bromoform, dibromochloromethane, and bromodichloromethane) are the most abundant by-products of chlorination. People are exposed to THMs through ingestion, dermal contact and inhalation. The objective of this study was to compare two methods for assessing THM inhalation: a direct method with personal monitors assessing continuous exposure and an indirect one with microenvironmental sampling and collection of time-activity data during the main event exposures: bathing, showering and swimming. This comparison was conducted to help plan a future epidemiologic study of the effects of THMs on the upper airways of children. 30 children aged from 4 to 10 years were included. They wore a 3M 3520 organic vapor monitor for 7 days. We sampled air in their bathrooms (during baths or showers) and in the indoor swimming pools they visited and recorded their time-activity patterns. We used stainless steel tubes full of Tenax to collect air samples. All analyses were performed with Gas Chromatography and Mass Spectrometry (GC-MS). Chloroform was the THM with the highest concentrations in the air of both bathrooms and indoor swimming pools. Its continuous and event exposure measurements were significantly correlated (r(s)=0.69 p<0.001). Continuous exposures were higher than event exposures, suggesting that the event exposure method does not take into account some influential microenvironments. In an epidemiologic study, this might lead to random exposure misclassification, thus underestimation of the risk, and reduced statistical power. The continuous exposure method was difficult to implement because of its poor acceptability and the fragility of the personal monitors. These two points may also reduce the statistical power of an epidemiologic study. It would be useful to test the advantages and disadvantages of a second sample in the home or of modeling the baseline concentration of THM in the home to improve the event exposure method.

Reporting disease activity in clinical trials of patients with rheumatoid arthritis: EULAR/ACR collaborative recommendations

OBJECTIVE

To make recommendations on how to report disease activity in clinical trials of rheumatoid arthritis (RA) endorsed by the European League Against Rheumatism (EULAR) and the American College of Rheumatology (ACR).

METHODS

The project followed the EULAR standardised operating procedures, which use a three-step approach: (1) expert-based definition of relevant research questions (November 2006); (2) systematic literature search (November 2006 to May 2007); and (3) expert consensus on recommendations based on the literature search results (May 2007). In addition, since this is the first joint EULAR/ACR publication on recommendations, an extra step included a meeting with an ACR panel to approve the recommendations elaborated by the expert group (August 2007).

RESULTS

Eleven relevant questions were identified for the literature search. Based on the evidence from the literature the expert panel recommended that each trial should report the following items: (1) disease activity response and disease activity states; (2) appropriate descriptive statistics of the baseline, the endpoints and change of the single variables included in the core set; (3) baseline disease activity levels (in general); (4) the percentage of patients achieving a low disease activity state and remission; (5) time to onset of the primary outcome; (6) sustainability of the primary outcome; (7) fatigue.

CONCLUSIONS

These recommendations endorsed by EULAR and ACR will help harmonise the presentations of results from clinical trials. Adherence to these recommendations will provide the readership of clinical trials with more details of important outcomes, while the higher level of homogeneity may facilitate the comparison of outcomes across different trials and pooling of trial results, such as in meta-analyses.

Evaluation of a modified ACR20 scoring system in patients with rheumatoid arthritis receiving treatment with etanercept

OBJECTIVE

To evaluate a modified American College of Rheumatology 20 (mACR20) scoring system for patients with rheumatoid arthritis.

METHODS

The data were evaluated from one study on patients with methotrexate (MTX)-naive early rheumatoid arthritis (ERA) and another study on patients with DMARD-refractory late rheumatoid arthritis (LRA). For mACR20 scoring, acute-phase reactant measurements were excluded, and 20% improvement from baseline was determined by 2 or 3 of the 4 remaining ACR components.

RESULTS

For full joint counts with data from patients with ERA, marked differences favoured 25 mg etanercept (ETN) over 10 mg ETN by using the unmodified ACR20 (69% v 55%), the mACR20(3 of 4) (63% v 49%) and the mACR20(2 of 4) (72% v 58%). An assessment of 28 joints showed similar findings. In the trial on patients with LRA, considerably more patients in both ETN groups achieved a clinical response compared with placebo by using the ACR20, the mACR20(3 of 4) and the mACR20(2 of 4), whether using full or 28 joint counts. The mACR20(3 of 4) and full joint counts with data on patients with ERA showed a marked difference between the MTX and 10 mg ETN groups (63% v 49%), which was not observed with the ACR20.

CONCLUSION

Patterns of improvement indicated by mACR20 scores were consistent with standard ACR20 scores.

Inteins as enzymes

The term "self-catalyzed" as applied to protein processing reactions might be considered a contradiction, since catalysis implies that the catalyst is regenerated without change. However, as our understanding of protein autoprocessing reactions such as protein splicing advances, it is becoming clear that they have many of the hallmarks of enzymatic reactions. In this review, we will examine the properties of protein splicing elements, or inteins, and show how these can be understood in terms of enzyme catalysis, both with respect to substrate specificity and the stabilization of reactive intermediates.

Reversible inhibition of protein splicing by zinc ion

Protein splicing involves the self-catalyzed excision of a protein-splicing element, the intein, from flanking polypeptides, the exteins, which are concomitantly joined by a peptide bond. Taking advantage of recently developed in vitro systems in which protein splicing occurs in trans to assay for protein-splicing inhibitors, we discovered that low concentrations of Zn(2+) inhibited splicing mediated both by the RecA intein from Mycobacterium tuberculosis and by the naturally split DnaE intein from Synechocystis sp. PCC6803. Inhibition by Zn(2+) was also observed with a cis-splicing system involving the RecA intein. In all experimental systems used, inhibition by Zn(2+) could be completely reversed by the addition of EDTA. Zinc ion also inhibited hydroxylamine-dependent N-terminal cleavage of the RecA intein. All other divalent transition metal ions tested were less effective as inhibitors than Zn(2+). The reversible inhibition by Zn(2+) should be useful in studies of the mechanism of protein splicing and allow structural studies of unmodified protein-splicing precursors.

Minimal clinically important difference in radiological progression of joint damage over 1 year in rheumatoid arthritis: preliminary results of a validation study with clinical experts

To determine the minimal clinically important difference (MCID) between hand and foot films with a 1 year interval assessed with the Sharp/van der Heijde or Larsen/Scott scoring method. Progression scores of the 2 methods were compared with the opinion of an international expert panel on clinical relevance of radiological joint damage in 4 predefined clinical settings. The expert panel consisted of 3 rheumatologists, who evaluated 46 pairs of hand and foot films, taken with 1 year intervals, of patients with early rheumatoid arthritis. Receiver operating characteristics curves analyzed the accuracy of different threshold values (progression scores) of the 2 scoring methods to detect the presence or absence of clinically important difference, as defined by the expert panel as external criterion. The threshold value with the highest accuracy was subsequently chosen as the score representing the MCID. Five Sharp/van der Heijde units and 2 Larsen/Scott units were the best cutoffs. The accompanying sensitivities ranged from 77% to 100% for the Sharp/van der Heijde method and from 73% to 84% for the Larsen/Scott method for the 4 clinical settings. The specificities were between 78% and 84% for the Sharp/van der Heijde method and between 74% and 94% for the Larsen/Scott method. The smallest progression score that can be detected apart from interobserver measurement error, the smallest detectable difference (SDD), was equal to or larger than the calculated MCID, 5 Sharp/van der Heijde units and 6 Larsen/Scott units in our study, if the mean progression scores of the same 2 observers were used. The SDD is a conservative estimate of the MCID; our panel rated progression at or below this level as clinically significant.

Protein trans-splicing to produce herbicide-resistant acetolactate synthase

Protein splicing in trans has been demonstrated both in vivo and in vitro by biochemical and immunological analyses, but in vivo production of a functional protein by trans-splicing has not been reported previously. In this study, we used the DnaE intein from Synechocystis sp. strain PCC6803, which presumably reconstitutes functional DnaE protein by trans-splicing in vivo, to produce functional herbicide-resistant acetolactate synthase II (ALSII) from two unlinked gene fragments in Escherichia coli. The gene for herbicide-resistant ALSII was fused in frame to DnaE intein segments capable of promoting protein splicing in trans and was expressed from two compatible plasmids as two unlinked fragments. Cotransformation of E. coli with the two plasmids led to production of a functional enzyme that conferred herbicide resistance to the host E. coli cells. These results demonstrate the feasibility of expressing functional genes from two unlinked DNA loci and provide a model for the design of nontransferable transgenes in plants.

Protein splicing and related forms of protein autoprocessing

Protein splicing is a form of posttranslational processing that consists of the excision of an intervening polypeptide sequence, the intein, from a protein, accompanied by the concomitant joining of the flanking polypeptide sequences, the exteins, by a peptide bond. It requires neither cofactors nor auxiliary enzymes and involves a series of four intramolecular reactions, the first three of which occur at a single catalytic center of the intein. Protein splicing can be modulated by mutation and converted to highly specific self-cleavage and protein ligation reactions that are useful protein engineering tools. Some of the reactions characteristic of protein splicing also occur in other forms of protein autoprocessing, ranging from peptide bond cleavage to conjugation with nonprotein moieties. These mechanistic similarities may be the result of convergent evolution, but in at least one case-hedgehog protein autoprocessing-there is definitely a close evolutionary relationship to protein splicing.

Copper(II) and copper(I) complexes with an open-chain N4 Schiff base ligand modeling CuZn superoxide dismutase: structural and spectroscopic characterization and kinetics of electron transfer

The structure of the complex [CuII(PuPy)](ClO4)2 (PuPy = L = 1,8-bis(2-pyridyl)-2,7-diazaoctadiene-1,7) and the structure of the corresponding copper(I) complex were determined. In CuIIL(ClO4)2, a model compound with CuZnSOD activity, the unit CuIIL2+ has a tetrahedrally distorted square-planar N4 coordination geometry. The copper(I) complex with L was found to be dimeric, (CuIL)2(ClO4)2.DMF (DMF = N,N-dimethylformamide). The binuclear unit (CuIL)2(2+) has a helical structure with two ligands L bridging the two copper atoms to provide tetrahedral N4 coordination of each copper(I). In solutions of (CuIL)2(ClO4)2.DMF, solvent-dependent dissociation occurs according to D reversible 2M (D = (CuIL)2(2+); M = CuILSx+; S = solvent). Stopped-flow spectrophotometry was used to determine the rate constants for the dissociation of the dimer D (kM) and dimerization of the monomer M (kD) for S = acetonitrile and DMF. Equilibrium constants Kdim = kM/kD were determined spectrophotometrically. In aqueous solution, the oxidation of the dimer (CuIL)2(2+) by CoIII(NH3)5Cl2+ and cis- and trans-CoIII(en)2Cl2+ follows a second-order rate law, rate = kox[(CuIL)2(2+)][Co(III)]. Data for rate constant kox and for the activation parameters delta H++ and delta S++ are presented. In DMF, the oxidation of (CuIL)2(2+) by CoIII(NH3)5Cl2+ occurs via the monomer CuIL(DMF)x+ and the dissociation of (CuIL)2(2+) becomes rate-controlling. The reduction of CuIIL2+ by RuII(edta)H2O2- was found to be too fast to be resolved by stopped-flow spectrophotometry. The kinetic results are discussed mechanistically in terms of the redox switch aspects of the system.

Characteristics of protein splicing in trans mediated by a semisynthetic split intein

Protein splicing in trans results in the ligation of two protein or peptide segments linked to appropriate intein fragments. We have characterized the trans-splicing reaction mediated by a naturally expressed, approximately 100-residue N-terminal fragment of the Mycobacterium tuberculosis intein and a synthetic peptide containing the 38 C-terminal intein residues, and found that the splicing reaction was very versatile and robust. The efficiency of splicing was nearly independent of temperature between 4 and 37 degrees C and pH between 6.0 and 7.5, with only a slight decline at pH values as high as 8.5. In addition, there was considerable flexibility in the choice of the C-terminal intein fragment, no significant difference in protein ligation efficiency being observed between reactions utilizing the N-terminal fragment and either the naturally expressed 107-residue C-terminal portion of the intein, much smaller synthetic peptides, or the 107-residue C-terminal intein fragment modified by fusion of a maltose binding protein domain to its N-terminus. The ability to use different types of the C-terminal intein fragments and a broad range of reaction conditions make protein splicing in trans a versatile tool for protein ligation.

Reactivity of the cysteine residues in the protein splicing active center of the Mycobacterium tuberculosis RecA intein

Protein splicing involves the self-catalyzed excision of an intervening polypeptide segment, an intein, from a precursor protein. The first two steps in the protein splicing process lead to the formation of ester intermediates through nucleophilic attacks by the side chains of cysteine, serine, or threonine residues adjacent to the splice junctions. Since both nucleophilic residues in the Mycobacterium tuberculosis RecA intein are cysteine, their reactivities could be compared by sulfhydryl group titration. This was accomplished by using fusion proteins containing a truncated RecA intein modified by mutation to prevent protein splicing, in which the cysteines at the splice junctions were the only sulfhydryl groups. The ability to undergo hydroxylamine-induced cleavage at the upstream splice junction showed that the modified intein was not impaired in the ability to form ester intermediates. Sulfhydryl titration with iodoacetamide, monitored by quantitating the residual thiols after reaction with a maleimide derivative of biotin, revealed a striking difference in the apparent pK(a) values of the cysteines at the two splice junctions. The apparent pK(a) of the cysteine at the upstream splice junction, which initiates the N-S acyl rearrangement leading to the linear ester intermediate, was approximately 8.2, whereas that of the cysteine residue at the downstream splice junction, which initiates the transesterification reaction converting the linear ester to the branched ester intermediate, was about 5.8. This suggests that the transesterification step is facilitated by an unusually low pK(a) of the attacking thiol group. Comparison of the rates of cleavage of the linear ester intermediates derived from the M. tuberculosis RecA and the Saccharomyces cerevisiae VMA inteins by dithiothreitol and hydroxylamine revealed that the former reacted relatively more slowly with dithiothreitol, suggesting that the RecA intein has diverged in the course of evolution to react preferentially with thiolate anions and thus lacks the basic groups that may facilitate nucleophilic attack by thiols in other inteins.

Patient self-report tender and swollen joint counts in early rheumatoid arthritis. Western Consortium of Practicing Rheumatologists

OBJECTIVE

To determine the correlation between patient self-report joint counts and standard physician joint counts, and to compare pictorial (Mannequin) and text (Rapid Assessment of Disease Activity in Rheumatology, RADAR) formats for obtaining patient self-reports.

METHODS

Baseline patient self-report joint counts were mailed and completed by 60 patients with early rheumatoid arthritis (RA) one day before and one day after being examined by a physician. Twenty-seven were randomized to the Mannequin tender and Mannequin swollen joint counts; 33 were randomized to the RADAR tender and swollen joint counts. Agreement between patient and physician self-report joint counts, diagnostic characteristics, and test-retest reliability of patient self-report joint counts was computed. Stepwise regression analyses were performed to identify predictors of patient-physician differences in total joint count.

RESULTS

Means and standard deviations of paired patient and physician total joint counts were not different for Mannequin or RADAR forms. Spearman correlations were moderate (0.58 to 0.69 for Mannequin, 0.37 to 0.58 for RADAR). Agreement (intraclass correlations) was 0.65 for the Mannequin and 0.56 for the RADAR forms. Patient test-retest reproducibility was moderate for RADAR tenderness (0.58) and high (r>0.90) for RADAR swollen and both Mannequin forms. Level of patient education predicted patient-physician differences on the RADAR swollen joint counts (p = 0.003), but was not significant in Mannequin forms, suggesting that education was not a factor in accurate completion of Mannequin forms.

CONCLUSION

Both pictorial and text format patient self-report joint counts are significantly correlated with physician joint counts. In addition to moderately high patient test-retest reproducibility, this suggests that patient self-reports in both formats may yield accurate measures of improvement in disease activity.

Enantioseparation of amfepramone (rac-diethylpropion): preparative separation of the enantiomers and enantioselective analysis

The enantiomers of the anorectic drug amfepramone [rac-diethylpropion, rac-2-(diethylamino)-1-phenyl-1-propanone; rac-DEP] were separated in the preparative scale by crystallization. With enantiopure di-O-benzoyltartaric acid as salt-forming chiral selector, diastereoisomeric salts of DEP enantiomers with a final purity of more than 97.5% were obtained. Analytical liquid chromatographic and electrophoretic methods for the control of the enantiomeric purity and the stoichiometry of the salts were developed. The enantioseparation of rac-DEP by capillary electrophoresis (CE) using hydroxypropyl-beta-cyclodextrin (HP-beta-CD) as chiral discriminator and phosphate buffer (pH 3.3) as run buffer led to good separations. HPLC methods were developed using polysaccharide chiral stationary phases (CSP). The separation of the two enantiomers and the two main degradation products (1-phenyl-1,2-propanedione and propiophenone), known from solid and liquid pharmaceutical preparations, was attained in one run on the silica-based CSP cellulose tris(3,5-dimethylphenylcarbamate) (Chiralcel OD). The conditions which might affect the enantioselectivity and the quality of the enantiomeric separation were investigated for Chiralcel OD and the related CSP amylose tris(3,5-dimethylphenylcarbamate) (Chiralpak AD). Both CSPs showed very similar chromatographic properties. The separation factors could be influenced significantly by varying the polar organic modifier added to the mobile phase.

Imaging in rheumatoid arthritis: results of group discussions

None of the current scoring methods for radiological damage in rheumatoid arthritis (RA) is ideal. The objective for RA imaging at OMERACT IV was to start discussion about the problems and applicability of the current scoring methods for radiological damage and to start discussion on the challenge of new imaging techniques. The RA imaging module comprised preconference reading material, plenary sessions, small group discussions, and a plenary report of the group sessions, combined with interactive voting. The OMERACT filter guided the discussions. Priorities for further research in imaging studies were: (1) pathologies versus features on radiographs; (2) relation with longterm outcome; and (3) definition of minimum clinically important difference.

Costs attributable to osteoarthritis

OBJECTIVE

To estimate charges attributable to osteoarthritis (OA) in a managed care organization.

METHODS

Longitudinal study based on insurance claims incurred and filed between 1991 and 1993 in a national managed care organization. Patients with claims for OA were randomly sampled to yield 20,000 study subjects. Charges per person-year were determined for these patients and compared to those of comparison subjects matched for age, sex, and insurance plan without claims for OA.

RESULTS

Total charges per patient-year adjusted to 1993 dollars for patients with OA <65 and > or =65 years of age were $5,294 and $5,704, respectively, while charges for controls were $2,467 and $3,741, respectively. Thus, charges due to OA were $2,827 and $1,963, accounting for 5% of total plan charges.

CONCLUSION

Patients with symptomatic OA incur charges for medical care at about twice the rate of plan enrollees without claims for OA and account for a substantial proportion of total charges in a managed care plan.

When are bioavailability studies required? A German proposal

The Bundesinstitut für Arzneimittel und Medizinprodukte (BfArM), the German drug regulation authority, issued guidelines for determining whether bioavailability/bioequivalence studies are required for certain drugs. This decision tree is based on pharmacodynamic, pharmacokinetic, and physicochemical criteria. Details of this decision tree were worked out by an expert panel, the Bioavailability Commission at the BfArM. The decision tree has been in use by German regulatory authorities for more than 10 years. In the meantime, its essentials were adopted by the European Committee for Proprietary Medicinal Products (CPMP) and by the World Health Organization (WHO) for their "Guidelines on interchangeability of multisource pharmaceutical products." This article reviews the original decision tree of the BfArM and provides examples of drugs that have been assessed according to its rules. The current procedure of the German regulatory authorities for judging the necessity of bioavailability trials, which reflects the status quo of regulatory practice in Germany, is also discussed.

Protein splicing in vitro with a semisynthetic two-component minimal intein

Protein splicing elements, or inteins, catalyze their own excision from flanking polypeptide sequences, or exteins, thereby leading to the formation of new proteins in which the exteins are linked directly by a peptide bond. A trans-splicing system, using separately purified and expressed N- and C-terminal intein fragments of about 100 amino acids each, fused to appropriate exteins, was recently derived from the Mycobacterium tuberculosis RecA intein (Mills, K. V., Lew, B. M., Jiang, S.-Q., and Paulus, H. (1998) Proc. Natl. Acad. Sci. U. S. A. 95, 3543-3548). We have replaced the C-terminal intein fragment of this system with synthetic peptides comprising 35-50 of the C-terminal residues of the RecA intein. The N-terminal intein fragment and the synthetic peptide were reconstituted by renaturation from guanidinium chloride. In the absence of added reductants, a disulfide-linked dimer of the N-terminal fragment and the peptide accumulated and could be induced to splice by reduction of its disulfide bond. The intermediate and spliced products were identified by polyacrylamide gel electrophoresis, mass spectrometry, and derivatization with thiol-reactive biotin followed by Western blotting with a streptavidin-enzyme conjugate. This is the first example of protein splicing involving a synthetic intein fragment and opens the way for studying the active site structure and function of the intein by the use of different synthetic peptides, including ones with non-natural amino acids.

Kinetics of racemization of (+)- and (-)-diethylpropion: studies in aqueous solution, with and without the addition of cyclodextrins, in organic solvents and in human plasma

The configurational stability of (+)- and (-)-diethylpropion [(+)- and (-)-2-(diethyl)-1-phenyl-1-propanone or (+)- and (-)-DEP] was investigated systematically from chemical, pharmaceutical, and pharmacological aspects. The enantiomeric ratio was monitored directly with a recently developed stability-indicating enantioselective HPLC method. In aqueous solutions, the rate of racemization increased non-linearly with increasing pH and with increasing phosphate buffer concentration. The racemization rate showed a positive slope with increasing temperature and decreasing ionic strength. The racemization rates of (+)- and (-)-DEP in the presence of cyclodextrins (CDs) did not differ significantly. CDs that were added to (+)- and (-)-DEP in a molar ratio 5:1 showed the following effects after dissolution in 10 mM phosphate buffer (final pH 6.7): sulfobutyl ether-beta-CD (SBE-beta-CD) and methylated-beta-CD (Me-beta-CD) retarded racemization; whereas hydroxypropyl-beta-CD (HP-beta-CD), acetyl-gamma-CD (Ac-gamma-CD), acetyl-beta-CD (Ac-beta-CD), gamma-CD, and beta-CD showed a weak destabilising effect. In contrast to the described CDs, alpha-CD distinctly accelerated the rate of racemization. The configurational stability of (+)- and (-)-DEP was also studied under physiological conditions. The half-life of racemization in heparinised human plasma was for both enantiomers determined to be approximately 23-25 min. In phosphate buffer (10 mM, pH 7.4), rac-DEP showed a high, but unselective affinity towards human alpha 1-acid glycoprotein (orosomucoid) immobilised on silica (Chiral AGP). The rate of racemization of the free base of (-)-DEP dissolved in organic solutions generally increases with the polarity of the solvating agent.

Characterization and functional analysis of the cis-autoproteolysis active center of glycosylasparaginase

Glycosylasparaginase is an N-terminal nucleophile hydrolase and is activated by intramolecular autoproteolytic processing. This cis-autoproteolysis possesses unique kinetics characterized by a reversible N-O acyl rearrangement step in the processing. Arg-180 and Asp-183, involved in binding of the substrate in the mature enzyme, are also involved in binding of free amino acids in the partially formed substrate pocket on certain mutant precursors. This binding site is sequestered in the wild-type precursor. Binding of free amino acids on mutant precursors can either inhibit or accelerate their processing, depending on the individual mutants and amino acids. The polypeptide sequence at the processing site, which is highly conserved, adopts a special conformation. Asp-151 is essential for maintaining this conformation, possibly by anchoring its side chain into the partially formed substrate pocket through interaction with Arg-180. The reactive nucleophile Thr-152 is activated not only by deprotonation by His-150 but also by interaction with Thr-170, suggesting a His-Thr-Thr active triad for the autoproteolysis.

Protein splicing in trans by purified N- and C-terminal fragments of the Mycobacterium tuberculosis RecA intein

Protein splicing involves the self-catalyzed excision of protein splicing elements, or inteins, from flanking polypeptide sequences, or exteins, leading to the formation of new proteins in which the exteins are linked directly by a peptide bond. To study the enzymology of this interesting process we have expressed and purified N- and C-terminal segments of the Mycobacterium tuberculosis RecA intein, each approximately 100 amino acids long, fused to appropriate exteins. These fragments were reconstituted into a functional protein splicing element by renaturation from 6 M urea. When renaturation was carried out in the absence of thiols, the reconstituted splicing element accumulated as an inactive disulfide-linked complex of the two intein fragments, which could be induced to undergo protein splicing by reduction of the disulfide bond. This provided a useful tool for separately investigating the requirements for the reconstitution of the intein fragments to yield a functional protein splicing element and for the protein splicing process per se. For example, the pH dependence of these processes was quite different, with reconstitution being most efficient at pH 8.5 and splicing most rapid at pH 7.0. The availability of such an in vitro protein splicing system opens the way for the exploration of intein structure and the unusual enzymology of protein splicing. In addition, this trans-splicing system is a potential protein ligase that can link any two polypeptides fused to the N- and C-terminal intein segments.

Molecular dissection of the Mycobacterium tuberculosis RecA intein: design of a minimal intein and of a trans-splicing system involving two intein fragments

Most protein-splicing elements (inteins) function both as catalysts of protein splicing and as homing endonucleases. In order to identify the domains of inteins that are essential for protein splicing, the intein sequence embedded in the recA gene of Mycobacterium tuberculosis was genetically dissected. The effect of various modifications of the intein on the ability to mediate splicing was studied in Escherichia coli transformed with plasmids in which the coding sequence for the RecA intein was inserted in-frame between coding regions for the E. coli maltose-binding protein and a polypeptide containing a hexahistidine sequence as the N- and C-exteins, respectively. One type of genetic alteration of the RecA intein involved deletion of the central region encoding 229 amino acids (aa), representing the entire homing endonuclease homology domain. The residual intein (211 aa plus an undecapeptide spacer) was able to promote protein splicing as efficiently as the wild-type intein, indicating that the homing endonuclease domain plays no role in the protein-splicing process and that the protein-splicing active center is confined to the N- and C-terminal segments of the intein, less than 110 aa each. Another type of alteration involved the introduction of overlapping translation termination and initiation codons in-frame into the intein coding region. The modified RecA intein, although synthesized as two separate components, could nevertheless mediate protein splicing, indicating that the N- and C-terminal protein-splicing domains can interact with sufficient affinity and specificity to allow protein-splicing to occur in trans. The efficiency of trans-splicing was much enhanced when the homing endonuclease domain was entirely deleted so that the length of the interacting N- and C-terminal intein fragments was only about 110 aa each.

Protein splicing and autoproteolysis mechanisms

It has generally been assumed that the conversion of all inactive protein precursors to biologically active proteins is mediated by specific processing enzymes. However, numerous examples of self-catalyzed protein rearrangements have recently been discovered, including protein splicing and autoproteolysis of hedgehog proteins, glycosylasparaginases and pyruvoyl enzyme precursors. The initial formation of an ester bond by the acyl rearrangement of a peptide bond is a common feature of all of these autoprocessing reactions, which manifest themselves in diverse biological functions, which manifest themselves in diverse biological functions ranging from protein splicing to protein targeting, proenzyme activation, and the generation of enzyme-bound prosthetic groups. Although such acyl rearrangements are thermodynamically unfavorable, their coupling to diverse types of self-catalyzed irreversible steps drives the protein rearrangements to completion.

Identification of ribosomal protein S1 as a poly(A) binding protein in Escherichia coli

To elucidate the metabolic function of mRNA polyadenylation in Escherichia coli. we searched for a polyadenylate-binding protein as a potential mediator of the function of the poly(A) moiety. Using a nitrocellulose filter-binding assay and a Northwestern blot technique, a protein in the ribosomal supernatant fraction of E coli was identified and purified to homogeneity. N-terminal sequence analysis yielded a 25-residue sequence which corresponded to the 25 N-terminal amino acids of protein S1, one of the proteins of the E coli 30S ribosomal subunit. Poly(A) binding to S1 protein was inhibited by Mg2+ and Mn2+ and by ATP and stimulated 8-fold by 100 mM KCl. The binding of S1 to poly(A) occurred with an association constant of 3 x 10(6) M-1 and seemed to be only mildly cooperative. Competition studies of the binding of poly(A) and poly(C) to purified S1 protein were consistent with the presence of two polynucleotide binding sites, of which one binds poly(A) five times more strongly than poly(C), whereas the other binds poly(C) 50 times more strongly than poly(A). Poly(A) bound to 30S ribosomal subunits but not to 50S ribosomes. To study possible association of S1 with the poly(A) tracts of E coli mRNA in the process of translation, poly(A) RNA was isolated from polysomes by oligo(dT) cellulose chromatography and the poly(A) RNA with bound protein was eluted either directly or after digestion with RNase T1 and A. When subjected to Western blot analysis with antibody to S1, both poly(A) RNA and isolated poly(A) tracts revealed bound S1 protein. The implications of these results for the possible interaction of poly(A) tracts of mRNA and the translational machinery of E coli are discussed.

Protein splicing: estimation of the rate of O-N and S-N acyl rearrangements, the last step of the splicing process

The last step in the sequence of reactions that lead to protein splicing is the intramolecular O-N or S-N acyl rearrangement of the ester or thioester linkage, respectively, between the two exteins and hydrolysis of the aminosuccinimide residue at the C-terminus of intein. This paper presents data on the rates of O-N and S-N acyl rearrangements of two model depsipeptides as a function of pH and temperature. The rates of rearrangement of both the oxygen ester and the thioester depsipeptide increased strikingly with pH, with the thioester being about 10(3) times more reactive at pH 5.5, and had a relatively low dependence on temperature, indicative of a low activating energy. The rates of O-N and S-N acyl rearrangement of these two model depsipeptides greatly exceed the rate of protein splicing, explaining why the last step of protein splicing can occur without catalysis by the intein.

Single-column purification of free recombinant proteins using a self-cleavable affinity tag derived from a protein splicing element

A novel protein purification system has been developed which enables purification of free recombinant proteins in a single chromatographic step. The system utilizes a modified protein splicing element (intein) from Saccharomyces cerevisiae (Sce VMA intein) in conjunction with a chitin-binding domain (CBD) from Bacillus circulans as an affinity tag. The concept is based on the observation that the modified Sce VMA intein can be induced to undergo a self-cleavage reaction at its N-terminal peptide linkage by 1,4-dithiothreitol (DTT), beta-mercaptoethanol (beta-ME) or cysteine at low temperatures and over a broad pH range. A target protein is cloned in-frame with the N-terminus of the intein-CBD fusion, and the stable fusion protein is purified by adsorption onto a chitin column. The immobilized fusion protein is then induced to undergo self-cleavage under mild conditions, resulting in the release of the target protein while the intein-CBD fusion remains bound to the column. No exogenous proteolytic cleavage is needed. Furthermore, using this procedure, the purified free target protein can be specifically labeled at its C-terminus.

The relationship between socioeconomic status and recently diagnosed rheumatoid arthritis

OBJECTIVE

To examine the role of socioeconomic status (SES) in physical functioning, pain, and depressive symptoms among newly diagnosed rheumatoid arthritis (RA) patients with severe disease.

METHODS

Data are from 118 non-Hispanic patients of European origin at baseline of a longitudinal study of early, severe RA. Outcome measures with the Health Assessment Questionnaire (HAQ) functional disability index, the HAQ visual analog pain scale, and the Center for Epidemiologic Studies Depression Scale. Hierarchical regression analyses were conducted using a health status block (disease activity and comorbidities), a non-SES related social structure block (age, sex and Lubben Social Network Scale), and indicators of SES (income and education).

RESULTS

Non-SES related social structure and SES were important independent determinants of functional disability and depressive symptoms, but both they and the health status variables were unrelated to pain. Further, neither income nor education was related to disease activity or comorbidities.

CONCLUSION

It cannot be argued from these data that poorer health status explains the link between SES and disability and depressive symptoms. Although, at baseline, the psychosocial effects of early RA are more severe for those with SES, the disease does not appear to be more severe. It may be that the biologic impact of status differentials will become clearer as the effects of treatment and the course of the disease unfold over time.

Protein splicing involving the Saccharomyces cerevisiae VMA intein. The steps in the splicing pathway, side reactions leading to protein cleavage, and establishment of an in vitro splicing system

Protein splicing involves the excision of an internal protein segment, the intein, from a precursor protein and the concomitant ligation of the flanking N- and C-terminal regions. It occurs in mesophilic bacteria, yeast, and thermophilic archaea. The ability to control protein splicing of a thermophilic intein by temperature and pH in a foreign protein context facilitated the study of the mechanism of protein splicing in thermophiles. On the other hand, no direct studies have been done on the mechanism of protein splicing in mesophiles. We examined the splicing of a chimeric protein containing the intein of the vacuolar ATPase subunit (VMA) of Saccharomyces cerevisiae that involves cysteines rather than serines at the reaction center. The steps in the splicing process were deduced by analyzing intermediates and side products that accumulated as a result of amino acid substitutions and were found to be analogous to those occurring in thermophiles. Moreover, appropriate amino acid replacements allowed us to develop the first mesophilic in vitro protein splicing system as well as strategies for modulating the rate of protein splicing and for converting the splicing reaction to an efficient protein cleavage reaction at either splice junction.

Lysine-induced premature transcription termination in the lysC operon of Bacillus subtilis

The expression of the Bacillus subtilis lysC operon, which encodes the first specific enzyme of lysine biosynthesis, is controlled by the availability of the end product, lysine. The question of whether lysine exerts its control by inducing premature termination of transcription was addressed using Northern blot analysis. Whereas lys-C-specific RNA from lysine-starved B. subtilis consisted primarily of the expected full-length mRNA (1.6 kb), that from bacteria grown with an excess of lysine consisted of a truncated 0.27 kb RNA in place of the full-length 1.6 kb transcript. On the other hand, a B. subtilis aecA mutant, in which the lysC operon was derepressed owing to a single nucleotide substitution in the region corresponding to the lysC leader transcript, produced full-length lysC mRNA, but no 0.27 kb RNA, even during growth with excess lysine. Mapping of the truncated 0.27 kb lysC RNA by hybridization with oligonucleotide probes showed that it corresponded to the upstream portion of the lysC leader transcript, extending from the transcription initiation site to a putative rho-independent terminator element. Quantitative transcript analysis by hybridization with specific oligonucleotides showed that lysine did not affect the number of lysC-specific RNA molecules but promoted the stoichiometric replacement of full-length mRNA with truncated 0.27 kb molecules. These results indicate that lysine regulates the expression of the lysC operon by effecting the premature termination of transcription at a rho-independent terminator site in the lysC leader region and that the site of the aecA mutation, far upstream of the putative terminator element, must play an essential role in premature transcription termination by a mechanism which is not yet understood.

Protein splicing: evidence for an N-O acyl rearrangement as the initial step in the splicing process

Protein splicing involves the self-catalyzed formation of a branched intermediate, which then resolves into the excised intervening sequence and the spliced protein. A possible mechanism for branched intermediate formation is an N-O rearrangement of the peptide bond involving the amino group of the conserved serine/cysteine residue at the upstream splice junction to yield a linear peptide ester intermediate. This possibility was examined in using an in vitro splicing system involving the intervening sequence from the DNA polymerase of the extremely thermophilic archeon, Pyrococcus sp. GB-D. Because thioesters react much more rapidly with nitrogen nucleophiles at neutral pH than do oxygen esters, protein-splicing precursors in which the serine residue of interest was replaced by cysteine were constructed and purified. In the presence of 0.25 M hydroxylamine or 0.1 M ethylene diamine at pH 6 or higher, these constructs underwent rapid cleavage at the upstream splice junction, consistent with the aminolysis of a thioester. The site of hydroxylaminolysis was identified by analysis of the C-terminus of the polypeptide cleavage products. Comparison of the C-terminal peptide hydroxamate with the synthetic peptide hydroxamates with respect to chromatographic mobility, colorimetric assay, amino acid composition, and high-resolution mass spectrometry showed that the hydroxylamine-sensitive site in the splicing precursor was the peptide bond adjacent to the serine residue at the upstream splice junction. These results provide evidence that the peptide bond at the upstream splice junction can undergo a self-catalyzed N-O or N-S acyl rearrangement to yield a linear polypeptide ester intermediate and suggest that this kind of rearrangement constitutes the first step in protein splicing.

Applications of SNMS in archaeometry

The recently developed High Frequency Mode HFM of electron gas SNMS allows investigations on insulating samples with the well known advantages of the SNMS Direct Bombardment Mode DBM for the analysis of conducting samples. HFM has been applied to analyses of different historic ceramic and glass samples in order to demonstrate the possibilities of SNMS in this field. It is shown that manufacturing places of ceramic samples could be distinguished by SNMS mass spectra ("fingerprints"). Furthermore questions of the constituents of colour remains on a painted ceramic ("Kaisermedaillon") could be answered by our SNMS analyses. SNMS investigations have been also applied to corrosion phenomena on different glass samples.

Protein splicing: characterization of the aminosuccinimide residue at the carboxyl terminus of the excised intervening sequence

Protein splicing is a self-catalyzed, posttranslational process which converts a precursor polypeptide into two new proteins by the excision of an internal polypeptide segment and the ligation of the flanking polypeptides. Evidence has been presented that protein splicing involves a branched intermediate, which is resolved into the two protein products by the cyclization of an asparagine residue to aminosuccinimide [Xu, M. Q., Comb, D. G., Paulus, H., Noren, C. J., Shao, Y., & Perler, F. (1994) EMBO J. 13, 5517-5522]. This report describes the chemical synthesis of a peptide with a C-terminal aminosuccinimide residue, corresponding to the putative C-terminus of the excised intervening sequence (intein) derived from the thermostable DNA polymerase of Pyrococcus species GB-D. The synthetic aminosuccinimide peptide was compared with the C-terminal cyanogen bromide peptide of the excised intein and found to be indistinguishable in terms of its chromatographic properties, high-resolution mass spectrum, and colorimetric assay involving reaction with hydroxylamine. This establishes definitively that protein splicing is accompanied by the cyclization of asparagine to yield an aminosuccinimide residue at the C-terminus of the excised intein and that this unusual residue is therefore a natural constituent of spliced proteins. The effects of pH and temperature on the stability of the synthetic aminosuccinimide peptide are described.(ABSTRACT TRUNCATED AT 250 WORDS)

American College of Rheumatology. Preliminary definition of improvement in rheumatoid arthritis

OBJECTIVE

Trials of rheumatoid arthritis (RA) treatments report the average response in multiple outcome measures for treated patients. It is more clinically relevant to test whether individual patients improve with treatment, and this identifies a single primary efficacy measure. Multiple definitions of improvement are currently in use in different trials. The goal of this study was to promulgate a single definition for use in RA trials.

METHODS

Using the American College of Rheumatology (ACR) core set of outcome measures for RA trials, we tested 40 different definitions of improvement, using a 3-step process. First, we performed a survey of rheumatologists, using actual patient cases from trials, to evaluate which definitions corresponded best to rheumatologists' impressions of improvement, eliminating most candidate definitions of improvement. Second, we tested 20 remaining definitions to determine which maximally discriminated effective treatment from placebo treatment and also minimized placebo response rates. With 8 candidate definitions of improvement remaining, we tested to see which were easiest to use and were best in accord with rheumatologists' impressions of improvement.

RESULTS

The following definition of improvement was selected: 20% improvement in tender and swollen joint counts and 20% improvement in 3 of the 5 remaining ACR core set measures: patient and physician global assessments, pain, disability, and an acute-phase reactant. Additional validation of this definition was carried out in a comparative trial, and the results suggest that the definition is statistically powerful and does not identify a large percentage of placebo-treated patients as being improved.

CONCLUSION

We present a definition of improvement which we hope will be used widely in RA trials.

Protein splicing: an analysis of the branched intermediate and its resolution by succinimide formation

Protein splicing involves the excision of an internal domain from a precursor protein and the ligation of the external domains so as to generate two new proteins. Study of this process has recently been facilitated by the isolation of a precursor and a branched intermediate from a thermophilic protein splicing element expressed in a foreign protein context. Two aspects of protein splicing are examined in this paper. We demonstrate a succinimide at the C-terminus of the spliced internal protein, implicating cyclization of asparagine in resolution of the branched intermediate, and we identify an alkali-labile bond in the branched intermediate. A revised protein splicing model based on these experimental results is presented.

Deoxyribonucleic acid replication in fetal cells

OBJECTIVES

Our purpose was to develop a sensitive method for assessing the replication time of specific human genes in cultured fetal cells and for detecting potential replication defects.

STUDY DESIGN

Synchronous progression of diploid human fetal lung cells through S phase was achieved by releasing from serum restriction with minimum essential medium alpha modification plus 10% fetal bovine serum, followed by hydroxyurea blockage at the G1/S boundary. Deoxyribonucleic acid replication was studied in permeabilized cells using mercurated nucleotides to label nascent deoxyribonucleic acid.

RESULTS

A high degree of synchrony in traversal of S phase was indicated by flow cytometry and a well-defined 7-hour period of deoxyribonucleic acid synthesis. The replication of the topoisomerase II gene occurred in a narrow time span 3 hours after entry into S phase.

CONCLUSIONS

Fetal cells have been highly synchronized at the beginning of S phase, and the replication time of a specific gene can be defined within a narrow time window.

The course of skin involvement in systemic sclerosis over three years in a trial of chlorambucil versus placebo

OBJECTIVE

To describe the course of cutaneous involvement in systemic sclerosis (SSc; scleroderma) over 3 years, in the context of a placebo-controlled drug trial.

METHODS

The course of skin tethering (assessed by a semiquantitative skin scoring technique) was documented annually for 3 years in 64 SSc patients with early (< 3 years duration at entry), intermediate (3-8 years duration), or late (> 8 years duration) diffuse or limited SSc.

RESULTS

Mean +/- SD entry skin scores were significantly greater in the 33 diffuse SSc patients (13.1 +/- 5.0) than in the 31 limited SSc patients (4.3 +/- 2.1) (P < 0.001). In patients with diffuse SSc, the skin score remained stable for the first 12 months, but had decreased significantly by 24 months (P < 0.022) and 36 months (P < 0.004). In those with limited SSc, the skin score did not change significantly over 3 years.

CONCLUSION

Trials of treatments designed to affect skin thickening/tethering should be conducted in patients who have diffuse SSc (of short, intermediate, or long duration) at entry. The best time to study therapies designed to affect skin thickening may be in the first year after entry.