Transporter-Mediated Hepatic Uptake Plays an Important Role in the Pharmacokinetics and Drug-Drug Interactions of Montelukast

Montelukast, a leukotriene receptor antagonist commonly prescribed for treatment of asthma, is primarily metabolized by cytochrome P450 (CYP)2C8, and has been suggested as a probe substrate for investigating CYP2C8 activity in vivo. We evaluated the quantitative role of hepatic uptake transport in its pharmacokinetics and drug-drug interactions (DDIs). Montelukast was characterized with significant active uptake in human hepatocytes, and showed affinity towards organic anion transporting polypeptides (OATPs) in transfected cell systems. Single-dose rifampicin, an OATP inhibitor, decreased montelukast clearance in rats and monkeys. Clinical DDIs of montelukast were evaluated using physiologically based pharmacokinetic modeling; and simulation of the interactions with gemfibrozil-CYP2C8 and OATP1B1/1B3 inhibitor, clarithromycin-CYP3A and OATP1B1/1B3 inhibitor, and itraconazole-CYP3A inhibitor, implicated OATPs-CYP2C8-CYP2C8 interplay as the primary determinant of montelukast pharmacokinetics. In conclusion, hepatic uptake plays a key role in the pharmacokinetics of montelukast, which should be taken into account when interpreting clinical interactions.

Utility of the carboxylesterase inhibitor bis-para-nitrophenylphosphate (BNPP) in the plasma unbound fraction determination for a hydrolytically unstable amide derivative and agonist of the TGR5 receptor

The potent, functional agonist of the bile acid Takeda G-protein-coupled receptor 5 (TGR5), (S)-1-(6-fluoro-2-methyl-3,4-dihydroquinolin-1(2H)-yl)-2-(isoquinolin-5-yloxy)ethanone (3), represents a useful tool to probe in vivo TGR5 pharmacology. Rapid degradation of 3 in both rat and mouse plasma, however, hindered the conduct of in vivo pharmacokinetic/pharmacodynamic investigations (including plasma-free fraction (f(u plasma)) determination) in rodent models of pharmacology. Studies were therefore initiated to understand the biochemical basis for plasma instability so that appropriate methodology could be implemented in in vivo pharmacology studies to prevent the breakdown of 3. Compound 3 underwent amide bond cleavage in both rat and mouse plasma with half-lives (T(1/2)) of 39 + or - 7 and 9.9 + or - 0.1 min. bis(p-nitrophenyl) phosphate (BNPP), a specific inhibitor of carboxylesterases, was found to inhibit hydrolytic cleavage in a time- and concentration-dependent manner, which suggested the involvement of carboxylesterases in the metabolism of 3. In contrast with the findings in rodents, 3 was resistant to hydrolytic cleavage in both dog and human plasma. The instability of 3 was also observed in rat and mouse liver microsomes. beta-Nicotinamide adenine dinucleotide phosphate, reduced form (NADPH)-dependent metabolism of 3 occurred more rapidly (T(1/2) approximately 2.22-6.4 min) compared with the metabolic component observed in the absence of the co-factor (T(1/2) approximately 89-130 min). Oxidative metabolism dominated the NADPH-dependent decline of 3, whereas NADPH-independent metabolism of 3 proceeded via simple amide bond hydrolysis. Compound 3 was highly bound (approximately 95%) to both dog and human plasmas. Rat and mouse plasma, pre-treated with BNPP to inhibit carboxylesterases activity, were used to determine the f(u plasma) of 3. A BNPP concentration of 500 microM was determined to be optimal for these studies. Higher BNPP concentrations (1000 microM) appeared to displace 3 from its plasma protein-binding sites in preclinical species and human. Under the conditions of carboxylesterases-inhibited rat and mouse plasma, the level of protein binding displayed by 3 was similar to those observed in dog and human. In conclusion, a novel system has been devised to measure f(u plasma) for a plasma-labile compound. The BNPP methodology can be potentially applied to stabilize hydrolytic cleavage of structurally diverse carboxylesterase substrates in the plasma (and other tissue), thereby allowing the characterization of pharmacology studies on plasma-labile compounds if and when they emerge as hits in exploratory drug-discovery programmes.

Block of slow axonal transport and axonal growth by brefeldin A in compartmented cultures of rat sympathetic neurons

Disruption of the Golgi by brefeldin A (BFA) has been reported to block fast axonal transport and axonal growth. We used compartmented cultures of rat sympathetic neurons to investigate its effects on slow axonal transport. BFA (1 micro g/ml) applied to cell bodies/proximal axons for 6-20 h disrupted the Golgi, reversibly blocked axonal growth, and reversibly blocked anterograde transport of all proteins, including tubulin. The retrograde transport of nerve growth factor (NGF) was also blocked. The phosphorylation of Erk1 and Erk2 in response to NGF was unaffected after 6 h of treatment with BFA, suggesting that the block of axonal transport was specific and direct. Consistent with its principal site of action at the Golgi, no effects were observed when BFA was applied only to the distal axons. Block of fast anterograde and retrograde axonal transport is consistent with the role of the Golgi in supplying transport vesicles. Block of slow axonal transport was surprising, and further results indicated that transport of tubulin en route along the axon was arrested by application of BFA to the cell bodies, suggesting that a continuous supply of anterograde transport vesicles from the Golgi is required to maintain slow axonal transport of cytoskeletal proteins.

Protein synthesis in axons and its possible functions

Proteins synthesized in neuronal cell bodies are transported along axons by fast and slow axonal transport. Cytoskeletal proteins and cytosolic proteins that travel by slow axonal transport could take years to reach the terminals of meter-long axons, and it is difficult to see how proteins could last long enough to make this journey. How then are proteins supplied to the distal regions of long axons? Evidence has accumulated indicating that axons contain specific mRNAs and ribosomes and can synthesize cytoskeletal proteins and some other proteins. This review considers the direct evidence that proteins can be synthesized in axons and considers the possible functional significance of axonal protein synthesis. It remains unclear whether local protein synthesis could supply the cytoskeletal proteins and other slow-transported proteins required for the maintenance, plasticity, and regeneration of long axons.

Mortality from cardiovascular diseases and its relationship to air temperature during the winter months in Dublin and Oslo/Akershus

In many countries increased winter mortality from cardiovascular diseases (CVD) has been documented. A causal relationship between change in air temperature and change in number of deaths has been suggested. There is also evidence for a delay between a fall in air temperature and death (lag effect). We have investigated these relationships using mortality data for CVD (ICD-9: 390-459) and daily air temperatures in selected winter months (December to March) from two densely populated areas in Norway and Ireland, Oslo/Akershus and Dublin. A specially designed computer programme was used to select data from specific days in the ten years period. The days selected depended on the temperature change chosen between two consecutive days. We examined 2 types of temperature change, a large change and little or no change. An analytical technique involving the use of Spearman's correlations coefficients was used to investigate delays in mortality following a particular change in temperature. For groups of selected days, an inverse relation between mortality and air temperature was found. For neither the Oslo/Akershus nor the Dublin data was it possible to see a sudden increase in mortality following a large, sudden decrease in temperature and no evidence for a delay between a change in temperature and a change in mortality rate was found.

The relationship between mortality caused by cardiovascular diseases and two climatic factors in densely populated areas in Norway and Ireland

BACKGROUND

Seasonal variations in mortality due to cardiovascular disease have been demonstrated in many countries, with the highest levels occurring during the coldest months of the year. It has been suggested that this can be explained by cold climate. In this study, we examined the relationship between mortality and two different climatic factors in two densely populated areas (Dublin, Ireland and Oslo/Akershus, Norway).

METHODS

Meteorological data (mean daily air temperatures and wind speed) and registered daily mortality data for three groups of cardiovascular disease for the period 1985-1994 were obtained for the two respective areas. The daily mortality ratio for both men and women of 60 years and older was calculated from the mortality data. The wind chill temperature equivalent was calculated from the Siple and Passels formula.

RESULTS

The seasonal variations in mortality were greater in Dublin than in Oslo/Akershus, with mortality being highest in winter. This pattern was similar to that previously shown for the two respective countries as a whole. There was a negative correlation between mortality and both air temperature and wind chill temperature equivalent for all three groups of diseases. The slopes of the linear regression lines describing the relationship between mortality and air temperature were a lot steeper for the Irish data than for the Norwegian data. However, the difference between the steepness of the linear regression lines for the relationship between mortality and wind chill temperature equivalent was considerably less between the two areas. This can be explained by the fact that Dublin is a much windier area than Oslo/Akershus.

CONCLUSION

The results of this study demonstrate that the inclusion of two climatic factors rather than just one changes the impression of the relationship between climate and cardiovascular disease mortality.

Bacteriology and antimicrobial choice in hepatolithiasis

BACKGROUND AND AIMS

Hepatolithiasis is prevalent in southeast Asia and presents a difficult management problem. Acute repeated episodes of cholangitis are frequently manifested in patients with hepatolithiasis. Without proper treatment, such infection can lead to liver abscess, secondary biliary cirrhosis, portal hypertension, and death from sepsis or hepatic failure. In addition to clearance of the stones and relief of bile stasis either by surgery or by interventional radiologic manipulation, effective antimicrobial therapy also plays a crucial role in the treatment of patients with hepatolithiasis. The aim of this study is to clarify the bacteriology in hepatolithiasis and to provide the information for an appropriate antimicrobial choice.

METHODS

From July 1993 to June 1996, 150 patients with hepatolithiasis underwent surgical intervention. Bile specimens were routinely obtained by syringe aspiration from common bile duct. The syringe was immediately capped, and the bile was subsequently cultured for both aerobes and anaerobes.

RESULTS

Bacteria were present in the bile of all patients. The bacteria most frequently found were gram-negative bacteria such as Klebsiella sp, Escherichia coli, and Pseudomonas sp, and the gram-positive Enterococcus sp. Bacteroides sp were the most frequently found anaerobes.

CONCLUSIONS

This study demonstrated the close relationship between acute cholangitis in hepatolithiasis and enteric bacteria and also displayed the detailed antibiotic sensitivity results. Armed with this fruitful information, we believe the antibiotic treatment for acute cholangitis in hepatolithiasis should first aim at enteric bacteria and be adjusted later according to the results of bacteriologic cultures and clinical situation to achieve an effective microbial control.

Association of extracellular matrix proteins fibulin-1 and fibulin-2 with fibronectin in bone marrow stroma

Extracellular matrix (ECM) molecules, together with growth factors and stromal cells, regulate haematopoietic cell development in bone marrow (BM). We report here expression of ECM proteins fibulin-1 and fibulin-2 in mouse BM. In other tissues, fibulin-1 and fibulin-2 associate with fibronectin and other ECM proteins. Fibulin-2 has also been found to adhere to cells via beta3 integrins. We studied the association of fibulins with fibronectin in BM stroma. By confocal microscopy, fibulin-1 and fibulin-2 immunostainings were co-localized with fibronectin in the adherent layer of long-term BM cultures. In cell adhesion assays using recombinant proteins, mouse fibulin-2 adhered to human erythroid-megakaryocytic leukaemia cell line HEL. This adhesion was mediated by beta3 integrins. However, HEL cells did not adhere to human fibulin-2. We therefore studied a possible species-specific cell-adhesive activity of mouse fibulin-2 by using mouse megakaryocytes, obtained by culture of BM cells in the presence of thrombopoietin. These megakaryocytes did not adhere to mouse fibulin-2. Our findings suggested that the functional role of fibulin-1 and fibulin-2 in BM stroma is related to binding to the major cell adhesion protein fibronectin, whereas adhesion of mouse fibulin-2 to human cells containing the integrin beta3 chain is not related to an apparent physiological function of the protein.

Recurrent and new hepatitis C virus infection after liver transplantation

Chronic infection with the hepatitis C virus (HCV) is the most common reason for liver transplantation. We examined the results of laboratory tests for HCV on a cohort of patients who received a liver transplant between 1990 and 1994 at three large centers. Seven hundred twenty-two recipients and 604 donors were tested for antibody to HCV (anti-HCV) using a second-generation enzyme-linked immunoassay (EIA-2), followed by recombinant immunoblot (RIBA-2) and HCV RNA confirmation by reverse-transcription polymerase chain reaction (RT-PCR) (with genotyping and viral quantification). Diagnosis of posttransplantation infection required detection of serum HCV RNA that could be genotyped by sequencing or was repeatedly positive despite being unsequenceable. Twenty-five percent of transplantation candidates were seropositive for anti-HCV. Approximately 86% of anti-HCV-positive, 93% of RIBA-positive, and 97% of HCV RNA-positive candidates developed infection after transplantation. Pretransplantation HCV RNA was superior to RIBA-2 for predicting posttransplantation infection. Whereas HCV genotype was identified in nearly all candidates and changed little after transplantation, serum viral levels rose markedly after transplantation. Fifteen donors were either anti-HCV- or HCV RNA-positive. Recipients of grafts from donors with HCV RNA all developed infection, whereas infection was not detected in recipients of grafts from donors with anti-HCV but without detectable HCV RNA. The rate of new infection fell significantly (P =.02) after the introduction of EIA-2 screening of blood. Donor and candidate markers for HCV predict posttransplantation infection.

Synthesis of beta-tubulin, actin, and other proteins in axons of sympathetic neurons in compartmented cultures

The proteins needed for growth and maintenance of the axon are generally believed to be synthesized in the cell bodies and delivered to the axons by anterograde transport. However, recent reports suggest that some proteins can also be synthesized within axons. We used [35S]methionine metabolic labeling to investigate axonal protein synthesis in compartmented cultures of sympathetic neurons from newborn rats. Incubation of distal axons for 4 hr with [35S]methionine resulted in a highly specific pattern of labeled axonal proteins on SDS-PAGE, with 4 prominent bands in the 43-55 kDa range. The labeled proteins in axons were not synthesized in the cell bodies, because they were also produced by axons after the cell bodies had been removed. Two of the proteins were identified by immunoprecipitation as actin and beta-tubulin. Axons synthesized <1% of the actin and tubulin synthesized in the cell bodies and transported into the axons, and 75-85% inhibition of axonal protein synthesis by cycloheximide and puromycin failed to inhibit axonal elongation. Nonetheless, the specific production by axons of the major proteins of the axonal cytoskeleton suggests that axonal protein synthesis arises from specific mechanisms and likely has biological significance. One hypothetical scenario involves neurons with long axons in vivo in which losses from turnover during axonal transport may limit the availability of cell body synthesized proteins to the distal axons. In this case, a significant fraction of axonal proteins might be supplied by axonal synthesis, which could, therefore, play important roles in axonal maintenance, regeneration, and sprouting.

Seasonal variations in mortality caused by cardiovascular diseases in Norway and Ireland

BACKGROUND

Seasonal variations in mortality resulting from cardiovascular diseases (CVD) have been demonstrated in many countries, with the highest levels observed during the coldest months of the year. We studied the seasonal changes in CVD mortality in Norway and the Republic of Ireland, two countries which are demographically quite similar, but climatically different; we also examined the relation between CVD mortality and air temperature.

METHODS

Registered monthly data for mortality from CVD for the period 1985-1995 were obtained from the Norwegian Central Bureau of Statistics and the Irish Central Statistics Office. Meteorological data were provided by the Norwegian Institute of Meteorology and Met Eireann, in Ireland. Monthly mortality ratio for both men and women aged 60 and older was calculated from the mortality date. Mean monthly air temperatures for the two countries were calculated from the meteorological data.

RESULTS

For the 10-year period investigated, the lowest and highest monthly mortality ratios were on average found in August and January, respectively, and mean excess winter mortality, expressed as the difference between the August and January values for the entire 10-year period, was 22% (Norway) and 35% (Ireland). However, when the percentage difference in the months with the respective highest and lowest mortality ratios were calculated for each year, the average of these differences for each of the 10 individual years was 29% and 45%. Mortality ratio was found to increase much more steeply with decreasing air temperature in Ireland than in Norway.

CONCLUSION

Although the seasonal variation between CVD mortality in both countries is similar, the different relation with climatic conditions may result from differences in housing standards, allowing outdoor temperatures to have a greater influence on indoor temperature in Ireland than in Norway.

Decreased beta2-adrenergic receptor density on peripheral blood mononuclear cells in myasthenia gravis

Beta2-adrenergic receptors (beta2AR) are present on both lymphocytes and skeletal muscle cells. Antibodies and T cells that react with these receptors are present in patients with myasthenia gravis (MG). Immune reactivity against the beta2AR may thus modify both the immune and the muscle functions in MG. In this study, we analysed the density and affinity of beta2AR on peripheral blood mononuclear cells using a radioligand binding assay. The density (Bmax) of the receptor on cells from patients with MG was significantly lower than that on cells from patients with other neurological disorders and healthy individuals. The affinity (Kd) of the receptor and the concentration of the second messenger, cAMP, in the cells did not differ between the groups. Serum antibodies against beta2AR were demonstrated in 22% of 27 MG patients vs. 0% of 26 healthy controls. Incubation of cells with serum or purified IgG containing antibodies against the beta2AR resulted in a decline in ligand binding of the receptor in samples from three out of five patients. Thus, this study suggests that a downregulation of the beta2AR may occur in MG. This downregulation might be of importance in the patho-genesis of the disease and its symptoms.

Effects of divalent cations on M-cadherin expression and distribution during primary rat myogenesis in vitro

In the process of myogenesis, cadherins are thought to be involved in the initial cell-cell recognition and possible initiation of myoblast fusion to form multinucleated myotubes. Of the cadherins, M-cadherin, but not N-cadherin, is down-regulated upon inhibition of myogenesis, suggesting that M-cadherin may be a key receptor involved in myogenesis. M-cadherin binds in a calcium-dependent manner, and depletion of divalent cations inhibits myoblast fusion. We analyzed the regulation of M-cadherin protein and mRNA levels in primary rat myogenic cultures in the presence and absence of divalent cations. In untreated cultures M-cadherin was localized to various myogenic cell-cell contacts. M-cadherin protein and mRNA levels showed a peak at day 2 after the initiation of growth. When divalent cations were removed from the cell culture medium, myoblast fusion was inhibited and immunocytochemical analysis revealed a failure of M-cadherin to localize to cell-cell contacts. Analysis of M-cadherin protein and mRNA in fusion-inhibited cultures still revealed a peak at day 2. However, by day 3, M-cadherin protein levels in the fusion-inhibited cultures were reduced in both the detergent-soluble and -insoluble fractions in comparison with the untreated cultures. Interestingly, beta-catenin, a protein associated with cadherins, was frequently observed at intercellular contacts in the fusion-inhibited cultures. We could also show that the intracellular levels of beta-catenin protein remained constant regardless of the presence or absence of divalent cations. In summary, the dynamic regulation of M-cadherin in muscle-fusion-related events is an indication of the importance of M-cadherin for myoblast fusion and myogenic differentiation.

Characterization of monoclonal antibodies against tenascin-C: no apparent effect on kidney development in vitro

Tenascin-C is an extracellular matrix glycoprotein found in embryonic mesenchyme. The precise biological function of tenascin-C is unknown, but different parts of the molecule have effects on cell adhesion and other cellular activities. We studied the expression and role of tenascin-C in the embryonic mouse kidney. By Northern blots, no tenascin-C was detectable in uninduced mesenchyme from day 11 embryonic kidneys, but after 24 hours of in vitro culture both major splice variants of tenascin-C were detected. The larger variant was the predominant form. By in situ hybridization tenascin-C mRNA in 13-day old embryonic kidneys was detected in the mesenchyme surrounding newly formed epithelial structures. In 17-day old embryonic kidneys, tenascin-C mRNA was detected in mesenchyme around the forming epithelial structures in the cortex, and expression was also seen in mesenchyme surrounding the capsular epithelium of glomeruli. In newborn kidneys, expression had shifted to the medulla but was still confined to mesenchymal areas. We have characterized 6 new monoclonal antibodies against mouse tenascin-C, which all stain embryonic kidneys from different stages in a pattern consistent with earlier reports and with the mRNA data. The binding sites of the monoclonal antibodies on the tenascin-C molecule were mapped to discrete regions of tenascin-C. These six and five previously described antibodies against tenascin-C were tested in antibody perturbation experiments. Three of these have been shown by in vitro assays to perturb function of other cell types. Despite this, none of them inhibited development of mouse kidneys in organ culture, although they were tested at 1 mg/ml. It raises the possibility that tenascin-C is not crucial for kidney development. Alternatively, tenascin-C has more subtle functions which could not be identified with the assays used here.

T and B lymphocytes reacting with the extracellular loop of the beta 2-adrenergic receptor (beta 2AR) are present in the peripheral blood of patients with myasthenia gravis

Eighteen percent of patients with myasthenia gravis (MG) have serum antibodies against a synthetic peptide corresponding to the second extracellular loop of the human beta 2AR (residues 172-197). In this study we examined T and B cell responses to the peptide, using assays to detect individual cells secreting interferon-gamma (IFN-gamma) and IL-4 or antibodies against the peptide, and by measuring thymidine incorporation in response to the peptide. The peptide from the beta 2AR induced cytokine secretion from blood mononuclear cells in 67% of MG patients, compared with 14-28% of the control groups. Cells secreting antibodies binding to the peptide were present in 54% of MG patients and in 19-28% of controls. The numbers of beta 2AR-reactive cells were higher in MG patients than in controls. Peptide-induced increase in thymidine incorporation in cells was also more frequently demonstrated in patients (26%) compared with controls (about 10%). Activation of cells was dependent on monocytes and on MHC class II DR antigen. Based on the pattern of the cytokine secretion induced, beta 2AR-reactive T cells comprise both T helper type-1 and type-2 subsets. In addition, control peptide-reactive T and B cells were much less frequently demonstrated in the patients, and the number of such cells did not differ between the groups. Our results show that beta 2AR-reactive cells are present in most patients with MG. Such autoreactive antibodies and cells might play a role in the pathogenesis of the disease by influencing the function of skeletal muscle and immune systems.

T-cell epitopes on the human acetylcholine receptor alpha-subunit residues 10-84 in myasthenia gravis

In myasthenia gravis the production of anti-acetylcholine receptor antibodies is modulated by acetylcholine receptor-specific T cells. Most B- and T-cell epitopes are located on the alpha-subunit of the receptor. In order to map the fine specificity of the antigen-specific T cells in myasthenia gravis, T-cell stimulation in response to 70 hexapeptides was studied in 24 patients and 24 healthy individuals. The hexapeptides overlapped with one amino acid and represented residues 10-84 of the NH2-terminal part of the alpha-subunit of the receptor. The IFN-gamma secretion from single T cells was used to detect T-cell stimulation. A significant difference in the T-cell response to several of the peptides was found between patients and healthy controls. The majority of the hexapeptides induced T-cell stimulation in at least one of the patients. Peptide-induced T-cell stimulation was evident in all but one of the patients. The results indicate that different epitopes and multiple T-cell clones are involved in the T-cell recognition of the acetylcholine receptor.

Beta 2-adrenergic receptor antibodies in myasthenia gravis

Although autoantibodies against the nicotinic acetylcholine receptor are the characteristic feature of the autoimmune disease myasthenia gravis (MG), no strong correlation is found between the autoantibody titer and the degree of clinical severity. Numerous studies have attempted to detect the presence of other autoantibody populations that might have a role in the pathology of the disease. We report, for the first time, that 18% of the MG patients we screened have antibodies in their serum to a peptide corresponding to the second extracellular loop of the human beta 2-adrenergic receptor (residues 172-197). Affinity purified antibodies to the beta 2-adrenergic receptor peptide 172-197 reacted with the human beta 2-adrenergic receptor protein obtained from transfected E. coli cell membrane extracts, but did not cross-react with the human AChR. Sufficient material was obtained from nine MG patients and it was found that the gamma globulin fraction from these patients immunoprecipitated the receptor, and that affinity purified IgG to peptide 172-197 competed for receptor binding with the beta-antagonist iodo-cyanopindolol. Using truncated peptides or amino acid modification procedures, no immunodominant B-cell epitope could be detected within region 172-197. Thus, a subpopulation of MG patients possesses anti-beta 2-adrenergic receptor antibodies which are a distinct set of autoantibodies with possible pharmacological activity.

B cell and autoantibody repertoire in a pair of monozygotic twins discordant for myasthenia gravis

A pair of identical twins, 47 years of age, who have been discordant for myasthenia gravis for 15 years were studied with regard to clinical status, neuromuscular function, and presence and properties of myasthenia specific autoantibodies. The autoantibody repertoire was tested in serum, as produced by peripheral lymphocytes in culture and as revealed by B cell lines. The healthy twin had no clinical signs of myasthenia and no signs of impaired neuromuscular function on electrophysiological tests. The autoantibody repertoire and the avidity of the anti-receptor antibodies were similar in both individuals. Epstein-Barr virus transformation of peripheral lymphocytes revealed a higher incidence of B cells committed to make autoantibodies in the healthy twin than in her myasthenic sister.

Idiotypic network in myasthenia gravis

Fluctuations in idiotypic and anti-idiotypic Ab levels over time in two myasthenia gravis patients were found to vary either inversely with one another or in relation to one another. A pair of 46-year-old female twins in which one of the twins developed myasthenia gravis while the other remained healthy were also studied. Ab specificities and immunoglobulin specificities available in the B cell repertoire were found to be similar in both twins.

Isolation of an antiidiotypic antibody with acetylcholine-receptor-like binding properties from myasthenia gravis patients

The network theory predicts that a subpopulation within the antiidiotypic (anti-Id) antibody response will be the internal image of the priming stimulus. In myasthenia gravis, a portion of the anti-acetylcholine-receptor (anti-AChR) antibody repertoire is directed against the ligand-binding site. These antibodies would be expected to elicit an "anti-idiotype" which is the internal image of the receptor-binding site and hence may also bind cholinergic ligands. We have utilized this theoretical specificity to isolate anti-Id antibodies with AChR-like ligand-binding properties from the serum of 4 myasthenia gravis patients using a choline affinity column. Affinity-purified antibodies from one patient were characterized and found to exhibit binding properties similar to the AChR for various cholinergic ligands.

Human monoclonal immunoglobulins that bind the human acetylcholine receptor

Myeloma immunoglobulins, once thought to be without any immunological function, are now known to be reactive with many antigens, including self components. We have screened 149 monoclonal immunoglobulin samples and found 14 (9%) to react with the human acetylcholine receptor (AChR). Such anti-AChR antibodies are often associated with the autoimmune disease myasthenia gravis (MG). The anti-AChR binding of the myeloma components was restricted to the F(ab')2 fragment and the affinities were similar to anti-AChR antibodies isolated from MG patients. Despite the presence of anti-AChR antibodies none of the patients exhibited any symptoms of MG.

Properties of urease from Ureaplasma urealyticum: kinetics, molecular weight, and demonstration of multiple enzyme isoelectric point forms

In the several strains of Ureaplasma urealyticum that we examined, all originally isolated from human sources, the ureases were found to have a pH optimum between 7.2 and 7.5, and the Km was approximately 2.5 mM urea. Using nonreducing, nondenaturing conditions for polyacrylamide gel electrophoresis, the molecular weight of the holoenzyme was determined to be approximately 380 000. Treatment with reducing agents did not affect the electrophoretic mobility and, therefore, the molecular weight of ureaplasma urease. Immunoblot analysis (using antiserum to U. urealyticum urease) after sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing, denaturing conditions revealed two antigenically reactive bands of molecular weight 174 000 and 179 000. Under reducing, denaturing conditions, a single band of molecular weight approximately 179 000 was detected. Multiple forms of urease were detected by isoelectrofocusing but not by zonal electrophoresis.