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Background: Current methods for evaluating liver health rely on nonspecific blood tests, elastography surrogates for fibrosis, and invasive procedures, none of which directly measure liver function and physiology. Herein we present the analytical validation of a unique, highly sensitive LC-MS/MS assay and dual-sample oral (DuO) cholate challenge test to reliably quantify serial serum concentrations of cholate isotopes administered to patients with liver diseases. The clearance of administered cholate isotopes measured by the assay provides information about liver function and physiology., Methods: Analytical method validation of the cholate assay analytes (endogenous unlabeled cholic acid, 24-13C-cholic acid, and 2,2,4,4-D4-cholic acid) in terms of accuracy, precision, analytical sensitivity, analytical specificity, and range of reliable response was completed in human serum samples spiked with quality controls and calibrators in accordance with applicable guidelines. DuO test parameters were validated using samples from 48 subjects representing various liver disease etiologies., Results: Accuracy (mean biases) for all analytes ranged from 0.1% to 3.7%. Using a nested components-of-variance design (20 days, 2 runs per day, 2 replicates per sample), total imprecision for all analytes ranged from 2.3% to 8.4%. Lower and upper limits of quantitation were established and validated at 0.1 to 10.0 µM. Matrix effects and potential interferents did not affect assay performance. DuO test validation met all prespecified acceptance criteria., Conclusions: The method validation studies described herein established the performance characteristics in terms of accuracy, precision, analytical sensitivity, analytical specificity, reportable ranges, and reference intervals of the LC-MS/MS cholate assay and DuO test., (© Association for Diagnostics & Laboratory Medicine 2024. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

New methods for measuring hepatic improvement in clinical trials and the clinic are needed. One new method, HepQuant SHUNT, detected dose-dependent improvements in hepatic function and portal physiology in the phase 1b study (NCT03842761) of avenciguat, an activator of soluble guanylyl cyclase that is being developed for the treatment of portal hypertension. Herein, we examined whether HepQuant Duo, an easy-to-administer test version, could similarly detect the effects of avenciguat. Twenty-three patients with Child-Pugh A cirrhosis and liver stiffness >15 kPa received either a placebo (n = 5) or a maximum twice-daily avenciguat dose of 1, 2, or 3 mg (n = 6 per group) for 28 days. The DuO test was performed at baseline and on days 11 and 27 in each subject. The test involved administering 40 mg of d4-cholate orally, measuring d4-cholate concentrations in serum at 20 and 60 minutes, and calculating portal hepatic filtration rate, disease severity index, portal-systemic shunting (SHUNT%), and hepatic reserve (HR%). Avenciguat demonstrated dose-dependent improvement in all test parameters. Changes from baseline in SHUNT% after 27 days' treatment were 0.1 ± 9.0% for placebo, 1.7 ± 5.5% for 1 mg twice-daily, -3.2 ± 2.7% for 2 mg twice-daily, and -6.1 ± 5.0% for 3 mg twice-daily (paired t test for change from baseline p = 0.98, 0.48, 0.04, and 0.03, respectively). The changes detected by HepQuant DuO were similar to those previously observed and reported for HepQuant SHUNT. The results support further study of avenciguat in treating portal hypertension and spotlight the utility of HepQuant DuO in the development of drug therapy for liver disease. HepQuant DuO facilitates the use of function testing to measure hepatic improvement in clinical trials and the clinic., (Copyright © 2024 American Association for the Study of Liver Diseases.)

HepQuant tests quantify liver function from clearance of deuterium- and 13C-labeled cholates administered either intravenously and orally (SHUNT) or orally (DuO). Hepatic impairment studies have relied on clinical or laboratory criteria like Child-Pugh classification to categorize the degree of hepatic dysfunction. We compared HepQuant tests with Child-Pugh classification in predicting the pharmacokinetics of ampreloxetine. Twenty-one subjects with hepatic impairment (8 Child-Pugh A, 7 Child-Pugh B, and 6 Child-Pugh C), and 10 age- and sex-matched controls were studied. The pharmacokinetics of ampreloxetine were measured after oral administration of a single dose of 10 mg. Disease severity index (DSI), portal-systemic shunting (SHUNT%), hepatic reserve, and hepatic filtration rates (HFRs) were measured from serum samples obtained after intravenous administration of [24- 13 C]-cholate and oral administration of [2,2,4,4- 2 H]cholate. Ampreloxetine plasma exposure (AUC 0-inf ) was similar to controls in Child-Pugh A, increased 1.7-fold in subjects with Child-Pugh B, and 2.5-fold in subjects with Child-Pugh C and correlated with both Child-Pugh score and HepQuant parameters. The variability observed in ampreloxetine exposure (AUC 0-inf ) in subjects with moderate (Child-Pugh B) and severe hepatic impairment (Child-Pugh C) was explained by HepQuant parameters. Multivariable regression models demonstrated that DSI, SHUNT%, and Hepatic Reserve from SHUNT and DuO were superior predictors of ampreloxetine exposure (AUC 0-inf ) compared to Child-Pugh score. HepQuant DSI, SHUNT%, and hepatic reserve were more useful predictors of drug exposure than Child-Pugh class for ampreloxetine and thus may better optimize dose recommendations in patients with liver disease. The simple-to-administer, oral-only DuO version of the HepQuant test could enhance clinical utility., (© 2024 The Authors. Clinical Pharmacology & Therapeutics © 2024 American Society for Clinical Pharmacology and Therapeutics.)

Current noninvasive liver tests measure fibrosis, inflammation, or steatosis and do not measure function. The HepQuant platform of noninvasive tests uniquely assesses both liver function and physiology through the hepatic uptake of stable isotopes of cholate. However, the prototypical HepQuant SHUNT test (SHUNT V1.0) is cumbersome to administer, requiring intravenous and oral administration of cholate and six peripheral venous blood samples over 90 min. To alleviate the burden of test administration, we explored whether an oral only (DuO) version, and other simplified versions, of the test could provide reproducible measurements of liver function. DuO requires only oral dosing and two blood samples over 60 min. The simplified SHUNT test versions were SHUNT V1.1 (oral and IV dosing but four blood samples) and SHUNT V2.0 (oral and IV dosing but only two blood samples over 60 min). In this paper, we describe the reproducibility of DuO and the simplified SHUNT tests relative to that of SHUNT V1.0; equivalency is described in a separate paper. Data from two studies comprising 236 SHUNT tests in 94 subjects were analyzed retrospectively by each method. All simplified methods were highly reproducible across test parameters with intraclass correlation coefficients >0.93 for test parameters Disease Severity Index (DSI) and Hepatic Reserve. DuO and SHUNT V2.0 improved reproducibility in measuring portal-systemic shunting (SHUNT%). These simplified tests, particularly DuO and SHUNT V2.0, are easier to administer and less invasive, thus, having the potential to be more widely accepted by care providers administering the test and by patients receiving the test., (© 2024 HepQuant LLC. Clinical and Translational Science published by Wiley Periodicals LLC on behalf of American Society for Clinical Pharmacology and Therapeutics.)

Introduction: Perturbations in aromatic (AAAs) and branched-chain amino acids (BCAAs) are seen in decompensated liver disease. The aim of this study was to evaluate the dynamic, postprandial relationship between hepatitis C virus-induced liver disease and amino acid concentrations in patients with compensated liver disease., Methods: Patients infected with hepatitis C virus underwent a baseline liver biopsy to determine Ishak Fibrosis Score and evaluate the liver transcriptome. Patients ate a standard meal and underwent peripheral vein sampling at defined intervals. Quantitative analysis of amino acids was performed using liquid chromatography-tandem mass spectrometry., Results: At baseline, there was no difference in AAA and BCAA concentrations between patients with cirrhosis and non-cirrhotic patients. After a standard meal, AAAs, but not BCAAs, were elevated in patients with cirrhosis compared with non-cirrhotic patients at every time point. The HepQuant SHUNT fraction was significantly higher in patients with cirrhosis and positively correlated with AAA concentration at all time points, but not BCAA. Analysis of the hepatic transcriptome demonstrated greater downregulation of the AAA degradation pathways than the BCAA degradation pathways., Discussion: At baseline, cirrhotic patients with compensated liver disease have adequate reserve liver function to metabolize AAAs and BCAAs. When faced with a metabolic stressor, such as a standard meal, patients with cirrhosis are less able to metabolize the increased load of AAAs. This impairment correlates with portosystemic shunting. Further evaluation of AAA levels in compensated liver disease might further the understanding of the liver-muscle axis and the role it may play in the development of sarcopenia in liver disease., (Copyright © 2024 Written work prepared by employees of the Federal Government as part of their official duties is, under the U.S. Copyright Act, a “work of the United States Government” for which copyright protection under Title 17 of the United States Code is not available. As such, copyright does not extend to the contributions of employees of the Federal Government.)

Current noninvasive liver tests are surrogates for fibrosis and lack ability to directly measure liver function. HepQuant tests measure liver function and physiology through hepatic uptake of stable cholate isotopes. HepQuant SHUNT (V1.0) involves oral and intravenous dosing and six blood samples over 90 min. We developed simplified test versions: SHUNT V2.0 (oral and intravenous dosing, two blood samples over 60 min) and DuO (oral dosing only, two blood samples over 60 min). The aim of this study was to evaluate equivalency of the simplified tests to the original SHUNT test. Data from three studies comprising 930 SHUNT tests were retrospectively analysed by each method. Equivalence was evaluated in terms of proportion of tests in which the difference between methods was less than any clinically meaningful difference and additionally by two one-sided t-test and bioequivalence methods. DuO and SHUNT V2.0 were equivalent to the original SHUNT test for Disease Severity Index, with >99% and >96% of tests falling within equivalence bounds. DuO and SHUNT V2.0 met equivalency criteria by two one-sided t-tests and bioequivalence. DuO and SHUNT V2.0 are easier to administer, are less invasive than the original SHUNT test and have potential to be more accepted by patients and providers., (© 2024 Nordic Association for the Publication of BCPT (former Nordic Pharmacological Society).)

The HepQuant SHUNT test quantifies hepatic functional impairment from the simultaneous clearance of cholate from the systemic and portal circulations for the purpose of monitoring treatment effects or for predicting risk for clinical outcome. Compartmental models are defined by distribution volumes and transfer rates between volumes to estimate parameters not defined by noncompartmental analyses. Previously, a noncompartmental analysis method, called the minimal model (MM), demonstrated reproducible and reliable measures of liver function (Translational Research 2021). The aim of this study was to compare the reproducibility and reliability of a new physiologically based compartmental model (CM) vs the MM. Data were analyzed from 16 control, 16 nonalcoholic steatohepatitis (NASH), and 16 hepatitis C virus (HCV) subjects, each with 3 replicate tests conducted on 3 separate days. The CM describes transfer of cholates between systemic, portal, and liver compartments with assumptions from measured or literature-derived values and unknown parameters estimated by nonlinear least-squares regression. The CM was compared to the MM for 6 key indices of hepatic disease in terms of intraclass correlation coefficient (ICC) with a lower acceptable limit of 0.7. The CM correlated well with the MM for disease severity index (DSI) with R 2 (95% confidence interval) of 0.96 (0.94-0.98, P < 0.001). Acceptable reproducibility (ICC > 0.7) was observed for 6/6 and 5/6 hepatic disease indices for CM and MM, respectively. SHUNT, a measure of the absolute bioavailability, had ICC of 0.73 (0.60-0.83, P = 0.3095) for MM and 0.84 (0.76-0.90, P = 0.0012) for CM. The CM, but not the MM, allowed determination of anatomic shunt and hepatic extraction and improved the within individual reproducibility., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Physicians use portal pressure measurements in clinical practice and research but the methods are invasive, can cause complications, and are resource intensive. 1-3 Herein we describe preliminary findings of the minimally invasive HepQuant-SHUNT test in the diagnosis of portal hypertension in precirrhotic and compensated cirrhotic patients., (Copyright © 2022 AGA Institute. Published by Elsevier Inc. All rights reserved.)

This study was designed to quantify and identify differences in protein levels between tumor and adjacent normal breast tissue from the same breast in 18 women with stage I/II ER positive/Her2/neu negative invasive breast cancer. Eighteen separate difference gel electrophoresis (DIGE) gels were run (1 gel per patient). Relative quantification was based on DIGE analysis. After excision and tryptic digestion, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and peptide mass mapping were used to identify protein spots. Two hundred and forty-three spots were differentially abundant between normal and cancer tissues. Fifty spots were identified: 41 were over abundant and nine were less abundant in cancers than in normal breast tissue. Western blotting provided independent confirmation for three of the most biologically and statistically interesting proteins. All 18 gels were replicated by another technician and 32% of the differentially abundant proteins were verified by the duplicate analysis. Follow-up studies are now examining these proteins as biomarkers in blood.

Class IIa histone deacetylases (HDACs) -4, -5, -7 and -9 undergo signal-dependent nuclear export upon phosphorylation of conserved serine residues that are targets for 14-3-3 binding. Little is known of other mechanisms for regulating the subcellular distribution of class IIa HDACs. Using a biochemical purification strategy, we identified protein kinase C-related kinase-2 (PRK2) as an HDAC5-interacting protein. PRK2 and the related kinase, PRK1, phosphorylate HDAC5 at a threonine residue (Thr-292) positioned within the nuclear localization signal (NLS) of the protein. HDAC7 and HDAC9 contain analogous sites that are phosphorylated by PRK, while HDAC4 harbors a non-phosphorylatable alanine residue at this position. We provide evidence to suggest that the unique phospho-acceptor cooperates with the 14-3-3 target sites to impair HDAC nuclear import., (Copyright 2010 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.)

The focus of this review is polycystic liver disease, a genetic disorder characterized by multiple macroscopic liver cysts that initially bud from biliary epithelium but subsequently lack communication with the biliary tree. There are two main clinical presentations: polycystic liver associated with autosomal dominant polycystic kidney disease and isolated polycystic liver disease. Both of these forms of polycystic liver disease exhibit an autosomal dominant pattern of inheritance. Clinical manifestations of polycystic liver disease are related to either mass effect of the volume of hepatic cysts or to complications arising within the cysts. Polycystic liver disease rarely progresses to hepatic failure or clinical complications of portal hypertension. Management is directed at counseling patients and families, treating complications and reducing cyst load by surgical techniques: cyst fenestration, hepatic resection or, rarely, hepatic transplantation. Recent research suggests that blockade of cyst secretion or inhibition of epithelial cells might be useful in halting progression of disease--these observations are discussed in this review.

Distinguishing between benign follicular thyroid adenoma (FTA) and malignant follicular thyroid carcinoma (FTC) by cytologic features alone is not possible. Molecular markers may aid distinguishing FTA from FTC in patients with indeterminate cytology. The aim of this study is to define protein abundance differences between FTC from FTA through a discovery (proteomics) and validation (immunohistochemistry) approach. Difference gel electrophoresis (DIGE) and peptide mass fingerprinting were performed on protein extracts from five patients with FTC and compared with six patients with FTA. Individual gel comparisons (i.e., each FTC extract versus FTA pool) were also performed for the five FTC patients. Immunohistochemical validation studies were performed on three of the identified proteins. Based on DIGE images, 680 protein spots were matched on individual gels. Of these, 102 spots showed statistically significant differences in abundance between FTC and FTA in the individual gel analyses and were therefore studied further. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was used to identify 54 of these protein spots. Three candidates involved in protein folding (heat shock protein gp96, protein disulfide isomerase A3, and calreticulin) were studied by immunohistochemistry. Moderate calreticulin immunohistochemical staining was the best single marker with a high negative predictive value (88%); combining all three markers (any marker less than moderate staining) had the best positive predictive value (75%) while still retaining a good negative predictive value (68%). With DIGE, we identified 54 proteins differentially abundant between FTC and FTA. Three of these were validated by immunohistochemistry. These findings provide further insights into the diagnosis, prognosis, and pathophysiology of follicular-derived thyroid neoplasms.

In this article we critically review the development and application of gas chromatography-mass spectrometry (GC-MS) techniques to the measurement of the nitric oxide (NO) metabolites, nitrite and nitrate, in human biological fluids. Our focus is on the issue of the fitness of any analytical strategy to its intended purpose and the validity of the analytical results generated. The accuracy, precision, recovery, selectivity and sensitivity of the various methods are evaluated and the potential pitfalls, both specific to the methods, and general to the area, are considered. Several examples of the applications of these techniques to clinical investigations of NO physiology are also critically evaluated.

In order to better understand basic mechanisms of tumor development and identify potential new biomarkers, we have performed difference gel electrophoresis (DIGE) and peptide mass fingerprinting on pooled protein extracts from patients with papillary thyroid carcinoma (PTC) compared with matched normal thyroid tissue. Image analysis of DIGE gels comparing PTC and matched normal thyroid tissue protein indicated that 25% of the protein spots were differentially expressed at a 2.5-fold cutoff and 35% at two-fold. Comparison between two different pools of protein from normal thyroid tissues revealed differential protein expression of only 4% at 2.5-fold and 6% at two-fold cutoff. One hundred ninety-two protein spots were identified by MALDI-TOFMS, representing 90 distinct proteins. Excluding albumin, globins and thyroglobulin, imaging software determined 31 proteins to be differentially expressed at the two-fold (or greater) level. Individual gel comparisons (PTC vs. matched normal) from five patients established that 15/31 (48%) of these proteins exhibited statistically significant differential expression. Previously identified molecular markers in this group of proteins include cathepsin B, cytokeratin 19, and galectin-3. Novel differentially expressed proteins include S100A6, moesin, HSP70 (BiP), peroxiredoxin 2, protein phosphatase 2, selenium binding protein 1, vitamin D binding protein, and proteins involved in mitochondrial function. The use of two-dimensional gel electrophoresis (2DGE) revealed a significantly altered protein mass and/or pI in 10%-15% of proteins, suggesting alternatively spliced forms and other posttranslational modification of proteins revealed by this approach. We confirmed S100A6 as a potentially useful biomarker using immunohistochemical analysis (85% sensitivity and 69% specificity for distinguishing benign from malignant thyroid neoplasms). In summary, proteomic analysis of PTC using DIGE and mass spectrometry has confirmed several known biomarkers, uncovered novel potential biomarkers, and provided insights into global pathophysiologic changes in PTC. Many of the differences observed would not have been detected by genomic or other proteomic approaches.

Myotonic dystrophy protein kinase (DMPK) was the initial representative of a ubiquitous protein kinase family that regulates cell size and shape. DMPK is highly expressed in heart and skeletal muscle and transgenic over-expression induces cardiac hypertrophy. The characterization of DMPK has been limited by the paucity of immunological reagents with high affinity and well-defined specificity. Amino acid sequence data was used to predict the surface exposure of the coil-coiled domain of DMPK. These exposed amino acids were substituted into an extremely stable coiled-coil template to produce a peptide antigen. Sera from mice immunized with the peptide conjugated to keyhole limpet hemocyanin were screened against recombinant DMPK using Western blots. Murine spleens expressing DMPK antibodies were used to produce hybridoma cell lines. Hybridoma supernatants were further screened against recombinant DMPK and four clonal hybridoma cell lines expressing DMPK antibodies were generated. These four monoclonal antibodies recognized recombinant DMPK in Western blots of COS-1 cell lysates expressing high levels of recombinant DMPK and immunoprecipitated recombinant DMPK from COS-1 cell lysates. The identity of the immunoprecipitated DMPK was confirmed by MALDI-TOF mass spectrometry and peptide mass fingerprinting. DMPK was the only protein detected in the immunoprecipitates, indicating the high specificity of the antibodies. Western blots immunostained with two of the monoclonal antibodies specifically recognized the two isoforms of endogenous DMPK, DMPK-1 and DMPK-2, that are expressed at low levels in the human heart. The recognition of low amounts of DMPK-1 and DMPK-2 indicates the high affinity of these antibodies. A human heart lysate was subjected to ammonium sulfate precipitation and column chromatography to produce a fraction that was enriched in DMPK. One of the monoclonal antibodies immunoprecipitated endogenous DMPK from this fraction. This antibody was used for immuno-localization studies of an adenoviral DMPK construct, expressed in adult mouse cardiac myocytes. This construct was localized to the intercalated disc, the site of endogenous DMPK, indicating that this antibody is applicable to immuno-localization studies. This study demonstrates the utility of the described procedure for generation of specific monoclonal antibodies with high affinity for epitopes in coiled-coiled domains of mammalian proteins expressed at low levels., (Copyright 2006 John Wiley & Sons, Ltd.)

The anterior pituitary gland (AP) secretes six established hormones that collectively control hundreds of biological and behavioral functions. Because of advances in mass spectrometry (MS), protein labeling, and bioinformatics, it is now possible to characterize, compare, and quantify the AP hormones together with large numbers of nonhormonal AP proteins. For example, by using high-performance liquid chromatography in line with tandem MS we characterized 145 proteins in sub-cellular fractions of the AP of young adult male Golden Syrian hamsters and 115 proteins in subcellular fractions of the AP of young adult male mice. These included hormones, proteins involved in hormone synthesis and release, and housekeeping proteins. We also used difference gel electrophoresis in conjunction with MS and peptide mass fingerprinting to quantify the effects of estrogen on the AP-soluble protein fraction in rats. Ovariectomized rats were administered 50 microg of estradiol valerate subcutaneously and studied 48 hrs later, before the onset of the anticipated surges of gonadotropins in blood. Following DeCyder image analysis, we identified by MS and peptide mass fingerprinting 26 protein spots that were upregulated and 19 protein spots that were downregulated. Estrogen increased levels of acidic isoforms of growth hormone and prolactin, several proteins involved in protein synthesis, folding and secretion, and several metabolic enzymes. Most of the downregulated proteins are involved in RNA or DNA interactions. We followed up on the results with RT-PCR and immunohistochemical techniques to demonstrate that one protein identified by MS in hamster AP, fertility protein SP22, is synthesized in the AP and localized primarily in somatotropes and thyrotropes. These experiments demonstrate the efficacy of our proteomics approach to characterize AP proteins and quantify changes in them. The approaches used to study the AP could serve as a model to investigate other heterogeneous organs.

Estrogen is known to affect the regulation of all six of the established anterior pituitary gland (AP) hormones, but little is known of the specifics of its regulation of the AP hormones, their isoforms, and nonhormonal AP proteins. We used difference gel electrophoresis in conjunction with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and peptide mass fingerprinting to quantify the effects of estrogen on the AP-soluble protein fraction in rats. Two-month-old rats were ovariectomized and used at 6 months of age. They were injected subcutaneously with sesame oil vehicle or 50 mug estradiol valerate in vehicle and studied 48 hrs later, approximately 3 hrs before the time of the anticipated onset of the estrogen-induced surges of gonadotropins in blood. The APs were pooled, and the soluble protein fraction was examined in replicate analyses. After DeCyder software analysis, we identified 26 protein spots that had a 1.5-fold or greater average increase in the experimental group relative to the controls. Nineteen showed a 1.5-fold or greater decrease. Estrogen increased levels of the more acidic isoforms of growth hormone and prolactin and of proteins involved in protein synthesis, folding, and secretion (e.g., eukaryotic translation elongation factor 2, ERp57, ERp29, Hsc70-ps1, calreticulin, coatomer delta subunit, and secretogranin II) and of some metabolic enzymes (e.g., arginosuccinate synthetase, enolase 1, creatine kinase B, phosphoglycerate mutase, malate dehydrogenase, pyruvate kinase, and aldolase A). The majority of the downregulated proteins were involved in RNA or DNA interactions (e.g., five heterogeneous nuclear ribonucleoproteins, DEAD-box proteins 17 and 48, ssDNA binding protein PUR-alpha, PTB-associated splicing factor, and Pigpen protein), but isovaleryl coenzyme A dehydrogenase, mitochondrial aldehyde dehydrogenase, stathmin 1, vinculin, radixin, and secretogranin III were also reduced. Our results indicate that estrogen acts in vivo within 48 hrs to modulate levels of a significant number of AP proteins.

Human heart failure is accompanied by repression of genes such as alpha myosin heavy chain (alphaMyHC) and SERCA2A and the induction of fetal genes such as betaMyHC and atrial natriuretic factor. It seems likely that changes in MyHC isoforms contribute to the poor contractility seen in heart failure, because small changes in isoform composition can have a major effect on the contractility of cardiac myocytes and the heart. Our laboratory has recently shown that YY1 protein levels are increased in human heart failure and that YY1 represses the activity of the human alphaMyHC promoter. We have now identified a region of the alphaMyHC promoter that binds a factor whose expression is increased sixfold in failing human hearts. Through peptide mass spectrometry, we identified this binding activity to be a heterodimer of Ku70 and Ku80. Expression of Ku represses the human alphaMyHC promoter in neonatal rat ventricular myocytes. Moreover, overexpression of Ku70/80 decreases alphaMyHC mRNA expression and increases skeletal alpha-actin. Interestingly, YY1 interacts with Ku70 and Ku80 in HeLa cells. Together, YY1, Ku70, and Ku80 repress the alphaMyHC promoter to an extent that is greater than that with YY1 or Ku70/80 alone. Our results suggest that Ku is an important factor in the repression of the human alphaMyHC promoter during heart failure.

We have developed a novel method for quantifying protein isoforms, in both relative and absolute terms, based on MALDI-TOF mass spectrometry. The utility of the approach is demonstrated by quantifying the alpha and beta protein isoforms of myosin heavy chain (MyHC) in human atrial tissue. Alpha-MyHC (726-741) and beta-MyHC (724-739) were identified as isoform-specific tryptic peptides. A calibration curve was constructed by plotting ion current ratios against molar ratios of the two peptides prepared synthetically. MyHC was digested by trypsin and the ion current ratio determined for the two tryptic peptides. The ion current ratio was converted to the peptide ratio and hence the isoform ratio by reference to the standard curve. The accuracy of the method was confirmed by a comparison between these results and those determined by an established method of MyHC isoform ratio determination. So that the molar ratio could be converted to absolute values, a third peptide, an analogue of the two peptides being measured, was synthesized for use as an internal standard (IS). The measured ion current ratios of synthetic alpha-MyHC (726-741), beta-MyHC (724-739), and IS peptides were used to generate standard curves. A known quantity of the IS was added to the MyHC digests. The measured ion current ratios were converted to the actual quantities of the isoform-specific peptides and hence the actual quantity of each protein isoform by reference to the standard curves. This method is of general applicability, especially when isoform quantification is required.

Comparison of mammalian cardiac alpha- and beta-myosin heavy chain isoforms reveals 93% identity. To date, genetic methodologies have effected only minor switches in the mammalian cardiac myosin isoforms. Using cardiac-specific transgenesis, we have now obtained major myosin isoform shifts and/or replacements. Clusters of non-identical amino acids are found in functionally important regions, i.e. the surface loops 1 and 2, suggesting that these structures may regulate isoform-specific characteristics. Loop 1 alters filament sliding velocity, whereas Loop 2 modulates actin-activated ATPase rate in Dictyostelium myosin, but this remains untested in mammalian cardiac myosins. Alpha --> beta isoform switches were engineered into mouse hearts via transgenesis. To assess the structural basis of isoform diversity, chimeric myosins in which the sequences of either Loop 1+Loop 2 or Loop 2 of alpha-myosin were exchanged for those of beta-myosin were expressed in vivo. 2-fold differences in filament sliding velocity and ATPase activity were found between the two isoforms. Filament sliding velocity of the Loop 1+Loop 2 chimera and the ATPase activities of both loop chimeras were not significantly different compared with alpha-myosin. In mouse cardiac isoforms, myosin functionality does not depend on Loop 1 or Loop 2 sequences and must lie partially in other non-homologous residues.

The genetic abnormality in myotonic muscular dystrophy, multiple CTG repeats lie upstream of a gene that encodes a novel protein kinase, myotonic dystrophy protein kinase (DMPK). Phospholemman (PLM), a major membrane substrate for phosphorylation by protein kinases A and C, induces Cl currents (I(Cl(PLM))) when expressed in Xenopus oocytes. To test the idea that PLM is a substrate for DMPK, we measured in vitro phosphorylation of purified PLM by DMPK. To assess the functional effects of PLM phosphorylation we compared I(Cl(PLM)) in Xenopus oocytes expressing PLM alone to currents in oocytes co-expressing DMPK, and examined the effect of DMPK on oocyte membrane PLM expression. We found that PLM is indeed a good substrate for DMPK in vitro. Co-expression of DMPK with PLM in oocytes resulted in a reduction in I(Cl(PLM)). This was most likely a specific effect of phosphorylation of PLM by DMPK, as the effect was not present in oocytes expressing a phos(-) PLM mutant in which all potential phosphorylation had been disabled by Ser --> Ala substitution. The biophysical characteristics of I(Cl(PLM)) were not changed by DMPK or by the phos(-) mutation. Co-expression of DMPK reduced the expression of PLM in oocyte membranes, suggesting a possible mechanism for the observed reduction in I(Cl(PLM)) amplitude. These data show that PLM is a substrate for phosphorylation by DMPK and provide functional evidence for modulation of PLM function by phosphorylation.

The investigation of the molecular properties of nerve growth cones depends to a significant degree on their isolation from fetal brain in the form of 'growth cone particles' (GCPs). The availability of markers for developing axons and dendrites, as well as glial cells, has made it possible to characterize the GCP fraction in much greater detail than before and to optimize its yield. Marker analyses show that a member of the N-CAM family (5B4-CAM), synaptophysin, and especially GAP-43 and non-phosphorylated tau, are enriched in the GCP fraction. In contrast, MAP2 and, particularly, glial fibrillary acidic protein and vimentin are fractionated away from GCPs. Furthermore, GCP yield can be doubled relative to the original procedure, without compromising purity, by raising the sucrose concentration of the fractionation gradient's uppermost layer. The results indicate that GCPs are highly purified growth cone fragments with very little glial contamination, and that they are primarily of axonal origin.

Growth-regulated proteins (GRPs) of the neuron are synthesized during outgrowth and regeneration at an increased rate and enriched in nerve growth cones. Therefore, they can be used to some degree as markers of neurite growth. However, these proteins are not unique to the growing neuron, and their properties are not known sufficiently to assign them a functional and/or causal role in the mechanisms of outgrowth. During synaptogenesis, GRPs decrease in abundance, and growth cone functions of motility and organelle assembly are being replaced by junctional contact and transmitter release. However, there is a stage during which growth cone and synaptic properties overlap to some degree. We propose that it is this overlap and its continuation that allow for synaptic plasticity in developing and adult nervous systems. We also propose a hypothesis involving (a) trophic factor(s) that might explain the regulation of synaptic sizes and collateral sprouting. Some GRPs, especially GAP43/B50/pp46/F1, are more prominent in adult brain regions of high plasticity, and they undergo change, such as phosphorylation, during long-term potentiation (LTP). Without precise functional knowledge of GRPs, it is impossible to use changes in such proteins to explain the plasticity mechanism. However, changes in these "growth markers" are likely to be an indication of sprouting activity, which would explain well the various phenomena associated with plasticity and learning in the adult. Thus, plasticity and memory may be viewed as a continuation of the developmental process into adulthood.

Despite numerous reports of solubilization of adenosine A1 receptors, little progress has been made in isolating or purifying the receptor, owing to the extreme lability of the preparations. The present solubilization strategies recognized the possible role of endogenous adenosine to produce adenosine-receptor-N-protein complexes, which are intrinsically unstable, and instead attempted to use caffeine to solubilize free adenosine receptors, which might be more stable. Endogenous adenosine was removed from membranes by using adenosine deaminase along with GTP to accelerate the release of receptor-bound adenosine. The receptors were then occupied with caffeine and solubilized with 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulphonate (CHAPS) in the presence of glycerol. These soluble preparations exhibited the characteristics of free adenosine receptors. They bound the A1-selective antagonist 8-cyclopentyl-1,3-dipropylxanthine (CPDPX) with high affinity to a single class of binding sites, which were insensitive to GTP. The binding activity was extremely stable, with a half-life of about 5 days at 4 degrees C; there was little change in either receptor number or affinity during 3 days at 4 degrees C. This methodology should greatly facilitate the characterization, isolation and purification of the adenosine A1 receptor.

A procedure for solubilization, fractionation, and reconstitution of sarcoplasmic reticulum (SR) protein is presented. The SR protein is solubilized with the zwitterionic detergent CHAPS in the presence of added 5-mM phosphatidylcholine and 20% glycerol, which stabilize the reconstitutable Ca2+ transport activity. For reconstitution the solubilized SR protein is incorporated into preformed French-pressed unilamellar vesicles that had been treated with 10-mM sodium cholate. By passing the proteoliposomes through a centrifuged Sephadex G-50 column that had been equilibrated with potassium oxalate, the detergent is removed, and the proteoliposomes become sealed with potassium oxalate trapped inside. This procedure requires less than 2 h and results in Ca2+ uptake active of over 1 mumol/min/mg of protein. The solubilized SR protein was fractionated on a DEAE-Biogel A column. A fraction containing the Ca2+-ATPase but not the Mr 55,000 glycoprotein had reconstitutable Ca2+ uptake activity of 2.2 mumol/min/mg of protein. Inclusion of the Mr 55,000 glycoprotein during the reconstitution procedure did not increase the Ca2+ uptake activity of the reconstituted fraction containing the Ca2+-ATPase. This result demonstrates that the glycoprotein is not required for Ca2+ uptake.