Lamivudine as initial treatment for chronic hepatitis B in the United States

BACKGROUND AND METHODS

Although the nucleoside analogue lamivudine has shown promise in patients with chronic hepatitis B, long-term data on patients from the United States are lacking. We randomly assigned previously untreated patients with chronic hepatitis B to receive either 100 mg of oral lamivudine or placebo daily for 52 weeks. We then followed them for an additional 16 weeks to evaluate post-treatment safety and the durability of responses. The primary end point with respect to efficacy was a reduction of at least 2 points in the score on the Histologic Activity Index. On this scale, scores can range from 0 (normal) to 22 (most severe abnormalities).

RESULTS

Of the 143 randomized patients, 137 were included in the efficacy analysis: 66 in the lamivudine group and 71 in the placebo group. The other six patients were excluded at the base-line visit because of the absence of a documented history of hepatitis B surface antigen for at least six months. After 52 weeks of treatment, lamivudine recipients were more likely than placebo recipients to have a histologic response (52 percent vs. 23 percent, P<0.001), loss of hepatitis B e antigen (HBeAg) in serum (32 percent vs. 11 percent, P=0.003), sustained suppression of serum hepatitis B virus (HBV) DNA to undetectable levels (44 percent vs. 16 percent, P<0.001), and sustained normalization of serum alanine aminotransferase levels (41 percent vs. 7 percent, P<0.001), and they were less likely to have increased hepatic fibrosis (5 percent vs. 20 percent, P=0.01). Lamivudine recipients were also more likely to undergo HBeAg seroconversion, defined as the loss of HBeAg, undetectable levels of serum HBV DNA, and the appearance of antibodies against HBeAg (17 percent vs. 6 percent, P=0.04). HBeAg responses persisted in most patients for 16 weeks after the discontinuation of treatment. Lamivudine was well tolerated. Self-limited post-treatment elevations in serum alanine aminotransferase were more common in lamivudine recipients: 25 percent had serum alanine aminotransferase levels that were at least three times base-line levels, as compared with 8 percent of placebo recipients (P=0.01). The clinical condition of all patients remained stable during the study.

CONCLUSIONS

In U.S. patients with previously untreated chronic hepatitis B, one year of lamivudine therapy had favorable effects on histologic, virologic, and biochemical features of the disease and was well tolerated. HBeAg responses were generally sustained after treatment.

Assembly of microarrays for genome-wide measurement of DNA copy number

We have assembled arrays of approximately 2,400 BAC clones for measurement of DNA copy number across the human genome. The arrays provide precise measurement (s.d. of log2 ratios=0.05-0.10) in cell lines and clinical material, so that we can reliably detect and quantify high-level amplifications and single-copy alterations in diploid, polyploid and heterogeneous backgrounds.

Sedative but not anxiolytic properties of benzodiazepines are mediated by the GABA(A) receptor alpha1 subtype

Inhibitory neurotransmission in the brain is largely mediated by GABA(A) receptors. Potentiation of GABA receptor activation through an allosteric benzodiazepine (BZ) site produces the sedative, anxiolytic, muscle relaxant, anticonvulsant and cognition-impairing effects of clinically used BZs such as diazepam. We created genetically modified mice (alpha1 H101R) with a diazepam-insensitive alpha1 subtype and a selective BZ site ligand, L-838,417, to explore GABA(A) receptor subtypes mediating specific physiological effects. These two complimentary approaches revealed that the alpha1 subtype mediated the sedative, but not the anxiolytic effects of benzodiazepines. This finding suggests ways to improve anxiolytics and to develop drugs for other neurological disorders based on their specificity for GABA(A) receptor subtypes in distinct neuronal circuits.

Identification and characterization of mutations in hepatitis B virus resistant to lamivudine. Lamivudine Clinical Investigation Group

Cirrhosis and hepatocellular carcinoma occur as long-term complications of chronic hepatitis B virus (HBV) infection. Antiviral therapy is potentially a successful approach for the treatment of patients with HBV infection, which includes the nucleoside analog, lamivudine [(-)2'-deoxy-3'-thiacytidine, 3TC]. Although resistance to lamivudine therapy has been reported in several HBV-infected patients, the pattern of resistance-associated mutations in HBV has not been fully characterized. We report a DNA sequence database that includes a 500-base pair region of the HBV polymerase gene from 20 patients with clinical manifestations of lamivudine resistance. Analysis of the database reveals two patterns of amino acid substitutions in the tyrosine, methionine, aspartate, aspartate (YMDD) nucleotide-binding locus of the HBV polymerase. HBV DNA from the sera of patients in Group I exhibits a substitution of valine for methionine at residue 552, accompanied by a substitution of methionine for leucine at residue 528. Patients in Group II had only an isoleucine-for-methionine substitution at position 552. Reconstruction of these mutations in an HBV replication-competent plasmid was performed in a transient transfection cell assay to determine the function/relevance of these mutations to lamivudine resistance. Both Group I and Group II mutations resulted in a substantial decrease in sensitivity to lamivudine treatment (> 10,000-fold shift in IC50 over wild-type [wt] IC50), strongly indicating that these mutations were involved in resistance to lamivudine. A hypothetical model of the HBV reverse transcriptase has been generated for further study of the role of these mutations in lamivudine resistance.

The arterial pole of the mouse heart forms from Fgf10-expressing cells in pharyngeal mesoderm

Development of the arterial pole of the heart is a critical step in cardiogenesis, yet its embryological origin remains obscure. We have analyzed a transgenic mouse line in which beta-galactosidase activity is observed in the embryonic right ventricle and outflow tract of the heart and in contiguous splanchnic and pharyngeal mesoderm. The nlacZ transgene has integrated upstream of the fibroblast growth factor 10 (Fgf10) gene and comparison with the expression pattern of Fgf10 in pharyngeal mesoderm indicates transgene control by Fgf10 regulatory sequences. Dil labeling shows a progressive movement of cells from the pharyngeal arch region into the growing heart tube between embryonic days 8.25 and 10.5. These data suggest that arterial pole myocardium originates outside the classical heart field.

Pharmacological characterization of a novel cell line expressing human alpha(4)beta(3)delta GABA(A) receptors

1: The pharmacology of the stable cell line expressing human alpha(4)beta(3)delta GABA(A) receptor was investigated using whole-cell patch-clamp techniques. 2: alpha(4)beta(3)delta receptors exhibited increased sensitivity to GABA when compared to alpha(4)beta(3)gamma(2) receptors, with EC(50)'s of 0.50 (0.46, 0.53) microM and 2.6 (2.5, 2.6) microM respectively. Additionally, the GABA partial agonists piperidine-4-sulphonate (P4S) and 4,5,6,7-tetrahydroisothiazolo-[5,4-c]pyridin-3-ol (THIP) displayed markedly higher efficacy at alpha(4)beta(3)delta receptors, indeed THIP demonstrated greater efficacy than GABA at these receptors. 3: The delta subunit conferred slow desensitization to GABA, with rate constants of 4.8+/-0.5 s for alpha(4)beta(3)delta and 2.5+/-0.2 s for alpha(4)beta(3)gamma(2). However, both P4S and THIP demonstrated similar levels of desensitization on both receptor subtypes suggesting this effect is agonist specific. 4: alpha(4)beta(3)delta and alpha(4)beta(3)gamma(2) demonstrated equal sensitivity to inhibition by the cation zinc (2-3 microM IC(50)). However, alpha(4)beta(3)delta receptors demonstrated greater sensitivity to inhibition by lanthanum. The IC(50) for GABA antagonists SR-95531 and picrotoxin, was similar for alpha(4)beta(3)delta and alpha(4)beta(3)gamma(2). Likewise, inhibition was observed on both subtypes at high and low pH. 5: alpha(4)beta(3)delta receptors were insensitive to modulation by benzodiazepine ligands. In contrast Ro15-4513 and bretazenil potentiated GABA responses on alpha(4)beta(3)gamma(2) cells, and the inverse agonist DMCM showed allosteric inhibition of alpha(4)beta(3)gamma(2) receptors. 6: The efficacy of neurosteroids at alpha(4)beta(3)delta receptors was greatly enhanced over that observed at alpha(4)beta(3)gamma(2) receptors. The greatest effect was observed using THDOC with 524+/-71.6% potentiation at alpha(4)beta(3)delta and 297.9+/-49.7% at alpha(4)beta(3)gamma(2) receptors. Inhibition by the steroid pregnenolone sulphate however, showed no subtype selectivity. The efficacy of both pentobarbitone and propofol was slightly augmented and etomidate greatly enhanced at alpha(4)beta(3)delta receptors versus alpha(4)beta(3)gamma(2) receptors. 7: We show that the alpha(4)beta(3)delta receptor has a distinct pharmacology and kinetic profile. With its restricted distribution within the brain and unique pharmacology this receptor may play an important role in the action of neurosteroids and anaesthetics. British Journal of Pharmacology (2002) 136, 965-974

ATL-derived factor (ADF), an IL-2 receptor/Tac inducer homologous to thioredoxin; possible involvement of dithiol-reduction in the IL-2 receptor induction

HTLV-I transformed T cells not only express a large number of interleukin-2 receptors [IL-2R/p55(Tac)], but also produce a factor named ATL-derived factor (ADF) that augments the expression of IL-2R/p55(Tac). Based on a partial N-terminal amino acid sequence, complementary DNA (cDNA) clones for human and mouse ADF were isolated and sequenced. Recombinant ADF produced by COS-7 monkey kidney cells showed IL-2R/Tac inducing activity on YT cells, which are sensitive for ADF. ADF mRNA was strongly expressed in HTLV-I(+) T cells lines, but not in inactivated cells (THP-1, unstimulated PBMC). Furthermore, in normal human peripheral blood mononuclear cells, the expression of ADF mRNA was enhanced by mitogens or phorbol myristate acetate, suggesting a possible involvement of ADF in the lymphocyte activation. Homology analysis revealed an unexpected relationship between ADF and dithiol-reducing enzyme, thioredoxin, involved in many important biological reactions such as the conversion of ribonucleotides into deoxyribonucleotides, or the stabilization of glucocorticoid receptors. The biological significance of the generation of a redox potential in lymphocyte activation, and the possible involvement of dithiol reduction in the induction of IL-2R/Tac are discussed.

The history of photodetection and photodynamic therapy

Light has been employed in the treatment of disease since antiquity. Many ancient civilizations utilized phototherapy, but it was not until early last century that this form of therapy reappeared. Following the scientific discoveries by early pioneers such as Finsen, Raab and Von Tappeiner, the combination of light and drug administration led to the emergence of photochemotherapy as a therapeutic tool. The isolation of porphyrins and the subsequent discovery of their tumor-localizing properties and phototoxic effects on tumor tissue led to the development of modern photodetection (PD) and photodynamic therapy (PDT). This review traces the origins and development of PD and PDT from antiquity to the present day.

Quantitation of rat embryonic development in vitro: a morphological scoring system

In order to realize the maximum potential of whole-embryo culture techniques, definitive parameters must be developed for the quantitative estimation of embryonic growth and development. An objective scoring system has been devised which provides a precise measure of morphological development. Examination of rat conceptuses from dams on pregnancy days 10, 11, 12, and 13 (sperm positive = day 1) led to the selection of 17 morphological features for use in the system. Up to six developmental stages of each feature were defined and assigned scores of 0 to 5. The numerical total of scores for an individual embryo is taken as the overall morphological score (MS). The system was applied prospectively to 103 Sprague-Dawley rat conceptuses aged 9 to 12.7 days (0 = time of copulation). The variation of score with embryonic age (EA, days) was highly linear: MS = 202.28 + 20.932 EA (R2 = 0.991). Thus, the morphological score can be used to compute apparent embryonic age, and the calculated standard error of prediction is +/- 2.2 hrs. The number of somites (SN) was also found to vary linearly with age over this period: SN = -126.23 + 13.217 EA (R2 = 0.982), and could be used to estimate development. However, the standard error for prediction of apparent embryonic age is greater (+/- 3.1 hours) than that for morphological score, and this single feature will not necessarily reflect overall development. Several parameters were examined as estimates of embryonic growth, as distinct from development. Yolk sac diameter, crown-rump length, and head length were found to vary with EA as quadratic functions over this time. Total embryonic protein increased logarithmically with EA and was considered to be the most suitable measure of embryonic growth. Use of the morphological scoring system in embryo culture experiments provides a precise index of embryonic development, aids the detection of retardation or dysmorphogenesis of specific primordia, and allows a quantitative comparison of development and growth.

An investigation of the rigor of interpretation rules for STRs derived from less than 100 pg of DNA

By increasing the PCR amplification regime to 34 cycles, we have demonstrated that it is possible routinely to analyse <100 pg DNA. The success rate was not improved (without impairing quality) by increasing cycle number further. Compared to amplification of 1 ng DNA at 28 cycles, it was shown that increased imbalance of heterozygotes occurred, along with an increase in the size (peak area) of stutters. The analysis of mixtures by peak area measurement becomes increasingly difficult as the sample size is reduced. Laboratory-based contamination cannot be completely avoided, even when analysis is carried out under stringent conditions of cleanliness. A set of guidelines that utilises duplication of results to interpret profiles originating from picogram levels of DNA is introduced. We demonstrate that the duplication guideline is robust by applying a statistical theory that models three key parameters - namely the incidence of allele drop-out, laboratory contamination and stutter. The advantage of the model is that the critical levels for each parameter can be calculated. This information may be used (for example) to determine levels of contamination that can be tolerated within the strategy employed. In addition we demonstrate that interpreting one banded loci, where allele dropout could have occurred, using LR=1/2f(a) was conservative provided that the band was low in peak area. Furthermore, we demonstrate that an apparent mis-match between crime-stain and a suspect DNA profile does not necessarily result in an exclusion. The method used is complex, yet can be converted into an expert system. We envisage this to be the next step.

Hepatitis-B-virus resistance to lamivudine given for recurrent infection after orthotopic liver transplantation

BACKGROUND

Orthotopic liver transplantation for end-stage hepatitis-B-virus (HBV) infection is commonly complicated by recurrence of HBV. Lamivudine, a cytosine nucleoside analogue, has been shown to suppress HBV infection. We report the development of resistance to lamivudine in three patients who underwent transplantation for end-stage liver disease secondary to hepatitis B.

METHODS

Two of the patients received lamivudine for recurrent HBV infection after transplantation, whereas the third patient began treatment 1 month before transplantation in an attempt to prevent HBV recurrence after transplantation. The three patients initially responded well to treatment, but viral recurrence occurred after 9-10 months of treatment in all patients. HBV DNA was amplified from serum and sequenced through a conserved polymerase domain-the tyrosine, methionine, aspartate, aspartate (YMDD) locus. We assessed the susceptibility of HBV to lamivudine by infecting primary human hepatocytes with serum taken before the start of treatment and after recurrence in varying concentrations of lamivudine.

FINDINGS

DNA sequencing showed a common mutation within the YMDD locus of the HBV polymerase gene in all patients during lamivudine treatment. In hepatocyte cultures infected with pretreatment serum, HBV DNA concentrations were reduced to less than 6% of those in control cultures by addition of lamivudine in concentrations as low as 0.03 mumol/L. By contrast, in cultures treated with serum taken after recurrence, HBV DNA concentrations did not fall below 20% of control values, even with lamivudine at 30 mumol/L.

INTERPRETATION

Resistance to lamivudine has been reported in HIV patients with mutations in the YMDD locus of the polymerase gene. Our findings indicate a common mechanism of lamivudine resistance for HIV and HBV that involves similar point mutations in homologous domains of the viral polymerases.

A multicenter United States-Canadian trial to assess lamivudine monotherapy before and after liver transplantation for chronic hepatitis B

Seventy-seven liver transplant candidates were enrolled in a multicenter study in which patients were treated with lamivudine (100 mg daily) without the adjunctive use of hepatitis B immune globulin. Treatment was begun while patients awaited liver transplantation and continued after transplantation. All were hepatitis B surface antigen (HBsAg) positive, and 61% had detectable hepatitis B e antigen (HBeAg) and HBV DNA when treatment was begun. Forty-seven underwent liver transplantation and 30 did not. Median study participation was 38 months (range, 2.7-48.5) in the transplanted patients and 26 months (range, 0.1-37) in the nontransplanted group. Twenty-five of 42 (60%) transplanted patients with 12 or more weeks of posttransplantation follow-up were HBsAg negative at the last study visit. At treatment week 156, 13 of 22 (59%) remained HBsAg negative, and all 9 reinfected patients were HBV-DNA positive before treatment. In the nontransplanted patients, HBeAg was initially detectable in 20 of 27 (74%) but this decreased to 3 of 17 (18%) after 104 weeks of treatment, and significant improvement in biochemical parameters was observed. HBV-DNA polymerase mutants were detected in 15 (21%) and 6 (20%) of the transplanted and nontransplanted patients, respectively. When compared with historical cohorts, lamivudine-treated patients appeared to have improved survival, and transplanted patients had a decrease in the rate of recurrent HBV infection. Lamivudine therapy was partially effective in preventing recurrent HBV infection when given before and after transplantation. Thus, future trials using a combination of HBIg and lamivudine are needed to assess the optimal prophylactic therapy.

Clinical experience over 48 years with pheochromocytoma

OBJECTIVE

To analyze the presentation, localization, surgical management, pathology, and long-term outcome of a large series of patients with pheochromocytomas.

SUMMARY BACKGROUND DATA

There are several areas of controversy pertaining to pheochromocytomas. Although many studies report a higher rate of malignancy for extraadrenal pheochromocytomas than for adrenal pheochromocytomas, the number of patients with the former tumor are small and statistical analysis is lacking. There has also been recent debate as to whether microscopic features of the tumor may be predictive of future behavior.

METHODS

From 1950 to 1998, the authors observed 108 pheochromocytomas in 104 patients. The outcome of these patients has been followed prospectively. The medical records of these patients were reviewed for data on the presentation, localization, surgical management, pathology, and outcome. Patient survival was analyzed using Kaplan-Meier survival distributions.

RESULTS

This study included 66 female patients and 38 male patients. The average age at surgery was 42.3 years. Sporadic cases accounted for 84% of the patients; the other 16% had multiple endocrine neoplasia type 2, von Recklinghausen's disease, von Hippel-Lindau disease, or Carney's syndrome. Of 64 adrenal tumors, 55 were initially considered benign, 6 had microscopic malignant features, and 3 had malignant disease. Mean patient follow-up was 12.6 years. To date, in five additional patients (none with microscopic disease) malignant disease developed (13% overall rate of malignancy). Recurrence occurred as late as 15 years after resection. Of 26 extraadrenal pheochromocytomas, 14 were initially considered benign, 8 had microscopic malignant features, and 4 had malignant disease. Thus, 46% of patients had either malignant disease or tumors with malignant features. Mean patient follow-up was 11.5 years. In one patient with benign disease and in one patient with malignant features, malignant disease developed (23% overall rate of malignancy). The difference in the rate of malignancy was not statistically significant between adrenal and extraadrenal pheochromocytomas. Patients with adrenal and extraadrenal pheochromocytomas also had similar rates of survival (p = NS).

CONCLUSIONS

The data suggest that patients with extraadrenal pheochromocytomas have the same risk of malignancy and the same overall survival as patients with adrenal pheochromocytomas. Lifelong follow-up of these patients is mandatory.

The development of handedness in left/right asymmetry

The development of handed asymmetry requires a special mechanism for consistently specifying a difference between left and right sides. This is to be distinguished from both random asymmetry, and from those left/right differences that are mirror symmetrical. We propose a model for the development of handedness in bilateral animals, comprising three components. (i) A process termed conversion, in which a molecular handedness is converted into handedness at the cellular level. A specific model for this process is put forward, based on cell polarity and transport of cellular constituents by a handed molecule. (ii) A mechanism for random generation of asymmetry, which could involve a reaction-diffusion process, so that the concentration of a molecule is higher on one side than the other. The handedness generated by conversion could consistently bias this mechanism to one side. (iii) A tissue-specific interpretation process which responds to the difference between the two sides, and results in the development of different structures on the left and right. There could be direct genetic control of the direction of handedness in this model, most probably through the conversion process. Experimental evidence for the model is considered, particularly the iv mutation in the mouse, which appears to result in loss-of-function in biasing, and so asymmetry is random. The model can explain the abnormal development of handedness observed in bisected embryos of some mammalian, amphibian and sub-vertebrate species. Spiral asymmetry, as seen in spiral cleavage and in ciliates, involves only conversion of molecular asymmetry to the cellular and multicellular level, with no separate interpretation step.

Pitx2c and Nkx2-5 are required for the formation and identity of the pulmonary myocardium

The pulmonary vein is sleeved by myocardium, which is a major source of atrial fibrillation and is involved in congenital sinus venosus defects. Little is known about the cellular origin and mechanism of formation of the pulmonary myocardium. We observed a biphasic process of pulmonary myocardium formation in mice. Firstly, a myocardial cell population forms de novo at the connection of the pulmonary vein and the atrium. Genetic labeling revealed that atrial cells do not contribute to this population, indicating it forms by differentiation of pulmonary mesenchymal cells. Secondly, these pulmonary myocardial cells initiate a phase of rapid proliferation and form the pulmonary myocardial sleeve. Pitx2c-deficient mice do not develop a pulmonary myocardial sleeve because they fail to form the initial pulmonary myocardial cells. Genetic-labeling analyses demonstrated that whereas the systemic venous return derives from Nkx2-5-negative precursors, the pulmonary myocardium derives from Nkx2-5-expressing precursors, indicating a distinct origin of the 2 venous systems. Nkx2-5 and its target gap-junction gene Cx40 are expressed in the atria and in the pulmonary myocardium but not in the systemic venous return, which expresses the essential pacemaker channel Hcn4. When Nkx2-5 protein level was lowered in a hypomorphic model, the pulmonary myocardium switched to a Cx40-negative, Hcn4-positive phenotype resembling that of the systemic venous return. In conclusion, our data suggest a cellular mechanism for pulmonary myocardium formation and highlight the key roles played by Pitx2c and Nkx2-5 in its formation and identity.

Molecular pathway for the localized formation of the sinoatrial node

The sinoatrial node, which resides at the junction of the right atrium and the superior caval vein, contains specialized myocardial cells that initiate the heart beat. Despite this fundamental role in heart function, the embryonic origin and mechanisms of localized formation of the sinoatrial node have not been defined. Here we show that subsequent to the formation of the Nkx2-5-positive heart tube, cells bordering the inflow tract of the heart tube give rise to the Nkx2-5-negative myocardial cells of the sinoatrial node and the sinus horns. Using genetic models, we show that as the myocardium of the heart tube matures, Nkx2-5 suppresses pacemaker channel gene Hcn4 and T-box transcription factor gene Tbx3, thereby enforcing a progressive confinement of their expression to the forming Nkx2-5-negative sinoatrial node and sinus horns. Thus, Nkx2-5 is essential for establishing a gene expression border between the atrium and sinoatrial node. Tbx3 was found to suppress chamber differentiation, providing an additional mechanism by which the Tbx3-positive sinoatrial node is shielded from differentiating into atrial myocardium. Pitx2c-deficient fetuses form sinoatrial nodes with indistinguishable molecular signatures at both the right and left sinuatrial junction, indicating that Pitx2c functions within the left/right pathway to suppress a default program for sinuatrial node formation on the left. Our molecular pathway provides a mechanism for how pacemaker activity becomes progressively relegated to the most recently added components of the venous pole of the heart and, ultimately, to the junction of the right atrium and superior caval vein.

Right ventricular myocardium derives from the anterior heart field

The mammalian heart develops from a primary heart tube, which is formed by fusion of bilateral cardiac territories in which myocardial and endothelial cells have already begun to differentiate from splanchnic mesoderm. A population of myocardial precursors has been identified in pharyngeal mesoderm, anterior to the early heart tube. Cell labeling studies have indicated that this novel territory, called the anterior heart field (AHF), gives rise to the myocardial wall of the outflow tract. We now report that not only the myocardium of the outflow tract but also myocardial cells of the embryonic right ventricle are derived from this source. Explants of pharyngeal mesoderm or of the early heart tube were cultured from transgenic mice in which transgene expression marks different regions of the heart. Pharyngeal mesoderm from 5 to 7 somite embryos gives rise to cardiomyocytes with right ventricular and outflow tract identities, whereas the heart tube as this stage has an essentially left ventricular identity. DiI labeling confirms that the early heart tube is destined to contribute to the embryonic left ventricle and indicates that right ventricular myocardium is added from extracardiac mesoderm. Retrospective clonal analysis of the heart at embryonic day (E) 10.5 reveals the existence of a clonal boundary in the interventricular region, which appears during ventricular septation, underlining different origins of the two ventricular compartments. This study demonstrates the differences in the embryological origin of right and left ventricular myocardium, which has important implications for congenital heart disease.

theta, a novel gamma-aminobutyric acid type A receptor subunit

gamma-Aminobutyric acid type A (GABA-A) receptors are a major mediator of inhibitory neurotransmission in the mammalian central nervous system, and the site of action of a number of clinically important drugs. These receptors exist as a family of subtypes with distinct temporal and spatial patterns of expression and distinct properties that presumably underlie a precise role for each subtype. The newest member of this gene family is the theta subunit. The deduced polypeptide sequence is 627 amino acids long and has highest sequence identity (50.5%) with the beta1 subunit. Within the rat striatum, this subunit coassembles with alpha2, beta1, and gamma1, suggesting that gamma-aminobutyric acid type A receptors consisting of arrangements other than alpha beta + gamma, delta, or epsilon do exist. Expression of alpha2beta1gamma1theta in transfected mammalian cells leads to the formation of receptors with a 4-fold decrease in the affinity for gamma-aminobutyric acid compared with alpha2beta1gamma1. This subunit has a unique distribution, with studies so far suggesting significant expression within monoaminergic neurons of both human and monkey brain.

Multicenter study of lamivudine therapy for hepatitis B after liver transplantation. Lamivudine Transplant Group

Hepatitis B after liver transplantation is often fatal, and no proven medical therapy exists for this condition. We chose to study the potential efficacy of lamivudine therapy for patients with chronic hepatitis B after liver transplantation. Fifty-two patients with chronic hepatitis B after liver transplantation were treated in an open label, multicenter study. Each had detectable hepatitis B virus (HBV) DNA in serum and 45 (87%) had detectable serum hepatitis B e antigen before treatment. Patients were treated for 52 weeks with lamivudine (100 mg daily). The primary endpoint was undetectability of HBV DNA; secondary endpoints included normalization of serum alanine transaminase (ALT) levels, disappearance of hepatitis B e antigen, and improvement in liver histology. After treatment, 60% of patients had undetectable HBV DNA by solution hybridization assay, 14 (31%) of the initially positive patients lost hepatitis B e antigen; hepatitis B surface antigen was undetectable in 3 (6%); and serum ALT levels normalized in 71%. Blinded histological assessments showed improvement in the histological activity index (P =.007 for periportal necrosis,.001 for lobular necrosis, and.013 for portal inflammation). YMDD variants of HBV, potentially associated with drug resistance, were detected in 14 (27%) of the patients. Repeat liver biopsies in 7 patients with the mutated virus were unchanged in 2, improved in 2, and worse in 3. We conclude that lamivudine is a potentially effective therapy for hepatitis B after liver transplantation.

The ECVAM international validation study on in vitro embryotoxicity tests: results of the definitive phase and evaluation of prediction models. European Centre for the Validation of Alternative Methods

From 1996 to 2000, ZEBET (Centre for Documentation and Evaluation of Alternative Methods to Animal Experiments at the BgVV, Berlin, Germany) coordinated the European Centre for the Validation of Alternative Methods (ECVAM) prevalidation and validation study on three embryotoxicity tests: a) a test employing embryonic stem cell lines (EST); b) the micromass (MM) test; and c) the postimplantation rat whole-embryo culture assay (WEC test). The main objectives of the study were to assess the performance of these three in vitro tests in discriminating between non- embryotoxic, weakly embryotoxic and strongly embryotoxic compounds. Phase I of the study (1997) was designed as a prevalidation phase, for test protocol optimisation, and for the establishment of a comprehensive database of in vivo and in vitro data on embryotoxic compounds. Phase II (1998-2000) involved a formal validation trial, conducted under blind conditions on 20 test compounds selected from the database, which were coded and distributed to the participating laboratories. In the preliminary phase of the validation study, six chemicals out of the 20, which showed embryotoxic potential, were tested. These results were used to define new biostatistically based prediction models (PMs) for the MM and WEC tests, and to evaluate those developed previously for the EST. As a next step, the PMs were evaluated by using the results for the remaining 14 chemicals of the definitive phase of the validation study. The three in vitro embryotoxicity tests proved to be applicable to testing a diverse group of chemicals with different embryotoxic potentials (non-embryotoxic, weakly embryotoxic, and strongly embryotoxic). The reproducibility of the three in vitro embryotoxicity tests were acceptable according to the acceptance criteria defined by the Management Team. The concordances between the embryotoxic potentials derived from the in vitro data and from the in vivo data were good for the EST and the WEC (PM2) test, and sufficient for the MM test and the WEC (PM1) tests according to the performance criteria defined by the Management Team before the formal validation study. When applying the PM of the EST to the in vitro data obtained in the definitive phase of the formal validation study, chemicals were classified correctly in 78% of the experiments. For the MM and the WEC tests, the PMs provided 70% and 80% (PM2) correct classifications, respectively. And, very importantly, an excellent predictivity (100%, except for PM1 of the WEC test, with 79%, considered as good) was obtained with strong embryotoxic chemicals in each of the three in vitro tests.

PITX2c is expressed in the adult left atrium, and reducing Pitx2c expression promotes atrial fibrillation inducibility and complex changes in gene expression

BACKGROUND

Intergenic variations on chromosome 4q25, close to the PITX2 transcription factor gene, are associated with atrial fibrillation (AF). We therefore tested whether adult hearts express PITX2 and whether variation in expression affects cardiac function.

METHODS AND RESULTS

mRNA for PITX2 isoform c was expressed in left atria of human and mouse, with levels in right atrium and left and right ventricles being 100-fold lower. In mice heterozygous for Pitx2c (Pitx2c(+/-)), left atrial Pitx2c expression was 60% of wild-type and cardiac morphology and function were not altered, except for slightly elevated pulmonary flow velocity. Isolated Pitx2c(+/-) hearts were susceptible to AF during programmed stimulation. At short paced cycle lengths, atrial action potential durations were shorter in Pitx2c(+/-) than in wild-type. Perfusion with the β-receptor agonist orciprenaline abolished inducibility of AF and reduced the effect on action potential duration. Spontaneous heart rates, atrial conduction velocities, and activation patterns were not affected in Pitx2c(+/-) hearts, suggesting that action potential duration shortening caused wave length reduction and inducibility of AF. Expression array analyses comparing Pitx2c(+/-) with wild-type, for left atrial and right atrial tissue separately, identified genes related to calcium ion binding, gap and tight junctions, ion channels, and melanogenesis as being affected by the reduced expression of Pitx2c.

CONCLUSIONS

These findings demonstrate a physiological role for PITX2 in the adult heart and support the hypothesis that dysregulation of PITX2 expression can be responsible for susceptibility to AF.

Genes regulating lymphangiogenesis control venous valve formation and maintenance in mice

Chronic venous disease and venous hypertension are common consequences of valve insufficiency, yet the molecular mechanisms regulating the formation and maintenance of venous valves have not been studied. Here, we provide what we believe to be the first description of venous valve morphogenesis and identify signaling pathways required for the process. The initial stages of valve development were found to involve induction of ephrin-B2, a key marker of arterial identity, by venous endothelial cells. Intriguingly, developing and mature venous valves also expressed a repertoire of proteins, including prospero-related homeobox 1 (Prox1), Vegfr3, and integrin-α9, previously characterized as specific and critical regulators of lymphangiogenesis. Using global and venous valve-selective knockout mice, we further demonstrate the requirement of ephrin-B2 and integrin-α9 signaling for the development and maintenance of venous valves. Our findings therefore identified molecular regulators of venous valve development and maintenance and highlighted the involvement of common morphogenetic processes and signaling pathways in controlling valve formation in veins and lymphatic vessels. Unexpectedly, we found that venous valve endothelial cells closely resemble lymphatic (valve) endothelia at the molecular level, suggesting plasticity in the ability of a terminally differentiated endothelial cell to take on a different phenotypic identity.

The Drosophila PS2 antigen is an invertebrate integrin that, like the fibronectin receptor, becomes localized to muscle attachments

We establish that the position-specific antigen 2 (PS2), a Drosophila cell surface glycoprotein complex, is an invertebrate member of the vertebrate fibronectin receptor (integrin) family. New monoclonal antibodies show that in Drosophila embryos and larvae PS2 alpha subunits have a size of ca. 140 kd. Analysis of cDNA and genomic clones revealed that the canonical PS2 alpha subunit contains 1394 amino acids and has extensive homology to the heavy and light chains of integrin alpha subunits. The distribution of the PS2 antigen is regulated at the level of PS2 alpha subunit mRNA. In early Drosophila development the protein is restricted to mesoderm and appears to be involved in muscle attachment. We suggest that PS2, like vertebrate fibronectin receptors, mediates changes in cell shape and cell-extracellular matrix adhesion by binding to a basement membrane protein.

Waves of mouse Lunatic fringe expression, in four-hour cycles at two-hour intervals, precede somite boundary formation

During somitogenesis, cells are recruited to the caudal presomitic mesoderm (PSM) from the primitive streak (and later the tail bud), while somites separate from the rostral end as epithelial cubes. This is a regular process, one somite forming every 2 hours in the mouse, that can be simulated by clock and wavefront models. The chick basic helix-loop-helix transcription factor encoded by c-hairy1 is expressed in dynamic waves in the PSM, undergoing one cycle for each somite formed. This is compatible with an underlying oscillating molecular clock. We have shown here that Lunatic fringe (L-fng) expression is indicative of it being one of the implementing outputs of this clock. Fringe genes regulate the Notch signalling pathway in boundary formation. Of the known mouse genes, only L-fng is expressed in PSM and it is required for somite segmentation and patterning. We have now shown that L-fng is expressed as dynamic, repetitive and complex waves within the mouse PSM. A wave takes 4 hours to complete one cycle and terminates immediately at, and prior to, somite boundary formation. Consecutive waves are temporally but not spatially overlapping, being initiated in the caudal PSM every 2 hours, so offset by one half-cycle. Waves of expression are not associated with cell movement and do not require cell contact for propagation, so appear to reflect a cell-autonomous clock that is synchronous in all PSM cells.