Development of intranasal implantable devices for schizophrenia treatment

In this work the preparation and characterisation of intranasal implants for the delivery of risperidone (RIS) is described. The aim of this work is to develop better therapies to treat chronic conditions affecting the brain such as schizophrenia. This type of systems combines the advantages of intranasal drug delivery with sustained drug release. The resulting implants were prepared using biodegradable materials, including poly(caprolactone) (PCL) and poly(lactic-co-glycolic acid) (PLGA). These polymers were combined with water-soluble compounds, such as poly(ethylene glycol) (PEG) 600, PEG 3000, and Tween® 80 using a solvent-casting method. The resulting implants contained RIS loadings ranging between 25 and 50%. The obtained implants were characterised using a range of techniques including thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), attenuated total reflectance-Fourier transform infrared (ATR-FTIR), X-ray diffraction (XRD), and Scanning Electron Microscopy (SEM). Moreover, in vitro RIS release was evaluated showing that the addition of water-soluble compounds exhibited significant faster release profiles compared to pristine PCL and PLGA-based implants. Interestingly, PCL-based implants containing 25% of RIS and PLGA-based implants loaded with 50% of RIS showed sustained drug release profiles up to 90 days. The former showed faster release rates over the first 28 days but after this period PLGA implants presented higher release rates. The permeability of RIS released from the implants through a model membrane simulating nasal mucosa was subsequently evaluated showing desirable permeation rate of around 2 mg/day. Finally, following in vitro biocompatibility studies, PCL and PLGA-based implants showed acceptable biocompatibility. These results suggested that the resulting implants displayed potential of providing prolonged drug release for brain-targeting drugs.

Development and validation of a high-performance liquid chromatography method for levothyroxine sodium quantification in plasma for pre-clinical evaluation of long-acting drug delivery systems

Levothyroxine (LEVO) sodium is an FDA-approved drug that is used to treat underactive thyroid (hypothyroidism) and other conditions. It is generally used as a thyroid-stimulating hormone administered orally. However, this approach has some drawbacks such as this drug should be taken every day 30 min to 1 h prior to breakfast with an empty stomach, moreover, some food interactions must be monitored. Thus, alternative innovative approaches capable of providing sustained LEVO release should be developed. Our research was designed to establish a simple quantitative determination method for LEVO in rat plasma for pre-clinical evaluation of long acting formulations using a high-performance liquid chromatography method, to validate the analytical method according to ICH guidelines and to characterise its pharmacokinetic behavior in rats. After simple protein precipitation with acetonitrile, LEVO was eluted on a Xselect CSH™ C18 column (Waters, 3.0 × 150 mm) with a particle size of 3.5 μm using a mobile phase of water and acetonitrile at a ratio of 65 : 35% v/v, including 0.1% v/v of trifluoracetic acid. The calibration standards used for plasma ranged between 0.5-1000 ng mL^-1 with a correlation coefficient (r²) of ≥0.998. The limit of detection was 0.44 ng mL^-1 and the lower limit of quantitation was 1.33 ng mL^-1. The extraction recovery of LEVO in rat plasma samples by this method was between 80 and 85%. The method was selective, sensitive, accurate and precise for detecting and quantifying LEVO in a pharmacokinetic study carried out in rats for pre-clinical evaluation of long acting formulations. The validated HPLC method meets the ICH established requirements and therefore offers a wide range of potential applications in pre-clinical therapeutic drug monitoring, pharmacokinetics and toxicology.

Poly(caprolactone)-based subcutaneous implant for sustained delivery of levothyroxine

This work aimed to develop a subcutaneous implant for prolonged delivery of LEVO to treat hypothyroidism. This could overcome challenges with patient compliance and co-administration and could improve treatment of this condition. For this purpose, implants were produced by solvent casting mixtures of poly(caprolactone) (PCL), poly(ethylene glycol) (PEG) and LEVO sodium. These implants contained mixtures of PCL of differing molecular weight, PEG and different LEVO sodium loadings (20% or 40% w/w). SEM images confirmed that the drug was evenly dispersed throughout the implant. In vitro release rates ranging from 28.37 ± 1.19 - 78.21 ± 19.93 µg/day and 47.39 ± 8.76 - 98.92 ± 4.27 µg/day were achieved for formulations containing 20% and 40% w/w drug loading, respectively. Implants containing higher amounts of low molecular weight PCL and 40% w/w of LEVO showed release profiles governed by zero order kinetics. On the other hand, implants containing higher amounts of high molecular weight PCL showed a release mechanism governed by Fickian diffusion. Finally, two representative formulations were tested in vivo. These implants were capable of providing detectable LEVO levels in plasma during the entire duration of the experiments (4 weeks) with LEVO plasma levels ranging between 5 and 20 ng/mL.

Fused deposition modelling for the development of drug loaded cardiovascular prosthesis

Cardiovascular diseases constitute a number of conditions which are the leading cause of death globally. To combat these diseases and improve the quality and duration of life, several cardiac implants have been developed, including stents, vascular grafts and valvular prostheses. The implantation of these vascular prosthesis has associated risks such as infection or blood clot formation. In order to overcome these limitations medicated vascular prosthesis have been previously used. The present paper describes a 3D printing method to develop medicated vascular prosthesis using fused deposition modelling (FDM) technology. For this purpose, rifampicin (RIF) was selected as a model molecule as it can be used to prevent vascular graft prosthesis infection. Thermoplastic polyurethane (TPU) and RIF were combined using hot melt extrusion (HME) to obtain filaments containing RIF concentrations ranging between 0 and 1% (w/w). These materials are capable of providing RIF release for periods ranging between 30 and 80 days. Moreover, TPU-based materials containing RIF were capable of inhibiting the growth of Staphylococcus aureus. This behaviour was observed even for TPU-based materials containing RIF concentrations of 0.1% (w/w). TPU containing 1% (w/w) of RIF showed antimicrobial properties even after 30 days of RIF release. Alternatively, these methods were used to prepare dipyridamole containing TPU filaments. Finally, using a dual extrusion 3D printer vascular grafts containing both drugs were prepared.

Multicenter retrospective evaluation of ileocecocolic perforations associated with diagnostic lower gastrointestinal endoscopy in dogs and cats

Background

Ileoscopy is increasingly performed in dogs and cats with gastrointestinal signs, but iatrogenic ileocecocolic (ICC) perforations have not been described.

Hypothesis/Objectives

To characterize endoscopic ICC perforations in dogs and cats.

Animals

Thirteen dogs and 2 cats.

Methods

This is a retrospective case series. Signalment, presentation, endoscopic equipment, colonic preparation, endoscopist's experience level, ileal intubation technique, method of diagnosis, perforation location, histopathology, management, and outcome data were collected and reviewed.

Results

Six ileal, 5 cecal, and 4 colonic perforations were identified between 2012 and 2019. Dogs weighed 2.4‐26 kg (median, 10.3 kg) and cats 4.6‐5.1 kg (median, 4.9 kg). Endoscopy was performed in dogs presented for vomiting (n = 4), as well as large (n = 5), mixed (n = 4), and small (n = 1) bowel diarrhea. Cats had large bowel diarrhea. Endoscopists included 1 supervised intern, 9 supervised internal medicine residents (2 first year, 6 second year, 1 third year), and 5 internal medicine diplomates. Diagnosis was delayed in 5 dogs, occurring 1‐5 days after endoscopy (median, 3 days); dogs were presented again with inappetence (n = 4), lethargy (n = 4), abdominal pain (n = 3), retching (n = 2), and syncope (n = 1). All animals underwent surgical correction. Histopathology did not identify lesions at the perforation site in any animal. Two dogs required a second surgery; 1 died 12 hours after surgery. Survival to discharge was 93%, with 78% surviving ≥8 months.

Conclusions and Clinical Importance

Iatrogenic endoscopic ICC perforation is not indicative of underlying disease and is associated with a good prognosis. Delayed diagnosis can occur. Therefore, perforation should be considered in the differential diagnosis for animals with clinical deterioration after endoscopy.

Development of a Biodegradable Subcutaneous Implant for Prolonged Drug Delivery Using 3D Printing

Implantable drug delivery devices offer many advantages over other routes of drug delivery. Most significantly, the delivery of lower doses of drug, thus, potentially reducing side-effects and improving patient compliance. Three dimensional (3D) printing is a flexible technique, which has been subject to increasing interest in the past few years, especially in the area of medical devices. The present work focussed on the use of 3D printing as a tool to manufacture implantable drug delivery devices to deliver a range of model compounds (methylene blue, ibuprofen sodium and ibuprofen acid) in two in vitro models. Five implant designs were produced, and the release rate varied, depending on the implant design and the drug properties. Additionally, a rate controlling membrane was produced, which further prolonged the release from the produced implants, signalling the potential use of these devices for chronic conditions.

Fused Deposition Modeling as an Effective Tool for Anti-Infective Dialysis Catheter Fabrication

Catheter-associated infections are a common complication that occurs in dialysis patients. Current strategies to prevent infection include catheter coatings containing heparin, pyrogallol, or silver nanoparticles, which all have an increased risk of causing resistance in bacteria. Therefore, a novel approach for manufacture, such as the use of additive manufacturing (AM), also known as three-dimensional (3D) printing, is required. Filaments were produced by extrusion using thermoplastic polyurethane (TPU) and tetracycline hydrochloride (TC) in various concentrations (e.g., 0, 0.25, 0.5, and 1%). The extruded filaments were used in a fused deposition modeling (FDM) 3D printer to print catheter constructs at varying concentrations. Release studies in phosphate-buffered saline, microbiology studies, thermal analysis, contact angle, attenuated total reflection-Fourier transform infrared, scanning electron microscopy, and X-ray microcomputer tomography (μCT) analysis were conducted on the printed catheters. The results suggested that TC was uniformly distributed within the TPU matrix. The microbiology testing of the catheters showed that devices containing TC had an inhibitory effect on the growth of Staphylococcus aureus NCTC 10788 bacteria. Catheters containing 1% TC maintained inhibitory effect after 10 day release studies. After an initial burst release in the first 24 h, there was a steady release of TC in all concentrations of catheters. 3D-printed antibiotic catheters were successfully printed with inhibitory effect on S. aureus bacteria. Finally, TC containing catheters showed resistance to S. aureus adherence to their surfaces when compared with catheters containing no TC. Catheters containing 1% of TC showed a bacterial adherence reduction of up to 99.97%. Accordingly, the incorporation of TC to TPU materials can be effectively used to prepare anti-infective catheters using FDM. This study highlights the potential for drug-impregnated medical devices to be created through AM.

Lignin and Cellulose Blends as Pharmaceutical Excipient for Tablet Manufacturing via Direct Compression

Extensive efforts are being made to find alternative uses for lignin (LIG). In the present work the use of this biopolymer as excipient to prepare tablets was studied. For this purpose, LIG was combined with microcrystalline cellulose (MCC) and used as excipients to prepare directly compressed tablets containing a model drug, tetracycline (TC). The excipients contained different concentrations of LIG: 100%, 75%, 50%, 25% and 0% (w/w). Two different compression forces were used (two and five tonnes). When formulations were prepared using LIG as the only excipient, tablets were formed, but they showed lower densities and crushing strength than the ones obtained with only MCC or LIG/MCC blends. Moreover, tablets prepared using five tonnes of compression force showed TC releases ranging from 40% to 70% of the drug loading. On the other hand, the tablets prepared using two tonnes of compression force showed a faster and more efficient TC release, between 60% and 90%. The presence of LIG in the tablets modified significantly the release profile and the maximum amount of TC released. Finally, a DPPH (2,2-diphenyl-1-picrylhydrozyl) assay was performed to confirm that the presence of LIG provided antioxidant properties to the formulations. Accordingly, LIG has potential as a pharmaceutical excipient.

Antioxidant PLA Composites Containing Lignin for 3D Printing Applications: A Potential Material for Healthcare Applications

Lignin (LIG) is a natural biopolymer with well-known antioxidant capabilities. Accordingly, in the present work, a method to combine LIG with poly(lactic acid) (PLA) for fused filament fabrication applications (FFF) is proposed. For this purpose, PLA pellets were successfully coated with LIG powder and a biocompatible oil (castor oil). The resulting pellets were placed into an extruder at 200 °C. The resulting PLA filaments contained LIG loadings ranging from 0% to 3% (w/w). The obtained filaments were successfully used for FFF applications. The LIG content affected the mechanical and surface properties of the overall material. The inclusion of LIG yielded materials with lower resistance to fracture and higher wettabilities. Moreover, the resulting 3D printed materials showed antioxidant capabilities. By using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) method, the materials were capable of reducing the concentration of this compound up to ca. 80% in 5 h. This radical scavenging activity could be potentially beneficial for healthcare applications, especially for wound care. Accordingly, PLA/LIG were used to design meshes with different designs for wound dressing purposes. A wound healing model compound, curcumin (CUR), was applied in the surface of the mesh and its diffusion was studied. It was observed that the dimensions of the meshes affected the permeation rate of CUR. Accordingly, the design of the mesh could be modified according to the patient’s needs.

Implantable Polymeric Drug Delivery Devices: Classification, Manufacture, Materials, and Clinical Applications

The oral route is a popular and convenient means of drug delivery. However, despite its advantages, it also has challenges. Many drugs are not suitable for oral delivery due to: first pass metabolism; less than ideal properties; and side-effects of treatment. Additionally, oral delivery relies heavily on patient compliance. Implantable drug delivery devices are an alternative system that can achieve effective delivery with lower drug concentrations, and as a result, minimise side-effects whilst increasing patient compliance. This article gives an overview of classification of these drug delivery devices; the mechanism of drug release; the materials used for manufacture; the various methods of manufacture; and examples of clinical applications of implantable drug delivery devices.

Synthetic hydrogels formed by thiol-ene crosslinking of vinyl sulfone-functional poly(methyl vinyl ether-alt-maleic acid) with α,ω-dithio-polyethyleneglycol

Polymer hydrogels formed by rapid thiol-ene coupling of macromolecular gel formers can offer access to versatile new matrices. This paper describes the efficient synthesis of cysteamine vinyl sulfone (CVS) trifluoroacetate, and its incorporation into poly(methyl vinyl ether-alt-maleic anhydride) (PMMAn) to form a series of CVS-functionalized poly(methyl vinyl ether-alt-maleic acid) polymers (PMM-CVS_x) containing 10 to 30 mol% pendant vinyl sulfone groups. Aqueous mixtures of these PMM-CVS and a dithiol crosslinker, α,ω-dithio-polyethyleneglycol (HS-PEG-SH, M_n = 1 kDa), gelled through crosslinking by Michael addition within seconds to minutes, depending on pH, degree of functionalization, and polymer loading. Gelation efficiency, Young's modulus, equilibrium swelling and hydrolytic stability are described, and step-wise hydrogel post-functionalization with a small molecule thiol, cysteamine, was demonstrated. Cytocompatibility of these crosslinked hydrogels towards entrapped 3T3 fibroblasts was confirmed using a live/dead fluorescence assay.

Nocturama gen. nov., Nothocladus s. lat. and other taxonomic novelties resulting from the further resolution of paraphyly in Australasian members of Batrachospermum (Batrachospermales, Rhodophyta)

The informal "Australasica Group" was established in 2009 to include several Australasian endemic Batrachospermum species, a few species of the cosmopolitan Batrachospermum section Setacea, and the South American endemic Petrohua bernabei. Although useful for communication purposes, no formal taxonomic designation was proposed due to weakly supported basal nodes. The present research took a two-pronged approach of adding more taxa (29 additional specimens) as well as more sequence data (LSU, cox1, psaA, and psbA markers added to rbcL data) to provide better resolution. The resulting tree showed improved statistical support values (Bayesian posterior probability and maximum likelihood bootstrap) for most nodes providing a framework for taxonomic revision. Based on our well-resolved phylogeny, a new genus, Nocturama, is proposed for a clade of Batrachospermum antipodites specimens. The circumscription of Nothocladus is expanded to include Batrachospermum section Setacea and four additional sections composed of at least 10 species, mostly from Australia and New Zealand. One new species added to the data set, N. diatyches, did not form a clade with the other species of section Setaceus, where it was classified previously, rendering that section paraphyletic. To resolve this, N. diatyches and the morphologically similar species N. latericius are included with N. theaquus, in the new section Theaquus within Nothocladus s. lat. A specimen from Australia unaligned to these clades was sister to the Australia-New Zealand genus Psilosiphon and the cosmopolitan B. cayennense, but lacked statistical support. This specimen has the gross morphology of Batrachospermum s. lat. and is here provisionally assigned to that genus, as B. serendipidum sp. nov.

Methylene Blue-Loaded Dissolving Microneedles: Potential Use in Photodynamic Antimicrobial Chemotherapy of Infected Wounds

Photodynamic therapy involves delivery of a photosensitising drug that is activated by light of a specific wavelength, resulting in generation of highly reactive radicals. This activated species can cause destruction of targeted cells. Application of this process for treatment of microbial infections has been termed “photodynamic antimicrobial chemotherapy” (PACT). In the treatment of chronic wounds, the delivery of photosensitising agents is often impeded by the presence of a thick hyperkeratotic/necrotic tissue layer, reducing their therapeutic efficacy. Microneedles (MNs) are an emerging drug delivery technology that have been demonstrated to successfully penetrate the outer layers of the skin, whilst minimising damage to skin barrier function. Delivering photosensitising drugs using this platform has been demonstrated to have several advantages over conventional photodynamic therapy, such as, painless application, reduced erythema, enhanced cosmetic results and improved intradermal delivery. The aim of this study was to physically characterise dissolving MNs loaded with the photosensitising agent, methylene blue and assess their photodynamic antimicrobial activity. Dissolving MNs were fabricated from aqueous blends of Gantrez^® AN-139 co-polymer containing varying loadings of methylene blue. A height reduction of 29.8% was observed for MNs prepared from blends containing 0.5% w/w methylene blue following application of a total force of 70.56 N/array. A previously validated insertion test was used to assess the effect of drug loading on MN insertion into a wound model. Staphylococcus aureus, Escherichia coli and Candida albicans biofilms were incubated with various methylene blue concentrations within the range delivered by MNs in vitro (0.1–2.5 mg/mL) and either irradiated at 635 nm using a Paterson Lamp or subjected to a dark period. Microbial susceptibility to PACT was determined by assessing the total viable count. Kill rates of >96%, were achieved for S. aureus and >99% for E. coli and C. albicans with the combination of PACT and methylene blue concentrations between 0.1 and 2.5 mg/mL. A reduction in the colony count was also observed when incorporating the photosensitiser without irradiation, this reduction was more notable in S. aureus and E. coli strains than in C. albicans.

Accidental entrapment of cats in front-loading washing machines

Two clinical cases of accidental entrapment of cats in front-loading washing machines are described. One cat died the day after presentation as a result of aspiration pneumonia and head trauma, despite supportive care. The second cat survived with supportive treatment, but developed dermatologic complications 10 d later.

FEN1 contributes to telomere stability in ALT-positive tumor cells

Abrogation of telomere stability through loss-of-function mutations in telomere binding proteins contributes to genomic instability and cancer progression. Recently, Flap endonuclease 1 (FEN1) was shown to contribute to telomere stability in human cells that had not yet activated a telomere maintenance mechanism, suggesting that abrogation of FEN1 function influences the transformation process by compromising telomere stability and driving genomic instability. Here, we analyse the telomeres in human cancer cells following FEN1 depletion. We show that FEN1 is required for telomere stability in cells that rely on the alternative lengthening of telomere (ALT) mechanism. Indeed, FEN1 depletion resulted in telomere dysfunction, characterized by formation of telomere dysfunction-induced foci (TIFs) and end-to-end fusions in ALT-positive cells. In contrast, no telomere phenotype was observed in telomerase-positive cells on FEN1 depletion, suggesting that ongoing telomerase activity protected telomeres. In consonance with this, we found that expression of the catalytic component of telomerase (hTERT) but not an inactive allele rescued telomere dysfunction on FEN1 depletion in ALT cells. Our data suggest that mutations that arise in FEN1 affect telomere stability and genome fidelity by promoting telomere fusions and anaphase-bridge-breakage cycles, which further drive genome instability and thereby contribute to the transformation process.

Glucocorticoids act directly on osteoclasts to increase their life span and reduce bone density

Glucocorticoid administration to mice results in a rapid loss of bone mineral density due to an imbalance in osteoblast and osteoclast numbers. Whereas excess glucocorticoids reduce both osteoblast and osteoclast precursors, cancellous osteoclast number surprisingly does not decrease as does osteoblast number, presumably due to the ability of glucocorticoids to promote osteoclast life span. Whether glucocorticoids act directly on osteoclasts in vivo to promote their life span and whether this contributes to the rapid loss of bone with glucocorticoid excess remains unknown. To determine the direct effects of glucocorticoids on osteoclasts in vivo, we expressed 11beta-hydroxysteroid dehydrogenase type 2, an enzyme that inactivates glucocorticoids, specifically in the osteoclasts of transgenic mice using the tartrate-resistant acid phosphatase promoter. Bone mass, geometry, and histomorphometry were similar in untreated wild-type and transgenic animals. Glucocorticoid administration for 7 d caused equivalent increases in cancellous osteoblast apoptosis, and equivalent decreases in osteoblasts, osteoid, and bone formation, in wild-type and transgenic mice. In contrast, glucocorticoids stimulated expression of the mRNA for calcitonin receptor, an osteoclast product, in wild-type but not transgenic mice. Consistent with the previous finding that glucocorticoids decrease osteoclast precursors and prolong osteoclast life span, glucocorticoids decreased cancellous osteoclast number in the transgenic mice but not wild-type mice. In accord with this decrease in osteoclast number, the loss of bone density observed in wild-type mice was strikingly prevented in transgenic mice. These results demonstrate for the first time that the early, rapid loss of bone caused by glucocorticoid excess results from direct actions on osteoclasts.

Effect of energy substrates on protein degradation in isolated small intestinal enterocytes from rats

BACKGROUND

Nutrients affect small intestinal protein mass and metabolism, but studies on the effect of nutrients on small intestinal protein degradation are very limited due to a lack of a proper method. The objectives of this study were to establish a method to directly estimate protein degradation in isolated enterocytes from rats and to test the effect of energy substrates on protein degradation.

METHODS

Male Sprague-Dawley rats (150-200 g, n>or=8 per treatment) were used. Cell viability, tyrosine release as an indicator of protein degradation, and the effect of osmolarity, 50 mmol/L glucose, 20 mmol/L beta-hydroxybutyrate, 4.7 mmol/L butyrate, and 30 mmol/L glutamine on protein degradation were measured.

RESULTS

The average viability of enterocytes at time 30 minutes was 85.8% (range, 81%-94%). Tyrosine release was linear over the course of experiments, indicating constant protein degradation (R2=0.9943; p<.05). Osmolarity, glucose, and glutamine had no effect on protein degradation in isolated enterocytes. Beta-hydroxybutyrate significantly decreased it (-16%; p<.05), whereas butyrate slightly increased it (+5%; p<.05).

CONCLUSIONS

A high viability and constant protein degradation indicate a successful establishment of a method to estimate protein degradation in isolated small intestinal enterocytes from rats. The large effect of beta-hydroxybutyrate suggests a potential positive role for ketone bodies to limit the loss of small intestinal protein mass by decreasing protein degradation.

Liver protein synthesis stays elevated after chemotherapy in tumour-bearing mice

We studied the effect of chemotherapy on liver protein synthesis in mice bearing colon 26 adenocarcinoma (C26). Liver protein mass decreased (-32%; P<0.05) in cachectic mice, but protein synthesis increased (20-35%; P<0.05) in cachectic mice, which is consistent with increased export protein synthesis. Increased protein synthesis in tumour-bearing mice was primarily mediated by increasing ( approximately 15%; P<0.05) the RNA concentration, i.e. the capacity for protein synthesis (Cs; mg RNA/g protein). Cystemustine, a nitrosourea chemotherapy that cures C26 with 100% efficacy, rapidly restored liver protein mass; protein synthesis however stayed higher than in healthy mice ( approximately 15%) throughout the initial and later stages of recovery. Chemotherapy had no significant effect on liver protein mass and synthesis in healthy mice. Reduced food intake was not a factor in this model. These data suggest a high priority for liver protein synthesis during cancer cachexia and recovery.

Reversal of bone loss in mice by nongenotropic signaling of sex steroids

We show that sex steroids protect the adult murine skeleton through a mechanism that is distinct from that used to preserve the mass and function of reproductive organs. The classical genotropic actions of sex steroid receptors are dispensable for their bone protective effects, but essential for their effects on reproductive tissues. A synthetic ligand (4-estren-3alpha,17beta-diol) that reproduces the nongenotropic effects of sex steroids, without affecting classical transcription, increases bone mass and strength in ovariectomized females above the level of the estrogen-replete state and is at least as effective as dihydrotestosterone in orchidectomized males, without affecting reproductive organs. Such ligands merit investigation as potential therapeutic alternatives to hormone replacement for osteoporosis in both women and men [corrected].

Integrin-mediated adhesion regulates ERK nuclear translocation and phosphorylation of Elk-1

Integrin-mediated adhesion to the extracellular matrix permits efficient growth factor-mediated activation of extracellular signal-regulated kinases (ERKs). Points of regulation have been localized to the level of receptor phosphorylation or to activation of the downstream components, Raf and MEK (mitogen-activated protein kinase/ERK kinase). However, it is also well established that ERK translocation from the cytoplasm to the nucleus is required for G1 phase cell cycle progression. Here we show that phosphorylation of the nuclear ERK substrate, Elk-1 at serine 383, is anchorage dependent in response to growth factor treatment of NIH 3T3 fibroblasts. Furthermore, when we activated ERK in nonadherent cells by expression of active components of the ERK cascade, subsequent phosphorylation of Elk-1 at serine 383 and Elk-1-mediated transactivation were still impaired compared with adherent cells. Elk-1 phosphorylation was dependent on an intact actin cytoskeleton, as discerned by treatment with cytochalasin D (CCD). Finally, expression of active MEK failed to predominantly localize ERK to the nucleus in suspended cells or adherent cells treated with CCD. These data show that integrin-mediated organization of the actin cytoskeleton regulates localization of activated ERK, and in turn the ability of ERK to efficiently phosphorylate nuclear substrates.

Telomerase and human tumorigenesis

Human cancer cells, unlike their normal counterparts, have shed the molecular restraints to limited cell growth and are immortal. Exactly how cancer cells manage this at the molecular level is beginning to be understood. Human cells must overcome two barriers to cellular proliferation. The first barrier, referred to as senescence, minimally involves the p53 and Rb tumor-suppressor pathways. Inactivation of these pathways results in some extension of lifespan. However, inactivation of these pathways is insufficient for immortalization. As normal cells undergo repeated rounds of DNA replication, their telomeres shorten due to the inability of traditional DNA polymerases to completely replicate the end of the chromosomal DNA. This shortening continues until the cells reach a second proliferative block referred to as crisis, which is characterized by chromosomal instability, end-to-end fusions, and cell death. Stabilization of the telomeric DNA through either telomerase activation or the activation of the alternative mechanism of telomere maintenance (ALT) is essential if the cells are to survive and proliferate indefinitely. Conversely, loss of telomere stabilization by an already-immortalized cell results in loss of immortality and cell death. Together this indicates that telomere maintenance is a critical component of immortality. In this review we attempt to describe our current understanding of the role of telomere maintenance in senescence, crisis, and tumorigenesis.

Human immunodeficiency virus type 1 vpr induces apoptosis through caspase activation

Human immunodeficiency virus type 1 (HIV-1) Vpr is a 96-amino-acid protein that is found associated with the HIV-1 virion. Vpr induces cell cycle arrest at the G(2)/M phase of the cell cycle, and this arrest is followed by apoptosis. We examined the mechanism of Vpr-induced apoptosis and found that HIV-1 Vpr-induced apoptosis requires the activation of a number of cellular cysteinyl aspartate-specific proteases (caspases). We demonstrate that ectopic expression of anti-apoptotic viral proteins, which inhibit caspase activity, and addition of synthetic peptides, which represent caspase cleavage sites, can inhibit Vpr-induced apoptosis. Finally, inhibition of caspase activity and subsequent inhibition of apoptosis results in increased viral expression, suggesting that therapeutic strategies aimed at reducing Vpr-induced apoptosis in vivo require careful consideration.

Lentiviral delivery of HIV-1 Vpr protein induces apoptosis in transformed cells

Most current anticancer therapies act by inducing tumor cell stasis followed by apoptosis. HIV-1 Vpr effectively induces apoptosis of T cells after arrest of cells at a G(2)/M checkpoint. Here, we investigated whether this property of Vpr could be exploited for use as a potential anticancer agent. As a potentially safer alternative to transfer of genes encoding Vpr, we developed a method to efficiently introduce Vpr protein directly into cells. Vpr packaged into HIV-1 virions lacking a genome induced efficient cell cycle arrest and apoptosis. Introduction of Vpr into tumor cell lines of various tissue origin, including those bearing predisposing mutations in p53, XPA, and hMLH1, induced cell cycle arrest and apoptosis with high efficiency. Significantly, apoptosis mediated by virion-associated Vpr was more effective on rapidly dividing cells compared with slow-growing cells, thus, in concept, providing a potential differential effect between some types of tumor cells and surrounding normal cells. This model system provides a rationale and proof of concept for the development of potential cancer therapeutic agents based on the growth-arresting and apoptotic properties of Vpr.

Sexual dimorphism and ontogenetic allometry of soft tissues in Rattus norvegicus

Most studies of sexual dimorphism in mammals focus on overall body size. However, relatively little is known about the differences in growth trajectories that produce dimorphism in organ and muscle size. We weighed six organs and four muscles in Rattus norvegicus to determine what heterochronic and allometric scaling differences exist between the sexes. This cross-sectional growth study included 113 males and 109 females with ages ranging from birth to 200 days of age. All muscle and organ weights were ultimately greater in males than in females, because males grew for a longer period of time, had a greater maximum rate of growth, and spent more time near the maximum rate. No ontogenetic scaling differences existed between the sexes in organ weight except for lungs and gonads. During growth, organ weights were negatively allometric to body weight. No scaling differences relative to body weight existed between the sexes for muscles; however, there was variation in the allometric relations among muscles relative to body weight. Sexual dimorphism in muscles and organs appears to be a size difference resulting from differences in the duration and rates of growth.

Inhibition of telomerase limits the growth of human cancer cells

Telomerase is a ribonucleoprotein enzyme that maintains the protective structures at the ends of eukaryotic chromosomes, called telomeres. In most human somatic cells, telomerase expression is repressed, and telomeres shorten progressively with each cell division. In contrast, most human tumors express telomerase, resulting in stabilized telomere length. These observations indicate that telomere maintenance is essential to the proliferation of tumor cells. We show here that expression of a mutant catalytic subunit of human telomerase results in complete inhibition of telomerase activity, reduction in telomere length and death of tumor cells. Moreover, expression of this mutant telomerase eliminated tumorigenicity in vivo. These observations demonstrate that disruption of telomere maintenance limits cellular lifespan in human cancer cells, thus validating human telomerase reverse transcriptase as an important target for the development of anti-neoplastic therapies.

Infrared Spectroscopic Imaging of the Biochemical Modifications Induced in the Cerebellum of the Niemann-Pick type C Mouse

We have applied Fourier transform infrared (IR) spectroscopic imaging to the investigation of the neuropathologic effects of a genetic lipid storage disease, Niemann-Pick type C (NPC). Tissue sections both from the cerebella of a strain of BALB/c mice that demonstrated morphology and pathology of the human disease and from control animals were used. These samples were analyzed by standard histopathological procedures as well as this new IR imaging approach. The IR absorbance images exhibit contrast based on biochemical variations and allow for the identification of the cellular layers within the tissue samples. Furthermore, these images provide a qualitative description of the localized biochemical differences existing between the diseased and control tissue in the absence of histological staining. Statistical analyses of the IR spectra extracted from individual cell layers of the imaging data sets provide concise quantitative descriptions of these biochemical changes. The results indicate that lipid is depleted specifically in the white matter of the NPC mouse in comparison to the control samples. Minor differences were noted for the granular layers, but no significant differences were observed in the molecular layers of the cerebellar tissue. These changes are consistent with significant demyelination within the cerebellum of the NPC mouse. © 1999 Society of Photo-Optical Instrumentation Engineers.

Cell cycle arrest by Vpr in HIV-1 virions and insensitivity to antiretroviral agents

Expression of human immunodeficiency virus-type 1 (HIV-1) Vpr after productive infection of T cells induces cell cycle arrest in the G2 phase of the cell cycle. In the absence of de novo expression, HIV-1 Vpr packaged into virions still induced cell cycle arrest. Naturally noninfectious virus or virus rendered defective for infection by reverse transcriptase or protease inhibitors were capable of inducing Vpr-mediated cell cycle arrest. These results suggest a model whereby both infectious and noninfectious virions in vivo, such as those surrounding follicular dendritic cells, participate in immune suppression.

Human immunodeficiency virus type 1 Vpr interacts with HHR23A, a cellular protein implicated in nucleotide excision DNA repair

The human immunodeficiency virus type 1 (HIV-1) vpr gene is an evolutionarily conserved gene among the primate lentiviruses HIV-1, HIV-2, and simian immunodeficiency viruses. One of the unique functions attributed to the vpr gene product is the arrest of cells in the G2 phase of the cell cycle. Here we demonstrate that Vpr interacts physically with HHR23A, one member of an evolutionarily conserved gene family involved in nucleotide excision repair. Interaction of Vpr with HHR23A was initially identified through a yeast two-hybrid screen and was confirmed by the demonstration of direct binding between bacterially expressed recombinant and transiently expressed or chemically synthesized protein products. Visualization of HHR23A and Vpr by indirect immunofluorescence and confocal microscopy indicates that the two proteins colocalize at or about the nuclear membrane. We also map the Vpr-binding domain in HHR23A to a C-terminal 45-amino-acid region of the protein previously shown to have homology to members of the ubiquitination pathway. Overexpression of HHR23A and a truncated derivative which includes the Vpr-binding domain results in a partial alleviation of the G2 arrest induced by Vpr, suggesting that the interaction between Vpr and HHR23A is critical for cell cycle arrest induced by Vpr. These results provide further support for the hypothesis that Vpr interferes with the normal function of a protein or proteins involved in the DNA repair process and, thus, in the transmission of signals that allow cells to transit from the G2 to the M phase of the cell cycle.

Two new species of Acanthobothrium in Narcine entemedor (Rajiformes: Narcinidae) from the northwest coast of Guanacaste Peninsula, Costa Rica

This paper describes 2 new species of Acanthobothrium collected in Narcine entemedor from Cuajiniquil, Guanacaste Province, Costa Rica (10 degrees 57'N, 85 degrees 42'W). Acanthobothrium franus n. sp. averages 27 mm long, composed of 110 proglottides, has bothridial hooks 344-469 microns long, and 24-56 testes per proglottis. This new species resembles Acanthobothrium colombianum, Acanthobothrium coquimbensis. Acanthobothrium dujardini, Acanthobothrium lineatum, Acanthobothrium lintoni, and Acanthobothrium paulum. The new species differs from these 6 species by having a relatively shorter cirrus sac length not reaching the middle region of the proglottis. Additionally, A. franus differs from these species by having longer bothridia (627-1,408 microns vs. 299-391 microns for A. colombianum, 312-480 microns for A. coquimbensis, 240-560 microns for A. dujardini, 275-624 microns for A. lineatum, 389-720 microns for A. lintoni, and 300-880 microns for A. paulum), and larger bothridial hooks (344-469 microns vs. 175-193 microns, 120-192 microns, 180-210 microns, 118-216 microns, 108-230 microns, and 104-229 microns, respectively). Acanthobothrium inbiorium n. sp. averages 59 mm long, composed of 198 proglottides, has bothridial hooks 95-120 microns long, and possesses 44-73 testes per proglottis. Among species of Acanthobothrium, the new species resembles Acanthobothrium electricolum, Acanthobothrium dasybati, Acanthobothrium dighaensis, Acanthobothrium icelandicum, Acanthobothrium indicum, Acanthobothrium microcephalum, and Acanthobothrium wedli. The new species closely, resembles A. dasybati, but differs from that species in average strobila length and number of proglottides (58 microns long and 198 proglottides in A. inbiorium vs. 20 and 80 in A. dasybati, respectively). The new species can be distinguished from A. electricolum by having a wider scolex (450-900 microns vs. 189-252 microns), from A. dighaensis by having a narrower scolex (450-900 vs. 1,050-1,429), and from A. indicum by average strobilar length and number of proglottides (58 mm and 198 for A. inbiorium vs. 25 mm and 145 for A. indicum). Finally, A. inbiorium differs from A. icelandicum by having a shorter cirrus sac (122-285 for A. inbiorium vs. 380-410 for A. icelandicum), and A. microcephalum and A. wedli by having longer bothridia (an average of 603 microns vs. 447 microns for A. microcephalum and 350 microns for A. wedli), and fewer testes per proglottis (44-73 vs. 105-115 and 80-100, respectively). Morphological similarities suggest that some components of the eastern Pacific fauna of Acanthobothrium might share historical associations with the Caribbean and the western Pacific/Indian Ocean fauna.

Human immunodeficiency virus type 1 Vpr induces apoptosis following cell cycle arrest

The human immunodeficiency virus type 1 (HIV-1) vpr gene encodes a protein which induces arrest of cells in the G2 phase of the cell cycle. Here, we demonstrate that following the arrest of cells in G2, Vpr induces apoptosis in human fibroblasts, T cells, and primary peripheral blood lymphocytes. Analysis of various mutations in the vpr gene revealed that the extent of Vpr-induced G2 arrest correlated with the levels of apoptosis. However, the alleviation of Vpr-induced G2 arrest by treatment with the drug pentoxifylline did not abrogate apoptosis. Together these studies indicate that induction of G2 arrest, but not necessarily continued arrest in G2, was required for Vpr-induced apoptosis to occur. Finally, Vpr-induced G2 arrest has previously been correlated with inactivation of the Cdc2 kinase. Some models of apoptosis have demonstrated a requirement for active Cdc2 kinase for apoptosis to occur. Here we show that accumulation of the hypophosphorylated or active form of the Cdc2 kinase is not required for Vpr-induced apoptosis. These studies indicate that Vpr is capable of inducing apoptosis, and we propose that both the initial arrest of cells and subsequent apoptosis may contribute to CD4 cell depletion in HIV-1 disease.

Human immunodeficiency virus type 1 vpr gene induces phenotypic effects similar to those of the DNA alkylating agent, nitrogen mustard

The product of the human immunodeficiency virus type 1 (HIV-1) vpr gene induces cell cycle arrest in the G2 phase of the cell cycle and is characterized by an accumulation of the hyperphosphorylated form of cdc2 kinase. This phenotype is similar to the effect of DNA-damaging agents, which can also cause cells to arrest at G2. We previously reported that Vpr mimicked some of the effects of a DNA alkylating agent known as nitrogen mustard (HN2). Here we extend these earlier observations by further comparing the activation state of cdc2 kinase, the kinetics of G2 arrest, and the ability to reverse the arrest with chemical compounds known as methylxanthines. Infection of cells synchronized in the G1 phase of the cell cycle with a pseudotyped HIV-1 resulted in arrest at G2 within 12 h postinfection, before the first mitosis. Similar to that induced by HN2, Vpr-induced arrest led to a decrease in cdc2 kinase activity. Vpr-mediated G2 arrest was alleviated by methylxanthines at concentrations similar to those needed to reverse the G2 arrest induced by HN2, and cells proceeded apparently normally through at least one complete cell cycle. These results are consistent with the hypothesis that Vpr induces G2 arrest through pathways that are similar to those utilized by DNA-damaging agents.

HTLV-1 gene expression in adult T-cell leukemia cells elicits an NK cell response in vitro and correlates with cell rejection in SCID mice

Human T-cell leukemia virus type 1 (HTLV-1) is the etiologic agent of adult T-cell leukemia (ATL). We have previously shown that the ATL cell line, RV-ATL, formed tumors when inoculated into severe combined immunodeficient (SCID) mice. In contrast, the HTLV-1 in vitro-transformed cell line, SLB-1, was nontumorigenic in SCID mice. ATL cells contain HTLV-1 proviral DNA sequences but lack detectable viral gene expression, in contrast to HTLV-1 in vitro-transformed cells, which express all viral gene products. We investigated the role of HTLV-1 gene expression in tumorigenesis by superinfecting RV-ATL cells with HTLV-1. The resulting cell line, HT-1RV, expressed HTLV-1. Injection of HT-1RV cells into SCID mice resulted in a reduced tumorigenic phenotype compared to the parental RV-ATL cells. In vitro natural killer (NK) cell cytotoxicity assays revealed that cell lines expressing HTLV-1 gene products, SLB-1 and HT-1RV, were sensitive to NK cell cytolysis. In contrast, nonexpressing RV-ATL cells were resistant to NK cell cytolysis. These studies indicate that lack of viral gene expression allows HTLV-1-infected cells to elude detection by murine NK cells and increases tumorigenicity in SCID mice. Thus the loss of HTLV-1 gene expression in ATL cells may be an important mechanism by which leukemic cells escape immune surveillance in humans.

A new reporter system for detection of retroviral infection

We describe a novel reporter molecule, the murine surface antigen Thy-1, useful for immunoselection and detection of retrovirus-mediated transduction by flow cytometry. A cDNA encoding the murine thy-1 gene was isolated, and cell surface expression of its gene product was demonstrated. The Thy-1 glycoprotein was tested as a cell surface reporter molecule in the context of replication-defective and -competent retroviruses. Cells transduced via murine retroviral vectors carrying the thy-1 and the neomycin phosphotransferase genes express Thy-1 glycoprotein on their surfaces. The Thy-1 marker is potentially useful in gene transfer protocols because selection of transduced cells can be achieved by immunoselection with anti-Thy-1 antibodies shortly after infection with the retroviral vector. In addition, a human immunodeficiency virus type 1 (HIV-1) recombinant expressing Thy-1 is described, which is replication-competent and syncytium-inducing in human peripheral blood mononuclear cells (PBMCs) and immortalized CD4-positive cell lines. Cells infected with this HIV-1 recombinant express Thy-1 on their surfaces and can be detected and purified by fluorescence-activated cell sorting (FACS). Because of these properties, retroviruses expressing this genetic marker can be useful for studies in gene therapy and of the retroviral life-cycle.

Potential role of natural killer cells in controlling tumorigenesis by human T-cell leukemia viruses

Human T-cell leukemia virus (HTLV) is the etiologic agent of adult T-cell leukemia (ATL), a malignancy of T lymphocytes that is characterized by a long latency period after virus exposure. Intraperitoneal inoculation of severe combined immunodeficient (SCID) mice with HTLV-transformed cell lines and ATL tumor cells was employed to investigate the tumorigenic potential of HTLV type I (HTLV-I)-infected cells. In contrast to inoculation of ATL (RV-ATL) cells into SCID mice, which resulted in the formation of lymphomas, inoculation of HTLV-I- and HTLV-II-transformed cell lines (SLB-I and JLB-II cells, respectively) did not result in tumor formation. Immunosuppression of SCID mice, either by whole-body irradiation or by treatment with an antiserum, anti-asialo GM1 (alpha-AGM1), which transiently abrogates natural killer cell activity in vivo, was necessary to establish the growth of tumors derived from HTLV-transformed cell lines. PCR and flow cytometric studies reveal that HTLV-I-transformed cells are eliminated from the peritoneal cavities of inoculated mice by 3 days postinoculation; in contrast, RV-ATL cells persist and are detected until the mice succumb to lymphoma development. The differing behaviors of HTLV-infected cell lines and ATL tumor cells in SCID mice suggest that ATL cells have a higher tumorigenic potential in vivo than do HTLV-infected cell lines because of their ability to evade natural killer cell-mediated cytolysis.

Meeting a person with AIDS in the classroom: an evaluation

Meeting a person with AIDS in the classroom was evaluated to determine if it had an impact on students' perceived susceptibility to HIV infection and attitudes toward persons with AIDS. The meeting was incorporated into the Grade 9 AIDS education program of a school district in Nova Scotia. Four schools participated in this study. Two schools were randomly assigned to the treatment group, which met the person with AIDS, and the remaining two schools formed the comparison group. Measures of the two attitudinal variables were collected using a self-report questionnaire that was administered both prior to and two weeks after the educational intervention. Meeting a person with AIDS in the classroom had no measurable impact on students perceived susceptibility to HIV infection nor on their attitudes toward persons with AIDS. Suggestions for using the educational intervention more effectively and for further research are made.

Prism adaptation for esotropia with a distance-near disparity

A series of 64 patients who had surgery for esotropia with a distance-near disparity of at least 10 prism diopters was reviewed. Thirty-three patients were prism adapted for their distance deviation (PA distance). Thirty-one patients were prism adapted for near deviation (PA near). Both groups were divided into responders and nonresponders. In the PA distance group, 22 (67%) patients were responders. All responders had surgery for their prism-adapted angle. Postoperatively, 19 (86%) responders had fusion. Thirteen (68%) required bifocals to maintain fusion. In the PA near group, 21 (68%) patients were responders. All responders had surgery for their prism-adapted angle. Ninety-four percent of responders had fusion postoperatively. None needed bifocals for fusion postoperatively and none were overcorrected. The results show that those patients who were prism adapted for their near angle, responded with fusion, and had surgery for their full amount of esotropia at prism response obtained better postoperative fusion, without the need for a bifocal at near and without overcorrection at distance.

The diagnosis of amblyopia in cross-fixation

Customarily, it is taught that cross-fixation, in a patient with congenital esotropia, obviates the development of amblyopia. However, our clinical experience has shown significant amblyopia in 50% of cross-fixators. In our hands, the diagnosis of amblyopia is made based on the point at which alternation of fixation takes place. By this method, if there is equal visual acuity, alternation will occur at the midline with each eye. If amblyopia exists, the sound eye will continue to follow the target beyond midline, into abduction, before the poorer seeing eye picks up fixation. In order to test the reliability of this method, using Teller acuity cards as the standard, we compared estimates of objective and subjective vision in 25 consecutive patients with congenital esotropia and cross-fixation. Our findings suggest that there may be a significant prevalence of amblyopia in cross- fixating patients and that the point at which alternation of fixation occurs is a reliable means of detecting a difference in visual acuity between the two eyes.

Neuromyotonia in hereditary motor neuropathy

Two siblings with a distal motor neuropathy experienced cramping and difficulty in relaxing their muscles after voluntary contraction. Electromyographic recordings at rest revealed repetitive high voltage spontaneous electrical discharges that were accentuated after voluntary contraction and during ischaemia. Regional neuromuscular blockage with curare indicated hyperexcitability of peripheral nerve fibres and nerve block suggested that the ectopic activity originated in proximal segments of the nerve. Symptoms were improved with diphenylhydantoin, carbamazepine and tocainide.

The surgical overcorrection of intermittent exotropia

Many strabismus surgeons recommend an initial surgical overcorrection for intermittent exotropia. Others caution against overcorrection because of possible nasal suppression and amblyopia in children, or because of possible diplopia in adults. We reviewed the records of 69 patients who were initially overcorrected following surgery for an intermittent exotropia. The mean postoperative follow-up was 3.1 years. Eight patients (11.6%) had a persistent overcorrection of 3 prism diopters or more and three patients (4.3%) had persistent diplopia. Patients with a persistent overcorrection had a greater mean age (P less than .02) and a greater mean initial overcorrection (P less than .005) compared with the patients who were not overcorrected 3 delta or more. No child lost stereoacuity or developed amblyopia due to the overcorrection.

ERCC2: cDNA cloning and molecular characterization of a human nucleotide excision repair gene with high homology to yeast RAD3

Human ERCC2 genomic clones give efficient, stable correction of the nucleotide excision repair defect in UV5 Chinese hamster ovary cells. One clone having a breakpoint just 5' of classical promoter elements corrects only transiently, implicating further flanking sequences in stable gene expression. The nucleotide sequences of a cDNA clone and genomic flanking regions were determined. The ERCC2 translated amino acid sequence has 52% identity (73% homology) with the yeast nucleotide excision repair protein RAD3. RAD3 is essential for cell viability and encodes a protein that is a single-stranded DNA dependent ATPase and an ATP dependent helicase. The similarity of ERCC2 and RAD3 suggests a role for ERCC2 in both cell viability and DNA repair and provides the first insight into the biochemical function of a mammalian nucleotide excision repair gene.

Biochemical and genetic analysis of the Chinese hamster mutants irs1 and irs2 and their comparison to cultured ataxia telangiectasia cells

Two mutants of the Chinese hamster cell line V79-4 (irs1 and irs2) were previously isolated on the basis of their hypersensitivity (2- to 3-fold) to cell inactivation by ionizing radiation. One of these mutants, irs1, displays an unusual phenotype of cross-sensitivity to other varied genotoxic agents including UV light (2- to 3-fold), ethyl methanesulphonate (approximately 10-fold) and mitomycin C (approximately 60-fold). The possibility that these sensitivities might be due to more than one gene mutation in irs1 was investigated. Hybrids formed between irs1 and human lymphocytes were isolated in which the mitomycin C (MMC) sensitivity of irs1 was corrected by complementing human chromosomal material. These MMC-resistant hybrids and their subclones also showed concordant correction of the gamma-ray, UV and EMS sensitivities of irs1, suggesting that a single gene defect is most likely responsible for the phenotype of irs1. In addition it was shown that the MMC-sensitivity of irs1 is complemented by four CHO cell mutants (UV20, UV41, UV-1 and irs1SF), which also display extreme sensitivity to MMC. Mutants irs1, irs1SF and UV-1 define three new complementation groups for MMC sensitivity. The biochemical nature of the ionizing radiation sensitivity of irs1 and irs2 was also investigated. The production and repair of DNA single- and double-strand breaks were studied using the techniques of alkaline and neutral elution, respectively. Irs1 and irs2 both showed repair kinetics for each lesion that are indistinguishable from wild-type. Analysis of the rate of DNA synthesis following gamma-irradiation showed irs1 to have a dose-dependent inhibition similar to that of wild-type.(ABSTRACT TRUNCATED AT 250 WORDS)

CHO mutant UV61 removes (6-4) photoproducts but not cyclobutane dimers

The CHO mutant UV61 was previously assigned to complementation group 6 of UV-sensitive rodent cell mutants. UV61 is less sensitive to killing by UV radiation than mutants such as UV5, which is highly defective in the incision process that acts on UV-induced lesions. The D37 for cell survival is approximately 4 J/m2 for UV61, compared with 10 J/m2 for the parental AA8 line and approximately 2 J/m2 for UV5. Similarly, mutation induction at the hprt and aprt loci shows an intermediate response to UV61. In a post-replication recovery assay, the kinetics of maturation of pulse-labelled nascent DNA were normal after UV irradiation in UV61. Data from alkaline elution and alkaline unwinding assays showed that the rates of break accumulation and resealing, measured 0-120 min after irradiation, were also normal in the mutant. This repair incision correlated with the rapid, normal removal of pyrimidine(6-4)pyrimidone photoproducts in UV61 measured using a radioimmunoassay that is specific for this class of damage. In contrast, after exposure to 10 or 15 J/m2, no detectable removal of cyclobutane dimers from DNA was found in UV61 while AA8 cells removed 32% by 24 h. We suggest that the mutation in UV61 specifically lowers the affinity of a repair protein for cyclobutane dimers, which are also inefficiently removed from the bulk DNA of normal CHO cells. The resistance of UV61 to killing by the direct acting chemical 7-bromomethylbenz[a]anthracene was only slightly greater than that of UV5, indicating defective repair of bulky chemical adducts in addition to cyclobutane dimers.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular cloning and biological characterization of a human gene, ERCC2, that corrects the nucleotide excision repair defect in CHO UV5 cells

The UV-sensitive Chinese hamster ovary (CHO) cell line UV5, which is defective in the incision step of nucleotide excision repair, was used to identify and clone a complementing human gene, ERCC2, and to study the repair process. Genomic DNA from a human-hamster hybrid cell line was sheared and cotransferred with pSV2gpt plasmid DNA into UV5 cells to obtain five primary transformants. Transfer of sheared DNA from one primary transformant resulted in a secondary transformant expressing both gpt and ERCC2. The human repair gene was identified with a probe for Alu-family repetitive sequences. For most primary, secondary, and cosmid transformants, survival after UV exposure showed a return to wild-type levels of resistance. The levels of UV-induced mutation at the aprt locus for secondary and cosmid transformants varied from 50 to 130% of the wild-type level. Measurements of the initial rate of UV-induced strand incision by alkaline elution indicated that, whereas the UV5 rate was 3% of the wild-type level, rates of cosmid-transformed lines were similar to that of the wild type, and the secondary transformant rate was about 165% of the wild-type rate. Analysis of overlapping cosmids determined that ERCC2 is between 15.5 and 20 kilobases and identified a closely linked gpt gene. Cosmids were obtained with functional copies of both ERCC2 and gpt. ERCC2 corrects only the first of the five CHO complementation groups of incision-defective mutants.

Genotoxicity of compounds from cooked beef in repair-deficient CHO cells versus Salmonella mutagenicity

A series of compounds isolated on the basis of their mutagenicity in the Ames/Salmonella reversion assay were previously identified in fried beef and chemically synthesized for further evaluation. In this study three of these compounds were tested for genotoxic effects in the UV5 line of Chinese hamster ovary (CHO) cells, which is deficient in nucleotide excision repair. Both 2-amino-3,4-dimethyl-imidazo]4,5-f]quinoline (MeIQ) and 2-amino-3,8-dimethyl-imidazo[4,5-f]quinoxaline (MeIQx) gave very weak responses for cell killing, hprt mutation induction and sister chromatid exchange. These effects occurred at doses in the range of 100-800 micrograms/ml (approximately solubility limit), and dose-dependent increases were not observed. Induction of chromosomal aberrations did not occur with either compound. Nor did either of these compounds produce differential cytotoxicity in normal CHO cells versus UV5 cells, indicating that potentially repairable DNA damage was not responsible for the observed cell killing. In contrast to these results, 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine (PhIP), which constitutes greater than 90% of the mass of bacterial mutagens in beef, was strongly positive for all endpoints at doses in the range 1-3 micrograms/ml. PhIP also gave marked differential cytotoxicity (ratio of 6) and cell survival curves that were strongly dependent on repair capacity. Because PhIP is 50- to 300-fold less mutagenic than MeIQ and MeIQx in Salmonella TA1538, these results point to major differences between the bacterial and mammalian assays in terms of the relative potency of these food-related compounds.

Identification of nucleotide-excision-repair genes on human chromosomes 2 and 13 by functional complementation in hamster-human hybrids

The CHO UV-sensitive mutants UV24 and UV135 (complementation groups 3 and 5, respectively) are defective in nucleotide excision repair. After fusing each mutant with human lymphocytes, resistant hybrid clones showing genetic complementation were isolated by repeated exposure to UV radiation. Using a combination of isozyme markers, DNA probes, and cytogenetic methods to analyze the primary hybrids and their subclones, correction of the repair defect was shown to be correlated with the presence of a specific human chromosome in each case. Chromosome 2 corrected UV24, and the gene responsible was designated ERCC3. Line UV135 was corrected by human chromosome 13 and the gene designated ERCC5. The UV-sensitive mouse cell line, Q31, was shown not to complement UV135 and thus appears to be mutated in the same genetic locus (homologous to ERCC5) as UV135. Breakage of complementing chromosomes with retention of the genes correcting repair defects allowed the following provisional assignments: regional localization of ERCC5 to 13q14-q34, exclusion of ERCC3 from the region of chromosome 2 distal to p23, and relief of the ambiguity of ACP1 assignment (2p23 or 2p25) to 2p23 proximal to MDH1.

Recent progress with the DNA repair mutants of Chinese hamster ovary cells

Repair-deficient mutants of Chinese hamster ovary (CHO) cells are being used to identify human genes that correct the repair defects and to study mechanisms of DNA repair and mutagenesis. Five independent tertiary DNA transformants were obtained from the EM9 mutant, which is noted for its very high sister-chromatid exchange frequencies. In these clones a human DNA sequence was identified that correlated with the resistance of the cells to chlorodeoxyuridine (CldUrd). After EcoRI digestion, Southern transfer, and hybridization of transformant DNAs with the BLUR-8 Alu family sequence, a common fragment of 25-30 kilobases (kb) was present. Since the DNA molecules used to produce these transformants were sheared to less than 50 kb in size, the correcting gene should be small enough to clone in a cosmid vector. Using drug-resistance markers to select for hybrids after fusion, we have done complementation experiments with ultraviolet light (u.v.)-sensitive mutants and have identified a sixth complementation group, line UV61. Additionally, CHO mutants UV27-1 and MMC-2, isolated in other laboratories, were found to belong to UV group 3, which is represented by line UV24. To study the behaviour of transfected DNA molecules in repair-deficient cells, we treated plasmid pSV2gpt with either u.v. radiation or cis-diamminedichloroplatinum(II) (cis-DDP) and introduced the damaged DNA into normal CHO cells (AA8) and mutants UV4 and UV5. Unrepaired damage to the plasmid was indicated by loss of colony-forming ability of the transfected cells in selective medium containing mycophenolic acid. With u.v. damage, the differential survival of the cell lines was similar to that seen when whole cells are treated with u.v. However, with cis-DDP damage, mutant UV4 did not exhibit the extreme hypersensitivity (50-fold) that occurs when cells are treated. This result suggests that UV4 cells may be able to repair cross-links in transfected DNA.