Continuing benefits of the Montreal Protocol and protection of the stratospheric ozone layer for human health and the environment

The protection of Earth's stratospheric ozone (O3) is an ongoing process under the auspices of the universally ratified Montreal Protocol and its Amendments and adjustments. A critical part of this process is the assessment of the environmental issues related to changes in O3. The United Nations Environment Programme's Environmental Effects Assessment Panel provides annual scientific evaluations of some of the key issues arising in the recent collective knowledge base. This current update includes a comprehensive assessment of the incidence rates of skin cancer, cataract and other skin and eye diseases observed worldwide; the effects of UV radiation on tropospheric oxidants, and air and water quality; trends in breakdown products of fluorinated chemicals and recent information of their toxicity; and recent technological innovations of building materials for greater resistance to UV radiation. These issues span a wide range of topics, including both harmful and beneficial effects of exposure to UV radiation, and complex interactions with climate change. While the Montreal Protocol has succeeded in preventing large reductions in stratospheric O3, future changes may occur due to a number of natural and anthropogenic factors. Thus, frequent assessments of potential environmental impacts are essential to ensure that policies remain based on the best available scientific knowledge.

Effects of UV radiation on natural and synthetic materials

The deleterious effects of solar ultraviolet (UV) radiation on construction materials, especially wood and plastics, and the consequent impacts on their useful lifetimes, are well documented in scientific literature. Any future increase in solar UV radiation and ambient temperature due to climate change will therefore shorten service lifetimes of materials, which will require higher levels of stabilisation or other interventions to maintain their lifetimes at the present levels. The implementation of the Montreal Protocol and its amendments on substances that deplete the ozone layer, controls the solar UV-B radiation received on Earth. This current quadrennial assessment provides a comprehensive update on the deleterious effects of solar UV radiation on the durability of natural and synthetic materials, as well as recent innovations in better stabilising of materials against solar UV radiation-induced damage. Pertinent emerging technologies for wood and plastics used in construction, composite materials used in construction, textile fibres, comfort fabric, and photovoltaic materials, are addressed in detail. Also addressed are the trends in technology designed to increase sustainability via replacing toxic, unsustainable, legacy additives with 'greener' benign substitutes that may indirectly affect the UV stability of the redesigned materials. An emerging class of efficient photostabilisers are the nanoscale particles that include oxide fillers and nanocarbons used in high-performance composites, which provide good UV stability to materials. They also allow the design of UV-shielding fabric materials with impressive UV protection factors. An emerging environmental issue related to the photodegradation of plastics is the generation of ubiquitous micro-scale particles from plastic litter exposed to solar UV radiation.

The Montreal Protocol and the fate of environmental plastic debris

Microplastics (MPs) are an emerging class of pollutants in air, soil and especially in all aquatic environments. Secondary MPs are generated in the environment during fragmentation of especially photo-oxidised plastic litter. Photo-oxidation is mediated primarily by solar UV radiation. The implementation of the Montreal Protocol and its Amendments, which have resulted in controlling the tropospheric UV-B (280-315 nm) radiation load, is therefore pertinent to the fate of environmental plastic debris. Due to the Montreal Protocol high amounts of solar UV-B radiation at the Earth's surface have been avoided, retarding the oxidative fragmentation of plastic debris, leading to a slower generation and accumulation of MPs in the environment. Quantifying the impact of the Montreal Protocol in reducing the abundance of MPs in the environment, however, is complicated as the role of potential mechanical fragmentation of plastics under environmental mechanical stresses is poorly understood.

Oxidation and fragmentation of plastics in a changing environment; from UV-radiation to biological degradation

Understanding the fate of plastics in the environment is of critical importance for the quantitative assessment of the biological impacts of plastic waste. Specially, there is a need to analyze in more detail the reputed longevity of plastics in the context of plastic degradation through oxidation and fragmentation reactions. Photo-oxidation of plastic debris by solar UV radiation (UVR) makes material prone to subsequent fragmentation. The fragments generated following oxidation and subsequent exposure to mechanical stresses include secondary micro- or nanoparticles, an emerging class of pollutants. The paper discusses the UV-driven photo-oxidation process, identifying relevant knowledge gaps and uncertainties. Serious gaps in knowledge exist concerning the wavelength sensitivity and the dose-response of the photo-fragmentation process. Given the heterogeneity of natural UV irradiance varying from no exposure in sediments to full UV exposure of floating, beach litter or air-borne plastics, it is argued that the rates of UV-driven degradation/fragmentation will also vary dramatically between different locations and environmental niches. Biological phenomena such as biofouling will further modulate the exposure of plastics to UV radiation, while potentially also contributing to degradation and/or fragmentation of plastics independent of solar UVR. Reductions in solar UVR in many regions, consequent to the implementation of the Montreal Protocol and its Amendments for protecting stratospheric ozone, will have consequences for global UV-driven plastic degradation in a heterogeneous manner across different geographic and environmental zones. The interacting effects of global warming, stratospheric ozone and UV radiation are projected to increase UV irradiance at the surface in localized areas, mainly because of decreased cloud cover. Given the complexity and uncertainty of future environmental conditions, this currently precludes reliable quantitative predictions of plastic persistence on a global scale.

Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: UNEP Environmental Effects Assessment Panel, Update 2021

The Environmental Effects Assessment Panel of the Montreal Protocol under the United Nations Environment Programme evaluates effects on the environment and human health that arise from changes in the stratospheric ozone layer and concomitant variations in ultraviolet (UV) radiation at the Earth’s surface. The current update is based on scientific advances that have accumulated since our last assessment (Photochem and Photobiol Sci 20(1):1–67, 2021). We also discuss how climate change affects stratospheric ozone depletion and ultraviolet radiation, and how stratospheric ozone depletion affects climate change. The resulting interlinking effects of stratospheric ozone depletion, UV radiation, and climate change are assessed in terms of air quality, carbon sinks, ecosystems, human health, and natural and synthetic materials. We further highlight potential impacts on the biosphere from extreme climate events that are occurring with increasing frequency as a consequence of climate change. These and other interactive effects are examined with respect to the benefits that the Montreal Protocol and its Amendments are providing to life on Earth by controlling the production of various substances that contribute to both stratospheric ozone depletion and climate change.

Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: UNEP Environmental Effects Assessment Panel, Update 2020

This assessment by the Environmental Effects Assessment Panel (EEAP) of the United Nations Environment Programme (UNEP) provides the latest scientific update since our most recent comprehensive assessment (Photochemical and Photobiological Sciences, 2019, 18, 595-828). The interactive effects between the stratospheric ozone layer, solar ultraviolet (UV) radiation, and climate change are presented within the framework of the Montreal Protocol and the United Nations Sustainable Development Goals. We address how these global environmental changes affect the atmosphere and air quality; human health; terrestrial and aquatic ecosystems; biogeochemical cycles; and materials used in outdoor construction, solar energy technologies, and fabrics. In many cases, there is a growing influence from changes in seasonality and extreme events due to climate change. Additionally, we assess the transmission and environmental effects of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is responsible for the COVID-19 pandemic, in the context of linkages with solar UV radiation and the Montreal Protocol.

Environmental effects of stratospheric ozone depletion, UV radiation and interactions with climate change: UNEP Environmental Effects Assessment Panel, update 2019

This assessment, by the United Nations Environment Programme (UNEP) Environmental Effects Assessment Panel (EEAP), one of three Panels informing the Parties to the Montreal Protocol, provides an update, since our previous extensive assessment (Photochem. Photobiol. Sci., 2019, 18, 595-828), of recent findings of current and projected interactive environmental effects of ultraviolet (UV) radiation, stratospheric ozone, and climate change. These effects include those on human health, air quality, terrestrial and aquatic ecosystems, biogeochemical cycles, and materials used in construction and other services. The present update evaluates further evidence of the consequences of human activity on climate change that are altering the exposure of organisms and ecosystems to UV radiation. This in turn reveals the interactive effects of many climate change factors with UV radiation that have implications for the atmosphere, feedbacks, contaminant fate and transport, organismal responses, and many outdoor materials including plastics, wood, and fabrics. The universal ratification of the Montreal Protocol, signed by 197 countries, has led to the regulation and phase-out of chemicals that deplete the stratospheric ozone layer. Although this treaty has had unprecedented success in protecting the ozone layer, and hence all life on Earth from damaging UV radiation, it is also making a substantial contribution to reducing climate warming because many of the chemicals under this treaty are greenhouse gases.

An xQTL map integrates the genetic architecture of the human brain's transcriptome and epigenome

We report a multi-omic resource generated by applying quantitative trait locus (xQTL) analyses to RNA sequence, DNA methylation and histone acetylation data from the dorsolateral prefrontal cortex of 411 older adults who have all three data types. We identify SNPs significantly associated with gene expression, DNA methylation and histone modification levels. Many of these SNPs influence multiple molecular features, and we demonstrate that SNP effects on RNA expression are fully mediated by epigenetic features in 9% of these loci. Further, we illustrate the utility of our new resource, xQTL Serve, by using it to prioritize the cell type(s) most affected by an xQTL. We also reanalyze published genome wide association studies using an xQTL-weighted analysis approach and identify 18 new schizophrenia and 2 new bipolar susceptibility variants, which is more than double the number of loci that can be discovered with a larger blood-based expression eQTL resource.

Mitochondrial-targeted peptide rapidly improves mitochondrial energetics and skeletal muscle performance in aged mice

Mitochondrial dysfunction plays a key pathogenic role in aging skeletal muscle resulting in significant healthcare costs in the developed world. However, there is no pharmacologic treatment to rapidly reverse mitochondrial deficits in the elderly. Here, we demonstrate that a single treatment with the mitochondrial-targeted peptide SS-31 restores in vivo mitochondrial energetics to young levels in aged mice after only one hour. Young (5 month old) and old (27 month old) mice were injected intraperitoneally with either saline or 3 mg kg(-1) of SS-31. Skeletal muscle mitochondrial energetics were measured in vivo one hour after injection using a unique combination of optical and (31) P magnetic resonance spectroscopy. Age-related declines in resting and maximal mitochondrial ATP production, coupling of oxidative phosphorylation (P/O), and cell energy state (PCr/ATP) were rapidly reversed after SS-31 treatment, while SS-31 had no observable effect on young muscle. These effects of SS-31 on mitochondrial energetics in aged muscle were also associated with a more reduced glutathione redox status and lower mitochondrial H2 O2 emission. Skeletal muscle of aged mice was more fatigue resistant in situ one hour after SS-31 treatment, and eight days of SS-31 treatment led to increased whole-animal endurance capacity. These data demonstrate that SS-31 represents a new strategy for reversing age-related deficits in skeletal muscle with potential for translation into human use.

An accelerated exposure and testing apparatus for building joint sealants

The design, fabrication, and implementation of a computer-controlled exposure and testing apparatus for building joint sealants are described in this paper. This apparatus is unique in its ability to independently control and monitor temperature, relative humidity, ultraviolet (UV) radiation, and mechanical deformation. Each of these environmental factors can be controlled precisely over a wide range of conditions during periods of a month or more. Moreover, as controlled mechanical deformations can be generated, in situ mechanical characterization tests can be performed without removing specimens from the chamber. Temperature and humidity were controlled during our experiments via a precision temperature regulator and proportional mixing of dry and moisture-saturated air; while highly uniform UV radiation was attained by attaching the chamber to an integrating sphere-based radiation source. A computer-controlled stepper motor and a transmission system were used to provide precise movement control. The reliability and effectiveness of the apparatus were demonstrated on a model sealant material. The results clearly show that this apparatus provides an excellent platform to study the long-term durability of building joint sealants.

Viscoelastic Characterization of Polymers Using Dynamic Instrumented Indentation

Dynamic nanoindentation was performed on a poly(methyl methacrylate, PMMA), and two different poly(dimethyl siloxane, PDMS) samples having different crosslink densities. Comparison was made between dynamic nanoindentation and rheological instrumentation measurements in the glassy and rubbery plateau regions of polymeric materials. Excellent agreement between bulk rheological data and dynamic nanoindentation data was observed for the two glassy materials and the less compliant of the two PDMS samples. Results were divergent for the more compliant PDMS sample.

Design, fabrication, and implementation of thermally driven outdoor testing devices for building joint sealants

The paper describes the development, implementation, and testing of two thermally driven outdoor exposure instruments. These devices are unique in their ability to impose field generated thermally induced strain on sealant specimens while monitoring their resulting load and displacement. The instruments combine a fixed wood and steel supporting frame with a moving polyvinyl chloride frame, and employ differences in the coefficients of thermal expansion between the supporting frame and moving frame to induce strain on the sealant specimens. Two different kinds of instruments have been fabricated, "winter/tension" and "winter/compression" designs. In the winter/tension design, the thermally induced dimensional change is directly transferred to the specimens; while in the winter/compression design, the samples are loaded in an opposite direction with the dimensional change. Both designs are instrumented to monitor load and displacement and are built so that the strain on the specimen does not exceed ±25% over the range of temperatures expected in Gaithersburg, MD. Additionally, a weather station is colocated with the device to record environmental conditions in 1 min intervals. This combination of weather information with mechanical property data enables a direct link between environmental conditions and the corresponding sealant response. The reliability and effectiveness of these instruments are demonstrated with a typical sealant material. The results show that the instruments work according to the design criteria and provide a meaningful quantitative platform to monitor the mechanical response of sealant exposed to outdoor weathering.

Neurotoxicity of domoic Acid in cerebellar granule neurons in a genetic model of glutathione deficiency

This study investigated the role of cellular antioxidant defense mechanisms in modulating the neurotoxicity of domoic acid (DomA), by using cerebellar granule neurons (CGNs) from mice lacking the modifier subunit of glutamate-cysteine ligase (Gclm). Glutamate-cysteine ligase (Glc) catalyzes the first and rate-limiting step in glutathione (GSH) biosynthesis. CGNs from Gclm (-/-) mice have very low levels of GSH and are 10-fold more sensitive to DomA-induced toxicity than CGNs from Gclm (+/+) mice. GSH ethyl ester decreased, whereas the Gcl inhibitor buthionine sulfoximine increased DomA toxicity. Antagonists of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate receptors and of N-methyl-D-aspartate (NMDA) receptors blocked DomA toxicity, and NMDA receptors were activated by DomA-induced l-glutamate release. The differential susceptibility of CGNs to DomA toxicity was not due to a differential expression of ionotropic glutamate receptors, as evidenced by similar calcium responses and L-glutamate release in the two genotypes. A calcium chelator and several antioxidants antagonized DomA-induced toxicity. DomA caused a rapid decrease in cellular GSH, which preceded toxicity, and the decrease was primarily due to DomA-induced GSH efflux. DomA also caused an increase in oxidative stress as indicated by increases in reactive oxygen species and lipid peroxidation, which was subsequent to GSH efflux. Astrocytes from both genotypes were resistant to DomA toxicity and presented a diminished calcium response to DomA and a lack of DomA-induced L-glutamate release. Because polymorphisms in the GCLM gene in humans are associated with low GSH levels, such individuals, as well as others with genetic conditions or environmental exposures that lead to GSH deficiency, may be more susceptible to DomA-induced neurotoxicity.

Development of A High Throughput Method Incorporating Traditional Analytical Devices

A high-throughput (high throughput is the ability to process large numbers of samples) and companion informatics system has been developed and implemented. High throughput is defined as the ability to autonomously evaluate large numbers of samples, while an informatics system provides the software control of the physical devices, in addition to the organization and storage of the generated electronic data. This high throughput system includes both an ultra-violet and visible light spectrometer (UV-Vis) and a Fourier transform infrared spectrometer (FTIR) integrated with a multi sample positioning table. This method is designed to quantify changes in polymeric materials occurring from controlled temperature, humidity and high flux UV exposures. The integration of the software control of these analytical instruments within a single computer system is presented. Challenges in enhancing the system to include additional analytical devices are discussed.

The effects of Neotrofin on septodentate sprouting after unilateral entorhinal cortex lesions in rats

PURPOSE

Recent research on the purine derivative of hypoxanthine Neotrofin (4-[[3-(1,6-dihydro-6-oxo-9-purin-9-yl)-1-oxopropyl]amino]benzoic acid; AIT-082) has indicated that Neotrofin treatment elevates the mRNA levels of various neurotrophic factors, including nerve growth factor (NGF), in the CNS. Several previous studies have indicated that NGF may regulate septodentate sprouting after entorhinal cortex lesions in rats. Thus, the objective of this investigation was to determine whether Neotrofin treatment would enhance lesion-induced septodentate sprouting from 4 to 15 days postlesion.

METHODS

Sham-operated rats or rats with EC lesions were injected (i.p.) with either Neotrofin (30 mg/kg) or saline (0.9%) immediately after surgery and every day thereafter until the end of the treatment regimen. Septodentate sprouting, as indicated by intensity of acetylcholinesterase (AChE) label in the dentate gyrus, was assessed with optical densitometry.

RESULTS

We observed that Neotrofin elevated the AChE-label in the outer molecular layer of the ventral dentate gyrus at 4 days postlesion and of the dorsal dentate gyrus at 15 days postlesion.

CONCLUSIONS

Neotrofin appears to have exerted limited stimulatory effects on lesion-induced sprouting by a cholinergic pathway.

Enhanced acetaminophen hepatotoxicity in transgenic mice overexpressing BCL-2

Mitochondria play an important role in the cell death induced by many drugs, including hepatotoxicity from overdose of the popular analgesic, acetaminophen (APAP). To investigate mitochondrial alterations associated with APAP-induced hepatotoxicity, the subcellular distribution of proapoptotic BAX was determined. Based on the antiapoptotic characteristics of BCL-2, we further hypothesized that if a BAX component was evident then BCL-2 overexpression may be hepatoprotective. Mice, either with a human bcl-2 transgene (-/+) or wild-type mice (WT; -/-), were dosed with 500 or 600 mg/kg (i.p.) APAP or a nonhepatotoxic isomer, N-acetyl-m-aminophenol (AMAP). Immunoblot analyses indicated increased mitochondrial BAX-beta content very early after APAP or AMAP treatment. This was paralleled by disappearance of BAX-alpha from the cytosol of APAP treated animals and, to a lesser extent, with AMAP treatment. Early pathological evidence of APAP-induced zone 3 necrosis was seen in bcl-2 (-/+) mice, which progressed to massive panlobular necrosis with hemorrhage by 24 h. In contrast, WT mice dosed with APAP showed a more typical, and less severe, centrilobular necrosis. AMAP-treated bcl-2 (-/+) mice displayed only early microvesicular steatosis without progression to extensive necrosis. Decreased complex III activity, evident as early as 6 h after treatment, correlated well with plasma enzyme activities at 24 h (AST r(2) = 0.89, ALT r(2) = 0.87) thereby confirming a role for mitochondria in APAP-mediated hepatotoxicity. In conclusion, these data suggest for the first time that BAX may be an early determinant of APAP-mediated hepatotoxicity and that BCL-2 overexpression unexpectedly enhances APAP hepatotoxicity.

Gonadotropin regulation of glutathione synthesis in the rat ovary

Glutathione (GSH), an antioxidant and conjugator of electrophilic toxicants, prevents toxicant-mediated destruction of ovarian follicles and oocytes. Ovarian GSH has previously been shown to change with estrous cycle stage in rats, suggesting that the gonadotropin hormones may regulate ovarian GSH synthesis. The present studies tested the hypotheses that [1] estrous cycle-related changes in ovarian GSH result from cyclic changes in protein and mRNA expression of the rate-limiting enzyme in GSH synthesis, glutamate cysteine ligase (GCL, also called gamma-glutamylcysteine synthetase), and [2] that these changes result from gonadotropin-mediated regulation of GCL subunit expression. In the first experiment, ovaries were harvested from cycling adult female rats on each stage of the estrous cycle. In the second experiment immature female rats were injected with pregnant mare's serum gonadotropin (PMSG) to stimulate follicular development or with vehicle and killed 8, 24, or 48 h later. In both experiments the ovaries were harvested for [1] total GSH assay, [2] Western analysis for GCL catalytic (GCLc) and regulatory (GCLm) subunit protein levels, or [3] Northern analysis for Gclc and Gclm mRNA levels. Ovarian GSH concentrations and Gclc and Gclm mRNA levels, but not GCL subunit protein levels, varied significantly with estrous cycle stage. PMSG administration significantly increased ovarian GSH concentrations 24 and 48 h later. GCLm protein levels increased significantly at 24 h and 48 h following PMSG. GCLc protein levels did not increase significantly following PMSG. Gcl subunit mRNA levels were not significantly increased at any time point by the planned ANOVA; however, an increase in Gelc at 48 h was identified by t-testing. These results support the hypothesis that gonadotropins regulate ovarian GSH synthesis by modulating GCL subunit expression.

Tissue specific changes in the expression of glutamate-cysteine ligase mRNAs in mice exposed to methylmercury

Glutamate-cysteine ligase (GLCL), the rate-limiting enzyme in glutathione (GSH) synthesis is composed of two subunits, a catalytic (GLCLc) and a regulatory subunit (GLCLr). These two subunits are known to be differentially regulated in vitro, in different cell types and in response to various xenobiotic exposures. In this study, we examined whether these two subunits can also be differentially regulated in vivo. We found that GLCLc and GLCLr are differentially regulated at the transcriptional level in a tissue-dependent manner in female mice treated with methylmercury (MeHg). MeHg caused a downregulation of both subunit mRNAs in the liver, upregulation of both subunit mRNAs in the kidney and upregulation of only the catalytic subunit mRNA in the small intestine of female mice treated with a single dose of MeHg (6 mg/kg) by intraperitoneal injection. These results suggest that GLCLc and GLCLr can be differentially regulated in vivo, and that this regulation is tissue dependent in the mouse.

A model for predicting chloride concentrations in river water in a relatively unpolluted catchment in north-east Scotland

The River Dee is an oligotrophic soft water system, in the NE of Scotland, with a catchment area of approximately 2100 km2. The river rises in the Cairngorm Mountains and enters the North Sea at Aberdeen, approximately 140 km from its source. Water chemical quality data was collected every 2 weeks over 12 months for 59 sites distributed throughout the catchment. River water chloride concentrations increased significantly from west to east. In depth investigation of the relationship with distance from the coast revealed the significant difference in spatial distribution of river water chloride concentrations between upland and lowland/agricultural areas, suggesting the possible importance of agricultural practices to streamwater chloride concentrations. Thirty of the sample sites are independent and have been used to develop a simple model for prediction of streamwater Cl- concentration throughout the catchment. The model has been validated using data from the remaining sub-catchments. The model shows that mean Cl- concentration may be reliably predicted from distance from the coast and the percentage of improved grassland and arable land cover in each sub-catchment (r2 = 0.98). It is postulated that the land use effects may be partly due to the evolved link between landuse and catchment altitude characteristics, rather than just the direct effect of applied potassium chloride fertiliser on agricultural land. It was noted that there was insufficient forestry within the River Dee Catchment to reliably include % forest cover in the model.

Modulation of glutathione and glutamate-L-cysteine ligase by methylmercury during mouse development

The antioxidant tripeptide glutathione has been proposed to be important in defense against oxidative stress and heavy metal toxicity. We evaluated alterations in glutathione regulation and synthesis associated with low-level chronic methylmercury (MeHg) exposure in the developing mouse fetus. Female C57Bl/6 mice were given 0, 3, or 10 ppm MeHg in the drinking water for 2 weeks prior to breeding and throughout pregnancy. Fetuses were collected on gestational days (gd) 12 and 16. Total glutathione, reduced glutathione (GSH), oxidized glutathione (GSSR), and glutamate-L-cysteine ligase (Glcl) activity were assessed in yolk sacs and fetuses at gd 16. Western and Northern blots for Glcl-catalytic (Glclc) and Glcl-regulatory (Glclr) subunits were performed on gd 12 and gd 16 fetuses. There were no changes in total glutathione in gd 16 mouse fetuses with exposure, but there were dose-related decreases in GSH and increases in GSSR. In contrast, visceral yolk sacs exhibited an increase in total glutathione in the low-dose groups, but no changes in the high-dose group. There were no changes in Glcl activity in fetuses, but there was a 2-fold increase in Glcl activity in yolk sacs from both low-dose and high-dose groups. There was a 2-fold induction in GLCLC: mRNA and protein in the gd 16 yolk sacs at both 3 and 10 ppm MeHg. No treatment-related changes in Glclr protein in either gd 12 or gd 16 yolk sacs or fetuses were found. Thus, the yolk sac is capable of up-regulating Glclc and GSH synthetic capacity in response to MeHg exposure. This increase appears to be sufficient to resist MeHg-induced GSH depletion in the yolk sac; however fetal glutathione redox status is compromised with exposure to 10 ppm MeHg.

Induction of glutamate-cysteine ligase (gamma-glutamylcysteine synthetase) in the brains of adult female mice subchronically exposed to methylmercury

Methylmercury (MeHg) is widely known for its potent neurotoxic properties. One proposed mechanism of action of MeHg relates to its high affinity for sulfhydryl groups, especially those found on glutathione (GSH) and proteins. Previous studies have shown that acute MeHg exposure results in an increase in the mRNA for the rate-limiting enzyme in GSH synthesis, glutamate-cysteine ligase (GLCL) (also known as gamma-glutamylcysteine synthetase). In this study, we evaluated the effects of subchronic (12-week) MeHg exposure at 0, 3 or 10 ppm in the drinking water on GSH levels, GLCL catalytic (GLCLC) and regulatory subunit mRNA and protein levels, and GLCL activity in brain, liver and kidney tissue of C57B1/6 female mice. Contrary to previous findings in rats, there were no changes in GSH concentration in any of the tissues examined. However, there was an increase in GLCLC protein in the brain, which was accompanied by a 30% increase in GLCL activity. We conclude that up-regulation of GSH synthetic capacity in the brains of mice is a sensitive biomarker of subchronic MeHg exposure.

The role of intracellular glutathione in methylmercury-induced toxicity in embryonic neuronal cells

Previous studies indicate that the ability of cells to up-regulate levels of intracellular glutathione (GSH) synthesis may determine their sensitivity to MeHg exposure. The purpose of the current study is two-fold. First, we determined whether the vulnerability of the developing central nervous system (CNS) to MeHg lies in its intracellular GSH content. The intracellular GSH content and the activity of gamma-glutamyl cysteine synthetase (GCS) were determined with and without MeHg exposure in primary cultures of rat embryonic CNS cells. In addition, the effect of GSH modulation on MeHg-induced cytotoxicity was determined. Second, we characterized the mechanism of GCS regulation, initially by studying the GCS heavy chain subunit (GCS-HC). Primary embryonic limb bud cells were used as a reference cell type for comparing the response of CNS cells. The results indicate that constitutive intracellular GSH content, GCS activity, and GCS-HC mRNA and protein levels of CNS cells were approximately ten-, two-, five-, and ten-fold higher, respectively, than those in limb bud cells. A dose-dependent increase in GSH levels and GCS activity was observed in CNS and limb bud cells following 1 and 2 microM MeHg exposure for 20 hr. Further characterization of GCS up-regulation in CNS cells showed that the increase in GCS activity following MeHg exposure, unlike limb bud cells, was not accompanied by an elevation of GCS-HC mRNA and protein levels. Pretreatment with N-acetylcysteine led to a significant increase in intracellular GSH, while L-buthionine-(S,R)-sulfoximine (BSO) resulted in decreased GSH levels, however neither pretreatment had a significant impact on MeHg-induced cytotoxicity in either cell type. Our results suggest that although oxidative stress may mediate aspects of MeHg toxicity, disruption of GSH homeostasis alone is not responsible for the sensitivity of embryonic CNS cells to MeHg.

Functions of the Caenorhabditis elegans regulatory myosin light chain genes mlc-1 and mlc-2

Caenorhabditis elegans contains two muscle regulatory myosin light chain genes, mlc-1 and mlc-2. To determine their in vivo roles, we identified deletions that eliminate each gene individually and both genes in combination. Functions of mlc-1 are redundant to those of mlc-2 in both body-wall and pharyngeal muscle. mlc-1(0) mutants are wild type, but mlc-1(0) mlc-2(0) double mutants arrest as incompletely elongated L1 larvae, having both pharyngeal and body-wall muscle defects. Transgenic copies of either mlc-1(+) or mlc-2(+) rescue all defects of mlc-1(0) mlc-2(0) double mutants. mlc-2 is redundant to mlc-1 in body-wall muscle, but mlc-2 performs a nearly essential role in the pharynx. Approximately 90% of mlc-2(0) hermaphrodites arrest as L1 larvae due to pharyngeal muscle defects. Lethality of mlc-2(0) mutants is sex specific, with mlc-2(0) males being essentially wild type. Four observations suggest that hermaphrodite-specific lethality of mlc-2(0) mutants results from insufficient expression of the X-linked mlc-1(+) gene in the pharynx. First, mlc-1(0) mlc-2(0) double mutants are fully penetrant L1 lethals in both hermaphrodites and males. Second, in situ localization of mlc mRNAs demonstrates that both mlc-1 and mlc-2 are expressed in the pharynx. Third, transgenic copies of either mlc-1(+) or mlc-2(+) rescue the pharyngeal defects of mlc-1(0) mlc-2(0) hermaphrodites. Fourth, a mutation of the dosage compensation gene sdc-3 suppresses hermaphrodite-specific lethality of mlc-2(0) mutants.

Zonal differences in DNA synthesis activity and cytochrome P450 gene expression in livers of male F344 rats treated with five nongenotoxic carcinogens

Both increased cell proliferation and "altered" CYP gene expression are prominent phenomena associated with liver tumor promotion by nongenotoxic carcinogen treatment. To further characterize these two responses, groups of rats were kept on powdered rat chow diet containing 0.05% phenobarbital (PB) or 0.025% ciprofibrate (Cip) for 8 days or given 8 daily doses by gavage of pregnenolone 16 alpha-carbonitrile (PCN, 150 mg/kg/ml corn oil), 3,3',4,4'-tetrachlorobiphenyl (PCB-MC, 3 mg/kg/ml corn oil) or 2,2',4,4'-tetrachlorobiphenyl (PCB-PB, 7.5 mg/kg/ml corn oil). A minipump was implanted in the rat abdominal cavity to release bromodeoxyuridine (BRDU) 5 days after the start of nongenotoxic carcinogen treatment and the experiment was terminated 3 days later. BRDU-labeled parenchymal nuclei were observed primarily in the periportal area independent of nongenotoxic carcinogen treatment. Treatment with each of the 5 nongenotoxic carcinogens resulted in profound alterations in CYP gene expression at both the transcriptional and translational levels. Expression of CYP1A1, 1A1/2, 3A1, 2B1/2, and 4A immunoproteins demonstrated nongenotoxic carcinogen-specific patterns in both magnitude and zonal distribution. In agreement with the CYP immunoprotein data, treatment with each of the five nongenotoxic carcinogens resulted in a unique composition of mRNAs of CYP2B1, 2B2, 2C6, 2C11, 3A1, 3A2, and 4A1, which were variably increased or decreased relative to the untreated control livers, depending on the treatment. Similarly, the rate and pattern of CYP enzyme-mediated hydroxylation toward testosterone, 17 beta-estradiol, corticosterone, and lauric acid were greatly altered by nongenotoxic carcinogen treatment. According to the zonal distribution patterns of CYP immunoproteins, each hepatocyte in the cell plate from the periportal triad to the central vein has a characteristic and nongenotoxic carcinogen-specific composition of CYP enzymes. Because many endogenous substrates are modulators of DNA and RNA synthesis, intracellular kinetics of endogenous substrates of CYP enzymes in the corresponding hepatocytes could contribute, at least in part, to the differences in gene expression, differentiation, and cell proliferation among the hepatocytes in the cell plate.

From the archives of the AFIP. Malignant pleural mesothelioma: radiologic-pathologic correlation

Malignant pleural mesothelioma (MPM) is a rare malignant neoplasm that typically affects individuals occupationally exposed to asbestos through a variety of industries. The patients experience an insidious onset of symptoms, including dyspnea, chest pain, cough, malaise, and weight loss. The pathologic diagnosis of MPM is difficult, and special stains or immunohistochemical or ultrastructural analysis may be required to differentiate MPM from metastatic adenocarcinoma. The tumor affects both the parietal and visceral pleural surfaces and progresses to encase the lung and invade the lung, mediastinum, and chest wall. Radiologically, MPM manifests as unilateral pleural effusion, pleural nodules, or pleural masses. Imaging studies are useful for diagnosis and staging in patients who are potential surgical candidates. Although a variety of multimodality therapies are available and radical surgical procedures have been developed, the prognosis remains dismal.

Inhibition of cell proliferation by ciprofibrate in glutathione S-transferase P1-1-positive rat hepatic hyperplastic nodules

Previous studies have demonstrated that short-term treatment with a peroxisome proliferator (PP) decreased the size and number of genotoxic carcinogen-induced hepatic hyperplastic lesions identified by gamma-glutamyl transpeptidase (GGT) or glutathione S-transferase P1-1 (rGSTP1-1) staining. However, longer-term PP treatment of animals bearing similar hepatic hyperplastic lesions produced an increase in both the size and number of liver tumors. To characterize the hepatic hyperplastic lesions which are inhibited or promoted by PP, a unique double labeling technique was developed to determine the relative rate of cell division (e.g., DNA synthesis) in rGSTP1-1-positive nodules before and after ciprofibrate (Cip) treatment. rGSTP1-1-positive nodules were induced with the Solt-Farber resistance protocol (diethylnitrosamine-2-acetylaminofluorene partial hepatectomy). Eleven weeks after diethylnitrosamine initiation, 3 groups of rats were maintained on a control chow diet or switched to a powdered chow diet containing 0.025% Cip or 0.05% phenobarbital (PB) for the last 8 days of the experiment. A minipump implanted in the abdominal cavity released [methyl-3H]thymidine continuously for 72 h and was then removed prior to CIp or PB treatment. A second minipump was then implanted which released bromodeoxyuridine to the abdominal cavity 5 days after the start of Cip or PB administration and lasted for 72 h until the termination of the experiment. Both the [methyl-3H]thymidine and bromodeoxyuridine labeling indices (LIs) were determined in the same group of cells within individual rGSTP1-1-positive nodules in the right posterior lobes of livers. PB treatment increased both the average number of persistent GGT-positive nodules and the ratio of persistent GGT-positive to rGSTP1-1-positive nodules/cm2. In contrast, Cip treatment greatly decreased the average number and area of persistent GGT-positive nodules, as well as the ratio between persistent GGT-positive and rGSTP1-1-positive nodules/cm2. Cip treatment also resulted in a 40% decrease in the average LI in the rGSTP1-1-positive nodules. In some rGSTP1-1-positive nodules, the LI was decreased from > 40% prior to Cip treatment to < 5% afterward, suggesting that Cip treatment interrupted progression in these nodules. Such drastic changes in the LI before and after treatments were not observed in either PB- or vehicle-treated (control) animals. A number of small nodules with a high bromodeoxyuridine LI but with no or very few [methyl-3H]thymidine-labeled nuclei and negative GGT and rGSTP1-1 staining were detected only in the Cip group.(ABSTRACT TRUNCATED AT 400 WORDS)

Enhancement of glutathione content in glutathione synthetase-deficient fibroblasts from a patient with 5-oxoprolinuria via metabolic cooperation with normal fibroblasts

Fibroblasts from patients with the disease 5-oxoprolinuria have reduced glutathione synthetase activity and are thus glutathione (GSH) deficient. In this study, 5-oxoprolinuria fibroblasts (GM3877 cells) contained less GSH than normal diploid fibroblasts as determined by biochemical analysis and by flow cytometry using monochlorobimane. They also contained lower gamma-glutamylcysteine synthetase activity than normal cells. However, cocultures of GM3877 cells and normal cells displayed either normal or slightly elevated GSH content, depending upon the assay used. When differentially labeled with fluorescent beads, cocultured, and then isolated by fluorescence-activated cell sorting, both GM3877 cells and normal cells had GSH content similar to that of sorted normal cells cultured alone, whereas sorted GM3877 cells cultured alone showed depressed GSH content. GM3877 cells had detectable levels of gamma-glutamylcysteine (gamma-GC) when cultured alone, but gamma-GC was undetectable in these cells when they were cocultured with normal cells, indicating that it was efficiently metabolized to GSH by the normal cells. These changes in low-molecular-weight thiols were likely to have been mediated by metabolic cooperation across gap junctions because they were dependent upon confluency and because media conditioned by either cell type failed to significantly alter the GSH content of the other cell type. Cocultures exposed to moderate levels of hydrogen peroxide showed less depletion of GSH than GM3877 cells cultured alone, suggesting that the sharing of low-molecular-weight thiols or other reductants via metabolic cooperation can protect cells from oxidative stress.

Decreased expression of cytochrome P450 mRNAs and related steroid hydroxylation activities in hepatic hyperplastic nodules in male F344 rats

To explore the mechanism(s) underlying the relationship between expression of cytochrome P450 (CYP) enzymes and growth of hepatic hyperplastic nodules, mRNA of CYP1A1, 1A2, 2B1, 2B2, 2C6, 2C11, and 3A1, and CYP enzyme-mediated hydroxylation of testosterone (T), 17 beta-estradiol (E), and corticosterone (C) were determined in a group of selected large nodules from livers of male F344 rats given the modified Solt-Farber resistance protocol and compared with control and surrounding tissue. Slot-blot analysis with specific oligonucleotides showed little or no mRNA of CYP2B1, 2B2, and 2C6 in nodules, surrounding tissue, and control liver without PB treatment. Constitutive expression of CYP1A2, 2C11, and 3A1 in nodules was from 2 to 10 times less in nodules than in control liver. BP treatment increased mRNA of CYP2B1, 2B2, 2C6, 2C11, and 3A1 in control and surrounding tissue substantially, but was 3 to 11 times less in the nodules than in the control liver. Messenger RNA of CYP1A1 was not detected in either nodules or control livers independent of PB treatment. HPLC determination demonstrated a general pattern of a decrease in CYP enzyme-mediated hydroxylation of T, E, and C in the nodules relative to the surrounding tissue and control liver. The differences between nodules and control liver were usually 3 to 10-fold for the 12 metabolites detected although smaller decreases were observed for a few metabolites in some nodules. PB increased the rate of hydroxylation for 11 of the 12 metabolites and resulted in 2 additional metabolites of both T and E in control liver and some nodules. However, the general pattern of lower hydroxylation activities in the nodules relative to the surrounding tissue remained the same as that in the non-PB group. These observations are consistent with the hypothesis that intracellular kinetics of endogenous CYP enzyme substrates may differ in some nodules, relative to the surrounding tissue, as a result of decreased expression of CYP genes. This difference in CYP expression pattern in turn may contribute to the selective growth and progression to cancer of certain nodules, as many endogenous CYP enzyme substrates are modulators of DNA and RNA synthesis and cellular growth and differentiation.

The effect of 1-chloro-2,4-dinitrobenzene exposure on antigen receptor (CD3)-stimulated transmembrane signal transduction in purified subsets of human peripheral blood lymphocytes

The intracellular low-molecular-weight thiol glutathione (GSH) is an important scavenger of free radicals and plays a role in the maintenance of the redox status of protein sulfhydryl groups. We have previously shown that human peripheral blood lymphocytes sorted on their basal GSH content proliferate proportionately to their GSH levels, and that an early event in lymphocyte activation appeared to be dependent on GSH. We have now analyzed transmembrane signal transduction in cells treated with 1-chloro-2,4-dinitrobenzene (CDNB), a GSH-depleting agent. Transmembrane signal transduction was measured as changes in intracellular free calcium and in protein tyrosine phosphorylation after stimulation with anti-CD3 monoclonal antibody. The results show a CDNB dose-dependent reduction in GSH content, the magnitude of intracellular free calcium mobilization, and the extent of tyrosine phosphorylation of several proteins, including phospholipase C-gamma 1. This suggests a role for GSH and/or protein thiol redox status in one of the earliest events controlling the ability of lymphocytes to respond to important proliferative signals in their environment and implies that agents which deplete lymphocyte GSH may be immunosuppressive through effects on CD3/T cell receptor-dependent transmembrane signal transduction.

Longitudinal change and interstate variability in the size of residential facilities for persons with mental retardation

Changes in the size and type of operation of residential facilities for persons with mental retardation in the United States over the past 2 decades were discussed and current (June 30, 1988) interstate variability in residential services along these same dimensions examined. Considerable progress was noted nationally in securing relatively small, community-based residential opportunities for persons with mental retardation. However, this progress has not been uniformly realized in all states or for all types of facilities. Standards for federal policy that would make the official national commitment to community-based services more consistent among all the states were considered.

Longitudinal patterns in ICF-MR utilization, 1977-1986

The development of the ICF-MR program and the issue to which the ICF-MR program was intended to respond was briefly reviewed. National and state-by state statistics on changing patterns and interstate variations in use of ICF-MR services as of June 30, 1977, June 30, 1982, and June 30, 1986 were presented and ICF-MR problems and issues were discussed within the context of the evolving system of long-term care.

The Behavioral Risk Factor Surveys: IV. The descriptive epidemiology of exercise

Telephone interview data from aggregated state surveys showed that about 21 percent of the U.S. adult population expends greater than or equal to 3 kcal/kg-day in vigorous leisure-time exercise. Three kilocalories per kilogram-day is equivalent to the amount commonly recommended to maximally reduce the incidence of coronary heart disease. Approximately 36 percent of the U.S. population reported no vigorous leisure-time exercise. Men, younger persons, and the more highly educated were most likely to expend greater than or equal to 3 kcal/kg-day, but for no subgroup did the rate exceed 30 percent. People who did not smoke, were not obese, and who did wear seat belts are also more likely to expend energy in vigorous leisure-time exercise. The prevalence of alcohol misuse is similar for all exercise categories. The proportion of people who expend greater than or equal to 3 kcal/kg-day is unrelated to self-reported occupational physical effort. Given the established and presumed benefits of physical activity, a substantial portion of the U.S. population would probably benefit from regular, vigorous, leisure-time exercise.

A comparison of the effect of two bovine serum albumin preparations on benzo(alpha)pyrene hydroxylase in rat liver and lung microsomes

One of two commercial bovine serum albumin preparations caused decreases in rat liver and lung microsomal benzo(alpha)pyrene hydroxylase activities when measured by the fluorescence assay. The decreased activities were not due to a decreased recovery of a reaction product, 3-hydroxybenzo (alpha)pyrene, the presence of unmasked fatty acid binding sites or decreased content of cytochrome P450. The decreased enzyme activity may be due to a component present in the preparation. The results indicate that bovine serum albumin preparations should be carefully checked before use in the benzo(alpha)pyrene hydroxylase assay.

Benefits, risks and costs of immunization for measles, mumps and rubella

For a single year, 1983, we compared the actual and estimated morbidity, mortality, and costs attributable to measles, mumps, and rubella with having or not having a childhood immunization program using the combined measles-mumps-rubella (MMR) vaccine. Without an immunization program, an estimated 3,325,000 cases of measles would occur as compared to 2,872 actual cases in 1983 with a program. Instead of an expected 1.5 million rubella cases annually, there were only 3,816 actual cases. Mumps cases were lowered from an expected 2.1 million to 32,850 actual cases. Comparable reductions in disease-associated complications, sequelae, and deaths are gained with an immunization program. Without a vaccination program, disease costs would have been almost $1.4 billion. Based on the actual incidence of disease in 1983, costs were estimated to be approximately +14.5 million. Expenditures for immunization, including vaccine administration costs and the costs associated with vaccine reactions, totaled $96 million. The resulting benefit-cost ratio for the MMR immunization program is approximately 14:1. The savings realized due to the use of combination rather than single antigen vaccine total nearly $60 million.

A descriptive epidemiology of leisure-time physical activity

Eight national surveys conducted in the United States and Canada between 1972 and 1983 are reviewed for evidence of leisure-time physical activity patterns in the population. The authors' major conclusion is that it is difficult to make reliable generalizations when definitions of exercise used in the surveys vary so widely. Nevertheless, the young and persons of relatively high socioeconomic status are definitely more active than average in their leisure time; this is probably also true of westerners and suburbanites. Males and females are about equally likely to be involved in conditioning activities, but males are more likely to participate in vigorous exercise and sport. It appears likely that exercise prevalence has increased in recent years, and a maximum of 20 percent of the population exercises at a level frequently recommended for cardiovascular benefit. Major areas of uncertainty and ignorance remain, and the authors identify 15 such areas. Secondary analysis is recommended to help resolve several questions currently impeding a complete description of the exercise patterns of the population. For future surveys, five recommendations are offered on definitions and essential data items. Existing time series studies are generally inadequate. The authors recommend that detailed surveys of exercise patterns be conducted every 5 years to supplement the continual monitoring that is also essential to detect shifts in this important health behavior.

National census of residential facilities: a 1982 profile of facilities and residents

A national census of all state-licensed residential facilities for mentally retarded persons was conducted in 1982. This census enumerated 243,669 mentally retarded residents living in 15,633 facilities on June 30, 1982. Information on characteristics of facilities (e.g., type, location, size, type of operator, reimbursement rates) is presented along with demographic/functional characteristics of residents (e.g., age, level of retardation, previous and subsequent placement). The census verified the existence of an extensive variety of residential living alternatives available to mentally retarded people.

Decision analytic approach to the management of gonorrhea contacts

We used a combination of decision analytic and modeling techniques in constructing a model for study of the management of an asymptomatic woman presenting to a sexually transmitted disease clinic as a contact of a man with gonorrhea. Total cost (physical, emotional, and economic) is expressed in units of dysutility. Initially the probabilities and "costs" of anogenital gonorrhea, incubating syphilis, carriage of the agents of nongonococcal urethritis, and coincident pharyngeal gonorrhea are considered; complications and sequelae are then accounted for. The best strategy is to culture for Neisseria gonorrhoeae, treat immediately with tetracycline, and follow up sexual partners if the culture is positive. Dysutility values calculated for the strategies of just treating with standard regimens of tetracycline, procaine penicillin, or amoxicillin are 288, 310, and 560, respectively. Sensitivity analyses show that the most important factors in determining optimal strategy are the probabilities and costs associated with the patient's carriage of the agents of nongonococcal urethritis. In order for this decision to change, the dysutility value for nongonococcal urethritis would have to decrease to 17% of our best estimate, or the overall prevalence of nongonococcal urethritis would have to be reduced to 16% of our best estimate.

Decision aid development for use in ambulatory health care settings

An approach is presented using interactive microcomputers for the development of diagnostic decision aids applicable to some complaints encountered in ambulatory care. The central feature of the descriptive phase of the approach is the use of the underlying (and perhaps dynamic) state of patient health. The central feature of the prescriptive phase of the approach is quick, simple assessment which produces a set of nondominated diagnostic tests, the selection of which is biased by the subjectively determined disease(s) that the diagnostician wishes to rule out or confirm. We present an application of the approach to the complaint, "diarrhea of recent onset in adults," discuss the hardware/software implementation, and summarize preliminary evaluation results.