Predictive value of the ToxCast/Tox21 high throughput toxicity screening data for approximating in vivo ecotoxicity endpoints and ecotoxicological risk in eco- surveillance applications

Ecotoxicology has long relied on assessing the hazard potential of chemicals through traditional in vivo testing methods to understand the possible risk exposure could pose to ecological taxa. In the past decade, the development of non-animal new approach methods (NAMs) for assessing chemical hazard and risk has quickly grown. These methods are often cheaper and faster than traditional toxicity testing, and thus are amenable to high-throughput toxicity testing (HTT), resulting in large datasets. The ToxCast/Tox21 HTT programs have produced in vitro data for thousands of chemicals covering a large space of biological activity. The relevance of these data to in vivo mammalian toxicity has been much explored. Interest has also grown in using these data to evaluate the risk of environmental exposures to taxa of ecological importance such as fish, aquatic invertebrates, etc.; particularly for the purpose of estimating the risk of exposure from real-world complex mixtures. Understanding the relationship and relative sensitivity of NAMs versus standardized ecotoxicological whole organism models is a key component of performing reliable read-across from mammalian in vitro data to ecotoxicological in vivo data. In this work, we explore the relationship between in vivo ecotoxicity data from several publicly available databases and the ToxCast/Tox21 data. We also performed several case studies in which we compare how using different ecotoxicity datasets, whether traditional or ToxCast-based, affects risk conclusions based on exposure to complex mixtures derived from existing large-scale chemical monitoring data. Generally, predictive value of ToxCast data for traditional in vivo endpoints (EPs) was poor (r ≤ 0.3). Risk conclusions, including identification of different chemical risk drivers and prioritized monitoring sites, were different when using HTT data vs. traditional in vivo data.

A generic avian physiologically-based kinetic (PBK) model and its application in three bird species

Physiologically-based kinetic (PBK) models are effective tools for designing toxicological studies and conducting extrapolations to inform hazard characterization in risk assessment by filling data gaps and defining safe levels of chemicals. In the present work, a generic avian PBK model for male and female birds was developed using PK-Sim and MoBi from the Open Systems Pharmacology Suite (OSPS). The PBK model includes an ovulation model (egg development) to predict concentrations of chemicals in eggs from dietary exposure. The model was parametrized for chicken (Gallus gallus), bobwhite quail (Colinus virginianus) and mallard duck (Anas platyrhynchos) and was tested with nine chemicals for which in vivo studies were available. Time-concentration profiles of chemicals reaching tissues and egg compartment were simulated and compared to in vivo data. The overall accuracy of the PBK model predictions across the analyzed chemicals was good. Model simulations were found to be in the range of 22-79% within a 3-fold and 41-89% were within 10- fold deviation of the in vivo observed data. However, for some compounds scarcity of in-vivo data and inconsistencies between published studies allowed only a limited goodness of fit evaluation. The generic avian PBK model was developed following a "best practice" workflow describing how to build a PBK model for novel species. The credibility and reproducibility of the avian PBK models were scored by evaluation according to the available guidance documents from WHO (2010), and OECD (2021), to increase applicability, confidence and acceptance of these in silico models in chemical risk assessment.

Utility of the avian sub-acute dietary toxicity test in ecological risk assessment and a path forward to reduce animal use

The United States Environmental Protection Agency (USEPA) has long required both avian sub-acute dietary and acute oral studies to inform risk assessments for pesticides. Recently, the USEPA collaborated with People for the Ethical Treatment of Animals to determine whether the results of the acute oral avian toxicity test or the sub-acute dietary toxicity test consistently generated the greatest risk predictions in USEPA tier 1 assessments for pesticides first registered between 1998 and 2017. Their study concluded that in 99% of the cases, risk conclusions were driven by the acute oral study (OPPTS 850.2100, OCSPP 850.2100, or similar) because using these data results in higher risk quotients than sub-acute dietary data. Shortly after publishing these results, the USEPA released a formal memorandum providing guidance for waiving the sub-acute dietary study for most pesticides. The USEPA will, however, retain the option to require sub-acute dietary studies for pesticides with certain chemical properties. However, as the avian sub-acute dietary study has an exposure regimen that is often more representative of how birds are exposed to pesticides under actual use conditions than does the acute oral study (i.e., as part of a dietary item eaten over the course of a day and not a bolus dose), this study can provide useful context for risk assessment on a case-by-case basis. Decision criteria are needed to determine a path forward that both minimizes vertebrate animal testing and positions the avian sub-acute dietary data as an option for risk refinement. Decision criteria are proposed here with recommendations for refining the design of avian sub-acute dietary studies to ensure that the data generated are optimized to support a science-based acute avian risk assessment, supported by a case study demonstrating when and how sub-acute dietary studies may be used in a higher-tier risk assessment. Integr Environ Assess Manag 2022;18:1629-1638. © 2022 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Quantitative Morphometric, Physiological, and Metabolic Characteristics of Chickens and Mallards for Physiologically Based Kinetic Model Development

Physiologically based kinetic (PBK) models are a promising tool for xenobiotic environmental risk assessment that could reduce animal testing by predicting in vivo exposure. PBK models for birds could further our understanding of species-specific sensitivities to xenobiotics, but would require species-specific parameterization. To this end, we summarize multiple major morphometric and physiological characteristics in chickens, particularly laying hens (Gallus gallus) and mallards (Anas platyrhynchos) in a meta-analysis of published data. Where such data did not exist, data are substituted from domesticated ducks (Anas platyrhynchos) and, in their absence, from chickens. The distribution of water between intracellular, extracellular, and plasma is similar in laying hens and mallards. Similarly, the lengths of the components of the small intestine (duodenum, jejunum, and ileum) are similar in chickens and mallards. Moreover, not only are the gastrointestinal absorptive areas similar in mallard and chickens but also they are similar to those in mammals when expressed on a log basis and compared to log body weight. In contrast, the following are much lower in laying hens than mallards: cardiac output (CO), hematocrit (Hct), and blood hemoglobin. There are shifts in ovary weight (increased), oviduct weight (increased), and plasma/serum concentrations of vitellogenin and triglyceride between laying hens and sexually immature females. In contrast, reproductive state does not affect the relative weights of the liver, kidneys, spleen, and gizzard.

Quantitative Comparison of Avian and Mammalian Physiologies for Parameterization of Physiologically Based Kinetic Models

Physiologically based kinetic (PBK) models facilitate chemical risk assessment by predicting in vivo exposure while reducing the need for animal testing. PBK models for mammals have seen significant progress, which has yet to be achieved for avian systems. Here, we quantitatively compare physiological, metabolic and anatomical characteristics between birds and mammals, with the aim of facilitating bird PBK model development. For some characteristics, there is considerable complementarity between avian and mammalian species with identical values for the following: blood hemoglobin and hemoglobin concentrations per unit erythrocyte volume together with relative weights of the liver, heart, and lungs. There are also systematic differences for some major characteristics between avian and mammalian species including erythrocyte volume, plasma concentrations of albumin, total protein and triglyceride together with liver cell size and relative weights of the kidney, spleen, and ovary. There are also major differences between characteristics between sexually mature and sexually immature female birds. For example, the relative weights of the ovary and oviduct are greater in sexually mature females compared to immature birds as are the plasma concentrations of triglyceride and vitellogenin. Both these sets of differences reflect the genetic "blue print" inherited from ancestral archosaurs such as the production of large eggs with yolk filled oocytes surrounded by egg white proteins, membranes and a calciferous shell together with adaptions for flight in birds or ancestrally in flightless birds.

The Extended Amphibian Metamorphosis Assay: A Thyroid-Specific and Less Animal-Intensive Alternative to the Larval Amphibian Growth and Development Assay

The amphibian metamorphosis assay (AMA; US Environmental Protection Agency [USEPA] test guideline 890.1100 and Organisation for Economic Co-Operation and Development test guideline 231) has been used for more than a decade to assess the potential thyroid-mediated endocrine activity of chemicals. In 2013, in the context of the Endocrine Disruptor Screening Program of the USEPA, a Scientific Advisory Panel reviewed the results from 18 studies and recommended changes to the AMA test guideline, including a modification to a fixed-stage design rather than a fixed-time (i.e., 21-d) design. We describe an extended test design for the AMA (or EAMA) that includes thyroid histopathology and time to metamorphosis (Nieuwkoop-Faber [NF] stage 62), to address both the issues with the fixed-time design and the specific question of thyroid-mediated adversity in a shorter assay than the larval amphibian growth and development assay (LAGDA; Organisation for Economic Co-Operation and Development test guideline 241), using fewer animals and resources. A demonstration study was conducted with the EAMA (up to NF stage 58) using sodium perchlorate. Data analyses and interpretation of the fixed-stage design of the EAMA are more straightforward than the fixed-time design because the fixed-stage design avoids confounded morphometric measurements and thyroid histopathology caused by varying developmental stages at test termination. It also results in greater statistical power to detect metamorphic delays than the fixed-time design. By preferentially extending the AMA to NF stage 62, suitable data can be produced to evaluate thyroid-mediated adversity and preclude the need to perform a LAGDA for thyroid mode of action analysis. The LAGDA remains of further interest should investigations of longer term effects related to sexual development modulated though the hypothalamus-pituitary-gonadal axis be necessary. However, reproduction assessment or life cycle testing is currently not addressed in the LAGDA study design. This is better addressed by higher tier studies in fish, which should then include specific thyroid-related endpoints. Environ Toxicol Chem 2021;40:2135-2144. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Critical Review of Read-Across Potential in Testing for Endocrine-Related Effects in Vertebrate Ecological Receptors

Recent regulatory testing programs have been designed to evaluate whether a chemical has the potential to interact with the endocrine system and could cause adverse effects. Some endocrine pathways are highly conserved among vertebrates, providing a potential to extrapolate data generated for one vertebrate taxonomic group to others (i.e., biological read-across). To assess the potential for biological read-across, we reviewed tools and approaches that support species extrapolation for fish, amphibians, birds, and reptiles. For each of the estrogen, androgen, thyroid, and steroidogenesis (EATS) pathways, we considered the pathway conservation across species and the responses of endocrine-sensitive endpoints. The available data show a high degree of confidence in the conservation of the hypothalamus-pituitary-gonadal axis between fish and mammals and the hypothalamus-pituitary-thyroid axis between amphibians and mammals. Comparatively, there is less empirical evidence for the conservation of other EATS pathways between other taxonomic groups, but this may be due to limited data. Although more information on sensitive pathways and endpoints would be useful, current developments in the use of molecular target sequencing similarity tools and thoughtful application of the adverse outcome pathway concept show promise for further advancement of read-across approaches for testing EATS pathways in vertebrate ecological receptors. Environ Toxicol Chem 2020;39:739-753. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Primary Cell Phenotypic Screening Illuminates ADRs and AOPs

Preclinical, in vitro screening for adverse drug reactions continues to present challenges in the field of drug development. In this issue of Cell Chemical Biology, Shah et al. (2017) employ a phenotypic screening strategy using a panel of human primary cells to define a signature response and an adverse outcome pathway for delayed type IV skin hypersensitivity.

AHR2 morpholino knockdown reduces the toxicity of total particulate matter to zebrafish embryos

The zebrafish embryo has been proposed as a 'bridge model' to study the effects of cigarette smoke on early development. Previous studies showed that exposure to total particulate matter (TPM) led to adverse effects in developing zebrafish, and suggested that the antioxidant and aryl hydrocarbon receptor (AHR) pathways play important roles. This study investigated the roles of these two pathways in mediating TPM toxicity. The study consisted of four experiments. In experiment I, zebrafish embryos were exposed from 6h post fertilization (hpf) until 96hpf to TPM0.5 and TPM1.0 (corresponding to 0.5 and 1.0μg/mL equi-nicotine units) in the presence or absence of an antioxidant (N-acetyl cysteine/NAC) or a pro-oxidant (buthionine sulfoximine/BSO). In experiment II, TPM exposures were performed in embryos that were microinjected with nuclear factor erythroid 2-related factor 2 (Nrf2), AHR2, cytochrome P450 1A (CYP1A), or CYP1B1 morpholinos, and deformities were assessed. In experiment III, embryos were exposed to TPM, and embryos/larvae were collected at 24, 48, 72, and 96hpf to assess several genes associated with the antioxidant and AHR pathways. Lastly, experiment IV assessed the activity and protein levels of CYP1A and CYP1B1 after exposure to TPM. We demonstrate that the incidence of TPM-induced deformities was generally not affected by NAC/BSO treatments or Nrf2 knockdown. In contrast, AHR2 knockdown reduced, while CYP1A or CYP1B1 knockdowns elevated the incidence of some deformities. Moreover, as shown by gene expression the AHR pathway, but not the antioxidant pathway, was induced in response to TPM exposure, providing further evidence for its importance in mediating TPM toxicity.

Silver toxicity across salinity gradients: the role of dissolved silver chloride species (AgCl x ) in Atlantic killifish (Fundulus heteroclitus) and medaka (Oryzias latipes) early life-stage toxicity

The influence of salinity on Ag toxicity was investigated in Atlantic killifish (Fundulus heteroclitus) early life-stages. Embryo mortality was significantly reduced as salinity increased and Ag(+) was converted to AgCl(solid). However, as salinity continued to rise (>5 ‰), toxicity increased to a level at least as high as observed for Ag(+) in deionized water. Rather than correlating with Ag(+), Fundulus embryo toxicity was better explained (R(2) = 0.96) by total dissolved Ag (Ag(+), AgCl2 (-), AgCl3 (2-), AgCl4 (3-)). Complementary experiments were conducted with medaka (Oryzias latipes) embryos to determine if this pattern was consistent among evolutionarily divergent euryhaline species. Contrary to Fundulus data, medaka toxicity data were best explained by Ag(+) concentrations (R(2) = 0.94), suggesting that differing ionoregulatory physiology may drive observed differences. Fundulus larvae were also tested, and toxicity did increase at higher salinities, but did not track predicted silver speciation. Alternatively, toxicity began to increase only at salinities above the isosmotic point, suggesting that shifts in osmoregulatory strategy at higher salinities might be an important factor. Na(+) dysregulation was confirmed as the mechanism of toxicity in Ag-exposed Fundulus larvae at both low and high salinities. While Ag uptake was highest at low salinities for both Fundulus embryos and larvae, uptake was not predictive of toxicity.

Silver nanoparticle toxicity to Atlantic killifish (Fundulus heteroclitus) and Caenorhabditis elegans: a comparison of mesocosm, microcosm, and conventional laboratory studies

The use of silver nanoparticles (AgNPs) in consumer products and industrial applications, as well as their recent detection in waste streams, has created concern about potential impacts on aquatic ecosystems. The effect of complex environmental media on AgNP toxicity was investigated using wetland mesocosms and smaller scale microcosms. Mesocosms were dosed with 2.5 mg Ag/L as gum arabic (GA)-coated AgNPs, polyvinylpyrrolidone (PVP)-coated AgNPs, or AgNO3. Water samples were taken from mesocosms 24 h after dosing for acute toxicity tests with embryos and larvae of Atlantic killifish (Fundulus heteroclitus) and the nematode Caenorhabditis elegans. Acute toxicity tests were also performed on Atlantic killifish with AgNO3, GA AgNPs, and PVP AgNPs prepared in the laboratory with similar water. For killifish embryos, mesocosm samples were much less toxic than laboratory samples for all types of silver. For larvae, in contrast, all 3 silver mesocosm treatments exhibited toxicity. Interestingly, mesocosm samples of AgNO3 were less toxic than laboratory samples; samples containing GA AgNPs were similar in toxicity, and samples containing PVP AgNPs were more toxic. For C. elegans, results were similar to killifish larvae. Results obtained from the mesocosms were not replicated on the smaller scale of the microcosms. These results indicate that environmental factors unique to the mesocosms acted differentially on AgNO3 to reduce its toxicity in a manner that does not translate to AgNPs for larval fish.

Resistance to teratogenesis by F1 and F2 embryos of PAH-adapted Fundulus heteroclitus is strongly inherited despite reduced recalcitrance of the AHR pathway

Atlantic killifish (Fundulus heteroclitus) inhabiting the Atlantic Wood Superfund site on the Elizabeth River (Portsmouth, VA, USA) are exposed to a complex mixture of polycyclic aromatic hydrocarbons (PAHs) from former creosote operations, but are resistant to the acute toxicity and cardiac teratogenesis caused by PAHs. The resistance is associated with a dramatic recalcitrance to induction of cytochrome P450 (CYP1) metabolism enzymes following exposure to aryl hydrocarbon receptor (AHR) agonists, along with an elevated antioxidant response and increased expression of several other xenobiotic metabolism and excretion enzymes. However, the heritability of the resistance in the absence of chemical stressors has been inconsistently demonstrated. Understanding the heritability of this resistance will help clarify the nature of population-level responses to chronic exposure to PAH mixtures and aid in identifying the important mechanistic components of resistance to aryl hydrocarbons. We compared the response of Atlantic Wood F1 and F2 embryos to benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), 3,3',4,4',5-pentachlorobiphenyl (PCB-126), and a mixture of BkF and fluoranthene (Fl) to that of F1 embryos of reference site killifish. Resistance to cardiac teratogenesis and induction of CYP mRNA expression and CYP activity was determined. We found that both Atlantic Wood F1 and F2 embryos were highly resistance to cardiac teratogenesis. However, the resistance by Atlantic Wood F2 embryos to induction of CYP mRNA expression and enzyme activity was intermediate between that of Atlantic Wood F1 embryos and reference embryos. These results suggest that resistance to cardiac teratogenesis in Atlantic Wood fish is conferred by multiple factors, not all of which appear to be fully genetically heritable.

Expression of the enteroviral capsid protein VP1 in the islet cells of patients with type 1 diabetes is associated with induction of protein kinase R and downregulation of Mcl-1

AIMS/HYPOTHESIS

Immunohistochemical staining reveals that the enteroviral capsid protein VP1 is present at higher frequency in the insulin-containing islets of patients with recent-onset type 1 diabetes than in controls. This is consistent with epidemiological evidence suggesting that enteroviral infection may contribute to the autoimmune response in type 1 diabetes. However, immunostaining of VP1 is not definitive since the antibody widely used to detect the protein (Clone 5D8/1) might also cross-react with additional proteins under some conditions. Therefore, we sought to verify that VP1 immunopositivity correlates with additional markers of viral infection.

METHODS

Antigen immunoreactivity was examined in formalin-fixed, paraffin-embedded, pancreases from two different collections of type 1 diabetes and control cases: a historical collection from the UK and the nPOD (network of Pancreatic Organ donors with Diabetes) cohort from the USA.

RESULTS

VP1 immunoreactivity was present in ~20% of insulin-containing islets of both cohorts under stringent conditions but was absent from insulin-deficient islets. The presence of VP1 was restricted to beta cells but only a minority of these contained the antigen. The innate viral sensor, protein kinase R (PKR) was upregulated selectively in beta cells that were immunopositive for VP1. The anti-apoptotic protein myeloid cell leukaemia sequence-1 (Mcl-1) was abundant in beta cells that were immunonegative for VP1 but Mcl-1 was depleted in cells containing VP1.

CONCLUSIONS/INTERPRETATION

The presence of immunoreactive VP1 within beta cells in type 1 diabetes is associated with a cellular phenotype consistent with the activation of antiviral response pathways and enhanced sensitivity to apoptosis. However, definitive studies confirming whether viral infections are causal to beta cell loss in human diabetes are still awaited.

Long-term transformation and fate of manufactured ag nanoparticles in a simulated large scale freshwater emergent wetland

Transformations and long-term fate of engineered nanomaterials must be measured in realistic complex natural systems to accurately assess the risks that they may pose. Here, we determine the long-term behavior of poly(vinylpyrrolidone)-coated silver nanoparticles (AgNPs) in freshwater mesocosms simulating an emergent wetland environment. AgNPs were either applied to the water column or to the terrestrial soils. The distribution of silver among water, solids, and biota, and Ag speciation in soils and sediment was determined 18 months after dosing. Most (70 wt %) of the added Ag resided in the soils and sediments, and largely remained in the compartment in which they were dosed. However, some movement between soil and sediment was observed. Movement of AgNPs from terrestrial soils to sediments was more facile than from sediments to soils, suggesting that erosion and runoff is a potential pathway for AgNPs to enter waterways. The AgNPs in terrestrial soils were transformed to Ag(2)S (~52%), whereas AgNPs in the subaquatic sediment were present as Ag(2)S (55%) and Ag-sulfhydryl compounds (27%). Despite significant sulfidation of the AgNPs, a fraction of the added Ag resided in the terrestrial plant biomass (~3 wt % for the terrestrially dosed mesocosm), and relatively high body burdens of Ag (0.5-3.3 μg Ag/g wet weight) were found in mosquito fish and chironomids in both mesocosms. Thus, Ag from the NPs remained bioavailable even after partial sulfidation and when water column total Ag concentrations are low (<0.002 mg/L).

Biotic and abiotic interactions in aquatic microcosms determine fate and toxicity of Ag nanoparticles. Part 1. Aggregation and dissolution

To better understand their fate and toxicity in aquatic environments, we compared the aggregation and dissolution behavior of gum arabic (GA) and polyvinylpyrrolidone (PVP) coated Ag nanoparticles (NPs) in aquatic microcosms. There were four microcosm types: surface water; water and sediment; water and aquatic plants; or water, sediment, and aquatic plants. Dissolution and aggregation behavior of AgNPs were examined using ultracentrifugation, ultrafiltration, and asymmetrical flow field flow fractionation coupled to ultraviolet-visible spectroscopy, dynamic and static laser light scattering, and inductively coupled plasma mass spectrometry. Plants released dissolved organic matter (DOM) into the water column either through active or passive processes in response to Ag exposure. This organic matter fraction readily bound Ag ions. The plant-derived DOM had the effect of stabilizing PVP-AgNPs as primary particles, but caused GA-AgNPs to be removed from the water column, likely by dissolution and binding of released Ag ions on sediment and plant surfaces. The destabilization of the GA-AgNPs also corresponded with X-ray absorption near edge spectroscopy results which suggest that 22-28% of the particulate Ag was associated with thiols and 5-14% was present as oxides. The results highlight the potential complexities of nanomaterial behavior in response to biotic and abiotic modifications in ecosystems, and may help to explain differences in toxicity of Ag observed in realistic exposure media compared to simplified laboratory exposures.

Immunohistochemical analysis of the relationship between islet cell proliferation and the production of the enteroviral capsid protein, VP1, in the islets of patients with recent-onset type 1 diabetes

AIMS/HYPOTHESIS

The enteroviral capsid protein, VP1, was recently shown to be present in some beta cells in more than 60% of patients with recent-onset type 1 diabetes but in very few age-matched controls. The rate of proliferation of islet cells was also markedly increased in the type 1 diabetic patients. As it has been suggested that enteroviruses replicate most efficiently in proliferating cells, we have investigated whether VP1 is preferentially present in proliferating beta cells in type 1 diabetes.

METHODS

Combined immunoperoxidase and immunofluorescence staining was used to record the presence of enteroviral VP1, insulin and Ki67 in the islets of recent-onset type 1 diabetic patients.

RESULTS

From a total of 1,175 islets, 359 (30.5%) contained insulin. VP1-producing endocrine cells were found in 72 islets (6.1% of total), all of which retained insulin. Ki67(+) endocrine cells were present in 52 (4.4%) islets, with 44 (84.6%) of these being insulin-positive. Overall, 28 of 1,175 (2.4%) islets contained both Ki67(+) cells and VP1(+) cells. Dual positivity of these markers accounted for 38.9% of the total VP1(+) islets and 53.8% of the total Ki67(+) islets. No individual islet cells were dual-positive for Ki67 and VP1.

CONCLUSIONS/INTERPRETATION

Ki67(+) cells were frequently observed in islets that also contained VP1(+) cells, suggesting that the factors facilitating viral replication may also drive islet cell proliferation. However, in an individual cell, VP1 production does not require concurrent beta cell proliferation.

Evidence of increased islet cell proliferation in patients with recent-onset type 1 diabetes

AIMS/HYPOTHESIS

In adults, the rate of beta cell replication is normally very low, but recent evidence suggests that it may increase during insulitis. We therefore studied tissue from donors with recent-onset type 1 diabetes to establish whether islet cell proliferation is increased during the disease process.

METHODS

Paraffin-embedded pancreatic sections from ten donors with recent-onset type 1 diabetes and a range of relevant controls were stained by immunohistochemical techniques with antibodies against the proliferation markers Ki67 and minichromosome maintenance protein-2 (MCM-2). A combination staining technique involving immunoperoxidase and immunofluorescence methods was developed to quantify the numbers of alpha and beta cells with Ki67-positive nuclei and to investigate the relationship between insulitis and islet cell proliferation.

RESULTS

In non-diabetic control donors, only 1.1 +/- 0.3% (mean +/- SEM) of islets contained one or more Ki67(+) islet cells, whereas this proportion was increased markedly in recent-onset type 1 diabetes (10.88 +/- 2.5%; p < 0.005). An equivalent increase in Ki67(+) staining occurred in alpha and beta cells and was correlated positively with the presence of insulitis. A significant increase in the labelling of islet cells from type 1 diabetic donors was also seen when MCM-2 staining was employed. Increased islet cell proliferation was not evident in three donors with longer duration type 1 diabetes or in ten type 2 diabetic donors.

CONCLUSIONS/INTERPRETATION

Alpha and beta cells undergo a marked increase in proliferation during the progression of type 1 diabetes in humans. The results imply that islet cell proliferation is re-initiated in response to the autoimmune attack associated with type 1 diabetes.

The prevalence of enteroviral capsid protein vp1 immunostaining in pancreatic islets in human type 1 diabetes

AIMS/HYPOTHESIS

Evidence that the beta cells of human patients with type 1 diabetes can be infected with enterovirus is accumulating, but it remains unclear whether such infections occur at high frequency and are important in the disease process. We have now assessed the prevalence of enteroviral capsid protein vp1 (vp1) staining in a large cohort of autopsy pancreases of recent-onset type 1 diabetic patients and a range of controls.

METHODS

Serial sections of paraffin-embedded pancreatic autopsy samples from 72 recent-onset type 1 diabetes patients and up to 161 controls were immunostained for insulin, glucagon, vp1, double-stranded RNA activated protein kinase R (PKR) and MHC class I.

RESULTS

vp1-immunopositive cells were detected in multiple islets of 44 out of 72 young recent-onset type 1 diabetic patients, compared with a total of only three islets in three out of 50 neonatal and paediatric normal controls. vp1 staining was restricted to insulin-containing beta cells. Among the control pancreases, vp1 immunopositivity was also observed in some islets from ten out of 25 type 2 diabetic patients. A strong correlation was established between islet cell vp1 positivity and PKR production in insulin-containing islets of both type 1 and type 2 diabetic patients, consistent with a persistent viral infection of the islets.

CONCLUSIONS/INTERPRETATION

Immunoreactive vp1 is commonly found in the islets of recent-onset type 1 diabetes patients, but only rarely in normal paediatric controls. vp1 immunostaining was also observed in some islets of type 2 diabetes patients, suggesting that the phenomenon is not restricted to type 1 diabetes patients.

Analysis of islet inflammation in human type 1 diabetes

The immunopathology of type 1 diabetes (T1D) has proved difficult to study in man because of the limited availability of appropriate samples, but we now report a detailed study charting the evolution of insulitis in human T1D. Pancreas samples removed post-mortem from 29 patients (mean age 11.7 years) with recent-onset T1D were analysed by immunohistochemistry. The cell types constituting the inflammatory infiltrate within islets (insulitis) were determined in parallel with islet insulin content. CD8(+) cytotoxic T cells were the most abundant population during insulitis. Macrophages (CD68(+)) were also present during both early and later insulitis, although in fewer numbers. CD20(+) cells were present in only small numbers in early insulitis but were recruited to islets as beta cell death progressed. CD138(+) plasma cells were infrequent at all stages of insulitis. CD4(+) cells were present in the islet infiltrate in all patients but were less abundant than CD8(+) or CD68(+) cells. Forkhead box protein P3(+) regulatory T cells were detected in the islets of only a single patient. Natural killer cells were detected rarely, even in heavily inflamed islets. The results suggest a defined sequence of immune cell recruitment in human T1D. They imply that both CD8(+) cytotoxic cells and macrophages may contribute to beta cell death during early insulitis. CD20(+) cells are recruited in greatest numbers during late insulitis, suggesting an increasing role for these cells as insulitis develops. Natural killer cells and forkhead box protein P3(+) T cells do not appear to be required for beta cell death.

Apoptosis and disease progression in the spontaneously diabetic BB/S rat

AIMS/HYPOTHESIS

Type I (insulin-dependent) diabetes mellitus is an autoimmune disease culminating in pancreatic beta-cell destruction. A role for apoptosis in this destruction has been suggested, although controversy exists over the identity of the apoptotic cells and the time of onset of apoptosis. This study investigates the extent and timing of islet cell apoptosis in vivo in the spontaneously diabetic BB/S rat.

METHODS

Pancreatic biopsies were taken from 30 diabetes-prone and 6 diabetes-resistant BB/S rats matched for age. Animals were serially biopsied before, during and after development of diabetes and apoptotic cells analysed in serial sections. The diabetes-prone group included animals (n = 6) that had insulitis but did not develop diabetes.

RESULTS

Apoptosis was not detected in any pancreatic sections from diabetes resistant animals at any age investigated or from any animal before 50 days of age. By 68 days, apoptosis was, however, detectable in both the diabetes-prone group and in the group that had insulitus but did not develop diabetes and this correlated with a decrease in pancreatic insulin staining and a development of insulitis. There was a further increase in apoptosis in the diabetes-prone group at 85 days, which coincided with the time of onset of diabetes (84 days). In addition, there was a sixfold increase in intra-islet apoptosis between 68 and 85 days in the diabetes-prone group and at 85 days intra-islet apoptosis was threefold higher in the diabetes-prone group than in the group that had insulitus but did not develop diabetes. At 107 days, apoptosis (total and intra-islet) was higher in the group that had insulitus but did not develop diabetes (OND-DP) than in either the diabetes resistant (DR) or diabetes-prone (DP) groups.

CONCLUSION/INTERPRETATION

We have shown significant islet cell apoptosis in the pancreas of diabetes-prone BB/S rats, which coincides with the appearance of insulitis and the onset of diabetes. We have also detected differences in the levels of apoptosis between diabetic and non-diabetic animals and suggest that such differences could be an important determinant of disease progression in this animal model of Type I diabetes.

Insulitis and mechanisms of disease resistance: studies in an animal model of insulin dependent diabetes mellitus

Insulin dependent diabetes mellitus (IDDM) is an autoimmune disease characterised by extreme insulin deficiency due to an overall decrease in the mass of properly functioning beta-cells. This reduction occurs as a result of insulitis. the outcome of which will depend upon the intensity of the cytotoxic attack and the ability of beta-cells to resist and repair immune mediated cell damage. To further elucidate the relationship between the insulitis process and beta-cell defence and repair mechanisms in the prevention of diabetes we have studied a unique subgroup of diabetes prone (DP) BB/S rats which have demonstrated an ability to recover from IDDM (BB/S-R). Animals were diagnosed as diabetic at 115 days of age, subsequently receiving insulin therapy (1.49+/-0.1 IU/day) for a total of 19.7 days during 1 to 4 episodes of IDDM. Following a prolonged symptom-free period of 90 days, an IPGTT revealed that BB/S-R rats possessed normal glycaemic control. Islets were isolated from the BB/S-R rats and their glucose-stimulated insulin response was shown to be comparable to Wistar control islets. Furthermore, control and BB/S-R islets showed both a similar structural integrity and insulin content. BB/S-R islets cultured for 24 hr in IL-1beta (10(-13) M) maintained a significant insulin secretory response to glucose in contrast to Wistar controls in which the response was completely inhibited. Nitrite production was induced by IL-1beta, in a dose-dependent manner, in control islets whereas there was no significant increase in production in the islets of BB/S-R rats. These findings suggest that previous immune directed beta-cell attack may induce a state of increased resistance to subsequent deleterious effects of cytokine-mediated cytotoxicity. Overall therefore, the present study shows how the "recovered" BB/S-R rat model provides a unique opportunity to assess the direct effects of insulitis on pancreatic islets and how this interaction may subsequently determine disease outcome.

Tumor necrosis factor-alpha and interferon-gamma inhibit insulin secretion and cause DNA damage in unweaned-rat islets. Extent of nitric oxide involvement

Nitric oxide has been implicated as one possible mediator of interleukin-1 beta (IL-1)-induced inhibition of insulin secretion and islet cell damage. The aim of this study was to define the effects of tumor necrosis factor-alpha (TNF) and interferon-gamma (IFN) on nitric oxide production, insulin secretion, and DNA damage in islets from unweaned rats. Treatment of islets with 0.5-500 U/ml of either TNF or IFN on their own inhibited glucose-stimulated insulin secretion in a dose-dependent manner (minimum effective dose 5 U/ml). In combination, the cytokines exerted a pronounced synergistic inhibitory effect on secretion and were equipotent at causing a significant and concentration-dependent increase in culture medium nitrite levels, islet cyclic GMP formation, and DNA damage. Used alone or in combination, TNF and IFN significantly enhanced the activity of inducible nitric oxide synthase as determined by measuring the conversion of 14C-labeled arginine to 14C-labeled citrulline and nitric oxide. Use of arginine-free medium, without or with NG-monomethyl-L-arginine, resulted in inhibition of nitrite formation by 5-1,000 U/ml IFN+TNF and partial restoration of the insulin secretory response to glucose. Treatment of rat islets with increasing doses of TNF+IFN (5, 50, and 500 U/ml) resulted in a progressive increase in DNA damage, as shown by the comet assay, which detects DNA strand breaks in individual islet cells. The DNA damage caused by an intermediate concentration (50 U/ml) of TNF+IFN was comparable to that generated by IL-1 when used at 20 U/ml. We conclude that TNF and IFN induce nitric oxide formation, which partially inhibits glucose-induced insulin secretion and causes significant DNA strand breakage, but that as cytokine concentrations increase, non-nitric-oxide-mediated events predominate.

Serum biopterin--a novel marker for immune activation during pre-diabetes in the BB rat

Tetrahydrobiopterin (BH4) is a pteridine product which is released by rodent macrophages on activation by cytokines. We have used serial pancreatic biopsy, and measurement of serum biopterin at 30, 60, 90 and 120 days in the BB/S rat to relate histological change to macrophage activation during the course of pre-diabetes. Using immunohistochemistry, and an arbitrary scoring system read blind and standardised against day 30, we found that pancreatic MHC class I, MHC class II and infiltrating macrophage staining were up-regulated in the BB/S diabetes-prone rats (n = 17) at day 60, markedly so at day 90, and less so at day 120. Staining for resident pancreatic macrophages remained unchanged throughout in diabetes prone, diabetes resistant and Wistar (n = 28) control animals. Serum biopterin fell progressively and identically with age in BB diabetes resistant rats (n = 11) and Wistar controls. No change in weight gain or biopterin levels was observed in the biopsied animals. Mean serum biopterin levels in diabetes prone rats (of which 13 of 17 became diabetic at median 85 days) were the same as in diabetes resistant and Wistar rats at days 30, 60 and 120, but showed a striking and highly significant elevation (p < 0.001) at day 90. Although macrophages infiltrate the islet early in pre-diabetes, the timing of their activation is unknown. The rise in biopterin we observed is a potentially important immunological event which occurred late in the progression of pre-diabetes. This acute terminal event has not been reported previously, and may modify current concepts concerning the tempo of cell destruction during pre-diabetes.

Metabolic control in streptozotocin diabetic rats following transplantation of microencapsulated pancreatic islets

Microencapsulated islet grafts implanted into the peritoneal cavity of a variety of animal models of diabetes have been shown to reverse hyperglycaemia over prolonged periods without immunosuppression. Here, effects of these grafts on intermediary metabolites, diurnal blood glucose and glycated haemoglobin were studied in streptozotocin-diabetic Wistar rats. Following transplantation (approximately 3000 islets) glucose and the ketone 3-hydroxybutyrate fell significantly (glucose: 19.1 +/- 0.6 (SD) to 9.2 +/- 4.3 mmol/l, p < 0.01; 3-hydroxybutyrate: 1.51 +/- 0.48 to 0.55 +/- 0.38 mmol/l, p < 0.02) and remained within/close to the normal range for at least four weeks. In control diabetic animals, values remained abnormally elevated. There was no difference in lactate, alanine or glycerol between the two groups. In transplanted animals there was a marked variation in blood glucose over a 24h period, values being low during daylight hours but with nocturnal peaks (up to 25 mmol/l) during the animals' normal feeding time. Glycated haemoglobin was also lower in transplanted animals but did not return to normal and the difference was not significant. In conclusion, microencapsulated islet grafts ameliorated the diabetic state. However, normal metabolic homeostasis was not achieved. The intraperitoneal site precludes direct graft vascular access and this may be a contributory factor. Additionally, daytime blood sugar values in murine models of diabetes may be a poor guide to graft function and glucose tolerance.

Expression of an islet regenerating (reg) gene in isolated rat islets: effects of nutrient and non-nutrient growth factors

The expression of a novel regenerating (reg) gene has been reported previously in the regenerating islets of a surgical model of diabetes in rats. We exposed collagenase-isolated rat islets for three days to nutrient and non-nutrient growth factors in minimally supplemented RPMI medium (2.7 mmol/l glucose, 2% fetal calf serum), and investigated the relationship between reg gene expression and islet cell replication. RNA was prepared from half of the islets by homogenisation in guanidinium isothiocyanate followed by phenol/chloroform extraction. Northern/dot blot analyses were used to semi-quantify reg mRNA. Islet cell replication was estimated by culturing the remaining islets in radiolabelled thymidine to determine de novo DNA synthesis. Thymidine uptake was stimulated by the following factors: 11 mmol/l glucose (50% increase); 10% amino acids (126% increase); 10% fetal calf serum (39% increase); 100 ng/ml insulin (45% increase); 250 ng/ml growth hormone (65% increase); 1.5 nmol/l aldosterone (29% increase); 2 U/ml platelet derived growth factor (116% increase). The results are expressed as a percentage of the thymidine incorporated into control islets cultured in minimal RPMI (1118 +/- 100 (SD) cpm/microgram protein, n = 15). Increased islet cell replication was paralleled in each case by a clear rise in reg mRNA expression compared to controls. Furthermore, the rank order for reg gene expression was the same as that for thymidine uptake (r = 0.90). The present findings suggest a clear association between reg gene expression and islet cell replication in vitro, and are the first to demonstrate reg gene expression in response to individual growth factors.

Insulin-mimicking anti-idiotypic antibodies in development of spontaneous autoimmune diabetes in BB/E rats

BB/E rats spontaneously develop a form of autoimmune diabetes resembling insulin-dependent diabetes mellitus (IDDM) in humans. IDDM results from central destruction of the insulin-producing beta-cells of the pancreatic islets. Herein, we report that the outbreak of IDDM in BB/E rats is preceded by the spontaneous development of an anti-idiotypic antibody to a particular antibody to insulin made by the rats. This anti-idiotype, designated anti-DM-id, behaves as an antibody to the insulin-hormone receptor. Thus, a spontaneous anti-idiotypic antibody network whose products can affect the peripheral utilization of insulin seems to accompany the central destruction of beta-cells in developing IDDM.

Comparison of an enzyme-linked immunosorbent assay (ELISA) with a radioimmunoassay (RIA) for the measurement of rat insulin

A recently developed competitive enzyme-linked immunosorbent assay (ELISA) was compared with a conventional competitive radioimmunoassay (RIA) for the measurement of rat insulin in culture medium. Fifty-six samples were analysed by both assays. There was a correlation coefficient of r = 0.783 between results obtained using the two assay systems. The binding curves of the two assays were differently shaped, so that the ELISA gave good reproducibility over the concentration range 5-50 microU/ml insulin with inter- and intra-assay coefficients of variation less than 14%, but poor reproducibility at higher concentrations. Conversely, the RIA showed excellent reproducibility at concentrations greater than 50 microU/ml insulin, but poor sensitivity and high coefficients of variation below this level. The ELISA procedure offers practical advantages over the RIA, and performs well when measuring physiological concentrations of insulin.

Increased preproinsulin mRNA in pancreatic islets incubated with islet cell-stimulating antibodies from serums of type I diabetic patients

We recently described autoantibodies that stimulate the release of insulin from pancreatic beta-cells both in vitro and in vivo. The aim of this study was to establish whether islet cell-stimulating antibodies (ICSTAs) also increase islet cell preproinsulin mRNA content. Wistar rat islets, isolated by collagenase digestion, were exposed to 2.7 and 11.1 mM glucose. Insulin release increased 10-fold in response to the higher glucose concentration, and dot-blot analysis of islet mRNA with a rat preproinsulin cDNA probe showed a concomitant increase in mRNA levels. The globulin fractions of four test serums, three from patients with type I (insulin-dependent) diabetes and one from a patient with the insulin autoimmune syndrome, showed clear (5- to 8-fold) stimulation of insulin release. The nonglobulin fractions of these serums and both fractions of three control serums failed to stimulate secretion of insulin. The insulin mRNA content of islets incubated with the ICSTA globulin fractions was greatly increased compared with levels observed in islets treated with control serum globulin fractions. We conclude that ICSTAs not only can stimulate the release of insulin but also increase the preproinsulin mRNA content of islet cells.

HbA1 in assessment of metabolic control in diabetic BB/E rats

Estimations of HbA1 levels have been used to assess long-term glycaemic control in spontaneously diabetic BB/E rats. The degree of metabolic control achieved by once daily insulin injections and continuous insulin infusion by osmotic minipump was compared. Citrate gel electrophoresis of lysed erythrocytes, previously washed and incubated in 0.9% NaCl, gave accurate HbA1 values without interference from either abnormal Hb variants or labile glycosylation products. Over a 12 week period there was no significant difference in the mean random weekly plasma glucose concentrations between diabetic rats maintained on insulin injections or continuous infusion therapy. The HbA1 values in the injection-treated animals remained unchanged throughout the study period (mean +/- SEM = 5.1 +/- 0.1%). Diabetic rats treated by osmotic minipump showed a steady decline in values over the same period (4.1 +/- 0.1%; p less than 0.001 vs injected rats) but levels remained higher than those recorded in non-diabetic control rats (2.9 +/- 0.01%; p less than 0.001 vs pump-treated rats). These differences in HbA1 were reflected in the plasma glucose values obtained during a 30 h glucose profile performed after six weeks of insulin therapy. Diabetic rats on injection therapy showed considerable diurnal variation in plasma glucose concentration (5.5-11.2 mmol/l; mean 8.9 +/- 0.5) but continuous insulin infusion eliminated the fluctuations giving a significantly lower mean glucose level over the 30 h period (7.3 +/- 0.1 mmol/l; p less than 0.005). HbA1 levels show a poor correlation with random plasma glucose estimations (r = 0.43) but provide a simple and accurate assessment of long-term glycaemic control without the need for multiple 24 h glucose profiles.

Effect of cyclosporin on pancreatic events and development of diabetes in BB/Edinburgh rats

The effect of cyclosporin administered from 30 to 100 days of age on pancreatic events and the development of insulin-dependent diabetes has been studied by serial pancreatic biopsy of individual diabetes-prone BB/Edinburgh rats. Cyclosporin completely prevented the development of diabetes up to 150 days of age and reduced the incidence to 50% of controls at 452 days of age. Islet cell surface antibodies paralleled the development of diabetes. Insulin autoantibodies were unrelated to diabetes and not affected by cyclosporin. Immunohistochemical analysis of pancreatic biopsies from untreated control diabetes-prone rats with monoclonal antibodies specific for rat MHC molecules and T- and B-lymphocyte and macrophage subsets showed that the first abnormality seen in rats that subsequently developed diabetes was hyperexpression of MHC class I molecules on vascular endothelium and islet cells. This was followed by accumulation of ED1+ macrophages at perivascular and periductal sites adjacent to noninfiltrated islets. Increased expression of MHC class II molecules on vascular endothelial cells was also noted. Most cells infiltrating the islets initially were also ED1+ macrophages, followed by increasing numbers of other activated effector cells including helper and cytotoxic-suppressor T lymphocytes and natural killer cells. Obliteration of insulin-containing cells was associated with regression of the infiltrate. Treatment with cyclosporin had no effect on pancreatic hyperexpression of MHC class I molecules but markedly inhibited accumulation of ED1+ cells at extraislet sites, the subsequent recruitment of immune effector cells, and islet infiltration. This resulted in a delay of the onset of diabetes in some rats and prevention of diabetes in others.

Elevated neuropeptide Y concentrations in the central hypothalamus of the spontaneously diabetic BB/E Wistar rat

Insulin-deficient diabetes causes hypothalamic and pituitary dysfunction. The possible role of hypothalamic regulatory peptides in mediating these disturbances was investigated in spontaneously diabetic BB/E Wistar rats. Concentrations of 10 regulatory peptides were measured in the central (nucleus-rich) and lateral parts of the hypothalamus in 18 diabetic and 5 non-diabetic BB/E rats. Diabetic rats were treated with either intensified or low-dose insulin schedules to achieve moderate or severe hyperglycaemia (mean blood glucose concentrations, 8 and 20 mmol l-1 respectively). Neuropeptide Y concentration and content in the central hypothalamus were increased by 30-40% in both moderately and severely hyperglycaemic diabetic groups (p less than 0.01). Lateral hypothalamic neuropeptide Y levels did not differ significantly between the groups. The only other peptide to show any significant difference between diabetic and control rats was calcitonin gene-related peptide, whose central hypothalamic concentrations were significantly increased in the severely hyperglycaemic animals. Alterations of hypothalamic neuropeptide Y, which has potent experimental effects on hypothalamo-pituitary function, may contribute to certain neuroendocrine disturbances in insulin-deficient diabetes.

Timed interruption of insulin therapy in diabetic BB/E rat pregnancy: effect on maternal metabolism and fetal outcome

Experimental and clinical studies have suggested that periods of poor metabolic control in early diabetic pregnancy have an adverse effect on the developing embryo, but the precise nature and mechanism of this damaging influence have not been defined. In this study the effect of withdrawing treatment with insulin for 2 days at various times during early gestation on maternal metabolism and fetal outcome has been investigated in the spontaneously diabetic BB/E rat. Non-diabetic BB/E rats and diabetic BB/E rats treated continuously with insulin throughout pregnancy served as controls. Continuously treated diabetic rats had a higher rate of fetal resorption and bigger placentae and their offspring had fewer ossification centres, lower extractable pancreatic insulin content, larger hearts, and smaller kidneys and lungs than the offspring of non-diabetic rats. Interruption of treatment with insulin further aggravated the adverse effect of diabetes on the outcome of pregnancy by resulting in a further increase in the rate of fetal resorption, a rise in the neonatal death rate, a reduction in fetal body weight, and retardation of skeletal development. These effects were more apparent when interruption of treatment with insulin occurred during the period of organogenesis, i.e. during gestational days 8 and 9, and 10 and 11. Two severe malformations were seen, both in litters originating from mothers whose treatment with insulin was interrupted during and immediately before fetal organogenesis. We conclude that a period of disturbed maternal metabolism during fetal organogenesis is capable of affecting the survival, growth, and organ development of the fetus and that the spontaneously diabetic insulin-dependent BB rat appears to be a good model for studies of the effect of diabetes and its treatment on the outcome of pregnancy.

Graves' disease of the beta cell: glucose dysregulation due to islet-cell stimulating antibodies

The immunoglobulin fractions of serum from patients with spontaneous hyperinsulinaemic hypoglycaemia and others with type 1 diabetes stimulated insulin release both in islet-cell cultures and in vivo in rats. Serum from patients with type 2 diabetes, which is not an autoimmune disease, did not stimulate insulin release. The discovery of islet-cell-stimulating antibodies (ICSTA) completes for the islet the triad of autoantibodies (anticytoplasmic, antiproduct, and antireceptor) previously described in autoimmune thyroid disease. ICSTA may be important modulators of islet-cell secretion in man.

Distinct macrophage subpopulations in pancreas of prediabetic BB/E rats. Possible role for macrophages in pathogenesis of IDDM

Use of monoclonal antibodies directed against rat macrophages and serial pancreatic biopsy in the prediabetic period have enabled us to document the involvement of macrophages in the pancreatic events leading to onset of diabetes in the spontaneously diabetic BB/E rat. A few weeks before onset of disease, there is marked recruitment and accumulation of ED1+ macrophages at periductal and perivascular locations adjacent to noninfiltrated islets. These recruited cells, distinct from the resident ED2+ tissue macrophages, then infiltrate the islets. Infiltration of the pancreas by ED1+ macrophages is therefore a very early event in the prediabetic period and suggests a possible role for macrophages in the pathogenesis of insulin-dependent diabetes mellitus (IDDM) in this animal model.

Pre-diabetes in the spontaneously diabetic BB/E rat: pancreatic infiltration and islet cell proliferation

A cohort of BB/E rats derived from litters with a high and low incidence of IDDM was studied prospectively to examine the relationship between circulating autoantibodies, islet insulin secretion, pancreatic infiltration, and islet cell replication during the pre-diabetic period. Although a higher incidence of islet cell surface (ICSA) and insulin autoantibodies (IAA) was detected in the diabetes-prone than in the low diabetic-incidence BB/E rats there was no correlation between the two antibodies in individual animals. Moreover, ICSA, but not IAA, were associated with loss of first phase islet insulin release. Between 75 and 105 days of age the number of diabetes-prone rats with ICSA and impaired islet insulin secretory function increased. Over the same period, there was a concomitant increase in the proportion of diabetes-prone animals with pancreatic infiltration, and increased islet endocrine cell proliferation. All these interrelated phenomena were observed in diabetes-prone BB/E rats at a time when the animals were normoglycaemic.

Insulin autoantibodies, islet cell surface antibodies and the development of spontaneous diabetes in the BB/Edinburgh rat

The presence of insulin autoantibodies (IAA) and islet cell surface antibodies (ICSA) was sought in two longitudinal studies, involving BB/Edinburgh rats of high (BB/E/H, n = 157) and low (BB/E/L, n = 61) susceptibility to diabetes development. Both studies were designed to correlate pancreatic morphology with cellular and humoral immunity. In Study I, groups of eight male and eight female non-diabetic rats of the BB/E/H line were killed at 15 day intervals from 30-105 days and plasma samples were obtained by cardiac puncture. In study II, 61 BB/E/H and 41 BB/E/L rats underwent pancreatic biopsy 1-3 times from 30 days of age until onset of diabetes or 150 days, plasma samples being taken from the tail vein at biopsy. Both studies revealed a higher prevalence for ICSA than IAA in BB/E rats. Whereas a highly significant association of ICSA with diabetes development was observed in study II (chi 2 = 8.30, P less than 0.005), IAA were associated with diabetes development only weakly (P less than 0.03, Mann-Witney U-rank test). No correlation between the presence of ICSA and IAA in individual rats was observed and IAA were not significantly associated with BB/E/H in preference to BB/E/L rats, although positive IAA values were significantly elevated in the former compared with the latter (P less than 0.01). These observations support the concept that IAA form part of a background of heightened autoimmunity against which frank diabetes develops in some animals.

Immunological responses of the BB rat colony in Edinburgh

Several immunological responses of the spontaneously diabetic BB rat colony in Edinburgh designated (BB/E) have been studied. The proliferative responses to Con A and LPS, ability to make IL-2 and to show NK activity have been studied using diabetic and non-diabetic BB/E rats and normal Wistar rats. Our data suggest that the diabetic animals in the BB/E colony do not have marked deficiencies in any of these parameters. Lymphopenia and depressed T-cell responses do not appear to be a prerequisite for the development of diabetes in the BB/E colony.

Xiaoke, a traditional Chinese treatment for diabetes. Studies in streptozotocin diabetic mice and spontaneously diabetic BB/E rats

Xiaoke tea is consumed as a traditional herbal treatment for diabetes mellitus in China. An aqueous extract of Xiaoke (1 g of dried plant preparation in 64 ml of water), supplied ad lib in place of drinking water during the induction and development of streptozotocin diabetes in mice, reduced (about 30%) plasma glucose concentrations by 25 days. The polydipsia and hyperphagia of the streptozotocin diabetic mice were also reduced by Xiaoke, and the effects lapsed after treatment was withdrawn. Xiaoke did not significantly alter plasma insulin concentrations. Consumption of the Xiaoke extract by insulin-treated diabetic BB/E Wistar rats did not affect glycaemic control or body wt. When insulin treatment was reduced and discontinued, Xiaoke failed to prevent the progression of severe hyperglycaemia and weight loss. The results suggest that the slowly generated antihyperglycaemic effect of Xiaoke in streptozotocin diabetic mice may involve an extrapancreatic effect on food intake, glucose production or glucose clearance. However, as evidenced in BB/E rats, Xiaoke does not substitute for insulin in the absence of endogenous insulin secretion.

Induction of class II MHC antigens in vitro on pancreatic B cells isolated from BB/E rats

The ability of recombinant Interferon-gamma to induce class II expression in vitro on pancreatic islet B cells has been investigated by exposing islets isolated from BB/E and normal Wistar rats to Interferon-gamma and then staining successively with monoclonal antibodies specific for rat class II MHC antigens and insulin. Induction of class II expression was never observed on islet cells obtained from either normal Wistar rats or rats from the BB/E low diabetes incidence (less than 2%) subline. In contrast, pancreatic B cells from rats from the BB/E high diabetes incidence (60-70%) subline expressed class II antigen following culture with Interferon-gamma.

Islet cell surface antibodies in genetically obese hyperglycaemic (ob/ob) mice

A quantitative method for circulating islet cell surface antibodies (ICSA), based on the binding of 125I-protein A to insulin-producing RINm5F cells, was used to evaluate ICSA in plasma of 4- to 40-week-old Aston obese hyperglycaemic (ob/ob) mice and normal control (+/+) mice. RINm5F cells bound 2502 +/- 1196 c.p.m. 125I-protein A per 10(5) cells (mean +/- S.D., n = 54) after incubation with +/+ plasma. ICSA positive plasma (defined as 125I-protein A binding, mean +/- 2 S.D. of +/+ plasma) was detected in 3 out of 54 +/+ mice and 3 out of 54 ob/ob mice. ICSA were not observed in ob/ob mice before the onset of diabetes (7 weeks of age), but were detected at 9, 20 and 40 weeks. At 20 weeks 125I-protein A binding produced by ob/ob plasma was 35% greater than +/+ plasma (P less than 0.05). The low occurrence of ICSA in ob/ob mice (6%) suggests that factors other than ICSA are responsible for B-cell dysfunction and eventual islet degeneration observed in Aston ob/ob mice.

Pre-diabetes in the spontaneously diabetic BB/E rat: lymphocyte subpopulations in the pancreatic infiltrate and expression of rat MHC class II molecules in endocrine cells

Use of monoclonal antibodies specific for rat lymphocyte subsets and an anti-insulin marker has allowed us to document the following sequence of events leading to the development of clinical diabetes in this animal model. The first change observed in the pancreas is increased expression of MHC class II molecules on vascular endothelium and this precedes lymphocytic infiltration. Next, T cells of the T helper phenotype infiltrate the pancreas around blood vessels. Many of the infiltrating T cells show class II expression indicating that they are activated. A few cytotoxic and suppressor cells and B lymphocytes are also present and their numbers increase proportionately with rat age. Some macrophages are also seen. Finally, at a late stage class II MHC molecules can be detected in partially destroyed islets on beta cells which are still actively synthesising insulin. We have never observed expression of class II molecules on glucagon or somatostatin secreting cells which are invariably well preserved.

Assessment of the antidiabetic activity of epicatechin in streptozotocin-diabetic and spontaneously diabetic BB/E rats

(-)-Epicatechin has previously been suggested to rapidly reverse alloxan diabetes in rats. We have assessed the therapeutic value of the compound in two further animal models of insulin-dependent diabetes mellitus, namely streptozotocin-diabetic rats and the spontaneously diabetic BB/E rat. There was no indication of a reversal of established diabetes in either the streptozotocin-diabetic or the spontaneously diabetic BB/E rats. Moreover, epicatechin also failed to halt the progression of the disease in prediabetic BB/E rats. Earlier claims of the potential use of epicatechin as an antidiabetic agent must therefore be treated with some caution.

The effect of valproate on blood metabolite concentrations in spontaneously diabetic, ketoacidotic, BB/E Wistar rats

Valproate is an effective anticonvulsant which is rarely associated with hepatotoxicity. It has profound effects on the intermediary metabolism of isolated rat hepatocytes. In this paper the effect of valproate on blood metabolite concentrations in spontaneously diabetic BB/E rats has been studied. Valproate causes a marked fall in blood ketone body concentrations and a smaller fall in blood glucose concentrations following either oral or intraperitoneal administration. Valproate may have a role in the treatment of patients with "brittle" diabetes.