Liver hypertrophy: a review of adaptive (adverse and non-adverse) changes--conclusions from the 3rd International ESTP Expert Workshop

Preclinical toxicity studies have demonstrated that exposure of laboratory animals to liver enzyme inducers during preclinical safety assessment results in a signature of toxicological changes characterized by an increase in liver weight, hepatocellular hypertrophy, cell proliferation, and, frequently in long-term (life-time) studies, hepatocarcinogenesis. Recent advances over the last decade have revealed that for many xenobiotics, these changes may be induced through a common mechanism of action involving activation of the nuclear hormone receptors CAR, PXR, or PPARα. The generation of genetically engineered mice that express altered versions of these nuclear hormone receptors, together with other avenues of investigation, have now demonstrated that sensitivity to many of these effects is rodent-specific. These data are consistent with the available epidemiological and empirical human evidence and lend support to the scientific opinion that these changes have little relevance to man. The ESTP therefore convened an international panel of experts to debate the evidence in order to more clearly define for toxicologic pathologists what is considered adverse in the context of hepatocellular hypertrophy. The results of this workshop concluded that hepatomegaly as a consequence of hepatocellular hypertrophy without histologic or clinical pathology alterations indicative of liver toxicity was considered an adaptive and a non-adverse reaction. This conclusion should normally be reached by an integrative weight of evidence approach.

Peptidoglycan from Staphylococcus aureus induces T(H)2 immune response in mice

BACKGROUND AND OBJECTIVE

Atopic dermatitis patients have an increased number of type 2 helper (T(H)2) cells in their peripheral blood and superficial Staphylococcus aureus colonization. The purpose of this study was to clarify the effects of peptidoglycan (PEG) from S aureus on the induction of the TH2 immune response in mice.

METHODS

Mice were primed with PEG- and ovalbumin (OVA)-pulsed Langerhans cells (LCs) and given a booster OVA injection 2 days later via the hind footpad. Five days later, the cytokine response in the draining popliteal lymph nodes was investigated by reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay (ELISA). IL-12 production from cultured LCs was detected by ELISA and Western blot analysis.

RESULTS

Administration of PEG- and OVA-pulsed LCs into the hind footpads of the mice induced a T(H)2-prone immune response as represented by the enhanced interleukin (IL) 4 expression in the lymph nodes. We further showed that higher levels of IL-12 p40 production by PEG-stimulated LCs relative to IL-12 p70 (p35/p40) production were associated with the induction of the T(H)2 immune response.The LC-derived IL-12 p40 protein induced by PEG stimulation was detected mainly as monomeric and homodimeric IL-12 p40 subunits; other heterodimers including the L-12 p40 subunit, such as IL-23, were undetected.

CONCLUSION

These results suggest that PEG may have the ability to induce the development of T(H)2 cells through insufficient production of IL-12 p70 and excessive production by LCs of homodimeric IL-12 p40, a known antagonist of bioactive IL-12 p70, offering a possible explanation for the role of S aureus colonization in patients with atopic dermatitis.

Percutaneous application of peptidoglycan from Staphylococcus aureus induces infiltration of CCR4+ cells into mouse skin

BACKGROUND

The lesional skin of patients with atopic dermatitis has an increased number of type 2 helper T (TH2) cells in the dermis and is superficially colonized by Staphylococcus aureus. The purpose of this study was to determine the effects of peptidoglycan (PEG) from S aureus on TH2 cell induction in murine skin.

METHODS

Mice were sensitized with house dust mite antigen (MA) by topical application to barrier-disrupted abdominal skin. Seven days after sensitization, PEG was applied to the barrier-disrupted dorsal skin. After a further 3 days, C-C chemokine receptor type 4-positive (CCR4+) cells were counted in the PEG-treated skin.The production of chemokine (C-C) motif ligand 17 (CCL17) (thymus- and activation-regulated chemokine) and CCL22 (macrophage-derived chemokine) in the skin was investigated using reverse transcriptase polymerase chain reaction and immunohistological analysis.

RESULTS

Application of PEG to the dorsal skin of MA-sensitized mice led to a significant increase in the number of cells expressing CCR4 in the dermis. The skin of PEG-treated mice showed an increased level of CCL17 mRNA expression, which coincided with TH2 cytokine mRNA expression. Immunohistological analysis demonstrated that levels of CCL17 transcripts corresponded to those of protein synthesis in the epidermis. CCL17 production was induced mainly by Langerhans cells stimulated with PEG. Furthermore, intraperitoneal injection of anti-CCL17 antibody abrogated the induction of CCR4+ cells in the skin.

CONCLUSION

These results suggest that PEG may induce TH2 cells in the skin through the production of CCL17 by Langerhans cells and would explain the role of colonization by S aureus in patients with atopic dermatitis.

Investigation of carcinogenicity for levamisole administered in the diet to F344 rats

A two year carcinogenicity study of anthelmintic drug levamisole (LV) was performed using 50 male and 50 female F344 rats at dietary drug concentrations of 0, 60, or 300 ppm. The daily intakes of LV were calculated to be 2.6, 12.9 mg/kg b.w./day for males and 2.9, 14.1mg/kg b.w./day for females, respectively. No significant differences in general condition and survival rate (82%, 74%, 80% in males and 84%, 84%, 84% in females, respectively) were observed. In the 300 ppm group, suppression of body weight gain was observed from the onset of treatment and reduction in final body weights was 6% in males and 11% in females. Significant increases in the absolute and/or relative weights of the lungs, heart, spleen, liver, kidneys, and adrenals were observed in males and/or females treated with 300 ppm. Some of high incidences neoplasms were observed, and there were also tendencies to increase for mammary gland fibroma and thoracic/abdominal cavity mesothelioma in males. However, there were no significant inter-group differences in incidences, histopathological types or differences compared with historical control data. Thus, it was concluded that LV was not carcinogenic to male and female F344 rats under the experimental conditions.

Inhibitory effects of Schefflera leucantha extract on production of allergic mediators by Langerhans cells and mast cells

BACKGROUND

Schefflera leucantha Viguier is used as a traditional medicine in Thailand and China to relieve chronic cough and asthma. However, little is known about its anti-allergic effects.

OBJECTIVE

This study was designed to investigate the effects of S leucantha ethanol extract (SLEE) on chemokine production by epidermal Langerhans cells (LCs) stimulated with peptidoglycan (PEG) from Staphylococcus aureus and histamine release from mast cells.

METHODS

LCs were purified from murine epidermal cells using the panning method with anti-IA(d) monoclonal antibody. Chemokine production by LCs was investigated by reverse transcription polymerase chain reaction and enzyme-linked immunosorbent assay (ELISA). Mast cells for histamine release assay were induced by long-term culture of mouse spleen cells. Histamine release from these mast cells was measured by a competitive ELISA.

RESULTS

Production of the eosinophil chemoattractant CCL5 and the type 2 T helper (TH2)-associated chemokine CCL17 from PEG-stimulated LCs was significantly inhibited by SLEE. Furthermore, SLEE significantly decreased the release of histamine from mast cells by IgE-mediated degranulation.

CONCLUSION

These results suggest that S leucantha may offer a new therapeutic approach for the control of atopic dermatitis associated with S aureus colonization through inhibition of the production of allergic mediators.

Molecular analysis of the cutaneous Malassezia microbiota from the skin of patients with atopic dermatitis of different severities

Cutaneous Malassezia is an exacerbating factor in patients with atopic dermatitis. We analysed the Malassezia microbiota of adult patients with head and neck atopic dermatitis of different severities (mild, moderate and severe). Of the nine human-associated Malassezia species, the number detected was similar (3.5-4.2 species per case) among the members of all severity groups. However, the ratio of the two major Malassezia species, M. globosa and M. restricta, was different in the severe group.

A 13-week subchronic toxicity study of dietary administered saponin-rich and isoflavones-containing soybean extract in F344 rats

A subchronic toxicity study of soybean extract was performed in F344 rats with dietary administration at concentrations of 0%, 1.25%, 2.5% and 5% for 13 weeks. No mortality or abnormal clinical signs in any group were observed. Body weight gains were decreased with a tendency for reduction of feed intake in the 1.25% and above female and 5% male groups. In males, absolute and relative liver weights were increased in the 1.25% and above groups. In females relative kidney weights were increased in the 1.25% and above groups. Other significant changes such as decreased RBC and hematocrit and increased urea nitrogen were detected in the 2.5% and/or 5% groups. On histopathological observation, atrophy of the ventral prostate was observed in all animals in the 5% male group. Mucification and atrophy of the vaginal epithelium and increased atretic follicles in ovaries were noted in 2.5% and 5% female rats. Based on the above findings the lowest-observed-adverse-effect level for male and female rats was estimated to be 1.25% (707.2 and 751.8 mg/kg b.w./day, respectively).

Percutaneous application of peptidoglycan from Staphylococcus aureus induces eosinophil infiltration in mouse skin

BACKGROUND

Atopic dermatitis (AD) is a chronic inflammatory skin disease with immunopathologic features that vary depending on the duration of the lesion. The lesioned skin of AD patients shows an increased number of inflammatory cells such as eosinophils, mast cells and mononuclear cells in the dermis and superficial Staphylococcus aureus colonization.

OBJECTIVE

The purpose of this study was to determine the effects of peptidoglycan (PEG) from S. aureus on eosinophil induction in murine skin.

METHODS

PEG was applied to the barrier-disrupted abdominal skin of mice every 5 days. Twenty days later, the number of eosinophils in the abdominal skin was counted. The cytokine response in the skin was investigated by RT-PCR and immunohistological analysis. The regulated-upon activation in normal T cells expressed and secreted (RANTES) production from cultured epidermal cells was measured by ELISA.

RESULTS

The skin of mice treated with PEG showed a significantly increased number of eosinophils compared with that of mice treated with vehicle alone. In addition, application of PEG to the abdominal skin of mice increased the expression of mRNA for RANTES, but not that of mRNA for eotaxin, eotaxin-2 and monocyte chemotactic protein-3 in the skin. Immunohistologic analysis demonstrated that the levels of RANTES transcripts corresponded with those of protein synthesis in the epidermis. In vitro experiments using epidermal Langerhans cells (LCs) and keratinocytes (KCs) showed that RANTES production was induced by LCs but not by KCs stimulated with PEG. Furthermore, an intraperitoneal injection of anti-RANTES antibody neutralized the induction of eosinophils in the skin.

CONCLUSION

These results suggest that PEG may have an ability to induce eosinophil infiltration in the skin through RANTES production by LCs, and would explain the role of S. aureus colonization in AD patients.

Evaluation of certain food additives and contaminants

This report represents the conclusions of a Joint FAO/WHO Expert Committee convened to evaluate the safety of various food additives, including flavouring agents, with a view to recommending acceptable daily intakes (ADIs) and to preparing specifications for identity and purity. The Committee also evaluated the risk posed by two food contaminants, with the aim of advising on risk management options for the purpose of public health protection. The first part of the report contains a general discussion of the principles governing the toxicological evaluation and assessment of intake of food additives (in particular flavouring agents) and contaminants. A summary follows of the Committee's evaluations of technical, toxicological and intake data for certain food additives (acidified sodium chlorite, asparaginase from Aspergillus oryzae expressed in Aspergillus oryzae, carrageenan and processed Eucheuma seaweed, cyclotetraglucose and cyclotetraglucose syrup, isoamylase from Pseudomonas amyloderamosa, magnesium sulfate, phospholipase A1 from Fusarium venenatum expressed in Aspergillus oryzae, sodium iron(III) ethylenediaminetetraacetic acid (EDTA) and steviol glycosides); eight groups of related flavouring agents (linear and branched-chain aliphatic, unsaturated, unconjugated alcohols, aldehydes, acids and related esters; aliphatic acyclic and alicyclic terpenoid tertiary alcohols and structurally related substances; simple aliphatic and aromatic sulfides and thiols; aliphatic acyclic dials, trials and related substances; aliphatic acetals; sulfur-containing heterocyclic compounds; aliphatic and aromatic amines and amides; and aliphatic alicyclic linear alpha, beta -unsaturated di- and trienals and related alcohols, acids and esters); and two food contaminants (aflatoxin and ochratoxin A). Specifications for the following food additives were revised: maltol and ethyl maltol, nisin preparation, pectins, polyvinyl alcohol, and sucrose esters of fatty acids. Specifications for the following flavouring agents were revised: maltol and ethyl maltol, maltyl isobutyrate, 3-acetyl-2,5-dimethylfuran and 2,4,5-trimethyl-delta-oxazoline (Nos 1482, 1506 and 1559), and monomenthyl glutarate (No. 1414), as well as the method of assay for the sodium salts of certain flavouring agents. Annexed to the report are tables summarizing the Committee's recommendations for intakes and toxicological evaluations of the food additives and contaminants considered.

cDNA cloning and functional characterization of Xenopus laevis DNase γ

We report here the cDNA cloning and functional analysis of Xenopus DNase gamma (xDNase gamma). Two forms of cDNAs are isolated from adult spleen: one composing a 933 bp open reading frame for the enzymatically active xDNase gamma protein, and the other encoding an inactive short alternative form. Northern blot analysis revealed that the xDNase gamma mRNA is expressed in spleen, liver, testis, and ovary. xDNase gamma expression is scarcely detected in the tail muscle of tadpoles; however, it increases during metamorphosis and reaches a maximum during the late metamorphic climax. The ectopic expression of xDNase gamma results in the appearance of extensive DNA fragmentation in C2C12 myoblasts after the induction of apoptosis. In contrast, Xenopus DNase I fails to induce apoptotic DNA ladder formation under the same conditions. Our results suggest a possible involvement of xDNase gamma in apoptosis during amphibian metamorphosis.

Percutaneous application of peptidoglycan from Staphylococcus aureus induces mast cell development in mouse spleen

BACKGROUND

Previously, we found that percutaneous application of peptidoglycan (PEG) from Staphylococcus aureus increased the number of mast cells in the dermis, as seen in patients with atopic dermatitis. However, the origin of the mast cells infiltrating the dermis was not known. Our aim was to determine the origin of the skin mast cells induced by the percutaneous PEG application in mice.

METHODS

PEG was applied to barrier-disrupted abdominal skin of mice every 5 days. Twenty days after the first application, mast cells were detected in the spleen cells by alcian blue-safranin staining. Expression of mast cell proteases and cytokines in the skin or spleen was investigated by reverse transcription-polymerase chain reaction.

RESULTS

Percutaneous application of PEG increased the numbers of alcian blue-positive and safranin-negative mast cells in the spleen. Reverse transcription-polymerase chain reaction analysis of the spleen showed that these mast cells expressed mouse mast cell protease (MMCP)-1, MMCP-4, MMCP-5, and mast cell carboxypeptidase, suggesting that they were immature cells positioned developmentally between mucosal mast cells and connective tissue mast cells. In vitro long-term culture of spleen cells in the presence of PEG induced mast cell development. The features of these mast cells were coincident with those seen in the spleens of PEG-applied mice. Furthermore, when mice were intradermally injected, their skin showed increased levels of expression of mRNAs of MMCP-4, MMCP-5, and mast cell carboxypeptidase, but not MMCP-1. Similar mRNA expression was observed in the skin of PEG-applied mice.

CONCLUSIONS

Percutaneous application of PEG may lead to the development of mast cells in the spleens of mice and contribute to an increase in mast cell numbers in the dermis, as seen in the skin lesions of atopic dermatitis patients.