Two samples of diesel exhaust particles (DEPs) predominate in health effects research: an automobile-derived DEP (A-DEP) sample and the National Institute of Standards Technology standard reference material (SRM 2975) generated from a forklift engine. A-DEPs have been tested extensively for their effects on pulmonary inflammation and exacerbation of allergic asthmalike responses. In contrast, SRM 2975 has been tested thoroughly for its genotoxicity. In the present study, we combined physical and chemical analyses of both DEP samples with pulmonary toxicity testing in CD-1 mice to compare the two materials and to make associations between their physicochemical properties and their biologic effects. A-DEPs had more than 10 times the amount of extractable organic material and less than one-sixth the amount of elemental carbon compared with SRM 2975. Aspiration of 100 micro g of either DEP sample in saline produced mild acute lung injury; however, A-DEPs induced macrophage influx and activation, whereas SRM 2975 enhanced polymorphonuclear cell inflammation. A-DEPs stimulated an increase in interleukin-6 (IL-6), tumor necrosis factor alpha, macrophage inhibitory protein-2, and the TH2 cytokine IL-5, whereas SRM 2975 only induced significant levels of IL-6. Fractionated organic extracts of the same quantity of DEPs (100 micro g) did not have a discernable effect on lung responses and will require further study. The disparate results obtained highlight the need for chemical, physical, and source characterization of particle samples under investigation. Multidisciplinary toxicity testing of diesel emissions derived from a variety of generation and collection conditions is required to meaningfully assess the health hazards associated with exposures to DEPs. Key words: automobile, diesel exhaust particles, forklift, mice, pulmonary toxicity, SRM 2975.

Many pulmonary toxicity studies of diesel exhaust particles (DEPs) have used an automobile-generated sample (A-DEPs) whose mutagenicity has not been reported. In contrast, many mutagenicity studies of DEPs have used a forklift-generated sample (SRM 2975) that has been evaluated in only a few pulmonary toxicity studies. Therefore, we evaluated the mutagenicity of both DEPs in Salmonella coupled to a bioassay-directed fractionation. The percentage of extractable organic material (EOM) was 26.3% for A-DEPs and 2% for SRM 2975. Most of the A-EOM (~55%) eluted in the hexane fraction, reflecting the presence of alkanes and alkenes, typical of uncombusted fuel. In contrast, most of the SRM 2975 EOM (~58%) eluted in the polar methanol fraction, indicative of oxygenated and/or nitrated organics derived from combustion. Most of the direct-acting, base-substitution activity of the A-EOM eluted in the hexane/dichloromethane (DCM) fraction, but this activity eluted in the polar methanol fraction for the SRM 2975 EOM. The direct-acting frameshift mutagenicity eluted across fractions of A-EOM, whereas > 80% eluted only in the DCM fraction of SRM 2975 EOM. The A-DEPs were more mutagenic than SRM 2975 per mass of particle, having 227 times more polycyclic aromatic hydrocarbon-type and 8-45 more nitroarene-type mutagenic activity. These differences were associated with the different conditions under which the two DEP samples were generated and collected. A comprehensive understanding of the mechanisms responsible for the health effects of DEPs requires the evaluation of DEP standards for a variety of end points, and our results highlight the need for multidisciplinary studies on a variety of representative samples of DEPs.

No abstract

SummaryMacrophages are the major source of the chemokines macrophage inflammatory protein-2 (MIP-2) and keratinocyte-derived chemokine (KC), which play a major role in neutrophil migration to sites of inflammation. Although extracellular ATP from inflammatory tissues induces several immune responses in macrophages, it is unclear whether ATP-stimulated macrophages affect neutrophil migration. Therefore, the aim of the present study was to investigate the role of ATP-induced MIP-2 production by macrophages. When ATP was injected intraperitoneally into mice, the number of neutrophils within the peritoneal cavity markedly increased, along with the levels of MIP-2 and KC in the peritoneal lavage fluid. Consistent with this, ATP induced MIP-2 production, but not that of KC, by peritoneal exudate macrophages (PEMs) in vitro. This occurred via interactions with the P2X 7 receptor and P2Y 2 receptor. Furthermore, treatment of PEMs with ATP led to the production of reactive oxygen species. The ATP-induced MIP-2 production was inhibited by treatment with the antioxidant N-acetyl-L-cysteine. Also, MIP-2 production was inhibited by pre-incubating PEMs with inhibitors of extracellular signal-regulated kinase 1/2 or p38 mitogen-activated protein kinase. The MIP-2 neutralization reduced the increase in neutrophil numbers observed in ATP-treated mice. Taken together, these results suggest that increased production of reactive oxygen species by ATP-stimulated macrophages activates the signalling pathways that promote MIP-2 production which, in turn, induces neutrophil migration.

Ras GTPase-activating proteins negatively regulate the Ras/Erk signaling pathway, thereby playing crucial roles in the proliferation, function, and development of various types of cells. In this study, we identified a novel Ras GTPase-activating proteins protein, RASAL3, which is predominantly expressed in cells of hematopoietic lineages, including NKT, B, and T cells. We established systemic RASAL3-deficient mice, and the mice exhibited a severe decrease in NKT cells in the liver at 8 weeks of age. The treatment of RASAL3-deficient mice with α-GalCer, a specific agonist for NKT cells, induced liver damage, but the level was less severe than that in RASAL3-competent mice, and the attenuated liver damage was accompanied by a reduced production of interleukin-4 and interferon-γ from NKT cells. RASAL3-deficient NKT cells treated with α-GalCer in vitro presented augmented Erk phosphorylation, suggesting that there is dysregulated Ras signaling in the NKT cells of RASAL3-deficient mice. Taken together, these results suggest that RASAL3 plays an important role in the expansion and functions of NKT cells in the liver by negatively regulating Ras/Erk signaling, and might be a therapeutic target for NKT-associated diseases.Keywords: α-GalCer r IL-4 r Liver injury r NKT cell r Ras r RasGAP Additional supporting information may be found in the online version of this article at the publisher's web-site IntroductionRas proteins have been shown to play pivotal roles in proliferation, differentiation, and oncogenesis by functioning as a molecular switch for intracellular signaling pathways [1,2]. In order to act as a switch, Ras has two forms, an inactive GDP-bound form and an active GTP-bound form. GDP-bound Ras is dominant under the steady-state condition. Upon agonist binding to its receptor on the cell membrane, GDP-bound Ras is converted into active GTPbound Ras, which stimulates downstream signaling cascades, such as the Raf/Erk and phosphoinositide-3 kinase/Akt pathways [3]. Such switching of Ras forms is controlled by its intrinsic GTPase activity, and a balance between Ras guanine nucleotide exchange factors (RasGEFs) and Ras GTPase-activating proteins (RasGAPs) [4]. While RasGEFs act as a positive factor for Ras signaling by stimulating the conversion of Ras-GDP into Ras-GTP, RasGAPs act as negative factors by stimulating the rate of GTP hydrolysis from Ras-GTP into Ras-GDP [4]. Ras regulates the activation, differentiation, and proliferation of lymphoid cells. For instance, p21ras (K-Ras) regulates the function and growth of T cells and thymocytes during both immune activation and T-cell development [5][6][7]. In addition, TCR activation in T cells stimulates Ras, which initiates downstream signaling pathways leading to the production of cytokines such as IL-2, and subsequent IL-2-induced proliferation [8,9]. A deficiency of the RasGRP1 gene, a RasGEF, in mice inactivates the TCR activation-induced Ras signaling in thymocytes, and the mice have reduced single-positive (CD4 + CD8 − and CD4 − CD8 + ) thymocytes [10]....

No abstract

Renal stone formation and renal failure among Chinese infants administered melamine-containing formula were increasingly reported in 2008. We investigated the mechanism by which melamine and cyanuric acid induce renal stone formation and renal failure. Ten-week-old rats were administered either melamine [2.4, 24, or 240 mg/kg/day], both melamine and cyanuric acid [each at 1.2, 12, or 120 mg/kg/day], or water (controls). Blood and 24-h urine samples and kidney sections were evaluated on days 3, 7, and 14. In rats administered melamine alone or the low-dose melamine/cyanuric acid combination [1.2 mg/kg/day], crystals were not detected. On day 3, crystal formation was observed in the renal distal tubular lumens and collecting ducts of rats administered the intermediate-dose melamine/cyanuric acid [12 mg/kg/day], and the number of crystals increased during the course of the experiment. In rats administered the high-dose melamine/cyanuric acid [120 mg/kg/day], crystals were found in the proximal tubular lumens of the renal cortex on day 3, but acute renal failure resulted in death by day 7. Polarized light optical microphotography and scanning electron microscopy revealed tubular lumens occluded by a layer of axle-shaped crystals. X-ray diffraction findings revealed a nitrogen component but no calcium. The upper regions of occluded tubes were expanded, and the epithelium was thin. Melamine and cyanuric acid in combination, but not by melamine alone induce crystal formation and affected renal functioning. Renal failure due to melamine cyanurate crystals appears to occur via tubular occlusion.

No abstract