Increased exposure of plankton to arsenic in contaminated weakly-stratified lakes.

Arsenic, a priority Superfund contaminant and carcinogen, is a legacy pollutant impacting aquatic ecosystems in urban lakes downwind of the former ASARCO copper smelter in Ruston, WA, now a Superfund site. We examined the mobility of arsenic from contaminated sediments and arsenic bioaccumulation in phytoplankton and zooplankton in lakes with varying mixing regimes. In lakes with strong seasonal thermal stratification, high aqueous arsenic concentrations were limited to anoxic bottom waters that formed during summer stratification, and arsenic concentrations were low in oxic surface waters. However, in weakly-stratified lakes, the entire water column, including the fully oxic surface waters, had elevated concentrations of arsenic (up to 30µgL-1) during the summer. We found enhanced trophic transfer of arsenic through the base of the aquatic food web in weakly-stratified lakes; plankton in these lakes accumulated up to an order of magnitude more arsenic on multiple sampling days than plankton in stratified lakes with similar levels of contamination. We posit that greater bioaccumulation in weakly-stratified lakes was due to elevated arsenic in oxic waters. Aquatic life primarily inhabits oxic waters and in the oxic water column of weakly-stratified lakes arsenic was speciated as arsenate, which is readily taken up by phytoplankton because of its structural similarities to phosphate. Our study indicates that mobilization of arsenic from lake sediments into overlying oxic water columns in weakly-stratified lakes leads to increased arsenic exposure and uptake at the base of the aquatic food web.

Material Parameter Determination of an L4-L5 Motion Segment Finite Element Model Under High Loading Rates.

Underbody blast (UBB) events impart vertical loads through a victim’s lumbar spine, resulting in fracture, paralysis, and disc rupture. Validated biofidelic lumbar models allow characterization of injury mechanisms and development of personal protective equipment. Previous studies have focused on lumbar mechanics under quasi-static loading. However, it is unclear how the role and response of individual spinal components of the lumbar spine change under dynamic loading. The present study leverages high-rate impacts of progressively dissected two-vertebra lumbar motion segments and Split-Hopkinson pressure bar tissue characterization to identify and validate material properties of a high-fidelity lumbar spine finite element model for UBB. The annulus fibrosus was modeled as a fiber-reinforced Mooney-Rivlin material, while ligaments were represented by nonlinear spring elements. Optimization and evaluation of material parameters was achieved by minimizing the root-mean-square (RMS) of compressive displacement and sagittal rotation for selected experimental conditions. Applying dynamic based material models and parameters resulted in a 0.42% difference between predicted and experiment axial compression during impact loading. This dynamically optimized lumbar model is suited for cross validation against whole-lumbar loading scenarios, and prediction of injury during UBB and other dynamic events.

Donor-derived soluble MHC antigens plus low-dose cyclosporine induce transplantation unresponsiveness independent of the thymus by down-regulating T cell-mediated alloresponses in a rat transplantation model.

BACKGROUND: In vitro, soluble MHC (sMHC) antigens modulate and induce apoptosis in alloreactive and antigen-specific T cells, demonstrating their potency to regulate T cell-mediated immune responses. However, their efficacy to regulate immunological responses in vivo remains unclear. Here, we report that repetitive intraperitoneal injection of recombinant Lewis rat-derived MHC class I antigens in Dark Agouti (DA) rats modulates alloreactivity. METHODS: RT1.A1 (Lewis derived) genes were cloned into mammalian expression vectors, and RT1.Aa (DA derived) genes were used to transfect a rat myeloma cell line. RT1.A1 molecules were injected intraperitoneally in DA recipients that subsequently underwent transplantation with Lewis-derived cardiac allografts. RESULTS: Soluble class I antigens were secreted by the transfected cells and were shown to be heterodimeric, peptide-loaded, and conformationally folded. Injection of donor-derived soluble MHC significantly reduced the ability of recipient animals to mount a cytotoxic T-cell response to donor-derived tissue. More interestingly, this treatment significantly prolonged donor-graft survival and allowed 60% of treated animals to develop graft tolerance (>120 days), when donor sMHC were combined with a single subtherapeutic dosage of cyclosporine. Thymectomy of recipient animals before transplantation did not interfere with induction of peripheral tolerance. CONCLUSIONS: Donor-derived sMHC are potential tolerogens for down-regulating the cytotoxic T-cell response of animals that undergo transplantation. Thus, these data provide for the first time a rationale for the application of directly injected sMHC in vivo to down-regulate immunological responses and aid the induction of graft tolerance.

Co-transplantation of donor-derived hepatocytes induces long-term tolerance to cardiac allografts in a rat model.

BACKGROUND: Liver allografts transplanted between MHC-disparate mice, rats, and swine are spontaneously accepted in most strain combinations without requirement for immunosuppression. The underlying mechanism has, however, remained elusive. Here, we demonstrate that co-transplantation of donor-derived hepatocytes protect Lewis (RT1.A1) cardiac allografts from acute and chronic rejection in DA (RT1.Aa) recipients indefinitely. METHODS: Livers of donor Lewis rats were harvested and the hepatocytes separated from hepatic leukocytes by collagenase digestion and gradient separation. DA recipient animals were transplanted Lewis cardiac allografts and simultaneously intraportally infused either Lewis-derived hepatocytes or hepatic leukocytes. Recipient animals were either not further treated or received a single dose of 15 mg/kg cyclosporine. RESULTS: Donor hepatocytes alone significantly protected syngeneic cardiac allografts from rejection, whereas hepatic leukocytes failed to influence graft survival. In combination with cyclosporine, recipient cardiac allografts were indefinitely protected from rejection. Graft-infiltrating cells in tolerant animals presented as clusters of CD4+ T cells and stained mostly positive for interleukin-4, whereas graft-infiltrating cells in rejected allografts were predominantly positive for interferon-gamma. Adoptive transfer of splenocytes derived from tolerant animals protected Lewis cardiac allografts from rejection in DA recipients without immunosuppression. In contrast, hepatic leukocytes protected only 50% of the allografts from rejection. CONCLUSION: We propose that donor hepatocytes induce permanent engraftment of syngeneic allografts by establishing a Th2 type alloresponse that is transferable to new graft recipients. The results of this study demonstrate that liver parenchymal cells significantly mediate spontaneously liver-induced tolerance.

Inhibition of c-kit receptor tyrosine kinase activity by STI 571, a selective tyrosine kinase inhibitor.

STI 571 (formerly known as CGP 57148B) is a known inhibitor of the c-abl, bcr-abl, and platelet-derived growth-factor receptor (PDGFR) tyrosine kinases. This compound is being evaluated in clinical trials for the treatment of chronic myelogenous leukemia. We sought to extend the activity profile of STI 571 by testing its ability to inhibit the tyrosine kinase activity of c-kit, a receptor structurally similar to PDGFR. We treated a c-kit expressing a human myeloid leukemia cell line, M-07e, with STI 571 before stimulation with Steel factor (SLF). STI 571 inhibited c-kit autophosphorylation, activation of mitogen-activated protein (MAP) kinase, and activation of Akt without altering total protein levels of c-kit, MAP kinase, or Akt. The concentration that produced 50% inhibition for these effects was approximately 100 nmol/L. STI 571 also significantly decreased SLF-dependent growth of M-07e cells in a dose-dependent manner and blocked the antiapoptotic activity of SLF. In contrast, the compound had no effect on MAP kinase activation or cellular proliferation in response to granulocyte-macrophage colony-stimulating factor. We also tested the activity of STI 571 in a human mast cell leukemia cell line (HMC-1), which has an activated mutant form of c-kit. STI 571 had a more potent inhibitory effect on the kinase activity of this mutant receptor than it did on ligand-dependent activation of the wild-type receptor. These findings show that STI 571 selectively inhibits c-kit tyrosine kinase activity and downstream activation of target proteins involved in cellular proliferation and survival. This compound may be useful in treating cancers associated with increased c-kit kinase activity.

Oral feeding of an immunodominant MHC donor-derived synthetic class I peptide prolongs graft survival of heterotopic cardiac allografts in a high-responder rat strain combination.

The efficacy of two synthetic major histocompatibility complex (MHC)-derived DA (RT1.Aa) 25-mer peptides (residues 56-80 and 96-120) to modulate alloreactivity was tested in Lewis (RT1.A1) responder animals. The DA peptide 56-80, but not peptide 96-120, induced delayed-type hypersensitivity (DTH). DTH was significantly reduced by oral feeding of peptide 56-80, P = 0.004. In addition, oral feeding of this peptide in combination with a short course of cyclosporin A (CsA) prolonged graft survival of 60% of heterotope transplanted DA cardiac allografts in Lewis recipient rats. Long-term survivors developed low levels of allo-antibodies against donor tissue as compared to rejecting animals and increased levels of interleukin-4 (IL-4) within the allograft. Similarly, IL-4-secreting splenocytes were identified by flow cytometry in these animals, indicating a Th2-type cytokine pattern. However, graft survival was particularly limited to cardiac allografts because donor-type skin grafts were acutely rejected in tolerant animals. It is interesting that residue alignment of peptide 56-80 to the motif of the RT1.A1 molecule showed a preferred class I motif within this sequence, suggesting indirect presentation of this peptide to recipient T cells. Thus, peptide 56-80 appears to represent a dominant epitope that can be exploited for establishing tolerance in this transplantation strain combination.

Rat MHC class I peptides are immunogenic.

We postulated that indirect recognition of MHC-derived peptides might modulate the alloresponse to donor antigen. In this study, we looked at the potential of two class I peptides derived from the alpha 1 and alpha 2 regions of the DA RT1Aa molecule. Lew responder rats were immunized by varying concentrations of two 25mer peptides covering residues 56-81 and 96-120. The injections were under the footpad and were repeated on day 14. The thickness of the footpads was measured to control delayed-type hypersensitivity (DTH). The animals were sacrificed on day 16 and the splenocytes were tested in mixed lymphocyte culture as responders against DA stimulator cells and CAP third-party splenocytes. In addition, the phenotype of the cells was measured using flow cytometry with antibodies against CD4, CD8, CD5, MHC class II, CD25, CD14 and CD19. Peptide 96-120 induced strong sensitization of the Lew recipient animals at concentrations of 200-500 micrograms (n = 4). The stimulation index was 2-3 times higher than that of untreated animals. Peptide 56-81 failed to induce sensitization at the concentrations used, but surprisingly induced a concentration-dependent immunosuppression that was highest at 400 micrograms (n = 4). In proliferation experiments responder Lew rats proliferated only to peptide 56-81 in vitro.