Activated protein C ameliorates Bacillus anthracis lethal toxin-induced lethal pathogenesis in rats

Simulation of Hemorrhage Pathogenesis in Mice through Dual Stimulation with Dengue Envelope Protein Domain III-Coated Nanoparticles and Antiplatelet Antibody

Dengue hemorrhagic fever (DHF) is a severe form of dengue virus (DENV) infection that can lead to abnormal immune responses, endothelial vascular dysfunction, and hemorrhage pathogenesis. The virion-associated envelope protein domain III (EIII) is thought to play a role in the virulence of DENV by damaging endothelial cells. However, it is unclear whether EIII-coated nanoparticles simulating DENV virus particles could cause a more severe pathogenesis than soluble EIII alone. This study aimed to investigate whether EIII-coated silica nanoparticles (EIII-SNPs) could elicit greater cytotoxicity in endothelial cells and hemorrhage pathogenesis in mice compared to EIII or silica nanoparticles alone. The main methods included in vitro assays to assess cytotoxicity and in vivo experiments to examine hemorrhage pathogenesis in mice. EIII-SNPs induced greater endothelial cytotoxicity in vitro than EIII or silica nanoparticles alone. Two-hit combined treatment with EIII-SNPs and antiplatelet antibodies to simulate DHF hemorrhage pathogenesis during secondary DENV infections resulted in higher endothelial cytotoxicity than either treatment alone. In mouse experiments, two-hit combined treatment with EIII-SNPs and antiplatelet antibodies resulted in more severe hemorrhage pathogenesis compared to single treatments of EIII, EIII-SNPs, or antiplatelet antibodies alone. These findings suggest that EIII-coated nanoparticles are more cytotoxic than soluble EIII and could be used to develop a tentative dengue two-hit hemorrhage pathogenesis model in mice. Additionally, our results indicated that EIII-containing DENV particles could potentially exacerbate hemorrhage pathogenesis in DHF patients who have antiplatelet antibodies, highlighting the need for further research on the potential role of EIII in DHF pathogenesis.

Thioacetamide-induced liver damage and thrombocytopenia is associated with induction of antiplatelet autoantibody in mice

Thrombocytopenia is usually associated with liver injury, elevated plasma aspartate aminotransferase and alanine aminotransferase levels, and high antiplatelet immunoglobulin (Ig) titers, although the mechanism behind these effects remains elusive. Deciphering the mechanism behind acute liver disease–associated thrombocytopenia may help solve difficulties in routine patient care, such as liver biopsy, antiviral therapy, and surgery. To determine whether liver damage is sufficient per se to elicit thrombocytopenia, thioacetamide (TAA)-induced hepatitis rodent models were employed. The analysis results indicated that TAA treatment transiently induced an elevation of antiplatelet antibody titer in both rats and mice. B-cell-deficient (BCD) mice, which have loss of antibody expression, exhibited markedly less thrombocytopenia and liver damage than wild-type controls. Because TAA still induces liver damage in BCD mice, this suggests that antiplatelet Ig is one of the pathogenic factors, which play exacerbating role in the acute phase of TAA-induced hepatitis. TNF-α was differentially regulated in wild-type versus BCD mice during TAA treatment, and anti-TNF treatment drastically ameliorated antiplatelet Ig induction, thrombocytopenia, and liver injury, suggesting that the TNF pathway plays a critical role in the disease progression.

A fucoidan-quaternary chitosan nanoparticle adjuvant for anthrax vaccine as an alternative to CpG oligodeoxynucleotides

We examined the efficacy of fucoidan-N-(2-hydroxy-3-trimethylammonium)propylchitosan nanoparticles (FUC-HTCC NPs) as adjuvants for anthrax vaccine adsorbed (AVA). Positively and negatively surface-charged FUC-HTCC NPs were prepared via polyelectrolyte complexation by varying the mass ratio of FUC and HTCC. When cultured with L929 cells or JAWS II dendritic cells, both charged NPs showed high cell viability and low cytotoxicity, observed via MTT assay and lactate dehydrogenase release assay, respectively. In addition, we have monitored excellent NPs uptake efficacy by dendritic cells and observed that combining FUC-HTCC NPs with AVA significantly increases the magnitude of IgG-anti-protective antigen titers in A/J mice compared to that by CpG oligodeoxynucleotides plus AVA or AVA alone, and PA-specific IgG1 and IgG2a analysis confirmed that FUC-HTCC NPs strongly stimulated humoral immunity. Furthermore, FUC-HTCC NPs plus AVA provided a superior survival rate (100%) of A/J mice compared to CpG oligodeoxynucleotides plus AVA (75%) or AVA alone (50%) following anthrax lethal toxin challenge. The findings support FUC-HTCC NPs as a potential adjuvant of AVA for rapid induction of protective immunity.

TRPM8 and RAAS-mediated hypertension is critical for cold-induced immunosuppression in mice

Mechanisms underlying cold-induced immunosuppression remain unclear. Here we found that cold exposure leads to transient receptor potential melastatin 8 (TRPM8)-dependent, renin–angiotensin–aldosterone system (RAAS)-mediated hypertension, which subsequently induces small molecule and fluid extravasation, increases plasma Ig levels, and elicits immunosuppression. An effect is similar to the clinically-used immunosuppressive treatments of intravenous immunoglobulin (IVIg) against various inflammatory diseases, such as immune thrombocytopenia (ITP). Essential roles of TRPM8 and Ig in cold-induced immunosuppression are supported by the cold-mediated amelioration of ITP and the cold-mediated suppression of bacterial clearance, which were observed in wild-type mice but not in Ig- and TRPM8-deficient mutants. Treatment with antihypertensive drugs aliskiren and losartan drastically reversed high plasma Ig levels and ameliorated cold-induced immunosuppression, indicating the involvement of the RAAS and hypertension. These results indicated that the natively increased plasma Ig level is associated with immunosuppression during periods of cold exposure, and antihypertensive drugs can be useful to manage cold-induced immunosuppression.

Soluble P-selectin rescues mice from anthrax lethal toxin-induced mortality through PSGL-1 pathway-mediated correction of hemostasis

As one of the virulence factors of Bacillus anthracis, lethal toxin (LT) induces various pathogenic responses including the suppression of the coagulation system. In this study, we observed that LT markedly increased the circulating soluble P-selectin (sP-sel) levels and microparticle (MP) count in wild-type but not P-selectin (P-sel, Selp^-/-) or P-sel ligand-1 (PSGL-1, Selplg^-/-) knockout mice. Because sP-sel induces a hypercoagulable state through PSGL-1 pathway to generate tissue factor-positive MPs, we hypothesized that the increase in plasma sP-sel levels can be a self-rescue response in hosts against the LT-mediated suppression of the coagulation system. In agreement with our hypothesis, our results indicated that compared with wild-type mice, Selp^-/- and Selplg^-/- mice were more sensitive to LT. In addition, the recombinant sP-sel treatment markedly ameliorated LT-mediated pathogenesis and reduced mortality. As a result, elicitation of circulating sP-sel is potentially a self-rescue response, which is beneficial to host recovery from an LT-induced hypocoagulation state. These results suggest that the administration of sP-sel is likely to be useful in the development of a new strategy to treat anthrax.

Antibacterial Properties of Visible-Light-Responsive Carbon-Containing Titanium Dioxide Photocatalytic Nanoparticles against Anthrax

The bactericidal activity of conventional titanium dioxide (TiO₂) photocatalyst is effective only on irradiation by ultraviolet light, which restricts the applications of TiO₂ for use in living environments. Recently, carbon-containing TiO₂ nanoparticles [TiO₂(C) NP] were found to be a visible-light-responsive photocatalyst (VLRP), which displayed significantly enhanced antibacterial properties under visible light illumination. However, whether TiO₂(C) NPs exert antibacterial properties against Bacillus anthracis remains elusive. Here, we evaluated these VLRP NPs in the reduction of anthrax-induced pathogenesis. Bacteria-killing experiments indicated that a significantly higher proportion (40%–60%) of all tested Bacillus species, including B. subtilis, B. cereus, B. thuringiensis, and B. anthracis, were considerably eliminated by TiO₂(C) NPs. Toxin inactivation analysis further suggested that the TiO₂(C) NPs efficiently detoxify approximately 90% of tested anthrax lethal toxin, a major virulence factor of anthrax. Notably, macrophage clearance experiments further suggested that, even under suboptimal conditions without considerable bacterial killing, the TiO₂(C) NP-mediated photocatalysis still exhibited antibacterial properties through the reduction of bacterial resistance against macrophage killing. Our results collectively suggested that TiO₂(C) NP is a conceptually feasible anti-anthrax material, and the relevant technologies described herein may be useful in the development of new strategies against anthrax.

Soluble P-selectin rescues viper venom-induced mortality through anti-inflammatory properties and PSGL-1 pathway-mediated correction of hemostasis

Venomous snakebites are lethal and occur frequently worldwide each year, and receiving the antivenom antibody is currently the most effective treatment. However, the specific antivenom might be unavailable in remote areas. Snakebites by Viperidae usually lead to hemorrhage and mortality if untreated. In the present study, challenges of rattlesnake (Crotalus atrox) venom markedly increased the circulating soluble P-selectin (sP-sel) level, but not P-selectin (P-sel, Selp^−/−) mutants, in wild-type mice. Because sP-sel enhances coagulation through the P-selectin ligand 1 (PSGL-1, Selplg) pathway to produce tissue factor–positive microparticles, we hypothesized that increasing the plasma sP-sel level can be a self-rescue response in hosts against snake venom–mediated suppression of the coagulation system. Confirming our hypothesis, our results indicated that compared with wild-type mice, Selp^−/− and Selplg^−/− mice were more sensitive to rattlesnake venom. Additionally, administration of recombinant sP-sel could effectively reduce the mortality rate of mice challenged with venoms from three other Viperidae snakes. The antivenom property of sP-sel is associated with improved coagulation activity in vivo. Our data suggest that the elevation of endogenous sP-sel level is a self-protective response against venom-suppressed coagulation. The administration of recombinant sP-sel may be developed as a new strategy to treat Viperidae snakebites.

Nanodiamonds protect skin from ultraviolet B-induced damage in mice

BACKGROUND

Solar ultraviolet (UV) radiation causes various deleterious effects, and UV blockage is recommended for avoiding sunburn. Nanosized titanium dioxide and zinc oxide offer effective protection and enhance cosmetic appearance but entail health concerns regarding their photocatalytic activity, which generates reactive oxygen species. These concerns are absent in nanodiamonds (NDs). Among the UV wavelengths in sunlight, UVB irradiation primarily threatens human health.

RESULTS

The efficacy and safety of NDs in UVB protection were evaluated using cell cultures and mouse models. We determined that 2 mg/cm(2) of NDs efficiently reduced over 95% of UVB radiation. Direct UVB exposure caused cell death of cultured keratinocyte, fibroblasts and skin damage in mice. By contrast, ND-shielding significantly protected the aforementioned pathogenic alterations in both cell cultures and mouse models.

CONCLUSIONS

NDs are feasible and safe materials for preventing UVB-induced skin damage.

Acquired coagulant factor VIII deficiency induced by Bacillus anthracis lethal toxin in mice

Mice treated with anthrax lethal toxin (LT) exhibit hemorrhage caused by unknown mechanisms. Moreover, LT treatment in mice induced liver damage. In this study, we hypothesized that a suppressed coagulation function may be associated with liver damage, because the liver is the major producing source of coagulation factors. The hepatic expression of coagulant factors and the survival rates were analyzed after cultured cells or mice were exposed to LT. In agreement with our hypothesis, LT induces cytotoxicity against hepatic cells in vitro. In addition, suppressed expression of coagulation factor VIII (FVIII) in the liver is associated with a prolonged plasma clotting time in LT-treated mice, suggesting a suppressive role of LT in coagulation. Accordingly, we further hypothesized that a loss-of-function approach involving treatments of an anticoagulant should exacerbate LT-induced abnormalities, whereas a gain-of-function approach involving injections of recombinant FVIII to complement the coagulation deficiency should ameliorate the pathogenesis. As expected, a sublethal dose of LT caused mortality in the mice that were non-lethally pretreated with an anticoagulant (warfarin). By contrast, treatments of recombinant FVIII reduced the mortality from a lethal dose of LT in mice. Our results indicated that LT-induced deficiency of FVIII is involved in LT-mediated pathogenesis. Using recombinant FVIII to correct the coagulant defect may enable developing a new strategy to treat anthrax.

Anti-inflammatory functions of protein C require RAGE and ICAM-1 in a stimulus-dependent manner

By binding β₂-integrins both ICAM-1 and the receptor for advanced glycation end products (RAGE) mediate leukocyte recruitment in a stimulus-dependent manner. Using different inflammatory mouse models we investigated how RAGE and ICAM-1 are involved in anti-inflammatory functions of protein C (PC; Ceprotin, 100 U/kg). We found that, depending on the stimulus, RAGE and ICAM-1 are cooperatively involved in PC-induced inhibition of leukocyte recruitment in cremaster models of inflammation. During short-term proinflammatory stimulation (trauma, fMLP, and CXCL1), ICAM-1 is more important for mediation of anti-inflammatory effects of PC, whereas RAGE plays a major role after longer proinflammatory stimulation (TNFα). In contrast to WT and Icam-1^−/− mice, PC had no effect on bronchoalveolar neutrophil emigration in RAGE^−/− mice during LPS-induced acute lung injury, suggesting that RAGE critically mediates PC effects during acute lung inflammation. In parallel, PC treatment effectively blocked leukocyte recruitment and improved survival of WT mice and Icam-1-deficient mice in LPS-induced endotoxemia, but failed to do so in RAGE-deficient mice. Exploring underlying mechanisms, we found that PC is capable of downregulating intracellular RAGE and extracellular ICAM-1 in endothelial cells. Taken together, our data show that RAGE and ICAM-1 are required for the anti-inflammatory functions of PC.

RAGE controls activation and anti-inflammatory signalling of protein C

AIMS

The receptor for advanced glycation endproducts, RAGE, is a multiligand receptor and NF-κB activator leading to perpetuation of inflammation. We investigated whether and how RAGE is involved in mediation of anti-inflammatory properties of protein C.

METHODS AND RESULTS

We analyzed the effect of protein C on leukocyte adhesion and transmigration in WT- and RAGE-deficient mice using intravital microscopy of cremaster muscle venules during trauma- and TNFα-induced inflammation. Both, protein C (PC, Ceprotin, 100 U/kg) and activated protein C (aPC, 24 µg/kg/h) treatment significantly inhibited leukocyte adhesion in WT mice in these inflammation models. The impaired leukocyte adhesion after trauma-induced inflammation in RAGE knockout mice could not be further reduced by PC and aPC. After TNFα-stimulation, however, aPC but not PC treatment effectively blocked leukocyte adhesion in these mice. Consequently, we asked whether RAGE is involved in PC activation. Since RAGE-deficient mice and endothelial cells showed insufficient PC activation, and since thrombomodulin (TM) and endothelial protein C receptor (EPCR) are reduced on the mRNA and protein level in RAGE deficient endothelial cells, an involvement of RAGE in TM-EPCR-dependent PC activation is likely. Moreover, TNFα-induced activation of MAPK and upregulation of ICAM-1 and VCAM-1 are reduced both in response to aPC treatment and in the absence of RAGE. Thus, there seems to be interplay of the RAGE and the PC pathway in inflammation.

CONCLUSION

RAGE controls anti-inflammatory properties and activation of PC, which might involve EPCR and TM.

Targeting the host hemostatic system function in bacterial infection for antimicrobial therapies

The hemostatic system is an important player in host's response to infection. It has been shown that host hemostatic factors as well as platelets, interact with various proteins from bacteria and play important roles in host defense against infections. This review summarizes studies of function of host hemostatic system in host defense against bacterial infections and efforts to target hemostatic system interaction with pathogens to develop potential antimicrobial therapies.

Suppressive effects of anthrax lethal toxin on megakaryopoiesis

Anthrax lethal toxin (LT) is a major virulence factor of Bacillus anthracis. LT challenge suppresses platelet counts and platelet function in mice, however, the mechanism responsible for thrombocytopenia remains unclear. LT inhibits cellular mitogen-activated protein kinases (MAPKs), which are vital pathways responsible for cell survival, differentiation, and maturation. One of the MAPKs, the MEK1/2-extracellular signal-regulated kinase pathway, is particularly important in megakaryopoiesis. This study evaluates the hypothesis that LT may suppress the progenitor cells of platelets, thereby inducing thrombocytopenic responses. Using cord blood-derived CD34(+) cells and mouse bone marrow mononuclear cells to perform in vitro differentiation, this work shows that LT suppresses megakaryopoiesis by reducing the survival of megakaryocytes. Thrombopoietin treatments can reduce thrombocytopenia, megakaryocytic suppression, and the quick onset of lethality in LT-challenged mice. These results suggest that megakaryocytic suppression is one of the mechanisms by which LT induces thrombocytopenia. These findings may provide new insights for developing feasible approaches against anthrax.