Lead alters intracellular protein signaling and suppresses pro-inflammatory activation in TLR4 and IFNR-stimulated murine RAW 264.7 cells, in vitro

Lead (Pb) is a persistent environmental pollutant that has a structure and charge similar to many ions, such as calcium, that are essential for normal cellular function. Pb may compete with calcium for protein binding sites and inhibit signaling pathways within the cell affecting many organ systems including the immune system. The aim of the current study was to assess whether the calcium/calmodulin pathway is a principal target of environmentally relevant Pb during pro-inflammatory activation in a RAW 264.7 macrophage cell line. RAW 264.7 cells were cultured with 5 μM Pb(NO₃)₂, LPS, rIFNγ, or LPS+rIFNγ for 12, 24, or 48 hr. Intracellular protein signaling and multiple functional endpoints were investigated to determine Pb-mediated effects on macrophage function. Western blot analysis revealed that Pb initially modulated nuclear localization of NFκB p65 and cytoplasmic phosphorylation of CaMKIV accompanied by increased phosphorylation of STAT1β at 24 hr. Macrophage proliferation was significantly decreased at 12 hr in the presence of Pb, while nitric oxide (NO) was significantly reduced at 12 and 24 hr. Cells cultured with Pb for 12, 24, or 48 hr exhibited altered cytokine levels after specific stimuli activation. Our findings are in agreement with previous reports suggesting that macrophage pro-inflammatory responses are significantly modulated by Pb. Further, Pb-induced phosphorylation of CaMKIV (pCaMKIV), observed in the present study, may be a contributing factor in metal-induced autophagy noted in our previous study with this same cell line.

Exposure of juvenile Leghorn chickens to lead acetate enhances antibiotic resistance in enteric bacterial flora

Heavy metals have been implicated for their ability to increase antibiotic resistance in bacteria collected from polluted waters, independent of antibiotic exposure. Specific-pathogen-free Leghorn chickens were therefore given Pb acetate in the drinking water to expose the enteric bacteria to Pb and to determine if antibiotic resistance changed in these bacteria. Concentrations of Pb used were 0.0, 0.01, 0.1, 1.0, or 10.0 mM; birds given the highest 2 concentrations showed signs of moribundity and dehydration and were removed from the study. Vent culture samples were collected for bacterial cultures on d 0 before Pb exposure, d 7 and 14, and then birds were euthanized by CO2 gas for necropsy on d 14, at which time intestinal contents were also collected for bacterial cultures. Fecal swabs but not intestinal samples from Pb-exposed birds contained isolates that had significantly elevated antibiotic resistance. Some of the isolates contained bacteria that were resistant to up to 20 antibiotics. These results suggest the need for repeated studies in chickens infected with zoonotic pathogens.

A single mid-gestation exposure to TCDD yields a postnatal autoimmune signature, differing by sex, in early geriatric C57BL/6 mice

We recently observed an autoimmune profile in 24-week-old C57BL/6 mice that received a 2.5 or 5.0μg/kg mid-gestation dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (Mustafa et al., 2008). The clinical signs were consistent with a lupus-like syndrome and included: increased autoantibody levels, renal IgG and C3 immune complex deposition with associated inflammation, and increased peripheral Vβ(+) T cells. No studies currently exist following the progression of such disease into middle or advanced ages, when human autoimmune diseases may manifest. Therefore in the present study, littermates of mice from the previous 24 week prenatal TCDD study were allowed to age to 48 weeks, considered early geriatric in mice. Similarities and differences in the disease profile based on age and sex were observed. Peripheral autoreactive Vβ(+) T cells were increased in both sexes at 48 weeks, in contrast to males only at 24 weeks. Activated T cells from 48-week-old prenatal TCDD females over-produced the pro-inflammatory cytokine IFN-γ while males over-produced IL-10, effects again not seen at 24 weeks. Splenic transitional-2 B cells (CD21(int)CD24(hi)) were increased in males while transitional-1 B cells (CD23(neg) CD1(neg)) were increased in females at 48 weeks. Autoantibodies to cardiolipin and CD138(+) spleen plasma cells were significantly increased in the aged males but not females. Anti-IgG and anti-C3 immune complex renal deposition were also significantly increased in the prenatal TCDD males but not females. These selective changes in the aged male mice may be noteworthy, in that the prevalence of SLE in humans shifts dramatically toward males with aging. The collective findings in aged mice suggest that prenatal TCDD permanently biases the postnatal immune response in C57BL/6 mice toward autoimmunity, and support a significant B cell component to the induced renal autoimmune disease.