Topical Permethrin Exposure Causes Thymic Atrophy and Persistent Inhibition of the Contact Hypersensitivity Response in C57BI/6 Mice

Developmental exposure to diuron causes splenotoxicity in male Sprague-Dawley rat pups

This study investigated whether perinatal exposure to diuron [3-(3,4-dichlorophenyl)-1-1-dimethylurea] might exert adverse effects on rat lymphoid organs. Pregnant Sprague-Dawley (SD) rats were exposed to diuron at 500, 750 or 1250 ppm in the diet from gestational days (GD) 12-21 and during lactation. At postnatal day (PND) 42, male pups were euthanized and thymus, spleen, mesenteric lymph node and femur were collected for histopathological analysis. Food consumption and body weight gain were significantly reduced in dams exposed to 1250 ppm during gestation period. Also, Diuron at 750 and 1250 ppm produced: (1) increased relative spleen weight associated histologically with severe congestion in red pulp, (2) enhanced extramedullary hematopoiesis and hemosiderosis as well as (3) depletion of lymphoid follicles in white pulp. Flow cytometric analysis revealed a significant reduction in B lymphocytes (CD45RA+) in male pups but T lymphocytes (CD4+, CD8+ and CD4+/CD8+) were not markedly affected. Thus, data suggest that Diuron-induced maternal toxicity in dams exposed to high dose and perinatal exposure to this herbicide produced spleen toxicity as evidenced by a reduction in B lymphocyte number in male SD pups.

Combined dermal exposure to permethrin and cis-urocanic acid suppresses the contact hypersensitivity response in C57BL/6N mice in an additive manner

Cutaneous exposure to the pyrethroid insecticide permethrin significantly suppresses contact hypersensitivity (CH) response to oxazolone in C57BL/6N mice. Additionally, cis-urocanic acid (cUCA), an endogenous cutaneous chromophore isomerized to its active form following exposure to ultraviolet radiation, modulates cell-mediated cutaneous immune responses. This study describes cutaneous immune alterations following combined topical permethrin and intradermal cUCA exposure. Female C57BL/6N mice were administered 5, 50 or 100 microg cUCA daily for 5 consecutive days. CH was then evaluated by the mouse ear swelling test (MEST) response to oxazolone. Decreased responses of 52.3%, 76.3% and 76.3%, respectively, as compared to controls were observed. Then, mice were co-exposed to 5 microg cUCA daily for 5 days and 1.5, 5, 15, or 25 microL permethrin, on either day 1, 3 or 5 of the cUCA treatment to evaluate combined immunomodulatory effects of the two chemicals, or cUCA daily for 5 days followed by permethrin on day 3, 5, or 7 after the last cUCA injection to demonstrate prolonged immunosuppressive effects. Two days after final treatment, mice were sensitized with oxazolone and MEST was performed. Mice receiving five cUCA injections and permethrin topically on cUCA injection day 1 showed up to 93.3% suppression of MEST compared to vehicle control. CH was suppressed by 87.5%, 86.6% and 74.2% in mice treated with 25 muL permethrin on days 3, 5 and 7 after cUCA, respectively, compared to vehicle control. Taken together, these data indicate co-exposure to cUCA and permethrin profoundly suppresses cell-mediated cutaneous immunity.

Molecular mechanisms of cis-urocanic acid and permethrin-induced alterations in cutaneous immunity

BACKGROUND/PURPOSE

Cutaneous cis-urocanic acid (cUCA) or ultraviolet B exposure has been shown to cause diminished cutaneous contact hypersensitivity (CH) and to induce systemic tolerance (increased regulatory T lymphocytes) in mice. Permethrin is also a known CH inhibitor, but the molecular mechanisms are currently poorly understood. In this study, CH was evaluated in four strains of mice: an immunosensitive strain (C57BL/6N), an immunoresistant strain (SvImJ), a strain developed from C57BL/6N mice but genetically altered at both the tumor necrosis factor-alpha receptors (TNFalphap55R and p75R), and a strain developed from C57BL/6N but genetically deleted at the interferon-gamma (IFNgamma) locus.

METHODS

CH was evaluated in each group via oxazolone challenge following a 5-day exposure to intradermal (ID) cUCA or a single exposure to topical permethrin, or co-exposure to both chemicals in 5-week-old female C57BL/6N, SvImJ, and C57BL/6N mice genetically altered at the TNFalpha or IFNgamma locus.

RESULTS

A 5-day exposure to ID cUCA or a single exposure to topical permethrin resulted in diminished CH response in C57BL/6N mice, and this effect was exacerbated with concurrent exposure to both chemicals. CH in SvImJ was both cUCA- and permethrin-resistant relative to C57BL/6N mice, as 5-day cUCA or a single exposure to permethrin did not diminish CH, nor did concurrent exposure to cUCA and permethrin. Mice deleted at both TNFalphaR loci displayed similar but somewhat blunted diminished CH responses to cUCA or permethrin. This trend became significant with combined chemical exposure. IFNgamma knockout mice displayed similar diminished CH responses to cUCA or permethrin alone. Unlike C57BL/6N mice, the IFNgamma knockout mice did not show a further reduction in CH with combined chemical exposure.

CONCLUSIONS

These results suggest the following: (1)Mouse strains show variable susceptibility to permethrin- and cUCA-induced immunomodulation. (2)TNFalpha may be involved in the immunomodulatory effects of cUCA and permethrin. (3)IFNgamma may be required for the more than additive depression of CH caused by cUCA+permethrin.

Cis-urocanic acid increases immunotoxicity and lethality of dermally administered permethrin in C57BL/6N mice

Immunomodulatory effects of a single topical permethrin exposure, 5-day exposure to cis-urocanic acid (cUCA), or a combination of the two chemicals were evaluated in 4- to 5-week-old female C57BL/6N mice. Permethrin alone decreased thymic weight and cellularity. Although cUCA alone did not affect thymic end points, coexposure to topical permethrin and cUCA exacerbated the thymolytic effects of permethrin. The single topical dose of permethrin also depressed several immune responses in isolated splenic leukocytes. This included splenic T-cell proliferative response to mitogen, splenic macrophage hydrogen peroxide production, and splenic B lymphocyte-specific antibody production. Unlike the effect of coexposure to these agents on thymic end points, cUCA did not exacerbate permethrin's adverse effect on any of the splenic end points examined. These results appear to suggest divergent mechanisms by which these compounds affect precursor and functionally mature T cells. At the doses used in this study, permethrin caused neurotoxic effects, including lethality, in a portion of the mice. For undetermined reasons, cUCA significantly increased the rate of lethality caused by permethrin. Although the permethrin doses used in this study exceed that typically used in human medicine, these results raise some concerns about the possibility that sunlight, via cUCA, may increase the risk of adverse central nervous system and immune effects caused by permethrin alone.

Single-dose topical exposure to the pyrethroid insecticide, permethrin in C57BL/6N mice: effects on thymus and spleen

Immunomodulatory effects of single topical exposure to permethrin were evaluated in 5-week-old female C57BL/6N mice. Mice exposed to 5-25 microl permethrin (equivalent to 220-1100 mg/kg body weight) on shaved interscapular skin were evaluated for altered body weight; splenic and thymic organ weight and cellularity; thymocyte cell surface expression, cellular apoptosis; splenic macrophage phagocytosis and hydrogen peroxide production; splenic B cell antibody production and T cell cytolytic activity; and mitogen-induced proliferation of splenocytes and thymocytes after in vivo or in vitro permethrin exposure. Topical permethrin application (25 microl) caused 32% inhibition of splenic T cell proliferation; in vitro exposure to permethrin also diminished splenocyte proliferation by 72% at 25 microM and 86% at 100 microM. permethrin did not appear to affect other leukocyte functional assays. Dose-related decreases in thymic cellularity of 52 and 80% were seen in mice exposed to 15 and 25 microl permethrin, respectively. Apoptosis was significantly increased in CD4(-)8(-) and CD4(-)8(+) thymocytes, and the CD4(+)CD8(+) thymocyte subpopulation was most severely diminished, suggesting possible chemical-induced apoptotic mechanism of thymic atrophy. Permethrin also caused splenic hypocellularity by 31% at 15 microl, and by 50% at 25 microl, an effect that may relate to inhibited proliferation or reduced seeding from the hypocellular thymus.

Topical permethrin exposure inhibits antibody production and macrophage function in C57Bl/6N mice

Permethrin was applied to the shaved dorsal interscapular region of C57Bl/6N mice at doses of 0.5, 1.5 or 5.0 microl/day. These doses corresponded to approximately 22-220 mg/kg/day topical insecticide. Mice were exposed to permethrin in this manner daily for 10 or 30 consecutive days, or every other day for 7 or 14 exposures. The splenic macrophage chemiluminescent response was depressed in a dose-dependent manner at 2 and 10 days post-exposure to permethrin. Phagocytic ability of macrophages was not inhibited. Antibody production as shown by plaque-forming cell (PFC) assay decreased significantly after 10 consecutive days of exposure to permethrin. These data indicate that topical permethrin exposure may produce systemic immune effects.