Immunotoxicity of epicutaneously applied anticoagulant rodenticide warfarin: evaluation by contact hypersensitivity to DNCB in rats

Effects of Low-level Brodifacoum Exposure on the Feline Immune Response

Anticoagulant rodenticides have been implicated as a potential inciting factor in the development of mange in wild felids, but a causative association between anticoagulant rodenticide exposure and immune suppression has not been established. Specific-pathogen-free domestic cats were exposed to brodifacoum over a 6-week period to determine whether chronic, low-level exposure altered the feline immune response. Cats were vaccinated with irrelevant antigens at different points during the course of the experiment to assess recall and direct immune responses. Measures of immune response included delayed-type hypersensitivity tests and cell proliferation assays. IgE and antigen-specific antibodies were quantified via ELISA assays, and cytokine induction following exposure to vaccine antigens was also analyzed. While cats had marked levels of brodifacoum present in blood during the study, no cats developed coagulopathies or hematologic abnormalities. Brodifacoum-exposed cats had transient, statistically significant decreases in the production of certain cytokines, but all other measures of immune function remained unaffected throughout the study period. This study indicates that cats may be more resistant to clinical effects of brodifacoum exposure than other species and suggests that the gross impacts of environmentally realistic brodifacoum exposure on humoral and cell-mediated immunity against foreign antigen exposures in domestic cats are minimal.

Oral warfarin intake affects skin inflammatory cytokine responses in rats

Warfarin is an anticoagulant used in prevention/prophylaxis of thromboembolism. Besides the effects on coagulation, non-hemorrhagic reactions have also been documented. Although cutaneous reactions were reported in some patients, the impact on skin immunity was not explored. In the present paper, the effect of 30-day oral warfarin intake on skin cytokine responses in rats was analyzed. Increased release of inflammatory cytokines (TNF, IL-1β and IL-10) was noted by skin explants from rats which received warfarin, but without effect on IL-6. No impact on epidermal cell cytokine secretion was seen, except a tendency of an increase of IL-6 response to stimulation with microbial product lipopolysaccharide (LPS). Topical application of contact allergen dinitrochlorobenzene (DNCB) resulted in slight (numerical solely) increase of TNF release by skin explants of warfarin-treated animals, while epidermal cells responded by increased secretion of all four cytokines examined. The data presented provide new information on the potential of oral warfarin to modulate skin innate immune activity.

Transdermal toxicity of topically applied anticoagulant rodenticide warfarin in rats

Occupational/accidental exposure data have showed hemorrhage as a result of transdermal exposure to warfarin, however, other effects are not known. In the present study, the impact of epicutaneous application of 10 μg or 100 μg of warfarin (three times, once a day) on peripheral blood polymorphonuclear (PMN) and mononuclear cells (PBMC) was examined in rats. Both doses resulted in prolongation of prothrombin time and changes in hematologic parameters. Increases in PMN intracellular myeloperoxidase (MPO) activity were seen at higher warfarin dose and both doses resulted in higher percentages of granular CD11b(+) cells. In contrast, a decrease in PMN TNF and IL-6 production (ELISA) and gene expression (RT-PCR) was observed. Epicutaneous application of warfarin resulted in decreased numbers of PBMC, higher numbers of mononuclear CD11b(+) cells, but without effect on PMBC cytokine production. The data obtained showed differential effects of transdermal exposure to warfarin depending on leukocyte type and activity.

Oral warfarin affects peripheral blood leukocyte IL-6 and TNFα production in rats

Warfarin is a Vitamin K (VK) antagonist that affects Vitamin K-dependent (VKD) processes, including blood coagulation, as well as processes unrelated to hemostasis such as bone growth, calcification, and growth of some cell types. In addition, warfarin exerts influence on some non-VKD-related activities, including anti-tumor and immunomodulating activity. With respect to the latter, both immune stimulating and suppressive effects have been noted in different experimental systems. To explore the in vivo immunomodulatory potential of warfarin on one type of activity (i.e., cytokine production) in two different immune cell populations (i.e., mononuclear or polymorphonuclear cells), effects of subchronic oral warfarin intake in rats on pro-inflammatory cytokine (i.e., TNFα, IL-6) production by peripheral blood mononuclear and polymorphonuclear cells (granulocytes) was examined. Differential effects of warfarin intake on TNFα and IL-6 were noted, depending on the type of peripheral blood leukocytes and on the cytokine examined. Specifically, a lack of effect on TNFα and a priming of IL-6 production by mononuclear cells along with a decrease in TNFα and a lack of effect on IL-6 in polymorphonuclear cells were seen in warfarin-exposed hosts. The cell- and cytokine-dependent effects from subchronic oral warfarin intake on peripheral blood leukocytes demonstrated in this study could, possibly, differentially affect reactions mediated by these cells. Ultimately, the observed effects in rats might have implications for those humans who are on long-term/prolonged warfarin therapy.

Epicutaneous Exposure to Anticoagulant Rodenticide Warfarin Modulates Local Skin Activity in Rats

Dermatotoxic effects of epicutaneous application of a first generation anticoagulant, warfarin (WF), were examined in rats. Selected parameters of skin activity were determined 24 hours following warfarin application by histomorphological and immunohistochemical analysis and by assessing some aspects of immunomodulatory potential of warfarin in skin. Increased number of mast cells, with degranulation at higher doses of warfarin was noted in warfarin treated skin. Mast cell presence coincided with changes in blood vessels and fibroblast appearance suggesting mast cell activity in warfarin treated skin. Signs of nuclear hypertrophy and anysonucleosys were noted by analysis of PCNA(+) cells in epidermis following warfarin application. Histomorphological changes were accompanied by immunemodulating activity in warfarin treated skin. This was judged by slightly increased numbers of CD3(+) cells in epidermis and superficial dermis and by production of organ cultured full thickness skin explants of factors with costimulatory activity in T-cell activation/proliferation assay. Presented data demonstrates the potential of warfarin to modulate local skin activity in rats.

Immunosuppressive effect of subchronic exposure to a mixture of eight heavy metals, found as groundwater contaminants in different areas of India, through drinking water in male rats

Immunotoxicity is an important health hazard of heavy metal exposure. Because the risk of combined exposure in the population cannot be neglected, we examined whether subchronic exposure to a mixture of metals (arsenic, cadmium, lead, mercury, chromium, nickel, manganese, and iron) via drinking water at contemporary Indian groundwater contamination levels and at concentrations equivalent to the WHO maximum permissible limit (MPL) in drinking water can induce immunotoxicity in male rats. Data on groundwater contamination with metals in India were collected from literature and metals were selected on the basis of their frequency of occurrence and contamination level above the MPL. Male albino Wistar rats were exposed to the mixture at 0, 1, 10, and 100 times the mode concentrations (the most frequently occurring concentration) of the individual metals in drinking water for 90 days. In addition, one group was exposed to the mixture at a concentration equal to the MPL of the individual metal and another group was used as positive control for immune response studies. The end points assessed were weights of organs, hematological indices, humoral and cell-mediated immune responses, and histopathology of skin and spleen. The MPL and 1x doses did not significantly affect any of the parameters and none of the doses induced any significant changes after 30 days of exposure. The mixture at 10x and 100x doses increased the relative weight of the spleen, but that of thymus, adrenals, and popliteal lymphnodes were increased with the 100x dose. After 90 days, 10x and 100x doses decreased serum protein and globulin contents and increased the albumin:globulin ratio; the albumin level was decreased only with the 100x dose. After 60 days, the total erythrocyte count (TEC), hemoglobin (Hb) level, and packed cell volume (PCV) were decreased with the 100x dose, whereas after 90 days, 10x and 100x doses reduced the TEC, total leukocyte count, Hb level, PCV, mean corpuscular volume, and mean corpuscular hemoglobin. With the 100x dose, the lymphocyte count was decreased after 60 and 90 days, but the neutrophil number was increased after 90 days. Antibody titer was decreased after 75 days with the 100x dose, but after 90 days, it was decreased with both the 10x and 100x doses. In delayed-type hypersensitivity response, these two doses decreased ear thickness after 24 and 48 h and skin biopsies showed a dose-dependent decrease in inflammatory changes. Histologically, the spleen revealed depletion of lymphoid cells and atrophic follicles with reduced follicular activity with higher doses. The findings suggest that hematopoietic and immune systems are toxicologically sensitive to the mixture, which could lead to anemia and suppression of humoral and cell-mediated immune responses in male rats at 10 and 100 times the mode concentrations of the individual components in contaminated groundwater.

Dermatotoxicity of epicutaneously applied anticoagulant warfarin

Dermatotoxic effects of epicutaneous application of a first-generation anticoagulant, warfarin (WF) were examined in rats. Selected parameters of skin activity were determined 24h following warfarin application, including metabolic viability of skin explants, some aspects of oxidative activity in skin tissue homogenates and inflammatory/immune relevant activity of epidermal cells from warfarin-treated skin. No changes in skin metabolic viability (MTT reduction) were noted ex vivo following WF application, suggesting the absence of immediate toxicity for skin. In contrast, increased formation of malondialdehyde (MDA), with a decrease in protein and non-protein thiols in homogenates of warfarin-treated skin was demonstrated, pointing to prooxidant activity in warfarin-treated skin. Increased costimulatory activity of epidermal cells isolated from warfarin-exposed skin in Con-A-stimulated T-cell activation/proliferation assay was noted, reflecting proinflammatory and immune-modulating capacity of warfarin for epidermis. No evident differences in skin histology between control and warfarin-treated skin were found at that time point, while striking changes in tissue integrity, cellularity and appearance 72 h following WF application were noted. The observed histological picture probably reflects a regenerative/inflammatory program related to oxidant/inflammation-type warfarin-evoked injury to the skin. Presented data demonstrate the potential of epicutaneously applied warfarin to modulate local skin activity in rats.