Vitamins A and D and Zinc Affect the Leshmanicidal Activity of Canine Spleen Leukocytes

SIMPLE SUMMARY: Canine leishmaniasis (CanL) is a zoonosis caused by the protozoan Leishmania infantum, with dogs being considered the main domestic reservoirs of the parasite and potential transmitters to humans through the phlebotomine vector. CanL is a chronic infectious disease that characteristically occurs in underdeveloped and developing countries, with a broad spectrum of clinical and immunopathological manifestations. Despite the efforts in the fight against the disease, many endemic sites of CanL persist, preceding human infection and representing a serious public health problem. The therapeutic arsenal for the treatment of leishmaniasis is limited by toxicity, high costs, and inefficacy, in some cases. Treatment failure implies the permanence of dogs as reservoirs of the parasite, with further aggravation of the public health problem, indicating that new therapies should be evaluated in order to increase the treatment efficacy. Recent studies have shown that nutrients can regulate the immune response in many clinical conditions, but no study has been conducted using spleen leukocytes in CanL. In this paper, we demonstrate for the first time that nutrients added to cultures of spleen leukocytes from dogs infected with CanL can modulate the immune response and parasite load compared to healthy dogs. ABSTRACT: Canine leishmaniasis (CanL) is a chronic disease caused by Leishmania infantum, and the limitations of the current treatments have encouraged new alternatives, such as the use of immunomodulatory nutrients. The objective of this study was to determine the serum levels of vitamin A (retinol), vitamin D (25(OH)VD(3)), and zinc (Zn) in dogs with CanL and the effect of in vitro supplementation with the respective active forms ATRA, 1,25(OH)(2)VD(3), and SZn on spleen leukocyte cultures. Serum retinol, 25(OH)VD(3), and Zn were determined by HPLC, ELISA, and ICP-MS, respectively. Spleen leukocyte cultures were used for the detection of NO and ROS by flow cytometry; the IFN-γ, TNF-α, and IL-10 levels were determined by ELISA; and the parasite load was determined by microscopy. We detected low serum levels of retinol and Zn and high levels of 25(OH)VD(3) in the CanL group. The in vitro supplementation of CanL spleen leukocytes with ATRA, 1,25(OH)(2)VD(3), and SZn, in addition to a soluble leishmania antigen (SLA) treatment, increased the NO and ROS levels, while the treatments with only ATRA and SZn increased the TNF-a levels. Increased IL-10 and IFN-g levels were observed with the addition of SLA to the medium, although the addition of the three nutrients led to a reduction of the IL-10 levels, and the addition of 1,25(OH)(2)VD(3) and SZn led to a reduction of IFN-g. A supplementation with 1,25(OH)(2)VD(3) and SZn reduced the parasite load but only in the absence of SLA. We suggest that the nutrients we tested are involved in the leishmanicidal mechanism, showing a potential for investigation in future studies.