Elementos traço na Leishmaniose visceral canina: correlações com aspectos clínicos, histopatológicos e estresse oxidativo

Abstract

Dogs are the main domestic reservoirs acting as sources of parasites for transmission and infection of human visceral leishmaniasis. Trace elements, like cooper (Cu), iron (Fe), zinc (Zn) and selenium (Se) are found at low levels in the body of mammals and participate in some immunological process as maturation as function of T and B lymphocytes, innate immunity development and acting as anti-oxidants, preventing tissue damage. The immune response against Leishmania parasites is especially triggered by macrophages, as these cells can produce microbicidal substances such as, reactive molecular oxygen species (ROS) and nitric oxide that can kill the parasite and promote lipoperoxidation. Vertebrate hosts have an anti-oxidant system as catalase, superóxido dismutase and glutationa-peroxidase, dependent of Fe, Cu, Zn and Se. The aim of this work was to investigate possible alterations in trace elements and correlate these alterations with clinical and histopathological aspects and oxidative stress in visceral canine leishmaniasis. To answer these questions we studied 30 mongrel adult dogs, males and females, naturally infected with L. infantum from control of zoonosis center in the city of Ribeirão das Neves, MG. Their positivity for the disease was assayed by serological (RIFI, ELISA) and parasitological diagnostic (histology, immunohistochemistry) and PCR. After testing positive, animals were divided in 2 groups based on clinical features: 19 dogs were symptomatic and 11 were asymptomatic. Control animals were obtained from a nonendemic gerographical area, Carandaí, MG and tested negative for Leishmania in all assays mentioned above. All the animals were sedated, then euthanized with a lethal dose of Thiopental sodium. Samples of blood and fragments of liver, spleen, and cervical lymph node were obtained. The trace elements and NO were tested in the serum, the LPO in the plasma, the activity of anti-oxidant enzymes CAT, SOD and GSH-PX were measured in the blood and tissues. We also did some histochemical stainings to detect iron deposition and to visualize fibrotic areas. Finally, we did immunohistochemistry for iNOS and immature macrophage detection (calprotectin). When we analyzed trace elements, we observed a reduction in the serum levels of Se, Zn and Fe and an increase in Cu levels. At the same time there was an increase in plasma levels of LPO and a decrease in the blood levels of the enzymes CAT and GSH-Px. In spite of these results, we detected a higher activity of SOD enzyme in infected animals, especially the symptomatic ones. Regarding the organs and tissues of symptomatic animals, we found a decrease in the activity of anti-oxidant enzymes and innumerous macroscopic lesions: as a consequence of an intense, difuse and chronic inflammatory process as (1) congestion and deposition of hemosiderin with a high parasitic load; (2) congestion associated with high levels of iron deposition ;(3) increase in fibrilopoiesis; (4) decrease in the levels of iNOS and NO (5) high number of L1 positive macrophages. We found some positive correlations between iron deposition and degree of inflammation/fibroses and LPO and hemosiderin deposition. However there is a negative correlation between iron deposition and iNOS and NO. Together, these data suggest that the clinical status marked by injuries, higher parasite burden and lower NO production in dogs naturally infected with L. infantum chagasi, are directly related to the imbalance of trace elements, especially Fe, oxidative stress and exudation of immature macrophages.