Kidney Histology of Mice After Seven Days Oral Intake of Cyanobacterial Extract

Abstract

At the end of the dry season, during October 2004, a dense cyanobacteria bloom was observed in Monjolinho Reservoir (São Carlos city, São Paulo State, Brazil), and a great amount of scum accumulated on the water surface. Samples were collected in order to identify phytoplankton species and to determine its toxicity. Anabaena circinalis and Anabaena spiroides were the dominant species in this bloom. Initially, mouse bioassays (LD₅₀-24 h) and analysis by ELISA were performed, to detect toxic compounds in crude extracts of the natural samples. After toxicity was confirmed, an oral chronic toxicity test was carried out using three doses of cyanotoxins, in male Swiss albino mice, for 7 days. To prepare the extract, cyanobacterial cells were broken by repeated freeze and thaw cycles. Mice received the following doses of crude cyanobacterial extract diluted in drinking test solutions: 0.5 mg L_–1; 1.0 mg L_–1 and 2.0 mg L_–1. Mortality, clinical signs, body weight and weight gain were recorded during the study. In addition, histological slides were prepared to detect toxic injuries to the kidney. Toxin analysis by ELISA revealed 1.77 to 6.12 μg L^–1 total microcystins in the mouse drinking water. This study indicated that administration of low doses of cyanotoxins in mouse drinking test solutions did not result in histological injury in the kidney of animals exposed to cyanotoxins, as observed by optical microscopy.