Moreover, the urine formation process could be acting to concentrate MCYST in the tubular fluid. In this sublethal dose experiment the analyses of free MCYST in tissues and samples of excreta showed the presence of the toxin (mean ± SD) in liver (data not shown), kidney (113.5 ± 21.3 ng/g), serum (0.46 ± 0.20 ng/ml), urine (2348 ± 354 ng – total amount) and feces (663 ± 331 ng – total amount). Despite the fact that the ELISA method only detects the non-protein conjugated amount of toxin (a minor percentage of the total), the data show that MCYST was circulating

in the organism and was partially eliminated through feces and urine in a period of 24 h. It was also observed that MCYST and/or its

GSH conjugates (MCYST-GSH, MCYST-Cys; also detectable by ELISA antibodies; Metcalf et al., 2000) were detected in the urine at a concentration that indicates click here a process of secretion, since FEMCYST is about 138% (see Table 1). This secretion of the toxin probably occurs along the renal JQ1 tubules and confirms the active role of kidney in the elimination of MCYST from the organism. Ito et al. (2002) have already detected the toxin in this organ, and not only MCYST itself, but also its conjugates. These ones result from the main route of MCYST detoxication which is through the activity of GST. That conjugation makes the toxin more hydrophilic and less toxic (Wiegand et al., 2002; Gehringer Methamphetamine et al., 2004). However, despite being less toxic, these conjugates can still induce damage in renal tissue (Kondo et al., 1992). The generation of reactive oxygen species (ROS) in the MCYST group is shown by increased formation of MDA, a known lipid peroxidation indicator (Fig. 2A) and also by a significant decrease in catalase enzyme activity (Fig. 2B). The observed oxidative damage verified by the lipid peroxidation process indicates a higher production

of ROS by renal cells exposed to MCYST. An excessive amount of ROS could reduce some antioxidant enzyme activities. If superoxide dismutase is affected, the consequent excess of superoxide anion radical can inhibit catalase activity (Kono and Fridovich, 1982), consistent with the reduced catalase activity observed after MCYST-LR exposure. Moreover, according to Ding et al. (2000), MCYST-LR induces damage to mitochondria by altering its membrane potential and permeability transition (MPT). The toxin may disrupt the mitochondrial electron transport chain, followed by ROS production and then change in MPT. This presence of ROS in renal tissue could also contribute to the formation of collagen in the interstitial space observed in cortex and medulla regions (Fig. 1D and F). In a recent study, using a skeletal muscle cell model, Cabello-Verrugio et al.