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Supernatants from macrophages stimulated with microcystin-LR induce electrogenic intestinal response in rabbit ileum
M F Rocha1, J J Sidrim, A M Soares
1Department of Physiology and Pharmacology, Federal University of Ceará, Fortaleza-CE, Brazil.
Abstract:
Microcystin-LR is a cyclic heptapeptide hepatotoxin produced by the cyanobacterium Microcystis aeruginosa. This microorganism often forms toxic blooms in freshwater lakes and reservoirs for drinking water supply, producing serious disorders in humans and animals. Some have suggested that certain biological activities of microcystin may depend upon the stimulation of immune cells. Therefore, the aims of this research were to examine electrogenic intestinal secretion, in vitro, caused by the supernatants from macrophages stimulated with microcystin-LR, as well as to investigate the presence of interleukin-1beta and tumour necrosis factor-alpha in these supernatants. We found that the supernatants of macrophages stimulated with microcystin-LR (0.1, 0.3 and 1.0 microg/ml) caused electrogenic intestinal effects (change in short circuit currents (delta SCC)=57.6, 50.8 and 73.3, respectively, versus control=19.6 microA.cm(-2)) in a time-dependent way (microcystin-LR (1.0 microg/ml)=63.2, 108.8, 120.4 and 132.3 microA.cm(-2) at time 0, 40, 50 and 60 min., respectively). In addition, the intestinal secretory activity present in these supernatants was blocked (57%) by the prior treatment of macrophages with dexamethasone. We also demonstrated that microcystin-LR (0.1, 0.3 and 1.0 ,microg/ml) is capable of stimulating the synthesis of tumour necrosis factor-alpha (375.4, 369.0 and 610.8 pg/ml, respectively, versus control=165.0 pg/ml) and interleukin-1beta (198.9, 189.3 and 522.1 pg/ml, respectively, versus control=39.7 pg/ml). These findings demonstrate that microcystin-LR induces the release of interleukin-1beta and tumour necrosis factor-alpha by peritoneal macrophages in vitro, and that the supernatants from these macrophages induce electrogenic secretion in rabbit ileal mucosa.
Insights
Microcystin-LR, a toxin from cyanobacteria, stimulates immune cells to release inflammatory cytokines. These cytokines then induce intestinal secretion, potentially impacting health through contaminated water sources.
Area of Science:
- Environmental Toxicology
- Immunology
- Gastroenterology
Background:
- Microcystin-LR is a potent hepatotoxin produced by cyanobacteria, frequently contaminating freshwater supplies.
- Cyanobacterial blooms pose risks to human and animal health, with potential immune system involvement.
- Understanding microcystin-LR's biological activities is crucial for assessing public health risks.
Purpose of the Study:
- To investigate the effect of microcystin-LR-stimulated macrophage supernatants on intestinal electrogenic secretion in vitro.
- To determine the presence and levels of interleukin-1beta and tumor necrosis factor-alpha in these supernatants.
- To elucidate the role of immune cell activation in microcystin-LR-induced physiological responses.
Main Methods:
- Cultured peritoneal macrophages were stimulated with varying concentrations of microcystin-LR.
- Supernatants from stimulated macrophages were applied to rabbit ileal mucosa to measure electrogenic secretion (change in short-circuit current).
- Cytokine levels (interleukin-1beta and tumor necrosis factor-alpha) in supernatants were quantified using immunoassays.
Main Results:
- Macrophage supernatants from microcystin-LR stimulation induced significant, time-dependent electrogenic intestinal secretion.
- The observed intestinal secretory activity was partially blocked by dexamethasone treatment of macrophages.
- Microcystin-LR significantly increased the synthesis and release of tumor necrosis factor-alpha and interleukin-1beta by macrophages.
Conclusions:
- Microcystin-LR stimulates peritoneal macrophages to release key inflammatory cytokines, TNF-α and IL-1β.
- The supernatants containing these cytokines induce electrogenic secretion in the intestinal mucosa.
- These findings highlight a potential mechanism for microcystin-LR toxicity impacting the gastrointestinal system.