Does the midgut of the tardigrade Paramacrobiotus experimentalis respond to the effects of ibuprofen?

In recent years, the pollution of aquatic environments with pharmaceuticals, including non-steroidal anti-inflammatory drugs (NSAIDs), has increased. This research investigated the effects of 7- and 28-day exposure to ibuprofen on the midgut ultrastructure of the tardigrade Paramacrobiotus experimentalis. The conducted research will enrich the knowledge on the effect of ibuprofen with histological analyses. In addition, the effect of ibuprofen has not been studied on tardigrades so far. Specimens were incubated in three concentrations of this drug: 0.1 μg/L (concentration commonly found in surface waters worldwide), 16.8 μg/L (concentration found in the rivers of large cities), and 1 mg/L (experimental concentration). In addition, the lethal concentration 50 (LC50) after 24 h incubation in ibuprofen was determined. Ultrastructural analyses showed the presence of degenerated mitochondria and autophagic structures in midgut digestive cells after incubation in ibuprofen, which was confirmed by LysoTracker Red staining. TUNEL staining showed DNA fragmentation–a marker of cell apoptosis–in digestive cells treated with ibuprofen. Furthermore, dihydroethidium (DHE) revealed signals emitted by ROS+ positive cells in midgut digestive cells, indicating oxidative stress. Ultrastructural changes and the number of signals indicating damage in the cell were correlated with increases in concentration and time of exposure to the stressor. The lack of ultrastructural changes in regenerative cells supports the theory that digestive cells of the midgut are one of the first barriers protecting the body against stressors.