The Effects of Doxapram Blocking the Response of Gram-Negative Bacterial Toxin (LPS) at Glutamatergic Synapses

SIMPLE SUMMARY: The actions of bacterial toxin lipopolysaccharides (LPS) can lead to the development of illness in humans and animals by triggering an immune system response. LPS is known to negatively affect ion channels within mammalian cells and block receptors in flies. There are currently no pharmacological blockers for LPS. In recent studies, the compound doxapram has been shown to block some of the negative effects of LPS. In the crayfish model, LPS is thought to increase transmission at neuromuscular junctions. The effects of doxapram on the crayfish model are relatively unknown. This study aimed to determine the general effect of doxapram on the crayfish model and if doxapram could also block the ability of LPS to increase transmission at synapses. It was shown that high concentrations of doxapram rapidly decreased transmission, while lower concentrations increased transmission for a short time and then decreased transmission. When exposed to a combination of LPS and doxapram, the increase in transmission typically seen with LPS did not occur and transmission was completely decreased. These results could suggest that LPS and doxapram are working through the same pathways. This study provides further information regarding bacterial infections and how pharmacological agents may affect their development. ABSTRACT: Lipopolysaccharides (LPS) associated with Gram-negative bacteria are one factor responsible for triggering the mammalian immune response. Blocking the action of LPS is key to reducing its downstream effects. However, the direct action of LPS on cells is not yet fully addressed. LPS can have rapid, direct effects on cells in the absence of a systemic immune response. Recent studies have shown that doxapram, a blocker of a subset of K2P channels, also blocks the acute actions of LPS. Doxapram was evaluated to determine if such action also occurs at glutamatergic synapses in which it is known that LPS can increase synaptic transmission. Doxapram at 5 mM first enhanced synaptic transmission, then reduced synaptic response, while 10 mM rapidly blocked transmission. Doxapram at 5 mM blocked the excitatory response induced by LPS. Enhancing synaptic transmission with LPS and then applying LPS combined with doxapram also resulted in retarding the response of LPS. It is possible doxapram and LPS are mediated via a similar receptor or cellular responses. The potential of designing pharmacological compounds with a similar structure to doxapram and determining the binding of such compounds can aid in addressing the acute, direct actions by LPS on cells.