Homoanatoxins

Homoanatoxins are a group of potent neurotoxic alkaloids produced by certain cyanobacteria and are structural homologues of anatoxin-A. The best known member is homoanatoxin-a, which differs from anatoxin-A by an extra methylene group in the side chain. These toxins are typically produced by freshwater cyanobacterial blooms and can accumulate in surface waters used for drinking, irrigation, or recreation.

Mechanism of action is through agonism at nicotinic acetylcholine receptors at the neuromuscular junction. By mimicking acetylcholine, homoanatoxins cause sustained depolarization of nerve and muscle cells, leading to rapid motor dysfunction and potentially fatal respiratory paralysis.

Toxicity and exposure risk are significant in sensitive environments. Human cases are rare but can be severe, with symptoms such as tremors, drooling, vomiting, muscular weakness, and respiratory distress occurring soon after exposure. Animals and livestock are also at risk when drinking contaminated water. The toxins are relatively stable to heat and some food-processing conditions, allowing them to persist in water and sediments under bloom conditions.

Diagnosis and treatment rely on detecting the toxin in water or biological samples using analytical methods such as liquid chromatography–mass spectrometry. There is no specific antidote; management is supportive, focusing on airway management and breathing support, plus measures to prevent further exposure.

Prevention centers on reducing cyanobacterial blooms through nutrient management and effective water treatment. Public health guidance during bloom events emphasizes avoiding contact with affected waters and using safe drinking-water sources.

See also anatoxin, cyanotoxins.