Neosaxitoxin

Neosaxitoxin is a potent neurotoxin produced by certain species of marine dinoflagellates, particularly those belonging to the genera *Alexandrium* and *Pyrodinium*. It belongs to the broader class of toxins known as saxitoxins, which are responsible for paralytic shellfish poisoning (PSP) in humans and other marine animals. Neosaxitoxin is structurally similar to saxitoxin but differs slightly in its chemical composition, contributing to its unique biological activity.

The toxin is synthesized by dinoflagellates during their growth phases and can accumulate in filter-feeding organisms such as clams, mussels, and oysters, which are commonly consumed by humans. When contaminated shellfish are ingested, neosaxitoxin binds to voltage-gated sodium channels in nerve and muscle cells, blocking the influx of sodium ions and disrupting normal electrical signaling. This interference leads to paralysis, starting with the muscles controlling respiration, which can be fatal if untreated.

Neosaxitoxin is highly water-soluble and stable under acidic conditions, making it resistant to degradation during food processing. Its toxicity is measured in mouse units (MU), where a single microgram of neosaxitoxin can be lethal to a 20-gram mouse. Symptoms of poisoning in humans typically include numbness of the lips and tongue, followed by progressive paralysis, difficulty breathing, and, in severe cases, death. Treatment primarily involves supportive care, such as mechanical ventilation, as there is no specific antidote.

The toxin’s presence in marine environments is monitored through regulatory programs that test shellfish for saxitoxin and its analogs, including neosaxitoxin. Harmful algal blooms, often referred to as "red tides," are a primary concern, as they can lead to widespread contamination of coastal waters and shellfish beds. Research continues to improve detection methods and understand the ecological factors influencing neosaxitoxin production in marine ecosystems.