*2.4.3 Neurotoxins*

Alkaloids are poisonous in a short amount of time and are usually lethal, as they cause paralysis of the surrounding skeletal muscles, followed by paralysis of the respiratory muscles, resulting in incapacity to breathe and death. Several forms of these toxins have been identified (e.g., *Oscillatoria* and *Trichodesmium*).


i. **Anatoxin**: It is produced by the species (Anabaena flos-aquae) with a molecular weight of (765 Da), and it is also produced by species of the genus (*Oscillatoria*) as well.

#### **Table 1.**

*Cyanotoxins with public health significance from acute exposures [6].*


#### **2.5 Hepatotoxins**

Toxins of this sort cause a variety of types and strains that belong to the genera (*Microcystis*, *Anabaena*, *Nodularia*, *Cylindrospermopsis*, *Oscillatoria* and *Nostoc*). These toxins are the most frequent among cyanobacterial toxins, and they have a strong toxic impact. However, they take longer to kill than neurotoxins, and death can take anywhere from 5 min to a few days, depending on numerous factors such as the animal's weight, the type of poison, and the dose. These toxins are divided into three categories [9].

## *2.5.1 Microcystins*

They're monocyclic seven-chain peptides with an unique amino acid named Adda connecting the side chains. Because the peptide ring comprises five amino acids that are used in the synthesis of all forms of microcystins produced by the species (*Microcystis aeruginosa*), it was named after it. Other species from the genera (*Oscillatoria*, *Nodularia*, *Anabaena*, *Nostoc*) and others are used to make it. So far, more than a million microcystins have been identified (60 species). Microcystins MC-LR, MC-RR, and MC-YR are the most frequent and poisonous kinds of microcystins. Microcystins have a molecular weight of 909–1044 Da, depending on the species. Microcystins are known for their long-term resilience to high temperatures, however it has been discovered that they can tolerate boiling without denaturation. It withstands pH changes and dissolves easily in water, ethanol, methanol, and acetone, and cells require energy to consume the poison [10].

#### *2.5.2 Nodularin*

It's a pentacyclic monocyclic peptide that looks a lot like MC–LR but is smaller. The peptide ring has a molecular weight of 824 Da and comprises amino acids similar to those found in MC–LR. Only one variety has been identified as being produced by the species (*Nodularia spumigena*), and this proliferation has a poisonous impact identical to that of MC-LR.

#### *2.5.3 Cylindrospermopsin*

It is one of the toxins produced by the type (*Cylindrospermopsis mceberskii*), and it is the only alkaloid compound among the hepatotoxicants, as it shares this

characteristic with neurotoxins, and its toxic effect is not limited to the liver, as it has been discovered that it also affects the kidneys, causing tissue destruction [11].

## **2.6 Endotoxins**

It refers to the lipo polysaccharide (LPS) that forms the cell wall of pan cyanobacteria, and it has been discovered that these chemicals are hazardous to humans. When injected into the peritoneal membranes at a dose of (1–1.2 mg/kg after 48 h), it was likewise proven to be deadly to rats [12].
