Tomatine

Tomatine (sometimes called tomatin or lycopersicin) is a glycoalkaloid, found in the stems and leaves of tomato plants, and in the fruits at much lower concentrations. It has fungicidal, antimicrobial, and insecticidal properties. Chemically pure tomatine is a white crystalline solid at standard temperature and pressure. Tomatine, as well as the closely related aglycon (or aglycone) derivative tomatidine have been shown to have multiple health benefits.Tomatoes were brought to Europe in the early 1500s. The English botanist John Gerard was one of the first cultivators of the tomato plant. In his publication Grete Herball, he considered tomatoes as poisonous due to their levels of what would later be called tomatine, plus high acid content. Consequently, tomatoes were generally not eaten in Britain until the mid-18th century.Alpha-tomatine (α-tomatine) belongs to the compound group steroidal glycoalkaloids. These compounds consist of an aglycon, which is a cholesterol derivative, and a carbohydrate chain, which in the case of α-tomatine consists of two d-glucose units, a d-galactose unit, and a d-xylose unit. In α-tomatine, the tetrasaccharide called lycotetraose is attached to the O-3 of the steroidal aglycone. At first it was thought that the synthesis of steroidal alkaloids only involved multiple steps of hydroxylation, oxidation and amination of cholesterol with arginine as the source of the incorporated nitrogen. Later the glycoalkaloid metabolism genes were discovered. These genes produce the glycoalkaloid metabolism enzymes, which are responsible for the synthesis of steroidal alkaloid aglycones in potato and tomato plants. The reaction these enzymes perform are shown in the figure 1.Tomatine may play a major role in resistance of the tomato plant against fungal, microbial, insect, and herbivoral attack.Even now, little is known about the bioavailability, pharmacokinetics and metabolism of the glycoalkaloids in humans. One important factor is the poor uptake of tomatine into general blood circulation. When tomatine is orally ingested, much tomatine may form complexes with cholesterol from the other food present in the stomach. The complexes of tomatine and cholesterol are not absorbed in the intestine, but are excreted. For the complexation with cholesterol to occur, the presence of a carbohydrate chain is essential. The aglycon tomatidine, which is tomatine without the sugars, does not form the complexes. The complexation probably occurs in the duodenum, because the acidic conditions in the stomach itself lead to protonation of the tomatine, and the protonated form of tomatine does not bind to cholesterol.Tomatine has been used as a reagent in analytical chemistry for precipitating cholesterol from solution. Also, tomatine is known to be an immune adjuvant in connection with certain protein antigens.Studies showed that the molecule possesses antibiotic properties against the human pathogens E.coli and Staphylococcus aureus, and a variety of fungi. The presence of sterols in cell membranes of fungi and other pathogens makes it possible for glycoalkaloids to form complexes with sterols. Such binding results in the disruption of cell membranes, leakage of cell components and finally cell death.The possible risks of tomatine for humans have not been formally studied, so no NOAEL can be deduced. The toxicity of tomatine has only been studied on laboratory animals. The symptoms of acute tomatine poisoning in animals are similar to the symptoms of poisoning by solanine, a potato glycoalkaloid. These symptoms include vomiting, diarrhea, abdominal pain, drowsiness, confusion, weakness, and depression. Generally, tomatine is regarded to cause less toxic effects to mammals than other alkaloids such as solanine. The amount of tomatine absorbed by the human body as well as the possible metabolism is unknown. There is no evidence that consumption of tomatoes causes acute toxic or genotoxic effects.