Solanine

SOLANINE, a glycoalkaloid found in various species of the nightshade family: in black nightshade (Solanum nigrum L.), in tomatoes (Solanum lycopersicum L.), in bittersweet nightshade (Solanum dulcamara L.), and in potatoes (Solanum tuberosum L.), in which solanine is contained in the haulm, more in the berries, and least of all in the tubers. In the latter, the amount of solanine increases significantly during sprouting and storage of potatoes: in good, healthy potatoes, the amount of solanine rose from 0.04‰ in January to 0.11‰ by July, and after 1.5 years of storage, when the tubers had already shriveled significantly and turned black in places, the solanine content reached 1.3‰. Fresh potato sprouts, if they are no more than 1 cm long, are especially rich in solanine—up to 5‰. In young, immature potatoes, there is more solanine than in mature ones. Diseased, soft, wrinkled potatoes contain 2–3 times more solanine than good, healthy ones. Solanine possesses poisonous properties, and this must be taken into account in cases of food poisoning consisting mainly of potatoes, although some authors consider the cause of the illnesses here to be not solanine, but poisonous products formed as a result of bacterial growth (for example, Bacillus proteus) on the potatoes.

Solanine is extracted from potatoes. Solanine consists of delicate, white, shiny, bitter-tasting, needle-like crystals that melt at 254°C with decomposition; it is almost insoluble in water and alcohol at 15°C; in boiling water, the solubility is 1:8,000, and the solution has a weakly alkaline reaction; it dissolves well in hot alcohol. With acids, it forms amorphous salts that are easily soluble in water and alcohol, very unstable, and easily decompose with the release of free solanine. With reagents for alkaloids, it gives characteristic reactions, and under the influence of dilute HCl or H₂SO₄, it splits into grape sugar, galactose, indulcide, and the poisonous solanidine. Thus, solanine exhibits a dual character, which is why it is classified as a glycoalkaloid. Solanine was first isolated in 1821 from black nightshade by Desfosses, but the composition of solanine still remains not fully clarified to this day. Solanine is precipitated by cholesterol, which brings solanine closer to saponin, with which solanine has much in common in a pharmacodynamic respect. The effect of solanine on animals is expressed locally by strong irritation, causing inflammation, abscesses, and tissue necrosis. Solanine is absorbed with difficulty and slowly, therefore its effect is clearly manifested only upon direct introduction into the blood. In such cases, muscle twitching, convulsions, strengthening and then weakening of respiration, a comatose state, muscle paralysis, respiratory paralysis, and death occur. These phenomena depend on the action of solanine on the central nervous system. In the intestines, solanine increases peristalsis and causes nausea, vomiting, and diarrhea; at autopsy, swelling and redness of the follicular apparatus of the small intestine, rejection of the epithelium, ecchymoses, and the exit of leukocytes from the vessels are discovered. In the kidneys, phenomena of acute parenchymatous nephritis are found as a result of the irritating action of solanine, which is excreted during the animal's life through the kidneys. Protein, hemoglobin, and many granular casts are found in the urine. Blood becomes laky from solanine. For solanine poisoning to occur in a human, it is necessary to ingest at least 0.4 g of this poison (Rote); in such a case, a decrease and weakening of the pulse, difficulty in breathing, nausea, sometimes vomiting, rarely diarrhea, a feeling of heaviness in the head, a tendency to sleep, general weakness, cramps of the calf muscles, dryness of the skin, itching, and protein in the urine occur. The phenomena of solanine poisoning in humans and animals are generally similar. Solanine is excreted from the body in the urine and partly in unchanged form in the feces. Poisoning by solanine (potatoes) with a fatal outcome in humans has not been described. Therapeutically, solanine is not currently used.