Glycerol belongs to the sugar alcohols and is involved in numerous metabolic processes. Medical science uses it, among other things, to treat cerebral edema, as a laxative in suppositories, and tentatively for stabilization during some surgeries.
What is glycerol?
Glycerin is an alcohol. Carl Wilhelm Scheele discovered the substance as early as 1779, when he obtained it from olive oil during the production of soap. But it was not until the next century, in 1813, that Michel-Eugène Chevreul finally proved that glycerol is a component of fats – along with fatty acids. However, it took another ten years before glycerin was given its name. Today, the substance is also known as glycerol, propanetriol, propane-1,2,3-triol or 1,2,3-propanetriol. The E number for glycerol is 422. In its pure form, it is colorless and liquid; it has a melting point of 18 °C and a sweetish taste. Heating causes glycerol to evaporate. In the process, it converts to propenal.
Function, effect and tasks
In various biological processes, glycerol is used or can intervene in the course of the processes. Above all, it is found in metabolic processes. The digestion of fats releases glycerol in the intestine. The tissue reabsorbs the substance and it eventually reaches the liver. There, the enzyme glycerol kinase converts the glycerol into glycerol-3-phosphate. For this process, the enzyme requires not only the substrate but also adenosine triphosphate (ATP). The cleavage of ATP releases energy, which glycerol kinase uses to catalyze the biochemical reaction with glycerol-3-phosphate. The body does not always convert ingested glycerol to glycerol-3-phosphate. Alternatively, the substance can oxidize and phosphorylate – the product is then glyceraldehyde-3-phosphate or glyceric acid-2-phosphate. In this form, it interferes with metabolism and plays a role in the processing of fats and carbohydrates, for example. The body can use glyceraldehyde in glycolysis. Glycolysis is the process in which cells break down the sugar glucose in a specific way. Glycolysis follows the Embden-Meyerhof scheme, which includes other molecules with glycerol. Glycerol also plays a role in biomembranes such as the cell membrane. Phospholipids form the lipid bilayer that makes up the membrane. The content of phospholipids in the membrane depends on the type of cell; Schwann’s cells, for example, have a very high content. Phospholipids are composed of fatty acids and phosphoric acids esterified with an alcohol, among others. In addition to glycerol, sphingosine can also serve this purpose.
Formation, occurrence, properties, and optimal values
Glycerol is found primarily in fats and fatty acid esters. Biochemistry also refers to the latter as triglycerides because they are triple esters of glycerol. The concentration of triglycerides in the blood is an indicator of a person’s health. A value above 150 mg per dl is considered elevated and may, for example, indicate a lipid metabolism disorder (hypertriglyceridemia). Glycerol is composed of carbon, hydrogen and oxygen and has the molecular formula C3H8O3. It is the simplest trivalent alcohol. Glycerol often appears in combination with carboxylic acids, which are organic compounds and have at least one carboxyl group. Together with carboxylic acids, glycerol forms organic esters that form compounds with other building blocks in many molecules.
Diseases and disorders
An increase in triglycerides in the blood may indicate a lipid metabolism disorder. Medicine refers to this clinical picture as hypertriglyceridemia. Various causes are possible for the disorder. One variant of hypertriglyceridemia is genetic. Affected individuals suffer from a deficiency of certain enzymes. Lipoprotein lipase is one such enzyme. It converts triglycerides and water into diacylglycerol and fatty acid. Body cells need the fatty acids to synthesize fats and store them as reserves, for example. A mutation causes defects in the formation of the enzyme lipoprotein lipase, which disrupts fat synthesis. In this case, a change in the LPL gene is responsible for hypertriglyceridemia. Another cause of the disease is found in apolipoprotein C2. It represents a component of the lipoproteins, with the help of which the transport of lipids through the blood is possible.As a result of a mutation in the corresponding DNA segment, not only can hypertriglyceridemia occur; the disturbed fat metabolism also increases the risk of arteriosclerosis, which medicine calls arteriosclerosis. Arteriosclerosis can result from blood fats such as triglycerides being deposited in the blood vessels, causing the veins to narrow. Complete vascular occlusion is also possible. In addition, the deposits can become detached and block finer veins. Possible consequences include stroke, heart attack and pulmonary embolism. Lifestyle factors such as poor diet, tobacco use, lack of exercise and high blood pressure further increase the risk of such complications. Glycerin is also used as a basic ingredient in ointments and creams. It is also used as a drug: in suppositories, glycerin has a laxative effect, and it expels gallstones and urinary stones. Doctors also use glycerin to treat cerebral edema (water retention in the brain). Furthermore, there are initial attempts to use glycerin during long operations: This would allow doctors to further lower body temperature during surgery, potentially increasing the likelihood of a successful intervention. Orally administered glycerol is potentially harmful to health in larger amounts if ingested for nonmedical reasons and without medical supervision.
