Why is urine yellow? It seems like such a simple question, but the answer was only given this week. American researchers have discovered that an enzyme produced by intestinal bacteria is responsible for the yellow color.
The discovery of this enzyme, called bilirubin reductase, paves the way for further research into the role of the gut microbiome – or the billions of bacteria, viruses, yeasts and fungi that live together in your gastrointestinal system – and possible new treatment methods for diseases. such as jaundice and inflammatory bowel disease. The best known are Crohn’s disease and ulcerative colitis. In the Netherlands, one in two hundred people has one of these invisible and often shame-related conditions.
Better treatment of intestinal diseases
The explanation for yellow urine can therefore contribute to better treatment. “The discovery of this enzyme has finally solved the mystery behind the yellow color of urine,” said lead researcher Brantley Hall of the University of Maryland. “It is fascinating that the origins of such an everyday biological phenomenon have remained unclear for so long.”
But the scientists can now explain it perfectly: when red blood cells are broken down after about six months, a bright orange pigment called bilirubin is created as a byproduct. This bilirubin is then secreted in the intestines, after which it is directed towards the exit, but in the meantime part of this dye is reabsorbed by the body. If the blood absorbs too much bilirubin, this can lead to jaundice. This is a phenomenon in which the skin and eyes yellow. But fortunately, a number of microbial intestinal inhabitants are able to convert this bilirubin into other substances.
Age-old mystery
“Intestinal bacteria produce the enzyme bilirubin reductase, which converts bilirubin into the colorless byproduct urobilinogen,” explains biologist Hall. “The substance urobilinogen then spontaneously breaks down and turns into a molecule called urobilin, which is the substance that gives urine the yellow color we all know so well.”
Scientists have known for some time that urobilin is responsible for the yellow tint, but the discovery of the microbial enzyme makes it clear how this yellow substance is found in the urine; a question that has puzzled scientists for more than a century.
Jaundice
It is of course wonderful that this scientific mystery has finally been solved, but this new knowledge could also have great practical use for people with certain digestive diseases. The research team found that bilirubin reductase is present in the gastrointestinal tract of almost all adult humans, but is often absent in infants and patients with intestinal diseases. It strongly appears that the absence of bilirubin reductase is an important cause of jaundice in newborns and the development of gallstones.
“We have now successfully identified this enzyme. The next step is to find out how the gut microbiome influences bilirubin levels and what impact this has on conditions such as jaundice,” says researcher Xiaofang Jiang. “This discovery lays the foundation for a better understanding of the intestinal-liver axis.”
Healing effect of microbiome
The gut microbiome has been linked to everything from Crohn’s and ulcerative colitis to allergies, rheumatoid arthritis and the skin condition psoriasis. This discovery brings science closer to a holistic understanding of the complex role of the gut microbiome for human and animal health. To achieve this, the researchers collaborated with many different labs. “This multidisciplinary approach has allowed us to solve the physiological puzzle at the molecular level,” says Hall. “This is the culmination of many years of hard work and shows once again why the diverse collection of microbes in our gastrointestinal tract are so incredibly important for public health.”
2024-01-08 13:32:21
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