uric acid

As uric acid is the name given to the end product of the purine metabolism. Purine is necessary for the structure of ribonucleic acid (RNA) and deoxyribonucleic acid (DNA), which are found in the body's own cells and which carry genetic information.

What is uric acid?

Purine is ingested with food (e.g. meat) and is therefore not essential. During the purine metabolism, uric acid is produced, which is excreted with the urine via the kidneys or the intestines.

Uric acid is only very slightly soluble in the blood, the solubility being determined by the pH value. For example, if the urine pH is 7.0, uric acid excretion is ten times worse than at a pH value of 5.7. If the purine metabolism is disturbed and the urine concentration rises, this can lead to various diseases.

Function, effect & tasks

Uric acid arises as a breakdown product of the purine bases from xanthine or hypoxanthine. 75 percent of the uric acid is excreted via the kidneys, the rest of the excretion occurs via the intestines, saliva or sweat.

The amount of uric acid in the body depends on gender, age and diet. In men, the uric acid levels are between 3.6 mg / dl (lower limit) and 8.2 mg / dl (upper limit), in women between 2.3 mg / dl (lower limit) and 6.1 mg / dl (upper limit). The uric acid level is mainly determined in the following diseases:

• Renal failure
• leukemia
• Radiation therapy or chemotherapy
• Joint inflammation
• Type II diabetes
• Obesity

The concentration of uric acid is measured both in the urine and in the blood serum. Therefore, no alcohol or offal should be consumed for three days before blood collection. Uric acid has an antioxidant effect in the blood and also protects the blood vessels from damage that can occur due to oxidative processes. When the uric acid level rises sharply, the acid forms crystals that can be deposited in the kidneys or joints.

Education, occurrence, properties & optimal values

Purine bodies are made up of two nitrogen-containing rings. They can be found in the RNA or DNA but also in energy carriers (e.g. GTP, ATP). The nitrogen bases adenine and guanine, which play an essential role in energy metabolism, can be found in the RNA or DNA molecule. When the two purine derivatives are broken down, the phosphate residue is first split off with the help of certain enzymes, then the base is separated from the sugar.

Uric acid is then produced from the nitrogen base through various reactions. The acid is formed in the small intestine and in the liver, part of which is produced by endogenous purine breakdown, the other part is formed from purines that are ingested with food.

There are foods that contain a lot of purines and can be of both vegetable and animal origin. If foods that tend to be low in purine are consumed, the body can remove the uric acid, which is produced during breakdown, with the urine without problems. When foods rich in purine are consumed, the metabolism also produces a lot of uric acid, which can often not be completely excreted. Therefore, it remains in the blood and the uric acid level increases.

There are also products that are purine-free, but which still raise the uric acid level because they inhibit the excretion of uric acid and promote the breakdown of purine. This group mainly includes alcoholic beverages such as beer or schnapps. Another source is fructose, especially when used as a sweetener. If fructose is broken down, the uric acid level rises sharply and the risk of gout is increased. If the concentration of uric acid in the blood is increased, the doctor speaks of what is known as hyperuricemia. A distinction is made between primary and secondary hyperuricemia:

• Primary hyperuricemia is caused by a disorder in the urea metabolism.
• Secondary hyperuricemia is caused by various diseases or by taking medication.

Diseases & Disorders

If the uric acid concentration is high, so-called uric acid crystals develop, especially in the joints. This causes inflammatory reactions and those affected suffer an attack of gout.

The excess uric acid is subsequently deposited in the tissue, whereby the toe and finger joints or the kidneys are particularly affected. The uric acid crystals cause severe pain and also lead to malfunctions and deformations. The deposits lead to kidney stones or inflammation on the kidney. To reduce elevated uric acid levels, those affected should eat a low-fat diet and avoid alcohol.

If the uric acid level remains high, it is necessary to take medication to reduce the production of uric acid. The increased amount of uric acid in gout or in Lesch-Nyhan syndrome are genetic. An excessively high uric acid level can also have the following reasons:

• Kidney dysfunction
• Increased production of purine in the body
• Increased intake of purine through food

In addition, the body produces more uric acid in:

• Thrombocythemia
• leukemia
• Poisoning
• underactive thyroid
• Overactive parathyroid gland
• Taking medication such as acetylsalicylic acid, antihypertensive drugs or tuberculostatics

A uric acid level that is too low occurs when there is a lack of xanthine oxidase or when drugs such as probeneciol or allopurinol are taken.