In general, the water solubility of uric acid and its alkali metal and alkaline earthsalts is rather low. All these salts exhibit greater solubility in hot water than cold, allowing for easy recrystallization. This low solubility is significant for the etiology of gout. The solubility of the acid and its salts in ethanol is very low or negligible. In ethanol/water mixtures, the solubilities are somewhere between the end values for pure ethanol and pure water.
Solubility of urate salts (grams of water per gram of compound)
Ammonium hydrogen urate
Lithium hydrogen urate
Sodium hydrogen urate
Potassium hydrogen urate
Magnesium dihydrogen diurate
Calcium dihydrogen diurate
The figures given indicate what mass of water is required to dissolve a unit mass of compound indicated. The lower the number the more soluble the substance in the said solvent.
Humans. The normal concentration range of uric acid (or hydrogen urate ion) in human blood is 25 to 80 mg/L for men and 15 to 60 mg/L for women (but see below for slightly different values). An individual can have serum values as high as 96 mg/L and not have gout. In humans, about 70% of daily uric acid disposal occurs via the kidneys, and in 5-25% of humans, impaired renal (kidney) excretion leads to hyperuricemia. Normal excretion of uric acid in the urine is 250 to 750 mg per day (concentration of 250 to 750 mg/L if one litre of urine is produced per day - higher than the solubility of uric acid because it is in the form of dissolved acid urates).
Dogs. The Dalmatian dog has a genetic defect in uric acid uptake by the liver and kidneys, resulting in decreased conversion to allantoin, so this breed excretes uric acid, and not allantoin, in the urine.
Birds and reptiles. In birds and reptiles, and in some desert dwelling mammals (such as the kangaroo rat), uric acid also is the end-product of purine metabolism, but it is excreted in feces as a dry mass. This involves a complex metabolic pathway that is energetically costly in comparison to processing of other nitrogenous wastes such as urea (from the urea cycle) or ammonia, but has the advantages of reducing water loss and preventing dehydration.
In human blood plasma, the reference range of uric acid is typically 3.4-7.2 mg per 100 ml (200-430 µmol/l) for men, and 2.4-6.1 mg per 100 ml for women (140-360 µmol/l). Uric acid concentrations in blood plasma above and below the normal range are known as, respectively, hyperuricemia and hypouricemia. Likewise, uric acid concentrations in urine above and below normal are known as hyperuricosuria and hypouricosuria. Uric acid levels in saliva may be associated with blood uric acid levels.
High uric acid
Hyperuricemia (high levels of uric acid), which induces gout, has various potential origins:
Excess blood uric acid can induce gout, a painful condition resulting from needle-like crystals of uric acid precipitating in joints, capillaries, skin, and other tissues. Gout can occur where serum uric acid levels are as low as 6 mg per 100 ml (357 µmol/l), but an individual can have serum values as high as 9.6 mg per 100 ml (565 µmol/l) and not have gout.
In humans, purines are metabolized into uric acid which is then excreted in the urine. Consumption of some types of purine-rich foods, particularly meat and seafood, increases gout risk. Gout may arise from regular consumption of meats, such as liver, kidney, and sweetbreads, and certain types of seafood including anchovies, herring, sardines, mussels, scallops, trout, haddock, mackerel and tuna. Moderate intake of purine-rich vegetables, however, is not associated with an increased risk of gout.
One treatment for gout in the 19th century was administration of lithium salts; lithium urate is more soluble. Today, inflammation during attacks is more commonly treated with NSAIDs, colchicine, or corticosteroids, and urate levels are managed with allopurinol. Allopurinol, which weakly inhibits xanthine oxidase, is an analog of hypoxanthine that is hydroxylated by xanthine oxidoreductase at the 2-position to give oxipurinol.
Lesch-Nyhan syndrome, a rare inherited disorder, is also associated with high serum uric acid levels. Spasticity, involuntary movement, and cognitive retardation as well as manifestations of gout are seen in this syndrome.
Saturation levels of uric acid in blood may result in one form of kidney stones when the urate crystallizes in the kidney. These uric acid stones are radiolucent and so do not appear on an abdominal plain X-ray. Uric acid crystals can also promote the formation of calcium oxalate stones, acting as "seed crystals".
Meta-analysis of 10 case-control studies found that the serum uric acid levels of patients with multiple sclerosis were significantly lower compared to those of healthy controls, possibly indicating a diagnostic biomarker for multiple sclerosis.
Normalizing low uric acid
Correcting low or deficient zinc levels can help elevate serum uric acid.
Theacrine or 1,3,7,9-tetramethyluric acid, a purine alkaloid found in some teas
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