Uric acid

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Uric acid


General
Systematic name	7,9-dihydro-1H-purine- 2,6,8(3H)-trione
Other names	2,6,8 Trioxypurine
Molecular formula	C₅H₄N₄O₃
SMILES	C12NC(=O)NC(=O)C=2NC(=O)N1
Molar mass	168g/mol
Appearance	White Crystals
CAS number	69-93-2
Properties
Density and phase	1.87
Solubility in water	Slightly
Melting point	decomposes on heating
Boiling point	N/A
Acidity (pK_a)	3.89
Structure
Molecular shape	?
Coordination geometry	?
Crystal structure	?
Dipole moment	?
Hazards
MSDS	?
Main hazards	?
Flash point	? °C
R/S statement	R: ? S: ?
RTECS number	?
Supplementary data page
Structure & properties	?
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Related compounds
Related compounds	hypoxanthine, xanthine, purine, urea, urate, ammonia
Except where noted otherwise, data are given for materials in their standard state (at 25°C, 100 kPa) Infobox disclaimer and references

Uric acid (or urate) is an organic compound of carbon, nitrogen, oxygen and hydrogen with the formula C₅H₄N₄O₃.

1 Metabolic processes
2 Medical issues
3 See also
4 External links
5 External links

[edit] Metabolic processes

Xanthine oxidase oxidizes oxypurines such as xanthine and hypoxanthine to uric acid. In humans and higher primates, uric acid is the final oxidation product of purine metabolism. In most other mammals, the enzyme uricase further oxidizes uric acid to allantoin. The loss of uricase in higher primates parallels the similar loss of the ability to synthesize ascorbic acid [1]. This may be because in higher primates uric acid (urate) partially replaces ascorbic acid [2] Both urate and ascorbate are strong reducing substances (electron donors) and potent antioxidants. In humans, about half the antioxidant capacity of plasma comes from uric acid.

Uric acid is also the end product of nitrogen metabolism in birds and reptiles. In such species, it is excreted in feces as a dry mass. While this compound is produced through a complex and energetically costly metabolic pathway (in comparison to other nitrogenated wastes such as urea or ammonia), its elimination minimizes water loss. It is therefore commonly found in the excretions of animals that live in very dry environments like the kangaroo rat.

[edit] Medical issues

Humans produce only small quantities of uric acid with excess accumulation leading to a type of arthritis known as gout.

In human blood, uric acid concentrations between 3.6 mg/dL (~214µmol/L) and 8.3 mg/dL (~494µmol/L) (1mg/dL=59.48 µmol/L)[3] are considered normal by the American Medical Association, although significantly lower levels are common in vegetarians due to a decreased intake of purine-rich meat.[4]

The disease gout in humans is associated with elevated blood levels of uric acid [5]. Saturation levels of uric acid in blood may result in one form of kidney stones when the urate crystallizes in the kidney. Some patients with gout eventually get uric kidney stones. Lesch-Nyhan syndrome is also associated with very high serum uric acid levels [6].

Gout can occur where serum uric acid levels are as low as 6 mg/dL (~357µmol/L), but an individual can have serum values as high as 9.5 mg/dL (~565µmol/L) and not have gout [7] (no abstract available; levels reported at [8]).

Multiple sclerosis patients have been found to have serum uric acid levels ~194µmol/L, with patients in relapse averaging ~160µmol/L and patients in remission averaging ~230µmol/L. Serum uric acid in healthy controls was ~290µmol/L.[9] (1mg/dL=59.48 µmol/L)[10]

A 1998 study completed a statistical analysis of 20 million patient records, comparing serum uric acid values in patients with gout and patients with multiple sclerosis. Almost no overlap between the groups was found [11].

Uric acid has been successfully used in the treatment and prevention of the animal (murine) model of MS. A 2006 study found that elevation of serum uric acid values in multiple sclerosis patients, by oral supplementation with inosine, resulted in lower relapse rates, and no adverse effects. [12]

Purine-rich foods that are known to elevate uric acid levels include:

High animal sources: sweetbreads, anchovies, sardines, liver, beef kidneys, brains, meat extracts (e.g Oxo, Bovril), herring, mackerel, scallops, game meats, gravy

Moderate animal sources: beef, pork, poultry, fish and seafood

Moderate vegetable/grain sources: asparagus, cauliflower, spinach, mushrooms, green peas, lentils, dried peas, beans, oatmeal, wheat bran and wheat germ [13]

Moderate intake of purine-containing food is not associated with an increased risk of gout [14].

Uric acid may be a marker of oxidative stress [15], and may have a potential therapeutic role as an antioxidant (PMID 16375736). On the other hand, like other strong reducing substances such as ascorbate, uric acid can also act as a prooxidant [16], particularly at elevated levels. Thus, it is unclear whether elevated levels of uric acid in diseases associated with oxidative stress such as stroke and atherosclerosis are a protective response or a primary cause [17].

For example, some researchers propose that hyperuricemia-induced oxidative stress is a cause of Metabolic syndrome [18] [19]. On the other hand, plasma uric acid levels correlate with longevity in primates and other mammals[20]. This is presumably a function of urate's antioxidant properties.

The high nitrogen content of uric acid makes guano a useful agricultural fertilizer.

The crystalline form of uric acid is used as a reflector in certain species of fireflies.