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uric acid

 
Dictionary: uric acid
 

n.

A semisolid compound, C5H4N4O3, that is a nitrogenous end product of protein and purine metabolism and is the chief nitrogenous component of the urine in birds, terrestrial reptiles, and insects.


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Sci-Tech Encyclopedia: Uric acid
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The main excretory end product of protein metabolism in certain species of birds and reptiles. In mammals, uric acid is derived from purines; in higher primates, including humans, it is excreted as such and is not oxidized to allantoin, the main excretory purine metabolism product of most species. In humans, uric acid levels are increased following excessive intake of dietary purines, primary synthesis in certain diseases (gout, Lesch-Nyhan syndrome), endogenous nucleic acid metabolism (leukemia, an abnormal number of erythrocytes in blood, chemotherapy-induced tumor lysis), and restricted renal excretion (renal diseases, ketoacidosis, lacticidosis, diuretics). Uric acid levels are lowered by the use of drugs causing increased uric acid excretion, and by renal tubular defects. See also Gout; Kidney disorders; Leukemia; Liver; Nucleic acid; Protein metabolism; Purine; Tumor.


 
Food and Nutrition: uric acid
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The end-product of purine metabolism in human beings and other apes; other mammals have the enzyme uricase, which converts the uric acid to allantoin, which is more soluble in water. See also gout.

 
Dental Dictionary: uric acid
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(yoor′ik)
n

A product of protein metabolism and present in the blood and urine. See also gout.

 

Heterocyclic compound of the purine type, the end product of metabolism of the purines in nucleic acids in many animals, including humans. It is excreted by reptiles and birds as the chief nitrogenous end product of protein breakdown. Small quantities are normally found in human blood; in gout, levels are abnormally high. Uric acid is used industrially in organic synthesis.

For more information on uric acid, visit Britannica.com.

 

An end-product of the metabolism of nucleic acids (e.g. DNA) that is normal constituent of urine. Excessive amounts of uric acid in the blood are associated with gout.

 
Columbia Encyclopedia: uric acid
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uric acid (yʊr'ĭk) , white, odorless, tasteless crystalline substance formed as a result of purine degradation in man, other primates, dalmatians, birds, snakes, and lizards. The last three groups of animals also channel all amino acid degradation into the formation of glycine, aspartic acid, and glutamine, which combine to form purines and finally uric acid; these so-called uricotelic organisms thus excrete uric acid as the major end-product of the metabolism of all nitrogen-containing compounds. Uric acid is a very weak organic acid that is barely soluble in water and insoluble in alcohol and ether. The urates are its salts. Uric acid is present in human urine only in extremely small amounts but constitutes a large part of the body waste matter of birds (see guano) and of reptiles. It collects sometimes in the human kidneys or bladder in calculi, or stones, and is responsible, when present in tissues or deposited upon bones in the form of urates, for gouty conditions (see gout). It occurs also in normal human blood. The pure acid is obtained from guano and other similar substances. Upon decomposition urea is obtained. A common test for the presence of the acid in urine depends upon the formation of murexide (an ammonium salt), which is an intense reddish purple. Nitric acid is added to the urine, which is then evaporated. If uric acid is present, murexide is formed when ammonia is added to the residue.


 
Wikipedia: Uric acid
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Uric acid
IUPAC name
Other names 2,6,8 Trioxypurine
Identifiers
CAS number [69-93-2]
PubChem 1175
EC number 200-720-7
KEGG C00366
SMILES
InChI
ChemSpider ID 1142
Properties
Molecular formula C5H4N4O3
Molar mass 168g/mol
Appearance White Crystals
Density 1.87
Melting point

decomposes on heating

Boiling point

N/A

Solubility in water Slightly
Acidity (pKa) 3.89
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox references

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

Contents

Biology

Uric acid is produced by xanthine oxidase from xanthine and hypoxanthine, which in turn are produced from purine. Uric acid is more toxic to tissues than either xanthine or hypoxanthine.

In humans and higher primates, uric acid is the final oxidation (breakdown) product of purine metabolism and is excreted in urine. In most other mammals, the enzyme uricase further oxidizes uric acid to allantoin.[2] The loss of uricase in higher primates parallels the similar loss of the ability to synthesize ascorbic acid.[3] Both uric acid and ascorbic acid are strong reducing agents (electron donors) and potent antioxidants. In humans, over half the antioxidant capacity of blood plasma comes from uric acid.

The Dalmatian dog has a genetic defect in uric acid uptake by the liver, resulting in decreased conversion to allantoin, so this breed excretes uric acid, and not allantoin, in the urine.[4]

In birds and reptiles, and in some desert dwelling mammals (eg 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 urea cycle) or ammonia, but has the advantage of reducing water loss.

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.[5]

Genetics

A proportion of people have mutations in the proteins responsible for the excretion of uric acid by the kidneys. Four genes have so far been identified: SLC22A12, SLC2A9, ABCG2 and SLC17A3).[6] SLC2A9 is known to transport both uric acid and fructose.[5] [7]

Medicine

In human blood plasma, the reference range of uric acid is between 3.6 mg/dL (~214µmol/L) and 8.3 mg/dL (~494µmol/L) (1mg/dL=59.48 µmol/L).[8] This range is considered normal by the American Medical Association. Uric acid concentrations in blood plasma above and below the normal range are known, respectively, as hyperuricemia and hypouricemia. Similarly, uric acid concentrations in urine above and below normal are known as hyperuricosuria and hypouricosuria. Such abnormal concentrations of uric acid are not medical conditions, but are associated with a variety of medical conditions.

Reference ranges for blood tests, comparing blood content of uric acid (shown in green) with other constituents.
Shown in molarity rather than mass. Uric acid shown in yellow.

High uric acid

This is the main focus of Biosensors researchers. They are developing techniques to detect higher concentrations of uric acid.

Gout

Excess serum accumulation of uric acid can lead to a type of arthritis known as gout.[9]

Elevated serum uric acid (hyperuricemia) can result from high intake of purine-rich foods, high fructose intake (regardless of fructose's low glycemic index (GI) value) and/or impaired excretion by the kidneys. 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 or CT scan. Their presence must be diagnosed by ultrasound for this reason. Very large stones may be detected on x-ray by their displacement of the surrounding kidney tissues. Some patients with gout eventually get uric kidney stones.

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 9.6 mg/dL (~565µmol/L) and not have gout[10] (no abstract available; levels reported at [11]).

Lesch-Nyhan syndrome

Lesch-Nyhan syndrome, an extremely rare inherited disorder, is also associated with very high serum uric acid levels.[12]

Spasticity, involuntary movement and cognitive retardation as well as manifestations of gout are seen in cases of this syndrome.[13]

Cardiovascular disease

Although uric acid can act as an antioxidant, excess serum accumulation is often associated with cardiovascular disease. It is not known whether this is causative (e.g., by acting as a prooxidant ) or a protective reaction taking advantage of urate's antioxidant properties.

[14]

Diabetes

The association of high serum uric acid with insulin resistance has been known since the early part of the 20th century, nevertheless, recognition of high serum uric acid as a risk factor for diabetes has been a matter of debate. In fact, hyperuricemia has always been presumed to be a consequence of insulin resistance rather than its precursor [15]. However, it was shown in a prospective follow-up study that high serum uric acid is associated with higher risk of type 2 diabetes independent of obesity, dyslipidemia, and hypertension [16].

Metabolic syndrome

Hyperuricemia is associated with components of metabolic syndrome and it has been debated for a while to be a component of it. It has been shown in a recent study that fructose-induced hyperuricemia may play a pathogenic role in the metabolic syndrome. This agrees with the increased consumption of fructose-base drinks in recent decades and the epidemic of diabetes and obesity [17].

Uric acid stone formation

Uric acid stones, which form in the absence of secondary causes such as chronic diarrhea, vigorous exercise, dehydration, and animal protein loading, are felt to be secondary to obesity and insulin resistance seen in metabolic syndrome. Increased dietary acid leads to increased endogenous acid production in the liver and muscles which in turn leads to an increased acid load to the kidneys. This load is handled more poorly because of renal fat infiltration and insulin resistance which are felt to impair ammonia excretion (a buffer). The urine is therefore quite acidic and uric acid becomes insoluble, crystallizes and stones form. In addition, naturally present promotor and inhibitor factors may be affected. This explains the high prevalence of uric stones and unusually acidic urine seen in patients with type 2 diabetes. Uric acid crystals can also promote the formation of calcium oxalate stones, acting as "seed crystals" (heterogenous nucleation).[18]

Low uric acid

Multiple sclerosis

Lower serum values of uric acid have been associated with Multiple Sclerosis. Multiple sclerosis (MS) patients have been found to have serum 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.[19] Conversion factor: 1 mg/dL=59.48 µmol/L[8]

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.[20]

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.[21]

Oxidative stress

Uric acid may be a marker of oxidative stress,[22] and may have a potential therapeutic role as an antioxidant.[23] On the other hand, like other strong reducing substances such as ascorbate, uric acid can also act as a prooxidant,[24] 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.[25][26]

For example, some researchers propose that hyperuricemia-induced oxidative stress is a cause of metabolic syndrome.[27][28] On the other hand, plasma uric acid levels correlate with longevity in primates and other mammals.[29] This is presumably a function of urate's antioxidant properties.

Sources of uric acid

  • In many instances, people have elevated uric acid levels for hereditary reasons. Diet may also be a factor, eating large amounts of sea salt can cause increased levels of uric acid. (Medical consultation is recommended before using large quanities of sea salt in daily cooking.)
  • Purines are found in high amounts in animal internal organ food products, such as liver.[30] A moderate amount of purine is also contained in beef, pork, poultry, fish and seafood, asparagus, cauliflower, spinach, mushrooms, green peas, lentils, dried peas, beans, oatmeal, wheat bran and wheat germ.[31]
  • Moderate intake of purine-containing food is not associated with an increased risk of gout.[32]
  • Serum uric acid can be elevated due to high fructose intake [27], reduced excretion by the kidneys, and or high intake of dietary purine.

Causes of low uric acid

Low uric acid (hypouricemia) can have numerous causes.
Low dietary zinc intakes cause lower uric acid levels. This effect can be even more pronounced in women taking oral contraceptive medication. [33]
Sevelamer, a drug indicated for prevention of hyperphosphataemia in patients with chronic renal failure, can significantly reduce serum uric acid.[34]

Normalizing low uric acid

Correcting low or deficient zinc levels can help elevate serum uric acid [35]
Inosine can be used to elevate uric acid levels. [36]

Other uric acid facts

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.

The uric acid in urine can also dry in a baby's diaper to form a pinkish powder that is harmless.

See also

External links

References

  1. ^ "Uric Acid." Biological Magnetic Resonance Data Bank. Indicator Information Retrieved on 18 February 2008.
  2. ^ Purine and Pyrimidine Metabolism
  3. ^ Proctor, P. (1970). "Similar Functions of Uric Acid and Ascorbate in Man". Nature 228: 868. doi:10.1038/228868a0. http://www.ncbi.nlm.nih.gov/pubmed/5477017. 
  4. ^ Friedamman, M; S.O Byers (01 Sep 1948). "Observations concerning the causes of the excess excretion of uric acid in the dalmatian dog". Journal of Biological Chemistry 175(2) (2): 727–35. http://www.jbc.org/cgi/reprint/175/2/727. 
  5. ^ a b Vitart V, Rudan I, Hayward C, et al. (2008). "SLC2A9 is a newly identified urate transporter influencing serum urate concentration, urate excretion and gout". Nature Genetics 40 (4): 437. doi:10.1038/ng.106. 
  6. ^ Aringer M, Graessler J (2008). "Understanding deficient elimination of uric acid". Lancet 372 (9654): 1929–1930. doi:10.1016/S0140-6736(08)61344-6. 
  7. ^ Döring A, Gieger C, Mehta D, et al. (2008). "SLC2A9 influences uric acid concentrations with pronounced sex-specific effects". Nature Genetics 40 (4): 430. doi:10.1038/ng.107. 
  8. ^ a b SI Units for Clinical Data
  9. ^ Tausche AK et al. (2006). "Hyperuricemia and gout: diagnosis and therapy. Article in German". Internist (Berl). 47(5): 509–20. doi:10.1007/s00108-006-1578-y. http://www.ncbi.nlm.nih.gov/pubmed/17190309. 
  10. ^ Laster L, Howell RR. (1963). "Biochemistry of uric acid and its relation to gout". N Engl J Med 268: 764–73. http://www.ncbi.nlm.nih.gov/pubmed/16586130. 
  11. ^ Uric Acid, Serum
  12. ^ Luo YC et al. (2006). "An amperometric uric acid biosensor based on modified Ir-C electrode". Biosens Bioelectron 22(4): 482–8. doi:10.1016/j.bios.2006.07.013. http://www.ncbi.nlm.nih.gov/pubmed/16908130. 
  13. ^ Nyhan WL (2005). "Lesch-Nyhan Disease". J Hist Neurosci 14(1): 1–10. doi:10.1080/096470490512490. http://www.ncbi.nlm.nih.gov/pubmed/15804753. 
  14. ^ Heinig M, Johnson RJ. (2006). "Role of uric acid in hypertension, renal disease, and metabolic syndrome". Cleve Clin J Med. 73(12): 1059–64. doi:10.3949/ccjm.73.12.1059. http://www.ncbi.nlm.nih.gov/pubmed/17190309. 
  15. ^ Cappuccio FP, et al. (1993). "Uric acid metabolism and tubular sodium handling. Results from a population-based study". Jama 270--- (3): 354–359. doi:10.1001/jama.270.3.354. PMID 8315780. http://www.ncbi.nlm.nih.gov/pubmed/8315780. 
  16. ^ Dehghan A. et al. (2007). "High serum uric acid as a novel risk factor for type 2 diabetes mellitus". Diabetes Care 31: 361. doi:10.2337/dc07-1276. PMID 17977935. http://www.ncbi.nlm.nih.gov/pubmed/17977935. 
  17. ^ Nakagawa T, Hu H, Zharikov S, et al. (2006). "A causal role for uric acid in fructose-induced metabolic syndrome". Am J Physiol Renal Physiol. 290 (3): F625–631. http://www.ncbi.nlm.nih.gov/pubmed/16234313. 
  18. ^ Charles Y.C. Pak (2008). "Metabolic Stone Management: 35 Years of Advances.". Journal of Urology 180 pages = 813-819. 
  19. ^ Toncev G, et al. (2002). "Serum uric acid levels in multiple sclerosis patients correlate with activity of disease and blood-brain barrier dysfunction". Eur J Neurol. 9(3): 221–6. doi:10.1046/j.1468-1331.2002.00384.x. http://www.ncbi.nlm.nih.gov/pubmed/11985629. 
  20. ^ Hooper DC, et al. (1998). "Uric acid, a natural scavenger of peroxynitrite, in experimental allergic encephalomyelitis and multiple sclerosis". Proc Natl Acad Sci U S A. 95(2): 675–80. doi:10.1073/pnas.95.2.675. PMID 9435251. http://www.ncbi.nlm.nih.gov/pubmed/9435251. 
  21. ^ Toncev G (2006). "Therapeutic value of serum uric acid levels increasing in the treatment of multiple sclerosis". Vojnosanit Pregl. 63(10): 879–82. http://www.ncbi.nlm.nih.gov/pubmed/17121380. 
  22. ^ Becker BF (June 1993). "Towards the physiological function of uric acid". Free radical biology & medicine 14 (6): 615–31. doi:10.1016/0891-5849(93)90143-I. PMID 8325534. http://linkinghub.elsevier.com/retrieve/pii/0891-5849(93)90143-I. 
  23. ^ Glantzounis GK, Tsimoyiannis EC, Kappas AM, Galaris DA (2005). "Uric acid and oxidative stress". Current pharmaceutical design 11 (32): 4145–51. doi:10.2174/138161205774913255. PMID 16375736. http://www.bentham-direct.org/pages/content.php?CPD/2005/00000011/00000032/0006B.SGM. 
  24. ^ Proctor P. (1972). "Electron-transfer factors in psychosis and dyskinesia". Physiol Chem Phys. 4(4): 349–60. http://www.ncbi.nlm.nih.gov/pubmed/4680784. 
  25. ^ Free Radicals and Human Disease
  26. ^ Uric Acid, Neuroprotective or Neurotoxic ?
  27. ^ a b Nakagawa T, et al. (2006). "A causal role for uric acid in fructose-induced metabolic syndrome". Am J Physiol Renal Physiol. 290(3): F625–31. http://www.ncbi.nlm.nih.gov/pubmed/16234313. 
  28. ^ Hayden MR, Tyagi SC. (2004). "Uric acid: A new look at an old risk marker for cardiovascular disease, metabolic syndrome, and type 2 diabetes mellitus: The urate redox shuttle". Nutr Metab. 1(1): 10. doi:10.1186/1743-7075-1-10. http://www.ncbi.nlm.nih.gov/pubmed/15507132. 
  29. ^ Cutler RG. (1984). "Urate and ascorbate: their possible roles as antioxidants in determining longevity of mammalian species". Arch Gerontol Geriatr. 3(4): 321–48. doi:10.1016/0167-4943(84)90033-5. http://www.ncbi.nlm.nih.gov/pubmed/6532339. 
  30. ^ Gout Causes: List of Diet/Food Sources High or Low in Purine Content
  31. ^ Gout Diet / Low Purine Diet - Limit High Purine foods
  32. ^ Choi HK, et al. (2004). "Purine-rich foods, dairy and protein intake, and the risk of gout in men". N Engl J Med. 350(11): 1093–103. doi:10.1056/NEJMoa035700. PMID 15014182. http://www.ncbi.nlm.nih.gov/pubmed/15014182. 
  33. ^ Hess FM, King JC and Margen S (1977). "Effect of Low Zinc Intake and Oral Contraceptive Agents on Nitrogen Utilization and Clinical Findings in Young Women". The Journal of Nutrition 107: 2219–2227. 
  34. ^ Garg JP, Chasan-Taber S, Blair A, et al. (January 2005). "Effects of sevelamer and calcium-based phosphate binders on uric acid concentrations in patients undergoing hemodialysis: a randomized clinical trial". Arthritis and rheumatism 52 (1): 290–5. doi:10.1002/art.20781. PMID 15641045. 
  35. ^ Umeki S, Ohga R, Konishi Y et al. (1986). "Oral zinc therapy normalizes serum uric acid level in Wilson's disease patients". American Journal of the Medical Sciences 292 (5): 289–292. doi:10.1097/00000441-198611000-00007. 
  36. ^ Toncev G, et al. (2002). "Serum uric acid levels in multiple sclerosis patients correlate with activity of disease and blood-brain barrier dysfunction". Eur J Neurol. 9(3): 221–6. doi:10.1046/j.1468-1331.2002.00384.x. http://www.ncbi.nlm.nih.gov/pubmed/11985629. 

 
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