Urine 3-hydroxybutyric acid

Higher than normal quantities of ketone bodies present in the blood or urine constitute ketonemia (hyperke-tonemia) or ketonuria, respectively. The overall condition is called ketosis. Acetoacetic and 3-hydroxybutyric acids are both moderately strong acids and are buffered when present in blood or other tissues. However, their continual excretion in quantity progressively depletes the alkah reserve, causing ketoacidosis. This may be fatal in uncontrolled diabetes mellitus. 

When male F-344 rats were injected with NNN-2 -14c, 75-95% of the dose was excreted in the 48 hr urine. In one experiment, the urine was collected in vessels containing DNP reagent. However, the DNPs of 4-hydroxy-l-(3-pyridyl)-l-butanone and 4-hy-droxy-4-C3-pyridy1)butanal were not detected. Since this was likely due to further oxidation in vivo, methods were developed for isolation of their probable oxidation products. This resulted in identification of the lactone, 5- C3-pyridyl)—tetrahydrofuran-2-one (1-2%), the keto acid, 4-(3-pyridyl).-4-oxobutyric acid (1-2%) and the hydroxy acid, 4-(3-pyridyl)-4-hydroxybutyric acid (26-40%) as urinary metabolites. These metabolites resulted. 

Carnitine, L-3-hydroxy-4-(trimethylammonium)butyrate, is a water-soluble, tri-methylammonium derivative of y-amino-jS-hydroxybutyric acid, which is formed from trimethyllysine via y-butyrobetaine [40]. About 75% of carnitine is obtained from dietary intake of meat, fish, and dairy products containing proteins with trimethyllysine residues. Under normal conditions, endogenous synthesis from lysine and methionine plays a minor role, but can be stimulated by a diet low in carnitine. Carnitine is not further metabolized and is excreted in urine and bile as free carnitine or as conjugated carnitine esters [1, 41, 42]. Adequate intracellular levels of carnitine are therefore maintained by mechanisms that modulate dietary intake, endogenous synthesis, reabsorption, and cellular uptake. 

Disposition in the Body. Readily absorbed after oral administration. The major metabolite is free bromide ion hydrolysis to an active metabolite, 2-bromo-2-ethylbutyramide, also occurs followed by oxidation to 2-bromo-2-ethyl-3-hydroxybutyramide other metabolites include 2-ethylbutyrylurea and 2-ethyl-2-hydroxybutyric acid. Carbromal is excreted in the urine mainly as bromide ion and partly as 2-ethyl-2-hydroxybutyric acid, with very little as unchanged drug. Peak bromide excretion is attained after about 48 hours. 

Disposition in the Body. Readily absorbed after oral administration, and extensively metabolised to active metabolites. A number of metabolites have been identified including (i) 4-(biphenyl-4-yl)-4-hydroxybutyric acid, (ii) biphenyl-4-ylacetic acid, (iii) (4 -hydroxybiphenyl-4-yl)acetic acid, and (iv) 4-hydroxy-(4 -hydroxybiphenyl-4-yl)butyric acid. About 40% of a dose is excreted in the urine in 24 hours. The major urinary metabolites are metabolite (iii), about 11% of the dose, and metabolite (iv), about 17% of the dose metabolites (i) and (ii) are excreted in amounts less than about 3% of the dose. Very little unchanged drug is excreted in the urine. Less than 2% of the dose is eliminated in the faeces in 24 hours. 

In known metabolic states and disorders, the nature of metabolites excreted at abnormal levels has been identified by GC-MS. Examples of this are adipic and suberic acids found in urine from ketotic patients [347], 2-hydroxybutyric acid from patients with lactic acidosis [348], and methylcitric acid (2-hydroxybutan-l,2,3-tricarboxylic acid) [349] in a case of propionic acidemia [350,351]. In the latter instance, the methylcitric acid is thought to be due to the condensation of accumulated propionyl CoA with oxaloacetate [349]. Increased amounts of odd-numbered fatty acids present in the tissues of these patients due to the involvement of the propionyl CoA in fatty acid synthesis, have also been characterised [278]. A deficiency in a-methylacetoacetyl CoA thiolase enzyme in the isoleucine pathway prevents the conversion of a-methylacetoacetyl CoA to propionyl CoA and acetyl CoA [352,353]. The resultant urinary excretion of large amounts of 2-hydroxy-3-methylbutanoic acid (a-methyl-/3-hydroxybutyric acid) and an excess of a-methylacetoacetate and often tiglyl glycine are readily detected and identified by GC-MS. 

Ammonia is released into the urine, where it buffers the hydrogen ions produced by phosphoric acid, sulfuric acid (produced from cysteine), and various metabolic acids (e.g., lactic acid and the ketone bodies, ace-toacetic acid and P-hydroxybutyric acid). 

Strong acids, such as sulfuric, hydrochloric, and phosphoric, are fully ionized at the pH of urine and are excreted only after the H" derived from these acids reacts with a buffer base. Excretion of the anions of these acids is accompanied by the simultaneous removal of an equal number of cations, such as Nak IC, or NHJ, to provide electrochemical balance. However, some acids, such as acetoacetic acid (piC = 3.58) and p-hydroxybutyric acid (piC= 4.7), are present in blood almost entirely in ionized form at the acid pH frequently prevailing in urine, some are nondissociated and thus may be excreted partially as the nondissociated acid (see Figure 46-11). For example, 50% of 3-hydroxybutyric acid at pH 4.7 is nonionized. 

The SPE method used by the Miami-Dade County Medical Examiner s Office, Toxicology Laboratory, in Miami, Florida (Andollo and Hearn, 1998) uses Chem-Elute - SPE columns, p-hydroxybutyric acid internal standard, pretreatment of urine with sulfuric acid and pretreatment of blood with sodium tungstate and sulfuric acid. The Dade County method gave an absolute recovery of 30% with a limit of detection of 2 pg mL and a limit of quantitation of 10 pgmL ... 

Ferrara, S.D., Tedeschi, L., Prison, G., Castagna, F, Gallimberti, L., Giorgetti, R., Gessa, G.L. and Palatini, P. (1993). Therapeutic gamma-hydroxybutyric acid monitoring in plasma and urine by gas chromatography-mass spectrometry. J. Pharm. Biomed. Anal. 11 483 487. 

Prison, G.,Tedeschi, L, Maietti, S. and Ferrara, S.D. (1998). Determination of gamma-hydroxybutyric Acid (GHB) in plasma and urine by headspace solid-phase microextraction (SPME) and gas chromatography-positive ion chemical ionization-mass spectrometry. In Proceedings of the 1998 Joint Society of Forensic Toxicologists and the International Association of Forensic Toxicologists SOFT/TIAFT International Meeting, Spiehler, V. (Ed.), pp. 394 404. 

Hydroxybutyric Acid. P-Hydroxybutyric acid is present in normal human plasma (at a concentration of 0.3-0.9mg%) (K14) and in normal urine (F2). 

Fig. 3.22. GC separation of keto and hydroxy acids from the urine of a patient with maple syrup urine disease. Top chromatogram, the patient before dietary treatment middle chromatogram, the same patient after two days on a diet bottom chromatogram, a mixture of reference compounds. Peaks 1, lactic acid 2, 2-hydroxyisobutyric acid 3, 2-hydroxybutyric acid 4, pyruvic acid 5, 3-hydroxyisobutyric acid 6, 3-hydroxybutyric acid 7, 2-hydroxyisovaleric acid 8, 2-ketobutyric acid 9, malonic acid (internal standard) 10, 2-methyl-3-hydroxybutyric acid 11, 2-hydroxy-n-valeric acid 12. methylmalonic acid 13, 3-hydroxyisovaleric acid 14a and b, 2-ketoisovaleric acid IS, acetoacetic add 16, 2-hydroxyisocaproic acid 17, 2-hydroxy-3-methylvaleric acid 18a, L-2-keto-3-methylvaleric add 18b, D-2-keto-3-methyl-valeric acid 19, 2-ketoisocaproic acid. Reproduced from [386],...

Saudan et al. [180] evaluated the use of GC-IRMS for the measurement of carbon isotope values for the detection of exogenous gamma-hydroxybutyric acid (GHB) in human urine. Preliminary results indicate possible differentiation between endogenous and exogenous GHB. 

Polyhydroxybutyric acid is a storage compound for excess carbon in many microorganisms (E 2.2). It may be used in the production of plastics (F 4). Acetoacetic acid, acetone, and /S-hydroxybutyric acid are excreted in the urine of people with a pathologically high blood sugar level (diabetes mellitus) (E 1). Their appearance is of diagnostic value. Butyric acid, butanol, and acetone are products of microbial fermentations. 

Acetyl CoA derivatives Acetoacetic acid, 3-hydroxybutyric acid, acetone (D 3.1) Urine... 

The activity of hydroxymethylglutarate CoA reductase, which produces mevalonic acid—a precursor of cholesterol—was unchanged in diabetic rats. The observations made on diabetic rats contrast with those made in fasted animals in which ketosis is likely to result from activation of the hydroxymethylglutarate CoA shunt pathway, probably due to decreased activity of the hydroxymethylglutarate CoA reductase. In the presence of NADH and a specific mitochondrial dehydrogenase, acetoacetic acid is reduced to yield j8-hydroxybutyric acid, one of the ketone bodies that is excreted in the urine in ketosis. In fact, D-jS-hydroxy-butyric acid represents 50-75% of the blood content of ketone bodies. Therefore, hydroxybutyric acid metabolism assumes a particular importance. 

Among the organic acidemias, 3-oxothiolase deficiency is the one that is likely to remain undiagnosed even after organic acid analysis of the urine has been performed. At the time of acute ketoacidosis there may be little or no tiglylglycine or 2-methyl-3-hydroxybutyrate in the urine, and the latter may be elevated amounts in the urine of anyone who is ketotic. With resolution of the acute illness, it is not unusual for urine organic acid analysis to be normal. The isoleucine load is invaluable in this situation. 

The appearance of 8-hydroxybutyric acid, acetoacetic acid, and acetone in the blood and urine of diabetics is explained most readily by the /8-oxidation theory of fat metabolism. 

During the course of this study it was decided to investigate the excretion of urinary organic acids by the technique of GC-Mass Spectrometry. Large quantities of lactic acid and beta-hydroxybutyric acid were found in the urine and also some alpha-hydroxybutyric acid. 

Methylacetoacetyl-CoA thiolase deficiency (McKusick 20 375) was originally described by Daum et al. (1971), who reported briefly on a 6-year-old boy with metabolic acidosis in whose urine they identified 2-methylacetoacetic and 2-methyl-3-hydroxybutyric acids. Subsequently they identified two further affected families and reported the details of the disease (Daum etaL, 1973). A number of other cases have subsequently been reported and the variety of presenting features and findings warrants their individual discussion here. 

This chapter describes the case reports of these enzyme deficiencies and the underlying biochemistry of the disorders and their associations. It is not the intention to discuss keto acidosis associated with other diseases, for example juvenile diabetes, or ketogenesis and its control which are reviewed elsewhere (Wildenhoff, 1975, 1977 McGarry and Foster, 1976 Halperin, 1977). In addition to the common occurrence of 3-hydroxybutyrate and acetoacetate in body fluids of patients with keto acidosis, secondary organic acids have been observed in urine, including adipic and suberic acids (Pettersen et aL, 1972), 3-hydroxyisovaleric acid (Landaas, 1974), 3-hydroxyisobutyric acid and 2-methyl-3-hydroxybutyric acid (Landaas, 1975). The dicarboxylic acids occur as a result of initial co-oxidation of accumulating long-chain fatty acids followed by )8-oxidation (Pettersen, 1972), and metabolites of the branched-chain amino acids occur because of inhibition of their metabolic pathways by 3-hydroxybutyrate and acetoacetate (Landaas and Jakobs, 1977). 

Acid-base status—pH, HC03y PC02, /3-hydroxybutyrate Renal function (creatinine, urine output)... 

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