Trihydroxycholestanoic acid

Alkyl PAT, alkyl-dihydroxy phosphate synthase Bif, bifunctional enzyme DHAPAT, dihydroxyphosphate acyltransferase deficiency DHCA, dihydroxycholestanoic acid N, normal nd, not determined Ox, acyl-CoA oxidase Rac, 2-methylacyl-CoA racemase RCDP, rhizomelic chondrodysplasia punctata Ref, Refsum s disease THCA, trihydroxycholestanoic acid VLCFA, very-long-chain fatty acid. 

Other fatty acids including long-chain fatty acids were normal, provided the first clue that the mitochondrial and peroxisomal P-oxidation systems might have different substrate specificities. Subsequent studies indeed revealed that peroxisomes are the primary site of oxidation of very-long-chain fatty acids whereas oxidation of long-chain fatty acids occurs predominantly in mitochondria. Later studies showed that oxidation of pristanic acid and the bile acid intermediates di- and trihydroxycholestanoic acid is also primarily peroxisomal. 

Di- and trihydroxycholestanoic acid are intermediates in the complex formation of bile acids from cholesterol. The two cholestanoic acids are activated to their CoA-esters at the endoplasmic reticulum membrane " and undergo P-oxidation to chenodeoxycholoyl-CoA and choloyl-CoA in the peroxisome. This is followed by conjugation with either taurine or glycine to produce chenodeoxytauro- or glycocholate and tauro- or glycocholate, respectively, which can pass the canalicular membrane to end up in the bile fluid. 

As discussed above, the peroxisomal fatty acid P-oxidation system is specifically involved in the degradation of a specific group of fatty acids including very-long-chain fatty acids, pristanic acid and di- and trihydroxycholestanoic acid. Several inherited diseases in man have been described in which peroxisomal P-oxidationis impaired at some level as reflected in the differential acciunulation of very-long-chain fatty acids, pristanic acid and the bile acid intermediates in plasma from patients. The following disorders can be distinguished ... 

We recently identified a new peroxisomal disorder in a patient showing signs and symptoms comparable to those observed in Zellweger syndrome. In the patients plasma, veiy-long-chain fatty acids, pristanic acid, and di- and trihydroxycholestanoic acid were elevated suggesting a defect in the peroxisomal P-oxidation system. Subsequent studies identified the defect in this patient at the level of the 3-hydroxyacyl-CoA dehydrogenase component of the newly identified D-bifunctional protein.""... 

Dihydroxycholestanoic acid CoA ester and trihydroxycholestanoic acid CoA ester IS d4-CA CoA ester Rat liver homogenate (0.1 g) extraction (ethyl acetate) RP-SPE Synergi HydroRP 80A (150 x 2.0 mm I.D., Phenomenex), isojHX>panol— acetonitrile—water adjusted to pH 2.7 with formic acid and 0.4 ml/min API 365 (Sciex), positive ESI, SRM ([M + p oduct ion) LOD 0.1 nmol [65]... 

Dihydroxycholestanoic acid, trihydroxycholestanoic acid and their taurine conjugates IS d4-CA and taurine conjugate of d4-CA Human plasma (50 pi) deproteinization (acetonitrile) AUtima Cig (250 x 2.1 mm I.D., AUtima), gradient (ethanol-5 mAf ammonium formate) and 0.3 ml/min Quattro II (Micromass), negative ESI, SRM ([M-H] — product ion, unconjugates), SIM ([M-H] , taurine conjugates) LOD 0.05 nmol/ml [67]... 

Ferdinandusse, S. Overmars, H. Denis, S. Waterham, H.R. Wanders, R.J. Vreken, P. Plasma analysis of di- and trihydroxycholestanoic acid diastereomers in peroxisomal a-methylacyl-CoA racemase deficiency. J. Lipid Res. 2001, 42 (1), 137-141. 

The most important substrates handled by the peroxisomal fatty acid oxidation system from the perspective of peroxisomal disorders are (1) very-long-chain fatty acids (VLCFA), notably hexacosanoic acid (C26 0), (2) pris-tanic acid (2,6,10,14-tetramethylpentadecanoic acid), as derived from dietary sources either directly or indirectly from phytanic acid and (3) di- and trihydroxycholestanoic acid (DHCA and THCA). The latter two compounds are intermediates in the formation of the primary bile acids cholate and chenodeoxycholate from cholesterol in the liver. 

Fig. 25.1. Schematic representation of the role of the peroxisomal / -oxidation system in the oxidation of C26 0, pristanic acid, di- and trihydroxycholestanoic acid and C24 6...

Trihydroxycholestanoic acid (THCA) Dihydroxycholestanoic acid (DHCA) Phytanic acid Pristanic acid... 

Very-long-chain fatty acids (VLCFA), trihydroxycholestanoic acid (THCA), phytanic acid and pristanic acid can all be measured in plasma/serum (> 1 ml). From the same blood sample erythrocytes, platelets and/or leukocytes can be prepared for determination of plasmalogens and dihydroxyacetone-phosphate acyltransferase (DHAPAT), respectively. 

Figure 4 Peroxisomal fatty-acid (FA) /3-oxidation pathways. While saturated long-chain fatty acids (LCFA) are preferentially degrade in mitochondria, saturated very-long-chain fatty acids (VLCFA) and some LCFA are shortened by peroxisomal /3-oxidation. Degradation of pristanic acid, the product of phytanic acid a-oxidation, and the conversion of the cholesterol-derived 27-carbon bile-acid precursors dihydroxycholestanoic acid (DHCA) and trihydroxycholestanoic acid (THCA) to 24-carbon bile acids also require this pathway. The mechanism by which these substrates enter peroxisomes is unknown. Four enzymatic reactions serve to shorten the substrates by either two (LCFA, VLCFA) or three (pristanic acid, DHCA, THCA) carbon atoms. The 2-methyl group of the latter substrates is shown in brackets. SCPx thiolase refers to the thiolase activity of sterol carrier protein x.

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