Lithocholic acid sulfate

Deconjugation and dehydroxylation reactions occur in the colon, leading to the formation of dozens of new distinct BAs, by the action of the colonic bacteria. The final products enter the enterohepatic circulation and reach the liver where they are reconjugated mostly to either glycine or taurine. Some lithocholic acid, the most toxic substance produced in the body and a known carcinogen, enters the liver where it is sulfated or esterified to glucuronic acid and excreted. 

As a consequence of the 7a-dehydroxylation process, the bile acid composition of bile in healthy subjects usually comprises around 30 to 40% conjugated cholic acid, 30 to 40% conjugated chenodeoxycholic acid, 10 to 30% conjugated deoxycholic acid, and less than 5% conjugated lithocholic acid, of which the majority is sulfated (H18). 

Palmer [56-58] first reported the presence in human bile of a sulfate ester of lithocholate in as much as 40-80% of the small amounts of available glyco- and taurolithocholate. Following intragastric or intraduodenal intubation of glyco-[24- C]lithocholic acid 3-sulfate to rats with bile fistulas, 70-89% of the radioactivity was recovered in bile [59] allolithocholate 3-sulfate was also reported in rat bile [60]. The radioactive conjugate was absorbed intact without loss of the sulfate, and was not metabolized in the liver (e.g., to the muricholates or chenodeoxycholate) [58,59]. Similarly, chenodeoxycholate 3-sulfate was not metabolized after intravenous infusion into rats or hamsters with or without obstruction of the biliary tract [58,59,61]. Lithocholate 3-sulfate is efficiently removed from the body [62]. 

The intestinal microflora of man and animals can biotransform bile acids into a number of different metabolites. Normal human feces may contain more than 20 different bile acids which have been formed from the primary bile acids, cholic acid and chenodeoxycholic acid [1-5], Known microbial biotransformations of these bile acids include the hydrolysis of bile acid conjugates yielding free bile acids, oxidation of hydroxyl groups at C-3, C-6, C-7 and C-12 and reduction of oxo groups to give epimeric hydroxy bile acids. In addition, certain members of the intestinal microflora la- and 7j8-dehydroxylate primary bile acids yielding deoxycholic acid and lithocholic acid (Fig. 1). Moreover, 3-sulfated bile acids are converted into a variety of different metabolites by the intestinal microflora [6,7]. 

Huijghebaert et al. [23] isolated a bile salt sulfatase-producing strain designated, Clostridium S, from rat feces. This bacterium hydrolyzed the 3-sulfates of lithocholic acid, chenodeoxycholic acid, deoxycholic acid and cholic acid but not the 7-or 12-monosulfates. Sulfatase activity required the 3-sulfate group to be in the equatorial position. A free C-24 or C-26 carboxyl group was also required for sulfatase activity in whole cells of this bacterium. The 3-sulfate of cholesterol, Cj,-and Cji-steroids were not hydrolyzed by Clostridium S, [24]. Nevertheless, C,9- and C2]-steroid sulfates are hydrolyzed in the gut by microbial activity suggesting that the intestinal microflora may contain bacteria with steroid sulfatases possessing different substrate specificities. However, it should be noted that enzyme substrate specificity studies carried out in whole cells may reflect both cell wall permeability and enzyme specificity. 

Palmer (133) has isolated labeled glycolithocholic acid 3-sulfate and taurolithocholic acid 3-sulfate from human bile after oral administration of labeled lithocholic acid. No further information concerning sulfate esters of bile acids is available at present. 

Figure 13 Chromatograms of gall bladder extracts from the pacific lamprey (A), western brook lamprey (B), and sea lamprey (C). Petromyzonol sulfate (PZS) and allocholic acid (ACA) cleanly separate from each other and hyocholic acid (HA) and lithocholic acid (LCA) are the internal standards. (Reprinted with permission from Steroids, 68 (2003) 515-523 Elsevier.)...

SULFATED LITHOCHOLIC ACID CONJUGATES AND CHOLESTASIS CLINICAL IMPLICATIONS AND PROTECTING FACTORS... 

It originates mainly from bacterial 7a-dehydroxylation of chenode-oxycholic acid in the intestine, but can also be formed in the liver by an alternative pathway involving 26-hydroxylation of choles-terol[9]. Little is known about the significance of lithocholic acid in the pathogenesis of cholestasis in man. It has been claimed that the human liver is protected from lithocholic acid-hepatoxicity by the efficient sulfation of the 3a-hydroxy group[10], which increases the bile acids polarity. Sulfated bile acids are poorly absorbed from the intestine[11,12] and their renal clearance is relatively high[13]. Therefore, sulfation of lithocholic acid should promote its elimination from the body[14]. 

Serum concentration of sulfated lithocholic acid conjugates (SGLC) and glycocholic acid (GC) in two brothers with benign recurrent intrahepatic cholestasis after oral fat loading at t = 0 hours A. during a symptom-free period B. as A, cholestyramine added C. during a pre-icteric period. 

Serum transaminases tend to double or triple in the early weeks of treatment with chenodeoxycholic acid in about one-third of patients (10). There is a hypothesis that this is due to impaired lithocholate sulfation. Lithochohc acid is... 

Some bile salts are quite toxic in the liver, leading to cholestasis and morphologic changes in bile canalicular membranes associated with this toxicity. Some of these toxic bile salts, such as lithocholate and 3 hydroxy-5a-cholanic acid are not detoxified by sulfation, but the sulfate conjugates retain their toxic effects almost completely. Although strictly speaking this is no toxlficatlon by sulfation, yet sulfation does not alleviate toxicity of these compounds (42-45). 

The liver, and also bacteria in the small and large intestine, can cause other structural modifications to bile acids as they undergo their entero-hepatic cycle. The formation of sulfate esters, already mentioned with respect to lithocholate in Section 4.2.1, is carried out primarily in the liver in man by a sulfotransferase (Lll). Other bile acids can also be sulfoconjugated to a small extent, mainly at the 3a-hydroxyl position. Bacteria, which have been isolated anaerobically from human feces, are known to possess bile acid sulfatase activity, which removes the 3a-sul te group of chenodeoxycholic and cholic acids (H24). The action of this bacterial enzyme probably explains why only trace amounts of sul ted bile acids, which are poorly absorbed in the intestine, are detected in the feces (12). Another type of bile acid conjugate, which has been identified in the urine of healthy subjects and patients with hepatobiliary disease, is the glucuronide (A7, S41). Both the liver and extrahepatic tissues, such as the kidney and small intestinal mucosa, are capable of glucuronidation of bile acids in man (M14). 

A cytosolic sulfotransferase has been identified in rat liver and kidney which utilizes 3 -phosphoadenosine-5 -phosphosulfate (PAPS) and shows a greater rate of sulfation for glycolithocholate than lithocholate. In an assay with the enzyme preparation, PAPS, and conjugated bile acids, 3 unidentified products were formed from taurocholate suggesting multiple sulfation of more polar conjugated bile acids [64]. The enzyme from liver, proximal intestine or adrenals of hamster produced only glycochenodeoxycholate 7-sulfate. Comparable results with the enzyme from kidney will be discussed in Section VI.3. Hepatic enzyme from the female hamster shows 4-fold greater activity than that of the male [65]. 

Although cholesterol is the major source of 5)9-bile acids, an unsaturated acid, 3)8-hydroxy-5-cholenic acid [174] has been found in meconium, mainly as the sulfate [175], in bile of a boy with a deficiency of 3)8-hydroxysteroid dehydrogenase [176], and in urine of healthy persons and individuals with liver disease [164]. The details of metabolism of 3)8-hydroxy-5-cholenic acid to lithocholate have not been entirely elucidated, but the mechanism for conversion of the 3/8-hydroxy-A to the 3-oxo-A derivative has been formulated in the C27 series (cf. Chapter 9). Briefly, the 3)8-ol is dehydrogenated by a microsomal enzyme fortified with NAD to provide the 3-oxo-A system [177,178]. Whether a A - A" isomerase is essential is not known, since there is no direct evidence for the formation of the intermediary 3-oxo-A system the rate-limiting step is the dehydrogenation of the 3)8-ol which may prevent accumulation of the 3-oxo-A system [177]. The reduction of the double bond at 4-5 to the 5)8- or 5a-bile acid is catalyzed by the respective A -3-oxosteroid 5)8- or 5 -reductase obtained from liver cytosol [170], and has been purified about 10-fold [178]. The formation of the 3-oxo-5/9 derivative requires the enzyme and NADPH the proton from the A side (4A-NADPH) appeared in the product as the 5)8-H, whereas the proton at C-4 is derived from the aqueous medium. Formation of the 5a derivative requires (4B-NADPH) in a similar mechanism (Fig. 4) [179], Reduction of the 3-0X0 product is then catalyzed by 3a-hydroxysteroid dehydrogenase as discussed above. 

Bile acids in meconium also reflect atypical synthesis. Back and Walter [209] reported on the presence of 14 bile acids obtained from meconium of 6 healthy infants (Table 2B). On the average 21% of chenodeoxycholate and of hyocholate and 8% of cholate were sulfated. Deoxycholate was the major bile acid of the sulfate fraction lithocholate, 3/8-hydroxy-5-cholenate [175] and 3, 12a-dihydroxy-5-cholenate were found only in the sulfate fraction, but quantities of lithocholate (range 0.3-1.4%) and 3i8,12a-dihydroxy-5-cholenate were small. The amount of l, 3tt,7a,12a-tetrahydroxy acid (79% as the taurine conjugate and 21% unconjugated) ranged from 3.6 to 11.1% of the total bile acids [209]. The feta bile adds of a number of animals, normal, adrenalectomized, thyroidectomized, or diabetic, are reviewed by Subbiah and Hassan ]210]. 

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