Bile salts in serum

Ah SS, Javitt NB (1970) Quantitative estimation of bile salts in serum. Can J Biochem 48 1054-1057... 

The concentrations of the primary bile salts in serum are very nearly equal but sufficiently small so that they approach in magnitude the error of the method. For this reason, a primary bile salt concentration ratio has little or no significance when the concentrations are not increased above the normal range. If the concentration of at least one of the bile salts is increased above the normal range, however, the error remains the same, the concentration is not significantly altered by error, and thus the concentration ratio becomes valid. The general observation has been made that when serum bile salt concentrations are elevated in the presence of severe liver injury, chenodeoxycholate predominates and the cholate/chenodeoxycholate ratio is usually less than 1 (50). A primary bile salt ratio of greater than 1 is most commonly found in jaundiced patients who have bile duct disease, either intra- or extrahepatic (50). 

Depending upon their severity, liver diseases may impair bile salt reabsorption, interfere with bile salt conjugation, or both. Detailed discussion of the changes in bile salt concentration in feces, urine, and bile is not necessary it suffices to remark that the concentration of biliary bile salts in serum depends on the rate of production and on intestinal and hepatic reabsorption. The ability of the liver cells to reabsorb bile salts is believed to be the most critical factor therefore, measurements of the bile salt levels in serum can be helpful for diagnosing certain liver diseases. The concentration of primary bile salts in the serum is significant, whereas that of secondary bile salts is too low to influence distribution changes markedly. 

The enhancement of nasal absorption of insulin by hydrophobic bile salts has also been investigated. It was found that minor differences in the number, position, and orientation of the nuclear hydroxyl groups as well as alterations to side-chain conjugation can improve the adjuvant potency of bile salts. Moreover, the absorption of insulin positively correlated with an increase in the hydrophilicity of the steroid nucleus of the bile salts. In the presence of bile salts, nasal absorption of insulin reached peak levels within about lOmin, and some 10-20% of the dose was found to have been absorbed into the circulation. Marked increases in serum insulin levels were seen with sodium deoxycholate, the most lipophilic of the bile salts, whereas the least elevation—as well as least lowering of blood glucose levels—was seen with the most hydrophobic bile salt, sodium ursodeoxycholate [63],... 

Etiology of generalized itching Increased serum bile salts and accumulation of bile salts in the dermis of the skin. 

There are several methods available for the extraction of bile salts from serum or plasma. The most convenient methods utilize some form of liquid-solid extraction. An early procedure involved the anion-exchange resin, Amberlyst A-26 (S8), but considerable time and effort was required to perform column chromatography and to concentrate the eluate from the column. The introduction in 1972 of the neutral resin, Amberlite XAD-2, improved the ease of extracting bile acids and their conjugates from serum samples (M6). Further improvement occurred in 1977 with the description of a batch extraction technique using the related neutral resin, Amberlite XAD-7 (B5). With this technique, serum is diluted in 0.1 M sodium hydroxide to release bile acids from albumin and mixed with resin for 1 hour. After washing the resin in dilute alkali, bile acids are eluted with methanol, which cdn be removed on a rotary evaporator (B5). 

As will be discussed in a later section, patients with certain types of liver injury have chenodeoxycholate as the predominant primary bile salt in their serum. Primary bile salt concentration ratios in serum are a fairly accurate reflection of the primary bile salt concentration ratio in bile. The evidence for this is given in Fig. 3, in which the primary bile salt concentration ratio in serum is plotted against that in bile in 14 patients. The correlation coefficient for these two variables is 0.86 (p<0.01). When chenodeoxycholate predominates in bile its metabolites (lithocholate and others) predominate in feces, and when cholate predominates in bile its metabolites (de-oxycholate and others) predominate in feces (27). This relationship is shown in Fig. 4. It thus appears that primary bile salt concentrations in blood and bile are related to their relative synthesis rates and that the predominant bile salt in blood and bile has the greater synthesis rate, since its metabolites predominate in feces. This assumes of course that there is a steady state and... 

Despite some conflicting observations (55), the bulk of recent evidence supports the hypothesis that increased concentrations of bile salts in the skin, resulting from sustained elevations in serum concentrations, are the responsible circumstance for pruritic jaundice. Higher concentrations of bile salts occur in the skin of patients who itch than in those who do not (56). A reduction in high skin bile salt concentrations in a jaundiced patient with pancreatic carcinoma followed cholecystojejunostomy, and this was accompanied... 

A nonabsorbable strongly basic anion exchange resin which binds bile salts in the intestinal lumen, thereby removing them from the enterohepatic circulation for excretion in the feces, will relieve pruritus in patients who do not have complete biliary obstruction. When serum bile salt concentrations are measured serially at frequent intervals during cholestyramine feeding, it can be shown that concentrations reach near normal levels before pruritus stops, and when cholestyramine is withheld, high serum concentrations are reached before pruritus starts. This lag period, which may be a day or more, may represent the period of time required for concentrations of bile salts sufficient to induce pruritus to accumulate in or leave the skin (57). 

The serum bile salt pattern is altered in patients with bacterial proliferation in the small intestinal content (stagnant loop or blind loop syndrome). Bacterial deconjugation of bile salts in the lumen of the small intestine per-... 

The shape and fragility of red cell membranes are greatly influenced by their free cholesterol content, and bile salts have been shown to affect the free cholesterol content of red cell membranes in at least two ways (79). Serum cholesterol transesterase activity is inhibited by bile salts, and thus removal of free cholesterol from the membrane, which is facilitated by esterification, is delayed. Bile salts induce a shift in the cell/serum free cholesterol partition ratio in favor of the cell, so that supranormal concentrations of cholesterol occur in the cells. Such cells are flat and osmotically resistant and appear as target cells on stained smears. Patients with jaundice, especially obstructive jaundice, have numerous target cells, and it has been postulated that increased concentrations of bile salts in the serum of such patients may account for the target cell formation (79). 

Cholestyramin is a basic anion exchange resin which is used to ameliorate watery diarrhea in cases of ileal dysfunction, ileal resection, and vagotomy. It is also used to relieve pruritus due to elevated serum and skin levels of bile salts in patients with intrahepatic cholestasis and to lower cholesterol levels in familial hypercholes-... 

Increased levels of bile acids in the serum are found in hepatitis and obstructive jaundice. In cholestatic liver disease, there can be a deficiency of bile salts in the intestine and this leads to fat malabsorption. Disturbances in bile acid composition may be one of the factors involved in gallstone formation because it may lead to conditions favouring cholesterol precipitation. 

Cherry and Crandall in 1932 (86) used olive oil as substrate with gum acacia as the emufsTfier. This method has served as the basis for a number of modifications that increased the stability of the emulsion, decreased incubation time and gave better precision. When a serum sample is incubated with a stabilized olive oil emulsion, lipase acts at the interface of substrate and water to hydrolyze olive oil into fatty acid plus diglycerides, and to a small extent to monoglycerides and glycerol. The bile salt sodium deoxycholate activates the reaction. These methods measure the liberated fatty acids by titration with a standardized NaOH solution. An indicator such as phenolphatalein, thymolphthalein or methyl red or a pH meter are used to detect the end point. 

Highly insoluble molecules are in part transported in the GIT by partitioning into the mixed micelles injected into the lumen from the biliary duct in the duodenum (Fig. 2.3). Mixed micelles consist of a 4 1 mixture of bile salts and phospholipids (Fig. 7.13). In contrast, at the point of absorption in the BBB, highly insoluble molecules are transported by serum proteins. This distinction is expected to be important in in vitro assay modeling. The use of simulated intestinal fluids is appealing. 

Liver injury is clinically defined as an increase of serum alanine amino transferase (ALT) levels of more than three times the upper limit of normal and a total bilirubin level of more than twice the upper limit of normal [4]. The clinical patterns of liver injury can be characterized as hepatocellular (with a predominant initial elevation of ALT), cholestatic (with an initial elevation of alkaline phosphatase) or mixed. The mechanisms of drug-induced hepatotoxicity include excessive generation of reactive metabolites, mitochondrial dysfunction, oxidative stress and inhibition of bile salt efflux protein [5]. Better understandings of these mechanisms in the past decades led to the development of assays and models suitable for studying such toxic mechanisms and for selecting better leads in the drug discovery stage. 

Two complementary experiments show that the orientation and hiding of one or the other face of the steroid ring of cholate can occur when mixtures of lecithin and bile salt are considered. One of these experiments was performed by Etienne (4), who observed the following facts incidentally while extracting lipids from the serum lipoproteins by Delsal s method. This method utilizes a mixture of methanol and methylal (1 to 4) in the cold. The proteins are precipitated, while the lipids are dissolved in the methanol-methylal solvent mixture. If this solution of the lipids is evaporated, the residue is soluble in nonpolar solvents, such as chloroform. However, if sodium cholate is added to the lipoproteins before their extraction, the residue obtained after the methylal-methanol solvent evaporates is insoluble in chloroform. More precisely, while cholesterol and the triglycerides of the lipidic residue are extracted by chloroform, all of the lecithin remains insoluble, associated to the bile salt. The explanation is probably as follows. During evaporation, methylal with its low boiling point (44°C.), evaporates first, and the solvent becomes more and more concentrated with methanol and the residual water from the lipoprotein aqueous solution. Therefore, in the lecithin plus... 

Recently the means by which pectin lowers cholesterol levels and even the validity of this effect have been questioned. Upon finding no bile salt binding capacity for soluble pectin, Baig and Cerda (76) proposed that pectin lowered serum cholesterol levels by forming insoluble complexes with the serum low density lipoproteins (LDL) which transport circulating cholesterol. Complexing of LDL by citrus pectin was observed in vitro, but the way in which pectin or some component thereof enters the blood stream to effect such binding in vivo has not been determined. 

About 500 mg cholesterol is converted every day to bile salts. This may be increased if the patient is given bile salt binding resins, such as cholestyramine, which diminishes bile salt resorption, causing increased bile salt excretion in the feces. Cholestyramine and similar substances are given to individuals with high serum cholesterol levels. Most of the cholesterol that enters the small intestine via bile (see earlier) is also excreted. Fecal cholesterol amounts to about 1 g/day and is a major means of removing cholesterol from the organism. 

It is clear from Equation (19.4) that saturated fat, not cholesterol, is the single most important factor that raises serum cholesterol. Some cases of hyperlipoproteinemia type IV (high VLDL) respond to low-carbohydrate diets, because the excess of VLDL comes from intestinal cells, where it is produced from dietary carbohydrate. Resins, such as cholestyramine and cholestipol, bind and cause the excretion of bile salts, forcing the organism to use more cholesterol. Lovastatin decreases endogenous cholesterol biosynthesis (see later), and niacin (nicotinic acid) apparently decreases the production of VLDL and, consequently, LDL. It also results in an HDL increase. Antioxidants that inhibit the conversion of LDL to oxidized LDL have also been used with some success. These are high doses of vitamin E and the drug probucol. 

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