Correlation of cholesterol and bilirubin solubilization in bile salt solution

Bile pigment pharmacokinetics and absorption in the rat: therapeutic potential for enteral administration

BACKGROUND AND PURPOSE

Bilirubin and biliverdin possess antioxidant and anti-inflammatory properties and their exogenous administration protects against the effects of inflammation and trauma in experimental models. Despite the therapeutic potential of bile pigments, little is known about their in vivo parenteral or enteral absorption after exogenous administration. This study investigated the absorption and pharmacokinetics of bile pigments after i.v., i.p. and intraduodenal (i.d.) administration in addition to their metabolism and routes of excretion.

EXPERIMENTAL APPROACH

Anaesthetized Wistar rats had their bile duct, jugular and portal veins cannulated. Bile pigments were infused and their circulating concentrations/biliary excretion were measured over 180 min. KEY RESULTS After i.v. administration of unconjugated bilirubin, biliverdin and bilirubin ditaurate, their plasma concentrations decreased exponentially over time. Subsequently, native and metabolized compounds appeared in the bile. When administered i.p., their absolute bioavailabilities equalled 14.0, 16.1 and 33.1%, respectively, and correspondingly 38, 28 and 34% of the same bile pigment doses were excreted in the bile. Administration of unconjugated bilirubin and bilirubin ditaurate i.d. increased their portal and systemic concentrations and their systemic bioavailability equalled 1.0 and 2.0%, respectively. Correspondingly, 2.7 and 4.6%, of the doses were excreted in the bile. Biliverdin was rapidly metabolized and these products were absorbed and excreted via the urine and bile.

CONCLUSIONS AND IMPLICATIONS

Bile pigment absorption from the peritoneal and duodenal cavities demonstrate new routes of administration for the treatment of inflammatory and traumatic pathology. Oral biliverdin administration may lead to the production of active metabolite that protect from inflammation/complement activation.

Quantitative analysis of gallstones in Libyan patients

Gallstone disease is one of the major surgical problems in the Libyan population; it is probably related to diet, especially excessive consumption of meat. The study was conducted to determine the composition of gallstones and their possible etiology in a Libyan population. The chemical composition of gallstones from 41 patients (six males and 35 females) was analyzed. The stones were classified into cholesterol, pigment, and mixed stones (MS). Cholesterol stones (CS) showed a significantly higher cholesterol content than pigment stones (PS) (p=0.0085) though not significantly higher than MS. Their phospholipid content and inorganic phosphates were higher than in the other types of stones and oxalate content was significantly elevated in comparison with MS (p=0.0471). In MS, the cholesterol, bile acids, and bilirubin were intermediate between cholesterol and PS, whereas triglycerides were significantly more than PS (p=0.0004). Bilirubin (0.0001) and bile acids (p=0.0009) were significantly higher than CS (p=0.0001). However, they contained the lowest amounts of sodium, potassium, magnesium, and oxalate. In PS, bilirubin (p=0.0001) was significantly higher than both groups. Bile acid content was significantly higher than CS (p=0.0001) but not significantly more than MS. They showed the highest values of calcium, sodium, potassium, magnesium, and chlorides compared to the other types of stones. High levels of cholesterol in stones and dyslipidemia associated with mixed as well as cholesterol gallstones suggest an etiological association and efforts to reduce dietary fat among the Libyan population may lead to decreased cholesterol and mixed gallstones.

Quantitative analysis of gallstones in Libyan patients

Gallstone disease is one of the major surgical problems in the Libyan population; it is probably related to diet, especially excessive consumption of meat. The study was conducted to determine the composition of gallstones and their possible etiology in a Libyan population. The chemical composition of gallstones from 41 patients (six males and 35 females) was analyzed. The stones were classified into cholesterol, pigment, and mixed stones (MS). Cholesterol stones (CS) showed a significantly higher cholesterol content than pigment stones (PS) (p=0.0085) though not significantly higher than MS. Their phospholipid content and inorganic phosphates were higher than in the other types of stones and oxalate content was significantly elevated in comparison with MS (p=0.0471). In MS, the cholesterol, bile acids, and bilirubin were intermediate between cholesterol and PS, whereas triglycerides were significantly more than PS (p=0.0004). Bilirubin (0.0001) and bile acids (p=0.0009) were significantly higher than CS (p=0.0001). However, they contained the lowest amounts of sodium, potassium, magnesium, and oxalate. In PS, bilirubin (p=0.0001) was significantly higher than both groups. Bile acid content was significantly higher than CS (p=0.0001) but not significantly more than MS. They showed the highest values of calcium, sodium, potassium, magnesium, and chlorides compared to the other types of stones. High levels of cholesterol in stones and dyslipidemia associated with mixed as well as cholesterol gallstones suggest an etiological association and efforts to reduce dietary fat among the Libyan population may lead to decreased cholesterol and mixed gallstones.

The effect of parenteral nutrition on biliary calcium and bilirubin

Recent studies have suggested that patients maintained on prolonged total parenteral nutrition (TPN) are at increased risk for gallstone formation. Animal and human data suggest that TPN causes calcium bilirubinate sludge and pigment gallstones. However, the effect of TPN on bile bilirubin and calcium concentrations has not previously been investigated. We, therefore, tested the hypothesis that TPN alters biliary bilirubin and calcium. Eight adult male prairie dogs received TPN (dextrose 15%, FreAmine III 4.25%, Intralipid 10%, insulin 25 U, electrolytes, and vitamins) at a rate of 80 cc/kg/day for 10 days. Eight additional animals maintained on a trace cholesterol diet served as controls. Gallbladder and hepatic bile samples were assayed for bilirubin and calcium. Cholesterol saturation index (CSI) and Rsa, a measure of gallbladder stasis, were also calculated. Calcium bilirubinate crystals were seen in gallbladder bile or wall scrapings of 7 of 8 TPN animals but in none of the controls (P less than 0.001). Animals that received TPN had bilirubin levels that were significantly higher in gallbladder bile (24.8 +/- 7.0 vs 5.1 +/- 0.9, P less than 0.05). Similarly, TPN animals had calcium levels that were significantly higher in gallbladder (30.0 +/- 3.6 vs 13.9 +/- 2.1, P less than 0.005) as well as hepatic (10.5 +/- 0.6 vs 7.4 +/- 0.6, P less than 0.005) bile. The Rsa values were also significantly lower (P less than 0.01) in TPN animals (0.57 +/- 0.07 vs 1.06 +/- 0.14). CSI, serum bilirubin, serum calcium, hematocrit, and reticulocyte counts did not differ between groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Bilirubin chemistry, ionization and solubilization by bile salts

Bilirubin is a linear tetrapyrrole whose conformation is affected by internal hydrogen bonds formed between the carboxyl side chains and dipyrromethenone rings. Structural variations include: constitutional isomerism of the vinyl or carboxyethyl side chains, geometric isomerism of the methene bridges, tautomerism of the lactam groups, conformational rotations about the central methylene bridge and ionization of one or both carboxyl groups. Aggregation of the dianion into dimers and multimers may occur. The pKa' values of the two carboxyl groups are affected greatly by the environment and may differ widely in micellar solutions like bile. Solubility of bilirubin in water is less than 1 nM at pH = 7 and about 0.1 microM at pH = 8. Nonetheless, it dissolves poorly in most lipid solvents, except for asymmetrical chloroalkanes. Hydrogen bond-breaking solvents, especially dimethyl sulfoxide, are most effective in solubilizing bilirubin. In bile salt solutions, solubility of bilirubin is well above the concentrations of unconjugated bilirubin found in normal human gallbladder bile, and is impaired by lecithin but unaffected by cholesterol. At physiological pH in bile salt solutions, bilirubin is predominantly in its monoanion form that binds readily to the micelles. In such solutions, addition of physiological concentrations of calcium precipitates calcium bilirubinate, leaving residual bilirubin concentrations of up to 15 microM in 50 mM taurocholate or close to the maximum bilirubin concentrations in normal bile. Studies in which disodium bilirubinate is dissolved in bile salt solutions and pH is adjusted to the physiological range reveal that metastable supersaturation with bilirubin may occur and that a mesophase may also form in the presence of lecithin, akin to that seen with cholesterol.(ABSTRACT TRUNCATED AT 250 WORDS)

Reappraisal of cholesterol solubilization in bile salt-lecithin solution and the stability of bile

On the basis obtained in a preceding study, cholesterol solubilization in aqueous bile salt-lecithin solution was investigated. The alteration of mixing sequence was found to yield differences not only in the rate but also in the magnitude of cholesterol solubilization. Both the rate and the magnitude were remarkably bigger in the system solubilizing cholesterol and lecithin mixture by bile salt than that solubilizing cholesterol crystal by bile salt with solubilized lecithin. A linear relation between the quantity of solubilized cholesterol and the concentration of bile salt except for lower concentration range was obtained for every bile salt-lecithin system. Values of k, the slope of the partial straight line, determined for cholate, chenodeoxycholate, deoxycholate and equimolar cholate-deoxycholate systems were 5.85 X 10(-2), 7.60 X 10(-2), 9.50 X 10(-2) and 7.17 X 10(-2), respectively. Cholesterol solubilizing power of bile salt was thus enhanced by the addition of lecithin. Since the solubilizing power could be given by the ratio of the solubilizate to the solubilizer, it was expressed graphically by the ratio of cholesterol to bile salt as ordinate and the concentration of bile salt as abscissa. The saturability of cholesterol solubilization in bile was purposefully exhibited in this graph by plotting assayed data of biliary lipid components.