Apolipoproteins A-1 and A-2 were purified from human plasma. At concentrations present in human bile these proteins prolonged the nucleation time of cholesterol monohydrate crystals when added to model systems of supersaturated bile. In contrast, apolipoprotein C-3 and other serum proteins did not have this effect. Also, when human gallbladder bile was fractionated by gel filtration chromatography, apolipoproteins A-1 and A-2 were among the proteins present in a fraction of bile enriched in potent inhibitors of cholesterol crystal nucleation. These findings suggest that apolipoproteins A-1 and A-2 in supersaturated human gallbladder bile could inhibit the rate of formation of solid cholesterol crystals and thus help to prevent spontaneous cholesterol gallstone formation in humans.

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As bstract. The onset time for cholesterol crystal nucleation of supersaturated normal human gallbladder biles is consistently prolonged when compared with biles from patients with cholesterol gallstone disease. Investigation of the factor(s) responsible for the suspended supersaturation (metastability) of normal human biles revealed that model bile solutions of cholesterol saturation index (CSI) and molar lipid composition identical to individual gallbladder bile specimens had much shorter crystal nucleation times, i.e., exhibited decreased metastability. Unsaturated normal biles, after supplementation with lecithin, cholesterol, and sodium taurocholate to a 'standard' supersaturated lipid composition, also demonstrated nucleation times three-to 15-fold longer than the comparable standard model bile. Total lipid extracts of normal biles, however, when similarly supplemented, did not differ in nucleation time from the control model solution. Gallbladder biles were fractionated by gel chromatography and the eluted fractions were pooled into two fractions. The fractions eluting in about the first 25% of the included volume when mixed with the supersaturated standard model bile induced a modest increase in nucleation time of -1.5 times the control value. The fractions eluting in the second 25% of the included volume and which contained all ofthe bile lipids, were concentrated and supplemented with lipids to the standard composition. The nucleation times of these supPart ofthis work was presented at

The effect of oral administration of taurine (200-300 mg daily) on the metabolism of bile acids was studied in male guinea pigs which have predominantly glycine conjugated bile acids. The results were summarized as follows: (a) oral administration of taurine for 10 days increased taurine-conjugated bile acids and the ratio of glycine- to taurine-conjugated bile acids (G:T ratio) shifted from 3.95 to 0.19; (b) in taurine fed guinea pigs, the half-life of chenodeoxycholic acid (CDC) was about 40% shorter than that in controls and the fractional turnover rate increased by 70%; (c) the synthetic rate (mg/day/500 g body weight) of bile acids increased from 4.28 to 7.27 by taurine feeding; (d) hepatic cholesterol 7 alpha-hydroxylase activity was increased 2.4-fold by taurine feeding; (e) the total pool size of bile acids did not change significantly but the amount of lithocholic acid in the caecum and large intestine increased by about 40%; (f) neither free cholesterol nor cholesterol ester levels in liver and serum changed significantly. Results of this study suggest that changing the G:T ratio in the bile acid conjugation pattern may influence the rate of hepatic bile acid synthesis.