Apolipoprotein E polymorphism and lithogenic factors in gallbladder bile

Background Associations between the polymorphism of apolipoprotein E, which plays an important role in cholesterol metabolism and cholesterol gallston e formation, have been reported recently. Patients with the apo E4 isoform showed increased numbers and cholesterol contents of their stones, a higher frequency of cholesterol crystals in bile, increased susceptibility to gal lstone fragmentation by extracorporeal shock-wave lithotripsy and an increa se in recurrence rate after dissolution. A recent study, however, showed th at fast cholesterol crystallization in bile is associated with multiple sto nes but not with apo E4. Therefore the mechanism for an increased risk of g allstone formation in patients with the apo E4 isoform still remains under debate. Design To clarify this issue we investigated 37 patients with gallstones (1 0 with the apo E4 allele and 27 without the allele). Gallbladder biles were examined for total cholesterol and other lipids, cholesterol saturation in dex, crystal observation time, crystal mass, total protein and mucin. Moreo ver, number of gallstones and cholesterol in gallstones was compared in bot h groups. Results The crystal observation time (2.5 vs. 2.0 days, median) and the cho lesterol saturation index (1.34 +/- 0.45 vs. 1.43 +/- 0.74) did not differ significantly between the apo E4 and the non apo E4 group. Total biliary li pids (11.6 +/- 3.8 vs. 9.3 +/- 3.9 g 100 mL(-1) P = 0.126) and total biliar y cholesterol (21.8 +/- 9.7 vs. 15.7 +/- 7 mmol L-1, P = 0.067) tended to b e elevated in the apo E4 group. Crystal mass (3.60 +/- 4.10 vs. 2.38 +/- 2. 70 mmol L-1), biliary total protein (8.6 +/- 3.5 vs. 8.3 +/- 6.6 mg mL(-1)) and mucin (0.55 +/- 0.38 vs. 0.66 +/- 0.67 mg mL(-1)), number (solitary/mu ltiple) of gallstones and cholesterol in gallstones were not different in b oth groups of patients. Conclusions In comparison to the non apo E4 patients the apo E4 group showe d a trend to elevated biliary cholesterol whereas crystal observation time, cholesterol saturation index, crystal mass, number of gallstones, choleste rol content of gallstones and total protein and mucin were not different. T hese findings do not suggest an association of the apo E isoform. and the f ormation of cholesterol gallstones