A minimally invasive technique for the evaluation of the regulatory steps of the two major pathways of bile acid synthesis.
BACKGROUND
Bile acid synthesis accounts for more than 95% of total cholesterol catabolism per day. We have developed a minimally invasive technique in humans that quantifies the rates of plasma appearance of 7alpha- and 27-hydroxycholesterol, representing the first steps of the "classical" and "alternative" pathways of bile acid synthesis, respectively.


METHODS
For this purpose, during the intravenous infusion of synthetic deuterated isotopomers of 7alpha-hydroxycholesterol and 27-hydroxycholesterol plasma samples are collected and analysed by a GC-MS based method that allows to quantify the exogenous/natural isotopomer ratio of the two sterols. From this data, the rates of plasma appearance of 7alpha- and 27-hydroxycholesterol are calculated.


RESULTS
In a group of healthy individuals steady state kinetics are obtained during a 2 h period yielding mean values of 2.0+/-0.8 and 3.7+/-0.6 mg/h for 7alpha- and 27-hydroxycholesterol, respectively. The data are consistent with findings using older techniques that require studies over several days.


CONCLUSIONS
Considering that at steady state of the exogenous/natural isotopomer ratio the plasma appearance of the two regulatory hydroxysterols are related to the rate of bile acid synthesis via the "classical" and the "alternative" pathways, respectively, the proposed method could be used to evaluate the immediate effects of different diets and drugs and other determinants on cholesterol catabolism.
Del Puppo
Marina
M
Dipartimento di Medicina Sperimentale, Ambientale e Biotecnologie Mediche (DIMESAB), University of Milano-Bicocca, Via Cadore 48, 20052 Monza, Italy. marina.delpuppo@unimib.it
Crosignani
Andrea
A
Longo
Matteo
M
Zuin
Massimo
M
Podda
Mauro
M
Galli
Giovanni
G
De Fabiani
Emma
E
Ciuffreda
Pierangela
P
Santaniello
Enzo
E
Javitt
Norman B
NB
Kienle
Marzia Galli
MG
D000328:Adult; D001647:Bile Acids and Salts / Q000096:biosynthesis*; D003903:Deuterium; D005260:Female; D006801:Humans; D006888:Hydroxycholesterols / Q000378:metabolism*; D008099:Liver / Q000201:enzymology; D008297:Male
D001647:Bile Acids and Salts; D006888:Hydroxycholesterols; C011724:cholest-5-en-3 beta,7 alpha-diol; C076996:27-hydroxycholesterol; D003903:Deuterium