Oxysterols in the circulation of patients with the Smith-Lemli-Opitz syndrome: abnormal levels of 24S- and 27-hydroxycholesterol.
Infants with the cholesterol synthesis defect Smith- Lemli-Opitz syndrome (SLO) have reduced activity of the enzyme 7-dehydrocholesterol-7-reductase and accumulate 7-dehydrocholesterol, with the highest concentration in the brain. As a result of the generally reduced content of cholesterol, plasma levels of oxysterols would be expected to be reduced. 24S-hydroxycholesterol is almost exclusively formed in the brain, whereas 27-hydroxycholesterol is mainly formed from extrahepatic and extracerebral cholesterol. In accordance with the expectations, sterol-correlated plasma levels of 24S-hydroxycholesterol were reduced in infants with SLO (by about 50%). In contrast, the sterol-correlated levels of 27-hydroxycholesterol in the circulation were markedly increased. No side-chain oxidized metabolites of 7-dehydrocholesterol were detected in the circulation. Recombinant human CYP27 had markedly lower 27-hydroxylase activity toward 7-dehydrocholesterol than towards cholesterol. HEK293 cells expressing 24S-hydroxylase active toward cholesterol had no significant activity towards 7-dehydrocholesterol. The plasma levels of 3 beta,7 alpha-dihydroxy-5-cholestenoic in the patients acid were reduced, suggesting a generally reduced metabolism of 27-oxygenated steroids. It is concluded that the accumulation of 7-dehydrocholesterol in the brains of patients with SLO reduces formation of 24S-hydroxycholesterol. The condition is associated with markedly increased circulating levels of 27-hydroxycholesterol, most probably due to reduced metabolism of this oxysterol. We discuss the possibility that the circulating levels of 24S-hydroxycholesterol may be used as a marker for the severity of the disease.--Björkhem, I., L. Starck, U. Andersson, D. Lütjohann, S. von Bahr, I. Pikuleva, A. Babiker, and U. Diczfaulsy. Oxysterols in the circulation of patients with the Smith-Lemli-Opitz syndrome: abnormal levels of 24S- and 27-hydroxycholesterol. J. Lipid Res. 2001. 42: 366--371.
Björkhem
I
I
Division of Clinical Chemistry, Huddinge University Hospital, Sweden. Ingemar.Bjorkhem@chemlab.hs.sll.se
Starck
L
L
Andersson
U
U
Lütjohann
D
D
von Bahr
S
S
Pikuleva
I
I
Babiker
A
A
Diczfalusy
U
U
D000293:Adolescent; D000818:Animals; D019556:COS Cells; D002460:Cell Line; D002648:Child; D002675:Child, Preschool; D002775:Cholestadienols / Q000097:blood; D053493:Cholestanetriol 26-Monooxygenase; D000072556:Cholesterol 24-Hydroxylase; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D003684:Dehydrocholesterols / Q000097:blood / Q000494:pharmacology; D015870:Gene Expression; D006801:Humans; D006888:Hydroxycholesterols / Q000097:blood*; D007223:Infant; D011994:Recombinant Proteins / Q000378:metabolism; D019082:Smith-Lemli-Opitz Syndrome / Q000097:blood*; D013250:Steroid Hydroxylases / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity; D014162:Transfection
D002775:Cholestadienols; D003684:Dehydrocholesterols; D006888:Hydroxycholesterols; D011994:Recombinant Proteins; C044563:24-hydroxycholesterol; C076996:27-hydroxycholesterol; C026359:cholesta-5,8-dien-3 beta-ol; D003577:Cytochrome P-450 Enzyme System; C016705:7-dehydrocholesterol; D013250:Steroid Hydroxylases; D000072556:Cholesterol 24-Hydroxylase; C506831:CYP27A1 protein, human; D053493:Cholestanetriol 26-Monooxygenase