A novel specific bioassay for the determination of glucocorticoid bioavailability in human serum.
OBJECTIVE
Some patients develop side-effects even on relatively low doses of topically administered glucocorticoids (GCs), while others appear to be less sensitive to GCs. We have developed and validated a bioassay which can measure glucocorticoid bioavailability directly from small amounts of human serum to help elucidate underlying mechanisms.


METHODS
We have stably transfected the human embryonic kidney cell line HEK293 with a plasmid expressing the glucocorticoid receptor, and a plasmid containing the luciferase gene preceded by three concatenated steroid response elements, bringing luciferase expression under control of the liganded glucocorticoid receptor.


RESULTS
The assay, with an intra- and interassay coefficient of variance (CV) better than 10%, showed the expected difference in potency between different GCs (fluticasone propionate > budesonide > dexamethasone > hydrocortisone). No cross-reactivity was detected with other steroid hormones such as progesterone, testosterone and oestradiol. The bioassay easily detects the rise and subsequent fall of bioavailable GCs in human serum following ingestion of only 0.5 mg dexamethasone, and clearly reflects the diurnal cortisol rhythm. Moreover, systemic availability following inhalation of 2 x 250 micro g fluticasone propionate using a pressure dose inhaler could be demonstrated.


CONCLUSIONS
This assay can be used to determine levels of bioavailable GCs in serum, both endogenous and administered, and thus may help in optimizing treatment regimens. The small amount of serum needed to perform an analysis makes this assay applicable even to infants.
Vermeer
H
H
Department of Pediatric Endocrinology, University Medical Center Utrecht, The Netherlands.
Hendriks-Stegeman
B I
BI
van den Brink
C E
CE
van der Saag
P T
PT
van der Burg
B
B
van Buul-Offers
S C
SC
Jansen
M
M
D000280:Administration, Inhalation; D000730:Androstadienes / Q000097:blood / Q000627:therapeutic use; D001681:Biological Assay / Q000379:methods*; D001682:Biological Availability; D019819:Budesonide / Q000097:blood / Q000627:therapeutic use; D002460:Cell Line; D003907:Dexamethasone / Q000097:blood / Q000627:therapeutic use; D000068298:Fluticasone; D005938:Glucocorticoids / Q000097:blood* / Q000627:therapeutic use; D006801:Humans; D006854:Hydrocortisone / Q000097:blood / Q000627:therapeutic use; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D011965:Receptors, Glucocorticoid / Q000235:genetics / Q000378:metabolism; D012680:Sensitivity and Specificity; D014162:Transfection
D000730:Androstadienes; D005938:Glucocorticoids; D011965:Receptors, Glucocorticoid; D019819:Budesonide; D003907:Dexamethasone; D000068298:Fluticasone; D008156:Luciferases; D006854:Hydrocortisone