Androstenedione, LC/MS

Androstenedione (also known as 4-androstenedione and δ₄-androstenedione) is a 19-carbon steroid hormone produced in the adrenal glands and the gonads that is the common precursor in the biochemical pathway that produces the androgen testosterone and the estrogens estrone and estradiol.^1-7 Androstenedione has approximately one tenth of the androgenic potency of testosterone.¹ Androstenedione is synthesized by means of two biochemical pathways. The predominant pathway involves conversion of 17-hydroxypregnenolone to dehydroepiandrosterone (DHEA) catalyzed by the enzyme 17,20-lyase, with subsequent conversion of DHEA to androstenedione catalyzed by the enzyme 3-β-hydroxysteroid dehydrogenase. A secondary pathway for androstenedione production involves conversion of 17-hydroxyprogesterone to androstenedione directly by 17,20-lyase. 17,20-lyase is required for both pathways of androstenedione synthesis.

The production of adrenal androstenedione is controlled by ACTH, whereas production of gonadal androstenedione is governed by the gonadotropins, luteinizing hormone (LH), and follicle stimulating hormone (FSH). Androstenedione produced in the adrenal gland of both men and women is further converted to testosterone by the enzyme 17-β-hydroxysteroid dehydrogenase.¹ In women, androstenedione produced by theca cells of the ovary is converted to estrogen by the enzyme aromatase in the granulosa cells of the ovary.⁵ Androstenedione secreted into the plasma by either the adrenal or ovary can be converted to testosterone and estrogens by the same enzymes in peripheral tissues. Androstenedione, largely of ovarian origin, is the only circulating androgen that is higher in premenopausal women than in men.¹ After menopause, androstenedione production is about halved, primarily due to the reduction of the steroid secreted by the ovary. Nevertheless, androstenedione is the principal steroid produced by the postmenopausal ovary.

Congenital adrenal hyperplasia (CAH) is a family of disorders caused by defects in one of the enzymes of the adrenal steroidogenic pathway.^1,3,6 The most common form of CAH results from mutations in the gene that codes for the 21-hydroxylase enzyme.^1,3,6 Patients with CAH develop varying degrees of glucocorticoid and mineralocorticoid deficiency due to the inability to produce cortisol and aldosterone, respectively.^1,3,6 Diminished cortisol levels cause an increase in pituitary adrenocorticotrophic hormone (ACTH) secretion due to a lack of negative feedback. The resultant high levels of ACTH lead to adrenal hyperplasia and dramatically increased production of adrenal steroids proximal to the enzyme block.^1,3,6 These steroids (progesterone and 17-hydroxyprogesterone) are shunted into the adrenal androgen pathway that leads to increased concentrations of dehydroepiandrosterone and androstenedione.^1,3,6 These weakly androgenic steroids are then peripherally converted to testosterone that produces the androgenic symptoms frequently associated with CAH.^1,3,6

The diagnosis and therapeutic monitoring of CAH is based on clinical parameters and the measurement of the concentrations of adrenal steroid products and their metabolites.^1,3,6 Recent clinical guidelines have recommended the use of 17-hydroxyprogesterone (17OHP) as the primary marker for diagnosis and monitoring of CAH.⁶ Other steroid products--including androstenedione and testosterone--can provide additional clinical information in some circumstances.^3,6,8-11 There is generally a good correlation between 17OHP, androstenedione, and testosterone concentrations in a single blood sample, suggesting these hormone concentrations are all under similar influences.⁹ Random serum steroid levels in CAH patients tend to fluctuate with time of day and timing relative to glucocorticoid administration.³ For this reason, samples for a given patient should be collected at a consistent time before the administration of the morning glucocorticoid dose.³

Polycystic ovary syndrome (PCOS) is a syndrome of ovarian dysfunction characterized by hyperandrogenism, menstrual irregularities, and polycystic ovaries.^9,12 PCOS is associated with an increased risk of diabetes and cardiovascular disease.¹ The measurement of circulating androstenedione levels has been applied to the diagnosis of PCOS in several studies.^6,12-14