Pathophysiology of free cortisol in plasma

Regulation of cortisol bioavailability--effects on hormone measurement and action

Routine assessment of the hypothalamic-pituitary-adrenal axis relies on the measurement of total serum cortisol levels. However, most cortisol in serum is bound to corticosteroid-binding globulin (CBG) and albumin, and changes in the structure or circulating levels of binding proteins markedly affect measured total serum cortisol levels. Furthermore, high-affinity binding to CBG is predicted to affect the availability of cortisol for the glucocorticoid receptor. CBG is a substrate for activated neutrophil elastase, which cleaves the binding protein and results in the release of cortisol at sites of inflammation, enhancing its tissue-specific anti-inflammatory effects. Further tissue-specific modulation of cortisol availability is conferred by corticosteroid 11β-dehydrogenase. Direct assessment of tissue levels of bioavailable cortisol is not clinically practicable and measurement of total serum cortisol levels is of limited value in clinical conditions that alter prereceptor glucocorticoid bioavailability. Bioavailable cortisol can, however, be measured indirectly at systemic, extracellular tissue and cell levels, using novel techniques that have provided new insight into the transport, metabolism and biological action of glucocorticoids. A more physiologically informative approach is, therefore, now possible in the assessment of the hypothalamic-pituitary-adrenal axis, which could prove useful in clinical practice.

Quantification of unbound prednisolone, prednisone, cortisol and cortisone in human plasma by ultrafiltration and direct injection into liquid chromatrography tandem mass spectrometry

BACKGROUND

The existing methods for quantitative analysis of free corticosteroids require high volume of plasma and laborious extraction processes. Development of ultrafiltration followed by the liquid chromatrography tandem mass spectrometry (LC-MS/MS) method that requires 300 microL of plasma, does not entail any offline extraction and achieves good sensitivity was described.

METHODS

Unbound corticosteroids were separated by the ultrafiltration of plasma using Microcon centrifugal filter devices (10,000 Dal nominal molecular weight limit). A 30 microL aliquot of the ultrafiltrate was directly injected into a two-dimensional high-performance liquid chromatography clean-up and separation system coupled with API-4000 mass spectrometer. The clean-up was performed on a Strata-X on-line extraction cartridge. A Zorbax-SB Phenyl, Rapid Resolution HT (2.1 x 100 mm) column was employed to chromatographically resolve cortisol and prednisolone from each other, from cortisone and prednisone as well as from interferences found in plasma from stable kidney transplant recipients.

RESULTS

Intra- and inter-run imprecision and inaccuracy within +/-15% were achieved during a three-batch validation for quality control samples at six concentrations in ultrafiltrate from charcoal-stripped plasma and three concentrations from normal plasma, over a 2000-fold dynamic range. The lower limit of quantification was 0.100 ng/mL for all four corticosteroids.

CONCLUSIONS

A highly selective, sensitive, simple and robust LC-MS/MS method was developed for the simultaneous quantification of free cortisol, cortisone, prednisolone and prednisone. The performance of the Strata-X on-line extraction cartridge was maintained for over 700 injections. The assay was successfully applied for the analysis of the analytes in over 500 plasma samples from stable kidney transplant recipients.

The effect of glucocorticoids on ERK-1/2 phosphorylation during maturation of lamb oocytes and their subsequent fertilization and cleavage ability in vitro

High levels of glucocorticoids may alter reproduction, but little is known about their direct actions on oocyte maturation, fertilization and subsequent development. Earlier work suggested negative effects of cortisol or dexamethasone on oocyte maturation but differences were noted between animal models. Both glucocorticoids reduce the p34(cdc2)-cyclin B1 complex but it is unknown if other signaling pathways important for meiosis progression are affected. In this study, using sheep oocytes as a model system, we assessed in vitro the effects of increasing concentration of glucocorticoids (0-250 microM) on oocyte maturation and underlying changes in the MAP kinase pathway, and the ability of oocytes to undergo fertilization and embryo development. Cortisol decreased oocyte maturation but only at the highest concentration, whereas dexamethasone had no effect. Fertilization and cleavage were not affected. On the other hand, both cortisol and dexamethasone inhibited ERK-1/2 activation in a concentration-dependent manner. It thus seems that oocytes can overcome deleterious effects of glucocorticoids during maturation despite the decrease in ERK-1/2 activity, but repercussions in vivo should be further explored.

Biological activities of the shrub Salsola tuberculatiformis Botsch.: contraceptive or stress alleviator?

Plants belonging to the genus Salsola (Family: Chenopodiaceae) are common in the arid and semiarid regions of our planet with no less than 69 different Salsola species found in Namibia and the Republic of South Africa. This genus is used as a traditional medicine and aqueous extracts of Salsola have been used by Bushmen women as an oral contraceptive. Ingestion of the Namibian shrub Salsola tuberculatiformis Botsch. by pregnant Karakul sheep leads to prolonged gestation and fetal post-maturity and, as a result, the pelts of the new-born karakul lambs are worthless. This initiated an investigation into the active agents in the plant, using the terminal enzyme in adrenal corticosteroidogenesis, cytochrome P450-dependent 11beta-hydroxylase (P450c11), as a bioassay. Although the active fraction, S2, was extremely labile, partial structure determination suggested the presence of synephrine and a highly reactive aziridine. Therefore a more stable analogue, 2-(4-acetoxyphenyl)2-chloro-N-methylethylammonium-chloride (compound A), was synthesised, which, like the active plant extracts, inhibited adrenal steroidogenesis and acted as a contraceptive. In addition, compound A was stabilised by interaction with steroid-binding globulins in plasma thus enhancing biological activity in vivo. These findings provided explanations for the complex biological effects of the shrub as well as a new insight into the mode of action of chemically labile plant products in vivo.

Free serum cortisol during the postoperative acute phase response determined by equilibrium dialysis liquid chromatography-tandem mass spectrometry

In severely ill patients low concentrations of the corticosteroid binding globulin are typically found; the aim of this study was to quantify directly free bioactive cortisol concentrations in the sera of postoperative cardiosurgical patients. Serum samples of 12 consecutive patients undergoing aortocoronary bypass surgery taken preoperatively and on the postoperative days 1 to 4 were analyzed. Total serum cortisol was quantified using liquid chromatography-tandem mass spectrometry with an on-line sample extraction system and tri-deuterated cortisol as the internal standard, and free serum cortisol was measured after over-night equilibrium dialysis. Whereas on the first postoperative day, the median total serum cortisol concentration was approximately two-fold increased compared to preoperative samples (preoperatively, 245 nmol/l (interquartile range (IQR) 203-293 nmol/l); first postoperative day, 512 nmol/l (IQR 410-611 nmol/l)), median dialyzable free cortisol concentration was almost seven-fold increased (preoperatively, 14.2 nmol/l (IOR 10.9-20.7 nmol/l); first postoperative day, 98.3 nmol/l (IQR 81.3-134 nmol/l)). On the fourth postoperative day, median free cortisol was still significantly increased compared to baseline sampling (p < 0.05), whereas median total cortisol was not. A median of 5.7% (IQR 5.4-7.0%) of total cortisol was found as free cortisol on the preoperative day, 21.2% (IQR 18.9-23.5%) on the first postoperative day and 10.5% (IQR 9.8-14.0%) on the fourth postoperative day. It is concluded that during the postoperative period the free-to-bound ratio of cortisol is highly variable and that during the acute phase response direct quantification of free bioactive cortisol concentrations seems to be biologically more appropriate than the measurement of total cortisol concentrations.

Dialyzable free cortisol after stimulation with Synacthen

OBJECTIVES

To compare the changes in free vs. total serum cortisol concentrations after acute stimulation of the adrenal cortex.

DESIGN AND METHODS

Paired serum samples of ten individuals taken immediately before and 1 h after stimulation with 250 microg ACTH (1-24) (Synacthen) given i.v. were analyzed. Total cortisol was quantified using liquid chromatography tandem-mass spectrometry with an online sample extraction system and tri-deuterated cortisol as the internal standard. Free cortisol was measured with the same method after equilibrium dialysis. Concentrations of the corticosteroid-binding globulin (CBG) were determined by radioimmuno assay.

RESULTS

Total cortisol increased by a mean of 106% (mean basal cortisol 312 nmol/L (SD 140 nmol/L), stimulated 686 nmol/L (SD 163 nmol/L); p < 0.001, paired t-test for differences); no significant change of CBG concentrations was found (874 nmol/L (SD 179 nmol/L) before stimulation, 869 nmol/L (SD 225 nmol/L) after stimulation). The mean increase of free cortisol was 263% (mean basal free cortisol 20.3 nmol/L (SD 13.2 nmol/L), stimulated 73.8 nmol/L (SD 26.7 nmol/L); p < 0.001) and thus substantially more pronounced compared to the increase of total cortisol (p < 0.01). The ratio of free to total serum cortisol was significantly increased after stimulation (6.1% (SD 1.7%) before stimulation, 10.6% (SD 1.9%) after stimulation; p < 0.001).

CONCLUSIONS

After acute neuroendocrine stimulation of the adrenal cortex the relative increase of free bioactive cortisol concentrations is substantially more pronounced than the increase of total cortisol concentrations.