Both cortisol and corticosterone circulate in human plasma however corticosterone has been relatively neglected in human research to date. There is evidence of distinct regulation within different tissues with the transmembrane transporter ABCB1, highly expressed in the brain, exporting cortisol but not corticosterone. This may account for the relative accumulation of corticosterone in the CNS. In contrast, ABCC1, highly expressed in adipose tissue and skeletal muscle, exports corticosterone but not cortisol, suggesting cortisol is the principal glucocorticoid acting in these tissues. We tested the hypotheses that: (i) corticosterone physiology in humans is different to that of cortisol; (ii) inhibition of ABCC1 increases binding of corticosterone to corticosteroid receptors in adipose tissue and skeletal muscle but has no central CNS effect; and (iii) corticosterone is superior to cortisol as a basis for glucocorticoid replacement therapy with fewer metabolic side effects. We compared paired salivary and plasma samples from 10 healthy individuals. Plasma corticosterone showed a similar diurnal variation to cortisol but salivary corticosterone was low and did not correlate with plasma concentrations. A placebo-controlled randomised crossover study was carried out in 14 healthy individuals comparing receptor occupancy of glucocorticoids centrally and peripherally with and without ABCC1 inhibition. Receptor occupancy was assessed through displacement with MR and GR antagonists potassium canrenoate and mifepristone. Centrally, ABCC1 inhibition caused increased activation of the HPA axis after MR and GR antagonism. Peripherally, we were unable to show displacement from adipose tissue or skeletal muscle. A further placebo-controlled randomised crossover study is still ongoing in 16 patients with congenital adrenal hyperplasia, comparing metabolic effects of placebo, cortisol and corticosterone infusions over 6 hours. We present interim data for n=8. ACTH and 17-OHP were suppressed with corticosterone. Metabolic parameters were similar between placebo, cortisol and corticosterone phases. These data suggest corticosterone physiology is distinct compared with cortisol in humans. We have shown ABCC1 inhibition alters the HPA axis after receptor antagonism which suggests ABCC1 may play more of a key role centrally than previously thought. Corticosterone suppresses ACTH and 17-OHP in the short term in congenital adrenal hyperplasia, highlighting the possibility of its use as an alternative glucocorticoid replacement therapy in the future.

The circadian clock drives ~24hr rhythms in a variety of processes, from gene expression through to behaviour, facilitating anticipation of daily changes in the external environment and temporal separation of internal processes. This pacemaker is a critical regulator of immune function and many inflammatory diseases show time-of-day variation in symptom severity. Disruption of the pacemaker by manipulation of the daily cycle of light and dark exposure (experimental 'jet lag') is known to exacerbate inflammatory responses to innate immune challenge, and recent evidence has highlighted immuno-modulatory roles for components of the molecular oscillator in peripheral tissues. The adrenal-derived glucocorticoid hormones are potent anti-inflammatory molecules and are capable of modulating circadian oscillations in peripheral tissues. This, along with their rhythmic secretion profile, makes them key candidates as mediators of circadian regulation of inflammatory signalling. Utilising adrenalectomy, timed glucocorticoid administration, hormone clamp and genetic targeting of the glucocorticoid receptor in mice, I present evidence for an interaction between glucocorticoid signalling and the circadian pacemaker in regulating the pulmonary inflammatory response to lipopolysaccharide (LPS) challenge. The neutrophilic response to aerosolised LPS exhibits a clear time-of-day effect in vivo, which is lost after disruption of endogenous glucocorticoid production via adrenalectomy. However, replacement of a rhythmic circulating glucocorticoid concentration with a flat daily average using a subcutaneous hormone clamp does not disrupt the inflammatory rhythm. Finally, a novel mouse strain was produced with disrupted expression of the glucocorticoid receptor (GR) in bronchial epithelial cells (Ccsp-GR-/-). These cells are critical regulators of circadian rhythmicity in the lung and drive rhythmic neutrophil influx in response to LPS stimulation through production of the chemokine CXCL5. Loss of GR in the bronchial epithelium was associated with a loss of rhythmic neutrophil influx after challenge, but anti-inflammatory sensitivity to the synthetic glucocorticoid dexamethasone remained. Collectively, these data show that appropriate temporal modulation of pulmonary inflammation requires functional glucocorticoid signalling, although the ligand itself does not need to oscillate. The retention of anti-inflammatory dexamethasone sensitivity suggests a role for cross-talk between the bronchial epithelium and additional cell populations, consistent with recent evidence for immuno-suppressive macrophage-epithelium communication in the lung. These are the first studies to dissect the mechanistic links between clocks, glucocorticoids and immunological responses in a target tissue.

Thesis (M.S.)--Duquesne University, 2007. / Title from document title page. Abstract included in electronic submission form. Includes bibliographical references (p. 54-60) and index.

Glucocorticoids (GCs) are commonly used in the clinic as a treatment for Chronic Lymphocytic Leukemia (CLL). The exact mechanism of GC action remains unclear and patients eventually develop resistance to this group of agents. Our findings show that GC-cytotoxicity in circulating CLL cells is caused by bioenergetic restriction resulting from the down-regulation of a key glycolytic enzyme, pyruvate kinase, muscle isozyme 2 (PKM2). Conversely, GCs were shown to promote fatty acid oxidation instead by up-regulating the expression of peroxisome proliferator activated receptor α (PPARα). These findings establish PPARα and fatty acid oxidation as novel mediators of GC resistance in CLL. Our findings also demonstrate that GCs enhance the cytotoxic effects of membrane-damaging agents such as ionophores and complement-mediated cytotoxicity. A clinically relevant agent known to intercalate in the cell membrane, Danazol was also found to have activity against CLL and can be combined safely with GCs for enhanced treatment efficacy.

Glucocorticoids (GCs) are commonly used in the clinic as a treatment for Chronic Lymphocytic Leukemia (CLL). The exact mechanism of GC action remains unclear and patients eventually develop resistance to this group of agents. Our findings show that GC-cytotoxicity in circulating CLL cells is caused by bioenergetic restriction resulting from the down-regulation of a key glycolytic enzyme, pyruvate kinase, muscle isozyme 2 (PKM2). Conversely, GCs were shown to promote fatty acid oxidation instead by up-regulating the expression of peroxisome proliferator activated receptor α (PPARα). These findings establish PPARα and fatty acid oxidation as novel mediators of GC resistance in CLL. Our findings also demonstrate that GCs enhance the cytotoxic effects of membrane-damaging agents such as ionophores and complement-mediated cytotoxicity. A clinically relevant agent known to intercalate in the cell membrane, Danazol was also found to have activity against CLL and can be combined safely with GCs for enhanced treatment efficacy.

Diss. (sammanfattning) Uppsala : Univ., 2002. / Härtill 5 uppsatser.

Thesis (Ph. D.)--Michigan State University. Biochemistry and Molecular Biology, 2008. / Title from PDF t.p. (viewed on July 8, 2009) Includes bibliographical references. Also issued in print.

Thesis (M.S.)--Marshall University, 2004. / Title from document title page. Includes abstract. Document formatted into pages; contains vi, 40 p. Includes bibliographical references (p. 38-40).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1958. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.Sc.)--York University, 2009. Graduate Programme in Kinesiology and Health Science. / Typescript. Includes bibliographical references (leaves 76-87). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR51561