**3.3 Understanding adverse effects of GC therapy**

The functions of endogenous GC are numerous. It is estimated that GC influence the transcription of ~1% of the entire genome and 20% of genes expressed on human leukocytes through their direct effects on transcription and their interaction with coactivators and transcription factors (Galon et al., 2002; Goulding & Flower, 2001). These include effects on metabolism, homeostasis and immune function. Most of the therapeutic effects are mediated via repression of gene activation in pro-inflammatory pathways. However, only certain adverse effects result from repression of gene transcription such as suppression of the hypothalamic-pituitary-adrenal axis while others are mediated via activation of gene transcription as is the case with diabetes. In some instances such as osteoporosis, there may be a complex interaction between gene activation and repression and the exact mechanism remains unclear in many cases (Schäcke et al., 2002) (Fig 6).


It is now thought that GC also have specific non-genomic effects that are mediated through membrane bound GCRs which are found in small numbers on human peripheral blood mononuclear cells (Bartholome et al., 2004). Moreover, stimulation of these cells in vitro by lipopolyscaharide (LPS) increases the percentage of membrane GCR expressing monocytes indicating an active upregulation of this process (Bartholome et al., 2004). Interestingly in patients with RA who have an activated immune system, the percentage memebrane GCR expressing monocytes is increased, in keeping with the in-vitro observations. These membrane expressed receptors are thought to be variants of the classical cytoplasmic GCRs (Löwenberg et al., 2007) and have recently been shown to also interact with the MAP kinase pathway (Strehl et al., 2011) Moreover, the engagement of these receptors is thought to inhibit T cell signalling by acting through downstream TCR associated signalling proteins lymphocytespecific tyrosine kinase (LCK) and FYN oncogene (Lowenberg et al., 2006). It is possible that

The functions of endogenous GC are numerous. It is estimated that GC influence the transcription of ~1% of the entire genome and 20% of genes expressed on human leukocytes through their direct effects on transcription and their interaction with coactivators and transcription factors (Galon et al., 2002; Goulding & Flower, 2001). These include effects on metabolism, homeostasis and immune function. Most of the therapeutic effects are mediated via repression of gene activation in pro-inflammatory pathways. However, only certain adverse effects result from repression of gene transcription such as suppression of the hypothalamic-pituitary-adrenal axis while others are mediated via activation of gene transcription as is the case with diabetes. In some instances such as osteoporosis, there may be a complex interaction between gene activation and repression and the exact mechanism

memberane glucocorticoid receptors will prove to have therapeutic implications.

**3.3 Understanding adverse effects of GC therapy** 

remains unclear in many cases (Schäcke et al., 2002) (Fig 6).

Fig. 5. Cellular action of glucocorticoids

Fig. 6. Adverse effect associated proteins: regulation by GC and mechanisms. Reproduced from Schäcke et al, Pharmacology and therapeutics 96 (2002) 23-43

PEPCK X

sgk X

POMC/ACTH X

 AAT X G6Pase X

Hypertension αENAC X

TAT X

CRH X

HPA suppression

Diabetes Mellitus

The Clinical Role of Glucocorticoids in the Management of Rheumatoid Arthritis 13

Dissociating the beneficial and adverse effects of GC was suggested over 10 years ago but has so far proved largely elusive. The first such compound was RU24858 which was described in 1997 by Vayssiere et al (Vayssière et al., 1997). Despite showing initial promise in dissociation of GC mediated gene activation and repression, the in-vivo effects were more disappointing and the drug did not make it into clinical trials (Belvisi et al., 2001). Other drugs such as A276575 have again shown promise but fared little better (Lin et al., 2002). The only SEGRA in clinical trials at the moment is ZK 245186 which is in Phase III trials for topical use post cateract surgery after initial results from animal models showed promise (Proksch et al., 2011). The Pahse II trail was concluded at the end of 2010 but results have not yet been released. The struggle to take SEGRAs from the bench to the bedside has been quite disappointing but not entirely surprising given the sheer number of biological mechanisms

Modelling of the diurnal variation of the HPA axis and its effects on the secretion of systemic inflammatory cytokines in RA has been a novel approach which has yielded positive results. The cytokine IL-6 has been unequivocally shown to have a diurnal variation which causes an increase in serum concentrations during the night, before the natural increase in serum cortisol, and which reaches a peak at the time of morning waking (Perry et al., 2009). This has opened the door for the development of a modified release form of GC tablet which is taken at night and releases the active ingredients in the early hours of the morning (approximately 2 am) in order to target the peak in IL-6 levels (Kirwan, 2011). The rationale behind this approach suggests that better targeting of glucocorticoids within the HPA axis may produce better efficacy hence allowing clinicians to use smaller doses of GC. Indeed a multi-centre RCT comparing a modified release GC preparation with the equivalent prednisolone dose showed significant improvements in the duration of early morning stiffness in RA (Buttgereit et al., 2008). Interestingly, a recent study by Clarke et al. (Fig 8), which measured overnight cortisol concentrations as well as IL-6 in RA patients treated with modified release GC, showed the normal pre-treatment cortisol response to be suppressed in active RA and this suppression was reversed using the correctly timed modified release therapy with a corresponding decrease in IL-6 levels and clinical

 Fig. 8. Effects of modified release GC on 24 hour diurnal variation of systemic IL-6 and

**4.1 SEGRAs** 

influenced by GC in vivo.

symptoms (Clarke et al., 2011).

cortisol in RA patients

**4.2 Modified release glucocorticoids** 

GC have a mixture of genomic and non-genomic therapeutic effects depending on the dosage used. Broadly speaking genomic effects occur at lower doses while non-genomic effects become relevant at higher doses with the combined effect of the two mechanisms accounting for the total effect of GC therapy (Fig 7). This has implications for therapeutics as at the lower doses not all the mechanisms are activated therefore the adverse effect profile may significantly differ. In essence low dose GC therapy is a very different treatment compared to high dose therapy both in terms of therapeutic effects and safety (Kirwan & Power, 2007).

Fig. 7. Contribution of genomic and non genomic therapeutic effects of GC action is dose dependent.
