The molecular basis for the effectiveness, toxicity, and resistance to glucocorticoids: focus on the treatment of rheumatoid arthritis.

Glucocorticoids (GCs) have powerful and potent anti-inflammatory and immunomodulatory effects in rheumatoid arthritis (RA) and many other diseases. These effects are mediated by up to four different mechanisms of action: cytosolic glucocorticoid receptor (cGCR)-mediated classical genomic and rapid non-genomic effects, membrane-bound glucocorticoid receptor (mGCR)-mediated non-genomic effects and non-specific non-genomic effects. On the basis of this detailed knowledge of mechanisms there are currently interesting approaches being considered that may lead to the development of GC drugs and GCR ligands with an improved benefit to side-effect ratio. Another interesting field of GC research is the phenomenon of GCR resistance. Several different mechanisms may mediate this phenomenon; among them are alterations in number, binding affinity, or phosphorylation status of the GCR. Other mechanisms of GC resistance being investigated are polymorphic changes and/or overexpression of (co-)chaperones, the increased expression of inflammatory transcription factors, overexpression of the GCR beta isoform, the multidrug resistance pump, and an altered mGCR expression.