New Aspects in the Diagnosis and Treatment of Cushing Disease

Cushing disease, which is caused by the excessive production of ACTH, is a rare and complex endocrine disorder that still represents a major challenge for the physician in terms of accurate diagnosis and efficient treatment. Diagnosing Cushing syndrome and its etiology is an elaborate procedure and no single test is sensitive and specific enough to provide sufficient accuracy. Therefore, an ordered cascade of tests is necessary recommended by a consensus statement in 2002. The proposed diagnostic algorithm will be summarized in the following section. In the absence of efficient drug therapy, transsphenoidal resection of the pituitary adenoma is the treatment of choice for the reduction of ACTH secretion. However, not all patients can be cured by surgery. In the present article, we examine recent studies that have investigated the therapeutic potential of new generations of drugs for the treatment of Cushing disease such as cabergoline and SOM230. The role of nuclear receptors: retinoic acid receptors and peroxisome proliferator-activated receptor-gamma as new approaches for treating pituitary tumors is also discussed.

New perspectives in the treatment of Cushing's syndrome

Regardless of etiology, all cases of endogenous Cushing's syndrome are due to increased production of cortisol by the adrenal gland. Most are caused by adrenocorticotrophic hormone (ACTH)-secreting pituitary adenomas. Alternatively, the glucocorticoid excess may be due to adrenal neoplasia or to ectopic ACTH-secreting tumors. Cushing's syndrome is characterized by endocrine and metabolic alterations such as truncal obesity, hypertension, weakness, amenorrhea, hyperglycemia, osteoporosis and depression. Unless treated, the disease is associated with high morbidity, and ultimately, mortality. Depending on the etiology of Cushing's syndrome two different treatment modalities are possible: reduction of pituitary ACTH production or reduction of adrenocortical cortisol secretion. In the absence of efficient drug therapy, transsphenoidal resection of the pituitary adenoma is the primary treatment of choice for the reduction of ACTH secretion. In the last years there was much progress in understanding the molecular mechanisms that control the function of the hypothalamic-pituitary-adrenal axis. Thus, new insights made it possible to identify potential drug targets for the treatment of Cushing's syndrome. The present article reviews different drug targets and therapeutic options including drugs that control the central ACTH regulation, e.g. by modulating signaling pathways and transcriptional regulation of ACTH biosynthesis, corticotrophin releasing hormone (CRH) or glucocorticoid receptor antagonists, inhibitors of glucocorticoid synthesis, ketoconazole, somatostatin and dopamine analogs. Some of these substances might be useful for the treatment of Cushing's syndrome.

Migratory Activity and Functional Changes of Green Fluorescent Effector Cells before and during Experimental Autoimmune Encephalomyelitis

Homing behavior and function of autoimmune CD4+ T cells in vivo was analyzed before and during EAE, using MBP-specific T cells retrovirally engineered to express the gene of green fluorescent protein. The cells migrate from parathymic lymph nodes to blood and to the spleen. Preceding disease onset, large numbers of effector cells invade the CNS, with only negligible numbers left in the periphery. In early EAE, most (>90%) infiltrating CD4+ cells were effector cells. Migratory effector cells downregulate activation markers (CD25, OX-40) but upregulate several chemokine receptors and adsorb MHC class II on their membranes. Within the CNS, the effector cells are reactivated, with upregulated proinflammatory cytokines and downmodulated T cell receptor-associated structures, presumably reflecting autoantigen recognition in situ.

Transfection of immature murine bone marrow-derived dendritic cells with the granulocyte-macrophage colony-stimulating factor gene potently enhances their in vivo antigen-presenting capacity

Ag presentation by dendritic cells (DC) is crucial for induction of primary T cell-mediated immune responses in vivo. Because DC culture from blood or bone marrow-derived progenitors is now clinically applicable, this study investigated the effectiveness of in vitro-generated murine bone marrow-derived DC (Bm-DC) for in vivo immunization protocols. Previous studies demonstrated that GM-CSF is an essential growth and differentiation factor for DC in culture and that in vivo administration of GM-CSF augments primary immune responses, which renders GM-CSF an attractive candidate to further enhance the effectiveness of DC-based immunotherapy protocols. Therefore, immature Bm-DC were transiently transfected with the GM-CSF gene and tested for differentiation, migration, and Ag-presenting capacity in vitro and in vivo. In vitro, GM-CSF gene-transfected Bm-DC were largely unaltered with regard to MHC and costimulatory molecule expression as well as alloantigen or peptide Ag-presenting capacity. When used for in vivo immunizations, however, the Ag-presenting capacity of GM-CSF gene-transfected Bm-DC was greatly enhanced compared with mock-transfected or untransfected cells, as determined by their effectiveness to induce primary immune reactions against hapten, protein Ag, and tumor Ag, respectively. Increased effectiveness in vivo correlated with the better migratory capacity of GM-CSF gene-transfected Bm-DC. These results show that GM-CSF gene transfection significantly enhances the capacity of DC to induce primary immune responses in vivo, which might also improve DC-based vaccines currently under clinical investigation.

TRH receptor on immune cells: in vitro and in vivo stimulation of human lymphocyte and rat splenocyte DNA synthesis by TRH

This work examined whether (1) immune cells express thyrotrophin releasing hormone (TRH) receptor mRNA and (2) TRH modulates lymphocyte activation. By Northern blot of RNA extracted from human peripheral blood mononuclear cells (PBMC) and rat splenocytes, a single TRH receptor mRNA band of about 3.8 kb (identical to that obtained from pituitary cells) was obtained, under both basal and stimulated conditions. A significant increase in DNA synthesis was observed in phytohemagglutinin-stimulated PBMC and concanavalin A (Con A) stimulated splenocytes when TRH (10(-6) M-10(-12) M) was added. After 5, 30, 60, 180 min and 24 h of TRH administration in vivo, a significant increase in the rat splenocyte proliferative response to Con A was observed. In vivo administration of anti-rat TSH antibody (1/1000) blocked the increase observed after 30 min of TRH administration on the Con A stimulated splenocyte response. TRH possess immunostimulatory functions directly via its receptor and indirectly via release of other immunostimulatory factors such as thyrotrophin.

Glucocorticoids suppress interleukin-1 receptor antagonist synthesis following induction by endotoxin

Glucocorticoids, as part of their physiological role in the control of inflammatory and immune processes, suppress the expression of IL-1 and other cytokines. We have found a dose-dependent inhibition by dexamethasone (10 nM to 10 microM) of mRNA levels of the recently cloned IL-1 receptor antagonist (IL-1ra) in endotoxin-stimulated human monocytes. At the same concentrations, both dexamethasone and cortisol inhibited the secretion of IL-1ra. These inhibitory effects were reversed by blocking glucocorticoid receptors with the specific antagonist RU 38486, but not by adding exogenous IL-1, even up to 100 ng/ml, to the monocytes. A similar inhibition of IL-1ra mRNA and protein secretion was found in monocytes obtained after dexamethasone administration in vivo. In addition, we observed parallel increases in glucocorticoid and IL-1ra levels following endotoxin administration to normal volunteers. Our results show that glucocorticoids shut down not only IL-1 but also IL-1ra expression, ruling out induction of IL-1ra as part of the glucocorticoid antiinflammatory mechanism. The control of the delicate immunoregulatory balance of the IL-1/IL-1ra system during endotoxemia underscores the physiological importance of glucocorticoids in the final control of immune responses.

Lesions of the medial septal nucleus produce a long-lasting inhibition of T lymphocyte proliferation

The influence of the central cholinergic system on the immune system was studied in Wistar rats by lesioning the medial septal nucleus. This lesion inhibited T cell proliferation of splenocytes and thymocytes induced by the mitogens concanavalin A (Con A), phytohemagglutinin (PHA) and pokeweed mitogen (PWM) up to 25 days and did not affect proliferation at 40 days after lesioning. In contrast, the response to the B cell mitogen lipopolysaccharide from E. coli (LPS) was not affected at any time. These findings suggest a regulatory role of the cholinergic medial septal nucleus on T lymphocyte proliferation.