Altered function of the hypothalamic stress axes in patients with moderately active systemic lupus erythematosus. II. Dissociation between androstenedione, cortisol, or dehydroepiandrosterone and interleukin 6 or tumor necrosis factor.

OBJECTIVE: To investigate adrenocorticotropin, androstenedione (ASD), cortisol, or dehydroepiandrosterone sulfate (DHEAS) before and during a corticotropin releasing hormone (hCRH) test in patients with moderately active systemic lupus erythematosus (SLE) undergoing low dose longterm glucocorticoid therapy, and to examine these hormones in relation to interleukin 6 (IL-6) or tumor necrosis factor (TNF). METHODS: Serum levels of hormones and cytokines were measured before and during an hCRH test. The results of 12 patients with SLE were compared to 12 healthy subjects (HS) and 12 healthy subjects given prior short term prednisolone (HS+P). RESULTS: Baseline and stimulated serum ASD, cortisol, and DHEAS were lower in patients with SLE vs. HS (p<0.005), but baseline and stimulated plasma adrenocorticotropin was normal in SLE. In SLE, but not in HS+P or HS, baseline and stimulated DHEAS was low in relation to cortisol or ASD (i.e., shift from DHEAS to cortisol or ASD). In patients with SLE, baseline and stimulated serum levels of adrenal hormones were lower in relation to IL-6 or TNF compared to HS or HS+P (p< 0.001). In contrast, in SLE patients, the baseline and stimulated pituitary hormone adrenocorticotropin was normal in relation to these cytokines. CONCLUSION: We found marked adrenal insufficiency and a shift in steroidogenesis to cortisol in patients with SLE, but a completely normal pituitary function (in absolute values and in relation to IL-6 or TNF). This may depend in part on prior longterm glucocorticoid therapy and changes of steroidogenesis due to cytokines. The situation in patients with SLE was not mimicked by high dose short term prednisolone in healthy subjects. Further longitudinal studies in untreated patients are needed to investigate the endocrine-immune interplay and its consequences during the course of SLE.

Differential selenium-dependent expression of type I 5'-deiodinase and glutathione peroxidase in the porcine epithelial kidney cell line LLC-PK1.

The Se-dependent expression of two selenoproteins, cytosolic glutathione peroxidase (cGPx) and type I iodothyronine-5'-deiodinase (5'DI), was investigated in the porcine epithelial kidney cell line LLC-PK1 in serum-free medium. The selenite-dependent expression of cGPx and 5'DI was revealed by enzyme-activity measurements, affinity labelling of 5'DI, metabolic labelling of proteins with 75Se and steady-state mRNA analysis. The expression of the two enzymes strongly depended on selenite concentrations of the culture medium. cGPx required 2-fold higher selenite levels than 5'DI to reach half-maximal activity. The Se-dependent enzyme activities were approximately paralleled by the corresponding steady-state mRNA levels. The response of the two enzymes to Se supply was further characterized by kinetic Se-depletion and -repletion experiments. Upon removal of medium selenite, cGPx activity decreased exponentially, whereas after an initial decrease over 1-2 days, 5'DI levels completely recovered during a further 2 days. These data indicate a differential Se-dependent regulation of the two selenoproteins, with 5'DI being preferentially supplied with the trace element Se, thus ensuring a continuous cellular capacity for thyroid-hormone activation, even under Se-deficient conditions. The abundant cGPx in cells with sufficient Se supply might serve as a cellular Se store which can be mobilized for the synthesis of more vital selenoproteins such as 5'DI under shortage conditions. Thus, a cellular hierarchy of selenoprotein expression, reflected by different individual regulation mechanisms at the transcriptional and post-transcriptional level, adds to the previously recognized tissue-specific hierarchy of Se retention.

Selenium-dependent regulation of type I 5'-deiodinase expression.

Selenite concentration regulates activity and expression of the p27 substrate-binding subunit of type I 5'deiodinase (5'-D) and of a protein labeled with bromoacetylthyroxin (BrAcT4), or p30, with yet unknown function in a porcine-kidney epithelial cell line (LLC-PK1) cultured in serum-free medium. p27 is metabolically labeled by 75-selenite and affinity labeled by BrAc[125I]T4. Compared with glutathione peroxidase, expression of the p27 5'D subunit (5'-DI) is observed at 10-fold-lower concentrations of selenium in the growth medium, suggesting an intracellular hierarchy of selenite utilization. Selenium deficiency retards cell growth and prevents 5'-DI expression and may thus impair thyroid hormone action in vivo.

Selenium supply regulates thyroid function, thyroid hormone synthesis and metabolism by altering the expression of the selenoenzymes Type I 5'-deiodinase and glutathione peroxidase.

Selenium supply appears to be insufficient in several regions of Europe as indicated by analysis of plasma and tissue selenium content and measurements of selenium dependent glutathione peroxidases (GPx). Selenium deficiency alters both thyroid hormone synthesis and tissue specific activation by 5'deiodinase isoenzymes. Human and rat Type I 5'deiodinase have been identified as selenoprotein containing selenocysteine in its active site. Regulation of selenium dependent expression of Type I 5'deiodinase occurs at the transcriptional and posttranscriptional level and a cellular hierarchy of selenite incorporation was found for Type I 5'deiodinase over GPx in LLC-PK1 kidney cells. The role of other newly discovered selenoproteins for thyroid hormone synthesis, activation, and action has to be investigated.