Journal of Clinical Endocrinology & Metabolism, Vol 78, 872-877, Copyright © 1994 by Endocrine Society

ARTICLES

Inhibition of lysozyme synthesis by dexamethasone in human mononuclear leukocytes: an index of glucocorticoid sensitivity

M Panarelli, CD Holloway, P Mulatero, R Fraser and CJ Kenyon
Medical Research Council Blood Pressure Unit, Western Infirmary, Glasgow, Scotland.

Glucocorticoids inhibit translation of the lysozyme gene. This effect may be the basis of an improved method of measuring glucocorticoid responsiveness in human tissues. We have compared lysozyme synthesis in various types of white blood cells and examined the specificity of inhibitory responses to various steroid hormones. The dose-related effects of the glucococorticoid receptor antagonist RU486 on dexamethasone responses were also assessed. Glucocorticoid receptor binding in mononuclear leukocytes (HML) was characterized by homologous displacement of [3H]dexamethasone and compared with the dose-related inhibitory effect of dexamethasone on lysozyme synthesis. Lysozyme activity was measured photometrically as the ability to cause lysis of Micrococcus lysodeikticus in the medium. The greatest effect of dexamethasone was observed after 72 h of culture. Qualitatively similar effects of dexamethasone were observed on cell lysozyme content and lysozyme activity in the medium, but for convenience, activity in medium, rather than cell content, was measured in subsequent assays. Lysozyme activities in various cell types prepared from the blood of healthy volunteers were ranked as follows: polymorphonuclear cells > monocytes > mononuclear cells > lymphocytes. However, dexamethasone inhibited lysozyme synthesis to a similar degree for all types. As mononuclear cells are more conveniently prepared in greater yield compared with other cells, this HML fraction formed the basis of a method of assessing glucocorticoid responsiveness and sensitivity. Lysozyme activity from HML was not significantly affected by incubation with 1 mumol/L estradiol, progesterone, dehydroepiandrosterone, or aldosterone. Dexamethasone and cortisol at 1 mumol/L both inhibited release by 45-50%. Although RU486 when added alone partially inhibited lysozyme activity, the same concentration (1 mumol/L) antagonized glucocorticoid responses and shifted the IC50 and threshold values for the effect of dexamethasone from 1.2 nmol/L to more than 1 mumol/L and from less than 1.0 to 19 nmol/L, respectively. The equilibrium dissociation constants (Kd) for dexamethasone binding to the glucocorticoid receptor ranged from 2.8-12.5 nmol/L and were positively correlated with dexamethasone IC50 values for lysozyme synthesis (r = 0.57; P = 0.002). In conclusion, the inhibition of lysozyme synthesis by dexamethasone in human mononuclear cells is a convenient and specific method of measuring responsiveness to glucocorticoids.

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