HYDROXYUREA INDUCES THE GENE-EXPRESSION AND SYNTHESIS OF PROINFLAMMATORY CYTOKINES IN-VIVO

The anticancer agent hydroxyurea (HU) was previously found to cause do se-dependent adrenal activation in the rat. The increased secretion of corticosterone (CORT) that results appeared to protect animals agains t HU toxicity, which was dramatically enhanced in adrenalectomized (AD X) rats. Similarities with the endocrine and toxicological profiles of proinflammatory cytokines such as interleukin (IL)-1 and tumor necros is factor (TNF) led us to suggest that these effects of HU might be me diated by an increased synthesis of these cytokines. The goal of this study was therefore to demonstrate that HU induces the gene expression and synthesis of proinflammatory cytokines in vivo. Intact and ADX ra ts were treated with HU, mRNA was extracted from spleen cells 2 and 24 hr after treatment and message levels for IL-1 alpha, IL-2, IL-4, IL- 6, TNF alpha and interferon-gamma were evaluated using the reverse tra nscriptase-polymerase chain reaction technique. In some experiments, c irculating levels of CORT and TNF were also measured. We found that tr anscripts of the proinflammatory cytokines, TNF, IL-6 and (though less clearly) IL-1 alpha, were expressed in the majority of intact rats tr eated with HU but were absent or less evident in most controls. In con trast, gene expression of IL-2, IL-4 and interferon-gamma was not infl uenced by drug treatment. Adrenalectomy markedly enhanced the effects of HU. Twenty-four hours after administration of the drug, the express ion of TNF and IL-6 mRNAs was still higher in ADX rats compared with i ntact animals. Parallel measurements of plasma CORT levels revealed th at gene expression of IL-1 alpha and, to a lesser extent, TNF was inve rsely related to levels of circulating CORT. Adrenalectomy per se caus ed a significant increase in plasma TNF levels compared with intact co ntrols. Hydroxyurea elicited significant increases in circulating TNF in both ADX and intact rats. These findings lend support to our workin g hypothesis and provide an explanation for both the rise in glucocort icoid secretion induced by HU in intact rats and the increase in letha lity observed in animals with disruptions of the hypothalamo-pituitary -adrenal axis.