Hydroxyurea induces vasopressin release and cytokine gene expression in the rat hypothalamus.

We previously showed that the cytostatic drug hydroxyurea (HU) activates the hypothalamo-pituitary-adrenal (HPA) axis in intact rats, whereas it is lethal in rats with impaired HPA function. In these animals, HU toxicity is mediated by increased circulating levels of proinflammatory cytokines, whose secretion cannot be counteracted by glucocorticoids, suggesting that HPA activation blunts HU toxicity. Here we investigated the mechanisms through which HU activates the HPA axis, looking at the direct effects of the drug on the isolated hypothalamus. We found that HU significantly increases the release of arginine vasopressin but not that of corticotrophin-releasing hormone in short-term incubation experiments. The levels of arginine vasopressin are also increased in the hypothalamus and systemic circulation 2 h after the in vivo administration of the drug. Furthermore, HU increased significantly the expression of interleukin-6 and, to a lesser extent, interleukin-1beta in the hypothalamus. Interestingly, experiments with HU on primary cultures of rat microglia and astrocytes suggested that the increase in cytokine gene expression observed in hypothalamic explants is not accounted for by glial cells. Since both vasopressin and cytokines can activate the HPA axis, our present findings provide a reasonable explanation of the HPA activation elicited by HU in vivo in the rat.

Metallic but not ceramic wear particles increase prostaglandin E2 release and interleukin-1beta gene expression in human blood monocytes in vitro.

In this study the potential of clinically relevant alumina ceramic and metal wear particles to induce an in vitro inflammatory response was assessed in human monocytes and lymphocytes isolated from healthy donors by measuring prostaglandin E2 (PGE2) levels and mRNA expression of various pro-inflammatory cytokines. Bacterial lipopolysaccharide (LPS) was used as positive control. LPS significantly increased PGE2 levels in the incubation medium of monocyte cultures after 24 h. Alumina had no effect on PGE2 production, whereas metals induced a concentration-dependent increase in PGE2 release, that was statistically significant at the dose of 0.1 mg/ml. In lymphocytes, LPS elicited a weak but significant increase in PGE2 release, whereas both alumina and metals did not modify PGE2 amounts at any of the concentrations tested. The gene expression of a number of pro- and anti-inflammatory cytokines was assessed in monocytes and lymphocytes exposed to LPS, 0.1 mg/ml alumina or 0.1 mg/ml metals for 24 h. In monocytes, LPS caused a 2-fold increase in interleukin-1beta (IL-1beta) mRNA levels. The exposure of monocytes to metals resulted in a selective increase in IL-1beta mRNA accumulation (+48% compared to control). By contrast, alumina did not modify IL-1beta mRNA levels. None of the test substances elicited any response on purified lymphocyte population. These findings suggest that PGE2 production and IL-1 mRNA expression are a reliable marker to study the pro-inflammatory effects of wear debris in vitro. The lower activity of alumina compared to metals suggests that the former should be preferred in implants for its favorable biological and mechanical behavior.

Interleukin-18 displays effects opposite to those of interleukin-1 in the regulation of neuroendocrine stress axis.

The effects of interleukin-18 (IL-18), a putative member of the IL-1 family, were investigated on basal and stimulated release of corticotropin-releasing hormone (CRH) and prostanoids from rat hypothalamic explants and glial cells in vitro. We found that IL-18 decreases basal and KCl-stimulated CRH release from the hypothalamus. IL-18 also reduced CRH gene expression after 1- and 3-h incubation. The cytokine did not modify basal PGE2 production by hypothalamic explants but abolished production stimulated by IL-1beta. Similar effects were also observed on cultured glial cells. The present findings show that IL-18 possesses a profile of in vitro neuroendocrine activities opposing to, and even antagonizing, those of IL-1beta.