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By activating the Toll-like receptor 4-nuclear factor-kappaB signal transduction pathway, the bacterial endotoxin lipopolysaccharide (LPS) induces anorexia, weight loss, fever, and other components of the sickness response. By comparison, the hormones leptin and insulin cause anorexia without sickness via a central mechanism involving the phosphatidylinositol-3 kinase signaling pathway. In the current study, we investigated whether a common Toll-like receptor 4 and phosphatidylinositol-3 kinase signaling intermediate, atypical protein kinase Czeta/lambda (aPKC), contributes to changes of energy balance induced by these stimuli. Immunohistochemistry analysis revealed that aPKC is expressed in the arcuate and paraventricular nuclei of the hypothalamus, key sites of leptin, insulin, and LPS action. Although administration of LPS, insulin, and leptin each acutely increased hypothalamic aPKC activity at doses that also reduce food intake, LPS treatment caused over 10-fold greater activation of hypothalamic a PKC signaling than that induced by leptin or insulin. Intracerebroventricular pretreatment with an aPKC inhibitor blocked anorexia induced by LPS but not insulin or leptin. Similarly, LPS-induced hypothalamic inflammation (as judged by induction of proinflammatory cytokine gene expression) and neuronal activation in the paraventricular nucleus (as judged by c-fos induction) were reduced by central aPKC inhibition. Although intracerebroventricular aPKC inhibitor administration also abolished LPS-induced fever, it had no effect on sickness-related hypoactivity or weight loss. We conclude that although hypothalamic aPKC signaling is not required for food intake inhibition by insulin or leptin, it plays a key role in inflammatory anorexia and fever induced by LPS.

Anorexia is a debilitating manifestation of many malignancies. The etiology of cancer anorexia is poorly understood, and effective treatment options are limited. To investigate the role of central melanocortin receptor signaling in the pathogenesis of cancer anorexia, we assessed the effects on food intake of the melanocortin receptor antagonist SHU9119 administered into the third cerebral ventricle of Lobund-Wistar rats that were anorexic from prostate cancer. In anorexic tumor-bearing rats, daily treatment with SHU9119 (0.35 nmol, intracerebroventricularly) increased food intake from 71 +/- 3% to 110 +/- 6% of preanorectic baseline and caused significant weight gain (13 +/- 5 vs. 5 +/- 1 g/3 d, SHU9119 vs. baseline in tumor-bearing rats). In control rats pair-fed to the intake of tumor-bearing animals, SHU9119 was ineffective at increasing food intake. The specificity of the SHU9119 feeding response was assessed using two other orexigenic peptides, NPY and the novel hormone ghrelin. Treatment of tumor-bearing rats with intracerebroventricular ghrelin (10 microg) increased food intake, but the effect was blunted relative to that in controls. Intracerebroventricular injections of NPY (1 microg) also failed to reverse anorexia in tumor-bearing rats. Because SHU9119 completely reverses cancer anorexia in this model, whereas ghrelin and NPY do not, increased central nervous system melanocortin signaling is implicated in the pathogenesis of this disorder. This suggests that new targets for the treatment of cancer anorexia may be found in the melanocortin pathways.