Muscle wasting and cachexia have long been postulated to be key determinants of cancer-related death, but there has been no direct experimental evidence to substantiate this hypothesis. Here, we show that in several cancer cachexia models, pharmacological blockade of ActRIIB pathway not only prevents further muscle wasting but also completely reverses prior loss of skeletal muscle and cancer-induced cardiac atrophy. This treatment dramatically prolongs survival, even of animals in which tumor growth is not inhibited and fat loss and production of proinflammatory cytokines are not reduced. ActRIIB pathway blockade abolished the activation of the ubiquitin-proteasome system and the induction of atrophy-specific ubiquitin ligases in muscles and also markedly stimulated muscle stem cell growth. These findings establish a crucial link between activation of the ActRIIB pathway and the development of cancer cachexia. Thus ActRIIB antagonism is a promising new approach for treating cancer cachexia, whose inhibition per se prolongs survival.

Increased blood flow and vascular leakage of proteins preferentially affect tissues that are sites of diabetic complications in humans and animals. These vascular changes in diabetic rats are largely prevented by aminoguanidine. Glucose-induced vascular changes in nondiabetic rats are also prevented by aminoguanidine and by A^-monomethyl-L-arginine (NMMA), an established inhibitor of nitric oxide (NO) formation from L-arginine. Aminoguanidine and NMMA are equipotent inhibitors of interleukin-1 p-induced 1) nitrite formation (an oxidation product of NO) and cGMP accumulation by the rat p-cell insulinoma cell line RINm5F, and 2) inhibition of glucose-stimulated insulin secretion and formation of iron-nitrosyl complexes by islets of Langerhans. In contrast, NMMA is ~40 times more potent than aminoguanidine in elevating blood pressure in nondiabetic rats. These results demonstrate that aminoguanidine inhibits NO production and suggest a role for NO in the pathogenesis of diabetic vascular complications. Diabetes 41:552-56, 1992 N itric oxide synthase catalyzes the mixed functional oxidation of a guanidino nitrogen atom of L-arginine to yield L-citrulline and NO-(1,2). The constitutive isoform of NO-synthase is Ca 2+ dependent and produces small amounts of NO-that activate guanylate cyclase, resulting in the formation of cGMP, which mediates endothelium-dependent relaxation (2) and neural transmission (3). NO-is produced in much larger amounts by the cytokine-and endotoxininducible isoform of NO-synthase, which is Ca 2+ inde-

Cytokines have been implicated s immunological effector molecules that mediate beta cell destruction asciated with insulin-dependent diabetes mellitus. In this report we demonstrate that the cytokine combination of human recombinant interieukin lp (IL-1*), tumor necrosis factor a (TNF-a), and interferon y (IFN-y) induces the formation of nitric oxide by human islets. This combination of cytokines stimulates both the formation of the nitric oxide derivative, nitrite, and the accumulation of cGMP by human iWets. The nitric oide synthase inhibitor NG.monomethyl-L-argIne prevents formation of both cGMP and nitrite. IL-1,B and IFN-y are sufcient to induce nitric oide formation by human islets, whereas TNF-a potentiates nitrite production. This combination of cytokines (IL-1f3, TNF-a, and IFN-y) also influences insulin secretion by human idets. Pretreatment of human iWets with low concentrations of this cytokne combination (IL-lp at 15 units/ml, 0.7 nM TNF-a, and IFN-y at 150 units/ml) appears to slightly stimulate insulin secretion. Higher concentrations (IL-l1 at 75 units/nl, 3.5 nM TNF-a, and IFN-yat 750 units/ml) inhibit inlin secretion from human islets, and the inhibitory effect is prevented by NG-monomethyl-L-argine. This higher concentration of cytokines also induces the formation of an electron paramagnetic resonance-detectable g = 2.04 axial feature by human islets that is characteristic of the formation of an iron-diho-dinitrosyl complex. The formation of this complex is prevented by NG-monomethyl-L-arginine, thus confirming that this cytokine combination induces the formation of nitric oxide by human islets. These results indicate that nitric oxide mediates the inhibitory effects of cytoldnes on glucosestimulated insulin secretion by human Wets and suggest that nitric oidde may participate in beta-cell dysfunction associated with insulin-dependent diabetes mellitus.Insulin-dependent diabetes mellitus (IDDM) is an autoimmune disease characterized by specific destruction of the pancreatic islet beta cell (1). The destruction of beta cells is believed to be mediated by infiltrating lymphocytes. The ability of T cells to adoptively transfer diabetes in diabetesprone BB rats (2) and in the NOD mouse indicates that T cells participate in beta-cell destruction (3). Cytokines, released by infiltrating lymphocytes, have also been implicated as possible mediators of beta-cell destruction. Pretreatment of isolated rat islets with the cytokine human recombinant interleukin 1,B (IL-1*8) results in a concentration-and timedependent inhibition of glucose-stimulated insulin secretion that is followed by islet destruction after prolonged exposures to this cytokine (4, 5).The free-radical nitric oxide has been implicated as the cellular effector molecule that mediates the inhibitory and cytotoxic effects of IL-1,3 on rat islets (6). Pretreatment of rat islets for 18-24 hr with IL-1lB results in nearly complete inhibition of glucose-stimulated insulin secretion that is prevented by the nitric oxide synthase inhibitor...

IntroductionNitric oxide has recently been implicated as the effector molecule that mediates IL-1(3-induced inhibition of glucose-stimulated insulin secretion and (3-cell specific destruction. The pancreatic islet represents a heterogeneous cell population con-

Nitric oxide has recently been implicated as a cellular molecule that mediates interleukin-1 beta (IL-1 beta)-induced inhibition of glucose-stimulated insulin secretion by islets of Langerhans. In this study evidence is presented which demonstrates that islets contain both the cytokine inducible and the constitutive isoforms of nitric oxide synthase as determined by NADPH diaphorase staining and immunohistochemical localization. Untreated islets contain NADPH diaphorase activity, and the intensity of NADPH diaphorase staining is dramatically increased after culture for 18 hrs with IL-1 beta. Both control and IL-1 beta-induced NADPH diaphorase staining of islets is inhibited by the nitric oxide synthase inhibitor NG-monomethyl-L-arginine (NMMA). Importantly, approximately 60-70% of islet cells stained positive for NADPH diaphorase (under both IL-1 beta treated and control conditions), suggesting that a subset of islet cells contain nitric oxide synthase. The beta-cell appears to be the endocrine cell type which contains constitutive nitric oxide synthase as demonstrated by immunohistochemical co-localization of constitutive nitric oxide synthase and insulin. IL-1 beta is believed to stimulate the expression of cytokine inducible nitric oxide synthase because the synthetic glucocorticoid, dexamethasone, prevents IL-1 beta induced inhibition of glucose stimulated insulin secretion and cGMP accumulation by islets. Both dexamethasone, and the nitric oxide synthase inhibitors NMMA and aminoguanidine also prevent IL-1 beta induced islet degeneration. These results indicate that nitric oxide produced by the inducible isoform of nitric oxide synthase mediates cytokine induced islet dysfunction and destruction, and that the beta-cell is the islet endocrine cellular source of constitutive nitric oxide synthase.