Brian N. Finck

In Vivo and in Vitro Evidence for the Involvement of Tumor Necrosis Factor-α in the Induction of Leptin by Lipopolysaccharide

To examine the role of tumor necrosis factor-α (TNFα) in mediating leptin secretion during an immunological challenge, we studied the effects of lipopolysaccharide (LPS) and TNFα on leptin secretion in endotoxin-sensitive C3H/HeOuJ (OuJ) mice, endotoxin-insensitive C3H/HeJ (HeJ) mice, and primary adipocytes cultured from both. Intraperitoneal injection of LPS increased plasma concentrations of TNFα and leptin in OuJ mice, but not in HeJ mice, suggesting a causal relationship between the induction of TNFα and leptin. Consistent with this idea, ip injection of recombinant murine TNFα increased plasma leptin in both OuJ and HeJ mice. To determine whether TNFα induces leptin secretion by acting directly on fat cells, primary adipocytes from OuJ and HeJ mice were cultured in the presence of TNFα or LPS. Whereas LPS was without effect on leptin secretion by adipocytes, TNFα induced a marked increase in the cell supernatant leptin concentration. These data demonstrate that TNFα plays a role in regulating the inc...

Interleukin (IL)-10 inhibits IL-6 production in microglia by preventing activation of NF-κB

The purpose of this study was to determine if interleukin (IL)-10 inhibits lipopolysaccharide (LPS)-induced IL-6 production in microglia by inhibiting activation of nuclear factor-kappaB (NF-kappaB). N13 microglia (a murine microglial cell line) and primary microglia from neonatal mice were cultured in the presence or absence of LPS and increasing amounts of murine IL-10 for 24 h. As predicted, LPS treatment increased supernatant IL-6 concentration in both N13 and primary microglia cultures. Pretreatment with IL-10, however, decreased LPS-induced IL-6 secretion in a dose-dependent manner in both culture systems. Likewise, ribonuclease protection assays showed that LPS increased steady-state IL-6 mRNA levels, but that pretreatment with IL-10 blocked the LPS-induced increase in IL-6 mRNA. Because NF-kappaB is the predominant transcription factor responsible for IL-6 transcription in response to inflammatory stimuli, it was hypothesized that IL-10 inhibited IL-6 production by preventing nuclear translocation of NF-kappaB. Consistent with this idea, LPS increased nuclear translocation of NF-kappaB as assessed by gel mobility shift assay. Supershift assays and immunocytochemical staining showed that both the p50 and p65 subunits of NF-kappaB translocated from the cytoplasm to the nucleus upon LPS stimulation. Pretreatment with IL-10, however, inhibited LPS-induced activation of NF-kappaB. Furthermore, inhibition of NF-kappaB activity with tosyl-Phe-chloromethlyketone (a serine protease inhibitor that prevents degradation of the NF-kappaB-IkappaB complex), completely blocked LPS-induced IL-6 production. These data suggest that IL-10 inhibited IL-6 production in microglia by decreasing the activity of NF-kappaB and, therefore, extend what little is known of the intricate relationship between anti-inflammatory and inflammatory cytokines in the central nervous system.

Coincidental Changes in Behavior and Plasma Cortisol in Unrestrained Pigs after Intracerebroventricular Injection of Tumor Necrosis Factor-α1

The coincidental behavioral and physiological responses to inflammatory stimuli administered either peripherally or centrally were evaluated. In the first study, twenty castrated male pigs were injected ip with 0, 0.5, 5, or 50 μg/kg BW lipopolysaccharide (LPS). Body temperature was monitored telemetrically, and serial blood samples were collected via an indwelling jugular catheter for determination of plasma cortisol and tumor necrosis factor-α (TNF-α) concentrations. Sickness behaviors were measured during 10-min tests at 0, 2, 4, 8, 12, and 24 h post injection. The 5 and 50 μg/kg doses of LPS increased plasma concentrations of cortisol and TNF-α, while inducing anorexia, hypersomnia, and fever. In contrast, although 0.5 μg/kg LPS induced acute anorexia, hypersomnia, and fever, it did not increase plasma TNF-α; and the cortisol response was small and transient, suggesting the behavioral system in pigs is more responsive to LPS than the hypothalamic-pituitary-adrenal (HPA) axis. Because LPS-induced behav...

Tumor necrosis factor-α regulates secretion of the adipocyte-derived cytokine, Leptin

The seminal observation that secretion of the adipocyte‐derived hormone leptin was induced by inflammatory challenge has been expanded upon to demonstrate the importance of the pro‐inflammatory cytokines, especially tumor necrosis factor (TNF)‐α, in inflammatory hyperleptinemia. Initially, it was thought that cytokine‐induced hyperleptinemia might somehow be involved in the anorexia and cachexia that often accompany chronic infectious, neoplastic, and autoimmune disease. While the role of leptin in disease‐associated anorexia and cachexia appears tenuous in light of recent findings, there is evidence that the hyperleptinemia induced by cytokines is an integral part of the acute phase response and necessary for comprehensive immunocompetence. This hints at the existence of an integrated communication network, wherein the energy status of the animal impacts its ability to fight pathogens. Microsc. Res. Tech. 50:209–215, 2000.

Anorexia, weight loss and increased plasma interleukin-6 caused by chronic intracerebroventricular infusion of interleukin-1 β in the rat

Pro-inflammatory cytokines produced in the central nervous system (CNS) have been suggested to have a role in the anorexia and cachexia of disease. In the present study, the effects of chronic exposure of the CNS to interleukin-1beta (IL-1beta) on several indicators of cachexia were studied. Rats were prepared with an intracerebroventricular (i.c.v.) cannula and an osmotic minipump that delivered vehicle or 1.56 ng/h recombinant murine IL-1beta for 4 days. Food intake and body weight were determined daily during the 4-day infusion period and plasma IL-6 and corticosterone concentrations were determined from plasma collected postinfusion. Chronic i.c.v. infusion of IL-1beta resulted in a chronic reduction in food intake. Rats infused i.c.v. with IL-1beta ate less food each day compared to vehicle controls and, at the end of the 4-day infusion period, consumed an average of 17.2 g less. Intracerebroventricular infusion of IL-1beta also caused an immediate and substantial loss of body weight that was sustained throughout the infusion period. In addition, rats infused with IL-1beta had plasma levels of IL-6 double those of vehicle controls (401 pg/ml vs. 185 pg/ml). Plasma corticosterone concentrations were similar between treatments. These results suggest that chronic exposure of the CNS to cytokines such as IL-1beta may be sufficient to induce anorexia and cachexia.

Intracerebroventricular injection of lipopolysaccharide increases plasma leptin levels.

Leptin regulates adiposity by reducing caloric intake and increasing energy expenditure. Because loss of body weight is common during infectious, neoplastic, and autoimmune diseases of the central nervous system, we examined whether an injection of lipopolysaccharide (LPS) into the lateral cerebral ventricle increases circulating leptin levels in fasted mice. Centrally injected LPS (100 ng) induced a two-fold elevation in plasma leptin 6, 12, and 18 h post-injection. Peripheral injection of the same dose of LPS did not affect leptin secretion. This suggests that inflammatory stimuli localized in the CNS are sufficient to induce leptin secretion in the periphery. The induction of leptin by inflammatory stimuli in the brain may be part of a feed-back loop that contributes to anorexia and cachexia in many CNS-oriented diseases.