Inhibition of vagally mediated immune-to-brain signaling by vanadyl sulfate speeds recovery from sickness

Abstract

To the ill patient with diabetes, the behavioral symptoms of sickness such as fatigue and apathy are debilitating and can prevent recuperation. Here we report that peripherally administered insulin-like growth factor 1 (IGF-1) attenuates LPS-dependent depression of social exploration (sickness) in nondiabetic (db/+) but not in diabetic (db/db) mice. We show that the insulin/IGF-1 mimetic vanadyl sulfate (VS) is effective at augmenting recovery from sickness in both db/+ and db/db mice. Specifically, peak illness was reached at 2 h for both VS and control animals injected with LPS, and VS mice recovered 50% faster than non-VS-treated animals. Examination of the mechanism of VS action in db/+ mice showed that VS paradoxically augmented peritoneal macrophage responsivity to LPS, increasing both peritoneal and ex vivo macrophage production of IL-1beta and IL-6 but not TNF-alpha. The effects of VS in promoting recovery from sickness were not restricted to LPS, because they were also observed after direct administration of IL-1beta. To explore the possibility that VS impairs immune-to-brain communication via vagal afferents, the vagally mediated satiety-inducing effects of cholecystokinin 8 were tested in db/+ mice. Cholecystokinin decreased food intake in saline-injected mice but not in VS-treated mice. VS also inhibited LPS-dependent up-regulation of IL-1beta and IL-6 mRNA in the brain, while increasing by 50% the cerebral expression of transcripts of the specific antagonist of IL-1 receptors IL-1RA and IL-1R2. Taken together, these data indicate that VS improves recovery from LPS-induced sickness by blocking vagally mediated immune-to-brain signaling and by up-regulating brain expression of IL-1beta antagonists.

Fig. 1.

VS improves sickness in response to LPS. (A) db/+ or db/db mice were pretreated with or without i.p. IGF-1 (1 μg). Sixty minutes later, LPS (5 μg) or vehicle control (PBS) was administered i.p. SE was measured at 8 h after LPS injection. Results are expressed as a percentage of the pre-LPS SE baseline measurement and shown as means ± SEM; n = 4(*, P < 0.05). (B) db/db mice, as indicated, were treated with VS (0.5 mg/kg per day) or vehicle control (PBS) for 7 days before i.p. injection of LPS (5 μg). SE was measured immediately before and at 2, 4, 8, 12, and 24 h after injection. Results are expressed as percentages of the baseline measurement and shown as means ± SEM; n = 6. *, P < 0.05 VS-LPS vs. PBS-LPS. (C) db/+ were treated with VS (0.5 mg/kg) or vehicle control (PBS) for 7 days before i.p. injection of LPS (100 μg/kg). SE was measured immediately before and at 2, 4, 8, 12, and 24 h after injection. Results are expressed as percentages of the baseline measurement and shown as means ± SEM; n = 5. *, P < 0.05 VS-LPS vs. PBS-LPS.

Fig. 2.

VS increases peritoneal production of IL-1β and IL-6 in response to LPS. Mice (db/+) were treated with VS (0.5 mg/kg) or vehicle control (Control) for 7 days before i.p. injection of LPS (100 μg/kg). At the times indicated, peritoneal IL-1β (A) and IL-6 (B) were assayed by ELISA. Data in A represent means ± SEM; n = 5. *, P < 0.05 VS vs. control.

Fig. 3.

Peripheral to central neural communication is blunted by VS. (A) Mice (db/+) were treated with VS (0.5 mg/kg) or vehicle control (PBS) for 7 days before i.p. injection of IL-1β (2 μg). SE was measured immediately before and at 2, 4, 8, 12, and 24 h after injection. Results are expressed as percentages of the baseline measurement and shown as means ± SEM; n = 5. *, P < 0.05 VS-IL-1β vs. PBS-IL-1β. (B) Mice (db/+) were treated with or without VS as above. Mice were then fasted for 16 h before administration of CCK-8 (CCK). Food was reintroduced, and food intake was measured at 60 and 90 min. Data represent means ± SEM; n = 8. * and +, P < 0.05.

Fig. 4.

VS inhibits LPS-dependent up-regulation of IL-1β and IL-6 in the brain. (A and B) Mice (db/+) were treated with VS (0.5 mg/kg) or vehicle control (PBS) for 7 days before i.p. injection of LPS (100 μg/kg). At the times indicated, total RNA was extracted from whole brains. Real-time RT-PCR was used to quantify IL-1β (A) and IL-6 (B) mRNAs relative to that of β actin. Results are expressed as relative change in mRNA expression (ΔmRNA) and are shown as means ± SEM; n = 5. *, P < 0.05 VS-LPS vs. PBS-LPS.

Fig. 5.

VS up-regulates IL-1RA and IL-1R2 in the brain. Mice (db/+) were treated with VS (0.5 mg/kg) or vehicle control (PBS) for 7 days. Total RNA was extracted from whole brains. Real-time RT-PCR was used to quantify IL-1RA and IL-1R2 mRNAs relative to that of β actin. Results are expressed as relative change in mRNA expression (ΔmRNA) and shown as means ± SEM; n = 5. *, P < 0.05 VS vs. PBS.