Interleukin-1 stimulates the central release of corticotropin-releasing hormone in the primate

Proopiomelanocortin, agouti-related protein, and leptin in human cerebrospinal fluid: correlations with body weight and adiposity

Leptin and its neuronal targets, which produce proopiomelanocortin (POMC) and agouti-related protein (AgRP), regulate energy balance. This study characterized leptin, POMC, and AgRP in the cerebrospinal fluid (CSF) of 47 healthy human subjects, 23 lean and 24 overweight/obese (OW/OB), as related to BMI, adiposity, plasma leptin, soluble leptin receptor (s-OB-R), and insulin. POMC was measured since the POMC prohormone is the predominant POMC peptide in CSF and correlates with hypothalamic POMC in rodents. Plasma AgRP was similarly characterized. CSF leptin was 83-fold lower than in plasma and correlated strongly with BMI, body fat, and insulin. The relative amount of leptin transported into CSF declined with increasing BMI, ranging from 4.5 to 0.52%, consistent with a saturable transport mechanism. CSF sOB-R was 78-fold lower than in plasma and correlated negatively with plasma and CSF leptin. CSF POMC was higher in lean vs. OW/OB subjects (P < 0.001) and correlated negatively with CSF leptin (r = -0.60, P < 0.001) and with plasma leptin, insulin, BMI, and adiposity. CSF AgRP was not different in lean vs. OW/OB; however, plasma AgRP was higher in lean subjects (P = 0.001) and correlated negatively with BMI, adiposity, leptin, insulin, and HOMA (P < 0.005). Thus, CSF measurements may provide useful biomarkers for brain leptin and POMC activity. The striking negative correlation between CSF leptin and POMC could be secondary to leptin resistance and/or neuronal changes associated with obesity but may also indicate that POMC plays a primary role in regulating body weight and adiposity. The role of plasma AgRP as a neuroendocrine biomarker deserves further study.

Neuroprotective properties of tianeptine: interactions with cytokines

Tianeptine is an antidepressant with proven clinical efficacy and effects on hippocampal plasticity. Hypoxia increased lactate dehydrogenase (LDH) release from cortical neuronal cultures, and tianeptine (1, 10 and 100 microM) inhibited LDH release as efficiently as the N-methyl-D-aspartate (NMDA) antagonist, MK-801. However, tianeptine did not block apoptosis in cultured cortical neurones caused by NMDA, but reduced apoptosis when interleukin-1beta (IL-1beta) was included with NMDA. In 5-day old mice, intracerebral injection of ibotenate induced reproducible lesions in cortex and white matter. Lesion size was markedly reduced by co-administration of MK-801 (1 mg/kg i.p.) but neither by tianeptine or its enantiomers administered acutely (1, 3 or 10 mg/kg i.p.) nor by tianeptine administered chronically (10 mg/kg i.p. for 5 days). Chronic administration of IL-1beta (10 ng/kg i.p. for 5 days) prior to ibotenate injection exacerbated lesion size in cortex and white matter, and this exacerbation was prevented by chronic pre-treatment with tianeptine (10 mg/kg i.p.) or by acute administration of tianeptine (10 mg/kg i.p.) concomitantly with ibotenate. Thus tianeptine has neuroprotective effects against hypoxia in tissue culture and against the deleterious effects of cytokines in cortex and white matter, but not against NMDA receptor-mediated excitotoxicity.

Potential mechanisms of interleukin-1 involvement in cerebral ischaemia

Interleukin-1 (IL-1) has pleiotropic actions in the central nervous system. During the last decade, a growing corpus of evidence has indicated an important role of this cytokine in the development of brain damage following cerebral ischaemia. The expression of IL-1 in the brain is dramatically increased during the early and chronic stage of infarction. The most direct evidence that IL-1 contributes significantly to ischaemic injury is that (1) central administration of IL-1beta exacerbates brain damage, and (2) injection or over-expression of interleukin-1 receptor antagonist, and blockade of interleukin-1beta converting enzyme activity reduce, dramatically, infarction and improve behavioural deficit. The mechanisms underlying IL-1 actions in stroke are not definitively elucidated, and it seems likely that its effects are mediated through stimulation and inhibition of wide range of pathophysiological processes.

Intracerebroventricular injection of interleukin-1 stimulates the release of high levels of interleukin-6 and interleukin-1 receptor antagonist into peripheral blood in the primate

Previous studies in the rodent have shown that the cytokine IL-1 can act within the brain to influence peripheral IL-6 secretion. In order to determine if such an interaction occurs in the primate, we have compared the effects of intracerebroventricular vs. intravenous injection of IL-1beta on the release of IL-6 into the peripheral circulation of the monkey. The effects of i.c.v. IL-1beta on the release of the IL-1 receptor antagonist (IL-1ra) were studied in parallel. For comparison, we have also measured the release of both IL-6 and IL-1ra into lumbar CSF after i.c.v. IL-1beta injection. Ten ovariectomized rhesus monkeys with indwelling lateral ventricular and peripheral venous cannulae were studied. Human rIL-1beta (400 ng) was infused either i.c.v. or i.v. over 30 min and blood samples were collected for IL-6 and IL-1ra measurement by monoclonal human ELISAs. Although both i.c.v. and i.v. IL-1beta stimulated IL-6 and IL-1ra release into peripheral blood, the stimulation was much more profound after i.c.v. injection (p < 0.001). Peak IL-6 levels were 2010 +/- 590 pg/ml after i.c.v. IL-1beta compared to 243 +/- 60 pg/ml after i.v. IL-1beta. Peak IL-1ra levels were 61,310 +/- 16,190 pg/ml after i.c.v. IL-1beta compared to 18,175 +/- 4270 pg/ml after i.v. IL-1beta. There was no significant effect of an i.c.v. saline infusion on peripheral IL-6 or IL-1ra levels. In four animals, lumbar CSF was collected 7 h after i.c.v. IL-1beta injection. The mean concentration of IL-6 in CSF was 103, 570 +/- 13,780 pg/ml after i.c.v. IL-1beta vs. 224 +/- 190 pg/ml after i.c.v. saline injection; IL-1ra was 47,460 +/- 6290 pg/ml vs. 1040 +/- 550 pg/ml. As expected, both i.c.v. and i.v. IL-beta stimulated ACTH and cortisol release; the stimulation was significantly greater after i.c.v. compared to i.v. administration (p < 0.001). Thus, in the monkey, i.c.v. injection of IL-1beta stimulates the release of large amounts of IL-6 and IL-1ra into the CSF and the peripheral circulation. Both IL-6 and IL-1ra were released into the peripheral circulation to a much greater extent after i.c.v. compared to i.v. IL-1beta infusion. These studies provide further support in the primate for a mechanism by which inflammation within the brain could induce a variety of systemic responses.

Cytokine-induced transcription of protein-tyrosine-phosphatases in human astrocytoma cells

Interleukin-1 (IL-1) and Tumor Necrosis Factor-a (TNFalpha) are potent mediators of inflammatory reactions in the brain. Although much is known about the effects of IL-1 on expression of secretory proteins, few studies have addressed the question of a selective, IL-1-dependent expression of genes involved in neuromodulatory effects of inflammation. Protein-tyrosine-phosphatases (PTP's) have been shown to regulate signal transduction and adhesion processes in the developing nervous system. They are candidates for inflammation-induced neuromodulation. Therefore, we investigated if IL-1 regulates expression of PTP's. We applied a DNA-fingerprinting method based on the PCR-amplification of conserved domains of gene families and observed IL-1-dependent induction of two PTP's, cytoplasmic PTPvarepsilon and receptor-PTPgamma, RPTPgamma, in human U373-MG astrocytoma cells. Using Northern blot analysis, we confirmed this result and also show that in addition to IL-1, TNFalpha but not IL-6 induces the transcription of cytoplasmic PTPvarepsilon and RPTPgamma in human astrocytoma cells. Given the important role for PTP's in neuromodulatory aspects such as axonal guidance and neurite outgrowth, cytokine-induced induction of PTP's may play an important pathenogenic role in the development of chronic inflammatory diseases in the brain.

Stress-related disturbances of the menstrual cycle

Stress is a common cause of hypothalamic amenorrhoea. In our laboratory, we have studied the effects of an inflammatory-like stress on gonadotropin secretion and on the menstrual cycle in a nonhuman primate model. In this short review, we summarize some of our findings regarding the mechanisms whereby stress induces disturbances of reproductive function. Our data indicate that the hypothalamic-pituitary-adrenal axis, through the release of corticotropin-releasing hormone and vasopressin, plays a mediatory role. One type of action is exerted through a central process resulting in the inhibition of the gonadotropin-releasing hormone pulse generator. The other type is mediated by a peripheral pathway stimulatory to gonadotropin secretion. Activation of one or the other pathway is determined by the ovarian endocrine milieu. Both actions presumably result in deleterious effects on the menstrual cycle.