Peripheral anti-inflammatory actions of corticotropin-releasing factor

Steroid utility, immunotherapy, and brain tumor management: an update on conflicting therapies

Steroid use is a widely accepted practice for both the treatment and prevention of tumor-induced edema, but there are many unknowns regarding their current clinical utility with modern anti-tumor therapies. This decreases edema and relieves the symptomatic mass effect. There are clearly understood benefits and commonly accepted complications of methylprednisolone (MP) use, but the topic is recently controversial. With immunotherapy advancing, a robust immune response is crucial for full therapeutic efficacy. The immunosuppression of MP may interfere with future and current therapeutics relying on the integrity of the patient’s immune system. This further emphasizes the need for alternative agents to effectively treat tumor-induced cerebral edema. This review highlights the current clinical utility of steroids to treat brain tumor-related edema and the underlying pathophysiology. It also reviews details regarding different steroid formulations and dosing. Research available regarding concurrent steroid use with immunotherapy is detailed next, followed by alternatives to steroids and barriers to their adoption. Finally, this paper discusses pre-clinical findings and emerging treatments aimed to augment or replace steroid use.

Comparison of corticotropin-releasing factor, dexamethasone, and temozolomide: treatment efficacy and toxicity in U87 and C6 intracranial gliomas

PURPOSE/EXPERIMENTAL DESIGN: Treatment of cerebral tumors and peritumoral brain edema remains a clinical challenge and is associated with high morbidity and mortality. Dexamethasone is an effective drug for treating brain edema, but it is associated with well-documented side effects. Corticorelin acetate (Xerecept) or human corticotrophin-releasing factor (hCRF) is a comparatively new drug and has been evaluated in two orthotopic glioma models (U87 and C6), by a direct comparison with dexamethasone and temozolomide.

RESULTS

In vitro combination therapy and monotherapy showed a variable response in 6 different glioma cell lines. In vivo studies showed a dose-dependent effect of hCRF (0.03 and 0.1 mg/kg q12h) on survival of U87 intracranial xenograft-bearing animals [median survival: control--41 days (95% CI 25-61); "low-hCRF" 74.5 days (95% CI 41-88); "high-hCRF" >130 days (95% CI not reached)]. Dexamethasone treatment had no effect on survival, but significant toxicity was observed. A survival benefit was observed with temozolomide and temozolomide + hCRF-treated animals but with significant temozolomide toxicity. C6-bearing animals showed no survival benefit, but there were similar treatment toxicities. The difference in hCRF treatment response between U87 and C6 intracranial gliomas can be explained by a difference in receptor expression. RT-PCR identified CRF2r mRNA in U87 xenografts; no CRF receptors were identified in C6 xenografts.

CONCLUSIONS

hCRF was more effective than either dexamethasone or temozolomide in the treatment of U87 xenografts, and results included improved prognosis with long-term survivors and only mild toxicity. The therapeutic efficacy of hCRF seems to be dependent on tumor hCRF receptor (CRFr) expression. These results support further clinical assessment of the therapeutic efficacy of hCRF and levels of CRFr expression in different human gliomas.

Corticotropin releasing hormone and related peptides can act as bioregulatory factors in human keratinocytes

Following previous findings in human skin of the functional expression of genes for the corticotropin releasing hormone (CRH) receptor type 1 (CRH-R1) and CRH itself, we searched for local phenotypic effects for peptides related to CRH. We now report that CRH, sauvagine, and urocortin inhibit proliferation of human HaCaT keratinocytes in a dose-dependent manner. The peptides produced variable cyclic adenosine 3':5'-monophosphate stimulation, with CRH having the highest potency. Binding of iodine 125 CRH to intact keratinocytes was inhibited by increasing doses of CRH, sauvagine, or urocortin, all showing equal inhibitory potency. Immunocytochemistry identified CRH-R1 immunoreactivity in HaCaT keratinocytes. In conclusion, CRH (exogenous or produced locally) and the related urocortin and sauvagine peptides can modify human keratinocyte phenotype through a receptor-mediated pathway.

Sex steroid regulation of the inflammatory response: sympathoadrenal dependence in the female rat

To investigate the role of sex steroids in sex differences in the response of rats to the potent inflammatory mediator bradykinin (BK), we evaluated the effect of sex steroid manipulation on the magnitude of BK-induced synovial plasma extravasation (PE). The magnitude of BK-induced PE is markedly less in females. Ovariectomy of female rats increased BK-induced PE, and administration of 17beta-estradiol to ovariectomized female rats reconstituted the female phenotype. Castration in male rats decreased BK-induced PE, and administration of testosterone or its nonmetabolizable analog dihydrotestosterone reconstituted the male phenotype. The results of these experiments strongly support the role of both male and female sex steroids in sex differences in the inflammatory response. Because the stress axes are sexually dimorphic and are important in the regulation of the inflammatory response, we evaluated the contribution of the hypothalamic-pituitary-adrenal and the sympathoadrenal axes to sex differences in BK-induced PE. Neither hypophysectomy nor inhibition of corticosteroid synthesis affected BK-induced PE in female or male rats. Adrenal denervation in females produced the same magnitude increase in BK-induced PE as adrenalectomy or ovariectomy, suggesting that the adrenal medullary factor(s) in females may account for the female sex steroid effect on BK-induced PE. Furthermore, we have demonstrated that in female but not male rats, estrogen receptor alpha immunoreactivity is present on medullary but not cortical cells in the adrenal gland. These data suggest that regulation of the inflammatory response by female sex steroids is strongly dependent on the sympathoadrenal axis, possibly by its action on estrogen receptors on adrenal medullary cells.

Corticotropin-Releasing Factor Receptor 1 in Mouse Spleen: Expression After Immune Stimulation and Identification of Receptor-Bearing Cells

A specific polyclonal Ab against the N-terminal domain of corticotropin-releasing factor (CRF) receptor, type 1 (CRF-R1), was employed to an immunohistochemical analysis of the spleen from naive mice and mice exposed to an immune challenge. Cell types stained with anti-CRF-R1 Ab were identified by their nuclear shapes and colocalization with the cell type-specific markers ER-MP58, ER-MP20, Moma-1, Moma 2, anti-CD3e mAbs, and anti-Ig Ab. Only a few clusters of CRF-R1+ cells were found in spleen sections of naive mice at sites typical for granulopoietic islands. However, a 17-fold increase in the mean number of CRF-R1+ cells was noted within hours following a challenge of acute systemic inflammation induced by i.p. administration of LPS. The majority of these cells were identified as mature neutrophils. CRF-R1 was shown to mediate suppression of the IL-1β secretion by these cells. However, at later time points a large number of granulocyte-macrophage precursors was strongly labeled with anti-CRF-R1 Ab. Western blot analysis of splenic membranes from animals treated with LPS revealed a m.w. of approximately 70,000 for CRF-R1. Subcellular staining patterns were suggestive for the predominant localization of CRF-R1 on granule membranes. CRF-R1 mRNA was detected in spleen but not in bone marrow and peripheral blood leukocytes from naive mice. Thus, it was indicated that CRF-R1 was not produced constitutively by mature or immature neutrophils. Its production was rather triggered by inflammatory stimuli.

Corticotropin-releasing hormone inhibits lowering of interstitial pressure in rat trachea after neurogenic inflammation

Increased negativity of interstitial fluid pressure (Pif) is a key determinant of edema formation after tissue injury. In this study, we addressed the question of whether the anti-inflammatory effects of corticotropin-releasing hormone (CRH) shown by others are mediated by changes in interstitial fluid pressure. CRH, 25 to 50, but not 5 and 11 microg/kg s.c., administered 45 min before antidromic stimulation of the vagal nerve inhibited the lowering of interstitial fluid pressure in rat trachea produced by nerve stimulation. This inhibitory effect of CRH was blocked by pretreatment with the CRH receptor antagonist, alpha-helical CRH-(9-41), 0.15 mg/kg i.v., administered 5 min before CRH. These results suggest that CRH receptors modulate the structural integrity of the extracellular matrix in rat trachea for its response to inflammatory stimuli.

D-amino acid-substituted analogs of corticotropin-releasing hormone (CRH) and urocortin with selective agonist activity at CRH1 and CRH2beta receptors

The activities of corticotropin-releasing hormone (CRH)-related peptides and several analogs were examined in cells transfected with either CRH1 or CRH2beta receptors, in suppression of heat-induced rat paw edema in pentobarbital-anesthetised animals and in stimulation of release of immunoreactive corticotropin (ir-ACTH) from rat anterior pituitary tissue in vitro. The peptides tested were human/rat (h/r)-CRH, r-urocortin, h-urocortin, white sucker fish or maggy sole urotensin I and some analogs of these peptides substituted with D-amino acids at residues 4 (urocortin), 5 (CRH and urotensin I) and 20 (CRH). In cells transfected with CRH1 receptors, these peptides were similar in potency in stimulation of cAMP accumulation. By contrast, at CRH2beta receptors peptides of the urocortin and urotensin series were more potent than h/r-CRH while [D-Glu20]-h/r-CRH was 6.5-fold less active than h/r-CRH. I.v. administration of h/r-CRH or related peptides 10 min prior to a thermal stimulus produced a significant dose-dependent inhibition of rat paw edema formation. Comparison of the ED50's showed that urocortins ([D-Ser4]-h-urocortin, h-urocortin, [D-Pro4]-r-urocortin, r-urocortin) were approximately 2 to 3 times more active than h/r-CRH, but [D-Glu20]-h/r-CRH was 18.5-fold less active. In the assay for ir-ACTH release, the activity of h/r-CRH and [D-Glu20]-h/r-CRH was similar but [D-Pro5]-h/r-CRH and [D-Pro4]-r-urocortin was less potent than the native peptide. These results provide further evidence that D-amino acid substitution at residue 20 reduces the potency of h/r-CRH at endogenous (anti-edema effect) and transfected (cAMP accumulation) CRH2beta receptors whilst activity at the CRH1 receptor is retained (ACTH-release and cAMP accumulation). On the other hand substitutions at residues 4 or 5 in r-urocortin or h/r-CRH respectively appear to decrease activity at CRH1 but not CRH2beta receptors The modified CRH and urocortin analogs described here may provide clues for the further design of receptor selective ligands.

Corticotropin releasing factor-like immunoreactivity in afferent projections to the sacral spinal cord of the cat

Distribution and origin of corticotropin releasing factor (CRF) in the thoraco-lumbar and sacral spinal cord of the cat has been studied using immunohistochemical method. CRF immunoreactive (CRF-IR) nerve fibers and terminals were most prominent in dorsal part of sacral spinal cord. In the sacral segments of the spinal cord, immunoreactivity for CRF was detected in a prominent bundle of axons and varicosities extending from Lissauer's tract (LT) along the lateral edge of the superficial dorsal horn (laminae I and II) to laminae V at the base of the dorsal horn. Individual CRF-IR fibers passed from the bundle in ventral medial and ventrolateral directions to the dorsal commissure and the sacral preganglionic nucleus (SPN), respectively. The bundle of CRF-IR axons closely resembled vasoactive intestinal polypeptide (VIP) containing fibers in LT and on the lateral edge of the dorsal horn. Sacral dorsal root transection eliminated both the CRF and VIP fiber staining in the dorsal horn. Spinal transection at the T12-T13 segmental level did not influence the CRF- or VIP-IR. Less intense CRF-IR was also present in fibers in: (1) the dorsal lateral funiculus adjacent to LT, (2) the superficial layers of the dorsal horn and intermediolateral nucleus at thoracolumbar spinal levels, (3) the ventral horn, including Onuf's nucleus, (4) the intermediate gray matter including the dorsal gray commissure, and (5) the SPN. The similarity in the distribution of CRF-IR and pelvic nerve afferent projections in the sacral spinal cord raises the possibility that CRF may be a transmitter in afferent neurons innervating the pelvic viscera.