Inhibition of peroxisome-proliferator-activated receptor (PPAR)alpha by MK886

Although MK886 was originally identified as an inhibitor of 5-lipoxygenase activating protein (FLAP), recent data demonstrate that this activity does not underlie its ability to induce apoptosis [Datta, Biswal and Kehrer (1999) Biochem. J. 340, 371--375]. Since FLAP is a fatty-acid binding protein, it is conceivable that MK886 may affect other such proteins. A family of nuclear receptors that are activated by fatty acids and their metabolites, the peroxisome-proliferator-activated receptors (PPARs), have been implicated in apoptosis and may represent a target for MK886. The ability of MK886 to inhibit PPAR-alpha, -beta and -gamma activity was assessed using reporter assay systems (peroxisome-proliferator response element--luciferase). Using a transient transfection system in monkey kidney fibroblast CV-1 cells, mouse keratinocyte 308 cells and human lung adenocarcinoma A549 cells, 10--20 microM MK886 inhibited Wy14,643 activation of PPAR alpha by approximately 80%. Similar inhibition of PPAR alpha by MK886 was observed with a stable transfection reporter system in CV-1 cells. Only minimal inhibitory effects were seen on PPAR beta and PPAR gamma. MK886 inhibited PPAR alpha by a non-competitive mechanism as shown by its effects on the binding of arachidonic acid to PPAR alpha protein, and a dose-response study using a transient transfection reporter assay in COS-1 cells. An assay assessing PPAR ligand-receptor interactions showed that MK886 prevents the conformational change necessary for active-complex formation. The expression of keratin-1, a protein encoded by a PPAR alpha-responsive gene, was reduced by MK886 in a culture of mouse primary keratinocytes, suggesting that PPAR inhibition has functional consequences in normal cells. Although Jurkat cells express all PPAR isoforms, various PPAR alpha and PPAR gamma agonists were unable to prevent MK886-induced apoptosis. This is consistent with MK886 functioning as a non-competitive inhibitor of PPAR alpha, but may also indicate that PPAR alpha is not directly involved in MK886-induced apoptosis. Although numerous PPAR activators have been identified, the results show that MK886 can inhibit PPAR alpha, making it the first compound identified to have such an effect.

Fatty acid oxidation and signaling in apoptosis

It is well established that fatty acid metabolites of cyclooxygenase, lipoxygenase (LOX), and cytochrome P450 are implicated in essential aspects of cellular signaling including the induction of programmed cell death. Here we review the roles of enzymatic and non-enzymatic products of polyunsaturated fatty acids in controlling cell growth and apoptosis. Also, the spontaneous oxidation of polyunsaturated fatty acids yields reactive aldehydes and other products of lipid peroxidation that are potentially toxic to cells and may also signal apoptosis. Significant conflicting data in terms of the role of LOX enzymes are highlighted, prompting a re-evaluation of the relationship between LOX and prostate cancer cell survival. We include new data showing that LNCaP, PC3, and Du145 cells express much lower levels of 5-LOX mRNA and protein compared with normal prostate epithelial cells (NHP2) and primary prostate carcinoma cells (TP1). Although the 5-LOX activating protein inhibitor MK886 killed these cells, another 5-LOX inhibitor AA861 hardly showed any effect. These observations suggest that 5-LOX is unlikely to be a prostate cancer cell survival factor, implying that the mechanisms by which LOX inhibitors induce apoptosis are more complex than expected. This review also suggests several mechanisms involving peroxisome proliferator activated receptor activation, BCL proteins, thiol regulation, and mitochondrial and kinase signaling by which cell death may be produced in response to changes in non-esterified and non-protein bound fatty acid levels. Overall, this review provides a context within which the effects of fatty acids and fatty acid oxidation products on signal transduction pathways, particularly those involved in apoptosis, can be considered in terms of their overall importance relative to the much better studied protein or peptide signaling factors.

Transcriptional regulation of intracellular IL-1 receptor antagonist gene by IL-1 alpha in primary mouse keratinocytes

The inflammatory cytokine IL-1alpha mediates inflammatory reactions in skin and up-regulates the expression of other proinflammatory genes. We previously found that IL-1alpha also increases steady state mRNA levels for intracellular IL-1 receptor antagonist (icIL-1Ra) in primary mouse keratinocytes; however, the mechanism for this was unknown. Here we show that increased expression in primary keratinocytes is due to increased rates of transcription. To study the transcriptional regulation of icIL-1Ra expression induced by IL-1alpha, we functionally characterized 4.5 kb of the 5'-flanking region of the human icIL-1Ra gene. Deletion analysis showed that regulatory elements were contained in the -598- and -288-bp region upstream of the transcription start site. Then we investigated cis- and trans-acting factors required for icIL-1Ra expression and found that a NF-IL-6 site and a NF-kappaB site in the icIL-1Ra promoter were responsible for IL-1alpha-induced icIL-1Ra expression. Moreover, gel shift assays and cotransfection experiments showed that CCAAT/enhancer-binding proteins alpha, beta, and p65 bind to the NF-IL-6 site and NF-kappaB site, respectively, and functionally trans-activate the icIL-1Ra promoter. Finally, mutational analysis confirmed that these elements were both essential for maximal transcription induced by IL-1alpha.

Fatty acid release and oxidation are factors in lipoxygenase inhibitor-induced apoptosis

MK886, an inhibitor of 5-lipoxygenase activating protein (FLAP), and the lipoxygenase (LOX) inhibitors baicalein and nordihydroguaiaretic acid (NDGA), induce apoptosis by mechanisms independent of both LOX and FLAP. One possible mechanism for these agents is through an effect on the binding of fatty acids to LOX and fatty acid binding proteins resulting in increased intracellular levels of unbound fatty acids, particularly arachidonic acid (AA), that in turn, activate apoptosis signaling pathways either directly or following oxidation. In FL5.12 murine pro-B lymphocytic cells, exogenous fatty acids induced apoptosis proportional to their degree of unsaturation. MK886, baicalein, and NDGA significantly enhanced the release of [3H]-AA two to threefold within 2 h and induced apoptosis by 8 h. Neither MK886-induced AA release, nor apoptosis were affected by quinacrine, a phospholipase A2 inhibitor. The presence of peroxides 1 h after treatment of FL5.12 cells with these agents was evident by a two to threefold increase in the ferrous oxidation-xylenol orange (FOX) assay as well as dichlorofluorescein fluorescence measured with flow cytometry. Isoprostane formation, an additional index of lipid peroxidation, was increased threefold by 2 h, and fourfold at 4 h after MK886 or baicalein, but not after NDGA. Antioxidants were able to protect against NDGA-induced apoptosis but had no effect on baicalein and resulted in enhanced apoptosis with MK886. These data support the hypothesis that release of fatty acids and generation of oxidized species contribute to apoptosis induced by these LOX inhibitors, but that more complex mechanisms are likely involved.

Role of intracellular interleukin-1 receptor antagonist in skin carcinogenesis

Interleukin 1 (IL-1) is a major mediator of inflammation and exerts pleiotropic effects on many systems. To elucidate the role of its endogenous inhibitor, intracellular IL-1 receptor antagonist (icIL-1Ra), in mouse skin, we produced an icIL-1Ra-overexpressing skin carcinoma cell line (icIL-1Ra-JWF2). Altered expression of icIL-1Ra did not change IL-1alpha mRNA levels in these transfected cells. In icIL-1Ra-JWF2 cells, however, cyclooxygenase-2 mRNA levels were dramatically reduced and shown to be transcriptionally regulated by icIL-1Ra. To determine the effect of icIL-1Ra on cell proliferation, cell counts were done 24 h after plating equal numbers of cells. Cells from three icIL-1Ra-JWF2 clones showed significantly reduced growth rates compared with parental JWF2 cells. We subcutaneously injected five independent clones of icIL-1Ra-JWF2 cells into nude mice and measured the tumor doubling time by weekly measurements of tumor volume. IcIL-1Ra appeared to significantly slow the growth of tumors in vivo. Collectively these observations suggest that IL-1Ra has antiproliferative effects in murine skin carcinoma cells.

Regulation of transcription of the intracellular interleukin-1 receptor antagonist gene by AP-1 in mouse carcinoma cells

Interleukin-1 receptor antagonist (IL-1Ra) is involved in many processes, including epidermal inflammation and hyperplasia after irritation or injury. However, the mechanism by which intracellular IL-1Ra (icIL-1Ra) expression is regulated in mouse keratinocytes has not been reported. We found that the CH72 mouse carcinoma cell line constitutively expresses the icIL-1Ra mRNA. To study the transcriptional factors responsible for the constitutive expression of icIL-1Ra, we functionally characterized 4.5 kb of the 5' flanking region of the human icIL-1Ra gene in these cells. We first demonstrated that icIL-1Ra expression in these cells was regulated at the level of transcription. Deletion analysis of the promoter showed that regulatory elements for constitutive expression were located -158 to -49 bp upstream of the transcription start site for icIL-1Ra. We investigated the cis- and trans-acting factors required for icIL-1Ra expression. An activating protein-1 (AP-1) site was identified as the positive regulatory element necessary for the constitutive expression of the icIL-1Ra promoter in CH72 cells. Moreover, electrophoretic mobility shift assay and cotransfection experiments showed that c-jun and c-fos proteins bound to the AP-1 site and functionally transactivated the icIL-1Ra promoter in mouse carcinoma CH72 cells.

Effect of spray-dried yogurt and lactic acid bacteria on the initiation and promotion stages of chemically induced skin carcinogenesis in mice

The effects of dietary spray-dried yogurt powder product (YPP) and two strains of lactic acid bacteria on the initiation and promotion stages of carcinogenesis were investigated using the 7,12-dimethylbenz[a]anthracene (DMBA)-12-O-tetradecanoylphorbol-13-acetate (TPA) mouse skin carcinogenesis model. In two independent studies, Sencar mice were fed a diet containing 86%, 43%, or 0% YPP or the 0% YPP diet supplemented with viable cultures of Lactobacillus acidophilus or bifidobacteria. Animals were initiated with a single topical application of DMBA (10 nmol). Promotion began three weeks later with twice weekly treatment of TPA (1 microgram/200 microliters acetone). During the initiation study (Study 1) the experimental diets were fed for four weeks before and one week after DMBA treatment. All mice were then switched to the AIN-76 diet. For the promotion study (Study 2) the experimental diets were begun one week after initiation and fed during the remainder of the study. Gross appearance of tumors was assessed weekly. No statistically significant differences in body weight or food disappearance were observed among the diet groups during the studies. For Studies 1 and 2, final histologically verified papilloma incidence and multiplicity and carcinoma incidence were not statistically different. These data suggest that different levels of YPP or lactic acid bacteria fed during the initiation or promotion stage of carcinogenesis do not significantly affect chemically induced skin tumor development.

P-568 The effect of recombinant hCG on FSH-induced ovarian stimulation in rats depends on the FSH dose and can be detrimental at high concentrations

Study question

What is the effect of choriogonadotropin beta (CG beta) on FSH-induced ovarian stimulation and multifollicular development in a rat model?

Summary answer

CG beta dose-dependently potentiates effects of low-to-mid FSH doses but has inhibitory effects at high concentrations: optimal CG beta/FSH ratio depends on the FSH dose.

What is known already

Similarly to follitropin delta (rFSH), CG beta (FE 999302) is a novel recombinant hCG purified from the human PER.C6®cell line. A recent placebo-controlled trial in women undergoing ovarian stimulation with follitropin delta demonstrated that the addition of 1 to 12 µg CG beta reduced the number of intermediate follicles and related hormones. This observation required further preclinical research to (1) evaluate whether the pharmacology of CG beta at LH/CGR was different than other hCG forms used in the clinic and/or (2) assess the effect of high concentrations of hCG and different hCG/FSH ratios on multiple follicular development and follicle atresia.

Study design, size, duration

Signaling properties of CG beta and other LH/hCG forms were compared at downstream pathways of LH/CGR in recombinant systems and human granulosa cells. To evaluate the effects of FSH±hCG in vivo, juvenile female rats were injected subcutaneously twice daily with follitropin delta ± CG beta/alfa for three days followed by an ovulatory dose of hCG. Oviducts were then collected for oocyte enumeration, ovaries and uteri were weighed, and ovaries were fixed for histological analysis.

Participants/materials, setting, methods

The pharmacology of CG beta and other LH/hCG forms was evaluated in a cAMP assay in human granulosa cells from follicular fluid from IVF patients and in recombinant systems, at the Gs, Gq and arrestin pathways. In the rat model, a dose response of follitropin delta (Rekovelle) was first evaluated, followed by evaluation of the dose-dependent effects of CG beta (0.00117-2.4 µg/kg), or CG alfa (Ovidrel/Ovitrelle), in combination with 1, 3 or 10 µg/kg rFSH.

Main results and the role of chance

The in vitro pharmacology (potency and efficacy) of CG beta was similar to recombinant LH, urinary hCG and recombinant hCG (CG alfa) tested at all proximal pathways evaluated downstream of LH/CGR as well as in human granulosa cells.

In vivo, treatment with follitropin delta induced a bell-shaped dose-response curve for oocyte release with a maximum response of 40-50 oocytes at 8-10 µg/kg follitropin delta dose.

The addition of CG beta dose-dependently potentiated the effects at low-to-mid follitropin delta doses but had inhibitory effects on the number of ovulated oocytes at high CG beta concentrations. The lowest CG beta dose that clearly reduced the number of ovulated oocytes was 2.4, 0.6 and 0.3 µg/kg in combination with a fixed dose of 1, 3 and 10 µg/kg follitropin delta, respectively, which indicated that the optimal hCG/FSH ratio and corresponding hCG efficacious dose was inversely related to the FSH dose. There was no difference between CG beta and CG alfa for the dose effect on the number of ovulated oocytes or ovarian weight. Histology data indicated many cystic follicles following high CG beta exposure which may represent atretic follicles prior to triggering follicular maturation and ovulation.

Limitations, reasons for caution

This is the first study demonstrating that the FSH dose in combination with the hCG dose determines the effect on multiple follicle growth, ovulation, and atresia. These observations need to be confirmed in clinical research, as doses and ratios applied in the rat cannot be extrapolated to the clinical setting.

Wider implications of the findings

A better understanding of the effect of different FSH to hCG ratios will help to improve current mixed protocols and design future recombinant combination products providing the optimal treatment outcome for each individual patient.

Trial registration number

not applicable

Altered expression of interleukin-1 receptor antagonist in different stages of mouse skin carcinogenesis

Interleukin-1 receptor antagonist (IL-1Ra) is an endogenous inhibitor of interleukin-1. The expression of IL-1Ra and interleukin-1alpha (IL-1alpha) was measured in murine epidermis after treatment with tumor promoters and in tumor cell lines. A single treatment with three different tumor promoters (12-O-tetradecanoylphorbol-13-acetate (TPA), anthralin, and thapsigargin) induced IL-1Ra mRNA with different kinetics in mouse skin. The expression of IL-1Ra mRNA also was induced by TPA and IL-1alpha in a dose-related and time-dependent manner in cultured mouse keratinocytes. Expression of IL-1Ra mRNA peaked 6 h after treatment. Both IL-1Ra and IL-1alpha protein and IL-1Ra and IL-1alpha mRNA were measured in various keratinocyte tumor cell lines (C50, MT1/2, HEL30, JWF2, CH72, and BPCC2). The expression of IL-1alpha was increased in papilloma and squamous cell carcinoma cell lines. IL-1Ra protein also was increased in nontumorigenic and papilloma cell lines; however, the expression was dramatically reduced in some carcinoma cell lines. Finally, we detected IL-1alpha and IL-1Ra protein in mouse skin tumors by western blot analysis, and localization was assessed by immunohistochemical analysis. Positive staining for both IL-1alpha and IL-1Ra was observed in the cytoplasm and was most prominent in the suprabasal layer. Although IL-1Ra protein increased in papillomas and carcinomas, IL-1alpha protein was not significantly increased above basal level in most tumors.