Biomedical subjects

N E Hubbard

Publications and source records attributed to N E Hubbard.

34 records · Page 2Linked to original sources

PubMed1995

Modulation of signal transduction in macrophages by dietary fatty acids.

Tumor growth can be altered by the amount and type of fat in the diet. Although there are several possible mechanisms for this, recent work suggests that alterations in the immune system by dietary fat may affect tumorigenesis. The focus of recent studies has been on dietary fat modulation of macrophage function because that cell plays a pivotal role in many immune responses, including anti-tumor activity. One possible mechanism of dietary fat effects on macrophages is altered signal transduction, which, in turn, could alter gene regulation and macrophage function. Initial studies tested the effects of dietary fat on kinase activity after stimulation with interferon-gamma. Macrophages from mice fed menhaden fish oil (MFO) had slightly decreased protein kinase C activity compared with macrophages from mice fed safflower oil (SAF). No differences among the diets were observed when the activity of protein kinase A and G were tested. When calcium mobilization was tested, we found that macrophages from mice fed MFO had an increased response compared with macrophages from mice fed SAF. Dietary fat also modified the response of macrophages to platelet-activating factor with respect to the induction of Ia expression. In studies to identify genes involved in dietary fat effects on macrophage function, we screened a cDNA library of macrophages treated with prostaglandin E2 (PGE2), a lipid-based mediator that can modulate macrophage function and be altered by dietary fat. The cloned gene, BTG1, was enhanced in macrophages treated with PGE2, but the relationship with dietary fat remains to be determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

A possible mechanism by which dietary fat can alter tumorigenesis: lipid modulation of macrophages function.

It has been known for at least 20 years that fatty acids can alter immune functions in vitro. More recently we have begun to understand the role that dietary fats play in immunity [formula: see text] and specifically how they may alter macrophage function. In the future it will be important not simply to redefine that fatty acids can alter select macrophage functions but to understand the mechanisms by which that occurs. Whether the same or different mechanisms are operational for those functions that are altered by dietary fat remains to be determined. Nevertheless, tumoricidal responses can be modified depending on the fatty acids in the diet. Hopefully, these recent observations will expand our understanding of how lipids regulate macrophage tumoricidal function and thus, might lead to new insights of how dietary fat may be manipulated to affect breast tumor regression.

Animals↗

PubMed1994

Effect of dietary linseed oil on tumoricidal activity and eicosanoid production in murine macrophages.

Diets that contain high levels of n-3 fatty acids from fish oil have been shown to significantly effect macrophage cytolytic capacity, tumor necrosis factor alpha production and eicosanoid production. The present study was undertaken to determine whether n-3 fatty acids from vegetable origin [linseed oil (LIN)] would have the same effects on murine macrophage tumoricidal capacity and eicosanoid production as would fish oil. Mice were fed for three weeks diets that contained 10% (wt/wt) of either LIN, which is high in linolenic acid (18:3n-3), menhaden fish oil (MFO), which is high in eicosapentaenoic (20:5n-3) and docosahexaenoic (22:6n-3) acids, or safflower oil (SAF), which is high in linoleic acid (18:2n-6). In vivo- or in vitro-activated macrophages were assessed for select functions. As expected, macrophages from mice fed LIN and MFO produced significantly lower levels of both prostaglandins and leukotriene C4 when compared with macrophages from mice fed SAF. In addition, LIN and MFO macrophages were able to synthesize leuko-triene C5, which could not be produced by macrophages from mice fed SAF. The effects of LIN, however, were not as pronounced as those of MFO. With respect to specific functions, macrophages from mice fed LIN did not have altered cytolytic capacity when compared with macrophages from mice fed SAF and activated in vitro with either lipopolysaccharide (LPS) alone for 24 h or with LPS plus interferon gamma (IFN gamma) for 5 h. Diet did not significantly alter tumoricidal capacity of macrophages activated completely in vivo either.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Effects of in vitro exposure to arachidonic acid on TNF-alpha production by murine peritoneal macrophages.

Modifying the fatty acid composition of macrophages through diet can significantly alter some of their functions, such as tumoricidal capacity and tumor necrosis factor alpha (TNF-alpha) production. The mechanism of that modification, however, is unknown. In this report, we provide evidence that fatty acids added to macrophages in culture can significantly alter macrophage TNF-alpha production. For example when inflammatory macrophages were incubated with various doses of arachidonic acid [20:4(n-6)] during activation with lipopolysaccharide (LPS), we observed a dose-dependent decrease in the level of bioactive TNF-alpha with complete inhibition at 2-5 microM. This inhibition was specific for 20:4(n-6) because in vitro treatment with other fatty acids, such as eicosapentaenoic [20:5(n-3)] or docosahexaenoic [22:6(n-3)] acids, had differential effects. The inhibitory action of 20:4(n-6) did not involve toxicity because cell viability was not affected and in vitro interferon-gamma and lipopolysaccharide (LPS) activation of macrophages for killing of P815 tumor targets was not altered. Inhibition by 20:4(n-6) occurred posttranscriptionally, and could be reversed when macrophages were treated with indomethacin during activation. Arachidonic acid treatment also significantly increased the production of immunoreactive prostaglandin E2 (PGE2) by LPS-treated and untreated macrophages. These results suggest that in vitro treatment of macrophages with 20:4(n-6) may inhibit TNF-alpha production through an alteration in the levels of PGE2 at a posttranscriptional level. These results provide evidence that some dietary fats may affect macrophage activity through modification of eicosanoid synthesis.

Animals↗

PubMed1991

Effect of dietary fish oil on development and selected functions of murine inflammatory macrophages.

Inflammatory macrophages from mice fed diets containing menhaden fish oil (MFO) have a reduced capacity for cytotoxicity of mastocytoma cells upon activation with interferon-gamma (IFN gamma) and lipopolysaccharide due to an altered responsiveness to IFN gamma. In an effort to elucidate further how dietary MFO effects macrophage function, we have studied the maturation of inflammatory macrophages from mice fed MFO compared with mice fed safflower oil (SFO) using several processes that serve as markers of the activational state. No significant differences in the recruitment or percentage of peritoneal exudate cells as macrophages after thioglycollate injection and no differences in spreading, binding, or phagocytosis of sheep erythrocytes or phagocytosis of yeast by inflammatory macrophages were observed when the dietary groups were compared. However, MFO macrophages had an altered capacity for peroxide release when stimulated with unopsonized zymosan (10-200 micrograms/ml). Furthermore, to elucidate how MFO feeding could alter IFN gamma-induced responses of inflammatory macrophages, we assessed phorbol-12-myristate-13-acetate-induced hydrogen peroxide production and expression of class II MHC determinants (Ia). There were no differences between macrophages from mice fed the two diets with respect to the production of peroxide when they were preincubated with 0.1-10 U/ml of IFN gamma. However, MFO macrophages had greater peroxide production after enhancement with 100 U/ml of IFN gamma. With respect to Ia induction, the percentage of macrophages responding to IFN gamma was not altered by diet, and there were no differences in expression of Ia induced by 24 hr exposure to IFN gamma. Thus the differential effect of MFO compared with SFO is probably mediated not by an alteration in the maturation of inflammatory macrophages but rather through the alteration of IFN gamma-induced functions such as peroxide production.

Administration, Oral↗

PubMed1991

Role of dietary oleic acid in linoleic acid-enhanced metastasis of a mouse mammary tumor.

We have previously shown that a high fat diet (20% w/w) containing 12% linoleic acid (18:2) can significantly increase the metastasis of mammary tumor cells when compared with high fat diets that contain 8% or less 18:2 with a constant level of oleic acid (18:1). This effect may have been due to an alteration of eicosanoid metabolism because the cyclooxygenase inhibitor, indomethacin, abolished the increase. Because 18:1 may interfere with the metabolism of 18:2 to 20:4, we have now tested whether the 18:1 that supplements the 18:2 diet can have an effect on spontaneous or experimental metastasis of the line 4526 murine mammary tumor. For this, six 20% fat diets were formulated with 1%, 6%, and 12% 18:2 and either high or low levels of 18:1. Our results indicate that the amount of select fatty acids other than 18:2 at 12% has no significant effect on mouse growth, tumor growth, or tumor latency. When spontaneous metastatic burden was calculated, no significant differences between mice fed diets containing 1% and 6% 18:2 were observed. However, 4 to 5 times more of a metastatic burden was observed in mice fed diets containing 12% 18:2. No significant differences were observed between high and low 18:1 diets when the 18:2 content was 1 or 12%. However, at 6% 18:2, 18:1 significantly decreased metastatic burden. When experimental metastasis was assessed, relatively low levels of surface lung nodules were observed at 1% and 6% 18:2, but significantly higher levels were observed at 12% 18:2.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Eicosanoids and linoleate-enhanced growth of mouse mammary tumor cells.

Metastatic mouse mammary tumor cell line 4526 was used to determine whether linoleate (LN)-derived cyclooxygenase metabolites were involved in the mechanism of LN-enhanced 4526 tumor growth. Unstimulated line 4526 cells converted LN to both PGE1 and PGE2 in serum free medium (SFM). However, neither prostaglandin (PG) influenced growth, while db-cGMP, but not db-cAMP, stimulated growth to the same extent as LN. Cyclooxygenase inhibitors stimulated growth while suppressing PG synthesis. Lipoxygenase inhibitors decreased growth in a dose dependent manner. Supplemental LN had no effect on cyclooxygenase inhibition while the IC50s for lipoxygenase inhibition were increased several fold. These results indicate that lipoxygenase products rather than cyclooxygenase metabolites play a major role in LN-stimulated growth of line 4526 cells.

Adenocarcinoma↗

PubMed1990

5-series peptido-leukotriene synthesis in mouse peritoneal macrophages: modulation by dietary n-3 fatty acids.

This study was undertaken to elucidate the metabolic fate of dietary eicosapentaenoic acid (20:5n-3), a major n-3 polyunsaturated fatty acid constituent of fish oil, in the mouse peritoneal macrophage. Mice were fed diets containing menhaden fish oil (FO) or safflower oil (SO). After 3 weeks, resident or responsive peritoneal macrophages were isolated and stimulated with zymosan and A23187, respectively. We demonstrate the novel synthesis of leukotriene C5 (LTC5), derived from 20:5n-3, in addition to LTC4 in both resident and responsive macrophages from FO fed mice. The structures of these peptido-leukotrienes were characterized by their retention times on reverse phase high pressure liquid chromatography, by their u.v. absorbance spectra, and by cross-reactivity with peptido-leukotriene antibody. These results demonstrate for the first time that macrophages are capable of metabolizing dietary 20:5n-3 to LTC5, a pentaene peptido-leukotriene.

Animals↗

PubMed1990

Dietary fat and tumor metastasis.

Evidence from several types of studies indicates a relationship between fat intake and occurrence of malignant tumors at specific sites. When rodents are fed high-fat diets, the incidence of mammary tumors sharply increases and latency of tumor appearance is greatly diminished, as compared with the same parameters in animals fed low levels of fat. Despite advances in surgical technique and the development of aggressive therapies for the treatment of primary cancers, most deaths in humans with cancer are caused by metastasis. Accordingly, we have reviewed the process of metastasis and have focused on the question of whether dietary fat can play a role. Metastasis is a complex, multistep, progressive process, and dietary fats may affect specific events such as implantation, survival, and proliferation of tumors. Finally, we discuss possible mechanisms by which dietary fat can modulate metastasis. Available data lead us to stress the importance of assessment of metastasis in studies of the effects of dietary fat on tumorigenesis.

Dietary Fats↗

PubMed1989

Linoleic acid metabolism in metastatic and nonmetastatic murine mammary tumor cells.

The mechanism(s) by which dietary linoleic acid (18:2n-6) enhances mammary tumor growth and metastasis is not known. Since arachidonic acid (20:4n-6)-derived prostaglandins (PG) may play a role in the metastatic dissemination of tumor cells, the ability of two murine mammary tumor cell lines, 4526 (metastasis positive) and line 168 (spontaneous metastasis negative), to convert 18:2n-6 into prostaglandins was examined. Cells were initially incubated with [14C]18:2n-6 and after 8-24 h the [14C]fatty acids were quantitated by high-performance liquid chromatography following transesterification. [14C]18:2n-6 was metabolized primarily to [14C]dihomogammalinolenic acid (20:3n-6) in line 4526 cells and [14C]20:4n-6 in line 168 cells. Examination of cellular fatty acid levels revealed a 20:3n-6/20:4n-6 ratio of 1.79 +/- 0.36 and 0.20 +/- 0.02 in line 4526 and 168 cells, respectively. These data are consistent with an inherently lower delta 5 desaturase activity in line 4526 relative to 168. To assess the metabolism of 18:2n-6 into eicosanoid products, the cell lines were prelabeled with [14C]18:2n-6 or 0-40 microM nonradiolabeled 18:2n-6 overnight and subsequently stimulated with calcium ionophore A23187 for 1 h. Total PGE production, as determined by radioimmunoassay, was greater in 168 relative to 4526 cells at all 18:2n-6 concentrations. 14C-prostaglandins detected by high-performance liquid chromatography and argentation thin-layer chromatography were: PGF1 alpha and PGE1 (derived from 20:3n-6) and PGF2 alpha and PGE 2 (derived from 20:4n-6) from line 4526; PGE1 and PGE2 from line 168. PGE1/PGE2 ratios were 1.43 +/- 0.07 and 0.23 +/- 0.03 for 4526 and 168 lines, respectively. Neither cell line synthesized lipoxygenase products following [14C]18:2n-6 or [3H]-20:4n-6 incubations under the conditions employed. Additional studies are warranted in order to define the biological properties of 1- and 2-series cyclooxygenase products as they relate to tumor cell metastasis.

Animals↗

PubMed1989

Effect of dietary linoleic acid level on lodgement, proliferation and survival of mammary tumor metastases.

High levels of dietary linoleic acid (18:2) have been shown to increase the spontaneous metastasis of line 4526 mouse mammary tumors. In this report, the influence of 18:2 on specific events of tumor metastasis, namely, lodgement, proliferation and survival, were studied using spontaneous and experimental metastasis assays with line 4526 cells. A significantly greater number of radiolabeled tumor cells lodged in the lungs of mice fed 4, 8 and 12% 18:2 when compared with mice fed lower levels of 18:2. The effect of dietary 18:2 appeared to be on the host tissue (lungs) and not the tumor cells. Lodgement of tumor cells first cultured in serum of mice fed 18:2 then injected into mice fed 1% 18:2 was not affected. There were no significant differences in the percentage of [3H]thymidine labeled metastatic cells from lungs of mice fed different levels of 18:2. However, the number of surface lung nodules that appeared in mice 21 days after injection of unlabeled line 4526 cells increased in mice fed 8 and 12% 18:2 compared with those fed lower levels of 18:2. Thus, dietary 18:2 may increase metastasis by influencing the lodgement, implantation and survival but not proliferation of line 4526 mouse mammary tumor cells.

Animals↗

PubMed1988

Inhibition of growth and linoleate-enhanced metastasis of a transplantable mouse mammary tumor by indomethacin.

The influence of the cyclo-oxygenase inhibitor, indomethacin (IM), on the metastasis, development and prostaglandin E (PGE) levels of line 4526 mammary tumors grown in mice fed high fat (HF, 20%, w/w) diets containing various levels of linoleic acid (18:2) was investigated. Control mice that grew primary tumors and were fed HF diets containing 12% 18:2 (w/w) had 2-3 times the number of lung metastases than mice fed 1%, 4%, or 8% 18:2. Chronic treatment of mice with 10 micrograms/ml IM in drinking water reduced metastasis in 1% and 4% 18:2-fed mice compared to controls and completely inhibited the increased metastasis of mice fed the 12% 18:2 diet. Treatment with IM also increased the latency and decreased the growth rates of primary 4526 tumors of all dietary groups. Treatment of mice with a higher dosage of IM (20 micrograms/ml), decreased tumor metastasis even further compared to controls, but did not decrease tumor growth rate compared to the lower dosage of IM (10 micrograms/ml). Tumor PGE levels, measured by radioimmunoassay (RIA), were decreased by IM treatment. These data provide evidence that arachidonic acid metabolites such as PGE may be involved in the metastasis of 4526 mammary tumors.

Animals↗

PubMed1987

Enhancement of metastasis from a transplantable mouse mammary tumor by dietary linoleic acid.

The influence of quantitative differences in dietary linoleic acid (18:2) on the metastasis as well as the development of line 4526 mouse mammary tumors was investigated. High fat diets (20%, w/w) that contained either 1, 2, 4, 8, or 12% 18:2 by weight, were prepared by using mixtures of coconut and safflower oil and fed to female BALB/c mice that were subsequently inoculated with 10(4) 4526 tumor cells s.c., either at the lateral abdominal wall (LAW) or in the mammary fat pad (MFP). Latency of LAW tumors was influenced by the level of dietary 18:2, whereas the latency of MFP tumors was not. When metastasis was assessed, mice with MFP tumors fed 1, 2, 4, or 8% 18:2 diets had 62-73% fewer lung surface tumor nodules than similar mice fed 12% 18:2. Mice in all dietary groups with LAW tumors had fewer metastatic lung nodules than mice with MFP tumors; mice with LAW tumors fed diets containing 1, 2, or 4% 18:2 had 52-69% fewer nodules than similar mice fed diets containing 8 or 12% 18:2. There were no significant differences in the rate of increase of body weight or the daily mean tumor volumes when compared with dietary 18:2 level. Fatty acid composition of the tumor, particularly the level of 18:2, was significantly altered by diet. This study demonstrates that while the level of dietary 18:2 does not enhance the growth rate of primary 4526 tumors and does or does not affect the latency depending on the primary site, it does significantly alter the metastasis. These results stress the importance of metastasis assessment in future studies involving dietary fat effects on tumorigenesis.

Animals↗

PubMed1987

Influence of dietary fats on cell populations of line 168 mouse mammary tumors: a morphometric and ultrastructural study.

The effect of dietary fat concentration and saturation on cell composition and structure of line 168 mouse mammary tumors in vivo was studied using morphometry and electron microscopy. Both the concentration and saturation of fat fed to mice had a significant influence on the volume ratio of mast cells infiltrating line 168 tumors. Tumors of mice fed diets containing a high concentration (20%) of either safflower oil (SO) or palm oil (PO) had 2-3 times the volume ratio of mast cells than mice fed diets containing a low concentration (5%) of either fat. There were no significant differences among diets with respect to other inflammatory cell populations. Mice fed either one of the high fat diets had tumor cells with inclusions that ultrastructurally, appeared to consist of lipid. Dietary fat, however, had no observable affect on cell junctions or other morphological characteristics. Greater infiltration of mast cells in tumors of mice fed high fat diets and the eventual formation of new blood capillaries may explain the decreased latency of tumor onset and enhanced growth of tumors in mice fed diets with high concentrations of fat.

Animals↗

PubMed1986

Morphological changes in the blastocyst of the western spotted skunk during activation from delayed implantation.

Blastocysts collected from the spotted skunk during delay of implantation, early activation and late activation demonstrate three-tiered growth and developmental changes. The slow-growing blastocyst from the several months of delay is small (less than 1.1 mm) with a rounded inner cell mass consisting of clusters of rounded, lipid-filled cells. During the several days of early activation, the lipid in both inner cell mass and trophoblast diminishes, polyribosomes increase in number, and the endodermal layer differentiates as the blastocyst grows (1.2-1.6 mm). At activation the inner cell mass flattens, becomes uncovered by polar trophoblast, and forms a disc of columnar epiblast cells. The blastocyst expands rapidly during the last 24-48 h prior to implantation to 1.7-2.0 mm, and the trophoblast becomes cuboidal with a marked endocytotic apparatus. The morphological evidence, together with previous studies of protein and RNA synthesis, suggests a tooling-up period during early activation with progressive increases in rates of growth and differentiation in the last hours as implantation approaches.

Animals↗

PubMedDate not supplied

Differential mRNA expression of prostaglandin receptor subtypes in macrophage activation.

Assessing the regulation of macrophage receptors for prostaglandin (PGE2) is essential to understanding the control which that potent lipid mediator has in modulating macrophage activities. The purpose of this study was to assess the differential mRNA expression of PGE2 receptor subtypes (EP) during macrophage exposure to activating and transducing agents. RAW 264.7 macrophages constitutively expressed mRNA for EP2,EP3 and EP4 receptor subtypes. Messenger RNA for EP4 was expressed at a much higher level when compared to EP2 in unstimulated macrophages as assessed by kinetic quantitative RT-PCR. When macrophages were stimulated with LPS, EP2 m RNA levels were 12-fold higher when compared to unstimulated macrophages, while EP4 m RNA remained unchanged. Conversely, mRNA levels of both EP2 and EP4 receptors were lower after macrophages were treated with IFN-gamma. Messenger RNA levels of both receptors were lower in macrophages after treatment with PGE2 or dibutyryl (db) cAMP Addition of the PKA inhibitor H89 reversed the effects of PGE2 and dbcAMP to varying degrees. Proteosome and p38 MAP kinase inhibitors blocked the LPS-stimulated increase in EP2 mRNA levels. Those inhibitors had no effect on EP4 mRNA.Thus, activating agents such as LPS and IFN-gamma may differentially regulate mRNAfor PGE2 receptor types in macrophages but the ligand and its associated signal transducing factors probably have similar regulatory effects.

Animals↗