Vitamin B12 uptake by intestinal microorganisms: mechanism and relevance to syndromes of intestinal bacterial overgrowth.

The mechanism of bacterial uptake of vitamin B(12), the spectrum of microorganisms capable of such uptake, and the factors involved were the subject of this study. Bacterial uptake of vitamin B(12) was found to be at least a two stage process. A primary uptake phase which was rapid (1 min or less), pH dependent, nontemperature dependent, did not require viable organisms and was insensitive to either the metabolic inhibitor dinitrophenol or to the sulfhydryl inhibitor N-ethyl-maleimide. Protein denaturation (formalin treatment or autoclaving) abolished all B(12) uptake. This primary uptake phase is thought to represent adsorption to binding or "receptor" sites on the cell wall. Second stage uptake was slower, pH and temperature dependent, required living bacteria, and was abolished by either dinitrophenol or N-ethyl-maleimide. This phase is dependent upon metabolic processes and may reflect transfer of B(12) from surface "receptor" sites into the bacterial cell. Although differences among organisms were observed in total 1 hr uptake, number of surface "receptor" sites, and relative avidities for B(12), all organisms except Streptococcus fecalis shared the two stage mechanism. Two Gram-positive organisms. Bacillus subtilis and Group A streptococcus, demonstrated the highest 1 hr vitamin B(12) uptake values; Gram-negative bacteria required 2,000-10,000 the number of organisms for comparable uptake. Binding constants (K(m)) varied from 5.05 +/-1.67 x 10(-10)M for B. subtilis to 6.18 +/-3.08 x 10(-9)M for Klebsiella pneumoniae which approximate the Km for human intrinsic factor (0.38 x 10(-10)M). Competition between bacteria and intrinsic factor for vitamin B(12) may be inferred from the similarity of these constants. These observations suggest that a variety of enteric and nonenteric organisms, not requiring exogenous B(12), may play a role in the pathogenesis of the vitamin B(12) malabsorption found in the intestinal bacterial overgrowth syndromes.

Effect of diet upon intestinal disaccharidases and disaccharide absorption.

The administration of a carbohydrate-containing diet for 24 hours to rats previously fasted for 3 days led to a twofold increase in total intestinal sucrase and sucrase specific activity. The specific activity of maltase was similarly increased, but lactase activity was unaffected. The sucrose-containing diet led to a greater increase in sucrase than maltase activity, whereas the converse was true of the maltose-containing diet. A carbohydrate-free isocaloric diet led to a slight increase in the total intestinal sucrase, but sucrase specific activity was unchanged. Assay of sucrase activity of mixed homogenates from casein-fed and sucrose-fed rats or fasted and sucrose-fed animals yielded activities that were additive. The Michaelis constant (Km) of the enzyme hydrolyzing sucrose was similar in the fasted, casein-fed, and sucrose-fed rats. The maximal velocity (Vmax) was twice greater in sucrose-fed as compared to casein-fed or fasted rats, suggesting an increased quantity of enzyme subsequent to sucrose feeding. Adrenalectomized rats maintained on 1.0% salt intake had sucrase and maltase levels comparable to those of controls. Steroid administration did not significantly increase their activities. The response to sucrose feeding was similar in both control and adrenalectomized rats, indicative of the absence of steroidal control on sucrase and maltase activity in the adult animal. Studies using intestinal ring preparations indicated that sucrose hydrolysis by the intact cells proceeded more rapidly when animals were fed sucrose. Additional corroboration of the physiologic significance of the increased enzyme levels in homogenates was afforded by intestinal perfusion studies. Sucrose hydrolysis increased twofold and fructose absorption fourfold in animals fed sucrose when compared to either fasted or casein-fed rats.

Demonstration and immunochemical characterization of carcinoembryonic antigen in human pancreatic juice.

Pancreatic juice collected from 10 patients without evidence of malignant disease of the pancreas or other organs was pooled, extracted, and fractionated by Sepharose 6-B and Sephadex G-200 gel filtration. The carcinoembryonic antigen (CEA) activity in the material was demonstrated and studied by: a) radioimmunoassay, b) competitive binding to antibodies against CEA, c) precipitin inhibition, and d) Ouchterlony analysis. The immunochemical identity of the active material to CEA purified from liver metastases of colon cancer was demonstrated.

Cholesterol excretion and colon cancer.

Populations consuming diets high in fat and cholesterol exhibit a greater incidence of colon cancer than those consuming less fat and cholesterol. Lowering elevated serum cholesterol levels experimentally or clinically is associated with increased large-bowel tumorigenesis. Thus, cholesterol lost to the gut, either dietary or endogenously synthesized, appears to have a role in large-bowel cancer. Whether the effect(s) is mediated by increases in fecal bile acid excretion or some other mechanism is not clear.

Lipids and immune function.

There is in vitro and in vivo evidence to suggest that dietary lipids play a role in modulating immune function. A review of the current literature on the interrelationships among dietary lipids, blood cholesterol levels, immunosuppression, and tumorigenesis makes for a very strong argument that (a) immunosuppression may be causally related to lymphoproliferative disorders, as well as to tumorigenesis and (b) diets high in polyunsaturated fat, relative to diets high in saturated fat, are more immunosuppressive and are better promotors of tumorigenesis. The effects of dietary fat on immune function seem to be mediated though its component parts, the unsaturated fatty acids, specially linoleic, linolenic, and arachidonic. It is not clear how these components affect immune function. Several studies suggest that one effect is mediated by altering the lipid component of the cell membrane and thus its fluidity; the more fluid the membrane, the less responsive it is. Thus, fluidity of both immune cells and those to be destroyed or protected may be affected. The effects of saturated as well as unsaturated fatty acids may be mediated by modulating serum lipoprotein levels, prostaglandin metabolism, and cholesterol concentrations and metabolism.

Evidence for deficiency of low density lipoprotein receptor on human colonic carcinoma cell lines.

Cells from six human colonic adenocarcinoma lines (CaCo-2, HT29, LS174T, SW480, SW403, and SW1417) and a normal skin fibroblast cell line (AG1519) were assayed in vitro for their ability to use low density lipoprotein (LDL). All tumor cell lines grew well in lipoprotein-deficient serum, implying that LDL in culture medium was not critical for cell growth. When cell growth was inhibited with mevinolin, a cholesterol synthesis inhibitor, the addition of LDL to the medium had no effect on the growth of cells from five of six tumor cell lines. CaCo-2 cells showed a moderate reversal while the fibroblast control showed total reversal of inhibition. A monoclonal antibody to bovine/human LDL receptor, used in an enzyme-linked immunosorbent assay, indicated that only CaCo-2 cells and human skin fibroblast cells consistently demonstrated the presence of LDL receptors. Thus, five of six colon tumor cell lines were unable to overcome a mevinolin block in cholesterol metabolism indicating that these cells were deficient in LDL receptors.

Postpromotional effects of dietary marine or safflower oils on large bowel or pulmonary implants of CT-26 in mice.

Marine oils containing n-3 fatty acids exhibit variable antineoplastic effects. Diets containing low (11.6% of kcal) or high (46.5% of kcal) levels of marine oils as the exclusive fat source were compared to diets containing identical amounts of safflower oil (n-6) in weanling, male BALB/c ByJ mice. All diets provided approximately 90 kcal/100 g body weight/day, and contained identical quantities of vitamins, minerals, protein, and fiber. The growth of transplantable colon carcinoma, CT-26, (10(6) cells/animal) implanted, subserosally, into the descending colon via laparotomy, was observed weekly over 28 days by necropsy in all dietary groups. At each time period animals fed safflower oil had larger tumors than those fed marine oil. Tumor volumes at 21 days postimplantation were as follows: low fat marine, 55 mm3 (5-196 mm3) [median (range)]; high fat marine, 70 (26-194); low fat safflower, 216 (32-800); high fat safflower, 247 (70-1352). Marine oil tumors were smaller than safflower oil tumors (P less than 0.005 by analysis of variance; P less than 0.01 by Scheffe test). Metastatic potential was assessed by pulmonary colonization. CT-26 was injected i.v. in tail veins (10(5) cells/animal). Mice were sacrificed and colonies were counted after 21 days. Mice fed low fat marine, high fat marine, and low fat safflower oil diets, 10-14 colonies; high fat safflower, 55 colonies (P less than 0.001 by analysis of variance). Hence, dietary marine oil significantly suppressed growth of this colon carcinoma at all intake levels studied and inhibited pulmonary colonization at higher intakes relative to safflower oil.

Receptor-mediated endocytosis of carcinoembryonic antigen by rat liver Kupffer cells.

In vivo, carcinoembryonic antigen (CEA) is removed from the circulation by the liver Kupffer cells. Immunologically identifiable CEA is transferred from these macrophages to the hepatocytes, where degradation is completed. Circulatory clearance of CEA is specific, rapid [t1/2 = 3.7 +/- 0.9 (S.D.) min], and saturable. In vitro, Kupffer cells take up CEA by a saturable process which is time/temperature dependent and colchicine sensitive. Isolated Kupffer cells endocytose CEA with an apparent Km of 6 X 10(-8) M. There are approximately 16,000 CEA binding sites per cell. Nonspecific cross-reacting antigen (NCA), a glycoprotein structurally similar to CEA, is recognized with lower affinity by the same receptor. Endocytosis is independent of the nonreducing terminal sugars on the molecule: CEA modified by Smith degradation inhibits Kupffer cell recognition of native CEA. Since performic acid oxidized CEA also inhibits endocytosis, receptor binding is similarly independent of intact protein conformation. Isolated Kupffer cells have mannose and/or N-acetyl glucosamine receptor activity but do not internalize CEA by that mechanism. Galactose-terminated glycoproteins impede CEA and NCA clearance in vivo but not Kupffer cell endocytosis in vitro. Radiolabeled CEA released from isolated Kupffer cells following endocytosis shows no apparent molecular weight change. However, the released CEA contains species with higher isoelectric points, suggesting that perhaps the removal of sialic acid and the resulting exposure of galactose residues mediate the subsequent transfer to the hepatocyte.

Beneficial effects of post-transfusional hepatitis in acute myelogenous leukemia may be mediated by lipopolysaccharides, tumor necrosis factor alpha and interferon gamma.

Post-transfusional hepatitis is often a complication in patients with acute myelogenous leukemia (AML) in whom survival is paradoxically prolonged. The etiology is unknown. In previous studies, we showed that impaired hepatic endotoxin (lipopolysaccharide, LPS) clearance in patients with acute viral hepatitis A, B, or C versus controls results in endotoxemia and tumor necrosis factor alpha (TNF-alpha) release. TNF-alpha mediates anti-proliferative and differentiating effects in AML cell lines. Interferon-gamma (IFN-gamma) released in acute viral hepatitis, acts in synergy with TNF-alpha. HL60, KG1, and U937 AML cells treated 3, 6, and 9 days with physiologically attainable TNF-alpha (10 U/ml), IFN-gamma (100 U/ml) and LPS (10 ng/ml) levels, have significantly diminished viability and cell growth versus controls. Treatment of HL60 AML cells with LPS/TNF-alpha/IFN-gamma also resulted in significantly increased monocytic pathway differentiation not seen with KG1 or U937 AML cells. HL60 AML cells treated with TNF-alpha/IFN-gamma for 6 days released endogenous TNF-alpha (1.57 U/10(6) cells) upon LPS stimulation compared to less than 0.01 U/10(6) cells in non-LPS-stimulated TNF-alpha/IFN-gamma-treated cells or untreated cells (p less than 0.0001). Untreated HL60 AML cells co-cultured with HL60 cells pretreated for 6 days with TNF-alpha/IFN-gamma and then subjected to LPS stimulation had significantly diminished cell growth compared to controls (p less than 0.0001). This effect could be reversed with anti-TNF-alpha antibody, supporting the concept that endogenous TNF-alpha release by LPS/TNF-alpha/IFN-gamma treated HL60 AML cells may act by paracrine means to suppress growth of other AML cells. The beneficial effects of post-transfusional hepatitis in AML patients may be mediated via LPS/TNF-alpha/IFN-gamma-induced AML cell growth suppression and/or terminal differentiation in which AML cells participate by releasing TNF-alpha after being acted upon by LPS/TNF-alpha/IFN-gamma. Endogenously released TNF-alpha might then act by autocrine/paracrine means to mediate further suppression and terminal differentiation.

Growth restraint and differentiation by LPS/TNF-alpha/IFN-gamma reorganization of the microtubule network in human leukemia cell lines.

The microtubule (MT) network of the cytoskeleton has been implicated as a mediator of cellular signal transduction; disorganization of this network may allow for mitogenesis. In previous work, loss of MT network organization in human MOLT4 and HUT78 T-cell leukemias was demonstrated in contrast to an organized "spoke-wheel-like arrangement" in normal human T-lymphocytes. In this study, loss of MT network organization was shown in several representative acute myeloid leukemia (AML) cell lines: KG1 myeloblastic, HL60 promyelocytic, and U937 myelomonocytic cells. Re-organization of the MT network was observed in HL60 and U937 AML cells treated with combined lipopolysaccharide (LPS), tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma). This re-organization paralleled earlier work which showed this combination was effective in inducing monocytic pathway differentiation and growth restraint in HL60 cells, and growth restraint in U937 cells. In contrast, KG1 cells exhibited growth restraint, but did not re-organize with LPS/TNF-alpha/IFN-gamma treatment. These results are consistent with a role for the MT network in mitogenesis. Loss of MT network organization appeared to parallel the neoplastic phenotype in three AML cell lines, whereas MT network re-organization accompanied recovery of growth control in 2 of 3 AML cell lines.

Pathophysiological aspects of coxsackievirus B intestinal infection.

Our findings reveal that intestinal infection with coxsackie B5 results in decreased intestinal epithelial cell division in association with an increase in carbohydrate (glucose) and amino acid (leucine) absorption in the small intestine. These findings are contrasted with those occurring during Salmonella infection, which results in increased intestinal cell division rate but decreased carbohydrate (glucose) absorption. The changes in intestinal function and physiology that have been described occurred during an asymptomatic viral infection characterized by normal intestinal histology. A reasonable hypothesis is that these pathophysiological changes may be due not only to a variety of local factors but also to hormonal effects induced by systemic spread of coxsackievirus B.

CD14 mediated endogenous TNF-alpha release in HL60 AML cells: a potential model for CD14 mediated endogenous cytokine release in the treatment of AML.

In previous studies, HL60 AML cells treated with tumor necrosis factor-alpha (TNF), interferon-gamma (IFN), and lipopolysaccharides (LPS) displayed decreased growth and viability, enhanced monocytic pathway differentiation and endogenous TNF release. Endogenous TNF release by LPS/TNF/IFN treated HL60 cells was postulated to play a role with the above findings. In these studies, HL60 cells expressed CD14 when treated with TNF, IFN, and LPS. CD14 mediates TNF release in monocytes/macrophages in response to binding of LPS with LPS binding protein (LBP). CD14 was not expressed in either untreated or LPS only treated HL60 cells. CD14 expression was present and greater with HL60 cells cultured with LPS/TNF/IFN vs TNF/IFN (47.47% vs 9.07% positive, respectively) suggesting synergism for LPS in CD14 induction. CD14 expression was associated with endogenous TNF release, and with significantly higher levels by HL60 cells treated with LPS/TNF/IFN vs TNF/IFN (p < 0.001). Addition of anti-CD14 antibody significantly reduced release of TNF in TNF/IFN (p < 0.001) and LPS/TNF/IFN (p = 0.0013) treated cells. KG1 and U937 AML cells treated with LPS, TNF, and IFN did not express CD14, nor release TNF. A model for inducing release of endogenous growth inhibitory cytokines by CD14 bearing AML cells is proposed as an approach to AML therapy.

E. coli peritonitis and bacteremia cause increased blood-brain barrier permeability.

Impaired mental status is a poorly understood manifestation of sepsis and may be associated with altered permeability of the blood-brain barrier. To examine the possibility that sepsis affects permeability of the blood-brain barrier, rats were infected with a peritoneal implant consisting of sterilized feces, barium sulfate, and 10(8) colony forming units (CFU) of Escherichia coli. Using this model, reproducible episodes of peritonitis with bacteremia resulted. Rats were sacrificed hourly after 5 min circulation of 100 mg horseradish peroxidase. Animals were perfused-fixed and the brains removed. Representative coronal sections were stained for peroxidase reaction product and cerebral blood vessels were examined microscopically for evidence of HRP staining and extravasation. The number of stained cerebral vessels from infected rats was increased at all times compared to uninfected control rats. Extravasation of horseradish peroxide within neuropil was significantly higher in hours 1, 4 and 5 as compared to controls. The lack of significant increase in hours 2 and 3 may suggest transient closing or repair of the tight junctions. We conclude that peritonitis and bacteremia are associated with increased permeability of the blood-brain barrier.

R-(+)-perillyl alcohol-induced cell cycle changes, altered actin cytoskeleton, and decreased ras and p34(cdc2) expression in colonic adenocarcinoma SW480 cells.

Monoterpenes as S-(-)-perillyl alcohol (PA) have been shown to inhibit the isoprenylation of such growth regulatory proteins as ras. In this study, we investigated the effects of the R-(+) enantiomer of PA on cell cycle, signaling, and cytoskeletal control in the colonic adenocarcinoma cell line SW480, which carries a K-ras mutation. Cell cycle analysis by flow cytometry of SW480 cells treated with 1 mM PA for 24 hours demonstrated an increase in the number of cells in G0/G1 with a decrease in S phase, compared with untreated control cells. These cell cycle changes correlated with an inhibition of protein isoprenylation from (14)C-mevalonate and decreased expression of the cell cycle regulatory kinase p34(cdc2). Additionally, PA-treated cells acquired a flattened morphology with a condensation of cytoskeletal actin spikes to the periphery. This was in contrast to treatment with 15 microM mevinolin (MVN), a direct mevalonate synthesis inhibitor, which imparted to SW480 cells a more rounded and spindly morphology, associated with the depolymerization of actin microfilaments. Together, these data suggest that fluctuations in mevalonate and isoprenoid pools may involve different morphologic phenomenon. Because ras mediated signaling is related to the organization of the actin cytoskeleton, we investigated the effects of PA on the isoprenylation of ras. Although MVN treatment inhibited ras farnesylation, PA treatment decreased the expression of total ras protein. In summary, R-(+)-PA-induced cell signaling events correlated with alterations in the organization of cytoskeletal actin and decreased protein expression of growth regulatory proteins, such as ras and cdc2 kinase. These effects may contribute to the growth inhibitory activity of R-(+)-PA.

Regulation of cholesterol synthesis in four colonic adenocarcinoma cell lines.

Colon tumor cells, unlike normal human fibroblasts, exhibited an uncoupling of low density lipoprotein (LDL)-derived cholesterol from cellular growth, when endogenous cholesterol synthesis was inhibited by mevinolin, a hydroxymethylglutaryl-CoA reductase (HMG-CoAR) competitive inhibitor [Fabricant, M., and Broitman, S.A. (1990) Cancer Res. 50, 632-636]. Further evaluation of cholesterol metabolism was conducted in two undifferentiated (SW480, SW1417) and two differentiated (HT29, CACO2) colonic adenocarcinoma (adeno-CA) cell lines and an untransformed human fibroblast, AG1519A. Cells grown in monolayer culture to near subconfluency were used to assess endogenous cholesterol synthesis by 14C-acetate incorporation, in response to the following treatments in lipoprotein-deficient serum (LPDS)-supplemented minimum essential medium (MEM): LPDS alone, LDL, mevinolin, mevinolin with LDL, and 25-hydroxy-cholesterol (25-OH-CH). Complete fetal bovine serum (FBS)-supplemented MEM was used as control. All colon tumor lines exhibited similarly high endogenous cholesterol synthesis in both FBS and LPDS relative to the fibroblasts which demonstrated low basal levels in FBS and maximal synthesis in LPDS. LDL treatment did not inhibit cholesterol synthesis in colon tumor cells, but suppressed that in the fibroblast by 70%. Sterol repression of cholesterol synthesis mediated by 25-OH-CH occurred in all cells. Mevinolin caused a reduction in cholesterol synthesis in the colonic cancer cell lines, which was not further decreased by concurrent addition of LDL. In contrast, in mevinolin-treated fibroblasts, LDL further inhibited cholesterol synthesis. When the effect of cell density on cholesterol synthesis regulation was evaluated under conditions of sparse density in SW480 and SW147, results indicated that (i) basal rates of cholesterol synthesis were higher, (ii) LDL inhibited cholesterol synthesis more effectively, and (iii) mevinolin or 25-OH-CH had a more pronounced effect than in subconfluent cells. Evaluation of LDL receptor activity through 125I-LDL binding and internalization studies demonstrated LDL receptor expression was reduced by 37% in normal density cells relative to the low density cultures. In contrast to cholesterol synthesis, exogenous LDL could inhibit LDL receptor activity at both densities. Thus subconfluent growing colonic adenoCA cell lines retain the capacity for sterol repression, but, in contrast to normal fibroblasts, exhibit a high endogenous cholesterol synthesis which LDL cannot regulate.

Incorporation of polyunsaturated fatty acids into CT-26, a transplantable murine colonic adenocarcinoma.

Previous studies in our laboratory have shown that marine oils, with high levels of eicosapentaenoic (EPA, 20:5n-3) and docosahexaenoic acids (DHA, 22:6n-3), inhibit the growth of CT-26, a murine colon carcinoma cell line, when implanted into the colons of male BALB/c mice. An in vitro model was developed to study the incorporation of polyunsaturated fatty acids (PUFA) into CT-26 cells in culture. PUFA-induced changes in the phospholipid fatty acid composition and the affinity with which different fatty acids enter the various phospholipid species and subspecies were examined. We found that supplementation of cultured CT-26 cells with either 50 microM linoleic acid (LIN, 18:2n-6), arachidonic acid (AA, 20:4n-6), EPA, or DHA significantly alters the fatty acid composition of CT-26 cells. Incorporation of these fatty acids resulted in decreased levels of monounsaturated fatty acids, while EPA and DHA also resulted in lower levels of AA. While significant elongation of both AA and EPA occurred, LIN remained relatively unmodified. Incorporation of radiolabeled fatty acids into different phospholipid species varied significantly. LIN was incorporated predominantly into phosphatidylcholine and had a much lower affinity for the ethanolamine phospholipids. DHA had a higher affinity for plasmenylethanolamine (1-O-alk-1'-enyl-2-acyl-sn-glycero-3-phosphoethanolamine) than the other fatty acids, while EPA had the highest affinity for phosphatidylethanol-amine (1,2-diacyl-sn-glycero-3-phosphoethanolamine). These results demonstrate that, in vitro, significant differences are seen between the various PUFA in CT-26 cells with respect to metabolism and distribution, and these may help to explain differences observed with respect to their effects on tumor growth and metastasis in the transplantable model.

Enhancement of sterol synthesis by the monoterpene perillyl alcohol is unaffected by competitive 3-hydroxy-3-methylglutaryl-CoA reductase inhibition.

Monoterpenes such as limonene and perillyl alcohol (PA) are currently under investigation for their chemotherapeutic properties which have been tied to their ability to affect protein isoprenylation. Because PA affects the synthesis of isoprenoids, such as ubiquinone, and cholesterol is the end product of the synthetic pathway from which this isoprenoid pathway branches, we investigated the effects of this compound upon cholesterol metabolism in the colonic adenocarcinoma cell line SW480. PA (1 mM) inhibited incorporation of 14C-mevalonate into 21-26 kDa proteins by 25% in SW480 cells. Cholesterol (CH) biosynthesis was assessed by measuring the incorporation of 14C-acetate and 14C-mevalonate into 27-carbon-sterols. Cells treated with PA (1 mM) exhibited a fourfold increase in the incorporation of 14C-acetate but not 14C-mevalonate into cholesterol. Mevinolin (lovastatin), an inhibitor of 3-hydroxy-3-methylglutaryl-CoA(HMG-CoA) reductase, at 2 microM concentration, inhibited CH synthesis from 14C-acetate by 80%. Surprisingly, concurrent addition of mevinolin and PA did not significantly alter the stimulatory effects of PA. As observed differences in 14C-acetate and 14C-mevalonate precursor labeling could indicate PA affects early pathway events, the effects of this monoterpene on HMG-CoA reductase activity were evaluated. Unexpectedly, 1 mM PA did not stimulate activity of this enzyme. Consistent with its action as a reversibly bound inhibitor, in washed microsomes, 2 microM mevinolin pretreatment increased reductase protein expression causing a 12.7 (+/- 2.4)-fold compensatory HMG-CoA reductase activity increase; concurrent treatment with 1 mM PA attenuated this to a 5.3 (+/- 0.03)-fold increase. Gas chromatographic analysis confirmed CH was the major lipid present in the measured thin-layer chromatography spot. Since 14C-acetate incorporation into free fatty acid and phospholipid pools was not significantly affected by PA treatment, nonspecific changes in whole acetate pool sizes were not indicated. Because increases in endogenous CH synthesis should result in compensatory changes in exogenous sterol utilization, the effects of PA upon low density lipoprotein (LDL) receptor activity were evaluated. Consistent with the observed increases in CH synthesis, 1 mM PA decreased 125I-LDL internalization to 50% of the fetal bovine serum control; concurrent addition of 2 microM mevinolin attenuated this effect to a reduction of 80% of the control value. Data suggest that in certain colonic tumor cells PA strongly affects cholesterol metabolism via a mechanism of action that is insensitive to the HMG-CoA reductase inhibitor mevinolin.

Monoclonal antibody therapy in the treatment of Reye's syndrome.

A role for lipopolysaccharides (endotoxins, LPS) in 7 the pathogenesis of Reye's syndrome (RS) has previously been suggested. Impairment of hepatic LPS clearance can lead to systemic endotoxemia as previous studies by this and other laboratories have suggested for several hepatic disorders including RS. Systemic LPS may mediate many of the clinical findings associated with RS by eliciting monokines such as tumor necrosis factor-alpha, interleukin-1, interleukin-6, and interleukin-8. Monoclonal antibody therapy directed at LPS, and monokines may represent a novel approach to the treatment of RS.

Dietary cholesterol, serum cholesterol, and colon cancer: a review.

Observational and case-control epidemiologic data supported by experimental studies indicate that dietary cholesterol may contribute to colon tumorigenesis. A mechanism for this possible relationship is currently under investigation. Additional international epidemiologic data, although not uniformly consistent, indicate an inverse relationship between serum or plasma cholesterol levels and risk for colon cancer. This risk is greatest at serum cholesterol levels of less than 180 mg/dl. It has been suggested but not proven that individuals consuming diets high in dietary fat and cholesterol may have variations in cholesterol dynamics that account for lowered serum cholesterol levels and enhanced risk for colon cancer. Clinical evidence in both men and women indicates that age-sex-adjusted, low serum cholesterol levels may precede the detection of colon cancer by more than 5 years. Preclinical colon cancer is associated with a further decrease in serum cholesterol levels. It is not clear whether progression of the disease before metastatic spread results in continued lowering of serum cholesterol levels. In men with markedly elevated serum cholesterol levels who have been placed on cholesterol-lowering drugs such as clofibrate or cholestyramine, there was no evidence that such regimens increased the risk for colon cancer. It is possible that reductions in serum cholesterol associated with the use of these drugs are insufficient to lower cholesterol levels to a range associated with an increased risk for colon cancer.

A model system for studying nutritional interventions on colon tumor growth: effects of marine oil.

Lipid nutrition effects were evaluated on the growth of a transplantable colon tumor (CT-26) at various sites in the BALB/c mouse. CT-26 implanted into the back or flank of these mice grew well independent of the quality or quantity of fat in the diet. However, when implanted in the mid-portion of the descending colon, tumor growth was related to the level of dietary saturated (coconut oil) or n-6 unsaturated (safflower oil) fat in the diet. Similar findings were obtained when the tumor was utilized in a pulmonary colonization assay. Dietary marine oil (mainly EPA, and DHA n-3 polyunsaturated oils) was found to markedly impair the growth of CT-26 implanted in the bowel and lung, but not in the back. Thus, CT-26 exhibits nutrition responsiveness at certain sites, but not at others. This may help to explain contradictory findings concerning dietary lipids in certain studies. Inhibition of tumor growth by marine oils may afford preventive or chemotherapeutic implications as its mode of action unfolds. Histologic findings in bowel tumors from mice fed marine oil but not other oils revealed focal areas of necrosis. It is appreciated that arachidonate metabolism is competitively interfered with by EPA in both cyclooxygenase and lipoxygenase pathways. The possibility is raised that the metabolism of marine oils in this model system may generate lipid peroxidation products to a greater extent than n-6 lipids and in turn is associated with focal areas of necrosis. A model system of nutritionally non-responsive and nutritionally responsive sites for the post-promotional growth of a bowel tumor affords the opportunity to explore lipid effects with control and test tumors in hosts fed identical lipid nutriture.