The role of the Peyer's patch in carcinogenesis. II. 3-Methylcholanthrene-induced lymphoid malignancies in rat Peyer's patches

The role of dietary factors in the epidemiology of non-Hodgkin's lymphoma

The incidence of non-Hodgkin's lymphoma (NHL) has risen dramatically over recent decades and, despite some known risk factors, such as compromised immunity, the etiology of NHL and the reasons for most of this increase are unknown. Dietary components may be a common and critical source of immunologic antigens and promoters, which needs to be incorporated more in the etiologic research of NHL. To date, epidemiologic evidence suggests that obesity and fat intake, in particular saturated or animal fat, may increase the risk of NHL; whereas whole-grains, vegetables and moderate consumption of alcohol may be inversely associated with NHL risk. Much of the current evidence is obtained from case-control studies, which are subject to dietary recall bias; therefore, this area of research requires further study within prospective cohorts with detailed dietary information and with a large number of cases to examine disease sub-type heterogeneity.

Tobacco, alcohol, diet and risk of non-Hodgkin's lymphoma: a case-control study in Uruguay

To test whether high meat intake is associated with the development of non-Hodgkin lymphoma (NHL) in the Uruguayan population, a case-control study was performed at the Instituto Nacional de Oncologia, Montevideo, Uruguay. After controlling for age, sex, residence, education, urban/rural status and the habit of drinking the beverage 'mate', red meat intake was associated with an increased risk of NHL of 2.5. This finding was similar in both sexes separately. Odds ratios (OR) for the highest tertile of barbecued meat was 1.7 among men, whereas salted meat was associated with an increased risk of NHL (OR 4.9, 95% CI 1.4-17.7). The effect of processed and salted meat among women was of much less magnitude and the OR's were non-significant. Also, cumulative exposure to 'mate' drinking displayed an OR of 2.4 (95% CI 1.0-5.6). Smokers of black tobacco and hand-rolled cigarettes were associated with an increased risk of 3.5 (95% 1.1-10.9), whereas beer drinkers showed an increased OR of 5.5 (95% 1.1-26.7) in men. It could be concluded that red or salted meat intake, smoking of black tobacco, and beer and 'mate' drinking are risk factors for NHL in the Uruguayan population.

Pristane-induced effects on cytochrome P-4501A, ornithine decarboxylase and putrescine in rats

The effects of pristane (2,6,10,14-tetramethylpentadecane) on cytochrome P-4501A (cP4501A) activity in microsomes, as well as on ornithine decarboxylase (ODC) activity and concomitant putrescine levels were examined in Copenhagen rats. In general, pristane treatment led to increased cP4501A levels when compared to basal levels, while co-treatment with 3-methylcholanthrene (3-MC) and pristane elicited augmented cP4501A responses when compared to responses induced by 3-MC alone. Increases in both ODC activity and putrescine levels were also observed in pristane treated rats. Collectively, these results indicate that pristane influences cP4501A activity and elicits promoter-like responses as reflected in elevated ODC activity and increased amount of putrescine.

Analysis of transcriptional activation of a cyclic AMP response element by 2,6,10,14-tetramethylpentadecane (pristane) in JB6 mouse epidermal cells

Pristane is a naturally occurring isoprenoid that is believed to be derived from the phytyl moiety of chlorophyll. Thus, it is not surprising that pristane is present in many common fruits and vegetables. Furthermore, pristane can be detected in the tissues of fish and mammals. In animal models using rodents, pristane can function as a potent tumor promoter. At the molecular level, pristane can induce changes in the plasma membrane, alter the conformation of chromatin, and selectively activate gene expression. Addition of pristane to a mouse epidermal cell line (JB6 P+) allows these cells to grow in an anchorage-independent manner. In contrast, JB6 P-cells are not transformed by pristane. Our study was undertaken to correlate transformation of P+ cells with changes induced by pristane. Transcriptional activation of a cyclic AMP response element (CRE) was induced by pristane in P+ and P-cells. Point mutations in the CRE abolished activation by pristane, thus indicating that an intact CRE was necessary for pristane activation. In P+ cells, pristane repressed phosphodiesterase activity. However, protein kinase A was activated by pristane in P+ and P-cells. Taken together, these results indicated pristane induced novel changes in P+ cells that in turn may facilitate neoplastic transformation.

The tumor promoter pristane activates transcription by a cAMP dependent mechanism

Pristane is a naturally occurring isoprenoid which is believed to be derived from the phytyl moiety of chlorophyll. Thus it is not surprising that pristane is present in many common fruits or vegetables and furthermore can be detected in tissues of fish and mammals. Using the rat as an animal model, pristane can function as a potent tumor promoter. It is conceivable that pristane could play a role in the development of certain malignancies in higher mammals since it is commonly found in the diet. At the molecular level, pristane can induce changes in the plasma membrane, alter the conformation of chromatin, as well as selectively activate gene expression. This study was undertaken to identify specific transcriptional motifs which are responsive to pristane. A transcriptional promoter which contained a cAMP response element (CRE) was consistently stimulated by pristane in several mouse and primate cell lines. A promoter construct which contained a single copy of the TPA response element (TRE) was also activated by pristane but surprisingly a promoter which contained multiple copies of the TRE was not. Activation of the TRE required 10 fold higher concentrations of pristane relative to activation of the CRE. Within two hours after addition of pristane to monkey fibroblasts (CV-1) levels of cAMP were increased more than two fold relative to controls. These data indicated that pristane can increase the level of cAMP in CV-1 cells and consequently stimulate transcriptional promoters which contain a CRE.

Pristane induced gene activation

Studies were performed to examine the effects of 2,6,10,14-tetramethyl pentadecane (pristane) versus 12-O-tetradecanoylphorbol 13-acetate (TPA) on the activation of the CAT gene under the regulatory control of viral promoter/enhancer elements transfected into NIH-3T3, CV-1 and COS-7 cells. The results of these studies demonstrated that (1) pristane or TPA induced trans-activation of SV2cat, HIVcat, RSVcat and MMTVcat in cells transfected with each respective plasmid construct, (2) only pristane induced activation of pA10cat and pOSP/11 and (3) neither TPA nor pristane trans-activated pSV0cat. Furthermore, treatment with either pristane or TPA elicited changes in the morphology of each of the cell lines. Collectively these results indicate that pristane is a potent inducer of gene expression and exhibits similar characteristics as the tumor promoter, TPA.

The uptake of pristane (2,6,10,14-tetramethylpentadecane) into phospholipid bilayers as assessed by NMR, DSC, and tritium labeling methods

Unilamellar dioleoylphosphatidylcholine (DOPC) liposomes (250 microM) incorporated 2 mol% of [3H]pristane at 37 degrees C after addition of 50 microM pristane solubilized with beta-cyclodextrin. Conventional solubilization in dimethyl sulphoxide resulted in much lower uptake. Premixing of perdeuterated pristane with DOPC and dipalmitoylphosphatidylcholine (DPPC) prior to the formation of multilamellar liposomes resulted in homogeneous incorporation of up to 5 mol% pristane at 22 degrees C and 50 degrees C, respectively, as observed by 2H-NMR. Lipid order parameters measured by 31P and 2H-NMR remained unchanged after pristane uptake. Pristane induced the transformation of part of the dioleoylphosphatidylethanolamine (DOPE)/DOPC (3:1, mol/mol) liquid crystalline lamellar phase into an inverse hexagonal phase. 5 mol% pristane in DPPC bilayers decreased the midpoint of the main phase transition temperature of DPPC from 41.5 degrees C to 40.9 degrees C. Upon cooling in the temperature range from 41 degrees C to 36 degrees C, pristane was either displaced from the DPPC bilayer or the mode of incorporation changed. These results may aid in defining the mechanisms whereby pristane, an isoprenoid C19-isoalkane, induces plasmacytomagenesis in mice.

Pristane induced effects on chromatin of rat lymphoid cells

The effects of pristane on the conformation of chromatin in cells isolated from the lymphoid tissues of pristane-treated Copenhagen rats were examined by flow cytometry, thermal denaturation, sensitivity to enzymatic digestion, and histone protein analyses. Decreases were observed in the fluorescent intensities of propidium iodide (PI) stained nuclei isolated from lymphoid cells of pristane-treated rats when compared with normal rat lymphoid nuclei. Studies to address the possible basis for the pristane-induced changes in the DNA staining characteristics of lymphocytes demonstrated that 1) there were no decreases in the amount of DNA present in the nuclei, 2) nuclei isolated from pristane treated rats were less sensitive to thermal denaturation, as well as DNase I enzymatic digestion, and 3) there were apparent increases in the expression of the H1 histone proteins. Collectively, these results suggest that pristane elicits a conformational change in the chromatin which may be mediated by altered expression of nuclear-associated histone proteins.

The role of the Peyer's patch in the carcinogenesis of lymphoid cells

The dose response to 3-methylcholanthrene (3-MC), the promoter effects of 2,6,10,14-tetramethylpentadecane (pristane) and the target-organ specificity in the preferential induction of B-lymphoid malignancies versus thymic tumors were examined. Lymphoid malignancies were induced in approximately 30% of the Copenhagen rats treated with injections in Peyer's patches (PP) of low, intermediate or high doses of 3-MC. A low dose of 3-MC induced B-lymphocytic leukemias or B lymphomas, whereas thymic tumors were detected in rats treated with high doses. Co-treatment of rats with pristane and 3-MC resulted in increased incidences and decreased latency of the lymphoid malignancies observed, suggesting that pristane acts as a tumor promoter. To address the possible role of PP in the induction events, PP were surgically removed after 3-MC treatment and the remaining small intestine anastomosed. Thymic tumors, but no B-lymphoid malignancies, were observed, indicating that the PP environment was important in the induction of the B-lymphoid malignancies. Radiotracer studies also revealed that appreciable amounts of 3-MC were disseminated to the thymus within 24 hr after treatment of PP with a high dose of 3-MC. Furthermore, direct intrathymic injection of the thymus with 3-MC resulted in the development of thymic tumors only. These results support the hypothesis that the PP has an important role in early events in the carcinogenesis of B lymphocytes and in the dissemination of 3-MC to the thymus.

Thymic tumors induced by 3-methylcholanthrene treatment of rat Peyer's patches

Studies were performed to characterize thymic tumors which were induced after a single injection of 500 microgram or 3-methylcholanthrene (3-MC) into surgically exposed Peyer's patches (PP) of Copenhagen rats. Detailed gross, histological, and morphological analyses revealed thymic tumors differing in size and weight (1 to greater than 8 g) with distorted architecture and infiltration by lymphocytes and epithelial cells in varying proportions. Approximately 25% of the rats with thymic tumors exhibited abnormal spleens, whereas 66% developed low grade leukemias. A majority of the thymic tumors contained cells which exhibited (1) phenotypic markers characteristic of normal thymocytes, (2) abnormal DNA, and (3) increased percentages in S + G2 phases of the cell cycle. Further studies of tumor cell isolates demonstrated an increased frequency of colony formation on soft agar, as well as the ability to elicit thymic tumors upon transplantation. Collectively these studies describe chemically induced thymic lymphomas.

The Ah receptor, cytochrome P450IA1 mRNA induction, and aryl hydrocarbon hydroxylase in a human lymphoblastoid cell line

The immunosuppressive and carcinogenic effects of aryl hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 3-methylcholanthrene (MC) on B lymphocytes of adult rodents and the induction of cytochrome P450IA1 and aryl hydrocarbon hydroxylase (AHH) in human mitogen-activated lymphocytes and B-lymphoblastoid cell lines are believed to be mediated by the Ah receptor. However, there has not been a direct demonstration or characterization of the Ah receptor in defined populations of any of these cells. We report here the detection and characterization of an abundant, high-affinity B lymphocyte Ah receptor in the AHH-inducible human B lymphoblastoid cell line BCR-5. Our results represent the first characterization of a human lymphocyte receptor in a well-defined lymphocyte population. Sucrose density gradient analysis of BCR-5 cytosols incubated with [3H]TCDD revealed a characteristic 9 S specific binding peak. The maximum concentration of Ah receptor was about 200 fmol/mg protein. Specific binding to the Ah receptor was also detected with [3H]MC and, to a lesser extent, with [3H]benzo[alpha]pyrene. The apparent binding affinity (Kd) for [3H]TCDD (determined by saturation analyses) was about 5 nM. A specific [3H]TCDD-Ah receptor complex which sedimented at 5 S was extracted from nuclei of BCR-5 cells incubated at 37 degrees with [3H]TCDD. The Ah receptor of BCR-5 cells is thus similar in characteristics to that identified in other cell lines. When BCR-5 cells were exposed in culture for 24 hr to increasing concentrations of benz[alpha]anthracene there was a concentration-dependent increase in induction and a good correlation (r = 0.98) between the level of induced AHH activity and the relative abundance of cytochrome P450IA1 mRNA. The human B lymphoblastoid cell line BCR-5, therefore, has a complete regulatory mechanism for Ah receptor-mediated induction of cytochrome P450IA1 that is essentially the same as that which has been well established in many rodent species. The accessibility of human blood lymphocytes and the ease of establishment of B lymphoblastoid cell lines from any donor provide a source of pure cultures of human B lymphocytes which can be grown continuously in vitro for the study of mechanisms related to Ah receptor-mediated cytochrome P450IA1 induction, immunosuppression and carcinogenesis.

Dietary effects of pristane on rat lymphoid tissues

Studies were conducted to assess the normal tissue-associated levels of pristane (2,6,10,14,-tetramethylpentadecane) in Copenhagen rats during ontogeny and adult life and to address whether or not dietary pristane can be adsorbed from the gut and disseminated throughout the body. During the course of this study the possible effects of dietary pristane on chromatin conformation of lymphoid cells were also examined by flow cytometry. The data indicated that 1) pristane crossed the placenta and accumulated in fetal tissues, 2) neonates were exposed to pristane via the colostrum, 3) there were significant increases in the amount of tissue-associated pristane in young adults and subsequent redistribution of the pristane to the muscle and adipose tissues in older rats and 4) after dietary exposure, significantly elevated levels of pristane were associated with the tissues and concomitant changes in chromatin conformation were observed. Collectively, these results suggest that pristane was adsorbed from dietary sources, disseminated to the tissues and exerted a transient, yet marked effect on chromatin of lymphoid cells in rats.

Conformational changes in the DNA of hybridoma cells from pristane treated mice

The effects of pristane on the DNA of hybridoma cells propagated as ascitic tumors in pristane-primed BALB/c mice were determined using flow cytometric analyses. Hybridoma cells maintained in vitro or cell isolates from solid tumors which developed in unprimed mice injected with hybridoma cells exhibited similar propidium iodide (PI) staining characteristics. In contrast, PI stained cells isolated from ascites which developed in pristane-primed mice injected with the hybridoma cells displayed significant decreases in fluorescence intensity. Diphenylamine studies and analyses of pH 10 treated cells indicated that the actual DNA content of the hybridoma cells was not altered by exposure to pristane. Furthermore, the altered staining characteristics of the ascitic tumor cells were reversible in that the fluorescence intensity after serial in vitro passage of the ascites cells was similar to that of the parent cell line which had not been exposed to pristane. In addition, there was a direct correlation between the altered PI staining characteristics and the presence of cell-associated pristane as determined by gas-liquid chromatography analyses of cell extracts. Collectively these results suggest that pristane may have a direct effect on the DNA conformation of hybridoma cells which may in turn enhance their growth as ascitic tumors. The possible role of such an altered DNA conformation in hybridoma cells on the in vivo development of ascites is discussed.

Changes in the DNA of lymphocytes from pristane treated rats

The effects of pristane (2,6,10,14-tetramethylpentadecane) on the cellular DNA of lymphoid cells from Copenhagen rats were examined by flow cytometry. Significant reductions in the mean relative fluorescent intensities of propidium iodide (PI) stained lymphocytes from peripheral blood, spleen, thymus and lymph nodes were observed after a single intraperitoneal injection of pristane. The altered PI staining characteristics were observed as early as 4 days and reached a maximum decrease between 1-4 weeks (depending upon the lymphoid cells examined) post pristane treatment. The pristane-induced effects on peripheral blood lymphocytes were observed to be dose dependent, transient and reinducible by a subsequent exposure to pristane. Further analyses, using gas-liquid chromatography to detect pristane in the blood and lymphoid tissues of treated rats, indicated significant increases over normal amounts of pristane. Furthermore, correlations existed between the times of maximum decrease in the fluorescence of PI stained cells and the amounts of pristane detected within the respective lymphoid tissues. By contrast no changes in the PI staining characteristics of kidney cells were observed, even though appreciable amounts of pristane were detected in this organ. Diphenylamine analyses indicated no differences in the amounts of DNA in lymphoid cells from pristane treated and untreated rats. Furthermore, lymphocytes from pristane-treated rats did not exhibit decreased fluorescence when fixed at pH 10 rather than pH 7.4 prior to PI staining. Collectively these results suggest that pristane may preferentially induce qualitative rather than quantitative changes in the DNA of lymphocytes.