Premalignant alterations in the lipid composition and fluidity of colonic brush border membranes of rats administered 1,2 dimethylhydrazine

Phospholipids as cancer biomarkers: Mass spectrometry-based analysis

Lipids, particularly phospholipids (PLs), are key components of cellular membrane. PLs play important and diverse roles in cells such as chemical-energy storage, cellular signaling, cell membranes, and cell-cell interactions in tissues. All these cellular processes are pertinent to cells that undergo transformation, cancer progression, and metastasis. Thus, there is a strong possibility that some classes of PLs are expected to present in cancer cells and tissues in cellular physiology. The mass spectrometric soft-ionization techniques, electrospray ionization (ESI), and matrix-assisted laser desorption/ionization (MALDI) are well-established in the proteomics field, have been used for lipidomic analysis in cancer research. This review focused on the applications of mass spectrometry (MS) mainly on ESI-MS and MALDI-MS in the structural characterization, molecular composition and key roles of various PLs present in cancer cells, tissues, blood, and urine, and on their importance for cancer-related problems as well as challenges for development of novel PL-based biomarkers. The profiling of PLs helps to rationalize their functions in biological systems, and will also provide diagnostic information to elucidate mechanisms behind the control of cancer, diabetes, and neurodegenerative diseases. The investigation of cellular PLs with MS methods suggests new insights on various cancer diseases and clinical applications in the drug discovery and development of biomarkers for various PL-related different cancer diseases. PL profiling in tissues, cells and body fluids also reflect the general condition of the whole organism and can indicate the existence of cancer and other diseases. PL profiling with MS opens new prospects to assess alterations of PLs in cancer, screening specific biomarkers and provide a basis for the development of novel therapeutic strategies. © 2016 Wiley Periodicals, Inc. Mass Spec Rev 37:107-138, 2018.

Imaging mass spectrometry distinguished the cancer and stromal regions of oral squamous cell carcinoma by visualizing phosphatidylcholine (16:0/16:1) and phosphatidylcholine (18:1/20:4)

Most oral cancers are oral squamous cell carcinoma (OSCC). The anatomical features of OSCC have been histochemically evaluated with hematoxylin and eosin. However, the border between the cancer and stromal regions is unclear and large portions of the cancer and stromal regions are resected in surgery. To reduce the resected area and maintain oral function, a new method of diagnosis is needed. In this study, we tried to clearly distinguish the border on the basis of biomolecule distributions visualized by imaging mass spectrometry (IMS). In the IMS dataset, eleven signals were significantly different in intensity (p < 0.01) between the cancer and stromal regions. Two signals at m/z 770.5 and m/z 846.6 were distributed in each region, and a clear border was revealed. Tandem mass spectrometric (MS/MS) analysis identified these signals as phosphatidylcholine (PC) (16:0/16:1) at m/z 770.5 in the cancer region and PC (18:1/20:4) at m/z 846.6 in the stromal region. Moreover, the distribution of PC species containing arachidonic acid in the stromal region suggests that lymphocytes accumulated in response to the inflammation caused by cancer invasion. In conclusion, the cancer and stromal regions of OSCCs were clearly distinguished by use of these PC species and IMS analysis, and this molecular identification can provide important information to elucidate the mechanism of cancer invasion.

Alterations in membrane fluidity and dynamics in experimental colon cancer and its chemoprevention by diclofenac

We examined the role of membrane fluidity and dynamics as important early events in the carcinogenic transformation of colonic epithelial cells. 1,2-Dimethylhydrazine dihydrochloride (DMH) was used to induce initial stages of colon cancer and diclofenac was used for chemoprevention. To determine alterations of membrane fluidity of rat colonic epithelial cells, fluidity (inverse of fluorescence polarization) and order parameter were studied with 1,6-diphenylhexatriene (DPH) polarization. Order parameter as well as fluorescence polarization was found to be significantly decreased, thus demonstrating an increase in the fluidity of the membrane. To further confirm the fluidity changes, microviscosity of the cell membrane was studied using pyrene excimer formation, which showed a significant decrease in microviscosity and hence elevated membrane fluidity (translational diffusion). The colonocytes were stained with merocyanine 540 (MC540) to further elaborate the changes in membrane fluidity and lipid packing. The increased number of colonocytes showing high MC540 fluorescence pointed towards the wide spaces and hence, high fluidity in the membrane after DMH treatment. Membrane dynamics studies, i.e., lipid phase separation and membrane phase state were carried out using N-NBD-PE and Laurdan, respectively. We saw a transition from the gel to a more liquid crystalline state of the membrane in the Laurdan experiment. Further more percentage quenching (%Q) value of N-NBD-PE showed less phase separation (or domain formation). Diclofenac co-administration with DMH was successful in reverting the changes observed, confirming the role of these anti-inflammatory drugs in considerable lipid affinity and consequently in the chemoprevention of early stages of colon cancer.

Inhibitory effect of morin on DMH-induced biochemical changes and aberrant crypt foci formation in experimental colon carcinogenesis

Morin is a flavonoid present in fruits and Chinese herbs, exhibits various beneficial biological activities. There are numerous evidence suggesting that total dietary fat intake is generally associated with early promotion of colon cancer, the alterations in the lipid profile is important for malignant transformation and tumor development and carbohydrate moieties of glycoproteins reflect the stage of cancer. Aberrant crypt foci (ACF) consisting of morphologically irregular crypts, are thought to be precancerous lesions for colon cancer. Our aim was to study the inhibitory effect morin on aberrant crypt foci and alterations in the levels of lipids, and glycoconjugates in experimental rat colon cancer. Group 1 served as control, groups 2 and 4 received 50mg/kg b.w. morin orally everyday for 30 weeks. Groups 3 and 4 were given subcutaneous injection of 1,2-dimethylhydrazine (DMH) 20mg/kg b.w. for the first 15 weeks. Administration of morin at the dose of 50mg/kg b.w., significantly suppressed the formation of ACF its multiplicity and lowered levels of serum and tissue lipids, cholesterol-phospholipid ratio, glycoconjugate and also increased the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG CoA reductase). These results indicate that morin has a protective effect against DMH-induced colon carcinogenesis.

MALDI-based imaging mass spectrometry revealed abnormal distribution of phospholipids in colon cancer liver metastasis

We present the results of matrix-assisted laser desorption/ionization (MALDI) imaging and direct molecular identification using tandem mass spectrometry (MS/MS) in colon cancer liver metastasis. Cancer tissue was removed from a Japanese patient and frozen immediately without any fixations. The sections were sliced to a thickness of 3 microm. The matrix for lipid ionization was 2,6-dihydroxy acetophenone. The matrix solution was applied with an airbrush into a thin uniform matrix layer on the tissue surface. After two-dimensional laser scanning, the images were reconstructed as a function of m/z from a few hundred obtained spectra. In the obtained images, the existence of molecules was represented by a pseudo-color corresponding to the signal intensity. In a feasibility study, we picked up a localized signal, m/z 725 in a cancerous area. The MS/MS result suggested that m/z 725 was sphingomyelin(16:0)+Na. Thus, we successfully show the feasibility of MALDI imaging as a tool for the analysis of pathological specimens.

Ursodeoxycholic acid differentially affects three types of sphingomyelinase in human colon cancer Caco 2 cells

We investigated the effects of UDCA on sphingomyelinase (SMase) in Caco 2 cells cultured in monolayer and polarized conditions. Alkaline SMase activity was high in polarized cells whereas, acid and neutral SMase activities were high in monolayer cells. In polarized cells, UDCA increased alkaline SMase expression and caspase 3 activity but had no effect on acid and neutral SMases. In monolayer cells, UDCA reduced both acid and neutral SMase activities, inhibited cell proliferation, but had little effect on alkaline SMase and caspase 3 activities. In conclusion, UDCA differentially affects SMase activity, cell proliferation, and apoptosis in colonic cells depending on the cell conditions.

Purification, localization, and expression of human intestinal alkaline sphingomyelinase

Sphingomyelin (SM) metabolism in the gut may have an impact on colon cancer development. In this study, we purified alkaline sphingomyelinase (alk-SMase) from human intestinal content, and studied its location in the mucosa, expression in colon cancer, and function on colon cancer cells. The enzyme was purified by a series of chromatographies. The molecular mass of the enzyme is 60 kDa, optimal pH is 8.5, and isoelectric point is 6.6. Under optimal conditions, 1 mg of the enzyme hydrolyzed 11 mM SM per hour. The properties of the enzyme are similar to those of rat intestinal alk-SMase but not to those of bacterial neutral SMase. Immunogold electronmicroscopy identified the enzyme on the microvillar membrane in endosome-like structures and in the Golgi complexes of human enterocytes. The expression and the activity of the enzyme were decreased in parallel in human colon cancer tissues compared with the adjacent normal tissue. The enzyme inhibited DNA biosynthesis and cell proliferation dose dependently and caused a reduction of SM in HT29 cells. Intestinal alk-SMase is localized in the enterocytes, down-regulated in human colon cancer, and may have antiproliferative effects on colon cancer cells.

Dietary copper affects azoxymethane-induced intestinal tumor formation and protein kinase C isozyme protein and mRNA expression in colon of rats

Previous studies have show that changes in protein kinase C (PKC) isoform expression may be related to increased susceptibility of copper-deficient rats to aberrant crypt formation. The purpose of this study was to determine whether dietary copper would affect azoxymethane-induced intestinal tumor formation and PKC isozyme expression in normal colonic mucosa and tumor samples. Eighty weanling Fischer-344 rats were randomly assigned to diets that contained either 0.8 or 5.3 microg Cu/g diet. After 24 and 31 d of diet consumption, 30 rats/diet were administered azoxymethane (15 mg/kg i.p.) and 10 rats/diet were administered saline. Rats continued to consume their respective diets for an additional 38 wk. Rats injected with azoxymethane and fed the low copper diet had a significantly (P < 0.0001) greater small intestinal and total tumor incidence compared with rats fed adequate dietary copper. However, dietary copper did not affect colon tumor incidence. Low dietary copper significantly (P < 0.004) decreased PKC alpha protein expression in normal but not in tumor tissue. In contrast, low dietary copper did not affect PKC delta or zeta protein expression in either the normal or tumor tissue. PKC alpha and delta protein and mRNA expression were lower in tumor tissue than in normal tissue. These results along with previous observations suggest that dietary copper-mediated changes in PKC alpha, delta and zeta protein expression are not as important for colon tumor promotion/progression as they are for tumor initiation.

Dietary copper and dimethylhydrazine affect protein kinase C isozyme protein and mRNA expression and the formation of aberrant crypts in colon of rats

Low dietary copper has been shown to decrease the expression of various protein kinase C (PKC) isozymes and increase the risk of colon cancer development in experimental animals. The purpose of this study was to investigate the relationship between dietary copper and carcinogen administration on PKC isozyme accumulation and aberrant crypt foci (ACF) formation in rats fed 0.9 and 7.7 microg Cu/g diet. After 24 and 31 d on the diets, the rats were injected with either dimethylhydrazine (DMH) (25 mg/kg i.p.) or saline and killed at two time points (2 wk and 8 wk after DMH). Rats fed low dietary copper had significantly lower (p<0.0001) hematocrits, hemoglobin, ceruloplasmin activity and plasma and liver copper concentrations than rats fed adequate dietary copper. Ingestion of low dietary copper significantly (p<0.005) increased the formation of DMH-induced ACF (116.8 vs 59.6). Low dietary copper significantly (p<0.05) decreased the concentration of PKC alpha, delta, and zeta in the colon at 2 wk but not at 8 wk. Thus, changes in PKC isoform protein concentration may be related to increased susceptibility of copper-deficient animals to colon cancer.

Phospholipid profiles of human colon cancer using 31P magnetic resonance spectroscopy

Phospholipids of 16 malignant and 11 non-malignant human colon specimens were analyzed using a chloroform-methanol analytical reagent in conjunction with 31P magnetic resonance spectroscopy (MRS) at 202.4 MHz. Sixteen individual generic phospholipids were identified and quantified for statistical intergroup comparisons. Statistically significant elevations in the relative concentrations of lysophosphatidylcholine and phosphatidylcholine plasmalogen were seen in malignant tissues along with significantly depressed levels of sphingomyelin and phosphatidylethanolamine plasmalogen. The malignant and non-malignant tissue groups were further differentiated by the detection of the minor phospholipids, lysophosphatidylcholine plasmalogen, lysophosphatidylethanolamine plasmalogen, lysophosphatidic acid and phosphatidylglycerol exclusively present in the malignant tissues and by significant changes in computed phospholipid metabolic indices that were dominated by choline containing lipids. The 31P MRS methods used represent an advancement over previous protocols for identifying and quantifying major and minor tissue phospholipids making this the first direct study of membrane phospholipids in human colon tissues using 31P MRS. The phospholipid profiles obtained may provide important information regarding the nature of the malignant cell's membrane system and identify markers which may be used to estimate malignant propensity, aggressiveness of disease and provide prognostic information.

Down-regulation of protein kinase C activity in 1,2-dimethylhydrazine-induced rat colonic tumors

Recent studies by our laboratory have indicated that alterations in protein kinase C activity may be involved in the early stage(s) of malignant transformation in the 1,2-dimethylhydrazine model of colonic adenocarcinoma. In order to further evaluate the possible role of protein kinase C in this multistage process, rats were given subcutaneous weekly injections of this procarcinogen (20 mg/kg body weight) or diluent for 26 weeks. One week after receiving the last injection, animals were killed and control colonic tissue, tumor tissue and tissue at least 1 cm away from these tumors ('uninvolved mucosa') were harvested. The activity and distribution of protein kinase C in the cytosolic and membrane fractions of these preparations as well as their 1,2-diacylglycerol mass were then examined and compared. The results of these studies demonstrated that: (1) total protein kinase C activity was reduced by approximately 35% and 60%, respectively, in the 'uninvolved' colonic mucosa and tumors of carcinogen-treated rats compared to their control counterpart values; (2) in the 'uninvolved' mucosa, this decrease in total activity was secondary to a decrease solely in cytosolic protein kinase C, whereas, in tumors both membrane and cytosolic activities were reduced; and (3) 1,2-diacylglycerol mass was significantly increased in colonic tumors versus control values. Based on these findings, it would appear that alterations in the cellular distribution and total activity of protein kinase C, possibly secondary to increases in 1,2-diacylglycerol mass, may also play a role in the latter stage(s) of malignant transformation in this experimental model.

Sphingomyelin and derivatives as cellular signals

This comprehensive review was necessitated by recent observations suggesting that sphingomyelin and derivatives may serve second messenger functions. It has attempted to remain true to the theme of cellular signalling. Hence, it has focussed on the lipids involved primarily with respect to their metabolism and properties in mammalian systems. The enzymology involved has been emphasized. An attempt was made to define directions in which signals may be flowing. However, the evidence presented to date is insufficient to conclusively designate the mechanisms of stimulated lipid metabolism. Hence, the proposed pathways must be viewed as preliminary. Further, the biologic functions of these lipids is for the most part uncertain. Thus, it is difficult to presently integrate this sphingomyelin pathway into the greater realm of cell biology. Nevertheless, the present evidence appears to suggest that a sphingomyelin pathway is likely to possess important bioregulatory functions. Hopefully, interest in this novel pathway will grow and allow a more complete understanding of the roles of these sphingolipids in physiology and pathology.

1,2-Dimethylhydrazine-induced alterations in lipid peroxidation in preneoplastic and neoplastic colonic tissues

To determine whether alterations in lipid peroxidation existed in the preneoplastic and neoplastic colonic tissues of animals treated with the procarcinogen 1,2-dimethylhydrazine, rats were injected subcutaneously with this agent (20 mg/kg body weight per week) or diluent for 5, 10, 15 and 26 weeks. At each of these time periods, animals from both groups were sacrificed, their distal colonic mucosa and/or tumors harvested, and examined and compared with respect to malondialdehyde and lipofuscin-like pigments levels. Additionally, at 26 weeks, the fatty acid composition of microsomes prepared from control, 'uninvolved' and tumor colonic tissues were analyzed and compared. The results of these experiments demonstrated that: (1) the levels of these products of lipid peroxidation were similar in the distal colons of all animals at 5 and 10 weeks; (2) at 15 weeks, however, lipid peroxidation was decreased in the distal colons of animals treated with dimethylhydrazine; (3) at 26 weeks, the levels of these products of lipid peroxidation remained lower in dimethylhydrazine-treated distal 'uninvolved' colonic mucosa and was, moreover, markedly decreased in colonic tumors; and (4) at this latter time period, differences in the fatty acid composition between tumor, 'uninvolved' and control tissues were found. These differences, however, did not appear to underlie the changes noted in the lipid peroxidation products seen in these tissues. Taken together, these findings suggest that alterations in lipid peroxidation may be involved in the colonic malignant transformation process in this experimental model.

1,2-Dimethylhydrazine-induced alterations in N1-acetylspermidine levels in rat distal colonic mucosa: effects of 2-difluoromethylornithine

Recently, our laboratory has demonstrated that N1-acetylspermidine levels were increased in the distal colonic mucosa of rats administered 1,2-dimethylhydrazine for 15 and 26 weeks. In order to further explore the possible role of this acetylated polyamine in the malignant transformation process induced by this carcinogen, groups of rats were subcutaneously injected weekly with dimethylhydrazine (20 mg/kg body wt.) or diluent for 5, 10, 15 and 26 weeks +/- 1% 2-difluoromethylornithine in the drinking water. The latter agent, an irreversible inhibitor of ornithine decarboxylase, has previously been shown to inhibit colonic tumor formation in this experimental model. At each of these time periods, rats from each group were killed, their proximal and distal colonic mucosa harvested and examined, and compared with respect to polyamine levels, including N1-acetylspermidine, as well as the activities of ornithine decarboxylase, S-adenosylmethionine decarboxylase, spermidine N1-acetyltransferase and polyamine oxidase. The results of these experiments demonstrated that: (1) N1-acetylspermidine levels in the proximal colonic segment of all animals were similar at each time point; (2) N1-acetylspermidine levels were also similar in the distal colons of all animals at 5 and 10 weeks. At 15 weeks, however, the level of N1-acetylspermidine was increased in the dimethylhydrazine-treated distal colonic segment secondary to increases in the activity of spermidine N1-acetyltransferase; and (3) at 26 weeks, the level of this acetylated polyamine remained higher in dimethylhydrazine-treated distal 'uninvolved' colonic mucosa and was markedly elevated in colonic tumors; (4) co-administration of difluoromethylornithine decreased the elevated levels of N1-acetylspermidine to control values in the distal colons of animals treated with carcinogen for 15 and 26 weeks; and (5) difluoromethylornithine markedly reduced the number of tumors induced by dimethylhydrazine in the distal but not proximal colonic mucosa at 26 weeks.

Premalignant alterations in rat colonic N1-acetylspermidine levels induced by 1,2-dimethylhydrazine: effects of a high corn oil dietary regimen

Recently, our laboratory has demonstrated that elevations in the levels of N1-acetylspermidine could be detected in the colonic mucosa of rats after administration of 1,2-dimethylhydrazine for 15 weeks, i.e., before the development of colon tumors. Since prior studies have indicated that diets high in fat, particularly unsaturated fat, promote the development of dimethylhydrazine-induced tumors, it was of interest to examine the effect of a corn oil dietary regimen (20% by weight) on colonic N1-acetylspermidine levels in this model of colonic adenocarcinoma. Four groups of rats were used in these studies: chow, chow + carcinogen, corn oil and corn oil + carcinogen. The carcinogen groups received weekly s.c. injections of 1,2-dimethylhydrazine (20 mg/kg body wt) for 15 weeks, while the control groups received diluent. 1 week after the last injection, animals from each group were killed, and their proximal and distal colons were resected, examined and compared with respect to polyamine levels, including N1-acetylspermidine, as well as the activities of ornithine decarboxylase, spermidine N1-acetyltransferase, and polyamine oxidase. In view of previous studies which suggested that N1-acetylspermidine levels may be elevated in the urine of patients with various malignancies, it was also of interest to examine and compare the urinary levels of this acetylated polyamine in animals from each group. The results of these experiments demonstrated that: (1) the levels of N1-acetylspermidine in the distal colonic segment were found to be increased approx. 25 and 80% in the chow + carcinogen and corn oil + carcinogen groups, respectively, compared to their control counterparts; (2) the activities of spermidine N1-acetyltransferase in the distal colonic segments of chow + carcinogen and corn oil + carcinogen animals were increased 1.5- and 2-fold, respectively, compared to control values; (3) dimethylhydrazine administration did not affect the levels of this acetylated polyamine or spermidine N1-acetyltransferase activities in the proximal colon, but, in general, did increase the levels of putrescine and spermidine as well as ornithine decarboxylase activities in both colonic segments of animals fed chow or corn oil diets; and (4) elevated urinary levels of N1-acetylspermidine did not appear to be a reliable 'premalignant' marker in this experimental model of colonic adenocarcinoma.

Structurally distinct plasma membrane regions give rise to extracellular membrane vesicles in normal and transformed lymphocytes

Shedding of extracellular membranes from the cell surface may be one of the means through which cells communicate with one another. In an attempt to elucidate whether cell surface exfoliation is a directed or random process, we investigated the membrane lipid and protein composition and membrane lipid order of shed extracellular membranes and of plasma membranes from which they arose in normal circulating lymphocytes and in the B-lymphoblastoid cell lines Raji, WI HF2 729 and the T-lymphoblastoid cell line Jurkat. Extracellular membranes derived from transformed cell lines were more rigid as assessed by steady state polarization of 1,6-diphenylhexatriene (DPH) and were highly enriched in cholesterol when compared with the corresponding plasma membrane. The extracellular membranes from normal lymphocytes, on the other hand, were more fluid and contained more polyunsaturated acyl chains than did the plasma membranes from these cells. Our results suggest that extracellular membranes are shed from specialized regions of the lymphocyte plasma membrane and that membrane exfoliation is likely to be a directed event.

1,2-Dimethylhydrazine-induced premalignant alterations in the S-adenosylmethionine/S-adenosylhomocysteine ratio and membrane lipid lateral diffusion of the rat distal colon

Prior studies by our laboratory, utilizing the 1,2-dimethylhydrazine experimental model of colonic cancer, had shown that administration of this procarcinogen for 5 weeks was found to increase phospholipid methyltransferase activity and the fluidity of rat distal colonic brush-border membranes. The present studies were conducted to further explore these 'premalignant' colonic phenomena. Male albino rats of the Sherman strain were subcutaneously injected with dimethylhydrazine (20 mg/kg body weight per week) or diluent for 5 weeks. Animals from each group were killed, distal colonic tissue harvested and the levels of S-adenosylmethionine, S-adenosylhomocysteine and decarboxylated S-adenosylmethionine measured by high performance liquid chromatography. The activity of methionine adenosyltransferase was also examined in these tissues. Additionally, brush-border membranes were isolated from the distal colonocytes of control and treated-animals and examined and compared with respect to their phospholipid methylation activities as well as their lipid fluidity as assessed by the rotational mobilities of the probes 1,6-diphenyl-1,3,5-hexatriene and DL-12-(9-anthroyl)stearic acid and translational mobility of the fluorophore pyrenedecanoic acid. The results of these studies demonstrated: (1) phospholipid methyltransferase activity in rat colonic plasma membranes was increased concomitantly with increases in the cellular levels of S-adenosylmethionine and the S-adenosylmethionine/S-adenosylhomocysteine ratio in the distal colonic segment of treated-animals; and (2) the lateral diffusion of rat distal colonic brush-border membrane lipids, as assessed by the ratio of excimer/monomer fluorescence intensities of the fluorophore pyrenedecanoate, was also increased after dimethylhydrazine administration to these animals for 5 weeks.

Premalignant alterations in the glycosphingolipids of small intestinal mucosa of rats treated with 1,2-dimethylhydrazine

1,2-Dimethylhydrazine is a procarcinogen with selectivity for the colon and proximal small intestine. In weekly subcutaneous (s.c.) doses of 20 mg/kg body weight, this agent produces colonic and proximal small intestinal tumors in a high percentage of rodents with a latency period of approximately six months. To determine whether alterations in the glycosphingolipid content of rat proximal and/or distal small intestinal mucosa existed before the development of dimethylhydrazine-induced cancer, rat were given s.c. injections of this agent (20 mg/kg body weight per wk) or diluent for five wk. Animals were killed at this time, and mucosa was isolated from each small intestinal segment of both groups. Glycosphingolipids then were extracted from these tissues and analyzed by high performance thin layer chromatography and gas liquid chromatography. The results of these studies demonstrated that (1) the content of neutral and acidic glycosphingolipids was significantly decreased (approximately 20%) in the proximal small intestine of treated rats compared with their control counterparts; (2) no significant difference in the glycosphingolipid content was seen, however, in the distal small intestinal mucosa of control and treated rats; and (3) while significant differences were noted in the majority of fatty acids of GM3, glucosyl- and globotriaosylceramide in the proximal small intestine of control and treated animals, differences in the fatty acids of these glycosphingolipids in the distal segment of these groups were confined to stearic (18:0) acid and/or arachidic (20:0) acid.

Effect of hypothyroidism on the lipid composition and fluidity of rat colonic apical plasma membranes

Prior studies have suggested that the lipid composition and lipid fluidity of cellular membranes of various organs are altered in the hypothyroid rat. To date, the effects of hypothyroidism on these parameters have not been examined in rat colonic apical plasma membranes. In the present experiments, male Sprague-Dawley rats were fed a pelleted diet (control group) or the same diet containing 0.1% propylthiouracil (hypothyroid group) for 3 weeks. The lipid composition and lipid fluidity of apical plasma membranes prepared from colonocytes of these two groups of animals were then examined and compared. Membranes prepared from the hypothyroid animals were found to possess a higher level of linoleic acid (18:2) and a lower level of arachidonic acid (20:4) than membranes from control animals. The molar ratio of cholesterol/phospholipid was also lower in hypothyroid membranes secondary to a decreased cholesterol content compared to their control counterparts. Moreover, the lipid fluidity of colonic apical plasma membranes, as assessed by (1) the ratio of excimer to monomer fluorescence intensities of the lipid-soluble fluorophore pyrenedecanoic acid and (2) the anisotropy values of the fluorophore DL-12-(9-anthroyloxy)stearic acid using steady-state fluorescence polarization techniques, was greater in hypothyroid animals. These data, therefore, indicate that alterations in the lipid composition and fluidity of colonic apical plasma membranes can be detected in hypothyroid rats.

1,2-Dimethylhydrazine-induced alterations in Na+-H+ exchange in rat colonic brush-border membrane vesicles

1,2-Dimethylhydrazine, in weekly subcutaneous (s.c.) doses of 20 mg/kg body weight, produces colonic tumors in virtually 100% of rodents, with a latency period of approximately 6 months. To determine whether alterations in Na+-H+ exchange existed before the development of dimethylhydrazine-induced colon cancer, rats were given s.c. injections of this agent (20 mg/kg body wt. per per week) or diluent for 5 weeks. Animals were then killed, rat colonic brush-border membrane vesicles prepared and amiloride-sensitive sodium-stimulated proton efflux was measured and compared in control and treated-preparations. The results of these studies demonstrated that dimethylhydrazine treatment: (1) significantly increased the Vmax of this exchange without altering the Km for sodium of this exchange process, utilizing the fluorescent pH-sensitive dye, acridine orange; 22Na flux experiments also demonstrated an increase in amiloride-sensitive proton-stimulated sodium influx across treated-membrane vesicles; (2) did not appear to significantly influence Na+ permeability or proton conductance in treated-preparations compared to their control counterparts; and (3) did not significantly affect the kinetic parameters of amiloride-sensitive sodium-stimulated proton efflux in renal cortex brush-border membrane vesicles using acridine orange. This data, therefore, suggests that alterations in Na+-H+ exchange in rat colonic brush-border membranes may be involved in the malignant transformation process induced by this procarcinogen in the large intestine.

1,2-Dimethylhydrazine-induced alterations in colonic plasma membrane fluidity: restriction to the luminal region

Recently, work in this laboratory has shown that changes in the 'dynamic' component of fluidity, lipid composition and phospholipid methylation activity of distal colonic brush-border membranes could be detected after administration of 1,2-dimethylhydrazine to rats of the Sherman strain for 5-15 weeks, i.e., before the development of colon cancer. The present experiments were therefore conducted to: determine whether similar 'premalignant' biochemical changes could be detected in basolateral membranes of Sherman rats treated with this agent; and clarify the relationship of these membrane changes to the malignant transformation process by examining the effect of 1,2-dimethylhydrazine on these biochemical parameters in colonic antipodal plasma membranes of rats of the Lobund-Wistar strain. This particular strain of rats has previously been shown to be total resistant to the induction of tumors by 1,2-dimethylhydrazine. The results of the present experiments demonstrate that similar biochemical alterations could not be detected in the colonic plasma membranes prepared from either strain of rat treated with 1,2-dimethylhydrazine. These data support the contention that the prior biochemical membrane alterations noted in brush-border membranes of 1,2-dimethylhydrazine-treated animals are, in fact, related to the malignant transformation process and, furthermore, are confined to the luminal surface of distal colonic epithelial cells.

The role of sphingomyelin synthetase and sphingomyelinase in 1,2-dimethylhydrazine-induced lipid alterations of rat colonic plasma membranes

Recently, our laboratory, utilizing the 1,2-dimethylhydrazine model of colonic adenocarcinoma, demonstrated alterations in the 'dynamic component' of fluidity in brush-border membranes prepared from distal colonocytes of rats administered this agent for 5, 10 and 15 weeks, i.e., before the development of colon cancer. Furthermore, changes in the sphingomyelin content and sphingomyelin/phosphatidylcholine molar ratio of these membranes appeared, at least partially, to be responsible for these fluidity alterations. In an attempt to elucidate the mechanism(s) involved in these dimethylhydrazine-induced lipid changes, in the present studies the activities of sphingomyelin synthetase and magnesium-dependent neutral sphingomyelinase, enzymes involved in the synthesis and degradation of this phospholipid, respectively, were examined and compared in distal colonic brush-border membranes prepared from rats after 5, 10 or 15 weeks administration of dimethylhydrazine or diluent. The results of these studies demonstrate that alterations in both these enzymatic activities can be detected after administration of dimethylhydrazine and appear to, at least in part, be responsible for the changes in membrane sphingomyelin composition noted previously. These results as well as a discussion of their possible serve as the basis for the present report.