Biomedical subjects

Robert S Chapkin

Publications and source records attributed to Robert S Chapkin.

At least 19 recordsLinked to original sources

PubMed2007

Immunomodulatory effects of (n-3) fatty acids: putative link to inflammation and colon cancer.

Chronic inflammation and colorectal cancer are closely linked. Although the overall mechanisms of inflammation-associated gastrointestinal carcinogenesis are complex, it is clear that antiinflammatory therapy is efficacious against neoplastic progression and malignant conversion. From a dietary perspective, fish oil containing (n-3) polyunsaturated fatty acids (PUFAs) has antiinflammatory properties, but for years the mechanism has remained obscure. Of relevance to the immune system in the intestine, we showed that (n-3) PUFA feeding alters the balance between CD4+ T-helper (Th1 and Th2) subsets by directly suppressing Th1 cell development (i.e., clonal expansion). This is noteworthy because Th1 cells mediate inflammatory diseases and resistance to intracellular pathogens or allergic hypersensitivity, and Th2 cells mediate resistance to extracellular pathogens. Therefore, any changes induced by (n-3) PUFAs in T-cell subset balance and function are important because the outcome is expected to suppress the development of autoimmune diseases and possibly the occurrence of colon cancer. Precisely how the immunomodulatory effects of (n-3) PUFAs influence inflammation-associated colonic tumor development is the subject of an ongoing investigation.

Animals↗

PubMed2007

Colon cancer, fatty acids and anti-inflammatory compounds.

PURPOSE OF REVIEW: To outline recent findings on the efficacy of n-3 polyunsaturated fatty acids in the prevention/treatment of inflammatory bowel disease and colorectal cancer. RECENT FINDINGS: Compelling data indicate a functional link between chronic inflammation and colon cancer. With respect to environmental risk factors, there is growing evidence that long-chain n-3 polyunsaturated fatty acids found in fish oil suppress inflammatory bowel diseases and colon cancer risk in humans. Unfortunately, the molecular basis of the effect of n-3 polyunsaturated fatty acids on inflammation/colitis-associated colon cancer risk is still largely obscure. In this review, we focus on recent studies which address three emerging mechanisms of n-3 polyunsaturated fatty acids action: (1) metabolic interconversion into bioactive eicosanoids, (2) modulation of nuclear receptor activation, and (3) alteration of membrane phospholipid composition and functionality of lipid microdomains. SUMMARY: The consumption of dietary fish oil may prove to be an effective adjuvant therapy in colon cancer. Therefore, it is both appropriate and timely to determine precisely how n-3 polyunsaturated fatty acids modulate cell signaling networks, and reduce the risk of developing colon cancer and inflammatory disorders of the intestine.

Anti-Inflammatory Agents↗

PubMed2006

Docosahexaenoic acid selectively inhibits plasma membrane targeting of lipidated proteins.

Membrane localization of lipidated cytosolic signaling proteins is mediated by interactions between specific lipid anchors and membranes, but little is known about the regulatory role of membrane composition in lipidated protein membrane targeting. Here, using green fluorescent protein (GFP) chimeras and quantitative fluorescence microscopy in living mouse colonocytes, we show that docosahexaenoic acid (DHA), a dietary polyunsaturated fatty acid (PUFA) with membrane lipid-modifying properties, selectively inhibits plasma membrane (PM) targeting and increases the endomembrane localization of lipidated proteins that are cytoplasmic cargo in the exocytic pathway, without affecting the exocytic pathway itself. DHA selectivity seems to be dictated by the protein trafficking route, independent of the functional state of proteins and the location and composition of membrane anchors. DHA enrichment in cell membranes was required to elicit the inhibitory effect. These data reveal that membrane lipid composition influences cell signaling by modulating intracellular trafficking and localization of membrane proteins, providing a potential molecular mechanism for the documented health benefits of DHA.

Animals↗

PubMed2006

Dietary fish oil inhibits antigen-specific murine Th1 cell development by suppression of clonal expansion.

To determine the mechanisms by which dietary fish oil (FO) affects antigen-stimulated Th1 cell development, DO11.10 Rag 2(-/-) T cell receptor transgenic mice were fed a control diet (5% corn oil (CO) or a FO diet (1% CO + 4% FO, (n-3) PUFA) for 2 wk. CD4(+) T cells were cultured under neutral or Th1 polarizing conditions. FO feeding suppressed (P < 0.05) ovalbumin peptide-induced proliferation of nonpolarized CD4(+) T cells. Differentiation in vitro to Th1 cells was not affected by dietary FO, as evidenced by similar percentages of KJ1-26(+), IFN-gamma(+), IL-4(-) Th1 cells in cultures from CO-fed (99%) and FO-fed (97%) mice. However, the absolute number of viable Th1 cells in polarized cultures from FO-fed mice was less than half that observed in CO-fed mice (P < 0.05), indicating that FO inhibits in vitro Th1 clonal expansion. The reduced number of Th1 cells in FO cultures was not a result of increased apoptosis, because similar percentages of apoptotic Th1 cells were observed in cultures from FO- and CO-fed mice. IL-2-induced cell proliferation was significantly decreased in polarized Th1 cells from the FO group; however, the suppressed proliferation was not linked to reduced CD25 surface expression on antigen-stimulated CD4(+) T cells. Adoptively transferred CFSE-labeled DO11.10 CD4(+) cells into immunized mice (Th1 polarizing agents) showed that dietary FO reduced (P < 0.05) the number of cell divisions in vivo. These studies suggest that the attenuated inflammatory response which accompanies FO feeding may be explained, at least in part, by suppression of Th1 clonal expansion.

Adoptive Transfer↗

PubMed2005

Suppression of colon carcinogenesis by bioactive compounds in grapefruit.

This study evaluated the hypothesis that untreated and irradiated grapefruit as well as the isolated citrus compounds naringin and limonin would protect against azoxymethane (AOM)-induced aberrant crypt foci (ACF) by suppressing proliferation and elevating apoptosis through anti-inflammatory activities. Male Sprague-Dawley rats (n = 100) were provided one of five diets: control (without added grapefruit components), untreated or irradiated (300 Gy, 137Cs) grapefruit pulp powder (13.7 g/kg), naringin (200 mg/kg) or limonin (200 mg/kg). Rats were injected with saline or AOM (15 mg/kg) during the third and fourth week and colons were resected (6 weeks post second injection) for evaluation of ACF, proliferation, apoptosis, and cyclooxygenase (COX)-2 and inducible nitric oxide synthase (iNOS) protein levels. Experimental diets had no effect on the variables measured in saline-injected rats. However, in AOM-injected rats, the experimental diets suppressed (P < or = 0.02) aberrant crypt and high multiplicity ACF (HMACF; P < or = 0.01) formation and the proliferative index (P < or = 0.02) compared with the control diet. Only untreated grapefruit and limonin suppressed (P < or = 0.04) HMACF/cm and expansion (P < or = 0.008) of the proliferative zone that occurred in the AOM-injected rats consuming the control diet. All diets elevated (P < or = 0.05) the apoptotic index in AOM-injected rats, compared with the control diet; however, the greatest enhancement was seen with untreated grapefruit and limonin. Untreated grapefruit and limonin diets suppressed elevation of both iNOS (P < or = 0.003) and COX-2 (P < or = 0.032) levels observed in AOM-injected rats consuming the control diet. Although irradiated grapefruit and naringin suppressed iNOS levels in AOM-injected rats, no effect was observed with respect to COX-2 levels. Thus, lower levels of iNOS and COX-2 are associated with suppression of proliferation and upregulation of apoptosis, which may have contributed to a decrease in the number of HMACF in rats provided with untreated grapefruit and limonin. These results suggest that consumption of grapefruit or limonin may help to suppress colon cancer development.

Animals↗

PubMed2005

Dietary eicosapentaenoic acid modulates CTLA-4 expression in murine CD4+ T-cells.

We have demonstrated that downregulation of proliferation by CD4(+) T-cells in mice fed n-3 PUFA diets is dependent on the involvement of CD28. Therefore, we hypothesized that the balance of co-stimulatory and downregulatory properties of CD28 and CTLA-4, respectively, would be altered by diet. Mice were fed a control corn oil (CO)-enriched diet devoid of n-3 PUFA, or diets enriched with either docosahexaenoic acid (DHA) or eicosapentaenoic acid (EPA) for 14d. The proliferation of splenic CD4(+) T-cells was suppressed by DHA and EPA following stimulation with anti-CD3 and anti-CD28. Surprisingly, the number of surface CD28 molecules was not reduced in activated CD4(+) T-cells from either group of n-3 PUFA-fed mice. However, in mice fed EPA, CTLA-4 protein levels were enhanced significantly 72 h post-activation (P<0.01). Therefore, we conclude that dietary EPA may suppress CD4(+) T-cell activation by enhancing the downregulatory co-receptor CTLA-4, while not altering the levels of CD28.

Animals↗

PubMed2005

A two-stage normalization method for partially degraded mRNA microarray data.

MOTIVATION: The goal of the study is to obtain genetic information from exfoliated colonocytes in the fecal stream rather than directly from mucosa cells within the colon. The latter is obtained through invasive procedures. The difficulties encountered by this procedure are that certain probe information may be compromised due to partially degraded mRNA. Proper normalization is essential to obtaining useful information from these fecal array data. RESULTS: We propose a new two-stage semiparametric normalization method motivated by the features observed in fecal microarray data. A location-scale transformation and a robust inclusion step were used to roughly align arrays within the same treatment. A non-parametric estimated non-linear transformation was then used to remove the potential intensity-based biases. We compared the performance of the new method in analyzing a fecal microarray dataset with those achieved by two existing normalization approaches: global median transformation and quantile normalization. The new method favorably compared with the global median and quantile normalization methods. AVAILABILITY: The R codes implementing the two-stage method may be obtained from the corresponding author.

Algorithms↗

PubMed2005

The role of docosahexaenoic acid in mediating mitochondrial membrane lipid oxidation and apoptosis in colonocytes.

Docosahexaenoic acid (DHA, 22:6 n-3) from fish oil, and butyrate, a fiber fermentation product, work coordinately to protect against colon tumorigenesis in part by inducing apoptosis. We have recently demonstrated that dietary DHA is incorporated into mitochondrial membrane phospholipids, thereby enhancing oxidative stress induced by butyrate metabolism. In order to elucidate the subcellular origin of oxidation induced by DHA and butyrate, immortalized young adult mouse colonocytes were treated with 0-200 microM DHA or linoleic acid (LA, 18:2 n-6; control) for 72 h with or without 5 mM butyrate for the final 24 h. Cytosolic reactive oxygen species, membrane lipid oxidation, and mitochondrial membrane potential (MP), were measured by live-cell fluorescence microscopy. After 24 h of butyrate treatment, DHA primed cells exhibited a 151% increase in lipid oxidation (P < 0.01), compared with no butyrate treatment, which could be blocked by a mitochondria-specific antioxidant, 10-(6'-ubiquinoyl) decyltriphenylphosphonium bromide (MitoQ) (P < 0.05). Butyrate treatment of LA pretreated cells did not show any significant effect. In the absence of butyrate, DHA treatment, compared with LA, increased resting MP by 120% (P < 0.01). In addition, butyrate-induced mitochondrial membrane potential (MP), dissipation was 21% greater in DHA primed cells as compared with LA at 6 h. This effect was reversed by preincubation with inhibitors of the mitochondrial permeability transition pore, cyclosporin A or bongkrekic acid (1 microM). The functional importance of these events is supported by the demonstration that DHA and butyrate-induced apoptosis is blocked by MitoQ. These data indicate that DHA and butyrate potentiate mitochondrial lipid oxidation and the dissipation of MP which contribute to the induction of apoptosis.

Animals↗

PubMed2005

Comparing automatic and manual image processing in FLARE assay analysis for colon carcinogenesis.

Measurement of the amount of oxidative damage to DNA is one tool that can be used to estimate the beneficial effect of diet on the prevention of colon carcinogenesis. The FLARE assay is a modification of the single-cell gel electrophoresis (Comet) assay, and provides a measure of the 8OHdG adduct in the cells. In this paper, we present two innovations to the existing methods of analysis. The first one is related to the FLARE assay itself. We describe automated image analysis techniques that can be expected to measure oxidative damage faster, reproducibly, with less noise, and hence achieve greater statistical power. The proposed technique is compared to an existing technique, which was more manual and thus slower. The second innovation is our statistical analysis: we exploit the shape of FLARE intensity histograms, and show statistically significant diet effects in the duodenum. Previous analyses of this data concentrated on simple summary statistics, and found only marginally statistically significant diet effects. With the new imaging method and measure of oxidative damage, we show cells in the duodenum exposed to fish oil as having more oxidative damage than cells exposed to corn oil.

Journal Article↗

PubMed2005

Folate transport gene inactivation in mice increases sensitivity to colon carcinogenesis.

Low dietary folate intake is associated with an increased risk for colon cancer; however, relevant genetic animal models are lacking. We therefore investigated the effect of targeted ablation of two folate transport genes, folate binding protein 1 (Folbp1) and reduced folate carrier 1 (RFC1), on folate homeostasis to elucidate the molecular mechanisms of folate action on colonocyte cell proliferation, gene expression, and colon carcinogenesis. Targeted deletion of Folbp1 (Folbp1(+/-) and Folbp1(-/-)) significantly reduced (P < 0.05) colonic Folbp1 mRNA, colonic mucosa, and plasma folate concentration. In contrast, subtle changes in folate homeostasis resulted from targeted deletion of RFC1 (RFC1(+/-)). These animals had reduced (P < 0.05) colonic RFC1 mRNA and exhibited a 2-fold reduction in the plasma S-adenosylmethionine/S-adenosylhomocysteine. Folbp1(+/-) and Folbp1(-/-) mice had larger crypts expressed as greater (P < 0.05) numbers of cells per crypt column relative to Folbp1(+/+) mice. Colonic cell proliferation was increased in RFC1(+/-) mice relative to RFC1(+/+) mice. Microarray analysis of colonic mucosa showed distinct changes in gene expression specific to Folbp1 or RFC1 ablation. The effect of folate transporter gene ablation on colon carcinogenesis was evaluated 8 and 38 weeks post-azoxymethane injection in wild-type and heterozygous mice. Relative to RFC1(+/+) mice, RFC1(+/-) mice developed increased (P < 0.05) numbers of aberrant crypt foci at 8 weeks. At 38 weeks, RFC1(+/-) mice developed local inflammatory lesions with or without epithelial dysplasia as well as adenocarcinomas, which were larger relative to RFC1(+/+) mice. In contrast, Folbp1(+/-) mice developed 4-fold (P < 0.05) more lesions relative to Folbp1(+/+) mice. In conclusion, Folbp1 and RFC1 genetically modified mice exhibit distinct changes in colonocyte phenotype and therefore have utility as models to examine the role of folate homeostasis in colon cancer development.

Animals↗

PubMed2005

Dietary (n-3) polyunsaturated fatty acids modulate murine Th1/Th2 balance toward the Th2 pole by suppression of Th1 development.

We showed that dietary long-chain (n-3) PUFAs present in fish oil (FO) affect CD4(+) T cell proliferation and cytokine production in C57BL/6 mice. To test the hypothesis that the anti-inflammatory effect of dietary (n-3) PUFAs could be due to the indirect suppression of T helper (Th)1 cells by cross-regulation of enhanced Th2 activation, mice were fed a wash-out control diet [5% corn oil (CO), (n-6) PUFA] for 1 wk, followed by the control diet or a fish oil diet [1% CO + 4% FO, (n-3) PUFA] for 2 wk. Splenic CD4+ T cells were cultured under both neutral and Th2 polarizing conditions for 2 d. Cells were reactivated and analyzed for interleukin-4 and interferon-gamma by intracellular cytokine staining. Dietary fish oil significantly increased the percentage of Th2 polarized cells and suppressed Th1 cell frequency under neutral conditions. However, under Th2 polarizing conditions, although the suppression of Th1 cells was maintained in FO-fed mice, no effect was observed in Th2 cells. Dietary fish oil increased the Th2/Th1 ratio in the presence of homologous mouse serum under both neutral (P = 0.0009) and Th2 polarizing conditions (P = 0.0185). The FO diet did not significantly affect proliferation under Th2 polarizing conditions. Thus, the anti-inflammatory effects of FO may be explained in part by a shift in the Th1/Th2 balance, due to the direct suppression of Th1 development, and not by enhancement of the propensity of CD4+ T cells to be polarized toward a Th2 phenotype, at least in vitro.

Animals↗

PubMed2005

Tissue-specific attenuation of endogenous DNA I-compounds in rats by carcinogen azoxymethane: possible role of dietary fish oil in colon cancer prevention.

I-compounds are bulky covalent DNA modifications that are derived from metabolic intermediates of nutrients. Some I-compounds may play protective roles against cancer, aging, and degenerative diseases. Many carcinogens and tumor promoters significantly reduce I-compound levels gradually during carcinogenesis. Colon cancer is the second leading cause of cancer death in the United States, whereas cancer of the small intestine is relatively rare. Here we have studied levels of I-compounds in DNA of colon and duodenum of male Sprague-Dawley rats treated with azoxymethane. The effects of dietary lipids (fish oil or corn oil) on colon and duodenal DNA I-compounds were also investigated. Rats fed a diet containing fish oil or corn oil were treated with 15 mg/kg azoxymethane. Animals were terminated 0, 6, 9, 12, or 24 hours after injection. I-compound levels were analyzed by the nuclease P1-enhanced (32)P-postlabeling assay. Rats treated with azoxymethane displayed lower levels of I-compounds in colon DNA compared with control groups (0 hour). However, I-compound levels in duodenal DNA were not diminished after azoxymethane treatment. Animals fed a fish oil diet showed higher levels of I-compounds in colonic DNA compared with corn oil groups (mean adduct levels for fish and corn oil groups were 13.35 and 10.69 in 10(9) nucleotides, respectively, P = 0.034). Taken together, these results support claims that fish oil, which contains a high level of omega-3 polyunsaturated fatty acids, may have potent chemopreventive effects on carcinogen-induced colon cancer. The fact that duodenal I-compounds were not diminished by azoxymethane treatment may have been due to the existence of tissue-specific factors protecting against carcinogenesis. In conclusion, our observations show that endogenous DNA adducts may serve not only as sensitive biomarkers in carcinogenesis and cancer prevention studies, but are also helpful to further our understanding of the chemopreventive properties of omega-3 fatty acids and mechanisms of carcinogenesis.

Analysis of Variance↗

PubMed2005

Differential response to DNA damage may explain different cancer susceptibility between small and large intestine.

Although large intestine (LI) cancer is the second-leading cause of cancer-related deaths in the United States, small intestine (SI) cancer is relatively rare. Because oxidative DNA damage is one possible initiator of tumorigenesis, we investigated if the SI is protected against cancer because of a more appropriate response to oxidative DNA damage compared with the LI. Sixty rats were allocated to three treatment groups: 3% dextran sodium sulfate (DSS, a DNA-oxidizing agent) for 48 hrs, withdrawal (DSS for 48 hrs + DSS withdrawal for 48 hrs), or control (no DSS). The SI, compared with the LI, showed greater oxidative DNA damage (P < 0.001) as determined using a quantitative immunohistochemical analysis of 8-oxodeoxyguanosine (8-oxodG). The response to the DNA adducts in the SI was greater than in the LI. The increase of TdT-mediated dUTP-biotin nick end labeling (TUNEL)-positive apoptosis after DSS treatment was greater in the SI compared with the LI (P < 0.001), and there was a positive correlation (P = 0.031) between DNA damage and apoptosis in the SI. Morphologically, DSS caused an extensive loss of crypt structure shown in lower crypt height (P = 0.006) and the number of intact crypts (P = 0.0001) in the LI, but not in the SI. These data suggest that the SI may be more protected against cancer by having a more dynamic response to oxidative damage that maintains crypt morphology, whereas the response of the LI makes it more susceptible to loss of crypt architecture. These differential responses to oxidative DNA damage may contribute to the difference in cancer susceptibility between these two anatomic sites of the intestine.

8-Hydroxy-2'-Deoxyguanosine↗

PubMed2005

Fish oil decreases oxidative DNA damage by enhancing apoptosis in rat colon.

To determine if dietary fish oil protects against colon cancer by decreasing oxidative DNA damage at the initiation stage of colon tumorigenesis, oxidative DNA damage, proliferation, and apoptosis were assessed by colonic crypt cell position using quantitative immunohistochemical analysis of 8-hydroxydeoxyguanosine (8-OHdG), Ki-67, and TUNEL assay, respectively. Sixty rats were provided one of two diets (corn oil or fish oil) and dextran sodium sulfate (DSS, an inducer of oxidative DNA damage) treatments (no DSS, 3% DSS, or DSS withdrawal). Fish oil feeding resulted in lower 8-OHdG levels (P = 0.038), higher levels of apoptosis (P = 0.035), and a lower cell proliferative index (P = 0.05) compared with corn oil feeding. In the top third of the crypt, fish oil caused an incremental stimulation of apoptosis with increased DNA damage (P = 0.043), whereas there was no such relationship with corn oil. Because polyps and tumors develop from DNA damage that leads to loss of growth and death control, the significant difference in fish oil vs. corn oil on these variables may account, in part, for the observed protective effect of fish oil against oxidatively induced colon cancer.

Animals↗

PubMed2004

Dietary docosahexaenoic acid suppresses T cell protein kinase C theta lipid raft recruitment and IL-2 production.

To date, the proximal molecular targets through which dietary n-3 polyunsaturated fatty acids (PUFA) suppress the inflammatory process have not been elucidated. Because cholesterol and sphingolipid-enriched rafts have been proposed as platforms for compartmentalizing dynamically regulated signaling assemblies at the plasma membrane, we determined the in vivo effects of fish oil and highly purified docosahexaenoic acid (DHA; 22:6n-3) on T cell microdomain lipid composition and the membrane subdomain distribution of signal-transducing molecules (protein kinase C (PKC)theta;, linker for activation of T cells, and Fas/CD95), before and after stimulation. Mice were fed diets containing 5 g/100 g corn oil (control), 4 g/100 g fish oil (contains a mixture of n-3 PUFA) plus 1 g/100 g corn oil, or 4 g/100 g corn oil plus 1 g/100 g DHA ethyl ester for 14 days. Dietary n-3 PUFA were incorporated into splenic T cell lipid raft and soluble membrane phospholipids, resulting in a 30% reduction in raft sphingomyelin content. In addition, polyclonal activation-induced colocalization of PKCtheta; with lipid rafts was reduced by n-3 PUFA feeding. With respect to PKCtheta; effector pathway signaling, both AP-1 and NF-kappaB activation, IL-2 secretion, and lymphoproliferation were inhibited by fish oil feeding. Similar results were obtained when purified DHA was fed. These data demonstrate for the first time that dietary DHA alters T cell membrane microdomain composition and suppresses the PKCtheta; signaling axis.

Animals↗

PubMed2004

Chemopreventive n-3 polyunsaturated fatty acids reprogram genetic signatures during colon cancer initiation and progression in the rat.

The mechanisms by which n-3 polyunsaturated fatty acids (PUFAs) decrease colon tumor formation have not been fully elucidated. Examination of genes up- or down-regulated at various stages of tumor development via the monitoring of gene expression relationships will help to determine the biological processes ultimately responsible for the protective effects of n-3 PUFA. Therefore, using a 3 x 2 x 2 factorial design, we used Codelink DNA microarrays containing approximately 9000 genes to help decipher the global changes in colonocyte gene expression profiles in carcinogen-injected Sprague Dawley rats. Animals were assigned to three dietary treatments differing only in the type of fat (corn oil/n-6 PUFA, fish oil/n-3 PUFA, or olive oil/n-9 monounsaturated fatty acid), two treatments (injection with the carcinogen azoxymethane or with saline), and two time points (12 hours and 10 weeks after first injection). Only the consumption of n-3 PUFA exerted a protective effect at the initiation (DNA adduct formation) and promotional (aberrant crypt foci) stages. Importantly, microarray analysis of colonocyte gene expression profiles discerned fundamental differences among animals treated with n-3 PUFA at both the 12 hours and 10-week time points. Thus, in addition to demonstrating that dietary fat composition alters the molecular portrait of gene expression profiles in the colonic epithelium at both the initiation and promotional stages of tumor development, these findings indicate that the chemopreventive effect of fish oil is due to the direct action of n-3 PUFA and not to a reduction in the content of n-6 PUFA.

Animals↗

PubMed2004

Interactions of phospholipase D and cytochrome P450 protein stability.

Previous studies have suggested a relationship between cytochrome P450 (P450) 3A (CYP3A) conformation and the phospholipid composition of the associated membrane. In this study, we utilized a novel microsomal incubation system that mimics many of the characteristics of CYP3A degradation pathway that have been observed in vivo and in cultured cells to study the effects of phospholipid composition on protein stability. We found that addition of phosphatidylcholine-specific phospholipase D (PLD) stabilized CYP3A in this system, but that phosphatidylinositol-specific phospholipase C (PLC) was without effect. Addition of phosphatidic acid also stabilized CYP3A protein in the microsomes. The use of 1,10-phenanthroline (phenanthroline), an inhibitor of PLD activity, decreased CYP3A stability in incubated microsomes. Similarly, 6-h treatment of primary cultures of rat hepatocytes with phenanthroline resulted in nearly complete loss of CYP3A protein. Treatment of rats with nicardipine or dimethylsulfoxide (DMSO), which have been shown to affect CYP3A stability, altered the phospholipid composition of hepatic microsomes. It did not appear, though, that the changes in phospholipid composition that resulted from these in vivo treatments accounted for the change in CYP3A stability observed in hepatic microsomes from these animals.

Analysis of Variance↗

PubMed2004

Pro-oxidant environment of the colon compared to the small intestine may contribute to greater cancer susceptibility.

The colon and small intestine have inherent differences (e.g. redox status) that may explain the variation in cancer occurrence at these two sites. This study examined basal and induced (oxidative challenge) reactive oxygen species (ROS) generation, antioxidant enzyme activity and oxidative DNA damage. Basal ROS and antioxidant enzyme activities in the colon were greater than in the small intestine. During oxidative stress, 8-oxo-deoxyguanosine (8-oxodG) DNA adducts in the colon exceeded levels in the small intestine concomitant with increased ROS. Thus the colon responds to oxidative stress less effectively than the small intestine, possibly contributing to increased cancer incidence at this site.

Animals↗