[show abstract][hide abstract] ABSTRACT: We have demonstrated that fish oil- and pectin-containing (FO/P) diets protect against colon cancer compared with corn oil and cellulose (CO/C) by upregulating apoptosis and suppressing proliferation. To elucidate the mechanisms whereby FO/P diets induce apoptosis and suppress proliferation during the tumorigenic process, we analyzed the temporal gene expression profiles from exfoliated rat colonocytes. Rats consumed diets containing FO/P or CO/C and were injected with azoxymethane (AOM; 2 times, 15 mg/kg body weight, subcutaneously). Feces collected at initiation (24 h after AOM injection) and at aberrant crypt foci (ACF) (7 wk postinjection) and tumor (28 wk postinjection) stages of colon cancer were used for poly (A)+ RNA extraction. Gene expression signatures were determined using Codelink arrays. Changes in phenotypes (ACF, apoptosis, proliferation, and tumor incidence) were measured to establish the regulatory controls contributing to the chemoprotective effects of FO/P. At initiation, FO/P downregulated the expression of 3 genes involved with cell adhesion and enhanced apoptosis compared with CO/C. At the ACF stage, the expression of genes involved in cell cycle regulation was modulated by FO/P and the zone of proliferation was reduced in FO/P rats compared with CO/C rats. FO/P also increased apoptosis and the expression of genes that promote apoptosis at the tumor endpoint compared with CO/C. We conclude that the effects of chemotherapeutic diets on epithelial cell gene expression can be monitored noninvasively throughout the tumorigenic process and that a FO/P diet is chemoprotective in part due to its ability to affect expression of genes involved in apoptosis and cell cycle regulation throughout all stages of tumorigenesis.
Journal of Nutrition 06/2011; 141(6):1029-35. · 4.20 Impact Factor
[show abstract][hide abstract] ABSTRACT: Epidemiological evidence suggests that a diet abundant in fruits and vegetables may protect against colon cancer. Bioactive compounds, including flavonoids and limonoids, have been shown to possess antiproliferative and antitumorigenic effects in various cancer models. This experiment investigated the effects of four citrus flavonoids and one limonoid mixture at the promotion stage of chemically induced colon cancer in rats. Male Sprague-Dawley rats (n = 10 rats/group) were randomly allocated to one of six diets formulated to contain 0.1% apigenin, 0.02% naringenin, 0.1% hesperidin, 0.01% nobiletin, 0.035% limonin glucoside/obacunone glucoside mixture or a control diet (0% flavonoid/limonoid). Rats received experimental diets for 10 weeks and were injected with azoxymethane (15 mg/kg) at weeks 3 and 4. Excised colons were evaluated for aberrant crypt foci (ACF) formation, colonocyte proliferation (proliferating cell nuclear antigen assay), apoptosis (terminal deoxynucleotidyl transferase dUTP nick end labeling assay) and expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) (immunoblotting). When compared with the control diet, apigenin lowered the number of high multiplicity ACF (HMACF >4 aberrant crypts/focus) by 57% (P < 0.05), while naringenin lowered both the number of HMACF by 51% (P < 0.05) and the proliferative index by 32% (P < 0.05). Both apigenin and naringenin increased apoptosis of luminal surface colonocytes (78% and 97%, respectively; P < 0.05) when compared with the control diet. Hesperidin, nobiletin and the limonin glucoside/obacunone glucoside mixture did not affect these variables. The colonic mucosal protein levels of iNOS or COX-2 were not different among the six diet groups. The ability of dietary apigenin and naringenin to reduce HMACF, lower proliferation (naringenin only) and increase apoptosis may contribute toward colon cancer prevention. However, these effects were not due to mitigation of iNOS and COX-2 protein levels at the ACF stage of colon cancer.
Experimental Biology and Medicine 06/2010; 235(6):710-7. · 2.80 Impact Factor
[show abstract][hide abstract] ABSTRACT: We introduce a new class of functional generalized linear models, where the response is a scalar and some of the covariates are functional. We assume that the response depends on multiple covariates, a finite number of latent features in the functional predictor, and interaction between the two. To achieve parsimony, the interaction between the multiple covariates and the functional predictor is modeled semiparametrically with a single-index structure. We propose a two step estimation procedure based on local estimating equations, and investigate two situations: (a) when the basis functions are pre-determined, e.g., Fourier or wavelet basis functions and the functional features of interest are known; and (b) when the basis functions are data driven, such as with functional principal components. Asymptotic properties are developed. Notably, we show that when the functional features are data driven, the parameter estimates have an increased asymptotic variance, due to the estimation error of the basis functions. Our methods are illustrated with a simulation study and applied to an empirical data set, where a previously unknown interaction is detected. Technical proofs of our theoretical results are provided in the online supplemental materials.
Journal of the American Statistical Association 06/2010; 105(490):621-633. · 1.83 Impact Factor
[show abstract][hide abstract] ABSTRACT: n-3 Polyunsaturated fatty acids (PUFA) are considered to be authentic immunosuppressors and appear to exert beneficial effects with respect to certain immune-mediated diseases. In addition to promoting T-helper 1 (Th1) cell to T-helper 2 (Th2) cell effector T-cell differentiation, n-3 PUFA may also exert anti-inflammatory actions by inducing apoptosis in Th1 cells. With respect to mechanisms of action, effects range from the modulation of membrane receptors to gene transcription via perturbation of a number of second messenger cascades. In this review, the putative targets of anti-inflammatory n-3 PUFA, activated during early and late events of T-cell activation will be discussed. Studies have demonstrated that these fatty acids alter plasma membrane micro-organization (lipid rafts) at the immunological synapse, the site where T-cells and antigen-presenting cells (APC) form a physical contact for antigen initiated T-cell signaling. In addition, the production of diacylglycerol and the activation of different isoforms of protein kinase C (PKC), mitogen-activated protein kinase (MAPK), calcium signaling, and nuclear translocation/activation of transcriptional factors, can be modulated by n-3 PUFA. Advantages and limitations of diverse methodologies to study the membrane lipid raft hypothesis, as well as apparent contradictions regarding the effect of n-3 PUFA on lipid rafts will be critically presented.
Progress in lipid research 02/2010; 49(3):250-61. · 10.67 Impact Factor
[show abstract][hide abstract] ABSTRACT: Developing and evaluating new technology that enables researchers to recover gene-expression levels of colonic cells from fecal samples could be key to a non-invasive screening tool for early detection of colon cancer. The current study, to the best of our knowledge, is the first to investigate and report the reproducibility of fecal microarray data. Using the intraclass correlation coefficient (ICC) as a measure of reproducibility and the preliminary analysis of fecal and mucosal data, we assessed the reliability of mixture density estimation and the reproducibility of fecal microarray data. Using Monte Carlo-based methods, we explored whether ICC values should be modeled as a beta-mixture or transformed first and fitted with a normal-mixture. We used outcomes from bootstrapped goodness-of-fit tests to determine which approach is less sensitive toward potential violation of distributional assumptions.
The graphical examination of both the distributions of ICC and probit-transformed ICC (PT-ICC) clearly shows that there are two components in the distributions. For ICC measurements, which are between 0 and 1, the practice in literature has been to assume that the data points are from a beta-mixture distribution. Nevertheless, in our study we show that the use of a normal-mixture modeling approach on PT-ICC could provide superior performance.
When modeling ICC values of gene expression levels, using mixture of normals in the probit-transformed (PT) scale is less sensitive toward model mis-specification than using mixture of betas. We show that a biased conclusion could be made if we follow the traditional approach and model the two sets of ICC values using the mixture of betas directly. The problematic estimation arises from the sensitivity of beta-mixtures toward model mis-specification, particularly when there are observations in the neighborhood of the the boundary points, 0 or 1. Since beta-mixture modeling is commonly used in approximating the distribution of measurements between 0 and 1, our findings have important implications beyond the findings of the current study. By using the normal-mixture approach on PT-ICC, we observed the quality of reproducible genes in fecal array data to be comparable to those in mucosal arrays.
[show abstract][hide abstract] ABSTRACT: With respect to functional mapping of gene expression signatures, the steady-state mRNA expression level does not always accurately reflect the status of critical signaling proteins. In these cases, control is exerted at the epigenetic level of recruitment of mRNAs to polysomes, the factories of ribosomes that mediate efficient translation of many cellular messages. However, to date, a genome-wide perspective of the effect of carcinogen and chemoprotective bioactive diets on actively translated (polysomal) mRNA populations has not been done. Therefore, we used an established colon cancer model, i.e., the azoxymethane (AOM)-treated rat, in combination with a chemoprotective diet extensively studied in our laboratory, i.e., n-3 polyunsaturated fatty acids, to characterize the molecular processes underlying the transformation of normal colonic epithelium. The number of genes affected by AOM treatment 10 weeks after carcinogen injection was significantly greater in the polysome RNA fraction compared with the total RNA fraction as determined using a high-density microarray platform. In particular, polysomal loading patterns of mRNAs associated with the Wnt-beta catenin, phospholipase A(2)-eicosanoid and the mitogen-activated protein kinase signaling axes were significantly upregulated at a very early period of tumor development in the colon. These data indicate that translational alterations are far more extensive relative to transcriptional alterations in mediating malignant transformation. In contrast, transcriptional alterations were found to be more extensive relative to translational alterations in mediating the effects of diet. Therefore, during early stage colonic neoplasia, diet and carcinogen seem to predominantly regulate gene expression at multiple levels via unique mechanisms.
Cancer Prevention Research 11/2009; 2(11):984-94. · 4.89 Impact Factor
[show abstract][hide abstract] ABSTRACT: We have hypothesized that dietary modulation of intestinal non-coding RNA [microRNA (miRNA)] expression may contribute to the chemoprotective effects of nutritional bioactives (fish oil and pectin). To fully understand the effects of these agents on the expression of miRNAs, Sprague-Dawley rats were fed diets containing corn oil or fish oil with pectin or cellulose and injected with azoxymethane (AOM, a colon-specific carcinogen) or saline (control). Real-time polymerase chain reaction using miRNA-specific primers and Taq Man probes was carried out to quantify effects on miRNA expression in colonic mucosa. From 368 mature miRNAs assayed, at an early stage of cancer progression (10 week post AOM injection), let-7d, miR-15b, miR-107, miR-191 and miR-324-5p were significantly (P < 0.05) affected by diet x carcinogen interactions. Overall, fish oil fed animals exhibited the smallest number of differentially expressed miRNAs (AOM versus saline treatment). With respect to the tumor stage (34 week post AOM injection), 46 miRNAs were dysregulated in adenocarcinomas compared with normal mucosa from saline-injected animals. Of the 27 miRNAs expressed at higher (P < 0.05) levels in tumors, miR-34a, 132, 223 and 224 were overexpressed at >10-fold. In contrast, the expression levels of miR-192, 194, 215 and 375 were dramatically reduced (< or = 0.32-fold) in adenocarcinomas. These results demonstrate for the first time the utility of the rat AOM model and the novel role of fish oil in protecting the colon from carcinogen-induced miRNA dysregulation.
[show abstract][hide abstract] ABSTRACT: Inflammatory bowel disease (IBD) patients are at high risk for developing folate deficiency and colon cancer. Since it is difficult to study the subtle global and gene-specific epigenetic mechanisms involved in folate-mediated tumor initiation and promotion, we have generated genetically modified mouse models by targeting the reduced folate carrier (RFC1) and folate-binding protein (Folbp1) genes. The transgenic mice were fed semi-purified diets for 8 weeks containing either normal (2 mg) or deficient (0.1 mg folate/kg diet) levels of folate. Compound heterozygous mice (Folbp1(+/-); RFC1(+/-)) fed an adequate folate diet exhibited a reduction in plasma folate concentrations compared to heterozygous (Folbp1(+/-)) and littermate wild-type mice (P<.05). In contrast, no differences were observed in colonic mucosa. Consumption of a low folate diet significantly reduced (three- to fourfold) plasma and tissue folate levels in all animal models, although plasma homocysteine levels were not altered. In order to elucidate the relationship between folate status and inflammation-associated colon cancer, animals were injected with azoxymethane followed by dextran sodium sulphate treatment in the drinking water. Mice were fed a normal folate diet and were terminated 5 weeks after carcinogen injection. The number of high multiplicity aberrant crypt foci per centimeter of colon was significantly elevated (P<.05) in compound Folbp1(+/-); RFC1(+/-) (3.5+/-0.4) mice as compared to Folbp1(+/-) (1.9+/-0.3) and wild-type control mice (1.1+/-0.1). These data demonstrate that the ablation of two receptor/carrier-mediated pathways for folate transport increases the risk for developing inflammation-associated colon cancer.
The Journal of nutritional biochemistry 10/2008; 20(8):649-55. · 4.29 Impact Factor
[show abstract][hide abstract] ABSTRACT: We recently generated nutritional data suggesting that chemoprotective dietary n-3 polyunsaturated fatty acids (n-3 PUFA) are capable of displacing acylated proteins from lipid raft microdomains in vivo [D.W. Ma, J. Seo, L.A. Davidson, E.S. Callaway, Y.Y. Fan, J.R. Lupton, R.S. Chapkin, n-3 PUFA alter caveolae lipid composition and resident protein localization in mouse colon, FASEB J. 18 (2004) 1040-1042; Y.Y. Fan, L.H. Ly, R. Barhoumi, D.N. McMurray, R.S. Chapkin, Dietary docosahexaenoic acid suppresses T cell protein kinase Ctheta lipid raft recruitment and IL-2 recruitment, J. Immunol. 173 (2004) 6151-6160]. A primary source of very long chain n-3 PUFA in the diet is derived from fish enriched with docosahexaenoic acid (DHA, 22:6n-3). In this study, we sought to determine the effect of DHA on cell surface microdomain organization in situ. Using immuno-gold electron microscopy of plasma membrane sheets coupled with spatial point analysis of validated microdomain markers, morphologically featureless microdomains were visualized in HeLa cells at high resolution. Clustering of probes within cholesterol-dependent (GFP-tH) versus cholesterol-independent (GFP-tK) nanoclusters was differentially sensitive to n-3 PUFA treatment of cells. Univariate K-function analysis of GFP-tH (5 nm gold) revealed a significant increase in clustering (p<0.05) by pre-treatment with DHA and linoleic acid (LA, 18:2(Delta9,12)) compared to control fatty acids; whereas LA significantly (p<0.05) reduced GFP-tK clustering. These novel data suggest that the plasma membrane organization of inner leaflets is fundamentally altered by PUFA-enrichment. We speculate that our findings may help define a new paradigm to better understand the complexity of n-3 PUFA modulation of signaling networks.
Biochimica et Biophysica Acta 03/2008; 1778(2):466-71. · 4.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: We study a mixed-effects model in which the response and the main covariate are linked by position. While the covariate corresponding to the observed response is not directly observable, there exists a latent covariate process that represents the underlying positional features of the covariate. When the positional features and the underlying distributions are parametric, the expectation-maximization (EM) is the most commonly used procedure. Though without the parametric assumptions, the practical feasibility of a semi-parametric EM algorithm and the corresponding inference procedures remain to be investigated. In this paper, we propose a semiparametric approach, and identify the conditions under which the semiparametric estimators share the same asymptotic properties as the unachievable estimators using the true values of the latent covariate; that is, the oracle property is achieved. We propose a Monte Carlo graphical evaluation tool to assess the adequacy of the sample size for achieving the oracle property. The semiparametric approach is later applied to data from a colon carcinogenesis study on the effects of cell DNA damage on the expression level of oncogene bcl-2. The graphical evaluation shows that, with moderate size of subunits, the numerical performance of the semiparametric estimator is very close to the asymptotic limit. It indicates that a complex EM-based implementation may at most achieve minimal improvement and is thus unnecessary.
Statistics and its interface 01/2008; 1(1):75. · 0.40 Impact Factor
[show abstract][hide abstract] ABSTRACT: In longitudinal and spatial studies, observations often demonstrate strong correlations that are stationary in time or distance lags, and the times or locations of these data being sampled may not be homogeneous. We propose a nonparametric estimator of the correlation function in such data, using kernel methods. We develop a pointwise asymptotic normal distribution for the proposed estimator, when the number of subjects is fixed and the number of vectors or functions within each subject goes to infinity. Based on the asymptotic theory, we propose a weighted block bootstrapping method for making inferences about the correlation function, where the weights account for the inhomogeneity of the distribution of the times or locations. The method is applied to a data set from a colon carcinogenesis study, in which colonic crypts were sampled from a piece of colon segment from each of the 12 rats in the experiment and the expression level of p27, an important cell cycle protein, was then measured for each cell within the sampled crypts. A simulation study is also provided to illustrate the numerical performance of the proposed method.
The Annals of Statistics 11/2007; · 2.53 Impact Factor
[show abstract][hide abstract] ABSTRACT: Butyrate, a short-chain fatty acid fiber fermentation product, induces colonocyte apoptosis in part via a Fas-mediated (extrinsic) pathway. In previous studies, we demonstrated that docosahexaenoic acid (DHA, 22:6(Delta4,7,10,13,16,19)) enhances the effect of butyrate by increasing mitochondrial lipid oxidation and mitochondrial Ca(2+)-dependent apoptosis in the colon. In this study, we further examined the mechanism of DHA-butyrate synergism in 1) human colon tumor (HCT-116 isogenic p53+/+ vs. p53-/-) cells and 2) primary cultures of rat colonic crypts. Herein, we show that DHA and butyrate promote apoptosis by enhancing mitochondrial Ca(2+) accumulation in both isogenic cell lines. Ca(2+) accumulation and apoptosis were inhibited by blockade of mitochondrial uniporter-mediated Ca(2+) uptake. In addition, Mito-Q, a mitochondria-targeted antioxidant, also blocked apoptosis induced by DHA and butyrate. In complementary experiments, rats were fed diets supplemented with either corn oil (control, contains no DHA) or fish oil (contains DHA). Colonic crypts were isolated and incubated with or without butyrate, after which the mitochondria-to-cytosol Ca(2+) ratio and crypt viability were measured. No significant difference (P > 0.05) in basal mitochondrial Ca(2+) levels was observed between fish oil- or corn oil-fed animals. In contrast, when fish oil was the dietary lipid source, crypts incubated with butyrate exhibited a significant increase (3.6-fold, P < 0.001) in mitochondrial Ca(2+) compared with corn oil plus butyrate treatment. On the basis of these data, we propose that the combination of DHA and butyrate compared with butyrate alone further enhances colonocyte apoptosis by inducing a p53-independent, oxidation-sensitive, mitochondrial Ca(2+) -dependent (intrinsic) pathway.
[show abstract][hide abstract] ABSTRACT: A DNA microarray experiment simultaneously measures the expression levels of thousands of genes. An important question is to identify genes that express differentially between two types of tissues or at different experimental conditions. Since large numbers of genes are compared simultaneously, simple use of significance tests can easily lead to false positive findings. We propose a sequential procedure for estimating the empirical null distribution of multiple hypothesis testing and apply the procedure to identify differentially expressed genes in microarray experiments. Our procedure can be viewed as a new method to estimate the q-value proposed by Storey (2002). The key intuition is to obtain an estimate of the null distribution that is robust to the observations from the alternative distribution. Technically, we borrow strength from the missing data literature so that we can avoid estimating the density function corresponding to differentially expressed genes nonparametrically, but can focus on estimating the null density. Numerical comparisons between our method and Storey's original method were conducted in simulated and real data examples. The numerical results show that our procedure outperforms the originally estimated q-values in almost all scenarios.
[show abstract][hide abstract] ABSTRACT: The increasing use of microarray technologies is generating a large amount of data that must be processed to extract underlying gene expression patterns. Existing clustering methods could suffer from certain drawbacks. Most methods cannot automatically separate scattered, singleton and mini-cluster genes from other genes. Inclusion of these types of genes into regular clustering processes can impede identification of gene expression patterns. In this paper, we propose a general clustering method, namely a dynamic agglomerative clustering (DAC) method. DAC can automatically separate scattered, singleton and mini-cluster genes from other genes and thus avoid possible contamination to the gene expression patterns caused by them. For DAC, the scattered gene filtering step is no longer necessary in data pre-processing. In addition, we propose a criterion for evaluating clustering results for a dataset which contains scattered, singleton and/or mini-cluster genes. DAC has been applied successfully to two real datasets for identification of gene expression patterns. Our numerical results indicate that DAC outperforms other clustering methods, such as the quality-based and model-based clustering methods, in clustering datasets which contain scattered, singleton and/or mini-cluster genes.
[show abstract][hide abstract] ABSTRACT: 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.
Journal of Nutrition 10/2006; 136(9):2391-8. · 4.20 Impact Factor
[show abstract][hide abstract] ABSTRACT: We study the heteroscedastic partially linear model with an unspecified partial baseline component and a nonparametric variance function. An interesting finding is that the performance of a naive weighted version of the existing estimator could deteriorate when the smooth baseline component is badly estimated. To avoid this, we propose a family of consistent estimators and investigate their asymptotic properties. We show that the optimal semiparametric efficiency bound can be reached by a semiparametric kernel estimator in this family. Building upon our theoretical findings and heuristic arguments about the equivalence between kernel and spline smoothing, we conjecture that a weighted partial-spline estimator could also be semiparametric efficient. Properties of the proposed estimators are presented through theoretical illustration and numerical simulations. Copyright 2006, Oxford University Press.
[show abstract][hide abstract] ABSTRACT: 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.
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.
The R codes implementing the two-stage method may be obtained from the corresponding author.
[show abstract][hide abstract] ABSTRACT: 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.
[show abstract][hide abstract] ABSTRACT: We consider marginal generalized semiparametric partially linear models for clustered data. Lin and Carroll derived the semiparametric efficient score function for this problem in the multivariate Gaussian case, but they were unable to construct a semiparametric efficient estimator that actually achieved the semiparametric information bound. Here we propose such an estimator and generalize the work to marginal generalized partially linear models. We investigate asymptotic relative efficiencies of the estimators that ignore the within-cluster correlation structure either in nonparametric curve estimation or throughout. We evaluate the finite-sample performance of these estimators through simulations and illustrate it using a longitudinal CD4 cell count dataset. Both theoretical and numerical results indicate that properly taking into account the within-subject correlation among the responses can substantially improve efficiency.
Journal of the American Statistical Association 02/2005; 100(March):147-157. · 1.83 Impact Factor
[show abstract][hide abstract] ABSTRACT: We consider a partially linear single-index model Y = η(Z T α0)+X T β0+ε when X is measured with additive error. Estimators in the literature are biased when the measurement errors are ignored. We propose two estimators in this setting and develop their asymptotic normality. We apply the proposed estimators to the analysis of dietary data, and provide the results of a simulation experiment to illustrate our approach.