339 research outputs found
Homogenization Model for Aberrant Crypt Foci
Several explanations can be found in the literature about the origin of
colorectal cancer. There is however some agreement on the fact that the
carcinogenic process is a result of several genetic mutations of normal cells.
The colon epithelium is characterized by millions of invaginations, very small
cavities, called crypts, where most of the cellular activity occurs. It is
consensual in the medical community, that a potential first manifestation of
the carcinogenic process, observed in conventional colonoscopy images, is the
appearance of Aberrant Crypt Foci (ACF). These are clusters of abnormal crypts,
morphologically characterized by an atypical behavior of the cells that
populate the crypts. In this work an homogenization model is proposed, for
representing the cellular dynamics in the colon epithelium. The goal is to
simulate and predict, in silico, the spread and evolution of ACF, as it can be
observed in colonoscopy images. By assuming that the colon is an heterogeneous
media, exhibiting a periodic distribution of crypts, we start this work by
describing a periodic model, that represents the ACF cell-dynamics in a
two-dimensional setting. Then, homogenization techniques are applied to this
periodic model, to find a simpler model, whose solution symbolizes the averaged
behavior of ACF at the tissue level. Some theoretical results concerning the
existence of solution of the homogenized model are proven, applying a fixed
point theorem. Numerical results showing the convergence of the periodic model
to the homogenized model are presented.Comment: 26 pages, 4 figure
Effects of bran from sorghum grains containing different classes and levels of bioactive compounds in colon carcinogenesis
In order to test the dietary effects of bioactive compounds present in whole
grains, we decided to observe the effect of varying types of sorghum bran on colon
cancer promotion. We used 40 rats consuming diets containing 6% fiber from either
cellulose or bran from white (contains phenolic acids), brown (contains tannins), or
black (contains anthocyanins) sorghum (n=10). Diets were fed for 10 wk, during which
two azoxymethane (AOM) injections (15 mg/kg BW) were administered in wk 3 and 4.
We observed that the total number of aberrant crypts (AC) and high multiplicity
aberrant crypt foci (HMACF) were lower in rats consuming black (p < 0.04) and brown
(p < 0.006) sorghum diets when compared to the cellulose diet, and that these decreases
were an inverse function of diet antioxidant activity (ABTS). These observations led us
to evaluate the effect of these diets on endogenous enzymatic activities (superoxide
dismutase, SOD; catalase, CAT; and glutathione peroxidase, GPx), redox status as
measured by reduced and oxidized glutathione, and cell cycle processes, proliferation
and apoptosis, in the rat colon. Total SOD activity was higher (p < 0.04) in rats
consuming black sorghum when compared to all other diets. A similar, but not significant, trend occurred in mitochondrial SOD. The white sorghum diet had enhanced
(p < 0.02) CAT activity compared to the cellulose diet, but the black and brown sorghum
diets were intermediate. Finally, all sorghum diets suppressed GPx activity relative to
cellulose (p < 0.04). However, no changes were seen in levels of reduced and oxidized
glutathione or the ratio of the two.
The black sorghum fed rats had a lower proliferative index (p < 0.01) and zone (p
< 0.04) compared to cellulose; brown and white sorghum rats were intermediate.
Apoptotic index was highest in brown sorghum rats compared to cellulose (p < 0.03),
while other sorghum diets were intermediate. These data suggest that the suppression of
AC and HMACF formation in rats consuming sorghum bran may have resulted through
the differential actions of the sorghum brans on endogenous antioxidant enzymes, which
may affect colonocyte proliferation and apoptosis
Effects of bran from sorghum grains containing different classes and levels of bioactive compounds in colon carcinogenesis
In order to test the dietary effects of bioactive compounds present in whole
grains, we decided to observe the effect of varying types of sorghum bran on colon
cancer promotion. We used 40 rats consuming diets containing 6% fiber from either
cellulose or bran from white (contains phenolic acids), brown (contains tannins), or
black (contains anthocyanins) sorghum (n=10). Diets were fed for 10 wk, during which
two azoxymethane (AOM) injections (15 mg/kg BW) were administered in wk 3 and 4.
We observed that the total number of aberrant crypts (AC) and high multiplicity
aberrant crypt foci (HMACF) were lower in rats consuming black (p < 0.04) and brown
(p < 0.006) sorghum diets when compared to the cellulose diet, and that these decreases
were an inverse function of diet antioxidant activity (ABTS). These observations led us
to evaluate the effect of these diets on endogenous enzymatic activities (superoxide
dismutase, SOD; catalase, CAT; and glutathione peroxidase, GPx), redox status as
measured by reduced and oxidized glutathione, and cell cycle processes, proliferation
and apoptosis, in the rat colon. Total SOD activity was higher (p < 0.04) in rats
consuming black sorghum when compared to all other diets. A similar, but not significant, trend occurred in mitochondrial SOD. The white sorghum diet had enhanced
(p < 0.02) CAT activity compared to the cellulose diet, but the black and brown sorghum
diets were intermediate. Finally, all sorghum diets suppressed GPx activity relative to
cellulose (p < 0.04). However, no changes were seen in levels of reduced and oxidized
glutathione or the ratio of the two.
The black sorghum fed rats had a lower proliferative index (p < 0.01) and zone (p
< 0.04) compared to cellulose; brown and white sorghum rats were intermediate.
Apoptotic index was highest in brown sorghum rats compared to cellulose (p < 0.03),
while other sorghum diets were intermediate. These data suggest that the suppression of
AC and HMACF formation in rats consuming sorghum bran may have resulted through
the differential actions of the sorghum brans on endogenous antioxidant enzymes, which
may affect colonocyte proliferation and apoptosis
Quercetin and Dietary Lipids Alter the Cellular Redox Environment of the Colonocyte in the Promotion Stage of Colon Carcinogenesis.
Quercetin (Q), a water-soluble flavonoid that is ubiquitous to foods of plant
origin is postulated to protect against colon cancer due to its antioxidant activity. In
contrast, we have shown that a dietary combination of fish oil (FO; n-3 fatty acids) and
pectin may protect against colon cancer by decreasing endogenous antioxidant enzyme
activities leading to increased reactive oxygen species (ROS), an inducer of apoptosis.
We hypothesized that adding an antioxidant to a FO diet may negate the beneficial
effects of FO by counteracting FO effects on colonocyte redox status. To test this, we
provided 40 rats with FO or CO (fiber = pectin) diets with Q being 0 or 0.45% of the diet
for 10 wk. All rats were injected with azoxymethane (AOM) on d 21 and 28.
Measurements included: aberrant crypt (AC) enumeration (colon cancer marker);
apoptosis (TUNEL assay); catalase (CAT), superoxide dismutase (SOD), and
glutathione peroxidase (GPx) activities; reduced and oxidized glutathione concentrations
(GSH/GSSG); and oxidative DNA damage (8-OHdG adducts). AC numbers were lower
in FO vs CO rats (p<0.0001), but tended to increase for FO diets containing Q
(P<0.098). The apoptotic index was higher (p<0.0001) when Q was added to the FO and
CO diets. Total SOD (lipid main effect, p=0.0136) and GPX activity (p=0.0025) was elevated in CO rats. CAT activity was higher (p=0.0204) in FO rats, however Q
diminished this effect. GSH was not affected by diet; yet, GSSG accumulated
(p=0.0554) in CO rats with Q as compared to CO rats without Q. The GSH/GSSG ratio
was lower (p=0.0314) in CO rats than in FO rats. There was no difference in 8-OHdG
adduct levels in FO vs CO rats, however, Q decreased 8-OHdG adducts in CO rats
(p=0.0428). Despite increasing apoptosis, Q did not significantly lower AC formation.
These data suggest that the distinct effects of the CO/Q and FO/Q combinations are
functioning through different mechanisms to induce apoptosis. The long-term
consequences of adding antioxidants such as Q to a diet thought to exert its anticancer
effect through a pro-oxidant mechanism are unknown and deserve further study
Análise numérica de métodos multiescala para problemas elíticos-parabólicos com aplicação na dinâmica celular durante a formação do câncer colorretal
Orientador: Giuseppe RomanazziTese (doutorado - Universidade Estadual de Campinas, Instituto de Matemática, Estatística e Computação CientíficaResumo: O cólon humano é propício ao desenvolvimento de câncer devido à sua renovação celular que consiste em um alto número de proliferações por dia, localizadas em pequenas cavidade chamadas de criptas. O epitélio do cólon é formado por milhões de criptas e é conhecido que mutações no processo de proliferação (dentro das criptas) podem conduzir à carcinogênese. A proliferação de células colônicas pode ser modelada usando multiescalas (FIGUEIREDO et al., 2013). Em particular, nós podemos usar uma cripta de referência como um domínio microescala, que é periodicamente distribuído em um domínio macroescala, onde este é associado a uma porção do epitélio do cólon. O modelo final resulta em um sistema de EDPs acoplado formado por uma equação elítica e uma parabólica na qual as variáveis são a densidade de células proliferativas e a pressão celular exercida. Apresentamos o processo de homogenização desse sistema de equações supondo a existência de uma expansão assintótica da solução e das demais funções que compõem o problema, veja (D.; P., 1999). Aplicamos um método de resolução multiescala baseado em elementos finitos (HMM-FEM) para aproximar a solução homogenizada encontrado em alguns trabalhos como (ABDULLE, 2009; ABDULLE, 2011; ABDULLE; HUBER, 2016). No cenário onde o problema é acoplado e não linear, a implementação de métodos se torna mais robusta e custosa computacionamente, portanto optamos por resolver primeiro o problema elítico e depois o parabólico como uma forma de amenizar essa complexidade. Como poderemos ver mais em frente, essa estratégia não afeta as ordens de convergência dos métodos. Em uma única escala, estudamos estabilidade e convergência de um esquema supraconvergente baseado em diferenças finitas centradas para malhas não uniformes que é equivalente à um esquema baseado em elementos finitos. Em um cenário mais simplificado, estudamos convergência e estabilidade do método apresentado. Já para um caso mais geral provamos, para s = 1, 2, ordem O(h^s) de convergência para a solução e gradiente se a solução exata está em H^(1)(omega). Para o problema homogenizado, apresentamos uma estratégia supraconvergente que permite aproximar a solução do problema homogenizado acoplado, onde numericamente obtemos uma ordem de convergência O(H^2+h^2). Por fim, buscamos apresentar o esboço de um esquema para resolver problemas multiescala usando dos bons resultados de convergência discutidos acima. Esse modelo é baseado em resolover um problema microescala que posteriormente será usado para construir uma solução macroescala para o sistema homogenizado. Os primeiros indícios de convergência surgem dos resultados numéricos obtidos.Abstract: The human colon is prone to develop a cancer due to its cell renovation that consists in a large number of cell divisions per day located in small cavities of the colon epithelium, called crypts. The colon epithelium is filled by millions of crypts, and it is known that mutations in the cell proliferation process (inside the crypts) can lead to the carcinogenesis. Colonic cell proliferation can be modeled by using multiscales (FIGUEIREDO et al., 2013). In particular, we can use a reference crypt, as a microscale domain, that is periodically distributed in a macroscale domain that is a portion of the colon epithelium. The final model results in a coupled PDE system formed by an elliptic and parabolic equations whose unknowns are the proliferative cell density and the exerted cell pressure. We present a homogenization for the final PDE model where it is supposed to exist a asymptotic expansion for the exact solution of the problem , see (D.; P., 1999). We apply a multiscale method based on finite elements (HMM-FEM) to approximate the homogenized solution as in (ABDULLE, 2009; ABDULLE, 2011; ABDULLE; HUBER, 2016). The coupling and the non-linearity of the system implies a more complex implementation and increase the computational effort, thus we first solve the elliptic problem and then the parabolic one to make it easier. As we can see later, that strategy does not affect the convergence rates. Furthermore, in a single scale, we study a supraconvergent method based on centered finite difference to nonuniform mesh which is equivalent to a fully discrete linear finite element method. Firstly we study convergence and stability of a simpler model and then we prove for s = 1, 2 order O(h^s) convergence of solution and gradient if the exact solution is in H^1(omega). Numerical results illustrate the methods above. For the multiscale problem, we present a supraconvergent scheme which provides approximations to the coupled system with O(H^2+h^2) of convergence rate. This is done by solving the homogenized problem with the supraconvergent method discussed before. Our last contribution is a multiscale model in development which can be useful to solve multiscale problems with the good convergence rates discussed above. That model is based on solving a microscale problem that will be used to construct a macroscale solution for the homogenized system. Numerical results for this model suggest a supraconvergence.DoutoradoMatemática AplicadaDoutor em Matemática Aplicada001CAPE
Spatiotemporal Effects of Dietary Bioactives on Lgr5+ Stem Cells during Colon Tumorigenesis
To better understand how the stem cells respond to environmental factors such as diet and carcinogen, we investigated the chemo-protective effects of dietary agents (n-3 PUFA and curcumin) on DNA damage response in colonic stem cells isolated from Lgr5-EGFP-IRES-CreER^T2 knock in mice injected with AOM. We demonstrated that n-3 PUFA and curcumin synergize to promote targeted apoptosis of damaged Lgr5⁺ stem cells in part by enhancing p53 signaling in Lgr5⁺ stem cells at the tumor initiation stage. In addition, at the pre-tumor stage of tumorigenesis in colon cancer, we demonstrated n-3 PUFA and curcumin combination synergistically reduces nuclear -catenin levels in aberrant crypt foci, a surrogate marker of colon cancer. In order to assess the dose-dependency of n-3 PUFA and curcumin action, we also calculated the median effective concentration and the Human equivalent dose of n-3 PUFA + curcumin required to remove DNA damaged Lgr5⁺ stem cells by targeted apoptosis.
In order to further elucidate the effects of oncogenesis on the biophysical properties of the colonocyte plasma membrane at the pre tumor stage, we generated CDX2P-CreER^T2 –Apc^580S/+; KrasLSL-^G12D/+ (ACK) transgenic mice. Our findings demonstrate for the first time that oncogenic Apc and Kras increase plasma membrane order by perturbing cholesterol homeostasis and promoting cell proliferation. Genes associated with cholesterol uptake and de novo synthesis of cholesterol are enhanced in ACK mice. This process is associated with the upregulation of Myc signaling, a well-known upstream mediator of cholesterol homeostasis. Our preliminary findings also indicate that the addition of exogenous cholesterol can dose-dependently promote cell proliferation in colonic cell lines and mouse colonic organoids. In complementary experiments, we also investigated the chemo-protective effects of dietary agents on cholesterol homeostasis and plasma membrane order in ACK mice. Our findings indicate that perturbed plasma membrane order and cholesterol homeostasis is ameliorated by n-3 PUFA + curcumin feeding.
In summary, our results indicate for the first time that fish oil plus curcumin synergistically reduce colon cancer risk in part by modulating (i) p53 signaling in Lgr5+ stem cells, and (ii) plasma membrane properties implicated in the regulation of the colon cancer cells and tumor development
Assessment of the cell cycle proteins Cdc7 and PCNA as markers of colon carcinogenesis in obese and lean rats
Obesity increases the risk of colon cancer as well as the expression of many cancer markers, ostensibly due to the interaction between insulin resistance and adipocyte production of hormones, mitogens and cytokines which collaborate to enhance proliferation signaling and impair the DNA damage response. Cdc7 and PCNA are both proteins involved in the DNA damage response as well as DNA replication. Both have also been shown to be upregulated in human tumours. To assess Cdc7 and PCNA roles during the DNA damage response in obese and lean animals, we administered azoxymethane (AOM), a colon-specific carcinogen, to obese and lean rats. Cdc7 and PCNA levels in colonic mucosal protein extracts from obese Zucker rats were compared with those from their lean counterparts. Significant differences were seen between lean and obese animals 3 hours post-AOM (lean Cdc7 levels > obese Cdc7 levels) and 24 hours post-AOM (lean PCNA levels > obese PCNA levels). This result suggests an impaired checkpoint response in obese animals relative to lean animals and supports a previously reported early role for Cdc7 in the checkpoint signaling cascade relative to a later role of PCNA in DNA damage repair. At the time tumours appeared (32 weeks post-AOM), colonic mucosal Cdc7 levels of obese rats exceeded that of their lean counterparts, suggesting that the obese metabolic environment causes upregulation of Cdc7 in obese rat epithelia. Cdc7 and PCNA levels were then compared between tumours and mucosa in obese and Sprague Dawley rats. Tumour Cdc7 levels were upregulated relative to mucosal levels in more samples than tumour PCNA levels, suggesting Cdc7 may be a more sensitive tumour marker. No significant differences in Cdc7 levels were seen between obese tumours and mucosa, likely due to elevation of obese mucosal Cdc7 levels. However, Sprague Dawley (non-obese) rats showed significantly higher Cdc7 and PCNA levels in tumours than mucosa, consistent with previous studies in human tissues. These results suggest that Cdc7 may be a more sensitive tumour marker than PCNA, but that its utility as a biomarker of colon cancer is dependent on the metabolic state (leanness) of the individual
Detection and Characterization of Oncogene Mutations in Preneoplastic and Early Neoplastic Lesions
While it has been nearly 30 years since its discovery, the ras family of genes has not yet lost its impact on basic and clinical oncology. These genes remain central to the field of molecular oncology as tools for investigating carcinogenesis and oncogenic signaling, as powerful biomarkers for the identification of those who have or are at high risk of developing cancer, and as oncogene targets for the design and development of new chemotherapeutic drugs. Mutational activation of the K-RAS proto-oncogene is an early event in the development and progression of the colorectal, pancreatic, and lung cancers that are the major causes of cancer death in the world. The presence of point mutational "hot spots" at sites necessary for the activation of this proto-oncogene has led to the development of a number of highly sensitive PCR-based methods that are feasible for the early detection of K-RAS oncogene mutations in the clinical setting. In light of these facts, mutation at the K-RAS oncogene has the potential to serve as a useful biomarker in the early diagnosis and risk assessment of cancers with oncogenic ras signaling. This chapter describes a highly sensitive method for detecting mutant K-RAS, enriched PCR, and its application to early detection of alterations in this oncogene in preneoplastic and early neoplastic lesions of the colon and rectum
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