A high-fat diet generates alterations in nuclear receptor expression: prevention by vitamin A and links with cyclooxygenase-2 and beta-catenin

Ferulic acid in synergy with retinol alleviates oxidative injury of HaCaT cells during UVB-induced photoaging

Application of retinol (Vitamin A, VA) in skincare is limited for instability, poor water solubility, and skin intolerance that combats skin aging. We employed computer-aided virtual screening and cell experiments with transcriptomics, thereby unveiling the comprehensive gene expression and regulation pathway of photoaging HaCaT cell treated with ferulic acid (FA) in synergizing with VA. Through network pharmacology analysis, the combined use of VA and FA exhibited highly correlated cross-targets with skin aging acting on EGFR, PTPN1, ESR2, GSK3B, BACE1, PYGL, PTGS2 and APP. The indicators of oxidative stress, such as SOD, GSH, MDA, CAT and ROS in HaCaT cells after co-administration, were significantly improved from those in photoaging group (p<0.0001). 155 differential expressed genes (DEGs) were specific between groups, while reducing the expression of PTGS2 was identified as an important regulatory factor in photoaging HaCaT cells by VA and FA. Those DEGs of co-administration group focused on oxidative-reduction enzyme activity, skin growth, keratinization, and steroid biosynthesis. Apparently, the co-administration of VA and FA effectively mitigated the process of UVB-induced photoaging by reducing oxidative stress injury, inflammation responses, and regulating cell growth. This synergistic approach significantly slowed down the photoaging progression and improved the applied performance of VA in HaCaT cells.

Dietary trans fatty acids and risk of colorectal cancer: a systematic review and meta-analysis of observational studies

PURPOSE

Although trans fatty acid has been associated with diabetes and cardiovascular disorders, studies gave conflicting results when examined their impact on colorectal cancer (CRC). The present systematic review and meta-analysis aimed to summarize the current evidence regarding the association between dietary and tissue trans fatty acids and the risk of CRC.

METHODS

We searched PubMed/MEDLINE, EMBASE, Scopus, Web of Science (ISI), and Google Scholar without date and language limitation up to May 2022 and included the eligible studies. The quality of included studies was assessed using the Newcastle-Ottawa scale. The overall odds ratios (ORs) were derived using a random-effects model.

RESULTS

In assessment of dietary trans fatty acids 18 studies, including eight cohort, 10 case-control, and observational data from one randomized control trial were included. Although Dietary trans fats were associated with higher risk of CRC (OR = 1.093, 95% CI 1.017, 1.176, P = 0.016; I² = 61.3%), Subgroup analysis by study design yielded an insignificant effect for case-control (OR = 1.152, 95% CI 1.000, 1.328, P = 0.050; I² = 77.2%) and cohort (OR = 1.027, 95% CI 0.976, 1.081, P = 0.299; I² = 0%) studies. Although there was no significant association of trans fatty acids with rectal cancer (OR = 1.093, 95% CI 0.984 to 1.215, P = 0.098; I² = 0%), there was for colon cancer (OR = 1.91, 95% CI 1.062 to 1.335, P = 0.003; I² = 37.6%).The analysis of four studies that evaluated the relation between tissue trans fat and CRC revealed meaningful result (OR = 0.745, 95% CI 0.619, 0.896, P = 0.002; I² = 42.6%). While subgroup assessments for colon cancer (OR = 0.804, 95% CI 0.583, 1.109, P = 0.183; I² = 0%) and plasma trans fatty acids OR = 0.853, 95% CI 0.633, 1.150, P = 0.298; I² = 0%) were insignificant.

CONCLUSION

Dietary trans fatty acids increased the risk of CRC, whereas tissue trans fatty acids had a protective effect on CRC. Nonetheless, neither type of trans fatty acid increased the risk of colon or rectal cancer; thus, more prospective studies are needed to determine the validity of these associations.

Intestinal Barrier Function and Immune Homeostasis Are Missing Links in Obesity and Type 2 Diabetes Development

Noncommunicable diseases, such as type 2 diabetes (T2D), place a burden on healthcare systems worldwide. The rising prevalence of obesity, a major risk factor for T2D, is mainly attributed to the adoption of Westernized diets and lifestyle, which cause metabolic dysfunction and insulin resistance. Moreover, diet may also induce changes in the microbiota composition, thereby affecting intestinal immunity. The critical role of intestinal immunity and intestinal barrier function in the development of T2D is increasingly acknowledged, however, limited studies have investigated the link between intestinal function and metabolic disease. In this review, studies reporting specific roles of the intestinal immune system and intestinal epithelial cells (IECs) in metabolic disease are highlighted. Innate chemokine signaling, eosinophils, immunoglobulin A (IgA), T helper (Th) 17 cells and their cytokines were associated with obesity and/or dysregulated glucose homeostasis. Intestinal epithelial cells (IECs) emerged as critical modulators of obesity and glucose homeostasis through their effect on lipopolysaccharide (LPS) signaling and decontamination. Furthermore, IECs create a link between microbial metabolites and whole-body metabolic function. Future in depth studies of the intestinal immune system and IECs may provide new opportunities and targets to develop treatments and prevention strategies for obesity and T2D.

Nuclear Receptors in Asthma: Empowering Classical Molecules Against a Contemporary Ailment

The escalation in living standards and adoption of 'Western lifestyle' has an allied effect on the increased allergy and asthma burden in both developed and developing countries. Current scientific reports bespeak an association between allergic diseases and metabolic dysfunction; hinting toward the critical requirement of organized lifestyle and dietary habits. The ubiquitous nuclear receptors (NRs) translate metabolic stimuli into gene regulatory signals, integrating diet inflences to overall developmental and physiological processes. As a consequence of such promising attributes, nuclear receptors have historically been at the cutting edge of pharmacy world. This review discusses the recent findings that feature the cardinal importance of nuclear receptors and how they can be instrumental in modulating current asthma pharmacology. Further, it highlights a possible future employment of therapy involving dietary supplements and synthetic ligands that would engage NRs and aid in eliminating both asthma and linked comorbidities. Therefore, uncovering new and evolving roles through analysis of genomic changes would represent a feasible approach in both prevention and alleviation of asthma.

Colon Cancer Risk of a Westernized Diet Is Reduced in Mice by Feeding Cruciferous or Apiaceous Vegetables at a Lower Dose of Carcinogen but Not a Higher Dose

Western-style diets (WD) are associated with greater risk of colon cancer. Exposure to 2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP), a food-borne carcinogen, is linked to increased colon cancer risk. In contrast, intake of apiaceous and cruciferous vegetables (APIs and CRUs) is associated with reduced risk. Here we evaluated effects of a WD alone or a WD containing API or CRU, relative to a purified diet (basal), on colon cancer risk in mice. All diets were fed at one of two concentrations of PhIP (100 or 400 ppm). The activity of the hepatic PhIP-activating enzyme, cytochrome P450 (CYP) 1A2, was examined at week 4 and colonic precancerous lesions (aberrant crypt foci, ACF) were enumerated at week 12. In low PhIP-fed groups, CYP1A2 activity was greater for CRU than all other groups, which did not differ from one another. WD had a significantly greater effect on the formation of ACF than the basal diet. In groups fed API or CRU, the ACF number was reduced to the level observed in the basal diet-fed group. In high PhIP-fed groups, all WD-based diets had greater CYP1A2 activity than the basal diet-fed group. Surprisingly, the basal diet group had more ACF than the WD group, and API and CRU groups did not differ from the WD alone group. Thus, at the lower dose of PhIP, the WD increased colon cancer risk in mice, compared to a purified diet, and APIs and CRUs reduced the risk of the WD. However, at the higher dose of PhIP, the enhancement of colon cancer risk by the WD was not evident, nor was the chemopreventive effect of these vegetables.

Tucum-do-cerrado (Bactris setosa Mart.) modulates oxidative stress, inflammation, and apoptosis-related proteins in rats treated with azoxymethane

Oxidative and inflammatory responses play an important role in the development and prevention of cancer, with both responses being modulated by phytochemical compounds. This study investigated the chemopreventive effect of tucum-do-cerrado fruit in rats treated with azoxymethane. Wistar rats were treated for 12 weeks with: a control diet (CT); a control diet + AOM (CT/DR); a control diet + 15% tucum-do-cerrado (TU); or a control diet + 15% tucum-do-cerrado + AOM (TU/DR). The association of tucum-do-cerrado and AOM (TU/DR) increased glutathione-S-transferase activity, decreased MDA levels, increased levels of COX2, TNFα and BAX, and decreased Bcl2/Bax ratio, compared to the CT/DR group. Carbonyl levels, IL-1β and IL-6 mRNA levels, and aberrant crypt foci showed no difference between the treatments. In conclusion, tucum-do-cerrado reduced lipid oxidative damage, induced a pro-inflammatory effect, and promoted a pro-apoptotic “environment” in rats treated with AOM; however no changes in aberrant crypts were observed.

Characterization of Cyclooxygenase-2 and its induction pathways in response to high lipid diet-induced inflammation in Larmichthys crocea

The present study was conducted to investigate the effects of a high-lipid diet (HLD) on cyclooxygenase (Cox)-2 expression and the signalling pathways related to low-grade inflammation in the large yellow croaker (Larmichthys crocea). An isolated 2508 bp cDNA clone of cox-2 contained an open reading frame spanning 1827 bp encoding a protein with 608 amino acid residues. The over-expression of cox-2 was consistent with the activation of c-Jun N-terminal kinases (JNKs) and p38 mitogen-activated protein kinase (MAPK) in HLD-fed fish. The activation of the activator protein-1 (AP-1) and the nuclear transcription factor kappa-B (NF-κB) signalling pathways in HLD-fed fish and the significant increase of cox-2 promoter-luciferase activity in vitro indicated that AP-1 and NF-κB could combine cox-2 promoter to promote its transcription, respectively. Together, HLD-induced inflammation up-regulates cox-2 expression via JNKs and p38 MAPK-dependent NF-κB and AP-1 pathways. The present study provides important insight into the signal transduction pathways involved in HLD-induced inflammation, which is detrimental to the health and production of fish as well as to the health of fish consumers.

Role of retinoids in the prevention and treatment of colorectal cancer

Vitamin A and its derivatives, retinoids, have been widely studied for their use as cancer chemotherapeutic agents. With respect to colorectal cancer (CRC), several critical mutations dysregulate pathways implicated in progression and metastasis, resulting in aberrant Wnt/β-catenin signaling, gain-of-function mutations in K-ras and phosphatidylinositol-3-kinase/Akt, cyclooxygenase-2 over-expression, reduction of peroxisome proliferator-activated receptor γ activation, and loss of p53 function. Dysregulation leads to increased cellular proliferation and invasion and decreased cell-cell interaction and differentiation. Retinoids affect these pathways by various mechanisms, many involving retinoic acid receptors (RAR). RAR bind to all-trans-retinoic acid (ATRA) to induce the transcription of genes responsible for cellular differentiation. Although most research concerning the chemotherapeutic efficacy of retinoids focuses on the ability of ATRA to decrease cancer cell proliferation, increase differentiation, or promote apoptosis; as CRC progresses, RAR expression is often lost, rendering treatment of CRCs with ATRA ineffective. Our laboratory focuses on the ability of dietary vitamin A to decrease CRC cell proliferation and invasion via RAR-independent pathways. This review discusses our research and others concerning the ability of retinoids to ameliorate the defective signaling pathways listed above and decrease tumor cell proliferation and invasion through both RAR-dependent and RAR-independent mechanisms.

Effect of vitamin A deficiency on the immune response in obesity

Obesity has been associated with low-grade systemic inflammation and with micronutrient deficiencies. Obese individuals have been found to have lower vitamin A levels and lower vitamin A intake compared with normal-weight individuals. Vitamin A plays a major role in the immune function, including innate immunity, cell-mediated immunity and humoral antibody immunity. It has also been recognised recently that vitamin A has important regulatory functions. Vitamin A status has an important effect on the chronic inflammatory response. Vitamin A deficiency increases a T-helper type 1 (Th1) response, elevates levels of pro-inflammatory cytokines, increases the expression of leptin, resistin and uncoupling proteins (UCP) and promotes adipogenesis. The effect of vitamin A deficiency on obesity might be increasing the risk of fat deposition and also the risk of chronic inflammation associated with obesity. Supplementation with vitamin A in vitro and in animal models has been found to reduce concentrations of adipocytokines, such as leptin and resistin. In conclusion, vitamin A deficiency increases a Th1 response in the presence of obesity and thus, increases the inflammatory process involved in chronic inflammation and fat deposition. The metabolism of leptin and other adipocytokines may play a critical role in the effect of vitamin A deficiency in the inflammatory response observed in obesity.

The Mediterranean diet: effects on proteins that mediate fatty acid metabolism in the colon

A Mediterranean diet appears to have health benefits in many domains of human health, mediated perhaps by its anti-inflammatory effects. Metabolism of fatty acids and subsequent eicosanoid production is a key mechanism by which a Mediterranean diet can exert anti-inflammatory effects. Both dietary fatty acids and fatty acid metabolism determine fatty acid availability for cyclooxygenase- and lipoxygenase-dependent production of eicosanoids, namely prostaglandins and leukotrienes. In dietary intervention studies and in observational studies of the Mediterranean diet, blood levels of fatty acids do reflect dietary intakes but are attenuated. Small differences in fatty acid levels, however, appear to be important, especially when exposures occur over long periods of time. This review summarizes how fat intakes from a Greek-style Mediterranean diet can be expected to affect fatty acid metabolizing proteins, with an emphasis on the metabolic pathways that lead to the formation of proinflammatory eicosanoids. The proteins involved in these pathways are ripe for investigation using proteomic approaches and may be targets for colon cancer prevention.

PPAR Action in Human Placental Development and Pregnancy and Its Complications

During pregnancy crucial anatomic, physiologic, and metabolic changes challenge the mother and the fetus. The placenta is a remarkable organ that allows the mother and the fetus to adapt to the new metabolic, immunologic, and angiogenic environment imposed by gestation. One of the physiologic systems that appears to have evolved to sustain this metabolic regulation is mediated by peroxisome proliferator-activated receptors (PPARs). In clinical pregnancy-specific disorders, including preeclampsia, gestational diabetes, and intrauterine growth restriction, aberrant regulation of components of the PPAR system parallels dysregulation of metabolism, inflammation and angiogenesis. This review summarizes current knowledge on the role of PPARs in regulating human trophoblast invasion, early placental development, and also in the physiology of clinical pregnancy and its complications. As increasingly indicated in the literature, pregnancy disorders, such as preeclampsia and gestational diabetes, represent potential targets for treatment with PPAR ligands. With the advent of more specific PPAR agonists that exhibit efficacy in ameliorating metabolic, inflammatory, and angiogenic disturbances, further studies of their application in pregnancy-related diseases are warranted.

Abnormal Savda Munziq, an Herbal Preparation of Traditional Uighur Medicine, May Prevent 1,2-dimethylhydrazine-Induced Rat Colon Carcinogenesis

The study tried to assess the chemoprotective effect of abnormal Savda Munziq (ASMq) on 1,2-dimethylhydrazine (DMH)-induced rat colon carcinogenesis. Male F344 rats were randomized into eight groups: Group 1 was served as control, no DMH injection was given and treated daily with normal saline. Rats in Groups 2–8 were given a single intraperitoneal injection of DMH (20 mg/kg body weight) at the beginning of the study. Group 2 was served as negative control, administered with normal saline until the end of the experiment after the single DMH injection. Groups 3–5 were served as pretreatment group, administered with ASMq ethanol extract at 400, 800 and 1600 mg/kg body weight, respectively, until the 45th day, continued by normal saline administration for another 45 days. Groups 6–8 were served as the treatment group, administered with normal saline for the first 45 days from the day of DMH injection, ASMq ethanol extract at three different doses to be administered until the end of the second 45th day. All rats were sacrificed at 91st day and the colons were analyzed for aberrant crypt foci (ACF) formation and crypt multiplicity. Results showed that ASMq ethanol extract reduced the number of ACF, AC and crypt multiplicity significantly (P < .05). It suggested that ASMq ethanol extract had chemoprotective effects on DMH-induced colon carcinogenesis, by suppressing the development of preneoplastic lesions, and probably exerted protection against the initiation and promotion steps of colon carcinogenesis.

Celecoxib increases retinoid sensitivity in human colon cancer cell lines

Retinoid resistance has limited the clinical application of retinoids as differentiation-inducing and apoptosis-inducing drugs. This study was designed to investigate whether celecoxib, a selective COX-2 inhibitor, has effects on retinoid sensitivity in human colon cancer cell lines, and to determine the possible mechanism of said effects. Cell viability was measured using the MTT assay. Apoptosis was detected via Annexin-V/PI staining and the flow cytometry assay. PGE₂ production was measured with the ELISA assay. The expression of RARβ was assayed via western blotting. The results showed that celecoxib enhanced the inhibitory effect of ATRA in both COX-2 high-expressing HT-29 and COX-2 low-expressing SW480 cell lines. Further study showed the ATRA and celecoxib combination induced greater apoptosis, but that the addition of PGE₂ did not affect the enhanced growth-inhibitory and apoptosis-inducing effects of the combination. Moreover, NS398 (another selective COX-2 inhibitor) did not affect the inhibitory effects of ATRA in the two cell lines. Western blotting showed that the expression of RARβ in HT-29 cell lines was increased by celecoxib, but not by NS398, and that the addition of PGE₂ did not affect the celecoxib-induced expression of the retinoic acid receptor beta. In conclusion, celecoxib increased the expression of RARβ and the level of cellular ATRA sensitivity through COX-2-independent mechanisms. This finding may provide a potential strategy for combination therapy.

RARgamma and TRbeta expressions are decreased in PBMC and SWAT of obese subjects in weight gain

In order to evaluate the expression of nuclear receptors at the peripheral level in obese subjects, messenger RNA (mRNA) levels of different isoforms of retinoic acid receptor (RAR), triiodothyronine (TR), and peroxisome proliferator-activated receptor (PPAR) were determined and compared in peripheral mononuclear blood cells (PBMC) and subcutaneous white adipose tissue (SWAT). Twelve lean subjects and 68 obese subjects divided into weight gain (WG), weight-stable (WS), and weight loss (WL) groups were studied. Nuclear receptor mRNA levels were assessed in PBMC and SWAT using a quantitative real-time reverse transcription polymerase chain reaction method. mRNA levels of RARgamma were significantly lower in PBMC of obese subjects (WG -19%, WS -30%, and WL -24.7%) as in SWAT of WG (-50%). Lower mRNA levels of TRbeta were observed in PBMC and SWAT of WG (-50.7% and -28%, respectively) just as for TRalpha in PBMC of WG (-19%). In contrast, retinoid X receptors alpha (RXRalpha) and RARalpha mRNA levels were higher in PBMC of obese subjects (+53% and +54.5% in WG, +56% and +67% in WS, and +68% and +49.7% in WL, respectively), while expression of RXRalpha was lower in SWAT of WG (-24.5%). As for PPARgamma, its mRNA level was significantly higher in PBMC of WG subjects (+34%) while its expression was not modified in SWAT, contrary to the PPARgamma2 isoform which was significantly higher. These data show that in both adipose tissue and blood compartment of obese subjects, expressions of RARgamma and TRbeta were downregulated. Thus, we suggest that the expression in PBMC of obese subjects may constitute new cellular indicators of nuclear receptor retinoid and thyroid status.

A high-fat diet induces lower expression of retinoid receptors and their target genes GAP-43/neuromodulin and RC3/neurogranin in the rat brain

Numerous studies have reported an association between cognitive impairment in old age and nutritional factors, including dietary fat. Retinoic acid (RA) plays a central role in the maintenance of cognitive processes via its nuclear receptors (NR), retinoic acid receptor (RAR) and retinoid X receptor (RXR), and the control of target genes, e.g. the synaptic plasticity markers GAP-43/neuromodulin and RC3/neurogranin. Given the relationship between RA and the fatty acid signalling pathways mediated by their respective NR (RAR/RXR and PPAR), we investigated the effect of a high-fat diet (HFD) on (1) PUFA status in the plasma and brain, and (2) the expression of RA and fatty acid NR (RARbeta, RXRbetagamma and PPARdelta), and synaptic plasticity genes (GAP-43 and RC3), in young male Wistar rats. In the striatum of rats given a HFD for 8 weeks, real-time PCR (RT-PCR) revealed a decrease in mRNA levels of RARbeta ( - 14 %) and PPARdelta ( - 13 %) along with an increase in RXRbetagamma (+52 %). Concomitantly, RT-PCR and Western blot analysis revealed (1) a clear reduction in striatal mRNA and protein levels of RC3 ( - 24 and - 26 %, respectively) and GAP-43 ( - 10 and - 42 %, respectively), which was confirmed by in situ hybridisation, and (2) decreased hippocampal RC3 and GAP-43 protein levels (approximately 25 %). Additionally, HFD rats exhibited a significant decrease in plasma ( - 59 %) and brain ( - 6 %) n-3 PUFA content, mainly due to the loss of DHA. These results suggest that dietary fat induces neurobiological alterations by modulating the brain RA signalling pathway and n-3 PUFA content, which have been previously correlated with cognitive impairment.

Epidermal growth factor receptor is required for colonic tumor promotion by dietary fat in the azoxymethane/dextran sulfate sodium model: roles of transforming growth factor-{alpha} and PTGS2

PURPOSE

Colon cancer is a major cause of cancer deaths. Dietary factors contribute substantially to the risk of this malignancy. Western-style diets promote development of azoxymethane-induced colon cancer. Although we showed that epidermal growth factor receptors (EGFR) controlled azoxymethane tumorigenesis in standard fat conditions, the role of EGFR in tumor promotion by high dietary fat has not been examined.

EXPERIMENTAL DESIGN

A/J x C57BL6/J mice with wild-type Egfr (Egfr(wt)) or loss-of-function waved-2 Egfr (Egfr(wa2)) received azoxymethane followed by standard (5% fat) or western-style (20% fat) diet. As F(1) mice were resistant to azoxymethane, we treated mice with azoxymethane followed by one cycle of inflammation-inducing dextran sulfate sodium to induce tumorigenesis. Mice were sacrificed 12 weeks after dextran sulfate sodium. Tumors were graded for histology and assessed for EGFR ligands and proto-oncogenes by immunostaining, Western blotting, and real-time PCR.

RESULTS

Egfr(wt) mice gained significantly more weight and had exaggerated insulin resistance compared with Egfr(wa2) mice on high-fat diet. Dietary fat promoted tumor incidence (71.2% versus 36.7%; P < 0.05) and cancer incidence (43.9% versus 16.7%; P < 0.05) only in Egfr(wt) mice. The lipid-rich diet also significantly increased tumor and cancer multiplicity only in Egfr(wt) mice. In tumors, dietary fat and Egfr(wt) upregulated transforming growth factor-alpha, amphiregulin, CTNNB1, MYC, and CCND1, whereas PTGS2 was only increased in Egfr(wt) mice and further upregulated by dietary fat. Notably, dietary fat increased transforming growth factor-alpha in normal colon.

CONCLUSIONS

EGFR is required for dietary fat-induced weight gain and tumor promotion. EGFR-dependent increases in receptor ligands and PTGS2 likely drive diet-related tumor promotion.

Retinol Increases beta-catenin-RXRalpha binding leading to the increased proteasomal degradation of beta-catenin and RXRalpha

Retinol utilizes a retinoid X receptor (RXR)-mediated degradation pathway to decrease beta-catenin protein in all-trans retinoic acid (ATRA)-resistant human colon cancer cells. In this study, we examined interactions between RXRalpha and beta-catenin in ATRA-resistant human colon cancer cells treated with retinol. Retinol treatment triggers relocation of beta-catenin and RXRalpha proteins. Cells treated with retinol for 8 and 24 h displayed increased cytosolic but decreased nuclear beta-catenin and RXRalpha. Retinol treatment increased beta-catenin and RXRalpha protein interaction. Previously, we showed that 24 h of retinol treatment increased RXRalpha protein. Here we show this increase in RXRalpha levels is due to increased RXRalpha messenger RNA. Treatment with 48 h with retinol decreased RXRalpha protein levels. Last, by transfecting HCT-116 cells with a RXRalpha construct lacking the activation function-1 and DNA binding domains, we show RXRalpha and beta-catenin binding is required for proteosomal degradation of beta-catenin. These results suggest retinol induces RXRalpha and beta-catenin binding and transport to the cytosol where they are proteasomally degraded.

The effect of body weight on altered expression of nuclear receptors and cyclooxygenase-2 in human colorectal cancers

Background

Epidemiological studies on risk factors for colorectal cancer (CRC) have mainly focused on diet, and being overweight is now recognized to contribute significantly to CRC risk. Overweight and obesity are defined as an excess of adipose tissue mass and are associated with disorders in lipid metabolism. Peroxisome proliferator-activated receptors (PPARs) and retinoid-activated receptors (RARs and RXRs) are important modulators of lipid metabolism and cellular homeostasis. Alterations in expression and activity of these ligand-activated transcription factors might be involved in obesity-associated diseases, which include CRC. Cyclooxygenase-2 (COX-2) also plays a critical role in lipid metabolism and alterations in COX-2 expression have already been associated with unfavourable clinical outcomes in epithelial tumors. The objective of this study is to examine the hypothesis questioning the relationship between alterations in the expression of nuclear receptors and COX-2 and the weight status among male subjects with CRC.

Method

The mRNA expression of the different nuclear receptor subtypes and of COX-2 was measured in 20 resected samples of CRC and paired non-tumor tissues. The association between expression patterns and weight status defined as a body mass index (BMI) was statistically analyzed.

Results

No changes were observed in PPARγ mRNA expression while the expression of PPARδ, retinoid-activated receptors and COX-2 were significantly increased in cancer tissues compared to normal colon mucosa (P ≤ 0.001). The weight status appeared to be an independent factor, although we detected an increased level of COX-2 expression in the normal mucosa from overweight patients (BMI ≥ 25) compared to subjects with healthy BMI (P = 0.002).

Conclusion

Our findings show that alterations in the pattern of nuclear receptor expression observed in CRC do not appear to be correlated with patient weight status. However, the analysis of COX-2 expression in normal colon mucosa from subjects with a high BMI suggests that COX-2 deregulation might be driven by excess weight during the colon carcinogenesis process.

Tumor-suppressive activity of retinoic acid receptor-beta in cancer

Retinoids, a group of structural and functional analogs of vitamin A, are known to regulate a large number of essential biological processes and to suppress carcinogenesis. The effects of retinoids are mainly mediated by nuclear retinoid receptors, which include retinoic acid receptors (RARs) and retinoid X receptors (RXRs). Each receptor has three subtypes (alpha, beta, and gamma) and each subtype has different isoforms. Retinoic acid receptor-beta (RAR-beta) has four isoforms that have different affinities to retinoids and different biological functions. Loss of expression of RAR-beta(2) during cancer development is associated with tumorigenesis and retinoid resistance; induction of its expression, on the other hand, can suppress carcinogenesis. Expression of another isoform, RAR-beta(4), is increased in various types of cancer. RAR-beta(4) transgenic mice develop hyperplasia and neoplasia in various tissues, and induction of RAR-beta(4) expression increases the growth of tumor cells that do not express RAR-beta(2). Future studies will focus on molecular pathways involving RAR-beta(2) and the role of RAR-beta(4) in cancer development.

Retinol decreases beta-catenin protein levels in retinoic acid-resistant colon cancer cell lines

The beta-catenin signaling pathway is dysregulated in most cases of colon cancer resulting in an accumulation of nuclear beta-catenin and increased transcription of genes involved in tumor progression. This study examines the effect of retinol on beta-catenin protein levels in three all-trans retinoic acid (ATRA)-resistant human colon cancer cell lines: HCT-116, WiDr, and SW620. Each cell line was treated with increasing concentrations of retinol for 24 or 48 h. Retinol reduced beta-catenin protein levels and increased ubiquitinated beta-catenin in all cell lines. Treatment with the proteasomal inhibitor MG132 blocked the retinol-induced decrease in beta-catenin indicating retinol decreases beta-catenin by increasing proteasomal degradation. Multiple pathways direct beta-catenin to the proteasome for degradation including a p53/Siah-1/adenomatous polyposis coli (APC), a Wnt/glycogen synthase kinase-3beta/APC, and a retinoid "X" receptor (RXR)-mediated pathway. Due to mutations in beta-catenin (HCT-116), APC (SW620), and p53 (WiDr), only the RXR-mediated pathway remains functional in each cell line. To determine if RXRs facilitate beta-catenin degradation, cells were treated with the RXR pan-antagonist, PA452, or transfected with RXRalpha small interfering RNA (siRNA). The RXR pan-antagonist and RXRalpha siRNA reduced the ability of retinol to decrease beta-catenin protein levels. Nuclear beta-catenin induces gene transcription via interaction with T cell factor/lymphoid enhancer factor (TCF/LEF) proteins. Retinol treatment decreased the transcription of a TOPFlash reporter construct and mRNA levels of the endogenous beta-catenin target genes, cyclin D1 and c-myc. These results indicate that retinol may reduce colon cancer cell growth by increasing the proteasomal degradation of beta-catenin via a mechanism potentially involving RXR.