Chemopreventive N-(4-hydroxyphenyl)retinamide (fenretinide) targets deregulated NF-{kappa}B and Mat1A genes in the early stages of rat liver carcinogenesis

Retinoids Delivery Systems in Cancer: Liposomal Fenretinide for Neuroectodermal-Derived Tumors

Retinoids are a class of natural and synthetic compounds derived from vitamin A. They are involved in several biological processes like embryogenesis, reproduction, vision, growth, inflammation, differentiation, proliferation, and apoptosis. In light of their important functions, retinoids have been widely investigated for their therapeutic applications. Thus far, their use for the treatment of several types of cancer and skin disorders has been reported. However, these therapeutic agents present several limitations for their widespread clinical translatability, i.e., poor solubility and chemical instability in water, sensitivity to light, heat, and oxygen, and low bioavailability. These characteristics result in internalization into target cells and tissues only at low concentration and, consequently, at an unsatisfactory therapeutic dose. Furthermore, the administration of retinoids causes severe side-effects. Thus, in order to improve their pharmacological properties and circulating half-life, while minimizing their off-target uptake, various retinoids delivery systems have been recently developed. This review intends to provide examples of retinoids-loaded nano-delivery systems for cancer treatment. In particular, the use and the therapeutic results obtained by using fenretinide-loaded liposomes against neuroectodermal-derived tumors, such as melanoma, in adults, and neuroblastoma, the most common extra-cranial solid tumor of childhood, will be discussed.

Chemosensitization by 4-hydroxyphenyl retinamide-induced NF-κB inhibition in acute myeloid leukemia cells

PURPOSE

Inherent and/or acquired multi-drug resistance might be the instigator of treatment failure for acute myeloid leukemia (AML). In the current study, we aimed to explored the chemosensitizing effect of 4-HPR on AML therapy.

METHODS

Luciferase reporter assays were used to test the effect of 4-HPR on transcriptional signaling pathways. The quantitative real-time polymerase chain reaction and immunoblots were used to confirm the role of 4-HPR in NF-κB inhibition, apoptosis, and drug resistance. MTT and flow cytometry assays were applied to test the drug response and chemosensitizing effect of 4-HPR with AML cell lines and primary AML samples.

RESULTS

4-HPR suppressed tumor necrosis factor-α- and daunorubin-induced NF-κB activation in AML cell lines. The expression of anti-apoptotic gene, BCL2, was downregulated, while expressions of pro-apoptotic genes, cIAP, XIAP, and BID, were increased after 4-HPR treatment. Immunoblots showed decreased p65-NF-κB, IκBα, and MDR1, but increased cleaved poly (ADP-ribose) polymerase and BIM. A low concentration of 4-HPR chemosensitized AML cells to daunorubin treatment in vitro.

CONCLUSION

4-HPR-induced NF-κB inhibition was the main driver of the chemosensitizing effect observed in AML cell lines and primary AML samples. These results highlight that 4-HPR might be a promising chemosensitizing agent in AML therapy.

The dual role of iNOS in cancer

Nitric oxide (NO) is one of the 10 smallest molecules found in nature. It is a simple gaseous free radical whose predominant functions is that of a messenger through cGMP. In mammals, NO is synthesized by the enzyme nitric oxide synthase (NOS) of which there are three isoforms. Neuronal (nNOS, NOS1) and endothelial (eNOS, NOS3) are constitutive calcium-dependent forms of the enzyme that regulate neural and vascular function respectively. The third isoform (iNOS, NOS2), is calcium-independent and is inducible. In many tumors, iNOS expression is high, however, the role of iNOS during tumor development is very complex and quite perplexing, with both promoting and inhibiting actions having been described. This review will aim to summarize the dual actions of iNOS-derived NO showing that the microenvironment of the tumor is a contributing factor to these observations and ultimately to cellular outcomes.

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NO is pro- and anti-tumorigenic. High concentrations of NO maybe anti-tumorigenic.

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iNOS produces high concentrations of NO and relates to tumor growth or its inhibition.

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iNOS is associated with cytotoxicity, apoptosis and bystander anti-tumor effects.

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Tumor- and stromal-iNOS, and the ‘cell situation’ contribute to anti or pro-tumor effects.

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Dual role of iNOS is influenced by the cell situation and is environment dependent.

The role of inflammation and liver cancer

Persistent inflammation is known to promote and exacerbate malignancy. Primary liver cancer, mostly hepatocellular carcinoma (HCC), is a clear example of inflammation-related cancer as more than 90 % of HCCs arise in the context of hepatic injury and inflammation. HCC represents the fifth most common malignancy and the third leading cause of cancer-related death worldwide with about one million new cases diagnosed every year with almost an equal number of deaths. Chronic unresolved inflammation is associated with persistent hepatic injury and concurrent regeneration, leading to sequential development of fibrosis, cirrhosis, and eventually HCC. Irrespective of the intrinsic differences among various etiological factors, a common denominator at the origin of HCC is the perpetuation of a wound-healing response activated by parenchymal cell death and the resulting inflammatory cascade. Hence, the identification of fundamental inflammatory signaling pathways causing transition from chronic liver injury to dysplasia and HCC could depict new predictive biomarkers and targets to identify and treat patients with chronic liver inflammation. This chapter critically discusses the roles of several major cytokines, chemokines, growth factors, transcription factors, and enzymes as well as a distinct network of inflammatory signaling pathways in the development and progression of HCC. It also highlights and analyzes preclinical animal studies showing innovative approaches of targeting inflammatory mediators and signaling by a variety of natural compounds and synthetic agents to achieve effective therapy as well as prevention of hepatic malignancy. Additionally, current limitations and potential challenges associated with the inhibition of inflammatory signaling as well as future directions of research to accelerate clinical development of anti-inflammatory agents to prevent and treat liver cancer are presented.

Retinoids: novel immunomodulators and tumour-suppressive agents?

Retinoids play important roles in the transcriptional activity of normal, degenerative and tumour cells. Retinoid analogues may be promising therapeutic agents for the treatment of immune disorders as different as type I diabetes and systemic lupus erythematosus. In addition, the use of retinoids in cancer treatment has progressed significantly in the last two decades; thus, numerous retinoid compounds have been synthesized and tested. In this paper, the actual or potential use of retinoids as immunomodulators or tumour-suppressive agents is discussed.

The protective effects of quercetin on the cytotoxicity of atrazine on rat Sertoli-germ cell co-culture

To evaluate the direct effect of atrazine (ATZ) and the protective effect of quercetin (QT) on testicular cells, we used primary cultures of rat Sertoli-germ cells (SGCs). ATZ (232 μm) up-regulated the mRNA expression of GATA-4, androgen receptor (AR), androgen-binding protein (ABP), steroidogenic acute regulatory protein (StAR), cytochrome P450 side-chain cleavage enzyme (CYP11A1), cyclooxygenase-2 (COX-2) and NF-κappaB (NF-κB) and down-regulated the expression of stem cell factor (SCF) mRNA. There was no change on the mRNA expression of oestrogen receptor-alpha (ER-α). Simultaneous supplementation of QT in the culture normalizes the expression of these genes. The stimulatory action of follicle stimulating hormone (10 ng/mL) on ATZ-induced StAR and CYP11A1 mRNA levels were also prevented by QT. Furthermore, ATZ-stimulatory action on AR mRNA was opposed in a dose-dependent manner in the presence of increasing concentrations of QT (10-50 μm).The dislodgement of germ cells from the Sertoli cells monolayer and decrease in SGCs viability was prevented by QT. To show whether or not the disrupted interactions of Sertoli and germ cells impaired spermatogenesis, adult male rats exposed in vivo to ATZ (50 mg/kg b.wt) for 1 week had their daily spermatozoa production (DSP) per gram testis lowered by 30%. DSP was significantly increased in the QT(10 mg/kg) + ATZ-treated rats as compared with the ATZ-treated rats. Taken together, ATZ can alter SGCs expression of spermatogenesis- and steroiodogenesis-related genes resulting in a decrease in sperm production in the testis as well as cell viability. QT might block these molecular events-induced by ATZ thereby protecting testicular Sertoli-germ cells from ATZ-induced toxicity.

Folic acid supplementation during early hepatocarcinogenesis: cellular and molecular effects

Folic acid (FA) supplementation during carcinogenesis is controversial. Considering the impact of liver cancer as a public health problem and mandatory FA fortification in several countries, the role of FA supplementation in hepatocarcinogenesis should be elucidated. We evaluated FA supplementation during early hepatocarcinogenesis. Rats received daily 0.08 mg (FA8 group) or 0.16 mg (FA16 group) of FA/100 g body weight or water (CO group, controls). After a 2-week treatment, animals were subjected to the "resistant hepatocyte" model of hepatocarcinogenesis (initiation with diethylnitrosamine, selection/promotion with 2-acetylaminofluorene and partial hepatectomy) and euthanized after 8 weeks of treatment. Compared to the CO group, the FA16 group presented: reduced (p < 0.05) number of persistent and increased (p < 0.05) number of remodeling glutathione S-transferase (GST-P) positive preneoplastic lesions (PNL); reduced (p < 0.05) cell proliferation in persistent GST-P positive PNL; decreased (p < 0.05) hepatic DNA damage; and a tendency (p < 0.10) for decreased c-myc expression in microdissected PNL. Regarding all these parameters, no differences (p > 0.05) were observed between CO and FA8 groups. FA-treated groups presented increased hepatic levels of S-adenosylmethionine but only FA16 group presented increased S-adenosylmethionine/S-adenosylhomocysteine ratio. No differences (p > 0.05) were observed between experimental groups regarding apoptosis in persistent and remodeling GST-P positive PNL, and global DNA methylation pattern in microdissected PNL. Altogether, the FA16 group, but not the FA8 group, presented chemopreventive activity. Reversion of PNL phenotype and inhibition of DNA damage and of c-myc expression represent relevant FA cellular and molecular effects.

Prognostic markers and putative therapeutic targets for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fifth most frequent human cancer and a fatal disease. Therapies with pharmacological agents do not improve the prognosis of patients with unresectable HCC. This emphasizes the need to identify new targets for early diagnosis, chemoprevention, and treatment of the disease. Available evidence indicates that clinical outcome of HCC could reflect the genetic predisposition to cancer development and progression. Numerous loci controlling HCC progression have been identified in rodents. In this review, we describe results of recent studies on effector mechanisms of susceptibility/resistance genes, responsible for HCC progression, aimed at identifying new putative prognostic markers and therapeutic targets of this tumor. Highest c-myc amplification and overexpression, alterations of iNOS crosstalk with IKK/NF-kB and RAS/ERK signaling, ubiquitination of ERK and cell cycle inhibitors, and deregulation of FOXM1 and cell cycle key genes occur in rapidly progressing dysplastic nodules and HCC, induced in genetic susceptible rat strains, compared to the lesions of resistant rats. Notably, alterations of these mechanisms in human HCC subtypes with poorer or better prognosis, are similar to those present in genetically susceptible and resistant rats, respectively, and function as prognostic markers and therapeutic targets. Attempts to cure advanced HCC by molecular therapy directed against specific targets led to modest survival benefit. Thus, efforts are necessary to identify and test, in pre-clinical and clinical studies, new therapeutic targets for combined molecular treatments of HCC. They may take advantage from the comparative analysis of signal transduction in HCCs differently prone to progress, in rats and humans.

Genetic and epigenetic control of molecular alterations in hepatocellular carcinoma

Comparative analysis of hepatocellular carcinoma (HCC) in rat strains that are either susceptible or resistant to the induction of HCC has allowed the mapping of genes responsible for inherited predisposition to HCC. These studies show that the activity of several low penetrance genes and a predominant susceptibility gene regulate the development of hepatocarcinogenesis in rodents. These studies shed light on the epidemiology of human HCC. The identified genes regulate resistance to hepatocarcinogenesis by affecting the capacity of the initiated cells to grow autonomously and to progress to HCC. Analysis of the molecular alterations showed highest iNos cross-talk with IKK/NF-kB and RAS/ERK pathways in most aggressive liver lesions represented by HCC in the susceptible F344 rats. Unrestrained extracellular signal-regulated kinase (Erk) activity linked to proteasomal degradation of dual-specificity phosphatase 1 (Dusp1), a specific ERK inhibitor, by the CKS1-SKP2 ubiquitin ligase complex was highest in more aggressive HCC of genetically susceptible rats. Furthermore, deregulation of G1 and S phases of the cell cycle occurs in HCC of susceptible F344 rats, leading to pRb hyperphosphorylation and elevated DNA synthesis, whereas a block to G1-S transition is present in the HCC of resistant BN rats. Importantly, similar alterations in the signaling pathways that regulate cell cycle progression were found in human HCC with poorer prognosis (as defend by patients' survival length), whereas human HCC with better prognosis had molecular characteristics similar to the lesions in the HCC of resistant rat strains. This review discusses the role of molecular alterations involved in the acquisition of resistance or susceptibility to HCC and the importance of genetically susceptible and resistant rat models for the identification of prognostic markers, and chemopreventive or therapeutic targets for the biological network therapy of human disease.

Interaction of major genes predisposing to hepatocellular carcinoma with genes encoding signal transduction pathways influences tumor phenotype and prognosis

Studies on rodents and humans demonstrate an inherited predisposition to hepatocellular carcinoma (HCC). Analysis of the molecular alterations involved in the acquisition of a phenotype resistant or susceptible to hepatocarcinogenesis showed a deregulation of G1 and S phases in HCC of genetically susceptible F344 rats and a G1-S block in lesions of resistant Brown norway (BN) rats. Unrestrained extracellular signal-regulated kinase (ERK) activity linked to proteasomal degradation of dual-specificity phosphatase 1 (DUSP1), a specific ERK inhibitor, by the CKS1-SKP2 ubiquitin ligase complex occurs in more aggressive HCC of F344 rats and humans. This mechanism is less active in HCC of BN rats and human HCC with better prognosis. Upregulation of iNos cross-talk with IKK/NF-κB and RAS/ERK pathways occurs in rodent liver lesions at higher levels in the most aggressive models represented by HCC of F344 rats and c-Myc-TGF-α transgenic mice. iNOS, IKK/NF-κB, and RAS/ERK upregulation is highest in human HCC with a poorer prognosis and positively correlates with tumor proliferation, genomic instability and microvascularization, and negatively with apoptosis. Thus, cell cycle regulation and the activity of signal transduction pathways seem to be modulated by HCC modifier genes, and differences in their efficiency influence the susceptibility to hepatocarcinogenesis and probably the prognosis of human HCC.

Gene expression and MR diffusion-weighted imaging after chemoembolization in rabbit liver VX-2 tumor model

AIM: To investigate the dynamic characteristics and the correlation between PCNA, Bax, nm23, E-cadherin expression and apparent diffusion coefficient (ADC) on MR diffusion-weighted imaging (DWI) after chemoembolization in rabbit liver VX-2 tumor model.

METHODS: Forty New Zealand rabbit liver VX-2 tumor models were included in the study. DWI was carried out periodically after chemoembolization. All VX-2 tumor samples in each group were examined by histopathology and Strept Avidin-Biotin Complex (SABC) immunohistochemical staining.

RESULTS: The PCNA expression index in VX-2 tumors was higher than in the normal parenchyma around the tumor (P < 0.001). Nm23, Bax or E-caderin expression index in VX-2 tumors were lower than in the normal parenchyma around the tumor (all P < 0.001). PCNA and nm23 expression in the VX-2 tumor periphery first increased and then decreased (P < 0.001 and P = 0.03, respectively), while the expression of Bax and E-cadherin before and after chemoembolization was insignificant. When b-value was 100 s/mm², there was a linear correlation between PCNA expression and ADC in the area of VX-2 tumor periphery (P < 0.001), and PCNA expression in VX-2 tumor periphery influenced the ADC.

CONCLUSION: The potential of VX-2 tumor infiltrating and metastasizing decreases, while its ability to proliferate increases for a short time after chemoembolization. To some degree, the ADC value indirectly reflects the proliferation of VX-2 tumor cells.

Persistent and remodeling hepatic preneoplastic lesions present differences in cell proliferation and apoptosis, as well as in p53, Bcl-2 and NF-κB pathways

During rat hepatocarcinogenesis preneoplastic lesions (PNL) emerge which may persist (pPNL) and be sites of progress to cancer or suffer remodeling (rPNL) tending to disappear. Cellular and molecular mechanisms involved in both phenotypes are not sufficiently elucidated. pPNL and rPNL cellular proliferation and apoptosis were evaluated in rats submitted to the resistant hepatocyte (RH) model, and an adjusted growth index (AGI) was established. p53, Bcl-2, and NF-kappaB p65 subunit expression was evaluated by immunohistochemistry in pPNL and rPNL. p65 expression and NF-kappaB activation was evaluated by Western blot assays in whole livers. A lower number of BrdU-stained hepatocyte nuclei/mm(2) and higher number of apoptotic bodies (AB) per mm(2) were observed in remodeling compared to pPNL. Cytoplasmic p53 accumulation is related to increased hepatocarcinoma malignancy. We observed that 71.3% pPNL and 25.4% rPNL (P < 0.05) presented p53 staining in the cytoplasm. Similarly, 67.7% pPNL and 23.1 % rPNL (P < 0.05) presented increased Bcl-2 staining. Thirty-two percent pPNL and 15.6% rPNL (P < 0.05) presented p65 staining. Compared to normal rats, increase (P < 0.05) of hepatic p65 expression and NF-kappaB activation in rats submitted to the RH model was observed. In agreement to previous studies hepatic pPNL and rPNL differ regarding cell proliferation and apoptosis. Moreover, persistence and remodeling involve differences in p53, Bcl-2, and NF-kappaB pathways. These data point to molecular pathways that may direct preneoplastic lesions to spontaneously regress or to progress to cancer. J. Cell. Biochem. 103: 538-546, 2008. (c) 2007 Wiley-Liss, Inc.

Fenretinide-induced apoptosis of Huh-7 hepatocellular carcinoma is retinoic acid receptor beta dependent

BACKGROUND

Retinoids are used to treat several types of cancer; however, their effects on liver cancer have not been fully characterized. To investigate the therapeutic potential of retinoids on hepatocellular carcinoma (HCC), the present study evaluates the apoptotic effect of a panel of natural and synthetic retinoids in three human HCC cell lines as well as explores the underlying mechanisms.

METHODS

Apoptosis was determined by caspase-3 cleavage using western blot, DNA double-strand breaks using TUNEL assay, and phosphatidylserine translocation using flow cytometry analysis. Gene expression of nuclear receptors was assessed by real-time PCR. Transactivation assay and chromatin immunoprecipitation (ChIP) were conducted to evaluate the activation of RXRalpha/RARbeta pathway by fenretinide. Knockdown of RARbeta mRNA expression was achieved by siRNA transfection.

RESULTS

Our data revealed that fenretinide effectively induces apoptosis in Huh-7 and Hep3B cells. Gene expression analysis of nuclear receptors revealed that the basal and inducibility of retinoic acid receptor beta (RARbeta) expression positively correlate with the susceptibility of HCC cells to fenretinide treatment. Furthermore, fenretinide transactivates the RXRalpha/RARbeta-mediated pathway and directly increases the transcriptional activity of RARbeta. Knockdown of RARbeta mRNA expression significantly impairs fenretinide-induced apoptosis in Huh-7 cells.

CONCLUSION

Our findings reveal that endogenous expression of retinoids receptor RARbeta gene determines the susceptibility of HCC cells to fenretinide-induced apoptosis. Our results also demonstrate fenretinide directly activates RARbeta and induces apoptosis in Huh-7 cells in a RARbeta-dependent manner. These findings suggest a novel role of RARbeta as a tumor suppressor by mediating the signals of certain chemotherapeutic agents.

Predictive toxicogenomics approaches reveal underlying molecular mechanisms of nongenotoxic carcinogenicity

Toxicogenomics technology defines toxicity gene expression signatures for early predictions and hypotheses generation for mechanistic studies, which are important approaches for evaluating toxicity of drug candidate compounds. A large gene expression database built using cDNA microarrays and liver samples treated with over one hundred paradigm compounds was mined to determine gene expression signatures for nongenotoxic carcinogens (NGTCs). Data were obtained from male rats treated for 24 h. Training/testing sets of 24 NGTCs and 28 noncarcinogens were used to select genes. A semiexhaustive, nonredundant gene selection algorithm yielded six genes (nuclear transport factor 2, NUTF2; progesterone receptor membrane component 1, Pgrmc1; liver uridine diphosphate glucuronyltransferase, phenobarbital-inducible form, UDPGTr2; metallothionein 1A, MT1A; suppressor of lin-12 homolog, Sel1h; and methionine adenosyltransferase 1, alpha, Mat1a), which identified NGTCs with 88.5% prediction accuracy estimated by cross-validation. This six genes signature set also predicted NGTCs with 84% accuracy when samples were hybridized to commercially available CodeLink oligo-based microarrays. To unveil molecular mechanisms of nongenotoxic carcinogenesis, 125 differentially expressed genes (P<0.01) were selected by Student's t-test. These genes appear biologically relevant, of 71 well-annotated genes from these 125 genes, 62 were overrepresented in five biochemical pathway networks (most linked to cancer), and all of these networks were linked by one gene, c-myc. Gene expression profiling at early time points accurately predicts NGTC potential of compounds, and the same data can be mined effectively for other toxicity signatures. Predictive genes confirm prior work and suggest pathways critical for early stages of carcinogenesis.

Organ-specific expression profiles of rat mammary gland, liver, and lung tissues treated with targretin, 9-cis retinoic acid, and 4-hydroxyphenylretinamide

A rexinoid, targretin, and two retinoids, 9-cis retinoic acid (9cRA) and 4-hydroxyphenylretinamide (4HPR), were examined for their effects on gene expression in rat mammary gland, liver, and lung tissues. The chemopreventive effects of these agents have largely been attributed to their ability to interact with retinoic acid receptors (RAR) and/or retinoid X receptors (RXR). Targretin interacts with the RXR receptors. 9cRA interacts with both the RAR and RXR receptors, whereas 4HPR has a moderate affinity primarily for RAR gamma. Based on previous studies on mammary chemoprevention, targretin (150 mg/kg diet), 9cRA (100 mg/kg diet), and 4HPR (782 mg/kg diet), were administered to rats continually in their diet for 7 days. Tissue- and agent-specific expression differences were determined by comparing tissues from treated rats with those from rats given a control diet. There were significantly more changes associated with targretin than 9cRA or 4HPR. Only a limited number of expression changes were found with 4HPR treatment. For each organ, targretin- and 9cRA-treated tissues clustered closely together, whereas 4HPR-treated tissues clustered with the tissues from the control diet group. In contrast to 9cRA treatment, targretin treatment altered genes that involved fatty acid metabolism and modulation of various cytochromes P450 in the liver, clearly demonstrating the very disparate nature of these two retinoids. These expression signatures could provide useful pharmacodynamic biomarkers for retinoid treatment and chemoprevention.

Dietary sphingolipids suppress a subset of preneoplastic rat liver lesions exhibiting high PTEN, low phospho-Akt and high levels of ceramide species

Rat liver glutathione-S-transferase Pi-(GST-P)-positive enzyme-altered foci (EAF) are preneoplastic lesions that develop in response to carcinogenic stress. They are often used as endpoints in e.g. chemopreventive studies. In this study we characterize a pAkt-negative/ceramide-positive (pAkt-/cer+) EAF phenotype, as defined by immunohistochemistry for pAkt and ceramide species, in diethylnitrosamine(DEN)-, phenobarbital- or aflatoxinB1-treated rats. There was a close to 100% overlap for the pAkt and the ceramide marker. Furthermore, serial sections stained for PTEN indicated a close correlation between PTEN-positive and pAkt-negative lesions in DEN-treated rats. Experiments with DEN-treated rats given sphingomyelin in the diet suggested that sphingomyelin selectively targeted these lesions. In in vitro experiments sphingosine rapidly decreased pAkt levels in hepatocytes, and in experiments with hepatocytes from DEN-treated rats sphingosine selectively killed EAF cells. Furthermore, pretreatment with antisense Akt oligonucleotides in vitro sensitized non-EAF hepatocytes, so that EAF and non-EAF cells became equally sensitive to sphingosine. It is concluded that rat liver, in response to carcinogenic stress, develops a distinct EAF phenotype exhibiting low pAkt levels and concomitant alterations in sphingolipid metabolism. Our data also suggest that pAkt-/cer+ EAF are selectively targeted by sphingolipids in the diet and that lesions with this phenotype should be of particular interest for future studies on chemopreventive effects that may affect sphingolipid metabolism.

All- trans and 9- cis retinoic acids, retinol and β-carotene chemopreventive activities during the initial phases of hepatocarcinogenesis involve distinct actions on glutathione S -transferase positive preneoplastic lesions remodeling and DNA damage

Chemopreventive activities of all-trans retinoic acid (AtRA), 9-cis retinoic acid (9cRA), retinol (ROL) and beta-carotene (betaC) were evaluated during hepatocarcinogenesis. Rats received 1 mg/100 g body wt AtRA (AtRA group), 9cRA (9cRA group), ROL (ROL group), 7 mg/100 g body wt betaC (betaC group) or corn oil (CO group, controls). Hepatocyte nodule incidence was reduced (P < 0.05) in betaC group (46%), but not (P > 0.05) in AtRA (92%), 9cRA (92%) and ROL (82%) groups, compared with the CO group (100%). Multiplicity of these preneoplastic lesions (PNL) was different (P < 0.05) between CO group (44 +/- 9) and 9cRA (11 +/- 4), ROL (7 +/- 3) and betaC (4 +/- 2) groups, except for AtRA group (27 +/- 9; P > 0.05). Number/cm(2) liver section, mean area (mm(2)) and percent liver section area occupied by total (persistent + remodeling) placental glutathione S-transferase (GST-P) positive PNL was reduced (P < 0.05) in AtRA (107 +/- 13; 0.12 +/- 0.06; 13.9 +/- 3.9), 9cRA (71 +/- 12; 0.12 +/- 0.06; 6.8 +/- 2.2), ROL (96 +/- 13; 0.11 +/- 0.22; 6.8 +/- 2.0) and betaC (106 +/- 13; 0.08 +/- 0.03; 10.8 +/- 2.5) groups compared with CO group (166 +/- 14; 0.18 +/- 0.09; 28.6 +/- 5.2). Percent of remodeling GST-P positive PNL was increased (P < 0.05) in 9cRA (92 +/- 1), ROL (96 +/- 1) and betaC (93 +/- 1) groups, but not (P > 0.05) in AtRA group (90 +/- 2), compared with the CO group (86 +/- 1). Compared with the CO group, all groups present in PNL reduced (P < 0.05) cell proliferation and no differences (P > 0.05) in apoptosis. DNA damage [comet length (mum)] was reduced (P < 0.05) in ROL (87.9 +/- 2.6) and betaC (89.2 +/- 4.0) groups, but not in AtRA (94.8 +/- 4.1) and 9cRA (94.2 +/- 1.5) groups, compared with the CO group (100.4 +/- 3.9). AtRA, 9cRA, ROL and betaC presented chemopreventive activities against hepatocarcinogenesis. These involve inhibition of cell proliferation, but not induction of apoptosis. Increased remodeling of GST-P positive PNL relates to 9cRA, ROL and betaC actions, while inhibition of DNA damage relates to ROL and betaC actions.