Irma Martha Medina-Díaz

Retinoic acid modulates retinaldehyde dehydrogenase 1 gene expression through the induction of GADD153–C/EBPβ interaction

Mammalian class I aldehyde dehydrogenase (ALDH) plays an important role in the biosynthesis of the hormone retinoic acid (RA), which modulates gene expression and cell differentiation. RA has been shown to mediate control of human ALDH1 gene expression through modulation of the retinoic acid receptor alpha (RARalpha) and the CCAAT/enhancer binding protein beta (C/EBPbeta). The positive activation of these transcription factors on the ALDH1 promoter is inhibited by RA through a decrease of C/EBPbeta binding to the ALDH1 CCAAT box response element. However, the mechanism of this effect remains unknown. Here we report that the RARalpha/retinoid X receptor beta (RXRbeta) complex binds to the mouse retinaldehyde dehydrogenase 1 (Raldh1) promoter at a non-consensus RA response element (RARE) with similar affinity to that of the consensus RARE. We found that C/EBPbeta binds to a Raldh1 CCAAT box located at -82/-58bp, adjacent to the RARE. Treatment with RA increases GADD153 and GADD153-C/EBPbeta interaction resulting in a decreased cellular availability of C/EBPbeta for binding to the Raldh1 CCAAT box. These data support a model in which high RA levels inhibit Raldh1 gene expression by sequestering C/EBPbeta through its interaction to GADD153.

Pregnane X Receptor-Dependent Induction of the CYP3A4 Gene by o,p′-1,1,1,-Trichloro-2,2-Bis (p-Chlorophenyl)ethane

CYP3A4, the predominant cytochrome P450 (P450) expressed in human liver and intestine, contributes to the metabolism of approximately half the drugs in clinical use today. CYP3A4 catalyzes the 6β-hydroxylation of a number of steroid hormones and is involved in the bioactivation of environmental procarcinogens. The expression of CYP3A4 is affected by several stimuli, including environmental factors such as insecticides and pesticides. The o,p′-1,1,1,-trichloro-2,2-bis (p-chlorophenyl)ethane (DDT) isomer of DDT comprises approximately 20% of technical grade DDT, which is an organochloride pesticide. We have recently shown that o,p′-DDT exposure increases CYP3A4 mRNA levels in HepG2 cells. To determine the mechanism by which o,p′-DDT induces CYP3A4 expression, transactivation and electrophoretic mobility shift assays were carried out, revealing that o,p′-DDT activates the CYP3A4 gene promoter through the pregnane X receptor (PXR). CYP3A4 gene promoter activation resulted in both an increase in CYP3A4 mRNA levels and an increase in the total CYP3A4 activity in HepG2 cells. We also observed induction of CYP3A4 and mouse Cyp3a11 mRNA in the intestine of CYP3A4-transgenic mice after exposure to 1 mg/kg o,p′-DDT. At higher doses, a decrease of CYP3A4 inducibility was observed together with an increase in levels of interleukin 6 mRNA, a proinflammatory cytokine that strongly represses CYP3A4 transcription. The present study indicates that regulation of other genes under PXR control may be altered by o,p′-DDT exposure.

Oxidative stress and genetic damage among workers exposed primarily to organophosphate and pyrethroid pesticides

The indiscriminate use of pesticides in agriculture and public health campaigns has been associated with an increase of oxidative stress and DNA damage, resulting in health outcomes. Some defense mechanisms against free radical‐induced oxidative damage include the antioxidant enzyme systems. The aim of this study was to determine the levels of malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), and the relationship of antioxidant enzyme levels with DNA damage among sprayers (workers) occupationally exposed to pesticides. The determinations of MDA and antioxidant enzymes were performed spectrophotometrically. The genotoxic effects were evaluated using the comet assay. The results showed a marginally significant decrease in SOD and CAT activities in the high exposure group compared to the control group. For MDA, statistically significant differences were found among people working long term vs. those working temporarily (P = 0.02) as sprayers. In the moderate exposure group, a positive correlation was observed between MDA levels and GPx activity. In the high exposure group, a negative correlation was observed between GR and CAT activities, and between MDA levels and GPx activities. Furthermore, in the high exposure group, a positive correlation between DNA damage parameters and MDA levels was observed. The results suggest an important role of antioxidant enzymes for the protection of DNA damage caused by occupational exposure to pesticides.

Downregulation of human paraoxonase 1 (PON1) by organophosphate pesticides in HepG2 cells

Paraoxonase 1 (PON1) is a calcium‐dependent esterase synthesized primarily in the liver and secreted into the plasma where it is associated with high‐density lipoproteins (HDL). PON1 hydrolyzes and detoxifies some toxic metabolites of organophosphorus compounds (OPs) such as methyl parathion and chlorpyrifos. Thus, PON1 activity and expression levels are important for determining susceptibility against OPs poisoning. Some studies have demonstrated that OPs can modulate gene expression through interactions with nuclear receptors. In this study, we evaluated the effects of methyl parathion and chlorpyrifos on the modulation of PON1 in Human Hepatocellular Carcinoma (HepG2) cells by real‐time PCR, PON1 activity assay, and western blot. The results showed that the treatments with methyl parathion and chlorpyrifos decreased PON1 mRNA and immunoreactive protein and increased inflammatory cytokines in HepG2 cells. The effects of methyl parathion and chlorpyrifos on the downregulation of PON1 gene expression in HepG2 cells may provide evidence of OPs cytotoxicity related to oxidative stress and an inflammatory response. A decrease in the expression of the PON1 gene may increase the susceptibility to OPs intoxication and the risk of diseases related to inflammation and oxidative stress.

Relationship between LINE-1 methylation pattern and pesticide exposure in urban sprayers

Recently a relationship has been reported between pesticide exposure and changes in global DNA methylation patterns. Urban sprayers are a particularly vulnerable population because of the high risk of pesticide exposure that their work implies. Therefore, the aim of this study was to estimate the changes in the Long Interspersed Nucleotide Element (LINE-1) in urban sprayers and its relationship with pesticide exposure. The study population consisted of 190 individuals stratified into three study groups: no occupational pesticide exposure; moderate exposure, and high exposure. Pesticide exposure and other external factors such as diet, lifestyle, and others were evaluated through a validated questionnaire, and the butyrylcholinesterase enzyme activity was evaluated spectrophotometrically and used as exposure biomarker. DNA methylation was evaluated by pyrosequencing on bisulfite-treated DNA. The results showed a significant decrease of %5mC in both the moderate- and high-exposure groups with respect to the non-exposed group (p < 0.05). In addition, alcohol intake was associated with a higher percentage of LINE- 1 methylation. In conclusion, our results suggest that occupational pesticide exposure and external factors appears to modify the DNA methylation pattern measured through LINE-1.

Human papilloma virus genotypes in women from Nayarit, Mexico, with squamous intraepithelial lesions and cervical cancer

OBJECTIVE In Mexico cervical cancer (CC) is the most common cause of death from neoplasia in women. Study aimed to analyze the current distribution of Human papillomavirus (HPV) types in women from Nayarit, Mexico, with Squamous intraepithelial lesions (SIL) and Cervical cancer (CC). METHODOLOGY Between January 2011 and July 2013, cervical samples were collected from female residents of the Mexican state of Nayarit and were analyzed by means of a LINEAR ARRAY® HPV genotyping test. Data analyses were performed using Stata ver. 8.0 statistical software. RESULTS Of the samples analyzed, 91.2%, HPV DNA was detected. Of these positive samples, 82% were High-risk (HR) viral types. The most prevalent HPV genotypes identified were 16, 58, 31, 18, and 70. Forty two percent of participants had a single infection, while 23 and 26% of participants were infected with two or more HPV genotypes, respectively. HPV 16 was the most prevalent genotype identified and was frequently present as a co-infection with HPV types 18, 51, 52, 59, 66, or 70. CONCLUSION Women <20 years of age were most often infected with HPV, and the HPV Quadrivalent vaccine (types 16, 18, 6, and 11), currently available in Mexico, no confers protection against a subset of the HPV genotypes identified in the present study (58, 31, 70, and 35). Thus, it is important evaluate the geographical distribution of specific HPV genotypes in all health of center across Mexico in order to implement a successful vaccination program and to diagnose CC in its early stages.