The mycotoxin PAT (4-hydroxy-4-furo[3,2]pyran-2[6]-one) is a secondary metabolic product of molds such as ,, and species. PAT is a common contaminant of fruit and vegetable based products, most notably apples. Despite PAT's original discovery as an antibiotic, it has come under heavy scrutiny for its potential to impart negative health effects. Studies investigating these health effects have proved its toxic potential. PAT occurrence in the food commodities poses a serious threat and necessitates novel and cost-effective mitigation methods to remove it from food products. It also creates a demand to improve handling and food processing techniques. With this being the case, several studies have been devoted to understanding the key biological and chemical attributes of PAT. While past research has elucidated a great deal, PAT contamination continues to be a challenge for the food industry. Here, we review its influence within the mammalian system, including its regulation, incidences of experimental evidence of PAT toxicity, its interaction with intracellular components, and the effects of PAT induced systemic toxicity on vital organs. Finally, key areas where future PAT research should focus to best control the PAT contamination problem within the food industry have been addressed.

Although prostaglandin E 2 (PGE 2 ) has been shown by pharmacologic and genetic studies to be important in skin cancer, the molecular mechanism(s) by which it contributes to tumor growth is not well understood. In this study, we investigated the mechanisms by which PGE 2 stimulates murine keratinocyte proliferation using in vitro and in vivo models. In primary mouse keratinocyte cultures, PGE 2 activated the epidermal growth factor receptor (EGFR) and its downstream signaling pathways as well as increased cyclic AMP (cAMP) production and activated the cAMP response element binding protein (CREB). EGFR activation was not significantly inhibited by pretreatment with a c-src inhibitor (PP2), nor by a protein kinase A inhibitor (H-89). However, PGE 2 -stimulated extracellularly regulated kinase 1/2 (ERK1/2) activation was completely blocked by EGFR, ERK1/2, and phosphatidylinositol 3-kinase (PI3K) pathway inhibitors. In addition, these inhibitors attenuated the PGE 2 -induced proliferation, nuclear factor-KB, activator protein-1 (AP-1), and CREB binding to the promoter regions of the cyclin D1 and vascular endothelial growth factor (VEGF) genes and expression of cyclin D1 and VEGF in primary mouse keratinocytes. Similarly, in vivo, we found that WT mice treated with PGE 2 and untreated cyclooxygenase-2 -overexpressing transgenic mice had higher levels of cell proliferation and expression of cyclin D1 and VEGF, as well as higher levels of activated EGFR, nuclear factor-KB, AP-1, and CREB, than vehicle-treated WT mice. Our findings provide evidence for a link between cyclooxygenase-2 overexpression and EGFR-, ERK-, PI3K-, cAMP-mediated cell proliferation, and the tumor-promoting activity of PGE 2 in mouse skin.

No abstract

The EP2 prostanoid receptor is one of the four subtypes of receptors for prostaglandin E2 (PGE2). We previously reported that deletion of EP2 led to resistance to chemically induced mouse skin carcinogenesis, whereas overexpression of EP2 resulted in enhanced tumor development. The purpose of this study was to investigate the underlying molecular mechanisms. We found that EP2 knockout mice had reduced cyclooxygenase-2 (COX-2) expression after 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment compared with wild-type (WT) mice. Further, primary keratinocytes from EP2 transgenic mice had increased COX-2 expression after either TPA or PGE2 treatment and COX-2 expression was blocked by 10 microM SQ 22,536, an adenylate cyclase inhibitor. EP2 knockout mice had significantly decreased, whereas EP2 transgenic mice had significantly increased PGE2 production in response to a single treatment of TPA. Cyclic AMP response element-binding protein (CREB) phosphorylation was elevated to a greater extent in keratinocytes from EP2 transgenic mice compared with those of WT mice following PGE2 treatment. A protein kinase A (PKA) inhibitor reduced PGE2-mediated CREB phosphorylation in keratinocytes from EP2 transgenic mice. Furthermore, we found that there was no CREB phosphorylation in EP2 knockout mice following PGE2 treatment. PGE2-induced DNA synthesis (cell proliferation) was significantly decreased in keratinocytes from EP2 knockout mice following pretreatment with 10 microM SQ 22,536. Taken together, EP2 activation of the PKA/CREB-signaling pathway is responsible for keratinocyte proliferation and our findings reveal a positive feedback loop between COX-2 and PGE2 that is mediated by the EP2 receptor.

The mycotoxin, citrinin (CTN), is a contaminant of various food and feed materials. Several in vivo and in vitro studies have demonstrated that CTN has broad toxicity spectra; however, dermal toxicity is not known. In the present investigation, dermal exposure to CTN was undertaken to study oxidative stress, DNA damage, cell cycle arrest, and apoptosis in mouse skin. A single topical application of CTN caused significant change in oxidative stress markers, such as lipid peroxidation, protein carbonyl content, glutathione (GSH) content, and antioxidant enzymes in a dose-dependent (25-100 μg/mouse) and time-dependent (12-72 h) manner. Single topical application of CTN (50 μg/mouse) for 12-72 h caused significant enhancement in (1) reactive oxygen species (ROS); (2) cell cycle arrest at the G0/G1 phase (30-71%) and G2/M phase (56-65%) along with the induction of apoptosis (3.6-27%); (3) expression of p53, p21/waf1; (4) Bax/Bcl₂ ratio and cytochome c release; and (5) activities of caspase 9 (22-46%) and 3 (42-54%) as well as increased poly(ADP-ribose) polymerase cleavage. It was also observed that pretreatment with bio-antioxidants viz butylated hydroxyanisole (55 μmol/100 μl), quercetin (10 μmol/100 μl), or α-tocopherol (40 μmol/100 μl) resulted in decreases of ROS generation, arrest in the G0/G1 phase of the cell cycle, and apoptosis. These data confirm the involvement of ROS in apoptosis and suggest that these bio-antioxidants may be useful in the prevention of CTN-induced dermal toxicity.

Skin cancer is one of the most common forms of cancer and 2–3 million new cases are being diagnosed globally each year. Along with UV rays, environmental pollutants/chemicals including mycotoxins, contaminants of various foods and feed stuffs, could be one of the aetiological factors of skin cancer. In the present study, we evaluated the DNA damaging potential and dermal carcinogenicity of a mycotoxin, ochratoxin A (OTA), with the rationale that dermal exposure to OTA in workers may occur during their involvement in pre and post harvest stages of agriculture. A single topical application of OTA (20–80 µg/mouse) resulted in significant DNA damage along with elevated γ-H2AX level in skin. Alteration in oxidative stress markers such as lipid peroxidation, protein carbonyl, glutathione content and antioxidant enzymes was observed in a dose (20–80 µg/mouse) and time-dependent (12–72 h) manner. The oxidative stress was further emphasized by the suppression of Nrf2 translocation to nucleus following a single topical application of OTA (80 µg/mouse) after 24 h. OTA (80 µg/mouse) application for 12–72 h caused significant enhancement in- (a) reactive oxygen species generation, (b) activation of ERK1/2, p38 and JNK MAPKs, (c) cell cycle arrest at G0/G1 phase (37–67%), (d) induction of apoptosis (2.0–11.0 fold), (e) expression of p53, p21/waf1, (f) Bax/Bcl-2 ratio, (g) cytochrome c level, (h) activities of caspase 9 (1.2–1.8 fold) and 3 (1.7–2.2 fold) as well as poly ADP ribose polymerase cleavage. In a two-stage mouse skin tumorigenesis protocol, it was observed that a single topical application of OTA (80 µg/mouse) followed by twice weekly application of 12-O-tetradecanoylphorbol-13-acetate for 24 week leads to tumor formation. These results suggest that OTA has skin tumor initiating property which may be related to oxidative stress, MAPKs signaling and DNA damage.

Nexrutine(®) (NX), a herbal extract from Phellodendron amurense, has been shown to possess antitumor, antimicrobial, anti-inflammatory and other biological activities. In the present investigation, we explored the mechanism of chemopreventive/chemotherapeutic efficacy of NX against skin cancer. Single application of NX (1.0mg/mouse) prior to 12-O-tetradecanoylphorbol 13-acetate (TPA) application significantly inhibited TPA-induced skin edema, hyperplasia, thymidine incorporation and ornithine decarboxylase (ODC) activity; expression of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS); phosphorylation of extracellular signal-regulated kinases (ERK) 1/2, p38 and c-jun N-terminal kinase (JNK) mitogen-activated protein kinases (MAPKs); and activation of I kappa B kinase (IKK), IκBα and nuclear factor-kappa B (NF-κB) in mouse skin. In a two-stage mouse skin tumorigenesis model, it was found that twice-weekly treatment of NX prior to TPA application in 7,12-dimethylbenz[α]anthracene (DMBA)-initiated animals showed reduced tumor incidence, lower tumor body burden and significant delay in latency period compared with DMBA-initiated and TPA-promoted animals. Furthermore, the therapeutic efficacy of NX was assessed against human squamous carcinoma (A431) and human melanoma (A375) cells. A431 and A375 cells treated with NX (2.5-10.0 μg/ml, 48h) showed a decrease in viability and enhanced cell cycle arrest at the G(0)/G(1) phase and apoptosis; however, NX had minimal cytotoxic effect on HaCaT cells and primary murine keratinocytes, suggesting its high therapeutic index. In addition, NX treatment also modulates the levels of Bax and Bcl-2 proteins along with cytochrome c release, cleavage and enhanced expression of poly (adenosine diphosphate-ribose) polymerase as well as catalytic activities of caspases 3 and 9 in both A431 and A375 cells. Based on our in vivo and in vitro studies, NX could be useful in the management (chemoprevention as well as chemotherapy) of skin cancer.

No abstract