Role of the p50 subunit of NF-kappaB in vitamin E-induced changes in mice treated with the peroxisome proliferator, ciprofibrate

Evaluation of Polymer Nanoformulations in Hepatoma Therapy by Established Rodent Models

Hepatoma is one of the most severe malignancies usually with poor prognosis, and many patients are insensitive to the existing therapeutic agents, including the drugs for chemotherapy and molecular targeted therapy. Currently, researchers are committed to developing the advanced formulations with controlled drug delivery to improve the efficacy of hepatoma therapy. Numerous inoculated, induced, and genetically engineered hepatoma rodent models are now available for formulation screening. However, animal models of hepatoma cannot accurately represent human hepatoma in terms of histological characteristics, metastatic pathways, and post-treatment responses. Therefore, advanced animal hepatoma models with comparable pathogenesis and pathological features are in urgent need in the further studies. Moreover, the development of nanomedicines has renewed hope for chemotherapy and molecular targeted therapy of advanced hepatoma. As one kind of advanced formulations, the polymer-based nanoformulated drugs have many advantages over the traditional ones, such as improved tumor selectivity and treatment efficacy, and reduced systemic side effects. In this article, the construction of rodent hepatoma model and much information about the current development of polymer nanomedicines were reviewed in order to provide a basis for the development of advanced formulations with clinical therapeutic potential for hepatoma.

The PPARα-dependent rodent liver tumor response is not relevant to humans: addressing misconceptions

A number of industrial chemicals and therapeutic agents cause liver tumors in rats and mice by activating the nuclear receptor peroxisome proliferator-activated receptor α (PPARα). The molecular and cellular events by which PPARα activators induce rodent hepatocarcinogenesis have been extensively studied elucidating a number of consistent mechanistic changes linked to the increased incidence of liver neoplasms. The weight of evidence relevant to the hypothesized mode of action (MOA) for PPARα activator-induced rodent hepatocarcinogenesis is summarized here. Chemical-specific and mechanistic data support concordance of temporal and dose-response relationships for the key events associated with many PPARα activators. The key events (KE) identified in the MOA are PPARα activation (KE1), alteration in cell growth pathways (KE2), perturbation of hepatocyte growth and survival (KE3), and selective clonal expansion of preneoplastic foci cells (KE4), which leads to the apical event-increases in hepatocellular adenomas and carcinomas (KE5). In addition, a number of concurrent molecular and cellular events have been classified as modulating factors, because they potentially alter the ability of PPARα activators to increase rodent liver cancer while not being key events themselves. These modulating factors include increases in oxidative stress and activation of NF-kB. PPARα activators are unlikely to induce liver tumors in humans due to biological differences in the response of KEs downstream of PPARα activation. This conclusion is based on minimal or no effects observed on cell growth pathways and hepatocellular proliferation in human primary hepatocytes and absence of alteration in growth pathways, hepatocyte proliferation, and tumors in the livers of species (hamsters, guinea pigs and cynomolgus monkeys) that are more appropriate human surrogates than mice and rats at overlapping dose levels. Despite this overwhelming body of evidence and almost universal acceptance of the PPARα MOA and lack of human relevance, several reviews have selectively focused on specific studies that, as discussed, contradict the consensus opinion and suggest uncertainty. In the present review, we systematically address these most germane suggested weaknesses of the PPARα MOA.

Effects of adenosine A2a receptor agonist and antagonist on cerebellar nuclear factor-kB expression preceded by MDMA toxicity

BACKGROUND

Adenosine is an endogenous purine nucleoside that has a neuromodulatory role in the central nervous system. The amphetamine derivative (±)-3,4-methylenedioxymethamphetamine (MDMA or ecstasy) is a synthetic amphetamine analogue used recreationally to obtain an enhanced affiliated emotional response. MDMA is a potent monoaminergic neurotoxin with the potential of damage to brain neurons. The NF-kB family of proteins are ubiquitously expressed and are inducible transcription factors that regulate the expression of genes involved in disparate processes such as immunity and ingrowth, development and cell-death regulation. In this study we investigated the effects of the A2a adenosine receptor (A2a-R) agonist (CGS) and antagonist (SCH) on NF-kB expression after MDMA administration.

METHODS

Sixty three male Sprague-Dawley rats were injected to MDMA (10 and 20mg/kg) followed by intraperitoneal CGS (0.03 mg/kg) or SCH (0.03mg/kg) injection. The cerebellum were then removed forcresylviolet staining, western blot and RT- PCR analyses. MDMA significantly elevated NF-kB expression. Our results showed that MDMA increased the number of cerebellar dark neurons.

RESULTS

We observed that administration of CGS following MDMA, significantly elevated the NF-kB expression both at mRNA and protein levels. By contrast, administration of the A2a-R antagonist SCH resulted in a decrease in the NF-kB levels.

CONCLUSION

These results indicated that, co-administration of A2a agonist (CGS) can protect against MDMA neurotoxic effects by increasing NF-kB expression levels; suggesting a potential application for protection against the neurotoxic effects observed in MDMA users.

Mode of action framework analysis for receptor-mediated toxicity: The peroxisome proliferator-activated receptor alpha (PPARα) as a case study

Several therapeutic agents and industrial chemicals induce liver tumors in rodents through the activation of the peroxisome proliferator-activated receptor alpha (PPARα). The cellular and molecular events by which PPARα activators induce rodent hepatocarcinogenesis has been extensively studied and elucidated. This review summarizes the weight of evidence relevant to the hypothesized mode of action (MOA) for PPARα activator-induced rodent hepatocarcinogenesis and identifies gaps in our knowledge of this MOA. Chemical-specific and mechanistic data support concordance of temporal and dose-response relationships for the key events associated with many PPARα activators including a phthalate ester plasticizer di(2-ethylhexyl) phthalate (DEHP) and the drug gemfibrozil. While biologically plausible in humans, the hypothesized key events in the rodent MOA, for PPARα activators, are unlikely to induce liver tumors in humans because of toxicodynamic and biological differences in responses. This conclusion is based on minimal or no effects observed on growth pathways, hepatocellular proliferation and liver tumors in humans and/or species (including hamsters, guinea pigs and cynomolgous monkeys) that are more appropriate human surrogates than mice and rats at overlapping dose levels. Overall, the panel concluded that significant quantitative differences in PPARα activator-induced effects related to liver cancer formation exist between rodents and humans. On the basis of these quantitative differences, most of the workgroup felt that the rodent MOA is "not relevant to humans" with the remaining members concluding that the MOA is "unlikely to be relevant to humans". The two groups differed in their level of confidence based on perceived limitations of the quantitative and mechanistic knowledge of the species differences, which for some panel members strongly supports but cannot preclude the absence of effects under unlikely exposure scenarios.

Effects of adenosine A2a receptor agonist and antagonist on hippocampal nuclear factor-kB expression preceded by MDMA toxicity

There is an abundance of evidence showing that repeated use of 3,4-methlylenedioxymethamphetamine (MDMA; ecstasy) is associated with brain dysfunction, memory disturbance, locomotor hyperactivity, and hyperthermia. MDMA is toxic to both the serotonergic neurons and dopaminergic system. Adenosine is an endogenous purine nucleoside with a neuromodulatory function in the central nervous system. Nuclear factor kappa-B (NF-kB) plays a pivotal role in the initiation and perpetuation of an immune response by triggering the expression of major inflammatory mediators such as cytokines, chemokines, and adhesion molecules. Here, we investigated the effects of the A2a adenosine receptor (A2a-R) agonist (CGS) and antagonist (SCH) on NF-kB expression after MDMA administration. Male Sprague-Dawley rats were injected to MDMA (10 mg/kg) followed by intraperitoneal injection of either CGS or SCH (0.03 mg/kg each) to animals. The hippocampi were then removed for western blot and RT- PCR analyses. MDMA significantly elevated NF-kB expression. Our results show that administration of CGS following MDMA significantly elevated the NF-kB expression both at mRNA and protein levels. By contrast, administration of the A2a-R antagonist SCH resulted in a decrease in the NF-kB levels. Taken together, these results indicate that, co-administration of A2a agonist (CGS) can protect against MDMA neurotoxic effects by increasing NF-kB expression levels; suggesting a potential application for protection against the neurotoxic effects observed in MDMA users.

Effect of vitamin E on hepatic cell proliferation and apoptosis in mice deficient in the p50 subunit of NF-κB after treatment with phenobarbital

Phenobarbital (PB) is an efficacious and well-studied hepatic tumor promoting agent. Nuclear factor-κB (NF-κB) is a transcription factor activated by reactive oxygen and is involved in cell proliferation and apoptosis. We previously found that PB activates NF-κB and that dietary vitamin E is effective in decreasing PB-induced NF-κB DNA binding. We therefore hypothesized that dietary vitamin E influences PB-induced changes in cell proliferation and apoptosis through its action on NF-κB. NF-κB1 deficient mice (p50-/-) and wild-type B6129 mice were fed a purified diet containing 10 or 250ppm vitamin E (α-tocopherol acetate) for 28days. At that time, half of the wild-type and half of the p50-/- mice were placed on the same diet with 0.05% PB for 10days. Compared to wild-type mice, the p50-/- mice had higher levels of cell proliferation and apoptosis. Cell proliferation was significantly increased by PB, but vitamin E did not affect hepatic cell proliferation. Apoptosis was not changed in mice fed PB, and there was no significant difference in apoptosis between control and high vitamin E treated mice. Thus, vitamin E does not appear to influence cell growth parameters in either wild-type or p50-/- mice.

DietaryRRR-α-tocopherol succinate attenuates lipopolysaccharide-induced inflammatory cytokines secretion in broiler chicks

The anti-inflammatory effects of two esters of α-tocopherol (α-TOH),all-rac-α-TOH acetate (dl-α-TOA) andRRR-α-TOH succinate (d-α-TOS), on broilers repeatedly challenged with lipopolysaccharide (LPS) were investigated. Three hundred and twenty 1-d-old broiler chicks were allotted into four treatment groups and fed on a control diet (30 mg/kgdl-α-TOA) or diets containing 10, 30, 50 mg/kgd-α-TOS. Half of the birds from each treatment group were challenged with 0·9 % NaCl solution or LPS (250 μg/kg body weight) at 16, 18 and 20 d of age. The results indicated that the pretreatment of birds with 50 mg/kgd-α-TOS markedly reduced serum PGE2secretion and increased the concentrations of serum or hepatic α-TOH. When LPS-challenged birds were pretreated with 30 or 50 mg/kgd-α-TOS, the increases of plasma and splenic concentrations of interferon-γ, IL-1β, IL-2, IL-6, IL-4 and IL-10 were dramatically attenuated. Also, a significant decrease of hepatic reactive oxygen species (ROS) and hepatic or splenic phosphokinase C (PKC) activities was found in birds pretreated with 30 or 50 mg/kgd-α-TOS. Furthermore,d-α-TOS inhibited the activation of NF-κB by preventing the degradation of inhibitory-κBα. In conclusion, D-α-TOS is able to prevent LPS-induced inflammation responsein vivo.The beneficial effect may depend on suppressing the secretion of various plasma and splenic inflammatory mediators through inhibiting NF-κB activation and by blocking ROS signalling, in which PKC may play an assistant role.

The role of vitamin E and oxidative stress in diabetes complications

Diabetes is a disease characterized by poor glycemic control for which risk of the type 2 form increases with age. A rise in blood glucose concentration causes increased oxidative stress which contributes to the development and progression of diabetes-associated complications. Studies have shown that primary antioxidants or genetic manipulation of antioxidant defenses can at least partially ameliorate this oxidative stress and consequentially, reduce severity of diabetic complications in animal models. Data from humans is less clear and will be summarized in this review. We highlight results from studies performed to investigate the role of vitamin E in preventing diabetes-induced oxidative damage in cell culture, animal models, and human participants, and summarize evidence testing whether this nutrient has an effect on outcomes related to the diabetic complications of nephropathy, retinopathy, and neuropathy. The most compelling evidence for an effect of vitamin E in diabetes is on protection against lipid peroxidation, whereas effects on protein and DNA oxidation are less pronounced. More studies are required to make definitive conclusions about the effect of vitamin E treatment on diabetes complications in human subjects.

Experimental mouse models for hepatocellular carcinoma research

Every year almost 500,000 new patients are diagnosed with hepatocellular carcinoma (HCC), a primary malignancy of the liver that is associated with a poor prognosis. Numerous experimental models have been developed to define the pathogenesis of HCC and to test novel drug candidates. This review analyses several mouse models useful for HCC research and points out their advantages and weaknesses. Chemically induced HCC mice models mimic the injury-fibrosis-malignancy cycle by administration of a genotoxic compound alone or, if necessary, followed by a promoting agent. Xenograft models develop HCC by implanting hepatoma cell lines in mice, either ectopically or orthotopically; these models are suitable for drug screening, although extrapolation should be considered with caution as multiple cell lines must always be used. The hollow fibre assay offers a solution for limiting the number of test animals in xenograft research because of the ability for implanting multiple cell lines in one mouse. There is also a broad range of genetically modified mice engineered to investigate the pathophysiology of HCC. Transgenic mice expressing viral genes, oncogenes and/or growth factors allow the identification of pathways involved in hepatocarcinogenesis.

The Role of NF-kappaB in PPARalpha-Mediated Hepatocarcinogenesis

In this review, the role of NF-kappaB in the induction of hepatocarcinogenesis by peroxisome proliferators is examined. The administration of peroxisome proliferators for more than a three-day period leads to the activation of NF-kappaB in the livers of rats and mice. On the other hand, peroxisome proliferator activated receptor-alpha (PPARalpha) activation in non-hepatic tissues can lead to the inhibition of NF-kappaB activation. Several lines of evidence support the hypothesis that the activation of NF-kappaB by peroxisome proliferators in the liver is mediated by oxidative stress. The role of NF-kappaB in peroxisome proliferator-induced hepatocarcinogenesis has been examined using NF-kappaB knockout models. Specifically, the induction of cell proliferation and the promotion of liver carcinogenesis are inhibited in mice lacking the p50 subunit of NF-kappaB. Overall, the activation of NF-kappaB appears to be important in the carcinogenic activity of peroxisome proliferators.