Spotlight pubs.acs.org/crt
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A BETTER MOUSE MODEL FOR STUDYING LIVER CARCINOGENESIS
Liver cancer incidence is on the rise in developed countries worldwide, but despite awareness of certain etiological contributors to the disease (including viral infections, excessive alcohol consumption, and environmental carcinogens), the mechanism of its pathogenesis is not fully understood. One problem with investigating the development of hepatocellular carcinoma (HCC) is that in commonly used rodent models, tumorigenesis is seldom accompanied by liver fibrosis or cirrhosis, whereas these forms of liver damage are presented in most human cases of HCC. Thus, Ivan Rusyn and co-workers set out to develop a more humanrelevant mouse model for studying HCC pathogenesis ((2013) Toxicol. Sci. 132, 53−63). The researchers repeatedly dosed mice with low amounts of the known profibrogenic agent carbon tetrachloride (CCl4) to instigate the development of liver fibrosis, which was accompanied with eventual formation of liver tumors in some mice receiving this treatment. All mice that received a single dose of the genotoxic agent diethylnitrosamine (DEN) prior to CCl4treatment developed tumors, more than double the incidence of mice treated with CCl4 alone. Compared with control mice, both CCl4− and CCl4+ DEN-treated mice showed increased expression of profibrogenic chemokines and liver cell proliferation. Expression of certain fetal stage-specific genes, cancer stem cell marker genes, and a cell-cycle inhibitor were found to be one potential mechanism for the fibrosis-associated promotion of liver carcinogenesis. Collectively, these results show that the current model of human HCC pathogenesis, in which liver fibrosis induces hepatocyte senescense and activates hepatic progenitor cells (thus increasing the potential for neoplastic transformation) can be effectively reproduced in the mouse. Heidi A. Dahlmann
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CYTOTOXIC COMPOUND OSW-1 CAUSES INCREASED MITOCHONDRIAL CALCIUM UPTAKE IN LEUKEMIA CELLS
Huntington’s disease (HD) is a heritable neurodegenerative disorder that typically manifests itself in early adulthood. Expansion of a CAG repeat within the huntingtin gene results in mutant huntingtin protein, which has been shown to bind to type 1 inositol 1,4,5-triphosphate receptors (InsP3R1) and disrupt Ca+ signaling in neurons. Oxidative damage to mitochondrial DNA (mtDNA), particularly in striatal medium spiny neurons (MSNs) in the brain, is one of the hallmarks of HD in both human patients and in HD mouse models. Recently, researchers led by Tie-Shan Tang have investigated the potential connection between mitochondrial Ca+ concentrations and oxidative mtDNA damage ((2013) J. Biol. Chem. 288, 3070−3084). The research team demonstrated that HD model mouse embryonic fibroblasts (MEFs) and MSNs as well as human HD fibroblasts had significantly higher mitochondrial Ca+ concentration and superoxide levels than did wild-type (WT) MEFs, MSNs, and normal human fibroblasts during both Ca+ loading and basal states. When InsP3R1 was inhibited or knocked down in both WT and HD MEFs, an expected decrease in Ca+ levels was observed; importantly, superoxide levels also declined as a result. Finally, quantitative PCR was used to show that the increase in mtDNA damage in cells stimulated to take up Ca+ could be circumvented when the protein responsible for mitochondrial Ca+ uptake was blocked. Thus, the authors propose that mutant huntingtin binds to InsP3R1, causing an excessive release of Ca+ that subsequently accumulates in mitochondria, which triggers the production of superoxide that damages mtDNA. Heidi A. Dahlmann
A critical trait of anticancer chemotherapeutic agents is their selective cytotoxicity or the ability to kill malignant cells in preference to normal cells. The natural product OSW-1, originally isolated from the bulbs of the African garden plant Ornithogalum saundersiae, shows selective cytotoxicity toward leukemia cells. Previous studies indicated that cells with defective mitochondria are less sensitive to OSW-1 and that OSW-1 cytoxicity may be mediated by the disruption of Ca+ homeostasis. A recent report by Peng Huang and co-workers ((2013) J. Biol. Chem. 288, 3240−3250) further elaborates on the role of mitochondria and Ca+ in OSW-1 cytotoxicity. The researchers observed that human leukemia cells had elevated levels of cytosolic and mitochondrial Ca+ following treatment with OSW-1. OSW-1-treated cells also showed decreased mitochondrial membrane potential (MMP) and activation of caspase-3, while cells cotreated with OSW-1 and cyclosporin A, which blocks mitochondrial Ca+ entry, showed significantly lower loss of MMP and caspase-3 activation. Ultimately, the research team identified the sodium−calcium exchanger NCX, a protein which localizes in both plasma and mitochondrial membranes, as a potential target of OSW-1. The authors propose that OSW-1 inhibits NCX, causing an increase in cytosolic Ca+ that ultimately results in mitochondrial Ca+ overload, loss of MMP, and induction of apoptosis. Heidi A. Dahlmann © 2013 American Chemical Society
MUTANT HUNTINGTIN PROTEIN CAUSES INCREASED MITOCHONDRIAL CALCIUM UPTAKE IN HUNTINGTON’S DISEASE
Published: April 15, 2013 509
dx.doi.org/10.1021/tx400113h | Chem. Res. Toxicol. 2013, 26, 509−510
Chemical Research in Toxicology
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Spotlight
GUT MICROBIOTA MEDIATE MELAMINE TOXICITY IN MICE
raised in completely germ-free (GF) environments, while the gender bias returned among mice raised in less stringent (specific pathogen free, SPF) conditions. Additionally, female GF mice had higher testosterone levels than female SPF mice, while male GF mice had lower testosterone levels than male SPF mice. Although both male and female SPF mice had indistinguishable gut microbiota at weanling stage, noticeable gender-specific differences emerged at puberty. Since male T1D resistance was dependent on microbial colonization and adult male and female gut microbiomes were distinct from each other, the research team explored whether inoculating female mice with male gut microbiota would alter their hormonal status and confer T1D resistance. Indeed, female mice that received gavage transfer of male cecal material formed microbiomes distinct from male and female control mice, had significantly higher testosterone levels than female control mice, and were strongly protected from T1D development. The authors note that early manipulation of gut microbiome composition may potentially be useful for conferring resistance to autoimmune disease in high-risk human populations as well. Heidi A. Dahlmann
Melamine poisoning, which can result in renal failure and death, has become a hot topic for research following recent incidents in which manufacturers used melamine as an additive to boost apparent protein content of pet food and infant formula. While melamine was shown to be toxic to Wistar rats at high doses, similar toxicity occurred when the rats received low doses of melamine along with an equivalent dose of cyanuric acid, a deaminated derivative of melamine. Studies confirmed that renal toxicity stems from the cocrystallization of melamine and cyanuric acid in the kidney. It was also known that bacterial strains such as Klebsiella terrigena (K. terrigena), which reside in mammalian intestines, are capable of deaminating melamine to produce cyanuric acid. Thus, a research team led by Aihua Zhao and Wei Jia hypothesized that gut microbes may mediate the conversion of melamine to cyanuric acid, facilitating melamine poisoning in mammals ((2013) Sci. Transl. Med. 5, 172ra22). The researchers initially found that following oral exposure to melamine, the kidneys of rats with suppressed gut microbiota were less severely damaged than those of rats that did not receive microbial suppression. Cultures of fecal-derived rat gut microbes, eventually confirmed to contain K. terrigena, were shown to mediate the conversion of melamine to cyanuric acid. When the researchers specifically colonized rats with K. terrigena and administered melamine, they observed elevated pathological and biochemical markers of kidney damage and a 5-fold increase of kidney cyanuric acid concentration compared with those in noninoculated control rats. The authors note that gut microbiota-mediated conversion of melamine to cyanuric acid may also be responsible for melamine toxicity in humans since K. terrigena has been detected in human populations at an incidence similar to that observed for urinary tract abnormalities in children recently exposed to melaminecontaminated dairy products in rural China. Heidi A. Dahlmann
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GUT MICROBIOTA MEDIATE TYPE 1 DIABETES DEVELOPMENT IN MICE Autoimmune diseases are often definitively linked to genetic polymorphisms that are readily identifiable through genomewide studies. In other cases, environmental factors and gender play a role in the pathogenesis of autoimmune diseases, but the pathogenic mechanisms are less simple to elucidate. To illustrate, female nonobese diabetic (NOD) mice are more than twice as likely to develop type 1 diabetes (T1D) than male NOD mice; subsequently, it was established that testosterone regulation is involved in T1D development. Complicating matters was the decades-old observation that NOD colonies with better hygiene status have elevated incidences of T1D, while NOD colonies exposed to bacterial antigens have reduced T1D incidence. Jayne Danska and co-workers recently investigated the link between testosterone regulation and microbial exposure in NOD mouse T1D pathogenesis ((2013) Science 339, 1084− 1088). T1D incidence was similar in male and female mice 510
dx.doi.org/10.1021/tx400113h | Chem. Res. Toxicol. 2013, 26, 509−510
