Spotlight pubs.acs.org/crt
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FASTING BEFORE CHEMOTHERAPY PROTECTS MICE FROM TREATMENT TOXICITY BY SHIELDING SMALL INTESTINE STEM CELLS FROM DNA DAMAGE Patients receiving chemotherapy often experience debilitating side effects. Interestingly, fasting can protect against the toxic effects of chemotherapy. Gastrointestinal (GI) toxicity is a common complication of chemotherapy treatment, and David Piwnica-Worms, Helen Piwnica-Worms, and their collaborators studied whether fasting could mitigate high-dose chemotherapyinduced GI toxicity ((2015) PNAS, 112, E7148−E7154). The authors fasted mice for 24 h or allowed them to feed at will and then treated them with etoposide, a chemotherapeutic agent that causes DNA double-strand breaks. Although the drug exited the plasma of both groups at an equal rate, mice fed pretreatment became sedentary, displayed signs of toxicity, and died 5−6 days post-treatment. In contrast, mice who fasted before drug administration were active after treatment, showed no signs of distress, and survived the lethal etoposide dose. Whereas small intestine (SI) mucosa of fed mice displayed post-treatment atrophy, the scientists found that pretreatment fasting protected mice from drug-induced SI damage. Additionally, neutrophils infiltrated the SI of fed mice post-treatment, whereas fasting mice were shielded against this proinflammatory response and its accompanying structural damage. Furthermore, the authors found that fasting protects SI stem cells from chemotherapy toxicity; although many stem cells in fasting mice were killed by etoposide, a subset was able to survive, maintain structural and functional viability, and repopulate the SI epithelium after drug exposure. Microarray analysis showed enhanced expression of DNA damage response and repair genes in SI stem cells from fasted mice 3 h after drug treatment compared to that from fed mice, along with differential regulation of metabolic and cellular stress response genes. The researchers found that fasting increased the ability and rapidity of murine SI stem cells to resolve the DNA double-strand breaks caused by etoposide and that it also reduced apoptosis, alleviating GI side effects associated with chemotherapy. Abigail Druck Shudofsky
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COPPER AND ZINC IONS INDUCE AGGREGATION OF EYE LENS PROTEIN HUMAN γD CRYSTALLIN
thermal stability of HγD and promoted disulfide-bridged dimer formation, causing significant changes to HγD crystallin’s folding and conformation. Although the specific protein residues involved in metal-induced aggregation remain to be discovered through site-directed mutagenesis studies, the researchers demonstrated that Cu(II) and Zn(II) display distinct site-specific interactions with the protein, resulting in varying mechanisms of metal-induced HγD crystallin aggregation. Abigail Druck Shudofsky
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COMPENSATORY HUMAN-SPECIFIC ALLELES MAY PREVENT POSTREPRODUCTIVE COGNITIVE DECLINE Humans, along with two species of whales, are the only vertebrates known to have prolonged postreproductive lifespans. As older individuals can care for and transfer information to younger generations, this can increase the fitness of the human species. However, if older individuals are affected with declining cognitive capacity, then group resources are instead diverted to care for them. Late-onset Alzheimer’s disease (LOAD) is a uniquely human neurodegenerative disease. As such, human-specific alleles may exist to protect from it. Pascal Gagneux, Ajit Varki, and their teams investigated the relationship between the immunoregulatory receptor CD33 and LOAD ((2015) PNAS, 113, 74−79). The CD33 gene is expressed in innate immune system cells and inhibits proinflammatory cascades in the presence of sialic acids. There are two alternative splice forms of CD33 whose protein products differ in their ability to bind sialic acid: CD33M is full-length, whereas CD33m is missing an exon. The single-nucleotide polymorphism rs3865444 in the CD33 promoter region is associated with LOAD susceptibility; people homozygous for the rs3865444C LOAD-risk allele have greater
Adapted from L. Quintanar et al. (2015) ACS Chem. Biol., DOI: 10.1021/acschembio.5b00966. Copyright 2015 American Chemical Society.
The eye lens is composed of differentiated fiber cells that have a high content of crystallins, which are proteins that maintain lens transparency through their stability and solubility. Monomeric, β-sheet-rich human γD (HγD) crystallin is abundant in the lens and is highly stable, resisting chemical and heat denaturation. However, partially folded HγD crystallin molecules are prone to aggregation, and these high-molecular-weight complexes cause lens opacity and cataract formation. Metals have been implicated in protein aggregation, and because copper (Cu(II)) and zinc (Zn(II)) concentrations are significantly increased in lenses with cataracts, Liliana Quintanar and Jonathan A. King led a team to investigate the effects of these ions on HγD crystallin aggregation ((2016) ACS Chem. Biol., 11, 263−272). The authors assessed the effect of six divalent metal ions on HγD crystallin and found that only Cu(II) and Zn(II) specifically induced the loss of soluble monomeric protein and the formation of larger aggregates. The scientists found that Cu(II) ions had a more pronounced effect than Zn(II) ions on HγD crystallin and induced the formation of larger protein aggregates; Cu(II) also substantially decreased the © 2016 American Chemical Society
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DOI: 10.1021/acs.chemrestox.6b00062 Chem. Res. Toxicol. 2016, 29, 235−236
Chemical Research in Toxicology
Spotlight
tumors and patients. Given this variability, it would be advantageous to predict TNP impact on an individual before treatment to maximize success. Omid C. Farokhzad, Ralph Weissleder, and their collaborators investigated whether magnetic NPs (MNPs) could predict TNP distribution in vivo and therapeutic efficacy ((2015) Sci. Transl. Med., 7, 314ra183). The authors utilized intravital high-resolution time-lapse microscopy to visualize fluorescently labeled carboxymethyl dextran-coated MNPs. Despite their different sizes and compositions, the NPs demonstrated similar intratumoral pharmacokinetics and uptake. MNPs could predict TNP localization with >85% accuracy within the tumor microenvironment and with >95% accuracy within microvasculature circulation. The researchers utilized magnetic resonance imaging (MRI) to visualize the biodistribution of the MNPs and sought to determine if this correlated with TNP distribution. They scanned tumor-bearing mice before and after MNP treatment and observed that the particles amassed in the tumors heterogeneously among the animals; they classified the MNP accumulation within animals as low, medium, and high. The scientists then administered the same dose of TNPs to all mice, but the drug response differed in each classification group. Mice with high-MNP tumor accumulation had more tumor cell DNA damage and substantially more cells that were drug-responsive. Moreover, the MNP MRI predicted post-TNP tumor growth; high-MNP tumors did not increase in size after TNP drug treatment, whereas low-MNP tumors grew twice as fast as medium-MNP tumors. The authors further determined that tumor MNP levels correlated with TNP drug accumulation, establishing that MNPs could be used as imaging agents to predict TNP response. Abigail Druck Shudofsky
cell surface expression of CD33M compared with that in individuals homozygous with the rs3865444A LOAD-protective allele. CD33M expression in microglial cells suppresses uptake and clearance of amyloid β peptide, which accumulates in the central nervous system and contributes to LOAD. The authors analyzed aggregated genomic data and discovered that rs3865444A is found only in modern humans; Neanderthal and other human ancestors and nonhuman primates contain only the rs3865444C allele. It is possible that this LOADprotective allele evolved to adjust CD33 splicing and decrease the CD33M isoform, an adaptation that protects people against the distinct human liability of postreproductive cognitive decline. The authors also found that other genes associated with human age-related neurodegeneration, diabetes, and cerebrovascular disease have similarly derived human-specific protective alleles. Abigail Druck Shudofsky
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DIFFERENTIATION OF EPIGENETIC CYTOSINE STRUCTURAL VARIANTS IN DNA USING A COUPLED FLUORESCENCE SENSING ASSAY
Adapted from J.-L.H.A. Duprey et al. (2015) ACS Chem. Biol., DOI: 10.1021/acschembio.5b00796. Copyright 2015 American Chemical Society.
Epigenetic modifications of cytosine (C) include methylation (mC) and hydroxymethylation (hmC) at the C5 position. While such modifications play a crucial role in genetic regulation, it can be challenging to identify these nucleobase variants given their similarity in structure and size. James H. R. Tucker and his group developed a fluorescent probe assay to discriminate among C, mC, and hmC bases in a DNA strand ((2015) ACS Chem. Biol., DOI: 10.1021/acschembio.5b00796). The authors synthesized 15-mer oligonucleotide probes with anthracene tags incorporated in the center of each sequence. Upon room-temperature hybridization with a target DNA strand, the photoexcited anthracene chromophore emits a fluorescent output; this signal differs in emission intensity depending on the identity of the base directly opposite it. When compared to the emission intensity of anthracene in an unbound probe, the greatest change occurs when C is present in a target strand, followed by the change that occurs in the presence of mC and then by the change that occurs in the presence of hmC. As differing methylation status leads to either an increase or a decrease in emission intensity, the researchers were able to distinguish among C, mC, and hmC using two different probes per sample; the “up” or “down” changes in fluorescence readings that take place upon duplex formation allow users to easily discern the cytosine methylation status at a single locus. Abigail Druck Shudofsky
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MRI OF MAGNETIC NANOPARTICLES CAN PREDICT INTRATUMORAL THERAPEUTIC NANOPARTICLE ACCUMULATION AND EFFICACY Therapeutic nanoparticles (TNPs) offer controlled drug release but produce inconsistent results in clinical trials. TNP uptake and accumulation in tumors are affected by a variety of factors, and consequently, drug distribution and efficacy differ across 236
DOI: 10.1021/acs.chemrestox.6b00062 Chem. Res. Toxicol. 2016, 29, 235−236
