Poly(ADP-ribosyl)ation by PARP1: reaction mechanism and regulatory proteins.

Poly(ADP-ribosyl)ation (PARylation) is posttranslational modification of proteins by linear or branched chains of ADP-ribose units, originating from NAD+. The central enzyme for PAR production in cells and the main target of poly(ADP-ribosyl)ation during DNA damage is poly(ADP-ribose) polymerase 1 (PARP1). PARP1 ability to function as a catalytic and acceptor protein simultaneously made a considerable contribution to accumulation of contradictory data. This topic is directly related to other questions, such as the stoichiometry of PARP1 molecules in auto-modification reaction, direction of the chain growth during PAR elongation and functional coupling of PARP1 with PARylation targets. Besides DNA damage necessary for the folding of catalytically active PARP1, other mechanisms appear to be required for the relevant intensity and specificity of PARylation reaction. Indeed, in recent years, PARP research has been enriched by the discovery of novel PARP1 interaction partners modulating its enzymatic activity. Understanding the details of PARP1 catalytic mechanism and its regulation is especially important in light of PARP-targeted therapy and may significantly aid to PARP inhibitors drug design. In this review we summarize old and up-to-date literature to clarify several points concerning PARylation mechanism and discuss different ways for regulation of PAR synthesis by accessory proteins reported thus far.

Inhibition of autophagy potentiates the apoptosis-inducing effects of photodynamic therapy on human colon cancer cells.

BACKGROUND: Photodynamic therapy (PDT) has been reported to be a promising therapy for colon cancer because of its substantial safety features and its ability to induce a systematic reaction rather than local effects on the focal lesion in the intestine. Autophagy and apoptosis play important roles in the response to PDT. However, the role of autophagy after PDT treatment has not yet been clarified. METHODS: In this study, we investigated the relationship between apoptosis and autophagy in porphyrin IX (PpIX)-mediated PDT (PpIX-PDT) in HCT116 colon cancer cells. PpIX-PDT decreased cell viability in a concentration- and light dose-dependent manner. RESULTS: PpIX-PDT results in nuclear condensation, increased the expression of Caspase-3, Bax, and PARP, and decreased expression of Bcl-2. PpIX-PDT also induces the double membrane autophagosome, up-regulates LC3B, Atg7, Beclin-1, and Bcl-2 expression and down-regulates P62 expression. Inhibition of autophagy using chloroquine (CQ) or Atg7 knockdown with a shRNA enhances apoptotic cell death. Based on these findings, autophagy plays a self-protective role in HCT116 cells in response to PpIX-PDT treatment. DISCUSSION: Both autophagy and apoptosis were induced by PpIX-PDT in HCT116 cells, and the inhibition of autophagy strengthened the proapoptotic effect of PpIX-PDT. Thus, the appropriate modulation of autophagy may be as a potential therapeutic target for colon cancer cells treated with PpIX-PDT.

Single molecule detection of PARP1 and PARP2 interaction with DNA strand breaks and their poly(ADP-ribosyl)ation using high-resolution AFM imaging.

PARP1 and PARP2 are implicated in the synthesis of poly(ADP-ribose) (PAR) after detection of DNA damage. The specificity of PARP1 and PARP2 interaction with long DNA fragments containing single- and/or double-strand breaks (SSBs and DSBs) have been studied using atomic force microscopy (AFM) imaging in combination with biochemical approaches. Our data show that PARP1 localizes mainly on DNA breaks and exhibits a slight preference for nicks over DSBs, although the protein has a moderately high affinity for undamaged DNA. In contrast to PARP1, PARP2 is mainly detected at a single DNA nick site, exhibiting a low level of binding to undamaged DNA and DSBs. The enhancement of binding affinity of PARP2 for DNA containing a single nick was also observed using fluorescence titration. AFM studies reveal that activation of both PARPs leads to the synthesis of highly branched PAR whose size depends strongly on the presence of SSBs and DSBs for PARP1 and of SSBs for PARP2. The initial affinity between the PARP1, PARP2 and the DNA damaged site appears to influence both the size of the PAR synthesized and the time of residence of PARylated PARP1 and PARP2 on DNA damages.

Negative prognostic value of high levels of intracellular poly(ADP-ribose) in non-small cell lung cancer.

BACKGROUND: Cisplatin-resistant non-small cell lung cancer (NSCLC) cells are often characterized by alterations in vitamin B-related metabolic processes, including the overexpression and hyperactivation of poly(ADP-ribose) polymerase 1 (PARP1) and the downregulation of pyridoxal kinase (PDXK), correlating with elevated apoptosis resistance. Low PDXK expression is an established negative prognostic factor in NSCLC. PATIENTS AND METHODS: We determined by immunohistochemistry the expression of PARP1 and the level of its product, poly(ADP-ribose) (PAR), in two independent cohorts of patients with resected NSCLC. RESULTS: Intratumoral high levels (above median) of PAR (but not PARP1 protein levels) had a negative prognostic impact in both the training (92 stage I subjects) and validation (133 stage I and II subjects) cohorts, as determined by univariate and multivariate analyses. The simultaneous assessment of PAR and PDXK protein levels improved risk stratification. CONCLUSION: NSCLC patients with high intratumoral PARP1 activity (i.e. elevated PAR levels above median) and low PDXK expression (below median) had a dismal prognosis, while patients with low PARP1 activity and high PDXK expression had a favorable outcome. Altogether, these results underscore the clinical potential and possible therapeutic relevance of these biomarkers.

ARTD1-induced poly-ADP-ribose formation enhances PPARγ ligand binding and co-factor exchange.

PPARγ-dependent gene expression during adipogenesis is facilitated by ADP-ribosyltransferase D-type 1 (ARTD1; PARP1)-catalyzed poly-ADP-ribose (PAR) formation. Adipogenesis is accompanied by a dynamic modulation of the chromatin landscape at PPARγ target genes by ligand-dependent co-factor exchange. However, how endogenous PPARγ ligands, which have a low affinity for the receptor and are present at low levels in the cell, can induce sufficient co-factor exchange is unknown. Moreover, the significance of PAR formation in PPARγ-regulated adipose tissue function is also unknown. Here, we show that inhibition of PAR formation in mice on a high-fat diet reduces weight gain and cell size of adipocytes, as well as PPARγ target gene expression in white adipose tissue. Mechanistically, topoisomerase II activity induces ARTD1 recruitment to PPARγ target genes, and ARTD1 automodification enhances ligand binding to PPARγ, thus promoting sufficient transcriptional co-factor exchange in adipocytes. Thus, ARTD1-mediated PAR formation during adipogenesis is necessary to adequately convey the low signal of endogenous PPARγ ligand to effective gene expression. These results uncover a new regulatory mechanism of ARTD1-induced ADP-ribosylation and highlight its importance for nuclear factor-regulated gene expression.

Nucleolar integrity is required for the maintenance of long-term synaptic plasticity.

Long-term memory (LTM) formation requires new protein synthesis and new gene expression. Based on our work in Aplysia, we hypothesized that the rRNA genes, stimulation-dependent targets of the enzyme Poly(ADP-ribose) polymerase-1 (PARP-1), are primary effectors of the activity-dependent changes in synaptic function that maintain synaptic plasticity and memory. Using electrophysiology, immunohistochemistry, pharmacology and molecular biology techniques, we show here, for the first time, that the maintenance of forskolin-induced late-phase long-term potentiation (L-LTP) in mouse hippocampal slices requires nucleolar integrity and the expression of new rRNAs. The activity-dependent upregulation of rRNA, as well as L-LTP expression, are poly(ADP-ribosyl)ation (PAR) dependent and accompanied by an increase in nuclear PARP-1 and Poly(ADP) ribose molecules (pADPr) after forskolin stimulation. The upregulation of PARP-1 and pADPr is regulated by Protein kinase A (PKA) and extracellular signal-regulated kinase (ERK)--two kinases strongly associated with long-term plasticity and learning and memory. Selective inhibition of RNA Polymerase I (Pol I), responsible for the synthesis of precursor rRNA, results in the segmentation of nucleoli, the exclusion of PARP-1 from functional nucleolar compartments and disrupted L-LTP maintenance. Taken as a whole, these results suggest that new rRNAs (28S, 18S, and 5.8S ribosomal components)--hence, new ribosomes and nucleoli integrity--are required for the maintenance of long-term synaptic plasticity. This provides a mechanistic link between stimulation-dependent gene expression and the new protein synthesis known to be required for memory consolidation.

Phosphoproteomic approach to characterize protein mono- and poly(ADP-ribosyl)ation sites from cells.

Poly(ADP-ribose), or PAR, is a cellular polymer implicated in DNA/RNA metabolism, cell death, and cellular stress response via its role as a post-translational modification, signaling molecule, and scaffolding element. PAR is synthesized by a family of proteins known as poly(ADP-ribose) polymerases, or PARPs, which attach PAR polymers to various amino acids of substrate proteins. The nature of these polymers (large, charged, heterogeneous, base-labile) has made these attachment sites difficult to study by mass spectrometry. Here we propose a new pipeline that allows for the identification of mono(ADP-ribosyl)ation and poly(ADP-ribosyl)ation sites via the enzymatic product of phosphodiesterase-treated ADP-ribose, or phospho(ribose). The power of this method lies in the enrichment potential of phospho(ribose), which we show to be enriched by phosphoproteomic techniques when a neutral buffer, which allows for retention of the base-labile attachment site, is used for elution. Through the identification of PARP-1 in vitro automodification sites as well as endogenous ADP-ribosylation sites from whole cells, we have shown that ADP-ribose can exist on adjacent amino acid residues as well as both lysine and arginine in addition to known acidic modification sites. The universality of this technique has allowed us to show that enrichment of ADP-ribosylated proteins by macrodomain leads to a bias against ADP-ribose modifications conjugated to glutamic acids, suggesting that the macrodomain is either removing or selecting against these distinct protein attachments. Ultimately, the enrichment pipeline presented here offers a universal approach for characterizing the mono- and poly(ADP-ribosyl)ated proteome.

Different involvement of extracellular calcium in two modes of cell death induced by nanosecond pulsed electric fields.

Exposure of cultured cells to nanosecond pulsed electric fields (nsPEFs) induces various cellular responses, including the influx of extracellular Ca2+ and cell death. Recently, nsPEFs have been regarded as a novel means of cancer therapy, but their molecular mechanism of action remains to be fully elucidated. Here, we demonstrate the involvement of extracellular Ca2+ in nsPEF-induced cell death. Extracellular Ca2+ was essential for necrosis and consequent poly(ADP-ribose) (PAR) formation in HeLa S3 cells. Treatment with a Ca2+ ionophore enhanced necrosis as well as PAR formation in nsPEF-exposed HeLa S3 cells. In the absence of extracellular Ca2+, HeLa S3 cells were less susceptible to nsPEFs and exhibited apoptotic proteolysis of caspase 3 and PARP-1. HeLa S3 cells retained the ability to undergo apoptosis even after nsPEF exposure but instead underwent necrosis, suggesting that necrosis is the preferential mode of cell death. In K562 and HEK293 cells, exposure to nsPEFs resulted in the formation of necrosis-associated PAR, whereas Jurkat cells exclusively underwent apoptosis independently of extracellular Ca2+. These observations demonstrate that the mode of cell death induced by nsPEFs is cell-type dependent and that extracellular Ca2+ is a critical factor for nsPEF-induced necrosis.

PARP-1 dependent recruitment of the amyotrophic lateral sclerosis-associated protein FUS/TLS to sites of oxidative DNA damage.

Amyotrophic lateral sclerosis (ALS) is associated with progressive degeneration of motor neurons. Several of the genes associated with this disease encode proteins involved in RNA processing, including fused-in-sarcoma/translocated-in-sarcoma (FUS/TLS). FUS is a member of the heterogeneous nuclear ribonucleoprotein (hnRNP) family of proteins that bind thousands of pre-mRNAs and can regulate their splicing. Here, we have examined the possibility that FUS is also a component of the cellular response to DNA damage. We show that both GFP-tagged and endogenous FUS re-localize to sites of oxidative DNA damage induced by UVA laser, and that FUS recruitment is greatly reduced or ablated by an inhibitor of poly (ADP-ribose) polymerase activity. Consistent with this, we show that recombinant FUS binds directly to poly (ADP-ribose) in vitro, and that both GFP-tagged and endogenous FUS fail to accumulate at sites of UVA laser induced damage in cells lacking poly (ADP-ribose) polymerase-1. Finally, we show that GFP-FUS(R521G), harbouring a mutation that is associated with ALS, exhibits reduced ability to accumulate at sites of UVA laser-induced DNA damage. Together, these data suggest that FUS is a component of the cellular response to DNA damage, and that defects in this response may contribute to ALS.

SET7/9-dependent methylation of ARTD1 at K508 stimulates poly-ADP-ribose formation after oxidative stress.

ADP-ribosyltransferase diphtheria toxin-like 1 (ARTD1, formerly PARP1) is localized in the nucleus, where it ADP-ribosylates specific target proteins. The post-translational modification (PTM) with a single ADP-ribose unit or with polymeric ADP-ribose (PAR) chains regulates protein function as well as protein-protein interactions and is implicated in many biological processes and diseases. SET7/9 (Setd7, KMT7) is a protein methyltransferase that catalyses lysine monomethylation of histones, but also methylates many non-histone target proteins such as p53 or DNMT1. Here, we identify ARTD1 as a new SET7/9 target protein that is methylated at K508 in vitro and in vivo. ARTD1 auto-modification inhibits its methylation by SET7/9, while auto-poly-ADP-ribosylation is not impaired by prior methylation of ARTD1. Moreover, ARTD1 methylation by SET7/9 enhances the synthesis of PAR upon oxidative stress in vivo. Furthermore, laser irradiation-induced PAR formation and ARTD1 recruitment to sites of DNA damage in a SET7/9-dependent manner. Together, these results reveal a novel mechanism for the regulation of cellular ARTD1 activity by SET7/9 to assure efficient PAR formation upon cellular stress.

Nanosecond pulsed electric fields induce poly(ADP-ribose) formation and non-apoptotic cell death in HeLa S3 cells.

Nanosecond pulsed electric fields (nsPEFs) have recently gained attention as effective cancer therapy owing to their potency for cell death induction. Previous studies have shown that apoptosis is a predominant mode of nsPEF-induced cell death in several cell lines, such as Jurkat cells. In this study, we analyzed molecular mechanisms for cell death induced by nsPEFs. When nsPEFs were applied to Jurkat cells, apoptosis was readily induced. Next, we used HeLa S3 cells and analyzed apoptotic events. Contrary to our expectation, nsPEF-exposed HeLa S3 cells exhibited no molecular signs of apoptosis execution. Instead, nsPEFs induced the formation of poly(ADP-ribose) (PAR), a hallmark of necrosis. PAR formation occurred concurrently with a decrease in cell viability, supporting implications of nsPEF-induced PAR formation for cell death. Necrotic PAR formation is known to be catalyzed by poly(ADP-ribose) polymerase-1 (PARP-1), and PARP-1 in apoptotic cells is inactivated by caspase-mediated proteolysis. Consistently, we observed intact and cleaved forms of PARP-1 in nsPEF-exposed and UV-irradiated cells, respectively. Taken together, nsPEFs induce two distinct modes of cell death in a cell type-specific manner, and HeLa S3 cells show PAR-associated non-apoptotic cell death in response to nsPEFs.

Roles of poly(ADP-ribose) glycohydrolase in DNA damage and apoptosis.

Poly(ADP-ribose) glycohydrolase (PARG) is the primary enzyme that catalyzes the hydrolysis of poly(ADP-ribose) (PAR), an essential biopolymer that is synthesized by poly(ADP-ribose) polymerases (PARPs) in the cell. By regulating the hydrolytic arm of poly(ADP-ribosyl)ation, PARG participates in a number of biological processes, including the repair of DNA damage, chromatin dynamics, transcriptional regulation, and cell death. Collectively, the research investigating the roles of PARG in the cell has identified the importance of PARG and its value as a therapeutic target. However, the biological role of PARG remains less understood than the role of PAR synthesis by the PARPs. Further complicating the study of PARG is the existence of multiple PARG isoforms in the cell, the lack of optimal PARG inhibitors, and the lack of viable PARG-null animals. This review will present our current knowledge of PARG, with a focus on its roles in DNA-damage repair and cell death.

p63 involvement in poly(ADP-ribose) polymerase 1 signaling of topoisomerase I-dependent DNA damage in carcinoma cells.

Poly(ADP-ribose)polymerase 1 (PARP-1) inhibitors are thought as breakthrough for cancer treatment in solid tumors such as breast cancer through their effects on PARP's enzymatic activity. Our previous findings showed that the hydrophilic PARP inhibitor PJ34 enhances the sensitivity of p53 proficient MCF7 breast carcinoma cells to topotecan, a DNA Topoisomerase I (TOP 1) inhibitor. In the present study, we combine the classical TOP 1 poison camptothecin or its water-soluble derivative topotecan with PJ34 to investigate the potentiation of chemotherapeutic efficiency in MCF7 (p53(WT)), MDA-MB231 (p53(mut)) breast carcinoma cells and SCC022 (p53(null)) squamous carcinoma cells. We show that, following TPT-PJ34 combined treatment, MCF7 cells exhibit apoptotic death while MDA-MB231 and SCC022 cells are more resistant to these agents. Specifically, in MCF7, (i) PJ34 in combination with TPT causes a G2/M cell cycle arrest followed by massive apoptosis; (ii) PJ34 addition reverts TPT-dependent PARP-1 automodification and triggers caspase-dependent PARP-1 proteolysis; (iii) TPT, used as a single agent, stimulates p53 expression while in combination with PJ34 increases p53, TAp63α and TAp63γ protein levels with a concomitant reduction of MDM2 protein. The identification of p63 proteins as new players involved in the cancer cell response to TPT-PJ34 is relevant for a better understanding of the PARP1-dependent signaling of DNA damage. Furthermore, our data indicate that, in response to TPT-PJ34 combined chemotherapy, a functional cooperation between p53 and TAp63 proteins may occur and be essential to trigger apoptotic cell death.

Hyperactivation of PARP triggers nonhomologous end-joining in repair-deficient mouse fibroblasts.

Regulation of poly(ADP-ribose) (PAR) synthesis and turnover is critical to determining cell fate after genotoxic stress. Hyperactivation of PAR synthesis by poly(ADP-ribose) polymerase-1 (PARP-1) occurs when cells deficient in DNA repair are exposed to genotoxic agents; however, the function of this hyperactivation has not been adequately explained. Here, we examine PAR synthesis in mouse fibroblasts deficient in the base excision repair enzyme DNA polymerase ß (pol ß). The extent and duration of PARP-1 activation was measured after exposure to either the DNA alkylating agent, methyl methanesulfonate (MMS), or to low energy laser-induced DNA damage. There was strong DNA damage-induced hyperactivation of PARP-1 in pol ß nullcells, but not in wild-type cells. In the case of MMS treatment, PAR synthesis did not lead to cell death in the pol ß null cells, but instead resulted in increased PARylation of the nonhomologous end-joining (NHEJ) protein Ku70 and increased association of Ku70 with PARP-1. Inhibition of the NHEJ factor DNA-PK, under conditions of MMS-induced PARP-1 hyperactivation, enhanced necrotic cell death. These data suggest that PARP-1 hyperactivation is a protective mechanism triggering the classical-NHEJ DNA repair pathway when the primary alkylated base damage repair pathway is compromised.

Large-scale preparation and characterization of poly(ADP-ribose) and defined length polymers.

Poly(ADP-ribose) (pADPr) is a large, structurally complex polymer of repeating ADP-ribose units. It is biosynthesized from NAD⁺ by poly(ADP-ribose) polymerases (PARPs) and degraded to ADP-ribose by poly(ADP-ribose) glycohydrolase. pADPr is involved in many cellular processes and exerts biological function through covalent modification and noncovalent binding to specific proteins. Very little is known about molecular recognition and structure-activity relationships for noncovalent interaction between pADPr and its binding proteins, in part because of lack of access to the polymer on a large scale and to units of defined lengths. We prepared polydisperse pADPr from PARP1 and tankyrase 1 at the hundreds of milligram scale by optimizing enzymatic synthesis and scaling up chromatographic purification methods. We developed and calibrated an anion exchange chromatography method to assign pADPr size and scaled it up to purify defined length polymers on the milligram scale. Furthermore, we present a pADPr profiling method to characterize the polydispersity of pADPr produced by PARPs under different reaction conditions and find that substrate proteins affect the pADPr size distribution. These methods will facilitate structural and biochemical studies of pADPr and its binding proteins.

PARP-1 inhibition induces a late increase in the level of reactive oxygen species in cells after ionizing radiation.

Poly(ADP-ribose) polymerase 1 (PARP1), an enzyme activated by DNA strand breaks, synthesizes polymers of poly(ADP-ribose) (PAR) that modify chromatin and other proteins and play a role in DNA repair. Inhibition of PARP1 activity is considered a potentially important strategy in clinical practice, especially to sensitize tumor cells to chemo- and radio-therapy. Here we examined the influence of inhibition of PARP1 on formation of reactive oxygen species (ROS) and on DNA repair in cells exposed to ionizing radiation (IR). K562 (human myelogenous leukaemia) cells were grown and exposed to 4 or 12 Gy of ionizing radiation in presence or absence of the PARP inhibitor NU1025 (100 µM). Intracellular ROS were assayed using the probe 2,7-dichlorofluorescein with detection by flow cytometry and the rejoining of DNA strand breaks were followed by alkaline single cell gel electrophoresis (comet) assays. In untreated cells a significant increase in PAR formation occurred during the first 5 min after IR, followed by a gradual decrease up to 30 min. Addition of a PARP inhibitor arrested the production of PAR almost completely and decreased the rate of rejoining of DNA strand breaks significantly; however, 3h after irradiation we observed no difference in the amount of DNA strand breaks between PARP inhibitor-treated and untreated cells. Twelve to 48 h after irradiation, an increase of ROS concentration was observed in irradiated cells and ROS levels in PARP inhibitor-treated cells were significantly higher than in cells without inhibitor. Irradiated cells grown in the presence or absence of PARP inhibitor did not differ in the frequencies of apoptotic and necrotic cells or in the activity of caspases at 24, 48 and 72 h after irradiation. Poly(ADP-ribosylation) and inhibition of PARP1 appeared to modulate DNA strand break rejoining and influence the concentration of ROS in irradiated cells.

cGMP-Prkg1 signaling and Pde5 inhibition shelter cochlear hair cells and hearing function.

Noise-induced hearing loss (NIHL) is a global health hazard with considerable pathophysiological and social consequences that has no effective treatment. In the heart, lung and other organs, cyclic guanosine monophosphate (cGMP) facilitates protective processes in response to traumatic events. We therefore analyzed NIHL in mice with a genetic deletion of the gene encoding cGMP-dependent protein kinase type I (Prkg1) and found a greater vulnerability to and markedly less recovery from NIHL in these mice as compared to mice without the deletion. Prkg1 was expressed in the sensory cells and neurons of the inner ear of wild-type mice, and its expression partly overlapped with the expression profile of cGMP-hydrolyzing phosphodiesterase 5 (Pde5). Treatment of rats and wild-type mice with the Pde5 inhibitor vardenafil almost completely prevented NIHL and caused a Prkg1-dependent upregulation of poly (ADP-ribose) in hair cells and the spiral ganglion, suggesting an endogenous protective cGMP-Prkg1 signaling pathway that culminates in the activation of poly (ADP-ribose) polymerase. These data suggest vardenafil or related drugs as possible candidates for the treatment of NIHL.

Role of poly(ADP-ribose) glycohydrolase in the regulation of cell fate in response to benzo(a)pyrene.

Poly(ADP-ribosyl)ation is a crucial regulator of cell fate in response to genotoxic stress. Poly(ADP-ribosyl)ation plays important roles in multiple cellular processes, including DNA repair, chromosomal stability, chromatin function, apoptosis, and transcriptional regulation. Poly(ADP-ribose) (PAR) degradation is carried out mainly by poly(ADP-ribose) glycohydrolase (PARG) enzymes. Benzo(a)pyrene (BaP) is a known human carcinogen. Previous studies in our laboratory demonstrated that exposure to BaP caused a concentration-dependent DNA damage in human bronchial epithelial (16HBE) cells. The role of PARG in the regulation of DNA damage induced by BaP is still unclear. To gain insight into the function of PARG and PAR in response to BaP, we used lentiviral gene silencing to generate 16HBE cell lines with stably suppressed PARG, and determined parameters of cell death and cell cycle following BaP exposure. We found that PARG was partially dependent on PAR synthesis, PARG depletion led to PAR accumulation. BaP-induced cell death was regulated by PARG, the absence of which was beneficial for undamaged cells. Our results further suggested that PARG probably has influence on ATM/p53 pathway and metabolic activation of BaP. Experimental evidences provided from this study suggest significant preventive properties of PAR accumulation in the toxicity caused by BaP.

Glutamine treatment attenuates the development of organ injury induced by zymosan administration in mice.

Glutamine is the most abundant amino acid in the bloodstream. It is important in nucleotide synthesis, is anti-catabolic, has anti-oxidant properties via metabolism to glutathione, may enhance immune responsiveness and possesses immunoregulatory functions. Moreover, it reduces atrophy of intestinal mucosa in animals on total parenteral nutrition and prevents intestinal mucosal injury accompanying small bowel transplantation, chemotherapy and radiation. In the present study, we investigated the effects of glutamine on development of non-septic shock caused by zymosan. Mice received either zymosan (500 mg/kg, administered i.p., as a suspension in saline) or vehicle (saline). Glutamine (1.5 mg/kg i.p.) was administered 1 and 6h after zymosan administration. Organ failure and systemic inflammation in mice were assessed 18 h after administration of zymosan and/or glutamine. Glutamine-treatment reduced the peritoneal exudation and the migration of polymorphonuclear cells caused by zymosan-injection and also attenuated the pancreatic and gut injury. Inflammatory and apoptotic parameters were evaluated to better investigate the effects of the glutamine-administration. So, by immunohistochemical analysis and in vitro assays, we have clearly showed that glutamine reduces: 1) the histological damage in pancreas and gut; 2) the inducible nitric oxide synthase expression; 3) nitrotyrosine and poly (ADP-ribose) formation; 4) TNF-α and IL-1ß tissue and plasma levels; 5) FasL localization; and 6) alteration of the balance between Bax and Bcl-2. In addition, at the end of the observation period (7 days), zymosan causes severe illness in the mice characterized by a systemic toxicity, significant loss of body weight and mortality. Glutamine-treatment significantly reduced all these parameters.

Expression of proliferative and inflammatory markers in a full-thickness human skin equivalent following exposure to the model sulfur mustard vesicant, 2-chloroethyl ethyl sulfide.

Sulfur mustard is a potent vesicant that induces inflammation, edema and blistering following dermal exposure. To assess molecular mechanisms mediating these responses, we analyzed the effects of the model sulfur mustard vesicant, 2-chloroethyl ethyl sulfide, on EpiDerm-FT™, a commercially available full-thickness human skin equivalent. CEES (100-1000 µM) caused a concentration-dependent increase in pyknotic nuclei and vacuolization in basal keratinocytes; at high concentrations (300-1000 µM), CEES also disrupted keratin filament architecture in the stratum corneum. This was associated with time-dependent increases in expression of proliferating cell nuclear antigen, a marker of cell proliferation, and poly(ADP-ribose) polymerase (PARP) and phosphorylated histone H2AX, markers of DNA damage. Concentration- and time-dependent increases in mRNA and protein expression of eicosanoid biosynthetic enzymes including COX-2, 5-lipoxygenase, microsomal PGE2 synthases, leukotriene (LT) A4 hydrolase and LTC4 synthase were observed in CEES-treated skin equivalents, as well as in antioxidant enzymes, glutathione S-transferases A1-2 (GSTA1-2), GSTA3 and GSTA4. These data demonstrate that CEES induces rapid cellular damage, cytotoxicity and inflammation in full-thickness skin equivalents. These effects are similar to human responses to vesicants in vivo and suggest that the full thickness skin equivalent is a useful in vitro model to characterize the biological effects of mustards and to develop potential therapeutics.