The mast cell-T lymphocyte axis impacts cancer: Friend or foe?

Crosstalk between mast cells (MCs) and T lymphocytes (TLs) releases specific signals that create an environment conducive to tumor development. Conversely, they can protect against cancer by targeting tumor cells for destruction. Although their role in immunity and cancer is complex, their potential in anticancer strategies is often underestimated. When peripheral MCs are activated, they can affect cancer development. Tumor-infiltrating TLs may malfunction and contribute to aggressive cancer and poor prognoses. One promising approach for cancer patients is TL-based immunotherapies. Recent reports suggest that MCs modulate TL activity in solid tumors and may be a potential therapeutic layer in multitargeting anticancer strategies. Pharmacologically modulating MC activity can enhance the anticancer cytotoxic TL response in tumors. By identifying tumor-specific targets, it has been possible to genetically alter patients' cells into fully humanized anticancer cellular therapies for autologous transplantation, including the engineering of TLs and MCs to target and kill cancer cells. Hence, recent scientific evidence provides a broader understanding of MC-TL activity in cancer.

Loss of PARP7 Increases Type I Interferon Signaling in EO771 Breast Cancer Cells and Prevents Mammary Tumor Growth by Increasing Antitumor Immunity

PARP7 is a member of the ADP-ribosyltransferase diphtheria toxin-like (ARTD) family and acts as a repressor of type I interferon (IFN) signaling. PARP7 inhibition causes tumor regression by enhancing antitumor immunity, which is dependent on the stimulator of interferon genes (STING) pathway, TANK-binding kinase 1 (TBK1) activity, and cytotoxic CD8⁺ T cells. To better understand PARP7's role in cancer, we generated and characterized PARP7 knockout (Parp7^KO) EO771 mouse mammary cancer cells in vitro and in a preclinical syngeneic tumor model using catalytic mutant Parp7^H532A mice. Loss of PARP7 expression or inhibition of its activity increased type I IFN signaling, as well as the levels of interferon-stimulated gene factor 3 (ISGF3) and specifically unphosphorylated-ISGF3 regulated target genes. This was partly because PARP7's modification of the RelA subunit of nuclear factor κ-B (NF-κB). PARP7 loss had no effect on tumor growth in immunodeficient mice. In contrast, injection of wildtype cells into Parp7^H532A mice resulted in smaller tumors compared with cells injected into Parp7^+/+ mice. Parp7^H532A mice injected with Parp7^KO cells failed to develop tumors and those that developed regressed. Our data highlight the importance of PARP7 in the immune cells and further support targeting PARP7 for anticancer therapy.

Increased sensitivity to chemically induced colitis in mice harboring a DNA-binding deficient aryl hydrocarbon receptor

The aryl hydrocarbon receptor (AHR), a transcription factor best known for mediating toxic responses of environmental pollutants, also integrates metabolic signals to promote anti-inflammatory responses, intestinal homeostasis, and maintain barrier integrity. AHR regulates its target genes through direct DNA-binding to aryl hydrocarbon response elements (AHREs) but also through tethering to other transcription factors in a DNA-binding independent manner. However, it is not known if AHR's anti-inflammatory role in the gut requires its ability to bind to AHREs. To test this, we determined the sensitivity of Ahrdbd/dbd mice, a genetically modified mouse line that express an AHR protein incapable of binding to AHREs, to dextran sulfate sodium (DSS)-induced colitis. Ahrdbd/dbd mice exhibited more severe symptoms of intestinal inflammation than Ahr+/+ mice. None of the Ahrdbd/dbd mice survived after the 5-day DSS followed by 7-day washout period. By day 6, the Ahrdbd/dbd mice had severe body weight loss, shortening of the colon, higher disease index scores, enlarged spleens, and increased expression of several inflammation genes, including interleukin 1b (Il-1b), Il-6, Il-17, C-x-c motif chemokine ligand 1 (Cxcl1), Cxcl2, Prostaglandin-endoperoxide synthase (Ptgs2), and lipocalin-2. Our findings show that AHR's DNA-binding domain and ability to bind to AHREs are required to reduce inflammation, maintain a healthy intestinal environment, and protect against DSS-induced colitis.

Structurally distinct PARP7 inhibitors provide new insights into the function of PARP7 in regulating nucleic acid-sensing and IFN-β signaling

The mono-ADP-ribosyltransferase PARP7 has emerged as a key negative regulator of cytosolic NA-sensors of the innate immune system. We apply a rational design strategy for converting a pan-PARP inhibitor into a potent selective PARP7 inhibitor (KMR-206). Consistent with studies using the structurally distinct PARP7 inhibitor RBN-2397, co-treatment of mouse embryonic fibroblasts with KMR-206 and NA-sensor ligands synergistically induced the expression of the type I interferon, IFN-β. In mouse colon carcinoma (CT-26) cells, KMR-206 alone induced IFN-β. Both KMR-206 and RBN-2397 increased PARP7 protein levels in CT-26 cells, demonstrating that PARP7's catalytic activity regulates its own protein levels. Curiously, treatment with saturating doses of KMR-206 and RBN-2397 achieved different levels of PARP7 protein, which correlated with the magnitude of type I interferon gene expression. These latter results have important implications for the mechanism of action of PARP7 inhibitors and highlights the usefulness of having structurally distinct chemical probes for the same target.

2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD)-Inducible Poly-ADP-Ribose Polymerase (TIPARP/PARP7) Catalytic Mutant Mice (TiparpH532A) Exhibit Increased Sensitivity to TCDD-Induced Hepatotoxicity and Lethality

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-inducible poly-adenosine diphosphate (ADP)-ribose polymerase (TIPARP/PARP7), an aryl hydrocarbon receptor (AHR) target gene and mono-ADP-ribosyltransferase, acts as part of a negative feedback loop to repress AHR signaling. This process is prevented by a single H532A mutation in TIPARP that destroys its catalytic activity. We hypothesized that the loss of TIPARP catalytic activity would increase sensitivity to TCDD-induced toxicity in vivo. To test this, we created a catalytically deficient mouse line (Tiparp^H532A) by introducing a single H532A mutation in TIPARP. Treatment of mouse embryonic fibroblasts or hepatocytes isolated from Tiparp^H532A mice confirmed the increased TCDD-induced expression of the AHR target genes Cyp1a1, Cyp1b1, and Tiparp. Tiparp^H532A mice given a single injection of 10 µg/kg TCDD, a nonlethal dose in Tiparp^+/+ mice, did not survive beyond day 10. All Tiparp^+/+ mice survived the 30-day treatment. TCDD-treated Tiparp^H532A mice displayed increased expression of AHR target genes, increased steatohepatitis and hepatotoxicity. Hepatic RNA-sequencing revealed 7-fold more differentially expressed genes in Tiparp^H532A mice than in Tiparp^+/+ mice (4542 vs 647 genes) 6 days after TCDD treatment. Differentially expressed genes included genes involved in xenobiotic metabolism, lipid homeostasis and inflammation. Taken together, these data further support TIPARP as a critical negative regulator of AHR activity and show that loss of its catalytic activity is sufficient to increase sensitivity to TCDD-induced steatohepatitis and lethality. Since TIPARP inhibition has recently emerged as a potential anticancer therapy, the impact on AHR signaling, TCDD and polycyclic aromatic hydrocarbon toxicity will need to be carefully considered under conditions of therapeutic TIPARP inhibition.

Chemical genetics and proteome-wide site mapping reveal cysteine MARylation by PARP-7 on immune-relevant protein targets

Poly(ADP-ribose) polymerase 7 (PARP-7) has emerged as a critically important member of a large enzyme family that catalyzes ADP-ribosylation in mammalian cells. PARP-7 is a critical regulator of the innate immune response. What remains unclear is the mechanism by which PARP-7 regulates this process, namely because the protein targets of PARP-7 mono-ADP-ribosylation (MARylation) are largely unknown. Here, we combine chemical genetics, proximity labeling, and proteome-wide amino acid ADP-ribosylation site profiling for identifying the direct targets and sites of PARP-7-mediated MARylation in a cellular context. We found that the inactive PARP family member, PARP-13-a critical regulator of the antiviral innate immune response-is a major target of PARP-7. PARP-13 is preferentially MARylated on cysteine residues in its RNA binding zinc finger domain. Proteome-wide ADP-ribosylation analysis reveals cysteine as a major MARylation acceptor of PARP-7. This study provides insight into PARP-7 targeting and MARylation site preference.

Cell Type-Specific Roles of CD38 in the Interactions of Isoniazid with NAD+ in the Liver

NAD⁺ is a critical molecule that is involved in multiple cellular functions. CD38 is a multifunctional enzyme with NAD⁺ nucleosidase activity. Our previous work revealed the CD38-dependent interactions of isoniazid (INH), an antituberculosis drug, with NAD⁺ to form INH-NAD adduct. In the current work, our metabolomic analysis discovered a novel NAD⁺ adduct with acetylisoniazid (AcINH), a primary INH metabolite mediated by N-acetyltransferase (NAT), and we named it AcINH-NAD. Using Nat1/2(-/-) and Cd38(-/-) mice, we determined that AcINH-NAD formation is dependent on both NAT and CD38. Because NAT is expressed in hepatocytes (HP), whereas CD38 is expressed in Kupffer cells (KC) and hepatic stellate cells (HSC), we explored cell type-specific roles of CD38 in the formation of AcINH-NAD as well as INH-NAD. We found that both INH-NAD and AcINH-NAD were produced in the incubation of INH or AcINH with KC and HSC but not in HP. These data suggest that hepatic nonparenchymal cells, such as KC and HSC, are the major cell types responsible for the CD38-dependent interactions of INH with NAD⁺ in the liver. SIGNIFICANCE STATEMENT: The current study identified AcINH-NAD as a novel metabolite of INH in the liver. Our work also revealed the essential roles of nonparenchymal cells, including Kupffer cells and hepatic stellate cells, in the CD38-dependent interactions of NAD⁺ with INH, leading to the formation of both INH-NAD and AcINH-NAD in the liver. These data can be used to guide the future studies on the mechanisms of INH and NAD⁺ interactions and their contributions to INH-induced liver injury.

A readout of metabolic efficiency in arylamine N-acetyltransferase-deficient mice reveals minor energy metabolism changes

Recent studies have revealed a possible link between the activities of polymorphic arylamine N-acetyltransferases (NATs) and energy metabolism. We used a Nat1/Nat2 double knockout (KO) mouse model to demonstrate that ablation of the two Nat genes is associated with modest, intermittent alterations in respiratory exchange rate. Pyruvate tolerance tests show that double KO mice have attenuated hepatic gluconeogenesis when maintained on a high-fat/high-sucrose diet. Absence of the two Nat genes also leads to an increase in the hepatic concentration of coenzyme A in mice fed a high-fat/high-sucrose diet. Our results suggest a modest involvement of NAT in energy metabolism in mice, which is consistent with the absence of major phenotypic deregulation of energy metabolism in slow human acetylators.

Hepatocyte-Specific Deletion of TIPARP, a Negative Regulator of the Aryl Hydrocarbon Receptor, Is Sufficient to Increase Sensitivity to Dioxin-Induced Wasting Syndrome

The aryl hydrocarbon receptor (AHR) mediates the toxic effects of dioxin (2, 3, 7, 8-tetrachlorodibenzo-p-dioxin; TCDD), which includes thymic atrophy, steatohepatitis, and a lethal wasting syndrome in laboratory rodents. Although the mechanisms of dioxin toxicity remain unknown, AHR signaling in hepatocytes is necessary for dioxin-induced liver toxicity. We previously reported that loss of TCDD-inducible poly(adenosine diphosphate [ADP]-ribose) polymerase (TIPARP/PARP7/ARTD14), an AHR target gene and mono-ADP-ribosyltransferase, increases the sensitivity of mice to dioxin-induced toxicities. To test the hypothesis that TIPARP is a negative regulator of AHR signaling in hepatocytes, we generated Tiparpfl/fl mice in which exon 3 of Tiparp is flanked by loxP sites, followed by Cre-lox technology to create hepatocyte-specific (Tiparpfl/flCreAlb) and whole-body (Tiparpfl/flCreCMV; TiparpEx3-/-) Tiparp null mice. Tiparpfl/flCreAlb and TiparpEx3-/- mice given a single injection of 10 μg/kg dioxin did not survive beyond days 7 and 9, respectively, while all Tiparp+/+ mice survived the 30-day treatment. Dioxin-exposed Tiparpfl/flCreAlb and TiparpEx3-/- mice had increased steatohepatitis and hepatotoxicity as indicated by greater staining of neutral lipids and serum alanine aminotransferase activity than similarly treated wild-type mice. Tiparpfl/flCreAlb and TiparpEx3-/- mice exhibited augmented AHR signaling, denoted by increased dioxin-induced gene expression. Metabolomic studies revealed alterations in lipid and amino acid metabolism in liver extracts from Tiparpfl/flCreAlb mice compared with wild-type mice. Taken together, these data illustrate that TIPARP is an important negative regulator of AHR activity, and that its specific loss in hepatocytes is sufficient to increase sensitivity to dioxin-induced steatohepatitis and lethality.

Deficiency of N-acetyltransferase increases the interactions of isoniazid with endobiotics in mouse liver

Acetylation is the major metabolic pathway of isoniazid (INH) mediated by N-acetyltransferases (NATs). Previous reports suggest that slow acetylators have higher risks of INH hepatotoxicity than rapid acetylators, but the detailed mechanisms remain elusive. The current study used Nat1/2(-/-) mice to mimic NAT slow metabolizers and to investigate INH metabolism in the liver. We found that INH acetylation is abolished in the liver of Nat1/2(-/-) mice, suggesting that INH acetylation is fully dependent on NAT1/2. In addition to the acetylation pathway, INH can be hydrolyzed to form hydrazine (Hz) and isonicotinic acid (INA). We found that INA level was not altered in the liver of Nat1/2(-/-) mice, indicating that deficiency of NAT1/2 has no effect on INH hydrolysis. Because INH acetylation was abolished and INH hydrolysis was not altered in Nat1/2(-/-) mice, we expected an extremely high level of INH in the liver. However, we only observed a modest accumulation of INH in the liver of Nat1/2(-/-) mice, suggesting that there are alternative pathways in INH metabolism in NAT1/2 deficient condition. Our further studies revealed that the conjugated metabolites of INH with endobiotics, including fatty acids and vitamin B6, were significantly increased in the liver of Nat1/2(-/-) mice. In summary, this study illustrated that deficiency of NAT1/2 decreases INH acetylation, but increases the interactions of INH with endobiotics in the liver. These findings can be used to guide future studies on the mechanisms of INH hepatotoxicity in NAT slow metabolizers.

Analysis of bovine viral diarrhoea virus: Biobank and sequence database to support eradication in Scotland

Samples from bovine viral diarrhoea virus (BVDV)-positive cattle were gathered by Scottish diagnostic laboratories and used to produce a Biobank of samples with associated location and identification data in support of the Scottish BVDV eradication scheme. The samples were subject to direct amplification and sequencing of the 5'-untranslated region (5'-UTR) to define the viral types and subtypes present. From 2693 samples collected prior to 2016, approximately 2300 sequences were obtained, representing 8 BVDV type 1 subtypes. No BVDV type 2 samples were detected. The samples came from all regions of the UK but 66 per cent were from Scotland. Analysis of the sequences showed great diversity in the 5'-UTR, with 1206 different sequences. Many samples carried virus with identical 5'-UTR sequences; often from single locations, but there were also examples of the same sequence being obtained from samples at several different locations. This work provides a resource that can be used to analyse the movement of BVDV strains both within Scotland and between Scotland and other nations, particularly in the latter stages of the Scottish eradication programme, and so inform the advice available to both livestock keepers and policymakers.

Development of Fluorinated Analogues of Perhexiline with Improved Pharmacokinetic Properties and Retained Efficacy

We designed and synthesized perhexiline analogues that have the same therapeutic profile as the parent cardiovascular drug but lacking its metabolic liability associated with CYP2D6 metabolism. Cycloalkyl perhexiline analogues 6a-j were found to be unsuitable for further development, as they retained a pharmacokinetic profile very similar to that shown by the parent compound. Multistep synthesis of perhexiline analogues incorporating fluorine atoms onto the cyclohexyl ring(s) provided a range of different fluoroperhexiline analogues. Of these, analogues 50 (4,4-gem-difluoro) and 62 (4,4,4',4'-tetrafluoro) were highly stable and showed greatly reduced susceptibility to CYP2D6-mediated metabolism. In vitro efficacy studies demonstrated that a number of derivatives retained acceptable potency against CPT-1. Having the best balance of properties, 50 was selected for further evaluation. Like perhexiline, it was shown to be selectively concentrated in the myocardium and, using the Langendorff model, to be effective in improving both cardiac contractility and relaxation when challenged with high fat buffer.

Influence of sex and developmental stage on acute hepatotoxic and inflammatory responses to liver procarcinogens in the mouse

The incidence of liver cancer is higher in men than in women. This sex difference is also observed in murine tumor induction models that result in the appearance of liver tumors in adult mice following their exposure on postnatal days 8 and/or 15 to carcinogens such as 4-aminobiphenyl (ABP) or diethylnitrosamine (DEN). Previous studies performed in adult mice showed that acute hepatotoxic and inflammatory responses to high-dose DEN exposure were greater in males than in females, leading to the suggestion that these responses could account for the sex difference in tumor development. We also recently observed that female but not male mice exposed postnatally to ABP had slightly increased expression of the antioxidant defense genes Nqo1 and Ggt1, which are regulated by the oxidative stress response protein nuclear factor erythroid 2-related factor 2 (NRF2), while expression of Hmox1 was increased in both sexes. The goal of the present study was therefore to compare selected acute hepatotoxic, inflammatory and oxidative stress defense responses to ABP, DEN, or the prototype hepatotoxicant carbon tetrachloride (CCl₄), in male and female mice exposed to these chemicals either postnatally or as adults. Exposure of adult mice to ABP, DEN or CCl₄ produced a 2-fold greater acute elevation in serum levels of the hepatotoxicity biomarker alanine aminotransferase (ALT) in males than in females, while levels of the inflammatory biomarker interleukin-6 (IL-6) showed no sex difference. However, treatment of immature mice with either ABP or DEN using standard tumor-inducing postnatal exposure protocols produced no increase in serum ALT or IL-6 levels in either males or females, while CCl₄ produced a 40-fold ALT elevation but with no sex difference. Basal expression of the NRF2-responsive gene Nqo1 was higher in adult females than in males, but there was no sex difference in basal expression of Ggt1 or Hmox1. Sexually immature animals showed no sex difference in basal expression of any of the three genes. Postnatal DEN exposure modestly increased the expression of Ggt1 only in male mice and Nqo1 in both sexes, while CCl₄ slightly increased expression of Ggt1 in both males and females and Nqo1 only in females. Taken together, our results make it unlikely that acute hepatotoxic, inflammatory or NRF2-activated gene responses account for the male predominance in liver tumor growth following postnatal carcinogen exposure in mice. Our findings also suggest that acute toxicity studies performed in adult mice should be interpreted with caution when extrapolating potential mechanisms to liver carcinogenesis models that commonly use postnatally exposed mice.

Caffeine Consumption Contributes to Skin Intrinsic Fluorescence in Type 1 Diabetes

BACKGROUND

A variant (rs1495741) in the gene for the N-acetyltransferase 2 (NAT2) protein is associated with skin intrinsic fluorescence (SIF), a noninvasive measure of advanced glycation end products and other fluorophores in the skin. Because NAT2 is involved in caffeine metabolism, we aimed to determine whether caffeine consumption is associated with SIF and whether rs1495741 is associated with SIF independently of caffeine.

MATERIALS AND METHODS

SIF was measured in 1,181 participants with type 1 diabetes from the Epidemiology of Diabetes Interventions and Complications study. Two measures of SIF were used: SIF1, using a 375-nm excitation light-emitting diode (LED), and SIF14 (456-nm LED). Food frequency questionnaires were used to estimate mean caffeine intake. To establish replication, we examined a second type 1 diabetes cohort.

RESULTS

Higher caffeine intake was significantly associated with higher SIF1(LED 375 nm[0.6, 0.2]) (P=2×10(-32)) and SIF14L(ED 456 nm[0.4, 0.8]) (P=7×10(-31)) and accounted for 4% of the variance in each after adjusting for covariates. When analyzed together, caffeine intake and rs1495741 both remained highly significantly associated with SIF1(LED 375 nm[0.6, 0.2]) and SIF14(LED 456 nm[0.4, 0.8]). Mean caffeinated coffee intake was also positively associated with SIF1(LED 375 nm[0.6, 0.2]) (P=9×10(-12)) and SIF14(LED 456 nm[0.4, 0.8]) (P=4×10(-12)), but no association was observed for decaffeinated coffee intake. Finally, caffeine was also positively associated with SIF1(LED 375 nm[0.6, 0.2]) and SIF14(LED 456 nm[0.4, 0.8]) (P<0.0001) in the replication cohort.

CONCLUSIONS

Caffeine contributes to SIF. The effect of rs1495741 on SIF appears to be partially independent of caffeine consumption. Because SIF and coffee intake are each associated with cardiovascular disease, our findings suggest that accounting for coffee and/or caffeine intake may improve risk prediction models for SIF and cardiovascular disease in individuals with diabetes.

Loss of the Mono-ADP-ribosyltransferase, Tiparp, Increases Sensitivity to Dioxin-induced Steatohepatitis and Lethality

The aryl hydrocarbon receptor (AHR) mediates the toxic effects of the environmental contaminant dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin; TCDD). Dioxin causes a range of toxic responses, including hepatic damage, steatohepatitis, and a lethal wasting syndrome; however, the mechanisms are still unknown. Here, we show that the loss of TCDD-inducible poly(ADP-ribose) polymerase (Tiparp), an ADP-ribosyltransferase and AHR repressor, increases sensitivity to dioxin-induced toxicity, steatohepatitis, and lethality. Tiparp(-/-) mice given a single injection of 100 μg/kg dioxin did not survive beyond day 5; all Tiparp(+/+) mice survived the 30-day treatment. Dioxin-treated Tiparp(-/-) mice exhibited increased liver steatosis and hepatotoxicity. Tiparp ADP-ribosylated AHR but not its dimerization partner, the AHR nuclear translocator, and the repressive effects of TIPARP on AHR were reversed by the macrodomain containing mono-ADP-ribosylase MACROD1 but not MACROD2. These results reveal previously unidentified roles for Tiparp, MacroD1, and ADP-ribosylation in AHR-mediated steatohepatitis and lethality in response to dioxin.

Relative Contributions of CYP1A2 and CYP2E1 to the Bioactivation and Clearance of 4-Aminobiphenyl in Adult Mice

4-Aminobiphenyl (ABP), a prototypical aromatic amine carcinogen in rodents and humans, requires bioactivation to manifest its toxic effects. A traditional model of ABP bioactivation, based on in vitro enzyme kinetic evidence, had postulated initial N-hydroxylation by the cytochrome P450 isoform CYP1A2. This is followed by phase 2 O-conjugation and hydrolysis to form a reactive nitrenium ion that covalently binds to DNA and produces tumor-initiating mutations. However, Cyp1a2(-/-) mice still possess significant liver ABP N-hydroxylation activity, DNA damage, and incidence of ABP-induced liver tumors, and in vivo induction of CYP1A2 paradoxically reduces levels of ABP-induced DNA damage. Competing ABP detoxification pathways can include N-acetylation by arylamine N-acetyltransferase 1 (NAT1) and/or NAT2; however, wild-type and Nat1/2(-/-) mice have similar in vivo ABP clearance rates. Together, these studies suggest the existence of novel ABP bioactivating and clearance/detoxification enzymes. In the present study, we detected similar reductions in Vmax for ABP N-hydroxylation by liver microsomes from Cyp1a2(-/-) and Cyp2e1(-/-) mice when compared with wild-type mice. In addition, recombinant mouse CYP1A2 and CYP2E1 were both able to N-hydroxylate ABP in mouse hepatoma cells. However, the in vivo clearance of ABP was significantly reduced in Cyp1a2(-/-) but not in Cyp2e1(-/-) mice. Our results support a significant role for CYP2E1 as a novel ABP N-oxidizing enzyme in adult mice, and suggest a more important contribution of CYP1A2 to the in vivo plasma clearance and thus detoxification of ABP.

N-hydroxylation of 4-aminobiphenyl by CYP2E1 produces oxidative stress in a mouse model of chemically induced liver cancer

4-Aminobiphenyl (ABP) is a trace component of cigarette smoke and hair dyes, a suspected human carcinogen and a potent rodent liver carcinogen. Postnatal exposure of mice to ABP results in a higher incidence of liver tumors in males than in females, paralleling the sex difference in human liver cancer incidence. A traditional model of ABP tumorigenesis involves initial CYP1A2-mediated N-hydroxylation, which eventually leads to production of mutagenic ABP-DNA adducts that initiate tumor growth. However, several studies have found no correlation between sex or CYP1A2 function and the DNA-damaging, mutagenic, or tumorigenic effects of ABP. Oxidative stress may be an important etiological factor for liver cancer, and it has also been linked to ABP exposure. The goals of this study were to identify novel enzyme(s) that contribute to ABP N-oxidation, and to investigate a potential role for oxidative stress in ABP liver tumorigenicity. Isozyme-selective inhibition experiments using liver microsomes from wild-type and genetically modified mice identified CYP2E1 as a major ABP N-hydroxylating enzyme. The N-hydroxylation of ABP by transiently expressed CYP2E1 produced oxidative stress in cultured mouse hepatoma cells. In vivo postnatal exposure of mice to a tumorigenic dose of ABP also produced oxidative stress in male wild-type mice, but not in male Cyp2e1(-/-) mice or in female mice. However, a stronger NRF2-associated antioxidant response was observed in females. Our results identify CYP2E1 as a novel ABP-N-oxidizing enzyme, and suggest that sex differences in CYP2E1-dependent oxidative stress and antioxidant responses to ABP may contribute to the observed sex difference in tumor incidence.

5-methyl-tetrahydrofolate and the S-adenosylmethionine cycle in C57BL/6J mouse tissues: gender differences and effects of arylamine N-acetyltransferase-1 deletion

Folate catabolism involves cleavage of the C⁹-N¹⁰ bond to form p-aminobenzoylgluamate (PABG) and pterin. PABG is then acetylated by human arylamine N-acetyltransferase 1 (NAT1) before excretion in the urine. Mice null for the murine NAT1 homolog (Nat2) show several phenotypes consistent with altered folate homeostasis. However, the exact role of Nat2 in the folate pathway in vivo has not been reported. Here, we examined the effects of Nat2 deletion in male and female mice on the tissue levels of 5-methyl-tetrahydrofolate and the methionine-S-adenosylmethionine cycle. We found significant gender differences in hepatic and renal homocysteine, S-adenosylmethionine and methionine levels consistent with a more active methionine-S-adenosylmethionine cycle in female tissues. In addition, methionine levels were significantly higher in female liver and kidney. PABG was higher in female liver tissue but lower in kidney compared to male tissues. In addition, qPCR of mRNA extracted from liver tissue suggested a significantly lower level of Nat2 expression in female animals. Deletion of Nat2 affected liver 5- methyl-tetrahydrofolate in female mice but had little effect on other components of the methionine-S-adenosylmethionine cycle. No N-acetyl-PABG was observed in any tissues in Nat2 null mice, consistent with the role of Nat2 in PABG acetylation. Surprisingly, tissue PABG levels were similar between wild type and Nat2 null mice. These results show that Nat2 is not required to maintain tissue PABG homeostasis in vivo under normal conditions.

Three-dimensional culture and cAMP signaling promote the maturation of human pluripotent stem cell-derived hepatocytes

Human pluripotent stem cells (hPSCs) represent a novel source of hepatocytes for drug metabolism studies and cell-based therapy for the treatment of liver diseases. These applications are, however, dependent on the ability to generate mature metabolically functional cells from the hPSCs. Reproducible and efficient generation of such cells has been challenging to date, owing to the fact that the regulatory pathways that control hepatocyte maturation are poorly understood. Here, we show that the combination of three-dimensional cell aggregation and cAMP signaling enhance the maturation of hPSC-derived hepatoblasts to a hepatocyte-like population that displays expression profiles and metabolic enzyme levels comparable to those of primary human hepatocytes. Importantly, we also demonstrate that generation of the hepatoblast population capable of responding to cAMP is dependent on appropriate activin/nodal signaling in the definitive endoderm at early stages of differentiation. Together, these findings provide new insights into the pathways that regulate maturation of hPSC-derived hepatocytes and in doing so provide a simple and reproducible approach for generating metabolically functional cell populations.

Abstract 4795: N-hydroxylation of 4-aminobiphenyl (ABP) and associated oxidative stress may influence ABP carcinogenicity in the mouse liver

Liver cancer is the 3rd most common cause of death from cancer worldwide due to poor prognosis and lack of treatment options. A prominent sex difference is observed in human liver cancer such that men have a 3 to 5 fold higher incidence than women even after accounting for known etiological factors. In a tumor study carried out previously in our laboratory, two doses of the human carcinogen 4-aminobiphenyl (ABP) given to mice on postnatal days 8 and 15 resulted in the formation of liver tumors at 1 year. Moreover, female mice were dramatically protected from liver tumors compared to males, which parallels the sex difference found in human liver cancer. Our goal is to elucidate the molecular mechanisms behind the sex differences in ABP carcinogenesis in mouse liver with the hope of extrapolating to the human condition.

Oxidative stress may play an important role in human liver carcinogenesis since all major etiological factors for human liver cancer, including viral hepatitis, alcohol, obesity and chemical carcinogens have been shown to be associated with oxidative stress. To determine whether oxidative stress is involved in ABP-mediated carcinogenesis in the mouse, we first assessed the ability of ABP to generate oxidative stress in the mouse Hepa1c1c7 hepatoma cell line. ABP did not produce reactive oxygen species (ROS) or oxidative DNA damage in Hepa1c1c7 cells. However, N-hydroxy-ABP (HOABP), an in vivo metabolite of ABP, was a potent inducer of both ROS and oxidative DNA damage. Furthermore, HOABP-induced oxidative stress was dose-dependent and could be blocked by co-treatment with the antioxidant N-acetylcysteine. These results suggest that HOABP may be a potential source of oxidative stress in mouse liver. We subsequently characterized the kinetics of ABP N-hydroxylation by mouse liver microsomes, and found that more than one cytochrome P450 (CYP) appears to be involved in the reaction. As predicted by the traditional model of ABP bioactivation, the high affinity ABP N-hydroxylation reaction is mediated by CYP1A2, while at least one additional low affinity site belonging to an as yet unidentified CYP is responsible for significant ABP N-hydroxylation at higher concentrations of ABP that would be expected following the doses of ABP used in our tumor study. However, no sex difference was found in either high or low affinity ABP N-hydroxylation activities between liver microsomes from male and female postnatal (day 15) or adult mice. Future studies will focus on quantifying both acute and chronic changes in oxidative stress and antioxidant levels in the mouse liver following carcinogenic doses of ABP, and correlating such changes to tumor formation.

Citation Format: Shuang Wang, Kim S. Sugamori, Denis M. Grant. N-hydroxylation of 4-aminobiphenyl (ABP) and associated oxidative stress may influence ABP carcinogenicity in the mouse liver. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4795. doi:10.1158/1538-7445.AM2013-4795

Transient serum exposure regimes to support dual differentiation of human mesenchymal stem cells

Human mesenchymal stem cells (MSCs), which can generate both osteoblasts and chondrocytes, represent an ideal resource for orthopaedic repair using tissue-engineering approaches. One major difficulty for the development of osteochondral constructs using undifferentiated MSCs is that serum is typically used in culture protocols to promote differentiation of the osteogenic component, whereas existing chondrogenic differentiation protocols rely on the use of serum-free conditions. In order to define conditions which could be compatible with both chondrogenic and osteogenic differentiation in a single bioreactor, we have analysed the efficiency of new biphasic differentiation regimes based on transient serum exposure followed by serum-free treatment. MSC differentiation was assessed either in serum-free medium or with a range of transient exposure to serum, and compared to continuous serum-containing treatment. Although osteogenic differentation was not supported in the complete absence of serum, marker expression and extensive mineralization analyses established that 5 days of transient exposure triggered a level of differentiation comparable to that observed when serum was present throughout. This initial phase of serum exposure was further shown to support the successful chondrogenic differentiation of MSCs, comparable to controls maintained in serum-free conditions throughout. This study indicates that a culture based on temporal serum exposure followed by serum-free treatment is compatible with both osteogenic and chondrogenic differentiation of MSCs. These results will allow the development of novel strategies for osteochondral tissue engineering approaches using MSCs for regenerative medicine.

Influence of arylamine N-acetyltransferase, sex, and age on 4-aminobiphenyl-induced in vivo mutant frequencies and spectra in mouse liver

One model for cancer initiation by 4-aminobiphenyl (ABP) involves N-oxidation by cytochrome P450 CYP1A2 followed by O-conjugation by N-acetyltransferase(s) NAT1 and/or NAT2 and decomposition to a DNA-binding nitrenium ion. We recently observed that neonatal ABP exposure produced liver tumors in male but not in female mice, and that NAT deficiency reduced liver tumor incidence. However, ABP-induced liver tumor incidence did not correlate with liver levels of N-(deoxyguanosin-8-yl)-ABP adducts 24 hr after exposure. In this study, we compared in vivo ABP-induced DNA mutant frequencies and spectra between male and female wild-type and NAT-deficient Muta™Mouse using both the tumor-inducing neonatal exposure protocol and a 28-day repetitive dosing adult exposure protocol. ABP produced an increase in liver DNA mutant frequencies in both neonates and adults. However, we observed no sex or strain differences in mutant frequencies in neonatally exposed mice, and higher frequencies in adult females than males. Neonatal ABP exposure of wild-type mice increased the proportion of G-T transversions in both males and females, while exposure of Nat1/2(-/-) mice produced increased G-T transversions in males and a decrease in females, even though females had higher levels of N-(deoxyguanosin-8-yl)-4-ABP adducts. There was no correlation of mutant frequencies or spectra between mice dosed as neonates or as adults. These results suggest that observed sex- and NAT-dependent differences in ABP-induced liver tumor incidence in mice are not due to differences in either mutation rates or mutational spectra, and that mechanisms independent of carcinogen bioactivation, covalent DNA binding and mutation may be responsible for these differences.

Abstract 4423: Transgenic liver expression of human arylamine N-acetyltransferase NAT2 restores sensitivity of male Nat1/2 null mice to 4-aminobiphenyl-induced liver tumorigenesis

We recently observed that male Nat1/2(-/-) mice, which are deficient in the arylamine N-acetyltransferases Nat1 and Nat2, have a significantly lower incidence and multiplicity of liver tumors than wild-type C57BL/6 mice after their neonatal exposure to the aromatic amine carcinogen 4-aminobiphenyl (ABP). Female mice showed low or no liver tumors from ABP exposure regardless of Nat1/2 status. The goal of the present study was to determine the effect of liver-selective transgenic expression of human NAT2 on ABP-induced liver tumorigenicity in male and female Nat1/2(-/-) mice. We generated a hNAT2tgNat1/2(-/-) strain of mice that express human NAT2 selectively in liver on a Nat1/2 null background, exposed male and female mice to either DMSO vehicle, a low dose (600 nmoles) or a high dose (1200 nmoles) of ABP during the second postnatal week, and assessed mice for tumor growth at one year of age. Male hNAT2tgNat1/2(-/-) mice had liver tumor incidences of 29% (low dose) and 61% (high dose), which more closely resembled those of C57BL/6 mice (60% and 69%, respectively) than those of Nat1/2(-/-) mice (0% and 35%, respectively). This suggests that human NAT2 is capable of substantially restoring the sensitivity of mice to ABP-induced liver tumorigenicity that is lost by the absence of mouse Nat1 and Nat2. On the other hand, female hNAT2tgNat1/2(-/-) mice were still as resistant to liver tumors as C57BL/6 or Nat1/2(-/-) mice. No tumors were observed in any other organs. These results suggest that the human and mouse NAT enzymes play similar roles in enhancing liver tumor growth, and that the mechanism of female protection against ABP-induced tumor growth is unrelated to NAT status. However, neither the sex nor the NAT status of the mice appear to be correlated with the ability of ABP to produce acute DNA-damaging or mutation-inducing effects in liver. This suggests that the role of the human and mouse NAT enzymes in promoting liver tumor growth in mice may be due to a mechanism that is independent of their ability to influence the process of ABP metabolic activation and subsequent DNA damage leading to tumor initiation.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4423. doi:1538-7445.AM2012-4423

Reduced 4-aminobiphenyl-induced liver tumorigenicity but not DNA damage in arylamine N-acetyltransferase null mice

The aromatic amine 4-aminobiphenyl (ABP) is a liver procarcinogen in mice, requiring enzymatic bioactivation to exert its tumorigenic effect. To assess the role of arylamine N-acetyltransferase (NAT)-dependent acetylation capacity in the risk for ABP-induced liver tumors, we compared 1-year liver tumor incidence following the postnatal exposure of wild-type and NAT-deficient Nat1/2(-/-) mice to ABP. At an ABP exposure of 1200 nmol, male Nat1/2(-/-) mice had a liver tumor incidence of 36% compared to 69% in wild-type males, and at 600 nmol there was a complete absence of tumors compared to 60% in wild-type mice. Only one female wild-type mouse had a tumor using this exposure protocol. However, levels of N-deoxyguanosin-8-yl-ABP-DNA adducts did not correlate with either the strain or sex differences in tumor incidence. These results suggest that female sex and NAT deficiency reduce risk for ABP-induced liver tumors, but by mechanisms unrelated to differences in DNA-damaging events.

A retrospective cohort study of the impact of biologic therapy initiation on medical resource use and costs in patients with moderate to severe psoriasis

BACKGROUND

Biologic therapy has become established as an important treatment option in patients with severe psoriasis, but is significantly more expensive in terms of drug costs than traditional treatment options. Relatively little is known about the total healthcare cost of treating severe psoriasis in daily clinical practice and what the budgetary impacts of such high-cost drugs are when compared with standard systemic therapy.

OBJECTIVES

To describe the impact of biologic therapy introduction on the use of medical resources, costs and where available, outcomes in patients with moderate to severe psoriasis.

METHODS

Data were extracted from case notes of a sequential patient cohort with psoriasis attending a tertiary referral severe psoriasis service and initiated on biologics (adalimumab, efalizumab, etanercept or infliximab) for treatment of their psoriasis. Data on hospital resource use (inpatient, outpatient, day ward, accident and emergency visits and phototherapy sessions) and drug usage (systemic nonbiologic and biologic psoriasis therapies and supportive drugs) were collected for 12 months prior to, and at least 6 months following initiation of biologic therapy. Outcome was measured using the Psoriasis Area and Severity Index (PASI). Differences in resource use and associated costs and outcomes, between 12 months before and after initiation of biologic therapy, were tested using Wilcoxon paired sign tests for continuous data and the McNemar test for categorical data. Confidence intervals (CI) around treatment costs were constructed using a 5000-sample bootstrap analysis.

RESULTS

The primary analysis population comprised 76 patients completing 12 months of biologic therapy: 71% males; mean age at time of study 47·3 years (range 23-74); mean duration of psoriasis 24·7 years (range 5·3-45·5). Significant reductions (P < 0·05) in the year following initiation of biologic therapy were observed for all hospital resource use categories, with mean annual costs reduced by £1682 (95% CI -3182 to -182·2; P = 0·05). Mean annual drug costs increased by £9456 (95% CI 8732-10,182; P < 0·001). Mean PASI fell by 8·9 points from 18·7 to 9·8 (95% CI -10·8 to -7·1; P < 0·001).

CONCLUSIONS

Total healthcare costs associated with treatment of severe psoriasis with biologic therapy are significantly greater than with traditional systemic therapy. However, some of these are offset by substantial reductions in the number and length of hospital admissions and use of photo- and systemic therapy, and result in significantly improved patient outcome (as inferred by improvement in PASI).

Liver-selective expression of human arylamine N-acetyltransferase NAT2 in transgenic mice

Human arylamine N-acetyltransferase 2 (NAT2) mediates the biotransformation of arylamine drugs and procarcinogens into either innocuous or reactive DNA-damaging metabolites and is expressed predominantly in liver. Interspecies differences and incongruous results between in vitro, in vivo, and epidemiological studies make it difficult to extrapolate animal results to human risk. We have generated human NAT2 transgenic mice on both C57BL/6 (hNAT2(tg)) and Nat1/2 null backgrounds [hNAT2(tg)Nat1/2(-/-)], in which liver-selective expression of human NAT2 is driven by the mouse albumin promoter. We detected expression of the human NAT2 transcript and protein in mouse liver by real-time PCR and Western blot analysis. NAT2 enzyme activity, measured using the human NAT2-selective substrate sulfamethazine (SMZ), was 40- to 80-fold higher in liver cytosols from hNAT2(tg)Nat1/2(-/-) mice than in wild-type mice. An unexpected gender difference was observed, with males displaying 2-fold higher activity than females. Transgenic mice also had an increased in vivo plasma clearance of SMZ and higher levels of N-acetylated SMZ than wild-type mice. Liver expression of human NAT2 did not affect the disposition of the human NAT1-selective substrate p-aminosalicylic acid (PAS), because hNAT2(tg)Nat1/2(-/-) mice displayed in vivo PAS pharmacokinetic profiles similar to those of Nat1/2(-/-) mice. The metabolism of 4-aminobiphenyl was similar between hNAT2(tg)Nat1/2(-/-) and wild-type mice with the exception of a more liver-restricted pattern in hNAT2(tg)Nat1/2(-/-) mice and lower activity in females. Overall, the hNAT2(tg)Nat1/2(-/-) mouse mimics human expression of NAT2 and may thus be of value in clarifying the role of human NAT2 in arylamine clearance, detoxification, and bioactivation.

Inheritance of chloroplast DNA in Chlamydomonas reinhardtii

Two symmetrically located deletions of approximately 100 base pairs each have been identified in chloroplast DNA of Chlamydomonas reinhardtii. Although present in a mutant strain that requires acetate for growth, both deletions have been shown to be distinct from the nonphotosynthetic phenotype of this strain. These physical markers in the chloroplast genome and maternally inherited genetic markers showed strict cotransmission in reciprocal crosses. Thus, our results are consistent with the location of the well-characterized maternally inherited genetic markers in chloroplast DNA of C. reinhardtii.

An appraisal of ultramicrotomy, FIBSEM and cryogenic FIBSEM techniques for the sectioning of biological cells on titanium substrates for TEM investigation

Ultramicrotomy, focused ion beam scanning electron microscopy (FIBSEM) and cryogenic FIBSEM (cryo-FIBSEM) techniques, as developed for the controlled cross-sectioning of mesenchymal stem cells (MSCs) and human osteoblasts (HObs) on titanium (Ti) substrates for transmission electron microscopy (TEM) investigation, are compared. Conventional ultramicrotomy has been used to section cells on Ti-foil substrates embedded in resin, but significant problems with cell detachment using this technique restricted its general applicability. Conventional FIBSEM 'lift-out' procedures were found to be effective for the preparation of uniform sections of fixed and dehydrated cell/Ti specimens, but the control of cell staining remains an issue. Cryo-FIBSEM procedures used with an 'H-bar' sample geometry enabled the sectioning of fixed and hydrated cell/Ti specimens, but issues remain over ion beam-induced artefacts and control of frost on the sample foils.

Ureteric stents: investigating flow and encrustation

Blockages of the ureter, e.g. due to calculi (kidney stones), can result in an increase in renal pelvic pressure. This may be relieved by inserting a stent (essentially a permeable hollow tube). However, a number of complications are associated with stent use. Stents can result in reflux (backflow of urine along the ureter), which will promote recurrent urinary infection and possible renal parenchymal damage. Furthermore, long-term stent use is associated with infection and precipitation of salts from the urine, which can lead to a build-up of crystalline deposits on the stent surface, making stent removal difficult and painful. This paper examines factors governing urine flow in a stented ureter, the implications for reflux, and the processes by which the stent surface encrusts, in particular focusing on the influence of bacterial infection. An interdisciplinary approach is adopted, involving a combination of theoretical investigations and novel experiments.

Structural Basis of Substrate-binding Specificity of Human Arylamine N-Acetyltransferases

The human arylamine N-acetyltransferases NAT1 and NAT2 play an important role in the biotransformation of a plethora of aromatic amine and hydrazine drugs. They are also able to participate in the bioactivation of several known carcinogens. Each of these enzymes is genetically variable in human populations, and polymorphisms in NAT genes have been associated with various cancers. Here we have solved the high resolution crystal structures of human NAT1 and NAT2, including NAT1 in complex with the irreversible inhibitor 2-bromoacetanilide, a NAT1 active site mutant, and NAT2 in complex with CoA, and have refined them to 1.7-, 1.8-, and 1.9-A resolution, respectively. The crystal structures reveal novel structural features unique to human NATs and provide insights into the structural basis of the substrate specificity and genetic polymorphism of these enzymes.

Effect of Arylamine AcetyltransferaseNat3Gene Knockout onN-Acetylation in the Mouse

Arylamine N-acetyltransferases (NAT) catalyze the biotransformation of many important arylamine drugs and procarcinogens. NAT can either detoxify or activate procarcinogens, complicating the manner in which these enzymes may participate in enhancing or preventing toxic responses to particular agents. Mice possess three NAT isoenzymes: Nat1, Nat2, and Nat3. Whereas Nat1 and Nat2 can efficiently acetylate many arylamines, few substrates appear to be appreciably metabolized by Nat3. We generated a Nat3 knockout mouse strain and used it along with our double Nat1/2(-/-) knockout strain to further investigate the functional role of Nat3. Nat3(-/-) mice showed normal viability and reproductive capacity. Nat3 expression was very low in wild-type animals and completely undetectable in Nat3(-/-) mice. In contrast, greatly elevated expression of Nat3 transcript was observed in Nat1/2(-/-) mice. We used a transcribed marker polymorphism approach to establish that the increased expression of Nat3 in Nat1/2(-/-) mice is a positional artifact of insertion of the phosphoglycerate kinase-neomycin resistance cassette in place of the Nat1/Nat2 gene region and upstream of the intact Nat3 gene, rather than a biological compensatory mechanism. Despite the increase in Nat3 transcript, the N-acetylation of p-aminosalicylate, sulfamethazine, 2-aminofluorene, and 4-aminobiphenyl was undetectable either in vivo or in vitro in Nat1/2(-/-) animals. In parallel, no difference was observed in the in vivo clearance or in vitro metabolism of any of these substrates between wild-type and Nat3(-/-) mice. Thus, Nat3 is unlikely to play a significant role in the N-acetylation of arylamines either in wild-type mice or in mice lacking Nat1 and Nat2 activities.

The effect of anisotropic architecture on cell and tissue infiltration into tissue engineering scaffolds

A common phenomenon in tissue engineering is rapid tissue formation on the outer edge of the scaffold which restricts cell penetration and nutrient exchange to the scaffold centre, resulting in a necrotic core. To address this problem, we generated scaffolds with both random and anisotropic open porous architectures to enhance cell and subsequent tissue infiltration throughout the scaffold for applications in bone and cartilage engineering. Hydroxyapatite (HA) and poly(D,L-lactic acid) (P(DL)LA) scaffolds with random open porosity were manufactured, using modified slip-casting and by supercritical fluid processing respectively, and subsequently characterised. An array of porous aligned channels (400 microm) was incorporated into both scaffold types and cell (human osteoblast sarcoma, for HA scaffolds; ovine meniscal fibrochondrocytes, for P(DL)LA scaffolds) and tissue infiltration into these modified scaffolds was assessed in vitro (cell penetration) and in vivo (tissue infiltration; HA scaffolds only). Scaffolds were shown to have an extensive random, open porous structure with an average porosity of 85%. Enhanced cell and tissue penetration was observed both in vitro and in vivo demonstrating that scaffold design alone can influence cell and tissue infiltration into the centre of tissue engineering scaffolds.

Attentional biases in social anxiety and dysphoria: does comorbidity make a difference?

This study examined whether comorbid symptoms influence the attentional biases associated with social anxiety and dysphoria using the Emotional Stroop Task (EST). Participants were recruited into three groups: a Social Anxiety group, a Dysphoric group, and a Social Anxiety/Dysphoric group. Four types of stimulus words were used: social anxiety threat, depressive threat, neutral words, and positive words. It was hypothesized that the Social Anxiety group would display an attentional bias to emotionally threatening stimuli whereas neither the dysphoric nor the Social Anxiety/Dysphoric group would display an attentional bias. Results found that the Social Anxiety group took longer to color name social threat and depressive words, whereas neither the Dysphoric nor the Comorbid group displayed an attentional bias. These results are discussed in light of their implications for cognitive theories of social anxiety and depression.

In Vivo and in Vitro Metabolism of Arylamine Procarcinogens in Acetyltransferase-Deficient Mice

Arylamine N-acetyltransferases (NATs) catalyze the biotransformation of a number of aromatic and heterocyclic amines, many of which are procarcinogenic agents. Interestingly, these enzymes are binary in nature, participating in both detoxification and activation reactions, and thus it is unclear what role NATs actually play in either preventing or enhancing toxic responses. The ultimate direction may be substrate-specific and dependent on its tissue-specific metabolism by competing, but genetically variable, drug-metabolizing enzymes. To investigate the effect of N-acetylation on the metabolism of some classical procarcinogenic arylamines, we have used our double knockout Nat1/2(-/-) mouse model to test both in vitro activity and the in vivo clearance of some of these agents. As expected, N-acetylation activity was undetectable in tissue cytosol preparations from Nat1/2(-/-) mice for 4-aminobiphenyl (ABP) and 2-aminofluorene (AF), whereas significant levels were measured in all wild-type tissue cytosols tested, indicating the widespread metabolism of these agents. Nat1/2(-/-) mice displayed a variable response with respect to in vivo pharmacokinetics. AF appeared to be most severely compromised, with a 3- to 4-fold increased area under the curve (AUC), whereas the clearance of ABP was found to be less dependent on N-acetylation, with no difference in ABP-AUC between wild-type and knockout animals. 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine was neither N-acetylated nor was its clearance affected by NAT genotype, signifying a dependence on other drug-metabolizing enzymes. The elucidation of the role that N-acetylation plays in the clearance of procarcinogenic agents is the first step in attempting to correlate metabolism by NATs to toxic outcome prevention or augmentation.

A new dehydrogenation mechanism for reversible multicomponent borohydride systems—The role of Li–Mg alloys

A new dehydrogenation mechanism for LiBH4-MgH2 mixtures revealed that magnesium destabilised the LiBH(4) resulting in complete dehydrogenation of the borohydride phase and the formation of a Li-Mg alloy.

Optically sectioned fluorescence lifetime imaging using a Nipkow disk microscope and a tunable ultrafast continuum excitation source

We demonstrate an optically sectioned fluorescence lifetime imaging microscope with a wide-field detector, using a convenient, continuously tunable (435-1150 nm) ultrafast source for fluorescence imaging applications that is derived from a visible supercontinuum generated in a microstructured fiber.

Thin-film theories for two-phase reactive flow models of active cell motion

The aim of this paper is to develop a broadly-applicable and self-consistent thin-film biphasic modelling framework for the full crawling cycle of a single animal cell. A hierarchy of thin-film two-phase 'reactive flow' models is derived; between them these cover a wide range of biologically relevant parameter regimes. The mathematical properties and biological implications of the resulting systems of high-order nonlinear degenerate parabolic-elliptic evolution equations are investigated. Linear-stability arguments suggest the formation of highly localized regions of high or low network density associated with small irregular oscillations or 'ruffling' of the plasma membrane. Local analyses at the contact line identify the classes of admissible contact-line conditions, through which we study for the first time the effect on the cell-scale motion of the 'mesoscopic' contact-line physics, which consists of the chemical and mechanical mechanisms for protrusive and retractive force generation near the outer cell periphery. One of the formulations is used to develop a minimal model for cell body translocation over a thin pseudopod, which predicts that myosin-driven contraction is not essential for rapid translocation. An analytic prediction for the translocation speed is given in terms of the network viscosity and slip coefficient (a parameter measuring the adhesion strength), of the membrane tension and of the thicknesses of the pseudopod and actin cortex; this is in good agreement with the translocation speed of osteoblasts on biomaterial substrates commonly used for orthopaedic implants. Limitations of the modelling approach and directions for future work are outlined.

The influence of dispersant concentration on the pore morphology of hydroxyapatite ceramics for bone tissue engineering

There is a clinical need for synthetic scaffolds that will promote bone regeneration. Important factors include obtaining an optimal porosity and size of interconnecting windows whilst maintaining scaffold mechanical strength, enabling complete penetration of cells and nutrients throughout the scaffold, preventing the formation of necrotic tissue in the centre of the scaffold. To address this we investigated varying slip deflocculation in order to control the resulting porosity, pore size and interconnecting window size whilst maintaining mechanical strength. Hydroxyapatite (HA) porous ceramics were prepared using a modified slip casting process. Rheological measurements of the HA slips were used to identify deflocculation conditions which resulted in changes in the cell and window sizes of the resulting ceramics. Sintered ceramics were characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Pore and window size distribution was determined by SEM. XRD analysis confirmed that the crystal structure remained HA after the sintering process. SEM showed that HA porous ceramics presented a highly interconnected porous network with average pore sizes ranging from 391+/-39 to 495+/-25 microm. The average window size varied from 73+/-5 to 135+/-7 microm. Pore diameters obtained were controllable in the range 200-500 microm. Window sizes were in the range 30-250 microm. The use of dispersant concentration allows pore and window size to be modified whilst maintaining control over porosity demonstrated by a porosity of 85% for seven different dispersant concentrations. The advantage of this approach allows the correlation between the rheological conditions of the slip and the resultant sintered ceramic properties. In particular, optimising the ceramic strength by controlling the agglomeration during the casting process.

Determination of age and gender differences in biochemical processes affecting the disposition of 2-butoxyethanol and its metabolites in mice and rats to improve PBPK modeling

2-Butoxyethanol (BE) is the most widely used glycol ether solvent. BEs major metabolite, butoxyacetic acid (BAA), causes hemolysis with significant species differences in sensitivity. Several PBPK models have been developed over the past two decades to describe the disposition of BE and BAA in male rats and humans to refine health risk assessments. More recent efforts by Lee et al. [Lee, K.M., Dill, J.A., Chou, B.J., Roycroft, J.H., 1998. Physiologically based pharmacokinetic model for chronic inhalation of 2-butoxyethanol. Toxicol. Appl. Pharmacol. 153, 211-226] to describe the kinetics of BE and BAA in the National Toxicology Program (NTP) chronic inhalation studies required the use of several assumptions to extrapolate model parameters from earlier PBPK models developed for young male rats to include female F344 and both sexes of B6C3F1 mice and the effects of aging. To replace these assumptions, studies were conducted to determine the impact of age, gender and species on the metabolism of BE, and the tissue partitioning, renal acid transport and plasma protein binding of BAA. In the current study, the Lee et al. PBPK model was updated and expanded to include the further metabolism of BAA and the salivary excretion of BE and BAA which may contribute to the forestomach irritation observed in mice in the NTP study. The revised model predicted that peak blood concentrations of BAA achieved following 6 h inhalation exposures are greatest in young adult female rats at concentrations up to 300 ppm. This is not the case predicted for old (> or =18 months) animals, where peak blood concentrations of BAA in male and female mice were similar to or greater than female rats. The revised model serves as a quantitative tool for integrating an extensive pharmacokinetic and mechanistic database into a format that can readily be used to compare internal dosimetry across dose, route of exposure and species.

The effect of surface chemistry and nanotopography of titanium nitride (TiN) films on primary hippocampal neurones

The cell-substrate interaction of primary hippocampal neurones with thin films of TiN was studied in vitro. TiN films of different surface chemistries and topographies were deposited by pulsed DC reactive magnetron sputtering and closed field unbalanced magnetron sputter ion plating by Teer Coatings Ltd., Hartlebury, UK to result in TiN films with similar surface chemistries but different topographical features. TiN films were characterised using X-ray diffraction, X-ray photoelectron spectroscopy and atomic force microscopy. The neuron-substrate interaction was examined using environmental scanning electron microscopy (FEG-ESEM) for morphological information. Bromodeoxyuridine and TUNEL assays were used to identify proliferating neurones as well as apoptotic neurones. Fluorescent staining for MAP-2 was used to label neuronal network formation. Primary hippocampal neurones were found to attach and spread to all of the TiN film chemistries and topographies investigated. Neuronal network morphology appeared to be more preferential on the nitrogen rich TiN films and also with reduced nanotopographical features.