Concurrent Umbilical Hernia Repair at the Time of Liver Transplantation: A Six-Year Experience from a Single Institution

BACKGROUND

Umbilical hernias are common in patients with end-stage liver disease undergoing liver transplantation. Management of those persisting at the time of liver transplantation is important to define.

OBJECTIVE

To evaluate the long-term results of patients undergoing simultaneous primary umbilical hernia repair (UHR) at the time of liver transplantation at a single institution.

METHODS

Retrospective chart review was performed on patients undergoing simultaneous UHR and liver transplantation from 2010 through 2016. 30-day morbidity and mortality outcomes and long-term hernia recurrence were investigated.

RESULTS

59 patients had primary UHR at the time of liver transplantation. All hernias were reducible with no overlying skin breakdown or leakage of ascites. 30-day morbidity and mortality included 5 (8%) superficial surgical site infections, 1 (2%) deep surgical site infection, and 7 (12%) organ space infections. Unrelated to the UHR, 10 (17%) patients had an unplanned return to the operating room, 16 (27%) were readmitted within 30 days of their index operation, and 1 (2%) patient died. With a mean follow-up of 21.8 months, 7 (18%) patients experienced an umbilical hernia recurrence.

CONCLUSION

Despite the high perioperative morbidity associated with the transplant procedure, concurrent primary UHR resulted in an acceptable long-term recurrence rate with minimal associated morbidity.

Retrospective study of porcine circovirus type 2 infection reveals a novel genotype PCV2f

Porcine postweaning multisystemic wasting syndrome (PMWS) caused by porcine circovirus type 2 (PCV2) is a disease causing severe economic losses annually worldwide to the pig industry. PCV2 infection was first reported in China in 2000, and currently has three major genotypes, PCV2a, b and d, circulating in this country. To further elucidate the origin and prevalence of PCV2 in China, 123 clinical pig tissue samples collected in 25 provinces between 1990 and 1999 were analysed by PCV2-specific PCR, resulting in identification of 23 PCV2 strains collected between 1996 and 1999. Phylogenetic analysis based on the nucleotide sequences of open reading frame 2 (ORF2) showed that 20 of the 23 grouped within PCV2a, while the remaining three strains formed an independent clade, so far unreported and therefore named PCV2f. This genotype shared lower sequence identity with other known genotypes. This study provides further understanding of the genetic diversity and evolution of PCV2 and has tracked PCV2 infection in China back to 1996 rather than 2000.

Abstract 5936: Comparison of carbonic anhydrase & activity between triple-negative & luminal breast cancer cells

Tumor microenvironment substantially influences the process of tumorigenesis. Extracellular acidification within the tumor microenvironment is an indicator of an aggressive cancer and a marker for poor patient outcome. In solid tumors, hypoxia leads to extracellular acidosis. Carbonic anhydrases (CA) are thought to regulate intracellular and extracellular pH (pHi and pHe, respectively). To explore the effect of CAs in breast cancer, we compared the expression and activity of two membrane bound CAs, CAIX and CAXII, between triple negative breast cancer cells (TNBCs) and luminal breast cancer cells (LBCs).

We chose five different TNBC and LBC lines. Our data show that, among the TNBC lines, CAIX expression increased in three of the five lines: HBL100, SUM159, and the new UFH-001 cells under hypoxic condition. UFH-001 cells also showed strong constitutive expression. None of these TNBC lines expressed CAXII or estrogen receptor (ER). In LBC lines, four of the five lines constitutively expressed CAXII: T47D, MCF7, SKBR and SUM52 cells. CAXII expression was not hypoxia-dependent. Each of the five luminal lines expressed ER. We also examined CA expression in a tumor graft model. In tumors grown from cells derived from TNBC patients, we observed CAIX expression in four of six sample sets. In tumors derived from ER-positive LBC patients, all five expressed CAXII.

We also used the 18O exchange method to assess CA activity. Two TNBC lines: UFH-001 and HBL100 cells showed that CAIX activity increased in hypoxic conditions which was blocked by an impermeant sulfonamide CA inhibitor (N3500). In the luminal lines, we detected CAXII activity in T47D and MCF7 cells that was also inhibited by N3500. Like CAXII protein expression in these cells, CAXII activity was not affected by hypoxia. We also evaluated the effect of pH on CA activity in TNBC and LBC lines. Both CAIX and CAXII showed increased activity in response to reduced pH, which is expected in a bicarbonate-based system. However, UFH-001 cells also exhibited a hypoxic-dependent increase in CAIX activity which is associated with increased protein expression.

In conclusion, these observations demonstrate that CAIX expression is associated with the TNBC phenotype. Based on our activity data, we would predict that CA activity in TNBC tumors will be sensitive to both hypoxia (based on enhanced expression) and reduced pH. This change in activity may serve to regulate pH in the tumor microenvironment favoring an aggressive phenotype. On the other hand, LBC tumors, which are ER-positive, are only associated with CAXII expression. In luminal cells, we expect that only pH and not hypoxia will affect CAXII activity. This may, in part, explain the more positive prognosis in patients with CAXII expression.

Note: This abstract was not presented at the meeting.

Citation Format: Zhijuan Chen, Mam Y. Mboge, Chingkuang Tu, Lingbao Ai, Coy Heldermon, Susan C. Frost. Comparison of carbonic anhydrase & activity between triple-negative & luminal breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5936. doi:10.1158/1538-7445.AM2017-5936

Correlation between circulating tumor cells EGFR expression and T cell subsets in advanced non-small cell lung cancer patients after tyrosine kinase inhibitor treatment

Research indicates that after EGFR-tyrosine kinase inhibitors (EGFR-TKIs) treatment of non-small cell lung cancer (NSCLC), patient immune function significantly improved, and that circulating tumor cells (CTCs) measurements and peripheral blood epidermal growth factor receptor (EGFR) mutation data can guide TKIs treatment. Sixty-six advanced NSCLC patients treated with TKIs were enrolled and CTCs, EGFR expression, T cell subsets and natural killer (NK) cells in peripheral blood were measured using flow cytometry before and after treatment and assessed with respect to patient prognosis. CTCs and EGFR expression were negatively correlated with cellular immune function and immune recovery after EGFR-TKI treatment. Thus, CD4+/ CD8+ ratios and NK cells may be useful prognostic indicators for advanced NSCLC patients who receive TKIs treatment.

The Structure of Carbonic Anhydrase IX Is Adapted for Low-pH Catalysis

Human carbonic anhydrase IX (hCA IX) expression in many cancers is associated with hypoxic tumors and poor patient outcome. Inhibitors of hCA IX have been used as anticancer agents with some entering Phase I clinical trials. hCA IX is transmembrane protein whose catalytic domain faces the extracellular tumor milieu, which is typically associated with an acidic microenvironment. Here, we show that the catalytic domain of hCA IX (hCA IX-c) exhibits the necessary biochemical and biophysical properties that allow for low pH stability and activity. Furthermore, the unfolding process of hCA IX-c appears to be reversible, and its catalytic efficiency is thought to be correlated directly with its stability between pH 3.0 and 8.0 but not above pH 8.0. To rationalize this, we determined the X-ray crystal structure of hCA IX-c to 1.6 Å resolution. Insights from this study suggest an understanding of hCA IX-c stability and activity in low-pH tumor microenvironments and may be applicable to determining pH-related effects on enzymes.

Mate choice and host discrimination behavior of the parasitoid Trichogramma chilonis

Trichogramma chilonis Ishii (Hymenoptera: Trichogrammatidae) is an important natural enemy of many species of lepidopterous pests and a widely used biological control agent. Detailed knowledge about its mate choice and host discrimination behavior is lacking. In this study, we studied the mate choice and host discrimination behavior of T. chilonis in experimental arenas through video tracking. Males' mate recognition capacity was realized by perceiving the sex pheromone of females. When offered two females of different species, male could distinguish the conspecific female from Trichogrammatoidea bactrae Nagaraja (Hymenoptera: Trichogrammatidae), a species that has overlapping hosts with T. chilonis. When placed with two females of different mating status, male preferred mating with the virgin female to the mated female. T. chilonis females could distinguish unparasitized host eggs from parasitized ones (parasitized by conspecific females or heterospecific females). They preferred to stay on and lay eggs in unparasitized host eggs. When T. chilonis females were only provided with parasitized host eggs (parasitized by T. chilonis and T. bactrae females), conspecific superparasitism occurred more often than heterospecific superparasitism. Furthermore, the host egg discrimination ability of T. chilonis females was mainly achieved through antennal perception.

Substrate Binding Mode and Molecular Basis of a Specificity Switch in Oxalate Decarboxylase

Oxalate decarboxylase (OxDC) catalyzes the conversion of oxalate into formate and carbon dioxide in a remarkable reaction that requires manganese and dioxygen. Previous studies have shown that replacing an active-site loop segment Ser¹⁶¹-Glu¹⁶²-Asn¹⁶³-Ser¹⁶⁴ in the N-terminal domain of OxDC with the cognate residues Asp¹⁶¹-Ala¹⁶²-Ser-¹⁶³-Asn¹⁶⁴ of an evolutionarily related, Mn-dependent oxalate oxidase gives a chimeric variant (DASN) that exhibits significantly increased oxidase activity. The mechanistic basis for this change in activity has now been investigated using membrane inlet mass spectrometry (MIMS) and isotope effect (IE) measurements. Quantitative analysis of the reaction stoichiometry as a function of oxalate concentration, as determined by MIMS, suggests that the increased oxidase activity of the DASN OxDC variant is associated with only a small fraction of the enzyme molecules in solution. In addition, IE measurements show that C–C bond cleavage in the DASN OxDC variant proceeds via the same mechanism as in the wild-type enzyme, even though the Glu¹⁶² side chain is absent. Thus, replacement of the loop residues does not modulate the chemistry of the enzyme-bound Mn(II) ion. Taken together, these results raise the possibility that the observed oxidase activity of the DASN OxDC variant arises from an increased level of access of the solvent to the active site during catalysis, implying that the functional role of Glu¹⁶² is to control loop conformation. A 2.6 Å resolution X-ray crystal structure of a complex between oxalate and the Co(II)-substituted ΔE162 OxDC variant, in which Glu¹⁶² has been deleted from the active site loop, reveals the likely mode by which the substrate coordinates the catalytically active Mn ion prior to C–C bond cleavage. The “end-on” conformation of oxalate observed in the structure is consistent with the previously published V/K IE data and provides an empty coordination site for the dioxygen ligand that is thought to mediate the formation of Mn(III) for catalysis upon substrate binding.

Activity and anion inhibition studies of the α-carbonic anhydrase from Thiomicrospira crunogena XCL-2 Gammaproteobacterium

Thiomicrospira crunogena XCL-2 expresses an α-carbonic anhydrase (TcruCA). Sequence alignments reveal that TcruCA displays a high sequence identity (>30%) relative to other α-CAs. This includes three conserved histidines that coordinate the active site zinc, a histidine proton shuttling residue, and opposing hydrophilic and hydrophobic sides that line the active site. The catalytic efficiency of TcruCA is considered moderate relative to other α-CAs (k(cat)/K(M)=1.1×10(7) M(-1) s(-1)), being a factor of ten less efficient than the most active α-CAs. TcruCA is also inhibited by anions with Cl(-), Br(-), and I(-), all showing Ki values in the millimolar range (53-361 mM). Hydrogen sulfide (HS(-)) revealed the highest affinity for TcruCA with a Ki of 1.1 μM. It is predicted that inhibition of TcruCA by HS(-) (an anion commonly found in the environment where Thiomicrospira crunogena is located) is a way for Thiomicrospira crunogena to regulate its carbon-concentrating mechanism (CCM) and thus the organism's metabolic functions. Results from this study provide preliminary insights into the role of TcruCA in the general metabolism of Thiomicrospira crunogena.

A sucrose-binding site provides a lead towards an isoform-specific inhibitor of the cancer-associated enzyme carbonic anhydrase IX

Human carbonic anhydrase (CA; EC 4.2.1.1) isoform IX (CA IX) is an extracellular zinc metalloenzyme that catalyzes the reversible hydration of CO2 to HCO3(-), thereby playing a role in pH regulation. The majority of normal functioning cells exhibit low-level expression of CA IX. However, in cancer cells CA IX is upregulated as a consequence of a metabolic transition known as the Warburg effect. The upregulation of CA IX for cancer progression has drawn interest in it being a potential therapeutic target. CA IX is a transmembrane protein, and its purification, yield and crystallization have proven challenging to structure-based drug design, whereas the closely related cytosolic soluble isoform CA II can be expressed and crystallized with ease. Therefore, we have utilized structural alignments and site-directed mutagenesis to engineer a CA II that mimics the active site of CA IX. In this paper, the X-ray crystal structure of this CA IX mimic in complex with sucrose is presented and has been refined to a resolution of 1.5 Å, an Rcryst of 18.0% and an Rfree of 21.2%. The binding of sucrose at the entrance to the active site of the CA IX mimic, and not CA II, in a non-inhibitory mechanism provides a novel carbohydrate moiety binding site that could be further exploited to design isoform-specific inhibitors of CA IX.

Structural and biophysical characterization of the α-carbonic anhydrase from the gammaproteobacterium Thiomicrospira crunogena XCL-2: insights into engineering thermostable enzymes for CO2 sequestration

Biocatalytic CO2 sequestration to reduce greenhouse-gas emissions from industrial processes is an active area of research. Carbonic anhydrases (CAs) are attractive enzymes for this process. However, the most active CAs display limited thermal and pH stability, making them less than ideal. As a result, there is an ongoing effort to engineer and/or find a thermostable CA to fulfill these needs. Here, the kinetic and thermal characterization is presented of an α-CA recently discovered in the mesophilic hydrothermal vent-isolate extremophile Thiomicrospira crunogena XCL-2 (TcruCA), which has a significantly higher thermostability compared with human CA II (melting temperature of 71.9°C versus 59.5°C, respectively) but with a tenfold decrease in the catalytic efficiency. The X-ray crystallographic structure of the dimeric TcruCA shows that it has a highly conserved yet compact structure compared with other α-CAs. In addition, TcruCA contains an intramolecular disulfide bond that stabilizes the enzyme. These features are thought to contribute significantly to the thermostability and pH stability of the enzyme and may be exploited to engineer α-CAs for applications in industrial CO2 sequestration.

Structural and catalytic effects of proline substitution and surface loop deletion in the extended active site of human carbonic anhydrase II

Bioengineering of a thermophilic enzyme starting from a mesophilic scaffold has proven to be a significant challenge, as several stabilizing elements have been proposed to be the foundation of thermal stability, including disulfide bridges, surface loop reduction, ionic pair networks, proline substitutions and aromatic clusters. This study emphasizes the effect of increasing the rigidity of human carbonic anhydrase II (HCA II; EC 4.2.1.1) via incorporation of proline residues at positions 170 and 234, which are located in surface loops that are able to accommodate restrictive main-chain conformations without rearrangement of the surrounding peptide backbone. Additionally, the effect of the compactness of HCA II was examined by deletion of a surface loop (residues 230-240) that had been previously identified as a possible source of thermal stability for the hyperthermophilic carbonic anhydrase isolated from the bacterium Sulfurihydrogenibium yellowstonense YO3AOP1. Differential scanning calorimetry analysis of these HCA II variants revealed that these structural modifications had a minimum effect on the thermal stability of the enzyme, while kinetic studies showed unexpected effects on the catalytic efficiency and proton transfer rates. X-ray crystallographic analysis of these HCA II variants showed that the electrostatic potential and configuration of the highly acidic loop (residues 230-240) play an important role in its high catalytic activity. Based on these observations and previous studies, a picture is emerging of the various components within the general structural architecture of HCA II that are key to stability. These elements may provide blueprints for rational thermal stability engineering of other enzymes.

DATABASE

Structural data have been submitted to the Protein Data Bank under accession numbers 4QK1 (K170P), 4QK2 (E234P) and 4QK3 (Δ230-240).

Wnt5a is involved in the pathogenesis of cutaneous lichen planus

BACKGROUND

Cutaneous lichen planus (CLP) is a chronic inflammatory and immune-mediated disease. Wnt5a is one of the most extensively studied Wnt proteins, and has important functions in stimulating inflammation, cell proliferation, cell fate determination and cell differentiation. Wnt5a expression in CLP has not been comprehensively studied to date.

AIM

To determine the expression and distribution of Wnt5a in CLP.

METHODS

Skin samples were obtained from patients with CLP and healthy controls (HCs). The WNT5A gene was detected by real-time quantitative PCR, and Wnt5a protein by immunohistochemical analysis and western blotting.

RESULTS

WNT5A mRNA was upregulated in CLP samples compared with the HC skin samples (P < 0.001). Wnt5a protein was overexpressed in all layers of the epidermis and dermis in CLP lesions compared with HC skin (all P < 0.001). These results were confirmed by western blotting.

CONCLUSIONS

The data presented in this study suggest that Wnt5a pathway may play an important role in the pathogenesis of CLP.

NMR studies of active-site properties of human carbonic anhydrase II by using (15) N-labeled 4-methylimidazole as a local probe and histidine hydrogen-bond correlations

By using a combination of liquid and solid-state NMR spectroscopy, (15) N-labeled 4-methylimidazole (4-MI) as a local probe of the environment has been studied: 1) in the polar, wet Freon CDF3 /CDF2 Cl down to 130 K, 2) in water at pH 12, and 3) in solid samples of the mutant H64A of human carbonic anhydrase II (HCA II). In the latter, the active-site His64 residue is replaced by alanine; the catalytic activity is, however, rescued by the presence of 4-MI. For the Freon solution, it is demonstrated that addition of water molecules not only catalyzes proton tautomerism but also lifts its quasidegeneracy. The possible hydrogen-bond clusters formed and the mechanism of the tautomerism are discussed. Information about the imidazole hydrogen-bond geometries is obtained by establishing a correlation between published (1) H and (15) N chemical shifts of the imidazole rings of histidines in proteins. This correlation is useful to distinguish histidines embedded in the interior of proteins and those at the surface, embedded in water. Moreover, evidence is obtained that the hydrogen-bond geometries of His64 in the active site of HCA II and of 4-MI in H64A HCA II are similar. Finally, the degeneracy of the rapid tautomerism of the neutral imidazole ring His64 reported by Shimahara et al. (J. Biol. Chem.- 2007, 282, 9646) can be explained with a wet, polar, nonaqueous active-site conformation in the inward conformation, similar to the properties of 4-MI in the Freon solution. The biological implications for the enzyme mechanism are discussed.

Human carbonic anhydrase II-cyanate inhibitor complex: putting the debate to rest

The binding of anions to carbonic anhydrase II (CA II) has been attributed to high affinity for the active-site zinc. An anion of interest is cyanate, for which contrasting binding modes have been reported in the literature. Previous spectroscopic data have shown cyanate behaving as an inhibitor, directly binding to the zinc, in contrast to previous crystallographic data that implied that cyanate acts as a substrate mimic that is not directly bound to the zinc but overlaps with the binding site of the substrate CO2. Wild-type and the V207I variant of CA II have been expressed and X-ray crystal structures of their cyanate complexes have been determined to 1.7 and 1.5 Å resolution, respectively. The rationale for the V207I CA II variant was its close proximity to the CO2-binding site. Both structures clearly show that the cyanate binds directly to the zinc. In addition, inhibition constants (∼40 µM) were measured using (18)O-exchange mass spectrometry for wild-type and V207I CA II and were similar to those determined previously (Supuran et al., 1997). Hence, it is concluded that under the conditions of these experiments the binding of cyanate to CA II is directly to the zinc, displacing the zinc-bound solvent molecule, and not in a site that overlaps with the CO2 substrate-binding site.

Insights into Activity Enhancement of H64A Carbonic Anhydrase by Imidazoles

Human carbonic anhydrases (CAs) are zinc metalloenzymes that catalyze the hydration and dehydration of CO2 and HCO3-, respectively. The reaction follows a ping-pong mechanism, where the rate limiting step is the transfer of a proton from the zinc-bound solvent out of the active site, via His64 which is widely believed to be the proton shuttling residue. Being involved in a number of physiological processes such as respiration, pH regulation, ureagenesis etc., CAs are therapeutic targets for inhibition to treat various diseases. However, the physiologically dominant isoform is CA II, which is catalytically highly efficient and is easily crystallizable. Thus, most of our knowledge in the design of CA inhibitors with pharmacological applications is based on detailed CA II crystallographic studies. The catalytic activity of a variant of CA II in which His64 is replaced with Ala (H64A CA II) can be enhanced by exogenous proton donors/acceptors, usually derivatives of imidazoles and pyridines. This article examines the mechanism through which this activity enhancement might occur. X-ray crystal structures of H64A CA II in complex with four imidazole derivatives have been determined and reveal multiple binding sites. We have identified two molecules of imidazoles that bind in region that is otherwise occupied by the "in" and "out" dual conformation of the side chain of His64 in wild-type CA II. The data presented here not only corroborates the importance of imidazole side chain of His64 in proton transfer during CA catalysis, but also provides a complete structural understanding of the mechanism by which imidazoles enhance (and inhibit when used in higher concentrations) the activity of H64A CA II. In addition to inhibition of CA by these imidazoles, the presence of a large number of binding sites also gives insights and preliminary data required to fragment addition approach of drug design against CA.

Membrane inlet mass spectrometry reveals that Ceriporiopsis subvermispora bicupin oxalate oxidase is inhibited by nitric oxide

Membrane inlet mass spectrometry (MIMS) uses a semipermeable membrane as an inlet to a mass spectrometer for the measurement of the concentration of small uncharged molecules in solution. We report the use of MIMS to characterize the catalytic properties of oxalate oxidase (E.C. 1.2.3.4) from Ceriporiopsis subvermispora (CsOxOx). Oxalate oxidase is a manganese dependent enzyme that catalyzes the oxygen-dependent oxidation of oxalate to carbon dioxide in a reaction that is coupled with the formation of hydrogen peroxide. CsOxOx is the first bicupin enzyme identified that catalyzes this reaction. The MIMS method of measuring OxOx activity involves continuous, real-time direct detection of oxygen consumption and carbon dioxide production from the ion currents of their respective mass peaks. (13)C2-oxalate was used to allow for accurate detection of (13)CO2 (m/z 45) despite the presence of adventitious (12)CO2. Steady-state kinetic constants determined by MIMS are comparable to those obtained by a continuous spectrophotometric assay in which H2O2 production is coupled to the horseradish peroxidase catalyzed oxidation of 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulphonic acid). Furthermore, we used MIMS to determine that NO inhibits the activity of the CsOxOx with a KI of 0.58±0.06 μM.