Isolation and characterization of a high affinity peptide inhibitor of ClC-2 chloride channels

The ClC protein family includes voltage-gated chloride channels and chloride/proton exchangers. In eukaryotes, ClC proteins regulate membrane potential of excitable cells, contribute to epithelial transport, and aid in lysosomal acidification. Although structure/function studies of ClC proteins have been aided greatly by the available crystal structures of a bacterial ClC chloride/proton exchanger, the availability of useful pharmacological tools, such as peptide toxin inhibitors, has lagged far behind that of their cation channel counterparts. Here we report the isolation, from Leiurus quinquestriatus hebraeus venom, of a peptide toxin inhibitor of the ClC-2 chloride channel. This toxin, GaTx2, inhibits ClC-2 channels with a voltage-dependent apparent K(D) of approximately 20 pm, making it the highest affinity inhibitor of any chloride channel. GaTx2 slows ClC-2 activation by increasing the latency to first opening by nearly 8-fold but is unable to inhibit open channels, suggesting that this toxin inhibits channel activation gating. Finally, GaTx2 specifically inhibits ClC-2 channels, showing no inhibitory effect on a battery of other major classes of chloride channels and voltage-gated potassium channels. GaTx2 is the first peptide toxin inhibitor of any ClC protein. The high affinity and specificity displayed by this toxin will make it a very powerful pharmacological tool to probe ClC-2 structure/function.

Reawakening retrocyclins: ancestral human defensins active against HIV-1

Human alpha and beta defensins contribute substantially to innate immune defenses against microbial and viral infections. Certain nonhuman primates also produce theta-defensins—18 residue cyclic peptides that act as HIV-1 entry inhibitors. Multiple human theta-defensin genes exist, but they harbor a premature termination codon that blocks translation. Consequently, the theta-defensins (retrocyclins) encoded within the human genome are not expressed as peptides. In vivo production of theta-defensins in rhesus macaques involves the post-translational ligation of two nonapeptides, each derived from a 12-residue “demidefensin” precursor. Neither the mechanism of this unique process nor its existence in human cells is known. To ascertain if human cells retained the ability to process demidefensins, we transfected human promyelocytic cells with plasmids containing repaired retrocyclin-like genes. The expected peptides were isolated, their sequences were verified by mass spectrometric analyses, and their anti-HIV-1 activity was confirmed in vitro. Our study reveals for the first time, to our knowledge, that human cells have the ability to make cyclic theta-defensins. Given this evidence that human cells could make theta-defensins, we attempted to restore endogenous expression of retrocyclin peptides. Since human theta-defensin genes are transcribed, we used aminoglycosides to read-through the premature termination codon found in the mRNA transcripts. This treatment induced the production of intact, bioactive retrocyclin-1 peptide by human epithelial cells and cervicovaginal tissues. The ability to reawaken retrocyclin genes from their 7 million years of slumber using aminoglycosides could provide a novel way to secure enhanced resistance to HIV-1 infection.

Defensins are a large family of small antimicrobial peptides that contribute to host defense against a broad spectrum of pathogens. In primates, defensins are divided into three subfamilies—alpha, beta, and theta—on the basis of their disulfide bonding pattern. Theta-defensins were the most recently identified defensin subfamily, isolated initially from white blood cells and bone marrow of rhesus monkeys. They are the only known cyclic peptides in mammals and act primarily by preventing viruses such as HIV-1 from entering cells. Whereas theta-defensin genes are intact in Old World monkeys, in humans they have a premature stop codon that prevents their expression; they thus exist as pseudogenes. In this work, we reveal that, upon correction of the premature termination codon in theta-defensin pseudogenes, human myeloid cells produce cyclic, antiviral peptides (which we have termed “retrocyclins”), indicating that the cells retain the intact machinery to make cyclic peptides. Furthermore, we exploited the ability of aminoglycoside antibiotics to read-through the premature termination codon within retrocyclin transcripts to produce functional peptides that are active against HIV-1. Given that the endogenous production of retrocyclins could also be restored in human cervicovaginal tissues, we propose that aminoglycoside-based topical microbicides might be useful in preventing sexual transmission of HIV-1.

Repairing an ancestral human pseudogene by mutagenesis, or by the application of aminoglycosides to suppress the termination codon, can restore the production of retrocyclins, which are peptides of the defensin family that are remarkable inhibitors of HIV-1 entry into cells.

Cationic polypeptides contribute to the anti-HIV-1 activity of human seminal plasma

Mucosal surfaces of the reproductive tract as well as their secretions have important roles in preventing sexual transmission of HIV-1. In the current study, the majority of the intrinsic anti-HIV-1 activity of human seminal plasma (SP) was determined to reside in the cationic polypeptide fraction. Antiviral assays utilizing luciferase reporter cells and lymphocytic cells revealed the ability of whole SP to prevent HIV-1 infection, even when SP was diluted 3200-fold. Subsequent fractionation by continuous flow acid-urea (AU)-PAGE and antiviral testing revealed that cationic polypeptides within SP were responsible for the majority of anti-HIV-1 activity. A proteomic approach was utilized to resolve and identify 52 individual cationic polypeptides that contribute to the aggregate anti-HIV-1 activity of SP. One peptide fragment of semenogelin I, termed SG-1, was purified from SP by a multistep chromatographic approach, protein sequenced, and determined to exhibit anti-HIV-1 activity against HIV-1. Anti-HIV-1 activity was transient, as whole SP incubated for prolonged time intervals exhibited a proportional decrease in anti-HIV-1 activity that was directly attributed to the degradation of semenogelin I peptides. Collectively, these results indicate that the cationic polypeptide fraction of SP is active against HIV-1, and that semenogelin-derived peptides contribute to the intrinsic anti-HIV-1 activity of SP.

Reawakening Retrocyclins: Ancestral Human Defensins Active Against HIV-1 (133.49)

Human alpha and beta defensins contribute substantially to innate immune defenses against microbial and viral infections. Certain nonhuman primates also produce theta-defensins - 18 residue cyclic peptides that act as HIV-1 entry inhibitors. Multiple human theta-defensin genes exist, but they harbor a premature stop codon that blocks translation. Consequently, the theta-defensins (retrocyclins) encoded within the human genome are not expressed as peptides. In vivo production of theta-defensins in rhesus macaques involves the post-translational ligation of two nonapeptides. Neither the mechanism of this unique process nor its existence in human cells is known. To ascertain if human cells retained the ability to process demidefensins, we transfected human promyelocytic cells with plasmids containing repaired retrocyclin-like genes. The expected peptides were isolated, their sequences were verified by mass spectrometric analyses, and their anti-HIV-1 activity was confirmed in vitro. Our study reveals for the first time that human cells have the ability to make cyclic theta-defensins. Given this evidence that human cells could make theta-defensins, we attempted to restore endogenous expression of retrocyclin peptides. Since human theta-defensin genes are transcribed, we used aminoglycosides to read-through the premature stop codon found in the mRNA transcripts. This treatment induced the production of intact, bioactive retrocyclin-1 peptide by human epithelial cells and cervicovaginal tissues. Since retrocyclins are broadly antiviral, the ability to reawaken retrocyclin genes from their 7 million years of slumber could provide a novel way to secure enhanced resistance to several major viral pathogens. AI052017; AI065430

Double-balloon endoscopy for retrograde cholangiography in patients with choledochojejunostomy and Roux-en-Y reconstruction

BACKGROUND

Choledochojejunal anastomoses with Roux-en-Y reconstruction excludes the biliary tract from conventional endoscopic retrograde cholangiography (ERC) with standard endoscopes due to the length of the interposed small bowel segment. Double-balloon enteroscopy (DBE) facilitates deep insertion into the small bowel and may be used to perform ERC in these patients. In the present case series we report our experience with diagnostic and therapeutic double-balloon ERC in patients with choledochojejunostomy to a long Roux-en-Y loop previously unavailable for standard length endoscopes.

PATIENTS AND METHODS

Between December 2004 and May 2008 15 patients (mean age: 60.2 years) with choledochojejunal anastomosis underwent a total of 25 DBE-ERC procedures.

RESULTS

Cannulation of the bile ducts was achieved in 22 / 25 procedures (84 %). Twenty-one therapeutic interventions, including stone removal, biliary duct dilation, stent placement and removal of previously placed stents were performed during 16 procedures in 8 patients. The mean total duration time of the procedures was 74.6 +/- 25.0 minutes. Postinterventional self-limiting fever occurred after 4 procedures in 3 patients with cholangitis. After therapeutic interventions all patients had a significant drop of bilirubin levels and all except one patient were free of complaints (follow-up 10.4 +/- 8.6 months).

CONCLUSIONS

The DBE system permits diagnostic and therapeutic ERC in surgically modified anatomy, previously unavailable for endoluminal access. In our experience this procedure is safe and has a high success rate with a favourable patient outcome.

Dual mechanisms of CYP3A protein regulation by proinflammatory cytokine stimulation in primary hepatocyte cultures

Whereas many cytochrome P450 enzymes are transcriptionally suppressed by inflammatory stimuli, down-regulation of CYP2B protein by the inflammatory cytokine interleukin (IL)-1beta is nitric oxide (NO)-dependent and occurs via polyubiquitination and proteasomal degradation. Here, we used iTRAQ proteomic analysis to search for other proteins that are potentially down-regulated by cellular NO in cultured rat hepatocytes, and we identified CYP3A1 as one such protein. Therefore, we examined whether CYP3A proteins, like CYP2B, undergo NO- and proteasome-dependent degradation in response to cytokine treatment of rat hepatocytes. In cultured rat hepatocytes treated with phenobarbital, IL-1beta stimulation failed to down-regulate CYP3A1 mRNA within 24 h of treatment, whereas CYP3A protein was down-regulated to 40% of control within 6 h, showing the post-transcriptional down-regulation of CYP3A1 protein. The down-regulation of CYP3A after 9 h of stimulation by IL-1beta was attenuated by inhibitors of NO synthase (NOS) and of the proteasome, showing NO- and proteasome-dependent down-regulation at earlier time points. However, the down-regulation of CYP3A evoked by IL-1beta measured 24 h after stimulation was not affected by the inhibition of NOS or by proteasomal inhibitors, showing that CYP3A1 down-regulation at later time points is NO- and proteasome-independent. IL-6, which did not evoke NO production nor affect CYP3A1 mRNA within 24 h, produced a delayed proteasome-independent down-regulation as well. Taken together, these observations show a novel dual mode of post-transcriptional CYP3A down-regulation by cytokines: NO- and proteasome-dependent at earlier time points and NO- and proteasome-independent at later times.

Hermansky-Pudlak syndrome protein complexes associate with phosphatidylinositol 4-kinase type II alpha in neuronal and non-neuronal cells

The Hermansky-Pudlak syndrome is a disorder affecting endosome sorting. Disease is triggered by defects in any of 15 mouse gene products, which are part of five distinct cytosolic molecular complexes: AP-3, homotypic fusion and vacuole protein sorting, and BLOC-1, -2, and -3. To identify molecular associations of these complexes, we used in vivo cross-linking followed by purification of cross-linked AP-3 complexes and mass spectrometric identification of associated proteins. AP-3 was co-isolated with BLOC-1, BLOC-2, and homotypic fusion and vacuole protein sorting complex subunits; clathrin; and phosphatidylinositol-4-kinase type II alpha (PI4KIIalpha). We previously reported that this membrane-anchored enzyme is a regulator of AP-3 recruitment to membranes and a cargo of AP-3 ( Craige, B., Salazar, G., and Faundez, V. (2008) Mol. Biol. Cell 19, 1415-1426 ). Using cells deficient in different Hermansky-Pudlak syndrome complexes, we identified that BLOC-1, but not BLOC-2 or BLOC-3, deficiencies affect PI4KIIalpha inclusion into AP-3 complexes. BLOC-1, PI4KIIalpha, and AP-3 belong to a tripartite complex, and down-regulation of either PI4KIIalpha, BLOC-1, or AP-3 complexes led to similar LAMP1 phenotypes. Our analysis indicates that BLOC-1 complex modulates the association of PI4KIIalpha with AP-3. These results suggest that AP-3 and BLOC-1 act, either in concert or sequentially, to specify sorting of PI4KIIalpha along the endocytic route.

Computed virtual chromoendoscopy versus standard colonoscopy with targeted indigocarmine chromoscopy: a randomised multicentre trial

OBJECTIVE

Colonoscopy is the accepted gold standard for screening of neoplastic colorectal lesions, but the substantial miss rate remains a challenge. Computed virtual chromoendoscopy with the Fujinon intelligent colour enhancement (FICE) system is a new dyeless imaging technique that might allow higher rates of adenoma detection.

METHODS

This is a prospective randomised five tertiary care centre trial of colonoscopy in the FICE mode versus standard colonoscopy with targeted indigocarmine chromoscopy (control group) in consecutive patients attending for routine colonoscopy. Histopathology of detected lesions was confirmed by evaluation of endoscopic resection or biopsy specimens.

RESULTS

871 patients were enrolled, and 764 patients (344 female, mean age 64 years) were subjected to final analysis (368 in the FICE group, 396 in the control group). In total, 236 adenomas (mean of 0.64 per case) were detected in the FICE group and 271 adenomas (mean of 0.68 per case) in the control group (p = 0.92). There was no statistically significant difference in the percentage of patients with >or=1 adenoma between the control group (35.4%) and the FICE group (35.6%) (p = 1.0). For the differential diagnosis of adenomas and non-neoplastic polyps, the sensitivity of FICE (92.7%) was comparable with that of indigocarmine (90.4%) (p = 0.44).

CONCLUSIONS

At colonoscopy, adenoma detection rates are not improved by virtual chromoendoscopy with the FICE system compared with white light endoscopy with targeted indigocarmine spraying. However, FICE can effectively substitute for chromoscopy concerning the differentiation of neoplastic and non-neoplastic lesions.

"Dry biopsies" with spraying of dilute epinephrine optimize biopsy mapping of long segment Barrett's esophagus

BACKGROUND AND STUDY AIMS

For surveillance of Barrett's esophagus random stepwise four-quadrant biopsy (4QB) is recommended for detecting macroscopically occult neoplasias. Thorough performance of the systematic protocol is commonly hampered by poor visibility due to oozing from biopsy sites. Topical application of dilute epinephrine may prevent bleeding by vasoconstriction of superficial microvessels and might therefore enable "dry biopsy" sampling. The aim of this study was to examine the safety and efficacy of spraying dilute epinephrine for optimal 4QB mapping of Barrett's esophagus.

PATIENTS AND METHODS

In this prospective, double-blind trial 40 patients with known long segment Barrett's esophagus were randomly allocated to undergo spraying with either dilute epinephrine (1 : 20 000) (epinephrine group; n = 20) or saline (control group; n = 20) before 4QB sampling. During endoscopies patients received continuous monitoring of vital parameters. Endoscopists blinded to randomization assessed visibility scores during biopsy sampling. Additionally, electronically stored images of the Barrett's esophagus segment after 4QB sampling were evaluated by blinded assessors.

RESULTS

The mean length of Barrett's segments was 5.5 +/- 1.8 cm and the mean number of 4QBs was 12.5 +/- 3.6 with no statistically significant differences between control and epinephrine groups. Epinephrine spraying did not affect patients' vital parameters. Visualization ratings by endoscopists on site and by the assessors of the stored images were significantly better in the epinephrine compared with the control group (P < 0.05). Moreover, epinephrine spraying reduced the time for 4QB sampling (P = 0.015) and the mean number of saline flushes needed to maintain visibility (P = 0.0003).

CONCLUSIONS

The novel "dry biopsy" technique with spraying of dilute epinephrine is safe, and facilitates thorough performance of systematic 4QB mapping of Barrett's esophagus by improvement of visibility.

A rapid LC-FTMS method for the analysis of cysteine, cystine and cysteine/cystine steady-state redox potential in human plasma

BACKGROUND

The steady-state redox potential of the cysteine/cystine couple in human plasma provides a measure of oxidative stress, yet available assays are limited by either specificity or speed of assay.

METHOD

The present study evaluated the use of LC-FTMS for identification based on accurate mass combined with quantification by stable isotopic dilution to rapidly determine cysteine and cystine concentration and cysteine/cystine steady-state redox potential in human plasma.

RESULTS

A simple extraction procedure followed by a rapid LC separation eluted cysteine in 4 min and cystine in 1.5 min with simultaneous measurement of glutathione (GSH) and glutathione disulfide (GSSG). A study of five young (mean age=25.7) subjects and 5 older (mean age=67.8 y) subjects showed an increased oxidation with age.

CONCLUSIONS

The analysis by LC-FTMS is suitable for high-throughput analysis of plasma cysteine, cystine and cysteine/cystine steady-state redox potential as clinical measures of oxidative stress.

Targeting tissue factor-expressing tumor angiogenesis and tumors with EF24 conjugated to factor VIIa

Tissue factor (TF) is aberrantly expressed on tumor vascular endothelial cells (VECs) and on cancer cells in many malignant tumors, but not on normal VECs, making it a promising target for cancer therapy. As a transmembrane receptor for coagulation factor VIIa (fVIIa), TF forms a high-affinity complex with its cognate ligand, which is subsequently internalized through receptor-mediated endocytosis. Accordingly, we developed a method for selectively delivering EF24, a potent synthetic curcumin analog, to TF-expressing tumor vasculature and tumors using fVIIa as a drug carrier. EF24 was chemically conjugated to fVIIa through a tripeptide-chloromethyl ketone. After binding to TF-expressing targets by fVIIa, EF24 will be endocytosed along with the drug carrier and will exert its cytotoxicity. Our results showed that the conjugate inhibits vascular endothelial growth factor-induced angiogenesis in a rabbit cornea model and in a Matrigel model in athymic nude mice. The conjugate-induced apoptosis in tumor cells and significantly reduced tumor size in human breast cancer xenografts in athymic nude mice as compared with the unconjugated EF24. By conjugating potent drugs to fVIIa, this targeted drug delivery system has the potential to enhance therapeutic efficacy, while reducing toxic side effects. It may also prove to be useful for treating drug-resistant tumors and micro-metastases in addition to primary tumors.

Severe paraneoplastic gastroparesis associated with anti-Hu antibodies preceding the manifestation of small-cell lung cancer

Gastroparesis is a common but challenging disorder which can be idiopathic or induced by a variety of underlying diseases, most frequently by diabetes, or post-surgical conditions of the upper abdomen. Clinicians must also consider rare causes of gastric motor dysfunction, such as collagen vascular disorders and paraneoplastic syndromes. Here we present the case of a patient with severe gastroparesis, who was admitted to our hospital for vomiting and weight loss of 25 kg within four months. Endoscopy showed a dilated fluid-filled stomach without peristalsis but no obstruction. High titres of anti-Hu antibodies were detected in patient's serum, supporting the diagnosis of severe paraneoplastic gastroparesis with chronic intestinal pseudo-obstruction. Fine-needle aspiration of suspicious mediastinal lymph nodes guided by endoscopic ultrasound revealed lymphatic metastases of a small-cell lung carcinoma. Jejunal tube feeding and chemotherapy with carboplatin and etoposide were initiated. Paraneoplastic gastrointestinal dysmotility is rare, however, clinicians should consider this differential diagnosis in otherwise unexplained gastrointestinal motor dysfunction. The pathophysiology of paraneoplastic gastroparesis, the diagnostic relevance of anti-Hu antibodies as well as therapeutic options are discussed.

Increased mitochondrial thioredoxin 2 potentiates N-ethylmaleimide-induced cytotoxicity

Thioredoxin 2 (Trx2) is a mitochondrially localized antioxidant and antiapoptotic protein, whose functions are mainly dependent on the conserved cysteines at its redox active center. In the current study, we showed by mass spectrometry that a thiol alkylating agent, N-ethylmaleimide (NEM), alkylated a single cysteine residue in the active center of Trx2. The interaction between NEM and Trx2 in intact cells was confirmed by redox Western analysis. Overexpression of Trx2 in cultured 143B osteosarcoma cells caused increased sensitivity to NEM. Covalent modification by NEM resulted in a dominant-negative effect and increased the interaction between Trx2 and peroxiredoxin 3 (Prx3). Our data suggest that the alkylation of the essential thiol(s) of Trx2 has profound impact on the mitochondrial redox circuitry and that such effects are distinct from the responses to agents causing reversible disulfide bond formation between the vicinal dithiols in the active center.

Reactive aldehyde modification of thioredoxin-1 activates early steps of inflammation and cell adhesion

Several lines of evidence suggest that an increase in aldehyde-modified proteins is associated with development of atherosclerosis. Acrolein and 4-hydroxynonenal (HNE) are reactive aldehydes generated during active inflammation as a consequence of lipid peroxidation; both react with protein thiols, including thioredoxin-1 (Trx1), a protein recently found to regulate antioxidant function in endothelial cells. The present study examined whether acrolein or HNE modification of Trx1 could potentiate monocyte adhesion to endothelial cells, an early event of atherosclerosis. We examined the function of acrolein and HNE-modified Trx1 in the regulation of the early events of atherosclerosis using cultured aortic endothelial cells as a vascular model system, for in vitro enzymatic assay, and in mass spectrometry analysis. Our data show that acrolein and HNE at 1:1 ratios with Trx1 modified Cys-73 and inhibited activity. In endothelial cells, adducts were detected at concentrations as low as 1 mumol/L including conditions in which there was no detectable change in glutathione. Acrolein and HNE modification of Trx1 was associated with increased production of reactive oxygen species. Microinjection of acrolein- and HNE-modified Trx1 into endothelial cells stimulated monocyte adhesion. Chemical modification of Trx1 by common environmental and endogenously generated reactive aldehydes can contribute to atherosclerosis development by interfering with antioxidant and redox signaling functions of Trx1.

ABRF ESRG 2006 study: Edman sequencing as a method for polypeptide quantitation

The Edman Sequencing Research Group (ESRG) designs studies on the use of Edman degradation for protein and peptide analysis. These studies provide a means for participating laboratories to compare their analyses against a benchmark of those from other laboratories that provide this valuable service. The main purpose of the 2006 study was to determine how accurate Edman sequencing is for quantitative analysis of polypeptides. Secondarily, participants were asked to identify a modified amino acid residue, N-epsilon-acetyl lysine [Lys(Ac)], present within one of the peptides. The ESRG 2006 peptide mixture consisted of three synthetic peptides. The Peptide Standards Research Group (PSRG) provided two peptides, with the following sequences: KAQYARSVLLEKDAEPDILELATGYR (peptide B), and RQAKVLLYSGR (peptide C). The third peptide, peptide C*, synthesized and characterized by ESRG, was identical to peptide C but with acetyl lysine in position 4. The mixture consisted of 20% peptide B and 40% each of peptide C and its acetylated form, peptide C*. Participating laboratories were provided with two tubes, each containing 100 picomoles of the peptide mixture (as determined by quantitative amino acid analysis) and were asked to provide amino acid assignments, peak areas, retention times at each cycle, as well as initial and repetitive yield estimates for each peptide in the mixture. Details about instruments and parameters used in the analysis were also collected. Participants in the study with access to a mass spectrometer (MALDI-TOF or ESI) were asked to provide information about the relative peak areas of the peptides in the mixture as a comparison with the peptide quantitation results from Edman sequencing. Positive amino acid assignments were 88% correct for peptide C and 93% correct for peptide B. The absolute initial sequencing yields were an average of 67% for peptide (C+C*) and 65.6 % for peptide B. The relative molar ratios determined by Edman sequencing were an average of 4.27 (expected ratio of 4) for peptides (C+C*)/B, and 1.49 for peptide C*/C (expected ratio of 1); the seemingly high 49% error in quantification of Lys(Ac) in peptide C* can be attributed to commercial unavailability of its PTH standard. These values compare very favorably with the values obtained by mass spectrometry.