Redox phospholipidomics analysis reveals specific oxidized phospholipids and regions in the diabetic mouse kidney

While it is generally accepted that oxidative stress impacts the diabetic kidney and contributes to pathogenesis, there is a substantial lack of knowledge about the molecular entity and anatomic location of a variety of reactive species. Here we provide a novel “oxidative stress map” of the diabetic kidney – the first of its kind, and identify specific, oxidized and other reactive lipids and their location. We used the db/db mouse model and Desorption Electrospray Ionization (DESI) mass spectrometry combined with heatmap image analysis. We analyzed a comprehensive array of phospholipid peroxide species in normal (db/m) and diabetic (db/db) kidneys using DESI imaging. Oxilipidomics heatmaps of the kidneys were generated focusing on phospholipids and their potential peroxidized products. We identified those lipids that undergo peroxidation in diabetic nephropathy. Several phospholipid peroxides and their spatial distribution were identified that were specific to the diabetic kidney, with significant enrichment in oxygenated phosphatidylethanolamines (PE) and lysophosphatidylethanolamine. Beyond qualitative and semi-quantitative information about the targets, the approach also reveals the anatomic location and the extent of lipid peroxide signal propagation across the kidney. Our approach provides novel, in-depth information of the location and molecular entity of reactive lipids in an organ with a very heterogeneous landscape. Many of these reactive lipids have been previously linked to programmed cell death mechanisms. Thus, the findings may be relevant to understand what impact phospholipid peroxidation has on cell and mitochondria membrane integrity and redox lipid signaling in diabetic nephropathy.

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Oxidative stress is one of the major players in the pathogenesis of diabetic nephropathy.

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Here, using an innovative mass spectrometry approach (DESI), we provide a novel oxilipidomics map of the diabetic kidney.

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Our analysis revealed enrichment of specific oxygenated phospholipid species at specific regions of the diabetic kidney.

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Our findings will likely further our understanding in how and where lipid peroxidation impacts the diabetic kidney.

Resilience and its association with post-traumatic stress disorder, anxiety, and depression symptomatology in the aftermath of trauma: a cross-sectional study from Nepal

Introduction

Resilience is a multidimensional construct. Despite being quoted as protective against mental disorders, it remains largely unexplored in our context.

Objectives

We attempted to explore the role of resilience in the development of various psychiatric symptoms as depression, anxiety and post-traumatic stress disorder following trauma in clinical population in a psychiatry outpatient of a university hospital.

Methods

We interviewed one hundred patients who sought treatment in psychiatry outpatient in a university hospital in Kathmandu, Nepal. We collected sociodemographic and trauma related information using semi-structured interview format. Other instruments used were the World Health Organization Composite International Diagnostic Interview version 2.1 for trauma categorization, the Post-Traumatic Stress Disorder Checklist-Civilian version to measure the post-traumatic stress disorder symptoms, and the 25-item Hopkins Symptom Checklist-25 to assess the level of depression and anxiety symptoms. We used Nepali adapted resilience scale derived from the original Wagnild and Young Resilience scale to measure resilience. We explored the associations between resilience scores and the scores on depression, anxiety and posttraumatic stress disorder using bivariate and multivariate analysis.

Results

Resilience had negative correlations with depression, anxiety, and post-traumatic stress disorder symptoms after adjusting for other variables such as gender, marital status, employment status, socioeconomic status and trauma types which were observed to have significant association in the bivariate analysis.

Conclusions

There was inverse correlation between resilience scores and depression, anxiety, and post-traumatic stress symptoms. Resilience should be considered in studies involving trauma population.

Disclosure

No significant relationships.

Abstract P2-08-05: Plasma lipidomics analysis to identify potential non-invasive biomarkers for breast white adipose inflammation and aromatase expression levels

Background: The presence of white adipose tissue inflammation (WATi) in the breast has been associated with increased breast cancer risk and a worse clinical course. Elevated body mass index (BMI) and the post-menopausal state are both associated with breast WATi. Breast WATi has also been associated with increased expression of aromatase, the rate-limiting enzyme for estrogen biosynthesis. Currently, WATi is diagnosed in surgical samples of breast tissue by the identification of crown-like structures (CLS), which are comprised of a dead or dying adipocyte enveloped by macrophages. In contrast to surgical specimens, core biopsies have been shown to be inadequate for assessing WATi. Hence, there is an unmet need for strategies to non-invasively diagnose WATi. Here we used a novel lipidomics platform to identify potential non-invasive blood signatures of breast WATi. Methods: We conducted a cross-sectional study which included 100 patients who underwent mastectomy for breast cancer treatment or risk reduction. WATi was detected by CD68 immunohistochemistry to identify CLS. Breast aromatase expression levels were measured by qPCR. Clinicopathologic data were abstracted from electronic medical records. Lipidomic data were measured from blood plasma in collaboration with Waters Technologies Corporation. Lipid levels in association with breast WATi (presence/absence) and levels of aromatase expression (high/low) in non-tumorous breast tissue were examined using Welch’s t-test. P-values were adjusted for multiple comparisons by controlling the false discovery rate (FDR) using the Benjamini-Hochberg method. A logistic regression model was used to develop predictive models that evaluated potential lipid biomarkers of the presence of breast WATi and high breast aromatase expression levels. Stepwise regression was used for variable selection. AUC of the ROC curves was used to evaluate the performance of the predictive models. Results: Among 140 lipids analyzed, 13 were identified to be associated with breast WATi (P<0.05, |log2FC|>0.3). Specifically, 8 lipids had lower levels, and 6 lipids had higher levels in patients with breast WATi compared to those without. Levels of 7 lipids were significantly higher in patients with an increased level of aromatase (P<0.05, |log2FC|>0.3). After variable selection, LPE(22:6) (P=0.018), LPE(20:3) ES-(P=0.006), along with menopausal status and BMI provided an 86.0% (95% CI, 77.6%-94.5%) accuracy in predicting higher breast aromatase levels. Combining the effect of two lipids improved the accuracy by 10.4%(P=0.030) compared to the model only using menopausal status and BMI. A model with 5 lipids and menopausal status provided an 88.8%(95% CI, 81.9%-95.8%) accuracy for predicting breast WATi. The model performance improved by 9.2% (P=0.026) compared to the model only using menopausal status and BMI. Conclusions: Our study identified several lipid species that showed significant changes in association with breast WATi and levels of aromatase expression. Further validation of these blood signatures could provide non-invasive assessment of WATi and aromatase levels. The availability of such a diagnostic algorithm could help, in turn, to both identify women at elevated risk for breast cancer and for monitoring the efficacy of interventions aimed at reducing inflammation and aromatase levels.

Citation Format: Xiao Cai, Siqi Wei, Zizhuo Xu, Xi K Zhou, Andrew Peck, Steven Lai, Giorgis Isaac, Hernando Olivos, Nayasha Munjoma, Suraj Dhungana, Rob Plumb, Andrew J Dannenberg, Neil M Iyengar. Plasma lipidomics analysis to identify potential non-invasive biomarkers for breast white adipose inflammation and aromatase expression levels [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-08-05.

Clinical and epidemiological features of COVID-19 deaths in Nepal

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has taken more than 1 million lives globally. This study, based on the official media releases of the Government of Nepal, analyses the clinical and epidemiological features of the individuals who died as a result of COVID-19 in Nepal from 23 January to 10 August 2020. We found that nearly half of the deaths were among people less than 50 years of age and being female increased the risk of death. The majority of deaths were associated with co-morbidities, the most common being cardiovascular diseases and diabetes followed by respiratory diseases. With the approaching festive season and relaxed lockdown, both government and citizens need to be more cautious about the severity of COVID-19 and take appropriate action.

COVID-19: the current situation in Nepal

The recent global pandemic of novel coronavirus disease 2019 (COVID-19) is increasingly alarming. As of 21 June 2020, there are more than 8.7 million cases worldwide, with 460 000 deaths. Nepal is not an exception to COVID-19 and is currently facing a challenge to prevent the spread of infection. The analysis of the detected cases, severity and outcomes of the cases within a country is important to have a clear picture of where the pandemic is heading and what measures should be taken to curb the infection before it becomes uncontrollable. We collected data regarding all the cases, recoveries and deaths attributed to COVID-19 in Nepal starting from the first case on 23 January to 21 June 2020. At present, COVID-19 has spread all over Nepal, with a rapid increase in the number of new cases and deaths, which is alarming in a low-income country with an inadequate healthcare system like Nepal. Although the government implemented early school closure and lockdown, the management to contain COVID-19 does not appear to be adequate. Understanding the current situation regarding COVID-19 in Nepal is important for providing a direction towards proper management of the disease.

Neuropsychiatric manifestations in General Paralysis of Insane (GPI)

General paralysis of insane is a form of neurosyphilis which brings parenchymatous changes in the central nervous system. Its manifestations include a variety of neuropsychiatric symptoms ranging from cognitive impairment to overt psychosis. Clinicians face difficulties in proper diagnosis as variety of symptoms changes from one form to other within a short period of time. Rarity of the disease at this modern era of penicillin is also another factor in timely diagnosis and management of such cases. Here we present a case of general paralysis of insane who presented with variety of neuropsychiatric symptoms and have had great difficulties to reach into the diagnosis.

Metabolomic approaches to study the tumor microenvironment

Tumors are characterized by metabolic dysregulation, reprogramming, and the presence of metabolites, which can act both as energy mediators and signaling messengers. Measuring the concentration and composition of metabolites in the tumor microenvironment can help to better understand the tumor pathology and might improve therapeutic treatments. Metabolomics can provide a description of the physiological and pathological status, as well as help to identify biomarkers of the disease. Additionally, mass spectrometry-based tissue imaging techniques can show the spatial distribution of metabolites. In this chapter we present protocols for the extraction and analysis of metabolites and lipids, with emphasis on liquid chromatography-mass spectrometry and mass spectrometry imaging.

The Effects of Glaucoma Drainage Devices on Oxygen Tension, Glycolytic Metabolites, and Metabolomics Profile of Aqueous Humor in the Rabbit

Purpose

Glaucoma drainage device (GDD) implantation can lead to corneal decompensation. We evaluated changes over time in oxygen tension and in the metabolic environment of the aqueous humor after GDD implantation in the rabbit eye.

Methods

Ahmed Glaucoma Valves were implanted in the left eyes of eight male New Zealand white rabbits. Right eyes were used as a control. Oxygen tension was measured immediately before surgery and at 1 and 2 months postoperation. Aqueous humor was collected from the surgical and control eyes at 1, 2, and 5 months postoperation. Aqueous humor samples collected at 1 and 5 months postoperation were selected for broad-spectrum metabolomics analysis using ultra-performance liquid chromatography-time of flight-mass spectrometry (UPLC TOF-MS). Multivariate analysis methods were used to identify metabolite profiles that separated the surgical and control eye at 1 and 5 months.

Results

There was a significant decrease in oxygen tension in aqueous humor of the surgical eyes (9 mm Hg, 95% confidence interval [CI]: -14.7 to -3.5). Differences in the metabolic profiles between the surgical and control eye at 1 and 5 months were observed, as were differences for the surgical eye at 1 and 5 months. In addition, a metabolite profile was identified that differentiated the surgical eyes at 1 and 5 months.

Conclusion

Changes in the oxygen tension and metabolic intermediates occur within the aqueous humor as early as 1 month after GDD implantation.

Translational Relevance

Corneal decompensation following GDD implantation could be secondary to disruption of the normal aqueous circulation, resulting in hypoxia and an altered metabolic profile. Alterations to the GDD design might minimize aqueous disruption and prevent corneal decompensation.

Yale school of public health symposium on lifetime exposures and human health: the exposome; summary and future reflections

The exposome is defined as "the totality of environmental exposures encountered from birth to death" and was developed to address the need for comprehensive environmental exposure assessment to better understand disease etiology. Due to the complexity of the exposome, significant efforts have been made to develop technologies for longitudinal, internal and external exposure monitoring, and bioinformatics to integrate and analyze datasets generated. Our objectives were to bring together leaders in the field of exposomics, at a recent Symposium on "Lifetime Exposures and Human Health: The Exposome," held at Yale School of Public Health. Our aim was to highlight the most recent technological advancements for measurement of the exposome, bioinformatics development, current limitations, and future needs in environmental health. In the discussions, an emphasis was placed on moving away from a one-chemical one-health outcome model toward a new paradigm of monitoring the totality of exposures that individuals may experience over their lifetime. This is critical to better understand the underlying biological impact on human health, particularly during windows of susceptibility. Recent advancements in metabolomics and bioinformatics are driving the field forward in biomonitoring and understanding the biological impact, and the technological and logistical challenges involved in the analyses were highlighted. In conclusion, further developments and support are needed for large-scale biomonitoring and management of big data, standardization for exposure and data analyses, bioinformatics tools for co-exposure or mixture analyses, and methods for data sharing.

Distribution and biomarkers of carbon-14-labeled fullerene C60 ([(14) C(U)]C60 ) in female rats and mice for up to 30 days after intravenous exposure

A comprehensive distribution study was conducted in female rats and mice exposed to a suspension of uniformly carbon-14-labeled C60 ([(14) C(U)]C60 ). Rodents were administered [(14) C(U)]C60 (~0.9 mg kg(-1) body weight) or 5% polyvinylpyrrolidone-saline vehicle alone via a single tail vein injection. Tissues were collected at 1 h and 1, 7, 14 and 30 days after administration. A separate group of rodents received five daily injections of suspensions of either [(14) C(U)]C60 or vehicle with tissue collection 14 days post exposure. Radioactivity was detected in over 20 tissues at all time points. The highest concentration of radioactivity in rodents at each time point was in liver, lungs and spleen. Elimination of [(14) C(U)]C60 was < 2% in urine and feces at any 24 h time points. [(14) C(U)]C60 and [(14) C(U)]C60 -retinol were detected in liver of rats and together accounted for ~99% and ~56% of the total recovered at 1 and 30 days postexposure, respectively. The blood radioactivity at 1 h after [(14) C(U)]C60 exposure was fourfold higher in rats than in mice; blood radioactivity was still in circulation at 30 days post [(14) C(U)]C60 exposure in both species (<1%). Levels of oxidative stress markers increased by 5 days after exposure and remained elevated, while levels of inflammation markers initially increased and then returned to control values. The level of cardiovascular marker von Willebrand factor, increased in rats, but remained at control levels in mice. This study demonstrates that [(14) C(U)]C60 is retained in female rodents with little elimination by 30 days after i.v. exposure, and leads to systemic oxidative stress.

Abstract 3752: Integrating proteomics and metabolomics characterizes active pathways and potential drug targets in small cell lung cancer

Small cell lung cancer (SCLC) accounts for 13-15% of all new lung cancer cases and represents the sixth most commonly diagnosed cancer in the US. However, it is an understudied cancer for which no molecularly targeted approaches have shown benefit. Using high-throughput techniques such as proteomics and metabolomics we can provide a more global, unbiased characterization to the inner workings of this disease. Integrating disparate data is a challenge in data analysis and bioinformatics, but this challenge is worth confronting due to the potential for combined proteomics / metabolomics analyses to better interrogate and capture the global landscape of active pathways and networks in SCLC than either technology alone. We accomplished this by comparing SCLC cell lines with non-small cell lung cancer (NSCLC) cell lines, differentiating characteristics of these two lung cancer cell types. We first used activity-based protein profiling (ABPP) combined with LC-MS/MS to profile the ATP-binding proteome of SCLC cell lines (n = 18) and NSCLC cell lines (n = 18). ABPP uses chemical probes that are directed against the active sites of enzymes to interrogate the functional state of ATP-binding enzymes, particularly kinases, in biological samples. These experiments identified 6937 peptides (2319 proteins), of which 3891 peptides (1543 proteins) were differentially expressed. Several pathways related to metabolism, such as purine biosynthesis and glycolysis / gluconeogenesis, were identified as over-represented in this list. These results led us to perform broad spectrum UPLC-TOF-MS metabolomics on ten SCLC and ten NSCLC cell lines. Multivariate analysis demonstrated distinct metabolite profiles for SCLC and NSCLC. Over 100 metabolites with variable importance to projection greater than 1 contributed to the differentiation of the two groups. These included metabolites related to purine metabolism such as inosinic acid and adenosine monophosphate and suggest a connection between our proteomics and metabolomics results. Statistical modeling approaches such as linear modeling, nonparametric nonlinear correlation, and Bayesian network analysis were used to integrate proteomics and metabolomics data to jointly characterize the key pathways and constituent components in SCLC. Multiple regression revealed a statistically significant interaction between endoglin (ENG) and phosphatidylethanolamine (PE), both of which are involved in angiogenesis. These findings and other statistical modeling results have the potential to facilitate the identification of new subtypes in SCLC and allow for the identification of novel targeted therapies. Future work will use these results to help characterize SCLC patient-derived xenograft models and surgically resected patient tissue samples. Funded, in part, by NIH Common Fund, 1U24DK097193.

Citation Format: Paul A. Stewart, Jiannong Li, Kate J. Fisher, Suraj Dhungana, Delisha Stewart, Susan Sumner, Eric Gardner, John Poirier, Charles M. Rudin, Eric A. Welsh, Steven Eschrich, Ann Chen, Eric B. Haura. Integrating proteomics and metabolomics characterizes active pathways and potential drug targets in small cell lung cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3752. doi:10.1158/1538-7445.AM2015-3752

Obesity Increases Mortality and Modulates the Lung Metabolome during Pandemic H1N1 Influenza Virus Infection in Mice

Obese individuals are at greater risk for hospitalization and death from infection with the 2009 pandemic H1N1 influenza virus (pH1N1). In this study, diet-induced and genetic-induced obese mouse models were used to uncover potential mechanisms by which obesity increases pH1N1 severity. High-fat diet-induced and genetic-induced obese mice exhibited greater pH1N1 mortality, lung inflammatory responses, and excess lung damage despite similar levels of viral burden compared with lean control mice. Furthermore, obese mice had fewer bronchoalveolar macrophages and regulatory T cells during infection. Obesity is inherently a metabolic disease, and metabolic profiling has found widespread usage in metabolic and infectious disease models for identifying biomarkers and enhancing understanding of complex mechanisms of disease. To further characterize the consequences of obesity on pH1N1 infection responses, we performed global liquid chromatography-mass spectrometry metabolic profiling of lung tissue and urine. A number of metabolites were perturbed by obesity both prior to and during infection. Uncovered metabolic signatures were used to identify changes in metabolic pathways that were differentially altered in the lungs of obese mice such as fatty acid, phospholipid, and nucleotide metabolism. Taken together, obesity induces distinct alterations in the lung metabolome, perhaps contributing to aberrant pH1N1 immune responses.

Distribution and biomarkers of carbon-14-labeled fullerene C60 ([(14) C(U)]C60 ) in female rats and mice for up to 30 days after intravenous exposure

A comprehensive distribution study was conducted in female rats and mice exposed to a suspension of uniformly carbon-14-labeled C60 ([(14) C(U)]C60 ). Rodents were administered [(14) C(U)]C60 (~0.9 mg kg(-1) body weight) or 5% polyvinylpyrrolidone-saline vehicle alone via a single tail vein injection. Tissues were collected at 1 h and 1, 7, 14 and 30 days after administration. A separate group of rodents received five daily injections of suspensions of either [(14) C(U)]C60 or vehicle with tissue collection 14 days post exposure. Radioactivity was detected in over 20 tissues at all time points. The highest concentration of radioactivity in rodents at each time point was in liver, lungs and spleen. Elimination of [(14) C(U)]C60 was < 2% in urine and feces at any 24 h time points. [(14) C(U)]C60 and [(14) C(U)]C60 -retinol were detected in liver of rats and together accounted for ~99% and ~56% of the total recovered at 1 and 30 days postexposure, respectively. The blood radioactivity at 1 h after [(14) C(U)]C60 exposure was fourfold higher in rats than in mice; blood radioactivity was still in circulation at 30 days post [(14) C(U)]C60 exposure in both species (<1%). Levels of oxidative stress markers increased by 5 days after exposure and remained elevated, while levels of inflammation markers initially increased and then returned to control values. The level of cardiovascular marker von Willebrand factor, increased in rats, but remained at control levels in mice. This study demonstrates that [(14) C(U)]C60 is retained in female rodents with little elimination by 30 days after i.v. exposure, and leads to systemic oxidative stress.

Systemic uptake, albumin and hemoglobin binding of [(14)C]2,3-butanedione administered by intratracheal instillation in male Harlan Sprague Dawley rats and oropharyngeal aspiration in male B6C3F1/N mice

2,3-Butanedione (BD) is a reactive diketone in artificial butter flavors that is thought to cause bronchiolitis obliterans in workers in microwave popcorn manufacturing. Bronchiolitis obliterans is generally not diagnosed until irreversible damage has occurred; therefore a biomarker of early exposure is needed. The potential systemic uptake of BD from inhalation exposure has not been evaluated. The objective here was to evaluate the systemic exposure of BD and binding to hemoglobin and albumin. [(14)C]BD was administered to male Harlan Sprague Dawley rats (100 mg/kg, intratracheal instillation) and B6C3F1/N mice (157 mg/kg, oropharyngeal aspiration). Blood and plasma was collected 24 h after administration and analyzed for (14)C content. At 24h, 0.88±0.07% of the administered dose was in rat blood, 0.66±0.06% in rat plasma, 0.38±0.13% in mouse blood and 0.17±0.05% in mouse plasma. Albumin binding in rats was 269±24.2 ng equiv./mg, which accounts for 38% of the radioactivity in plasma. In mice, binding was 85.0±22.3 ng equiv./mg albumin, which accounts for 51% of the radioactivity in plasma. The binding to hemoglobin in rats was 38.2±17.6 ng equiv./mg, and to globin was 29.1±3.96 ng equiv./mg. In mice, the binding to hemoglobin was 16.2±9.0 ng equiv./mg. The site(s) of adduction on hemoglobin and albumin was investigated by mass spectrometry. In rat globin, arginine adducts were detected at R-30 and R-104 of the beta chain in vitro and in vivo. In rat albumin, adducts were detected in vitro on R-219/221, R-360, and R-368, and in vivo on a variety of arginine residues. This study demonstrated that BD enters the systemic circulation and reacts with arginine on hemoglobin and albumin. These results indicate that hemoglobin and albumin adducts may be useful as biomarkers of BD exposure in humans.

Commensal microbiota is hepatoprotective and prevents liver fibrosis in mice

Translocation of bacteria and their products across the intestinal barrier is common in patients with liver disease, and there is evidence that experimental liver fibrosis depends on bacterial translocation. The purpose of our study was to investigate liver fibrosis in conventional and germ-free (GF) C57BL/6 mice. Chronic liver injury was induced by administration of thioacetamide (TAA) in the drinking water for 21 wk or by repeated intraperitoneal injections of carbon tetrachloride (CCl4). Increased liver fibrosis was observed in GF mice compared with conventional mice. Hepatocytes showed more toxin-induced oxidative stress and cell death. This was accompanied by increased activation of hepatic stellate cells, but hepatic mediators of inflammation were not significantly different. Similarly, a genetic model using Myd88/Trif-deficient mice, which lack downstream innate immunity signaling, had more severe fibrosis than wild-type mice. Isolated Myd88/Trif-deficient hepatocytes were more susceptible to toxin-induced cell death in culture. In conclusion, the commensal microbiota prevents fibrosis upon chronic liver injury in mice. This is the first study describing a beneficial role of the commensal microbiota in maintaining liver homeostasis and preventing liver fibrosis.

Association of thyroid dysfunction with depression in a teaching hospital

BACKGROUND

Thyroid dysfunction is common in patients with depression and depression is also common in patients with thyroid dysfunction. The purpose of this study was to estimate the prevalence of thyroid dysfunction in newly diagnosed depressed patients attending Psychiatry outpatient department of Tribhuvan University Teaching Hospital, Nepal and to find the correlation between the two.

METHODS

The study population comprised of 70 patients aged more than 15 years selected by simple random sampling technique who attended the Psychiatry OPD of Tribhuvan University Teaching Hospital, Kathmandu, Nepal and were diagnosed with first episode depression. A self- designed semi structured proforma was devised to obtain the socio- demographic characteristics of the study population. These patients were diagnosed as depression as per the ICD-10 DCR Criteria and HDRS scale was used at the same interview to verify it objectively.

RESULTS

Fifteen patients (21%) were found to have thyroid dysfunction, the most common being sub-clinical hypothyroidism, seen in 8 (11%). Thyroid dysfunction also showed positive correlation with depression severity. The diagnosis of depression by ICD- 10 DCR Criteria had positive correlation with HDRS grading of depression, though no significant association was found between different socio- demographic variables and depression.

CONCLUSIONS

This study concluded that thyroid dysfunction is common in depressed patients and larger studies are required in this field before TFTs are considered as an integral part of evaluation of these patients.

Leucine rich repeats and calponin homology containing protein 4 (Lrch4) is a novel regulator of Toll-like receptor signaling (68.8)

Toll-like receptor (TLR)4 signaling involves assembly of multi-protein complexes in lipid rafts. We identified Leucine rich repeats and calponin homology containing protein (Lrch)4 in a proteomic screen as a protein recruited to rafts of lipopolysaccharide (LPS)-exposed macrophages. Lrch4 had no published function, but structure predictions, including a transmembrane domain and leucine rich repeats, were suggestive of a receptor. Subcellular fractionation studies verified Lrch4 localization to the plasma membrane. qRT-PCR of 14 mouse tissues revealed that Lrch4 is ubiquitous. Lrch4 silencing in RAW 264.7 cells using lentiviral shRNAs and siRNAs attenuated LPS induction of TNFα and activation of mitogen-activated protein kinases and NF-κB. Lrch4 knockdown also reduced TNFα induction by ligands to several other TLRs. Lrch4 knockdown in TLR2 or TLR4 stable MD2-CD14-293 cells revealed that Lrch4 regulates human TLR but not TNFα -receptor signaling. Lrch4 and MD2 co-precipitated with biotin-LPS, and Lrch4 knockdown reduced cell binding of biotin-LPS without altering surface display of TLR4, together suggesting that Lrch4 interacts either directly or indirectly with LPS as part of a receptor complex. Lrch4 moreover co-precipitated with both MyD88 and TLR2. Lentiviral shRNA-mediated knockdown of Lrch4 in the murine airway reduced LPS-induced neutrophil influx into the airspaces in vivo. Taken together, we hypothesize that Lrch4 is a novel regulator of the innate immune response.

Proteomic profiling of S-acylated macrophage proteins identifies a role for palmitoylation in mitochondrial targeting of phospholipid scramblase 3

S-Palmitoylation, the reversible post-translational acylation of specific cysteine residues with the fatty acid palmitate, promotes the membrane tethering and subcellular localization of proteins in several biological pathways. Although inhibiting palmitoylation holds promise as a means for manipulating protein targeting, advances in the field have been hampered by limited understanding of palmitoylation enzymology and consensus motifs. In order to define the complement of S-acylated proteins in the macrophage, we treated RAW 264.7 macrophage membranes with hydroxylamine to cleave acyl thioesters, followed by biotinylation of newly exposed sulfhydryls and streptavidin-agarose affinity chromatography. Among proteins identified by LC-MS/MS, S-acylation status was established by spectral counting to assess enrichment under hydroxylamine versus mock treatment conditions. Of 1183 proteins identified in four independent experiments, 80 proteins were significant for S-acylation at false discovery rate = 0.05, and 101 significant at false discovery rate = 0.10. Candidate S-acylproteins were identified from several functional categories, including membrane trafficking, signaling, transporters, and receptors. Among these were 29 proteins previously biochemically confirmed as palmitoylated, 45 previously reported as putative S-acylproteins in proteomic screens, 24 not previously associated with palmitoylation, and three presumed false-positives. Nearly half of the candidates were previously identified by us in macrophage detergent-resistant membranes, suggesting that palmitoylation promotes lipid raft-localization of proteins in the macrophage. Among the candidate novel S-acylproteins was phospholipid scramblase 3 (Plscr3), a protein that regulates apoptosis through remodeling the mitochondrial membrane. Palmitoylation of Plscr3 was confirmed through (3)H-palmitate labeling. Moreover, site-directed mutagenesis of a cluster of five cysteines (Cys159-161-163-164-166) abolished palmitoylation, caused Plscr3 mislocalization from mitochondrion to nucleus, and reduced macrophage apoptosis in response to etoposide, together suggesting a role for palmitoylation at this site for mitochondrial targeting and pro-apoptotic function of Plscr3. Taken together, we propose that manipulation of protein palmitoylation carries great potential for intervention in macrophage biology via reprogramming of protein localization.

Synthesis and iron sequestration equilibria of novel exocyclic 3-hydroxy-2-pyridinone donor group siderophore mimics

The synthesis of a novel class of exocyclic bis- and tris-3,2-hydroxypyridinone (HOPO) chelators built on N(2) and N(3) aza-macrocyclic scaffolds and the thermodynamic solution characterization of their complexes with Fe(III) are described. The chelators for this study were prepared by reaction of either piperazine or N,N',N''-1,4,7-triazacyclononane with a novel electrophilic HOPO iminium salt in good yields. Subsequent removal of the benzyl protecting groups using HBr/acetic acid gave bis-HOPO chelators N(2)(etLH)(2) and N(2)(prLH)(2), and tris-HOPO chelator N(3)(etLH)(3) in excellent yields. Solution thermodynamic characterization of their complexes with Fe(III) was accomplished using spectrophotometric, potentiometric, and electrospray ionization-mass spectrometry (ESI-MS) methods. The pK(a)'s of N(2)(etLH)(2), N(2)(prLH)(2), and N(3)(etLH)(3), were determined spectrophotometrically and potentiometrically. The Fe(III) complex stability constants for the tetradentate N(2)(etLH)(2) and N(2)(prLH)(2), and hexadentate N(3)(etLH)(3), were measured by spectrophotometric and potentiometric titration, and by competition with ethylenediaminetetraacetic acid (EDTA). N(3)(etLH)(3) forms a 1:1 complex with Fe(III) with log β(110) = 27.34 ± 0.04. N(2)(prLH)(2) forms a 3:2 L:Fe complex with Fe(III) where log β(230) = 60.46 ± 0.04 and log β(110) = 20.39 ± 0.02. While N(2)(etLH)(2) also forms a 3:2 L:Fe complex with Fe(III), solubility problems precluded determining log β(230); log β(110) was found to be 20.45 ± 0.04. The pFe values of 26.5 for N(3)(etLH)(3) and 24.78 for N(2)(prLH)(2) are comparable to other siderophore molecules used in the treatment of iron overload, suggesting that these hydroxypyridinone ligands may be useful in the development of new chelation therapy agents.

Idiopathic intracranial hypertension

Idiopathic intracranial hypertension (IIH) is a condition which affects predominantly overweight women and is characterized by raised intracranial pressure without any identifiable pathology in the brain and with normal cerebrospinal fluid (CSF) composition. The cause of IIH is unclear and as such it remains a diagnosis of exclusion. Although the pathophysiology of IIH remains elusive, some observations have recently been added to our understanding of this, including the presence of transverse sinus stenosis on many patients and the possible role of leptin and inflammation in the disease pathogenesis. Headache is the most common symptom and papilloedema is the major clinical finding. Choices of medical treatment are limited to the use of diuretics particularly acetazolamide and encouragement of weight loss. Surgical therapies such as CSF diversion procedures and fenestration of the optic nerve may be necessary in some cases with persistent symptoms or progressive visual deterioration. While not life-threatening, IIH has a significant morbidity with up to 25% of patients developing visual impairment from optic atrophy. Visual surveillance is therefore vital. Long-term follow-up is recommended as the disease may worsen after an initial period of stability.

Epitope mapping by proteolysis of antigen-antibody complexes

The ability to accurately characterize an epitope on an antigen is essential to understand the pathogenesis of an infectious material, and for the design and development of drugs and vaccines. Emergence of a new contagious microbial or viral variant necessitates the need for robust identification and characterization of the antigenic determinant. Recent advances have made mass spectrometry (MS) a robust and sensitive analytical tool with high mass accuracy. The use of MS to characterize peptides and proteins has gained popularity in the research arena involving protein-protein interactions. Combining the modern mass spectrometric principles of protein-protein interaction studies with the classical use of limited proteolysis, a linear epitope on a peptide or a protein antigen can be accurately mapped in a short time, compared with other traditional techniques available for epitope mapping. Additionally, complete MS analyses can be achieved with very little sample consumption. Here we discuss the overall approach to characterize the detailed interaction between a linear antigen (either a peptide or a protein antigen) and its corresponding monoclonal antibody by using MS. The steps involved in epitope excision, epitope extraction, and indirect immunosorption are outlined thoroughly. Conditions required for MS analysis using either matrix assisted laser desorption ionization (MALDI) or electrospray ionization (ESI) sources are summarized, with special emphasis on the experimental protocols.

Epitope mapping by differential chemical modification of antigens

Matrix-assisted laser desorption ionization or electrospray ionization mass spectrometry combined with differential chemical modification have proven to be versatile tools for epitope mapping as well as for studying diverse protein-protein and protein-ligand interactions. Characterization of a discontinuous or a conformational epitope on an antigen demands the ability to map the three-dimensional protein surface along with the interface of two interacting proteins. Classical methods of differentially derivatizing amino acid residues have been successfully merged with highly sensitive and highly accurate mass spectrometric techniques to rapidly profile the three-dimensional protein surface and determine the surface accessibility of specific amino acid residues. Here we discuss the use of mass spectrometry to characterize discontinuous or conformational epitopes by studying antigen-antibody interactions. The steps involved in epitope mapping approaches using differential chemical modification and H/D exchange on the antigen are discussed in detail, with particular emphasis on the experimental protocols.

Quantitative proteomics analysis of macrophage rafts reveals compartmentalized activation of the proteasome and of proteasome-mediated ERK activation in response to lipopolysaccharide

Lipopolysaccharide (LPS), a glycolipid component of the outer membrane of Gram-negative bacteria, is a potent initiator of the innate immune response of the macrophage. LPS triggers downstream signaling by selectively recruiting and activating proteins in cholesterol-rich membrane microdomains called lipid rafts. We applied proteomics analysis to macrophage detergent-resistant membranes (DRMs) during an LPS exposure time course in an effort to identify and validate novel events occurring in macrophage rafts. Following metabolic incorporation in cell culture of heavy isotopes of amino acids arginine and lysine ([(13)C(6)]Arg and [(13)C(6)]Lys) or their light counterparts, a SILAC (stable isotope labeling with amino acids in cell culture)-based quantitative, liquid chromatography-tandem mass spectrometry proteomics approach was used to profile LPS-induced changes in the lipid raft proteome of RAW 264.7 macrophages. Unsupervised network analysis of the proteomics data set revealed a marked representation of the ubiquitin-proteasome system as well as changes in proteasome subunit composition following LPS challenge. Functional analysis of DRMs confirmed that LPS causes selective activation of the proteasome in macrophage rafts and proteasome inactivation outside of rafts. Given previous reports of an essential role for proteasomal degradation of IkappaB kinase-phosphorylated p105 in LPS activation of ERK mitogen-activated protein kinase, we tested for a role of rafts in compartmentalization of these events. Immunoblotting of DRMs revealed proteasome-dependent activation of MEK and ERK specifically occurring in lipid rafts as well as proteasomal activity upon raft-localized p105 that was enhanced by LPS. Cholesterol extraction from the intact macrophage with methyl-beta-cyclodextrin was sufficient to activate ERK, recapitulating the LPS-IkappaB kinase-p105-MEK-ERK cascade, whereas both it and the alternate raft-disrupting agent nystatin blocked subsequent LPS activation of the ERK cascade. Taken together, our findings indicate a critical, selective role for raft compartmentalization and regulation of proteasome activity in activation of the MEK-ERK pathway.

Petrobactin is produced by both pathogenic and non-pathogenic isolates of the Bacillus cereus group of bacteria

Petrobactin is the primary siderophore synthesized by Bacillus anthracis str Sterne and is required for virulence of this organism in a mouse model. The siderophore's biosynthetic machinery was recently defined and gene homologues of this operon exist in several other Bacillus strains known to be mammalian pathogens, but are absent in several known to be harmless such as B. subtilis and B. lichenformis. Thus, a common hypothesis regarding siderophore production in Bacillus species is that petrobactin production is exclusive to pathogenic isolates. In order to test this hypothesis, siderophores produced by 106 strains of an in-house library of the Bacillus cereus sensu lato group were isolated and identified using a MALDI-TOF-MS assay. Strains were selected from a previously defined phylogenetic tree of this group in order to include both known pathogens and innocuous strains. Petrobactin is produced by pathogenic strains and innocuous isolates alike, and thus is not itself indicative of virulence.

Iron Chelation Equilibria, Redox, and Siderophore Activity of a Saccharide Platform Ferrichrome Analogue

A complete characterization of the aqueous solution Fe(III) and Fe(II) coordination chemistry of a saccharide-based ferrichrome analogue, 1-O-methyl-2,3,6-tris-O-[4-(N-hydroxy-N-ethylcarbamoyl)-n-butyryl]-alpha-D-glucopyranoside (H3LN236), is reported including relevant thermodynamic parameters and growth promotion activity with respect to both Gram-negative and Gram-positive bacterial strains. The saccharide platform is an attractive backbone for the design and synthesis of ferrichrome analogues because of its improved water solubility and hydrogen-bonding capabilities, which can potentially provide favorable receptor recognition and biological activity. The ligand deprotonation constants (pKa values), iron complex (FeIII(LN236) and FeII(LN236)1-) protonation constants (KFeHxL-236-N), overall Fe(III) and Fe(II) chelation constants (beta110), and aqueous solution speciation were determined by spectrophotometric and potentiometric titrations, EDTA competition equilibria, and cyclic voltammetry. Log betaIII110 = 31.16 and pFe = 26.1 for FeIII(LN236) suggests a high affinity for Fe(III), which is comparable to or greater than ferrichrome and other ferrichrome analogues. The E1/2 for the FeIII(LN236)/FeII(LN236)1- couple was determined to be -454 mV (vs NHE) from quasi-reversible cyclic voltammograms at pH 9. Below pH 6.5, the E1/2 shifts to more positive values and the pH-dependent E1/2 profile was used to determine the FeII(LN236)1- protonation constants and overall stability constant log betaII110 = 11.1. A comparative analysis of similar data for an Fe(III) complex of a structural isomer of this exocyclic saccharide chelator (H3LR234), including strain energy calculations, allows us to analyze the relative effects of the pendant arm position and hydroxamate moiety orientation (normal vs retro) on overall complex stability. A correlation between siderophore activity and iron coordination chemistry of these saccharide-hydroxamate chelators is made.

Genetic diversity of coastal bottlenose dolphins revealed by structurally and functionally diverse hemoglobins

Studies of structure-function relationships in the respiratory proteins of marine mammals revealed unexpected variations in the number and types of hemoglobins (Hbs) present in coastal bottlenose dolphins, Tursiops truncatus. We obtained blood samples from free-ranging coastal bottlenose dolphins as a component of capture-release studies. We found that the oxygen-binding functions of bottlenose dolphin blood are poised between effector-saturated and unsaturated levels, enabling exercise-dependent shifts in oxygen transfer functions. Isolated bottlenose dolphin Hbs showed elevated pH sensitivities (Bohr effects) and appreciably lower oxygen affinities than adult human Hb in the absence of allosteric effectors. These properties may be an adaptive modification that enhances oxygen delivery during diving episodes when oxygen tensions and effector levels are low. The Hbs of individual dolphins showed similar oxygen affinities, responses to effectors, and expression of heme-heme interaction in oxygen binding, but differed in their redox potentials and rates of autoxidation. The heterogeneity suggested by these functional variations in Hbs of individual dolphins was born out by variations in the molecular weights and numbers of their alpha and beta globin chains. Although coastal bottlenose dolphins were expected to have a single type of Hb, the mass differences observed revealed considerable genetic diversity. There were multiple Hb forms in some individuals and differences in Hb patterns among individuals within the same community.

Effect of exogenous reductant on growth and iron mobilization from ferrihydrite by the Pseudomonas mendocina ymp strain

Growth of the Pseudomonas mendocina ymp strain on insoluble ferrihydrite is enhanced by exogenous reductants with concurrent increase in soluble iron concentrations. This shows that exogenous reductants play a substantial role in the overall microbial iron bioavailability. The exogenous reductants may work together with the siderophores, Fe-scavenging agents, to facilitate ferrihydrite dissolution.

Purification and characterization of rhodobactin: a mixed ligand siderophore from Rhodococcus rhodochrous strain OFS

The siderophore produced by Rhodococcus rhodochrous strain OFS, rhodobactin, was isolated from iron-deficient cultures and purified by a combination of XAD-7 absorptive/partition resin column and semi-preparative HPLC. The siderophore structure was characterized using 1D and 2D (1)H, (13)C and (15)N NMR techniques (DQFCOSY, TOCSY, NOESY, HSQC and LR-HSQC) and was confirmed using ESI-MS and MS/MS experiments. The structural characterization revealed that the siderophore, rhodobactin, is a mixed ligand hexadentate siderophore with two catecholate and one hydroxamate moieties for iron chelation. We further investigated the effects of Fe concentrations on siderophore production and found that Fe limiting conditions (Fe concentrations from 0.1 microM to 2.0 microM) facilitated siderophore excretion. Our interests lie in the role that siderophores may have in binding metals at mixed contamination sites (containing metals/radionuclides and organics). Given the broad metabolic capacity of this microbe and its Fe scavenging ability, R. rhodochrous OFS may have a competitive advantage over other organisms employed in bioremediation.

Kinetics of iron release from ferric binding protein (FbpA): mechanistic implications in bacterial periplasm-to-cytosol Fe3+ transport

The ferric binding protein (FbpA) transports iron across the periplasmic space of certain Gram-negative bacteria and is an important component involved in iron acquisition by pathogenic Neisseria spp. (Neisseria gonorrheae and Neisseria meningitidis). Previous work has demonstrated that the synergistic anion, required for tight Fe(3+) sequestration by FbpA, also plays a key role in inserting Fe(3+) into the FbpA binding site. Here, we investigate the iron release process from various forms of holo-FbpA, Fe(3+)FbpA-X, during the course of a chelator competition reaction using EDTA and Tiron. Fe(3+)FbpA-X represents the protein assembly complex with different synergistic anions, X = PO(4)(3)(-) and NTA. Stepwise mechanisms of Fe(3+) release are proposed on the basis of kinetic profiles of these chelator competition reactions. Fe(3+)FbpA-PO(4) and Fe(3+)FbpA-NTA react differently with EDTA and Tiron during the Fe(3+)-exchange process. EDTA replaces PO(4)(3)(-) and NTA from the first coordination shell of Fe(3+) and acts as a synergistic anion to give a spectroscopically distinguishable intermediate, Fe(3+)FbpA-EDTA, prior to pulling Fe(3+) out of the protein. Tiron, on the other hand, does not act as a synergistic anion but is a more efficient competing chelator as it removes Fe(3+) from FbpA at rate much faster than EDTA. These results reaffirm the contribution of the synergistic anion to the FbpA iron transport process as the anion, in addition to playing a facilitative role in iron binding, appears to have a "gatekeeper" role, thereby modulating the Fe(3+) release process.

SUPREX (Stability of Unpurified Proteins from Rates of H/D Exchange) analysis of the thermodynamics of synergistic anion binding by ferric-binding protein (FbpA), a bacterial transferrin

SUPREX (stability of unpurified proteins from rates of H/D exchange) is a H/D exchange- and matrix-assisted laser desorption/ionization (MALDI)-based technique for characterizing the equilibrium unfolding/refolding properties of proteins and protein-ligand complexes. Here, we describe the application of SUPREX to the thermodynamic analysis of synergistic anion binding to iron-loaded ferric-binding protein (Fe(3+)FbpA-X, X = synergistic anion). The in vivo function of FbpA is to transport unchelated Fe(3+) across the periplasmic space of certain Gram-negative bacteria, a process that requires simultaneous binding of a synergistic anion. Our results indicate that Fe(3+)FbpA-X is not a so-called "ideal" protein system for SUPREX analyses because it does not exhibit two-state folding properties and it does not exhibit EX2 H/D exchange behavior. However, despite these nonideal properties of the Fe(3+)FbpA-X protein-folding/unfolding reaction, we demonstrate that the SUPREX technique is still amenable to the quantitative thermodynamic analysis of synergistic anion binding to Fe(3+)FbpA. As part of this work, the SUPREX technique was used to evaluate the DeltaDeltaG(f) values of four synergistic anion-containing complexes of Fe(3+)FbpA (i.e., Fe(3+)FbpA-PO(4), Fe(3+)FbpA-citrate, Fe(3+)FbpA-AsO(4), and Fe(3+)FbpA-SO(4)). The DeltaDeltaG(f) value obtained for Fe(3+)FbpA-citrate relative to Fe(3+)FbpA-PO(4) (1.45 +/- 0.44 kcal/mol), is in good agreement with that reported previously (1.98 kcal/mol). The value obtained for Fe(3+)FbpA-AsO(4) (0.58 +/- 0.45 kcal/mol) was also consistent with that reported previously (0.68 kcal/mol), but the measurement error is very close to the magnitude of the value. This work (i) demonstrates the utility of the SUPREX method for studying anion binding by FbpA, (ii) provides the first evaluation of a DeltaDeltaG(f) value for Fe(3+)FbpA-SO(4), -1.43 +/- 0.17 kcal/mol, and (iii) helps substantiate our hypothesis that the synergistic anion plays a role in controlling the lability of iron bound to FbpA in the transport process.

Phosphate ester hydrolysis is catalyzed by a bacterial transferrin: potential implications for in vivo iron transport mechanisms

Two synergistic anions, p-nitrophenyl phosphate ester (NPP) and SO(4)(2-), were found to form new stable assemblies with Fe(3+) and a bacterial transferrin, FbpA (FbpA=ferric binding protein). Fe(3+)FbpA-SO(4) undergoes rapid anion exchange in the presence of NPP to form Fe(3+)FbpA-NPP. Formation of Fe(3+)FbpA-NPP was found to accelerate the rate of hydrolysis of the bound phosphate ester (k(hyd)=1.6 x 10(-6) s(-1) at 25 degrees C and pH 6.5) by >10(3) fold over the uncatalyzed reaction. These findings suggest a dual function for FbpA in vivo: transport of Fe(3+) across the periplasmic space to the inner membrane in certain gram-negative bacteria and hydrolysis of periplasmic polyphosphates.

Iron Chelation Properties of an Extracellular Siderophore Exochelin MS

The coordination chemistry of an extracellular siderophore produced by Mycobacterium smegmatis, exochelin MS (ExoMS), is reported along with its pK(a) values, Fe(III) and Fe(II) chelation constants, and aqueous solution speciation as determined by spectrophotometric and potentiometric titrations. Exochelin MS has three hydroxamic acid groups for Fe(III) chelation and has four additional acidic protons from a carboxylic acid group and three primary amine groups, on the backbone of the molecule. The pK(a) values for the three hydroxamic acid moieties, the carboxylic acid group and the alkylammonium groups on ExoMS, correspond well with the literature values for these moieties. Equilibrium constants for proton-dependent Fe(III)-ExoMS equilibria were determined using a model involving the sequential protonation of the Fe(III)-ExoMS complexes at the first and second coordination shells. The equilibrium constants (beta) for the overall formation of Fe(III)ExoMS(H(3))(2+) and Fe(II)ExoMS(H(3))(+) from Fe((aq))(3+) or Fe((aq))(2+) and the deprotonated hydroxamate coordinating group form of the siderophore, ExoMS(H(3))(-), are calculated as log beta(III) = 28.9 and log beta(II) = 10.1. A calculated pFe value of 25.0 is very similar to that of other linear trihydroxamic acid siderophores, and indicates that ExoMS is thermodynamically capable of removing Fe(III) from transferrin. The E(1/2) for the Fe(III)-ExoMS/Fe(II)-ExoMS couple was determined from quasi reversible cyclic voltammograms at pH = 6.5 and found to be -380 mV.

Redox Properties of Human Transferrin Bound to Its Receptor†

Virtually all organisms require iron, and iron-dependent cells of vertebrates (and some more ancient species) depend on the Fe(3+)-binding protein of the circulation, transferrin, to meet their needs. In its iron-donating cycle, transferrin is first captured by the transferrin receptor on the cell membrane, and then internalized to a proton-pumping endosome where iron is released. Iron exits the endosome to enter the cytoplasm via the ferrous iron transporter DMT1, a molecule that accepts only Fe(2+), but the reduction potential of ferric iron in free transferrin at endosomal pH (approximately 5.6) is below -500 mV, too low for reduction by physiological agents such as the reduced pyridine nucleotides with reduction potentials of -284 mV. We now show that in its complex with the transferrin receptor, which persists throughout the transferrin-to-cell cycle of iron uptake, the potential is raised by more than 200 mV. Reductive release of iron from transferrin, which binds Fe(2+) very weakly, is therefore physiologically feasible, a further indication that the transferrin receptor is more than a passive conveyor of transferrin and its iron.

Crystal and Molecular Structures of Ionophore−Siderophore Host−Guest Supramolecular Assemblies Relevant to Molecular Recognition

Ionophore-siderophore host-guest assemblies composed of 18-crown-6 and ferrioxamine B, benzo-18-crown-6 and ferrioxamine B, and cis-syn-cis-dicyclohexano-18-crown-6 and ferrioxamine B were successfully crystallized, and their structures were determined by single-crystal X-ray diffraction. All three crystal lattices also include solvated Mg(II) and perchlorate ions. The ionophore-siderophore host-guest assembly is noncovalently held together by a hydrogen bonding interaction between the pendant protonated amine in the second coordination sphere of ferrioxamine B and the hydrogen bond acceptor oxygen atoms in the crown ether. The crystals of 18-crown-6:ferrioxamine B host-guest assembly are monoclinic, with space group P2(1)/c, and four molecules per unit cell with dimensions a = 19.8327(11) A, b = 20.4111(11) A, c = 15.1698(8) A, and beta = 96.435(1) degrees. The crystals of benzo-18-crown-6:ferrioxamine B host-guest assembly are triclinic, with space group P(-)1, and two molecules per unit cell with dimensions a = 11.1747(10) A, b = 16.0580(15) A, c = 18.4175(17) A, alpha = 80.469(3) degrees, beta = 81.481(3) degrees and gamma = 70.212(2) degrees. The crystals of cis-syn-cis-dicyclohexano-18-crown-6:ferrioxamine B host-guest assembly are monoclinic, with space group P2(1)/c, and four molecules per unit cell with dimensions a = 20.1473(13) A, b = 21.5778(15) A, c = 14.8013(10) A, and beta = 94.586(2) degrees. The crystal structures of all three host-guest assemblies contain a racemic mixture of Lambda-N-cis, cis and Delta-N-cis, cis coordination isomers of ferrioxamine B. The crystal structures indicate that the steric rigidity of the benzo-18-crown-6 and cis-syn-cis-dicyclohexano-18-crown-6 cavity has a pronounced effect on the conformation of the crown ring and ultimately on the hydrogen bonding interactions between the crown ethers and ferrioxamine B. The structural parameters and the conformational features of the ferrioxamine B guests compare very well with each other and with those of the ferrioxamine B structure obtained in the absence of a host. Structural features relevant to siderophore molecular recognition are discussed.

Iron chelation properties of an extracellular siderophore exochelin MN

The coordination chemistry of an extracellular siderophore produced by Mycobacterium neoaurum, exochelin MN (ExoMN), is reported along with its pK(a) values, Fe(III) and Fe(II) chelation constants, and aqueous solution speciation as determined by spectrophotometric and potentiometric titration techniques. Exochelin MN is of particular interest as it can efficiently transport iron into pathogenic M. leprae, which is responsible for leprosy, in addition to its own parent cells. The Fe(III) coordination properties of ExoMN are important with respect to understanding the Fe(III) acquisition and uptake mechanism in pathogenic M. leprae, as the siderophores from this organism are very difficult to isolate. Exochelin MN has two hydroxamic acid groups and an unusual threo-beta-hydroxy-l-histidine available for Fe(III) chelation. The presence of threo-beta-hydroxy-l-histidine gives rise to a unique mode of Fe(III) coordination. The pK(a) values for the two hydroxamic acid moieties, the histidine imidazole ring and the alkylammonium groups on ExoMN, correspond well with the literature values for these moieties. Proton-dependent Fe(III)- and Fe(II)-ExoMN equilibrium constants were determined using a model involving sequential protonation of the Fe(III)- and Fe(II)-ExoMN complexes. These data were used to develop a model whereby deprotonation reactions on the surface of the complex in the second coordination shell result in first coordination shell isomerization. The overall formation constants were calculated: log beta(110) = 39.12 for Fe(III)-ExoMN and 16.7 for Fe(II)-ExoMN. The calculated pFe value of 31.1 is one of the highest among all siderophores and their synthetic analogues and indicates that ExoMN is thermodynamically capable of removing Fe(III) from transferrin. The E(1/2) for the Fe(III)ExoMN/Fe(II)ExoMN(-) couple was determined to be -595 mV from quasi-reversible cyclic voltammograms at pH = 10.8, and the pH-dependent E(1/2) profile was used to determine the Fe(II)-ExoMN protonation constants.

The influence of the synergistic anion on iron chelation by ferric binding protein, a bacterial transferrin

Although the presence of an exogenous anion is a requirement for tight Fe(3+) binding by the bacterial (Neisseria) transferrin nFbp, the identity of the exogenous anion is not specific in vitro. nFbp was reconstituted as a stable iron containing protein by using a number of different exogenous anions [arsenate, citrate, nitrilotriacetate, pyrophosphate, and oxalate (symbolized by X)] in addition to phosphate, predominantly present in the recombinant form of the protein. Spectroscopic characterization of the Fe(3+)anion interaction in the reconstituted protein was accomplished by UV-visible and EPR spectroscopies. The affinity of the protein for Fe(3+) is anion dependent, as evidenced by the effective Fe(3+) binding constants (K'(eff)) observed, which range from 1 x 10(17) M(-1) to 4 x 10(18) M(-1) at pH 6.5 and 20 degrees C. The redox potentials for Fe(3+)nFbpXFe(2+)nFbpX reduction are also found to depend on the identity of the synergistic anion required for Fe(3+) sequestration. Facile exchange of exogenous anions (Fe(3+)nFbpX + X' --> Fe(3+)nFbpX' + X) is established and provides a pathway for environmental modulation of the iron chelation and redox characteristics of nFbp. The affinity of the iron loaded protein for exogenous anion binding at pH 6.5 was found to decrease in the order phosphate > arsenate approximately pyrophosphate > nitrilotriacetate > citrate approximately oxalate carbonate. Anion influence on the iron primary coordination sphere through iron binding and redox potential modulation may have in vivo application as a mechanism for periplasmic control of iron delivery to the cytosol.

Fe(III) coordination properties of a new saccharide-based exocyclic trihydroxamate analogue of ferrichrome

The coordination chemistry of a saccharide-based ferrichrome analogue, 1-O-methyl-2,3,4-tris-O-[4-(N-hydroxy-N-methylcarbamoyl)-n-butyrate]-alpha-d-glucopyranoside (H(3)L), is reported, along with its pK(a) values, Fe(III) and Fe(II) chelation constants, and aqueous-solution speciation as determined by spectrophotometric and potentiometric titration techniques. The use of a saccharide platform to synthesize a hexadentate trihydroxamic acid chelator provides some advantages over other approaches to ferrichrome models, including significant water solubility and hydrogen-bonding capability of the backbone that can potentially provide favorable receptor recognition and biological activity. The pK(a) values for the hydroxamate moieties were found to be similar to those of other trihydroxamates. Proton-dependent Fe(III)-H(3)L and Fe(II)-H(3)L equilibrium constants were determined using a model involving the sequential protonation of the iron(III)- and iron(II)-ligand complexes. These results were used to calculate the formation constants, log beta(110) = 31.86 for Fe(III)L and 12.1 for Fe(II)L(-). The calculated pFe value of 27.1 indicates that H(3)L possesses an Fe(III) affinity comparable to or greater than those of ferrichrome and other ferrichrome analogues and is thermodynamically capable of removing Fe(III) from transferrin. E(1/2) for the Fe(III)L/Fe(II)L(-) couple was determined to be -436 mV from quasi-reversible cyclic voltammograms at pH = 9, and the pH-dependent E(1/2) profile was used to determine the Fe(II)L(-) protonation constants.

Fe(III) coordination properties of two new saccharide-based enterobactin analogues: methyl 2,3,4-tris-O-[N-[2,3-di(hydroxy)benzoyl-glycyl]-aminopropyl]-alpha-D-glucopyranoside and methyl 2,3,4-tris-O-[N-[2,3-di-(hydroxy)-benzoyl]-aminopropyl]-alpha-D-glucopyranoside

The synthesis of two saccharide-based enterobactin analogues, methyl 2,3,4-tris-O[-N[2,3-di(hydroxy)benzoyl-glycyl]-aminopropyl]-alpha-D-glucopyranoside (H(6)L(A)) and methyl 2,3,4-tris-O-[N-[2,3-di(hydroxy)benzoyl]-aminopropyl]-alpha-D-glucopyranoside (H(6)L(B)), are reported along with their pK(a) values, Fe(III) binding constants, and aqueous solution speciation as determined by spectrophotometric and potentiometric titration techniques. Use of a saccharide platform to synthesize a hexadentate triscatechol chelator provides some advantages over other approaches to enterobactin models, including significant water solubility, resistance to hydrolysis, and backbone chirality which may provide favorable recognition and availability to cells. The protonation constants for the catechol ligand hydroxyl moieties were determined for both ligands and found to be significantly different, which is attributed to the differences in the spacer chain of the two triscatechols. Proton dependent Fe(III)-ligand equilibrium constants were determined using a model involving the sequential protonation of the Fe(III)-ligand complex. These results were used to calculate the formation constants, log beta(110) = 41.38 for Fe(III)-H(6)L(A) and log beta(110) = 46.38 for Fe(III)-H(6)L(B). The calculated pM values of 28.6 for H(6)L(A) and 28.3 for H(6)L(B) indicate that these ligands possess Fe(III) affinities comparable to or greater than other enterobactin models and are thermodynamically capable of removing Fe(III) from transferrin.

Crystal structure of ferrioxamine B: a comparative analysis and implications for molecular recognition

Ferrioxamine B was successfully co-crystallized with ethanolpentaaquomagnesium(II) and perchlorate ions as counter ions, C27H62Cl3FeMgN6O26, and the crystal structure has been determined by single-crystal X-ray diffraction. The crystals are monoclinic, space group P2(1)/n, four molecules per unit cell with dimensions a=21.1945(7) A, b=10.0034(3) A, c=106.560(1) A, and beta=106.560(1) degrees. The crystal structure contains a racemic mixture of Lambda-N-cis,cis and Delta-N-cis,cis coordination isomers. The structural parameters and the conformational features of ferrioxamine B compare very well with those of ferrioxamines D1 and E, with an exception of the orientation of the pendant protonated amine, which is pointing away from the connecting amide chains and towards the carbonyl face of the inner coordination shell distorted octahedron. This pendant protonated amine, in conjunction with the carbonyl face of the Fe(III) coordination shell, is proposed to play an important role in the recognition and membrane transport processes.