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Cruz-Saavedra L, Caceres T, Ballesteros N, Posada-Forero B, Ramírez JD. Differential expression of meiosis and homologous recombination-related genes in the life cycle of Trypanosoma cruzi. Parasitol Res 2023:10.1007/s00436-023-07850-2. [PMID: 37272974 DOI: 10.1007/s00436-023-07850-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2023] [Accepted: 04/17/2023] [Indexed: 06/06/2023]
Abstract
Trypanosoma cruzi has a complex life cycle consisting of four morphological and distinct biological stages. Although some authors suggest that T. cruzi primarily follows clonal reproduction, recent genomic and transcriptomic studies indicate an unorthodox capacity for recombination. We aimed to estimate the differential gene expression of 10 meiosis/homologous recombination-related genes during the T. cruzi life cycle, including epimastigotes, under two different types of stress (oxidative stress and pH changes). We performed RT-qPCR tests using novel-designed primers to estimate the differential gene expression (∆Ct and ∆∆Ct) of nine genes (SPO11, HAP2, RAD50, MRN complex, BRCA2, DMC1, MND1, and RPA1) and RAD51, which was previously reported. Our results show basal expression of all genes during the life cycle, indicating their hypothetical role in several cellular processes but with specific signatures of differential gene expression during the life cycle (HAP2, RPA, RAD50, BRCA2, MND1, and DMC1) and oxidative stress (RPA, MRE11, NBS1, BRCA2, MND1, and RAD51). Additionally, we found that the MRN complex has an independent level of expression in T. cruzi, with profiles of MRE11 and NBS1 upregulated in some stages. Recent studies on other trypanosomatids have highlighted the influence of HAP2 and RPA in recombination and hybridization. If T. cruzi uses the same repertoire of genes, our findings could suggest that metacyclogenesis may be the putative step that the parasite uses to undergo recombination. Likewise, our study reveals the differential profiles of genes expressed in response to oxidative and pH stress. Further studies are necessary to confirm our findings and understand the recombination mechanism in T. cruzi.
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Affiliation(s)
- Lissa Cruz-Saavedra
- Centro de Investigaciones en Microbiología y Biotecnología-UR (CIMBIUR), Facultad de Ciencias Naturales, Universidad del Rosario, Bogotá, Colombia
| | - Tatiana Caceres
- Centro de Investigaciones en Microbiología y Biotecnología-UR (CIMBIUR), Facultad de Ciencias Naturales, Universidad del Rosario, Bogotá, Colombia
| | - Nathalia Ballesteros
- Centro de Investigaciones en Microbiología y Biotecnología-UR (CIMBIUR), Facultad de Ciencias Naturales, Universidad del Rosario, Bogotá, Colombia
| | | | - Juan David Ramírez
- Centro de Investigaciones en Microbiología y Biotecnología-UR (CIMBIUR), Facultad de Ciencias Naturales, Universidad del Rosario, Bogotá, Colombia.
- Molecular Microbiology Laboratory, Department of Pathology, Molecular and Cell-Based Medicine, Icahn School of Medicine at Mount Sinai, New York, NY, 10029, USA.
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MacLean ELH, Villa-Castillo L, Espinoza-Lopez P, Caceres T, Sulis G, Kohli M, Pai M, Ugarte-Gil C. Integrating tuberculosis and COVID-19 molecular testing in Lima, Peru: a cross-sectional, diagnostic accuracy study. Lancet Microbe 2023:S2666-5247(23)00042-3. [PMID: 37068500 PMCID: PMC10105319 DOI: 10.1016/s2666-5247(23)00042-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2022] [Revised: 12/23/2022] [Accepted: 02/07/2023] [Indexed: 04/19/2023]
Abstract
BACKGROUND Integrated molecular testing could be an opportunity to detect and provide care for both tuberculosis and COVID-19. Many high tuberculosis burden countries, such as Peru, have existing GeneXpert systems for tuberculosis testing with GeneXpert Xpert MTB/RIF Ultra (Xpert Ultra), and a GeneXpert SARS-CoV-2 assay, GeneXpert Xpert Xpress SARS-CoV-2 (Xpert Xpress), is also available. We aimed to assess the feasibility of integrating tuberculosis and COVID-19 testing using one sputum specimen with Xpert Ultra and Xpert Xpress in Lima, Peru. METHODS In this cross-sectional, diagnostic accuracy study, we recruited adults presenting with clinical symptoms or suggestive history of tuberculosis or COVID-19, or both. Participants were recruited from a total of 35 primary health facilities in Lima, Peru. Participants provided one nasopharyngeal swab and one sputum sample. For COVID-19, we tested nasopharyngeal swabs and sputum using Xpert Xpress; for tuberculosis, we tested sputum using culture and Xpert Ultra. We compared diagnostic accuracy of sputum testing using Xpert Xpress with nasopharyngeal swab testing using Xpert Xpress. Individuals with positive Xpert Xpress nasopharyngeal swab results were considered COVID-19 positive, and a positive culture indicated tuberculosis. To assess testing integration, the proportion of cases identified in sputum by Xpert Xpress was compared with Xpert Xpress on nasopharyngeal swabs, and sputum by Xpert Ultra was compared with culture. FINDINGS Between Jan 11, 2021, and April 26, 2022, we recruited 600 participants (312 [52%] women and 288 [48%] men). In-study prevalence of tuberculosis was 13% (80 participants, 95% CI 11-16) and of SARS-CoV-2 was 35% (212 participants, 32-39). Among tuberculosis cases, 13 (2·2%, 1·2-3·7) participants were concurrently positive for SARS-CoV-2. Regarding the diagnostic yield of integrated testing, Xpert Ultra detected 96% (89-99) of culture-confirmed tuberculosis cases (n=77), and Xpert Xpress-sputum detected 67% (60-73) of COVID-19 cases (n=134). All five study staff reported that integrated molecular testing was easy and acceptable. INTERPRETATION The diagnostic yield of Xpert Xpress on sputum was moderate, but integrated testing for tuberculosis and COVID-19 with GeneXpert was feasible. However, systematic testing for both diseases might not be the ideal approach for everyone presenting with presumptive tuberculosis or COVID-19, as concurrent positive cases were rare during the study period. Further research might help to identify when integrated testing is most worthwhile and its optimal implementation. FUNDING Canadian Institutes of Health Research and International Development Research Centre. TRANSLATION For the Spanish translation of the abstract see Supplementary Materials section.
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Affiliation(s)
- Emily Lai-Ho MacLean
- Department of Epidemiology, Biostatistics and Occupational Health, Faculty of Medicine and Health Sciences, McGill University, Montreal, QC, Canada; McGill International TB Centre, Research Institute of the McGill University Health Centre, Montreal, QC, Canada
| | - Luz Villa-Castillo
- Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia Lima, Peru
| | - Patricia Espinoza-Lopez
- Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia Lima, Peru
| | - Tatiana Caceres
- Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia Lima, Peru
| | - Giorgia Sulis
- McGill International TB Centre, Research Institute of the McGill University Health Centre, Montreal, QC, Canada; School of Epidemiology and Public Health, Faculty of Medicine, University of Ottawa, Ottawa, ON, Canada
| | | | - Madhukar Pai
- Department of Epidemiology, Biostatistics and Occupational Health, Faculty of Medicine and Health Sciences, McGill University, Montreal, QC, Canada; McGill International TB Centre, Research Institute of the McGill University Health Centre, Montreal, QC, Canada
| | - César Ugarte-Gil
- Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia Lima, Peru; School of Medicine, Universidad Peruana Cayetano Heredia, Lima, Peru.
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Shah M, Paradis S, Betz J, Beylis N, Bharadwaj R, Caceres T, Gotuzzo E, Joloba M, Mave V, Nakiyingi L, Nicol MP, Pradhan N, King B, Armstrong D, Knecht D, Maus CE, Cooper CK, Dorman SE, Manabe YC. Multicenter Study of the Accuracy of the BD MAX Multidrug-resistant Tuberculosis Assay for Detection of Mycobacterium tuberculosis Complex and Mutations Associated With Resistance to Rifampin and Isoniazid. Clin Infect Dis 2021; 71:1161-1167. [PMID: 31560049 PMCID: PMC7442848 DOI: 10.1093/cid/ciz932] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2019] [Accepted: 10/08/2019] [Indexed: 01/29/2023] Open
Abstract
BACKGROUND Tuberculosis (TB) control is hindered by absence of rapid tests to identify Mycobacterium tuberculosis (MTB) and detect isoniazid (INH) and rifampin (RIF) resistance. We evaluated the accuracy of the BD MAX multidrug-resistant (MDR)-TB assay (BD MAX) in South Africa, Uganda, India, and Peru. METHODS Outpatient adults with signs/symptoms of pulmonary TB were prospectively enrolled. Sputum smear microscopy and BD MAX were performed on a single raw sputum, which was then processed for culture and phenotypic drug susceptibility testing (DST), BD MAX, and Xpert MTB/RIF (Xpert). RESULTS 1053 participants with presumptive TB were enrolled (47% female; 32% with human immunodeficiency virus). In patients with confirmed TB, BD MAX sensitivity was 93% (262/282 [95% CI, 89-95%]); specificity was 97% (593/610 [96-98%]) among participants with negative cultures on raw sputa. BD MAX sensitivity was 100% (175/175 [98-100%]) for smear-positive samples (fluorescence microscopy), and 81% (87/107 [73-88%]) in smear-negative samples. Among participants with both BD MAX and Xpert, sensitivity was 91% (249/274 [87-94%]) for BD MAX and 90% (246/274 [86-93%]) for Xpert on processed sputa. Sensitivity and specificity for RIF resistance compared with phenotypic DST were 90% (9/10 [60-98%]) and 95% (211/222 [91-97%]), respectively. Sensitivity and specificity for detection of INH resistance were 82% (22/27 [63-92%]) and 100% (205/205 [98-100%]), respectively. CONCLUSIONS The BD MAX MDR-TB assay had high sensitivity and specificity for detection of MTB and RIF and INH drug resistance and may be an important tool for rapid detection of TB and MDR-TB globally.
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Affiliation(s)
- Maunank Shah
- Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Sonia Paradis
- Becton, Dickinson and Company, Sparks, Maryland, USA
| | - Joshua Betz
- Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Department of Biostatistics, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA
| | - Natalie Beylis
- Division of Medical Microbiology, University of Cape Town, Cape Town, South Africa.,Medical Microbiology Laboratory National Health Laboratory Services Groote Schuur Hospital, Cape Town, South Africa
| | - Renu Bharadwaj
- Byramjee Jeejeebhoy Government Medical College, Johns Hopkins University Clinical Research Site, Pune, Maharashtra, India
| | - Tatiana Caceres
- Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia, Lima, Peru
| | - Eduardo Gotuzzo
- Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia, Lima, Peru
| | - Moses Joloba
- Infectious Diseases Institute, College of Health Sciences, Makerere University, Kampala, Uganda
| | - Vidya Mave
- Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Byramjee Jeejeebhoy Government Medical College, Johns Hopkins University Clinical Research Site, Pune, Maharashtra, India
| | - Lydia Nakiyingi
- Infectious Diseases Institute, College of Health Sciences, Makerere University, Kampala, Uganda
| | - Mark P Nicol
- Division of Medical Microbiology, University of Cape Town, Cape Town, South Africa.,Division of Infection and Immunity, School of Biomedical Sciences, University of Western Australia, Perth, Australia
| | - Neeta Pradhan
- Byramjee Jeejeebhoy Government Medical College, Johns Hopkins University Clinical Research Site, Pune, Maharashtra, India
| | - Bonnie King
- Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Derek Armstrong
- Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | | | | | | | - Susan E Dorman
- Medical University of South Carolina, Charleston, South Carolina, USA
| | - Yukari C Manabe
- Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Infectious Diseases Institute, College of Health Sciences, Makerere University, Kampala, Uganda
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Nabeta P, Havumaki J, Ha DTM, Caceres T, Hang PT, Collantes J, Thi Ngoc Lan N, Gotuzzo E, Denkinger CM. Feasibility of the TBDx automated digital microscopy system for the diagnosis of pulmonary tuberculosis. PLoS One 2017; 12:e0173092. [PMID: 28253302 PMCID: PMC5333855 DOI: 10.1371/journal.pone.0173092] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2016] [Accepted: 02/15/2017] [Indexed: 11/19/2022] Open
Abstract
Background Improved and affordable diagnostic or triage tests are urgently needed at the microscopy centre level. Automated digital microscopy has the potential to overcome issues related to conventional microscopy, including training time requirement and inconsistencies in results interpretation. Methods For this blinded prospective study, sputum samples were collected from adults with presumptive pulmonary tuberculosis in Lima, Peru and Ho Chi Minh City, Vietnam. TBDx performance was evaluated as a stand-alone and as a triage test against conventional microscopy and Xpert, with culture as the reference standard. Xpert was used to confirm positive cases. Findings A total of 613 subjects were enrolled between October 2014 and March 2015, with 539 included in the final analysis. The sensitivity of TBDx was 62·2% (95% CI 56·6–67·4) and specificity was 90·7% (95% CI 85·9–94·2) compared to culture. The algorithm assessing TBDx as a triage test achieved a specificity of 100% while maintaining sensitivity. Interpretation While the diagnostic performance of TBDx did not reach the levels obtained by experienced microscopists in reference laboratories, it is conceivable that it would exceed the performance of less experienced microscopists. In the absence of highly sensitive and specific molecular tests at the microscopy centre level, TBDx in a triage-testing algorithm would optimize specificity and limit overall cost without compromising the number of patients receiving up-front drug susceptibility testing for rifampicin. However, the algorithm would miss over one third of patients compared to Xpert alone.
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Affiliation(s)
| | | | - Dang Thi Minh Ha
- TB Department, Pham Ngoc Thach Hospital, Ho Chi Minh City, Vietnam
| | - Tatiana Caceres
- Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia, Lima, Peru
| | - Pham Thu Hang
- TB Department, Pham Ngoc Thach Hospital, Ho Chi Minh City, Vietnam
| | - Jimena Collantes
- Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia, Lima, Peru
| | | | - Eduardo Gotuzzo
- Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia, Lima, Peru
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Quispe R, Valle GA, Huapaya JA, Novoa I, Giraldo J, Caceres T, Gotuzzo E, Zamudio C, Seas C. Manual MGIT™ system for the detection of Mycobacterium tuberculosis: insights from a high TB burden setting. Int J Tuberc Lung Dis 2016; 20:605-10. [PMID: 27084813 DOI: 10.5588/ijtld.15.0489] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
OBJECTIVE To evaluate the diagnostic performance of manual MGIT™ (MMGIT) compared to the gold standard, Löwenstein-Jensen (LJ), in the diagnosis of pulmonary tuberculosis (TB) in a high-burden setting. METHODS Individuals with suspected TB enrolled in parallel diagnostic trials during 2007-2011 were included. Two samples were obtained from each patient and inoculated into MMGIT and LJ medium. Diagnostic tests were performed, and the incremental yield of a second test and time to detection (TTD) were calculated. Analyses were performed per patient and per sample. Gold standard was based on LJ culture. RESULTS In the per patient and per sample analysis, we evaluated 1436 patients and 4142 samples. The sensitivity and specificity for smear and MMGIT per sample were respectively 89.9%/92.2% and 97.1%/98.9%. Contamination was observed in 1.4% of samples on MMGIT. The mean TTD (days) was 11.8 for MMGIT and 22.9 for LJ. The sensitivity and specificity for smear and MMGIT per patient were respectively 89.9% and 92.2% and 97.1% and 98.3%. A second MMGIT culture had an incremental yield of 1.6%. CONCLUSIONS MMGIT has high sensitivity and specificity, regardless of smear result, with a 50% reduction in TTD compared to LJ. These features make MMGIT an acceptable TB diagnostic method for use in resource-limited settings.
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Affiliation(s)
- R Quispe
- Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia, Lima, Peru
| | - G A Valle
- Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia, Lima, Peru
| | - J A Huapaya
- School of Medicine, Universidad Peruana Cayetano Heredia, Lima, Peru
| | - I Novoa
- Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia, Lima, Peru
| | - J Giraldo
- Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia, Lima, Peru
| | - T Caceres
- Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia, Lima, Peru
| | - E Gotuzzo
- Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia, Lima, Peru; Departamento de Enfermedades Infecciosas, Tropicales y Dermatológicas, Hospital Nacional Cayetano Heredia, Lima, Peru
| | - C Zamudio
- Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia, Lima, Peru
| | - C Seas
- Instituto de Medicina Tropical Alexander von Humboldt, Departamento de Enfermedades Infecciosas, Tropicales y Dermatológicas, Hospital Nacional Cayetano Heredia, Lima, Peru
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Boehme CC, Nicol MP, Nabeta P, Michael JS, Gotuzzo E, Tahirli R, Gler MT, Blakemore R, Worodria W, Gray C, Huang L, Caceres T, Mehdiyev R, Raymond L, Whitelaw A, Sagadevan K, Alexander H, Albert H, Cobelens F, Cox H, Alland D, Perkins MD. Feasibility, diagnostic accuracy, and effectiveness of decentralised use of the Xpert MTB/RIF test for diagnosis of tuberculosis and multidrug resistance: a multicentre implementation study. Lancet 2011; 377:1495-505. [PMID: 21507477 PMCID: PMC3085933 DOI: 10.1016/s0140-6736(11)60438-8] [Citation(s) in RCA: 677] [Impact Index Per Article: 52.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
BACKGROUND The Xpert MTB/RIF test (Cepheid, Sunnyvale, CA, USA) can detect tuberculosis and its multidrug-resistant form with very high sensitivity and specificity in controlled studies, but no performance data exist from district and subdistrict health facilities in tuberculosis-endemic countries. We aimed to assess operational feasibility, accuracy, and effectiveness of implementation in such settings. METHODS We assessed adults (≥18 years) with suspected tuberculosis or multidrug-resistant tuberculosis consecutively presenting with cough lasting at least 2 weeks to urban health centres in South Africa, Peru, and India, drug-resistance screening facilities in Azerbaijan and the Philippines, and an emergency room in Uganda. Patients were excluded from the main analyses if their second sputum sample was collected more than 1 week after the first sample, or if no valid reference standard or MTB/RIF test was available. We compared one-off direct MTB/RIF testing in nine microscopy laboratories adjacent to study sites with 2-3 sputum smears and 1-3 cultures, dependent on site, and drug-susceptibility testing. We assessed indicators of robustness including indeterminate rate and between-site performance, and compared time to detection, reporting, and treatment, and patient dropouts for the techniques used. FINDINGS We enrolled 6648 participants between Aug 11, 2009, and June 26, 2010. One-off MTB/RIF testing detected 933 (90·3%) of 1033 culture-confirmed cases of tuberculosis, compared with 699 (67·1%) of 1041 for microscopy. MTB/RIF test sensitivity was 76·9% in smear-negative, culture-positive patients (296 of 385 samples), and 99·0% specific (2846 of 2876 non-tuberculosis samples). MTB/RIF test sensitivity for rifampicin resistance was 94·4% (236 of 250) and specificity was 98·3% (796 of 810). Unlike microscopy, MTB/RIF test sensitivity was not significantly lower in patients with HIV co-infection. Median time to detection of tuberculosis for the MTB/RIF test was 0 days (IQR 0-1), compared with 1 day (0-1) for microscopy, 30 days (23-43) for solid culture, and 16 days (13-21) for liquid culture. Median time to detection of resistance was 20 days (10-26) for line-probe assay and 106 days (30-124) for conventional drug-susceptibility testing. Use of the MTB/RIF test reduced median time to treatment for smear-negative tuberculosis from 56 days (39-81) to 5 days (2-8). The indeterminate rate of MTB/RIF testing was 2·4% (126 of 5321 samples) compared with 4·6% (441 of 9690) for cultures. INTERPRETATION The MTB/RIF test can effectively be used in low-resource settings to simplify patients' access to early and accurate diagnosis, thereby potentially decreasing morbidity associated with diagnostic delay, dropout and mistreatment. FUNDING Foundation for Innovative New Diagnostics, Bill & Melinda Gates Foundation, European and Developing Countries Clinical Trials Partnership (TA2007.40200.009), Wellcome Trust (085251/B/08/Z), and UK Department for International Development.
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Lissi EA, Caceres T. Oxygen diffusion-concentration in erythrocyte plasma membranes studied by the fluorescence quenching of anionic and cationic pyrene derivatives. J Bioenerg Biomembr 1989; 21:375-85. [PMID: 2745401 DOI: 10.1007/bf00762728] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Fluorescence quenching by oxygen of cationic [pyrene-(CH2)nN(CH3)3+; n = 1, 4, and 11] and anionic [pyrene-(CH2)nCO2-, n = 3, 8, 11, and 15] probes was investigated in erythrocyte plasma membranes (leaky) in order to assess the ability of oxygen molecules to interact with solutes located at different positions in the membrane. The pseudounimolecular quenching rate constants measured increase, both for cationic and anionic probes, when n increases. These results are interpreted in terms of an increased oxygen solubility toward the center of the membrane interior, and imply that lateral diffusion contributes more than transverse diffusion to total oxygen mobility. For all of the probes considered, quenching rates increase when n-alkanols are added. The effect observed increases when n decreases and when the size of the n-alkanol alkyl chain increases. Arrhenius-type plots for the quenching rate constants show noticeable downward curvatures. Average (0-40 degrees C) activation energies are approximately 6 kcal/mol.
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Affiliation(s)
- E A Lissi
- Department of Chemistry, University of Santiago, Chile
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