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Koo BH, Lee YJ, Park NR, Heo SC, Hudson DM, Fernandes AA, Friday CS, Hast MW, Corr DT, Keene DR, Tufa SF, Dyment NA, Joeng KS. Characterization of TGFβ1-induced tendon-like structure in the scaffold-free three-dimensional tendon cell culture system. Sci Rep 2024; 14:9495. [PMID: 38664570 PMCID: PMC11045825 DOI: 10.1038/s41598-024-60221-4] [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] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2024] [Accepted: 04/19/2024] [Indexed: 04/28/2024] Open
Abstract
The biological mechanisms regulating tenocyte differentiation and morphological maturation have not been well-established, partly due to the lack of reliable in vitro systems that produce highly aligned collagenous tissues. In this study, we developed a scaffold-free, three-dimensional (3D) tendon culture system using mouse tendon cells in a differentially adherent growth channel. Transforming Growth Factor-β (TGFβ) signaling is involved in various biological processes in the tendon, regulating tendon cell fate, recruitment and maintenance of tenocytes, and matrix organization. This known function of TGFβ signaling in tendon prompted us to utilize TGFβ1 to induce tendon-like structures in 3D tendon constructs. TGFβ1 treatment promoted a tendon-like structure in the peripheral layer of the constructs characterized by increased thickness with a gradual decrease in cell density and highly aligned collagen matrix. TGFβ1 also enhanced cell proliferation, matrix production, and morphological maturation of cells in the peripheral layer compared to vehicle treatment. TGFβ1 treatment also induced early tenogenic differentiation and resulted in sufficient mechanical integrity, allowing biomechanical testing. The current study suggests that this scaffold-free 3D tendon cell culture system could be an in vitro platform to investigate underlying biological mechanisms that regulate tenogenic cell differentiation and matrix organization.
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Affiliation(s)
- Bon-Hyeock Koo
- McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104-6081, USA
| | - Yeon-Ju Lee
- McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104-6081, USA
- Research and Development Division, BioBricks Co., Ltd, Pohang, 37673, Republic of Korea
| | - Na Rae Park
- McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104-6081, USA
- Department of Molecular Medicine, Cell and Matrix Research Institute, School of Medicine, Kyungpook National University, Daegu, 41944, Republic of Korea
| | - Su Chin Heo
- McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104-6081, USA
| | - David M Hudson
- Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, WA, 98195, USA
| | - Aysel A Fernandes
- Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, WA, 98195, USA
| | - Chet S Friday
- McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104-6081, USA
| | - Michael W Hast
- McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104-6081, USA
| | - David T Corr
- Center for Modeling, Simulation, and Imaging in Medicine (CeMSIM), Department of Biomedical Engineering, Rensselaer Polytechnic Institute, Troy, NY, 12180-3590, USA
| | - Douglas R Keene
- Micro-Imaging Center, Shriners Children's, Portland, OR, 97239, USA
| | - Sara F Tufa
- Micro-Imaging Center, Shriners Children's, Portland, OR, 97239, USA
| | - Nathaniel A Dyment
- McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104-6081, USA
| | - Kyu Sang Joeng
- McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104-6081, USA.
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Kang H, Strong AL, Sun Y, Guo L, Juan C, Bancroft AC, Choi JH, Pagani CA, Fernandes AA, Woodard M, Lee J, Ramesh S, James AW, Hudson D, Dalby KN, Xu L, Tower RJ, Levi B. The HIF-1α/PLOD2 axis integrates extracellular matrix organization and cell metabolism leading to aberrant musculoskeletal repair. Bone Res 2024; 12:17. [PMID: 38472175 PMCID: PMC10933265 DOI: 10.1038/s41413-024-00320-0] [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] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2023] [Revised: 01/04/2024] [Accepted: 02/01/2024] [Indexed: 03/14/2024] Open
Abstract
While hypoxic signaling has been shown to play a role in many cellular processes, its role in metabolism-linked extracellular matrix (ECM) organization and downstream processes of cell fate after musculoskeletal injury remains to be determined. Heterotopic ossification (HO) is a debilitating condition where abnormal bone formation occurs within extra-skeletal tissues. Hypoxia and hypoxia-inducible factor 1α (HIF-1α) activation have been shown to promote HO. However, the underlying molecular mechanisms by which the HIF-1α pathway in mesenchymal progenitor cells (MPCs) contributes to pathologic bone formation remain to be elucidated. Here, we used a proven mouse injury-induced HO model to investigate the role of HIF-1α on aberrant cell fate. Using single-cell RNA sequencing (scRNA-seq) and spatial transcriptomics analyses of the HO site, we found that collagen ECM organization is the most highly up-regulated biological process in MPCs. Zeugopod mesenchymal cell-specific deletion of Hif1α (Hoxa11-CreERT2; Hif1afl/fl) significantly mitigated HO in vivo. ScRNA-seq analysis of these Hoxa11-CreERT2; Hif1afl/fl mice identified the PLOD2/LOX pathway for collagen cross-linking as downstream of the HIF-1α regulation of HO. Importantly, our scRNA-seq data and mechanistic studies further uncovered that glucose metabolism in MPCs is most highly impacted by HIF-1α deletion. From a translational aspect, a pan-LOX inhibitor significantly decreased HO. A newly screened compound revealed that the inhibition of PLOD2 activity in MPCs significantly decreased osteogenic differentiation and glycolytic metabolism. This suggests that the HIF-1α/PLOD2/LOX axis linked to metabolism regulates HO-forming MPC fate. These results suggest that the HIF-1α/PLOD2/LOX pathway represents a promising strategy to mitigate HO formation.
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Affiliation(s)
- Heeseog Kang
- Center for Organogenesis, Regeneration and Trauma, Department of Surgery, University of Texas Southwestern, Dallas, TX, 75390, USA
| | - Amy L Strong
- Section of Plastic Surgery, Department of Surgery, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Yuxiao Sun
- Center for Organogenesis, Regeneration and Trauma, Department of Surgery, University of Texas Southwestern, Dallas, TX, 75390, USA
| | - Lei Guo
- Quantitative Biomedical Research Center, Peter O'Donnell Jr. School of Public Health, University of Texas Southwestern, Dallas, TX, 75390, USA
| | - Conan Juan
- Center for Organogenesis, Regeneration and Trauma, Department of Surgery, University of Texas Southwestern, Dallas, TX, 75390, USA
| | - Alec C Bancroft
- Center for Organogenesis, Regeneration and Trauma, Department of Surgery, University of Texas Southwestern, Dallas, TX, 75390, USA
| | - Ji Hae Choi
- Center for Organogenesis, Regeneration and Trauma, Department of Surgery, University of Texas Southwestern, Dallas, TX, 75390, USA
| | - Chase A Pagani
- Center for Organogenesis, Regeneration and Trauma, Department of Surgery, University of Texas Southwestern, Dallas, TX, 75390, USA
| | - Aysel A Fernandes
- Department of Orthopedics and Sports Medicine, University of Washington, Seattle, WA, 98195, USA
| | - Michael Woodard
- Center for Organogenesis, Regeneration and Trauma, Department of Surgery, University of Texas Southwestern, Dallas, TX, 75390, USA
| | - Juhoon Lee
- Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, University of Texas at Austin, Austin, TX, 78712, USA
| | - Sowmya Ramesh
- Department of Pathology, Johns Hopkins University, Baltimore, MD, 21218, USA
| | - Aaron W James
- Department of Pathology, Johns Hopkins University, Baltimore, MD, 21218, USA
| | - David Hudson
- Department of Orthopedics and Sports Medicine, University of Washington, Seattle, WA, 98195, USA
| | - Kevin N Dalby
- Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, University of Texas at Austin, Austin, TX, 78712, USA
| | - Lin Xu
- Quantitative Biomedical Research Center, Peter O'Donnell Jr. School of Public Health, University of Texas Southwestern, Dallas, TX, 75390, USA
| | - Robert J Tower
- Center for Organogenesis, Regeneration and Trauma, Department of Surgery, University of Texas Southwestern, Dallas, TX, 75390, USA
| | - Benjamin Levi
- Center for Organogenesis, Regeneration and Trauma, Department of Surgery, University of Texas Southwestern, Dallas, TX, 75390, USA.
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Silva MET, Bessa JNM, Parente MPL, Mascarenhas T, Natal Jorge RM, Fernandes AA. Effect of mesh anchoring technique in uterine prolapse repair surgery: A finite element analysis. J Biomech 2021; 127:110649. [PMID: 34375905 DOI: 10.1016/j.jbiomech.2021.110649] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2020] [Revised: 05/28/2021] [Accepted: 07/25/2021] [Indexed: 11/17/2022]
Abstract
The female pelvic cavity involves muscles, ligaments, endopelvic fasciae and multiple organs where different pathologies may occur, namely the pelvic organ prolapse (POP). The synthetic implants are used for the reconstructive surgery of POP, but severe complications associated with their use have been reported, mainly related to their mechanical properties (e.g., implant stiffness) and microstructure. In this study, we mimicked a transvaginal reconstructive surgery to repair the apical ligaments (uterosacral ligaments (USLs) and cardinal ligaments (CLs)), by modeling, their impairment (90% and 50%) and/or total rupture. The implants to reinforce/replace these ligaments were built based on literature specifications and their mechanical properties were obtained through uniaxial tensile tests. The main aim of this study was to simulate the effect of mesh anchoring technique (simple stich and continuous stitch), and compare the displacement magnitude of the pelvic tissues, during Valsalva maneuver. The absence/presence of the synthetic implant was simulated when total rupture of the CLs and USLs occurs, causing a variation of the vaginal displacement (9% for the CLs and 27% for the USLs). Additionally, the simulations showed that there was a variation of the supero-inferior displacement of the vaginal wall between different anchoring techniques (simple stich and continuous stitch) being approximately of 10% for the simulation USLs and CLs implant. The computational simulation was able to mimic the biomechanical behavior of the USLs and CLs, in response to different anchoring techniques, which can be help improving the outcomes of the prolapse surgery.
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Affiliation(s)
- M E T Silva
- LAETA, INEGI, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias s/n, Porto 4200 - 465, Portugal.
| | - J N M Bessa
- Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias s/n, Porto 4200 - 465, Portugal.
| | - M P L Parente
- LAETA, INEGI, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias s/n, Porto 4200 - 465, Portugal.
| | - T Mascarenhas
- Dep. of Obstetrics and Gynecology, CHSJ-EPE / Faculty of Medicine, University of Porto, Alameda Professor Hernâni Monteiro, Porto 4200 - 319, Portugal.
| | - R M Natal Jorge
- LAETA, INEGI, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias s/n, Porto 4200 - 465, Portugal.
| | - A A Fernandes
- LAETA, INEGI, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias s/n, Porto 4200 - 465, Portugal.
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McAlinden A, Hudson DM, Fernandes AA, Ravindran S, Fernandes RJ. Biochemical and immuno-histochemical localization of type IIA procollagen in annulus fibrosus of mature bovine intervertebral disc. Matrix Biol Plus 2021; 12:100077. [PMID: 34337380 PMCID: PMC8313739 DOI: 10.1016/j.mbplus.2021.100077] [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] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Revised: 06/08/2021] [Accepted: 06/24/2021] [Indexed: 11/05/2022] Open
Abstract
For next generation tissue-engineered constructs and regenerative medicine to succeed clinically, the basic biology and extracellular matrix composition of tissues that these repair techniques seek to restore have to be fully determined. Using the latest reagents coupled with tried and tested methodologies, we continue to uncover previously undetected structural proteins in mature intervertebral disc. In this study we show that the “embryonic” type IIA procollagen isoform (containing a cysteine-rich amino propeptide) was biochemically detectable in the annulus fibrosus of both calf and mature steer caudal intervertebral discs, but not in the nucleus pulposus where the type IIB isoform was predominantly localized. Specifically, the triple-helical type IIA procollagen isoform immunolocalized in the outer margins of the inner annulus fibrosus. Triple helical processed type II collagen exclusively localized within the inter-lamellae regions and with type IIA procollagen in the intra-lamellae regions. Mass spectrometry of the α1(II) collagen chains from the region where type IIA procollagen localized showed high 3-hydroxylation of Proline-944, a post-translational modification that is correlated with thin collagen fibrils as in the nucleus pulposus. The findings implicate small diameter fibrils of type IIA procollagen in select regions of the annulus fibrosus where it likely contributes to the organization of collagen bundles and structural properties within the type I-type II collagen transition zone.
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Affiliation(s)
- Audrey McAlinden
- Department of Orthopaedic Surgery, Washington University School of Medicine, St Louis, MO, USA.,Department of Cell Biology & Physiology, Washington University School of Medicine, St Louis, MO, USA.,Shriners Hospitals for Children- St Louis, MO, USA
| | - David M Hudson
- Department of Orthopaedic & Sports Medicine, University of Washington, Seattle, WA, USA
| | - Aysel A Fernandes
- Department of Orthopaedic & Sports Medicine, University of Washington, Seattle, WA, USA
| | - Soumya Ravindran
- Department of Orthopaedic Surgery, Washington University School of Medicine, St Louis, MO, USA
| | - Russell J Fernandes
- Department of Orthopaedic & Sports Medicine, University of Washington, Seattle, WA, USA
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Ramião NG, Martins PS, Barroso ML, Santos DC, Fernandes AA. Biomechanical analysis of intact versus ruptured Poly Implant Prothèse breast implants. Interface Focus 2019; 9:20180086. [PMID: 31263530 DOI: 10.1098/rsfs.2018.0086] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/02/2019] [Indexed: 01/13/2023] Open
Abstract
Despite there being many studies that have evaluated breast implant rupture, there is no consensus about causes and incidence. Most studies lack a multifactorial analysis of what causes breast implants to rupture. To fill this gap, an experimental protocol was developed to compare ruptured and intact Poly Implant Prothèse (PIP) breast implants from the same woman. These conditions guarantee that the physical/biological variables are the same for each pair of ruptured and intact implants. A total of 1008 samples from 22 PIP explants (11 intact and 11 ruptured) and three control PIP implants were analysed. The mechanical properties (tensile strength) of the ruptured and intact implants were compared according to brand, lot, implantation time and demographic conditions. In general, statistically significant differences were found between the intact and ruptured PIP implants. Ruptured implants were thinner (0.73 ± 0.10 mm versus 0.91 ± 0.11 mm) and weaker (7.42 ± 2.65 MPa versus 9.59 ± 2.37 MPa) than intact implants. Intact and ruptured implants have shown distinct mechanical behaviours and variations in thickness. Our understanding is that these differences may be associated with the typical manufacturing process of breast implant shells. These results stress the importance of thorough control of the shell thickness. Given its relevance, shell thickness should be used as a quality control measure for homologation purposes. Thus, the homogeneity of the shell should be considered as a relevant parameter during the manufacturing process. This will translate into an improved quality of life for patients and will potentiate safer and longer lasting products.
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Affiliation(s)
- N G Ramião
- INEGI, LAETA, Faculty of Engineering of the University of Porto, Campus da FEUP, Rua Dr. Roberto Frias, 400, 4200-465 Porto, Portugal
| | - P S Martins
- INEGI, LAETA, Faculty of Engineering of the University of Porto, Campus da FEUP, Rua Dr. Roberto Frias, 400, 4200-465 Porto, Portugal
| | - M L Barroso
- Department of Plastic Surgery, Gaia Hospital Center, Vila Nova de Gaia, Portugal
| | - D C Santos
- Department of Plastic Surgery, Gaia Hospital Center, Vila Nova de Gaia, Portugal
| | - A A Fernandes
- INEGI, LAETA, Faculty of Engineering of the University of Porto, Campus da FEUP, Rua Dr. Roberto Frias, 400, 4200-465 Porto, Portugal
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Ribeiro Júnior RF, Ronconi KS, Jesus ICG, Almeida PWM, Forechi L, Vassallo DV, Guatimosim S, Stefanon I, Fernandes AA. Testosterone deficiency prevents left ventricular contractility dysfunction after myocardial infarction. Mol Cell Endocrinol 2018; 460:14-23. [PMID: 28606867 DOI: 10.1016/j.mce.2017.06.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/06/2016] [Revised: 05/17/2017] [Accepted: 06/08/2017] [Indexed: 11/30/2022]
Abstract
Testosterone may affect myocardial contractility since its deficiency decreases the contraction and relaxation of the heart. Meanwhile, testosterone replacement therapy has raised concerns because it may worsen cardiac dysfunction and remodeling after myocardial infarction (MI). In this study, we evaluate cardiac contractility 60 days after MI in rats with suppressed testosterone. Male Wistar rats underwent bilateral orchidectomy one week before the ligation of the anterior descending left coronary artery. The animals were divided into orchidectomized (OCT); MI; orchidectomized + MI (OCT + MI); orchidectomized + MI + testosterone (OCT + MI + T) and control (Sham) groups. Eight weeks after MI, papillary muscle contractility was analyzed under increasing calcium (0.62, 1.25, 2.5 and 3.75 mM) and isoproterenol (10-8 to 10-2 M) concentrations. Ventricular myocytes were isolated for intracellular calcium measurements and assessment of Ca2+ handling proteins. Contractility was preserved in the orchidectomized animals after myocardial infarction and was reduced when testosterone was replaced (Ca2+ 3.75 mM: Sham: 608 ± 70 (n = 11); OCT: 590 ± 37 (n = 16); MI: 311 ± 33* (n = 9); OCT + MI: 594 ± 76 (n = 7); OCT + MI + T: 433 ± 38* (n=4), g/g *p < 0.05 vs Sham). Orchidectomy also increased the Ca2+ transient amplitude of the ventricular myocytes and SERCA-2a protein expression levels. PLB phosphorylation levels at Thr17 were not different in the orchidectomized animals compared to the Sham animals but were reduced after testosterone replacement. CAMKII phosphorylation and protein nitrosylation increased in the orchidectomized animals. Our results support the view that testosterone deficiency prevents MI contractility dysfunction by altering the key proteins involved in Ca2+ handling.
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Affiliation(s)
- R F Ribeiro Júnior
- Department of Physiological Sciences, Universidade Federal do Espírito Santo, Vitória, ES, Brazil.
| | - K S Ronconi
- Department of Physiological Sciences, Universidade Federal do Espírito Santo, Vitória, ES, Brazil
| | - I C G Jesus
- Department of Physiology and Biophysics, Universidade Federal de Minas Gerais, Minas Gerais, MG, Brazil
| | - P W M Almeida
- Department of Physiology and Biophysics, Universidade Federal de Minas Gerais, Minas Gerais, MG, Brazil
| | - L Forechi
- Department of Physiological Sciences, Universidade Federal do Espírito Santo, Vitória, ES, Brazil
| | - D V Vassallo
- Department of Physiological Sciences, Universidade Federal do Espírito Santo, Vitória, ES, Brazil
| | - S Guatimosim
- Department of Physiology and Biophysics, Universidade Federal de Minas Gerais, Minas Gerais, MG, Brazil
| | - I Stefanon
- Department of Physiological Sciences, Universidade Federal do Espírito Santo, Vitória, ES, Brazil
| | - A A Fernandes
- Department of Physiological Sciences, Universidade Federal do Espírito Santo, Vitória, ES, Brazil
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Ramião NG, Martins PS, Barroso ML, Santos DC, Fernandes AA. An experimental analysis of shell failure in breast implants. J Mech Behav Biomed Mater 2017; 72:22-28. [PMID: 28437660 DOI: 10.1016/j.jmbbm.2017.04.005] [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] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2017] [Accepted: 04/05/2017] [Indexed: 11/18/2022]
Abstract
Breast implant durability and the mechanisms of rupture are important topics in the medical community, for patients, manufactures and regulatory medical agencies. After concerns about the Poly Implant Prosthesis (PIP) implants, the need for understanding the adverse outcomes and the failure mode to improve the breast implants increased. The objective of this research is to analyze and describe the rupture characteristics of failed explanted PIP implants to study the modes and causes of rupture. Eleven explanted PIP implants were analyzed by visual inspection and scanning electron microscopy (SEM). To simulate hypothetical ruptures caused by cyclic mechanical stress (fatigue) in the implant shell, two control implants were submitted to fatigue tests, and analyzed with SEM. Small ruptures (either Hole or split) striations were found, which normally appear due to fatigue phenomena. Similar striations were also found in specimens (control) tested under laboratory controlled conditions. In the context of this work, the striations found in explants constitute a significant finding as they point to the occurrence of fatigue phenomena associated with mammary implants rupture. This research, also demonstrates that rupture surface analysis of explanted breast implants has the potential to become a useful indicator for assessing implant rupture mechanisms.
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Affiliation(s)
- N G Ramião
- INEGI, LAETA, Faculdade de Engenharia da Universidade do Porto, Portugal.
| | - P S Martins
- INEGI, LAETA, Faculdade de Engenharia da Universidade do Porto, Portugal.
| | - M L Barroso
- Department of Plastic Surgery of Gaia Hospital Center, Vila Nova de Gaia, Portugal.
| | - D C Santos
- Department of Plastic Surgery of Gaia Hospital Center, Vila Nova de Gaia, Portugal.
| | - A A Fernandes
- INEGI, LAETA, Faculdade de Engenharia da Universidade do Porto, Portugal.
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8
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Ramião NG, Martins PS, Barroso ML, Santos DC, Fernandes AA. Breast implants rupture induced by fatigue phenomena. J Plast Reconstr Aesthet Surg 2017; 70:552-553. [PMID: 28159545 DOI: 10.1016/j.bjps.2017.01.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2016] [Revised: 11/16/2016] [Accepted: 01/04/2017] [Indexed: 10/20/2022]
Affiliation(s)
- N G Ramião
- INEGI, LAETA, Faculty of Engineering of the University of Porto, Portugal
| | - P S Martins
- INEGI, LAETA, Faculty of Engineering of the University of Porto, Portugal.
| | - M L Barroso
- Department of Plastic Surgery of Gaia Hospital Center, Vila Nova de Gaia, Portugal
| | - D C Santos
- Department of Plastic Surgery of Gaia Hospital Center, Vila Nova de Gaia, Portugal
| | - A A Fernandes
- INEGI, LAETA, Faculty of Engineering of the University of Porto, Portugal
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9
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Costa CMA, Sillero-Quintana M, Piñonosa Cano S, Moreira DG, Brito CJ, Fernandes AA, Pussieldi GA, Marins JCB. Daily oscillations of skin temperature in military personnel using thermography. J ROY ARMY MED CORPS 2015; 162:335-342. [PMID: 26385071 DOI: 10.1136/jramc-2015-000462] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2015] [Accepted: 08/29/2015] [Indexed: 11/04/2022]
Abstract
INTRODUCTION The human body makes many physiological adjustments throughout the day, including adjustments to body temperature. The purpose of this study was to determine oscillations in the skin temperature (Tsk-1-Tsk-25) at 25 body regions of interest (ROIs) over 1 day using infrared thermography. METHODS Tsk values of 31 male (age 22.9±3.0 years) Brazilian Air Force members were evaluated from five thermograms collected at 7, 11, 15, 19 and 23 h (Tsk7,11,15,19,23) by a Fluke imager. We applied one-way analysis of variance for repeated measures for the different times of the day and Tukey's post hoc test to determine significant Tsk differences between ROIs (α=0.05), and the cosinor analysis was used to determine the midline estimating statistic of rhythm, amplitude and acrophase of Tsk during the 24 h period. RESULTS The anterior hands showed the greatest Tsk variations throughout the day. In the lower limbs, scapula, abdomen, chest and lower back, Tsk-11, Tsk-15, Tsk-19 and Tsk-23 were significantly different (p<0.05) from Tsk-7. The lowest Tsk values were obtained in the early morning, with increases in the afternoon and levelling after 15:00. CONCLUSIONS The Tsk at all ROIs and the averaged Tsk showed oscillations throughout the day, with the lowest values in the early morning (07:00). Temperature fluctuations depended on the specific ROI, with thermal stabilisation in some regions in the afternoon and a central upward trend throughout the day in the hands.
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Affiliation(s)
- Carlos Magno Amaral Costa
- Federal University of Viçosa, Laboratory Human Performance, Minas Gerais, Brazil Aeronatutics Instruction and Adaptation Center, Minas Gerais, Brazil
| | - M Sillero-Quintana
- Faculty of Sport Sciences, Technical University of Madrid (UPM), Madrid, Spain
| | - S Piñonosa Cano
- Faculty of Sport Sciences, Technical University of Madrid (UPM), Madrid, Spain
| | - D G Moreira
- Federal University of Viçosa, Laboratory Human Performance, Minas Gerais, Brazil
| | - C J Brito
- Federal University of Viçosa, Laboratory Human Performance, Minas Gerais, Brazil
| | - A A Fernandes
- Federal University of Viçosa, Laboratory Human Performance, Minas Gerais, Brazil
| | - G A Pussieldi
- Federal University of Viçosa, Laboratory Human Performance, Minas Gerais, Brazil
| | - J C B Marins
- Federal University of Viçosa, Laboratory Human Performance, Minas Gerais, Brazil
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Fernandes AA, Faria TDO, Ribeiro Júnior RF, Costa GP, Marchezini B, Silveira EA, Angeli JK, Stefanon I, Vassallo DV, Lizardo JH. A single resistance exercise session improves myocardial contractility in spontaneously hypertensive rats. ACTA ACUST UNITED AC 2015; 48:813-21. [PMID: 26176315 PMCID: PMC4568809 DOI: 10.1590/1414-431x20154355] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2014] [Accepted: 03/20/2015] [Indexed: 01/03/2023]
Abstract
Resistance training evokes myocardial adaptation; however, the effects of a single
resistance exercise session on cardiac performance are poorly understood or
investigated. This study aimed to investigate the effects of a single resistance
exercise session on the myocardial contractility of spontaneously hypertensive rats
(SHRs). Male 3-month-old SHRs were divided into two groups: control (Ct) and exercise
(Ex). Control animals were submitted to sham exercise. Blood pressure was measured in
conscious rats before the exercise session to confirm the presence of arterial
hypertension. Ten minutes after the exercise session, the animals were anesthetized
and killed, and the hearts were removed. Cardiac contractility was evaluated in the
whole heart by the Langendorff technique and by isometric contractions of isolated
left ventricular papillary muscles. SERCA2a, phospholamban (PLB), and phosphorylated
PLB expression were investigated by Western blot. Exercise increased force
development of isolated papillary muscles (Ex=1.0±0.1 g/mg vs
Ct=0.63±0.2 g/mg, P<0.05). Post-rest contraction was greater in the exercised
animals (Ex=4.1±0.4% vs Ct=1.7±0.2%, P<0.05). Papillary muscles
of exercised animals developed greater force under increasing isoproterenol
concentrations (P<0.05). In the isolated heart, exercise increased left
ventricular isovolumetric systolic pressure (LVISP; Δ +39 mmHg; P<0.05) from
baseline conditions. Hearts from the exercised rats presented a greater response to
increasing diastolic pressure. Positive inotropic intervention to calcium and
isoproterenol resulted in greater LVISP in exercised animals (P<0.05). The results
demonstrated that a single resistance exercise session improved myocardial
contractility in SHRs.
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Affiliation(s)
- A A Fernandes
- Departamento de Morfologia, Universidade Federal do Espírito Santo, Vitória, ES, BR
| | - T de O Faria
- Departamento de Ciências Fisiológicas, Universidade Federal do Espírito Santo, Vitória, ES, BR
| | - R F Ribeiro Júnior
- Departamento de Ciências Fisiológicas, Universidade Federal do Espírito Santo, Vitória, ES, BR
| | - G P Costa
- Departamento de Ciências Fisiológicas, Universidade Federal do Espírito Santo, Vitória, ES, BR
| | - B Marchezini
- Departamento de Ciências Fisiológicas, Universidade Federal do Espírito Santo, Vitória, ES, BR
| | - E A Silveira
- Departamento de Ciências Fisiológicas, Universidade Federal do Espírito Santo, Vitória, ES, BR
| | - J K Angeli
- Departamento de Ciências Fisiológicas, Universidade Federal do Espírito Santo, Vitória, ES, BR
| | - I Stefanon
- Departamento de Ciências Fisiológicas, Universidade Federal do Espírito Santo, Vitória, ES, BR
| | - D V Vassallo
- Departamento de Ciências Fisiológicas, Escola Superior de Ciências da Santa Casa de Misericórdia de Vitória, Vitória, ES, BR
| | - J H Lizardo
- Departamento de Morfologia, Universidade Federal do Espírito Santo, Vitória, ES, BR
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11
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Fioresi M, Furieri LB, Simões MR, Ribeiro RF, Meira EF, Fernandes AA, Stefanon I, Vassallo DV. Acute exposure to lead increases myocardial contractility independent of hypertension development. Braz J Med Biol Res 2013; 46:178-85. [PMID: 23369976 PMCID: PMC3854357 DOI: 10.1590/1414-431x20122190] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2012] [Accepted: 09/24/2012] [Indexed: 11/22/2022] Open
Abstract
We studied the effects of the acute administration of small doses of lead over time on hemodynamic parameters in anesthetized rats to determine if myocardial contractility changes are dependent or not on the development of hypertension. Male Wistar rats received 320 µg/kg lead acetate iv once, and their hemodynamic parameters were measured for 2 h. Cardiac contractility was evaluated in vitro using left ventricular papillary muscles as were Na+,K+-ATPase and myosin Ca2+-ATPase activities. Lead increased left- (control: 112 ± 3.7 vs lead: 129 ± 3.2 mmHg) and right-ventricular systolic pressures (control: 28 ± 1.2 vs lead: 34 ± 1.2 mmHg) significantly without modifying heart rate. Papillary muscles were exposed to 8 µM lead acetate and evaluated 60 min later. Isometric contractions increased (control: 0.546 ± 0.07 vs lead: 0.608 ± 0.06 g/mg) and time to peak tension decreased (control: 268 ± 13 vs lead: 227 ± 5.58 ms), but relaxation time was unchanged. Post-pause potentiation was similar between groups (n = 6 per group), suggesting no change in sarcoplasmic reticulum activity, evaluated indirectly by this protocol. After 1-h exposure to lead acetate, the papillary muscles became hyperactive in response to a β-adrenergic agonist (10 µM isoproterenol). In addition, post-rest contractions decreased, suggesting a reduction in sarcolemmal calcium influx. The heart samples treated with 8 µM lead acetate presented increased Na+,K+-ATPase (approximately 140%, P < 0.05 for control vs lead) and myosin ATPase (approximately 30%, P < 0.05 for control vs lead) activity. Our results indicated that acute exposure to low lead concentrations produces direct positive inotropic and lusitropic effects on myocardial contractility and increases the right and left ventricular systolic pressure, thus potentially contributing to the early development of hypertension.
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Affiliation(s)
- M Fioresi
- Programa de Pós-Graduação em Ciências Fisiológicas, Centro de Ciências da Saúde, Universidade Federal do Espírito Santo, Vitória, ES, Brasil.
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12
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Stefanon I, Cade JR, Fernandes AA, Ribeiro Junior RF, Targueta GP, Mill JG, Vassallo DV. Ventricular performance and Na+-K+ ATPase activity are reduced early and late after myocardial infarction in rats. ACTA ACUST UNITED AC 2009; 42:902-11. [PMID: 19787147 DOI: 10.1590/s0100-879x2009005000015] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2008] [Accepted: 06/26/2009] [Indexed: 11/22/2022]
Abstract
Myocardial infarction leads to compensatory ventricular remodeling. Disturbances in myocardial contractility depend on the active transport of Ca2+ and Na+, which are regulated by Na+-K+ ATPase. Inappropriate regulation of Na+-K+ ATPase activity leads to excessive loss of K+ and gain of Na+ by the cell. We determined the participation of Na+-K+ ATPase in ventricular performance early and late after myocardial infarction. Wistar rats (8-10 per group) underwent left coronary artery ligation (infarcted, Inf) or sham-operation (Sham). Ventricular performance was measured at 3 and 30 days after surgery using the Langendorff technique. Left ventricular systolic pressure was obtained under different ventricular diastolic pressures and increased extracellular Ca2+ concentrations (Ca2+e) and after low and high ouabain concentrations. The baseline coronary perfusion pressure increased 3 days after myocardial infarction and normalized by 30 days (Sham 3 = 88 +/- 6; Inf 3 = 130 +/- 9; Inf 30 = 92 +/- 7 mmHg; P < 0.05). The inotropic response to Ca2+e and ouabain was reduced at 3 and 30 days after myocardial infarction (Ca2+ = 1.25 mM; Sham 3 = 70 +/- 3; Inf 3 = 45 +/- 2; Inf 30 = 29 +/- 3 mmHg; P < 0.05), while the Frank-Starling mechanism was preserved. At 3 and 30 days after myocardial infarction, ventricular Na+-K+ ATPase activity and contractility were reduced. This Na+-K+ ATPase hypoactivity may modify the Na+, K+ and Ca2+ transport across the sarcolemma resulting in ventricular dysfunction.
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Affiliation(s)
- I Stefanon
- Departamento de Ciências Fisiológicas, Universidade Federal do Espírito Santo, Vitória, ES, Brasil.
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13
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Afonso JS, Martins PALS, Girao MJBC, Natal Jorge RM, Ferreira AJM, Mascarenhas T, Fernandes AA, Bernardes J, Baracat EC, Rodrigues de Lima G, Patricio B. Mechanical properties of polypropylene mesh used in pelvic floor repair. Int Urogynecol J 2007; 19:375-80. [PMID: 17846702 DOI: 10.1007/s00192-007-0446-1] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2007] [Accepted: 08/07/2007] [Indexed: 10/22/2022]
Abstract
The aim of this study was the comparison of the stiffness of different meshes under two types of mechanical tests. Five different mesh types were mechanically tested. The methods used consisted on uniaxial tension test (tensile stiffness) and tape ring tests, experimental continuous compression of the mesh loops (flexural stiffness). The most significant difference of tensile stiffness behaviour appears between Aris and TVTO. From the analysis of the experimental data, we divided the flexural stiffness, in two main groups. The first group includes Auto Suture and Aris meshes. The two meshes seem to have a similar flexural behaviour. The second group includes TVTO, Uretex and Avaulta. The difference between these two groups is clearly evident comparing TVTO and Aris. This study shows that there are significant differences on the mechanical properties between urogynecology meshes.
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Affiliation(s)
- J S Afonso
- Department of Gynecology, Federal University of São Paulo, São Paulo, Brazil.
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14
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Parente MPL, Jorge RMN, Mascarenhas T, Fernandes AA, Martins JAC. Deformation of the pelvic floor muscles during a vaginal delivery. Int Urogynecol J 2007; 19:65-71. [PMID: 17522755 DOI: 10.1007/s00192-007-0388-7] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2007] [Accepted: 04/20/2007] [Indexed: 11/24/2022]
Abstract
Pelvic floor dysfunction is a hidden problem with a magnitude unknown to many. Statistics show that one in every ten women will have pelvic floor dysfunction so severe that it will require surgery. Several studies have shown that pelvic floor injuries during a vaginal delivery can be considered a significant factor in the development of urinary incontinence, fecal incontinence, and pelvic organ prolapse. The objective of the present work is to contribute to the clarification of the mechanisms behind pelvic floor disorders related to a vaginal delivery. For this purpose, a numerical simulation based on the finite element method was carried out. The finite element model intends to represent the effects that the passage of a fetal head can induce on the muscles of the pelvic floor, from a mechanical point of view. The model used for the simulation represents the pelvic bones, with the attached pelvic floor muscles and the fetus. In this work, we simulated the movements of the fetus during birth, in vertex position. We simulated the engagement, descent, flexion, internal rotation, and extension of the fetal head. Results for the pelvic floor stretch values obtained during the passage of the fetus head are presented; the deformation field is also shown. The results were obtained using the finite element method and a three-dimensional computer model of the pelvic floor and fetus. The maximum deformation obtained was 0.66 for a vertical displacement of the fetal head of approximately 60 mm.
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Affiliation(s)
- M P L Parente
- IDMEC, Faculty of Engineering, University of Porto, 4200-465 Porto, Portugal
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15
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Leite RC, Rodríguez Z, Faccini JL, Oliveira PR, Fernandes AA. First report of Haematobia irritans (L.) (Diptera: Muscidae) as vector of Dermatobia hominis (L.jr.) (Diptera: Cuterebridae) in Minas Gerais, Brazil. Mem Inst Oswaldo Cruz 1998; 93:761-2. [PMID: 9921299 DOI: 10.1590/s0074-02761998000600012] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Affiliation(s)
- R C Leite
- Departamento de Medicina Veterinária Preventiva, Escola de Veterinária, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brasil.
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16
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Carvalho LH, Fontes CJ, Fernandes AA, Marinuzzi HC, Krettli AU. Cross-reactive cellular immune response to circumsporozoite proteins of Plasmodium vivax and P. falciparum in malaria-exposed individuals. Parasite Immunol 1997; 19:47-59. [PMID: 9076807 DOI: 10.1046/j.1365-3024.1997.d01-182.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [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: 02/04/2023]
Abstract
Acquired immunity against the recombinant circumsporozoite protein of P. falciparum (rPfCS) or P. vivax (rPvCS) was studied in two malarious areas of the Brazilian Amazon. Cellular responsiveness, evaluated by proliferative assays, was detected in about 45% of individuals who had recovered from recent acute malaria infections. Peripheral blood mononuclear cells of individuals whose last malaria infection was by P. vivax responded more to the rCS proteins than those who had P. falciparum. Since in P. vivax infections hypnozoites in the liver retain CS antigen, this stage may have contributed to the increased cellular response. The unexpected result was that in primoinfections by P. falciparum or P. vivax the proliferative response did not correspond to the rPfCS and rPvCS, respectively. Furthermore, among the malaria-exposed individuals, there was a positive correlation between the intensity of the responses to the two rCS proteins. Our results suggest that cross-reactive epitopes exist in the CS protein of P. falciparum and P. vivax. In the areas studied, the frequency of antibodies against rPvCS and/or rPfCS ranged from 43% to 11%. Species-specific antibodies against the CS protein were detected in the primoinfected individuals. Some individuals living in the endemic area but with no clinical history of malaria were positive by serology (8%) or by in vitro proliferation (21%). However, antibodies and cellular responses against rCS were detected only in malaria-exposed individuals, since those living outside the endemic area were all negative.
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Affiliation(s)
- L H Carvalho
- Departamento de Parasitología, Universidade Federal de Minas Gerais, Brazil
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17
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Fernandes AA, Santamaria J, Bud'ko SL, Nakamura O, Guimpel J, Schuller IK. Effect of physical and chemical pressure on the superconductivity of high-temperature oxide superconductors. Phys Rev B Condens Matter 1991; 44:7601-7606. [PMID: 9998675 DOI: 10.1103/physrevb.44.7601] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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18
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Fernandes AA. Ferromagnetic resonance evidence for superparamagnetism in a partially crystallized metallic glass. Phys Rev B Condens Matter 1990; 42:527-529. [PMID: 9994569 DOI: 10.1103/physrevb.42.527] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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19
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Njoroge FG, Fernandes AA, Monnier VM. Mechanism of formation of the putative advanced glycosylation end product and protein cross-link 2-(2-furoyl)-4(5)-(2-furanyl)-1H-imidazole. J Biol Chem 1988; 263:10646-52. [PMID: 3392032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
2-(2-Furoyl)-4(5)-(2-furanyl)-1H-imidazole (FFI) is a fluorescent molecule which was originally discovered in chloroform extract of ammoniacal solution of acid-hydrolyzed glycated proteins and proposed to represent a protein cross-link. The absence of a lysyl residue side chain and other observations promoted a detailed study of its mechanism of formation. Glycated alpha-t-Butoxycarbonyllysine was incubated for 29 days and periodically assayed for FFI and FFI-like fluorescence. Whereas fluorescence increased over time, FFI recovery was unexpectedly highest on day 0 and lowest on day 29, suggesting that FFI was directly derived from Amadori products. FFI was also recovered from hydrolysates of glycated neopentylamine, furosine, and browned poly-L-lysine but was virtually undetectable in similar solutions basified with NaOH, triethylamine, or pyridine instead of ammonia. Gas chromatography-mass spectrometry analysis of FFI from similar hydrolysates basified in the presence of 15N-enriched NH4Cl revealed for all precursors a parent ion peak at 230 instead of 228 m/e units, suggesting that the two imidazole nitrogen atoms had been incorporated from free ammonia into FFI. Spontaneous FFI synthesis occurred when furosine was reacted with aqueous ammonia at room temperature. These results do not support the proposition that FFI is an advanced glycosylation end product or a protein cross-link. They suggest that FFI is formed from ammonia and furosine which are by-products of acid-hydrolyzed glycated proteins.
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Affiliation(s)
- F G Njoroge
- Institute of Pathology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106
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20
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Fernandes AA, Kalhan SC, Njoroge FG, Matousek GS. Quantitation of branched-chain alpha-keto acids as their N-methylquinoxalone derivatives: comparison of O- and N-alkylation versus -silylation. Biomed Environ Mass Spectrom 1986; 13:569-81. [PMID: 2947652 DOI: 10.1002/bms.1200131009] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Quantitative estimation of isotopic enrichment and concentrations of keto analogs of branched-chain amino acids in biological fluid has been used for the study of protein metabolism in animal and human studies. At present, O-trimethylsilyl-quinoxalinol derivative is used widely in the quantification of branched-chain alpha-keto acids. In the present study, N-methyl-quinoxalone derivative was developed and its use in quantification in human studies verified. O-phenylenediamine and alpha-keto acid react in acidic media to yield phenolic and amide tautomers. O-trimethylsilyl-quinoxalinol derivative of the phenolic tautomer is used at present for quantification by chemical ionization/selected ion monitoring. We have prepared N-methyl-quinoxalone derivative using N,N-dimethyl formamide dimethyl acetal. This derivative is characterized by a major amide form and a minor phenolic form. The mass spectrum has a characteristic fragment, which facilitates easy identification and quantitation by electron impact/selected ion monitoring. Because m/z 174 was observed as the base peak for alpha-ketoisocaproate, alpha-keto-beta-methylvalerate and alpha-ketoisovalerate, "single ion monitoring' could be performed for the quantification of isotopic enrichment as well as plasma concentration of these three branched-chain alpha-keto acids. Isotopic enrichment from 0.25 to 7.5 at% excess could be measured easily, with an average coefficient of variation of less than 8%. Plasma concentrations as low as 10 microM l-1 in a 200-microliters aliquot could be measured. Methyl migration was an interesting feature of the mass spectrometric fragmentation pattern of the alpha-keto acids. The mechanism of methyl migration is proposed and discussed. This paper also describes some of the studies involved in the formation of isomeric O- and N-alkyl, -quinoxaline and -quinoxalone using a number of N,N-dimethyl formamide dialkyl acetals.
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