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von der Burchard C, Kren C, Fleger JE, Theisen-Kunde D, Danicke V, Abbas HS, Kleyman V, Roider J, Brinkmann R. Real-Time Temperature-Controlled Retinal Laser Irradiation in Rabbits. Transl Vis Sci Technol 2024; 13:26. [PMID: 38639930 PMCID: PMC11037498 DOI: 10.1167/tvst.13.4.26] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2023] [Accepted: 02/19/2024] [Indexed: 04/20/2024] Open
Abstract
Purpose Subdamaging thermal retinal laser therapy has the potential to induce regenerative stimuli in retinal diseases, but validated dosimetry is missing. Real-time optoacoustic temperature determination and control could close this gap. This study investigates a first in vivo application. Methods Two iterations of a control module that were optically coupled in between a continuous-wave commercial laser source and a commercial slit lamp were evaluated on chinchilla rabbits. The module allows extraction of the temperature rise in real time and can control the power of the therapy laser such that a predefined temperature rise at the retina is quickly achieved and held constant. Irradiations with aim temperatures from 45°C to 69°C were performed on a diameter of 200 µm and a heating time of 100 ms. Results We analyzed 424 temperature-guided irradiations in nine eyes of five rabbits. The mean difference between the measured and aim temperature was -0.04°C ± 0.98°C. The following ED50 values for visibility thresholds could be determined: 58.6°C for funduscopic visibility, 57.7°C for fluorescein angiography, and 57.0°C for OCT. In all measurements, the correlation of tissue effect was higher to the temperature than to the average heating laser power used. Conclusions The system was able to reliably perform temperature-guided irradiations, which allowed for better tissue effect control than simple power control. This approach could enhance the accuracy, safety, and reproducibility of thermal stimulating laser therapy. Translational Relevance This study is a bridge between preclinical ex vivo experiments and a pilot clinical study.
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Affiliation(s)
| | | | - Jan-Erik Fleger
- Department of Ophthalmology, Christian-Albrechts-University of Kiel, Kiel, Germany
| | | | | | - Hossam S. Abbas
- Medical Laser Center Lübeck, Lübeck, Germany
- Institute for Electrical Engineering in Medicine, University of Lübeck, Lübeck, Germany
| | - Viktoria Kleyman
- Institute of Automatic Control, Leibniz University Hannover, Hannover, Germany
| | - Johann Roider
- Department of Ophthalmology, Christian-Albrechts-University of Kiel, Kiel, Germany
| | - Ralf Brinkmann
- Medical Laser Center Lübeck, Lübeck, Germany
- Institute of Biomedical Optics, University of Lübeck, Lübeck, Germany
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Veysset D, Zhuo Y, Hattori J, Buckhory M, Palanker D. Interferometric thermometry of ocular tissues for retinal laser therapy. BIOMEDICAL OPTICS EXPRESS 2023; 14:37-53. [PMID: 36698667 PMCID: PMC9842005 DOI: 10.1364/boe.475705] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2022] [Revised: 11/13/2022] [Accepted: 11/14/2022] [Indexed: 06/17/2023]
Abstract
Controlling the tissue temperature rise during retinal laser therapy is highly desirable for predictable and reproducible outcomes of the procedure, especially with non-damaging settings. In this work, we demonstrate a method for determining the optical absorption, the thermal conductivity, and the thermal expansion coefficients of RPE and choroid using phase-resolved optical coherence tomography (pOCT). These parameters are extracted from the measured changes in the optical path length (ΔOPL) using an axisymmetric thermo-mechanical model. This allows the calculation of the temperature rise during hyperthermia, which was further validated by imaging the temperature-sensitive fluorescence at the same location. We demonstrate that, with a temperature uncertainty of ±0.9°C and a peak heating of about 17°C following a laser pulse of 20 ms, this methodology is expected to be safe and sufficiently precise for calibration of the non-damaging retinal laser therapy. The method is directly translatable to in-vivo studies, where we expect a similar precision.
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Affiliation(s)
- David Veysset
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305, USA
- Department of Ophthalmology, Stanford University, Stanford, CA 94305, USA
| | - Yueming Zhuo
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305, USA
- Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA
| | - Junya Hattori
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305, USA
- Department of Mechanical Engineering, The University of Tokyo, Tokyo, Japan
| | - Mohajeet Buckhory
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305, USA
- Department of Ophthalmology, Stanford University, Stanford, CA 94305, USA
| | - Daniel Palanker
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305, USA
- Department of Ophthalmology, Stanford University, Stanford, CA 94305, USA
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Miura Y, Inagaki K, Hutfilz A, Seifert E, Schmarbeck B, Murakami A, Ohkoshi K, Brinkmann R. Temperature Increase and Damage Extent at Retinal Pigment Epithelium Compared between Continuous Wave and Micropulse Laser Application. Life (Basel) 2022; 12:life12091313. [PMID: 36143352 PMCID: PMC9504342 DOI: 10.3390/life12091313] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2022] [Revised: 08/14/2022] [Accepted: 08/18/2022] [Indexed: 11/16/2022] Open
Abstract
Continuous wave (CW) and microsecond pulse (MP) laser irradiations were compared regarding cell damage and laser-induced temperature rise at retinal pigment epithelium (RPE). The RPE of porcine RPE-choroid-sclera explants was irradiated with a 577 nm laser in CW or MP mode (5% or 15% duty cycle (DC)) for 20 ms or 200 ms at an average laser power of 20−90 mW. Cell viability was investigated with calcein-AM staining. Optoacoustic (OA) technique was employed for temperature measurement during irradiation. For 200 ms irradiation, the dead cell area (DCA) increased linearly (≈1600 µm2/mW) up to the average power of 40 mW for all modes without significant difference. From 50 mW, the increase of DCA of MP-5% significantly dropped to 610 µm2/mW (p < 0.05), likely due to the detected microbubble formation. OA temperature measurement showed a monotonic temperature increase in CW mode and a stepwise increase in MP mode, but no significant difference in the average temperature increase at the same average power, consistent with the temperature modeling. In conclusion, there is no difference in the average temperature rise between CW and MP modes at the same average power regardless of DC. At lower DC, however, more caution is required regarding mechanical damage due to microbubble formation.
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Affiliation(s)
- Yoko Miura
- Institute of Biomedical Optics, University of Lübeck, 23562 Lübeck, Germany
- Medical Laser Center Lübeck, 23562 Lübeck, Germany
- Department of Ophthalmology, University of Lübeck, 23562 Lübeck, Germany
- Correspondence: ; Tel.: +49-451-3101-3212; Fax: +49-451-3101-3204
| | - Keiji Inagaki
- Inagaki Eye Clinic, Chiba 279-0011, Japan
- Department of Ophthalmology, Faculty of Medicine, Juntendo University, Tokyo 113-8421, Japan
| | | | - Eric Seifert
- Medical Laser Center Lübeck, 23562 Lübeck, Germany
| | | | - Akira Murakami
- Department of Ophthalmology, Faculty of Medicine, Juntendo University, Tokyo 113-8421, Japan
| | - Kishiko Ohkoshi
- Department of Ophthalmology, Hiroo Hanezawa Internal Medicine and Ophthalmology Clinic, Tokyo 150-0012, Japan
- Department of Ophthalmology, St. Luke’s International Hospital, Tokyo 104-8560, Japan
| | - Ralf Brinkmann
- Institute of Biomedical Optics, University of Lübeck, 23562 Lübeck, Germany
- Medical Laser Center Lübeck, 23562 Lübeck, Germany
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Veysset D, Ling T, Zhuo Y, Pandiyan VP, Sabesan R, Palanker D. Interferometric imaging of thermal expansion for temperature control in retinal laser therapy. BIOMEDICAL OPTICS EXPRESS 2022; 13:728-743. [PMID: 35284191 PMCID: PMC8884207 DOI: 10.1364/boe.448803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2021] [Revised: 12/27/2021] [Accepted: 12/28/2021] [Indexed: 06/14/2023]
Abstract
Precise control of the temperature rise is a prerequisite for proper photothermal therapy. In retinal laser therapy, the heat deposition is primarily governed by the melanin concentration, which can significantly vary across the retina and from patient to patient. In this work, we present a method for determining the optical and thermal properties of layered materials, directly applicable to the retina, using low-energy laser heating and phase-resolved optical coherence tomography (pOCT). The method is demonstrated on a polymer-based tissue phantom heated with a laser pulse focused onto an absorbing layer buried below the phantom's surface. Using a line-scan spectral-domain pOCT, optical path length changes induced by the thermal expansion were extracted from sequential B-scans. The material properties were then determined by matching the optical path length changes to a thermo-mechanical model developed for fast computation. This method determined the absorption coefficient with a precision of 2.5% and the temperature rise with a precision of about 0.2°C from a single laser exposure, while the peak did not exceed 8°C during 1 ms pulse, which is well within the tissue safety range and significantly more precise than other methods.
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Affiliation(s)
- David Veysset
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305, USA
- Department of Ophthalmology, Stanford University, Stanford, CA 94305, USA
| | - Tong Ling
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305, USA
- Department of Ophthalmology, Stanford University, Stanford, CA 94305, USA
- Present address: School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637457, Singapore
| | - Yueming Zhuo
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305, USA
- Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA
| | | | - Ramkumar Sabesan
- Department of Ophthalmology, University of Washington, Seattle, WA 98109, USA
| | - Daniel Palanker
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305, USA
- Department of Ophthalmology, Stanford University, Stanford, CA 94305, USA
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Richert E, Papenkort J, von der Burchard C, Klettner A, Arnold P, Lucius R, Brinkmann R, Framme C, Roider J, Tode J. Selective retina therapy and thermal stimulation of the retina: different regenerative properties - implications for AMD therapy. BMC Ophthalmol 2021; 21:412. [PMID: 34847865 PMCID: PMC8630886 DOI: 10.1186/s12886-021-02188-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2020] [Accepted: 11/22/2021] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Selective Retina Therapy (SRT), a photodisruptive micropulsed laser modality that selectively destroys RPE cells followed by regeneration, and Thermal Stimulation of the Retina (TSR), a stimulative photothermal continuous wave laser modality that leads to an instant sublethal temperature increase in RPE cells, have shown therapeutic effects on Age-related Macular Degeneration (AMD) in mice. We investigate the differences between both laser modalities concerning RPE regeneration. METHODS For PCR array, 6 eyes of murine AMD models, apolipoprotein E and nuclear factor erythroid-derived 2- like 2 knock out mice respectively, were treated by neuroretina-sparing TSR or SRT. Untreated litter mates were controls. Eyes were enucleated either 1 or 7 days after laser treatment. For morphological analysis, porcine RPE/choroid organ cultures underwent the same laser treatment and were examined by calcein vitality staining 1 h and 1, 3 or 5 days after irradiation. RESULTS TSR did not induce the expression of cell-mediators connected to cell death. SRT induced necrosis associated cytokines as well as inflammation 1 but not 7 days after treatment. Morphologically, 1 h after TSR, there was no cell damage. One and 3 days after TSR, dense chromatin and cell destruction of single cells was seen. Five days after TSR, there were signs of migration and proliferation. In contrast, 1 h after SRT a defined necrotic area within the laser spot was seen. This lesion was closed over days by migration and proliferation of adjacent cells. CONCLUSIONS SRT induces RPE cell death, followed by regeneration within a few days. It is accompanied by necrosis induced inflammation, RPE proliferation and migration. TSR does not induce immediate RPE cell death; however, migration and mitosis can be seen a few days after laser irradiation, not accompanied by necrosis-associated inflammation. Both might be a therapeutic option for the treatment of AMD.
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Affiliation(s)
- Elisabeth Richert
- Department of Ophthalmology, Christian-Albrechts-University of Kiel, University Medical Center, Kiel, Germany
| | - Julia Papenkort
- Department of Ophthalmology, Christian-Albrechts-University of Kiel, University Medical Center, Kiel, Germany
| | - Claus von der Burchard
- Department of Ophthalmology, Christian-Albrechts-University of Kiel, University Medical Center, Kiel, Germany
| | - Alexa Klettner
- Department of Ophthalmology, Christian-Albrechts-University of Kiel, University Medical Center, Kiel, Germany
| | - Philipp Arnold
- Friedrich-Alexander-University Erlangen-Nürnberg, Nürnberg, Germany
| | - Ralph Lucius
- Christian-Albrechts-University of Kiel, Institute of Anatomy, Kiel, Germany
| | - Ralf Brinkmann
- Medical Laser Center Lübeck, Lübeck, Germany.,Institute for Biomedical Optics, University of Lübeck, Lübeck, Germany
| | - Carsten Framme
- Department of Ophthalmology, Hannover Medical School, Carl-Neuberg-Str. 1, 30625, Hannover, Germany
| | - Johann Roider
- Department of Ophthalmology, Christian-Albrechts-University of Kiel, University Medical Center, Kiel, Germany
| | - Jan Tode
- Department of Ophthalmology, Christian-Albrechts-University of Kiel, University Medical Center, Kiel, Germany. .,Department of Ophthalmology, Hannover Medical School, Carl-Neuberg-Str. 1, 30625, Hannover, Germany.
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Souissi S, Le Mer Y, Metge F, Portmann A, Baudouin C, Labbé A, Hamard P. An update on continuous-wave cyclophotocoagulation (CW-CPC) and micropulse transscleral laser treatment (MP-TLT) for adult and paediatric refractory glaucoma. Acta Ophthalmol 2021; 99:e621-e653. [PMID: 33222409 DOI: 10.1111/aos.14661] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2020] [Revised: 09/06/2020] [Accepted: 10/11/2020] [Indexed: 12/12/2022]
Abstract
PURPOSE Continuous-wave cyclophotocoagulation (CW-CPC) is often preferred to medical and surgical treatments for managing refractory glaucoma. This review summarizes diode CW-CPC indications, history, histopathology, methods, efficacy and safety. It also provides an overview of the latest data available on micropulse transscleral laser treatment (MP-TLT) that uses repetitive micropulses of diode laser energy in an off-and-on cyclical fashion. METHODS A literature review was conducted on transscleral CW-CPC (CW-TSCPC), endoscopic CPC (ECP) and MP-TLT. Relevant series of adult and paediatric patients were included for assessing the procedures. RESULTS Regarding CW-TCPC, highly variable success rates are reported in the literature, depending on the definition of success, type of underlying glaucoma, energy settings, follow-up duration and retreatment rates. CW-CPC often needs to be repeated, especially in paediatric patients. CW-CPC exposes to risks of inflammation and chronic ocular hypotony or phthisis with irreversible visual loss. CW-TSCPC has mainly been used in very severe forms of glaucoma, in painful eyes with limited visual potential or after filtering surgery failure. Published data on ECP are more limited but overall good success rates have been reported. Through the direct visualization of the targeted ciliary body in anatomically abnormal eyes, ECP is the preferred surgical procedure in paediatric refractory glaucoma. Complication rates are relatively low after ECP; however, large studies with long-term follow-up are needed. ECP may be used in difficult, refractory cases, but it is often used earlier when combined with cataract surgery. Despite limited data on the exact mechanism of action of MP-TLT and a lack of standardization of laser settings, the first data from heterogeneous case series shows that it has a similar efficacy and a better safety profile compared to CW-TSCPC in the medium term. CONCLUSION Although they may lead to sight-threatening complications, both CW-TSCPC and ECP seem effective. ECP appears to be superior to CW-TSCPC in paediatric refractory glaucoma. Unlike ECP combined with cataract surgery, evidence supporting a wider use of CW-TSCPC and MP-TLT in earlier stages of neuropathy is lacking. While it now appears that the safety profile of MP-TLT is superior to that of CW-CPC, robust prospective comparative studies including homogeneous and well-defined cohorts of patients are still needed to confirm an at least comparable efficacy in the long term.
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Affiliation(s)
- Soufiane Souissi
- Department of Vitreoretinal Surgery Adolphe de Rothschild Foundation Paris France
| | - Yannick Le Mer
- Department of Vitreoretinal Surgery Adolphe de Rothschild Foundation Paris France
| | - Florence Metge
- Department of Pediatric Ophthalmology Adolphe de Rothschild Foundation Paris France
| | - Alexandre Portmann
- Department of Pediatric Ophthalmology Adolphe de Rothschild Foundation Paris France
| | | | - Antoine Labbé
- Department of Ophthalmology III Quinze‐Vingts Hospital Paris France
| | - Pascale Hamard
- Department of Ophthalmology III Quinze‐Vingts Hospital Paris France
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The Need for Rigor in Evaluating Micropulse and Other New Procedures. Ophthalmol Glaucoma 2020; 3:171-173. [PMID: 32672611 DOI: 10.1016/j.ogla.2020.04.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2020] [Accepted: 04/08/2020] [Indexed: 12/24/2022]
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Richert E, Papenkort J, Klettner A, Tode J, Koinzer S, Brinkmann R, Fink C, Roeder T, Lucius R, Roider J. Response of Retinal Pigment Epithelium (RPE)-Choroid Explants to Thermal Stimulation Therapy of the RPE (TSR). Lasers Surg Med 2020; 53:359-369. [PMID: 32567146 DOI: 10.1002/lsm.23288] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2020] [Revised: 05/06/2020] [Accepted: 06/07/2020] [Indexed: 01/15/2023]
Abstract
BACKGROUND AND OBJECTIVES The thermal stimulation therapy of the retinal pigment epithelium (TSR) is a sublethal laser technique for thermal stimulation of the retinal pigment epithelium (RPE)-Bruch's membrane (BrM)-complex. The aim of this study was to investigate the influence of TSR on the release of age-related macular degeneration (AMD)-relevant cell mediators. STUDY DESIGN/MATERIALS AND METHODS Porcine RPE-BrM-choroid explants were irradiated with a 532 nm continuous wave laser using different spot sizes (100-300 µm, duration 100 milliseconds, 15-100 mW). Cell death was investigated by calcein staining. Explants were treated with grids of sublethal spots and cultivated in modified Ussing chambers. The effect on matrix metalloproteinase-2 (MMP-2) and -9 was investigated by zymography and quantitative reverse transcription polymerase chain reaction. Secretion of vascular endothelial growth factor (VEGF), pigment epithelium derived factor (PEDF), and transforming growth factor-β (TGF-β) was analyzed by enzyme-linked immunosorbent assay and expression of HSP70 was examined by western blot. Integrity of the RPE/BrM-complex was analyzed by scanning electron microscopy. RESULTS Laser powers of 15 mW (100 µm) and 45 mW (300 µm) did not induce RPE cell death. The integrity of the RPE/BrM-complex was not impaired after TSR. After TSR with 300 µm spot size, we observed a significant increase of active MMP-2 in the basal compartments. The content of PEDF significantly increased in treated explants in both compartments with 100 and 300 µm spot sizes. VEGF and TGF-β secretion was not triggered by TSR. CONCLUSIONS TSR represents a possible RPE stimulating treatment for dry AMD. TSR increases the basal release of active MMP-2, which might reverse age-related thickening of BrM. VEGF secretion was not triggered by TSR while anti-angiogenic PEDF was increased, indicating an induction of an anti-angiogenic and neuroprotective environment. Lasers Surg. Med. © 2020 Wiley Periodicals LLC.
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Affiliation(s)
- Elisabeth Richert
- Department of Ophthalmology, University Medical Center, Christian-Albrechts University of Kiel, Arnold-Heller-Street 3, House 3B, Kiel, 24105, Germany
| | - Julia Papenkort
- Department of Ophthalmology, University Medical Center, Christian-Albrechts University of Kiel, Arnold-Heller-Street 3, House 3B, Kiel, 24105, Germany
| | - Alexa Klettner
- Department of Ophthalmology, University Medical Center, Christian-Albrechts University of Kiel, Arnold-Heller-Street 3, House 3B, Kiel, 24105, Germany
| | - Jan Tode
- Department of Ophthalmology, University Medical Center, Christian-Albrechts University of Kiel, Arnold-Heller-Street 3, House 3B, Kiel, 24105, Germany
| | - Stefan Koinzer
- Department of Ophthalmology, University Medical Center, Christian-Albrechts University of Kiel, Arnold-Heller-Street 3, House 3B, Kiel, 24105, Germany
| | - Ralf Brinkmann
- Medical Laser Center Lübeck, Peter-Monnik-Weg 4, Lübeck, 23562, Germany
| | - Christine Fink
- Molecular Physiology, Zoological Institute, Christian-Albrechts University of Kiel, Am Botanischen Garten 1-9, Kiel, 24118, Germany
| | - Thomas Roeder
- Molecular Physiology, Zoological Institute, Christian-Albrechts University of Kiel, Am Botanischen Garten 1-9, Kiel, 24118, Germany
| | - Ralph Lucius
- Institute of Anatomy, Christian-Albrechts University of Kiel, Olshausenstraße, Kiel, 24118, Germany
| | - Johann Roider
- Department of Ophthalmology, University Medical Center, Christian-Albrechts University of Kiel, Arnold-Heller-Street 3, House 3B, Kiel, 24105, Germany
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Kern K, Mertineit CL, Brinkmann R, Miura Y. Expression of heat shock protein 70 and cell death kinetics after different thermal impacts on cultured retinal pigment epithelial cells. Exp Eye Res 2018; 170:117-126. [PMID: 29454858 DOI: 10.1016/j.exer.2018.02.013] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2017] [Revised: 01/25/2018] [Accepted: 02/14/2018] [Indexed: 12/19/2022]
Abstract
Recent technologies are broadening the possibility to treat the retinal pigment epithelium (RPE) with different thermal impacts, from sublethal to lethal ranges. Thus temperature-dependent subcellular molecular responses need to be elucidated in more detail. In this study, RPE cell viability and expression of heat shock protein 70 (Hsp70) were investigated after thermal irradiation with different temperature increase using an in-vitro model. Primary porcine RPE cell cultures were irradiated with different laser power of a thulium laser (λ = 1940 nm, beam-diameter 30 mm) for 10 s, such that the maximal temperatures at the center of the culture dish (Tmax) reach 40, 44, 47, 51 or 59 °C after 10-s irradiation. The temperature distribution across the culture dish shows a Gaussian decay from central position to the periphery of the dish. At 3, 24 and 48 h after irradiation cell viability was assessed with fluorescence microscopy using cell viability-indicating fluorescence dyes, followed by the determination of the threshold temperature for apoptotic change and death of RPE cells. Intracellular localization and amount of Hsp70 were investigated with immunofluorescence and western blotting, respectively. The threshold temperature (at the 10th second of irradiation: T10s) for cellular apoptosis and complete cell death showed a decrease over time after irradiation, suggesting a long-term process of thermally induced cell death. For complete cell death the threshold T10s was 52.1 ± 0.6 °C, 50.1 ± 1.4 °C, and 50.1 ± 0.8 °C, for 3, 24 and 48 h, respectively, whereas for the apoptotic changes 48.6 ± 1.8 °C, 47.2 ± 1.3 °C, and 46.7 ± 0.9 °C, respectively. Quantitative analysis of Hsp70 with western blotting showed a significant increase in intracellular Hsp70 at lethal irradiation with Tmax ≥ 51 °C, up to 19.6 ± 2.3 fold after 48 h at 59 °C, whereas sub-lethal irradiations with Tmax ≤ 44 °C led to a slight tendency of time-dependent increases (up to 1.8 ± 1.1 fold) over 48 h. Immunostainings for Hsp70 showed a circle- or ring-pattern of the Hsp70 staining during 3-48 h after irradiation, and the range of the 1st and 3rd quartiles of T10s for heat-induced Hsp70 expression over this time period was between 44.8 °C and 48.2 °C. A very strong staining of Hsp70 was observed at the border to the damaged zone, where many cells show the strong staining in the whole cytoplasmic space, while some cells in the nucleus, or some cells show the signs of cell migration and proliferation. Moreover, among the cells showing high intensity of Hsp70 staining, there are small round cells like apoptotic cells. Results suggest that RPE cell death after thermal irradiation may take time, and mostly undergoes through apoptosis, unless cells are immediately killed. Thermal irradiation-induced Hsp70 expression is not only temperature-dependent, but also depends largely on the existence of neighboring cell death, suggesting the crucial role of Hsp70 in apoptosis and wound healing processes of RPE cells. The increase of Hsp70 over 24-48 h indicates its long-term roles in cell responses both after sublethal and lethal thermal laser irradiations.
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Affiliation(s)
- Katharina Kern
- Institute of Biomedical Optics, University of Lübeck, Lübeck, Germany; Medical Laser Center Lübeck, Lübeck, Germany
| | | | - Ralf Brinkmann
- Institute of Biomedical Optics, University of Lübeck, Lübeck, Germany; Medical Laser Center Lübeck, Lübeck, Germany
| | - Yoko Miura
- Institute of Biomedical Optics, University of Lübeck, Lübeck, Germany; Medical Laser Center Lübeck, Lübeck, Germany; Department of Ophthalmology, University of Lübeck, Lübeck, Germany.
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