High-resolution contrast-enhanced optical coherence tomography in mice retinae Debasish Sen Elliott D. SoRelle Orly Liba Roopa Dalal Yannis M. Paulus Tae-Wan Kim Darius M. Moshfeghi Adam de la Zerda
Debasish Sen, Elliott D. SoRelle, Orly Liba, Roopa Dalal, Yannis M. Paulus, Tae-Wan Kim, Darius M. Moshfeghi, Adam de la Zerda, “High-resolution contrast-enhanced optical coherence tomography in mice retinae,” J. Biomed. Opt. 21(6), 066002 (2016), doi: 10.1117/1.JBO.21.6.066002.
Journal of Biomedical Optics 21(6), 066002 (June 2016)
High-resolution contrast-enhanced optical coherence tomography in mice retinae Debasish Sen,a,b,† Elliott D. SoRelle,a,c,d Orly Liba,a,b,d,e Roopa Dalal,f Yannis M. Paulus,a,‡ Tae-Wan Kim,a,§ Darius M. Moshfeghi,e,g and Adam de la Zerdaa,b,c,d,e,* a
Stanford University, Department of Structural Biology, 299 Campus Drive, Stanford, California 94305, United States Stanford University, Molecular Imaging Program at Stanford, 299 Campus Drive, Stanford, California 94305, United States Stanford University, Biophysics Program, 299 Campus Drive, Stanford, California 94305, United States d Stanford University, Department of Electrical Engineering, 299 Campus Drive, Stanford, California 94305, United States e Stanford University, Bio-X Program, 299 Campus Drive, Stanford, California, 94305, United States f Stanford University, Department of Ophthalmology, 300 Pasteur Drive, Palo Alto, California 94304, United States g Stanford University, Department of Ophthalmology, Stanford Byers Eye Institute, 2452 Watson Court, Palo Alto, California 94303, United States b c
Abstract. Optical coherence tomography (OCT) is a noninvasive interferometric imaging modality providing anatomical information at depths of millimeters and a resolution of micrometers. Conventional OCT images limit our knowledge to anatomical structures alone, without any contrast enhancement. Therefore, here we have, for the first time, optimized an OCT-based contrast-enhanced imaging system for imaging single cells and blood vessels in vivo inside the living mouse retina at subnanomolar sensitivity. We used bioconjugated gold nanorods (GNRs) as exogenous OCT contrast agents. Specifically, we used anti-mouse CD45 coated GNRs to label mouse leukocytes and mPEG-coated GNRs to determine sensitivity of GNR detection in vivo inside mice retinae. We corroborated OCT observations with hyperspectral dark-field microscopy of formalin-fixed histological sections. Our results show that mouse leukocytes that otherwise do not produce OCT contrast can be labeled with GNRs leading to significant OCT intensity equivalent to a 0.5 nM GNR solution. Furthermore, GNRs injected intravenously can be detected inside retinal blood vessels at a sensitivity of ∼0.5 nM, and GNR-labeled cells injected intravenously can be detected inside retinal capillaries by enhanced OCT contrast. We envision the unprecedented resolution and sensitivity of functionalized GNRs coupled with OCT to be adopted for longitudinal studies of retinal disorders. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE) [DOI: 10.1117/1.JBO.21.6.066002]
Keywords: optical coherence tomography; gold nanorods; retina; in vivo imaging; leukocyte. Paper 150578RR received Aug. 28, 2015; accepted for publication May 2, 2016; published online Jun. 6, 2016.
1
Introduction
‡ Current address: University of Michigan, Kellogg Eye Center, Grand Blanc, Michigan 48439, United States
contrast agents as a multifaceted technology for imaging single cells and blood vessels in vivo inside the mouse retina noninvasively at subnanomolar sensitivity. Following our development of numerous imaging agents for specifically labeling target proteins of interest in living mice,3–6 we recently designed a new OCT-based imaging system for the retina by developing nanoparticles based on gold nanorods (GNRs), which produce a strong OCT signal. GNRs have been recently used to enhance OCT signals in tissue mimicking phantoms,7–11 excised porcine eyes,8 vitreous of mice eyes,12 anterior chambers and cornea of mice eyes,13 and in mouse mammary tumors.14 Additionally, using our custom synthesized GNRs (∼100 × 30 nm), we have achieved ultrahigh detection sensitivity in vivo.15 Here we sought to address whether freshly isolated leukocytes could be labeled with GNRs to enhance scattering, and thus be detected in vitro and in vivo in the retina using OCT. We further determined the sensitivity for detection of GNRs inside retinal blood vessels using OCT in vivo. To our knowledge, this is a first demonstration of OCT-based cellular imaging at a high resolution and subnanomolar sensitivity, allowing single cell and blood capillary detection inside the retina in vivo. OCT has long been used to image human eyes for clinical diagnosis1,2,16 and several commercial OCT systems are FDA approved for ophthalmological use. GNRs were previously
§ Current address: Seoul Metropolitan Government, Seoul National University Boramae Medical Center, Department of Ophthalmology, Seoul, Republic of Korea
1083-3668/2016/$25.00 © 2016 SPIE
Optical coherence tomography (OCT) is a noninvasive imaging modality that uses low-coherence interferometry to detect optical scattering from tissue, cells, or objects with lateral spatial resolutions of a few microns up to several millimeters deep into tissue.1,2 Thus, a noninvasive technology like OCT can be very useful for longitudinal studies of the cellular and molecular foundations of diseased conditions. Because of the lack of an OCT based imaging system that is capable of providing information via functionalized contrast agents, our knowledge is currently limited to visual clues obtained with conventional OCT images of anatomical structures and/or anomalies within tissues. However, these anomalies are merely the outcome of complex molecular and cellular interactions. Without the benefit of enhanced molecular contrast in OCT imaging, it is difficult to determine the role of the aforementioned complex structural anomalies in a diseased condition. Here we seek to optimize an OCT-based imaging technique coupled with functionalized
*Address all correspondence to: Adam de la Zerda, E-mail: [email protected] † Current address: Asterias Biotherapeutics, Fremont, California 94555, United States
Journal of Biomedical Optics
066002-1
June 2016
•
Vol. 21(6)
Sen et al.: High-resolution contrast-enhanced optical coherence tomography in mice retinae
shown to be nontoxic13,17 and have also been used for clinical trials in cancer immunotherapy18 and photothermal cancer therapy.19,20 So, we expect our OCT imaging system paired with a nonsurgical minimally invasive procedure to be fully translatable to patients in the future. Additionally, depth and resolution offered by OCT, as well as the enhanced contrast of functionalized GNRs may complement existing clinical imaging techniques and help in better diagnosis and personalized treatments of disorders.
2 2.1
Methods Functionalized Gold Nanorods
GNRs stable in aqueous solutions were synthesized as previously reported.15 These GNRs (∼110 × 32 nm) exhibited peak longitudinal surface plasmon resonance between 824 and 830 nm, and a spectral full width at half maximum (FWHM) of 100 nm. GNR absorbance was verified using a UV–Vis spectrophotometer. After synthesis, GNRs were coated with poly(sodium 4-styrenesulfonate) (PSS), yielding GNR– PSS conjugates. Using thiol reactivity, GNR–PSS was further conjugated with either mPEG or PEG-Biotin to make GNR– mPEG conjugates (GNRmPEG ) or GNR–biotin conjugates, respectively. 10 nM GNR–biotin conjugates were incubated with NeutrAvidin at 2 μg∕mL final concentration and washed twice at 2250 × g at room temperature (RT, 25°C). The pellets of NeutrAvidin-conjugated GNRs (GNRNav ) were resuspended in distilled deionized water (diH2 O) to a final concentration of 10 nM. Stability of GNRNav was tested in various solutions as follows. 5 μL of GNRNav was added to 95 μL of either diH2 O or Dulbecco’s modified Eagle’s medium (DMEM, Gibco) alone, or diH2 O or DMEM containing 5 or 10% fetal bovine serum (FBS, Hyclone) and optical density (OD) was measured immediately. The solutions containing GNRNav were then incubated for 1 h at RT, centrifuged at 2250 × g for 10 min at RT, resuspended without discarding the supernatant, and then OD was measured again. The ratio of the OD before and after incubation was used to determine GNR stability in these solutions.
We observed that GNR stability was significantly reduced in physiological solutions in the absence of FBS. Thus, for all experiments involving GNRs in physiological solutions, 5% FBS was used.
2.2
Labeling of Leukocytes with Gold Nanorod
Eight-week-old nu/nu mice (Charles River) were euthanized using CO2 , and spleens and blood were harvested. The spleen was homogenized to get single cell suspensions and mixed with the blood [Fig. 1(a)]. The cells were then washed twice in DMEM, and red blood cells (RBCs) were lysed using 1× lysis buffer (Biolegend) following manufacturer’s protocol. 2.5 μg of biotin-conjugated anti-mouse CD45 (Biolegend, Clone 30-F11) was incubated for 20 min at RT with 50 μL of OD 200 GNRNav (see above) + diluted to 1 mL using diH2 O to make GNR–anti-CD45 conjugates (GNRCD45 ). GNRCD45 was washed twice in diH2 O by centrifuging at 2250 × g for 10 min at RT, and finally resuspended in 50 μL DMEM þ 5% FBS. The cells were resuspended in 200 μL DMEM þ 5% FBS (∼30 × 106 cells∕100 μL), mixed with the freshly prepared 50 μL GNRCD45 , and incubated for 2 h at RT. Cells were washed twice with DMEM þ 5% FBS by centrifuging at 340 × g for 2 min at RT each time, and finally resuspended in 1 mL DMEM. A tube containing 200 μm of DMEM þ 5% FBS and 50 μL GNRCD45 was subjected to the same staining and washing conditions as the labeled cells. Using this tube as a control, the amount of free GNRs post wash was measured to be
Debasish Sen, Elliott D. SoRelle, Orly Liba, Roopa Dalal, Yannis M. Paulus, Tae-Wan Kim, Darius M. Moshfeghi, Adam de la Zerda, “High-resolution contrast-enhanced optical coherence tomography in mice retinae,” J. Biomed. Opt. 21(6), 066002 (2016), doi: 10.1117/1.JBO.21.6.066002.
Journal of Biomedical Optics 21(6), 066002 (June 2016)
High-resolution contrast-enhanced optical coherence tomography in mice retinae Debasish Sen,a,b,† Elliott D. SoRelle,a,c,d Orly Liba,a,b,d,e Roopa Dalal,f Yannis M. Paulus,a,‡ Tae-Wan Kim,a,§ Darius M. Moshfeghi,e,g and Adam de la Zerdaa,b,c,d,e,* a
Stanford University, Department of Structural Biology, 299 Campus Drive, Stanford, California 94305, United States Stanford University, Molecular Imaging Program at Stanford, 299 Campus Drive, Stanford, California 94305, United States Stanford University, Biophysics Program, 299 Campus Drive, Stanford, California 94305, United States d Stanford University, Department of Electrical Engineering, 299 Campus Drive, Stanford, California 94305, United States e Stanford University, Bio-X Program, 299 Campus Drive, Stanford, California, 94305, United States f Stanford University, Department of Ophthalmology, 300 Pasteur Drive, Palo Alto, California 94304, United States g Stanford University, Department of Ophthalmology, Stanford Byers Eye Institute, 2452 Watson Court, Palo Alto, California 94303, United States b c
Abstract. Optical coherence tomography (OCT) is a noninvasive interferometric imaging modality providing anatomical information at depths of millimeters and a resolution of micrometers. Conventional OCT images limit our knowledge to anatomical structures alone, without any contrast enhancement. Therefore, here we have, for the first time, optimized an OCT-based contrast-enhanced imaging system for imaging single cells and blood vessels in vivo inside the living mouse retina at subnanomolar sensitivity. We used bioconjugated gold nanorods (GNRs) as exogenous OCT contrast agents. Specifically, we used anti-mouse CD45 coated GNRs to label mouse leukocytes and mPEG-coated GNRs to determine sensitivity of GNR detection in vivo inside mice retinae. We corroborated OCT observations with hyperspectral dark-field microscopy of formalin-fixed histological sections. Our results show that mouse leukocytes that otherwise do not produce OCT contrast can be labeled with GNRs leading to significant OCT intensity equivalent to a 0.5 nM GNR solution. Furthermore, GNRs injected intravenously can be detected inside retinal blood vessels at a sensitivity of ∼0.5 nM, and GNR-labeled cells injected intravenously can be detected inside retinal capillaries by enhanced OCT contrast. We envision the unprecedented resolution and sensitivity of functionalized GNRs coupled with OCT to be adopted for longitudinal studies of retinal disorders. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE) [DOI: 10.1117/1.JBO.21.6.066002]
Keywords: optical coherence tomography; gold nanorods; retina; in vivo imaging; leukocyte. Paper 150578RR received Aug. 28, 2015; accepted for publication May 2, 2016; published online Jun. 6, 2016.
1
Introduction
‡ Current address: University of Michigan, Kellogg Eye Center, Grand Blanc, Michigan 48439, United States
contrast agents as a multifaceted technology for imaging single cells and blood vessels in vivo inside the mouse retina noninvasively at subnanomolar sensitivity. Following our development of numerous imaging agents for specifically labeling target proteins of interest in living mice,3–6 we recently designed a new OCT-based imaging system for the retina by developing nanoparticles based on gold nanorods (GNRs), which produce a strong OCT signal. GNRs have been recently used to enhance OCT signals in tissue mimicking phantoms,7–11 excised porcine eyes,8 vitreous of mice eyes,12 anterior chambers and cornea of mice eyes,13 and in mouse mammary tumors.14 Additionally, using our custom synthesized GNRs (∼100 × 30 nm), we have achieved ultrahigh detection sensitivity in vivo.15 Here we sought to address whether freshly isolated leukocytes could be labeled with GNRs to enhance scattering, and thus be detected in vitro and in vivo in the retina using OCT. We further determined the sensitivity for detection of GNRs inside retinal blood vessels using OCT in vivo. To our knowledge, this is a first demonstration of OCT-based cellular imaging at a high resolution and subnanomolar sensitivity, allowing single cell and blood capillary detection inside the retina in vivo. OCT has long been used to image human eyes for clinical diagnosis1,2,16 and several commercial OCT systems are FDA approved for ophthalmological use. GNRs were previously
§ Current address: Seoul Metropolitan Government, Seoul National University Boramae Medical Center, Department of Ophthalmology, Seoul, Republic of Korea
1083-3668/2016/$25.00 © 2016 SPIE
Optical coherence tomography (OCT) is a noninvasive imaging modality that uses low-coherence interferometry to detect optical scattering from tissue, cells, or objects with lateral spatial resolutions of a few microns up to several millimeters deep into tissue.1,2 Thus, a noninvasive technology like OCT can be very useful for longitudinal studies of the cellular and molecular foundations of diseased conditions. Because of the lack of an OCT based imaging system that is capable of providing information via functionalized contrast agents, our knowledge is currently limited to visual clues obtained with conventional OCT images of anatomical structures and/or anomalies within tissues. However, these anomalies are merely the outcome of complex molecular and cellular interactions. Without the benefit of enhanced molecular contrast in OCT imaging, it is difficult to determine the role of the aforementioned complex structural anomalies in a diseased condition. Here we seek to optimize an OCT-based imaging technique coupled with functionalized
*Address all correspondence to: Adam de la Zerda, E-mail: [email protected] † Current address: Asterias Biotherapeutics, Fremont, California 94555, United States
Journal of Biomedical Optics
066002-1
June 2016
•
Vol. 21(6)
Sen et al.: High-resolution contrast-enhanced optical coherence tomography in mice retinae
shown to be nontoxic13,17 and have also been used for clinical trials in cancer immunotherapy18 and photothermal cancer therapy.19,20 So, we expect our OCT imaging system paired with a nonsurgical minimally invasive procedure to be fully translatable to patients in the future. Additionally, depth and resolution offered by OCT, as well as the enhanced contrast of functionalized GNRs may complement existing clinical imaging techniques and help in better diagnosis and personalized treatments of disorders.
2 2.1
Methods Functionalized Gold Nanorods
GNRs stable in aqueous solutions were synthesized as previously reported.15 These GNRs (∼110 × 32 nm) exhibited peak longitudinal surface plasmon resonance between 824 and 830 nm, and a spectral full width at half maximum (FWHM) of 100 nm. GNR absorbance was verified using a UV–Vis spectrophotometer. After synthesis, GNRs were coated with poly(sodium 4-styrenesulfonate) (PSS), yielding GNR– PSS conjugates. Using thiol reactivity, GNR–PSS was further conjugated with either mPEG or PEG-Biotin to make GNR– mPEG conjugates (GNRmPEG ) or GNR–biotin conjugates, respectively. 10 nM GNR–biotin conjugates were incubated with NeutrAvidin at 2 μg∕mL final concentration and washed twice at 2250 × g at room temperature (RT, 25°C). The pellets of NeutrAvidin-conjugated GNRs (GNRNav ) were resuspended in distilled deionized water (diH2 O) to a final concentration of 10 nM. Stability of GNRNav was tested in various solutions as follows. 5 μL of GNRNav was added to 95 μL of either diH2 O or Dulbecco’s modified Eagle’s medium (DMEM, Gibco) alone, or diH2 O or DMEM containing 5 or 10% fetal bovine serum (FBS, Hyclone) and optical density (OD) was measured immediately. The solutions containing GNRNav were then incubated for 1 h at RT, centrifuged at 2250 × g for 10 min at RT, resuspended without discarding the supernatant, and then OD was measured again. The ratio of the OD before and after incubation was used to determine GNR stability in these solutions.
We observed that GNR stability was significantly reduced in physiological solutions in the absence of FBS. Thus, for all experiments involving GNRs in physiological solutions, 5% FBS was used.
2.2
Labeling of Leukocytes with Gold Nanorod
Eight-week-old nu/nu mice (Charles River) were euthanized using CO2 , and spleens and blood were harvested. The spleen was homogenized to get single cell suspensions and mixed with the blood [Fig. 1(a)]. The cells were then washed twice in DMEM, and red blood cells (RBCs) were lysed using 1× lysis buffer (Biolegend) following manufacturer’s protocol. 2.5 μg of biotin-conjugated anti-mouse CD45 (Biolegend, Clone 30-F11) was incubated for 20 min at RT with 50 μL of OD 200 GNRNav (see above) + diluted to 1 mL using diH2 O to make GNR–anti-CD45 conjugates (GNRCD45 ). GNRCD45 was washed twice in diH2 O by centrifuging at 2250 × g for 10 min at RT, and finally resuspended in 50 μL DMEM þ 5% FBS. The cells were resuspended in 200 μL DMEM þ 5% FBS (∼30 × 106 cells∕100 μL), mixed with the freshly prepared 50 μL GNRCD45 , and incubated for 2 h at RT. Cells were washed twice with DMEM þ 5% FBS by centrifuging at 340 × g for 2 min at RT each time, and finally resuspended in 1 mL DMEM. A tube containing 200 μm of DMEM þ 5% FBS and 50 μL GNRCD45 was subjected to the same staining and washing conditions as the labeled cells. Using this tube as a control, the amount of free GNRs post wash was measured to be
