Multimodal In Vivo Fluorescent, Luminescent and X-ray Imaging in Preclinical Studies of Inflammation and Immunobiology

Author: Todd A Sasser , Sean P Orton , Matthew W Leevy

Preclinical models of inflammation and immunobiology in infection (Garside & Brewer, 2010), orthopedics (Mayer-Kuckulk et al., 2006), autoimmunity (‘t Hart et al., 2014), and oncology (Lu et al., 2014) are now routinely employed. Preclinical optical imaging has been applied in many of these studies. Optical inflammation probes to detect and monitor hyperaemia associated with inflammation (Meier et al., 2010), inflammatory cell infiltration (Eisenblaeatter et al., 2009), activated immune cell localization (Zhou et al., 2007), immune cell respiratory bursts, and other inflammatory biomarkers (Vogl et al., 2014) have been validated and used for studies in inflammatory disease. Additionally, optical preclinical imaging has been used to evaluate candidate therapeutics and drug delivery for treatment of inflammatory diseases (Gompels et al., 2011a; Capini et al., 2009). In some cases X-ray imaging has been employed to image anatomical changes associated with inflammatory conditions (Gompels et al., 2011a; 2011b; Fonseca et al., 2010).

 

Preclinical optical imaging allows researchers to longitudinally monitor molecular and cellular inflammatory markers. In general optical imaging, relative to standard in vivo studies, allows researchers to use fewer animals in studies of inflammation and immunobiology. The Bruker In-Vivo Multispectral (MS) FX PRO and In-Vivo Xtreme systems provide multimodal bioluminescence, fluorescence, radioisotopic and X-ray preclinical imaging. Here we provide an overview of representative reports on inflammation and immunobiology research performed using the Bruker In-Vivo optical imaging platform.

In Vivo Imaging Studies in Inflammation

In vivo optical reporters have been developed for monitoring cells and molecular events associated with inflammation. Clinically, autologous radiolabeled white blood cells are frequently used to detect inflammation and infection. In a similar fashion, Eisenblaetter et al. (2009) used fluorescently labeled macrophage (MΦ) cells in a model of granuloma formulation.


Here, MΦ cells were fluorescently labeled in culture using the lipophilic near-infrared (NIR) agent DiR (Invitrogen). Inflammation was induced in the hind flank of experimental mice using bacterial endotoxin lipopolysaccharide (LPS). DiR labeled MΦ cells were evaluated for viability and functionality and introduced via i.v. injection. In vivo MΦ infiltration was monitored for up to 7 days post cell administration. This technique provides a simple method for short term monitoring of MΦ infiltration.

 

A salient feature of inflammation is increased blood flow to the injured site. Indocyanine Green (ICG) quickly binds plasma proteins and via hyperemia collects at sites of inflammation. (ICG fluorescent in vivo imaging may also be employed in studies of the lymphatic system structure and drainage (see Figure 1)). Meier et al. (2010) demonstrated in a rat model of antigen induced arthritis that ICG administered IV served as an early and sensitive reporter for arthritic detection.

 

These studies were combined with complementary multimodal X-ray detection. Preclinical optical imaging has been used in other studies of arthritis models. Gompels et al. (2011b) developed a NIR probe with specificity to the endothelium leukocyte adhesion molecule E-selectin upregulated with inflammation associated with collagen-induced arthritis (CIA). Gompels et al. (2011a) employed their E-selectin probe in a CIA model to evaluate candidate therapeutic response with a bispecific ligand trap RB200.

Probes with specificity to inflammatory molecules associated with signaling cascades and respiratory burst have also been used in early and specific detection of inflammatory response. Recently, Vogl et al. (2014) validated an Alarmin specific NIR reporter for early and sensitive detection of inflammation. This compound was validated in in vivo models of contact dermatitis, CIA and Leishmania infection. Additionally, luminol reagent has been employed for luminescent detection of neutrophil myeloperoxidase (MPO) production (Gross et al., 2009). Figure 2 shows an unpublished example of MPO detection via in vivo luminescence imaging in a traumatic brain imaging (TBI) model.

Conclusions


Optical imaging has been employed in a range of inflammation and immunobiology preclinical studies. Reporters and protocols for immune cell tracking, drug delivery, and inflammatory marker detection have been established that will facilitate future in vivo optical imaging studies. The Bruker  In-Vivo systems provide for fluorescence, luminescence, and X-ray imaging that allow for flexible probe selection in in vivo inflammatory studies. 

Figure 1

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Lymph drainage using ICG. One nM ICG was administered SQ. Three hours PI in vivo fluorescent imaging was performed using the Bruker In-Vivo Xtreme. Inguinal lymph node and lymph vessels are clearly visible.

Figure 2

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Neutrophil MPO detection in TBI model. Fluorescent apoptosis specific probe PSVue794 (blue) and 5 mg luminol MPO (fire) were administered 1 hr and 4 hr respectively post TBI (cryolesion). Sequential X-ray, luminescence and fluorescence imaging was performed using the In-Vivo Xtreme (control animal at left).

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