Systemic delivery of fluorophore-conjugated antibodies enables ex vivo fluorescence mapping of intestinal GLP-1 and GIP: a preclinical feasibility study

Bariatric surgery provides substantial weight loss and metabolic improvements in severe obesity. RYGB, DS, OAGB, and SADI-S share a mechanism of diverting nutrient flow away from the duodenum and proximal jejunum, altering gut hormone signalling and incretin responses. However, bypass length is guided largely by surgeon experience and retrospective evidence, limiting precision due to variability in individual small-bowel anatomy. Target-specific visualization of enteroendocrine and absorptive markers could enable more precise bypass design. We evaluated the feasibility of systemic in vivo delivery and subsequent ex vivo fluorescence detection of fluorophore-conjugated antibodies targeting GLP-1, GIP, and SGLT-1 in rat small intestine. Following intravenous administration of fluorophore-conjugated monoclonal antibodies, rats were euthanized and the small intestine was harvested and divided into proximal, mid, and distal segments. Tissue was fixed in formalin and processed into paraffin sections for fluorescence imaging. Fluorescein-anti GLP-1 demonstrated detectable fluorescence localization in the terminal ileum, while IR800CW-anti GIP showed detectable fluorescence localization in the proximal small bowel. In both cases, fluorescence was localized predominantly to enterocytes and to capillary/vascular structures within the lamina propria and subserosal layers, consistent with segment-specific targeting. In contrast, MB633-anti SGLT-1 showed no detectable uptake across examined segments and dilutions, and this negative signal was interpreted as most likely technical rather than biological, including possibilities such as reduced antibody affinity after fluorophore conjugation, steric hindrance affecting epitope recognition, limited extracellular epitope accessibility following systemic delivery, and/or species/isoform mismatch. These findings demonstrate feasibility of detectable, segment-specific ex vivo localization of incretin-marker antibodies (GLP-1 and GIP) after systemic delivery, supporting future optimization and translation toward real-time intra-operative fluorescence imaging (e.g., probe-based confocal laser endomicroscopy or fluorescence laparoscopy).