Fluorescence Lifetime Imaging of Human Sub-RPE Calcification In Vitro Following Chlortetracycline Infusion

Area of Science:

• Ophthalmology
• Biomaterials Science
• Medical Imaging

Background:

• Sub-retinal pigment epithelial (sub-RPE) deposits are implicated in age-related macular degeneration (AMD) pathogenesis.
• These deposits are primarily composed of calcium phosphate minerals, including hydroxyapatite (HAP) and whitlockite (Wht).
• Current methods for detecting sub-RPE deposits have limitations in sensitivity and specificity.

Purpose of the Study:

• To investigate the potential of vascularly administered chlortetracycline for in vivo fluorescent labeling of sub-RPE HAP deposits.
• To assess the feasibility of using this method for early detection and monitoring of AMD and other deposit-related diseases.
• To evaluate the safety and efficacy of chlortetracycline in human cadaveric models.

Main Methods:

• Human cadaveric eyes were utilized for the study.
• Chlortetracycline was administered via vascular perfusion.
• Fluorescence lifetime imaging microscopy (FLIM) was employed to visualize HAP deposits labeled by tetracycline.
• Selective sensors (tetracycline antibiotics) were used to differentiate HAP from tissue autofluorescence.

Main Results:

• All examined sub-RPE deposits contained calcium phosphate minerals (HAP, Wht, or both).
• Vascular perfusion of chlortetracycline successfully and selectively labeled retinal HAP deposits in human cadavers.
• FLIM imaging demonstrated improved contrast for tetracycline-stained HAP deposits compared to background autofluorescence.

Conclusions:

• Sub-RPE calcium phosphate deposits are present in AMD and can be targeted by systemically administered tetracyclines.
• Vascular delivery of chlortetracycline offers a promising approach for in vivo imaging of sub-RPE deposits.
• This technique holds potential for ophthalmic monitoring of AMD, Alzheimer disease, and other conditions associated with deposit formation.