Time resolved spectroscopic studies on the intact human lens

Area of Science:

• Ophthalmology
• Photochemistry
• Biophysics

Background:

• The human lens is constantly exposed to photooxidative stress from ambient radiation.
• In young lenses, the glucoside of 3-hydroxy kynurenine (3-HKG) is the primary UV absorber (300-400 nm).
• Lens proteins yellow with age, absorbing light up to 450 nm.

Purpose of the Study:

• To investigate the photophysical properties of 3-HKG in young lenses.
• To understand the transient species formed in aged human lenses upon UV excitation.
• To elucidate the role of these compounds in lens protection and age-related changes.

Main Methods:

• Time-resolved fluorescence spectroscopy on isolated 3-HKG and intact human lenses.
• Time-resolved diffuse reflectance spectroscopy on intact older human lenses.
• Utilized two model systems to mimic age-related changes in lens proteins.

Main Results:

• The first excited singlet state of 3-HKG exhibits fast picosecond decay, minimizing energy transfer to harmful pathways.
• Excitation of aged human lenses generated long-lived (microseconds) transient species with absorption around 490 nm.
• Similar spectral characteristics were observed in model systems simulating aged lens proteins.

Conclusions:

• 3-HKG acts as a protective agent for the retina by efficiently quenching photoexcitation.
• The long-lived transient species in aged lenses may be implicated in age-related vision impairment.
• Understanding these photophysical processes is crucial for addressing lens aging and associated visual decline.