Gourami lenses convert tryptophan into 3-hydroxykynurenine

Area of Science:

• Biochemistry
• Ophthalmology
• Comparative Physiology

Background:

• Tryptophan metabolism is crucial for ocular health.
• The presence of tryptophan and its metabolites in fish lenses is not well-understood.
• Previous studies suggest potential differences in tryptophan metabolism between fish species.

Purpose of the Study:

• To investigate the presence and metabolism of tryptophan in fish lenses.
• To compare tryptophan metabolism in the kissing gourami (Helostoma temmincki) and the 3-spot gourami (Trichogaster trichopterus).
• To determine if lenticular tryptophan is converted to 3-hydroxykynurenine in fish lenses.

Main Methods:

• Analysis of free tryptophan and 3-hydroxykynurenine in fish lenses.
• In vitro radiolabel experiments using cultured 3-spot gourami lenses.
• Tracing the metabolic pathway of tryptophan conversion.

Main Results:

• Free tryptophan was detected in the lenses of both gourami species.
• 3-hydroxykynurenine was exclusively found in the lens of the 3-spot gourami.
• Radiolabel experiments confirmed that 3-spot gourami lenses convert tryptophan to 3-hydroxykynurenine, likely via kynurenine.

Conclusions:

• The 3-spot gourami possesses a tryptophan-to-3-hydroxykynurenine metabolic pathway in its lens, similar to humans.
• Kynurenine serves as a probable intermediate in this lenticular metabolic process.
• This finding contributes to understanding ocular biochemistry in fish and its evolutionary parallels.