Diurnal variation in human tear enzymes

Area of Science:

• Biochemistry
• Ophthalmology
• Physiology

Background:

• Lactate dehydrogenase (LDH) and malate dehydrogenase (MDH) are key enzymes in cellular metabolism.
• Tear fluid analysis offers insights into ocular surface health and metabolic status.
• Previous studies lacked a consistent method for analyzing diurnal enzyme patterns in tears.

Purpose of the Study:

• To develop a fluorometric assay for measuring LDH and MDH activities in human tears.
• To investigate the diurnal variation of tear LDH and MDH levels and their ratio.
• To explore the potential of the tear LDH/MDH ratio as a biomarker for corneal epithelial metabolic changes.

Main Methods:

• A novel fluorometric technique was employed to quantify LDH and MDH activities in individual human tear samples.
• Tear samples were collected throughout the day to assess diurnal fluctuations.
• The ratio of LDH to MDH activity was calculated for each sample.

Main Results:

• Individual measurements of tear LDH and MDH activities showed significant daily fluctuations without a clear pattern.
• A consistent diurnal pattern was observed for the tear LDH/MDH ratio, peaking upon waking and stabilizing thereafter.
• The tear LDH/MDH ratio was sensitive to environmental conditions, differing between open-eye and closed-eye states, suggesting corneal epithelial metabolic alterations.

Conclusions:

• The tear LDH/MDH ratio exhibits a distinct diurnal pattern, potentially reflecting corneal epithelial metabolic state.
• Lid closure, leading to hypoxia, may increase the tear LDH/MDH ratio by affecting intracellular LDH and cell permeability.
• This ratio may serve as a non-invasive indicator of corneal epithelial metabolic changes in response to environmental factors.