Sialic acid in human tear fluid.

Area of Science:

• Biochemistry
• Ophthalmology
• Analytical Chemistry

Background:

• Sialic acids are crucial components of glycoproteins involved in various biological functions.
• Understanding sialic acid levels in human tear fluid is important for ocular health research.
• Previous methods for sialic acid determination in tears were limited.

Purpose of the Study:

• To evaluate a simple enzymatic colorimetric assay for determining sialic acid (N-acetylneuraminic acid) in human tear fluid.
• To investigate the source of sialic acid in tears, assessing the contribution of major tear proteins.

Main Methods:

• Tear fluid samples were collected from healthy adults using glass capillaries and cellulose sponges.
• Sialic acid was released by neuraminidase treatment and quantified using an enzymatic colorimetric test.
• Protein content was measured, and sialic acid levels were normalized to protein concentration.

Main Results:

• Sialic acid levels (mmol l-1) did not significantly differ between capillary and sponge collection methods.
• Sialic acid normalized to protein (mmol g-1 protein) was significantly lower in tears collected with sponges.
• Recovery of sialic acid and protein from sponges exceeded 99%, and centrifugation did not alter levels.
• Tear sialic acid activity did not pass a 10,000 MWCO filter, excluding major tear proteins like sIgA.

Conclusions:

• The evaluated assay is suitable for determining sialic acid in human tear fluid.
• The primary source of detected sialic acid in tears is not secretory immunoglobulin A, lactoferrin, or lysozyme.
• Unknown soluble glycoproteins likely contribute significantly to the sialic acid content in human tears.