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Most of the lipid in purulent sputum is bound to mucus glycoprotein
C E Nadziejko1, B L Slomiany, A Slomiany
1Department of Medicine, New York Medical College, Valhalla 10595.
Abstract:
Mucus glycoprotein (mucin) is the principal biochemical constituent of sputum. Appreciable quantities of lipid, DNA, and nonmucin proteins are also present, particularly in purulent sputum. Previous studies have shown that purified mucin from respiratory tract secretions contains non-covalently bound lipid. However, it is not known whether lipids in purulent sputum are associated only with mucin or with nonmucin proteins and DNA as well. Purulent sputum was obtained from cystic fibrosis patients. Tracheal aspirates were obtained from noncystic patients with purulent secretions due to Pseudomonas species, as well as from noninfected, noncystic patients who had mucoid airway secretions. The lipid content of unfractionated airway secretions (sputum or tracheal aspirates), gel filtration-purified mucin, and nonmucin components of the airway secretions was analyzed. The purified mucin from all three groups had a significantly higher content of solvent-extractable lipid as compared to unfractionated airway secretions. The nonmucin fractions contained only small amounts of lipid. Density gradient centrifugation verified that the lipid recovered in the purified mucin fraction was complexed with the glycoprotein. The results of this study indicate that most of the lipids in purulent sputum are associated with mucin.
Insights
Most lipids in purulent sputum are bound to mucus glycoprotein (mucin), not other proteins or DNA. This study analyzed lipids in airway secretions from various patient groups, finding mucin consistently bound more lipids.
Area of Science:
- Biochemistry
- Pulmonary Medicine
- Microbiology
Background:
- Mucus glycoprotein (mucin) is the main component of sputum.
- Purulent sputum contains significant amounts of lipids, DNA, and non-mucin proteins.
- Previous research indicated lipids are non-covalently bound to respiratory mucin, but their association in purulent sputum remained unclear.
Purpose of the Study:
- To determine if lipids in purulent sputum associate exclusively with mucin or also with non-mucin proteins and DNA.
- To investigate the lipid content in airway secretions from cystic fibrosis patients, Pseudomonas-infected non-cystic patients, and non-infected non-cystic patients.
Main Methods:
- Analysis of lipid content in unfractionated airway secretions (sputum/tracheal aspirates).
- Gel filtration chromatography to purify mucin from airway secretions.
- Analysis of lipid content in purified mucin and non-mucin fractions.
- Density gradient centrifugation to confirm lipid-glycoprotein complexation.
Main Results:
- Purified mucin from all patient groups exhibited significantly higher solvent-extractable lipid content compared to unfractionated secretions.
- Non-mucin fractions contained only minimal amounts of lipid.
- Density gradient centrifugation confirmed that lipids in the purified mucin fraction were indeed complexed with the glycoprotein.
Conclusions:
- The majority of lipids present in purulent sputum are associated with mucin.
- Lipids are complexed with mucin glycoproteins in airway secretions.
- Findings clarify the biochemical composition of purulent sputum, highlighting mucin's role in lipid binding.