Original Article

A ¹³CO₂ breath test to assess the metabolism of triglyceride-rich lipoprotein remnants in mice

Correspondence to: Ian J. Martins.

Remnant-like emulsions were prepared with lipid compositions similar to remnants derived from triacylglycerol-rich lipoproteins. When injected into the bloodstream of conscious mice the remnant-like emulsions labeled with cholesteryl[¹³C]oleate were metabolized in the liver and the appearance of ¹³CO₂ in the breath was measured. In control mice injected with remnant-like emulsions labeled with cholesteryl[¹³C]oleate, enrichment of ¹³CO₂ in the breath peaked at 45 min and then decreased markedly by 3 h. In apoE-deficient (-/-) mice no enrichment was found and in low density lipoprotein receptor (LDLr)-deficient (-/-) mice the appearance of ¹³CO₂ in the breath was markedly decreased. These findings were consistent with the ability of the breath test to detect defects in remnant metabolism. The breath test was useful in detecting a defect in remnant metabolism in LDLr heterozygote (+/-) mice, in which the appearance of ¹³CO₂ in the breath was less by 45 min but remained elevated for the duration of the experiment when compared with control mice. In hepatic lipase-deficient (-/-) mice no defect in remnant metabolism was found. Under fasting conditions, the enrichment of ¹³CO₂ in the breath after injection of emulsion was markedly increased when compared with fed mice, indicating that the metabolism of the injected remnant-like emulsion was probably competed for by post-prandial particles under fed conditions.

Our findings show that a ¹³C breath test can be used to assess the metabolism of remnants. The test provides a useful and sensitive method for non-invasive testing of remnant metabolism in experimental animals.—Martins, I. J., and T. G. Redgrave. A ¹³CO₂ breath test to assess the metabolism of triglyceride-rich lipoprotein remnants in mice. J. Lipid Res. 1998. 39: 691–698.

Supplementary key words: cholesteryl oleate, emulsion, triolein, triglyceride-rich lipoproteins, remnants, cholesterol

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