1. Increased concentrations of plasma polyunsaturated fatty acids have been implicated in the pathogenesis of Crohn's disease. However, it is not known whether there are corresponding changes in circulating phospholipids - the major source of fatty acids in the plasma.
2. Fasting plasma samples were obtained from 17 control subjects and 13 patients with active Crohn's disease [Simple Index of Crohn's Disease Activity (SICDA) >6] before, and 2 and 8 weeks after, treatment with either a peptide diet or oral prednisolone.
3. Before treatment, the Crohn's disease patients had mildly active disease (SICDA 9.9 ± 0.8, erythrocyte sedimentation rate 26.4 ± 6.5 mm/h, serum C-reactive protein 2.8 ± 0.4 mg/l). The proportions of the polyunsaturated phosphatidylcholine species, 16:0–20:4 (10.0 ± 0.7%) and 16:0–22:6 (7.1 ± 0.8%), were both significantly higher than those in healthy controls (7.6 ± 0.5%, P < 0.01 and 5.3 ± 0.5%, P < 0.05 respectively).
4. After 2 weeks treatment, the SICDA in the Crohn's disease patients decreased to 3.2 ± 0.6 (P < 0.0001 compared with the pretreatment value), and there were corresponding falls in the erythrocyte sedimentation rate (to 12.6 ± 2.7 mm/h, P < 0.05) and C-reactive protein concentration (to 1.7 ± 0.3 mg/l, P < 0.05)—these improvements being maintained at 8 weeks. There was also a fall to normal values in 16:0–20:4 (to 7.7 ± 0.6%, P < 0.01 compared with the pretreatment value) and in 16:0–22:6 (to 5.7 ± 0.5%, P not significant), by week 8.
5. The proportions of polyunsaturated phosphatidylcholine molecular species were increased in the plasma of patients with active Crohn's disease, but fell to normal levels during disease remission. These observations are consistent with the theory that, in active Crohn's disease, the mucosal phospholipids containing polyunsaturated fatty acids are increased, contribute to eicosanoid synthesis and ‘spill’ into the plasma.