A membrane lipid imbalance plays a role in the phenotypic expression of cystic fibrosis in cftr(-/-) mice

Abstract

A deficiency in essential fatty acid metabolism has been reported in plasma from patients with cystic fibrosis (CF). However, its etiology and role in the expression of disease is unknown. The objective of this study was to determine whether alterations in fatty acid metabolism are specific to CF-regulated organs and whether they play a role in the expression of disease. A membrane lipid imbalance was found in ileum, pancreas, and lung from cftr(-/-) mice characterized by an increase in phospholipid-bound arachidonic acid and a decrease in phospholipid-bound docosahexaenoic acid (DHA). This lipid imbalance was observed in organs pathologically affected by CF including lung, pancreas, and ileum and was not secondary to impaired intestinal absorption or hepatic biosynthesis of DHA. As proof of concept, oral administration of DHA to cftr(-/-) mice corrected this lipid imbalance and reversed the observed pathological manifestations. These results strongly suggest that certain phenotypic manifestations of CF may result from remediable alterations in phospholipid-bound arachidonic acid and DHA levels.

Figures

Figure 1

AA and DHA levels in ileum, lung, and pancreas fromcftr−/− and wild-type mice. AA and DHA levels were quantitated from the respective organs fromcftr−/− (CF) and wild-type (WT) mice and expressed as nmol/mg protein. Results are expressed as the means ± SD (n = 7).

Figure 2

AA and DHA levels from other organs fromcftr−/− and wild-type mice. Homogenates from brain, heart, and kidney were prepared. AA and DHA were extracted from these organs fromcftr−/− (CF) and wild-type (WT) mice. Results are expressed as the means ± S.D (n = 3). Only results from heart were statistically significant.

Figure 3

Effects of oral DHA administration on AA and DHA levels in preparations of pancreatic acini (A) and lung cells (B). Varying doses of DHA were administered orally for 7 days to cftr−/− mice, and AA and DHA levels were determined. The results are expressed as the mean nanomoles of lipid/mg protein ± SD as a function of mg of DHA administered orally per day (n = 3). For reference, mean AA and DHA levels from wild-type mice (WT) are indicated by dashed lines.

Figure 4

DHA plasma levels in wild-type (WT) andcftr−/− (CF) mice as a function of oral DHA dosing. Mice were fed varying doses of DHA for 7 days, and DHA levels were measured in plasma. Results are expressed as mean plasma level ± SD (n = 3).

Figure 5

Pancreatic morphology and morphometry from wild-type (WT) andcftr−/− (CF) mice, andcftr−/− mice treated orally with 40 mg per day of DHA for 7 days (CF + DHA). Mice were fed Peptamen or Peptamen containing 40 mg of DHA/day for 7 days. Tissue then was prepared for light microscopy. Representative sections (×200) are shown in the three micrographs. The arrowheads indicate the dilated duct lumen in cftr−/− mice. As shown at far right, pancreatic duct diameter was quantitated and expressed as mean diameter (μm) ± SD (n = 6).

Figure 6

Ileal morphology and morphometry from wild-type (WT) andcftr−/− (CF) mice andcftr−/− mice treated orally with 40 mg per day of DHA for 7 days (CF + DHA). Mice were fed Peptamen or Peptamen containing 40 mg of DHA/day (+DHA) for 7 days. Tissue then was prepared for light microscopy. Representative sections are shown (×200) in the three micrographs. (Right) Villous height was quantitated by using nih image software and expressed as arbitrary mean diameter units ± SD (n = 6).

Figure 7

Neutrophil concentration in BAL fluid from wild-type (WT) andcftr−/− mice. Mice were fed Peptamen or Peptamen containing 40 mg of DHA/day (+DHA) for 7 days and then exposed to aerosolized Pseudomonas LPS daily for 3 days. Shown are the means ± SEM from at least five separate experiments. Statistically significant differences were observed in comparing CF with CF + DHA (P = 0.048), CF with WT (P = 0.0004), and CF with WT + DHA (P = 0.0107).