Rituximab therapy in pulmonary alveolar proteinosis improves alveolar macrophage lipid homeostasis.

Abstract

RATIONALE:

Pulmonary Alveolar Proteinosis (PAP) patients exhibit an acquired deficiency of biologically active granulocyte-macrophage colony stimulating factor (GM-CSF) attributable to GM-CSF specific autoantibodies. PAP alveolar macrophages are foamy, lipid-filled cells with impaired surfactant clearance and markedly reduced expression of the transcription factor peroxisome proliferator-activated receptor gamma (PPARγ) and the PPARγ-regulated ATP binding cassette (ABC) lipid transporter, ABCG1. An open label proof of concept Phase II clinical trial was conducted in PAP patients using rituximab, a chimeric murine-human monoclonal antibody directed against B lymphocyte specific antigen CD20. Rituximab treatment decreased anti-GM-CSF antibody levels in bronchoalveolar lavage (BAL) fluid, and 7/9 patients completing the trial demonstrated clinical improvement as measured by arterial blood oxygenation.

OBJECTIVES:

This study sought to determine whether rituximab therapy would restore lipid metabolism in PAP alveolar macrophages.

METHODS:

BAL samples were collected from patients pre- and 6-months post-rituximab infusion for evaluation of mRNA and lipid changes.

RESULTS:

Mean PPARγ and ABCG1 mRNA expression increased 2.8 and 5.3-fold respectively (p ≤ 0.05) after treatment. Lysosomal phospholipase A2 (LPLA2) (a key enzyme in surfactant degradation) mRNA expression was severely deficient in PAP patients pre-treatment but increased 2.8-fold post-treatment. In supplemental animal studies, LPLA2 deficiency was verified in GM-CSF KO mice but was not present in macrophage-specific PPARγ KO mice compared to wild-type controls. Oil Red O intensity of PAP alveolar macrophages decreased after treatment, indicating reduced intracellular lipid while extracellular free cholesterol increased in BAL fluid. Furthermore, total protein and Surfactant protein A were significantly decreased in the BAL fluid post therapy.

CONCLUSIONS:

Reduction in GM-CSF autoantibodies by rituximab therapy improves alveolar macrophage lipid metabolism by increasing lipid transport and surfactant catabolism. Mechanisms may involve GM-CSF stimulation of alveolar macrophage ABCG1 and LPLA2 activities by distinct pathways.

• Authors: Anagha Malur, Mani S Kavuru, Irene Marshall, Barbara P Barna, Isham Huizar, Reema Karnekar, Mary Jane Thomassen
• Journal: Respiratory research (Respir Res) Vol. 13 Pg. 46 (Jun 14 2012) ISSN: 1465-993X [Electronic] England
• PMID: 22697800 (Publication Type: Clinical Trial, Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• Antibodies, Monoclonal, Murine-Derived
• Membrane Lipids
• Rituximab

Topics

• Adult
• Animals
• Antibodies, Monoclonal, Murine-Derived (therapeutic use)
• Female
• Homeostasis (drug effects, immunology)
• Humans
• Macrophages, Alveolar (drug effects, immunology, pathology)
• Male
• Membrane Lipids (physiology)
• Mice
• Mice, Inbred C57BL
• Mice, Knockout
• Prospective Studies
• Pulmonary Alveolar Proteinosis (drug therapy, immunology, pathology)
• Pulmonary Alveoli (drug effects, immunology, pathology)
• Rituximab