AJP - Lung Cellular and Molecular Physiology, Vol 268, Issue 3 374-L380, Copyright © 1995 by American Physiological Society
Delivery of superoxide dismutase to pulmonary epithelium via pH-sensitive liposomes
P. Briscoe, I. Caniggia, A. Graves, B. Benson, L. Huang, A. K. Tanswell and B. A. Freeman
Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, 35233.
Respiratory insufficiency, when treated with oxygen supplementation, or
exposure to diverse pulmonary toxins can cause lung damage as a result of
increased oxygen radical production. Enzymes such as superoxide dismutase
(SOD) may attenuate this pathological process, but the intracellular
delivery and antioxidant action of SOD is impeded by its inability to cross
cellular membranes. One approach for facilitating intracellular delivery of
macromolecules is to entrap SOD into liposomes. The delivery of SOD to lung
cells was accomplished using pH-sensitive liposomes, made with
1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) and
1-oleoyl-2-oleoyl-sn-glycero-3-succinate (DOSG), added to cultured fetal
rat lung distal epithelial (FRLE) cells. FRLE cells, obtained from fetuses
at day 19 gestation, expressed a high-affinity receptor for surfactant
protein A (SP-A) with an apparent dissociation constant (Kd) = 3.6 +/- 0.2
micrograms/ml (5.5 x 10(-9) M) and a capacity of 130 +/- 3 ng/10(6) cells
(125,000 +/- 3,000 binding sites/cell). This receptor was utilized for
targeting liposomes to cells, after incorporating SP-A during liposome
membrane formation. Liposomes were uniformly small (180 +/- 77 nm; mean +/-
SD) and stable at 4 degrees C for 1 wk, entrapping 10 +/- 4% of initially
added SOD. After incubation of pH-sensitive liposomes containing entrapped
SOD with cultured FRLE cells, cell-associated SOD activity was increased
5.1-fold from 7.8 +/- 2.5 to 40.1 +/- 3.3 U SOD/mg cell protein.
Incorporation of SP-A into liposomes increased by 6.2-fold the delivery of
liposomal SOD to cells.(ABSTRACT TRUNCATED AT 250 WORDS)
