The document discusses the two-step process of pulmonary surfactant adsorption to an air-water interface. The initial step slowly reduces surface tension to around 35-50 mN/m. The later step then accelerates further to the final tension of around 25 mN/m. Experiments show that lysophosphatidylcholine (LPC) and DSPE-PEG inhibit the later fusion step by disrupting lipid structure and stability, but have mixed effects on the initial step, either delaying or accelerating the rate. This supports a model where the initial step involves decreased lipid ordering, while the later step requires formation of a negatively curved stalk structure through vesicle fusion.

1. THE EARLY AND LATE PROCESSES IN THE
ADSORPTION OF PULMONARY
SURFACTANT
Samares C. Biswas1, Shankar B. Rananavare2, Stephen B. Hall1
1Oregon Health & Science University, Portland, OR, USA,
2Portland State University, Portland, OR, USA.

2. ADSORPTION OF PULMONARY SURFACTANT
• Pulmonary surfactant adsorbs to an air-water interface
in two distinct steps
– initial fall in surface tension at slowing rates to an
inflection point at ~35-50mN/m
– later acceleration until reaching the final surface
tension of ~25mN/m.

3. ADSORPTION OF LIPID VESICLES
Formation of lipid layer at the alveolar A/W interface
Multiple steps
•Diffusion
•Insertion
•Fusion

4. Inflection point
EFFECTS OF HYDROPHOBIC SURFACTANT
PROTEINS (SP-B/-C) ON ADSORPTION

5. OBJECTIVES
Determine the mechanisms involved in the two
steps adsorption of pulmonary surfactant

6. MODEL
• Step 1: Initial adsorption of lipid vesicle
– Does not require hydrophobic surfactant proteins (SP-B/-C)
– Related to a process other than fusion
• Step 2: Later acceleration of adsorption
– Requires the presence of proteins
– Fusion of the lipid vesicles with the preformed lipid layer

7. EFFECTS OF LPC & DSPE-PEG ON LIPID
STRUCTURES
• LPC
– forms micelles
– induces positive curvature
• which inhibit fusion
– produces lipid disorder
•DSPE-PEG
– forms micelles
– produces sterically stabilized liposomes
• which inhibit fusion
– produces lipid disorder
LPC-diagram
DOPE-PEG-
diagram

8. PREDICTED EFFECTS OF LPC AND DSPE-PEG
ON ADSORPTION
• LPC should
– inhibit the final step
– inhibition of fusion
– destabilization of stalk intermediate
• DSPE-PEG should
– inhibit the final step
– inhibition of fusion
– steric stabilization of liposome

9. RESULTS

10. Effect of lysophosphatidylcholine
(LPC) on adsorption

15. LPC
Affected both the steps of adsorption.
Delayed the initiation of final acceleration.
Effect on the initial process is not clear.

16. LPC does have effect on the initial step, but it is
not clear. To determine the effect on the initial
step, we studied adsorption of LPC/DOPC and
LPC/N&PL systems.

17. Effects of LPC on adsorption of
DOPC and N&PL

22. LPC
Affected the initial fall in surface tension.
Effect was dose dependent.
Dialysis confirmed that the observed effect is
not due to the presence of free LPC.

23. Effects of DSPE-PEG on
adsorption

25. DOPC alone

27. Like LPC, DSPE-PEG also
Affected both the steps of adsorption
Delayed the initiation of final acceleration
Effects on initial process is not regular.
DSPE-PEG does accelerate the adsorption of
DOPC vesicles.

28. FINDINGS
Effects of LPC:
On CLSE and the model systems DOPE and GrA/DOPC-
Inhibit final steps of adsorption.
On N&PL and DOPC-
 Accelerate the initial rate of adsorption.
Effects of DSPE-PEG:
CLSE and GrA/DOPC
Inhibit the initial and final steps of adsorption.
ON DOPC
Accelerate the initial rate of adsorption

29. CONCLUSIONS
Our results supports a model in which
Adsorption proceeds by two distinct steps:
Associated with two different structural effects.
Initial step
 determined by different processes, such as
decreased bilayer order.
The final step
 involves formation of a negatively curved
structure