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Interaction of nitrogen dioxide with cholesterol-lecithin mixed monolayers
Atmospheric
Environment
Pergamon Press 1970. Vol. 4, pp. 475-480. Printed in Great Britain.
INTERACTION OF NITROGEN DIOXIDE WITH CHOLESTEROL-LECITHIN MIXED MONOLAYERS AIDA M. KAMEL, NORMAN D. WEINER and ALVIN FEL~WEISTER College of Pharmacy, Rutgers University, Newark, New Jersey and College. of Pharmaceutical Sciences, Columbia University, New York, New York. (First received 8 January
1969, and in final form 9 March
1970)
Abstract-The interaction of NO2 with cholesterol-dipahnitoyl lecithin and cholesterolegg lecithin mixed monomolecular !ilms was studied. Both lecithins inhibited the NOz-induced loss of cholesterol from the films, and the degree of inhibition was directly related to the mole fraction of these lipids in the 6lm. The dipalmitoyl lecithin was more efficient in producing this inhibition, apparently because of its greater tendency to associate with the NO+holesterol reaction products. A method is presented to calculate the percentage apparent loss of cholesterol from the mixed films after exposure to N02. INTRODUCTION RECENTLY, we reported the effect of NO1 on pure cholesterol monomolecular films (KAMEL et al., 1969). These films showed a condensation effect that, at least in part,
was due to the desorption of the NO,-reacted cholesterol from the interface. Since monomolecular films have been useful as a means of gaining some insight into the interactions that may occur at the cell membrane surface (PETHICA and SCHXLMAN, 1953; DE~IEL ef al., 1965), and since the loss of cholesterol from cell membranes has been shown to influence properties such as osmotic fragility and permeability (VAN GASTEL et al., 1965), it was of interest to study this NO+holesterol film interaction in more detail. Mixed monomolecular films of cholesterol-lecithin, which more closely resemble cell membranes than do pure cholesterol films, were utilized in this study in order to determine the effect of phospholipids on the observed NOz-induced cholesterol desorption. MATERIALS
AND METHODS
Chromatographically pure L-a-dipalmitoyl lecithin (DPL) and cholesterol (CH), were obtained from Mann Research Laboratories, New York, New York. Chromatographically pure egg lecithin (EL) was supplied by Pierce Chemical Company, Rockford, Illinois. Spectroscopic grade hexane was used to prepare the lipid solutions. All other chemicals were of reagent grade. Previously deionized water was distilled from an all glass still prior to use. A mixture of 0.5 per cent nitrogen dioxide (99.5 per cent pure) and 99.9 per cent prepurified grade nitrogen, Matheson Company, East Rutherford, New Jersey, was used as the source of NO,. The gas mixture was allowed to pass through a flow meter at the rate of 100 ml min-’ and directed into a short length of perforated Teflon tubing which was atied to the underside of a Lucite trough cover as previously described by FELMEISTER et al. (1968). This served to maintain a concentration of 175 i 25 ppm NO, over the film as determined by the method of SALTZMAN (1954). The film balance used to study the surface pressure-surface area (V-A) characteristics of the tim has been described previously (FELMEISTER et al., 1968). Surface pressures were measured by the Wilhehny plate method. 475
476
AIDA M. &MEL,
13. WEINER and ALVIXFELMEI~~R
NORMAN
Solutions of lipids inethanol-hexane (j-95, v/v) were spread on a 0.065 M phosphate buffer at pH 7.0 in order to maintain a constant pH of the subphase throughout the course of the experiment. x-A data were obtained for each of the films. The following procedure was used to determine the effects of NO1 on these films. Solutions of lipids were spread on the buffered subphase and the area of the trough adjusted so that the film pressure was initially 7 dyn cm- I. The gas was allowed to flow over the film for 35 min and the surface pressure values were determined periodically. At the end of the 35 min exposure period manual compression of the films was initiated and surface pressure readings obtained at various film areas.
RESULTS
AND DISCUSSION
FIGURE1 shows the n-A curves for the DPL-CH mixed films of molecular ratios of 3: 1, 2: I, 1: 1, 1: 2 and I : 3 before and after exposure to NO1. Exposure of the
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I
l
I
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I
.
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l
!.
3 40 50 Area/molecule,
A’
FIG. 1. Effect of NO, on the surface pressure-surface area curves for various mole fractions of dipalmitoyl lecithin (DPL): Cholesterol (CH); A, DPL:CH = 3: 1; B, DPL:CH = 2: 1; C, DPL:CH = 1:l; D, DPL:CH = 1:2; E, DPL:CH = 1:3; 0 prior to exposure; 0 after 35 min exposure to Not.
I : 1, 1: 2 and 1: 3 DPL-CH mixed films to NOz resulted in +A curves that were more condensed than the respective curves for the unexposed Glms, i.e., standard curves (FIG. lc, d and e), In contrast, the n-A curves for the mixed films of molecular ratios 3 : 1 and 2 : 1 exposed to NOz were more expanded than the unexposed films (FIG. la and b). Since it has been shown previously that NOz does not interact with DPL (FELMEISTERet al., 1968), these observed effects are not the result of any direct NO,-DPL
Interaction of Nitrogen Dioxide with Cholesterol-Lecithin Mixed Monolayers
477
interaction. However, pure cholesterol monolayers have been shown to become considerably condensed on exposure to NO1 (KAMEL et al., 1969). This effect apparently is due to the interaction of NO, with CH, followed by desorption of the reaction products. It would appear then, that a similar desorption occurs in the 1: 1, 1: 2, and 1: 3 DPL-CH f&s, though to a lesser degree. Furthermore, the extent of condensation observed in these mixed films decreases as the proportion of DPL increases, suggesting that DPL inhibits the desorption, through some type of association with the NO,-reacted cholesterol. This postulation is supported further by the fact that in the 3 : 1 and 2 : 1 DPL-CH films expansion is observed, rather than a total inhibition of the desorption effect. Apparently in these systems, CH is still able to react with the NOz, but now in the presence of the relatively high ratios of DPL, all or at least most of the reacted CH is retained at the surface. Although the possibility exists that DPL may also retard the extent of interaction between CH and NO*, this in itself could not fully explain the data. This effect could lead only to a decreased degree of condensation as a function of increasing DPL concentration, but not to expansion. FIGURE2 shows the n-A curves for EL-CH mixed films of molecular ratios 3 : 1, 2 : 1, 1: 1, 1: 2, and 1: 3, before and after exposure to NO1. Whereas exposure of the 3: 1 EL-CH mixed film to NO, resulted in a TVA curve which was more expanded than the standard curve (FIG. 2a), x-A curves of mixed films of EL-CH of all other molecular ratios studied after exposure to NO1, appeared to be more condensed than the standard curves (FIG. 2B, C, D and E). Although FEL~MEISTERet al. (1968) noted that exposure of pure EL films to NO2 produces a significant shift in the ~4 curve of EL after several hours of exposure,
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Area/molecule.
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A’
FIG. 2. Effect of Not on the surface pressure-surface area curves for various mole fractions of eggIecithin~L):Cholesterol(CH);A,EL:CH=3:1;B,EL:CH=2:1;C,EL:CH=l:l; d, EL:CH = 1:2; e, EL:CH = 1:3; 0 prior to exposure; 0 after 35 min exposure to NO1.
418
AIDA hi. CAMEL, XORUAS D. WEISER and ALLIN FELMEISTER
no shift was detected after the 35 min exposure used in this study. Thus, the observed changes in the 7-A curves of the EL-CH mixed films is, as in the case of the DPL-CH systems, not a function of an NOI-EL interaction. It appears also, that EL acts through the same mechanism as DPL to inhibit the desorption of the N02-reacted CH. A comparison of FIGS. 1 and 2 shows that although both DPL and EL tend to inhibit the loss of CH after exposure to N02, DPL starrs to produce this effect at a lower DPL: CH mole ratio than does EL. The effect of a 3.5 min exposure of NO2 on the Iilm pressure of various mixed films of DPL-CH and EL-CH at constant area at an initial 7 of 7 dyn cm-’ is shown in FIGS. 3a and 3b, respectively. It is apparent that not only the magnitude, but also the sign of the change in pressure (1:) as a result of NO2 exposure is a function of the mole fraction and degree of unsaturation of the phospholipid, and again DPL is shown to be more effective than EL jn inhibiting film condensation. SHAH and SCHULM~ (1967) pointed out that increasing saturation of the fatty acyl chains in phospholipids progressively decreases the intermolecular spacing monolayer. This in turn weakens the internal salt linkage between molecules in a
FIG. 3. Effect of 35 min exposure to NO, on the surface pressure of various mole fractions of cholesterol-lecithin mixtures at constant area at an initial surface pressure of 7 dyn cm - I. A, dipalmitoyl lecithin; B, egg lecithin.
Interaction
of Nitrogen Dioxide with Cholesesterol-Lecithin Mixed Monolayers
479
between the phosphate and t~methyl~mo~um groups, thereby increasing the ability of these compounds to engage in intermolecular ion-ion or ion-dipole interactions. The fact that DPL is somewhat more efficient than EL in inhibiting the loss of NOzreacted CH from the surface may be related to the weaker internal salt linkage between its phosphate and trimethylammonium groups and the subsequent increased ability of DPL to engage in ion-dipole interactions with the products of the NOzCH reaction. The influence of these lecithins on the stability of mixed cholesterol-lecithin films is made more evident by comparing the percent apparent loss (PAL) of CH for the various mixed films after exposure to NOz. Unfortunately, the actual loss of CH can not be determined from the available data because of the complexity of the processes involved in the observed condensation. Clearly, the effect is a combination of several factors such as desorption, dissolution, change in orientation, and chemical modification of the film molecules. However, the PAL, which summarizes the overall effect ofall of these processes, is a measure of the effectiveness of the lecithins on the stability of cholesterol-lecithin films in the presence of NOz. A surface pressure value of 30 dyn cm-’ was chosen to calculate values of PAL since the sensitivity of the method is improved at high surface pressures due to the higher percentage of the total area occupied by CH (SHAHet al., 1967). The percentage apparent loss (PAL) of CH from pure CH monolayers is calculated from the following relationship (KAMEL et al.,1969): PAL = (1 - K/A) loo, where A and A’ are the areas per moiecule of CH prior to and after exposure to N02, respectively. The apparent loss of CH from the mixed monolayers is calculated from the following relationship : PAL = {1 -
[F’( 1 - F)/F( 1 - F’)]]
. 100,
where F and F’ are the mole fractions of CH prior to and after exposure of the mixed lilms to N02, respectively. The mole fractions of CH after exposure to NO2 (F’) are obtained for each of their corresponding initialmole fraction values(F) by determining the change in the fraction of the total area occupied by CH prior to and after exposure to N02. These data can be obtained from the surface pressure vs. area per lecithin molecule curves for each of the mixed fihns prior to and after exposure to N02. Within the range of mole fractions used in this study, a linear relationship was found to exist between F and the fraction of the total film area occupied by CH. The data are presented in TABLE1. CONCLUSION
Though phospholipids, enzymes, fatty acids, and other cellular components have been implicated as possible sites of attack by air pollutants (FELMEISTER et al., 1968, THOMASet al., 1968, ORD~ et al., 1969), the effects of these pollutants on cholesterol and cholesterol-lecit~n systems have not been considered. The data presented here suggest that CH may be directly involved in some of the observed in vim effects of air pollutants on biological systems. Furthermore, the extent of interaction of NO2 on
480
AIDA ht. CAMEL,
NORMAS
D. WEIXR
and ALVIN FELME~STER
TABLE I. PERCENTAGEAPPARENTLoss (PAL) OF CHOLESTEROLPER 35min EXPOSLRE TO x;02 AS A FLYCI-IOS OF SIOLE FRACTIOS OF CHOLESTEROL(F) IN CHOLESTEROL-LECITHIS.LCXEDFK.MS AT AS I&W SuRFACE PRESSURE oF7dyncm-i PAL DPL
F 0.25 0.33 0.50 0.67 0.75 1.00’ *Data
0 0 30 4-t 62 67 from KARL
EL 0 26 44 63 61 67
et al. (1969).
cell membranes may be directly dependent on the ratio of CH to phospholipids and to the degree of unsaturation of the latter. Acknowledgements-This Control Administration, Service.
study is being supported by Grant Number AP 788, National Air Pollution Consumer Protection and Environmental Health Service, Public Health
REFERENCES DEMEL R. A., VAN DEENEN L. L. IM. and KLVSKY S. C. (1965) Penetration of lipid monolayers by polyene antibiotics. J. biol. Chem. UO,2749-2753. FEL.~TER A., AMANAT M. and WEINER N. D. (1968) Interaction of nitrogen dioxide+letin gas mixtures with lecithin monomolecular films. Emiron. Sci. Tech. 2,40-43. KA~CELA. M., FEL~IEDTERA. and WEIXER iL’. D. (1969) The interaction of nitrogen dioxide with cholesterol monomolecular films: effect of initial surface pressure, time of exposure and concentration of NOz. J. Pharm. Sci., in press. ORDM L., HALL M. A. and KWDINGER J. I. (1969) Oxidant-induced inhibition of enzymes involved in cell wall-polysaccharide synthesis. Archs. Emiron. Health 18, 623-626. PETHICA B. A. and SCHULMASJ. H. (1953) The physical chemistry of haemolysis by surface active agents. Biochem. J. 53, 177-185. SALTZMAN B. E. (1954) Calorimetric microdetermination of nitrogen dioxide in the atmosphere. AML Chem. 26, 1949-1955. SHAH D. 0. and SCHULMAN J. H. (1967) Inhuence of calcium, cholesterol, and unsaturation on lethithin monolayers. J. Lipid Res. 8, 215-226. THOMASH.V., MUELLER P. K. and LYMANR. L. (1967) Lipoperoxidation of lung lipids in rats exposed
to nitrogen dioxide. Science 159,532-534. VAY GASI-ELC., VANDEN BERG D., DE GIER J. and V.XVDEE&XX L. L. M. (1965) Some lipid characteristics of normal red blood cells of different age. Br. J. Huemat. 11, 193-199.
Environment
Pergamon Press 1970. Vol. 4, pp. 475-480. Printed in Great Britain.
INTERACTION OF NITROGEN DIOXIDE WITH CHOLESTEROL-LECITHIN MIXED MONOLAYERS AIDA M. KAMEL, NORMAN D. WEINER and ALVIN FEL~WEISTER College of Pharmacy, Rutgers University, Newark, New Jersey and College. of Pharmaceutical Sciences, Columbia University, New York, New York. (First received 8 January
1969, and in final form 9 March
1970)
Abstract-The interaction of NO2 with cholesterol-dipahnitoyl lecithin and cholesterolegg lecithin mixed monomolecular !ilms was studied. Both lecithins inhibited the NOz-induced loss of cholesterol from the films, and the degree of inhibition was directly related to the mole fraction of these lipids in the 6lm. The dipalmitoyl lecithin was more efficient in producing this inhibition, apparently because of its greater tendency to associate with the NO+holesterol reaction products. A method is presented to calculate the percentage apparent loss of cholesterol from the mixed films after exposure to N02. INTRODUCTION RECENTLY, we reported the effect of NO1 on pure cholesterol monomolecular films (KAMEL et al., 1969). These films showed a condensation effect that, at least in part,
was due to the desorption of the NO,-reacted cholesterol from the interface. Since monomolecular films have been useful as a means of gaining some insight into the interactions that may occur at the cell membrane surface (PETHICA and SCHXLMAN, 1953; DE~IEL ef al., 1965), and since the loss of cholesterol from cell membranes has been shown to influence properties such as osmotic fragility and permeability (VAN GASTEL et al., 1965), it was of interest to study this NO+holesterol film interaction in more detail. Mixed monomolecular films of cholesterol-lecithin, which more closely resemble cell membranes than do pure cholesterol films, were utilized in this study in order to determine the effect of phospholipids on the observed NOz-induced cholesterol desorption. MATERIALS
AND METHODS
Chromatographically pure L-a-dipalmitoyl lecithin (DPL) and cholesterol (CH), were obtained from Mann Research Laboratories, New York, New York. Chromatographically pure egg lecithin (EL) was supplied by Pierce Chemical Company, Rockford, Illinois. Spectroscopic grade hexane was used to prepare the lipid solutions. All other chemicals were of reagent grade. Previously deionized water was distilled from an all glass still prior to use. A mixture of 0.5 per cent nitrogen dioxide (99.5 per cent pure) and 99.9 per cent prepurified grade nitrogen, Matheson Company, East Rutherford, New Jersey, was used as the source of NO,. The gas mixture was allowed to pass through a flow meter at the rate of 100 ml min-’ and directed into a short length of perforated Teflon tubing which was atied to the underside of a Lucite trough cover as previously described by FELMEISTER et al. (1968). This served to maintain a concentration of 175 i 25 ppm NO, over the film as determined by the method of SALTZMAN (1954). The film balance used to study the surface pressure-surface area (V-A) characteristics of the tim has been described previously (FELMEISTER et al., 1968). Surface pressures were measured by the Wilhehny plate method. 475
476
AIDA M. &MEL,
13. WEINER and ALVIXFELMEI~~R
NORMAN
Solutions of lipids inethanol-hexane (j-95, v/v) were spread on a 0.065 M phosphate buffer at pH 7.0 in order to maintain a constant pH of the subphase throughout the course of the experiment. x-A data were obtained for each of the films. The following procedure was used to determine the effects of NO1 on these films. Solutions of lipids were spread on the buffered subphase and the area of the trough adjusted so that the film pressure was initially 7 dyn cm- I. The gas was allowed to flow over the film for 35 min and the surface pressure values were determined periodically. At the end of the 35 min exposure period manual compression of the films was initiated and surface pressure readings obtained at various film areas.
RESULTS
AND DISCUSSION
FIGURE1 shows the n-A curves for the DPL-CH mixed films of molecular ratios of 3: 1, 2: I, 1: 1, 1: 2 and I : 3 before and after exposure to NO1. Exposure of the
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I
l
I
C
E
l
I. \
I
.
\.
\
A-
l
!.
3 40 50 Area/molecule,
A’
FIG. 1. Effect of NO, on the surface pressure-surface area curves for various mole fractions of dipalmitoyl lecithin (DPL): Cholesterol (CH); A, DPL:CH = 3: 1; B, DPL:CH = 2: 1; C, DPL:CH = 1:l; D, DPL:CH = 1:2; E, DPL:CH = 1:3; 0 prior to exposure; 0 after 35 min exposure to Not.
I : 1, 1: 2 and 1: 3 DPL-CH mixed films to NOz resulted in +A curves that were more condensed than the respective curves for the unexposed Glms, i.e., standard curves (FIG. lc, d and e), In contrast, the n-A curves for the mixed films of molecular ratios 3 : 1 and 2 : 1 exposed to NOz were more expanded than the unexposed films (FIG. la and b). Since it has been shown previously that NOz does not interact with DPL (FELMEISTERet al., 1968), these observed effects are not the result of any direct NO,-DPL
Interaction of Nitrogen Dioxide with Cholesterol-Lecithin Mixed Monolayers
477
interaction. However, pure cholesterol monolayers have been shown to become considerably condensed on exposure to NO1 (KAMEL et al., 1969). This effect apparently is due to the interaction of NO, with CH, followed by desorption of the reaction products. It would appear then, that a similar desorption occurs in the 1: 1, 1: 2, and 1: 3 DPL-CH f&s, though to a lesser degree. Furthermore, the extent of condensation observed in these mixed films decreases as the proportion of DPL increases, suggesting that DPL inhibits the desorption, through some type of association with the NO,-reacted cholesterol. This postulation is supported further by the fact that in the 3 : 1 and 2 : 1 DPL-CH films expansion is observed, rather than a total inhibition of the desorption effect. Apparently in these systems, CH is still able to react with the NOz, but now in the presence of the relatively high ratios of DPL, all or at least most of the reacted CH is retained at the surface. Although the possibility exists that DPL may also retard the extent of interaction between CH and NO*, this in itself could not fully explain the data. This effect could lead only to a decreased degree of condensation as a function of increasing DPL concentration, but not to expansion. FIGURE2 shows the n-A curves for EL-CH mixed films of molecular ratios 3 : 1, 2 : 1, 1: 1, 1: 2, and 1: 3, before and after exposure to NO1. Whereas exposure of the 3: 1 EL-CH mixed film to NO, resulted in a TVA curve which was more expanded than the standard curve (FIG. 2a), x-A curves of mixed films of EL-CH of all other molecular ratios studied after exposure to NO1, appeared to be more condensed than the standard curves (FIG. 2B, C, D and E). Although FEL~MEISTERet al. (1968) noted that exposure of pure EL films to NO2 produces a significant shift in the ~4 curve of EL after several hours of exposure,
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.
.
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20-
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\
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10
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0
.
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.
.
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i
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‘
$
! 40
Area/molecule.
:J_ 50
I
)
30
40
I_
A’
FIG. 2. Effect of Not on the surface pressure-surface area curves for various mole fractions of eggIecithin~L):Cholesterol(CH);A,EL:CH=3:1;B,EL:CH=2:1;C,EL:CH=l:l; d, EL:CH = 1:2; e, EL:CH = 1:3; 0 prior to exposure; 0 after 35 min exposure to NO1.
418
AIDA hi. CAMEL, XORUAS D. WEISER and ALLIN FELMEISTER
no shift was detected after the 35 min exposure used in this study. Thus, the observed changes in the 7-A curves of the EL-CH mixed films is, as in the case of the DPL-CH systems, not a function of an NOI-EL interaction. It appears also, that EL acts through the same mechanism as DPL to inhibit the desorption of the N02-reacted CH. A comparison of FIGS. 1 and 2 shows that although both DPL and EL tend to inhibit the loss of CH after exposure to N02, DPL starrs to produce this effect at a lower DPL: CH mole ratio than does EL. The effect of a 3.5 min exposure of NO2 on the Iilm pressure of various mixed films of DPL-CH and EL-CH at constant area at an initial 7 of 7 dyn cm-’ is shown in FIGS. 3a and 3b, respectively. It is apparent that not only the magnitude, but also the sign of the change in pressure (1:) as a result of NO2 exposure is a function of the mole fraction and degree of unsaturation of the phospholipid, and again DPL is shown to be more effective than EL jn inhibiting film condensation. SHAH and SCHULM~ (1967) pointed out that increasing saturation of the fatty acyl chains in phospholipids progressively decreases the intermolecular spacing monolayer. This in turn weakens the internal salt linkage between molecules in a
FIG. 3. Effect of 35 min exposure to NO, on the surface pressure of various mole fractions of cholesterol-lecithin mixtures at constant area at an initial surface pressure of 7 dyn cm - I. A, dipalmitoyl lecithin; B, egg lecithin.
Interaction
of Nitrogen Dioxide with Cholesesterol-Lecithin Mixed Monolayers
479
between the phosphate and t~methyl~mo~um groups, thereby increasing the ability of these compounds to engage in intermolecular ion-ion or ion-dipole interactions. The fact that DPL is somewhat more efficient than EL in inhibiting the loss of NOzreacted CH from the surface may be related to the weaker internal salt linkage between its phosphate and trimethylammonium groups and the subsequent increased ability of DPL to engage in ion-dipole interactions with the products of the NOzCH reaction. The influence of these lecithins on the stability of mixed cholesterol-lecithin films is made more evident by comparing the percent apparent loss (PAL) of CH for the various mixed films after exposure to NOz. Unfortunately, the actual loss of CH can not be determined from the available data because of the complexity of the processes involved in the observed condensation. Clearly, the effect is a combination of several factors such as desorption, dissolution, change in orientation, and chemical modification of the film molecules. However, the PAL, which summarizes the overall effect ofall of these processes, is a measure of the effectiveness of the lecithins on the stability of cholesterol-lecithin films in the presence of NOz. A surface pressure value of 30 dyn cm-’ was chosen to calculate values of PAL since the sensitivity of the method is improved at high surface pressures due to the higher percentage of the total area occupied by CH (SHAHet al., 1967). The percentage apparent loss (PAL) of CH from pure CH monolayers is calculated from the following relationship (KAMEL et al.,1969): PAL = (1 - K/A) loo, where A and A’ are the areas per moiecule of CH prior to and after exposure to N02, respectively. The apparent loss of CH from the mixed monolayers is calculated from the following relationship : PAL = {1 -
[F’( 1 - F)/F( 1 - F’)]]
. 100,
where F and F’ are the mole fractions of CH prior to and after exposure of the mixed lilms to N02, respectively. The mole fractions of CH after exposure to NO2 (F’) are obtained for each of their corresponding initialmole fraction values(F) by determining the change in the fraction of the total area occupied by CH prior to and after exposure to N02. These data can be obtained from the surface pressure vs. area per lecithin molecule curves for each of the mixed fihns prior to and after exposure to N02. Within the range of mole fractions used in this study, a linear relationship was found to exist between F and the fraction of the total film area occupied by CH. The data are presented in TABLE1. CONCLUSION
Though phospholipids, enzymes, fatty acids, and other cellular components have been implicated as possible sites of attack by air pollutants (FELMEISTER et al., 1968, THOMASet al., 1968, ORD~ et al., 1969), the effects of these pollutants on cholesterol and cholesterol-lecit~n systems have not been considered. The data presented here suggest that CH may be directly involved in some of the observed in vim effects of air pollutants on biological systems. Furthermore, the extent of interaction of NO2 on
480
AIDA ht. CAMEL,
NORMAS
D. WEIXR
and ALVIN FELME~STER
TABLE I. PERCENTAGEAPPARENTLoss (PAL) OF CHOLESTEROLPER 35min EXPOSLRE TO x;02 AS A FLYCI-IOS OF SIOLE FRACTIOS OF CHOLESTEROL(F) IN CHOLESTEROL-LECITHIS.LCXEDFK.MS AT AS I&W SuRFACE PRESSURE oF7dyncm-i PAL DPL
F 0.25 0.33 0.50 0.67 0.75 1.00’ *Data
0 0 30 4-t 62 67 from KARL
EL 0 26 44 63 61 67
et al. (1969).
cell membranes may be directly dependent on the ratio of CH to phospholipids and to the degree of unsaturation of the latter. Acknowledgements-This Control Administration, Service.
study is being supported by Grant Number AP 788, National Air Pollution Consumer Protection and Environmental Health Service, Public Health
REFERENCES DEMEL R. A., VAN DEENEN L. L. IM. and KLVSKY S. C. (1965) Penetration of lipid monolayers by polyene antibiotics. J. biol. Chem. UO,2749-2753. FEL.~TER A., AMANAT M. and WEINER N. D. (1968) Interaction of nitrogen dioxide+letin gas mixtures with lecithin monomolecular films. Emiron. Sci. Tech. 2,40-43. KA~CELA. M., FEL~IEDTERA. and WEIXER iL’. D. (1969) The interaction of nitrogen dioxide with cholesterol monomolecular films: effect of initial surface pressure, time of exposure and concentration of NOz. J. Pharm. Sci., in press. ORDM L., HALL M. A. and KWDINGER J. I. (1969) Oxidant-induced inhibition of enzymes involved in cell wall-polysaccharide synthesis. Archs. Emiron. Health 18, 623-626. PETHICA B. A. and SCHULMASJ. H. (1953) The physical chemistry of haemolysis by surface active agents. Biochem. J. 53, 177-185. SALTZMAN B. E. (1954) Calorimetric microdetermination of nitrogen dioxide in the atmosphere. AML Chem. 26, 1949-1955. SHAH D. 0. and SCHULMAN J. H. (1967) Inhuence of calcium, cholesterol, and unsaturation on lethithin monolayers. J. Lipid Res. 8, 215-226. THOMASH.V., MUELLER P. K. and LYMANR. L. (1967) Lipoperoxidation of lung lipids in rats exposed
to nitrogen dioxide. Science 159,532-534. VAY GASI-ELC., VANDEN BERG D., DE GIER J. and V.XVDEE&XX L. L. M. (1965) Some lipid characteristics of normal red blood cells of different age. Br. J. Huemat. 11, 193-199.