Solubilization of liposomes by weak electrolyte drugs. II. Cefotaxime

The solubilization of dimyristoylphosphatidylcholine (DMPC) liposomes by the weak electrolyte drug, cefotaxime (CFX), has been studied as a function of pH, DMPC, temperature, presence of cholesterol (CHOL), and method of liposome preparation. At 7.5 mM CFX the lag time for solubilization increased, the rate of solubilization decreased, and the minimum turbidity reached increased as a function of DMPC at pH 1.0 and 40 degrees C. Solubilization was most pronounced at pHs below the pKa but inhibited at least one pH unit above the pKa. The critical mole ratio of unionized CFX:DMPC, Rec, for solubilization was estimated to be 0.12. Reducing the temperature slowed the rate of solubilization as did the addition of CHOL. Encapsulation of CFX in liposomes did not significantly reduce CFX degradation,. k1 = 0.048 h-1 at 40 degrees C and a complex of DMPC and a degradation product of CFX precipitated as rectangular crystals. As a result, an increase in the turbidity of solubilized systems was observed from about 20 h to 48 h depending on the conditions. Liposomes in the gel state or with at least 20% CHOL did not undergo an apparent reversal of solubilization. It is concluded that the inclusion of weak electrolyte drugs existing predominantly as the unionized species in liquid crystalline state liposomes may undergo a slow solubilization process not necessarily recognized during characterization.     

Partitioning and thermodynamics of dipyridamole in the n-octanol/buffer and liposome systems

Abstract— The thermodynamics of partitioning (K) of dipyridamole has been determined in n-octanol/buffer and liposome-buffer systems at pH 7·4. Dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) were used to prepare multilamellar liposomes. Partitioning of dipyridamole did not depend on the amount of n-octanol employed, however, partitioning was dependent upon the quantity of DMPC employed to prepare liposomes. Plots of log K vs 1/T were linear in the n-octanol and liposome systems. Partitioning was generally greater in liposomes than in the n-octanol/buffer system. Among liposomes, the partitioning was greater in DMPC liposomes at all temperatures. The values of enthalpy (ΔH) and entropy (ΔS) were positive in both the n-octanol and liposome systems. These values were lower in DMPC liposomes and were comparable in the n-octanol and DPPC liposomes. Thus, the interaction of dipyridamole depends on the rigidity of lipid bilayers and liposomes constitute a more selective partitioning system than the n-octanol/buffer system.     

Solubilization of liposomes by weak electrolyte drugs II. Cefotaxime

The solubilization of dimyristoylphosphatidylcholine (DMPC) liposomes by the weak electrolyte drug, cefotaxime (CFX), has been studied as a function of pH, DMPC, temperature, presence of cholesterol (CHOL), and method of liposome preparation. At 7.5mMCFX the lag time for solubilization increased, the rate of solubilization decreased, and the minimum turbidity reached increased as a function of DMPC at pH 1.0 and 40C. Solubilization was most pronounced at pHs below the pKa but inhibited at least one pH unit above the pKa. The critical mole ratio of unionized CFX:DMPC, Rec, for solubilization was estimated to be 0.12. Reducing the temperature slowed the rate of solubilization as did the addition of CHOL. Encapsulation of CFX in liposomes did not significantly reduce CFX degradation, k1=0.048h-1 at 40C and a complex of DMPC and a degradation product of CFX precipitated as rectangular crystals. As a result, an increase in the turbidity of solubilized systems was observed from about 20h to 48h depending on the conditions. Liposomes in the gel state or with at least 20% CHOL did not undergo an apparent reversal of solubilization. It is concluded that the inclusion of weak electrolyte drugs existing predominantly as the unionized species in liquid crystalline state liposomes may undergo a slow solubilization process not necessarily recognized during characterization.     

The Thermodynamics of Partitioning of Phenothiazines between Phosphate Buffer and the Lipid Phases of Cyclohexane,n-Octanol and DMPC Liposomes

The partitioning of six phenothiazines was determined between phosphate buffer (pH 6.0) and the lipid phases of cyclohexane, n-octanol and dimyristoyl phosphatidylcholine (DMPC). For DMPC liposomes studies were carried out both below and above the phase transition temperature (Tc) of the liposomes. The partitioning of chlorpromazine hydrochloride between n-octanol and phosphate buffer was both pH and concentration-dependent. A linear relationship between the absolute temperature (T^–1) and the logarithm of the equilibrium partition coefficient (ln K) was derived. The temperature dependence of the partition coefficient (K) over the temperature range 20–40° C in cyclohexane and n-octanol, and 5–40° C in DMPC liposomes, permitted the calculation of free-energy (G), enthalpy (H) and the entropy (S) of partitioning. Both the entropy and the enthalpy of partitioning of phenothiazines were positive in the three systems studied. In general, the partitioning of phenothiazines in cyclohexane, n-octanol and DMPC liposomes (both above and below the phase transition temperature (Tc)) is entropically controlled. Correlation was not however found between the free-energy of oil-water partitioning and liposome-water partitioning which may be attributed to the formation of surface associated phenothiazine in high concentrations at the liposome water interface. The concentration dependent partitioning of chlorpromazine in DMPC liposomes may be attributed to the adsorbed fraction of drug.     

Hydrolysis and Stability of Acetylsalicylic Acid in Stearylamine-containing Liposomes

Abstract— The hydrolysis and the stabilization of acetylsalicylic acid (ASA) in liposomes at 30°C were studied. The liposomes consisted of dimyristoylphosphatidylcholine (DMPC) and stearylamine. At pH 4·0 and 8·0, the pseudo-first-order rate constants (k_obs) in DMPC: stearylamine (2:1 mole ratio) liposomes were approximately 60% of the values in control solutions (k_B) if ASA was incorporated via the organic phase. In contrast, when ASA was added via the aqueous phase, k_obs = k_B at pH 4·0 but k_obs < kB at pH 8·0 and k_obs increased with the fraction of stearylamine in the liposomes. However, when ASA was added via the organic phase, reactions occurred which resulted in the loss of ASA as a function of the time period between phase admixture and the point of film hydration. A product of the reactions was determined by IR and TLC to be N-stearylacetamide. Both the initial loss of ASA and the increase in stability decreased as the DMPC: stearylamine mole ratio increased. A mechanism of aminolysis occurring in the organic solvent and at liposome surfaces between ASA and stearylamine or DMPC at pH 8·0 has been suggested. It is concluded that the orientation of ASA and the ordered structural environment of the bilayers minimizes the aminolytic and hydrolytic reactions.     

Interleukin-2-Containing Liposomes: Interaction of Interleukin-2 with Liposomal Bilayers and Preliminary Studies on Application in Cancer Vaccines

Interleukin-2 (IL-2) incorporation in liposomes was studied under different conditions. Information was obtained on the mechanism of interaction of glycosylated recombinant IL-2 with liposomal bilayers. This information was utilized to formulate liposomes with high levels of incorporated IL-2. Multilamellar vesicles were prepared by hydration of a lipid film with an IL-2 solution. The incorporation efficiency, measured with a bioassay after forced release of IL-2 from the vesicles, was strongly dependent on the charge of the liposomes and the pH and ionic strength of the hydration medium. Negatively charged liposomes composed of phosphatidylcholine/ phosphatidylglycerol (9:1) and prepared with IL-2 dissolved in 10 mM NaAc/270 mM glycerol, 0.1% BSA, pH 5, showed the highest incorporation efficiency (81%) among the investigated preparations. This type of liposome was selected for further study. Electrostatics play a crucial role in the process of IL-2 association with this type of liposome. Initial studies concerning induction of protective tumor immunity by immunization with reconstituted membranes with mu-ramyl tripeptide phosphatidylethanolamine indicate that coinjection of IL-2-containing liposomes provided a significant enhancement of the immune response.     

Liposomal Formulation of DIMIQ,Potential Antitumor Indolo[2,3-b]Quinoline Agent and Its Cytotoxicity on Hepatoma Morris 5123 Cells

The cytotoxic and antitumor activity of DIMIQ (5,11-dimethyl-5H-indolo[2,3-b]quinoline), synthetic analog of neocryptolepine, makes this compound a potential antitumor agent. An attempt to obtain liposomal form of DIMIQ·HCl was undertaken in the present study. Standard experimental conditions were chosen and information on the physicochemical parameters of the liposome dispersion containing studied indoloquinoline agent was collected. The effective and efficient encapsulation of DIMIQ·HCl (66.6%) in conventional liposomes (FAT-MLV, DMPC:DMPG 7:3 w/w at pH 7.0), uniformity of the size of liposomal vesicles, and high stability at pH 6.5 were demonstrated. Hemolysis of sheep erythrocytes induced by free form of DIMIQ·HCl was dramatically decreased after addition of liposome-entrapped DIMIQ·HCl. Treatment of hepatoma Morris 5123 cells for 24 hr with different concentrations of both free and its liposomal formulation of DIMIQ·HCl resulted in significant changes in cell morphology accompanied by reduction of cell viability.     

A high sensitivity differential scanning calorimetry study of the interaction between poloxamers and dimyristoylphosphatidylcholine and dipalmitoylphosphatidylcholine liposomes.

High sensitivity differential scanning calorimetry (HSDSC) has been used to measure the thermal behaviour of dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) liposomes to which poloxamer surfactants P338 or P407 had been added during or after preparation. The phospholipid pre-transition was more sensitive than the main transition to the association of poloxamers with liposomal bilayers. Poloxamers reduced the enthalpy of the pre-transition of liquid-crystalline state DMPC and DPPC MLVs but not that of gel state DPPC MLVs. Freezing and thawing DMPC and DPPC liposomes in the presence of poloxamers was shown to increase their interaction with the liposomal bilayers. Copyright     

Acacia-Gelatin Microencapsulated Liposomes: Preparation,Stability, and Release of Acetylsalicylic Acid

Liposomes of dipalmitoylphosphatidylcholine (DPPC) containing acetylsalicylic acid (ASA) have been microencapsulated by acacia-gelatin using the complex coacervation technique as a potential oral drug delivery system. The encapsulation efficiency of ASA was unaltered by the microencapsulation process. The stability of the microencapsulated liposomes in sodium cholate solutions at pH 5.6 was much greater than the corresponding liposomes. The optimum composition and conditions for stability and ASA release were 3.0% acacia-gelatin and a 1- to 2-hr formaldehyde hardening time. Approximately 25% ASA was released in the first 6 hr from microencapsulated liposomes at 23°C and the kinetics followed matrix-controlled release (Q t ^l/2). At 37°C, this increased to 75% released in 30 min followed by a slow constant release, likely due to lowering of the phase transition temperature of DPPC by the acacia-gelatin to near 37°C. At both temperatures, the release from control liposomes was even more rapid. Hardening times of 4 hr and an acacia-gelatin concentration of 5% resulted in a lower stability of liposomes and a faster release of ASA. It is concluded that under appropriate conditions the microencapsulation of liposomes by acacia-gelatin may increase their potential as an oral drug delivery system.     

The topography of acetylcholinesterase in dimyristoylphosphatidylcholine liposomes

Abstract

Unilamellar liposomes prepared from sn-3-(dimyristoyl)phosphatidylcholine (DMPC) in the presence and absence of acetylcholinesterase were examined by ESR for lipid/protein interactions. Using 5-, 12-, and 16-doxyl stearic acid probes incorporated into the phospholipid bilayers, no measurable differences in the gel to liquid-crystalline phase transition temperature of DMPC (as determined by ESR spectroscopy) were observed when the enzyme was present. These results have established that no significant incorporation of acetylcholinesterase into the hydrophobic region of the phospholipid bilayer is detectable at the protein : lipid ratios used in these experiments. Confirmation of these results was also obtained by differential scanning calorimetry. Interaction of the enzyme with the outermost region of the bilayer was established by trypsin digestion which indicated that as much as 25% of liposome-associated enzyme was removable and was, therefore, exposed to the outer surface. the results of this study have established that acetylcholinesterase associated with unilamellar DMPC liposomes was primarily entrapped within the aqueous compartment of the vesicles and was not present in the phospholipid bilayer.     

Characterization of porcine coronary muscarinic receptors

Summary To determine the muscarinic receptor subtype involved in the contractile response of coronary smooth muscle, we investigated the profiles of various muscarinic receptor antagonists competing for [³H]N-methyl-scopolamine ([³H]NMS) binding to membrane preparations from porcine coronary arteries. [³H]NMS binds to a single population of muscarinic binding sites with a K_D of 135 pM and a B_max of 57 fmol/mg. The affinity profiles of AF-DX 116 [11-2((–((diethylamino)methyl)-1-piperidinyl)acetyl)-5,11-dihydro-6H-pyrido(2,3-b)(1,4)-benzodiazepin-6-one], atropine, 4-DAMP [4-diphenylacetoxy-N-methylpiperidine methiodide], methoctramine [N,N-bis (6-((2-methoxybenzyl) amino)hexyl)-1,8-octane-diamine tetrahydrochloride], HHSiD [hexahydrosiladi-fenidol] and pirenzepine are consistent with binding to a mixed population of muscarinic binding sites, namely of the M₂ and M₃ subtype.Binding curves for AF-DX 116 and methoctramine are shallow with Hill-coefficients significantly less than unity. Comparison of data from binding studies with results obtained in functional experiments, i.e. antagonism of methacholine induced contraction of porcine coronary artery rings, it was found that only the low-affinity pK_i values of AF-DX 116 (6.26) and methoctramine (6.51) correlated well with functional pA₂ values.It is concluded that a mixed population of the M₂ and M₃ muscarinic receptor subtypes is present in porcine coronary arteries. Functional experiments do not support the contribution of the M₂ subtype to the contractile response. Cholinergic induced contractions of porcine coronary arteries appear to be evoked via stimulation of the muscarinic M₃ receptor subtype. However, since the compounds investigated here do not markedly discriminate between cloned m₃, m₄ and m₅ receptors the involvement of muscarinic receptors different from M₁, M₂ and M₃ cannot be excluded. Send offprint requests to M. Entzeroth at the above address     

Liposomal formulation of DIMIQ, potential antitumor indolo[2,3-b]quinoline agent and its cytotoxicity on hepatoma Morris 5123 cells

The cytotoxic and antitumor activity of DIMIQ (5,11-dimethyl-5H-indolo[2,3-b]quinoline), synthetic analog of neocryptolepine, makes this compound a potential antitumor agent. An attempt to obtain liposomal form of DIMIQ·HCl was undertaken in the present study. Standard experimental conditions were chosen and information on the physicochemical parameters of the liposome dispersion containing studied indoloquinoline agent was collected. The effective and efficient encapsulation of DIMIQ·HCl (66.6%) in conventional liposomes (FAT-MLV, DMPC:DMPG 7:3 w/w at pH 7.0), uniformity of the size of liposomal vesicles, and high stability at pH 6.5 were demonstrated. Hemolysis of sheep erythrocytes induced by free form of DIMIQ·HCl was dramatically decreased after addition of liposome-entrapped DIMIQ·HCl. Treatment of hepatoma Morris 5123 cells for 24 hr with different concentrations of both free and its liposomal formulation of DIMIQ·HCl resulted in significant changes in cell morphology accompanied by reduction of cell viability.     

Solubilization of ionized and un-ionized flavopiridol by ethanol and polysorbate 20

Because the ionized species is more polar than its un-ionized counterpart, it is often assumed that the ionized species of the drug does not make a meaningful contribution to solubilization by either cosolvents or surfactants. This report extends previous studies on solubilization of the ionic species by a combination of pH control and complexation to pH control and micellization and to pH control and cosolvency. The total aqueous solubility is expressed as the addition of the concentration of all contributing species: free un-ionized drug [Du], free ionized drug [Di], un-ionized drug micelle [DuM], and ionized drug micelle [DiM] for surfactant, and free un-ionized drug [Dcu] and free ionized drug [Dci] for cosolvent. The equations indicate that under certain conditions the ionized species can be more important in determining the drug total solubility than the un-ionized species. Flavopiridol, a weak base, is used to test these newly generated equations. As expected, the micellar partition coefficient and solubilization power for ionized flavopiridol are both less than those of the un-ionized species. However, at acidic pH, the solubilities of the ionized drug in surfactant micelles [DiM] and in cosolvent-water [Dci] are both much greater than that of the un-ionized drug. This difference is because the solubilization of the ionized drug is proportional to its aqueous solubility, and its solubility [Di] can be as much as 24-fold greater than that of the free un-ionized species [Du].     

Cell Handling,Membrane-Binding Properties and Membrane-Penetration Modeling Approaches of Pivampicillin and Phthalimidomethylampicillin,Two Basic Esters of Ampicillin,in Comparison with Chloroquine and Azithromycin

Purpose. The purpose of this work was to examine and understand the cellular pharmacokinetics of two basic esters of ampicillin, pivaloyloxymethyl (PIVA) and phthalimidomethyl (PIMA), in comparison with lysosomotropic drugs (chloroquine, azithromycin). Methods. Cell culture studies (J774 macrophages) were undertaken to study uptake and release kinetics and to assess the influence of concentration, pH, proton ionophore (monensin), and MRP and P-gp inhibitors (probenecid, gemfibrozil, cyclosporin A, GF 120918). Equilibrium dialysis with liposomes were performed to directly asses the extent of drug binding to bilayers. Conformational analysis modeling of the drug penetration in bilayers was conducted to rationalize the experimental observations. Results. PIVA and PIMA showed properties in almost complete contrast with those of chloroquine and azithromycin, i.e., fast apparent accumulation and fast release at 4°C as well as at 37°C, saturation of uptake (apparent K _d 40 M), no influence of monensin, MRP, or P-gp inhibitors; tight binding to liposomes (K _d approx. 40 M); and sharp increase in calculated free energy when forced in the hydrophobic domain. Conclusions. Although they are weak organic bases, PIVA and PIMA show none of the properties of lysosomotropic agents. We hypothesize that they remain locked onto the pericellular membrane and may never penetrate cells as such in significant amounts.     

Influence of ceramides in the solubilization of stratum corneum lipid liposomes by C(12)-betaine/sodium dodecyl sulfate mixtures.

The solubilization of liposomes modeling the stratum corneum (SC) lipid composition and those obtained varying the proportion of ceramides by means of dodecyl betaine (C(12)-Bet)/sodium dodecyl sulfate (SDS) mixtures was studied. The surfactant/lipid molar ratios (Re) and the bilayer/aqueous phase partition coefficients (K) were determined by monitoring the changes in the static light scattering of the system during solubilization. The fact that the free surfactant concentration was always similar to its critical micelle concentration (CMC) indicates that the liposome solubilization was mainly ruled by the formation of mixed micelles. The mole fraction of the zwitterionic component (X(zwitter)) of 0.4 showed the lowest ability to saturate or solubilize liposomes, although exhibiting the highest degree of partitioning into liposomes. This X(zwitter) corresponded to the highest derivation of the CMCs of these mixtures (negative synergism) and to the highest reduction in the skin irritation with respect to the anionic component. Higher and lower proportion of ceramides in the mixture led to a fall and to a rise in both the activity and the partitioning of a specific surfactant mixture (X(zwitter)=0.4). This finding could be related to the recently reported dependences of the level of ceramides in skin and function barrier abnormalities. Comparison of the present Re and K values with those reported for phosphatidylcholine (PC) liposomes shows that, although SC liposomes were more resistant to the action of surfactant mixtures, the surfactant partitioning into SC bilayers was similar to that reported for PC ones in all cases.     

Free Fatty Acids Cause pH-Dependent Changes in Drug-Lipid Membrane Interactions Around Physiological pH

Purpose. The influence of oleic acid (OA) and phosphatidylethanolamine (PhE) as membrane constituents on the partition behavior of (RS)-[³H]propranolol between unilamellar liposomes and buffer was studied as a function of pH. Methods. Partition studies were performed by means of equilibrium dialysis at 37°C over a broad pH range at a molar propranolol to lipid ratio in the membrane of 10^–6. Results. As compared to the standard phosphatidylcholine (PhC)-liposome/buffer partition system PhE and OA have an enhancing effect on the apparent partition coefficient (D) of (RS)-[³H]propranolol between pH 6 and 11. Data analysis with Henderson-Hasselbalch equations revealed that the neutral propranolol has a higher affinity to membranes containing net neutral charged PhE than to pure PhC-liposomes. Net negatively charged PhE seems to have no significant influence on the partitioning. Deprotonated OA caused an increase in the true partition coefficient (P) of the protonated propranolol. Neutral OA showed no influence on the partitioning. From the fit D vs pH curves and from zeta potential measurements of the liposomes the intrinsic pK_a values of the membranous lipids were calculated as 7.5 to 7.8 for OA and 9.7 to 9.8 for PhE. Conclusions. Since the pK_a of membranous OA is close to the physiological pH and D depends on the ionisation state of OA, small pH changes around the physiological pH may cause large differences in drug-lipid membrane interactions.     

Lymphatic Uptake and Biodistribution of Liposomes After Subcutaneous Injection: III. Influence of Surface Modification with Poly(ethyleneglycol)

Purpose. The aim of the present paper was to assess the effect of inclusion of distearoylphosphatidylethanolamine-poly(ethyleneglycol) (DSPE-PEG) into liposomal bilayers on the lymphatic uptake and lymph node localization of liposomes after subcutaneous administration. Methods. [³H]-Cholesteryloleylether labeled liposomes of various composition and sizes were injected s.c. into the dorsal side of the foot of rats. At several time-points after injection, blood levels of liposomes were determined. Lymphatic uptake from the s.c. site of injection and lymph node localization in regional lymph nodes were determined at the end of the 52 h observation period. Results. The results demonstrate that inclusion of DSPE-PEG into several types of liposomes has only a modest effect on lymphatic uptake. Also lymph node localization is only slightly affected by PEG-mediated steric stabilization. Conclusions. Factors other than the presence of a steric barrier are more important in determining lymphatic uptake from the s.c. injection site. The observation that lymph node localization was only slightly affected by PEG-coating strongly suggests that macrophage uptake is not the only important mechanism of lymph node localization of s.c. administered liposomes.     

Poly(4-vinylpyridine)-coated liposomes: stability studies and release of acetylsalicylic acid.

Liposomes of dimyristoylphosphatidylcholine (DMPC) and dicetylphosphate (DCP) reacted with 4-vinylpyridine (4-VP) to form a salt and, subsequently, autopolymerized for form poly(4-vinylpyridine) (poly(4-VP))-coated liposomes. The conditions for optimization of polymer coating have been determined; also, the effects of polymer coating on liposome stability, the encapsulation of ASA and its release kinetics have been measured. The coating efficiency was maximum at a DMPC:DCP 1:1 mole ratio, at pH 4.0 in acetate buffer, and a polymerization time of 40 min. The polymer-coated liposomes were stable in 2 mM sodium cholate and 4 per cent isopropanol solutions, as determined from turbidity measurements, versus a 20-25% decrease in stability of uncoated liposomes. The encapsulation efficiency of ASA reached a maximum of 9 per cent at DMPC:DCP 1:1 mole ratio. The release of ASA at 37 degrees C, pH 7.0 was characterized by an initial fast release (85 and 63 per cent in 20 min from uncoated and polymer-coated liposomes, respectively) followed by a slow, constant release rate up to 140 min. Thus, autopolymerization of a polymerizable monomer at liposome surfaces represents a potentially feasible stabilization approach for liposomes exposed to sodium cholate solutions with greater retention of solute than uncoated liposomes.     

Interactions of amiodarone with model membranes and amiodarone-photoinduced peroxidation of lipids.

The potent antiarrhythmic drug, amiodarone (AMIO) exhibits phototoxicity, which is thought to be related to its interaction with biological membranes. We report here a spectroscopic study of the interactions of this drug with phosphatidylglycerol (PG) and phosphatidylcholine (PC) liposomes used as membrane model systems. A linear increase in absorbance at 300 nm was observed with increasing addition of AMIO to dimyristoyl-DL-PC (DMPC) liposomes over all the drugs-lipid molar ratio (Ri)s tested. In contrast, in the dimyristoyl-DL-PG (DMPG) liposomes, there was a dramatic increase in absorbance at values of Ri above unity. Light scattering by DMPG liposomes at 350 nm increased with increasing AMIO concentration up to a Ri = 1, and then decreased with increasing drug concentration. Such changes were not observed with the DMPC liposomes. Moreover, addition of AMIO changed the fluorescence polarization rate of 1,6-diphenyl 1,3,5-hexatriene embedded in these liposomes. It reduced the rate below the phase transition temperature (Tt) of the lipid, but increased it above this temperature. These effects on the lipidic phases observed at low Ri were more pronounced on the DMPG than on the DMPC liposomes. The strong interactions of AMIO with phospholipids, especially the acidic ones, were confirmed by liposome size determinations. All these data strongly suggest that the drug was incorporated in the core of the lipid bilayers. Such a penetration would favor a drug-photoinduced peroxidation of lipids. Indeed, UV irradiation of AMIO-DOPG mixtures led to the disappearance of the unsaturated fatty acids of phospholipids, checked by gas chromatography measurements, which was correlated with the amount of oxygen consumed. This showed that AMIO did photosensitize phospholipid peroxidation.