Hepatic cysteamine and non-protein sulfhydryl levels following cystamine or cysteamine treatment of galactosamine-poisoned rats

Hepatic cysteamine and non-protein sulfhydryl (NPSH) levels were determined in galactosamine (GAL)-poisoned rats following hepatoprotective cystamine or cysteamine treatments to determine whether alterations of hepatic NPSH status could contribute to their observed protective actions. D(+)-Galactosamine HC1 (400 mg/kg, ip) was administered to male Sprague-Dawley rats at 8 pm. Cystamine diHC1 (300 mg/kg, po) or cysteamine HC1 (170 mg/kg, ip) were administered 12 hr after GAL. Hepatic NPSH levels were determined using Ellman's reagent. Hepatic cysteamine levels were determined by separating NPSH Ellman's derivatives by reversed phase HPLC. Cystamine and cysteamine caused transient elevation of NPSH levels of 1-2 nanomoles/mg liver which correlated with the presence of 1-2 nanomoles of cysteamine/mg liver. However, neither cystamine nor cysteamine prevented NPSH levels from falling to 3 nanomoles/mg tissue 24 hr after GAL. Hepatoprotective treatments did not affect long term NPSH status in GAL-poisoned rats. However, transient NPSH increases, due to the intrahepatic presence of cysteamine, may contribute to the therapeutic effects of these hepatoprotective agents.     

含硫亚硝基脲衍生物

本文报道一系列含硫亚硝基脲衍生物的合成、光谱学特征及对小鼠白血病L1210的作用。这些化合物都是CNC-半胱胺的衍生物,包括二硫化合物、2-氯乙基氨甲酸酯衍生物以及与羰基化合物环合而成的2,2-二取代的CNC-四氢噻唑。CNC-半胱胺及其二硫化合物、CNC-胱胺甲酰叠氮均有良好的抗L1210的作用;相应的氨甲酸酯衍生物和四氢噻唑衍生物的作用不明显。值得注意的是,2-甲基-2-乙氧羰甲基-3-CNC-四氢噻唑(15b)是一个例外,它对L1210有显著的抑制作用。     

Hepatic Cysteamine and Non-Protein Sulfhydryl Levels Following Cystamine or Cysteamine Treatment of Galactosamine-Poisoned Rats

ABSTRACT

Hepatic cysteamine and non-protein sulfhydryl (NPSH) levels were determined in galactosamine (GAL)-poisoned rats following hepatoprotective cystamine or cysteamine treatments to determine whether alterations of hepatic NPSH status could contribute to their observed protective actions. D(+)-Galactosamine HC1 (400 mg/kg, ip) was administered to male Sprague-Dawley rats at 8 pm. Cystamine diHCl (300 mg/kg, po) or cysteamine HC1 (170 mg/kg, ip) were administered 12 hr after GAL. Hepatic NPSH levels were determined using Ellman's reagent. Hepatic cysteamine levels were determined by separating NPSH Ellman's derivatives by reversed phase HPLC. Cystamine and cysteamine caused transient elevation of NPSH levels of 1–2 nanomoles/mg liver which correlated with the presence of 1-2 nanomoles of cysteamine/mg liver. However, neither cystamine nor cysteamine prevented NPSH levels from falling to 3 nanomoles/mg tissue 24 hr after GAL. Hepatoprotective treatments did not affect long term NPSH status in GAL-poisoned rats. However, transient NPSH increases, due to the intrahepatic presence of cysteamine, may contribute to the therapeutic effects of these hepatoprotective agents.     

Nano-based rescue of dysfunctional autophagy in chronic obstructive lung diseases

Introduction: ΔF508-CFTR (cystic fibrosis transmembrane conductance regulator) is a common CF-mutation that is known to induce oxidative-inflammatory stress through activation of reactive oxygen species (ROS), which induces autophagy-impairment resulting in accumulation of CFTR in aggresome-bodies. Cysteamine, the reduced form of cystamine, is a FDA-approved drug that has anti-oxidant, anti-bacterial, and mucolytic properties. This drug has been shown in a recent clinical trial to decrease lung inflammation and improve lung function in CF patients by potentially restoring autophagy and allowing CFTR to be trafficked to the cell membrane.

Areas covered: The delivery of cysteamine to airway epithelia of chronic subjects prerequisite the need for a delivery system to allow rescue of dysfunctional autophagy.

Expert opinion: We anticipate based on our ongoing studies that PLGA-PEG- or Dendrimer-mediated cysteamine delivery could allow sustained airway delivery over standard cysteamine tablets or delay release capsules that are currently used for systemic treatment. In addition, proposed nano-based autophagy induction strategy can also allow rescue of cigarette smoke (CS) induced acquired-CFTR dysfunction seen in chronic obstructive pulmonary disease (COPD)-emphysema subjects. The CS induced acquired-CFTR dysfunction involves CFTR-accumulation in aggresome-bodies that can be rescued by an autophagy-inducing antioxidant drug, cysteamine. Moreover, chronic CS-exposure generates ROS that induces overall protein-misfolding and aggregation of ubiquitinated-proteins as aggresome-bodies via autophagy-impairment that can be also be resolved by treatment with autophagy-inducing antioxidant drug, cysteamine.     

Transdermal lontophoretic delivery of colchicine encapsulated in liposomes

Iontophoresis is useful for the transdermal delivery of charged drugs. However, nonionized drugs either have a low flux (due to electro-osmosis) or cannot be delivered using this technique. Because ionized or nonionized drugs can be encapsulated in charged liposomes, it was hypothesized that charged liposomes can deliver neutral or nonionized drug efficiently by iontophoresis. Colchicine, a neutral drug, was encapsulated in large unilamellar vesicles (LUVs), prepared with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), and 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) along with cholesterol (1:0.5 mole ratio). Multilamellar vesicles (MLVs) were prepared by the thin-film hydration method and LUVs were obtained by extruding MLVs through polycarbonate filters of 200 nm pore size. Positive charge was induced in the liposomes by adding stearylamine and negative charge by adding dicetyl phosphate. Nonencapsulated drug was separated from LUVs by the Ficoll density gradient method. Positively charged LUVs were delivered under the anode, negatively charged LUVs under the cathode, and neutral LUVs without current using Franz cells and human cadaver skin. Plain colchicine as well as colchicine encapsulated in positively charged LUVs was delivered better under the anode compared with the cathode and passive conditions. Delivery of colchicine encapsulated in positively charged DSPC liposomes was four to five times greater than that of plain colchicine and two to three times greater than that of colchicine encapsulated in DMPC or DPPC liposomes. Because LUVs prepared with DMPC and DPPC were fluid at 37°C, the encapsulated drug leaked during iontophoresis and therefore the delivery was less. Delivery of colchicine was lower under the cathode due to the change in pH during iontophoresis, which, as observed in high-performance liquid chromatographic analysis, caused degradation of the drug. Thus, it can be concluded that iontophoresis of colchicine encapsulated in positively charged DSPC liposomes can improve its delivery across human cadaver skin     

Association of an acylated model peptide with DPPC-DPPS lipid membranes

The interaction between a small positively charged peptide with a N-terminally linked acyl chain and dipalmitoylphosphatidylcholine-dipalmitoylphosphatidylserine (DPPC-DPPS) lipid membranes has been studied by means of fluorescence resonance energy transfer. Two different lipid compositions were used: a neutral membrane (100 mol% DPPC), and a negatively charged membrane (30 mol% DPPS in DPPC). The fluorescence resonance energy transfer results reveal that the peptide associates with both types of membranes. Furthermore, it is found that the slope of the titration curve for the negatively charged membranes is much steeper than that for the neutral membranes. This indicates a higher binding affinity of the acylated peptide towards negatively charged lipid membranes as compared with neutral lipid membranes.     

Comparison of the effect of 4-hydroxycoumarin and umbelliferone on the phase transition of dipalmitoylphosphatidylcholine (DPPC) bilayers

The study compares the effect of the addition of two coumarins: 4-hydroxycoumarin (4-HC) and 7-hydroxycoumarin (umbelliferone; UMB) on dipalmitoylphosphatidylcholine (DPPC) membranes. The study was based on microcalorimetric and fluorescence measurements. The examinations have shown that 4-HC changes parameters of phase transition of DPPC membranes to a greater degree than UMB. It is associated with different location of each coumarin in the lipid membrane, which is caused by different orientation of polarity of coumarin molecules. 4-HC molecules that are amphiphilic "along" incorporate inside the membrane interacting with lipid carbohydrate chains. UMB molecules amphiphilic "across" the molecule are not incorporated inside the membrane and do not interact with acyl chains.     

Gastric acid stimulating action of cysteamine in the rat.

Cysteamine was previously found to produce duodenal ulcers in rats. In the present study, the effect of cysteamine on gastric secretion was studied. Cysteamine administered by a parenteral or intraduodenal route induced a marked and sustained increase in gastric secretion in conscious and in anesthetized rats. The response to cysteamine or its metabolite, cystamine, appeared gradually and the maximum response was observed in 2 or 3 hr after the administration. The response to cysteamine was completely inhibited by vagotomy and inhibited dose-dependently by atropine methylbromide or hexamethonium. Cysteamine stimulated gastric acid secretion in conscious rats with chronic gastric fistula but not in rats with denervated gastric pouch. Tissue histamine levels in the gastric mucosa, abdominal muscle and whole blood were not affected by cysteamine. These results suggest that a cholinergic mechanism is involved in the gastric secretion induced by cysteamine.     

琥珀酸胆固醇酯作为脂质体膜稳定剂的研究及其在制备柴胡皂苷-D脂质体中的应用

目的研究琥珀酸胆固醇酯(CHEMS)对二棕榈酰磷脂酰胆碱(DPPC)脂质体的膜稳定作用以及作用机制；以CHEMS和DPPC为膜材制备柴胡皂苷-D(SSD)脂质体，考察其包封率和溶血性。方法差示扫描量热法(DSC)和荧光释放实验考察CHEMS的膜稳定作用，傅立叶红外(FT-IR)研究CHEMS与DPPC膜的作用机制，沉降实验研究CHEMS与SSD相互作用，溶血实验考察了以CHEMS为膜材包裹SSD脂质体的溶血性。结果CHEMS在膜稳定性上优于胆固醇(CHOL)，CHEMS与DPPC的极性端头同时有氢键和静电作用；CHEMS与SSD不会形成不溶性复合物(INCOM)，用DPPC和CHEMS为膜材制备了稳定的SSD包裹的脂质体，其溶血性大大降低。结论CHEMS对DPPC膜的稳定作用大于CHOL，并可取代CHOL作为制备胆固醇依赖性的溶血性皂苷脂质体的膜稳定剂。     

Beneficial effects of N-acetylcysteine and cysteine in stunned myocardium in perfused rat heart.

1. The objective of this study was to evaluate the effects of three sulphydryl (SH) compounds, N-acetylcysteine (NAC), cysteine (Cys) and cystamine, on functional recovery and ventricular arrhythmias (VF) in stunned myocardium in the isolated perfused heart of the rat. 2. Hearts (n = 7-8 per group) were perfused by the Langendorff procedure for 20 min to stabilize and then assigned to one of five groups: saline, sham, NAC, Cys and cystamine. After the stabilizing period, the drugs (at 3.6 microM min-1) or their vehicle (saline) were infused into coronary vessels throughout the experimental period. Ten min after administration of drugs, the left anterior descending coronary artery (LAD) was ligatured for 20 min and then untied to reperfuse for 30 min. In the sham group, a ligature was placed around the LAD but not tied. 3. NAC and Cys had a significant effect in attenuating myocardial stunning: the percentage recovery of rate-pressure product measured 30 min after reperfusion as an index of heart function, was improved with the NAC (98.3 +/- 4.5) and Cys groups (104.0 +/- 6.5) compared with the saline (only 73.6 +/- 3.8, P < 0.01) group. Cystamine did not show these beneficial effects. This may be due to the difference in chemical structure between NAC, Cys and cystamine since the latter does not have a free SH group with a disulphide bond formed. This phenomenon suggests that a free SH group is essential for the protective effects of compounds like NAC and Cys in myocardial injury.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of polymer cation content on certain film properties

Mixing of two acrylate-methacrylate copolymers designated A and B and differing only in cation (quaternary ammonium) content in the ratio 2:1 (A:B) provided a means of varying polymer cation content in resulting films. Film permeability to the permeant urea, increased with increase in cation content; a two phase change characterized by a slow increase at a low cation content level followed by about 13 times more rapid increase at high cation content level. The point of transition from the slow to the rapid phase was 53 moles cation per mole polymer chain. On average a fold increase in cation content resulted in a 500 fold increase in permeation rate. Increases in film swelling and pore size also accompanied the increase in cation content, but the change in permeability was more positively correlated with the corresponding change in film pore size. Mutual repulsion by charged groups during film formation is suggested as a factor promoting the formation of large pores in the film at high cation content.     

Characterization of distribution behavior of 2-imidazolines into multilamellar liposomes.

The distribution of 2-imidazolines in neutral dimyristoylphosphatidylcholine (DMPC) liposomes, in negatively charged liposomes containing dicetylphosphate (DCP) or phosphatidylserine (PS), and in positively charged liposomes containing stearylamine (STA), has been investigated. Electrophoretic mobilities of multilamellar liposomes have also been measured as a function of drug concentration. Apparent equilibrium partition coefficients (log K'm) increased as a function of the DCP or PS concentration in DMPC liposomes whereas log K'm decreased with STA concentration, except for lofexidine and clonidine. Similarly, the electrokinetic parameters increased in DMPC liposomes that exhibited a small, positive surface charge, decreased in DMPC/cholesterol/DCP (7:1:2 mole ratio) liposomes, and increased in DMPC/STA (3:1 mole ratio) liposomes, except for clonidine which showed a decrease, as a function of the 2-imidazoline concentration. Surface potential change (delta psi o) due to drug inclusion in the liposomes obtained from theoretical considerations exhibited a positive linear relationship with log K'm. Values of delta psi o were greater but less sensitive to log K'm in negatively charged than in neutral or positively charged liposomes at 1 mM drug concentration. Likewise, surface charge densities varied in the same order as the surface potentials as a function of log K'm of the 2-imidazolines, except for clonidine and lofexidine. These data indicate the relative importance of the membrane surface characteristics on the partitioning behavior, and also possibly the membrane transport behavior, of the 2-imidazoline drugs.     

Effects of sulfhydryl-related compounds on indomethacin-induced gastric lesions in rats: role of endogenous sulfhydryls in the pathogenesis.

The role of mucosal sulfhydryl (SH) in the pathogenesis of indomethacin-induced gastric lesions was investigated in rats. Indomethacin (25 mg/kg, s.c.) caused high-amplitude gastric contractions, resulting in linear hemorrhagic lesions in the corpus mucosa within 4 hr, but did not induce any changes in the mucosal SH levels. These lesions were prevented significantly by prior s.c. administration of cysteamine, glutathione (GSH) or diethylmaleate (DEM), irrespective of whether the mucosal SH was increased by the former two agents or reduced by the latter. N-Ethylmaleimide (NEM) tended to worsen such lesions without any effect on the mucosal SH contents. Gastric hypermotility caused by indomethacin was inhibited significantly by DEM, cysteamine and GSH, while acid secretion was reduced by DEM and NEM. Both cysteamine and GSH prevented the indomethacin-induced linear lesions even in the stomach perfused with 150 mM HCl, whereas in the animals treated with DEM, nonlinear damage was induced exclusively in the antrum by indomethacin in the presence of acid. We conclude that the mucosal SH has no relation to the ulcerogenicity of indomethacin in the gastric corpus mucosa.     

The effect of electrolytes on rigidity and diffusion in gelatin--glycerin gels

The effect of electrolytes on the rigidity of and diffusion of dye from gelatin-glycerin gels has been examined. Cations, which might be expected to reduce the rigidity in the ratio of their valency, produced a fall in rigidity in the ratio Na⁺, 1: Ca⁺⁺, 1·25:A1⁺⁺⁺, 1·57. This approximate halving of the effect is attributed to interference by the chloride ion. The rigidity was proportional to the square root of the ionic concentration except with sodium ferrocyanide where no simple relation held. A simple expression G = G₀ (1 ± ***I) was found for the rigidity, the sign depending whether anion or cation was considered. The effect of anions and cations on diffusion was as varied as their effect on rigidity. The addition of chlorides increased the diffusion coefficient in the order Al > Ca > Na. Both multivalent anions examined produced a decrease in diffusion coefficient; the sulphate being less effective than the ferrocyanide.     

The entrapment of kojic oleate in bilayer vesicles

The entrapment of kojic acid and its newly synthesized ester (kojic oleate) has been evaluated. Kojic oleate was synthesized by DCC (N,N'-dicyclohexylcarbodiimide, DCC)/(4-(N,N-dimethylamino)pyridine, DMAP) esterification method and identified by FAB-MS and 1H NMR. The synthesized product was mainly 7-O-kojic oleate with more than 80% yield. It was entrapped in vesicular membrane prepared from 9.5:9.5:1.0 molar ratio of amphiphiles (Span 60, Tween 61 or DPPC), cholesterol and dicetyl phosphate. Kojic acid was encapsulated in the water compartment of these vesicles in order to confirm the vesicle formation. The morphology and particle size of the vesicles were characterized by an optical microscope and transmission electron microscope (TEM). The entrapment efficiencies of kojic acid and kojic oleate in the vesicles were investigated by dialysis and column chromatography, respectively. The contents of the entrapped kojic acid and kojic oleate were assayed by HPLC. The entrapment efficiency of kojic acid was 0.01-0.04 mol, whereas kojic oleate gave higher entrapment efficiency of 0.25-0.35 mol/mol of the total compositions of amphiphile/cholesterol/dicetyl phosphate. Structural modification of kojic acid improved its entrapment in the vesicles. Tween 61 vesicles could entrap kojic oleate more than did Span 60 vesicles. The pi-A isotherms revealed the lower area per molecule of Span 60, which formed a more rigid pack of its molecule on air/water interface than that of Tween 61. This implied the high rigidity of vesicular membrane prepared with Span 60 led to the lower amount of kojic oleate entrapped in the vesicles. From the release study of kojic acid through the dialysis membrane, it indicated that the intercalation of kojic oleate in the vesicular membranes did not significantly affect the release of kojic acid from the vesicles.     

Stability of SUV liposomes in the presence of cholate salts and pancreatic lipases: effect of lipid composition.

The effect of bile salts (sodium cholate and sodium taurocholate), and pancreatic lipases on the structural integrity of SUV liposomes of different lipid compositions was studied. Liposomal membrane integrity was judged by bile salt or pancreatin-induced release of vesicle encapsulated 5,6-carboxyfluorescein, and vesicle size distribution before and after incubations. Bile salt concentration was 10 mM, while a saturated solution of pancreatin (mixed with equal volume of liposomes) was utilized. Results agree with earlier studies, demonstrating the instability of liposomes composed of lipids with low transition temperatures (PC and DMPC) in presence of cholates. Addition of cholesterol (1:1 lipid:chol molar ratio) does not substantially increase the encapsulated molecule retention. Nevertheless, liposomes composed of lipids with high transition temperatures (DPPC, DSPC and SM), retain significantly higher amounts of encapsulated material, under all conditions studied. Furthermore, the vesicles formed by mixing cholesterol with these lipids will possibly be sufficiently stable in the gastrointestinal tract for long periods of time. Sizing results reveal that in most cases release of encapsulated molecules is mainly caused by their leakage through holes formed on the lipid bilayer. However, in stearylamine containing DPPC and DSPC vesicles, the cholate-induced drastic decrease in vesicle size suggests total liposome disruption as the possible mechanism of encapsulated material immediate release.     

Cholesterol alters the binding of Ca2+ channel blockers to the membrane lipid bilayer.

X-ray diffraction and equilibrium binding techniques were used to study the effect of cholesterol on membrane binding of the charged 1,4-dihydropyridine (DHP) Ca2+ channel antagonist amlodipine and uncharged isradipine, nimodipine, and nitrendipine. Increases in membrane cholesterol content resulted in a marked decrease in DHP binding to cardiac phospholipid membranes, as expressed by the equilibrium partition coefficient (Kp[mem]). Between a 0:1 and 0.3:1 cholesterol to phospholipid mole ratio, the Kp(mem) values for isradipine, nimodipine, and nitrendipine decreased by greater than 50%, whereas that for amlodipine decreased by only 10%. Electron density profiles calculated from the X-ray diffraction data showed that the time-averaged locations for the DHPs and cholesterol in the membrane overlap, leading to the conclusion that the addition of cholesterol alters the lipid bilayer hydrocarbon core structure in a manner that makes drug partitioning into the membrane less energetically favorable. These data support the idea that drug interactions with the anisotropic membrane environment are complex and may be greatly influenced by cholesterol composition. This effect of cholesterol was also observed for phenylalkylamine (verapamil) and benzothiazepine (diltiazem) Ca2+ channel blockers. The DHP amlodipine had the highest membrane partition coefficient (Kp[mem] greater than 10(4) and the slowest rate of dissociation and was affected least by membrane cholesterol content. The combination of electrostatic and hydrophobic bonding between amlodipine and membrane phospholipid may explain the high affinity of this drug for the membrane bilayer with normal and elevated cholesterol. The results of this study show that cholesterol content differentially affects the membrane-binding properties of the charged DHP amlodipine, compared with other Ca2+ channel blockers. These data help explain the biological distribution of these drugs and the distinct pharmacokinetics of amlodipine versus other Ca2+ channel blockers.     

Effects of soybean-derived sterol and its glucoside mixtures added in dipalmitoylphosphatidylcholine liposomes on the blood circulation and hepatic cellular distribution in mice

The effects of a soybean-derived sterol mixture (SS) and their glucoside mixture (SG) in dipalmitoylphosphatidylcholine (DPPC) liposomes on blood circulation and hepatic distribution were investigated by measuring the leakage of calcein after intravenous administration to mice. Four kinds of liposomes were prepared: liposomes consisting only of DPPC (DPPC liposomes); and DPPC liposomes containing SS, cholesterol (Ch) or SG (molar ratio of DPPC/X = 7:2, X = SS, Ch, SG; SS, Ch and SG liposome), respectively. The area under the blood concentration-time curve (AUC) was greater in the order, SS liposomes > DPPC liposomes > SG liposomes, and the order is the same for lower membrane fluidity. Hepatic cellular distribution of SG liposomes 2 h after intravenous injection was significantly high compared with that of DPPC and SS liposomes. The results indicated that SS liposomes were stable in the blood circulation; however, SG liposomes were not stable and appeared to have an enhancing effect on hepatic uptake. This difference might indicate that hepatic accumulation is primarily governed by the glucose group of SG.     

Differential gene expression in mouse liver associated with the hepatoprotective effect of clofibrate

Pretreatment of mice with the peroxisome proliferator clofibrate (CFB) protects against acetaminophen (APAP)-induced hepatotoxicity. Previous studies have shown that activation of the nuclear peroxisome proliferator activated receptor-alpha (PPARalpha) is required for this effect. The present study utilizes gene expression profile analysis to identify potential pathways contributing to PPARalpha-mediated hepatoprotection. Gene expression profiles were compared between wild type and PPARalpha-null mice pretreated with vehicle or CFB (500 mg/kg, i.p., daily for 10 days) and then challenged with APAP (400 mg/kg, p.o.). Total hepatic RNA was isolated 4 h after APAP treatment and hybridized to Affymetrix Mouse Genome MGU74 v2.0 GeneChips. Gene expression analysis was performed utilizing GeneSpring software. Our analysis identified 53 genes of interest including vanin-1, cell cycle regulators, lipid-metabolizing enzymes, and aldehyde dehydrogenase 2, an acetaminophen binding protein. Vanin-1 could be important for CFB-mediated hepatoprotection because this protein is involved in the synthesis of cysteamine and cystamine. These are potent antioxidants capable of ameliorating APAP toxicity in rodents and humans. HPLC-ESI/MS/MS analysis of liver extracts indicates that enhanced vanin-1 gene expression results in elevated cystamine levels, which could be mechanistically associated with CFB-mediated hepatoprotection.     

Combined surface pressure-interfacial shear rheology studies of the interaction of proteins with spread phospholipid monolayers at the air-water interface

The adsorption of two model proteins, catalase and lysozyme, to phospholipid monolayers spread at the air–water interface has been studied using a combined surface pressure-interfacial shear rheology technique. Monolayers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dipalmitoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (DPPG) and DPPC:DPPG (7:3) were spread on a phosphate buffer air–water interface at pH 7.4. Protein solutions were introduced to the subphase and the resultant changes in surface pressure and interfacial storage and loss moduli were recorded with time. The results show that catalase readily adsorbs to all the phospholipid monolayers investigated, inducing a transition from liquid-like to gel-like rheological behaviour in the process. The changes in surface rheology as a result of the adsorption of catalase increase in the order DPPC < DPPC:DPPG < DPPG. Lysozyme behaves in a similar manner beneath a DPPG monolayer, but shows no measurable differences when injected beneath DPPC or the DPPC:DPPG (7:3) mixed monolayer. It is proposed that DPPG monolayers are more susceptible to penetration by adsorbing protein molecules. The interaction between DPPG and lysozyme is further enhanced due to electrostatic interactions between the negatively charged DPPG and the positively charged lysozyme.