Second derivative spectrophotometric determination of partition coefficients of chlorpromazine and promazine between lecithin bilayer vesicles and water

Facile, eco-friendly and sensitive fluorimetric approach for detection of chlorpromazine: Application in biological fluids and tablet formulations as well as greenness evaluation of the analytical method

Monitoring antipsychotic drugs in biological fluids, such as human serum and urine, is important for ensuring the safety and efficacy of psychiatric treatments. This process helps maintain therapeutic drug levels, minimize side effects, and optimize patient well-being. Chlorpromazine (CZ) is a widely prescribed antipsychotic drug used for conditions like schizophrenia, bipolar disorder, and acute psychosis. Almost all existing sensing techniques for CZ are either insensitive spectrophotometric methods or involve long and complex chromatographic procedures, limiting their routine use. In this work, we introduce a facile, green, and sensitive fluorimetric strategy with high reproducibility for detecting CZ in its pure form, tablet formulation, and spiked human plasma and urine without the need for derivatization reactions. The proposed method relies on the inhibition of the intramolecular photoinduced electron transfer (PET) effect by using 2.0 M acetic acid. This approach enables the linear detection of CZ from 3.0 to 600 ng/mL with remarkably low quantitation and detection limits of 1.51 and 0.49 ng/mL, respectively. Moreover, the developed method's greenness was evaluated.

Lipophilicity Modulations by Fluorination Correlate with Membrane Partitioning

Bioactive compounds generally need to cross membranes to arrive at their site of action. The octanol-water partition coefficient (lipophilicity, logPOW ) has proven to be an excellent proxy for membrane permeability. In modern drug discovery, logPOW and bioactivity are optimized simultaneously, for which fluorination is one of the relevant strategies. The question arises as to which extent the often subtle logP modifications resulting from different aliphatic fluorine-motif introductions also lead to concomitant membrane permeability changes, given the difference in molecular environment between octanol and (anisotropic) membranes. It was found that for a given compound class, there is excellent correlation between logPOW values with the corresponding membrane molar partitioning coefficients (logKp ); a study enabled by novel solid-state 19 F NMR MAS methodology using lipid vesicles. Our results show that the factors that cause modulation of octanol-water partition coefficients similarly affect membrane permeability.

Investigation of Quercetin interaction behaviors with lipid bilayers: Toward understanding its antioxidative effect within biomembrane

Quercetin (QCT), existing in common dietary sources, is an abundant bioflavonoid with planar structure and exerts multiple pharmacological effects. Herein, four kinds of liposomes were prepared as model biomembranes, and then the partition coefficient, distribution in lipid membrane and influence of the QCT on the membrane properties were evaluated. The partition of QCT to lipid membranes was affected by both membrane phase state and the interference of QCT on membrane properties. The location of QCT in lipid membrane was related to the phase state of lipid membrane. In addition, influence of QCT on the compaction of the hydrocarbon tail in lipid membranes was dependent on the unsaturation degree of lipid molecules. Finally, about its antioxidant activity, from the results of 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay, it can be concluded that the interaction of QCT with lipid membrane greatly influences on QCT reductive activity in lipid membrane. Furthermore, mass spectrometry of DOPC molecule showed no lipid oxidation in the presence of QCT, indicating that in addition to the QCT ability toward radical scavenging, the ordering effect of QCT in unsaturated lipid membrane would be helpful to protect lipid membrane from oxidation by inhibiting radical diffusion (synergy effect). Based on lipid membrane analysis, our study made it clear that the effect of QCT on various lipid membrane and its relation with the antioxidant effect of QCT within lipid membrane. Therefore, our analytical method and findings would be also helpful for understanding the mechanism of other antioxidants effects on biomembrane.

Interface-Mediated Mechanism of Action-The Root of the Cytoprotective Effect of Immediate-Release Omeprazole

Omeprazole is usually administered under an enteric coating. However, there is a Food and Drug Administration-approved strategy that enables its release in the stomach. When locally absorbed, omeprazole shows a higher efficacy and a cytoprotective effect, whose mechanism was still unknown. Therefore, we aimed to assess the effect of the absorption route on the gastric mucosa. 2D and 3D models of dipalmitoylphosphatidylcholine (DPPC) at different pH values (5.0 and 7.4) were used to mimic different absorption conditions. Several experimental techniques, namely, fluorescence studies, X-ray scattering methodologies, and Langmuir monolayers coupled with microscopy, X-ray diffraction, and infrared spectroscopy techniques, were combined with molecular dynamics simulations. The results showed that electrostatic and hydrophobic interactions between omeprazole and DPPC rearranged the conformational state of DPPC. Omeprazole intercalates among DPPC molecules, promoting domain formation with untilted phospholipids. Hence, the local release of omeprazole enables its action as a phospholipid-like drug, which can reinforce and protect the gastric mucosa.

Binding of warfarin differently affects the thermal behavior and chain packing of anionic, zwitterionic and cationic lipid membranes

Warfarin is a coumarin derivative drug widely used for its anticoagulant properties. The interaction of warfarin with fully hydrated lipid bilayers has been studied by combining differential scanning calorimetry, spectrophotometry, electron spin resonance of chain-labelled lipids and molecular docking. Bilayers formed by lipids with different chemico-physical properties were considered, namely dimyristoyl-phosphatidylcholine (DMPC), dimyristoyl-phosphatidylglycerol (DMPG), and dioleoyltrimethyl-ammoniumpropane (DOTAP). We observed in all cases the binding of warfarin in proximity of the surface of the bilayers, leading to a variety of distinct effects on key molecular properties of the membranes. The drug associates with the lipid bilayers in the deprotonated open chain form, with an association constant similar for DMPC and DMPG (1.27·10⁴ and 2.82·10⁴ M^-1, respectively) and lower for DOTAP (0.46·10⁴ M^-1). In DMPC bilayers, which are zwitterionic and with saturated symmetrical chains, warfarin at 10 mol% suppresses the pre-transition, slightly stabilizes the fluid state and reduces the cooperativity of the main transition. Moreover, it alters the lateral packing density of the chain segments close to the polar/apolar interface at any temperature through the gel phase. In anionic DMPG bilayers, the drug slightly perturbs the thermotropic phase behavior, and at 10 mol% markedly loosens the compact gel phase packing of the first chain segments. In cationic DOTAP bilayers, possessing unsaturated acyl chains, the drug induces a slightly higher degree of order and motional restriction in the outer hydrocarbon region in the frozen state. In all cases, as a surface adsorbed molecule, warfarin does not affect the segmental chain order and dynamics for temperatures in the fluid phase. The overall results provide an outline of the action of warfarin on membranes formed by lipids of different types.

The Interaction of Temozolomide with Blood Components Suggests the Potential Use of Human Serum Albumin as a Biomimetic Carrier for the Drug

The interaction of temozolomide (TMZ) (the main chemotherapeutic agent for brain tumors) with blood components has not been studied at the molecular level to date, even though such information is essential in the design of dosage forms for optimal therapy. This work explores the binding of TMZ to human serum albumin (HSA) and alpha-1-acid glycoprotein (AGP), as well as to blood cell-mimicking membrane systems. Absorption and fluorescence experiments with model membranes indicate that TMZ does not penetrate into the lipid bilayer, but binds to the membrane surface with very low affinity. Fluorescence experiments performed with the plasma proteins suggest that in human plasma, most of the bound TMZ is attached to HSA rather than to AGP. This interaction is moderate and likely mediated by hydrogen-bonding and hydrophobic forces, which increase the hydrolytic stability of the drug. These experiments are supported by docking and molecular dynamics simulations, which reveal that TMZ is mainly inserted in the subdomain IIA of HSA, establishing π-stacking interactions with the tryptophan residue. Considering the overexpression of albumin receptors in tumor cells, our results propose that part of the administered TMZ may reach its target bound to plasma albumin and suggest that HSA-based nanocarriers are suitable candidates for designing biomimetic delivery systems that selectively transport TMZ to tumor cells.

Thermodynamics of selective serotonin reuptake inhibitors partitioning into 1,2-dioleoyl-sn-glycero-3-phosphocholine bilayers

Knowledge of thermodynamics of lipid membrane partitioning of amphiphilic drugs as well as their binding site within the membrane are of great relevance not only for understanding the drugs' pharmacology but also for the development and optimization of more potent drugs. In this study, the interaction between two representatives of selective serotonin reuptake inhibitors, including paroxetine and sertraline, and large unilamellar vesicles (LUVs) composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) was investigated by second derivative spectrophotometry and Fourier transform infrared spectroscopy (FTIR) to determine the driving force of the drug partitioning across lipid membranes. It was found that temperature increase from 25 to 42 °C greatly enhanced the partitioning of paroxetine and sertraline into DOPC LUVs, and sertraline intercalated into the lipid vesicles to a greater extent than paroxetine in the temperature range examined. The partitioning of both drugs into DOPC LUVs was a spontaneous, endothermic and entropy-driven process. FTIR measurements suggested that sertraline could penetrate deeply into the acyl tails of DOPC LUVs as shown by the considerable shifts in the lipid's CH₂ and C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O stretching modes induced by the drug. Paroxetine, however, could reside closer to the head groups of the lipid since its presence caused a larger shift in the PO₂⁻ bands of DOPC LUVs. The findings reported here provide valuable insights into the influence of small molecules' chemical structure on their molecular interaction with the lipid bilayer namely their possible binding sites within the lipid bilayer and their thermodynamics profiles of partitioning, which could benefit rational drug design and drug delivery systems.

Paroxetine and sertraline have the same thermodynamics profile of phospholipid bilayer partitioning but different location within the lipid bilayer.

Drug Exchange between Albumin Nanoparticles and Erythrocyte Membranes

The effects of thioridazine (TDZ) and chlorpromazine (CPZ) and bovine serum albumin nanoparticles (BSA-NPs) on erythrocyte membranes have been investigated. Two kinds of hemolytic assays were used; hemolysis under hypotonic conditions and hemolysis in physiological conditions. Under hypotonic conditions for 50% hemolysis, both TDZ and CPZ have a biphasic effect on membranes; namely, stabilization at low concentrations and destabilization after reaching a critical concentration. In physiological conditions, there are other critical concentrations above which both drugs hemolyse the erythrocites. In each case, the critical concentrations of TDZ are lower than those of CPZ, which is consistent with the ratio of their partition coefficients. When BSA-NPs are added to the erythrocyte suspension simultaneously with the drugs, the critical concentrations increase for both drugs. The effect is due to the incorporation of a portion of drug substances into the BSA-nanoparticles, which consequently leads to the decrease of the active drug concentrations in the erythrocyte suspension medium. Similar values of the critical concentrations are found when the BSA-NPs are loaded with the drugs before their addition to the erythrocyte suspension in which case the events of the partition are: desorption of the drug from BSA-NPs, diffusion through the medium, and adsorption on erythrocyte membranes. This result suggests that the drugs are not influenced by the processes of adsorption and desorption onto and out of the BSA-NPs, and that the use of BSA-NPs as drug transporters would allow intravenous administration of higher doses of the drug without the risk of erythrocyte hemolysis.

A Molecular Biophysical Approach to Diclofenac Topical Gastrointestinal Damage

Diclofenac (DCF), the most widely consumed non-steroidal anti-inflammatory drug (NSAID) worldwide, is associated with adverse typical effects, including gastrointestinal (GI) complications. The present study aims to better understand the topical toxicity induced by DCF using membrane models that mimic the physiological, biophysical, and chemical environments of GI mucosa segments. For this purpose, phospholipidic model systems that mimic the GI protective lining and lipid models of the inner mitochondrial membrane were used together with a wide set of techniques: derivative spectrophotometry to evaluate drug distribution at the membrane; steady-state and time-resolved fluorescence to predict drug location at the membrane; fluorescence anisotropy, differential scanning calorimetry (DSC), dynamic light scattering (DLS), and calcein leakage studies to evaluate the drug-induced disturbance on membrane microviscosity and permeability; and small- and wide-angle X-ray scattering studies (SAXS and WAXS, respectively), to evaluate the effects of DCF at the membrane structure. Results demonstrated that DCF interacts chemically with the phospholipids of the GI protective barrier in a pH-dependent manner and confirmed the DCF location at the lipid headgroup region, as well as DCF’s higher distribution at mitochondrial membrane contact points where the impairment of biophysical properties is consistent with the uncoupling effects reported for this drug.

Spectroscopic Studies as a Toolbox for Biophysical and Chemical Characterization of Lipid-Based Nanotherapeutics

The goal of this study is to provide tools to minimize trial-and-error in the development of novel lipid-based nanotherapeutics, in favor of a rational design process. For this purpose, we present case-study examples of biophysical assays that help addressing issues of lipid-based nanotherapeutics' profiling and assist in the design of lipid nanocarriers for therapeutic usage. The assays presented are rooted in spectroscopic methods (steady-state and time-resolved fluorescence; UV-Vis derivative spectroscopy; fluorescence anisotropy and fluorescence lifetime image microscopy) and allow accessing physical-chemical interactions between drugs and lipid nanocarriers, as well as studying interactions between lipid-based nanotherapeutics and membranes and/or proteins, as this is a key factor in predicting their therapeutic and off target effects. Derivative spectroscopy revealed Naproxen's high distribution (LogD ≈ 3) in different lipid-based nanocarriers (micelles and unilamellar or multilamellar vesicles) confirming the adequacy of such systems for encapsulating this anti-inflammatory drug. Fluorescence quenching studies revealed that the anti-inflammatory drugs Acemetacin and Indomethacin can reach an inner location at the lipid nanocarrier while being anchored with its carboxylic moiety at the polar headgroup. The least observed quenching effect suggested that Tolmetin is probably located at the polar headgroup region of the lipid nanocarriers and this superficial location may translate in a fast drug release from the nanocarriers. Fluorescent anisotropy measurements indicated that the drugs deeply buried within the lipid nanocarrier where the ones that had a greater fluidizing effect which can also translate in a faster drug release. The drug binding strength to serum albumin was also compared for a free drug (Clonixin) or for the same drug after encapsulation in a lipid nanocarrier DSPC:DODAP (2:1). Under both conditions there is a strong binding to serum albumin, at one binding site, suggesting the need to produce a stealth nanosystem. Finally the cellular uptake of lipid nanocarriers loaded with Daunorubicin was investigated in cancer cells using fluorescence lifetime imaging microscopy. From the images obtained it was possible to conclude that even at short incubation times (15 min) there was a distribution of the drug in the cytoplasm, whereas for longer incubation periods (4 h) the drug has reached the nucleus.

On the interaction between fluoxetine and lipid membranes: Effect of the lipid composition

Molecular interaction between the antidepressant fluoxetine and lipid bilayers was investigated in order to provide insights into the drug's incorporation to lipid membranes. In particular, the effects of lipid's unsaturation degree and cholesterol content on the partitioning of fluoxetine into large unilamellar vesicles (LUVs) comprised of unsaturated 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and saturated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) were evaluated using second derivative spectrophotometry and Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR). It was found that fluoxetine partitioned to a greater extent into the liquid-crystalline DOPC LUVs than into the solid-gel DPPC LUVs. The lipid physical state dependence of drug partitioning was verified by increasing the temperature in which the partition coefficient of fluoxetine significantly increased upon the change of the lipid phase from solid-gel to liquid-crystalline. The incorporation of 28mol% cholesterol into the LUVs exerted a significant influence on the drug partitioning into both DOPC and DPPC LUVs. The ATR-FTIR study revealed that fluoxetine perturbed the conformation of DOPC more strongly than that of DPPC due to the cis-double bonds in the lipid acyl chains. Fluoxetine possibly bound to the carbonyl moiety of the lipids through the hydrogen bonding formation while displaced some water molecules surrounding the PO₂^- regions of the lipid head groups. Cholesterol, however, could lessen the interaction between fluoxetine and the carbonyl groups of both DOPC and DPPC LUVs. These findings provided a better understanding of the role of lipid structure and cholesterol on the interaction between fluoxetine and lipid membranes, shedding more light into the drug's therapeutic action.

Lipophilicity assessement in drug discovery: Experimental and theoretical methods applied to xanthone derivatives

For the last several years, searching of new xanthone derivatives (XDs) with potential pharmacological activities has remained one of the main areas of interest of our group. The optimization of biological activity and drug-like properties of hits and leads is crucial at early stage of the drug discovery pipeline. Lipophilicity is one of the most important drug-like properties having a great impact in both pharmacokinetics and pharmacodynamics processes. In this work, we describe the lipophilicity of a small library of bioactive XDs, previously synthesized by our group, using different methods: computational, vortex-assisted liquid-liquid microextraction coupled with high-performance liquid chromatography (VALLME-HPLC), reversed-phase high-performance thin layer chromatography (RP-HPTLC), reversed-phase high-performance liquid chromatography (RP-HPLC), and biomembrane model by the partition between micelles and aqueous phase. The different results obtained by the used methods were compared and discussed. The methodologies and data gathered in this study will expand the investigation of lipophilicity of XDs, an important class of compounds in medicinal chemistry.

Fluorescence studies on the interaction between chlorpromazine and model cell membranes

The fluorescence quenching of membrane fluorophores and the fluorescence enhancement of chlorpromazine were simultaneously observed during chlorpromazine–lipid membrane interaction.

19F Nuclear Magnetic Resonance Spectrometric Determination of the Partition Coefficients of Flutamide and Nilutamide (Antiprostate Cancer Drugs) in a Lipid Nano-Emulsion and Prediction of Its Encapsulation Efficiency for the Drugs

To design a useful lipid drug carrier having a high encapsulation efficiency (EE%) for the antiprostate cancer drugs flutamide (FT) and nilutamide (NT), a lipid nano-emulsion (LNE) was prepared with soybean oil (SO), phosphatidylcholine (PC), and sodium palmitate, and the partition coefficients (K _ps) of the drugs for the LNE were determined by ¹⁹F nuclear magnetic resonance (NMR) spectrometry. The ¹⁹F NMR signal of the trifluoromethyl group of both drugs showed a downfield shift from an internal standard (trifluoroethanol) and broadening according to the increase in the lipid concentration due to their interaction with LNE particles. The difference in the chemical shift (Δδ) of each drug caused by the addition of LNE was measured under different amounts of LNE, and the K _p values were calculated from the Δδ values. The results showed that FT has higher lipophilicity than NT. The total lipid concentration (SO + PC) required to encapsulate each drug into LNE with an EE% of more than 95% was calculated from the K _p values as 93.3 and 189.9 mmol/L for FT and NT, respectively. For an LNE prepared with the total lipid concentration of 215 mmol/L, the predicted EE% values were 98 and 96% for FT and NT, respectively, while the experimental EE% values determined by a centrifugation method were approximately 99% for both drugs. Thus, the ¹⁹F NMR spectrometric method is a useful technique to obtain the K _p values of fluorinated drugs and thereby predict the theoretical lipid concentrations and prepare LNEs with high EE% values.

Partitioning of organophosphorus pesticides into phosphatidylcholine small unilamellar vesicles studied by second-derivative spectrophotometry

In order to quantitatively examine the lipophilicity of the widely used organophosphorus pesticides (OPs) chlorfenvinphos (CFVP), chlorpyrifos-methyl (CPFM), diazinon (DZN), fenitrothion (FNT), fenthion (FT), isofenphos (IFP), profenofos (PFF) and pyraclofos (PCF), their partition coefficient (Kp) values between phosphatidylcholine (PC) small unilamellar vesicles (SUVs) and water (liposome-water system) were determined by second-derivative spectrophotometry. The second-derivative spectra of these OPs in the presence of PC SUV showed a bathochromic shift according to the increase in PC concentration and distinct derivative isosbestic points, demonstrating the complete elimination of the residual background signal effects that were observed in the absorption spectra. The Kp values were calculated from the second-derivative intensity change induced by addition of PC SUV and obtained with a good precision of R.S.D. below 10%. The Kp values were in the order of CPFM>FT>PFF>PCF>IFP>CFVP>FNT⩾DZN and did not show a linear correlation relationship with the reported partition coefficients obtained using an n-octanol-water system (R(2)=0.530). Also, the results quantitatively clarified the effect of chemical-group substitution in OPs on their lipophilicity. Since the partition coefficient for the liposome-water system is more effective for modeling the quantitative structure-activity relationship than that for the n-octanol-water system, the obtained results are toxicologically important for estimating the accumulation of these OPs in human cell membranes.

A spectrophotometric and thermodynamic study of the charge-transfer complexes of N-aryl-N'-isopropyloxycarbonylsulfamides with DDQ and TCNE

Molecular charge-transfer complexes of three N-aryl-N'-isopropyloxycarbonylsulfamides derivatives with π-acceptors tetracyanoethylene (TCNE), and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), were studied by using zero and second order derivative UV spectrophotometry in different solvents at four different temperatures within the range of 20-35 °C. The stoichiometries of the complexes were found to be 1:1 ratio between donors and acceptors using Job's method. The data were analyzed in terms of their stability constant (K), molar extinction coefficient (εCT), thermodynamic standard reaction quantities (ΔG°, ΔH°, ΔS°), oscillator strength (f), transition dipole moment (μEN) and ionization potential (ID). The results show that the stability constant (K) for the complexes was found to be dependant upon the nature of electron acceptor, electron donor, and polarity of used solvents.

An in vitro spectrometric method for determining the partition coefficients of non-steroidal anti-inflammatory drugs into human erythrocyte ghost membranes

Usefulness of second derivative spectrophotometry for determining the partition coefficients (K(p)s) of four non-steroidal anti-inflammatory drugs (NSAIDs) between human erythrocyte ghost (HEG) membranes and buffer at simulated physiological conditions (pH=7.4, 37 °C) has been adequately emphasized. In the absorption spectra for each of the investigated NSAIDs, λ(max) was red-shifted in presence of HEG membranes, indicating that NSAIDs have the nature of metachromasy between lipid bilayer and water. Further quantitative spectral data for calculating K(p)s could not be obtained from the absorption spectra because of the presence of background signal impacts of HEG lipid bilayers. Second derivative spectra were calculated from absorption spectra and fortunately showed three isosbestic derivative points for each NSAID, indicating without doubt that the background signals were entirely eliminated. From the relation between the derivative intensity change (ΔD) induced by addition of HEG membranes, K(p)s were calculated and obtained with RSD of below 6%. Fractions of partitioned NSAIDs are in well-harmony with that derived from the experimental values. Moreover, validity of the proposed method was confirmed. Conclusively, the second derivative spectrometry has proven to be a facile, reliable and more expeditious method to obtain in vitro K(p)s of drugs to HEG without previous separation.

Binding of benzodiazepine drugs to bovine serum albumin: a second derivative spectrophotometric study

The binding constants (K values) of three benzodiazepine drugs to bovine serum albumin were determined by a second derivative spectrophotometric method. Despite the sample and reference samples were prepared in the same way to maintain the same albumin content in each sample and reference pair, the absorption spectra show that the baseline compensation was incomplete because of the strong background signals caused by bovine serum albumin. Accordingly, further quantitative spectral information could not be obtained from these absorption spectra. On the other hand, the calculated second derivative spectra clearly show isosbestic points indicating the complete removal of the residual background signal effects. Using the derivative intensity differences (ΔD values) of the studied benzodiazepine drugs before and after the addition of albumin, the binding constants were calculated and obtained with R.S.D. of less than 8%. The interactions of drugs with bovine serum albumin were investigated using Scatchard's plot. In addition, the consistency between the fractions of bound benzodiazepine calculated from the obtained K values and the experimental values were established. The results indicate that the second derivative method can be advantageously applicable to the determination of binding constants of drugs to serum albumin without prior separation. Moreover, the validity of the proposed method was confirmed.

Lipophilic phenolic antioxidants: correlation between antioxidant profile, partition coefficients and redox properties

Lipophilic compounds structurally based on caffeic, hydrocaffeic, ferulic and hydroferulic acids were synthesized. Subsequently, their antioxidant activity was evaluated as well as their partition coefficients and redox potentials. The structure-property-activity relationship (SPAR) results revealed the existence of a clear correlation between the redox potentials and the antioxidant activity. In addition, some compounds showed a proper lipophilicity to cross the blood-brain barrier. Their predicted ADME properties are also in accordance with the general requirements for potential CNS drugs. Accordingly, one can propose these phenolic compounds as potential antioxidants for tackling the oxidative status linked to the neurodegenerative processes.

Use of liposomes to evaluate the role of membrane interactions on antioxidant activity

Cellular membranes, which contain abundant phospholipids, such as phosphatidylcholine, are major targets subjected to the damage caused by free radicals. Cellular damage due to lipid oxidation is strongly associated with ageing, carcinogenesis and other diseases. In addition, lipid oxidation is an important deteriorative reaction in the processing and storage of lipid-containing foods. Liposomes have been used extensively as biological models for in vitro lipid oxidation studies. The resemblance between the liposomal and membrane bilayer core makes liposomes a very useful tool to investigate the significance of the antioxidant-membrane interactions for antioxidant activity. The antioxidant activity of a compound is strongly influenced by numerous factors including the nature of the lipid substrate, the hydrophilic-lipophilic balance of the antioxidant, the physical and chemical environments of the lipids, and various other interfacial interactions. Thus, compounds that are effective antioxidants in one model system or food matrix may be unsuitable in other systems.This chapter describes fluorescent probes-based methods commonly used for testing antioxidant activity in liposomes and stresses the need to combine antioxidant assays and drug-membrane interaction studies to get a better description of the antioxidants' profile considering their location in lipid bilayer and their effect on membrane fluidity and consequently provide additional information to that obtained currently from assays performed in aqueous buffer media.

Screening for the drug-phospholipid interaction: correlation to phospholipidosis

Phospholipid bilayers represent a complex, anisotropic environment fundamentally different from bulk oil or octanol, for instance. Even "simple" drug association to phospholipid bilayers can only be fully understood if the slab-of-hydrocarbon approach is abandoned and the complex, anisotropic properties of lipid bilayers reflecting the chemical structures and organization of the constituent phospholipids are considered. The interactions of drugs with phospholipids are important in various processes, such as drug absorption, tissue distribution, and subcellular distribution. In addition, drug-lipid interactions may lead to changes in lipid-dependent protein activities, and further, to functional and morphological changes in cells, a prominent example being the phospholipidosis (PLD) induced by cationic amphiphilic drugs. Herein we briefly review drug-lipid interactions in general and the significance of these interactions in PLD in particular. We also focus on a potential causal connection between drug-induced PLD and steatohepatitis, which is induced by some cationic amphiphilic drugs.

Interaction and micellar solubilization of diclofenac with cetyltrimethylammonium bromide: A spectrophotometric study

In this study, the interaction of diclofenac (Dic) with cationic surfactant cetyltrimethylammonium bromide (CTAB) was investigated. The effect of cationic micelles on solubilization of diclofenac in aqueous micellar solution was studied at pH 6.8, 29 °C and various drug concentrations. The binding of diclofenac to CTAB micelles was accompanied by a batochromic shift in the drug absorption spectra. The solubility of diclofenac increased with increasing surfactant concentration as a consequence of the association between the drug and micelles. From the results, the binding constants Kb, was obtained. By using the pseudo-phase model, the partition coefficient between the bulk water and CTAB micelles, Kx, and the Gibbs energy of binding were calculated. The value of binding constant and partition coefficient are increased by increasing of diclofenac concentration.

Membrane-thinning effect of curcumin

Interaction of curcumin with lipid bilayers is not well understood. A recent experiment showed that curcumin significantly affected the single-channel lifetime of gramicidin in a 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) bilayer without affecting its single-channel conductance. We performed two experiments to understand this result. By isothermal titration calorimetry, we measured the partition coefficient of curcumin binding to DOPC bilayers. By x-ray lamellar diffraction, we measured the thickness change of DOPC bilayers as a function of the curcumin/lipid ratio. A nonlinear membrane-thinning effect by curcumin was discovered. The gramicidin data were qualitatively interpreted by the combination of isothermal titration calorimetry and x-ray results. We show that not only does curcumin thin the lipid bilayer, it might also weaken its elasticity moduli. The result implies that curcumin may affect the function of membrane proteins by modifying the properties of the host membrane.

Curcumin is a Modulator of Bilayer Material Properties

Curcumin (1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione) is the major bioactive compound in turmeric (Curcuma longa) with antioxidant, antiinflammatory, anticarcinogenic, and antimutagenic effects. At low muM concentrations, curcumin modulates many structurally and functionally unrelated proteins, including membrane proteins. Because the cell membranes' lipid bilayer serves as a gate-keeper and regulator of many cell functions, we explored whether curcumin modifies general bilayer properties using channels formed by gramicidin A (gA). gA channels form when two monomers from opposing monolayers associate to form a conducting dimer with a hydrophobic length that is less than the bilayer hydrophobic thickness; gA channel formation thus causes a local bilayer thinning. The energetic cost of this bilayer deformation alters the gA monomer <--> dimer equilibrium, which makes the channels' appearance rate and lifetime sensitive to changes in bilayer material properties, and the gA channels become probes for changes in bilayer properties. Curcumin decreases bilayer stiffness, increasing both gA channel lifetimes and appearance rates, meaning that the energetic cost of the gA-induced bilayer deformation is reduced. These results show that curcumin may exert some of its effects on a diverse range of membrane proteins through a bilayer-mediated mechanism.

Drug-membrane interactions studied in phospholipid monolayers adsorbed on nonporous alkylated microspheres

Characterization of interactions with phospholipids is an integral part of the in vitro profiling of drug candidates because of the roles the interactions play in tissue accumulation and passive diffusion. Currently used test systems may inadequately emulate the bilayer core solvation properties (immobilized artificial membranes [IAM]), suffer from potentially slow transport of some chemicals (liposomes in free or immobilized forms), and require a tedious separation (if used for free liposomes). Here the authors introduce a well-defined system overcoming these drawbacks: nonporous octadecylsilica particles coated with a self-assembled phospholipid monolayer. The coating mimics the structure of the headgroup region, as well as the thickness and properties of the hydrocarbon core, more closely than IAM. The monolayer has a similar transition temperature pattern as the corresponding bilayer. The particles can be separated by filtration or a mild centrifugation. The partitioning equilibria of 81 tested chemicals were dissected into the headgroup and core contributions, the latter using the alkane/water partition coefficients. The deconvolution allowed a successful prediction of the bilayer/water partition coefficients with the standard deviation of 0.26 log units. The plate-friendly assay is suitable for high-throughput profiling of drug candidates without sacrificing the quality of analysis or details of the drug-phospholipid interactions.

Influence of structural factors on the enhanced activity of moxifloxacin: a fluorescence and EPR spectroscopic study

Partition coefficients of moxifloxacin in liposomes of dimyristoyl-L-alpha-phosphatidylcholine or dimyristoyl-L-alpha-phosphatidylglycerol and water were determined by spectrophotometry and fluorimetry. The K (p) values obtained were larger than those reported for most of the other fluoroquinolones, a consequence of the structural changes observed in the molecule of moxifloxacin, which in turn change its acid/base properties. Introduction of a methoxy group at position 8 and a diazabicyclonyl ring at position 7 in the basic fluoroquinolone structure alters the charge distribution at the physiological pH of 7.4, and these changes seem to be responsible for its improved antibacterial potency and broader spectrum of activity. Location studies have also been performed using fluorescence and electron paramagnetic resonance (EPR) spectroscopies. The results show that moxifloxacin must be located near the phospholipid headgroups, similar to other fluoroquinolones, but contributions from a hydrophobic component were also detected. These results suggest that the enhanced activity of this drug may be related to a more facilitated entrance into the bacterial cell, perhaps including a mediator step involving electrostatic interaction with a hydrophobic component; this step then controls the extent or orientation of insertion and improves the electrostatic interaction.

Antioxidant profile of dihydroxy- and trihydroxyphenolic acids--a structure-activity relationship study

Eight structurally similar dihydroxy and trihydroxyphenolic acids (protocatechuic acid, 3,4-dihydroxyphenylacetic acid, hydrocaffeic acid, caffeic acid, gallic acid, 3,4,5-trihydroxyphenylacetic acid, 3-(3,4,5-trihydroxyphenyl)propanoic acid and 3-(3,4,5-trihydroxyphenyl)propenoic acid) were examined for their total antioxidant capacity (TAC). Furthermore, their ability to scavenge peroxyl radicals, generated by AAPH in liposomes, was determined. The antioxidant/pro-oxidant activity of the compounds was screened using the 2'-deoxyguanosine assay. All compounds behave as radical scavengers, with 3,4,5-trihydroxyphenylacetic acid being the most potent. Nevertheless, in the lipid peroxidation assay an inverse ranking order was observed, 3,4-dihydroxyphenylacetic acid being the most effective compound. All the dihydroxylated compounds showed a pro-oxidant behaviour leading to an increase of 50% in 8-OH-dG induction. From the structure-antioxidant activity relationship studies performed it may be concluded that the number of phenolic groups and the type of the alkyl spacer between the carboxylic acid and the aromatic ring strongly influence the antioxidant activity.

Effects of Inorganic Ions on the Binding of Triflupromazine and Chlorpromazine to Bovine Serum Albumin Studied by Spectrometric Methods

The effects of inorganic salts, NaCl, NaBr, NaI, Na2SO4, KCl, KBr, KI, on the binding constants (Ks) of psychotropic phenothiazine drugs, triflupromazine (TFZ) and chlorpromazine, to bovine serum albumin (BSA) were examined by using second-derivative spectrophotometry. All of the salts examined, with the exception of Na2SO4, decreased the K values significantly, depending on the concentration of the salt, e.g., the decrease in the K values of both drugs were about 40% for 0.1 M NaCl. The results obtained with Na2SO4 indicated that neither Na+ nor SO4(2-) had any affect on the binding of the phenothiazines to BSA. Based on the Na2SO4 results and the finding that the effect of each potassium salt on binding was quite similar to that of the corresponding sodium salt, the effects of these halogen salts can be considered to be derived from their anions, although the phenothiazines are positively charged at pH 7.4. The effectiveness of the anions was determined to occur in the following order: I->>Br->Cl-; these results coincided with the published order of the binding affinity of these anions to albumin. The 19F-NMR spectra of TFZ in the presence of each of these halogen salts revealed a concentration-dependent decrease in the intensity of the signal at 13.8 ppm that had previously been assigned to the TFZ bound to Site II. Consequently, the effects of these anions on the binding of positively charged phenothiazine drugs are thought to be local steric effects caused by the binding of these anions to Site II.

A Simple Flow Injection Spectrophotometric Procedure for the Determination of Diazepam in Pharmaceutical Formulation

A single-channel flow injection (FI) manifold with spectrophotometric detection has been designed and fabricated for diazepam determination. A 100 microl sample and/or standard solution containing diazepam was injected into a flowing stream of 0.1 mol L(-1) hydrochloric acid with the optimum flow rate of 6.8 mL min(-1). As soon as the sample reached the detector, the FI signal as a peak was recorded at 360 nm. The optimum conditions for microg amounts of diazepam were achieved. A linear calibration graph over the range of 2-110 mg L(-1) diazepam was obtained with the regression equation Y = 0.2926X + 0.5896 (r2 = 0.9929). The method was very sensitive, since as little as 0.60 mg L(-1) could be detected; very reproducible with an RSD of 3.3% (n=11); and very rapid with a sampling rate of 100 h(-1). The limit of quantitation (10 sigma) was 2.0 mg L(-1). The proposed FI procedure has been satisfactorily applied to the quantitation of diazepam in commercial pharmaceutical formulations. The obtained results were in excellent agreement with those obtained by the conventional spectrophotometric method, verified by the student t-test at the 95% confidence level.

Structure-property studies on the antioxidant activity of flavonoids present in diet

The screening of natural flavonoids for their bioactivity as antioxidants is usually carried out by determinination of their profile as chain-breaking antioxidants, by the evaluation of their direct free radical-scavenging activity as hydrogen- or electron-donating compounds. Since this may not be the only mechanism underlying the antioxidant activity it is important to check the ability of these compounds to act as chelators of transition metal ions. Accordingly, in the present study the acidity constants of catechin and taxifolin, as well as the formation constants of the corresponding copper (II) complexes, were investigated by potentiometry and/or spectrophotometry. Moreover, a detailed quantitative examination of the coordination species formed is presented. In addition, the partition coefficients of both catechin and taxifolin in a biomimetic system (micelles) were determined, since these properties may also contribute to the antioxidant behavior of this type of compound. The log P values determined depend on the electrostatic interactions of the compounds with the differently charged micelles (the highest values were obtained for zwitterionic and cationic micelles). The prooxidant behavior of the compounds was assessed through the oxidation of 2'-deoxyguanosine, induced by a Fenton reaction, catalyzed by copper. The data obtained reveal that the flavonoids under study did not present prooxidant activity, in this particular system. The results obtained are evidence of a clear difference among the pKa, the complexation properties, and the lipophilicity of the flavonoids studied, which can partially explain their distinct antioxidant activity. The most stable geometries of the free compounds were determined by theoretical (ab initio) methods, in order to properly account for the electron correlation effects which occur in these systems, thus allowing a better interpretation of the experimental data.

Effects of diclofenac on EPC liposome membrane properties

In this work the interaction of a non-steroidal anti-inflammatory drug (NSAID), diclofenac, with egg yolk phosphatidylcoline (EPC) liposomes, used as cell-membrane models, was quantified by determination of the partition coefficient. The liposome/aqueous phase partition coefficient was determined by derivative spectrophotometry, fluorescence quenching, and measurement of zeta-potential. Theoretical models based on simple partition of the diclofenac between two different media, were used to fit the experimental data, enabling the determination of K(p). The three techniques used yielded similar results. The effects of the interaction on the membrane's characteristics were further evaluated, either by studying membrane potential changes or by effects on membrane fluidity. The liposome membrane potential and the size and size-homogeneity of liposomes were measured by light scattering. The effects of diclofenac on the internal viscosity or fluidity of the membrane were determined by use of spectroscopic probes-a series of n-(9-anthroyloxy) fatty acids in which the carboxyl terminal group is located at the interfacial region of the membrane and the fluorescent anthracene group is attached at different positions along the fatty acid chain. The location of the diclofenac on the membrane was also evaluated, by fluorescence quenching using the same series of fluorescent probes. Because the fluorescent anthracene group is attached at different positions along the fatty acid chain, it is possible to label at a graded series of depths in the bilayer. The interactions between the drug and the probe are a means of predicting the location of the drug on the membrane.