Interaction of the cholesterol reducing agent simvastatin with zwitterionic DPPC and charged DPPG phospholipid membranes

Process development of inhalation powders containing simvastatin loaded liposomes using spray drying technology

The development of an inhalation powder (IP) for cancer therapy is desired to improve the therapeutic response and patient compliance. The latest studies highlighted that statins, a class of drugs used in hypercholesterolemia, can have anticancer and antiinflammatory properties. Therefore, the aim of the study was to develop an IP containing liposomes loaded with simvastatin using spray drying technology, as well as to investigate the influence of formulation factors on the quality attributes of the IP by means of experimental design. Results highlighted that the composition of liposomes, namely type of phospholipid and cholesterol concentration, highly influences the quality attributes of IP, and the use of optimal concentrations of excipients, i.e. D-mannitol and L-leucine, is essential to preserve the characteristics of liposomes throughout the spray drying process. The in vitro characterization of the optimal IP formulation revealed that the total percentage of released drug is higher from the IP formulation compared to the powder of active substance (53.38 vs. 42.76%) over a period of six hours, and 39.67% of dry particles have a size less than 5 µm, making them suitable for inhalation. As a conclusion, spray drying technology can be effectively used in the development and preparation of IP containing liposomes.

Investigation of miltefosine-model membranes interactions at the molecular level for two different PS levels modeling cancer cells

Miltefosine (MLT) is a broad-spectrum drug included in the alkylphospholipids (APL) used against leishmania and various types of cancer. The most crucial feature of APLs is that they are thought to only kill cancerous cells without harming normal cells. However, the molecular mechanism of action of APLs is not completely understood. The increase in the phosphatidylserine (PS) ratio is a marker showing the stage of cancer and even metastasis. The goal of this research was to investigate the molecular effects of miltefosine at the molecular level in different PS ratios. The effects of MLT on membrane phase transition, membrane orders, and dynamics were studied using DPPC/DPPS (3:1) and DPPC/DPPS (1:1) multilayer (MLV) vesicles mimicking DPPS ratio variation, Differential Scanning Calorimetry (DSC), and Fourier Transform Infrared spectroscopy (FTIR). Our findings indicate that miltefosine is evidence at the molecular level that it is directed towards the tumor cell and that the drug's effect increases with the increase of anionic lipids in the membrane depending on the stage of cancer.

Interplay of Cholesterol and Actin in Neurotransmitter GPCR Signaling: Insights from Chronic Cholesterol Depletion Using Statin

Serotonin1A receptors are important neurotransmitter receptors in the G protein-coupled receptor (GPCR) family and modulate a variety of neurological, behavioral, and cognitive functions. We recently showed that chronic cholesterol depletion by statins, potent inhibitors of HMG-CoA reductase (the rate-limiting enzyme in cholesterol biosynthesis), leads to polymerization of the actin cytoskeleton that alters lateral diffusion of serotonin1A receptors. However, cellular signaling by the serotonin1A receptor under chronic cholesterol depletion remains unexplored. In this work, we explored signaling by the serotonin1A receptor under statin-treated condition. We show that cAMP signaling by the receptor is reduced upon lovastatin treatment due to reduction in cholesterol as well as polymerization of the actin cytoskeleton. To the best of our knowledge, these results constitute the first report describing the effect of chronic cholesterol depletion on the signaling of a G protein-coupled neuronal receptor. An important message arising from these results is that it is prudent to include the contribution of actin polymerization while analyzing changes in membrane protein function due to chronic cholesterol depletion by statins. Notably, our results show that whereas actin polymerization acts as a negative regulator of cAMP signaling, cholesterol could act as a positive modulator. These results assume significance in view of reports highlighting symptoms of anxiety and depression in humans upon statin administration and the role of serotonin1A receptors in anxiety and depression. Overall, these results reveal a novel role of actin polymerization induced by chronic cholesterol depletion in modulating GPCR signaling, which could act as a potential therapeutic target.

Modulators of cellular cholesterol homeostasis as antiproliferative and model membranes perturbing agents

Cholesterol is an important component of mammalian cell membranes affecting their fluidity and permeability. Together with sphingomyelin, cholesterol forms microdomains, called lipid rafts. They play important role in signal transduction forming platforms for interaction of signal proteins. Altered levels of cholesterol are known to be strongly associated with the development of various pathologies (e.g., cancer, atherosclerosis and cardiovascular diseases). In the present work, the group of compounds that share the property of affecting cellular homeostasis of cholesterol was studied. It contained antipsychotic and antidepressant drugs, as well as the inhibitors of cholesterol biosynthesis, simvastatin, betulin, and its derivatives. All compounds were demonstrated to be cytotoxic to colon cancer cells but not to non-cancerous cells. Moreover, the most active compounds decreased the level of free cellular cholesterol. The interaction of drugs with raft-mimicking model membranes was visualized. All compounds reduced the size of lipid domains, however, only some affected their number and shape. Membrane interactions of betulin and its novel derivatives were characterized in detail. Molecular modeling indicated that high dipole moment and significant lipophilicity were characteristic for the most potent antiproliferative agents. The importance of membrane interactions of cholesterol homeostasis-affecting compounds, especially betulin derivatives, for their anticancer potency was suggested.

The interaction of tryptophan enantiomers with model membranes is modulated by polar head type and physical state of phospholipids

The mutual influence of chiral bioactive molecules and supramolecular assemblies is currently being studied in many research fields, including medical-pharmaceutical applications. Model membranes of phospholipids, such as the zwitterionic dipalmitoylphosphatidylcholine (DPPC) and the anionic dipalmitoylphosphatidylglycerol (DPPG), interact with a variety of chiral compounds that include amino acids. In this work, the interaction of tryptophan enantiomers, L-Trp and D-Trp, on DPPC and DPPG bilayers was investigated by using differential scanning calorimetry, attenuated total reflectance-Fourier transform infrared and spin-label electron spin resonance spectroscopies as well as molecular docking simulations. The results show that Trp enantiomers slightly perturb the bilayer thermotropic phase transitions. For both membranes, O atoms in the carbonyl groups have a propensity to act as acceptors of a (weak) hydrogen bond. The Trp chiral forms also promote formation of hydrogen bonds and/or hydration in the PO₂^- moiety of the phosphate group, especially for the DPPC bilayer. In contrast, they interact more closely with the glycerol group of DPPG polar head. Only for DPPC bilayers, both enantiomers increase the packing of the first hydrocarbon chain segments for temperatures through the gel state, whereas they do not affect the lipid chain order and mobility in the fluid state. The results are consistent with a Trp association in the upper region of the bilayers without permeation in the innermost hydrophobic region. The findings suggest that neutral and anionic lipid bilayers are differently sensitive to amino acid chirality.

The recovery effect of Vitamin C on structural alterations due to Streptozotocin-Induced diabetes in rat testicular tissues

Type I Diabetes is a multisystem disease that causes alterations in carbohydrate, protein, and fat metabolisms due to hyperglycemia. It has an extensive pathology, especially the mechanism involving oxidative stress is still complex. Type I diabetes is correlated with increased formation of free radicals and decreased levels of antioxidant potential. Vitamin C (Vit C) is a powerful antioxidant that participates in antioxidant defense, protecting lipid membranes and proteins from oxidative damage by donating electrons to free radicals. The effect of type I diabetes and the recovery role of Vit C on the structure and composition of the biomolecular content of testicular tissue is still unknown. Therefore, the current study aimed to investigate the alterations in the biomolecules of rat testes due to Streptozotocin (STZ)-induced type I diabetes using Attenuated Total Reflectance (ATR)-Fourier Transform Infrared (FTIR) spectroscopy and histological staining. The results revealed that the biomolecular structure and composition of testicular tissue are highly affected due to the development of diabetes. We obtained decreased saturation levels and increased unsaturation index in the lipids indicating the presence of lipid peroxidation in the diabetic state. The elevated lipid peroxidation levels have been implicated in the pathogenesis of naturally occurring and chemically induced diabetes. On the other hand, the protein content of diabetic rat testicular tissue was shown to decrease considerably, indicating an increase in proteolysis processes. Supporting the ratio of protein structural and conformational change, protein secondary structural components were also found to alter substantially in the diabetic state. Diabetes was also shown to lead to a decrease in the content of nucleic acids compared to proteins. These diabetes-induced alterations were found to be substantially recovered with the administration of Vit C. Although different doses and administration types of Vit C have been reported in the literature, there is no consensus yet. Therefore, we used three different doses of Vit C in our study as high (100 mg/kg/day), medium (50 mg/kg/day) and low (15 mg/kg/day) doses intraperitoneally in the present study, and the medium dose was found to be the most effective in the recovery from the diabetes-induced structural damages on rat testicular tissue. Vit C may have a therapeutic effect to be used as a complementary therapy in the treatment of diabetes.

Co-Encapsulation of Simvastatin and Doxorubicin into pH-Sensitive Liposomes Enhances Antitumoral Activity in Breast Cancer Cell Lines

Doxorubicin (DOX) is a potent chemotherapeutic drug used as the first line in breast cancer treatment; however, cardiotoxicity is the main drawback of the therapy. Preclinical studies evidenced that the association of simvastatin (SIM) with DOX leads to a better prognosis with reduced side effects and deaths. In this work, a novel pH-sensitive liposomal formulation capable of co-encapsulating DOX and SIM at different molar ratios was investigated for its potential in breast tumor treatment. Studies on physicochemical characterization of the liposomal formulations were carried out. The cytotoxic effects of DOX, SIM, and their combinations at different molar ratios (1:1; 1:2 and 2:1), free or co-encapsulated into pH-sensitive liposomes, were evaluated against three human breast cancer cell lines (MDA-MB-231, MCF-7, and SK-BR-3). Experimental protocols included cell viability, combination index, nuclear morphological changes, and migration capacity. The formulations showed a mean diameter of less than 200 nm, with a polydispersity index lower than 0.3. The encapsulation content was ~100% and ~70% for DOX and SIM, respectively. A more pronounced inhibitory effect on breast cancer cell lines was observed at a DOX:SIM molar ratio of 2:1 in both free and encapsulated drugs. Furthermore, the 2:1 ratio showed synergistic combination rates for all concentrations of cell inhibition analyzed (50, 75, and 90%). The results demonstrated the promising potential of the co-encapsulated liposome for breast tumor treatment.

Smith-Lemli-Opitz syndrome: A pathophysiological manifestation of the Bloch hypothesis

The biosynthesis of cholesterol, an essential component of higher eukaryotic membranes, was worked out by Konrad Bloch (and Feodor Lynen) in the 1960s and they received the Nobel Prize around that time in recognition of their pioneering contributions. An elegant consequence of this was a hypothesis proposed by Konrad Bloch (the Bloch hypothesis) which suggests that each subsequent intermediate in the cholesterol biosynthesis pathway is superior in supporting membrane function in higher eukaryotes relative to its precursor. In this review, we discuss an autosomal recessive metabolic disorder, known as Smith-Lemli-Opitz syndrome (SLOS), associated with a defect in the Kandutsch-Russell pathway of cholesterol biosynthesis that results in accumulation of the immediate precursor of cholesterol in its biosynthetic pathway (7-dehydrocholesterol) and an altered cholesterol to total sterol ratio. Patients suffering from SLOS have several developmental, behavioral and cognitive abnormalities for which no drug is available yet. We characterize SLOS as a manifestation of the Bloch hypothesis and review its molecular etiology and current treatment. We further discuss defective Hedgehog signaling in SLOS and focus on the role of the serotonin_1A receptor, a representative neurotransmitter receptor belonging to the GPCR family, in SLOS. Notably, ligand binding activity and cellular signaling of serotonin_1A receptors are impaired in SLOS-like condition. Importantly, cellular localization and intracellular trafficking of the serotonin_1A receptor (which constitute an important determinant of a GPCR cellular function) are compromised in SLOS. We highlight some of the recent developments and emerging concepts in SLOS pathobiology and suggest that novel therapies based on trafficking defects of target receptors could provide new insight into treatment of SLOS.

Lipidomic and Membrane Mechanical Signatures in Triple-Negative Breast Cancer: Scope for Membrane-Based Theranostics

Triple-negative breast cancer (TNBC) is a highly aggressive form of breast cancer associated with poor prognosis, higher grade, and a high rate of metastatic occurrence. Limited therapeutic interventions and the compounding issue of drug resistance in triple-negative breast cancer warrants the discovery of novel therapeutic targets and diagnostic modules. To this view, in addition to proteins, lipids also regulate cellular functions via the formation of membranes that modulate membrane protein function, diffusion, and their localization; thus, orchestrating signaling hot spots enriched in specific lipids/proteins on cell membranes. Lipid deregulation in cancer leads to reprogramming of the membrane dynamics and functions impacting cell proliferation, metabolism, and metastasis, providing exciting starting points for developing lipid-based approaches for treating TNBC. In this review, we provide a detailed account of specific lipidic changes in breast cancer, link the altered lipidome with membrane structure and mechanical properties, and describe how these are linked to subsequent downstream functions implicit in cancer progression, metastasis, and chemoresistance. At the fundamental level, we discuss how the lipid-centric findings in TNBC are providing cues for developing lipid-inspired theranostic strategies while bridging existing gaps in our understanding of the functional involvement of lipid membranes in cancer.

Membrane Cholesterol Content and Lipid Organization Influence Melittin and Pneumolysin Pore-Forming Activity

Melittin, the main toxic component in the venom of the European honeybee, interacts with natural and artificial membranes due to its amphiphilic properties. Rather than interacting with a specific receptor, melittin interacts with the lipid components, disrupting the lipid bilayer and inducing ion leakage and osmotic shock. This mechanism of action is shared with pneumolysin and other members of the cholesterol-dependent cytolysin family. In this manuscript, we investigated the inverse correlation for cholesterol dependency of these two toxins. While pneumolysin-induced damage is reduced by pretreatment with the cholesterol-depleting agent methyl-β-cyclodextrin, the toxicity of melittin, after cholesterol depletion, increased. A similar response was also observed after a short incubation with lipophilic simvastatin, which alters membrane lipid organization and structure, clustering lipid rafts. Therefore, changes in toxin sensitivity can be achieved in cells by depleting cholesterol or changing the lipid bilayer organization.

A Screening Study for the Development of Simvastatin-Doxorubicin Liposomes, a Co-Formulation with Future Perspectives in Colon Cancer Therapy

An increasing number of studies published so far have evidenced the benefits of Simvastatin (SIM) and Doxorubicin (DOX) co-treatment in colorectal cancer. In view of this, the current study aimed to investigate the pharmaceutical development of liposomes co-encapsulating SIM and DOX, by implementing the Quality by Design (QbD) concept, as a means to enhance the antiproliferative effect of the co-formulation on C26 murine colon cancer cells co-cultured with macrophages. It is known that the quality profile of liposomes is dependent on the critical quality attributes (CQAs) of liposomes (drug entrapped concentration, encapsulation efficiency, size, zeta potential, and drug release profile), which are, in turn, directly influenced by various formulation factors and processing parameters. By using the design of experiments, it was possible to outline the increased variability of CQAs in relation to formulation factors and identify by means of statistical analysis the material attributes that are critical (phospholipids, DOX and SIM concentration) for the quality of the co-formulation. The in vitro studies performed on a murine colon cancer cell line highlighted the importance of delivering the optimal drug ratio at the target site, since the balance antiproliferative vs. pro-proliferative effects can easily be shifted when the molar ratio between DOX and SIM changes.

Urine analysis using FTIR spectroscopy: A study on healthy adults and children

Urine spectra from 108 healthy volunteers are studied by attenuated total refraction-Fourier transform infrared (ATR-FTIR) spectroscopy. The spectral features are correlated with observable urine components. The variation of spectra within a healthy population is quantified and a library of reference spectra is constructed. Using the band assignments, these spectra are compared with both age-wise and gender-wise. Children show the least intensity variations compared to both adult groups. Young adults show the highest variation, particularly in the 1650 to 1400 cm^-1 and 1200 to 900 cm^-1 regions. These results indicate the importance of the size of the control group in comparative studies utilizing FTIR. Age-wise comparisons reveal that phosphate and sulfate excretion decreases with age, and that the variance of phosphate among individuals is higher with adults. As for gender-wise comparisons, females show a slightly higher citrate content at 1390 cm^-1 regardless of the age and they show a higher variance in the 1200 to 1000 cm^-1 region when compared to men.

Facile L-Glutamine delivery to erythrocytes via DOPC-DPPG mixed liposomes

Sickle cell disease (SCD) is a mortal erythrocyte-based disease which is hard to treat effectively. Development of a treatment method that can prevent deoxygenation of erythrocytes or reduce the oxidative stress of sickle erythrocytes is one of the important issues towards SCD. Among a wide variety of potential drug carriers, liposomes are advantageous and preferable with their easy preparation and biocompatibility. In this study, L-Glutamine (Gln) loaded liposomes were prepared with 1,2-Dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-Dioleoyl-sn-glycero-3-phospho-rac-(1-glycerol) sodium salt (DPPG). Liposomes were characterized via zeta potential, size measurements, differential scanning calorimetry, Fourier Transform Infra-red Spectroscopy and they were visualized via transmission electron microscopy and scanning electron microscopy. Effect of the encapsulated amount of Gln was investigated by encapsulating Gln at three different concentrations (i.e0.20 mM, 40 mM and 60 mM). Drug encapsulation and release studies were implemented with high pressure liquid chromatography (HPLC). The encapsulation efficiency of Gln was determined to be the higher than the ones reported in the literature: 83.6%, 87.1% and 84.9% for 20 mM, 40 mM and 60 mM Gln, respectively. It was found that after 6 hours, liposomes loaded with 60 mM of Gln had released 45.7% of Gln. Optical microscopy images of the erythrocytes after 3 hours of incubation and haemolysis measurements proved that presence of liposomes did not cause any structural changes on the erythrocyte shape. Overall, it was concluded that L-Gln loaded PC/PG liposomes provide promising results in terms of developing a new drug delivery platform for SCD.

Incorporation of simvastatin into lipid membranes: Why deliver a statin in form of inclusion complex with hydrophilic cyclodextrin

In this work, the effects of simvastatin (SIM), (2-hydroxypropyl)-β-cyclodextrin (HPβCD) and their complex (SIM:HPβCD) on the structure and properties of lipid membranes were investigated for the first time by Langmuir technique combined with PM-IRRAS spectroscopy. An improved understanding of the differences of the interactions between free SIM, and SIM in the form of an inclusion complex with HPβCD with the lipid membrane will improve the development of preparation methods for in vivo applications. Monolayers of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), cholesterol (Chol) and their mixture DMPC:Chol (7:3) served as simple models of one leaflet of the cell membrane. The penetration of well-organized lipid layers by simvastatin lead to their fluidization but the extent of this unwanted effect was smaller when the drug was delivered in the form of the SIM:HPβCD complex. Surface pressure vs. time dependencies showed that the drug encapsulated with cyclodextrin dissociated from the complex upon contact with the lipid layer and the weak interactions between the exterior polar part of the HPβCD and the polar headgroups of the lipid layer facilitated smooth incorporation of the released lipophilic drug into the membrane. At a longer time-scale, the HPβCD ligand released from the complex removed some cholesterol, but not DMPC, from the lipid layer, hence, similarly to the enzyme inhibiting action of statins - it lead to the decrease of the amount of cholesterol in the membrane. Delivery of simvastatin in the form of an inclusion complex with HPβCD is proposed as an approach improving its bioavailability in the cholesterol-lowering therapies.

Membrane cholesterol regulates endocytosis and trafficking of the serotonin1A receptor: Insights from acute cholesterol depletion

Endocytosis and intracellular trafficking constitute important regulatory features associated with G protein-coupled receptor (GPCR) function. GPCR endocytosis involves several remodeling events at the plasma membrane orchestrated by a concerted interplay of a large number of proteins and membrane lipids. Although considerable literature exists on the protein framework underlying GPCR endocytosis, the role of membrane lipids in this process remains largely unexplored. In order to explore the role of membrane cholesterol (an essential and important lipid in higher eukaryotes) in GPCR endocytosis, we monitored the effect of acute cholesterol depletion using methyl-β-cyclodextrin (MβCD) on endocytosis and intracellular trafficking of the serotonin_1A receptor, an important neurotransmitter GPCR. Our results show that the serotonin_1A receptor exhibits agonist-induced clathrin-mediated endocytosis with a concentration-dependent inhibition in internalization with increasing concentrations of MβCD, which was restored upon cholesterol replenishment. Interestingly, subsequent to internalization under these conditions, serotonin_1A receptors were re-routed toward lysosomal degradation, instead of endosomal recycling observed under normal conditions, thereby implicating membrane cholesterol in modulation of intracellular trafficking of the receptor. This raises the possibility of a novel cholesterol-dependent role of intracellular sorting proteins in GPCR trafficking. These results differ from our previous observations on the endocytosis of the serotonin_1A receptor upon statin-induced chronic cholesterol depletion, in terms of endocytic pathway. We conclude that analysis of complex cellular trafficking events such as GPCR endocytosis under acute and chronic cholesterol depletion conditions should be carried out with caution due to fundamental differences underlying these processes.

The Role of Structure and Biophysical Properties in the Pleiotropic Effects of Statins

Statins are a class of drugs used to lower low-density lipoprotein cholesterol and are amongst the most prescribed medications worldwide. Most statins work as a competitive inhibitor of 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase (HMGR), but statin intolerance from pleiotropic effects have been proposed to arise from non-specific binding due to poor enzyme-ligand sensitivity. Yet, research into the physicochemical properties of statins, and their interactions with off-target sites, has not progressed much over the past few decades. Here, we present a concise perspective on the role of statins in lowering serum cholesterol levels, and how their reported interactions with phospholipid membranes offer a crucial insight into the mechanism of some of the more commonly observed pleiotropic effects of statin administration. Lipophilicity, which governs hepatoselectivity, is directly related to the molecular structure of statins, which dictates interaction with and transport through membranes. The structure of statins is therefore a clinically important consideration in the treatment of hypercholesterolaemia. This review integrates the recent biophysical studies of statins with the literature on the physiological effects and provides new insights into the mechanistic cause of statin pleiotropy, and prospective means of understanding the cholesterol-independent effects of statins.

New Insights Into Targeting Membrane Lipids for Cancer Therapy

Modulation of membrane lipid composition and organization is currently developing as an effective therapeutic strategy against a wide range of diseases, including cancer. This field, known as membrane-lipid therapy, has risen from new discoveries on the complex organization of lipids and between lipids and proteins in the plasma membranes. Membrane microdomains present in the membrane of all eukaryotic cells, known as lipid rafts, have been recognized as an important concentrating platform for protein receptors involved in the regulation of intracellular signaling, apoptosis, redox balance and immune response. The difference in lipid composition between the cellular membranes of healthy cells and tumor cells allows for the development of novel therapies based on targeting membrane lipids in cancer cells to increase sensitivity to chemotherapeutic agents and consequently defeat multidrug resistance. In the current manuscript strategies based on influencing cholesterol/sphingolipids content will be presented together with innovative ones, more focused in changing biophysical properties of the membrane bilayer without affecting the composition of its constituents.