The administration of methyl and butyl parabens interferes with the enzymatic antioxidant system and induces genotoxicity in rat testis: possible relation to male infertility

Parabens are esters of p-hydroxybenzoic acid, used for decades as a preservative in many products, including agrochemicals, pharmaceuticals, foods and cosmetics. Concerns regarding parabens toxicity include adverse effects on endocrine activity, carcinogenesis, infertility, spermatogenesis, and adipogenesis. The present study aimed to investigate the in vivo administration of methyl and butylparaben at concentrations of 100 and 200 mg/kg body weight, by subcutaneous injection, in variable murinometric measurements, antioxidant systems and genotoxicity. The administration of parabens did not affect the consumption of water and food. However, there was a decrease in the weight of the testes and the seminal vesicle (p < 0.05). The administration of parabens caused an increase in superoxide dismutase for methylparaben (200 mg/kg) and both concentrations of butylparaben (p < 0.05). Catalase showed increased activity in all groups treated with parabens. In contrast, glutathione reductase and glutathione S-transferase suffered a decrease in the groups treated with both parabens. These results show that parabens, especially butyl, can affect the rat testis enzymatic antioxidant system, decreasing the cellular antioxidant capacity, which was confirmed by the decrease in the glutathione reducing power, expressed by the reduced glutathione/oxidized glutathione ratio. Therefore, an increase in lipid peroxidation was observed, which was significant in the case of butyl. Genetic Damage Indicator values show that butylparaben treatments displayed significantly higher values than the control. This study shows for the first time that parabens can induce genotoxicity in the rat male reproductive organ.

Onion (Allium cepa L.) Skin Waste Valorization: Unveiling the Phenolic Profile and Biological Potential for the Creation of Bioactive Agents through Subcritical Water Extraction

Onion skin waste (OSW), the primary non-edible byproduct from onion processing, offers a renewable source of bioactive compounds. This study aims to valorize OSW through subcritical water extraction (SWE), aligning with a circular economy and biorefinery principles. SWE was carried out at 145 °C and 50 bar for 50 min in a discontinuous reactor, producing a phenolic-rich extract (32.3 ± 2.6 mg/g) dominated by protocatechuic acid (20.3 ± 2.5 mg/g), quercetin-4'-O-glucoside (7.5 ± 0.2 mg/g), and quercetin (3.2 ± 0.6 mg/g). Additionally, the extract contains sugars (207.1 ± 20.3 mg sucrose-Eq/g), proteins (22.8 ± 1.6 mg BSA-Eq/g), and free amino acids (20.4 ± 1.2 mg arginine-Eq/g). Its phenolic richness determines its scavenging activity against ●NO and O2●- radicals and its α-glucosidase and aldose-reductase inhibition without affecting α-amylase. Notably, the extract demonstrates significant α-glucosidase inhibition (IC50 = 75.6 ± 43.5 µg/mL), surpassing acarbose (IC50 = 129.5 ± 1.0 µg/mL) in both pure enzyme and cell culture tests without showing cytotoxicity to AGS, HepG2, and Caco-2 human cell lines. The extract's bioactivity and nutritional content make it suitable for developing antioxidant and antidiabetic nutraceutical/food components, highlighting SWE's potential for OSW valorization without using organic solvents.

Antifungal Activity of Guiera senegalensis: From the Chemical Composition to the Mitochondrial Toxic Effects and Tyrosinase Inhibition

Pest resistance against fungicides is a widespread and increasing problem, with impact on crop production and public health, making the development of new fungicides an urgent need. Chemical analyses of a crude methanol extract (CME) of Guiera senegalensis leaves revealed the presence of sugars, phospholipids, phytosterols, guieranone A, porphyrin-containing compounds, and phenolics. To connect chemical composition with biological effects, solid-phase extraction was used to discard water-soluble compounds with low affinity for the C18 matrix and obtain an ethyl acetate fraction (EAF) that concentrates guieranone A and chlorophylls, and a methanol fraction (MF) dominated by phenolics. While the CME and MF exhibited poor antifungal activity against Aspergillus fumigatus, Fusarium oxysporum and Colletotrichum gloeosporioides, the EAF demonstrated antifungal activity against these filamentous fungi, particularly against C. gloeosporioides. Studies with yeasts revealed that the EAF has strong effectiveness against Saccharomyces cerevisiae, Cryptococcus neoformans and Candida krusei with MICs of 8, 8 and 16 μg/mL, respectively. A combination of in vivo and in vitro studies shows that the EAF can function as a mitochondrial toxin, compromising complexes I and II activities, and as a strong inhibitor of fungal tyrosinase (Ki = 14.40 ± 4.49 µg/mL). Thus, EAF appears to be a promising candidate for the development of new multi-target fungicides.

An Experimental Approach to Address the Functional Relationship between Antioxidant Enzymes and Mitochondrial Respiratory Complexes

Mitochondrial dysfunction and cytosolic oxidative stress are pathological biomarkers interlinked in several chronic diseases and cellular toxicity promoted by high-energy radiation or xenobiotics. Thus, assessing the activities of the mitochondrial redox chain complexes and the cytosolic antioxidant enzymes in the same cell culture system is a valuable approach to addressing the challenge of chronic diseases or unveiling the molecular mechanisms underlying the toxicity of physical and chemical stress agents. The present article gathers the experimental procedures to obtain, from isolated cells, a mitochondria-free cytosolic fraction and a mitochondria-rich fraction. Furthermore, we describe the methodologies to evaluate the activity of the main antioxidant enzymes in the mitochondria-free cytosolic fraction (superoxide dismutase, catalase, glutathione reductase and glutathione peroxidase), and the activity of the individual mitochondrial complexes I, II and IV, as well as the conjugated activity of complexes I-III and complexes II-III in the mitochondria-rich fraction. The protocol to test the citrate synthase activity was also considered and used to normalize complexes. The procedures were optimized within an experimental setup to allow that each condition to be tested only requires sampling of one T-25 flask of cells 2D cultured, as the typical results presented and discussed here.

Mitochondria research and neurodegenerative diseases: on the track to understanding the biological world of high complexity

From the simple unicellular eukaryote to the highly complex multicellular organism like Human, mitochondrion emerges as a ubiquitous player to ensure the organism's functionality. It is popularly known as "the powerhouse of the cell" by its key role in ATP generation. However, our understanding of the physiological relevance of mitochondria is being challenged by data obtained in different fields. In this review, a short history of the mitochondria research field is presented, stressing the findings and questions that allowed the knowledge advances, and put mitochondrion as the main player of safeguarding organism life as well as a key to solve the puzzle of the neurodegenerative diseases.

Trichilia catigua and Turnera diffusa phyto-phospholipid nanostructures: physicochemical characterization and bioactivity in cellular models of induced neuroinflammation and neurotoxicity

Flavonoid-based therapies supported by nanotechnology are considered valuable strategies to prevent or delay age-related and chronic neurodegenerative disorders. Egg yolk phospholipids were combined with flavonoid-rich extracts obtained from Trichilia catigua A.Juss. (rich in flavan-3-ols and phenylpropanoid derivatives) or Turnera diffusa Willd. ex Schult (dominated by luteolin derivatives) to prepare nanophytosomes. The nanophytosomes showed that size and surface charge of the lipid-based vesicles are dependent of their phenolic composition. In vitro assays with SH-SY5Y cells showed that both formulations protect cells from glutamate-induced toxicity, but not from 6-hydroxydopamine/ascorbic acid. T. diffusa nanophytosomes promote a decrease of nitric oxide produced by BV-2 cells stimulated with interferon-γ. Nanophytosomes dialysed against a mannitol solution, and then lyophilised, allow to obtain freeze-dried products that after re-hydration preserve the essential physicochemical features of the original formulations, and exhibit improved colloidal stability. These results indicate that these flavonoid/phospholipid-based nanophytosomes have suitable features to be considered as tool in the development of therapeutic and food applications.

Topical Fixed-Dose Combinations: Current in vitro methodologies for pre-clinical development

The combination of two or more active pharmaceutical ingredients in the same dosage form - fixed-dose combination products - for topical administration represents a promising therapeutic approach for treating several pathologies, including pain. The pre-clinical development of fixed-dose combination products aims to characterize the interactions between the different APIs and ensure that the final medicinal product has the required safety characteristics. To this end, there are several regulatory accepted in vitro tests to assess the safety of medicinal products intended for cutaneous administration. In turn, the evaluation of anti-inflammatory activity should be based on models described in the scientific literature, as there are no models fully validated by competent entities. Therefore, the present work presents the information regarding accepted in vitro tests to assess the safety of topical products and the most used methods to assess anti-inflammatory activity. Additionally, a new approach to select a fixed-dose combination product with the potential to enhance the therapeutic effects of the individual active pharmaceutical ingredients is rationalized by integrating the overall effects on several targets relevant for inflammation and pain management in one numeric index.

In vivo methodologies to assist preclinical development of topical fixed-dose combinations for pain management

The combination in a fixed dose of two or more active pharmaceutical ingredients in the same pharmaceutical dosage form is an approach that has been used successfully in the treatment of several pathologies, including pain. In the preclinical development of a topical fixed-dose combination product with analgesic and anti-inflammatory activities for pain management, the main objective is to establish the nature of the interaction between the different active pharmaceutical ingredients while obtaining data on the medicinal product safety and efficacy. Despite the improvement of in vitro assays, animal models remain a fundamental strategy to characterise the interaction, efficacy and safety of active pharmaceutical ingredients at the physiological level, which cannot be reached by in vitro assays. Thus, the main goal of this review is to systematise the available animal models to evaluate the efficacy and safety of a new fixed-dose combination product for topical administration indicated for pain management. Particular emphasis is given to animal models that are accepted for regulatory purposes.

Inherited Metabolic Memory of High-fat Diet Impairs Testicular Fatty Acid Content and Sperm Parameters

Exposure to a high-fat diet (HFD) from early-life is associated with a testicular metabolic signature linked to abnormal sperm parameters up to two generations after exposure in mice. Hereby, we describe a testicular lipid signature associated with "inherited metabolic memory" of exposure to HFD, persisting up to two generations in mice. Diet-challenged mice (n = 36) were randomly fed after weaning with standard chow (CTRL); HFD for 200 days or transient HFD (HFD_t ) (60 days of HFD+140 days of standard chow). Subsequent generations (36 mice per generation) were fed with chow diet. Mice were euthanized 200 days post-weaning. Glucose homeostasis, serum hormones, testicular bioenergetics and antioxidant enzyme activity were evaluated. Testicular lipid-related metabolites and fatty acids were characterized by ¹ H-NMR and GC-MS. Sons of HFD display impaired choline metabolism, mitochondrial activity and antioxidant defenses, while grandsons show a shift in testicular ω3/ω6 ratio towards a pro-inflammatory environment. Grandsons of HFDt raise 3-hydroxybutyrate levels with possible implications to testicular insulin resistance. Sperm counts decrease in grandsons of HFD-exposed mice, regardless of the duration of exposure. HFD-induced "inherited metabolic memory" alters testicular fatty acid metabolism with consequences to sperm parameters up to two generations. This article is protected by copyright. All rights reserved.

Improving pollutants environmental risk assessment using a multi model toxicity determination with in vitro, bacterial, animal and plant model systems: The case of the herbicide alachlor

Several environmental pollutants, including pesticides, herbicides and persistent organic pollutants play an important role in the development of chronic diseases. However, most studies have examined environmental pollutants toxicity in target organisms or using a specific toxicological test, losing the real effect throughout the ecosystem. In this sense an integrative environmental risk of pollutants assessment, using different model organisms is necessary to predict the real impact in the ecosystem and implications for target and non-target organisms. The objective of this study was to use alachlor, a chloroacetanilide herbicide responsible for chronic toxicity, to understand its impact in target and non-target organisms and at different levels of biological organization by using several model organisms, including membranes of dipalmitoylphosphatidylcholine (DPPC), rat liver mitochondria, bacterial (Bacillus stearothermophilus), plant (Lemna gibba) and mammalian cell lines (HeLa and neuro2a). Our results demonstrated that alachlor strongly interacted with membranes of DPPC and interfered with mitochondrial bioenergetics by reducing the respiratory control ratio and the transmembrane potential. Moreover, alachlor also decreased the growth of B. stearothermophilus and its respiratory activity, as well as decreased the viability of both mammalian cell lines. The values of TC₅₀ increased in the following order: Lemna gibba < neuro2a < HeLa cells < Bacillus stearothermophilus. Together, the results suggest that biological membranes constitute a putative target for the toxic action of this lipophilic herbicide and point out the risks of its dissemination on environment, compromising ecosystem equilibrium and human health.

Homarine Alkyl Ester Derivatives as Promising Acetylcholinesterase Inhibitors

Reversible acetylcholinesterase (AChE) inhibitors are key therapeutic tools to modulate the cholinergic connectivity compromised in several degenerative pathologies. In this work, four alkyl esters of homarine were synthesized and screened by using Electrophorus electricus AChE and rat brain AChE-rich fraction. Results showed that all homarine alkyl esters are able to inhibit AChE by a competitive inhibition mode. The effectiveness of AChE inhibition increases with the alkyl side chain length of the homarine esters, being HO-C₁₆ (IC₅₀ =7.57±3.32 μM and K_i =18.96±2.28 μM) the most potent inhibitor. The fluorescence quenching studies confirmed that HO-C₁₆ is the compound with higher selectivity and affinity for the tryptophan residues in the catalytic active site of AChE. Preliminary cell viability studies showed that homarine esters display no toxicity for human neuronal SH-SY5Y cells. Thus, the long-chain homarine esters emerge as new anti-cholinesterase agents, with potential to be considered for therapeutic applications development.

Trichilia catigua and Turnera diffusa extracts: In vitro inhibition of tyrosinase, antiglycation activity and effects on enzymes and pathways engaged in the neuroinflammatory process

ETHNOPHARMACOLOGICAL RELEVANCE

Flavonoids interact with multiple targets in Central Nervous System resulting in a broad neuroprotection mediated by complementary processes and synergic interactions. Therefore, flavonoid-based therapies may input positive outcomes in the prevention and early management of neurodegenerative diseases. In Brazilian folk medicine Trichilia catigua is used for its neuroactive properties, such as neurostimulant, antioxidant and anti-neuroinflammatory, while Turnera diffusa is traditionally used as a tonic in neurasthenia. Both species are known to be rich in flavonoids.

AIM OF THE STUDY

To study aqueous extracts of T. catigua and T. diffusa in terms of their antioxidant and antiglycation effects, inhibition of tyrosinase activity, and interaction with enzymes and pathways engaged in neuroinflammation. Moreover, whenever possible, to establish a relationship between the studied activities and the traditional usage of the species.

MATERIALS AND METHODS

The phenolic profiles of the aqueous extracts were validated by HPLC-DAD. The effect of the extracts over mushroom tyrosinase and 5-lipoxygenase activities, as well as their capacity to impair bovine serum albumin glycation, were assessed by in vitro assays. The anti-neuroinflammatory potential of the same extracts was evaluated by their capacity to mitigate the pro-inflammatory stimulus induced in BV-2 microglia cells by interferon-gamma.

RESULTS

T. catigua extract, a rich mixture of phenolic acids, catechins and flavonolignans, excels by its ability to decrease lipid peroxidation (EC₅₀ = 227.18 ± 9.04 μg/mL), and to work as anti-glycation agent, and inhibitor of both tyrosinase and 5-lipoxigenase (IC₅₀ = 358.84 ± 19.05 and 56.25 ± 14.53 μg/mL, respectively). However, only T. diffusa extract, mainly composed by luteolin derivatives, is able to lower NO production by BV-2 microglia cells stimulated with interferon-gamma, despite its lower activities in the other assays.

CONCLUSIONS

Overall, this work highlights the value of medicinal plant extracts as sources of bioactive flavonoid-rich extracts with neuroactive effects. Furthermore, these results support their application as alternative strategies to develop functional foods and therapeutics to fight chronic neurodegenerative disorders.

Diet during early life defines testicular lipid content and sperm quality in adulthood

Childhood obesity is a serious concern associated with ill health later in life. Emerging data suggest that obesity has long-term adverse effects upon male sexual and reproductive health, but few studies have addressed this issue. We hypothesized that exposure to high-fat diet during early life alters testicular lipid content and metabolism, leading to permanent damage to sperm parameters. After weaning (day 21 after birth), 36 male mice were randomly divided into three groups and fed with a different diet regimen for 200 days: a standard chow diet (CTRL), a high-fat diet (HFD) (carbohydrate: 35.7%, protein: 20.5%, and fat: 36.0%), and a high-fat diet for 60 days, then replaced by standard chow (HFD_t). Biometric and metabolic data were monitored. Animals were then euthanized, and tissues were collected. Epididymal sperm parameters and endocrine parameters were evaluated. Testicular metabolites were extracted and characterized by 1H-NMR and GC-MS. Testicular mitochondrial and antioxidant activity were evaluated. Our results show that mice fed with a high-fat diet, even if only until early adulthood, had lower sperm viability and motility, and higher incidence of head and tail defects. Although diet reversion with weight loss during adulthood prevents the progression of metabolic syndrome, testicular content in fatty acids is irreversibly affected. Excessive fat intake promoted an overaccumulation of proinflammatory n-6 polyunsaturated fatty acids in the testis, which is strongly correlated with negative effects upon sperm quality. Therefore, the adoption of high-fat diets during early life correlates with irreversible changes in testicular lipid content and metabolism, which are related to permanent damage to sperm quality later in life.

Parabens enhance the calcium-dependent testicular mitochondrial permeability transition: Their relevance on the reproductive capacity in male animals

Parabens, alkyl ester derivatives from p-hydroxybenzoic acid, are extensively used as antimicrobial preservatives. Nonetheless, due to its widespread and massive employment, several studies highlighted the association between parabens and alterations in the reproductive system. This study aimed to relate the adverse effect of the most commonly used parabens in testis mitochondria with male fertility. From all the parabens used, propyl and butyl were the ones that most negatively decreased the respiratory control ratio. In the case of butyl, inhibitions of 20% and 60% were observed, respectively, at the lowest and highest concentration, when compared to the control group. The membrane potential was only significantly affected by propyl (14%) and butyl (31%), and at a concentration of 250 µM. Succinate dehydrogenase, cytochrome c oxidase, and ATPase activities showed a nonsignificant decrease. Cytochrome c reductase, on the other hand, showed statistically significant inhibitions for both propyl (56%) and butylparaben (55%). The susceptibility to the mitochondrial permeability transition pore (MPTP) opening was increased by all parabens, although this increase was markedly significant for propyl and butyl. These results show that the susceptibility of mitochondria to parabens is dependent on the alkyl chain length and parabens hydrophobicity, and the main mitochondrial target is Complex II-III and MPTP. Hence, this study demonstrates the contribution of parabens exposition to the inhibition of testis mitochondrial function and their putative noxious effect on the male reproductive system.

Adding value to polyvinylpolypyrrolidone winery residue: A resource of polyphenols with neuroprotective effects and ability to modulate type 2 diabetes-relevant enzymes

A polyphenols-rich extract was obtained from polyvinylpolypyrrolidone (PVPP) winery residue, and its neuroprotective effects and ability to modulate the kinetics of type 2 diabetes-relevant enzymes were characterized. The PVPP-white wine extract is a mixture of polyphenols (840.08 ± 161.25 µg/mg, dry weight) dominated by proanthocyanidins and hydroxycinnamic acids, affording strong antioxidant activity, as detected by the protection of membrane lipids against oxidation and superoxide radical anion scavenging activity. Regarding type 2 diabetes framework, the extract inhibits α-glucosidase (K_i = 166.9 µg/mL) and aldose reductase (K_i = 127.5 µg/mL) through non-competitive mechanisms. Despite the modest ability to inhibit rat brain acetylcholinesterase, it protects neuronal SH-SY5Y cells against oxidative damage promoted by glutamate, decreasing reactive oxygen species generation and preserving cell redox state. Thus, PVPP-white wine extract has potential to support the development of functional foods and/or nutraceuticals aiming neuroprotection and glucose homeostasis regulation, with high relevance in Alzheimeŕs disease and type 2 diabetes interlink.

Extraction of phospholipid-rich fractions from egg yolk and development of liposomes entrapping a dietary polyphenol with neuroactive potential

A new protocol to obtain egg yolk phospholipids in ethanol is presented. Rutin-phospholipids nanoliposomes were prepared and characterized. The procedure takes advantage of the different solubility of egg yolk lipids in ethanol and acetone at low temperature, to efficiently obtain a phospholipid-rich fraction of high purity degree. The phospholipid content in the final fraction is 208.65 ± 26.46 μmol/g fresh egg yolk (16%), accounting for ca. 96% of the extract's dry weight. The phospholipid-rich fraction contains cholesterol (0.069-0.082 cholesterol/phospholipid molar ratio), and vestigial amounts of lutein and zeaxanthin (89.24 ± 9.76 and 14.9 ± 2.16 ng/g of fresh egg yolk, respectively). Saturated fatty acids dominate the extracted phospholipids (50% of egg's total yolk phospholipids), the levels of monounsaturated ranging from 20 to 25%, and polyunsaturated up to 35%. Rutin-liposomes, prepared with phospholipid-rich fraction, presented mean diameter <140 nm, negative surface charge (Zeta potential ~ -13 mV), and entrapment efficiency of rutin up to 87%. In human neuroblastoma cell line SH-SY5Y, rutin-liposomes (lipid 25 μM + rutin 16.7 μM) attenuated glutamate-induced cytotoxicity, in part by reducing the formation of intracellular reactive species, pointing to their potential application as new functional neuroprotective agents.

Anti-Inflammatory Effects of 5α,8α-Epidioxycholest-6-en-3β-ol, a Steroidal Endoperoxide Isolated from Aplysia depilans, Based on Bioguided Fractionation and NMR Analysis

Sea hares of Aplysia genus are recognized as a source of a diverse range of metabolites. 5α,8α-Endoperoxides belong to a group of oxidized sterols commonly found in marine organisms and display several bioactivities, including antimicrobial, anti-tumor, and immunomodulatory properties. Herein we report the isolation of 5α,8α-epidioxycholest-6-en-3β-ol (EnP(5,8)) from Aplysia depilans Gmelin, based on bioguided fractionation and nuclear magnetic resonance (NMR) analysis, as well as the first disclosure of its anti-inflammatory properties. EnP(5,8) revealed capacity to decrease cellular nitric oxide (NO) levels in RAW 264.7 macrophages treated with lipopolysaccharide (LPS) by downregulation of the Nos2 (inducible nitric oxide synthase, iNOS) gene. Moreover, EnP(5,8) also inhibited the LPS-induced expression of cyclooxygenase-2 (COX-2), interleukin 6 (IL-6), and tumor necrosis factor alpha (TNF-α) at the mRNA and protein levels. Mild selective inhibition of COX-2 enzyme activity was also evidenced. Our findings provide evidence of EnP(5,8) as a potential lead drug molecule for the development of new anti-inflammatory agents.

Toxicity and structure-activity relationship (SAR) of α,β-dehydroamino acids against human cancer cell lines

A library of N-protected dehydroamino acids, namely dehydroalanine, dehydroaminobutyric acid and dehydrophenylalanine derivatives, was screened in three human cancer cell lines [(lung (A549), gastric (AGS) and neuroblastoma (SH-SY5Y)] in order to characterize their toxicological profile and identify new molecules with potential anticancer activity. Results showed N-protected dehydrophenylalanine and dehydroaminobutyric acid derivatives have no or low toxicity for all tested cell lines. The N-protected dehydroalanines exhibit significant toxic effects and the AGS and SH-SY5Y cells were significantly more vulnerable than A549 cells. Four α,β-dehydroalanine derivatives, with IC₅₀<62.5μM, were selected to investigate the pathways by which these compounds promote cell death. All compounds, at their IC₅₀ concentrations, were able to induce apoptosis in both AGS and SH-SY5Y cell lines. In both cell lines, loss of mitochondrial membrane potential (ΔΨm) was found and caspase activity was increased, namely endoplasmic reticulum-resident caspase-4 in AGS cells and caspase-3/7 in SH-SY5Y cells. When evaluated in a non-cancer cell line, the molecules displayed no to low toxicity, thus suggesting some degree of selectivity for cancer cells. The results indicate that α,β-dehydroalanine derivatives can be considered a future resource of compounds able to work as anticancer drugs.

Age-dependent biochemical dysfunction in skeletal muscle of triple-transgenic mouse model of Alzheimer`s disease

The emergence of Alzheimer`s disease as a systemic pathology shifted the research paradigm toward a better understanding of the molecular basis of the disease considering the pathophysiological changes in both brain and peripheral tissues. In the present study, we evaluated the impact of disease progression on physiological relevant features of skeletal muscle obtained from 3, 6 and 12 month-old 3xTg-AD mice, a model of Alzheimer`s disease, and respective agematched nonTg mice. Our results showed that skeletal muscle functionality is already affected in 3-month-old 3xTg-AD mice as evidenced by deficient acetylcholinesterase and catalase activities as well as by alterations in fatty acid composition of mitochondrial membranes. Additionally, an age-dependent accumulation of amyloid-β_1-40 peptide occurred in skeletal muscle of 3xTg-AD mice, an effect that preceded bioenergetics mitochondrial dysfunction, which was only detected at 12 months of age, characterized by decreased respiratory control ratio and ADP/O index and by an impairment of complex I activity. HPLC-MS/MS analyses revealed significant changes in phospholipid composition of skeletal muscle tissues from 3xTg-AD mice with 12 months of age when compared with age-matched nonTg mice. Increased levels of lyso-phosphatidylcholine associated with a decrease of phosphatidylcholine molecular species containing arachidonic acid were detected in 3xTg-AD mice, indicating an enhancement of phospholipase A₂ activity and skeletal muscle inflammation. Additionally, a decrease of phosphatidylethanolamine plasmalogens content and an increase in phosphatidylinositol levels was observed in 3xTg-AD mice when compared with age-matched nonTg mice. Altogether, these observations suggest that the skeletal muscle of 3xTg-AD mice are more prone to oxidative and inflammatory events.

Polymer encapsulated scorpionate Eu3+ complexes as novel hybrid materials for high performance luminescence applications

Tri-pyrazolyl methane europium complex, [Eu{HC(pz)₃}(H₂O)₆]Cl₃ with PMMA gel, PVA gel and HMS-PVA, have been synthesized and checked for unit mass luminescence emission and lifetime application.

Cardiolipin profile changes are associated to the early synaptic mitochondrial dysfunction in Alzheimer's disease

Brain mitochondria are fundamental to maintaining healthy functional brains, and their dysfunction is involved in age-related neurodegenerative disorders such as Alzheimer's disease (AD). In this study, we conducted a research on how both non-synaptic and synaptic mitochondrial functions are compromised at an early stage of AD-like pathologies and their correlation with putative changes on membranes lipid profile, using 3 month-old nontransgenic and 3xTg-AD mice, a murine model of experimental AD. Bioenergetic dysfunction in 3xTg-AD brains is evidenced by a decrease of brain ATP levels resulting, essentially, from synaptic mitochondria functionality disruption as indicated by declined respiratory control ratio associated with a 50% decreased complex I activity. Lipidomics studies revealed that synaptic bioenergetic deficit of 3xTg-AD brains is accompanied by alterations in the phospholipid composition of synaptic mitochondrial membranes, detected either in phospholipid class distribution or in the phospholipids molecular profile. Globally, diacyl- and lyso-phosphatidylcholine lipids increase while ethanolamine plasmalogens and cardiolipins content drops in relation to nontransgenic background. However, the main lipidomic mark of 3xTg-AD brains is that cardiolipin cluster-organized profile is lost in synaptic mitochondria due to a decline of the most representative molecular species. In contrast to synaptic mitochondria, results support the idea that non-synaptic mitochondria function is preserved at the age of 3 months. Although the genetically construed 3xTg-AD mouse model does not represent the most prevalent form of AD in humans, the present study provides insights into the earliest biochemical events in AD brain, connecting specific lipidomic changes with synaptic bioenergetic deficit that may contribute to the progressive synapses loss and the neurodegenerative process that characterizes AD.

Interaction of fullerene nanoparticles with biomembranes: from the partition in lipid membranes to effects on mitochondrial bioenergetics

Partition and localization of C60 and its derivative C60(OH)18-22 in lipid membranes and their impact on mitochondrial activity were studied, attempting to correlate those events with fullerene characteristics (size, surface chemistry, and surface charge). Fluorescence quenching studies suggested that C60(OH)18-22 preferentially populated the outer regions of the bilayer, whereas C60 preferred to localize in deeper regions of the bilayer. Partition coefficient values indicated that C60 exhibited higher affinity for dipalmitoylphosphatidylcholine and mitochondrial membranes than C60(OH)18-22. Both fullerenes affected the mitochondrial function, but the inhibitory effects promoted by C60 were more pronounced than those induced by C60(OH)18-22 (up to 20 nmol/mg of mitochondrial protein). State 3 and p-trifluoromethoxyphenylhydrazone-uncoupled respirations are inhibited by both fullerenes when glutamate/malate or succinate was used as substrate. Phosphorylation system and electron transport chain of mitochondria are affected by both fullerenes, but only C60 increased the inner mitochondrial membrane permeability to protons, suggesting perturbations in the structure and dynamics of that membrane. At concentrations of C60(OH)18-22 above 20 nmol/mg of mitochondrial protein, the activity of FoF1-ATP synthase was also decreased. The evaluation of transmembrane potential showed that the mitochondria phosphorylation cycle decreased upon adenosine diphosphate addition with increasing fullerenes concentration and the time of the repolarization phase increased as a function of C60(OH)18-22 concentration. Our results suggest that the balance between hydrophilicity and hydrophobicity resulting from the surface chemistry of fullerene nanoparticles, rather than the cluster size or the surface charge acquired by fullerenes in water, influences their membrane interactions and consequently their effects on mitochondrial bioenergetics.

Studies on the toxicity of an aqueous suspension of C60 nanoparticles using a bacterium (gen. Bacillus) and an aquatic plant (Lemna gibba) as in vitro model systems

The increasing use of C60 nanoparticles and the diversity of their applications in industry and medicine has led to their production in a large scale. C60 release into wastewaters and the possible accumulation in the environment has raised concerns about their ecotoxicological impact. In the present study, an aqueous suspension of C60 nanoparticles was prepared and its potential toxicity studied in laboratory, using a bacterium (Bacillus stearothermophilus) and an aquatic plant (Lemna gibba) as model systems. C60 nanoparticles inhibited the growth of L. gibba, in contrast to that of the bacterium. Consistently, the ultrastructure and respiratory activity of bacterial cells were not affected by C60, but the contents of chlorophylls a and b and chloroplast oxygen production decreased considerably in L. gibba. Altogether, our results suggest that C60 aqueous dispersions must be viewed as an environmental pollutant, potentially endangering the equilibrium of aquatic ecosystems.

Tacrine and its analogues impair mitochondrial function and bioenergetics: a lipidomic analysis in rat brain

Tacrine is an acetylcholinesterase (AChE) inhibitor used as a cognitive enhancer in the treatment of Alzheimer's disease (AD). However, its low therapeutic efficiency and a high incidence of side effects have limited its clinical use. In this study, the molecular mechanisms underlying the impact on brain activity of tacrine and two novel tacrine analogues (T1, T2) were approached by focusing on three aspects: (i) their effects on brain cholinesterase activity; (ii) perturbations on electron transport chain enzymes activities of non-synaptic brain mitochondria; and (iii) the role of mitochondrial lipidome changes induced by these compounds on mitochondrial bioenergetics. Brain effects were evaluated 18 h after the administration of a single dose (75.6 μmol/kg) of tacrine or tacrine analogues. The three compounds promoted a significant reduction in brain AChE and butyrylcholinesterase (BuChE) activities. Additionally, tacrine was shown to be more efficient in brain AChE inhibition than T2 tacrine analogue and less active than T1 tacrine analogue, whereas BuChE inhibition followed the order: T1 > T2 > tacrine. The studies using non-synaptic brain mitochondria show that all the compounds studied disturbed brain mitochondrial bioenergetics mainly via the inhibition of complex I activity. Furthermore, the activity of complex IV is also affected by tacrine and T1 treatments while FoF(1) -ATPase is only affected by tacrine. Therefore, the compounds' toxicity as regards brain mitochondria, which follows the order: tacrine >> T1 > T2, does not correlate with their ability to inhibit brain cholinesterase enzymes. Lipidomics approaches show that phosphatidylethanolamine (PE) is the most abundant phospholipids (PL) class in non-synaptic brain mitochondria and cardiolipin (CL) present the greatest diversity of molecular species. Tacrine induced significant perturbations in the mitochondrial PL profile, which were detected by means of changes in the relative abundance of phosphatidylcholine (PC), PE, phosphatidylinositol (PI) and CL and by the presence of oxidized phosphatidylserines. Additionally, in both the T1 and T2 groups, the lipid content and molecular composition of brain mitochondria PL are perturbed to a lesser extent than in the tacrine group. Abnormalities in CL content and the amount of oxidized phosphatidylserines were associated with significant reductions in mitochondrial enzymes activities, mainly complex I. These results indicate that tacrine and its analogues impair mitochondrial function and bioenergetics, thus compromising the activity of brain cells.

Toxicity assessment of the herbicide metolachlor comparative effects on bacterial and mitochondrial model systems

Metolachlor is one of the most intensively used chloroacetamide herbicides. However, its effects on the environment and on non-target animals and humans as well as its interference at a cell/molecular level have not yet been fully elucidated. The aim of this study was: firstly, to evaluate the potential toxicity of metolachlor at a cell/subcellular level by using two in vitro biological model systems (a strain of Bacillus stearothermophilus and rat liver mitochondria); secondly, to evaluate the relative sensibility of these models to xenobiotics to reinforce their suitability for pollutant toxicity assessment. Our results show that metolachlor inhibits growth and impairs the respiratory activity of B.stearothermophilus at concentrations two to three orders of magnitude higher than those at which bacterial cells are affected by other pesticides. Also at concentrations significantly higher than those of other pesticides, metolachlor depressed the respiratory control ratio, membrane potential and respiration of rat liver mitochondria when malate/glutamate or succinate were used as respiratory substrates. Moreover, metolachlor impaired the respiratory activity of rat liver mitochondria in the same concentration range at which it inhibited bacterial respiratory system (0.4-5.0 micromol/mg of protein). In conclusion, the high concentration range at which metolachlor induces toxicity in vitro suggests that this compound is safer than other pesticides previously studied in our laboratory, using the same model systems. The good parallelism between metolachlor effects on both models and the toxicity data described in the literature, together with results obtained in our laboratory with other compounds, indicate the suitability of these systems to assess toxicity in vitro.

Cerebrocrast promotes the cotransport of H+ and Cl- in rat liver mitochondria

Considering that cerebrocrast stimulates oligomycin-inhibited state 3 respiration simultaneously with mitochondrial transmembrane potential (Deltapsi) dissipation, the mechanism underlying the uncoupler activity of cerebrocrast was assessed by its ability to permeabilize the mitochondrial inner membrane to H(+) or to K(+) or to cotransport anions with H(+). The partition coefficient of cerebrocrast in mitochondrial membrane and its ability to act as a membrane-active compound disturbing membrane lipid organization were also investigated. Cerebrocrast induced no permeabilization of mitochondrial inner membrane to H(+) or K(+), but it was able to transport H(+) in association with Cl(-). Cerebrocrast showed a strong incorporation into the mitochondrial membrane, with a partition coefficient (Kp(m/w)) of 2.7(+/-0.1)x10(5). Cerebrocrast also reduced, in a concentration dependent manner, the phase transition temperature, the cooperative unit size, and the enthalpy associated with the phase transition temperature of DMPC membrane bilayers. It was concluded that the uncoupler activity of cerebrocrast is due to its ability to promote the cotransport of H(+) with Cl(-) through the rat liver mitochondrial inner membrane, and that this cerebrocrast mechanism of action may be potentiated by alterations of membrane lipid organization and membrane lateral heterogeneity.

Differential effects induced by alpha- and beta-endosulfan in lipid bilayer organization are reflected in proton permeability

The effects of two insecticides isomers, alpha- and beta-endosulfan, on the passive proton permeability of large unilamellar vesicles (LUV) reconstituted with dipalmitoylphosphatidylcholine (DPPC) or mitochondrial lipids were reported. In DPPC (LUV) gel phase, at 30 degrees C, the global kinetic constant (K) of proton permeability (proportional to the proton permeability) initially increased slightly with the increase of alpha-endosulfan/lipid molar ratio up to 0.143. In the range from 0.143 to 0.286, a discontinuity in the increment occurred and, above this range, the proton permeability increased substantially. In DPPC fluid phase, at 48 degrees C, the proton permeability showed a behavior identical to that observed in gel DPPC, with a sharp increase for alpha-endosulfan/lipid molar ratios ranging from 0.143 to 0.286. At these and higher concentrations, alpha-endosulfan induced phase separation in the plane of DPPC membranes, as revealed by differential scanning calorimetry (DSC). Conversely to alpha-endosulfan, beta-endosulfan induced only a slight increase in the proton permeability, either in the fluid or the gel phase of DPPC, for all beta-endosulfan/lipid molar ratios tested. Additionally, the effects of the endosulfan isomers on the proton permeability of mitochondrial fluid lipid dispersions, at 37 degrees C, are similar to those described for DPPC. The beta-isomer induced a very small effect, and alpha-endosulfan, at low concentrations, increased slightly the proton permeability, but for insecticide/lipid molar ratios above 0.143 the permeability increased substantially. Consequently, the membrane physical state of synthetic and native lipid dispersions, as affected by the structural features of alpha- and beta-endosulfan, influenced the proton permeability. The effects here observed in vitro suggest that the formation of lateral membrane domains may underlay the biological activity of alpha-endosulfan in vivo, contributing to its higher degree of toxicity as compared with beta-endosulfan.

Cholesterol modulates amiodarone-membrane interactions in model and native membranes

The effects of cholesterol, a lipid mostly found in the sarcolemmal membranes, on the interaction of amiodarone with synthetic models of dimyristoylphosphatidylcholine (DMPC) and with native models of mitochondria and brain microsomes was studied. Alterations on the structural order of lipids were assessed by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) probing the bilayer core, and of the propionic acid derivative 3-(p-(6-phenyl)-1,3,5-hexatrienyl)phenylpropionic acid (DPH-PA) probing the outer regions of the bilayer. As detected by the probes and according to classic observations, cholesterol progressively increased the molecular order in the fluid phase of DMPC. Additionally, it modulated the type and extension of amiodarone effects. For low cholesterol concentrations (< or =10-15 mol%), amiodarone (50 microM) ordered DMPC bilayers and the effects were almost identical to those observed in pure DMPC. For higher cholesterol concentrations, amiodarone ordering effects decreased slightly and faded for cholesterol concentrations as high as 25 and 30 mol%, when detected by DPH-PA and DPH, respectively. Above these high cholesterol concentrations, a crossover from ordering to disordering effects of amiodarone was apparent, either in the upper region of the bilayer or the hydrophobic core. The effects of amiodarone in native membranes of mitochondria and brain microsomes, in which "native" cholesterol accounts for about 0 and 25 mol%, respectively, correlated reasonably with the results in models of synthetic lipids. There is a close relationship between cholesterol concentration and amiodarone effects, in either synthetic models or native model membranes. Therefore, it may be predicted that the lipid physicochemical properties regulated by cholesterol concentration will also modulate the effects of amiodarone in sarcolemma.

Ethylazinphos interaction with membrane lipid organization induces increase of proton permeability and impairment of mitochondrial bioenergetic functions

Ethylazinphos increases the passive proton permeability of lipid bilayers reconstituted with dipalmitoylphosphatidylcholine (DPPC) and mitochondrial lipids. A sharp increase of proton permeability is detected at insecticide/lipid molar ratios identical to those inducing phase separation in the plane of DPPC bilayers, as revealed by differential scanning calorimetry (DSC). Ethylazinphos progressively depresses the transmembrane potential (DeltaPsi) of mitochondria supported by piruvate/malate, succinate, or ascorbate/TMPD. Additionally, a decreased depolarization induced by ADP depends on ethylazinphos concentration, reflecting a phosphorylation depression. This loss of phosphorylation is a consequence of a decreased DeltaPsi. A decreased respiratory control ratio is also observed, since ethylazinphos stimulates state 4 respiration and inhibits ADP-stimulated respiration (state 3). Ethylazinphos concentrations up to 100 nmol/mg mitochondrial protein increase the rate of state 4 together with a decrease in DeltaPsi, without significant perturbation of state 3 and carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP)-uncoupled respiration. For increased insecticide concentrations, the state 3 and FCCP-uncoupled respiration are inhibited to approximately the same extent. The perturbations are more pronounced when the energization is supported by pyruvate/malate and less effective when succinate is used as substrate. The present data, in association with previous DSC studies, indicate that ethylazinphos, at concentrations up to 100 nmol/mg mitochondrial protein, interacts with the lipid bilayer of mitochondrial membrane, changing the lipid organization and increasing the proton permeability of the inner membrane. The increased proton permeability explains the decreased oxidative phosphorylation coupling. Resulting disturbed ATP synthesis may significantly underlie the mechanisms of ethylazinphos toxicity, since most of cell energy in eukaryotes is provided by mitochondria.

Changes induced by malathion, methylparathion and parathion on membrane lipid physicochemical properties correlate with their toxicity

Perturbations induced by malathion, methylparathion and parathion on the physicochemical properties of dipalmitoylphosphatidylcholine (DPPC) were studied by fluorescence anisotropy of DPH and DPH-PA and by differential scanning calorimetry (DSC). Methylparathion and parathion (50 microM) increased the fluorescence anisotropy evaluated by DPH-PA and DPH, either in gel or in the fluid phase of DPPC bilayers, but mainly in the fluid phase. Parathion is more effective than methylparathion. On the other hand, malathion had almost no effect. All the three xenobiotics displaced the phase transition midpoint to lower temperature values and broadened the phase transition profile of DPPC, the effectiveness following the sequence: parathion>methylparathion>>malathion. A shifting and broadening of the phase transition was also observed by DSC. Furthermore, at methylparathion/lipid molar ratio of 1/2 and at parathion/lipid molar ratio of 1/7, the DSC thermograms displayed a shoulder in the main peak, in the low temperature side, suggesting coexistence of phases. For higher ratios, the phase transition profile becomes sharp as the control transition, but the midpoint is shifted to the previous shoulder position. Conversely to methylparathion and parathion, malathion did not promote phase separation. The overall data from fluorescence anisotropy and calorimetry indicate that the degree of effect of the insecticides on the physicochemical membrane properties correlates with toxicity to mammals. Therefore, the in vivo effects of organophosphorus compounds may be in part related with their ability to perturb the phospholipid bilayer structure, whose integrity is essential for normal cell function.

Perturbations induced by alpha- and beta-endosulfan in lipid membranes: a DSC and fluorescence polarization study

The interaction of alpha- and beta-endosulfan isomers with lipid bilayers was searched by differential scanning calorimetry (DSC) and fluorescence polarization of 2-, 6- and 12-(9-anthroyloxy) stearic acids (2-AS, 6-AS and 12-AS) and 16-(9-anthroyloxy) palmitic acid (16-AP). Both endosulfan isomers, at insecticide/lipid molar ratios ranging from 1/40 to 1/1, shift the phase transition midpoint to lower temperature values and broaden the transition profile of dipalmitoylphosphatidylcholine (DPPC) bilayers. At insecticide/lipid molar ratios of 1/40, the isomers fully abolish the bilayer pretransition. Conversely to beta-endosulfan, alpha-endosulfan promotes a new phase transition, centered at 35.4 degrees C, in addition to the main phase transition of DPPC. Therefore, the alpha-isomer may undergo a heterogeneous distribution in separate domains in the plane of the membrane, whereas the beta-isomer may undergo a homogeneous distribution. Fluorescence polarization data indicate that alpha-endosulfan increases the lipid structural order in the regions probed by 2-AS and decreases it in the regions probed by 6-AS, 12-AS and 16-AP. On the other hand, the beta-isomer produces disordering effects in the upper regions of the bilayers, probed by 2-AS, and ordering in deeper regions, probed by 6-AS, 12-AS and 16-AP, mainly in the gel phase. The incorporation of cholesterol into DPPC bilayers progressively decreases the effects of beta-isomer which are vanished at 20 mol% cholesterol. However, this and higher cholesterol concentrations did not prevent alpha-endosulfan membrane interaction, as revealed by DSC and fluorescence polarization. The distinct effects promoted by alpha- and beta-endosulfan are discussed in terms of molecular orientation and positioning within the bilayer. Apparently, the alpha-isomer preferentially locates closer to the phospholipid headgroups whereas the beta-isomer distributes in deeper domains of the bilayer.

Biophysical perturbations induced by ethylazinphos in lipid membranes

Perturbations induced by ethylazinphos on the physical organization of dipalmitoylphosphatidylcholine (DPPC) and DPPC/cholesterol membranes were studied by differential scanning calorimetry (DSC) and fluorescence polarization of 2-, 6-, 12-(9-anthroyloxy) stearic acids and 16-(9-anthroyloxy) palmitic acid. Ethylazinphos (50 and 100 microM) increases the fluorescence polarization of the probes, either in the gel or in the fluid phase of DPPC bilayers, and this concentration dependent effect decreases from the surface to the bilayer core. Additionally, the insecticide displaces the phase transition to a lower temperature range and broadens the transition profile of DPPC. A shifting and broadening of the phase transition is also observed by DSC. Furthermore at insecticide/lipid molar ratios higher than 1/7, DSC thermograms, in addition to the normal transition centered at 41 degrees C, also display a new phase transition centered at 45.5 degrees C. The enthalpy of this new transition increases with insecticide concentration, with a corresponding decrease of the main transition enthalpy. Ethylazinphos in DPPC bilayers with low cholesterol (< or = 20 mol%) perturbs the membrane organization as described above for pure DPPC. However, cholesterol concentrations higher than 20 mol% prevent insecticide interaction, as revealed by fluorescence polarization and DSC data. Apparently, cholesterol significantly modulates insecticide interaction by competition for similar distribution domains in the membrane. The present results strongly support our previous hypothesis that ethylazinphos locates in the cooperativity region, i.e. the region of C1-C9 atoms of the acyl chains, and extends to the lipid-water interface, where it increases lipid packing order sensed across all the thickness of the bilayer. Additionally, and, on the basis of DSC data, a lateral regionalization of ethylazinphos is here tentatively suggested.

Interaction of ethylazinphos with the physical organization of model and native membranes

The interaction of ethylazinphos with the physical organization of model and native membranes was investigated by means of fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) and of its propionic acid derivative (DPH-PA). Ethylazinphos shifts the phase transition midpoint to lower temperature values and broadens the phase transition profile of bilayers reconstituted with dimyristoyl-, dipalmitoyl- and distearoylphosphatidylcholines (DMPC, DPPC, DSPC), as detected by DPH and DPH-PA. Additionally, both probes detect significant effects of ethylazinphos in the fluid phase of the above lipid bilayers. The insecticide perturbations are more pronounced in bilayers of short-chain lipids, e.g., DMPC, in correlation with the higher partition in these membranes. On the other hand, the insecticide increases to some extent the ordering promoted by cholesterol in the fluid phase of DMPC, but high cholesterol concentrations (> or = 30 mol%) almost prevent insecticide interaction, as revealed by DPH and DPH-PA. In agreement with the results in models of synthetic lipids, the increase of intrinsic cholesterol in fluid native membranes depresses the partition values of ethylazinphos and consequently its effects.

Partition of DDE in synthetic and native membranes determined by ultraviolet derivative spectroscopy

Partition coefficients of DDE (2,2-bis(p-chlorophenyl)-1,1-dichloroethylene) were determined, in model and native membranes, as a function of temperature, lipid chain length, cholesterol content and DDE concentration, by means of second derivative ultraviolet spectrophotometry. DDE incorporation increases with the temperature, since the partition values in dimyristoylphosphatidylcholine (DMPC), at 24, 30 and 37 degrees C, are 5722 +/- 138, 10356 +/- 763 and 14006 +/- 740, respectively. The insecticide incorporates better into bilayers of DMPC as compared with DPPC (dipalmitoylphosphatidylcholine). The partition decreases from 10355 +/- 763 in DMPC to 6432 +/- 613 in DPPC, at temperatures 5-7 degrees C above the midpoint of their transitions. The addition of cholesterol to fluid membranes of DMPC depresses the partition of DDE. In agreement with the results in models of synthetic lipids, the partition of DDE into native membranes increases with the temperature and decreases with the intrinsic cholesterol. It is concluded that a fluid membrane favors the accumulation of DDE.

Amiodarone effects on membrane organization evaluated by fluorescence polarization

The effects of amiodarone (0-100 microM) on the physical state of synthetic and native membranes were investigated by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH), probing the bilayer core, and of its anionic propionic acid derivative (DPH-PA), probing the outer regions of the bilayer. In the gel phase of dimyristoylphosphatidylcholine (DMPC) bilayers, amiodarone broadens the transition profile and shifts the phase transition midpoint to lower temperature values, as evaluated by both probes. On the other hand, the drug orders the fluid phase of the lipid either in hydrophobic core or in the outer regions of the bilayer, as detected by DPH and DPH-PA, respectively. The effects of amiodarone on the thermotropic behaviour of DPPC confirm and extend data in DMPC. Cholesterol concentration modulates to a great extent the effects of amiodarone in the fluid phase of DMPC. Thus, both probes, DPH and DPH-PA, detect either ordering effects of amiodarone for low cholesterol concentrations (< or = 20 mol%) or disordering amiodarone effects at higher cholesterol levels (> 20 mol%). In agreement with the results in models of synthetic lipids, the ordering effects of amiodarone in fluid native membranes of mitochondria and brain microsomes are depressed with the increase in intrinsic cholesterol. The ordering effects in mitochondria may induce bioenergetic dysfunctions and consequently disturbances in the electromechanic functioning of myocardium.

Effects of parathion on membrane organization and its implications for the mechanisms of toxicity

The effects of the organophosphorus insecticide parathion (O,O-diethyl O-(p-nitrophenyl)phosphorothioate) on the physical state of synthetic and native membranes was investigated by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH), probing the bilayer core, and by its anionic propionic acid derivative (DPH-PA), probing the outer regions of the bilayer. Parathion disorders the gel phase of liposomes reconstituted with dimyristoylphosphatidylcholine (DMPC), broadening the transition profile and shifting the temperature midpoint of the phase transition, as detected by both probes. The insecticide strongly orders the fluid phase either in the hydrophobic core or in the outer regions of the membrane, as evaluated by DPH and DPH-PA, respectively. These ordering effects of parathion were further confirmed in fluid models of egg-yolk phosphatidylcholine. Parathion increases to some extent the ordering promoted by cholesterol in DMPC bilayers, but high cholesterol concentrations (> or = 30 mol%) prevent parathion interaction. The results in native membranes correlate reasonably with those obtained in models of synthetic lipids. Thus, parathion does not exert detectable effects in cholesterol-rich membranes, namely, erythrocytes, but moderate ordering effects of parathion are detected by both probes in brain microsomes, i.e., membranes with a lower content of cholesterol. Again, in agreement with the models of synthetic lipids, pronounced ordering effects of parathion are detected in cholesterol-poor membranes, e.g., sarcoplasmic reticulum and mitochondria.