Cholesterol oxidation products and their biological importance

Investigating the stability of RNA-lipid nanoparticles in biological fluids: Unveiling its crucial role for understanding LNP performance

Lipid nanoparticles (LNPs) are the most established and clinically advanced platform for RNA delivery. While significant efforts have been made to improve RNA delivery efficiency for improved protein production, the interplay between physiological stability, target specificity, and therapeutic efficacy of RNA-LNPs remains largely unexplored. This review highlights the crucial, yet often overlooked, impact of in vivo stability or instability of RNA-LNPs in contact with biological fluids on delivery performance. We discuss the various factors, including lipid composition, particle surface properties and interactions with proteins in physiological conditions, and provide an overview of the current methods for assessing RNA-LNP stability in biological fluids, such as dynamic laser light scattering, liquid chromatography, and fluorescent and radiolabeled techniques. In the final part, we propose strategies for enhancing stability, with a focus on shielding lipids. Therefore, this work highlights the importance of investigating and understanding the balance between stability and instability of LNPs in the biological context to achieve a more meaningful correlation between formulation properties and in vivo performance.

Disrupted homeostasis in sickle cells: Expanding the comprehension of metabolism adaptation and related therapeutic strategies

Sickle cell disease (SCD) is a hereditary hemolytic anemia associated with the alteration of the membrane composition of the sickle erythrocytes, the loss of glycolysis, dysregulation of the pyruvate phosphatase pathway, and changes in nucleotide metabolism of the sickle red blood cell (RBC). This review provides a comprehensive overview of the impact of the presence of Hb S, which leads to the disruption of the normal RBC metabolism. The intricate interplay between the redox and energetic balance in erythrocytic cells, where the glycolysis, pentose phosphate pathway, and methemoglobin reductase pathways are all altered in sickle RBC, is a key focus. Moreover, this review summarizes the current knowledge about the disease-modifying agents and their action mechanisms based on the sickle RBC alterations previously mentioned (i.e., their association with beneficial effects on the sickle cells' membrane, to their RBCs' energy metabolism, and to their oxidative status). Therefore, providing a comprehensive understanding of how sickle cells cope with the disruption of metabolic homeostasis and the most promising therapeutic agents able to ameliorate the various consequences of abnormal sickle RBC alterations.

Associations between plasma 24(S)-Hydroxycholesterol and neuropsychological profile in Fragile X Syndrome

Fragile X Syndrome (FXS) is caused by mutations in the fragile X mental retardation 1 gene, characterized by low plasma cholesterol levels. Considering the essential role of brain cholesterol in signaling and synaptogenesis, it is important to screen for brain cholesterol abnormalities in FXS and explore their link with neuropsychological profiles. Brain cholesterol is synthesized in situ, and the excess is primarily converted to 24(S)-hydroxycholesterol (24(S)-OHC). 27-hydroxycholesterol (27-OHC) is the major cholesterol oxidation metabolite that crosses the blood-brain barrier from peripheral circulation into the brain Plasma levels of 24(S)-OHC and 27-OHC were quantified in FXS and control individuals. The FXS group underwent transcranial magnetic stimulation to evaluate corticospinal excitability and inhibition. The clinical profile was assessed using questionnaires evaluating specific symptoms related to autism, aberrant behaviors, and anxiety. Study results show a significant decrease in plasma levels of 24(S)-OHC in FXS as compared to controls (78.48 nM ± 20.90 vs 99.53 nM ± 32.30; p = 0.006). Moreover, a negative correlation was observed between plasma levels of 24(S)-OHC and Motor-Evoked Potential (rs = -0.57; p = 0.05) in FXS. Similarly, a negative correlation was also found between plasma levels of 24(S)-OHC and the total score of the Social Communication Questionnaire (rs = - 0.72; p = 0.002) and the Anxiety Depression and Mood Scale (rs = - 0.61; p = 0.02). The 24(S)-OHC is associated with specific neurophysiological and behavioral characteristics in individuals with FXS. Larger studies are warranted to confirm the potential of 24(S)-OHC as a reliable biomarker for FXS.

A panel of altered blood oxysterols in patients with mild cognitive impairment: A novel combined diagnostic marker

Perturbed cholesterol metabolism may play an important role in the development of dementia and its preclinical stage, mild cognitive impairment (MCI). Oxysterols, the metabolites generated during cholesterol oxidation, also appear to be risk factors for MCI. Therefore, we aimed to investigate if the metabolic profile of blood oxysterols could be used to characterize MCI risk. This cross-sectional study incorporated 501 participants-253 patients with MCI and 248 cognitively normal controls. Serum levels of 22 free oxysterols were measured, and a set of 27 oxysterol-related gene polymorphisms was genotyped. Five [27-hydroxycholesterol (27-OHC), 27-OHC periphery-derived metabolite 3β-hydroxy-5-cholestenoic acid (27-CA) and brain-derived metabolite 7α-hydroxy-3-oxo-4-cholestenoic acid (7-HOCA), 4β-hydroxycholesterol (4β-OHC); 4α-hydroxycholesterol (4α-OHC)] of the twenty-two oxysterols detected in serum significantly differed between the patients with MCI and controls, greatly distinguishing patients with MCI from control individuals (AUC=0.834, 95 % CI: 0.804-0.866). Association analyses demonstrated significant correlations between these candidate oxysterol biomarkers with younger age, higher blood lipids, worse cognitive performance, and higher monounsaturated fatty acid intake. This panel of serum free oxysterols as candidate serum oxysterol biomarkers for MCI highlighted the essential role of 27-OHC in the pathogenesis of early dementia prevention. (The study registered in the Chinese Clinical Trial Registry as ChiCTR-OOC-17011882).

Targeting the mevalonate pathway potentiates NUAK1 inhibition-induced immunogenic cell death and antitumor immunity

The induction of immunogenic cell death (ICD) impedes tumor progression via both tumor cell-intrinsic and -extrinsic mechanisms, representing a robust therapeutic strategy. However, ICD-targeted therapy remains to be explored and optimized. Through kinome-wide CRISPR-Cas9 screen, NUAK family SNF1-like kinase 1 (NUAK1) is identified as a potential target. The ICD-provoking effect of NUAK1 inhibition depends on the production of reactive oxygen species (ROS), consequent to the downregulation of nuclear factor erythroid 2-related factor 2 (NRF2)-mediated antioxidant gene expression. Moreover, the mevalonate pathway/cholesterol biosynthesis, activated by spliced form of X-box binding protein 1 (XBP1s) downstream of ICD-induced endoplasmic reticulum (ER) stress, functions as a negative feedback mechanism. Targeting the mevalonate pathway with CRISPR knockout or the 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) inhibitor simvastatin amplifies NUAK1 inhibition-mediated ICD and antitumor activity, while cholesterol dampens ROS and ICD, and therefore also dampens tumor suppression. The combination of NUAK1 inhibitor and statin enhances the efficacy of anti-PD-1 therapy. Collectively, our study unveils the promise of blocking the mevalonate-cholesterol pathway in conjunction with ICD-targeted immunotherapy.

Interactions Determining Stereoselectivity in Two-Dimensional Systems─The Case of 22-Hydroxycholesterol Epimers

Oxidized derivatives of cholesterol play an important role in the functioning of biomembranes. Unlike other biomolecules, which are physiologically active in only one enantiomeric form, some oxysterols exist endogenously as two stereoisomers that exhibit strictly different biological effects. In this paper, we focused our attention on 22-hydroxycholesterol (22-OH) epimers, 22(R)-OH and 22(S)-OH, and examined their properties in Langmuir monolayers spread at the air/water interface, using classical surface manometry complemented with Brewster angle microscopy (BAM) images of the film texture. The studied epimers showed quite different monolayer characteristics. Namely, 22(S)-OH formed homogeneous, condensed monolayers of high collapse pressure, while 22(R)-OH films were more disordered and expanded with quite low collapse pressure. Interestingly, the latter compound showed in the course of the surface pressure-molecular area isotherm a temperature-dependent plateau transition, characterized by the coexistence of domains of molecules with different inclinations, visible in BAM images as patches of varying brightness. Molecular dynamics (MD) simulations confirmed this and revealed that the greater structural variability of 22(R)-OH is due to the greater hydration of the oxygen atom at C(22) compared to the other epimer. Next, we tested whether 22-OH epimers could differentiate interactions with sphingomyelin (SM). Although the strength of interaction with SM was similar for both epimers, the composition of the films corresponding to this minimum was different. With the aid of MD, it was found that these differences result directly from the interplay between 22-OH molecules and their ability for hydrogen bond formation. Therefore, the stereochemistry of oxysterols seems to play a crucial role in the overall structural organization of the membrane.

Interactions of sphingomyelin with biologically crucial side chain-hydroxylated cholesterol derivatives

Oxysterols are interesting molecules due to their dual nature, reflecting beneficial and harmful effects on the body. An issue that still needs to be solved is how slight modification of their structure owing to the location of the additional polar group in the molecules affects their biological activity. With this in mind, we selected three side chain-hydroxylated oxysterols namely: 20(S)-hydroxycholesterol (20(S)-OH), 24(S)-hydroxycholesterol (24(S)-OH), and 27-hydroxycholesterol (27-OH), and examined their behavior in mixtures with the bioactive sphingolipid - sphingomyelin (SM). Our research was based on the Langmuir monolayer technique supplemented with molecular dynamics (MD) and microscopic observation of the films texture (Brewster angle microscopy, BAM, and atomic force microscopy, AFM). Additionally, since 20(S)-hydroxycholesterol has not been studied so far, we thoroughly characterized this oxysterol in one-component monolayers. Our studies showed differences in the interactions of the studied oxysterols and sphingomyelin. Namely, it was found that 20(S)-OH binds to SM, unlike 24(S)-OH and 27-OH, which both weakly interact with SM. This distinct behavior was interpreted within the molecular dynamics as being due to weak intermolecular interactions between 20(S)-OH molecules, which allowed easy incorporation of SM into the 20(S)-OH monolayer. In contrast, the strong oxysterol-oxysterol interactions occurring in monolayers with 24(S)-OH or 27-OH make this process more difficult. This may be important in the process of bone formation/resorption. Other aspects derived from our study are: (i) the tendency of oxysterols to incorporate into lipid rafts (leading to their modification in structure and function), as well as (ii) the formation of multilayer structures, in which oxysterols are arranged in the characteristic forms of "strings of beads", which may facilitate their transport across the membrane.

Hepatic retinol dehydrogenase 11 dampens stress associated with the maintenance of cellular cholesterol levels

OBJECTIVE

Dysregulation of hepatic cholesterol metabolism can contribute to elevated circulating cholesterol levels, which is a significant risk factor for cardiovascular disease. Cholesterol homeostasis in mammalian cells is tightly regulated by an integrated network of transcriptional and post-transcriptional signalling pathways. Whilst prior studies have identified many of the central regulators of these pathways, the extended supporting networks remain to be fully elucidated.

METHODS

Here, we leveraged an integrated discovery platform, combining multi-omics data from 107 strains of mice to investigate these supporting networks. We identified retinol dehydrogenase 11 (RDH11; also known as SCALD) as a novel protein associated with cholesterol metabolism. Prior studies have suggested that RDH11 may be regulated by alterations in cellular cholesterol status, but its specific roles in this pathway are mostly unknown.

RESULTS

Here, we show that mice fed a Western diet (high fat, high cholesterol) exhibited a significant reduction in hepatic Rdh11 mRNA expression. Conversely, mice treated with a statin (3-hydroxy-3-methyl-glutaryl-coenzyme A reductase (HMGCR) inhibitor) exhibited a 2-fold increase in hepatic Rdh11 mRNA expression. Studies in human and mouse hepatocytes demonstrated that RDH11 expression was regulated by altered cellular cholesterol conditions in a manner consistent with SREBP2 target genes HMGCR and LDLR. Modulation of RDH11 in vitro and in vivo demonstrated modulation of pathways associated with cholesterol metabolism, inflammation and cellular stress. Finally, RDH11 silencing in mouse liver was associated with a reduction in hepatic cardiolipin abundance and a concomitant reduction in the abundance of proteins of the mitochondrial electron transport chain.

CONCLUSION

Taken together, these findings suggest that RDH11 likely plays a role in protecting cells against the cellular toxicity that can arise as a by-product of endogenous cellular cholesterol synthesis.

Formulation of lipid nanoparticles containing ginsenoside Rg2 and protopanaxadiol for highly efficient delivery of mRNA

Lipid nanoparticles (LNPs) are widely recognized as crucial carriers of mRNA in therapeutic and vaccine development. The typical lipid composition of mRNA-LNP systems includes an ionizable lipid, a helper lipid, a polyethylene glycol (PEG)-lipid, and cholesterol. Concerns arise regarding cholesterol's susceptibility to oxidation, potentially leading to undesired immunological responses and toxicity. In this study, we formulated novel LNPs by replacing cholesterol with phytochemical-derived compounds, specifically ginsenoside Rg2 and its derivative phytosterol protopanaxadiol (PPD), and validated their efficacy as mRNA delivery systems. The mRNA-LNP complexes were manually prepared through a simple mixing process. The biocompatibility of these Rg2-based LNPs (Rg2-LNP) and PPD-based LNPs (PPD-LNP) was assessed through cell viability assays, while the protective function of LNPs for mRNA was demonstrated by RNase treatment. Enhanced green fluorescent protein (EGFP) mRNA delivery and expression in A549 and HeLa cells were analyzed using optical microscopy and flow cytometry. The expression efficiency of Rg2-LNP and PPD-LNP was compared with that of commercially available LNPs, with both novel formulations demonstrating superior transfection and EGFP expression. Furthermore, in vivo tests following intramuscular (I.M.) injection in hairless mice demonstrated efficient luciferase (Luc) mRNA delivery and effective Luc expression using Rg2-LNP and PPD-LNP compared to commercial LNPs. Results indicated that the efficiency of EGFP and Luc expression in Rg2-LNP and PPD-LNP surpassed that of the cholesterol-based LNP formulation. These findings suggest that Rg2-LNP and PPD-LNP are promising candidates for future drug and gene delivery systems.

7-Ketocholesterol Effects on Osteogenic Differentiation of Adipose Tissue-Derived Mesenchymal Stem Cells

Some oxysterols were shown to promote osteogenic differentiation of mesenchymal stem cells (MSCs). Little is known about the effects of 7-ketocholesterol (7-KC) in this process. We describe its impact on human adipose tissue-derived MSC (ATMSC) osteogenic differentiation. ATMSCs were incubated with 7-KC in osteogenic or adipogenic media. Osteogenic and adipogenic differentiation was evaluated by Alizarin red and Oil Red O staining, respectively. Osteogenic (ALPL, RUNX2, BGLAP) and adipogenic markers (PPARƔ, C/EBPα) were determined by RT-PCR. Differentiation signaling pathways (SHh, Smo, Gli-3, β-catenin) were determined by indirect immunofluorescence. ATMSCs treated with 7-KC in osteogenic media stained positively for Alizarin Red. 7-KC in adipogenic media decreased the number of adipocytes. 7-KC increased ALPL and RUNX2 but not BGLAP expressions. 7-KC decreased expression of PPARƔ and C/EBPα, did not change SHh, Smo, and Gli-3 expression, and increased the expression of β-catenin. In conclusion, 7-KC favors osteogenic differentiation of ATMSCs through the expression of early osteogenic genes (matrix maturation phase) by activating the Wnt/β-catenin signaling pathway, while inhibiting adipogenic differentiation. This knowledge can be potentially useful in regenerative medicine, in treatments for bone diseases.

Immune Implications of Cholesterol-Containing Lipid Nanoparticles

The majority of clinically approved nanoparticle-mediated therapeutics are lipid nanoparticles (LNPs), and most of these LNPs are liposomes containing cholesterol. LNP formulations significantly alter the drug pharmacokinetics (PK) due to the propensity of nanoparticles for uptake by macrophages. In addition to readily engulfing LNPs, the high expression of cholesterol hydroxylases and reactive oxygen species (ROS) in macrophages suggests that they will readily produce oxysterols from LNP-associated cholesterol. Oxysterols are a heterogeneous group of cholesterol oxidation products that have potent immune modulatory effects. Oxysterols are implicated in the pathogenesis of atherosclerosis and certain malignancies; they have also been found in commercial liposome preparations. Yet, the in vivo metabolic fate of LNP-associated cholesterol remains unclear. We review herein the mechanisms of cellular uptake, trafficking, metabolism, and immune modulation of endogenous nanometer-sized cholesterol particles (i.e., lipoproteins) that are also relevant for cholesterol-containing nanoparticles. We believe that it would be imperative to better understand the in vivo metabolic fate of LNP-associated cholesterol and the immune implications for LNP-therapeutics. We highlight critical knowledge gaps that we believe need to be addressed in order to develop safer and more efficacious lipid nanoparticle delivery systems.

A rapid quantitative UPLC-MS/MS method for analysis of key regulatory oxysterols in biological samples for liver cancer

An UPLC-APCI-MS/MS method was developed for the simultaneous determination of cholesterol, 7-dehydrocholesterol (7DHC) and eight oxysterols including 27-hydroxycholesterol (27OHC), 7α-hydroxycholesterol (7αOHC), 7β-hydroxycholesterol (7βOHC), 24S-hydroxycholesterol (24SOHC), 25-hydroxycholesterol (25OHC), 7α,24S-dihydroxycholesterol (7α,24SdiOHC), 7α,25-dihydroxycholesterol (7α,25diOHC), and 7α,27-dihydroxycholesterol (7α,27diOHC). It has been used for quantitative analysis of cholesterol, 7DHC and eight oxysterols in hepatocellular carcinoma (HCC) cells, plasma and tumor tissue samples. And the above compounds were extracted from the biological matrix (plasma and tissue) using liquid-liquid extraction with hexane/isopropanol after saponification to cleave the steroids from their esterified forms without further derivatization. Then cholesterol, 7DHC and oxysterols were separated on a reversed phase column (Agilent Zorbax Eclipse plus, C18) within 8 min using a gradient elution with 0.1 % formic acid in H2O and methanol and detected by an APCI triple quadrupole mass spectrometer. The lower limit of quantification (LLOQ) of the cholesterol, 7DHC and oxysterols ranged from 3.9 ng/mL to 31.25 ng/mL, and the recoveries ranged from 83.0 % to 113.9 %. Cholesterol, 7DHC and several oxysterols including 27OHC, 7αOHC and 7βOHC were successfully quantified in HCC cells, plasma, tissues and urine of HCC mice. Results showed that 27OHC was at high levels in three kind of HCC cells and tumor tissues as well as plasma samples from both HepG2 and Huh7 bearing mice model，and the high levels of 27OHC in tumors were associated with HCC development. Moreover, the levels of cholesterol in HCC cells and tumor issues varied in different HCC cells and mice model. Oxysterols profiling in biological samples might provide complementary information in cancer diagnosis.

Statins in the Cause and Prevention of Cancer: Confounding by Indication and Mediation by Rhabdomyolysis and Phosphate Toxicity

Statins are drugs used in cardiovascular pharmacotherapy to decrease hypercholesterolemia and lower the risk of atherosclerosis. Statins also increase the risk of rhabdomyolysis, which is often minimized in comparison with large relative risk reductions of cardiovascular disease reported in clinical trials. By contrast, absolute risk reductions of cardiovascular disease are often clinically insignificant and unreported in statin clinical trials. Additionally, cytotoxic effects of statins inhibit cancer cell proliferation and reduce cancer risk, but other studies found that statins are carcinogenic. Due to an inverse association between incidence of cancer and atherosclerosis, the indication to prescribe statins likely biases the association of statins with cancer prevention. Dietary patterns associated with atherosclerosis and cancer contain inverse amounts of cholesterol and phosphate, an essential mineral that stimulates tumorigenesis. Accordingly, lower cancer risk is associated with high dietary cholesterol intake and increased risk of atherosclerosis. Furthermore, serum is exposed to excessive inorganic phosphate that could increase cancer risk as rhabdomyolysis induced by statins releases phosphate from skeletal muscle breakdown. Increased risk of comorbid conditions associated with statins may share the mediating factor of phosphate toxicity. More research is warranted on statins in the cause and prevention of cancer.

Effects of Phenols from Olive Vegetation Water on Mutagenicity and Genotoxicity of Stored-Cooked Beef Patties

This explorative study aimed to assess the mutagenicity and genotoxicity of stored-cooked beef patties formulated with and without phenols (7.00 mg of phenols/80-g patty) extracted from olive vegetation water (OVW), as related to the formation of cholesterol oxidation products (COPs) and heterocyclic amines (HCAs). The patties were packaged in a modified atmosphere, sampled during cold storage (4 °C) for 9 days, and grilled at 200 °C. The genotoxicity was evaluated by the Comet assay. The patty extract was found to be genotoxic on primary peripheral blood mononuclear cells (PBMCs), while no mutagenicity was detected. The addition of OVW phenols significantly decreased the genotoxicity of the patty extract and reduced the total COPs content in stored-cooked patties (4.59 times lower than control); however, it did not affect the content of total HCAs (31.51-36.31 ng/patty) and the revertants' number. Therefore, these results demonstrate that the OVW phenols were able to counteract the formation of genotoxic compounds in stored-cooked beef patties.

Mechanisms and Barriers in Nanomedicine: Progress in the Field and Future Directions

In recent years, steady progress has been made in synthesizing and characterizing engineered nanoparticles, resulting in several approved drugs and multiple promising candidates in clinical trials. Regulatory agencies such as the Food and Drug Administration and the European Medicines Agency released important guidance documents facilitating nanoparticle-based drug product development, particularly in the context of liposomes and lipid-based carriers. Even with the progress achieved, it is clear that many barriers must still be overcome to accelerate translation into the clinic. At the recent conference workshop "Mechanisms and Barriers in Nanomedicine" in May 2023 in Colorado, U.S.A., leading experts discussed the formulation, physiological, immunological, regulatory, clinical, and educational barriers. This position paper invites open, unrestricted, nonproprietary discussion among senior faculty, young investigators, and students to trigger ideas and concepts to move the field forward.

Oxysterols in Cell Viability, Phospholipidosis and Extracellular Vesicles Production in a Lung Cancer Model

The study carried out systematic research on the influence of selected oxysterols on cells viability, phospholipidosis and the level of secreted extracellular vesicles. Three oxidized cholesterol derivatives, namely 7α-hydroxycholesterol (7α-OH), 7- ketocholesterol (7-K) and 24(S)-hydroxycholesterol (24(S)-OH) were tested in three different concentrations: 50 μM, 100 μM and 200 μM for 24 h incubation with A549 lung cancer cell line. All the studied oxysterols were found to alter cells viability. The lowest survival rate of the cells was observed after 24 h of 7-K treatment, slightly better for 7α-OH while cells incubated with 24(S)-OH had the best survival rate among the oxysterols used. 7-K increased phospholipids accumulation in cells, however, most noticeable effect was noticed for 24(S)-OH. Changes in the level of extracellular vesicles secreted in cells culture after the treatment with oxysterols were also observed. It was found that all oxysterols used increased the level of secreted vesicles, both exosomes and ectosomes. The strongest effect was noticed for 24(S)-OH. Taken together, these results suggest that 7-K is the most potent inducer of cancer cell death, while 7α-OH is slightly less potent in this respect. The lower cytotoxic effect of 24(S)-OH correlates with greater phospholipids accumulation, extracellular vesicles production and better cells survival.

Excipient-related impurities in liposome drug products

Liposomes are widely used in the pharmaceutical industry as drug delivery systems to increase the efficacy and reduce the off-target toxicity of active pharmaceutical ingredients (APIs). The liposomes are more complex drug delivery systems than the traditional dosage forms, and phospholipids and cholesterol are the major structural excipients. These two excipients undergo hydrolysis and/or oxidation during liposome preparation and storage, resulting in lipids hydrolyzed products (LHPs) and cholesterol oxidation products (COPs) in the final liposomal formulations. These excipient-related impurities at elevated concentrations may affect liposome stability and exert biological functions. This review focuses on LHPs and COPs, two major categories of excipient-related impurities in the liposomal formulations, and discusses factors affecting their formation, and analytical methods to determine these excipient-related impurities.

Cholesterol and Its Oxidation Derivatives Content in Market Dairy Products

Cholesterol oxidation products (COPs) are contaminants of food of animal origin. Increased levels of these compounds in the human body are associated with an increased risk of many non-communicable diseases. Dairy products are mentioned among the main sources of these compounds in the diet. The objective of this study was to evaluate the contents of cholesterol and its oxidized derivatives in eleven groups of dairy products, willingly consumed in European countries. The levels of COPs were determined by applying the GC-TOF/MS method. In the tested products, cholesterol and its oxidation derivatives, such as 7-ketocholesterol, 7α-hydroxycholesterol, 7β-hydroxycholesterol, 5,6β-epoxycholesterol and 5,6α-epoxycholesterol, were determined. The studied dairy products differed in their contents and profiles of oxysterols. The highest contents of COPs were found in cheese with internal mold (13.8 ± 2.5 mg kg-1) and Cheddar (11.7 ± 3.5 mg kg-1), while the lowest levels were detected in yoghurt (0.94 ± 0.30 mg kg-1) and kefir (0.57 ± 0.11 mg kg-1). 7-ketocholesterol and 5,6β-epoxycholesterol were the dominant oxysterols. The ratio of oxidized derivatives to total cholesterol was on average 1.7%. Our results confirmed that dairy products are an important dietary source of COPs. Their levels should be monitored in dairy products to provide the best health quality.

Altered Brain Cholesterol Machinery in a Down Syndrome Mouse Model: A Possible Common Feature with Alzheimer's Disease

Down syndrome (DS) is a complex chromosomal disorder considered as a genetically determined form of Alzheimer's disease (AD). Maintenance of brain cholesterol homeostasis is essential for brain functioning and development, and its dysregulation is associated with AD neuroinflammation and oxidative damage. Brain cholesterol imbalances also likely occur in DS, concurring with the precocious AD-like neurodegeneration. In this pilot study, we analyzed, in the brain of the Ts2Cje (Ts2) mouse model of DS, the expression of genes encoding key enzymes involved in cholesterol metabolism and of the levels of cholesterol and its main precursors and products of its metabolism (i.e., oxysterols). The results showed, in Ts2 mice compared to euploid mice, the downregulation of the transcription of the genes encoding the enzymes 3-hydroxy-3-methylglutaryl-CoA reductase and 24-dehydrocholesterol reductase, the latter originally recognized as an indicator of AD, and the consequent reduction in total cholesterol levels. Moreover, the expression of genes encoding enzymes responsible for brain cholesterol oxidation and the amounts of the resulting oxysterols were modified in Ts2 mouse brains, and the levels of cholesterol autoxidation products were increased, suggesting an exacerbation of cerebral oxidative stress. We also observed an enhanced inflammatory response in Ts2 mice, underlined by the upregulation of the transcription of the genes encoding for α-interferon and interleukin-6, two cytokines whose synthesis is increased in the brains of AD patients. Overall, these results suggest that DS and AD brains share cholesterol cycle derangements and altered oxysterol levels, which may contribute to the oxidative and inflammatory events involved in both diseases.

Water thermodynamics and lipid oxidation in stored whey butter

Whey butter is the result of the rational use of the whey component, which is cream whey. It is an alternative to milk cream butter. The aim of the presented study was to analyze the effect of storage conditions on water thermodynamics and cholesterol oxidation products as reliable markers of quality and safety. After 4 mo of storage, the water loss (at 3°C and 13°C) and water activity in whey butter (only at 13°C) were reduced. Three-factorial ANOVA showed that the value of water activity was independent of the type of butter in interaction with the storage temperature. The duration of the translational movement of water molecules from the inside of whey butter was definitely longer than in butter and shortened with storage time. This was in contrast to butter. For whey butter stored at 13°C, the kinetics of the movement of water molecules was at the highest speed. In the case of whey butter and butter, the higher storage temperature almost doubled the gloss. Increasing the temperature to 13°C resulted in different yellowness index, chroma, and browning index between whey butter and butter. There were no statistically significant differences in the percentage of fatty acids and triacylglycerols in whey butter and milk cream butter during storage. In whey butter, compared with butter, the cholesterol content was higher, but the amount of cholesterol oxidation products was smaller. However, in whey butter, these amounts increased significantly. The presence of epoxides and their transformation products (i.e., triol cholesterol) was found in storage whey butter.

A Novel Method for the Determination of Squalene, Cholesterol and Their Oxidation Products in Food of Animal Origin by GC-TOF/MS

Cholesterol present in food of animal origin is a precursor of oxysterols (COPs), whose high intake through diet can be associated with health implications. Evaluation of the content of these contaminants in food is associated with many analytical problems. This work presents a GC-TOF/MS method for the simultaneous determination of squalene, cholesterol and seven COPs (7-ketocholesterol, 7α-hydroxycholesterol, 7β-hydroxycholesterol, 25-hydroxycholesterol, 5,6α-epoxycholesterol, 5,6β-epoxycholesterol, cholestanetriol). The sample preparation procedure includes such steps as saponification, extraction and silylation. The method is characterized by high sensitivity (limit of quantification, 0.02-0.25 ng mL-1 for instrument, 30-375 μg kg of sample), repeatability (RSD 2.3-6.2%) and a wide linearity range for each tested compound. The method has been tested on eight different animal-origin products. The COP to cholesterol content ratio in most products is about 1%, but the profile of cholesterol derivatives differs widely (α = 0.01). In all the samples, 7-ketocholesterol is the dominant oxysterol, accounting for 31-67% of the total COPs level. The levels of the other COPs range between 0% and 21%. In none of the examined products are cholestanetriol and 25-hydroxycholesterol present. The amount of squalene, which potentially may inhibit the formation of COPs in food, ranges from 2 to 57 mg kg-1.

Oxysterols as Biomarkers of Aging and Disease

Oxysterols derive from either enzymatic or non-enzymatic oxidation of cholesterol. Even though they are produced as intermediates of bile acid synthesis pathway, they are recognised as bioactive compounds in cellular processes. Therefore, their absence or accumulation have been shown to be associated with disease phenotypes. This chapter discusses the contribution of oxysterol to ageing, age-related diseases such as neurodegeneration and various disorders such as cancer, cardiovascular disease, diabetes, metabolic and ocular disorders. It is clear that oxysterols play a significant role in development and progression of these diseases. As a result, oxysterols are being investigated as suitable markers for disease diagnosis purposes and some drug targets are in development targeting oxysterol pathways. However, further research will be needed to confirm the suitability of these potentials.

Effects of Nitro-Oxidative Stress on Biomolecules: Part 1-Non-Reactive Molecular Dynamics Simulations

Plasma medicine, or the biomedical application of cold atmospheric plasma (CAP), is an expanding field within plasma research. CAP has demonstrated remarkable versatility in diverse biological applications, including cancer treatment, wound healing, microorganism inactivation, and skin disease therapy. However, the precise mechanisms underlying the effects of CAP remain incompletely understood. The therapeutic effects of CAP are largely attributed to the generation of reactive oxygen and nitrogen species (RONS), which play a crucial role in the biological responses induced by CAP. Specifically, RONS produced during CAP treatment have the ability to chemically modify cell membranes and membrane proteins, causing nitro-oxidative stress, thereby leading to changes in membrane permeability and disruption of cellular processes. To gain atomic-level insights into these interactions, non-reactive molecular dynamics (MD) simulations have emerged as a valuable tool. These simulations facilitate the examination of larger-scale system dynamics, including protein-protein and protein-membrane interactions. In this comprehensive review, we focus on the applications of non-reactive MD simulations in studying the effects of CAP on cellular components and interactions at the atomic level, providing a detailed overview of the potential of CAP in medicine. We also review the results of other MD studies that are not related to plasma medicine but explore the effects of nitro-oxidative stress on cellular components and are therefore important for a broader understanding of the underlying processes.

Advances and Challenges in Plant Sterol Research: Fundamentals, Analysis, Applications and Production

Plant sterols (PS) are cholesterol-like terpenoids widely spread in the kingdom Plantae. Being the target of extensive research for more than a century, PS have topped with evidence of having beneficial effects in healthy subjects and applications in food, cosmetic and pharmaceutical industries. However, many gaps in several fields of PS's research still hinder their widespread practical applications. In fact, many of the mechanisms associated with PS supplementation and their health benefits are still not fully elucidated. Furthermore, compared to cholesterol data, many complex PS chemical structures still need to be fully characterized, especially in oxidized PS. On the other hand, PS molecules have also been the focus of structural modifications for applications in diverse areas, including not only the above-mentioned but also in e.g., drug delivery systems or alternative matrixes for functional foods and fats. All the identified drawbacks are also superimposed by the need of new PS sources and technologies for their isolation and purification, taking into account increased environmental and sustainability concerns. Accordingly, current and future trends in PS research warrant discussion.

Plant sterols and cholesterol metabolism are associated with five-year cognitive decline in the elderly population

Dysregulations in cholesterol metabolism are associated with neurodegenerative and vascular pathologies, and dementia. Diet-derived plant sterols (phytosterols) have cholesterol-lowering, anti-inflammatory, and antioxidant properties and may interfere with neurodegeneration and cognitive decline. Here we performed multivariate analysis in 720 individuals enrolled in a population-based prospective study to determine whether circulating cholesterol precursors and metabolites, triglycerides, and phytosterols, are associated with cognitive impairment and decline in the older population. We report specific dysregulations of endogenous cholesterol synthesis and metabolism, and diet-derived phytosterols, and their changes over time associated with cognitive impairment, and decline in the general population. These findings suggest circulating sterols levels could be considered in risk evaluation and are relevant for the development of strategies to prevent cognitive decline in older people.

The Immunosuppressive Potential of Cholesterol Sulfate Through T Cell Microvilli Disruption

Cholesterol (CL) is required for various biomolecular production processes, including those of cell membrane components. Therefore, to meet these needs, CL is converted into various derivatives. Among these derivatives is cholesterol sulfate (CS), a naturally produced CL derivative by the sulfotransferase family 2B1 (SULT2B1), which is widely present in human plasma. CS is involved in cell membrane stabilization, blood clotting, keratinocyte differentiation, and TCR nanocluster deformation. This study shows that treatment of T cells with CS resulted in the decreased surface expression of some surface T-cell proteins and reduced IL-2 release. Furthermore, T cells treated with CS significantly reduced lipid raft contents and membrane CLs. Surprisingly, using the electron microscope, we also observed that CS led to the disruption of T-cell microvilli, releasing small microvilli particles containing TCRs and other microvillar proteins. However, in vivo, T cells with CS showed aberrant migration to high endothelial venules and limited infiltrating splenic T-cell zones compared with the untreated T cells. Additionally, we observed significant alleviation of atopic dermatitis in mice injected with CS in the animal model. Based on these results, we conclude that CS is an immunosuppressive natural lipid that impairs TCR signaling by disrupting microvillar function in T cells, suggesting its usefulness as a therapeutic agent for alleviating T-cell-mediated hypersensitivity and a potential target for treating autoimmune diseases.

Unification of medicines and excipients: The roles of natural excipients for promoting drug delivery

INTRODUCTION

Drug delivery systems (DDSs) formed by natural active compounds be instrumental in developing new green excipients and novel DDS from natural active compounds (NACs). 'Unification of medicines and excipients'(UME), the special inherent nature of the natural active compounds, provides the inspiration and conduction to achieve this goal.

AREAS COVERED

This review summarizes the typical types of NACs from herbal medicine, such as saponins, flavonoids, polysaccharides, etc. that act as excipients and their main application in DDS. The comparison of the drug delivery systems formed by NACs and common materials and the primary formation mechanisms of these NACs are also introduced to provide a deepened understanding of their performance in DDS.

EXPERT OPINION

Many natural bioactive compounds, such as saponins, polysaccharides, etc. have been used in DDS. Diversity of structure and pharmacological effects of NACs turn out the unique advantages in improving the performance of DDSs like targeting ability, adhesion, encapsulation efficiency(EE), etc. and enhancing the bioavailability of loaded drugs.

Identification and quantification of ionising radiation-induced oxysterol formation in membranes of lens fibre cells

Ionising radiation (IR) is a cause of lipid peroxidation, and epidemiological data have revealed a correlation between exposure to IR and the development of eye lens cataracts. Cataracts remain the leading cause of blindness around the world. The plasma membranes of lens fibre cells are one of the most cholesterolrich membranes in the human body, forming lipid rafts and contributing to the biophysical properties of lens fibre plasma membrane. Liquid chromatography followed by mass spectrometry was used to analyse bovine eye lens lipid membrane fractions after exposure to 5 and 50 Gy and eye lenses taken from wholebody 2 Gy-irradiated mice. Although cholesterol levels do not change significantly, IR dose-dependant formation of the oxysterols 7β-hydroxycholesterol, 7-ketocholesterol and 5, 6-epoxycholesterol in bovine lens nucleus membrane extracts was observed. Whole-body X-ray exposure (2 Gy) of 12-week old mice resulted in an increase in 7β-hydroxycholesterol and 7-ketocholesterol in their eye lenses. Their increase regressed over 24 h in the living lens cortex after IR exposure. This study also demonstrated that the IR-induced fold increase in oxysterols was greater in the mouse lens cortex than the nucleus. Further work is required to elucidate the mechanistic link(s) between oxysterols and IR-induced cataract, but these data evidence for the first time that IR exposure of mice results in oxysterol formation in their eye lenses.

Site of the Hydroxyl Group Determines the Surface Behavior of Bipolar Chain-Oxidized Cholesterol Derivatives─Langmuir Monolayer Studies Supplemented with Theoretical Calculations

Cholesterol oxidation products (called oxysterols) are involved in many biological processes, showing both negative (e.g., neurodegenerative) and positive (e.g., antiviral and antimicrobial) effects. The physiological activity of oxysterols is undoubtedly closely related to their structure (i.e., the type and location of the additional polar group in the cholesterol skeleton). In this paper, we focus on determining how a seemingly minor structural change (introduction of a hydroxyl moiety at C(24), C(25), or C(27) in the isooctyl chain of cholesterol) affects the organization of the resulting molecules at the phase boundary. In our research, we supplemented the classic Langmuir monolayer technique, based on the surface pressure and electric surface potential isotherms, with microscopic (BAM) and spectroscopic (PM-IRRAS) techniques, as well as theoretical calculations (DFT and MD). This allowed us to show that 24-OH behaves more like cholesterol and forms stable, rigid monolayers. On the other hand, 27-OH, similar to 25-OH, undergoes the phase transition from monolayer to bilayer structures. Theoretical calculations enabled us to conclude that the formation of bilayers from 27-OH or 25-OH is possible due to the hydrogen bonding between adjacent oxysterol molecules. This observation may help to understand the factors responsible for the unique biological activity (including antiviral and antimicrobial) of 27-OH and 25-OH compared to other oxysterols.

The Niemann-Pick type diseases – A synopsis of inborn errors in sphingolipid and cholesterol metabolism

Disturbances of lipid homeostasis in cells provoke human diseases. The elucidation of the underlying mechanisms and the development of efficient therapies represent formidable challenges for biomedical research. Exemplary cases are two rare, autosomal recessive, and ultimately fatal lysosomal diseases historically named "Niemann-Pick" honoring the physicians, whose pioneering observations led to their discovery. Acid sphingomyelinase deficiency (ASMD) and Niemann-Pick type C disease (NPCD) are caused by specific variants of the sphingomyelin phosphodiesterase 1 (SMPD1) and NPC intracellular cholesterol transporter 1 (NPC1) or NPC intracellular cholesterol transporter 2 (NPC2) genes that perturb homeostasis of two key membrane components, sphingomyelin and cholesterol, respectively. Patients with severe forms of these diseases present visceral and neurologic symptoms and succumb to premature death. This synopsis traces the tortuous discovery of the Niemann-Pick diseases, highlights important advances with respect to genetic culprits and cellular mechanisms, and exposes efforts to improve diagnosis and to explore new therapeutic approaches.

Role of reactive oxygen species in regulating 27-hydroxycholesterol-induced apoptosis of hematopoietic progenitor cells and myeloid cell lines

Oxysterols are oxygenated derivatives of cholesterol that contain an additional hydroxy, epoxide, or ketone group in the sterol nucleus and/or a hydroxyl group in the side chain of the cholesterol molecule. 27-Hydroxycholesterol (27HC) is a side-chain oxysterol that is oxygenated at the 27th carbon atom of cholesterol. The oxysterol (27HC) is produced via oxidation by sterol 27-hydroxylase (CYP27A1) and metabolized via oxysterol 7a-hydroxylase (CYP7B1) for bile acid synthesis in the liver. A previous study has demonstrated that treatment with the alternative Estrogen receptor alpha (ERα) ligand 27HC induces ERα-dependent hematopoietic stem cell (HSC) mobilization. In addition, Cyp27a1-deficient mice demonstrate significantly reduced 27HC levels and HSC mobilization. Here, we report that exogenous 27HC treatment leads to a substantial reduction in the hematopoietic stem and progenitor cell (HSPC) population owing to significantly increased reactive oxygen species (ROS) levels and apoptosis in the bone marrow (BM). However, 27HC does not influence the population of mature hematopoietic cells in the BM. Furthermore, exogenous 27HC treatment suppresses cell growth and promotes ROS production and apoptosis in leukemic cells. Moreover, acute myeloid leukemia (AML) patients with high CYP7B1 expression (expected to have inhibition of 27HC) had significantly shorter survival than those with low CYP7B1 expression (expected to have an elevation of 27HC). Single-cell RNA-sequencing (scRNA seq) analysis revealed that the expression of CYP7B1 was significantly increased in AML patients. Thus, our study suggests that 27HC may serve as a potent agent for regulating pools of HSPCs and may have an application as a novel therapeutic target for hematological malignancies. Collectively, pharmacological inhibition of CYP7B1 (expected to have an elevation of 27HC) would potentially have fewer long-term hematological side effects, particularly when used in combination with chemotherapy or radiation for the treatment of leukemia patients.

Profiling subcellular localization of nuclear-encoded mitochondrial gene products in zebrafish

Most mitochondrial proteins are encoded by nuclear genes, synthetized in the cytosol and targeted into the organelle. To characterize the spatial organization of mitochondrial gene products in zebrafish (Danio rerio), we sequenced RNA from different cellular fractions. Our results confirmed the presence of nuclear-encoded mRNAs in the mitochondrial fraction, which in unperturbed conditions, are mainly transcripts encoding large proteins with specific properties, like transmembrane domains. To further explore the principles of mitochondrial protein compartmentalization in zebrafish, we quantified the transcriptomic changes for each subcellular fraction triggered by the chchd4a ^-/- mutation, causing the disorders in the mitochondrial protein import. Our results indicate that the proteostatic stress further restricts the population of transcripts on the mitochondrial surface, allowing only the largest and the most evolutionary conserved proteins to be synthetized there. We also show that many nuclear-encoded mitochondrial transcripts translated by the cytosolic ribosomes stay resistant to the global translation shutdown. Thus, vertebrates, in contrast to yeast, are not likely to use localized translation to facilitate synthesis of mitochondrial proteins under proteostatic stress conditions.

The Effects of Cholesterol Oxidation on Erythrocyte Plasma Membranes: A Monolayer Study

Cholesterol plays a key role in the molecular and mesoscopic organisation of lipid membranes and it is expected that changes in its molecular structure (e.g., through environmental factors such as oxidative stress) may affect adversely membrane properties and function. In this study, we present evidence that oxidation of cholesterol has significant effects on the mechanical properties, molecular and mesoscopic organisation and lipid-sterol interactions in condensed monolayers composed of the main species found in the inner leaflet of the erythrocyte membrane. Using a combination of experimental methods (static area compressibility, surface dilatational rheology, fluorescence microscopy, and surface sensitive X-ray techniques) and atomistic molecular dynamics simulations, we show that oxidation of cholesterol to 7-ketocholesterol leads to stiffening of the monolayer (under both static and dynamic conditions), significant changes in the monolayer microdomain organisation, disruption in the van der Waals, electrostatic and hydrophobic interactions between the sterol and the other lipid species, and the lipid membrane hydration. Surface sensitive X-ray techniques reveal that, whilst the molecular packing mode is not significantly affected by cholesterol oxidation in these condensed phases, there are subtle changes in membrane thickness and a significant decrease in the coherence length in monolayers containing 7-ketocholesterol.

Oxysterols can act antiviral through modification of lipid membrane properties - The Langmuir monolayer study

In this paper we tested how oxysterols influence on fusion process between viral lipid envelope and host cells membranes. For this purpose, the Zika virus was selected, while dendritic cell (DC) and neural cell (NC) membranes were chosen as target membranes. The investigated systems were modeled as multicomponent Langmuir monolayers and characterized using surface manometry and imaging in micro- (Brewster angle microscopy, BAM) and nanoscale (Atomic Force Microscopy, AFM) to monitor local heterogeneity. The fusion process was conducted by mixing viral and host cell membranes devoid and in the presence of oxysterols: 25-hydroxycholesterol (25-OH) and 7β-hydroxycholesterol (7β-OH) as representatives of chain- and ring-oxidized oxysterols, respectively. Our results show that oxysterols hinder the fusion with host cell membranes by modifying their biophysical properties. Moreover, oxysterols applied to an already infected membrane reverse the changes caused by the infection. It could therefore be concluded that oxysterols may display antiviral activity in two ways: they prevent the healthy membrane from viral infection by blocking the fusion process; and protect already infected membrane from pathological changes induced by the virus.

Oxysterols are potential physiological regulators of ageing

Delaying and even reversing ageing is a major public health challenge with a tremendous potential to postpone a plethora of diseases including cancer, metabolic syndromes and neurodegenerative disorders. A better understanding of ageing as well as the development of innovative anti-ageing strategies are therefore an increasingly important field of research. Several biological processes including inflammation, proteostasis, epigenetic, oxidative stress, stem cell exhaustion, senescence and stress adaptive response have been reported for their key role in ageing. In this review, we describe the relationships that have been established between cholesterol homeostasis, in particular at the level of oxysterols, and ageing. Initially considered as harmful pro-inflammatory and cytotoxic metabolites, oxysterols are currently emerging as an expanding family of fine regulators of various biological processes involved in ageing. Indeed, depending of their chemical structure and their concentration, oxysterols exhibit deleterious or beneficial effects on inflammation, oxidative stress and cell survival. In addition, stem cell differentiation, epigenetics, cellular senescence and proteostasis are also modulated by oxysterols. Altogether, these data support the fact that ageing is influenced by an oxysterol profile. Further studies are thus required to explore more deeply the impact of the "oxysterome" on ageing and therefore this cholesterol metabolic pathway constitutes a promising target for future anti-ageing interventions.

Presence of cholesterol oxides in milk chocolates and their correlation with milk powder freshness

Cholesterol oxidation products (COPs) of non-enzymatic origin are mainly found in meat, fish, eggs and milk, mostly originating from the type of feeding, processing and storage. To verify the significance of COPs as biomarkers of cholesterol autoxidation and milk freshness, we quantified them in chocolates containing whole milk powders (WMPs) of increasing shelf-lives (i.e. 20, 120, and 180 days). Non-enzymatic total COPs (both free and esterified) ranged from 256.57 ± 11.97 to 445.82 ± 11.88 ng/g, increasing proportionally to the shelf-life of the WMPs, thus reflecting the ingredients’ freshness. Based on the expected theoretical COPs, the effect of processing was quantitatively less significant in the generation of oxysterols (41–44%) than the contribution of the autoxidation of the WMPs over time (56–59%), pointing to the shelf-life as the primary determinant of COPs. Lastly, we quantified COPs of major commercial milk chocolates on the Italian market, which followed a similar distribution (from 240.79 ± 11.74 to 475.12 ± 12.58 ng/g). Although further replications of this work are needed, this study reports preliminary results and a practical example of a first application of non-enzymatic COPs as markers to further quantify and characterize the nutritional quality and freshness, not only of ingredients but also of composite products.

Different effects of oxysterols on a model lipid raft - Langmuir monolayer study complemented with theoretical calculations

Three oxysterols (7β-hydroxycholesterol; 7β-OH, 7-ketocholesterol; 7-K and 25-hydroxycholesterol, 25-OH) differing in the site of oxidation (ring system versus chain) and kind of polar group (hydroxyl versus carbonyl) were studied in lipid raft environment using the Langmuir monolayer technique complemented with theoretical calculations. Experiments were performed for the unmodified raft system, composed of sphingomyelin (SM) and cholesterol (Chol), and in the next step the raft was modified by the incorporation of oxysterol in different proportions. In the examined three-component system (Chol:SM:oxysterol), apart from interactions between the lipid raft components, the affinity of Chol to its oxidized derivatives also plays an important role. 25-OH was found to enhance interactions between SM and Chol and thus stabilize the raft, contrary to 7β-OH and 7-K, which exterted the fluidizing effect as well as the destabilization of the raft. Different action of oxysterols on model raft was observed. 7β-OH and 7-K, which are highly potent inducers of cell dath caused raft destabilization, while 25-OH, which is the least toxic of the investigated oxysterols, was found to stabilize the raft.

New Function of Cholesterol Oxidation Products Involved in Osteoporosis Pathogenesis

Osteoporosis (OP) is a systemic bone disease characterized by decreased bone strength, microarchitectural changes in bone tissues, and increased risk of fracture. Its occurrence is closely related to various factors such as aging, genetic factors, living habits, and nutritional deficiencies as well as the disturbance of bone homeostasis. The dysregulation of bone metabolism is regarded as one of the key influencing factors causing OP. Cholesterol oxidation products (COPs) are important compounds in the maintenance of bone metabolic homeostasis by participating in several important biological processes such as the differentiation of mesenchymal stem cells, bone formation in osteoblasts, and bone resorption in osteoclasts. The effects of specific COPs on mesenchymal stem cells are mainly manifested by promoting osteoblast genesis and inhibiting adipocyte genesis. This review aims to elucidate the biological roles of COPs in OP development, starting from the molecular mechanisms of OP, pointing out opportunities and challenges in current research, and providing new ideas and perspectives for further studies of OP pathogenesis.

DNA damage in circulating hematopoietic progenitor stem cells as promising biological sensor of frailty

Frailty is an age-related syndrome that exposes individuals to increased vulnerability. Although it is potentially reversible, in most cases it leads to negative outcomes, including mortality. The different methods proposed identify frailty after the onset of clinical manifestations. An early diagnosis might make it possible to manage the frailty progression better. The frailty pathophysiology is still unclear although mechanisms, in particular, those linked to inflammation and immunosenescence, have been investigated. A common feature of several clinical aspects involved in senescent organisms is the increase of oxidative stress, described as one of the major causes of deoxyribonucleic acid (DNA) damage accumulation in aged cells including the adult stem cell compartment. Likely, this accumulation is implicated in frailty status. The oxidative status of our frail, pre-frail, and non-frail population was characterized. In addition, the DNA damage in hematopoietic cells was evidenced by analyzing the peripheral blood mononuclear cell and their T lymphocyte, monocyte, circulating hematopoietic progenitor stem cell (cHPSC) subpopulations. The phosphorylation of C-terminal of histone H2AX at amino acid Ser 139 (γ-H2AX), which occurs at the DNA double-strand break focus, was evaluated. In our frail population, increased oxidative stress and a high level of DNA damage in cHPSC were found. This study may have potential implications because the increment of DNA damage in cHPSC could be suggestive of an organism impairment preceding the evident frailty. In addition, it may open the possibility for attenuation of frailty progression throughout specific drugs acting on preventing DNA damage or removing damaged cells

SARS-CoV-2 treatment effects induced by ACE2-expressing microparticles are explained by the oxidized cholesterol-increased endosomal pH of alveolar macrophages

Exploring the cross-talk between the immune system and advanced biomaterials to treat SARS-CoV-2 infection is a promising strategy. Here, we show that ACE2-overexpressing A549 cell-derived microparticles (AO-MPs) are a potential therapeutic agent against SARS-CoV-2 infection. Intranasally administered AO-MPs dexterously navigate the anatomical and biological features of the lungs to enter the alveoli and are taken up by alveolar macrophages (AMs). Then, AO-MPs increase the endosomal pH but decrease the lysosomal pH in AMs, thus escorting bound SARS-CoV-2 from phago-endosomes to lysosomes for degradation. This pH regulation is attributable to oxidized cholesterol, which is enriched in AO-MPs and translocated to endosomal membranes, thus interfering with proton pumps and impairing endosomal acidification. In addition to promoting viral degradation, AO-MPs also inhibit the proinflammatory phenotype of AMs, leading to increased treatment efficacy in a SARS-CoV-2-infected mouse model without side effects. These findings highlight the potential use of AO-MPs to treat SARS-CoV-2-infected patients and showcase the feasibility of MP therapies for combatting emerging respiratory viruses in the future.

Mitochondrial respiratory chain dysfunction alters ER sterol sensing and mevalonate pathway activity

Mitochondrial dysfunction induces a strong adaptive retrograde signaling response; however, many of the downstream effectors of this response remain to be discovered. Here, we studied the shared transcriptional responses to three different mitochondrial respiratory chain inhibitors in human primary skin fibroblasts using QuantSeq 3′-RNA-sequencing. We found that genes involved in the mevalonate pathway were concurrently downregulated, irrespective of the respiratory chain complex affected. Targeted metabolomics demonstrated that impaired mitochondrial respiration at any of the three affected complexes also had functional consequences on the mevalonate pathway, reducing levels of cholesterol precursor metabolites. A deeper study of complex I inhibition showed a reduced activity of endoplasmic reticulum–bound sterol-sensing enzymes through impaired processing of the transcription factor Sterol Regulatory Element-Binding Protein 2 and accelerated degradation of the endoplasmic reticulum cholesterol-sensors squalene epoxidase and HMG-CoA reductase. These adaptations of mevalonate pathway activity affected neither total intracellular cholesterol levels nor the cellular free (nonesterified) cholesterol pool. Finally, measurement of intracellular cholesterol using the fluorescent cholesterol binding dye filipin revealed that complex I inhibition elevated cholesterol on intracellular compartments. Taken together, our study shows that mitochondrial respiratory chain dysfunction elevates intracellular free cholesterol levels and therefore attenuates the expression of mevalonate pathway enzymes, which lowers endogenous cholesterol biosynthesis, disrupting the metabolic output of the mevalonate pathway. We conclude that intracellular disturbances in cholesterol homeostasis may alter systemic cholesterol management in diseases associated with declining mitochondrial function.

Dietary cholesterol oxidation products: Perspectives linking food processing and storage with health implications

Dietary cholesterol oxidation products (COPs) are heterogeneous compounds formed during the processing and storage of cholesterol-rich foods, such as seafood, meat, eggs, and dairy products. With the increased intake of COPs-rich foods, the concern about health implications of dietary COPs is rising. Dietary COPs may exert deleterious effects on human health to induce several inflammatory diseases including atherosclerosis, neurodegenerative diseases, and inflammatory bowel diseases. Thus, knowledge regarding the effects of processing and storage conditions leading to formation of COPs is needed to reduce the levels of COPs in foods. Efficient methodologies to determine COPs in foods are also essential. More importantly, the biological roles of dietary COPs in human health and effects of phytochemicals on dietary COPs-induced diseases need to be established. This review summarizes the recent information on dietary COPs including their formation in foods during their processing and storage, analytical methods of determination of COPs, metabolic fate, implications for human health, and beneficial interventions by phytochemicals. The formation of COPs is largely dependent on the heating temperature, storage time, and food matrices. Alteration of food processing and storage conditions is one of the potent strategies to restrict hazardous dietary COPs from forming, including maintaining relatively low temperatures, shorter processing or storage time, and the appropriate addition of antioxidants. Once absorbed into the circulation, dietary COPs can contribute to the progression of several inflammatory diseases, where the absorbed dietary COPs may induce inflammation, apoptosis, and autophagy in cells in the target organs or tissues. Improved intake of phytochemicals may be an effective strategy to reduce the hazardous effects of dietary COPs.

Predicting the packing parameter for lipids in monolayers with the use of molecular dynamics

Lipid molecules form the backbone of biological membranes. Due to their amphiphilic structure, they can self-organize in a plethora of different structures when in contact with water. The type of self-assembled structure and its curvature depend on so-called shape factor or critical packing parameter, CPP, that can be derived knowing the molecular volume of a lipid (V), optimal surface area (a₀) and critical chain length (l_c) (see Intermolecular and Surface Forces by Jacob N. Israelachvili, Third Edition, 2011). The value of CPP allows not only to predict the type of self-assembled structure but also is a key factor for molecular interactions, which play a great role both in physiological and pathological conditions. The greatest difficulties arise when calculating the a₀ parameter, and although for some typical membrane lipids these values have been determined, there are a number of derivatives for which this parameter, and thus CPP, are unknown. The value of CPP allows not only to predict the type of self-assembled structure but also is a key factor for molecular interactions, which play a great role both in physiological and pathological conditions. So far, the determination of the packing parameter required the use of theoretical models with assumptions deviating from the physical conditions. Here we report a method based on molecular dynamics, which was applied to simulate lipid membranes consisting of cholesterol, oxysterols, sphingolipids, phosphatidylcholines, and phosphatidylethanolamines. For lipid molecules for which CPPs have already been determined, high compliance has been demonstrated. This proves that the method presented herein can be successfully used to determine packing parameters for other membrane lipids and amphiphilic molecules.

Can oxysterols work in anti-glioblastoma therapy? Model studies complemented with biological experiments

Despite the progress made in recent years in the field of oncology, the results of glioblastoma treatment remain unsatisfactory. In this paper, cholesterol derivatives - oxysterols - have been investigated in the context of their anti-cancer activity. First, the influence of three oxysterols (7-K, 7β-OH and 25-OH), differing in their chemical structure, on the properties of a model membrane imitating glioblastoma multiforme (GBM) cells was investigated. For this purpose, the Langmuir monolayer technique was applied. The obtained results clearly show that oxysterols modify the structure of the membrane by its stiffening, with the 7-K effect being the most pronounced. Next, the influence of 7-K on the nanomechanical properties of glioblastoma cells (U-251 line) was verified with AFM. It has been shown that 7-K has a dose-dependent cytotoxic effect on glioblastoma cells leading to the induction of apoptosis as confirmed by viability tests. Interestingly, significant changes in membrane structure, characteristic for phospholipidosis, has also been observed. Based on our results we believe that oxysterol-induced apoptosis and phospholipidosis are related and may share common signaling pathways. Dysregulation of lipids in phospholipidosis inhibit cell proliferation and may play key roles in the induction of apoptosis by oxysterols. Moreover, anticancer activity of these compounds may be related to the immobilization of cancer cells as a result of stiffening effect caused by oxysterols. Therefore, we believe that oxysterols are good candidates as new therapeutic molecules as an alternative to the aggressive treatment of GBM currently in use.

Impact of Fatty Acids on Obesity-Associated Diseases and Radical Weight Reduction

Purpose

Fatty acids (FA), particularly polyunsaturated (PUFA) ones, are involved in the regulation of glycemic control, lipid metabolism, and inflammation. The aim of the study was to assess patient FA profile in relation to obesity, lipid and carbohydrate metabolism disturbances, and weight loss.

Materials and Methods

The studied group consisted of 51 patients with extreme obesity, 23 of whom achieved radical weight reduction within 1 year after a laparoscopic sleeve gastrectomy (LSG). FA levels were determined using gas chromatography with flame ionization detection.

Results

Patients with extreme obesity and higher serum PUFA content have lower serum levels of SFA and MUFA (especially myristic, palmitic, lignoceric acids and palmitoleic, oleic acids), as well as lower triglyceride and higher HDL-cholesterol concentrations and it was not influenced by CEPT Taq1B variant. At baseline, the fatty acid profile of patients with type II diabetes differ from patients with dyslipidemia. In patients who had lost weight, significantly lower levels of selected saturated FA and major trans-fatty acid, elaidic, were found. Moreover, the proportion of PUFA was increased.

Conclusion

In extreme obesity, higher PUFA exert their favorable effects on serum lipids. Significant weight reduction after the bariatric surgery is associated with beneficial changes in the fatty acid profile.

Graphical Abstract

Interdomain exchange and the flip-flop of cholesterol in ternary component lipid membranes and their effects on heterogeneous cholesterol diffusion

Cell membranes are heterogeneous with a variety of lipids, cholesterol, and proteins and are composed of domains of different compositions. Such heterogeneous environments make the transport of cholesterol complicated: cholesterol not only diffuses within a particular domain but also travels between domains. Cholesterol also flip-flops between upper and lower leaflets such that cholesterol may reside both within leaflets and in the central region between two leaflets. How the presence of multiple domains and the interdomain exchange of cholesterol would affect the cholesterol transport, however, remains elusive. In this study, therefore, we perform molecular dynamics simulations up to 100μs for ternary component lipid membranes, which consist of saturated lipids (dipalmitoylphosphatidylcholine, DPPC), unsaturated lipids (dilinoleylphosphatidylcholine, DIPC), and cholesterol. The ternary component membranes in our simulations form two domains readily: DPPC and DIPC domains. We find that the diffusion of cholesterol molecules is much more heterogeneous and non-Gaussian than expected for binary component lipid membranes of lipids and cholesterol. The non-Gaussian parameter of the cholesterol molecules is about four times larger in the ternary component lipid membranes than in the binary component lipid membranes. Such non-Gaussian and heterogeneous transport of cholesterol arises from the interplay among the interdomain kinetics, the different diffusivity of cholesterol in different domains, and the flip-flop of cholesterol. This suggests that in cell membranes that consist of various domains and proteins, the cholesterol transport can be very heterogeneous. We also find that the mechanism of the interdomain exchange differs for different domains: cholesterol tends to exit the DIPC domain along the central region of the membrane for the DIPC-to-DPPC transition, while the cholesterol is likely to exit the DPPC domain within the membrane leaflet for the DPPC-to-DIPC transition. Also, the interdomain exchange kinetics of cholesterol for the DPPC-to-DIPC transition is up to 7.9 times slower than the DIPC-to-DPPC transition.

What Does Time-Dependent Fluorescence Shift (TDFS) in Biomembranes (and Proteins) Report on?

The organization of biomolecules and bioassemblies is highly governed by the nature and extent of their interactions with water. These interactions are of high intricacy and a broad range of methods based on various principles have been introduced to characterize them. As these methods view the hydration phenomena differently (e.g., in terms of time and length scales), a detailed insight in each particular technique is to promote the overall understanding of the stunning “hydration world.” In this prospective mini-review we therefore critically examine time-dependent fluorescence shift (TDFS)—an experimental method with a high potential for studying the hydration in the biological systems. We demonstrate that TDFS is very useful especially for phospholipid bilayers for mapping the interfacial region formed by the hydrated lipid headgroups. TDFS, when properly applied, reports on the degree of hydration and mobility of the hydrated phospholipid segments in the close vicinity of the fluorophore embedded in the bilayer. Here, the interpretation of the recorded TDFS parameters are thoroughly discussed, also in the context of the findings obtained by other experimental techniques addressing the hydration phenomena (e.g., molecular dynamics simulations, NMR spectroscopy, scattering techniques, etc.). The differences in the interpretations of TDFS outputs between phospholipid biomembranes and proteins are also addressed. Additionally, prerequisites for the successful TDFS application are presented (i.e., the proper choice of fluorescence dye for TDFS studies, and TDFS instrumentation). Finally, the effects of ions and oxidized phospholipids on the bilayer organization and headgroup packing viewed from TDFS perspective are presented as application examples.

Oxysterols in stored powders as potential health hazards

Cholesterol oxidation products (COPs) have greater biological activity than cholesterol itself. Oxysterols reduce the nutritional value of foods and exhibit a wide range of biological activity, including pro-oxidant, carcinogenic, and cytotoxic properties. The most commonly detected oxysterols in foods are 7α-HC, 7β-HC, a product of their dehydrogenation 7-KC and α-CE, β-CE. The main dietary sources of oxysterols are eggs and egg-derived products, thermally processed milk and milk-based products, fried meat. This study aimed to measure the amount of cholesterol oxidation products in milk powder, egg powder and milk-egg powder during 24 months of storage. The changes in the selected oxysterols (determined by gas chromatography) were recorded. In milk powder, after the production process, the amount of cholesterol was 0.2 g 100 g^-1 fat and in egg powder it was 3.4 g 100 g^-1. After 6 months of storage, the dominant oxysterol in milk and egg powder was 7α-HC and in milk-egg powder it was 7-KC. After the storage period, oxysterols in powdered milk reached 1.81% of total cholesterol.  The most stable cholesterol was in the milk-egg mixture and its oxidation was the slowest. This study showed the presence of COPs in milk powder, egg powder and milk-egg powder and the effect of storage on cholesterol oxidation.

The Influence of Supplementation with Zinc in Micro and Nano Forms on the Metabolism of Fatty Acids in Livers of Rats with Breast Cancer

The aim of this study was to investigate the effect of zinc supplementation (in the form of nano or microparticles) on the profile and metabolism of fatty acids in the liver microsomes of rats with induced breast cancer. The activity of desaturases (Δ5, Δ6, Δ9) and the level of cholesterol and its oxidized derivatives were measured. The aim of this study was also to determine the effect of various forms of zinc supplements on rats that were on 5-, 12- and 15-hydroxyeicosatetraenoic (5-, 12- and 15-HETE) and hydroxyoctadecadienoic (HODE) acids, and the level of prostaglandin E2 (PGE2). Female Spraque-Dawley rats (n = 24) were divided into 2 groups that were supplemented with zinc in the micro form (342 nm) or nano form (99 nm) particles, respectively, and a group with a standard diet (control group). All animals received 7,12-dimethylbenz[a]anthracene twice for the induction of breast cancer. Dietary nano-Zn supplementation increased vaccenic acid content (p = 0.032) and decreased Δ6-desaturase activity (p = 0.006), whereas micro-Zn increased cholesterol (p = 0.006), ∑COPs (total cholesterol-oxidation products) (p = 0.019) and PGE2 (p = 0.028) content. Dietary enrichment with Zn microparticles resulted in lower concentrations of the metabolites 15-, 12- and 5-HETE and HODE. Our study indicates that the effect of zinc supplementation on the metabolism of fatty acids in the liver microsomes under neoplastic conditions depends on the form in which it is administered.

Site of Cholesterol Oxidation Impacts Its Localization and Domain Formation in the Neuronal Plasma Membrane

Cholesterol is integral to the structure of mammalian cell membranes. Oxidation of cholesterol alters how it behaves in the membrane and influences the membrane biophysical properties. Elevated levels of oxidized cholesterol are associated with neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, multiple sclerosis, and Huntington's disease. Previous work has investigated the impact of oxidized cholesterol in the context of simple model membrane systems. However, there is a growing body of literature that shows that complex membranes possessing physiological phospholipid distributions have different properties from those of binary or trinary model membranes. In the current work, the impact of oxidized cholesterol on the biophysical properties of a complex neuronal plasma membrane is investigated using coarse-grained Martini molecular dynamics simulations. Comparison of the native neuronal membrane to neuronal membranes containing 10% tail-oxidized or 10% head-oxidized cholesterol shows that the site of oxidization changes the behavior of the oxidized cholesterol in the membrane. Furthermore, species-specific domain formation is observed between each oxidized cholesterol and minor lipid classes. Although both tail-oxidized and head-oxidized cholesterols modulate the biophysical properties of the membrane, smaller changes are observed in the complex neuronal membrane than seen in the previous work on simple binary or trinary model membranes. This work highlights the presence of compensatory effects of lipid diversity in the complex neuronal membrane. Overall, this study improves our molecular-level understanding of the effects of oxidized cholesterol on the properties of neuronal tissue and emphasizes the importance of studying membranes with realistic lipid compositions.