Cholesterol oxidase: sources, physical properties and analytical applications

The importance of choosing the appropriate cholesterol quantification method: enzymatic assay versus gas chromatography

Cholesterol is a major lipid of the animal realm with many biological roles. It is an important component of cellular membranes and a precursor of steroid hormones and bile acids. It is particularly abundant in nervous tissues, and dysregulation of cholesterol metabolism has been associated with neurodegenerative diseases such as Alzheimer's and Huntington's diseases. Deciphering the pathophysiological mechanisms of these disorders often involves animal models such as mice and Drosophila. Accurate quantification of cholesterol levels in the chosen models is a critical point of these studies. In the present work, we compare two common methods, gas chromatography coupled to flame-ionization detection (GC/FID) and a cholesterol oxidase-based fluorometric assay to measure cholesterol in mouse brains and Drosophila heads. Cholesterol levels measured by the two methods were similar for the mouse brain, which presents a huge majority of cholesterol in its sterol profile. On the contrary, depending on the method, measured cholesterol levels were very different for Drosophila heads, which present a complex sterol profile with a minority of cholesterol. We showed that the enzyme-based assay is not specific for cholesterol and detects other sterols as well. This method is therefore not suited for cholesterol measurement in models such as Drosophila. Alternatively, chromatographic methods, such as GC/FID, offer the required specificity for cholesterol quantification. Understanding the limitations of the quantification techniques is essential for reliable interpretation of the results in cholesterol-related research.

Mass Spectrometry Imaging of Cholesterol and Oxysterols

Mass spectrometry imaging (MSI) is a new technique in the toolbox of the analytical biochemist. It allows the generation of a compound-specific image from a tissue slice where a measure of compound abundance is given pixel by pixel, usually displayed on a color scale. As mass spectra are recorded at each pixel, the data can be interrogated to generate images of multiple different compounds all in the same experiment. Mass spectrometry (MS) requires the ionization of analytes, but cholesterol and other neutral sterols tend to be poorly ionized by the techniques employed in most MSI experiments, so despite their high abundance in mammalian tissues, cholesterol is poorly represented in the MSI literature. In this chapter, we discuss some of the MSI studies where cholesterol has been imaged and introduce newer methods for its analysis by MSI. Disturbed cholesterol metabolism is linked to many disorders, and the potential of MSI to study cholesterol, its precursors, and its metabolites in animal models and from human biopsies will be discussed.

Directed evolution of cholesterol oxidase with improved thermostability using error-prone PCR

Cholesterol oxidase is industrially important as it is frequently used as a biosensor in food and agriculture industries and measurement of cholesterol. Although, most natural enzymes show low thermostability, which limits their application. Here, we obtained an improved variant of Chromobacterium sp. DS1 cholesterol oxidase (ChOS) with enhanced thermostability by random mutant library applying two forms of error-prone PCR (serial dilution and single step). Wild-type ChOS indicated an optimal temperature and pH of 70 ºC and pH 7.5, respectively. The best mutant ChOS-M acquired three amino acid substitutions (S112T, I240V and A500S) and enhanced thermostability (at 50 °C for 5 h) by 30%. The optimum temperature and pH in the mutant were not changed. In comparison to wild type, circular dichroism disclosed no significant secondary structural alterations in mutants. These findings show that error-prone PCR is an effective method for enhancing enzyme characteristics and offers a platform for the practical use of ChOS as a thermal-resistance enzyme in industrial fields and clinical diagnosis.

An integrated microfluidic-based biosensor using a magnetically controlled MNPs-enzyme microreactor to determine cholesterol in serum with fluorometric detection

This work provides a microfluidic-based biosensor to determine total cholesterol in serum based on integrating the reaction/detection zone of a microfluidic chip of a magnetically retained enzyme microreactor (MREµR) coupled with the remote fluorometric detection through a bifurcated fiber-optic bundle (BFOB) connected with a conventional spectrofluorometer. The method is based on developing the enzymatic hydrolysis and oxidation of cholesterol at microscale size using both enzymes (cholesterol esterase (ChE) and cholesterol oxidase (ChOx)) immobilized on magnetic nanoparticles (MNPs). The biocatalyst reactions were followed by monitoring the fluorescence decreasing by the naphtofluorescein (NF) oxidation in the presence of the previous H₂O₂ formed. This microfluidic biosensor supposes the physical integration of a minimal MREµR as a bioactive enzyme area and the focused BFOB connected with the spectrofluorometer detector. The MREµR was formed by a 1 mm length of magnetic retained 2:1 ChE-MNP/ChOx-MNP mixture. The dynamic range of the calibration graph was 0.005-10 mmol L^-1, expressed as total cholesterol concentration with a detection limit of 1.1 µmol L^-1 (r² = 0.9999, s_y/x = 0.03, n = 10, r = 3). The precision expressed as the relative standard deviation (RSD%) was between 1.3 and 2.1%. The microfluidic-based biosensors showed a sampling frequency estimated at 30 h^-1. The method was applied to determine cholesterol in serum samples with recovery values between 94.8 and 102%. The results of the cholesterol determination in serum were also tested by correlation with those obtained using the other two previous methods.

Expression and characterization of cholesterol oxidase with high thermal and pH stability from Janthinobacterium agaricidamnosum

Cholesterol oxidases (COXases) have a diverse array of applications including analysis of blood cholesterol levels, synthesis of steroids, and utilization as an insecticidal protein. The COXase gene from Janthinobacterium agaricidamnosum was cloned and expressed in Escherichia coli. The purified COXase showed an optimal temperature of 60 °C and maintained about 96 and 72% of its initial activity after 30 min at 60 and 70 °C, respectively. In addition, the purified COXase exhibited a pH optimum at 7.0 and high pH stability over the broad pH range of 3.0-12.0. The pH stability of the COXase at pH 12.0 was higher than that of highly stable COXase from Chromobacterium sp. DS-1. The COXase oxidized cholesterol and β-cholestanol at higher rates than other 3β-hydroxysteroids. The Km, Vmax, and kcat values for cholesterol were 156 μM, 13.7 μmol/min/mg protein, and 14.4 s^-1, respectively. These results showed that this enzyme could be very useful in the clinical determination of cholesterol in serum and the production of steroidal compounds. This is the first report to characterize a COXase from the genus Janthinobacterium.

Improvement of thermostability of cholesterol oxidase from streptomyces Sp. SA-COO by random mutagenesis

To enhance the thermal stability of Streptomyces Sp. SA-COO cholesterol oxidase, random mutagenesis was used. A random mutant library was generated using two types of error-prone PCR (single step and serial dilution) and two mutants (ChOA-M1 and ChOA-M2) with improved thermostability were obtained. The best mutant ChOA-M1 acquired three amino acid substitutions (G49T, W52K, and F62V) and improved thermostability (at 50 °C for 5 h) by 40% and increased the kcat/Km value by 23%. The optimum pH was desirably changed to encompass a broad range from alkali to acid and circular dichroism revealed no significant secondary structure changes in mutants against wild type. These findings indicated that random mutagenesis was an effective technique for optimizing cholesterol oxidase properties and make a foundation for practical applications of Cholesterol oxidase in clinical diagnosis and industrial fields.

Metabolic signatures of cholesterol biosynthesis and absorption in patients with coronary artery disease

Due to the biochemical importance of cholesterol homeostasis in cardiovascular disease (CVD), this study was aimed to identify metabolic signatures of serum sterols according to atherosclerotic CVD severity. Biogically active free cholesterol and its 11 analogues in serum samples obtained from subjects who underwent cardiovascular intervention were quantitatively evaluated by gas chromatography-mass spectrometry (GCMS). Study groups were divided by 29 patients with stable angina (SA), 35 patients with acute coronary syndrome (ACS), and 41 controls. In all subjects, serum levels of cholesterol and its upstream precursors of 7-dehydrocholesterol, lathosterol, and lanosterol were closely associated with CVD risk factors, such as total cholesterol, low-density lipoprotein cholesterol (LDL-C), and LDL-C/high-density lipoprotein cholesterol (HDL-C) ratio (r = 0.407 ∼ 0.684, P < 0.03 for all). Metabolic ratios of lathosterol/cholesterol (control = 55.75 ± 34.34, SA = 51.04 ± 34.93, ACS = 36.52 ± 22.00; P < 0.03) and lanosterol/cholesterol (control = 12.27 ± 7.43, SA = 10.97 ± 9.13, ACS = 8.01 ± 5.82; P < 0.03), were remarkably decreased. Both metabolic ratios and individual concentrations of lathosterol and lanosterol were also decreased in subjects with statin treatment than those in the control group without statin treatment (P < 0.05 for all), whereas three metabolic ratios of dietary sterols (sitosterol, campesterol, and stigmasterol) to free cholesterol were increased after statin therapy (P < 0.05 for all) in both SA and ACS groups. The present metabolic signatures suggest that both lathosterol/cholesterol and lanosterol/cholesterol ratios corresponding to cholesterol biosynthesis may reflect statin response. Individual dietary sterols to cholesterol ratios resulted in higher intestinal cholesterol absorption after statin therapy.

MOF@MnO2nanocomposites prepared usingin situmethod and recyclable cholesterol oxidase-inorganic hybrid nanoflowers for cholesterol determination

In this work, through thein situgrowth of MnO₂nanosheets on the surface of terbium metal-organic frameworks (Tb-MOFs), MOF@MnO₂nanocomposites are prepared and the fluorescence of Tb-MOFs is quenched significantly by MnO₂. Additionally, the hybrid nanoflowers are self-assembled by cholesterol oxidase (ChOx) and copper phosphate (Cu₃(PO₄)₂·3H₂O). Then a new strategy for cholesterol determination is developed based on MOF@MnO₂nanocomposites and hybrid nanoflowers. Cholesterol is oxidized under the catalysis of hybrid nanoflowers to yield H₂O₂, which further reduces MnO₂nanosheets into Mn²⁺. Hence, the fluorescence recovery of Tb-MOFs is positively correlated to the concentration of cholesterol in the range of 10 to 360μM. The limit of detection (LOD) of cholesterol is 1.57μM. On the other hand, the hierarchical and confined structure of ChOx-inorganic hybrid nanoflowers greatly improve the stability of the enzyme. The activity of hybrid nanoflowers remains at a high level for one week when stored at room temperature. Moreover, the hybrid nanoflowers can be collected by centrifugation and reused. The activity of hybrid nanoflowers can continue at a high level for five cycles of determination. Therefore, it can be concluded that the hybrid nanoflowers are more stable and more economic than free enzymes, and they show a similar sensitivity and specificity to cholesterol compared with free ChOx. Finally, this strategy has been further validated for the determination of cholesterol in serum samples with satisfactory recoveries.

Impairing committed cholesterol biosynthesis in white matter astrocytes, but not grey matter astrocytes, enhances in vitro myelination

Remyelination is a regenerative process that is essential to recover saltatory conduction and to prevent neurodegeneration upon demyelination. The formation of new myelin involves the differentiation of oligodendrocyte progenitor cells (OPCs) toward oligodendrocytes and requires high amounts of cholesterol. Astrocytes (ASTRs) modulate remyelination by supplying lipids to oligodendrocytes. Remarkably, remyelination is more efficient in grey matter (GM) than in white matter (WM), which may relate to regional differences in ASTR subtype. Here, we show that a feeding layer of gmASTRs was more supportive to in vitro myelination than a feeding layer of wmASTRs. While conditioned medium from both gmASTRs and wmASTRs accelerated gmOPC differentiation, wmOPC differentiation is enhanced by secreted factors from gmASTRs, but not wmASTRs. In vitro analyses revealed that gmASTRs secreted more cholesterol than wmASTRs. Cholesterol efflux from both ASTR types was reduced upon exposure to pro-inflammatory cytokines, which was mediated via cholesterol transporter ABCA1, but not ABCG1, and correlated with a minor reduction of myelin membrane formation by oligodendrocytes. Surprisingly, a wmASTR knockdown of Fdft1 encoding for squalene synthase (SQS), an enzyme essential for the first committed step in cholesterol biosynthesis, enhanced in vitro myelination. Reduced secretion of interleukin-1β likely by enhanced isoprenylation, and increased unsaturated fatty acid synthesis, both pathways upstream of SQS, likely masked the effect of reduced levels of ASTR-derived cholesterol. Hence, our findings indicate that gmASTRs export more cholesterol and are more supportive to myelination than wmASTRs, but specific inhibition of cholesterol biosynthesis in ASTRs is beneficial for wmASTR-mediated modulation of myelination.

Binding of lactoferrin to the surface of low-density lipoproteins modified by myeloperoxidase prevents intracellular cholesterol accumulation by human blood monocytes

Myeloperoxidase (MPO) is a unique heme-containing peroxidase that can catalyze the formation of hypochlorous acid (HOCl). The strong interaction of MPO with low-density lipoproteins (LDL) promotes proatherogenic modification of LDL by HOCl. The MPO-modified LDL (Mox-LDL) accumulate in macrophages, resulting in the formation of foam cells, which is the pathognomonic symptom of atherosclerosis. A promising approach to prophylaxis and atherosclerosis therapy is searching for remedies that prevent the modification or accumulation of LDL in macrophages. Lactoferrin (LF) has several application points in obesity pathogenesis. We aimed to study LF binding to Mox-LDL and their accumulation in monocytes transformed into macrophages. Using surface plasmon resonance and ELISA techniques, we observed no LF interaction with intact LDL, whereas Mox-LDL strongly interacted with LF. The affinity of Mox-LDL to LF increased with the degree of oxidative modification of LDL. Moreover, an excess of MPO did not prevent interaction of Mox-LDL with LF. LF inhibits accumulation of cholesterol in macrophages exposed to Mox-LDL. The results obtained reinforce the notion of LF potency as a remedy against atherosclerosis.

The electrochemical reaction controlled optical response of cholestrol oxidase (COx) conjugated CdSe/ZnS quantum dots

This paper reports the enhanced performance of cholesterol oxidase (COx) conjugated CdSe/ZnS quantum dots (QDs) by using water-soluble mercaptoacitic acid (MAA) as linker. The functionalized MAA-CdSe/ZnS QDs conjugated in four different dilutions of cholesterol oxidase significantly affected QDs photoluminescence intensities, which affected the process of charge transfer from QDs to MAA. The conjugation of COx to MAA-QDs in increased dilutions resulted in the regain of PL intensities, which were attributed to the passivation of MAA HOMO/LUMO states. The electrochemical impedance spectroscopy and cyclic voltammetry of the conjugated QDs were performed to get study the charge transfer mechanism. The 1:1000 diluted COx conjugated MAA-CdSe/ZnS QDs was found to have the lowest charge transfer resistance of 228 Ω, the highest diffusion (~ 1.39 × 10^–13 cm²/s) and charge transfer rates (~ 4.5 × 10^–6 s⁻¹) between the electrode and the redox species. The current study demonstrated the sensitivity of electrochemical and optical based detection on the alkaline.

Cholesterol oxidase from Rhodococcus erythropolis with high specificity toward β-cholestanol and pytosterols

Two genes (choRI and choRII) encoding cholesterol oxidases belonging to the vanillyl-alcohol oxidase (VAO) family were cloned on the basis of putative cholesterol oxidase gene sequences in the genome sequence data of Rhodococcus erythropolis PR4. The genes corresponding to the mature enzymes were cloned in a pET vector and expressed in Escherichia coli. The two cholesterol oxidases produced from the recombinant E. coli were purified to examine their properties. The amino acid sequence of ChoRI showed significant similarity (57%) to that of ChoRII. ChoRII was more stable than ChoRI in terms of pH and thermal stability. The substrate specificities of these enzymes differed distinctively from one another. Interestingly, the activities of ChoRII toward β-cholestanol, β-sitosterol, and stigmasterol were 2.4-, 2.1-, and 1.7-fold higher, respectively, than those of cholesterol. No cholesterol oxidases with high activity toward these sterols have been reported so far. The cholesterol oxidation products from these two enzymes also differed. ChoRI and ChoRII oxidized cholesterol to form cholest-4-en-3-one and 6β-hydroperoxycholest-4-en-3-one, respectively.

Reagent-Free Colorimetric Cholesterol Test Strip Based on Self Color-Changing Property of Nanoceria

Paper-based test strip consisting of cerium oxide nanoparticles (nanoceria) as hydrogen peroxide (H₂O₂)-dependent color-changing nanozymes and cholesterol oxidase (ChOx) has been developed for convenient colorimetric determination of cholesterol without the need for chromogenic substrate. The construction of the cholesterol strip begins with physical adsorption of nanoceria on the paper surface, followed by covalent immobilization of ChOx via silanization, chitosan-mediated activation, and glutaraldehyde treatment of the nanoceria-embedded paper matrices. In the presence of cholesterol, ChOx catalyzes its oxidation to produce H₂O₂, which forms peroxide complex on the nanoceria surface and induces visual color change of the nanoceria-embedded paper from white/light yellow into intense yellow/orange, which was conveniently quantified with an image acquired by a conventional smartphone with the ImageJ software. Using this strategy, target cholesterol was specifically determined down to 40 μM with a dynamic linear concentration range of 0.1–1.5 mM under neutral pH condition, which is suitable to measure the serum cholesterol, with excellent stability during 20 days and reusability by recovering its original color-changing activity for 4 consecutive cycles. Furthermore, the practical utility of this strategy was successfully demonstrated by reliably determining cholesterol in human blood serum samples. This study demonstrates the potential of self color-changing nanozymes for developing colorimetric paper strip sensor, which is particularly useful in instrumentation-free point-of-care environments.

Medium Optimization by Response Surface Methodology for Improved Cholesterol Oxidase Production by a Newly Isolated Streptomyces rochei NAM-19 Strain

Cholesterol oxidase is an alcohol oxidoreductase flavoprotein with wide biotechnological applications. The current work describes the isolation of a potential cholesterol oxidase producing streptomycete from Egyptian soil. The isolated strain produced cholesterol oxidase in submerged culture using a medium containing glucose, yeast extract, malt extract, and CaCO₃ with the addition of cholesterol as an inducer. The isolated strain was identified as Streptomyces rochei NAM-19 based on 16S rRNA sequencing and phylogeny. Optimization of cholesterol oxidase production has been carried out using response surface methodology. The Plackett-Burman design method was used to evaluate the significant components of the production medium followed by Box-Behnken experimental design to locate the true optimal concentrations, which are significantly affecting enzyme production. Results showed that the predicted enzyme response could be closely correlated with the experimentally obtained production. Furthermore, the applied optimization strategy increased volumetric enzyme production by 2.55 times (65.1 U/mL) the initial production obtained before medium optimization (25.5 U/mL).

Identification of non-accumulating intermediate compounds during estrone (E1) metabolism by a newly isolated microbial strain BH2-1 from mangrove sediments of the South China Sea

Steroid estrogens are natural hormonal compounds produced by various animals and humans. Estrone (E1), estradiol (E2), and estriol (E3) are the most commonly known estrogens that are released into the environment along with human and animal excreta, which end up polluting water bodies. While these estrogens are usually biotransformed into their respective by-products by various microbial strains, E2 could also be transformed into E1 by 17β-hydroxysteroid dehydrogenases (17β-HSDs) under reducing environmental conditions. However, due to limited further biotransformation of E1, it accumulates to higher levels in water bodies compared to other natural estrogens in the aquatic environment. Given that E1 is one of the potential endocrine-disrupting compounds (EDCs), with several adverse effects on aquatic animals and consequently on the seafood industry, it is vital to remove E1 from the environment via improved steroid bioremediation. In the present study, we successfully isolated a potential E1-degrading microbial strain (named as BH2-1) from soil sediments collected from the Bai Hai mangrove region of the South China Sea. The strain BH2-1 has excellent E1-degrading potential and could degrade 89.5% of E1 after 6 days of incubation in a MSM-E1 medium containing 1% NaCl at pH 6. Besides, after 3 h and 6 h of extraction, two non-accumulating intermediate compounds [3-hydroxyandrosta-5,7,9(11)-trien-17-one and androsta-1,4,6-triene-3,17-dione (ATD)], respectively, were successfully identified using GC-MS analysis. These non-accumulating intermediate compounds have not previously been reported during E1 biodegradation and might be new intermediate metabolites. The identification of these new compounds also gives more insight into the mechanism of E1 metabolism and helps to establish a clear E1 biodegradation pathway, which further enriches our knowledge on the overall microbial steroid degradation pathway. Furthermore, whole-genome sequence analysis of strain BH2-1 revealed the presence of 46 genes that belong to 6 major steroid-degrading gene classes.

Immobilization of Cholesterol Oxidase from Streptomyces Sp. on Magnetite Silicon Dioxide by Crosslinking Method for Cholesterol Oxidation

Enzymatic biosensor has been paid much attention to the research fields due to its advantage in medical application. As one of the application, we determined the optimum value of cholesterol oxidase against cholesterol. In this work, we studied the behavior of cholesterol oxidation by enzymatic reaction to get the optimum condition for cholesterol oxidation. The enzyme that used were in two form, free cholesterol oxidase, and immobilized cholesterol oxidase. Cholesterol oxidase was produced from Streptomyces sp. by using solid state fermentation method and identified had high enzyme activity to be 5.12 U/mL. Cholesterol oxidase was simultaneously crosslinked immobilized onto magnetite coated by silicon dioxide (M-SiO₂). The support was characterized by Fourier transform infrared (FTIR) to determine the functional group of modified particle and scanning electron microscope (SEM) to observe the morphological or our prepared particle. Cholesterol oxidase sensitivity to substrate was analyzed by using HPLC with different interval time measurements. The oxidation of cholesterol by free enzyme and immobilized enzyme was also investigated. The best sensitivity of cholesterol oxidase was estimated to oxidize Cso (concentration of substrate) 1.46 mM of substrate with Ce (concentration of enzyme) 20 mg/mL for 180 min. Final oxidation value of cholesterol by immobilized enzyme was greater than 60%. The results of this study revealed that immobilized enzyme for cholesterol oxidation was stable, reproducible, and sensitive.

Solid state synthesis of docosahexaenoic acid-loaded zinc oxide nanoparticles as a potential antidiabetic agent in rats

Our goal in this study is to improve the efficiency of docosahexaenoic acid (DHA) toward the enhancement of insulin signaling pathway in vivo via loading with zinc oxide nanoparticles (ZnO NPs). To this end, two consecutive steps were undertaken, preparation of ZnO NPs by one-step solid-state reaction in dry conditions and calcinated followed by loading DHA. Both developed nanoparticles, with and without DHA were then characterized by TEM, SEM, EDX, and Zetasizer. For comparison between free and loaded DHA, four groups of rats were prepared to receive different treatments. Group I; healthy rats (reference), group II; diabetes (streptozotocin-induced), group III and group IV are diabetes orally administered with free DHA and DHA-loaded ZnO NPs (10 mg/kg bw/day), respectively. Blood samples were collected and analyzed where the results demonstrated that fasting blood sugar and insulin resistance were significantly increased in diabetic group along with upgrading in oxidative stress parameters emphasizing the oxidative properties of streptozotocin. HPLC analysis of cell membrane fatty acids resulted in the reduction of omega-6 and 9 and elevation of omega-3 after free DHA and DHA-loaded ZnO NPs streptozotocin treatments. DHA-loaded ZnO NPs had high performance in enhancing insulin signaling pathway as expressed in changes of phosphatidylinositol 3-kinase (PI3K) levels.

Microbial transformation of cholesterol: reactions and practical aspects-an update

Cholesterol is a C27-sterol employed as starting material for the synthesis of valuable pharmaceutical steroids and precursors. The microbial transformations of cholesterol have been widely studied, since they are performed with high regio- and stereoselectivity and allow the production of steroidal compounds which are difficult to synthesize by classical chemical methods. In recent years, ongoing research is being conducted to discover novel biocatalysts and to develop biotechnological processes to improve existing biocatalysts and biotransformation reactions. The main objective of this review is to present the most remarkable advances in fungal and bacterial transformation of cholesterol, focusing on the different types of microbial reactions and biocatalysts, biotransformation products, and practical aspects related to sterol dispersion improvement, covering literature since 2000. It reviews the conversion of cholesterol by whole-cell biocatalysts and by purified enzymes that lead to various structural modifications, including side chain cleavage, hydroxylation, dehydrogenation/reduction, isomerization and esterification. Finally, approaches used to improve the poor solubility of cholesterol in aqueous media, such as the use of different sterol-solubilizing agents or two-phase conversion system, are also discussed.

Expression optimization, purification, and functional characterization of cholesterol oxidase from Chromobacterium sp. DS1

Cholesterol oxidase is a bifunctional bacterial flavoenzyme which catalyzes oxidation and isomerization of cholesterol. This valuable enzyme has attracted a great deal of attention because of its wide application in the clinical laboratory, synthesis of steroid derived drugs, food industries, and its potentially insecticidal activity. Therefore, development of an efficient protocol for overproduction of cholesterol oxidase could be valuable and beneficial in this regard. The present study examined the role of various parameters (host strain, culture media, induction time, isopropyl ß-D-1-thiogalactopyranoside concentration, as well as post-induction incubation time and temperature) on over-expression of cholesterol oxidase from Chromobacterium sp. DS1. Applying the optimized protocol, the yield of recombinant cholesterol oxidase significantly increased from 92 U/L to 2115 U/L. Under the optimized conditions, the enzyme was produced on a large-scale, and overexpressed cholesterol oxidase was purified from cell lysate by column nickel affinity chromatography. K_m and V_max values of the purified enzyme for cholesterol were estimated using Lineweaver-Burk plot. Further, the optimum pH and optimum temperature for the enzyme activity were determined. This study reports a straightforward protocol for cholesterol oxidase production which can be performed in any laboratory.

Expression optimization of recombinant cholesterol oxidase in Escherichia coli and its purification and characterization

Cholesterol oxidase is a bacterial flavoenzyme which catalyzes oxidation and isomerization of cholesterol. This enzyme has a great commercial value because of its wide applications in cholesterol analysis of clinical samples, synthesis of steroid-derived drugs, food industries, and potentially insecticidal activity. Accordingly, development of an efficient protocol for overexpression of cholesterol oxidase can be very valuable and beneficial. In this study, expression optimization of cholesterol oxidase from Streptomyces sp. SA-COO was investigated in Escherichia coli host strains. Various parameters that may influence the yield of a recombinant enzyme were evaluated individually. The optimal host strain, culture media, induction time, Isopropyl ß-d-1-thiogalactopyranoside concentration, as well as post-induction incubation time and temperature were determined in a shaking flask mode. Applying the optimized protocol, the production of recombinant cholesterol oxidase was significantly enhanced from 3.2 to 158 U/L. Under the optimized condition, the enzyme was produced on a large-scale, and highly expressed cholesterol oxidase was purified from cell lysate by column nickel affinity chromatography. K_m and V_max values of the purified enzyme for cholesterol were estimated using Lineweaver–Burk plot. Further, the optimum pH and optimum temperature for the enzyme activity were also determined. We report a straightforward and easy protocol for cholesterol oxidase production which can be performed in any laboratory.

Analytical methods for cholesterol quantification

Cholesterol is an important lipid molecule in cell membranes and lipoproteins. Cholesterol is also a precursors of steroid hormones, bile acids, and vitamin D. Abnormal levels of cholesterol or its precursors have been observed in various human diseases, such as heart diseases, stroke, type II diabetes, brain diseases and many others. Therefore, accurate quantification of cholesterol is important for individuals who are at increased risk for these diseases. Multiple analytical methods have been developed for analysis of cholesterol, including classical chemical methods, enzymatic assays, gas chromatography (GC), liquid chromatography (LC), and mass spectrometry (MS). Strategy known as ambient ionization mass spectrometry (AIMS), operating at atmospheric pressure, with only minimal sample pretreatments for real time, in situ, and rapid interrogation of the sample has also been employed for quantification of cholesterol. In this review, we summarize the most prevalent methods for cholesterol quantification in biological samples and foods. Nevertheless, we highlight several new technologies, such as AIMS, used as alternative methods to measure cholesterol that are potentially next-generation platforms. Representative examples of molecular imaging of cholesterol in tissue sections are also included in this review article.

Co-localization of oxidase and catalase inside a porous support to improve the elimination of hydrogen peroxide: Oxidation of biogenic amines by amino oxidase from Pisum sativum

Diamine oxidase (DAO) from Pisum sativum is an enzyme that catalyzes the degradation of biogenic amines (BA) present in wine, producing harmless aldehydes and hydrogen peroxide (H2O2). H2O2 promotes a rapid inactivation of the immobilized enzyme. At first glance, co-immobilization of DAO and catalase (CAT) could improve the elimination of the released hydrogen peroxide. Two different co-immobilized derivatives were prepared: (a) both enzymes co-localized and homogeneously distributed across the whole structure of a porous support, and (b) both enzymes we de-localized inside the porous support: DAO immobilized on the outer part of the porous support and catalase immobilized in the inner part. Co-localized derivatives were seven-fold more effective than de-localized ones for the elimination of hydrogen peroxide inside the porous support. In addition to that, the degradation of putrescine by DAO was three-fold more rapid when using both co-localized enzymes. The optimal co-localized derivative (containing 1.25 mg of DAO plus 25 mg of CAT per g of support) promoted the instantaneous elimination of 91% H2O2 released inside the porous support during putrescine oxidation. This optimal derivative preserves 92% of activity after three reaction cycles and DAO immobilized without catalase only preserves 41% of activity. Co-localization seems to be the key strategy to immobilize two sequential enzymes. When enzymes are immobilized in close proximity to each other in a co-localized pattern, the generation of byproducts as H2O2 is strongly reduced.

Identification of unusual oxysterols and bile acids with 7-oxo or 3β,5α,6β-trihydroxy functions in human plasma by charge-tagging mass spectrometry with multistage fragmentation

7-Oxocholesterol (7-OC), 5,6-epoxycholesterol (5,6-EC), and its hydrolysis product cholestane-3β,5α,6β-triol (3β,5α,6β-triol) are normally minor oxysterols in human samples; however, in disease, their levels may be greatly elevated. This is the case in plasma from patients suffering from some lysosomal storage disorders, e.g., Niemann-Pick disease type C, or the inborn errors of sterol metabolism, e.g., Smith-Lemli-Opitz syndrome and cerebrotendinous xanthomatosis. A complication in the analysis of 7-OC and 5,6-EC is that they can also be formed ex vivo from cholesterol during sample handling in air, causing confusion with molecules formed in vivo. When formed endogenously, 7-OC, 5,6-EC, and 3β,5α,6β-triol can be converted to bile acids. Here, we describe methodology based on chemical derivatization and LC/MS with multistage fragmentation (MSⁿ) to identify the necessary intermediates in the conversion of 7-OC to 3β-hydroxy-7-oxochol-5-enoic acid and 5,6-EC and 3β,5α,6β-triol to 3β,5α,6β-trihydroxycholanoic acid. Identification of intermediate metabolites is facilitated by their unusual MSⁿ fragmentation patterns. Semiquantitative measurements are possible, but absolute values await the synthesis of isotope-labeled standards.

An update on oxysterol biochemistry: New discoveries in lipidomics

Oxysterols are oxidised derivatives of cholesterol or its precursors post lanosterol. They are intermediates in the biosynthesis of bile acids, steroid hormones and 1,25-dihydroxyvitamin D_3. Although often considered as metabolic intermediates there is a growing body of evidence that many oxysterols are bioactive and their absence or excess may be part of the cause of a disease phenotype. Using global lipidomics approaches oxysterols are underrepresented encouraging the development of targeted approaches. In this article, we discuss recent discoveries important in oxysterol biochemistry and some of the targeted lipidomic approaches used to make these discoveries.

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Oxysterols can regulate both the innate and adaptive immune systems.

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Oxysterols can be tumour suppressors and on cometabolites.

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Oxysterols can inhibit or activate the Hh signalling pathway.

An ARV1 homologue from a filarial nematode is functional in yeast

The transmembrane protein, ARV1, plays a key role in intracellular sterol homeostasis by controlling sterol distribution and cellular uptake. To date, only the ARV1s from yeast and humans have been characterized to some extent. In this study, the ARV1 of an animal filarial parasite, Setaria digitata (SdARV1), was characterized; its cDNA was 761 bp and encoded a protein of 217 amino acids, with a predicted molecular weight of 25 kDa, containing a highly conserved ARV1 homology domain and three transmembrane domains in the bioinformatic analyses. Information required to cluster members belonging to a particular taxon has been revealed in phylogenetic analyses of ARV1 sequences derived from different organisms. Reverse transcription-polymerase chain reaction (RT-PCR) analyses indicated that SdARV1 was expressed in different developmental stages - microfilariae and adult male and female worms. Experiments carried out with a single copy of the SdARV1 under the control of the PMA-1 promoter in a temperature-sensitive Saccharomyces cerevisiae mutant strain indicated full complementation of the mutant phenotype, with growth at a non-permissive temperature (37°C). Microscopic observations of cellular morphology with Gram staining revealed alteration of the shape from shrunken to oval, in mutant and complemented strains, respectively. Assessment of free sterol levels extracted from mutant yeast and complemented strains indicated that the level of sterol was significantly higher in the former compared to the latter, which had sterol levels similar to those of the wild type. Thus, the results of the current study suggest that SdARV1 is ubiquitously expressed in different developmental stages of S. digitata, and that it is a true functional homologue of mammalian and yeast ARV1s, which have crucial phylogenetic information that follows classical evolutionary trends. Finally, this is the first study to report the biological function of nematode ARV1.

Purification, characterization and amino acid content of cholesterol oxidase produced by Streptomyces aegyptia NEAE 102

BACKGROUND

There is an increasing demand on cholesterol oxidase for its various industrial and clinical applications. The current research was focused on extracellular cholesterol oxidase production under submerged fermentation by a local isolate previously identified as Streptomyces aegyptia NEAE 102. The crude enzyme extract was purified by two purification steps, protein precipitation using ammonium sulfate followed by ion exchange chromatography using DEAE Sepharose CL-6B. The kinetic parameters of purified cholesterol oxidase from Streptomyces aegyptia NEAE 102 were studied.

RESULTS

The best conditions for maximum cholesterol oxidase activity were found to be 105 min of incubation time, an initial pH of 7 and temperature of 37 °C. The optimum substrate concentration was found to be 0.4 mM. The higher thermal stability behavior of cholesterol oxidase was at 50 °C. Around 63.86% of the initial activity was retained by the enzyme after 20 min of incubation at 50 °C. The apparent molecular weight of the purified enzyme as sized by sodium dodecyl sulphate-polyacryalamide gel electrophoresis was approximately 46 KDa. On DEAE Sepharose CL-6B column cholesterol oxidase was purified to homogeneity with final specific activity of 16.08 U/mg protein and 3.14-fold enhancement. The amino acid analysis of the purified enzyme produced by Streptomyces aegyptia NEAE 102 illustrated that, cholesterol oxidase is composed of 361 residues with glutamic acid as the most represented amino acid with concentration of 11.49 μg/mL.

CONCLUSIONS

Taking into account the extracellular production, wide pH tolerance, thermal stability and shelf life, cholesterol oxidase produced by Streptomyces aegyptia NEAE 102 suggested that the enzyme could be industrially useful.

Biomedical Applications of Enzymes From Marine Actinobacteria

Marine microbial enzyme technologies have progressed significantly in the last few decades for different applications. Among the various microorganisms, marine actinobacterial enzymes have significant active properties, which could allow them to be biocatalysts with tremendous bioactive metabolites. Moreover, marine actinobacteria have been considered as biofactories, since their enzymes fulfill biomedical and industrial needs. In this chapter, the marine actinobacteria and their enzymes' uses in biological activities and biomedical applications are described.

Enzymes From Rare Actinobacterial Strains

Actinobacteria constitute rich sources of novel biocatalysts and novel natural products for medical and industrial utilization. Although actinobacteria are potential source of economically important enzymes, the isolation and culturing are somewhat tough because of its extreme habitats. But now-a-days, the rate of discovery of novel compounds producing actinomycetes from soil, freshwater, and marine ecosystem has increased much through the developed culturing and genetic engineering techniques. Actinobacteria are well-known source of their bioactive compounds and they are the promising source of broad range of industrially important enzymes. The bacteria have the capability to degrade a range of pesticides, hydrocarbons, aromatic, and aliphatic compounds (Sambasiva Rao, Tripathy, Mahalaxmi, & Prakasham, 2012). Most of the enzymes are mainly derived from microorganisms because of their easy of growth, minimal nutritional requirements, and low-cost for downstream processing. The focus of this review is about the new, commercially useful enzymes from rare actinobacterial strains. Industrial requirements are now fulfilled by the novel actinobacterial enzymes which assist the effective production. Oxidative enzymes, lignocellulolytic enzymes, extremozymes, and clinically useful enzymes are often utilized in many industrial processes because of their ability to catalyze numerous reactions. Novel, extremophilic, oxidative, lignocellulolytic, and industrially important enzymes from rare Actinobacterial population are discussed in this chapter.

Identification and statistical optimization of fermentation conditions for a newly isolated extracellular cholesterol oxidase-producing Streptomyces cavourensis strain NEAE-42

BACKGROUND

Due to broad range of clinical and industrial applications of cholesterol oxidase, isolation and screening of bacterial strains producing extracellular form of cholesterol oxidase is of great importance.

RESULTS

One hundred and thirty actinomycete isolates were screened for their cholesterol oxidase activity. Among them, a potential culture, strain NEAE-42 is displayed the highest extracellular cholesterol oxidase activity. It was selected and identified as Streptomyces cavourensis strain NEAE-42. The optimization of different process parameters for cholesterol oxidase production by Streptomyces cavourensis strain NEAE-42 using Plackett-Burman experimental design and response surface methodology was carried out. Fifteen variables were screened using Plackett-Burman experimental design. Cholesterol, initial pH and (NH4)2SO4 were the most significant positive independent variables affecting cholesterol oxidase production. Central composite design was chosen to elucidate the optimal concentrations of the selected process variables on cholesterol oxidase production. It was found that, cholesterol oxidase production by Streptomyces cavourensis strain NEAE-42 after optimization process was 20.521U/mL which is higher than result obtained from the basal medium before screening process using Plackett-Burman (3.31 U/mL) with a fold of increase 6.19.

CONCLUSIONS

The cholesterol oxidase level production obtained in this study (20.521U/mL) by the statistical method is higher than many of the reported values.

New methods for analysis of oxysterols and related compounds by LC-MS

Oxysterols are oxygenated forms of cholesterol or its precursors. They are formed enzymatically and via reactive oxygen species. Oxysterols are intermediates in bile acid and steroid hormone biosynthetic pathways and are also bioactive molecules in their own right, being ligands to nuclear receptors and also regulators of the processing of steroid regulatory element-binding proteins (SREBPs) to their active forms as transcription factors regulating cholesterol and fatty acid biosynthesis. Oxysterols are implicated in the pathogenesis of multiple disease states ranging from atherosclerosis and cancer to multiple sclerosis and other neurodegenerative diseases including Alzheimer's and Parkinson's disease. Analysis of oxysterols is challenging on account of their low abundance in biological systems in comparison to cholesterol, and due to the propensity of cholesterol to undergo oxidation in air to generate oxysterols with the same structures as those present endogenously. In this article we review the mass spectrometry-based methods for oxysterol analysis paying particular attention to analysis by liquid chromatography-mass spectrometry (LC-MS).

Elevated Basal Insulin Secretion in Type 2 Diabetes Caused by Reduced Plasma Membrane Cholesterol

Elevated basal insulin secretion under fasting conditions together with insufficient stimulated insulin release is an important hallmark of type 2 diabetes, but the mechanisms controlling basal insulin secretion remain unclear. Membrane rafts exist in pancreatic islet cells and spatially organize membrane ion channels and proteins controlling exocytosis, which may contribute to the regulation of insulin secretion. Membrane rafts (cholesterol and sphingolipid containing microdomains) were dramatically reduced in human type 2 diabetic and diabetic Goto-Kakizaki (GK) rat islets when compared with healthy islets. Oxidation of membrane cholesterol markedly reduced microdomain staining intensity in healthy human islets, but was without effect in type 2 diabetic islets. Intriguingly, oxidation of cholesterol affected glucose-stimulated insulin secretion only modestly, whereas basal insulin release was elevated. This was accompanied by increased intracellular Ca²⁺ spike frequency and Ca²⁺ influx and explained by enhanced single Ca²⁺ channel activity. These results suggest that the reduced presence of membrane rafts could contribute to the elevated basal insulin secretion seen in type 2 diabetes.

Ergosterols from the Culture Broth of Marine Streptomyces anandii H41-59

An actinomycete strain, H41-59, isolated from sea sediment in a mangrove district, was identified as Streptomyces anandii on the basis of 16S rDNA gene sequence analysis as well as the investigation of its morphological, physiological and biochemical characteristics. Three new ergosterols, ananstreps A-C (1-3), along with ten known ones (4-13), were isolated from the culture broth of this strain. The gross structures of these new compounds were elucidated on the basis of extensive analysis of spectroscopic data, including HR-ESI-MS, and NMR. The cytotoxicities of these isolates against human breast adenocarcinoma cell line MCF-7, human glioblastoma cell line SF-268, and human lung cancer cell line NCI-H460 and their antibacterial activities in inhibiting the growth of Candida albicans and some other pathogenic microorganisms were tested. Compounds 3-8, 10 and 11 displayed cytotoxicity with IC50 values in a range from 13.0 to 27.8 μg/mL. However, all the tested compounds showed no activity on C. albicans and other bacteria at the test concentration of 1 mg/mL with the paper disc diffusion method.

Modeling and optimization of a continuous bead milling process for bacterial cell lysis using response surface methodology

Schematic representation of the modeling and optimization of continuous bead milling process for efficient bacterial cell lysis.

Purification and Characterization of an Extracellular Cholesterol Oxidase of Bacillus subtilis Isolated from Tiger Excreta

A mesophilic Bacillus sp. initially isolated from tiger excreta and later identified as a Bacillus subtilis strain was used to produce an extracellular cholesterol oxidase (COX) in cholesterol-enriched broth. This bacterial isolate was studied for the production of COX by manipulation of various physicochemical parameters. The extracellular COX was successfully purified from the cell-free culture broth of B. subtilis by successive salting out with ammonium sulfate, dialysis, and riboflavin-affinity chromatography. The purified COX was characterized for its molecular mass/structure and stability. The enzyme possessed some interesting properties such as high native Mr (105 kDa), multimeric (pentamer of ∼21 kDa protein) nature, organic solvent compatibility, and a half-life of ∼2 h at 37 °C. The bacterial COX exhibited ∼22 % higher activity in potassium phosphate buffer (pH 7.5) in the presence of a nonionic detergent Triton X-100 at 0.05 % (v/v). The K m and V max value of COX of B. subtilis COX were found to be 3.25 mM and 2.17 μmol min ml(-1), respectively. The purified COX showed very little cytotoxicity associated with it.

Artificial Intelligence versus Statistical Modeling and Optimization of Cholesterol Oxidase Production by using Streptomyces Sp

Cholesterol oxidase (COD) is a bi-functional FAD-containing oxidoreductase which catalyzes the oxidation of cholesterol into 4-cholesten-3-one. The wider biological functions and clinical applications of COD have urged the screening, isolation and characterization of newer microbes from diverse habitats as a source of COD and optimization and over-production of COD for various uses. The practicability of statistical/ artificial intelligence techniques, such as response surface methodology (RSM), artificial neural network (ANN) and genetic algorithm (GA) have been tested to optimize the medium composition for the production of COD from novel strain Streptomyces sp. NCIM 5500. All experiments were performed according to the five factor central composite design (CCD) and the generated data was analysed using RSM and ANN. GA was employed to optimize the models generated by RSM and ANN. Based upon the predicted COD concentration, the model developed with ANN was found to be superior to the model developed with RSM. The RSM-GA approach predicted maximum of 6.283 U/mL COD production, whereas the ANN-GA approach predicted a maximum of 9.93 U/mL COD concentration. The optimum concentrations of the medium variables predicted through ANN-GA approach were: 1.431 g/50 mL soybean, 1.389 g/50 mL maltose, 0.029 g/50 mL MgSO₄, 0.45 g/50 mL NaCl and 2.235 ml/50 mL glycerol. The experimental COD concentration was concurrent with the GA predicted yield and led to 9.75 U/mL COD production, which was nearly two times higher than the yield (4.2 U/mL) obtained with the un-optimized medium. This is the very first time we are reporting the statistical versus artificial intelligence based modeling and optimization of COD production by Streptomyces sp. NCIM 5500.