Alkaline surface treatment and time-resolved reading of mn-doped nanocrystal signal transducer for enhanced bioassay sensitivity

Recently, Mn-doped semiconductor nanocrystals (NCs) with high brightness, long lifetimes, and low-energy excitation are emerging for time-resolved luminescence biosensing/imaging. Following our previous work on Mn-doped NCs, in this work we developed poly(styrene-co-maleic anhydride) (PSMA)-encapsulated Mn-doped AgZnInS/ZnS NCs as signal transducers for immunoassay of capsular polysaccharide (CPS), a surface antigen and also a biomarker of Burkholderia pseudomallei which causes a fatal disease called melioidosis. To enhance the assay sensitivity, a surface treatment for PSMA-encapsulated NCs (NC-probes) was performed to promote the presence of carboxyl groups that help conjugate more anti-CPS antibodies to the surface of NC-probes and thus enhance bioassay signals. Meanwhile, time-resolved reading on the luminescence of NC-probes was adopted to minimize the assay background autofluorescence. Both strategies essentially enhance the assay signal-to-background ratio (or equivalently the assay sensitivity) by increasing the signal and decreasing the background, respectively. Through performing and comparing immunoassays with different NC-probes (with and without surface treatment) and different signal reading methods (time-resolved reading and non-time-resolved reading), it was proven that the immunoassay adopting surface-treated NC-probes and time-resolved reading achieved a lower limit-of-detection (LOD) than the ones adopting non-surface-treated NC-probes or non-time-resolved reading. Moreover, the achieved LOD is comparable to the LOD of immunoassay using enzyme horseradish peroxidase as a signal transducer.

3-Methylglutarylcarnitine: A biomarker of mitochondrial dysfunction

The acylcarnitines comprise a wide range of acyl groups linked via an ester bond to the hydroxyl group of L-carnitine. Mass spectrometry methods are capable of measuring the relative abundance of hundreds of acylcarnitines in a single drop of blood. As such, acylcarnitines can serve as sensitive biomarkers of disease. For certain acylcarnitines, however, their biochemical origin, and biomedical significance, remain unclear. One such example is 3-methylglutaryl (3MG) carnitine (C5-3M-DC). Whereas 3MG carnitine levels are normally very low, elevated levels are detected in discrete inborn errors of metabolism (IEM) as well as different forms of heart disease. Moreover, acute injury, including γ radiation exposure, paraquat poisoning, and traumatic brain injury manifest elevated levels of 3MG carnitine in blood and/or urine. Recent evidence indicates that two distinct biosynthetic routes to 3MG carnitine exist. The first, caused by an inherited deficiency in the leucine catabolism pathway enzyme, 3-hydroxy-3-methylglutaryl (HMG) CoA lyase, leads to a buildup of trans-3-methylglutaconyl (3MGC) CoA. Reduction of the double bond in trans-3MGC CoA generates 3MG CoA, which is then converted to 3MG carnitine by carnitine acyltransferase. This route, however, cannot explain why 3MG carnitine levels increase in IEMs that do not affect leucine metabolism or various chronic and acute disease states. In these cases, disease-related defects in aerobic energy metabolism result in diversion of acetyl CoA to trans-3MGC CoA. Once formed, trans-3MGC CoA is reduced to 3MG CoA and esterified to form 3MG carnitine. Thus, 3MG carnitine, represents a potential biomarker of disease processes associated with compromised mitochondrial energy metabolism.

Characterization of trans-3-Methylglutaconyl CoA-Dependent Protein Acylation

3-methylglutaconyl (3MGC) CoA hydratase (AUH) is the leucine catabolism pathway enzyme that catalyzes the hydration of trans-3MGC CoA to 3-hydroxy, 3-methylglutaryl (HMG) CoA. In several inborn errors of metabolism (IEM), however, metabolic dysfunction can drive this reaction in the opposite direction (the dehydration of HMG CoA). The recent discovery that trans-3MGC CoA is inherently unstable and prone to a series of non-enzymatic chemical reactions provides an explanation for 3MGC aciduria observed in these IEMs. Under physiological conditions, trans-3MGC CoA can isomerize to cis-3MGC CoA, which is structurally poised to undergo intramolecular cyclization with the loss of CoA, generating cis-3MGC anhydride. The anhydride is reactive and has two potential fates; (a) hydrolysis to yield cis-3MGC acid or (b) a reaction with lysine side-chain amino groups to 3MGCylate substrate proteins. An antibody elicited against a 3MGC hapten was employed to investigate protein acylation in incubations containing recombinant AUH, HMG CoA, and bovine serum albumin (BSA). The data obtained show that, as AUH dehydrates HMG CoA to trans-3MGC CoA, BSA is acylated. Moreover, α-3MGC IgG immunoblot signal intensity correlates with AUH concentration, HMG CoA substrate concentration, and incubation time. Thus, protein 3MGCylation may contribute to the phenotypic features associated with IEMs that manifest 3MGC aciduria.

Isolation of recombinant apolipoprotein E4 N-terminal domain by foam fractionation

Apolipoprotein (apo) E functions in lipoprotein metabolism as a low density lipoprotein receptor ligand. ApoE is comprised of two structural domains, a 22 kDa N-terminal (NT) domain that adopts a helix bundle conformation and a 10 kDa C-terminal domain with strong lipid binding affinity. The NT domain is capable of transforming aqueous phospholipid dispersions into discoidal reconstituted high density lipoprotein (rHDL) particles. Given the utility of apoE-NT as a structural component of rHDL, expression studies were conducted. A plasmid construct encoding a pelB leader sequence fused to the N-terminus of human apoE4 (residues 1-183) was transformed into Escherichia coli. Upon expression, the fusion protein is directed to the periplasmic space where leader peptidase cleaves the pelB sequence, generating mature apoE4-NT. In shaker flask expression cultures, apoE4-NT escapes the bacteria and accumulates in the medium. In a bioreactor setting, however, apoE4-NT was found to combine with gas and liquid components in the culture medium to generate large quantities of foam. When this foam was collected in an external vessel and collapsed into a liquid foamate, analysis revealed that apoE4-NT was the sole major protein present. The product protein was further isolated by heparin affinity chromatography (60-80 mg/liter bacterial culture), shown to be active in rHDL formulation, and documented to serve as an acceptor of effluxed cellular cholesterol. Thus, foam fractionation provides a streamlined process to produce recombinant apoE4-NT for biotechnology applications.

Formulation and Characterization of Bioactive Agent Containing Nanodisks

The term nanodisk refers to a discrete type of nanoparticle comprised of a bilayer forming lipid, a scaffold protein, and an integrated bioactive agent. Nanodisks are organized as a disk-shaped lipid bilayer whose perimeter is circumscribed by the scaffold protein, usually a member of the exchangeable apolipoprotein family. Numerous hydrophobic bioactive agents have been efficiently solubilized in nanodisks by their integration into the hydrophobic milieu of the particle's lipid bilayer, yielding a largely homogenous population of particles in the range of 10-20 nm in diameter. The formulation of nanodisks requires a precise ratio of individual components, an appropriate sequential addition of each component, followed by bath sonication of the formulation mixture. The amphipathic scaffold protein spontaneously contacts and reorganizes the dispersed bilayer forming lipid/bioactive agent mixture to form a discrete, homogeneous population of nanodisk particles. During this process, the reaction mixture transitions from an opaque, turbid appearance to a clarified sample that, when fully optimized, yields no precipitate upon centrifugation. Characterization studies involve the determination of bioactive agent solubilization efficiency, electron microscopy, gel filtration chromatography, ultraviolet visible (UV/Vis) absorbance spectroscopy, and/or fluorescence spectroscopy. This is normally followed by an investigation of biological activity using cultured cells or mice. In the case of nanodisks harboring an antibiotic (i.e., the macrolide polyene antibiotic amphotericin B), their ability to inhibit the growth of yeast or fungi as a function of concentration or time can be measured. The relative ease of formulation, versatility with respect to component parts, nanoscale particle size, inherent stability, and aqueous solubility permits myriad in vitro and in vivo applications of nanodisk technology. In the present article, we describe a general methodology to formulate and characterize nanodisks containing amphotericin B as the hydrophobic bioactive agent.

Cardiac-specific deficiency of 3-hydroxy-3-methylglutaryl coenzyme A lyase in mice causes cardiomyopathy and a distinct pattern of acyl-coenzyme A-related biomarkers

Deficiency of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) lyase (HL) is an autosomal recessive inborn error of acyl-CoA metabolism affecting the last step of leucine degradation. Patients with HL deficiency (HLD) can develop a potentially fatal cardiomyopathy. We created mice with cardiomyocyte-specific HLD (HLHKO mice), inducing Cre recombinase-mediated deletion of exon 2 at two months of age. HLHKO mice survive, but develop left ventricular hypertrophy by 9 months. Also, within minutes after intraperitoneal injection of the leucine metabolite 2-ketoisocaproate (KIC), they show transient left ventricular hypocontractility and dilation. Leucine-related acyl-CoAs were elevated in HLHKO heart (e.g., HMG-CoA, 34.0 ± 4.4 nmol/g versus 0.211 ± 0.041 in controls, p < 0.001; 3-methylcrotonyl-CoA, 5.84 ± 0.69 nmol/g versus 0.282 ± 0.043, p < 0.001; isovaleryl-CoA, 1.86 ± 0.30 nmol/g versus 0.024 ± 0.014, p < 0.01), a similar pattern to that in liver of mice with hepatic HL deficiency. After KIC loading, HMG-CoA levels in HLHKO heart were higher than under basal conditions, as were the ratios of HMG-CoA/acetyl-CoA and of HMG-CoA/succinyl-CoA. In contrast to the high levels of multiple leucine-related acyl-CoAs, biomarkers in urine and plasma of HLHKO mice show isolated hyper-3-methylglutaconic aciduria (700.8 ± 48.4 mmol/mol creatinine versus 37.6 ± 2.4 in controls, p < 0.001), and elevated C5-hydroxyacylcarnitine in plasma (0.248 ± 0.014 μmol/L versus 0.048 ± 0.005 in controls, p < 0.001). Mice with liver-specific HLD were compared, and showed normal echocardiographic findings and normal acyl-CoA profiles in heart. This study of nonhepatic tissue-specific HLD outside of liver reveals organ-specific origins of diagnostic biomarkers for HLD in blood and urine and shows that mouse cardiac HL is essential for myocardial function in a cell-autonomous, organ-autonomous fashion.

Cardiolipin nanodisks confer protection against doxorubicin-induced mitochondrial dysfunction

Doxorubicin (DOX) is an aqueous soluble anthracycline therapeutic widely used in cancer treatment. Although DOX anti-cancer activity is dose-dependent, increased dosage enhances the risk of cardiotoxicity. Despite intensive investigation, the molecular basis of this undesirable side effect has yet to be established. In addition to serving as a DNA intercalation agent, DOX is known to bind to the signature mitochondrial phospholipid, cardiolipin (CL). Consistent with this, DOX associates with aqueous soluble nanoparticles, termed nanodisks (ND), comprised solely of CL and an apolipoprotein scaffold. Fluorescence microscopy analysis revealed that DOX uptake, and targeting to the nucleus of cultured hepatocarcinoma (HepG2) or breast cancer (MCF7) cells, was unaffected by its association with CL-ND. Subsequent studies revealed that free DOX and DOX-CL-ND were equivalent in terms of growth inhibition activity in both cell lines. By contrast, in studies with H9C2 cardiomyocytes, DOX-CL-ND induced a lesser concentration-dependent decline in cell viability than free DOX. Whereas incubation of H9C2 cardiomyocytes with free DOX caused a steep decline in maximal oxygen consumption rate, DOX-CL-ND treated cells were largely unaffected. The data indicate that association of DOX with CL-ND does not diminish its cancer cell growth inhibition activity yet confers protection to cardiomyocytes from DOX-induced effects on aerobic respiration. This study illustrates that interaction with CL plays a role in DOX-induced mitochondrial dysfunction and suggests CL-ND provide a tool for investigating the mechanistic basis of DOX-induced cardiotoxicity.

Role of non-enzymatic chemical reactions in 3-methylglutaconic aciduria

3-Methylglutaconic (3MGC) aciduria occurs in numerous inborn errors associated with compromised mitochondrial energy metabolism. In these disorders, 3MGC CoA is produced de novo from acetyl CoA in three steps with the final reaction catalysed by 3MGC CoA hydratase (AUH). In in vitro assays, whereas recombinant AUH dehydrated 3-hydroxy-3-methylglutaryl (HMG) CoA to 3MGC CoA, free CoA was also produced. Although HMG CoA is known to undergo non-enzymatic intramolecular cyclisation, forming HMG anhydride and free CoA, the amount of free CoA generated increased when AUH was present. To test the hypothesis that the AUH-dependent increase in CoA production is caused by intramolecular cyclisation of 3MGC CoA, gas chromatography-mass spectrometry analysis of organic acids was performed. In the absence of AUH, HMG CoA was converted to HMG acid while, in the presence of AUH, 3MGC acid was also detected. To determine which 3MGC acid diastereomer was formed, immunoblot assays were conducted with 3MGCylated BSA. In competition experiments, when α-3MGC IgG was preincubated with trans-3MGC acid or cis-3MGC acid, the cis diastereomer inhibited antibody binding to 3MGCylated BSA. When an AUH assay product mix served as competitor, α-3MGC IgG binding to 3MGCylated BSA was also inhibited, indicating cis-3MGC acid is produced in incubations of AUH and HMG CoA. Thus, non-enzymatic isomerisation of trans-3MGC CoA drives AUH-dependent HMG CoA dehydration and explains the occurrence of cis-3MGC acid in urine of subjects with 3MGC aciduria. Furthermore, the ability of cis-3MGC anhydride to non-enzymatically acylate protein substrates may have deleterious pathophysiological consequences.

Diversion of Acetyl CoA to 3-Methylglutaconic Acid Caused by Discrete Inborn Errors of Metabolism

A growing number of inborn errors of metabolism (IEM) have been identified that manifest 3-methylglutaconic (3MGC) aciduria as a phenotypic feature. In primary 3MGC aciduria, IEM-dependent deficiencies in leucine pathway enzymes prevent catabolism of trans-3MGC CoA. Consequently, this metabolite is converted to 3MGC acid and excreted in urine. In secondary 3MGC aciduria, however, no leucine metabolism pathway enzyme deficiencies exist. These IEMs affect mitochondrial membrane structure, electron transport chain function or ATP synthase subunits. As a result, acetyl CoA oxidation via the TCA cycle slows and acetyl CoA is diverted to trans-3MGC CoA, and then to 3MGC acid. Whereas the trans diastereomer of 3MGC CoA is the only biologically relevant diastereomer, the urine of affected subjects contains both cis- and trans-3MGC acids. Studies have revealed that trans-3MGC CoA is susceptible to isomerization to cis-3MGC CoA. Once formed, cis-3MGC CoA undergoes intramolecular cyclization, forming an anhydride that, upon hydrolysis, yields cis-3MGC acid. Alternatively, cis-3MGC anhydride can acylate protein lysine side chains. Once formed, cis-3MGCylated proteins can be deacylated by the NAD⁺-dependent enzyme, sirtuin 4. Taken together, the excretion of 3MGC acid in secondary 3MGC aciduria represents a barometer of defective mitochondrial function.

Foam fractionation of a recombinant biosurfactant apolipoprotein

Locusta migratoria apolipophorin III (apoLp-III) possesses the ability to exist as a water soluble amphipathic α-helix bundle and a lipid surface seeking apolipoprotein. The intrinsic ability of apoLp-III to transform phospholipid vesicles into reconstituted discoidal high-density lipoproteins (rHDL) has led to myriad applications. To improve the yield of recombinant apoLp-III, studies were performed in a bioreactor. Induction of apoLp-III expression generated a protein product that is secreted from E. coli into the culture medium. Interaction of apoLp-III with gas and liquid components in media produced large quantities of thick foam. A continuous foam fractionation process yielded a foamate containing apoLp-III as the sole major protein component. The yield of recombinant apoLp-III was ~0.2 g / liter bacterial culture. Mass spectrometry analysis verified the identity of the target protein and indicated no modifications or changes to apoLp-III occurred as a result of foam fractionation. The functional ability of apoLp-III to induce rHDL formation was evaluated by incubating foam fractionated apoLp-III with phosphatidylcholine vesicles. FPLC size exclusion chromatography revealed a single major population of particles in the size range of rHDL. The results described offer a novel approach to bioreactor-based apoLp-III production that takes advantage of its intrinsic biosurfactant properties.

Lutein nanodisks protect human retinal pigment epithelial cells from UV light-induced damage

The hydrophobic carotenoid, lutein, was conferred with aqueous solubility upon formulation into reconstituted discoidal high density lipoprotein particles, termed lutein nanodisks (ND). When formulated with phosphatidylcholine (PC), apolipoprotein (apo) A-I and lutein (formulation ratio = 5 mg PC/2 mg apoA-I/1 mg lutein), lutein solubilization efficiency in phosphate buffered saline (PBS) was ~90%. The UV/Vis absorbance maxima for lutein ND in PBS were red shifted by 6-13 nm versus the corresponding lutein absorbance maxima in ethanol. FPLC gel filtration chromatography gave rise to a single major absorbance peak in the size range of ND. Incubation of cultured ARPE-19 cells with lutein ND resulted in lutein uptake, as determined by HPLC analysis of cell extracts. Compared to control incubations, ARPE-19 cells incubated with lutein ND were protected from UV light-induced loss of cell viability. Consistent with this, reactive oxygen species generation, induced by exposure to UV irradiation, was lower in lutein-enriched cells than in control cells. Thus, uptake of ND-associated lutein protects ARPE-19 cells from UV light-induced damage. Taken together, the data indicate ND provide an aqueous lutein delivery vehicle for biotechnological or therapeutic applications.

Calcium-induced release of cytochrome c from cardiolipin nanodisks: Implications for apoptosis

Miniature bilayer membranes comprised of phospholipid and an apolipoprotein scaffold, termed nanodisks (ND), have been used in binding studies. When ND formulated with cardiolipin (CL), but not phosphatidylcholine, were incubated with cytochrome c, FPLC gel filtration chromatography provided evidence of a stable binding interaction. Incubation of CL ND with CaCl₂ resulted in a concentration-dependent increase in sample turbidity caused by ND particle disruption. Prior incubation of CL ND with cytochrome c increased CL ND sensitivity to CaCl₂-induced effects. Centrifugation of CaCl₂-treated CL ND samples yielded pellet and supernatant fractions. Whereas the ND scaffold protein, apolipophorin III, was recovered in the pellet fraction along with CL, the majority of the cytochrome c pool was in the supernatant fraction. Moreover, when cytochrome c CL ND were incubated with CaCl₂ at concentrations below the threshold to induce ND particle disruption, FPLC analysis showed that cytochrome c was released. Pre-incubation of CL ND with CaCl₂ under conditions that do not disrupt ND particle integrity prevented cytochrome c binding to CL ND. Thus, competition between Ca²⁺ and cytochrome c for a common binding site on CL modulates cytochrome c binding and likely plays a role in its dissociation from CL-rich cristae membranes in response to apoptotic stimuli.

Inborn errors of metabolism associated with 3-methylglutaconic aciduria

A growing number of inborn errors of metabolism (IEM) associated with compromised mitochondrial energy metabolism manifest an unusual phenotypic feature: 3-methylglutaconic (3MGC) aciduria. Two major categories of 3MGC aciduria, primary and secondary, have been described. In primary 3MGC aciduria, IEMs in 3MGC CoA hydratase (AUH) or HMG CoA lyase block leucine catabolism, resulting in a buildup of pathway intermediates, including 3MGC CoA. Subsequent thioester hydrolysis yields 3MGC acid, which is excreted in urine. In secondary 3MGC aciduria, no deficiencies in leucine catabolism enzymes exist and 3MGC CoA is formed de novo from acetyl CoA. In the "acetyl CoA diversion pathway", when IEMs directly, or indirectly, interfere with TCA cycle activity, acetyl CoA accumulates in the matrix space. This leads to condensation of two acetyl CoA to form acetoacetyl CoA, followed by another condensation between acetyl CoA and acetoacetyl CoA to form 3-hydroxy, 3-methylglutaryl (HMG) CoA. Once formed, HMG CoA serves as a substrate for AUH, producing trans-3MGC CoA. Non enzymatic isomerization of trans-3MGC CoA to cis-3MGC CoA precedes intramolecular cyclization to cis-3MGC anhydride plus CoA. Subsequent hydrolysis of cis-3MGC anhydride gives rise to cis-3MGC acid, which is excreted in urine. In reviewing 20 discrete IEMs that manifest secondary 3MGC aciduria, evidence supporting the acetyl CoA diversion pathway was obtained. This biochemical pathway serves as an "overflow valve" in muscle / brain tissue to redirect acetyl CoA to 3MGC CoA when entry to the TCA cycle is impeded.

Reconstituted HDL as a therapeutic delivery device

Studies of "pre β" high density lipoprotein (HDL) and reconstituted HDL (rHDL) have contributed to our understanding of the Reverse Cholesterol Transport pathway. The relative ease with which discoidal rHDL can be generated in vitro has led to novel applications including a) infusion of rHDL into patients to promote regression of atherosclerosis; b) use of rHDL as a miniature membrane for integration of transmembrane proteins in a native-like conformation and c) incorporation of hydrophobic bioactive molecules into rHDL, creating a delivery device. The present review is focused on bioactive agent containing rHDL. The broad array of hydrophobic bioactive molecules successfully incorporated into these particles is discussed, as well as the use of natural lipids and synthetic lipid analogs to confer distinctive binding activity. This technology remains in its infancy with the full potential of these simple, yet elegant, nanoparticles still to be discovered.

Coenzyme Q nanodisks counteract the effect of statins on C2C12 myotubes

Depletion of coenzyme Q (CoQ) is associated with disease, ranging from myopathy to heart failure. To induce a CoQ deficit, C2C12 myotubes were incubated with high dose simvastatin. This resulted in a concentration-dependent inhibition of cell viability. Simvastatin-induced effects were prevented by co-incubation with mevalonic acid. When myotubes were incubated with 60 μM simvastatin, mitochondrial CoQ content decreased while co-incubation with CoQ nanodisks (ND) increased mitochondrial CoQ levels and improved cell viability. Incubation of myotubes with simvastatin also led to a reduction in oxygen consumption rate (OCR). When myotubes were co-incubated with simvastatin and CoQ ND, the decline in OCR was ameliorated. The data indicate that CoQ ND represent a water soluble vehicle capable of delivering CoQ to cultured myotubes. Thus, these biocompatible nanoparticles have the potential to bypass poor CoQ oral bioavailability as a treatment option for individuals with severe CoQ deficiency syndromes and/or aging-related CoQ depletion.

Isomerization of trans-3-methylglutaconic acid

3-Methylglutaconic (3MGC) aciduria is a common phenotypic feature of a growing number of inborn errors of metabolism. "Primary" 3MGC aciduria is caused by deficiencies in leucine pathway enzymes while "secondary" 3MGC aciduria results from inborn errors of metabolism that impact mitochondrial energy production. The metabolic precursor of 3MGC acid is trans-3MGC CoA, an intermediate in the leucine catabolism pathway. Gas chromatography-mass spectrometry (GC-MS) analysis of commercially available trans-3MGC acid yielded a mixture of cis and trans isomers while 1H-NMR spectroscopy of trans-3MGC acid at 25°C provided no evidence for the cis isomer. When trans-3MGC acid was incubated under conditions used for sample derivatization prior to GC-MS (but with no trimethylsilane added), 1H-NMR spectroscopy provided evidence of trans to cis isomerization. Incubation of trans-3MGC acid at 37°C resulted in time-dependent isomerization to cis-3MGC acid. Cis-3MGC acid behaved in a similar manner except that, under identical incubation conditions, less isomerization occurred. In agreement with these experimental results, molecular modeling studies provided evidence that the energy minimized structure of cis-3MGC acid is 4 kJ/mol more stable than that for trans-3MGC acid. Once generated in vivo, trans-3MGC acid is proposed to isomerize via a mechanism involving π electron delocalization with formation of a resonance structure that permits bond rotation. The data presented are consistent with the occurrence of both diastereomers in urine samples of subjects with 3MGC aciduria.

trans-3-Methylglutaconyl CoA isomerization-dependent protein acylation

3-methylglutaconic (3MGC) aciduria is associated with a growing number of discrete inborn errors of metabolism. Herein, an antibody-based approach to detection/quantitation of 3MGC acid has been pursued. When trans-3MGC acid conjugated keyhole limpet hemocyanin (KLH) was inoculated into rabbits a strong immune response was elicited. Western blot analysis provided evidence that immune serum, but not pre-immune serum, recognized 3MGC-conjugated bovine serum albumin (BSA). In competition ELISAs using isolated immune IgG, the limit of detection for free trans-3MGC acid was compared to that for cis-3MGC acid and four structurally related short-chain dicarboxylic acids. Surprisingly, cis-3MGC acid yielded a much lower limit of detection (∼0.1 mg/ml) than trans-3MGC acid (∼1.0 mg/ml) while all other dicarboxylic acids tested were poor competitors. The data suggest trans-3MGC- isomerized during, or after, conjugation to KLH such that the immunogen was actually comprised of KLH harboring a mixture of cis- and trans-3MGC haptens. To investigate this unexpected isomerization reaction, trans-3MGC CoA was prepared and incubated at 37 °C in the presence of BSA. Evidence was obtained that non-enzymatic isomerization of trans-3MGC CoA to cis-3MGC CoA precedes intramolecular catalysis to form cis-3MGC anhydride plus CoASH. Anhydride-dependent acylation of BSA generated 3MGCylated BSA, as detected by anti-3MGC immunoblot. The results presented provide an explanation for the unanticipated detection of 3MGCylated proteins in a murine model of primary 3MGC aciduria. Furthermore, non-enzymatic hydrolysis of cis-3MGC anhydride represents a potential source of cis-3MGC acid found in urine of subjects with 3MGC aciduria.

Assembly and Characterization of Biocompatible Coenzyme Q10 -Enriched Lipid Nanoparticles

Coenzyme Q₁₀ (CoQ₁₀ ) is a strongly hydrophobic lipid that functions in the electron transport chain and as an antioxidant. CoQ₁₀ was conferred with aqueous solubility by incorporation into nanoparticles containing phosphatidylcholine (PtdCho) and apolipoprotein (apo) A-I. These particles, termed CoQ₁₀ nanodisks (ND), contain 1.0 mg CoQ₁₀ /5 mg PtdCho/2 mg apoA-I (97% CoQ₁₀ solubilization efficiency). UV/Vis absorbance spectroscopy of CoQ₁₀ ND revealed a characteristic absorbance peak centered at 275 nm. Incorporation of CoQ₁₀ into ND resulted in quenching of apoA-I tryptophan fluorescence emission. Gel filtration chromatography of CoQ₁₀ ND gave rise to a single major absorbance peak and HPLC of material extracted from this peak confirmed the presence of CoQ₁₀ . Incubation of cultured cells with CoQ₁₀ ND, but not empty ND, resulted in a significant increase in the CoQ₁₀ content of mitochondria as well as enhanced oxidative phosphorylation, as observed by a ~24% increase in maximal oxygen consumption rate. Collectively, a facile method to solubilize significant quantities of CoQ₁₀ in lipid nanoparticles has been developed. The availability of CoQ₁₀ ND provides a novel means to investigate biochemical aspects of CoQ₁₀ uptake by cells and/or administer it to subjects deficient in this key lipid as a result of inborn errors of metabolism, statin therapy, or otherwise.

Dye binding assay reveals doxorubicin preference for DNA versus cardiolipin

Doxorubicin (DOX) is a potent anticancer agent that binds both DNA and cardiolipin (CL). To investigate DOX binding to CL versus DNA, aqueous soluble, CL-enriched nanoparticles, termed nanodisks (ND), were employed. Upon incubation with CL-ND, but not with phosphatidylcholine ND, DOX binding was detected. DOX binding to CL-ND was sensitive to buffer pH and ionic strength. To investigate if a DOX binding preference for DNA versus CL-ND exists, an agarose gel-based dye binding assay was developed. Under conditions wherein the commercial fluorescent dye, GelRed, detects a 636 bp DNA template following electrophoresis, DOX staining failed to visualize this DNA band. Incubation of the template DNA with DOX prior to electrophoresis resulted in a DOX concentration-dependent attenuation of GelRed staining intensity. When the template DNA was pre-incubated with equivalent amounts of free DOX or DOX-CL-ND, no differences in the extent of GelRed staining intensity attenuation were noted. When DOX was incubated with DNA alone, or a mixture of DNA and CL-ND, the extent of DOX-induced GelRed staining intensity attenuation was equivalent. Thus, DOX has a binding preference for DNA versus CL and, moreover, DOX-CL-ND offer a potential strategy to prevent DOX-induced cardiotoxicity while not affecting its affinity for DNA.

3-Methylglutaric acid in energy metabolism

3-methylglutaric (3MG) acid is a conspicuous C6 dicarboxylic organic acid classically associated with two distinct leucine pathway enzyme deficiencies. 3MG acid is excreted in urine of individuals harboring deficiencies in 3-hydroxy-3-methylglutaryl (HMG) CoA lyase (HMGCL) or 3-methylglutaconyl CoA hydratase (AUH). Whereas 3MG CoA is not part of the leucine catabolic pathway, it is likely formed via a side reaction involving reduction of the α-ß trans double bond in the leucine pathway intermediate, 3-methylglutaconyl CoA. While the metabolic basis for the accumulation of 3MG acid in subjects with deficiencies in HMGCL or AUH is apparent, the occurrence of 3MG aciduria in a host of unrelated inborn errors of metabolism associated with compromised mitochondrial energy metabolism is less clear. Herein, a novel mitochondrial biosynthetic pathway termed "the acetyl CoA diversion pathway", provides an explanation. The pathway is initiated by defective electron transport chain function which, ultimately, inhibits acetyl CoA entry into the TCA cycle. When this occurs, 3MG acid is synthesized in five steps from acetyl CoA via a novel reaction sequence, providing a metabolic rationale for the connection between 3MG aciduria and compromised mitochondrial energy metabolism.

Correction to: Sphingadienes show therapeutic efficacy in neuroblastoma in vitro and in vivo by targeting the AKT signaling pathway

The authors would like to note an omission of disclosure in this paper. Author JDS is cofounder, equity-holder, and consultant of GILTRx Therapeutics.

Calcium-induced transformation of cardiolipin nanodisks

Miniature membranes comprised of tetramyristoylcardiolipin (CL) and apolipoprotein (apo) A-I, termed nanodisks (ND), are stable, aqueous soluble, reconstituted high density lipoproteins. When CL ND, but not dimyristoylphosphatidylcholine (PC) ND, were incubated with CaCl₂, a concentration dependent increase in sample turbidity occurred, consistent with CL undergoing a bilayer to non-bilayer transition. To assess the cation specificity of this reaction, CL ND were incubated with various mono- and divalent cations. Whereas monovalent cations had no discernable effect, MgCl₂ and SrCl₂ induced a response similar to CaCl₂. When ND were formulated using different weight ratios of CL and PC, those possessing 100% CL or 75% CL remained susceptible to CaCl₂ induced sample turbidity development while ND possessing 50% CL displayed reduced susceptibility. ND comprised of 25% CL and 75% PC were unaffected by CaCl₂ under these conditions. SDS PAGE analysis of insoluble material generated by incubation of CL ND with CaCl₂ revealed that nearly all apoA-I was recovered in the insoluble fraction along with CL. One h after addition of EDTA to CaCl₂-treated CL ND, sample clarity was restored. Collectively, the data are consistent with a model wherein Ca²⁺ forms a bidentate interaction with anionic phosphates in the polar head group of CL. As phosphate group repositioning occurs to maximize Ca²⁺ binding, CL acyl chains reposition, accentuating the conical shape of CL to an extent that is incompatible with the ND bilayer structure.

Evaluation of cardiolipin nanodisks as lipid replacement therapy for Barth syndrome

Barth syndrome (BTHS) is a mitochondrial disorder characterized by cardiomyopathy and skeletal muscle weakness. Disease results from mutations in the tafazzin (TAZ) gene, encoding a phospholipid transacylase. Defective tafazzin activity results in an aberrant cardiolipin (CL) profile. The feasibility of restoring the intracellular CL profile was tested by in vivo administration of exogenous CL in nanodisk (ND) delivery particles. Ninety mg/kg CL (as ND) was administered to doxycycline-inducible taz shRNA knockdown (KD) mice once a week. After 10 weeks of CL-ND treatment, the mice were sacrificed and tissues harvested. Liquid chromatography-mass spectrometry of extracted lipids revealed that CL-ND administration failed to alter the CL profile of taz KD or WT mice. Thus, although CL-ND were previously shown to be an effective means of delivering CL to cultured cells, this effect does not extend to an in vivo setting. We conclude that CL-ND administration is not a suitable therapy option for BTHS.

Sphingadienes show therapeutic efficacy in neuroblastoma in vitro and in vivo by targeting the AKT signaling pathway

Neuroblastoma is a childhood malignancy that accounts for approximately 15% of childhood cancer deaths. Only 20-35% of children with metastatic neuroblastoma survive with standard therapy. Identification of more effective therapies is essential to improving the outcome of children with high-stage disease. Sphingadienes (SD) are growth-inhibitory sphingolipids found in natural sources including soy. They exhibit chemopreventive activity in mouse models of colon cancer, where they mediate cytotoxicity by inhibiting key pro-carcinogenic signaling pathways. In this study, the effect of SD on neuroblastoma was analyzed. Low micromolar concentrations of SD were cytotoxic to transformed and primary neuroblastoma cells independently of N-Myc amplification status. SD induced both caspase-dependent apoptosis and autophagy in neuroblastoma cells. However, only inhibition of caspase-dependent apoptosis protected neuroblastoma cells from SD-mediated cytotoxicity. SD also inhibited AKT activation in neuroblastoma cells as shown by reduced phosphorylated AKT levels. Pre-treatment with insulin attenuated SD-mediated cytotoxicity in vitro. SD-loaded nanoparticles (NP) administered parenterally to immunodeficient mice carrying neuroblastoma xenografts resulted in cytotoxic levels of SD in the circulation and significantly reduced tumor growth compared to vehicle-treated controls. Analysis of tumor extracts demonstrated reduced AKT activation in tumors of mice treated with SD-NP compared to controls treated with empty NP. Our findings indicate SD are novel potential chemotherapeutic agents that promote neuroblastoma cell death and reduce tumorigenicity in vivo.

Effect of curcumin on amyloid-like aggregates generated from methionine-oxidized apolipoprotein A-I

Curcumin is a polyphenolic phytonutrient that has antineurodegenerative properties. In this study, we investigated the anti‐amyloidogenic properties of curcumin. Following incubation with curcumin, intrinsic tryptophan fluorescence emission of apolipoprotein (apo) A‐I was strongly quenched. At the same time, curcumin fluorescence emission was enhanced. The fluorescence emission spectra of curcumin in the presence of amyloid‐like aggregates formed by methionine‐oxidized (ox) apoA‐I varied, depending on whether curcumin was added before, or after, aggregate formation. The impact of curcumin on the structure of the aggregating material was revealed by the lower amount of β‐structure in ox‐apoA‐I amyloid‐like aggregates formed in the presence of curcumin, compared to aggregates formed without curcumin. However, the kinetics of ox‐apoA‐I amyloid‐like aggregate formation was not altered by the presence of curcumin. Moreover, electron microscopy analysis detected no discernable differences in amyloid morphology when ox‐apoA‐I amyloid‐like aggregates were formed in the presence or absence of curcumin. In conclusion, curcumin interacts with apoA‐I and alters the structure of ox‐apoA‐I amyloid‐like aggregates yet does not diminish the propensity of ox‐apoA‐I to form aggregates.

Characterization of secondary structure and lipid binding behavior of N-terminal saposin like subdomain of human Wnt3a

Wnt signaling is essential for embryonic development and adult homeostasis in multicellular organisms. A conserved feature among Wnt family proteins is the presence of two structural domains. Within the N-terminal (NT) domain there exists a motif that is superimposable upon saposin-like protein (SAPLIP) family members. SAPLIPs are found in plants, microbes and animals and possess lipid surface seeking activity. To investigate the function of the Wnt3a saposin-like subdomain (SLD), recombinant SLD was studied in isolation. Bacterial expression of this Wnt fragment was achieved only when the core SLD included 82 NT residues of Wnt3a (NT-SLD). Unlike SAPLIPs, NT-SLD required the presence of detergent to achieve solubility at neutral pH. Deletion of two hairpin loop extensions present in NT-SLD, but not other SAPLIPs, had no effect on the solubility properties of NT-SLD. Far UV circular dichroism spectroscopy of NT-SLD yielded 50-60% α-helix secondary structure. Limited proteolysis of isolated NT-SLD in buffer and detergent micelles showed no differences in cleavage kinetics. Unlike prototypical saposins, NT-SLD exhibited weak membrane-binding affinity and lacked cell lytic activity. In cell-based canonical Wnt signaling assays, NT-SLD was unable to induce stabilization of β-catenin or modulate the extent of β-catenin stabilization induced by full-length Wnt3a. Taken together, the results indicate neighboring structural elements within full-length Wnt3a affect SLD conformational stability. Moreover, SLD function(s) in Wnt proteins appear to have evolved away from those commonly attributed to SAPLIP family members.

Nutlin-3a Nanodisks Induce p53 Stabilization and Apoptosis in a Subset of Cultured Glioblastoma Cells

Nanodisks (ND) are ternary complexes of phospholipid, one or more hydrophobic bioactive agents and an apolipoprotein scaffold. These nanoscale assemblies are organized as a disk-shaped lipid bilayer whose perimeter is stabilized by an apolipoprotein scaffold. Solubilization of hydrophobic bioactive agents is achieved by their integration into the ND lipid milieu. When the cis-imidazoline, nutlin-3a, was incubated with phosphatidylcholine and apolipoprotein A-I, it was conferred with aqueous solubility as judged by spectroscopic analysis. Nondenaturing polyacrylamide gel electrophoresis yielded evidence of a homogeneous population of ND particles ~9 nm in diameter. Gel filtration chromatography experiments revealed the association of nutlin-3a with ND is reversible. Biological activity of nutlin-3a ND was examined in three distinct glioblastoma cell lines, U87MG, SF763 and SF767. Incubation of U87MG cells with nutlin-3a ND induced concentration-dependent cell growth arrest and apoptosis. SF763 cells demonstrated modest cell growth arrest only at high concentrations of nutlin-3a ND and no apoptosis. SF767 cells were unaffected by nutlin-3a ND. Immunoblot analysis revealed nutlin-3a ND induced time-dependent stabilization of the master tumor suppressor, p53, and up regulation of the E3 ubiquitin ligase, murine double minute 2 in U87MG cells, but not the other glioma cell lines. The nanoscale size of the formulation particles, their facile assembly and nutlin-3a solubilization capability suggest ND represent a potentially useful vehicle for in vivo administration of this anti-tumor agent.

A facile method for isolation of recombinant human apolipoprotein A-I from E. coli

Apolipoprotein (apo) A-I is the major protein component of high-density lipoprotein (HDL) and plays key roles in the Reverse Cholesterol Transport pathway. In the past decade, reconstituted HDL (rHDL) has been employed as a therapeutic agent for treatment of atherosclerosis. The ability of rHDL to promote cholesterol efflux from peripheral cells has been documented to reduce the size of atherosclerotic plaque lesions. However, development of apoA-I rHDL-based therapeutics for human use requires a cost effective process to generate an apoA-I product that meets "Good Manufacturing Practice" standards. Methods available for production and isolation of unmodified recombinant human apoA-I at scale are cumbersome, laborious and complex. To overcome this obstacle, a streamlined two-step procedure has been devised for isolation of recombinant untagged human apoA-I from E. coli that takes advantage of its ability to re-fold to a native conformation following denaturation. Heat treatment of a sonicated E. coli supernatant fraction induced precipitation of a large proportion of host cell proteins (HCP), yielding apoA-I as the major soluble protein. Reversed-phase HPLC of this material permitted recovery of apoA-I largely free of HCP and endotoxin. Purified apoA-I possessed α-helix secondary structure, formed rHDL upon incubation with phospholipid and efficiently promoted cholesterol efflux from cholesterol loaded J774 macrophages.

Barth Syndrome: Connecting Cardiolipin to Cardiomyopathy

The Barth syndrome (BTHS) is caused by an inborn error of metabolism that manifests characteristic phenotypic features including altered mitochondrial membrane phospholipids, lactic acidosis, organic acid-uria, skeletal muscle weakness and cardiomyopathy. The underlying cause of BTHS has been definitively traced to mutations in the tafazzin (TAZ) gene locus on chromosome X. TAZ encodes a phospholipid transacylase that promotes cardiolipin acyl chain remodeling. Absence of tafazzin activity results in cardiolipin molecular species heterogeneity, increased levels of monolysocardiolipin and lower cardiolipin abundance. In skeletal muscle and cardiac tissue mitochondria these alterations in cardiolipin perturb the inner membrane, compromising electron transport chain function and aerobic respiration. Decreased electron flow from fuel metabolism via NADH ubiquinone oxidoreductase activity leads to a buildup of NADH in the matrix space and product inhibition of key TCA cycle enzymes. As TCA cycle activity slows pyruvate generated by glycolysis is diverted to lactic acid. In turn, Cori cycle activity increases to supply muscle with glucose for continued ATP production. Acetyl CoA that is unable to enter the TCA cycle is diverted to organic acid waste products that are excreted in urine. Overall, reduced ATP production efficiency in BTHS is exacerbated under conditions of increased energy demand. Prolonged deficiency in ATP production capacity underlies cell and tissue pathology that ultimately is manifest as dilated cardiomyopathy.

On the origin of 3-methylglutaconic acid in disorders of mitochondrial energy metabolism

3-methylglutaconic acid (3MGA)-uria occurs in numerous inborn errors of metabolism (IEM) associated with compromised mitochondrial energy metabolism. This organic acid arises from thioester cleavage of 3-methylglutaconyl CoA (3MG CoA), an intermediate in leucine catabolism. In individuals harboring mutations in 3MG CoA hydratase (i.e., primary 3MGA-uria), dietary leucine is the source of 3MGA. In secondary 3MGA-uria, however, no leucine metabolism defects have been reported. While others have suggested 3MGA arises from aberrant isoprenoid shunting from cytosol to mitochondria, an alternative route posits that 3MG CoA arises in three steps from mitochondrial acetyl CoA. Support for this biosynthetic route in IEMs is seen by its regulated occurrence in microorganisms. The fungus, Ustilago maydis, the myxobacterium, Myxococcus xanthus and the marine cyanobacterium, Lyngbya majuscule, generate 3MG CoA (or acyl carrier protein derivative) in the biosynthesis of iron chelating siderophores, iso-odd chain fatty acids and polyketide/nonribosomal peptide products, respectively. The existence of this biosynthetic machinery in these organisms supports a model wherein, under conditions of mitochondrial dysfunction, accumulation of acetyl CoA in the inner mitochondrial space as a result of inefficient fuel utilization drives de novo synthesis of 3MG CoA. Since humans lack the downstream biosynthetic capability of the organisms mentioned above, as 3MG CoA levels rise, thioester hydrolysis yields 3MGA, which is excreted in urine as unspent fuel. Understanding the metabolic origins of 3MGA may increase its utility as a biomarker.

Wnt3a nanodisks promote ex vivo expansion of hematopoietic stem and progenitor cells

BACKGROUND

Wnt proteins modulate development, stem cell fate and cancer through interactions with cell surface receptors. Wnts are cysteine-rich, glycosylated, lipid modified, two domain proteins that are prone to aggregation. The culprit responsible for this behavior is a covalently bound palmitoleoyl moiety in the N-terminal domain.

RESULTS

By combining murine Wnt3a with phospholipid and apolipoprotein A-I, ternary complexes termed nanodisks (ND) were generated. ND-associated Wnt3a is soluble in the absence of detergent micelles and gel filtration chromatography revealed that Wnt3a co-elutes with ND. In signaling assays, Wnt3a ND induced β-catenin stabilization in mouse fibroblasts as well as hematopoietic stem and progenitor cells (HSPC). Prolonged exposure of HSPC to Wnt3a ND stimulated proliferation and expansion of Lin(-) Sca-1(+) c-Kit(+) cells. Surprisingly, ND lacking Wnt3a contributed to Lin(-) Sca-1(+) c-Kit(+) cell expansion, an effect that was not mediated through β-catenin.

CONCLUSIONS

The data indicate Wnt3a ND constitute a water-soluble transport vehicle capable of promoting ex vivo expansion of HSPC.

Apolipoprotein A-V is present in bile and its secretion increases with lipid absorption in Sprague-Dawley rats

Apolipoprotein (apo) A-V is a protein synthesized only in the liver that dramatically modulates plasma triglyceride levels. Recent studies suggest a novel role for hepatic apoA-V in regulating the absorption of dietary triglycerides, but its mode of action on the gut remains unknown. The aim of this study was to test for apoA-V in bile and to determine whether its secretion is regulated by dietary lipids. After an overnight recovery, adult male Sprague-Dawley bile fistula rats indeed secreted apoA-V into bile at a constant rate under fasting conditions. An intraduodenal bolus of intralipid (n = 12) increased the biliary secretion of apoA-V but not of other apolipoproteins, such as A-I, A-IV, B, and E. The lipid-induced increase of biliary apoA-V was abolished under conditions of poor lymphatic lipid transport, suggesting that the stimulation is regulated by the magnitude of lipids associated with chylomicrons transported into lymph. We also studied the secretion of apoA-V into bile immediately following bile duct cannulation. Biliary apoA-V increased over time (∼6-fold increase at hour 16, n = 8) but the secretions of other apolipoproteins remained constant. Replenishing luminal phosphatidylcholine and taurocholate (n = 9) only enhanced apoA-V secretion in bile, suggesting that the increase was not due to depletion of phospholipids or bile salts. This is the first study to demonstrate that apoA-V is secreted into bile, introducing a potential route of delivery of hepatic apoA-V to the gut lumen. Our study also reveals the uniqueness of apoA-V secretion into bile that is regulated by mechanisms different from other apolipoproteins.

Apolipoprotein A-V gene therapy for disease prevention / treatment: a critical analysis

Apolipoprotein (apo) A-V is a novel member of the class of exchangeable apo's involved in triacylglycerol (TG) homeostasis. Whereas a portion of hepatic-derived apoA-V is secreted into plasma and functions to facilitate lipoprotein lipase-mediated TG hydrolysis, another portion is recovered intracellularly, in association with cytosolic lipid droplets. Loss of apoA-V function is positively correlated with elevated plasma TG and increased risk of cardiovascular disease. Single nucleotide polymorphisms (SNP) in the APOA5 locus can affect transcription efficiency or introduce deleterious amino acid substitutions. Likewise, rare mutations in APOA5 that compromise functionality are associated with increased plasma TG and premature myocardial infarction. Genetically engineered mouse models and human population studies suggest that, in certain instances, supplementation with wild type (WT) apoA-V may have therapeutic benefit. It is hypothesized that individuals that manifest elevated plasma TG owing to deleterious APOA5 SNPs or rare mutations would respond to WT apoA-V supplementation with improved plasma TG clearance. On the other hand, subjects with hypertriglyceridemia of independent origin (unrelated to apoA-V function) may not respond to apoA-V augmentation in this manner. Improvement in the ability to identify individuals predicted to benefit, advances in gene transfer technology and the strong connection between HTG and heart disease, point to apoA-V supplementation as a viable disease prevention / therapeutic strategy. Candidates would include individuals that manifest chronic TG elevation, have low plasma apoA-V due to an APOA5 mutation/polymorphism and not have deleterious mutations/polymorphisms in other genes known to influence plasma TG levels.

Exogenous cardiolipin localizes to mitochondria and prevents TAZ knockdown-induced apoptosis in myeloid progenitor cells

The concentration and composition of cardiolipin (CL) in mitochondria are altered in age-related heart disease, Barth Syndrome, and other rare genetic disorders, resulting in mitochondrial dysfunction. To explore whether exogenous CL can be delivered to cells, CL was combined with apolipoprotein A-I to generate water-soluble, nanoscale complexes termed nanodisks (ND). Mass spectrometry of HL60 myeloid progenitor cell extracts revealed a 30-fold increase in cellular CL content following incubation with CL-ND. When CL-ND containing a fluorescent CL analogue was employed, confocal microscopy revealed CL localization to mitochondria. The ability of CL-ND to elicit a physiological response was examined in an HL60 cell culture model of Barth Syndrome neutropenia. siRNA knockdown of the phospholipid transacylase, tafazzin (TAZ), induced apoptosis in these cells. When TAZ knockdown cells were incubated with CL-ND, the apoptotic response was attenuated. Thus, CL-ND represent a potential intervention strategy for replenishment of CL in Barth Syndrome, age-related heart disease, and other disorders characterized by depletion of this key mitochondrial phospholipid.

Anti-CD20 single chain variable antibody fragment-apolipoprotein A-I chimera containing nanodisks promote targeted bioactive agent delivery to CD20-positive lymphomas

A fusion protein comprising an α-CD20 single chain variable fragment (scFv) antibody, a spacer peptide, and human apolipoprotein (apo) A-I was constructed and expressed in Escherichia coli. The lipid interaction properties intrinsic to apoA-I as well as the antigen recognition properties of the scFv were retained by the chimera. scFv•apoA-I was formulated into nanoscale reconstituted high-density lipoprotein particles (termed nanodisks; ND) and incubated with cultured cells. α-CD20 scFv•apoA-I ND bound to CD20-positive non-Hodgkins lymphoma (NHL) cells (Ramos and Granta) but not to CD20-negative T lymphocytes (i.e., Jurkat). Binding to NHL cells was partially inhibited by pre-incubation with rituximab, a monoclonal antibody directed against CD20. Confocal fluorescence microscopy analysis of Granta cells following incubation with α-CD20 scFv•apoA-I ND formulated with the intrinsically fluorescent hydrophobic polyphenol, curcumin, revealed α-CD20 scFv•apoA-I localizes to the cell surface, while curcumin off-loads and gains entry to the cell. Compared to control incubations, viability of cultured NHL cells was decreased upon incubation with α-CD20 scFv•apoA-I ND harboring curcumin. Thus, formulation of curcumin ND with α-CD20 scFv•apoA-I as the scaffold component confers cell targeting and enhanced bioactive agent delivery, providing a strategy to minimize toxicity associated with chemotherapeutic agents.

Apolipoprotein A-V deficiency enhances chylomicron production in lymph fistula mice

Apolipoprotein A-V (apoA-V), a liver-synthesized apolipoprotein discovered in 2001, strongly modulates fasting plasma triglycerides (TG). Little is reported on the effect of apoA-V on postprandial plasma TG, an independent predictor for atherosclerosis. Overexpressing apoA-V in mice suppresses postprandial TG, but mechanisms focus on increased lipolysis or clearance of remnant particles. Unknown is whether apoA-V suppresses the absorption of dietary lipids by the gut. This study examines how apoA-V deficiency affects the steady-state absorption and lymphatic transport of dietary lipids in chow-fed mice. Using apoA-V knockout (KO, n = 8) and wild-type (WT, n = 8) lymph fistula mice, we analyzed the uptake and lymphatic transport of lipids during a continuous infusion of an emulsion containing [(3)H]triolein and [(14)C]cholesterol. ApoA-V KO mice showed a twofold increase in (3)H (P < 0.001) and a threefold increase in (14)C (P < 0.001) transport into the lymph compared with WT. The increased lymphatic transport was accompanied by a twofold reduction (P < 0.05) in mucosal (3)H, suggesting that apoA-V KO mice more rapidly secreted [(3)H]TG out of the mucosa into the lymph. ApoA-V KO mice also produced chylomicrons more rapidly than WT (P < 0.05), as measured by the transit time of [(14)C]oleic acid from the intestinal lumen to lymph. Interestingly, apoA-V KO mice produced a steadily increasing number of chylomicron particles over time, as measured by lymphatic apoB output. The data suggest that apoA-V suppresses the production of chylomicrons, playing a previously unknown role in lipid metabolism that may contribute to the postprandial hypertriglyceridemia associated with apoA-V deficiency.

Isolation and characterization of recombinant murine Wnt3a

Wnt proteins are a family of morphogens that possess potent biological activity. Structure-function studies have been impeded by poor yield of biologically active recombinant Wnt as well as a propensity of isolated Wnt to self-associate in the absence of detergent. Using stably transfected Drosophila S2 cells, studies have been conducted to improve recovery of recombinant murine Wnt3a, establish conditions for a detergent-free Wnt preparation and examine the effects of limited proteolysis. S2 cell culture conditioned media was subjected to a 3-step protocol including dye-ligand chromatography, immobilized metal affinity chromatography and gel filtration chromatography. Through selective pooling of column fractions, homogeneous and purified Wnt3a preparations were obtained. Limited proteolysis of Wnt3a with thrombin resulted in site-specific cleavage within the N-terminal saposin-like motif. To generate detergent-free protein, Wnt3a was immobilized on Cu(2+)-charged, iminodiacetic acid-derivatized Sepharose beads, detergent-free buffer was applied and Wnt3a eluted from the beads with buffer containing imidazole plus 30mM methyl-ß-cyclodextrin (MßCD). Wnt3a recovered in MßCD-containing buffer was soluble and biologically active. Insofar as MßCD is a member of a family of non-toxic, low molecular weight compounds capable of binding and solubilizing small hydrophobic ligands, Wnt-cyclodextrin complexes may facilitate structure-activity studies in the absence of adverse detergent effects.

Aberrant hetero-disulfide bond formation by the hypertriglyceridemia-associated p.Gly185Cys APOA5 variant (rs2075291)

OBJECTIVE

Apolipoprotein A-V (apoA-V) is a low-abundance plasma protein that modulates triacylglycerol homeostasis. Gene transfer studies were undertaken in apoa5 (-/-) mice to define the mechanism underlying the correlation between the single-nucleotide polymorphism c.553G>T in APOA5 and hypertriglyceridemia.

APPROACH AND RESULTS

Adeno-associated virus (AAV) 2/8-mediated gene transfer of wild-type apoA-V induced a dramatic lowering of plasma triacylglycerol in apoa5 (-/-) mice, whereas AAV2/8-Gly162Cys apoA-V (corresponding to the c.553G>T single-nucleotide polymorphism: rs2075291; p.Gly185Cys when numbering includes signal sequence) had a modest effect. Characterization studies revealed that plasma levels of wild-type and G162C apoA-V in transduced mice were similar and within the physiological range. Fractionation of plasma from mice transduced with AAV2/8-G162C apoA-V indicated that, unlike wild-type apoA-V, >50% of G162C apoA-V was recovered in the lipoprotein-free fraction. Nonreducing SDS-PAGE immunoblot analysis provided evidence that G162C apoA-V present in the lipoprotein-free fraction, but not that portion associated with lipoproteins, displayed altered electrophoretic mobility consistent with disulfide-linked heterodimer formation. Immunoprecipitation followed by liquid chromatography/mass spectrometry of human plasma from subjects homozygous for wild-type APOA5 and c.553G>T APOA5 revealed that G162C apoA-V forms adducts with extraneous plasma proteins including fibronectin, kininogen-1, and others.

CONCLUSIONS

Substitution of Cys for Gly at position 162 of mature apoA-V introduces a free cysteine that forms disulfide bonds with plasma proteins such that its lipoprotein-binding and triacylglycerol-modulation functions are compromised.

Curcumin homing to the nucleolus: mechanism for initiation of an apoptotic program

Curcumin is a plant-derived polyphenol that displays antitumor properties. Incubation of cultured SF-767 glioma cells with curcumin gave rise to intense intranuclear foci of curcumin fluorescence. In vitro studies revealed that nuclear homing by curcumin is not a result of DNA/chromatin binding. On the other hand, curcumin fluorescence colocalized with nucleophosmin, a nucleolus marker protein. To determine the temporal relationship between curcumin-induced apoptosis and nucleolar homing, confocal live cell imaging was performed. The data show that curcumin localization to the nucleolus occurs prior to cell surface exposure of phosphatidylserine. In studies of the mechanism of curcumin-induced apoptosis in SF-767 cells, its effect on the subcellular location of p14(ARF) was determined. Whereas p14(ARF) was confined to the nucleolus in untreated cells, 2 h following incubation with curcumin, it displayed a diffuse nuclear distribution. Given the role of nuclear p14(ARF) in binding the E3 ubiquitin ligase, mouse double minute 2 homolog (MDM2), the effect of curcumin treatment on cellular levels of the tumor suppressor protein, p53, was examined. Between 2 and 4 h following curcumin treatment, p53 levels increased with maximum levels reached by 8 h. Thus, curcumin homing to the nucleolus induces redistribution of p14(ARF) to the nucleoplasm where interaction with MDM2 leads to stabilization of p53, with subsequent initiation of apoptosis.

Impact of apolipoprotein E on Alzheimer's disease

A key feature of Alzheimer's disease (AD) is deposition of extracellular amyloid plaque comprised chiefly of the amyloid β (Aβ) peptide. Studies of Aβ have shown that it may be catabolized by proteolysis or cleared from brain via members of the low-density lipoprotein receptor family. Alternatively, Aβ can undergo a conformational transition from α-helix to β-sheet, a conformer that displays a propensity to self-associate, oligomerize and form fibrils. Furthermore, β- sheet conformers catalyze conversion of other α-helical Aβ peptides to β-sheet, feeding the oligomer and fibril assembly process. A factor that influences the fate of Aβ in the extracellular space is apolipoprotein (apo) E. Polymorphism at position 112 or 158 in apoE give rise to three major isoforms. One isoform in particular, apoE4 (Arg at 112 and 158), has generated considerable interest since the discovery that it is the major genetic risk factor for development of late onset AD. Despite this striking correlation, the molecular mechanism underlying apoE4's association with AD remains unclear. A tertiary structural feature distinguishing apoE4 from apoE2 and apoE3, termed domain interaction, is postulated to affect the conformation and orientation of its' two independently folded domains. This feature has the potential to influence apoE4's interaction with Aβ, its sensitivity to proteolysis or its lipid accrual and receptor binding activities. Thus, domain interaction may constitute the principal molecular feature of apoE4 that predisposes carriers to late onset AD. By understanding the contribution of apoE4 to AD at the molecular level new therapeutic or prevention strategies will emerge.

Metabolic biology of 3-methylglutaconic acid-uria: a new perspective

Over the past 25 years a growing number of distinct syndromes/mutations associated with compromised mitochondrial function have been identified that share a common feature: urinary excretion of 3-methylglutaconic acid (3MGA). In the leucine degradation pathway, carboxylation of 3-methylcrotonyl CoA leads to formation of 3-methylglutaconyl CoA while 3-methylglutaconyl CoA hydratase converts this metabolite to 3-hydroxy-3-methylglutaryl CoA (HMG CoA). In "primary" 3MGA-uria, mutations in the hydratase are directly responsible for the accumulation of 3MGA. On the other hand, in all "secondary" 3MGA-urias, no defect in leucine catabolism exists and the metabolic origin of 3MGA is unknown. Herein, a path to 3MGA from mitochondrial acetyl CoA is proposed. The pathway is initiated when syndrome-associated mutations/DNA deletions result in decreased Krebs cycle flux. When this occurs, acetoacetyl CoA thiolase condenses two acetyl CoA into acetoacetyl CoA plus CoASH. Subsequently, HMG CoA synthase 2 converts acetoacetyl CoA and acetyl CoA to HMG CoA. Under syndrome-specific metabolic conditions, 3-methylglutaconyl CoA hydratase converts HMG CoA into 3-methylglutaconyl CoA in a reverse reaction of the leucine degradation pathway. This metabolite fails to proceed further up the leucine degradation pathway owing to the kinetic properties of 3-methylcrotonyl CoA carboxylase. Instead, hydrolysis of the CoA moiety of 3-methylglutaconyl CoA generates 3MGA, which appears in urine. If experimentally confirmed, this pathway provides an explanation for the occurrence of 3MGA in multiple disorders associated with compromised mitochondrial function.

Cationic lipid nanodisks as an siRNA delivery vehicle

The term nanodisk (ND) describes reconstituted high-density lipoprotein particles that contain one or more exogenous bioactive agents. In the present study, ND were assembled from apolipoprotein A-I, the zwitterionic glycerophospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), and the synthetic cationic lipid 1,2-dimyristoyl-3-trimethylammonium-propane (DMTAP). ND formulated at a DMPC:DMTAP ratio of 70:30 (by weight) were soluble in aqueous media. The particles generated were polydisperse, with diameters ranging from ∼20 to <50 nm. In nucleic acid binding studies, agarose gel retardation assays revealed that a synthetic 23-mer double-stranded oligonucleotide (dsOligo) bound to DMTAP containing ND but not to ND formulated with DMPC alone. Sucrose density gradient ultracentrifugation studies provided additional evidence for stable dsOligo binding to DMTAP-ND. Incubation of cultured hepatoma cells with DMTAP-ND complexed with a siRNA directed against glyceraldehyde 3-phosphate dehydrogenase showed 60% knockdown efficiency. Thus, incorporation of synthetic cationic lipid (i.e., DMTAP) to ND confers an ability to bind siRNA and the resulting complexes possess target gene knockdown activity in a cultured cell model.

ApoE enhances nanodisk-mediated curcumin delivery to glioblastoma multiforme cells

AIM

To evaluate the effect of incorporating the polyphenol, curcumin, into nanodisk (ND) particles on its biological activity.

MATERIALS & METHODS

Curcumin-NDs formulated with different scaffold proteins were incubated with cultured glioblastoma multiforme cells.

RESULTS

When ApoE was employed as the ND scaffold protein, enhanced curcumin uptake was observed. Furthermore, ApoE curcumin-NDs induced greater cell death than either free curcumin or ApoAI curcumin-NDs. A total of 1 h after exposure of glioblastoma multiforme cells to ApoE curcumin-NDs, significant curcumin uptake was detected while ApoE was localized at the cell surface. After 2 h, a portion of the curcumin had migrated to the nucleus, giving rise to enhanced fluorescence intensity in discrete intranuclear sites.

CONCLUSION

ApoE-mediated interaction of curcumin-NDs with glioblastoma multiforme cells leads to enhanced curcumin uptake and increased biological activity.

Abstract 1: Molecular Basis of Hypertriglyceridemia Associated with the APOA5 c553.G>T SNP

Objectives

Apolipoprotein (apo) A-V is a low abundance protein with profound effects on plasma triglyceride (TG) levels. Several APOA5 SNPs correlate with hypertriglyceridemia (HTG). The c.553 G>T SNP, substituting a Cys for Gly at position 162 of mature apoA-V, is prevalent in Asian populations and correlates with HTG. To investigate the mechanism underlying this association, gene transfer studies were performed in apoa5-/- mice.

Methods

Adeno-associated virus (AAV2/8) harboring the coding sequence for wild type apoA-V (AAV2/8-apoA-V), G162C apoA-V (AAV2/8-G162C) and LacZ (AAV2/8-LacZ) were injected (1x10e12 virus genome) into the tail vein of 8 apoa5-/- mice per group. Blood samples were collected weekly for 4 weeks and TG and apoA-V levels measured. FPLC was performed on plasma obtained from AAV2/8-apoA-V and AAV2/8-G162C mice. VLDL, LDL, HDL and the lipoprotein-free region were characterized.

Results

Compared to AAV2/8-LacZ mice, AAV2/8-apoA-V mice had significantly lower plasma TG levels (50% ±5). Unlike AAV2/8-apoA-V, mice injected with AAV2/8-G162C displayed little or no reduction in TG despite similar amounts of plasma apoA-V protein. Immunoblot analysis of FPLC fractionated plasma revealed that, whereas wild-type apoA-V was lipoprotein associated (VLDL and HDL), G162C apoA-V was largely recovered in the lipoprotein-free fraction. Immunoblot analysis following SDS-PAGE under non-reducing conditions revealed that lipoprotein-associated wild type apoA-V and G162C apoA-V are monomeric; by contrast, the electrophoretic mobility of G162C apoA-V recovered in the lipoprotein-free fraction was retarded.

Conclusions

Gene transfer of wild type apoA-V induces a significant reduction in plasma TG levels of apoa5-/- mice. By contrast, G162C apoA-V failed to induce a corresponding decrease in plasma TG, recapitulating effects observed in human populations harboring this SNP. The propensity of G162C apoA-V to form a disulfide bond with one or more plasma proteins interferes with its lipoprotein binding ability, resulting in loss of function. The results provide a molecular explanation for HTG associated with a common APOA5 SNP. The gene transfer strategy employed provides a platform for studies of other common apoA-V SNPs.

Abstract 388: Apolipoprotein A-V Deficiency in Mice Results In Increased Triglyceride and Cholesterol Absorption

Elevated plasma triglycerides constitute an independent risk factor for coronary heart disease. Discovered in 2001, apolipoprotein A-V (apoA-V) was found inversely proportional to plasma triglycerides (TG). Synthesized only in the liver, apoA-V exists in very low concentrations in the plasma (~10,000 fold lower than apoA-I). While apoA-V is proposed to enhance hydrolysis and reduce hepatic production of TG-rich lipoproteins, the role of apoA-V on intestinal lipid absorption has not been investigated. The aim of this study is to examine the effects of apoA-V deficiency on intestinal lipid absorption in chow-fed mice. Since mice lacking functional apoA-V have drastically elevated plasma TG, we hypothesize that apoA-V deficiency in mice elevates the lymphatic output of TG after a lipid meal. Using apoA-V knockout (n=8) and wildtype (n=8) control mice, we employed the conscious lymph fistula model to examine the transport of dietary TG and cholesterol into the lymph during a continuous lipid infusion. Interestingly, apoA-V knockout mice displayed a 2-fold elevation in dietary TG (P<0.001) and a 3-fold elevation in dietary cholesterol (P<0.001) transport into the lymph compared to wildtype mice, suggesting that a loss of apoA-V enhances transport across the enterocyte. However, apoA-V knockout mice displayed a 2-fold reduction (P<0.05) in dietary TG accumulated in the intestinal mucosa while there was no difference in the mucosal accumulation of dietary cholesterol between apoA-V knockout and wildtype mice, suggesting that apoA-V affected TG and cholesterol transport in the enterocyte differently. We conclude apoA-V deficiency results in increased TG and cholesterol absorption in mice, and therefore plays a previously unknown role in intestinal lipid absorption.

Influence of apolipoprotein A-V on the metabolic fate of triacylglycerol

PURPOSE OF REVIEW

Apolipoprotein (apo) A-V functions to modulate intracellular and extracellular triacylglycerol metabolism. The present review addresses molecular mechanisms underlying these effects. The relevance of apoA-V to human disease conditions is illustrated by the strong correlation between single nucleotide polymorphisms in APOA5, elevated plasma triacylglycerol and dyslipidemic disease.

RECENT FINDINGS

Despite undergoing processing for secretion from hepatocytes, a portion of apoA-V escapes this destiny and accumulates as a component of cytosolic lipid droplets. Expression of recombinant apoA-V in hepatocarcinoma cells results in increased lipid droplet size and number at the expense of triacylglycerol secretion.ApoA-V modulates atherosclerosis in hypercholesterolemic apoE null mice. ApoE null/human apoA-V transgenic mice had reduced levels of triacylglycerol and cholesterol in plasma along with decreased aortic lesion size.

SUMMARY

ApoA-V modulates triacylglycerol metabolic fate. Following its synthesis, apoA-V enters the endoplasmic reticulum and associates with membrane defects created by triacylglycerol accumulation. Association of apoA-V with endoplasmic reticulum membrane defects promotes nascent lipid droplets budding toward the cytosol. Despite its low concentration in plasma (∼150 ng/ml), apoA-V modulates lipoprotein metabolism by binding to glycosylphosphatidylinositol-anchored high-density lipoprotein binding protein 1. This interaction effectively localizes triacylglycerol-rich lipoproteins in the vicinity of glycosylphosphatidylinositol-anchored high-density lipoprotein binding protein1's other ligand, lipoprotein lipase.

Gene transfer of apolipoprotein A-V improves the hypertriglyceridemic phenotype of apoa5 (-/-) mice

OBJECTIVE

Apolipoprotein (apo) A-V is a low abundance protein with a profound influence on plasma triacylglycerol levels. In human populations, single nucleotide polymorphisms and mutations in APOA5 positively correlate with hypertriglyceridemia. As an approach to preventing the deleterious effects of chronic hypertriglyceridemia, apoA-V gene therapy has been pursued.

METHODS AND RESULTS

Recombinant adeno-associated virus (AAV) 2/8 harboring the coding sequence for human apoA-V or a control AAV2/8 was transduced into hypertriglyceridemic apoa5 (-/-) mice. After injection of 1×10(12) viral genome AAV2/8-apoA-V, maximal plasma levels of apoA-V protein were achieved at 3 to 4 weeks, after which the concentration slowly declined. Complementing the appearance of apoA-V was a decrease (50±6%) in plasma triacylglycerol content compared with apoa5 (-/-) mice treated with AAV2/8-β-galactosidase. After 8 weeks the mice were euthanized and plasma lipoproteins separated. AAV2/8-apoA-V-transduced mice displayed a dramatic reduction in very low-density lipoprotein triacylglycerol content. Vector generated apoA-V in plasma associated with both very low-density lipoprotein and high-density lipoprotein fractions.

CONCLUSIONS

Taken together, the data show that gene transfer of apoA-V improves the severe hypertriglyceridemia phenotype of apoa5 (-/-) mice. Given the prevalence of hypertriglyceridemia, apoA-V gene therapy offers a potential strategy for maintenance of plasma triacylglycerol homeostasis.

Influence of apolipoprotein A-V on hepatocyte lipid droplet formation

Apolipoprotein A-V (apoA-V) is postulated to modulate intra-hepatic triglyceride (TG) trafficking. Stably transfected McA-RH7777 hepatocarcinoma cells expressing human apoA-V displayed enhanced neutral lipid staining while conditioned media from these cells had 40±8% less TG than cells transfected with a control vector. To obtain homogeneous cell lines expressing different amounts of apoA-V, a strategy of clonal selection was pursued. Immunoblot analysis of two distinct apoA-V stable cell lines yielded one that expresses low amounts of apoA-V and another that expresses higher amounts. Confocal fluorescence microscopy of control cells and cells expressing low levels of apoA-V had similar numbers of lipid droplets while cells expressing higher amounts of apoA-V had twice as many lipid droplets, on average. Thus, apoA-V expression promotes lipid droplet accumulation in these cells.