Identification of protein disulfide isomerase 1 as a key isomerase for disulfide bond formation in apolipoprotein B100

Apolipoprotein (apo) B is an obligatory component of very low density lipoprotein (VLDL), and its cotranslational and posttranslational modifications are important in VLDL synthesis, secretion, and hepatic lipid homeostasis. ApoB100 contains 25 cysteine residues and eight disulfide bonds. Although these disulfide bonds were suggested to be important in maintaining apoB100 function, neither the specific oxidoreductase involved nor the direct role of these disulfide bonds in apoB100-lipidation is known. Here we used RNA knockdown to evaluate both MTP-dependent and -independent roles of PDI1 in apoB100 synthesis and lipidation in McA-RH7777 cells. Pdi1 knockdown did not elicit any discernible detrimental effect under normal, unstressed conditions. However, it decreased apoB100 synthesis with attenuated MTP activity, delayed apoB100 oxidative folding, and reduced apoB100 lipidation, leading to defective VLDL secretion. The oxidative folding–impaired apoB100 was secreted mainly associated with LDL instead of VLDL particles from PDI1-deficient cells, a phenotype that was fully rescued by overexpression of wild-type but not a catalytically inactive PDI1 that fully restored MTP activity. Further, we demonstrate that PDI1 directly interacts with apoB100 via its redox-active CXXC motifs and assists in the oxidative folding of apoB100. Taken together, these findings reveal an unsuspected, yet key role for PDI1 in oxidative folding of apoB100 and VLDL assembly.     

A comparison of the LDL-cholesterol lowering efficacy of plant stanols and plant sterols over a continuous dose range: results of a meta-analysis of randomized, placebo-controlled trials

Purpose

To determine if plant stanols and plant sterols differ with respect to their low-density lipoprotein cholesterol (LDL-CH) lowering efficacies across a continuous dose range.

Methods

Dose-response relationships were evaluated separately for plant stanols and plant sterols and reductions in LDL-CH, using a first-order elimination function.

Results

Altogether, 113 publications and 1 unpublished study report (representing 182 strata) complied with the pre-defined inclusion and exclusion criteria and were included in the assessment. The maximal LDL-CH reductions for plant stanols (16.4%) and plant stanol ester (17.1%) were significantly greater than the maximal LDL-CH reductions for plant sterols (8.3%) and plant sterol ester (8.4%). These findings persisted in several additional analyses.

Discussion and conclusions

Intakes of plant stanols in excess of the recommended 2 g/day dose are associated with additional and dose-dependent reductions in LDL-CH, possibly resulting in further reductions in the risk of coronary heart disease (CHD).     

Ethanol exposure modulates hepatic S-adenosylmethionine and S-adenosylhomocysteine levels in the isolated perfused rat liver through changes in the redox state of the NADH/NAD system

Methionine metabolism is disrupted in patients with alcoholic liver disease, resulting in altered hepatic concentrations of S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH), and other metabolites. The present study tested the hypothesis that reductive stress mediates the effects of ethanol on liver methionine metabolism. Isolated rat livers were perfused with ethanol or propanol to induce a reductive stress by increasing the NADH/NAD⁺ ratio, and the concentrations of SAM and SAH in the liver tissue were determined by high-performance liquid chromatography. The increase in the NADH/NAD⁺ ratio induced by ethanol or propanol was associated with a marked decrease in SAM and an increase in SAH liver content. 4-Methylpyrazole, an inhibitor the NAD⁺-dependent enzyme alcohol dehydrogenase, blocked the increase in the NADH/NAD⁺ ratio and prevented the alterations in SAM and SAH. Similarly, co-infusion of pyruvate, which is metabolized by the NADH-dependent enzyme lactate dehydrogenase, restored the NADH/NAD⁺ ratio and normalized SAM and SAH levels. The data establish an initial link between the effects of ethanol on the NADH/NAD⁺ redox couple and the effects of ethanol on methionine metabolism in the liver.     

Design and synthesis of pyridone inhibitors of non-nucleoside reverse transcriptase

Next generation NNRTIs are sought which possess both broad spectrum antiviral activity against key mutant strains and a high genetic barrier to the selection of new mutant viral strains. Pyridones were evaluated as an acyclic conformational constraint to replace the aryl ether core of MK-4965 (1) and the more rigid indazole constraint of MK-6186 (2). The resulting pyridone compounds are potent inhibitors of HIV RT and have antiviral activity in cell culture that is superior to other next generation NNRTI’s.     

A novel class of dual mPGES-1/5-LO inhibitors based on the α-naphthyl pirinixic acid scaffold

Dual inhibition of microsomal prostaglandin E₂ synthase-1 (mPGES-1) and 5-lipoxygenase (5-LO) represents a promising strategy in the development of novel anti-inflammatory drugs targeting the arachidonic acid cascade. Herein, a class of α-naphthyl pirinixic acids is characterized as dual mPGES-1/5-LO inhibitors. Systematic structural variation was focused on the lipophilic backbone of the scaffold and yielded detailed structure-activity relationships (SAR) with compound 16 (IC₅₀ mPGES-1 = 0.94 μM; IC₅₀ 5-LO = 0.1 μM) showing the most favorable in vitro pharmacological profile.     

Structure-based parallel medicinal chemistry approach to improve metabolic stability of benzopyran COX-2 inhibitors

Combination of the structure-based design and solid-phase parallel synthesis provided an integrated approach to rapidly develop the structure-activity relationship of benzopyran COX-2 inhibitors. Binding free energies predicted by free energy perturbation theory yielded good agreement with experimental results. New potent and selective lead compounds with improved metabolic properties were identified.     

Diblock glycopolymers promote colloidal stability of polyplexes and effective pDNA and siRNA delivery under physiological salt and serum conditions

A series of glycopolymers composed of 2-deoxy-2-methacrylamido glucopyranose (MAG) and the primary amine-containing N-(2-aminoethyl) methacrylamide (AEMA) were synthesized via aqueous reversible addition-fragmentation chain transfer (RAFT) polymerization. The colloidal stability of the polyplexes formed with three diblock glycopolymers and pDNA was assessed using dynamic light scattering, and the polyplexes were found to be stable against aggregation in the presence of salt and serum over the 4 h time period studied. Delivery experiments were performed in vitro to examine the cellular uptake, transfection efficiency, and cytotoxicity of the glycopolymer/pDNA polyplexes in cultured HeLa cells and the diblock copolymer with the shortest AEMA block was found to be the most effective. Additionally, the ability of the diblock glycopolymers to deliver siRNA to U-87 (glioblastoma) cells was screened, and the diblock copolymer with the longest AEMA block was found to have gene knockdown efficacy similar to Lipofectamine 2000.     

Methylmalonic acid quantification in low serum volumes by UPLC-MS/MS

Methylmalonic acid (MMA) is a metabolic intermediate transformed to succinic acid (SA) by a vitamin B(12)-dependent catalytic step, and is broadly used as a clinical biomarker of functional vitamin B12 status. However, reported methods use between 100 and 1000 μL of serum or plasma making them sub-optimal for sample-limited studies, including those with neonates and infants. LC-MS/MS based protocols to measure MMA as n-butyl esters in the presence of tri-deuterated MMA (MMA-d(3)) were modified for use with 25 μL of human serum by scaling down sample processing volumes and analysis by UPLC-MS/MS. Plasma-based calibration solutions were found to be unnecessary, and chromatographic resolution and peak shape of SA and MMA was optimized in <4 min with isocratic 53:47 methanol/1.67 mM (pH 6.5) ammonium formate. Additionally, 1-cyclohexyl-urido-3-dodecanoic acid (CUDA) was included as internal standard allowing direct assessment of MMA recovery. Sample concentrations in the low normal range produced a signal:noise of >100:1. MMA intra- and inter-assay variability was under 10%. MMA-d(3) surrogate recovery averaged 93±14%. MMA stability exceeded three years in frozen samples and was unaffected by up to five freeze/thaw cycles. In conclusion, we report that methylmalonic acid can be measured with 25 μL of serum using water based standards. The assay signal:noise per concentration indicates that the method could perform as implemented with as little as 5 μL of serum. The reported method is applicable for studies of functional B12 status in sample limited experiments including investigations of nutritional status in neonates and in studies where low normal MMA levels are expected.     

An efficient high-throughput screening method for MYST family acetyltransferases, a new class of epigenetic drug targets

Epigenetic aberrations are increasingly regarded as key factors in cancer progression. Recently, deregulation of histone acetyltransferases (HATs) has been linked to several types of cancer. Monocytic leukemia zinc finger protein (MOZ) is a member of the MYST family of HATs, which regulate gene expression in cell proliferation and differentiation. Deregulation of these processes through constitutively active MOZ fusion proteins gives rise to the formation of leukemic stem cells, rendering MOZ an excellent target for treating myeloid leukemia. The authors implemented a hit discovery campaign to identify small-molecule inhibitors of MOZ-HAT activity. They developed a robust, homogeneous assay measuring the acetylation of synthetic histone peptides. In a primary screening campaign testing 243 000 lead-like compounds, they identified inhibitors from several chemical classes. Secondary assays were used to eliminate assay-interfering compounds and prioritize confirmed hits. This study establishes a new high-throughput assay for HAT activity and could provide the foundation for the development of a new class of drugs for the treatment of leukemias.