David H. Peyton

Hidden Formaldehyde in E-Cigarette Aerosols

This letter reports a chemical analysis of vapor from electronic cigarettes that shows high levels of formaldehyde, a known carcinogen. The authors project that the associated incremental lifetime risk of cancer could be higher than that from long-term smoking.

HIV-1 Matrix Protein Binding to RNA

The matrix (MA) domain of the human immunodeficiency virus type 1 (HIV-1) precursor Gag (PrGag) protein plays multiple roles in the viral replication cycle. One essential role is to target PrGag proteins to their lipid raft-associated phosphatidylinositol-(4,5)-bisphosphate [PI(4,5)P(2)] assembly sites at the plasma membranes of infected cells. In addition to this role, several reports have implicated nucleic acid binding properties to retroviral MAs. Evidence indicates that RNA binding enhances the binding specificity of MA to PI(4,5)P(2)-containing membranes and supports a hypothesis in which RNA binding to MA acts as a chaperone that protects MA from associating with inappropriate cellular membranes prior to PrGag delivery to plasma membrane assembly sites. To gain a better understanding of HIV-1 MA-RNA interactions, we have analyzed the interaction of HIV MA with RNA ligands that were selected previously for their high affinities to MA. Binding interactions were characterized via bead binding, fluorescence anisotropy, gel shift, and analytical ultracentrifugation methods. Moreover, MA residues that are involved in RNA binding were identified from NMR chemical shift data. Our results indicate that the MA RNA and PI(4,5)P(2) binding sites overlap and suggest models for Gag-membrane and Gag-RNA interactions and for the HIV assembly pathway.

Sweet is stable: glycosylation stabilizes collagen

For most collagens, the melting temperature (T m) of the triple‐helical structure of collagen correlates with the total content of proline (Pro) and 4‐trans‐hydroxyproline (Hyp) in the Xaa and Yaa positions of the ‐Gly‐Xaa‐Yaa‐ triplet repeat. The cuticle collagen of the deep‐sea hydrothermal vent worm Riftia pachyptila, despite a very low content of Pro and Hyp, has a relatively high thermal stability. Rather than Hyp occupying the Yaa position, as is normally found in mammalian collagens, this position is occupied by threonine (Thr) which is O‐glycosylated. We compare the triple‐helix forming propensities in water of two model peptides, Ac‐(Gly‐Pro‐Thr)10‐NH2 and Ac‐(Gly‐Pro‐Thr(Galβ))10‐NH2, and show that a collagen triple‐helix structure is only achieved after glycosylation of Thr. Thus, we show for the first time that glycosylation is required for the formation of a stable tertiary structure and that this modification represents an alternative way of stabilizing the collagen triple‐helix that is independent of the presence of Hyp.

Optimization of Xanthones for Antimalarial Activity: the 3,6-Bis-ω-Diethylaminoalkoxyxanthone Series

ABSTRACT Hydroxyxanthones have been identified as novel antimalarial agents. The compounds are believed to exert their activity by complexation to heme and inhibition of hemozoin formation. Modification of the xanthone structure was pursued to improve their antimalarial activity. Attachment of R-groups bearing protonatable nitrogen atoms was conducted to enhance heme affinity through ionic interactions with the propionate side chains of the metalloporphyrin and to facilitate drug accumulation in the parasite food vacuole. A series of 3,6-bis-ω-diethylaminoalkoxyxanthones with side chains ranging from 2 to 8 carbon atoms were prepared and evaluated. Measurement of heme affinity for each of the derivatives revealed a strong correlation (R2 = 0.97) between affinity and antimalarial potency. The two most active compounds in the series contained 5- and 6-carbon side chains and exhibited low nanomolar 50% inhibitory concentration (IC50) values against strains of chloroquine-susceptible and multidrug-resistant Plasmodium falciparum in vitro. Both of these xanthones exhibit stronger heme affinity (8.26 × 105 and 9.02 × 105 M−1, respectively) than either chloroquine or quinine under similar conditions and appear to complex heme in a unique manner.

A spectroscopic investigation of the binding interactions between 4,5-dihydroxyxanthone and heme

In order to investigate one possible mechanism by which xanthones inhibit growth of malaria-causing Plasmodium parasites, optical and NMR spectroscopic studies were performed on a prototypic xanthone, 4,5-dihydroxyxanthone (45X2), upon its complexation to heme. The 45X2 x heme complex stoichiometry in aqueous solution was found to be 1:2; this interaction was non-cooperative, and exhibited a very similar heme complex dissociation constant (K(d)=5.1 x 10(-6)) as observed for the common antimalarial agents, chloroquine and quinine. The 45X2 x heme(2) complex formation was found to be both pH- and solvent-dependent, with clear evidence of the xanthone carbonyl moiety coordinating with the iron of heme. Hydrogen bonding between the hydroxyl groups of 45X2 and the propionate side chains of heme, as well as pi-pi stacking between both aromatic systems appeared to contribute to the overall stability of the 45X2 x heme(2) complex, as judged by 1H NMR. It was concluded that 45X2 forms a complex with a heme dimer in aqueous solution, and that this interaction can be generalized to account for its in vivo detrimental effect of parasite growth through an effective inhibition of hemozoin aggregate formation.

Effect of the ‐Gly‐3(S)‐hydroxyprolyl‐4(R)‐hydroxyprolyl‐ tripeptide unit on the stability of collagen model peptides

In order to evaluate the role of 3(S)‐hydroxyproline [3(S)‐Hyp] in the triple‐helical structure, we produced a series of model peptides with nine tripeptide units including 0–9 3(S)‐hydroxyproline residues. The sequences are H‐(Gly‐Pro‐4(R)Hyp)l‐(Gly‐3(S)Hyp‐4(R)Hyp)m‐(Gly‐Pro‐4(R)Hyp)n‐OH, where (l, m, n) = (9, 0, 0), (4, 1, 4), (3, 2, 4), (3, 3, 3), (1, 7, 1) and (0, 9, 0). All peptides showed triple‐helical CD spectra at room temperature and thermal transition curves. Sedimentation equilibrium analysis showed that peptide H‐(Gly‐3(S)Hyp‐4(R)Hyp)9‐OH is a trimer. Differential scanning calorimetry showed that replacement of Pro residues with 3(S)Hyp residues decreased the transition enthalpy, and the transition temperature increases by 4.5 °C from 52.0 °C for the peptide with no 3(S)Hyp residues to 56.5 °C for the peptide with nine 3(S)Hyp residues. The refolding kinetics of peptides H‐(Gly‐3(S)Hyp‐4(R)Hyp)9‐OH, H‐(Gly‐Pro‐4(R)Hyp)9‐OH and H‐(Gly‐4(R)Hyp‐4(R)Hyp)9‐OH were compared, and the apparent reaction orders of refolding at 10 °C were n = 1.5, 1.3 and 1.2, respectively. Replacement of Pro with 3(S)Hyp or 4(R)Hyp has little effect on the refolding kinetics. This result suggests that the refolding kinetics of collagen model peptides are influenced mainly by the residue in the Yaa position of the ‐Gly‐Xaa‐Yaa‐ repeated sequence. The experiments indicate that replacement of a Pro residue by a 3(S)Hyp residue in the Xaa position of the ‐Gly‐Xaa‐4(R)Hyp‐ repeat of collagen model peptides increases the stability, mainly due to entropic factors.

Reversed Chloroquine Molecules as a Strategy to Overcome Resistance in Malaria

This short review tells the story of how Reversed Chloroquine drugs (RCQs) were developed. These are hybrid molecules, made by combining the quinoline nucleus from chloroquine (CQ) with moieties which are designed to inhibit efflux via known transporters in the membrane of the digestive vacuole of the malaria parasite. The resulting RCQ drugs can have potencies exceeding that of CQ, while at the same time having physical chemical characteristics that may make them favorable as partner drugs in combination therapies. The need for such novel antimalarial drugs will continue for the foreseeable future.

Solvent Chemistry in the Electronic Cigarette Reaction Vessel

Knowledge of the mechanism of formation, levels and toxicological profiles of the chemical products in the aerosols (i.e., vapor plus particulate phases) of e-cigarettes is needed in order to better inform basic research as well as the general public, regulators, and industry. To date, studies of e-cigarette emissions have mainly focused on chromatographic techniques for quantifying and comparing the levels of selected e-cigarette aerosol components to those found in traditional cigarettes. E-cigarettes heat and aerosolize the solvents propylene glycol (PG) and glycerol (GLY), thereby affording unique product profiles as compared to traditional cigarettes. The chemical literature strongly suggests that there should be more compounds produced by PG and GLY than have been reported in e-cigarette aerosols to date. Herein we report an extensive investigation of the products derived from vaporizing PG and GLY under mild, single puff conditions. This has led to the discovery of several new compounds produced under vaping conditions. Prior reports on e-cigarette toxin production have emphasized temperature as the primary variable in solvent degradation. In the current study, the molecular pathways leading to enhanced PG/GLY reactivity are described, along with the most impactful chemical conditions promoting byproduct production.

The kinetics of uptake and accumulation of 3,6-bis-ω-diethylamino-amyloxyxanthone by the human malaria parasite Plasmodium falciparum

Malarial parasites rely on the digestion of hemoglobin during the intra-erythrocytic stage. The enzymatic degradation of hemoglobin yields amino acids for parasite survival, and free heme which is detoxified by conversion to an aggregate of dimeric heme known as hemozoin. Xanthones have been found to subvert this process by formation of soluble drug-heme complexes. We have optimized the simple hydroxyxanthone structure to include side chains with protonatable nitrogen atoms to enhance interaction with the propionate groups of heme and to target the drug to the parasite digestive vacuole. One member of this optimized class of compounds, 3,6-bis-omega-diethylaminoamyloxyxanthone (C5), was used as a prototype for mechanistic studies. By HPLC analysis we demonstrate that the drug accumulates in the digestive vacuole from 5 to approximately 33,000 microM within 1 h of exposure to parasitized red cells. Confocal fluorescence microscopy was used to visualize the accumulation process directly and to document the colocalization of the drug with the acidophilic dye, LysoTracker Red.

Antileishmanial drug development: exploitation of parasite heme dependency.

A rational approach in the search for new antiparasitic drugs is the exploitation of biochemical differences between the parasite and its mammalian host. One specific example in the case of Leishmania relates to the biosynthesis of heme, a critical prosthetic group for proteins involved in metabolism and electron transport. Like all Trypanosomatids, Leishmania parasites require heme or pre-formed porphyrins for survival because they lack several key enzymes in the heme biosynthetic pathway. Considering their specific nutritional requirements, we speculated that they would be particularly sensitive to the effects of heme-complexing xanthones. In this report, we document the antileishmanial activity of selected nitrogenated xanthones and correlate drug potency with heme affinity. In vitro tests demonstrated that 3,6-bis-omega-diethylaminoamyloxyxanthone, C5, was at least 100 times more active than pentamidine against intracellular amastigotes of Leishmania mexicana. Our findings provide practical guidance for optimizing the antileishmanial activity of the xanthone pharmacophore to better exploit parasite heme salvage processes.