Growth of Large Hematin Crystals in Biomimetic Solutions

Nonclassical mechanisms to irreversibly suppress β-hematin crystal growth

Hematin crystallization is an essential element of heme detoxification of malaria parasites and its inhibition by antimalarial drugs is a common treatment avenue. We demonstrate at biomimetic conditions in vitro irreversible inhibition of hematin crystal growth due to distinct cooperative mechanisms that activate at high crystallization driving forces. The evolution of crystal shape after limited-time exposure to both artemisinin metabolites and quinoline-class antimalarials indicates that crystal growth remains suppressed after the artemisinin metabolites and the drugs are purged from the solution. Treating malaria parasites with the same agents reveals that three- and six-hour inhibitor pulses inhibit parasite growth with efficacy comparable to that of inhibitor exposure during the entire parasite lifetime. Time-resolved in situ atomic force microscopy (AFM), complemented by light scattering, reveals two molecular-level mechanisms of inhibitor action that prevent β-hematin growth recovery. Hematin adducts of artemisinins incite copious nucleation of nonextendable nanocrystals, which incorporate into larger growing crystals, whereas pyronaridine, a quinoline-class drug, promotes step bunches, which evolve to engender abundant dislocations. Both incorporated crystals and dislocations are known to induce lattice strain, which persists and permanently impedes crystal growth. Nucleation, step bunching, and other cooperative behaviors can be amplified or curtailed as means to control crystal sizes, size distributions, aspect ratios, and other properties essential for numerous fields that rely on crystalline materials.

Assembly of Core/Shell Nanospheres of Amorphous Hemin/Acetone-Derived Carbonized Polymer with Graphene Nanosheets for Room-Temperature NO Sensing

Implementing parts per billion-level nitric oxide (NO) sensing at room temperature (RT) is still in extreme demand for monitoring inflammatory respiratory diseases. Herein, we have prepared a kind of core-shell structural Hemin-based nanospheres (Abbr.: Hemin-nanospheres, defined as HNSs) with the core of amorphous Hemin and the shell of acetone-derived carbonized polymer, whose core-shell structure was verified by XPS with argon-ion etching. Then, the HNS-assembled reduced graphene oxide composite (defined as HNS-rGO) was prepared for RT NO sensing. The acetone-derived carbonized polymer shell not only assists the formation of amorphous Hemin core by disrupting their crystallization to release more Fe-N₄ active sites, but provides protection to the core. Owing to the unique core-shell structure, the obtained HNS-rGO based sensor exhibited superior RT gas sensing properties toward NO, including a relatively higher response (R_a/R_g = 5.8, 20 ppm), a lower practical limit of detection (100 ppb), relatively reliable repeatability (over 6 cycles), excellent selectivity, and much higher long-term stability (less than a 5% decrease over 120 days). The sensing mechanism has also been proposed based on charge transfer theory. The superior gas sensing properties of HNS-rGO are ascribed to the more Fe-N₄ active sites available under the amorphous state of the Hemin core and to the physical protection by the shell of acetone-derived carbonized polymer. This work presents a facile strategy of constructing a high-performance carbon-based core-shell nanostructure for gas sensing.

Biodereplication of Antiplasmodial Extracts: Application of the Amazonian Medicinal Plant Piper coruscans Kunth

Improved methodological tools to hasten antimalarial drug discovery remain of interest, especially when considering natural products as a source of drug candidates. We propose a biodereplication method combining the classical dereplication approach with the early detection of potential antiplasmodial compounds in crude extracts. Heme binding is used as a surrogate of the antiplasmodial activity and is monitored by mass spectrometry in a biomimetic assay. Molecular networking and automated annotation of targeted mass through data mining were followed by mass-guided compound isolation by taking advantage of the versatility and finely tunable selectivity offered by centrifugal partition chromatography. This biodereplication workflow was applied to an ethanolic extract of the Amazonian medicinal plant Piper coruscans Kunth (Piperaceae) showing an IC50 of 1.36 µg/mL on the 3D7 Plasmodium falciparum strain. It resulted in the isolation of twelve compounds designated as potential antiplasmodial compounds by the biodereplication workflow. Two chalcones, aurentiacin (1) and cardamonin (3), with IC50 values of 2.25 and 5.5 µM, respectively, can be considered to bear the antiplasmodial activity of the extract, with the latter not relying on a heme-binding mechanism. This biodereplication method constitutes a rapid, efficient, and robust technique to identify potential antimalarial compounds in complex extracts such as plant extracts.

Dual nature of magnetic nanoparticle dispersions enables control over short-range attraction and long-range repulsion interactions

Competition between attractive and repulsive interactions drives the formation of complex phases in colloidal suspensions. A major experimental challenge lies in decoupling independent roles of attractive and repulsive forces in governing the equilibrium morphology and long-range spatial distribution of assemblies. Here, we uncover the 'dual nature' of magnetic nanoparticle dispersions, particulate and continuous, enabling control of the short-range attraction and long-range repulsion (SALR) between suspended microparticles. We show that non-magnetic microparticles suspended in an aqueous magnetic nanoparticle dispersion simultaneously experience a short-range depletion attraction due to the particulate nature of the fluid in competition with an in situ tunable long-range magnetic dipolar repulsion attributed to the continuous nature of the fluid. The study presents an experimental platform for achieving in situ control over SALR between colloids leading to the formation of reconfigurable structures of unusual morphologies, which are not obtained using external fields or depletion interactions alone.

CarbonIron Electron Transport Channels in Porphyrin-Graphene Complex for ppb-Level Room Temperature NO Gas Sensing

It is a great challenge to develop efficient room-temperature sensing materials and sensors for nitric oxide (NO) gas, which is a biomarker molecule used in the monitoring of inflammatory respiratory diseases. Herein, Hemin (Fe (III)-protoporphyrin IX) is introduced into the nitrogen-doped reduced graphene oxide (N-rGO) to obtain a novel sensing material HNG-ethanol. Detailed XPS spectra and DFT calculations confirm the formation of carbon-iron bonds in HNG-ethanol during synthesis process, which act as electron transport channels from graphene to Hemin. Owing to this unique chemical structure, HNG-ethanol exhibits superior gas sensing properties toward NO gas (R_a /R_g  = 3.05, 20 ppm) with a practical limit of detection (LOD) of 500 ppb and reliable repeatability (over 5 cycles). The HNG-ethanol sensor also possesses high selectivity against other exhaled gases, high humidity resistance, and stability (less than 3% decrease over 30 days). In addition, a deep understanding of the gas sensing mechanisms is proposed for the first time in this work, which is instructive to the community for fabricating sensing materials based on graphene-iron derivatives in the future.

What roles do alkali metal ions play in the pathological crystallization of uric acid?

Na+ and K+ regulate the crystal growth of uric acid dihydrate by kink blocking and rough growth mechanisms.

A Chemically Stable Fluorescent Mimic of Dihydroartemisinin, Artemether, and Arteether with Conserved Bioactivity and Specificity Shows High Pharmacological Relevance to the Antimalarial Drugs

Three novel tracers designed as fluorescent surrogates of artemisinin-derived antimalarial drugs (i.e., dihydroartemisinin, artemether, arteether, and artemisone) were synthesized from dihydroartemisinin. One of these tracers, corresponding to a dihydroartemisinin/artemether/arteether mimic, showed a combination of excellent physicochemical and biological properties such as hydrolytic stability, high inhibitory potency against blood-stage parasites, similar ring-stage survival assay values than the clinical antimalarials, high cytopermeability and specific labeling of live P. falciparum cells, alkylation of heme, as well as specific covalent labeling of drug-sensitive and drug-resistant P. falciparum proteomes at physiological concentrations, consistent with a multitarget action of the drugs. Our study demonstrates that probes containing the complete structural core of clinical artemisinin derivatives can be stable in biochemical and cellular settings, and recapitulate the complex mechanisms of these frontline, yet threatened, antimalarial drugs.

Computational insights into the inhibition of β-haematin crystallization by antimalarial drugs

During the red blood cell phase of their life cycle, malaria parasites digest their host's haemoglobin, with concomitant release of potentially toxic iron(iii) protoporphyrin IX (FePPIX). The parasites' strategy for detoxification of FePPIX involves its crystallization to haemozoin, such that the build-up of free haem in solution is avoided. Antimalarial drugs of both historical importance and current clinical use are known to be capable of disrupting the growth of crystals of β-haematin, which is the synthetic equivalent of haemozoin. Hence, the disruption of haemozoin crystal growth is implicated as a possible mode of action of such drugs. However, the details of β-haematin crystal poisoning at the molecular level have yet to be fully elucidated. In this study, we have used a combination of density functional theory (DFT) and molecular modelling to examine the possible modes of action of ten different antimalarial drugs, including quinine-type aliphatic alcohols, amodiaquine-type phenols, and chloroquine-type aliphatic diamines. The DFT calculations indicate that each of the drugs can form at least one molecular complex with FePPIX. These complexes have 1 : 1 or 2 : 1 FePPIX : drug stoichiometries and all of them incorporate Fe-O bonds, formed either by direct coordination of a zwitterionic form of the drug, or by deprotonation of water. Most of the drugs can form more than one such complex. We have used the DFT model structures to explore the possible formation of a monolayer of each drug-haem complex on four of the β-haematin crystal faces. In all cases, the drug complexes can form a monolayer on the fast-growing {001} and {011} faces, but not on the slower growing {010} and {100} faces. Additional modelling of the chloroquine and quinidine complexes shows that individual molecules of these species can also obstruct the growth of new layers on other crystal faces. The implications of these observations for antimalarial drug development are discussed.

Structuring of Organic Solvents at Solid Interfaces and Ramifications for Antimalarial Adsorption on β-Hematin Crystals

A critical aspect of material synthesis is solvent structuring at solid-liquid interfaces, which can impact the adsorption of solute and growth modifiers on an underlying substrate. In general, the impact of solvent structuring on molecular sorbate interactions with solid sorbents is poorly understood. This is particularly true for processes that occur in organic media, such as hematin crystallization, which is crucial to the survival of malaria parasites. Here, we use chemical force microscopy and molecular modeling to analyze the interactions between functional moieties of known antimalarials and the interface between β-hematin crystals and a mixed organic (octanol)-aqueous solvent. We show that the β-hematin surface, patterned in parallel hydrophobic and hydrophilic stripes, engenders the assembly of up to five layers of octanol molecules aligned parallel to the crystal surface. In contrast, studies of solvent structuring on a disordered glass surface reveal that octanol molecules align perpendicular to the interface. The distinct octanol arrays direct molecule adsorption at the respective interfaces. At both substrates, we also find stabilized pockets of aqueous nanophase lining the surfaces. A combination of experimental analyses and modeling of solvent structuring provides crucial insights into the association of hematin molecules with growing crystals as well as the adsorption and mobility of antimalarial drugs. Moreover, our findings offer a general perspective on the collective behaviors of complex organic solvents that may apply to a broad range of interactions at solid-liquid interfaces.

Histology of Brain Trauma and Hypoxia-Ischemia

Forensic pathologists encounter hypoxic-ischemic (HI) brain damage or traumatic brain injuries (TBI) on an almost daily basis. Evaluation of the findings guides decisions regarding cause and manner of death. When there are gross findings of brain trauma, the cause of death is often obvious. However, microscopic evaluation should be used to augment the macroscopic diagnoses. Histology can be used to seek evidence for TBI in the absence of gross findings, e.g., in the context of reported or suspected TBI. Estimating the survival interval after an insult is often of medicolegal interest; this requires targeted tissue sampling and careful histologic evaluation. Retained tissue blocks serve as forensic evidence and also provide invaluable teaching and research material. In certain contexts, histology can be used to demonstrate nontraumatic causes of seemingly traumatic lesions. Macroscopic and histologic findings of brain trauma can be confounded by concomitant HI brain injury when an individual survives temporarily after TBI. Here we review the histologic approaches for evaluating TBI, hemorrhage, and HI brain injury. Amyloid precursor protein (APP) immunohistochemistry is helpful for identifying damaged axons, but patterns of damage cannot unambiguously distinguish TBI from HI. The evolution of hemorrhagic lesions will be discussed in detail; however, timing of any lesion is at best approximate. It is important to recognize artifactual changes (e.g., dark neurons) that can resemble HI damage. Despite the shortcomings, histology is a critical adjunct to the gross examination of brains.

Insights into the initial stages of lipid-mediated haemozoin nucleation

Lipid-mediated haemozoin nucleation, as probed by molecular dynamics, proceeds via aggregation of ferrihaem π–π dimers at a lipid–aqueous interface.

Mechanisms of hematin crystallization and inhibition by the antimalarial drug chloroquine

Hematin crystallization is the primary mechanism of heme detoxification in malaria parasites and the target of the quinoline class of antimalarials. Despite numerous studies of malaria pathophysiology, fundamental questions regarding hematin growth and inhibition remain. Among them are the identity of the crystallization medium in vivo, aqueous or organic; the mechanism of crystallization, classical or nonclassical; and whether quinoline antimalarials inhibit crystallization by sequestering hematin in the solution, or by blocking surface sites crucial for growth. Here we use time-resolved in situ atomic force microscopy (AFM) and show that the lipid subphase in the parasite may be a preferred growth medium. We provide, to our knowledge, the first evidence of the molecular mechanisms of hematin crystallization and inhibition by chloroquine, a common quinoline antimalarial drug. AFM observations demonstrate that crystallization strictly follows a classical mechanism wherein new crystal layers are generated by 2D nucleation and grow by the attachment of solute molecules. We identify four classes of surface sites available for binding of potential drugs and propose respective mechanisms of drug action. Further studies reveal that chloroquine inhibits hematin crystallization by binding to molecularly flat {100} surfaces. A 2-μM concentration of chloroquine fully arrests layer generation and step advancement, which is ∼10(4)× less than hematin's physiological concentration. Our results suggest that adsorption at specific growth sites may be a general mode of hemozoin growth inhibition for the quinoline antimalarials. Because the atomic structures of the identified sites are known, this insight could advance the future design and/or optimization of new antimalarials.

Lipid or aqueous medium for hematin crystallization?

Hematin crystallization, the primary heme detoxification mechanism of malaria parasites infecting human erythrocytes, most likely requires the participation of lipid structures.