Characterization and optimization of the haemozoin-like crystal (HLC) assay to determine Hz inhibiting effects of anti-malarial compounds

Operando spectroscopy investigations of the redox reactions in heme and heme-proteins

Operando spectroscopic investigations during molecular redox processes provide unique insights into complex molecular structures and their transformations. Herein, a combination of a potentiodynamic method with spectroscopy has been employed to holistically investigate the structural transformations during Fe-redox (Fe3+ ↔ Fe2+) of hemin vis á vis heme-proteins, e.g. myoglobin (Mb), hemoglobin (Hb) and cytochrome-C (Cyt-C). The UV-vis findings reveal the formation of hemozoin (≈heme-dimer), which can be selectively prevented via a high concentration of strongly interacting ligands, e.g. histidine (the fifth coordinating ligand in the heme-based protein). On the other hand, methionine does not prevent the formation of hemozoin. In Mb, Hb, and Cyt-C, as the fifth coordination site is occupied by histidine, hemozoin formation is inhibited. During Fe3+→ Fe2+, operando circular dichroism exhibits a decrease in the initial helical component in Hb from nearly 40% to 28%, which is close to the initial helix component of Mb (≈25%), strongly indicating denaturation of the protein in the redox pathway. The rate of change of the helices versus potential is almost identical for Mb and Hb, but comparatively faster than Cyt-C. In addition, from the Raman bands of M-N dynamics and protein agglomeration, it is concluded that Cyt-C prefers to agglomerate in the 2+ state, whereas Mb/Hb in the 3+ state. In this report, the power of operando spectroscopy is utilized to unearth the dynamics of hemin and heme-based proteins for comprehending the underlying complexities associated with the molecular redox, which have deep implications in electrocatalysis, energy storage, and sensing.

Dual role of azo compounds in inhibiting Plasmodium falciparum adenosine deaminase and hemozoin biocrystallization

Protein-ligand (GOLD) docking of the NCI compounds into the ligand-binding site of Plasmodium falciparum adenosine deaminase (PfADA) identified three most active azo compounds containing 4-[(4-hydroxy-2-oxo-1H-quinolin-3-yl) moiety. These compounds showed IC₅₀ of 3.7-15.4 μM against PfADA, as well as inhibited the growth of P. falciparum strains 3D7 (chloroquine (CQ)-sensitive) and K1 (CQ-resistant) with IC₅₀ of 1.8-3.1 and 1.7-3.6 μM, respectively. The identified compounds have structures similar to the backbone structure (4-N-(7-chloroquinolin-4-yl)) in CQ, and NSC45545 could mimic CQ by inhibiting the bioformation of hemozoin in parasitic food vacuole. The amount of in situ hemozoin in the ring-stage parasite was determined using a combination of synchrotron transmission Fourier transform infrared microspectroscopy and Principal Component Analysis. Stretching of the C-O bond of hemozoin propionate group measured at 1220-1210 cm^-1 in untreated intraerythrocytic P. falciparum strains 3D7 and K1 was disappeared following treatment with 1.85 and 1.74 μM NSC45545, similar to those treated with 0.02 and 0.13 μM CQ, respectively. These findings indicate a novel dual function of 4-[(4-hydroxy-2-oxo-1H-quinolin-3-yl) azo compounds in inhibiting both PfADA and in situ hemozoin biocrystallization. These lead compounds hold promise for further development of new antimalarial therapeutics that could delay the onset of parasitic drug resistance.

Cryogenically induced signal enhancement of Raman spectra of porphyrin molecules

Raman spectroscopy is a powerful analytical technique in contemporary medicine and biomedical research due to its exceptional ability to provide an unambiguous spectroscopic signature of the molecular chemical composition, structure and atom arrangements. Among other applications, investigations of the Raman spectra of porphyrins and their derivatives have been critical in the study of ligand binding mechanisms and drug interactions with healthy and diseased blood cells, as well as for the analysis of blood, hemoproteins and the oxygenation process of human erythrocyte. However, obtaining Raman spectra with satisfactory definition of porphyrin-based molecules can be challenging due to their inherent photo- and thermal sensitivity which leads to laser damage even at low laser power. This severely affects the Raman spectra of porphyrins and limits the Raman signal strength and spectra quality. In this study, we examine two important porphyrins, hemin and protoporphyrin IX, at cryogenic temperatures down to 77 K using a 532 nm excitation Raman instrument in order to study the Raman signal strength and spectral quality dependence on the sample temperature at these extreme low temperatures. We report a significant Raman signal enhancement of up to 310% in the spectra at cryogenic temperatures compared to room temperature measurements. This provides a remarkable improvement of the quality and definition within the spectra and demonstrates that cryogenic Raman measurements can be used as an exceptionally effective method of enhancing the Raman signal and spectra quality for investigations of porphyrins and their derivatives regardless of the excitation wavelength selection. This can greatly improve the effectiveness of Raman spectroscopy in biomedical research, especially in the field of drug design and development, medical diagnostics and disease monitoring and analysis.

Quantitative imaging of intraerythrocytic hemozoin by transient absorption microscopy

Hemozoin, the heme detoxification end product in malaria parasites during their growth in the red blood cells (RBCs), serves as an important marker for diagnosis and treatment target of malaria disease. However, the current method for hemozoin-targeted drug screening mainly relies on in vitro β-hematin inhibition assays, which may lead to false-positive events due to under-representation of the real hemozoin crystal. Quantitative in situ imaging of hemozoin is highly desired for high-throughput screening of antimalarial drugs and for elucidating the mechanisms of antimalarial drugs. We present transient absorption (TA) imaging as a high-speed single-cell analysis platform with chemical selectivity to hemozoin. We first demonstrated that TA microscopy is able to identify β-hematin, the artificial form of hemozoin, from the RBCs. We further utilized time-resolved TA imaging to in situ discern hemozoin from malaria-infected RBCs with optimized imaging conditions. Finally, we quantitatively analyzed the hemozoin amount in RBCs at different infection stages by single-shot TA imaging. These results highlight the potential of TA imaging for efficient antimalarial drug screening and drug mechanism investigation.

Enhanced In-Vitro Hemozoin Polymerization by Optimized Process using Histidine-Rich Protein II (HRPII)

Conductive biopolymers, an important class of functional materials, have received attention in various fields because of their unique electrical, optical, and physical properties. In this study, the polymerization of heme into hemozoin was carried out in an in vitro system by the newly developed heme polymerase (histidine-rich protein 2 (HRP-II)). The HRP-II was produced by recombinant E. coli BL21 from the Plasmodium falciparum gene. To improve the hemozoin production, the reaction conditions on the polymerization were investigated and the maximum production was achieved after about 790 μM at 34 °C with 200 rpm for 24 h. As a result, the production was improved about two-fold according to the stepwise optimization in an in vitro system. The produced hemozoin was qualitatively analyzed using the Fourier transform infrared (FTIR) spectroscopy, energy dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM). Finally, it was confirmed that the enzymatically polymerized hemozoin had similar physical properties to chemically synthesized hemozoin. These results could represent a significant potential for nano-biotechnology applications, and also provide guidance in research related to hemozoin utilization.

New Method of Production and Characterization of Haemozoin and B-Haemozoin from Meccus longipennis

BACKGROUND

Understanding the significance of hemozoin (Hz) in the process through which Plasmodium is released from the heme group in the food vacuole during hemoglobin degradation, will allow the development of more effective drugs against malaria. Therefore, the development of methodologies to obtain Hz synthetically will facilitate an in vitro evaluation of new anti-malarial drugs.

METHODS

We present a methodology with good results to obtain Hz from fecal material of blood-sucking insects Meccus longipennis. The preparation of biological cultures of the parasite (Plasmodium) transmitter of the disease is not necessary.

RESULTS

The hemozoin molecule and its dimer were obtained using the method described and it was possible to validate a comparison with the positive and negative controls using different analytical techniques.

CONCLUSION

The proposed method allows obtaining hemozoin and its dimer demonstrating equivalence with positive controls that demonstrate that the present procedure may be an alternative for the evaluation of antimalarial drugs.