Evaluation of Gallium as a Tracer of Exogenous Hemoglobin-Haptoglobin Complexes for Targeted Drug Delivery Applications

Understanding the relationship between viral infections and trace elements from a metallomics perspective: implications for COVID-19

Recently, the World Health Organization (WHO) declared a pandemic situation due to a new viral infection (COVID-19) caused by a novel virus (Sars-CoV-2). COVID-19 is today the leading cause of death from viral infections in the world. It is known that many elements play important roles in viral infections, both in virus survival, and in the activation of the host's immune system, which depends on the presence of micronutrients to maintain the integrity of its functions. In this sense, the metallome can be an important object of study for understanding viral infections. Therefore, this work presents an overview of the role of trace elements in the immune system and the state of the art in metallomics, highlighting the challenges found in studies focusing on viral infections.

Antimicrobial photodynamic activity of gallium-substituted haemoglobin on silver nanoparticles

Methicillin-resistant Staphylococcus aureus (MRSA), a major scourge in skin and soft-tissue infections, expresses surface-bound haemoprotein receptors that can be exploited for the targeted delivery of photosensitizers. We have developed a nanosized agent for targeted antimicrobial photodynamic therapy (aPDT), comprised of GaPpIX (a hemin analog with potent photosensitizer activity) encapsulated in haemoglobin (GaHb), mounted on 10 nm Ag nanoparticles (AgNPs). The average GaHb-AgNP contains 28 GaPpIX units stabilized by Hb αβ-dimer units. Eradication (>6-log reduction) of S. aureus and MRSA can be achieved by a 10-second exposure to 405 nm irradiation from a light-emitting diode (LED) array (140 mW cm-2), with GaHb-AgNP loadings as low as 5.6 μg mL-1 for S. aureus and 16.6 μg mL-1 for MRSA, corresponding to nanomolar levels of GaPpIX. This reduction in bacterial count is several orders of magnitude greater than that of GaHb or free GaPpIX on a per mole basis. The GaHb-AgNP platform is also effective against persister MRSA and intracellular MRSA, and can provide comparable levels of aPDT with a 15-minute irradiation by an inexpensive compact fluorescent lightbulb. Collateral phototoxicity to keratinocytes (HaCaT cells) is low at the GaHb-AgNP concentrations and fluences used for aPDT. GaHb adsorbed on 10 nm AgNPs is much more potent than that on 40 nm AgNPs or 10 nm AuNPs, indicating that both size and plasmon-resonant coupling are important factors for enhanced aPDT. Electron microscopy analysis reveals that GaHb-AgNPs are not readily internalized by S. aureus but remain attached to the bacterial cell wall, the likely target of photo-oxidative damage.

Ruthenium coordination preferences in imidazole-containing systems revealed by electrospray ionization mass spectrometry and molecular modeling: Possible cues for the surprising stability of the Ru (III)/tris (hydroxymethyl)-aminomethane/imidazole complexes

Ruthenium is a platinoid that exhibits a range of unique chemical properties in solution, which are exploited in a variety of applications, including luminescent probes, anticancer therapies, and artificial photosynthesis. This paper focuses on a recently demonstrated ability of this metal in its +3 oxidation state to form highly stable complexes with tris (hydroxymethyl)aminomethane (H₂ NC(CH₂ OH)₃ , Tris-base or T) and imidazole (Im) ligands, where a single Ru^III cation is coordinated by two molecules of each T and Im. High-resolution electrospray ionization mass spectrometry (ESI MS) is used to characterize Ru^III complexes formed by placing a Ru^II complex [(NH₃ )₅ Ru^II Cl]Cl in a Tris buffer under aerobic conditions. The most abundant ionic species in ESI MS represent mononuclear complexes containing an oxidized form of the metal, ie, [X_n Ru^III T₂ - 2H]⁺ , where X could be an additional T (n = 1) or NH₃ (n = 0-2). Di- and tri-metal complexes also give rise to a series of abundant ions, with the highest mass ion representing a metal complex with an empirical formula Ru₃ C₂₄ O₂₁ N₆ H₆₆ (interpreted as cyclo(T₂ RuO)₃ , a cyclic oxo-bridged structure, where the coordination sphere of each metal is completed by two T ligands). The empirical formulae of the binuclear species are consistent with the structures representing acyclic fragments of cyclo(T₂ RuO)₃ with addition of various combinations of ammonia and dioxygen as ligands. Addition of histidine in large molar excess to this solution results in complete disassembly of poly-nuclear complexes and gives rise to a variety of ionic species in the ESI mass spectrum with a general formula [Ru^III His_k T_m (NH₃ )_n - 2H]⁺ , where k = 0 to 2, m = 0 to 3, and n = 0 to 4. Ammonia adducts are present for all observed combinations of k and m, except k = m = 2, suggesting that [His₂ Ru^III T₂ - 2H]⁺ represents a complex with a fully completed coordination sphere. The observed cornucopia of Ru^III complexes formed in the presence of histidine is in stark contrast to the previously reported selective reactivity of imidazole, which interacts with the metal by preserving the RuT₂ core and giving rise to a single abundant ruthenium complex (represented by [Im₂ Ru^III T₂ - 2H]⁺ in ESI mass spectra). Surprisingly, the behavior of a hexa-histidine peptide (HHHHHH) is similar to that of a single imidazole, rather than a single histidine amino acid: The RuT₂ core is preserved, with the following ionic species observed in ESI mass spectra: [HHHHHH·(Ru^III T₂ )_m - (3m-1)H]⁺ (m = 1-3). The remarkable selectivity of the imidazole interaction with the Ru^III T₂ core is rationalized using energetic considerations at the quantum mechanical level of theory.

Exploiting His-Tags for Absolute Quantitation of Exogenous Recombinant Proteins in Biological Matrices: Ruthenium as a Protein Tracer

Metal labeling and ICP MS detection offer an alternative to commonly accepted techniques that are currently used to quantitate exogenous proteins in vivo, but modifying the protein surface with metal-containing groups inevitably changes its biophysical properties and is likely to affect trafficking and biodistribution. The approach explored in this work takes advantage of the presence of hexa-histidine tags in many recombinant proteins, which have high affinity toward a range of metals. While many divalent metals bind to poly histidine sequences reversibly, oxidation of imidazole-bound Co^II or Ru^II is known to result in a dramatic increase of the binding strength. In order to evaluate the feasibility of using imidazole-bound metal oxidation as a means of attaching permanent tags to polyhistidine segments, a synthetic peptide YPDFEDYWMKHHHHHH was used as a model. Ru^II can be oxidized under ambient (aerobic) conditions, allowing any oxidation damage to the peptide beyond the metal-binding site to be avoided. The resulting peptide-Ru^III complex is very stable, with the single hexa-histidine segment capable of accommodating up to three metal ions. Localization of Ru^III within the hexa-histidine segment of the peptide was confirmed by tandem mass spectrometry. The Ru^III/peptide binding appears to be irreversible, with both low- and high-molecular weight biologically relevant scavengers failing to strip the metal from the peptide. Application of this protocol to labeling a recombinant form of an 80 kDa protein transferrin allowed Ru^III to be selectively placed within the His-tag segment. The metal label remained stable in the presence of ubiquitous scavengers and did not interfere with the receptor binding, while allowing the protein to be readily detected in serum at sub-nM concentrations. The results of this work suggest that ruthenium lends itself as an ideal metal tag for selective labeling of His-tag containing recombinant proteins to enable their sensitive detection and quantitation with ICP MS.

In Vitro Functional Quality Characterization of NOTA-Modified Somatropins

Chemical modifications on protein biopharmaceuticals introduce extra variability in addition to their inherent complexity, hence require more comprehensive analytical and functional characterization during their discovery, development, and manufacturing. Somatropin (i.e., recombinant human growth hormone, rhGH) modified with the chelating agent S-2-(4-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (p-SCN-Bn-NOTA) allows the incorporation of radiometals for research and possible theranostic purposes. We previously demonstrated that this conjugation leads to multiple substitution degrees and positional isomers within the product. In vitro techniques at the molecular and cellular levels were now applied to assess their functional quality: (i) size exclusion chromatography (SEC) demonstrated functional complexation with human growth hormone binding protein (hGHBp) to the different NOTA-modified somatropins as well as to gallium chelated NOTA-functionalities (Ga-10:1 NOTA-somatropin); (ii) native mass spectrometry (MS) offered in-depth information, a substitution degree up to four NOTAs was still functional; (iii) circular dichroism (CD) analysis confirmed the complexation of unmodified and NOTA-modified somatropin to hGHBp; and (iv) a hGHR bioassay demonstrated initiation of the signal transduction cascade, after binding of all investigated products to the receptor presented on cells with a similar potency (pEC₅₀ values between 9.53 and 9.78) and efficacy (E_max values between 130 and 160%). We conclude that the NOTA-modified somatropins do not possess a significantly different in vitro functionality profile compared to unmodified somatropin. Techniques such as SEC, MS, and CD, traditionally used in the physicochemical characterization of proteins have a demonstrated potential use in the functionality evaluation not only in drug discovery and development but also in quality control settings.