Integrative Salt Selection and Formulation Optimization: Perspectives of Disproportionation and Microenvironmental pH Modulation.

We report a novel utilization of a pH modifier as a disproportionation retardant in a tablet formulation. The drug molecule of interest has significant bioavailability challenges that require solubility enhancement. In addition to limited salt/cocrystal options, disproportionation of the potential salt(s) was identified as a substantial risk. Using a combination of Raman spectroscopy with chemometrics and quantitative X-ray diffraction in specially designed stress testing, we investigated the disproportionation phenomena. The learnings and insight drawn from crystallography drove the selection of the maleate form as the target API. Inspired by the fumarate form's unique stability and solubility characteristics, we used fumaric acid as the microenvironmental pH modulator. Proof-of-concept experiments with high-risk (HCl) and moderate-risk (maleate) scenarios confirmed the synergistic advantage of fumaric acid, which interacts with the freebase released by disproportionation to form a more soluble species. The resultant hemifumarate helps maintain the solubility at an elevated level. This work demonstrates an innovative technique to mediate the solubility drop during the "parachute" phase of drug absorption using compendial excipients, and this approach can potentially serve as an effective risk-mitigating strategy for salt disproportionation.

Developing In Situ Chemometric Models with Raman Spectroscopy for Monitoring an API Disproportionation with a Complex Polymorphic Landscape.

An in situ Raman method was developed to characterize the disproportionation of two salts involving a complex polymorphic landscape comprising up to two metastable and one stable freebase forms. Few precedents exist for Raman calibration procedures for solid form quantitation involving more than two polymorphs, while no literature examples were found for cases with multiple metastable forms. Therefore, a new Raman calibration procedure was proposed by directly using disproportionation experiments to generate multiple calibration samples encompassing a range of polymorph ratios through in-line Raman measurements complemented by off-line reference X-ray diffraction measurements. The developed Raman methods were capable of accurately quantitating each solid form in situ when solid concentration variation was incorporated into the calibration dataset. The kinetic understanding of the thermodynamically driven polymorphic conversions gained from this Raman method guided the selection of the salt best suited for the delivery of the active ingredient in the drug product. This work provided a spectroscopic and mathematical approach for simultaneously quantitating multiple polymorphs from a complex mixture of solids with the objective of real-time monitoring.

Influencia de los anticoagulantes EDTAK² y EDTAK³ en los resultados del hemograma / Influence of the EDTAK² and EDTAK³ anticoagulants on hematology testing results / Influência dos anticoagulantes EDTAK² e EDTAK³ nos resultados do hemograma

El International Council for Standardization in Haematology (ICSH) recomienda el uso de ácido etilendiaminotretaacético dipotásico (EDTAK2) como anticoagulante para el hemograma, mientras que el Clinical and Laboratory Standards Institute (CLSI) EDTAK2 o ácido etilendiaminotetraacético tripotásico (EDTAK3). El objetivo de este trabajo fue evaluar la influencia del tipo de sal de EDTA utilizado en la variación de los resultados de los parámetros hematológicos. Se recolectaron 24 muestras por venopunción, de cada una se cargó una alícuota en EDTAK3 y otra en EDTAK2. De los 23 parámetros evaluados en el autoanalizador Sysmex XN1000 (Roche Diagnostics), sólo los de la serie roja presentaron diferencias estadísticamente significativas en las muestras pareadas (p<0,05). El sesgo superó las especificaciones de calidad de Variabilidad Biológica Mínima para hematocrito (2,9%) y concentración de hemoglobina corpuscular media (1,7%), de Variabilidad Biológica Deseable para el volumen corpuscular medio (1,7%) y Variabilidad Biológica Óptima para hemoglobina (1,2%) y recuento de eritrocitos (1,2%). No se hallaron diferencias significativas en los parámetros de la serie blanca, ni en los plaquetarios y tampoco en los reticulocitarios. Para disminuir el error preanalítico, cada laboratorio debe estandarizar la extracción de los hemogramas empleando un único tipo de anticoagulante.

The International Council for Standardization in Haematology (ICSH) currently supports de use of ethylenediaminetetraacetic acid dipotassium (EDTAK2) anticoagulant for hematology testing, while the Clinical and Laboratory Standards Institute (CLSI) recommends EDTAK2 or ethylenediaminetetraacetic acid tripotassium (EDTAK3). The objective of this study was to evaluate the influence of the EDTA formulations in the results of hematologic parameters. A total of 24 samples were collected by venous puncture and two aliquots were loaded: one in EDTAK3 and another in EDTAK2. Of the 23 hematologic parameters tested with the use of Sysmex XN1000 (Roche diagnostics) hematologic analyser, only those in the red series showed statistically significant differences in the paired samples (p < 0.05). The bias exceeded the quality specifications of Minimum Biological Variability for hematocrit (2.9%) and mean corpuscular hemoglobin concentration (1.7%), Desirable Biological Variability for the mean corpuscular volume (1.7%) and Biological Variability Optimal for hemoglobin (1.2%) and erythrocyte count (1.2%). No significant differences were found in the parameters of white series, neither platelets, nor reticulocytes. To reduce the preanalytical error, each laboratory should standardize the extraction for complete blood cell count using a single type of anticoagulant.

A International Council for Standardization in Haematology (ICSH) recomenda a utilização do ácido etileno diamino treta-acético dipotássico (EDTAK2) como anticoagulante para hemograma, enquanto que a Clinical and Laboratory Standards Institute (CLSI) EDTAK2 ou ácido etileno diamino treta-acético tripotássico (EDTAK3). O objetivo deste trabalho foi avaliar a influência do tipo de sal de EDTA utilizado na variação dos resultados dos parâmetros hematológicos. Foram recolhidas 24 amostras por venopunção, de cada uma se carregou uma alíquota de EDTAK3 e outra de EDTAK2. Dos 23 parâmetros avaliados no autoanalisador Sysmex XN1000 (Roche Diagnostics), apenas aqueles da série vermelha apresentaram diferenças estatisticamente significativas nas amostras emparelhadas (p<0,05). O viés superou as especificações de qualidade da Variabilidade Biológica Mínima para o hematócrito (2,9%) e concentração de hemoglobina corpuscular média (1,7%), de Variabilidade Biológica Desejável para o volume corpuscular médio (1,7%) e Variabilidade Biológica Ótima para a hemoglobina (1,2%) e contagem de eritrócitos (1,2%). Não foram encontradas diferenças significativas nos parâmetros da série branca, nem nos plaquetários, nem nos reticulocitários. Para reduzir o erro pré-analítico, cada laboratório deve padronizar a extração dos hemogramas usando um único tipo de anticoagulante.

Biosynthesis of the [FeFe] Hydrogenase H Cluster: A Central Role for the Radical SAM Enzyme HydG.

Hydrogenase enzymes catalyze the rapid and reversible interconversion of H2 with protons and electrons. The active site of the [FeFe] hydrogenase is the H cluster, which consists of a [4Fe-4S]H subcluster linked to an organometallic [2Fe]H subcluster. Understanding the biosynthesis and catalytic mechanism of this structurally unusual active site will aid in the development of synthetic and biological hydrogenase catalysts for applications in solar fuel generation. The [2Fe]H subcluster is synthesized and inserted by three maturase enzymes-HydE, HydF, and HydG-in a complex process that involves inorganic, organometallic, and organic radical chemistry. HydG is a member of the radical S-adenosyl-l-methionine (SAM) family of enzymes and is thought to play a prominent role in [2Fe]H subcluster biosynthesis by converting inorganic Fe(2+), l-cysteine (Cys), and l-tyrosine (Tyr) into an organometallic [(Cys)Fe(CO)2(CN)](-) intermediate that is eventually incorporated into the [2Fe]H subcluster. In this Forum Article, the mechanism of [2Fe]H subcluster biosynthesis is discussed with a focus on how this key [(Cys)Fe(CO)2(CN)](-) species is formed. Particular attention is given to the initial metallocluster composition of HydG, the modes of substrate binding (Fe(2+), Cys, Tyr, and SAM), the mechanism of SAM-mediated Tyr cleavage to CO and CN(-), and the identification of the final organometallic products of the reaction.

Cysteine as a ligand platform in the biosynthesis of the FeFe hydrogenase H cluster.

Hydrogenases catalyze the redox interconversion of protons and H2, an important reaction for a number of metabolic processes and for solar fuel production. In FeFe hydrogenases, catalysis occurs at the H cluster, a metallocofactor comprising a [4Fe-4S]H subcluster coupled to a [2Fe]H subcluster bound by CO, CN(-), and azadithiolate ligands. The [2Fe]H subcluster is assembled by the maturases HydE, HydF, and HydG. HydG is a member of the radical S-adenosyl-L-methionine family of enzymes that transforms Fe and L-tyrosine into an [Fe(CO)2(CN)] synthon that is incorporated into the H cluster. Although it is thought that the site of synthon formation in HydG is the "dangler" Fe of a [5Fe] cluster, many mechanistic aspects of this chemistry remain unresolved including the full ligand set of the synthon, how the dangler Fe initially binds to HydG, and how the synthon is released at the end of the reaction. To address these questions, we herein show that L-cysteine (Cys) binds the auxiliary [4Fe-4S] cluster of HydG and further chelates the dangler Fe. We also demonstrate that a [4Fe-4S]aux[CN] species is generated during HydG catalysis, a process that entails the loss of Cys and the [Fe(CO)2(CN)] fragment; on this basis, we suggest that Cys likely completes the coordination sphere of the synthon. Thus, through spectroscopic analysis of HydG before and after the synthon is formed, we conclude that Cys serves as the ligand platform on which the synthon is built and plays a role in both Fe(2+) binding and synthon release.

X-ray crystallographic and EPR spectroscopic analysis of HydG, a maturase in [FeFe]-hydrogenase H-cluster assembly.

Hydrogenases use complex metal cofactors to catalyze the reversible formation of hydrogen. In [FeFe]-hydrogenases, the H-cluster cofactor includes a diiron subcluster containing azadithiolate, three CO, and two CN(-) ligands. During the assembly of the H cluster, the radical S-adenosyl methionine (SAM) enzyme HydG lyses the substrate tyrosine to yield the diatomic ligands. These diatomic products form an enzyme-bound Fe(CO)x(CN)y synthon that serves as a precursor for eventual H-cluster assembly. To further elucidate the mechanism of this complex reaction, we report the crystal structure and EPR analysis of HydG. At one end of the HydG (ßα)8 triosephosphate isomerase (TIM) barrel, a canonical [4Fe-4S] cluster binds SAM in close proximity to the proposed tyrosine binding site. At the opposite end of the active-site cavity, the structure reveals the auxiliary Fe-S cluster in two states: one monomer contains a [4Fe-5S] cluster, and the other monomer contains a [5Fe-5S] cluster consisting of a [4Fe-4S] cubane bridged by a µ2-sulfide ion to a mononuclear Fe(2+) center. This fifth iron is held in place by a single highly conserved protein-derived ligand: histidine 265. EPR analysis confirms the presence of the [5Fe-5S] cluster, which on incubation with cyanide, undergoes loss of the labile iron to yield a [4Fe-4S] cluster. We hypothesize that the labile iron of the [5Fe-5S] cluster is the site of Fe(CO)x(CN)y synthon formation and that the limited bonding between this iron and HydG may facilitate transfer of the intact synthon to its cognate acceptor for subsequent H-cluster assembly.

Ceftaroline is active against heteroresistant methicillin-resistant Staphylococcus aureus clinical strains despite associated mutational mechanisms and intermediate levels of resistance.

Methicillin-resistant Staphylococcus aureus (MRSA) is an important infectious human pathogen responsible for diseases ranging from skin and soft tissue infections to life-threatening endocarditis. ß-Lactam resistance in MRSA involves acquisition of penicillin-binding protein 2a (PBP2a), a protein with low affinity for ß-lactams that mediates cell wall assembly when the normal staphylococcal PBPs (PBP1 to -4) are blocked by these agents. Many MRSA strains display heterogeneous expression of resistance (HeR) against ß-lactam antibiotics. The ß-lactam-mediated homoresistant (HoR) phenotype is associated with both expression of the mecA gene and activation of the LexA-RecA-mediated SOS response, a regulatory network induced in response to DNA damage. Ceftaroline (CPT) is the only FDA-approved cephalosporin targeting PBP2a. We investigated the mechanistic basis of CPT activity against HeR-MRSA strains, including a set of strains displaying an intermediate level of resistance to CPT. Mechanistically, we found that 1 exposure of HeR-MRSA to subinhibitory concentrations of CPT selected for the HoR derivative activated the SOS response and increased mutagenesis. Importantly, CPT-selected HoR cells remained susceptible to CPT while still being resistant to most ß-lactams, and 2-CPT activity in HeR-MRSA resided in an attenuated induction of mecA expression in comparison to other ß-lactams. In addition, 3-CPT intermediate-resistant strains displayed a significant increase in CPT-induced mecA expression accompanied by mutations in PBP2, which together may interfere with the complete repression by CPT of both PBP2a and PBP2a-PBP2 interactions and thus be a determining factor in the low level of CPT resistance in the absence of mecA gene mutations. The present study provides mechanistic evidence that CPT represents an alternative therapeutic option for the treatment of heteroresistant MRSA strains.

TCA cycle-mediated generation of ROS is a key mediator for HeR-MRSA survival under ß-lactam antibiotic exposure.

Methicillin-resistant Staphylococcus aureus (MRSA) is a major multidrug resistant pathogen responsible for several difficult-to-treat infections in humans. Clinical Hetero-resistant (HeR) MRSA strains, mostly associated with persistent infections, are composed of mixed cell populations that contain organisms with low levels of resistance (hetero-resistant HeR) and those that display high levels of drug resistance (homo-resistant HoR). However, the full understanding of ß-lactam-mediated HeR/HoR selection remains to be completed. In previous studies we demonstrated that acquisition of the HoR phenotype during exposure to ß-lactam antibiotics depended on two key elements: (1) activation of the SOS response, a conserved regulatory network in bacteria that is induced in response to DNA damage, resulting in increased mutation rates, and (2) adaptive metabolic changes redirecting HeR-MRSA metabolism to the tricarboxylic acid (TCA) cycle in order to increase the energy supply for cell-wall synthesis. In the present work, we identified that both main mechanistic components are associated through TCA cycle-mediated reactive oxygen species (ROS) production, which temporally affects DNA integrity and triggers activation of the SOS response resulting in enhanced mutagenesis. The present work brings new insights into a role of ROS generation on the development of resistance to ß-lactam antibiotics in a model of natural occurrence, emphasizing the cytoprotective role in HeR-MRSA survival mechanism.

[Intestinal pseudo-obstruction due to sporadic visceral myopathy]. / Pseudo-obstrucción intestinal por miopatía visceral esporádica.

We report an unusual case of a patient with sporadic visceral myopathy and involvement of the entire gastrointestinal and urinary tract. Visceral myopathy is a form of chronic idiophatic intestinal pseudo-obstruction characterized by vacuolar degeneration, atrophy and fibrosis of the intestinal propia muscle layer without inflammatory cells. It can be found in childhood and adolescence affecting the gastrointestinal and urinary visceral muscle. The familial occurrence can be found in about 30% of cases and the mode of transmission is autosomal recessive in most families. It is crucial to exclude secondary forms of chronic intestinal pseudo-obstruction and to obtain full thickness intestinal biopsy for the diagnosis. Surgical treatment is only beneficial in cases with isolated segmental involvement of the gastrointestinal tract.

Pseudo-obstrucción intestinal por miopatía visceral esporádica. / [Intestinal pseudo-obstruction due to sporadic visceral myopathy]

We report an unusual case of a patient with sporadic visceral myopathy and involvement of the entire gastrointestinal and urinary tract. Visceral myopathy is a form of chronic idiophatic intestinal pseudo-obstruction characterized by vacuolar degeneration, atrophy and fibrosis of the intestinal propia muscle layer without inflammatory cells. It can be found in childhood and adolescence affecting the gastrointestinal and urinary visceral muscle. The familial occurrence can be found in about 30

of cases and the mode of transmission is autosomal recessive in most families. It is crucial to exclude secondary forms of chronic intestinal pseudo-obstruction and to obtain full thickness intestinal biopsy for the diagnosis. Surgical treatment is only beneficial in cases with isolated segmental involvement of the gastrointestinal tract.