BIOTRANSFORMATION OF HYDRAZINE DERVATIVES IN THE MECHANISM OF TOXICITY

Acute exposure to hydrazine reported to four United States regional poison centers: reconsidering a paradigm

INTRODUCTION

Exposures to hydrazines occur during aeronautic and space operations and pose a potential risk to personnel. Historically, extensive preparatory countermeasures have been taken due to concern for severe toxicity. This study seeks to better understand manifestations of acute occupational exposures to hydrazine to guide recommendations for management.

MATERIALS AND METHODS

A retrospective database review of records from four United States regional poison centers was conducted of all human exposures to hydrazine, monomethylhydrazine, or 1,1-dimethylhydrazine over two decades. Following case abstraction, descriptive statistics were performed to characterize demographics, manifestations, treatments, and outcomes.

RESULTS

One hundred and thirty-five cases were identified, and most were adult males exposed to inhaled hydrazine propellant vapors. Fifty-seven percent of patients were asymptomatic following exposure; otherwise, common symptoms were dyspnea, throat irritation, cough, ocular irritation, and headache. All patients were evacuated or received decontamination, with a few reports of symptomatic treatments, including oxygen supplementation and salbutamol (albuterol). Patients usually recovered quickly and were released after a brief healthcare facility evaluation or observed locally. No patients developed delayed symptoms. Symptoms of severe toxicity were not observed, and there were no deaths.

DISCUSSION

Acute exposures to hydrazines during operations within the aerospace industry appear to be limited primarily to mucosal and mild pulmonary irritation without significant neurologic, hepatic, or hematologic toxicity. These findings are contrary to previously established expectations and may be related to low-level exposures or possibly due to current emergency countermeasures.

CONCLUSIONS

Care in occupational hydrazine exposure will focus on evacuation, decontamination, and symptomatic management of chemical irritant properties of hydrazines. It is reasonable to manage mild cases outside of a healthcare facility. Continued endeavors in human space exploration and habitation will increase the risk of these exposures, making it imperative that clinicians be comfortable with the care and management of these patients.

DNA Adducts in Cancer Chemotherapy

DNA adducting drugs, including alkylating agents and platinum-containing drugs, are prominent in cancer chemotherapy. Their mechanisms of action involve direct interaction with DNA, resulting in the formation of DNA addition products known as DNA adducts. While these adducts are well-accepted to induce cancer cell death, understanding of their specific chemotypes and their role in drug therapy response remain limited. This perspective aims to address this gap by investigating the metabolic activation and chemical characterization of DNA adducts formed by the U.S. FDA-approved drugs. Moreover, clinical studies on DNA adducts as potential biomarkers for predicting patient responses to drug efficacy are examined. The overarching goal is to engage the interest of medicinal chemists and stimulate further research into the use of DNA adducts as biomarkers for guiding personalized cancer treatment.

Bis-chalcone Fluorescent Probe for Hydrazine Ratio Sensing in Environment and Organism

In this paper, four novel hydrazine fluorescent probes X1-X4 with bis-chalcone structure were designed and synthesized. Through the measurement of its optical properties, it is found that it can quickly identify hydrazine, high sensitivity, low detection limit, and good anti-interference ability. The recognition of hydrazine by probes X1-X4 is not affected in the pH range of 4-10, X2 has the highest sensitivity, and the detection limit is as low as 0.336 × 10-7 M. Through Gaussian quantization calculation of probe molecules and their reaction products with hydrazine, it is speculated that the recognition mechanism is the closure of intramolecular charge transfer effect. In addition, the cytotoxicity and imaging of HeLa cells were tested, which showed that probes X1-X4 could be used to detect hydrazine in cells.

Acid-base responsive multifunctional poly(formyl sulfide)s through a facile catalyst-free click polymerization of aldehyde-activated internal diynes and dithiols

Acid-base equilibria play a critical role in biological processes and environmental systems. The development of innovative fluorescent polymeric materials to monitor acid-base equilibria is highly desirable. Herein, a novel catalyst-free click polymerization of aldehyde-activated internal diynes and dithiols was established, and exclusively Markovnikov poly(formyl sulfide)s (PFSs) with high molecular weights and moderate stereoregularity were produced in high yields. Because of the aromatic units and sulfur atoms in their main chains, these polymers possessed high refractive index values. By introducing the fluorene and aldehyde moieties, the resulting PFSs could act as a fluorescent sensor for sensitive hydrazine detection. Taking advantage of the reaction of the aldehyde group and hydrazine, imino-PFSs with remarkable and reversible fluorescence change through alternating fumigation with HCl and NH3 were easily acquired and further applied in multicolor patterning, a rewritable material and quadruple-mode information encryption. Additionally, a test strip of protonated imino-polymer for the tracking of bioamines in situ generated from marine product spoilage was also demonstrated. Collectively, this work not only provides a powerful click polymerization to enrich the multiplicity of sulfur-containing materials, but also opens up enormous opportunities for these functional polysulfides in diverse applications.

Comprehensive Mechanistic View of the Hydrolysis of Oxadiazole-Based Inhibitors by Histone Deacetylase 6 (HDAC6)

Histone deacetylase (HDAC) inhibitors used in the clinic typically contain a hydroxamate zinc-binding group (ZBG). However, more recent work has shown that the use of alternative ZBGs, and, in particular, the heterocyclic oxadiazoles, can confer higher isoenzyme selectivity and more favorable ADMET profiles. Herein, we report on the synthesis and biochemical, crystallographic, and computational characterization of a series of oxadiazole-based inhibitors selectively targeting the HDAC6 isoform. Surprisingly, but in line with a very recent finding reported in the literature, a crystal structure of the HDAC6/inhibitor complex revealed that hydrolysis of the oxadiazole ring transforms the parent oxadiazole into an acylhydrazide through a sequence of two hydrolytic steps. An identical cleavage pattern was also observed both in vitro using the purified HDAC6 enzyme as well as in cellular systems. By employing advanced quantum and molecular mechanics (QM/MM) and QM calculations, we elucidated the mechanistic details of the two hydrolytic steps to obtain a comprehensive mechanistic view of the double hydrolysis of the oxadiazole ring. This was achieved by fully characterizing the reaction coordinate, including identification of the structures of all intermediates and transition states, together with calculations of their respective activation (free) energies. In addition, we ruled out several (intuitively) competing pathways. The computed data (ΔG^‡ ≈ 21 kcal·mol^-1 for the rate-determining step of the overall dual hydrolysis) are in very good agreement with the experimentally determined rate constants, which a posteriori supports the proposed reaction mechanism. We also clearly (and quantitatively) explain the role of the -CF₃ or -CHF₂ substituent on the oxadiazole ring, which is a prerequisite for hydrolysis to occur. Overall, our data provide compelling evidence that the oxadiazole warheads can be efficiently transformed within the active sites of target metallohydrolases to afford reaction products possessing distinct selectivity and inhibition profiles.

Crystal structures of 4-[(4-methyl-benz-yl)-oxy]benzohydrazide and its N'-[(thio-phen-2-yl)-methyl-idene]- derivative

The mol-ecular and crystal structures of a benzoyl-hydrazine bearing an ether group, 4-[(4-methyl-benz-yl)-oxy]benzohydrazide, C₁₅H₁₆N₂O₂, (I), and of the corresponding N'-[(thio-phen-2-yl)-methyl-idene]- derivative, 4-[(4-methyl-benz-yl)-oxy]-N'-[(thio-phen-2-yl)-methyl-idene]benzohydrazide, C₂₀H₁₈N₂O₂S, (II), are described. The supra-molecular structures of both compounds are governed by N-H⋯N and N-H⋯O hydrogen-bonding inter-actions. The hydrazine compound (I) shows a crystal packing with a more complex hydrogen-bonding scheme because of the NH-NH₂ entity, forming a di-periodic supra-molecular structure extending parallel to (100). Hydrazone mol-ecules in (II) are hydrogen-bonded through N-H⋯O inter-actions, giving rise to the formation of ribbons parallel to [010]. Mol-ecules of (I) and (II) show a different orientation of the carbohydrazide moiety likely to favor the crystal packing and thus hydrogen-bonding inter-actions.

Towards N-N-Doped Carbon Dots: A Combined Computational and Experimental Investigation

The introduction of N doping atoms in the carbon network of Carbon Dots is known to increase their quantum yield and broaden the emission spectrum, depending on the kind of N bonding introduced. N doping is usually achieved by exploiting amine molecules in the synthesis. In this work, we studied the possibility of introducing a N–N bonding in the carbon network by means of hydrothermal synthesis of citric acid and hydrazine molecules, including hydrated hydrazine, di-methylhydrazine and phenylhydrazine. The experimental optical features show the typical fingerprints of Carbon Dots formation, such as nanometric size, excitation dependent emission, non-single exponential decay of photoluminescence and G and D vibrational bands in the Raman spectra. To explain the reported data, we performed a detailed computational investigation of the possible products of the synthesis, comparing the simulated absorbance spectra with the experimental optical excitation pattern. The computed Raman spectra corroborate the hypothesis of the formation of pyridinone derivatives, among which the formation of small polymeric chains allowed the broad excitation spectra to be experimentally observed.

Photoactivatable Red Chemiluminescent AIEgen Probe for In Vitro/Vivo Imaging Assay of Hydrazine

Here, we have developed a novel photoactivatable red chemiluminescent AIEgen probe (ACL), based on the combination of the red-emission AIEgen fluorophore (TPEDC) that shows excellent singlet oxygen (¹O₂)-generation ability and the precursor of Schaap's dioxetane (the linker connected to adamantane is the C═C bond) that can be modified to target various analytes, for in vitro and in vivo measurement of hydrazine. Prior to applying for sensing detection, the C═C bond connected to adamantane in ACL was first converted into dioxetane by irradiation to form the activated chemiluminescent AIEgen probe (ACLD). Then, the self-immolative reaction was triggered upon the deprotection of the acylated phenolic hydroxyl group in ACLD in the presence of hydrazine, resulting in the release of the high energy held in the 1,2-dioxetanes, and then, the chemiexcitation was triggered, thereby producing red chemiluminescence through the intramolecular chemiluminescence resonance energy transfer from Schaap's dioxetane to TPEDC. This chemiluminescent AIEgen probe was evaluated in a clean buffer environment as well as using living cells and mouse models.

Dietary Energy Partition: The Central Role of Glucose

Humans have developed effective survival mechanisms under conditions of nutrient (and energy) scarcity. Nevertheless, today, most humans face a quite different situation: excess of nutrients, especially those high in amino-nitrogen and energy (largely fat). The lack of mechanisms to prevent energy overload and the effective persistence of the mechanisms hoarding key nutrients such as amino acids has resulted in deep disorders of substrate handling. There is too often a massive untreatable accumulation of body fat in the presence of severe metabolic disorders of energy utilization and disposal, which become chronic and go much beyond the most obvious problems: diabetes, circulatory, renal and nervous disorders included loosely within the metabolic syndrome. We lack basic knowledge on diet nutrient dynamics at the tissue-cell metabolism level, and this adds to widely used medical procedures lacking sufficient scientific support, with limited or nil success. In the present longitudinal analysis of the fate of dietary nutrients, we have focused on glucose as an example of a largely unknown entity. Even most studies on hyper-energetic diets or their later consequences tend to ignore the critical role of carbohydrate (and nitrogen disposal) as (probably) the two main factors affecting the substrate partition and metabolism.

Role of Oxygen and Nitrogen Radicals in the Mechanism of Anticancer Drug Cytotoxicity

Because of the emergence of drug-resistant tumor cells, successful treatments of human malignancies have been difficult to achieve in the clinic. In spite of various approaches to overcome multi drug resistance, it has remained challenging and elusive. It is, therefore, necessary to define and understand the mechanisms of drug-induced tumor cell killing for the future development of anticancer agents and for rationally designed combination chemotherapies. The clinically active antitumor drugs, topotecan, doxorubicin, etoposide, and procarbazine are currently used for the treatment of human tumors. Therefore, a great deal research has been carried to understand mechanisms of actions of these agents both in the laboratory and in the clinic. These drugs are also extensively metabolized in tumor cells to various reactive species and generate oxygen free radical species (ROS) that initiate lipid peroxidation and induce DNA damage. However, the roles of ROS in the mechanism of cytotoxicity remain unappreciated in the clinic. In addition to ROS, various reactive nitrogen species (RNS) are also formed in tumor cells and in vivo. However, the importance of RNS in cancer treatment is not clear and has remained poorly defined. This review discusses the current understanding of the formation and the significance of ROS and RNS in the mechanisms of various clinically active anticancer drugs.

A Straightforward Approach toward Multifunctionalized Pyridazines via Imination/Electrocyclization

A facile synthesis of functionalized 3-carbamide pyridazines starting from readily available chlorovinyl aldehydes and oxamic acid thiohydrazides via cascade imination/electrocyclization is reported. In the presence of p-toluenesulfuric acid, various ketones have been efficiently incorporated into the pyridazine derivatives through a two-step sequence involving a Vilsmeier-Haack reaction and imination. The synthetic value of this method has been demonstrated by efficient synthesis of steroidal pyridazines.