Activated charcoal significantly improved the reliability of methods for quantitative analysis of endogenous substances in biological specimens: Glutathione and cysteine as cases

2,2',4,4'-Tetrabromodiphenyl ether exposure disrupts blood-testis barrier integrity through CMA-mediated ferroptosis

2,2',4,4'-Tetrabromodiphenyl ether (PBDE-47), being the most prevalent congener of polybrominated diphenyl ethers (PBDEs), has been found to accumulate greatly in the environment and induce spermatogenesis dysfunction. However, the specific underlying factors and mechanisms have not been elucidated. Herein, male Sprague-Dawley (SD) rats were exposed to corn oil, 10 mg/kg body weight (bw) PBDE-47 or 20 mg/kg bw PBDE-47 by gavage for 30 days. PBDE-47 exposure led to blood-testis barrier (BTB) integrity disruption and aberrant spermatogenesis. Given that Sertoli cells are the main toxicant target, to explore the potential mechanism involved, we performed RNA sequencing (RNA-seq) in Sertoli cells, and the differentially expressed genes were shown to be enriched in ferroptosis and lysosomal pathways. We subsequently demonstrated that ferroptosis was obviously increased in testes and Sertoli cells upon exposure to PBDE-47, and the junctional function of Sertoli cells was restored after treatment with the ferroptosis inhibitor ferrostatin-1. Since glutathione peroxidase 4 (GPX4) was dramatically reduced in PBDE-47-exposed testes and Sertoli cells and considering the RNA-sequencing results, we examined the activity of chaperone-mediated autophagy (CMA) and verified that the expression of LAMP2a and HSC70 was upregulated significantly after PBDE-47 exposure. Notably, Lamp2a knockdown not only inhibited ferroptosis by suppressing GPX4 degradation but also restored the impaired junctional function induced by PBDE-47. These collective findings strongly indicate that PBDE-47 induces Sertoli cell ferroptosis through CMA-mediated GPX4 degradation, resulting in decreased BTB-associated protein expression and eventually leading to BTB integrity disruption and spermatogenesis dysfunction.

Integrated untargeted and targeted testicular metabolomics to reveal the regulated mechanism of Gushudan on the hypothalamic-pituitary-gonadal axis of kidney-yang-deficiency-syndrome rats

Modern studies have shown that neuroendocrine disorders caused by the dysfunction of the hypothalamic-pituitary-gonadal (HPG) axis are one of the important pathogenetic mechanisms of kidney-yang-deficiency-syndrome (KYDS). The preventive effect of Gushudan on KYDS has been reported, but its regulatory mechanisms on the HPG axis have not been elucidated. In this study, we developed an integrated untargeted and targeted metabolomics analysis strategy to investigate the regulatory mechanism of Gushudan on the HPG axis in rats with KYDS. In untargeted metabolomics, we screened 14 potential biomarkers such as glycine, lysine, and glycerol that were significantly associated with the HPG axis. To explore the effect of changes in the levels of potential biomarkers on KYDS, all of them were quantified in targeted metabolomics. With the quantitative results, correlations between potential biomarkers and testosterone, a functional indicator of the HPG axis, were explored. The results showed that oxidative stress, inflammatory response, and energy depletion, induced by metabolic disorders in rats, were responsible for the decrease in testosterone levels. Gushudan improves metabolic disorders and restores testosterone levels, thus restoring HPG axis dysfunction. This finding elucidates the special metabolic characteristics of KYDS and the therapeutic mechanism of Gushudan from a new perspective.

A new adsorptive 3D-printed sampling device for simultaneous determination of 63 urinary organic acids by LC-MS/MS

BACKGROUND

The detection and quantification of urinary metabolites play an important role in disease diagnosis. In most cases, urinary analyses are done with liquid urine samples, which must be quickly transported to the laboratory to avoid metabolites degradation that is associated with temperature fluctuations. Consequently, dried sampling devices have emerged to minimize analyte degradation. However, most commercial dried sampling devices are expensive, aggregate low volumes, and need better analytical sensitivity. Therefore, a new dry urine sampling device that is inexpensive, suitable for domestic sampling operation, and efficient for quantifying metabolites without requiring high-resolution instruments is proposed in the present study.

RESULTS

The newly designed dry urine sampling device was produced by 3D printing that efficiently determines 63 urinary organic acids using liquid chromatography coupled with mass spectrometry (LC-MS/MS). The system's efficiency was demonstrated with analytical figures of merit, such as precision, accuracy, and stability of analytes after the sampling and storing of ordinary urine samples. The limits of quantification ranged from 0.01 to 0.42 ng mL-1. Precision and accuracy tests showed relative standard deviations of less than 15 %. The urine stability in the sampling device was high within seven days without any significant degradation of the metabolites. The method was applied to the analysis of 10 human urine samples and compared to a conventional method without the use of the sampling device. The results showed no statistically significant differences, demonstrating the method's efficiency.

SIGNIFICANCE

The proposed 3-D printing device was developed with fast, low-cost manufacturing features and can be manufactured with different volumetric capacities, adaptable to the needs of each user. Furthermore, it is innovative because this is the first sampling device that is effective for the simultaneous storage and preservation of several important urinary metabolites. Thus, it is anticipated that its application would contribute significantly to the identification of metabolic disorders.

A potent phosphodiester Keap1-Nrf2 protein-protein interaction inhibitor as the efficient treatment of Alzheimer's disease

The Keap1-Nrf2 pathway has been established as a therapeutic target for Alzheimer's disease (AD). Directly inhibiting the protein-protein interaction (PPI) between Keap1 and Nrf2 has been reported as an effective strategy for treating AD. Our group has validated this in an AD mouse model for the first time using the inhibitor 1,4-diaminonaphthalene NXPZ-2 with high concentrations. In the present study, we reported a new phosphodiester containing diaminonaphthalene compound, POZL, designed to target the PPI interface using a structure-based design strategy to combat oxidative stress in AD pathogenesis. Our crystallographic verification confirms that POZL shows potent Keap1-Nrf2 inhibition. Remarkably, POZL showed its high in vivo anti-AD efficacy at a much lower dosage compared to NXPZ-2 in the transgenic APP/PS1 AD mouse model. POZL treatment in the transgenic mice could effectively ameliorate learning and memory dysfunction by promoting the Nrf2 nuclear translocation. As a result, the oxidative stress and AD biomarker expression such as BACE1 and hyperphosphorylation of Tau were significantly reduced, and the synaptic function was recovered. HE and Nissl staining confirmed that POZL improved brain tissue pathological changes by enhancing neuron quantity and function. Furthermore, it was confirmed that POZL could effectively reverse Aβ-caused synaptic damage by activating Nrf2 in primary cultured cortical neurons. Collectively, our findings demonstrated that the phosphodiester diaminonaphthalene Keap1-Nrf2 PPI inhibitor could be regarded as a promising preclinical candidate of AD.

A Substituted-Rhodamine-Based Reversible Fluorescent Probe for In Vivo Quantification of Glutathione

Quantifying glutathione (GSH) in cells and organisms is of great significance for understanding the mechanism of oxidative stress in various physiological and pathological processes. However, the quantification by fluorescence bioimaging in living tissues has much stricter requirements than the "Petri dish"-cultured cells in flat plates. Based on the evaluation of the electronic structure and steric hindrance-tuned reactivity of phospha-substituted rhodamine with GSH, a reversible Förster resonance energy transfer (FRET) probe ZpSiP with a distinct performance (K_d =4.9 mM, t_1/2 =0.57 s, k=81 M^-1  s^-1 ) is developed for real time quantifying GSH in living cells. Furthermore, the near-infrared (NIR) probe succeeded in sensitively tracking the dynamics of GSH in the real organisms bearing tumors, chronic renal failure, and liver fibrosis for unveiling the related pathological processes. We believe that the advance in chemistry with quantitative analysis methods will initiate more promising progress and broad applications.

Advancement in Analytical Strategies for Quantification of Biomarkers with a Special Emphasis on Surrogate Approaches

Accurate quantification of biomarkers has always been a challenge for many bioanalytical scientists due to their endogenous nature and low concentration in biological matrices. Different analytical approaches have been developed for quantifying biomarkers including enzyme-linked immunosorbent assay, immunohistochemistry, western blotting, and chromatographic techniques assisted with mass spectrometry. Liquid chromatography-tandem mass spectrometry-based quantification of biomarkers has gained more attention over other traditional techniques due to its higher sensitivity and selectivity. However, the primary challenge lies with this technique includes the unavailability of a blank matrix for method development. To overcome this challenge, different analytical approaches are being developed including surrogate analyte and surrogate matrix approach. Such approaches include quantification of biomarkers in a surrogate matrix or quantification of an isotopically labeled surrogate analyte in an authentic matrix. To demonstrate the authenticity of the surrogate approach, it is mandatory to establish quantitative parallelism through validation employing respective surrogate analytes and surrogate matrices. In this review, different bioanalytical approaches for biomarker quantification and recent advancements in the field aiming for improvement in the specificity of the techniques have been discussed. Liquid chromatography-tandem mass spectrometry-based surrogate approaches for biomarker quantification and significance of parallelism establishment in both surrogate matrix and surrogate analyte-based approaches have been critically discussed. In addition, different methods for demonstrating parallelism in the surrogate method have been explained.

Review of HPLC-MS methods for the analysis of nicotine and its active metabolite cotinine in various biological matrices

In recent years, tobacco smoking is a risk factor for a series of diseases including cardiovascular diseases, cerebrovascular diseases, and cancers. Nicotine, the primary component of tobacco smoke, is mainly transformed to its active metabolite cotinine, which is often used as biomarker for tobacco exposure for its higher blood concentration and longer residence time than nicotine. Various analytical methods have been developed for the determination of nicotine and cotinine in biological matrices. This article reviewed the HPLC-MS based methods for nicotine and/or cotinine analysis in various biological matrices. The sample preparation, mass and chromatographic conditions and method validation results of these methods have been summarized and analyzed. Sample was mainly pretreated by protein precipitation and/or extraction. Separation was achieved using methanol and/or acetonitrile:water (with or without ammonium acetate) on C18 columns, and acetonitrile:water (with formic acid, ammonium acetate/formate) on HILIC columns. Nicotine-d3, nicotine-d4 and cotinine-d3 were commonly used internal standards. Other non-deuterated IS were also used such as ritonavir, N-ethylnorcotinine, and milrinone. For both nicotine and cotinine, the calibration range was 0.005-35000 ng/mL, the matrix effect was 75.96% - 126.8% and the recovery was 53% - 124.5%. The two analytes were stable at room temperature for 1-10 days, at -80 °C for up to 6 months, and after 3-6 freeze-thaw cycles. Comedications did not affect nicotine and cotinine analysis.

High level nitrosamines in rat faeces with colorectal cancer determined by a sensitive GC-MS method

N-nitrosamines (NAs) are common toxic substances that have a strong correlation with many human diseases, such as liver damage and cancer. However, there is a lack of studies on methods involving the detection of NAs in biological samples, possibly owing to the interference of complex biological matrices and the influence of endogenous NAs. In this work, solid-phase extraction with mixed solid phases and adsorption sedimentation were used to successfully establish a gas chromatography-mass spectrometry (GC-MS) method for detecting eight NAs in rat faeces. Chromatographic separation of analytes was performed with Agilent VF-WAXms (30 m × 0.25 mm, 0.25 µm) GC columns. The LLOQs of eight NAs were set to the concentration of 0.5 ng/g and the obtained standard curves were linear, and correlation coefficients (r) were ≥ 0.99 for samples with concentration ranges of 0.5-500 ng/g. The inter and intra-assay precisions were< 15% for all analytes in the quality control samples, and the accuracies ranged from 88.67% to 108.33%. The extraction recoveries were above 78.56% for seven NAs, and a significant matrix effect was not observed. The application of this method revealed that the levels of NAS in the faeces of rats with colorectal cancer were higher than those of normal rats. Additionally, the effect of a high nitrite diet on NAs in faeces was analysed; the results confirmed that a high nitrite diet might contribute to an abnormal increase in NAs. Our work provides an analytical method for further in vivo study of NAs. Furthermore, a pilot study on the relationship between NAs and colorectal cancer was completed.

Characterization of the roles of activated charcoal and Chelex in the induction of PrfA regulon expression in complex medium

The foodborne pathogen Listeria monocytogenes is able to survive across a wide range of intra- and extra-host environments by appropriately modulating gene expression patterns in response to different stimuli. Positive Regulatory Factor A (PrfA) is the major transcriptional regulator of virulence gene expression in L. monocytogenes. It has long been known that activated charcoal is required to induce the expression of PrfA-regulated genes in complex media, such as Brain Heart Infusion (BHI), but not in chemically defined media. In this study, we show that the expression of the PrfA-regulated hly, which encodes listeriolysin O, is induced 5- and 8-fold in L. monocytogenes cells grown in Chelex-treated BHI (Ch-BHI) and in the presence of activated charcoal (AC-BHI), respectively, relative to cells grown in BHI medium. Specifically, we show that metal ions present in BHI broth plays a role in the reduced expression of the PrfA regulon. In addition, we show that expression of hly is induced when the levels of bioavailable extra- or intercellular iron are reduced. L. monocytogenes cells grown Ch-BHI and AC-BHI media showed similar levels of resistance to the iron-activated antibiotic, streptonigrin, indicating that activated charcoal reduces the intracellular labile iron pool. Metal depletion and exogenously added glutathione contributed synergistically to PrfA-regulated gene expression since glutathione further increased hly expression in metal-depleted BHI but not in BHI medium. Analyses of transcriptional reporter fusion expression patterns revealed that genes in the PrfA regulon are differentially expressed in response to metal depletion, metal excess and exogenous glutathione. Our results suggest that metal ion abundance plays a role in modulating expression of PrfA-regulated virulence genes in L. monocytogenes.