An LC-MS/MS method for determination of novel fungicide pyraoxystrobin in rat plasma and tissues: Toxicokinetics and tissue distribution study

Some evidence supporting the use of optically pure R-(-)-diniconazole: Toxicokinetics and configuration conversion on chiral diniconazole

Diniconazole is a chiral pesticide that exists in two enantiomers, R-(-)-diniconazole and S-(+)-diniconazole, with the R-enantiomer being much more active than the S-enantiomer. Previous enantioselective toxicology studies of diniconazole focused mostly on simple environmental model organisms. In this study, we evaluated the toxicokinetics of the two diniconazole enantiomers in rats and mice to provide a more comprehensive risk assessment. The two enantiomers displayed clear differences in their stereoselective contents in vivo. The t1/2 of R-(-)-diniconazole was 7.06 ± 3.35 h, whereas that of S-(+)-diniconazole was 9.14 ± 4.60 h, indicating that R-(-)-diniconazole was eliminated faster in vivo. The excretion rates of R-(-)-diniconazole and S-(+)-diniconazole were 4.08 ± 0.50 % and 2.68 ± 0.58 %, respectively, indicating more excretion of R-(-)-diniconazole. S-(+)-diniconazole had a higher bioavailability than R-(-)-diniconazole (52.19 % vs. 42.44 %). S-(+)-Diniconazole was also found in relatively high abundance in tissues such as the stomach, large intestine, small intestine, cecum, liver, kidney, brain, and testes, with the abundance being 1.71-2.48-fold that of R-(-)-diniconazole. The selective degradation of both enantiomers in the tissues and their mutual conversion in vivo were not observed, and this could indicate that configuration conversion did not contribute to the differences in the content of enantiomers in the tissues. Instead, such differences were mainly caused by the differences in affinity of each enantiomer for the tissues. Furthermore, investigation of the interconversion between optically pure R-(-)-diniconazole and S-(+)-diniconazole monomers in soil revealed no interconversion. All of the above results indicated no interconversion between R-(-)-diniconazole and S-(+)-diniconazole in vivo and in the soil, and that S-(+)-diniconazole tends to have a greater potential to accumulate in vivo. Thus, if only R-(-)-diniconazole is used as a pesticide, the negative impact on mammals and the environment will be reduced, suggesting that in agriculture, the application of optically pure R-(-)-diniconazole may be a better strategy.

An Efficient UPLC-MS/MS Method for the Determination of Pyrroloquinoline Quinone in Rat Plasma and Its Application to a Toxicokinetic Study

Pyrroloquinoline quinone (PQQ) is a powerful antioxidant coenzyme existing in diet, benefiting growth, development, cognition function, and the repair of damaged organs. However, a method for detecting PQQ in vivo was rarely described, limiting the research on the bioanalysis and metabolic properties of PQQ. In this study, a novel, simple, and efficient ultra-high performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS) method was developed and validated to quantify the concentration of PQQ in rat plasma. Detection through mass spectrometry was operated by multiple reaction monitoring (MRM) in negative electrospray ionization mode with ion transitions m/z 328.99→197.05 for PQQ and m/z 280.04→195.04 for the internal standard. The calibration curves were linear up to 10,000 ng/mL, with a lower limit of quantitation of 10 ng/mL. Inter-run and intra-run precision ranged from 1.79% to 10.73% and accuracy ranged from -7.73% to 7.30%. The method was successfully applied to a toxicokinetic study in Sprague-Dawley rats after the oral administration of PQQ disodium salt at doses of 250 mg/kg, 500 mg/kg, and 1000 mg/kg. The toxicokinetic parameters were subsequently analyzed, which may provide valuable references for the toxicokinetic properties and safety evaluation of PQQ.

Adverse effects of SYP-3343 on zebrafish development via ROS-mediated mitochondrial dysfunction

As a newly-invented and highly-efficiency strobilurin fungicide, pyraoxystrobin (SYP-3343) has been recognized as a highly poisonous toxin for a variety of aquatic organisms. Nevertheless, the developmental toxicity and potential mechanism of SYP-3343 have not been well-documented. The results showed that SYP-3343 was relatively stable and maintained within the range of 20 % in 24 h, and the LC₅₀ value to embryos at 72 hpf was 17.13 μg/L. The zebrafish embryotoxicity induced by 1, 2, 4, and 8 μg/L SYP-3343 is demonstrated by repressive embryo incubation, enhancive mortality rate, abnormal heart rate, malformed morphological characteristic, and impaired spontaneous coiling, indicating SYP-3343 mostly exerted its toxicity in a dose- and time-dependent manner. Besides SYP-3343 was critically involved in regulating cell cycle, mitochondrial membrane potential, and reactive oxygen species production as well as zebrafish primary cells apoptosis, which can be mitigated using antioxidant N-acetyl-L-cysteine. A significant change occurred in total protein content, the biochemical indices, and antioxidant capacities owing to SYP-3343 exposure. Additionally, SYP-3343 altered the mRNA levels of heart development-, mitochondrial function-, and apoptosis-related genes in zebrafish embryos. These results indicated that SYP-3343 induced apoptosis accompanying reactive oxygen species-initiated mitochondrial dysfunction in zebrafish embryos.

Simultaneous determination of strobilurin fungicides residues in bean samples by HPLC-UV-AD using boron-doped diamond electrode

The aim of this paper was the development of a method for the determination of six strobilurins (fungicides) using boron-doped diamond (BDD) electrode with amperometric detection (AD) homemade coupled to high performance liquid chromatography (HPLC/UV-Vis). HPLC separation of fungicides was performed in a C18 reverse phase column using both UV and AD detectors at 200 mn and 1.9 V, respectively. The linear range for each strobilurin was from 5 to 15 mg L^-1 and the correlation coefficients for all the compounds were above 0.997. Both detectors presented adequate detectability (LOD ranging from 1.33 to 1.57 μg kg^-1) respecting the limits pre-established by regulatory agencies. The method was validated presenting good values of recovery and accuracy. In the spiked samples the recoveries ranged from 61.6% (trifloxystrobin) to 98.8% (azoxystrobin) for UV and 62.3% (trifloxystrobin) to 95.2% (azoxystrobin) for AD. In blanks spikes the recovery varied from 77.8% (picoxystrobin) to 88.4% (kresoxim-methyl) for UV and 76.7% (picoxystrobin) to 87.1% (dimoxystrobin) for AD. The method showed good precision (RSD < 10%). The results obtained by amperometric and UV detections were statistically comparable. Seven bean samples were analyzed to detect fungicide residues.

Enantioseparation and Determination of Penconazole in Rat Plasma by Chiral LC-MS/MS: Application to a Stereoselective Toxicokinetic Study

In this study, a specific and sensitive method of liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) was developed for the determination of penconazole enantiomers in rat plasma. The enantioseparation was achieved on a Chiralpak IC column by using acetonitrile/water (80:20, v/v) as the mobile phase. Penconazole enantiomers and internal standard l-lansoprazole (IS) were detected in multiple reaction monitoring (MRM) mode with positive electrospray ionization source. The method was validated over the concentration range of 2.5–250.0 ng mL⁻¹ for penconazole enantiomers. Good linearity was obtained for both enantiomers with correlation coefficients (R) greater than 0.995. The relative error was well within the admissible range of −1.1–3.2%, and relative standard deviation was less than 6.0%. After validation, the established method was successfully applied to a stereoselective toxicokinetic study in female and male rats after oral administration of 50 mg kg⁻¹ racemic penconazole. This is the first experiment regarding the stereospecific toxicokinetic study of penconazole and the bioanalytical approach for its quantitation in vivo.

Evaluation of pyraoxystrobin bioconcentration in zebrafish (Danio rerio) using modified QuEChERS extraction

Pyraoxystrobin is a novel strobilurin fungicide that is widely used on many crops. The high log K_ow of pyraoxystrobin implies that it tends to accumulate in aquatic organisms. This study optimized the sorbents of QuEChERS (quick, easy, cheap, effective, rugged, and safe) using ¹³C-labelled pyraoxystrobin as the internal standard (IS). It has been established a QuEChERS-LC-MS/MS IS method to study the bioconcentration and elimination of pyraoxystrobin in zebrafish (Danio rerio). The results indicated that the method had satisfactory linearity between 0.234 and 15 μg L^-1 (R² = 0.9996). The limits of detection (LOD) and quantification (LOQ) for pyraoxystrobin were 0.01 and 0.03 μg L^-1, respectively. The LOQs of the method for water and zebrafish were 0.05 μg L^-1 and 0.01 mg/kg, respectively. The mean recovery of pyraoxystrobin in zebrafish and water at fortification levels of 0.01-0.3 mg kg^-1 and 0.05-1.5 μg L^-1 ranged from 98.31 to 105.61% and 101.87 to 108.48%, respectively, with a % RSD (relative standard deviation) of 0.94-3.57%. The bioconcentration has been evaluated. The bioconcentration factors for pyraoxystrobin in zebrafish were 1,792 and 3,505 after exposure to 0.5 μg L^-1 for 168 h and 0.05 μg L^-1 for 216 h, respectively. The half-life of pyraoxystrobin in zebrafish was 9.0-9.5 d.

Toxicokinetics, Tissue Distribution, and Excretion of Dufulin Racemate and Its R ( S)-Enantiomers in Rats

Dufulin is a plant antiviral agent with a novel molecular structure and has been used widely to prevent and control tobacco and rice viral diseases. In this study, an UHPLC-MS/MS method was developed for rapid determination of dufulin racemate ( rac-DFL) and its R ( S)-enantiomers in rat plasma, tissues, urine, and feces. A MALDI-MSI method was further used for visual research on tissue distribution after intragastric administration of the three analytes. Toxicokinetic study showed that both ( R)-enantiomer of dufulin (( R)-DFL) and ( S)-enantiomer of dufulin (( S)-DFL) had a faster ability to reach C_max than that of rac-DFL. ( R)-DFL and ( S)-DFL had a similar T_1/2, though both were significantly lower than rac-DFL. C_max of rac-DFL was obviously higher than ( R)-DFL or ( S)-DFL. Meanwhile, C_max of ( S)-DFL was only about 60% of ( R)-DFL. Rac-DFL and its R ( S)-enantiomers had a dose-dependent toxicokinetic profile. Tissue distribution results revealed rac-DFL, ( R)-DFL, and ( S)-DFL mainly distributed in the liver and kidney, but the maximum concentration was only ng/g grade and could significantly degrade within 3 h. This indicates that dufulin does not cause liver and kidney toxicity in animals. In addition, rac-DFL and its R ( S)-enantiomers have not been detected in brain tissue. Cumulative excretion of rac-DFL and its R ( S)-enantiomers within 24 h in urine and feces were less than 22.85% indicating that they mainly excreted as metabolites. These results could provide evidence for the in-depth toxicity evaluation of dufulin pesticide. In addition, its metabolic selectivity information in vivo has also been obtained.

Developmental toxicity and potential mechanisms of pyraoxystrobin to zebrafish (Danio rerio)

As a newly developed, highly efficient strobilurin fungicide, pyraoxystrobin has been reported to be highly toxic to some aquatic organisms. However, the toxicity of pyraoxystrobin to different life stages of fish and the potential underlying mechanisms are still unknown. Hence, in the present study, the acute toxicity of pyraoxystrobin to different life stages of zebrafish (embryo, larva, and adult) was assessed. The developmental toxicity of pyraoxystrobin to zebrafish embryos and its effects on gene transcription in the embryo were also investigated. The results showed that the 96-h LC₅₀ values of pyraoxystrobin to embryos [2h post-fertilization (hpf)], 12h post-hatching (hph) larvae (84 hpf), 72 hph larvae (144 hpf), and adult zebrafish were 4.099, 1.069, 3.236, and 5.970µg/L, respectively. This suggests that pyraoxystrobin has very high toxicity to different life stages of zebrafish, while the newly hatched larvae constitute the most sensitive period of zebrafish to pyraoxystrobin. Decreased heart rate, hatching inhibition, growth regression, and morphological deformities were observed in zebrafish embryos after acute exposure to different concentrations of pyraoxystrobin. The rate of malformation increased in a time- and concentration-dependent manner in embryos, and the most pronounced abnormality was pericardial edema and yolk sac edema. Pyraoxystrobin (2 and 4μg/L) significantly altered the mRNA levels of genes related to mitochondrial respiratory chain and ATP synthesis (NDI, uqcrc, and ATPo6), oxidative stress (Mn-Sod, Cat, and Gpx), apoptosis (p53, Bcl2, Bax, and Cas3), and immune system (TNFα, IFN, and IL-1b) in zebrafish embryos. This result indicates that the alteration of these genes is a potential mechanism underlying the toxic effects of pyraoxystrobin on zebrafish.