Mathematical Modeling of ROS Production and Diode-like Behavior in the SDHA/SDHB Subcomplex of Succinate Dehydrogenases in Reverse Quinol-Fumarate Reductase Direction

Succinate dehydrogenase (SDH) plays an important role in reverse electron transfer during hypoxia/anoxia, in particular, in ischemia, when blood supply to an organ is disrupted, and oxygen is not available. It was detected in the voltammetry studies about three decades ago that the SDHA/SDHB subcomplex of SDH can have such a strong nonlinear property as a "tunnel-diode" behavior in reverse quinol-fumarate reductase direction. The molecular and kinetic mechanisms of this phenomenon, that is, a strong drop in the rate of fumarate reduction as the driving force is increased, are still unclear. In order to account for this property of SDH, we developed and analyzed a mechanistic computational model of reverse electron transfer in the SDHA/SDHB subcomplex of SDH. It was shown that a decrease in the rate of succinate release from the active center during fumarate reduction quantitatively explains the experimentally observed tunnel-diode behavior in SDH and threshold values of the electrode potential of about -80 mV. Computational analysis of ROS production in the SDHA/SDHB subcomplex of SDH during reverse electron transfer predicts that the rate of ROS production decreases when the tunnel-diode behavior appears. These results predict a low rate of ROS production by the SDHA/SDHB subcomplex of SDH during ischemia.

Integration of transcriptomic and proteomic reveals the toxicological molecular mechanisms of decabromodiphenyl ethane (DBDPE) on Pleurotus ostreatus

Decabromodiphenyl ethane (DBDPE), as one of the most widely used new brominated flame retardants (NBFRs), can pose a potential threat to human health and the environment. An integrated transcriptome and proteome was performed for investigating the toxicological molecular mechanisms of Pleurotus ostreatus (P. ostreatus) during the biodegradation of DBDPE at the concentrations of 5 and 20 mg/L. A total of 1193/1018 and 92/126 differentially expressed genes/proteins (DEGs/DEPs) were found, respectively, with DBDPE exposure at 5 and 20 mg/L. These DEGs and DEPs were mainly involved in the cellular process as well as metabolic process. DEPs for oxidation-reduction process and hydrolase activity were up-regulated, and those for membrane, lipid metabolic process and transmembrane transport were down-regulated. The DEGs and DEPs related to some key enzymes were down-regulated, such as NADH dehydrogenase/oxidoreductase, succinate dehydrogenase, cytochrome C1 protein, cytochrome-c oxidase/reductase and ATP synthase, which indicated that DBDPE affected the oxidative phosphorylation as well as tricarboxylic acid (TCA) cycle. Cytochrome P450 enzymes (CYPs) might be involved in DBDPE degradation through hydroxylation and oxidation. Some stress proteins were induced to resist DBDPE toxicity, including major facilitator superfamily (MFS) transporter, superoxide dismutase (SOD), molecular chaperones, heat shock proteins (HSP20, HSP26, HSP42), 60S ribosomal protein and histone H4. The findings help revealing the toxicological molecular mechanisms of DBDPE on P. ostreatus, aiming to improve the removal of DBDPE.

Discovery of N-Methoxy-(biphenyl-ethyl)-pyrazole-carboxamides as Novel Succinate Dehydrogenase Inhibitors

Succinate dehydrogenase (SDH) inhibitor is one of the research hotspots for the development of fungicides. Herein, we describe the design and synthesis of N-methoxy-(biphenyl-ethyl)-pyrazole-carboxamide derivatives with enhanced fungicidal activity by employing fragment combination strategy. The SDH enzymatic activity was evaluated for 24 title compounds, and compound 7s was identified as the highest activity against porcine SDH with an IC₅₀ value of 0.014 μM, 205-fold greater than that of fluxapyroxad. Furthermore, the greenhouse experiments showed that compound 7u exhibited potent fungicidal activity against wheat powdery mildew with an EC₅₀ value of 0.633 mg/L, higher activity than fluxapyroxad and benzovindiflupyr. The computational results showed that the fluorine atom substituted on the pyrazole ring formed an extra dipolar-dipolar interaction with C_S42 and then increased the van der Waals interaction between the compound and SDH. The structural and mechanistic insights obtained from the present work will provide a valuable clue to developing novel SDH inhibitors.

The adverse effects of fluxapyroxad on the neurodevelopment of zebrafish embryos

Fluxapyroxad (Flu), one of the succinate dehydrogenase-inhibited (SDHI) fungicides, has been extensively used in crop fungal disease control. Despite its increasing use in modern agriculture and long-term retention in the environment, the potentially toxic effects of Flu in vivo, especially on neurodevelopment, remain under-evaluated. In this study, zebrafish embryos were exposed to Flu at concentrations of 0.5, 0.75, and 1 mg/L for 96 h to evaluate the neurotoxicity of Flu. The results showed that Flu caused concentration-dependent malformations, including shorter body length, smaller head and eyes, and yolk sac edema. After exposure to Flu, larval zebrafish exhibited severe motor aberrations. Flu at a concentration of 1 mg/L significantly decreased dopamine level and notably altered acetylcholinesterase (AChE) activity and acetylcholine (ACh) content. Abnormal central nervous system (CNS) neurogenesis and disordered motor neuron development were observed in Tg (HUC-GFP) and Tg (hb9-GFP) zebrafish in Flu-treated groups. The expression of key genes involved in neurotransmission and neurodevelopment further proved that Flu impaired the zebrafish nervous system. This work contributes to our understanding of the neurotoxic effects and mechanisms induced by Flu in zebrafish and may help us take precautions against the neurotoxicity of Flu.

Novel Pyrazole Carboxamide Containing a Diarylamine Scaffold Potentially Targeting Fungal Succinate Dehydrogenase: Antifungal Activity and Mechanism of Action

Succinate dehydrogenase (SDH) is known as an ideal target for the development of novel fungicides. Over the years, a series of novel pyrazole carboxamides containing a diarylamine scaffold have been reported as potent SDH inhibitors (SDHIs) in our laboratory. Among them, compound SCU3038 (EC₅₀ = 0.016 mg/L) against in vitro Rhizoctonia solani was better than fluxapyroxad (EC₅₀ = 0.033 mg/L). However, its mechanism of action is still unclear. In this paper, in pot tests, bioactivity evaluation indicated that in vivo antifungal activity of compound SCU3038 (EC₅₀ = 0.95 mg/L) against R. solani was better than that of fluxapyroxad (EC₅₀ = 2.29 mg/L) and thifluzamide (EC₅₀ = 1.88 mg/L). In field trials, control efficacy of compound SCU3038 (74.10%) at 200 g ai/ha against rice sheath blight was better than that of thifluzamide (71.40%). Furthermore, target evaluation showed that compound SCU3038 could inhibit the fungal SDH from R. solani and fix in the binding site of SDH by molecular docking, thereby it could dissolve and reduce mitochondria of R. solani as observed by electron microscopy. In addition, transcriptome results showed that compound SCU3038 affected the TCA cycle pathway in mitochondria, and this was manifested in the downregulation of eight genes and upregulation of one gene. The most important phenomenon was the repressed expression of SDH2 confirmed by qRT-PCR. It was observed that compound SCU3038 was a potent SDHI, and these results afforded further research on pyrazole carboxamides.

Pathological Features in Paediatric Patients with TK2 Deficiency

Thymidine kinase (TK2) deficiency causes mitochondrial DNA depletion syndrome. We aimed to report the clinical, biochemical, genetic, histopathological, and ultrastructural features of a cohort of paediatric patients with TK2 deficiency. Mitochondrial DNA was isolated from muscle biopsies to assess depletions and deletions. The TK2 genes were sequenced using Sanger sequencing from genomic DNA. All muscle biopsies presented ragged red fibres (RRFs), and the prevalence was greater in younger ages, along with an increase in succinate dehydrogenase (SDH) activity and cytochrome c oxidase (COX)-negative fibres. An endomysial inflammatory infiltrate was observed in younger patients and was accompanied by an overexpression of major histocompatibility complex type I (MHC I). The immunofluorescence study for complex I and IV showed a greater number of fibres than those that were visualized by COX staining. In the ultrastructural analysis, we found three major types of mitochondrial alterations, consisting of concentrically arranged lamellar cristae, electrodense granules, and intramitochondrial vacuoles. The pathological features in the muscle showed substantial differences in the youngest patients when compared with those that had a later onset of the disease. Additional ultrastructural features are described in the muscle biopsy, such as sarcomeric de-structuration in the youngest patients with a more severe phenotype.

Aggressiveness of Small-Spored Alternaria spp. and Their Sensitivity to Succinate Dehydrogenase Inhibitor Fungicides

Brown leaf spot of potato is caused by a number of small-spored Alternaria spp. Alternaria alternata sensu stricto, A. arborescens, and A. tenuissima have been reported with increasing frequency in commercial potato fields. Potato cultivars with resistance to small-spored Alternaria spp. have yet to be developed; therefore, the application of foliar fungicides is a primary management strategy. Greenhouse inoculation assays demonstrated that isolates of these three small-spored Alternaria spp. were pathogenic. Significant differences in aggressiveness were observed across isolates; however, there was no trend in aggressiveness based on species. Significant fungicide by isolate interactions in in vitro fungicide sensitivity and significant differences between baseline and nonbaseline isolates were observed in all three small-spored Alternaria spp. The ranges of in vitro sensitivity of A. alternata baseline isolates to boscalid (EC₅₀ <0.010 to 0.89 µg/ml), fluopyram (<0.010 to 1.14 µg/ml) and solatenol (<0.010 to 1.14 µg/ml) were relatively wide when compared with adepidyn (<0.010 to 0.023 µg/ml). The baseline sensitivities of A. arborescens and A. tenuissima isolates to all four fungicides were <0.065 µg/ml. Between 10 and 21% of nonbaseline A. alternata isolates fell outside the baseline range established for the four succinate dehydrogenase inhibitor (SDHI) fungicides evaluated. In A. arborescens, 10 to 80% of nonbaseline isolates had higher sensitivities than the baseline. A. tenuissima isolates fell outside the baseline for boscalid (55%), fluopyram (14%), and solatenol (14%), but none fell outside the baseline range for adepidyn. Evaluations of in vivo fungicide efficacy demonstrated that most isolates were equally controlled by the four SDHI fungicides. However, reduced boscalid efficacy was observed for four isolates (two each of A. arborescens and A. tenuissima) and reduced fluopyram control was observed in one A. alternata isolate. Results of these studies demonstrate that isolates of all three species could be contributing to the brown leaf spot pathogen complex and that monitoring both species diversity and fungicide sensitivity could be advantageous for the management of brown leaf spot in potatoes with SDHI fungicides.

Design, Synthesis, and Fungicidal Evaluation of Novel 1,3-Benzodioxole-Pyrimidine Derivatives as Potential Succinate Dehydrogenase Inhibitors

A series of novel 1,3-benzodioxole-pyrimidine derivatives were designed and synthesized. The in vitro bioassay indicated that compounds 4e, 4g, 4n, 5c, and 5e displayed excellent fungicidal activities against test fungal strains. Especially, in the in vitro experiments, 5c exhibited a broad spectrum of fungicidal activity against Botrytis cinerea, Rhizoctonia solani, Fusarium oxysporum, Alternaria solani, and Gibberella zeae with EC₅₀ values of 0.44, 6.96, 6.99, 0.07, and 0.57 mg/L, respectively, which were significantly more potent than those of positive control boscalid (EC₅₀: 5.02, >50, >50, 0.16, and 1.28 mg/L). In vivo testing on tomato fruits and leaves showed that 5c displayed considerable protective and curative efficacy against A. solani. Scanning electron microscopy analysis indicated that 5c possessed a strong ability to destroy the surface morphology of mycelia and seriously interfere with the growth of the fungal pathogen. In the in vitro enzyme inhibition assay, 5c exhibited pronounced succinate dehydrogenase (SDH) inhibitory activity with an IC₅₀ value of 3.41 μM, equivalent to that of boscalid (IC₅₀: 3.40 μM). In addition, fluorescence quenching experiment further confirmed the strong interaction of 5c with SDH. Through chiral resolution, 5c was separated into two enantiomers. Among them, (S)-5c exhibited stronger fungicidal activity (EC₅₀: 0.06 mg/L) and SDH inhibitory (2.92 μM) activity than the R-enantiomer (EC₅₀: 0.17 mg/L and SDH IC₅₀: 3.68 μM), which was in accordance with the molecular docking study (CDOCKER Interaction Energy for (R)-5c and (S)-5c: -28.23 and -29.98 kcal/mol, respectively). These results presented a promising lead for the discovery of novel SDHIs as antifungal pesticides.

Rational Design, Synthesis, and Biological Evaluation of Fluorine- and Chlorine-Substituted Pyrazol-5-yl-benzamide Derivatives as Potential Succinate Dehydrogenase Inhibitors

To develop novel succinate dehydrogenase inhibitors (SDHIs), two series of novel N-4-fluoro-pyrazol-5-yl-benzamide and N-4-chloro-pyrazol-5-yl-benzamide derivatives were designed and synthesized, and their antifungal activities were evaluated against Valsa mali, Sclerotinia sclerotiorum, FusaHum graminearum Sehw, Physalospora piricola, and Botrytis cinerea. The bioassay results showed that some of the target compounds exhibited good antifungal activities in vitro against V. mali and S. sclerotiorum. Remarkably, compound 9Ip displayed good in vitro activity against V. mali with an EC₅₀ value of 0.58 mg/L. This outcome was 21-fold greater than that of fluxapyroxad (12.45 mg/L) and close to that of the commercial fungicide tebuconazole (EC₅₀ = 0.36 mg/L). In addition, in vivo experiments proved that compound 9Ip has good protective fungicidal activity with an inhibitory rate of 93.2% against V. mali at 50 mg/L, which was equivalent to that of the positive control tebuconazole (95.5%). The results of molecular docking indicated that there were obvious hydrogen bonds and p-π interactions between compound 9Ip and succinate dehydrogenase (SDH), which could explain the probable action mechanism. In addition, the SDH enzymatic inhibition assay was carried out to further prove its mode of action. Our studies suggest that compound 9Ip could be a fungicidal lead to discover more potent SDHIs for crop protection.

Discovery of Novel Pyrazole Amides as Potent Fungicide Candidates and Evaluation of Their Mode of Action

A rational molecule design strategy based on scaffold hopping was applied to discover novel leads, and then a series of novel pyrazole amide derivatives were designed, synthesized, characterized, and evaluated for their antifungal activities. Bioassay results indicated that some target compounds such as S3, S12, and S26 showed good in vivo antifungal activities; among them, S26 exhibited commendable in vivo protective activity with an 89% inhibition rate against Botrytis cinerea on cucumber at 100 μg/mL that is comparable to positive controls boscalid, isopyrazam, and fluxapyroxad. Microscopy observations suggested that S26 affects the normal fungal growth. Fluorescence quenching analysis and SDH (succinate dehydrogenase) enzymatic inhibition studies validated that S26 may not be an SDH inhibitor. Based on induction of plant defense responses testing, S26 enhanced the accumulation of RBOH, WRKY6, WRKY30, PR1, and PAL defense-related genes expression and the defense-associated enzyme phenylalanine ammonia lyase (PAL) expression on cucumber. These findings support that S26 not only displayed direct fungicidal activity but also exhibited plant innate immunity stimulation activity, and it could be used as a promising plant defense-related fungicide candidate.

Case Report: Giant Paraganglioma of the Skull Base With Two Somatic Mutations in SDHB and PTEN Genes

Head and neck paragangliomas (HNPGLs) are neuroendocrine tumors. They arise from the parasympathetic ganglia and can be either sporadic or due to hereditary syndromes (up to 40%). Most HNPGLs do not produce significant amounts of catecholamines. We report a case of a giant paraganglioma of the skull base with an unusually severe presentation secondary to excessive release of norepinephrine, with a good outcome considering the severity of disease. A 39-year-old Caucasian woman with no prior medical history was found unconscious and emaciated in her home. In the intensive care unit (ICU) the patient was treated for multi-organ failure with multiple complications and difficulties in stabilizing her blood pressure with values up to 246/146 mmHg. She was hospitalized in the ICU for 72 days and on the 31^st day clinical assessment revealed jugular foramen syndrome and paralysis of the right n. facialis. A brain MRI confirmed a right-sided tumor of the skull base of 93.553 cm³. Blood tests showed high amounts of normetanephrine (35.1-45.4 nmol/L, ref <1.09 nmol/L) and a tumor biopsy confirmed the diagnosis of a paraganglioma. Phenoxybenzamine and Labetalol were used in high doses ((Dibenyline^®, 90 mg x 3 daily) and labetalol (Trandate^®, 200 + 300 + 300 mg daily) to stabilize blood pressure. The patient underwent two tumor embolization procedures before total tumor resection on day 243. Normetanephrine and blood pressure normalized after surgery (0.77 nmol/L, ref: < 1.09 nmol/L). The damage to the cranial nerve was permanent. Our patient was comprehensively examined for germline predisposition to PPGLs, however we did not identify any causal aberrations. A somatic deletion and loss of heterozygosity (LOH) of the short arm (p) of chromosome 1 (including SDHB) and p of chromosome 11 was found. Analysis showed an SDHB (c.565T>G, p.C189G) and PTEN (c.834C>G, p.F278L) missense mutation in tumor DNA. The patient made a remarkable recovery except for neurological deficits after intensive multidisciplinary treatment and rehabilitation. This case demonstrates the necessity for an early tertiary center approach with a multidisciplinary expert team and highlights the efficacy of the correct treatment with alpha-blockade.

Sensitivity of Rhizoctonia solani Anastomosis Group 2-2 Isolates from Soybean and Sugar Beet to Selected SDHI and QoI Fungicides

Rhizoctonia solani causes root and stem diseases on soybean and sugar beet, and fungicides are commonly used to manage these diseases. Quinone outside inhibitor (QoI) fungicides (pyraclostrobin and azoxystrobin) have been used for in-furrow and postemergence application since 2000. Succinate dehydrogenase inhibitor (SDHI) fungicides (sedaxane, penthiopyrad, and fluxapyroxad) became popular seed treatments after their registration in Minnesota and North Dakota between 2012 and 2016. Periodic monitoring of sensitivity to these fungicides in R. solani anastomosis group (AG) 2-2 is important to detect potential shifts in sensitivity over time. R. solani AG 2-2 isolates (n = 35) collected from soybean and sugar beet in Minnesota and North Dakota were evaluated in vitro for sensitivity. Isolates were considered as baseline or nonbaseline for the above-mentioned fungicides based on previous potential exposure. The effective concentration (EC50) required to suppress radial fungal growth by 50% was determined. The mean EC50 values for sedaxane, penthiopyrad, fluxapyroxad, and pyraclostrobin were 0.1, 0.15, 0.16, and 0.25 (µg ml-1), respectively. The mean EC50 value for azoxystrobin for 22 isolates was 0.76 to 1.56 µg ml-1; and EC50 could not be determined for 13 isolates because of <50% inhibition at the highest concentrations used. The EC50 values for the QoI fungicides did not differ significantly between baseline and nonbaseline isolates. EC50 values for SDHI fungicides were significantly higher for isolates collected from soybean than from sugar beet, and isolates collected from both crops had similar EC50 values for pyraclostrobin. All SDHI fungicides and pyraclostrobin effectively suppressed R. solani isolates from soybean and sugar beet at low concentrations in vitro.

Toxic effects of benzovindiflupyr, a new SDHI-type fungicide on earthworms (Eisenia fetida)

Benzovindiflupyr has received increasing attention as a new novel succinate dehydrogenase inhibitor (SDHI)-type fungicide. Nonetheless, its traces remaining in soil potentially trigger an ecotoxicological threat to soil organisms including earthworms. This paper evaluates the eco-toxicity of different benzovindiflupyr doses (0.1, 1, 5, and 10 mg kg-1) on earthworms (Eisenia fetida) after long-term exposure. Consequently, benzovindiflupyr at higher doses significantly inhibited the activities of respiratory chain complex II and succinate dehydrogenase (SDH) in E. fetida. Besides, the reactive oxygen species (ROS) and lipid peroxidation (LPO) were significantly induced in earthworms when treated with this fungicide. After benzovindiflupyr exposure, activities of antioxidant enzymes including catalase, peroxidase, and superoxide dismutase were activated. However, glutathione S-transferase activity in E. fetida was initially induced then inhibited in earthworms after treatment. Furthermore, benzovindiflupyr exposure induced the protein carbonylation (PCO) level in cells indicating oxidative damage to the cellular protein. Due to the destruction of the normal function in the coelomocytes, the phagocytic activity was initially activated, then inhibited when earthworms were treated at 5 and 10 mg kg-1 concentrations. Additionally, DNA damage was induced (larger olive tail moment (OTM) values) with the increase of benzovindiflupyr doses and exposure time. The weight was significantly decreased after benzovindiflupyr exposure on days 21 and 28. Benzovindiflupyr at higher doses significantly decreased the reproduction (number of cocoons and juveniles) of E. fetida. These findings reveal that benzovindiflupyr potentially induces a potential toxicological risk to earthworms when applied in the mentioned above dosages.

Activity of A Novel Succinate Dehydrogenase Inhibitor Fungicide Pydiflumetofen Against Fusarium fujikuroi causing Rice Bakanae Disease

New fungicides are tools to manage fungal diseases and overcome emerging resistance in fungal pathogens. In this study, a total of 121 Fusarium fujikuroi isolates were collected from various geographical regions of China and their sensitivity to a novel succinate dehydrogenase inhibitor (SDHI) fungicide 'pydiflumetofen' was evaluated. The 50% effective concentration (EC₅₀) value of pydiflumetofen for mycelial growth suppression ranged from 0.0101 to 0.1012 μg/ml and for conidial germination inhibition ranged from 0.0051 to 0.1082 μg/ml. Pydiflumetofen-treated hyphae showed contortion and increased branching, cell membrane permeability, and glycerol content significantly. The result of electron microscope transmission indicated that pydiflumetofen damaged the mycelial cell wall and the cell membrane, and almost broke up the cells, which increased the intracellular plasma leakage. There was no cross-resistance between pydiflumetofen and the widely used fungicides such as carbendazim, prochloraz, and phenamacril. Pydiflumetofen was found safe to seeds and rice seedlings of four rice cultivars, used up to 400 μg/ml. Seed treatment significantly decreased the rate of diseased plants in the greenhouse as well as in field trials in 2017 and 2018. Pydiflumetofen showed superb results against the rice bakanae disease (RBD), when used at 10 or 20 g a.i./100 kg of treated seeds, providing over 90% control efficacy (the maximum control efficacy was up to 97%), which was significantly higher than that of 25% phenamacril (SC) at 10 g or carbendazim at 100 g. Pydiflumetofen is highly effective against F. fujikuroi growth and sporulation as well as RBD in the field.

Multiple, large intra-abdominal cystic lesions and iron deficiency anaemia as the presenting symptoms of SDHD gastrointestinal stromal tumour (GIST) in a young sub-Saharan woman

We report the case of a 27-year-old female patient from sub-Saharan Africa who presented with non-specific abdominal complaints, iron deficiency anaemia and multiple, large intra-abdominal cystic lesions on imaging. The lesions appeared to be a most unusual presentation of gastrointestinal stromal tumour (GIST). GIST is a sarcomatous tumour that comprises only 0.2% of all gastrointestinal (GI) tumours; it is the most common mesenchymal malignancy of the GI tract. Our patient had the succinate dehydrogenase-deficient (SDHD) subtype, identified in some 5%-10% of patients with GIST only, commonly found in women and younger patients. The differential diagnosis of intra-abdominal cystic lesions is briefly discussed, including the relevance of a correct pathological diagnosis. This impacts medical and surgical management decisions, including predicting response to targeted therapy. Tyrosine kinase inhibitor therapy has been a breakthrough in the treatment of GISTs, although with extensive disease, and certainly in case of the SDHD subtype, long-term outcome remains disappointing.

Superoxide produced by mitochondrial site IQ inactivates cardiac succinate dehydrogenase and induces hepatic steatosis in Sod2 knockout mice

Superoxide produced by mitochondria has been implicated in numerous physiologies and pathologies. Eleven different mitochondrial sites that can produce superoxide and/or hydrogen peroxide (O₂^.-/H₂O₂) have been identified in vitro, but little is known about their contributions in vivo. We introduce novel variants of S1QELs and S3QELs (small molecules that suppress O₂^.-/H₂O₂ production specifically from mitochondrial sites I_Q and III_Qo, respectively, without compromising bioenergetics), that are suitable for use in vivo. When administered by intraperitoneal injection, they achieve total tissue concentrations exceeding those that are effective in vitro. We use them to study the engagement of sites I_Q and III_Qo in mice lacking functional manganese-superoxide dismutase (SOD2). Lack of SOD2 is expected to elevate superoxide levels in the mitochondrial matrix, and leads to severe pathologies and death about 8 days after birth. Compared to littermate wild-type mice, 6-day-old Sod2^-/- mice had significantly lower body weight, lower heart succinate dehydrogenase activity, and greater hepatic lipid accumulation. These pathologies were ameliorated by treatment with a SOD/catalase mimetic, EUK189, confirming previous observations. A 3-day treatment with S1QEL352 decreased the inactivation of cardiac succinate dehydrogenase and hepatic steatosis in Sod2^-/- mice. S1QEL712, which has a distinct chemical structure, also decreased hepatic steatosis, confirming that O₂^.- derived specifically from mitochondrial site I_Q is a significant driver of hepatic steatosis in Sod2^-/- mice. These findings also demonstrate the ability of these new S1QELs to suppress O₂^.- production in the mitochondrial matrix in vivo. In contrast, suppressing site III_Qo using S3QEL941 did not protect, suggesting that site III_Qo does not contribute significantly to mitochondrial O₂^.- production in the hearts or livers of Sod2^-/- mice. We conclude that the novel S1QELs are effective in vivo, and that site I_Q runs in vivo and is a significant driver of pathology in Sod2^-/- mice.

Surgical treatment and management of syndromic paraganglioma. The experience of a referral center

BACKGROUND

Paragangliomas (PGL) are neuroendocrine tumors arising from neural crest-derived chromaffin cells in the parasympathetic ganglia or in sympathetic ganglia located in the adrenal glands (Pheochromocytoma, PHEO), or extra-adrenal location and around 30-40% of PGL can be hereditary (MEN2, Von Hippel Lindau syndrome, von Reklingausen syndrome and Pheochromocytoma-Paraganglioma syndrome).

METHODS

We retrospectively evaluate 127 patients with PHEO/PGL treated at our Institution from 1992 to 2018 and report our experience, focusing on different surgical treatment based on hereditary syndrome. Genetic analysis was performed in patients with features suspected for hereditary syndrome to search genetic mutations of RET, VHL, SDHD and SDHB.

RESULTS

Hereditary syndrome was diagnosed in 30 patients (7 patients affected by MEN2A, 6 VHL, 9 NF1, 2 PGL- 1, and 6 PGL-4). 17 patients with monolateral PHEO underwent adrenalectomy (laparoscopic approach since 1998); 8 patients with bilateral adrenal lesions underwent bilateral adrenalectomy with cortical-sparing approach of almost one gland.

CONCLUSIONS

Syndromic PGLs are rare conditions; surgery is the treatment of choice. Adrenal PGL requires laparoscopic adrenalectomy with transperitoneal lateral approach as gold standard. For genetic syndrome such as MEN2 and VHL, laparoscopic cortical sparing adrenalectomy of at least one gland should be considered.

KEY WORDS

Adrenalectomy, Endocrine Surgery, Hereditary Syndromes, Paraganglioma, Pheochromocytoma.

Low shear stress induced vascular endothelial cell pyroptosis by TET2/SDHB/ROS pathway

Vascular endothelial cell (VEC) inflammation induced by low shear stress plays key roles in the initiation and progression of atherosclerosis (As). Pyroptosis is a form of inflammatory programmed cell death that is critical for As. However, the effect of low shear stress on VEC pyroptosis and the underlying mechanisms were not clear. Here we show that low shear stress promoted VEC pyroptosis and reduced the expression of Ten-Eleven Translocation 2 (TET2) methylcytosine dioxygenase. Loss of TET2 resulted in the upregulation of the expression and activity of mitochondrial respiratory complex II subunit succinate dehydrogenase B (SDHB) by decreasing the recruitment of histone deacetylase 2, independent of DNA demethylation modification. The overexpression of SDHB mediated mitochondrial injury and increased the production of reactive oxygen species (ROS). The administration of ROS scavenger NAC alleviated VEC pyroptosis induced by SDHB overexpression and TET2 shRNA. These findings show that low shear stress induced endothelial cell pyroptosis through the TET2/SDHB/ROS pathway and offer new insights into As.

Fluxapyroxad induces developmental delay in zebrafish (Danio rerio)

Succinate dehydrogenase inhibitor (SDHI) fungicides are extensively used in agriculture. Some SDHI fungicides show developmental toxicity, immune toxicity and hepatotoxicity to fish. Fluxapyroxad (FLU) is a broad spectrum pyrazole-carboxamide SDHI fungicide and its potential impacts on fish embryonic development are unknown. We exposed zebrafish embryos to 1, 2 and 4 μM FLU. Developmental malformations, including yolk sac absorption disorder, decreased pigmentation and hatch delay were induced after FLU exposure. FLU caused significantly increased transcription levels in the ectoderm marker foxb1a but no significant changes in endoderm and mesoderm development markers (foxa2, ntl and eve1). Transcription levels of genes in the early stage embryos (gh, crx, neuroD and nkx2.4b) decreased significantly after FLU treatments. The content of glutathione (GSH) increased after FLU exposure. This study shows that FLU is toxic to zebrafish through its developmental effects and oxidative stress. FLU may pose risks to other non-target aquatic organisms.

Activity of the Succinate Dehydrogenase Inhibitor Fungicide Penthiopyrad Against Sclerotinia sclerotiorum

In present study, the morphological and physiological characteristics of Sclerotinia sclerotiorum (Lib.) de Bary to a novel succinate dehydrogenase inhibitor (SDHI) fungicide penthiopyrad has been reported. The baseline sensitivity of S. sclerotiorum to penthiopyrad was determined using 119 strains by inhibition of mycelial growth. The median effective concentration (EC₅₀) values for penthiopyrad ranged from 0.0096 to 0.2606 μg/ml, and the mean value was 0.0578 (±0.0626) μg/ml. After 1 μg/ml penthiopyrad treatment, mycelia of S. sclerotiorum strains showed increased apical branching and were denser compared with control, and cell membrane permeability significantly increased. In addition, glycerol content, oxalic acid (OA), and exopolysaccharide (EPS) content decreased markedly and mycelial respiration was distinctly inhibited. The number and dry weight of sclerotia significantly decreased after being treated with 2 μg/ml penthiopyrad. Penthiopyrad exhibited both protective and curative activity on the detached rapeseed leaves. Importantly, the above results will provide us more information on penthiopyrad for management of diseases caused by S. sclerotiorum and increase our understanding of action of penthiopyrad against S. sclerotiorum.

Thifluzamide induces the toxic effects on zebrafish (Danio rerio) via inhibition of succinate dehydrogenase (SDH)

Thifluzamide is widely used in treatment of rice diseases and has potential toxicity on aquatic organism. Although previous studies have focused on the toxic effect of thifluzamide in zebrafish, no consistent conclusions have been reached. To help to elucidate the toxic mechanism, qualities of liver and mitochondria were evaluated. The global changes in the transcriptome of zebrafish after exposure to thifluzamide were measured. Based on this, the expression and activities of chitinase and succinate dehydrogenase (SDH) were further assayed. And the targeted site of thifluzamide in zebrafish was confirmed by dock study and co-exposure study. Here we report that developmental inhibition was observed along with presence of liver and mitochondrial damage. The expression of SDHa-d and genes related to mitochondrial DNA (mtDNA) replicate and mitochondrial complexes were significantly altered. And, as the top differentially expressed genes, the expression of chia.1-6 did show apparent changes, but differences of chitinase activity between exposure groups and the controls did not reach significance. In line with that, dock study showed that the binding potentials of thifluzamide toward zebrafish chitinase and SDH exhibited in the following order: SDH> chitinase. And sdhb-sdhc-sdhd (Qp site) showed the highest binding activity toward thifluzamide. The joint exposure (thifluzamide + Q10) significantly improved the survival of zebrafish compared with single thifluzamide exposure. These results indicate that SDH, especially Qp-site, may be the target of thifluzamide in zebrafish and inhibition of SDH activity may be at least in partial responsible for the toxicity of thifluzamide in zebrafish. In addition, the antagonistic effect of Q10 on thifluzamide toxicity in zebrafish suggests that Q10 may be a useful adjunct to detoxification.

Resistance to succinate dehydrogenase inhibitors in field isolates of Podosphaera xanthii on cucumber: Monitoring, cross-resistance patterns and molecular characterization

New succinate dehydrogenase inhibitor fungicides (SDHIs), isopyrazam, pyraziflumid and isofetamid were introduced in the Japanese market in 2017-2018 to control powdery mildew on cucumber. SDHI resistance of the disease fungus (Podosphaera xanthii) was first reported during 2008-2009 against boscalid. Then, penthiopyrad which belongs to SDHIs was introduced in 2010, but subsequent monitoring study was not performed. We investigated the sensitivity of P. xanthii field isolates from Ibaraki Prefecture, Japan, to SDHIs and SdhB, SdhC and SdhD gene mutations, using a leaf disc assay and SDH gene analysis. A total of 19 out of the 22 selected isolates showed resistance to SDHIs. The 19 isolates were phenotypically categorized into three types: Resistant I as moderately and Resistant II as highly resistant to penthiopyrad, isopyrazam and pyraziflumid but sensitive to isofetamid and Resistant III as highly resistant to isofetamid but sensitive to the other three SDHIs. SDH gene analysis revealed that Resistant I and III isolates carried a substitution in PxD-S121P and PxC-A86V, respectively. Resistant II carried three different substitutions: PxC-G151R, PxC-G172D, and PxD-H137R. Among 127 isolates sampled from 16 cucumber greenhouses, 54 exhibited Resistant I phenotype and carried only PxD-S121P. Fifty-six isolates exhibited Resistant II and carried PxC-G151R (four isolates), PxC-G172D (24), and PxD-H137R (28). Only two isolates expressed the Resistant III phenotype carrying PxC-A86V. To the best of our knowledge, this is the first report demonstrating cross-resistance patterns and the molecular characterization of SDHIs in P. xanthii.

The relationship between features enabling SDHI fungicide binding to the Sc-Sdh complex and its inhibitory activity against Sclerotinia sclerotiorum

BACKGROUND

A new generation of succinate dehydrogenase inhibitors (SDHIs) with high efficiency and broad-spectrum antifungal activity has been frequently used in crop production. Sclerotinia stem rot is a major disease of various plants and crops caused by Sclerotinia sclerotiorum. Although benzovindiflupyr and isopyrazam reportedly have high activity against S. sclerotiorum, little is known about the bioactivity of different SDHIs classes against S. sclerotiorum or the mechanism of their differential antifungal activity.

RESULTS

The in vitro tests revealed that the pyrazole-4-carboxamides of SDHIs (benzovindiflupyr, isopyrazam, fluxapyroxad, pydiflumetofen) had the highest activity against S. sclerotiorum followed by pyridine carboxamides (boscalid), pyridinyl-ethyl benzamides (fluopyram) and thiazole carboxamides (thifluzamide), and of these thifluzamide showed poor antifungal activity with EC₅₀ values greater than 6.01 mg L^-1 . The pyrazole-4-carboxamides of SDHIs showed satisfactory protective and curative activity against Sclerotinia stem rot. After treatment with the pyrazole-4-carboxamides of SDHIs, mitochondrial function in S. sclerotiorum decreased significantly. The enzyme activity assays revealed a lower affinity between thifluzamide and the Sc-Sdh complex than was observed for the other six fungicides, with IC₅₀ values ranging from 0.0036 to 1.2088 μmol L^-1 . Additionally, the docking positions of fungicides were similar, yet binding energies were different in the docking study with the Sdh complex. The correspondingly weaker hydrogen bonds may be responsible for the poor activity of thifluzamide against S. sclerotiorum.

CONCLUSION

Understanding different binding features of various SDHIs classes with the Sc-Sdh complex might be beneficial for the design and development of highly effective broad-spectrum fungicides to ensure high yield and quality in crops by reducing fungicide use. © 2020 Society of Chemical Industry.

Activity of the Novel Succinate Dehydrogenase Inhibitor Fungicide Pydiflumetofen Against SDHI-Sensitive and SDHI-Resistant Isolates of Botrytis cinerea and Efficacy Against Gray Mold

Succinate dehydrogenase inhibitor (SDHI) fungicides are currently the most frequently used fungicides for controlling gray mold. However, isolates of Botrytis cinerea resistant to SDHI fungicides have emerged in the field. Pydiflumetofen is a new SDHI fungicide that can control a variety of fungal diseases, but its efficacy against gray mold and whether the activity of pydiflumetofen is affected by the current SDHI-resistant isolates is currently unknown. The sensitivity of 291 single-spore B. cinerea isolates collected from 2017 to 2019 to pydiflumetofen was determined by spore germination inhibition assays. The mean EC₅₀ value (fungicide concentration resulting in a 50% inhibition compared with that of the control) of pydiflumetofen was 0.06 ± 0.01, 0.07 ± 0.02, and 0.05 ± 0.02 mg/liter in 2017, 2018, and 2019, respectively. There was no significant difference in the sensitivity of B. cinerea to pydiflumetofen among the 3 years. Furthermore, pydiflumetofen at 300 mg/liter effectively controlled gray mold on cucumber leaves (80.9%), and its efficacy was superior to that of boscalid at 400 mg/liter (42.7%). The isolates carrying P225F, N230I, H272Y, and H272R mutations in the SdhB subunit were associated with the less sensitivity of B. cinerea to SDHI fungicides. After establishing the baseline sensitivity of B. cinerea to pydiflumetofen (EC₅₀ of 0.03 ± 0.003 mg/liter), we found that the P225F and H272Y mutant isolates showed low to moderate levels of resistance to pydiflumetofen, and the H272R and N230I mutant isolates showed low levels of resistance. The reduced sensitivity to pydiflumetofen resulted from the positive correlation of pydiflumetofen with the other four SDHI fungicides (i.e., boscalid, fluopyram, isopyrazam, and benzovindiflupyr). These results suggest that pydiflumetofen provides effective control for the management of gray mold but must be used with caution.

Studies on the novel pyridine sulfide containing SDH based heterocyclic amide fungicide

BACKGROUND

Succinate dehydrogenase (SDH) has been identified as one of the most significant targets for fungicide discovery. To date, 23 commercial SDH inhibitor (SDHI) fungicides have been approved for plant protection since the first launch of carboxin in 1966, and extensively applied to combat destructive plant fungi.

RESULTS

In this project, 20 novel pyridine sulfide derivatives containing SDH-based heterocyclic amide fungicide were designed, synthesized, and characterized by proton nuclear magnetic resonance (¹ H-NMR), carbon-13 (¹³ C)-NMR and high-resolution mass spectrometry (HRMS). In vitro fungicidal activity experiment, the target compound I-1 displayed excellent inhibitory rates against the common agricultural pathogens with half maximal effective concentration (EC₅₀ ) values of 5.2 to 39.8 μg mL^-1 . The in vivo fungicidal activities demonstrated that the compound I-1 could effectively prevent Botrytis cinerea from infecting tomato and cucumber leaves with the preventative rates of 67% and 50%. The mitochondrial membrane potential detection, SDH enzyme assay and the molecular docking simulation revealed that the mechanism of action of the compound I-1 and the relevant interactions with the target enzyme may be similar to those of the control fluopyram.

CONCLUSION

The biological activity screening and validation of mechanism of action indicated that the compound I-1 could be identified as a potential SDH inhibitor for further study. © 2020 Society of Chemical Industry.