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.

Resistance risk assessment for Fusarium graminearum to pydiflumetofen, a new succinate dehydrogenase inhibitor

BACKGROUND

Pydiflumetofen is a new generation succinate dehydrogenase inhibitor currently undergoing the process of registration in China for the control of Fusarium head blight in wheat. A resistance risk assessment of Fusarium graminearum to pydiflumetofen was undertaken in this study.

RESULTS

A total of 75 pydiflumetofen-resistant mutants were generated through spontaneous selection and displayed high resistance with an average resistance factor (RF) value of 78. Four mutants were generated through UV mutagenesis and displayed very high resistance with an RF value >1000. The sequence analysis results for Sdh genes and fitness studies revealed the existence of four types of mutations. In particular, 32 spontaneous selection mutants (SP mutants) had an arginine (R) to histidine (H) transition at position 86 in FGSdhC, resulting in seriously reduced fitness. Seven SP mutants had an R to cysteine (C) transition at position 86 in FGSdhC, resulting in reduced fitness. Thirty-six SP mutants had an alanine (A) to valine (V) transition at position 83 in FGSdhC and had no fitness penalties. The efficacy of pydiflumetofen towards a mutant carrying A83V in FGSdhC in vivo was significantly decreased at 42.7%. Four UV mutants had no mutations on all Sdh genes and no fitness penalties. Cross-resistance among boscalid, fluopyram and pydiflumetofen was observed.

CONCLUSION

Sdhc mutations were found and other target site resistance may be present in laboratory PR mutants of F. graminearum. An overall moderate risk of resistance development in F. graminearum was recommended for pydiflumetofen. © 2019 Society of Chemical Industry.

Baseline Sensitivity of Botrytis cinerea Isolates from Strawberry to Isofetamid Compared to other SDHIs

Succinate dehydrogenase inhibitors (SDHIs) are the fungicides most commonly used to control Botrytis fruit rot on commercial strawberry in Florida. The medium-to-high risk of selection of resistance in the causal agent Botrytis cinerea is a threat to the efficacy of this fungicide group. In this study, we characterized the sensitivity of B. cinerea to the SDHI isofetamid, evaluated the SdhB gene mutation associated with resistance, and monitored resistance frequencies to five SDHI fungicides for two consecutive seasons. EC₅₀ values of 70 isolates were obtained using the spiral gradient dilution (SGD) method and averaged 0.098 µg/ml of isofetamid. EC₅₀ averages of 3.04 and >500.00 µg/ml were obtained for isolates with the N230I and P225F mutations indicating moderate and high resistance to isofetamid, respectively. A total of 565 B. cinerea isolates collected during 2015-2016 and 2016-2017 seasons from strawberry nurseries and Florida production fields were evaluated using conidial germination assays. Results for the first season showed resistance frequencies of 95, 33, 21, 25, and 0% to boscalid, penthiopyrad, fluopyram, benzovindiflupyr, and isofetamid, respectively. The respective resistance frequencies for the following season were 91, 95, 44, 27, and 1.3%. Only three isolates were found to be moderately resistant to isofetamid during the second season, and the mutation N230I was identified after sequence analysis. These isolates were confirmed to be resistant to isofetamid in fruit assays with disease incidence of 55.6 to 77.0%; however, the conidial production of the isolates was inhibited by an average of 83.9%. In general, isofetamid efficacy was higher than the other evaluated SDHIs, but a slight increase in resistance frequencies was observed in our study.

A bioactivity-oriented modification strategy for SDH inhibitors with superior activity against fungal strains

In this work, a total of 36 novel 5-(nicotinamido)-1-phenyl-1H-pyrazole-4-carboxylic acid derivatives were designed and synthesized successfully by introducing a carboxyl group based on the N-(1-(4-chlorophenyl)-4-cyano-1H-pyrazol-5-yl)-6-methoxynicotinamide. Among them, the growth inhibition assays on agar plates showed that compound 5IV-d(5-(2-chloronicotinamido)-1-(p-tolyl)-1H-pyrazole-4-carboxylic acid) exhibited the significant antifungal activity against four important fruit and main crop disease fungi (i.e., Valsa mali Miyabe et Yamada, Botryosphaeria dothidea, Helminthosporium maydis and Rhizoctonia cerealis) with EC₅₀ values of 22.6, 14.5, 17.6 and 18.2 μM, respectively. In addition, 5IV-d showed the excellent inhibitory effect against SDH enzymes with IC₅₀ values ranging from 9.4 to 15.6 μM. In vivo bioassay and molecular docking were applied to explore the potential in practical application and combination of modified structure and SDH. The results of structure-activity relationships indicates that the methoxy substitution at the benzene ring attached to the pyrazole ring and a wide variety of substituents could be responsible for the promising antifungal efficacy of the designed compounds. This study demonstrated that the compound 5IV-d can act as the most potent SDH inhibitor in the reported series of compounds.

Temozolomide Is a Potential Therapeutic Tool for Patients With Metastatic Pheochromocytoma/Paraganglioma-Case Report and Review of the Literature

Context: Metastatic pheochromocytoma/paraganglioma (MPP) therapy mainly involves radionuclide therapy, chemotherapy, and targeted therapy. In recent years, temozolomide (TMZ) showed great promise in some MMP patients, especially those with SDHB germline mutation. We reported a patient with MPP who did not have any known germline genetic change and responded remarkably well to TMZ monotherapy. Case presentation: The patient was a 41-year-old woman with local and distant recurrence (soft tissues and bone metastases) of retroperitoneal paraganglioma. She suffered from dizziness, palpitation, sweating, weight loss and constipation, with the blood pressure fluctuating substantially from 130/100 mmHg to 190/120 mmHg, although she was on phenoxybenzamine and metoprolol medication. The patient showed clinical and radiological response after 3-cycle TMZ therapy. Upon 15 cycles of TMZ therapy, her symptoms were dramatically alleviated, urinary norepinephrine excretion decreased from 1,840 μg/24 h to 206 μg/24 h, and CT showed that the lesions further shrank. Molecular profiling of the tumor tissue of the patient revealed hypermethylation of the O6-methylguanine-DNA-methyltransferase (MGMT) promoter and a negative immunostaining for MGMT. Globally, only 26 cases of MPP treated with TMZ have been described so far. TMZ is effective, especially in patients with SDHB mutation, which can be explained by the silencing of MGMT expression as a consequence of MGMT promoter hypermethylation in SDHB-mutated tumors. Although, in general, patients with SDHB mutation or MGMT promoter hypermethylation have better response to TMZ, there are also exceptions. Severe side effects are uncommon, with only 17.4% patients experiencing Grade 3 toxicities, including lymphopenia, and hypertension. Conclusions: TMZ is effective and safe in MPP patients, and, it may work better on patients with SDHB-related MPP. Measurement of MGMT expression might help assess the tumor sensitivity to TMZ but this needs further systematic investigation.

Sdhd ablation promotes thyroid tumorigenesis by inducing a stem-like phenotype

Mutations in genes encoding enzymes in the tricarboxylic acid cycle (TCA, also known as the Krebs cycle) have been implicated as causative genetic lesions in a number of human cancers, including renal cell cancers, glioblastomas and pheochromocytomas. In recent studies, missense mutations in the succinate dehydrogenase (SDH) complex have also been proposed to cause differentiated thyroid cancer. In order to gain mechanistic insight into this process, we generated mice lacking the SDH subunit D (Sdhd) in the thyroid. We report that these mice develop enlarged thyroid glands with follicle hypercellularity and increased proliferation. In vitro, human thyroid cell lines with knockdown of SDHD exhibit an enhanced migratory capability, despite no change in proliferative capacity. Interestingly, these cells acquire stem-like features which are also observed in the mouse tumors. The stem-like characteristics are reversed by α-ketoglutarate, suggesting that SDH-associated tumorigenesis results from dedifferentiation driven by an imbalance in cellular metabolites of the TCA cycle. The results of this study reveal a metabolic vulnerability for potential future treatment of SDH-associated neoplasia.

Primary Renal Paragangliomas and Renal Neoplasia Associated with Pheochromocytoma/Paraganglioma: Analysis of von Hippel-Lindau (VHL), Succinate Dehydrogenase (SDHX) and Transmembrane Protein 127 (TMEM127)

Alterations of von Hippel-Lindau (VHL), succinate dehydrogenase (SDHX), and TMEM127 have been associated with the development of pheochromocytomas (PCs) and paragangliomas (PGLs) and are also associated with the development of renal neoplasms. This study involved 2 primary renal PGL and 12 cases of PC/PGL with associated renal neoplasia with a mean follow up of 74 months. Germline VHL and SDHX mutation status was obtained from the medical record. Immunohistochemistry for SDHB and mutation analysis for TMEM127 was performed, in addition to analysis of The Cancer Genome Atlas datasets for SDHX and TMEM127 mutated renal cell carcinomas (RCCs). The spectrum of renal neoplasia included clear cell and tubulocystic and papillary RCC, as well as a case of multiple papillary adenomas. Three patients had metastatic PC/PGL and three patients had VHL syndrome. Previously unreported TMEM127 alterations were identified in two patients, both without evidence of VHL syndrome or SDH-deficiency, and were classified as variants of uncertain significance. Primary renal PGL and neoplasia was associated with about 2% of 710 cases of PC/PGL. These were diagnosed concurrently or on average 27 months prior to the PC/PGL, and most were low-grade, low-stage clear cell RCCs. Up to half of patients with PC/PGL and renal neoplasia had VHL syndrome, SDH deficiency, or alterations in TMEM127. One (of three) case of metastatic PC/PGL had SDHB mutation and loss of SDHB by immunohistochemistry. The other two cases had retained SDHB expression.

Aerobic biogenesis of selenium nanoparticles by Enterobacter cloacae Z0206 as a consequence of fumarate reductase mediated selenite reduction

In the present study, we examined the ability of Enterobacter cloacae Z0206 to reduce toxic sodium selenite and mechanism of this process. E. cloacae Z0206 was found to completely reduce up to 10 mM selenite to elemental selenium (Se°) and form selenium nanoparticles (SeNPs) under aerobic conditions. The selenite reducing effector of E. cloacae Z0206 cell was to be a membrane-localized enzyme. iTRAQ proteomic analysis revealed that selenite induced a significant increase in the expression of fumarate reductase. Furthermore, the addition of fumarate to the broth and knockout of fumarate reductase (frd) both significantly decreased the selenite reduction rate, which revealed a previously unrecognized role of E. cloacae Z0206 fumarate reductase in selenite reduction. In contrast, glutathione-mediated Painter-type reactions were not the main pathway of selenite reducing. In conclusion, E. cloacae Z0206 effectively reduced selenite to Se° using fumarate reductase and formed SeNPs; this capability may be employed to develop a bioreactor for treating Se pollution and for the biosynthesis of SeNPs in the future.

IMPROVED TECHNIQUE FOR THE HISTOCHEMICAL DEMONSTRATION OF SUCCINIC DEHYDROGENASE IN BRAIN TISSUE

A tissue cutting technique for the histochemical demonstration of succinic dehydrogenase activity in brain tissue is described. The demonstration of succinic dehydrogenase in fine and delicate structures depends on a tissue temperature of –3 to –2°C. during cutting. Artefacts such as coarse granules, loss of activity and diffusion of stain are prevented by minimizing of traumatic effects due to this improved technique.

Delayed Onset and Reduced Cognitive Deficits through Pre-Conditioning with 3-Nitropropionic Acid is Dependent on Sex and CAG Repeat Length in the R6/2 Mouse Model of Huntington's Disease

BACKGROUND

Impairments in energy metabolism are implicated in Huntington's disease (HD) pathogenesis. Reduced levels of the mitochondrial enzyme succinate dehydrogenase (SDH), the main element of complex II, are observed post mortem in the brains of HD patients, and energy metabolism defects have been identified in both presymptomatic and symptomatic HD patients.

OBJECTIVE

Chemical preconditioning with 3-nitropropionic acid (3-NP), an irreversible inhibitor of SDH, has been shown to increase tolerance against experimental hypoxia in both heart and brain. Here we studied the effect of chronic preconditioning in the R6/2 mouse model of HD using mice carrying CAG repeat lengths of either 250 or 400 repeats. Both are transgenic fragment models, with 250CAG mice having a more rapid disease progression than 400CAG mice.

METHODS

Low doses of 3-NP (24 mg/kg) were administered via the drinking water and the effect on phenotype progression and cognition function assessed.

RESULTS

After 3-NP treatment there were significant improvements in all aspects of the behavioural phenotype, apart from body weight, with timing and magnitude of improvements dependent on both CAG repeat length and sex. Specifically, a delay in the deterioration of general health (as shown by delayed onset of glycosuria and increased survival) was seen in both male and female 400CAG mice and in female 250CAG mice and was consistent with improved appearance of 3-NP treated R6/2 mice. Male 250CAG mice showed improvements but these were short term, and 3-NP treatment eventually had deleterious effects on their survival rate. When cognitive performance of 250CAG mice was assessed using a two-choice discrimination touchscreen task, we found that female mice showed significant improvements.

DISCUSSION

Together, our results support the idea that energy metabolism contributes to the pathogenesis of HD, and suggest that improving energy deficits might be a therapeutically useful target.

HISTO- AND CYTOCHEMICAL LOCALIZATION OF DEHYDROGENASES IN RABBIT LENS EPITHELIUM

Dehydrogenase distributions were determined with Nitro BT in fresh flat mounts of the rabbit lens epithelium and capsule. The capsule was unreactive and the epithelium displayed high lactic and malic dehydrogenase activities, and minimal uridine diphosphate glucose and glucose-6-phosphate dehydrogenase activities. In addition, lactic and malic dehydrogenases were present in higher amounts in the peripheral (pre-equatorial and equatorial) than in the central areas of the epithelium. Lactic dehydrogenase activity was specifically inhibited by sodium and potassium iodide, oxalic acid and sodium pyruvate, the latter effect reversed with cyanide. High lactic dehydrogenase activity in lens epithelium correlates adequately with previous microchemical determinations and points to a possible role of the epithelium in the active lactate production of the lens.

HISTOCHEMICAL LOCALIZATION OF ENZYME ACTIVITY IN THE KIDNEYS OF THREE MAMMALIAN SPECIES DURING THEIR POSTNATAL DEVELOPMENT

The activities of various enzymes were studied histochemically in two species which at birth have a kidney with an active nephrogenic zone, the rat and rabbit, and one (the guinea pig) in which this organ is at this time apparently fully matured. The histochemical reactions, in general, reflect the degree of maturity found in kidneys of newborn and growing animals. Immature proximal convoluted tubules lack enzymatic activity or show only minimal amounts. As these tubules mature, the adult pattern is noted at about the 14th to 16th day after birth in rat, and after 21 to 28 days in rabbit. Within this general pattern, however, considerable variations are noted. Glucose-6-phosphatase, e.g., is less active at birth, even in mature tubules, while acid phosphatase localized in granular "lysosomal" bodies is as prominent in newborn kidney as in adult. Newborn guinea pig kidney lacks glomerular adenosine triphosphatase activity in spite of its general enzymatic maturity, while rat kidney at birth has no tubular adenosine triphosphatase activity, even in more mature proximal convolutions.

Oxidative enzymes, particularly succinic dehydrogenase, and acid phosphatase are active in tubules of the inner portion of medulla in rat and rabbit at birth. This appears to be an expression of the immaturity of newborn kidney. With the progress of zonal differentiation, this enzyme activity is no longer found in the papillary portion of medulla where thin limbs of Henle's loop are now located. In rat kidney, best seen in cryostat sections briefly postfixed in very cold neutral formalin, single cells are found in the collecting ducts with striking 5-nucleotidase activity. The number of these cells is greater in neonatal kidney than in adult kidney. The physiological significance of many of the findings described in this report has still to be clarified.

HISTOCHEMICAL STUDY OF OXIDATIVE ENZYMES IN VERTEBRATE MUSCLES

A histochemical study was carried out on oxidative enzymes, succinic dehydrogenase, diphosphopyridine nucleotide (DPN)-dependent dehydrogenases (lactic, malic, α-glycerophosphate, glutamic, and β-hydroxybutyric dehydrogenases), DPNH-diaphorase, triphosphopyridine nucleotide (TPN)-dependent dehydrogenases (isocitrate, and glucose-6-phosphate dehydrogenase) and TPNH-diaphorase on various kinds of vertebrate muscles. The results obtained were as follows:

1. Most of the mammalian striated muscle fibers fell into three types following a histochemical demonstration of oxidative enzyme reaction: Small red muscle fibers showed higher activities of oxidative enzymes, while large white fibers lower activities and the third type of fibers, "medium fiber" which were intermediate in size showed activities between red and white muscle fibers.

2. The intrafusal fibers of mammalian muscle spindles are classified into three types by oxidative enzyme reactions, i.e., red intrafusal fibers, medium intrafusal fibers and white intrafusal fibers.

3. Regarding birds, chicken muscle was composed of three types of fibers, while pigeon and lovebird muscles displayed two types of fibers.

4. Reptile and amphibian muscle fibers were classed as small red fibers showing higher activities, medium fibers moderate activities and white fibers lower activities.

5. Fish red muscle was composed only of red fibers, and the white muscle of white fibers. The transitional part of red and white muscles, revealed three types of fibers.

6. Generally, succinic dehydrogenase, lactic dehydrogenase, malic dehydrogenase, α-glycerophosphate dehydrogenase showed a higher activity, DPNH-diaphorase, TPNH-diaphorase a moderate activity, glutamic dehydrogenase, isocitrate dehydrogenase a lower activity and β-hydroxybutyric dehydrogenase and glucose-6-phosphate dehydrogenase a trace or nonactivity in most vertebrate striated muscles.

SUCCINIC DEHYDROGENASE IN PIGEON PECTORALIS DURING DISUSE ATROPHY

Quantitative and histochemical changes in succinic dehydrogenase activity in pigeon breast muscle was studied during one to sixty days of disuse after immobilization of the wings. Muscle enzyme activity was found to decrease from the first day, reaching its lowest level after seven days. Histochemical observations on red and white muscle fibers showed that after seven days atrophy, the majority of red fibers had lower enzyme activity; a few others showed higher activity. In white fibers on the other hand, a uniform increase over normal in enzyme activity and mitochondrial number was seen. These changes in the two types of fibers were less conspicuous during the later stages of atrophy. Thus the general level of oxidative metabolism in muscle as a whole was lowered in spite of the slight increase in level of SDH in white fibers. It is suggested that in both red and white fibers there was a shift, of aerobic to anaerobic metabolism, or vice versa.

HISTOCHEMICAL STUDY OF OXIDATIVE ENZYMES IN INVERTEBRATE MUSCLES

A histochemical study of oxidative enzymes was carried out on various kinds of invertebrate muscles and the results obtained were as follows:

1. Insect flight muscles showed the presence of the most intense activity of succinic dehydrogenase and high activity of α-glycerophosphate and glutamic dehydrogenases.

2. Regarding crustacean striated muscles, prawn muscle was distinguished into types of fibers by oxidative enzyme reactions.

3. In molluscan muscles, the squid and octopus muscle fibers were distinguished into two types by their oxidative enzyme activities.

4. The earthworm body wall muscle was made of only one type of fibers, whose oxidative enzyme activities were low.

MONOAMINE OXIDASE DISTRIBUTION IN THE RABBIT EYE

Monoamine oxidase distribution in the different components of the eye has been described in detail. The degree of enzyme activity varied from one component of the eye to another, the corneal stroma and Descemet's membrane being completely negative. The corneal epithelium, choroid and nonpigmented cells of the iris stroma showed mild positive activity. Strong positive activity was present in the myelin sheaths of optic and oculomotor nerves and also in the ciliary epithelium. The irido-corneal angle (meshwork) showed a moderately strong positive activity against the surrounding tissues. The most interesting observations were made in the retina. The pigment epithelial cell layer and the outer plexiform layer showed moderate positive activity while the activity in the inner plexiform layer, the outer and inner nuclear layers and in the ganglion cell layer was negligible. The layer of nerve fibers and internal limiting membranes were completely negative. In the layer of neuroreceptors, the outer half of this layer gave a very strong positive reaction and the inner half a very mild positive reaction.

The significance of this varied distribution in the neuroreceptor layer is discussed. A comparison of distribution of some important enzymes in the myelin sheaths of peripheral nerves, pigment epithelial cells of the retina, and the inner and outer segments of the neuroreceptor layer is made to show that each tissue is differently equipped with various enzymes, due probably to a fundamental difference in their functions.

HISTOCHEMISTRY OF TISSUE CULTURE CELLS: A STUDY OF THE EFFECTS OF FREEZING AND OF SOME FIXATIVES

It has been shown that a) the membranes of HeLa and L cell lysosomes are readily permeable to naphthol AS-AM phosphate when used as a substrate for acid phosphatase, b) freezing as well as fixation affect the permeability of the lysosomal membrane to both naphthol AS-AM phosphate and β-glycerophosphate, c) none of these treatments seem to affect greatly the plasma or the mitochondrial membranes and d) the distribution of phospholipids in the cells is also affected by freezing or fixation.