[Molluscicidal activity of the secondary metabolites from Streptomyces nigrogriseolus XD 2-7 against Oncomelania hupensis and its preliminary mechanisms of molluscicidal actions]

OBJECTIVE

To evaluate the storage stability of metabolites from actinomycetes Streptomyces nigrogriseolus XD 2-7 and the mollcuscicidal activity against Oncomelania hupensis in the laboratory, and to preliminarily explore the mechanisms of the molluscicidal activity.

METHODS

The fermentation supernatant of S. nigrogriseolus XD 2-7 was prepared and stored at -20, 4 °C and 28 °C without light for 10 d; then, the molluscicidal effect was tested against O. hupensis following immersion for 72 h. The fermentation supernatant was boiled in a 100 °C water bath for 30 min and recovered to room temperature, and then the molluscicidal effect was tested against O. hupensis following immersion for 72 h. The pH values of the fermentation supernatant were adjusted to 4.0, 6.0 and 9.0 with concentrated hydrochloric acid and sodium hydroxide, and the fermentation supernatant was stilled at room temperature for 12 h, with its pH adjusted to 7.0; then, the molluscicidal effect was tested against O. hupensis following immersion for 72 h. The fermentation product of S. nigrogriseolus XD 2-7was isolated and purified four times with macroporous resin, silica gel and octadecylsilane bonded silica gel. The final products were prepared into solutions at concentrations of 10.00, 5.00, 2.50, 1.25 mg/L and 0.63 mg/L, and the molluscicidal effect of the final productswas tested against O. hupensis following immersion for 72 h, while dechlorination water served as blank controls, and 0.10 mg/L niclosamide served as positive control. The adenosine triphosphate (ATP) and adenosine diphosphate (ADP) levels were measured in in O. hupensis soft tissues using high performance liquid chromatography (HPLC) following exposure to the final purified fermentation products of S. nigrogriseolus XD 2-7.

RESULTS

After the fermentation supernatant of S. nigrogriseolus XD 2-7 was placed at -20, 4 °C and 28 °C without light for 10 d, immersion in the stock solution and solutions at 10- and 50-fold dilutions for 72 h resulted in a 100% (30/30) O. hupensis mortality. Following boiling at 100 °C for 30 min, immersion in the stock solution and solutions at 10- and 50-fold dilutions for 72 h resulted in a 100.00% (30/30) O. hupensis mortality. Following storage at pH values of 4.0 and 6.0 for 12 h, immersion in the fermentation supernatant of S. nigrogriseolus XD 2-7 for 72 h resulted in a 100.00% (30/30) O. hupensis mortality, and following storage at a pH value of 9.0 for 12 h, immersion in the fermentation supernatant of S. nigrogriseolus XD 2-7 for 72 h resulted in a 33.33% (10/30) O. hupensis mortality (χ² = 30.000, P < 0.05). The minimum concentration of the final purified fermentation products of S. nigrogriseolus XD 2-7 was 1.25 mg/L for achieving a 100% (30/30) O. hupensis mortality. The ATP level was significantly lower in O. hupensis soft tissues exposed to 0.10 mg/L and 1.00 mg/L of the final purified fermentation products of S. nigrogriseolus XD 2-7 than in controls (F = 7.274, P < 0.05), while no significant difference was detected in the ADP level between the treatment group and controls (F = 2.485, P > 0.05).

CONCLUSIONS

The active mollcuscicidal ingredients of the S. nigrogriseolus XD 2-7 metabolites are maintained stably at -20, 4 °C and 28 °C for 10 d, and are heat and acid resistant but not alkali resistant. The metabolites from S. nigrogriseolus XD 2-7 may cause energy metabolism disorders in O. hupensis, leading to O. hupensis death.

[Activity of aromatic pyrrole-based compounds against of Schistosoma japonicum cercariae and acute toxicity to fish]

OBJECTIVE

To test the activity of aromatic pyrrole-based compounds against cercariae of Schistosoma japonicum and test their acute toxicity to fish.

METHODS

A series of aromatic pyrrole-based compounds were synthesized using 4-benzyl-5-(trifluoromethyl)-1H-pyrrole-3-nitrile as the lead compound. The synthesized compounds were prepared into solutions at concentrations of 10.00, 1.00, 0.10, 0.01 mg/L, and the activity of these solutions against S. japonicum cercariae was tested in 30 min, while 0.10 mg/L and 0.01 mg/L niclosamide solutions served as a positive control and dechlorinated water with 1% dimethyl sulfoxide (DMSO) was used as a negative control, with 10 to 30 cercariae of S. japonicum in each group. In addition, the compounds were prepared into solutions at concentrations of 0.50, 0.25, 0.12, 0.06, 0.03 mg/L, and their toxicity to zebrafish was tested in 72 h, while 0.15 mg/L and 0.30 mg/L niclosamide solutions served as a positive control and dechlorinated water with 1% DMSO was used as a negative control, with 10 zebrafishes in each group.

RESULTS

A total of 7 aromatic pyrrole-based compounds were successfully synthesized. Treatment with compounds 102, 104 and 106 at a concentration of 0.01 mg/L for 30 min killed all S. japonicum cercariae, and compounds 105 and 107 showed no activity against cercariae. No death of cercariae was found in the blank control group, while treatment with 0.10 mg/L niclosamide for 10 min caused a 100% mortality rate of S. japonicum cercariae and 0.01 mg/L niclosamide failed to kill S. japonicum cercariae. No zebrafish death was found 72 h post-treatment with compounds 101, 104 and 105 at a concentration of 0.03 mg/L, and exposure to compounds 102, 103 and 106 at a concentration of 0.03 mg/L for 12 h resulted in a 100% mortality rate of zebrafish. No zebrafish death occurred 72 h post-treatment with 0.50 mg/L Compound 104, and no zebrafish death was found in the blank control group, while treatment with 0.30 mg/L niclosamide for 24 h resulted in a 100% mortality rate of zebrafish.

CONCLUSIONS

Compound 104 achieves a 100% mortality rate against S. japonicum cercariae at a concentration of 0.01 mg/L for 30 min, and causes no death of zebrafish at a concentration of 0.50 mg/L for 72 h, which may serve as a cercaricide candidate.

[Effects of praziquantel isomers on the proliferation and activation of the LX-2 human hepatic stellate cell line]

OBJECTIVE

To compare the effects of levo-praziquantel (L-PZQ) and dextro-praziquantel (D-PZQ) on the proliferation and activation of the human hepatic stellate cell line LX-2 in vitro.

METHODS

LX-2 cells were stimulated with transforming growth factor-β (TGF-β). LX-2 cell proliferation was measured using the CCK-8 assay after 24 h stimulation with 0 to 50 μg/mL concentrations of praziquantel, and the gene and protein expression of type Ⅰ collagen (collagen Ⅰ), type Ⅲ collagen (collagen Ⅲ) and α-smooth muscle actin (α-SMA) was quantified in LX-2 cells using quantitative real-time PCR (qPCR) and Western blotting assays 24 h and 48 h following stimulation with 15 μg/mL praziquantel to detect LX-2 cell activation.

RESULTS

There were significant differences in the survival rate of LX-2 cells between L-PZQ and D-PZQ treatments at all concentrations (F = 6.119 and 79.180, both P values < 0.05). Either L-PZQ or D-PZQ at a concentration of < 30 μg/mL showed no remarkableeffectsonthe LX-2 cell proliferation (both P values > 0.05), and L-PZQ at a concentration of > 50 μg/mL and D-PZQ at a concentration of > 40 μg/mL inhibited the LX-2 cell proliferation (both P values < 0.05), while D-PZQ at concentrations of 40 μg/mL and 50 μg/mL showed greater inhibition on LX-2 cell proliferation than L-PZQ (t = 3.419 and 8.776, both P values < 0.05). There were significant differences in the collagen Ⅰ, collagen Ⅲ and α-SMA expression in LX-2 cells at both transcriptional (F = 21.55, 79.99 and 46.70, all P values < 0.05) and translational levels (F = 20.12, 30.29 and 32.93, all P values < 0.05) among the blank control group, TGF-β stimulation group, L-PZQ treatment group and D-PZQ treatment group. L-PZQ treatment resulted in remarkable inhibition on collagen Ⅲ and α-SMA gene expression in LX-2 cells (both P values < 0.05); however, the treatment showed no remarkable inhibition collagen Ⅰ gene expression or collagen Ⅰ, collagen Ⅲ or α-SMA protein expression in LX-2 cells (all P values > 0.05). In addition, D-PZQ treatment resulted in significant inhibition on collagen Ⅰ, collagen Ⅲ and α-SMA expression in LX-2 cells at both translational and transcriptional levels (all P values < 0.05), and D-PZQ showed higher inhibition on collagen Ⅰ, collagen Ⅲ and α-SMA gene expression in LX-2 cells than L-PZQ (all P values < 0.05).

CONCLUSIONS

Both L-PZQ and D-PZQ inhibit the proliferation and activation of LX-2 cells, and D-PZQ shows a higher inhibitory activity than L-PZQ.

[Studies on resistance of Schistosoma to praziquantel XVIII Sensitivity to praziquantel in filial generations of praziquantel-resistant and -sensitive Schistosoma japonicum mixed infections]

OBJECTIVE

To investigate the sensitivity of adult worms of filial generations from praziquantel-resistant and -sensitive Schistosoma japonicum mixed infections to praziquantel.

METHODS

Mice were infected with the cercariae of an experimentally generated praziquantel-resistant S. japonicum isolate [median effective dose (ED₅₀) = 277.4 mg/kg] and a laboratory-maintained praziquantel-sensitive S. japonicum isolate (ED₅₀ = 99.6 mg/kg) at a mixture ratio of 1:1 and 2:1, which was maintained in the laboratory via the mouse-snail cycle for 8 generations. Then, mice were infected with the cercariae of the 8th filial-generation parasite, and grouped 35 days post-infection. Mice in the 5 treatment groups were given praziquantel treatment by gavage at a single oral dose of 37.5, 75, 150, 300 mg/kg and 600 mg/kg, while animals in the control group was administered orally with 2.5% cremophor EL. All mice were sacrificed 14 days post-treatment and adult worms were collected by perfusion of the portal vein. The worm burden reductions and praziquantel ED₅₀ values were calculated. The praziquantel-resistant S. japonicum isolate generated from experimental induction with 12 rounds of praziquantel treatment with sub-curative doses was maintained in the laboratory via the mouse-snail cycle, and mice were infected with the cercariae of the 8th filial-generation parasite. The praziquantel ED₅₀ value against the 8th filial-generation adults was measured.

RESULTS

After mice were infected with the mixture of cercariae of PZQ-resistant and -sensitive S. japonicum isolates at a ratio of 1:1, the praziquantel ED₅₀ was 135.2 mg/kg against the adults of the 8th filial-generation parasite. After mice were infected with the mixture of cercariae of PZQ-resistant and -sensitive S. japonicum isolates at a ratio of 2:1, the praziquantel ED₅₀ was 129.2 mg/kg against the adults of the 8th filial-generation parasite. In addition, the praziquantel ED₅₀ was 208.4 mg/kg against the adults of the 8th filial-generation S. japonicum without the selection pressure of praziquantel.

CONCLUSIONS

Compared with the experimentally induced praziquantel-resistant S. japonicum isolate, the adult worms of the filial-generation S. japonicum show a reduced sensitivity to praziquantel in the same host following infection with the mixture of cercariae of praziquantel-resistant and -sensitive S. japonicum isolates. The adult worms of the filial generation of the praziquantel-resistant S. japonicum isolate without the selection pressure of praziquantel may still maintain the resistance to praziquantel.

[Study on the factors affecting the degradation of niclosamide in the soil]

OBJECTIVE

To investigate the factors affecting the degradation of niclosamide in the soil, so as to provide the evidence for the assessment of the environmental safety in the field snail control with niclosamide.

METHODS

A high performance liquid chromatography was established for the determination of niclosamide in the field. Then, the degradation of niclosamide was investigated in soils with different moistures (10%, 30%, 50%, 70% and 90%), temperatures [(15 ± 1), (25 ± 1), (35 ± 1) °C], initial concentrations (1, 5, 10 mg/kg) and in sterilized and non-sterilized soils. In addition, the degradation of niclosamide was fitted with the first-order kinetics equation, and the degradation half-life was calculated.

RESULTS

The niclosamide residues gradually decreased over time in soils with different moistures, and a higher rate of degradation was seen in soils with a higher moisture. The degradation half-life of niclosamide reduced from 4.258 d in the soil with a 10% moisture to 2.412 d in the soil with a 90% moisture. The niclosamide residues gradually decreased over time in soils with different temperatures, and a higher rate of degradation was seen in soils with a higher temperature. The degradation half-life of niclosamide reduced from 4.398 d in the soil with a temperature of (15 ± 1) °C to 2.828 d in the soil with a temperature of (35 ± 1) °C. The degradation half-lives of niclosamide were 3.212, 3.333 d and 3.448 d in soils containing niclosamide at initial concentrations of 1, 5 mg/kg and 10 mg/kg, and > 30 d and 3.273 d in sterilized and non-sterilized soils. Multiple linear regression analysis revealed that soil microorganisms (P = 0.010), moisture (P = 0.000) and temperature (P = 0.002) affected the half-life of niclosamide degradation.

CONCLUSIONS

The degradation of niclosamide in soils fits the first-order kinetics equation, and presence of microorganisms, a high temperature and high moisture may accelerate the degradation of niclosamide in the soil.

Expression of calcitonin gene-related peptide (CGRP) mRNA in rat lymphocytes

We recently found that calcitonin gene-related peptide (CGRP)-like immunoreactivity was present in lymphocytes of rat thymus and lymph node. In order to investigate whether these cells were capable of synthesizing CGRP, CGRP mRNA of rat dorsal root ganglia, thymocytes and mesenteric lymph node lymphocytes were determined by reverse transcription and polymerase chain reaction (RT-PCR) utilizing synthetic oligonucleotides bracketing a portion of the calcitonin/CGRP gene. A discrete band of the expected size of 90 base pairs was found in the dorsal root ganglia (positive control), and in both thymocytes and mesenteric lymph node lymphocytes. These data strongly suggest that CGRP is not only an important neuropeptide, but it is also synthesized in lymphocytes of both thymus and lymph nodes, which is identical to that in sensory neurons. CGRP from lymphocytes may act as an immunomodulator and serve as a common ligand in immune and nervous systems.

[Changes of CGRP levels in plasma and CGRP mRNA in dorsal root ganglia during endotoxicosis in the rat]

To investigate the changes of both CGRP release and synthesis during endotoxicosis, CGRP mRNA in thoracolumbar dorsal root ganglia (DRG) was determined by the semi-quantity RT-PCR and the CGRP levels in plasma were measured by RIA. The results showed that plasma CGRP, but not mRNA, began to increase 30 min after endotoxin (5 mg/kg, i.v.) administration. On the other hand, the CGRP levels in plasma and CGRP mRNA in DRG were significantly increased by 142% and 32% respectively at the 3 h of injection and by 216% and 85% respectively at the 8 h of injection. The data suggest that not only the release of CGRP from the peripheral organs, but also the transcription of CGRP mRNA and synthesis of CGRP in sensory neurons are increased during the development of endotoxicosis in the rat. Presumably the DRG is an important source of CGRP release in the response to endotoxicosis.