[Study on insecticide resistance of Culex pipiens pallens in southwest region of Shandong Province]

OBJECTIVE

To explore the sensitivity of Culex pipiens pallens to common chemical insecticides in the southwestern region of Shandong Province, so as to provide a theoretical basis for the development of reasonable and effective mosquito control measures.

METHODS

The resistance of Cx. pipiens pallens larvae to 5 chemical insecticides, such as cypermethrin, deltamethrin, DDVP, propoxur, and acetofenate were tested by using the WHO biological test method in 2018, and the co-toxicity coefficients after compounding the above-mentioned insecticides were tested by using a drug compounding method.

RESULTS

The resistance indexes of Cx. pipiens pallens to cypermethrin, deltamethrin, DDVP, propoxur, and acetofenate in 3 cities were 144.43-557.54, 118.17-445.33, 6.44-19.00, 2.37-8.10, and 0.88-2.98, respectively, and expect the difference between the DDVP resistances of Cx. pipiens pallens in Jining City and Heze City was not statistically significant (P > 0.05), all the other differences were statistically significant (all P < 0.05). The synergistic coefficients of cypermethrin + DDVP, cypermethrin + propoxur, DDVP + acetofenate, and propoxur + acetofenate were 199.58 - 456.95, 190.56 - 292.37, 123.32 - 319.24, and 192.31 - 367.32, respectively. The lower synergism was observed by using the mixture of DDVP + propoxur (synergistic coefficient: 99.87-108.36) .

CONCLUSIONS

After decades of chemical control, Cx. pipiens pallens in the southwestern region of Shandong Province has produced different degrees of resistance to common chemical insecticides. Therefore, comprehensive control measures should be taken to control mosquito breeding and prevent the development of insecticide resistance.

Imaging adipose tissue browning using the TSPO-18kDa tracer [18F]FEPPA

Objectives

The browning of white adipose tissue (WAT) into beige has been proposed as a strategy to enhance energy expenditure to combat the growing epidemic of obesity. Research into browning strategies are hampered by the lack of sensitive, translatable, imaging tools capable of detecting beige fat mass non-invasively. [¹⁸F]FDG is able to detect activated beige fat but provides little information on unstimulated beige fat mass. We have assessed the use of [¹⁸F]FEPPA, a tracer for the TSPO-18KDa found on the outer mitochondrial membrane, as an alternative imaging agent capable of detecting unstimulated brown fat (BAT) and beige fat.

Methods

Female Balb/c mice (n = 5) were treated for 7 days with the β3 adrenergic agonist CL-316,243 to induce the browning of inguinal WAT (beige fat). Animals were imaged longitudinally with [¹⁸F]FDG and [¹⁸F]FEPPA and uptake in interscapular BAT and inguinal WAT assessed. The browning of inguinal WAT was confirmed using H&E and immunohistochemical detection of UCP-1 and TSPO.

Results

Repeated dosing with β3-adrenergic agonist CL-316,243 caused a significant increase in [¹⁸F]FDG uptake in both interscapular BAT and inguinal WAT associated with the increased metabolic activity of brown and beige adipocytes respectively. [¹⁸F]FEPPA uptake was likewise increased in inguinal WAT but showed no increase in BAT uptake due to stimulation over the same time course. Furthermore, inguinal WAT uptake was unaffected by pharmacological blockade, indicating that [¹⁸F]FEPPA uptake is associated with the expression of mitochondria in BAT and beige adipocytes and independent of activation.

Conclusion

These data show that [¹⁸F]FEPPA can detect BAT and newly formed beige fat under non-stimulated, thermoneutral conditions and that uptake after stimulation is linked to mitochondrial expression as opposed to activation.

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TSPO-18kDa tracers can detect BAT under non-stimulated, thermoneutral conditions.

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TSPO-18kDa tracers can detect the formation of beige adipocytes in white adipose tissue.

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TSPO-18kDa tracers may aid in the development of new approaches to treat obesity.

Preparation and evaluation of tilmicosin microspheres and lung-targeting studies in rabbits

Tilmicosin (TMS) is a macrolide used extensively for pulmonary infections in clinical veterinary medicine. However, TMS has frequent administration and short elimination half-life. Therefore, tilmicosin-gelatine microspheres (TMS-GMS) were prepared by an emulsion-chemical cross-linking technique as a sustained-release formulation to extend drug half-life. The particle size distribution, in-vitro sustained-release properties, stability, and physical characteristics, as well as pharmacokinetic (PK) characteristics, were evaluated in rabbits. TMS-GMS were spherical in shape and had a mean diameter of 11.34±1.20μm; 95.65% of the microspheres varied in size from 5.0 to 25.0μm. Light and thermal stability tests indicated no significant changes in all observed indices. Importantly, compared to crude TMS, slower release of TMS from TMS-GMS was noted in drug release studies (in vitro). Pharmacokinetic (PK) characteristics were examined in the lung, liver, heart, kidney and muscle tissue of rabbits following IM injection of TMS-GMS or TMS-injection at a dose of 10mg/kg. The elimination half-life of TMS-GMS (59.21±0.21h) was longer than that of TMS-injection (38.56±0.13h) in the lung. The ratio of peak concentration (C_e) of TMS-GMS to TMS-injection was 2.19 (>1) in the lung, demonstrating the selectivity of TMS-GMS to target the lung compared to that of other tissues (C_e<1). Interestingly, the uptake value of TMS from TMS-GMS was 8.48 times higher in the lung than that for the TMS-injection, and was slightly higher than in the liver (1.85), heart (1.72), kidney (2.44) and muscle (2.79) tissues. TMS-GMS is a sustained-release formulation of TMS with potential to be used in veterinary clinical applications; possible benefits include lung-targeting and prolonged elimination half-life.