Chronic tributyltin exposure induces metabolic disruption in an invertebrate model animal, Lymnaea stagnalis

Over the last 20 years, tributyltin (TBT) has been reported to cause metabolic disruption in both invertebrates and vertebrates, highlighting the need for further detailed analysis of its physiological effects. This study aimed to investigate the metabolic-disrupting effects of TBT from the behavioral to the molecular level. Adult specimens of the great pond snail (Lymnaea stagnalis) were exposed to an environmentally relevant concentration (100 ng L-1) of TBT for 21 days. After the chronic exposure, behavioral alterations as well as histological, cellular, and molecular changes were investigated in the central nervous system, kidney, and hepatopancreas. TBT exposure significantly decreased feeding activity, while locomotor activity remained unchanged. At the histological level, the cellular localization of tin was demonstrated in all tissues investigated and, in addition, characteristic morphological changes were observed in the kidney and hepatopancreas. Tissue-specific changes in lipid profiles confirmed TBT-induced disruption of lipid homeostasis in mollusks, characterized by a consistent reduction in the proportion of polyunsaturated fatty acids and a shift toward more saturated lipids. The expression of 17β-hydroxysteroid dehydrogenase type 12 (HSD17B12) enzyme, involved in lipid metabolism in vertebrates, was reduced in all three tissues after TBT exposure. Our results show that TBT induces significant multi-level metabolic changes in Lymnaea, including direct alterations in feeding activity and lipid composition. Our findings also suggest that HSD17B12 enzyme plays a key role in lipid metabolism in mollusks, as in mammals, and is likely involved in TBT-induced metabolic disruption. Overall, our study extends the findings of previous studies on mollusks by providing novel behavioral as well as tissue-specific histological and metabolic data and highlights the complexity and evolutionary conserved way of TBT-induced metabolic disruption.

Multi-omics analysis reveals the toxic mechanism of tributyltin exposure causing digestive gland oxidative stress in cuttlefish (Sepia pharaonis)

Tributyltin (TBT) is known for its environmental persistence and high toxicity, posing a significant threat to benthic aquatic organisms in coastal zones. The present study employed physiological, histological, and multi-omics techniques to investigate the toxic effects of TBT exposure and the detoxification mechanisms in Sepia pharaonis. The results revealed that TBT exposure resulted in reduced growth performance, elevated activity of the antioxidant enzyme system, and pronounced histopathological alterations in the digestive glands, suggesting substantial oxidative stress within these tissues. Transcriptome analysis indicated that differentially expressed genes were significantly enriched in pathways related to reactive oxygen species (ROS) metabolism, oxidative stress, the mitochondrial respiratory chain, antioxidant activity, and stress responses. Furthermore, levels of metabolites involved in ROS scavenging-including oxidized glutathione, L-arginine, L-glutamate, γ-glutamyl-L-alanine, and L-glycine-were markedly elevated, reflecting the organism's response to reduce the excess ROS induced by TBT stress. Additionally, the integrated analysis of transcriptome and metabolome data indicated that the cuttlefish could effectively counteract TBT-induced oxidative stress via its antioxidant enzyme system. However, exposure to high concentrations of TBT prompted a shift from reliance on the antioxidant enzyme system to the activation of detoxification defense mechanisms, with a pronounced effect on glutathione metabolism and arginine biosynthesis. In conclusion, our findings enhance the understanding of S. pharaonis's adaptability to TBT-stressed environments and offer new insights into the molecular mechanisms underlying TBT-induced detoxification.

In-feed oxolinic acid induces oxidative stress and histopathological alterations in Nile tilapia Oreochromis niloticus

The aquaculture industry urgently requires effective bacterial disease management strategies, necessitating better regulation of antibiotic application. This study investigated the effects of oral oxolinic acid (OA) administration on Oreochromis niloticus at the recommended dose of 12 mg (1 ×) and overdose of 36 mg (3 ×)/kg biomass/day for 7 consecutive days in terms of growth, oxidative stress, residue accretion and histopathology relative to the control. The 1 × and 3 × groups experienced dose-dependent mortalities (3.33-8.33 %). The OA residues peaked in the liver and kidney tissues with dosing and declined upon discontinuation. The residues persisted in the kidney even on day 35 post-dosing. Elevated malondialdehyde and total nitric oxide levels signified oxidative stress and correlated with the tissue level changes in various organs. Histologically, glycogen-type vacuolation and cellular hypertrophy were observed in the liver. The kidney had hydropic swelling, renal epithelium degradation, nephrocalcinosis, vacuolation, and necrosis. Splenic alterations were confined to necrosis and a slight increase in sinusoidal space. Intestinal tissues exhibited a depletion of absorptive vacuoles, epithelial layer degradation, mucinous degeneration, and necrosis. Gills displayed epithelial hyperplasia, thickening of secondary lamellae, and erosion. Nevertheless, the cohort administered the recommended dose exhibited recovery with OA discontinuation. However, none of the assessed parameters normalized in the overdosed group even after 35 days of dose suspension. The results indicated that O. niloticus can safely adapt to and tolerate the toxic effects of OA. As the recommended dose of OA elicited reversible bioresponses effectively in tilapia, it can be utilized in aquaculture with due caution following regulations.

Pharmacokinetics/pharmacodynamics of gamithromycin for treating Pasteurella multocida infection in cattle using a tissue cage model

In this study, gamithromycin, a long-acting azalide antibiotic recently introduced for bovine respiratory disease (BRD) treatment, was evaluated for its effectiveness against Pasteurella multocida using a cattle tissue cage model. Gamithromycin (6 mg/kg) was administered via both intravenous and subcutaneous routes and the gamithromycin contents in sera, transudates, and exudates were measured using HPLC/MS-MS. Non-compartmental methods were utilized for assessing pharmacokinetic parameters and an inhibitory sigmoid Emax model determined associations between the pharmacokinetic/pharmacodynamic (PK/PD) indices and antibacterial activity. The area under the 24-h concentration-time curve/minimum inhibitory concentration (AUC0-24h/MIC) was found to be an optimal measure of antibacterial activity. The AUC0-24h/MIC values over 24 h in sera, transudates, and exudates were 0.27, 0.17, and 0.14, respectively, for bacteriostatic effects, while for bactericidal activity, the AUC0-24h/MIC values over 24 h in sera and exudates 3.76 and 5.31, respectively, and for bacterial eradication, the serum value was 18.46. These findings contribute valuable insights into the optimization of gamithromycin dosing regimens for treating respiratory conditions caused by Pasteurella multocida in cattle.

Research Progress on the Application of Nanoenzyme Electrochemical Sensors for Detecting Zearalenone in Food

Zearalenone (ZEN) is a common mycotoxin widely found in food crops such as corn. The toxicity of ZEN is manifested as multiple hazards to reproduction, genes, cells, and immune systems. Long-term exposure may have a serious impact on health, so it has received extensive attention due to its potential harm to human and animal health. In order to ensure food safety, countries have formulated corresponding ZEN content limit standards and promoted the development of efficient and rapid detection technologies. This paper reviews the research progress of ZEN detection in food based on nanoenzyme electrochemical sensors. Firstly, the basic situation of ZEN was introduced, including its physical and chemical properties, toxicity, and related regulations and standards. Secondly, the advantages and disadvantages of traditional detection methods and new detection technologies are analyzed, and the application progress of electrochemical sensors in ZEN detection is discussed, especially aptamer electrochemical sensors, immune-electrochemical sensors, and nanoenzyme electrochemical sensors. In this paper, the advantages of nanoenzyme electrochemical sensors in ZEN detection are discussed in detail, especially in terms of sensitivity, selectivity, and rapid detection. However, nanoenzyme electrochemical sensors still face some challenges in practical applications, such as high production costs, control of signal amplification effects, and safety issues of nanomaterials. Finally, this paper looks forward to the future development direction of nanoenzyme electrochemical sensors and proposes possible solutions to further improve their stability, reduce costs, and optimize sensing performance.

Population Pharmacokinetics of Enrofloxacin in Micropterus salmoides Based on a Nonlinear Mixed Effect Model After Intravenous and Oral Administration

This study aimed to investigate the PPK of EF in largemouth bass after oral and intravenous administration based on a nonlinear mixed effect model. Samples were collected using the sparse sampling method at pre-designed time points determined by high-performance liquid chromatography with a fluorescent detector. The initial PK parameters were estimated by reference search and the calculation of a naïve pooled approach. The covariate model included a variation in body weight. The oral dose data were best fitted by a one-compartment model. The injection dose data were best fitted by a two-compartment model. The results demonstrated that body weight had no marked effect on the parameters of PPK. Finally, the bioavailability was calculated to be 12.24%. The area under the concentration-time curve/minimum inhibitory concentration was estimated to be ≥408.16, indicating that EF at 20 mg/kg has high effectiveness for aquatic pathogens.

Population Pharmacokinetics of Enrofloxacin in Ctenopharyngodon idella Based on the Sparse Sampling Method and a Nonlinear Mixed Effect Model Following Intravenous and Oral Administration

The objective of this study was to implement population pharmacokinetic (PPK) of enrofloxacin (EF) in grass carp (Ctenopharyngodon idella) after a single oral administration and a single intravenous administration based on a nonlinear mixed effect model. The plasma samples collected by the sparse sampling method were detected by high-performance liquid chromatography with a fluorescent detector. The initial pharmacokinetic (PK) parameters were evaluated by reference search and the calculation of a naïve pooled method. After oral administration, the concentration-time profile was best described by a one-compartment open model. The absorption rate constant (Ka), apparent distribution volume (V), and systemic clearance (CL) were estimated to be 3.11/h, 4.36 L/kg, and 0.079 L/h/kg, respectively. After intravenous administration, the concentration-time curve was best simulated by a two-compartment open model. The apparent distribution volume of the central compartment (V1), apparent distribution volume of the peripheral compartment (V2), CL, and clearance from the central compartment to the peripheral compartment (CL2) were estimated to be 0.42, 2.05 L/kg, 0.067, and 2.94 L/h/kg, respectively. Finally, the bioavailability was calculated to be 84.81%. The parameter of AUC/minimum inhibitory concentration value was estimated to be more than 506.32 for Aeromonas hydrophila, Aeromonas sobria, and Flavobacterium columnare indicating that EF at 20 mg/kg has high effectiveness for these pathogens. This study supported a concise method for conducting PK study in aquatic animals that facilitated the development of PK methodology in aquaculture.

Residue Behavior and Risk Assessment of Diazepam and Its Metabolites in Crucian Carp (Carassius auratus) After Oral Administration

Diazepam (DZP), a benzodiazepine medication, is extensively utilized in both human and veterinary medicine and has been frequently detected in fish populations. The use of DZP-laced bait is identified as a predominant contributor to drug residue contamination in fish. Nonetheless, our understanding of the residue profile of DZP in fish and its potential implications for human health remains constrained. This study investigated the residue behavior and dietary intake risks of DZP and its primary metabolites in crucian carp (Carassius auratus) following oral administration. A rapid and sensitive UHPLC-MS/MS method was developed and validated for the reliable quantification of DZP and its identified metabolites. The findings revealed rapid absorption and extensive distribution of DZP in crucian carp, with peak concentrations in plasma and tissues occurring at 1 h. The distribution pattern of DZP, based on calculated AUC, was kidney > liver > plasma > gill > muscle plus skin. The distribution of DZP in plasma and tested tissues followed the decreasing order of kidney > liver > plasma > gill > muscle plus skin according to the calculated AUC. DZP elimination was notably slow, particularly in muscle plus skin, with an elimination half-life of 619.31 h, necessitating at least 70 days for concentrations to fall below the limit of quantitation, suggesting a high likelihood of residue formation in fish from oral DZP administration. DZP was metabolized into nordiazepam and temazepam in crucian carp; nordiazepam is the main metabolite of DZP, which is gradually higher than the parent drug in the elimination phase. The dietary risk assessment suggested that a possible health risk (HQ ≥ 0.1) was found within 1 day via ingestion of crucian carp after an oral dose of DZP, suggesting that frequent consumption of high-residue crucian carp may cause harm to human health.

Doxycycline pharmacokinetics and tissue depletion in striped catfish (Pagasianodon hypophthalmus) after oral administration

The pharmacokinetics and residue depletion of doxycycline (DOX) in striped catfish (Pagasianodon hypophthalmus) after oral dosage were investigated. The pharmacokinetic experiment was conducted in an aquarium, while the experiment of residue depletion was performed in both an aquarium and earth ponds. Medicated feed was administered orally using the gavage method at a dosage of 20 mg/kg body weight. Blood, liver, and kidney from medicated fish samples were collected. In the depletion experiments, fish were fed medicated feed for five consecutive days at a dosage of 20 mg/kg body weight, with samples collected during and after medication. The concentrations of DOX were quantified using an LC-MS/MS system. The pharmacokinetics parameters of DOX in striped catfish included the absorption rate constant (ka), absorption half-life (T1/2abs), maximal plasma concentration (Cmax), time to maximal plasma concentration (Tmax), and area under the plasma concentration-time curve from time 0 to 96 h (AUC0-96 h) which were 0.12 h-1, 5.68 h, 1123.45 ng/mL, 8.19 h, and 25,018 ng/mL/h, respectively. Residue depletion results indicated that the withdrawal times of DOX in muscle (with skin) from fish kept in the aquarium were slightly longer than that in fish raised in earth ponds, corresponding to 194 degree-days compared with 150 degree-days. In conclusion, administration of DOX at the dosage of 20 mg/kg body weight can be used for treatment of bacterial infections in striped catfish, and a withdrawal time of 5 days at 29.4°C will ensure consumer food safety due to the rapid depletion of DOX from muscle and skin.

The Glutamatergic System Regulates Feather Pecking Behaviors in Laying Hens Through the Gut-Brain Axis

Feather pecking (FP) is a significant welfare and economic problem in laying hen husbandry. While there is growing evidence that the glutamatergic system plays a crucial role in regulating FP behavior, the biological mechanisms remain unclear, largely due to the limited uptake of peripheral glutamate across the blood-brain barrier (BBB). Here, we applied a multi-omics approach combined with physiology assays to answer this question from the perspective of the gut-brain axis. A total of 108 hens were randomly assigned to two groups (treatment and control) with six replicates each, and the treatment group was subjected to chronic environmental stressors including re-housing, noise, and transport. We found that chronic exposure to environmental stressors induced severe FP, accompanied by reduced production performance and increased anxiety- and depression-related behaviors, compared to controls. In addition, the immune system was potentially disrupted in FP chickens. Notably, gut microbiota diversity and composition were significantly altered, leading to decreased microbial community stability. Non-targeted metabolomic analysis identified a variety of differential metabolites, primarily associated with arginine and histidine biosynthesis. A significant increase in glutamate levels was also observed in the hippocampus of FP chickens. Transcriptome analysis revealed the upregulated expressions of glutamate-related receptors GRIN2A and SLC17A6 in the hippocampus. Correlation analysis indicated that GRIN2A and SLC17A6 are positively associated with arginine levels in the duodenum, while Romboutsia in the duodenum is negatively correlated with arginine. These findings suggest that intestinal bacteria, including Romboutsia, may influence FP behavior by altering plasma arginine and histidine levels. These changes, in turn, affect glutamate levels and receptor gene expression in the hippocampus, thereby regulating the glutamatergic system. Our research offers insights into novel strategies for mitigating harmful behaviors in poultry farming, with potential benefits for animal performance and welfare.

Influence of N-Acetyl-L-Cysteine on the Pharmacokinetics and Antibacterial Activity of Marbofloxacin in Chickens

Background/Objectives: Marbofloxacin, a second-generation fluoroquinolone, is used to control economically significant poultry diseases caused by pathogenic bacteria such as Staphylococcus aureus and Escherichia coli. Although synergistic antimicrobial activity between fluoroquinolones and N-acetyl-L-cysteine (NAC) has been observed in vitro, data on their pharmacokinetic interactions in vivo remain limited. This study aimed to evaluate the effect of NAC on the oral pharmacokinetics of marbofloxacin in broiler chickens and its antibacterial activity against E. coli ATCC 25922 and S. aureus ATCC 25923, assessing the potential benefits of their combined administration. Methods: The pharmacokinetics of marbofloxacin was evaluated in broilers (5 mg/kg dose) after a single intravenous (n = 12) or single oral (n = 12) administration into the crop. The protocol for the co-administration of marbofloxacin and NAC (400 mg/kg via feed) was as follows: on the first day, the poultry (n = 12) received a single oral dose of marbofloxacin via the crop and over the next four days the fluoroquinolone drug was administered via their drinking water. The plasma levels of the drugs were determined using LC-MS/MS analyses, and minimum inhibitory concentrations were determined using the microbroth dilution method. Results: NAC significantly reduced the bioavailability of marbofloxacin after a single oral administration into the crop and decreased the elimination rate constant following the administration of both drugs. At a concentration of 20 μg/mL, NAC led to a 3.8-fold reduction in the MIC of marbofloxacin against E. coli ATCC 25922 and a 2-fold decrease at concentrations between 1 μg/mL and 6 μg/mL, while no change was observed in marbofloxacin's effect on S. aureus ATCC 25923. Conclusions: Oral co-administration of NAC and marbofloxacin reduced the fluoroquinolone's bioavailability by two-fold while enhancing its antibacterial activity against E. coli ATCC 25922.

Pharmacokinetics and Tissue Distribution of Florfenicol in Pacific White Shrimp (Litopenaeus vannamei) Following Oral Gavage and Medicated Feed Administration

Information on pharmacokinetics (PK) and tissue residues is critical for responsible drug use. The present study aimed to investigate PK characteristics and tissue distribution of florfenicol (FF) in Pacific white shrimp following a single dose of 150 mg/kg administered via oral gavage and medicated feed. Tissue depletion study and withdrawal time determination were performed after FF-medicated feed administration at a dosage of 150 mg/kg/day for 10 days. Furthermore, the effectiveness of FF against shrimp pathogens, Vibrio spp., was tested in vitro and in vivo, using broth microdilution technique and bacterial challenge experiment (immersion with Vibrio parahaemolyticus 105 CFU/mL), respectively. Following the oral gavage, the peak concentration (Cmax) in hemolymph was 162.81 μg/mL (at 0.14 h), and the area under the concentration-time curve (AUC) was 71.44 h·μg/mL, whereas those of the medicated feed method were much lower, being 6.84 μg/mL (at 0.40 h) and 8.25 h·μg/mL, respectively. The elimination half-lives (t1/2β) of the two routes were very short and comparable, being 0.77 and 0.75 h, respectively. The hemolymph protein binding was 10.42%. FF was well distributed to the muscle, producing an AUC comparable to that of the hemolymph, but it was depleted at a slower rate. Drug residue was not found in the hemolymph and muscle at 24 h after the 10-day multiple dosing. The extremely fast drug elimination renders it practically ineffective in treating vibriosis in shrimp, despite demonstrating high efficacy against Vibrio spp. in vitro. Consequently, FF may not be an ideal treatment option for Vibrio spp. infections in shrimp aquaculture.

Impact of milbemycin oxime on fluconazole resistance in Candida auris

Background

Candida auris is a pathogenic yeast that can develop resistance to multiple antifungals, particularly to azoles (e.g. fluconazole). Milbemycin oxime potentiates the effect of fluconazole against Candida spp. by inhibiting ABC transporters, such as Cdr1, which is involved in azole drug efflux.

Objectives

This study aimed to assess the interaction of milbemycin oxime and fluconazole against clinical (n = 4) and laboratory-generated (n = 4) C. auris isolates with different mechanisms of azole resistance.

Methods

Interactions of milbemycin oxime and fluconazole were assessed by chequerboard assays and defined as synergistic, indifferent or antagonistic according to the FIC index (FICI) values. The fluorescent substrate rhodamine 6 g (R6G) was used to measure ABC transporter activity in the absence or presence of milbemycin oxime.

Results

A synergistic interaction between milbemycin oxime and fluconazole was observed against most isolates, including those harbouring Cdr1-independent mechanisms of azole resistance (e.g. ERG11 mutations). The highest synergism was observed in a laboratory-generated strain overexpressing CDR1, while the interaction was indifferent in a strain lacking CDR1. R6G experiments confirmed the inhibitory effect of milbemycin oxime on ABC transporters.

Conclusions

Milbemycin oxime could represent an interesting adjunctive therapy against azole-resistant C. auris, particularly those with CDR1 overexpression.

In vivo Pharmacokinetic/pharmacodynamic relationship of florfenicol in combination with doxycycline against Riemerella anatipestifer in ducks and the effect upon resistance development

Antimicrobial chemotherapy is necessary to control Riemerella anatipestifer (RA), among which florfenicol (FF) is regarded as one of the preferred options. Based on the consideration of drug combination to improve efficacy, the pharmacokinetics and pharmacodynamics of FF combined with doxycycline (DOX) against RA were studied. FF was administered at doses of 20 or 40 mg/kg in combination with DOX (1, 2.5, 5, 10, or 20 mg/kg) via a single intramuscular injection (i.m.). DOX showed slow elimination in ducks with elimination half-life (T1/2kel) in plasma, lung, and liver of 11.21, 11.53, and 13.01 h, respectively. A single dose of DOX (≥10 mg/kg) combined with FF (20 mg/kg) could exert a bactericidal effect on some tissues (heart, liver, spleen, lungs) in a model of RA strain CVCC3857 (minimum inhibitory concentration (MIC) of FF = 1 µg/mL, MIC of DOX = 2 µg/mL) infection within 24 h, and bactericidal effects (3.01-4.36 log10 CFU/mL) were achieved in various tissues at a FF dose of 40 mg/kg. The AUC24h/MIC of DOX combined with FF at 20 mg/kg required to produce a drop of 3 Log10CFU/mL was 39.19 h (predicted dose of 25.03 mg/kg) and the value was 19.98 h (predicted dose of 12.76 mg/kg) when the dose of FF was 40 mg/kg. Combination of these two drugs could be used against insensitive strains (RA38 infection model with MIC of FF = 4 µg/mL, MIC of DOX = 2 µg/mL) by administering them twice for 24 h. Continuous passage under antibiotic pressure for 30 days suggested that resistance to FF was delayed in the presence of DOX. Genome resequencing and analyses of single-nucleotide polymorphisms revealed seven mutated genes (fahA, pfam, TonB-dependent receptor gene, proS, porU, RpiB). TonB-dependent receptor genes play a role in bacterial susceptibility. Additionally, both TonB-dependent receptor genes and fahA are involved in bacterial virulence and biofilm formation capabilities. Antimicrobial-treated strains were different from ancestor strains in terms of growth and virulence. Our study provides a data basis for the clinical use of FF and DOX against RA.

Unveiling the silent threat: A comprehensive review of Riemerella anatipestifer - From pathogenesis to drug resistance

Riemeralla anatipestifer, a predominant bacterium with multidrug resistance, has caused tremendous economic losses in the poultry farming industry. However, there are few studies on its identification, pathogenic mechanisms, and virulence factors and effective and systematic prevention and control strategies. The emergence and spread of antibacterial resistance has prompted increased focus on R. anatipestifer. However, studies on the mechanisms underlying gene aggregation and dissemination are lacking. This review summarizes recent studies on R. anatipestifer and explores its epidemiology, pathobiology, serotype classification, and preventive and treatment measures. Our findings illuminate the characteristics of virulence-related and drug resistance factors that have pivotal roles in the pathogenesis of R. anatipestifer infection. This study provides a comprehensive reference and guidance for in-depth research on R. anatipestifer.

Pharmacokinetics of tolfenamic acid in ducks (Anas platyrhynchos domestica) after different administration routes

1. The objective of this research was to compare the pharmacokinetics and bioavailability of tolfenamic acid, analgesic, antipyretic and anti-inflammatory compound, after administration through different routes to Pekin ducks. The investigation was carried out over four time periods using a randomised cross-pharmacokinetic design.2. Tolfenamic acid was administered to ducks intravenously, intramuscularly, subcutaneously and orally at a dose of 2 mg/kg. Tolfenamic acid analysis was performed using HPLC-UV and pharmacokinetic data were conducted by non-compartmental analysis.3. The total clearance, volume of distribution at steady state and terminal elimination half-life after intravenous administration were 0.14 l/h/kg, 0.29 l/kg and 1.80 h, respectively. The peak plasma concentration and bioavailability for intramuscular, subcutaneous and oral administration were 4.59, 3.55 and 2.23 μg/ml and 93.62, 74.30 and 43.43%, respectively.4. Tolfenamic acid was absorbed rapidly, eliminated quickly and exhibited a small distribution volume in Pekin ducks. Pharmacokinetic parameters, including maximum concentration, area under the plasma concentration - time curve and bioavailability, were found to be different in ducks from other bird species.

Comparative Pharmacological Assessment of Amoxicillin in Five Cultured Fish Species: Implications for Off-Label Use in Aquaculture

Background: Amoxicillin (AMOX) is widely used in aquaculture for bacterial infections due to its efficacy and safety. Despite official approval for select species, off-label use is common. This study evaluated the antibacterial efficacy and residue depletion of AMOX in five aquaculture species: olive flounder (Paralichthys olivaceus), rainbow trout (Oncorhynchus mykiss), Japanese eel (Anguilla japonica), black rockfish (Sebastes schlegelii), and Israeli carp (Cyprinus carpio). Methods: Fish were administered AMOX orally at 40 mg/kg and 80 mg/kg for seven days. Antibacterial efficacy was assessed by bacterial load reduction and survival rates following artificial infection. Residue depletion was analyzed using HPLC-MS/MS to determine the time required for AMOX levels to fall below the maximum residue limit (MRL, 0.05 mg/kg). Results: AMOX, at 40 mg/kg, significantly reduced bacterial loads in olive flounder, rainbow trout, and Japanese eel (p < 0.05), while Israeli carp exhibited a limited response (p = 0.54). Black rockfish showed moderate efficacy (RPS 72.7%) but increased mortality at 80 mg/kg. Residue levels fell below the MRL within 10 days for all species except Israeli carp (~30 days). Conclusions: These findings highlight species-specific differences in AMOX efficacy and residue depletion rates, emphasizing the necessity of tailored dosing regimens and withdrawal periods to ensure optimal therapeutic outcomes and food safety compliance in aquaculture. Further pharmacokinetic studies are needed to refine dosing strategies, particularly for species with extended residue retention and potential dose-dependent adverse effects.

Dual-Mode Quantitative Immunochromatographic Assay for Highly Sensitive On-Site Detection of Ciprofloxacin in Fish Products

Ciprofloxacin has been extensively utilized in aquaculture due to its remarkable efficacy in preventing and treating bacterial infections in fish animals. However, the widespread application of ciprofloxacin has led to significant residue accumulation, necessitating the development of rapid, sensitive and specific detection methods. In this study, we developed a novel dual-mode quantitative immunochromatographic assay based on a portable reader and a photothermal instrument, enabling on-site ciprofloxacin detection. Under optimized conditions, the portable reader mode (Mode 1) achieved a detection range of 0.1-100.0 ng/L with a limit of detection (LOD) of 0.1 ng/mL. The photothermal instrument mode (Mode 2) achieved a detection range of 0.1-500.0 ng/mL with an LOD of 0.1 ng/mL. The sensitivity and accuracy of the method were validated using an Enzyme-Linked Immunosorbent Assay. This developed method successfully detected ciprofloxacin residues in samples of Parabramis pekinensis, Larimichthys crocea, Channa argus, Carassius auratus and Micropterus salmoides, with satisfactory recovery rates. The results demonstrated excellent specificity and applicability across various fish product matrices, offering a reliable and efficient solution for the on-site monitoring of ciprofloxacin residues in fish products.

Mycotoxins in Feed: Hazards, Toxicology, and Plant Extract-Based Remedies

Background: Mycotoxins, which are secondary metabolites produced by fungi, are prevalent in animal feed and pose a serious risk to the healthy growth of livestock and poultry. Methods: This review aims to conclude current knowledge on the detrimental effects of mycotoxins on animal health and to demonstrate the potential of plant extracts as a means to counteract mycotoxin toxicity in feed. A systematic review of the literature was conducted to identify studies on the impact of mycotoxins on livestock and poultry health, as well as research into the use of plant extracts as feed additives to mitigate mycotoxin effects. Studies were selected based on their relevance to the topic, and data were extracted regarding the mechanisms of action and the efficacy of plant extracts. Results: Excessive mycotoxins in feed can lead to reduced appetite, impaired digestion, and general health issues in animals, resulting in decreased food intake, slowed weight gain, and instances of acute poisoning. Plant extracts with antioxidant, anti-inflammatory, and anti-mutagenic properties have shown the potential to improve production efficiency and reduce the toxic effects of mycotoxins. Conclusion: This comprehensive review not only consolidates the well-documented adverse effects of mycotoxins on animal health but also introduces a novel perspective by highlighting the potential of plant extracts as a promising and natural solution to counteract mycotoxin toxicity.

Ex Vivo Pharmacokinetic/Pharmacodynamic Integration Model of Cefquinome Against Escherichia coli in Foals

Cefquinome is used to treat septicemia caused by Escherichia coli (E. coli) and respiratory infections caused by Streptococcus equi subsp. zooepidemicus in foals. However, studies reporting the use of cefquinome to target E. coli as pathogens of sepsis are lacking. Therefore, this study aimed to determine the optimal dosage regimen for cefquinome against E. coli using a PK/PD model. After the administration of 1 mg/kg cefquinome (intramuscularly or intravenously), blood samples were collected at different time points to determine the serum concentration of cefquinome via HPLC. The pharmacokinetic parameters were evaluated via NCA (WinNonlin 5.2.1 software). The main pharmacokinetic parameters of cefquinome in foals were as follows: after intravenous administration, the elimination half-life (T1/2β) was 2.35 h, the area under the curve (AUC0-last) was 12.33 μg·h/mL, the mean residence time (MRT0-last) was 2.67 h, and the clearance rate (CL) was 0.09 L/h/kg. After intramuscular administration, the peak concentration (Cmax) was 0.89 μg/mL, the time to reach the maximum serum concentration (Tmax) was 2.16 h, T1/2β was 4.16 h, AUC0-last was 5.41 μg·h/mL, MRT0-last was 4.92 h, CL was 0.15 L/h/kg, and the absolute bioavailability (F) was 43.86%. An inhibitory sigmoid Emax model was used to integrate the PK/PD indices with ex vivo antimicrobial effects to identify pharmacodynamic targets (PDTs). According to the dose calculation formula, the doses of intramuscularly administered cefquinome required to achieve bacteriostatic effects, bactericidal effects, and bactericidal elimination were 1.10, 1.66, and 2.28 mg/kg, respectively. However, further studies are warranted to verify the therapeutic efficacy of cefquinome in clinical settings.

Comparative bioavailability study of two oral formulations of amoxicillin-clavulanic acid in healthy dogs

BACKGROUND

Amoxicillin-clavulanic acid combination (AMX-CA) is a widely used oral antibiotic for companion animals. In Thailand, various AMX-CA formulations are available. This study aimed to evaluate and compare the pharmacokinetic profiles and relative bioavailability of two AMX-CA formulations using a randomized, two-period, two-treatment crossover design in six healthy Beagle dogs. Each dog received a 250 mg AMX-CA tablet (formulation A or B) at a dosage of 20.5 ± 2.5 mg/kg, with a 7-day washout period between treatments. Blood samples were collected over a 24-h period post-administration, then AMX and CA concentrations were measured using LC-MS/MS. Bioequivalence was assessed based on the 90% confidence intervals (CI) for peak plasma concentration (Cmax) and the area under the plasma concentration-time curve extrapolated to infinity (AUC0-∞), which required to fall within 80%-125%.

RESULTS

The relative bioavailability of formulation B was 76.5% for AMX and 72.7% for CA, compared to formulation A. Only CA's Cmax met the bioequivalence criteria, while the CIs for AUC0-∞ and Cmax of AMX and AUC0-∞ of CA were outside the acceptable range.

CONCLUSIONS

Bioequivalence between the two formulations was not established, indicating that these formulations are not interchangeable.

Systematic transcriptome-wide analysis and validation of tributyltin-induced differential changes in the liver with sex-specific effects

BACKGROUND

Tributyltin (TBT), a prevalent environmental antiseptic, contaminates seafood, fish, and drinking water, posing health risks. While TBT's hepatic toxicity is well-known, its sex-specific effects on liver function remain poorly understood.

METHODS

To address this gap, a comprehensive analysis was conducted utilizing the Toxicant Exposures and Responses by Genomic and Epigenomic Regulators of Transcription (TaRGET) dataset. Chromatin accessibility changes and transcriptomic alterations were analyzed via ATAC-seq and RNA-seq in liver tissues from TBT-exposed male and female mice. In vitro experiments were performed to validate the key bioinformatic findings.

RESULTS

TBT exposure induced significant chromatin accessibility changes and transcriptomic alterations in male liver compared to female counterparts. Notably, Signal transducer and activator of transcription 3 (STAT3) was identified as a central regulator among differentially expressed genes (DEGs) in male liver cells. Functional validation experiments confirmed that TBT-mediated downregulation of STAT3 impaired liver cell function and contributed to increased hepatotoxicity in males.

CONCLUSIONS

Our study highlights significant sex-dependent differences in TBT-induced hepatotoxicity and identifies STAT3 as a critical mediator in male liver cells, providing a novel perspective on the toxicology of TBT.

Microalgae in health care and functional foods: β-glucan applications, innovations in drug delivery and synthetic biology

Microalgae are emerging as a key player in healthcare, functional foods, and sustainable biotech due to their capacity to produce bioactive compounds like β-glucans, omega-3 fatty acids, and antioxidants in an eco-friendly manner. This review comprehensively discusses the role of microalgae in healthcare and functional foods, focusing particularly on β-glucan therapeutics, drug delivery innovations, and synthetic biology applications. In healthcare, microalgae-derived compounds show immense promise for treating diseases, boosting immunity, and tackling oxidative stress. Euglena-derived paramylon, a type of β-glucan, has shown potential in various medical applications, including immunomodulation and anticancer therapy. Synthetic biology and bioprocess engineering are enhancing microalgae's therapeutic and nutritional value, with applications in drug delivery and personalized medicine. To maximize the potential of microalgae, further research and development are needed to address scalability, regulatory alignment, and consumer acceptance, with a focus on interdisciplinary collaboration and sustainable practices to align healthcare innovation with environmental conservation.

Recent Advances in Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-Associated Proteins System-Based Biosensors

High-sensitivity and high-specificity biodetection is critical for advancing applications in life sciences, biosafety, food safety, and environmental monitoring. CRISPR/Cas systems have emerged as transformative tools in biosensing due to their unparalleled specificity, programmability, and unique enzymatic activities. They exhibit two key cleavage behaviors: precise ON-target cleavage guided by specific protospacers, which ensures accurate target recognition, and bystander cleavage activity triggered upon target binding, which enables robust signal amplification. These properties make CRISPR/Cas systems highly versatile for designing biosensors for ultra-sensitive detection. This review comprehensively explores recent advancements in CRISPR/Cas system-based biosensors, highlighting their impact on improving biosensing performance. We discuss the integration of CRISPR/Cas systems with diverse signal readout mechanisms, including electrochemical, fluorescent, colorimetric, surface-enhanced Raman scattering (SERS), and so on. Additionally, we examine the development of integrated biosensing systems, such as microfluidic devices and portable biosensors, which leverage CRISPR/Cas technology for point-of-care testing (POCT) and high-throughput analysis. Furthermore, we identify unresolved challenges, aiming to inspire innovative solutions and accelerate the translation of these technologies into practical applications for diagnostics, food, and environment safety.

Chemical risk assessment in food animals via physiologically based pharmacokinetic modeling - Part I: Veterinary drugs on human food safety assessment

Veterinary drugs and environmental pollutants can enter food animals and remain as residues in food chains threatening human food safety and health. Performing health risk and food safety assessments to derive safety levels of these xenobiotics can protect human health. Physiologically based pharmacokinetic (PBPK) modeling is a mathematical tool to quantitatively describe chemical disposition in humans and animals informing human food safety and health risk assessments. However, few reviews focus on the application of PBPK models in food animals and discuss their relationship to human food safety and health risk assessments in the last five years (2020-2024). In this series of reviews, we introduce the methodology, recent progress and challenges of PBPK modeling in food animals. The present review is Part I of this series of reviews and it focuses on applications of PBPK models of veterinary drugs in food animals, whereas Part II is a companion review focusing on environmental chemicals. Advanced strategies of PBPK modeling in risk and food safety assessment, including population PBPK, interactive PBPK web dashboard, and generic PBPK are also summarized in Part I. Additionally, we share our perspective on the existing challenges and future direction for PBPK modeling of veterinary medicines in food animals.

Detection and Analysis of Florfenicol Residues and Metabolites in Nile Tilapia (Oreochromis niloticus) Tissues Post-Oral Administration in Tropical Waters

Water temperature is a critical environmental parameter that significantly influences fish metabolism. This study assessed the metabolism of florfenicol (FF) in tilapia (Oreochromis niloticus) at water temperatures typical of tropical and subtropical regions. Fish were treated with FF by oral administration of a dose of 10 mg kg-1 bw for 10 consecutive days. Fish fillet, liver, and kidney were sampled during the treatment phase (1, 5, and 10 days) and posttreatment (1, 2, 3, and 5 days after the last FF administration). FF, florfenicol amine (FFA), monochloro florfenicol (FFCl), and florfenicol alcohol (FFOH) were determined in the sampled tissues using a validated LC-LC-MS/MS method. The highest FF, FFA, and FFOH concentrations were determined on day 5 during the treatment phase. For FF, the concentration order is kidney > liver > fillet, while for the metabolites FFOH and FFA, the order is liver > kidney > fillet. In fillet and liver, the concentrations of FFOH were higher than the FFA concentrations, indicating that FFOH was the primary metabolite in these tissues. FFCl was only quantified at concentrations lower than 90 μg kg-1 in all tissues. The results indicated that FF can be readily absorbed and rapidly eliminated in tilapia cultivated in warm water environments. This study revealed FFOH as the primary and most persistent metabolite in tilapia farmed in warm water, followed by FFA.

Pharmacokinetics of Milbemycin Oxime in Pekingese Dogs after Single Oral and Intravenous Administration

OBJECTIVE

This study aimed to characterize the pharmacokinetic profiles of milbemycin oxime in Pekingese dogs following a single oral (PO) and intravenous (IV) dose. Six clinically healthy Pekingese dogs, with an average body weight (BW) of 4.75 kg, were included. Each dog received an IV injection of milbemycin oxime solution and PO doses of both milbemycin oxime tablets and nanoemulsion, all administered at 1 mg/kg BW.

METHODS

Blood samples (∼0.6 mL) were collected at various time points, and milbemycin oxime concentrations were measured using a validated high-performance liquid chromatography (HPLC) method with ultraviolet (UV) detection. Pharmacokinetic parameters were obtained through non-compartmental analysis (NCA) using WinNonLin software.

RESULTS

Oral administration of milbemycin oxime tablets resulted in a peak concentration (Cmax) of 0.33 ± 0.07 µg/mL at 2.47 ± 1.90 h, with a mean residence time (MRT) of 21.96 ± 14.43 h and an absolute bioavailability of 51.44% ± 21.76%. In contrast, the nanoemulsion achieved a significantly higher Cmax of 8.87 ± 1.88 µg/mL, with a much quicker time to peak concentration (Tmax) at 0.33 ± 0.13 h, an MRT of 21.74 ± 18.21 h, and an absolute bioavailability of 99.26% ± 12.14%. After IV administration, total clearance (Cl) and steady-state volume of distribution (VSS) were 0.13 ± 0.06 mL/kg/h and 2.36 ± 0.73 mL/kg, respectively.

CONCLUSIONS

These findings demonstrate that the milbemycin oxime nanoemulsion is absorbed more rapidly and completely, with significantly higher bioavailability than the tablet form. This suggests that the nanoemulsion could effectively overcome the issues of poor diffusion and low bioavailability associated with tablet formulations, positioning it as a promising alternative to traditional milbemycin oxime tablets.

Recent Advances in Biosensor Technologies for Meat Production Chain

Biosensors are innovative and cost-effective analytical devices that integrate biological recognition elements (bioreceptors) with transducers to detect specific substances (biomolecules), providing a high sensitivity and specificity for the rapid and accurate point-of-care (POC) quantitative detection of selected biomolecules. In the meat production chain, their application has gained attention due to the increasing demand for enhanced food safety, quality assurance, food fraud detection, and regulatory compliance. Biosensors can detect foodborne pathogens (Salmonella, Campylobacter, Shiga-toxin-producing E. coli/STEC, L. monocytogenes, etc.), spoilage bacteria and indicators, contaminants (pesticides, dioxins, and mycotoxins), antibiotics, antimicrobial resistance genes, hormones (growth promoters and stress hormones), and metabolites (acute-phase proteins as inflammation markers) at different modules along the meat chain, from livestock farming to packaging in the farm-to-fork (F2F) continuum. By providing real-time data from the meat chain, biosensors enable early interventions, reducing the health risks (foodborne outbreaks) associated with contaminated meat/meat products or sub-standard meat products. Recent advancements in micro- and nanotechnology, microfluidics, and wireless communication have further enhanced the sensitivity, specificity, portability, and automation of biosensors, making them suitable for on-site field applications. The integration of biosensors with blockchain and Internet of Things (IoT) systems allows for acquired data integration and management, while their integration with artificial intelligence (AI) and machine learning (ML) enables rapid data processing, analytics, and input for risk assessment by competent authorities. This promotes transparency and traceability within the meat chain, fostering consumer trust and industry accountability. Despite biosensors' promising potential, challenges such as scalability, reliability associated with the complexity of meat matrices, and regulatory approval are still the main challenges. This review provides a broad overview of the most relevant aspects of current state-of-the-art biosensors' development, challenges, and opportunities for prospective applications and their regular use in meat safety and quality monitoring, clarifying further perspectives.

Roughage Sources During Late Gestation and Lactation Alter Metabolism, Immune Function and Rumen Microbiota in Ewes and Their Offsprings

Maternal metabolic intensity significantly increases during late gestation and lactation, placing significant stress on cells and tissues. This heightened metabolic demand can lead to inflammatory responses and metabolic disorders, adversely affecting the health of both the mother and her offspring. Diet plays a key role in modulating host health by influencing the gastrointestinal microbiome. This study examined the impact of two roughage sources, corn straw (CS), and alfalfa hay (AH), on ewes and their offspring during late gestation and lactation, with a focus on metabolism, immunity, and the microbiome. Thirty-six multiparous Inner Mongolia cashmere goats, approximately 60 days pregnant, were assigned to CS and AH groups. Samples were collected from the ewes on day 140 of gestation (G140) and day 28 of lactation (L28) for analysis. The results showed that ewes fed AH had reduced body weight loss during lactation (p < 0.05), and increased serum metabolic factors levels (p < 0.05). Additionally, ewes in the AH group exhibited a reduced inflammatory response during both gestation and lactation compared to those in the CS group, as evidenced by a significant decrease in TNF-α and LPS levels and a notable increase in IL-10 (p < 0.05). The rumen microbiomes of ewes in the AH and CS groups exhibited stark differences, with specific microbial markers identified at G140 and L28. Correlation analysis revealed associations between microbiome, volatile fatty acids, cytokines, and metabolic markers. The analysis of the lambs demonstrated that their immune status and microbial composition were significantly influenced by the immune health and microbial community structure of the ewe. Moreover, microbial and immune-related components from the ewes were transmitted to the lambs, further shaping their immune development and rumen microbiota. Overall, different roughage sources during late gestation and lactation had minimal impact on the growth performance of ewes and lambs, given that both diets were iso-nitrogen and iso-energetic. However, ewes fed AH exhibited significant improvements in immune function and overall health for both them and their lambs.

A brief review on models for birds exposed to chemicals

"A Who's Who of pesticides is therefore of concern to us all. If we are going to live so intimately with these chemicals eating and drinking them, taking them into the very marrow of our bones - we had better know something about their nature and their power."-Rachel Carson, Silent Spring. In her day, Rachel Carson was right: plant protection products (PPP), like all the other chemical substances that humans increasingly release into the environment without further precaution, are among our worst enemies today (Bruhl and Zaller, 2019; Naidu et al., 2021; Tang et al., 2021; Topping et al., 2020). All compartments of the biosphere, air, soil and water, are potential reservoirs within which all species that live there are impaired. Birds are particularly concerned: PPP are recognized as a factor in the decline of their abundance and diversity predominantly in agricultural landscapes. Due to the restrictions on vertebrates testing, in silico-based approaches are an ideal choice alternative given input data are available. This is where the problem lies as we will illustrate in this paper. We performed an extensive literature search covering a long period of time, a wide diversity of bird species, a large range of chemical substances, and as many model types as possible to encompass all our future need to improve environmental risk assessment of chemicals for birds. In the end, we show that poultry species exposed to pesticides are the most studied at the individual level with physiologically based toxicokinetic models. To go beyond, with more species, more chemical types, over several levels of biological organization, we show that observed data are crucially missing (Gilbert, 2011). As a consequence, improving existing models or developing new ones could be like climbing Everest if no additional data can be gathered, especially on chemical effects and toxicodynamic aspects.

Pharmacokinetics of difloxacin after single intravenous, oral and intramuscular administration in pigeons

This study aimed to investigate the pharmacokinetics of difloxacin in pigeons following oral (PO), intramuscular (IM), and intravenous (IV) administration. Thirty pigeons were randomly divided into three groups (IM, IV, and PO; n = 10 per group). Difloxacin was administered at 10 mg/kg body weight (BW) via each route. Blood samples were collected at various intervals from 0 to 48 h, and plasma was analyzed for difloxacin concentrations using a validated high-performance liquid chromatography (HPLC) method. Pharmacokinetic parameters were determined using Phoenix software and a non-compartmental analysis (NCA) approach. After PO and IM administration, peak plasma concentrations (Cmax) were observed as 1.81 ± 0.47 and 6.52 ± 1.62 μg/mL, occurring at 2.60 ± 0.97 and 0.63 ± 0.24 h, respectively. Bioavailability (F) was 38.35 % ± 10.45 % for PO and 90.25 % ± 26.14 % for IM administration. Following IV administration, difloxacin was widely distributed, with a volume of distribution (VZ) of 2.52 ± 0.65 L/kg and a steady-state volume of distribution (VSS) of 1.87 ± 0.27 L/kg. Difloxacin exhibited slow elimination, with elimination half-lives (t1/2λzs) of 1.61 ± 0.3, 2.64 ± 0.64, and 4.27 ± 1.14 h after IM, PO, and IV administration, respectively. Based on the AUC/MIC ratios calculated here, the current IM or IV administration at 10 mg/kg BW is effective against bacterial infections with MIC values ≤ 0.1 μg/mL, while the current oral dose (10 mg/kg BW) may be insufficient, particularly for infections caused by pathogens with MIC values exceeding 0.1 μg/mL.

Development of a physiologically based pharmacokinetic model for flunixin in cattle and swine following dermal exposure

Flunixin meglumine is a nonsteroidal anti-inflammatory drug (NSAID). Banamine Transdermal is a pour-on formulation of flunixin approved for pain control in beef and dairy cattle, but not for calves and some classes of dairy cattle or swine. Violative flunixin residues in edible tissues in cattle and swine have been reported and are usually attributed to non-compliant drug use or failure to observe an appropriate withdrawal time. This project aimed to develop a physiologically based pharmacokinetic (PBPK) model for flunixin in cattle and swine to predict withdrawal intervals (WDI) after exposures to different therapeutic regimens of Banamine Transdermal. Due to the lack of comprehensive skin physiological data in cattle, the model was initially developed for swine and then adapted for cattle. Monte Carlo simulation was employed for population variability analysis. The model predicted WDIs were rounded to 1 and 2 d for liver and muscle in cattle, respectively, under FDA tolerance levels, while under EU maximum residue limits, the WDIs were rounded to 1, 3, 2, and 2 d for liver, kidney, muscle, and fat, respectively, following a labeled single transdermal 3.3 mg/kg dose in cattle. The model was converted into a user-friendly interactive PBPK (iPBPK) interface. This study reports the first transdermal absorption model for drugs in cattle. This iPBPK model provides a scientifically based tool for the prediction of WDIs in cattle and swine administered with flunixin in an extra-label manner, especially by the transdermal route.

Residue depletion and withdrawal time estimation of tilmicosin in black-bone silky fowls after administration via drinking water

In this study, residue depletion and withdrawal time estimation of tilmicosin were examined in Taihe black-bone silky fowls (TBSFs) after oral administration for three consecutive days at a dose of 75 mg/L in water. The tilmicosin concentrations in liver, kidney, muscle, and skin/fat of TBSFs collected from different time points (0.16, 1, 3, 5, 7, 9, 12, 20, 30, 40 days after last administration) were determined by UPLC-MS/MS. The results indicated that the tilmicosin concentrations in TBSFs tissues varied significantly, and kidney had the highest average concentrations (2604.65 ± 4625.20 μg/kg), followed by liver (1125.54 ± 1479.24 μg/kg), skin/fat (372.81 ± 428.33 μg/kg), and muscle (104.52 ± 143.95 μg/kg). Meanwhile, tilmicosin was still detected in all the four studied tissues (liver, kidney, skin/fat, and muscle) of TBSFs at the last time point (40th day after administration), suggesting that tilmicosin in TBSFs depleted slowly. Based on our experiments, the recommended withdrawal time of tilmicosin for TBSFs after oral administration for three consecutive days at a dose of 75 mg/L in water should be 32 days, which is much longer than the duration specified by Chinese regulatory authorities (10 days), and the abundance of melanin in TBSFs might be responsible for this phenomenon. Hence, a special use and withdrawal procedure of veterinary drugs in TBSFs is needed, and it is essential to focus on potential involvement of melanin in tilmicosin accumulation.

Pharmacokinetics and Tissue Distribution of Albendazole and Its Three Metabolites in Yellow River Carp (Cyprinus carpio haematopterus) after Single Oral Administration

This study aimed to evaluate the pharmacokinetics and tissue distribution of albendazole (ABZ) and its three metabolites─albendazole sulfoxide (ABZSO), albendazole sulfone (ABZSO2), and albendazole-2-aminosulfone (ABZ-2-NH2-SO2)─in Yellow River carp (Cyprinus carpio haematopterus) reared at 17.2 ± 1.1 °C after single oral administration of 12 mg/kg body weight (BW) ABZ. The concentrations of ABZ and its metabolites in different samples were measured using high performance liquid chromatography (HPLC). Pharmacokinetic parameters for ABZSO2 and ABZ-2-NH2-SO2 were not estimated due to their low levels. Pharmacokinetic analysis of ABZ and ABZSO was conducted using average concentration-time data with Phoenix software. The Cmax values (μg/mL or μg/g) of ABZ in skin-on muscle, plasma, bile, kidney, gills, liver, and intestine were 0.65, 0.70, 1.01, 1.61, 1.71, 2.42, and 3.34, respectively. The elimination half-life (t1/2λZ) of ABZ was longest in skin-on muscle (37.92 h), followed by the liver (32.07 h), gills (31.92 h), bile (31.51 h), kidney (26.96 h), intestine (20.81 h), and plasma (19.86 h). For ABZSO, the Cmax values (μg/mL or μg/g) in plasma, skin-on muscle, gills, intestine, liver, kidney, and bile were 0.46, 0.76, 0.89, 1.13, 1.54, 1.89, and 3.78, respectively. These findings indicate that ABZ and ABZSO are widely distributed and metabolized slowly in Yellow River carp after single oral administration. The higher ABZ concentrations in the liver and kidney suggest that these are the main metabolic organs for ABZ, while the elevated levels of ABZSO in bile indicate that bile excretion is the main pathway of ABZSO elimination. Based on the marker residue (ABZ-2-NH2-SO2) and its maximum residue limit (MRL) of 0.1 μg/g in skin-on muscle recommended by China, no withdrawal period was required for ABZ in Yellow River carp after a single oral dose of 12 mg/kg BW. However, using the marker residue (the sum of ABZ and its three metabolites) and the MRL of 0.1 μg/g for ruminants recommended by the EU, the withdrawal period was calculated to be 7 days or 118 °C-day under the same dosing regimen.

Pharmacokinetics of Enrofloxacin and Its Metabolite Ciprofloxacin in Nanyang Cattle

The objective of this study was to determine the pharmacokinetics of enrofloxacin and its metabolite, ciprofloxacin, in Nanyang cattle after a single intravenous (IV), and intramuscular (IM) administration of enrofloxacin at 2.5 mg/kg body weight (BW). Blood samples were collected at predetermined time points. Enrofloxacin and ciprofloxacin concentrations in plasma were simultaneously determined using a high-performance liquid chromatography (HPLC) assay method and subjected to a non-compartmental analysis. After IV administration, enrofloxacin had a mean (±SD) volume of distribution at steady state (V SS) of 1.394 ± 0.349 L/kg, a terminal half-life (t 1/2λz ) of 3.592 ± 1.205 h, and a total body clearance (Cl) of 0.675 ± 0.16 L/h/kg. After IM administration, enrofloxacin was absorbed relatively slowly but completely, with a mean absorption time (MAT) of 6.051 ± 1.107 h and a bioavailability of 99.225 ± 7.389%. Both compounds were detected simultaneously in most plasma samples following both routes of administration, indicating efficient biotransformation of enrofloxacin to ciprofloxacin. After IV injection, the peak concentration (C max) of ciprofloxacin was 0.315 ± 0.017 μg/mL, observed at 0.958 ± 0.102 h. Following IM injection, the corresponding values were 0.071 ± 0.006 μg/mL and 3 ± 1.095 h, respectively. Following IV and IM administration, the conversion ratio of enrofloxacin to ciprofloxacin was calculated as 59.2 ± 9.6% and 31.2 ± 7.7%, respectively. The present results demonstrated favorable pharmacokinetic profiles for enrofloxacin, characterized by complete absorption with relatively slow kinetics, extensive distribution, efficient biotransformation to ciprofloxacin, and prolonged elimination in Nanyang cattle.

Deciphering Oxidative Stress in Cardiovascular Disease Progression: A Blueprint for Mechanistic Understanding and Therapeutic Innovation

Oxidative stress plays a pivotal role in the pathogenesis and progression of cardiovascular diseases (CVDs). This review focuses on the signaling pathways of oxidative stress during the development of CVDs, delving into the molecular regulatory networks underlying oxidative stress in various disease stages, particularly apoptosis, inflammation, fibrosis, and metabolic imbalance. By examining the dual roles of oxidative stress and the influences of sex differences on oxidative stress levels and cardiovascular disease susceptibility, this study offers a comprehensive understanding of the pathogenesis of cardiovascular diseases. The study integrates key findings from current research in three comprehensive ways. First, it outlines the major CVDs associated with oxidative stress and their respective signaling pathways, emphasizing oxidative stress's central role in cardiovascular pathology. Second, it summarizes the cardiovascular protective effects, mechanisms of action, and animal models of various antioxidants, offering insights into future drug development. Third, it discusses the applications, advantages, limitations, and potential molecular targets of gene therapy in CVDs, providing a foundation for novel therapeutic strategies. These tables underscore the systematic and integrative nature of this study while offering a theoretical basis for precision treatment for CVDs. A major contribution of this study is the systematic review of the differential effects of oxidative stress across different stages of CVDs, in addition to the proposal of innovative, multi-level intervention strategies, which open new avenues for precision treatment of the cardiovascular system.

Machine learning and molecular docking prediction of potential inhibitors against dengue virus

Introduction

Dengue Fever continues to pose a global threat due to the widespread distribution of its vector mosquitoes, Aedes aegypti and Aedes albopictus. While the WHO-approved vaccine, Dengvaxia, and antiviral treatments like Balapiravir and Celgosivir are available, challenges such as drug resistance, reduced efficacy, and high treatment costs persist. This study aims to identify novel potential inhibitors of the Dengue virus (DENV) using an integrative drug discovery approach encompassing machine learning and molecular docking techniques.

Method

Utilizing a dataset of 21,250 bioactive compounds from PubChem (AID: 651640), alongside a total of 1,444 descriptors generated using PaDEL, we trained various models such as Support Vector Machine, Random Forest, k-nearest neighbors, Logistic Regression, and Gaussian Naïve Bayes. The top-performing model was used to predict active compounds, followed by molecular docking performed using AutoDock Vina. The detailed interactions, toxicity, stability, and conformational changes of selected compounds were assessed through protein-ligand interaction studies, molecular dynamics (MD) simulations, and binding free energy calculations.

Results

We implemented a robust three-dataset splitting strategy, employing the Logistic Regression algorithm, which achieved an accuracy of 94%. The model successfully predicted 18 known DENV inhibitors, with 11 identified as active, paving the way for further exploration of 2683 new compounds from the ZINC and EANPDB databases. Subsequent molecular docking studies were performed on the NS2B/NS3 protease, an enzyme essential in viral replication. ZINC95485940, ZINC38628344, 2',4'-dihydroxychalcone and ZINC14441502 demonstrated a high binding affinity of -8.1, -8.5, -8.6, and -8.0 kcal/mol, respectively, exhibiting stable interactions with His51, Ser135, Leu128, Pro132, Ser131, Tyr161, and Asp75 within the active site, which are critical residues involved in inhibition. Molecular dynamics simulations coupled with MMPBSA further elucidated the stability, making it a promising candidate for drug development.

Conclusion

Overall, this integrative approach, combining machine learning, molecular docking, and dynamics simulations, highlights the strength and utility of computational tools in drug discovery. It suggests a promising pathway for the rapid identification and development of novel antiviral drugs against DENV. These in silico findings provide a strong foundation for future experimental validations and in-vitro studies aimed at fighting DENV.

Residue Elimination Patterns and Determination of the Withdrawal Times of Seven Antibiotics in Eggs of Taihang Chickens

The objective of this study was to examine the residue elimination patterns of seven antibiotics in the eggs of Taihang chickens under free-range conditions and develop suitable withdrawal times (WDTs). A total of 240 healthy Taihang chickens, aged 180 days, were randomly divided into eight groups of 30 birds each. The first seven groups were administered oxytetracycline, chlortetracycline, erythromycin, tylosin, tylvalosin, lincomycin, and tiamulin, respectively, in accordance with the maximum dosages and longest durations of treatment recommended by the Veterinary Pharmacopoeia of the People's Republic of China. Group 8 served as the control group, and the test period continued until no drug residue could be detected. The results demonstrate that the residues of oxytetracycline, chlortetracycline, tylosin, tylvalosin, and tiamulin throughout the test period were below the maximum residue limits (MRLs) outlined in GB 31650-2019, "National food safety standard-Maximum residue limits for veterinary drugs in foods". The egg yolk was identified as the target tissue for estimating the withdrawal time periods (WDTs) of these seven drugs. It was thus concluded that the recommended withdrawal time for tiamulin should be 0 days. However, the WDTs of oxytetracycline, chlortetracycline, tylosin, tylvalosin, were 2.8, 0.3, 2.4, and 7.4, respectively, when the upper limit of the 95% confidence interval was found to be lower than the MRLs. It was thus determined that the recommended WDTs for oxytetracycline, chlortetracycline, tylosin, and tylvalosin should be 3, 1, 3, and 8 days, respectively. In contrast, erythromycin and lincomycin exhibited concentrations below the permitted MRLs on days 7 and 8, respectively. However, the upper limits of the 95% confidence intervals for erythromycin and lincomycin were found to be below the MRLs when the WDTs were 11 and 8.9, respectively. This suggests that the recommended WDTs for these two antibiotics should be 11 days and 9 days.

Pharmacokinetics and Pharmacodynamics Evaluation of Amoxicillin Against Staphylococcus pseudintermedius in Dogs

Antibiotic resistance in bacteria from companion animals poses significant public health risks. Prudent antibiotic use, particularly through pharmacokinetics/pharmacodynamics modeling, is crucial for minimizing resistance. We investigated the pharmacokinetics/pharmacodynamics of amoxicillin (AMX) against Staphylococcus pseudintermedius. A pharmacokinetic study was conducted on healthy dogs subcutaneously injected with a dose of 15 mg/kg AMX. The antibacterial efficacy of AMX was evaluated against a standard strain from animals (KCTC 3344) and clinical isolates from dogs (B-2, B-7, and B-8), with minimum inhibitory concentrations (MICs) of 0.25, 0.5, 64, and 16 μg/mL, respectively. The half-life of AMX was 7 h, allowing for extended drug efficacy. The time above MIC (%T > MIC) values indicated that the AMX concentrations were maintained above MICs of the two susceptible strains (KCTC 3344 and B-2) for more than 80% of the time when dosed at a one-day interval, suggesting an effective treatment. The area under the curve over 24 h/MIC ratios confirmed the bacteriostatic, bactericidal, and bacterial eradication effects of AMX against S. pseudintermedius strains, except for B-7 (the most resistant strain). These results support improved clinical dosing strategies for AMX against S. pseudintermedius infections in dogs.

Pharmacokinetics, optimal dosages and withdrawal time of amoxicillin in Nile tilapia (Oreochromis niloticus) reared at 25 and 30 °C

Knowledge of amoxicillin (AMX) pharmacokinetics (PK) and tissue residues in fish, which is necessary for prudent drug use, remains limited. The study aimed to explore the PK characteristics of AMX in Nile tilapia (Oreochromis niloticus) reared at 25 and 30 °C as well as to determine optimal dosages and drug withdrawal time (WDT). In the PK investigation, the fish received a single dose of 40 mg/kg AMX via oral gavage, and the optimal dosage was determined by the pharmacokinetic-pharmacodynamic approach. In the tissue residue study, the fish were orally gavaged with 40 mg/kg/day AMX once daily for 5 days and the WDT was established by the linear regression analysis. The results revealed the temperature-dependent drug elimination; the clearance relative to bioavailability (CL/F) and elimination half-life at 30 °C (0.180 L/kg/h and 6.06 h, respectively) were about twice those at 25 °C (0.090 L/kg/h and 10.49 h, respectively). The optimal dosages at the minimum inhibitory concentration (MIC) of 2 μg/mL were 10.97 (25 °C) and 41.03 (30 °C) mg/kg/day, respectively. Finally, following the multiple oral administration, the muscle/skin residue of AMX on day 1 after the last dosing at 25 and 30 °C were 548 and 264 ng/g, respectively. The average tissue residues were depleted below the maximum residue limits (MRL) of 50 μg/kg on day 5 (25 °C) and 3 (30 °C), respectively, and the WDT were 6 and 4 days when rearing at 25 and 30 °C, respectively. This knowledge serves as a practical guideline for responsible use of AMX in treating bacterial diseases in Nile tilapia aquaculture.

Dynamic Shifts in Antibiotic Residues and Gut Microbiome Following Tilmicosin Administration to Silkie Chickens

Tilmicosin, an antibiotic widely used in animal husbandry to prevent and treat bacterial infections, raises concerns due to its residual accumulation, which impacts both animal health and food safety. In this study, we conducted a comprehensive analysis of tilmicosin clearance patterns in different tissues, assessed physiological impacts through blood biochemistry, and investigated changes in gut microbial composition with 16S rRNA sequencing of the tilmicosin-treated Silkie chickens. Initially, we observed rapid peaks in tilmicosin residues in all tissues within 1 day after treatment, but complete metabolism took longer, extending beyond 9 days. Moreover, tilmicosin treatment significantly decreased serum levels of total bile acid, blood urea nitrogen, and uric acid, while increasing the levels of direct bilirubin, total bilirubin, and glutathione peroxidase at day 3, followed by a decrease from day 5 onwards. The effects of tilmicosin use on microbial composition and diversity lasted for an extended period, with the relative abundance of Proteobacteria remaining significantly different between the control and tilmicosin-treated groups at 120 days. Additionally, correlation analysis revealed a strong positive correlation between Mucispirillum_schaedleri and tilmicosin residue in all tissues, while Parabbacteroide_distasonis, Faecalibacterium_prausnitzii, and others exhibited negative correlations with tilmicosin residue. Overall, our study indicates a significant correlation between intestinal microbes and antibiotic residues, providing a theoretical basis for guiding the withdrawal period after antibiotic use.

Comparison of the Minimum Inhibitory and Mutant Prevention Drug Concentrations for Pradofloxacin and 7 Other Antimicrobial Agents Tested Against Swine Isolates of Actinobacillus pleuropneumoniae and Pasteurella multocida

Pradofloxacin is a dual targeting, bactericidal fluoroquinolone recently approved for treating bacteria causing swine respiratory disease. Currently, an abundance of in vitro data does not exist for pradofloxacin. We determined the minimum inhibitory concentration (MIC) and mutant prevention concentrations (MPC) of pradofloxacin compared to ceftiofur, enrofloxacin, florfenicol, marbofloxacin, tildipirosin, tilmicosin and tulathromycin against swine isolates of Actinobacillus pleuropneumoniae and Pasteurella multocida. Overall, pradofloxacin had the lowest MIC and MPC values as compared to the other agents tested. For example, pradofloxacin MIC values for 50%, 90% and 100% of A. pleuropneumoniae strains were ≤0.016 µg/mL, ≤0.016 µg/mL and ≤0.016 µg/mL and for P. multocida were ≤0.016 µg/mL, ≤0.016 µg/mL and 0.031 µg/mL, respectively. The MPC values for 50%, 90% and 100% of A. pleuropneumoniae strains were 0.031 µg/mL, 0.063 µg/mL and 0.125 µg/mL and for P. multocida were ≤0.016 µg/mL, 0.031 µg/mL and 0.0.063 µg/mL, respectively. By MPC testing, all strains were at or below the susceptibility breakpoint. Based on MPC testing, pradofloxacin appears to have a low likelihood for resistance selection. This study represents the most comprehensive in vitro comparison of the above noted drugs and the first report for pradofloxacin and tildipirosin.

Effect of Body Size on Plasma and Tissue Pharmacokinetics of Danofloxacin in Rainbow Trout (Oncorhynchus mykiss)

Danofloxacin is a fluoroquinolone antibiotic approved for use in fish. It can be used for bacterial infections in fish of all body sizes. However, physiological differences in fish depending on size may change the pharmacokinetics of danofloxacin and therefore its therapeutic efficacy. In this study, the change in the pharmacokinetics of danofloxacin in rainbow trout of various body sizes was revealed for the first time. The objective of this investigation was to compare the plasma and tissue pharmacokinetics of danofloxacin in rainbow trout of different body sizes. The study was conducted at 14 ± 0.5 °C in fish of small, medium, and large body size and danofloxacin was administered orally at a dose of 10 mg/kg. Concentrations of this antimicrobial in tissues and plasma were quantified by high performance liquid chromatography with ultraviolet detector. The plasma elimination half-life (t1/2ʎz), volume of distribution (Vdarea/F), total clearance (CL/F), peak concentration (Cmax), and area under the plasma concentration-time curve (AUC0-last) were 27.42 h, 4.65 L/kg, 0.12 L/h/kg, 2.53 µg/mL, and 82.46 h·µg/mL, respectively. Plasma t1/2ʎz, AUC0-last and Cmax increased concomitantly with trout growth, whereas CL/F and Vdarea/F decreased. Concentrations in liver, kidney, and muscle tissues were higher than in plasma. Cmax and AUC0-last were significantly higher in large sizes compared to small and medium sizes in all tissues. The scaling factor in small, medium, and large fish was 1.0 for bacteria with MIC thresholds of 0.57, 0.79, and 1.01 µg/mL, respectively. These results show that therapeutic efficacy increases with body size. However, since increases in danofloxacin concentration in tissues of large fish may affect withdrawal time, attention should be paid to the risk of tissue residue.

Liver damage and lipid metabolic dysregulation in adult zebrafish (Danio rerio) induced by spirotetramat

Spirotetramat, an insecticide derived from cycloketone and extensively utilized in agricultural production, has been reported to be toxic to an array of aquatic organisms. Previous studies have indicated that spirotetramat can cause toxicity such as impaired ovarian development and apoptosis in zebrafish, but its toxicological effects on lipid metabolism and liver health in zebrafish remain unclear. In this study, we explored the effects of spirotetramat exposure on zebrafish (Danio rerio) by examining key markers of lipid metabolism, alterations in gene expression related to this process, and histological characteristics of the liver. Spirotetramat significantly reduced the condition factor, triglycerides and low-density lipoprotein cholesterol levels at 2 mg/L. The expression of genes related to fatty acid synthesis (acacb), β-oxidation (acox1, pparda) and pro-inflammatory cytokines (tnf-α, il-1β) was downregulated. However, the expression of genes related to lipid transport and uptake (cd36, ppara) and output (apob) was upregulated. The activity of alanine aminotransferase was significantly inhibited. Histopathology results showed that spirotetramat exposure led to liver cell vacuolation and necrosis. In addition, molecular docking results of spirotetramat and lipid transport related protein (ACC, ApoB) in both zebrafish and human showed the binding energy of human proteins is lower than that for zebrafish, and that the number of hydrogen bonds formed was higher. It is speculated that spirotetramat may also pose a significant potential hazard to humans, potentially affecting human lipid metabolism and health. This study expunge shed light on the ecological toxicity of spirotetramat by showing how it disrupts lipid metabolism and causes tissue damage specifically in zebrafish liver, contributing to a deeper understanding of its harmful effects in aquatic environment.

Effect of tributyltin exposure on the embryonic development and behavior of a molluscan model species, Lymnaea stagnalis

The presence of the organotin compound tributyltin (TBT) in aquatic ecosystems has been a serious environmental problem for decades. Although a number of studies described the negative impact of TBT on mollusks at different levels, investigations connected to its potential effects during embryogenesis have been neglected. For a better understanding of the impact of TBT on mollusks, in the present study, embryos of previously TBT-treated or not treated specimens of the great pond snail (Lymnaea stagnalis) were exposed to 100 ng L-1 TBT from egg-laying (single-cell stage) until hatching. According to our results, TBT significantly delayed hatching and caused shell malformation. TBT transiently decreased the locomotion (gliding) and also reduced the feeding activity, demonstrating for the first time that this compound can alter the behavioral patterns of molluscan embryos. The heart rate was also significantly reduced, providing further support that cardiac activity is an excellent indicator of metal pollution in molluscan species. At the histochemical level, tin was demonstrated for the first time in TBT-treated hatchlings with intensive reaction in the central nervous system, kidney, and hepatopancreas. Overall, the most notable effects were observed in treated embryos derived from TBT treated snails. Our findings indicate that TBT has detrimental effects on the development and physiological functions of Lymnaea embryos even at a sub-lethal concentration, potentially influencing their survival and fitness. Highlighting our observations, we have demonstrated previously unknown physiological changes (altered heart rate, locomotion, and feeding activity) caused by TBT, as well as visualized tin at the histochemical level in a molluscan species for the first time following TBT exposure. Further studies are in progress to reveal the cellular and molecular mechanisms underlying the physiological and behavioral changes described in the present study.

Residue depletion profiles and withdrawal intervals of florfenicol and its metabolite florfenicol amine in plasma and milk of lactating goats after repeated subcutaneous administrations

Florfenicol is a broad-spectrum and bacteriostatic antibiotic with a time-dependent killing action. It is commonly used to treat respiratory diseases in goats in an extra-label manner. This study aimed to determine the plasma pharmacokinetics and milk residue depletion profiles and calculate the milk withdrawal interval (WDI) of florfenicol and its main metabolite florfenicol amine in lactating goats. Five healthy lactating goats were administered with 40 mg/kg florfenicol by subcutaneous injection, twice, 96 h apart. Plasma and milk samples were collected up to 864 h post the first injection. Non-compartmental analysis was used to estimate the plasma pharmacokinetic parameters. Milk WDIs were calculated using the U.S. Food and Drug Administration (FDA) method and European Medicines Agency (EMA) method. A Monte Carlo simulation was performed to generate simulated data for five virtual animals to meet the data requirement of the FDA method. The calculated milk WDIs based on florfenicol, florfenicol amine, and the combined (the sum of florfenicol and florfenicol amine) were 720.28, 690.45, and 872.69 h after the last injection using the FDA method. In conclusion, this study improves our understanding on the plasma pharmacokinetics and milk residue depletion kinetics of florfenicol and florfenicol amine in lactating ruminants after subcutaneous injections.

Effect of single parenteral administration of marbofloxacin on bacterial load and selection of resistant Enterobacteriaceae in the fecal microbiota of healthy pigs

BACKGROUND

Antimicrobial resistance (AMR) is a global concern impacting both humans, animals and their environment. The use of oral antimicrobials in livestock, particularly in pigs, has been identified as a driver in the selection of AMR bacteria. The aim of the present study was to evaluate the effects of a single intramuscular (IM) dose of marbofloxacin (8 mg/kg) on Enterobacteriaceae and E. coli populations, as well as on fluoroquinolone resistance within the fecal microbiota of pigs. Twenty healthy pigs, 60-days old, were divided into two groups: a treated group (n = 13) and a control group (n = 7) and were monitored over a 28-day experimental period. Fecal samples were collected from all animals for the isolation of E. coli and Salmonella strains. The minimum inhibitory concentration (MIC) of marbofloxacin for the isolates recovered on MacConkey agar supplemented with 1 or 4 µg/mL of marbofloxacin and for some generic E. coli isolates (recovered from MacConkey agar not supplemented with marbofloxacin) was determined using the broth microdilution method. Genomic DNA was extracted from the confirmed bacterial strains and sequenced using the Sanger method to identify mutations in the quinolone resistance determining regions (QRDRs) of the gyrA and parC genes.

RESULTS

The single IM administration of marbofloxacin resulted in a significant decrease in Enterobacteriaceae and E. coli fecal populations from days 1 to 3 post- treatment. No Salmonella isolates were detected in either group, and no marbofloxacin-resistant E. coli isolates were identified. The MIC of the selected generic E. coli strains (n = 100) showed an increase to up to 0.5 µg/mL between days 1 and 3 post-treatment but remained below the clinical breakpoint of marbofloxacin resistance (4 µg/mL). Sequencing of these isolates revealed no mutations in gyrA and parC genes.

CONCLUSIONS

The present study showed that this dosing regimen of marbofloxacin significantly decreases the fecal shedding of Enterobacteriaceae and E. coli populations in pigs, while limiting the selection of marbofloxacin-resistant E. coli isolates. These findings warrant validation in sick pigs to support the selective use of this antibiotic solely in cases of clinical disease, thereby minimizing the reliance on conventional (metaphylactic) group treatments in pigs.

The outer membrane protein, OMP71, of Riemerella anatipestifer, mediates adhesion and virulence by binding to CD46 in ducks

The Riemerella anatipestifer bacterium is known to cause infectious serositis in ducklings. Moreover, its adherence to the host's respiratory mucosa is a critical step in pathogenesis. Membrane cofactor protein (MCP; CD46) is a complement regulatory factor on the surface of eukaryotic cell membranes. Bacteria have been found to bind to this protein on host cells. Outer membrane proteins (OMPs) are necessary for adhesion, colonisation, and pathogenicity of Gram-negative bacteria; however, the mechanism by which R. anatipestifer adheres to duck cells remains unclear. In this study, pull-down assays and LC-MS/MS identified eleven OMPs interacting with duck CD46 (dCD46), with OMP71 exhibiting the strongest binding. The ability of an omp71 gene deletion strain to bind dCD46 is weaker than that of the wild-type strain, suggesting that this interaction is important. Further evidence of this interaction was obtained by synthesising OMP71 using an Escherichia coli recombinant protein expression system. Adhesion and invasion assays and protein and antibody blocking assays confirmed that OMP71 promoted the R. anatipestifer YM strain (RA-YM) adhesion to duck embryo fibroblasts (DEFs) by binding to CD46. Tests of the pathogenicity of a Δomp71 mutant strain of RA-YM on ducks compared to the wild-type parent supported the hypothesis that OMP71 was a key virulence factor of RA-YM. In summary, the finding that R. anatipestifer exploits CD46 to bind to host cells via OMP71 increases our understanding of the molecular mechanism of R. anatipestifer invasion. The finding suggests potential targets for preventing and treating diseases related to R. anatipestifer infection.