Natalie Norton

Polymyxin B protects horses against induced endotoxaemia in vivo

REASONS FOR PERFORMING STUDY A safe, affordable and effective treatment for endotoxaemia in horses is needed in order to reduce the incidence of this potentially fatal condition. OBJECTIVE To evaluate the effect of polymyxin B (PMB) on signs of experimentally-induced endotoxaemia. HYPOTHESIS PMB ameliorates the adverse effects of endotoxaemia without causing nephrotoxicity. METHODS Four groups of 6 healthy mature horses each received 20 ng endotoxin/kg bwt i.v. over 30 mins. Additionally, each group received one of the following i.v.; 5000 u PMB/kg bwt 30 mins before endotoxin infusion; 5000 u PMB/kg bwt 30 mins after endotoxin infusion; 1000 u PMB/kg bwt 30 mins prior to endotoxin infusion; or saline. Clinical response data and samples were collected to determine neutrophil count, serum tumour necrosis factor (TNF) activity, plasma thromboxane B2 concentration and urine gamma glutamyltranspeptidase (GGT) to creatinine ratio. RESULTS Treatment with PMB before or after administration of endotoxin significantly reduced fever, tachycardia and serum TNF, compared to horses receiving saline. The differences in response to endotoxin were greatest between horses that received saline vs. those that received 5000 u PMB/kg bwt prior to endotoxin. Urine GGT:creatinine did not change significantly. CONCLUSIONS AND POTENTIAL RELEVANCE This study indicates that PMB may be a safe and effective treatment of endotoxaemia, even when administered after onset. Although nephrotoxicity was not demonstrated with this model, caution should be exercised when using PMB in azotaemic patients.

Rapid infusion of a phospholipid emulsion attenuates the effects of endotoxaemia in horses

REASONS FOR PERFORMING STUDY Endotoxaemia currently is associated with a poor prognosis in horses. The results of recent trials in other species indicate that phospholipid emulsions reduce the deleterious effects of endotoxin (LPS). However, in a previous study in horses, a 2 h infusion of emulsion caused an unacceptable degree of haemolysis. HYPOTHESIS Rapid administration of a lower total dose of emulsion would reduce the effects of LPS and induce less haemolysis; the emulsion would reduce inflammatory effects of LPS in vitro. METHODS Twelve healthy horses received an i.v. infusion either of saline or a phospholipid emulsion (100 mg/kg), followed immediately by E. coli 055:B5 LPS (30 ng/kg). Clinical parameters, haematological profiles, serum tumour necrosis factor (TNF) activity, serum lipid profiles, urine analyses and severity of haemolysis were monitored before and at selected times after LPS. Monocytes were also incubated in vitro with LPS in the presence or absence of emulsion, after which TNF and tissue factor activities were determined. RESULTS Clinical signs of endotoxaemia were reduced in horses receiving the emulsion, including clinical score, heart rate, rectal temperature, serum TNF activity, and the characteristic leucopenic response to LPS, when compared to horses not receiving the emulsion. Three horses receiving the emulsion had none, 2 had mild and one had moderate haemolysis. There were no differences in urinalysis results and creatinine concentrations, either within the groups over time or between the groups. Serum concentrations of phosphatidylcholine, bile acids and triglycerides peaked immediately after the infusion; there were no significant changes in concentrations of nonesterified fatty acids or cholesterol. Incubation of equine monocytes with emulsion prevented LPS-induced TNF and tissue factor activities. CONCLUSIONS Rapid administration of emulsion significantly reduced inflammatory effects of LPS in vivo and caused a clinically insignificant degree of haemolysis. The results of the in vitro studies indicate that emulsion prevents not only LPS-induced synthesis of cytokines, but also expression of membrane-associated mediators (i.e. tissue factor). POTENTIAL RELEVANCE Rapid i.v. administration of emulsions containing phospholipids that bind endotoxin may provide a clinically useful method of treating endotoxaemia in horses.

Hypothalamic-Pituitary-Adrenal Axis Assessment in Healthy Term Neonatal Foals Utilizing a Paired Low Dose/High Dose ACTH Stimulation Test

BACKGROUND Hypothalamic-pituitary-adrenal (HPA) axis function is dynamic in the neonatal foal. The paired low dose/high dose cosyntropin (ACTH) stimulation test allows comprehensive HPA axis assessment, but has not been evaluated in neonatal foals. HYPOTHESIS Foal age will significantly affect cortisol responses to a paired 10 and 100 microg dose cosyntropin stimulation test in healthy neonatal foals. ANIMALS Twenty healthy neonatal foals. METHODS HPA axis function was assessed in 12 foals at birth and at 12-24, 36-48 hours, and 5-7 days of age. At each age, basal cortisol and ACTH concentrations were measured and cortisol responses to 10 and 100 microg cosyntropin were assessed with a paired ACTH stimulation test protocol. Eight additional 36-48-hour-old foals received saline instead of 10 microg cosyntropin in the same-paired ACTH stimulation test design. RESULTS At birth, foals had significantly higher basal cortisol and ACTH concentrations and higher basal ACTH : cortisol ratios compared with foals in all other age groups. A significant cortisol response to both the 10 and 100 microg doses of cosyntropin was observed in all foals. The magnitude of the cortisol response to both doses of cosyntropin was significantly different across age groups, with the most marked responses in younger foals. There was no effect of the paired ACTH stimulation test design itself on cortisol responses. CONCLUSIONS AND CLINICAL IMPORTANCE A paired 10 and 100 microg cosyntropin stimulation test can be used to evaluate HPA axis function in neonatal foals. Consideration of foal age is important in interpretation of HPA axis assessment.

Rhizobium Sin-1 Lipopolysaccharide (LPS) Prevents Enteric LPS-induced Cytokine Production

Endotoxin (lipopolysaccharide (LPS)), a component of Gram-negative bacteria, is among the most potent proinflammatory substances known. The lipid-A region of this molecule initiates the production of multiple host-derived inflammatory mediators, including cytokines (e.g. tumor necrosis factor-α (TNFα)). It has been a continuous effort to identify methods of interfering with the interaction between enteric LPS and inflammatory cells using natural and synthetic LPS analogs. Some of these LPS analogs (e.g. Rhodobacter spheroides LPS/lipid-A derivatives) are antagonists in human cells but act as potent agonists with cells of other species. Data reported here indicate that structurally novel LPS from symbiotic, nitrogen-fixing bacteria found in association with the root nodules of legumes do not stimulate human monocytes to produce TNFα. Furthermore, LPS from one of these symbiotic bacterial species,Rhizobium sp. Sin-1, significantly inhibits the synthesis of TNFα by human cells incubated with Escherichia coli LPS. Rhizobium Sin-1 LPS exerts these effects by competing with E. coli LPS for binding to LPS-binding protein and by directly competing with E. coli LPS for binding to human monocytes. Rhizobial lipid-A differs significantly from previously characterized lipid-A analogs in phosphate content, fatty acid acylation patterns, and carbohydrate backbone. These structural differences define the rhizobial lipid-A compounds as a potentially novel class of LPS antagonists that might well serve as therapeutic agents for the treatment of Gram-negative sepsis.

Efficacy of cyclo-oxygenase inhibition by two commercially available firocoxib products in horses

REASONS FOR PERFORMING STUDY Two firocoxib preparations for oral use are approved for use in animals in many countries: a chewable canine tablet and an equine paste. In order to reduce costs, many veterinarians use the canine product in horses even though this is an off-label use of the preparation. OBJECTIVE To determine the relative efficacy of 2 commercially available firocoxib products to inhibit prostaglandin E₂ (PGE2) synthesis after oral dosing in horses. STUDY DESIGN A crossover design using 8 adult horses (n = 4 for each preparation during each treatment period). Body weight range 532-614 kg. METHODS Horses received 57 mg of the assigned firocoxib preparation orally once daily for 7 days, with a 14 day washout period between drug crossover. Ten healthy adult light breed horses were used as no-treatment controls. During each treatment period, blood was taken before dosing on Days 0 and 7 and on Day 7 1 h after dosing for ex vivo lipopolysaccharide (LPS) stimulation to induce (PGE₂ ) synthesis. Heparinised plasma was also collected on Day 7 immediately prior to and 1 h after dosing to determine plasma firocoxib concentrations. RESULTS In the control group, there was no significant change in LPS-induced PGE2 over time. In contrast, immediately prior to and 1 h after treatment on Day 7, the mean LPS-induced PGE₂ concentration decreased significantly compared to Day 0 values in all treated horses. There was no difference in PGE₂ or plasma firocoxib concentrations between firocoxib treatment groups. CONCLUSION In this model, the canine chewable preparation of firocoxib was as effective as the equine paste formulation at reducing LPS-induced PGE₂ synthesis. POTENTIAL RELEVANCE The canine chewable preparation of firocoxib may be a suitable alternative to the paste formulation in horses for situations where extra-label drug use can be legally justified. The Summary is available in Chinese - see Supporting information.

Effect of Age, Season, Body Condition, and Endocrine Status on Serum Free Cortisol Fraction and Insulin Concentration in Horses

Background Increased free cortisol fraction is associated with insulin dysregulation (ID) in people with Metabolic Syndrome and Cushings Disease. Free cortisol has not been investigated in equine endocrine disorders. Hypotheses (1) In healthy horses, sex, age, body condition score (BCS), and season impact free cortisol; (2) free cortisol is increased in horses with Pituitary Pars Intermedia Dysfunction (PPID) or Equine Metabolic Syndrome (EMS). Animals Fifty‐seven healthy horses; 40 horses and ponies with PPID (n = 20) or EMS (n = 20). Methods Prospective study. Serum collected seasonally from healthy animals and archived serum from PPID and EMS animals was analyzed for insulin, total and free cortisol concentrations, and free cortisol fraction (FCF). Linear mixed models were used to determine effects of age, sex, season, and BCS on hormones in controls. Hormone measurements were compared between disease groups and age‐ and season‐matched controls with t‐tests. EMS and hyperinsulinemic PPID animals were combined in an ID (hyperinsulinemia) group. Results Free cortisol concentrations were increased in overweight/obese controls (0.3 ± 0.1 μg/dL) compared to lean controls (0.2 ± 0.1 μg/dL; P = .017). Mean FCF was significantly higher in animals with PPID (8.8 ± 5.8 μg/dL, P = .005) or ID (8.8 ± 10.2 μg/dL, P = .039) than controls (5.0 ± 0.9 μg/dL), but total cortisol concentrations were similar (P ≥ .350) (PPID: 4.2 ± 4.3 μg/dL; ID: 5.0 ± 4.5 μg/dL; controls: 4.6 ± 1.7 and 5.1 ± 2.1 μg/dL). Conclusions and Clinical Importance Increased FCF is associated with obesity in healthy horses and with ID (hyperinsulinemia) in horses and ponies with endocrine disease. Decreased plasma cortisol‐binding capacity could be a component of these endocrine disorders in horses.

Feline mesenchymal stem cells and supernatant inhibit reactive oxygen species production in cultured feline neutrophils

Feline bone marrow-derived MSCs (BMMSCs), adipose-derived MSCs (AMSCs) and fibroblasts (FBs) were isolated and cultured. Tri-lineage differentiation assays and flow cytometry were used to characterize MSCs. Neutrophils (NPs) were isolated from whole blood and the NPs production of reactive oxygen reactive oxygen species (ROS) was measured. NPs were cultured alone, with MSC culture supernatant (SN), BMMSCs or AMSCs. NPs incubated with BMMSCs had significantly lower ROS production than NPs incubated with AMSCs (p=0.0006) or FB (p<0.0001); NPs ROS production significantly decreased with increasing BMMSC cell number (p=0.0023) and significantly increased with NPs were incubated with FB compared to BMMSC (p=0.0003). Both BMMSC SN and AMSC SN had statistically significantly lower ROS production than FB SN when incubated with NPs (both p<0.0001). ROS production was significantly reduced with increased fractions of SN from BMMSCs (p=0.0467) and AMSCs (p=0.0017).

Daily endogenous cortisol production and hydrocortisone pharmacokinetics in adult horses and neonatal foals.

OBJECTIVE To compare daily endogenous cortisol production rate and the pharmacokinetics of an i.v. bolus of hydrocortisone between neonatal foals and adult horses. ANIMALS 10 healthy full-term 2- to 4-day-old foals and 7 healthy adult horses. PROCEDURES Blood samples were collected from each horse every 15 to 20 minutes for 24 hours for determination of 24-hour mean cortisol concentration. Afterward, dexamethasone (0.08 mg/kg) was administered i.v. to suppress endogenous cortisol production. Twelve hours afterward, hydrocortisone sodium succinate (1.0 mg/kg) was administered as a rapid i.v. bolus and serial blood samples were collected to determine hydrocortisone pharmacokinetics. Cortisol concentrations, daily cortisol production rate, and hydrocortisone pharmacokinetics were determined, and results were compared between adult horses and foals. RESULTS The mean ± SD 24-hour cortisol concentration was significantly lower in foals (20 ± 4 ng/mL) than in horses (26 ± 6 ng/mL), but the daily cortisol production rate was significantly greater in foals (6,710 ± 320 ng/kg/d) than in horses (2,140 ± 400 ng/kg/d). For hydrocortisone, foals had a significantly greater volume of distribution at steady state (1.92 ± 1.11 L/kg) and total body clearance (1.39 ± 0.108 L/kg/h) and significantly lower peak plasma concentration (1,051 ± 343 ng/mL) than did horses (0.58 ± 0.15 L/kg, 0.349 ± 0.065 L/kg/h, and 8,934 ± 3,843 ng/mL, respectively). CONCLUSIONS AND CLINICAL RELEVANCE Important differences were detected in cortisol production and metabolism between neonatal foals and adult horses consistent with lower plasma protein binding of cortisol in foals. This decrease may contribute to cortisol insufficiency during prolonged critical illness in neonatal foals.

Detection of endogenous cortisol in equine tears and blood at rest and after simulated stress.

OBJECTIVE To determine whether cortisol is present in equine tears at rest and during simulated stress and compare tear cortisol to serum free and total cortisol. MATERIALS AND METHODS Fourteen healthy adult horses were included. Paired tear total cortisol and serum total and free cortisol concentrations were measured with ELISA, chemiluminescent immunoassay, and ultrafiltration methodology, respectively, in 10 horses at rest once daily for five consecutive days. In an additional four horses, paired tear and serum samples were collected for cortisol measurement before and after adrenocorticotropic hormone (ACTH) stimulation (cosyntropin, 1 μg/kg IV). RESULTS Cortisol was detectable in equine tears at rest. Following ACTH stimulation, tear cortisol increased significantly from baseline at 60-120 min (P ≤ 0.001). Serum total and free cortisol also increased significantly at 30-180 min after ACTH stimulation (P ≤ 0.001). Both serum and tear cortisol returned to baseline concentrations by 360 min. Changes in tear cortisol were similarly associated with changes in serum total and free cortisol, although high tear cortisol concentrations suggest a portion of tear cortisol may be protein-bound. DISCUSSION Cortisol is present in equine tears and increases in concert with serum cortisol following ACTH stimulation. Further study is needed to determine whether endogenous cortisol in tears contributes to ocular pathology.

Validation of commercial ELISAs for quantifying anabolic growth factors and cytokines in canine ACD-A anticoagulated plasma

Platelet-rich plasma has been studied extensively in dogs, but validation of enzyme-linked immunosorbent assays (ELISAs) for quantifying anabolic growth factors and inflammatory cytokines in canine plasma prepared with citrate-based anticoagulants is not available. We performed a validation of commercial ELISAs for transforming growth factor–beta 1 (TGF-β1), platelet-derived growth factor–BB (PDGF-BB), vascular endothelial growth factor (VEGF), tumor necrosis factor–alpha (TNF-α), and interleukin–1 beta (IL-1β) for use with canine plasma prepared with acid–citrate–dextrose, solution A (ACD-A). Platelet-poor plasma (PPP) anticoagulated with ACD-A as well as PPP anticoagulated with ACD-A and spiked with the relevant canine recombinant proteins were evaluated with each ELISA to calculate the efficiency of spike recovery. Replicates of the spiked PPP were also assessed in 2 additional assays to quantify intra-assay and interassay precision. The efficiency of spike recovery was within 75–125% of the expected concentration for the TGF-β1, PDGF-BB, and VEGF ELISAs. The intra- and interassay variability were <25% for the TGF-β1, PDGF-BB, VEGF, and TNF-α ELISAs. The TGF-β1, PDGF-BB, and VEGF ELISAs demonstrate acceptable efficiency of spike recovery and intra- and interassay variability, whereas the TNF-α and IL-1β ELISAs did not meet industry standards of performance with ACD-A anticoagulated canine plasma.