Effects of administration of ascorbic acid and low-dose hydrocortisone after infusion of sublethal doses of lipopolysaccharide to horses

Application of blood parameters for the early diagnosis of natural ascending placentitis in pregnant mares

Placental infection is an important cause of late-term pregnancy loss and neonatal diseases in horses. Detection of changes in blood parameters especially during early placentitis could improve the diagnostic accuracy, treatment decision, and potential outcomes. The objectives of this 2-part study were to identify differences in circulating immunological, inflammatory, and hormonal parameters between mares with natural ascending placentitis and control mares; evaluate each and combination of parameters as predictors of placentitis; and determine how these parameters indicate severity of placentitis. Reproductive examination and blood sampling were prospectively performed on pregnant mares in a natural setting. Study 1 enrolled mares diagnosed with early stage of ascending placentitis based on ultrasonographic findings (n = 12), and gestationally age-matched mares with healthy pregnancies as controls (n = 12). Blood samples were classified as pre-onset (before) and early onset (at the time of ultrasonographic changes) of placentitis. There were no detected statistically significant differences between groups and timepoints in immunological and inflammatory parameters, including peripheral lymphocyte subpopulations, cytokine, and serum amyloid A concentrations. The placentitis group showed a reduced (P = 0.01) DHP/20α-DHP ratio when compared to the control group at the early onset timepoint. Plasma estradiol-17β concentration <359 pg/mL predicted ascending placentitis with acceptable accuracy (area under the curve, AUC = 0.71). Combined albumin <3.7 g/dL, estradiol-17β < 499 ng/mL, and DHP <33 ng/mL predicted 100 % of cases of ascending placentitis. In study 2, samples were classified according to the presence and severity of the abnormal ultrasonographic findings as mild (n = 11) and moderate-severe (n = 23), and gestationally age-matched with samples from control mares (n = 34). Mares with moderate-severe ascending placentitis had increased (P = 0.03) plasma 20α-DHP concentration and reduced (P = 0.03) DHP/20α-DHP ratio when compared to control mares. Our results suggest that the early events of ascending placentitis detected by ultrasonographic findings include hormonal alterations of feto-placental metabolism measurable in the mare's circulation, yet without obvious systemic immunological and inflammatory changes. Additional studies are warranted to further assess how hormonal markers and cutoff values could guide decisions for timely therapeutic intervention.

Pharmacologic Interventions to Immunologic and Immune-Mediated Conditions in Horses

Immunomodulators can stimulate, suppress, or regulate one or many aspects of the immune response. Use of a variety of immunostimulants, immunosuppressors, and anti-inflammatory drugs are described in horses, but the evidence supporting their efficacy is variable. Corticosteroids and nonsteroidal anti-inflammatory drugs are the best characterized immunomodulators in horses, but further study is needed to fully define their ideal dosing protocols and indications and to characterize the efficacy of other immunomodulators in equine medicine.

Monoclonal antibodies for equine IL-1β enable the quantification of mature IL-1β in horses

Interleukin-1β (IL-1β) is one of the key mediators of inflammation during innate immune responses. Mature bioactive IL-1β mediates essential host defense mechanisms but also has a mechanistic role in several autoinflammatory and degenerative diseases. In horses, specific and sensitive assays for IL-1β are crucial for immunological research on inflammatory processes and diseases. In this article, we describe the development of four monoclonal antibodies (mAbs) against equine IL-1β. The specificity of the new IL-1β mAbs was confirmed using a panel of equine recombinant cytokines and chemokines. The mAbs were validated for detection of native mature IL-1β in a fluorescent bead-based assay and for staining of IL-1β-producing immune cells by flow cytometry. The bead-based assay for equine IL-1β had a linear quantification range between 60 pg/ml to 960 ng/ml. Horse peripheral blood mononuclear cells (PBMC) secreted IL-1β after lipopolysaccharide (LPS) stimulation in time and dose dependent manner as quantified by the new equine IL-1β bead-based assay. A comparison of two commercial equine IL-1β ELISA kits with the new IL-1β fluorescent bead-based assay revealed that the bead-based assay improved the quantification of native equine IL-1β in LPS stimulated PBMC supernatants by detecting it with high intensity and a broad linear quantification range, while both ELISAs resulted in low signals and poor native IL-1β recognition. Intracellular staining and flow cytometric analysis confirmed that the main cellular source of IL-1β in equine PBMC after LPS stimulation were CD14+ monocytes. IL-1β secretion from PBMC was inhibited by a caspase inhibitor but protein translation within the cells was not, supporting the accumulation of pro-IL-1β within the cells even when proteolytic cleavage for IL-1β activation is missing. This confirmed the importance of specific mAbs for analyzing the biologically active, mature IL-1β in horses.

Retrospective evaluation of the effects of a single intraoperative dose of dexamethasone in horses undergoing exploratory laparotomy for small intestinal lesions (2008-2019): 240 cases

OBJECTIVE

To determine the effect of a single intraoperative dose of dexamethasone on the risk of postoperative reflux (POR) in horses undergoing small intestinal surgery and to investigate its association with incisional complications and short-term survival.

DESIGN

Retrospective cohort study over an 11-year period (2008-2019).

SETTING

UK-based private referral center.

ANIMALS

Two hundred and forty client-owned horses >6 months of age undergoing exploratory laparotomy for treatment of a small intestinal lesion.

INTERVENTIONS

Ninety-seven horses received a single intraoperative dose of dexamethasone (0.1 mg/kg, IV).

MEASUREMENTS AND MAIN RESULTS

Of 97 horses that received dexamethasone, 52 (53.6%) required small intestinal resection. Of 143 horses that did not receive dexamethasone, small intestinal resection was performed in 78 (54.5%). A total of 70 horses (29%) developed POR. There was no difference in the risk of POR between horses that received dexamethasone (25/97; 26%) and those that did not (45/143; 31%, P = 0.34). Risk factors associated with the development of POR included small intestinal resection (odds ratio [OR]: 4.55, 95% confidence interval [CI]: 2.27-9.11, P < 0.001), a PCV >40% 24 hours postoperatively (OR: 4.11, 95% CI: 2-8.45, P < 0.001), and a WBC count >10 × 109/L on admission (OR: 3.29, 95% CI: 1.47-7.41, P = 0.004). Dexamethasone was not associated with the odds of POR. Horses undergoing repeat laparotomy had a higher risk of incisional infection (OR: 8.07, 95% CI: 1.98-32.81, P = 0.004). Dexamethasone administration was not associated with incisional infection. The development of POR was negatively associated with short-term survival (OR: 0.07, 95% CI: 0.03-0.17, P ≤ 0.001). Dexamethasone administration was not retained in the final multivariable model for survival.

CONCLUSIONS

Intraoperative dexamethasone was not associated with the development of POR in this study population, nor did it have an effect on postoperative survival or incisional infection in horses undergoing surgical management of small intestinal disease.

Effects of intravenous administration of ascorbic acid (vitamin C) on oxidative status in healthy adult horses

BACKGROUND

Ascorbic acid (AA) is an antioxidant that might be beneficial for adjunctive treatment of sepsis in horses. The optimal dose and effects on oxidative status are unknown.

HYPOTHESIS

Ascorbic acid administration will increase plasma AA concentrations and decrease determinants of reactive oxygen metabolites (dROM), basal and stimulant-induced intraerythrocytic reactive oxygen species (ROS) concentrations, and stimulant-induced neutrophil ROS production, and increase plasma antioxidant capacity (PAC) in a dose-dependent manner.

ANIMALS

Eight healthy horses.

METHODS

Randomized placebo-controlled crossover study. Each horse received 4 single-dose IV treatments including AA at 25, 50, and 100 mg/kg and saline (placebo) with each treatment separated by ≥1 week. Blood was collected at baseline, 2 and 6 hours for assessment of plasma dROM and PAC via photometer, intraerythrocytic ROS by flow cytometry, and stimulant-induced neutrophil ROS by a fluorometric assay. Plasma AA concentrations were measured by high-performance liquid chromatography/electrochemical detection.

RESULTS

Ascorbic acid at 100 mg/kg resulted in decreased dROM 2 hours after treatment (P = .03, 95% CI 5.51-121.2, point estimate 63.3). There was no effect of AA on basal or stimulant-induced intraerythrocytic ROS (P = .88, 95% CI -0.156 to 0.081, point estimate -0.037; P = .93, 95% CI -0.123 to 0.112, point estimate -0.006, respectively), basal or stimulant-induced neutrophil ROS (P ≥ .12, 95% CI -644.9 to 56.2, point estimate -294.4), or PAC (P ≥ .64, 95% CI -1567 to 463.4, point estimate -552.0) at any dose or timepoint. Plasma AA concentrations increased in a dose-dependent manner.

CONCLUSIONS AND CLINICAL IMPORTANCE

High-dose administration of AA might provide antioxidant benefits in horses.

TLR4 and MD2 variation among horses with differential TNFα baseline concentrations and response to intravenous lipopolysaccharide infusion

Gram-negative bacterial septicemia is mediated through binding of lipopolysaccharide (LPS) to mammalian toll-like receptor protein 4 (TLR4). TLR4 and its cognate protein, myeloid differentiation factor 2 (MD2) form a heterodimeric complex after binding LPS. This complex induces a cascade of reactions that results in increased proinflammatory cytokine gene expression, including TNFα, which leads to activation of innate immunity. In horses, the immune response to LPS varies widely. To determine if this variation is due to differences in TLR4 or MD2, DNA from 15 healthy adult horses with different TNFα dynamics after experimental intravenous LPS infusion was sequenced across exons of TLR4 and MD2. Haplotypes were constructed for both genes using all identified variants. Four haplotypes were observed for each gene. No significant associations were found between either TNFα baseline concentrations or response to LPS and haplotype; however, there was a significant association (P value = 0.0460) between the baseline TNFα concentration and one MD2 missense variant. Three-dimensional structures of the equine TLR4-MD2-LPS complex were built according to haplotype combinations observed in the study horses, and the implications of missense variants on LPS binding were modeled. Although the sample size was small, there was no evidence that variation in TLR4 or MD2 explains the variability in TNFα response observed after LPS exposure in horses.

Equine peripheral blood CD14+ monocyte-derived macrophage in-vitro characteristics after GM-CSF pretreatment and LPS+IFN-γ or IL-4+IL-10 differentiation

Macrophages are a heterogeneous population of immune cells that exhibit dynamic plasticity, polarize into inflammatory or regulatory/pro-resolving macrophages, and influence the healing tissue microenvironment. This study evaluated the in-vitro morphological, proliferative, cell surface marker expression and cytokine/soluble factor secretion characteristics of control, GM-CSF pretreated and inflammatory (LPS+IFN-γ) and regulatory (IL-4 + IL-10) differentiated equine CD14+ monocyte-derived macrophages. Phase contrast microscopy demonstrated that LPS+IFN-γ-primed macrophages exhibited a rounded, granular morphology, whereas IL-4 +IL-10-primed macrophages were elongated with a spindle-shaped morphology. GM-CSF enhanced the proliferation rate of monocytes/macrophages during adherent in-vitro culture. Flow cytometry analysis showed that GM-CSF alone and GM-CSF pretreatment with LPS+IFN-γ or IL-4 +IL-10 priming increased CD86 immunopositivity by 2-fold (p = 0.6); and CD206 immunopositivity remained unchanged. GM-CSF pretreatment and subsequent priming with LPS and IFN-γ yielded inflammatory macrophages that secrete significantly increased quantities of IL-1β compared to control (p = 0.012) and IL-4 +IL-10-primed (p = 0.0047) macrophages. GM-CSF pretreatment followed by both LPS + IFN-γ and IL-4 + IL-10 priming significantly increased IL-1Ra secretion by 6-fold (p < 0.05). There were no differences in TGFβ-1 secretion among control, LPS+IFN-γ or IL-4 + IL-10 primed macrophages (p = 0.85). All groups contained an average of 643 ± 51.5 pg/mL of TGFβ1. Among the culture conditions evaluated, IL-4 +IL-10 priming for 24 h after 6 days of adherent culture yielded macrophages that were the least inflammatory compared to GM-CSF pretreated and LPS+IFN-γ or IL-4 +IL-10-primed macrophages. These results provide a basis for subsequent in-vitro and in-vivo studies that investigate macrophage-tissue cell interactions and related biological mechanisms relevant to the field of immunomodulatory approaches for enhancing tissue healing.

Effects of intravenous administration of peripheral blood-derived mesenchymal stromal cells after infusion of lipopolysaccharide in horses

BACKGROUND

A systemic and dysregulated immune response to infection contributes to morbidity and mortality associated with sepsis. Peripheral blood-derived mesenchymal stromal cells (PB-MSC) mitigate inflammation in animal models of sepsis. Allogeneic PB-MSC administered IV to horses is well-tolerated but therapeutic benefits are unknown.

HYPOTHESIS

After IV lipopolysaccharide (LPS) infusion, horses treated with PB-MSC would have less severe clinical signs, clinicopathological abnormalities, inflammatory cytokine gene expression, and oxidative stress compared to controls administered a placebo.

ANIMALS

Sixteen horses were included in this study.

METHODS

A randomized placebo-controlled experimental trial was performed. Sixteen healthy horses were assigned to 1 of 2 treatment groups (1 × 10⁹  PB-MSC or saline placebo). Treatments were administered 30 minutes after completion of LPS infusion of approximately 30 ng/kg. Clinical signs, clinicopathological variables, inflammatory cytokine gene expression, and oxidative stress markers were assessed at various time points over a 24-hour period.

RESULTS

A predictable response to IV LPS infusion was observed in all horses. At the dose administered, there was no significant effect of PB-MSC on clinical signs, clinicopathological variables, or inflammatory cytokine gene expression at any time point. Antioxidant potential was not different between treatment groups, but intracellular ROS increased over time in the placebo group. Other variables that changed over time were likely due to effects of IV LPS infusion.

CONCLUSIONS AND CLINICAL IMPORTANCE

Administration of allogeneic PB-MSC did not cause clinically detectable adverse effects in healthy horses. The dose of PB-MSC used here is unlikely to exert a beneficial effect in endotoxemic horses.

Pharmacokinetics of thiamine (vitamin B1) in adult horses after administration of three single intravenous doses

Thiamine is a vital co-factor for several anti-inflammatory and antioxidant processes that are critical for mitigation of sepsis-associated inflammation, but pharmacokinetic (PK) analysis has not been reported in horses. We hypothesized that IV thiamine hydrochloride (TH) at increasing dosages would result in corresponding increases in plasma thiamine concentrations without causing adverse effects. A randomized cross-over study was performed in 9 healthy horses that each received TH at 5, 10, and 20 mg/kg IV. Blood was collected immediately prior to drug administration and at several time points thereafter. High-performance liquid chromatography with mass spectrometry was used to quantify thiamine concentrations at each time point. Non-compartmental PK methods showed that IV TH resulted in supraphysiologic plasma concentrations with a short half-life (0.77-1.12 h) and no adverse clinical signs were observed. The terminal rate constant decreased as the dosage increased (p < .0001) and clearance significantly decreased at the 20 mg/kg dosage (p = .0011). The area under the curve (AUC) increased in a non-linear fashion. These findings suggest that thiamine follows non-linear elimination kinetics in horses, which is likely due to saturation of renal elimination. Future studies are needed to identify therapeutic plasma concentrations and develop thiamine dosing recommendations for horses.

Effects of administration of ascorbic acid and low-dose hydrocortisone after infusion of sublethal doses of lipopolysaccharide to horses

Background

Sepsis is associated with ascorbic acid (AA) depletion and critical illness‐related corticosteroid insufficiency (CIRCI) in humans.

Hypotheses

Intravenous infusion of lipopolysaccharide (LPS) would (a) decrease endogneous AA concentrations, (b) induce CIRCI and (c) administration of a combination of AA and hydrocortisone (HC) would have decreased indices of inflammation compared to either drug alone.

Animals

Thirty‐two healthy horses.

Methods

Randomized placebo‐controlled experimental trial. Horses were assigned to 1 of 4 groups (saline, AA and HC, AA only, or HC only). Treatments were administered 1 hour after completion of LPS infusion. Clinical signs, clinicopathological variables, pro‐inflammatory cytokine gene expression and production, and plasma AA concentrations were assessed at various time points. Serum cortisol concentrations and ACTH stimulation tests were used to detect CIRCI.

Results

There was no effect of drug on clinical signs or pro‐inflammatory cytokine gene expression or production compared to controls at any time point. Administration of AA was associated with higher blood neutrophil counts 6 hours after LPS infusion (11.01 ± 1.02 K/μl) compared to other groups (8.99 ± 0.94 K/μL; P < .009). Adminstration of HC was associated with higher blood neutrophil counts 12 hours after LPS infusion (10.40 ± 0.75 K/μl) compared to other groups (6.88 ± 0.68 K/μl; P < .001). Serum cortisol increased from 5.11 ± 1.48 μg/dL before LPS administration to 9.59 ± 1.83 μg/dL 1 h after completion of LPS infusion (T1) without an effect of treatment (P = 0.59).

Conclusions and Clinical Importance

Ascorbic acid and HC appeared to protect against LPS‐induced neutrophil depletion and could be considered as adjunctive therapy in horses with endotoxemia.