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

Abstract

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.

Keywords: corticosteroid; endotoxemia; equine; sepsis.

FIGURE 1

Daily schedule from T‐1h (baseline) to 24h post‐LPS infusion in 32 adult horses. The asterisk indicates that ACTH stimulation was performed only on horses administered 0.9% sodium chloride (placebo) and AA only. AA, ascorbic acid; ACTH, adrenocorticotropic hormone; LPS, lipopolysaccharide; MAP, mean arterial blood pressure; PE, physical examination; SAA, serum amyloid A; SBA, serum biochemical analysis; WBC, white blood cell

FIGURE 2

Segmented neutrophil count over time in horses administered 0.9% sodium chloride (placebo; pink box), AA and HC (green box), AA only (blue box), and HC only (yellow box). Within each box, the median is represented by a horizontal line, and brackets represent interquartile range (IQR). Closed circles are outliers, which represent data points outside the IQR with a value >1.5*IQR. Significance between groups is denoted by “a” and “b.” AA, ascorbic acid; HC, hydrocortisone

FIGURE 3

Serum amyloid A (μg/mL), median log TNF‐α plasma concentration, median log IL‐1β plasma concentration, and median log IL‐6 plasma concentration in all horses (n = 32) over time. Within each box, the median is represented by a horizontal line, and brackets represent interquartile range (IQR). Closed circles are outliers, which represent data points outside the IQR with a value >1.5*IQR. IL‐1β, interleukin 1 beta; IL‐6, interleukin 6; SAA, serum amyloid A; TNF‐α, tumor necrosis factor alpha