Markers of Hepatic Insulin Clearance and Their Association With Steatosis in Hyperinsulinaemic Horses

Abstract

Background: Hyperinsulinaemia (HI) is an important feature of Equine Metabolic Syndrome (EMS). It has been suggested that reduced hepatic clearance of insulin contributes to HI, particularly in humans affected by metabolic dysfunction-associated steatotic liver disease (MASLD).

Hypothesis: In obese horses with HI, insulin clearance is impaired and associated with MASLD.

Animals: Tissue samples were collected at post-mortem from clinically well-characterized horses with HI (n = 13; basal insulin > 20 mIU/l) and without HI (control; n = 20).

Methods: Retrospective observational study. Molecular drivers of hepatic clearance (CAECAM-1, an insulin chaperone protein and IDE-Insulin Degrading Enzyme) were quantified by RT-qPCR and activity, respectively, in liver tissue. Fixed liver sections stained with hematoxylin and eosin (H&E) were assigned a histological score by two blinded observers using an equine liver disease score and a human MASLD score. Triglyceride (TG) content in liver sections, serum liver enzymes, ACTH, basal insulin, and serum triglycerides were also measured.

Results: IDE activity was 2.73 (IQR 4.00 activity/mg of protein) in HI horses and 2.18 (IQR 0.55) in controls (p = 0.07). IDE activity correlated negatively with insulin (rho = 0.561, p = 0.04) but not with liver or serum TG. CEACAM-1 gene expression was higher in the HI group (2.09 ± 1.79 folds) than in controls (0.69 ± 0.62, p = 0.03). Liver disease and MASLD scores were no different between groups, whereas triglyceride liver content was higher in horses with HI (504.83 IQR 217.51 nmol/g) compared to controls (363.58 IQR 67.32 nmol/g, p = 0.04).

Conclusions and clinical relevance: MASLD is not consistently present in HI horses, but CAECAM-1 expression is higher.

Keywords: MASLD; CEACAM‐1; equine metabolic syndrome; insulin degrading enzyme.

FIGURE 1

Graph showing IDE activity in control horses (3.00 IQR 4.04 activity/mg of protein; n = 8) compared to HI (2.18 IQR 0.40 activity/mg of protein, n = 5; p = 0.07).

FIGURE 2

Graph showing difference in CEACAM‐1 in HI horses (1.86 SD ±1.81 folds, n = 9) compared to control horses (0.69 ± 0.62folds, n = 11, p = 0.03).

FIGURE 3

Graphic representation of the distribution of the study sample based on the MASLD scale. For simplicity, scores were reduced to binary (score = 0 for absence of the histopathological change, presence of changes all scores ≥ 1). For this analysis 14/22 controls and 8/13 HI horses' livers were available (magnification 20×, scale bar 50 μm).

FIGURE 4

Graph comparing liver TG content in control horses (363.58 IQR 67.32 nmol/g, 480 n = 15) compared to HI horses (504.83 IQR 217.51 nmol/g, n = 8; p = 0.04).