Leukocyte-derived and endogenous matrix metalloproteinases in the lamellae of horses with naturally acquired and experimentally induced laminitis

Vet Immunol Immunopathol. 2009 Jun 15;129(3-4):221-30. doi: 10.1016/j.vetimm.2008.11.003. Epub 2008 Nov 7.


Rationale: Inflammation and dysregulation of endogenous matrix metalloproteinase (MMP) production are implicated in the development of equine laminitis. In this study, we examine quantitative relationships among levels of leukocyte-derived proMMP-9 and MMP-9, lamellar proMMP-2 and MMP-2, and expression of proMMP-2 processing enzymes, MT1-MMP/PACE4, as steps towards determining whether inflammation and dysregulation of endogenous MMP production are independent or co-dependent processes.

Animals: Archived samples of lamellae from horses with naturally acquired laminitis (n = 12), and from horses administered a pro-laminitic gastric bolus of starch gruel were used, the latter horses falling into two groups: (i) responders (CHO-R, n = 7), which developed Obel grade 3-lameness and (ii) non-responders (CHO-NR, n = 4), which did not become lame.

Methods: Lamellar tissue extracts were analyzed by gelatin zymography to determine gelatinase content and by a myeloperoxidase ELISA to quantify relative monocyte/neutrophil content in the tissue. Real-time PCR was employed to measure gene expression of MT1-MMP and PACE4.

Results and conclusions: Extracts of lamellae from control horses, CHO-NR and horses with chronic (non-aggravated) laminitis had similarly low levels of pro and processed MMP-9 and MMP-2. In contrast, proMMP-9 was significantly elevated in extracts of lamellae from CHO-R and horses with naturally acquired acute and aggravated chronic laminitis. Lamellar MMP-2 was also increased significantly in the CHO-R and aggravated chronic laminitis groups, although not in the horses with naturally acquired acute laminitis. Concentrations of proMMP-9 correlated directly with myeloperoxidase content in lamellar extracts, suggesting production/induction by inflammatory leukocytes. In contrast, concentrations of proMMP-2 and MMP-2 were unrelated to concentrations of myeloperoxidase or proMMP-9 suggesting that leukocyte infiltration and dysregulation of endogenous MMP-2 are independent processes most likely with distinct inducers. Neither MT1-MMP nor PACE4 gene expression was elevated relative to controls in any group; this is discussed with respect to proMMP-2 processing in disease. In addition, variability in relative concentrations of lamellar MMPs observed among horses with Obel grade 3-lameness is discussed in the context of laminitis risk assessment and disease outcome.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Carbohydrates / toxicity
  • Female
  • Foot Diseases / chemically induced
  • Foot Diseases / enzymology
  • Foot Diseases / veterinary*
  • Gene Expression Regulation, Enzymologic / drug effects
  • Gene Expression Regulation, Enzymologic / physiology
  • Hoof and Claw / enzymology*
  • Hoof and Claw / pathology
  • Horse Diseases / chemically induced
  • Horse Diseases / metabolism*
  • Horses
  • Inflammation / chemically induced
  • Inflammation / enzymology
  • Inflammation / veterinary
  • Leukocytes / enzymology*
  • Male
  • Matrix Metalloproteinases / genetics
  • Matrix Metalloproteinases / metabolism*


  • Carbohydrates
  • Matrix Metalloproteinases