MMP-9 Concentration in Peritoneal Fluid Is a Valuable Biomarker Associated with Endotoxemia in Equine Colic

Serum and Urinary Matrix Metalloproteinase-9 Concentrations in Dehydrated Horses

Matrix metalloproteinase-9 is increased in renal tissue in human kidney disease, but its role as a biomarker for kidney disease has not been fully evaluated yet. The aim of this study was to evaluate serum MMP-9 (sMMP-9) and urinary MMP-9 (uMMP-9) concentrations in dehydrated horses. Dehydrated horses were prospectively included. Blood and urinary samples were taken at admission, and after 12, 24, and 48 h (t0, t12, t24, t48), an anti-equine MMP-9 sandwich ELISA was used. Four healthy horses served as the controls. Serum creatinine, urea, symmetric dimethylarginine (SDMA), urine-specific gravity, urinary protein concentration, fractional sodium excretion, and urinary gamma-glutamyl transferase/creatinine ratio (uGGT/Cr) were measured. Statistical analysis included a repeated measures ANOVA and mixed linear regression model. Overall, 40 dehydrated horses were included (mild dehydration 13/40, moderate 16/40, severe 11/40). Acute kidney injury was found in 1/40 horses; 7/40 horses showed elevated serum creatinine, 11/40 horses elevated serum SDMA, and 5/28 elevated uGGT/Cr at presentation. In dehydrated horses, sMMP-9 concentrations were significantly higher on t0 (median: 589 ng/mL, range: 172-3597 ng/mL) compared to t12 (340 ng/mL, 132-1213 ng/mL), t24 (308 ng/mL, 162-1048 ng/mL), and t48 (258 ng/mL, 130-744 ng/mL). In healthy horses, sMMP-9 (239 ng/mL, 142-508 ng/mL) showed no differences over time or compared to patients. uMMP-9 and uMMP-9/creatinine did not differ over time or to the controls. No differences were found between dehydration groups. Urinary casts (p = 0.001; estimate = 135) and uGGT/Cr (p = 0.03; estimate = 6.5) correlated with sMMP-9. Serum urea was associated with uMMP-9/Cr (p = 0.01, estimate 0.9). In conclusion, sMMP-9 was elevated at arrival in dehydrated patients compared to later measurements. Correlations to uGGT/Cr and urinary casts need further evaluation.

Lymphocyte immunophenotyping and concentration of MMP-9 in transudates and exudates in horses

This study is the first to provide information on the lymphocyte subpopulations in peritoneal effusions in horses. Peritoneal transudates (n = 12), peritoneal exudates (n = 6) and a pleural exudate (n = 1) were analyzed. The total nucleated cell count (TNCC), total protein (TP) and matrix metalloproteinase-9 (MMP-9) concentration determined by ELISA were measured and routine cytological evaluation was performed. CD3, CD4, CD8 and CD21 positive cells were detected by flow cytometry. A higher percentage of neutrophils (P < 0.05) and higher MMP-9 (P < 0.01) levels were found in exudates. A higher percentage of macrophages (P < 0.05) and lymphocytes (P < 0.01) were found in transudates. CD4 + lymphocytes were the most common lymphocyte subpopulation in all samples. CD21 + lymphocytes were the least common in all samples. A large variability in the percentage of CD21 + lymphocytes was found in exudates. The percentage of CD21 + lymphocytes positively correlated with the level of total protein (r = 0.5704, P < 0.05). The correlation was even stronger in the group of exudates. The percentages of lymphocyte subpopulations did not correlate with the level of MMP-9 or with cytological findings. The level of MMP-9 positively correlated with the percentage of neutrophils (r = 0.4980, P < 0.05), the level of TP (r = 0.7855, P < 0.01) and TNCC (r = 0.6129, P < 0.01). A significantly higher level of MMP-9 was detected in euthanized horses than in horses that survived (P < 0.05). However, it was shown that the level of MMP-9 in the peritoneal fluid can change significantly in a short time. More studies on repeated abdominocentesis could contribute to elucidating the role of MMP-9 as a prognostic indicator.

Equine Placentitis in Mares Induces the Secretion of Pro-Inflammatory Cytokine eIL-1β and the Active Extracellular Matrix Metalloproteinase (MMP)-9

Equine placentitis is characterized by infection and inflammation of the placenta. Different biomarkers associated with this inflammatory response have been evaluated in experimentally induced equine placentitis, but not in pregnant mares with spontaneous placentitis. The aim of the current study was to determine the concentration of eIL-1β and the activity of proMMP-2 and proMMP-9 in the serum of healthy mares and mares with placentitis on days 240 and 320 of gestation to explore whether these biomarkers are associated with equine maternal placentitis and/or with the birth of an infected or inviable foals. Serum samples were collected from sixteen pregnant English Thoroughbred mares, retrospectively classified as follows: (1) healthy mares with full-term gestation; and (2) mares with ultrasonographic signs of placentitis. The health of each foal was examined at birth, and it was decided to classify the cases into four groups: (1) healthy mares delivering a healthy foals (HM-HF, n = 6); (2) mares with USP delivering a healthy foal (USP-HF, n = 3); (3) mares with USP delivering a live septic foal (USP-LSeF, n = 4); and (4) mares with USP delivering a dead foal (USP-DF, n = 3). eIL-1β was quantified by ELISA, and proMMP-2 and proMMP-9 activity by gelatin zymography electrophoresis. In healthy mares, the serum concentrations of eIL-1β underwent a significant 16.5-fold increase from day 240 to day 320 of gestation. Although similar results were found in the mares with ultrasonographic signs of placentitis that delivered a healthy foal, those delivering a live septic or nonviable foal exhibited much higher concentrations of eIL-1β. proMMP-2 and proMMP-9 activity was not associated with maternal placentitis, foal infection, or death. Hence, the presence of placentitis severe enough to affect the health of the foal can be confirmed or discarded by determining the eIL-1β concentration in mares that have shown ultrasonographic signs of placentitis.

Biomarkers of Intestinal Injury in Colic

Biomarkers are typically proteins, enzymes, or other molecular changes that are elevated or decreased in body fluids during the course of inflammation or disease. Biomarkers pose an extremely attractive tool for establishing diagnoses and prognoses of equine gastrointestinal colic, one of the most prevalent causes of morbidity and mortality in horses. This topic has received increasing attention because early diagnosis of some forms of severe colic, such as intestinal ischemia, would create opportunities for rapid interventions that would likely improve case outcomes. This review explores biomarkers currently used in equine medicine for colic, including acute phase proteins, proinflammatory cytokines, markers of endotoxemia, and tissue injury metabolites. To date, no single biomarker has been identified that is perfectly sensitive and specific for intestinal ischemia; however, L-lactate has been proven to be a very functional and highly utilized diagnostic tool. However, further exploration of other biomarkers discussed in this review may provide the key to accelerated identification, intervention, and better outcomes for horses suffering from severe colic.