Evaluation of myeloid-related protein 126, cardiac troponin C and serum amyloid A as potential plasma biomarkers of health and disease in sea turtles

Abstract

Sea turtle health assessments can be strengthened by developing conserved biomarkers that discriminate between healthy and diseased states. Serum amyloid A, myeloid-related protein 126 and cardiac troponin C (CTNC) were explored as potential biomarkers of sea turtle health. Plasma concentrations initially quantified using a targeted SPARCL™ assay significantly differed between moribund (n = 15) and recovered (n = 5) loggerhead turtles (Caretta caretta). There was a negative correlation between myeloid-related protein 126 and packed cell volume (r = -0.612, P = 0.005) and total solids (r = -0.497, P = 0.03) and between and Fulton's body condition index (r = -0.684, P = 0.001). Serum amyloid A showed a relatively high interquartile range (IQR) in moribund turtles and no significant correlations with clinical parameters. Myeloid-related protein 126 and cardiac troponin C were further evaluated by an enzyme-linked immunosorbent assay in a larger dataset of loggerhead, Kemp's ridley (Lepidochelys kempii) and green (Chelonia mydas) turtles. Plasma myeloid-related protein 126 was significantly lower in captive healthy (n = 7) and recovered (n = 23) turtles than in moribund (n = 25) and nesting green (n = 58) turtles. Green turtles with fibropapillomatosis (n = 10) were not significantly different from any group. Discriminating values between healthy/recovered and moribund turtles were 1.89 and 1.97 ng/ml by receiver operating characteristic and logistic regression analyses, respectively. Myeloid-related protein 126 decreased in successfully rehabilitated turtles (n = 18 turtles; n = 67 blood samples) and was negatively correlated with body condition score (r = -0.672, P < 0.001) and packed cell volume (r = -0.443, P = 0.009). Cardiac troponin C was significantly higher (P = 0.049) in moribund turtles (n = 16) compared to healthy/recovered turtles (n = 7) and in moribund samples (n = 11) compared to recovered samples (n = 11) in serially sampled turtles (P = 0.015), but was not predictive of health status. Myeloid-related protein 126 represents a strong biomarker candidate in sea turtles. Cardiac troponin C warrants further evaluation in a larger dataset and serum amyloid A requires examination of variables affecting pathophysiologic responses in sea turtles.

Keywords: Biomarkers; MRP-126; cardiac troponin C; health; plasma; sea turtles; serum amyloid A.

Figure 1

Median and IQR of plasma concentrations of (A) serum amyloid A (SAA), (B) MRP-126 and (C) CTNC in recovered and moribund loggerhead sea turtles (C. caretta) quantified by SPARCL™ assay. Asterisks indicate significant differences (*P = 0.026; ***P < 0.001; **P = 0.003).

Figure 2

Simple linear regression of plasma concentrations of MRP-126 quantified by SPARCL™ assay and (A) PCV, (B) TS and CTNC and (C) BCI in recovered and moribund loggerhead sea turtles (C. caretta). Corresponding P-values: (A) P = 0.006, (B) P = 0.046 (C) P = 0.001.

Figure 3

Median and IQR of MRP-126 concentrations in green (C. mydas), loggerhead (C. caretta) and Kemp’s ridley (L. kempii) turtles quantified by ELISA comprising captive healthy (0.71 ng/ml, 0.57–0.93), clinically recovered (1.92 ng/ml, 1.21–3.98) and moribund (11.83 ng/ml, 4.61–20.24) groups and green turtles that were nesting (6.29 ng/ml, 4.42–8.45) and wild-caught with FP (3.68 ng/ml, 3.10–8.80). Statistical groups are noted by letter. Significance was set to P < 0.050.

Figure 4

MRP-126 concentrations quantified by ELISA showed a mean downward trend (red arrow) for serially sampled turtles undergoing successful treatment and recovery. The exceptions were (A) one green turtle (C. mydas) (ID: C22005) that was euthanized after not responding to treatment and (B) one loggerhead sea turtle (C. caretta) (ID: C21298) that was a healthy resident turtle.

Figure 5

Simple linear regression of plasma concentrations of MRP-126 quantified by ELISA and (A) PCV and (B) subjective BCS in healthy/recovered and moribund sea turtles. Corresponding P-values: (A) P = 0.009, (B) P = 0.001.