Exploring Serum Ferritin's Connection to the Acute Phase Response in Zoo-Managed African Rhinoceroses

Abstract

Despite serum ferritin's potential as an iron status indicator, its concentrations vary significantly throughout a black rhinoceros's (Diceros bicornis) life, sometimes irrespective of iron load. We explored acute phase response-related biomarkers, serum amyloid A (SAA) and ceruloplasmin (Cp), to better understand the mechanisms influencing serum ferritin changes in managed black rhinoceroses. The objective was to evaluate the relationships between circulating levels of ferritin, SAA, and Cp in black and white rhinoceroses (Ceratotherium simum). We analyzed banked serum samples collected serially from 11 black (n = 222) and 7 white (n = 134), rhinoceroses (rhinos) and classified samples based on SAA values: clinically healthy (< 1 mg/L), subclinical (1-7 mg/L), or clinically abnormal (> 7 mg/L). In black rhinos, serum ferritin was not different between health status categories (p = 0.5292), nor was it correlated with SAA (p = 0.4164). However, Cp activity was significantly lower in clinically healthy sera (p < 0.0001) and had a moderate positive association with SAA (r = 0.477, p < 0.0001). Among the white rhino samples, only five had SAA values greater than 1 mg/L, limiting the assessment of ferritin and Cp activity in the health context. Minor, yet significant, relationships were observed between serum ferritin and Cp activity, negative in black rhinos (r = -0.206; p = 0.0022) and positive in white rhinos (r = 0.289, p = 0.0008). Cp activity may aid in diagnosing illness in black and white rhinos, based on values observed in sera collected near the time of death. However, acute inflammatory processes do not appear to be one of the primary drivers of the high ferritin concentrations detected in some black rhinos.

Keywords: black rhinoceros; ceruloplasmin; serum amyloid A; white rhinoceros.

Figure 1

Profile of serum ferritin (red), serum amyloid A (SAA; black), and ceruloplasmin (Cp) activity (blue) from a black (Diceros bicornis) rhinoceros (female #3). These profiles depict ~2 years of collections, 11 years before (A) and the 2 years leading up to death (B). Clinical signs of illness developed during the period presented in (B). Systemic hemosiderosis was determined postmortem. Please note logarithmic axis was used for SAA values and that scales are identical between panels.

Figure 2

Profile of serum ferritin (red), serum amyloid A (SAA; black), and ceruloplasmin (Cp) activity (blue) from a white (Ceratotherium simum) rhinoceros (male #3). Includes samples collected ~14 years before death (A) and the 4 months immediately before death (B). The presence of cancer throughout his body was determined postmortem. Please note logarithmic axis was used for SAA values and that scales are identical between panels.

Figure 3

Distribution of serum ferritin (upper panel), and ceruloplasmin activity (lower panel) values observed in black (Diceros bicornis) rhinoceros sera (n = 222) in relationship to serum amyloid A classification (A, clinically healthy [< 1 mg/L SAA]; B, subclinical [1–7 mg/L SAA]; C, clinically abnormal [> 7 mg/L SAA]). Each symbol type within biomarker denotes whether the value came from a female (red circle) or male (blue plus) rhino. Please note logarithmic axis was used for serum ferritin values (scale 100–100,000).

Figure 4

Distribution of serum ferritin (upper panel), and ceruloplasmin activity (lower panel) values observed in white (Ceratotherium simum) rhinoceros sera (n = 134) in relationship to serum amyloid A classification (A, clinically healthy [< 1 mg/L SAA]; B, subclinical [1–7 mg/L SAA]; C, clinically abnormal [> 7 mg/L SAA]). Each symbol type within biomarker denotes whether the value came from a female (red circle) or male (blue plus) rhino. Please note logarithmic axis was used for serum ferritin values (scale 10–10,000).