Erythroid hypoplasia and anemia following administration of recombinant human erythropoietin to two horses.

The research article discusses a study on two horses that were observed to have developed anemia upon receiving doses of recombinant human erythropoietin (rhEPO). The paper suggests the possibility that this occurred due to developed anti-rhEPO antibodies which hindered the occurrence of erythropoiesis, the process of producing red blood cells.

Background and Case Overview

• Two horses, a Standardbred gelding and a colt, were studied because they showed signs of poor performance and had anemia. The horses were given recombinant human erythropoietin (rhEPO) doses, specifically 4,000 IU on two instances within the preceding 2-4 months.

Clinical Examination and Findings

• The examination included different blood parameters including hematocrit (Hct), serum iron concentration, total iron binding capacity, the percentage saturation of transferrin by iron, and serum ferritin concentrations.
• Both horses showed low Hct levels, significantly above normal serum iron and transferrin saturation percentages, and markedly increased serum ferritin concentrations, which all signify abnormal iron metabolism and a decreased red blood cell count.

Investigation of Cause of Anemia

• The researchers found no clinical or laboratory evidence of immune-mediated hemolysis or an infectious or inflammatory cause of the anemia.
• When the researchers examined sternebral marrow biopsy specimens, they found general bone marrow hypoplasia and confirmed a diagnosis of moderate-to-marked erythroid hypoplasia – decreased production of red blood cells – in both horses.

Antibody Hypothesis and Confirmation

• The medical researchers hypothesized that the horses might have developed antibodies against rhEPO that was cross-reacting with the horses’ natural erythropoietin, which is an essential hormone for red blood cell production. This cross-reactivity could have prevented erythropoiesis, leading to anemia.
• To confirm this, they compared the serum from the affected horses to serum from a healthy control horse. The serum from the affected horses significantly inhibited rhEPO-induced proliferation of erythroid progenitors in vitro, thus substantiating their hypothesis.

Post Study Follow Up

• The horses were prescribed to discontinue rhEPO administration and to take dexamethasone instead.
• Five months after these instructions, the horses were found to be back in training. For one horse, the Hct had increased to 35% (an improvement), while the other horse was not available for examination.