Daily propranolol administration reduces persistent injury-associated anemia after severe trauma and chronic stress

Abstract

Background: After severe trauma, patients develop a norepinephrine-mediated persistent, injury-associated anemia. This anemia is associated with suppression of bone marrow (BM) erythroid colony growth, along with decreased iron levels, and elevated erythropoietin (EPO) levels, which are insufficient to promote effective erythropoiesis. The impact of norepinephrine on iron regulators, such as ferroportin, transferrin, and transferrin receptor-1 (TFR-1), is unknown. Using a clinically relevant rodent model of lung contusion (LC), hemorrhagic shock (HS), and chronic stress (CS), we hypothesize that daily propranolol (BB), a nonselective β blocker, restores BM function and improves iron homeostasis.

Methods: Male Sprague-Dawley rats were subjected to LCHS ± BB and LCHS/CS ± BB. BB was achieved with propranolol (10 mg/kg) daily until the day of sacrifice. Hemoglobin, plasma EPO, plasma hepcidin, BM cellularity and BM erythroid colony growth were assessed. RNA was isolated to measure transferrin, TFR-1 and ferroportin expression. Data are presented as mean ± SD; *p < 0.05 versus untreated counterpart by t test.

Results: The addition of CS to LCHS leads to persistent anemia on posttrauma day 7, while the addition of BB improved hemoglobin levels (LCHS/CS: 10.6 ± 0.8 vs. LCHS/CS + BB: 13.9 ± 0.4* g/dL). Daily BB use after LCHS/CS improved BM cellularity, colony-forming units granulocyte, erythrocyte, monocyte megakaryocyte, burst-forming unit erythroid and colony-forming unit erythroid cell colony growth. LCHS/CS + BB significantly reduced plasma EPO levels and increased plasma hepcidin levels on day 7. The addition of CS to LCHS resulted in decreased liver ferroportin expression as well as decreased BM transferrin and TFR-1 expression, thus, blocking iron supply to erythroid cells. However, daily BB after LCHS/CS improved expression of all iron regulators.

Conclusion: Daily propranolol administration after LCHS/CS restored BM function and improved anemia after severe trauma. In addition, iron regulators are significantly reduced after LCHS/CS, which may contribute to iron restriction after injury. However, daily propranolol administration after LCHS/CS improved iron homeostasis.

Figure 1

Seven days following LCHS and LCHS/CS, daily administration of BB restored bone marrow function. A. BB treatment after LCHS and LCHS/CS significantly improved bone marrow cellularity. B–D. The addition of BB after LCHS and LCHS/CS improved all erythroid progenitor colony growth, including CFU-GEMM, BFU-E and CFU-E. BM=bone marrow; BB=propranolol; LCHS= lung contusion followed by hemorrhagic shock; LCHS= LCHS followed by daily chronic stress; *p <0.05 vs. naïve; **p <0.05 vs. untreated counterpart

Figure 2

Seven days following LCHS and LCHS/CS, daily BB administration improved hemoglobin levels. BB=propranolol; LCHS= lung contusion followed by hemorrhagic shock; LCHS= LCHS followed by daily chronic stress; *p <0.05 vs. naïve; **p <0.05 vs. untreated counterpart

Figure 3

A. BB use after LCHS and LCHS increased liver ferroportin expression. B–C. Seven days following LCHS and LCHS/CS, bone marrow transferrin and TFR-1 expression was significantly reduced. The use of daily BB after LCHS and LCHS/CS increased bone marrow transferrin and TFR-1 expression. BM=bone marrow; BB=propranolol; LCHS= lung contusion followed by hemorrhagic shock; LCHS= LCHS followed by daily chronic stress; *p <0.05 vs. naïve; **p <0.05 vs. untreated counterpart

Figure 4

A. Following LCHS and LCHS/CS, daily BB administration reduced plasma EPO levels. B. Daily BB administration after LCHS and LCHS/CS increased plasma hepcidin levels. EPO=erythropoietin; BB=propranolol; LCHS= lung contusion followed by hemorrhagic shock; LCHS= LCHS followed by daily chronic stress; *p <0.05 vs. naïve; **p <0.05 vs. untreated counterpart

Figure 5

A. Norepinephrine stimulates IL-6 which stimulates hepcidin and inhibits iron export by reducing ferroportin which leads to reduction in systemic iron availability. 5B. Norepinephrine mediates a decrease in iron availability to erythroid cells in the bone marrow by either disrupting the bond between iron and transferrin in the peripheral blood or by reducing TFR-1 in the bone marrow. EPO=erythropoietin; EPOr=erythropoietin receptor; TFR1=transferrin receptor, NE=norepinephrine.