Effects of bilirubin and phototherapy on osmotic fragility and haematoporphyrin‐induced photohaemolysis of normal erythrocytes and spherocytes

Abstract

Aim: To study the effects of phototherapy on erythrocyte haemolysis in vitro and to determine possible differences in sensitivity to phototherapy between normal erythrocytes and spherocytes. Methods: Erythrocytes from four normal healthy donors and two donors with hereditary spherocytosis were treated with bilirubin (160 μM) in the presence of human serum albumin in the molecular ratio bilirubin/albumin 0.8. Treated cells were maintained either in the dark or in blue light (450 nm, 8 mW/cm2, 30 min). The experimental light dose was comparable to 2 h of clinical phototherapy. The osmotic fragility of the treated cells was measured by scoring haemolysis in hypo‐osmolar solutions (0.10–0.90% NaCl). The sensitivity to photohaemolysis of cells pre‐treated with bilirubin (BR) and/or phototherapy was tested by exposing the cell suspensions to haematoporphyrin and UVA radiation. The delayed (18 h) photohaemolysis was measured by spectrophotometry. Results: Osmotic fragility, expressed as percentage haemolysis, of normal erythrocytes was more than doubled in the presence of BR combined with phototherapy (n=6, p<0.05). In contrast, osmotic fragility of spherocytes was unaffected by either treatment (n=8, p<0.05). Increased photohaemolysis was seen in spherocytes treated with BR (n=13, p<0.05), phototherapy (n=13, p<0.05) and a combination of the two agents (n=13, p<0.05) compared with spherocytes without BR in the dark (n=6). Conclusion: Bilirubin may make the plasma membrane of normal erythrocytes more fragile. Newborns with hereditary spherocytosis may be sensitive to phototherapy.

Phototherapy: Old questions, new answers

“…Failure of phototherapy to be effective in reducing TSB levels in some infants with hereditary spherocytosis and hyperbilirubinemia has been hypothesized to be due to increased hemolysis from the absorption of light and photosensitization of cell membrane contents. In an in vitro study using RBCs from healthy donors and patients with hereditary spherocytosis, the investigators showed that the osmotic fragility of normal RBCs was increased in the presence of bilirubin or bilirubin and phototherapy 5. Phototherapy in the absence of bilirubin did not affect normal RBCs.…”

“…Why does phototherapy fail in some patients with hereditary spherocytosis and hemolytic jaundice? In this month's issue, Bruzell Roll et al present three studies that shed some light on these areas 3–5.…”