Impact of Some Pharmaceuticals on Red Cell Survival

Red Cells

• In adult humans, there are approximately 5.5 imes 10^{12}/L red blood cells (RBCs), which are essential for transporting oxygen and carbon dioxide throughout the body.

• Each red cell is synthesized in the bone marrow, where hematopoiesis occurs. This process involves the differentiation of hematopoietic stem cells into erythroid progenitor cells, which eventually mature into erythrocytes.

• Each red cell survives in circulation for approximately 120 days before it is phagocytosed by macrophages in the spleen or liver.

• Red cells contain Hemoglobin, a protein that binds oxygen in the lungs and transports it to the tissues. Hemoglobin also plays a role in the regulation of blood pH and the transport of carbon dioxide from tissues to the lungs to be exhaled.

• If the rate of destruction of red cells exceeds their production, it results in a condition known as HAEMOLYTIC ANEMIA, which can lead to symptoms such as fatigue, pallor, and shortness of breath.

• Immature red cells are referred to as reticulocytes, which can be identified in a blood smear by the presence of residual ribosomal RNA.

• The production of reticulocytes can increase in response to anemia, indicating the bone marrow's efforts to compensate for the loss of RBCs.

Penicillin Case Study

• A married woman aged 64 presented with a medical history significant for subacute bacterial endocarditis affecting the aortic valve. In 1998, she was successfully treated with intramuscular penicillin for a duration of 13 weeks without any adverse reactions.

• Years later, she was readmitted to the hospital with a new infection and was administered Penicillin G. Fifteen days post-administration, she developed a rash, prompting further investigation through a complete blood count.

• Parameter changes observed 15 days after Penicillin G administration:

  • Haemoglobin: Decreased from 145 g/L (within normal range) to 101 g/L at admittance and subsequently to 79 g/L, indicating significant anemia.

  • Haematocrit: Decreased from 0.45 (normal) to 0.32 at admittance, further dropping to 0.21, showing a reduced volume percentage of red cells in blood.

  • Reticulocytes: Increased significantly from approximately 1% (normal) to 1.4% at admittance, peaking at 17.2%, which suggests a compensatory response of the bone marrow to the reduced red cell mass.

  • WBC: Decreased from 4.5-11 X 10^9 /L (within normal limits) to 10.1 X 10^9 /L at admittance, and then falling to 3.1 X 10^9 /L, which may indicate a reaction to hemolysis or infection.

• The patient's second exposure to penicillin triggered an immune-mediated hemolytic response, as evidenced by the markedly elevated reticulocyte count, signifying increased red blood cell production in response to hemolysis.

Anti-Human Globulin Test

• The Anti-Human Globulin Test involves isolating red cells from a patient and testing them with anti-human globulin to identify antibodies bound to the RBC surface.

• The test result was POSITIVE, indicating an immune reaction against the patient's RBCs.

• The Direct Antiglobulin Test (DAT), also known as the direct Coombs test, is performed by adding anti-IgG to detect IgG that is attached to the RBCs and can also identify C3 complement fragments on the RBC surface. This test is critical in the investigation of immune hemolytic anemia and transfusion reactions.

Antibody Binding to Red Cell - Why?

• During the first treatment with penicillin in 1998, the drug was administered at a high dose and was adsorbed onto the surface of the red cells, modifying their antigenic properties.

• The immune system incorrectly recognizes the penicillin-coated red cells as foreign, leading to the production of antibodies (IgG) and memory T cells.

• Upon the second exposure to penicillin several years later, the plasma contained a higher titer of IgG antibodies which bind to the penicillin-coated red cells, leading to their destruction.

What Happens Next to The Coated Cells?

• The penicillin-coated red cells are then targeted by macrophages, which engulf and destroy them through phagocytosis.

• Alternatively, the binding of complement proteins via the classical pathway can occur, leading to the formation of a membrane attack complex that lyses the red cells directly.

How does the Bone Marrow Respond?

• In response to hemolysis, the bone marrow increases the production of red blood cells, releasing reticulocytes into circulation. This includes the appearance of:

  • Polychromatic red cells: These mature erythrocytes exhibit a mix of colors due to varying levels of hemoglobin and residual RNA.

  • Microspherocytes: These are sphere-shaped red blood cells that result from antibody-mediated destruction.

  • The action of macrophages is crucial in clearing damaged red cells and recycling hemoglobin.

Treatment

• The first step in management was discontinuing penicillin treatment; no antibody was detected in circulation 77 days post-cessation of the drug.

• Additionally, corticosteroids were administered to suppress the immune response and reduce hemolysis.

• In severe cases, plasmapheresis may be indicated to remove circulating antibodies, along with blood transfusions to manage significant anemia.

Dapsone

• Dapsone is an antibacterial agent commonly used in treating Mycobacterium tuberculosis and leprosy.

• It has the ability to oxidize hemoglobin to a form known as methemoglobin, which is functionally deficient and unable to transport oxygen effectively.

• Dapsone can lead to the formation of Heinz bodies through the induction of oxidative stress, which results in denaturation of hemoglobin and subsequent red cell damage.

Heinz Bodies

• Heinz bodies are aggregates of denatured hemoglobin that form within the red blood cells due to oxidative damage.

• These bodies are recognized and removed by macrophages, particularly in the liver and spleen, resulting in the formation of bite cells in circulation, which are indicative of hemolytic processes.

Bite Cells

• Bite cells are red blood cells that have been partially phagocytosed by macrophages, leading to characteristic morphology that reflects their compromised functionality.

Conclusions

• Various treatments can profoundly affect red cell morphology and viability, and understanding the mechanisms is vital in clinical settings.

• Penicillin can induce antibody-mediated destruction of red cells in sensitized individuals, leading to hemolytic anemia.

• Dapsone affects hemoglobin integrity, resulting in oxidative damage and Heinz body formation, further contributing to hemolysis.