Reasons for Macrocytic Red Cells and Megaloblastic Change
• A typical cause of megaloblastic anemia is a deficit in folic acid or vitamin B12 (cyanocobalamin), which are coenzymes needed for the synthesis of thymidine, one of the four nucleotide bases found in DNA.
• Nuclear maturation is slowed or stopped when there is a deficiency of folic acid or vitamin B12.
• proper RNA and protein synthesis leads to proper maturation of the cytoplasm.
As a result, nuclear maturation proceeds more slowly than cytoplasmic maturation, and cytoplasmic hemoglobinization takes a very long time. It causes the erythroid, myeloid, and megakaryocyte lineages of cells in the bone marrow to proliferate abnormally quickly.
Delays in cell division, longer intervals between divisions, greater cell growth, and larger cells are all results of impaired DNA synthesis. This nuclear to cytoplasmic asynchrony in the erythroid series leads to the development of massive nucleated erythrocyte precursors known as megaloblasts. The chromatin pattern of the megaloblasts is lacy, stippled, and open. The early nucleated red cell precursors exhibit the most pronounced megaloblastic alterations.
• A significant portion of megaloblastic precursors in the bone marrow are killed there due to inefficient erythropoiesis, meaning they do not mature enough to be released into the blood.
The peripheral blood also exhibits moderate hemolysis of red blood cells. Large amounts of lactate dehydrogenase (LDH) are released as a result, raising blood levels. • Erythroid precursor cells undergo fewer mitoses and maintain normal hemoglobin synthesis. These megaloblasts give rise to mature red blood cells (RBCs), which are oval-shaped, massive, and highly hemoglobinized.
• Aberrant proliferation in the bone marrow results in dysplastic megakaryocytes from the megakaryocyte series and gigantic metamyelocytes from the myeloid series.
• The body's rapidly dividing cells, such as those in the skin, GI tract, and bone marrow, display megaloblastic alterations, and anemia is merely a symptom of a more widespread malfunction in DNA synthesis.
FOLIC ACID AND VITAMIN B12 METABOLISM
Folic acid metabolism and vitamin B12 metabolism are intimately linked, and both are necessary for healthy nuclear maturation and DNA synthesis. While other conditions can be linked to macrocytosis, folic acid or vitamin B12 deficiencies are typically the cause of megaloblastic hematopoiesis.
Metabolism of Vitamin B12
Animal products are the only source of vitamin B12 that humans can obtain through diet.
Vegetable-based diet does not include vitamin B12. As a result, severe vegans do not consume enough vitamin B12. A well-balanced diet—not a strict vegetarian diet—contains a substantial amount of vitamin B12, which builds up in the liver and lasts for several years. Because of this sufficient storage, clinical signs of any vitamin B12 malabsorption or dietary shortage don't show up for two to four years. Cobalamin, a complex vitamin B12 molecule, is needed daily in amounts of two to 3 µg.
Transport, Storage, and Absorption
• Deoxyadenosylcobalamin and methylcobalamin, the coenzymes that makeup vitamin B12 in food, are often bound to binding proteins.
• Peptic digestion, or low pH digestion in the stomach, is necessary for the release of vitamin B12 from food-bound protein. The salivary protein known as haptocorrin, which is secreted in salivary fluids, binds to the released vitamin B12.
• Along with the unbound unique protein known as intrinsic factor (IF), which is produced by gastric (fundus and cardia) parietal (oxyntic) cells, these haptocorrin-B12 complexes exit the stomach (intrinsic factor is also termed as Castle intrinsic factor).
• Pancreatic proteases liberate vitamin B12 from haptocorrin when the haptocorrin-B12 complexes enter the duodenum's second section. Following this, vitamin B12 combines with the intrinsic factor to produce the IF-B12 complex. • After being delivered to the ileum, ileal enterocytes endocytose the stable IF-vitamin B12 complex. These ileal enterocytes have a surface receptor for the intrinsic element. We refer to these receptors as cubilin.
• Vitamin B12 reacts with transcobalamin, a significant carrier protein, in the ileal epithelium. II, and is actively transferred into the bloodstream via the mucosal cells.
• The liver and other cells of the body receive vitamin B12 from the transcobalamin II-vitamin B12 complex. The body, especially the quickly multiplying bone marrow cells and mucosal lining of the digestive system
Vitamin B12's function
A lack of vitamin B12 affects the production of DNA since it is indirectly needed for DNA synthesis in several metabolic processes.
• The primary form of vitamin B12 found in plasma is methylcobalamin, which is also a necessary cofactor for the conversion of homocysteine to methionine and the synthesis of tetrahydrofolate (THF) from methyl THF. The primary form of folic acid in plasma, methyl THF, replaces the methyl group that vitamin B12 lost during the previous reaction. The production of deoxythymidine monophosphate (dTMP), a precursor to DNA, requires tetrahydrofolate.
The primary reason for reduced DNA synthesis in vitamin B12 insufficiency is the failure of methyl THF to convert to THF. Methyl THF is the term for the accumulated methyl THF.
• According to Figure 4.3, vitamin B12 is also necessary for the transformation of methylmalonyl CoA into succinyl malonyl CoA. Elevated plasma and urine levels of methylmalonic acid are a result of vitamin B12 deficiency. As a result, aberrant fatty acids are formed and integrated into the lipids that make up neurons. Thus, this increases the risk of myelin deterioration and is most likely accountable for vitamin B12 deficiency's neurologic side effects.
Metabolism of Folic Acid
For the folic acid that they need, humans rely solely on food sources. A daily dose of 50–200 mg is needed. The best sources of folic acid include green vegetables, yeast, legumes, fruits, and animal proteins; most typical diets also contain adequate levels of the vitamin. These foods mostly include polyglutamate, which are a kind of folic acid. Since polyglutamate is heat-sensitive (thermolabile), most of the folic acid is destroyed when they boil, steam, fry, or otherwise cook.
The polyglutamates are broken down into monoglutamates by intestinal conjugases, which the proximal jejunum may easily absorb. They are changed to 5 methyltetrahydrofolate, the regular form of folic acid transport, after intestinal absorption.
ANALYZATION OF MEGALOBLASTIC ANEMIA IN THE LAB
A few characteristics shared by all types of megaloblastic anemia are addressed together. Blood results in vitamin B12 and/or folic acid insufficiency are comparable, with red cell macrocytosis and bone marrow megaloblastosis being the main characteristics.
auxiliary blood
• Hemoglobin: Usually seen in the range of 5 to 10 g/dL, hemoglobin levels are reduced.
The hematocrit dropped.
• Indexes of red cells:
- A mean corpuscular volume (MCV) exceeding 100 fl (average 82–98 fl).
- Because of the proportionate rise in hemoglobin content in red blood cells, mean corpuscular hemoglobin concentration (MCHC) stays normal.
There is an increase in mean corpuscular hemoglobin (MCH).
• Peripheral smear: RBCs: The majority of red blood cells (macro-ovalocytes) are oval and macrocytic, and their varied sizes are indicative of megaloblastic anemia. Macrocytes have greater volume, thickness, and diameter.
Most macrocytes lack the core pallor of normal red blood cells and may even seem hyperchromic due to their thickness and high hemoglobinization.
Anisopoikilocytosis causes a noticeable variation in the size and form of red blood cells. Dyserythropoiesis symptoms include the following: ◆ Basophilic stippling: these are blue-black cytoplasmic inclusions that indicate ribosomal RNA that has precipitated.
Radiation remains known as Howell-Jolly bodies can be seen in a small percentage of red blood cells.
The Cabot ring denotes nuclear remains and is stained pink-blue.
- WBCs: Hypersegmented neutrophils (with five to six nuclear lobes or more) and reduced white blood cells (leukopenia) are observed. The earliest and distinct morphologic symptom of megaloblastic anemia is their presence. These neutrophils (macro polymorphonuclear) are also bigger than typical neutrophils.
- Platelets: Reduced and variable in count (thrombocytopenia).
Dimorphic anemia: A peripheral smear shows a dual population of macrocytes and hypochromic microcytes in cases of a combination of vitamin B12/folic acid and iron insufficiency. On the other hand, bone marrow exhibits a normoblastic response with massive metamyelocytes and no marrow iron at all.
• The reticulocyte count is either low or normal. Considering that this is a dyserythropoietic anemia, reticulocytosis does not happen. In cases of severe anemia, nucleated red cells can occasionally be seen in the bloodstream.
Bone Marrow
The physical characteristics of bone marrow are distinctive.
The marrow exhibits moderate to notable hypercellularity, primarily as a result of the proliferation of erythroid precursors, which have the potential to replace the fatty marrow entirely.
• M: E (Myeloid: Erythroid) ratio: This ratio is elevated due to erythroid hyperplasia. from 1:1 to 1:6 in reverse (often 2:1 to 4:1).
• Erythropoiesis: Unlike normal, it is of the megaloblastic type. type normoblasts.
- Megaloblasts: The distinguishing characteristics of these gigantic, aberrant counterparts of normal normoblasts. At every step of red cell development, megaloblastic alteration is observed. They show that nuclear and cytoplasmic maturation are asynchronous, with cytoplasm undergoing normal hemoglobinization while nuclear chromatin fails to develop due to compromised DNA synthesis.
- Ineffective erythropoiesis: More primitive cells predominate in untreated megaloblastic anemia. The megaloblast forms that are in the late stage of death in the bone marrow are referred to as intramedullary hemolysis or inefficient erythropoiesis.
Note: The phrase "ineffective erythropoiesis" refers to erythropoiesis in which non-viable red cells are produced or developing erythroid cells at the production site die.
- Dyserythropoiesis: This condition is characterized by inefficient erythropoiesis and aberrant erythropoiesis with peculiar bone marrow shape. The morphological aspects of dyserythropoietic in megaloblasts are as follows:
◆ Howell-Jolly bodies and aberrant hemoglobinization in the cytoplasm
◆ Within the nucleus: Abnormal mitosis, internuclear bridging, and irregular nuclear boundaries brought forth by nuclear budding.
