Erythrocyte, folate vitamin

A cross-sectional study showed a 20% lower serum vitamin B12 concentration in patients taking lithium (n = 81) than in controls (n = 14) (serum and erythrocyte folate concentrations were normal) (346). 

Concentrations of plasma homocysteine, plasma pyridoxal 5 -phosphate (active vitamin B6), serum folate, erythrocyte folate, and serum vitamin B12 have been measured both during fasting and after methionine in 60 epileptic patients (aged 14-18 years) and 63 sex- and age-matched controls before therapy and after 1 year of therapy with valproate or carbamazepine (33). After 1 year the patients who took valproate and carbamazepine had significantly increased plasma homocysteine concentrations compared with both baseline and control values and there was a significant fall in serum folate and plasma pyridoxal 5 -phosphate. Serum vitamin B12 and erythrocyte folate were unchanged. 

It is of paramount importance to rule out vitamin B12 deficiency when folate deficiency is detected, as symptoms are similar. Laboratory changes associated with folate deficiency are similar to those seen in vitamin Bn deficiency, except vitamin Bn levels are normal. Decreases occur in the serum folate level (<3 ng/mL) within a few days of dietary folate limitations. The RBC folate level (<150 ng/mL) also declines and may be a better indicator of deficiency, as levels remain constant throughout the life span of the erythrocyte. Serum folate levels are sensitive to short-term changes such as dietary restrictions or alcohol intake, which may result in a short-term decline in serum levels with adequate tissue stores. It should be noted that an estimated 60% of patients with pernicious anemia have falsely low RBC folate levels, in all probability due to the requirement of cobal-amin for the normal transfer of methyltetrahydrofolate from plasma to cells. Additionally, if serum or erythrocyte folate levels are borderline, serum homocysteine is usually increased with a folic acid deficiency. If serum MMA levels are also elevated, vitamin B12 deficiency needs to be ruled out. 

Davis et al. found that folate was not the only B group vitamin which was reduced in patients receiving treatment with anticonvulsant drugs (D4). In a study of 68 patients suffering from severe epileptic seizures they found that 18 patients had a low folate, 10 a low serum pyridoxal, and in 15 both the folate and pyridoxal were reduced. Only two patients in this series had a reduced erythrocyte folate, and this is in accord with the infrequency with which a macrocytic anemia is seen in these patients. All the patients in this series had a normal hemoglobin concentration and a normal mean corpuscular volume. However, in a study of 75 epileptic children Maxwell (M3) found both the serum and erythrocyte folate levels to be reduced in 60% and similar observations have been made by other workers (M4, N2). 

One patient has been found with this deficiency (All). Hie patient, an infant, was mentally retarded, had a megaloblastic anemia and abnormally high levels of serum and erythrocyte folate. In spite of the high serum folate concentration there was a marked rise in the reticulocyte count when the patient was treated with folate. It was thought that the patient had impaired utilization of -methyltetrahydrofolate. Assay of liver W -methyltetrahy-drofolate transferase showed it to be reduced. It was suggested that folate accumulated at the N -methyltetrahydrofolate block and could therefore not be further utilized. Treatment with pteroylglutamic acid provided a means of producing active folate up to the point of the block. Unfortunately this patient was also treated with pyridoxine, and it is not clear which vitamin was responsible for the reticulocyte response. Further studies are required to determine the precise nature of this metabolic disorder. 

There have been other single reports of megaloblastic anemia associated with an apparent abnormality of folate metabolism. One child had a normal serum folate of 6 p,g/liter, an erythrocyte folate of 1480 p.g/liter, and a megaloblastic anemia which responded to treatment with folic acid (VI). Lampkin (Lll) described two sisters with a severe megaloblastic anemia and normal vitamin 6 2 folate levels. Absorption of vitamin 6, 2 normal and both patients excreted an increased amount of formiminoglutamic acid. It was thought that they required both vitamin B 2 and folate to restore normoblastic hemopoiesis. 

Patients with homozygous sickle cell disease (SS) had a mean serum folate of 5.8 JLg/liter compared with 7.2 p.g/liter in patients with sickle cell trait and 7.9 p.g/liter in healthy controls. However, there was no correlation between the serum folate and the hematocrit or reticulocyte count. Since reticulocytes may have a higher folate concentration than mature erythrocytes, Liu found that the erythrocyte folate, measured before and after removal of the reticulocytes, was a reliable indicator of the folate status in patients with sickle cell disease despite the variable degree of re-ticulocytosis. Using this technique only one of nine patients was found to have a low erythrocyte concentration of the vitamin. Treatment with fohc acid resulted in higher hematocrits in three of four patients with low serum and erythrocyte folate concentrations, but only one of 12 patients with a normal folate concentration showed any improvement when treated with folate. 

Little is known about other aspects of folate metabolism, such as the factors that determine plasma clearance, in either normal subjects or users of oral contraceptive steroids. As described earlier, maximum serum folate concentrations after oral folate polyglutamate are lower in contraceptive users than in nonusers, when subjects are not presaturated (S19). This may be due to increased clearance from plasma, because poor absorption was not found. Stephens et al. (S19) felt that this was probably not due to tissue folate depletion because there was no correlation with initial fasting serum folate concentrations. However, erythrocyte folate concentrations were not measured and might have been a better index of tissue saturation with the vitamin. 

Low levels of serum folate are often associated with low levels of erythrocyte folate (intracellular). The mean corpuscular volume (MCV) of erythrocytes may increase slightly with low folate levels, though overt macrocytic anaemia occurs infrequently. Carbamazepine (CBZ) therapy may cause leukopenia and neutropenia. In a randomized trial in patients on CBZ, subjects on folic acid had higher leucocyte counts and less neutropenia compared with subjects without vitamin supplements. Other studies found no connection between folate and AED-induced haematological abnormalities. 

Nutrition The effect of warfarin therapy for 6 months on folate status has been studied in 114 patients, using measurements of erythrocyte folate and 5-methyltetrahydro-folate and plasma folate, total homocysteine, phylloquinone, vitamin B12, and methylmalonic acid [ll. There were significant falls in total erythrocyte folate and 5-methyltetrahydrofolate and a concurrent increase in plasma phylloquinone, attributed to altered vitamin K metabolism. 

Pernicious anemia arises when vitamin B,2 deficiency blocks the metabohsm of folic acid, leading to functional folate deficiency. This impairs erythropoiesis, causing immature precursors of erythrocytes to be released into the circulation (megaloblastic anemia). The commonest cause of pernicious anemia is failure of the absorption of vitamin B,2 rather than dietary deficiency. This can be due to failure of intrinsic factor secretion caused by autoimmune disease of parietal cells or to generation of anti-intrinsic factor antibodies. 

Erythrocyte and plasma folate concentrations are reduced in protein-calorie malnutrition, but the serum vitamin Bj2 concentration is unaffected or may even be slightly increased. The plasma concentrations of vitamins A and E are much reduced. Although the blood hemoglobin concentration is reduced, the serum iron concentration is initially little affected by malnutrition. 

Many epileptics receiving anticonvulsants excrete increased amounts of copper and zinc in their urine. Increased serum ceruloplasmin also increases the total serum copper concentration. In 20% to 30% of epileptic children receiving anticonvulsant therapy, erythrocyte aspartate aminotransferase activity is low, indicating a lowered pyridoxal (vitamin Bg) status. In as many as 50% of the adults receiving phenytoin for some time, there will be folate deficiency, manifested by reduced erythrocyte and serum folate concentrations. The mechanism for the deficiency has not yet been established conclusively. In about 10% of adults taking phenytoin, the serum vitamin is low. 

Hemolysis, if sufficiently severe, produces an LD isoenzyme pattern similar to that in myocardial infarction. Megaloblastic anemias, usually resulting from the deficiency of folate or vitamin cause the erythrocyte precursor cell to break down in the bone marrow (ineffective erythropoiesis), resulting in the release of large quantities of LD-1 and LD-2 isoenzymes. Marked elevations of the total LD activity in serum— up to 50 times the upper reference limit—have been observed in the megaloblastic anemias. These elevations rapidly return to normal after appropriate treatment. 

There are several vitamin Bg-responsive inborn errors of metabolism that include (1) cases of infantile convulsions in which the apoenzyme for glutamate decarboxylase has a poor affinity for the coenzyme (2) a type of chronic anemia in which the number but not morphological abnormality of erythrocytes is improved by pyridoxine supplementation (3) xanthurenic aciduria in which affinity of the mutant kynureninase for PLP is decreased (4) primary cystathion-inuria caused by similarly defective cystathionase and (5) homocystinuria in which there is less of the normal cystathionine synthetase. In these cases increased levels (200 to lOOOmg/day) of administered vitamin Bg are required for life. Low vitamin Bg status (together with low vitamin B12 and folate status) in humans has been linked to hyperho-mocysteinemia and as an independent risk factor for cardiovascular disease. ... 

Orotic aciduria is characterized by failure of normal growth and by the presence of hypochromic erythrocytes and megaloblastic bone marrow, none of which are improved by the usual hematinic agents (e.g., iron, pyridoxine, vitamin B 2, and folate). Leukopenia is also present. Treatment with uridine 2-A g/d) results in marked improvement in the hematological abnormalities, in growth and development, and in decreased excretion of orotic acid. These patients are pyrimidine auxotrophs and require an exogenous source of... 

MCV represents the average volume of RBCs. Cells are said to be macrocytic if they are larger than normal, microcytic if they are smaller than normal, and normocytic if their size falls within normal limits. Folic acid and vitamin B12 deficiency anemias yield macrocytic morphology, whereas iron deficiency and thalassemia are examples of microcytic anemias. A falsely elevated MCV occurs with reticulo-cytosis because reticulocytes are larger than erythrocytes. The MCV is also falsely elevated in the presence of cold agglutinins and hyperglycemia. When IDA (decreased MCV) is accompanied by folate deficiency (increased MCV), failure to understand that the MCV rep-... 

The resnlts of folic acid measnrements may vary depending on the assay method nsed. Decreased serum folic acid levels indicate a folate deficiency megaloblastic anemia that may coexist with a vitamin B12 deficiency anemia. An erythrocyte folic acid level is less volatile than sernm levels, as it is slow to decrease in an acnte process such as drug-induced folic acid deficiency, and slow to increase with oral folic acid replacement. However, the clinical ntflity of determining the erythrocyte folic acid level is qnestionable, and the procedure should be reserved for cases in which the clinician snspects folic acid depletion and the serum folic acid may be falsely elevated or depleted. 

In vitamin B12 or folate deficiency anemia, megaloblastosis results from interference in fohc acid-and vitamin B -interdependent nucleic acid synthesis in the immature erythrocyte. The rate of RNA and cytoplasm production exceeds the rate of DNA production. The maturation process is retarded, resulting in immature large RBCs (macrocytosis). Synthesis of the RNA and DNA necessary for cell division depends on a series of reactions catalyzed by vitamin B12 and folic acid, as they have a role in the conversion of midine to thymidine. As shown in Fig. 99-4, dietary folates are absorbed in this process and converted (A) to 5-methyl tetrahydrofolate, which is then converted via a Bi2-dependent reaction (B) to tetrahydrofolate (C). After gaining a carbon, tetrahydrofolate is converted to a folate cofactor (D), 5,10-methyl-tetrahydrofolate, used by thymidylate synthetase (E) in the... 

B. Excess folate, by overwhelming the folate pool trapped as N -methyltetrahydrofolate, can allow for formation of AI, A4°-methyl-enetetrahydrofolate which is required for the thymidylate synthase reaction for DNA synthesis and red blood cell formation. Folate is not recognized as a methyl donor by methionine synthase. Folate does not inhibit destruction of erythrocytes. Cobalamin is an important critical vitamin not synthesized by humans. 

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