FOLIC ACID

 

Q1) What are other names of folic acid?

A1-

Folic acid is known as Vitamin B9, folacin, ptero-glutamic acid, anti anemia factor, L-casei factor etc.

 

Q2) How folic acid was discovered?

A2-

      The discovery of folic acid group of vitamins is the result of many different investigations. The research proceeded along two chief lines.

 

1.      Certain substances were found to be essential for the growth of microorganisms, particularly L casei and streptococcus lactis.

 

2.      Other investigations dealt with factors found to be necessary in the nutrition of chicks, guinea pigs, and monkeys. Since these substances were not the same as the known vitamins. They were given new names as their functions became apparent.

            1931 Wills demonstrated factor form yeast active in treating anemia.

            1938 Day et al found yeast or liver extracts active in treating anemia in monkeys.

            1938 Snell and Peterson isolated L. casei growth factor from liver and yeast.

1938 Snell, Williams, et al isolated bacterial growth factor similar to L.casei factor from yeast and name it -folic acid.

 

Not until later was it evident that the factor required for chick growth and bacterial growth factor were probably a single substance.

 

In other words, liver factor, fermentation L-casei factor, vitamin M, factor R, S, U, yeast factor, all are vitamins of the same group related to folic acid. The generic name preferred to be folacin.

1946 Angier et al isolated petro-monoglutamic acid, proved structure and synthesized it.

 

Q3) What is the structure of folic acid?

A3-

b9

 

·        Folic acid is a conjugated molecule consisting of a pteridine ring (bicyclic nitrogenous compound) structure linked to para-aminobenzoic acid (PABA) that forms pteroic acid.

·        This pteroic acid is further conjugated with glutamic acid to form ptero-glutamate

 

Q4) What are physical properties of folic acid?

A4-

·        It is Yellow crystalline substance, slightly soluble in water but it’s sodium salt is more soluble in water.

·        It is inactivated by light.

·        Storing at room temperature a considerable loss occurs.

·        It is stable in neutral and alkaline medium.

 

Q5) What are dietary sources of folic acid?

A5-

Folic acid widely occurs in nature primarily in leafy (foliage) vegetables, yeast and liver.       

 

High dietary source- (90—300) micro grams/100 gm.

                                     Liver (pork, lamb, chicken, Beef)

                                     Spinach, asparagus, yeast

 

Medium dietary source, 30---90 micro gram/100gm.

                                     Wheat, lentils, beans, Lima beans, barely, oat etc.

                                     Cauliflower, broccoli, beet, greens

                                     Nuts—peanuts, almonds, walnuts,

 

Low dietary source-   up to 30 micro gram/100 gm

                                     Cheese, milk, meat

                                     Cabbage, carrots

 

Q6) what are recommended daily allowances of folic acid?

A6-     

            Children and adults---require   400 micro gram /day

Pregnancy-------800 microgram/day

Lactation   -------500 micro gram/day

            Intestinal bacteria synthesize folic acid.

 

Q7) How folic acid is absorbed and transported?

A7-

·        Folic acid usually occurs as polyglutamate derivatives with two to seven glutamic acid residues.

§        These polygutamate are not absorbable. These compounds are taken up by intestinal mucosal cell and extra glutamate residues are removed by a enzyme conjugase, a lysosomal enzyme.

§        The removal of glutamate residues makes folate less negatively charged and therefore readily absorbable.

§        Only 20 to 50 % dietary folacin is absorbed and is nutritionally available.                          

§        The free folic acid then reduced to tetrahydrofolate by the enzyme dihydrofolate reductase and converted to N5-methyl derivative of tetra hydro folate in intestine and circulated in the plasma.

§        In plasma, about 2/3 of the folate is protein bound which is taken up by tissues upon requirement.

§        Inside the cells, tetra hydro folate is found primarily as polyglutamate derivative and it appears to be the biologically most potent forms.

§        Folic acid is also stored to some extent as a polyglutamate (pentaglutamate) derivative of TH4 in the liver.

 

Q8) What is role of folic acid and one carbon pool?

A 8-

 

             The one carbon pool refers to single carbon units attached to folic acid coenzyme carriers.

 

·        Single carbon atom can exist in a variety of oxidation states. These include methane, methanol, formaldehyde, formic acid and carbonic acid.

[Carbonic acid, the hydrated form of CO2, is carried by the vitamin biotin, which participates in                 carboxylation reactions but is not considered a member of one carbon pool].

·        It is possible to incorporate carbon units at each of these oxidation states, except methane (CH4) into other organic compounds.

·        These single carbon units can be transferred from carrier compounds such as tetrahydrofolate and S-adenosyl methionine to specific structures that are being synthesized or modified.

·        There are several active species of the folic acid group. Different species function as one-carbon carriers in different metabolic processes.

·        The carbon is carried in a covalent linkage to one or both of the nitrogen atoms at N5 and N10 positions of the pteroic acid.

 

Q 9) What are the different forms of co-enzymes of folic acid?

A 9-

           Known forms of co-enzymes of folic acid are given as below--

1)     5- methyl FH4

2)     5-OH methyl FH4

3)     5,10 methylene FH4

4)     5-10 methynyl FH4

5)     5 formyl FH4

6)     10 –formyl FH4

7)     -formimino FH4

 

Q 10) How different forms of co-enzymes of folic acid are formed?

A 10-

1) Serine is the principal source of one carbon unit.

 

Glycine

Serine         --------+ TH4 --------------àN5 N10 methylene TH4    (-CH2 group) for purine synthesis       

 

2) N5 N10 methylene TH4 is an important coenzyme because it can be oxidized to form N5 N10methenyl FH4 or reduction will convert it to N5 methyl TH4.

 

3) N5 N10 methylene TH4 can be oxidize as follows

N5 N10 methylene TH4 + NADP+<=è N5 N10methenyl FH4 +NADPH+ H+

 

4) Reduction reaction of N5 methenyl TH4 coenzyme

N5 N10 methylene TH4 + NADPH + H+--------à N5 methyl TH4 +NAD+ (CH3 group)

 

5) Hydrolysis of N5 N10methenyl FH4   by a cyclohydrolase yields N5 Formyl FH4 (folanic acid) and N10 formyl FH4

N5 N10methenyl FH4 +H2O==== N10 formyl FH4

 

 6) N10 formyl TH4 can be formed directly from formate.

Formate  + TH4------àN10 formyl TH4   (-CHO group)

 

7) FH4+ HCOO-+ ATP------àN5 formyl FH4 + ADP + Pi

Formaldehyde is toxic compound, which reacts spontaneously with amino groups of proteins and nucleic acids hydroxymethylating them, and forming Methylene Bridge cross-links between them.

 

The fundamental biochemical importance of TH4 is to maintain formaldehyde and format in chemically poised fates, not so reactive as to have toxic effects on cell but available for essential processes by specific enzyme action.

 

 8)  N5 formimino FH4      -------HC=NH (at N5)

catabolite of histidine forms formimino FH4

 

N5 formimino glutamate undergoes deamination to N5 N10methenyl FH4.

In folic acid deficiency if a loading dose of histidine is given to a patient urinary excretion of figlu (formimino glutamate) is increased. This figlu excretion test is useful in the diagnosis of folate deficiency, which clinically is manifested as a megaloblastic anemia.

Conversion of coenzymes reaction chart

 

Q 11) What is metabolic role of folic acid? 

A 11-

1) Various one-carbon tetrahydrofolate derivatives are required in biosynthetic reactions.  They are required for synthesis of choline, serine, glycine, purines and dTMP.

            2) Formation of thymidine from uridine

            Metylation of deoxy uridine to thymidine require N5 –N10methylene TH4

3) Synthesis of formyl-methoinine t RNA for initiation of protein synthesis (N10 Formyl   FH4) it is required for the synthesis of purine nucleotides (N10-formyl FH4)

4) Conversion of homocysteine to methionine N5 methyl TH4.

 

 

Q 12) What deficiency manifestation of folic acid are observed?

A 12-

      Deficiency symptoms are…

1)     Glossitis

2)     Intestinal disturbances syndrome characterized by a sore mouth and gastro intestinal disturbances including periodic diarrhea and steatorrhea is associated with folate deficiency

3)     Leucopenia, thrombocytopenia

4)     Macrocytic anemia

5)     Hydrocephalus

6)     Endocrine disturbances

7)     Impairment of antibody formation

8)     Cell division from metaphase----anaphase is blocked

 

 

Q13) Why deficiency of folic acid results in megaloblastic anemia?

A13-

·        The most pronounced effect of folate deficiency is inhibition of DNA synthesis due to decrease availability of purines and dTMP.            

·        This leads to characteristic megaloblastic change in size and shape of nuclei of rapidly dividing cells.

·        The block in DNA synthesis slows down maturation of red blood cells, resulting in production of abnormally large ‘macrocytic’ red blood cells with fragile membranes.

·        Thus macrocytic anemia associated with megaloblastic changes in the bone marrow is characteristic of folate deficiency.

 

Q14) What is role of folic acid in homocysteinemia?

A14-

·        Hyper homocysteinemia is fairly common in elderly population and appears to be due to inadequate intake and /or decreased utilization of folate, vitamin B6 and vitamin B12.

·        Folic acid might prevent heart disease in adults by lowering levels of an artery damaging substance called homocysteine.

·        Elevated homocysteine levels usually respond to supplementation with these vitamins.

 

Q 15) Which factors are responsible for folic acid deficiency?

A 15-

§        Folate deficiency is common in alcoholics, in malabsorption diseases, due to a combination of poor dietary habits and poor absorption.

§        Number of drugs that interfere folate metabolism e.g. anticonvulsants and oral contraceptives. They may interfere with folate absorption and anticonvulsant appears to increase catabolism of folate.

§        In disorder of hereditary folate malabsorption, which may be associated (with a defective carrier), failure of growth, megaloblastic anemia and severe mental retardation may result.

 

Q 16) For treating megaloblastic anemia why vitamin B12 should be included with folic acid

A 16-

A close relationship exists between metabolism of the folate and of vitamin B12.

§        Deficiency of either produces megaloblastic anemia and symptoms of vitamin. B12 deficiency.

§        Anemia is reversed by large doses of folate; however folate does not reverse the neurological abnormalities, which are associated with vitamin B12 deficiency hence?????

 

Q 17) what is folate trap hypothesis?

A17-

       The common point in metabolism of folate and vitamin B12 is methylation of homocysteine to methionine. 

 

§        In human and some other species, this is the only route for conversion of N5 methyl FH4, to other folate derivatives.

§        According to methyl folate trap hypothesis, inhibition of this reaction by cobalamin deficiency leads to accumulation of folate as N5 methyl FH4, deprives the cell of other folate cofactors and leads to blockage of several enzymatic reactions. The role of vitamin B12 and N5-methyl-THF in the conversion of homocysteine to methionine also can have a significant impact on the ability of cells to regenerate needed THF.

§        Inherited disorders of folate transport and metabolism may be due to:

-         Defects in folate carrier (hereditary folate malabsorption),

-         Deficiency of N5 N10methyleneFH4 reductase

-         Functional deficiency of N5 –methyl FH4 methyl transferase

-         Formimino transferase

-         Or due defects of vitamin B12 metabolism

 

Q 18) Which analogues compounds of folic acid are used for therapeutic purposes?

A 18-

·        Methothrexate, a structural analogue of FH2, is a potent inhibitor of di hydro folate reductase and is used in chemotherapy for neoplastic disease.

·        Methothrexate is not effective against bacteria and protozoa infections since these organisms are impermeable to folate and its analogue.

·        Pyrimethamine is very effective against protozoan (e.g. malarial parasite) but ineffective against bacteriaaal infection.it is mild inhibitor of mammalian enzyme.

·        Trimethoprim- effective inhibitor for bacteria and protozoal enzymes but has minimal inhibition against the mammalian enzymes.

 

These selective enzyme inhibitors have been used in the treatment of bacterial and malarial infections.