Vitamin D2

Absorption

Ergocalciferol is absorbed in the intestine and carried to the liver in chylomicrons. Its intestinal absorption does not present limitations unless the presence of conditions related to fat malabsorption. However, for absorption to take place, the presence of bile is required.

Toxicity

The reported LD50 for orally administered ergocalciferol in the rat is of 10 mg/kg. Overdosage with this agent is reported to produce hypervitaminosis characterized by hypercalcemia, renal impairment, calcification of soft tissues, a decline in the rate of linear growth and increase in bone mineralization.
Once an overdose state is registered, immediate withdrawal of vitamin D is required along with a calcium diet, generous intake of fluids and symptomatic treatment. The administration of loop diuretics is an option to increase renal calcium excretion. On the other hand, dialysis and administration of citrates, sulfates, phosphates, corticosteroids, EDTA and mithramycin are recommended.
There haven't been long term studies analyzing the carcinogenic and mutagenic potential of ergocalciferol or its effects in fertility.

Description

Vitamin D aids in the absorption of calcium and has central roles in bone formation and maintenance, hypertension, cancer and immunity. Vitamin D may be obtained from many dietary sources, including eggs and fish, and is synthesized in the skin by the conversion of 7-dehydrocholesterol to vitamin D₃ by ultraviolet light. Vitamin D₂ is produced in fungi, including yeast, and invertebrates from ergosterol in response to ultraviolet radiation. In vertebrates as well as host organisms, vitamin D₂ is metabolized first to 25-hydroxyvitamin D₂ and subsequently to the active 1,25-dihydroxyvitamin D₂. Differences in the metabolism and action of vitamin D₂ vs. vitamin D₃ in mammals is a current topic of research interest.

The Uses of Vitamin D2

Vitamin d2 is fat-soluble, and is stable unless oxidized. It is necessary for growth and maintenance of teeth and bones and the normal utilization of calcium and phosphorus; it is used medicinally in the treatment of rickets and as a dietary supplement. Its sources include fish liver and vitamin d-fortified milk.

Background

Ergocalciferol is an inactivated vitamin D analog. It is synthesized by some plants in the presence of UVB light. The production of ergocalciferol was prompted by the identification of dietary deficiency, more specifically vitamin D, as the main causative factor for the development of rickets. Ergocalciferol was isolated for the first time from yeast in 1931 and its structure was elucidated in 1932.
Ergocalciferol is considered the first vitamin D analog and is differentiated from cholecalciferol by the presence of a double bond between C22 and C23 and the presence of a methyl group at C24. These modifications reduce the affinity of ergocalciferol for the vitamin D binding protein resulting in faster clearance, limits its activation, and alters its catabolism.
The first approved product containing ergocalciferol under the FDA records was developed by US Pharm Holdings and was FDA approved in 1941.

Indications

Ergocalciferol is indicated for the treatment of hypoparathyroidism, refractory rickets, and familial hypophosphatemia.
Hypoparathyroidism is the result of inadequate parathyroid hormone production that occurs due to the presence of damage or removal of the parathyroid glands. This condition produces decreased calcium and increased phosphorus levels.
Rickets is a condition produced due to a deficiency in vitamin D, calcium or phosphorus. However, this condition can also be related to renal diseases. It is characterized to present weak or soft bones.
Familial hypophosphatemia is characterized by the impaired transport of phosphate and an altered vitamin D metabolism in the kidneys. The presence of this condition can derive in the presence of osteomalacia, bone softening and rickets.

What are the applications of Application

Vitamin D2 is a cell differentiation inducer and DNA polymerase inhibitor

Pharmacokinetics

After the activation of the vitamin D receptor, some of the biological changes produced by ergocalciferol include mobilization and accretion of calcium and phosphorus in the bone, absorption of calcium and phosphorus in the intestine, and reabsorption of calcium and phosphorus in the kidney.
Some other effects known to be produced due to the presence of vitamin D are osteoblast formation, fetus development, induction of pancreatic function, induction of neural function, improvement of immune function, cellular growth and cellular differentiation.
When compared to its vitamin D counterpart cholecalciferol, ergocalciferol has been shown to present a reduced induction of calcidiol and hence, it is less potent.
Ergocalciferol supplementation in patients with end-stage renal disease has been shown to generate a significant benefit in lab parameters of bone and mineral metabolism as well as improvement in glycemic control, serum albumin levels and reduced levels of inflammatory markers.

Metabolism

Ergocalciferol is inactive and hence, the first step in the body is ruled by the conversion of this parent compound to 25-hydroxyvitamin D by the action of CYP2R1 followed by the generation of the major circulating metabolite, 1,25-dihydroxyvitamin D or calcitrol. The generation of this major metabolite is ruled by the activity of CYP27B1 which is a key 1-hydroxylase and CYP24A1 which is responsible for the 25-hydroxylation.
As part of the minor metabolism, ergocalciferol is transformed into 25-hydroxyvitamin D in the liver by the activity of D-25-hydroxylase and CYP2R1. As well, the formation of 24(R),25dihydroxyvitamin D is performed mainly in the kidneys by the action of 25-(OH)D-1-hydroxylase and 25-(OH)D-24-hydroxylase.
Additionally, there are reports indicating significant activity of 3-epimerase in the metabolism of ergocalciferol which modifies the hydroxy group in C3 from the alpha position to a beta. The epimers formed seemed to have a reduced affinity for the vitamin D plasma proteins and to the vitamin D receptor.
An alternative activation metabolic pathway has been reported and this process is characterized by the activity of CYP11A1 and its hydroxylation in the C-20. This 20-hydroxylated vitamin D seems to have similar biological activity than calcitriol.