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Calcifediol is also known as 25-hydroxyvitamin D2.
Answer: False
Calcifediol is specifically 25-hydroxycholecalciferol (25(OH)D3). 25-hydroxyvitamin D2 (25(OH)D2) is known as ercalcidiol, a metabolite derived from vitamin D2 (ergocalciferol).
The chemical formula for calcifediol is C27H44O2.
Answer: True
The molecular formula for calcifediol is indeed C27H44O2, with a molar mass of 400.64 g/mol.
Calcifediol's ATC code is A11CC01.
Answer: False
The correct Anatomical Therapeutic Chemical (ATC) classification code for calcifediol is H05BX05, not A11CC01.
In the US, 25(OH)D levels are typically reported in nmol/L, while other countries use ng/mL.
Answer: False
The United States typically reports 25(OH)D levels in ng/mL, whereas many other countries use nmol/L.
Michael F. Holick's laboratory identified calcifediol and the enzyme responsible for its synthesis.
Answer: False
While Michael F. Holick's laboratory identified the enzyme responsible for calcifediol synthesis (cholecalciferol 25-hydroxylase), the identification of calcifediol itself was established in Hector DeLuca's laboratory.
The Preferred IUPAC name for calcifediol is a simple designation like '25-hydroxyvitamin D3'.
Answer: False
The Preferred IUPAC name for calcifediol is highly complex, reflecting its intricate chemical structure, and is not a simple designation.
What are the common names and abbreviations for calcifediol mentioned in the source?
Answer: Calcifediol, 25-hydroxycholecalciferol, and 25(OH)D3
The source identifies calcifediol by names such as calcidiol, 25-hydroxycholecalciferol, and 25-hydroxyvitamin D3, with the common abbreviation 25(OH)D3.
What is the chemical formula of calcifediol?
Answer: C27H44O2
The chemical formula for calcifediol is C27H44O2.
What is the Anatomical Therapeutic Chemical (ATC) classification code for calcifediol?
Answer: H05BX05
Calcifediol is classified under the ATC system with the code H05BX05.
What is the conversion factor between US units (ng/mL) and common international units (nmol/L) for 25(OH)D levels?
Answer: 1 ng/mL = 2.5 nmol/L
The conversion factor is 1 ng/mL equals 2.5 nmol/L for 25(OH)D measurements.
Who were the key researchers associated with the initial identification of calcifediol and its synthesizing enzyme?
Answer: DeLuca and Holick
Hector DeLuca's laboratory identified calcifediol, while Michael F. Holick's laboratory isolated the enzyme responsible for its synthesis.
The Preferred IUPAC name for calcifediol is extremely complex, suggesting what about its chemical structure?
Answer: It has a complex, multi-ring structure with specific stereochemistry.
The highly complex nature of calcifediol's Preferred IUPAC name indicates a sophisticated chemical structure involving multiple rings and specific stereochemical configurations.
What is the CAS Number listed for calcifediol?
Answer: 19356-17-3
The CAS Number listed for calcifediol is 19356-17-3.
What is the molar mass of calcifediol?
Answer: 400.64 grams per mole
The molar mass of calcifediol is 400.64 grams per mole.
Which of the following is NOT a name or abbreviation used for calcifediol according to the source?
Answer: Ercalcidiol
Ercalcidiol refers to 25-hydroxyvitamin D2 (25(OH)D2), a metabolite of vitamin D2, whereas calcifediol is 25-hydroxyvitamin D3 (25(OH)D3).
The initial production of calcifediol occurs in the kidneys via vitamin D 25-hydroxylase.
Answer: False
The initial hydroxylation step to produce calcifediol occurs in the liver, mediated by the enzyme vitamin D 25-hydroxylase (CYP2R1).
Calcifediol is the active hormonal form of vitamin D.
Answer: False
Calcifediol is a precursor metabolite. The active hormonal form of vitamin D is calcitriol (1,25-dihydroxyvitamin D3), which is synthesized from calcifediol.
CYP27A1 is the primary enzyme responsible for the 25-hydroxylation of vitamin D3 in the liver.
Answer: False
While CYP27A1 can contribute, the primary enzyme responsible for the 25-hydroxylation of vitamin D3 in the liver is CYP2R1. CYP27A1 is primarily involved in other metabolic pathways.
The enzyme 25(OH)D-1α-hydroxylase converts calcifediol into calcitriol, primarily in the liver.
Answer: False
The enzyme 25(OH)D-1α-hydroxylase converts calcifediol into calcitriol, but this process occurs primarily in the kidneys, not the liver.
Parathyroid hormone is a key regulator of the CYP27B1 enzyme activity in the kidneys.
Answer: True
Parathyroid hormone (PTH) is a primary regulator of the CYP27B1 enzyme, which is responsible for the final activation step of vitamin D in the kidneys.
The enzyme CYP27B1, responsible for calcitriol synthesis, is exclusively found in the kidneys.
Answer: False
While predominantly active in the kidneys, CYP27B1 is also expressed in various extra-renal tissues, allowing for local calcitriol synthesis.
The enzyme CYP24A1 is involved in the 24-hydroxylation pathway, leading to the inactivation of vitamin D metabolites.
Answer: True
CYP24A1 catalyzes the 24-hydroxylation of vitamin D metabolites, which is a key step in their inactivation and degradation.
The 24-hydroxylation pathway results in the production of the most potent form of active vitamin D.
Answer: False
The 24-hydroxylation pathway, mediated by CYP24A1, leads to the inactivation of vitamin D metabolites, not the production of the most potent active form (which is calcitriol).
According to the pathway map, calcitriol is the direct precursor to calcifediol.
Answer: False
The pathway map indicates that calcifediol is the precursor to calcitriol; calcitriol is the active hormonal form derived from calcifediol.
The enzyme CYP24A1 is responsible for the activation of vitamin D metabolites into their active hormonal forms.
Answer: False
CYP24A1 is responsible for the 24-hydroxylation pathway, which leads to the inactivation of vitamin D metabolites, not their activation into hormonal forms.
Where does the initial hydroxylation step to produce calcifediol take place in the body?
Answer: Liver
The initial 25-hydroxylation of vitamin D3 to form calcifediol occurs primarily in the liver, mediated by the enzyme vitamin D 25-hydroxylase.
Which enzyme is primarily responsible for converting vitamin D3 into calcifediol in the liver?
Answer: Vitamin D 25-hydroxylase (CYP2R1)
The enzyme primarily responsible for the hepatic conversion of vitamin D3 to calcifediol is vitamin D 25-hydroxylase, commonly identified as CYP2R1.
What is the role of calcifediol in the vitamin D metabolic pathway?
Answer: It is the precursor that is further hydroxylated to form calcitriol.
Calcifediol serves as an intermediate metabolite, undergoing further hydroxylation primarily in the kidneys to yield calcitriol, the active hormonal form of vitamin D.
Which enzyme is responsible for converting calcifediol to calcitriol, and where does this primarily occur?
Answer: 25(OH)D-1α-hydroxylase (CYP27B1) in the kidneys
The conversion of calcifediol to calcitriol is catalyzed by the enzyme 25(OH)D-1α-hydroxylase (CYP27B1), primarily within the renal tissue.
What factors primarily regulate the activity of the 25(OH)D-1α-hydroxylase (CYP27B1) enzyme?
Answer: Parathyroid hormone, FGF23, and calcitriol
The activity of CYP27B1 is primarily regulated by parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), and calcitriol itself.
What is the function of the enzyme CYP24A1 in vitamin D metabolism?
Answer: To perform 24-hydroxylation, leading to the inactivation of vitamin D metabolites.
CYP24A1 catalyzes the 24-hydroxylation of vitamin D metabolites, which is a key step in their inactivation and subsequent degradation.
According to the pathway map, what is the immediate precursor to calcifediol?
Answer: Cholecalciferol (Vitamin D3)
The Vitamin D Synthesis pathway map indicates that cholecalciferol (vitamin D3) is the direct precursor to calcifediol.
Which enzyme is responsible for the 24-hydroxylation of calcifediol?
Answer: CYP24A1
The enzyme CYP24A1 is responsible for catalyzing the 24-hydroxylation of calcifediol and other vitamin D metabolites.
The conversion of calcifediol to calcitriol involves adding a hydroxyl group at which position?
Answer: The 1-alpha position
The conversion of calcifediol to calcitriol involves the addition of a hydroxyl group at the 1-alpha position of the molecule.
The 24-hydroxylation pathway eventually leads to the formation of which substance?
Answer: Calcitroic acid
The 24-hydroxylation pathway, mediated by CYP24A1, ultimately results in the formation of calcitroic acid, an inactive metabolite.
In the bloodstream, calcifediol is primarily transported freely without binding to proteins.
Answer: False
Calcifediol is strongly bound in the bloodstream to the vitamin D-binding protein (VDBP), also known as gc-globulin, which is essential for its transport and bioavailability.
Obesity is associated with increased activity of the CYP2R1 enzyme, leading to higher calcifediol levels.
Answer: False
Obesity is generally associated with decreased expression or activity of the CYP2R1 enzyme, potentially leading to lower calcifediol levels, rather than increased activity.
Peak calcifediol levels are reached within 24 hours after taking a large dose of vitamin D3.
Answer: False
Peak calcifediol levels following a large dose of vitamin D3 are typically reached approximately 7 days post-administration, not within 24 hours.
Calcifediol has a relatively short elimination half-life of about 1-2 days.
Answer: False
Calcifediol has a significantly longer elimination half-life, estimated to be between 15 to 30 days.
Increasing calcifediol levels above 80 nmol/L are associated with significantly enhanced calcium absorption.
Answer: False
Calcium absorption is significantly enhanced by increasing calcifediol levels up to approximately 80 nmol/L; levels above this threshold do not confer further significant increases in absorption.
Calcifediol is generally considered less effective than cholecalciferol in correcting vitamin D deficiency due to slower absorption.
Answer: False
Calcifediol is generally considered more effective than cholecalciferol due to its better intestinal absorption and higher bioavailability.
The pharmacokinetic advantages of calcifediol are particularly useful in patients with normal liver function.
Answer: False
The pharmacokinetic advantages of calcifediol, such as improved absorption, are particularly beneficial in conditions like intestinal malabsorption or obesity, rather than being specifically tied to normal liver function.
Calcifediol binds weakly to the vitamin D-binding protein, allowing for rapid distribution.
Answer: False
Calcifediol binds strongly to the vitamin D-binding protein (VDBP), which influences its transport and distribution, rather than allowing for rapid distribution due to weak binding.
Calcifediol exhibits lower bioavailability compared to cholecalciferol due to poor intestinal absorption.
Answer: False
Calcifediol demonstrates higher bioavailability than cholecalciferol, attributed to better intestinal absorption and higher affinity for vitamin D-binding protein.
How is calcifediol primarily transported in the bloodstream?
Answer: Strongly bound by vitamin D-binding protein (gc-globulin)
Calcifediol is predominantly transported in the bloodstream via strong binding to the vitamin D-binding protein (VDBP), also known as gc-globulin.
How does obesity potentially influence calcifediol levels?
Answer: By potentially lowering the expression or activity of the CYP2R1 enzyme.
Obesity may be associated with reduced expression or activity of the hepatic CYP2R1 enzyme, potentially impacting calcifediol synthesis and circulating levels.
Approximately how long does it take for calcifediol levels to peak after taking a large dose of vitamin D3?
Answer: 7 days
Following a substantial dose of vitamin D3, serum calcifediol levels typically reach their peak concentration around 7 days later.
What is the approximate elimination half-life of calcifediol?
Answer: 15-30 days
Calcifediol exhibits an elimination half-life that ranges approximately from 15 to 30 days.
How do increasing calcifediol levels impact calcium absorption?
Answer: They enhance calcium absorption up to a certain level (approx. 80 nmol/L).
Increasing calcifediol levels enhance intestinal calcium absorption up to approximately 80 nmol/L (32 ng/mL); higher levels do not yield further significant increases.
Compared to cholecalciferol, calcifediol is suggested to have which potential advantage in treating deficiency?
Answer: Better absorption and higher bioavailability
Calcifediol offers potential advantages over cholecalciferol, including superior intestinal absorption and higher bioavailability.
In which patient population might the pharmacokinetic properties of calcifediol be particularly advantageous?
Answer: Patients experiencing intestinal malabsorption
The pharmacokinetic benefits of calcifediol, such as improved absorption, are especially valuable for patients with intestinal malabsorption.
The strong binding of calcifediol to vitamin D-binding protein affects its:
Answer: Transport and bioavailability
The strong binding of calcifediol to vitamin D-binding protein significantly influences its transport within the bloodstream and its overall bioavailability.
Which of the following is a potential advantage of calcifediol over cholecalciferol mentioned in the text?
Answer: Higher affinity for vitamin D-binding protein
A potential advantage of calcifediol over cholecalciferol is its higher affinity for vitamin D-binding protein, contributing to increased bioavailability.
Why might calcifediol be particularly beneficial for obese individuals compared to cholecalciferol?
Answer: It is absorbed better and has higher bioavailability.
Calcifediol's improved absorption and higher bioavailability make it potentially more beneficial than cholecalciferol for obese individuals, who may have altered vitamin D metabolism and distribution.
Measuring serum calcifediol levels is the standard method for assessing an individual's vitamin D status.
Answer: True
Serum calcifediol concentration is the principal biomarker used clinically to determine an individual's overall vitamin D status, reflecting both endogenous production and dietary intake.
Standard blood tests for vitamin D status measure calcifediol (25(OH)D3) and ercalcidiol (25(OH)D2) separately.
Answer: False
Standard clinical assays typically measure the total 25-hydroxyvitamin D, combining the levels of both calcifediol (25(OH)D3) and ercalcidiol (25(OH)D2) into a single value.
The 25(OH)D blood test is primarily used to monitor calcium levels in the blood.
Answer: False
The 25(OH)D blood test is the standard measure for assessing vitamin D status, not for monitoring calcium levels.
Individuals with osteoporosis are considered at lower risk for vitamin D deficiency.
Answer: False
Individuals with osteoporosis are generally considered at higher risk for vitamin D deficiency due to factors related to bone metabolism and potential absorption issues.
Vitamin D screening tests (25(OH)D) are routinely recommended for all individuals regardless of risk factors.
Answer: False
Routine 25(OH)D screening is generally not recommended for the entire general population; it is typically reserved for individuals with specific risk factors or symptoms.
A 25(OH)D level between 50 and 100 nmol/L is generally considered sufficient for vitamin D status.
Answer: True
A serum 25(OH)D concentration within the range of 50 to 100 nmol/L (equivalent to 20-40 ng/mL) is commonly accepted as indicative of vitamin D sufficiency.
The main circulating metabolite of vitamin D, calcifediol, is the most reliable indicator of overall vitamin D status.
Answer: True
As the primary circulating form, calcifediol levels are considered the most accurate and reliable measure for assessing an individual's vitamin D status.
Why is measuring serum calcifediol levels clinically significant?
Answer: It is the standard test to determine an individual's vitamin D status.
Serum calcifediol measurement is the established clinical standard for assessing overall vitamin D status, reflecting both dietary intake and endogenous production.
When measuring total 25(OH)D in blood tests, how are the metabolites of vitamin D2 and D3 typically handled?
Answer: The test combines both calcifediol and ercalcidiol into a single total 25(OH)D value.
Standard clinical assays for vitamin D status typically report a combined total 25(OH)D value, encompassing both calcifediol (from D3) and ercalcidiol (from D2).
What is the main clinical utility of the 25(OH)D blood test?
Answer: To assess the body's overall vitamin D status.
The primary clinical utility of the 25(OH)D blood test is to evaluate an individual's overall vitamin D status.
Which of the following patient groups is NOT typically considered at higher risk for vitamin D deficiency?
Answer: Young adults with regular outdoor physical activity
Young adults engaging in regular outdoor physical activity are generally at lower risk for vitamin D deficiency compared to individuals with chronic kidney disease, osteoporosis, or malabsorption issues.
What does the source suggest regarding routine 25(OH)D testing for the general population?
Answer: It is not typically recommended for the entire general population.
The source indicates that routine 25(OH)D testing is not typically recommended for the general population, with screening usually reserved for those with specific risk factors.
Which range is generally considered sufficient for 25(OH)D levels, according to MedlinePlus cited in the source?
Answer: 20 to 40 ng/mL (50 to 100 nmol/L)
According to MedlinePlus, a serum 25(OH)D level between 20 to 40 ng/mL (50 to 100 nmol/L) is generally considered sufficient.
Calcifediol is not available as a medication and can only be obtained through sun exposure and diet.
Answer: False
Calcifediol is available as a prescription medication in certain countries and is used therapeutically to supplement vitamin D status.
In Canada, calcifediol is available over-the-counter without a prescription.
Answer: False
In Canada, calcifediol is classified and regulated as a prescription-only medication.
Vitamin D2 (ergocalciferol) is also hydroxylated to form 25-hydroxyvitamin D2, also known as ercalcidiol.
Answer: True
Vitamin D2 (ergocalciferol) undergoes 25-hydroxylation to produce 25-hydroxyvitamin D2, which is commonly referred to as ercalcidiol.
Calcifediol supplementation is indicated for conditions like hypoparathyroidism and renal osteodystrophy.
Answer: True
Calcifediol supplementation is a recognized treatment modality for conditions such as hypoparathyroidism and renal osteodystrophy, among others.
A formulation of calcifediol was approved by the FDA in 2016 to treat secondary hyperparathyroidism in chronic kidney disease patients.
Answer: True
In 2016, the FDA approved a calcifediol formulation (Rayaldee) for the treatment of secondary hyperparathyroidism in individuals with chronic kidney disease.
In teleost fish, calcifediol is converted to calcitriol mainly in the kidneys, similar to humans.
Answer: False
In teleost fish, calcifediol is primarily converted to calcitriol in the liver, unlike in humans where this occurs mainly in the kidneys.
Dietary calcifediol supplementation has been shown to improve growth rates in salmonid fish.
Answer: True
Studies have demonstrated that dietary supplementation with calcifediol can enhance growth rates and improve food conversion ratios in salmonid fish species.
In Canada, what is the regulatory status of calcifediol?
Answer: Prescription-only medication
In Canada, calcifediol is classified as a prescription-only medication.
What is the product formed when vitamin D2 (ergocalciferol) undergoes 25-hydroxylation?
Answer: Ercalcidiol (25(OH)D2)
The 25-hydroxylation of vitamin D2 (ergocalciferol) yields 25-hydroxyvitamin D2, also known as ercalcidiol.
Calcifediol supplementation might be used for which of the following conditions?
Answer: Refractory rickets
Calcifediol supplementation is indicated for conditions such as refractory rickets, hypoparathyroidism, and renal osteodystrophy.
What specific FDA-approved indication does calcifediol (Rayaldee) have related to chronic kidney disease?
Answer: To treat secondary hyperparathyroidism
Calcifediol (Rayaldee) received FDA approval for treating secondary hyperparathyroidism in patients with chronic kidney disease.
How does calcifediol metabolism differ in teleost fish compared to humans?
Answer: Fish convert calcifediol to calcitriol mainly in the liver, not the kidneys.
In teleost fish, calcifediol is predominantly converted to calcitriol in the liver, contrasting with the primary renal conversion observed in humans.
What benefit has been observed from using dietary calcifediol supplementation in salmonids?
Answer: Improved food conversion ratios and growth rates
Dietary calcifediol supplementation in salmonid fish has been shown to improve growth rates and enhance food conversion ratios.
A checkmark ('Y') next to data in the infobox signifies that the information requires verification.
Answer: False
A checkmark ('Y') indicates confirmed data, while an 'X' mark or a 'verify' link suggests information that requires verification.
The statement 'Except where otherwise noted, data are given for materials in their standard state' implies that properties are measured under varying temperature and pressure conditions.
Answer: False
The statement indicates that properties are measured under standard conditions (typically 25°C and 100 kPa), ensuring consistency, not varying conditions.
The 'Interactive pathway map' allows users to click on biological components to access related articles.
Answer: True
The 'Interactive pathway map' feature is designed to enable users to click on various biological components within the pathway to navigate to related informational articles.
The navboxes at the end of the article suggest calcifediol is only related to vitamin D metabolism.
Answer: False
The presence of multiple navboxes (e.g., Vitamins, Calcium homeostasis, Vitamin D receptor modulators) indicates that calcifediol is relevant to broader biological systems beyond just vitamin D metabolism.
What is the significance of the 'verify' link and the 'X' mark in the infobox data?
Answer: They suggest the data might be unverified or requires confirmation.
The 'verify' link and 'X' mark serve as indicators that the associated data may require further verification or confirmation.
The multiple navboxes associated with calcifediol indicate its role in:
Answer: Broader biological systems like calcium homeostasis and receptor modulation.
The presence of multiple navboxes, such as those for Vitamins, Calcium homeostasis, and Vitamin D receptor modulators, signifies calcifediol's involvement in a wide array of biological systems and processes.