Vitamin C Flashcards
What was written by James Lind in 1753, that showed that scurvy was easily treated with citrus fruits?
Treatise of the Scurvy
What do plants synthesize Vitamin C from?
glucose & fructose
Most mammals can synthesize Vitamin C from glucose in their…
liver or kidneys
- Most mammals: dogs, cats, mice, cows, horses
- Reptiles
- Amphibians
Why can’t mammals synthesize Vitamin C?
Lack the enzyme to convert glucose to Vitamin C
Where is fat soluble Vitamin C stored in the body? (3)
- Adrenal gland
- Pituitary gland
- Eyes
Vitamin C = ________ = ascorbate
L-ascorbic acid
L-ascorbic acid (ascorbate) is what kind of acid?
- Weak acid
- 6 carbon alpha-ketolactone
Vitamin C can donate what to other compounds which are at risk of becoming oxidized.
2 electrons
- Vitamin C is an electron donor, which makes it a reducing agent
Why is Vitamin C known as an outstanding antioxidant?
- Its reduction potential as an electron donor is very high.
- Readily “gives up” electrons
How is Vitamin C assessed?
Serum Ascorbic Acid levels
Serum Ascorbic Acid levels are …
Dose-dependent
*No further increase following additional doses of VIt. C
What is Serum Ascorbic Acid levels lowered by? (7)
- Smoking
- Oral contraceptive use (birth control)
- Cold
- Fever
- Acute or chronic stress
- Infection
- Inflammatory Bowel Disease
What 2 ways can Vitamin C be absorbed?
Active transport & Simple diffusion
Where does the active transport of Vitamin C occur?
Active transport occurs through out the small intestine.
Simple diffusion of Vitamin C occurs with?
Simple diffusion occurs with higher intake of Vitamin C
Absorption of Vitamin C is modulated by what?
Glucose transporters (GLUT)
What form of Vitamin C is typically absorbed more in the lumen?
Dehydroascorbate
Dehydroascorbic acid (DHAA) is converted to ascorbate in enterocytes via?
DHAA reductase
In what form does Vitamin C circulate?
Freely, unbound to any proteins
*Water-soluble nutrient available for cellular transport and accumulation inside tissues.
Vitamin C is uptaken into cells via?
SVCT1 & SVCT2 - sodium-dependent Vitamin C transporters
Both SVCTs are dependent on what?
Na & ATP
Neither of the SVCTs transport …
Dehydroascorbic acid
In what forms is Vitamin C excreted as?
intact or in form of metabolites
Where does the metabolism of Vitamin C occur?
Liver & also kidney
What are the final excretory products of Vitamin C metabolism? (2)
Oxalic acid & 4-C threonic acid
Vitamin C can also be excreted as …
A variety of 5-C sugars
- Xylose, xylonate, lyxonate
Ascorbic acid concentrations in plasma are tightly regulated by what?
Kidney
What patients is Vitamin C excretion problematic?
End-stage renal disease
Why is Vitamin C excretion problematic in patients with end-stage renal disease?
Due to lack of glomerular filtration
In patients with end-stage renal disease Vitamin C doses higher than 200mg can accumulate and produce?
hyperoxalemia
Why do dialysis patients often have chronically low plasma Vitamin C concentrations?
To prevent to much oxalate formation in the blood.
* hyperoxalemia
Vitamin C is required as a cofactor for how many different enzymes?
8
What are the 2 families of enzymes that require Vitamin C as a cofactor?
Monooxygenases & Dioxygenases
What incorporates a single oxygen molecule into a substrate?
Monooxygenases
What enzyme is responsible for:
Dopamine -> Norepinephrine synthesis
Dopamine Beta-monooxygenases
What incorporates molecular oxygen (O2) into a substrate?
Dioxygenases
Dioxygenases adds hydroxyl groups to ____ or ____.
Proline or lysine
Adding hydroxyl groups to proline or lysine for the …
formation of collagen molecule
Dioxygenases are used in the biosynthesis of …
Carnitine
What is carnitine is essential for?
Fatty acid transport into mitochondria
Dioxygenases are used in the metabolism of?
Tyrosine
What symptoms are related to the impaired function of these two families of enzymes?
* (Especially in impairment of collagen formation)
Scurvy symptoms
Vitamin C acts as an antioxidant by preventing intracellular?
Protein oxidation
The prevention of intracellular protein oxidation is relevant in which tissues with high oxidant production?
- Neutrophils
- Monocytes
- Macrophages
The prevention of intracellular protein oxidation is relevant in which tissues with high oxygen concentrations?
- Lungs
- Tissues of the eye exposed to light
Vitamin C acts as an antioxidant extracellularly by preventing?
Oxidant-mediated damage extracellularly
Vitamin C prevents oxidant-mediated damage extracellularly by quenching … (2)
- Aqueous peroxyl radicals
- Lipid peroxidation products (rancid fats)
Vitamin C is preferentially used before what? (3)
- Tocopherols (Vit. E)
- Bilirubin
- Uric acid
Vitamin C affects several pathways involved in what?
Atherogenesis
Vitamin C protects LDL from what?
Metal catalyzed oxidation
- Hypothesized to be an initiating factor in atherogenesis
Vitamin C can regenerate oxidized …
alpha - tocopherol (Vitamin E)
Vitamin C affects several pathways involved in atherogenesis, and can decrease …
Lipid peroxidation
Vitamin C can decrease adhesion of ______ to endothelium of vascular system?
Monocytes
Vitamin C can decrease aggregation of ______ & _______.
Platelets and leukocytes
Vitamin C can quench oxidants that ‘leak’ from activated ______ or ______, which prevents damage to supporting tissues such as collagen and surrounding fibroblasts.
Neutrophils or macrophages
Vitamin C is involved in cholesterol degradation for …
Bile acid synthesis
What retards cholesterol transformation into bile acids?
Vitamin C deficiency
What has been implicated as a risk factor in CVD?
Hypovitaminosis C
Vitamin C is involved in the conversion of folacin to
Tetrahydrofolate (THF)
Vitamin C is involved in the synthesis of
adrenal tissue steroids (noradrenaline)
Vitamin C helps iron absorption by …?
- reducing ferric to ferrous form
- and is involved in transfer from plasma transferrin to liver ferritin
Vitamin C improves immune response by increasing? (4)
- Immunologic activity of leukocytes
- Interferon production
- Integrity of mucous membrane
- Processes of inflammatory reactions
What was found to be lower in HIV subjects?
Plasma ascorbate
What treatment is commonly used in HIV subjects?
Interferon treatment
Tolerable upper limit was set due to what at higher doses?
Gi adverse affects
Who is at risk for deficiency? (3)
- Smokers
- Individuals with limited food variety
- Females using oral contraceptives
Smokers have lower ____ & _____ vitamin C levels, and require additional 35mg/day of vitamin C.
plasma & leukocyte
What are the best sources of vitamin C?
Fruits and vegetables
What are the earliest symptoms of scurvy?
Weakness & lassitude (a state of physical or mental weariness; lack of energy)
A symptom of vitamin C deficiency results in an autoimmune disease in which sufferers experience dry mouth & dry eyes.
Sjogren’s Syndrome
Ingestion of 3g of Vitamin C or more per day can cause what? (4)
- Osmotic diarrhea
- Bloating
- Hyperuricosuria
- Iron overload in certain cases
Presence of excessive amounts of uric acid in urine, associated with kidney stones.
Hyperuricosuria
