Introduction of Zinc, Zinc Chemistry, Zinc functions, Zinc metabolism , Role in diarrhea , role in wound healing, immunity , hormones , catalytic zinc atom structure zinc atom , zinc enzyme, acrodermatitis enteropathica, toxicity

1. Zinc
Hari Sharan Makaju
M.Sc.Clinical Biochemistry
1st year
2076/4/27

2. Outlines
• Introduction
• Chemistry
• Dietary sources
• Absorption
• Transport
• Excretion
• Functions
• Clinical deficiency

3. Zinc
Introduction
• Zinc is an essential trace element
• Second most abundant trace element (next to
iron) in the human body, containing
approximately 2–4 g.
• About 99% of the total body is intracellular
• Zinc is present in all body tissues
• 60% is in skeletal muscle
• 30% in bone
• 4–6% in the skin.

4. Zinc
• In the circulation
• 80% is contained within red cells,
• While in the plasma,
• 80% associated with albumin
• Most of the remainder is loosely bound to α2-
macroglobulin.
• Cellular zinc
• 30-40% in the nucleus,
• ~50% is in the cytoplasm and its organelles,
• the remainder is in the cell membrane and/or wall

5. Zinc Chemistry
• Atomic number :30; Atomic weight 65.37
• Zinc has fast ligand exchange kinetics and flexible
coordination geometry
• Good electron acceptor (Strong Lewis acid) with no redox
reaction
• Zinc Binding Ligands
• Zn2+ can coordinate with atoms N, O or S
• In protein zinc-binding sites, Zn2+ is coordinated by different
combinations of protein side chains, including the nitrogen of
histidine (H), the sulfur of cysteine (C), the oxygen of aspartate (D)
and glutamate (E)
• Other more rarely observed ligands include the hydroxyl of
tyrosine (Y), the carbonyl oxygen of the protein backbone and the
carbonyl oxygen of either glutamine (Q) or asparagine (N)

6. Dietary sources
• Widely distributed in food mainly bound to proteins
• Bioavailability of dietary zinc is depend on :
• the digestion of these proteins to release zinc
• and allow it to bind to peptides , amino acid , phosphate and other
ligand within the intestinal tract.
• The best dietary sources of zinc are
• Oysters, red meat, shellfish, nuts and cereals,
• Although processing food tends to remove zinc (e.g. white flour is
a poor source)

7. Recommended Dietary Allowance
(RDA) in US
Infants
• 0 - 6 months:2mg/d
• 7 - 12 months: 3mg/d
Children
• 1 - 3 years: 3 mg/d
• 4 - 8 years: 5 mg/d
• 9 - 13 years: 8 mg/d
Adolescents and Adults
• Males age 14 and over: 11mg/d
• Females age 14 to 18 yrs: 9 mg/d
• Pregnant and lactating mothers:
25mg/day

8. Absorption
• Absorbed in the jejunum and ileum
• Presence of glucose in the intestinal lumen assists its
uptake
• Absorption occurs through by both passive diffusion
and (unknown) carrier mediated processes
• Zinc entry increasing in relation to requirement
• Exchange of zinc across membranes is mediated :
• two solute-linked carrier (SLC) families:
• SLC30(ZnT-1 to ZnT-10)
• SLC39(Zrt, Irt-like protein ZIP1 to ZIP14)family.

9. Absorption
• Influenced by the foods consumed
• 40% of zinc from dietary source is absorbed if body’s needs are great
• Dependent on body’s need
• Presence of phytic acid decreases absorption
• Calcium supplement decreases zinc absorption
• Competes with copper and iron absorption

10. Transport
• 1-14 ZIP(SLC 39) transporters that have critical roles in the
transport of zinc into cytoplasm from
• Extracellular sources
• Intracellular storage compartments such as the Golgi apparatus and
endoplasmic reticulum.
• The ZIP transporters are regulated by intracellular and
extracellular zinc concentrations, and hormones and
cytokines.
• 1-10 ZnT (SLC30) transporters–transport of zinc
• Into subcellular organelles from the cytosol
• From the cytosol through the plasma membrane into the
extracellular space

14. Fig. Predicted structure of the zinc transporters ZIP and ZnT. ZIP transporters are
predicted to have eight transmembrane domains (TMDs) with a long histidine loop
between TMDs 3 and 4. The ZnT transporters are predicted to have six TMDs with
a histidine loop between TMDs 4 and 5.
Source:Figure was produced using Servier Medical Art, http://www.servier.com

15. Overview of major zinc transporters expressed in intestinal epithelial cells. ZIP4 is a
major importer and is regulated by zinc. ZIP14 is responsive to proinflammatory
conditions and is postulated to be at both the apical and basolateral surface of
enterocytes. ZnT1 and ZIP5 influence zinc trafficking at the basolateral
membrane.ZnT7 influences the apparent transcellular movement of zinc.

16. Fig.Cellular and subcellular localization of zinc transporters ZIP and ZnT.The primary
localization of ZIP transporters (red arrow heads) and ZnT transporter (purple arrows) is
shown representing the direction of zinc transport

18. Transport
• Metallothionein, an intracellular metal buffer, and the
transporter ZnT1 at the basolateral membrane
• Regulate the amount of zinc released to the portal circulation for
systemic distribution.
• Absorbed zinc is transported to the liver by the portal
circulation
• Active incorporation into metalloenzymes and plasma
protein such as albumin and α2-macroglobulin.

19. Excretion
Zinc is excreted through:
• Gastrointestinal tract
• Urinary losses
• 0.5mg/day
• Sweat :
• 500 to 600pg/day

21. PHYSIOLOGICAL FUNCTIONS OF ZINC
• Biochemical functions :
 Cofactor for enzymes
 Activity of zinc finger proteins
• Cellular functions :
 Growth & cell development
 Cell membrane integrity
 Tissue growth & repair
 Wound healing
 Immunological functions :
 Function of neutrophils,T cells, B cells and NK cells

22. PHYSIOLOGICAL FUNCTIONS OF ZINC
• Endocrinological functions:
 Reproduction: spermatogenesis
 Thyroid function
 Pancreatic function-Insulin storage and release
 Prolactin secretion
 Thymopoetin synthesis
 Neurological function: Cognition, memory, taste
acuity, vision
 Hematological function : coagulation factors
 Skeletal function : Bone mineralization

23. Function
• More than 300 Zinc metalloenzymes occurs in all six
categories of enzymes.
• Important example : Carbonic anhydrase, Alkaline phosphatase,
DNA and RNA polymerase, Thymidine kinase, Carboxypeptidase
and Alcohol dehydrogenase
• For their catalytic activation, thus participating in various
enzymatic and metabolic cellular processes in human
body

24. Class I: Oxidoreductases
Alcohol dehydrogenase, Lactate dehydrogenase, Lactate
cytochrome reductase,Superoxide dismutase
Class II:Transferases
Transcarboxylase, Aspartate transcarbamylase,
Phosphoglucomutase,RNA polymerase, Reverse transcriptase,
Nuclear poly(A) polymeraseTerminal deoxyribonucleotidyl
transferase
Class III : Hydrolases
Leukotriene A, hydrolase, Alkaline phosphatase, 5’-
Nucleotidase, Fructose-1,6- bisphosphatase, Phospholipase C,
Aminopeptidase, Angiotensin-converting enzyme,Carboxypeptidase
A, Carboxypeptidase B, Collagenase ,Protein kinaseC
Class IV: Lyases
Carbonic anhydrase, δAminolevulinic acid dehydratase
ClassV: Isomerases
Phosphomannose isomerase,DNA topoisomerase I
ClassVI: Ligases
tRNA synthetase, Pyruvate carboxylase

25. Zinc Enzymes
• Zinc has three function in zinc enzymes:
• Catalytic
• Coactive (or cocatalytic)
• Structural
• Catalytic
• A catalytic role specifies that the metal participates directly in
enzyme catalysis.
• If the metal is removed by chelating or other agents, the enzyme
becomes inactive.
• Alcohol dehydrogenase, Angiotensin-converting enzyme,
Collagenase

26. Zinc Enzyme
Coactive (or cocatalytic) :
• Zinc atom enhances or diminishes catalytic function in
conjunction with another active site zinc atom in the
same enzyme
• but is not indispensable of itself for either enzyme
activity or stability .
• An amino acid forms a ligand bridge between two zinc or
a zinc plus a different metal atom.
• There are two such bridged metal atoms
• Zinc and magnesium, in alkaline phosphatase
• Two zinc atoms in phospholipaseC zinc and possibly
• Zinc and copper in erythrocyte superoxide dismutase

27. superoxide dismutase

28. Zinc Enzyme
Structural zinc atom
• Are required solely for structural stability of the protein
• Help stabilize the quaternary structure of oligomeric
holoenzymes.
• Aalcohol dehydrogenase , Aspartate transcarbamylase
, and Protein kinase C, nitric oxide synthase
• Alcohol dehydrogenases of vertebrates are the only enzymes
known thus far to contain both a catalytic and a structural zinc
atom.

29. Zinc Proteins
• Protein can form domain able to bind tetrahedral zinc
atom by coordination with histidine and cysteine to form
folded structurer that have become known as “Zinc
Finger”
• Two other classes of zinc proteins
• Metallothioneins
• Gene regulatory proteins
• The key role of Zinc in protein and nucleic acid synthesis
explain the failure of growth and impaired wound healing
observed in individual with zinc deficiency .

30. Metallothionein (MW: 9000-10000Da)
• First isolated as a cadmium- and zinc-containing species from
equine kidney cortex in 1957
• Composed of 62 amino acids, including 20 cysteines,
• Metallothionein-like proteins and peptides
• Have found in numerous unicellular and multicellular
organisms
• Grouped together as a family composed of three
• Class I - mammalian organisms, and their primary structures
are highly conserved.
• Class II- unicellular eukaryotes, such as yeast
• Class III- is present in plants, composed of chains varying from
2 to 11 y-glutamylcysteinyl units

31. Metallothionein
• Some remaining zinc in enterocytes bound to a
metallothionein
• the proportion depending on the amount of metallothionein
present.
• Important in intracellular zinc trafficking and helps to
maintain intracellular zinc concentration

32. Gene regulatory proteins
• Many nucleoproteins directly involved with replication
and transcription of DNA are now known to contain
functionally important zinc atoms
Protein Zinc/mole Ligand/Zinc
TFIIIA 7-11 2 Cys, 2 His
Glucocorticoid
receptor
2 4 Cys
Estrogen receptor 2 4 cys
Gene 32 protein
(g32p)
1 3Cys, 1His
GAL 4 2 4Cys
Zinc in replication and transcription regulatory proteins

33. Gene regulatory proteins
• Zinc is required for DNA binding ofTFIIIA.
• The protein will not bind to the internal control region of the 5s RNA
gene if zinc is removed by chelating agents.
• Zinc is believed to function by organizing a subdomain
within residues 22-253 of g32p
• that is required to maintain the protein-protein interaction as that
are essential for cooperative binding to single-stranded DNA

34. Gene regulatory proteins
Glucocorticoid and Estrogen receptors are also zinc proteins.
• They are members of a multigene family that includes
receptors
• For thyroid hormone, retinoic acid, and vitamin D,
• That incorporate three polypeptide domains, each
interacting with a different ligand.
• The first domain binds to a specific hormone, e.g., cortisol or
estrogen;
• the second interacts with enhancer like DNA segments;
• the third binds to RNA polymerase .
• Hormone-receptor complex facilitates the interaction
between the DNA binding domain and the enhancer region
.

35. • Zinc is required forGAL4 function
• GAL4 protein from yeast activates the genes utilized for
galactose metabolism

36. Functions
Zinc has a critical role in maintaining human health,
especially in terms of anti-oxidative stress and anti-
inflammation
• Zinc is not redox active
• Antioxidant function of zinc is through some indirect mechanisms
of action.
• Zinc competes with redox active metals for negative
charges in lipid bilayer; and as such, it protects the cell
membrane from lipid oxidation
• Zinc is also able to interact with thiol or sulfhydryl groups
in proteins and peptides
• to reduce the reactivity of sulfhydryl groups.
• This stabilization prevents intramolecular disulfide
formation, and thus zinc functions as an antioxidant

37. Functions
• Zinc also protects cells from oxidative stress
• By increasing glutathione (GSH) biosynthesis
• Responsible for the maintenance of cellular redox state.
• Zinc additionally serves as a cofactor in antioxidant
enzymes
• such as superoxide dismutase 1 (SOD1) that scavenges superoxide
anions.

38. Function
Zn as an intracellular signaling molecule, or the second
messenger
• The released zinc, termed the ‘zinc wave’,
• Activates two mitogen-activated protein kinase
(MAPK) pathways
• the extracellular signal-related kinase (ERK)
• the c-Jun N-terminal kinase(JNK).
• MAPKs are serine/threonine protein kinases activation
by extracellular or intracellular signals,
• Phosphorylate proteins involved in regulating cell
proliferation, differentiation and apoptosis

39. Prostate function
• Secretion by the prostate of large amount of zinc
• key role to the function of sperm, maintaining both vitality
and antibacterial environment.
• Decrease seminal Zn can be a risk factor for sperm
abnormality and idiopathic male infertility.
• Seminal plasma zinc concentration normal in chronic
prostatitis and adenoma
• Prostatic neoplasm – Decrease

40. Role of Zinc in the body
Zinc and the endocrine system
• Manifold influences on the endocrine system
• Role in the metabolism of androgen hormones, estrogen,
and progesterone, together with the prostaglandins
• Role in the secretion of insulin,
• Role in the regulation of thymic hormones
• An involvement of zinc in the regulation of sex hormones in
males and females can be concluded indirectly.

41. Zinc and the immune system
• Zinc status of an individual affects the majority of
immunological events such as
• Hematopoiesis
• Immune cell function and survival,
• Humoral immunity,
• Cytokinesecretion
• Zinc is necessary for intracellular binding of tyrosine
kinase to the T-cell receptors CD4 and CD8, which are
required for T-lymphocyte activation

42. Causes of Zinc Deficiency
 Lack of nutrition
 Excessive alcohol intake
 Long term exposure to environmental toxins
 Malabsorption syndrome
 Chronic diseases e.g. sickle cell anemia, Wilson's disease,
renal and liver diseases

43. Clinical deficiency
• Multiple biochemical function of Zinc , the clinical
presentation of deficiency disease is varied, nonspecific
and related to the degree and duration of depletion.
• Sign and symptoms
• Depressed growth with stunting
• Increased incidence of infection
• Possibly related to alternation in immune function
• Diarrhea
• Skin lesion
• Alopecia
• Defect ion carbohydrate use
• Other adverse clinical outcomes

44. Effect of Growth

45. Acrodermatitis Enteropathica.
• AR inherited partial defect in intestinal zinc absorption.
• Encodes a protein that appears to be involved in zinc
transportation
• Erythematous and vesiculobullous dermatitis

47. Parenteral Nutrition.
• Some patients requiring intravenous feeding after surgery
are likely to be significantly zinc depleted
• because of poor oral intake before and after surgery.
• may have increased zinc losses from the intestinal tract via
diarrhea and in urine from catabolism of muscle during periods of
negative nitrogen balance.
• Diarrhea, mental depression, dermatitis, delayed wound
healing, and alopecia are seen during the anabolic period
of weight regain when zinc is insuffient in the nutritional
regimen to support tissue repair.
• Provision of adequate zinc intravenously to achieve a
positive zinc balance is associated with improvement in
nitrogen balance.

48. Infectious Disease.
• Zinc depletion impairs immunity and has a direct
effect on the gastrointestinal tract
• This increases the severity of enteric infections.
• In populations at risk of zinc and vitamin A
deficiency, provision of zinc alone increased the
incidence of respiratory infection, but when vitamin
A was added, respiratory infections were decreased.

49. Subclinical Effects of Deficiency
• When zinc deficiency is not severe enough to cause
clinical signs and symptoms, it still may have a subclinical
affects on
• immune function,
• the synthesis and action of hormones
• neurologic function

50. Immune Function
• In zinc deficiency, a reduction in the activity of serum
thymulin, the thymus specific hormone involved in
• T-cell function,
• Imbalance betweenTh 1 andTh 2 helper cells.
• The lytic activity of natural killer cells also decreases.
• These complex changes result in impairment of cell-
mediated immunity and may serve as the
basis for increased infection rates seen in marginal zinc
depletion.

51. Immune function
• Moderate deficiencies in Zn occur in
• sickle cell anemia, renal disease, chronic gastrointestinal
disorders HIV; Children with diarrhea; & elderly persons.
• Zn deficiency greatly alters host defense systems,
leading to in opportunistic infections & mortality rates

55. Hormones
• Zinc is thought to have a role in the synthesis and actions of
many hormones via zinc transcription factors.
• Zinc depletion is associated with low circulating
concentrations of testosterone, freeT4, insulin-like growth
factor (IGF)- 1, and thymulin.
• Both plasma IGF-1 and growth velocity are increased in
zinc-supplemented children.
• Production of testosterone has been shown to be improved
in patients given zinc supplements when initial plasma
concentrations indicated zinc defiiency.
• Hence zinc may play an important role in modulating serum
testosterone concentrations in normal men.

57. Hormone
• Zinc deficiency and the depletion of testosterone result in
an inhibition of spermatogenesis in males.
• Hypogonadism is a major manifestation of zinc deficiency.
• A low zinc status has been associated with diabetes (types 1
and 2)
• Zinc supplementation was reported capable of restoring
insulin secretion

58. Hormone
ZnT8 and type 2 diabetes
• ZnT 8 predominant in pancreatic β-cells
• For the synthesis, storage and action of insulin .
• A strong association between a mutation in ZnT8 and
type 2 diabetes was noticed in different populations
• An Arg instead of a Trp at position 325 in the
cytoplasmic domain of ZnT8 increases the risk for
developing diabetes.

59. Neurologic Effects.
• Severe zinc deficiency is known to affect mental well
being, with varying degrees of confusion and depression
consistent with zinc enzymes having important activity in
brain development and function.
• Alterations in zinc homeostasis may be associated with
brain dysfunction, including brain inflammatory status.
• Zinc ion dyshomeostasis may also play a role in the aging
neuron through deterioration of synapses.

60. Zinc Deficiency
• Upon zinc depletion, SOD1 mutants underwent
conformational changes due to zinc dissociation,
• Resulted in oxidative stress and endoplasmic reticulum
(ER) stress
• The excess oxidative stress react with nitric oxide (NO) to
form RNS
• Turn to oxidize endothelial nitric oxide synthase (eNOS)
and uncouple functional eNOS dimers.
• Accumulating evidence has demonstrated that the eNOS
dimer uncoupling increases pathologic ROS production
and decreases NO synthesis by the endothelium.

61. Zinc deficiency
• Lowering of plasma zinc in the acute-phase response
associated with inflammatory conditions
• Zinc deficiency results in the impairment of antibody-mediated
and cell-mediated immune response
• Causes increased auto-reactivity likely due to damaged
immune tolerance and/or inefficient removal of autoreactive T-
cells.
• In addition, zinc deficiency contributes to chronic inflammatory
conditions, where no inducer appears to be required.
• These conditions coincide with and are likely to contribute to
CVDs, type 2 diabetes (T2DM), and
other chronic diseases

63. Role of Zinc Diarrhea
Physiological effects of zinc

64. • Zinc supplementation in the
treatment and prevention of
bloody diarrhea
Zinc therapy was associated with enhanced antigen-specific antibody
responses.
◦The bactericidal antibody titers against Shigella increased the proportions
of B cells and plasma cells, as also higher lymphocyte proliferation
responses in the peripheral circulation, during the early convalescent phase
of shigellosis.
For all these reasons, zinc supplementation should be given as an adjunct to
antimicrobial treatment in bloody diarrhea.

65. Role of zinc in wound healing
In experimental animal studies-
• In the skin, the highest concentration of zinc is found in the
epidermis, especially in the keratinocytes closest to the
basement membrane.
• In the initial inflammatory phase, zinc levels rise at the edges
of the wound
• this concentration increases during granulation and epithelialization
phase.
• This is due to increased expression of membrane transporters in
keratinocytes, fibroblasts and macrophages.
• In the final stage of wound healing, these levels are reduced,
with the consequent decrease in cell division.

66. Role of zinc in wound healing
• Although the exact action mechanism of zinc
is unknown
• Different pathways in which it could be involved have
been proposed
• Cell replication and migration
• Protein synthesis and cell repair.
• In addition, it has also been shown that topical zinc in
wounds promotes autolytic debridement.
• Due to the collagenase activity of the
matrix metalloproteinases of which zinc is a cofactor.
This benefit has been observed in pressure ulcers,
diabetic foot and burns.

67. Role of zinc in wound healing
• when zinc is applied directly on the wound and damaged
perilesional skin
• the elimination of non-viable tissue is promoted, the risk of
superinfection decreases
• inflammation is reduced and epithelialization is stimulated.

69. Toxicity
• U.S. Nutrition Board has set the tolerable upper amount
of intake for adults at 40 mg/d.
Clinical effects
• Abdominal pain, diarrhea, nausea, and vomiting .
• Single doses of 225 to 450 mg of Zn can induce vomiting
with milder forms of gastrointestinal upset reported at 50
to 150 mg Zn/d (dosages that were initially used in
therapy).
• More than 60 mg Zn/d can result in copper depletion by
causing intestinal blockade of intestinal absorption.

73. References
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74. References
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75. THANKYOU