PLASMA PROTEINS

Dr.Jasmin.A.S

Composition of blood and plasma

Plasma constitutes water (90%),proteins,electrolytes,nutrients and metabolites

PLASMA PROTEINS

Albumin Globulin

Fibrinogen Others

Albumin 60%Globulin 35%Fibrinogen 4%Others 1%

PLASMA PROTEINS

Total protein content - 6-8 g/dl Almost all plasma proteins except

immunoglobulins are synthesised in liver

Mainly glycoproteins Albumin ,globulin and fibrinogen are

the major plasma proteins

ALBUMIN

Predominant plasma protein,water soluble

Synthesised in liver The name is derived from the white

precipitate formed when egg is boiled[albus means white in Latin]

Normal blood level is 3.5-5 g/dl Migrates fastest in electrophoresis at

alkaline pH and precipitates last in salting out methods

ALBUMIN…continued

Structure and synthesis Has one polypeptide chain consisting

of 585 AAs with 17 disulfide bonds Mol wt :69 KD,relatively low mol.wt Daily production:12g/day Estimation of albumin is a

component of liver function test [LFT] Has a PI of 4.7

Its signal peptide is removed as it passes into the cisternae of the rough endoplasmic reticulum, and a hexapeptide at the resulting amino terminal is subsequently cleaved off farther along the secretory pathway Albumin can come out of vascular compartment,so it is present in CSF and interstitial fluid

Albumin is initially synthesized as a preproprotein

ALBUMIN-Functions

1. Maintenance of blood volume by maintaining the colloid osmotic pressure Total osmolality of serum is 278-305 milliosmol/kg Albumin is responsible for 75-80% of the osmotic

pressure of human plasma due to its large concentration and relatively small mol.wt

Maintenance of blood volume and body fluid distribution is dependent on EOP

According to Starling hypothesis,at the capillary end,the BP expels water out and EOP takes water into the vascular compartment at the venous end

At arterial end BP is 35 mm Hg,EOP is 25 mm Hg;thus water is expelled by a pressure of 10 mm Hg

At the venous end,BP is 15 mm Hg and EOP is 25 mm Hg;thus water is imbibed with a pressure of 10 mm Hg

Thus no of water molecules escaping out at the arterial side will be exactly equal to those returned at the venous end and thus blood volume remains the same

In hypo albuminemia,[decreased blood levels of albumin] the EOP is correspondingly decreased return of water to blood vessels decreased accumulation/retention of water in tissues EDEMA

Edema usually occurs when blood albumin level is < 2g/dl

2. Transport function Carrier of various hydrophobic substances

i. Bilirubin and non esterified fatty acidsii. Drugs like

sulpha,aspirin,salicylate,dicoumarol, phenytoin

iii. Hormones like steroid hormones,thyroxine

iv. Metals like copper,calcium and heavy metals

3. Buffering action Albumin has maximum buffering

capacity as it has the highest concentration in blood

Albumin has 16 histidine residues which contributes to this buffering action

4. Nutritional function Albumin is a complete protein Albumin is taken up by pinocytosis It may be considered as the transport

form of essential AAs from liver to extra hepatic cells

Albumin thus serves as a source of AAs especially in cases of nutritional deprivation

ALBUMIN- Clinical significance1. Blood brain barrier

Alb-FA complex cannot cross the BBB,so FAs cannot be taken up by brain

Unconjugated bilirubin can cross the BBB : so in cases of unconjugated hyperbilirubinemia in infants,as occurs in Rh incompatibility,the free bilirubin can get deposited in the brain leading to kernicterus and mental retardation

2. Drug interactions Drugs having high affinity to albumin will

compete each other for the available sites with consequent displacement of one drug leading to significant drug interactions

Eg : phenytoin – dicoumarol interaction

3. Blood calcium levels In hypo albuminemia,blood levels of

calcium decreases Serum total calcium may be decreased Ionic calcium remains same Tetany does not occur For a fall of 1g/dl of albumin,Ca is

lowered by 0.8mg/dl

4. Therapeutic use Human albumin is therapeutically useful

to treat burns,hemorrhage and shock

5. Hypo albuminemia and edemaa. Malnutrition - albumin synthesis is

depressed [generalised edema]b. Nephrotic syndrome - albumin is lost

through urine facial edema]c. Cirrhosis of liver – decreased albumin

synthesis [ascites]d. c/c congestive heart failure – pitting

edema of feet

6. Albuminuria Presence of albumin in urine Always pathological Micro albuminuria – 30-300mg/day ;

occurs in acute nephritis,inflammatory conditions of urinary tract

Macro albuminuria - >300mg/day ;occurs in nephrotic syndrome

8. Protein losing enteropathy Large quantities of albumin is lost from

GIT9. Analbuminemia – absence of

albumin synthesis defective mutation in the gene; very rare condition

ALBUMIN-GLOBULIN RATIO or A/G ratio

Normal is 1.2:1 – 1.5:1 In hypo albuminemia,there will be

compensatory increase in globulin synthesis

A/G ratio is either altered or even reversed leading to edema

Common causes include cirrhosis,nephrotic syndrome,multiple myeloma

GLOBULINS

Multiple proteins which are separated into 4 distinct bands a1,a2,band gamma

Higher mol.wt than albumin; ranges from 90,000 to 13,00,000

Have a variety of functions including transport and immunity

Normal blood concentration is 2.5 – 3.5 g/dl

Separated by half saturation with ammo.sulfate

Α1-globulinsA1 antitrypsin Inhibitor of trypsin and

other serine proteasesOroso mucoid Transports progesteroneA1 lipoproteins Transports cholesterol

from tissues to liverAFP Principal fetal proteinRetinol binding protein [RBP]

Transports retinol

Thyroxine binding globulin [TBG]

Transports thyroxine

Cortisol binding globulin [CBG]or transcortin

Transports cortisol and corticosterol

A2 globulins2 macroglobulin Inhibitor of proteasesHaptoglobins Binds with Hb and

prevents its excretionProthrombin Essential for blood

clottingCeruloplasmin Transports Cu,oxdn of

ferrous to ferric ionTranscobalamine Transports vit B12

B globulinsB lipoproteins [LDL] Transports cholesterol

and triglycerides to tissues

B2 microglobulin Used to test renal tubular function

Transferrin Transports ironHemopexins Transports hemePlasminogen Involved in

fibrinolysis

Gamma globulins Eg: CRP [C reactive protein] Non specific defence against infectious

agents

FIBRINOGEN Synthesised by liver Mol.wt 3,40,000 D Acute phase protein Has important role in blood clotting process Also called clotting factor1 Constitutes 4-6% of total protein (200-400

mgdl) Imparts maximum viscosity to blood Precipitated with 1/5 th saturation with

ammonium sulphate

SEPARATION OF PLASMA PROTEINS1. Salting out technique

Albumin – full saturation with ammo.sulphate Globulin – half saturation with ammo.sulphate Fibrinogen - ⅕ saturation with ammo.sulphate

2. Electrophoresis Most commonly used method used Proteins are separated into 5 distinct bands ;

albumin,a1,a2,b and gamma globulins

Normal electrophoretic pattern

Reference ranges:

Total protein 6.0 – 8.0 g/dLAlbumin 3.5 – 5.0 g/dLα1-globulins 0.1 – 0.4 g/dLα2-globulins 0.4 – 1.3 g/dLβ-globulins 0.6 – 1.3 g/dLγ-globulins 0.6 – 1.5 g/dL

Acute infections

• Immediate response occurs with stress or inflammation caused by infection, injury or surgical trauma

• normal or ↓ albumin• ↑ α1 and α2 globulins

Chronic infections•Late response is correlated with chronic infection(autoimmune diseases, chronic liver disease, chronic infection, cancer)• normal or ↓ albumin•↑α1 or α2 globulins•↑↑ γ globulins

Cirrhosis of liver• Cirrhosis can be caused by

chronic alcohol abuse or viral hepatitis

• ↓ albumin• ↓ α1, α2 and β globulins• ↑ Ig A in γ-fraction

Nephrotic syndrome• the kidney damage illustrates the

long term loss of lower molecular weight proteins

(↓ albumin and IgG – they are filtered in kidney)

• retention of higher molecular weight proteins (↑↑ α2-macroglobulin and ↑β-globulin)

Multiple myeloma

SEPARATION ..continued

3. Ultra centrifugation technique Based on the difference in densities of

various proteins4. Cohn’s fractionation5. Gel filtration

ACUTE PHASE PROTEINS

A class of proteins whose plasma concentrations increase (positive acute phase proteins) or decrease (negative acute phase proteins) in response to various inflammatory and neoplastic conditions

ACUTE PHASE PROTEINS

Positive acute phase proteins

Negative acute phase proteins

C reactive protein Albumin

Ceruloplasmin Transthyretin Alpha 1 antitrypsin Retinol binding

proteinAlpha 2 macroglobulin

Transferrin

C reactive protein (CRP)Named so because it reacts with C

polysaccharide of capsule of Pneumococci

Beta globulin with mol.wt of 115-140 KDSynthesised by liverIt can stimulate complement activity and

macrophage phagocytosisClinically important marker in predicting

the risk of coronary artery diseases

Ceruloplasmin Copper containing α2-globulin Glycoprotein with enzyme activities

(ferroxidase) It has a blue color because of its high

copper content Each molecule of ceruloplasmin binds six

atoms of copper very tightly, so that the copper is not readily exchangeable

Normal plasma concentration approximately 30mg/dL

Synthesized in liver in the form of apo ceruloplasmin, when copper atoms get attached it becomes Ceruloplasmin.

It carries 90% of the Cu present in plasma &binds so tightly that the Cu is not readily exchangeable.

Albumin carries the other 10% of the plasma Cu but binds less tightly

Albumin thus donates its Cu to tissues more readily than ceruloplasmin and appears to be more important in Cu transport

Clinical significance Normal level- 25-50 mg/dl Low levels of ceruloplasmin are found in Wilson

disease (hepatolenticular degeneration), a disease due to abnormal metabolism of copper.

The amount of ceruloplasmin in plasma is also decreased in liver diseases, mal nutrition and nephrotic syndrome.

Increased in active hepatitis,biliary cirrhosis,hemochromatosis,obstructive biliary disease,pregnancy,estrogen therapy,inflammatory conditions,collagen disorders and in malignancies

A1 antitrypsin Also called α1-antiprotease It is a single-chain protein of 394 amino

acids, contains three oligosaccharide chains

It is the major component (> 90%) of the α 1 fraction of human plasma.

It is synthesized by hepatocytes and macrophages and is the principal serine protease inhibitor of human plasma.

It inhibits trypsin, elastase, and certain other proteases by forming complexes with them.A deficiency of this protein has a role in certain cases (approximately 5%) of emphysema.

Transport proteins1. Albumin 2. Retinol binding protein3. Thyroxine binding globulin4. Cortisol binding globulin5. Haptoglobin6. Transferrin7. Hemopexin8. HDL and LDL