Plasma Proteins Dr. Sara Mariyum

Centrifuged Blood Sample Add anticoagulants (heparin, potassium oxalate) Centrifuged Blood Sample

Components of Plasma Blood plasma Consists of: Other components: Water 90% Plasma Proteins 6-8 % Electrolytes (Na+ & Cl-) 1% Other components: Nutrients (e.g. Glucose and amino acids) Hormones (e.g. Cortisol, thyroxine) Wastes (e.g. Urea) Blood gases (e.g. CO2, O2)

Separation of Components Plasma = Less Dense Platelets / WBCs RBCs More Dense

Plasma vs. serum Anticoagulated Clotted serum= plasma - fibrinogen Plasma is the liquid, cell-free part of blood, that has been treated with anti-coagulants. Serum is the liquid part of blood AFTER coagulation, therfore devoid of clotting factors as fibrinogen. Anticoagulated Clotted serum= plasma - fibrinogen

Origin Liver ( except immunoglobulin's) Derived from dietary protein Normal level 6.3 to 8 gm/dl

TOTAL PLASMA PROTEINS The normal serum protein level is 6.3-8.3 g/L. The type of proteins in plasma include: a. Albumin b. Globulins α− globulin: α1 & α2−globulins β− globulin: β1 & β2 globulins γ− globulins c. Fibrinogen

Under different pathological conditions the protein levels depart from the normal range Over 300 proteins have been detected in plasma

General functions of plasma proteins include: Tissue formation Viscosity Transport Maintaining plasma osmotic pressure Buffering pH changes Immunity Enzyme activity

Clotting The acute inflammatory response Precursors of active substances

Transport: Transferrin transports iron. Ceruloplasmin transports copper. Albumin transports fatty acids, bilirubin calcium, many drugs etc. Transcortin transports cortisol and corticosterone

Retinol binding protein transports retinol. Lipoproteins transport lipids. Haptoglobin transports free haemoglobin. Thyroxin binding globulin transports thyroxin

Tissue formation Dynamic equilibrium Continuously replenished 10 to 12 grams of albumin

Viscosity Resistance to the blood flow Hyper viscosity syndrome

Osmotic regulation:- Plasma proteins are colloidal and non-diffusable and exert a colloidal osmotic pressure which helps to maintain a normal blood volume and a normal water content in the interstitial fluid and the tissues.

Albumin content is most important in regulation of colloidal osmotic or oncotic pressure. Decrease in albumin level results in loss of water from blood and its entry into interstitial fluids causing edema

Blood clotting:- Many factors are involved in clotting mechanism and prevent loss of excessive amount of blood. e.g. clotting factors IX, VIII, thrombin, fibrinogen etc. An excess or deficiency leads to a disease. e.g hemophilia, thrombus formation.

Anticoagulant activity (thrombolysis): Plasmin breaks down thrombin and dissolves the clot Buffering capacity: - Proteins in plasma help to maintain acid-base balance

Immunity Gamma globulins Complement system

Precursors of active substances Hydrolyzed to liberate active biological products Kinin kininogen Angiotensin angiotensinogen

Hormones Protein in nature circulate in plasma PTH, insulin, glucagon GIT

Enzymes Diagnosing disease Physiological importance ( ACE, renin , plasmin)

Cytokines Non antibody proteins Regulation of growth, development Mediation of inflammatory response

Measurement of plasma proteins A) Quantitative measurement of a specific protein: by chemical or immunological methods B) Semiquantitative measurement by electrophoresis: Proteins are separated on the basis of their electrical charge.

In normal cases, electrophoresis separates the proteins into five broad fractions: Albumin, α1-globulin, α2-globulin, β-globulin γ-globulin Each of the globulin fractions consists of a mixture of several proteins

Amount of protein Mobility albumin globulins + -

Protein Electrophoresis - + Albumin a1 a2 b g Electrophoresis pattern for normal serum proteins

C-Reactive Protein ( CRP) Electrophoretic BAND Proteins Albumin a1-globulin a1-Antitrypsin Prothrombin a1-Fetoprotein (AFT) a2-globulin Ceruoplasmin Haptaglobin a2-macroglobulin b- globulin C-Reactive Protein ( CRP) Transferrin b2-microglobulin g-globulin Immunoglobulins (A, G, M, D & F)

Prealbumin Prealbumin migrates faster than albumin in the classic electrophoresis. It is the transport protein for: - Thyroid hormones - Retinol (vitamin A) Prealbumin is decreased in: Liver disease Nephrotic syndrome Malnutrition

Albumin Albumin is present in higher concentrations than other plasma proteins Albumin is synthesized in the liver & has a half-life of 20 days. Very small amounts of albumin cross the glomerular capillary wall.

Accordingly, no more than traces of albumin may normally appear in urine that can not be detected by ordinary laboratory means. Albuminuria : In this case, albumin can be detected in urine by ordinary laboratory means due to physiological or pathological conditions.

1- Osmotic pressure: Functions of albumin: Albumin is responsible for ~ 80% of the plasma osmotic pressure. It is a major determinant of the distribution of fluids between intravascular & extravascular compartments. Hypoalbuminemia leads to edema. 2- Buffering.  

3- Transport: bound to albumin e.g. Lipid-soluble substances Many substances are transported in the blood bound to albumin e.g. Lipid-soluble substances Hormones e.g. thyroid hormones & steroid hormones Calcium Drugs e.g. salicylates Free fatty acids (FFA) Billirubin

Colloid osmotic pressure Low albumin, causing edema.

Causes of Albumin Deficiency Liver diseases (cirrhosis) – decrease in the ratio of albumin to globulins Protein malnutrition Excessive excretion by kidneys (renal disease)

GLOBULINS Heterogeneous group can be separated into different fractions on the basis of their electrophoretic mobility and sedimentation coefficient: α1-Globulin α1-Fetoprotein α1-Antitrypsin α2-Globulin α2-Fetoprotein Haptoglobin β-Globulin Transferrin Ceruloplasmin γ-Globulin Antibodies (immunoglobulins)

Positive Acute Phase Proteins Stresses increases the levels of some of plasma proteins as occur in infection, inflammation , malignancy, trauma or major surgery. These proteins are termed acute phase reactants and their synthesis is a part of body’s response to injury. 1-Antitypsin Haptoglobin Ceruloplasmin Fibrinogen C-reactive protein

Acute phase reactants (APRs) Their levels change during acute inflammatory response Cause conditions where there is: the destruction of cells the reversible cell damage and subsequent repair the metabolic activation of certain cells (immune cells) APRs concentration changes in: infection surgery injury cancer

α1-antitrypsin Main globulin of α1 fraction (90 %) Synthesized in the liver in hepatocytes and macrophages glycoprotein, highly polymorphous (≈75 forms) Function: Main plasma inhibitor of serine proteases (trypsin, elastase)

Haptoglobin (Hp) 2- globulin, tetramer a2b2 chains Exists in 3 polymorphic forms Functions: binds free hemoglobin and delivers it to the reticuloendothelial cells complex Hb-Hp is too large to pass through glomerulus  prevention of loss of free Hb (and Fe) Free Hb passes through glomerulus, enters tubules and tends to precipitate there  kidney damage

Transferrin Transferrin is a β-globulin It binds free iron in serum Normally it is about one third saturated with iron Transferrin levels are decreased in: liver disease (e.g. cirrhosis) Chronic infections Nephrosis Congenitalatransferrinaemia Increased serum transferrin levels occur during increased transferrin synthesis caused as a result of iron deficiency anemia

Fibrinogen Synthesized in the liver. Its function is to form a fibrin clot (when activated by thrombin) Its level rises with pregnancy and the use of oral contraceptives Decreased values generally reflects extensive coagulation during which the fibrinogen is consumed.

Ceruloplasmin Synthesized by the liver Contains over 90% of serum copper It is important in acute phase response as it is able to inactivate reactive oxygen species (ROS) that produce tissue damage It is important for iron absorption from the intestine. Plasma levels are usually low in Wilson’s disease in which copper is accumulated in the liver leading to cirrhosis , and in the basal ganglia of the brain.

C-Reactive Protein (CRP) It is an acute-phase protein synthesized by liver It precipitates the polysaccharide (fraction C) of pneumococcal cell walls It is important for phagocytosis . Very large increase in plasma CRP occurs in many inflammatory conditions e.g., rheumatoid arthritis. CRP measurement with a sensitive assay (Ultra-sensitive CRP) is used for risk assessment of patients with ischemic heart disease.

Immunoglobulins Immunoglobulin(Ig)/antibody(Ab): Glycoprotein molecules that are produced by plasma cells in response to an immunogen and which function as antibodies, mostly associated with γ fraction.

General Functions of Immunoglobulin Antigen(Ag) binding - Ig binds to a specific antigenic determinant Effector functions - Complement activation - Binding to various cells such as phagocytic cells, lymphocytes, mast cells: antibody-mediated phagocytosis or antibody-dependent cell-mediated cytotoxicity (ADCC).

1 Define origin of plasma proteins 2 Classify plasma proteins 3 Enumerate functions of plasma proteins