Lecture 3: Plasma Proteins & Dysproteinemia

Where are plasma proteins synthesized?

• liver: most plasma proteins

• lymphoid organs: immunoglobulins

What 3 proteins made up blood composition?

mostly albumin and globulins, small amount of fibrinogen

What are the functions of plasma proteins?

• transport of nutrients, small hormones, waste, drugs

• colloid osmotic effects

• acid-base

• regulatory proteins: cell production, inflammation

• immune defense hemostasis

What is the difference between neonate vs adult total PP concentrations and why?

neonate concentration is lower than adult because they lack immunoglobulin until colostrum ingestion and absorption

What are the three protein measurement methods?

• physical: refractometric

• biochemical: spectrophotometric

• fractionation: electrophoresis

What is a microhematocrit tube used for?

PCV or Hct

What is contained in the buffy coat in a microhematocrit tube?

leukocytes and platelets

What is used to determine plasma protein determination and fibrinogen determination?

microhematocrit tube

How would you physically measure total solids in plasma or urine?

using a refractometer

True or false: the amount of nonprotein solids in plasma (electrolytes, glucose, etc) is normally relatively constant at about 1.5 g/dL.

true

What could erroneously increase plasma protein concentration?

• hemolysis in sample: hemoglobin is not a plasma protein

• lipemia: interference with light transmission

What is the biochemical colorimetric method?

adding a reagent to change the color of a substance and measuring the intensity of the color change

True or false: total protein and albumin concentrations in serum (or plasma) are measured separately using 2 different spectrophotometric assays.

true

How is total globulin concentration calculated?

subtracting albumin concentration from total protein concentration

How would you fractionate serum/plasma proteins?

protein electrophoresis

Why is serum protein electrophoresis performed?

• unexplained hyperglobulinemia is present

• immunoglobulin deficiency is suspected

What single homogenous protein has a small molecular weight and contains minimal carbohydrate?

albumin

What are the transport functions of albumin?

• organic and inorganic substances

• cations (mostly Ca2+), metabolites, certain hormones, poorly soluble drugs, toxic substances

True or false: hypoalbuminemia can lead to high calcium in the blood.

false: low calcium

What are acute phase proteins (APPs)?

proteins with more than 25% change in serum concentrations in response to inflammatory cytokines (IL-1, TNFalpha, IL-6)

How are APPs categorized?

positive: increasing serum concentration

negative: decreasing serum concentration

What is the universal positive APP?

serum amyloid A

What positive APP is useful in dogs?

C-reactive protein

What positive APP is useful in ruminants?

haptoglobin

What positive APP binds free plasma Hb irreversibly?

haptoglobin

What is the optimal platelet aggregate classified as coagulation factor I?

fibrinogen

What is the function of fibrinogen?

scaffolding for inflammatory cells fibroblasts, and endothelial cells when deposited in tissues, precursor to fibrin in coagulation

How is fibrinogen estimated?

heat a hematocrit tube for 3 mins at 56C and fibrinogen will separate after heating and centrifugation

What causes fibrinogen to increase?

• active inflammation

• dehydration (all plasma proteins)

What causes fibrinogen to decrease?

• disseminated intravascular coagulation (DIC) somtimes

• liver failure, snake venom

What is the function of ceruloplasmin?

• copper transport

• plasma antioxidant

What is the function of transferrin?

• iron-binding

• correlates with total iron binding capacity (TIBC)

• negative APP

What APP contains iron, is found in low concentrations in plasma, and correlates with total body iron stores?

ferritin

What is the function of hormone binding proteins?

bind small MW hormones, preventing them from being rapidly filtered by the kidney

What are three hormone binding proteins?

– Corticosteroid-binding globulin

– Thyroxine-binding globulin

– Sex hormone-binding globulin

What is the function of antithrombin?

• protease inhibitor

• inhibits thrombin and certain other coagulation factors

What is required by antithrombin for optimal activity?

GAGS (ex. heparin)

What negative APP concentration falls gradually and reduction is more noticeable in chronic inflammatory disease?

albumin

What is allowed by reduction in production of albumin?

greater increase in the amount of amino acids available for positive APP production

What could cause hyperproteinemia?

• dehydration

• hyperglobulinemia

What could cause hypoproteinemia?

• dilution- overhydration

• decreased production

• increased loss

• sequestration in body cavities

What effect does inflammation have on proteins?

• increased loss of some proteins due to increased vascular permeability

• increased and decreased synthesis of some proteins due to altered cytokines

What causes hypoalbuminemia mixed with hypoglobulinemia?

hypoproteinemia

Why does dehydration cause a relative hyperproteinemia and erythrocytosis?

only fluid component of blood is lost, NOT proteins and erythrocytes

What components of blood are lost in external hemorrhage?

all components lost equally

How does external hemorrhage cause hypoproteinemia and anemia?

all components of blood lost equally, but fluid is replaced more rapidly than protein and cells

What could cause hypoalbuminemia?

• excessive fluid therapy

• decreased synthesis (chronic liver failure, inflammation)

• loss from body (protein losing glomerulopathy, hemorrhage, protein losing enteropathy)

• sequestration (accumulation of protein-rich fluids in body cavities)

What may cause hypoglobulinemia?

• hemorrhage

• protein-losing enteropathy

• failure of passive transfer via colostrum

• overhydration

• decreased production (humoral immunodeficiency)

What can cause hyperglobulinemia?

• increased immunoglobulins due to immune-mediated response or neoplastic lymphoid cells

• increased APP concentrations due to inflammation (haptoglobin, fibrinogen)

What is polyclonal hyperglobulinemia?

excess Ig from many lymphoid clones

What causes hyperglobulinemia?

antigentic stimulation:

• infections

• immune-mediated

• immune response to neoplasia

What is monoclonal hyperglobulinemia?

excess ig from a single lymphoid clone

What causes monoclonal hyperglobulinemia?

neoplasia: multiple myeloma, lymphoma/leukemia

Where are lipoproteins synthesized?

GI and liver

What is the function of lipoproteins?

transport of water insoluble lipids in blood

How are lipoproteins classified?

• density determined using ultracentrifugation

• migration on electrophoresis

What are lipoproteins composed of?

• lipid complexes and proteins called apolipoproteins

• Pseudomicellar particles with hydrophilic apolipoproteins and

  charged phospholipids on the surface

• ‘Hydrophobic triglycerides and cholesterol esters inside

Where are chylomicrons formed?

in the mucosal cells of the duodenum and jejunum following digestion of fat in the diet

What happens to chylomicrons in capillary beds?

Their core triglycerides are rapidly hydrolyzed by the action of lipoprotein lipase where resultant fatty acids and glycerol are metabolized

What is postprandial lipemia?

white cloudy plasma because of chylomicronemia after eating meal containing fat

What are very low density lipoproteins responsibly for?

transporting the bulk of endogenous triglycerides

In a lipemic sample, when is a cream layer not present in a sample that stood overnight in a refridgerator?

when very low density lipoproteins are present

What are low density lipoproteins (LDLs)?

metabolic products from VLDLs that are the major mechanism by which cholesterol is transported to peripheral tissues

Where are HDL precursors formed?

in the liver and complete molecules are formed in the plasma by addition of remnants form other lipoproteins

What transports cholesterol from tissues back to the liver?

HDLs

What is caused by hypertriglyceridemia, but NOT hypercholesterolemia?

lipemia in plasma or serum

What are the primary causes of lipemia in plasma or serum?

– Hyperchylomicronemia in cats with lipoprotein lipase deficiency

– Hereditary hypertriglyceridemia in miniature schnauzer dogs (unknown etiology)

What are the secondary causes of lipemia in plasma or serum?

– Postprandial hyperchylomicronemia

– Diabetes mellitus

– Acute pancreatitis

– Hyperadrenocorticism

– Hypothyroidism