Lecture 2 -- Proteins and Lipids

These flashcards cover key concepts of protein and lipid biochemistry, including measurement techniques, types of proteins, pathophysiological conditions, and the roles of lipoproteins in the body.

What are the methods of measuring globulins?

1. Calculated by subtracting albumin from total protein (TP − albumin)

2. Measured directly using serum protein electrophoresis (SPE)

What is serum protein electrophoresis (SPE)?

Laboratory technique that separates serum proteins into distinct fractions (bands) based on their electrical charge and molecular size

SPE from a dogs. What is the most likely diagnosis?

Normal

• Albumin (Narrow base and spiky)

SPE from a dogs. What is the most likely diagnosis?

Chronic inflammation (Polyclonal gammopathy)

• Increased production of gamma globulin BUT those gamma globulin are produced by different clones of B lymphocytes

SPE from a dogs. What is the most likely diagnosis?

Actue phase or active inflammation (Polyclonal gammopahty)

• Increased both alpha and gamma globulin

SPE from a dogs. What is the most likely diagnosis?

B cell neoplasia (Monoclonal gammopathy)

• Only one clone of B lymphocytes or plasma cell producing the gamma globulin

What acute phase proteins are produced in response to inflammation?

1. Positive acute phase proteins:

   • C-reactive protein (CRP) in dogs

   • Serum amyloid A in ruminants, horses, and cats

   • Alpha-1 acid glycoprotein in cats

2. Negative acute phase proteins

   • Albumin

   • Transferrin

3. Delayed acute phase proteins

   • Complement proteins

   • Immunoglobulins

What is alpha-1 acid glycoprotein used for diagnosing in cats?

Feline infectious peritonitis (FIP)

What stimulates the liver to produce acute phase proteins?

Pro-inflammatory cytokines such as IL-1, IL-6, and TNF

What are the causes of hyperproteinaemia?

1. Inflammation (Increased globulin)

2. B-cell neoplasia (Increased globulin)

3. Vomiting, diarrhoea, polyuria

   • Relative increase due to dehydration or hemoconcentration, which leads to an increase in total protein without a true increase in protein production

What are the causes of hypoproteinaemia?

1. Blood loss

2. Third-space loss

3. Protein-losing dermatopathy

4. Protein-losing enteropathy

5. Protein-losing nephropathy

6. Hepatic insufficiency

7. Inflammation (decreased albumin)

8. Malabsorption

9. Malnutrition

10. Failure of passive transfer (in foals or calves)

Why is protein-losing nephropathy considered selective protein loss?

Globulin has a larger molecular size than albumin → Only albumin can pass through glomerulus

Why can hepatic insufficiency cause non-selective hypoproteinaemia?

The liver produces albumin and clotting factors, but immunoglobulins are produced by B lymphocytes, so protein changes are mixed

Which protein is selectively decreased in hypoproteinaemia caused by inflammation? Why?

Albumin

• It a negative acute phase protein = Protein that decreases during inflammation

What are the causes of increased fibrinogen?

• Increased fibrinogen + Decreased albumin → Indicates inflammation

• Increased fibrinogen + albumin + total protein → Indicates Dehydration

What are the causes of decreased fibrinogen?

• Decrease synthesis of fibrinogen

  • Hepatic insufficiency

  • Congenital deficiency

    • Afibrinogenaemia or hypofibrinogenaemia

• Increased fibrinogen consumption

  • Disseminated intravascular coagulation (DIC)

How are dietary lipids digested, transported, and used in the body?

• Dietary lipids are digested in the intestine

• With the help of bile acids, cholesterol, and lipase, producing free fatty acids and monoglycerides

• Inside enterocytes, they are reassembled into triglycerides

• With apolipoproteins and phospholipids, triglycerides form chylomicrons

• Chylomicrons travel through the lymphatic system via the thoracic duct into the bloodstream

• Insulin activates lipoprotein lipase → Breaks down the triglycerides in chylomicrons into free fatty acids

• These fatty acids are then used by…

  • Adipose tissue for storage

  • Muscle for energy

How is VLDL metabolized and what is the role of LDL?

• The liver synthesizes VLDL, which contains a high level of triglycerides

• VLDL is broken down by lipoprotein lipase into free fatty acids, which are used by …

  • Adipose tissue for storage

  • Muscle for energy

• VLDL is hydrolysed into intermediate-density lipoprotein (IDL) → Then hydrolysed into low-density lipoprotein (LDL)

• LDL contains a high level of cholesterol, which is important for …

  • Maintaining cell membranes

  • Steroid hormone synthesis

What is the function of high density lipoproteins?

Pick up the cholesterol from tissues for reutilisation or degradation

What are the causes of increased serum cholesterol?

1. Cholestasis

2. Acute pancreatitis

   • Because pancreatitis often associate with cholestasis

3. Nephrotic syndrome

4. Postprandial state/

5. Diet e.g. high fat diet

6. Obesity

7. Endocrine diseases (diabetes mellitus, hyperadrenocorticism, hypothyroidism)

8. Drug administration (e.g. glucocorticoids)

What are the causes of decreased serum cholesterol?

• Pancreatic insufficiency

  • Cannot produce lipase → No breakdown into free fatty acid and monoglyceride)

• Hepatic insufficiency

• Portosystemic shunt (PSS)

• Hypoadrenocorticism

• Malabsorption or malnutrition

What are the causes of increased serum triglycerides?

Similar to causes of increased cholesterol

BUT NOT nephrotic syndrome and chloestasis