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Clinical Pathology > Enzymes > Flashcards

Enzymes Flashcards

1
Q

What is an enzyme?

A

Protein that catalyze chemical reactions

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2
Q

What are isoenzymes?

A

Different enzyme structure but catalyze the same chemical reaction

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3
Q

What are isoforms?

A

Different structure is created by post-translational modification of the same gene product

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4
Q

What is the source of serum enzymes?

A

Cells: cytoplasm, mitochondria, membrane

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5
Q

What does serum enzyme activity increase?

A

Enzyme entry into plasma > inactivation/removal

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6
Q

What are the mechanisms of serum enzyme activity?

A 
Increased release from damaged cells
Induction of enzyme synthesis
Cell proliferation--> more enzyme produced
Decreased enzyme clearance
Ingestion and absorption
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7
Q

What is decreased tissue mass associated with?

A

Decreased serum enzyme activity or concentration

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8
Q

Why does decreased activity of most enzymes not have diagnostic importance?

A

Poor sample handling
Presence of inhibitor in sample
Not appropriate reference interval for the patient
Decreased mass of origin tissue

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9
Q

What is the nomenclature for enzymes?

A

Name of substrate + type of reaction

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10
Q

What is the transfer of an amino group?

A

Transaminase

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11
Q

What is the transfer of amino group?

A

Kinase

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12
Q

What is oxidizing or reducing?

A

Oxidoreductases

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13
Q

When interpreting enzymes, what is the degree of increase determined by?

A

Patient’s value divided by the URL of the interval

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14
Q

What can indicate possible explanations when interpreting enzymes

A

Magnitude of increased enzyme activity

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15
Q

What does an ALT of 15x URL suggest?

A

Hepatocyte damage

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16
Q

What does an ALP of 10x URL indicate?

A

Too great from B-ALP, could be due to L- or C-ALP

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17
Q

Why should you consider the half life of enzymes?

A

CK has a shorter half life than AST

After a single injury, CK might return to the reference interval sooner

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18
Q

What is the significance of increased enzyme acitivities?

A

Markers or indicators of pathologic processes, not a specific diseae

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19
Q

What may the magnitude of increase of cytoplasmic enzymes relate to?

A

Severity of damage

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20
Q

What are the enzyme values with slight damage?

A

<2x URL

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21
Q

What are the enzyme values with severe damage?

A

> 50x URL

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22
Q

What does alanine transaminase (ALT/GPT) do?

A

Catalyzes deamination of alanine to form pyruvate –> can enter gluconeogenesis pathway or Krebs cycle

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23
Q

Where is ALT made?

A

Cytoplasmic enzyme:
Hepatocytes
Skeletal myocytes

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24
Q

What does it mean if there is increased ALT?

A

Hepatocyte damage

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25
Q

What are the most common causes of hepatocyte damage causing increased ALT?

A

Degenerative: hypoxia by anemia or congestion
Metabolic: lipidosis, diabetes, feline hyperthyroidism
Neoplastic: lymphoma, metastatic neoplasia, hepatocellular carcinoma
Infectious: lepto, histo, FIP, bacterial cholangiohepatitis
Inflammation of chronic hepatitis and cirrhosis
Toxic: steroid hepatopathy, anesthetic agents, tetracycline, carprofen, phenobarbital
Trauma: HBC

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26
Q

What is ALT a major marker of in dogs and cats?

A

Hepatocyte damage

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27
Q

What is ALT a major marker of in horses and cattles?

A

Hepatocytes heave very little ALT, thus it is not a useful marker

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28
Q

What does aspartate trasaminase (AST/GOT) do?

A

Catalyzes deamination of sspartate to form oxalacetate, which can enter the Krebs cycle

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29
Q

Where is AST made?

A 
Cytoplasmic and mitochondrial enzyme:
Hepatocytes
Skeletal myocytes
Cardiac myocytes
Erythrocytes
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30
Q

What are causes of increased AST?

A

Hepatocyte damage
Skeletal or cardiac muscle damage
In vitro hemolysis or delayed removal of serum from clot: mild to moderate increase

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31
Q

What are the most common causes of hepatocyte damage causing increased AST in dogs and cats?

A

Same as ALT

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32
Q

What are the most common causes of hepatocyte damage causing increased AST in horses and cattle?

A

Degenerative: hypoxia by anemia, congestion, or cholelithiasis
Metabolic: lipidosis, diabetes mellitus, equine hyperlipidemia
Infectious: bacterial hepatitis, bacterial cholangiohepatitis, infectious necrotic hepatitis, hepatic abscess

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33
Q

What is AST a common marker for in horses and cattle?

A

Hepatocyte damage and muslce

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34
Q

What can AST be an indicator of? Why?

A

Active hepatocyte damage

It has a shorter half-life than ALT

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35
Q

What does lactate dehydrogenase (LD/LDH) do?

A

Catalyzes pyruvate to lactate in anaerobic glycolysis

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36
Q

Where is LD made?

A 
Cytoplasmic:
Hepatocytes
Skeletal mycocytes
Cardiac myocytes
Erythrocytes
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37
Q

What is increased LD a marker for in all species?

A

Hepatocyte damage

Also increased by muscle damage and hemolysis

38
Q

What conditions involved in hepatocyte damage increase LD?

A

Same as those listed for AST

39
Q

What does iditol dehydrogenase (ID/SDH) do?

A

Catalyzes fructose to sorbitol

40
Q

Where is ID made?

A

Cytoplasmic:

Hepatocytes

41
Q

What causes increased serum activity of ID?

A

Hepatocyte damage

42
Q

What species is ID primarily used in? What for?

A

Primarily used in horses and cattle: specific for the liver

43
Q

What does glutamate dehydrogenase (GMD) do?

A

Catalyzes conversion of glutamate to 2-oxoglutarate

44
Q

Where is GMD made?

A

Mitochondrial:
Mostly hepatocytes
Also present in other tissues

45
Q

What increases the serum activity of GMD?

A

Hepatocyte damage

46
Q

What is GMD a sensitive indicator of in dogs?

A

Hepatic diseases (mores sensitive than ALT, AST, ALP, and GGT)

47
Q

What does alkaline phosphatase (ALP) do?

A

Phosphatase activity in an alkaline environment

48
Q

What are the tissue sources of ALP?

A

Hepatocytes (L-ALP)
Biliary epithelium (L-LAP)
Osteoblasts (B-LAP)
Mammary epithelium

49
Q

What is an increase in ALP in young animals due to?

A

B-LAP

50
Q

Why do calves and pups have a higher ALP in the first days of age/

A

Colostrum intake

51
Q

What are cause of increased ALP?

A 
Cholestasis
Induction by drugs or hormone
Increased osteoblastic activity
Canine mammary neoplasms
Benign familial hyperphosphatemia in Suberian huskies
52
Q

What is cholestasis primarily caused by?

A

Increased production of L-ALP by hepatocytes and biliary epithelium

53
Q

In dogs, what do corticosteroids do to ALP?

A

Induce synthesis of L- and C-LAP

54
Q

In pups, why is ALP increased?

A

B-ALP is typically mild

55
Q

What is the ALP diagnostic sensitivity for detecting cholestasis in cats? Dogs? Horses? Cattle?

A

Poor in cats
High sensitivity in dogs
Poor in horses
Moderate in cattle

56
Q

What does it mean if ALP has poor sensitivity for cholestasis?

A

Animal will be icteric before ALP increases

57
Q

What does it mean if ALP has good sensitivity for cholestasis?

A

Animal will have an increase in ALP before being icteric

58
Q

What happens to the ALP:GGT ratio in cats with lipidosis?

A

Increased; ALP increased more than GGT

59
Q

What causes increased activities of ALP in hyperthyroid cats?

A

L-ALP and B-ALP

60
Q

What does gamma-glutamyltransferase (GGT) do?

A

Catalyzes transfer of glutamyl groups between peptides and is involved in glutathione reactions

61
Q

What is GGT associated with?

A

Cell membrane

62
Q

What cells have GGT activity?

A 
Biliary epithelial cells
Hepatocytes
Mammary epithelium
Pancreatic acinar cells
Renal tubular epithelial cells
63
Q

What has a high activity of GGT in cattle?

A

Colostrum

Postsuckling calves have up to 16x the presuckling values

64
Q

What are the values of GGT in pups compared to adults?

A

Values are up to 100x URL of adults

65
Q

What may the synthesis of GGT be stimulated by?

A

Similar to ALP, increased constituents of bile

66
Q

What is increased serum GGT activity associated with?

A

Drugs or hormones (phenobarbital)

67
Q

What is a cause of hepatocyte damage in horses related to GGT?

A

Acute hepatocellular necrosis –> mild increase

68
Q

In horses, what has better diagnostic activity for cholestasis, ALP or GGT? Cattle? Dogs?

A

GGT for horses and cattle

Probably ALP in dogs

69
Q

What are the increases of GGT like in dogs with cholestatic diseases?

A

Tend to parallel increase in ALP activity

70
Q

What causes GGT activity in urine?

A

Damage to renal epithelial cells increases urinary excretion of renal GGT and no changes in serum GGT

71
Q

What does creatine kinase (CK) do?

A

Catalyzes transfer of phosphate from creatine-PO4 to adenosine diphosphate to form ATP

72
Q

Where is CK made?

A

Cytoplasm of:
Skeletal mycocytes
Cardiac myocytes
Smooth muscle myocytes

73
Q

What causes increased serum CK activity?

A

Damage to muscle fibers
Mild to marked increases in anorectic cats with nasophageal tubes
Hypothyroidism in dogs
In vitro hemolysis will cause falsely increased CK activity
Smooth muscle damage

74
Q

What is the CK activity in animal with neurologic disease?

A

Brain and other tissues of CNS contain high CK activity

Necrosis or demyelination may cause increase CK activity

75
Q

What does amylase (AMS) do?

A

Catalyzes hydrolysis of complex starches

76
Q

Where is amylase made?

A

Cytoplasm:

Pancreatic acinar cells

77
Q

What is the route of plasma AMS excretion or inactivation?

A

Kidneys

78
Q

What causes increased AMS?

A

Pancreatic acinar cell damage

Decreased renal inactivation or excretion

79
Q

What is the most common cause of pancreatic acinar cell damage?

A

Acute pancreatitis

80
Q

What is the AMS value for dogs with pancreatic acinar cell damage?

A

WRI to >10x URI

81
Q

What is the AMS value for cats with pancreatic acinar cell damage?

A

WRI to <3x

82
Q

What does lipase (LPS) do?

A

Catalyzes hydrolysis of triglycerides

83
Q

Where is LPS made?

A

Cytoplasmic:
Pancreatic acinar cells
Liver neoplasms
Gastric mucosa

84
Q

What causes increased LPS?

A

Pancreatic acinar cell damage (acute pancreatitis)
Proliferation of cells in pancreatic or extrapancreatic neoplasia
Decreased renal inactivation or excretion
Dexmethasone treatment in dogs

85
Q

What is the value of LPS in a dog with acute pancreatitis?

A

WRI to >10x URL

86
Q

What is the value of LPS in a cat with spontaneous pancreatitis?

A

WRI to <5x URL

87
Q

When is pancreatic lipase immunoreactivity (PLI) decreased?

A

Exocrin pancreatic insufficiency

88
Q

What has the greater diagnostic sensitivity for pancreatitis, PLI, LPS, or TLI?

A

PLI

89
Q

What was PLI like in cats with experimental pancreatitis?

A

PLI increased more and was more persistent than TLI

90
Q

What has more diagnostic sensitivity for spontaneous pancreatitis, PLI, TLI, or abdominal US?

A

PLI

91
Q

When is TLI increased?

A

Active pancreatitis

92
Q

When is TLI decreased?

A

Exocrine pancreatic insufficiency

Clinical Pathology (16 decks)

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