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Enzymes Flashcards

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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
What are the most common causes of hepatocyte damage causing increased ALT?
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
26
What is ALT a major marker of in dogs and cats?
Hepatocyte damage
27
What is ALT a major marker of in horses and cattles?
Hepatocytes heave very little ALT, thus it is not a useful marker
28
What does aspartate trasaminase (AST/GOT) do?
Catalyzes deamination of sspartate to form oxalacetate, which can enter the Krebs cycle
29
Where is AST made?
``` Cytoplasmic and mitochondrial enzyme: Hepatocytes Skeletal myocytes Cardiac myocytes Erythrocytes ```
30
What are causes of increased AST?
Hepatocyte damage Skeletal or cardiac muscle damage In vitro hemolysis or delayed removal of serum from clot: mild to moderate increase
31
What are the most common causes of hepatocyte damage causing increased AST in dogs and cats?
Same as ALT
32
What are the most common causes of hepatocyte damage causing increased AST in horses and cattle?
Degenerative: hypoxia by anemia, congestion, or cholelithiasis Metabolic: lipidosis, diabetes mellitus, equine hyperlipidemia Infectious: bacterial hepatitis, bacterial cholangiohepatitis, infectious necrotic hepatitis, hepatic abscess
33
What is AST a common marker for in horses and cattle?
Hepatocyte damage and muslce
34
What can AST be an indicator of? Why?
Active hepatocyte damage | It has a shorter half-life than ALT
35
What does lactate dehydrogenase (LD/LDH) do?
Catalyzes pyruvate to lactate in anaerobic glycolysis
36
Where is LD made?
``` Cytoplasmic: Hepatocytes Skeletal mycocytes Cardiac myocytes Erythrocytes ```
37
What is increased LD a marker for in all species?
Hepatocyte damage | Also increased by muscle damage and hemolysis
38
What conditions involved in hepatocyte damage increase LD?
Same as those listed for AST
39
What does iditol dehydrogenase (ID/SDH) do?
Catalyzes fructose to sorbitol
40
Where is ID made?
Cytoplasmic: | Hepatocytes
41
What causes increased serum activity of ID?
Hepatocyte damage
42
What species is ID primarily used in? What for?
Primarily used in horses and cattle: specific for the liver
43
What does glutamate dehydrogenase (GMD) do?
Catalyzes conversion of glutamate to 2-oxoglutarate
44
Where is GMD made?
Mitochondrial: Mostly hepatocytes Also present in other tissues
45
What increases the serum activity of GMD?
Hepatocyte damage
46
What is GMD a sensitive indicator of in dogs?
Hepatic diseases (mores sensitive than ALT, AST, ALP, and GGT)
47
What does alkaline phosphatase (ALP) do?
Phosphatase activity in an alkaline environment
48
What are the tissue sources of ALP?
Hepatocytes (L-ALP) Biliary epithelium (L-LAP) Osteoblasts (B-LAP) Mammary epithelium
49
What is an increase in ALP in young animals due to?
B-LAP
50
Why do calves and pups have a higher ALP in the first days of age/
Colostrum intake
51
What are cause of increased ALP?
``` Cholestasis Induction by drugs or hormone Increased osteoblastic activity Canine mammary neoplasms Benign familial hyperphosphatemia in Suberian huskies ```
52
What is cholestasis primarily caused by?
Increased production of L-ALP by hepatocytes and biliary epithelium
53
In dogs, what do corticosteroids do to ALP?
Induce synthesis of L- and C-LAP
54
In pups, why is ALP increased?
B-ALP is typically mild
55
What is the ALP diagnostic sensitivity for detecting cholestasis in cats? Dogs? Horses? Cattle?
Poor in cats High sensitivity in dogs Poor in horses Moderate in cattle
56
What does it mean if ALP has poor sensitivity for cholestasis?
Animal will be icteric before ALP increases
57
What does it mean if ALP has good sensitivity for cholestasis?
Animal will have an increase in ALP before being icteric
58
What happens to the ALP:GGT ratio in cats with lipidosis?
Increased; ALP increased more than GGT
59
What causes increased activities of ALP in hyperthyroid cats?
L-ALP and B-ALP
60
What does gamma-glutamyltransferase (GGT) do?
Catalyzes transfer of glutamyl groups between peptides and is involved in glutathione reactions
61
What is GGT associated with?
Cell membrane
62
What cells have GGT activity?
``` Biliary epithelial cells Hepatocytes Mammary epithelium Pancreatic acinar cells Renal tubular epithelial cells ```
63
What has a high activity of GGT in cattle?
Colostrum | Postsuckling calves have up to 16x the presuckling values
64
What are the values of GGT in pups compared to adults?
Values are up to 100x URL of adults
65
What may the synthesis of GGT be stimulated by?
Similar to ALP, increased constituents of bile
66
What is increased serum GGT activity associated with?
Drugs or hormones (phenobarbital)
67
What is a cause of hepatocyte damage in horses related to GGT?
Acute hepatocellular necrosis --> mild increase
68
In horses, what has better diagnostic activity for cholestasis, ALP or GGT? Cattle? Dogs?
GGT for horses and cattle | Probably ALP in dogs
69
What are the increases of GGT like in dogs with cholestatic diseases?
Tend to parallel increase in ALP activity
70
What causes GGT activity in urine?
Damage to renal epithelial cells increases urinary excretion of renal GGT and no changes in serum GGT
71
What does creatine kinase (CK) do?
Catalyzes transfer of phosphate from creatine-PO4 to adenosine diphosphate to form ATP
72
Where is CK made?
Cytoplasm of: Skeletal mycocytes Cardiac myocytes Smooth muscle myocytes
73
What causes increased serum CK activity?
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
What is the CK activity in animal with neurologic disease?
Brain and other tissues of CNS contain high CK activity | Necrosis or demyelination may cause increase CK activity
75
What does amylase (AMS) do?
Catalyzes hydrolysis of complex starches
76
Where is amylase made?
Cytoplasm: | Pancreatic acinar cells
77
What is the route of plasma AMS excretion or inactivation?
Kidneys
78
What causes increased AMS?
Pancreatic acinar cell damage | Decreased renal inactivation or excretion
79
What is the most common cause of pancreatic acinar cell damage?
Acute pancreatitis
80
What is the AMS value for dogs with pancreatic acinar cell damage?
WRI to >10x URI
81
What is the AMS value for cats with pancreatic acinar cell damage?
WRI to <3x
82
What does lipase (LPS) do?
Catalyzes hydrolysis of triglycerides
83
Where is LPS made?
Cytoplasmic: Pancreatic acinar cells Liver neoplasms Gastric mucosa
84
What causes increased LPS?
Pancreatic acinar cell damage (acute pancreatitis) Proliferation of cells in pancreatic or extrapancreatic neoplasia Decreased renal inactivation or excretion Dexmethasone treatment in dogs
85
What is the value of LPS in a dog with acute pancreatitis?
WRI to >10x URL
86
What is the value of LPS in a cat with spontaneous pancreatitis?
WRI to <5x URL
87
When is pancreatic lipase immunoreactivity (PLI) decreased?
Exocrin pancreatic insufficiency
88
What has the greater diagnostic sensitivity for pancreatitis, PLI, LPS, or TLI?
PLI
89
What was PLI like in cats with experimental pancreatitis?
PLI increased more and was more persistent than TLI
90
What has more diagnostic sensitivity for spontaneous pancreatitis, PLI, TLI, or abdominal US?
PLI
91
When is TLI increased?
Active pancreatitis
92
When is TLI decreased?
Exocrine pancreatic insufficiency

Clinical Pathology (16 decks)

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