Role of alcohol in pancreatitis
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Role of alcohol in pancreatitis
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[post_date] => 2024-12-23 18:28:09
[post_date_gmt] => 2024-12-23 23:28:09
[post_content] => Practice Passage (Question 1-6)
*This passage is the property of Khan Academy and has been reformatted into an AAMC-style interface in their entirety by MedLife Mastery. MedLife Mastery does not endorse and is not an affiliate of Khan Academy.
Researchers studying the pathogenesis of alcoholic pancreatitis recognize the importance of acinar cells in the disease. Acinar cells constitute an “enzyme factory” that produces millions of digestive enzyme molecules per day. It has been shown in animal models that one of the first events in acute experimental pancreatitis is the premature activation of digestive enzymes within acinar cells by co-segregation of zymogen granules with lysosomal enzymes, especially cathepsin B.
Scientists hypothesize that ethanol, ethanol metabolites, and oxidative stress exert toxic effects on pancreatic acinar cells, which predispose the gland to autodigestive injury. These toxic effects include:
(1) Destabilization of lysosomes (L) and zymogen granules (ZG): This destabilization is mediated by oxidative stress, cholesteryl esters (CEs) (which are known to accumulate in the pancreas during ethanol consumption), and fatty acid ethyl esters (FAEEs) (which are non-oxidative metabolites of alcohol).
(2) Increased digestive and lysosomal enzyme content attributed to increased synthesis (increased mRNA levels) and impaired secretion
These changes sensitize the cell such that overt injury is initiated (alcoholic acute pancreatitis) in the presence of an appropriate trigger. Cytokines released during alcohol-induced necroinflammation activate pancreatic stellate cells (PSCs). In addition, PSCs are activated directly by ethanol, most likely via its metabolism to acetaldehyde (Ac) and the subsequent generation of oxidative stress. Activated PSCs then synthesize excess amounts of extracellular matrix proteins leading to pancreatic fibrosis.
A summary of these proposed mechanisms is shown in Figure 1.
Figure 1 Hypothesized mechanisms of the pathogenesis of alcoholic pancreatitis
A major piece of evidence for this theory is the effect that alcohol and its metabolites have on fibrogenesis in PSCs. In a study conducted in 2000, pancreatic cell cultures were treated with ethanol and acetaldehyde, a product of ethanol oxidation, and collagen production by PSCs was measured. The results of this study are shown in Figure 2. The vertical axis of the graph, which measures the incorporation of proline into collagen, can be interpreted as a measure of total collagen synthesis.
Figure 2 Effects of ethanol (E) and acetaldehyde (A) at concentrations of 10 mmol/L, 50 mmol/L, 100 mmol/L, and 200 mmol/L on collagen synthesis in pancreatic stellate cells
Sources: Apte, M. (2000). Does alcohol directly stimulate pancreatic fibrogenesis? Studies with rat pancreatic stellate cells. Gastroenterology, 780-794. Vonlaufen, A. (2007). Role of alcohol metabolism in chronic pancreatitis. Alcohol Res Health, 48-54.
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[question] => What is the main mechanism that normally prevents pancreatic enzymes from being activated before they reach the small intestine?
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[answer] => 3
[description] => Reason for Correct Answer:
The small intestine is slightly alkaline, at around pH 8.5. Bicarbonate and bile enter via the pancreatic duct to neutralize the acidic chyme coming in from the stomach.
The pancreas creates enzymes in their zymogen form – an inactive form.
The majority of the pancreatic enzymes must be cleaved by another enzyme for activation. These activating enzymes are normally found in the small intestine.
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[answers] => Array
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[0] => Array
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[each_answer] => A. Chaperone proteins in the pancreas bind the zymogens and release them upon secretion into the pancreatic duct.
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[each_answer] => B. The higher pH of the pancreas destabilizes the enzymes’ structures, rendering them inactive.
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[each_answer] => C. Enzymes in the small intestine are responsible for activating pancreatic enzymes.
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[each_answer] => D. Pancreatic enzymes do not activate until they come in contact with their target molecules.
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[quiz_unique_key] => 1403770772
[question] => The addition of which of the following to the pancreatic cell culture would be LEAST likely to decrease collagen production in PSCs?
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[answer] => 4
[description] => Reason for Correct Answer:
You’re looking for something that will NOT counter the pathophysiology of pancreatitis, which the passage says leads to collagen production by PSCs.
The passage says that pancreatitis is attributable to “ethanol, its metabolites, and oxidative stress.” Paragraph 3 states that “PSCs are activated directly by ethanol, most likely via its metabolism to acetaldehyde (Ac) and the subsequent generation of oxidative stress.”
Therefore, 4MP, which prevents the breakdown of alcohol into its metabolites (specifically acetaldehyde), would likely help, and vitamin E, an antioxidant, would hypothetically help as well.
The passage also mentions the involvement of cathepsin B, as well as the role of cholesterol esters and fatty acid ethyl esters in the pathogenesis of pancreatitis.
Therefore, a cathepsin B inhibitor would counter the pathogenesis of pancreatitis, but palmitic acid ethyl ester, a fatty acid ethyl ester, would worsen it.
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[answers] => Array
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[each_answer] => A. 4MP, an alcohol dehydrogenase inhibitor
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[each_answer] => B. Leupeptin hemisulfate, a cathepsin B inhibitor
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[each_answer] => C. Vitamin E
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[each_answer] => D. Palmitic acid ethyl ester
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[quiz_unique_key] => 1403770772
[question] => Which enzyme category most likely includes cathepsin B?
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[answer] => 1
[description] => Reason for Correct Answer:
Paragraph 1 mentions cathepsin B is a lysosomal enzyme that causes the premature activation of pancreatic enzymes.
Lysosomes are membrane-bound organelles within cells that contain various hydrolytic enzymes that help digest molecules.
Lysosomal enzymes include acid hydrolases, such as proteases – including endopeptidases and exopeptidases, lipases, glycosidases, nucleases, as well other hydrolytic enzymes that cleave their target molecules.
Of the answers given, it is most likely that cathepsin B is an endopeptidase considering it’s a lysosomal enzyme that cleaves/activates proteins. This also explains why it contributes to the premature activation of zymogens in the pancreas.
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[each_answer] => A. Endopeptidase
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[each_answer] => B. Polymerase
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[each_answer] => C. Kinase
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[each_answer] => D. Ligase
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[quiz_unique_key] => 1403770772
[question] => **What is responsible for the increased lysosomal enzyme concentrations during pancreatitis?”
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[answer] => 3
[description] => Reason for Correct Answer:
Zymogen cleavage activates digestive enzymes destined for the small intestine, not lysosomal enzymes. The passage does not suggest it is responsible for the increased activation of lysosomal enzymes.
The passage states that “impaired secretion” is one of the reasons for increased lysosomal enzyme concentrations.
The passage states that “increased… lysosomal enzyme content [is] attributed to increased synthesis (increased mRNA levels) and impaired secretion,” and increased mRNA levels are shown in Figure 1.
Because the increase in enzyme concentration is attributable to increased mRNA, it must result from increased transcription of genes.
)
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[0] => Array
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[each_answer] => A. Decreased protein breakdown
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[each_answer] => B. Increased zymogen cleavage
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[each_answer] => C. Increased rates of transcription
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[each_answer] => D. Increased rates of secretion
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[quiz_unique_key] => 1403770772
[question] => If scientists added 4MP, an alcohol dehydrogenase inhibitor, to the conditions found in Figure 2, which graph would likely represent relative collagen synthesis in pancreatic cells?
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[answer] => 3
[description] => Reason for Correct Answer:
Figure 2 shows the results of collagen production in PSCs in a control group of pancreatic cells and in groups to which ethanol or acetaldehyde was added. Here, you’re looking for the relative collagen production in pancreatic cells in these conditions: control, ethanol treatment, 4MP treatment only, and combined ethanol + 4MP treatment.
Figure 2 already shows that ethanol increases collagen production in pancreatic cells. So, the beginning of the graph must look like this:
The passage states PSCs are activated by ethanol because of its conversion to acetaldehyde (Ac) and other effects of alcohol and its metabolites.
Alcohol dehydrogenase (ADH) is an enzyme that helps turn alcohol into acetaldehyde. So the addition of 4MP, an ADH antagonist, would prevent the breakdown of alcohol into acetaldehyde and other metabolites.
This would be expected to counter the effect of alcohol metabolism/production of metabolites in stellate cells, returning collagen production levels closer to those of the control:
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[each_answer] => A. 
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[each_answer] => B.
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[each_answer] => C.
)
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[each_answer] => D.
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[quiz_unique_key] => 1997864699
[question] => Which of the following would most likely help relieve the symptoms of pancreatitis?
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[answer] => 1
[description] => Reason for Correct Answer:
According to the passage, pancreatitis is the inflammation of the pancreas that is partially attributed to the buildup of enzymes in the pancreas.
The hepatobiliary sphincter, also known as the sphincter of Oddi, is a muscular valve that controls the flow of bile and pancreatic juice into the small intestine.
https://en.wikipedia.org/wiki/Ampulla_of_Vater#/media/File:Biliary_system_new.svg
When this sphincter is relaxed, it allows for better drainage of pancreatic juices and bile, which could help alleviate the symptoms of pancreatitis.
Reason for Incorrect Answer:
B. While probiotics can be beneficial for gut health, they would not directly affect these issues in the pancreas.
C. Cholecystokinin (CCK) is a hormone that stimulates the release of bile and pancreatic enzymes, which could worsen the inflammation in pancreatitis.
D. A high-fat diet can be taxing on the pancreas, as it requires more enzyme production to digest the fats, potentially aggravating pancreatitis.
)
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[each_answer] => A. Relaxation of the hepatobiliary sphincter
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[each_answer] => B. Administration of probiotics to improve colon health
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[each_answer] => C. Administration of a cholecystokinin (CCK) agonist
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[each_answer] => D. Adhering to a high-fat diet
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[554755|4] => C
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Figure 1
Figure 2
