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Old 05-07-2015
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Default Biochemistry

What is the rationale behind alkalinization of urine in cystinuria?
Wouldn't it make it less water soluble?
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Old 05-08-2015
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Who?


Why?

Cystine may precipitate out of the urine, if the urine is neutral or acidic, and form crystals or stones in the kidneys, ureters, or bladder.

What?
See that -SH group of cysteine molecule its has got a pK2=8.3 so I guess if we can alkalinize the urine sufficiently that -SH will ionize to -S and will not be able to react with another cystiene to form cystine and thus reduce precipitation.

Just a guess
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Old 05-08-2015
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Originally Posted by datson View Post
What is the rationale behind alkalinization of urine in cystinuria?
Wouldn't it make it less water soluble?
Nope, you are just understanding it backwards. Making the urine more alkaline makes an ACID like cysteine/cysteine more soluble by removing more protons.
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Nope, you are just understanding it backwards. Making the urine more alkaline makes an ACID like cysteine/cysteine more soluble by removing more protons.
but cystiene aint an acid its a polar amino acid with a side chain of -SH!

Or you are saying ingeneral if we alkalinize the urine it improves the clearance of all amino acids?
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but cystiene aint an acid its a polar amino acid with a side chain of -SH!

Or you are saying ingeneral if we alkalinize the urine it improves the clearance of all amino acids?
I think you're confusing the term 'clearance' here, though yes, as a rule, alkaline urine would make any acid more soluble -- that's just basic chemistry. Remember that the problem in this disease is a failure to reabsorb cysteine in the first place; you and I probably reabsorb it just fine and it doesn't matter how acidic or alkaline our urine is!

You are also correct in that alkaline urine will make it harder for the cysteine AAs to complex into cystine.

From a clinical standpoint, there are some limits to how much we can alkalinize the urine and a pH of 8 would be pushing it, so this therapy often fails and these people form stones anyhow. From a Step 1 and Step2CK standpoint, remember that additional treatments are dietary modifications such as low protein diets and low acid diets, both to help reduce how much cysteine ultimately makes it to the kidney and how acidic the urine is to start with.
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