Binding of anti-Parkinson's disease drugs to human serum albumin is allosterically modulated

Benserazide-induced diarrhea - A retrospective clinical study

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A largely unknown and unrecognized side effect of L-DOPA/benserazide is severe diarrhea in rare cases, which can lead to physicians initiating misguided and drug treatments or patients discontinuing their L-DOPA medication altogether.

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A simple change to L-DOPA/carbidopa has proven to be an effective solution in virtually all cases of benserazide-induced diarrhea, usually leading to full remission within days.

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A cohort of 50 patients is examined in search for a possible biochemical basis for benserazide intolerance.

Background

Although diarrhea has been reported as a side effect of L-3,4- dihydroxyphenylalanine (L-DOPA)/benserazide, it is largely unknown and unrecognized, presumably because it is very rare. There is almost no literature on benserazide-induced diarrhea (BID), no pharmacological explanation and, crucially, no treatment recommendation. This can lead to physicians misdiagnosing BID, for example as colitis, and initiating misguided and ultimately ineffective drug treatments. Or it can lead to erroneous assumptions about a general intolerance and subsequent discontinuation of L-DOPA medication – for lack of a better solution – at the high price of living with the recurring symptoms of Parkinson’s disease. Thus, our study aims to fill these gaps, beginning with a treatment recommendation: A simple switch to LDOPA/ carbidopa has proven to be an effective solution in virtually all cases of BID, usually leading to full remission within days. Finding a possible pharmacological explanation was the next objective of this study.

Methods

We retrospectively analyzed 50 case files of patients with BID, searching for patterns that could potentially explain this intolerance.

Results

The most frequent concomitant disease was hypertension, likely due to high average age. Beta-blockers and acetylsalicylic acid were the most frequent concomitant medications. Otherwise, no conspicuous pattern emerged in this seemingly rather heterogeneous sample.

Conclusions

Plasma protein binding (PPB) was suspected as a key difference between benserazide and carbidopa that might potentially explain why some patients can tolerate carbidopa but not benserazide. However, reports on PPB of carbidopa and benserazide vary wildly from one source to another, making definitive conclusions impossible.

A Comprehensive Computational Study of the Interaction between Human Serum Albumin and Fullerenes

Human serum albumin (HSA) is the most abundant blood plasma protein, which transports fatty acids, hormones, and drugs. We consider nanoparticle-HSA interactions by investigating the binding of HSA with three fullerene analogs. Long MD simulations, quantum mechanical (fragment molecular orbital, energy decomposition analysis, atoms-in-molecules), and free energy methods elucidated the binding mechanism in these complexes. Such a systematic study is valuable due to the lack of comprehensive theoretical approaches to date. The main elements of the mechanism include the following: binding to IIA site results in allosteric modulation of the IIIA and heme binding sites with an increase in α-helical structure of IIIA. Fullerenes displayed high binding affinities for HSA; therefore, HSA can be used as a fullerene carrier, facilitating any toxic function the fullerene may exert. Complex formation is driven by hydrogen bonding, van der Waals, nonpolar, charge transfer, and dispersion energy contributions. Proper functionalization of C60 has enhanced its binding to HSA by more than an order of magnitude. This feature may be important for biological applications (e.g., photodynamic therapy of cancer). Satisfactory agreement with relevant experimental and theoretical data has been obtained.