Knowing where a prodrug is converted is different from knowing which enzyme performs the conversion. A historical 2014 study of lisdexamfetamine made progress on the first question while leaving the second unresolved. That distinction matters when a pharmacological explanation is presented as an established molecular identity.
What experiment was performed?
Sharman and Pennick studied lisdexamfetamine dimesylate, a prodrug in which d-amphetamine is linked to l-lysine. This was an in-vitro investigation using blood pooled from three healthy male donors, rather than a clinical dosing trial. Blood and prepared fractions were incubated with lisdexamfetamine at 1 microgram/mL, at 37°C, for up to four hours.
The researchers measured intact lisdexamfetamine and released d-amphetamine using liquid chromatography–tandem mass spectrometry. Preparation included plasma, blood-cell lysate, cytosolic extract and a membrane fraction. Other blood cells were not separately removed; the paper’s attribution to red blood cells also relied on earlier research.
What did the fractions show?
Conversion was prominent in whole blood and cytosolic extract. Plasma remained stable over four hours, with d-amphetamine below the reported 10 ng/mL detection limit. In the membrane fraction, there was no detectable loss of intact prodrug, although a small d-amphetamine signal was measured. The authors acknowledged that fraction purity had not been verified.
A sample below a detection limit should retain that qualifier. It is not the same claim as proving that no molecule was present. Likewise, a small product signal in a prepared fraction cannot establish a second biological pathway when contamination between fractions has not been excluded.
Did the inhibitor results identify aminopeptidase B?
No. A protease-inhibitor mixture reduced conversion. Bestatin and EDTA also strongly inhibited d-amphetamine production in cytosolic extract, a pattern consistent with aminopeptidase-like activity. But purified recombinant aminopeptidase B did not generate detectable d-amphetamine from lisdexamfetamine, despite activity against a separate reporter substrate.
The reporter control matters: a negative result with lisdexamfetamine was not simply accompanied by an inactive enzyme preparation. Even so, the experiment did not identify the responsible enzyme. Inferring a class of activity from an inhibitor profile is a narrower conclusion than assigning the reaction to a named protein.
Do pooled donors establish consistency between people?
Pooling can provide material for comparing laboratory conditions, but it removes the donor-by-donor contrast. Three donors contributing to a pool are not three independently characterized conversion curves. Replicate incubations assess repeatability of the prepared material, not the distribution of responses across patients.
The authors also performed no statistical comparisons between measured concentrations in different sample types. The experiment therefore should not be recast as a population study quantifying sex differences, individual variability, anemia effects, or the probability of an unusual clinical response.
Can these laboratory findings date use or establish impairment?
They cannot. Incubating a known starting concentration in blood outside the body differs from oral administration, absorption, distribution and elimination in a living person. A laboratory conversion curve supplies no direct measure of a patient’s attention, driving performance or symptom duration.
The practical lesson is to preserve both analytes and the experimental setting. Lisdexamfetamine disappearance and d-amphetamine appearance describe prodrug activation in the tested preparation. This paper supports a cytosolic site and a constrained enzyme hypothesis; it does not provide an individual dosing recommendation or a forensic time-since-use calculator.
Source
Sharman J, Pennick M. Lisdexamfetamine prodrug activation by peptidase-mediated hydrolysis in the cytosol of red blood cells. Neuropsychiatric Disease and Treatment. 2014;10:2275–2280. DOI: 10.2147/NDT.S70382. Full text; bibliographic record.