Respecting the Patient’s Choice: A Case of Possible Drug-Induced Parkinsonism

This report describes a case of likely drug-induced Parkinsonism (DIP) identified by the pharmacist. A 54-year-old female patient was referred by a physician to the pharmacist in a rural, integrated care team for a comprehensive medication review (CMR) to address the patient’s concerns of possible Parkinson’s disease (PD). While PD may occur over the progression of age, medications that affect dopamine transport can also cause DIP, a secondary form of Parkinson’s disease. Although PD and DIP may be clinically indistinguishable, differentiation may be possible by reviewing a patient’s medication history for any potential causative drugs correlating to the timeline of the onset of symptoms. In this case, the pharmacist reviewed the medication profile and identified medications that could be responsible for causing DIP, specifically bupropion. The pharmacist suggested discontinuing bupropion and identifying another option for treating depression. The patient appreciated the suggestion and education, but ultimately preferred continuing her bupropion therapy instead of discontinuing therapy or changing to an alternative agent. At a follow-up meeting with the pharmacist, not only was the patient still experiencing tremors despite taking carbidopa/levodopa, but additional medications known to be potential inducers of tremors were added to her regimen. Although the pharmacist repeatedly discussed DIP with the patient and believed stopping bupropion would determine whether her Parkinsonism was PD or DIP, ultimately the patient continued taking bupropion because of concerns related to depression severity and the impact on her well-being. The patient’s wishes were respected.

Presumed topography of basal ganglion: Derived from TRODAT images in a case of hemorrhagic stroke complicated with asymmetrical cogwheel rigidity

Introduction: Systemic maps of basal ganglion lesion corresponding to clinical symptoms are lacking at present. Only the framework of functional domains in striatum was presumed. We present a case with asymmetrical cogwheel rigidity which is related to the lesion site of the basal ganglion in his functional brain image. Case presentations: A 50-year-old male who suffered from subarachnoid hemorrhage and intracranial hemorrhage presented with upper limbs cogwheel rigidity. The symptom was more severe in the right side than the left side. Dopamine transport images revealed bilateral decreased dopamine transporter binding capacity in bilateral striatum. In left striatum, decreased uptake in dorsal region is more severe than ventral region. Cogwheel rigidity was mildly improved after use of pramipexole. Conclusions: This case report suggests that asymmetrical cogwheel rigidity is linked to the lesion site of the basal ganglion. Topography exists in the striatum and is related to dysfunctional site of parkinsonism. Keywords: cogwheel rigidity; asymmetrical cogwheel rigidity; parkinsonism; basal ganglion; topography

The dopamine transporter counter-transports potassium to increase the uptake of dopamine

The dopamine transporter (DAT) facilitates dopamine reuptake from the extracellular space, and thereby terminates neurotransmission and refills cellular stores of dopamine. DAT belongs to the neurotransmitter:sodium symporter (NSS) family, which includes similar transporters for serotonin, norepinephrine, and GABA. A hallmark of NSS proteins is their ability to utilize the energy stored in the inward-directed Na+ gradient to drive the uphill transport of substrate. Decades ago, it was shown that the serotonin transporter also counter-transports K+, but investigations of K+-coupled transport in other NSSs have been inconclusive. Here, we show that the Drosophila dopamine transporter (dDAT) counter-transports K+. We found that ligand binding to both dDAT and human DAT is inhibited by K+ and that the conformational dynamics of dDAT in K+ is highly divergent from both the apo- and Na+-bound conformations. Furthermore, we found that K+ increased dopamine uptake by purified dDAT reconstituted in liposomes, and we visualized, in real-time, Na+ and K+ fluxes in single proteoliposomes using fluorescent ion indicators. Our results expand on the fundamentals of dopamine transport and prompt a reevaluation of the impact of K+ on other NSSs, including whether K+ counter-transport is a common mechanism for this pharmacologically important protein family.

Mutations of Human DopamineTransporter at Tyrosine88, Aspartic Acid206, and Histidine547 Influence Basal and HIV-1 Tat‐inhibited Dopamine Transport

HIV-1 transactivator of transcription (Tat) has a great impact on the development of HIV-1 associated neurocognitive disorders through disrupting dopamine transmission. This study determined the mutational effects of human dopamine transporter (hDAT) on basal and Tat-induced inhibition of dopamine transport. Compared to wild-type hDAT, the maximal velocity (Vmax) of [3H]dopamine uptake was decreased in D381L and Y88F/D206L/H547A, increased in D206L/H547A, and unaltered in D206L. Recombinant TatR1 − 86 inhibited dopamine uptake in wild-type hDAT, which was attenuated in either DAT mutants (D206L, D206L/H547A, and Y88F/D206L/H547A) or mutated TatR1 − 86 (K19A and C22G), demonstrating perturbed Tat-DAT interaction. Mutational effects of hDAT on the transporter conformation were evidenced by attenuation of zinc-induced increased [3H]WIN35,428 binding in D206L/H547A and Y88F/D206A/H547A and enhanced basal MPP+ efflux in D206L/H547A. H547A-induced outward-open transport conformational state was further validated by enhanced accessibility to MTSET ([2-(trimethylammonium)ethyl]-methanethiosulfonate) of an inserted cysteine (I159C) on a hDAT background.. Furthermore, H547A displayed an increase in palmitoylation inhibitor-induced inhibition of dopamine uptake relative to wide-type hDAT, indicating a change in basal palmitoylation in H547A. These results demonstrate that Y88F, D206L, and H547A attenuate Tat inhibition while preserving DA uptake, providing insights into identifying targets for improving DAT-mediated dopaminergic dysregulation. Graphical Abstract HIV-1 Tat inhibits dopamine uptake through human dopamine transporter (hDAT) on the presynaptic terminal through a direct allosteric interaction. Key hDAT residues D-H547, D-Y88, and D-D206 are predicted to be involved in the HIV-1 Tat-DAT binding. Mutating these residues attenuates this inhibitory effect by disrupting the Tat-hDAT interaction

Highly enriched hiPSC-derived midbrain dopaminergic neurons robustly models Parkinson’s disease

The development of human induced pluripotent stem cells (hiPSC) has greatly aided our ability to model neurodegenerative diseases. However, generation of midbrain dopaminergic (mDA) neurons is a major challenge and protocols are variable. Here, we developed a method to differentiate hiPSCs into enriched populations (>80%) of mDA neurons using only small molecules. We confirmed the identity of the mDA neurons using single-cell RNA-sequencing and detection of classical markers. Single-cell live imaging demonstrated neuronal calcium signalling and functional dopamine transport. Electrophysiology measures highlighted the ability to form synapses and networks in culture. Patient-specific hiPSC lines differentiated to produce functional mDA neurons that exhibit the hallmarks of synucleinopathy including: aggregate formation, oxidative stress as well as mitochondrial dysfunction and impaired lysosomal dynamics. In summary, we establish a robust differentiation paradigm to generate enriched mDA neurons from hiPSCs, which can be used to faithfully model key aspects of Parkinson’s disease (PD), providing the potential to further elucidate molecular mechanisms contributing to disease development.