Identification and characterization of ambroxol as an enzyme enhancement agent for Gaucher disease

Acetal functionalized iminosugars for targeting β-glucocerebrosidase modulation

Novel pH-sensitive drug delivery systems offer significant potential for personalized medicine by enabling targeted therapy and minimizing side effects. These systems are designed to release therapeutic agents in acidic environments to achieve localized pharmacological effects. Dysfunctions in lysosomal enzyme β-glucocerebrosidase (GCase) play a crucial role in Gaucher and Parkinson's diseases. While pharmacological chaperones (PCs) stabilize GCase, the overall efficacy in restoring enzyme functionality is often abolished by their reluctance to dissociate from the enzyme once in lysosomes. To address this limitation, we developed pH-sensitive acetal functionalized iminosugars that hydrolyze under weakly acidic conditions, exploiting the pH difference between the endoplasmic reticulum and lysosomes to promote dissociation. Additionally, antioxidant moieties, derived from coniferyl aldehyde and vanillin, were incorporated to counteract oxidative stress, which is prevalent in Gaucher and Parkinson's diseases. The newly synthesized compounds 1-4 exhibit varying degrees of pH sensitivity and GCase stabilization in fibroblast ex vivo assays, with acetal 4 showing promising response, here validated both in lysates and in intact cells.

Developing nanobodies as allosteric molecular chaperones of glucocerebrosidase function

The enzyme glucocerebrosidase (GCase) catalyses the hydrolysis of glucosylceramide to glucose and ceramide within lysosomes. Homozygous or compound heterozygous mutations in the GCase-encoding GBA1 gene cause the lysosomal storage disorder Gaucher disease, while heterozygous and homozygous mutations are the most frequent genetic risk factor for Parkinson's disease. These mutations commonly affect GCase stability, trafficking or activity. Here, we report the development and characterization of nanobodies (Nbs) targeting and acting as molecular chaperones for GCase. We identify several Nb families that bind with nanomolar affinity to GCase. Based on biochemical characterization, we group the Nbs in two classes: Nbs that improve the activity of the enzyme and Nbs that increase GCase stability in vitro. A selection of the most promising Nbs is shown to improve GCase function in cell models and positively impact the activity of the N370S mutant GCase. These results lay the foundation for the development of new therapeutic routes.

Allosteric Modulation of GCase Enhances Lysosomal Activity and Reduces ER Stress in GCase-Related Disorders

Variants in the GBA1 gene, encoding the lysosomal enzyme glucosylceramidase beta 1 (GCase), are linked to Parkinson's disease (PD) and Gaucher disease (GD). Heterozygous variants increase PD risk, while homozygous variants lead to GD, a lysosomal storage disorder. Some GBA1 variants impair GCase maturation in the endoplasmic reticulum, blocking lysosomal transport and causing glucosylceramide accumulation, which disrupts lysosomal function. This study explores therapeutic strategies to address these dysfunctions. Using Site-directed Enzyme Enhancement Therapy (SEE-Tx®), two structurally targeted allosteric regulators (STARs), GT-02287 and GT-02329, were developed and tested in GD patient-derived fibroblasts with relevant GCase variants. Treatment with GT-02287 and GT-02329 improved the folding of mutant GCase, protected the GCaseLeu444Pro variant from degradation, and facilitated the delivery of active GCase to lysosomes. This enhanced lysosomal function and reduced cellular stress. These findings validate the STARs' mechanism of action and highlight their therapeutic potential for GCase-related disorders, including GD, PD, and Dementia with Lewy Bodies.

The modifying effect of mutant LRRK2 on mutant GBA1-associated Parkinson disease

Parkinson disease (PD) is the second most common neurodegenerative disease. While most cases are sporadic, in ~ 5%-10% of PD patients the disease is caused by mutations in several genes, among them GBA1 (glucocerebrosidase beta 1) and LRRK2 (leucine-rich repeat kinase 2), both prevalent among the Ashkenazi Jewish population. LRRK2-associated PD tends to be milder than GBA1-associated PD. Several recent clinical studies have suggested that carriers of both GBA1 and LRRK2 mutations develop milder PD compared to that observed among GBA1 carriers. These findings strongly suggested an interplay between the two genes in the development and progression of PD. In the present study Drosophila was employed as a model to investigate the impact of mutations in the LRRK2 gene on mutant GBA1-associated PD. Our results strongly indicated that flies expressing both mutant genes exhibited milder parkinsonian signs compared to the disease developed in flies expressing only a GBA1 mutation. This was corroborated by a decrease in the ER stress response, increase in the number of dopaminergic cells, elevated levels of tyrosine hydroxylase, reduced neuroinflammation, improved locomotion and extended survival. Furthermore, a significant decrease in the steady-state levels of mutant GBA1-encoded GCase was observed in the presence of mutant LRRK2, strongly implying a role for mutant LRRK2 in degradation of mutant GCase.

Precision Medicine in Parkinson's Disease

The continually accumulating knowledge of Parkinson's disease (PD) genetics presents potential disease modification opportunities through targeting specific genes and associated metabolic pathways. Glucosylceramidase beta 1-associated PD and leucine-rich repeat kinase 2-associated PD are attractive drug targets, since their respective mutations significantly increase PD risk and, at the same time, are relatively prevalent in the PD population. Here, we review clinical trials and preclinical efforts whose mechanisms target genetic forms of PD, focusing on these 2 genes and their metabolic pathways. Such therapies could also potentially modify sporadic (ie, without a clear genetic risk factor) PD.

Impact of ER stress and the unfolded protein response on Fabry disease

Fabry disease (FD) is a lysosomal storage disorder caused by pathogenic missense and nonsense variants in the α-galactosidase A (GLA) gene, leading to absent or reduced enzyme activity. The resulting lysosomal accumulation of the substrate globotriaosylceramide leads to progressive renal failure, cardiomyopathy with (malignant) cardiac arrhythmias and progressive heart failure as well as recurrent strokes, which significantly limits the life expectancy of patients affected with FD. There is increasing evidence that pathogenic GLA missense variants as well as formally benign GLA variants can cause retention in the endoplasmic reticulum (ER), resulting in ER stress, which in turn triggers an unfolded protein response (UPR) leading to cellular dysregulation including inflammation, irreversible cell damage, and apoptosis. This review aims to provide an update on the pathogenetic significance of ER stress and UPR in FD, current treatment options, including pharmaceutical and chemical chaperones, and an outlook on current research and future treatment options in FD.

Sidransky Syndrome-GBA1-Related Parkinson's Disease and Its Targeted Therapies

Sidransky syndrome represents a distinct variant of Parkinson's disease (PD) that is linked to pathogenic variants in the glucocerebrosidase (GBA1) gene. This disorder exhibits an earlier onset, a more severe course, and a higher dementia prevalence compared to idiopathic PD. While the pathogenesis remains debated between loss-of-function and gain-of-function mechanisms, targeted therapies are emerging. Pharmacological chaperones (PCs), like high-dose Ambroxol, aim to mitigate enzyme misfolding-a primary driver of this disorder-rather than addressing metabolic deficiencies seen in Gaucher disease. Despite failed trials of substrate reduction therapies, current clinical trials with Ambroxol and other PCs highlight promising avenues for disease modification. This commentary advocates for increased awareness of Sidransky syndrome to advance diagnostic strategies, promote genetic testing, and refine targeted treatments, with the potential to transform care for GBA1-related PD and prodromal stages of the disease.

Development of selective nanomolar cyclic peptide ligands as GBA1 enzyme stabilisers

The stabilisation of recombinant glycosidases by exogenous ligands, known as pharmacological chaperones or enzyme stabilisers, has recently garnered great clinical interest. This strategy can prevent enzyme degradation in the blood, reducing required dosages of recombinant enzyme and extending IV injection intervals, thereby reducing side effects, improving patient lifestyles and treatment costs. While this therapeutic approach has been successfully implemented for treating Pompe and Fabry diseases, clinical studies for Gaucher disease using chaperones alone or in combination with enzyme replacement therapy (ERT) have been limited, and no small molecule chaperones have yet been approved for this condition. Developing such therapies requires selective and effective reversible GBA1 ligands. Here, we describe the development of a new class of selective macrocyclic peptide GBA1 ligands using random nonstandard peptides integrated discovery (RaPID) technology, and demonstrate their ability to bind and stabilise rhGBA1 in plasma at nanomolar concentrations. These cyclic peptides do not inhibit endogenous GBA1 in cells due to poor cell permeability but can stabilise extracellular rhGBA1 in plasma, presenting significant potential as a combinatorial ERT-pharmacological chaperone therapy for Gaucher disease.

Evidence of α-Synuclein/Glucocerebrosidase Dual Targeting by Iminosugar Derivatives

Intrinsically disordered proteins (IDPs) are highly flexible molecules often linked to the onset of incurable diseases. Despite their great therapeutic potential, IDPs are often considered as undruggable because they lack defined binding pockets, which constitute the basis of drug discovery approaches. However, small molecules that interact with the intrinsically disordered state of α-synuclein, the protein linked to Parkinson's disease (PD), were recently identified and shown to act as chemical chaperones. Glucocerebrosidase (GCase) is an enzyme crucially involved in PD, since mutations that code for GCase are among the most frequent genetic risk factors for PD. Following the "dual-target" approach, stating that one carefully designed molecule can, in principle, interfere with more than one target, we identified a pharmacological chaperone for GCase that interacts with the intrinsically disordered monomeric form of α-synuclein. This result opens novel avenues to be explored in the search for molecules that act on dual targets, in particular, with challenging targets such as IDPs.

Drug Repositioning and Repurposing for Disease-Modifying Effects in Parkinson's Disease

Parkinson's disease (PD) is the second most prevalent neurodegenerative disorder and is characterized by progressive dopaminergic and nondopaminergic neuronal loss and the presence of Lewy bodies, which are primarily composed of aggregated α-synuclein. Despite advancements in symptomatic therapies, such as dopamine replacement and deep brain stimulation, no disease-modifying therapies (DMTs) have been identified to slow or arrest neurodegeneration in patients with PD. Challenges in DMT development include disease heterogeneity, the absence of reliable biomarkers, and the multifaceted pathophysiology of PD, encompassing neuroinflammation, mitochondrial dysfunction, lysosomal impairment, and oxidative stress. Drug repositioning and repurposing strategies using existing drugs for new therapeutic applications offer promising approaches to accelerate the development of DMTs for PD. These strategies minimize time, cost, and risk by using compounds with established safety profiles. Prominent candidates include glucagon-like peptide-1 receptor agonists, dipeptidyl peptidase-4 inhibitors, ambroxol, calcium channel blockers, statins, iron-chelating agents, c-Abl inhibitors, and memantine. Although preclinical and early clinical studies have demonstrated encouraging results, numerous phase III trials have yielded unfavorable outcomes, elucidating the complexity of PD pathophysiology and the need for innovative trial designs. This review evaluates the potential of prioritized repurposed drugs for PD, focusing on their mechanisms, preclinical evidence, and clinical trial outcomes, and highlights the ongoing challenges and opportunities in this field.

Product Development of High-Dose Ambroxol HCl Capsules for an n-of-1 Clinical Trial Involving Dutch Patients with Gaucher Disease Type 3

Background/Objectives: Ambroxol hydrochloride (AMB) is a promising chaperone for treating neurological manifestations in Gaucher disease type 3 (GD3). The Amsterdam University Medical Center planned to conduct an n-of-1 clinical trial using high-dose AMB (25 mg/kg/day). As an adequate commercial AMB formulation is unavailable for this high target dosage, we aimed to develop high-dose AMB capsules and assess the formulated capsule's quality. Methods: AMB API was sourced and tested according to the requirements of the European Pharmacopoeia. Capsule formulations of 75 mg and 200 mg AMB were developed. Drug product specifications were set following international guidelines (ICH Q6A) and the European Pharmacopoeia. Analytical methods were developed and validated, and three validation batches of each capsule strength were produced and analyzed. Results: The contents and the Acceptance Values (AVs) of the initial AMB batches (both strengths) varied between 89.1% to 92.7% (specification: 90% to 110%) and 12.4 to 17.6 (specification ≤ 15.0), respectively, indicating non-uniform AMB distribution. Consequently, the production of 200 mg capsules was discontinued, and modifications were made to the 75 mg capsule formulation, followed by the production of three optimized 75 mg validation batches. These batches met the specified criteria, with an AMB content and AV values ranging from 93.9% to 96.5% and 12.4 to 14.9, respectively. Furthermore, rapid dissolution profiles were observed (>80% dissolution within 15 min). No degradation products or microbiological impurities were detected after production. Conclusions: The optimized formulation of 75 mg AMB capsules formulated within the hospital pharmacy setting resulted in qualitative and uniform capsules which can be used in clinical trials.

Does drug repurposing bridge the gaps in management of Parkinson's disease? Unravelling the facts and fallacies

Repurposing the existing drugs for the management of both common and rare diseases is increasingly appealing due to challenges such as high attrition rates, the economy, and the slow pace of discovering new drugs. Drug repurposing involves the utilization of existing medications to treat diseases for which they were not originally intended. Despite encountering scientific and economic challenges, the pharmaceutical industry is intrigued by the potential to uncover new indications for medications. Medication repurposing is applicable across different stages of drug development, with the greatest potential observed when the drug has undergone prior safety testing. In this review, strategies for repurposing drugs for Parkinson's disease (PD) are outlined, a neurodegenerative disorder predominantly impacting dopaminergic neurons in the substantia nigra pars compacta region. PD is a debilitating neurodegenerative condition marked by an amalgam of motor and non-motor symptoms. Despite the availability of certain symptomatic treatments, particularly targeting motor symptoms, there remains a lack of established drugs capable of modifying the clinical course of PD, leading to its unchecked progression. Although standard drug discovery initiatives focusing on treatments that relieve diseases have yielded valuable understanding into the underlying mechanisms of PD, none of the numerous promising candidates identified in preclinical studies have successfully transitioned into clinically effective medications. Due to the substantial expenses associated with drug discovery endeavors, it is understandable that there has been a notable shift towards drug reprofiling strategies. Assessing the efficacy of an existing medication offers the additional advantage of circumventing the requirement for preclinical safety assessments and formulation enhancements, consequently streamlining the process and reducing both the duration of time and financial investments involved in bringing a treatment to clinical fruition. Furthermore, repurposed drugs may benefit from lower rates of failure, presenting an additional potential advantage. Various strategies for repurposing drugs are available to researchers in the field of PD. Some of these strategies have demonstrated effectiveness in identifying appropriate drugs for clinical trials, thereby providing validation for such strategies. This review provides an overview of the diverse strategies employed for drug reprofiling from approaches that place emphasis on single-gene transcriptional investigations to comprehensive epidemiological correlation analysis. Additionally, instances of previous or current research endeavors employing each strategy have been discussed. For the strategies that have not been yet implemented in PD research, their strategic efficacy is demonstrated using examples involving other disorders. In this review, we assess the safety and efficacy potential of prominent candidates repurposed as potential treatments for modifying the course of PD undergoing advanced clinical trials.

Current and Emerging Therapies for Lysosomal Storage Disorders

Lysosomal storage disorders (LSDs) are rare inherited metabolic disorders characterized by defects in the function of specific enzymes responsible for breaking down substrates within cellular organelles (lysosomes) essential for the processing of macromolecules. Undigested substrate accumulates within lysosomes, leading to cellular dysfunction, tissue damage, and clinical manifestations. Clinical features vary depending on the degree and type of enzyme deficiency, the type and extent of substrate accumulated, and the tissues affected. The heterogeneous nature of LSDs results in a variety of treatment approaches, which must be tailored to patient presentation and characteristics. The treatment landscape for LSDs is rapidly evolving. An up-to-date discussion of current evidence is required to provide clinicians with an appropriate overview of treatment options. Therefore, we aimed to review current and ongoing trials pertaining to the treatment of common LSDs.

Current opinion on pluripotent stem cell technology in Gaucher's disease: challenges and future prospects

Gaucher's disease (GD) is a rare autosomal recessive genetic disorder caused by mutations in the GBA1 gene. Mutations in the gene lead to the deficiency of glucocerebrosidase, an enzyme that helps in the breakdown of glucosylceramide (GlcCer) into ceramide and glucose. The lack of the enzyme causes GlcCer accumulation in macrophages, resulting in various phenotypic characteristics of GD. The currently available therapies, including enzyme replacement therapy and substrate reduction therapy, only provide symptomatic relief. However, they grapple with limitations in efficacy, accessibility, and potential side effects. These observations laid the foundation to search for new approaches in the management of GD. Induced pluripotent stem cells (iPSCs) technology emerges as a beacon of hope, offering novel avenues for future GD therapies. The true magic of iPSCs lies in their ability to differentiate into various cell types. By reprogramming patient-derived cells into iPSCs, researchers can generate personalized models that recapitulate the genetic and phenotypic characteristics of the GD. These models are valuable tools for dissecting intricate disease pathways, developing novel therapeutic targets, and enhancing the drug development process for GD. This review emphasizes the significance of iPSCs technology in GD management. Further, it addresses several challenges that are being encountered in the application of iPSC technology in the management of GD. In addition, it provides several insights into the future aspects of iPSC technology in the management of GD.

Chaperone therapy: Stabilization and enhancement of endogenous and exogenous lysosomal enzymes

Chaperone therapy is a new concept of molecular therapeutic approach to protein misfolding diseases, particularly to lysosomal diseases. Initially we started molecular analysis of culture cells, model animals and patients with Fabry disease and GM1-gangliosidosis. Some mutant enzyme proteins did not express the catalytic activity because of unstable molecular structure in somatic cells. The small molecule compound (chaperone) corrected misfolding of the unstable mutant protein, resulting in restoration of the enzyme activity (chaperone therapy). This pathological molecular event was studied first in endogenous mutant enzymes. Then a similar molecular interaction was found between the chaperone and the exogenous protein supplied for enzyme replacement therapy (ERT) in Pompe disease. This new chaperone-ERT combination therapy will become another useful technology in order to expand the application of chaperone therapy to a wide range of lysosomal diseases. Thus, chaperone therapy is expected in future for stabilization and enhancement of exogenously supplied ERT enzymes as well as endogenous mutant enzymes.

Improvement of Mutant Galactose-1-Phosphate Uridylyltransferase (GALT) Activity by FDA-Approved Pharmacochaperones: A Preliminary Study

Classic galactosemia is a rare disease with long-term consequences that seriously affect the quality of life of patients. To date, various therapeutic approaches are being developed, but treatments that target the molecular defects in the mutant galactose-1-phosphate uridylyltransferase (GALT) gene are lacking. We conducted a computational search for putative pharmacochaperones by applying a drug repurposing strategy, and we found that one compound, already active as a pharmacochaperone in another pathology, doubled the enzymatic activity of the purified mutant enzyme in an in vitro test. Furthermore, an extensive computational search in a database of known active molecules found another compound able in its turn to improve in vitro enzymatic activity. Both compounds are predicted to interact with a cavity at the enzyme interface previously supposed to be an allosteric site for the GALT enzyme. In vitro tests confirmed also the reduced accumulation of galactose-1-phosphate (G1P) in fibroblasts of patients. Although these results must be considered preliminary, our findings pave the way for future research lines focused on the search for promising pharmacochaperones that can directly rescue the activity of the enzyme.

Multivalent GCase Enhancers: Synthesis and Evaluation of Glyco-Gold Nanoparticles Decorated with Trihydroxypiperidine Iminosugars

The present study reports the preparation of the first multivalent iminosugars built onto a glyco-gold nanoparticle core (glyco-AuNPs) capable of stabilizing or enhancing the activity of the lysosomal enzyme GCase, which is defective in Gaucher disease. An N-nonyltrihydroxypiperidine was selected as the bioactive iminosugar unit and further functionalized, via copper-catalyzed alkyne-azide cycloaddition, with a thiol-ending linker that allowed the conjugation to the gold core. These bioactive ligands were obtained with either a linear monomeric or dendritic trimeric arrangement of the iminosugar. The concentration of the bioactive iminosugar on the gold surface was modulated with different amounts of a glucoside bearing a short thiol-ending spacer as the inner ligand. The new mixed-ligand coated glyco-AuNPs were fully characterized, and those with the highest colloidal stability in aqueous medium were subjected to biological evaluation. Glyco-AuNPs with trimeric iminosugar bioactive units showed the ability to stabilize recombinant GCase in a thermal denaturation assay, while Glyco-AuNPs with monomeric iminosugar bioactive units were able to enhance the activity of mutant GCase in Gaucher patient's fibroblasts by 1.9-fold at 2.2 μM.

Prospects for Disease Slowing in Parkinson Disease

The increasing prevalence of Parkinson disease (PD) highlights the need to develop interventions aimed at slowing or halting its progression. As a result of sophisticated disease modeling in preclinical studies, and refinement of specific clinical/genetic/pathological profiles, our understanding of PD pathogenesis has grown over the years, leading to the identification of several targets for disease modification. This has translated to the development of targeted therapies, many of which have entered clinical trials. Nonetheless, up until now, none of these treatments have satisfactorily shown disease-modifying effects in PD. In this review, we present the most up-to-date disease-modifying pharmacological interventions in the clinical trial pipeline for PD. We focus on agents that have reached more advanced stages of clinical trials testing, highlighting both positive and negative results, and critically reflect on strengths, weaknesses, and challenges of current disease-modifying therapeutic avenues in PD.

Genetic-based diagnostics of Parkinson's disease and other Parkinsonian syndromes

INTRODUCTION

Parkinson's disease (PD) is a complex disorder with vast clinical heterogeneity. Recent genetic, imaging and clinical evidence suggest that there are multiple subtypes of PD, and perhaps even distinct clinical entities, which are being diagnosed under the umbrella of PD. These might have similar clinical presentation, but potentially different underlying mechanisms, which, in future, will require different treatments. Despite extensive genetic research progress, genetic testing is still not a common practice in clinical patient care.

AREAS COVERED

This review examines the numerous genes that have been discovered to affect the risk of, or cause, PD. We also outline genetic variants that affect PD age at onset, its progression, and the presence or severity of motor and non-motor symptoms. We differentiate between PD, other synucleinopathies, and atypical parkinsonism syndromes, and describe genes responsible for familial forms of typical PD and atypical parkinsonism. Lastly, we present current clinical trails that are underway for targeted therapies, particularly for GBA1-PD and LRRK2-PD which are the most significant subtypes.

EXPERT OPINION

While genetic studies alone cannot be diagnostic for PD, proper utilization of genetic screening for PD could improve diagnostic accuracy and predictions for prognosis, guide treatment, and identify individuals that qualify for clinical trials.

Targeting Protein Aggregation in ALS

Proteinopathies involve the abnormal accumulation of specific proteins. Maintaining the balance of the proteome is a finely regulated process managed by a complex network of cellular machinery responsible for protein synthesis, folding, and degradation. However, stress and ageing can disrupt this balance, leading to widespread protein aggregation. Currently, several therapies targeting protein aggregation are in clinical trials for ALS. These approaches mainly focus on two strategies: addressing proteins that are prone to aggregation due to mutations and targeting the cellular mechanisms that maintain protein homeostasis to prevent aggregation. This review will cover these emerging drugs. Advances in ALS research not only offer hope for better outcomes for ALS patients but also provide valuable insights and methodologies that can benefit the broader field of neurodegenerative disease drug discovery.

High-throughput screening for small-molecule stabilizers of misfolded glucocerebrosidase in Gaucher disease and Parkinson's disease

Glucocerebrosidase (GCase) is implicated in both a rare, monogenic disorder (Gaucher disease, GD) and a common, multifactorial condition (Parkinson's disease, PD); hence, it is an urgent therapeutic target. To identify correctors of severe protein misfolding and trafficking obstruction manifested by the pathogenic L444P-variant of GCase, we developed a suite of quantitative, high-throughput, cell-based assays. First, we labeled GCase with a small proluminescent HiBiT peptide reporter tag, enabling quantitation of protein stabilization in cells while faithfully maintaining target biology. TALEN-based gene editing allowed for stable integration of a single HiBiT-GBA1 transgene into an intragenic safe-harbor locus in GBA1-knockout H4 (neuroglioma) cells. This GD cell model was amenable to lead discovery via titration-based quantitative high-throughput screening and lead optimization via structure-activity relationships. A primary screen of 10,779 compounds from the NCATS bioactive collections identified 140 stabilizers of HiBiT-GCase-L444P, including both pharmacological chaperones (ambroxol and noninhibitory chaperone NCGC326) and proteostasis regulators (panobinostat, trans-ISRIB, and pladienolide B). Two complementary high-content imaging-based assays were deployed to triage hits: The fluorescence-quenched substrate LysoFix-GBA captured functional lysosomal GCase activity, while an immunofluorescence assay featuring antibody hGCase-1/23 directly visualized GCase lysosomal translocation. NCGC326 was active in both secondary assays and completely reversed pathological glucosylsphingosine accumulation. Finally, we tested the concept of combination therapy by demonstrating synergistic actions of NCGC326 with proteostasis regulators in enhancing GCase-L444P levels. Looking forward, these physiologically relevant assays can facilitate the identification, pharmacological validation, and medicinal chemistry optimization of small molecules targeting GCase, ultimately leading to a viable therapeutic for GD and PD.

Functional Analysis of Human GBA1 Missense Mutations in Drosophila: Insights into Gaucher Disease Pathogenesis and Phenotypic Consequences

The human GBA1 gene encodes lysosomal acid β-glucocerebrosidase, whose activity is deficient in Gaucher disease (GD). In Drosophila, there are two GBA1 orthologs, Gba1a and Gba1b, and Gba1b is the bona fide GCase encoding gene. Several fly lines with different deletions in the Gba1b were studied in the past. However, since most GD-associated GBA1 mutations are point mutations, we created missense mutations homologous to the two most common GD mutations: the mild N370S mutation (D415S in Drosophila) and the severe L444P mutation (L494P in Drosophila), using the CRISPR-Cas9 technology. Flies homozygous for the D415S mutation (dubbed D370S hereafter) presented low GCase activity and substrate accumulation, which led to lysosomal defects, activation of the Unfolded Protein Response (UPR), inflammation/neuroinflammation, and neurodegeneration along with earlier death compared to control flies. Surprisingly, the L494P (called L444P hereafter) flies presented higher GCase activity with fewer lysosomal defects and milder disease in comparison to that presented by the D370S homozygous flies. Treatment with ambroxol had a limited effect on all homozygous fly lines tested. Overall, our results underscore the differences between the fly and human GCase enzymes, as evidenced by the distinct phenotypic outcomes of mutations in flies compared to those observed in human GD patients.

Neuronopathic Gaucher disease: Rare in the West, common in the East

Gaucher disease (GD) stands as one of the most prevalent lysosomal disorders, yet neuronopathic GD (nGD) is an uncommon subset characterized by a wide array of clinical manifestations that complicate diagnosis, particularly when neurological symptoms are understated. nGD may manifest as the acute neuronopathic type, or GD type 2 (GD2), either prenatally or within the first weeks to months of life, whereas GD type 3 (GD3) symptoms may emerge at any point during childhood or occasionally in adolescence. The clinical presentation encompasses severe systemic involvement to mild visceral disease, often coupled with a spectrum of progressive neurological signs and symptoms such as cognitive impairment, ataxia, seizures, myoclonus, varying degrees of brainstem dysfunction presenting with stridor, apneic episodes, and/or impaired swallowing. This manuscript aims to provide a comprehensive review of the incidence, distinctive presentations, and diverse clinical phenotypes of nGD across various countries and regions. It will explore the natural history of the neurodegenerative process in GD, shedding light on its various manifestations during infancy and childhood, and offer insights into the diagnostic journey, the challenges faced in the clinical management, and current and investigative therapeutic approaches for GD's neurological variants.

Gaucher disease provides a unique window into Parkinson disease pathogenesis

An exciting development in the field of neurodegeneration is the association between the rare monogenic disorder Gaucher disease and the common complex disorder Parkinson disease (PD). Gaucher disease is a lysosomal storage disorder resulting from an inherited deficiency of the enzyme glucocerebrosidase, encoded by GBA1, which hydrolyses the glycosphingolipids glucosylceramide and glucosylsphingosine. The observation of parkinsonism in a rare subgroup of individuals with Gaucher disease first directed attention to the role of glucocerebrosidase deficiency in the pathogenesis of PD. PD occurs more frequently in people heterozygous for Gaucher GBA1 mutations, and 3-25% of people with Parkinson disease carry a GBA1 variant. However, only a small percentage of individuals with GBA1 variants develop parkinsonism, suggesting that the penetrance is low. Despite over a decade of intense research in this field, including clinical and radiological evaluations, genetic studies and investigations using model systems, the mechanism underlying GBA1-PD is still being pursued. Insights from this association have emphasized the role of lysosomal pathways in parkinsonism. Furthermore, different therapeutic strategies considered or developed for Gaucher disease can now inform drug development for PD.

Molecular mechanisms of the ambroxol action in Gaucher disease and GBA1 mutation-associated Parkinson disease

Glucocerebrosidase (GCase), encoded by the GBA1 gene, is one of the lysosomal enzymes responsible for hydrolyzing the glycosphingolipids. Deficiency in GCase activity (in patients with two defective alleles of GBA1) leads to glucosylceramide storage in lysosomes which in turn results in the development of the Gaucher diseases, a lysosomal storage disorder, while a heterozygous state may be correlated with the GBA1 mutation-associated Parkinson disease. One of the proposed forms of therapy for these two conditions is the use of pharmacological chaperones which work by facilitating the achievement of the correct conformation of abnormally folded enzymes. Several compounds with chaperone activities against GCase have already been tested, one of which turned out to be ambroxol. Studies conducted on the action of this compound have indeed indicated its effectiveness in increasing GCase levels and activity. However, some data have begun to question its activity as a chaperone against certain GCase variants. Then, a number of articles appeared pointing to other mechanisms of action of ambroxol, which may also contribute to the improvement of patients' condition. This paper summarizes the biological mechanisms of action of ambroxol in Gaucher disease and GBA1 mutation-associated Parkinson disease, focused on its activity as a chaperone, modulator of ERAD pathways, inducer of autophagy, and pain reliever in cellular and animal models as well as in patients. The effects of these activities on the reduction of disease markers and symptoms in patients are also discussed. Consideration of all the properties of ambroxol can help in the appropriate choice of therapy and the determination of the effective drug dose.

Clinical and preclinical insights into high-dose ambroxol therapy for Gaucher disease type 2 and 3: A comprehensive systematic review

RATIONALE

Gaucher disease (GD), an autosomal recessive lysosomal storage disease, results from GBA1 variants causing glucocerebrosidase (GCase) deficiency. While enzyme replacement therapy (ERT) helps with systemic symptoms, neurological complications in GD2 and GD3 persist due to the blood-brain-barrier (BBB) limiting ERT efficacy. Ambroxol, a BBB-permeable chaperone, enhances GCase activity. Our review explores high-dose ambroxol's therapeutic potential, both preclinical and clinical, in GD2 and GD3.

METHODS

PubMed was searched for studies published before March 2023, including clinical, animal, and in vitro studies focusing on the effect of high-dose ambroxol in GD2 and GD3. A narrative synthesis was performed.

RESULTS

Nine in vitro, three animal, and eight clinical studies were included, demonstrating varied responses to ambroxol across diverse outcome measures. In vitro and animal studies demonstrated reduced endoplasmatic reticulum stress due to the relocation of GCase from the ER to the lysosomes. In vitro cell lines exhibited varying degrees of increased GCase activity. Clinical trials observed reduced lyso-GL1 levels in plasma (41-89%) and cerebrospinal fluid (CSF) (26-97%), alongside increased GCase activity in GD3 patients. Ambroxol exhibited varying effects on neurological outcomes and development. No severe adverse events were reported.

CONCLUSION

High-dose ambroxol shows promise in managing neurological manifestations in GD3, albeit with uncertainties resulting from genetic heterogeneity and variable response. Further clinical trials, are essential for elucidating dosage-response relationships and refining treatment outcomes and strategies for neuronopathic GD.

The lysosomal β-glucocerebrosidase strikes mitochondria: implications for Parkinson's therapeutics

Parkinson's disease is a neurodegenerative disorder primarily known for typical motor features that arise due to the loss of dopaminergic neurons in the substantia nigra. However, the precise molecular aetiology of the disease is still unclear. Several cellular pathways have been linked to Parkinson's disease, including the autophagy-lysosome pathway, α-synuclein aggregation and mitochondrial function. Interestingly, the mechanistic link between GBA1, the gene that encodes for lysosomal β-glucocerebrosidase (GCase), and Parkinson's disease lies in the interplay between GCase functions in the lysosome and mitochondria. GCase mutations alter mitochondria-lysosome contact sites. In the lysosome, reduced GCase activity leads to glycosphingolipid build-up, disrupting lysosomal function and autophagy, thereby triggering α-synuclein accumulation. Additionally, α-synuclein aggregates reduce GCase activity, creating a self-perpetuating cycle of lysosomal dysfunction and α-synuclein accumulation. GCase can also be imported into the mitochondria, where it promotes the integrity and function of mitochondrial complex I. Thus, GCase mutations that impair its normal function increase oxidative stress in mitochondria, the compartment where dopamine is oxidized. In turn, the accumulation of oxidized dopamine adducts further impairs GCase activity, creating a second cycle of GCase dysfunction. The oxidative state triggered by GCase dysfunction can also induce mitochondrial DNA damage which, in turn, can cause dopaminergic cell death. In this review, we highlight the pivotal role of GCase in Parkinson's disease pathogenesis and discuss promising examples of GCase-based therapeutics, such as gene and enzyme replacement therapies, small molecule chaperones and substrate reduction therapies, among others, as potential therapeutic interventions.

Iminosugar-Dihydroazulenes as Mutant L444P Glucocerebrosidase Enhancers

A remarkable enhancer of human glucocerebrosidase enzyme (GCase) was identified among a set of dihydroazulene-tagged iminosugars. An unprecedented 3.9-fold increase in GCase activity was detected on fibroblasts bearing the homozygous L444P mutation, which is frequently associated with neuronopathic Gaucher forms, and which commonly results refractory to chaperone-induced refolding.

Fragment-Based Discovery of a Series of Allosteric-Binding Site Modulators of β-Glucocerebrosidase

β-Glucocerebrosidase (GBA/GCase) mutations leading to misfolded protein cause Gaucher's disease and are a major genetic risk factor for Parkinson's disease and dementia with Lewy bodies. The identification of small molecule pharmacological chaperones that can stabilize the misfolded protein and increase delivery of degradation-prone mutant GCase to the lysosome is a strategy under active investigation. Here, we describe the first use of fragment-based drug discovery (FBDD) to identify pharmacological chaperones of GCase. The fragment hits were identified by using X-ray crystallography and biophysical techniques. This work led to the discovery of a series of compounds that bind GCase with nM potency and positively modulate GCase activity in cells.

GBA1-Associated Parkinson's Disease Is a Distinct Entity

GBA1-associated Parkinson's disease (GBA1-PD) is increasingly recognized as a distinct entity within the spectrum of parkinsonian disorders. This review explores the unique pathophysiological features, clinical progression, and genetic underpinnings that differentiate GBA1-PD from idiopathic Parkinson's disease (iPD). GBA1-PD typically presents with earlier onset and more rapid progression, with a poor response to standard PD medications. It is marked by pronounced cognitive impairment and a higher burden of non-motor symptoms compared to iPD. Additionally, patients with GBA1-PD often exhibit a broader distribution of Lewy bodies within the brain, accentuating neurodegenerative processes. The pathogenesis of GBA1-PD is closely associated with mutations in the GBA1 gene, which encodes the lysosomal enzyme beta-glucocerebrosidase (GCase). In this review, we discuss two mechanisms by which GBA1 mutations contribute to disease development: 'haploinsufficiency,' where a single functional gene copy fails to produce a sufficient amount of GCase, and 'gain of function,' where the mutated GCase acquires harmful properties that directly impact cellular mechanisms for alpha-synuclein degradation, leading to alpha-synuclein aggregation and neuronal cell damage. Continued research is advancing our understanding of how these mechanisms contribute to the development and progression of GBA1-PD, with the 'gain of function' mechanism appearing to be the most plausible. This review also explores the implications of GBA1 mutations for therapeutic strategies, highlighting the need for early diagnosis and targeted interventions. Currently, small molecular chaperones have shown the most promising clinical results compared to other agents. This synthesis of clinical, pathological, and molecular aspects underscores the assertion that GBA1-PD is a distinct clinical and pathobiological PD phenotype, necessitating specific management and research approaches to better understand and treat this debilitating condition.

Cost-effectiveness of ambroxol in the treatment of Gaucher disease type 2

Objective

Our aim was to compare the costs and efficacy of ambroxol in combination with imiglucerase with the costs and efficacy of imiglucerase only in the treatment of Gaucher disease type 2 (GD2) in the socio-economic settings of the Republic of Serbia, an upper-middle-income European economy.

Methods

The perspective of the Serbian Republic Health Insurance Fund was chosen for this study, and the time horizon was 6 years. The main outcomes of the study were quality-adjusted life years gained with ambroxol + imiglucerase and comparator, and direct costs of treatment. The study was conducted through the generation and simulation of the Markov chain model. The model results were obtained after Monte Carlo microsimulation of a sample with 1,000 virtual patients.

Results

Treatment with ambroxol in combination with imiglucerase was cost-effective when compared with imiglucerase only and was associated with positive values of net monetary benefit regardless of the onset of the disease. Such beneficial result for ambroxol and imiglucerase combination is primarily driven by the low cost of ambroxol and its considerable clinical effectiveness in slowing the progression of neural complications of GD2.

Conclusion

If ambroxol and imiglucerase are used in combination for the treatment of GD2, it is more cost-effective than using imiglucerase alone.

Rapid and long-lasting efficacy of high-dose ambroxol therapy for neuronopathic Gaucher disease: A case report and literature review

Gaucher disease (GD) is a lysosomal storage disorder caused by a deficiency in the GBA1-encoded enzyme, β-glucocerebrosidase. Enzyme replacement therapy is ineffective for neuronopathic Gaucher disease (nGD). High-dose ambroxol has been administered as an alternative treatment for a group of patients with nGD. However, little is known about the clinical indication and the long-term outcome of patients after ambroxol therapy. We herein report a case of a female patient who presented with a progressive disease of GD type 2 from 11 months of age and had the pathogenic variants of p.L483P (formerly defined as p.L444P) and p.R502H (p.R463H) in GBA1. A combined treatment of imiglucerase with ambroxol started improving the patient's motor activity in 1 week, while it kept the long-lasting effect of preventing the deteriorating phenotype for 30 months. A literature review identified 40 patients with nGD, who had received high-dose ambroxol therapy. More than 65% of these patients favorably responded to the molecular chaperone therapy, irrespective of p.L483P homozygous, heterozygous or the other genotypes. These results highlight the long-lasting effect of ambroxol-based chaperone therapy for patients with an expanding spectrum of mutations in GBA1.

A recent update on drugs and alternative approaches for parkinsonism

Parkinson's disease, often known as PD, is a more common age-related neurological disorder that affects a huge number of older adults worldwide. Parkinson's disease is predominantly a movement-related pathosis and is distinguished by the deposition of intra-neuronal aggregates, as the alpha-synuclein gene is expressed as Lewy bodies (LB) causing dopaminergic neurons to die. Stress in early life may contribute to the development of depression, and depression in patients may result in the development of Parkinson's disease as they mature. Depression is a non-motor condition that leads to motor symptoms, such as Parkinson's disease. PD Patients are currently utilizing a variety of other therapies like utilizing nutritional supplements, herbal remedies, vitamins, and massage. When a patient's functional ability is impaired, drug treatment is usually initiated according to the individual's condition and the severity of signs and symptoms. The current marketed anti-Parkinson drugs, has low brain distribution and failing to repair dopaminergic neurons or delaying the progression of the disease these negative effects were unavoidable. To overcome these disadvantages, this review considers the inclusion of drugs used in Parkinson's disease, focusing on strategies to reuse existing compounds to speed up drug development, their capacity to traverse the BBB, and drug dispersion in the brain. We look at cellular therapies and repurposed drugs. We also investigate the mechanisms, effectiveness, as well as safety of several new medications that are being repositioned for Parkinson's disease pharmacotherapy. In this study, we focus on global trends in Parkinson's disease research. We hope to raise awareness about the present state of major factors for disability worldwide, including yearly prevalence's from international and national statistics. The pathophysiology of Parkinsonism and also analyze existing therapies for Parkinson's disease, moreover new and innovative drug therapies, and to assess the prospects for disease modification.

Development of quantitative high-throughput screening assays to identify, validate, and optimize small-molecule stabilizers of misfolded β-glucocerebrosidase with therapeutic potential for Gaucher disease and Parkinson's disease

Glucocerebrosidase (GCase) is implicated in both a rare, monogenic disorder (Gaucher disease, GD) and a common, multifactorial condition (Parkinson's disease); hence, it is an urgent therapeutic target. To identify correctors of severe protein misfolding and trafficking obstruction manifested by the pathogenic L444P-variant of GCase, we developed a suite of quantitative, high-throughput, cell-based assays. First, we labeled GCase with a small pro-luminescent HiBiT peptide reporter tag, enabling quantitation of protein stabilization in cells while faithfully maintaining target biology. TALEN-based gene editing allowed for stable integration of a single HiBiT-GBA1 transgene into an intragenic safe-harbor locus in GBA1-knockout H4 (neuroglioma) cells. This GD cell model was amenable to lead discovery via titration-based quantitative high-throughput screening and lead optimization via structure-activity relationships. A primary screen of 10,779 compounds from the NCATS bioactive collections identified 140 stabilizers of HiBiT-GCase-L444P, including both pharmacological chaperones (ambroxol and non-inhibitory chaperone NCGC326) and proteostasis regulators (panobinostat, trans-ISRIB, and pladienolide B). Two complementary high-content imaging-based assays were deployed to triage hits: the fluorescence-quenched substrate LysoFix-GBA captured functional lysosomal GCase activity, while an immunofluorescence assay featuring antibody hGCase-1/23 provided direct visualization of GCase lysosomal translocation. NCGC326 was active in both secondary assays and completely reversed pathological glucosylsphingosine accumulation. Finally, we tested the concept of combination therapy, by demonstrating synergistic actions of NCGC326 with proteostasis regulators in enhancing GCase-L444P levels. Looking forward, these physiologically-relevant assays can facilitate the identification, pharmacological validation, and medicinal chemistry optimization of new chemical matter targeting GCase, ultimately leading to a viable therapeutic for two protein-misfolding diseases.

Exploring the efficacy and safety of Ambroxol in Gaucher disease: an overview of clinical studies

Gaucher disease (GD) is mainly caused by glucocerebrosidase (GCase) enzyme deficiency due to genetic variations in the GBA1 gene leading to the toxic accumulation of sphingolipids in various organs, which causes symptoms such as anemia, thrombocytopenia, hepatosplenomegaly, and neurological manifestations. GD is clinically classified into the non-neuronopathic type 1, and the acute and chronic neuronopathic forms, types 2 and 3, respectively. In addition to the current approved GD medications, the repurposing of Ambroxol (ABX) has emerged as a prospective enzyme enhancement therapy option showing its potential to enhance mutated GCase activity and reduce glucosylceramide accumulation in GD-affected tissues of different GBA1 genotypes. The variability in response to ABX varies across different variants, highlighting the diversity in patients' therapeutic outcomes. Its oral availability and safety profile make it an attractive option, particularly for patients with neurological manifestations. Clinical trials are essential to explore further ABX's potential as a therapeutic medication for GD to encourage pharmaceutical companies' investment in its development. This review highlights the potential of ABX as a pharmacological chaperone therapy for GD and stresses the importance of addressing response variability in clinical studies to improve the management of this rare and complex disorder.

Inhibition of cysteine protease cathepsin L increases the level and activity of lysosomal glucocerebrosidase

The glucocerebrosidase (GCase) encoded by the GBA1 gene hydrolyzes glucosylceramide (GluCer) to ceramide and glucose in lysosomes. Homozygous or compound heterozygous GBA1 mutations cause the lysosomal storage disease Gaucher disease (GD) due to severe loss of GCase activity. Loss-of-function variants in the GBA1 gene are also the most common genetic risk factor for Parkinson's disease (PD) and dementia with Lewy bodies (DLB). Restoring lysosomal GCase activity represents an important therapeutic approach for GBA1-associated diseases. We hypothesized that increasing the stability of lysosomal GCase protein could correct deficient GCase activity in these conditions. However, it remains unknown how GCase stability is regulated in the lysosome. We found that cathepsin L, a lysosomal cysteine protease, cleaves GCase and regulates its stability. In support of these data, GCase protein was elevated in the brain of cathepsin L-KO mice. Chemical inhibition of cathepsin L increased both GCase levels and activity in fibroblasts from patients with GD. Importantly, inhibition of cathepsin L in dopaminergic neurons from a patient GBA1-PD led to increased GCase levels and activity as well as reduced phosphorylated α-synuclein. These results suggest that targeting cathepsin L-mediated GCase degradation represents a potential therapeutic strategy for GCase deficiency in PD and related disorders that exhibit decreased GCase activity.

The use of Ambroxol for the treatment of Gaucher disease: A systematic review

Gaucher disease (GD) is a heterogeneous condition requiring tailored treatment approaches. The aim of this systematic review was to synthesise and evaluate current evidence pertaining to the use of Ambroxol for the treatment of GD. Published and unpublished literature databases, conference proceedings and the reference lists of included studies were searched until 23 November 2023. A narrative synthesis was performed. Database search and risk of bias assessment were performed independently by two reviewers. Twenty-one studies (182 patients) were included. The evidence was low in quality. Variable responses to Ambroxol were observed. Response rates were 36% and 55% in two studies reporting on type 1 GD. One study found a 22% response rate in type 2 GD, whereas another study found 29% of patients with type 3 GD reported neurological improvements. No severe adverse events were reported in the literature, with mild and reversible side effects reported. Varying response rates are to be expected (29%-100%) when treating neurological manifestations. Varying degrees of symptomatic improvement for the treatment of GD were noted in the literature. Multidisciplinary team input and clinical judgement are advised to provide personalized treatment of this complex and multi-faceted condition.

Twelve Years of Drug Prioritization to Help Accelerate Disease Modification Trials in Parkinson's Disease: The International Linked Clinical Trials Initiative

In 2011, the UK medical research charity Cure Parkinson's set up the international Linked Clinical Trials (iLCT) committee to help expedite the clinical testing of potentially disease modifying therapies for Parkinson's disease (PD). The first committee meeting was held at the Van Andel Institute in Grand Rapids, Michigan in 2012. This group of PD experts has subsequently met annually to assess and prioritize agents that may slow the progression of this neurodegenerative condition, using a systematic approach based on preclinical, epidemiological and, where possible, clinical data. Over the last 12 years, 171 unique agents have been evaluated by the iLCT committee, and there have been 21 completed clinical studies and 20 ongoing trials associated with the initiative. In this review, we briefly outline the iLCT process as well as the clinical development and outcomes of some of the top prioritized agents. We also discuss a few of the lessons that have been learnt, and we conclude with a perspective on what the next decade may bring, including the introduction of multi-arm, multi-stage clinical trial platforms and the possibility of combination therapies for PD.

Ambroxol as a disease-modifying treatment to reduce the risk of cognitive impairment in GBA-associated Parkinson's disease: a multicentre, randomised, double-blind, placebo-controlled, phase II trial. The AMBITIOUS study protocol

Background

Heterozygous mutations in the GBA gene, encoding the lysosomal enzyme β-glucocerebrosidase (GCase), are the most frequent genetic risk factor for Parkinson's disease (PD). GBA-related PD (GBA-PD) patients have higher risk of dementia and reduced survival than non-carriers. Preclinical studies and one open-label trial in humans demonstrated that the chaperone ambroxol (ABX) increases GCase levels and modulates α-synuclein levels in the blood and cerebrospinal fluid (CSF).

Methods and analysis

In this multicentre, double-blind, placebo-controlled, phase II clinical trial, we randomise patients with GBA-PD in a 1:1 ratio to either oral ABX 1.2 g/day or placebo. The duration of treatment is 52 weeks. Each participant is assessed at baseline and weeks 12, 26, 38, 52 and 78. Changes in the Montreal Cognitive Assessment score and the frequency of mild cognitive impairment and dementia between baseline and weeks 52 are the primary outcome measures. Secondary outcome measures include changes in validated scales/questionnaires assessing motor and non-motor symptoms. Neuroimaging features and CSF neurodegeneration markers are used as surrogate markers of disease progression. GCase activity, ABX and α-synuclein levels are also analysed in blood and CSF. A repeated-measures analysis of variance will be used for elaborating results. The primary analysis will be by intention to treat.

Ethics and dissemination

The study and protocols have been approved by the ethics committee of centres. The study is conducted according to good clinical practice and the Declaration of Helsinki. The trial findings will be published in peer-reviewed journals and presented at conferences.

Trial registration numbers

NCT05287503, EudraCT 2021-004565-13.

Animal Models for the Study of Gaucher Disease

In Gaucher disease (GD), a relatively common sphingolipidosis, the mutant lysosomal enzyme acid β-glucocerebrosidase (GCase), encoded by the GBA1 gene, fails to properly hydrolyze the sphingolipid glucosylceramide (GlcCer) in lysosomes, particularly of tissue macrophages. As a result, GlcCer accumulates, which, to a certain extent, is converted to its deacylated form, glucosylsphingosine (GlcSph), by lysosomal acid ceramidase. The inability of mutant GCase to degrade GlcSph further promotes its accumulation. The amount of mutant GCase in lysosomes depends on the amount of mutant ER enzyme that shuttles to them. In the case of many mutant GCase forms, the enzyme is largely misfolded in the ER. Only a fraction correctly folds and is subsequently trafficked to the lysosomes, while the rest of the misfolded mutant GCase protein undergoes ER-associated degradation (ERAD). The retention of misfolded mutant GCase in the ER induces ER stress, which evokes a stress response known as the unfolded protein response (UPR). GD is remarkably heterogeneous in clinical manifestation, including the variant without CNS involvement (type 1), and acute and subacute neuronopathic variants (types 2 and 3). The present review discusses animal models developed to study the molecular and cellular mechanisms underlying GD.

Novel beta-glucocerebrosidase chaperone compounds identified from cell-based screening reduce pathologically accumulated glucosylsphingosine in iPS-derived neuronal cells

The beta-glucocerebrosidase (GBA1) gene encodes the lysosomal beta-glucocerebrosidase (GCase) that metabolizes the lipids glucosylceramide (GlcCer) and glucosylsphingosine (GlcSph). Biallelic loss-of-function mutations in GBA1 such as L444P cause Gaucher disease (GD), which is the most prevalent lysosomal storage disease and is histopathologically characterized by abnormal accumulation of the GCase substrates GlcCer and GlcSph. GD with neurological symptoms is associated with severe mutations in the GBA1 gene, most of which cause impairment in the process of GCase trafficking to lysosomes. Given that recombinant GCase protein cannot cross the blood-brain barrier due to its high molecular weight, it is invaluable to develop a brain-penetrant small-molecule pharmacological chaperone as a viable therapeutic strategy to boost GCase activity in the central nervous system. Despite considerable efforts to screen potent GCase activators/chaperones, cell-free assays using recombinant GCase protein have yielded compounds with only marginal efficacy and micromolar EC50 that would not have sufficient clinical efficacy or an acceptable safety margin. Therefore, we utilized a fluorescence-labeled GCase suicide inhibitor, MDW933, to directly monitor lysosomal GCase activity and performed a cell-based screening in fibroblasts from a GD patient with homozygotic L444P mutations. Here, we identified novel compounds that increase the fluorescence signal from labeled GCase with L444P mutations in a dose-dependent manner. Secondary assays using an artificial cell-permeable lysosomal GCase substrate also demonstrated that the identified compounds augment lysosomal GCase L444P in the fibroblast. Moreover, those compounds increased the total GCase L444P protein levels, suggesting the pharmacological chaperone-like mechanism of action. To further elucidate the effect of the compounds on the endogenous GCase substrate GlcSph, we generated iPSC-derived dopaminergic neurons with a GBA1 L444P mutation that exhibit GlcSph accumulation in vitro. Importantly, the identified compounds reduce GlcSph in iPSC-derived dopaminergic neurons with a GBA1 L444P mutation, indicating that the increase in lysosomal GCase resulting from application of the compounds leads to the clearance of pathologically-accumulated GlcSph. Together, our findings pave the way for developing potent and efficacious GCase chaperone compounds as a potential therapeutic approach for neurological GD.

GBA1 Variants and Parkinson's Disease: Paving the Way for Targeted Therapy

Glucosylceramidase beta 1 (GBA1) variants have attracted enormous attention as the most promising and important genetic candidates for precision medicine in Parkinson's disease (PD). A substantial correlation between GBA1 genotypes and PD phenotypes could inform the prediction of disease progression and promote the development of a preventive intervention for individuals at a higher risk of a worse disease prognosis. Moreover, the GBA1-regulated pathway provides new perspectives on the pathogenesis of PD, such as dysregulated sphingolipid metabolism, impaired protein quality control, and disrupted endoplasmic reticulum-Golgi trafficking. These perspectives have led to the development of novel disease-modifying therapies for PD targeting the GBA1-regulated pathway by repositioning treatment strategies for Gaucher's disease. This review summarizes the current hypotheses on a mechanistic link between GBA1 variants and PD and possible therapeutic options for modulating GBA1-regulated pathways in PD patients.

Therapeutic Role of Pharmacological Chaperones in Lysosomal Storage Disorders: A Review of the Evidence and Informed Approach to Reclassification

The treatment landscape for lysosomal storage disorders (LSDs) is rapidly evolving. An increase in the number of preclinical and clinical studies in the last decade has demonstrated that pharmacological chaperones are a feasible alternative to enzyme replacement therapy (ERT) for individuals with LSDs. A systematic search was performed to retrieve and critically assess the evidence from preclinical and clinical applications of pharmacological chaperones in the treatment of LSDs and to elucidate the mechanisms by which they could be effective in clinical practice. Publications were screened according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) reporting guidelines. Fifty-two articles evaluating 12 small molecules for the treatment of seven LSDs are included in this review. Overall, a substantial amount of preclinical and clinical data support the potential of pharmacological chaperones as treatments for Fabry disease, Gaucher disease, and Pompe disease. Most of the available clinical evidence evaluated migalastat for the treatment of Fabry disease. There was a lack of consistency in the terminology used to describe pharmacological chaperones in the literature. Therefore, the new small molecule chaperone (SMC) classification system is proposed to inform a standardized approach for new, emerging small molecule therapies in LSDs.

Potential Binding Sites of Pharmacological Chaperone NCGC00241607 on Mutant β-Glucocerebrosidase and Its Efficacy on Patient-Derived Cell Cultures in Gaucher and Parkinson's Disease

Mutations in the GBA1 gene, encoding the lysosomal enzyme glucocerebrosidase (GCase), cause Gaucher disease (GD) and are the most common genetic risk factor for Parkinson's disease (PD). Pharmacological chaperones (PCs) are being developed as an alternative treatment approach for GD and PD. To date, NCGC00241607 (NCGC607) is one of the most promising PCs. Using molecular docking and molecular dynamics simulation we identified and characterized six allosteric binding sites on the GCase surface suitable for PCs. Two sites were energetically more preferable for NCGC607 and located nearby to the active site of the enzyme. We evaluated the effects of NCGC607 treatment on GCase activity and protein levels, glycolipids concentration in cultured macrophages from GD (n = 9) and GBA-PD (n = 5) patients as well as in induced human pluripotent stem cells (iPSC)-derived dopaminergic (DA) neurons from GBA-PD patient. The results showed that NCGC607 treatment increased GCase activity (by 1.3-fold) and protein levels (by 1.5-fold), decreased glycolipids concentration (by 4.0-fold) in cultured macrophages derived from GD patients and also enhanced GCase activity (by 1.5-fold) in cultured macrophages derived from GBA-PD patients with N370S mutation (p < 0.05). In iPSC-derived DA neurons from GBA-PD patients with N370S mutation NCGC607 treatment increased GCase activity and protein levels by 1.1-fold and 1.7-fold (p < 0.05). Thus, our results showed that NCGC607 could bind to allosteric sites on the GCase surface and confirmed its efficacy on cultured macrophages from GD and GBA-PD patients as well as on iPSC-derived DA neurons from GBA-PD patients.

Targeting the GBA1 pathway to slow Parkinson disease: Insights into clinical aspects, pathogenic mechanisms and new therapeutic avenues

The GBA1 gene encodes the lysosomal enzyme glucocerebrosidase (GCase), which is involved in sphingolipid metabolism. Biallelic variants in GBA1 cause Gaucher disease (GD), a lysosomal storage disorder characterised by loss of GCase activity and aberrant intracellular accumulation of GCase substrates. Carriers of GBA1 variants have an increased risk of developing Parkinson disease (PD), with odds ratio ranging from 2.2 to 30 according to variant severity. GBA1 variants which do not cause GD in homozygosis can also increase PD risk. Patients with PD carrying GBA1 variants show a more rapidly progressive phenotype compared to non-carriers, emphasising the need for disease modifying treatments targeting the GBA1 pathway. Several mechanisms secondary to GCase dysfunction are potentially responsible for the pathological changes leading to PD. Misfolded GCase proteins induce endoplasmic reticulum stress and subsequent unfolded protein response and impair the autophagy-lysosomal pathway. This results in α-synuclein accumulation and spread, and promotes neurodegenerative changes. Preclinical evidence also shows that products of GCase activity can promote accumulation of α-synuclein, however there is no convincing evidence of substrate accumulation in GBA1-PD brains. Altered lipid homeostasis secondary to loss of GCase activity could also contribute to PD pathology. Treatments that target the GBA1 pathway could reverse these pathological processes and halt/slow the progression of PD. These range from augmentation of GCase activity via GBA1 gene therapy, restoration of normal intracellular GCase trafficking via molecular chaperones, and substrate reduction therapy. This review discusses the pathways associated with GBA1-PD and related novel GBA1-targeted interventions for PD treatment.

High-Dose Ambroxol Therapy in Type 1 Gaucher Disease Focusing on Patients with Poor Response to Enzyme Replacement Therapy or Substrate Reduction Therapy

Ambroxol hydrochloride (ABX), an oral mucolytic drug available over the counter for many years, acts as a pharmacological chaperone for mutant glucocerebrosidase, albeit at higher doses. Proof-of-concept reports have been published over the past decade on all three types of Gaucher disease (GD). Here, we assess the safety and efficacy of 12 months of 600 mg ambroxol per day in three groups of Type 1 GD patients with a suboptimal response to enzyme replacement therapy (ERT) or substrate reduction therapy (SRT), defined as platelet count < 100 × 10³/L, lumbar spine bone density T-score < -2.0, and/or LysoGb1 > 200 ng/mL, and for a group of naïve patients who had abnormal values in two of these three parameters. We enrolled 40 patients: 28 ERT- or SRT-treated, and 12 naïve. There were no severe adverse effects (AEs). There were 24 dropouts, mostly due to AEs (n = 12), all transient, and COVID-19 (n = 7). Among the 16 completers, 5 (31.2%) had a >20% increase in platelet count, 6 (37.5%) had a >0.2 increase in T-score, and 3 (18.7%) had a >20% decrease in Lyso-Gb1. This study expands the number of patients exposed to high-dose ABX, showing good safety and satisfactory efficacy, and provides an additional rationale for adding off-label ABX to the arsenal of therapies that could be offered to patients with GD1 and a suboptimal response or those unable to receive ERT or SRT.

Pharmacological Chaperones and Protein Conformational Diseases: Approaches of Computational Structural Biology

Whenever a protein fails to fold into its native structure, a profound detrimental effect is likely to occur, and a disease is often developed. Protein conformational disorders arise when proteins adopt abnormal conformations due to a pathological gene variant that turns into gain/loss of function or improper localization/degradation. Pharmacological chaperones are small molecules restoring the correct folding of a protein suitable for treating conformational diseases. Small molecules like these bind poorly folded proteins similarly to physiological chaperones, bridging non-covalent interactions (hydrogen bonds, electrostatic interactions, and van der Waals contacts) loosened or lost due to mutations. Pharmacological chaperone development involves, among other things, structural biology investigation of the target protein and its misfolding and refolding. Such research can take advantage of computational methods at many stages. Here, we present an up-to-date review of the computational structural biology tools and approaches regarding protein stability evaluation, binding pocket discovery and druggability, drug repurposing, and virtual ligand screening. The tools are presented as organized in an ideal workflow oriented at pharmacological chaperones' rational design, also with the treatment of rare diseases in mind.

Chaperone therapy for lysosomal and non-lysosomal protein misfolding diseases

Chaperone therapy was introduced first as a new molecular therapeutic approach to lysosomal diseases. In a recent article, I reviewed the development of chaperone therapy mainly for lysosomal diseases. Then, more data have been collected particularly on non-lysosomal protein misfolding diseases. In this short review, I propose the concept of chaperone therapy to be classified into two different therapeutic approaches, for pH-dependent lysosomal, and pH-independent non-lysosomal protein misfolding diseases. The concept of lysosomal chaperone therapy is well established, but the non-lysosomal chaperone therapy is heterogeneous and to be investigated further for various individual diseases. As a whole, these two-types of new molecular therapeutic approaches will make an impact on the treatment of a wide range of pathological conditions caused by protein misfolding, not necessarily lysosomal but also many non-lysosomal diseases caused by gene mutations, metabolic diseases, malignancy, infectious diseases, and aging. The concept will open a completely new aspect of protein therapy in future.

Biochemical Characteristics of iPSC-Derived Dopaminergic Neurons from N370S GBA Variant Carriers with and without Parkinson's Disease

GBA variants increase the risk of Parkinson's disease (PD) by 10 times. The GBA gene encodes the lysosomal enzyme glucocerebrosidase (GCase). The p.N370S substitution causes a violation of the enzyme conformation, which affects its stability in the cell. We studied the biochemical characteristics of dopaminergic (DA) neurons generated from induced pluripotent stem cells (iPSCs) from a PD patient with the GBA p.N370S mutation (GBA-PD), an asymptomatic GBA p.N370S carrier (GBA-carrier), and two healthy donors (control). Using liquid chromatography with tandem mass spectrometry (LC-MS/MS), we measured the activity of six lysosomal enzymes (GCase, galactocerebrosidase (GALC), alpha-glucosidase (GAA), alpha-galactosidase (GLA), sphingomyelinase (ASM), and alpha-iduronidase (IDUA)) in iPSC-derived DA neurons from the GBA-PD and GBA-carrier. DA neurons from the GBA mutation carrier demonstrated decreased GCase activity compared to the control. The decrease was not associated with any changes in GBA expression levels in DA neurons. GCase activity was more markedly decreased in the DA neurons of GBA-PD patient compared to the GBA-carrier. The amount of GCase protein was decreased only in GBA-PD neurons. Additionally, alterations in the activity of the other lysosomal enzymes (GLA and IDUA) were found in GBA-PD neurons compared to GBA-carrier and control neurons. Further study of the molecular differences between the GBA-PD and the GBA-carrier is essential to investigate whether genetic factors or external conditions are the causes of the penetrance of the p.N370S GBA variant.

Promising biomarkers and therapeutic targets for the management of Parkinson's disease: recent advancements and contemporary research

Parkinson's disease (PD) is one of the progressive neurological diseases which affect around 10 million population worldwide. The clinical manifestation of motor symptoms in PD patients appears later when most dopaminergic neurons have degenerated. Thus, for better management of PD, the development of accurate biomarkers for the early prognosis of PD is imperative. The present work will discuss the potential biomarkers from various attributes covering biochemical, microRNA, and neuroimaging aspects (α-synuclein, DJ-1, UCH-L1, β-glucocerebrosidase, BDNF, etc.) for diagnosis, recent development in PD management, and major limitations with current and conventional anti-Parkinson therapy. This manuscript summarizes potential biomarkers and therapeutic targets, based on available preclinical and clinical evidence, for better management of PD.