L-carnitine Supplements May Help Augment Enzyme Replacement Therapy
L-carnitine — a molecule often taken as an oral dietary supplement — boosts the efficacy of enzyme replacement therapy (ERT), increasing by four times the activity of acid alpha-glucosidase (GAA), the faulty enzyme in Pompe disease, in patient-derived cells, a study shows.
The molecule was found to stabilize GAA, working as a potential chaperone therapy but without the suppressing effects of those currently in development for Pompe.
These findings suggest that adding L-carnitine to standard ERT may help increase treatment efficacy in this patient population, the researchers noted.
The study, “Carnitine is a pharmacological allosteric chaperone of the human lysosomal α-glucosidase,” was published in the Journal of Enzyme Inhibition and Medicinal Chemistry.
Pompe disease is a lysosomal storage disorder caused by low to no levels of working GAA enzyme due to mutations in the GAA gene.
GAA breaks down glycogen — a large sugar molecule used for energy storage — within small recycling structures inside cells called lysosomes, and its deficiency leads to the toxic buildup of glycogen inside lysosomes of several tissues.
ERT, the standard and only approved treatment approach for Pompe disease, delivers a lab-made version of GAA directly to a patient’s bloodstream to prevent further damage. However, its efficacy can vary between patients and is not the same in all tissues.
As such, chaperone therapy — which works by stabilizing and correcting the folding of the faulty enzyme, thereby preventing its degradation — has gained increasing interest for the treatment of Pompe.
However, chaperones that bind to the active site of their target enzyme can potentially suppress their activity. In addition, they can typically rescue faulty enzymes associated with only a subset of disease-causing mutations, making them effective on a limited number of patients.
“An ideal chaperone should be able to protect the enzymes from degradation without interfering with its activity, be largely bioavailable in tissues and organs, reach therapeutic levels in cellular compartments where its action is required, show high specificity for the target enzyme with negligible effects on other enzymes, and have a good safety profile,” the researchers wrote.
With this in mind, the researchers, based in Italy and France, screened for potential chaperones that would not bind to GAA’s active site among molecules already approved as medications or supplements.
This repurposing of compounds already used in the clinic or with proven safety cuts both the costs and time required for the development of a safe and effective therapy.
Among the molecules analyzed, L-carnitine, D-carnitine, and the related compound acetyl-D-carnitine were found to be strong candidates.
L-carnitine is commonly used as an oral dietary supplement. Given that D-carnitine, a different form of L-carnitine, was previously associated with side effects, most of the study was conducted with L-carnitine
The team found that L-carnitine could stabilize ERT-delivered GAA in a dose-dependent manner across several pH and temperature conditions, without interfering with its activity.
Also, L-carnitine boosted the effects of active site-directed chaperones for Pompe, confirming that it did not bind to GAA’s active site.
Next, the researchers analyzed the effects of L-carnitine in lab-grown cells derived from three patients with early-onset Pompe disease and who carried different disease-causing mutations.
Treatment with the dietary molecule did not have noteworthy effects on GAA activity in cells from two patients. However, it significantly increased the enzyme’s activity in cells from one patient, who had a mutation already reported to be responsive to active site-directed chaperones, including miglustat.
In addition, adding L-carnitine to ERT significantly increased GAA activity relative to ERT alone in cells from all three patients. This activity difference was already detectable at two hours post-treatment and became progressively more pronounced up to 24 hours.
The GAA activity levels achieved with this combination treatment were up to four times greater than those previously reported for Pompe patient-derived cells treated with ERT plus miglustat.
Moreover, the ERT-L-carnitine combo improved the maturation and lysosomal trafficking of ERT-delivered GAA.
Therefore, L-carnitine may be a new potential chaperone, “with excellent perspectives for the treatment of Pompe disease alone and in combination with ERT,” the researchers wrote.
Particularly, a combination of ERT and L-carnitine “has the potential to determine remarkable increases of specific activity, independently of mutations affecting individual patients,” they added.
More studies are needed to confirm the therapeutic potential of L-carnitine, as well as to better understand the mechanism of action of this molecule.