Evidence of an intracellular creatine-sensing mechanism that modulates creatine biosynthesis via AGAT expression in human HAP1 cells.

Cellular homeostasis of creatine (CT), integral part of the energy buffering and transducing system connecting intracellular sites of ATP production and utilization, comprises of mechanisms that increase CT, i.e., biosynthesis and cellular uptake, and CT-lowering processes, such as export and non-enzymatic conversion to creatinine. The biosynthesis of CT is controlled by negative feedback loop via suppression of the rate-limiting enzyme arginine:glycine amidinotransferase (AGAT). Although the regulatory mechanism involved is not well understood, AGAT suppression is successfully used in patients with guanidinoacetate methyltransferase (GAMT) deficiency to reduce the neurotoxic accumulation of the AGAT-mediated guanidinoacetate production by supplementing patients with CT. Utilizing the CT-dependent feedback loop for the upregulation of AGAT expression may well represent a therapeutic target for an additional CT deficiency syndrome, the CT transporter (CrT) defect, for which no effective treatment option is available so far. We have used CRISPR to tag the C-terminus of AGAT with a nanoluc luciferase (NLuc) reporter in HAP1 cells. A biphasic decay of AGAT-NLuc in response to increasing extracellular CT was observed, whereas the decrease in AGAT-NLuc expression was directly proportional to the rise in intracellular CT levels with an approximate IC50 of 1-2 mM. CRISPR generated HAP1 CrT null cells and HAP1 CrT null cells stably expressing a CrT-GFP fusion protein further demonstrated that the biphasic response to extracellular CT is mediated by a high-affinity (Km 9-10 µM) CrT dependent, saturable mechanism and a CrT independent, unsaturable uptake process. The direct response to intracellular CT suggests the existence of an intracellular CT sensing system enabling a dynamic cell response to changing CT concentration that is relevant for cellular CT homeostasis.

Construction of a hybrid ß-hexosaminidase subunit capable of forming stable homodimers that hydrolyze GM2 ganglioside in vivo.

Tay-Sachs or Sandhoff disease result from mutations in either the evolutionarily related HEXA or HEXB genes encoding respectively, the α- or ß-subunits of ß-hexosaminidase A (HexA). Of the three Hex isozymes, only HexA can interact with its cofactor, the GM2 activator protein (GM2AP), and hydrolyze GM2 ganglioside. A major impediment to establishing gene or enzyme replacement therapy based on HexA is the need to synthesize both subunits. Thus, we combined the critical features of both α- and ß-subunits into a single hybrid µ-subunit that contains the α-subunit active site, the stable ß-subunit interface and unique areas in each subunit needed to interact with GM2AP. To facilitate intracellular analysis and the purification of the µ-homodimer (HexM), CRISPR-based genome editing was used to disrupt the HEXA and HEXB genes in a Human Embryonic Kidney 293 cell line stably expressing the µ-subunit. In association with GM2AP, HexM was shown to hydrolyze a fluorescent GM2 ganglioside derivative both in cellulo and in vitro. Gene transfer studies in both Tay-Sachs and Sandhoff mouse models demonstrated that HexM expression reduced brain GM2 ganglioside levels.

Pyrimethamine Derivatives: Insight into Binding Mechanism and Improved Enhancement of Mutant ß-N-acetylhexosaminidase Activity.

In order to identify structural features of pyrimethamine (5-(4-chlorophenyl)-6-ethylpyrimidine-2,4-diamine) that contribute to its inhibitory activity (IC50 value) and chaperoning efficacy toward ß-N-acetylhexosaminidase, derivatives of the compound were synthesized that differ at the positions bearing the amino, ethyl, and chloro groups. Whereas the amino groups proved to be critical to its inhibitory activity, a variety of substitutions at the chloro position only increased its IC50 by 2-3-fold. Replacing the ethyl group at the 6-position with butyl or methyl groups increased IC50 more than 10-fold. Surprisingly, despite its higher IC50, a derivative lacking the chlorine atom in the para-position was found to enhance enzyme activity in live patient cells a further 25% at concentrations >100 µM, while showing less toxicity. These findings demonstrate the importance of the phenyl group in modulating the chaperoning efficacy and toxicity profile of the derivatives.

Synthesis of 1,5-dideoxy-1,5-iminoribitol C-glycosides through a nitrone-olefin cycloaddition domino strategy: identification of pharmacological chaperones of mutant human lysosomal ß-galactosidase.

We report herein a newly developed domino reaction that facilitates the synthesis of new 1,5-dideoxy-1,5-iminoribitol iminosugar C-glycosides 7a-e and 8. The key intermediate in this approach is a six-membered cyclic sugar nitrone that is generated in situ and trapped by an alkene dipolarophile via a [2 + 3] cycloaddition reaction to give the corresponding isooxazolidines 10a-e in a "one-pot" protocol. The iminoribitol C-glycosides 7a-e and 8 were found to be modest ß-galactosidase (bGal) inhibitors. However, compounds 7c and 7e showed "pharmacological chaperone" activity for mutant lysosomal bGal activity and facilitated its recovery in GM1 gangliosidosis patient fibroblasts by 2-6-fold.

Transcutaneous electrical nerve stimulation as a novel method of remote preconditioning: in vitro validation in an animal model and first human observations.

Remote ischemic preconditioning (rIPC) induced by transient limb ischemia (li-rIPC) leads to neurally dependent release of blood-borne factors that provide potent cardioprotection. We hypothesized that transcutaneous electrical nerve stimulation (TENS) is a clinically relevant stimulus of rIPC. Study 1: seven rabbits were subjected to lower limb TENS; six to li-rIPC, and six to sham intervention. Blood was drawn and used to prepare a dialysate for subsequent analysis of cardioprotection in rabbit Langendorff preparation. Study 2: 14 healthy adults underwent upper limb TENS stimulation on one study day, 10 of whom also underwent li-rIPC on another study day. Blood was drawn before and after each stimulus, dialysate prepared, and cardioprotective activity assessed in mouse Langendorff preparation. The infarct size and myocardial recovery were measured after 30 min of global ischemia and 60 or 120 min of reperfusion. Animal validation: compared to control, TENS induced marked cardioprotection with significantly reduced infarct size (TENS vs. sham p < 0.01, rIPC vs. sham p < 0.01, TENS vs. rIPC p = ns) and improved functional recovery during reperfusion. Human study: compared to baseline, dialysate after rIPC (pre-rIPC vs. post-rIPC, p < 0.001) and TENS provided potent cardioprotection (pre-TENS vs. post-TENS p < 0.001) and improved myocardial recovery during reperfusion. The cardioprotective effects of TENS dialysates were blocked by pretreatment of the receptor heart with the opioid antagonist naloxone. TENS is a novel method for inducing cardioprotection and may provide an alternative to the limb ischemia stimulus for induction of rIPC clinically.

Remote cardioprotection by transfer of coronary effluent from ischemic preconditioned rabbit heart preserves mitochondrial integrity and function via adenosine receptor activation.

BACKGROUND: Coronary effluent from an isolated perfused heart undergoing ischemic preconditioning can be transferred to precondition another naïve isolated heart. We investigated the effects of this effluent on mitochondrial integrity and function following a global infarct model of ischemia/reperfusion and the role of adenosine in this model of remote preconditioning. METHODS AND RESULTS: Coronary effluent from isolated perfused rabbit hearts was collected prior to (control effluent) and during three cycles of 5-min ischemia and 10-min reperfusion (IPC effluent). Adenosine concentration was significantly increased in IPC effluent (2.6 ± 1.1 µM) versus control effluent (0.21 ± 0.06 µM, P < 0.01). Infarct size (% necrotic LV mass) after 30-min global ischemia and 90-min reperfusion was significantly reduced in hearts preconditioned with IPC effluent (IPC(eff), 23 ± 7 %) and control effluent supplemented with 2.5 µM exogenous adenosine (C(eff)+ 2.5 µM ADO, 25 ± 10 %) when compared to control effluent perfused hearts (C(eff), 41 ± 8 %, P < 0.05). Compared to C(eff) mitochondria, IPC(eff) mitochondria had preserved complex I/State3 and complex IV/State 3 respiration and outer membrane integrity, and reduced cytochrome c release. In contrast, C(eff) + 2.5 µM ADO mitochondria had improved state 2 respiration and coupling to oxidative phosphorylation, reduced reactive oxygen species production and preserved outer membrane integrity. Administration of adenosine receptor blocker 8-(p-sulfophenyl)theophylline abolished the infarct limiting effect (46 ± 7 %) and the mitochondrial integrity and function preservation of IPC effluent. CONCLUSION: Remote cardioprotection by IPC effluent preserves mitochondrial integrity and function in an adenosine receptor dependent mechanism, and although infarct size reduction can be mimicked by adenosine, IPC effluent contains additional factor(s) contributing to modulation of the mitochondrial response to ischemia/reperfusion injury.

Evaluation of N-nonyl-deoxygalactonojirimycin as a pharmacological chaperone for human GM1 gangliosidosis leads to identification of a feline model suitable for testing enzyme enhancement therapy.

Deficiencies of lysosomal ß-D-galactosidase can result in GM1 gangliosidosis, a severe neurodegenerative disease characterized by massive neuronal storage of GM1 ganglioside in the brain. Currently there are no available therapies that can even slow the progression of this disease. Enzyme enhancement therapy utilizes small molecules that can often cross the blood brain barrier, but are also often competitive inhibitors of their target enzyme. It is a promising new approach for treating diseases, often caused by missense mutations, associated with dramatically reduced levels of functionally folded enzyme. Despite a number of positive reports based on assays performed with patient cells, skepticism persists that an inhibitor-based treatment can increase mutant enzyme activity in vivo. To date no appropriate animal model, i.e., one that recapitulates a responsive human genotype and clinical phenotype, has been reported that could be used to validate enzyme enhancement therapy. In this report, we identify a novel enzyme enhancement-agent, N-nonyl-deoxygalactonojirimycin, that enhances the mutant ß-galactosidase activity in the lysosomes of a number of patient cell lines containing a variety of missense mutations. We then demonstrate that treatment of cells from a previously described, naturally occurring feline model (that biochemically, clinically and molecularly closely mimics GM1 gangliosidosis in humans) with this molecule, results in a robust enhancement of their mutant lysosomal ß-galactosidase activity. These data indicate that the feline model could be used to validate this therapeutic approach and determine the relationship between the disease stage at which this therapy is initiated and the maximum clinical benefits obtainable.

Pharmacological chaperones facilitate the post-ER transport of recombinant N370S mutant ß-glucocerebrosidase in plant cells: evidence that N370S is a folding mutant.

Gaucher disease is a prevalent lysosomal storage disease in which affected individuals inherit mutations in the gene (GBA1) encoding lysosomal acid ß-glucosidase (glucocerebrosidase, GCase, EC 3.2.1.45). One of the most prevalent disease-causing mutations in humans is a N370S missense mutation in the GCase protein. As part of a larger endeavor to study the fate of mutant human proteins expressed in plant cells, the N370S mutant protein along with the wild-type- (WT)-GCase, both equipped with a signal peptide, were synthesized in transgenic tobacco BY2 cells, which do not possess lysosomes. The enzymatic activity of plant-recombinant N370S GCase lines was significantly lower (by 81-95%) than that of the WT-GCase lines. In contrast to the WT-GCase protein, which was efficiently secreted from tobacco BY2 cells, and detected in large amounts in the culture medium, only a small proportion of the N370S GCase was secreted. Pharmacological chaperones such as N-(n-nonyl) deoxynojirimycin and ambroxol increased the steady-state mutant protein levels both inside the plant cells and in the culture medium. These findings contradict the assertion that small molecule chaperones increase N370S GCase activity (as assayed in treated patient cell lysates) by stabilizing the enzyme in the lysosome, and suggest that the mutant protein is impaired in its ability to obtain its functional folded conformation, which is a requirement for exiting the lumen of the ER.

Rapid assembly of a library of lipophilic iminosugars via the thiol-ene reaction yields promising pharmacological chaperones for the treatment of Gaucher disease.

A highly divergent route to lipophilic iminosugars that utilizes the thiol-ene reaction was developed to enable the rapid synthesis of a collection of 16 dideoxyiminoxylitols bearing various different lipophilic substituents. Enzyme kinetic analyses revealed that a number of these products are potent, low-nanomolar inhibitors of human glucocerebrosidase that stabilize the enzyme to thermal denaturation by up to 20 K. Cell based assays conducted on Gaucher disease patient derived fibroblasts demonstrated that administration of the compounds can increase lysosomal glucocerebrosidase activity levels by therapeutically relevant amounts, as much as 3.2-fold in cells homozygous for the p.N370S mutation and 1.4-fold in cells homozygous for the p.L444P mutation. Several compounds elicited this increase in enzyme activity over a relatively wide dosage range. The data assembled here illustrate how the lipophilic moiety common to many glucocerebrosidase inhibitors might be used to optimize a lead compound's ability to chaperone the protein in cellulo. The flexibility of this synthetic strategy makes it an attractive approach to the rapid optimization of glycosidase inhibitor potency and pharmacokinetic behavior.

Remote cardioprotection by direct peripheral nerve stimulation and topical capsaicin is mediated by circulating humoral factors.

We have previously shown that remote ischemic preconditioning by limb ischemia (rIPC) or intra-arterial adenosine releases a dialyzable cardioprotective circulating factor(s), the release of which requires an intact neural connection to the limb and is blocked by pretreatment with S-nitroso-N-acetylpenicillamine (SNAP). Remote cardioprotection can be induced by other forms of peripheral stimulation including topical capsaicin, but the mechanisms of their signal transduction are incompletely understood. Rabbits were anesthetized by intravenous pentobarbital, intubated and ventilated, then randomized (4-7 animals in each group) to receive sham procedure, rIPC (4 cycles of 5 min lower limb ischemia, 5 min reperfusion), direct femoral nerve stimulation, topical capsaicin, pretreatment with intra-arterial SNAP + capsaicin, pretreatment with topical DMSO (a sensory nerve blocker) + topical capsaicin, or pretreatment with intra-arterial SNAP + femoral nerve stimulation, topical DMSO alone, or intra-arterial SNAP alone. Blood was then rapidly drawn from the carotid artery to produce the plasma dialysate which was used to perfuse a naïve heart from an untreated donor rabbit. The infarct size and recovery of LV-developed pressure and end-diastolic pressure were measured after 30 min of global ischemia and 120 min of reperfusion. Compared to sham, dialysate from rIPC, femoral nerve stimulation, and topical capsaicin groups all produced significant cardioprotection with significantly reduced infarct size, and improved the post-ischemic cardiac performance. Cardioprotection was not seen in the topical DMSO-capsaicin, SNAP + capsaicin, and SNAP + FNS groups. These results confirm the central role of peripheral nerves in the local signal transduction of remote cardioprotection. Direct electrical or peripheral neural stimulation evokes the release of cardioprotective substances into the bloodstream, with comparable effects to that of rIPC induced by limb ischemia.

Production of active human glucocerebrosidase in seeds of Arabidopsis thaliana complex-glycan-deficient (cgl) plants.

There is a clear need for efficient methods to produce protein therapeutics requiring mannose-termination for therapeutic efficacy. Here we report on a unique system for production of active human lysosomal acid ß-glucosidase (glucocerebrosidase, GCase, EC 3.2.1.45) using seeds of the Arabidopsis thaliana complex-glycan-deficient (cgl) mutant, which are deficient in the activity of N-acetylglucosaminyl transferase I (EC 2.4.1.101). Gaucher disease is a prevalent lysosomal storage disease in which affected individuals inherit mutations in the gene (GBA1) encoding GCase. A gene cassette optimized for seed expression was used to generate the human enzyme in seeds of the cgl (C5) mutant, and the recombinant GCase was mainly accumulated in the apoplast. Importantly, the enzymatic properties including kinetic parameters, half-maximal inhibitory concentration of isofagomine and thermal stability of the cgl-derived GCase were comparable with those of imiglucerase, a commercially available recombinant human GCase used for enzyme replacement therapy in Gaucher patients. N-glycan structural analyses of recombinant cgl-GCase showed that the majority of the N-glycans (97%) were mannose terminated. Additional purification was required to remove ∼15% of the plant-derived recombinant GCase that possessed potentially immunogenic (xylose- and/or fucose-containing) N-glycans. Uptake of cgl-derived GCase by mouse macrophages was similar to that of imiglucerase. The cgl seed system requires no addition of foreign (non-native) amino acids to the mature recombinant GCase protein, and the dry transgenic seeds represent a stable repository of the therapeutic protein. Other strategies that may completely prevent plant-like complex N-glycans are discussed, including the use of a null cgl mutant.

1-Deoxy-D-galactonojirimycins with dansyl capped N-substituents as ß-galactosidase inhibitors and potential probes for GM1 gangliosidosis affected cell lines.

Two simple and reliably accessible intermediates, N-carboxypentyl- and N-aminohexyl-1-deoxy-D-galactonojirimycin were employed for the synthesis of a set of terminally N-dansyl substituted derivatives. Reaction of the terminal carboxylic acid of N-carboxypentyl-1-deoxy-D-galactonojirimycin with N-dansyl-1,6-diaminohexane provided the chain-extended fluorescent derivative. Employing bis(6-dansylaminohexyl)amine, the corresponding branched di-N-dansyl compound was obtained. Partially protected N-aminohexyl-1-deoxy-D-galactonojirimycin served as intermediate for two additional chain-extended fluorescent 1-deoxy-D-galactonojirimycin (1-DGJ) derivatives featuring terminal dansyl groups in the N-alkyl substituent. These new compounds are strong inhibitors of d-galactosidases and may serve as leads en route to pharmacological chaperones for GM1-gangliosidosis.

An open-label Phase I/II clinical trial of pyrimethamine for the treatment of patients affected with chronic GM2 gangliosidosis (Tay-Sachs or Sandhoff variants).

Late-onset GM2 gangliosidosis is an autosomal recessive, neurodegenerative, lysosomal storage disease, caused by deficiency of ß-hexosaminidase A (Hex A), resulting from mutations in the HEXA (Tay-Sachs variant) or the HEXB (Sandhoff variant) genes. The enzyme deficiency in many patients with juvenile or adult onset forms of the disease results from the production of an unstable protein, which becomes targeted for premature degradation by the quality control system of the smooth endoplasmic reticulum and is not transported to lysosomes. In vitro studies have shown that many mutations in either the α or ß subunit of Hex A can be partially rescued, i.e. enhanced levels of both enzyme protein and activity in lysosomes, following the growth of patient cells in the presence of the drug, pyrimethamine. The objectives of the present clinical trial were to establish the tolerability and efficacy of the treatment of late-onset GM2 gangliosidosis patients with escalating doses of pyrimethamine, to a maximum of 100 mg per day, administered orally in a single daily dose, over a 16-week period . The primary objective, tolerability, was assessed by regular clinical examinations, along with a panel of hematologic and biochemical studies. Although clinical efficacy could not be assessed in this short trial, treatment efficacy was evaluated by repeated measurements of leukocyte Hex A activity, expressed relative to the activity of lysosomal ß-glucuronidase. A total of 11 patients were enrolled, 8 males and 3 females, aged 23 to 50 years. One subject failed the initial screen, another was omitted from analysis because of the large number of protocol violations, and a third was withdrawn very early as a result of adverse events which were not drug-related. For the remaining 8 subjects, up to a 4-fold enhancement of Hex A activity at doses of 50 mg per day or less was observed. Additionally marked individual variations in the pharmacokinetics of the drug among the patients were noted. However, the study also found that significant side effects were experienced by most patients at or above 75 mg pyrimethamine per day. We concluded that pyrimethamine treatment enhances leukocyte Hex A activity in patients with late-onset GM2 gangliosidosis at doses lower than those associated with unacceptable side effects. Further plans are underway to extend these trials and to develop methods to assess clinical efficacy.

Remote preconditioning provides potent cardioprotection via PI3K/Akt activation and is associated with nuclear accumulation of ß-catenin.

rIPC [remote IPC (ischaemic preconditioning)] has been shown to invoke potent myocardial protection in animal studies and recent clinical trials. Although the important role of PI3K (phosphoinositide 3-kinase)/Akt activation in the cardioprotection afforded by local IPC is well described, our understanding of the intracellular signalling of rIPC remains incomplete. We therefore examined the hypothesis that the myocardial protection afforded by rIPC is mediated via the PI3K/Akt/GSK3ß (glycogen synthase kinase 3ß) signalling pathway, activation of which is associated with nuclear accumulation of ß-catenin. rIPC was induced in mice using four cycles of 5 min of ischaemia and 5 min of reperfusion of the hindlimb using a torniquet. This led to reduced infarct size (19 ± 4% in rIPC compared with 39 ± 7% in sham; P<0.05), improved functional recovery and reduced apoptosis after global I/R (ischaemia/reperfusion) injury using a Langendorff-perfused mouse heart model. These effects were reversed by pre-treatment with an inhibitor of PI3K activity. Furthermore, Western blot analysis demonstrated that, compared with control, rIPC was associated with activation of the PI3K/Akt signalling pathway, resulting in phosphorylation and inactivation of GSK3ß, accumulation of ß-catenin in the cytosol and its translocation to the nucleus. Finally, rIPC increased the expression of ß-catenin target genes involved in cell-survival signalling, including E-cadherin and PPARδ (peroxisome-proliferator-activated receptor δ). In conclusion, we show for the first time that the myocardial protection afforded by rIPC is mediated via the PI3K/Akt/GSK3ß signalling pathway, activation of which is associated with nuclear accumulation of ß-catenin and the up-regulation of its downstream targets E-cadherin and PPARδ involved in cell survival.

Fluorous iminoalditols: a new family of glycosidase inhibitors and pharmacological chaperones.

A collection of new reversible glycosidase inhibitors of the iminoalditol type featuring N-substituents containing perfluorinated regions has been prepared for evaluation of physicochemical, biochemical and diagnostic properties. The vast variety of feasible oligofluoro moieties allows for modular approaches to customised structures according to the intended applications, which are influenced by the fluorine content as well as the distance of the fluorous moiety from the ring nitrogen. The first examples, in particular in the D-galacto series, exhibited excellent inhibitory activities. A preliminary screen with two human cell lines showed that, at subinhibitory concentrations, they are powerful pharmacological chaperones enhancing the activities of the catalytically handicapped lysosomal D-galactosidase mutants associated with GM1 gangliosidosis and Morquio B disease.

1-Deoxynojirimycins with dansyl capped N-substituents as probes for Morbus Gaucher affected cell lines.

Cyclization by double reductive amination of d-xylo-hexos-5-ulose with methyl 6-aminohexanoate gave (methoxycarbonyl)pentyl-1-deoxynojirimycin. Reaction of the terminal carboxylic acid with N-dansyl-1,6-diaminohexane provided the corresponding chain-extended fluorescent derivative. By reaction with bis(6-dansylaminohexyl)amine, the corresponding branched di-N-dansyl compound was obtained. Both compounds are strong inhibitors of d-glucosidases and could also be shown to distinctly improve, at sub-inhibitory concentrations, the activity of beta-glucocerebrosidase in a Gaucher fibroblast (N370S) cell-line through chaperoning of the enzyme to the lysosome.

A sensitive fluorescence-based assay for monitoring GM2 ganglioside hydrolysis in live patient cells and their lysates.

Enzyme enhancement therapy, utilizing small molecules as pharmacological chaperones, is an attractive approach for the treatment of lysosomal storage diseases that are associated with protein misfolding. However, pharmacological chaperones are also inhibitors of their target enzyme. Thus, a major concern with this approach is that, despite enhancing protein folding within, and intracellular transport of the functional mutant enzyme out of the endoplasmic reticulum, the chaperone will continue to inhibit the enzyme in the lysosome, preventing substrate clearance. Here we demonstrate that the in vitro hydrolysis of a fluorescent derivative of lyso-GM2 ganglioside, like natural GM2 ganglioside, is specifically carried out by the beta-hexosaminidase A isozyme, requires the GM2 activator protein as a co-factor, increases when the derivative is incorporated into anionic liposomes and follows similar Michaelis-Menten kinetics. This substrate can also be used to differentiate between lysates from normal and GM2 activator-deficient cells. When added to the growth medium of cells, the substrate is internalized and primarily incorporated into lysosomes. Utilizing adult Tay-Sachs fibroblasts that have been pre-treated with the pharmacological chaperone Pyrimethamine and subsequently loaded with this substrate, we demonstrate an increase in both the levels of mutant beta-hexosaminidase A and substrate-hydrolysis as compared to mock-treated cells.