Lysosomal ceroid depletion by drugs: Therapeutic implications for a hereditary neurodegenerative disease of childhood

Abstract

Neuronal ceroid lipofuscinoses (NCLs) are the most common hereditary neurodegenerative diseases of childhood. The infantile form, INCL, is caused by lysosomal palmitoyl-protein thioesterase (PPT) deficiency, which impairs the cleavage of thioester linkages in palmitoylated proteins, preventing their hydrolysis by lysosomal proteinases. Consequent accumulation of these lipid-modified proteins (constituents of ceroid) in lysosomes leads to INCL. Because thioester linkages are susceptible to nucleophilic attack, drugs with this property may have therapeutic potential for INCL. We report here that two such drugs, phosphocysteamine and N-acetylcysteine, disrupt thioester linkages in a model thioester compound, [14C]palmitoyl approximately CoA. Most importantly, in lymphoblasts derived from INCL patients, phosphocysteamine, a known lysosomotrophic drug, mediates the depletion of lysosomal ceroids, prevents their re-accumulation and inhibits apoptosis. Our results define a novel pharmacological approach to lysosomal ceroid depletion and raise the possibility that nucleophilic drugs such as phosphocysteamine hold therapeutic potential for INCL.

Substrate Reduction Therapy in Four Patients with Milder CLN1 Mutations and Juvenile-Onset Batten Disease Using Cysteamine Bitartrate

“…Cysteamine bitartrate (Cystagon), a lysosomotropic agent, has been shown in vitro to inhibit the formation of cysteine thioesters, the storage material in PPT1 deficient cells (Zhang et al 2001). It was thus suggested that Cystagon might be used as a substrate reduction agent in infantile NCL due to CLN1 mutations (Zhang et al 2001). This effect on substrate accumulation was not replicated in later experiments (Lu and Hofmann 2006).…”

“…The cysteamine bitartrate (Cystagon) was shown to be able to metabolize the storage material in INCL. Study of phosphocysteamine, an agent with very similar structure and activity to Cystagon, was shown to prevent accumulation of storage material and to inhibit apoptosis in lymphoblasts of INCL patients (Zhang et al 2001). However, later in vitro experiments with cysteamine showed inefficient cleavage of PTT substrates by this agent and by related aminothiols (Lu and Hofmann 2006).…”

“…PPT1 is a lysosomal enzyme that is abundant in the brain, and removes long chain fatty acids bound to cysteine residues of S-fatty acylated proteins (Hofmann et al 1997). Cysteamine bitartrate (Cystagon), a lysosomotropic agent, has been shown in vitro to inhibit the formation of cysteine thioesters, the storage material in PPT1 deficient cells (Zhang et al 2001). It was thus suggested that Cystagon might be used as a substrate reduction agent in infantile NCL due to CLN1 mutations (Zhang et al 2001).…”

Axonal Transport of Human Immunodeficiency Virus Type 1 Envelope Protein Glycoprotein 120 Is Found in Association with Neuronal Apoptosis

“…When lysosomes cannot recycle/degrade efficiently, an excess storage of various molecules within the cells is created. This abnormal accumulation of undigested material within neurons can lead to cell death (Zhang et al, 2001). In particular, there is evidence that abnormal ceramide metabolism in relation to aberrant lysosomal function can cause neurodegenerative diseases (DitarantoDesimone et al, 2003).…”

Neuronal ceroid lipofuscinosis/Batten disease: the lysosomal proteinoses

“…A substrate depletion strategy employing the drug cysteamine has shown promise in cell culture experiments. 12 Cysteamine has a relatively long history for treatment of the lysosomal storage disorder cystinosis and can be tested expeditiously in mice and in humans with the infantile form of NCL. Enzyme replacement therapy (for CLN1 and CLN2 disease) and gene therapy experiments for several of these NCLs are underway.…”