Intravenous high-dose enzyme replacement therapy with recombinant palmitoyl–protein thioesterase reduces visceral lysosomal storage and modestly prolongs survival in a preclinical mouse model of infantile neuronal ceroid lipofuscinosis

Abstract

PPT1-related neuronal ceroid lipofuscinosis (NCL) is a lysosomal storage disorder caused by deficiency in a soluble lysosomal enzyme, palmitoyl-protein thioesterase-1 (PPT1). Enzyme replacement therapy (ERT) has not been previously examined in a preclinical animal model. Homozygous PPT1 knockout mice reproduce the known features of the disease, developing signs of motor dysfunction at 5 months of age and death by around 8 months. In the current study, PPT1 knockout mice were treated with purified recombinant PPT1 (0.3 mg, corresponding to 12 mg/kg or 180 U/kg for a 25 g mouse) administered intravenously weekly either 1) from birth; or 2) beginning at 8 weeks of age. The treatment was surprisingly well tolerated and neither anaphylaxis nor antibody formation was observed. In mice treated from birth, survival increased from 236 to 271 days (p<0.001) and the onset of motor deterioration was similarly delayed. In mice treated beginning at 8 weeks, no increases in survival or motor performance were seen. An improvement in neuropathology in the thalamus was seen at 3 months in mice treated from birth, and although this improvement persisted it was attenuated by 7 months. Outside the central nervous system, substantial clearance of autofluorescent storage material in many tissues was observed. Macrophages in spleen, liver and intestine were especially markedly improved, as were acinar cells of the pancreas and tubular cells of the kidney. These findings suggest that ERT may be an option for addressing visceral storage as part of a comprehensive approach to PPT1-related NCL, but more effective delivery methods to target the brain are needed.

Histochemical localization of palmitoyl protein thioesterase-1 activity

“…Interestingly, it seems reasonable to speculate that even less intense or inconspicuous blue stain might correlate with decreased neuropathological markers. Two previous studies [9, 15] indicate that doses similar to ours result in relatively low brain PPT1 activity while still decreasing GFAP and CD68 and increasing lifespan. As such, highly intense blue staining may not be required to indicate therapeutic levels of PPT1 activity.…”

“…Enzyme treatment in both infants and adults resulted in conspicuously low levels of PPT1 activity in the brain. This at least partially explains the lack of efficacy in the treatment of murine INCL using intravenous enzyme replacement alone [15] and confirms that PPT1 does not readily cross the BBB. This is not a surprising finding but indicates that while peripheral enzyme treatment may effectively treat the systemic disease associated with INCL [4], it cannot be expected to address the central nervous system aspects of the disease.…”

Pathogenesis and therapies for infantile neuronal ceroid lipofuscinosis (infantile CLN1 disease)

“…Lysosomal enzymes, in general, do not cross the blood brain barrier (BBB) effectively. Although some systemically delivered recombinant human PPT1 (rhPPT1) does appear to cross the BBB in the mouse model of infantile CLN1 disease, this was in very small amounts (Hu, et al 2012). Nonetheless, intravenous rhPPT1 delivery was tested for tolerability, tissue distribution, and efficacy in Ppt1 −/− mice.…”

Synergistic effects of treating the spinal cord and brain in CLN1 disease

“…Various experimental therapies have been tested to treat forebrain pathology in Ppt1 −/− mice, including antioxidants (19,20), enzyme replacement therapy (ERT) (21,22), human neuronal stem cells (23), and forebrain-directed gene therapy (12,(24)(25)(26)(27). Of these, adeno-associated virus (AAV) vector-mediated gene transfer has been the most promising (3,28).…”