Inhibition of Protease-Resistant Prion Protein Accumulation In Vitro by Curcumin

Abstract

Inhibition of the accumulation of protease-resistant prion protein (PrP-res) is a prime strategy in the development of potential transmissible spongiform encephalopathy (TSE) therapeutics. Here we show that curcumin (diferoylmethane), a major component of the spice turmeric, potently inhibits PrP-res accumulation in scrapie agent-infected neuroblastoma cells (50% inhibitory concentration, ϳ10 nM) and partially inhibits the cell-free conversion of PrP to PrP-res. In vivo studies showed that dietary administration of curcumin had no significant effect on the onset of scrapie in hamsters. Nonetheless, other studies have shown that curcumin is nontoxic and can penetrate the brain, properties that give curcumin advantages over inhibitors previously identified as potential prophylactic and/or therapeutic anti-TSE compounds.Transmissible spongiform encephalopathies (TSE) or prion diseases are untreatable, fatal neurodegenerative diseases that include bovine spongiform encephalopathy, chronic wasting disease, scrapie, and Creutzfeldt-Jakob disease. A central event in TSE diseases is the conversion of the normal, protease-sensitive isoform of prion protein (PrP-sen or PrP C ) to an abnormal, protease-resistant form, PrP-res or PrP Sc . Numerous compounds have been identified as inhibitors of PrPres formation in scrapie agent-infected murine neuroblastoma (ScNB) cells (1-3, 5). The most potent of these inhibitors can also protect rodents against scrapie if they are administered near the time of infection (7,8,10,11,14). Unfortunately, none of these compounds are known to be both safe and effective for use in humans and animals (8, 10, 11). One therapeutic weakness of most of these compounds is likely an inability to penetrate the brain where most of the PrP-res accumulates and TSE pathogenesis occurs.Curcumin, the major component of the spice turmeric and the yellow pigment in curry powder, has several properties that make it of interest as a possible anti-TSE drug. First, its structure resembles Congo red, the most potent of the small-molecule PrP-res inhibitors that have been assayed in ScNB cells (Fig. 1) in that both are potentially planar compounds that have two aromatic rings or ring systems with conjugated linkers. Structure-activity studies have provided evidence that the potential for coplanarity of the rings and linker is important for the inhibitory potency of Congo red (6). Second, unlike Congo red, curcumin is uncharged and is thought to have at least limited bioavailability to the brain after consumption. Indeed, recent studies with a rat model of Alzheimer's disease reported that dietary curcumin reduces ␤-peptide deposition in the brain as well as associated neuropathology and cognitive deficits (9, 12). Third, curcumin has antioxidant activity, a factor that may be important given that oxidative damage is a feature in TSE neuropathogenesis (13). Fourth, humans consume curcumin in large amounts with no apparent toxicity. Toxicology studies have indicated that rodents can tolerate for a long period up to 5%...

Inhibition of Protease-Resistant Prion Protein Formation in a Transformed Deer Cell Line Infected with Chronic Wasting Disease

“…Thus, it is tempting to speculate that PPS or In-TSP may help prevent the spread of CWD on game farms and in the wild, where most transmissions would be expected to occur via peripheral routes of infection. In addition, our findings attest to the broad inhibitory activities of both sulfated glycans and porphyrins, which differ from some other inhibitors that have strain and/or species specificities (10,22,23). The CWD infection in MDB CWD cells appears to be persistent because PrP CWD production has been stable and robust through 32 serial passes despite the fact that, in the first dilution cloning, 33% of the subclones were apparently negative for PrP CWD .…”

“…Numerous inhibitors of PrP-res accumulation have been identified initially using scrapie-infected cell lines, and many of these inhibitors have proven to have at least prophylactic activity against experimental scrapie in rodents. Nonetheless, striking TSE strain and species dependence has been observed with some antiscrapie compounds, and thus, it cannot be assumed that a compound that works against one TSE strain will be effective against others, such as CWD (10,19,23).…”

Progress and problems in the biology, diagnostics, and therapeutics of prion diseases

“…Many substances appear to possess prion-curing properties in vitro, including Congo red (68), amphotericin B, anthracyclines (69), sulfated polyanions (70), porphyrins (71), branched polyamines (72), �-sheet breakers (73), the spice curcumin (74), and recently even small interfering RNAs (75). The majority of these molecules exert their biological effects by directly or indirectly interfering with conversion of PrP C to PrP Sc , thereby also aiding clearance of PrP Sc .…”

Neuroprotective Effects of Curcumin

“…Because curcumin resembles Congo red and its chrysamine G homologue Congo red, its anti-amyloid-binding protein properties are generic and should extend to other protein-misfolding diseases with a β-pleated sheet, including the polyglutamine dieases like Huntington's disease (HD). 67 Evidence for a protective effect in an HD transgenic model has been recently obtained by a UCLA investigator, 68 leading to a pilot curcumin clinical trial with HD patients at UCLA. Marie-Charcot Tooth disorder is another example of a similar protein-misfolding neuropathy and curcumin protects against this disorder in vitro 69 ( and in vivo in a transgenic model (Lupski, personal communication).…”