Curcumin also impacts aluminum binding to chromatin DNA, which is of relevance. After aluminum mordanting of chicken blood smears, several chelating dyes and reagents were found to detect metal binding to chromatin DNA by fluorescence microscopy. One of them [the reagents] was curcumin. Aluminum is a risk factor for AD.

References:
A.R. Llorente, P. Del Castillo, J.C. Stockert, Aluminum binding to chromatin DNA as revealed by formation of fluorescent complexes with 8-hydroxyquinoline and other ligands. J. Microsc 155 (Pt. 2) (1989) 227-30

View all comments by Erik Jansson

In the 29 October issue of Science, Gestwicki, Crabtree, and Graef report results of a beautiful series of experiments testing the hypothesis that small-molecule inhibition of protein assembly can work, as long as the inhibitor isn't small! Gestwicki et al. synthesized a bifunctional compound containing one binding site for the amyloid β-protein (Aβ) and a second binding site for the chaperone FK506 binding protein (FKBP). The Aβ-binding moiety was the amyloidophilic dye Congo red (CR). The FKBP ligand was a synthetic ligand for FKBP, abbreviated SLF. The SLF-CR compound then was tested in a variety of assays to determine its effects. The assays included turbidometric and fluorescent (ThT) monitoring of fibril assembly and associated β-sheet formation, electron (EM) and atomic force (AFM) microscopic visualization of fibril morphology, light microscopic and immunofluorescent visualization of neuron morphology and TUNEL staining, MTT assays for cellular metabolism, and quantitative determination of oligomer distributions. Controls included Aβ, CR,...  Read more

In the 29 October issue of Science, Gestwicki, Crabtree, and Graef report results of a beautiful series of experiments testing the hypothesis that small-molecule inhibition of protein assembly can work, as long as the inhibitor isn't small! Gestwicki et al. synthesized a bifunctional compound containing one binding site for the amyloid β-protein (Aβ) and a second binding site for the chaperone FK506 binding protein (FKBP). The Aβ-binding moiety was the amyloidophilic dye Congo red (CR). The FKBP ligand was a synthetic ligand for FKBP, abbreviated SLF. The SLF-CR compound then was tested in a variety of assays to determine its effects. The assays included turbidometric and fluorescent (ThT) monitoring of fibril assembly and associated β-sheet formation, electron (EM) and atomic force (AFM) microscopic visualization of fibril morphology, light microscopic and immunofluorescent visualization of neuron morphology and TUNEL staining, MTT assays for cellular metabolism, and quantitative determination of oligomer distributions. Controls included Aβ, CR, FKBP, SLF, and SLF-CR tested singly and in the appropriate combinations.

Bottom line—the hypothesis holds.

By adding SLF-CR and the chaperone FKBP to Aβ fibril assembly reactions, fibril formation was blocked. Few, if any, fibrils could be observed by EM or AFM, and Aβ samples treated in this manner were no longer able to damage (MTT) or kill (TUNEL and morphology) primary cultures of hippocampal neurons. The inhibitory effect did not result from the complete prevention of peptide self-assembly because AFM revealed a population of "approximately uniform" particles of size 28 square nm. PICUP analysis, a photochemical cross-linking method which blocks the interconversion of monomer, oligomer, and higher-order species, thus allowing their quantitation by SDS-PAGE, showed that the SLF-CR/FKBP treatment produced an abundance of tetramers. The authors suggest that fibril formation might be "interrupted…at a discrete step." It is interesting that the area of the particles observed by AFM corresponds to particles of size similar to that of paranuclei, small oligomers of Aβ42 described previously using the same technique (Bitan et al., 2003). Whether paranuclei correspond to the fibril intermediates present at the "discrete step" at which the assembly path is blocked by SLF-CR/FKBP remains to be determined.

Having demonstrated the efficacy of the SLF-CR "lead compound," Gestwicki et al. did what any good medicinal chemists would do: They began to make systematic alterations in the compound's structure. The first site they examined was the linker connecting the two functional groups. Glycyl, butyl, and benzyl linkers produced successively more potent compounds that were active both in inhibiting fibril formation and neurotoxicity.

Even at this embryonic stage of drug development, the fact that IC50 values of 50 nm were obtained is quite encouraging. However, now comes the hard part. The strategy must work in the body. Here, the bifunctional compound and its targets, Aβ and the chaperone protein, must be colocalized. In addition, the site of colocalization must be relevant to the pathogenetic mechanism of Aβ-induced toxicity. Is the site in the ER, lipid rafts, or an extracellular compartment? Although toxicity was blocked in experiments on ex vivo neurons, will the effect be reproducible in the brain? An important related question is whether the small oligomers (tetramers) produced by the treatment are themselves toxic in vivo. Only future experiments will answer these questions.

View all comments by David Teplow

This is an interesting paper that describes a clever approach for targeting amyloid-β and preventing further aggregation. It is particularly interesting that a relatively uniform Aβ oligomer results from treatment that prevents the formation of fibrils. This could help in understanding the natural history of aggregate formation.

It would be very interesting to try and develop similar analogues that would be useful clinically, but this would probably be quite difficult. The current "small molecules" are quite large, and probably will not enter the CNS. Nonetheless, the bifunctional model compound represents an interesting new approach to this problem.

View all comments by Brian Bacskai

Reply to Frautschy, Teter Comment

In response to the comments by Frautschy and others, the objectives of our paper are first to explain the immune mechanisms of amyloidosis in Alzheimer disease patients and second to find out what can be done about clearance of amyloidosis from the patient’s brain. The emerging answers are that amyloidosis is contributed by insufficient clearance by the Alzheimer patients’ innate immune system and that modulation of the innate immune system has positive effects on amyloid-β clearance.

There is no problem in distinguishing FITC-amyloid-β by fluorescence microscopy from curcuminoids, which (at 0.1 microM) are not visible by fluorescence microscopy. Amyloid-β is also revealed by immunostaining with amyloid-β antibody or by electron microscopy. This can be seen in the pictures of FITC-Aβ in Figs. 2, 3, 5 in the current PNAS publication (1) or the Figs. 2 and 3 (using anti-Aβ immunofluorescence or electron microscopy) in our previous publication (2). The responses of individual patients and...  Read more

Reply to Frautschy, Teter Comment

In response to the comments by Frautschy and others, the objectives of our paper are first to explain the immune mechanisms of amyloidosis in Alzheimer disease patients and second to find out what can be done about clearance of amyloidosis from the patient’s brain. The emerging answers are that amyloidosis is contributed by insufficient clearance by the Alzheimer patients’ innate immune system and that modulation of the innate immune system has positive effects on amyloid-β clearance.

There is no problem in distinguishing FITC-amyloid-β by fluorescence microscopy from curcuminoids, which (at 0.1 microM) are not visible by fluorescence microscopy. Amyloid-β is also revealed by immunostaining with amyloid-β antibody or by electron microscopy. This can be seen in the pictures of FITC-Aβ in Figs. 2, 3, 5 in the current PNAS publication (1) or the Figs. 2 and 3 (using anti-Aβ immunofluorescence or electron microscopy) in our previous publication (2). The responses of individual patients and clinical data correlations were examined in a previous publication (3).

Our work relates to human tissues and blood cells from patients with Alzheimer disease, which makes a direct comparison with transgenic animals (which do not have a specific immune defect) difficult. We performed the studies in macrophages and monocytes from Alzheimer patients over a 6-year period. Logistically, it is difficult to ask that the blood specimens of over 140 patients collected over a 6-year period would be analyzed by the same techniques that were developed later during the course of this study. However, the immune defects in phagocytosis have been observed by fluorescence microscopy in a majority of patients and the biochemical defects in a small number of patients (MGAT3 in over 20 patients, TLR defects in four patients) but with a remarkable consistency. Without doubt, many factors might affect the immune system, including drugs, hormones, stress, infection, etc. However, the patients in Phase 1 – preclinical study (where we are now) have to be examined, as they present themselves. Phase 2 and 3 studies will be possible at a later stage of investigation.

Bisdemethoxycurcumin showed greatest effect on phagocytosis when compared to unfractionated curcuminoids or other fractions. In order to obtain the most reproducible results, we chose to work with a pure chemical, bisdemethoxycurcumin, not the unfractionated material.

Regarding MGAT3 and TLR results, the data, such as Fig. 4, speak for themselves since they are consistent (patients vs. controls). Recent results continue to support the conclusions about transcriptional effects of curcuminoids. The studies of MGAT3 protein levels in the brain are difficult since a good antibody is not available. We agree that more flow cytometric testing of TLR proteins in PBMCs treated with bisdemethoxycurcumin is warranted (the legend had an error and we plan to correct this).

The results of PBMC clearance of Aβ in brain sections in Fig. 6 are striking and deserve closer scrutiny of the legends. Similar results have been obtained in at least five other experiments. The tissues were obtained from the UCLA brain bank. We have not seen the effects on neuritic plaques in these frozen tissues, but further work is ongoing.

Our intention in this study was to identify and characterize the most potent anti-Alzheimer disease agent in mixture of curcuminoids, not to study curcumin SAR. In fact, bisdemethoxycurcumin does possess antioxidant activity (4). In the AAPH-induced linoleic acid antioxidation test or the DPPH-radical scavenging test, bisdemethoxycurcumin does possess significant activity as an antioxidant.

We are aware of the chemical properties of curcumins and related materials, and the compounds are readily handled with proper care. All of the compounds were fully characterized spectrally, and instability was not a problem during our analytical and synthetic studies. We are aware of the metabolic properties of curcumins and in fact “Dynamic Medicinal Chemistry” has been a major effort leading our studies in this and other areas (5). Our intention was not to study bisdemethoxycurcumin in a pharmaceutical sense. For our purposes, of greatest relevance was the apparent effective concentration of the active pharmacological agent at the target site and not the relative percent of material in dietary supplements.

The purpose of the study was to biotrack the most pharmacologically active constituent. That no curcumin was present in the final HPLC in the purification of bisdemethoxycurcumin was not surprising and speaks to the alacrity of our separation approach. Agreeably, the retention time was short, but the solvent polarity gradient was steep and quite effective. Of course, elution profiles are a function of the matrix employed and the history of the matrix. To confirm the activity of bisdemethoxycurcumin, indeed, synthetic bisdemethoxycurcumin was prepared and fully characterized spectrally. That synthetic bisdemethoxycurcumin is also highly active supports the exciting observation that the minor constituent in curcuminoids contains remarkable biological properties.

It was beyond the scope of this study to examine the glucuronidation of bisdemethoxycurcumin, but it is important to point out that 1) glucuronides undergo enterohepatic cycling, and urinary metabolite levels may not reflect metabolic disposition in the blood; 2) bisdemethoxycurcumin may not be “free” in the biological context but in fact associated with proteins, thus confounding apparent observations about solution stability study data; and 3) the effective concentration or accumulation of bisdemethoxycurcumin in the target tissue or cell may be much different than that estimated from plasma levels. The examination of these points is the subject of additional studies.

References:
1. Fiala M, Liu PT, Espinosa-Jeffrey A, Rosenthal MJ, Bernard G, Ringman JM, Sayre J, Zhang L, Zaghi J, Dejbakhsh S, Chiang B, Hui J, Mahanian M, Baghaee A, Hong P, Cashman J. Innate immunity and transcription of MGAT-III and Toll-like receptors in Alzheimer's disease patients are improved by bisdemethoxycurcumin. Proc Natl Acad Sci U S A. 2007 Jul 31;104(31):12849-54. Epub 2007 Jul 24. Abstract

2. Fiala M, Lin J, Ringman J, Kermani-Arab V, Tsao G, Patel A, Lossinsky AS, Graves MC, Gustavson A, Sayre J, Sofroni E, Suarez T, Chiappelli F, Bernard G. Ineffective phagocytosis of amyloid-beta by macrophages of Alzheimer's disease patients. J Alzheimers Dis. 2005 Jun;7(3):221-32; discussion 255-62. Abstract

3. Zhang L, Fiala M, Cashman J, Sayre J, Espinosa A, Mahanian M, Zaghi J, Badmaev V, Graves MC, Bernard G, Rosenthal M. Curcuminoids enhance amyloid-beta uptake by macrophages of Alzheimer's disease patients. J Alzheimers Dis. 2006 Sep;10(1):1-7. Abstract

4. Somparn P, Phisalaphong C, Nakornchai S, Unchern S, Morales NP. Comparative antioxidant activities of curcumin and its demethoxy and hydrogenated derivatives. Biol Pharm Bull. 2007 Jan;30(1):74-8. Abstract

5. Cashman JR, MacDougall JM. Dynamic medicinal chemistry in the elaboration of morphine-6-glucuronide analogs. Curr Top Med Chem. 2005;5(6):585-94. Review. Abstract

View all comments by Milan Fiala

This new data on curcumin stimulated neurogenesis look pretty good and the dosing at 500nM to get the effect in vitro and via stimulation of MAPK is credible and consistent with other literature. Their in vivo results are the most important demonstration of possible utility. The dosing is higher than what people achieve with current supplements and the blood and brain levels represent estimates. They are at the high end, but the authors get the neurogenesis effect without toxicity, suggesting that it may be realizable within a therapeutic window.

One caveat for the relevance to AD for this and for most of the other studies showing stimulation of hippocampal neurogenesis is that the effects shown are usually in the dentate gyrus rather than in more AD vulnerable regions like CA1, entorhinal cortex and other areas showing neuron loss. That said, the increases in areas with normal neurogenesis, in the DG and in the cortical subventricular zone, suggests an effect might extend to other areas and might redistribute to areas of neuron loss in the presence of regional pathology.

View all comments by Gregory Cole

This interesting paper of Thomas Willnow and colleagues confirms that SORLA/LR11 has a significant role in the regulation of APP processing, thus giving further support to the hypothesis that reduced SORLA expression could be a risk factor for sporadic AD (Rogaeva et al., 2007).

In addition, the results suggest some other reflections. First, they confirm that, at least in mice, altered neuronal function and survival are not directly correlated with the amount of Aβ produced and with plaque burden. This is the umpteenth observation that draws our attention to this point, but we still don’t have a clear explanation for that. Second, the results contribute to the unsolved issue of APP functions. The observed molecular phenotypes are actually due to an increased processing of APP that leads to accumulation of secreted soluble APP. However, we should also take into account that increased processing of APP is also expected to affect AICD intracellular concentration. Thus, we cannot exclude that the observed phenotype could be due to altered AICD-dependent signaling. This...  Read more

This interesting paper of Thomas Willnow and colleagues confirms that SORLA/LR11 has a significant role in the regulation of APP processing, thus giving further support to the hypothesis that reduced SORLA expression could be a risk factor for sporadic AD (Rogaeva et al., 2007).

In addition, the results suggest some other reflections. First, they confirm that, at least in mice, altered neuronal function and survival are not directly correlated with the amount of Aβ produced and with plaque burden. This is the umpteenth observation that draws our attention to this point, but we still don’t have a clear explanation for that. Second, the results contribute to the unsolved issue of APP functions. The observed molecular phenotypes are actually due to an increased processing of APP that leads to accumulation of secreted soluble APP. However, we should also take into account that increased processing of APP is also expected to affect AICD intracellular concentration. Thus, we cannot exclude that the observed phenotype could be due to altered AICD-dependent signaling. This possibility is also supported by the recent data of Quan-Hong Ma and colleagues (Quan-Hong Ma et al., 2008) indicating that TAG1-APP signaling modulates neurogenesis through AICD-Fe65. The problem is that the two papers observed an increased neurogenesis in two apparently opposite conditions, namely, increased processing of APP (with overproduction of APPs and Aβ) and absence of APP (no production of AICD), respectively. However, this is not the first time that increased production of Aβ and APPs is associated with low levels of AICD. The SORLA-/- background could be a good tool to address this point.

References:
Rogaeva E, Meng Y, Lee JH, Gu Y, Kawarai T, Zou F, Katayama T, Baldwin CT, Cheng R, Hasegawa H, Chen F, Shibata N, Lunetta KL, Pardossi-Piquard R, Bohm C, Wakutani Y, Cupples LA, Cuenco KT, Green RC, Pinessi L, Rainero I, Sorbi S, Bruni A, Duara R, Friedland RP, Inzelberg R, Hampe W, Bujo H, Song YQ, Andersen OM, Willnow TE, Graff-Radford N, Petersen RC, Dickson D, Der SD, Fraser PE, Schmitt-Ulms G, Younkin S, Mayeux R, Farrer LA, St George-Hyslop P. The neuronal sortilin-related receptor SORL1 is genetically associated with Alzheimer disease. Nat Genet. 2007 Feb 1;39(2):168-77. Abstract

Ma QH, Futagawa T, Yang WL, Jiang XD, Zeng L, Takeda Y, Xu RX, Bagnard D, Schachner M, Furley AJ, Karagogeos D, Watanabe K, Dawe GS, Xiao ZC. A TAG1-APP signalling pathway through Fe65 negatively modulates neurogenesis. Nat Cell Biol. 2008 Mar;10(3):283-94. Abstract

View all comments by Tommaso Russo