Progress and New Cautions in an "Universal Amyloid Strategy"

Posted by Michael Rae on June 07, 2010 | Chief Science Officer's Team

In late 2008, we reviewed then-unpublished work by Dr. Mark Pepys, who was working on an ambitious project anticipated to allow for the disaggregation of nearly all disease-associated amyloids. Dr. Pepys subsequently accepted an invitation to present those early results at the fourth SENS scientific conference(1). His strategy is based on the fact that the pentraxin serum amyloid P component (SAP) is an "universal constituent of the abnormal tissue deposits in amyloidosis, including Alzheimer disease". (2) As we reviewed:

A quarter century ago, Pepys suggested that because circulating SAP is believed to exist in a state of dynamic equilibrium with the SAP in amyloid deposits, lowering circulating SAP might lead plaque SAP to dissociate, leading to the breakup of the integrity of the plaque and ultimate clearance of amyloid deposits.

Early in this century, Pepys' team began ... search[ing for] a small molecule that might inhibit the binding of SAP in Abeta, and came across one that was particularly effective: R-1-[6-[R-2-carboxy-pyrrolidin-1-yl]-6-oxo-hexanoyl] pyrrolidine-2-carboxylic acid, or CPHPC, which "also crosslinks and dimerizes SAP molecules",([3]) blocking the binding face of the molecule in the process. They quickly moved from this in vitro finding through animal studies for efficacy and toxicity, and the initial results being favorable, moved into pilot human studies.([4])

In 2002, Pepys reported that adminstration of IV CPHPC over the course of 2 days into 8 amyloidosis patients resulted in almost total removal of SAP from the circulation, apparently through "very rapid" hepatic clearance, since tracer studies found a large amount of SAP in the liver of one patients 6 h after initiating treatment.([4]) They quickly sent CPHPC sailing down the drug-development pipeline, to results that, although still preliminary, were extremely exciting.

The promise

We reviewed some preliminary findings from subsequent pilot studies in light chain (AL) amyloidosis and other diseases, some of which were later reported and elaborated at SENS4 -- including very brief allusion to some work on AD patients. To surprisingly little fanfare (so little that it was not noticed by the present author), Dr. Pepys reported  results from those pilot studies late in 2009:

We therefore conducted a pilot proof of concept study in 5 patients aged 53–67 years with mild to moderate probable Alzheimer's disease who received 60 mg CPHPC by s.c. injection 3 times daily for 12 weeks. The drug was well tolerated with no adverse effects other than transient local discomfort on injection. Compliance was confirmed by the presence of CPHPC in all serum samples ... [and] in the cerebrospinal fluid. The concentration of SAP in the serum fell dramatically ... 1 week after starting CPHPC, remained around this value throughout the treatment period, and had [normalized] ... at 4 weeks after drug discontinuation (Fig. 1B). The SAP concentration in the CSF also fell remarkably [my emphasis], ...and then remained scarcely detectable throughout the treatment period. Because depletion of circulating SAP by CPHPC involves clearance by the liver, these observations ... suggest that entry of CPHPC into the brain is not required for removal of intracerebral SAP but the presence of CPHPC in CSF should additionally block effects of any residual or locally produced SAP.

There was no significant difference between the clinical measures before and after CPHPC and importantly no deterioration in [cognitive scores] ...  nor any structural change in MRI brain scans... [nor] in CSF concentrations of Aβ40, Aβ42, total or phosphorylated tau, or S100B or in any of the comprehensive routine hematological, biochemical, endocrine, or serological blood tests.  ... [I]t would have been astonishing if there had been any improvement in cognition or change in the CSF biomarkers during this brief study ... However, the clinical stability and absence of biochemical signs of cerebral damage importantly confirm the safety in patients with dementia both of CPHPC itself and of profound depletion of systemic and cerebral SAP and support longer-term studies of clinical efficacy.(5)

 As Pepys also notes, there are additional possible pathogenic roles for SAP in AD beyond their direct effect in Aß aggregation:

the universal presence of serum amyloid P component (SAP) in cerebrospinal fluid (CSF) and bound to cerebral and cerebrovascular amyloid deposits and to neurofibrillary tangles in Alzheimer disease [my emphasis] is consistent with a role of SAP in pathogenesis.  .... Furthermore, human SAP has been reported to bind to and enter neurons in culture and in rat brain in vivo, to cause apoptotic cell death, and to activate human microglia synergistically with Aβ and C1q [required for immune complex binding to phagocytes] in vitro, provoking increased production of pro-inflammatory cytokines and Aβ itself. The presence of tangles composed of hyperphosphorylated tau protein, to which SAP binds in non-Alzheimer dementias, also raises the possibility of targeting SAP in those conditions.(5)

While preliminary, these results are promising, and we are pleased to see the work published and advancing. However, there is also reason for caution. At its core, the therapeutic use of CPHPC is based on what the authors rightly characterize as its ability to induce the "unprecedented, profound depletion" (by >99%) of a physiological protein from the systemic circulation and CSF. Few side-effects have been observed in the small human studies conducted to date,(4,5) but these studies have been performed in patients rendered very ill by massive, prevalent accumulations of a single -- and, in most patients' case, a mutant -- protein.  If SAP depletion is to be used to target the more gradual, ongoing accumulation of multiple distinct species of extracellular aggregates formed from wild-type proteins during aging, its physiological roles will ipso facto be arrested for an extended percentage of the year, for each year of a current adult life expectancy and beyond. As with all such "gerontological" interventions against aging, such interference in body's homeostasis can be expected to come with significant potential for adverse outcomes -- and it is exceptionally difficult to predict the unintended side-effects of extended intermittent interference in the case of SAP, as its physiological functions  (such as its complex dual role in bacterial immunity(6)) are as yet little-understood.

As it happens, an hypothetical complication of chronic SAP suppression, conducted even intermittently over many decades, has just emerged.

The peril?

A group of researchers at the Harvard Institutes of Medicine and Harvard Medical School recently became interested in the possible role of SAP in controlling the fibrotic response to tissue injury.

[The] unique binding activities of SAP and in vitro biology studies suggest that SAP may localize specifically to sites of injury and aid in the removal of damaged tissue and pathogenic organisms.  ... Despite extensive characterization of SAP in vitro, its potential participation in natural regulation of the innate injury response has only recently been appreciated. ... Because FcγR [Fcγ receptor] expression is restricted predominantly to cells of the innate immune system, and many of the ligands for SAP are concentrated at sites of tissue injury, we predicted that SAP binding to ligands might affect innate immune cell activation events in a localized fashion and thereby potentially modulate the innate injury response. ...

Pilling et al. ... showed that purified rat SAP could suppress development of lung fibrosis in the bleomycin model, which correlated with reduced fibrocyte numbers within the lung tissue. However, fibrocytes play no obvious role in the development of fibrosis of the kidney; therefore, we wished to determine whether SAP would have an antifibrotic effect in this tissue setting and, if so, what mechanisms mediated its biologic effect....

Here we show that fibrosis progression in the mouse kidney is significantly inhibited by therapeutic administration of human serum amyloid P, regulated by activating Fcγ receptors, and dependent on inflammatory monocytes and macrophages, but not fibrocytes. Human serum amyloid P-mediated inhibition of mouse kidney fibrosis correlated with specific binding of human serum amyloid P to cell debris and with subsequent suppression of inflammatory monocytes and kidney macrophages in vitro and in vivo, and was dependent on regulated binding to activating Fcγ receptors and interleukin-10 expression.

These studies uncover previously unidentified roles for Fcγ receptors in sterile inflammation and highlight serum amyloid P as a potential antifibrotic therapy through local generation of interleukin-10.[emphasis mine](7)

This is an important finding in its own right, as SAP's physiological function is currently so poorly-understood. But from the viewpoint of biomedical gerontology, an antifibrotic role of SAP suggests a possible long-term risk associated with suppression of this key immunological protein as a potential prophylactic against the damage of aging. In addition to Aß, an universal anti-amyloid therapeutic would potentially be used to target a wide swath of age-related extracellular aggregates, including notably the age-related cardiac amyloidoses, which have emerged as critical-path targets for rejuvenation biotechnology.

The prevalence of age-related cardiac amyloidoses (notably senile cardiac amyloidosis (caused by aggregated wild-type transthyretin (TTR)) and isolated atrial amyloidosis (IAA) (caused by aggregated atrial natriureptide (ANP)) rises dramatically late in a currently-normal life expectancy(9,10) and appears to be responsible for, or a significant contributor to, a large number of deaths in centenarians and especially supercentenarians.(11) At the same time, fibrosis and "ectopic" collagen infiltration are prominent findings in the aging myocardium.(8) Cardiac remodeling replaces lost cardiomyocytes with fibrotic tissue in order to preserve the gross structural integrity of the aging heart, but as (7) notes absent this context, "Fibrosis itself causes parenchymal cell ischemia, distortion, and contraction of normal organ architecture and contributes directly to functional demise." A parallel statement could readily be inserted in the opening paragraphs of a report on age-related cardiac amyloidosis. Intermittent inhibition of the organism's ability to counterregulate the fibrotic response to injury in the heart could reasonably be hypothesized to accelerate this age-related degeneration of tissue architecture. And clearly, the brief months of clinical trials of SAP clearance with CPHPC to date(3-5) would not be sufficient to reveal any such long-term acceleration of this pathological structural decay, particularly in biologically aged patients with severe pre-existing pathology,

Of note, upon being informed of this new report,(7) Stan Primmer of the Supercentenarian Research Foundation (SRF) disclosed to  the present author (personal communication, 2010-05-31 9:59 PM)  that the autopsies of several supercentenarians have revealed the occurrence of fibrosis; in fact, one recent supercentenarian death could be attributed to pneumonia due to idiopathic pulmonary fibrosis -- and, by coincidence or not, this subject had an uncharacteristic lack of amyloidosis. While a single case report cannot be counted as evidence of any merit, this finding would be consistent with the idea that low levels or activity of endogenous SAP would at once result in slower progression of age-related amyloidoses, while simultaneously accelerating the deposition of fibrotic tissue by limiting the body's ability to counterregulate the fibrotic response in pulmonary and other tissue.  Irrespectively, the reasonable concern that repeated bouts of active pharmacological suppression of SAP for many decades would haunt its clinical use to retard or arrest the accumulation of age-related amyloidoses.

A Planned Collaboration in Rejuvenation Biotechnology

The "engineering" heuristic of anti-aging biomedicine is to target not the metabolic basis of age-related pathology, but the inert  damage of aging itself. I am therefore delighted to have the privilege to be given permission by Stan Primmer to make the first public announcement that the SRF has recently helped to facilitate a collaboration between Drs. Sudhir Paul and Brian O’Nuallain, researchers already working in amyloid diseases, to develop antibodies to cleave aggregated wild-type and mutant transthyretin -- the form responsible for senile cardiac amyloidosis (a prevalent, but not exclusive, cardiac amyloidosis in supercentenarians).

The project will proceed in four phases. Phase 1 will consist of in vitro generation of ... monoclonal... catalytic antibodies that can directly destroy TTR amyloid ... After the initial breakdown cycle, the catalytic antibody would be re-used again and again to disintegrate additional TTR molecules. Thus, only a small amount of the catalytic antibody should be needed to remove large amounts of TTR amyloidogenic precursors and TTR amyloid. ... Phase 2 will consist of studies in an animal model of TTR amyloidosis to determine the safety and efficacy of the potential ... therapeutic antibodies discovered in Phase 1. Phase 3 will involve clinical trials on the diagnostic and therapeutic potential of the novel antibodies for comparatively young human subjects who develop amyloidosis due to mutation(s) in the TTR molecule. Initial testing of the methodology in the younger cohort is designed to avoid risk to the uniquely fragile group consisting of supercentenarians. Phase 4 will then serve to apply the results of previous research to volunteer supercentenarians in order to improve their health and extend their lives beyond what they would otherwise be expected to live.(11)

SENS Foundation recognizes the importance of this project. In conception and ambition, this collaboration offers the potential to be exceptionally exciting, pioneering research, probing the extremes of human longevity with a bold new therapeutic strategy. Actual implementation of this proposal currently awaits the availability of funding, which has not yet been secured.  At this time, we can only wish these experienced specialists good luck and godspeed. 

References
1.Pepys M. Treatment and prevention of amyloidosis. Rejuvenation Res. 2009;12 (Suppl 1):S46–S47.

2. Pepys MB, Rademacher TW, Amatayakul-Chantler S, Williams P, Noble GE, Hutchinson WL, Hawkins PN, Nelson SR, Gallimore JR, Herbert J, et al. Human serum amyloid P component is an invariant constituent of amyloid deposits and has a uniquely homogeneous glycostructure. Proc Natl Acad Sci U S A. 1994 Jun 7;91(12):5602-6. PMID: 8202534 [PubMed - indexed for MEDLINE]

3. Pepys MB. Science and serendipity. Clin Med. 2007 Dec;7(6):562-78.Links PMID: 18193704

4. Pepys MB, Herbert J, Hutchinson WL, Tennent GA, Lachmann HJ, Gallimore JR, Lovat LB, Bartfai T, Alanine A, Hertel C, Hoffmann T, Jakob-Roetne R, Norcross RD, Kemp JA, Yamamura K, Suzuki M, Taylor GW, Murray S, Thompson D, Purvis A, Kolstoe S, Wood SP, Hawkins PN. Targeted pharmacological depletion of serum amyloid P component for treatment of human amyloidosis. Nature. 2002 May 16;417(6886):254-9. PMID: 12015594 [PubMed - indexed for MEDLINE]

5. Kolstoe SE, Ridha BH, Bellotti V, Wang N, Robinson CV, Crutch SJ, Keir G, Kukkastenvehmas R, Gallimore JR, Hutchinson WL, Hawkins PN, Wood SP, Rossor MN, Pepys MB. Molecular dissection of Alzheimer's disease neuropathology by depletion of serum amyloid P component. Proc Natl Acad Sci U S A. 2009 May 5;106(18):7619-23. Epub 2009 Apr 16. PubMed PMID: 19372378; PubMed Central PMCID: PMC2669789.

6. Noursadeghi M, Bickerstaff MC, Gallimore JR, Herbert J, Cohen J, Pepys MB. Role of serum amyloid P component in bacterial infection: protection of the host or protection of the pathogen. Proc Natl Acad Sci U S A. 2000 Dec 19;97(26):14584-9. PubMed PMID: 11121061; PubMed Central PMCID: PMC18962.

7. Castaño AP, Lin SL, Surowy T, Nowlin BT, Turlapati SA, Patel T, Singh A, Li S, Lupher ML Jr, Duffield JS. Serum amyloid P inhibits fibrosis through Fc gamma R-dependent monocyte-macrophage regulation in vivo. Sci Transl Med. 2009 Nov 4;1(5):5ra13. Erratum in: Sci Transl Med. 2009 Nov 4;1(5):5ra13. PubMed PMID: 20368175; PubMed Central PMCID: PMC2852889.

8. de Souza RR. Aging of myocardial collagen. Biogerontology. 2002;3(6):325-35. Review. PubMed PMID: 12510171.

9. Kholová I, Niessen HW. Amyloid in the cardiovascular system: a review. J Clin Pathol. 2005 Feb;58(2):125-33. Review. PubMed PMID: 15677530; PubMed Central PMCID: PMC1770576.

10. Steiner I, Hájková P. Patterns of isolated atrial amyloid: a study of 100 hearts on autopsy. Cardiovasc Pathol. 2006 Sep-Oct;15(5):287-90. 16979036

11. Primmer SR, Paul S, O’Nuallain B. Research project to extend lives of supercentenarians by diagnosing and treating transthyretin amyloidosis. Unpublished MS, Supercentenarian Research Foundation. 2010 Mar 25.