CA2373150A1 - Method for diagnosis of alzheimer's disease - Google Patents

Abstract

The present invention is directed to a method of diagnosing Alzheimer's disease involving analysis of a plasma or serum sample in such a way that .beta.-amyloid1-42 or A.beta.3pE is completely or nearly completely (ie., thoroughly) dissociated from binding proteins prior to the analysis of the levels of .beta.-amyloid1-42 or A.beta.3pE.

Description

Title of the Invention to Method for Diagnosis of Alzheimer's Disease Cross-Reference to Related Application This application claims priority from United States provisional applications Serial Nos. 60/133,161 filed May 7, 1999 and 60/179,975 filed February 3, 2000, the contents both of which are hereby incorporated by reference.
Field of the Invention The present invention provides a method for diagnosing Alzheimer's disease (AD) in a subject. More particularly, a 2o method for diagnosing AD by completely or nearly-completely releasing (3-amyloidl-92 or A~i3pE from plasma or serum proteins and then analyzing the quantity of elevated levels of (3-amyloidl-92 or A~3pE found in AD patients, or those who are in the early stages of AD, or who will develop AD in the future.
Background of the Invention Neurodegenerative disorders such as Alzheimer's 3o disease (AD) and Parkinson' s disease (PD) afflict humanity with great suffering and financial loss. AD is characterized by neurofibrillary tangles, neuritic plaques, and neuronal cell death. AD appears as either the familial, early onset (<60 yrs) or late-onset (>60 yrs) forms, with the latter being more prevalent. AD is the major cause of age-related dementia and cognitive impairment (Wisniewski, T.; Ghiso, J.; Frangione, B.
Neurobiol. of Disease 1997, 4, 313-328). The amyloid s various recently identified mutations accounting for certain types of inherited AD. Such mutations in the presenilin (PS1 and PS2) genes are probably the cause of the most frequent form of familial, early-onset AD

(Rogaev, E. I. Molecular Biology 1998, 32, 58). In 1o these cases, as with APP mutations, more A~31_~2 is observed relative to A(3140. Extensive studies have shown that A(31_~~ has a greater ability than A(31_qo to aggregate into the amyloid fibrils that constitute the plaques characteristic of AD (Lansbury, P. T., Jr.

15 Accts. Ch em. Res. 1996, 29, 317) . Even though A(31_qo is generally present to a much larger degree in the cerebrospinal fluid than A(31_42, it is A(31_Yz that is present to a greater degree in AD plaques. Another major amyloid related peptide found in plaques is an N-2o terminally truncated variant in which the two N-terminal amino acids are removed, and glutamic acid at position three has formed a pyroglutamyl residue. (Saido, T. C.;

Iwatsubo, T.; Mann, D. M. A.; Shimada, H.; Ihara, Y.;

Kawashima, S. Neuron 1995, 14, 457. Iwatsubo, T.;

25 Saido, T. C.; Mann, D. M. A.; Lee, V. M.-Y.;

Trojanowski, J. Q. Am. J. Path. 1996, 149, 1823. Russo, C.; Saido, T. C.; DeBusk, L. M.; Tabaton, M.; Gambetti, P.; Teller, J. K. FEBS Lett. 1997, 409, 411.) This peptide is termed A(33pE - pyroglutamyl at what was 3o previously residue 3 of either A(31_qo or A~31_4z. In fact, some plaques may contain this particular pyroglutamyl derivative to the extent of >500 (Kuo, Y.-M.; Emmerling, M. R.; Woods, A. S.; Cotter, R. J.; Roher, A. E.

Biochem. Biophys. Res. Commun. 1997, 237, 188). The 35 A~33pE has an increased tendency to form ~3-pleated sheets and aggregate than the parent amyloid peptides (He, W.;

z s Barrow, C. J. Biochemistry 1999, 38, 10871). Another minor, related amyloid peptide is that in which the aspartic acid at residue one is present as the isoaspartic acid.
io The A(3 peptides can inhibit cholinergic neurotransmitter function independent of neurotoxicity (Auld, D. S.; Kar, S.; Quirion, R. Trends Neurosci.
1998, 21, 43). A(3 peptides bind to a number of natural substances such as apoE3, apoE4, apoJ, transthyretin, 15 and albumin. In addition, A~3 has been reported to interact with a membrane-bound receptor for advanced glycation end products and to the class A scavenger receptor (SR) associated with the production of reactive oxygen species.
Recently, it has been described that circulating levels of (3-amyloidl_42 in plasma are elevated ca. 6X in patients with AD compared to age-matched controls (Kuo, Y.-M.; Emmerling, M. R.; Lampert, H. C.; Hempelman, S.
R.; Kokjohn, T. A.; Woods, A. S.; Cotter, R. J.; Roher, A. E. Biochem. Biophys. Res. Commun. 1999, 257, 787-791).
The pretreatment of plasma with formic acid was found to be absolutely critical in dissociating the (3-amyloidl_42 from plasma proteins, prior to evaluation of the (3-3o amyloidl_42 levels. Without the pretreatment, levels of (3-amyloidl_~~ are significantly lower. The present invention incorporates a step involving the complete or nearly-complete dissociation of (3-amyloidl_42, or related amyloid peptides such as A~33pE, from serum or plasma samples obtained from humans, prior to analysis of ~3-amyloidl_42 or s A(33pE levels, as part of a diagnostic assay for the early detection of AD, or the propensity to develop AD in the future.
Summary of the Invention The present invention is directed to a method of diagnosing Alzheimer's disease involving analysis of a plasma or serum sample ir~ such a way that ~3-amyloidl42 or A~33pE is completely or nearly completely (ie., thoroughly) dissociated from binding proteins prior to the analysis of the levels of (3-amyloidl_~2 or A(33pE.
We propose to diagnose patients with AD, or those who are gradually developing AD, or those who might 2o develop AD in the future, by a procedure which involves analysis of plasma by completely or nearly-completely dissociating ~3-amyloidl_42 or A(33pE from plasma proteins, such as albumin, followed by evaluation of the levels of (3-amyloidl_42 or A(33pE. Those patients whose (3-amyloidl_YZ
z5 or A(33pE levels are determined to be above a certain threshold level would be considered to either have AD or have a high probability of developing AD in the future.
Further, the procedure could be done at different times, and the relative increase in the levels of (3-amyloidl_42 or 3o A(33pE could be taken as a diagnostic component as to the presence of AD or the liability for developing AD in the future. Also, the relative increase in the levels of (3-amyloidl_42 or A~33pE could be taken as a prognostic marker and a marker to monitor the progression of the disease.
35 Levels of (3-amyloid,_42 or A~33pE could be determined along with standard cognitive testing for additional assessment for prognosis and progression of the disease.
Detailed Description of the Invention io The present invention provides a method of diagnosing Alzheimer's disease in a subject in need thereof comprising:
(a) obtaining a plasma or serum sample from a subject wherein the plasma or serum sample contains an A(3 peptide and a binding protein;
(b) contacting the plasma or serum sample with a dissociation reagent thereby thoroughly dissociating the A(3 peptide from the binding protein; and (c) measuring the quantity of A~3 peptide in the plasma or serum sample.
Alternatively, the method may be further defined by adding a step to neutralize the dissociation reagent prior to analysis. This method is useful where the assay used to measure the quantity of A(3 peptide may be affected by the presence of an active dissociation reagent. For example a highly acidic or basic dissociation reagent may alter the pH of the plasma or serum sample such that an immunoassay technique is not possible. The present invention also 3o provides a method of diagnosing Alzheimer's disease in a subject in need thereof comprising:
(a) obtaining a plasma or serum sample from a subject wherein the plasma or serum sample contains an A(3 peptide and a binding protein;

(b) contacting the plasma or serum sample with a dissociation reagent thereby thoroughly dissociating the A~3 peptide from the binding protein;
(c) contacting the plasma or serum sample with a neutralizing reagent; and to (d) measuring the quantity of A(3 peptide in the plasma or serum sample.
The term "subject" as used herein, refers to an animal, preferably a mammal, most preferably a human, who has been the object of treatment, observation, biochemical screening, or experiment.
As used herein the term "A(3 peptide" is a ~3-amyloid peptidel_4z or enzymatically modified (3-amyloid peptide, such as where aspartic acid at position one is modified to 2o isoaspartic acid. Particularly preferred A(3 peptides are selected from the group consisting of (3-amyloid,_s2 and A(33pE .
As used herein the term "binding protein" is any protein to which ~3-amyloid peptides naturally bind, such as apoE3, apoE4, apoJ, transthyretin, and albumin. The inventors contemplate that there are cell surface receptors that also bind A(3 peptides.
The term "dissociation reagent" is a material, preferably a solution, that causes A(3 peptide to dissociate 3o from the binding protein, and optionally causes denaturation of the binding protein. Preferred dissociation reagents include acids, including formic acid, hydrochloric acid, acetic acid, sulfuric acid, bases, including sodium hydroxide, miscible organic solvents, including ethanol, methanol, DMSO, and DMF. The dissociation reagent may also be a detergent or surfactant including Triton X-100, Tween 20, Tween 80, and sodium dodecyl sulfate ("SDS") or a chaotropic agent icluding urea, and guanidinium chloride. Yet another type of dissociation reagent is a compound that inhibits (3-amyloid to aggregation, such as raloxifene and those compounds described in Curr. Med. Chem. 1997, 4, 159; and Exp. Opin.
Ther. Pat. 1997, 7, 1115.
The term "neutralizing reagent" is a material, preferably a solution, that counteracts the dissociation reagents so that the final plasma or serum sample composition is suitable for an assay to measure the dissociated A(3 peptide. Where the dissociation reagent is an acid, a suitable amount of a base, as the neutralizing reagent, may be added to the plasma or serum sample to 2o prepare it for an assay. Alternatively where the dissociation reagent is a base, a suitable amount of acid, as the neutralizing reagent, may be added to the plasma or serum sample. Not all dissociation reagents will require a neutralizing reagent, including miscible organic solvents or compounds that inhibit ~3-amyloid aggregation.
The terms "thoroughly dissociated" and/or "thoroughly dissociating" as used herein when referring to dissociation of A(3 peptide from binding protein means that the A(3 peptide is completely or nearly completely dissociated from 3o the binding protein; that is, greater than 80% (preferably, >90%, more preferably, >95%).
The levels of A~i peptide are measured by methods known in the art including, but not limited to, immunoassay techniques, HPLC analysis, HPLC/MS (mass spectral) analysis, MALDI/TOF (matrix-assisted laser desorption /
time-of-flight) mass spectral analysis, size exclusion s chromatography, thioflavin-T or Congo Red staining, or ES/MS (electrospray ionization mass spectral) analysis. By comparing the levels of (3-amyloidl_4Z or A~33pE with normal (control) patients, one of ordinary skill in the art can readily determine whether the patient is suffering from AD, to is at risk for developing AD, or one can monitor the progression of AD.
A particularly preferred assay format is the immunoassay format, wherein the A(3 peptide is isolated from the plasma or serum sample using one affinity capture 15 reagent, and is detected with a affinity label reagent.
The affinity capture or affinity label reagents comprise compounds capable of specific interaction with the A(3 peptide to the exclusion of similar compounds. These compounds include, for example, synthetic or natural amino 2o acid polypeptides, proteins (including antibodies), small synthetic organic molecules, or deoxy- or ribo- nucleic acid sequences with about 20-fold or greater affinity for the A(3 peptide compared to other proteins or peptides.
The labeled compounds useful in the present invention 2s may be labeled compounds, with means of direct detection, or may be detected by an indirect means, for example by a second labeled compound.
The phrase "labeled compound" refers to moieties capable of measurement comprising radioactive atoms, 3o enzymes, fluorescent molecules, or alternative tags, for example biotin. Particular radioisotopes useful as a label in the present invention are 3H, 125I , 13~I , 3sS 32p or 33p, particular examples of enzymes suitable for use in the present invention are horseradish peroxidase, alkaline 35 phosphatase, or luciferase. A preferred example of a detectable label is an enzyme that cleaves a substrate to s yield a chromogenic or luminescent product. Particular examples of fluorescent molecules are fluorescein (FITC), rhodamine, R-phycoerythrin (PE) or AlexaT~ dyes (Molecular Probes). Direct measurement is conducted by observing the presence of the radioactive atom to or flourogenic molecule, or by observation of enzymatic activity of a colorimetric or luminescent substrate.
Indirect measurement is conducted by adding an additional compound including a label to the plasma or serum sample so that it can interact with the compound bound to the plasma 15 or serum sample. A well-known example is when the labeled compound comprises biotin, and a second compound comprises avidin or streptavidin and a detectable label. A second well-known example is when a first antibody is used to bind to the A(3 peptide and is detected with an anti-antibody 2o comprising a detectable label. In this case the first antibody comprises a label in that there are specific regions capable of detection within the structure of the first antibody.
z5 Also included in the invention is a diagnostic kit in which all of the components required for a viable diagnostic determination are packaged together sufficient for complete or nearly-complete dissociation of A(3 peptide from a plasma or serum sample and subsequent analysis of 3o the levels of the A(3 peptide such as by an ELISA (enzyme linked immunosorbant assay). The components of an immunoassay diagnostic kit include a dissociation reagent, optionally a neutralizing reagent, and an affinity capture reagent, for instance, an affinity coated resin, an 35 affinity label reagent, and optionally immunoassay control reagents. Immunoassay control reagents are those that s confirm proper function of the assay system and serve to validate interpretation of the sample. A negative control is one that yields no signal from the affinity label reagent, and is often used to determine the background noise of an assay system or used to calculate the signal to io noise ratio for a positive sample using calculations well known in the art. A positive control is one that yields a signal from the affinity label reagent, and is often used to validate the assay system or to compare to a sample to interpret the status of the sample. This can be done 15 empirically using a "yes/no" system or can be made quantitative by comparing the signal generated by control samples containing known quantities of AD peptide with a test sample.
While the foregoing specification teaches the principles of the present invention, with examples provided for the purpose of illustration, it will be understood that the practice of the invention encompasses all of the usual variations, adaptations and/or modifications as come within the scope of the following claims and their equivalents.
to

Claims (21)

WHAT IS CLAIMED IS:

1. A method of diagnosing Alzheimer's disease in a subject in need thereof comprising:
(a) obtaining a plasma or serum sample from a subject wherein the plasma or serum sample contains an A.beta. peptide and a binding protein;
(b) contacting the plasma or serum sample with a dissociation reagent thereby thoroughly dissociating the A.beta.
peptide from the binding protein; and (c) measuring the quantity of A.beta. peptide in the plasma or serum sample.

2. The method of Claim 1 wherein the A.beta. peptide is selected from the group consisting of .beta.-amyloid1-42 and A.beta.3pE.

3. The method of claim 1 wherein the dissociation reagent is selected from the group consisting of formic acid, hydrochloric acid, acetic acid, sulfuric acid, sodium hydroxide, ethanol, methanol, DMSO, DMF, Triton X-100, Tween 20, Tween 80, Sodium dodecyl sulfate (SDS), and raloxifene.

4. The method of Claim 1 wherein the subject is suffering from cognitive impairment and/or other clinical manifestations sufficient to warrant a possible diagnosis of Alzheimer's disease.

5. The method of Claim 1 wherein the subject is suspected of developing Alzheimer's disease in the future because of family history or genetic screening.

6. The method of Claim 1 wherein the subject requests a diagnostic for Alzheimer's disease, or a diagnostic is recommended by a physician, because of the subject's age, or because of suspected early signs of forgetfulness or other possible loss of cognitive function.

7. The method of Claim 1 wherein the subject's relative propensity to develop full Alzheimer's disease is monitored periodically, with increasing levels of .beta.-amyloid1-42 or A.beta.3pE over time indicating an increased propensity of developing Alzheimer's disease.

8. An immunoassay diagnostic kit useful for diagnosing Alzheimer's disease according to the method of claim 1 comprising a package containing;
(a) a dissociation reagent (b) an affinity capture reagent, and (c) an affinity label reagent.

9. The immunoassay diagnostic kit of claim 8 further comprising immunoassay control reagents.

10. A method of diagnosing Alzheimer's disease in a subject in need thereof comprising:
(a) obtaining a plasma or serum sample from a subject wherein the plasma or serum sample contains an A.beta. peptide and a binding protein;
(b) contacting the plasma or serum sample with a dissociation reagent thereby thoroughly dissociating the A.beta.
peptide from the binding protein;

(c) contacting the plasma or serum sample with a neutralizing reagent; and (d) measuring the quantity of A.beta. peptide in the plasma or serum sample.

11. The method of Claim 10, wherein the A.beta. peptide is selected from the group consisting of .beta.-amyloid1-42 and A.beta.3pE.

12. The method of claim 10 wherein the dissociation reagent is selected from the group consisting of formic acid, hydrochloric acid, acetic acid, sulfuric acid, sodium hydroxide, ethanol, methanol, DMSO, DMF, Triton X-100, Tween 20, Tween 80, Sodium dodecyl sulfate (SDS), and raloxifene.

13. The method of Claim 10 wherein the subject is suffering from cognitive impairment and/or other clinical manifestations sufficient to warrant a possible diagnosis of Alzheimer's disease.

14. The method of Claim 10 wherein the subject is suspected of developing Alzheimer's disease in the future because of family history or genetic screening.

15. The method of Claim 10 wherein the subject requests a diagnostic for Alzheimer's disease, or a diagnostic is recommended by a physician, because of the subject's age, or because of suspected early signs of forgetfulness or other possible loss of cognitive function.

16. The method of Claim 10 wherein the subject's relative propensity to develop full Alzheimer's disease is monitored periodically, with increasing levels of .beta.-amyloid 1-42 or A.beta.3pE over time indicating an increased propensity of developing Alzheimer's disease.

17. An immunoassay diagnostic kit useful for diagnosing Alzheimer's disease according to the method of claim 10 comprising a package containing;
(a) a dissociation reagent (b) a neutralization reagent, (c) an affinity capture reagent, (d) an affinity label reagent.

18. The immunoassay diagnostic kit of claim 17 further comprising immunoassay control reagents.

19. A method of diagnosing Alzheimer's disease in a subject in need thereof comprising:
(a) obtaining a plasma or serum sample from a subject wherein the sample contains a binding protein and an A.beta.
peptide selected from the group consisting of .beta.-amyloid 1-42 and A.beta.3pE;
(b) contacting the sample with a dissociation reagent selected from the group consisting of formic acid, hydrochloric acid, acetic acid, sulfuric acid, sodium hydroxide, ethanol, methanol, DMSO, DMF, Triton X-100, Tween 20, Tween 80, Sodium dodecyl sulfate (SDS), and raloxifene, thereby thoroughly dissociating the A.beta. peptide from the binding protein; and (c) measuring the quantity of A.beta. peptide in the test sample.

20. A method of diagnosing Alzheimer's disease in a subject in need thereof comprising:
(a) obtaining a serum or plasma sample from a subject wherein the sample contains a binding protein and an A.beta.
peptide selected from the group consisting of .beta.-amyloid 1-42 and A.beta.3pE;
(b) contacting the test sample with a dissociation reagent selected from the group consisting of formic acid, hydrochloric acid, acetic acid, sulfuric acid, and sodium hydroxide thereby thoroughly dissociating the A.beta. peptide from the binding protein;
(d) contacting the test sample with a neutralizing reagent; and (e) measuring the quantity of A.beta. peptide in the test sample by immunoassay.

21. The method of claim 19 or 20 wherein the quantity of A.beta.
peptide is detected using a labeled compound selected from the group consisting of horseradish peroxidase, alkaline phosphatase, luciferase, fluorescein (FITC), rhodamine, R-phycoerythrin (PE), and Alexa TM dyes (Molecular Probes).