AU750582B2 - Method for diagnosing Alzheimer's disease - Google Patents

Description

WO 99/24830 PCTIUS98/23198 METHOD FOR DIAGNOSING ALZHEIMER'S DISEASE Field of the Invention The present invention relates to a method for diagnosing Alzheimer's disease by detecting the presence or absence of functioning calcium-dependent potassium channels in human blood platelets, the absence of such potassium channels indicating a positive diagnosis of Alzheimer's disease.

Background of the Invention Alzheimer's disease is a progressive neurodegenerative disorder which causes irreversible damage to brain cells leading to dementia and ultimately death.

It is characterized by formation of amyloid plaques and neurofibrillary tangles in-the brain. Currently, it is primarily diagnosed by exclusion of other known causes of dementia. Diagnosis at an early stage prior to irreversible changes is practically non-existent.

In order for a therapeutic intervention to be significantly effective, it will have to be administered very early on prior to irreversible changes.

Accordingly, a non-invasive diagnostic test for early diagnosis of Alzheimer's disease would be a most welcomed addition to the diagnostician's armamentarium.

Calcium-dependent potassium channels have been found to be implicated with Alzheimer's disease. Abnormalities of potassium channel function have been reported in cultured cells in Alzheimer's disease (AD) 1 Depending upon the single channel conductance, a calcium-dependent potassium (Kca) channel is termed highconductance or maxi-K (100-250 picosiemens intermediate-conductance (18-50 pS), or low-conductance (10-14 pS)Kca 2 The high conductance Kca is present in neurons, cardiac cells and various types of smooth muscles 3 The intermediate-conductance channel has been shown to be 1 WO 99/24830 PCT/US98/23198 present in red blood cells 4 and in smooth muscle 5 The low-conductance channel is present in a variety of cell types 6 The most important tools to distinguish between lowand high-conductance KCa are the toxins apamin 7 and charybdotoxin 8 Atwal, footnote 2 at page 581, points out that "while charybdotoxin specifically blocks maxi-K, apamin is a potent blocker of the low conductance Kca. However, in certain tissues, for example, rat brain, charybdotoxin may block Kca of all three types." Mahaut-Smith 8a discloses that blood platelets contain a 30pS conductance charybdotoxin-sensitive channel.

It is also known that iberiotoxin specifically 15 inhibits maxi-K channels (Elelvez et al 8 b).

A 113 pS K+ channel sensitive to tetraethylammonium has been described as being absent or not functional in cultured fibroblasts from patients with AD 9 and this S. defect was mimicked in normal fibroblasts by the addition 20 of amyloid beta-protein (Ap) 1 0 which is also plentiful in platelets 11 12 However, tetraethylammonium is not a selective inhibitor of K* channels, and so the pharmacological identity of the abnormal channel in cultured fibroblasts is not clear.

25 U.S. Patent No. 5,580,748 to Alkon et al (issued December 3, 1996) discloses a method for the diagnosis of Alzheimer's disease using human cells such as fibroblasts, buccal mucosal cells, neurons, and blood cells such as erythrocytes, lymphocytes and lymphoblastoid cells, wherein the absence of a functional 133 pS potassium channel in the.

test cells indicates the presence of Alzheimer's disease.

Tetraethylammonium is employed as a potassium channel blocker to aid in detecting the presence of the functioning 113 pS potassium channel.

The discussion of the background to the invention herein is included to explain the context of the invention. This is not to be taken as an admission that any of the material referred to was published, known or part of the common general knowledge in Australia as at the priority date of any of the claims.

Throughout the description and claims of the specification the word "comprise" Tand variations of the word, such as "comprising" and "comprises", is not intended to exclude other additives, components, integers or steps.

4 uo WO 99/24830 PCT/US98/23198 Description of the Invention In accordance with the present invention, a method is provided for diagnosing Alzheimer's disease which includes the steps of obtaining a sample of platelets from a human subject, and detecting the presence or absence in such platelets of functioning calciumdependent potassium (Kca) channels, the absence of such functioning Kca channel indicating a positive diagnosis for Alzheimer's disease.

Detection of the absence of the functioning calciumdependent potassium channel will be indicated by lack of inhibition by a potassium channel blocker which has the ability to block the functioning Kca channel, and may, for example, include apamin, charybdotoxin, or a combination thereof, depending upon the specific functioning calciumdependent potassium channel involved.

In addition, in accordance with the present invention, a method is provided for diagnosing Alzheimer's disease which includes the step of detecting the presence or absence of one or more functioning small-conductance calcium-dependent potassium (SKca) channels in blood platelets of a human subject, the absence of a functioning SKca channel in such platelets indicating a positive diagnosis for Alzheimer's disease.

Detection of the absence of the functioning SKca channel will be indicated by lack of inhibition by a SKca channel blocker which has the ability to block the functioning SKca channel, and may, for example, include apamin, charybdotoxin, or a combination thereof, depending upon the specific SKca channel involved.

In addition, in accordance with the present invention, a method is provided for diagnosing Alzheimer's disease which includes the step of detecting the presence or absence of a functioning charybdotoxin-sensitive potassium (Kch) channel in blood platelets of a human 3 WO 99/24830 PCT/US98/23198 subject, the absence of a functioning KCh channel in such platelets indicating a positive diagnosis for Alzheimer's disease.

Detection of the absence of the functioning Kch channel will be indicated by lack of inhibition by charybdotoxin which has the ability to block the functioning Kch channel.

Detection of the presence or absence of the functional Kca channel, SKCa channel and/or Kch channel may be determined by conventional techniques for measuring electrical currents in cells such as the patch clamp technique disclosed by Sakmann, B. et a1 28 The presence or absence of the functional potassium channel may also be detected by loading blood platelets with 86 Rb+, (2) stimulating 86 Rb+ efflux (from the platelets via KCa channels) with thrombin or ionomycin, subjecting the thrombin- or ionomycin-stimulated 86 Rb efflux to the action of an appropriate potassium channel blocker, such as apamin, charybdotoxin or a combination thereof, depending upon the particular functional Kca channel involved, and determining if the Kca channel blocker significantly inhibits the thrombin- or ionomycin-stimulated 86 Rb+ efflux to cause significant reductions in the 86Rb+ efflux, a lack of significant inhibition and significant reduction in the 86Rb+ efflux indicating a positive diagnosis for Alzheimer's disease.

Thus, where the Kca channel is a small-conductance calcium dependent potassium (SKca) channel, the potassium channel blocker employed will preferably be apamin or a combination of apamin and charybdotoxin (weight ratio apamin:charybdotoxin from about 4:1 to about 1:1, preferably from about 3:1 to about 1.5:1).

Where the Kca channel is a charybdotoxin-sensitive potassium (Kch) channel, the potassium channel blocker employed will be charybdotoxin or a combination of 4 WO 99/24830 PCT/US98/23198 charybdotoxin and apamin (weight ratio charybdotoxin:apamin from about 4:1 to about 1:1, preferably from about 3:1 to about 1.5:1).

Brief Description of the Figures Figures la and lb are graphs showing the effects of apamin and charybdotoxin on thrombin-stimulated 86 Rb+ efflux in Control subjects (Figure la) and in patients with Alzheimer's disease (Figure Ib); Figures 2a and 2b are graphs showing the effect of a-dendrotoxin on thrombin-stimulated 8 6Rb+ efflux in Control subjects (Figure 2a) and in patients with Alzheimer's disease (Figure 2b); and Figures 3a and 3b are graphs showing the effect of apamin and charybdotoxin on ionomycin-stimulated 86Rb+ efflux in Control subjects (Figure 3a) and in patients with Alzheimer's disease (Figure 3b).

Example The following clinical experiments were carried out to determine if there is abnormal function of potassium channels in the platelets of patients with Alzheimer's disease.

Methods Patient selection. Subjects with and without cognitive dysfunction were rigorously assessed annually, with a full range of blood tests to exclude metabolic or other causes of dementia and to assess cognitive function using the Cambridge Examination for Mental Disorders of the Elderly (CAMDEX) 2 Diagnoses were made according to criteria of the National Institutes of Neurology and Communicative Disorders-Alzheimer's Disease and Related Disorders Association Work Group (NINCDS-ADRDA) 1 3 and the criteria described in the Diagnostic and Statistical Manual of Mental Disorders, Third Edition, Revised (DSM-IIIR) 14 in 5 WO 99/24830 PCT/US98/23198 addition to data from CT scans, 15 26 and the SPET regional cerebral blood flow data 15 16 Those with an OPTIMA (Oxford Project to Investigate Memory and Aging) diagnosis of 'probable AD' not only had no evidence of any other significant metabolic or psychiatric process that was thought to contribute to the dementia, but also had evidence of both significant medial temporal lobe atrophy on CT 26 without evidence of moderate or greater white matter change on axial images, and moderate or greater parietotemporal blood flow deficits on SPET 15 16 If there was clinical evidence of another process in addition to or other than AD, which the clinician considered could have contributed to the clinical presentation or have given rise to it, then a diagnosis of 'possible AD' was made (four cases, one with ischaemia and three with possible frontal lobe dementia). If, however, the clinical presentation could have been attributed to either AD or another dementia, but the imaging and longitudinal data were highly suggestive of AD on the basis of previously reported necropsy-confirmed cases 16 and overall the clinician's impression was of AD, then a diagnosis of 'probable AD' was made (four cases, two of frontal lobe dementia, one of vascular disease, and one of hypoxia). In six cases the diagnosis was clearly 'probable AD' In a previous necropsy-confirmed cohort, the use of these criteria, using CT and SPET changes alone, without taking into account the clinical history or cognitive profile, had a sensitivity of over 85% and a specificity of over 95%16. In the cases with 'probable AD' studied in this series, all of whom remain alive, the likelihood that AD accounted for the dementia is thought to be extremely high. Controls were selected to be age-and sex-matched (Table had no evidence of cognitive dysfunction, i.e.

their CAMCOG scores were over 79/10827, complained of no memory problems, and did not have the combination of a minimum medial temporal lobe width on CT of less than the fifth centile for controls of the same age with a moderate 6 WO 99/24830 PCT/US98/23198 or greater parietotemporal perfusion deficit on SPET.

Subjects recruited as part of OPTIMA were 14 patients with dementia of the Alzheimer type and 14 non-demented age- and sex-matched controls (details in Table each experiment was performed on 11 or 12 of these individuals.

Platelet perfusion 1 7 Blood was drawn by venepuncture and anticoagulated with acid-citratedextrose (ACD). Platelets were prepared by centrifugation within an hour of venesection and incubated with 86 Rb+ for 2 h. The platelet suspension (2.5 x 107 platelets per ml) was then injected into perfusion chambers, where the cells settled and became immobilized on inert filters (Millipore). The platelets were then continuously perfused with Krebs solution, to allow them to stabilize for 20 min before the start of each experiment. The perfusion buffer was then changed for 5 min to Krebs solution containing thrombin (0.3 IU/ml) or ionomycin (1 pM), after which the perfusion was switched to the original solution and continued for another 20 min. From 0 to 10 min after the addition of thrombin or ionomycin the perfusate was collected at 1-min intervals and thereafter at 2-min intervals. The solutions used for perfusion were bubbled with 95% 02 and 5% CO 2 throughout the experiment (pH At the end of the experiment the polycarbonate filters were retrieved and placed in scintillation vials, to which 3.5 ml of Aquasafe 500 scintillation fluid was added. The radioactivity in the perfusates and filters was determined by liquid scintillation counting in a Beckmann LS 6000 SE counter and the loss of radioactivity from the cells was calculated.

The amount of 86 Rb+ (pmol) in each fraction of perfusate collected was determined using the specific activity of the isotope. The radioactivity was measured in each fraction and the results were plotted as the cumulative efflux of 86 Rb+ against time.

Buffers and drugs. ACD contained citric acid (15 g trisodium citrate (25 and dextrose (20 g) in 1 1 of distilled water. Krebs buffer contained (mmol/l): NaCl 7 WO 99/24830 PCT/US98/23198 (119); KC1 CaCl2 NaH 2 PO4 MgC12 NaHCO 3 and glucose Apamin, charybdotoxin, adendrotoxin, iberiotoxin, ionomycin, and human thrombin were purchased from Sigma Chemical Company, Poole, Dorset.

8 6 RbCl was purchased from Amersham International plc (Amersham, Bucks).

Thrombin and ionomycin. Solutions of thrombin were prepared freshly in distilled water for each experiment and further diluted to a concentration of 0.3 IU/ml in Krebs solution. Stock solutions of ionomycin (10 mM in dimethylsulphoxide) were prepared and stored in aliquots at 4 0 C. On the day of the experiment ionomycin was further diluted in Krebs solution to a concentration of 1 pM.

Apamin, charvbdotoxin, iberiotoxin, and adendrotoxin. Apamin, charybdotoxin, iberiotoxin, and adendrotoxin were freshly prepared for each experiment.

Apamin, (100 nM), charybdotoxin (300 nM), iberiotoxin (300 nM), and a-dendrotoxin (200 nM) were reconstituted in distilled water and stored in aliquots at -20 0 C. On the day of the experiment the toxins were further diluted in Krebs solution. Apamin was pre-incubated with the platelets (added at time -20 min) and charybdotoxin, iberiotoxin,, and a-dendrotoxin were added with thrombin (at 0 min) for a period of 5 min.

Data presentation and analysis. The results in Figures 1-3 are shown as cumulative effluxes of 86 Rb+ from 0 to 14 min. The data are shown as means SEMs (n number of experiments with platelets obtained from different volunteers). The efflux data were analyzed using analysis of variance with repeated measures.

K± channel fluxes. Platelets were prepared and their K+ channel fluxes studied as described by DeSilva, H.A. et a1 17 by loading fresh platelets with 8 6Rb+ (used as a radioactive analogue of K 18 19 and stimulating 86 Rb+ efflux with thrombin and ionomycin. It has already been shown that thrombin and ionomycin stimulate 86 Rb+ efflux from platelets via K+ channels, and that the efflux occurs 8 WO 99/24830 PCT/S98/23198 via KCa channels, sensitive to the highly selective inhibitors apamin and charybdotoxin small-conductance calcium-dependent, SKca, channels and charybdotoxinsensitive, Kch, channels), and via voltage-gated (Ky) channels, sensitive to a-dendrotoxin 2 0 2 1 Uptake of rubidium by platelets. The uptake of 86 Rb+ by the platelets was the same in both groups (not shown).

Since over 90% of this uptake in platelets is inhibitable by ouabain and attributable to the sodium/potassium pump (de Silva Aronson, unpublished observations), this result suggests that the sodium/potassium pump functions normally in AD.

Non-stimulated 86Rb- efflux. Non-stimulated cumulative 8 6Rb+ efflux was linear with time (open circles; Figures 1-3) and did not differ between AD patients and controls. This efflux is partly mediated by the Na+/K /2C1- co-transport system 1 7 Thrombin-stimulated .86Rb efflux. Figures la and lb show the effects of apamin and charybdotoxin on thrombinstimulated 8 6Rb+ efflux. Figure la relates to Control subjects, and shows that thrombin 0.3 IU/ml (4-filled circles) increased 86 Rb efflux over the non-stimulated efflux (1-open circles). Apamin 100 nM (3-open squares) and charybdotoxin 300 nM (2-open triangles) inhibited the stimulated 86 Rb+ efflux (n=ll; P <0.0001).

Figure lb relates to patients with Alzheimer's disease and shows that thrombin 0.3 IU/ml (4-filled circles) increased 86Rb+ efflux over the non-stimulated efflux (1-open circles) to the same extent as in controls (P 0.996). Apamin 100 nM (3-open squares) and charybdotoxin 300 nM (2-open triangles) had no significant effect on the stimulated 86 Rb+ efflux (n=12; P 0.941).

Figures 2a and 2b show the effect of a-dendrotoxin on thrombin-stimulated 86Rb+ efflux. Figure 2a relates to Control subiects and shows that thrombin 0.3 IU/ml (filled circles) increased 8 6 Rb+ efflux over the non-stimulated 9 WO 99/24830 PCT/US98/23198 ef flux (open circles). a-dendrotoxin 200 nM (open triangles) inhibited the thrombin-stimulated ef flux (n=ll; P <0.0001). Figure 2b relates to patients with Alzheimer's disease and shows that thrombin 0.3 IU/ml (filled circles) increased 86 Rb+ ef flux over the non-stimulated ef flux (open circles). a-dendrotoxin 200 nM (open triangles) inhibited the thrombin-stimulated efflux (n=12; P <0.0001).

Control subjects. In control subjects, thrombin stimulated an increase in 86 Rb+ efflux from platelets (Figures la and 2a). In 8 of 11 control subjects, apamin and charybdotoxin inhibited the thrombin-stimulated 86 Rb+ efflux by at least 18% and 16% respectively, while in the other three subjects these toxins had minimal effects (less than 10% inhibition). When the data from all the control subjects were pooled, both apamin and charybdotoxin caused significant reductions in 86 Rb+ efflux (Figures la; Table In addition, a-dendrotoxin inhibited thrombinstimulated 86 Rb+ efflux from the platelets of all the controls (Figure 2a; Table These results are similar to the effects of these toxins on thrombin-stimulated 8 6 Rb+ efflux in the platelets of young volunteers 20 21 and they confirm that there are SKca, Kch, and Kv channels in normal human platelets.

Alzheimer's disease. Thrombin also stimulated 86 Rb+ efflux from the platelets of 12 patients with AD (Figures lb and 2b), to the same extent as in controls (cf. Figures la and 2a with Figures lb and 2b). In contrast to the results in controls, apamin and charybdotoxin had minimal effects on thrombin-stimulated 86Rb+ efflux (less than inhibition) in 9 of 12 patients with AD, while in the other three patients each toxin inhibited the thrombin-stimulated efflux by at least 16%. When the data from all the patients with AD were pooled, neither apamin nor charybdotoxin caused significant reductions in 86 Rb efflux (Figure lb; Table In contrast, a-dendrotoxin inhibited the thrombin-stimulated 86 Rb+ efflux from the platelets of all the patients with AD (Figure 2b; Table 2).

10 WO 99/24830 PCT/US98/23198 Ionomvcin-stimulated 86Rb efflux.

Figures 3a and 3b show effect of apamin and charybdotoxin on ionomycin-stimulated 86 Rb+ efflux.

As seen in Figure 3a, Control subjects; Ionomycin 1 pM (5-filled circles) increased 86Rb+ efflux over the nonstimulated efflux (1-open circles). Apamin 100 nM (4-open squares) and charybdotoxin 300 nM (3-open triangles) inhibited the stimulated 86 Rb+ efflux (P <0.0001). Apamin and charybdotoxin combined (2-filled squares) inhibited the stimulated efflux more than either toxin alone (n=ll; P <0.0001).

As seen in Figure 3b, Alzheimer's disease; Ionomycin 1 pM (5-filled circles) stimulated 86Rb efflux over the non-stimulated efflux (1-open circles) to the same extent as in controls (P 0.960). Apamin 100 nM (4-open squares) and charybdotoxin 300 nM (3-open triangles), either alone or in combination (2-filled squares), had no significant effect on the stimulated 86 Rb+ efflux (n=ll; P 0.883).

Control subjects. In 9 of 11 control subjects, apamin and charybdotoxin inhibited the ionomycin-stimulated 86 Rb efflux by at least 18% and 22% respectively, while in two subjects these toxins had minimal effects (less than 12% inhibition). When the data from all the controls were pooled, both apamin and charybdotoxin caused significant reductions in 86 Rb+ efflux (Figure 3a; Table The two toxins combined had a greater effect than either toxin alone (Figure 3a; Table These results are similar to those seen in young volunteers 2 0 2 1 and they confirm the presence of SKca and Kch channels in human platelets.

Alzheimer's disease. Ionomycin also stimulated 86 Rb+ efflux from the platelets of 11 patients with AD (Figure 3b), to the same extent as in controls (cf. Figures 3a and 3b). However, apamin, charybdotoxin, and their combination had minimal effects on the ionomycin-stimulated 86 Rb efflux in 8 of 11 patients with AD (less than 12% inhibition). When the data from all the patients with AD 11 WO 99/24830 PCT/US98/23198 were pooled, apamin and charybdotoxin, either alone or in combination, had minimal effects on 86Rb+ efflux (Figure 3b; Table 2).

Although abnormalities of K* channels have been reported in AD in neural cells (reduced post-mortem binding of 125 I-apamin to hippocampal neurones 2 2 and in fibroblasts (absence of a 113 pS channel sensitive to tetraethylammonium 9 this study is the first to show functional abnormalities of K+ channels in the platelets of patients with AD. The 86 Rb+ effluxes in platelets in response to both thrombin and ionomycin were quantitatively normal in AD, and the thrombin-stimulated efflux showed normal sensitivity to inhibition with a-dendrotoxin, suggesting that the Kv channels are normal in platelets in AD. However, the lack of inhibition of both thrombinstimulated and ionomycin-stimulated effluxes by apamin and charybdotoxin suggests either that the SKca and Kch channels are not present in platelets in AD or, if they are present, that they are not sensitive to inhibition by these toxins.

If SKca and Kch channels are present in platelets in AD, but unresponsive to inhibition, that would be consistent with the observation that the binding of 125Iapamin is reduced in post-mortem hippocampal neurones in

AD

22 This might be due to a change in the structure of the binding sites of the inhibitors. Alternatively, it might be due to an abnormality of the specific interaction of calcium with the channels, since the efflux stimulated by ionomycin, which increases the intracellular concentration of calcium, was not inhibitable.

Furthermore, the Ky channels were not affected, suggesting that Kca channels are selectively impaired in AD.

Alternatively, SKca and Kch channels may not be present at all in AD. However, if that is so, then 86 Rb+ efflux must be occurring through other K channels, since the thrombin-stimulated and ionomycin-stimulated effluxes were quantitatively normal. However, normal human 12 WO 99/24830 PCT/US98/3198 platelets do not contain large-conductance calciumdependent (BKCa) channels 21 and iberiotoxin, a selective inhibitor of BKca channels, had no effect on ionomycinstimulated effluxes in platelets from any individual (Table while the only other type of K channel found in platelets, Ky channels 20 21 responded normally to adendrotoxin. These observations argue against upregulation of other normal channels in AD. On the other hand, metabolites of the beta-amyloid precursor protein (3-APP) are capable of de novo formation of K channels 23 that are insensitive to some inhibitorsl, and the 86Rb+ efflux detected in AD might be via such channels.

Absence or non-functionality of the Kca channels might also explain the observation 2 4 that platelets from patients with AD had a higher thrombin-stimulated rise in intracellular Ca 2 since that might represent an exaggerated attempt to switch on non-existent or nonfunctional channels.

The frequencies of alleles E2, E3, and E4 of the apolipoprotein E gene in the patients and controls are shown in Table 3. As expected, significantly more patients with AD had one or two e4 alleles. Nine of the 13 individuals (patients and controls) who had one or two £4 alleles had abnormalities of inhibition of Kca channels, compared with only five of the 15 who had no e4 alleles suggesting a link between the K 1 channel abnormalities and the presence of the E4 allele. No such relationship was found between the K+ channel abnormalities and either the E2 or the e3 allele.

In conclusion, there were abnormalities of inhibition of SKca and Kch channels in the platelets of patients with AD compared with matched controls. Thus, Kca channel abnormalities provide a marker for patients with

AD.

13 WO 99/24830 PCT/US98/23198 Table 1. Patient data. The data are given as mean There were no significant differences between the groups.

Alzheimer's disease Controls (n 14) (n 14) Measure Age (y) Sex (M/F) Systolic blood pressure (mmHg) Diastolic blood pressure (mmHg) Serum Sodium (mM) Serum potassium (mM) Serum Calcium (mM) Serum urea (M) Serum creatinine (pM) Blood glucose (mM) Platelet count (x10 9 /1) Haemoglobin (g/dl) Mean cell volume (fl) White cell count (x10 9 /1) Total serum cobalamins (ng/1) 67.1 (7.5) 9/5 154 (16) 90 (14) 139 (3) 3.9 (0.4) 2.43 (0.10) 5.7 (1.3) 104 (12) 5.9 (2.1) 233 (58) 13.9 (0.8) 89 (4) 6.9 (1.5) 270 (90) 67.9 (7.7) 140 81 (14) 139 (2) 4.0 (0.3) 2.32 (0.13) 6.3 (2.7) 103 (24) 5.6 (1.1) 233 (62) 14.2 (1.1) 90 6.5 315 (125) 14 WO 99/24830 WO 9924830PCTIUS98/23 198 Table 2. Inhibition of thrombin-stimulated and ionomycin- stimulated i.9-Rb-± eff luxes by anainn charvbdotoxin. ax-dendrotoxin. and iberiotoxin in platelets of p~atients with AD and acge- and sexmatched controls. Data are given as median (interquartile range) percentages. Statistical comparisons by rank sum tests.

Thrombin- stimulated 8 6 Rb+ efflux Inhibition in Inhibition in Alzheimer's Toxin controls M% disease M% P value Apaxnin 26 (20-27) 0 01 Charybdotoxin 22 (18-29) 0 <0.01 a-dendrotoxin 26 (20-29) 19 (18-27) N lonomycin- stimulated 8 6 Rb+ efflux Inhibition in Inhibition in Alzheimer's Toxin controls M% disease M% P value Apamin 30 (20-31) 1 (0-20) <0.01 charybdotoxin 28 (20-34) 4 (1-26) <0.01 Apamin Charybdotoxin 51 (34-52) 2 (0-40) <0.01 Iberiotoxin 2 0 NS 15 WO 99/24830 PCT/US98/23198 Table 3. Numbers of normal and abnormal results in patients and controls. An abnormal result was defined as less than 15% inhibition by apamin and charybdotoxin. Statistical comparisons were by chi-square test. For comparison the distributions of apolipoprotein E alleles in the two groups are also shown.

Alzheimer's P disease Controls value Agonist Thrombin No. with an 9 3 abnormal result <0.02* No. with a 3 8 normal result lonomycin No. with an 9 3 abnormal result =0.01* No. with a 2 8 normal result Apolipoprotein E allele frequencies E2/2 0 2 e2/3 1 0 £3/3 4 8 <0.03t E3/4 5 4 E4/4 4 0 *chi-squared test tchi-squared test for trend 16 WO 99/24830 PCT/US98/23198 References 1. Fraser, S.P. et al, Ionic effects of the Alzheimer's disease -amyloid precursor protein and its metabolic fragments. Trends Neurosci. 20, 67-72 (1997).

2. K. Atwal, Med. Res. Rev. 12, 6, 579; N.S. Cook, Trends Pharmacol. Sci. 9, 21 (1988).

3. J.J. Singer et al, Pflugers Archiv. 408, 98 (1987), I. Baro et al, Pfltigers Archiv. 414, Suppl. 1), S168 (1989); and F. Ahmed et al, Br. J. Pharmacol. 83, 227 (1984).

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R. Inoue et al, PflOgers Archiv. 406, 138 (1986).

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85, 3329 (1988).

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8b. Galvez et al, Purification and characterization of a unique, potent, peptidyl probe for the high conductance calcium-activated potassium channel from the venom of the scorpion Buthus tamulus, J. Biol. Chem. 1990; 265:11083-90.

9. Etcheberrigaray, R. et al, Potassium channel dysfunction in fibroblasts identifies patients with Alzheimer's disease. Proc. Natl. Acad. Sci. USA 90, 8209- 8213 (1993).

Etcheberrigaray, R. et al, Soluble P-amyloid induction of Alzheimer's phenotype for human fibroblast K channels. Science 264, 276-279 (1994).

11. Van Nostrand, W.E. et al, Protease nexin-II (amyloid beta-protein precursor): a platelet alpha granule protein. Science 248, 745-748 (1990).

17 WO 99/24830 PCT/US98/23198 12. Chen, et al, Platelets are the primary source of amyloid -peptide in human blood. Biochem. Biophys. Res.

Comm. 213, 96-103 (1995).

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14. American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders. 3rd Revised ed. Washington: American Psychiatric Association (1987).

Jobst, K.A. et al, Association of atrophy of the medial temporal lobe with reduced blood flow in the posterior parietotemporal cortex in patients with a clinical and pathological diagnosis of Alzheimer's disease.

J. Neurol. Neurosurg. Psychiatry 55, 190-194 (1992).

16. Jobst, K.A. et al, on behalf of OPTIMA.

Accurate prediction of confirmed Alzheimer's disease and the differential diagnosis of dementia: the use of 99 mTc- HMPAO SPET and X-ray CT in medial temporal lobe dementias.

Int. Psychogeriatr. In press (1997).

17. De Silva, H.A. et al, Effects of high external concentrations of potassium on 8 6 rubidium efflux in human platelets: evidence for Na /K+/2C1- co-transport. Clin.

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18. de Allie, F.A. et al, Characterization of Ca 2 activated 86 Rb fluxes in rat C6 glioma cells: a system for identifying novel IKca-channel toxins. Br. J. Pharmacol.

117, 479-487 (1996).

19. Andersson, T.G.L. et al, The efflux of 86 Rb+ and 3 H]5-HT from human platelets during continuous perfusion: effects of potassium-induced membrane depolarization and thrombin stimulation. Acta Physiol. Scand. 141, 421-428 (1991).

18 WO 99/24830 PCT/US98/23198 De Silva, H.A. et al, Evidence for calciumdependent (Kca) and voltage-dependent (Kv) potassium channels in human platelets. Pharmacologist 39, 57 (1997).

21. De Silva, H.A. et al, Pharmacological evidence of calcium-activated and voltage-gated potassium channels in human platelets. Clin. Sci. 1997,; 93:249-55.

22. Ikeda, M. et al, Selective reduction of 125 I]apamin binding sites in Alzheimer hippocampus: a quantitative autoradiographic study. Brain Res. 567, 51- 56 (1991).

23. Furukawa, K. et al, Activation of K channels and suppression of neuronal activity by secreted P-amyloid precursor protein. Nature 379, 74-78 (1996).

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19

Claims (13)

1. A method for diagnosing Alzheimer's disease, which comprises obtaining a sample of platelets from a human subject, and detecting the presence or absence of functioning calcium-dependent potassium (Kca) channels of specified slope conductance in such platelets, the absence of said functioning Kca channel indicating a positive diagnosis for Alzheimer's disease.

2. The method as defined in Claim 1 wherein the absence of said functioning Kca channel is indicated by lack of inhibition by a potassium channel blocker which has the ability to block the functioning Kca channel. The method as defined in Claim 2 wherein the potassium channel blocker is apamin or charybdotoxin or a S 15 combination thereof.

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4. The method as defined in any one of Claims 1-3 wherein the presence or absence of the calcium-dependent potassium channel is determined by loading blood platelets with 86 Rb+, stimulating 8 6 Rb+ efflux (from the platelets via 20 Kca channels) with thrombin or ionomycin, subjecting the thrombin- or ionomycin-stimulated 86 Rb+ efflux to the action of a.potassium channel blocker, and determining if the potassium channel blocker significantly inhibits the thrombin- or ionomycin-stimulated 86 Rb+ efflux to cause 25 significant reductions in the 86 Rb+ efflux, a lack of significant inhibition and significant reduction in the 86 Rb efflux indicating a positive diagnosis for Alzheimer's disease.

A method for diagnosing Alzheimer's disease, which comprises detecting the presence or absence of one or more functioning small-conductance calcium-dependent potassium (SKca) channels in blood platelets of a human subject, the absence of a functioning SKCa channel in such platelets indicating a positive diagnosis for Alzheimer's disease. 20 WO 99/24830 PCT/US98/23198

6. The method as defined in Claim 5 wherein the absence of a functioning SKca channel is indicated by lack of significant inhibition by a SKca channel blocker which has the ability to block the functioning SKca channel.

7. The method as defined in Claim 6 wherein the potassium channel blocker is apamin.

8. The method as defined in Claim 6 wherein the potassium channel blocker is a combination of apamin and charybdotoxin.

9. The method as defined in any one of Claims 5-8 wherein the presence or absence of the SKca channel is determined by loading blood platelets with 8 6 Rb+, stimulating 8 6 Rb+ efflux (from the platelets via Kca channels) with thrombin or ionomycin, subjecting the thrombin- or S 15 ionomycin-stimulated 86 Rb efflux to the action of a SKca :channel blocker, and determining if the SKca channel blocker significantly inhibits the thrombin- or ionomycin- stimulated 86Rb+ efflux to cause significant reductions in the 86 Rb+ efflux, a lack of significant inhibition and significant reduction in the 86 Rb+ efflux indicating a positive diagnosis for Alzheimer's disease.

A method for diagnosing Alzheimer's disease, which comprises detecting the presence or absence of a functioning charybdotoxin-sensitive potassium (Kch) channel 25 in blood platelets of a human subject, the absence of a functioning Kch channel in such platelets indicating a positive diagnosis for Alzheimer's disease.

11. The method as defined in Claim 10 wherein the absence of a functioning Kch channel is indicated by lack of significant inhibition by charybdotoxin which has the ability to block the functioning Kch channel.

12. The method as defined in Claim 10 wherein the absence of a functioning Kch channel is indicated by lack of significant inhibition by a combination of charybdotoxin and apamin. 21 WO 99/24830 PCT/US98/23198

13. The method as defined in any one of Claims 10-12 wherein the presence or absence of the charybdotoxin-sensitive channel is determined by loading blood platelets with 86Rb+, stimulating 86 Rb efflux (from the platelets via Kca channels) with thrombin or ionomycin, subjecting the thrombin- or ionomycin-stimulated 8 6 Rb+ efflux to the action of a Kch channel blocker, and determining if the Kch channel blocker significantly inhibits the thrombin- or ionomycin-stimulated 86 Rb+ efflux to cause significant reductions in the 86Rb+ efflux, a lack of significant inhibition and significant reduction in the 8 6 Rb+ efflux indicating a positive diagnosis for Alzheimer's disease. 22