EP0607125A1 - Composition for the treatment of alzheimer's disease and process for preparing the same - Google Patents

Abstract

The present invention relates to a pharmaceutical composition for the treatment of Alzheimer's disease. The composition comprises a synergistic mixture of physostigmine and 4-aminopyridine. The invention also relates to a process for preparing the above-mentioned compositions. In a method for the treatment of Alzheimer's disease according to the invention, patients are administered effective amounts of physostigmine as well as 4-aminopyridine.

Description

Composition for the treatment of Alzheimer's disease and process for preparing the same

TECHNICAL FIELD

The invention relates to a composition for the

treatment of Alzheimer's disease comprising the synergistic mixture of physostigmin and 4-amino-pyridin as active ingredient. Another object of the present invention is the preparation of the said pharmaceutical composition. A further object of the invention is a method for treating Alzheimer's disease.

BACKGROUND ART

Damages of cognitive functions, the adjustment to recognition of situations in everyday life in the old age is a frequent diagnosis of dementia. 15,5% of the population over 65 and 20% of those over 80 suffers from one of the forms of dementia. The Alzheimer's type of dementia has recently become of high professional interest as the disease is associated with elongation of average age and due to the great public interest thereto. Such an interest is obvious as dementia occurs in almost every family. This occurance, however, burdens the families both in .social (material) and emotional aspects. Contrary to the 10 billion in 1982 (Terry and Katzman) 34 billion dollars were spent for nursing patients suffering from any form of dementia in 1985. The number of people connected with the disease exceeded 2,5 million in 1985.

The Alzheimer's disease was described first by Alois Alzheimer, German neurologist, in 1906 as a presenile type of dementia. The patient, though only 51, showed the most serious symptoms of senile dementia. The deterioration of condition was very rapid and the patient died after a few days. After autopsy of brain Alzheimer described that the neurofibrils, which, under normal conditions, showed a coordinated, thread-like formation, appeared as an entangled bunch. These neurofibrillar bundles were described as

characteristic symptoms of the disease called as presenile dementia. Istvan Tariska (1965) summarized the neuropathological characteristics of the disease entity and called attention to certain symptoms thereof being diagnostically important to distinguish the Alzheimer's and Pick's diseases.

In the sixties, it became obvious that Alzheimer's disease appears not. only in presenium but also in the late old age and generally comprises a greater part of senile dementiae. The term: Senile dementia of Alzheimer type (SDAT) is generally used. According to this most modern theory, no difference is made between Alzheimer's disease and senile" dementiae, though this theory is sometimes disagreed. It has also been found that the disease entity is one of the most common symptoms. This turn-about is associated not only with the development of the neurological and psychiatric diagnostics, resp., but also the revolutionary development in the health care in the 20th century. This latter resulted in extension of human age, but on the other hand, led to an increase of social and clinical troubles of the old age.

It is well-known that presenile and senile dementia are clinically and pathologically similar. The Alzheimer's disease can appear at any age, however, it forms usually over 50. In case of a definite diagnosis the expected mean length of life is 7 years (McGeer and McGear, 1976).

The morphological symptoms of the disease appear in the area of neurocortex as well as that of the temporal, parietal and occipital cortex, but symptoms can also be found in amygdalin and hippocampus.

1. intraneurally situated neurofibrillar tangles,

essentially accumulations of cytosomal neurofilaments.

Tariska (1965) describes these as being situated diffusely in certain areas of the brain.

2. intraneiαronal granulovacuolar degenerations and 3. extraneuronal senile (neuritic) argentophylic plaques,

4. decrease of cerebral volume and neuron number (about 18%). Note, however, that the decrease in the neuron number is so high over an age of 80 that it is not characteristic for those suffering in Alzheimer's disease.

The functional symptoms of the disease are as follows:

1. Dementia

A characteris.tic of the memory disturbance, which is never functional, like in case of neuropaths and psychopaths, that it extends to all memory components. This disturbance can be interpreted by serious neurophysiological damages of organic origin. A characteristic symptom is presbiophrenia, the complete deterioration of memory: the patient does not remember the happenings of the previous day and even

repeatedly reading a text it appears to be novel. Storage of memory traces, turning of short-term memory to long-term memory, i.e. consolidation does not take place, and

accordingly, learning, obtaining new knowledge becomes impossible. The loss of manual memory necessary for activity leads to apraxia; e.g., sewing on a button or tieing a necktie forms an insoluble problem. The early dementia is characterized by the disappearance of the EEG alpha rythm. The late dementia, however, may be detected even by CT scanning. The emotional disturbances, fear and depression may also be attributed partly to frustrations caused by the forgetfulness.

2. Decline of intelligence

Another main group of symptoms of the disease is the rapid decline of intelligence, i.e. that of the standard of proper thinking and the corresponding suitable activity. The patient's mental field narrows down, broader contexts become immense, the patient adheres to details, cannot make

difference between essential and non-essential. Power of discernment, capability of abstraction and combination, as well as intuition also decline. Mental work is becoming more and more difficult, and in the advanced stage, even carrying out simple household activities gets impossible. Sometimes serious activity disordes appear: e.g. the patient gets up in the night and performs a series of unsuitable activities, turning down and again making the bed, sweeping, etc.

Orientation in time and space and the ability to determine the ego therein decline as well.

The patient becomes unable to follow the daily events, the verbal expression ability gets disturbed and later disphasial (Schneck et al, 1982), i.e., the loss of

intellectual functions becomes the most characteristic symptom. Subsequently, the patient becomes disoriented, apathy, the total insusceptibility to other's feelings, depression, paranoid reactions, hallucinations take place.

The patient mixes up the seasons and cannot use the calendar. Sometimes they even cannot recognize their own husband or wife and become totally impossible to social life. The disease is also called "double death" referring to the intellectual declining associated with a total physical decay.

The above symptoms may be associated with real

psychotic actions, like hallucinations, paranoid reactions, etc. Disturbances can also occur in the affective (emotional) field: the initial emotional lability turns into increasing depression and finally, the patient falls into total lethargy and apathy. All these result in a slow breakdown of the personality, and, even if somatically the patient is

sometimes in acceptable state, psychiatrically, the state is near to death. These psychiatric symptoms are followed by neurological ones, like incontinency, motor weakness,

extrapyramidal symptoms and spasms. Finally, the patiens completely looses the sensibility, the sense of thinking and communicating, and slowly becomes akinetic. The final cause of death is generally an intercurrent infection or other chronic disease (Schneck et al, 1982).

The Alzheimer ' s disease is very difficult to

distinguish from othe types of senile dementia. I.e., in the old age, dementia may be caused by a number of diseases, like arteriosclerosis, apoplexy, tumors, dipsomania, anaemia, undernutrition, thyroid insufficiency, etc. In these cases, mental deterioration is a secondary process; it is formed on basis of an other illness, and accordingly, treatment is equal to curing the original disease. The situation is same with the dementation symptoms of Parkinson's disease, paralytic progressiva and senile psychosis. After exclusion of the above symptoms, the Alzheimer's disease should be differentiated from the Kraepelin's disease and Pickatrophy occuring in the presenium, which, themselves are also primary dementiae. Differentiated diagnosis of both diseases is more or less possible by encephalography. If the presence of all the above diseases can be excluded, the diagnosis of Alzheimer's disease is probable. According to statistics, about 50% of the senile dementiae is of Alzheimer's type.

There are different theories about the origin of the disease:

1. Cholinerg theory

One of the best known and most important chemical impulse conducting materials is the acetylcholin which is released from the cholinerg neurons. The abnormal function of cholinerg system results in innumerous disease entities.

E.g., deficiencies in the cortical cholinerg neuron functions result in Alzheimer's disease and myasthenia gravis is probably in connection with a decreased cholinerg transmission of motor plate.

There are neurochemical proofs concerning the

connection between Alzheimer's disease and reduced function of cholinerg system. The activity of cholinacetyl-transferase (CAT), the enzyme responsible for acetylcholin synthesis, was significantly lower in biopsy material of brain and in nucleus basalis (Meynert's nucleus) of autopsy material

(Bowen et al, 1976) . Lower activities were also found in the hippocampus. Moreover, an inverse relationship was found between the frontal - but not pariental - CAT activity and the disease (Bowen et al, 1976, Rossor et al, 1984) .

Consequently, it is right to conclude that less acetylcholin is released in these cortical areas. The neural uptake of cholin is also reduced in Alzheimer's disease. The CAT activity is in inverse relationship with appearance of the senile plaques (Perry et al, 1979).

The cholinesterase (ChE) activity is also reduced. It has been established that there is a close correlation between the degree of dementia and the defective function of the cholinerg system (Perry et al, 1978) . It is thought that destruction of the Nissl-stained cells of the basal nucleus, as well as the number of plaques are in close correlation with the severity of the disease entity (Whitehouse et al, 1982). In histological experiments 70% of the nuclei showed degeneration. Though, Perry et al (1982) regarded the destruction of the cytosomes secondary only. The cholinerg feature of these cells was also proved immunocytochemically (Nagai et al, 1983).

The connection between the cortical cholinerg system (about 50-60% of nucleus basalis, 20-40 % of interneuronal origin) and Alzheimer's disease is proved by the observation that in Huntington's disease associated with dementia

cardinalis as clinical symptom, the CAT activity does not decrease. The binding ability of the cerebral muscarine receptors does not change: there is no difference in ³H-QNB (quinuclidyl benzylate) binding and affinity between brain tissues obtained from normal patients and those died in Alzheimer's disease. It is to be noted, however, that no decisive result could be expected from this measurement as only about 10% of the cerebral neurons is cholinerg and the muscarine receptor occurs on neurons of other type as well. Accordingly, a change in only 10% of the cortical neurons can result in a minimal change in the cholinerg system only, when taking all binding sites into consideration. Accordingly, data like glycolysis, CO₂ production, etc., obtained on the cortex and interpreted as a result of the modified function of the cholinerg fibers, are hard to accept. Of course, it holds true for the reverse, i.e., detection of no

modification would not mean that the function of cholinerg neurons is unchanged.

The cholinerg theory is supported by observations that symptoms of patients suffering from Alzheimer's disease are relieved by the ChE-inhibiting physostigmin, but aggravated by scopolamine, and there is a close correlation between the cortical CAT-activity (postmortem measurement) and the seriousness of dementia (Mountjoy et al, 1984). 2. Noradrenerσ theory

In Alzheimer's disease both the dopaminerg and noradrenerg pathes are injured. The DOPA-decarboxylase (DOPA-DC) activity is e.g. by 80% lower than on patients with

Parkinson's disease (Bowen and Davison, 1976), and of course, also the NA and dopamin content is lower (Gershon and Herman, 1982, Gottfries, 1985). The DA-content is by 60% lower in the hypothalamus. The inhibition of the DA metabolism is characterized by a lower homovanillic acid (HVA) level in these patients (Gottfries, 1985). Clinically detected

parkinsonian symptoms, occuring in 50% of the cases, can be explained by this phenomenon. 3. Gamma-aminobutyric acid

Mountjoy et al (1984) found that in humans, contrary to the data on rats, the cerebral GABA level does not change postmortem. No essential correlation was found between the GABA level in different cerebral areas and the neuropathological changes.

4. Other theories

The disease entity is also characterized, among other neurochemical modifications, by changes in the somatostatin and other neuropeptide content.

Different methods have been used in the treatment of the disease. Some of them are discussed herebelow:

1. Acetylcholin precursor therapy

To reduce the defective function of the cholinerg system, chollne, the precursor of ACh is added in high doses (16 g/day). Similarily, phosphatidyl choline is also

administered (25 to 100 g/day). Most of these treatments proved to be ineffective in "double blind" tests (Jones et al, 1983). Similar results were obtained by the treatment with deanol (Fishman et al, 1981), which is transformed to choline in the liver. Insufficiency of this treatments is supported by the fact that choline is present in the neurons in a great excess, and accordingly, deficiency seems to be unlikely. 2. Cholinesterase blocking

In this treatment decomposition of ACh is inhibited in the synaptic space to enhance the activity of ACh released in a decreased ratio. Davis et al (1982, 1983) observed interim improvement after treatment by cholinesterase blocking. In the experiments memory-tests were used. Physostigmin, 2,3,3a, 8-tetrahydro-l,3a, 8-trimethyl-pirrolo [ 2 , 3-b] indol-5-yl-methyl-carbamate , in a dosis of 6 x 2-2 , 5 mg/day proved to be optimal. Unfortunately, administration caused different side-effects (nausea, vomitus). According to other opinions, cholinesterase blocking improves memory disturbances in the first line (Mesulam et al, 1987).

Mohs et al (1985) and Hollander et al (1986) also showed improvement by the administration of physostigmin. According to the general opinion, however, the improvement is only transitional and provisional (Johns et al). Some

scientists are convinced of its inefficiency as beside the deficiencies in the cholinerg system likely other

neurochemical changes should also play an important role (Hardy et al, 1985). Formation of memory disturbancies are likely caused by other neurotransmittance systems as well.

Physostigmin was administered to patients suffering from Alzheimer's disease in a dosis of 1 to 1,5 mg/day (Davis et al , 1976, Goodnick and Gershon, 1984 ) and improvement of cognitive functions was observed. Accordingly, the reduced function of central noradrenerg, serotoninerg pathes was described. The formation of memory disturbances is likely promoted by other transmittance systems. Though physostigmin increases the ACh concentration in the synaptic space, the enhancing effect on the ACh release negative feedback

mechanism inhibits the former effect (Vizy et al, 1985). This negative feedback inhibition is effected through the

muscarine receptors, and accordingly, it can be suspended by atropin. Unfortunately, atropin inhibits the muscarine receptors also postsynaptically, and thus, though enhancing the cholinerg transmission by the presynaptic effect, this favourable effect is inhibited by the postsynaptic effect. This theory is supported by the literature describing chat administration of atropin damages learning ability and memory (Watts et al , 1981 ) , while the same are improved by the effect of physostigmin (Murray and Fibiger, 1985).

The efficiency of orally administered tetrahydro-amino-acidine (Tacrin, THA) is likely also associated with the cholinesterase blocking effect (Koopmans, Summers et al, Engl. J. Med., 315, 1241-1245 [1987]). Nilsson et al

(J.Neural Transm., 70, 357-368 [1987]) described that on cortex segments obtained from patients died in Alzheimer's disease both Tacrin and physostigmin enhanced the ACh

release. A critical evaluation is described in the April 1989 issue of the British Medical Journal [Lancet, 298. 845-846 (1989)]. Multicentric test of Tacrin in the USA, however, was suspended [Jarvik, L.F., Alzheimer's disease and Associated Disorders, 1, 123-127 (1987)] due to hepatoxic effect of the compound [Wilcock et al, Lancet 1305 (1988); Arnes et al, 887 (1988)].

Considering all the data obtained from biopsy tests from patients suffering from Alzheimer's disease, the

following information can be summarized:

1. ACh synthesis is under inhibition (Sims et al, 1980),

2. The number of M₂ muscarine receptors is reduced (Mash et al, 1985),

3. The choline-acetyltransferase activity is reduced.

4. Postmortem examination of patients died in Alzheimer's disease showed that the nucleus basalis (Meynert nucleus) had been damaged selectively (Whitehouse et al, 1981, Bowen et al, 1976).

These data lead to the conclusion that there is a causal connection between certain symptoms of Alzheimer's disease (cognitive disorders) and the deficit of the

cholinerg system [Lancet, 139-141 (1987); Cholinergic

treatment in Alzheimer's diseases: Encouraging results].

It has been found that the 4-aminopyridin (4-AP) increases the amount of acetylcholin released by stimulation (Vizy et al, 1977, Fδldes et al, 1988).

Wessling et al, New England Med.J. (1984) described that administration of 4-aminopyridin in Alzheimer's disease proved to be partially effective. Clinical administration of the compound had already been partially known in the

following indications: human botulism intoxication (Ball et al, 1979), therapy of sclerosis multiplex (Jones et al, 1983; Stefoski et al, 1987) and in ketamin-diazepin anesthesia antagonizing (Agoston et al, 1980). However, Davidson et al [Biol.Psychiatry, 23, 485-490 (1988)] found 4-AP in a daily dosis of 2,5 to 10 mg on patients aged 66 ± 10.6 to be ineffective.

DISCLOSURE OF THE INVENTION

The present invention aims to provide an improved therapy to eliminate the disadvantegous effects of the above treatments and to provide a pharmaceutical composition which results in an effective therapy by using reasonably low drug concentrations.

The present invention relates to a pharmaceutical composition which comprises the mixture of physostigmin and 4-aminopyridin as active ingredient. The composition does not possess the disadvantages caused by the negative feedback inhibition caused by the physostigmin and at the same time the total amount of the two components may be substantially lower than the effective amount of either the physostigmin or 4-aminopyridin when taken alone.

Neurochemical tests showed that the 4-aminopyridin, a K canal inhibitor, enhances the ACh release in the cortex

(Földes et al, 1988) and suspends the negative feedback inhibition, thus promoting ACh release.

Atropin also promotes ACh release as resulting in suspension of the negative feedback inhibition (see Table 1). In the presence of 4-AP which itself also has the same effect, atropin did not enhance ACh release to a higher level, i.e., the S2/S1 value did not raise. Accordingly, the negative feedback did not function in the presence of 4-AP. Similar results were obtained at the suspension of the inhibiting effect of oxotremorin in the presence of 4-AP (see Table 2). Oxotremorin is a compound stimulating the presynaptic muscarine receptors as well as inhibits ACh release.

BRIEF DESCRIPTION OF DRAWINGS

Fig 1 shows that 4-AP has a higher ACh release

increasing effect in the presence of a cholinesterase inhibitor (Physostigmin).

BEST MODE TO CARRY OUT THE INVENTION

The above phenomenon might be explained by blocking the negative feedback - which otherwise functions more

expressively in the presence of ChE-blocking [Vizi et al, J.Pharmac.Exp.Therapy, 230. 493-499 (1984)] - in the presence of 4-AP and consequently, the ACh release is further

promoted.

Accordingly, in the composition according to the present composition the physostigmin, which was inactive due to the enhanced negative feedback inhibition, i.e. destroyed its own good effect by the function of its own negative feedback inhibition, results in enhanced ACh release and prolonged effect. A substantially lower concentration of physostigmin and 4-aminopyridin is sufficient to re-establish the normal cholinerg transmission, i.e. to improve cognitive disturbances. Accordingly, at least the most difficult problem caused by Alzheimer's disease, i.e. the social breakdown of the patient can be improved, at least partly, by the treatment according to the invention. Davidson et al (1988) administered to patients

suffering from Alzheimer's disease aged 66.1 years average 4-aminopyridin for four days in a dosis of 5 to 20 mg/day, Wesselin et al (1984) used also an oral dosis of 20 mg/day to patients of 84.6 years average age. Physostigmin was used in 3x0.5 mg dosis by Davis et al (1978).

The composition of the present invention comprises the synergistic mixture of physostigmin and 4-amino-pyridin as active ingredient. The ratio of the components within the mixture may vary within a broad range, preferably it is 1:1 to 1:20. Of course, the above preferred ratio may be exceeded in both directions. The suitable weight ratio is 1:2 to 1;10, most preferably 1:5.

A preferred oral dosis unit contains e.g. 0,2 mg physostigmin and 1 mg 4-aminopyridin, the daily supply being suitably 3 dosis units.

The compositions can be prepared by methods well-known in the pharmaceutical industry, e.g. by mixing the two active components with usual formulation auxiliaries and forming the mixture into suitable dosis forms.

The invention also relates to the process for the treatment of Alzheimer's disease, wherein physostigmin and 4-amino-pyridin are added to the patient. Clinical tests showed that the following components and preferred doses should be used:

1. Physostigmin salycilicum (Ph.Hg. VII) preferred dosis: 3x0,2 mg p.os.

2. 4-aminopyridin (Pymadin, Pharmachim, Bulgaria), 3x1 mg p.os, preferably the two components being administered together.

If desired, the 4-aminopyridin dosis may be raised to 2 mg.

Clinical tests carried out on more than 200 patients showed that partial inhibition of K canal, by the effect of small dosis of 4-AP suspends negative feedback modulation of transmitter release, which, in turn, leads to an enhanced ACh and noradrenalin release, without the appearance of the characteristic side effects. Small dosis of physostigmin results in a partial cholinesterase inhibition, but due to the partial inhibition of the K canal the negative feedback, i.e. the self-inhibiting effect of the ACh on the release is eliminated. This effect is clearly shown on Fig 1.

Table 1

Rat frontal cortex, ³H-ACh release in the presence of physostigmin

Additive S₂/S₁ no 0.83 ± 0.05

Atropin 0.5 μM 1.64 ± 0.07

4-aminopyridin 40 μ M 2.36 ± 0.13 4-aminopyridin, 40 μM +

Atropin, 0.5 μM 2.52 ± 0.16

Table 2

Rat frontal cortex, ³H-ACh release Additive S₂/S₁ no 0.85 ± 0.07 oxotremorin, 0.3 μM 0.48 ± 0.03 oxotremorin, 3.0 μM 0.22 ± 0.02

4-aminopyridin, 40 μM 1.53 ± 0.10

4-aminopyridin, 40 μM +

oxotremorin, 0.3 μM 1.47 ± 0.12

4-aminopyridin, 40 μM +

oxotremorin, 3.0 μM 1.42 ± 0.11

Note: 4-aminopyridin inhibited the ³H-ACh release inhibiting effect of oxotremorin.

Claims

1. Pharmaceutical composition for the treatment of Alzheimer's disease characterized by containing a synergistic mixture of physostigmin and 4-aminopyridin as active

ingredient.

2. The composition of claim 1 characterized in that the weight ratio of physostigmin to 4-aminopyridin is 1:1 to 1:20.

3. The composition of 1 or 2 characterized in that the weight ratio of the physostigmin to 4-aminopyridin is 1:5.

4. Process for preparing a pharmaceutical composition against Alzheimer's disease characterized by mixing a

synergistic mixture of physostigmin and 4-aminopyridin with pharmaceutically acceptable carriers.

5. Method for treating Alzheimer's disease

characterized by administering to the patient an effective amount of physostigmin and 4-aminopyridin.

6. The method of claim 5 characterized by using the physostigmin in a dosis of 0,4-0,5 mg/day and the 4-aminopyridin in a dosis of 2-4 mg/day.