Use of Disulfiram to Prevent Cardiovascular Damage

This invention is in the field of drugs, pharmacology, and neurology. It relates to drugs that can protect the nervous and cardiovascular systems against conditions such as ischemia and hypoxia.

Ischemia refers to a condition of inadequate blood supply to an internal organ or portion of an organ. This condition is encountered during events such as stroke, heart attack, cardiac arrest, injury or trauma, shock, and internal hemorrhaging due to rupture of an aneurysm. Hypoxia refers to a state of inadequate oxygen supply to an organ. Hypoxia and ischemia are closely related, since ischemia will lead directly to hypoxia. However, they can also occur separately; for example, hypoxia can occur despite normal blood flow in conditions such as anemia, carbon monoxide poisoning, drowning, suffocation, or asphyxia.

Ischemia and hypoxia can lead to severe and permanent damage to the brain and central nervous system (CNS), even when they last only a few minutes. They are often fatal, and even when not, they can lead to widespread cell death in the central nervous system (CNS) causing crippling and irreversible damage such as paralysis, loss of speech or memory, and other effects that are physically, emotionally, and financially devastating.

In addition, "peripheral" hypoxia and/or ischemia can occur sympathetic and parasympathetic nervous systems, and in tissue where blood flow is blocked or hindered by processes such as phlebitis, blood clots, shock, or loss of blood due to injury or hemorrhage.

Hypoxic/ischemic damage does not stop during "reperfusion," when oxygen or blood flow are restored to an organ or region of the brain; instead, the damage often increases sharply when oxygen is reintroduced after an anoxic period. During anoxia, certain metabolites and enzymes can accumulate which, when the anoxia ends, convert oxygen into a highly reactive free radical known as superoxide (O.sub.2.sup.-). Superoxide can attack any molecule, and it also promotes the release of iron ions from ferritin, which in turn promotes a process called "lipid peroxidation" which destroys cell membranes, as discussed in more detail below.

For more information on the cellular and molecular mechanisms involved in damage caused by hypoxia and/or ischemia, and on the various pharmaceutical approaches that are being studied in the hope of developing effective treatments for stroke, cardiac arrest, and other hypoxic or ischemic events, see Krause et al 1988. For additional background information on the structure, functioning, and biochemistry of the central and peripheral nervous systems, see Adelman 1987.

To date, to the best of the Applicant's knowledge, no other researchers studying drugs that are useful for preventing damage due to stroke or other hypoxic/ischemic events have published any reports discussing a drug called "disulfiram."

Disulfiram is a common name for tetraethylthiuram disulfide. The chemical structure is as follows: ##STR1## By itself, disulfiram is relatively nontoxic; most people are completely unaffected by disulfiram when it is administered alone. However, when disulfiram is administered in conjunction with ethyl alcohol (the form of alcohol found in intoxicating beverages), it causes severe adverse reactions, including severe headaches, nausea, vomiting, sweating, thirst, weakness, and low blood pressure. Therefore, it is widely used under the trademark "Antabuse" to help treat chronic alcoholism. After an alcoholic swallows a tablet of disulfiram, it persists in the blood for several days, and the alcoholic knows that if he or she drinks alcohol during those days, he or she will become severely ill. This helps alcoholics increase their resolve not to drink alcohol.

On a molecular level, disulfiram is believed to perform this function primarily by blocking the metabolism of acetaldehyde. When people drink alcohol, acetaldehyde is formed as a product of alcohol metabolism in the body. Acetaldehyde is toxic and causes symptoms which can become severe if the acetaldehyde accumulates to significant concentrations. In most people, this doesn't occur, since acetaldehyde is quickly converted into other compounds by enzymes such as aldehyde dehydrogenase (ALDH). However, in alcoholics who are treated with disulfiram, the disulfiram blocks the activity of the ALDH enzyme. This causes acetaldehyde to accumulate to levels that cause severe adverse effects.

Disulfiram also causes various other effects, some of which are difficult to precisely identify and quantify. For example, direct injection of acetaldehyde into animals usually causes an increase in blood pressure; however, administration of disulfiram in conjunction with alcohol causes a drop in blood pressure, for reasons that are not entirely understood. It is suspected that disulfiram might deactivate dopamine-beta-hydroxylase (DBH), an enzyme that is involved in the synthesis of epinephrine (adrenalin) in sympathetic nerve terminals.

Disulfiram also is known to form chemical complexes with certain metal ions, especially copper and iron. This chelating effect make the metal ions unavailable for other metabolic functions. Since a wide variety of enzymes and other proteins require metal ions for activity, this can cause various effects that are difficult to quantify and can vary between different individuals.

In addition, U.S. Pat. Nos. 4,870,101 and 5,011,857 (Ku et al, 1989 and 1991) indicate that disulfiram and certain other anti-oxidants can suppress the release of interleukin-1, a natural hormone that can aggravate inflammation in various conditions such as rheumatoid arthritis and psoriasis.

Although disulfiram is normally administered in oral form (usually 250 mg tablets or capsules), U.S. Pat. No. 4,687,809 (Phillips 1987) describes a slow-release injectable formulation. By mixing disulfiram with a biodegradable polymer, or by forming a slurry of disulfiram (which is very insoluble in water) in aqueous saline solution, substantial concentrations of disulfiram in blood serum can be maintained for periods up to about 90 days. Injection of a slow-release formulation can overcome the failure or refusal of many chronic alcoholics to diligently take disulfiram each day.

For more information on the chemistry and clinical use of disulfiram, see Banys 1988 (a review article) and the various articles cited therein.

As mentioned above, the Applicant is not aware of any prior publications which suggest that disulfiram could or would be useful to treat hypoxic and/or ischemic damage. Similarly, the Applicant is not aware of any prior publications which suggest that disulfiram could or would be useful to prevent the damage caused by progressive neurodegenerative diseases such as Alzheimer's, Parkinson's, or Huntington's disease or amyotrophic lateral sclerosis (ALS, also called Lou Gehrig's disease or motoneuron disease).

Accordingly, one object of this invention is to disclose that disulfiram can be useful in treating patients suffering from stroke, heart attack, and other conditions which generate hypoxia and/or ischemia, either inside the brain or in other parts of the body such as the heart.

Another object of this invention is to provide an effective treatment to minimize the damage caused by stroke, heart attack, cardiac arrest, and other conditions involving hypoxia and/or ischemia, using a drug that has already been extensively tested and widely used, which has few adverse side effects.

A third object of this invention is to disclose a treatment which can help reduce some of the oxidative, excitotoxic, and other damaging processes that are involved in some neurodegenerative diseases.

This invention discloses a method of reducing neurologic and cardiovascular damage in the mammalian body, caused by hypoxic or ischemic events or conditions such as stroke, heart attack, cardiac arrest, hemorrhage, drowning or suffocation, blood clots, or blood loss due to injury. This method involves the administration of disulfiram, or a suitable salt or analog of disulfiram, to a susceptible person or animal in need of such treatment. Disulfiram can perform at least three functions which are useful in reducing neurologic damage: (1) it can inhibit enzymes such as xanthine oxidase which would otherwise generate oxygenated free radicals, which are highly reactive chemical compounds that non-specifically attack and damage essential molecules and cells; (2) it can chelate copper and iron, thereby suppressing lipid peroxidation and protecting cell membranes from destruction; (3) it generates metabolites such as tryptophol, which can reduce the rate of metabolic activity in neurons and affected tissue, which can be useful during cytotoxic events.

This invention relates to a method of reducing or preventing damage in the mammalian body by means of administering disulfiram (or a pharmaceutically acceptable analog thereof which functions in a similar manner) to a person or animal suffering from a hypoxic or ischemic event or condition such as stroke, cardiac arrest, heart attack, or hemorrhage.

One useful effect of disulfiram involves suppressing the formation of oxygenated free radicals. In chemical terminology, a free radical is an atom or molecule with an unpaired electron. Except in certain very limited situations that are not relevant here, oxygen-containing free radicals are extremely reactive, and they will non-specifically attack nearly any type of molecule they encounter inside the body.

One of the most important enzymes involved in the generation of oxidative free radicals under ischemic conditions is xanthine oxidase. This enzyme usually exists in a form known as the "D" form, which is often called xanthine dehydrogenase. The D form is involved in the degradation of adenosine triphosphate through two intermediate metabolites (hypoxanthine and xanthine) into uric acid, which is secreted and eliminated from the body in urine. The metabolic steps involving xanthine dehydrogenase generate water as a byproduct.

However, under ischemic conditions, the D form of xanthine dehydrogenase is converted into a different form known as xanthine oxidase (also known as the "O" form) which generates highly reactive superoxide (O.sub.2.sup.-) free radicals (instead of water) as the byproduct when adenosine is degraded into uric acid. The superoxide radicals created by xanthine oxidase cause major damage to ischemic or hypoxic cells and tissue. By inhibiting the activity of xanthine oxidase (and possibly other oxidative enzymes as well), disulfiram can suppress the formation of oxygenated free radicals. This will reduce the amount of damage caused by the oxidative free radicals.

A second benefit that can arise when disulfiram is used as a cytoprotective agent involves the chelation of copper and iron. Iron ions are normally coupled to various proteins such as ferritin (a storage protein) and transferrin (a transport protein). When superoxide is present (which can occur under ischemic conditions, as discussed above), ferric ions (Fe.sup.3+) stored inside ferritin are converted into ferrous ions (Fe.sup.2+), which are released from the ferritin. These ions can catalyze a process called lipid peroxidation, a complex process involving lipid hydroperoxides and lipid peroxyl free radicals. In this process, lipids (which are the partly polar, partly non-polar molecules that form cell membranes) are attacked, and the double bonds in the fatty acid side chains are altered, which destroys the ability of the lipids to function as the structural components of cell membranes. Lipid peroxidation is a chain reaction; the molecules that destroy lipids are not inactivated or bound up by the reaction, so a single such molecule can destroy thousands of lipid molecules until something stops the process.

Transition metals such as iron or copper can act as catalysts for lipid peroxidation; the peroxidation process does not occur in the absence of transition metals, and it can be inhibited by agents which chelate (i.e., which chemically tie up and inactivate) transition metals. Therefore, in mammals that are treated with disulfiram as a cytoprotective agent, the disulfiram, which chelates and thereby inactivates iron and copper, will suppress lipid peroxidation and reduce lipid peroxidation damage to cell membranes.

In addition to these beneficial effects, disulfiram may also have various other beneficial effects when used to treat hypoxia/ischemia. For example, when administered to mammals, disulfiram induces the biosynthesis of a compound known as tryptophol (also called 3-indole ethanol). This compound reduces the rate of glucose utilization and other metabolic activity in neurons, and can reduce body temperature (Cornford et al 1981). When treating someone suffering from hypoxia or ischemia, the suppression of metabolic activity and temperature can be very useful, since it can delay the onset of neuronal damage. This can provide additional time for the neurons to try to reestablish homeostasis and proper metabolic functioning; it can also provide additional time for the introduction of additional drug treatments, such as blood clot dissolving agents or drugs that suppress excitotoxic activity mediated by neuronal receptors.

For all of these reasons, disulfiram can help prevent or reduce neurologic damage when used to treat ischemia and hypoxia.

An important aspect of this invention is that disulfiram has already been extensively tested and widely used to treat chronic alcoholism. It has no adverse side effects in most people, and the side effects that occasionally occur in some patients are usually mild if the patient does not also consume alcohol. In the words of Banys 1988, "Disulfiram is remarkably safe and well tolerated in the 250 mg per day recommended dosage."

The preferred mode of administration of disulfiram for use to treat stroke, heart attack, cardiac arrest, and other catastrophic events involves parenteral injection (preferably intravenous injection) to achieve rapid delivery to the affected organs. To the best of the Applicant's knowledge, the only prior method of injecting disulfiram involves slow-release formulations described in U.S. Pat. No. 4,678,809 (Phillips 1987). Those slow-release formulations release disulfiram into the circulating blood over a span of at least 30 and up to 90 days, which is useful for treating chronic alcoholics who might fail to take disulfiram tablets regularly. Clearly, a slow-release formulation would not be suitable for rapid delivery of disulfiram to reduce the catastrophic damage of a stroke, cardiac arrest, or hemorrhaging aneurysm.

Accordingly, one aspect of the subject invention comprises a rapid-release injectable formulation. As used herein, "rapid release" and "rapid diffusion into circulating blood" refer to the release of a substantial fraction (such as about 20% or more) of the disulfiram contained in a formulation, within a short span of time (such as an hour or less) after the formulation is injected into the bloodstream. One type of suitable rapid-release carrier liquid contains water mixed with a soluble or miscible organic compound which has a plurality of hydroxyl groups, such as propylene glycol, in roughly 1:1 proportions, which also contains a suitable quantity (such as about 5%) of a buffer, such as mixture of a carboxylic acid and a salt thereof (such as benzoic acid and sodium benzoate). Such carrier liquids are used to inject various other hydrophobic compounds, such as diazepam (Valium).

If desired, a rapid-release injection of disulfiram can be supplemented by a slow-release injection and/or oral administration, to maintain desired concentrations over a prolonged period of time.

Various salts or analogs of disulfiram may also be used, provided that (1) they must be pharmaceutically acceptable, and (2) they must be therapeutically effective when used as described herein. In general, a salt or analog can be presumed to have beneficial therapeutic effects if it can chelate iron or copper ions or inhibit the enzymatic activity of xanthine oxidase, which can be determined using in vitro screening tests. Salts or analogs which function in a desirable manner in in vitro screening tests can be tested for physiological acceptability and therapeutic effectiveness using in vivo tests using laboratory animals such as rodents. For example, surgical interventions which temporarily shut off blood supply to the brain or heart of a lab animal are widely used for research involving methods of treating stroke or heart attack and various convulsant and other drugs are used to cause oxidative or excitotoxic damage in the brain or to model neurodegenerative diseases such as Parkinson's disease. Such procedures and compounds are well known to those skilled in the art, and they can be used to test salts and analogs of disulfiram for therapeutic effectiveness.

In addition to the use of disulfiram to prevent hypoxic ischemic damage, it also appears that disulfiram, due to its ability to inhibit oxidative enzymes and chelate metal ions that promote lipid peroxidation, can also reduce some of the damage which occurs in at least some progressive neurodegenerative diseases, such as Parkinson's disease, Alzheimer's disease, Huntington's disease, and ALS. Destructive oxidative processes are believed to be involved in Parkinson's and Alzheimer's disease, and certain other activities such as excitotoxicity (which involves neural over-excitation and excessive neurotransmitter activity), which can be triggered by hypoxic or ischemic conditions, are also believed to occur in Parkinson's and Alzehimer's disease (Sonsalla et al 1989; Tanner 1989; Maragos et al 1987). Since some of the damaging processes involved in hypoxia/ischemia are also implicated in various neurodegenerative diseases, it appears that disulfiram may be useful in helping to reduce or delay the damage caused by at least some progressive neurodegenerative diseases.

In long-term use for purposes such as slowing or preventing the progression and damage of a degenerative disease, oral ingestion of 125 or 250 mg disulfiram tablets or capsules is the preferred method of administration.

Another aspect of this invention involves the joint administration of disulfiram and a second active agent which normally is degraded by oxidation enzymes. As an example, various drugs are referred to as NMDA antagonists, since they suppress excitatory activity at the NMDA (N-methyl-D-aspartate) class of receptors on the surfaces of neurons. NMDA antagonists are promising therapeutic agents that can reduce hypoxic and ischemic damage; see, e.g., U.S. Pat. Nos. 4,888,347 (Woodruff et al 1989) and 5,034,400 (Olney 1991). However, at least some NMDA antagonists such as dextromethorphan are rapidly degraded by oxidative enzymes such as cytochrome P-450. By reducing the rate at which other therapetuic drugs such as NMDA antagonists are degraded by oxidative enzymes, disulfiram administered in conjunction with such other drugs can function as an anti-oxidant to sustain desirable concentrations of the other drugs in the blood for longer periods of time, while also exerting its own neuroprotective effects.

Thus there has been shown and described a new method of using disulfiram as a cytoprotective agent. It will be apparent to those skilled in the art that various changes and modifications to the specific embodiments described herein are possible. Such changes that do not depart from the spirit and scope of the invention are deemed to be covered by the invention, which is limited only by the claims that follow.

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Krause, G. S., et al, "Brain cell death following ischemia and reperfusion: a proposed biochemical sequence," Critical Care Medical 16(7): 714-726 (1988)

Maragos, W. F., et al, "Glutamate dysfunction in Alzeheimer's disease: An hypothesis," Trends in Neuroscience 10(2): 65-68 (1987)

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Tanner, C. M., "The role of environmental toxins in the etiology of Parkinson's disease," Trends in Neuroscience 12(2): 49-54 (1987)