Testimony of

Beatrice Alexandra Golomb, M.D., Ph.D.

C. Ross Anthony, Ph.D.

RAND

Before The Subcommittee on Health, and

The Subcommittee on Oversight

Committee on Veteran’s Affairs

U.S. House of Representatives

 November 16, 1999

 

Mr. Chairman and distinguished Members of the Subcommittees, it is a pleasure for us to address you today on RAND’s review of the scientific literature as it pertains to pyridostigmine bromide (PB) and illnesses among Gulf War veterans. RAND is a nonprofit institution that helps improve policy and decision making through research and analysis. At RAND I am the Director of the Center for Military Health Policy Research and Co-Leader of this project. I am joined today by Dr. Beatrice Golomb, who prepared this exhaustive new PB study. Dr. Golomb, a RAND consultant, is a physician who also has a Ph.D. in biology specializing in neurobiology. She is a staff physician at the San Diego VA Medical Center, an Assistant Professor of Medicine at the U.C. San Diego, and a Research Associate Professor in the University of Southern California’s Psychology Department. This statement is based on a variety of sources, including research conducted at RAND. However, the opinions and conclusions expressed are those of the author and should not be interpreted as representing those of RAND or any of the agencies or others sponsoring its research.

I would like to describe briefly the context for this study. Dr. Golomb will then summarize her research findings.

After the Office of the Special Assistant for Gulf War Illnesses (OSAGWI) was formed in late 1996, the Special Assistant determined that there were at least two key kinds of information that were needed in the office’s efforts to leave no stone unturned in looking into the possible causes of illness among Gulf War veterans. OSAGWI has extensively investigated what happened and what exposures occurred in the Gulf while RAND was asked to summarize the scientific literature on the health effects of possible causes of illness. It was hoped that combining these sources of information would produce a more complete understanding of illnesses among veterans.

The PB report is the fourth of eight literature reviews published by RAND to date. Literature reviews on the health effects of wartime stress, oil well fires, and depleted uranium were published previously; while reviews on chemical and biological warfare agents, pesticides, immunizations, and infectious diseases are to follow. The PB report differs from the other reviews to date, in that we are unable to rule out an agent as a possible contributing factor to illnesses among some veterans. As Dr. Golomb will explain, she exhaustively examined seven hypotheses and found enough supporting evidence that she was not able to dismiss PB as a potential contributing factor.

These findings must be interpreted carefully. Even if enough evidence is found that a hypothesis can not be rejected, this does not necessarily imply that the agent in question is a causal factor. It only means that, based on the available scientific evidence, the possibility cannot be dismissed. Also note that although this report has clear policy implications, RAND was not asked to and did not examine the policy issues related to PB and its use.

Dr. Golomb will now summarize her study for you.

PB Report Background

Mr. Chairman and Members of the Sub-Committees, over the past several years, I have looked extensively at the scientific information as it relates to pyridostigmine bromide.

As the Committee knows, pyridostigmine bromide was a drug taken during the Persian Gulf War by an estimated 250,000 U.S. troops as a pretreatment to protect against the nerve agent soman. PB was approved by the Food and Drug Administration in 1955 for treatment of myasthenia gravis, an autoimmune disease that affects the muscles, and it is also approved for certain post-anesthesia applications. During the Gulf War, it was designated an "investigational new drug" for pretreatment for soman and was supplied to U.S. forces under a FDA waiver of informed consent with the possibility of an Iraqi nerve agent attack in mind. Technically, PB is a "pretreatment adjunct"—a drug that must be taken before exposure to be effective but that only confers benefit if post-exposure treatments are given as well.

RAND was asked to perform a literature review to evaluate whether PB could plausibly be related to increased health symptoms experienced by Persian Gulf War (PGW) veterans. I examined over 10,000 titles, 6,000 abstracts, several thousand papers and reports, interviewed over 80 people, and reviewed dozens of declassified British studies and reports. This extensive review has resulted in the lengthy report before you, which includes more than 1,000 citations.

The literature review was used first to identify theories that might link PB to symptoms in ill PGW veterans, and then to assess the evidence pertaining to these theories. (In addition, the issue of efficacy of PB as a pretreatment for nerve agent was addressed, but will not be reviewed here due to time constraints.) A total of 7 theories were identified that pertain to a link between PB and health effects. Each has its own chapter in the report, but two are closely related and will be discussed together.

These theories fall roughly into two categories each containing three theories.

• The first group of theories describes possible mechanisms that may produce heightened individual susceptibility to effects of PB in some circumstances – so that some individuals might experience effects, including perhaps toxic effects, while others do not.

• The second group of theories describes ways that PB may actually lead to chronic symptoms, perhaps selectively in those with heightened susceptibility.

I will discuss each of these theories briefly.

Theories on Individual Susceptibility

Regarding theories of possible heightened susceptibility to PB, one theory proposes that there may be widespread individual differences in processing of PB. Indeed, our review found evidence of differences at many levels. First, the desired dose of PB was not taken by all the veterans in the approved manner; some took more and many took less. However, even supposing the same oral dose of PB, there are 7-fold differences in the resulting steady-state blood level of PB in humans. Moreover, for the same blood level of PB, there are many-fold differences in the percent of enzyme inhibition induced by PB; thus depending when after PB administration one looks, there may be up to 15 to 25 fold differences in enzyme inhibition for the same oral dose. Finally, for the same measured enzyme inhibition, there are widespread differences in clinical effects, including toxic effects of PB. These widespread differences in processing of PB from one individual to another could potentially lead to substantial differences in susceptibility to effects of PB, including chronic effects if any occur.

The second theory notes that whereas ordinarily most PB is excluded from entering the brain by what is termed the "blood brain barrier," which bars access of many substances, some of the recent evidence from animal studies suggests that quite a bit of PB may access the brain under some conditions, such as stress, heat, and chemical combinations. These are conditions to which some PGW veterans may have been exposed, thus increasing the chance for brain effects of PB to occur. In addition, there is literature that indicates PB itself may enhance access to the brain of normally excluded substances, such as infectious viruses.

A third theory notes that toxic effects of PB may be greatly enhanced, in some cases in a synergistic fashion, by concomitant exposure to other factors like pesticides and nerve agent, to which some veterans may have been exposed.

These three theories, which describe mechanisms by which some individuals may have increased susceptibility to effects of PB – due to differences in processing, differences in environmental exposures, or combinations of these – were all found to be viable (i.e. had enough supporting evidence that they could not be rejected).

 

Mechanisms Linking PB with Chronic Symptoms

Of the theories in this category, the literature allowed us to reject bromism (from accumulation of the bromide in PB) as a likely factor in illnesses in Gulf War veterans, and the literature was inadequate to seriously evaluate multiple chemical sensitivity.

The most important theory regarding mechanisms by which PB may lead to chronic illness – perhaps selectively in those with heightened susceptibility – suggests that PB may change regulation of a key nerve signaling chemical called "acetylcholine" (ACh). ACh is known to be vitally involved in regulating muscle action, pain, mood, memory, and sleep, domains that figure prominently in complaints of ill PGW veterans.

 

PB acts by blocking the enzyme that normally breaks down excess ACh. The consequence is increased, unregulated action by this nerve-signaling chemical. The body responds to this inappropriate increase in ACh action by putting into place mechanisms to suppress the excess ACh activity. Thus, signaling cells may reduce production and release of ACh, and may withdraw nerve terminals from receiving cells. Receiving cells may reduce the number of receptors to which ACh may bind, and reduce the affinity of these receptors for binding to the signaling chemical. And there may be increased breakdown of ACh.

Since these mechanisms designed to suppress ACh action occur in response to the excess ACh action induced by PB, one might expect that they would go away as PB is withdrawn. But in fact, existing evidence from studies in animals suggests that the timecourses of these effects differ widely from one another. Some are short lived, and are unlikely to explain chronic illness in PGW veterans. However other effects are long lasting or permanent, lasting in some instances as long after stopping PB as anyone has looked.

Could such long lasting or permanent changes in regulation of ACh action relate to chronic symptoms reported by PGW veterans? The answer is, we don’t know; much more needs to be understood about the specifics of these changes, and what their relation may be to clinical effects. However we do know that ACh is critical to regulation of muscle action, pain, memory, and sleep – domains that are disrupted in ill PGW veterans; thus it is plausible that chronic changes in regulation of ACh could produce symptoms of the types veterans report.

 

Conclusions

Three major conclusions emerged from the study:

• We can not rule out pyridostigmine bromide as a possible contributor to the increased health symptoms in some Gulf War veterans.

• Further research is needed to determine the effectiveness of the current dose of PB in protecting against soman.

• More research is needed to clarify the role, if any, of PB in chronic health effects in ill PGW veterans. Some research of this kind is already being funded by the DoD, VA, and HHS.

The issue now is the very complex one of trading off uncertain health risks – but risks now known to be biologically plausible – against uncertain gains from use of PB in the warfare setting.

Attachment:

Preface

This literature review, one of eight commissioned by the Special Assistant to the Deputy Secretary of Defense for Gulf War Illnesses, summarizes the existing scientific literature on the health effects of pyridostigmine bromide that may have affected service members who served in Operations Desert Shield and Desert Storm. The eight RAND reviews are intended to complement efforts by the Defense Department and other federal agencies as they attempt to understand the full range of health implications of service in that conflict.

While many veterans have reported an array of physical and mental health complaints since the war, it is not yet clear the extent to which veterans are experiencing either higher-than-expected rates of identifiable illnesses with known etiologies or any other illnesses from as yet unidentified origins.

The other seven RAND literature reviews deal with chemical and biological warfare agents, depleted uranium, pesticides, oil well fires, immunizations, infectious diseases, and stress. The topics of these reviews all represent plausible causes of some of the illnesses Gulf War veterans have reported.

These reviews are intended principally to summarize the scientific literature on the known health effects of given exposures to these risk factors. Where available evidence permits, the reviews also summarize what is known about the range of actual exposures in the Gulf and assess the plausibility of the risk factor at hand as a cause of illnesses. Statements related to the Gulf War experience should be regarded as suggestive rather than definitive, for much more research both on health effects and exposures remains to be completed before more definitive statements are made. Recommendations for additional research where appropriate are also made.

These reviews are limited to literature published or accepted for publication in peer-reviewed journals, books, government publications, and conference proceedings. Unpublished information was occasionally used, but only to develop hypotheses.

This work is sponsored by the Office of the Special Assistant and was carried out jointly by RAND Health’s Center for Military Health Policy Research and the Forces and Resources Policy Center of the National Defense Research Institute. The latter is a federally funded research and development center sponsored by the Office of the Secretary of Defense, the Joint Staff, the unified commands, and the defense agencies.

 

Summary

Pyridostigmine bromide (PB) is a drug, often given as a tablet, that has been approved since 1955 by the U.S. Food and Drug Administration for treatment of myasthenia gravis, a disease characterized by weakness and fatigability of the muscles. During the Persian Gulf War (PGW), PB was used as an “investigational new drug” (IND) by the U.S. military and some other allied forces as a pretreatment adjunct to protect military personnel from death in event of attack with the nerve agent soman. (IND status conferred by the FDA does not permit unrestricted use but may, as in this case, have conditions attached.) PB is called a pretreatment adjunct because it must be given before exposure to be effective. Also, it is not effective alone but only confers benefit if postexposure treatments are given as well.

PB is used primarily to protect troops against attack by one particular nerve agent, soman. During the PGW, Iraq was known to have nerve agents, including sarin, and had weaponized them by putting them into rockets, bombs, and missile warheads. While it was not known whether Iraq had militarized the nerve agent soman, it was known that the former Soviet Union had soman, and there were concerns, particularly since the fragmentation of the former Soviet Union, that Iraq may have purchased soman. Iraq used chemical weapons against Iran and the Kurds. Because of the possibility that Iraq had soman, coalition troops were provided with PB, to be used for protection when the threat of chemical warfare was deemed high. Evidence from that time and subsequent to the PGW suggests that Iraq had weaponized the nerve agents sarin, cyclosarin, and perhaps tabun and VX, but no evidence uncovered suggests they had soman or had weaponized it.

This report examines issues surrounding the safety and to a lesser degree the effectiveness of PB. The sections on safety consider seven hypotheses of how PB might lead to negative health effects. Each hypothesis is investigated to determine if it can be rejected as a possible causal factor. If sufficient evidence cannot be marshaled to rule out a hypothesis, this does not imply that it is necessarily a causal factor, only that the possibility cannot be dismissed.

How PB Protects Against soman Exposure

To understand how PB protects against soman requires understanding the action of nerve agents. Nerve agents act by irreversibly binding to, and inhibiting, the normal action of acetylcholinesterase (AChE), an enzyme. Acetylcholine (ACh) is a major neurotransmitter, or nerve-signaling chemical, and acts as a signaling chemical both in the brain and elsewhere in the body; for example, it is the main signaling chemical used by nerves to tell muscles to contract. AChE breaks down ACh in the synapse, the area where a nerve sends signals to another nerve, or to a muscle (see Figure S.1). Thus, AChE serves a critical role in regulating nerve signaling to other nerve cells or to muscle cells. When AChE is inhibited by a nerve agent, an excessive accumulation of ACh occurs in the synapse, followed by excessive binding of ACh to the receptors on the receiving cell (see Figure S.2). Consequently, cells are overstimulated. This condition leads to an array of possible symptoms based on ACh binding to different types of receptors.

For most nerve agents, postexposure treatment confers adequate protection from death with amounts of nerve agent that are presumed likely in warfare. The postexposure treatments in use by the military are atropine and pralidoxime (also called “2PAM”). Atropine antagonizes (blocks) the effects of ACh at one type of receptor, and pralidoxime pulls the nerve agent off the AChE, restoring the action of AChE to normal. In addition to PB, troops were given three “Mark I” kits containing injections of both atropine and pralidoxime for use after a nerve agent attack (Army and possibly Marines) or were given individual injectors of these agents (Air Force and Navy).

Figure S.1—How Normal Neurotransmission Works

Figure S.2—Nerve Agent Blocks AChE Enzyme

Unfortunately, in the case of soman, a reaction termed “aging” takes place in the nerve agent–AChE complex within only minutes of exposure. Once this reaction has taken place, pralidoxime can no longer pull the nerve agent off the AChE molecule. Thus, troops would not have enough time to administer pralidoxime before AChE is permanently inactivated, which could ultimately result in death. Aging also happens with other nerve agents, but it takes hours to occur after sarin, cyclosarin, tabun, or VX exposure, which allows troops adequate time to administer pralidoxime before aging has taken place, helping to restore AChE action. Animal evidence suggests that to ensure adequate protection against death in the event of a soman attack, PB pretreatment must be employed.

PB acts—it is thought—by reversibly binding to (and, incidentally, inhibiting) the AChE on the site where the nerve agent would bind, thus blocking soman from permanently inactivating the AChE (see Figure S.3). As soman is cleared from the body, PB spontaneously leaves the AChE and restores functional

Figure S.3—PB Prevents Nerve Agent from Binding to AChE Enzyme

AChE. The dose of PB used by troops, 30 mg each eight hours, is chosen to inhibit 20 to 40 percent of the AChE. The goal is to ensure that at least this proportion of AChE is relatively safe from permanent inactivation in case of exposure to soman, while allowing enough residual AChE activity (60–80 percent) to prevent significant side effects and to allow personnel to adequately carry out their functions. It is believed that to protect most troops from death by amounts of soman that might realistically occur in a combat setting, a person must be able to withstand approximately five times the normal lethal dose. This level of protection has not been achieved with postexposure treatments alone (that is, with atropine and pralidoxime) but requires use of PB as a pretreatment adjunct in tests in nonhuman primates.

How Effective Is PB?

The dose of PB needed to protect humans against the effects of soman is not clear and may be higher than previously thought. Tests done in primates to determine the protection by PB against soman have used higher doses of PB (three to 50 times as high on a mg/kg basis), as well as higher doses of atropine (four times as high on a mg/kg basis) than those actually used in humans for nerve agent protection. In addition, these tests commonly have given the equivalent of all three atropine-pralidoxime postexposure treatments at once. Higher doses of PB are given to achieve a similar percentage of AChE inhibition, while the higher doses of atropine are given on the grounds that the nonhuman primates tested are this much “less sensitive” to the effects of atropine. The extrapolation of these data to humans then rests on the assumption that the percentage of AChE inhibition is the exclusive relevant “measure” of the “pharmacologically equivalent” dose of PB (with an analogous argument for atropine), which may or may not be so. According to the only identified study (Smith, 1981) that directly compared the ability of PB to protect against the effects of soman in human and primate muscle tissue, 10 times as high an in vitro dose of PB was needed in humans as in monkeys to provide comparable protection (whereas we give only one-tenth the oral dose to achieve a comparable AChE percentage inhibition). These data arouse concerns about the validity of extrapolation from primate data to humans. It is known that the protective ability of PB, atropine, and oximes vary widely from one species to another.

In monkeys and to a lesser extent in other animals, PB protects against the lethal effects of the nerve agent soman; but it does not prevent severe incapacitation of the animals from high doses of the nerve agent. So even if data signifying protection in primates at higher doses of PB do extrapolate to humans at lower doses, troops are likely to be incapacitated in the presence of a soman attack. Moreover, in animal studies, PB appears to reduce somewhat the protection (conferred by postexposure atropine and pralidoxime) against lethal effects of some other nerve agents, such as sarin and cyclosarin. This apparent reduction in protection still provides for high protection in some animals (with “protective ratios,” characterizing protection against lethal effects, that are still several times higher than the fivefold protection that has been designated as desirable). However, no direct evidence ensures that the increased vulnerability to death (reduced protection) that PB may bring for such nerve agents as sarin leaves high or “adequate” (fivefold) protection intact in humans. Again, substantial interspecies differences have been seen, with changes not only in magnitude but also in the sign (direction) of the effect of PB, and testing of protection by PB against lethal effects of nerve agents in humans cannot, of course, be done.

Is PB Safe? Safety Considerations of Using PB

The short-term side effects of taking PB—which also may occur with exposure to any nerve agent—are those of AChE inhibition and the resulting excess of ACh action. These effects may include muscle twitching, muscle spasms, weakness or paralysis, and secretions from glands. Consequences may include difficulty in breathing, cramping, feeling of urge to urinate or frequent urination, tearing, runny nose, salivation, increased bronchial secretions, diarrhea, and sweating.

PB is normally largely excluded from entry to the brain by the “blood-brain barrier," which bars access to the brain of many chemicals and organisms that circulate in the blood. If PB gains entry to the brain, adverse effects can result from the binding of PB to ACh receptors in the brain. These effects may include confusion, emotional changes such as depression, sleep alterations, and difficulties with concentration and memory.

This report explores whether PB—with this panoply of acute effects—could plausibly have contributed to chronic symptoms reported by ill PGW veterans. Far higher doses of PB, used for far longer times (typically lifelong) have been employed for decades to treat patients with myasthenia gravis, and this has been assumed by many to indicate that lower-dose, briefer use in nerve agent pretreatment will be safe. However, data from patients with myasthenia might not extrapolate completely to those taking PB for other purposes. For one thing, PB is used in patients with myasthenia gravis to restore nicotinic cholinergic function (at least in the muscles) toward normal. In those without myasthenia gravis, PB raises ACh function away from normal. Thus, extrapolating evidence of safety from patients with myasthenia gravis is somewhat analogous to assuming that, since high doses of insulin are tolerated—or even necessary—in some patients with diabetes (to bring their blood sugar toward normal), therefore a smaller dose of insulin should surely be safe in those without diabetes. We know this is not the case and that smaller doses of insulin given to normal individuals can cause adverse effects and even death. There are other important reasons PB may not be safe for nonmyasthenic individuals, which are discussed later.

Hypotheses Relating PB Use to Illnesses in PGW Veterans

A literature review was performed to identify hypotheses or theories that might link PB to illnesses in PGW veterans and to evaluate evidence pertaining to these hypotheses. Hypotheses are divided into two categories: those that may explain how some individuals may have had heightened susceptibility to PB and those that purport to link exposure to PB—perhaps enabled by such heightened susceptibility—to development of chronic illnesses.

Hypotheses regarding heightened susceptibility to effects of PB include the following:

• Stressful or other special conditions may allow PB to breach the blood-brain barrier and penetrate the brain, producing effects that would not “normally” occur.

• Individual differences in physiology may lead to widely different levels of and susceptibility to PB.

• Interactions between PB and other chemicals may produce toxicity greater than that produced by either alone.