The Art of Scientific Scrutiny: Investigating the Poppers-AIDS Hypothesis By Christine Weber, B.Sc.
As a science writer and researcher, I recently became interested in a scientific controversy I thought had been put to bed many years earlier. In the 1980s, when HIV/AIDS research was in its earliest and possibly most feverish stages, a relationship was discovered between the incidence of AIDS-like symptoms in homosexual men, the largest portion of the population displaying these symptoms at the time, and the use of alkyl nitrites, more commonly called “poppers”. This relationship was later extrapolated to link popper use to Kaposi’s sarcoma, a cancer frequently seen in immunocompromised individuals, including those with AIDS. Mainstream science and soon to be dissident AIDS researchers alike investigated this relationship, and while the former found it to be purely correlational, the latter continue to this day, ardently supported by members of the alternative press, to vigorously argue that a link exists between drug and disease. To this group, AIDS was not caused by the HIV retrovirus, a hypothesis now accepted as near fact by mainstream science, but by a popular recreational inhalant. A brief review of the controversy left me with more questions than I had begun with. For instance, why do two groups of scientists, both educated in universities on the basic tenants of science and established in their fields of research, continue to disagree about the cause of what is possibly the most researched disease of our generation? And more importantly, which of these two hypotheses best stands up to the scrutiny of science?
The case isn’t as unusual as you may think. The history of science is littered with such disagreements over opposing hypotheses. Scientists wouldn’t be practicing good science if they were not questioning their hypotheses every step of the way. That is what hypotheses are there for after all, to either stand or crumble under scientific scrutiny. By definition, a hypothesis is an educated guess, and it’s considered scientific only if it is a) testable and b) falsifiable. Its interesting, I find, that the very foundation science sits upon is designed to be tested and, if the case, proven wrong. But this is the safety net that science needs to operate. Without it scientists would only discover exactly what they were looking for, stubbornly sticking to their favorite hypothesis even if the data indicates that they should turn in a new direction. Often it’s only by identifying the wrong path that we stumble upon the right one. And I do mean stumble. Some of science’s greatest discoveries were a direct result of such happy accidents, possibly the most famous being the discovery of penicillin. Coming back to the AIDS hypothesis, let’s consider our two groups of scientists. One argues that the HIV virus causes AIDS; the other argues that it is linked to poppers. Which is correct? Many more scientists support the first hypothesis, but try to keep that out of your assessment. I can think of more than one scientist who was discredited by his peers, only to later win the Nobel Prize. Instead, clear your mind of bias and follow me on a journey of scientific analysis where logic, scientific procedure and experimental design act as our only guides.
Getting to Know Poppers
To begin with, what are alkyl nitrites, the drugs at the center of this controversy? Essentially, alkyl nitrites are any chemical with the general formula R-O-N=O, where the R is any organic (carbon containing) subgroup. Admittedly, this is a rather dull description of a drug with a long and colorful history. Unbiased Internet sources reviewing the history of alkyl nitrites are, as I quickly found, few and far between. A two-hour search on the subject still left much to the imagination. Fortunately for the frustrated researcher, there is always Wikipedia. According to the cyberspace encyclopedia, amyl nitrite, the most familiar form of the chemical, has been used for over 150 years as a treatment of angina, or heart pain (Wikipedia 2006). It was also used as part of the treatment protocol for cyanide poisoning. While other drugs have replaced amyl nitrite for this medicinal use, for the last 50 years alkyl nitrites have been used mainly as a component of room odorant products (Wikipedia 2006). Sold in small glass bottles or capsules nostalgically referred to as poppers, in reminiscence of the glass capsules that housed amyl nitrite as a heart medication, these compounds are also widely used as a recreational inhalant to enhance sexual experience (Wikipedia 2006). Because of their ability to relax smooth muscle tissue in the body, which includes the anal sphincter (their success as an angina treatment was based on their ability to dilate the blood vessels), their use has long been popular in the male homosexual population to enhance sensation during anal intercourse and to prolong and intensify orgasm (Wikipedia 2006).
Many of us were first introduced to poppers through Hollywood, which depicted the drug in such cult classics as Score and Fear and Loathing in Las Vegas, and through the mainstream media, which was awash with stories concerning the use of the inhalant in the 1970s and 80s (Wikipedia 2006). Although more popular with adults than youths, the drug has been widely used in rave subculture to enhance the experience of lights and music on the dance floor since the insurgence of the phenomenon in the 1980s (Wikipedia 2006). Currently illegal in the United States after a long and particularly convoluted legal history, poppers are still easily accessible through the Internet and other adult sources (Wikipedia 2006). While the concern over a possible poppers-AIDS connection has certainly lapsed since the near hysteria surrounding this issue in the 1980s, it nonetheless still lingers, albeit under a new guise. Where researchers once looked for a direct connection between compound and disease, findings are more recently presented to support the idea that alkyl nitrites act as a co-factor in the development of Kaposi’s sarcoma in AIDS patients, and also as an immune suppressant accelerating the progression of AIDS. Is it possible that the majority of the world’s AIDS researchers erroneously discounted a link between poppers and AIDS? It’s an interesting possibility, but does the link stand up to scientific scrutiny?
A Brief History of the AIDS-Alkyl Nitrite Hypothesis
Before looking at the studies that support or deny the AIDS-alkyl nitrite hypothesis, I found it helpful to gather some background information about the emergence of AIDS to put the dispute into context. AIDS burst onto the scene in 1981, when clinical investigators became aware that some very rare diseases were occurring in unusually high rates in young homosexual men with no previous health problems. These diseases included Kaposi’s sarcoma (KS) (CDC 1981b; CDC 1982a,e), a rare connective tissue cancer that previously had been seen mainly in older men of Mediterranean or Jewish origin, in Africa among young people and children (American Cancer Society 2006), and in transplant patients receiving immunosuppressive therapy to reduce organ rejection (Gange and Jones 1978; Safai and Good 1981). Opportunistic infections such as Pneumocystis carinii pneumonia (PCP), a rare form of pneumonia, and chronic enlargement of the lymph nodes were also present in many instances (CDC 1981a,b, 1982a; Masur et al. 1981; Gottlieb et al. 1981). With further research, it became clear that that these men had one thing in common: Their immune function was compromised because the cell-mediated aspect of their immune system was impaired by a loss of T-helper cells bearing the CD4 marker on their surface (Gottlieb et al. 1981; Masur et al. 1981; Siegal et al. 1981; Ammann et al. 1983a).
Such rare diseases in young men with no history of illness or immunosuppressive therapy had never been seen before in the history of medicine. Thus began the long and frustrating search for a cause. Not surprisingly, in the early stages of this research, scientists came to the rational conclusion that, because initially only homosexual men displayed this unique set of symptoms, some aspect of the gay lifestyle might be playing a role in the development of this disease (Goedert et al. 1982; Sonnabend et al. 1983; Mavligit et al. 1984). Many young men with AIDS symptoms also reported using poppers, a popular recreational inhalant among homosexuals at the time. As one of several behavioral aspects unique to the homosexual lifestyle, poppers were investigated during these early stages as a possible link to the syndrome. It was an interesting hypothesis, but one that would be ruled out relatively quickly. The first cracks in the hypothesis occurred when clinicians began to see the syndrome in populations outside of the homosexual community. Hemophiliacs and other recipients of blood products, injection drug users, female sexual partners of bisexual males, and infants born to females with the syndrome or a past history of injection drug use—all of these cases pointed to a new hypothesis that the disease was caused by a blood borne agent, such as a virus (CDC 1982b,c,d,e, Masur et al. 1982; 1983a; Ammann et al. 1983b; Davis et al. 1983; Elliot et al. 1983; Harris et al. 1983; Poon et al. 1983; Rubinstein et al. 1983).
Despite these findings, scientists continued to pursue the AIDS-alkyl nitrite hypothesis by completing a series of large and well-designed research studies that investigated the link. Although it may seem counterintuitive, it is simply good science to investigate a hypothesis until it is either repeatedly shown to be false or continues to stand up under continued scientific scrutiny. In this case, the hypothesis failed to stand up to the scrutiny of several studies. The results of the largest of these studies, referred to as the MACS (Multicenter AIDS Cohort Study) Project, were published in the prestigious New England Journal of Medicine in 1987 (Polk et al. 1987). This study investigated 1835 HIV positive homosexual men, 59 of which developed AIDS in the course of the 15-month study. One of many aspects studied in this long-term investigation was the possible role of alkyl nitrites in both AIDS and KS; no link was found (Polk et al. 1987; Voeller 1990). Another large-scale study by the New York Blood Center supported these findings (Stevens et al. 1986), as did other smaller studies (Vandenbroucke 1989; Schechter et al. 1993). The Schechter study was particularly definitive. In this study, 715 homosexual men were studied for nearly nine years. Of the 365 HIV-positive men, 136 subsequently developed AIDS. No cases of AIDS occurred in the HIV-negative men, even though they reported considerable use of alkyl nitrite inhalants (Schechter et al. 1993).
In my mind, these studies cleanly sever any possible link between AIDS and inhalation of alkyl nitrites. Science has confirmed what my mind had already surmised: a compound used for over 150 years by countless people to treat angina and cyanide poisoning could not be a casual factor in a disease that first appeared 25 years ago. It simply doesn’t make sense. It seems that many proponents of the alkyl nitrite-AIDS connection also saw the light. Leaving this initial hypothesis behind, researchers soon began to entertain new questions: Could alkyl nitrites accelerate the progression of AIDS by further compromising the immune system? Could they play a role in the development in KS, a disease seen mainly in the homosexual AIDS population? Here are two more interesting questions in the quest for definitive answers. How would the research findings deal with these new questions? Would well-designed studies support or refute these hypotheses?
Taking the Alkyl Nitrite-AIDS Hypotheses One Step Further
I approached these studies with an unbiased mind, searching for both solid and faulty logic, and for strength and weakness in experimental design. I urge you to do the same as you follow me through this further analysis of the AIDS-alkyl nitrite hypotheses. First on the list is the hypothesis that alkyl nitrites suppress the immune system, thereby either encouraging the development of AIDS in HIV-positive individuals or increasing the likelihood that an individual will become infected with the AIDS virus in the first place.
How does the data either support or refute this hypothesis? The first thing that struck me in researching the numerous studies on this topic was that while some immune suppression was found, numerous factors have confounded these findings to the point where they cannot be considered scientifically valid. On first glance, a large number of studies seem to support the immune suppression hypothesis, but further study of the experimental design used in these studies, as well as other shortcomings reveal these claims are on very shaky ground. I began my analysis by looking more closely at a problem found in most of the studies I came across, that of proper dosing.
Not surprisingly, most of these studies are experiments where either mice or cells were exposed to varying concentrations of alkyl nitrites, through various means of delivery. The first question that popped into my mind was how relevant are these experiments to real life? While helpful information is sometimes gained from these types of studies, more often, the findings cannot be transferred to human beings. Many new drugs are studied outside of the human context and, while the lab reports show they are a promising means of treatment, the drug fails to act the same way in human patients (Voeller 1986). Contrasting these experiments to the MACS Project and other studies where humans were studied, I found it impossible to compare the two. The next question that came to mind was how did the researchers adjust for the fact that they are using mice or cells, which differ from human subjects in many ways? Perhaps the most obvious difference is one of scale. Mice and cells are much smaller than human beings. How were doses adjusted to account for this size difference? Most frequently, I discovered, they weren’t.
Let’s look at a study completed by a group of researchers at M.D. Hospital in Houston, Texas (Hersh et al. 1983). The researchers investigated the effects of butyl nitrite (a type of alkyl nitrite) on laboratory cultures of white blood cells. So far, so good. We know the limitations of such an experiment, but let’s continue and look at the dosing regime. Hersh and colleagues reported that when exposed to a 1% concentration of butyl nitrite for 24 hours, many of these cells were killed, while at 0.5%, the cell number and viability were unaffected. What do these findings mean for an average human being? To establish a 1% concentration of butyl nitrite in an average human with six liters of blood even from a brief moment (we are not considering the 24 hour time period here yet), 60 mL of butyl nitrite needs to be added to the blood. A bottle of poppers contains 10 to 12 mL of the compound. This means that five or six bottles of the compound would have to be injected into a human to replicate the conditions of the experiment. Since nitrites are inhaled rather than injected (injecting nitrites is toxic) and only a small fraction of the compound is actually absorbed by the lungs, this study tells us nothing in reality except that a 1% concentration of butyl nitrite kills cells in a test tube. (Voeller 1986)
Numerous experiments conducted on mice also fail to adjust the doses for differences in lung size or body weight. Adjusting dose for body weight is a fundamental aspect of studies using experimental animals. When non-physiological doses (higher or lower than the comparable human dose) are used in animal studies, the results cannot be meaningfully compared to humans. Interestingly, many of the studies I reviewed administered doses that were at near lethal levels, so that it’s also unclear if the observed effect was due to toxicity (Lotzova et al. 1984; Gaworski et al. 1992; Soderberg et al. 1996a; Soderberg and Barnett 1996; Soderberg 1998; Tran et al. 2003). Imagine administering a near lethal dose of any compound, such as aspirin. Would the research findings tell us anything about the behavior of the compound at the normally consumed dose? I’m afraid not. Although it is clear that such data in no way test the hypothesis that alkyl nitrites impair the human immune system, I was completely taken aback to see how many advocates cite numerous studies of similar design to support the AIDS-poppers hypothesis.
In addition to dosing problems, many of the experiments that advocates reference in support of the AIDS-poppers hypothesis report changes in immune function only after administering the compound for an extended duration that simply does not reflect human use. For instance, in the 1983 study by Hersh et al. mentioned earlier, the cells in the experiment were exposed to butyl nitrite continuously for 24-72 hours. I was surprised that this and other studies (Gaworski et al. 1992; Tran et al. 2003) did not administer the compound for a briefer duration to better mimic human inhalation of the compound. Interestingly, I did come across one study that exposed mice to 300 ppm of alkyl nitrites for 6.5 hours a day for five days over 18 weeks, a level and duration that better reflects human use (Lewis 1985). No changes in immune function were observed.
In review, what did these experimental findings say about the effect of alkyl nitrites on immune function? In general, most of the findings stated that immune impairment occurred, but the doses were administered in a manner that rendered the findings invalid. This of course is a matter of scientific opinion. Suppose you don’t agree that the experimental designs were flawed? If so, I have a last point that may interest and surprise you. Many of the studies that saw immune impairment at near toxic doses of alkyl nitrites also reported that these effects were entirely reversible within days of stopping the dose (Soderberg and Barnett 1993; Dax et al. 1991; Soderberg et al. 1996b). Another interesting point to consider is that when immune cell function was compromised, the data often revealed that other cell types experienced cytotoxic effects, showing that nitrites did not act selectively against immune cells, but were harmful to other cell lines as well, suggesting that lethal doses of the compound were administered (Hersh et al. 1983). Additionally, published results were often contradictory. For instance, in 1996 Soderberg and Barnett (Soderberg et al. 1996a) repeated experiments that they had previously published in 1995 (Soderberg and Barnett 1995). The results of these experiments were opposite to those obtained when the same steps were followed previously. In science it’s important to repeat experiments to either support or invalidate a hypothesis. In this case, inconsistent findings help us see that the original hypothesis was invalid.
What About the Relationship Between Alkyl Nitrites and KS?
Named after Dr. Moritz Kaposi who first described the condition in 1872, Kaposi’s sarcoma has been with us for many years. Until the 1980s, the sarcoma (a cancer that effects the connective tissue such as bone, cartilage, fat, muscle, blood vessels and ligaments) was considered a rare disease. In the past it occurred in three main populations: elderly men of Mediterranean or Jewish heritage, organ transplant recipients receiving immune suppression therapy, and young people in Africa (American Cancer Association, 2006). It will probably strike you that these are not populations that typically use nitrites. With the advent of AIDS, Kaposi’s sarcoma reached epidemic proportions in the homosexual male population. Prior to the AIDS epidemic, the cancer occurred in only 0.02 to 0.06 individuals per 100,000 (Oettle 1962). By 1984, never-married men in the San Francisco area were 2000 times more likely to develop the disease than they were in the previous decades (Williams et al. 1994). Fortunately, as new AIDS treatments evolved, the number of cases of Kaposi’s sarcoma has fallen by about 85% (American Cancer Association 2006). These numbers and dates are interesting as they correspond directly with the emergence and treatment of the HIV virus, not with use of poppers, which was at it height in the 1960s and 1970s, prior to the AIDS epidemic (Lau et al. 1992; Stall and Purcell 2000) Scientists suggesting a connection between KS and alkyl nitrites often refer to the fact that KS occurs about 20 times more frequently in homosexual men with AIDS than in heterosexual individuals suffering from the disease (Beral 1989), citing that these findings support the hypothesis that alkyl nitrites may be a cofactor of KS (Wikipedia 2006). While the hypothesis is interesting, I find continued claims of this nature surprising, considering that they were refuted by the MACS study (reviewed earlier in the text) in 1987 (Polk et al. 1987), among other studies (Voeller 1990). In fact, researchers from the Johns Hopkins School of Hygiene and Public Health reanalyzed data from the MACS study and actually found that higher use of alkyl nitrites corresponded with lower incidence of KS (Palenicek et al. 1992).
This leaves us with the million-dollar question: If alkyl nitrites are not causing KS, what is? Many recent studies support the hypothesis that KS is caused by a sexually transmitted herpes virus, HHV-8, also called KSHV (Kaposi’s Sarcoma Associated Herpes Virus) (Whitby et al. 1995; Ziegler and Katongole-Mbidde 1996; Gnann et al. 2000). This hypothesis supports data that shows a low prevalence of KS among intravenous drug users and blood product recipients suffering from AIDS, as these individuals typically contract HIV through non-sexual (blood to blood) means. As a herpes virus, HHV-8 travels through nerve endings, and although it is sexually transmissible, it is unlikely to be transmitted through the blood (Gnann et al. 2000). Many studies support the HHV-8 hypothesis. As early as 1989, the Centers for Disease Control recognized that if an infectious agent caused KS, it was likely transmitted by some form of homosexual contact rather than by blood (Beral 1989). Six years later in a 1995 study by Whitby et al., HHV-8 was consistently detected in the biopsy samples of patients with both AIDS related and non-AIDS related (classical) KS. Further, HHV-8 was detected in the blood cells of over half of the KS patients, but not in those of the non-KS patients used as controls. Further studies support these findings (Bobroski et al. 1998; Gnann et al. 2000). In a 1996, study of children in Uganda published in the International Journal of Cancer, Ziegler and colleagues studied 100 cases of KS in children under age 15. They reported that the incidence of childhood KS in Uganda in 1996 was 40 times as great as it was in the pre-AIDS era. DNA from HHV-8 was found in all cases of childhood KS tested. Distribution patterns of the tumors suggested the virus entered during birth or breast-feeding (Ziegler 1996).
But what about the correlational findings linking high use of alkyl nitrites to KS? When reviewing these findings, it’s important to bear in mind that correlation does not equal cause. An interesting case in point comes from a 1985 study by Haverkos et al. that is widely cited in support of the KS-alkyl nitrite connection. While the authors found a correlation between the high levels of nitrite use and KS, they also found many other statistically significant correlations. For instance, homosexual men with KS tend to have had hepatitis B; use drugs such as amphetamines, barbiturates, cocaine, LSD, and marijuana to name a few; had a greater number of sexual partners than those without KS; and have an income over $20,000 per year (Haverkos et al. 1985).
Not surprisingly, correlation is easily confused with fact. I’ve found that a semi-ridiculous analogy often helps bring the point home. For instance, while homosexual men with KS may also be more likely to own a three-legged dog than those without KS, there is no proven causal link between KS and three-legged dog ownership. It’s the same with alkyl nitrite use. Because we cannot prove the link is more than a correlation, the conclusions remain unclear. Often upon further analysis, as was the case with a reanalysis study done by Marmor et al. in 1982, when other variables are controlled for, nitrite use is shown to no longer be a significant factor.
Summing It All Up
Bringing our scientific analysis to an end, we’ve learned a good deal about scientific research methods and how a scientific hypothesis can either stand against or fall under the weight of solid research. The main problem with the research supporting the alkyl nitrite-AIDS hypotheses is that many of the standards of experimental design are simply not upheld. Most experiments are in vitro (test tube) or involve mice. Results of these studies are then used by advocates to support the poppers-AIDS hypotheses, disregarding the fact that doses were not adjusted for body weight and lung size in mice, and were often administered at near toxic levels over a duration that failed to reflect human alkyl nitrite use. Under these conditions, it is simply impossible to extrapolate the findings to human beings. Not to mention that results derived from the same experimental design were often inconsistent. Even if one fails to consider these experimental design flaws, the small number of studies supporting a connection between poppers and AIDS or KS still do not stand up under the tremendous weight of the large number of well-designed research studies incriminating viruses, not poppers or other compounds, as the causal agent in both AIDS and KS. Advocates of the poppers hypotheses seem to want to sweep this burgeoning body of research under the carpet. To prove something is true in science, you also need try to show that the alternative is false. There are numerous web sites on the Internet that support the popper-AIDS/KS connection. I haven’t seen one that braves the waters to explore the data gathered by mainstream AIDS/KS research. The current is simply too strong to risk a swim.
“By continuing up a wrong path, we lose time finding the right one.
On the AIDS clock, time is measured in deaths.”
~ Dr. Bruce Voeller, Internationally Renowned AIDS Researcher (Voeller 1986)
Literature Cited
Ammann AJ, Abrams D, Conant M, Chudwin D, et al. 1983a. Acquired immune dysfunction in homosexual men: immunologic profiles. Clinical Immunology and Immunopathology. 27(3):315-25.
Ammann AJ, Cowan MJ, Wara DW, Weintrub P, et al. 1983b. Acquired immunodeficiency in an infant: possible transmission by means of blood products. Lancet. 1(8331):956-8.
American Cancer Society. 2006. Detailed Guide: Kaposi’s Sarcoma, What is Kaposi’s Sarcoma? Retrieved on March 21, 2006. http://www.cancer.org/docroot/cri/content/cri_2_4_1x_what_is_kaposis_sarcoma_21.asp?sitearea=cri
Beral V, Peterman TA, Berkelman RL, Holmberg SD, Jaffe HW. 1990. Kaposi's sarcoma among persons with AIDS: a sexually transmitted infection? Lancet. 335(8682):123-8.
Bobroski L, Bagasra AU, Patel D, Saikumari P et al. 1998. Localization of human herpesvirus type 8 (HHV-8) in the Kaposi's sarcoma tissues and the semen specimens of HIV-1 infected and uninfected individuals by utilizing in situ polymerase chain reaction. Journal of Reproductive Immunology. 41(1-2):149-60.
CDC (Centers for Disease Control). 1981a. Epidemiologic notes and reports Pneumocystis pneumonia - Los Angeles. Morbidity and Mortality Weekly Reports. 30:1-3.
CDC. 1981b. Kaposi's sarcoma and pneumocystis pneumonia among homosexual men - New York City and California. Morbidity and Mortality Weekly Reports. 30:305-8.
CDC. 1982a . Epidemiologic notes and reports persistent, generalized lymphadenopathy among homosexual males. Morbidity and Mortality Weekly Reports. 31:249-51.
CDC. 1982b. Current trends update on acquired immune deficiency syndrome (AIDS) - United States. Morbidity and Mortality Weekly Reports. 31:577-80.
CDC. 1982c. Epidemiologic notes and reports Pneumocytsis carinii pneumonia among persons with hemophilia A. Morbidity and Mortality Weekly Reports. 31:365-7.
CDC. 1982d. Epidemiologic notes and reports possible transfusion-associated acquired immune deficiency syndrome (AIDS) - California. Morbidity and Mortality Weekly Reports. 31:652-4.
CDC. 1982 e. A cluster of Kaposi’s sarcoma and Pneumocystis carinii pneumonia among homosexual male residents of Los Angeles and Range counties, California. Morbidity and Mortality Weekly Reports 31:305-307.
Davis KC, Horsburgh CR Jr, Hasiba U, Schocket AL et al. 1983. Acquired immunodeficiency syndrome in a patient with hemophilia. Annals of Internal Medicine. 98(3):284-6.
Dax EM, Alder WH, Nagel JE, Lange WR et al. 1991. Amyl nitrite alters human in vitro immune function. Immunopharmacology and Immunotoxicology, 13(4):577-87.
Elliott JL, Hoppes WL, Platt MS, Thomas JG et al. 1983. The acquired immunodeficiency syndrome and Mycobacterium avium-intracellulare bacteremia in a patient with hemophilia. Annals of Internal Medicine. 98(3):290-3.
Gange RW, Jones EW. 1978. Kaposi's sarcoma and immunosuppressive therapy: an appraisal. Clinical and Experimental Dermatology. 3(2):135-46.
Gaworski CL, Aranyi C, Hall A 3rd, Levine BS et al. 1992. Prechronic inhalation toxicity studies of isobutyl nitrite. Fundamental and Applied Toxicology. 19(2):169-75.
Gnann JW Jr, Pellett PE, Jaffe HW. 2000. Human herpesvirus 8 and Kaposi's sarcoma in persons infected with human immunodeficiency virus. Clinical Infectious Diseases. Suppl 1:S72-6.
Goedert JJ, Neuland CY, Wallen WC, Greene MH et al. 1982. Amyl nitrite may alter T lymphocytes in homosexual men. Lancet. 1(8269):412-6.
Gottlieb MS, Schroff R, Schanker HM, Weisman JD et al. 1981. Pneumocystis carinii pneumonia and mucosal candidiasis in previously healthy homosexual men: evidence of a new acquired cellular immunodeficiency. New England Journal of Medicine. 305(24):1425-31.
Harris C, Small CB, Klein RS, Friedland GH et al. 1983. Immunodeficiency in female sexual partners of men with the acquired immunodeficiency syndrome. New England Journal of Medicine. 308(20):1181-4.
Haverkos, H W. Pinsky, P F. Drotman, D P. Bregman, D J. 1985. Disease manifestation among homosexual men with acquired immunodeficiency syndrome: a possible role of nitrites in Kaposi's sarcoma. Sexually Transmitted Diseases. 12(4):203-8.
Hersh EM, Reuben JM, Bogerd H, Rosenblum M et al. 1983. Effect of the recreational agent isobutyl nitrite on human peripheral blood leukocytes and on in vitro interferon production. Cancer Research. 43(3):1365-71.
Jaffe HW, Choi K. Thomas PA, Haverkos HW et al. 1983. National case-control study of Kaposi's sarcoma and Pneumocystis carinii pneumonia in homosexual men: part 1. epidemiologic results. Annals of Internal Medicine. 99(2):145-51.
Lau RK, Jenkins P, Caun K, Forster SM et al. 1992. Trends in sexual behaviour in a cohort of homosexual men: a 7 year prospective study. International Journal of STDs and AIDS. 3(4):267-72.
Lewis DM, Koller WA, Lynch DW, Spira TJ. 1985. Subchronic inhalation toxicity of isobutyl nitrite in BALB/c mice. II. Immunotoxicity studies. Journal of Toxicological and Environmental Health. 15(6):835-46.
Lotzova E, Savary CA, Hersh EM, Khan AA et al. 1984. Depression of murine natural killer cell cytotoxicity by isobutyl nitrite. Cancer Immununology Immunotherapy. 17(2):130-4.
Marmor M, Friedman-Kien A E, Laubenstein L, Byrum RD et al. 1982. Risk factors for Kaposi's sarcoma in homosexual men. Lancet. 1(8281):1083-7.
Masur H, Michelis MA, Greene JB, Onorato I et al. 1981. An outbreak of community-acquired Pneumocystis carinii pneumonia: initial manifestation of cellular immune dysfunction. New England Journal of Medicine. 305(24):1431-8.
Masur H, Michelis MA, Wormser GP, Lewin S et al. 1982. Opportunistic infection in previously healthy women. Initial manifestations of a community-acquired cellular immunodeficiency. Annals of Internal Medicine. 97(4):533-9.
Mavligit GM, Talpaz M, Hsia FT, Wong W et al. 1984. Chronic immune stimulation by sperm alloantigens: support for the hypothesis that spermatozoa induce immune dysregulation in homosexual males. Journal of the American Medical Association. 251(2):237-41.
Oettle AG. 1962. Geographical and racial differences in the frequencies of Kaposi's sarcoma as evidence of environmental or genetic causes. Acta Unio Internationalis Contra Cancrum. 18:330-63.
Palenicek J, Fox R, Margolick J, Farzadegan H et al. 1992. Longitudinal study of homosexual couples discordant for HIV-1 antibodies in the Baltimore MACS Study. Journal of Acquired Immune Deficiency Syndromes. 5(12):1204-11.
Polk BF, Fox R, Brookmeyer R, Kanchanakaksa S et al. 1987. Predictors of the acquired immunodeficiency syndrome developing in a cohort of seropositive homosexual men. New England Journal of Medicine. 316(2):61-6.
Poon MC, Landay A, Prasthofer EF, Stagno S. 1983. Acquired immunodeficiency syndrome with Pneumocystis carinii pneumonia and Mycobacterium avium-intracellulare infection in a previously healthy patient with classic hemophilia. Clinical, immunologic, and virologic findings. Annals of Internal Medicine. 98(3):287-90.
Rubinstein A, Sicklick M, Gupta A, Bernstein L et al. 1983. Acquired immunodeficiency with reversed T4/T8 ratios in infants born to promiscuous and drug-addicted mothers. Journal of the American Medical Association. 249(17):2350-6.
Safai B, Good RA. Kaposi's sarcoma: a review and recent developments. 1981. CA: A Cancer Journal for Clinicians. 31(1):2-12.
Schechter MT, Craib KJ, Gelmon KA, Montaner JS et al. 1993. HIV-1 and the aetiology of AIDS. Lancet. 341(8846):658-9.
Soderberg LS. 1998. Immunomodulation by nitrite inhalants may predispose abusers to AIDS and Kaposi's sarcoma. Journal of Neuroimmunology. 83(1-2):157-61.
Soderberg LS. 1999. Increased tumor growth in mice exposed to isobutyl nitrtite. Toxicology Letters. 104(1-2):35-41.
Soderberg LS, Barnett JB. 1993. Inhaled isobutyl nitrite compromises T-dependent, but not T-independent, antibody induction. International Journal of Immunopharmacology. 15(7):821-7
Soderberg LS, Barnett JB. 1995. Inhalated exposure to isobutyl nitrite inhibits macrophage tumoricidal activity and modulates inducible nitric oxide. Journal of Leukocyte Biology. 57(1):135-40.
Soderberg LS, Barnett JB. 1996. Leukopenia and altered hematopoietic activity in mice exposed to the abused inhalant, isobutyl nitrite. Experimental Hematology. 24(7):848-53.
Soderberg LS, Chang LW, Barnett JB. 1996a. Elevated TNF-a and inducible nitric oxide production by alveolar macrophages after exposure to a nitrite inhalant. Journal of Leukocyte Biology. 60(4):459-64.
Soderburg LS, Flick JT, Barnett JB. 1996b. Acute inhalation exposure to isobutyl nitrite causes nonspecific blood cell destruction. Experimental Hematology. 24(5):592-6.
Sonnabend J, Witkin SS, Purtilo DT. 1983. Acquired immunodeficiency syndrome, opportunistic infections, and malignancies in male homosexuals. A hypothesis of etiologic factors in pathogenesis. Journal of the American Medical Association. 249(17):2370-4.
Siegal FP, Lopez C, Hammer GS, Brown AE et al. 1981. Severe acquired immunodeficiency in male homosexuals, manifested by chronic perianal ulcerative herpes simplex lesions. New England Journal of Medicine. 305(24):1439-44.
Stall R, Purcell DW. 2000. Intertwining epidemics: a review of research on substance use among men who have sex with men and its connection to the AIDS epidemic. AIDS and Behavior. 4(2):181-92.
Stevens CE, Taylor PE, Zang EA, Morrison JM et al. 1986. Human T-cell lymphotropic virus type III infection in a cohort of homosexual men in New York City. Journal of the Americam Medical Association. 255(16):2167-72.
Tran DC, Yeh KC, Brazeau DA, Fung HL. 2003. Inhalant nitrite exposure alters mouse hepatic angiogenic gene expression. Biochemical and Biophysical Research Communications. 310(2):439-45.
Vandenbroucke JP, Pardoel VP. 1989. An autopsy of epidemiologic methods: the case of "poppers" in the early epidemic of the acquired immunodeficiency syndrome (AIDS). American Journal of Epidemiology. 129(3):455-57.
Voeller B. 1986. Are poppers safe? Mariposa Occasional Paper 6. Mariposa Education and Research Foundation, Topanga, California.
Voeller B. 1990. Personal letter to Hon. Henry Waxman, Chairman, Health and Environmental Subcommittee. May 23, 1990.
Whitby D, Howard MR, Tenant-Flowers M, Brink NS et al. 1995. Detection of Kaposi sarcoma associated herpesvirus in peripheral blood of HIV-infected individuals and progression to Kaposi's sarcoma. Lancet. 346(8978):799-802.
Wikipedia. 2006. Retrieved Mar 21, 2006. http://en.wikipedia.org/wiki/Alkyl_nitrites
Williams CKO et al. 1994. AIDS-associated cancers. In Essex M, et al., eds. AIDS in Africa. New York, Raven Press, pp. 325-71.
Ziegler JL, Katongole-Mbidde E. 1996. Kaposi's sarcoma in childhood: an analysis of 100 cases from Uganda and relationship to HIV infection. International Journal of Cancer. 65(2):200-3.
