1992, 143, 145-148
Oxidative Stress, HIV and AIDS
E. Papadopulos-Eleopulos (1) V.F. Turner (2) and J.M. Papadimitriou
(1) Department of Medical Physics, (2) Emergency
Department and (3) Department of Pathology, (University of Western Australia),
Royal Perth Hospital, Wellington St., Perth 6001 (Western Australia)
As long ago as 1983, one of us (E.P.-E.) proposed that oxidative mechanisms
are of critical significance in the genesis of AIDS (acquired immune deficiency
syndrome). A prediction of this hypothesis was that the mechanisms responsible
for AIDS could be reversed by the administration of reducing agents, especially
those containing sulphydryl groups (SH groups). The discovery of HIV resulted
in a broadening of this hypothesis in that it considered oxidative stress
as a principal mechanism in both the development of AIDS and expression
of HIV (Papadopulos-Eleopulos, 1988; Papadopulos-Eleopulos et al., 1989).
However, the general acceptance of the HIV hypothesis of AIDS completely
overshadowed this alternative hypothesis, and although many other scientists
have questioned the role of HIV in the causation of AIDS (Duesberg, 1987;
Root-Bernstein, 1990) Robert Gallo and most AIDS researchers consider HIV
to be the sole "sine qua non" cause of AIDS.
Notwithstanding, some flaws, especially recently, have appeared which
cast serious doubt on the prevailing HIV/AIDS hypothesis. Luc Montagnier,
the discoverer of HIV, is presently of the opinion that cofactors are necessary
for the appearance of AIDS (Lemaitre et al., 1990). It has been accepted
by researchers at the CDC that KS (Kaposi's sarcoma), the first and most
specific of the AIDS indicator diseases, for which the explanation of the
HIV hypothesis was put forward by Gallo in 1982, is not caused directly
or indirectly by HIV (Beral et al., 1990). On the other hand, recent empirical
observations from three seemingly unrelated areas of AIDS research are
in agreement with the hypothesis that oxidative mechanisms play a critical
role in HIV expression and AIDS development.
(1) Pompidou et al. (1985a) and more recently researchers from many
other institutions (Lang et al., 1988; Brewton et al., 1989; Reisinger
et al., 1990; Hersh et al., 1991) have shown that a reducing agent, diethyl
dithiocarbonate, previously used as an immunomodulator, and inhibitor of
tumour promotion, may be useful in improving the immune response in HIV
infected individuals and in preventing and treating AIDS. Other reducing
agents have also been found to have similar effects (Schulof et al., 1986;
Wu et al., 1989).
(2) In 1989, Eck et al. measured the level of acid soluble-SH groups
in plasma and the intracellular concentration of reduced glutathione (GSH)
in peripheral blood mononuclear cells (PBMC) and monocytes in HIV-infected
patients: both were found to be significantly decreased. Following the
above report, Buhl et al. (1989) determined the glutathione concentration
(reduced, oxidised and total) in plasma and lung epithelial lining fluid
of symptom-free HIV seropositive individuals: in both tissues, both the
reduced and total GSH concentration was found to be significantly decreased.
(3) In 1985, Pompidou et al. (1985b) and more recently many other researchers
including Anthony Fauci have shown that reducing agents suppress the expression
of HIV (Scheib et al., 1987; Bitterlich et al., 1989; Kalebic et al., 1991).
Because of the possible therapeutic implications of reducing agents
in AIDS patients it is important to have a basic understanding as to why:
- reducing agents suppress the expression of HIV;
- asymptomatic HIV-infected individuals and AIDS patients have decreased
sulphydryl and total glutathione levels.
HIV expression and reducing agents
The answer to the first question is encompassed in basic retroviral
research conducted over half a century. It is well known that all cells
contain retroviral genomic sequences (Martin et al., 1981 ; Callahan et
al., 1989; Nakamura et al., 1991). Recently French researchers suggested
that human DNA also contains sequences which are homologous with the HIV
genome (Parravicini et al., 1988). Many eminent retrovirologists, including
Weiss, did not exclude the possibility that retroviruses with gene sequences
not originally present in cells may arise during the lifetime of the animal
by duplication and/or recombination of endogenous proviruses or even by
rearrangement of cellular DNA, caused by many factors including the pathogenic
process itself, and that retroviruses may be the effect and not the cause
of the disease (Weiss et al., 1971).
According to Temin (1974) who shared the Nobel prize with Baltimore
for the discovery of reverse transcriptase (RT) and who, from the time
of its discovery considered the enzyme to be constituent of all cells not
just retroviruses, the genome of a retrovirus (ribodeoxyvirus) may arise
by rearrangement of the normal cell genome by the following mechanism.
"A section of a cell genome becomes modified in successive DNA(w)
to RNA(-) to DNA transfers until it becomes a ribodeoxyvirus genome. First,
these sequences evolve as part of a cellular genome. After they have escaped
as a virus they evolve independently as a virus genome. The time may be
millions of years in germ-line cells and days in somatic cells". In
fact, Temin and Baltimore (1972) did not exclude the possibility that,
in at least some cases, particles which band at 1. 16 g/ml contain RT and
have morphological characteristics similar to retroviruses, may be nothing
more than cellular fragments. Irrespective of the mechanism it is a fact,
firmly established from basic retroviral research, that retroviruses can
appear even in virus-free cultures with a rate that can be accelerated
a million-fold by radiation, infection with other viruses and mitogens
(Weiss et al., 1971 Aaronson et al., 1971).
Of particular relevance to the present discussion is the fact that all
mitogenic agents including radiation exert their biological effect by oxidation
of cellular sulphydryl groups (Papadopulos-Eleopulos, 1982).
Montagnier and his associate David Klatzmann were the first to draw
attention to the fact that LAV infection of T4 cells in vitro does not
lead to HIV expression unless the cells are stimulated. "Infection
of resting T4 cells does not lead to viral replication or to expression
of viral antigens on the cell surface, while stimulation by lectins or
antigens of the same cells results in production of viral particles, antigenic
expression and the cytopathic effect" (Klatzmann and Montagnier, 1986).
Gallo also expressed the view that without "activation" the T4
cells do not express virus (Zagury et al., 1986). But, apparently, they
did not realise that oxidative phenomena are implicated in human T-cell
stimulation (Sekkat et al., 1988).
As early as 1984 it was realised that in vivo HIV genomic sequences
are not always detected in tissues obtained from patients with ARC and
AIDS or, when found, the "signal" is low. According to Gallo
and his colleagues "this low signal intensity could also be explained
by the presence of a virus distantly homologous to HTLV-III in these cells"
(Shaw et al., 1984).
Anthony Fauci and his colleagues, on comparing the evidence obtained
from the study of macrophages in vivo and in vitro, concluded: "These
data indicate that the ability to isolate in vitro macrophage tropic strains
of HIV does not reflect in vivo infection of circulating monocytes, but
is related to phenomena of in vitro selection or adaptation" (Massari
et al., 1990).
Furthermore, (a) to date, with perhaps one exception, no two identical
HIV have been isolated, not even from the same person; in one case where
two sequential isolates were made 16 months apart, none of the provirus
in the first isolate was found in the second (Saag et al., 1988); (b) the
genetic data obtained in vitro does not correlate with the data obtained
in vivo - "To culture is to disturb" (Meyerhans et al., 1989);
(c) many, if not all, of the proviruses detected in vivo and in vitro are
This data led researchers at the Pasteur Institute and their associates
to conclude that (1) "the task of defining HIV infection in molecular
terms will be difficult", (2) "virus isolated from PBMC may be
produced by the complementation of defective genes or by recombination
between two of them" (Meyerhans et al., 1989; Wain-Hobson, 1989).
Be this as it may, of particular relevance to the present discussion is
the fact that:
a) HIV has been isolated only from in vitro cultures;
b) no HIV can be isolated, unless the cultures, one way or the other,
are subjected to oxidative stress, even although the tissue from AIDS patients
is already oxidised; it may be then that oxidative stress is of pivotal
significance in the detection of all retroviruses including HIV. If oxidation
is a prerequisite for HIV expression, it follows that reducing agents will
have the opposite effect: HIV will not be expressed in their presence.
Oxidative factors in AIDS patients
AIDS patients suffer from many opportunistic microorganisms. Like all
cells, these microorganisms require reducing equivalents, including SH,
for division and survival (Papadopulos-Eleopulos, 1982) which they obtain
to the detriment of body tissues. In AIDS patients, a decrease in the level
of SH may also result from malnutrition and diarrhoea. However, opportunistic
infections, diarrhoea and malnutrition cannot account for the low level
of GSH and acid-soluble SH found in HIV-positive, symptom-free, well-nourished
homosexuals and haemophiliacs.
Since viral production also requires thiols, which they obtain from
the host, it may be reasonable to assume that the decreased SH level in
HIV-positive individuals may be the result of HIV infection, as has already
been proposed for SIV-infected monkeys (Eck et al., 1991). However, because
for both HIV and SIV expression, oxidative stress is a prerequisite, this
cannot be the case, i.e. oxidation cannot be both the cause and the effect
of HIV expression (Papadopulos-Eleopulos et al., 1991).
At first sight it appears that there is no common factor, apart from
HIV infection, linking the various AIDS risk groups. However, homosexuals
are exposed to relatively high levels of nitrites and anally deposited
sperm, drug abusers to opiates and nitrites, haemophiliacs to factor VIII.
All these are known potent oxidising agents which oxidise many cellular
reducing equivalents such as NADPH and all sulphydryl groups, including
those of cysteine (acid-soluble thiols) (Papadopulos-Eleopulos, 1988).
In normal tissue almost all glutathione is found intracellularly in
the reduced form (GSH) where it is also synthesised from glutamic acid,
cysteine and glycine, in the presence of ATP and magnesium. Cysteine which
is the rate-limiting amino acid cannot be substituted by its oxidised form,
cystine. Oxidation of cysteine (acid-soluble SH) is also known to decrease
cellular ATP and magnesium concentration (Tateishi and Higashi, 1978; Siliprandi
et al., 1987). Malnutrition and diarrhoea may also lead to cysteine, magnesium
and ATP deficiency.
As a result of the decrease in cysteine, ATP and magnesium concentration,
the synthesis of glutathione will be inhibited. The oxidising agents to
which the AIDS risk groups are exposed would also directly oxidise GSH
to GSSG. GSSG is efficiently excreted from cells (Sies and Akerbrum, 1984).
Glutathione exported across the cell membrane interacts with gamma-glutamyl
transpeptidase, an enzyme which catalyses the breakdown of glutathione
by transferring the gamma-glutamyl group to an acceptor.
It should be noted that: cystine is one of the best acceptors for the
gamma-glutamyl group; with exception of the kidney and pancreas, the highest
activity of the enzyme is in the epididymis and seminal vesicles; the highest
concentration of its soluble form, apart from urine and pancreatic juice,
is in seminal fluid (Meister and Anderson, 1983). Thus, the systemic decrease
of glutathione concentration in HIV seropositive individuals may result
from both, decrease in synthesis and increased degradation. The oxidative
stress to which the AIDS patients are subjected would lead to cellular
anomalies in many cells, including lymphocytes, resulting in opportunistic
infection, immunological abnormalities and neoplasia.
All this argues in favour of oxidation as being a critical factor in
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