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mitochondrial function in AZT-treated HIV-infected patients. In vivo studies
using the rat model were indeed very useful to de®ne pathogenetic molecular,
biochemical, and ultrastructural toxic events in skeletal muscle, and supported
clinical and in vitro ®ndings (Lewis et al., 1992). Electron microscopy was used
to analyze patients in whom a 16-week AZT treatment was supposed to pro-
voke either hepatic or muscle toxicity, and such techniques could demonstrate
characteristic enlarged mitochondria with paracrystalline inclusions, allowing
the distinction of myopathies caused by either HIV or zidovudine (Chen et al.,
1992). Flow cytometry was ®nally used to assess apoptosis and proliferative
response to polyclonal mitogens in cells from macaques infected with the simian
immunode®ciency virus (SIV ), and combined with assessment of the mitochon-
drial metabolic activity of freshly isolated blood mononuclear cells to determine
a novel three-parametric staging system that provided a new prognostic tool in
the longitudinal study of SIV infection ( Del Llano et al., 1993).
Mitochondria were then studied to ascertain whether HIV had the capacity
to damage these organelles directly. Using in situ hybridization detected by
electron microscopy and cellular fractionation, researchers found viral RNA in
signi®cantly increased amounts in mitochondria relative to the cytoplasm and
nucleus (Somasundaran et al., 1994). In contrast, cellular poly(A) RNA or viral
Gag proteins were not increased in the mitochondria. Concomitant with HIV
expression was a decrease in mitochondrial viability. An inverse relationship
between the amount of viral RNA and mitochondrial integrity was demon-
strated using immuno¯uorescent markers to detect probes for HIV RNA tran-
scripts and antibodies to mitochondrial proteins simultaneously in single cells.
High levels of viral RNA in mitochondria were present in acutely (but not
chronically) infected cells, suggesting that HIV RNA import into mitochondria
can compromise mitochondrial function.
The role of proin¯ammatory cytokines, capable of increasing HIV produc-
tion (Poli et al., 1990a, 1990b, 1994), was analyzed by immunocytochemistry
for interleukin ( IL)-1a, IL-1b, IL-6, and tumor necrosis factor ( TNF )-a on
frozen muscle biopsy specimens from HIV-infected patients with various myo-
pathies and from seronegative individuals, some of whom had mitochondrial
cytopathies (Gherardi et al., 1994). HIV-infected patients showed positive re-
activities in vessels ( IL-1) and in in¯ammatory cells (IL-1 and TNF-a). In AZT
myopathy, a majority of ®bers showed mild to marked IL-1 expression, which
was much weaker in the other mitochondrial myopathies. IL-1b messenger
RNA was demonstrated in muscle ®bers by in situ hybridization, implying that
IL-1 was produced in muscle cells. Immunoelectron microscopy showed that
IL-1a was mainly bound to mitochondrial membranes in AZT ®bers. Proin-
¯ammatory and destructive e¨ects of the studied cytokines might be responsible
for several myopathological changes observed in HIV-infected patients, in-
cluding in¯ammation and hemosiderin deposits in muscle tissue, and prominent
myo®brillar breakdown in AZT ®bers.
To examine the long-term e¨ects of AZT exposure on representative pre-
cursors of immune cells, investigators cultured human T-lymphocytic H9 cells
