Int. J. Med. Sci. 2004 1(3): 152-164
152
International Journal of Medical Sciences
ISSN 1449-1907 www.medsci.org 2004 1(3): 152-164
©2004 Ivyspring International Publisher. All rights reserved
An Increased Risk of Osteoporosis during Acquired
Immunodeficiency Syndrome
Review
Received: 2004.4.20
Accepted: 2004.7.05
Published: 2004.8.05
N. Annapoorna, G.Venkateswara Rao, N.S. Reddy, P. Rambabu
1
and K.R.S.Samabasiva
Rao
Centre for Biotechnology, Acharya Nagarjuna University, Nagarjunanagar, Guntur- 522 510,
A.P., India.
1
Department of Venereology, GGH/SMC, NTR University Of Health Sciences, Vijayawada-
520 002, A.P., India.
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Osteoporosis is characterized by decreased bone mineral density and
mechanistic imbalances of bone tissue that may result in reduced skeletal
strength and an enhanced susceptibility to fractures. Osteoporosis in its most
common form affects the elderly (both sexes) and all racial groups of human
beings. Multiple environmental risk factors like acquired immune deficiency
syndrome (AIDS) are believed to be one of the causes of osteoporosis.
Recently a high incidence of osteoporosis has been observed in human
immunodeficiency virus (HIV) infected individuals. The etiology of this
occurrence in HIV infections is controversial. This problem seems to be more
frequent in patients receiving potent antiretroviral therapy. In AIDS, the
main suggested risk factors for the development of osteoporosis are use of
protease inhibitors, longer duration of HIV infection, lower body weight
before antiretroviral therapy, high viral load. Variations in serum
parameters like osteocalcin, c-telopeptide, levels of elements like Calcium,
Magnesium, Phosphorus, concentration of vitamin-D metabolites, lactate
levels, bicarbonate concentrations, amount of alkaline phosphatase are
demonstrated in the course of development of osteoporosis.
OPG/RANKL/RANK system is final mediator of bone remodeling. Bone
mineral density (BMD) test is of added value to assess the risk of
osteoporosis in patients infected with AIDS. The biochemical markers also
aid in this assessment. Clinical management mostly follows the lines of
treatment of osteoporosis and osteopenia.
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Osteoporosis, AIDS, HIV, Bone mineral density, HAART, Protease inhibitor,
OPG/RANKL/RANK
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K.R.S.Samabasiva Rao
is Associate Professor and Head of Centre for Biotechnology at
Acharya Nagarjuna University. He is specialized in the area Environmental Biotechnology
and has been involved in teaching and research of Biochemistry. His major research interests
are in the molecular diagnosis of pathological diseases, and role of anti-oxidants in diseased
conditions.
…Continued at the end of paper.
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Dr. K.R.S.Samabasiva Rao. krssrao@yahoo.com. Phone - 91- 863- 2293400. Fax - 91-863-
2293378
Int. J. Med. Sci. 2004 1(3): 152-164
153
1. INTRODUCTION
Osteoporosis is a significant cause of morbidity and mortality worldwide with an estimated ten
million people in the United States already living with this disease [1]. It is a disease characterized by
abnormalities in the amount and architectural arrangement of bone tissue, which lead to impaired
skeletal strength and an increased susceptibility to fractures [2]. Bone is composed of organic
component consisting of collagen which gives bone its flexibility, and a mineral component that
includes calcium and phosphate salts, which combine to form hydroxyapatite crystals and add hardness
to the collagen matrix. Osteoporotic condition manifests reduced bone mass with a loss of both
collagen and minerals. Inspite of this loss, the collagen - calcium ratio is maintained at normal levels.
However the reduced levels of both collagen and calcium compromise the bone strength leading to risk
of fracture. Osteoporosis is characterized as either primary or secondary. Primary osteoporosis occurs
in both sexes at all ages but often follows menopause in women and occurs later in life in men. In
contrast secondary osteoporosis is a result of medication, other conditions, or diseases [3]. Many of the
commonly occurring diseases like endocrine disorders, malabsorption disorders, bone marrow
disorders and inflammatory diseases were reported to be associated with osteoporosis. In addition
AIDS or HIV infection is also reported to play an important role in osteoporosis. In the recent days,
high incidence of osteoporosis has been observed in HIV infected individuals [4-8].
AIDS is one of the known multiple environmental risk factors of osteoporosis [9]. HIV infection is
associated with numerous metabolic and endocrine complications, leading to loss of appetite and
hypogonadism. Medication during therapy also affect bone metabolism and contribute to bone loss
[4,5]. Bone remodeling process is altered in HIV-infections which contributes to bone loss [6]. Weight
loss, reduced lean body mass, and impaired functional capacity are the factors which may further
predispose HIV infected individuals with wasting to bone loss. Reduced bone mineral density (BMD)
has been demonstrated in HIV-infected men with hypogonadism [7] as well as in non-wasted HIV
infected men [8]. Anabolic effects of testosterone and progressive resistance training therapy on lean
body mass and muscle function in men with AIDS wasting have recently been reported [10,11].
Osteoporosis problem seems to be more frequent in patients receiving potent antiretroviral therapy,
although a specific contribution of the drugs used in different combination regimens is yet to be
established [12-15].
The introduction of highly active antiretroviral therapy (HAART) with the use of protease
inhibitors (PI) has resulted in significant reductions in morbidity and mortality from HIV infection in
recent years [16,17]. Practitioners have now become more cautious in early initiation of HAART in
light of reports concerning serious and potentially irreversible toxicities associated with numerous
antiretroviral drugs [18-24]. These toxicities include the development of diabetes mellitus, insulin
resistance, hyperlipidemia, lipodystrophy and lactic acidosis [19-24]. The current review focuses on
the possible factors that affect bone turnover and cause related bone disorders in AIDS.
2. EPIDEMIOLOGY OF OSTEOPOROSIS
A. MAGNITUDE OF THE PROBLEM
The number of people considered to have osteoporosis depends entirely on the way the condition
is defined in practice. A committee of the World Health Organization (WHO) recommended
the definitions shown in Table-1 [25]. It is possible to diagnose and treat osteoporosis (bone density
levels more than 2.5 standard deviations (SD) below the young normal mean) prior to the occurrence of
fractures (established osteoporosis). This avoids the need to restrict treatment to end-stage disease,
where it may be of limited effectiveness. It also circumvents the conceptual confusion that previously
existed when a fracture occurred, without any change in underlying bone density [26]. Women with
bone density levels between 1.0 and 2.5 SD below young normal mean levels have low bone mass, or
osteopenia. Thus perimenopasual women with bone density that is 1 SD below the young normal mean
might not have pathologically low bone mass but still they are at sufficiently high risk of fracture over
their remaining lifetime that preventive therapy is indicted [27]. This is particularly important since
currently available treatments can conserve existing bone mass but cannot restore osteoporotic bone to
biomechanical normality [28].
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154
Table 1: World Health Organization Definition of Osteoporosis
Bone Disorder Bone Density in standard deviation
(below the young adult mean)
Normal >1
Osteopenia 1-2.5
Osteoporosis >2.5
Severe Osteoporosis >2.5 with fracture
Source of table – Reference [25]
B. RISK FACTORS FOR OSTEOPOROSIS IN AIDS
The risk factors for osteoporosis are fairly straight forward (fig 1).
Fig.1 Schema of the object of environmental and genetic risk factors on the interaction between bone
strength and trauma that leads to osteoporotic fracture. Source of Fig. - Reference [29]
Osteoporosis in its most common form occurs in both the sexes of elderly and all racial groups
affecting the BMD. The variations in bone mineral density in men and women are shown in fig. 2 [29].
A person’s bone mass later in life is determined by the maximal bone mass achieved in young
adulthood, as well as by the subsequent rate of bone loss. At the of age 70 years, these two
determinants of bone mass are equally important [30]. The bone loss results from age-related factors
that occur universally in the population and account for slow bone loss over life in both sexes. An
accelerated phase of bone loss is associated with the menopause in women and hypogonadism in some
men; and from medical and surgical conditions that produce secondary osteoporosis [28]. Thus race
and sex differences in osteoporosis are explained in part by the heritability of skeletal size. Bone mass
is greatest in those of African heritage, who have the lowest fracture rates, and is least in Caucasian
women of Northern European origin, who have the highest fracture rates [32]. Similarly the accelerated
phase of bone loss in perimenopasual women is superimposed upon the slower, age-related bone loss
seen in both sexes and explains in part the two fold higher incidence of fractures among women than
men later in life [28]. Other genetic risk factors play a major role in the heritability of many
components of bone strength. There are a small number of cytogenetic [32,33] and monogenetic
diseases causing osteoporosis [34-39]. Quantitative traits in bone strength in the normal population do
not conform to a monogenetic mode of inheritance. The common form of osteoporosis is generally
considered to be polygenic arising from the interactions of common polymorphic alleles at quantitative
trait loci (QTL) with multiple environmental factors. Finding the genes underlying osteoporosis
typically requires identification of its key heritable phenotypes and demonstrating in family and
population studies that these phenotypes are coinherited with specific alleles. With progress in
developing statistical methods to detect QTL and biochemical techniques to identify and map abundant
Environmental Risk Factors
Susceptibility Genes
Skeletal Fracture
Bone strength
Mass
Shape
Structure
Quality
Trauma
Severity
Frequency
Direction
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155
polymorphisms throughout the genome studies [40,41] for identifying the susceptibile genes for
osteoporosis made easy for timely study.
Microbial genome sequencing is likely to play an increasingly important role in the analysis of
newly discovered human genes and provide further clues to the molecular basis of the diseases [42].
Because of the close correspondence among mammalian genomes, it is a hope that identification of the
genes underlying bone strength in mammals such as the mouse [43] will be of major assistance for
human studies. The identification of susceptibile genes for osteoporosis is expected to be a major
contributing factor toward the long-term goal of understanding the molecular biology of the normal
variation in bone strength and how it may be modified to prevent osteoporotic fractures. As with all
genetic studies in humans, these scientific advances are need to be made in an environment of legal and
ethical safeguards that are acceptable to the general public [44].
Fig 2. Normal variation (mean and 2 8D) and change in BMD with age in healthy men (black circle)
and women in (open circle) (Normal population Data base, DPX-IQ Reference Manual, Documentation
Version 5/96, Lunar Corp., Maidson, WI). Peak bone mass at hip and spine for measurement on Lunar
machines is taken as the mean BMD between age 20 and 40 yr, but this age range varies with DXA
machine manufacture. Source of Fig. - Reference [29]
In AIDS, the mainly suggested risk factors for the development of osteopoenia and osteoporosis
are the use of protease inhibitors, longer duration of HIV infection, high viral load, high lactate
levels, low bicarbonate levels, raised alkaline phosphatase level, and lower body weight before
antiretroviral therapy. There have also been a few case reports of pathologic fractures in AIDS patients
with antiretroviral therapy-induced osteopenia and osteoporosis. The underlying mechanism triggering
bone loss in HIV infected patients is still unknown [3].
3. BONE TURNOVER
A. BONE REMODELING
Growth in bone size and strength occurs during childhood, but bone accumulation is not
completed until the cessation of linear growth (till the third decade of life). Even after bone
accumulation has ended, there is a constant state of remodeling with repeated cycles of resorption
followed by the deposition of new bone [3].
The cellular process of bone activity by which both cortical and cancellous bone is maintained is
referred to as bone remodeling. This bone remodeling process takes place in discrete packets known as
multicellular units [45]. Initially, a cell from the hematopoietic granulocyte-macrophage colony-
forming unit lineage (along a bone surface) is activated and proliferates or transforms into an osteoclast
[46]. An osteoclast creates bone cavity and subsequently, osteoblasts, derived from pleuripotent
mesenchymal stem cells of the bone marrow, fill in the area of resorption with type 1 collagen [47].
Type I collagen ultimately becomes mineralized, probably as a function of the osteoblasts, thereby
completing the process of new bone formation. There is an interdependency of the osteoclastic and
osteoblastic activities where by osteoclasts are initially recruited to a particular site on the bone
surface, and when their task is completed, they signal the osteoblasts to attend to that same site. This
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interrelationship is known as coupling and is crucial link in the chain of bone-remodelling events [48].
A situation that interferes with coupling process or that causes imbalances between bone forming and
resorbing relationship leads to significant loss of bone over the time.
Regulation of the bone-remodeling process is complex. Undoubtedly, there are numerous systemic
hormones, such as parathyroid hormone, 1, 2 5-dihydroxy-vitamin D (calcitriol), calcitonin, estrogens,
and androgens that regulate the process. Vitamin D is recognized as a stimulator of osteoclastic
formation and a promoter of osteoblast differentiation [49]. There are also numerous local factors that
play an important role in the physiology of bone remodeling like interleukins (IL-1 and IL-6),
transforming growth factors (TGF), prostaglandins, tumor necrosis factor (TNF), lymphotoxin, colony
stimulating factors (CSF), and gamma interferons [50-53].
OPG/RANKL/RANK system is the dominant, final mediator of osteoclastogenesis. This system
explains the precise mechanisms by which preosteoblastic stromal cells control the osteoclast
development. It is a specific factor produced by preosteoblastic/stromal cells that is both necessary and
sufficient for osteoclast development. Osteoprotegerin (OPG) is a secreted soluble member of the
tumor necrosis factor receptor superfamily (TNFR), also known as osteoclastogenesis inhibitory factor
(OCIF) [54,55]. It has specificity for OPG/OCIF function for inhibiting osteoclast differentiation. The
initial cloning and characterization of OPG as a soluble, decoy receptor belonging to the TNF receptor
superfamily is the first step that eventually led to an unraveling of this system. Soon thereafter, the
molecule blocked by OPG, initially called OPG-ligand/osteoclast differentiating factor (ODF).
RANKL, is the key mediator of osteoclastogenesis in both a membrane-bound form expressed on
preosteoblastic/stromal cells as well as a soluble form. RANKL, in turn, binds to its receptor, RANK,
on osteoclast lineage cells. The decisive role played by these factors in regulating bone metabolism was
demonstrated by the findings of extremes of skeletal phenotypes (osteoporosis vs. osteopetrosis) in
mice with altered expression of these molecules. Identifying the factors regulating this system, the
signaling mechanisms involved in the RANKL/ RANK pathway, and finally, potential alterations in
this system in metabolic bone disorders that develop during HIV infections are crucial in understanding
the mechanism underlying osteoclastogenesis in this particular type [56].
B. INTERACTIONS BETWEEN SKELETAL , IMMUNE AND HORMONAL SYSTEMS
The entry of HIV-1 into target cells requires the binding of the viral envelope glycoprotein (Env)
with the target cell CD4 and an additional target cell co-receptor [57].
The co-receptors required for the
fusion of the T cell-tropic and macrophage-tropic viruses with their target cells have now been
identified to be fusin and CCR-5, respectively [58,59]. Fusin is a 7 TM domain protein with significant
amino acid sequence homology to the IL-8 receptors. A CXC chemokine, PBSF/SDF-1, has recently
been identified to be a ligand for fusin [60,61] The identification of CCR-5 as the co-receptor for
macrophage-tropic viruses is consistent with an earlier report identifying the CCR-5 ligands (RANTES,
MIP-1α and MIP-1β) as the major HIV suppressive factors produced by CD8
+
T cells for macrophage-
tropic, but not T cell tropic, HIV isolates [62]. Besides fusin and CCR-5, use of other chemokine
receptors such as CCR-2B and CCR-3 by a minority of HIV isolates has also been reported [63].
The hypothesis that the systemic activation of T cells in vivo leads to an osteoprotegerin ligand-
mediated increase in osteoclastogenesis and bone loss [64]. This explains the interaction of HIV
infection and bone mineralization. When the homeostasis between RANK/RANKL- osteoprotegerin is
lost, there is an increased incidence of loss of bone mineral density. Interactions between cells of
skeletal and immune system are important for the maintenance of bone homeostasis [65]. These
cellular circuits are in part mediated by specific cytokines and changes in levels of these mediations
may result in altered bone remodeling and disease [65-67]. Cytokines such as IL-1, IL-6, IL-11 and
TNF-α may stimulate osteoclast activity [66-68] and enhanced IL-6 levels appear to play a pathogenic
role in the enhanced bone resorption of post menopasual osteoporosis [69]. Some of these cytokines
may also inhibit bone formation exerted by their negative regulatory effects on osteoblasts [65, 70,71].
This inhibitory effect on osteoblats combined with stimulation of osteoclasts suggest a pathogenic role
for these cytokines in bone disorders characterized by increased resorption combined with decreased
formation of bone [65].
Persistent activation of proinflamatory cytokines such as IL-1 and in particular TNF- α appears to
play an important pathogenic role in HIV [72-75]. This proinflamatory activation may enhance HIV
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replication, contributing to the development of immunodeficiency and certain clinical manifestations
[74,75] and also be related to the endocrine abnormalities seen in HIV infected individuals [76,77].
Vitamin D metabolites and elements like Calcium, Magnesium, Phosphorus have complex effects in
the bone system, with stimulatory effects on both formation and resorption [65,78].
Estrogen deficiency causes an increase in osteoclastic resorbing capacity [79-81]. Estrogen
deficiency both directly and indirectly decreases the efficiency of intestinal and renal calcium
absorption and reabsorption respectively. Testosterone deficiency in men is the major identifiable
cause of male osteoporosis. It has analogous mineral metabolism effects. Evidence in support of
gonadal hormone deficiency as the cause of increasing bone resorption is that specific receptors for
estrogen and testosterone have been identified on the surface of the bone cells [82].
4. BONE MINERAL DENSITY IN HIV INFECTIONS
Bone mineral density is widely accepted as a measure of bone strength. BMD measurements have
been shown to correlate strongly with the load bearing capacity of the hip and spine and with the risk
of fracture. In patients with osteoporosis, there is a four fold to five fold increase in risk for fracture.
And for patients with osteoporosis and a history of fracture, the risk of another fracture occurring is
increased twenty fold.
While decreased BMD is certainly an important prediction of fracture risk, it is not the only
parameter to consider. Fracture risk is also associated with a history of falls, low physical function such
as slow gait speed and decreased quadriceps, impaired cognition and vision, and the presence of
environmental hazards [3].
A. BMD in HIV infected individuals prior to use of Highly Active Anti Retroviral Therapy
(HAART)
Prior to the widespread use of HAART, studies indicated that bone metabolism was altered, albeit
minimally, in HIV infected individuals. Before the availability of protease inhibitors (PIs), low BMD
was rarely observed in HIV infected individuals. However, the role of HAART in the reduction of
BMD is controversially reported. According to some reports the direct correlation between the use of
PI and osteoporosis is not so evident. BMD was significantly lower in HIV-seropositive patients in
comparison with controls in lumbar spine, proximal femur and total body, without significant
differences among treatment-naive patients and either of the treatment groups. Only time with HIV
infection and not specific therapy was associated with BMD decreases [83] patients not receiving
antiretrovirals also have a higher than expected prevalence of reduced BMD, which suggests that HIV
itself may be a contributing factor, mediated by immune activation and cytokines [84]
In one analysis, 45 HIV-infected patients had statistically significant lower lumbar spine BMD
scores than did HIV-negative controls. The subjects and controls did not differ in total or hip BMD. A
small decrease in total body BMD was observed in a longitudinal follow up after 15 months. No
significant reduction was found in spine and hip BMD. This matched the lines of osteopenia rather than
osteoporosis [85]. But advanced stages of HIV infection demonstrated lower BMD of the individuals
than HIV-negative controls. Several additional studies suggest a significant prevalence of low BMD in
HAART-naive patients. This shows the probable role of HIV infection itself in decreasing BMD. The
prevalence of osteoporosis in HAART-naive population is found to be approximately 28%, compared
with the expected 16% in the general population [86-88]
Studies associated with biochemical markers of bone metabolism and bone biopsy of therapy-
naïve HIV-infected individuals show a significant decrease in osteocalcin, a marker of bone formation
and a marked increase in C-telopeptide, a marker of bone resorption in a comparison with healthy HIV-
seronegative controls. These facts correlate with enhanced activation of the tumor necrosis factor
system and increasing severity of HIV disease [89-91]. Numerous cytokines are known to induce
differentiation of bone marrow precursors into osteoclasts. Hence bone resorption and osteoporosis are
probably favoured. Abnormal immune system activation may be one of the probable causes that lead to
bone resorption.
A study of bone samples from anti-retroviral therapy-naïve HIV infected subjects compared with
healthy controls showed only decreased levels of osteocalcin in individuals with lower CD4 counts. No
alterations in BMD or biochemical differences in bone metabolism were demonstrated [92].
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B. BMD in HIV infected individuals after the use of HAART
A cross-sectional analysis of whole body, lumbar spine and proximal femur BMD in male subjects
receiving HAART that included a protease inhibitor (PI), HIV-infected patients not receiving a PI and
healthy seronegative adults using dual x-ray absorptiometry (DXA) scans was performed. Men
receiving PI had lower lumbar spine BMD compared with the other two groups. 50% of the subjects on
PIs were classified as osteopenic or osteoporotic according to WHO classification [13]. An assessment
of bone metabolism in HIV infected subjects receiving HAART with 2 nucleosides and a PI [93]
showed 43% of the subjects to be osteopenic or osteoporotic according to the WHO definition.
Increased markers of bone resorption and bone formation, including elevations in urine pyridinolines,
bone alkaline phosphatase, and osteocalcin. Another study in HIV-infected children also demonstrated
HAART-associated losses in BMD that were associated with an increased rate of bone turnover [94].
Other studies have shown a more accelerated loss of BMD in individuals receiving potent antiretroviral
therapy, but the association with PI use remains speculative and needs to be confirmed [14-15].
It is impossible to attribute cause and effect and to measure the cumulative effects of other
important but common risk factors for BMD loss in HIV-infected individuals. Prospective and
longitudinal studies are necessary to determine the exact nature and mechanism of each individual
factor in the pathogenesis of HIV-related bone mineral loss.
5. ASSESSMENT OF BONE REMODELING
Bone remodeling can be assessed using surrogate markers of bone turnover in the blood or urine.
These markers include bone-specific alkaline phosphatase and osteocalcin, which are indices of bone
formation. There are also urinary levels of pyridinolines and deoxypyridinolines and serum and urine
levels of type 1 collagen telopeptides (CTX and NTX), which are indices of bone resorption. The level
of these markers may identify changes in bone remodeling within a relatively short time - several days
to months - before changes in bone density can be detected. It is important to realize, however, that
marker levels cannot predict fracture risk and are only weakly associated with changes in bone mass.
Therefore, they are of limited utility in the clinical evaluation of individual parametres [3].
6. CLINICAL MANAGEMENT
Current diagnosis and treatment of osteoporosis is primarily based on recommendations used for
the management of disease in HIV-seronegative adults. Measurement of BMD as a routine test in HIV-
infected patients is not recommended. However, plain radiographs and magnetic resonance imaging are
the cornerstones of diagnosis. A detailed history of the past, physical examination, evaluation of
nutritional status and potential secondary causes of osteoporosis are to be taken into consideration
before the onset of the treatment of HIV-infected patients. Abnormal laboratory values of elevated
alkaline phosphatase or low testosterone obtained during the course of HIV treatment should not be
ignored during treatment [94]. The primary diagnosis of osteoporosis is based on the WHO definitions
according to measurements of BMD. The most widely used technique for determining BMD is DXA.
DXA scanning measures bone mass and density in central regions of interest (hip and spine) as well as
appendicular regions (wrist, forearm, heel). It has become the gold standard to which all other bone
densitometry techniques are compared [95-97] Techniques for determining bone mineral density at
various sites are summarized in Table 2. DXA studies are also useful to define fracture risk as well as
to measure the efectiveness of various therapies on bone mass. Biochemical markers of bone turnover
can provide complemetnary information to DXA scans, including changes in bone remodeling that can
be identified before changes in BMD [1]. However the exact effectiveness of such markers remains
controversial.
Table 2: Techniques for determining bone mineral density at various sites
Technique Sites
Central dual-energy x-ray absorptiometry Spine, hip, whole body
Peripheral dual-energy x-ray absorptiometry Middle finger, wrist, heel, forearm
Single-energy x-ray absorptiometry Forearm, heel
Quantitative computed tomography Trabecular bone only; vertebral body
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Peripheral quantitative computed tomography Forearm
Ultrasound Heel, patella, ankle
Management is dependent on the stage of bone disease and ranges from observation to total joint
arthroplasty. Clinicians may help to prevent HIV-associated osteonecrosis by encouraging patients to
limit their exposure to the established risk factors for the disease [98]. The treatment strategies that are
effective in the general population should be pursued. Reversible causes of secondary osteoporosis
should be studied. Vitamin D and calcium intake should be optimized. Other nutrients are also
important in relation to bone health. Diets with very high protein content, excess caffeine, phosphorus,
and sodium can increase calcium losses. Moderate physical activity is also recommended. The
treatment for such conditions usually follows the general lines of management of osteoporosis [1].
Patients undergoing long-term corticosteroid treatment should begin primary prevention measures
as soon as such agents are prescribed. Attempts to preserve bone should not be delayed until the
underlying disease process is under way. Any patient taking glucocorticoids who has a T score of less
than -1.0 should immediately be given pharmacologic treatment [99]. The most commonly used
pharmacologic treatments for osteoporosis (excluding calcium and vitamin D supplements) are
antiresorptive agents (estrogen, bisphosphonates, calcitonins, and selective estrogen receptor
modulators). Other agents under development or already in use outside the United States include
fluoride salts, parathyroid hormone, active forms of vitamin D (calcitriol, alfacalcidol), and anabolic
steroids.
HRT
The utility of HRT (estrogen) for prevention of bone loss in early menopause is well established. HRT
that is started at menopause retards or prevents bone loss and increases BMD somewhat. HRT
continues to prevent bone loss for as long as it is taken, but bone loss resumes when estrogen is
discontinued [100,101]. HRT is also effective in older women with established osteoporosis. Added
potential benefits of HRT include controlling menopausal symptoms and reducing the risk of heart
disease. Despite its documented benefits, however, some women find that the side-effect profile of
HRT (eg, breast tenderness, abnormal uterine bleeding, endometrial hyperplasia, migraine, deep venous
thrombosis) is unacceptable. Additionally, women may fear the relationship between HRT and breast
cancer. Nevertheless, hormone replacement is considered first-line therapy in most postmenopausal
patients.
Bisphosphonates
Candidates for bisphosphonate treatment include premenopausal women at increased risk for
osteoporosis, postmenopausal women who forgo HRT, men with osteoporosis [102,103], and all
individuals receiving high-dose corticosteroid therapy. In controlled clinical trials [104,105],
bisphosphonates reduced the risk of fractures of the spine, hip, and wrist by 40% to 50% in
postmenopausal women. These data are particularly significant because no randomized clinical trials
have actually measured the effect of HRT on hip fracture, the most serious consequence of
osteoporosis, even though observed studies consistently show that postmenopausal women who have
been receiving HRT for 5 to 10 years have a lower risk of hip fracture than their counterparts who have
not [106]
Several studies have shown bisphosphonates to be highly effective for prevention of
glucocorticoid-induced bone loss, and these drugs have been approved by the US Food and Drug
Administration (FDA) for this indication. Risedronate sodium (Actonel), a pyridinyl
bisphosphonate with FDA approval for the treatment of Paget's disease of bone, has recently been
approved for prevention and treatment of postmenopausal and glucocorticoid-induced osteoporosis.
Recent data from two controlled studies showed that this agent reduced the incidence of vertebral
fractures by 70% in patients beginning corticosteroid therapy (when bone loss is most rapid) compared
with controls [107].
Clinical experience with bisphosphonates has shown that patients may experience upper
gastrointestinal disturbance, particularly esophageal symptoms (heartburn, painful or difficult
swallowing) .Alendronate sodium (Fosamax) should be taken with 6 to 8 oz of plain water at least one-
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half hour before the first food, beverage, or medication of the day. Other beverages (including mineral
water), food, and other medications can reduce the absorption of oral bisphosphonates. Also, patients
should not lie down until at least 30 minutes after taking alendronate and until after the first food of the
day [108]. Clinical trials of risedronate have included postmenopausal women with ongoing
gastrointestinal disease and those using aspirin or nonsteroidal anti-inflammatory drugs. Preliminary
results [109] indicate that the incidence and severity of gastrointestinal events with use of risedronate
are similar to those reported in the control group. Alternative dosage formulation and administration of
bisphosphonates is under investigation.
Calcitonins
For patients who are unable or choose not to undergo HRT or take a bisphosphonate, a calcitonin is a
viable alternative. Calcitonin-salmon is administered as a nasal spray (Miacalcin) or by injection.
Calcitonin prevents bone loss and fracture in established osteoporosis, although it is somewhat less
effective than HRT and bisphosphonates [110]. Recent results of a large controlled study (Prevent
Recurrence of Osteoporotic Fracture) showed that calcitonin-salmon nasal spray reduced the incidence
of new spinal fractures by 36% over a 5-year period, compared with placebo, in postmenopausal
women who had previously experienced fracture. To date, calcitonin has shown no effect on
nonvertebral fractures, and it has not been shown to reduce fracture risk in corticosteroid-treated
patients [111]. However, calcitonin has modest analgesic properties, which may decrease opioid use
and allow earlier ambulation in patients with acute vertebral fractures.
Selective estrogen receptor modulators
A selective estrogen receptor modulator may serve as an alternative to HRT for selected patients.
Raloxifene (Evista) is the most studied of these drugs to date; its estrogenlike effects increase BMD .
Raloxifene decreases total and low-density lipoprotein cholesterol levels, but unlike HRT, it does not
affect high-density lipoprotein cholesterol. Also, unlike HRT, raloxifene does not appear to stimulate
the endometrium . Recent data from the multiple outcomes of Raloxifene evaluation showed that 60-
and 120-mg daily doses of raloxifene significantly decreased vertebral fracture risk during the first 36
months of treatment, compared with placebo. All patients also received calcium and cholecalciferol. At
36 months, raloxifene did not significantly lower the risk of nonvertebral fractures compared with
placebo, although the cumulative incidence of nonvertebral fractures in active and placebo groups
begins to diverge at 2 years. The effect of raloxifene on hip fracture is under investigation [112,113].
Specific studies with HIV-infected individuals should be conducted to determine the most effective
way of this treatment.
7. CONCLUSION
Osteoporosis has been the recently recognized complication affecting HIV-positive patients.
Etiology and pathogenesis of osteoporosis in HIV infection are still uncertain. Progression in HIV
infection and HAART with PI are the possible factors that precipitate osteoporosis in HIV–sero-
positive patients. Further studies should be extended to look into the natural history of bone loss
during HIV disease. This would help to understand the mechanisms of uncoupled bone turnover and
effects of PI therapy on HIV infected patients. As the number and life expectancy of HIV-positive
patients treated with HAART increases, the development and treatment of osteoporosis in HIV
infection should be taken into consideration in the long term management of HIV disease.
Conflict of interest
The authors have declared that no conflict of interest exists.
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