Metabolic effects – bone density and avascular necrosis

17 October 2000. Related: Conference reports, Side effects, Lipodystrophy and metabolic complications, Lipodystrophy Workshop (IWADRLH) 2nd Toronto 2000.

Simon Collins, HIV i-Base

Osteoporosis, osteonecrosis and bone metabolism changes

There have been increasing reports of changes in bone mineral metabolism over the last two years in patients receiving anti-retroviral treatment. These are often individual case studies and range from relatively minor osteoporosis (reduction in mass and volume of bone) to more serious osteonecrosis (death of bone cells due to poor blood supply).

Osteoporosis is much more common in the general population, particularly in older women, and age and gender are risk factors. Disorders in which osteoporosis is a common feature include hypogonadism, hyperadrenocorticism, chronic corticoid administration, hyperparathyroidism, thyrotoxicosis, malabsorption, malnutrition, calcium deficiency, immobilization, chronic heparin administration, alcoholism, cigarette smoking, reduced physical activity etc. Although painless, it leaves bones more brittle and increases the risk of fractures. Osteonecrosis is less common but can be very painful, affecting particularly the femoral head, and often requiring replacement surgery. DEXA scan is routinely used for diagnosing both conditions.

At the Retrovirus conference in 1999, Luna and colleagues found a reduction in bone mineral density (BMD) in total body, but not at spine or hip, and without evidence of changes in calcium and phosphorus metabolism, in 17 HIV-positive men (mean age 37.5, range 26-50). [1] At the same meeting Timpone and colleagues presented results from a retrospective case review of 600 patients that had identified 8 cases (7.8 male, mean age 39) of avascular necrosis (AVN) with an estimated prevalence of 1.33%. Prior to 1996, only 23 cases of AVN had been reported. [2]

At this years Retrovirus meeting an incidence of osteopenia of 28% and osteoporosis of 9% was identified in a group of 80 Australian patients receiving HAART [3] and severe osteonecrosis in 21% of 64 PI-receiving patients in a study from Washington University. [4] Researchers from both these studies presented an update of their work at this year’s Lipodystrophy workshop.

A further six posters (three of which concerned women) at Durban this summer also addressed these concerns. [5] Although a link to PI-based regimens has been reported, this has not been established and two switching studies have so far failed to show an improvement over 24 weeks following the change to an NNRTI-based regimen.

The following report covers oral and poster presentations from both the Lipodystrophy meeting and ICAAC.

Potential mechanisms

Dr Pablo Tabas from the Washington University School of Medicine looked at serum and urine markers in 73 HIV-positive patients on a PI-containing regimen to identify whether the pathogenesis of decreases in BMD previously reported by this group involved either the impaired bone formation or the resorption process. [6] Bone is a living tissue, 10% of which is replaced each year in a continuous turnover. It is resorbed by osteoclasts that release calcium and collagen metabolites and formed by osteoblasts. An imbalance in these two processes leads to bone loss. Bone consists of mineralised organic matrix, 90% of which is type 1 collagen and calcification provides the degree of ‘hardness’.

Bone serum markers determined in the study included: creatinine, PTH panel, bone-specific alkaline, phosphatase, osteocalcin, 25-OH-vitamin D3, 1,25-(OH)2-vitamin D3. Urine markers included: creatinine, free cortisol, calcium, pyridinoline, deoxypyridinoline and urine N-teleopeptide. Spine and hip BMD was assessed by DEXA scan. Distribution of lumber t-scores showed 5% of patients in this group to have osteoporosis and 40% osteopenia. Mean CD4 count was 560 (±45), viral load was undetectable in 95% of patients. PI-use included indinavir in about half the patients, nelfinavir in 25% and various dual-PI combinations in the remainder.

Markers of bone formation (alkaline phoshatase, 188±152IU/L, p=0.006 and osteocalcin, 20 ± 26ug/l) and of resorption (urine pyridinoline, 41 ±22nmol/mmol creat, and deoxypyridoniline 10 ±6nmol/mmol creat) were significantly elevated compared to a normal range and there was a strong correlation between the two processes (p<0.0001, r=.581). There was an inverse correlation with these markers and t- and z- scores for the lumbar spine. Dr Tebas concluded that this strongly suggested an increase rate of bone turnover in patients with DEXA evidence of bone demineralisation.

In a second presentation Dr Tebas suggested that a mechanism for this could be through protease inhibitor inhibition of the hepatic P450 enzyme which also mediates vitamin D to its most potent circulating metabolite, part of an essential process for vitamin D control of calcium homeostasis. [7] In vitro studies were run in the human monocyte-macrophage cell line THP-1 which expresses a 1alpha-hydroxylase identical to the renal enzyme responsible for the final formation of bioactive 1,25-(OH)2-vitamin D. The level of inhibition of the most active metabolite in this cells line by the three PIs studied was 80% by ritonavir, 66% by indinavir and 32% by nelfinavir.

As with many presentations at this meeting, this provided a glimpse into what may be occurring but little indication to help clinical practice. The researchers themselves thought this may only be one of several mechanisms that affects multiple steps of a very delicate metabolic balance. High-dose vitamin D supplement was specifically not recommended due to toxicity concerns although an adequate intake of calcium and Vitamin D was recommended. It was also noted that patients in the study retained normal levels of vitamin D and PTH and although higher levels of calcium were contained in urine, calcium levels in serum remained normal.

A French poster presented at ICAAC also found a disparity between estimated calcium intake in patients with osteopenia (mean=1077 mg) and those without symptoms (mean=799 mg) that couldn’t be explained by the investigators. [8]

Dr Allanena and colleagues from the Hospital Hotel-Dieu, Nantes, enrolled 85 HIV-positive patients consecutively (70 men, 15 women) in a cross-sectional study to measure fat mass, lumber spine (L1-L4) and proximal femur BMD with t- and z-scores. The levels of both osteopenia and osteoporosis were again found to be high in patients on ARV treatment at 43% and 6.6% respectively. Osteopenia was also detected in 3/15 (20%) of patients not on treatment, with no cases of osteoporosis.

When women in the study were analysed separately rates of osteopenia and osteoporosis were 6/17 (35%) had 2/17 (12%) respectively, although there were confounding factors in this group (hormonal treatment n=8, amenorrhea n=3, menopause n=4, prolonged corticoid treatment n=1). Mean z-score for men in the study was 83% of normal for an age-matched population, and although it is difficult to accurately estimate time of infection, this correlated with risk of altered bone metabolism. No clear association however was found between osteopenia or osteoporosis and use of ARV treatment.

When Andrew Carr and David Cooper assessed bone density (t-score, z-score and total BMD) by DEXA in a cohort of 221 otherwise well HIV-positive men enrolled in a lipodystrophy study, they also failed to find a link between BMD changes and PI type or duration. This group included 32 treatment naive patients, 42 who were nuke-only experienced and 147 using PIs in a triple combination. However, 32 patients (14%) had NRTI-associated lactic acidemia (>2 mmol/L) and only this and lower weight prior to starting therapy had an independent association with risk of osteopenia and osteoporosis. These were detected in 3% and 22% of people in the study respectively. [9]

Table: Parameters associated with osteopenia

The link between osteopenia and HIV itself, and the possibility that antiretroviral therapy could reduce the risk of osteopenia was suggested in a poster presented by Graeme Moyle from the Chelsea and Westminster Hospital, London. [10] Whole body DEXA scans on 52 patients (51 male) with physical signs of lipodystrophy found a similar level of BMD between PI (n=22), RTI-only (n=10) and treatment naive control (n=19) arms (1.17, 1.17 and 1.21 respectively). T-scores were non-significantly lower in the control group (-0.6, -0.69 and – 0.12 respectively).

In this study, time from HIV test to diagnosis of osteopenia showed use of antiretroviral therapy to have a protective effect on BMD (p=0.02 log rank). This was confirmed in a Cox proportional hazards model in which PI and non-PI therapy were associated with reduced hazard ratio of osteopenia (0.17 [95%CI0.06-0.56] and 0.32 [95%CI 0.13-0.82], respectively).

Avascular necrosis (AVN)

Marshall Glesby from Cornell University presented a retrospective review of 14 male patients from a New York clinic, with AVN of femoral head from 1992-2000, 12/14 since 1996 [11]. 8 patients had bilateral AVN and one had AVN of hips and humeral head. Mean CD4 count at diagnosis was 164 cells/mm3, 36% patients had HIV RNA <400 copies/ml.

Cases and controls were matched for year of HIV diagnosis, race, gender, HBV/HCV status, and history of alcoholism, smoking, cancer, diabetes and pancreatitis, CD4, viral load and random TG and glucose. The study aimed to look at potential risk factors, particularly use of PI. Although cases had a longer ARV-use prior to AVN compared to controls (32 vs 14 months respectively, p=0.06), higher PI-use (71% vs 57%, p=0.5) and PI use at diagnosis (57% vs 32%, p=0.18) this was not found to be predictive in a multivariate analysis (Adj OR 1.1, 95%CI 0.11-11, p=0.94).

In fact, only previous PCP was independently associated with AVN in this study, which may have been a surrogate marker for corticosteroid use. Although the study concluded that pathogenisis of AVN in HIV remains unknown and may be multifactorial 11/14 cases vs 17/28 controls had at least one traditional risk factor (matched OR 2.2, 95%CI 0.95-5.0, p=0.06). Increased awareness of AVN allowing early diagnosis of this still rare condition would lead to improvements in surgical outcome.

Summary

We are only just recognising this new complication to affect HIV-positive patients and it may be several years before the mechanism for these changes is understood. Underlying reduction of BMD at around 20-40% in many lipodystrophy cohorts – when it is looked for – should clearly be a concern. Increased reporting and the seriousness of AVN, whether HIV or ARV mediated should alert clinicians to the possibility of diagnosis in patients reporting symptoms particularly if they have other risk factors.

Although not studied in HIV-positive patients, two potential treatments for BMD have been reported this year Alendronate significantly increased spine, hip and total body bone mineral density in a placebo controlled study in HIV-negative men (N Engl J Med 2000;343:604-10). Interestingly, experimental evidence suggested that the cholesterol-lowering statins increased bone formation in a UK study of 41 post-menopausal women receiving statin treatment compared to 100 non-statin controls (Edwards, C J et al. Lancet 2000; 355: 2218 – 2219).

References:

Abstracts referenced from the Conference of Retrovirus & Opportunistic Infections (CROI) are available on-line at:

http://www.retroconference.org/2001

1. Luna, N et al – Bone mineral diminuation in HIV patients treated with HAART. 6th CROI, Abstract 679. http://www.retroconference.org/99abstracts/679.htm
2. Timpone, J et al – Avascular necrosis in HIV+ patients – a potential link to protease inhibitors. 6th CROI, Abstract 680. http://www.retroconference.org/99abstracts/680.htm
3. Hoy, J et al – Osteopenia in a randomised, multicentre study of protease inhibitor substitution in patients with the lipodystrophy syndrome and well vontrolled HIV viremia. 7th CROI, Abstract 208. http://www.retroconference.org/2000abstracts/208.htm
4. Tebas, P et al – Accelerated bone mineral loss in HIV-infected patients receiving potent anti-retroviral therapy. 7th CROI, Abstract 207. http://www.retroconference.org/2000abstracts/207.htm
5. XIII International World AIDS Conference, Durban. Abstracts TuPeB3178, WePeB4235, WePeB4278, ThPpB1485, ThPpB1487, ThPpB1488. Not published on the internet. Copies available through HIV I-Base office if required.
6. Tebas, J – Serum and urine markers of bone mineral metabolism in HIV-infected patients taking PI-containing ART. Abstract 029. 2nd Intl Workshop on Adverse Drug Interactions and Lipodystrophy, Toronto, Sep 2000.
7. Dusso, A – Protease inhibitors inhibit in vitro conversion on 25(OH)-vitamin D to 1,25(OH)2-vitamin D. Abstract 030. 2nd Intl Workshop on Adverse Drug Interactions and Lipodystrophy, Toronto, Sep 2000.
8. Billaud E, Allavena C et al – Osteopenia and osteoperosis in HIV-infected patients: Role of ARV Therapy? – 40th ICAAC, Toronto, 2000. Poster 1304
9. Carr, A et al – Osteopenia in HIV-infected men: association with lactic acidemia and lower weight pre-antiretroviral therapy. Abstract O32. 2nd Intl Workshop on Adverse Drug Interactions and Lipodystrophy, Toronto, Sep 2000.
10. Moyle, G et al – Osteopenia: A Consequence of HIV? Abstract P33. 2nd Intl Workshop on Adverse Drug Interactions and Lipodystrophy, Toronto, Sep 2000.
11. Glesby, M – Case-control study of avascular necrosis in HIV-infected patients. Abstract 033. 2nd Intl Workshop on Adverse Drug Interactions and Lipodystrophy, Toronto, Sep 2000.