Bone mineral content in girls perinatally infected with HIV

Endogenous fecal losses of calcium compromise calcium balance in pancreatic-insufficient girls with cystic fibrosis

OBJECTIVE

Bone mineral density is compromised in individuals with cystic fibrosis (CF); calcium is the major bone mineral. This study examined the impact of endogenous fecal calcium (V(endo)) losses on calcium balance in girls with CF. Study design V(endo) was measured in 12 girls with CF (aged 7-18 years): 7 younger, premenarcheal girls with compromised nutritional status; and 5 older, postmenarcheal girls with adequate nutritional status. V(endo) was measured as the amount of intravenously administered (42)Ca, a calcium stable isotope, in stool relative to urine over 6 days. V(endo) was compared between pre- and postmenarcheal girls by Student's t test. Actual calcium balance [absorbed calcium-(urinary calcium (V(u))+V(endo))] was compared with estimated balance (assuming V(endo)=1.6 mg/kg/day calcium) by paired t test.

RESULTS

V(endo) was 99.3+/-42.3 mg/day. By body weight, V(endo) was highest among premenarcheal girls (3.37+/-1.09 mg/kg/day), resulting in excess losses (>1.6 mg/kg/day) of 55.0+/-45.7 mg/day. Over 1 year, this represents 20.1+/-16.7 g of unattained bone calcium or 6.7+/-4.2% of the bone calcium content of these girls.

CONCLUSIONS

V(endo) is a significant source of calcium loss in individuals with CF and may limit calcium availability for bone mineral deposition.

HIV infection--a risk factor for osteoporosis

Osteopenia and osteoporosis have recently been described as complications of antiretroviral therapy in HIV-infected patients. The advent of highly active antiretroviral therapy in conjunction with improved standard antiviral and antibiotic regimens has dramatically changed the clinical course of HIV infection, resulting in prolonged survival. The pathogenesis and role of each individual medication are poorly understood. Avascular necrosis has also been described in AIDS patients receiving or not receiving antiretroviral therapy. This article is a clinically focused review of the literature on osteopenia, osteoporosis, and mineral metabolism related to HIV infection. In patients with HIV infection, the risks of osteopenia and osteoporosis are not very clear. The suggested risk factors for the development of osteopenia are 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 unknown. The proinflammatory cytokines tumor necrosis factor and interleukin-6 have been found to be constitutionally produced in increased amounts in HIV-positive individuals, and they may have a role in osteoclast activation and resorption. Serum markers of bone formation are decreased and resorption is increased in patients with advanced clinical disease. Hypocalcemia, hypercalcemia, and abnormalities of the parathyroid hormone axis have been described in HIV infection. Histomorphometric analyses have shown altered bone remodeling in HIV-infected patients when compared with controls. Patients with known risk factors for osteoporosis-advancing age, low body weight, and prolonged duration of HIV infection-and those receiving protease inhibitor treatment should be considered for dual x-ray absorptiometry imaging. If bone mineral density is osteopenic or osteoporotic, then the patient should also be screened for other known medical causes of osteoporosis and consider treatment with a bisphosphonate or, if hypogonadal, testosterone replacement under close monitoring.

Altered bone metabolism in children infected with human immunodeficiency virus

AIM

Data on bone homoeostasis of children infected with human immunodeficiency virus (HIV), at the time of the gain in bone mass, are very rare. To determine possible alterations in bone metabolism, 13 prepubertal vertically HIV-infected children were studied.

METHODS

Viral load, CD4 count, interleukin-6 (IL-6), growth hormone, insulin-like growth factor-I (IGF-I), IGF binding protein-3 (IGFBP-3), acid-labile subunit (ALS), IGFBP-3 proteolysis, osteocalcin in blood and N-terminal telopeptide of type I collagen in urine were determined. Lumbar spine bone mineral density was examined by dual-energy X-ray absorptiometry.

RESULTS

Low osteocalcin levels were found in all patients. Low IGF-I was found in only six children, who had low CD4 count and high IL-6 levels, with normal levels of IGFBP-3 and ALS, absent IGFBP-3 proteolysis and decreased bone mineral density, irrespective of viral load or growth.

CONCLUSION

Low serum osteocalcin levels appear to be an initial warning sign of possible altered bone metabolism in HIV-infected children. However, only when the immune system becomes more seriously compromised is bone loss measurable by bone densitometry.

Osteopenia in HIV-infected women prior to highly active antiretroviral therapy

BACKGROUND AND OBJECTIVES

Multiple endocrine and metabolic consequences of human immunodeficiency (HIV) infection exist that alter bone metabolism in patients with acquired immune deficiency syndrome (AIDS). Osteopenia in AIDS patients has been associated with antiretroviral therapy particularly with protease inhibitors. However, there is very little data on bone metabolism in female subjects with AIDS prior to highly active antiretroviral therapy.

METHODS

Bone mineral density (BMD) was assessed by dual-energy X-ray absorptiometry (DEXA) in 50 HIV-infected female outpatients (mean age 37 years) both in the lumbar spine and the Ward's triangle of the left hip. Additional parameter assessed were demographics, smoking, CD4 counts, fasting metabolic parameters and biochemical markers of bone metabolism. None of the patients received reverse transcriptase inhibitors or protease inhibitors, vitamin D or calcium-supplementation.

RESULTS

The serum levels of parathyroid hormone and 1,25-dihydroxyvitamin D (1,25(OH2)D) were significantly reduced compared to 50 age-matched female healthy controls. Urinary calcium and pyridinium crosslinks-excretion corrected for creatinine excretion were elevated (P<0.01) and were likewise significantly correlated with the loss of CD4 cells (P<0.05). Serum osteocalcin was significantly lowered (P<0.01). Reduced BMD of the lumbar spine (t -score <-2.5 SD below normal) was found in seven patients (14%) and osteopenia (t -score -1.0 to -2.5 SD below normal) was diagnosed in 31 (62%). No patient had a fracture since being infected with HIV. The BMD was reduced both in lumbar spine and the hip measured in the left Ward's triangle. There were significant positive correlation between the CD4 counts and 1,25(OH2)D (P<0.05). Neither the CD4 counts nor the duration of disease correlated with BMD. The reduced bone formation rate was linked to progressive loss of CD4-cell count.

CONCLUSION

Osteopenia in HIV-infected female subjects is commonly manifested both in lumbar spine and Ward's triangle of the hip. There is a dissociation between lowered markers of bone formation rate and the increased bone resorption expressed as elevated urinary crosslinks and calcium excretion. Furthermore, the decreased levels of 1,25(OH2)D may contribute to a negative calcium balance and inhibition of bone formation. Our results suggest that further research is necessary to determine, whether low levels of 1,25(OH2)D lead to an accelerated inflammatory process in AIDS, since 1,25(OH)2D is known as an endogenous immune modulator suppressing formation of activated T cells and cell proliferation.

Tenofovir treatment at 30 mg/kg/day can inhibit cortical bone mineralization in growing rhesus monkeys (Macaca mulatta)

The acyclic nucleoside phosphonate analog, 9-[2-(R)-(phosphonomethoxy)propyl]adenine (PMPA; Tenofovir: Gilead Sciences, Inc., Foster City, CA), has been shown to effectively inhibit simian immunodeficiency virus (SIV) replication in rhesus macaques by blocking reverse transcription. However, chronic long-term tenofovir treatment at 30 mg/kg/day, intended to reduce viral replication and illness, has been shown to result in bone deformities and spontaneous fractures in rhesus monkeys. Based on these findings, we studied the effects of tenofovir treatment and pathogenic SIV infection on cortical bone remodeling in rhesus monkeys. Tibiae from tenofovir-treated or untreated, SIV-infected or uninfected, rhesus macaques were evaluated for bone microdamage and remodeling. We found that tenofovir treatment had a significant effect on osteoid (unmineralized bone) seam width in tibial cross-sections. Regardless of SIV infection status, half of the tenofovir-treated animals had significantly increased osteoid seam widths in tibial cortical bone resulting in an osteomalacia-like condition. Pathogenic SIV infection significantly increased tibial resorption cavity density. and this increase was normalized by tenofovir treatment. These results suggest that tenofovir treatment at 30 mg/kg/day inhibits mineralization of newly formed bone. SIV infection results in increased tibial resorption cavity density, while tenofovir treatment tends to minimize this increase. Both defective mineralization of newly formed bone and increased resorption cavity density may result in greater bone fragility.

Osteonecrosis of the hip (Legg-Calvé-Perthes disease) in human immunodeficiency virus-infected children

OBJECTIVE

Osteonecrosis of the hip has been reported in human immunodeficiency virus (HIV)-infected adults; whether this is related to HIV infection or its treatment is unknown. There has been 1 report of osteonecrosis among HIV-infected children. Specifically, avascular necrosis of the hip consistent with Legg-Calvé-Perthes disease (LCPD) was reported in 3 HIV-infected children with AIDS from Spain in 1992. We evaluated the prevalence and incidence of LCPD, the pediatric equivalent of adult osteonecrosis of the hip, in HIV-infected children participating in a prospective cohort study of long-term outcomes in HIV-infected and HIV-exposed children-Pediatric AIDS Clinical Trials Group (PACTG) protocol 219.

METHODS

PACTG 219 enrolled 2014 HIV-infected and 849 HIV-exposed, uninfected children between April 1993 and September 2000. Children had periodic examinations with collection of clinical and laboratory data. The database was reviewed for reports of LCPD and other bone disorders. A prevalent case was defined as LCPD diagnosis preceding PACTG 219 enrollment and an incident case had to have occurred between enrollment and September 2000. A case-control study (matching on age, gender, and race/ethnicity, which are known to be associated with risk of LCPD and HIV infection status) was performed to investigate factors possibly associated with LCPD.

RESULTS

Six cases of LCPD (4 prevalent cases reported at study entry; 2 diagnosed during 5837 person-years of follow-up) were observed; LCPD was seen only in children with perinatal HIV infection. LCPD prevalence was 199 per 100 000 compared with an estimated general pediatric population prevalence of 23 per 100 000. Based on age-adjusted general population rates, the expected number of prevalent cases at PACTG 219 study entry would have been 0.44; the age-adjusted LCPD prevalence rate ratio was 9.0 (95% confidence interval [CI]: 8.3-9.7) for HIV-infected children compared with the general population. LCPD incidence was 34 per 100 000 person-years (95% CI: 0.42-124) compared with the estimated general population incidence of 6 per 100 000 person-years (95% CI: 5-7). Based on age-adjusted general population rates, the expected incidence of LCPD in PACTG 219 would have been 0.42; the age-adjusted relative risk of LCPD in HIV-infected PACTG 219 children was 4.8 (95% CI: 0.56-10.4). No cases were observed in uninfected children during 1919 person-years of follow-up on PACTG 219; the age-adjusted expected number of cases was 0.09. Median onset age was 7 years; 67% were of Hispanic or black race/ethnicity and 33% were female. Four of the 6 LCPD cases had received antiretroviral therapy before diagnosis; treatment was primarily with nucleoside reverse transcriptase inhibitors, and 2 had received protease inhibitors. Three of the LCPD cases had corticosteroid exposure before the diagnosis, but only 1 child had systemic exposure and the remaining 2 had topical exposure exclusively. In the case-control study, antiretroviral and corticosteroid therapy, CD4 cell percentage, birth weight, height for age and gender percentile, and triglyceride levels were not significantly associated with LCPD. However, the case-control study had limited power to evaluate possible associations.

CONCLUSION

Similar to HIV-infected adults, children with perinatal HIV infection have an increased risk for osteonecrosis of the hip, and clinicians should be alert to this diagnosis when HIV-infected children present with limp or hip pain. Whether LCPD is attributable to HIV infection itself, HIV-associated complications that could predispose to hypercoagulopathy, HIV-related therapies, or to the growth abnormalities in HIV-infected children is unknown and deserves additional evaluation.

Z score prediction model for assessment of bone mineral content in pediatric diseases

The objective of this study was to develop an anthropometry-based prediction model for the assessment of bone mineral content (BMC) in children. Dual-energy X-ray absorptiometry (DXA) was used to measure whole-body BMC in a heterogeneous cohort of 982 healthy children, aged 5-18 years, from three ethnic groups (407 European- American [EA], 285 black, and 290 Mexican-American [MA]). The best model was based on log transformations of BMC and height, adjusted for age, gender, and ethnicity. The mean +/- SD for the measured/predicted in ratio was 1.000 +/- 0.017 for the calibration population. The model was verified in a second independent group of 588 healthy children (measured/predicted In ratio = 1.000 +/- 0.018). For clinical use, the ratio values were converted to a standardized Z score scale. The whole-body BMC status of 106 children with various diseases (42 cystic fibrosis [CF], 29 juvenile dermatomyositis [JDM], 15 liver disease [LD], 6 Rett syndrome [RS], and 14 human immunodeficiency virus [HIV]) was evaluated. Thirty-nine patients had Z scores less than -1.5, which suggest low bone mineral mass. Furthermore, 22 of these patients had severe abnormalities as indicated by Z scores less than -2.5. These preliminary findings indicate that the prediction model should prove useful in determining potential bone mineral deficits in individual pediatric patients.