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Sundeep Khosla

Publications and source records attributed to Sundeep Khosla.

69 records · Page 4Linked to original sources
PubMed2002

Subcutaneous administration of insulin-like growth factor (IGF)-II/IGF binding protein-2 complex stimulates bone formation and prevents loss of bone mineral density in a rat model of disuse osteoporosis.

Elevated serum levels of insulin-like growth factor binding protein-2 (IGFBP-2) and a precursor form of IGF-II are associated with marked increases in bone formation and skeletal mass in patients with hepatitis C-associated osteosclerosis. In vitro studies indicate that IGF-II in complex with IGFBP-2 has high affinity for bone matrix and is able to stimulate osteoblast proliferation. The purpose of this study was to determine the ability of the IGF-II/IGFBP-2 complex to increase bone mass in vivo. Osteopenia of the femur was induced by unilateral sciatic neurectomy in rats. At the time of surgery, 14-day osmotic minipumps containing vehicle or 2 microg IGF-II+9 microg IGFBP-2/100g body weight/day were implanted subcutaneously in the neck. Bone mineral density (BMD) measurements were taken the day of surgery and 14 days later using a PIXImus small animal densitometer. Neurectomy of the right hindlimb resulted in a 9% decrease in right femur BMD (P<0.05 vs. baseline). This loss in BMD was completely prevented by treatment with IGF-II/IGFBP-2. On the control limb, there was no loss of BMD over the 14 days and IGF-II/IGFBP-2 treatment resulted in a 9% increase in left femur BMD (P<0.05). Bone histomorphometry indicated increases in endocortical and cancellous bone formation rates and in trabecular thickness. These results demonstrate that short-term administration of the IGF-II/IGFBP-2 complex can prevent loss of BMD associated with disuse osteoporosis and stimulate bone formation in adult rats. Furthermore, they provide proof of concept for a novel anabolic approach to increasing bone mass in humans with osteoporosis.

Animals↗
PubMed2002

Sex steroids and the construction and conservation of the adult skeleton.

Here we review and extend a new unitary model for the pathophysiology of involutional osteoporosis that identifies estrogen (E) as the key hormone for maintaining bone mass and E deficiency as the major cause of age-related bone loss in both sexes. Also, both E and testosterone (T) are key regulators of skeletal growth and maturation, and E, together with GH and IGF-I, initiate a 3- to 4-yr pubertal growth spurt that doubles skeletal mass. Although E is required for the attainment of maximal peak bone mass in both sexes, the additional action of T on stimulating periosteal apposition accounts for the larger size and thicker cortices of the adult male skeleton. Aging women undergo two phases of bone loss, whereas aging men undergo only one. In women, the menopause initiates an accelerated phase of predominantly cancellous bone loss that declines rapidly over 4-8 yr to become asymptotic with a subsequent slow phase that continues indefinitely. The accelerated phase results from the loss of the direct restraining effects of E on bone turnover, an action mediated by E receptors in both osteoblasts and osteoclasts. In the ensuing slow phase, the rate of cancellous bone loss is reduced, but the rate of cortical bone loss is unchanged or increased. This phase is mediated largely by secondary hyperparathyroidism that results from the loss of E actions on extraskeletal calcium metabolism. The resultant external calcium losses increase the level of dietary calcium intake that is required to maintain bone balance. Impaired osteoblast function due to E deficiency, aging, or both also contributes to the slow phase of bone loss. Although both serum bioavailable (Bio) E and Bio T decline in aging men, Bio E is the major predictor of their bone loss. Thus, both sex steroids are important for developing peak bone mass, but E deficiency is the major determinant of age-related bone loss in both sexes.

Animals↗
PubMed2002

Effect of estrogen versus testosterone on circulating osteoprotegerin and other cytokine levels in normal elderly men.

Recent studies have shown that estrogen (E) likely plays a dominant role in inhibiting bone resorption in normal elderly men. Because both E and T inhibit osteoclast development and activity, stimulate osteoclast apoptosis, and inhibit osteoblast production of IL-6, it is unclear why T is less potent than E in inhibiting bone resorption in vivo. Osteoprotegerin (OPG) binds to and inactivates RANKL, the final mediator of osteoclastogenesis. In vitro, OPG production is stimulated by E, and preliminary data suggest that T has the opposite effect. Thus, we analyzed serum for OPG levels from a study in which 59 elderly men (mean age, 68 yr) were made acutely hypogonadal using a GnRH agonist and were also placed on an aromatase inhibitor to block conversion of androgens to estrogens. They were studied first under conditions of physiologic E and T replacement, and then randomized to no replacement, replacement with E alone, T alone, or both E and T. E alone resulted in an 18.6 +/- 7.9% (mean +/- SEM) increase in serum OPG levels (P < 0.05), whereas T alone tended to decrease OPG levels (by 10.0 +/- 8.5%; P < 0.05 compared with E alone). Using a two-factor ANOVA model, there was a highly significant T effect (P = 0.006) on decreasing serum OPG levels. Serum TNF-alpha, IL-6, and IL-6 soluble receptor levels increased significantly in the men who had both E and T withdrawn, and the increases in TNF-alpha and IL-6sR were absent in the men treated with either E or T. However, due to the variability in these cytokine measurements, the ANOVA models were not significant for E or T effects. Taken together, these data suggest that in vivo, T decreases OPG levels, whereas E tends to have the opposite effect. These differential effects of E vs. T on OPG production may explain, at least in part, why T has weaker effects than E on inhibiting bone resorption in vivo in humans.

Aged↗
PubMed2002

Clinical review 144: Estrogen and the male skeleton.

Because estrogen (E) and T are the major sex steroids in women and men, respectively, the traditional view had been that E primarily regulated bone turnover in women and T played the analogous role in men. The description of ER- deficient and aromatase-deficient males, however, initiated a major shift in our thinking on the relative roles of T and E in regulating the male skeleton, because these individuals all had unfused epiphyses, high bone turnover, and osteopenia. Similar, albeit less striking, findings were noted in mouse models with knock-out of either the ER-alpha or the aromatase genes. Although these human experiments of nature and mouse knock-out models clearly demonstrated an important role for E in the growth and maturation of the male skeleton, they did not define the role of E vs. T in regulating the adult male skeleton. The past several years have witnessed an accumulation of evidence from observational as well as direct interventional studies that now clearly indicates that E plays a major, and likely dominant, role in bone metabolism in men. These data also suggest that a threshold level of bioavailable (or non-SHBG bound) E is needed for skeletal E sufficiency in the male, and that with aging, an increasing percentage of elderly men begin to fall below this level. It is this subset of men who may be at greatest risk for the development of age-related bone loss and osteoporosis. Moreover, these men may also be the ones most likely to respond favorably to treatment with selective E receptor modulators, or perhaps even to T replacement, because the skeletal effects of the latter may be mediated largely via aromatization to E.

Animals↗
PubMed2002

Use of site-specific antibodies to characterize the circulating form of big insulin-like growth factor II in patients with hepatitis C-associated osteosclerosis.

Hepatitis C-associated osteosclerosis (HCAO) is a rare syndrome of adult-onset osteosclerosis. An understanding of the factor(s) leading to the stimulation of bone formation in these patients may provide novel anabolic approaches for the treatment of osteoporosis. We have demonstrated that HCAO patients have a specific increase in circulating big IGF-II (IGF-IIE) and IGF-binding protein-2 (IGFBP-2) levels, and that IGF-IIE and IGFBP-2 circulate together in a bioavailable, 50-kDa complex. Patients with nonislet cell tumor hypoglycemia (NICTH) also have increased circulating IGF-IIE and IGFBP-2 levels. However, HCAO patients do not exhibit hypoglycemia, nor do NICTH patients exhibit obvious osteosclerosis. Thus, to better understand the reason(s) for the differing clinical manifestations of the IGF-IIE excess in the two syndromes, we characterized IGF-IIE in HCAO and NICTH sera using recently developed antibodies (Ab) recognizing either the full-length IGF-IIE 89-amino acid C-terminal extension peptide (IIE(138-156) Ab) or specific cleavage forms of IGF-IIE (IIE(78-88) Ab and IIE(89-101) Ab). The predominant IGF-IIE form in HCAO serum migrated on SDS-PAGE as a single band at approximately 18 kDa that reacted with the IIE(89-101) Ab. On the other hand, the predominant form in NICTH serum migrated as a doublet of 14 and 16 kDa that reacted with the IIE(78-88) Ab. There results are consistent with differential processing of the IGF-IIE precursor at predicted cleavage sites producing IGF-IIE(1-104) and IGF-IIE(1-88) in HCAO and NICTH, respectively. As these two forms may have differing biological activities and/or targeting properties, our findings may explain at least in part the different manifestations of IGF-IIE overproduction in the two syndromes.

Antibody Specificity↗
PubMed2002

Role of low levels of endogenous estrogen in regulation of bone resorption in late postmenopausal women.

Although median levels of bone turnover are increased in postmenopausal women, it is unclear whether the low circulating levels of endogenous estrogen exert a regulatory role on these levels. This issue was evaluated by assessing the effect of a blockade of estrogen synthesis on bone turnover markers in 42 normal women (mean age +/- SD, 69 +/- 5 years) randomly assigned to groups receiving the potent aromatase inhibitor letrozole or placebo for 6 months. Letrozole treatment reduced serum estrone (E1) and estradiol (E2) to near undetectable levels (p < 0.0001). This treatment did not affect bone formation markers but, as compared with the placebo group, increased bone resorption markers (urine 24-h pyridinoline [PYD] by 13.3% [p < 0.05] and 24-h urine deoxypyridinoline [DPD] by 14.2% [p < 0.05]) and decreased serum parathyroid hormone (PTH) by 22% (p = 0.002). These data indicate that in late postmenopausal women even the low serum estrogen levels present exert a restraining effect on bone turnover and support the concept that variations in these low levels may contribute to differences in their rate of bone loss.

Aged↗
PubMed2002

Estrogen receptor isoform-specific induction of progesterone receptors in human osteoblasts.

Estrogen induction of progesterone receptor (PR) expression may be important to bone physiology because progesterone has been implicated in the control of bone formation and resorption. Although PR gene expression can be induced in osteoblasts by estrogen signaling through the estrogen receptor (ER) a isoform, it is unknown whether the ER-beta isoform is involved in this regulation. The effect of estrogen on PR expression was examined in human fetal osteoblast (hFOB) cell lines stably transfected with either ER-alpha or ER-beta. Estrogen treatment of hFOB/ER-a cells induced PR messenger RNA (mRNA) steady-state levels after 24 h and protein levels after 48 h, as established by competitive reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blotting. Interestingly, no induction of PR expression was observed in the hFOB/ER-beta cells during this period. However, PR mRNA was induced progressively after 48 h of treatment with estrogen with maximum levels achieved at 12 days posttreatment. ER protein also was increased after 12 days of treatment. Both A and B isoforms of PR (PRA and PRB) were induced by estrogen in the hFOB/ER-a cells as well as much later in hFOB/ER-beta cells. The pure antiestrogen ICI 182,780 prevented PR induction by estrogen in both cell lines. An ER-beta-selective antagonist R, R-tetrahydrochrysene (THC) abolished the induction of PR mRNA in hFOB/ER-beta but not in hFOB/ER-a cells, verifying that the response in the former cell line was ER-beta-mediated. Transient cotransfection of hFOB cells with ER-a or ER-beta together with either a human PRA or PRB promoter linked to a reporter plasmid revealed that although the PRB promoter was stimulated equally by estrogen activation of either ER isoform, PRA was activated preferentially by ER-alpha. Together, these results show that although estrogen can up-regulate endogenous PR gene expression in osteoblasts via both ER isoforms, ER-alpha is the predominant inducer.

Blotting, Western↗
PubMed2002

Regulation of osteoprotegerin production by androgens and anti-androgens in human osteoblastic lineage cells.

BACKGROUND: Estrogens and androgens have anti-resorptive effects on bone, although recent evidence indicates that, even in men, estrogen is the dominant sex steroid regulating bone resorption. The receptor activator of NF-kappaB ligand is essential for osteoclastic bone resorption, and its effects are blocked by the decoy receptor, osteoprotegerin (OPG). While estrogen has been shown to induce osteoblastic OPG production, the effects of androgens on OPG production have not been defined. METHODS: In this study, we assessed the regulation of OPG by androgens in hFOB/AR-6, an immortalized fetal osteoblastic cell line stably transfected with the human androgen receptor (AR), and MSC cells, primary human pluripotent marrow stromal cells capable of differentiating towards mature osteoblasts. RESULTS AND CONCLUSIONS: 5Alpha-dihydrotestosterone (DHT) dose-dependently decreased OPG mRNA levels and protein concentrations in hFOB/AR-6 cells by up to 50 and 60% respectively (P<0.001). Inhibition of OPG mRNA levels and protein production by 5alpha-DHT was completely abrogated by the AR antagonist, hydroxyflutamide (OHF), indicating that these effects are directly mediated by the AR. Of note, OHF alone increased OPG mRNA levels and protein secretion by 2- to 3-fold. Moreover, 5alpha-DHT and testosterone also decreased OPG protein secretion by 40-46% in the untransformed MSC cells, while OHF stimulated it. In conclusion, we demonstrate that androgens specifically inhibit OPG mRNA levels and protein secretion by osteoblastic cells.

Androgen Antagonists↗
PubMed2002

Osteopenia in adults with a history of juvenile rheumatoid arthritis. A population based study.

OBJECTIVE: To determine the extent of osteopenia in a population based cohort of adults with a history of juvenile rheumatoid arthritis (JRA). METHODS: The Rochester Epidemiology Project database was used to identify all cases of JRA diagnosed among Rochester, Minnesota residents under the age of 16 years between January 1, 1960, and December 31, 1993. Thirty-two of the 57 adult patients in this population based cohort (ages 19-53 years, mean 35) participated in this study. Average length of followup from the time of diagnosis was 27.1 years (median 26.9, range 7.7-39.1). Dual energy x-ray absorptiometry scans were used to assess bone density of the lumbar spine, hip, distal one-third radius, and whole body. In addition, a number of variables that influence bone mass were analyzed. RESULTS: Although many participants had T scores within the normal range (T score > -1) at all measured sites, 41% (n = 13) were osteopenic (T score < or = -1) at either the lumbar spine or femoral neck. Twenty-eight percent (n = 9) had T scores < or = -1 in the lumbar spine (p = 0.058 relative to expected). Thirty-two percent (n = 10) had T scores < or = -1 in the femoral neck (p = 0.012 relative to expected). Several variables were significantly (p < 0.05) associated with low bone density in this cohort of adults with a history of JRA, including: (1) revised Steinbrocker functional class > or = 2 during adolescence, indicating poorer physical functioning; (2) lack of participation in organized sports during adolescence (a surrogate measure of physical activity); (3) tobacco use during adolescence; and (4) lower calcium intake during adolescence. CONCLUSION: Although many adults with a history of JRA have normal bone density, a substantial subset are osteopenic, placing them at increased risk of fractures later in life. This observation is particularly striking given the predominance of patients with pauciarticular JRA in this population based group. We identified several variables associated with osteopenia in this cohort. Further work is needed to identify those patients with JRA who may benefit from aggressive therapy targeted at preventing the longterm morbidity associated with osteopenia.

Absorptiometry, Photon↗
PubMed2002

Fracture risk in primary hyperparathyroidism.

A key component in the decision to perform surgery on patients with primary hyperparathyroidism (HPT) is their skeletal status. Consequently, fracture risk in these patients has been investigated in a number of observational studies. Our group reported on a population-based cohort of residents from Rochester, MN, with primary HPT recognized during a 28-year period (1965-1992). The majority of these patients were asymptomatic, and most (77%) were managed conservatively. By contrast, a recent Danish study reported on a cohort of 674 patients, all of whom had surgery for primary HPT. Nonetheless, the risk of fracture was increased remarkably similarly in the two populations: vertebrae, approximately 3-fold; forearm, approximately 2-fold; hip, approximately 1.5-fold; and all fractures, approximately 1.5-fold. In both studies, parathyroid surgery seemed to have a protective effect. These (and previous studies) indicate that overall fracture risk is increased in primary HPT patients. An increase in forearm fracture risk is a relatively uniform finding and is consistent with known effects of parathyroid hormone (PTH) on cortical bone. However, the increase in vertebral fracture risk seen in most (but not all) studies does not fit with the observation that cancellous bone mass/structure is preserved in primary HPT patients. Based on these findings, future directions for research include (1) rigorously testing, in prospective studies, whether vertebral fracture risk is, in fact, increased in this disorder, and if so, determining the possible biomechanical mechanism(s) for this increase; and (2) testing whether the trend to increased hip fracture risk seen in some studies is real and whether it is more closely linked to cervical or intertrochanteric fractures.

Adolescent↗
PubMedDate not supplied

Effect of estrogen replacement therapy on parathyroid hormone secretion in elderly postmenopausal women.

OBJECTIVE: Women undergo two phases of involutional bone loss that have opposing effects on parathyroid hormone (PTH) secretion. During the early phase, the loss of the direct restraining effect of estrogen on bone resorption causes an outflow of skeletal calcium into the extracellular fluid. This causes a compensatory decrease in PTH secretion. In the late phase, loss of extraskeletal effects of estrogen (on intestinal and renal calcium handling) leads to increases in whole body losses of calcium and a compensatory increase in PTH secretion. Moreover, long-term estrogen replacement therapy (ERT) suppresses both basal and stimulated PTH secretion in these women. Whereas the effects of estrogen on PTH secretion have been assumed to be due to its extraskeletal actions, estrogen may also have direct effects on the parathyroid glands. The goal of the present study was to test for these possible direct effects of estrogen on PTH secretion. DESIGN: Basal and ethylenediaminetetraacetic acid (EDTA)-stimulated PTH secretion was assessed in 10 elderly postmenopausal women (mean age, 76.4 years) before and after acute (3 days) estrogen replacement with transdermal estradiol, 0.1 mg/day. In addition, similar studies were performed in 10 age-matched women (mean age, 74.5 years) who had been on long-term ERT. These women were studied before and after 3 days of estrogen withdrawal. RESULTS: Estrogen treatment or withdrawal had no significant effect on either basal or stimulated PTH secretion. CONCLUSIONS: These data provide evidence that, in elderly postmenopausal women, estrogen does not have significant direct effects on PTH secretion and point to the importance of the actions of estrogen on intestinal and renal calcium handling as the major mechanisms for its effects on modulating calcium homeostasis and, indirectly, PTH secretion.

Administration, Cutaneous↗