Spontaneous release of interleukin-I and interleukin-6 by peripheral blood mononuclear cells after oophorectomy

The Interleukin-6 inflammation pathway from cholesterol to aging--role of statins, bisphosphonates and plant polyphenols in aging and age-related diseases

We describe the inflammation pathway from Cholesterol to Aging. Interleukin 6 mediated inflammation is implicated in age-related disorders including Atherosclerosis, Peripheral Vascular Disease, Coronary Artery Disease, Osteoporosis, Type 2 Diabetes, Dementia and Alzheimer's disease and some forms of Arthritis and Cancer. Statins and Bisphosphonates inhibit Interleukin 6 mediated inflammation indirectly through regulation of endogenous cholesterol synthesis and isoprenoid depletion. Polyphenolic compounds found in plants, fruits and vegetables inhibit Interleukin 6 mediated inflammation by direct inhibition of the signal transduction pathway. Therapeutic targets for the control of all the above diseases should include inhibition of Interleukin-6 mediated inflammation.

Serum levels of soluble vascular cell adhesion molecule-1 are decreased in women receiving oral contraceptives compared with normally menstruating women: implications in atherosclerosis

OBJECTIVE

The primary objective was to assess whether short-term changes in estradiol (E2), such as those observed in the menstrual cycle, alter serum levels of soluble vascular cell adhesion molecule-1 (sVCAM-1), and whether VCAM-1 expression is suppressed in long-term users of exogenous estrogens. The secondary objective was to assess the association, if any, between inflammatory cytokines and expression of sVCAM-1.

DESIGN

Prospective collection of serum samples in healthy volunteers.

SETTING

University hospital.

PATIENTS(S)

Thirty-one normally menstruating women and 37 oral contraceptive (OC) users. Interventions included serum collection in the early follicular, late follicular, and midluteal phases of the menstrual cycle and once in oral contraceptive users.

MAIN OUTCOME MEASURE(S)

Samples were assayed for sVCAM-1, tumor necrosis factor alpha (TNF-alpha), and interleukin (IL)-6 by enzyme-linked immunoabsorbent assay (ELISA). Estradiol (E2) was measured by radioimmunoassay (RIA).

RESULT(S)

Oral contraceptive users had significantly lower serum levels of sVCAM-1 compared with normally menstruating women. No significant change was noted in the mean values of sVCAM-1 throughout the menstrual cycle, despite the significant change in 17beta-estradiol levels. Throughout the menstrual cycle, a significant correlation was noted between the serum levels of TNF-alpha and sVCAM-1. The serum levels of IL-6 correlated with those of sVCAM-1 in the late follicular and midluteal phase of the cycle. Similar correlations were observed in OC users.

CONCLUSION(S)

Long-term exposure to exogenous estrogens suppresses serum levels of sVCAM-1. Short-term changes in endogenous estrogens, as observed during the menstrual cycle, may not alter VCAM-1 expression; TNF-alpha and IL-6 may play a role in the regulation of VCAM-1 expression in vivo.

Hormonal modulation of interleukin-6, tumor necrosis factor and associated receptor secretion in postmenopausal women

Hormone replacement therapy (HRT) reduces the risk for osteoporosis but transiently increases cardiovascular risk for some postmenopausal women. This study investigated the hypothesis that these risks are associated with HRT-induced changes in mononuclear cell secretion of interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-alpha), and associated soluble receptors. Compared to the untreated condition (n=8), estrogen therapy (n=7) and estrogen+progestin therapy (n=7) both caused 2-fold elevations in TNF-alpha secretion. IL-6 secretion was increased (48%, P=0.04) only by estrogen+progestin therapy. Although soluble receptor secretion was not different among groups, soluble TNF receptor type I and IL-6 receptor secretion were inversely related to plasma follicle stimulating hormone (P<0.05). Both therapies reduced plasma osteocalcin (a marker for osteoporosis) by approximately 50% (P<0.002). Plasma C-reactive protein (CRP, a marker for cardiovascular risk) was 3-fold higher in women receiving only estrogen, compared to untreated women (P=0.01), and twice as high as those receiving estrogen+ progestin (P=0.045). Simple linear relationships were not observed between cytokine secretion and these markers, but a significant HRT/TNF-alpha interaction with osteocalcin (P=0.022) and an HRT/IL-6 interaction with CRP (P =0.016) indicated more complex relationships between hormone replacement, cytokine activity, and health risks associated with menopause.

Nonassociation of interleukin-1 receptor antagonist genotypes with bone mineral density, bone turnover status, and estrogen responsiveness in Korean postmenopausal women

Interleukin-1 receptor antagonist (IL-1ra), a natural inhibitor of interleukin-1 (IL-1), completely inhibits the stimulatory effects of IL-1 on bone resorption. Bioactivity of IL-1 increases in the estrogen-deficient state with an increased IL-1:IL-1ra ratio and decreases after estrogen replacement therapy with a decreased IL-1:IL-1ra ratio. An association was found between an 86 basepair variable number tandem-repeat (VNTR) polymorphism of the IL-1ra gene and an increased production of IL-1ra in a cultured monocyte system. The IL-1ra VNTR polymorphism, therefore, is an attractive candidate gene for osteoporosis susceptibility as well as hormone responsiveness after estrogen replacement. We examined the association of this VNTR polymorphism with bone mass, bone turnover, and the change of bone mineral density (BMD) after 1 year of hormone replacement therapy (HRT). The frequencies of the five alleles were as follows: A1, 90.8% (410 bp, four repeats); A2, 7.2% (240 bp, two repeats); A3, 1.6% (500 bp, five repeats); A4, 0.4% (326 bp, three repeats); and A5, 0% (595 bp, six repeats), in 714 healthy ethnically Korean postmenopausal women, aged 41-74 years (55.2 +/- 6.3 years mean +/- SD). Spine (L2-4) and femoral neck BMD were not significantly different among IL-1ra genotypes, and no significant genotypic differences were found in bone markers. There were no differences in genotypic proportions when we categorized the subjects into a high-loss group and a normal-loss group with regard to levels of bone marker. No significant genotypic differences were found in changes in lumbar and femoral neck BMD and those in bone markers before and after 1 year of HRT in 312 women. Our data suggest that these IL-1ra polymorphisms are not associated with BMD, bone turnover, or the change of BMD after 1 year of HRT in Korean women.

Relative contributions of testosterone and estrogen in regulating bone resorption and formation in normal elderly men

Young adult males who cannot produce or respond to estrogen (E) are osteopenic, suggesting that E may regulate bone turnover in men, as well as in women. Both bioavailable E and testosterone (T) decrease substantially in aging men, but it is unclear which deficiency is the more important factor contributing to the increased bone resorption and impaired bone formation that leads to their bone loss. Thus, we addressed this issue directly by eliminating endogenous T and E production in 59 elderly men (mean age 68 years), studying them first under conditions of physiologic T and E replacement and then assessing the impact on bone turnover of withdrawing both T and E, withdrawing only T, or only E, or continuing both. Bone resorption markers increased significantly in the absence of both hormones and were unchanged in men receiving both hormones. By two-factor ANOVA, E played the major role in preventing the increase in the bone resorption markers, whereas T had no significant effect. By contrast, serum osteocalcin, a bone formation marker, decreased in the absence of both hormones, and both E and T maintained osteocalcin levels. We conclude that in aging men, E is the dominant sex steroid regulating bone resorption, whereas both E and T are important in maintaining bone formation.

Age-associated increased interleukin-6 gene expression, late-life diseases, and frailty

Interleukin-6 (IL-6) is a proinflammatory cytokine that is normally tightly regulated and expressed at low levels, except during infection, trauma, or other stress. Among several factors that down-regulate IL-6 gene expression are estrogen and testosterone. After menopause or andropause, IL-6 levels are elevated, even in the absence of infection, trauma, or stress. IL-6 is a potent mediator of inflammatory processes, and it has been proposed that the age-associated increase in IL-6 accounts for certain of the phenotypic changes of advanced age, particularly those that resemble chronic inflammatory disease [decreased lean body mass, osteopenia, low-grade anemia, decreased serum albumin and cholesterol, and increased inflammatory proteins such as C-reactive protein (CRP) and serum amyloid A]. Furthermore, the age-associated rise in IL-6 has been linked to lymphoproliferative disorders, multiple myeloma, osteoporosis, and Alzheimer's disease. This overview discusses the data relating IL-6 to age-associated diseases and to frailty. Like the syndrome of inappropriate antidiuretic hormone, it is possible that certain clinically important late-life changes are due to an inappropriate presence of IL-6.

Hyperparathyroidism is augmented by ovariectomy in Nagase analbuminemic rats

The role of albumin in bone metabolism was studied in Nagase analbuminemic (NA) rats. Serum calcium (Ca), inorganic phosphate (Pi) and magnesium (Mg) concentrations did not differ between female NA and control Sprague-Dawley (SD) rats at the time of ovariectomy (ovx), although serum ionized Ca was significantly lower in NA rats than in SD rats. Serum parathyroid hormone (PTH) and osteocalcin (OC) concentrations and urinary Ca excretion were significantly greater in NA rats than in SD rats, suggesting hyperparathyroidism and the resultant enhanced bone turnover in NA rats. Paradoxically, ovx increased serum PTH and OC in NA rats but not in SD rats. Ovx-induced exacerbation of hyperparathyroidism was confirmed by significantly greater conversion of 25-hydroxyvitamin D to 1, 25-dihydroxyvitamin D in ovx NA rats even after normalization to vitamin D-binding protein. Bone mineral density (BMD) in proximal tibia increased similarly in a time-dependent manner in sham-operated NA and SD rats. However, ovx ablated the time-dependent increase of BMD in SD rats and significantly decreased BMD in NA rats by 2 wk after ovx, resulting in a significantly lower BMD in ovx NA rats than in ovx SD rats. In summary, NA rats, which are analbuminemic with compensatory increases in lipid and protein synthesis, developed hyperparathyroidism, possibly due to an increase in serum Pi and a reduction of ionized Ca, and ovx induced a greater BMD reduction in NA rats than in SD rats, probably by exacerbating hyperparathyroidism.

Cytokine RNA levels in transiliac bone biopsies from healthy early postmenopausal women

The cytokines interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), and IL-6 induce osteoclast formation and may contribute to the development of postmenopausal osteoporosis. Cross-sectional studies have suggested that both IL-1 and IL-1ra secretion increase on estrogen withdrawal, and that postmenopausal osteoporosis is associated with an inadequate increase in monocyte IL-1ra secretion with age. We measured cytokine mRNA (IL-1beta, IL-1ra, IL-6, and TNF-alpha) directly in bone biopsies from early postmenopausal women to determine if a lower compensatory increase in IL-1ra mRNA could be demonstrated in women with rapid bone loss after the menopause. Biopsies were obtained from 23 early postmenopausal women (mean age 53.9 years) who participated in a randomized study of hormone replacement therapy (HRT) and risk factors for osteoporosis. Bone mineral density was assessed by duel energy X-ray absorptiometry at 0, 1, 2, and 5 years. Women in the control group were recruited to the biopsy study based on their observed rate of bone loss (upper or lower tertile). Consent was also obtained from 11 participants receiving HRT. Biopsies were taken at 2 years, frozen in nitrogen, and homogenized. Cytokine mRNA was measured by competitive reverse transcriptase polymerase chain reaction. The IL-1ra/IL-1beta mRNA slope for the slow-loss group was steeper (deltaF = 23.3, p < 0.01) than that observed in the fast-loss group, indicating that slower bone loss was associated with higher IL-1ra mRNA levels relative to IL-1beta. During HRT, the IL-1beta mRNA level was inversely correlated with serum estradiol (log r2 = 0.77, p < 0.01), and women with a serum estradiol below 200 pmol/L during HRT had IL-1beta, mRNA levels identical to the control group. In contrast, IL-1ra mRNA was independent of serum estradiol. Histomorphometric analysis revealed weak correlations between IL-1beta mRNA and activation frequency (r2 = 0.26, p = 0.06) and between IL-1ra and volume referent bone resorption rate (r2 = 0.19, p = 0.11). TNF-alpha was not associated with the bone loss rates or with serum estradiol, and only three samples were positive for IL-6 mRNA. The findings support the hypothesis that IL-1beta production within bone increases with declining estrogen levels, and that an increase in II-1ra protects against accelerated bone loss.

Ovariectomy does not induce osteopenia through interleukin-6 in rhesus monkeys (Macaca mulatta)

To characterize the role of interleukin-6 (IL-6) in estrogen (E2)-depletion bone loss, we utilized a nonhuman primate model of human skeletal physiology. Adult female rhesus monkeys were sham-operated (S; n = 5), ovariectomized (ovx; n = 10), or ovx followed by E2 replacement (ovx + E2; n = 10) and evaluated for the indicated parameters at 0, 3, 6, and 9 months post-ovx. Lumbar spine bone mineral density (BMD) decreased by 3 months and continued to decline through 9 months in the ovx, but not in the ovx + E2 or S groups. Middle and distal radius BMD was decreased at 9 months in the ovx, but not in the ovx + E2 or S groups. The S group had marked fluctuations in bone remodeling parameters, and cytokine levels in S animals were consistent with menstrual cycling, and therefore only those values in the ovx and ovx + E2 groups are reported. Serum osteocalcin and skeletal-specific alkaline phosphatase were elevated in the ovx group compared with the ovx + E2 group. There was no difference in serum or bone marrow plasma IL-6 levels between the ovx and ovx + E2 groups. Similarly, there was no difference in basal or phorbol ester-stimulated IL-6 levels of peripheral blood mononuclear cell or bone marrow cell culture supernatants between groups. There was no difference in serum or bone marrow soluble IL-6 receptor between groups. However, the bone marrow plasma soluble IL-6 receptor levels were transiently increased from baseline at 3 months in the ovx but not in the ovx + E2 group. In summary, there was no bone loss in the ovx + E2 group, although the serum and bone marrow IL-6 levels were similar to those of the ovx group. These data suggest that modulation of IL-6 is not the key mechanism through which estrogen deprivation mediates bone loss in rhesus monkeys.

Correlation of estradiol, parathyroid hormone, interleukin-6, and soluble interleukin-6 receptor during the normal menstrual cycle

Rodent models suggest that estradiol deficiency promotes bone loss through increasing interleukin-6 (IL-6) activity. However, it is controversial as to whether these findings are applicable to humans. To evaluate estradiol-mediated modulation of IL-6 activity in relation to bone metabolism in humans, we measured serum IL-6, soluble interleukin-6 receptor (sIL-6R), estradiol (E2), progesterone, luteinizing hormone, follicle-stimulating hormone, intact parathyroid hormone (PTH), serum and urine Ca, and bone biochemical markers (serum bone-specific alkaline phosphatase, osteocalcin, and serum and urine deoxypyridinoline [Dpd]) across one menstrual cycle for 211 women. Neither IL-6 nor sIL-6R levels differed between the follicular phase (FP) and the luteal phases (LP). However, IL-6 was negatively correlated with E2 during the FP (p =0.003). Furthermore, IL-6 correlated positively with serum Ca over the entire cycle (p = 0.0091. Serum Ca correlated positively with serum (p = 0.040) and urine (p = 0.006) Dpd. PTH was significantly higher during the FP than in the LP (p = 0.004). PTH was negatively related to E2 (p = 0.002), serum Ca (p < 0.001), and urine Ca (p = 0.036), whereas it was positively correlated with IL-6 (p = 0.027). These data demonstrate that IL-6 and PTH fluctuate with E2, and serum II-6 is associated with PTH levels during the menstrual cycle. However, the role of 11-6 in bone remodeling during the normal menstrual cycle remains to be determined.

Oestrogens prevent the increase of human serum soluble interleukin-6 receptor induced by ovariectomy in vivo and decrease its release in human osteoblastic cells in vitro

OBJECTIVE

Interleukin-6 (IL-6) seems to be a key mediator of the increased bone loss that follows loss of ovarian function. Based on this and on evidence that oestrogen deficiency may also increase cell sensitivity to IL-6, we studied the effects of ovariectomy and of oestrogen replacement therapy on the serum levels of IL-6 and of soluble IL-6 receptor (sIL-6R) in vivo.

DESIGN AND PATIENTS

Thirty-seven fertile women undergoing surgery for benign uterine diseases were divided into 3 groups and monitored for 12 months: hysterectomized women (n = 9), ovariectomized untreated women (n = 12) and ovariectomized women starting treatment with transdermal estradiol (E2, 50 microg/d) 1 month after surgery (n = 16).

RESULTS

Hysterectomy alone caused no significant changes of sIL6R whereas serum levels of sIL-6R rose progressively after ovariectomy (mean +/- SEM: 31 +/- 9% and 38 +/- 7% over baseline, at 6 and 12 months, respectively; P < 0.01). Oestrogen replacement therapy prevented the increase of sIL6R over a 1-year period. A similar pattern was also found for serum IL-6 but the changes did not reach statistical significance. In ovariectomized (OVX) women there were significant correlations between serum sIL-6R levels and FSH (r = 0.59; P < 0. 01), oestradiol (r = - 0.43; P < 0.01), testosterone (r = - 0.41; P < 0.05), osteocalcin (r = 0.42; P < 0.05) and bone alkaline phosphatase (r = 0.44; P < 0.05). To examine whether oestrogen directly regulates sIL-6R secretion by bone cells, we studied in vitro the basal and phorbol ester (PMA) stimulated release of sIL-6R in a human osteoblastic cell-line (MG-63) and in a tumour-derived osteoclastic cell line (GCT-51). Osteoblastic (but not osteoclastic) cells spontaneously produced considerable amounts of sIL-6R and the protein kinase-C activator PMA (10-8 M) increased the release of sIL-6R by osteoblasts more than 3-fold. More strikingly, 17beta E2 (but not 17alpha) significantly inhibited both the spontaneous- and PMA-induced release of sIL-6R by osteoblastic cells (P < 0.05).

CONCLUSIONS

These results indicate that oestrogen loss causes alterations of the IL-6 system, and that sIL-6R is under the direct inhibitory control of oestrogens both in vivo and in vitro.

IL-1alpha, IL-1beta, IL-6, and TNF-alpha steady-state mRNA levels analyzed by reverse transcription-competitive PCR in bone marrow of gonadectomized mice

Loss of gonadal function in both females and males is associated with increased rates of bone loss by a yet unidentified mechanism. There is ample evidence that cytokines that are produced in the bone microenvironment and stimulate the activity and/or formation of osteoclasts are involved. In the present study, we examined whether gonadectomy increases cytokine production via increased transcription in the bone marrow of mice. For this, the in vivo steady-state mRNA levels of multiple cytokines were determined in the central bone marrow compartment of mice at different time points following ovariectomy or orchidectomy by reverse transcription-competitive polymerase chain reaction. The limit of detectable differences in mRNA expression was approximately 2-fold. Bone marrow mRNA levels of the cytokines interleukin-1alpha (IL-1alpha), interleukin-1beta (IL-1beta), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha) were elevated up to 30-fold after treatment of mice with lipopolysaccharide. Following gonadectomy, there were no differences in the mRNA expression of these cytokines in bone marrow of female and male mice 4, 7, and 14 days after surgery. Gender steroid deficiency does not, therefore, increase steady-state mRNA levels of IL-1alpha, IL-1beta, IL-6, and TNF-alpha in cells of the central bone marrow compartment in mice. If changes have occurred these should have been less than 2-fold or in a small cell population. These results do not preclude an important role of these cytokines in the induction of bone loss after gonadectomy. For example, bone marrow cells situated close to the bone surface or bone cells may be responsible for increased cytokine synthesis. Alternatively, the loss of gender steroids may alter post-transcriptional events in cytokine synthesis and activity or may modify the responsiveness of target cells.

Estradiol down-regulates LPS-induced cytokine production and NFkB activation in murine macrophages

PROBLEM

In vivo and in vitro studies have indicated that estradiol can affect cytokine production in different cell types. This study examines whether estradiol affects inflammatory cytokine production by murine splenic macrophages.

METHODS

Mouse splenic macrophages were first treated with 17 beta-estradiol, followed by lipopolysaccharide (LPS) stimulation. The production of cytokines by macrophages with or without estradiol treatment was determined at both the protein and mRNA levels. The nuclear factor-kB (NFkB) activity of activated mouse splenic macrophages was also evaluated by electrophoretic mobility shift assay.

RESULT

Our results show that 17 beta-estradiol decreases LPS-induced IL-1 alpha, IL-6, and TNF-alpha production but not IL-10, IL-12, and macrophage inflammatory protein (MIP) production by splenic macrophages. Furthermore, inhibition of cytokine production by 17 beta-estradiol was associated with a decreased LPS-induced NFkB-binding activity.

CONCLUSION

Because cytokines are important mediators of immune function, the alteration of cytokine production by 17 beta-estradiol may thus have a profound effect on the outcome of immune response during inflammation.

Estrogen, cytokines, and pathogenesis of postmenopausal osteoporosis

In summary, available data demonstrate that IL-1 and TNF are the causative agents underlying the bone loss induced by estrogen deficiency. Indeed, these factors are produced in bone and the bone marrow, released in larger amounts from cells of estrogen-deficient subjects, and indispensable for reproducing the effects of estrogen deficiency in bone. These observations support the hypothesis that the bone sparing effect of estrogen is due to the ability of the hormone to block osteoclastogenesis, the activation of mature osteoclasts and, as recently demonstrated, the rate of apoptotic osteoclast death. Although IL-1 and TNF play a prominent causal role in these events, the bone-sparing effect of estrogen is mediated by numerous cytokines which, by simultaneously stimulating multiple target cells, induce effects that are not accounted for by any one single factor (Fig. 2). The ability of estrogen to regulate some, but not all, the cytokines involved in this process is not inconsistent with this hypothesis because cytokines have potent synergistic effects. Thus, a considerable increase in bone resorption may result from a relatively small increase in the concentration of only a few of the bone-resorbing factors present in the bone microenvironment. This concept is best illustrated by the study of Miyaura et al. demonstrating that the concentrations of either IL-1, IL-6, IL-6 receptor, or prostaglandins detected in the bone marrow of OVX mice are insufficient to account for the increased bone resorption caused by estrogen withdrawal. In contrast, the increase in bone resorption induced by OVX can be explained by the cumulative effects of these cytokines. Thus, a better understanding of the cooperative effects of cytokines and a recognition that the contribution of individual cytokines to postmenopausal bone loss varies with the passage of time after menopause are necessary to fully understand the mechanism of action of estrogen in bone. Although the relevance of individual bone-targeting cytokines in species specific, the development of transgenic mice with activatable or deactivatable promoters is likely to result in a further clarification of the integrated action of estrogen-regulated cytokines in human bone cells and lay the foundations for the use of cytokine inhibitors in the treatment of postmenopausal osteoporosis.

Interleukin-4 inhibits prostaglandin G/H synthase-2 and cytosolic phospholipase A2 induction in neonatal mouse parietal bone cultures

We have shown previously that prostaglandin (PG) production in 7-day-old neonatal mouse calvarial cultures is regulated largely by changes in prostaglandin G/H synthase-2 (PGHS-2) expression and to a lesser extent by changes in arachidonic acid (AA) release. In this study, we examined the effects of interleukin-4 (IL-4), and its interactions with other cytokines and with parathyroid hormone (PTH), on mRNA levels of PGHS-2, PGHS-1, and cytosolic phospholipase A2 (cPLA2) and on medium protaglandin E2 (PGE2) levels in calvarial cultures. IL-1 and tumor necrosis factor-alpha (TNF-alpha), both at 1-100 ng/ml, and PTH at 0.1-10 nM increased PGHS-2 and cPLA2 mRNA and medium PGE2 levels dose-dependently after 4 h of treatment. IL-6 and IL-11 at 1-100 ng/ml did not affect mRNA or PGE2 levels. IL-4 at 1-100 ng/ml decreased PGHS-2 and cPLA2 mRNA and PGE2 levels in control as well as IL-1, TNF-alpha, and PTH-stimulated cultures. The inhibition of PGHS-2 and cPLA2 mRNA expression by IL-4 (10 ng/ml) was present at 1 h, reached a maximum at 4 h, and persisted for 24 h. The effects were maintained in the presence of cycloheximide. IL-4 also decreased PGHS-2 protein levels in control and IL-1-stimulated cultures. PGHS-1 mRNA levels were not stimulated by any of the factors studied nor inhibited by IL-4. IL-4 partially inhibited control and PTH-stimulated 45Ca release from prelabeled mouse calvariae at 4 days. However, neither the inhibition of resorption by IL-4 nor the stimulation by IL-1 and PTH were altered by indomethacin (1 microM). We conclude that (1) IL-1, TNF-alpha, and PTH, but not IL-6 nor IL-11, can increase the expression of PGHS-2, cPLA2, and PGE2 production in cultured mouse calvariae; (2) IL-4 inhibits PGE2 production in both control and stimulated calvarial cultures by inhibiting PGHS-2 and cPLA2; and (3) IL-4 has an inhibitory effect on bone resorption which is independent of PG production.

Menopause is associated with a significant increase in blood monocyte number and a relative decrease in the expression of estrogen receptors in human peripheral monocytes

PROBLEM

The clinical significance of the differential expression of estrogen receptor (ER) in human monocytes was evaluated.

METHOD

Two color flow cytometry analysis was used on peripheral blood samples of young and postmenopausal females and postmenopausal females treated with estrogen replacement therapy. In addition, the monocyte and lymphocyte counts and the blood estrogen levels of each patient were determine.

RESULTS

During menopause there is a significant decrease in the percentage of ER positive monocytes, and an increase in blood monocyte number, which declines following estrogen replacement therapy to values of the young.

CONCLUSIONS

These findings suggest that estrogen modulates the monocyte numbers and its effects may be mediated through the ER in the monocytes.

Immunoresponsiveness in endometriosis: implications of estrogenic toxicants

Endometriosis is a reproductive disease characterized by the growth of endometrial cells at sites outside the uterus. This disease is a serious disorder associated with chronic pain and infertility, which may be present in 6 million women in this country. Traditional medical therapy has consisted of hormonal regimens that limit the action of endogenous estrogen. The etiology of endometriosis is unknown, but studies suggest that soluble factors known as cytokines play a role in disease pathogenesis. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD or dioxin) is an environmental toxicant that alters the action of estrogen in reproductive organs and adversely affects immunocompetence. The incidence of endometriosis was determined in rhesus monkeys that were chronically exposed to dioxin for a period of approximately 4 years. Ten years after termination of dioxin treatment, the presence and severity of endometriosis was assessed by surgical laparoscopy. The incidence of endometriosis correlated with dioxin exposure and disease severity was dependent upon the dose administered. Moderate to severe endometriosis was not found in control animals but was documented in three of seven animals exposed to 5 ppt dioxin (43%) and in five of seven animals exposed to 25 ppt dioxin (71%). The frequency of spontaneous disease in the control group was 33%, similar to an overall prevalence of 30% in 304 rhesus monkeys with no history of dioxin exposure. This study indicates that endometriosis may be associated with dioxin exposure in the rhesus. In view of overwhelming evidence that cytokines participate in the mediation of reproductive-endocrine phenomena and regulation of endometrial growth, future assessment of the effects of environmental toxicants on reproductive health may depend upon our understanding of the bidirectional cytokine network between the immune and endocrine systems.

Molecular mechanisms of bone resorption

This review focuses on osteoclast ontogeny and function, emphasizing three aspects. We describe how a combination of laboratory models available to study the cell plus examination of the osteopetroses, a family of sclerotic diseases of the skeleton, have yielded major insights into osteoclast ontogeny and function. We proceed to describe the cell and molecular machinery enabling osteoclasts to resorb bone. The final, and most speculative, aspect of the review addresses possible mechanisms by which the osteoclast assumes its characteristic morphology, that of a polarized cell on bone. Since little direct information has been forthcoming as to how the osteoclast polarizes, we draw on other polarized cells. In particular, we examine the role of microtubules and members of the small GTPase family, the latter mediating polarized targeting of intracellular vesicles. In the case of the osteoclast, such vesicles probably represent the origin of the highly convoluted ruffled membrane, the cell's characteristic bone resorptive organ.

Ovariectomy enhances and estrogen replacement inhibits the activity of bone marrow factors that stimulate prostaglandin production in cultured mouse calvariae

To examine PG production in estrogen deficiency, we studied effects on cultured neonatal mouse calvariae of bone marrow supernatants (MSup) from sham-operated (SHAM), ovariectomized (OVX), or 17 beta-estradiol (OVX+E)-treated mice. MSups were obtained 3 wk after OVX when bone density had decreased significantly. 10-60% MSup increased medium PGE2 and levels of mRNA for inducible and constitutive prostaglandin G/H synthase (PGHS-2 and PGHS-1) and cytosolic phospholipase A2 in calvarial cultures. OVX MSups had twofold greater effects on PGHS-2 and medium PGE2 than other MSups. IL-1 receptor antagonist and anti-IL-1 alpha neutralizing antibody decreased MSup-stimulated PGHS-2 mRNA and PGE2 levels and diminished differences among OVX, sham-operated, and OVX+E groups. In contrast, antibodies to IL-1 beta, IL-6, IL-11, and TNF alpha had little effect. There were no significant differences in IL-1 alpha concentrations or IL-1 alpha mRNA levels in MSups or marrow cells. PGHS-2 mRNA in freshly isolated tibiae from OVX mice was slightly greater than from sham-operated. We conclude that bone marrow factors can increase PG production through stimulation of PGHS-2; that OVX increases and estrogen decreases activity of these factors; and that IL-1 alpha activity, together with additional unknown factors, mediates the differential MSup effects.

Estrogen modulates the inducible expression of platelet-derived growth factor mRNA by monocyte/macrophages

We examined the effects of estrogen, 12-O-tetradecanoylphorbol 13 acetate (TPA), and lipopolysaccharide (LPS) on the gene expression of platelet-derived growth factor (PDGF) by the monocyte/macrophage cell line, THP-1. THP-1 cells were exposed to TPA for 48 or 96 hours to induce differentiation. Some were treated with LPS in the last 3 hours and/or ethinyl estradiol (estrogen) (10(-9) M) in the last 20 hours. Total cellular RNA was isolated and cDNA was synthesized and then coamplified (with an internal control, beta-actin, product size 1126 bp) using polymerase chain reaction (PCR) and a set of primers for PDGF-A (product size 225 bp), PDGF-B (217 bp), or PDGF beta-receptor (PDGF-R) (228 bp). The products were separated on an agarose gel and the ratios of radioactivity incorporated into PDGF PCR products to beta-actin products were used to assess the relative changes in the levels of PDGF mRNA abundance in response to various inducers. TPA induced the expression of PDGF-A mRNA, whereas LPS had no effect. Treatment of TPA-stimulated cells with estrogen caused a 61% and 190% increase in PDGF-A mRNA (p < 0.05) at 48 and 96 hours, respectively. Addition of estrogen to cells treated with both TPA and LPS did not cause any significant change in the amounts of the transcripts. In contrast to PDGF-A mRNA, attempts to visualize and estimate PDGF-B and PDGF-R mRNA were unsuccessful. This was probably due to low levels of these transcripts in THP-1 cells. The results indicate that estrogen modulates PDGF-A gene expression by monocyte/macrophages and suggest that estrogen may influence atherogenesis at the vascular level.

Interleukin-1 receptor antagonist and tumor necrosis factor binding protein decrease osteoclast formation and bone resorption in ovariectomized mice

To investigate the contribution of IL-1, IL-6, and TNF to the increased osteoclastogenesis induced by estrogen deficiency, ovariectomized (ovx) mice were treated with either IL-1 receptor antagonist (IL-1ra), a competitive inhibitor of IL-1, TNF binding protein (TNFbp), an inhibitor of TNF, or the anti-IL-6 antibody (Ab) 20F3 for the first 2 wk after surgery. ovx increased the bone marrow cells secretion of IL-1 and TNF, but not IL-6, and the formation of TRAP-positive osteoclast-like multinucleated cells (MNCs) in bone marrow cultures treated with 1,25(OH)2D3. The increase in MNC formation induced by ovx was prevented by in vivo treatment with either 17 beta estradiol, IL-1ra, TNFbp, or anti-IL-6 Ab. However, the percent change in MNC formation induced by the anti-IL-6 Ab was similar in ovx and sham-operated animals, whereas IL-1ra and TNFbp were effective only in ovx mice. MNC formation was also decreased by in vitro treatment of bone marrow cultures with IL-1ra and TNFbp, but not with anti-IL-6 Ab. Ovx also increased bone resorption in vivo and in vitro, as assessed by the urinary excretion of pyridinoline cross links and the formation of resorption pits, respectively. IL-1ra, TNFbp and estrogen decreased bone resorption in vivo and in vitro whereas the anti-IL-6 Ab inhibited bone resorption in vitro but not in vivo. In conclusion, these data indicate that IL-1 and TNF play a direct role in mediating the effects of ovx on osteoclastogenesis and bone resorption. The data also suggest that IL-6 is not essential for increasing bone resorption in the early postovariectomy period.

Circulating levels of cytokines that modulate bone resorption: effects of age and menopause in women

Interleukin 1 alpha (IL-1 alpha), interleukin 1 beta (IL-1 beta), and interleukin 6 (IL-6) are cytokines with potent bone-resorbing effects; some of these biologic effects are opposed by interleukin-1 receptor antagonist (IL-1ra). In vitro and animal model studies suggest that these cytokines are paracrine mediators of the increased bone resorption associated with estrogen deficiency, and increases in their production also could contribute to age-related bone loss. Therefore, we measured serum concentrations of these cytokines in 80 normal women who were 24-87 years old. IL-6 concentration correlated highly with age (p < 0.001) and increased three-fold during life. However, multiple-regression analysis showed no significant correlation between serum IL-6 levels and menopausal status, serum estradiol concentration, or markers for bone turnover (serum bone alkaline phosphatase, osteocalcin, carboxyl-terminal telopeptide of type I collagen, or 24 h urinary free pyridinoline excretion). Serum IL-1 alpha, IL-1 beta, or IL-1ra level did not change with age and, by multiple-regression analysis, did not correlate with markers of bone turnover, except IL-1ra weakly with ICTP. We found no relationship between bone-resorbing cytokines and ovarian function. Although the large age-related increase in serum IL-6 concentration could contribute to age-related bone loss, the lack of correlation with markers for bone turnover argues against this. However, based on the strong evidence in experimental animals that these cytokines are involved in estrogen action on bone, further studies in humans are warranted.

Interleukin-1 receptor antagonist decreases bone loss and bone resorption in ovariectomized rats

Interleukin-1 (IL-1), a cytokine produced by bone marrow cells and bone cells, has been implicated in the pathogenesis of postmenopausal osteoporosis because of its potent stimulatory effects on bone resorption in vitro and in vivo. To investigate whether IL-1 plays a direct causal role in post ovariectomy bone loss, 6-mo-old ovariectomized rats were treated with subcutaneous infusions of IL-1 receptor antagonist (IL-1ra), a specific competitor of IL-1, for 4 wk, beginning either at the time of surgery or 4 wk after ovariectomy. The bone density of the distal femur was measured non invasively by dual-energy X-ray absorptiometry. Bone turnover was assessed by bone histomorphometry and by measuring serum osteocalcin, a marker of bone formation, and the urinary excretion of pyridinoline cross-links, a marker of bone resorption. Ovariectomy caused a rapid increase in bone turnover and a marked decrease in bone density which were blocked by treatment with 17 beta estradiol. Ovariectomy also increased the production of IL-1 from cultured bone marrow cells. Ovariectomy induced-bone loss was significantly decreased by IL-1ra treatment started at the time of ovariectomy and completely blocked by IL-1ra treatment begun 4 wk after ovariectomy. In both studies IL-1ra also decreased bone resorption in a manner similar to estrogen, while it had no effect on bone formation. In contrast, treatment with IL-1ra had no effect on the bone density and the bone turnover of sham-operated rats, indicating that IL-1ra specifically blocked estrogen-dependent bone loss. In conclusion, these data indicate that IL-1, or mediators induced by IL-1, play an important causal role in the mechanism by which ovariectomy induces bone loss in rats, especially following the immediate post ovariectomy period.