Alterations in the growth plate cartilage of rats with renal failure receiving corticosteroid therapy

mTORC1 Inhibits NF-κB/NFATc1 Signaling and Prevents Osteoclast Precursor Differentiation, In Vitro and In Mice

The mechanistic target of rapamycin complex 1 (mTORC1) is a critical sensor for bone homeostasis and bone formation; however, the role of mTORC1 in osteoclast development and the underlying mechanisms have not yet been fully established. Here, we found that mTORC1 activity declined during osteoclast precursors differentiation in vitro and in vivo. We further targeted deletion of Raptor (mTORC1 key component) or Tsc1 (mTORC1 negative regulator) to constitutively inhibit or activate mTORC1 in osteoclast precursors (monocytes/macrophages), using LyzM-cre mice. Osteoclastic formation was drastically increased in cultures of Raptor deficient bone marrow monocytes/macrophages (BMMs), and Raptor-deficient mice displayed osteopenia with enhanced osteoclastogenesis. Conversely, BMMs lacking Tsc1 exhibited a severe defect in osteoclast-like differentiation and absorptive function, both of which were restored following rapamycin treatment. Importantly, expression of nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) and nuclear factor of activated T cells, cytoplasmic 1 (NFATc1), transcription factors that are essential for osteoclast differentiation was negatively regulated by mTORC1 in osteoclast lineages. These results provide evidence that mTORC1 plays as a critical role as an osteoclastic differentiation-limiting signal and suggest a potential drawback in treating bone loss-related diseases with mTOR inhibitors clinically. © 2017 American Society for Bone and Mineral Research.

Effects of corticosterone on the metabolic activity of cultured chicken chondrocytes

Background

Corticosterone is one of the most crucial glucocorticoids (GCs) in poultry. Our previous study shows that corticosterone can retard the longitudinal growth of bones by depressing the proliferation and differentiation of chondrocytes in broilers. The present study was designed to investigate whether corticosterone affect the development of chondrocytes and the synthesis of collagen in vitro. The chondrocytes were isolated from proximal tibial growth plates of 6-week-old broiler chickens and cultured with different doses of corticosterone for 48 h. Then the cell viability, alkaline phosphatase (ALP) activity and the expression of parathyroid hormone-related peptide (PTHrP) and type X collagen (Col X) were detected.

Results

At 10⁻⁹-10⁻⁶ M concentration, corticosterone significantly inhibited the viability and differentiation of chondrocytes, as indicated by decreases in ALP and type X collagen expression. Conversely, there was completely opposite effect at 10⁻¹⁰ M. In addition, the expression of PTHrP was significantly downregulated at 10⁻⁶ M and 10⁻⁸ M, and was upregulated at 10⁻¹⁰ M.

Conclusions

The results suggested that corticosterone regulated chicken chondrocytes performance depending on its concentration with high concentrations inhibiting the viability and differentiation of chondrocytes and light concentrations promoting them, and these roles of corticosterone may be in part mediated through PTHrP.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-015-0398-5) contains supplementary material, which is available to authorized users.

Recent research on the growth plate: Impact of inflammatory cytokines on longitudinal bone growth

Children with inflammatory diseases usually display abnormal growth patterns as well as delayed puberty. This is a result of several factors related to the disease itself, such as malnutrition, hypercortisolism, and elevated levels of pro-inflammatory cytokines. These factors in combination with glucocorticoid treatment contribute to growth retardation during chronic inflammation by systemically affecting the major regulator of growth, the GH/IGF1 axis. However, recent studies have also shown evidence of a direct effect of these factors at the growth plate level. In conditions of chronic inflammation, pro-inflammatory cytokines are upregulated and released into the circulation. The most abundant of these, tumor necrosis factor α, interleukin 1β (IL1β), and IL6, are all known to directly act on growth plate cartilage to induce apoptosis and thereby suppress bone growth. Both clinical and experimental studies have shown that growth retardation can partly be rescued when these cytokines are blocked. Therefore, therapy modulating the local actions of these cytokines may be effective for preventing growth failure in patients with chronic inflammatory disorders. In this review, we report the current knowledge of inflammatory cytokines and their role in regulating bone growth.

Beneficial effect of interleukin-1 receptor antagonist protein on spinal cord injury recovery in the rat

We assessed the effect of treatment with the interleukin-1 receptor antagonist protein (IRAP) on morphological and functional recovery in a rat model of SCI. All sections were processed for immunohistochemistry, hematoxylin-eosin, and Nissl staining. Rats were assessed for hind limb motor function using the Basso, Beattie, and Bresnahan (BBB) hind limb locomotor rating scale and the inclined plane test. At 1, 48, and 72 h after operation, there was a significant increase in neurofilament proteins and brain-derived neurotrophic factor expression in the IRAP group I when compared with the saline group I and the sham-operated group I (P < 0.05). The mean inclined plane scores and BBB scores for the IRAP group II were higher than the saline group II at 1, 2, 3, and 4 weeks post-injury (P < 0.05). In conclusion, treatment with IRAP enhanced neuronal survival after SCI.

The role of α-zearalanol in reversing bone loss induced by ovarian hormone deficiency in rats

To assess the ability of α-zearalanol (α-ZAL) to prevent bone loss in an ovariectomized (OVX) rat model of osteoporosis, α-ZAL was administered intragastrically to rats. After 35 days, the total body bone mineral density (BMD) was assessed in all rats. All sections were processed for immunohistochemistry and hematoxylin and eosin staining. One-way ANOVA and an LSD multiple-range test were used to determine the significant differences between groups. BMD was lower in the OVX and OVX + α-ZAL high-dose (OVX + High) groups compared to the sham-operated (Sham), OVX + 17β-ethinylestradiol (OVX + E(2)), OVX + α-ZAL medium-dose (OVX + Medium) and OVX + α-ZAL low-dose (OVX + Low) groups (P < 0.05). Clear bone trabeculae arrangements were observed in the OVX + E(2,) OVX + Medium and OVX + Low groups. The expressions of bone morphogenetic proteins and basic fibroblast growth factor were up-regulated in the OVX + E(2), OVX + Medium and OVX + Low groups compared to the OVX and OVX + High groups (P < 0.05). The OVX + E(2), OVX + Medium and OVX + Low groups showed lower levels of bone Gla protein, bone alkaline phosphatase, tartrate-resistant acid phosphatase and tumor necrosis factor α expressions than the OVX and OVX + High groups (P < 0.05). The administration of α-ZAL to ovariectomized rats reverses bone loss and prevents osteoporosis.

Chondrocyte p21(WAF1/CIP1) expression is increased by dexamethasone but does not contribute to dexamethasone-induced growth retardation in vivo

It has been shown that cell cycle genes play an important role in the coordination of chondrocyte proliferation and differentiation. The inhibitory effects of glucocorticoids (GCs) on chondrocyte proliferation are consistent with GCs disrupting cell cycle progression and promoting cell cycle exit. Cyclin-dependent kinase inhibitors (CDKIs) force cells to exit the cell cycle and differentiate, and studies have shown that expression of the CDKI p21(CIP1/WAF1) is increased in terminally differentiated cells. In this study, p21 mRNA and protein expression was increased during chondrocyte differentiation and after exposure to dexamethasone (Dex, 10(-6 )M) in murine chondrogenic ATDC5 cells. In 4-week-old mice lacking a functional p21 gene, Dex caused a reduction in body weight compared to saline control null mice, but this was consistent with the reduction in body weight observed in Dex-treated wild-type littermates. In addition, p21 ablation had no effect on the reduction in width of the growth plate or reduced mineral apposition rate in Dex-treated mice. However, an alteration in growth rate and epiphyseal structure is evident when comparing p21(-/-) and wild-type mice. These findings suggest that p21 does not directly contribute to GC-induced growth retardation in vivo but is involved in the maintenance of the growth plate.

Bone growth during rapamycin therapy in young rats

BACKGROUND

Rapamycin is an effective immunosuppressant widely used to maintain the renal allograft in pediatric patients. Linear growth may be adversely affected in young children since rapamycin has potent anti-proliferative and anti-angiogenic properties.

METHODS

Weanling three week old rats were given rapamycin at 2.5 mg/kg daily by gavage for 2 or 4 weeks and compared to a Control group given equivalent amount of saline. Morphometric measurements and biochemical determinations for serum calcium, phosphate, iPTH, urea nitrogen, creatinine and insulin-growth factor I (IGF-I) were obtained. Histomorphometric analysis of the growth plate cartilage, in-situ hybridization experiments and immunohistochemical studies for various proteins were performed to evaluate for chondrocyte proliferation, chondrocyte differentiation and chondro/osteoclastic resorption.

RESULTS

At the end of the 2 weeks, body and tibia length measurements were shorter after rapamycin therapy associated with an enlargement of the hypertrophic zone in the growth plate cartilage. There was a decrease in chondrocyte proliferation assessed by histone-4 and mammalian target of rapamycin (mTOR) expression. A reduction in parathyroid hormone/parathyroid hormone related peptide (PTH/PTHrP) and an increase in Indian hedgehog (Ihh) expression may explain in part, the increase number of hypertrophic chondrocytes. The number of TRAP positive multinucleated chondro/osteoclasts declined in the chondro-osseous junction with a decrease in the receptor activator of nuclear factor kappa beta ligand (RANKL) and vascular endothelial growth factor (VEGF) expression. Although body and tibial length remained short after 4 weeks of rapamycin, changes in the expression of chondrocyte proliferation, chondrocyte differentiation and chondro/osteoclastic resorption which were significant after 2 weeks of rapamycin improved at the end of 4 weeks.

CONCLUSION

When given to young rats, 2 weeks of rapamycin significantly decreased endochondral bone growth. No catch-up growth was demonstrated at the end of 4 weeks, although markers of chondrocyte proliferation and differentiation improved. Clinical studies need to be done to evaluate these changes in growing children.

Dexamethasone-induced expression of the glucocorticoid response gene lipocalin 2 in chondrocytes

Glucocorticoids (GC) are commonly used anti-inflammatory drugs, but long-term use can result in marked growth retardation in children due to their actions on growth plate chondrocytes. To gain an insight into the mechanisms involved in GC-induced growth retardation, we performed Affymetrix microarray analysis of the murine chondrogenic cell line ATDC5, incubated with 10(-6) M dexamethasone (Dex) for 24 h. Downregulated genes included secreted frizzled-related protein and IGF-I, and upregulated genes included serum/GC-regulated kinase, connective-tissue growth factor, and lipocalin 2. Lipocalin 2 expression increased 40-fold after 24-h Dex treatment. Expression increased further after 48-h (75-fold) and 96-h (84-fold) Dex treatment, and this response was Dex concentration dependent. Lipocalin 2 was immunolocalized to both proliferating and hypertrophic growth plate zones, and its expression was increased by Dex in primary chondrocytes at 6 h (3-fold, P < 0.05). The lipocalin 2 response was blocked by the GC-receptor antagonist RU-486 and was increased further by the protein synthesis blocker cycloheximide. Proliferation in lipocalin 2-overexpressing cells was less than in control cells (49%, P < 0.05), and overexpression caused an increase in collagen type X expression (4-fold, P < 0.05). The effects of lipocalin 2 overexpression on chondrocyte proliferation (64%, P < 0.05) and collagen type X expression (8-fold, P < 0.05) were further exacerbated with the addition of 10(-6) M Dex. This synergistic effect may be explained by a further increase in lipocalin 2 expression with Dex treatment of transfected cells (45%, P < 0.05). These results suggest that lipocalin 2 may mediate Dex effects on chondrocytes and provides a potential novel mechanism for GC-induced growth retardation.

Bone growth during daily or intermittent calcitriol treatment during renal failure with advanced secondary hyperparathyroidism

Calcitriol is a standard therapy for secondary hyperparathyroidism in chronic renal failure. We evaluated whether the effect of daily or intermittent calcitriol administration is more efficient in enhancing bone growth in renal failure with advanced secondary hyperparathyroidism in weanling 5/6 nephrectomized rats loaded with phosphorus to induce severe secondary hyperparathyroidism. The animals were treated daily or three times weekly with calcitriol for 4 weeks but the total weekly dose of calcitriol was the same. Although calcitriol increased the serum calcium, it did not lower parathyroid hormone (PTH) or improve tibia and body length. Animals with renal failure and advanced secondary hyperparathyroidism had decreased PTH/PTHrP, which was accompanied by an increase in the cyclin kinase inhibitor p57(Kip2). Calcitriol treatment upregulated the PTH/PTHrP receptor but also increased inhibitors of cell proliferation such as p21(Waf1/Cip1), IGFBP3, and FGFR3. Calcitriol also enhanced markers of chondrocyte differentiation, such as IGF1, Vitamin D receptor, FGF23, and bone morphogenetic protein-7. Receptor activator of nuclear factor-kappabeta ligand levels improved with calcitriol treatment but without changes in osteoprotegerin suggesting an enhancement of osteo/chondroclastogenesis and mineralization. Overall, both daily and intermittent calcitriol had similar effects on endochondral bone growth in phosphorus-loaded rats with renal failure.

The effects of immunosuppressive agents on the function of human hepatocytes in vitro

Calcineurin inhibitors (tacrolimus) and steroids continue to be an important component of hepatocyte transplantation protocols, despite reports of hepatotoxicity and inhibitory effects of steroids on cell proliferation. The aim of the study was to investigate whether isolated human hepatocytes were more vulnerable to the toxicity of these agents and also to investigate their effects on hepatocyte VEGF secretion, a vascular permeability factor suggested to be involved in the cell engraftment process. Human hepatocytes were isolated from donor livers/segments rejected or unused for orthotopic liver transplantation using a collagenase perfusion technique. Hepatocytes were plated for cell function tests and to determine VEGF production. Tacrolimus (0-50 ng/ml) and methylprednisolone (0-500 ng/ml) were added to the culture media and cells incubated for 24 h. Cell metabolic activity was assessed using the MTT assay, cell number using the SRB assay, and cell attachment from hepatocyte total protein content and protein synthesis using [14C]leucine incorporation. VEGF in culture supernatants was measured by ELISA. Tacrolimus and methylprednisolone had no statistically significant inhibitory effects on metabolic activity or protein synthesis compared to controls at all concentrations of the agents tested when added after plating. There were also no significant effects on cell attachment when tacrolimus or methylprednisolone was added at the time of cell plating. There were no differences in the responses obtained when either fresh or cryopreserved hepatocytes were used. The amount of VEGF secreted by untreated hepatocytes was highly variable (0-1400 pg/10(6) cells/24 h). VEGF levels in the culture supernatant from hepatocytes isolated from < or = 20-year-old donors (687 +/- 59 pg/10(6) cells/24 h) was significantly greater than from older donors (61 +/- 7 pg/10(6) cells/24 h; p = 0.003). Tacrolimus and methylprednisolone did not significantly affect VEGF secretion by hepatocytes. Tacrolimus and methylprednisolone did not have detrimental effects on the metabolic function of human hepatocytes, cell attachment, or VEGF secretion after cell isolation.

Response of the growth plate of uremic rats to human growth hormone and corticosteroids

Children with chronic renal failure in general present growth retardation that is aggravated by corticosteroids. We describe here the effects of methylprednisolone (MP) and recombinant human growth hormone (rhGH) on the growth plate (GP) of uremic rats. Uremia was induced by subtotal nephrectomy in 30-day-old rats, followed by 20 IU kg-1 day-1 rhGH (N = 7) or 3 mg kg-1 day-1 MP (N = 7) or 20 IU kg-1 day-1 rhGH + 3 mg kg-1 day-1 MP (N = 7) treatment for 10 days. Control rats with intact renal function were sham-operated and treated with 3 mg kg-1 day-1 MP (N = 7) or vehicle (N = 7). Uremic rats (N = 7) were used as untreated control animals. Structural alterations in the GP and the expression of anti-proliferating cell nuclear antigen (PCNA) and anti-insulin-like growth factor I (IGF-I) by epiphyseal chondrocytes were evaluated. Uremic MP rats displayed a reduction in the proliferative zone height (59.08 +/- 4.54 vs 68.07 +/- 7.5 microm, P < 0.05) and modifications in the microarchitecture of the GP. MP and uremia had an additive inhibitory effect on the proliferative activity of GP chondrocytes, lowering the expression of PCNA (19.48 +/- 11.13 vs 68.64 +/- 7.9% in control, P < 0.0005) and IGF-I (58.53 +/- 0.96 vs 84.78 +/- 2.93% in control, P < 0.0001), that was counteracted by rhGH. These findings suggest that in uremic rats rhGH therapy improves longitudinal growth by increasing IGF-I synthesis in the GP and by stimulating chondrocyte proliferation.

The growth plate sparing effects of the selective glucocorticoid receptor modulator, AL-438

Long-term use of glucocorticoids (GC) can cause growth retardation in children due to their actions on growth plate chondrocytes. AL-438, a non-steroidal anti-inflammatory agent that acts through the glucocorticoid receptor (GR) retains full anti-inflammatory efficacy but has reduced negative effects on osteoblasts compared to those elicited by prednisolone (Pred) or dexamethasone (Dex). We have used the murine chondrogenic ATDC5 cell line to compare the effects of AL-438 with those of Dex and Pred on chondrocyte dynamics. Dex and Pred caused a reduction in cell proliferation and proteoglycan synthesis, whereas exposure to AL-438 had no effect. LPS-induced IL-6 production in ATDC5 cells was reduced by Dex or AL-438, showing that AL-438 has similar anti-inflammatory efficacy to Dex in these cells. Fetal mouse metatarsals grown in the presence of Dex were shorter than control bones whereas AL-438 treated metatarsals paralleled control bone growth. These results indicate that the adverse effects Dex or Pred have on chondrocyte proliferation and bone growth were attenuated following AL-438 exposure, suggesting that AL-438 has a reduced side effect profile on chondrocytes compared to other GCs. This could prove important in the search for new anti-inflammatory treatments for children.

Damage and recovery of the bone growth mechanism in young rats following 5-fluorouracil acute chemotherapy

Chemotherapy-induced bone growth arrest and osteoporosis are significant problems in paediatric cancer patients, and yet how chemotherapy affects bone growth remains unclear. This study characterised development and resolution of damage caused by acute chemotherapy with antimetabolite 5-fluorouracil (5-FU) in young rats in the growth plate cartilage and metaphyseal bone, two important tissues responsible for bone lengthening. In metaphysis, 5-FU induced apoptosis among osteoblasts and preosteoblasts on days 1-2. In growth plate, chondrocyte apoptosis appeared on days 5-10. Interestingly, Bax was induced prior to apoptosis and Bcl-2 was upregulated during recovery. 5-FU also suppressed cell proliferation on days 1-2. While proliferation returned to normal by day 3 in metaphysis, it recovered partially on day 3, overshot on days 5-7 and normalised by day 10 in growth plate. Histologically, growth plate heights decreased by days 4-5 and returned normal by day 10. In metaphysis, primary spongiosa height was also reduced, mirroring changes in growth plate thickness. In metaphyseal secondary spongiosa, a reduced bone volume was observed on days 7-10 as there were fewer but more separated trabeculae. Starting from day 4, expression of some cartilage/bone matrix proteins and growth factors (TGF-beta1 and IGF-I) was increased. By day 14, cellular activity, histological structure and gene expression had returned normal in both tissues. Therefore, 5-FU chemotherapy affects bone growth directly by inducing apoptosis and inhibiting proliferation at growth plate cartilage and metaphyseal bone; after the acute damage, bone growth mechanism can recover, which is associated with upregulated expression of matrix proteins and growth factors.

Impaired growth plate chondrogenesis in children with chronic illnesses

In mammals, statural growth is primarily accomplished by endochondral ossification, which takes place at the growth plate. Growth plate chondrocyte proliferation, hypertrophy/differentiation, apoptosis, and cartilage matrix synthesis all contribute to chondrogenesis or cartilage formation, a process tightly coupled to the simultaneous remodeling of the cartilage into bone at the metaphyseal border of the growth plate. Growth plate chondrogenesis is regulated by the complex interaction of molecular signals acting systemically as well locally within the growth plate. This network is often dysregulated during chronic illnesses, thus resulting in impaired growth plate chondrogenesis and, in turn, growth failure. The principal events responsible for altered growth plate chondrogenesis in chronic illness are inflammation, protein/calorie deprivation, uremia/metabolic acidosis, glucocorticoids, and impaired GH/IGF-I axis.

Alterations of the growth plate in chronic renal failure

Chronic renal failure modifies the morphology and dynamics of the growth plate (GP) of long bones. In young uremic rats, the height of cartilage columns of GP may vary markedly. The reasons for this variation are unknown, although the severity and duration of renal failure and the type of renal osteodystrophy have been shown to influence the height of GP cartilage. Expansion of GP cartilage is associated with that of the hypertrophic stratum. The interference of uremia with the process of chondrocyte differentiation is suggested by some morphological features. However, analysis by immunohistochemistry and/or in situ hybridization of markers of chondrocyte maturation in the GP of uremic rats has yielded conflicting results. Thus, there have been reported normal and reduced mRNA levels for collagen X, parathyroid hormone/parathyroid hormone-related peptide receptor, and matrix metalloproteinase 9, as well as normal mRNA and protein expression for vascular endothelial growth factor and chondromodulin I, peptides related to the control of angiogenesis. In addition, a decreased immunohistochemical signal for growth hormone receptor and low insulin-like growth factor I mRNA in the proliferative zone of uremic GP are supportive of reduced chondrocyte proliferation. Growth hormone treatment improves chondrocyte maturation and activates bone metabolism in the primary spongiosa.

Daily or intermittent calcitriol administration during growth hormone therapy in rats with renal failure and advanced secondary hyperparathyroidism

Growth hormone (GH) improves growth in children with chronic renal failure. The response to GH may be affected by the degree of secondary hyperparathyroidism and concurrent treatment with vitamin D. Forty-six rats underwent 5/6 nephrectomy (Nx) and were given a high-phosphorus diet (Nx-Phos) to induce advanced secondary hyperparathyroidism and divided into the following groups: (1) Nx-Phos (n = 10) received saline, (2) GH at 10 IU/kg per d (Nx-Phos+GH; n = 9), (3) GH and daily calcitriol (D) at 50 ng/kg per d (Nx-Phos+GH+daily D; n = 8), (4) GH and intermittent D (three times weekly) at 350 ng/kg per wk (Nx-Phos+GH+int D; n = 9), and (5) intact-control (n = 10). Serum parathyroid hormone (PTH) levels were elevated in Nx-Phos, but IGF-I levels did not change with growth hormone. Body length, tibial length, and growth plate width did not increase with either GH or calcitriol. Proliferating cell nuclear antigen staining, PTH/PTHrP receptor, bone morphogenetic protein-7, and fibroblast growth factor receptor-3 expression increased with GH alone or with intermittent calcitriol but were slightly diminished during daily calcitriol administration. GH enhanced IGF-I, IGF binding receptor-3, and GH receptor but declined with daily and intermittent calcitriol. Overall, there was no improvement in body length, tibial length, and growth plate width at the end of GH therapy, but selected markers of chondrocyte proliferation and chondrocyte differentiation increased, although these changes were attenuated by calcitriol. The combination of GH and calcitriol that is frequently used in children with renal failure and secondary hyperparathyroidism require further studies to evaluate the optimal dose and frequency of administration to increase linear growth and prevent bone disease.

Bone elongation in rats with renal failure and mild or advanced secondary hyperparathyroidism

BACKGROUND

Impairment of growth in children with chronic renal failure may be due, in part to the insensitivity to the actions of growth hormone by insulin-like growth factor-I (IGF-I) because of accumulations of IGF binding proteins. There are a few studies describing the changes that occur in the growth plate in renal failure. None of these studies has simultaneously compared the modifications in the expression of selected markers of endochondral bone formation in renal failure with mild or advanced secondary hyperparathyroidism.

METHODS

Forty-six rats that underwent 5/6 nephrectomy (Nx) were fed either standard rodent diet (Nx-control) or high phosphorus diet to induce advanced secondary hyperparathyroidism (Nx-phosphorus) for 4 weeks. Sections of the tibia were obtained for growth plate histomorphometry, immunohistochemistry studies, and in situ hybridization experiments for selected markers of endochondral bone formation.

RESULTS

Weight gain, gain in length, and tibial length were less in Nx animals. Serum parathyroid hormone (PTH) and phosphorus levels were higher and serum calcium levels were lower in the Nx-phosphorus group. The width of the growth plate was much shorter in the Nx-phosphorus group due to a decrease in both proliferative and hypertrophic zones. IGF-I protein and IGF binding protein-3 staining were diminished in both Nx groups without changes in the IGF-I receptor expression; the decline in IGF-I protein expression was much lower in the Nx-phosphorus group. PTH/PTH receptor protein (PTHrP) receptor mRNA transcripts decline and tartrate-resistant acid phosphastase (TRAP) staining increased only in the Nx-phosphorus group.

CONCLUSION

The growth impairment in renal failure may be worsened by the severity of secondary hyperparathyroidism.

Effects of acute 5-fluorouracil chemotherapy and insulin-like growth factor-I pretreatment on growth plate cartilage and metaphyseal bone in rats

With the intensified use of chemotherapy and improved survival rates for childhood malignancies, it has become increasingly apparent that some children or adult survivors show poor bone growth and develop osteoporosis. As a step to investigate underlying mechanisms, this project examined short-term effects in rats of chemotherapy agent 5-fluorouracil (5-FU) on cell proliferation, apoptosis, and bone formation at tibial growth plate cartilage and its adjacent bone-forming region metaphysis. In addition, since insulin-like growth factor (IGF-I) is important for bone growth, we examined whether IGF-I pretreatment would potentially protect growth plate cartilage and bone cells from chemotherapy damage. Two days after a single high dose of 5-FU injection, proliferation of growth plate chondrocytes and metaphyseal osteoblasts/preosteoblasts was dramatically suppressed, and apoptosis was induced among osteoblasts and preosteoblasts. As a result, there was a reduction in the chondrocyte number and zonal height at the proliferative zone and a decline in the number of osteoblasts and preosteoblasts on the metaphyseal trabecular bone surface. At day 2, no obvious deleterious effects were observed on the height of the growth plate hypertrophic zone and the bone volume fraction of the metaphyseal primary spongiosa trabeculae. At day 10, while cell proliferation and growth plate structure returned to normal, there were slight decreases in trabecular bone volume, body length increase, and tibial length. While pretreatment with 1-week IGF-I systemic infusion did not attenuate the suppressive effect of 5-FU on proliferation in both growth plate and metaphysis, it significantly diminished apoptotic induction in metaphysis. These results indicate that growth plate cartilage chondrocytes and metaphyseal bone cells are sensitive to chemotherapy drug 5-FU and that IGF-I pretreatment has some anti-apoptotic protective effects on metaphyseal bone osteoblasts and preosteoblasts.

Growth hormone therapy in calcium-loaded rats with renal failure

GH increases linear growth in children with chronic renal failure, but the response remains suboptimal in some patients. Some of the factors that may explain the poor response to GH include high doses of calcitriol and exogenous calcium loading to prevent hyperphosphatemia. High doses of exogenous calcium adversely affect chondrocyte proliferation and delay mineralization in the growth plate of rats with renal failure; bone histomorphometric changes in these animals are comparable to adynamic bone. To evaluate GH effects on adynamic bone in renal failure, 48 weanling rats underwent sham nephrectomy (Intact-Control) or 5/6 nephrectomy (Nx). Nx animals were fed a high-calcium diet (Nx-Ca(2+)) to induce adynamic bone. After 4 wk, the Nx-Ca(2+) animals were treated with GH (Nx-Ca(2+) + GH), calcitriol (Nx-Ca(2+) + D), or a combination of GH and calcitriol (Nx-Ca(2+)GH + D) for 2 wk. Serum intact PTH and IGF-I levels did not differ among all nephrectomized groups given high calcium. GH did not increase body length or tibial length at the end of study period. In the proximal tibia, the width of the growth plate and the growth plate architecture did not improve with GH. There was a decline in histone-4 expression, IGF-I protein, IGF binding protein-3, and bone morphogenetic protein-7 staining and a mild increase in IGF-I receptor, GH receptor, and gelatinase B expression in the Nx-Ca(2+) + GH group when compared with the Intact-Control group. Calcitriol blunted some of the mitogenic effects of GH in the growth plate. Thus, there was a poor response to GH therapy in calcium-loaded animals with renal failure.

Short-term glucocorticoid treatment of piglets causes changes in growth plate morphology and angiogenesis

OBJECTIVE

Glucocorticoid treatment of children often leads to growth retardation, and the precise target(s) in the growth plate responsible for this effect are unknown. Angiogenesis is an important part of the endochondral ossification process, and VEGF expressed in the growth plate is essential for proper angiogenesis to occur. Since glucocorticoid treatment down-regulates VEGF expression in cultured chondrocytes, we hypothesized that in vivo glucocorticoid treatment could result in VEGF down-regulation in the growth plate and disturbed angiogenesis, thus contributing to the growth retardation.

DESIGN

We treated 6-week-old prepubertal piglets (10 kg) for 5 days with prednisolone (50 mg/day). Tibial growth plate sections were studied for apoptosis and the expression of VEGF protein and mRNA and MMP-9 protein. Capillaries in the metaphysis were visualized by CD31 immunostaining. Growth plate morphology (width of various zones) was determined by interactive measurements on hematoxylin/eosin stained sections and apoptotic cells were detected by TUNEL assay.

RESULTS

In the prednisolone-treated animals, the total width of the growth plate decreased to 81% of controls (P<0.02), which was explained by a decrease of the width of the proliferative zone to 73% (P<0.05). The treatment had no effect on the orderly organization of the chondrocyte columns. In the growth plates of control animals, apoptosis was shown in 5.8% of the hypertrophic chondrocytes and was limited to the terminal hypertrophic chondrocytes. In prednisolone-treated animals, 40.5% of the hypertrophic chondrocytes was apoptotic (P<0.02), with apoptotic chondrocytes also appearing higher in the hypertrophic zone. We observed fewer capillaries and loss of their parallel organization in the metaphysis in the prednisolone-treated animals. The capillaries were shorter and chaotic in appearance. In contrast to controls, in prednisolone-treated animals VEGF mRNA and protein could not be detected in the hypertrophic zone of the growth plate. Trabecular bone length in the primary spongiosa was also diminished by the treatment. No changes were observed in the expression pattern of MMP-9, a matrix metalloproteinase, which is also important for angiogenesis and bone formation.

CONCLUSIONS

These results indicate that short-term glucocorticoid treatment of growing piglets severely disturbs the width of the growth plate, apoptosis of chondrocytes, VEGF expression by hypertrophic chondrocytes, the normal invasion of blood vessels from the metaphysis to the growth plate and bone formation at the chondro-osseous junction. These effects could alter the dynamics of endochondral ossification and thus contribute to glucocorticoid-induced growth retardation.

Effects of thyroparathyroidectomy, exogenous calcium, and short-term calcitriol therapy on the growth plate in renal failure

Several factors have been implicated in the development of adynamic bone, including the use of calcium-containing phosphate binding agents, aggressive calcitriol therapy, and parathyroidectomy. To evaluate the effects of these interventions on the growth plate, weanling rats underwent sham nephrectomy (Control, n = 10) and 5/6 nephrectomy (Nx). In the nephrectomized group, animals underwent (a) thyroparathyroidectomy (Nx-TPTX, n = 7), (b) received exogenous calcium (Nx-Calcium, n = 10), (c) received short-term calcitriol therapy (Nx-D, n = 10), or (d) nephrectomized control (Nx-Control, n = 10). Higher serum calcium and lower PTH levels were demonstrated in Nx-Calcium and Nx-D animals. A decline in growth was demonstrated in Nx-Calcium and Nx-TPTX accompanied by shorter tibial lengths. The width of the growth plate was wider in Nx-Calcium animals due to an increase in the width of the hypertrophic zone and a decrease in the proliferative zone; these changes were accompanied by an impairment of chondroclastic resorption, lower gelatinase B/MMP-9 activity, decline in insulin-like growth factor-I (IGF-I) receptor, and lower histone-4 mRNA expression. Such findings in the growth plate, may partially contribute to the diminution of growth in these animals. Although growth was impaired in the Nx-TPTX animals, there were no significant changes demonstrated in the growth plate cartilage. Histone-4 transcripts, IGF-I receptor expression, and histochemical staining for chondroclasts were decreased in Nx-D animals. Thus, treatments used in the management of secondary hyperparathyroidism in renal failure have diverse effects on the growth plate of the young skeleton, and concurrent use of these interventions needs further evaluation.