Diabetes Mellitus y pérdida de masa ósea / Diabetes Mellitus and bone mass loss

La diabetes mellitus es una enfermedad que afecta a unos 200 millones de personas en el mundo. Estudios epidemiológicos y experimentales demuestran la existencia de una pérdida de masa ósea asociada a la diabetes de tipo 1. Esta pérdida parece estar mediada por diversos factores endocrinos y/o locales, entre los que se incluyen: la insulina, el factor similar a la insulina tipo 1 (IGF-1), péptidos pancreáticos (amilina, leptina y preptina), hormonas intestinales (GLP-1 y GLP-2) y la vitamina D. Sin embargo, en la diabetes tipo 2 no existen datos concluyentes que la relacionen con una disminución de la masa ósea

Diabetes mellitus is a disease affecting about 200 million people worldwide. Both epidemiological and experimental studies have demonstrated the existence of a diabetes-related bone loss in type 1 diabetic patients. This relationship seems to be mediated by different endocrine and local factors, namely insulin, insulin-like growth factor 1 (IGF-1), pancreatic peptides (amylin, leptin, and preptin), intestinal hormones (GLP-1 y GLP-2), and vitamin D. However, no such relationship has been demonstrated in type 2 diabetes

Transient exposure to PTHrP (107-139) exerts anabolic effects through vascular endothelial growth factor receptor 2 in human osteoblastic cells in vitro.

Intermittent administration of the N-terminal fragment of parathyroid hormone (PTH) and PTH-related protein (PTHrP) induces bone anabolic effects. However, the effects of the C-terminal domain of PTHrP on bone turnover remain controversial. We examined the putative mechanisms whereby this PTHrP domain can affect osteoblastic differentiation, using human osteosarcoma MG-63 cells and osteoblastic cells from human trabecular bone. Intermittent exposure to PTHrP (107-139), within 10-100 nM, for only

Age-related changes in parathyroid hormone-related protein and vascular endothelial growth factor in human osteoblastic cells.

Osteogenesis and angiogenesis occur in a coordinated manner in skeletal tissue, so that impaired angiogenesis is associated with decreased bone formation in aged subjects. However, the interaction between bone endothelium and osteoblastic cells is poorly understood. Parathyroid hormone-related protein (PTHrP), a bone factor which modulates osteoblastic cell growth and/or differentiation, stimulates vascular endothelial growth factor (VEGF), a potent angiogenic factor, in primary cultures of human osteoblastic (hOB) cells. In the present study, we examined the age-related changes of both factors in these cells. Human OB cells were isolated from trabecular bone samples from knee or hip explants obtained from 45 osteoarthritic patients: 12 <60 years (21-59 years), 5 women and 7 men, and 33 >60 years (61-82 years), 20 women and 13 men. Cell total RNA was isolated, and mRNA analysis was performed by reverse transcription-polymerase chain reaction. Relative ratios of amplified products with respect to glyceraldehyde-3-phosphate dehydrogenase were then calculated. PTHrP and VEGF were measured in the cell-conditioned medium, after stimulation with (or without) 10 nM 1,25(OH)(2)D(3) for 72 h, using specific immunoradiometric assay and a competitive immunoassay, respectively. A positive correlation was found between PTHrP and VEGF (both mRNA and secreted protein), and also between PTHrP mRNA and the secreted protein levels, in these cells. PTHrP, both mRNA and protein secretion levels, and VEGF secreted values were higher in knee hOB cells than in hip hOB cells only in the younger group. In addition, a decrease in the secreted levels of these factors occurs with aging only in hOB cells from knee. Treatment with 10 nM 1,25(OH)(2)D(3) induced a lower inhibitory response of PTHrP secretion, and a higher stimulatory response of secreted VEGF, in hOB cells with age. These findings indicate that age-related bone loss in humans is associated with a decrease in the osteoblastic secretion of both PTHrP and VEGF in the knee, a predominantly trabecular bone. These data might provide a rationale to explain the impaired angiogenesis associated with trabecular bone loss in aging.

Cambios estructurales y calcificaciones vasculares en la uremia / No disponible

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Role of vascular endothelial growth factor in the response to vessel injury.

In the post-embryonic life, physiological angiogenesis is tightly controlled. Angiogenesis also occurs in pathological circumstances such as tumor vessel proliferation, retinal neovascularization and ischemia. The development of collateral circulation is not only not deleterious, but life saving. Other cases such as neoplastic neovascularization are the basis of the continuous growth of tumors and metastases, and therefore constitute a target of therapeutical efforts. Among a list of molecules able to control angiogenesis, we emphasize the pivotal role of vascular endothelial growth factor (VEGF). VEGF is a potent mitogen for endothelial cells, but is devoid of mitogenic activity for other cell types. VEGF is a polypeptide with four main different isoforms that are remarkably different in terms of solubility and affinity for matrix proteins. VEGF interacts with two endothelial cell-specific tyrosine kinase receptors. The main interest of its study lies in VEGF's role in pathological angiogenic processes, where an increase in the VEGF mRNA expression has been consistently observed. An interesting example is the up-regulation of VEGF's and VEGF receptors' mRNA in a considerable number of human tumors and retina, where they have a critical role in the development of neovascularization. In recent work in our laboratory, we have found further potential interactions of VEGF with pathophysiological mechanisms, namely, the increase in VEGF gene expression under exposure to reactive oxygen species and the positive interaction between VEGF and erythropoietin. VEGF has outstanding possibilities for therapeutic applications aimed at inhibiting or favoring the development of new vessels.

Role of vascular endothelial growth factor on erythropoietin-related endothelial cell proliferation.

The vascular actions of recombinant human erythropoietin (rhEPO) are of particular relevance for fully understanding rhEPO effects. This study examines the mechanisms of action of rhEPO on endothelial cells from bovine aorta (BAEC). First, the studies demonstrated that rhEPO acts on BAEC proliferation as a comitogenic growth factor in the presence of fetal calf serum (FCS). The main experimental findings disclosed that an interaction between rhEPO and vascular endothelial growth factor (VEGF) is instrumental for the growth-promoting action of rhEPO, as shown by the blockade (92.8+/-2.2% inhibition, P < 0.01) of the rhEPO-induced BAEC proliferation by a specific anti-VEGF antibody and by the capability of VEGF for substituting FCS in the induction of rhEPO-related BAEC proliferation (increase in BAEC number in the absence of FCS: 20 U/ml rhEPO alone, 0.3+/-2.8%; 5 x 10(-11) M VEGF alone, 52.9+/-3.1%; 20 U/ml rhEPO + 5 X 10(-11) M VEGF, 117.8+/-6.9%, P < 0.01 between the two agents combined with respect to each agent alone). The existence of a positive interaction between rhEPO and VEGF was further demonstrated by observing an increased cytosolic Ca2+ ([Ca2+]i) mobilization response to VEGF (10(-11)M) in BAEC pretreated or not with 20 U/ml rhEPO (delta[Ca2+]i = 704+/-111 versus 246+/-36 nM, respectively, P < 0.01). To further examine the mechanism of the potentiation of VEGF effect by rhEPO, we analyzed the mRNA expression of the VEGF receptors KDR/flk-1 and flt-1. The results disclosed that BAEC pretreatment with rhEPO upregulated the expression of both KDR/flk-1 and flt-1, therefore providing a structural basis for the aforementioned positive interactions between VEGF and rhEPO. Furthermore, inhibition by genistein suggests that tyrosine phosphorylation was involved in the VEGF receptor upregulation. The mechanisms identified in the present study disclose an interaction at the level of mRNA expression and functional effects between a hormone with predominantly hemopoietic effects, namely, erythropoietin, and an angiogenic factor, namely, VEGF. This relationship between rhEPO and VEGF might be of particular importance in neovascularization processes and in patients receiving rhEPO as a treatment.

Effects of angiotensin II on endothelial cell growth: role of AT-1 and AT-2 receptors.

Angiotensin II (AngII) is a main mediator in the regulation of vascular tone. Although its effects on vascular smooth muscle cells are well known, data on its role on endothelial biology are still insufficient. The present study examined the effect of endogenous and exogenous AngII on bovine aortic endothelial cells possessing both AT-1 and AT-2 receptors. A DNA synthesis-promoting effect of AT-2 blockade by PD123319 (10(-9) to 10(-7) M) was demonstrated. This effect was transduced through an AT-1-mediated pathway, as shown by using the AT-1 antagonist, losartan. In addition, an AT-1-mediated effect of AngII was demonstrated on bovine aortic endothelial cell proliferation, which occurred despite the absence of AngII-induced Ca2+ transients. In summary, the present study disclosed relevant characteristics of the effect of AngII on endothelial cell growth that have potential pathophysiologic projections, particularly for the use of selective AngII blocking agents.

Role of nitric oxide-related mechanisms in renal function in ageing rats.

BACKGROUND: The impaired renal function and vasodilatation that accompany age need to be re-addressed based upon the new knowledge concerning vascular nitric oxide (NO)-dependent systems. The present study examined the effects of age on the NO-related renal response. METHODS: The study was performed in euvolaemic, conscious Wistar rats, aged 5 and 18 months. Renal function and haemodynamic measurements with fluorescent microspheres were employed to assess differences between groups. RESULTS: A first set of experiments showed that ageing rats had a reduced natriuretic and diuretic response to acetylcholine, whereas the response to sodium nitroprusside was preserved. In the same regard, a reduction of the renal functional effects of L-arginine (L-Arg) and L-glycine (L-Gly) was found in the older rats. In the ageing rats, these responses were accompanied by an enhanced effect of the L-Arg competitive analogue, NwNLA, which provoked a marked reduction of renal function. This effect of NwNLA was blocked by the simultaneous administration of a small dose of L-Arg in the ageing but not in the young rats. Systemic haemodynamic studies revealed that in ageing rats, NwNLA reduced renal blood flow and increased renal vascular resistances in a significantly higher proportion than in younger animals. However, flow to other organs, namely, brain, spleen or liver, was affected in a similar manner in both young and old rats. Ultrastructural alterations were found in endothelial cells, which might constitute the anatomical basis for the observed functional derangements. CONCLUSIONS: The present experiments reveal that ageing is accompanied by significant differences in NO-related responses in the kidney which do not appear to affect blood flow to other organs. The response to L-Arg and L-Arg competitive analogues supports the existence of a marked dependency on NO-related mechanisms in the ageing rats, but not of a decreased baseline activity of the NO-dependent pathways.

[Nephrolithiasis and bone involvement in primary hyperparathyroidism. The relative role of vitamin D]. / Nefrolitiasis y participación ósea en el hiperparatiroidismo primario. Papel relativo de la vitamina D.

In order to analyze the role of 1,25(OH)2 D3 in bone and renal presentation forms of primary hyperparathyroidism (PHP), 61 patients, whose diagnosis had been confirmed surgically, were studied. An increase in serum 1,25(OH)2 D3 levels was found in PHP when compared to normal controls (49.1 +/- 2.8 pg/ml vs 34.1 +/- 1.4 pg/ml) (p less than 0.5). This increase directly correlates with serum alkaline phosphatase and creatinine clearance and inversely correlates with age. When patients were divided into two groups: A (n = 35) and B (n = 26) according to normal or increased 1,25(OH)2 D3 respectively, no difference was found in the clinical presentation forms of PHP. However, higher values of the biochemical parameters and bone remodeling markers were found in group B than in group A. This suggests the role of 1,25(OH)2 D3 as a modulator of metabolic activity in PHP and its possible therapeutic character in the clinical control of asymptomatic forms.

Role of citric acid in primary hyperparathyroidism with renal lithiasis.

Nephrolithiasis is presented in 18-40% of patients with primary hyperparathyroidism. Our work suggests that citrate, an inhibitor of calcium salts, could be involved in the presence of renal lithiasis because hyperparathyroid stone formers show less citrate elimination than nonstone formers.

Correlation between 1.25 dihydroxyvitamin D serum levels and fractional rate of intestinal calcium absorption in hypercalciuric nephrolithiasis. Role of phosphate.

Different mechanisms could explain the elevated calcium elimination, the main cause of calcium oxalate renal stones. Our results suggest that phosphate levels are decreased in patients with absorptive hypercalciuric nephrolithiasis and elevated serum dihydroxyvitamin D. This could be the reason why in this group of patients oral phosphate treatment prevented hypercalciuria and renal lithiasis.

Hypocitraturia as a pathogenic risk factor in the mixed (calcium oxalate/uric acid) renal stones.

A small group of patients with nephrolithiasis who forms mixed (calcium oxalate and uric acid) calculi presents particular problems in their clinical management. In 3,158 stones analyzed in our laboratory, we found 158 mixed calculi in 86 of the patients. In this work, the clinical and biochemical results obtained from 27 patients with mixed stones were compared with those from 27 control patients with calcium oxalate renal lithiasis. A significant difference was found in oxalate and citrate urinary elimination (mean +/- SD) in mixed stone formers versus pure calcium oxalate stone formers: oxaluria (mg/24 h: 38 +/- 15 vs. 28 +/- 12; p less than 0.01) and citraturia (mg/24 h: 214 +/- 139 vs. 437 +/- 303; p less than 0.01). Citraturia was decreased in a high proportion (77%) in mixed stone formers, and only a reduced percentage of them (23%) presented normal values, although in the low limit of normality. As treatment and prophylactic measure, we proposed oral administration of citrates in mixed stone patients because citrate inhibits spontaneous nucleation of calcium salts and crystal growth, and it also increases the urinary pH with a consequent increase in uric acid solubility.

Correlation between serum osteocalcin and 24,25-dihydroxyvitamin D levels in Paget's disease of bone.

We have studied the possible correlation between serum 24,25-dihydroxyvitamin D [24,25-(OH)2D] and osteocalcin levels (sBGP) in Paget's disease of bone. We measured serum calcium, phosphate, PTH, 25-hydroxyvitamin D, 1,25-(OH)2D, 24,25-(OH)2D, alkaline phosphatase (sAP), and the urinary hydroxyproline/creatinine ratio (UOH prol/creat) in 19 patients with Paget's disease of bone and 16 age- and sex-matched controls. As expected, sAP, UOH prol/creat, and sBGP levels were significantly elevated, and there was a tendency to a decrease in serum levels of 24,25-(OH)2D in Pagetic patients with respect to the control group. There was no significant difference between patients and controls in serum calcium, phosphate, PTH, 25-hydroxyvitamin D, and 1,25-(OH)2D. The Pagetic patients were subdivided into two subgroups; subgroup A had normal sBGP levels (less than 5 ng/mL), and subgroup B had increased sBGP levels (greater than 5 ng/mL). Serum 24,25-(OH)2D levels in subgroup B were significantly lower than those in controls, while subgroup A showed levels similar to those in the control group. We also found a positive linear correlation between sAP and sBGP and between sAP and UOH prol/creat as well as a negative linear correlation between sBGP and 24,25-(OH)2D and between 24,25-(OH)2D and UOH prol/creat in Pagetic patients. These results point to a possible role of 24,25-(OH)2D in disease activity.