Trabecular bone score (TBS) is associated with sub-clinical vertebral fractures in HIV-infected patients

Fragility fractures risk is increased among HIV infected patients. Bone microstructure alterations, in addition to bone mineral density (BMD) reduction, might be responsible for the increased risk. The aim of this study was to determine the prevalence of vertebral fractures (VFs) and their association with trabecular bone score (TBS), an indirect index of bone microstructure, in a cohort of HIV-infected subjects. One-hundred and forty-one HIV-infected patients (87% males, median age 43 years, 94% on stable antiretroviral therapy with undetectable viral load) underwent viro-immunological and bone metabolism biochemical screenings. Lumbar TBS and BMD at femoral neck, total hip, and lumbar spine, were measured with dual-energy X-ray absorptiometry (DXA). VFs were identified using the semiquantitative method and quantitative morphometric analysis from thoracic and lumbar spine X-ray images. VFs were observed in 19 patients (13.5%). BMD was below the expected range for age in 18 (12.8%) subjects. No significant differences were found stratifying VFs prevalence by BMD, whereas patients with lower TBS showed a higher prevalence of VFs (p = 0.03). In multivariate analysis, TBS was the only factor significantly associated to VFs (OR = 0.56; 95% CI = 0.33-0.96; p = 0.034), with increased fracture risk for lower TBS values. VFs are prevalent and associated with low TBS among HIV-positive patients, whereas no significant association was found with BMD.

Correlates of muscle strength in diabetes: The study on the assessment of determinants of muscle and bone strength abnormalities in diabetes (SAMBA)

BACKGROUND AND AIMS

Apart from late motor nerve dysfunction, factors affecting muscle strength in diabetes are largely unknown. This study was aimed at assessing muscle strength correlates in diabetic subjects encompassing a wide range of peripheral nerve function and various degrees of micro and macrovascular complications.

METHODS AND RESULTS

Four-hundred consecutive patients with type 1 and 2 diabetes (aged 46.4 ± 13.9 and 65.8 ± 10.3 years, respectively) from the Study on the Assessment of Determinants of Muscle and Bone Strength Abnormalities in Diabetes (SAMBA) were examined for upper and lower body muscle isometric maximal voluntary contraction by dynamometry. Univariate and multivariate regression analyses were applied to identify strength correlates. Isometric force at both the upper and lower limbs was significantly lower in subjects with than in those without any complication. At univariate analysis, it was strongly associated with age, diabetes duration, physical activity (PA) level, cardio-respiratory fitness, anthropometric parameters, surrogate measures of complications, and parameters of sensory and autonomic, but not motor (except amplitude) neuropathy. Multivariate analysis revealed that upper and lower body strength correlated independently with male gender and, inversely, with age, autonomic neuropathy score (or individual autonomic function abnormalities), and vibration perception threshold, but not sensory-motor neuropathy score. Diabetes duration and PA level were excluded from the model.

CONCLUSIONS

Both upper and lower body muscle strength correlate with measures of diabetic complications and particularly with parameters of sensory and especially autonomic nerve function, independently of diabetes duration and PA level, thus suggesting the involvement of mechanisms other than manifest motor nerve impairment.

Importance of gluten in the induction of endocrine autoantibodies and organ dysfunction in adolescent celiac patients

OBJECTIVE

It is well known that a high number of celiac patients may develop autoantibodies against endocrine glands, but it has not yet been clarified if this increased autoimmune response and the impaired organ function that can develop may be related to the presence or absence of gluten in the diet. The aim of the present study was to evaluate the effect of gluten on the autoimmunity and function of the endocrine glands in adolescent celiac patients.

METHODS

To clarify this aspect we investigated 44 patients (28 females), aged 11-20 yr (15.21+/-2.7 yr): 25 (mean age, 15.1+/-2.2 yr) on a gluten-free diet (treated patients) and 19 (mean age 15.4+/-2.9 yr) with a diet containing gluten (untreated patients). Forty adolescent subjects, aged 14-19 yr (mean age, 14.9+/-2.7 yr), of whom 20 were females, were studied as controls. Antibodies against the thyroid, adrenal, and pancreas were evaluated. Thyroid-stimulating hormone FT3, FT4, T3, T4, dehydroepiandrosterone sulphate, 17-OH progesterone, and cortisol, analyzed basally and 60 min after intravenous ACTH stimulation, were assayed to evaluate thyroid and adrenal function. The fasting glycemia level was used to evaluate the endocrine pancreas function. An ultrasonogram of the thyroid gland was performed on all patients. HLA class II typing for DR3 and DQB1 was performed in 32 of 44 patients.

RESULTS

Seven of 44 (15.9%) patients were positive for antibodies against peroxidase. Six of 44 (13.6%) were positive for antibodies against thyreoglobulin and four of them also showed positive antibodies against peroxidase. Therefore, in nine of 44 at least one antibody directed against thyroid tissue was positive. Seven of 44 (15.9%) were positive for antibodies against islet cell, one of 44 (2.3%) positive for antibodies against glutamic acid decarboxilase, one of 44 (2.3%) positive for antibodies against insulin, and none for antibodies against islet cell- 512bdc. In 15 of 44 (34%) at least one antibody against an endocrine tissue was positive. The genotype DR3 was found in 21 of 32 (65.6%) celiac patients (10 in the untreated and 11 in the treated group, respectively) and the genotype DQB1*02 (DQ2) was found in 30 of 32 (93.8%) patients (16 in the treated and 14 in the untreated group, respectively). DHA-S values were significantly lower in the untreated (30.5+/-28.5 microg/dl) than in the treated group (61.3+/-59.4 microg/dl, p < 0.05), and both showing significantly (p < 0.01) lower levels with respect to the controls (161+/-52 microg/dl). One patient showed diabetes, another one clinical hypothyroidism (thyroid-stimulating hormone > 6), and two patients showed preclinical hypothyroidism. Interestingly, at least one antibody was positive in 10 of 19 untreated patients (52.6%) but only in five of 25 treated patients (20%), with a significantly different distribution (p < 0.001) between the two groups and without differences in the HLA genotype. The ultrasonographic evaluation of the thyroid resulted in a pathological score in six patients of the 44 examined (13.6%), suggesting the presence of thyropathy.

CONCLUSIONS

The main results of this study are the high incidence of thyroid and pancreatic antibodies, and the possible role of gluten in the induction of the antibodies as well as, in few cases, the consequent organ dysfunction.

Growth hormone and insulin-like growth factor I responses to moderate submaximal acute physical exercise in man: effects of octreotide, a somatostatin analogue, administration

We evaluated growth hormone (GH) and insulin-like growth factor I (IGF-I) response to moderate submaximal acute short-term physical exercise under basal conditions and after the administration of octreotide, a somatostatin analogue (SA), in a double-blind, counter-balanced experimental protocol. Seven untrained male volunteers performed two identical exercise tests, each on a treadmill (2.5% slope) for 30 minutes (min) at 60% of VO2max. Before starting the exercise test all the subjects received a single administration of placebo or octreotide and vice versa at two different sessions. Plasma GH, IGF-I and lactate assays were evaluated before starting, during, at the end and in the recovery phase. In the placebo-treated group GH rose significantly both during exercise and recovery whereas no significant modifications in IGF-I levels were observed. SA administration inhibited the exercise-dependent GH secretion, which showed a small rise only during exercise and returned to basal levels during recovery. In the same group, IGF-I decreased significantly after exercise compared to basal values. The results suggest that 1) in our experimental conditions acute physical exercise at aerobic threshold does not modify IGF-I concentration 2) SA is able to inhibit the exercise-dependent GH secretion and to decrease post-exercise IGF-I concentration.

A novel line of transgenic mice (RSV/LTR-bGH) expressing growth hormone in cardiac and striated muscle

In order to further investigate the deleterious effects of GH overexpression, we generated a novel line of transgenic mice featuring stable and specific expression of bovine GH in the heart and striated muscle. A DNA construct, containing a region with promoter activity from the Long Terminal Repeat of Rous Sarcoma Virus (RSV-LTR) and the entire structural gene of bovine GH (bGH), was microinjected by standard techniques in male pronuclei of fertilized mice eggs. Transgenic mice expressed bGH mRNA in the heart and striated muscle starting at 5-6 weeks of age. They featured circulating levels of a 22 kDa form of bGH up to 700 ng/ml and enhanced growth starting at 6 weeks of age. No pathologic changes of the myocardium and striated muscle fibers, other than hypertrophy, were noticed, although severe glomerulosclerosis and liver alteration occurred in older mice. Future studies on this new line of transgenic GH mice and integration with the existing data might improve our understanding of the molecular mechanism underlying the detrimental effects of elevated GH levels on various organs and functions.

Mouse glomerular endothelial cells have an insulin receptor

An insulin receptor was found on the surface of cloned mouse glomerular endothelial cells in vitro. Total specific binding was 2.5 +/- 0.3%/10(6) cells at 90 min and 22 degrees C. Analysis according to Scatchard resulted in a curvilinear plot, with a kd for the high and low affinity sites estimated at 1.41 x 10(-10) and 8.2 x 10(-8) respectively. Insulin binding decreased following 12 hour exposure to 50 ng/ml of insulin suggesting that down regulation of the receptor had occurred, an effect which was reversible. Covalent crosslinking of the receptor to 125I insulin revealed one band at Mr 125,000 by SDS-PAGE which disappeared following preincubation with excess unlabeled insulin. Insulin was also able to stimulate phosphorylation of the beta subunit. The characteristics of this insulin receptor appear very similar to that of endothelial cell types from other microvascular beds.

Binding of insulin-like growth factor-I by glomerular endothelial and epithelial cells: further evidence for IGF-I action in the renal glomerulus

The renal glomerulus is both a site of action and synthesis of IGF-I. We previously demonstrated the presence of IGF-I receptor and synthesis in glomerular mesangial cells. In this study we investigated the presence of specific IGF-I receptors on mouse glomerular endothelial and epithelial cells in culture. [125I]IGF-I specifically bound to the cell surface of both cell types. Maximum specific binding, 0.141 B/F for endothelial cells and 0.301 B/F for epithelial cells, was obtained at 22 degrees C after 150 min incubation. The estimated Kd values were 2.25 x 10(-9) for endothelial cells and 1.5 x 10(-9) for epithelial cells. Cross-linking studies showed a single band of radioactivity with an estimated mol wt of 145K, consistent with the alpha-subunit of the IGF-I receptor. Radiolabelled IGF-I was not degraded by either cell types. These findings suggest a possible paracrine action of IGF-I in the renal glomerulus.

Insulinlike growth factor-1 is a progression factor for human mesangial cells

Mesangial cell hyperplasia is a feature common to several human glomerular diseases. The cause of this increased cell number is unknown. The authors assessed human mesangial cells in vitro and found that they possessed an insulinlike growth factor-1 (IGF-1) receptor consisting of alpha and beta units (Mr, 130 k and 90 k respectively). Fifty percent inhibition of IGF-1 specific binding to the receptor required 1 X 10(-9) M IGF-1, greater than 1 X 10(-6) M insulin and 1 X 10(-7) M multiplication stimulating activity (MSA). Analysis of binding by the method of Scatchard revealed one type of IGF-1 receptor with a Kd of 1.35 X 10(-9) M, and a number per cell of 1.04 X 10(5). Binding studies on whole glomeruli had similar specificity and there were 7.17 X 10(7) receptors per glomerulus (Kd, 1.12 X 10(-9) M). Examination of the effect of IGF-1 on the cell cycle revealed that exposure of cells to both IGF-1 and platelet-derived growth factor (PDGF) led to a significant increase in 3H-thymidine incorporation into cell layers. Antibody to PDGF abolished only that response due to PDGF. Similarly, the labeling index of cells pretreated with PDGF, washed, and then exposed to IGF-1 was increased, whereas if the order of ligand exposure was reversed, there was no such additive effect. Finally, PDGF increased RNA and protein synthesis, and this response was not enhanced by IGF-1. In summary, human mesangial cells and whole glomeruli possess IGF-1-specific receptors and IGF-1 was found to act as a progression factor in the cell cycle.

Synthesis and release of insulinlike growth factor I by mesangial cells in culture

Mesangial cell proliferation is a common hallmark of many glomerular diseases. The exact mechanisms inducing cell proliferation in glomerulosclerosis are not completely understood, and it remains to be determined whether growth factors play a role in this process. Insulinlike growth factor I (IGF I) has been shown to be synthesized in the kidney, and glomerular mesangial cells have receptors for and exhibit mitogenic response to IGF I. We found that mouse glomerular mesangial cells in culture synthesized and released into the culture medium a molecule with immunological and biological features of IGF I. This molecule specifically bound to mesangial cell IGF I receptors; high-pressure liquid chromatographic analysis provided further evidence of its similarity to human recombinant IGF I. Mesangial cells released into the culture medium 6 ng/10(6) cells of IGF I-like material per 24 h in a time-dependent and actinomycin-D inhibitable fashion. These data suggest that IGF I might be locally released by mesangial cells in the glomerulus and act in an autocrine and paracrine fashion.

Studies on binding and mitogenic effect of insulin and insulin-like growth factor I in glomerular mesangial cells

The mesangial cells, as part of their smooth muscle cell function, are actively involved in regulating glomerular hemodynamics. Their overlying endothelium is fenestrated; therefore, these cells are directly exposed to plasma substances, including hormones such as insulin and insulin-like growth factor I (IGF-I). These peptides may contribute to the mesangial sclerosis and cellular hyperplasia that characterize diabetic glomerulopathy. We report herein the characterization of the receptors and the mitogenic effects of IGF-I and insulin on mouse glomerular mesangial cells in culture. The IGF-I receptor was characterized on intact cells. The Kd of the IGF-I receptor was 1.47 X 10(-9) M, and the estimated number of sites was 64,000 receptors/cell. The binding was time, temperature, and pH dependent, and the receptor showed down-regulation after exposure to serum. The expression of the receptor did not change on cells at different densities. The specific binding for insulin was too low to allow characterization of the insulin receptor on intact cells. However, it was possible to identify the insulin receptor in a wheat germ agglutinin-purified preparation of solubilized mesangial cells. This receptor showed the characteristic features of the insulin receptor, including pH dependence of binding and a curvilinear Scatchard plot. The mitogenic effects of insulin and IGF-I on mesangial cells were measured by the incorporation of [3H]thymidine into DNA. IGF-I was more potent than insulin. The half-maximal response to IGF-I stimulation occurred at 1.3 X 10(-10) M, and a similar increase with insulin was observed at concentrations in the range of 10(-7) M, suggesting that this insulin action was mediated through the IGF-I receptor. These data show that the mouse microvascular smooth muscle cells of the glomerulus express a cell surface receptor for IGF-I in vitro and that this peptide is a potent mitogen for these mesangial cells. It may, therefore, play a role in glomerular proliferative lesions. The insulin receptor is present in small numbers and does not mediate mitogenesis in mesangial cells.

Progressive glomerulosclerosis develops in transgenic mice chronically expressing growth hormone and growth hormone releasing factor but not in those expressing insulinlike growth factor-1

An increase in glomerular size occurs in normal maturation after subtotal renal ablation and disease states such as diabetes mellitus. The role that growth hormone (GH), growth hormone releasing factor (GHRF), and insulinlike growth factor-1 (IGF-1) play in these processes has been investigated using transgenic mice chronically expressing these hormones. The glomeruli were enlarged in all 3 strains of mice. Mesangial proliferation followed by progressive glomerulosclerosis was observed in the GH and GHRF animals only. In the IGF-1 mice the large glomeruli remained morphologically normal except for the enlargement. These data suggest that the glomerulosclerosis was due, in part, to disordered mesangial cell growth in response to circulating GH. The mesangial lesions in mice with chronically high plasma GH levels mimicked those in human diabetes mellitus. These models provide a means to study the hormonal regulation of glomerular growth and the role that specific hormones might play in the pathogenesis of glomerulosclerosis.