Action of molecular switches in GPCRs--theoretical and experimental studies.

G protein coupled receptors (GPCRs), also called 7TM receptors, form a huge superfamily of membrane proteins that, upon activation by extracellular agonists, pass the signal to the cell interior. Ligands can bind either to extracellular N-terminus and loops (e.g. glutamate receptors) or to the binding site within transmembrane helices (Rhodopsin-like family). They are all activated by agonists although a spontaneous auto-activation of an empty receptor can also be observed. Biochemical and crystallographic methods together with molecular dynamics simulations and other theoretical techniques provided models of the receptor activation based on the action of so-called "molecular switches" buried in the receptor structure. They are changed by agonists but also by inverse agonists evoking an ensemble of activation states leading toward different activation pathways. Switches discovered so far include the ionic lock switch, the 3-7 lock switch, the tyrosine toggle switch linked with the nPxxy motif in TM7, and the transmission switch. The latter one was proposed instead of the tryptophan rotamer toggle switch because no change of the rotamer was observed in structures of activated receptors. The global toggle switch suggested earlier consisting of a vertical rigid motion of TM6, seems also to be implausible based on the recent crystal structures of GPCRs with agonists. Theoretical and experimental methods (crystallography, NMR, specific spectroscopic methods like FRET/BRET but also single-molecule-force-spectroscopy) are currently used to study the effect of ligands on the receptor structure, location of stable structural segments/domains of GPCRs, and to answer the still open question on how ligands are binding: either via ensemble of conformational receptor states or rather via induced fit mechanisms. On the other hand the structural investigations of homoand heterodimers and higher oligomers revealed the mechanism of allosteric signal transmission and receptor activation that could lead to design highly effective and selective allosteric or ago-allosteric drugs.

Peptic ulcer disease and calcium intake as risk factors of osteoporosis in women.

INTRODUCTION: Low dietary intake and decreased absorption of calcium are known as important risk factors of osteoporosis. Peptic ulcer disease may be accompanied by dietary restrictions influencing negatively calcium intake. Inflammation of gastric and duodenal mucosa as well as alkali used may significantly decrease calcium absorption. Additionally, bone metabolism may be changed by inflammatory mediators released as a result of mucosal inflammation. AIMS: Comparison of bone mineral density and calcium dietary intake in women with and without (control group) peptic ulcer disease. METHODS: Two hundred and sixty-three women were studied: 143 (mean age 60.3 years) with peptic ulcer disease diagnosed by endoscopy and/or upper gastrointestinal X-ray, and 120 (mean age 58.4 years) as controls. History of alimentary tract diseases and presence of risk factors of osteoporosis, as well as history of hormone replacement therapy, were collected based on specially designed questionnaires. Women with present risk factors of secondary osteoporosis and with previously diagnosed osteoporosis were excluded. The calcium dietary intake was determined using a standard questionnaire assessing milk and milk products intake as well as calcium supplementation when used. Bone mineral density of the lumbar spine and femoral bone was determined by DXA. RESULTS: Women with peptic ulcer disease not using hormone replacement therapy had lower bone mineral density in all studied regions as compared to control group without peptic ulcer disease. In the subgroup not using hormone replacement therapy all studied values differed significantly. In the smaller subgroup of women using hormone replacement therapy not all values were statistically significant. There was no statistical significance between studied groups in dietary calcium intake as milk, milk products, and calcium supplements. CONCLUSIONS: Calcium intake in women with ulcer disease is similar to healthy subjects. Peptic ulcer disease is an independent risk factor for osteoporosis in women.

Imaging of bone in the diagnostics of renal osteodystrophy in children with chronic renal failure.

BACKGROUND: In the last two decades considerable advances have been made in the development of imaging tests of the skeletal system. This progress in diagnostic techniques, along with the growing availability of the tests, renders it necessary to review and evaluate their suitability for daily clinical practice. The aim of this article is to compare the results of radiological testing of bone with densitometrical, histomorphometric, and biochemical tests in children with chronic renal failure. MATERIAL AND METHODS: The research involved 31 children with renal failure, of whom 10 were being treated conservatively, 17 by continuous ambulatory peritoneal dialysis (CADO), and 4 by hemodialysis (HD). In all these children, radiological examinations of bone were performed in the arms, knees, and hips, along with tests for the serum concentration of parathormone (iPTH), calcium (Ca), and phosphates (P), and for the activity of alkaline phosphatase (AP). Bone density tests by the DXA method and bone biopsies were also performed. On the basis of radiological evaluation, the patients were divided into two groups: Group I, consisting of 14 children with a normal bone structure image, and Group II, consisting of 17 children with bone atrophy. RESULTS: No statistically significant differences were discovered in the mean values of the tested biochemical parameters between the two groups. The mineral density of total body was normal in 9 of the 14 patients in Group I (64%), and in 7 of 17 (41%) from Group II. The mineral density of total lumbar spine gave similar results. Lower bone density results were obtained in Group II than in Group I, though only in the case of the lumbar spine were the differences statistically significant. In Group I, 5 cases were discovered of chronic osteodystrophy without osteomalacia and hyperparathyroidism (NB), 2 cases of adynamic bone disease (ABD), 4 cases of hyperparathyroidism (HP), 2 cases of moderate hyperparathyroidism (MHP), and one mixed form (Mix); in Group II, there were 6 NBs, 2 ABDs, 1 case of osteomalacia (OM), 5 HPs, and 3 mixed. Radiological examinations revealed one male in Group I with features of prior Perthes's disease, one with fibrous cortical defect, and four cases of valgity of the coxa valga. In Group II, there were 3 children with radiological changes typical for osteomalacia, and in 1 case typical radiological signs of hyperparathyroidism. CONCLUSIONS: Given the lack of consistency in the results of the tests here presented, an entire panel of available tests should be performed for the comprehensive evaluation of the status of the skeleton.

[Risk factors of adynamic bone disease in children with end-stage renal failure: personal experience]. / Czynniki ryzyka adynamicznej choroby kosci u dzieci ze schylkowa niewydolnoscia nerek--doswiadczenia wlasne.

The aim of the study was to estimate predisposing factors which can cause adynamic bone disease (ABD) and biochemical markers, bone densitometry results, bone histomorphometry in 17 children with this from of the renal osteodystrophy. Half of these of patients were treated with alphacalcidol pulses. In 47% of patients hypercalcemic episodes were noted, 76% had PTH level < 50 pg/ml. Four patients with osteoporosis (low bone volume at histological analysis) were distinguished. Two of them were treated with corticosteroids, 1 was immobilized for a long time.

[Bone metabolism markers and bone histomorphometry in children with chronic renal failure in predialysis period during growth hormone treatment]. / Markery metabolizmu kostnego u dzieci z przewlekla niewydolnoscia nerek leczonych hormonem wzrostu w okresie przeddializacyjnym.

The aim of the study was to estimate biochemical bone metabolism markers and bone histomorphometric parameters in children with chronic renal failure (CRF) treated with recombinant human growth hormone (rhGH). Twelve children with CRF aged 2-13.4 years were treated with rhGH 1-1.1 IU/kg per week and alfacalcidol. Bone biopsies were performed before and after 12 months of therapy. An increase in the biochemical markers of bone formation and bone resorption were noted. A statistically significant increase in mineral apposition rate (MAR) was observed in bone histomorphometry. The administration of active vitamin D metabolites enable proper bone mineralization in fast growing children with CRF during rhGH treatment.

Bone biopsy results and serum bone turnover parameters in uremic children.

UNLABELLED: The aim of the study was to evaluate the prevalence of renal osteodystrophy types in children undergoing haemodialysis and continuous ambulatory peritoneal dialysis and to assess the usefulness of biochemical parameters in diagnosis of renal osteodystrophy. Bone biopsy and measurements of serum parathormone (iPTH) level, alkaline phosphatase (AP), osteocalcin (OC), procollagen 1C, calcium and phosphorus levels were performed in 51 children aged 11.5 +/- 2.9 y with end-stage renal failure. Renal osteodystrophy (ROD) was diagnosed as follows: adynamic bone disease (ABD) in 14 (27%); normal bone histology (NB) in 19 (37%), osteomalacia (OM) in 1 (2%), mixed lesion (Mix) in 5 (10%) and hyperparathyroidism (HP) in 12 (24%) children. There was no difference in prevalence of ROD types between children on CAPD and HD. We found significant differences in the mean value of iPTH, OC levels and AP activity in HP vs NB and HP vs ABD. The prevalence of ABD was significantly higher in patients with PTH below 50 pg/ml than in patients with PTH above 50 pg/ml (p < 0.05). In 69% of children with NB the iPTH level was between 50 and 150 pg/ml. Most HP cases (75%) were diagnosed in patients with iPTH above 200 pg/ml. A high correlation between BFR and iPTH, BFR and OC, AP levels was found. CONCLUSION: The biochemical markers of bone turnover have only limited value in the differentiation of renal osteodystrophy types.

Vitamin D metabolite requirements in dialysed children receiving recombinant human growth hormone.

BACKGROUND: The aim of the study was to assess the requirement of active vitamin D in dialysed children during treatment with recombinant human growth hormone (rhGH). METHODS: Twenty-six children (aged 5-15 years) were treated with rhGH for 6 months. The serum concentration of parathyroid hormone (PTH), alkaline phosphatase (AP), and calcium and phosphorus were measured in two groups of patients studied in the years 1994-1995 (group I) and 1995-1998 (group II) respectively. Group I received a constant dose of alfacalcidol that was sufficient to keep PTH below 200 pg/ml before rhGH treatment began. The serum PTH level was checked every 3 months. Alfacalcidol was administered to group II according to serum PTH levels checked on a monthly basis. RESULTS: In group I the PTH level increased after 3 and 6 months of rhGH treatment from mean level 73+/-60; 155+/-156 and 344+/-249 pg/ml respectively; P<0.05. AP activity increased after 6 months of treatment from 206+/-99 to 325+/-124 U/l respectively; P<0.01. The calcium level decreased from baseline after 3 months of treatment from 2.36+/-0.21 to 2.17+/-0.12 mmol/l respectively; P<0.05. In group II AP activity increased after 3 and 6 months of treatment from 272+/-169 to 332+/-192 and 404. 9+/-219.8 U/l respectively; P<0.01. The mean level of phosphorus decreased after 6 months from 2.15+/-0.28 to 1.70+/-0.39 mmol/l respectively; P<0.01. In group II the mean dose of alfacalcidol increased by 60.9%. CONCLUSIONS: In children with end-stage renal failure, higher doses of vitamin D are needed during rhGH treatment. During rhGH treatment, frequent control of serum PTH level is necessary.