Ca, Mg metabolism, bone diseases. Tamás Kőszegi Pécs University, Department of Laboratory Medicine Pécs, Hungary - PDF

Ca, Mg metabolism, bone diseases Tamás Kőszegi Pécs University, Department of Laboratory Medicine Pécs, Hungary Calcium homeostasis Ca 1000g in adults 99% in bones (extracellular with Mg, P) Plasma/intracellular

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Ca, Mg metabolism, bone diseases Tamás Kőszegi Pécs University, Department of Laboratory Medicine Pécs, Hungary Calcium homeostasis Ca 1000g in adults 99% in bones (extracellular with Mg, P) Plasma/intracellular concentration as total 10-3 mol/l water Intracellular concentration as ionized 10-7 mol/l water Ionized Ca - muscle contraction, blood coagulation, enzyme activation, signalling, regulation of absorption/excretion Calcium homeostasis Parathyroid hormone (peptide) in PTH gland Ca release from bones (osteoclast) Increased 1-alpha hydroxylation of vitamin D in kidneys (1:25DHCC) 1:25DHCC Increased Ca absorption in gut Increased mineralization in bones (osteoblast) Calcitonin (katacalcin) in C-cells Decreased Ca release from bones Increased Ca (P) excretion Calcium homeostasis PTH half life: 4 minutes! Calcium homeostasis Calcitonin: tumor marker Procalcitonin: sepsis marker Beneficial effects of vitamin D Annual age-standardized incidence rate per 100,000 population, Colon Cancer, Colon Cancer Projected 25(OH)D concentration in ng/ml Source: GLOBOCAN Database of the International Agency for Research on Cancer. Composition of bone Minerals 65% dry weight Hydroxyapatite Matrix 35% dry weight Collagen 90% Other proteins Lipids, sugars Cells Osteoblasts Lining cells Osteocytes Osteoclasts Water Biochemical markers of bone formation and resorption Interpretation of plasma Ca values (2,10-2,60 mmol/l total) Fractions of plasma Ca Fraction as % of total Ca Ionized calcium (Ca 2+ ) Protein (albumin) bound Ca Complexed Ca 5-10 Influence of plasma albumin on total Ca Influence of H + on ionized Ca (respiratory alkalosis - tetany) Lab data useful in assessment of disorders in Ca metabolism Plasma: Ca, ionized Ca, P Kidney function tests ALP, bone specific ALP Acid base balance Total protein, albumin Parathormon, 25-HCC Urine: Ca, P excretion/day or /creatinine Type I collagen fragments Hypercalcemia: hyperparathyroidism Primary Ca Increased P Decreased ph Metabolic acidosis Kidney function Might be impaired ALP Increased PTH Increased (normal) Collagen fragments Increased Q P T H ( p g / m l) Intraoperative PTH testing Intraoperative Monitoring of PTH Baseline PI 5 Min 10 Min 20 Min Hypercalcemia: hyperparathyroidism Secondary Ca Decreased (normal) PTH Increased Kidney function Might be impaired Tertiary Ca, P Increased Kidney function Impaired PTH Increased Other hypercalcemias Osteolytic bone metastases Multiple myelome Vitamin D overdose Thyreotoxicosis Hypocalcemia Hypoalbuminemia Malabsorption Vitamin D deficiency (kidney disease) Low PTH (after surgery) or resistency Acute pancreatitis, alkalosis Ca replacement therapy with normal albumin concentration (tetany) Magnesium metabolism 24 g in adults, mostly intracellularly Plasma: 0,7-1,1 mmol/l (30% protein bound) Deficiency: rare, develops slowly Functional test (oral) 24h urinary Mg - baseline excretion 24h urinary Mg - after oral administration Functional test (intravenous) 48h urinary Mg ( 90% should be excreted) Magnesium and migraine Biochemical markers of bone formation and resorption Bone remodelling Bone turnover is characterised by two metabolic processes - formation of new bone (osteoblasts) - resorption of old bone (osteoclasts) Bone mass density (BMD) depends on the balance between formation and resorption There is a continuous loss in BMD during our life span (age and sex dependent) Age Sex Factors influencing bone turnover Mineral absorption and vitamin D supply Function of parathyroid gland Biological response modifiers, hormones Physical activity Metabolic bone diseases (Paget s) Impaired kidney function Cancer metastasis in bone Changes in BMD and bone turnover with age Bone turnover Resorption Formation Resorption Formation Age (yrs) Markers of bone formation Total alkaline phosphatase age! - activity changes with Bone specific alkaline phosphatase (in osteoblasts, isoenzyme) - amount changes with age Osteocalcin (vitamin K dependent) in extracellular matrix, degrades rapidly in plasma (N-MIDosteocalcin) - increases with high bone turnover Procollagen propeptides: cleavage products during formation of type I collagen (C/N-terminal peptides) Markers of bone resorption Calcium and hydroxyproline - minor significance, correction for kidney function necessary Tartrate resistant acid phosphatase - in osteoclast lysosomes, immunological determination Pyridinolines (deoxy): cross-linking collagen, cleavage products, urinary excretion corrected for creatinine - good specificity N-terminal cross-links (NTx): pyridinoline cross-link in peptide bound form, urinary excretion corrected for creatinine - good specificity β-crosslaps: C-telopeptide related collagen degradation product - urinary, serum, good specificity Collagen type I degradation products Structure of collagen type I degradation products Bone aging:β- Asp Cross-linked N-telopeptide C-terminal cross-link (β-crosslaps) (NTx) Diurnal variation is significant Reference ranges of bone metabolic tests done in our lab Laboratory parameter Intact parathormone Osteocalcin Vitamin D total β-crosslaps (serum) Pyrilinks-D/creatinine (urine) Total ALP Reference range (adult) 0,7-5,6 pmol/l 4,0-20,0 ng/ml nmol/l 0,010-5,94 ng/ml 2,3-7,4 nmol/mmol 100 IU/l Osteocalcin levels during antiresorptive treatment Β-crosslaps levels during bisphosphonate therapy in Paget s disease Use of biochemical markers in osteoporosis Imaging methods can not be avoided Combination of markers in early postmenopausal women can predict the rate of bone loss Rate of bone loss may predict fracture risk Monitoring the bone turnover rate is a good measure of the effects of antiresorptive therapies (HRT, bisphosphonate) Other conditions than osteoporosis can also cause increased bone turnover!
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