Alkaline Phosphatase Isoenzymes Research Articles

Alkaline phosphatase: a novel treatment target for cardiovascular disease in CKD.

Cardiovascular disease is the main cause of early death in the settings of chronic kidney disease (CKD), type 2 diabetes mellitus (T2DM), and ageing. Cardiovascular events can be caused by an imbalance between promoters and inhibitors of mineralization, which leads to vascular calcification. This process is akin to skeletal mineralization, which is carefully regulated and in which isozymes of alkaline phosphatase (ALP) have a crucial role. Four genes encode ALP isozymes in humans. Intestinal, placental and germ cell ALPs are tissue-specific, whereas the tissue-nonspecific isozyme of ALP (TNALP) is present in several tissues, including bone, liver and kidney. TNALP has a pivotal role in bone calcification. Experimental overexpression of TNALP in the vasculature is sufficient to induce vascular calcification, cardiac hypertrophy and premature death, mimicking the cardiovascular phenotype often found in CKD and T2DM. Intestinal ALP contributes to the gut mucosal defence and intestinal and liver ALPs might contribute to the acute inflammatory response to endogenous or pathogenic stimuli. Here we review novel mechanisms that link ALP to vascular calcification, inflammation, and endothelial dysfunction in kidney and cardiovascular diseases. We also discuss new drugs that target ALP, which have the potential to improve cardiovascular outcomes without inhibiting skeletal mineralization.

Enzymatic kinetics regarding reversible metabolism of CS-0777, a sphingosine 1-phosphate receptor modulator, via phosphorylation and dephosphorylation in humans

1. CS-0777, a candidate compound for autoimmune diseases, becomes phosphorylated active metabolite, M1, by fructosamine 3-kinase (FN3K), FN3K-related protein (FN3K-RP); and M1 is reverted back to CS-0777 by alkaline phosphatase (ALP) in the body. We performed enzyme kinetic analysis of phosphorylation of CS-0777 by FN3K, FN3K-RP, human erythrocytes and human platelets; and dephosphorylation of M1 by various ALP isozymes and human liver, kidney, lung and small intestine microsomes.2. The Michaelis constants of human FN3K, FN3K-RP and erythrocytes for CS-0777 phosphorylation were in the range from 498 μM to 1060 μM. FN3K inhibitor, 1-deoxy-1-morpholinofructose, suppressed only about 20% of CS-0777 phosphorylation activity in human erythrocyte lysate. Immunodepletion of FN3K and FN3K-RP decreased M1 formation activity by about 25% and 50%, respectively, in human erythrocyte lysate.3. The Michaelis constants of four human ALPs and microsomes were in the range from 10.9 μM to 32.1 μM. The ALP inhibitor, levamisole, suppressed over 50% of M1 dephosphorylation activity in liver, kidney and lung microsomes.4. FN3K-RP is expected to take a prominent role in the phosphorylation of CS-0777 in human erythrocytes; dephosphorylation of M1 was observed in all ALPs and human tissue microsomes examined, with a similar affinity towards M1 among them.

Hypophosphatasia: An overview For 2017

Hypophosphatasia (HPP) is the inborn-error-of-metabolism that features low serum alkaline phosphatase (ALP) activity (hypophosphatasemia) caused by loss-of-function mutation(s) of the gene that encodes the tissue-nonspecific isoenzyme of ALP (TNSALP). Autosomal recessive or autosomal dominant inheritance from among >300 TNSALP (ALPL) mutations largely explains HPP's remarkably broad-ranging severity. TNSALP is a cell-surface homodimeric phosphohydrolase richly expressed in the skeleton, liver, kidney, and developing teeth. In HPP, TNSALP substrates accumulate extracellularly. Among them is inorganic pyrophosphate (PPi), a potent inhibitor of mineralization. Superabundance of extracellular PPi explains the hard tissue complications of HPP that feature premature loss of deciduous teeth and often rickets or osteomalacia as well as calcific arthropathies in some affected adults. In infants with severe HPP, blocked entry of minerals into the skeleton can cause hypercalcemia, and insufficient hydrolysis of pyridoxal 5′-phosphate (PLP), the major circulating form of vitamin B6, can cause pyridoxine-dependent seizures. Elevated circulating PLP is a sensitive and specific biochemical marker for HPP. Also, the TNSALP substrate phosphoethanolamine (PEA) is usually elevated in serum and urine in HPP, though less reliably for diagnosis. Pathognomonic radiographic changes occur in pediatric HPP when the skeletal disease is severe. TNSALP mutation analysis is essential for recurrence risk assessment for HPP in future pregnancies and for prenatal diagnosis. HPP was the final rickets/osteomalacia to have a medical treatment. Now, significant successes using asfotase alfa, a mineral-targeted recombinant TNSALP, are published concerning severely affected newborns, infants, and children. Asfotase alfa was approved by regulatory agencies multinationally in 2015 typically for pediatric-onset HPP.

Analysis of serum corticosteroid-induced alkaline phosphatase isoenzyme in dogs with hepatobiliary diseases.

To reveal the relationship between canine corticosteroid-induced alkaline phosphatase isoenzyme activity and hepatobiliary diseases. Retrospective analysis of the relationship between serum corticosteroid-induced alkaline phosphatase activity and diagnosis, serum cortisol concentration and alanine transferase activity in dogs with hepatobiliary diseases. Dogs with a history of glucocorticoid administration were excluded. Seventy-two dogs with hepatobiliary diseases were analysed. The serum corticosteroid-induced alkaline phosphatase concentration was increased in dogs with hepatobiliary diseases. There was no correlation between serum cortisol concentration and serum corticosteroid-induced alkaline phosphatase percentage or activity. Dogs with hepatobiliary disease can exhibit high serum alkaline phosphatase activity even if the dogs have not been administrated glucocorticoids and the serum cortisol concentration is normal.

Hypophosphatasia: Enzyme Replacement Therapy Brings New Opportunities and New Challenges.

Hypophosphatasia (HPP) is caused by loss-of-function mutation(s) of the gene that encodes the tissue-nonspecific isoenzyme of alkaline phosphatase (TNSALP). Autosomal inheritance (dominant or recessive) from among more than 300 predominantly missense defects of TNSALP (ALPL) explains HPP's broad-ranging severity, the greatest of all skeletal diseases. In health, TNSALP is linked to cell surfaces and richly expressed in the skeleton and developing teeth. In HPP,TNSALP substrates accumulate extracellularly, including inorganic pyrophosphate (PPi), an inhibitor of mineralization. The PPi excess can cause tooth loss, rickets or osteomalacia, calcific arthropathies, and perhaps muscle weakness. Severely affected infants may seize from insufficient hydrolysis of pyridoxal 5'-phosphate (PLP), the major extracellular vitamin B6 . Now, significant successes are documented for newborns, infants, and children severely affected by HPP given asfotase alfa, a hydroxyapatite-targeted recombinant TNSALP. Since fall 2015, this biologic is approved by regulatory agencies multinationally typically for pediatric-onset HPP. Safe and effective treatment is now possible for this last rickets to have a medical therapy, but a number of challenges involving diagnosis, understanding prognosis, and providing this treatment are reviewed herein. © 2017 American Society for Bone and Mineral Research.

Synthesis, characterization and biological evaluation of novel chalcone sulfonamide hybrids as potent intestinal alkaline phosphatase inhibitors

Alkaline phosphatase (AP) and ecto-5′-nucleotidase (e5′NT) belong to same family that hydrolyze the extracellular nucleotides and ensure the bioavailability of nucleotides and nucleosides at purinergic receptors. During pathophysiological conditions, the over expression of AP and e5′NT lead to an increased production of adenosine that enhance tumor proliferation, invasiveness, neoangiogenesis and disrupts the body antitumor response. As both enzymes are abundantly expressed in above mentioned conditions, therefore it is of great interest to synthesize and develop potent inhibitors of these enzymes that augment the antitumor therapy. Herein we reported the synthesis and biological activity of a new series of chalcone-sulfonamide hybrids (4a-j). These derivatives were then evaluated for their inhibitory potential against two members of ecto-nucleotidase family, e5′NT (human and rat) and APs isozyme (intestinal and tissue nonspecific). Only six derivatives were found to inhibit both human and rat e5′NT enzymes. Compounds 4e and 4d showed maximum inhibition of human and rat e5′NT with an IC50±SEM=0.26±0.01 and 0.33±0.004μM, respectively. Moreover, on APs, these derivatives were identified as the selective inhibitors of calf intestinal AP (c-IAP). The derivative 4a exhibited maximum inhibition of c-IAP with an IC50±SEM=0.12±0.02μM. In conclusion, these chalcone-sulfonamide hybrids exhibited dual inhibition of both family of isozymes but was more selective towards c-IAP enzyme.

自然発症糖尿病WBN/Kobラットにおけるアルカリホスファターゼについて

The male WBN/Kob rat is an animal model of chronic pancreatitis and spontaneous diabetes. Here, we performed a kinetic study of alkaline phosphatase (ALP) in WBN/Kob rats. The level of serum ALP activities in the WBN/Kob rats was three times higher than that of the control group (p<0.001). Specific ALP activities in bone tissues or the ileum increased significantly (p<0.01 and p<0.05, respectively). By 4-20% gradient polyacrylamide gel electrophoresis, serum ALP isozymes were separated into two bands. One was heat-unstable, showing the same mobility as an ALP preparation from bone tissue, and the other was heat-stable. We considered these isozymes to be bone-type and intestinal-type ALPs, respectively, and both of them were enhanced in the WBN/Kob rats. These results demonstrate the enzyme kinetics of ALP isozymes in WBN/Kob rats, and further studies will be necessary to reveal the association with diabetes.

Median lethal dose (LD50) and cytotoxicity of Adriamycin in female albino mice

The median lethal dose of Adriamycin and its cytotoxicity in three vital organs (heart, liver and kidney) was studied. The median lethal dose (LD50) was 56.875mg/kg b.wt. . High doses of Adriamycin induced significant increases in heart tissues enzymes (lactate dehydrogenase, alkaline phosphatase and Creatine Kinase-MB isoenzyme (CKMB)). Hepatotoxicity figured in significant increment in liver function enzymes (aspartate aminotransferase (AST) and Alanine aminotransferase (ALT) activities) and lipid profile (cholesterol and triglycerides) and significant reduction in total protein and albumin. Moreover, urea and creatinine recorded significant increases in kidney tissues after interpretoneal administration of high doses of Adriamycin (100, 90 and 80 mg/kg b.wt.).

Effect of incubation period on measurement of alkaline phosphatase enzyme activity at 37°C

Background: Laboratory analysis of alkaline phosphatase (ALP) from blood can detect abnormalities which reflect changes in certain health conditions, including liver disease and bone disease. Despite the importance of measuring different isoenzymes activity in different diseases, total ALP test is often requested, which is not specific to identify the type and the extent of tissue damage. ALP activity measurement at different incubation period may affect the actual measurement as ALP is a heat labile enzyme and specific ALP isoenzymes have different sensitivity to heat inactivation which creates lab to lab variability and significant change if particular isoenzyme is predominant in patient’s sera. Objectives: The study was performed to measure the loss of activity of ALP at different 37°C incubation periods during ALP measurement in serum. Materials and Methods: Quality control materials were analyzed for ALP enzyme activity in 2-amino, 2-methyl, 1-propanol buffer, and 4-nitrophenyl phosphate substrate with different incubation periods. Result: There is a gradual decrease in enzyme activity on increase of incubation period. Conclusion: The effect of incubation period on ALP activity measurement at 37°C may be clinically relevant if one of the isoenzymes is predominant in the patient sera.

Effects of reduced food intake for 4 weeks on physiological parameters in toxicity studies in dogs.

This study sought to clarify the effects of reduced feeding on physiological parameters in dogs to enable appropriate evaluations of the safety and toxicity of test compounds. We measured alkaline phosphatase isozymes and the circulating blood volume, as well as clinical signs, body weight, hematology, blood chemistry, electrocardiography, organ weight, and histopathology, in male beagle dogs fed a diet consisting of 300 g/day or 150 g/day for 4 weeks. There were no abnormal clinical signs in any of the dogs. In the 150-g/day feeding group, a decreased alkaline phosphatase 3 suggesting effects on the bone and a decreased circulating blood volume associated with body weight loss were observed. Additionally, the following changes were also observed in the 150-g/day group: a decrease in body weight; hematologic changes including decreases in white blood cells, neutrophils, red blood cells, hemoglobin, hematocrit and reticulocytes; blood chemical changes including decreases in aspartate aminotransferase, lactate dehydrogenase and calcium and an increase in the creatinine at week 1 or thereafter; electrocardiographic changes including a decrease in the heart rate, a prolonged QRS duration and the occurrence of a second-degree atrioventricular block at week 3 or thereafter; and pathological changes including decreases in the weights of the liver and thymus, a decrease in hepatocyte rarefaction, and thymic atrophy. These results provide useful information for assessing the safety of compounds in toxicological studies, enabling direct treatment effects and secondary changes caused by decreased food intake to be distinguished.

Synthesis, alkaline phosphatase inhibition studies and molecular docking of novel derivatives of 4-quinolones

New and convenient methods for the functionalization of the 4-quinolone scaffold at positions C-1, C-3 and C-6 were developed. The 4-quinolone derivatives were evaluated for their inhibitory potential on alkaline phosphatase isozymes. Most of the compounds exhibit excellent inhibitory activity and moderate selectivity. The IC50 values on tissue non-specific alkaline phosphatase (TNAP) were in the range of 1.34 ± 0.11 to 44.80 ± 2.34 μM, while the values on intestinal alkaline phosphatase (IAP) were in the range of 1.06 ± 0.32 to 192.10 ± 3.78 μM. The most active derivative exhibits a potent inhibition on IAP with a ≈14 fold higher selectivity as compared to TNAP. Furthermore, molecular docking calculations were performed for the most potent inhibitors to show their binding interactions within the active site of the respective enzymes.

Isonicotinohydrazones as inhibitors of alkaline phosphatase and ecto-5'-nucleotidase.

A series of isonicotinohydrazide derivatives was synthesized and tested against recombinant human and rat ecto-5'-nucleotidases (h-e5'NT and r-e5'NT) and alkaline phosphatase isozymes including both bovine tissue-non-specific alkaline phosphatase (b-TNAP) and tissue-specific calf intestinal alkaline phosphatase (c-IAP). These enzymes are implicated in vascular calcifications, hypophosphatasia, solid tumors, and cancers, such as colon, lung, breast, pancreas, and ovary. All tested compounds were active against both enzymes. The most potent inhibitor of h-e5'NT was derivative (E)-N'-(1-(3-(4-fluorophenyl)-5-phenyl-4,5-dihydro-1H-pyrazol-1-yl)ethylidene)isonicotinohydrazide (3j), whereas derivative (E)-N'-(4-hydroxy-3-methoxybenzylidene)isonicotinohydrazide (3g) exhibited significant inhibitory activity against r-e5'NT. In addition, the derivative (E)-N'-(4'-chlorobenzylidene)isonicotinohydrazide (3a) was most potent inhibitor against calf intestinal alkaline phosphatase and the derivative (E)-N'-(4-hydroxy-3-methoxybenzylidene)isonicotinohydrazide (3g) was found to be most potent inhibitor of bovine tissue-non-specific alkaline phosphatase. Furthermore, putative binding modes of potent compounds against e5'NT (human and rat e5'NT) and AP (including b-TNAP and c-IAP) were determined computationally.

Menaquinone-4 (vitamin K2) up-regulates expression of human intestinal alkaline phosphatase in Caco-2 cells

Alkaline phosphatase (ALP) hydrolyzes several monophosphate esters into inorganic acid and alcohol. In humans, 4 kinds of ALP isozymes have been identified: tissue-nonspecific ALP, intestinal ALP, placental ALP, and germ cell ALP. Intestinal ALP is expressed at a high concentration in the brush border membrane of intestinal epithelial cells and is known to be affected by several kinds of nutrients, such as lipids, but the physiological function of intestinal ALP has remained elusive. Vitamin K is an essential cofactor for the posttranslational carboxylation of glutamate residues into γ-carboxy glutamate. Menaquinone-4 (MK-4) with 4 isoprene units, vitamin K2, has been shown to induce bone-type ALP activity and osteoblastogenesis in human bone marrow cells. In this study, we investigated the effects of MK-4 on the level of ALP activity and expression of ALP messenger RNA in the human colon carcinoma cell line Caco-2, which is known to differentiate into small intestinal epithelial cells in vitro. After treatment with MK-4, there were significant increases in the ALP activities of Caco-2 cells. Inhibitor and thermal inactivation experiments demonstrated that the increased ALP had properties of intestinal-type ALP. Semiquantitative reverse transcription–polymerase chain reaction analysis revealed that expressions of human intestinal ALP and sucrase-isomaltase, which are intestinal differentiation markers, were highly enhanced in Caco-2 cells by MK-4. This is the first report concerning ALP messenger RNA expression induced by vitamin K2 in Caco-2 cells. Further studies on the physiological functions of human intestinal ALP will provide useful data on the novel effects of vitamin K.

Hypophosphatasia: Natural history study of 101 affected children investigated at one research center

Hypophosphatasia (HPP) is the inborn-error-of-metabolism that features deficient activity of the tissue-nonspecific isoenzyme of alkaline phosphatase (TNSALP). Resultant extracellular accumulation of inorganic pyrophosphate, a TNSALP substrate and potent inhibitor of mineralization, typically leads to tooth loss and sometimes to rickets or osteomalacia. HPP's remarkably broad-ranging severity is largely explained by autosomal dominant versus autosomal recessive transmission from among several hundred usually missense mutations positioned throughout the gene that encodes TNSALP. In 2015, our cross-sectional investigation of 173 affected children validated and expanded the clinical nosology commonly used for pediatric HPP.Herein, for the 101 patients in that cohort with longitudinal data, we explored the natural history of pediatric HPP by assessing their z-scores for height and then for weight, grip strength, and bone mineral density (BMD) determined by dual energy X-ray absorptiometry (DXA) also after adjusting for patient height. Eighteen patients contributed to “across” puberty evaluation.According to increasing HPP severity, there were 28 odonto HPP, 28 mild childhood HPP, 37 severe childhood HPP, and 8 infantile HPP patients typically studied from early to mid-childhood. The individual values for each parameter were wide-ranging within, and overlapping between, the four successive patient groups. Final mean/median z-scores, like the published initial values, paralleled the nosology. Longitudinal findings were similar for the boys versus girls and across puberty. Mean/median height z-scores remained constant for all four patient groups. In contrast, mean/median weight z-scores increased with aging, including after height-adjustment, resembling the recent trend for American children. However, excessive weight gain was typically not observed and mean/median values became average for height. Mean/median z-scores calculated routinely for chronologic age did not change for grip strength or for lumbar spine or total hip BMD. However, height-correction of the cohort suggested some worsening of grip strength z-scores and indicated improvement in spine BMD z-scores.Overall, in affected children and adolescents, HPP represents a clinically stable but chronic disorder.

A concise review on hypophosphatasia with case report

Hypophosphatasia (HPP) is an inherited dento-osseous metabolic disease characterized by inactivating mutations in the gene encoding the tissue-nonspecific isoenzyme of alkaline phosphatase (TNSALP) which lead to a deficiency in TNSALP enzymatic activity. Low TNSALP activity results in increased levels of 3 known phosphocompound substrates: inorganic pyrophosphate (PPi), pyridoxal 5’-phosphate (PLP; the major circulating form of vitamin B6), and phosphoethanolamine (PEA). We discussed a systematic review with novel approach and a case report in which patient had multiple jaw reconstructive surgeries and early tooth loss in his childhood age but remained undiagnosed till his 60s. It should raise awareness among health care providers regarding low TNSALP and performing thorough etiological investigations which can ensure optimal clinical care and decision making for their patients by preventing complications like chondrocalcinosis, arthritis, early tooth loss, pseudo/complete fractures and pseudogout among the patients diagnosed with HPP even later in their life.

Adult Hypophosphatasia Treated with Teriparatide: Report of 2 Patients and Review of the Literature

Hypophosphatasia (HPP) is a rare inherited metabolic bone disease from deficient activity of the tissue-nonspecific isoenzyme of alkaline phosphatase (TNSALP). Reportedly, teriparatide (parathyroid hormone 1-34) can benefit the adult form of HPP, including fracture healing. We studied 2 women with adult HPP given teriparatide and reviewed the reports of 6 additional patients. A 68-year-old black woman (patient 1) described low-trauma fractures and had subnormal serum alkaline phosphatase (ALP) activity. Biochemical findings were consistent with HPP. Mutation analysis revealed a heterozygous defect in exon 10 of TNSALP (ALPL). Teriparatide was injected daily for 2 years. Four years later, she fractured her right hip. Treatment was resumed for 8 months without further fractures. A 53-year-old white woman (patient 2) reported low-trauma fractures and had subnormal serum ALP. Mutation analysis revealed a heterozygous defect in exon 8 of TNSALP. She injected teriparatide daily for 2 years. One year later, bone mineral density (BMD) declined and treatment was resumed for 3 months. When she sustained a sacral fracture, teriparatide was administered for a further 18 months. Patient 1's serum ALP increased while receiving teriparatide and returned to baseline after its discontinuation. BMD remained unchanged, but no fractures were sustained. Patient 2's serum ALP increased, but the improvement was not sustained. Femoral neck BMD increased significantly during the first cycle, declined significantly afterwards, and was regained during a second course of teriparatide. Teriparatide shows some benefit for adult HPP. ALP = alkaline phosphatase BMD = bone mineral density BSAP = bone-specific alkaline phosphatase CTX = C-telopeptide DXA = dual-energy X-ray absorptiometry FN = femoral neck HPP = hypophosphatasia LS = lumbar spine PEA = phosphoethanolamine PLP = pyridoxal 5'-phosphate PTH = parathyroid hormone SQ = subcutaneous TNSALP = tissue-nonspecific isoenzyme of alkaline phosphatase TPTD = teriparatide.

Increased Bone Resorption: A Possible Pathophysiological Link Between Hypovitaminosis D and Peripheral Arterial Disease

Vitamin D deficiency has been associated with the prevalence and severity of peripheral arterial disease (PAD); nevertheless, data on bone turnover in patients with PAD is lacking. The present study investigates a possible relationship between the markers of bone turnover and the presence and severity of PAD. The study examined 143 patients, with a mean±SD age of 75.3±8.5 years (range 50.0-93.0 years), of both sexes, admitted to a department of internal medicine. All patients underwent ankle brachial index (ABI) assessment by Doppler velocimetry. Serum levels of 25(OH) vitamin D and two markers of bone turnover, C-terminal telopeptide of type I collagen (sCTX) and bone isoenzyme of alkaline phosphatase, were measured. The differences between patients with normal ABI and patients with PAD were analyzed. Pearson and Spearman correlation coefficients were calculated and independent predictors were identified through a stepwise linear regression analysis. Odds ratios were calculated with a logistic regression model. Compared with patients with a normal ABI (≥0.90), patients with PAD (ABI<0.90) presented with significantly lower levels of 25(OH) vitamin D (12.2±9.6ng/mL vs. 16.7±8.7ng/mL; p=.006) and a significantly higher concentration of sCTX (1.1±0.7ng/mL vs. 0.6±0.4ng/mL; p<.001). There was a positive correlation between ABI and serum concentration of 25 (OH) vitamin D (r=0.3; p<.001), whereas ABI was inversely correlated with the concentration of sCTX (r=-0.358; p<.001). At logistic regression analysis, age, cigarette smoking, and both vitamin D and sCTX were independent predictors of an ABI<0.90. These results support the hypothesis that hypovitaminosis D and increased bone turnover are risk factors for the presence and severity of PAD. Furthermore, the presence of PAD, even if asymptomatic and diagnosed by a reduced ABI, could identify a population at risk for osteoporosis and osteomalacia.

Atypical femoral fracture in a 51-year-old woman: Revealing a hypophosphatasia

We report a 51-year old woman who suffered 2 atypical subtrochanteric femoral fractures (AFFs). She had a history of several metatarsal fractures. She had a normal bone densitometry. An adult form of hypophosphatasia (HPP) was diagnosed from low serum alkaline phosphatase (ALP), and tissue nonspecific isoenzyme of ALP (TNSALP) mutation analysis revealing 2 heterozygous mutations: c.299C>T (p. T100M) and c.571G>A (p. E191K). Low ALP is the hallmark of the diagnosis of HPP; which is associated in adults with premature loss of deciduous teeth, recurrent metatarsal stress fractures, and joints and tendons disorders. The incidence of AFFs in the population is 5.9 per 100,000 person-years. Physicians and patients with bone fragility must pay attention to prodromal pain, which require urgent radiographic evaluation of both femurs. Rheumatoid arthritis, use of glucocorticoids, and proton pump inhibitors have been associated with an excess risk of AFFs. Healthy subjects carrying a TNSALP mutation with low ALP value may be exposed to develop AFF spontaneously or while receiving potent anti-resorptive drugs. Low ALP must be checked as a cause of bone fragility.

Hypophosphatasia - aetiology, nosology, pathogenesis, diagnosis and treatment.

Hypophosphatasia is the inborn error of metabolism characterized by low serum alkaline phosphatase activity (hypophosphatasaemia). This biochemical hallmark reflects loss-of-function mutations within the gene that encodes the tissue-nonspecific isoenzyme of alkaline phosphatase (TNSALP). TNSALP is a cell-surface homodimeric phosphohydrolase that is richly expressed in the skeleton, liver, kidney and developing teeth. In hypophosphatasia, extracellular accumulation of TNSALP natural substrates includes inorganic pyrophosphate, an inhibitor of mineralization, which explains the dento-osseous and arthritic complications featuring tooth loss, rickets or osteomalacia, and calcific arthopathies. Severely affected infants sometimes also have hypercalcaemia and hyperphosphataemia due to the blocked entry of minerals into the skeleton, and pyridoxine-dependent seizures from insufficient extracellular hydrolysis of pyridoxal 5'-phosphate, the major circulating form of vitamin B6, required for neurotransmitter synthesis. Autosomal recessive or dominant inheritance from ~300 predominantly missense ALPL (also known as TNSALP) mutations largely accounts for the remarkably broad-ranging expressivity of hypophosphatasia. High serum concentrations of pyridoxal 5'-phosphate represent a sensitive and specific biochemical marker for hypophosphatasia. Also, phosphoethanolamine levels are usually elevated in serum and urine, though less reliably for diagnosis. TNSALP mutation detection is important for recurrence risk assessment and prenatal diagnosis. Diagnosing paediatric hypophosphatasia is aided by pathognomic radiographic changes when the skeletal disease is severe. Hypophosphatasia was the last type of rickets or osteomalacia to await a medical treatment. Now, significant successes for severely affected paediatric patients are recognized using asfotase alfa, a bone-targeted recombinant TNSALP.

HYPOPHOSPHATASIA IN ADULTS: CLINICAL CASES AND LITERATURE REVIEW

Hypophosphatasia is a rare inborn error of metabolism caused by mutations in the gene encoding tissue-nonspecific isoenzyme of alkaline phosphatase. Inexpressive clinical picture of the disease in adults is often difficult to diagnose. We present two clinical observations: in one case, the patient was treated for a long time with alfacalcidol and calcium supplementation due to misdiagnosis of systemic osteoporosis with pathologic fractures of the vertebras, although at the presentation the patient had a typical for hypophosphatasia decrease of alkaline phosphatase. In another case, a patient with diagnosis of aseptic necrosis of the femoral head had a sharp decrease in alkaline phosphatase levels at presurgical evaluation. In both cases, the diagnosis was confirmed by genetic testing. For patients with aseptic necrosis the confirmation of the diagnosis of hypophosphatasia determines the need for treatment with asfotase alfa in the postoperative period to preserve the stability of the endoprosthesis.