Differential glycosylation of tissue non-specific alkaline phosphatase in mesenchymal stromal cells differentiated into either an osteoblastic or adipocytic phenotype.

It has long been known that tissue non-specific alkaline phosphatase (TNAP) is essential for the correct formation of bone, as altered expression or function of this enzyme results in hypophosphatasia, a disease characterised by compromised bone structure, density and strength. However, recent evidence strongly suggests that the enzyme also has a role in lipid accrual and adipogenesis, a function that seems far removed from bone formation. Given that mesenchymal stromal cells (MSCs) are progenitors of both osteoblasts and adipocytes, the question arises of how TNAP is regulated to potentially have a different function when MSCs undergo either osteogenesis or adipogenesis. As the primary protein sequence is unchanged for the enzyme during both types of differentiation, any differences in function must be attributed to post-translational modification and/or localisation. We therefore examined the location of TNAP in bone- or adipose-derived MSCs differentiated into an adipocytic phenotype and compared the glycosylation state of the enzyme in MSCs differentiated into either osteoblasts or adipocytes. TNAP was found to co-locate with perilipin around lipid droplets in MSCs from bone, subcutaneous- and visceral adipose tissue during adipocytic differentiation. Treatment of TNAP with wheat germ lectin followed by electrophoresis showed minor differences in glycosylation between the phosphatase isolated from cells from these tissues, whereas electrophoresis after neuraminidase digestion highlighted differential glycosylation between cell types and during adipogenesis and osteoblastogenesis. This infers that post-translational modification of TNAP is altered during differentiation and is dependent on the eventual phenotype of the cells.

A new perspective on the function of Tissue Non-Specific Alkaline Phosphatase: from bone mineralization to intra-cellular lipid accumulation.

Tissue-nonspecific alkaline phosphatase (TNAP) is one of four isozymes, which include germ cell, placental and intestinal alkaline phosphatases. The TNAP isozyme has 3 isoforms (liver, bone and kidney) which differ by tissue expression and glycosylation pattern. Despite a long history of investigation, the exact function of TNAP in many tissues is largely unknown. Only the bone isoform has been well characterised during mineralization where the enzyme hydrolyses pyrophosphate to inorganic phosphate, which combines with calcium to form hydroxyapatite crystals deposited as new bone. The inorganic phosphate also increases gene expression of proteins that support tissue mineralization. Recent studies have shown that TNAP is expressed in preadipocytes from several species, and that inhibition of TNAP activity causes attenuation of intracellular lipid accumulation in these and other lipid-storing cells. The mechanism by which TNAP stimulates lipid accumulation is not known; however, proteins that are important for controlling phosphate levels in bone are also expressed in adipocytes. This review examines the evidence that inorganic phosphate generated by TNAP promotes transcription that enhances the expression of the regulators of lipid storage and consequently, that TNAP has a major function of lipid metabolism.

The Relationship of VO2 Peak and the Blood Lactate Transition Threshold with Metabolic Syndrome and Its Component Disorders.

Background: Improvements in cardiorespiratory fitness attenuate the risk for metabolic syndrome (MetS). However, the determinants of cardiorespiratory fitness measurements such as oxygen consumption (VO2) peak and anaerobic threshold (AT) have not been investigated in persons with MetS. Therefore, the main aim of this study was to compare VO2 peak and AT between subjects with and without MetS and to investigate determinants of cardiorespiratory fitness and its effects on the odds for MetS and its individual components. Methods: Thirty-one males with MetS and 24 healthy male participants each performed a VO2 peak and a blood lactate transition threshold test. Waist circumference, body mass index (BMI), blood pressure, fasting plasma triglyceride, total cholesterol, high-density lipoprotein cholesterol, glucose, and insulin levels were measured. Separate multivariable linear regression models were developed in which VO2 peak, AT, and the components of MetS were used as the dependent variables, while a multivariable logistic regression model was used for MetS. Results: The VO2 peak [median (interquartile range)] was lower in subjects with MetS compared with controls [27.9 (23.0-31.0) vs. 35.0 (32.0-45.0) mL·min-1·kg-1; P < 0.0001]. Multivariable regression analysis demonstrated that there was a bidirectional association between MetS and VO2 peak that was mediated by waist circumference and blood pressure. The VO2 peak was a strong negative determinant of waist circumference (ß = -0.36, P < 0.0001), but not of BMI (ß = -0.13, P = 0.21). Conclusions: A higher VO2 peak is associated with a lower odds ratio for MetS, which is related to greater cardiorespiratory fitness in a cyclical relationship that is mediated by blood pressure and waist circumference. A higher VO2 peak is specifically associated with lower waist circumference, and vice versa, possibly by effects on visceral fat.

Reproducibility and levels of blood lactate transition thresholds in persons with metabolic syndrome.

BACKGROUND: The optimal exercise load/intensity for exercise programs for individuals with metabolic syndrome has not been investigated. One method of determining optimal exercise load is to measure the blood lactate transition threshold (BLTT), referred to as the anaerobic threshold (AT). This study investigated the reproducibility of BLTT testing and the consequent determination of AT via the Mader method and a modified form of the Automatic Data Analysis for Progressive Tests (ADAPT) method in patients with metabolic syndrome. METHODS: Fifteen, male patients diagnosed with metabolic syndrome and 15 healthy, male subjects each performed BLTT measurements on a treadmill at the same daily times on three different days. Peak oxygen consumption was also determined during testing. RESULTS: There was no significant difference in treadmill velocity at AT determined by the Mader method or the modified ADAPT method within both groups (P>0.05). Both methods yielded good coefficients of variation. When combining both groups, the typical error also demonstrated good reproducibility. The mean treadmill velocity at AT was higher in the healthy compared to the metabolic syndrome group using both the Mader and the ADAPT method. Regression analysis and analysis of covariance (ANCOVA) demonstrated that this difference was largely due to a higher oxygen consumption (VO2) peak in the healthy group. The study also found an association between VO2 peak and waist circumference among the metabolic syndrome group. CONCLUSIONS: This study demonstrated that BLTT tests are reproducible in persons with metabolic syndrome. The modified ADAPT method may be the preferred method of determining treadmill velocity at AT because fewer factors are known to influence its determination.

Adiponectin and atherosclerosis risk factors in African hemodialysis patients: a population at low risk for atherosclerotic cardiovascular disease.

Atherosclerotic cardiovascular disease (CVD) is the major cause of morbidity and mortality in hemodialysis (HD) patients. Adiponectin (ADPN), a recently discovered collagen-like protein, is secreted exclusively by adipocytes. It has anti-atherogenic properties and reduced serum ADPN levels have been shown to be predictive of cardiovascular events. In this study, we determined the atherosclerotic risk and the significance of ADPN levels in our HD patients and also examined its relationship to other traditional CVD risk factors. A cross-sectional study of 84 patients on maintenance HD (58 Blacks and 26 non-Blacks) and 63 healthy controls matched for age, sex and race (35 Blacks and 28 non-Blacks) was undertaken. Serum ADPN levels and other risk factors, including blood pressure, serum lipid, and C-reactive protein, were studied in HD patients and were compared with the controls. Carotid artery intima-media thickness and plaque occurrence was measured by B-mode ultrasonography while echocardiography was done according to American Society of Echocardiography guidelines. Serum ADPN levels were higher in the HD group compared with the control subjects (22.19 ± 0.98 mg/mL vs. 9.93 ± 0.68 mg/mL; P < 0.001). Higher ADPN levels in HD patients were associated with lower triglyceride levels. ADPN correlated positively (r = 0.49, P < 0.0001) with left ventricular mass index (LVMI) in the total study population. ADPN levels were raised in HD patients and correlated with LVMI, possibly because of the confounding effect of low glomerular filtration rate. ADPN levels were inversely related to risk factors for atherosclerosis and may provide possible targets for therapeutic interventions.

The influence of metabolic syndrome components on plasma PAI-1 concentrations is modified by the PAI-1 4G/5G genotype and ethnicity.

Coronary artery disease (CAD) is less common in African than Indian or White subjects and elevated plasminogen activator inhibitor (PAI)-1 levels may be a risk factor for CAD. Therefore, PAI-1 levels were measured in the three populations and related to the -675 PAI-1 4G/5G promoter genotype. PAI-1 levels and anthropometric variables were measured in 310 Indian, 269 White and 107 African subjects. The PAI-1 4G allele frequency was lower in the African (0.13) than Indian (0.54) or White (0.58) populations and explained the lower PAI-1 levels in African (41.5+/-25.1 versus 68.0+/-33.3 and 70.5+/-35.7 ng/ml, respectively; p<0.0001) subjects. Except for White subjects, PAI-1 levels were higher in those with metabolic syndrome or type 2 diabetes. PAI-1 genotype did not associate with either disorder. Metabolic syndrome-related factors had little influence on PAI-1 levels in White subjects but in African and Indians subjects these variables had a major influence on PAI-1 levels in those with the 5G/5G genotype but not in subjects with the 4G/4G genotype. Ethnic differences in PAI-1 levels are largely due to differences in the frequency of the 4G and 5G alleles at the -675 locus. In Indian and African, but not White populations, the ability of metabolic syndrome-related factors to influence PAI-1 levels is modulated by the -675 genotype.

Metabolic function and the prevalence of lipodystrophy in a population of HIV-infected African subjects receiving highly active antiretroviral therapy.

OBJECTIVE: This study measured the prevalence of lipodystrophy and the metabolic effects of highly active antiretroviral therapy (HAART) in HIV-infected African subjects. METHODS: Prevalence was measured in 571 Rwandans receiving HAART for > or = 6 months. Metabolic variables were measured in 100 HIV-positive adults with lipodystrophy, 50 HIV-positive nonlipodystrophic adults, and 50 HIV-negative controls. RESULTS: A HAART regimen of stavudine, lamivudine, and nevirapine was used by 81.6% of subjects; none received protease inhibitors. Lipodystrophy was observed in 34% (48.5% in urban groups and 17.3% in rural groups) of subjects, with a prevalence of 69.6% in those receiving HAART for >72 weeks. Peripheral lipoatrophy combined with abdominal lipohypertrophy was observed in 72% of lipodystrophic subjects. HIV-positive adults with lipodystrophy had a significantly higher waist-to-hip ratio (WHR; 0.99 +/- 0.05 vs. 0.84 +/- 0.03: P < 0.0005) than HIV-positive nonlipodystrophic adults. Total cholesterol concentrations (median [interquartile range], mmol/L) were significantly higher in the HIV-positive adults with lipodystrophy (3.60 [1.38]) than in HIV-positive nonlipodystrophic adults (3.19 [0.65]; P < 0.005) and control (3.13 [0.70]; P < 0.0005) groups. Impaired fasting glucose was observed in 18% of HIV-positive adults with lipodystrophy, 16% of HIV-positive nonlipodystrophic adults, and 2% of controls, but insulin levels did not differ. CONCLUSIONS: African subjects with lipodystrophy have increased WHR, glucose, and cholesterol levels. Glucose concentrations are also elevated in nonlipodystrophic HIV-positive subjects. Therefore, factors other than body fat redistribution contribute to the glucose intolerance.