Assessment of Urine Proteomics in Type 1 Primary Hyperoxaluria.

BACKGROUND: Primary hyperoxaluria type 1 (PH1) and idiopathic hypercalciuria (IHC) are stone-forming diseases that may result in the formation of calcium (Ca) oxalate (Ox) stones, nephrocalcinosis, and progressive chronic kidney disease (CKD). Poorer clinical outcome in PH1 is segregated by the highest urine (Ur)-Ox (UrOx), while IHC outcomes are not predictable by UrCa. We hypothesized that differences would be found in selected Ur-protein (PRO) patterns in PH1 and IHC, compared to healthy intra-familial sibling controls (C) of PH1 patients. We also hypothesized that the PRO patterns associated with higher UrOx levels would reflect injury, inflammation, biomineralization, and abnormal tissue repair processes in PH1. METHODS: Twenty four-hour Ur samples were obtained from 3 cohorts: PH1 (n = 47); IHC (n = 35) and C (n = 13) and were analyzed using targeted platform-based multi-analyte profile immunoassays and for UrOx and UrCa by biochemical measurements. RESULTS: Known stone matrix constituents, osteopontin, calbindin, and vitronectin were lowest in PH1 (C > IHC > PH1; p < 0.05). Ur-interleukin-10; chromogranin A; epidermal growth factor (EGF); insulin-like growth factor-1 (IGF-1), and macrophage inflammatory PRO-1α (MIP-1α) were higher in PH1 > C (p = 0.03 to p < 0.05). Fetuin A; IGF-1, MIP-1α, and vascular cell adhesion molecule-1 were highest in PH1 > IHC (p < 0.001 to p = 0.005). CONCLUSION: PH1 Ur-PROs reflected overt inflammation, chemotaxis, oxidative stress, growth factors (including EGF), and pro-angiogenic and calcification regulation/inhibition compared to the C and IHC cohorts. Many of the up- and downregulated PH1-PROs found in this study are also found in CKD, acute kidney injury, stone formers, and/or stone matrices. Further data analyses may provide evidence for PH1 unique PROs or demonstrate a poorer clinical outcome.

Fibroblast growth factor-23 in obese, normotensive adolescents is associated with adverse cardiac structure.

OBJECTIVES: Fibroblast growth factor-23 (FGF23) is a biomarker for cardiovascular disease. Obesity may promote FGF23 production in the absence of chronic kidney disease. We sought to determine among normotensive African American adolescents whether FGF23 levels are greater in obese compared with normal-weight adolescents and to determine the relationship of FGF23 with markers of cardiac structure and insulin resistance. STUDY DESIGN: Cross-sectional data were obtained from a cohort of 130 normotensive, African American adolescents ages 13-18 years without chronic kidney disease; 74 were obese; 56 were normal weight. Plasma C-terminal FGF23, fasting glucose and insulin, and high-sensitivity C-reactive protein were measured; participants underwent M-mode echocardiography. RESULTS: FGF23 was skewed and approximately normally distributed after natural log transformation (logFGF23). FGF23 levels were greater in obese vs normal-weight participants (geometric mean 43 vs 23 RU/mL, P < .01). FGF23 values were significantly greater in participants with eccentric or concentric cardiac hypertrophy compared with those without hypertrophy P < .01). LogFGF23 directly correlated with body mass index, body mass index z-score, waist circumference, fasting insulin levels, and homeostasis model assessment scores. Regression models adjusted for age, sex, and high-sensitivity C-reactive protein suggest that each 10% increase in FGF23 is associated with a 1.31 unit increase in left ventricular mass (P < .01), a 0.29-unit increase in left ventricular mass index (P < .01), and a 0.01-unit increase in left atrial dimension indexed to height (P = .02). CONCLUSIONS: In this sample of obese African American adolescents, FGF23 blood levels were associated with abnormal cardiac structure. We postulate that FGF23 may be an early marker of cardiac injury in obese but otherwise-healthy African American adolescents.

Hyperphosphatemic familial tumoral calcinosis: response to acetazolamide and postulated mechanisms.

Hyperphosphatemic familial tumoral calcinosis (HFTC) is characterized by enhanced renal phosphate absorption, hyperphosphatemia, and tumor-like extraosseous calcifications due to inactivating mutations in FGF23 or associated proteins. Surgical excision is needed when low phosphate diet and phosphate binders are ineffective. Sporadic reports have supported acetazolamide use. We report on a 7-year-old African American boy who presented with severe HFTC requiring numerous surgical excisions. Tumors continued to appear and others reoccurred despite phosphate restriction and sevelamer carbonate. At the age of 9.5 years, acetazolamide (40 mg/kg/day) was added and resulted in mild metabolic acidosis (bicarbonate 25.3 mEq/L vs. 21.4 mEq/L, P < 0.001; serum pH 7.38 vs. 7.31, P = 0.013, pre- and post-acetazolamide, respectively) but no change in tubular reabsorption of phosphate (TRP) (96.9% vs. 95.9%, P = 0.34) or serum phosphate (6.6 mg/dl vs. 6.9 mg/dl, P = 0.52 pre- and post-acetazolamide, respectively). Following the initiation of acetazolamide therapy, the patient experienced significant improvement in disease course as indicated by resolution of localized bone pain, cessation of tumor formation, and no tumor recurrence. Despite mild metabolic acidosis, our patient had improved linear growth and did not develop any other side effects related to therapy. Intact FGF23 remained abnormally low throughout disease course, while C-terminal FGF23 increased with acetazolamide. We conclude that acetazolamide can control severe HFTC by inducing mild metabolic acidosis despite no change in serum phosphate or TRP. This effect may be exerted though improved calcium-phosphate complex solubility and increased FGF23 locally.

Longitudinal trajectory of vitamin D status from birth to early childhood in the development of food sensitization.

BACKGROUND: Increasing evidence supports the immunomodulatory effect of vitamin D on allergic diseases. The combined role of prenatal and postnatal vitamin D status in the development of food sensitization (FS) and food allergy remains understudied. METHODS: Plasma 25-hydroxyvitamin D (25(OH)D) levels of 460 children in the Boston Birth Cohort (BBC) were measured at birth and early childhood, and the subjects were genotyped for rs2243250 (C-590T) in the IL4 gene. We defined FS as specific IgE levels of ≥0.35 kUA/l to any of eight common food allergens; we defined persistently low vitamin D status as cord blood 25(OH)D <11 ng/ml and postnatal 25(OH)D <30 ng/ml. RESULTS: We observed a moderate correlation between cord blood 25(OH)D at birth and venous blood 25(OH)D measured at 2-3 y (r = 0.63), but a weak correlation at <1 y (r = 0.28). There was no association between low vitamin D status and FS at any single time point alone. However, in combination, persistence of low vitamin D status at birth and in early childhood increased the risk of FS (odds ratio (OR) = 2.03, 95% confidence interval (CI): 1.02-4.04), particularly among children carrying the C allele of rs2243250 (OR = 3.23, 95% CI: 1.37-7.60). CONCLUSION: Prenatal and early postnatal vitamin D levels, along with individual genetic susceptibility, should be considered in assessing the role of vitamin D in the development of FS and food allergy.

The role of exchange and emotion on commitment: A study of teachers.

Recent experimental work in social exchange offers keen insight into factors that enhance commitment to individuals, groups, and relationships. In this article we explore the relevance of this work to school settings. Specifically, we use structural equation modeling and data from the 2004 Schools and Staffing Survey (SASS) to test whether the commitment-enhancing processes laid out in Lawler's affect theory of social exchange might reduce teacher turnover, an issue plaguing school districts across the country. Our results support such a model and demonstrate the importance of interdependence for fostering commitment among teachers, with interaction, affect, and cohesion as intervening factors.

A stakeholder-driven method for selecting implementation strategies: a case example of pediatric hypertension clinical practice guideline implementation.

BACKGROUND: This article provides a generalizable method, rooted in co-design and stakeholder engagement, to identify, specify, and prioritize implementation strategies. To illustrate this method, we present a case example focused on identifying strategies to promote pediatric hypertension (pHTN) Clinical Practice Guideline (CPG) implementation in community health center-based primary care practices that involved meaningful engagement of pediatric clinicians, clinic staff, and patients/caregivers. This example was chosen based on the difficulty clinicians and organizations experience in implementing the pHTN CPG, as evidenced by low rates of guideline-adherent pHTN diagnosis and treatment. METHODS: We convened a Stakeholder Advisory Panel (SAP), comprising 6 pediatricians and 5 academic partners, for 8 meetings (~12 h total) to rigorously identify determinants of pHTN CPG adherence and to ultimately develop a testable multilevel, multicomponent implementation strategy. Our approach expanded upon the Expert Recommendations for Implementation Change (ERIC) protocol by incorporating a modified Delphi approach, user-centered design methods, and the Implementation Research Logic Model (IRLM). At the recommendation of our SAP, we gathered further input from youth with or at-risk for pHTN and their caregivers, as well as clinic staff who would be responsible for carrying out facets of the implementation strategy. RESULTS: First, the SAP identified 17 determinants, and 18 discrete strategies were prioritized for inclusion. The strategies primarily targeted determinants in the domains of intervention characteristics, inner setting, and characteristics of the implementers. Based on SAP ratings of strategy effectiveness, feasibility, and priority, three tiers of strategies emerged, with 7 strategies comprising the top tier implementation strategy package. Next, input from caregivers and clinic staff confirmed the feasibility and acceptability of the implementation strategies and provided further detail in the definition and specification of those strategies. CONCLUSIONS: This method-an adaptation of the ERIC protocol-provided a pragmatic structure to work with stakeholders to efficiently identify implementation strategies, particularly when supplemented with user-centered design activities and the intuitive organizing framework of the IRLM. This generalizable method can help researchers identify and prioritize strategies that align with the implementation context with an increased likelihood of adoption and sustained use.

Optimizing the implementation of a population panel management intervention in safety-net clinics for pediatric hypertension (The OpTIMISe-Pediatric Hypertension Study).

BACKGROUND: Though clinical practice guidelines are available, the diagnosis of pediatric hypertension (HTN) is often missed. Management may not follow guidelines due to the measurement challenges in children, complexity of interpreting youth blood pressure standards that are dependent on height, age, and sex, familiarity with diagnostic criteria, and variable comfort with management of pediatric HTN among providers. Evidence suggests that wide adoption and adherence to pediatric HTN guidelines would result in lower cardiovascular disease and kidney damage in adulthood. The proposed project will develop an implementation strategy package to increase adherence to clinical practice guidelines for pediatric HTN within safety-net community health centers (CHCs). The centerpiece of which is a provider-facing population panel management (PPM) tool and point-of-care clinical decision support (CDS). Prior research indicates that multiple discrete implementation strategies (e.g., stakeholder involvement, readiness planning, training, ongoing audit and feedback) are needed to institute practice- and provider-level adoption of such tools. METHODS: Using participatory research methods involving stakeholders from a practice-based research network of CHCs, with input from scientific advisors, the project aims to (1) employ user-centered design methods to tailor an existing CDS tool for use at the point of care and optimize cohort management with a PPM tool to support adherence to the latest pediatric HTN guidelines, and (2) use a stakeholder-driven method for selecting implementation strategies that support tool adoption and increase guideline-adherent physician behaviors. Multilevel process evaluation using surveys and key informant interview data will assess the acceptability, adoption, appropriateness, cost, and feasibility of the PPM tool and its multicomponent implementation strategy package. Usability testing will be conducted with the PPM tool to iteratively refine features and ensure proper functionality. DISCUSSION: The proposed research has the potential to improve identification, diagnosis, and management of HTN in primary care settings for high-risk youth by assisting healthcare providers in implementing the American Academy of Pediatrics' 2017 guidelines using an EHR-integrated PPM tool with CDS. Should the strategy package for PPM tool adoption be successful for pediatric HTN, findings will be translatable to other settings and PPM of other chronic cardiovascular conditions affecting overall population health.

The disruption of murine tumor neovasculature by low-intensity ultrasound-comparison between 1- and 3-MHz sonication frequencies.

RATIONALE AND OBJECTIVES: The goal was to determine whether the tumor vascular disrupting actions of low-intensity ultrasound were frequency dependent. MATERIALS AND METHODS: The effect of the frequency (1 MHz at 2.2 W/cm2 or 3 MHz at 2.4 W/cm2) of low-intensity ultrasound as a neovascular disrupting modality was investigated in 15 murine melanomas (K1735(22)) insonated for 3 minutes after the intravenous injection of a microbubble contrast agent (Definity). In contrast-enhanced power Doppler observations of each tumor (before and after treatment), measurements were made of the size of the area of the tumor that was perfused with blood containing the ultrasound contrast agent (percentage area of flow [PAF]), and the volume of contrast agent flowing through the unit volume of the tumor (color-weighted fractional area [CWFA]). During insonation of the tumor, the temperature was measured with a fine wire thermocouple in an additional eight mice. RESULTS: The antivascular action of low-intensity ultrasound was significantly enhanced (PAF by 64%; CWFA by 106%) when the tumor was treated with 3-MHz ultrasound rather than 1 MHz (analysis of variance: PAF, P=.02; CWFA, P=.04). The average rate of tumor temperature increase was 2.6+/-1.3 degrees C/min for 1 MHz and 5.0+/-1.7 degrees C/min for 3 MHz; these increases were significantly different (P=.04). CONCLUSIONS: Insonation of the tumor at a higher frequency amplified the heating of the neoplasm and led to greater disruption of the tumor vasculature; 3-MHz ultrasound was more efficacious than 1 MHz for antivascular cancer therapy.

Bioelectric impedance predicts total body water, blood pressure, and heart rate during hemodialysis in children and adolescents.

OBJECTIVE: The purposes of our study were to: (1) assess if changes in the volemic status of children and adolescents over the course of standard dialysis could be observed using bioelectric impedance (BIA); and (2) evaluate whether the variability of blood pressure (systolic blood pressure, SBP; diastolic blood pressure, DBP) and heart rate (HR) could be explained by independent variables from BIA data. DESIGN: We used a randomized, single-blinded treatment and repeated-measures design. SETTING: This study took place at the DaVita Children's Dialysis Center (Chicago, IL). PATIENTS: There were 7 subjects, aged 10 to 16 years. INTERVENTION: Two identical standard hemodialysis (HD) sessions were completed, with data collected five times during each HD session: pre-HD, intra-HD (hours 1, 2, and 3), and post-HD. Endpoints included total body water (TBW), resistance (R), reactance (Xc), bioimpedance vector |Z|, supine and sitting SBP, DBP, and HR. Standing SBP, DBP, and HR were collected pre-HD and post-HD. RESULTS: No differences were observed in TBW between HD sessions for all subjects. However, TBW decreased throughout the HD sessions for all subjects (although no significant differences were seen between hour 3 and post-HD). Reactance (representative of extracellular water) correlated with supine, sitting, and standing SBP (r = 0.55, 0.59, and 0.51, respectively; P < or = .008). The bioimpedance vector increased beginning at hour 1 (P < .001), reflective of a decline in tissue hydration over the course of HD. CONCLUSIONS: Weight gain in end-stage kidney disease patients is largely fluid. Thus, the use of BIA during HD may aid in the prediction of cardiovascular instability before the development of symptoms, because intravascular hypovolemia and hypotension can result from excessive ultrafiltration below the critical dry weight. In addition, BIA explains, in part, the variability of SBP, DBP, and HR during HD. We suggest that our data also demonstrates the delay in mobilization of fluid from the interstitial space for plasma refill, as evidenced by the delayed change in |Z| over HD. Bioelectric impedance is useful for explaining changes in volemic status and, in part, the variability of SBP, DBP, and HR during HD.

Maternal BMI Associations with Maternal and Cord Blood Vitamin D Levels in a North American Subset of Hyperglycemia and Adverse Pregnancy Outcome (HAPO) Study Participants.

OBJECTIVE: Obesity in pregnancy may be associated with reduced placental transfer of 25-hydroxyvitamin D (25-OHD). The objective of this study was to examine associations between maternal BMI and maternal and cord blood levels of 25-OHD in full term neonates born to a single racial cohort residing at similar latitude. Secondary objectives were to examine associations between maternal glucose tolerance with maternal levels of 25-OHD and the relationship between cord blood 25-OHD levels and neonatal size. METHODS: This study was conducted among participants of the Hyperglycemia and Adverse Pregnancy Outcomes (HAPO) Study meeting the following criteria: residing at latitudes 41-43°, maternal white race, and gestational age 39-41 weeks. Healthy pregnant women underwent measures of height, weight, and a 75-g fasting oral glucose tolerance test (OGTT) at approximately 28 weeks gestation. Maternal and cord blood sera were analyzed for total 25-OHD by HPLC tandem mass spectrometry. Statistical analyses included ANOVA and linear regression models. RESULTS: Maternal and cord blood (N = 360) mean levels (sd) of 25-OHD were 37.2 (11.2) and 23.4 (9.2) ng/ml, respectively, and these levels were significantly different among the 3 field centers (ANOVA p< 0.001). Maternal serum 25-OHD was lower by 0.40 ng/ml for BMI higher by 1 kg/m2 (p<0.001) in an adjusted model. Maternal fasting plasma glucose, insulin sensitivity, and presence of GDM were not associated with maternal serum 25-OHD level when adjusted for maternal BMI. Cord blood 25-OHD was lower by 0.26 ng/ml for maternal BMI higher by 1 kg/m2 (p<0.004). With adjustment for maternal age, field center, birth season and maternal serum 25-OHD, the association of cord blood 25-OHD with maternal BMI was attenuated. Neither birth weight nor neonatal adiposity was significantly associated with cord blood 25-OHD levels. CONCLUSION: These results suggest that maternal levels of 25-OHD are associated with maternal BMI. The results also suggest that interpretation of neonatal 25-OHD levels may need to incorporate specific maternal factors in addition to season of birth and latitude.

Serum soluble urokinase-type plasminogen activator receptor levels and idiopathic FSGS in children: a single-center report.

BACKGROUND AND OBJECTIVES: FSGS is the primary cause of childhood nephrotic syndrome leading to ESRD. Permeability factors, including circulating serum soluble urokinase-type plasminogen activator receptor (suPAR), have been postulated as putative causes in adults with primary FSGS. Similar results have yet to be proven in children. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: This cross-sectional single-center study assessed the association of serum suPAR in children with FSGS or other glomerular and nonglomerular kidney diseases. RESULTS: This study examined 110 samples retrieved from 99 individuals (between January 2011 and April 2012), aged 1-21 years; of these individuals, 20 had primary FSGS, 24 had non-FSGS glomerular disease, 26 had nonglomerular kidney disease, and 29 were healthy controls. suPAR levels were not significantly different in children with FSGS, non-FSGS glomerular disease, and healthy controls (P>0.05). However, suPAR levels (median [25%-75%]) were higher in children with nonglomerular kidney disease (3385 pg/ml [2695-4392]) versus FSGS (2487 pg/ml [2191-3351]; P<0.05). Female patients with nephrotic-range proteinuria (U-Pr/Cr >2) had lower suPAR levels than those without proteinuria (2380 pg/ml [2116-2571] versus 3125 pg/ml [2516-4198], respectively; P<0.001). This trend was not seen among male participants; suPAR levels in all female participants were lower than in male participants (P=0.03). Thirty-four patients studied were kidney transplant recipients; transplant status was not associated with suPAR levels in patients with FSGS or non-FSGS diagnoses, independent of proteinuria, race, or sex (P>0.05). CONCLUSIONS: On the basis of these results, circulating suPAR is unlikely the leading cause for childhood idiopathic FSGS.

Maternal obesity and vitamin D sufficiency are associated with cord blood vitamin D insufficiency.

CONTEXT: An inverse relationship between total serum 25-hydroxyvitamin D (25-OH D) and increased adiposity has been established in children, adolescents, and adults. However, the relationship between neonatal adiposity and vitamin D status has not been reported. Both maternal obesity and vitamin D deficiency in pregnancy are common and are associated with adverse pregnancy outcomes. OBJECTIVE: The aim of the study was to determine the relationship between vitamin D levels in mothers and newborns, as influenced by maternal obesity, and evaluate these associations with neonatal adiposity. DESIGN, SETTING, AND PATIENTS: Sixty-one maternal-neonatal pairs participated in this cross-sectional study at an academic medical center. Mothers had a prepregnancy body mass index that was normal or obese. OUTCOME MEASURES: Maternal and cord blood sera were assayed for 25-OH D, and neonatal body composition was measured by air displacement plethysmography. RESULTS: Mothers had similar and sufficient levels of 25-OH D when measured at 36-38 wk gestation, irrespective of body mass index category (normal weight, 46.05, vs. obese, 49.84 ng/ml; P = not significant). However, cord blood 25-OH D was higher in neonates of normal-weight mothers compared to neonates of obese mothers (27.45 vs. 20.81 ng/ml; P = 0.02). The variance in cord blood 25-OH D was explained by four factors: maternal 25-OH D level, the presence of maternal obesity, maternal age, and neonatal adiposity (r(2) = 0.66). CONCLUSION: Obese women transfer less 25-OH D to offspring than normal-weight women, despite similar serum levels. Cord blood 25-OH D levels directly correlate to neonatal percentage body fat. These novel findings underscore the evolving relationships between maternal obesity, vitamin D nutritional status, and adiposity in the neonatal period that may influence subsequent childhood and adulthood vitamin D-dependent processes.

Vitamin D deficiency in children with chronic kidney disease: uncovering an epidemic.

BACKGROUND: Vitamin D deficiency in children adversely affects bone development by reducing mineralization. Children with chronic kidney disease are at risk for altered bone development from renal osteodystrophy and concomitant vitamin D deficiency. The pediatric Kidney Disease Outcomes Quality Initiative guidelines suggest measuring serum 25-hydroxyvitamin D (25[OH]D) levels if serum parathyroid hormone levels are above the target range for chronic kidney disease stages 2 and beyond, but the magnitude of vitamin D deficiency in children with chronic kidney disease is not well studied. OBJECTIVES: The purpose of this work was to determine whether children with chronic kidney disease had vitamin D deficiency, to evaluate whether the prevalence of vitamin D deficiency changed over time, and to examine seasonal and ethnic differences in 25(OH)D levels. METHODS: 25(OH)D levels in children with chronic kidney disease (stages 1-5) were measured over a 10-year period from 1987 to 1996. Data were also collected for a contemporary group of patients from 2005 to 2006. RESULTS. The prevalence of vitamin D deficiency ranged from 20% to 75% in the decade studied. There was a significant trend for decreasing 25(OH)D levels over the decade, both at the group and individual levels. Seasonal variation was noted. In our contemporary population with chronic kidney disease, the mean 25(OH)D level was 21.8 ng/mL; we found a prevalence of vitamin D deficiency of 39%. Black and Hispanic patients had lower levels of 25(OH)D than white patients. CONCLUSIONS: Children with chronic kidney disease have great risk for vitamin D deficiency, and its prevalence was increasing yearly in the studied decade. Contemporary data show that vitamin D deficiency remains a problem in these children. Sunlight exposure and ethnicity play a role in levels of 25(OH)D. Our data support the recent pediatric Kidney Disease Outcomes Quality Initiative guidelines for measurement of 25(OH)D levels in children with chronic kidney disease and secondary hyperparathyroidism.

Methylated arginine derivatives in children and adolescents with chronic kidney disease.

Asymmetric dimethylarginine (ADMA), a methylated L: -arginine (Arg) derivative is associated with endothelial dysfunction, vasoconstriction, and hypertension in animals and humans. We examined the relationship between these derivatives, estimated glomerular filtration rate (eGFR), and awake (AW) and asleep (AS) blood pressure (BP) load in children and adolescents (n = 28) with stage 2-3 chronic kidney disease (CKD) and in matched intra-familial controls (n = 10). Plasma L: -Arg, ADMA, and symmetric dimethylarginine (SDMA) levels were measured by high-performance liquid chromatography-tandem mass spectrometry. Subjects wore a 24-hr ambulatory BP monitor with BP load >95th percentile. ADMA, SDMA/ADMA ratio and SDMA were 38-200% higher in CKD patients while L: -Arg/ADMA and L: -Arg/SDMA ratios and the L: -Arg level were 11-64% lower. The eGFR explained 42-60% of L: -Arg/SDMA, SDMA/ADMA, and SDMA variability (n = 38). Using linear regression, SDMA and SDMA/ADMA separately explained 15-38% of AW and AS systolic (S) BP and diastolic (D) BP load variability (p < 0.001-0.022). Using multivariate stepwise regression with eGFR held constant, SDMA/ADMA was a significant independent variable for AW DBP load (p = 0.03). In conclusion, BP load and a disproportionate elevation of SDMA are seen in children and adolescents with stage 2-3 (mild-moderate) CKD. SDMA is a strong marker for reduced eGFR and serves as a moderate but significant indicator of 24-hr BP load variability.

Measurement of arginine derivatives in pediatric patients with chronic kidney disease using high-performance liquid chromatography-tandem mass spectrometry.

BACKGROUND: The arginine derivatives asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) interfere with endothelial nitric oxide synthesis. Plasma ADMA and SDMA have been shown to be risk factors for cardiovascular disease and/or kidney function deterioration in a variety of patient populations. METHODS: We developed a method to quantitatively measure arginine, ADMA, and SDMA using HPLC-tandem mass spectrometry. 13C6-L-Arginine was used as the internal standard, while the derivatives were separated on a silica column in less than 14 min. Plasma levels of ADMA, SDMA, and arginine were measured in children with stage II or III chronic kidney disease (CKD) and age- and gender-matched siblings. RESULTS: The chromatography exhibited no observable ion suppression in the patient specimens tested. There was no apparent carryover for any of the analytes. The assay was linear over 0.32-2.29, 0.23-4.43, and 1.00-303.89 micromol/L for ADMA, SDMA, and arginine, respectively. Plasma ADMA, SDMA, and arginine (mean+/-SD) were 1.10+/-0.35, 2.06+/-1.11, and 57.93+/-22.10 mumol/L for children with CKD, and 0.78+/-0.16, 0.71+/-0.23, and 65.29+/-21.30 micromol/L for the healthy siblings. CONCLUSIONS: The method exhibited no observable ion suppression in the patient specimens tested and has an acceptably short analytical cycle time. Children with CKD had higher levels of ADMA and SDMA than the healthy siblings.

RANKL:osteoprotegerin ratio and bone mineral density in children with untreated juvenile dermatomyositis.

OBJECTIVE: To determine bone mineral density (BMD) in patients at the time of diagnosis of juvenile dermatomyositis (DM), to compare the RANKL:osteoprotegerin (OPG) ratio in patients with juvenile DM with that in healthy control subjects, and to evaluate whether BMD is associated with the RANKL:OPG ratio and the duration of untreated disease. METHODS: Thirty-seven children with juvenile DM were enrolled. Dual x-ray absorptiometry (DXA) was performed before treatment, and Z scores for the lumbar spine (L1-L4) were determined. The duration of untreated disease was defined as the period of time from the onset of rash or weakness to the time at which DXA was performed. Serum specimens obtained at the time of DXA were analyzed for concentrations of RANKL and OPG, using enzyme-linked immunosorbent assay. The RANKL:OPG ratio was also determined in 44 age-matched healthy control subjects. RESULTS: At the time of diagnosis of juvenile DM, patients had a significantly increased RANKL:OPG ratio compared with that in healthy children (mean +/- SD 2.19 +/- 3.03 and 0.13 +/- 0.17, respectively; P < 0.0001). In patients with a lumbar spine BMD Z score of -1.5 or lower, the RANKL:OPG ratio was significantly higher than that in patients with a lumbar spine BMD Z score higher than -1.5 (P = 0.038). Lumbar spine BMD Z scores (mean +/- SD -0.13 +/- 1.19 [range -2.10 to 2.85]) were inversely associated with the duration of untreated disease (R = -0.50, P = 0.003). CONCLUSION: Children with juvenile DM have an elevated RANKL:OPG ratio at the time of diagnosis, resulting in expansion of the number of osteoclasts and activation of the bone resorptive function. This may lead to a lack of normal bone mineral accretion and a subsequent reduction in the lumbar spine BMD Z score. Patients with a longer duration of untreated juvenile DM have reduced lumbar spine BMD Z scores. These data suggest that early diagnosis could reduce the likelihood of reduced lumbar spine BMD in these patients by prompting intervention strategies at an early stage.