Refining genome-wide associated loci for serum uric acid in individuals with African ancestry.

OBJECTIVE: Serum uric acid is the end-product of purine metabolism and at high levels is a risk factor for several human diseases including gout and cardiovascular disease. Heritability estimates range from 0.32 to 0.63. Genome-wide association studies (GWAS) provide an unbiased approach to identify loci influencing serum uric acid. Here, we performed the first GWAS for serum uric acid in continental Africans, with replication in African Americans. METHODS: Africans (n = 4126) and African Americans (n = 5007) were genotyped on high-density GWAS arrays. Efficient mixed model association, a variance component approach, was used to perform association testing for a total of ~ 18 million autosomal genotyped and imputed variants. CAVIARBF was used to fine map significant regions. RESULTS: We identified two genome-wide significant loci: 4p16.1 (SLC2A9) and 11q13.1 (SLC22A12). At SLC2A9, the most strongly associated SNP was rs7683856 (P = 1.60 × 10-44). Conditional analysis revealed a second signal indexed by rs6838021 (P = 5.75 × 10-17). Gene expression and regulatory motif data prioritized a single-candidate causal variant for each signal. At SLC22A12, the most strongly associated SNP was rs147647315 (P = 6.65 × 10-25). Conditional analysis and functional annotation prioritized the missense variant rs147647315 (R (Arg) > H (His)) as the sole causal variant. Functional annotation of these three signals implicated processes in skeletal muscle, subcutaneous adipose tissue and the kidneys, respectively. CONCLUSIONS: This first GWAS of serum uric acid in continental Africans identified three associations at two loci, SLC2A9 and SLC22A12. The combination of weak linkage disequilibrium in Africans and functional annotation led to the identification of candidate causal SNPs for all three signals. Each candidate causal variant implicated a different cell type. Collectively, the three associations accounted for 4.3% of the variance of serum uric acid.

Distinct inflammatory profile in preeclampsia and postpartum preeclampsia reveal unique mechanisms.

Preeclampsia (PE) is a poorly understood pregnancy complication. It has been suggested that changes in the maternal immune system may contribute to PE, but evidence of this remains scarce. Whilst PE is commonly experienced prepartum, it can also occur in the postpartum period (postpartum PE-PPPE), and the mechanisms involved are unknown. Our goal was to determine whether changes occur in the maternal immune system and placenta in pregnancies complicated with PE and PPPE, compared to normal term pregnancies. We prospectively recruited women and collected blood samples to determine the circulating immune profile, by flow cytometry, and assess the circulating levels of inflammatory mediators and angiogenic factors. Placentas were collected for histological analysis. Levels of alarmins in the maternal circulation showed increased uric acid in PE and elevated high-mobility group box 1 in PPPE. Analysis of maternal immune cells revealed distinct profiles in PE vs PPPE. PE had increased percentage of lymphocytes and monocytes whilst PPPE had elevated NK and NK-T cells as well. Elevated numbers of immune cells (CD45+) were detected in placentas from women that developed PPPE, and those were macrophages (CD163+). This work reveals changes within the maternal immune system in both PE and PPPE, and indicate a striking contrast in how this occurs. Importantly, elevated immune cells in the placenta of women with PPPE strongly suggest a prenatal initiation of the pathology. A better understanding of these changes will be beneficial to identify women at high risk of PPPE and to develop novel therapeutic targets.

Persistent elevation of fibroblast growth factor 23 concentrations in healthy appropriate-for-gestational-age preterm infants.

OBJECTIVE: To explore the temporal evolution of 25-hydroxyvitamin D [25(OH)D], its epimer, parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), and minerals in healthy appropriate-for-gestational-age preterms. PATIENTS: A prospective study was undertaken in infants born at 28-32 weeks with monitoring at 1, 3, 5 weeks and term. METHODS: Morning plasma and urine calcium; phosphorus; creatinine; PTH, C-terminal and intact FGF23 (iFGF23) and liquid chromatography-tandem mass spectrometry measurements of 25(OH)D were undertaken. Analyses included regression models. RESULTS: Some 11 infants (5 males) were recruited at a median gestational age of 31.2 weeks (interquartile range: 28.1-31.8). Standard chemistries were normal. No infant was vitamin D deficient; 58% achieved 50 nmol/L with a median intake of 540 IU/day. High concentrations of C-3 epimer were detected. iFGF23 and C-terminal concentrations were persistently elevated (double and ten times adult norms, respectively). Tubular resorption of phosphorus was normal (88%±8%). CONCLUSIONS: Most infants achieved acceptable 25(OH)D3 concentrations. The biologic significance of the elevated FGF23 is unclear.

The granin VGF promotes genesis of secretory vesicles, and regulates circulating catecholamine levels and blood pressure.

Secretion of proteins and neurotransmitters from large dense core vesicles (LDCVs) is a highly regulated process. Adrenal LDCV formation involves the granin proteins chromogranin A (CgA) and chromogranin B (CgB); CgA- and CgB-derived peptides regulate catecholamine levels and blood pressure. We investigated function of the granin VGF (nonacronymic) in LDCV formation and the regulation of catecholamine levels and blood pressure. Expression of exogenous VGF in nonendocrine NIH 3T3 fibroblasts resulted in the formation of LDCV-like structures and depolarization-induced VGF secretion. Analysis of germline VGF-knockout mouse adrenal medulla revealed decreased LDCV size in noradrenergic chromaffin cells, increased adrenal norepinephrine and epinephrine content and circulating plasma epinephrine, and decreased adrenal CgB. These neurochemical changes in VGF-knockout mice were associated with hypertension. Germline knock-in of human VGF1-615 into the mouse Vgf locus rescued the hypertensive knockout phenotype, while knock-in of a truncated human VGF1-524 that lacks several C-terminal peptides, including TLQP-21, resulted in a small but significant increase in systolic blood pressure compared to hVGF1-615 mice. Finally, acute and chronic administration of the VGF-derived peptide TLQP-21 to rodents decreased blood pressure. Our studies establish a role for VGF in adrenal LDCV formation and the regulation of catecholamine levels and blood pressure.

Aging and human hormonal and pressor responsiveness to angiotensin II infusion with simultaneous measurement of exogenous and endogenous angiotensin II.

A decline in the function of the renin angiotensin aldosterone system may induce adaptive changes in response to angiotensin II (ANG II) with age. We have examined platelet ANG II receptor density, blood pressure and aldosterone responses to ANG II [Asn1, Val5-ANG II] (Hypertensin, Ciba Geigy, Horsham, Sussex, England) infusion in 8 young, 24 to 30 years, and 8 older, 54 to 65 years, healthy volunteers. To measure circulating ANG II, we established a new method for specific and simultaneous measurement of exogenous [Asn1, Val5] (Hypertensin) and endogenous [Asp1,Ile5] ANG II in plasma by using isocratic HPLC and radioimmunoassays with cross-reacting antibodies and compared results with immunoreactive ANG II which was measured conventionally using monoclonal antibodies. Baseline endogenous ANG II (Asp1,Ile5-ANG II) levels in venous plasma were marginally, but not significantly, lower in the old [mean (95% confidence limits): 3.4 (< 0.1 to 7.7) v 3.7 (1.2 to 6.2), fmol/mL] and during suppression by the Hypertensin infusion appeared consistently, but not significantly, lower in the old [0.9 (0 to 3.1) v 2.1 (0.6 to 3.7), after 3 ng/kg/min], while the same infusion rate in young and old resulted in similar plasma Hypertensin levels. Baseline systolic blood pressure (SBP) was similar in both groups but the percentage increases in SBP at infusion rates of 1, 3.0, and 10 ng/kg/min were greater in the old than in the young (9.1 v 2.8, P < .05; 16.3 v 8.0, P < .01; 30.4 v 14.0%, P < .001, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

[Therapy of Bartter syndrome with indomethacin]. / Zur Therapie des Bartter-Syndroms mit Indomethazin.

In two children with typical clinical and laboratory findings of the B. S., the therapeutic effect of the prostaglandin synthetase inhibitor indomethacin could be unequivocally proved in balance studies performed under inpatient conditions. Under this medication, the serum potassium rose significantly and the potassium balance became positive. In parallel to this, the plasma renin (and in the case in which it could be regularly investigated also the plasma aldosterone) fell significantly. In one of the two patients, the hypertensin-test was performed before and under indomethacin treatment; the initial angiotensin resistance could be eliminated by Indocid. Both children have now already received Indocid for twenty-four and sixteen months. The preparation was adequately tolerated, and the clinical symptoms of B. S. have largely subsided. Noteworthy is a substantial catching up of growth in one of the two patients. Despite normal renin and aldosterone values, there was no complete normalization of the serum potassium, indicating that besides the elevation of certain renal prostaglandins in the pathogenesis of B. S. described by several authors, an additional (probably superordinate) mechanism is likely to play a role.

The half-lives of angiotensin II, angiotensin II-amide, angiotensin III, Sar1-Ala8-angiotensin II and renin in the circulatory system of the rat.

1. Methods are described for estimating the half-life of angiotensin analogues and renin in the rat, from the time course of the blood pressure changes they evoke. 2. The following half-life values were measured: angiotensin II, 16 +/- 1 sec; angiotensin III, 14 +/- 1 sec; angiotensin II-amide, 15 +/- 1 sec; Sar1-Ala8-angiotensin II, 6.4 +/- 0.6 min; renin, 3.0 +/- 0.4 min. The distribution volume of angiotensin was found to be 18 ml./kg body wt. 3. It is inferred that the Asp1 residue does not reduce the rate of angiotensin II catabolism, but that substitution of this residue by sarcosine may inhibit catabolism while substitution by asparagine has no effect. 4. Five experimental criteria were identified which indicate that these methods give reliable estimates of the half-life. It is suggested that these results are more accurate than most previous half-life estimates. 5 When tachyphylaxis to angiotensin II-amide occurs, the pressor activity of the plasma is not reduced.