👤 Belen Barcelona

Age at menarche and age at natural menopause occur significantly earlier in African American women than in other ethnic groups. African American women also have twice the prevalence of cardiometabolic disorders related to the timing of these reproductive traits. The objectives of this integrative review were to (a) summarize the genome-wide association studies of reproductive traits in African American women, (b) identify genes that overlap with reproductive traits and cardiometabolic risk factors in African American women, and (c) propose biological mechanisms explaining the link between reproductive traits and cardiometabolic risk factors. PubMed was searched for genome-wide association studies of genes associated with reproductive traits in African American women. After extracting and summarizing the primary genes, we examined whether any of the associations with reproductive traits had also been identified with cardiometabolic risk factors in African American women. Seven studies met the inclusion criteria. Associations with both reproductive and cardiometabolic traits were reported in or near the following genes: FTO, SEC16B, TMEM18, APOE, PHACTR1, KCNQ1, LDLR, PIK3R1, and RORA. Biological pathways implicated include body weight regulation, vascular homeostasis, and lipid metabolism. A better understanding of the genetic basis of reproductive traits in African American women may provide insight into the biological mechanisms linking variation in these traits with increased risk for cardiometabolic disorders in this population. Show less

The urea cycle disease carbamoyl-phosphate synthetase deficiency (CPS1D) has been associated with many mutations in the CPS1 gene [Häberle et al., 2011. Hum Mutat 32:579-589]. The disease-causing potential of most of these mutations is unclear. To test the mutations effects, we have developed a system for recombinant expression, mutagenesis, and purification of human carbamoyl-phosphate synthetase 1 (CPS1), a very large, complex, and fastidious enzyme. The kinetic and molecular properties of recombinant CPS1 are essentially the same as for natural human CPS1. Glycerol partially replaces the essential activator N-acetyl-l-glutamate (NAG), opening possibilities for treating CPS1D due to NAG site defects. The value of our expression system for elucidating the effects of mutations is demonstrated with eight clinical CPS1 mutations. Five of these mutations decreased enzyme stability, two mutations drastically hampered catalysis, and one vastly impaired NAG activation. In contrast, the polymorphisms p.Thr344Ala and p.Gly1376Ser had no detectable effects. Site-limited proteolysis proved the correctness of the working model for the human CPS1 domain architecture generally used for rationalizing the mutations effects. NAG and its analogue and orphan drug N-carbamoyl-l-glutamate, protected human CPS1 against proteolytic and thermal inactivation in the presence of MgATP, raising hopes of treating CPS1D by chemical chaperoning with N-carbamoyl-l-glutamate. Show less

We previously reported that isobutylmethylxanthine (IBMX), a derivative of oxypurine, inhibits citrulline synthesis by an as yet unknown mechanism. Here, we demonstrate that IBMX and other oxypurines containing a 2,6-dione group interfere with the binding of glutamate to the active site of N-acetylglutamate synthetase (NAGS), thereby decreasing synthesis of N-acetylglutamate, the obligatory activator of carbamoyl phosphate synthase-1 (CPS1). The result is reduction of citrulline and urea synthesis. Experiments were performed with (15)N-labeled substrates, purified hepatic CPS1, and recombinant mouse NAGS as well as isolated mitochondria. We also used isolated hepatocytes to examine the action of various oxypurines on ureagenesis and to assess the ameliorating affect of N-carbamylglutamate and/or l-arginine on NAGS inhibition. Among various oxypurines tested, only IBMX, xanthine, or uric acid significantly increased the apparent K(m) for glutamate and decreased velocity of NAGS, with little effect on CPS1. The inhibition of NAGS is time- and dose-dependent and leads to decreased formation of the CPS1-N-acetylglutamate complex and consequent inhibition of citrulline and urea synthesis. However, such inhibition was reversed by supplementation with N-carbamylglutamate. The data demonstrate that xanthine and uric acid, both physiologically occurring oxypurines, inhibit the hepatic synthesis of N-acetylglutamate. An important and novel concept emerging from this study is that xanthine and/or uric acid may have a role in the regulation of ureagenesis and, thus, nitrogen homeostasis in normal and disease states. Show less

Carbamoyl phosphate synthetase 1 (CPS1) plays a paramount role in liver ureagenesis since it catalyzes the first and rate-limiting step of the urea cycle, the major pathway for nitrogen disposal in humans. CPS1 deficiency (CPS1D) is an autosomal recessive inborn error which leads to hyperammonemia due to mutations in the CPS1 gene, or is caused secondarily by lack of its allosteric activator NAG. Proteolytic, immunological and structural data indicate that human CPS1 resembles Escherichia coli CPS in structure, and a 3D model of CPS1 has been presented for elucidating the pathogenic role of missense mutations. Recent availability of CPS1 expression systems also can provide valuable tools for structure-function analysis and pathogenicity-testing of mutations in CPS1. In this paper, we provide a comprehensive compilation of clinical CPS1 mutations, and discuss how structural knowledge of CPS enzymes in combination with in vitro analyses can be a useful tool for diagnosis of CPS1D. Show less

Carbamoyl-phosphate synthetase I (CPS1) deficiency (CPS1D), a recessively inherited urea cycle error due to CPS1 gene mutations, causes life-threatening hyperammonemia. The disease-causing potential of missense mutations in CPS1 deficiency can be ascertained with the recombinant CPS1 expression and purification system reported here, which uses baculovirus and insect cells. We study with this system the effects of nine clinical mutations and one polymorphism on CPS1 solubility, stability, activity, and kinetic parameters for NAG. Five of the mutations (p.T471N, p.Q678P, p.P774L, p.R1453Q, and p.R1453W) are first reported here, in three severe CPS1D patients. p.P774L, p.R1453Q, and p.R1453W inactivate CPS1, p.T471N and p.Y1491H greatly decrease the apparent affinity for NAG, p.Q678P hampers correct enzyme folding, and p.S123F, p.H337R, and p.P1411L modestly decrease activity. p.G1376S is confirmed a trivial polymorphism. The effects of the C-terminal domain mutations are rationalized in the light of this domain crystal structure, including the NAG site structure [Pekkala et al. Biochem J 424:211-220]. The agreement of clinical observations and in vitro findings, and the possibility to identify CPS1D patients who might benefit from specific treatment with NAG analogues because they exhibit reduced affinity for NAG highlight the value of this novel CPS1 expression/purification system. Show less