Genome-wide association identifies nine common variants associated with fasting proinsulin levels and provides new insights into the pathophysiology of type 2 diabetes.

OBJECTIVE: Proinsulin is a precursor of mature insulin and C-peptide. Higher circulating proinsulin levels are associated with impaired β-cell function, raised glucose levels, insulin resistance, and type 2 diabetes (T2D). Studies of the insulin processing pathway could provide new insights about T2D pathophysiology. RESEARCH DESIGN AND METHODS: We have conducted a meta-analysis of genome-wide association tests of ∼2.5 million genotyped or imputed single nucleotide polymorphisms (SNPs) and fasting proinsulin levels in 10,701 nondiabetic adults of European ancestry, with follow-up of 23 loci in up to 16,378 individuals, using additive genetic models adjusted for age, sex, fasting insulin, and study-specific covariates. RESULTS: Nine SNPs at eight loci were associated with proinsulin levels (P < 5 × 10(-8)). Two loci (LARP6 and SGSM2) have not been previously related to metabolic traits, one (MADD) has been associated with fasting glucose, one (PCSK1) has been implicated in obesity, and four (TCF7L2, SLC30A8, VPS13C/C2CD4A/B, and ARAP1, formerly CENTD2) increase T2D risk. The proinsulin-raising allele of ARAP1 was associated with a lower fasting glucose (P = 1.7 × 10(-4)), improved β-cell function (P = 1.1 × 10(-5)), and lower risk of T2D (odds ratio 0.88; P = 7.8 × 10(-6)). Notably, PCSK1 encodes the protein prohormone convertase 1/3, the first enzyme in the insulin processing pathway. A genotype score composed of the nine proinsulin-raising alleles was not associated with coronary disease in two large case-control datasets. CONCLUSIONS: We have identified nine genetic variants associated with fasting proinsulin. Our findings illuminate the biology underlying glucose homeostasis and T2D development in humans and argue against a direct role of proinsulin in coronary artery disease pathogenesis

Nuclear magnetic resonance and conformational investigations of the pentasaccharide of the Forssman antigen and overlapping di-, tri-, and tetra-saccharide sequences

The 1H and 13C NMR parameters, i.e., chemical shifts and coupling constants, for the pentasaccharide of the Forssman antigen and overlapping di-, tri-, and tetra-saccharide sequences thereof have been measured and assigned completely using 1D and 2D techniques, and the oligosaccharide structures have thereby been confirmed. Nuclear Overhauser effect (NOE) experiments have been carried out at three different temperatures to assess the preferred conformations of the pentasaccharide and the component oligosaccharides. The conformational preferences of the compounds mentioned above have subsequently been investigated by theoretical calculations. The flexibity and dynamics of the molecules have been studied by Metropolis Monte Carlo simulations using a modified HSEA force field, and ensemble average data have been generated and compared to data obtained experimentally

A STRATEGY FOR ISOLATION AND STRUCTURAL ANALYSIS OF GLYCOPROTEIN OLIGOSACCHARIDES

A general strategy is described for release, separation and structural analysis of Nand O-linked glycans from glycoproteins. Following sugar analysis, to determine the monosaccharide composition and the total carbohydrate content, the glycoprotein is degraded by chemical and/or enzymatic methods. The N- and O-linked glycans are separated and further fractionated into pure compoundsby gelfiltration, affinity chromatography and high performance ion exchange chromatography. Structural analysis is carried out by chemical analyses, fast atom bombardment mass spectrometry and 500 MHz 1H-NMR spectroscopy. Complete structural analysis is obtained of each glycan as well as determination of the glycosylationsites

Oligosaccharides from feces of preterm infants fed on breast milk

Nine neutral and five acidic oligosaccharides were isolated from feces of a preterm (30th postmenstrual week) blood group A nonsecretor infant fed on pooled breast milk. Structural analyses were carried out using sugar and methylation analyses, fast atom bombardment mass spectrometry, and 1H NMR. The acidic oligosaccharides are well-known components of human milk. The neutral oligosaccharides are characteristic of nonsecretor milk. Surprisingly, no secretor gene-dependent oligosaccharides were present in the feces. Another preterm (27th postmenstrual week) blood group A, secretor infant fed on pooled breast milk showed the same fecal oligosaccharide pattern as above during the first week after birth, despite being a secretor individual. Also notable was the absence of blood group A-active oligosaccharides in this sample. Another sample of feces collected 8 weeks later from the latter infant contained the expected blood group A-active oligosaccharides. Furthermore, free sialic acid was present at the cost of the sialyl oligosaccharides seen earlier. Thus, infants born prematurely do not show the same degree of development of oligosaccharide metabolism as their more mature counterparts

Oligosaccharides from faeces of a blood-group B, breast-fed infant

Eight oligosaccharides have been isolated from faeces of a blood group B, secretor, breast-fed infant and characterized by sugar and methylation analysis, f.a.b. mass spectrometry and 1H-n.m.r. spectroscopy. One of these oligosaccharides has not previously been reported and is a tri-L-fucosyl derivative of lacto-N-hexaose. The other compounds were identical to oligosaccharides found in human milk. Several of the reported compounds require the secretor dependent 2'-fucosyltransferase for their biosynthesis. Since the mother of this child was an O(H) non-secretor, an intestinal biosynthesis of at least some of these compounds is strongly indicated. No blood group B active oligosaccharides were detected which is in sharp contrast to the oligosaccharide excretion in faeces from a blood group A infant [Sabharwal et al., Mol. Immunol., 21 (1984) 1105-1112] in which all the major oligosaccharides isolated were blood group A active