Ve controls and methylation data were further normalized using quantile normalization [37]. ComBat was used

Ve controls and methylation data were further normalized using quantile normalization [37]. ComBat was used to adjust for batch effects between arrays [38]. A linear regression model was used to identify differences in DNA methylation between control and palmitate-treated islets in a paired fashion as described elsewhere [39]. As -values are biologically easier to interpret, M-values were reconverted to -values when describing the DNA methylation results. The DNA methylation probes on the Infinium HumanMethylation450K BeadChip have been annotated to different genomic regions depending on their location in relation to a gene or a CpG island [33].Hall PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/28154141 et al. BMC Medicine 2014, 12:103 http://www.biomedcentral.com/1741-7015/12/Page 4 ofFigure 1 Study design and work flow. Study design for the lipotoxicity study in human pancreatic islets is presented in panel a Work flow for the analysis of mRNA expression data in combination with DNA methylation data in human pancreatic islets exposed to palmitate is presented in panel b.KEGG pathway analysisKyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of expression data was performed with the online tool WebGestalt [40,41] (accessed 27 March 2012 and 12 February 2014). For the pathway analysis of mRNA expression data, Affymetrix probe IDs were used to identify unique genes and AffymetrixGeneChip?Human Gene 1.0 ST genes were used as background in this analysis. For the pathway analysis of the DNA methylation data, the gene symbol was used to identify unique genes and the human genome was used as background in this analysis. The Benjamini and Hochberg method was used to correct P-values for multiple testing.Hall et al. BMC Medicine 2014, 12:103 http://www.biomedcentral.com/1741-7015/12/Page 5 ofGlucose-stimulated insulin secretionGlucose-stimulated insulin secretion was analyzed in control and palmitate-treated human islets from nine donors. After 48 h culture in control or palmitate-containing medium, 10 replicates of 10 human islets per culture condition (control and palmitate-treated) and donor were pre-incubated in HEPES-balanced salt solution (HBSS) containing (in mM) 114 NaCl, 4.7 KCl, 1.2 KH2PO4, 1.16 MgSO4, 20 HEPES, 25.5 NaHCO3, 2.5 CaCl2 at pH 7.2 with 0.575 BSA and 3.3 mM purchase Lasalocid (sodium) glucose (1.65 mM glucose for one sample) for 1 h at 37 . Thereafter, for each donor, glucose was added to five of the replicates to a final concentration of 16.7 mM glucose (15.05 mM glucose for one sample) to study glucose-stimulated insulin secretion and the other five replicates were kept in 3.3 mM glucose to study basal insulin secretion and the incubation was continued for one more hour. The supernatant was immediately removed and the insulin concentration in the medium was measured by radioimmunoassay (RIA) (Millipore, Uppsala, Sweden).Assessment of apoptosis in human pancreatic isletsas mean ?standard error of mean (sem), unless stated otherwise.ResultsImpaired insulin secretion in human islets exposed to palmitateTo investigate the physiological response to 1 mM palmitate treatment for 48 h, we measured glucose-stimulated insulin secretion in human islets cultured under control (5.56 mM glucose) or lipotoxic (5.56 mM glucose and 1 mM palmitate) conditions. We found decreased glucosestimulated insulin secretion measured as fold change (insulin secretion at high glucose levels/insulin secretion at low glucose levels) in the palmitate-treated compared with control-treated human islets (Figure 2a). We also.