In mammals, ceramide kinase (CerK)-mediated phosphorylation of ceramide is the only known pathway to ceramide-1-phosphate (C1P), a recently identified signaling sphingolipid metabolite. To help delineate the roles of CerK and C1P, we knocked out the gene of CerK in BALB/c mice by homologous recombination. All in vitro as well as cell-based assays indicated that CerK activity is completely abolished in Cerk−/− mice. Labeling with radioactive orthophosphate showed a profound reduction in the levels of de novo C1P formed in Cerk−/− macrophages. Consistently, mass spectrometry analysis revealed a major contribution of CerK to the formation of C16-C1P. However, the significant residual C1P levels in Cerk−/− animals indicate that alternative routes to C1P exist. Furthermore, serum levels of proapoptotic ceramide in these animals were significantly increased while levels of dihydroceramide as the biosynthetic precursor were reduced. Previous literature pointed to a role of CerK or C1P in innate immune cell function. Using a variety of mechanistic and disease models, as well as primary cells, we found that macrophage- and mast cell-dependent readouts are barely affected in the absence of CerK. However, the number of neutrophils was strikingly reduced in blood and spleen of Cerk−/− animals. When tested in a model of fulminant pneumonia, Cerk−/− animals developed a more severe disease, lending support to a defect in neutrophil homeostasis following CerK ablation. These results identify ceramide kinase as a key regulator of C1P, dihydroceramide and ceramide levels, with important implications for neutrophil homeostasis and innate immunity regulation.

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Summary Background Eighty percent of adolescents with severe obesity suffer from non‐alcoholic fatty liver disease (NAFLD). Non‐invasive prediction models have been tested in adults, however, they performed poorly in paediatric populations. Objective This study aimed to investigate novel biomarkers for NAFLD and to develop a score that predicts liver fat in youth with severe obesity. Methods From a population with a BMI >97th percentile aged 9‐19 years (n = 68), clinically thoroughly characterized including MRI‐derived proton density fat fraction (MRI‐PDFF), amino acids and acylcarnitines were measured by HPLC‐MS. Results In children with NAFLD, higher levels of plasma branched‐chain amino acids (BCAA) were determined. BCAAs correlated with MRI‐PDFF (R = 0.46, p < .01). We identified a linear regression model adjusted for age, sex and pubertal stage consisting of BCAAs, ALT, GGT, ferritin and insulin that predicted MRI‐PDFF (R = 0.75, p < .01). ROC analysis of this model revealed AUCs of 0.85, 0.85 and 0.92 for the detection of any, moderate and severe steatosis, respectively, thus markedly outperforming previously published scores. Conclusion BCAAs could be an important link between obesity and other metabolic pathways. A BCAA‐based metabolic score can predict steatosis grade in high‐risk children and adolescents and may provide a feasible alternative to sophisticated methods like MRI or biopsy in the future.

Background Obesity-associated chronic low-grade inflammation leads to dysregulation of central lipid and glucose metabolism pathways leading to metabolic disorders. MicroRNAs (miRNAs) are known to control regulators of metabolic homeostasis. We aimed to assess the relationship of circulating miRNAs with inflammatory modulators and metabolic disorders in pediatric obesity. Methods From a pediatric cohort with severe obesity (n = 109), clinically thoroughly characterized including diverse routine blood parameters, oral glucose tolerance test, and liver MRI, a panel of 16 circulating miRNAs was quantified using qRT-PCR. Additionally, markers of inflammation TNFα, IL1 receptor antagonist, procalcitonin, CRP, and IL-6 were measured. Results Markers of obesity-associated inflammation, TNFα, IL-1Ra, and procalcitonin, all significantly correlated with concentrations of miRNAs 122 and 192. Concentrations of these miRNAs negatively correlated with serum adiponectin and were among those strongly linked to parameters of dyslipidemia and liver function. Moreover, miRNA122 concentrations correlated with HOMA-IR. Several miRNA levels including miRNAs 34a, 93, 122, and 192 were statistically significantly differing between individuals with prediabetes, impaired glucose tolerance, metabolic syndrome, or nonalcoholic fatty liver disease compared to the respective controls. Additionally, miRNA 192 was significantly elevated in metabolically unhealthy obesity. Conclusions A miRNA pattern associated with obesity-associated inflammation and comorbidities may be used to distinguish metabolically healthy from unhealthy pediatric patients with obesity. Moreover, these changes in epigenetic regulation could potentially be involved in the etiology of obesity-linked metabolic disease in children and adolescents.