Skin biomarkers predict development of atopic dermatitis in infancy.

BACKGROUND: There is currently no insight into biomarkers that can predict the onset of pediatric atopic dermatitis (AD). METHODS: Nested in a prospective birth cohort study that examined the occurrence of physician-diagnosed AD in 300 children, 44 random children with onset of AD in the first year of life were matched on sex and season of birth with 44 children who did not develop AD. Natural moisturizing factor (NMF), corneocyte surface protrusions, cytokines, free sphingoid bases (SBs) of different chain lengths and their ceramides were analyzed from tape strips collected at 2 months of age before onset of AD using liquid chromatography, atomic force microscopy, multiplex immunoassay, and liquid chromatography mass spectrometry, respectively. RESULTS: Significant alterations were observed for four lipid markers, with phytosphingosine ([P]) levels being significantly lower in children who developed AD compared with children who did not (median 240 pmol/mg vs. 540 pmol/mg, p < 0.001). The two groups of children differed in the relative amounts of SB of different chain lengths (C17, C18 and C20). Thymus- and activation-regulated chemokine (TARC/CCL17) was slightly higher in children who developed AD, whereas NMF and corneocyte surface texture were similar. AD severity assessed by the eczema area and severity index (EASI) at disease onset was 4.2 (2.0;7.2). [P] had the highest prediction accuracy among the biomarkers (75.6%), whereas the combination of 5 lipid ratios gave an accuracy of 89.4%. CONCLUSION: This study showed that levels and SB chain length were altered in infants who later developed AD, and that TARC/CCL17 levels were higher.

Glucosylated cholesterol in mammalian cells and tissues: formation and degradation by multiple cellular ß-glucosidases.

The membrane lipid glucosylceramide (GlcCer) is continuously formed and degraded. Cells express two GlcCer-degrading ß-glucosidases, glucocerebrosidase (GBA) and GBA2, located in and outside the lysosome, respectively. Here we demonstrate that through transglucosylation both GBA and GBA2 are able to catalyze in vitro the transfer of glucosyl-moieties from GlcCer to cholesterol, and vice versa. Furthermore, the natural occurrence of 1-O-cholesteryl-ß-D-glucopyranoside (GlcChol) in mouse tissues and human plasma is demonstrated using LC-MS/MS and (13)C6-labeled GlcChol as internal standard. In cells, the inhibition of GBA increases GlcChol, whereas inhibition of GBA2 decreases glucosylated sterol. Similarly, in GBA2-deficient mice, GlcChol is reduced. Depletion of GlcCer by inhibition of GlcCer synthase decreases GlcChol in cells and likewise in plasma of inhibitor-treated Gaucher disease patients. In tissues of mice with Niemann-Pick type C disease, a condition characterized by intralysosomal accumulation of cholesterol, marked elevations in GlcChol occur as well. When lysosomal accumulation of cholesterol is induced in cultured cells, GlcChol is formed via lysosomal GBA. This illustrates that reversible transglucosylation reactions are highly dependent on local availability of suitable acceptors. In conclusion, mammalian tissues contain GlcChol formed by transglucosylation through ß-glucosidases using GlcCer as donor. Our findings reveal a novel metabolic function for GlcCer.

Contributions of amino acid, acylcarnitine and sphingolipid profiles to type 2 diabetes risk among South-Asian Surinamese and Dutch adults.

INTRODUCTION: People of South Asian origin are at high risk of type 2 diabetes (T2D), but the underpinning mechanisms are not fully understood. We determined ethnic differences in acylcarnitine, amino acid and sphingolipid concentrations and determined the associations with T2D. RESEARCH DESIGN AND METHODS: Associations between these metabolites and incident T2D among Dutch and South-Asian Surinamese were determined in participants from the Healthy Life in an Urban Setting (HELIUS) study (Amsterdam, the Netherlands) using Prentice-weighted Cox regression. The HELIUS study includes 95 incident T2D cases and a representative subcohort of 700 people from a cohort of 5977 participants with a mean follow-up of 4 years. RESULTS: Concentrations of acylcarnitines were comparable between both ethnic groups. Amino acid and lactosylceramide concentrations were higher among South-Asian Surinamese than Dutch (eg, isoleucine 65.7 (SD 16.3) vs 60.7 (SD 15.6) µmol/L). Ceramide concentrations were lower among South-Asian Surinamese than Dutch (eg, Cer d18:1 8.48 (SD 2.04) vs 9.08 (SD 2.29) µmol/L). Metabolic dysregulation preceded T2D without evidence for a multiplicative interaction by ethnicity. Most amino acids and (dihydro)ceramides were associated with increased risk (eg, Cer d18:1 HR 2.38, 95% CI 1.81 to 3.12) while acylcarnitines, glycine, glutamine and lactosylceramides were associated with decreased risk for T2D (eg, LacCer d18:2 HR 0.56, 95% CI 0.42 to 0.77). CONCLUSIONS: Overall, these data suggest that the disturbances underlying amino acid and sphingolipid metabolism may be predictive of T2D risk in populations of both South Asian and European background. These observations may be used as starting point to unravel the underlying metabolic disturbances.

Detection of chitinase activity by 2-aminobenzoic acid labeling of chito-oligosaccharides.

Chitinases are hydrolases capable of hydrolyzing the abundant natural polysaccharide chitin. Next to artificial fluorescent substrates, more physiological chito-oligomers are commonly used in chitinase assays. Analysis of chito-oligosaccharides products is generally accomplished by UV detection. However, the relatively poor sensitivity poses a serious limitation. Here we report on a novel, much more sensitive assay for the detection of chito-oligosaccharide reaction products released by chitinases, based on fluorescent detection, following chemical labeling by 2-aminobenzoic acid. Comparison with existing UV-based assays, shows that the novel assay offers the same advantages yet allows detection of chito-oligosaccharides in the low picomolar range.

Prominent increase in plasma ganglioside GM3 is associated with clinical manifestations of type I Gaucher disease.

BACKGROUND: Patients with Gaucher disease show signs of insulin resistance. The ganglioside GM3 has recently shown to be a negative regulator of insulin sensitivity. In fibroblasts of Gaucher patients, deficient in degradation of glucosylceramide, an increased anabolism of this lipid to gangliosides occurs. The goal of the current study was to establish whether GM3 is elevated in plasma of type I Gaucher disease patients, and is related to disease manifestations. METHODS: Plasma GM3, glucosylceramide, and ceramide were determined and compared to overall severity of disease, hepatomegaly, and plasma chitotriosidase activity. RESULTS: The ceramide concentration in plasma of untreated Gaucher patients was slightly but not significantly lower than in controls (median: 9.8 micromol/L, range: 5.7-14.7 micromol/L, (n=40) vs. median: 11.0 micromol/L, range: 5.1-18.0 micromol/L, (n=30)). Glucosylceramide was significantly (p<0.0001) elevated. GM3 was also significantly (p<0.0001) increased (median: 10.2 micromol/L, range: 4.3-19.1 micromol/L, (n=40) vs. median: 3.6 micromol/L, range: 2.7-5.4 micromol/L, (n=30)). Plasma GM3 concentrations correlated with those of plasma chitotriosidase activity (rho=0.45, p=0.0036), overall severity of disease (rho=0.39, p=0.012), and hepatomegaly (rho=0.49, p=0.0015). CONCLUSIONS: GM3 is strikingly elevated in plasma of most Gaucher patients. The increase is comparable to that of glucosylceramide, the primary storage lipid. The marked elevations in GM3 may play a role in the insulin resistance of Gaucher patients.

Ethnic differences in metabolite signatures and type 2 diabetes: a nested case-control analysis among people of South Asian, African and European origin.

Accumulation of metabolites may mark or contribute to the development of type 2 diabetes mellitus (T2D), but there is a lack of data from ethnic groups at high risk. We examined sphingolipids, acylcarnitines and amino acids, and their association with T2D in a nested case-control study among 54 South Asian Surinamese, 54 African Surinamese and 44 Dutch in the Netherlands. Plasma metabolites were determined at baseline (2001-2003), and cumulative prevalence and incidence of T2D at follow-up (2011-2012). Weighted linear and logistic regression analyses were used to study associations. The mean level of most sphingolipids was lower, and amino-acid levels higher, in the Surinamese groups than among the Dutch. Surinamese individuals had higher mono- and polyunsaturated acylcarnitines and lower plasma levels of saturated acylcarnitine species than the Dutch. Several sphingolipids and amino acids were associated with T2D. Although only the shorter acylcarnitines seemed associated with prevalent T2D, we found an association of all acylcarnitines (except C0, C18 and C18:2) with incident T2D. Further analyses suggested a potentially different association of several metabolites across ethnic groups. Extension and confirmation of these findings may improve the understanding of ethnic differences and contribute to early detection of increased individual risk.

Common G102S polymorphism in chitotriosidase differentially affects activity towards 4-methylumbelliferyl substrates.

Chitotriosidase (CHIT1) is a chitinase that is secreted by activated macrophages. Plasma chitotriosidase activity reflects the presence of lipid-laden macrophages in patients with Gaucher disease. CHIT1 activity can be conveniently measured using fluorogenic 4-methylumbelliferyl (4MU)-chitotrioside or 4MU-chitobioside as the substrate, however, nonsaturating concentrations have to be used because of apparent substrate inhibition. Saturating substrate concentrations can, however, be used with the newly designed substrate 4MU-deoxychitobioside. We studied the impact of a known polymorphism, G102S, on the catalytic properties of CHIT1. The G102S allele was found to be common in type I Gaucher disease patients in the Netherlands ( approximately 24% of alleles). The catalytic efficiency of recombinant Ser102 CHIT1 was approximately 70% that of wild-type Gly102 CHIT1 when measured with 4MU-chitotrioside at a nonsaturating concentration. However, the activity was normal with 4MU-deoxychitobioside as the substrate at saturating concentrations, consistent with predictions from molecular dynamics simulations. In conclusion, interpretation of CHIT1 activity measurements with 4MU-chitotrioside with respect to CHIT1 protein concentrations depends on the presence of Ser102 CHIT1 in an individual, complicating estimation of the body burden of storage macrophages. Use of the superior 4MU-deoxychitobioside substrate avoids such complications because activity towards this substrate under saturating conditions is not affected by the G102S substitution.

Reducing glycosphingolipid content in adipose tissue of obese mice restores insulin sensitivity, adipogenesis and reduces inflammation.

Adipose tissue is a critical mediator in obesity-induced insulin resistance. Previously we have demonstrated that pharmacological lowering of glycosphingolipids and subsequently GM3 by using the iminosugar AMP-DNM, strikingly improves glycemic control. Here we studied the effects of AMP-DNM on adipose tissue function and inflammation in detail to provide an explanation for the observed improved glucose homeostasis. Leptin-deficient obese (Lep(Ob)) mice were fed AMP-DNM and its effects on insulin signalling, adipogenesis and inflammation were monitored in fat tissue. We show that reduction of glycosphingolipid biosynthesis in adipose tissue of Lep(Ob) mice restores insulin signalling in isolated ex vivo insulin-stimulated adipocytes. We observed improved adipogenesis as the number of larger adipocytes was reduced and expression of genes like peroxisome proliferator-activated receptor (PPAR) gamma, insulin responsive glucose transporter (GLUT)-4 and adipsin increased. In addition, we found that adiponectin gene expression and protein were increased by AMP-DNM. As a consequence of this improved function of fat tissue we observed less inflammation, which was characterized by reduced numbers of adipose tissue macrophages (crown-like structures) and reduced levels of the macrophage chemo attractants monocyte-chemoattractant protein-1 (Mcp-1/Ccl2) and osteopontin (OPN). In conclusion, pharmacological lowering of glycosphingolipids by inhibition of glucosylceramide biosynthesis improves adipocyte function and as a consequence reduces inflammation in adipose tissue of obese animals.

Transglycosidase activity of chitotriosidase: improved enzymatic assay for the human macrophage chitinase.

Chitotriosidase is a chitinase that is massively expressed by lipid-laden tissue macrophages in man. Its enzymatic activity is markedly elevated in serum of patients suffering from lysosomal lipid storage disorders, sarcoidosis, thalassemia, and visceral Leishmaniasis. Monitoring of serum chitotriosidase activity in Gaucher disease patients during progression and therapeutic correction of their disease is useful to obtain insight in changes in body burden on pathological macrophages. However, accurate quantification of chitotriosidase levels by enzyme assay is complicated by apparent substrate inhibition, which prohibits the use of saturating substrate concentrations. We have therefore studied the catalytic features of chitotriosidase in more detail. It is demonstrated that the inhibition of enzyme activity at excess substrate concentration can be fully explained by transglycosylation of substrate molecules. The potential physiological consequences of the ability of chitotriosidase to hydrolyze as well as transglycosylate are discussed. The novel insight in transglycosidase activity of chitotriosidase has led to the design of a new substrate molecule, 4-methylumbelliferyl-(4-deoxy)chitobiose. With this substrate, which is no acceptor for transglycosylation, chitotriosidase shows normal Michaelis-Menten kinetics, resulting in major improvements in sensitivity and reproducibility of enzymatic activity measurements. The novel convenient chitotriosidase enzyme assay should facilitate the accurate monitoring of Gaucher disease patients receiving costly enzyme replacement therapy.