Biomedical subjects

Roel J Vonk

Publications and source records attributed to Roel J Vonk.

12 recordsLinked to original sources

PubMed2007

Proteomics profiling of urine with surface enhanced laser desorption/ionization time of flight mass spectrometry.

BACKGROUND: Urine consists of a complex mixture of peptides and proteins and therefore is an interesting source of biomarkers. Because of its high throughput capacity SELDI-TOF-MS is a proteomics technology frequently used in biomarker studies. We compared the performance of seven SELDI protein chip types for profiling of urine using standard chip protocols. RESULTS: Performance was assessed by determining the number of detectable peaks and spot to spot variation for the seven array types and two different matrices: SPA and CHCA. A urine sample taken from one healthy volunteer was applied in eight-fold for each chip type/matrix combination. Data were analyzed for total number of detected peaks (S/N > 5). Spot to spot variation was determined by calculating the average CV of peak intensities. In addition, an inventory was made of detectable peaks with each chip and matrix type. Also the redundancy in peaks detected with the different chip/matrix combinations was determined. A total of 425 peaks (136 non-redundant peaks) could be detected when combining the data from the seven chip types and the two matrices. Most peaks were detected with the CM10 chip with CHCA (57 peaks). The Q10 with CHCA (51 peaks), SEND (48 peaks) and CM10 with SPA (48 peaks) also performed well. The CM10 chip with CHCA also has the best reproducibility with an average CV for peak intensity of 13%. CONCLUSION: The combination of SEND, CM10 with CHCA, CM10 with SPA, IMAC-Cu with SPA and H50 with CHCA provides the optimal information from the urine sample with good reproducibility. With this combination a total of 217 peaks (71 non-redundant peaks) can be detected with CV's ranging from 13 to 26%, depending on the chip and matrix type. Overall, CM10 with CHCA is the best performing chip type.

Journal Article↗

PubMed2006

SELDI-TOF mass spectra: a view on sources of variation.

Adequate interpretation of mass spectrometry data can yield valuable biomarkers. However, spectrum interpretation is a complicated task. This paper reviews the various factors that determine a sample's spectrum and demonstrates the role of these factors in the interpretation process. We derive a simulation model that adequately predicts the expected spectrum based on known sample content and, in the reverse mode, obtain an analysis model that adequately fits an observed spectrum based on the hypothesized sources of variation.

Algorithms↗

PubMed2006

Peak quantification in surface-enhanced laser desorption/ionization by using mixture models.

Surface-enhanced laser desorption/ionization (SELDI) time of flight (TOF) is a mass spectrometry technology for measuring the composition of a sampled protein mixture. A mass spectrum contains peaks corresponding to proteins in the sample. The peak areas are proportional to the measured concentrations of the corresponding proteins. Quantifying peak areas is difficult for existing methods because peak shapes are not constant across a spectrum and because peaks often overlap. We present a new method for quantifying peak areas. Our method decomposes a spectrum into peaks and a baseline using so-called statistical finite mixture models. We illustrate our method in detail on 8 samples from culture media of adipose tissue and globally on 64 samples from serum to compare our method to the standard Ciphergen method. Both methods give similar estimates for singleton peaks, but not for overlapping peaks. The Ciphergen method overestimates the heights of such peaks while our method still gives appropriate estimates. Peak quantification is an important step in pre-processing SELDI-TOF data and improvements therein will pay off in the later biomarker discovery phase.

Adipose Tissue↗

PubMed2006

Low lactase activity in a small-bowel biopsy specimen: should dietary lactose intake be restricted in children with small intestinal mucosal damage?

OBJECTIVE: Small intestinal mucosal damage can result in decreased lactase activity (LA). When LA is low in a small-bowel biopsy (SBB) specimen, a reduction of dietary lactose intake is usually advised. This is often done by reducing dietary dairy products, which also reduces the intake of calcium, protein and vitamins. Since intestinal damage can have a patchy character and LA varies along the horizontal axis of the small intestine, the relevance of SBB measurement for intestinal LA could be questioned. We compared LA in the SBB with the in vivo capacity to digest lactose using the Lactose Digestion Index (LDI). MATERIAL AND METHODS: LA was measured in 18 children aged 0.8-10.9 years (mean 3.9, SD 2.4) undergoing SBB for various indications. In all children the LDI was determined using the (13)C-lactose/(2)H-glucose test. RESULTS: In 9/18 biopsy specimens LA was low (<10 U/g protein). LDI was normal in 14/18 patients. In 8 out of 9 patients with normal lactase activity, LDI was also normal, while in 6 out of 9 patients LDI was normal despite low LA in the biopsy. In patients with normal LDI, histology was normal in 6/14, in 4/14 mild histological changes (Marsh II) were seen and in 4 patients histological damage was severe (grade III). CONCLUSIONS: In children with small-bowel mucosal damage, lactose digestive capacity can remain high despite low LA and histological changes in an SBB. Extrapolation of LA in SBB specimens to overall lactose digestive capacity may not be reliable. The advice concerning the restriction of intake of dairy products cannot be based on the data of the SBB only.

Biopsy↗

PubMed2006

Colonic fermentation may play a role in lactose intolerance in humans.

The results of our previous study suggested that in addition to the small intestinal lactase activity and transit time, colonic processing of lactose may play a role in lactose intolerance. We investigated whether colonic fermentation of lactose is correlated with lactose intolerance. After 28 Chinese subjects had undergone 1 glucose (placebo) and 2 lactose challenges, consistent lactose tolerant (n = 7) and intolerant (n = 5) subjects with no complaints after glucose administration were classified on the basis of the 6-h symptom scores. Before the challenges, fecal samples were collected for in vitro incubation with lactose. The incubation was carried out in a static system under anaerobic conditions for 5 h during which samples were taken for measurement of short-chain fatty acids, lactate, lactose, glucose, and galactose. Fecal bacterial composition was determined by fluorescent in situ hybridization. The tolerant and intolerant groups did not differ in the rate or degree of hydrolysis of lactose or production of glucose and galactose. The intolerant group produced d- and l-lactate, acetate, propionate, and butyrate significantly faster than the tolerant group. In the intolerant group, the amounts of acetate, propionate, butyrate, and l-lactate produced were higher than those in the tolerant group. Fecal bacterial composition did not differ between the 2 groups. The results indicate that the degree and rate of lactose hydrolysis in the colon do not play a role in lactose intolerance. However, after lactose is hydrolyzed, a faster and higher production of microbial intermediate and end metabolites may be related to the occurrence of symptoms.

Adult↗

PubMed2006

The rate of intestinal glucose absorption is correlated with plasma glucose-dependent insulinotropic polypeptide concentrations in healthy men.

Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) both play a role in the control of glucose homeostasis, and GIP is implicated in the regulation of energy storage. The capacity of carbohydrates to induce secretion of these incretin hormones could be one of the factors determining the metabolic quality of different types of carbohydrates. We analyzed the correlation between the rate of intestinal absorption of (starch-derived) glucose and plasma concentrations of GLP-1 and GIP after ingestion of glucose and starchy foods with a different content of rapidly and slowly available glucose. In a crossover study, glucose, insulin, GLP-1, and GIP concentrations were monitored for 6 h after consumption of glucose, uncooked cornstarch (UCCS) or corn pasta in 7 healthy men. All test meals were naturally labeled with 13C. Using a primed, continuous D-[6,6-2H2]glucose infusion, the rate of appearance of exogenous glucose (RaEx) was estimated, reflecting the rate of intestinal glucose absorption. GLP-1 concentrations increased significantly from 180 to 300 min after ingestion of UCCS, the starch product with a high content of slowly available glucose. A high GIP response in the early postprandial phase (15-90 min) occurred after consumption of glucose. There was a strong positive within-subject correlation between RaEx and GIP concentrations (r = 0.73, P < 0.01) across the test meals. Rapidly and slowly digestible carbohydrates differ considerably in their ability to stimulate secretion of incretin hormones; the metabolic consequences of such differences warrant exploration.

Adult↗

PubMed2005

Identification of bacteria with beta-galactosidase activity in faeces from lactase non-persistent subjects.

Previous studies suggest that, besides the maldigestion of lactose in the small intestine, the colonic processing of lactose might play a role in lactose intolerance. beta-Galactosidase is the bacterial enzyme which catalyzes the first step of lactose fermentation in the colon. We propose a practical method to differentiate and identify bacteria with beta-galactosidase activity in faeces which combines a colony-lift filter assay with X-gal (5-bromo-4-chloro-3-indolyl-beta-d-galactopyranoside) as substrate for differentiation and the fluorescent in situ hybridization technique for identification. The method was applied to faeces from lactase non-persistent subjects. After 28 subjects had undergone one glucose and two lactose challenges, consistent intolerant (n=5) and tolerant (n=7) groups were defined according to their symptom scores. Of the 28 faecal samples, 80.6% (mean, SD: 12.1, range: 47.8-100%) of the total cultured bacteria were found to possess beta-galactosidase activity, which indicates that the bacterial beta-galactosidase is abundant in the colon. The tolerant and intolerant groups did not differ in the percentage or composition of the bacteria with beta-galactosidase activity or beta-galactosidase activity in faeces. Results suggest that the percentage or composition of the bacteria with beta-galactosidase activity in faeces do not play a role in lactose intolerance.

Adult↗

PubMed2005

Complementary feeding with cow's milk alters sleeping metabolic rate in breast-fed infants.

Although it is widely accepted that energy expenditure in infants is a function of feeding pattern, the mechanism behind this is not well understood. The objectives of this observational study were as follows: 1) to compare minimal observable energy expenditure (MOEE) between 2 subgroups of breast-fed infants, a BM group in which breast milk was the only source of milk and a BCM group given cow's milk in addition to breast milk; and 2) to identify potential mediators of a feeding pattern effect. For this purpose, infants were classified by feeding group on the basis of a mother's recall. Respiration calorimetry was used to measure MOEE in 62 infants (n = 35 BM, n = 27 BCM) aged 8.7 mo in Pelotas, southern Brazil. Breast-milk intake was measured using deuterium oxide, complementary food intake by 1-d food weighing, total energy expenditure and total body water using doubly labeled water; anthropometric indices were calculated. MOEE was 1672 +/- 175 kJ/d in BM compared with 1858 +/- 210 kJ/d in BCM infants (P < 0.001). Mass-specific MOEE was 201 +/- 24.6 and 216 +/- 31.9 kJ/(kg . d) in BM and BCM infants, respectively (P = 0.041). MOEE (kJ/d) was mediated by protein intake and fat-free mass (R(2) = 41.4%). We conclude that complementary feeding with cow's milk alters the sleeping metabolic rate in breast-fed infants. These findings deserve attention in relation to "metabolic programming" and the development of obesity later in life.

Animals↗

PubMed2004

Proteomic analyzes of copper metabolism in an in vitro model of Wilson disease using surface enhanced laser desorption/ionization-time of flight-mass spectrometry.

In Wilson disease, mutations in the ATP7B-gene lead to hepatic accumulation of copper that becomes toxic when the hepatic binding capacity is exceeded, leading to oxidative stress and acute liver failure. Several proteins are probably involved in dealing with the excess copper and oxidative stress. As a first step towards biomarker discovery and analyzes of copper metabolism in Wilson disease patients we characterized copper-induced changes in protein expression in cell lysates and culture media from an in vitro copper-overload model using surface enhanced laser desorption/ionization (SELDI) proteomics technology. HepG2 cells were cultured for 48 h with a physiological (0.5 microM) or a pathological (100 microM) copper concentration. Samples were applied to weak cation exchange (WCX) proteinchip arrays and chips were analyzed by time of flight (TOF)-mass spectrometry. Copper-coated IMAC chips were used to detect copper-binding proteins in cell lysate of copper depleted cells using buffers with increasing imidazole concentrations. Data from the 2 to 50 kDa range indicate that high extra-cellular copper substantially altered both intra-cellular protein expression as well as the composition of the secretome. In the lysate 15 proteins were found up-regulated, while 6 proteins were down-regulated. In culture media 21 proteins were increased while 4 proteins were decreased in abundance. Copper-coated protein chips revealed the presence of 18 high-affinity copper-binding proteins. Further identification is necessary to determine the exact cellular roles of the discovered proteins.

Carcinoma, Hepatocellular↗

PubMed2004

The role of colonic microbiota in lactose intolerance.

In a previous study we observed a clear difference in lactose intolerance symptoms after a 25-g lactose load in two groups of persons with lactase nonpersistence and similar small intestinal lactase activity. From this observation we hypothesized a colon resistance factor. To identify this factor, the microbial composition of fecal samples of the two lactose intolerant groups (one with mild symptoms, n = 16, and one with diarrhea-predominant symptoms, n = 11) was compared using the fluorescent in situ hybridization technique. Large interindividual differences were found in the numbers of total bacteria and main groups of bacteria (CV: 0.65 and 0.64-0.82 respectively). The bacterial numbers were not significantly different between the two groups. A significant negative correlation, however, was found between the individual symptom scores of the intolerant persons and the numbers of total hybridizable bacteria (r(s) = -0.42, P = 0.03). The results suggest that an increased number of bacteria might contribute--by means of a higher fermentative capacity--to the reduction of lactose intolerance symptoms.

Adult↗

PubMed2002

The physiology of colonic metabolism. Possibilities for interventions with pre- and probiotics.

The awareness is increasing that in the colon many metabolic processes take place in relation to the fermentation of our food, which might be relevant for health and disease. However, the relation between food, colon metabolism and health or disease is far from clear. In this overview, the physiology of colonic metabolism and possibilities for its modification by the use of pre- and probiotics are discussed. Results of in vitro and animal studies indicate a beneficial impact of probiotics on adverse metabolic processes in the colon, but confirmation in human studies has to be extended. The administration of prebiotics seems to be promising with regard to their capacity to modulate the bacterial composition in the colon and there are indications that prebiotics can beneficially influence colonic metabolism. Whether these modulations brought about by pre- or probiotics have an effect on the health of the host, however, needs to be established in most cases.

Animals↗

PubMed2002

Functional development of fat absorption in term and preterm neonates strongly correlates with ability to absorb long-chain Fatty acids from intestinal lumen.

Our goal for this study was to determine whether the maturation of fat absorption in neonatal life is functionally related to an increased ability to hydrolyze dietary fat, to absorb long-chain fatty acids, or to do both. In 16 preterm and in eight term neonates, the intestinal ability to hydrolyze triacylglycerols and the capacity to absorb long-chain fatty acids were determined at several times between birth and 5 mo after the term age. These processes were compared with the percentage of fat absorption (formula-fed infants) or with fecal fat excretion (breast-fed infants). The functional capacity to digest triacylglycerols and to absorb the lipolytic products was evaluated by measuring serum concentrations of the lipolytic product [1-(13)C]palmitate after the enteral administration of tri-1-(13)C palmitoyl-glycerol. Long-chain fatty acids absorption (i.e. independent of lipolysis) was determined by measuring serum concentrations of [1-(13)C]stearate after its enteral administration. The efficacy of fat absorption increased in preterm infants (formula-fed) from 91.2 +/- 1.1% (mean +/- SEM) at 32.3 wk postconceptional age (PCA) to 97.3 +/- 0.6% at 53.6 wk PCA (p < 0.001), and in term infants from 91.7 +/- 1.8% (40.0 wk PCA) to 97.4 +/- 1.3% (58.9 wk PCA, p = 0.07). Both the serum concentration of [1-(13)C]stearate and that of [1-(13)C]palmitate appeared highly correlated with the efficacy of fat absorption (r = 0.82, p = 0.02; and r = 0.91, p = 0.004; respectively) and with PCA (r = 0.99, p < 0.001; and r = 0.85, p < 0.02; respectively). These results indicate that the functional development of fat absorption in preterm and term infants is related to the capacity to absorb long-chain fatty acids from the intestine.

Dietary Fats↗