Service Group Stable Isotope Tracer & Nutrient Analytics

This service group deals with qualitative and quantitative analysis of metabolites and nutrients, either labelled with stable-isotopes or unenriched, isolated from biological fluids (blood, saliva, urine, milk), tissues (e.g., liver, muscle) and excreta of e.g. cattle, pig, sheep, chicken and mice as well as feedstuffs.

This allows functional phenotyping of metabolic processes related to nutrition such as

• Nutrient oxidation (e.g. glucose, amino acids),
• Incorporation of nutrients into animal tissue or products (e.g. glucose into milk lactose),
• Protein synthesis (whole body or selected tissue protein),
• Nutrient fluxes (e.g. glucose, amino or fatty acids),
• Gluconeogenesis (using D₂O tracer),
• Energy expenditure (by quantifying CO₂-production with ¹³C bicarbonate or D₂¹⁸O tracers)

by dosing animals in vivo with stable-isotope labelled tracers and then follow-up on their fate in the body.

Chromatographic techniques

• Gas-chromatography (GC)-flame ionisation detection (e.g. short-chain fatty acids, alcohols)
• GC-mass spectrometry (e.g. long-chain fatty acids, glucose)
• High performance liquid chromatography (HPLC) with fluorescence, diode array (UV-VIS) or refractive index detection  (e.g. amino acids, peptides, sugars / sugar alcohols, low molecula organic acids)
• Thin layer chromatography (TLC, e.g. preparative isolation of lipid components)

Mass spectrometry-based stable isotope techniques

To analyse nutrients or metabolites chemically labelled with stable isotopes or at natural abundance (²H, ¹³C, ¹⁵N, ¹⁸O) to quantify nutrient and energy metabolism in vivo.

• Elemental analysis–combustion-isotope ratio mass spectrometry (IRMS) to quantify ¹³C, ¹⁵N abundance in feedstuffs, tissues or biological fluids
• Gas chromatography-combustion-IRMS to measure isotopic enrichment of individual substances (e.g. ¹³C natural abundance in fatty or amino acids)
• Gas bench - Continuous Flow - IRMS to measure ¹³C or ¹⁸O abundance in breath gas-CO₂ or ²H and ¹⁸O abundance in biological fluids (e.g. plasma, saliva, urine, milk)
• Molecular mass spectrometry (GC-quadrupole-MS in electron impact (EI), positive (PCI) or negative (NCI) chemical ionisation mode) to identify or quantify the abundance of nutrients or metabolites (e.g. glucose, amino or keto acids) unenriched or labelled with stable isotopes in plasma or tissue

Clinical chemistry analytics

• Measurement of enzyme and substrate concentrations in blood plasma or serum and urine by automated spectrophotometry (clinical chemistry benchtop analyser, ABX Pentra 400)
• Metabolites: alanine amino transferase, albumin, aspartate amino transferase, gamma-glutamyl-transferase, lactate-dehydrogenase, beta-hydroxybutyrate, bilirubin, calcium, total cholesterol, HDL-cholesterol, LDL-cholesterol, glucose, glutamate-dehydrogenase, urea, uric acid, creatine-kinase, creatinine, lactate, non-esterified fatty acids, phosphor, total protein, triglycerides