Quantitative evaluation of sebum lipid components with nuclear magnetic resonance.

A NMR spectroscopic method is described that enables the quantitation of specific lipid classes and components, independent of fatty acid composition. We demonstrate this method for measuring cholesterol, squalene, and pools of sterol esters, wax esters (WEs), and triglyceride (TG) components in sebum and meibum. When 600 MHz NMR equipment is used in conjunction with highly sensitive cryogenically cooled probes, this method has adequate sensitivity, and for some applications, advantages over commonly used HPLC-evaporative light-scattering detection and mass spectrometry-based approaches. This method is shown to be useful for preclinical and clinical monitoring of the efficacy of sebum-reducing agents in animals and humans. In Syrian hamsters, 3% topical flutamide and 20 mg/kg oral isotretinoin reduced sterol esters by 18.7% and 30.0%, respectively, and reduced WEs by 32.9% and 31.8%, respectively, as measured in a punch biopsy of the ear. In a 72 patient clinical methodology study, the assay delivered reproducible and noninvasive measurements of WEs, cholesteryl esters, TGs, and squalene from Sebutape skin blots. The quantitative results of sebum analysis obtained by the NMR method correlate well with those obtained with HPLC-based approaches. This approach may be broadly applicable to cases in which fatty acid-independent quantification of lipid classes is desired.

Metabonomic evaluation of Schaedler altered microflora rats.

Previously, we identified two distinct metabonomic phenotypes in Sprague-Dawley rats sourced from two different rooms (colonies) in the Charles River, Raleigh facility [Robosky, L. C., Wells, D. F., Egnash, L. A., Manning, M. L., Reily, M. D., and Robertson, D. G. (2005) Metabonomic identification of two distinct phenotypes in Sprague-Dawley (Crl:CD(SD)) rats. Toxicol. Sci. 87, 277-284]. On the basis of literature reports and cohabitation experiments, we concluded that the differing phenotypes were due to different gut flora populations. One hypothesis explaining this phenomenon was attributed to the practice of initiating new colonies with rats derived from foundation colonies that had limited gut floral populations, the Charles River altered Schaedler flora (CRASF) rats. We hypothesized that the lack of differentiation of CRASF rats to the full complement of microflora was responsible for the altered phenotype characterized by increased urinary chlorogenic acid metabolites and decreased hippurate (CA rats) as opposed to the prevalent phenotype characterized by the inverse ratio of these metabolites (HIP rats). Upon receipt, it was confirmed that the CRASF rats exhibited a metabonomic profile similar to CA rats that remained constant while animals were housed individually in a dedicated animal room. However, exposure of CRASF rats to HIP rats, or their bedding, led to a relatively rapid but variable rate of reversion to the historic HIP type metabolic profile. On the basis of the results, we conclude that CRASF rats have a unique metabolic profile due to their limited gut flora constitution. If rigorous isolation procedures are not employed, the CRASF phenotype will eventually differentiate into the more typical HIP phenotype with a time course that may be quite variable. Given the marked metabolic heterogeneity between the phenotypes, this work highlights the importance of monitoring rat metabolic profiles.

DFTMP, an NMR reagent for assessing the near-neutral pH of biological samples.

A new NMR chemical shift standard and pH indicator, difluorotrimethylsilanylphosphonic acid (DFTMP), is described, and the utility of this reagent is demonstrated for in situ determination of pH in complex biofluids. The pH dependence of this reagent allows accurate in situ determination of aqueous solution pH to within an RMSE of 0.02 pH units over a pH range of 5 to 8. Advantages of this reagent over previously described pH-sensitive components include (1) lack of metal binding affinity, (2) minimal disturbance of endogenous spectral regions, and (3) the potential to function as a multinuclear pH indicator and chemical shift reference point for 19F, 1H, and 31P nuclei. This reagent will be generally useful for NMR experiments on biological systems where the pH needs to be accurately measured at the moment of data acquisition.

Metabonomic identification of two distinct phenotypes in Sprague-Dawley (Crl:CD(SD)) rats.

Genetic drift in animal populations has been a recognized concern for many years. Less understood is the potential for phenotypic "drift" or variation that is not related to any genetic change. Recently, stock Sprague-Dawley (Crl:CD(SD)) rats obtained from the Charles River Raleigh facility demonstrated a distinct endogenous urinary metabonomic profile that differed from historical control SD urine spectral profiles obtained over the past several years in our laboratory. In follow-up studies, the origin of the variant phenotype was narrowed down to animals of both sexes that were housed in one specific room (Room 9) in the Raleigh facility. It is likely that the two phenotypes are related to distinct populations of gut flora that particularly impact the metabolism of aromatic molecules. The most pronounced difference between the two phenotypes is the relative amounts of hippuric acid versus other aromatic acid metabolites of chlorogenic acid. Though both molecular species are present in either phenotype, the marked variation in levels of these molecules between the two phenotypes has led to the designation of high hippuric acid (HIP) and high chlorogenic acid metabolites (CA) phenotypes. Specific urinary components that distinguish the phenotypes have been thoroughly characterized by NMR spectroscopy with additional, limited characterization by LC-MS (high performance liquid chromatography coupled with mass spectrometry). Co-habitation of rats from the two phenotypes rapidly facilitated a switch of the CA phenotype to the historical Sprague-Dawley phenotype (HIP). The impact of these variant phenotypes on drug metabolism and long-term safety assessment studies (e.g., carcinogenicity bioassays) is unknown.