Reversed-phase high-performance liquid chromatographic analysis of hydroxyproline and proline from collagen by derivatization with dabsyl chloride

Chromatographic separation by RPLC-ESI-MS of all hydroxyproline isomers for the characterization of collagens from different sources

During collagen biosynthesis, proline is post-translationally converted to hydroxyproline by specific enzymes. This amino acid, unique to collagen, plays a crucial role in stabilizing the collagen triple helix structure and could serve as an important biomarker for collagen content and quality analysis. Hydroxyproline has four isomers, depending on whether proline is hydroxylated at position 4 or 3 and on whether the cis- or trans- conformation is formed. Moreover, as extensive hydrolysis of collagen is required for its amino acid analysis, epimerization may also occur, although to a lesser extent, giving a total of eight possible isomers. The aim of the present study was to develop a reversed-phase high-performance liquid chromatography-UV-mass spectrometry (RPLC-UV-MS) method for the separation and quantification of all eight hydroxyproline isomers. After the chiral derivatization of the hydroxyproline isomers with Nα-(2,4-dinitro-5-fluorophenyl)-L-valinamide (L-FDVA), to enable their UV detection, the derivatized diastereoisomers were separated by testing different C18 column technologies and morphologies and optimizing operative conditions such as the mobile phase composition (solvent, additives), elution mode, flow rate and temperature. Baseline resolution of all eight isomers was achieved on a HALO® ES-C18 reversed-phase column (150×1.5 mm, 2.7 μm, 160 Å) using isocratic elution and MS-compatible mobile phase. The optimized method was validated for the quantification of hydroxyproline isomers and then applied to different collagen hydrolysates to gain insight and a deeper understanding of hydroxyproline abundances in different species (human, chicken) and sources (native, recombinant).

Does long intestinal tube splinting aggravate intestinal adhesions?

OBJECTIVE

Long intestinal tube splinting (LITS) is useful for clinically reducing the recurrence of adhesive small bowel obstruction (ASBO). However, a controversy exists whether LITS aggravates intestinal adhesions. This study evaluated the postoperative effects of LITS relative to simple enterolysis on intestinal adhesions in an experimental porcine model.

METHODS

A porcine model (n = 24) of dense intestinal adhesion was established by abrading the ileal wall with sterile P240 sandpaper. Enterolysis was performed on postoperative day 14. Animals were randomly divided into a group that underwent enterolysis only (control; n = 12) and those who underwent LITS as well as enterolysis (LITS; n = 12). The long intestinal tube was removed on post-LITS day 14, after abdominal radiography. All animals were euthanized on postenterolysis day 28 for assessment of intestinal adhesions using a semiquantitative macroscopic grading scale, hematoxylin-eosin histology, and hydroxyproline assay.

RESULTS

Prior to enterolysis, the experimentally induced intestinal adhesions of the two groups were similar in extent and severity. On postenterolysis day 28 the LITS and control groups were comparable with regard to adhesion loop length (p = .440), macroscopic adhesion severity (p = .820), serosal fibrosis grading (p = .450), and hydroxyproline content of the adhesion ileal segment (p = .630).

CONCLUSION

Placement of the long intestinal tube did not aggravate intestinal adhesions over that of simple enterolysis in this intestinal adhesion porcine model.

Cationic amino acid transporter gene expression in cultured vascular smooth muscle cells and in rats

Immunostimulants trigger vascular smooth muscle cells (VSMC) to express the inducible isoform of NO synthase (iNOS) and increased arginine transport activity. Although arginine transport in VSMC is considered to be mediated via the y+ system, we show here that rat VSMC in culture express the cat-1 gene transcript as well as an alternatively spliced transcript of the cat-2 gene. An RT-PCR cloning sequence strategy was used to identify a 141-base nucleotide sequence encoding the low-affinity domain of alternatively spliced CAT-2A and a 138-base nucleotide sequence encoding the high-affinity domain of CAT-2B in VSMC activated with lipopolysaccharide (LPS) in combination with interferon-gamma (IFN). With this sequence as a probe, Northern analyses showed that CAT-1 mRNA and CAT-2B mRNA are constitutively present in VSMC, and the expression of both mRNAs was rapidly stimulated by treatment with LPS-IFN, peaked within 4 h, and decayed to basal levels within 6 h after LPS-IFN. CAT-2A mRNA was not detectable in unstimulated or stimulated VSMC. Arginine transporter activity significantly increased 4-10 h after LPS-IFN. iNOS activity was reduced to almost zero in the absence of extracellular arginine uptake via system y+. Induction of arginine transport seems to be a prerequisite to the enhanced synthesis of NO in VSMC. Moreover, this work demonstrates tissue expression of CAT mRNAs with use of a model of LPS injection in rats. RT-PCR shows that the expression of CAT-1 and CAT-2B mRNA in the lung, heart, and kidney is increased by LPS administration to rats, whereas CAT-2A mRNA is abundantly expressed in the liver independent of LPS treatment. These findings suggest that together CAT-1 and CAT-2B play an important role in providing substrate for high-output NO synthesis in vitro as well as in vivo and implicate a coordinated regulation of intracellular iNOS enzyme activity with membrane arginine transport.

Rapid determination of dabsylated hydroxyproline from cultured cells by reversed-phase high-performance liquid chromatography

A high-performance liquid chromatographic method was modified for the determination of hydroxyproline in cultured cells derived from rat liver. First, the primary amino group in the cell hydrolysate was blocked with o-phthalaldehyde, then the secondary amino group was derivatized with 4-dimethylaminoazobenzene-4'-sulfonyl chloride (dabsyl chloride). The dabsylated sample was treated with ethyl acetate to obtain a simple chromatographic elution profile of the cell hydrolysate. Dabsylhydroxyproline and proline were separated from other compounds by high-performance liquid chromatography in the gradient elution mode, and eluted at 4.71 and 8.00 min, respectively. The method was applied to the determination of hydroxyproline contained in cultured cells, the result being 25.4 +/- 3.6 pmol/microgram.