Research
Gynecology
A systematic evaluation of collagen cross-links in the human cervix

Presented in poster form at the 34th annual meeting of the Society for Maternal-Fetal Medicine, New Orleans, LA, Feb. 3-8, 2014.
https://doi.org/10.1016/j.ajog.2014.09.036Get rights and content

Objective

The mechanical strength of the cervix relies on the cross-linking of the tissue’s collagen network. Clinically, the internal os is functionally distinct from the external os. We sought to detect specific collagen cross-links in human cervical tissue and determine whether cross-link profiles were similar at the internal and external os.

Study Design

Transverse slices of cervical tissue were obtained at the internal and external os from 13 nonpregnant, premenopausal women undergoing a benign hysterectomy. To understand how cross-links were distributed throughout the entire cervix and at the internal and external os, biopsies were obtained from 3 circumferential zones in 4 quadrants from each slice. Biopsies were pulverized, lyophilized, reduced with sodium borohydride, hydrolyzed with hydrochloric acid, and reconstituted in heptafluorobutyric acid buffer. Hydroxyproline was measured by ultraperformance liquid chromatography-electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS), converted to total collagen, and normalized by dry weight. Collagen cross-links pyridinoline (PYD), deoxypyridinoline (DPD), dihydroxylysinonorleucine (DHLNL), and the nonenzymatic advanced glycation end product pentosidine (PEN) were measured by UPLC-ESI-MS/MS and reported as cross-link density ratio (cross-link/total collagen). Generalized estimated equation analysis was used to compare results between the internal and external os and to compare quadrants and zones within slices from the internal and external os to determine if cross-link profiles were similar.

Results

A total of 592 samples from 13 patients were analyzed. Collagen cross-links are detectable in the human cervix by UPLC-ESI-MS/MS. When comparing all samples from the internal and external os, similar levels of collagen content, PYD, DHLNL, and DPD were found, but PEN density was higher at the external os (0.005 vs 0.004, P = .001). When comparing all internal os samples, significant heterogeneity was found in collagen content and cross-link densities across zones and quadrants. The external os exhibited heterogeneity only across zones.

Conclusion

Collagen cross-links (PYD, DPD, DHLNL, and PEN) are detectable by UPLC-ESI-MS/MS in the human cervix. The internal os exhibits significant collagen cross-link heterogeneity compared with the external os. Further studies are needed to evaluate how collagen cross-link heterogeneity correlates to the mechanical strength and function of the human cervix.

Section snippets

Materials and Methods

This study was approved by the Columbia University Medical Center Institutional Review Board (institutional review board no. AAAI0337). Nonpregnant, premenopausal women undergoing a total hysterectomy for benign indications were identified and consented to participate. Women were excluded if they were older than 50 years of age, had an abnormal Papanicolaou smear, or had prior cervical surgery. Demographic information (age, race, body mass index, obstetric history) and indication for procedure

Results

Thirteen patients were consented and cervical tissue collected. A total of 624 biopsies were collected. Biopsies were excluded if an error was made during processing or if the collagen content was higher than 100%. This left a total of 592 samples for analysis. The average age was 45.2 years, average body mass index was 28.8 kg/m2, and the mean uterine weight was 1011 g (Table 1).

Comment

This study establishes that specific immature and mature collagen cross-links are present in detectable amounts in the human cervix. The most abundant collagen cross-link is PYD followed by DHLNL and then DPD. PEN is present but in smaller amounts compared with the other cross-links. This trend appears to persist despite location in the cervix.

PEN was shown to be present in higher amounts at the external os compared with the internal os. PEN is a nonenzymatic advanced glycation product that is

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The views expressed herein are those of the authors and do not necessarily represent the official views of the National Institutes of Health.

This study was supported by the Society for Maternal-Fetal Medicine Foundation/American Association of Obstetricians and Gynecologists Foundation Scholarship and the National Center for Advancing Translational Sciences, National Institutes of Health, through grant UL1 TR000040.

The authors report no conflict of interest.

Cite this article as: Zork NM, Myers KM, Yoshida K, et al. A systematic evaluation of collagen cross-links in the human cervix. Am J Obstet Gynecol 2015;212:321.e1-8.

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