The impact of cholesterol deposits on the fibrillar architecture of the Achilles tendon in a rabbit model of hypercholesterolemia

Abstract

Background Increased tendon pain and tendon damage is a significant complication related to hyperlipidemia. Unlike the well-established pathogenesis associated with increased serum concentrations of total cholesterol, triglycerides, and low-density lipoprotein in atherosclerotic cardiovascular disease, the role of hyperlipidemia in promoting tendon damage remains controversial and requires mechanistic clarity. Methods In this study, we analyzed the consequences of hypercholesterolemia on the integrity of the collagen-based architecture of the Achilles tendon. The Achilles tendons from rabbits fed with normal-cholesterol (nCH) and high-cholesterol (hCH) diets were analyzed. We studied the morphology of tendons, distribution of lipids within their collagen-rich milieu, the relative amounts of fibrillar collagen I and collagen III, and selected biomechanical parameters of the tendons at the macroscale and the nanoscale. Results Histological assays of hCH tendons and tenosynovium demonstrated hypercellular areas with increased numbers of macrophages infiltrating the tendon structure as compared to the nCH tendons. While Oil Red staining revealed lipid-rich deposits in the hCH tendons, hybridization of tendon tissue with the collagen hybridizing peptide (CHP) demonstrated damage to the collagen fibers. Fourier-transform infrared (FTIR) spectra showed the presence of distinct peaks consistent with the presence of cholesterol ester. Additionally, the hCH tendons displayed regions of poor collagen content that overlapped with lipid-rich regions. The hCH tendons had a substantial fourfold increase in the collage III to collagen I ratio as compared to the nCH tendons. Tendons from the hCH rabbits showed poor biomechanical characteristics in comparison with control. The biomechanical changes were evident at the macrolevel and the nanolevel of tendon structure. Conclusions Our findings support the hypothesis that hypercholesterolemia coincides with the weakening of the tendons. It is likely that the intimate contact between collagen fibrils and cholesterol deposits contributes to the weakening of the fibrillar structure of the tendons.

Mechanisms of reducing joint stiffness by blocking collagen fibrillogenesis in a rabbit model of posttraumatic arthrofibrosis

“…As references, we selected a protein-specific amide II peak and a peak corresponding to sulfated glycosaminoglycans (GAGs). Consequently, the sulfated GAGs peak/collagen peak ratios and amide II peak/collagen peak ratios were measured to determine the relative collagen content (S1 Table in S1 File ) [ 40 , 41 ]. Please note that the relation between the ratio values and collagen amount is negative.…”

Influence of Achilles tendon rupture site on surgical repair outcomes

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Collagen‐rich deposit formation in the sciatic nerve after injury and surgical repair: A study of collagen‐producing cells in a rabbit model

“…Following deparaffinization, we scanned the samples using an FTIR spectrometer (Spotlight 400; Perkin Elmer), as previously described (Steplewski et al., 2019). The imaging mode was set at 4,000 to 748 cm −1 wavenumber spectral range, pixel resolution at 25 µm, with 32 scans per pixel, and spectral resolution at 8 cm −1 .…”

“…Then, each scan was used to generate FTIR spectra (Spectrum Image software; PerkinElmer, Inc.). Subsequently, employing the Spectrum software (PerkinElmer, Inc.), we calculated the AI/C ratios of the areas of the integrated amide I peak centered around 1,650 cm −1 and of the collagen peak centered around 1,338 cm −1 , as described (Bi, Yang, Bostrom, & Camacho, 2006; Kim et al., 2010; Steplewski et al., 2019; West, Bostrom, Torzilli, & Camacho, 2004). Please note that the value of the AI/C ratio is inversely proportional to the relative collagen content.…”