Molecular assessment of collagen denaturation in decellularized tissues using a collagen hybridizing peptide

Decellularized extracellular matrix (ECM) derived from tissues and organs are emerging as important scaffold materials for regenerative medicine. Many believe that preservation of the native ECM structure during decellularization is highly desirable. However, because effective techniques to assess the structural damage in ECM are lacking, the disruptive effects of a decellularization method and the impact of the associated structural damage upon the scaffold’s regenerative capacity are often debated. Using a novel collagen hybridizing peptide (CHP) that specifically binds to unfolded collagen chains, we investigated the molecular denaturation of collagen in the ECM decellularized by four commonly used cellremoving detergents: sodium dodecyl sulfate (SDS), 3-[(3-cholamidopropyl)dimethylammonio]-1-propa nesulfonate (CHAPS), sodium deoxycholate (SD), and Triton X-100. Staining of the detergent-treated porcine ligament and urinary bladder matrix with carboxyfluorescein-labeled CHP demonstrated that SDS and Triton X-100 denature the triple helical collagen molecule while CHAPS and SD do not, although second harmonic generation imaging and transmission electron microscopy (TEM) revealed that all four detergents disrupt collagen fibrils. Our findings from the CHP staining were further confirmed by the circular dichroism spectra of intact triple helical collagen molecules in CHAPS and SD solutions, and the TEM images of CHP-conjugated gold nanoparticles binding only to the SDS and Triton X-100 treated collagen fibrils. CHP is a powerful new tool for direct and reliable measurement of denatured collagen molecules in decellularized tissues. It is expected to have wide applications in the development and standardization of the tissue/organ decellularization technology.

Mechanical and microstructural analysis of a radially expandable vascular conduit for neonatal and pediatric cardiovascular surgery

In pediatric cardiovascular surgery, there is a significant need for vascular prostheses that have the potential to grow with the patient following implantation. Current clinical options consist of nonexpanding conduits, requiring repeat surgeries as the patient outgrows the device. To address this issue, PECA Labs has developed a novel ePTFE vascular conduit with the capability of being radially expanded via balloon catheterization. In the described study, a systematic characterization and comparison of two proprietary ePTFE expandable conduits was conducted. Conduit sizes of 8 and 16 mm inner diameters for both conduits were evaluated before and after expansion with a 26 mm balloon. Comprehensive mechanical testing was completed, including quantification of circumferential, and longitudinal tensile strength, suture retention strength, burst strength, water entry pressure, dynamic compliance, and kink radius. Scanning electron microscopy was used to investigate the microstructural properties. Automated extraction of the fiber architectural features for each scanning electron micrograph was achieved with an algorithm for each conduit before and after expansion. Results showed that both conduits were able to expand significantly, to as much as 2.5× their original inner diameter. All mechanical properties were within clinically acceptable values following expansion. Analysis of the microstructure properties of the conduits revealed that the circumferential main angle of orientation, orientation index, and spatial periodicity did not significantly change following expansion, whereas the node area fraction decreased post expansion. Successful proof-of-concept of this novel product represents a critical step toward clinical translation and provides hope for newborns and growing children with congenital heart disease. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 659-671, 2018.

The impact of detergents on the tissue decellularization process: A ToF-SIMS study

Biologic scaffolds are derived from mammalian tissues, which must be decellularized to remove cellular antigens that would otherwise incite an adverse immune response. Although widely used clinically, the optimum balance between cell removal and the disruption of matrix architecture and surface ligand landscape remains a considerable challenge. Here we describe the use of time of flight secondary ion mass spectroscopy (ToF-SIMS) to provide sensitive, molecular specific, localized analysis of detergent decellularized biologic scaffolds. We detected residual detergent fragments, specifically from Triton X-100, sodium deoxycholate and sodium dodecyl sulphate (SDS) in decellularized scaffolds; increased SDS concentrations from 0.1% to 1.0% increased both the intensity of SDS fragments and adverse cell outcomes. We also identified cellular remnants, by detecting phosphate and phosphocholine ions in PAA and CHAPS decellularized scaffolds. The present study demonstrates ToF-SIMS is not only a powerful tool for characterization of biologic scaffold surface molecular functionality, but also enables sensitive assessment of decellularization efficacy.

STATEMENT OF SIGNIFICANCE

We report here on the use of a highly sensitive analytical technique, time of flight secondary ion mass spectroscopy (ToF-SIMS) to characterize detergent decellularized scaffolds. ToF-SIMS detected cellular remnants and residual detergent fragments; increased intensity of the detergent fragments correlated with adverse cell matrix interactions. This study demonstrates the importance of maintaining a balance between cell removal and detergent disruption of matrix architecture and matrix surface ligand landscape. This study also demonstrates the power of ToF-SIMS for the characterization of decellularized scaffolds and capability for assessment of decellularization efficacy. Future use of biologic scaffolds in clinical tissue reconstruction will benefit from the fundamental results described in this work.

Solubilized liver extracellular matrix maintains primary rat hepatocyte phenotype in-vitro

Whole organ engineering and cell-based regenerative medicine approaches are being investigated as potential therapeutic options for end-stage liver failure. However, a major challenge of these strategies is the loss of hepatic specific function after hepatocytes are removed from their native microenvironment. The objective of the present study was to determine if solubilized liver extracellular matrix (ECM), when used as a media supplement, can better maintain hepatocyte phenotype compared to type I collagen alone or solubilized ECM harvested from a non-liver tissue source. Liver extracellular matrix (LECM) from four different species was isolated via liver tissue decellularization, solubilized, and then used as a media supplement for primary rat hepatocytes (PRH). The four species of LECM investigated were human, porcine, canine and rat. Cell morphology, albumin secretion, and ammonia metabolism were used to assess maintenance of hepatocyte phenotype. Biochemical and mechanical characterization of each LECM were also conducted. Results showed that PRH's supplemented with canine and porcine LECM maintained their phenotype to a greater extent compared to all other groups. PRH's supplemented with canine and porcine LECM showed increased bile production, increased albumin production, and the formation of multinucleate cells. The findings of the present study suggest that solubilized liver ECM can support in-vitro hepatocyte culture and should be considered for therapeutic and diagnostic techniques that utilize hepatocytes.

Decellularization and cell seeding of whole liver biologic scaffolds composed of extracellular matrix

The definitive treatment for patients with end-stage liver disease is orthotropic transplantation. However, this option is limited by the disparity between the number of patients needing transplantation and the number of available livers. This issue is becoming more severe as the population ages and as the number of new cases of end-stage liver failure increases. Patients fortunate enough to receive a transplant are required to receive immunosuppressive therapy and must live with the associated morbidity. Whole organ engineering of the liver may offer a solution to this liver donor shortfall. It has been shown that perfusion decellularization of a whole allogeneic or xenogeneic liver generates a three-dimensional ECM scaffold with intact macro and micro architecture of the native liver. A decellularized liver provides an ideal transplantable scaffold with all the necessary ultrastructure and signaling cues for cell attachment, differentiation, vascularization, and function. In this review, an overview of complementary strategies for creating functional liver grafts suitable for transplantation is provided. Early milestones have been met by combining stem and progenitor cells with increasingly complex scaffold materials and culture conditions.

ECM hydrogel coating mitigates the chronic inflammatory response to polypropylene mesh

Polypropylene has been used as a surgical mesh material for several decades. This non-degradable synthetic polymer provides mechanical strength, a predictable host response, and its use has resulted in reduced recurrence rates for ventral hernia and pelvic organ prolapse. However, polypropylene and similar synthetic materials are associated with a chronic local tissue inflammatory response and dense fibrous tissue deposition. These outcomes have prompted variations in mesh design to minimize the surface area interface and increase integration with host tissue. In contrast, biologic scaffold materials composed of extracellular matrix (ECM) are rapidly degraded in-vivo and are associated with constructive tissue remodeling and minimal fibrosis. The objective of the present study was to assess the effects of an ECM hydrogel coating on the long-term host tissue response to polypropylene mesh in a rodent model of abdominal muscle injury. At 14 days post implantation, the ECM coated polypropylene mesh devices showed a decreased inflammatory response as characterized by the number and distribution of M1 macrophages (CD86+/CD68+) around mesh fibers when compared to the uncoated mesh devices. At 180 days the ECM coated polypropylene showed decreased density of collagen and amount of mature type I collagen deposited between mesh fibers when compared to the uncoated mesh devices. This study confirms and extends previous findings that an ECM coating mitigates the chronic inflammatory response and associated scar tissue deposition characteristic of polypropylene.

The effect of detergents on the basement membrane complex of a biologic scaffold material

The basement membrane complex (BMC) is a critical component of the extracellular matrix (ECM) that supports and facilitates the growth of cells. This study investigates four detergents commonly used in the process of tissue decellularization and their effect upon the BMC. The BMC of porcine urinary bladder was subjected to 3% Triton-X 100, 8mM 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS), 4% sodium deoxycholate or 1% sodium dodecyl sulfate (SDS) for 24h. The BMC structure for each treatment group was assessed by immunolabeling, scanning electron microscopy (SEM) and second harmonic generation (SHG) imaging of the fiber network. The composition was assessed by quantification of dsDNA, glycosaminoglycans (GAG) and collagen content. The results showed that collagen fibers within samples treated with 1% SDS and 8mM CHAPS were denatured, and the ECM contained fewer GAG compared with samples treated with 3% Triton X-100 or 4% sodium deoxycholate. Human microvascular endothelial cells (HMEC) were seeded onto each BMC and cultured for 7 days. Cell-ECM interactions were investigated by immunolabeling for integrin β-1, SEM imaging and semi-quantitative assessment of cellular infiltration, phenotype and confluence. HMEC cultured on a BMC treated with 3% Triton X-100 were more confluent and had a normal phenotype compared with HMEC cultured on a BMC treated with 4% sodium deoxycholate, 8mM CHAPS and 1% SDS. Both 8mM CHAPS and 1% SDS damaged the BMC to the extent that seeded HMEC were able to infiltrate the damaged sub-basement membrane tissue, showed decreased confluence and an atypical phenotype. The choice of detergents used for tissue decellularization can have a marked effect upon the integrity of the BMC of the resultant bioscaffold.

Intestinal stem cells remain viable after prolonged tissue storage

Intestinal stem cells (ISCs) are responsible for renewal of the epithelium both during normal homeostasis and following injury. As such, they have significant therapeutic potential. However, whether ISCs can survive tissue storage is unknown. We hypothesize that, although the majority of epithelial cells might die, ISCs would remain viable for at least 24 h at 4 °C. To explore this hypothesis, jejuna of C57Bl6/J or Lgr5-LacZ mice were removed and either processed immediately or placed in phosphate-buffered saline at 4 °C. Delayed isolation of epithelium was performed after 24, 30, or 48 h storage. At the light microscope level, despite extensive apoptosis of villus epithelial cells, small intestinal crypts remained morphologically intact for 30 h and ISCs were identifiable via Lgr5-LacZ positivity. Electron microscopy showed that ISCs retained high integrity for 24 h. When assessed by flow cytometry, ISCs were more resistant to degeneration than the rest of the epithelium, including neighboring Paneth cells, with higher viability across all time points. Cultured isolated crypts showed no loss of capacity to form complex enteroids after 24 h tissue storage, with efficiencies after 7 days of culture remaining above 80 %. By 30 h storage, efficiencies declined but budding capability was retained. We conclude that, with delay in isolation, ISCs remain viable and retain their proliferative capacity. In contrast, the remainder of the epithelium, including the Paneth cells, exhibits degeneration and programmed cell death. If these findings are recapitulated in human tissue, storage at 4 °C might offer a valuable temporal window for the harvesting of crypts or ISCs for therapeutic application.

Catheter-deliverable hydrogel derived from decellularized ventricular extracellular matrix increases endogenous cardiomyocytes and preserves cardiac function post-myocardial infarction

OBJECTIVES

This study evaluated the use of an injectable hydrogel derived from ventricular extracellular matrix (ECM) for treating myocardial infarction (MI) and its ability to be delivered percutaneously.

BACKGROUND

Injectable materials offer promising alternatives to treat MI. Although most of the examined materials have shown preserved or improved cardiac function in small animal models, none have been specifically designed for the heart, and few have translated to catheter delivery in large animal models.

METHODS

We have developed a myocardial-specific hydrogel, derived from decellularized ventricular ECM, which self-assembles when injected in vivo. Female Sprague-Dawley rats underwent ischemia reperfusion followed by injection of the hydrogel or saline 2 weeks later. The implantation response was assessed via histology and immunohistochemistry, and the potential for arrhythmogenesis was examined using programmed electrical stimulation 1 week post-injection. Cardiac function was analyzed with magnetic resonance imaging 1 week pre-injection and 4 weeks post-MI. In a porcine model, we delivered the hydrogel using the NOGA-guided MyoStar catheter (Biologics Delivery Systems, Irwindale, California), and utilized histology to assess retention of the material.

RESULTS

We demonstrate that injection of the material in the rat MI model increases endogenous cardiomyocytes in the infarct area and maintains cardiac function without inducing arrhythmias. Furthermore, we demonstrate feasibility of transendocardial catheter injection in a porcine model.

CONCLUSIONS

To our knowledge, this is the first in situ gelling material to be delivered via transendocardial injection in a large animal model, a critical step towards the translation of injectable materials for treating MI in humans. Our results warrant further study of this material in a large animal model of MI and suggest this may be a promising new therapy for treating MI.

Intestinal crypts reproducibly expand in culture

BACKGROUND

In vitro growth techniques for intestinal crypts and single intestinal stem cells have been recently described, but several questions of translational importance remain unaddressed. The purpose of this study was to first, evaluate if intestinal crypts reproducibly expand in vitro; second, determine the impact of age and region of intestine on crypt growth in vitro; and third, determine the effects of cryopreservation on crypt growth in vitro.

METHODS AND MATERIALS

Crypts were harvested from 5 cm of proximal, middle, and distal small intestine of C57BL/6J mice aged 4 wk, 6-8 wk, 12-14 wk, and 18-20 wk (n = 4-6 animals) and cultured. For each region, we determined the efficiency of crypts forming enterospheres (day 1) and progressing to enteroids (day 7). Subsequently, enteroids were passaged and cryopreserved to determine if growth was changed by these manipulations.

RESULTS

Forty-three to 99% of intestinal crypts formed enterospheres, with higher efficiency in proximal small intestine and in younger mice. Twenty-five to 64% of enterospheres progressed to budding enteroids within 7 d. In vitro expansion was greater in proximal enteroids. This expansion continued in a logarithmic fashion, with ≈ 97% replating efficiency of isolated enteroid crypt buds. Following cryopreservation, ≈ 90% of enteroids recovered normal proliferative capacity.

CONCLUSIONS

Intestinal crypt culture is efficient and significantly expands intestinal tissue in a reproducible manner. Regional and age growth differences may reflect distinct stem cell characteristics or differences in support cells. The ability to culture and expand intestinal tissue in vitro provides a potential translational approach toward understanding and treating patients with short bowel syndrome.

Maintenance of human hepatocyte function in vitro by liver-derived extracellular matrix gels

Tissue engineering and regenerative medicine (TE&RM) approaches to treating liver disease have the potential to provide temporary support with biohybrid-liver-assist devices or long-term therapy by replacing the diseased liver with functional constructs. A rate-limiting step for TE&RM strategies has been the loss of hepatocyte-specific functions after hepatocytes are isolated from their highly specialized in vivo microenvironment and placed in in vitro culture systems. The identification of a biologic substrate that can maintain a functional hepatocyte differentiation profile during in vitro culture would advance potential TE&RM therapeutic strategies. The present study compared two different biologic substrates for their ability to support human hepatocyte function in vitro: porcine-liver-derived extracellular matrix (PLECM) or Matrigel. Because Matrigel has been shown to be the most useful matrix for static, traditional hepatocyte culture, we directly compared PLECM with Matrigel in each experiment. Albumin secretion, hepatic transport activity, and ammonia metabolism were used to determine hepatocyte function. Hepatocytes cultured between two layers of PLECM or Matrigel showed equally high levels of albumin expression and secretion, ammonia metabolism, and hepatic transporter expression and function. We conclude that like Matrigel, PLECM represents a favorable substrate for in vitro culture of human hepatocytes.

Strategies for the preflight circadian shifting of Space Shuttle crews

In June, 1990, a workshop was put together at NASA/Johnson Space Center to address difficulties the astronauts were having in adjusting their wake and sleep schedule, both immediately before and during Space Shuttle missions. The workshop members, prominent investigators in human circadian research, developed a number of strategies by which astronauts could tackle the problem of circadian adaptation within the demanding timetable of a Space Shuttle mission. The strategies included both abrupt and gradual methods, and some approaches used artificial "very bright lights" to reset the physiologic circadian pacemaker. The strategies have since been operationally implemented on Space Shuttle flights, with good success. This is a report of the problems addressed by the workshop and its recommendations.

Results of a structured psychiatric interview to evaluate NASA astronaut candidates

One hundred six astronaut applicants who had passed initial screening were evaluated for Axis I and Axis II DSM-III-R diagnoses using a structured psychiatric interview. Nine of 106 candidates (8.5%) met diagnostic criteria for six Axis I (including V-code), or Axis II disorders. The use of the NASA structured interview was effective in identifying past and present psychopathology in a group of highly motivated and healthy astronaut applicants. This was the first time that a structured interview had been used in such a setting for this purpose. The methodology described is applicable to any situation where the presence or history of psychopathology requires evaluation for job selection (e.g. pilot selection).

Psychiatric diagnoses in a group of astronaut applicants

Between 1959 and 1987, the psychiatric evaluation of astronaut candidates evolved from a 30-h intensive examination evaluating applicants for psychopathology, and studying their performance under stress, to a 2-h clinical interview whose structure and contents were determined by the individual examiner. Evaluations done during these years applied both psychiatric (or, "select-out") criteria and psychological (or, "select-in") criteria. In an attempt to more rigorously define the psychiatric, "select-out" component, a standardized, semi-structured clinical interview was developed to identify the presence or history of psychiatric disorders listed in the Diagnostic and Statistical Manual of Mental Disorders, 3rd Ed. ("DSM-III"). A total of 117 astronaut applicants underwent this clinical interview as part of a comprehensive medical evaluation during a recent astronaut selection. Of the 117 applicants, 9 (7.7%) met DSM-III criteria for a variety of Axis I and Axis II diagnoses, including V-code diagnoses.

Effects of phenytoin on N100 augmenting/reducing and the late positive complex of the event-related potential: a topographic analysis

The effects of 100 mg of phenytoin on the topographic distribution of augmenting/reducing (amplitude response/nonresponse to increases in stimulus intensity) of the visual N100 component of the event-related potential (ERP) were examined. In normal subjects, visual N100 augmenting is associated with impulsivity and attentional distraction. Effects of phenytoin on the topographic distributions of the P300 and slow-wave cognitive ERP components were also examined. Subjects counted the total number of light flashes presented at two highly discriminable but equiprobable intensities. Results indicated that phenytoin had a significant reducing effect on the intensity response of N100 at the vertex and anterior temporal electrode sites, and approached significance at the frontal pole. That is, at these loci N100 showed less of an increase in amplitude (or, in some subjects, more of a decrease) in going from baseline to drug than in going from baseline to placebo. Results also indicated that phenytoin significantly enhanced the amplitude of the frontal, negative portion of slow wave, but not the posterior, positive portion or the P300 component. These findings are consistent with behavioral evidence that phenytoin reduces impulsivity and improves concentration.