Meloche, Ryan

Combined histopathological and metabolomic analysis of the same tissue specimen can reduce biological variability compared to independent analyses of similar samples. However, conventional workflows are incompatible: tissue fixation leads to metabolite loss through dilution and chemical reactions with fixative, while metabolomic extraction typically destroys the specimen. We propose a method that reconciles these conflicting requirements by enabling metabolite recovery from fixative while preserving tissue for histopathology. In this approach, tissue is initially fixed in a small volume of fixative; an aliquot of the fixative is then collected for nuclear magnetic resonance-based metabolomic analysis before additional fixative is added for standard processing. As a proof-of-concept, mouse kidneys from the same subject were analyzed using two protocols: standard perchloric acid extraction (ensuring complete metabolite recovery but destroying tissue) and metabolite extraction from fixative. Several metabolites were fully recoverable from the fixative, others partially, while some were lost due to chemical reactions. Despite some limitations, this strategy may be useful for analyzing precious specimens, such as human biopsies, that must remain intact for further studies. Moreover, using the same specimen for dual analyses reduces the number of animals required and enhances statistical robustness.

Key Points Robotic ultrasound performed favorably compared with magnetic resonance imaging for evaluating total kidney volume. Collagen evaluation by two novel methods of picrosirius red imaging were more informative than the standard method by brightfield imaging. Findings can improve research by increasing speed and access to total kidney volume determination and sensitivity of collagen assessment. Background 3D imaging and histology are critical tools for assessing polycystic kidney disease (PKD) in patients and animal models. Magnetic resonance (MR) imaging provides micron resolution but is time consuming and expensive, and access to equipment and expertise is limited. Robotic ultrasound (US) imaging has lower spatial resolution but is faster, more cost-effective, and accessible. Similarly, picrosirius red (PSR) staining and brightfield microscopy are commonly used to assess fibrosis; however, alternative methods have been shown in non-kidney tissues to provide greater sensitivity and more detailed structural characterization. Methods In this study, we evaluated the utility of robotic US and alternative methods of quantifying PSR staining for PKD research. We compared longitudinal total kidney volume measurements using US and MR imaging. We additionally compared PSR imaging and quantification using standard brightfield microscopy with that by circularly polarized light with hue analysis and fluorescence imaging analyzed using curvelet transform fiber extraction software for automatic detection of individual collagen fibers. Results Increased total kidney volume was detected by US in Pkd1 RC/RC versus wild-type (WT) at time points spanning from early to established disease. US interobserver variability was greater but allowed scanning in 2–5 minutes/mouse, whereas MR imaging required 20–30 minutes/mouse. While no change in fibrotic index was detected in this cohort of relatively mild disease using brightfield microscopy, polarized light showed fibers skewed thinner in Pkd1 RC/RC versus WT. Fluorescence imaging showed a higher density of collagen fibers in Pkd1 RC/RC versus WT, and fibers were thinner and curvier with no change in length. In addition, fiber density was higher in both glomeruli and tubules in Pkd1 RC/RC , and glomeruli had a higher fiber density than tubules in Pkd1 RC/RC and trended higher in WT. Conclusions These studies show robotic US is a rigorous imaging tool for preclinical PKD research. In addition, they demonstrate the increased sensitivity of polarized and fluorescence analysis of PSR-stained collagen.

To describe transverse relaxation of water in fixed tissue, we propose a model of transverse relaxation accelerated by diffusion and exchange (TRADE) that assumes exchange between free (visible) and bound (invisible) water, which relax by the dipole–dipole interaction, chemical exchange, and translation in the field gradient. Depending on the prevailing mechanism, transverse relaxation time (T2) of water in fixed tissue could increase (when dipole–dipole interaction prevails) or decrease with temperature (when diffusion in the field gradient prevails). Chemical exchange can make T2 even temperature independent. Also, variation of resolution from 100 to 15 μm/pxl (or less) affects effective transverse relaxation. T2 steadily decreases with increased resolution ( , is the read direction resolution). TRADE can describe all of these observations (semi)quantitatively. The model has been experimentally verified on water phantoms and on formalin‐fixed zebrafish, mouse brain, and rabbit larynx tissues. TRADE could help predict optimal scanning parameters for high‐resolution MRM from much faster measurements at lower resolution.

AbstractObjectivesTo examine the degree of agreement between MRI and histologically generated volumetric measurements of residual injection laryngoplasty material.MethodsFollowing left recurrent laryngeal nerve transection, rabbit vocal cords were injected with jellyfish collagen, Cymetra®, or Restylane®. Laryngeal tissue was harvested 4 or 12 weeks post injection followed by MRI imaging and histologic cross‐sectioning. Two raters estimated the volume of remaining injection material in specimens within MRI and histologic axial cross sections. Wilcoxon signed rank tests were employed to detect gross differences between inter‐rater measurements and between imaging modalities across time. Agreement between rater measurements and imaging (histology and MRI) was assessed using intra‐class correlation coefficients.ResultsData was available from 16 rabbits sacrificed at 4 weeks (n = 8) and 12 weeks (n = 8). Inter‐rater testing of MRI imaging revealed no significant differences (p > .05) between rater measurements across time points, and excellent agreement (0.93; 95% confidence interval 0.80–0.98) while histologically estimated volumes demonstrated a significant difference at 4 weeks (p < .05) and overall good agreement (0.89; 95% confidence interval 0.59–0.97). Comparison of MRI and histologically estimated volume measurements revealed significant differences at the 4‐week time point (p < .05) but not at 12 weeks (p > .05). Overall, there is only moderate agreement between MRI and histology estimates (0.72; 95% confidence interval 0.22–0.90).ConclusionsMRI imaging demonstrates good reliability and similar estimates of volume to histologically estimated measurements of residual injection laryngoplasty material at time points clinically relevant for future injection laryngoplasty experiments.Level of EvidenceNA.

AbstractObjectives/HypothesisTest a new jellyfish collagen biomaterial aimed to increase duration of injection medialization laryngoplasty (IL) against two products in clinical practice.Study DesignAnimal model.MethodsLeft recurrent laryngeal nerve sectioning and IL were performed in New Zealand White rabbits (N = 6/group). Group 1 received micronized cross‐linked jellyfish collagen (MX‐JC) and adipose derived stem cells (ADSCs), Group 2, MX‐JC alone, Group 3, cross‐linked hyaluronic acid (X‐HA), and Group 4, micronized acellular dermis (MACD). Animals were sacrificed at 4 and 12 weeks. Major outcomes were MRI tissue volumes and histopathology.ResultsAfter 100 μL IL MRI volumes (means ± STD) at 4 and 12 weeks were: Group 1: 27.2 ± 15.6 and 13.1 ± 5.2 μL, Group 2: 60.8 ± 18 and 27.8 ± 2.47 μL, Group 3: 27.4 ± 12 and 10.6 ± 8 μL, and Group 4: 37.5 ± 11 and 9.85 ± 1 μL. Group 2 volumes were largest and Group 3 were smallest in all comparisons (P < .05). Histologically, low grade inflammatory responses were observed in Group 1, mild histiocytic infiltration in Group 2, widespread muscle fiber loss in Group 3, and plasmocytic infiltration in Group 4.ConclusionsMX‐JC showed the least resorption at 4 and 12 weeks among all groups. T cell inflammatory responses were observed with MX‐JC but were reduced by 12 weeks while B cell immune responses, indicative of antibody priming, were predominantly noted with MACD. MX‐JC + ADSC showed low grade immunity while the XHA showed greater myocyte loss compared to the other groups.Level of EvidenceNA Laryngoscope, 131:E2452–E2460, 2021