Comparison of fecal preservation and extraction methods for steroid hormone metabolite analysis in wild crested macaques

Validating the underpinnings of water corticosterone measurement for aquatic amphibians

Background

Good animal welfare is important ethically but also to ensure animals provide valid scientific models. Despite thousands of amphibians in research laboratories there is minimal quantitative evidence pertaining to their management and welfare. This study validated methods to non-invasively measure corticosterone, the amphibian 'stress' hormone, from tank water to provide a robust and reliable welfare assessment tool.

Methods

We report experiments (A) that evaluate parameters linked to the performance of our biochemical extraction methods for waterborne corticosterone and, importantly, associated sampling procedures. We evaluate appropriate sampling water type, sampling vessel, filtration methods, potential degradation of waterborne corticosterone over time and the impact of sampling procedures on animal corticosterone levels. We wanted to determine sampling parameters that yielded the least background corticosterone and had minimum negative impact on the animals. The second series of experiments (B) evaluated parameters linked to the biology of Xenopus, including the influence of circadian rhythm, sex and snout-vent length on waterborne corticosterone levels, since fundamental knowledge of a species' biology is essential for designing robust experiments and in the interpretation of the results.

Results

We propose collecting corticosterone samples in deionised water in either plastic or glass containers. The filtering process does not impact the amount of corticosterone measured in the water sample. Levels of corticosterone collected in the water change over a 48-hr period so we advocate standardising time from hormone collection to storage at - 20 °C. Repeated transfer of frogs to sampling containers does not increase corticosterone, suggesting our methods are not cumulatively stressful. Corticosterone levels were not impacted by circadian phase, sex or snout-vent length.

Conclusion

We have developed and validated robust methods to quantify waterborne corticosterone. We hope they provide a template for researchers wishing to develop methods to measure waterborne corticosterone in aquatic amphibians.

Validation of a Commercial ELISA Kit for Non-Invasive Measurement of Biologically Relevant Changes in Equine Cortisol Concentrations

The measurement of fecal cortisol/corticosterone metabolites (FCMs) is often used to quantify the stress response. The sampling method is relatively non-invasive, reduces concern for elevation of cortisol from the sampling method, and has been shown to measure cortisol more consistently without the daily diurnal rhythm observed in blood. Commercial ELISA (enzyme-linked immunoassay) kits offer benefits over previously validated immunoassay methods but lack validation. The objective of this study was to evaluate a commercial ELISA kit (Arbor AssaysTM DetectX® Cortisol ELISA kit, K003-H1, Ann Arbor, MI, USA) and provide analytical and biologic validation of equine fecal and plasma samples. Horses (4 male, 4 female, mean ± SD: 4 ± 5 yr) were transported for 15 min with limited physical and visual contact via a livestock trailer. Blood and fecal samples were collected pre- and post-transportation. Parallelism, accuracy, and precision tests were used to analytically validate this kit. Data were analyzed using PROC MIXED in SAS 9.4. Plasma cortisol concentrations increased in response to trailering (254.5 ± 26.4 nmol/L, 0 min post-transportation) compared to pre-transportation (142.8 ± 26.4 nmol/L). FCM concentrations increased 24 h post-trailering (10.8 ± 1.7 ng/g) when compared to pre-transportation (7.4 ± 1.7 ng/g). These data support that changes in FCMs can be observed 24 h post-stressor. In conclusion, the Arbor AssaysTM DetectX® Cortisol ELISA kit is a reliable, economic option for the measurement of biologically relevant changes in cortisol in equine plasma and FCMs.

Validation of a field-friendly faeces drying and storage method for quantifying faecal glucocorticoid metabolites in African elephants (Loxodonta africana) opens up new perspectives for conservationists

Faecal glucocorticoid metabolites (fGCMs) are a relevant means of non-invasively assessing adrenocortical activity and thus, a key physiological stress response in wildlife populations. However, the widespread use of fGCMs as a stress-related biomarker in conservation biology is often hampered by the logistical challenge of storing collected faecal material frozen until it reaches the laboratory for analysis. Although alternative approaches to minimize potential alteration of fGCM composition post-defecation have been recently identified, there is to our knowledge, no satisfactory alternative method established for the preservation of elephant dung. In this study, we validated a field-friendly protocol for dehydrating African elephant faeces samples using a food dehydrator with desiccant and investigated the stability of fGCM concentrations in the dehydrated faeces when stored at ambient temperature. We collected 40 faecal samples from African elephants and compared fGCM concentrations of freeze-dried and dehydrated sample sub-sets. Samples dried in the field showed a slight but significant overall -6% reduction in fGCM concentration compared with frozen control samples. However, fGCM concentrations following field dehydration protocol match those of control samples with high accuracy, as evidenced by the low bias and strong coefficient of determination between the two approaches (R2 = 0.88). In addition, over nearly 2 months, storage time at ambient temperature of the dehydrated samples had no effect on the fGCM concentrations compared with those measured in the control samples (F-statistic = 1.82; P = 0.18). Dehydrating the samples in the field thus provides an easy and cost-effective alternative to freezing, especially when working in remote areas with unstable electrical supply. Our results encourage the widespread use of fGCMs by conservationists as non-invasive means of steroid monitoring of African elephants in the current context of a general increase in wildlife welfare research. Future studies are needed to extend the use of this protocol to other species and to other steroid classes.

Variability in fecal metabolome depending on age, PFBS pollutant, and fecal transplantation in zebrafish: A non-invasive diagnosis of health

To protect the wellbeing of research animals, certain non-invasive measures are in increasing need to facilitate an early diagnosis of health and toxicity. In this study, feces specimen was collected from adult zebrafish to profile the metabolome fingerprint. Variability in fecal metabolite composition was also distinguished as a result of aging, perfluorobutanesulfonate (PFBS) toxicant, and fecal transplantation. The results showed that zebrafish feces was very rich in a diversity of metabolites that belonged to several major classes, including lipid, amino acid, carbohydrate, vitamin, steroid hormone, and neurotransmitter. Fecal metabolites had functional implications to multiple physiological activities, which were characterized by the enrichment of digestion, absorption, endocrine, and neurotransmission processes. The high richness and functional involvement of fecal metabolites pinpointed feces as an abundant source of diagnostic markers. By comparison between young and aged zebrafish, fundamental modifications of fecal metabolomes were caused by aging progression, centering on the neuroactive ligand-receptor interaction pathway. Exposure of aged zebrafish to PFBS pollutant also significantly disrupted the metabolomic structure in feces. Of special concern were the changes in fecal hormone intermediates after PFBS exposure, which was concordant with the in vivo endocrine disrupting effects of PFBS. Furthermore, it was intriguing that transplantation of young zebrafish feces efficiently mitigated the metabolic perturbation of PFBS in aged recipients, highlighting the health benefits of therapeutic strategies based on gut microbiota manipulation. In summary, the present study provides preliminary clues to evidence the non-invasive advantage of fecal metabolomics in the early diagnosis and prediction of physiology and toxicology.

Transplantation of Aceh cattle ovary into the uterus of pseudopregnant local rabbits: Effect of post-transplant stress on uterine histopathology and ovarian follicle dynamics

Background and Aim

The increase in the levels of the cortisol hormone caused by the stress conditions generated by an ovary transplantation procedure can damage the uterus of the transplant recipient as well as the transplanted ovaries. This study aimed to analyze the histopathological changes that occur in the uterine horn of pseudopregnant local rabbits (recipients), as well as the ovarian follicular integrity of the donor Aceh cattle after transplantation.

Materials and Methods

After 30 days of adaptation, all rabbits were divided into three treatment groups: R1 (the group of rabbits that underwent ovarian transplantation for 3 days, n = 5), R2 (the group of rabbits that underwent ovarian transplantation for 5 days, n = 5), and R3 (the group of rabbits that underwent ovarian transplantation for 7 days, n = 5). Pseudopregnancy induction was performed using the pregnant mare's serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG) methods. The rabbits were injected with 100 IU of PMSG intramuscularly, followed by an injection of 75 IU of hCG intravenously 3 days later. Ovarian transplantation was performed on day 8 (day 0 was the day of hCG injection). The concentration of cortisol hormone metabolites was measured from fecal samples using an enzyme-linked immunosorbent assay technique. The uterus and ovaries were collected for histopathological and follicular dynamics examination after the transplantation process was completed.

Results

The mean cortisol levels (ng/g) recorded before versus after the transplant in the R1, R2, and R3 groups were 146.23 ± 17.60 versus 338.84 ± 302.79, 128.97 ± 81.56 versus 174.79 ± 101.70, and 124.88 ± 43.61 versus 321.91 ± 221.63 (p < 0.05), respectively. The examination of the histopathological appearance of the uterus revealed edema in the uterine lumen, hyperemia and hemorrhage in the endometrium, necrosis of the epithelium, and infiltration of inflammatory cells. Hemorrhage and hyperemia were severe and filled the endometrium in the R1 compared with the R2 and R3 animals. Ovarian follicle development occurred in all treatment groups, although some histopathological features were observed. The number of tertiary follicles in R1, R2, and R3 animals was 24.67 ± 7.37, 20.67 ± 7.57, and 9.67 ± 3.79 (p < 0.05), respectively.

Conclusion

Based on the results of this study, it can be concluded that the transplantation of ovaries from Aceh cattle into pseudopregnant local rabbits triggered an increase in the levels of the cortisol hormone and uterine histological changes; however, follicles were still detected at various stages of development in the transplanted Aceh cattle ovaries. The results of this study are valuable for clinicians and researchers because they provide information regarding an alternative in vivo ovarian preservation technique using pseudopregnant rabbits.

An Optimised Monophasic Faecal Extraction Method for LC-MS Analysis and Its Application in Gastrointestinal Disease

Liquid chromatography coupled with mass spectrometry (LC-MS) metabolomic approaches are widely used to investigate underlying pathogenesis of gastrointestinal disease and mechanism of action of treatments. However, there is an unmet requirement to assess faecal metabolite extraction methods for large-scale metabolomics studies. Current methods often rely on biphasic extractions using harmful halogenated solvents, making automation and large-scale studies challenging. The present study reports an optimised monophasic faecal extraction protocol that is suitable for untargeted and targeted LC-MS analyses. The impact of several experimental parameters, including sample weight, extraction solvent, cellular disruption method, and sample-to-solvent ratio, were investigated. It is suggested that a 50 mg freeze-dried faecal sample should be used in a methanol extraction (1:20) using bead beating as the means of cell disruption. This is revealed by a significant increase in number of metabolites detected, improved signal intensity, and wide metabolic coverage given by each of the above extraction parameters. Finally, we addressed the applicability of the method on faecal samples from patients with Crohn's disease (CD) and coeliac disease (CoD), two distinct chronic gastrointestinal diseases involving metabolic perturbations. Untargeted and targeted metabolomic analysis demonstrated the ability of the developed method to detect and stratify metabolites extracted from patient groups and healthy controls (HC), highlighting characteristic changes in the faecal metabolome according to disease. The method developed is, therefore, suitable for the analysis of patients with gastrointestinal disease and can be used to detect and distinguish differences in the metabolomes of CD, CoD, and HC.

Effects of faecal inorganic content variability on quantifying glucocorticoid and thyroid hormone metabolites in large felines: Implications for physiological assessments in free-ranging animals

Faecal glucocorticoid (GC) and triiodothyronine (T3) metabolites and their interactions are increasingly used to monitor perceived stress and nutritional challenges in free-ranging animals. However, a number of extrinsic and intrinsic factors including hormone-inert dietary materials, inorganic matters etc. are known to affect reliable hormone metabolite quantifications. In this study, the impacts of inorganic matter (IOM) on faecal GC (fGCMs) and T3 (fT3Ms) metabolite measure were addressed in wild tiger (n = 193 from Terai Arc landscape, India) and captive lion (n = 120 from Sakkarbaug Zoological Garden, Gujarat, India) and possible corrective measures were evaluated. The wild tiger samples contained highly variable IOM content (9-98%, mostly with > 40% IOM) compared to captive Asiatic lion (17-57%, majority with < 40% IOM). Significant correlations were observed between IOM content and tiger fGCM (r = -0.46, p = 0.000), fT3M (r = -0.58, p = 0.000) and lion fT3M measures (r = -0.43, p = 0.003). Two corrective measures viz. removing samples with ≥ 80% IOM and subsequently expressing concentrations as per gram of organic dry matter (instead of total dry matter) reduced IOM influence on tiger fGCM, fT3M and lion fT3M, without affecting lion fGCM measures. The corrective measures changed the interpretations of fT3M data of field-collected tiger samples with no significant changes in fGCM (both tiger and lion) and fT3M (lion) data. As faecal IOM content is common in many wild species, the results emphasize the need to reduce IOM-driven hormone data variation for ecologically relevant interpretations towards species conservation.

Preservation of fecal glucocorticoid metabolites and immunoglobulin A through silica gel drying for field studies in horses

Non-invasive methods enable stress evaluation through measuring fecal glucocorticoid metabolites (FGMs), and immunoglobulin A (IgA) in the feces avoiding stressful blood drawing or stressful restraining of animals in the field. However, FGMs and IgA are mostly analysed in freshly frozen samples, which is difficult when fresh samples cannot be frozen immediately or frozen samples cannot be stored or transported. Good results were also derived from air-dried fecal samples, which are hampered by unstable air humidity in the field. These difficulties may be overcome, when drying of samples could be induced with colorless silica gel (SiO₂) granules in a secure set-up, such as an air tight tube. We determined the speed of drying 1.5 g of a fresh fecal sample from six horses on air and on silica gel. Furthermore, FGMs and IgA were analysed in differently stored subsamples from 12 horses: in frozen fecal samples, in air- or silica gel-dried samples stored for 1 day and for 7 days, and in wet fecal samples kept in a tube at room temperature for 7 days. FGM levels remained stable in feces dried on air or on silica gel for 7 days, whereas IgA quantities showed a significant loss. Under field conditions, when freezing or transporting the frozen samples is not possible and humidity hampers air drying, drying samples on silica gel in air tight tubes appears to be very helpful and reliable for analysing FGMs.

The validation of a commercial enzyme-linked immunosorbent assay and the effect of freeze-thaw cycles of serum on the stability of cortisol and testosterone concentrations in Aceh cattle

Background: To obtain accurate measurements of cortisol (C) and testosterone (T) in Aceh cattle, commercial enzyme-linked immunosorbent assay (ELISA) kits need to be carefully validated. Moreover, repeated freeze-thaw cycles during the storage of the samples may affect the stability of the hormones in the serum. Here, the reliability of C and T concentration measurements in the serum of Aceh cattle, was tested using commercial C and T ELISA kits designed to measure human C and T concentrations. Further, the effect of repeated freeze-thaw cycles on the stability of C and T concentrations in the serum was evaluated. Methods: Commercial C (Cat. no. EIA-1887) and T (Cat. no. EIA-1559) ELISA kits from DRG Instruments GmbH were validated through an analytical validation test (i.e., parallelism, accuracy, and precision) and a biological validation test (for C: effect of transportation on the C secretion; for T: the concentrations of T between bulls and cows). To test the effects of freeze-thaw cycles, cattle serum was subjected to the following treatments: (i) remained frozen at -20 OC (control group); (ii) exposed to freeze-thaw cycles for two, four, six, and eight times (test groups).   Results: Parallelism, accuracy, and precision tests showed that both  C and T ELISA kits adequately measured C and T in the serum of Aceh cattle. Concentrations of C post-transportation were significantly higher than pre-transportation (p<0.01). Concentrations of T in bulls were significantly higher than in cows (p<0.01). After four to eight freeze-thaw cycles, C concentrations were significantly lower compared to the control group (all p < 0.05). In contrast, T concentrations remained stable (all p>0.05). Conclusions: Commercial C (EIA-1887) and T (EIA-1559) ELISA kits are reliable assays for measuring serum C and T, respectively, in Aceh cattle. Repeated freeze-thaw cycles significantly affected the stability of serum C, but did not for T.

The validation of a commercial enzyme-linked immunosorbent assay and the effect of freeze-thaw cycles of serum on the stability of cortisol and testosterone concentrations in Aceh cattle

Background: To obtain accurate measurements of cortisol (C) and testosterone (T) in Aceh cattle, commercial enzyme-linked immunosorbent assay (ELISA) kits need to be carefully validated. Moreover, repeated freeze-thaw cycles during the storage of the samples may affect the stability of the hormones in the serum. Here, the reliability of C and T concentration measurements in the serum of Aceh cattle, was tested using commercial C and T ELISA kits designed to measure human C and T concentrations. Further, the effect of repeated freeze-thaw cycles on the stability of C and T concentrations in the serum was evaluated. Methods: Commercial C (Cat. no. EIA-1887) and T (Cat. no. EIA-1559) ELISA kits from DRG Instruments GmbH were validated through an analytical validation test (i.e., parallelism, accuracy, and precision) and a biological validation test (for C: effect of transportation on the C secretion; for T: the concentrations of T between bulls and cows). To test the effects of freeze-thaw cycles, cattle serum was subjected to the following treatments: (i) remained frozen at -20 OC (control group); (ii) exposed to freeze-thaw cycles for two, four, six, and eight times (test groups).   Results: Parallelism, accuracy, and precision tests showed that both  C and T ELISA kits adequately measured C and T in the serum of Aceh cattle. Concentrations of C post-transportation were significantly higher than pre-transportation (p<0.01). Concentrations of T in bulls were significantly higher than in cows (p<0.01). After four to eight freeze-thaw cycles, C concentrations were significantly lower compared to the control group (all p < 0.05). In contrast, T concentrations remained stable (all p>0.05). Conclusions: Commercial C (EIA-1887) and T (EIA-1559) ELISA kits are reliable assays for measuring serum C and T, respectively, in Aceh cattle. Repeated freeze-thaw cycles significantly affected the stability of serum C, but did not for T.

The validation of a commercial enzyme-linked immunosorbent assay and the effect of freeze-thaw cycles of serum on the stability of cortisol and testosterone concentrations in Aceh cattle

Background: To obtain accurate measurements of cortisol (C) and testosterone (T) in Aceh cattle, commercial enzyme-linked immunosorbent assay (ELISA) kits need to be carefully validated. Moreover, repeated freeze-thaw cycles during the storage of the samples may affect the stability of the hormones in the serum. Here, the reliability of C and T concentration measurements in the serum of Aceh cattle, was tested using commercial C and T ELISA kits designed to measure human C and T concentrations. Further, the effect of repeated freeze-thaw cycles on the stability of C and T concentrations in the serum was evaluated. Methods: Commercial C (Cat. no. EIA-1887) and T (Cat. no. EIA-1559) ELISA kits from DRG Instruments GmbH were validated through an analytical validation test (i.e., parallelism, accuracy, and precision) and a biological validation test (for C: effect of transportation on the C secretion; for T: the concentrations of T between bulls and cows). To test the effects of freeze-thaw cycles, cattle serum was subjected to the following treatments: (i) remained frozen at -20 ^OC (control group); (ii) exposed to freeze-thaw cycles for two, four, six, and eight times (test groups).   Results: Parallelism, accuracy, and precision tests showed that both  C and T ELISA kits adequately measured C and T in the serum of Aceh cattle. Concentrations of C post-transportation were significantly higher than pre-transportation (p<0.01). Concentrations of T in bulls were significantly higher than in cows (p<0.01). After four to eight freeze-thaw cycles, C concentrations were significantly lower compared to the control group (all p < 0.05). In contrast, T concentrations remained stable (all p>0.05). Conclusions: Commercial C (EIA-1887) and T (EIA-1559) ELISA kits are reliable assays for measuring serum C and T, respectively, in Aceh cattle. Repeated freeze-thaw cycles significantly affected the stability of serum C, but did not for T.

Non-invasive measurement of glucocorticoids: Advances and problems

Glucocorticoids (GCs; i.e. cortisol/corticosterone) are a central component of the stress response and thus their measurement is frequently used to evaluate the impact of stressful situations. Their metabolites from faeces of various animal species are more and more taken as a non-invasive aid to assess GC release and thus adrenocortical activity. The current literature review includes an extensive collection (1327 papers) and evaluation (see also Supplementary Tables) of the literature on faecal cortisol/corticosterone metabolite (FCM) analysis published to date. It aims at giving reference for researchers interested in implementing FCM analysis into their study or seeking to improve such methods by providing background knowledge on GC metabolism and excretion, conveying insights into methodological issues and stating caveats of FCM analysis and by highlighting prerequisites for and some examples of a successful application of such methods. Collecting faecal samples and analysing FCMs may appear simple and straightforward, but researchers have to select and apply methods correctly. They also need to be aware of the many pitfalls and potentially confounding factors and, last but not least, have to carefully interpret results. Applied properly, measurement of FCMs is a powerful non-invasive tool in a variety of research areas, such as (stress) biology, ethology, ecology, animal conservation and welfare, but also biomedicine.