Analytic Evaluation of a Human ELISA Kit for Measurement of Inhibin B in Rat Samples

Circulating microRNAs as promising testicular translatable safety biomarkers: current state and future perspectives

Drug-induced testicular injury (DITI) is one of the often-observed and challenging safety issues seen during drug development. Semen analysis and circulating hormones currently utilized have significant gaps in their ability to detect testicular damage accurately. In addition, no biomarkers enable a mechanistic understanding of the damage to the different regions of the testis, such as seminiferous tubules, Sertoli, and Leydig cells. MicroRNAs (miRNAs) are a class of non-coding RNAs that modulate gene expression post-transcriptionally and have been indicated to regulate a wide range of biological pathways. Circulating miRNAs can be measured in the body fluids due to tissue-specific cell injury/damage or toxicant exposure. Therefore, these circulating miRNAs have become attractive and promising non-invasive biomarkers for assessing drug-induced testicular injury, with several reports on their use as safety biomarkers for monitoring testicular damage in preclinical species. Leveraging emerging tools such as 'organs-on-chips' that can emulate the human organ's physiological environment and function is starting to enable biomarker discovery, validation, and clinical translation for regulatory qualification and implementation in drug development.

Effects of doxorubicin on sperm DNA methylation in mouse models of testicular toxicity

Testicular toxicity is a frequent adverse effect of cancer chemotherapy that has no effective clinical biomarker. To find new biomarkers, we focused on epigenetic mechanisms in the male germline. We investigated the DNA methylation status of the male germline during testicular toxicity induced by doxorubicin (DXR), a widely used anticancer agent. We established mouse models of early stage testicular toxicity and testicular pre-toxicity by the administration of 0.2 mg/kg and 0.02 mg/kg DXR, respectively, twice weekly for 5 weeks. Histological analysis showed sparse abnormalities in testicular tissue; however, western blotting analysis revealed reduced testicular expression levels of DNA methyltransferases DNMT3a and DNMT3b in both DXR-treated groups. Interestingly, comprehensive sperm DNA methylation analysis using Methyl-CpG binding domain protein-enriched genome sequencing revealed that hypomethylation was the most frequent change induced by DXR. These findings suggest that sperm DNA methylation status may be used as an early diagnostic marker for testicular changes not detected by conventional toxicity analysis.

A technical and clinical evaluation of a new assay for inhibin A and its use in second trimester Down syndrome screening

BACKGROUND

The objective of the study was to compare a new AutoDELFIA® Inhibin A kit (B064-102) with the Access Inhibin A kit (A36097) using clinical specimens and to evaluate the AutoDELFIA® Inhibin A assay performance in screening for Down syndrome in the second trimester of pregnancy.

METHODS

Using clinical samples, we performed a method comparison between new and existing inhibin A kits and assessed AutoDELFIA® Inhibin A kit precision performance. Normal median values for the second trimester of pregnancy were also determined. Finally, we evaluated the screening performance of the AutoDELFIA® Inhibin A kit together with other second trimester biomarkers for the detection of Down syndrome.

RESULTS

The two methods showed a high degree of correlation (r=0.99, Pearson and Spearman correlation), and the average relative level difference between the methods at a concentration range of 41.7-1925 pg/mL was 19.6% [95% confidence interval (CI) from 17.6% to 21.5%]. The acceptable precision of the AutoDELFIA® Inhibin A kit was demonstrated: the within-lot CV% varied from 1.9% to 3.9%. The screening performance results show that AutoDELFIA® Inhibin A when added to a combination of other second trimester serum markers [human alpha foetoprotein (hAFP), free beta subunit of human chorionic gonadotropin (free hCGβ) and unconjugated estriol (uE3) or hAFP and free hCGβ] improves the detection rate of screening in both combinations.

CONCLUSIONS

The performance of the AutoDELFIA® Inhibin A assay is highly acceptable for routine laboratory use for screening Down syndrome in the second trimester of pregnancy.

SOT Symposium Highlight: Translatable Indicators of Testicular Toxicity: Inhibin B, MicroRNAs, and Sperm Signatures

Testicular toxicity is an important safety endpoint in drug development and risk assessment, but reliable and translatable biomarkers for predicting injury have eluded researchers. However, this area shows great potential for improvement, with several avenues currently being pursued. This was the topic of a symposium session during the 2013 Society of Toxicology Annual Meeting in San Antonio, TX, entitled "Translatable Indicators of Testicular Toxicity: Inhibin B, MicroRNAs, and Sperm Signatures." This symposium brought together stakeholders from academia, government, and industry to present the limitations and drawbacks of currently used indicators of injury and discussed the ongoing efforts in developing more predictive biomarkers of injury. The presentations highlighted the early challenges of using circulating inhibin B and microRNA levels, and sperm messenger RNA transcript abundance and DNA methylation profiles, as novel biomarkers of testicular toxicity.

The inhibin B response in male rats treated with a GnRH agonist and an endothelin receptor antagonist

BACKGROUND

This study examined the correlation between Inhibin B and testicular pathology.

METHODS

Male Han Wistar rats (approximately 10 weeks old) were administered either vehicle or an endothelin receptor antagonist (ET-An) orally for 28 days or a Gonadotropin Releasing Hormone (GnRH) agonist (GnRH-A) as a subcutaneous implant on day 1. Ten animals/group/time point were killed on days 4, 8, 15, and 29 (controls on days 15 and 29) for testes weights and histopathology. In-life blood samples were taken on days 4, 8, 15, and 29 to measure Inhibin B, Follicle-Stimulating Hormone (FSH), and Lutenising Hormone (LH), and at necropsy for the same hormones plus testosterone.

RESULTS

Plasma Inhibin B showed a wide concentration range in controls (group means 76.4-184.2 pg/ml; individual animals 17.8-381 pg/ml). GnRH-A caused decreased testes weights plus degenerative testicular pathology from day 4 with partial recovery by day 29. Statistically significant reductions in Inhibin B were observed at all time points and appeared to track the development and partial recovery of the pathology (generally <50 pg/ml on days 4-15; group mean 92 pg/ml on day 29). ET-An produced an increase in testes weights and a nondegenerative lesion of minimal tubular dilatation. There was a trend for lower Inhibin B values (30-50%) at all time points, including on day 4 when tubular dilatation was not yet evident.

CONCLUSION

Inhibin B showed a good correlation with testicular pathology for GnRH-A, and following ET-An administration appeared to give a signal that might reflect changes in tubular function in the absence of degenerative pathology.

Inhibin B response to testicular toxicants hexachlorophene, ethane dimethane sulfonate, di-(n-butyl)-phthalate, nitrofurazone, DL-ethionine, 17-alpha ethinylestradiol, 2,5-hexanedione, or carbendazim following short-term dosing in male rats

BACKGROUND

Inhibin B is a heterodimer glycoprotein that downregulates follicle-stimulating hormone and is produced predominantly by Sertoli cells. The potential correlation between changes in plasma Inhibin B and Sertoli cell toxicity was evaluated in male rats administered testicular toxicants in eight studies. Inhibin B fluctuations over 24 hr were also measured.

METHODS

Adult rats were administered one of eight testicular toxicants for 1 to 29 days. The toxicants were DL-ethionine, dibutyl phthalate, nitrofurazone, 2,5-hexanedione, 17-alpha ethinylestradiol, ethane dimethane sulfonate, hexachlorophene, and carbendazim. In a separate study plasma was collected throughout a 24-hr period via an automatic blood sampler.

RESULTS

Histomorphologic testicular findings included seminiferous tubule degeneration, round and elongate spermatid degeneration/necrosis, seminiferous tubule vacuolation, aspermatogenesis, and interstitial cell degeneration. There was a varying response of plasma Inhibin B levels to seminiferous tubule toxicity, with three studies showing high correlation, three studies with a response only at a certain time or dose, and two studies with no Inhibin B changes. In a receiver operating characteristics exclusion model analysis, where treated samples without histopathology were excluded, Inhibin B showed a sensitivity of 70% at 90% specificity in studies targeting seminiferous tubule toxicity.

CONCLUSION

Decreases in Inhibin B correlated with Sertoli cell toxicity in the majority of studies evaluated, demonstrating the value of Inhibin B as a potential biomarker of testicular toxicity. There was no correlation between decreases in Inhibin B and interstitial cell degeneration. In addition, a pattern of Inhibin B secretion could not be identified over 24 hr.

The inhibin B response in male rats treated with two drug candidates

BACKGROUND

Serum Inhibin B was measured in two studies of known testis-toxic drug candidates.

METHODS AND RESULTS

Study 1 was for a compound for Hepatitis C, and utilized a 10-week dosing period, followed by mating and necropsy of half of each group, and then a 12-week recovery period for the remaining animals. At the postmating necropsy, 6 of 15 high-dose males had testis lesions; Inhibin B was significantly reduced in all animals in that group. The mid-dose group had no lesions but significantly reduced serum Inhibin B. At recovery, 9 of 15 high-dose males showed damage in testes; serum Inhibin B levels were not different from controls. Inhibin B appeared to both overreport and underreport testis damage in Study 1. Study 2 was an acute pathogenesis study for an antibacterial compound, using control and two dose levels and multiple time points (days 5, 8, 15, 22, and then untreated until day 71). At each time point blood was sampled from all remaining rats and five/group were killed for histologic evaluation. The low-dose group had minimal to moderate lesions, while serum Inhibin B was never changed. The high-dose animals progressed quickly from minimal lesions to being broadly and moderately affected; serum Inhibin B levels were reduced at days 8 and 15 only. In Study 2, Inhibin B appeared less sensitive than histology, except at the extremes of testis damage, when Inhibin B was routinely low.

CONCLUSION

We conclude that in these two studies there was a poor correlation between changes in serum levels of Inhibin B and testis histopathology.

Inhibin B in plasma samples from male volunteer panel selected for health but not fertility: sources of variability

BACKGROUND

Inhibin B was measured in plasma samples obtained from 34 healthy male subjects selected on criteria typical for a phase I clinical trial across a wide age range (19-70 years).

METHODS

Mutiple samples (up to seven per subject) were obtained as a set consisting of one baseline sample then three pairs of morning and evening samples. This allowed assessment of the fed/fasted state and diurnal effects. Samples were analyzed using a commercially available inhibin B ELISA assay. Across all time points, the mean plasma inhibin B was 197 pg/ml ± 67pg/ml.

RESULTS

The results confirmed a diurnal effect where inhibin B concentration is on average about 40 pg/ml greater in the morning and showed a negative influence of age on inhibin B concentrations. There was no overt influence of body mass index on inhibin B. A variance components analysis revealed that more than 80% of the total variability was due to the variability observed between individuals. Within the fed-fasted sampling schedule of this study, inhibin B levels were slightly lower when volunteers had eaten but the magnitude of this effect was within the variance encountered between occasions.

CONCLUSION

These results illustrate that when undertaking longitudinal monitoring of inhibin B in clinical trials as means of monitoring testicular function, it is important to obtain samples from an individual at the same time of day and to use statistical methods which analyze the magnitude of deviation of an individual from their personal baseline as well as looking at group means and influence of study duration.