Recent Successes in the Identification, Development, and Qualification of Translational Biomarkers

The development of novel safety or efficacy biomarkers has increasingly been used to improve safety monitoring and minimize attrition during drug development; however, for new biomarkers, the failure rate can equal or exceed that of new chemical entities. Drug-induced kidney injury is recognized to occur throughout the drug development process, with histopathology considered to be the gold standard for preclinical toxicologic screening. Renal biomarkers used clinically are primarily biomarkers of renal function and are considered insensitive for the detection of drug-induced kidney injury during first-in-man studies, particularly for compounds known to induce renal injury in preclinical species. Recent efforts by public–private partnerships have led to unprecedented success in the identification, development, and qualification of several new translatable biomarkers of kidney injury in the rat. To optimize the chance of success in current and future biomarker efforts in preclinical species and man, selection and development of biomarkers should emphasize biological considerations including marker variability and biology in both health and disease. The research to support the qualification of novel renal safety markers for routine use in the clinical setting is currently underway, and results from this work are greatly anticipated.

Use of urinary renal biomarkers to evaluate the nephrotoxic effects of melamine or cyanuric acid in non-pregnant and pregnant rats

Although traditional assessments of renal damage detect loss of kidney function, urinary renal biomarkers are proposed to indicate early changes in renal integrity. The recent adulteration of infant formula and other milk-based foods with melamine revealed a link between melamine ingestion and nephropathy. Thus, the effects of melamine and related analogs (e.g., cyanuric acid) should be assessed in other potentially sensitive groups. We evaluated whether urinary Kim-1, clusterin, and osteopontin could detect the effects of high doses of melamine or cyanuric acid in pregnant and non-pregnant female rats gavaged with 1000 mg/kg bw/day for 10 days. We demonstrate that these biomarkers can differentiate the severity of effects induced by melamine or cyanuric acid. All melamine-treated animals experienced adverse effects; however, pregnant rats were most sensitive as indicated by increased SCr, BUN, and kidney weights, decreased body weight, and presence of renal crystals. These effects coincided with elevated urinary biomarker levels as early as day 2 of exposure. One cyanuric acid-treated rat displayed effects similar to melamine, including increased urinary biomarker levels. This work illustrates that these biomarkers can detect early effects of melamine or cyanuric acid crystal-induced nephropathy and further supports the use of urinary protein immunoassays as a powerful, non-invasive method to assess nephrotoxicity.

Evaluation of the usefulness of novel biomarkers for drug-induced acute kidney injury in beagle dogs

As kidney is a major target organ affected by drug toxicity, early detection of renal injury is critical in preclinical drug development. In past decades, a series of novel biomarkers of drug-induced nephrotoxicity were discovered and verified in rats. However, limited data regarding the performance of novel biomarkers in non-rodent species are publicly available. To increase the applicability of these biomarkers, we evaluated the performance of 4 urinary biomarkers including neutrophil gelatinase-associated lipocalin (NGAL), clusterin, total protein, and N-acetyl-β-D-glucosaminidase (NAG), relative to histopathology and traditional clinical chemistry in beagle dogs with acute kidney injury (AKI) induced by gentamicin. The results showed that urinary NGAL and clusterin levels were significantly elevated in dogs on days 1 and 3 after administration of gentamicin, respectively. Gene expression analysis further provided mechanistic evidence to support that NGAL and clusterin are potential biomarkers for the early assessment of drug-induced renal damage. Furthermore, the high area (both AUCs=1.000) under receiver operator characteristics (ROC) curve also indicated that NGAL and clusterin were the most sensitive biomarkers for detection of gentamicin-induced renal proximal tubular toxicity. Our results also suggested that NAG may be used in routine toxicity testing due to its sensitivity and robustness for detection of tissue injury. The present data will provide insights into the preclinical use of these biomarkers for detection of drug-induced AKI in non-rodent species.

Systemic toxic effects during early phases of topical 4-NQO-induced oral carcinogenesis in rats

BACKGROUND

Most studies have demonstrated 4-NQO toxicity to oral epithelium during oral carcinogenesis induction, but systemic toxicity has been poorly addressed. The aim of this study was to describe the systemic effect of 4-NQO topical application during early phases of oral cancer induction.

METHODS

A 4-NQO propylene glycol ointment was topically applied on the rat tongue three times a week for 16 weeks. Local and systemic 4-NQO toxicity was evaluated by body weight gain, hematology, and serum chemistry analyses, histopathology, and proliferating cell nuclear antigen (PCNA) immunohistochemistry.

RESULTS

Significant reduction in body weight gain and in white blood cell count as well as significant increase in serum ALT and AST was observed after 16 weeks of 4-NQO topical application. Focal hepatic lobular necrosis, renal tubular degeneration, and decreased cellularity in the splenic white pulp were also detected.

CONCLUSIONS

4-NQO topical application on the tongue of rats for 16 weeks seems to have caused hepatic, renal, and splenic toxicity. Potential systemic toxicity should be considered to monitor for variables that could interfere in topical oral carcinogenesis experiments.

Usefulness of urinary kidney injury molecule-1 (Kim-1) as a biomarker for cisplatin-induced sub-chronic kidney injury

We explored biomarkers suitable for monitoring sub-chronic kidney injury using the three rat models of cisplatin (CDDP)-induced kidney injury, which were designed to extend the current knowledge beyond the sub-acute exposure period. In the pilot study, a single intravenous administration of 1.5 mg kg(-1) CDDP to rats was confirmed to result in no histopathological changes. Subsequently, CDDP was intravenously administered to rats at a dose of 1.5 mg kg(-1) for 4 days at 24-h intervals (Experimental model 1) and for up to 10 weeks at weekly intervals (Experimental models 2 and 3), and the changes in blood and urine components, such as recently recommended urinary biomarkers (Kim-1, clusterin and so on) and traditional blood biomarkers (blood urea nitrogen and serum creatinine), were examined together with the histopathological changes in renal tissues during the development of the kidney injury in each model. In these experimental models, a significant increase in urinary Kim-1 was observed prior to the histopathological changes in renal tissues, and these changes were retained after the adverse histopathological changes. Significant changes in all of the other urinary biomarkers examined occurred along with the histopathological changes. In addition, the increase in urinary Kim-1 after weekly treatment with CDDP for 4 weeks was reduced in a time-dependent manner after cessation of the drug. The present findings indicate that urinary Kim-1 is the most useful biomarker for CDDP-induced rat sub-chronic kidney injury among the biomarkers examined.

Comparison between male and female Sprague-Dawley rats in the response of urinary biomarkers to injury induced by gentamicin

Differences were examined between male and female Sprague-Dawley rats in the response of 16 urinary biomarkers (measured using several assay platforms) to renal injury produced by gentamicin administered subcutaneously for 10 days at a dosage of 75 mg/kg. Urinary biomarkers expressed as fold difference from contemporaneous controls and renal histopathology were assessed after 3 and 10 doses. On day 4, minimal proximal tubular changes were observed microscopically in all males but no females; on day 11, more extensive and more severe injury was observed to a similar extent in all animals of both sexes. Modest increases (maximum 5-fold) in all urinary biomarkers (except epidermal growth factor [EGF], which was decreased) on day 4 and marked elevations (maximum 271-fold) on day 11 were seen consistently in both sexes. However, the magnitude of the increases differed between the sexes. On day 4, despite the lack of tubular injury, many biomarkers were more elevated in females than males but this rarely led to statistically significant sex differences; only 2 biomarkers (β2-microglobulin and total protein) showed a greater increase in males than females in line with the histopathology. On day 11, there were many more biomarkers that showed a statistically significant difference between the sexes in fold change with treatment; in line with the results on day 4, the majority of biomarkers were more increased in females than males. It remains unresolved if sex differences in the magnitude of biomarker response at injury threshold would lead to any difference in diagnostic interpretation between the sexes. These data highlight the need for publication of more studies using animals of both sexes to fully explore the influence of sex on the diagnostic performance of the novel biomarkers.

Normal Ranges and Variability of Novel Urinary Renal Biomarkers in Sprague-Dawley Rats

Differences were examined between male and female Sprague-Dawley rats in basal levels of a wide range of urinary biomarkers, including 7 recently qualified biomarkers. The data were generated from urine samples collected on 3 occasions from untreated rats included in a study of the effect of gentamicin nephrotoxicity on urinary renal biomarkers, reported in a companion article in this journal (Gautier et al. 2014). The performance of multiple assays (9 singleplex assays and 2 multiplex platforms from Rules Based Medicine [RBM] and Meso Scale Discovery [MSD]) was evaluated, and normal ranges and variability estimates were derived. While variability was generally greater on the RBM platform than other assays, the more striking difference in the results from different assays was in magnitude. Where differences were observed between assays for an individual biomarker, they were seen in both sexes and consistent across samples collected at different time points. Differences of up to 15-fold were observed for some biomarker values between assays indicating that results generated using different assays should not be compared. For 8 biomarkers, there was compelling evidence for a sex difference. Baseline values in males were significantly higher than in females for total protein, β2-microglobulin, clusterin, cystatin-C, glutathione-S-transferase (GST-α), tissue inhibitor of metalloproteinases (TIMP-1), and vascular endothelial growth factor (VEGF); female values were significantly higher than that of males for albumin. The largest sex differences (male greater than female by 2- to 11-fold) were seen with β2-microglobulin, GST-α, and TIMP-1. These data add substantially to the limited body of knowledge in this area and provide a useful framework for evaluation of the potential relevance of sex differences in the diagnostic performance of these biomarkers.

Characterization of renal biomarkers for use in clinical trials: biomarker evaluation in healthy volunteers

BACKGROUND

Several preclinical urinary biomarkers have been qualified and accepted by the health authorities (US Food and Drug Administration, European Medicines Agency, and Pharmaceuticals and Medical Devices Agency) for detecting drug-induced kidney injury during preclinical toxicologic testing. Validated human assays for many of these biomarkers have become commercially available, and this study was designed to characterize some of the novel clinical renal biomarkers. The objective of this study was to evaluate clinical renal biomarkers in a typical Phase I healthy volunteer population to determine confidence intervals (pilot reference intervals), intersubject and intrasubject variability, effects of food intake, effect of sex, and vendor assay comparisons.

METHODS

Spot urine samples from 20 male and 19 female healthy volunteers collected on multiple days were analyzed using single analyte and multiplex assays. The following analytes were measured: α-1-microglobulin, β-2-microglobulin, calbindin, clusterin, connective tissue growth factor, creatinine, cystatin C, glutathione S-transferase-α, kidney injury marker-1, microalbumin, N-acetyl-β-(D) glucosaminidase, neutrophil gelatinase-associated lipocalin, osteopontin, Tamm-Horsfall urinary glycoprotein, tissue inhibitor of metalloproteinase 1, trefoil factor 3, and vascular endothelial growth factor.

RESULTS

Confidence intervals were determined from the single analyte and multiplex assays. Intersubject and intrasubject variability ranged from 38% to 299% and from 29% to 82% for biomarker concentration, and from 24% to 331% and from 10% to 67% for biomarker concentration normalized to creatinine, respectively. There was no major effect of food intake or sex. Single analyte and multiplex assays correlated with r (2)≥0.700 for five of six biomarkers when evaluating biomarker concentration, but for only two biomarkers when evaluating concentration normalized to creatinine.

CONCLUSION

Confidence intervals as well as intersubject and intrasubject variability were determined for novel clinical renal biomarkers/assays, which should be considered for evaluation in the next steps of the qualification process.

MicroRNA-34c-3p is an early predictive biomarker for doxorubicin-induced glomerular injury progression in male Sprague-Dawley rats

Increased microRNA-34c-3p appeared as a novel biomarker for doxorubicin nephrotoxicity in rats; alterations showed greater specificity than and comparable sensitivity to albuminuria for early prediction of glomerular injury.

Safety biomarkers in preclinical development: translational potential

The identification, application, and qualification of safety biomarkers are becoming increasingly critical to successful drug discovery and development as companies are striving to develop drugs for difficult targets and for novel disease indications in a risk-adverse environment. Translational safety biomarkers that are minimally invasive and monitor drug-induced toxicity during human clinical trials are urgently needed to assess whether toxicities observed in preclinical toxicology studies are relevant to humans at therapeutic doses. The interpretation of data during the biomarker qualification phase should include careful consideration of the analytic method used, the biology, pharmacokinetic and pharmacodynamic properties of the biomarker, and the pathophysiology of the process studied. The purpose of this review is to summarize commonly employed technologies in the development of fluid- and tissue-based safety biomarkers in drug discovery and development and to highlight areas of ongoing novel assay development.

Time Course of Renal Proximal Tubule Injury, Reversal, and Related Biomarker Changes in Rats Following Cisplatin Administration

Cisplatin (CDDP) is known to produce renal proximal tubule injury. Various renal biomarkers have been related to CDDP nephrotoxicity in previous research, but the temporal and spatial relationship of these biomarkers to injury reversal has not been well defined. In this study, the progression and reversal of renal histopathology findings relative to serum and urinary biomarker changes were examined during a 4-week postdose period following single intraperitoneal administration of CDDP (1 mg/kg) or 0.9% saline. Degeneration, vacuolation, inflammation, and regeneration of the S3 segment of proximal tubules were evident 72 hours following CDDP administration. Tubular degeneration and regeneration were also observed at 1 and 1.5 weeks but at lower incidences and/or severity indicating partial reversal. Complete histologic reversal was observed by 2 weeks following CDDP administration. Urinary kidney injury molecule 1 (KIM-1), α-glutathione-S-transferase (α-GST), and albumin levels increased at 72 hours postdosing, concurrently with the earliest histologic evidence of tubule injury. Changes in urinary KIM-1 correlated with KIM-1 immunostaining in the proximal tubular epithelial cells. No significant changes in serum biomarkers occurred except for a minimal increase in urea nitrogen at 1.5 weeks postdosing. Of the novel renal biomarkers examined, urinary KIM-1, α-GST, and albumin showed excellent concordance with CDDP-induced renal injury progression and reversal; and these biomarkers were more sensitive than traditional serum biomarkers in detecting early, acute renal tubular damage confirmed by histopathology. Furthermore, urinary KIM-1, α-GST, and albumin outperformed other biomarkers in correlating with the time of maximum histologic injury.

Clinical use of biomarkers for toxicant-induced acute kidney injury

Toxicant-induced acute kidney injury (ToxAKI) causes substantial morbidity and retards drug development. ToxAKI is relatively underexplored compared with ischemia–reperfusion injury in clinical biomarker studies. We highlight the rationale for novel AKI biomarkers in management of ToxAKI, and review the contemporary evidence supporting their clinical use. Directly-acting nephrotoxins, such as cisplatin, aminoglycosides, vancomycin and radiocontrast, remain widely used and highlight how novel biomarkers can either improve the detection of changes in glomerular filtration rate or directly signal cellular injury and structural damage. Serum cystatin C has already improved clinical risk prediction and drug dosing although its clinical use for early diagnosis awaits validation. The use of novel functional and structural biomarkers to stage ToxAKI and aid prognosis requires robust validation and better understanding of the relationship between biomarkers, morbidity and mortality. Biomarkers that illustrate the probable mechanisms and phase of ToxAKI may guide mechanism-specific diagnosis and therapy.

Meeting report: Urinary Pathology; sixth Research Triangle Park Rodent Pathology Course

Urinary system toxicity is a significant concern to pathologists in the hazard identification, drug and chemical safety evaluation, and diagnostic service industries worldwide. There are myriad known human and animal urinary system toxicants, and investigatory renal toxicology and pathology is continually evolving. The system-specific Research Triangle Park (RTP) Rodent Pathology Course biennially serves to update scientists on the latest research, laboratory techniques, and debates. The Sixth RTP Rodent Pathology Course, Urinary Pathology, featured experts from the government, pharmaceutical, academic, and diagnostic arenas sharing the state of the science in urinary pathology. Speakers presented on a wide range of topics including background lesions, treatment-related non-neoplastic and neoplastic lesions, transgenic rodent models of human disease, diagnostic imaging, biomarkers, and molecular analyses. These seminars were accompanied by case presentation sessions focused on usual and unusual lesions, grading schemes, and tumors.

Histone deacetylase inhibitor, sodium butyrate, attenuates gentamicin-induced nephrotoxicity by increasing prohibitin protein expression in rats

The major purpose in our study was to investigate the effects of sodium butyrate (NaBu) on nephrotoxicity induced by gentamicin in rats and determine further whether the protective effect is mediated by modulation of prohibitin protein expression. Gentamicin was injected intraperitoneally (100 mg/kg body weight) once daily for 8 days to induce nephrotoxicity. The effect of acute and chronic treatment of sodium butyrate on nephrotoxicity induced by gentamicin was assessed. Various doses of sodium butyrate (50, 100, 200 mg/kg, i.p.) was administered 30 min prior to the daily gentamicin injection. Histological analysis was used to evaluate the lesions in kidney after gentamicin administration. Expression of prohibitin was evaluated with immunohistochemical and western blot analysis. The present study demonstrated that gentamicin treatment for 8 consecutive days significantly increased in the levels of blood urea nitrogen, creatinine, kidney injury molecule (KIM-1) and neutrophil gelatinase-associated lipocalin (NGAL) which indicated nephrotoxicity induced by gentamicin. In addition, chronic treatment with NaBu significantly attenuated gentamicin-induced nephrotoxicity by increasing activities of superoxide dismutase, catalase and reduced glutathione. Immunohistochemical studies in gentamicin-induced rats also demonstrated an increase in the levels of inducible prohibitin after treatment with sodium butyrate. Our results indicated that sodium butyrate, a histone deacetylase inhibitor, decreased gentamicin-induced nephrotoxicity by enhancing renal antioxidant enzymes activity and the expression of prohibitin protein.

Bioengineered 3D human kidney tissue, a platform for the determination of nephrotoxicity

The staggering cost of bringing a drug to market coupled with the extremely high failure rate of prospective compounds in early phase clinical trials due to unexpected human toxicity makes it imperative that more relevant human models be developed to better predict drug toxicity. Drug–induced nephrotoxicity remains especially difficult to predict in both pre-clinical and clinical settings and is often undetected until patient hospitalization. Current pre-clinical methods of determining renal toxicity include 2D cell cultures and animal models, both of which are incapable of fully recapitulating the in vivo human response to drugs, contributing to the high failure rate upon clinical trials. We have bioengineered a 3D kidney tissue model using immortalized human renal cortical epithelial cells with kidney functions similar to that found in vivo. These 3D tissues were compared to 2D cells in terms of both acute (3 days) and chronic (2 weeks) toxicity induced by Cisplatin, Gentamicin, and Doxorubicin using both traditional LDH secretion and the pre-clinical biomarkers Kim-1 and NGAL as assessments of toxicity. The 3D tissues were more sensitive to drug-induced toxicity and, unlike the 2D cells, were capable of being used to monitor chronic toxicity due to repeat dosing. The inclusion of this tissue model in drug testing prior to the initiation of phase I clinical trials would allow for better prediction of the nephrotoxic effects of new drugs.

Strategic regulatory approaches for the qualification of a biomarker assay for safety use

Biomarkers can be defined as key molecular or cellular events that link a specific biological event to a health outcome. As such, biomarkers play an important role in understanding the relationships between exposure to a xenobiotic, the development of chronic human diseases, and the identification of subgroups that are at increased risk of disease. Much progress has been made in identifying and validating new biomarkers to be used in population-based studies. The increasing availability and use of biomarkers to aid informed decision-making in risk–benefit decisions highlights the need for careful assessment of the validity of such models. In particular, models involving new biomarkers require careful validation and regulatory acceptance.

Toxicity of melamine: the public health concern

Melamine contamination in food has resulted in sickness and deaths of human infants, pets, and farm animals in the past decade. The majority of the victims suffered from acute kidney injury, nephrolithiasis, and urolithiasis. Since then, animal studies have revealed the possible target organs of the melamine toxicity and the extent of the adverse effects of the contaminant. State-of-the-art analytical methods have been developed to achieve the "zero tolerance" aim for such economically motivated adulteration. These studies provide in-depth understanding of the melamine toxicity and promising analytical methods, which can help us safeguard our dairy food source.

Renal biomarker changes associated with hyaline droplet nephropathy in rats are time and potentially compound dependent

Alpha 2u-globulin mediated hyaline droplet nephropathy (HDN) is a male rat specific lesion induced when a compound or metabolite binds to alpha 2u-globulin. The objective of this study was to investigate if the newer and more sensitive renal biomarkers would be altered with HDN as well as be able to distinguish between HDN and oxidative stress-induced kidney injury. Rats were dosed orally for 7 days to determine (1) if HDN (induced by 2-propanol or D-limonene) altered the newer renal biomarkers and not BUN or creatinine, (2) if renal biomarkers could distinguish between HDN and oxidative stress-induced kidney injury (induced by potassium bromate), (3) sensitivity of HDN-induced renal biomarker changes relative to D-limonene dose, and (4) reversibility of HDN and renal biomarkers, using vehicle or 300 mg/kg/day D-limonene with 7 days of dosing and necropsies scheduled over the period of Days 8-85. HDN-induced renal biomarker changes in male rats were potentially compound specific: (1) 2-propanol induced mild HDN without increased renal biomarkers, (2) potassium bromate induced moderate HDN with increased clusterin, and (3) D-limonene induced marked HDN with increased αGST, μGST and albumin. Administration of potassium bromate did not result in oxidative stress-induced kidney injury, based on histopathology and renal biomarkers creatinine and BUN. The compound D-limonene induced a dose dependent increase in HDN severity and renal biomarker changes without altering BUN, creatinine or NAG: (1) minimal induction of HDN and no altered biomarkers at 10 mg/kg/day, (2) mild induction of HDN with increased αGST and μGST at 50 mg/kg/day and (3) marked induction of HDN with increased αGST, μGST and albumin at 300 mg/kg/day. HDN induced by D-limonene was reversible, but with a variable renal biomarker pattern over time: Day 8 there was increased αGST, μGST and albumin; on Day 15 increased clusterin, albumin and Kim-1. In summary, HDN altered the newer and more sensitive renal biomarkers in a time and possibly compound dependent manner.

Correlation of histopathology, urinary biomarkers, and gene expression responses following hexachloro-1:3-butadiene-induced acute nephrotoxicity in male Hanover Wistar rats: a 28-day time course study

Hexachloro-1:3-butadiene (HCBD) causes segment-specific injury to the proximal renal tubule. A time course study of traditional and more recently proposed urinary biomarkers was performed in male Hanover Wistar rats receiving a single intraperitoneal (ip) injection of 45 mg/kg HCBD. Animals were killed on days 1, 2, 3, 4, 5, 6, 7, 10, 14, and 28 postdosing and the temporal response of renal biomarkers was characterized using kidney histopathology, urinary and serum biochemistry, and gene expression. Histopathologic evidence of tubular degeneration was seen from day 1 until day 3 postdosing and correlated with increased urinary levels of α-glutathione S-transferase (α-GST), albumin, glucose, and kidney injury molecule-1 (KIM-1), and increased gene expression of KIM-1, NAD(P)H dehydrogenase, quinone 1, and heme oxygenase (decycling) 1. Histopathologic evidence of tubular regeneration was seen from day 2 postdosing and correlated with raised levels of urinary KIM-1 and osteopontin and increased gene expression of KIM-1 and annexin A7. Traditional renal biomarkers generally demonstrated low sensitivity. It is concluded that in rat proximal tubular injury, measurement of a range of renal biomarkers, in conjunction with gene expression analysis, provides an understanding of the extent of degenerative changes induced in the kidney and the process of regeneration.

Kidney Injury Biomarkers in Hypertensive, Diabetic, and Nephropathy Rat Models Treated with Contrast Media

Contrast-induced nephropathy (CIN) refers to a decline in renal function following exposure to iodinated contrast media (CM). The present study was initiated to explore the role of known human risk factors (spontaneous hypertension, diabetes, protein-losing nephropathy) on CIN development in rodent models and to determine the effect of CM administration on kidney injury biomarkers in the face of preexisting kidney injury. Spontaneously hypertensive rats (hypertension), streptozotocin-treated Sprague Dawley rats (diabetes), and Dahl salt-sensitive rats (protein-losing nephropathy) were given single intravenous injections of the nonionic, low osmolar contrast medium, iohexol. Blood urea nitrogen (BUN), serum creatinine (sCr), and urinary biomarkers; albumin, lipocalin 2 (Lcn-2), osteopontin (Opn), kidney injury molecule 1 (Kim-1), renal papillary antigen 1 (Rpa-1), α-glutathione S-transferase (α-Gst), µ-glutathione S-transferase (µ-Gst), and beta-2 microglobulin (β2m) were measured in disease models and appropriate controls to determine the response of these biomarkers to CM administration. Each disease model produced elevated biomarkers of kidney injury without CM. Preexisting histopathology was exacerbated by CM but little or no significant increases in biomarkers were observed. When 1.5-fold or greater sCr increases from pre-CM were used to define true positives, receiver–operating characteristic curve analysis of biomarker performance showed sCr was the best predictor of CIN across disease models. β2m, Lcn-2, and BUN were the best predictors of histopathology defined kidney injury.

Performance of urinary and gene expression biomarkers in detecting the nephrotoxic effects of melamine and cyanuric acid following diverse scenarios of co-exposure

Although standard nephrotoxicity assessments primarily detect impaired renal function, KIM-1, clusterin, NGAL, osteopontin and TIMP-1 were recently identified biomarkers proposed to indicate earlier perturbations in renal integrity. The recent adulteration of infant and pet food with melamine (MEL) and structurally-related compounds revealed that co-ingestion of MEL and cyanuric acid (CYA) could form melamine-cyanurate crystals which obstruct renal tubules and induce acute renal failure. This study concurrently evaluated the ability of multiplexed urinary biomarker immunoassays and biomarker gene expression analysis to detect nephrotoxicity in F344 rats co-administered 60ppm each of MEL and CYA in feed or via gavage for 28days. The biomarkers were also evaluated for the ability to differentiate the effects of the compounds when co-administered using diverse dosing schedules (i.e., consecutive vs. staggered gavage) and dosing matrixes (i.e., feed vs. gavage). Our results illustrate the ability of both methods to detect and differentiate the severity of adverse effects in the staggered and consecutive gavage groups at much lower doses than previously observed in animals co-exposed to the compounds in feed. We also demonstrate that these urinary biomarkers outperform traditional diagnostic methods and represent a powerful, non-invasive indicator of chemical-induced nephrotoxicity prior to the onset of renal dysfunction.

Qualified kidney biomarkers and their potential significance in drug safety evaluation and prediction

The kidney is one of the major organs drug toxicity may target. Some renal safety biomarkers have been proposed to measure kidney injury and function accordingly. Despite the widespread use for diagnosis and monitoring of renal injury and function for decades, serum creatinine and blood urea nitrogen are nonspecific biomarkers with insensitive and delayed response in the clinical setting. There is an urgent need to identify and qualify novel kidney safety biomarkers that would be used to detect and predict drug-induced nephrotoxicity in preclinical toxicological studies, clinical trials and patient care in sequence. To do that, eight novel renal safety biomarkers have been well characterized and qualified for preclinical drug safety screening, and their clinical bridging validation is underway as well. Of them, some are used to detect or predict proximal tubular injury, and others are used to diagnose and monitor glomerular damage. Thus, measurement of a panel of kidney safety biomarkers in parallel would help maximally capture all potential safety signals for a more informative decision to be made in drug research and development as well as for optimal selection of the drug and its dose in clinical practice.

Thyroid hormone and estradiol have overlapping effects on kidney glutathione S-transferase-α gene expression

α-Class GST (Gsta) represents an essential component of cellular antioxidant defense mechanisms in both the liver and the kidney. Estrogens and thyroid hormones (TH) play central roles in animal development, physiology, and behavior. Evidence of the overlapping functions of thyroid hormones and estrogens has been shown, although the molecular mechanisms are not always clear. We evaluated an interaction between TH and estradiol in regulating kidney Gsta expression and function. First, we observed that female mice expressed greater amounts of Gsta compared with males and showed an opposite pattern of expression in TRβ knock-in mice. To further investigate these sex differences, hypothyroidism was induced by a 5-propyl-2-thiouracil diet, and hyperthyroidism was induced by daily T₃ injections. Hypothyroidism increased kidney Gsta expression in male mice but not in female mice, indicating that sex hormones could be influencing the regulation of Gsta by thyroid hormones. To analyze this hypothesis, ovariectomized females were subjected to hypo- and hyperthyroidism, which led to a male profile of Gsta expression. When hypo- or hyperthyroid ovariectomized mice were treated with 17β-estradiol benzoate, we were able to confirm that estradiol was interfering with TH modulation; Gsta expression is increased by T₃ when estradiol is present and decreased by T₃ when estradiol is absent. Using proximal tubule cells, we also showed that estradiol and T₃ worked together to modulate Gsta expression in an overlapping fashion. In summary, 1) the sex difference in the basal expression of Gsta impacts the detoxification process, 2) kidney Gsta expression is regulated by TH in males and females but in opposite directions, and 3) T₃ and estradiol interact directly in renal proximal cells to regulate Gsta expression in females.

Kidney Toxicity Induced by 13 Weeks Exposure to the Fruiting Body of Paecilomyces sinclairii in Rats

Paecilomyces sinclairiis (PS) is known as a functional food or human health supplement. However concerns have been raised about its kidney toxicity. This study was performed to investigate the kidney toxicity of PS by 13 week-oral administration to rats. Blood urea nitrogen (BUN), serum creatinine, and kidney damage biomarkers including beta-2-microglobulin (β2m), glutathione S-transferase alpha (GST-α), kidney injury molecule 1 (KIM-1), tissue inhibitor of matrix metalloproteinase 1 (TIMP-1), vascular endothelial growth factor (VEGF), calbindin, clusterin, cystatin C, neutrophil gelatinase-associated lipocalin (NGAL) and osteopontin were measured during or after the treatment of PS. BUN, creatinine and kidney damage biomarkers in serum were not changed by PS. However, kidney cell karyomegaly and tubular hypertrophy were observed dose-dependently with higher severity in males. KIM-1, TIMP-1 and osteopontin in kidney and urine were increased dose dependently in male or at the highest dose in female rats. Increased urinary osteopontin by PS was not recovered at 2 weeks of post-exposure in both genders. Cystatin C in kidney was decreased at all treatment groups but inversely increased in urine. The changes in kidney damage biomarkers were more remarkable in male than female rats. These data indicate that the PS may provoke renal cell damage and glomerular filtration dysfunction in rats with histopathological lesions and change of kidney damage biomarkers in kidney or urine. Kidney and urinary KIM-1 and cystatin C were the most marked indicators, while kidney weight, BUN and creatinine and kidney damage biomarkers in serum were not influenced.

Fibrinogen excretion in the urine and immunoreactivity in the kidney serves as a translational biomarker for acute kidney injury

Fibrinogen (Fg) is significantly up-regulated in the kidney after acute kidney injury (AKI). We evaluated the performance of Fg as a biomarker for early detection of AKI. In rats and mice with kidney tubular damage induced by ischemia/reperfusion (I/R) or cisplatin administration, respectively; kidney tissue and urinary Fg increased significantly and correlated with histopathological injury, urinary kidney injury molecule-1 (KIM-1) and N-acetyl glucosaminidase (NAG) corresponding to the progression and regression of injury temporally. In a longitudinal follow-up of 31 patients who underwent surgical repair of abdominal aortic aneurysm, urinary Fg increased earlier than SCr in patients who developed postoperative AKI (AUC-ROC = 0.72). Furthermore, in a cohort of patients with biopsy-proven AKI (n = 53), Fg immunoreactivity in the tubules and interstitium increased remarkably and was able to distinguish patients with AKI from those without AKI (n = 59). These results suggest that immunoreactivity of Fg in the kidney, as well as urinary excretion of Fg, serves as a sensitive and early diagnostic translational biomarker for detection of AKI.

Cosupplementation with a synthetic, lipid-soluble polyphenol and vitamin C inhibits oxidative damage and improves vascular function yet does not inhibit acute renal injury in an animal model of rhabdomyolysis

We investigated whether cosupplementation with synthetic tetra-tert-butyl bisphenol (BP) and vitamin C (Vit C) ameliorated oxidative stress and acute kidney injury (AKI) in an animal model of acute rhabdomyolysis (RM). Rats were divided into groups: Sham and Control (normal chow), and BP (receiving 0.12% w/w BP in the diet; 4 weeks) with or without Vit C (100mg/kg ascorbate in PBS ip at 72, 48, and 24h before RM induction). All animals (except the Sham) were treated with 50% v/v glycerol/PBS (6 mL/kg injected into the hind leg) to induce RM. After 24h, urine, plasma, kidneys, and aortae were harvested. Lipid oxidation (assessed as cholesteryl ester hydroperoxides and hydroxides and F(2)-isoprostanes accumulation) increased in the kidney and plasma and this was coupled with decreased aortic levels of cyclic guanylylmonophosphate (cGMP). In renal tissues, RM stimulated glutathione peroxidase (GPx)-4, superoxide dismutase (SOD)-1/2 and nuclear factor kappa-beta (NFκβ) gene expression and promoted AKI as judged by formation of tubular casts, damaged epithelia, and increased urinary levels of total protein, kidney-injury molecule-1 (KIM-1), and clusterin. Supplementation with BP±Vit C inhibited the two indices of lipid oxidation, down-regulated GPx-4, SOD1/2, and NF-κβ gene responses and restored aortic cGMP, yet renal dysfunction and altered kidney morphology persisted. By contrast, supplementation with Vit C alone inhibited oxidative stress and diminished cast formation and proteinuria, while other plasma and urinary markers of AKI remained elevated. These data indicate that lipid- and water-soluble antioxidants may differ in terms of their therapeutic impact on RM-induced renal dysfunction.

Proteomic candidate biomarkers of drug-induced nephrotoxicity in the rat

Improved biomarkers of acute nephrotoxicity are coveted by the drug development industry, regulatory agencies, and clinicians. In an effort to identify such biomarkers, urinary peptide profiles of rats treated with two different nephrotoxins were investigated. 493 marker candidates were defined that showed a significant response to cis-platin comparing a cis-platin treated cohort to controls. Next, urine samples from rats that received three consecutive daily doses of 150 or 300 mg/kg gentamicin were examined. 557 potential biomarkers were initially identified; 108 of these gentamicin-response markers showed a clear temporal response to treatment. 39 of the cisplatin-response markers also displayed a clear response to gentamicin. Of the combined 147 peptides, 101 were similarly regulated by gentamicin or cis-platin and 54 could be identified by tandem mass spectrometry. Most were collagen type I and type III fragments up-regulated in response to gentamicin treatment. Based on these peptides, classification models were generated and validated in a longitudinal study. In agreement with histopathology, the observed changes in classification scores were transient, initiated after the first dose, and generally persistent over a period of 10–20 days before returning to control levels. The data support the hypothesis that gentamicin-induced renal toxicity up-regulates protease activity, resulting in an increase in several specific urinary collagen fragments. Urinary proteomic biomarkers identified here, especially those common to both nephrotoxins, may serve as a valuable tool to investigate potential new drug candidates for the risk of nephrotoxicity.

Biomarkers of Collecting Duct Injury in Han-Wistar and Sprague-Dawley Rats Treated with N-Phenylanthranilic Acid

N-phenylanthranilic acid is a chloride channel blocker that causes renal papillary necrosis in rats. Studies were conducted in two strains of male rats to evaluate novel biomarkers of nephrotoxicity. Han-Wistar rats were given daily oral doses of 50, 350, or up to 700 mg/kg/day of NPAA, and Sprague-Dawley rats were given 50 or 400 mg/kg/day of NPAA. Rats were euthanized on days 8 and 15. The candidate kidney injury biomarkers renal papillary antigen-1 (RPA-1, for collecting duct injury), clusterin (for general kidney injury), α-glutathione-S-transferase (a proximal tubular marker), and µ-glutathione-S-transferase (a distal tubular marker) were measured in urine by enzyme immunoassay. Characteristic degeneration and necrosis of the collecting duct and renal papilla were observed in Han-Wistar rats at the high dose on day 8 and at the mid and high doses on day 15, and in Sprague-Dawley rats given the high dose on days 8 and 15. Increases in urinary RPA-1, and to a lesser extent urine clusterin, were generally associated with the presence of collecting duct injury and were more sensitive than BUN and serum creatinine. On the other hand, decreases in α-glutathione-S-transferase without proximal tubule lesions in both strains and decreases in µ-glutathione-S-transferase in Sprague-Dawley rats only were not associated with morphological proximal or distal tubule abnormalities, so both were of less utility. It was concluded that RPA-1 is a new biomarker with utility in the detection of collecting duct injury in papillary necrosis in male rats.

Comparison of the course of biomarker changes and kidney injury in a rat model of drug-induced acute kidney injury

OBJECTIVE

To aid in evaluating the performance of biomarkers, we measured kidney injury biomarkers in rat models of drug-induced acute kidney injury.

METHODS AND RESULTS

Rats were treated with site-specific nephrotoxins, puromycin, gentamicin, cisplatin, or 2-bromoethylamine. Fifteen biomarkers (β-2-microglobulin, calbindin, clusterin, cystatin-C, KIM-1, GST-α, GST-μ, NGAL, osteopontin, EGF, TIMP-1, VEGF, albumin, RPA-1, and urinary total protein) were examined in comparison with BUN, serum creatinine, and NAG. Some biomarkers, which were different depending in each nephrotoxin, showed ability to detect the prodromal stage of drug-induced kidney injury. Characteristic changing patterns of biomarkers were also found depending on the specific lesion site in the kidney.

CONCLUSION

These data suggested that establishment of a suitable biomarker panel would facilitate detection of site-specific kidney injury with high sensitivity.