Development and validation of an LC-MSMS method to quantify creatinine from dried blood spots

Introduction

Screening for chronic kidney disease relies on accurate and precise creatinine measurements. Traditionally, creatinine is measured in serum or plasma using high-throughput chemistry analyzers. However, dried blood spots (DBS) can also be utilized to improve testing access.

Methods

Samples were obtained from a 6 mm DBS punch, which was reconstituted in water before undergoing an acetonitrile crash. The resulting supernatant was diluted using an 80:20 acetonitrile: water before injection. Creatinine was identified using an isocratic gradient, and detected using an API 4000 triple quadrupole mass analyzer. Quantification relied on matrix-matched calibrators, with values harmonized to the Roche Cobas enzymatic assay. Validation studies assessing method performance included precision, linearity, accuracy, method comparison, stability, interference, and matrix effects.

Results

The LC-MSMS assay was linear from 0.3 to 20 mg/dL (y = 1.02x-0.11; R2 = 0.996). Precision ranged from 5.2 to 8.1 % using matrix-matched controls (n = 4) that spanned the analytical measurement range. LC-MSMS results corresponded to the enzymatic assay (Roche) with a fitted line equation of y = 0.956x-0.07 (R2 = 0.995; n = 173). The Siemens and Roche enzymatic assays demonstrated higher accuracy in correlating to the DBS creatinine concentration (n = 40 paired venous/DBS collections) compared to the Beckman Jaffe assay (-2.5 % and -0.8 % versus -6.3 % and -4.1 %, respectively) or the iSTAT (-28.4 % and -27.1 %, respectively). Accuracy was unaffected by hematocrit, blood spot volume, excess IgG or IgA, or hypertriglyceridemia. No matrix effects were observed, and both extraction and processing efficiency were robust.Ambient stability extended to at least 10 days, and exposure to extreme temperature did not affect the creatinine results.

Conclusion

We successfully developed an accurate and precise LC-MSMS method for quantifying creatinine in DBS.

A Holistic Framework for the Evaluation of Kidney Function in a Gender-Diverse Landscape

The most commonly used equations to estimate glomerular filtration rate incorporate a binary male-female sex coefficient, which has important implications for the care of transgender, gender-diverse, and nonbinary (TGD) people. Whether "sex assigned at birth" or a binary "gender identity" is most appropriate for the computation of estimated glomerular filtration rate (eGFR) is unknown. Furthermore, the use of gender-affirming hormone therapy (GAHT) for the development of physical changes to align TGD people with their affirmed gender is increasingly common, and may result in changes in serum creatinine and cystatin C, the biomarkers commonly used to estimate glomerular filtration rate. The paucity of current literature evaluating chronic kidney disease (CKD) prevalence and outcomes in TGD individuals on GAHT makes it difficult to assess any effects of GAHT on kidney function. Whether alterations in serum creatinine reflect changes in glomerular filtration rate or simply changes in muscle mass is unknown. Therefore, we propose a holistic framework to evaluate kidney function in TGD people. The framework focuses on kidney disease prevalence, risk factors, sex hormones, eGFR, other kidney function assessment tools, and the mitigation of health inequities in TGD people.

Reconsidering the use of race adjustments in maternal serum screening

The use of race in maternal serum screening is problematic because race is a social construct rather than a distinct biological classifier. Nevertheless, laboratories offering this testing are encouraged to use race-specific cutoff values for maternal serum screening biomarkers to determine the risk of fetal abnormalities. Large cohort studies examining racial differences in maternal serum screening biomarker concentrations have yielded conflicting results, which we postulate may be explained by genetic and socioeconomic differences between racial cohorts in different studies. We recommend that the use of race in maternal serum screening should be abandoned. Further research is needed to identify socioeconomic and environmental factors that contribute to differences in maternal serum screening biomarker concentrations observed between races. A better understanding of these factors may facilitate accurate race-agnostic risk estimates for aneuploidy and neural tube defects.

AACC/NKF Guidance Document on Improving Equity in Chronic Kidney Disease Care

BACKGROUND

Kidney disease (KD) is an important health equity issue with Black, Hispanic, and socioeconomically disadvantaged individuals experiencing a disproportionate disease burden. Prior to 2021, the commonly used estimated glomerular filtration rate (eGFR) equations incorporated coefficients for Black race that conferred higher GFR estimates for Black individuals compared to non-Black individuals of the same sex, age, and blood creatinine concentration. With a recognition that race does not delineate distinct biological categories, a joint task force of the National Kidney Foundation and the American Society of Nephrology recommended the adoption of the CKD-EPI 2021 race-agnostic equations.

CONTENT

This document provides guidance on implementation of the CKD-EPI 2021 equations. It describes recommendations for KD biomarker testing, and opportunities for collaboration between clinical laboratories and providers to improve KD detection in high-risk populations. Further, the document provides guidance on the use of cystatin C, and eGFR reporting and interpretation in gender-diverse populations.

SUMMARY

Implementation of the CKD-EPI 2021 eGFR equations represents progress toward health equity in the management of KD. Ongoing efforts by multidisciplinary teams, including clinical laboratorians, should focus on improved disease detection in clinically and socially high-risk populations. Routine use of cystatin C is recommended to improve the accuracy of eGFR, particularly in patients whose blood creatinine concentrations are confounded by processes other than glomerular filtration. When managing gender-diverse individuals, eGFR should be calculated and reported with both male and female coefficients. Gender-diverse individuals can benefit from a more holistic management approach, particularly at important clinical decision points.

The impact of environmental factors on external and internal specimen transport

The environment that a clinical specimen is exposed to is an important preanalytical factor in laboratory testing. There are numerous environmental conditions that a specimen may experience before it arrives at the clinical laboratory for analysis. Specimens collected at offsite locations are typically stored at the site and transported to the clinical laboratory via courier. Depending on the geographic location, season, method of storage and method of transport, the specimen can experience varying climate conditions that can lead to inaccurate test results. Specimens collected within the healthcare institution are not exempt from suboptimal storage and transport environments. For example, specimens transported via pneumatic tube systems can experience extreme agitation and rapid accelerations and decelerations. Suboptimal storage and transport temperatures occur less frequently within health systems due to multiple regulatory requirements for temperature monitoring; however, temperature monitoring may not occur at every stage of the preanalytical phase. This review will highlight both internal and external environmental conditions that can cause preanalytical errors in clinical laboratory testing. Strategies to mitigate environmentally-induced preanalytical errors and regulatory gaps for environmental monitoring in the preanalytical phase will also be discussed.

Outdoor Courier Lockboxes in Summer Are a Significant Source of Preanalytical Error

OBJECTIVES

To determine the impact of short-term (<4-hour) exposure of summer-like temperatures on lithium heparin (uncentrifuged and centrifuged) samples stored in outdoor courier lockboxes in the Mid-Atlantic United States.

METHODS

Healthy adults (n = 8) were recruited to investigate the impact of the short-term exposure of lithium heparin samples (centrifuged and uncentrifuged) inside 2 LabLocker-KF300 courier lockboxes placed outside in direct sunlight during summer. Each courier lockbox was monitored every 5 minutes with a temperature data logger and contained either the standard number (n = 2) of cold packs (cold) or no standard cold packs (warm). Acceptable tolerance limits were defined for each analyte by significant change limit (SCL) analysis (P < .05), as previously described.

RESULTS

Significant changes were identified in each study condition for warm and cold lockbox conditions. Aspartate aminotransferase, glucose, lactate dehydrogenase, and potassium commonly crossed SCLs from mean baseline (t0) in the majority of conditions.

CONCLUSIONS

Outdoor courier lockboxes are an underrecognized source of preanalytical error.

Dancing from bottoms up - Roles of the POZ-ZF transcription factor Kaiso in Cancer

The POZ-ZF transcription factor Kaiso was discovered two decades ago as a binding partner for p120^ctn. Since its discovery, roles for Kaiso in diverse biological processes (epithelial-to-mesenchymal transition, apoptosis, inflammation) and several signalling pathways (Wnt/β-catenin, TGFβ, EGFR, Notch) have emerged. While Kaiso's biological role in normal tissues has yet to be fully elucidated, Kaiso has been increasingly implicated in multiple human cancers including colon, prostate, ovarian, lung, breast and chronic myeloid leukemia. In the majority of human cancers investigated to date, high Kaiso expression correlates with aggressive tumor characteristics including proliferation and metastasis, and/or poor prognosis. More recently, interest in Kaiso stems from its apparent correlation with racial disparities in breast and prostate cancer incidence and survival outcomes in people of African Ancestry. This review discusses Kaiso's role in various cancers, and Kaiso's potential for driving racial disparities in incidence and/or outcomes in people of African ancestry.

Kaiso differentially regulates components of the Notch signaling pathway in intestinal cells

Background

In mammalian intestines, Notch signaling plays a critical role in mediating cell fate decisions; it promotes the absorptive (or enterocyte) cell fate, while concomitantly inhibiting the secretory cell fate (i.e. goblet, Paneth and enteroendocrine cells). We recently reported that intestinal-specific Kaiso overexpressing mice (Kaiso^Tg) exhibited chronic intestinal inflammation and had increased numbers of all three secretory cell types, hinting that Kaiso might regulate Notch signaling in the gut. However, Kaiso’s precise role in Notch signaling and whether the Kaiso^Tg secretory cell fate phenotype was linked to Kaiso-induced inflammation had yet to be elucidated.

Methods

Intestines from 3-month old Non-transgenic and Kaiso^Tg mice were “Swiss” rolled and analysed for the expression of Notch1, Dll-1, Jagged-1, and secretory cell markers by immunohistochemistry and immunofluorescence. To evaluate inflammation, morphological analyses and myeloperoxidase assays were performed on intestines from 3-month old Kaiso^Tg and control mice. Notch1, Dll-1 and Jagged-1 expression were also assessed in stable Kaiso-depleted colon cancer cells and isolated intestinal epithelial cells using real time PCR and western blotting. To assess Kaiso binding to the DLL1, JAG1 and NOTCH1 promoter regions, chromatin immunoprecipitation was performed on three colon cancer cell lines.

Results

Here we demonstrate that Kaiso promotes secretory cell hyperplasia independently of Kaiso-induced inflammation. Moreover, Kaiso regulates several components of the Notch signaling pathway in intestinal cells, namely, Dll-1, Jagged-1 and Notch1. Notably, we found that in Kaiso^Tg mice intestines, Notch1 and Dll-1 expression are significantly reduced while Jagged-1 expression is increased. Chromatin immunoprecipitation experiments revealed that Kaiso associates with the DLL1 and JAG1 promoter regions in a methylation-dependent manner in colon carcinoma cell lines, suggesting that these Notch ligands are putative Kaiso target genes.

Conclusion

Here, we provide evidence that Kaiso’s effects on intestinal secretory cell fates precede the development of intestinal inflammation in Kaiso^Tg mice. We also demonstrate that Kaiso inhibits the expression of Dll-1, which likely contributes to the secretory cell phenotype observed in our transgenic mice. In contrast, Kaiso promotes Jagged-1 expression, which may have implications in Notch-mediated colon cancer progression.

Electronic supplementary material

The online version of this article (doi:10.1186/s12964-017-0178-x) contains supplementary material, which is available to authorized users.

Methylation-dependent regulation of hypoxia inducible factor-1 alpha gene expression by the transcription factor Kaiso

Low oxygen tension (hypoxia) is a common characteristic of solid tumors and strongly correlates with poor prognosis and resistance to treatment. In response to hypoxia, cells initiate a cascade of transcriptional events regulated by the hypoxia inducible factor-1 (HIF-1) heterodimer. Since the oxygen-sensitive HIF-1α subunit is stabilized during hypoxia, it functions as the regulatory subunit of the protein. To date, while the mechanisms governing HIF-1α protein stabilization and function have been well studied, those governing HIF1A gene expression are not fully understood. However, recent studies have suggested that methylation of a HIF-1 binding site in the HIF1A promoter prevents its autoregulation. Here we report that the POZ-ZF transcription factor Kaiso modulates HIF1A gene expression by binding to the methylated HIF1A promoter in a region proximal to the autoregulatory HIF-1 binding site. Interestingly, Kaiso's regulation of HIF1A occurs primarily during hypoxia, which is consistent with the finding that Kaiso protein levels peak after 4 h of hypoxic incubation and return to normoxic levels after 24 h. Our data thus support a role for Kaiso in fine-tuning HIF1A gene expression after extended periods of hypoxia.

Kaiso overexpression promotes intestinal inflammation and potentiates intestinal tumorigenesis in Apc(Min/+) mice

Constitutive Wnt/β-catenin signaling is a key contributor to colorectal cancer (CRC). Although inactivation of the tumor suppressor adenomatous polyposis coli (APC) is recognized as an early event in CRC development, it is the accumulation of multiple subsequent oncogenic insults facilitates malignant transformation. One potential contributor to colorectal carcinogenesis is the POZ-ZF transcription factor Kaiso, whose depletion extends lifespan and delays polyp onset in the widely used Apc(Min/+) mouse model of intestinal cancer. These findings suggested that Kaiso potentiates intestinal tumorigenesis, but this was paradoxical as Kaiso was previously implicated as a negative regulator of Wnt/β-catenin signaling. To resolve Kaiso's role in intestinal tumorigenesis and canonical Wnt signaling, we generated a transgenic mouse model (Kaiso(Tg/+)) expressing an intestinal-specific myc-tagged Kaiso transgene. We then mated Kaiso(Tg/+) and Apc(Min/+) mice to generate Kaiso(Tg/+):Apc(Min/+) mice for further characterization. Kaiso(Tg/+):Apc(Min/+) mice exhibited reduced lifespan and increased polyp multiplicity compared to Apc(Min/+) mice. Consistent with this murine phenotype, we found increased Kaiso expression in human CRC tissue, supporting a role for Kaiso in human CRC. Interestingly, Wnt target gene expression was increased in Kaiso(Tg/+):Apc(Min/+) mice, suggesting that Kaiso's function as a negative regulator of canonical Wnt signaling, as seen in Xenopus, is not maintained in this context. Notably, Kaiso(Tg/+):Apc(Min/+) mice exhibited increased inflammation and activation of NFκB signaling compared to their Apc(Min/+) counterparts. This phenotype was consistent with our previous report that Kaiso(Tg/+) mice exhibit chronic intestinal inflammation. Together our findings highlight a role for Kaiso in promoting Wnt signaling, inflammation and tumorigenesis in the mammalian intestine.

Kaiso represses the cell cycle gene cyclin D1 via sequence-specific and methyl-CpG-dependent mechanisms

Kaiso is the first member of the POZ family of zinc finger transcription factors reported to bind DNA with dual-specificity in both a sequence- and methyl-CpG-specific manner. Here, we report that Kaiso associates with and regulates the cyclin D1 promoter via the consensus Kaiso binding site (KBS), and also via methylated CpG-dinucleotides. The methyl-CpG sites appear critical for Kaiso binding to the cyclin D1 promoter, while a core KBS in close proximity to the methyl-CpGs appears to stabilize Kaiso DNA binding. Kaiso's binding to both sites was demonstrated in vitro using electrophoretic mobility shift assays (EMSA) and in vivo using Chromatin immunoprecipitation (ChIP). To elucidate the functional relevance of Kaiso's binding to the cyclin D1 promoter, we assessed Kaiso overexpression effects on a minimal cyclin D1 promoter-reporter that contains both KBS and CpG sites. Kaiso repressed this minimal cyclin D1 promoter-reporter in a dose-dependent manner and transcriptional repression occurred in a KBS-specific and methyl-CpG-dependent manner. Collectively our data validates cyclin D1 as a Kaiso target gene and demonstrates a mechanism for Kaiso binding and regulation of the cyclin D1 promoter. Our data also provides a mechanistic basis for how Kaiso may regulate other target genes whose promoters possess both KBS and methyl-CpG sites.

Abstract 1239: The transcription factor Kaiso negatively regulates the hypoxia inducible factor-1 alpha

Introduction: Hypoxia (reduced oxygen levels) is a common characteristic of solid tumors, and is strongly correlated with poor prognosis and resistance to treatment. In response to hypoxia, cells initiate a cascade of transcriptional events regulated by the Hypoxia Inducible Factor 1 (HIF-1) heterodimer. During hypoxia, the oxygen sensitive HIF-1α subunit is stabilized and translocates to the nucleus where it interacts with the HIF-1β subunit to form a functional HIF-1 transcription factor that regulates genes to facilitate cellular adaptation to hypoxia. To date, while the mechanisms governing HIF-1α stabilization and function have been well studied, those governing HIF-1α gene expression are not fully understood. Recent studies have revealed that the transcription factor Kaiso, a member of the POZ-ZF family of transcription factors implicated in tumorigenesis, is aberrantly expressed and mislocalized at the hypoxic core of various tumors. Mounting evidence suggests that, like other POZ-ZF proteins, Kaiso has a role in tumorigenesis. More importantly, the HIF-1α promoter contains several copies of the consensus Kaiso Binding Site (KBS) suggesting that HIF-1α may be a Kaiso target gene. Since HIF-1α is a key regulator of many hypoxia-induced pathways, and Kaiso is aberrantly expressed in hypoxia, some feed-back mechanism may exist between Kaiso and HIF-1α. These studies seek to elucidate the relationship between Kaiso and HIF-1α during the adaptive response to hypoxia.

Methods: Western blot analysis was performed on whole cell lysates harvested from cultured cells that were incubated in hypoxia for varying time periods to compare Kaiso expression levels in these cells. Electrophoretic Mobility Shift Assays (EMSAs) were used to determine the specificity of Kaiso binding to the HIF-1α promoter. To assess the effect of Kaiso on HIF-1α transcription, promoter-reporter assays were performed in cultured cells using a HIF-1α promoter-luciferase construct and a Kaiso expression plasmid.

Results: During hypoxia, Kaiso protein levels steadily decline and are significantly reduced after 24 hours in the MCF7 tumor epithelial cell line. Interestingly, the decrease in Kaiso protein levels is less apparent in the non-tumor MCF10A breast cell line. Kaiso binds 3 of the 6 putative Kaiso binding sites as well as a CpG rich region in the HIF-1α promoter in a methylation-dependent manner. Furthermore, Kaiso represses transcription of the HIF-1α promoter in MCF7, MCF10A and HCT116 cell lines.

Conclusion: These results indicate that Kaiso negatively regulates HIF-1α and thus implicates HIF-1α as a Kaiso target gene. The fluctuation of Kaiso expression during hypoxia suggests that HIF-1 may also regulate Kaiso and that a feedback mechanism may exist between Kaiso and HIF-1α. Ongoing studies are being performed to elucidate the functional interaction between HIF-1α and Kaiso.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1239.

Kaiso regulates Znf131-mediated transcriptional activation

Kaiso is a dual-specificity POZ-ZF transcription factor that regulates gene expression by binding to sequence-specific Kaiso binding sites (KBS) or methyl-CpG dinucleotide pairs. Kaiso was first identified as a binding partner for the epithelial cell adhesion regulator p120(ctn). The p120(ctn)/Kaiso interaction is reminiscent of the beta-catenin/TCF interaction and several studies have suggested that Kaiso is a negative regulator of the Wnt/beta-catenin TCF signaling pathway. To gain further insight into Kaiso's function, we performed a yeast two-hybrid screen using the Kaiso POZ domain as bait. This screen identified the POZ-ZF protein, Znf131, as a Kaiso-specific binding partner. GST pull-down assays confirmed that the interaction is mediated via the POZ domain of each protein, and co-immunoprecipitation experiments further supported an in vivo Kaiso-Znf131 interaction. Using a Cyclic Amplification and Selection of Targets (CAST) approach, we identified the 12-base pair DNA palindrome sequence GTCGCR-(X)(n)-YGCGAC as a potential Znf131 binding element (ZBE). In vitro studies using electrophoretic mobility shift assay (EMSA) demonstrated that Znf131 binds the ZBE via its zinc finger domain. Znf131 DNA-binding specificity was confirmed using competition assays and ZBE mutational analyses. An artificial promoter-reporter construct containing four tandem copies of the ZBE was constructed and used to assess Znf131 transcriptional properties. We observed dose-dependent transcriptional activation of this artificial promoter-reporter by Znf131 in both epithelial and fibroblast cells, suggesting that Znf131 is a transcriptional activator. Kaiso overexpression significantly decreased the Znf131-mediated transcriptional activation, and interestingly, co-expression of the Kaiso-specific interaction partner p120(ctn) relieved Kaiso's inhibition of Znf131-mediated transcriptional activation. These findings indicate that Znf131 is a transcriptional activator, a less common function of POZ-ZF proteins, that is negatively regulated by its heterodimerization partner Kaiso.