Correlation Between Saliva and Plasma Levels of Endothelin Isoforms ET-1, ET-2, and ET-3
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Hindawi Publishing Corporation International Journal of Peptides Volume 2015, Article ID 828759, 7 pages http://dx.doi.org/10.1155/2015/828759 Research Article Correlation between Saliva and Plasma Levels of Endothelin Isoforms ET-1, ET-2, and ET-3 Roma Gurusankar,1 Prem Kumarathasan,2 Anusha Saravanamuthu,2 Errol M. Thomson,1 and Renaud Vincent1 1 Inhalation Toxicology Laboratory, Environmental Health Science and Research Bureau, Health Canada, Ottawa, ON, Canada K1A 0K9 2Analytical Biochemistry and Proteomics Laboratory, Environmental Health Science and Research Bureau, Health Canada, Ottawa, ON, Canada K1A 0K9 Correspondence should be addressed to Renaud Vincent; [email protected] Received 17 January 2015; Revised 17 March 2015; Accepted 18 March 2015 Academic Editor: Kazuhiro Takahashi Copyright © 2015 Roma Gurusankar et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Although saliva endothelins are emerging as valuable noninvasive cardiovascular biomarkers, reports on the relationship between isoforms in saliva and plasma remain scarce. We measured endothelins in concurrent saliva and plasma samples (=30males; age 18–63) by HPLC-fluorescence. Results revealed statistically significant positive correlations among all isoforms between saliva and plasma: big endothelin-1 (BET-1, 0.55 ± 0.27 versus 3.35 ± 1.28 pmol/mL; = 0.38, = 0.041), endothelin-1 (ET-1, 0.52 ± 0.21 versus 3.45 ± 1.28 pmol/mL; = 0.53, = 0.003), endothelin-2 (ET-2, 0.21 ± 0.07 versus 1.63 ± 0.66 pmol/mL; = 0.51, = 0.004), and endothelin-3 (ET-3, 0.39 ± 0.19 versus 2.32 ± 1.44 pmol/mL; = 0.75, < 0.001). Correlations of BET-1, ET-1, and ET-3 within each compartment were positive in both plasma ( < 0.05)andsaliva( ≤ 0.1), whereas ET-2 was not significantly correlated with other isoforms in either plasma or saliva. For all isoforms, concentrations varied on average fivefold between individuals (90th/10th percentiles); individuals with high plasma endothelin levels generally had high saliva endothelin levels. Our results reveal that salivary ET isoform profiles portray the plasmatic profiles and support the view of coordinated regulation of ET-1 and ET-3, but distinct regulatory pathways for ET-2. 1. Introduction cardiovascular disease [9]. Endothelins are a family of potent vasoconstrictor peptides consisting of three distinct isoforms, As a diagnostic fluid, saliva has several advantages over blood endothelin-1 (ET-1), endothelin-2 (ET-2), and endothelin-3 [1, 2]. Saliva is inexpensive and easier to collect, and sufficient (ET-3) coded by distinct genes [10]. The mature endothelins volume can be obtained to allow performance of a variety areproducedthroughcleavageofthebigendothelin(BET) of analyses. For patients, particularly children, the noninva- precursors by endothelin-converting enzymes [11, 12]. Endo- sive sample collection reduces anxiety and discomfort and thelin-1, the most studied isoform, has been implicated in simplifies procurement of repeated samples for time-series several diseases, particularly in the progression of cardiovas- analyses. Saliva contains a wide array of proteins and peptides cular diseases [13, 14]. It has been known for two decades that that are responsive to pathological conditions [3]. Advanced ET-1, ET-2, and ET-3 are present in saliva [15, 16]. However, instrumentation and refined analytical techniques have been only recently have levels of saliva ET-1 been related to successfully applied for discovering oncological [4], hor- conditions such as chronic heart failure [17], upper gastroin- monal [5], immunological [6], and cardiovascular [7, 8] testinal diseases [18], vibration-induced white finger [19], biomarkers that can be informative for early detection and and oral cancer [20, 21]. The relationship between saliva and assessment of progression of oral and systemic diseases. plasmaET-2andET-3isoformsiscomparativelylesswell Of particular interest, saliva is known to contain understood. Because of the emerging significance of all three detectable levels of endothelins, an important risk marker for isoforms in health and disease, notably the role of ET-2 in 2 International Journal of Peptides the cardiovascular system, in ovulation, immunology, and Scientific, Guelph, ON), a Gilson autosampler (model 231 XL; cancer [22], we sought to extend the data on the relationships Middleton, WI), a Supelcosil LC-318 reverse-phase column between the three endothelin isoforms in concurrent saliva (25 cm length, 4.6 mm id, 5 m particle size, and 300 A˚ and plasma samples. pore dimension; Supelco, Oakville, ON), and a RF 551 model fluorescence detector (Shimadzu, Japan). Endothelins 2. Materials and Methods (20 L injection volume) were separated using a gradient elution with acetonitrile/water mobile phase at a flow rate of 2.1. Reagents. Ethylenediaminetetraacetic acid (EDTA), tri- 1 mL/min and detected at EX 280 nm and EM 340 nm [23]. fluoroacetic acid (TFA), phenylmethyl sulfonyl fluoride Blanks were analyzed after each set of four samples in order (PMSF), 3,4-dichloroisocoumarin, molecular weight cut-off to assess the extent of analyte carryover. filters (30 kDa), endothelin-1 (ET-1, human), endothelin- 2 (ET-2, human), and endothelin-3 (ET-3, human) were 2.5. Statistical Analyses. Student’s -test or Mann-Whitney obtained from Sigma Aldrich (Oakville, Ontario). Big endo- RankSumTestwascarriedoutasappropriateusingSigmaStat thelin-1 (BET-1, human) was obtained from Bachem Bio- v 11.0 (SPSS Inc., Chicago, IL). Results are presented as mean science (American Inc., CA, USA). Acetonitrile, acetone, ± standard deviation. Correlation between different endothe- methanol, and hydrochloric acid were purchased from Sigma lin isoforms in plasma and saliva was tested using Pearson’s Aldrich (Oakville, Ontario). Amber glass vials and screwcaps Product Moment correlation revealing and values. Statis- with septa were purchased from Chromatographic Special- tical significance was accepted for = 0.05. ities (Brockville, Ontario). Deionized water was obtained from a Super-Q Plus high purity water system (Millipore Corporation, Bedford, MA). Compressed gaseous nitrogen 3. Results and Discussion wasofUHPgradequalityandwassuppliedbyMathesonGas Products (Whitby, Ontario). We used HPLC-fluorescence to measure simultaneously the isoforms BET-1, ET-1, ET-2, and ET-3 (Figures 1(a)-1(b))in time-matched plasma and saliva sample pairs (=30) 2.2. Biological Samples. Anonymous, paired human plasma obtained from anonymous individuals (Table 1). Our results and saliva samples (from males) certified free of HIV, HEP- confirm and extend previous reports of the presence of A, and HEP-B were purchased commercially (Innovative endothelins in saliva [15, 16] and of a relationship between ResearchInc.,MI).Salivasampleswerecollectedbyspitting saliva and circulating endothelins [17–19], and the correlated in a sterile cup, without stimulation. Both plasma and saliva measurements provide additional insight into the relation- samples were treated on site with PMSF (final, 1.7 mg/mL) ship of ET-2 to the other two isoforms [22]. The recoveries, and EDTA (final, 10 mg/mL) to stabilize endothelins [23], ∘ analytical precision, and accuracy of the HPLC-fluorescence shipped to our laboratory in dry ice, and stored at −80 Cuntil procedure [23] are comparable to values reported by Walczak further use. Saliva samples containing phlegm or low volume et al. for HPLC with electrospray tandem mass spectrometry of fluid were discarded. Thirty (30) sample pairs of good qual- detection [24]: recoveries of endothelins from spiked plasma ity and in sufficient amounts for analysis were retained for this are between 60% (ET-2) and 97% (ET-1), depending on the study. endothelin isoforms; analytical precision is on the order of ±4% for replicate peptide standards; analytical accuracy is 2.3. Extraction of Endothelins from Plasma and Saliva. ±20% for replicate measurements of plasma samples; limit of Plasma and saliva endothelins were extracted following Kum- detection is 0.2–0.5 pmol; and linearity is 1–100 pmol on the arathasan et al. [23]. Briefly, plasma (250 L) and saliva (1 mL) column (20 L injection volume). Both methods detect the samples were treated with ice-cold 3,4-dichloroisocumarin separated peptides directly (i.e., on the basis of autofluores- solution in isopropanol to prevent conversion of BET-1 cence of aromatic amino acids by HPLC [23, 25]orfrom toET-1duringthesampleprocessing.Thesampleswere mass ion fingerprints in MS/MS24 [ ]), which is different deproteinized with ice-cold acid-acetone mix (acetone : 1 N from ELISA detection of immunoreactive endothelin in total × HCl : water, 40 : 1 : 5) and centrifuged at 9000 gfor10min, plasma [26, 27]. For this reason, we have verified identities and the supernatants obtained were concentrated by evapora- of analytes by pulling down of ET-1 and ET-3 with mon- tion under nitrogen flow. Deproteinization and concentration oclonal antibodies during sample processing, confirming stages were repeated once more to ensure the removal of the correspondence between immunoreactive endothelins in abundant proteins. Samples were then loaded onto 30 kDa plasma and the peptides measured by direct autofluorescence molecular weight cut-off filters (prewashed with deionised detection after separation on column [23]. × water) and centrifuged at 5000 g for 30 min. These