Essential hypertension: A filtered serum based metabolomics study

Abstract

Despite the easy and reliable methods of blood pressure measurement, the screening of essential hypertension (EH) is usually ignored due to delayed onset of symptoms. A probe into the biochemical changes in hypertension would serve as a welcome asset to provide insight into the mechanistic aspects of EH. Filtered serum samples from 64 EH patients and 59 healthy controls (HC) were analysed using 800 MHz nuclear magnetic resonance (NMR) spectroscopy. Application of principal component analysis (PCA) and orthogonal partial least-squares discriminant analysis (OPLS-DA) following receiver operating characteristic (ROC) curve of NMR data reveals significantly perturbed metabolites: alanine, arginine, methionine, pyruvate, adenine, and uracil. This set of metabolites correctly classified 99% of cases from HC and also showed excellent correlation in both isolated elevated diastolic blood pressure (DBP) cases and combined elevated systolic-diastolic blood pressure cases. Proton NMR metabolomics of EH may prove helpful in defining associated biomarkers and serve as an alternate diagnostic tool with judicious clinical assessment.

Figure 1

A typical ¹H NMR spectrum of serum samples after removal of proteins and lipoproteins (A) healthy control (B) essential hypertension, showing assignment of various metabolites.

Figure 2

Three-dimensional score plots of (A) unsupervised PCA (B) supervised OPLS-DA (C) OPLS-DA of training data and (D) Y-prediction of test data. Here; green color circles denote EH; blue color stars denote HC.

Figure 3

(A) Alterations in OPLS-DA coefficients (±SE) of filtered serum metabolites from EH patients as compared to HC. (B) Defines receiver operating characteristic (ROC) curve obtained from a combination of the six metabolites. Discrimin Pred Prob; Discriminant predicted probability.

Figure 4

A simplified metabolic pathway showing up-regulated and down-regulated metabolites in EH patients as compared to HC.

Figure 5

A flowchart representing possible dynamics of metabolites describing results and implications of elevated blood pressure (green colour represents decreased concentrations and red colour represents elevated concentration in EH milieu; DDAH; dimethylarginine dimethylamino-hydrolase, ADMA; asymmetrical dimethyl arginine, NO; Nitric oxide, NOS; NO synthase, PRMT; protein methyltransferase, ROS; reactive oxygen species, SAM; S-adenosylmethionine, SAH; S-adenosylhomocysteine). 1; competitive inhibition, 2; NOS inhibition, 3; Nitric oxide synthase, 4; peroxy nitrite formation, 5; decrease in methionine synthase, 6; hydrolysis, 7; PRMT, 8; decrease in norepinephrine release, 9; alanine aminotransaminase, 10; Mitochondrial metabolism is also activated by alanine resulting in increase in ATP/ADP ratio in cytosol, that triggers insulin exocytosis via increased cytosolic Ca²⁺ concentration, 11; insulin resistance, 12; insulin release, 13; arginine uptake, 14; increases NO via insulin signalling.