**1. Introduction**

Arterial hypertension is highly prevalent in kidney transplant recipients (KTRs) as a consequence of common pretransplant hypertension and as an additional effect of immunosuppressive medications [1,2]. It has been shown that blood pressure (BP) control is suboptimal (systolic BP > 140 mmHg) in 50% of KTRs [3–5]. In addition, higher BP values were associated with reduced graft and patient survival [5]. Notably, cardiovascular disease is the primary cause of mortality among kidney transplant recipients, mostly due to long-term consequences of chronic kidney disease (CKD) [6]. CKD-related systemic inflammation, calcium-phosphate abnormalities, and oxidative stress promote endothelial dysfunction, vascular calcification, and accelerated atherosclerosis in addition to the traditional risk factors [7,8]. Vascular

injury caused by the uremic milieu results in an increased arterial stiffness and reduced flow-mediated dilation (FMD) [9,10].

Chronic hepatitis C virus (HCV) infection has been shown to independently worsen posttransplant survival [11]. HCV infection is a risk factor for increased aortic stiffness and cardiovascular events in dialysis patients [12], whereas advanced HCV-derived liver fibrosis is associated with increased endothelial dysfunction, independently of common cardiovascular risk factors [13]. On the other hand, patients with chronic HCV infection also demonstrate impaired autonomic nervous system function [14]. All the above disturbances caused by coexisting HCV infection may partially worsen blood pressure control in KTRs.

A few years ago a breakthrough in the treatment of chronic hepatitis C occurred. The previous interferon-based therapy, which was contraindicated for kidney transplanted patients due to increased risk of organ rejection, was replaced by new, direct acting antiviral (DAA) drug regimens. In our observation, the effectiveness of this therapy, based on sofosbuvir, reached 100% [15]. We hypothesized that the successful eradication of HCV infection may directly or indirectly improve the endothelial function. In the present study, patients were prospectively evaluated regarding different measures of their vascular function, including endothelial function, arterial stiffness measurement, and blood pressure control. Concurrently, we assessed the liver stiffness and steatosis before and after the DAA treatment. As we observed the improvement of blood pressure control in some individuals, we conducted an analysis of potential explanatory mechanisms behind this finding.

#### **2. Material and Methods**

#### *2.1. Study Group*

The study protocol was accepted by the Bioethics Committee of the Medical University of Silesia in Katowice (KNW/0022/KB1/119/16) and all participants provided written informed consent. The study was conducted in accordance with the Declaration of Helsinki. We prospectively studied all eligible adult kidney transplant recipients (KTRs) who completed treatment with DAA therapy due to HCV infection and completed both baseline and follow-up examination at least 12 months after the start of DAA therapy.

#### *2.2. Clinical, Anthropometric, and Laboratory Measurements*

Body weight and height were measured following standard procedures and body mass index (BMI) was then calculated (kg/m2). Body surface area (BSA) was calculated according to the DuBois formula and was expressed in m2.

Kidney graft function was measured by the estimated glomerular filtration rate (eGFR), which was calculated according to the abbreviated Modification of Diet in Renal Disease formula.

HOMA-IR (Homeostatic model assessment of insulin resistance) was calculated to assess insulin resistance.

HCV RNA was measured with COBAS® AmpliScreen HCV v.1.0, with lower limit of detection of 15 IU/mL (Roche Diagnostics, USA). HCV genotyping and viral load was performed with Linear Array Genotyping Test and COBAS®TaqMan® Quantitative test v.1.0, with lower limit of detection of 21 IU/mL (TaqMan; Roche Diagnostics, Branchburg, NJ, USA).

Concentrations of blood glycated hemoglobin (HbA1C), serum creatinine, total cholesterol, triglycerides, and total bilirubin concentrations, as well as aspartate aminotransferase (AST), alanine aminotransferase (ALT), and gamma glutamyl transpeptidase (GGT) activity were routinely measured during standard outpatient visits. Additional blood samples were withdrawn in a closed system into tubes containing citrate and ethylenediaminetetraacetic acid (EDTA) for nonroutine analyses. The tubes were allowed to stand for 2 h at room temperature, then centrifuged (15 min, 3000 rpm), and finally plasma aliquots were preserved at −70 ◦C.

The plasma concentrations of high-sensitivity C-reactive protein (hsCRP) were assessed with the use of an enzyme-linked immunosorbent assay (ELISA) (Immundiagnostic AG, Bensheim, Germany), with the limit of quantification (LoQ) of 0.09 mg/L, intra-assay variation <6%, and inter-assay variation <11.6%. Plasma concentrations of interleukin-6 (IL-6) were assessed with an ELISA (R&D Systems, Minneapolis, MN, USA) with a LoQ of 0.7 pg/mL, intra-assay variation <4.2%, and inter-assay variation <6.4%. Plasma concentrations of fibroblast growth factor 21 (FGF-21) were assessed with an ELISA (Biovendor, Brno, Czech Republic) with a LoQ of 7 pg/mL, intra-assay variation <2.0%, and inter-assay variation <3.3%. Plasma concentrations of C-peptide and insulin were measured using a Cobas E411 analyzer with intermediate precision <5.0% and <2.8%, respectively.

Each study examination consisted of the measurement of office BP and central arterial pressure parameters. Echocardiography, pulse wave velocity (PWV), FMD, liver stiffness measurement (LSM), and liver steatosis assessment (controlled attenuation parameter (CAP)) were also performed at the same time points.

Attended office blood pressure measurements (OBP) were performed three times in the sitting position after more than a 5-min rest in the sitting position on the arm without arterio-venous fistula at the beginning of the study. Patients with systolic BP values ≥140 mmHg and/or diastolic BP values ≥90 mmHg or those who received antihypertensive medication were diagnosed as hypertensive. For the present post hoc analysis, the OBP control improvement was defined as the decline of attended office systolic pressure by at least 20 mmHg without pharmacotherapeutic changes or the reduction of antihypertensive treatment due to the BP decline during the follow-up period. The cut-off value (20 mmHg) was established based on doubled maximum measurement error of 10 mmHg [16,17]. Patients were divided into two study subgroups based on the BP control improvement during the follow-up period.
