**1. Introduction**

Due to the ongoing organ shortage, there has been an increased interest in utilizing moderately steatotic donor liver allografts to maximize opportunities for transplantation. Historically, the use of liver allografts with significant steatosis has been associated with increased risk of primary nonfunction, poor early graft function, and decreased patient and allograft survival [1–5]. The degree of steatosis, as well as its histological pattern, appears to impact patient and allograft survival [2,6]. While allografts with severe macrovesicular steatosis (>60%) carry a very high risk of primary non-function, those with mild macrovesicular steatosis (<30%) yield results similar to those of non-steatotic liver allografts [2]. The outcomes of liver allografts with moderate steatosis (30% to 60%) remain variable and the impact of graft steatosis on renal function has not been well described [7,8]. As such, the objectives of this

study were to: (1) evaluate postoperative acute kidney injury (AKI) patterns in recipients of steatotic grafts; (2) assess biopsy-findings predictive of AKI in the use of steatotic livers; (3) examine one-year patient and allograft outcomes.

#### **2. Materials and Methods**

#### *2.1. Study Population*

This was an eight-year, two-center retrospective study of patients who underwent a liver transplant at Mayo Clinic Arizona and Mayo Clinic Minnesota between January 2009 and December 2016 (*n* = 810). This study was approved by the Mayo Clinic Institutional Review Board. Outcomes were compared between moderately steatotic (>30% macrovesicular steatosis) and non-steatotic (<30% macrovesicular steatosis) grafts. In order to assess post-liver transplant (LT) acute kidney injury (AKI) patterns, patients with pre-LT acute kidney injury (AKI) (*n* = 143) were excluded. The majority of LT were performed via piggyback technique; 2.7% (*n* = 14) were performed via caval interposition. The data that supports the findings of this study is available from the corresponding author upon reasonable request.

Pre-LT AKI was defined using the Kidney Disease Improving Global Outcomes (KDIGO) guidelines by an increase in serum creatinine > 0.3 mg/dL or 1.5–1.9 times baseline. Post-LT AKI was defined by those patients satisfying the KDIGO guidelines within 48 h post-LT and maintaining the criteria for > 48 h. Patients with pre-existing chronic kidney disease were not excluded unless they had pre-LT AKI. Mean follow-up was 4.2 years.

All liver allografts were biopsied at the time of transplant and the biopsies were reviewed by a group of designated liver pathologists. Biopsy reports were retrospectively reviewed and macrovesicular steatosis percentage was recorded (less than 30% vs. greater than 30%). Early allograft dysfunction was defined as an aspartate aminotransferase (AST) greater than 2000 U/L within the first 7 days post-LT.

Liver biopsies reported as having moderate (>30% macrovesicular) steatosis were prospectively re-reviewed by a single liver pathologist (M.S.) to specifically assess for macro- and microvesicular steatosis, the percentage of small- and large droplet macrovesicular steatosis, zonation, features of steatohepatitis, fibrosis, preservation reperfusion injury (PRI), and lipopeliosis. Percentages of steatosis were based on the percentage of hepatic parenchyma involved by fat and were estimated using previously published reference figures [9].

Operative hemodynamics were quantified using a modified operative inotrope score (inotrope score = dopamine (×1) + dobutamine (×1) + amrinone (×1) + milrinone (×15) + epinephrine (×100) + norepinephrine (×100) + phenylephrine (×1) + vasopressin (×1), with each drug dosed in μg/kg/min). The inotrope score was calculated during the pre-anhepatic, anhepatic, and post-reperfusion phases for the moderately macrovesicular steatosis cohort [10]. An average of systolic blood pressure (SBP) and mean arterial pressure (MAP) was also recorded for these operative periods.

Immunosuppression was maintained per our center's protocol. All recipients were started on mycophenolate mofetil (MMF), tacrolimus, and prednisone post-LT. MMF was withdrawn at 2–4 months; prednisone was discontinued at 4 months. Tacrolimus trough levels were set at 7–10 ng/mL for the first 2 months post-LT; at one-year post-LT, trough levels were reduced to 4–6 ng/mL. By protocol at our centers, tacrolimus is typically started immediately following transplant unless there are concerns for renal insufficiency. In the setting of post-LT renal insufficiency (defined as creatinine >2.0 mg/dL, estimated glomerular filtration rate (eGFR) <40 mL/minute or dialysis), Basiliximab 20 mg is given on post-operative days 0 and 4 to allow for a delay in tacrolimus initiation. In this setting, tacrolimus initiation is delayed until postoperative day 5.

#### *2.2. Statistical Methods*

Descriptive analysis was performed using t-tests for continuous variables and Chi-square for categorical variables. Continuous variables are shown using mean and standard deviation; categorical

variables using count and percentage. Wilcoxon rank-sum tests were used for non-normally distributed continuous variables. Survival analysis was performed using Kaplan-Meier analysis. Logistic regression was applied to clinically significant variables. Statistical analysis was performed using Prism software version 7.03 (La Jolla, CA, USA) and SAS version 9.4. A *p* value of <0.05 was considered significant.
