*Article* **Human Red Blood Cells as Oxygen Carriers to Improve Ex-Situ Liver Perfusion in a Rat Model**

**Daniele Dondossola 1,2,\*, Alessandro Santini 3, Caterina Lonati 3,4, Alberto Zanella 2,3, Riccardo Merighi 4, Luigi Vivona 3, Michele Battistin 3, Alessandro Galli 3, Osvaldo Biancolilli 3, Marco Maggioni 5, Stefania Villa <sup>6</sup> and Stefano Gatti <sup>4</sup>**


Received: 29 September 2019; Accepted: 5 November 2019; Published: 8 November 2019

**Abstract:** Ex-situ machine perfusion (MP) has been increasingly used to enhance liver quality in different settings. Small animal models can help to implement this procedure. As most normothermic MP (NMP) models employ sub-physiological levels of oxygen delivery (DO2), the aim of this study was to investigate the effectiveness and safety of different DO2, using human red blood cells (RBCs) as oxygen carriers on metabolic recovery in a rat model of NMP. Four experimental groups (n = 5 each) consisted of (1) native (untreated/control), (2) liver static cold storage (SCS) 30 min without NMP, (3) SCS followed by 120 min of NMP with Dulbecco-Modified-Eagle-Medium as perfusate (DMEM), and (4) similar to group 3, but perfusion fluid was added with human RBCs (hematocrit 15%) (BLOOD). Compared to DMEM, the BLOOD group showed increased liver DO2 (*p* = 0.008) and oxygen consumption (*VO*˙ 2) (*p* < 0.001); lactate clearance (*p* < 0.001), potassium (*p* < 0.001), and glucose (*p* = 0.029) uptake were enhanced. ATP levels were likewise higher in BLOOD relative to DMEM (*p* = 0.031). *VO*˙ <sup>2</sup> and DO2 were highly correlated (*p* < 0.001). Consistently, the main metabolic parameters were directly correlated with DO2 and *VO*˙ 2. No human RBC related damage was detected. In conclusion, an optimized DO2 significantly reduces hypoxic damage-related effects occurring during NMP. Human RBCs can be safely used as oxygen carriers.

**Keywords:** normothermic machine perfusion; rat; human red blood cells; oxygen consumption; oxygen delivery
