Therapeutics administered during ex vivo liver machine perfusion: An overview

Table 3 Summary of proposed advantages and limitations of liver machine perfusion therapeutics

Therapeutic	Advantages	Limitations/future considerations
RNAi pathway	Selectively targets and silences/degrades specific genes	Most beneficial/effective siRNA target against liver IRI in transplantation remains to be identified
	Mechanism of siRNA silencing pathway is generally understood	Potential for administration of multiple siRNA constructs each with a different target
	Organ-specific uptake	Requires design of siRNA against target mRNA and validation of target silencing
	Permits imaging studies visualizing tissue uptake and distribution
Defatting cocktails	Ability to restore liver function by defatting	Steatotic livers are already predisposed to IRI[32]
	Aimed at enhancing natural lipid metabolism via lipid export, reduction of triglyceride levels, and stimulation of lipid oxidation and ketogenesis	Mechanisms of glucose and lipid control in liver remain poorly defined[69]
		Undefined consensus for quantifying degree of steatosis[70]
		Need for perfusate exchange protocol as secreted triglycerides recirculate causing further increase in lipid deposition[47]
		Kinetics of defatting may surpass average timeframe of liver transplantation[48]
Vasodilators	Focused on improving intrinsic function of liver to improve blood flow via smooth muscle relaxation and vasodilation	Effects of vasodilators in marginal grafts remains unclear[61]
	Act to increase arterial flow and decrease post-sinusoidal resistance[71]	Combination of agents does not allow for specific identification of most beneficial agent(s)
Anti-inflammatory agents	Some agents also act as vasodilators[68,72,73]	Mechanisms of anti-inflammatory agents remains unexplored in context of ex vivo liver perfusion[9]
	Act to scavenge free radicals to prevent IRI[74]	Combination of agents does not allow for determination of which specific agents were beneficial[9]
	Ability to protect other cell types such as endothelial cells[75,76]
HLSC-EV	Regenerative and hepatoprotective properties[77,78]	Unknown mechanism of hypoxic protection[65]
	Diverse differentiating capabilities[77]	Timing of EV uptake during NMP currently unknown[65]
	Contain mRNA and miRNA subsets that modulate activity of target cells[79]
	May serve as option for liver diseases without need for stem cells transplantation[65]
δ-opioid agonist (Enkephalin)	Protects against oxidative stress[66]	Unknown therapeutic role in setting of post-perfusion liver transplant model with measured outcomes of graft function[66]
	Prevention of mitochondrial dysfunction via opioid receptor signaling[66]
	Protection against IRI by slowing cellular metabolism[80,81]	Unknown role in cold ischemia conditions for liver transplant models[66]
NLRP3 inflammasome inhibitor (mcc950)	Blocks NLRP3-inflammsome activation preventing inflammatory liver damage[82,83]	mcc950 half-life is 3.27 h, while NLRP3 inflammasome activation lasts for several days after reperfusion[84,85]
	Reduces apoptosis post liver transplantation[67]	Additional mcc950 inhibition studies involving in vitro and in vivo models needed[67]

HLSC-EV: Human liver stem cells extracellular vesicles; NLRP3: Nucleotide-binding domain leucine-rich repeat containing family pyrin domain containing 3.