Necroptosis contributes to non-alcoholic fatty liver disease pathoetiology with promising diagnostic and therapeutic functions

Table 1 The unique morphological and biochemical hallmarks of regulated cell deaths

		Morphological characteristics	Biochemical hallmarks
Apoptotic RCD	Apoptosis	Cell and nucleus shrinkage, nuclear chromatin condensation, karyorrhexis, the formation of apoptotic bodies, and cell fragmentation	↑CASPs (8, 9, 3, and 7), ↑BAD and BAX, ↓BCL2
Non-apoptotic RCDs	Pyroptosis	Inflammasomes caused membrane rupture, cell swelling/cell lysis, DNA fragmentation, nuclear condensation, and nuclear pores	↑CASPs (1 and 7), ↑GSDMs (D, E, etc.), ↑IL-18, ↑IL-1β
	Ferroptosis	Cell swelling, mitochondria shrinkage, cristae disappearance, increased density of mitochondrial membrane, the rupture of the outer mitochondrial membrane	↑Fe2+, ROS, lipid peroxidation, ↑ACSL4 and PTGS2, ↓GPX4 and GSH
	Necroptosis	Organelles swelling, cell membrane rupture, cell lysis, loss of cell membrane integrity, nuclear chromatin deficiency	↑RIPK1, ↑RIPK3, ↑MLKL, ↓CASP-8

RIPK1: Receptor-interacting protein kinase 1; MLKL: Mixed lineage kinase domain-like pseudokinase; RCD: Regulated cell death; CASP: Caspase; ROS: Reactive oxygen species; GSDM: Gasdermin; IL: Interleukin; ACSL4: Acyl-CoA synthetase long-chain family member 4; GPX4: Glutathione peroxidase 4; GSH: Glutathione.

Table 2 Participation of necroptosis in the occurrence and progression of the disease and its effectiveness as a diagnostic marker and therapeutic target

Function	Advantages/limitations
Pathoetiology	The upregulation of RIPK1, RIPK3, and MLKL leads to the necroptosis of hepatocytes in the fatty liver, which along with inflammatory responses contributes to the induction of NAFLD. In addition, the intensification of necroptotic death of hepatocytes is followed by the aggravation of the disease and its progress toward NASH and HCC
Diagnosis	Most of the presented biomarkers are related to the upstream inflammatory inducers of necroptosis such as TNF and ILs. Although the aforementioned markers have provided diagnostic and prognostic properties, changes in inflammatory markers occur in a variety of disorders. In addition, the uncertainty of the sensitivity and specificity of the few suggested markers complicates the evaluation of their diagnostic value. Therefore, more studies that evaluate specific necroptotic biomarkers in NAFLD patients are encouraged
Therapy	Direct inhibitors of necroptosis (RIPK1 inhibitors for example) and a variety of herbal antioxidants with anti-necroptotic, anti-inflammatory, and regulating lipid metabolism properties have been proposed in experimental and human studies. However, no clinical trial has been registered in this direction, which reveals the necessity of designing further studies

NAFLD: Nonalcoholic fatty liver disease; NASH: Non-alcoholic steatohepatitis; HCC: Hepatocellular carcinoma; TNF: Tumor necrosis factor; IL: Interleukin; RIPK1: Receptor-interacting protein kinase 1; MLKL: Mixed lineage kinase domain-like pseudokinase.