Table 1.

Brief etiology and the direct/indirect involvement of MPO in different types of diseases.

No.	Name of Disease	Brief Etiology and Possible Role of MPO	Reference
1	CVD and atherosclerosis	Raised level of MPO causes RBCs deformability, accumulation of cholesterol and its esters, ruptures in atherosclerotic plaque	[8,60]
2	Obesity	Neutrophil infiltration and activation of MPO in adipose tissue	[84,85]
3	Neurodegenerative diseases	Release of neurotoxic mediators by many factors spearheaded by MPO from neurons, astrocytes, microglia cells	[11]
4	Cancer	MPO-derived ROS/RNS react with major biomolecules causing mutagenesis, gene polymorphism, SNPs, acrolein-protein adduct formation	[86,87,88]
5	Diabetes/diabetic retinopathy	Neutrophil activation and the release of MPO in vessels and retina, upregulation of leukocyte adhesion molecules, and increased production of anti-MPO antibodies	[89,90]
6	Renal diseases	MPO-initiated HOCl-modified proteins in glomerular peripheral basement membranes	[91]
7	Liver diseases	Neutrophil infiltration, hepatic fibrosis by activation of Kupffer cells cause production of oxidants, impaired signaling events	[92,93]
8	Lung injury	Activation and expression of proinflammatory cytokines and mediators by MPO	[5]
9	Cystic fibrosis	Bacterial infiltration, especially Pseudomonas aeruginosa and infiltrating neutrophils	[94]
10	Multiple sclerosis	MPO-generated ROS cause axonal damage by proteolytic enzymes and cytotoxic oxidants by activated immune cells and glia	[95]
11	Alzheimer’s disease	Increased production of oxidants like advanced glycation end products, o,o′-dityrosine, lipid oxidation products, protein carbonyls, oxidized DNA, and 3-nitrotyrosine in neuronal tissues proposed by increased expression of MPO	[96]
12	Parkinson’s disease	Upregulation of MPO and its byproduct, 3-chlorotyrosine, in ventral midbrain	[97]
13	Tuberculosis	Enhanced MPO expression along with TNF-α and IL-12 activation	[98]
14	Asthma	Excessive MPO release from neutrophils in lower respiratory tract cells	[99]
15	Rheumatoid arthritis	Inflamed synovium intervened by lymphocytes and neutrophils leads to the release of proinflammatory mediators	[100,101]
16	Chronic sinusitis	Enhanced level of MPO and IL-8 in sinuses	[102]
17	Peptic ulcer	Free radicals formation initiated by MPO	[103]
18	Gastric ulcer	Neutrophil infiltration and the release of MPO into gastric mucosal tissue	[104]
19	Duodenal ulcer	MPO and other pro-inflammatory agents	[105]
20	Colitis	Increased activity of MPO and pro-inflammatory mediators like IL-1β and TNF-α	[106,107,108]
21	Pancreatitis	Increased MPO activity causes increased ROS that leads to this disease	[109]
22	Chronic periodontitis	Increased MPO activity in gingival crevicular fluid	[110]

MPO: myeloperoxidase; CVD: cardiovascular disease; RBCs: red blood cells; ROS: reactive oxygen species; RNS: reactive nitrogen species; SNP: single nucleotide polymorphism; IL: interleukin; TNF-α: tumor necrosis factor-α. The descriptions of some of the diseases through the perspective of MPO are reviewed in this paper.