Table 2.

Review of reported effects on oxidative stress in varying skin models upon exposure to PM

Model	PM type	Dose and application	Exposure time	Main findings	Ref.
Ex vivo human skin	SRM® 1649b	2 mg/cm2, topical	24 h	- Lipid peroxidation.	[119]
Mice, C-57	Diesel PM	4.5, 11.1 and 26.7 mg/cm2, topical	80 h	- Increased DNA adduct formation.	[166]
Mice, FVB/N	SRM® 1650b	1 mg/time (PAH extracted), topical	12 h	- Increased CYP1B1 mRNA expression.	[167]
Mice, HR-1	SRM® 1650b	100 μg/mL, topical	7 d	- Increased protein carbonylation and lipid peroxidation.	[168]
	SRM® 1650b	100 μg/mL, topical	7 d	- ER stress: upregulation protein expression of CHOP and GRP78. - Lipid peroxidation: increased expression of HNE protein. - Mitochondrial and ER swelling. - Increased protein carbonylation. - Apoptosis: increased protein expression of BAX, active caspase-3, and caspase-9, and DNA breakage. - Autophagy: increased protein expression of LC3B-II.	[123]
	SRM® 1650b	100 μg/mL, topical	7 d	- Increased protein carbonylation. - Increased NOX4 protein expression.	[169]
HSE	SRM® 2975	200 μg/mL, systemic	2 d repetitive exposure, 6 d total	- Increased protein expression of cleaved caspase-3.	[125]
HEE	CAPs, PM2.5	0.5 and 2.0 μg/cm2, topical	24 and 48 h	- Increased isoprostanes protein level. - Increased HNE protein expression. - Increased CYP1A1 protein expression. - Increased DNA fragmentation.	[128]
	CAPs, PM2.5	25 μg/mL, topical	24 and 48 h	- Increased protein carbonylation.	[170]
	PM0.3–2.5 from Benin, West-Africa	30 μg/cm2, topical	24 h	- Increased HNE protein expression. - Increased HMOX1, metallothionein 1G and 1E, cyclin dependent kinase inhibitor 2A, and caspase 3 mRNA expression. - Decreased BIRC5 mRNA expression.	[133]
	CRM no. 28	25 mg, topical	6 h	- Upregulated mRNA expression of CYP1A1, CYP1B1, and SOD2.	[129]
	SRM® 1975	5 mg/mL, topical	48 h	- Increased level of carbonylated proteins	[171]
	SRM® 1648a	2.2, 8.9, and 17.9 μg/cm2, topical	24 and 48 h	- Decreased AhR and increased NOTCH1 protein expression.	[131]
NHDF	SRM® 2787	30 μg/cm2, systemic	24 h	- Autophagy: accumulation of LC3-II. - Mitochondrial stress: deformed mitochondria. - Increased CYP1A1 and CYP1B1 mRNA expression.	[135]
	ERM-CZ100	50–400 μg/mL, systemic	3.3 h	- Increased levels of intracellular ROS.	[136]
	The pre-conditioned medium of HaCaT treated with CRM no. 28	125 μg/mL, systemic	30 m, 48 h post-incubation	- Increased levels of intracellular ROS. - Increased number of apoptotic bodies.	[137]
	SRM® 1649b	50 μg/mL, systemic	24 h	- Increased intracellular ROS levels. - Activation of AhR (XRE activity). - Upregulation of CYP1A1 mRNA expression.	[119]
	SRM® 1649b	100–400 μg/mL, systemic	24 h	- Nuclear translocation of AhR. - Increased mRNA expression of CYP1A1. - Induced apoptosis.	[172]
NHEK	Diesel PM or vapour	0.05% (v/v), systemic	20 d	- Increased Nrf2 protein expression. - Mitochondrial dysfunction: overexpression of proteins from mitochondrial complex I and IV.	[127]
	SRM® 1975	5 mg/mL, systemic	1 and 24 h	- Increased intracellular ROS levels. - Increased of CYP1A1 mRNA expression. - Nuclear translocation of AhR.	[171]
	ERM-CZ120	3, 10, 30 and 100 μg/mL, systemic	24 and 48 h	- Increased ROS levels after 24 h. - Increased NOX1 and NOX2 mRNA expression after 24 h.	[173]
	PM ≤1 μm from Seoul, Korea	40 μg/cm2, systemic	24 h	- Increased ROS production. - Inhibition of ROS inhibited cytokine secretion.	[121]
	PM2.5 from Seoul, Korea	25 μg/mL, systemic	24 h	- Top upregulated genes from transcriptomics analysis are CYP1A1 and CYP1B1.	[132]
	PM2.5 from Xi’an, China	50 μg/mL, systemic	24 h	- Top upregulated genes from transcriptomics analysis are CYP1A1 and SOD2.	[134]
	Asian dust storm particles from Seoul, Korea	25 μg/mL, systemic	24 h	- Increased CYP1A1, CYP1A2, and CYP1B1 mRNA expression.	[139]
	Diesel PM	30 and 60 μg/mL, systemic	24 h	- Increased ROS production. - Increased HMOX1 mRNA and protein expression. - Increased Nrf2 mRNA expression.	[138]
	SRM® 2786	1 mg/mL, systemic	6 h	- RNA-Seq analysis: Downregulation of ER stress apoptosis-related genes such as ATF4 and CHOP. No activation of BCL2, BAX, caspase 3, and caspase 8. - Upregulation of HMOX1, CYP1A1, CYP1B1, and NQO1.	[141]
	SRM® 1650b and 2975	10 and 100 μg/mL, systemic	1 and 24 h	- Increased radical production.	[174]
NHEK, HaCaT, and HEK001	SRM® 1650b	50 μg/mL, systemic	72 h	- Induced senescence: increased β-galactosidase activity.	[124]
NHEK and HaCaT	SRM® 1650b	50 μg/mL, systemic	0.5–48 h	- Increased intracellular ROS levels. - Nuclear translocation of AhR (0.5 h). - Induced senescence: upregulation of P16INK4A and increased number of SAHF/nuclei. Decreased colony-forming ability. - Senescence is AhR dependent. - Transcriptional regulation of P16INK4A correlates with DNA demethylation: lower methylation of the P16INK4A promoter region.	[124]
NHDF and HaCaT	SRM® 1650b	50 μg/mL, systemic	30 m and 24 h	- Increased levels of lipid peroxidation and protein carbonylation after 24 h. - Increased levels of superoxide anion, hydroxyl radicals, and intracellular ROS (30 m). - Increased intracellular and mitochondrial calcium levels after 24 h. - Increased protein expression of CHOP, GRP78, active caspase-3, caspase-9, PARP, and BAX after 24 h. - Downregulated protein expression of Bcl-1 and Mcl-1 after 24 h. - Increased mitochondrial permeability after 24 h. - Reduced ATP levels after 24 h. - Increased DNA degradation and the number of apoptotic bodies after 24 h.	[175]
HaCaT	PM2.5 from Bangkok, Thailand	100 μg/mL, systemic	30 m	- Increased intracellular ROS levels.	[176]
	PM2.5 from Taoyuan, China	25, 50, 100 and 200 μg/mL, systemic	24 h	- Increased intracellular ROS levels. - Decreased SOD activity. - Increased lipid peroxidation: accumulation of MDA protein. - Induced formation of apoptotic bodies. - Induced protein expression of cytochrome c, active caspase-3, and caspase-9. - DNA damage.	[177]
	SRM® 1648a	50–200 ppm, systemic	24 and 48 h	- Increased ROS production.	[130]
	SRM® 1648a SRM® 1649b	50 μg/cm2, systemic	24 h	- Nuclear translocation of AhR. - Increased CYP1A1 and CYP1B1 mRNA expression.	[178]
	SRM® 1649b	50 μg/cm2, systemic	1 h	- Increased levels of intracellular ROS.	[142]
	SRM® 1649b	50 μg/cm2, systemic	2 and 24 h	- Increased cellular and mitochondrial ROS levels after 2 h. - Increased HMOX1 protein expression after 24 h.	[143]
	SRM® 1649b	25 and 50 μg/cm2, systemic	4 and 24 h	- Increased ROS production. - Increased NOX activity.	[122]
	SRM® 1649b	25–100 μg/cm2, systemic	4 and 24 h	- Increased NOX2 protein expression. - Increased ROS production.	[179]
	SRM® 1649b	25 μg/mL, systemic	2 and 24 h	- Increased ROS production.	[180]
	SRM® 1649b	50 μg/cm2, systemic	1 and 4 h	- Increased ROS production. - Increased NOX2 activity.	[181]
	SRM® 1649b	25 and 50 μg/cm2, systemic	4 and 24 h	- Increased ROS production - Increased NOX activity.	[122]
	SRM® 1649b	100–400 μg/mL, systemic	24 h	- Nuclear translocation of AhR. - Increased CYP1A1 mRNA expression. - Induced apoptosis.	[172]
	SRM® 1650b	50 μg/mL, systemic	24 h	- Increased cellular and mitochondrial ROS levels and mitochondrial stress. - Increased lipid peroxidation and protein carbonylation. - Increased cleaved caspase-3 and BAX and decreased Bcl-2 protein expression. - Induced DNA damage. - Increased number of apoptotic bodies.	[182]
	SRM® 1650b	50 μg/mL, systemic	1 and 24 h	- Increased intracellular ROS and superoxide anion levels. - Increased levels of protein carbonylation and lipid peroxidation after 24 h. - Induced DNA damage and apoptotic body formation. - Increased mitochondrial permeability after 24 h. - Increased BAX, active caspase-3, and PARP and decreased Bcl-2 protein expression.	[183]
	SRM® 1650b	50 μg/mL, systemic	24 h	- Increased intracellular ROS and calcium levels. - Increased levels of lipid peroxidation and protein carbonylation. - DNA damage. - Increased mitochondrial ROS, calcium, and permeability. - Apoptosis: increased protein expression of ATF6, GRP78, p-IRE1, BAX, and active caspase-3 and caspase-9. Decreased protein expression of Bcl2. Increased number of apoptotic bodies. - Autophagy: autophagic lysosomes. Increased protein expression of LC3B-II and beclin-1.	[168]
	SRM® 1650b	50 μg/mL, systemic	24 h	- Increased intracellular ROS and superoxide levels. - Induced NOX activity. - Increased intracellular calcium levels and mitochondrial membrane permeability. - Induced lipid peroxidation and protein carbonylation. - DNA damage. - Increased number of apoptotic bodies.	[184]
	SRM® 1650b	50 μg/mL, systemic	1, 4, 8, 12, and 24 h	- Increased intracellular ROS. - Increased levels of intracellular calcium. - ER stress: Increased protein expression of CHOP, GRP78, and p-PERK. - Increased mitochondrial permeability. - DNA damage. - Increased lipid peroxidation and protein carbonylation. - Apoptosis: Increased protein expression of BAX, DNA breakage, apoptotic body formation, and increased expression of active caspase-3 and caspase-9. - Autophagy: Increased protein expression of LC3B-II.	[123]
	SRM® 1650b	50 μg/mL, systemic	30 m, 1 h, and 24 h	- Increased ROS production. - Increased levels of intracellular calcium. - Induced senescence.	[185]
	SRM® 1650b	50 μg/mL, systemic	24 h	- Increased ROS production. - Increased lipid peroxidation. - Increased number of apoptotic bodies.	[186]
	SRM® 1650b and 2975	10 and 100 μg/mL, systemic	1 and 24 h	- No changes in radical production.	[174]
	SRM® 2975	100 and 200 μg/mL, systemic	24 h	- Increased protein expression of cleaved caspase-3 and PARP. - Increased protein expression of BAX and p53.	[125]
	CRM no. 28	125 μg/mL, systemic	30 m, 24 h post-incubation	- Increased levels of intracellular ROS.	[137]
	ERM-CZ120	100 μg/mL, systemic	30 m	- Increased intracellular ROS production.	[126]
	ERM-CZ120	25–100 μg/mL, systemic	3 and 24 h	- Increased CYP1A1 protein expression. - Decreased AhR protein expression. - Increased LC3-II and p62 protein expression.	[187]
	CAPs, PM2.5	5–25 μg/mL, systemic	1, 3, 6, and 24 h	- Increased HNE protein adduct formation. - Increased nuclear translocation of Nrf2. - No changes in GPX, GR, and NPQO1 mRNA expression.	[145]

Abbreviations: h, hour; d, day; m, minute; HSE, human skin equivalent; HEE, human epidermal equivalent; NHEK, normal human epidermal keratinocyte; SRM, standard reference material; PM, particulate matter; CAP, concentrated ambient particles; ppm, parts per million; CRM, certified reference material; ROS, reactive oxygen species; PARP, poly (ADP-ribose) polymerase; Nrf2, nuclear factor erythroid 2-related factor 2; AhR, aryl hydrocarbon receptor; LC3-II, light-chain 3 II; BIRC5, baculoviral IAP repeat containing 5; NQO1, NAD(P) H quinone dehydrogenase 1; HMOX1, heme oxygenase 1; NOX, NADPH oxygenase; HNE, 4-hydroxy-2-nonenal; ER, endoplasmic reticulum; CYP1A1, cytochrome P450 family 1 subfamily A member 1