Table 1.

Low molecular weight substances increased in CKD and examined for causal effects on cardiovascular calcification or associated readouts.

Effect	Substance	Species	Tissue or Cell Type	Type of Study		Analysis of Calcification or Calcification-Associated Process * by	Reference	Plasma Level in CKD	Classified as Uremic Toxin **
				In Vitro	Animal
INHIBITION	Asymmetric dimethylarginine (ADMA)	Human	VSMC	V $		Alizarin red staining	Schepers [29]	↑ [§]	V
	Symmetric dimethylarginine (SDMA)	Human	VSMC	V $		Alizarin red staining	Schepers [29]	↑ [§]	V
	Guanidinosuccinic acid (GSA)	Human	VSMC	V $		Alizarin red staining	Schepers [29]	↑ [§]	V
INDUCTION	Phosphate (P)	Human	VSMC	V		Calcium content Alizarin red staining	Bouabdallah [30]	↑ [31]
		Human	VSMC	V		Alizarin red staining Upregulation of MSX2, SOX9 and OPN Increased apoptosis	Cazana-Perez [32]
		Human	VSMC	V		Calcium content Upregulation of CBFA1/RUNX2 and BMP2	Guerrero [33]
		Human	VSMC	V		Alizarin red staining	Schepers [29]
		Human	VSMC	V $		High binding affinity of calcium to ECM	Shigematsu [34] 1
		Rat	VSMC	V		Von Kossa staining	Shibata [35]
		Rat	Aorta	V		Calcium content	Guerrero [33]
		Mouse	Aorta		V 2	Von Kossa staining	Belmokhtar [36]
		Mouse	VSMC	V		Alizarin red staining Increased ROS generation Upregulation of PIT-1, BMP2 and CBFA1/RUNX2	Belmokhtar [36]
		Mouse	VSMC	V		Upregulation of BMP2 and OPN	Sage [37] 1
		Rat	Aorta		V 3	Von Kossa staining	Shibata [35]
	Calcium	Rat	Aorta	V		Calcium content	Azpiazu [38] 1	↑ [39]
		Human	VSMC	V		Calcium content	Yang [40] 1
	Cytidine	Human	MSC	V $		ALP activity Calcium content	Hegner [41]	↑ [§]	V
	Urea	Human	MSC	V $		ALP activity Calcium content	Hegner [41]	↑ [§]	V
	Threitol	Human	MSC	V $		ALP activity Calcium content	Hegner [41]	↑ [§]	V
NO EFFECT	Guanidino compounds:	Human	VSMC	V		Alizarin red staining	Schepers [29]
	ADMA							↑ [§]	V
	SDMA							↑ [§]	V
	GSA							↑ [§]	V
	Creatine							↑ [§]	V
	Creatinine							↑ [§]	V
	Guanidine							↑ [§]	V
	Guanidino acetic acid							↑ [§]	V
	Guanidino butyric acid							↑ [§]	V
	Guanidino propionic acid							↑ [§]	V
	Methylguanidine							↑ [§]	V

ALP—alkaline phosphatase; BMP2—bone morphogenetic protein 2; CBFA1/RUNX2—core-binding factor subunit alpha-1/runt-related transcription factor 2; CT—computed tomography; ECM—extracellular matrix; MSC–mesenchymal stromal cells (as progenitors of VSMC); MSX2—msh homeobox 2; OPN—osteopontin; PIT-1—sodium Pi co-transporter-1; ROS—reactive oxygen species; SOX9—SRY-box transcription factor 9; VSMC—vascular smooth muscle cells. * Readouts of calcification-associated processes, such as cell signaling and gene/protein expression, are shown in italic. [§] As described in comprehensive uremic toxins reviews [19,20]. ** As described in comprehensive uremic toxins reviews [19,20,21]. ^$ In pro-calcifying medium. ¹ Literature added manually after checking reference lists of included studies or recent reviews. ² In vivo mouse model: 5/6 nephrectomy in Apoe^−/−mice on a high- phosphorus diet vs. 5/6 nephrectomy in Apoe^-/- mice on a control diet for twelve weeks. ³ In vivo rat model: 5/6 nephrectomy in rats on a high- phosphorus and low-calcium diet vs. 5/6 nephrectomy in rats on a control diet for eight weeks; ↑ indicates increased plasma levels in CKD patients.