Signal pathways underlying homocysteine-induced production of MCP-1 and IL-8 in cultured human whole blood¹

Aim: To elucidate the mechanisms underlying homocysteine (Hcy)-induced
chemokine production.
Methods: Human whole blood was pretreated with inhibitors
of calmodulin (CaM), protein kinase C (PKC), protein tyrosine kinase
(PTK), mitogen-activated protein kinase (MAPK), and NF-κB and activators of
PPARγ for 60 min followed by incubation with Hcy 100 μmol/L for 32 h. The
levels of mitogen chemokine protein (MCP)-1 and interleukin-8 (IL-8) were determined
by enzyme-linked immunosorbant assay (ELISA).
Results: Inhibitors
of PKC (calphostin C, 50-500 nmol/L and RO-31-8220, 10–100 nmol/L), CaM
(W7, 28–280 μmol/L), ERK1/2 MAPK (PD 98059, 2–20 μmol/L), p38 MAPK
(SB 203580, 0.6–6 μmol/L), JNK MAPK (curcumin, 2–10 μmol/L), and NF-κB
(PDTC, 10-100 nmol/L) markedly reduced Hcy 100 μmol/L-induced production
of MCP-1 and IL-8 in human cultured whole blood, but the inhibitors of PTK
(genistein, 2.6–26 μmol/L and tyrphostin, 0.5-5 μmol/L) had no obvious effect on
MCP-1 and IL-8 production. PPARγ activators (ciglitazone 30 μmol/L and
troglitazone 10 μmol/L) depressed the Hcy-induced MCP-1 production but not
IL-8 production in the cultured whole blood.
Conclusion: Hcy-induced MCP-1
and IL-8 production is mediated by activated signaling pathways such as PKC,
CaM, MAPK, and NF-κB. Our results not only provide clues for the signal transduction
pathways mediating Hcy-induced chemokine production, but also offer a
plausible explanation for a pathogenic role of hyperhomocysteinemia in these
diseases.