Anti-inflammatory effects of 1,25-dihydroxyvitamin D3 in monocytes cultured in serum from patients with type 2 diabetes mellitus and diabetic nephropathy with uremia via Toll-like receptor 4 and nuclear factor-B p65

Type 2 diabetes mellitus (T2DM) and diabetic nephropathy (DN) seriously affect the quality of human life. 1,25-dihydroxyvitamin D3 (VD3) is known to exert anti-inflammatory and immunomodulatory effects. The present study investigated the effects of VD3 on Toll-like receptor 4 (TLR4) and nuclear factor (NF)-B p65 expression in monocytes from patients with T2DM and investigated the underlying mechanisms. Serum from subjects of the control, T2DM and DN with uremia groups was isolated, and THP-1 monocytes were cultured in these sera with or without VD3. After treatment with lipopolysaccharide (LPS) and interleukin (IL)-15, monocytes and culture supernatants were collected. The expression of TLR4, TLR9 and IL-15 mRNA was detected using reverse-transcription polymerase chain reaction analysis. Furthermore, the protein expression of TLR4, NF-B p65 and inhibitor of NF-B (IB) was determined using western blot analysis. The levels of IL-6 and monocyte chemotactic protein in culture supernatants were detected using ELISAs. The impact of LPS, IL-15 and VD3 on the TLR/NF-B signaling pathway in the T2DM and DN uremia groups was also investigated. In the T2DM and DN uremia groups, LPS and IL-15 downregulated the expression of IB and upregulated levels of proteins, including TLR4, NF-B p65, IL-6 and monocyte chemoattractant protein 1, as well as TLR4 and IL-15 mRNA. There was no significant difference in TLR9 mRNA protein expression among the three groups. VD3 partially blocked the above effects; However, pre-treatment with VD3 had no significant effect on TLR4 mRNA expression, protein expression of NF-B p65 and IB, or the levels of associated inflammatory cytokines. In conclusion, the present study indicated that anti-inflammatory effects of VD3 in inflammatory immune responses in T2DM and DN uremia are associated with the TLR4/NF-B p65 signaling pathway.