The anti-proliferative effect of calcitriol on HL-60 cells is neutralized by uraemic biological fluids

Background. It has been demonstrated that uraemic serum/ultrafiltrate inhib its cell-mediated immune response in vitro, and that it suppresses calcitri ol synthesis and its biological actions. Methods. In the present in vitro study, the effect of calcitriol, uraemic u ltrafiltrate (UUF) and a combination of both on the human promyelocytic leu kaemia cell line, HL-60, was studied by evaluating bromodeoxyuridine (BrdU) incorporation into the DNA, luminol-amplified chemiluminescence (CL) produ ction, expression of CD14, and levels of vitamin D receptor mRNA (VDR mRNA) and CD14 mRNA. Results. The ability of calcitriol to block cell proliferation (37.4 +/- 5. 4 to 30.5 +/- 5.6% cells incorporating BrdU, P <0.01) was neutralized when UUF was applied together with calcitriol (53.4 +/- 21.3% cells incorporatin g Brdu, P <0.01 vs calcitriol alone). Similarly to what was observed for Br dU incorporation, the CL production of HL-60 cells was enhanced in the pres ence of calcitriol (20126 +/- 10154 to 61528 +/- 24021 cpm, P < 0.01), and was suppressed again in the presence of calcitriol and UUF (20916 +/- 12075 cpm, P <0.01 vs calcitriol alone); finally UUF also inhibited the calcitri ol-induced CD14 expression (71.1 +/- 11.2 to 54.9 +/- 17.7% CD14 positive c ells, P <0.05). On the other hand, the calcitriol-induced CD14 mRNA levels were not significantly different in the presence of calcitriol and UUF comp ared to calcitriol alone. This points to an inhibition by UUF at a post-tra nscriptional level. Similar data were found for VDR mRNA levels. UUF was fr actionated by HPLC in four fractions, hydrophilic uraemic solutes being elu ted first (F1) and hydrophobic solutes being eluted last (F4); fractions 1, 2 and 3 simultaneously affected both BrdU incorporation and CL production in a significant way. Conclusions. It is concluded that UUF contains factors that impair calcitri ol-activated function of HL-60 cells. Hence, the differentiation and immune response of these promyelocytic leukaemia cells, as induced by the supplem entation of calcitriol, is neutralized in the presence of uraemic biologica l fluids. This may be of relevance for the propensity to infection and mali gnancy of the uraemic patient.