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

The Calcitriol/Vitamin D Receptor System Regulates Key Immune Signaling Pathways in Chronic Lymphocytic Leukemia

Simple Summary

Calcitriol, the biologically active form of vitamin D, modulates a plethora of cellular processes following its receptor ligation, namely the vitamin D receptor (VDR). Epidemiological studies have linked low blood levels of vitamin D to adverse disease outcome in several B cell malignancies, including chronic lymphocytic leukemia (CLL), for as yet undetermined reasons. In this study, we sought to obtain deeper biological insight into the role of vitamin D in the pathophysiology of CLL. To this end, we investigated whether the calcitriol/VDR system is functional in CLL and analyzed key signaling pathways that are regulated by calcitriol supplementation, while also exploring the role of microenvironmental signals in the regulation of calcitriol/VDR system. Overall, we provide evidence that the calcitriol/VDR system is functional in CLL, regulating signaling pathways critical for cell survival/proliferation. Although microenvironmental triggers can modulate VDR expression and function, calcitriol appears to act independently, alluding to a potential clinical utility of vitamin D supplementation in CLL.

Abstract

It has been proposed that vitamin D may play a role in prevention and treatment of cancer while epidemiological studies have linked vitamin D insufficiency to adverse disease outcomes in various B cell malignancies, including chronic lymphocytic leukemia (CLL). In this study, we sought to obtain deeper biological insight into the role of vitamin D and its receptor (VDR) in the pathophysiology of CLL. To this end, we performed expression analysis of the vitamin D pathway molecules; complemented by RNA-Sequencing analysis in primary CLL cells that were treated in vitro with calcitriol, the biologically active form of vitamin D. In addition, we examined calcitriol effects ex vivo in CLL cells cultured in the presence of microenvironmental signals, namely anti-IgM/CD40L, or co-cultured with the supportive HS-5 cells; and, CLL cells from patients under ibrutinib treatment. Our study reports that the calcitriol/VDR system is functional in CLL regulating signaling pathways critical for cell survival and proliferation, including the TLR and PI3K/AKT pathways. Moreover, calcitriol action is likely independent of the microenvironmental signals in CLL, since it was not significantly affected when combined with anti-IgM/CD40L or in the context of the co-culture system. This finding was also supported by our finding of preserved calcitriol signaling capacity in CLL patients under ibrutinib treatment. Overall, our results indicate a relevant biological role for vitamin D in CLL pathophysiology and allude to the potential clinical utility of vitamin D supplementation in patients with CLL.

Enhancement by other compounds of the anti-cancer activity of vitamin D(3) and its analogs

Differentiation therapy holds promise as an alternative to cytotoxic drug therapy of cancer. Among compounds under scrutiny for this purpose is the physiologically active form of vitamin D(3), 1,25-dihydroxyvitamin D(3), and its chemically modified derivatives. However, the propensity of vitamin D(3) and its analogs to increase the levels of serum calcium has so far precluded their use in cancer patients except for limited clinical trials. This article summarizes the range of compounds that have been shown to increase the differentiation-inducing and antiproliferative activities of vitamin D(3) and its analogs, and discusses the possible mechanistic basis for this synergy in several selected combinations. The agents discussed include those that have differentiation-inducing activity of their own that is increased by combination with vitamin D(3) or analogs, such as retinoids or transforming growth factor-beta and plant-derived compounds and antioxidants, such as curcumin and carnosic acid. Among other compounds discussed here are dexamethasone, nonsteroidal anti-inflammatory drugs, and inhibitors of cytochrome P450 enzymes, for example, ketoconazole. Thus, recent data illustrate that there are extensive, but largely unexplored, opportunities to develop combinatorial, differentiation-based approaches to chemoprevention and chemotherapy of human cancer.

In vitro study of the potential role of guanidines in leukocyte functions related to atherogenesis and infection

BACKGROUND

The blunted immune response upon stimulation in chronic renal failure (CRF) is often coupled to a baseline inflammatory status which has been related to atherogenesis. Uremic biologic fluids and several specific uremic retention solutes alter cell-mediated immune responses, as well as the interaction of calcitriol with the immune system.

METHODS

The present study evaluated the influence of different guanidino compounds on DNA synthesis, chemiluminescence production, and CD14 expression of undifferentiated and calcitriol-differentiated HL-60 cells. In a second setup, these guanidino compounds were evaluated for their specific effect on normal human leukocyte oxidative burst activity and tumor necrosis factor-alpha (TNF-alpha) expression.

RESULTS

First, several guanidino compounds elicited proinflammatory effects on leukocytes. Methylguanidine and guanidine stimulated the proliferation of undifferentiated HL-60 cells and the antiproliferative effect of calcitriol (P < 0.05) was neutralized in the presence of methylguanidine (P < 0.05) and guanidinosuccinic acid (P < 0.05). The phorbol-myristate-acetate (PMA)-stimulated chemiluminescence production of the calcitriol differentiated HL-60 cells was enhanced in the presence of guanidine (P < 0.05). Methylguanidine and guanidinoacetic acid enhanced the lipopolysaccharide (LPS)-stimulated intracellular production of TNF-alpha by normal human monocytes (P < 0.05). Second, several guanidino compounds inhibited the function of leukocytes if they were activated. The PMA-stimulated chemiluminescence production of the calcitriol differentiated HL-60 cells was inhibited by the presence of methylguanidine (P < 0.05), guanidinoacetic acid (P < 0.05) and guanidinosuccinic acid (P < 0.05). After incubation of whole blood in the presence of methylguanidine, the Escherichia coli stimulated oxidative burst activity of the granulocyte population was significantly inhibited (P < 0.05). In addition, guanidinosuccinic acid had an inhibitory effect on the LPS-stimulated intracellular production of TNF-alpha by human monocytes (P < 0.01).

CONCLUSION

Guanidino compounds exert proinflammatory as well as anti-inflammatory effects on monocyte/macrophage function. This could contribute to the altered prevalence of cardiovascular disease and propensity to infection in patients with CRF.