Vitamin D supplementation was reported to improve the probability of achieving a sustained virological response when combined with antiviral treatment against hepatitis C virus (HCV). Our aim was to determine the in vitro potential of vitamin D to inhibit HCV infectious virus production and explore the mechanism(s) of inhibition. Here we show that vitamin D 3 remarkably inhibits HCV production in Huh7.5 hepatoma cells. These cells express CYP27B1, the gene encoding for the enzyme responsible for the synthesis of the vitamin D hormonally active metabolite, calcitriol. Treatment with vitamin D 3 resulted in calcitriol production and induction of calcitriol target gene CYP24A1, indicating that these cells contain the full machinery for vitamin D metabolism and activity. Notably, treatment with calcitriol resulted in HCV inhibition. Collectively, these findings suggest that vitamin D 3 has an antiviral activity which is mediated by its active metabolite. This antiviral activity involves the induction of the interferon signaling pathway, resulting in expression of interferon-b and the interferon-stimulated gene, MxA. Intriguingly, HCV infection increased calcitriol production by inhibiting CYP24A1 induction, the enzyme responsible for the first step in calcitriol catabolism. Importantly, the combination of vitamin D 3 or calcitriol and interferon-a synergistically inhibited viral production. Conclusion: This study demonstrates for the first time a direct antiviral effect of vitamin D in an in vitro infectious virus production system. It proposes an interplay between the hepatic vitamin D endocrine system and HCV, suggesting that vitamin D has a role as a natural antiviral mediator. Importantly, our study implies that vitamin D might have an interferon-sparing effect, thus improving antiviral treatment of HCV-infected patients. (HEPATOLOGY 2011;54:1570-1579 H epatitis C virus (HCV) is a major cause of chronic hepatitis and the leading cause of endstage liver disease including liver cirrhosis and hepatocellular carcinoma. 1 It is a major global health challenge affecting an estimated 2.7 million people worldwide. 2 HCV is a small enveloped positive-strand RNA virus classified in the Hepacivirus genus within the Flaviviridae family. 3 It is characterized by a high genetic variability that reflects the low-fidelity rate together with the lack of a proofreading function of the viral RNA-dependant RNA polymerase. 1,3 HCV variability, which facilitates rapid development of antiviral resistance, provides a strong rationale for the development and implementation of antiviral combination therapies. 3 The best available HCV antiviral therapy is a combination of pegylated interferon-a (IFNa) and ribavirin-based therapy. 4 This treatment is aimed to obtain a sustained viral response (SVR), which is defined as undetectable serum HCV RNA 24 weeks posttherapy.Abbreviations: 1a-hydroxylase, 25-hydroxyvitamin-D 1a-hydroxylase; 1a,25(OH) 2D, 1a, 25(OH)D,

MMP-9, a member of the matrix metalloproteinase family that degrades collagen IV and processes chemokines and cytokines, participates in epidermal remodeling in response to stress and injury. Limited activity of MMP-9 is essential while excessive activity is deleterious to the healing process. Tumor necrosis factor (TNFalpha), a key mediator of cutaneous inflammation, is a powerful inducer of MMP-9. Calcitriol, the hormonally active vitamin D metabolite, and its analogs are known to attenuate epidermal inflammation. We aimed to examine the modulation of MMP-9 by calcitriol in TNFalpha-treated keratinocytes. The immortalized HaCaT keratinocytes were treated with TNFalpha in the absence of exogenous growth factors or active ingredients. MMP-9 production was quantified by gelatin zymography and real-time RT-PCR. Activation of signaling cascades was assessed by western blot analysis and DNA-binding activity of transcription factors was determined by EMSA. Exposure to TNFalpha markedly increased the protein and mRNA levels of MMP-9, while pretreatment with calcitriol dose dependently reduced this effect. Employing specific inhibitors we established that the induction of MMP-9 by TNFalpha was dependent on the activity of the epidermal growth factor receptor, c-Jun-N-terminal kinase (JNK), NFkappaB and extracellular signal-regulated kinase-1/2. The effect of calcitriol was associated with inhibition of JNK activation and reduction of DNA-binding activities of the transcription factors activator protein-1 (AP-1) and NFkappaB following treatment with TNFalpha. By down-regulating MMP-9 levels active vitamin D derivatives may attenuate deleterious effects due to excessive TNFalpha-induced proteolytic activity associated with cutaneous inflammation.

In addition to its known effects on keratinocyte proliferation and differentiation, the hormonal form of vitamin D, 1,25-dihydroxyvitamin D 3 (1,25(OH) 2 D 3 ), has been shown to protect keratinocytes from UV-and chemotherapy-induced damage. Epidermal keratinocytes contain both the machinery needed to produce 1,25(OH) 2 D 3 and vitamin D receptors. The activation of the stress-activated protein kinases (SAPKs), such as c-Jun N-terminal kinase (JNK) and p38, is an early cellular response to stress signals and an important determinant of cell fate. This study examines whether modulation of these SAPKs is associated with the effects of 1,25(OH) 2 D 3 on keratinocytes under stress. HaCaT keratinocytes were exposed to heat shock, hyperosmotic concentrations of sorbitol, the epidermal growth factor receptor tyrosine kinase inhibitor AG1487, the pro-inflammatory cytokine tumor necrosis factor , and H 2 O 2 . These stresses activated both SAPKs. Pretreatment with 1,25(OH) 2 D 3 inhibited the activation of JNK by all stresses and the activation of p38 by heat shock, AG1478 and tumor necrosis factor . Under the same conditions, treatment with 1,25(OH) 2 D 3 protected HaCaT keratinocytes from cytotoxicity induced by exposure to H 2 O 2 and hyperosmotic shock. The effect of 1,25(OH) 2 D 3 was dosedependent, already apparent at nanomolar concentrations, and time-dependent, maximal after a 24-h pre-incubation. We suggest that inhibition of SAPK activation may account for some of the well-documented protective effects of 1,25(OH) 2 D 3 on epidermal cells during exposure to UV or chemotherapy and may also be related to the anti-inflammatory actions of the hormone in skin.

Agents that are known to be scavengers of hydroxyl radicals inhibit lymphocyte mitogenesis induced by phorbol myristate acetate (PMA) to a greater extent than they inhibit mitogenesis induced by concanavalin A or phytohemagglutinin. These agents include dimethyl suffoxide, benzoate, thiourea, dimethylurea, tetramethylurea, L-tryptophan, mannitol, and several other alcohols. Their inhibitory effect is not associated with cytotoxicity.

Polar organic compounds, such as dimethylsulfoxide and butyric acid, are known to induce differentiation in Friend erythroleukemia cells as well as in other cell types. It has been found that many of the compounds that induce cellular differentiation, inhibit 3H‐thymidine incorporation and induce cell damage when incubated with leukemic cells from patients with acute or chronic myelogenous or acute lymphocytic leukemia. These effects are time and dose dependent. Among the compounds tested, butyrate was the most potent. Parenteral administration of butyrate (500 mg/kg/day) for ten days to a child with acute myelogenous leukemia in relapse, and resistant to conventional therapy, resulted in elimination of myeloblasts from the peripheral blood, an increase in mature myeloid cells and a reduction in 3H‐thymidine uptake by the patient's peripheral blood cells. Bone marrow myeloblasts were reduced from 70‐80% to 20% following the course of intravenous butyrate. No impairment of liver or renal function and no coagulation abnormalities were observed during butyrate treatment. Organic agents that induce cell differentiation may provide additional reagents for the clinical management of selected cases of leukemia.

The epidermis is confronted with multiple environmental and pathophysiological stresses. This study shows that TNFalpha, oxidative stress, hyperosmotic and heat shock induced both caspase-dependent and independent cell death in human HaCaT keratinocytes. The hormonal form of vitamin D, 1,25(OH)2D3, which is an autocrine hormone in the epidermis, protected the cells from all the examined stresses and pathways leading to cell death. We aimed to define the signaling pathways that determine the life-death balance of stressed keratinocytes and participate in their protection by 1,25(OH)2D3. As assessed by employing specific inhibitors, the survival pathways mediated by the EGF receptor, ERK, PI-3K or Src kinase, or basal transcriptional activity are important for unstressed cell survival. However, only the EGF receptor, PI-3K and the Src kinase pathways mediate the survival of stressed cells in a stimulus-specific manner. Inhibition of the p38 and/or the JNK death pathways reduced caspase activation induced by oxidative stress, hyperosmotic shock and TNFalpha. The protective effect of 1,25(OH)2D3 was not mediated by the examined survival pathways. 1,25(OH)2D3 inhibited the stress-induced activation of p38 and JNK. Since mimicking this effect by pharmacological inhibition resulted in the attenuation of caspase activation, we infer that these pathways are involved in keratinocyte protection by 1,25(OH)2D3.

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Calcitriol, the hormonal form of vitamin D, potentiates the activity of some common anticancer drugs and agents of the anticancer immune system, including tumor necrosis factor ␣ (TNF␣). TNF␣-induced cytotoxicity is due to both caspasedependent and -independent pathways. Cotreatment with calcitriol enhanced both modes of TNF␣-induced death in MCF-7 breast cancer cells. It increased caspase-3-like activity as assayed by the cleavage of poly-(ADP-ribose)polymerase and of the fluorogenic substrate ac-DEVD-AMC. It also enhanced TNF␣-induced caspase-independent cytotoxicity in the presence of the pan-caspase inhibitor zD-2,6-dichlorobenzoyloxymethylketone. The antioxidants N-acetylcysteine, reduced glutathione, lipoic acid and ascorbic acid markedly reduced the enhancing effect of the hormone on TNF␣-induced caspase activation. N-acetylcysteine and reduced glutathione also decreased caspase-independent cytotoxicity in the presence or absence of calcitriol, indicating that reactive oxygen species (ROS) have a key role in the cross talk between TNF␣ and calcitriol. Mitochondrial damage is common to both TNF␣-induced caspase-dependent and -independent pathways and may underlie excessive production of ROS. Mitochondrial membrane potential (⌬⌿) was assessed by the specific potential-sensitive fluorescent probe JC-1. The hormone augmented the drop in ⌬⌿ and release of cytochrome c from mitochondria, induced by TNF␣. The effect of calcitriol on ⌬⌿ was mimicked by rotenone, which increased both the drop in ⌬⌿ and caspase activation induced by TNF␣. It is possible that the interaction of TNF␣ and calcitriol on the level of the mitochondria is the underlying mechanism responsible for the enhancement of TNF␣-induced, ROS-mediated caspase-dependent and -independent cell death.