Reduction of monocyte 5'nucleotidase activity by gamma-interferon in multiple sclerosis and autoimmune diseases

Complex regulation of ecto-5'-nucleotidase/CD73 and A2AR-mediated adenosine signaling at neurovascular unit: A link between acute and chronic neuroinflammation

The review summarizes available data regarding the complex regulation of CD73 at the neurovascular unit (NVU) during neuroinflammation. Based on available data we propose the biphasic pattern of CD73 regulation at NVU, with an early attenuation and a postponed up-regulation of CD73 activity. Transient attenuation of CD73 activity on leukocyte/vascular endothelium and leukocyte/astrocyte surface, required for the initiation of a neuroinflammatory response, may be effectuated either by catalytic inhibition of CD73 and/or by shedding of the CD73 molecule from the cell surface, while postponed induction of CD73 is effectuated by transcriptional up-regulation of Nt5e and posttranslational modifications. Neuroinflammatory conditions are also associated with significant enhancement and gain-of-function of A_2AR-mediated adenosine signaling. However, in contrast to the temporary prevalence of A_2AR over A₁R signaling during an acute inflammatory response, prolonged induction of A_2AR and resulting perpetual CD73/A_2AR coupling may be a contributing factors in the transition between acute and chronic neuroinflammation. Thus, pharmacological targeting of the CD73/A_2AR axis may attenuate inflammatory response and ameliorate neurological deficits in chronic neuroinflammatory conditions.

Dys-regulation of peripheral transcript levels of ecto-5'-nucleotidase in multiple sclerosis patients

CD73, also entitled as ecto-5'-nucleotidase (NT5E), is an ecto-nucleotidase that contributes in the breakage of extracellular ATP to adenosine and the preservation of immune balance. In spite of acknowledged role for immune response imbalance in the pathogenesis of multiple sclerosis (MS), data regarding NT5E expression in MS patients are scarce. In the current study, we assessed expression of NT5E in peripheral blood of MS patients and healthy subjects to unravel its role in the pathogenesis of MS. Results of Multilevel Bayesian model showed no significant difference in NT5E expression between total MS patients and healthy subjects. However, its expression was significantly lower in male MS patients compared with male controls (P= 0.031, 95% credible intervals: [-6.93, -0.56]). No significant correlation was found between expression of NT5E and age in any study subgroups. Remarkably, NT5E transcript levels had 92.31% sensitivity and 80% specificity in diagnosis of MS disease. The diagnostic power of NT5E transcripts was 86.2% based on AUC values. Consequently, the current study indicates the role of NT5E in the pathogenesis of MS disease in male subjects. Moreover, expression level of this gene might be used as a putative marker especially in male MS patients.

Effect of tenofovir on nucleotidases and cytokines in HIV-1 target cells

Tenofovir (TFV) has been widely used for pre-exposure prophylaxis of HIV-1 infection with mixed results. While the use of TFV in uninfected individuals for prevention of HIV-1 acquisition is actively being investigated, the possible consequences of TFV exposure for the HIV-target cells and the mucosal microenvironment are unknown. In the current study, we evaluated the effects of TFV treatment on blood-derived CD4⁺ T cells, monocyte-derived macrophages and dendritic cells (DC). Purified HIV-target cells were treated with different concentrations of TFV (0.001-1.0 mg/ml) for 2 to 24 hr. RNA was isolated and RT-PCR was performed to compare the levels of mRNA expression of nucleotidases and pro-inflammatory cytokine genes (MIP3α, IL-8 and TNFα) in the presence or absence of TFV. We found that TFV increases 5'-ecto-nucleotidase (NT5E) and inhibits mitochondrial nucleotidase (NT5M) gene expression and increases 5' nucleotidase activity in macrophages. We also observed that TFV stimulates the expression and secretion of IL-8 by macrophages, DC, and activated CD4⁺ T cells and increases the expression and secretion of MIP3α by macrophages. In contrast, TFV had no effect on TNFα secretion from macrophages, DC and CD4⁺ T cells. Our results demonstrate that TFV alters innate immune responses in HIV-target cells with potential implications for increased inflammation at mucosal surfaces. As new preventive trials are designed, these findings should provide a foundation for understanding the effects of TFV on HIV-target cells in microbicide trials.

The 5'-nucleotidases as regulators of nucleotide and drug metabolism

The 5'-nucleotidases are a family of enzymes that catalyze the dephosphorylation of nucleoside monophosphates and regulate cellular nucleotide and nucleoside levels. While the nucleoside kinases responsible for the initial phosphorylation of salvaged nucleosides have been well studied, many of the catabolic nucleotidases have only recently been cloned and characterized. Aside from maintaining balanced ribo- and deoxyribonucleotide pools, substrate cycles that are formed with kinase and nucleotidase activities are also likely to regulate the activation of nucleoside analogues, a class of anticancer and antiviral agents that rely on the nucleoside kinases for phosphorylation to their active forms. Both clinical and in vitro studies suggest that an increase in nucleotidase activity can inhibit nucleoside analogue activation and result in drug resistance. The physiological role of the 5'-nucleotidases will be covered in this review, as will the evidence that these enzymes can mediate resistance to nucleoside analogues.

Tumor-promoting functions of adenosine

Tumor growth is a multifactorial process that, in addition to mutations leading to dysregulated expression of oncogenes and tumor suppressive genes, requires specific conditions that provide a supportive physiological environment at the primary and metastatic sites of the disease. Adenosine is one of the factors potentially contributing to tumor growth that thus far has not received adequate attention, despite evidence for a broad range of cytoprotective, growth-promoting, and immunosuppressive activities. Adenosine accumulates in solid tumors at high concentrations, and has been shown to stimulate tumor growth and angiogenesis and to inhibit cytokine synthesis, adhesion of immune cells to the endothelial wall, and the function of T-cells, macrophages, and natural killer cells. However, the mechanisms whereby adenosine accumulates in cancer and the specific effects that result from this accumulation are not well understood. This article surveys the available evidence that supports an important role of adenosine in cancer.

Relationship between tumour necrosis factor-alpha (TNFalpha) production and a specific multiple sclerosis (MS) associated TNF gene haplotype

OBJECTIVE

To determine if monocyte TNFalpha production from patients homozygous for a specific MS associated TNF gene haplotype is different from that produced in patients either heterozygous for, or without this haplotype.

BACKGROUND

The balance between pro- and anti-inflammatory cytokines is important in the clinical outcome of inflammatory reactions. Levels of TNFalpha, a pro-inflammatory cytokine, is raised in MS as well as being found in acute and chronic MS lesions. A previous population based study in Northern Ireland with polymorphisms spanning the TNF gene region identified a conserved MS associated haplotype in relation to three markers (130: 118: 127 TNF d:a:b) for which 19 MS patients were homozygous.

METHODS

Venous blood collected in EDTA to give a concentration of 10(-3) M was drawn from 16 patients with the conserved MS associated haplotype, 19 patients heterozygous for the haplotype and 17 patients without the haplotype. Mononuclear cells were separated and cultured by standard techniques and levels of TNFalpha and of TNF binding proteins I and II were determined by commercial enzyme-linked immunosorbent assays.

RESULTS

There were no significant differences in TNFalpha production in the 3 h (P = 0.28) or 24 h cultures (P = 0.18) or following stimulation with interferon-gamma (P = 0.17) between the group positive for the conserved haplotype and the group negative for this haplotype. There was also no significant difference when compared to the heterozygote group. No association was found between the MS associated haplotype and levels of either TNF binding protein. A greater proportion of patients with the conserved haplotype had a benign clinical course (P = 0.06).

CONCLUSION

We conclude that whilst a trend exists, we have found no significant association between peripheral TNFalpha production and a specific MS associated TNF haplotype in this population. Paradoxically this haplotype may also predict a more favourable clinical course.

Effects of immunomodulators on ecto-5'-nucleotidase activity on blood mononuclear cells in vitro

In this study the effects of immunomodulators on the ecto-5'-nucleotidase (ecto-5'-NT) activity on blood mononuclear cells (BMC) were examined in vitro. Interleukin-4 (IL-4) and interferon-gamma (IFN-gamma) decreased the level of ecto-5'-NT activity on BMC whereas prostaglandin E2 (PGE2) increased the ecto-5'-NT level. All three immunomodulators influenced the ecto-5'-NT activity of isolated monocytes whereas only IL-4 and PGE2 had an effect on the enzyme level on isolated lymphocytes. The effect was dependent upon protein synthesis. The effect was dose dependent: IL-4 was effective at concentrations down to 0.5 U/ml, IFN-gamma down to 40 U/ml and PGE2 at nanomolar concentrations. These data indicate that immunomodulators may also take part in the regulation of ecto-5'-NT activity on BMC in vivo. BMC from 7 patients with different immunodeficiency syndromes showed decreased ecto-5'-NT activity on freshly isolated cells. However, following culture ecto-5'-NT activity was increased above the level found on freshly isolated BMC from healthy persons. On BMC from 3 patients with hypogammaglobulinaemia, the effect of IL-4 on the level of ecto-5'-NT activity was identical to that found on BMC from healthy donors, whereas PGE2 increased ecto-5'-NT activity on BMC from only 1 of the 3 patients investigated. The decreased ecto-5'-NT activity of BMC from patients with immunodeficiency may thus be due to a defective regulation of ecto-5'-NT activity in vivo.

Class II major histocompatibility complex antigen expression on unstimulated and gamma-interferon stimulated monocytes from patients with multiple sclerosis, rheumatoid arthritis and normal controls

HLA-DR, HLA-DQ, and HLA-DP antigen expression was assessed by immunofluorescent flow cytometry on monocytes from 19 patients with active multiple sclerosis (MS), 19 with inactive MS, 7 patients with early active rheumatoid arthritis (RA), and 19 normal controls. Percentage positivity and median channel fluorescence (MCF) were determined after separation of the monocytes (TO) and following 48 h culture with (T48 + IFN) and without (T48) recombinant gamma interferon (rIFN-gamma). The percentage positivity of the cells was normal at TO for all groups of patients for each of the HLA types but statistically significantly increased above normal, on monocytes from patients with inactive MS, after culture with rIFN-gamma. At TO, the MCF values for HLA-DQ, and HLA-DP were statistically significantly increased above normal on monocytes from patients with active MS indicating some pre-programming of the cells in vivo. After culture, when the carry-over from baseline TO values was eliminated, the increment in MCF for HLA-DR, on monocytes from patients with inactive MS, was statistically significantly lower than normal in the non-gamma-IFN cultures but was normal in the presence of rIFN-gamma. Conversely, the increment in MCF for HLA-DP on monocytes from patients with active MS was significantly lower than normal after culture with rIFN-gamma. Therefore, the stimulation required to increase antigen density on cells already expressing antigen may be different to that required to stimulate de novo expression on negative cells. Both systems appear to be abnormal in MS, possibly reflecting differences in disease activity, while only one system appears abnormal in RA.