Effect of immunosuppressive drugs on DNA repair in human peripheral blood mononuclear cells

Disturbed Antioxidant Capacity in Patients with Systemic Sclerosis Associates with Lung and Gastrointestinal Symptoms

The correct balance between reactive oxygen species and antioxidant defense in an organism is disturbed in oxidative stress. To assess oxidative balance in 36 SSc patients and 26 healthy controls (HCs), we measured reactive oxidative metabolites (ROMs), total antioxidant capacity (TAC), lipid peroxidation (measuring 4-HNE), and DNA oxidative damage (measuring 8-OHdG) in serum. Furthermore, DNA breaks in leukocytes of 35 SSc patients and 32 HCs were evaluated using COMET. While we report high ROMs for both SSc patients and age/sex matched HC samples, there was a significant increase in TAC in SSc patients as compared to HCs, and thus also a significantly higher oxidative stress index in SSc patients. TAC was significantly higher in SSc patients with ILD and gastrointestinal involvement, as well as in patients with anti-topoisomerase antibodies. We observe no difference in serum lipid peroxidation status or oxidative DNA damage. However, SSc patients had significantly more leukocyte DNA breaks than HCs; the most damage was observed in patients treated with immunosuppressives. Thus, our study confirms presence of oxidative stress and increased DNA damage in leukocytes of SSc patients; however, it points toward increased antioxidant capacity, which needs to be further studied.

Influence of the Photodegradation of Azathioprine on DNA and Cells

Azathioprine (AZA) is a pharmacologic immunosuppressive agent administrated in various conditions such as autoimmune disease or to prevent the rejection of organ transplantation. The mechanism of action is based on its biologically active metabolite 6-mercaptopurine (6-MP), which is converted, among others, into thioguanine nucleotides capable of incorporating into replicating DNA, which may act as a strong UV chromophore and trigger DNA oxidation. The interaction between azathioprine and DNA, before and after exposure to solar simulator radiation, was investigated using UV-vis spectrometry and differential pulse voltammetry at a glassy carbon electrode. The results indicated that the interaction of AZA with UV radiation was pH-dependent and occurred with the formation of several metabolites, which induced oxidative damage in DNA, and the formation of DNA-metabolite adducts. Moreover, the viability assays obtained for the L929 cell culture showed that both azathioprine and degraded azathioprine induced a decrease in cell proliferation.

Human Variation in DNA Repair, Immune Function, and Cancer Risk

DNA damage constantly threatens genome integrity, and DNA repair deficiency is associated with increased cancer risk. An intuitive and widely accepted explanation for this relationship is that unrepaired DNA damage leads to carcinogenesis due to the accumulation of mutations in somatic cells. But DNA repair also plays key roles in the function of immune cells, and immunodeficiency is an important risk factor for many cancers. Thus, it is possible that emerging links between inter-individual variation in DNA repair capacity and cancer risk are driven, at least in part, by variation in immune function, but this idea is underexplored. In this review we present an overview of the current understanding of the links between cancer risk and both inter-individual variation in DNA repair capacity and inter-individual variation in immune function. We discuss factors that play a role in both types of variability, including age, lifestyle, and environmental exposures. In conclusion, we propose a research paradigm that incorporates functional studies of both genome integrity and the immune system to predict cancer risk and lay the groundwork for personalized prevention.

Risk of lip cancer after solid organ transplantation in the United States

Solid organ transplant recipients have an increased risk of lip cancer, but the reasons are uncertain. Using data from the Transplant Cancer Match Study, we describe the epidemiology of lip cancer among 261 500 transplant recipients in the United States. Two hundred thirty-one lip cancers were identified, corresponding to elevated risks for both invasive and in situ lip cancers (standardized incidence ratios of 15.3 and 26.2, respectively). Invasive lip cancer incidence was associated with male sex (adjusted incidence rate ratio [aIRR] 2.01, 95% CI 1.44-2.82), transplanted organ (0.33, 0.20-0.57, for liver transplants and 3.07, 1.96-4.81, for lung transplants, compared with kidney transplants), and racial/ethnic groups other than non-Hispanic whites (0.09, 0.04-0.2). In addition, incidence increased with age and during the first 3 years following transplant, and was higher in recipients prescribed cyclosporine/azathioprine maintenance therapy (aIRR 1.79, 95% CI 1.09-2.93, compared with use of tacrolimus/mycophenolate mofetil) and following a diagnosis of cutaneous squamous cell carcinoma (4.21, 2.69-0.94). The elevation in lip cancer incidence is consistent with an effect of immunosuppression. Notably, the very strong associations with white race and history of prior skin cancer point to an important role for ultraviolet radiation exposure, and cyclosporine and azathioprine may contribute as photosensitizing or DNA damaging agents.

From Early Immunomodulatory Triggers to Immunosuppressive Outcome: Therapeutic Implications of the Complex Interplay Between the Wavebands of Sunlight and the Skin

Phototherapy is an efficient treatment for many cutaneous diseases that involve the activation of inflammatory pathways or the overgrowth of cells with aberrant phenotype. In this review, we discuss recent advances in photoimmunology, focusing on the effects of UV-based therapies currently used in dermatology. We describe the molecular responses to the main forms of photo(chemo)therapy such as UVB, UVA-1, and PUVA that include the triggering of apoptotic or immunosuppressive pathways and help to clear diseased skin. The early molecular response to UV involves DNA photoproducts, the isomerization of urocanic acid, the secretion of biophospholipids such as platelet activating factor (PAF), the activation of aryl hydrocarbon receptor and inflammasome, and vitamin D synthesis. The simultaneous and complex interaction of these events regulates the activity of the immune system both locally and systemically, resulting in apoptosis of neoplastic and/or benign cells, reduction of cellular infiltrate, and regulation of cytokines and chemokines. Regulatory T-cells and Langerhans cells, among other skin-resident cellular populations, are deeply affected by UV exposure and are therefore important players in the mechanisms of immunomodulation and the therapeutic value of UV in all its forms. We weigh the contribution of these cells to the therapeutic application of UV and how they may participate in transferring the direct impact of UV on the skin into local and systemic immunomodulation. Moreover, we review the therapeutic mechanisms revealed by clinical and laboratory animal investigations in the most common cutaneous diseases treated with phototherapy such as psoriasis, atopic dermatitis, vitiligo, and cutaneous T-cell lymphoma. Better understanding of phototherapeutic mechanisms in these diseases will help advance treatment in general and make future therapeutic strategies more precise, targeted, personalized, safe, and efficient.

DNA damage in kidney transplant patients. Role of organ origin

Chronic kidney disease (CKD) patients are characterized by elevated levels of genomic damage. This damage increases when kidney function decreases being maximum in hemodialysis patients. As kidney transplantation improves renal function, and it is related with better survival, the aim of our study was to evaluate potential changes in DNA damage levels after kidney transplantation, and comparing living donor recipients with cadaveric donor recipients. The alkaline comet assay was used to determine DNA breaks and oxidative damaged DNA; and the micronucleus assay was used to determine chromosomal breakage and/or aneuploidy. Fifty CKD patients were followed up after 6 and 12 months of their kidney transplantation. All patients increased their genomic damage levels after 6 and 12 months of renal transplantation, compared with those observed before transplantation, despite of the improvement of their metabolic functions. Donor advanced age correlated positively with higher DNA damage. Genomic damage was lower in living donor transplants with respect to cadaveric donor transplants. Our conclusion is that DNA damage increased in kidney transplantation patients, whereas their renal function improved. Higher levels of DNA damage were found in cadaveric donor transplants when compared to living donor transplants. Environ. Mol. Mutagen. 58:712-718, 2017. © 2017 Wiley Periodicals, Inc.

Oxidative stress-induced DNA damage and repair in human peripheral blood mononuclear cells: protective role of hemoglobin

BACKGROUND

DNA repair is a cellular defence mechanism responding to DNA damage caused in large part by oxidative stress. There is a controversy with regard to the effect of red blood cells on DNA damage and cellular response.

AIM

To investigate the effect of red blood cells on H2O2-induced DNA damage and repair in human peripheral blood mononuclear cells.

METHODS

DNA breaks were induced in peripheral blood mononuclear cells by H2O2 in the absence or presence of red blood cells, red blood cells hemolysate or hemoglobin. DNA repair was measured by (3)H-thymidine uptake, % double-stranded DNA was measured by fluorometric assay of DNA unwinding. DNA damage was measured by the comet assay and by the detection of histone H2AX phosphorylation.

RESULTS

Red blood cells and red blood cells hemolysate reduced DNA repair in a dose-dependent manner. Red blood cells hemolysate reduced % double-stranded DNA, DNA damage and phosphorylation of histone H2AX. Hemoglobin had the same effect as red blood cells hemolysate on % double-stranded DNA.

CONCLUSION

Red blood cells, via red blood cells hemolysate and hemoglobin, reduced the effect of oxidative stress on peripheral blood mononuclear cell DNA damage and phosphorylation of histone H2AX. Consequently, recruitment of DNA repair proteins diminished with reduction of DNA repair. This suggests that anemia predisposes to increased oxidative stress induced DNA damage, while a higher hemoglobin level provides protection against oxidative-stress-induced DNA damage.

Effect of immunosuppressive drugs on spontaneous DNA repair in human peripheral blood mononuclear cells

INTRODUCTION

Immunosuppressive treatment increases the risk of post-transplant cancer. Cyclosporine reduced UV-induced DNA repair by peripheral blood mononuclear cells (PBMC) and increased cancer incidence in kidney transplant recipients. Calcineurin inhibitors (CNI), but not mammalian target of rapamycin (mTOR) inhibitors or mycophenolic acid, suppressed H₂O₂-induced DNA repair in human peripheral blood mononuclear cells (PBMC) in vitro at maintenance drug concentrations. DNA repair, when measured in quiescent cells, is named spontaneous DNA repair, and represents a basal ongoing DNA repair in response to endogenous DNA damage. The effect of immunosuppressive drugs on spontaneous DNA repair has not been investigated.

AIM

To investigate the effect of currently used immunosuppressive drugs on spontaneous DNA repair.

METHODS

Spontaneous DNA repair by human PBMC was tested in vitro in the presence of the CNI-cyclosporine and tacrolimus; mycophenolic acid (MPA); and the mTOR inhibitors-sirolimus and everolimus, at low to high nontoxic concentrations.

RESULTS

Cyclosporine and tacrolimus suppressed spontaneous DNA repair throughout the tested dose range. In contrast, MPA, sirolimus and everolimus did so only at the high doses.

CONCLUSION

A reduction in CNI dosage may lead to a decrease in the occurrence of post-transplant malignancy.