Relationship between Vitamin B6, DNA damage and diabetes

The active form of vitamin B6, the pyridoxal-5’ phosphate (PLP) is a cofactor for more than 150 reactions involved in protein, carbohydrate and lipid metabolism. In addition, it is able to counteract Reactive Oxygen Species (ROS) and Advanced Glycation End products (AGEs). In eucaryotes PLP is produced, in the salvage pathway, by the concerted action of pyridoxal kinase (PDXK) and pyridoxamine/pyridoxine oxidase (PNPO) which recycle PLP precursor from food. PLP has been associated to different pathologies including diabetes and cancer although underlying mechanisms remain in large part still unknown. It has been previously demonstrated that mutations in Drosophila Pdxkgene (dPdxk1) cause diabetes and chromosome aberrations (CABs) and also that these phenotypes are linked by a causeeffect relationship. The first aim of this thesis has been to verify whether also the inactivation of the other gene of the salvage pathway, PNPO, encoded by sgll gene, produced the same phenotypes observed in dPdxk1 mutants. To this purpose we silenced sgll gene by RNA interference and characterized the resulting phenotypes. This analysis revealed a significant frequency of CABs and diabetic phenotypes such as hyperglycemia, small body size, impaired lipid storage and accumulation of AGEs associated to Sgll depletion. These results allowed us to confirm the hypothesis that PLP deficiency produces CABs through the genotoxic effect of AGEs in turn triggered by high glucose. Our second aim has been to investigate whether human PDXK variants present in the population can impact on DNA integrity and can be considered predictive of cancer risk. For this purpose, we expressed four human PDXK variants (carrying missense mutations) into dPdxk1 mutant flies and tested them for CABs as well as for diabetic phenotypes, finding that none of them was able to completely rescue the CAB phenotype, hyperglycemia nor AGE accumulation. Biochemical analysis of these variants revealed a compromised catalytic activity and/or a reduced affinity for their substrates, which explained their “loss of function” behaviour. These results suggested that mutations in PDXK human gene can impact on genome integrity via AGEs and predispose to cancer. Our third purpose was to test whether low PLP levels can impact on cancer in Drosophila. Thus we tested the effects of the PLP inhibitor 4-deoxypyridoxine (4-DP) on Ras and Ras/Scr cancer models generated by mosaic analysis with repressible marker (MARCM) strategy. This analysis showed that 4-DP caused enlargement of primary tumors as well as appearance of secondary tumors in both cancer models. Taken together all the results collected in this work have contributed to confirm and elucidate the relationship between vitamin B6 diabetes and cancer

The Relationship Between Vitamin B6, Diabetes and Cancer

Pyridoxal 5\u2032-phosphate (PLP), the active form of vitamin B6, works as cofactor in numerous enzymatic reactions and it behaves as antioxidant molecule. PLP deficiency has been associated to many human pathologies including cancer and diabetes and the mechanism behind this connection is now becoming clearer. Inadequate intake of this vitamin increases the risk of many cancers; furthermore, PLP deprivation impairs insulin secretion in rats, whereas PLP supplementation prevents diabetic complications and improves gestational diabetes. Growing evidence shows that diabetes and cancer are correlated not only because they share same risk factors but also because diabetic patients have a higher risk of developing tumors, although the underlying mechanisms remain elusive. In this review, we will explore data obtained in Drosophila revealing the existence of a connection between vitamin B6, DNA damage and diabetes, as flies in the past decade turned out to be a promising model also for metabolic diseases including diabetes. We will focus on recent studies that revealed a specific role for PLP in maintaining chromosome integrity and glucose homeostasis, and we will show that these aspects are correlated. In addition, we will discuss recent data identifying PLP as a putative linking factor between diabetes and cancer

Vitamin B6 rescues insulin resistance and glucose-induced DNA damage caused by reduced activity of Drosophila PI3K

: The insulin signaling pathway controls cell growth and metabolism, thus its deregulation is associated with both cancer and diabetes. Phosphatidylinositol 3-kinase (PI3K) contributes to the cascade of phosphorylation events occurring in the insulin pathway by activating the protein kinase B (PKB/AKT), which phosphorylates several substrates, including those involved in glucose uptake and storage. PI3K inactivating mutations are associated with insulin resistance while activating mutations are identified in human cancers. Here we show that RNAi-induced depletion of the Drosophila PI3K catalytic subunit (Dp110) results in diabetic phenotypes such as hyperglycemia, body size reduction, and decreased glycogen content. Interestingly, we found that hyperglycemia produces chromosome aberrations (CABs) triggered by the accumulation of advanced glycation end-products and reactive oxygen species. Rearing PI3KRNAi flies in a medium supplemented with pyridoxal 5'-phosphate (PLP; the catalytically active form of vitamin B6) rescues DNA damage while, in contrast, treating PI3KRNAi larvae with the PLP inhibitor 4-deoxypyridoxine strongly enhances CAB frequency. Interestingly, PLP supplementation rescues also diabetic phenotypes. Taken together, our results provide a strong link between impaired PI3K activity and genomic instability, a crucial relationship that needs to be monitored not only in diabetes due to impaired insulin signaling but also in cancer therapies based on PI3K inhibitors. In addition, our findings confirm the notion that vitamin B6 is a good natural remedy to counteract insulin resistance and its complications

Short-Term Exposure to Bisphenol A Does Not Impact Gonadal Cell Steroidogenesis In Vitro

: Bisphenol A (BPA) is a ubiquitous, synthetic chemical proven to induce reproductive disorders in both men and women. The available studies investigated the effects of BPA on male and female steroidogenesis following long-term exposure to the compound at relatively high environmental concentrations. However, the impact of short-term exposure to BPA on reproduction is poorly studied. We evaluated if 8 and 24 h exposure to 1 nM and 1 µM BPA perturbs luteinizing hormone/choriogonadotropin (LH/hCG)-mediated signalling in two steroidogenic cell models, i.e., the mouse tumour Leydig cell line mLTC1, and human primary granulosa lutein cells (hGLC). Cell signalling studies were performed using a homogeneous time-resolved fluorescence (HTRF) assay and Western blotting, while gene expression analysis was carried out using real-time PCR. Immunostainings and an immunoassay were used for intracellular protein expression and steroidogenesis analyses, respectively. The presence of BPA leads to no significant changes in gonadotropin-induced cAMP accumulation, alongside phosphorylation of downstream molecules, such as ERK1/2, CREB and p38 MAPK, in both the cell models. BPA did not impact STARD1, CYP11A1 and CYP19A1 gene expression in hGLC, nor Stard1 and Cyp17a1 expression in mLTC1 treated with LH/hCG. Additionally, the StAR protein expression was unchanged upon exposure to BPA. Progesterone and oestradiol levels in the culture medium, measured by hGLC, as well as the testosterone and progesterone levels in the culture medium, measured by mLTC1, did not change in the presence of BPA combined with LH/hCG. These data suggest that short-term exposure to environmental concentrations of BPA does not compromise the LH/hCG-induced steroidogenic potential of either human granulosa or mouse Leydig cells

The genetics of diabetes: what we can learn from Drosophila

Diabetes mellitus is a heterogeneous disease characterized by hyperglycemia due to impaired insulin secretion and/or action. All diabetes types have a strong genetic component. The most frequent forms, type 1 diabetes (T1D), type 2 diabetes (T2D) and gestational diabetes mellitus (GDM), are multifactorial syndromes associated with several genes' effects together with environmental factors. Conversely, rare forms, neonatal diabetes mellitus (NDM) and maturity onset diabetes of the young (MODY), are caused by mutations in single genes. Large scale genome screenings led to the identification of hundreds of putative causative genes for multigenic diabetes, but all the loci identified so far explain only a small proportion of heritability. Nevertheless, several recent studies allowed not only the identification of some genes as causative, but also as putative targets of new drugs. Although monogenic forms of diabetes are the most suited to perform a precision approach and allow an accurate diagnosis, at least 80% of all monogenic cases remain still undiagnosed. The knowledge acquired so far addresses the future work towards a study more focused on the identification of diabetes causal variants; this aim will be reached only by combining expertise from different areas. In this perspective, model organism research is crucial. This review traces an overview of the genetics of diabetes and mainly focuses on Drosophila as a model system, describing how flies can contribute to diabetes knowledge advancement

A new role for Drosophila Aurora-A in maintaining chromosome integrity

Aurora-A is a conserved mitotic kinase overexpressed in many types of cancer. Growing evidence shows that Aurora-A plays a crucial role in DNA damage response (DDR) although this aspect has been less characterized. We isolated a new aur-A mutation, named aur-A949, inDrosophila, and we showed that it causes chromosome aberrations (CABs). In addition, aur-A 949 mutants were sensitive to X-ray treatment and showed impaired γ-H2Av foci dissolution kinetics. To identify the pathway in which Aur-A works, we conducted an epistasis analysis by evaluating CAB frequencies in double mutants carrying aur-A 949 mutation combined to mutations in genes related to DNA damage response (DDR). We found that mutations in tefu (ATM) and in the histone variant H2Av were epistatic over aur-A 949 indicating that Aur-A works in DDR and that it is required for γ-H2Av foci dissolution. More interestingly, we found that a mutation in lig4, a gene belonging to the non-homologous end joining (NHEJ) repair pathway, was epistatic over aur-A 949. Based on studies in other systems, which show that phosphorylation is important to target Lig4 for degradation, we hypothesized that in aur-A 949 mutant cells, there is a persistence of Lig4 that could be, in the end, responsible for CABs. Finally, we observed a synergistic interaction between Aur-A and the homologous recombination (HR) repair system component Rad 51 in the process that converts chromatid deletions into isochromatid deletions. Altogether, these data indicate that Aur-A depletion can elicit chromosome damage. This conclusion should be taken into consideration, since some anticancer therapies are aimed at reducing Aurora-A expression

Hyponatremia as a predictor of outcome and mortality: results from a second-level urban emergency department population

Background Hyponatremia is the most common electrolyte disorder and it has been associated with increased mortality. Aims This study evaluated hyponatremia as a prognostic factor for severity and mortality. Methods We compared the prevalence of hyponatremia among patients who died during the year 2017 (from 1 January 2017 to 31 December 2017) with the prevalence of hyponatremia among subgroups of patients, i.e. outpatients, patients hospitalized for more than 2 days and patients admitted in the intensive care unit (ICU). We also described the mortality rate and the prevalence of comorbidities among hyponatremic patients, according to hyponatremia degree (slight, moderate, severe), basal characteristics, comorbidities and their outcome (discharged, hospitalized or died). Results In our population of a public hospital setting, hyponatremia was present at admission in 17% of deaths, and the comparison between hyponatremic and normonatremic patients in terms of mortality confirms the hypothesis that this disorder is in anyway strictly associated with vulnerability and with a poor prognosis. Conclusions We conclude that hyponatremia is a predictive marker for a bad clinical course, therefore patients with this electrolyte disorder should be carefully monitored