Protective role of vitamin B6 (PLP) against DNA damage in Drosophila models of type 2 diabetes

Chiara Merigliano,Elisa Mascolo,Fiammetta Vernì,Mattia La Torre,Isabella Saggio

doi:10.1038/s41598-018-29801-z

Chiara Merigliano, Elisa Mascolo + Show 3 more

Open Access

https://doi.org/10.1038/s41598-018-29801-z

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Abstract

Growing evidence shows that improper intake of vitamin B6 increases cancer risk and several studies indicate that diabetic patients have a higher risk of developing tumors. We previously demonstrated that in Drosophila the deficiency of Pyridoxal 5′ phosphate (PLP), the active form of vitamin B6, causes chromosome aberrations (CABs), one of cancer prerequisites, and increases hemolymph glucose content. Starting from these data we asked if it was possible to provide a link between the aforementioned studies. Thus, we tested the effect of low PLP levels on DNA integrity in diabetic cells. To this aim we generated two Drosophila models of type 2 diabetes, the first by impairing insulin signaling and the second by rearing flies in high sugar diet. We showed that glucose treatment induced CABs in diabetic individuals but not in controls. More interestingly, PLP deficiency caused high frequencies of CABs in both diabetic models demonstrating that hyperglycemia, combined to reduced PLP level, impairs DNA integrity. PLP-depleted diabetic cells accumulated Advanced Glycation End products (AGEs) that largely contribute to CABs as α-lipoic acid, an AGE inhibitor, rescued not only AGEs but also CABs. These data, extrapolated to humans, indicate that low PLP levels, impacting on DNA integrity, may be considered one of the possible links between diabetes and cancer.

Highlights

Growing evidence associates micronutrients as minerals and vitamins to genome integrity maintenance showing that their deficiency can damage DNA analogously to common carcinogens
We previously demonstrated that low Pyridoxal 5′ phosphate (PLP) levels, due to mutations in the encoding Pyridoxal kinase gene, cause chromosome aberrations (CABs) and increase glucose content in larval hemolymph[23]
In the first we examined chromosomes from Akt104226/Df, chicoRNAi and high sugar diet (HSD) fed third instar larvae in colchicine treated brain preparations (Fig. 2A), in the second, because of the low mitotic index induced by Insulin receptor (InR) silencing, we examined γ-H2Av foci in InRRNAi brains fixed and immunostained with the pS137 anti-phospho-histone antibody that recognizes γ-H2Av43 (Fig. 2C). γ-H2AV is the homolog of the mammalian γ-H2AX and represents a suitable marker to study DNA damage since it marks the DSBs44, which are known to be at the basis of CABs45

Summary

Introduction

Growing evidence associates micronutrients as minerals and vitamins to genome integrity maintenance showing that their deficiency can damage DNA analogously to common carcinogens. It has been shown that in human cells and rodents[2] the impairment of this reaction due to folate and B12 deficiency causes Uracil misincorporation, a mutagenic lesion leading to point mutation, micronuclei formation and chromosome aberrations (CABs) that are known to contribute to the genesis and progression of human cancers[3,4,5]. Treatment of dPdxk[1] mutant cells with α-lipoic acid (ALA), a well-known AGE inhibitor, lowers both AGE formation and CAB frequency, suggesting a possible AGE-CAB cause-effect relationship These findings indicate that a high intracellular glucose level has a dramatic clastogenic effect if combined with PLP deficiency and have prompted us to investigate if in diabetes low PLP levels can impair DNA integrity. In Drosophila malfunctioning of insulin signaling, induced either by mutations or by feeding flies with a sugar rich diet, produce diabetic hallmarks that mimic type 2 diabetes (reviewed in[34])

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