PLP or vitamin B6 is produced by Pyridoxal kinase (PDXK) enzyme. We recently demonstrated in Drosophila that PLP deficiency caused by dPdxk1 mutation or PLP inhibitors results in chromosome aberrations (CABs), a well-known tumorigenic factor, and impairs glucose homeostasis. Interestingly we found that glucose causes an increase of CABs in dPdxk1 mutants and in human cells depleted of PDXK enzyme, suggesting that the clastogenic effect of glucose in PLP-depleted cells is evolutionarily conserved. These results prompted us to speculate that low levels of PLP could increase cancer risk in diabetic patients.
This proposal is aimed at clarifying the mechanisms through which PLP protects from DNA and chromosome damage in high glucose conditions. We first planned to test whether the silencing of Drosophila insulin pathway genes (namely InR, chico/IRS1, Akt1, Dp110/PI3K, and GlyS) causes DNA damage enhanced by PLP depletion. Preliminary results indicated that the depletion of Insulin-like receptor (InR) and Insulin substrate (Chico/IRS1) results in CABs and gamma-H2AV foci accumulation, whose frequencies are increased by PLP inhibitors. We also observed that Drosophila brain cells depleted of InR and Chico/IRS1 accumulated Advanced Glycation End products (AGEs). Thus we will evaluate if the silencing of the other insulin pathway genes causes the same phenotype. To investigate the mechanism underlying the protective role of PLP in high sugar conditions we will determinate whether the antioxidant alpha-lipoic acid (ALA) compound decreases AGEs and CABs frequencies when insulin pathway is impaired. We planned to extend our experiments also to human cells studying the genes that will give the best results in Drosophila. Finally, we will test whether drugs used for diabetes treatment reduce the clastogenic effects of mutations in the dPdxk gene both in the presence and absence of high sugar.
To establish whether PLP can protect from chromosome damage either caused by PLP chronic deficiency alone or enhanced by high glucose concentrations impacts on several lines of research: from studies on the role of PLP in the diet and cancer in general and in diabetes in particular, to the deeper investigation of which -among the numerous reactions where PLP serves as co-enzyme- may be more relevant in the mechanism(s) of CABs formation. In addition, the rationale to study the effect of PLP supplementation and cancer incidence in diabetic patients will be also set if the role of PLP in preventing/protecting chromosome damage in the presence of high glucose concentrations will be firmly established (see https://ods.od.nih.gov/factsheets/VitaminB6-HealthProfessional/). Consequently, these studies can be the starting point for setting therapies that limit the risk of cancer caused by CABs in patients with diabetes. Our findings might suggest that patients suffering diabetes should avoid taking drugs that lower blood PLP levels (e.g. isoniazid, penicillamine and cycloserine) and obtain an optimal vitamin level by taking extra amounts of vitamin B6.
References
1.Hellmann H, Mooney S (2010) Molecules 15: 442-459.
2.Bowling FG (2011) Seminars in Cell & Developmental Biology 22: 611-618.
3.Williams ME, et al. (2007) Am J Nephrol 27: 605-614.
4.Shepler B, et al., (2012) Clin Ther 34: 1237-1246.
5.Milne R, Brownstein S (2013) Amino Acids 44:1397-1407.
6.Marzio A, et al. (2014) PLoS Genet. 10: e1004199.
7.Mitelman F, et al., (2007) Nat. Rev. Cancer 7: 233-245.
8.Aguilera A, Gòmez-Gonzàlez B (2008) Nat Rev Genet 9: 204-207.
9.Bunting SF, Nussenzweig A (2013) Nat Rev Cancer 13: 443-454.
10.Kanellis P et al. (2007). Plos genetics 3: e134.
11.Ames BN, Wakimoto P (2002) Nature 2: 694-704.
12.Ulrich CM, et al. (1999) Cancer Epidemiol Biomarkers Prev 8: 659-668.
13.Hartman TJ et al. (2001) Am J Epidemiol 153: 688-694
14.Galluzzi L et al. (2012) Cell reports 2: 257-269.
15.Musselman LP et al. (2011) Dis Model Mech 4: 842-849.
16.Booth AA et al., (1996) Biochem Biophys Res Commun. 220: 113-119.
17.Booth AA et al. J Biol Chem 272: 5430-5437.
18.Brownlee M (2001) Nature 414: 813-820.
19.Jafari et al. (2007) Biogerontology 8: 639-651.
20.Piersanti S et al. (2006) Calcified Tissue International 78: 372-384.
21.Gonzales et al.(2013) Nat Rev Cancer 13:172-183.
22.Teleman et al. (2012) Exp. Clin. Endocrinol Diabetes 120: 184-185.