Polymorphisms of the Gene Encoding Cytochrome b-245 Beta Chain of NADPH Oxidase: Relationship with Redox Homeostasis Markers and Risk of Type 2 Diabetes Mellitus

Molecular Genetics of Abnormal Redox Homeostasis in Type 2 Diabetes Mellitus

Numerous studies have shown that oxidative stress resulting from an imbalance between the production of free radicals and their neutralization by antioxidant enzymes is one of the major pathological disorders underlying the development and progression of type 2 diabetes (T2D). The present review summarizes the current state of the art advances in understanding the role of abnormal redox homeostasis in the molecular mechanisms of T2D and provides comprehensive information on the characteristics and biological functions of antioxidant and oxidative enzymes, as well as discusses genetic studies conducted so far in order to investigate the contribution of polymorphisms in genes encoding redox state-regulating enzymes to the disease pathogenesis.

Association between RAC1 gene variation, redox homeostasis and type 2 diabetes mellitus

BACKGROUND

Increased production of reactive oxygen species (ROS) and oxidative stress are known to play a key role in the pathogenesis of type 2 diabetes (T2D); however, the relationship between genes encoding a multi-subunit ROS-generated enzyme NADPH oxidase and disease susceptibility remains unexplored.

AIMS

The present pilot study investigated whether single-nucleotide polymorphisms (SNP) at the RAC1 gene (Rac family small GTPase 1), a molecular switcher of NADPH oxidase, are associated with the risk of T2D, glucose metabolism and redox homeostasis.

MATERIALS & METHODS

DNA samples from 3206 unrelated Russian subjects (1579 T2D patients and 1627 controls) were genotyped for six common SNPs rs4724800, rs7784465, rs10951982, rs10238136, rs836478 and rs9374 of RAC1 using the MassArray-4 system.

RESULTS

SNP rs7784465 was associated with an increased risk of T2D (p = .0003), and significant differences in the RAC1 haplotypes occurred between the cases and controls (p = .005). Seventeen combinations of RAC1 genotypes showed significant associations with T2D risk (FDR <0.05). Associations of RAC1 polymorphisms with T2D were modified by environmental factors such as sedentary lifestyle, psychological stresses, a dietary deficit of fresh fruits/vegetables and increased carbohydrate intake. RAC1 polymorphisms were associated with biochemical parameters in diabetics: rs7784465 (p = .015) and rs836478 (p = .028) with increased glycated haemoglobin, rs836478 (p = .005) with increased fasting blood glucose, oxidized glutathione (p = .012) and uric acid (p = .034). Haplotype rs4724800A-rs7784465C-rs10951982G-rs10238136A-rs836478C-rs9374G was strongly associated with increased levels of hydrogen peroxide (p < .0001).

CONCLUSION

Thus, polymorphisms in the RAC1 gene represent novel genetic markers of type 2 diabetes, and their link with glucose metabolism and disease pathogenesis is associated with the changes in redox homeostasis.

Polymorphism rs1046495 of the GFER Gene as a New Genetic Marker of Preposition to Type 2 Diabetes Mellitus

The study involving 2830 subjects (1444 patients with type 2 diabetes mellitus and 1386 healthy controls) an association of the rs1046495 polymorphism of the GFER gene encoding FADdependent sulfhydryl oxidase with low risk of the disease in non-obese patients (OR=0.76, 95%CI 0.57-0.99, p=0.029). The protective effect of the polymorphic gene variant remained significant in individuals who consumed fresh vegetables and fruits (p=0.014), proteins (p=0.0017), and did not consume carbohydrate- and fat-reach food (p=0.0047). The association of the minor allele rs1046495-C with type 2 diabetes mellitus can be explained by its more pronounced effect on the expression of the GFER enzyme that through glutathionation maintains the ROS level for optimal functioning of complexes III and IV of the electron transport chain and promotes the formation of disulfide bonds in the CHCHD4 chaperone molecule. Impaired activity of this molecule underlies mitochondrial dysfunction, one of the key pathological changes in patients with type 2 diabetes mellitus.