Research paperALA16VAL-MnSOD gene polymorphism and stroke: Association with dyslipidemia and glucose levels
Introduction
Stroke is the most frequent neurologic disease and the second most important cause of global mortality (Furie et al., 2011, Go et al., 2013, Lozano et al., 2012). Of all strokes, approximately 80% to 90% are of ischemic origin (Go et al., 2013). Ischemic stroke is a multifactorial disease involving various overlapping and interacting pathways, such as vascular disease, oxidative damage, and genetic factors (Go et al., 2013). Among these, vascular disease is the most important and has been the target of many preventive and therapeutic interventions. In this scenario, atherosclerosis is the most important risk factor for stroke (Bos et al., 2014) because is associated to clinic complications such as diabetes mellitus and hypercholesterolemia, which may result in cerebral embolization and consequent cerebral ischemia (Holm et al., 2011, Hansson, 2005).
Oxidative stress is potentially involved as trigger mediator in the onset and progression of the ischemic stroke damage through multiple pathways that disturb the neurovascular unit and alter homeostatic signaling among brain cells (Allen & Bayraktutan, 2009). Brain is susceptible to the deleterious effects of oxidative damage because requires large amounts of oxygen for energy production and is relatively poor in antioxidant defenses (Coultrap et al., 2011, Lo et al., 2005). Neuronal and endothelial nitric oxide synthases (nNOS and eNOS, respectively) generate reactive nitrogen species (RNS), such as nitric oxide (NO), a gaseous radical that plays a role in vascular homeostasis and brain plasticity is well known (Moro et al., 2004). Importantly, nitric oxide (NO) can be rapidly inactivated by reaction with superoxide (O2−), generating the strong oxidant peroxynitrite (ONOO−) (Guzik & Harrison, 2006). One of the major cellular defenses against O2– and peroxynitrite is a family of oxidoreductases known as superoxide dismutase (SODs), which catalyze the dismutation of O2– into oxygen and hydrogen peroxide (H2O2) (Fukai & Ushio-Fukai, 2011).
There are three SOD isoforms, including the manganese SOD (MnSOD), which is located in the mitochondria. A single gene containing five exons encodes MnSOD and it is located on chromosome 6q25 (Roy et al., 2006). Several single nucleotide polymorphisms (SNPs) have been described in the MnSOD gene, one of which is Ala16Val. The change of alanine (Ala) to valine (Val) at the 16th amino acid (Ala16Val) of the signal sequence of MnSOD (nine amino acids from the first amino acid of the mature protein) has been suggested to change the secondary structure of the protein and therefore the mitochondrial targeting of the enzyme (Rosemblum et al., 1996). The precursor sequence in the MnSOD protein is known as the mitochondrial target sequence (MTS). These SNPs may interfere in mitochondrial transport of human MnSOD, and it has been associated with MnSOD transport impairment in Val allele carries (Sutton et al., 2005). Corroborating this data, Sutton et al. showed that the Ala-MnSOD/mitochondrial-targeting sequence (MTS) allows a more efficient import into the mitochondrial matrix than Val variant (Bresciani et al., 2013), which is relevant considering that the influence of SNPs on redox status may affect cardiovascular homeostasis (Crawford et al., 2012).
Equally, investigations have shown that the Val allele is positively associated with cardiovascular disease risk and comorbidities, such as type 1 and 2 diabetes mellitus (Nakanishi et al., 2008, Mollsten et al., 2007); however, studies on its association with the late phase of stroke are still to be performed. The aim of this study was to investigate a possible relationship between the Ala16Val-MnSOD gene polymorphism with late phase stroke (> 6 months) and its influence on oxidative and glycolipidic metabolism in this population. Thus, it is of crucial importance studies that evaluate biochemistry and molecular mechanisms related to neurovascular damage to improve the clinic status and life quality of these patients.
Section snippets
Study population
We performed a case-control study with one hundred and nine participants that were divided into two groups: control group (44 healthy participants) and the stroke group (65 post-stroke participants). At first, participants were evaluated using a questionnaire. From the initial 65 stroke patients, 44 were selected according the following exclusion criteria: 1) systolic/diastolic blood pressure at rest ≥ 180/100 mm Hg, 2) rest heart rate ≥ 100 bpm and/or 3) alterations in two or more of the following
Results
Eighty-eight participants were enrolled in this study, consisting on 44 post-stroke and 44 controls. Baseline characteristics of the participants are described in Table 1. Statistical analysis showed that means of gender, body mass index (BMI), hypertension, smoking, diabetes and sedentary lifestyle were higher in the stroke group (P < 0.05). The stroke time was also higher than 6 months between study patients. Clinical characteristics of the study subjects are shown in Table 2. Statistical
Discussion
Our results showed, for the first time, a greater proportion of VV genotype among individuals in the late phase of stroke as compared to healthy counterparts. Furthermore, we showed that NOx, TBARS, and dsDNA levels as well as SOD and CAT activities were significantly higher in stroke participants compared to the control group. Interestingly, V allele carriers of stroke group showed higher levels of NOx with CHO and GLU levels in comparison to AA stroke and healthy participants when
Conclusion
Although the study cohort is small, results showed significant differences between stroke and control groups. This is a preliminary report and to our knowledge it is the first to point out an association between Ala16Val-MnSOD SNPs with nitrosative stress and metabolic dysfunction in late phase stroke. Then, we may suggest that CHO and GLU modulation influenced by SNPs could affect the neurovascular homeostasis and increase nitrosative damage, leading to stroke. Further studies with larger
Author contributions
MRF designed the study. MRF, AEF, ETP, ALCP selected the patients and control group. MRF diagnosed the cases to provide the relevant clinical information. AK and PG collected the blood samples. AK, GVB, FB, TD, MMMFD, RNM, and ARSS performed biochemical analyses and Ala16Val-MnSOD genotyping. MRF, AEF, IBMC, GB performed statistical analysis and variant validation. MRF, AEF, GB and LFFR wrote the paper.
Conflict of interest
The authors declare no conflict of interest.
Acknowledgements
This work was supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (307106/2013-6) and Coordenacao de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).
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