Methods: In this study, we scanned the MDR gene polymorphisms in peripheral blood samples of the 58 patients (41 males, 17 females; mean age 62.9±6.6 years) whom were operated on after the diagnosis of AAA, and of the 58 healthy individuals (38 males, 20 females; mean age 58.8±11.6 years) have normally measured aorta diameters on abdominal computed tomography scan.
Results: We found that MDR-1 C3435T gene CT variant (x2= 5.80; p=0.016) and MDR-1 C3435T gene TT variant (x2=11.47; p=0.001) polymorphisms was statistically significant in AAA cases (p<0.05). The demographic findings were similar in each group.
Conclusion: These obtained preliminary results suggest that the T allele polymorphism of the MDR-1 gene is associated with AAA. We belive that such molecular studies will blaze a trail for future studies on the understanding of AAA etiology.
The abdominal aortic aneurysm enlarges over time and if it has not been controlled, the final result is rupture.[4] The incidence of the disease is gradually increasing.[5] Approximately 50% of AAA will result in rupture if left untreated. Open surgery and endovascular aneurysm repair (EVAR) have been shown to be effective in preventing rupture. Even after surgical treatment, the mortality rate is about 15-30%, but there is lower morbidity risk with EVAR.[6] Long-term follow-up is required.[5] Furthermore, a second approach may be required in treatment with EVAR.[6]
The evaluation of molecular mechanisms that can lead to this pathology will be beneficial to explaining the pathophysiology of the disease.
The genetic transmission was first determined by Clifton in 1977.[7] The autoimmune diseases with genetic transmission were also described as a risk factor for AAA.[8]
Multi-drug resistance (MDR) gene is a gene group which is considered to be responsible for drug resistance. The gene of MDR-1 causes expression of the P-glycoprotein (P-gp), which takes place in active transport of various substrates. This gene play a role in elimination of toxic substances, intake of nutrients, transport of ions and peptides, and cellular signal transduction.[9] The expression of P-gp, a transport protein dependent on ATP, is decreased when there is a single nucleotide polymorphism in 26th exon of the MDR-1 gene.[10-12]
Furthermore, the evidence of previous studies has shown that cholesterol ester level binding to MDR-1 gene expression is positively correlated with cellular proliferation.[10] Besides it has been shown that MDR-1 was observed in pathologies that affect the vessel wall such as atherosclerosis.[10] In this study we aimed to investigate the relationship between MDR-1 gene polymorphism and AAA.
Polymorphism analysis
Total genomic DNA was extracted from 10 μl blood
samples by the Invitek kit extraction technique (Invitek,
Invisorb spin blood, Germany). The multidrug transporter
P-gp MDR-1 gene from healthy controls and
patients with AAA were simultaneously amplified in
a biotin-labeled single multiplex amplification reaction
(Viennelab, PGX-HIV Strip Assay, Austria) and
evaluated for 3435 C>T polymorphism. The polymerase
chain reaction (PCR) was performed in a Perkin Elmer
9600 and the protocol consisted of an initial melting
step of 2 minutes at 94 °C; followed by 35 cycles of 15
seconds at 94 °C, 30 seconds at 58 °C, and 30 seconds
at 72 °C; and a final elongation step of 3 minutes at
72 °C. The polymorphism analysis was performed by
Strip Assay technique (Vienna Lab, PGX-HIV Strip
Assay GmbH, and Austria), which is based on the
reverse-hybridization principle automatically. The normal,
heterozygous and homozygous mutant/non-mutant
genotype profiles of each of the genes were determined
using the enclosed CollectorTM sheet for each person.
Statistical analysis
The data were expressed as mean ± standard deviation
(SD) or percentage of column total. Analysis was
performed by using SPSS for Windows version 13.0
(SPSS I nc, C hicago, I L, U SA). Features of the
patients such as sex, hypertension, diabetes mellitus,
hyperlipidemia, smoking, coronary artery disease,
chronic obstructive pulmonary disease, and the genotype
frequencies were evaluated with chi square test.
Parametric data were compared with t-test for independent
samples. The test of importance between the
mean of two groups was used for accordance of two
groups and margin of error was set at p<0.05.
The mean abdominal aortic diameter was 54.9±8.6 mm in AAA cases and 26.4±2.9 mm in the control group.
Both groups were similar in terms of demographic data. The demographic data of the study and control groups are summarized in table 1.
Table 1: The demographic datas of control and patients with abdominal aortic aneurysm
Multi-drug resistance-1 genotype distribution and allele frequencies in each group are presented in tables 2 and 3. In the patient group, TT variant was detected in 20 (34.5%) patients, CT was detected in 24 (41.3%) patients, and CC was detected in 14 (24.2%) patients. In the control group, TT variant was detected in five (8.6%) patients, CT was detected in 12 (20.7%) patients, and CC was detected in 41 (70.7%) patients. MDR-1 homozygote T/T genotype polymorphism was more frequently observed in the patient group than in the control group (p=0.001), just as C3435T allele frequency (p=0.001). Based on univariate analysis, having T/T polymorphism was associated with 5.8 fold increased risk of having AAA.
Factors such as age, male gender, smoking, CAD, COPD, HT, DM cause adaptive alterations in AAA.[2,3,15] In our study, there were 33 individuals with HT, eight with HL, seven with DM, 10 with COPD, 21 with CAD and 21 smokers, while the mean age of patients with AAA was 62.9±6.6 years.
Apart from being associated with different drug levels, studies have suggested that MDR polymorphism may be significant in many diseases such as Parkinson disease, inflammatory bowel diseases, refractory epilepsies in cerebral arterial aneurysms, and regeneration of CD4 cells during treatment of HIV.[5,6,16] Previous studies have mentioned that MDR-1 protein plays a role in defense mechanisms versus toxic effects of smoking and may be effective in removal of stress metabolites.[17,18] Furthermore, t here are studies mentioning its role in cellular regeneration.[19] Shteinberg et al.[20] shown that inflammatory response is an important risk factor in AAA, together with genetic predisposition. The proinflammatory cytokines have been shown in the content of P-gp in the cellular secretion.[21] In experimental studies, a reduction has been observed in secretion and activity of P-gp in acute inflammation.[22] Accordingly, expression of P-gp decreases also in MDR-1 polymorphism6. On the other hand present reports show that the production of P-gp regulated by MDR increases MMP-2 and MMP-9.[23] It is already known that MMP-2 and MMP-9 play a role in enhancing aneurysm formation.[24] MDR can play a role in aneurysm formation through these mentioned mechanisms. In our study MDR-1 C3435T gene CT variant (x2Æ 5.80; p=0,016) and MDR-1 C3435T gene TT variant (x2Æ 11.47; p=0.001) MDR-1 polymorphism were significantly higher (p<0.05) in patients with AAA (Table 3). We also detected that T allele frequency for MDR-1 C3435T gene was significantly higher in patients with AAA (p<0.05; Table 2). As a result of our study, we detected that homozygote and heterozygote polymorphisms of MDR-1, which take place in serious metabolic activity, may be associated with AAA. Polymorphism of this gene may cause defects in one or more metabolic functions in which it is involved and may cause development of AAA.
In conclusion, AAA is a disease which is progressive and highly lethal, requiring its prevention because of both high morbidity and labor loss and high treatment costs despite early intervention. Understanding the etiology of the disease will be one of the most important steps in its treatment and prophylaxis. If the genome is revealed which leads to this disease with multifactorial etiology, individuals under threat of AAA can be easily detected and possible problems can be prevented earlier with less cost. We believe that genetic predisposition should be investigated in patients with AAA.
Declaration of conflicting interests
The authors declared no conflicts of interest with respect
to the authorship and/or publication of this article.
Funding
The authors received no financial support for the
research and/or authorship of this article.
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