Atherogenic Risk Factors among Young Indian Adults with Epilepsy on Treatment with Phenytoin: Need for Novel Therapeutic Strategies
Keywords: Dyslipidemia, metabolic syndrome, oxidative stress, phenytoin, systemic inflammationKey Message: Subjects with epilepsy especially when on long term treatment with phenytoin needs to be screened for the atherogenic risk factors and there is a need for introducing hypolipidemic, anti-oxidant and anti-inflammatory agents in their treatment protocols.
People with epilepsy are more prone to develop cardiovascular diseases. One of the causes for increased mortality among people with epilepsy is the cardiovascular diseases. Higher incidence of metabolic syndrome has been reported among the epileptic subjects on treatment with antiepileptic drugs., Development of metabolic syndrome is linked with impaired glucose tolerance and insulin resistance. In the metabolism of cholesterol, CYP450 enzyme system plays an important role. Antiepileptic drugs can induce CYP450 and development of dyslipidemia has been reported among Asian subjects treated with phenytoin. However, there is contradiction on the effect of phenytoin on serum triglyceride and HDL-cholesterol levels.,, Only limited information is available from the Indian adult population. Atherogenic risk in subjects with epilepsy may get enhanced by the prolonged use of phenytoin. Epilepsy subjects in the pediatric group have developed systemic inflammation. Redox imbalance has a major role in the origin and advancement of epilepsy. Free radical generation and the resulting subsequent biochemical derangements may be the cause for the onset of atherosclerosis in epilepsy on treatment with antiepileptic drugs. Comparisons of atherogenic risk factors have been carried out between epileptic patients treated with antiepileptic drugs (AEDs) and healthy control in the past. More studies need to be carried out to compare the atherogenic risk factors between drug naïve and treated subjects so that the role of AEDs in causing coronary heart diseases could be elucidated. In one of the reports from India, the authors have compared the lipid profile between treated epileptic patients and healthy control. In the realm of the epidemics of global diabetes, India ranks second after China. It has been observed that there is a change in the incidence of diabetes from urban, affluent, and older people towards rural, less privileged, and younger people. In India, over the years there is a tremendous increase in the number of people with diabetes. There are several causes for the origin of diabetes and vascular diseases. One among them could be oxidative stress resulting from nutritional, environmental, and genetic factors. Hence we carried out this study to compare the lipid profile, redox status, and systemic inflammation among healthy controls, newly diagnosed young epileptic patients, and those treated with phenytoin for more than six months.
We carried out a cross-sectional study with human subjects after getting approval from the ethics committee of our institute. There were three groups of 18–40 years who were age and gender matched.
Study groups: Twenty-eight patients were recruited in each of the three groups.
From the study, diabetic and hypertensive patients already on treatment were excluded. Further, we excluded smokers and alcoholics as well as those who had infection. Subjects with head injuries along with pregnant and lactating women did not find a place in the study. The participants of the study were from the Neurology outpatient department of our institute. Fasting blood samples were collected for the assay of biochemical parameters. From the subjects with epilepsy, the samples were collected only when they were free from seizures for at least one week. Body mass index (BMI) was calculated by the formula: BMI = Weight (kg)/Height (m2). Olympus 400 Clinical chemistry analyzer, Beckman Coulter, USA with commercial kits were used for the estimation of glucose and lipid profile. Commercial ELISA kits were used for the estimation of insulin, leptin, and hsCRP. Homeostatic Model Assessment of Insulin Resistance (HOMA – IR) index was calculated to assess the insulin resistance by the formula given below:
HOMA-IR = [fasting plasma glucose (mmol/dl) × fasting plasma insulin (IU/L)]/22.5.
Estimations of Malondialdehyde (MDA) and the total antioxidant status (TAS) were carried out by the methods of Kei Satoh and Benzie et al. respectively.
Statistical analysis was performed using SPSS version 19.0. Non-parametric values were expressed as median and interquartile range and parametric values were expressed as mean ± standard deviation. Kruskal–Wallis test or ANOVA were used for comparisons of continuous variables across the three groups of subjects. For statistical significance, a value of P < 0.05 was considered.
The duration and dosage of phenytoin monotherapy among the three groups and their clinical characteristics are presented in [Table 1]. There was no significant difference in the age between the groups. When compared to healthy subjects, the BMI of the patients who were already on treatment were significantly higher. The levels of total cholesterol, triglycerides, LDL-C, and VLDL-C of the newly diagnosed adult epileptic subjects were significantly higher when compared to healthy control. In the newly diagnosed epileptic subjects, The HDL- C level was significantly lower. The results are presented in [Table 1]. On treatment with phenytoin, there was further increment in the dyslipidemia, except the serum triglyceride levels.
Oxidative stress was significantly higher in the newly diagnosed epileptic subjects, which further increased on treatment with phenytoin [Table 2].
The hsCRP levels of newly diagnosed subjects were higher when compared to the healthy subjects which further increased on phenytoin treatment [Table 3]. There were no significant differences in the fasting insulin levels, HOMA-IR and serum leptin levels among the three groups.
Among the epileptic patients of our study who were not treated with phenytoin or were on treatment for less than 1 month, the LDL-cholesterol, total cholesterol and triglycerides, were higher, and HDL-cholesterol was lower in comparison to healthy subjects. This dyslipidemia further augmented on treatment with phenytoin for more than six months except for the serum triglyceride levels. Only limited studies have reported a significant increase in TG levels on phenytoin treatment. Several studies have reported only a trend for increase on treatment with phenytoin. There was no statistically significant increase in the TG levels on account of phenytoin treatment in the present study. Phenytoin is a potent inducer of the cytochrome P450 system. Phabphal et al. linked CYP450 induction by phenytoin with their observed increment in the serum values of total LDL-cholesterol, total cholesterol, and triglycerides in comparison to controls. Manimegalai et al. also found a strong association between phenytoin treatment and enhanced values LDL-C, TG, HDL-C, and TC. Chronic treatment with phenytoin in addition to inducing the cytochrome P450, makes it to compete with cholesterol for utilization by the hepatic microsomal enzymes CYP 450. This leads to less conversion of cholesterol to bile salts resulting in higher blood cholesterol. There is contradiction about HDL-cholesterol levels as a result of phenytoin treatment. While most of the studies report an increase or a trend for increase in HDL-C, some have reported a decrease. We found a decrease in the HDL-C on treatment with phenytoin. These opposing results could be explained in terms of the nutritional, environmental and the genetic factors of the study population. The lipid profile and its response to treatment may be related to the dietary habits of the population. Genetic polymorphism of the study subjects also has an influence on their lipid parameters including HDL – cholesterol. The other factors which could influence lipid profile in general and its changes on treatment are oxidative stress and the level of low-grade inflammation. Environmental factors like infections have a major influence on both these parameters.
Yet another cause for dyslipidemia in biological system could be the underlying oxidative stress. Hyperlipidemia occurs with redox imbalance. There was an enhancement in serum MDA among the newly diagnosed epileptic subjects of our study which further increased on treatment with phenytoin. Redox imbalance was found among epileptic subjects independent of antiepileptic drugs as reported by Bindu et al. They reported that antiepileptic drugs did not cause the redox imbalance and suggested seizure as the cause for free radical generation. In our observation, phenytoin treatment further increased oxidative stress which is in agreement with the progressive dyslipidemia on antiepileptic treatment observed in our study. Phenytoin mediated oxidative stress has been reported in female epileptics. The coexistence of oxidative stress and dyslipidemia may promote the oxidation of LDL. Supplementation of antioxidants may have an impact in epileptic patients in preventing or delaying atherosclerosis especially on treatment with phenytoin. Epilepsy-related neurodegenerative processes could be arrested with the discovery of new neuro-protective antioxidants which remains a great challenge at present.
Atherosclerosis can be viewed as a form of chronic inflammation that can be promoted by oxidative stress and perturbed by lipid accumulation. The serum hsCRP was higher among our study subjects which further increased on treatment with phenytoin. By animal experiments it has been proven that seizure activity by itself can result in brain inflammation. Further recurrent seizures can promote chronic inflammation. In addition, the redox imbalance promotes inflammation and is implicated in several chronic diseases including neurological diseases. Free radicals can activate several factors which promote transcription like Nrf2. This can lead to the increased expression of several genes like those for chemokines, inflammation, cell cycle, etc. The effect of phenytoin in promoting systemic inflammation observed in this study could be mediated through oxidative stress. Epilepsy per se causing oxidative stress and systemic inflammation and the treatment with phenytoin further augmenting these derangements is an alarming situation which needs to be addressed in the treatment strategies.
Brain inflammation promotes epileptic seizures. The proinflammatory markers like IL-6, and TNF and the complement system play important roles in the generation of epilepsy. Seizure by itself can lead to a state of inflammation which then promotes the severity and recurrence of seizures.
Experimentally induced seizures resulted in the destruction of hippocampus. Free radical generation and its associated proinflammatory state may be implicated in the neuronal destruction. Brain is more vulnerable to oxidative damage as it is rich in polyunsaturated fatty acids. Lipid peroxidation of the polyunsaturated sites can lead to cellular dysfunction. Inclusion of a combination of suitable antioxidants, anti-inflammatory agents and hypolipidemic agents to the existing treatment protocol may minimize the incidence and severity of seizures among the epilepsy patients. Supplementation of selenium has been reported to reduce seizure levels. By animal seizure models, the beneficial effects of several antioxidants have been identified. As an additional mode of therapy, only limited number of antioxidants had been tried out in subjects with epilepsy. Alternative medicine promotes the supplementation several naturally occurring phytochemicals. The antioxidant, anti-inflammatory and hypolipidemic effects of Amla, Soy Isoflavones and Insulin plant in animal models have been established.,, Clinical trials with some of these may provide an answer to the complications of treatment with phenytoin.
Yet another complication of redox imbalance as well as pro-inflammatory state in the biological system is development of insulin resistance. There is contradiction about the effect of treatment with phenytoin on the onset of insulin resistance. According to the study by Minaker et al., treatment with phenytoin improved the insulin action in subjects with insulin resistance. However, Al-Rubeaan reported the mechanism of phenytoin induced insulin resistance by in vitro studies. In yet another study with isolated rat islets, it has been proven that the release of insulin mediated by glucose was inhibited by phenytoin. This is mediated through its interference with Ca2+ channels for Ca2+ uptake. In our study we did not find any differences in the indices of glucose tolerance (serum fasting glucose, serum fasting insulin and by HOMA – IR) among the three groups. In agreement with this, no differences were found in leptin levels of serum among our three groups of patients. However, increased insulin resistance and leptin resistance are reported among epileptic subjects. At the same, we found weight gain among our third group of subjects who were on treatment with phenytoin for more than six months. In atherosclerosis as well as in epilepsy, leptin is implicated in the association between weight gain and impaired glucose tolerance.
One limitation in our study is that we could not measure the serum phenytoin levels in our patients. Further we had taken into consideration only few of the atherogenic risk factors. Future investigations are recommended to find out the serum levels of Vitamin B12, Folic acid, Homocysteine as well as other atherothrombotic risk factors such as vWF, Fibrinogen, Antithrombin III, etc., which may vary from population to population. In the view of the enormous increase in the burden of diabetes over the years, it is worth undertaking such studies in India.
From this study, we conclude that dyslipidemia, oxidative stress, and low-grade inflammation are identified among the newly diagnosed young adult Indian epileptic patients. Phenytoin treatment further augmented these complications. These observations warrant the need for introducing hypolipidemic, anti-oxidant, and anti-inflammatory agents in the treatment protocols for epileptic patients to minimize atherosclerosis and the recurrence and severity of epileptic seizures.
The authors gratefully acknowledge the receipt of intramural funds from JIPMER, Puducherry-6, India to the first author and corresponding author for the conduct of this study.
Financial support and sponsorship
This study was carried with the intramural funds received from JIPMER, Puducherry-6, India.
Conflicts of interest
There are no conflicts of interest.
[Table 1], [Table 2], [Table 3]