Statins for Oxidative Stress and Mitochondrial Function in Diabetic Polyneuropathy

Introduction Nerve dysfunction system in patients with diabetes is known as diabetic neuropathy and is considered as the most prevalent microvascular complication -up to 60%- in type 2 Diabetes Mellitus (T2DM) subjects. Diabetic polyneuropathy (DPN) comprise ≈70% of all cases. Its diagnosis is established by means of validated scores based on clinical features and abnormal nerve conduction studies (NCS). Pathophysiologic findings include loss of multifocal and focal nerve fibers secondary to axonal degeneration an segmental demyelinization, basically due to oxidative stress induced by chronic hyperglycemia, which leads to neural apoptosis. Other mechanisms involved in peripheral nerve injure is nitrosative stress induced by nitric oxide (NO).

Ezetimibe diminishes cholesterol esters content in chylomicrons by reducing liver cholesterol intake which in consequence increases LDL uptake and plasma depuration; as monotherapy it reduces LDL-C by 17%. When combined with simvastatin, cholesterol reduction is potentially increased; furthermore, pleiotropic effects of statins include an increase on nuclear factor kappa B activity and amelioration of superoxide ions after 12 week treatment. Another hydroxy-methyl-glutaryl coenzyme A inhibitor, rosuvastatin, has an antioxidant effect by acting as free radical carrier diminishing mitochondrial and cellular lipid peroxidation (LPO) production.

We conducted this study to evaluate the effect of ezetimibe/simvastatin and rosuvastatin on oxidative stress in patients with DPN.

Methods Study design A randomized, double blinded, placebo controlled phase II clinical trial was performed in the Clinic and Experimental Therapeutics Institute, University of Guadalajara, Mexico. Subjects were assigned to three group treatments in blocks with a parallel sequence 1:1:1 through a randomized computer-based list, generated by a different researcher unaware of drugs given. Patients were divided to: control group that received placebo, ezetimibe/simvastatin and rosuvastatin as a daily single dose for 16 weeks. The selection period was performed from February 2012 to January 2013. We selected 5 non-randomized healthy subjects (HS) from a blood bank to compare the oxidative stress status.

Study population Inclusion criteria were ≥18 years old, T2DM according to American Diabetes Association and DPN by Dyck et. al.3 criteria, HbA1c <12%, and informed consent signed. They were excluded if renal or hepatic failure, pregnant or breastfeeding, other neuropathies (alcohol-induced, radiculopathy, autoimmune, cancer-related), and eliminated if lack treatment adherence (<80% of drug intake), severe adverse drug reaction and/or serious health illness. Patients were selected by invitation in forums; outpatients recruited from primary care clinics; and database collected previously by our Institute from February 2010 to 2012. Patients were instructed to take their drugs only by night at the same time every day, as follows: placebo 100 mg, ezetimibe/simvastatin 10/20 mg, and rosuvastatin 20 mg. All drugs were similar in physical characteristics and presented in dark vials, carefully filled by another group researcher, who placed a respective tag with the patient code. Also, patients were provided with a diary where they would write down the date and time of drug administration, and drug adverse reactions felt. Such information was collected and registered every 4 weeks. Primary outcomes were oxidative stress markers LPO, NO, and TAC before and after 16 week intervention. Secondary outcomes were clinical, NCS and metabolic [fasting glucose, HbA1c, total cholesterol, high and low density lipoproteins (HDL, LDL), and triglycerides] parameters. Safety profile was assessed with drug adverse reactions, renal (urea, creatinin), and hepatic [(alamin- and aspartate-aminotransferase, gama-glutamyltransferase, bilirubins and phosphokinase] laboratory variables.

Oxidative stress and mitochondrial function markers LPO was measured according to kit specifications (Oxford Biomedical Research Inc., FR12), 200 μL of serum where processed with a chromogen substance that reacts with malondialdehyde (MDA) and 4-hydroxy-alkenals (HNA), the absorbance measured at 586 nm, and results expressed in nmol/mL.

Previous deproteinization of the samples, we performed a colorimetric for determining the concentration of NO with 85 µL of serum (Nitric Oxide Assay Kit, User protocol 482650), with results expressed as pmol/mL.

Total antioxidant capacity (TAC) was realized with 200 µL of serum, to obtain values of millimole (mM) equivalent of uric acid (Total Antioxidant Power Kit, No. 02090130, Oxford Biomedical Research®).

Clinical and nerve conduction variables Neuropathic symptoms (NSS) and disability scores (NIS) described by Dyck, et. al. were obtained by physical examination and anamnesis. We also measured the latency, duration, amplitude and motor nerve conduction velocity from fibula, tibial, median and ulnae nerves, and sensitivity parameters from sural, median and ulnae nerves, as required by the American Association of Electrodiagnostic Medicine.

Ethical considerations The study was approved by the Research and Ethics Committee of the Health Science University Center, University of Guadalajara, Mexico. Identification codes were assigned to each participant to guarantee patient confidentiality, and an informed consent form was signed before entering the protocol, according to national and international laws, and also as stipulated by the Helsinki Statements (http://www.wma.net/es/30 publications/ 10 policies/b3/17c.pdf, accessed January 2011).

Statistical analysis The sample size was obtained by a clinical study design formula taking in account a difference change of 0.05 nmol/mL in LPO, 95% confidence interval, 80% potency, and two-tailed p<0.05, which resulted in 21 for each group. Quantitative variables were expressed as mean ± standard deviation. Kolmogorov-Smirnov and Shapiro-Wilk tests were performed to determine the non-parametric distribution of variables. Friedman and Wilcoxon tests were realized for before and after measurements, and Kruskal-Wallis with Mann-Whitney´s U as post-hoc analysis for between group comparisons. Qualitative variables were expressed as frequencies and percentages. Chi square test was used to evaluate differences in dichotomy variables before and after treatment, between group comparisons were determined by Fisher´s exact test and χ2 as needed. Significance level was established with p value <0.05.