Life Sci J.2012 9(4):458-471.

Nerve Conduction Velocity of Sciatic Nerve in High Fat Diet Induced obesity in Rats: Effect of Corn Oil and Omega 3 Fatty Acids Supplement.

Laila Ahmed El sayed, Samah Elattar, and Nashwa Eltablawy

Department of Physiology, Faculty of Medicine, Cairo University, Cairo, Egypt. omarattar1993@yahoo.com

 

Abstract

Background: Obesity is a major susceptibility factor leading to the development of various conditions of the metabolic syndrome. In obese rats, slowing of motor nerve conduction velocity was observed. Fatty acids metabolism disturbance is very important in the occurrence of peripheral neuropathy. The aim of this work is  to consider the role that balanced diets high in omega 6&9 PUFA(corn oil) or supplying rats with omega 3,  play in modulating the impaired nerve  function in obese rats.

Methods: Thirty two adult male albino rats were randomly assigned to receive normal chow (NC) (n=8) or high  fat diet  HFD(n=24), for 12 weeks.  After 12 weeks ,  body weight and body mass index(BMI) were measured and the NC group(n=8) continue their normal chow diet, Group 1 (NC) and served as control group  and the obese rats were randomly divided into 3groups,  8rats  each.: Group 2: Ob + HFD group, they continue their high animal fat diet , Group 3: Ob+HFD + corn oil group, they are obese rats  received high  fat diet containing corn oil and  Group 4: Ob + HFD + Omega 3  group, they are obese  rats, fed high animal fat diet supplemented with omega 3 (0.4 g/kg) daily.  After five weeks, the final body weight was measured and BMI was calculated and blood samples were collected for measuring fasting plasma  glucose level, insulin level and homeostasis model assessment of insulin resistance ( HOMA-IR) test were evaluated. Plasma cholesterol, triglycerides and free fatty acids( FFAs) were measured. The rats were then killed and sciatic nerves were  carefully dissected for measuring of nerve conduction velocity.  Superoxide dismutase (SOD),  malondialdehyde (MDA) and  tumor necrosis factor alpha (TNFα) were  estimated  in the nerve tissue of the 4 groups.

Results: The results of this study showed a significant increase of body weight (gm) and BMI (kg/m2) in  high fat diet group ( p< 0.05) after 12weeks of the start of the diet when compared to   control  group (NC). There were significant  elevations in the final weight (gm)  and BMI(kg/m2), a significant  elevation in  insulin level (uIU/l)  and HOMA-IR test, a significant increase in nerve malondialdehyde (MDA), and tumor necrosis factor alpha (TNFα) and a significant decrease in superoxide dismutase (SOD) and  nerve conduction velocity (NCV)(m/s) after 5weeks of high fat diet in (Ob+HFD) group, when compared to NC group. Changing diet composition for 5weeks in Ob+ HFD+corn oil group and in Ob+HFD+omega 3  groups, did not induce any significant variation in body weight, BMI, or fasting blood glucose level as compared to Ob+HFD group. Insulin level (uIU/l)  and HOMA-IR test  were significantly decreased in  Ob+ HFD+corn oil group and in Ob+HFD+omega 3  groups compared to Ob+HFD group. Plasma  cholesterol levels (mg/dl), triglycerides (mg/dl), and free fatty acids(FFA) (mmol/l) were significantly decreased after 5weeks diet in Ob+ HFD+corn oil  or  Ob+HFD+ Omega 3 groups when compared to mean values of Ob+HFD group.  Tissue malondialdehyde (MDA and tumor necrosis factor alpha (TNFα) were significantly decreased but  superoxide dismutase (SOD) was significantly increased in Ob+HFD+corn oil and in Ob+HFD+omega3 groups compared to Ob+HFD. NCV(m/s) in Ob+HFD+ corn oil group was  significantly increased compared to Ob+ HFD+Omega 3 and their values in Ob+HFD+ corn oil group showed no significant variation as compared to NC group. While there was a significant increase in  NCV in Ob+ HFD+Omega 3 group as compared to Ob+ HFD group, there was still a significant decrease compared to NC group.

Conclusion

The results of this study may have important clinical and speculative implications. Corn oil  or omega 3 supplementation may be effective  in obesity induced neuropathy. The mechanism of their effects is multifactorial including improving insulin sensitivity, correction of dyslipdemia, reducing oxidative stress and an anti-inflammatory effect. This possibility should be carefully considered and examined in future trials of essential fatty acid supplementation.

Key words: nerve conduction velocity, obesity, oxidative stress, inflammation, corn oil, omega3, insulin resistance.

 

Supplements:

Thirty two adult male albino rats of body weight 80-100 gm, 3 to 4 weeks old, were included in this study. The rats were randomly assigned to receive normal chow; control group (NC) [16] (n=8), and HFD (n=24), for 12 weeks and then classified into:

Group 1: they are the normal rats (NC).

The HFD-fed rats were divided into 3 groups, 8 rats each:

Group 2: Ob + HFF group, they continue their high animal fat diet.

Group 3: Ob +HFD+ corn oil group, they are obese rats, received high fat diet. In this group of rats,  corn oil was administered as 20% of the diet, replacing the same percent of animal fat. Corn oil contains high omega 6&9 polyunsaturated fat.

Group 4: Ob + HFD + Omega 3  group, they are obese  rats, fed high fat diet rich in saturated animal fat  for 5 weeks and received omega 3 (0.4 g/kg BW) daily through gavage.

The body mass index was calculated at the end of the study period.

Rats were fasted overnight for at least 6 hours and blood samples were delivered into centrifuge tubes to which anticoagulant was added then centrifuged for measuring fasting blood glucose level, insulin level and HOMA-IR test were evaluated. Plasma cholesterol, triglycerides and FFAs were measured. The rats were then killed and sciatic nerves were  carefully dissected for measuring of nerve conduction velocity, tissue superoxide dismutase,  malondialdehyde and  tumor necrosis factor alpha.

The Sciatic nerve was mounted in a nerve champer for recording of action potential from isolated nerve. Conduction velocity  is measured by dividing the distance  between the stimulating and recording electrodes by latent period, which is  the time elapsed  between the application of stimulus until the peak of the maximum compound action potential.

The results of this study showed a significant increase of body weight (gm) and BMI (kg/m2) in  high fat diet group when compared to   control  group after 12weeks of the start of the diet.

There was a significant  elevation in the mean values final weight measurements and BMI in rats after 5weeks of high animal fat diet, when compared normal chow group (NC).

HFD yielded an  insignificant  elevation in the mean value of fasting blood glucose level, while there was a significant  elevation in  insulin level and HOMA-IR test after 5weeks of HFD compared to NC group. This reflects that  HFD  induced  insulin resistance.

There was a significant  elevation in their plasma levels  compared to NC  group,  and a significant increase in nerve tissue malondialdehyde, and tumor necrosis factor alpha and a significant decrease in superoxide dismutase after 5weeks of high animal fat diet in obese rats compared to NC group.

Interestingly, the current results recorded a significant decrease in nerve conduction velocity  after 5weeks of high animal fat diet (Ob+HFD), compared to values recorded from  normal chow group of rats.

When observing the values of final body weight and BMI measurements in rats after  changing diet composition for 5W, we can observe that there was no significant variation  in these values in Ob+HFD+ corn oil group or in Ob+HFD+omega 3 groups compared to values recorded in Ob+HFD group.

Furthermore, there  was no significant  variation in fasting blood glucose level in Ob+HFD+ corn oil and Ob+HFD+ Omega 3 group compared to Ob+HFD group. As regarding the mean values of  fasting insulin level and HOMA-IR test after 5 weeks there was no significant variation between Ob+HFD+corn oil group when compared to Ob+HFD,  however, the  plasma levels of these parameters in  the Ob+HFD+ corn oil and  Ob+HFD+ Omega 3 groups were significantly decreased when compared to Ob+HFD. Thus, these results reflect that changing the formula of diet from HFD only to addition of corn oil or of omega 3 to HFD improved insulin sensitivity and decreased the exposure to insulin resistance condition.

When observing levels of plasma cholesterol, triglycerides, and free fatty acids  after 5weeks diet (Ob+HFD+ corn oil  or  Ob+HFD+ Omega 3), there was no significant  change in the mean values recorded between these 2 groups, but the mean values of these parameters in the 2groups were significantly decreased when compared to mean values recorded in  Ob+HFD group. This indicates that the corn oil or omega3 protected against dyslipidemia.

There  was no significant  variation in mean values of  MDA, SOD or TNFα in  Ob+HFD+ corn oil group compared to  Ob+HFD+ Omega 3  group, but the 2 groups showed significantly decreased tissue malondialdehyde and tumor necrosis factor alpha and significantly increased superoxide dismutase  when compared to Ob+HFD.

Regarding NCVin Ob+HFD+ corn oil group there was a significant increase compared to Ob+HFD and their values in Ob+HFD+ corn oil group showed no significant variation as compared to control  group. While there was a significant increase in Ob+ HFD+Omega 3 group as compared to Ob+ HFD group, there was a significant decrease in values of this group as compared with the control group.

The results of this study have important clinical and speculative implications. Based on our findings, we suggest that  corn oil  or omega 3 supplementation may be effective in treatment of obesity induced neuropathy. The mechanism of their effects is multifactorial including improving insulin sensitivity, correction of dyslipdemia which could reflect on fatty acid composition of the nerve membrane structure and function, reducing oxidative stress and an anti-inflammatory effect. This possibility should be carefully considered and examined in future trials of essential fatty acid supplementation.

Omar Attar-1Figure 1: Plasma cholesterol levels (mg/dl) after 5weeks of normal chow(NC), high animal fat diet (Ob+HFD), high corn oil diet (Ob+HFD+corn oil), or high fat diet supplemented with omega 3 (Ob+HFD+Omega 3) in male rats. Results with different letters are significant (p< 0.05)  Results with the same  letter are   insignificant (p>0.05).

 

Omar Attar-2Figure 2: Plasma triglycerides (mg/dl) after 5weeks of normal chow(NC), high animal fat diet (Ob+HFD), high corn oil diet (Ob+HFD+corn oil), or high fat diet supplemented with omega 3 (Ob+HFD+Omega 3) in male rats. Results with different letters are significant (p< 0.05). Results with the same  letter are insignificant (p>0.05).

 

Omar Attar-3Figure 3: Plasma free fatty acids (mmol/l) after 5weeks of normal chow(NC), high animal fat diet (Ob+HFD), high corn oil diet (Ob+HFD+corn oil), or high fat diet supplemented with omega 3 (Ob+HFD+Omega 3) in male rats. Results with different letters are significant (p< 0.05). Results with the same  letter are   insignificant (p>0.05).

 

Omar Attar-4Figure 4: Tissue malondialdehyde (MDA) after 5weeks of normal chow(NC), high animal fat diet (Ob+HFD), high corn oil diet (Ob+HFD+corn oil), or high fat diet supplemented with omega 3 (HFD+Omega 3) in male rats. Results with different letters are significant (p< 0.05). Results with the same  letter are   insignificant (p>0.05).

 

Omar Attar-5Figure 5: Tissue tumor necrosis factor alpha (TNFα)  after 5weeks of normal chow(NC), high animal fat diet (Ob+HFD), high corn oil diet (Ob+HFD+corn oil), or high fat diet supplemented with omega 3 (HFD+Omega 3) in male rats. Results with different letters are significant (p< 0.05). Results with the same  letters are   insignificant (p>0.05).

 

Omar Attar-6Figure 6: Nerve conduction velocity (NCV)(m/s) after 5weeks of normal chow(NC), high animal fat diet (Ob+HFD), high corn oil diet (Ob+corn oil), or high fat diet supplemented with omega 3 (HFD+Omega 3) in male rats. Results with different letters are significant (p< 0.05); Results with the same  letter are   insignificant (p>0.05).

 

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