Are insulin-resistance and oxidative stress cause or consequence of aging

Abstract

Insulin resistance (IR) may be associated with oxidative stress and leads to cardiovascular disorders. Current research focuses on interplay between insulin-resistance indices and oxidant-antioxidant markers in elderly individuals with or without insulin-resistance. The assessment involved anthropometric data (weight, height, BMI, percentage of body fat (FAT)) and biochemical tests (glucose, lipids, serum insulin and plasma oxidant-antioxidant markers: Thiobarbituric Acid-Reacting Substances (TBARS), Cu,Zn-superoxide dismutase (SOD-1) and total antioxidant status). Insulin resistance index (IR) assuming a cut-off point of 0.3 allows to divides groups into: insulin sensitive group (InsS) IR < 0,3 (n = 35, median age 69.0 years) and insulin-resistant group (InsR) IR ≥ 0.3 (n = 51, median age 71.0 years). Lipids and antioxidant defense system markers did not differentiate the investigated groups. In the InsR elderly group, the FAT was increased (P < 0.000003) and TBARS (P = 0.008) concentration decreased in comparison with InsS group. A positive correlation for SOD-1 and total antioxidant status (P < 0.05; r =  0.434) and a negative correlation for TBARS and age (P < 0.05 with r = −0.421) were calculated in InsR individuals. In elderly individuals, oxidative stress persists irrespective of insulin-resistance status. We suggest that increased oxidative stress may be consequence of old age. An insulin action identifies those at high risk for atherosclerosis, via congruent associations with oxidative stress and extra- and intra-cellular antioxidant defense systems. Thus, we maintain that insulin-resistance is not the cause of aging.

Impact statement

Insulin resistance is associated with oxidative stress leading to cardiovascular diseases. However, little research has been performed examining elderly individuals with or without insulin-resistance. We demonstrate that antioxidant defense systems alone is not able to abrogate insulin action in elderly individuals at high risk for atherosclerosis, whereas the combined oxidant-antioxidant markers (thiobarbituric acid-reacting substances (TBARS), Cu,Zn-superoxide dismutase (SOD-1), and total antioxidant status (TAS)) might be more efficient and perhaps produce better clinical outcome. In fact, a decrease in oxidative stress and strong interaction between antioxidant defense can be seen only among insulin-resistant elderly individuals. This is, in our opinion, valuable information for clinicians, since insulin-resistance is considered strong cardiovascular risk factor.