Table 2.
Summary of indices of oxidative stress and diabetes mellitus.
| Index | General | Pertinence for diabetes |
|---|---|---|
| Lipid hydroperoxides (LOOH) | Peroxidation of lipids produces highly reactive aldehydes, including MDA, acrolein, 4-hydroxynonenal, 4-oxononenal, and isolevuglandins [68]. It has been reported that peroxyl radicals can remove hydrogen from lipids, producing hydroperoxides that further propagate the free-radical pathway [69] | Increased lipid peroxidation occurs in both type 1 and type 2 diabetes mellitus [38] LOOH increase particularly in patients with vascular complications [70]. Lipid peroxidation in diabetes induces many secondary chronic complications including atherosclerosis and neural disorders [71], [72] |
| Malondialdehyde (MDA) | MDA is a three carbon, low molecular weight aldehyde representing the main product of polyunsaturated fatty acid peroxidation. It is characterized by a high toxicity due to its ability to react with other molecules like DNA and protein [54], [55], [56], [57], [58], [28], [59], [30], [60], [61], [62], [63], [64], [65], [66], [67], [68], [69], [70], [71], [72], [73], [74], [75] MDA is documented as a primary biomarker of free radical mediated lipid damage and oxidative stress [74] |
Increased MDA level in plasma and many tissues was reported in diabetic patients [76], [77] Increased levels of MDA in diabetics suggests that peroxidative injury may be involved in the development of diabetic complications |
| Glutathione (GSH) | GSH is the most abundant nonprotein thiol that defends against oxidative stress [76]. GSH is an efficient antioxidant present in almost all living cells and is also considered as a biomarker of redox imbalance at cellular level [78], [79] | Reduced levels of GSH are found in diabetes [79]. Decreased GSH level may be one of the factors in the oxidative DNA damage in type 2 diabetics |
| Oxidized glutathione (GSSG) | GSSG is reduced back to GSH by the nicotinamide adenine dinucleotide phosphate (NADPH)-dependent catalysis of the flavoenzyme GSH reductase | GSSG levels in plasma from diabetic subjects were higher than those from controls |
| GSH to GSSG ratio | This ratio is used to evaluate oxidative stress status in biological systems | Plasma GSH/GSSG showed a significant decrease in type 2 diabetes as compared to normal. Hyperlipidemia, inflammation, and altered antioxidant profiles are the usual complications in diabetes mellitus as a result of decreased GSH/GSSG ratio |
| Total antioxidant capacity (TAC) | TAC is the primary measure and marker to evaluate the status and potential of oxidative stress in the body | TAC is significantly lower in diabetic subjects with poor glycaemic control than healthy subjects, while patients with good glycaemic control had plasma antioxidative values similar to controls [66]. Decrease in TAC of plasma is associated with increased complications of diabetes, which include cardiovascular disease, nerve damage, blindness, and nephropathy TAC is markedly reduced in sciatic nerve homogenates of diabetic animals [61] |