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Friday, May 15, 2009


M. ShanHH, Randeep Rajendran
National College of Pharmacy, Manassery, Calicut

Cite this: Mohan Shan, Randeep Rajendran, "EFFECT OF ANTIOXIDANT THERAPY ON DIABETES MELLITUS", B. Pharm Projects and Review Articles, Vol. 1, pp. 1680-1721, 2006. (


Diabetes mellitus is a group of metabolic disorders characterised by hyperglycemia; associated with abnormalities in carbohydrate, fat and protein metabolism and resulting in chronic microvascular macrovascular and neuropathic1 complications

Diabetes mellitus (Madhumeha) has been known since ages and the sweetness of diabetic urine has been mentioned in Ayurveda by Sushruta5. Its pharmacotherapy however is just over 80 yrs old5. The word DIABETES (to flow through) has coined by the Greek physician Aeretaeus in the 1st century AD5. In the 17th century, Willis observed that the urine of diabetics was "Wonderfully Sweet as if imbued with honey or sugar"5. The presence of sugar in urine of diabetics was demonstrated by Dobson in 17555. It is characterized by either a deficiency in insulin, or resistance to insulin. Diabetic patients also suffer from a wide variety of complications due to their disease, such as atherosclerosis, retinopathy, poor circulation, and liver and kidney problems. Diabetes also seems to be accompanied by a shortage of antioxidants and an increase in free radicals, the end result being oxidative stress. Research is being done to determine if the incurring oxidative stress is just another complication or if it may be a cause, in part or in full, of some of the diabetic complications. This paper will discuss the role of free radicals in the pathology of diabetes and its complications.

Diabetic patients have an increased level of blood glucose, but many patients also have secondary effects from the diabetes, such as poor circulation, ischemic brain injury, platelet adhesion and aggregation, excess free radicals, shortage of antioxidants, heart disease, cataracts and liver and kidney problems. Most of these are caused, at least in part, by too much glucose. Excess glucose, hyperglycaemia, can be toxic to cells in several ways, two of which are the formation of Advanced Glycation End products (AGEp) and free radicals such as O2•-, •OH. Both types of products can contribute to diabetic complications. Excessive free radicals can come from several pathways; ischemia, hyperglycemia, increased mitochondria leak, catecholamine oxidation and leukocytes11. Diabetic subjects have been shown to have increased levels of superoxide and hydrogen peroxide. Changes in antioxidant enzymes and small antioxidant molecules have also been documented.


    About 3% of the world population, approximately 100 million people suffer from diabetes, making this one of the most common non-communicable diseases4. Type 1 diabetes DM usually develops in childhood or early childhood, although some latent forms do occur. Type 1 DM accounts for up to 10% of all cases of DM1. In northern Europe the prevalence is approximately 0.3% in those under 30 years of age2. In United States, about 5% of all diabetic patients have Type 1 DM with an incidence of 18 per 100000 inhibitants per year.

    Type 2 DM is a heterogeneous disorder of glucose metabolism1. Type 2 DM accounts for as much as 90% of all cases of DM, and usually results from defects in insulin sensitivity and a relative defect in insulin secretion1. The overall prevalence of type 2 DM in the United States is about 6.6% in person of age 20 to 74 years1. Type 2 DM is much commoner than type 1, accounting for over 75% of all patients with diabetes in population2. The vast majority of diabetes patients have type 2 DM3. The incidence of type 2 DM increases with age and with increase in obesity2. In general non obese population the prevalence is 1 to 3%2. In the more obese secretion, there is a sharp increase in prevalence with figures of 6 to 8% in the USA increasing to values as high as 30% in Hindu Tamils in south Africa2. There are more than 125 million persons diabetes in the world today, and by 2010 this number is expected to approach 220 million3. Diabetes is 5 times more common among Asian immigrants in the UK than in the indigenous population2.


    The aetiology of type 1 has been the subject of considerable research2. Genetic factors are important but do not explain fully development of type 1. There is a strong immunological component to type 1 and a clear association with many organ specific auto immune disease2. Circulating islets cell antibodies (ICAs) are present in more than 70% of type 1 at the time of diagnosis2.

    Type 2 DM has a much stronger genetic relationship than type 1. Identical twins have concordance rate approaching 100%. Obesity and family history are risk factors for the development of NIDDM. Type I diabetes is treated with insulin supplementation, while type II can often be controlled with just diet and exercise. If these measures are insufficient, there are also a multitude of oral hypoglycaemic agents available for the treatment of this disease. Insulin is used only when the previous measures fail.


    The American Diabetes Association Expert Committee on the diagnosis and classification of diabetes mellitus recommends the use of Type 1 and Type 2 DM1.

Aetiological classification of DM by WHO 1999 as follows2
Type 1: (b-cell destruction usually leading to absolute insulin deficiency2) (Insulin dependent DM6, (IDDM) Juvenile onset DM6]
  • Autoimmune
  • Idiopathic
    Type 2: May range from predominantly insulin with relative insulin deficiency to a predominantly secretory defect with or without insulin resistance2] [Non insulin dependent DM6 (NIDDM) Maturity onset DM6].

  • Genetic defects b cell function2
  • Genetic defects in insulin action2
  • Diseases of the exocrine pancreas2
  • Endocrinopathies2
  • Drug or chemical induced eg. Miotinic acid, glucocorticoids, high dose     thiazides, pentramidine, interferone alpha infections2.
  • Uncommon forms of immune mediated diabetes2
  • Other genetic syndromes associated with diabetes2
  • Gestational diabetes2


    All patients with diabetes should receive healthy living advice2. This includes advice on appropriate physical activity, and lifestyle modificatin2 particularly smoking cessation and healthy eating2.

    The therapy for diabetes can be classified into two major classes.
  • Non-pharmacotherapy
    • Dietary therapy
    • Physical activity
  • Pharmcotherapy5
    • Insulin therapy
    • Oral hypoglycaemic agents
  • Stimulation of insulin by b cells eg. Sulphonyl ureas,                 meglitinides
  • Inhibitors of hepatic gluconeogenesis5 e.g. biguanides
  • Inhibitors of intestinal a glucosidases5 eg. Acarbose,                 miglitol
  • Drugs which reduce insulin resistance5
         eg. Thiozolidinediones

        A free radical is an item or molecule with one or more unpaired electrons5 or free radicals are chemical species with a single unpaired electron in an outer orbit4. Such chemical states are extremely unstable and readily react with inorganic or organic chemicals4. These oxidants are generated during the normal metabolic reactions in the body5. Small atoms of reactive oxygen are continually found in the body in the cell membrane and close to the cell organells5. Free radicals initiate autocatalytic reactions; molecules that react with free radicals are in turn converted into free radials further propagating the chain of damage4. Free radicals damage underlies chemicals and radiation injury, toxicity from oxygen and other gases cellular ageing, microbial killing by phagocytic cells, inflammatory cell damage, tumour destruction by macrophages and other injurious process4. Free radicals and other oxidants may be involved in the pathogenesis of cancer, DM, cardiovascular and neurological disorders5.


    Singlet O2
    Superoxide free radical 
    Hydroxide free radical 
    Alkoxyl free radical 
    Peroxyl free radical 
    Hydrogen peroxide 
    Lipid peroxide 







        The redox reactions that occur during normal physiological process, the free radicals are produced4. During normal respiration, e.g. Molecular oxygen is sequentially reduced in mitochondria by the addition of four electrons to generate water. In the process, small amounts of toxic intermediate species are generated. These includes
  • Superoxide radicals O2.
  • H2O2
  • OH.

        Some intracellular oxides (such as Xanthine oxidases) generate superoxide radicals as a direct consequence of their activity4. Transition metals such as copper and iron also accept or donate free electrons during certain intracellular reactions and thereby catalyse free radicals formation as in the Fenton reaction.

    Fe2+ + H2O2
    ® Fe3+ + OH. + OH

        Since most intracellular free iron is in the Fe3+ state it must first be reduced to the Fe2+ form to participate in the Fenton reaction. The reduction step is catalysed by superoxide ion and thus iron and superoxides synergise to elicit maximal oxidate cell injury.

  •     Nitric oxide (NO) an important chemical mediator normally synthesised by a variety of cell types that can act as a free radical or can be converted into highly reactive nitrite species.
  •     The absorption of radiant energy (eg. UV or X-rays) ionizing radiation can hydrolyse water into hydroxyl (OH.) and (H.) free radicals4.
  •     The enzymatic metabolism of exogenous chemicals e.g. CCl4
  •     Cycloxygenation5
  •     Lipoxygenation5
  •     Lipidperoxidation5
  •     Neutrophills stimulated by exposure to microbes5
  •     Reperfusion of ischemic organs5
  • Metabolism of xenobiotics (foreign chemicals) including, alcohol,          cigarette smoke, motor car exhaust5




Lipid peroxidation
of membranes4:Double bonds in membrane polyunsaturated lipids are vulnerable to be attacked by oxygen derived free radicals. Lipid radicals interaction yield peroxides which are themselves unstable and reactive and an autocatalytic chain reaction ensures4.

DNA fragmentation4: Free radicals reactions with thymine in nuclear and mitochondrial DNA produce single strand breaks such DNA damage has been implicated in both cell killing and the malignant transformation of cells.

Cross linking of proteins4: Free radicals promote sulphahydryl mediated proteins cross linking resulting in enhanced rates of degradation or loss of enzymatic activities. Free radicals reactions may also directly cause poly peptide fragmentation.
Hyperglycaemia can increase the levels of free radicals through protein glycation, autoxidation glycation, protein kinase and an increase in the polyol pathway. Autoxidation of glucose is the process by which it enolizes.

Figure 1. The process of autoxidation of a monosaccharide, showing how free radicals are produced when excess glucose is present
    This process entails the reduction of oxygen, producing oxidizing intermediates, such as Q2#~, #OH and H2O2, and alpha-ketoaldeydes11. See Figure 1. These molecules can damage important biomolecules such as DNA, proteins and lipids. The oxidizing intermediate formed by autoxidation is proposed to be a cause for some of the structural damage seen in diabetes. This reaction is often catalyzed by transition metals, and even with the catalyst, the reaction is very slow. These ketoaldehyde products may attach to proteins, in a process is called labile glycation. Protein fragmentation and labile glycation due to glucose autoxidation can be reduced by the use of a chelating agent, like DETAPAC11.
Glucose can also undergo glycation directly, where the glucose molecule covalently bonds to a protein to form a Schiff base. These molecules can then undergo rearrangement to form Amadori products. Amadori products can then decompose to form deoxyglucones, which are considerably more reactive than the sugar they derived from

Figure 2.
Glycation process and subsequent degradation of glycation products11
    These more reactive ketoaldeyhdes may go on to react with other proteins to form Advanced Glycation Endproducts (AGE) or Maillard products11. The Maillard products lead to the "browning" of the protein, the protein also becomes fluorescent and crosslinked. Glycation is a reversible process. When glycation follows autoxidation, also called glycoxidation, the products tend to be more permanent modifications such as protein crosslinking. Haemoglobin glycation is commonly used clinically to monitor the blood sugar level over several weeks. The amount of haemoglobin glycation can help doctors and patients monitor the glycaemia control.

An increase in the concentration of glucose contributes to an enhanced activity of the two enzymes used in the polyol pathway, aldose reductase and sorbitol dehydrogenase. With the increased activity of these two enzymes, the concentration of both sorbitol and fructose increase. This increased activity also causes the NADPH: NADP+ ratio to decrease and the NADH: NAD+ ratio to increase11. The change in these ratios can cause changes throughout various systems in the cell. The increase in the NADH:NAD+ ratio, also called hyperglycaemic pseudo-hypoxia, may cause an increase in free radical production which may lead to ischemia. It may also produce a reduction in glycolysis, which results in reduced pyruvate levels11. The reduction in the amount of NADPH may cause an inhibition in enzymes which are NADPH-dependent and lead to a shortage of the NADPH available for the many pathways it is involved in.

Glucose, once phosphorylated to glucose-6-phospate, is metabolized through two main processes in the cell, glycolysis and the pentose phosphate pathway. Glycolysis results in the production of pyruvate, which then goes on to react in the tricarboxylic acid cycle, among others and is also known to scavenge H2O2 and other hydroperoxides. The pentose phosphate pathway produces NADPH, which is the primary source of reducing equivalents for the glutathione reductase system, among many other oxidizing species. So not only is glucose a primary energy source, it is also a means of removing toxic H2O2 and hydroperoxides from cells.
Diabetic Complications and Free Radicals
Hyperglycaemia can produce a wide variety of secondary diabetic complications. Oxidative stress plays an integral role in the development of complications due to excess glucose.


Figure 3. Excessive glucose can cause multiple secondary complications through a variety of pathways, which are appearing to lead to oxidative stress11.

Diabetic patients have been shown to have platelets with increased adhesiveness and aggregation, increased concentrations of thromboxane A2, platelet factor 4 and |3-thromboglobulin11. Increase in platelet aggregation can cause a variety of effects: vasoconstriction, anoxia, ROS, atherosclerotic plaques, retinopathy, nephropathy and CV disease. Figure 3 shows how hyperglycaemia can be related to oxidative stress and further complications.




Antioxidants are the substances which prevent oxidation either by inhibiting the chain propagation step of free radical reaction (oil soluble antioxidants) e.g. butyrated - hydroxyl toluene or undergoing self oxidation (water soluble antioxidants) eg. Vitamin-C.

These antioxidants act against the free radicals and reduce the damaging properties of free radicals and act as a free radical scavenging units. Cells have developed several enzymatic and nonenzymatic systems to inactivate free radicals4.

The enzymes are4:
  • Superoxide dismutase (SODs)
  • Glutathione peroxidase (GSH)
  • Catalase


Nonenzymatic antioxidants4
  • Endogenous or exogenous antioxidants4:
e.g. Vitamin E, A, C and b carotene
Free ionised iron and copper catalyse the formation of reactive oxygen species these elements are usually segmented by storage aid and/or transport protein. (e.g. transferin, ferritine, ceruloplasmin).

    These antioxidants have been implicated in atherosclerosis (oxidised LDL is more altherogenic) cancers, neurodegenerative diseases and inflammatory diseases6.
Superoxide dismutase (SODs)4
    The rate of spontaneous decay in significantly increased by the actions of superoxide dismutase found in many cell types4.

Glutathione Peroxidase (GSH)4
    GSH also protects against injury by catalysing free radicals breakdown4.

    The intracellular ratio of oxidised GSSG to reduce to GSH Glutathione is a reflection of the oxidative state of the cell and an important aspect of the cell's ability to catabolise free radicals4.
    Catalases present in peroxisomes direct the degradation of H2O2

Endogenous and Exogenous antioxidants (Nonenzymatic antioxidants)
    Vitamin E, A, C and b carotene may either block the formation of free radical or scavenge them once they have formed.
Vitamin E is an antioxidant that resides in the lipid layer of the cell membrane. Its purpose is to stop the chain reaction begun by lipid radicals. Vitamin C then reacts with the octocpherol radical, thereby removing the radical from the lipid bilayer and moving it into the cytosol where it can be dealt with resident enzymes

Figure 4.Recycling of Vit E.
Alpha Lipoic Acid (ALA) is an antioxidant that is currently approved for diabetic neuropathy in Germany. A 50% reduction in nerve blood flow has been found in streptozotocin experimental diabetic animals. This reduction reverted to normal after one month of treatment with alpha-lipoic acid (100 mg/kg). The increase in nerve blood flow after ALA treatment appears to be dose-dependent (Figure 8). While this effect of ALA on experimental diabetic rats is impressive, it is yet to be seen if ALA will have such a substantial result on human diabetes.

Figure 5. The nerve blood flow and vascular resistance are shown for control animals, streptozotocin treated animals, which have had different doses of ALA over a month period (0-100 mg/kg)11

  1. Effect of vitamin E supplementation on diabetic induced oxidative stress in experimental diabetes in rats demonstrates that that vitamin E supplementation augments the antioxidant defence mechanism in diabetes and provides evidence that vitamin E may have a therapeutic role in free radical mediated diseases.7
  2. Chronic oral administration of vitamin C to diabetic or clinical research volunteers who are deficient in vitamin C will improve insulin sensitivity and endothelial function. Vitamin C levels in diabetic subjects and may suggest a potential therapy to significantly improve endothelial dysfunction and insulin resistance.8
  3. From a viewpoint of molecular mechanisms, HMG-CoA reductase inhibitors (statins) might inhibit the high glucose-induced NADPH oxidase activation through inhibition of Rac activity and finally prevent the increase in ROS production in diabetes. Actually, recent clinical trial suggested that statins prevent several vascular events in patients with type 2 diabetes without a high concentration of LDL-cholesterol. These pleiotropic effects of statins can be expected to improve endothelial dysfunction through nitric oxide production and/or an anti-oxidant effect on diabetic patients.9
  4. A cohort of 2,285 men and 2,019 women 40–69 years of age and free of diabetes at baseline (1967–1972) was studied. Food consumption during the previous year was estimated using a dietary history interview. The intake of vitamin C, four tocopherols, four tocotrienols, and six carotenoids was calculated. During a 23-year follow-up, a total of 164 male and 219 female incident cases occurred. Vitamin E intake was significantly associated with a reduced risk of type 2 diabetes which supports the hypothesis that development of type 2 diabetes may be reduced by the intake of antioxidants in the diet10
  5. .In the current study, intra-arterial administration of the antioxidant vitamin C restored endothelium-dependent vasodilatation in patients with insulin-dependent diabetes mellitus. This result supports the notion that oxygen-derived free radicals may contribute to abnormal vascular function in patients with diabetes mellitus. It is not certain that comparable effects would be observed after oral intake of vitamin C, because comparable plasma concentrations would be difficult to achieve. Further studies of the effects of long-term oral antioxidant therapy on vascular function are warranted as a means of reducing vascular disease in patients with diabetes

  1. The alterations of retinal glutamate, oxidative stress and NO appear to be inter-related in diabetes, and antioxidant therapy may be a suitable approach to determine the roles of these abnormalities in the development of diabetic retinopathy.
  2. In diabetics, there is increased superoxide release. With regard to diabetes, antioxidants such as alpha-tocopherol, alpha-lipoate, and ascorbic acid supplementation have been shown to be beneficial. Most importantly, alpha-tocopherol therapy, especially at high doses, clearly shows a benefit with regard to low-density lipoprotein oxidation, isoprostanes, and monocyte superoxide release. Thus, it appears that, in diabetes, antioxidant therapy could alleviate the increased attendant oxidative stress and emerge as an additional therapeutic modality12
  3. The antioxidant treatment suppressed apoptosis in β-cells without changing the rate of β-cell proliferation, supporting the hypothesis that in chronic hyperglycaemia, apoptosis induced by oxidative stress causes reduction of β-cell mass. The antioxidant treatment also preserved the amounts of insulin content and insulin mRNA, making the extent of insulin degranulation less evident. Furthermore, expression of pancreatic and duodenal homeobox factor-1 (PDX-1), a β-cell-specific transcription factor, was more clearly visible in the nuclei of islet cells after the antioxidant treatment. Observations indicate that antioxidant treatment can exert beneficial effects in diabetes, with preservation of in vivo β-cell function. This finding suggests a potential usefulness of antioxidants for treating diabetes and provides further support for the implication of oxidative stress in β-cell dysfunction in diabetes






  1. Data suggest that Cr supplementation was an effective treatment strategy to minimize increased oxidative stress in type 2 diabetes mellitus patients whose HbA1C level was >8.5%, and the Cr in EU groups might act as a pro-oxidant.


  1. It has been shown that oxidative stress has an adverse effect on glucose metabolism. Development of the disabling chronic complications
    of diabetes mellitus (DM) has also been attributed to oxidative stress. It has, been recommended that high doses of micronutrient antioxidant vitamins should be administered in combination rather than as single supplements. The use of certain antioxidant vitamin
    and mineral supplements may be beneficial as an adjunct therapy in the management of DM and its complications.13



  1. Accumulating evidence indicates that increased antioxidant
    defense systems reduce the susceptibility to IDDM in animal
    models or in human study. It is suggested that pancreas-specific
    ROS productions play a critical role in signaling the cellular
    autoimmune/inflammatory response by activating the transcription
    factor, NFB. Various diabetogenic factors may lead to an increase
    in ROS production, which activates the redox-sensitive NFB.
    This may be the initial event for the expression of cytokines
    and chemotactic agents involved in the autoimmune/inflammatory
    response. It is believed that this cascade results in a cyclic
    amplification of ROS and eventually leads to apoptosis and/or
    necrosis of ß cells. The specificity of antioxidants to
    inhibit NFB activation and the hyperglycemic response emphasizes
    the importance of selectivity in antioxidant therapy14.


I believe the evidence, though circumstantial in many ways, points to a distinct connection between free radicals and diabetic complications. An increase in free radical concentration has been shown for diabetic individuals. The increase in radicals can be caused by a variety of different factors. Accompanying this radical production is a decrease in many of the antioxidant defences of the cell. Antioxidant enzymes, such as SOD and catalase, are generally decreased, as are several small antioxidant molecules like vitamin C and vitamin E. This decrease in antioxidants and increase in free radicals indicates a potentially dangerous situation for the cells and the specimen as a whole. So from the current pre-clinical and clinical studies and experiments it can be concluded that the antioxidant therapy can be given to the DM patients for treating the complications and stress.



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  7. Effect of Vit E On DM induced Oxidative stress in experimental rats. IJEB 43(Feb 2)177-180(2005)

  8. Martin BC, Warram JH, Krolewski AS, Bergman RN, Soeldner JS Kahn CR. Role of glucose and insulin resistance in development of type 2 diabetes mellitus: results of a 25-year follow-up study. Lancet. 1992 Oct 17;340(8825):925-9

  9. Current Pharmaceutical Biotechnology, Volume 7, Number 2, April 2006, pp. 95-100(6)

  10. Diabetes Care 27:362-366, 2004Dietary Antioxidant Intake and Risk of Type 2 Diabetes Jukka Montonen, MSC1, Paul Knekt, PHD1,2, Ritva Järvinen, PHD3 and Antti Reunanen, PHD1
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    Cite this: Mohan Shan, Randeep Rajendran, "EFFECT OF ANTIOXIDANT THERAPY ON DIABETES MELLITUS", B. Pharm Projects and Review Articles, Vol. 1, pp. 1680-1721, 2006. (