Oxidative stress, micronutrients, diabetes mellitus and its complications

Beneficial effects of aminoguanidine on skin flap survival in diabetic rats

Random flaps in DM patients have poor reliability for wound coverage, and flap loss remains a complex challenge. The protective effects of aminoguanidine (AG) administration on the survival of dorsal random flaps and oxidative stress were studied in diabetic rats. Two months after the onset of DM, dorsal McFarlane flaps were raised. Forty rats were divided into four groups: (1) control, (2) AG, (3) DM, and (4) DM + AG groups. Flap viability, determined with the planimetric method, and free-radical measurements were investigated. In addition, HbA1c and blood glucose levels, body weight measurements, and histopathological examinations were evaluated. The mean flap necrotic areas (%) in Groups I to IV were 50.9 ± 13.0, 32.9 ± 12.5, 65.2 ± 11.5, and 43.5 ± 14.7, respectively. The malondialdehyde (MDA) and nitric oxide (NO) levels were higher in the DM group than in the nondiabetic group, while the reduced glutathione (GSH) levels and superoxide dismutase (SOD) activity were reduced as a result of flap injury. In the diabetic and nondiabetic groups, AG administration significantly reduced the MDA and NO levels and significantly increased GSH content and SOD enzyme activity. We concluded that AG plays an important role in preventing random pattern flap necrosis.

Increase in total antioxidant capacity of plasma despite high levels of oxidative stress in uncomplicated type 2 diabetes mellitus

OBJECTIVE

Oxidative stress is implicated in the pathophysiology of diabetes mellitus and its chronic complications. The aim of this study was to evaluate plasma antioxidant status in patients with uncomplicated type 2 diabetes, in order to understand the interactions between its components and the diabetic milieu.

METHODS

Plasma samples were collected from 15 patients with type 2 diabetes receiving oral antidiabetic agents and from 18 healthy control subjects without diabetes. Glycosylated haemoglobin was measured as an indicator of blood glucose control. Total and residual antioxidant activities were measured. Lipid peroxides were measured as indicators of plasma oxidative stress. Copper and caeruloplasmin were also assayed as possible pro-oxidants.

RESULTS

Antioxidant activities, lipid peroxide level, copper concentration and caeruloplasmin activity were significantly increased in the plasma of patients with diabetes compared with control subjects.

CONCLUSIONS

The total antioxidant capacity of plasma was increased, despite high levels of oxidative stress, in patients with uncomplicated type 2 diabetes. Increased levels of copper and caeruloplasmin characterized the diabetic milieu, despite an absence of chronic complications.

Hesperidin and naringin attenuate hyperglycemia-mediated oxidative stress and proinflammatory cytokine production in high fat fed/streptozotocin-induced type 2 diabetic rats

Abnormal regulation of glucose and impaired carbohydrate utilization that result from a defective or deficient insulin are the key pathogenic events in type 2 diabetes mellitus (T2DM). The present study was hypothesized to investigate the beneficial effects of hesperidin and naringin on hyperglycemia-induced oxidative damage in HFD/STZ-induced diabetic rats. Diabetes was induced by feeding rats with an HFD for 2 weeks followed by an intraperitoneal injection of STZ (35 mg/kg body weight). An oral dose of 50mg/kg hesperidin or naringin was daily given for 4 weeks after diabetes induction. At the end of the experimental period, blood was obtained from jugular vein and livers were rapidly excised and homogenized for biochemical assays. In the diabetic control group, levels of glucose, glycosylated hemoglobin (HbA1c%), MDA, NO, TNF-α and IL-6 were significantly increased, while serum insulin, GSH, vitamin C, and vitamin E levels were decreased. Both hesperidin and naringin administration significantly reversed these alterations. Moreover, supplementation with either compound significantly ameliorated serum and liver MDA, NO and glutathione, and liver antioxidant enzymes. Although detailed studies are required for the evaluation of the exact mechanism of the ameliorative effects of hesperidin and naringin against diabetic complications, these preliminary experimental findings demonstrate that both hesperidin and naringin exhibit antidiabetic effects in a rat model of T2DM by potentiating the antioxidant defense system and suppressing proinflammatory cytokine production.

Influence of therapy with metformin on the concentration of certain divalent cations in patients with non-insulin-dependent diabetes mellitus

Research was performed on a group of 30 patients with non-insulin-dependent diabetes mellitus (NIDDM), who never received antidiabetic medication before, and on a group of 17 healthy adults. The patients were administered treatment with metformin, 1,000 mg/day. Plasmatic and urinary concentration of magnesium have been measured, copper and zinc along with the concentrations of glucose, HDL, LDL, cholesterol, tryglicerides, HbA1c, and total erythrocyte magnesium, in advance and after 3 months of treatment. Data showed significant differences in the NIDDM group vs the control group: for plasma magnesium-1.95 ± 0.19 vs 2.20 ± 0.18 mg/dl, p < 0.001; urine magnesium-237.28 ± 34.51 vs 126.25 ± 38.22 mg/24 h, p < 0.001; erythrocyte magnesium-5.09 ± 0.63 vs 6.38 ± 0.75 mg/dl, p < 0.001; plasma zinc-67.56 ± 6.21 vs 98.41 ± 20.47 μg/dl, p < 0.001; urine zinc-1,347.54 ± 158.24 vs 851.65 ± 209.75 μg/24 h, p < 0.001; plasma copper-111.91 ± 20.98 vs 96.33 ± 8.56 μg/dl, p < 0.001; and urine copper-51.70 ± 23.79 vs 36.00 ± 11.70 μg/24 h, p < 0.05. Treatment with metformin for 3 months modified significant erythrocyte magnesium-5.75 ± 0.61 vs 5.09 ± 0.63 mg/dl, p < 0.001 and urine magnesium-198.27 ± 27.07 vs 237.28 ± 34.51 mg/24 h, p < 0.001, whereas it did not modify significant the plasmatic and urinary concentration of the other cations. The erythrocyte magnesium concentration was inversely correlated with HbA1c (r = -0.438, p = 0.015). The plasma level of copper was positively correlated with HbA1c (r = 0.517, p < 0.003), tryglicerides (r = 0.534, p < 0.003), and cholesterol (r = 0.440, p < 0.05), and the plasma level of zinc was inversely correlated with glycemia (r = -0.399, p = 0.029). Our data show a significant action of metformin therapy, by increasing the total intraerythrocyte magnesium concentration and decreasing the urinary magnesium elimination, positively correlated with the decrease of glycemia and HbA1c in NIDDM patients.

The effects of lipoic acid and α-tocopherol supplementation on the lipid profile and insulin sensitivity of patients with type 2 diabetes mellitus: a randomized, double-blind, placebo-controlled trial

Antioxidants probably play an important role in the etiology of type 2 diabetes (DM2). This study evaluated the effects of supplementation with lipoic acid (LA) and α-tocopherol on the lipid profile and insulin sensitivity of DM2 patients. A randomized, double-blind, placebo-controlled trial involving 102 DM2 patients divided into four groups to receive daily supplementation for 4 months with: 600 mg LA (n = 26); 800 mg α-tocopherol (n = 25); 800 mg α-tocopherol + 600 mg LA (n = 25); placebo (n = 26). Plasma α-tocopherol, lipid profile, glucose, insulin, and the HOMA index were determined before and after supplementation. Differences within and between groups were compared by ANOVA using Bonferroni correction. Student's t-test was used to compare means of two independent variables. The vitamin E/total cholesterol ratio improved significantly in patients supplemented with vitamin E+LA and vitamin E alone (p ≤ 0.001). There were improvements of the lipid fractions in the groups receiving LA and vitamin E alone or in combination, and on the HOMA index in the LA group, but not significant. The results suggest that LA and vitamin E supplementation alone or in combination did not affect the lipid profile or insulin sensitivity of DM2 patients.

Rescuing hepatocytes from iron-catalyzed oxidative stress using vitamins B1 and B6

In the following rescue experiments, iron-mediated hepatocyte oxidative stress cytotoxicity was found to be prevented if vitamin B1 or B6 was added 1h after treatment with iron. The role of iron in catalyzing Fenton-mediated oxidative damage has been implicated in iron overload genetic diseases, carcinogenesis (colon cancer), Alzheimer's disease and complications associated with the metabolic syndrome through the generation of reactive oxygen species (ROS). The objectives of this study were to interpret the cytotoxic mechanisms and intracellular targets of oxidative stress using "accelerated cytotoxicity mechanism screening" techniques (ACMS) and to evaluate the rescue strategies of vitamins B1 and B6. Significant cytoprotection by antioxidants or ROS scavengers indicated that iron-mediated cytotoxicity could be attributed to reactive oxygen species. Of the B6 vitamers, pyridoxal was best at rescuing hepatocytes from iron-catalyzed lipid peroxidation (LPO), protein oxidation, and DNA damage, while pyridoxamine manifested greatest protection against ROS-mediated damage. Thiamin (B1) decreased LPO, mitochondrial and protein damage and DNA oxidation. Together, these results indicate that added B1 and B6 vitamins protect against the multiple targets of iron-catalyzed oxidative damage in hepatocytes. This study provides insight into the search for multi-targeted natural therapies to slow or retard the progression of diseases associated with Fenton-mediated oxidative damage.

Management of cardiac fibrosis in diabetic rats; the role of peroxisome proliferator activated receptor gamma (PPAR-gamma) and calcium channel blockers (CCBs)

BACKGROUND

Diabetes mellitus (DM) and hypertension (HTN) are accused of being responsible for the development of the cardiac fibrosis due to severe cardiomyopathy.

METHODS

Blood glucose (BG) test was carried out, lipid concentrations, tumor necrosis factor alpha (TNF-α), transforming growth factor beta (TGF-β), matrix metalloproteinase (MMP-2), collagen-I and collagen-III were measured in male Albino rats weighing 179-219 g. The rats were divided into five groups, kept on either control diet or high fat diet (HFD), and simultaneously treated with rosiglitazone (PPAR-gamma) only for one group with 3 mg/kg/day via oral route for 30 days, and with rosiglitazone and felodipine combination for another group with 3 mg/kg/day and 5 mg/kg/day, respectively via oral route for 30 days.

RESULTS

Diabetic hypertensive (DH) rats which fed on a HFD, injected with streptozotocin (STZ) (i.p.) and obstruction for its right kidney was occurred develop hyperglycemia, hypertension, cardiac fibrosis, hypertriglyceridemia, hypercholesterolemia, increased TNF-α, increased TGF-β, decreased MMP-2, increased collagen-I and increased collagen-III, when compared to rats fed on control diet. Treating the DH rats with rosiglitazone only causes a significant decrease for BG levels by 52.79%, triglycerides (TGs) by 24.05%, total cholesterol (T-Chol) by 30.23%, low density lipoprotein cholesterol (LDL-C) by 40.53%, TNF-α by 20.81%, TGF-β by 46.54%, collagen-I by 48.11% and collagen-III by 53.85% but causes a significant increase for MMP-2 by 272.73%. Moreover, Treating the DH rats with rosiglitazone and felodipine combination causes a significant decrease for BG levels by 61.08%, blood pressure (BP) by 16.78%, TGs by 23.80%, T-Chol by 33.27%, LDL-C by 45.18%, TNF-α by 22.82%, TGF-β by 49.31%, collagen-I by 64.15% and collagen-III by 53.85% but causes a significant increase for MMP-2 by 290.91%. Rosiglitazone alone failed to decrease the BP in DH rats in the current dosage and duration.

CONCLUSION

Our results indicate that the co-existence of diabetes and hypertension could induce cardiomyopathy which could further result in cardiac fibrosis, and that combination treatment with rosiglitazone and felodipine has a great protective role against the metabolic abnormalities, meanwhile, the treatment with rosiglitazone alone has a protective role with a minimal effect against these abnormalities and has no effect on decreasing BP in these cases which may lead to coronary artery diseases (CADs) in future.

Resveratrol attenuates hyperglycemia-mediated oxidative stress, proinflammatory cytokines and protects hepatocytes ultrastructure in streptozotocin-nicotinamide-induced experimental diabetic rats

The present study was hypothesized to investigate the hepatoprotective nature of resveratrol in averting hyperglycemia-mediated oxidative stress by measuring extent of oxidant stress and levels of proinflammatory cytokines and antioxidant competence in the hepatic tissues of streptozotocin-nicotinamide-induced diabetic rats. After the experimental period of 30 days, the pathophysiological markers such as serum bilirubin and hepatic aspartate transaminase (AST), alanine transaminase (ALT) and alkaline phosphatase (ALP) were studied in addition to hepatic TNF-alpha, IL-1 beta, IL-6, NF-kappaB p65 and nitric oxide (NO) levels in control and experimental groups of rats. The levels of vitamin C, vitamin E and reduced glutathione (GSH) and activities of superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx), glutathione-S-transferase (GST) and glutathione reductase (GR) were determined in the liver tissues. Extent of oxidative stress was also assessed by hepatic lipid peroxides, hydroperoxides and protein carbonyls. A portion of liver was processed for histological and ultrastructural studies. Oral administration of resveratrol (5mg/kg b.w.) to diabetic rats showed a significant decline in hepatic proinflammatory cytokines and notable attenuation in hepatic lipid peroxides, hydroperoxides and protein carbonyls. The diminished activities of hepatic enzymic antioxidants as well as the decreased levels of hepatic non-enzymic antioxidants of diabetic rats were reverted to near normalcy by resveratrol administration. Moreover, the histological and ultrastructural observations evidenced that resveratrol effectively rescues the hepatocytes from hyperglycemia-mediated oxidative damage without affecting its cellular function and structural integrity. The findings of the present investigation demonstrated the hepatocyte protective nature of resveratrol by attenuating markers of hyperglycemia-mediated oxidative stress and antioxidant competence in hepatic tissues of diabetic rats.

Altered metabolism of copper, zinc, and magnesium is associated with increased levels of glycated hemoglobin in patients with diabetes mellitus

Diabetes mellitus (DM) is associated with the alterations in the metabolism of copper (Cu), zinc (Zn), and magnesium (Mg). The aim of the present study was to investigate plasma levels of these elements in patients with DM and in healthy subjects. Association between glycated hemoglobin and levels of metals was also evaluated. We studied 36 subjects with DM (type 1, 11; type 2, 25) and 34 healthy subjects matched for age, sex, and duration of diabetes. Plasma concentrations of Cu, Zn, and Mg were measured by atomic absorption spectrometry. An imbalance in the levels of studied metals was observed in both type 1 and type 2 DM. We found higher levels of Cu (P < .001) and Cu/Zn ratio (P < .0001) and decreased levels of Zn (P < .01) and Mg (P < .0001) in patients with DM when compared with controls. Negative correlation between Cu and Zn (r = -0.626, P < .0001) was found in patients with DM. Glycated hemoglobin levels were positively correlated with Cu (r = 0.709, P < .001) and Cu/Zn ratio (r = 0.777, P < .001) and inversely correlated with Zn (r = - 0.684, P < .001) and Mg (r = -0.646, P < .001). In conclusion, patients with DM had altered metabolism of Cu, Zn, and Mg; and this may be related to increased values of glycated hemoglobin. We concluded that impaired metabolism of these elements may contribute to the progression of DM and diabetic complications.

Amelioration of streptozotocin-induced diabetes mellitus, oxidative stress and dyslipidemia in rats by tomato extract lycopene

The effects of various doses of lycopene were studied in streptozotocin (STZ)-induced hyperglycaemic rats to evaluate its possible hypoglycaemic, hypolipidaemic and antioxidant activity in diabetes. Compared to the normoglycaemic group, the treatment of rats with a single dose of STZ (65 mg/kg body weight) revealed a significant increase (p<0.05) only in plasma hydrogen peroxide (H(2)O(2)), i.e. by 230%; it increased the thiobarbituric acid reactive substances (TBARS) as index of the lipid peroxidation level by 69%, while total antioxidant activity was decreased by 36%, with a consistently significant decrease (p<0.05) in the activity of erythrocytes antioxidative enzymes catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx). The levels of total lipid, triglycerides and total cholesterol in serum of hyperglycaemic rats were increased by 14%, 65% and 36%, respectively, while HDL-C decreased by 22% compared to the normoglycaemic group. Exogenous administration of individual gradual doses of lycopene to hyperglycaemic rats causes a dose-dependent decrease in glucose level, an increase of insulin concentration, a decrease of H(2)O(2) and TBARS levels, as well as increased total antioxidant status with increased antioxidant enzyme activities (CAT, SOD and GPx) with improvement in serum lipid profile. It is obvious from this study that lycopene acts as an antidiabetic agent through lowering the free radical and has an improving effect on serum that reaches the normal level; the greatest effect of lycopene was observed at 90 mg/kg body weight.

Implications for degenerative disorders: antioxidative activity, total phenols, flavonoids, ascorbic acid, beta-carotene and beta-tocopherol in Aloe vera

In order to demonstrate whether the known biological effects of Aloe vera (L.) Burm. fil. could correlate with the antioxidant activity of the plant, the antioxidant activity of the aqueous leaf extract was investigated. The present study demonstrated that the aqueous extract from A. vera leaves contained naturally occuring antioxidant components, including total phenols, flavonoids, ascorbic acid, beta-carotene and alpha-tocopherol. The extract exhibited inhibitory capacity against Fe(3+)/ascorbic acid induced phosphatidylcholine liposome oxidation, scavenged stable DPPH(*), ABTS(*+) and superoxide anion radicals, and acted as reductant. In contrast, the leaf inner gel did not show any antioxidant activity. It was concluded that the known beneficial effects of Aloe vera could be attributed to its antioxidant activity and could be related to the presence of phenolic compounds and antioxidant vitamins.

Medicinal plants of Cree communities (Québec, Canada): antioxidant activity of plants used to treat type 2 diabetes symptoms

Traditional medicines (TM) used to treat symptoms of diabetes by two Cree communities were assessed for their free radical scavenging activity using the stable 1,1-diphenyl-2-picrylhydrazyl radical, and their ability to protect human low-density lipoprotein from Cu2+-mediated oxidation by measuring lag time before the appearance of conjugated dienes and formation of thiobarbituric acid-reactive substances. Water-soluble phenolic content was also measured. A total of 20 medicinal plants from Whapmagoostui and 16 from Mistissini were compared with 16 extracts of plants that were not used medicinally. Medicinal plant extracts, particularly those from Larix laricina, displayed high antioxidant activity, comparable with ascorbic acid, Trolox, and the known antioxidant flavonoids quercetin, epicatechin, catechin. Extracts of Pinaceae and Ericaceae contained the highest levels of phenolics. Factors such as season and area of plant collection, as well as the plant part from which the extract was derived, affected antioxidant activity. Positive correlations were found between the established traditional knowledge of Cree Elders and Healers and the antioxidant activity for medicinal plants used in Mistissini (r = 0.3134; p = 0.058) and in Whapmagoostui (r = 0.5165; p = 0.001). Significant correlations between phenolic content were also seen with the existing ethnobotanical data (r = 0.5015; p = 0.003) and bioassays (r = 0.4178; p = 0.003). These results indicate that a clear majority of plants used by the Cree are excellent sources of antioxidants.

Metabolic syndrome and mitochondrial function: molecular replacement and antioxidant supplements to prevent membrane peroxidation and restore mitochondrial function

Metabolic syndrome consists of a cluster of metabolic conditions, such as hypertriglyceridemia, hyper-low-density lipoproteins, hypo-high-density lipoproteins, insulin resistance, abnormal glucose tolerance and hypertension, that-in combination with genetic susceptibility and abdominal obesity-are risk factors for type 2 diabetes, vascular inflammation, atherosclerosis, and renal, liver and heart disease. One of the defects in metabolic syndrome and its associated diseases is excess cellular oxidative stress (mediated by reactive oxygen and nitrogen species, ROS/RNS) and oxidative damage to mitochondrial components, resulting in reduced efficiency of the electron transport chain. Recent evidence indicates that reduced mitochondrial function caused by ROS/RNS membrane oxidation is related to fatigue, a common complaint of MS patients. Lipid replacement therapy (LRT) administered as a nutritional supplement with antioxidants can prevent excess oxidative membrane damage, restore mitochondrial and other cellular membrane functions and reduce fatigue. Recent clinical trials have shown the benefit of LRT plus antioxidants in restoring mitochondrial electron transport function and reducing moderate to severe chronic fatigue. Thus LRT plus antioxidant supplements should be considered for metabolic syndrome patients who suffer to various degrees from fatigue.

Vitamin E ameliorates some biochemical parameters in normal and diabetic rats

Diabetes is associated with hyperglycemia, one of the most important causes of oxidative stress. Endogenous antioxidants are able to destroy the reactive species and create a balance between antioxidant and free radicals. In diabetes, the oxidative stress is increased due to the deficiency in the antioxidant defense. The intake of antioxidants, such as vitamin E, may reduce the oxidative stress associated with diabetes and hence help to restore the antioxidant defense system. The aim of this article was to investigate the effect of different doses of vitamin E on the biochemical parameters of normal and streptozotocin (STZ)-induced diabetic rats. Biochemical analysis was used to study the effect of this vitamin on the biochemical parameters of normal and diabetic rats. The plasma levels of alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactic dehydrogenase (LDH), and gamma-glutamyl transferase (gamma-GT) were significantly increased after the onset of diabetes. In addition, STZ-induced diabetes also caused an increase in the level of blood urea nitrogen (BUN) and creatinine. Oral administration of vitamin E (0.2-0.4 mg daily) significantly (P < 0.05) decreased the plasma level of ALT, AST, and gamma-GT. In addition, there was a slight but not significant reduction in the plasma level of ALP. Parameters of kidney function, such as BUN and creatinine, were slightly reduced after the oral administration of vitamin E. The plasma level of electrolytes, such as calcium and sodium, also changed significantly (P < 0.00001) after the oral administration of vitamin E. Vitamin E ameliorates the metabolic and biochemical parameters of diabetic rats.

Comparison of the effects of zinc alone and zinc associated with selenium and vitamin E on insulin sensitivity and oxidative stress in high-fructose-fed rats

PURPOSE

In the present study, we investigated the effect of an association of micronutrients (zinc (Zn), selenium (Se) and vitamin E (vit E)) on insulin activity and antioxidant status in an animal model of insulin resistance, the high-fructose-fed rat.

PROCEDURES

Five experimental groups were compared: a control group (C) receiving a standard diet, a high-fructose-fed group (F) where 58% of the diet carbohydrate was fructose, a high-fructose-fed group supplemented with Zn alone (FZn group), a high-fructose-fed group supplemented micronutrients (Zn, Se and vit E) (FMicro group). A fifth group consumed a high-fructose diet and received metformin in the drinking water (200mg/day/rat) (FMet group). Insulin sensitivity was measured using the euglycemic hyperinsulinic glucose clamp technique. Metabolic parameters, trace elements and antioxidant parameters were measured in blood samples from all groups.

RESULTS

High-fructose-fed rats were resistant to insulin as indicated by the lower glucose infusion rate. The insulin sensitivity of FZn, FMicro and FMet groups was higher than that of F group, with the highest insulin sensitivity for the FMicro group. No statistically significant difference in glycemia between the groups was observed. The ratio of reduced to oxidized glutathione was higher in FZn and FMicro groups than in all other groups, as a consequence of decreased oxidized glutathione.

CONCLUSION

Our results provide direct evidence that micronutrients have a beneficial effect on insulin sensitivity and some components of the antioxidant defense system in an animal model of insulin resistance.

Oestrogen-receptors (ER) are likely to be promiscuous: wider role for oestrogens and mimics

The anti-breast cancer drug tamoxifen that binds to ER is metabolised in human liver by CYP2D6 isoenzyme, whilst the metabolism of 17beta-oestradiol (by hydroxylation) is by phase I biotransformation in the liver to 2-hydroxyoestradiol and to 4-hydroxyoestradiol respectively by two isoenzymes of this mixed function oxidase CYP cytochromes P450 (EC 1.14.14.1); CYP1A2 and by CYP1B1. Nevertheless, it appears that the receptor (AhR) itself causes the expression of oestrogen-regulated target genes (studied by binding of dioxin). This is the result of an unknown signalling mechanism at the genome that is triggered directly by this receptor by binding promiscuously to ER (alpha or beta) sites. This has been observed even in the absence of oestrogens or mimics therefore in genome-binding investigations of target tissues such as uterus: oestrogen-receptor (ER) is likely to be promiscuous therefore. Furthermore, AhR (polycyclic aromatic hydrocarbon receptor), when activated by the binding of aromatic hydrocarbons (Ah) forms a complex with the aryl hydrocarbon nuclear-translocator chaperone protein (Arnt). It is this binding to xenobiotic response elements in DNA that initiates expression of the appropriate oestrogen-regulated target-genes in the uterus and other target tissues (including mammary, ovaries, and brain). The likely promiscuity of oestrogen receptors is proposed to be the cause of numerous side effects when oestrogen is involved in therapy, these can be manifest in hormone replacement therapy (HRT) and in the incorporation of synthetic oestrogens in the wide varieties of oral contraceptives now available.

Gestational hyperglycemia, zinc, selenium, and antioxidant vitamins

OBJECTIVE

Lower levels of selenium and vitamin E have been described in gestational diabetes, a condition similar to type 2 diabetes, but few data are available about zinc (known to be associated with diabetes) and gestational hyperglycemia. This study evaluated the dietary intake of antioxidant vitamins, zinc, selenium, and serum levels of zinc and selenium in women with gestational hyperglycemia and normoglycemia.

METHODS

A food-frequency questionnaire was administered to 504 pregnant women (210 with hyperglycemia and 294 with normoglycemia). Serum levels of zinc and selenium were analyzed during pregnancy in a second cohort of 71 hyperglycemic and 123 normoglycemic women, with a mean age and body mass index similar to those in the first cohort.

RESULTS

Dietary intakes of zinc and selenium were significantly lower in hyperglycemic patients. In multiple logistic regression analysis, intakes were negatively associated with gestational hyperglycemia (odds ratios of 0.89 for zinc and 0.97 for selenium) after multiple adjustments. There were no significant differences in vitamin intakes. In the second cohort of 194 patients, serum levels of zinc and selenium were significantly lower in patients who had impaired glucose tolerance and negatively associated with gestational hyperglycemia in a multiple logistic regression model (odds ratios of 0.93 for serum zinc and 0.92 for serum selenium).

CONCLUSIONS

Our data suggested a significant inverse association of dietary intakes and serum levels of zinc and selenium with gestational hyperglycemia. If future studies confirm these results, it might be a useful interventional approach to appropriate dietary counseling in order to evaluate the possible decrease in gestational metabolic abnormalities and their adverse consequences.

Evaluation of some biochemical changes in diabetic patients

OBJECTIVE

Hyperglycemia is considered a primary cause of diabetic vascular complications and is associated with oxidative stress, impaired trace element and lipid metabolism as well as pancreatic enzyme abnormalities. The role of trace elements in some of the metabolic dysfunctions and their contributions in the development of vascular complications is not clear. Therefore, the present study investigates the relationship among diabetes mellitus, trace elements status, advanced glycation end products (AGEs), advanced oxidation protein products (AOPP), lipid profiles, antioxidant status, nitric oxide and pancreatic amylase activity in the sera of 55 non-insulin-dependent diabetes mellitus (NIDDM; 35 with microvascular complications and 20 without vascular complications), 40 insulin-dependent diabetes mellitus (IDDM; 25 with microvascular and 15 without microvascular complications), and 20 nondiabetic healthy control subjects. The mean age of the diabetic patients was similar to that of control. The mean duration of the disease was 11.8 +/- 6.8 years (3-27 years) in IDDM and 7.1 +/- 4.7 years (1-15 years) in NIDDM.

METHODS

Plasma Cu, Zn, Mg, Ca, thiobarbituric acid-reactive substance (i.e. malondialdehyde; MDA), nitric oxide (NO), glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), ceruloplasmin (Cp) and amylase activities as well as AOPP were assessed spectrophotometrically whereas AGEs were estimated spectrofluorometrically in two types of diabetes mellitus (DM) as well as control subjects of matched sex and ages.

RESULTS

SOD, CAT and Cp activities were decreased whereas serum alpha-amylase activity was increased in two types of DM in comparison to the corresponding activities of the control subjects. The plasma levels of MDA, NO and Cu were increased but GSH, Zn, Mg and Ca levels were significantly diminished in diabetic patients as compared to the controls. The averages of total cholesterol (CHOL), triglyceride (TG) and low-density lipoprotein-cholesterol (LDLc) were higher in both types of diabetes mellitus in comparison to the control subjects. The mean value of high-density lipoprotein-cholesterol (HDLc) was lower in both types of diabetes mellitus. Further, the mean values of AGEs and AOPP were elevated in diabetic patients vs. control. These parameters are significantly higher in NIDDM patients when compared to the IDDM subjects. Slight but not significant differences in these parameters were observed in patients with diabetic complications when compared to that of without diabetic complications.

CONCLUSION

These findings may explain the role of impaired trace element status, defect of antioxidants and increased of AGE and AOPP in the pathogenesis of pancreas and the vascular complications of diabetes mellitus. Oxidative stress is increased in both types of DM, but it is more in NIDDM patients than in IDDM subjects. In addition, oxidative stress also plays an important role in the formation of AGEs and AOPP in DM.

Oxidative stress in the pathogenesis of diabetic neuropathy

Oxidative stress results from a cell or tissue failing to detoxify the free radicals that are produced during metabolic activity. Diabetes is characterized by chronic hyperglycemia that produces dysregulation of cellular metabolism. This review explores the concept that diabetes overloads glucose metabolic pathways, resulting in excess free radical production and oxidative stress. Evidence is presented to support the idea that both chronic and acute hyperglycemia cause oxidative stress in the peripheral nervous system that can promote the development of diabetic neuropathy. Proteins that are damaged by oxidative stress have decreased biological activity leading to loss of energy metabolism, cell signaling, transport, and, ultimately, to cell death. Examination of the data from animal and cell culture models of diabetes, as well as clinical trials of antioxidants, strongly implicates hyperglycemia-induced oxidative stress in diabetic neuropathy. We conclude that striving for superior antioxidative therapies remains essential for the prevention of neuropathy in diabetic patients.

Insulin, C-peptide, hyperglycemia, and central nervous system complications in diabetes

Diabetes is an increasingly common disorder which causes and contributes to a variety of central nervous system (CNS) complications which are often associated with cognitive deficits. There appear to be two types of diabetic encephalopathy. Primary diabetic encephalopathy is caused by hyperglycemia and impaired insulin action, which evolves in a diabetes duration-related fashion and is associated with apoptotic neuronal loss and cognitive decline. This appears to be particularly associated with insulin-deficient diabetes. Secondary diabetic encephalopathy appears to arise from hypoxic-ischemic insults due to underlying microvascular disease or as a consequence of hypoglycemia. This type of cerebral diabetic complication is more common in the type 2 diabetic population. Here, we will review the clinical and experimental data supporting this conceptual division of diabetic CNS complications and discuss the underlying metabolic, molecular, and functional aberrations.

Role of Oxidative Stress in the Etiology of Type 2 Diabetes and the Effect of Antioxidant Supplementation on Glycemic Control

Oxidative stress is a situation in which the amount of reactive oxygen species (ROS) exceeds the levels of neutralizing substances referred to as antioxidants. Numerous studies have shown that oxidative stress is associated with type 2 diabetes, and there is compelling biochemical evidence that suggests that ROS may even play a role, if only secondary, in the pathogenesis of type 2 diabetes. These observations have provided sufficient impetus for the use of antioxidant supplements as adjunct therapy for control of blood sugar in diabetic patients. However, there is currently no optimum regimen of antioxidant supplementation for diabetic patients. Studies are required to determine appropriate doses of relevant individual micronutrients that perhaps should be used in combination to diminish oxidative stress and improve glycemic control in individuals afflicted with type 2 diabetes.

The Role of Antioxidant Micronutrients in the Prevention of Diabetic Complications

Diabetes mellitus is associated with an increased production of reactive oxygen species and a reduction in antioxidant defenses. This leads to oxidative stress, which is partly responsible for diabetic complications. Tight glycemic control is the most effective way of preventing or decreasing these complications. Nevertheless, antioxidant micronutrients can be proposed as adjunctive therapy in patients with diabetes. Indeed, some minerals and vitamins are able to indirectly participate in the reduction of oxidative stress in diabetic patients by improving glycemic control and/or are able to exert antioxidant activity. This article reviews the use of minerals (vanadium, chromium, magnesium, zinc, selenium, copper) and vitamins or cofactors (tocopherol [vitamin E], ascorbic acid [vitamin C], ubidecarenone [ubiquinone; coenzyme Q], nicotinamide, riboflavin, thioctic acid [lipoic acid], flavonoids) in diabetes, with a particular focus on the prevention of diabetic complications. Results show that dietary supplementation with micronutrients may be a complement to classical therapies for preventing and treating diabetic complications. Supplementation is expected to be more effective when a deficiency in these micronutrients exists. Nevertheless, many clinical studies have reported beneficial effects in individuals without deficiencies, although several of these studies were short term and had small sample sizes. However, a randomized, double-blind, placebo-controlled, multicenter trial showed that thioctic acid at an oral dosage of 800 mg/day for 4 months significantly improved cardiac autonomic neuropathy in type 2 diabetic patients. Above all, individuals with diabetes should be educated about the importance of consuming adequate amounts of vitamins and minerals from natural food sources, within the constraints of recommended sugar and carbohydrate intake.

Sea tangle supplementation lowers blood glucose and supports antioxidant systems in streptozotocin-induced diabetic rats

Diabetes mellitus is a chronic disease associated with serious complications that may be linked to increased lipid peroxidation. This study investigated the effects of dietary supplementation of sea tangle on lipid peroxidation and antioxidant systems in streptozotocin (STZ)-induced diabetes. Forty Sprague-Dawley rats were divided into four groups (n = 10 each) fed AIN76-based diets with either sea tangle powder, water extract of sea tangle, or sodium alginate, or a control diet with no supplement. On day 21 after beginning the diets, rats received intramuscular injections of STZ (45 mg/kg of body weight) to induce diabetes. Experimental diet feeding was continued for 3 more weeks. Dietary supplementation with water extract of sea tangle resulted in lower plasma glucose compared with the control and sodium alginate groups. There was no significant difference in plasma and hepatic lipid peroxides among the groups. Sea tangle and sodium alginate did not affect activities of catalase and glutathione peroxidase; however, supplementation of water extract of sea tangle resulted in higher superoxide dismutase activity as compared with the control and sodium alginate groups. The plasma concentration of alpha-tocopherol increased in the sea tangle water extract group, but the hepatic concentration of alpha-tocopherol was not affected by dietary supplementation. Plasma retinol was not different among experimental groups. In conclusion, our results showed that water extract of sea tangle reduces plasma glucose and protects the antioxidant system in diabetic rats. These results suggest that water extract of sea tangle contains unknown physiologically active components, other than alginic acid, that may exert a protective effect against diabetes.

Inhibitory effect of oolong tea on the oxidative state of low density lipoprotein (LDL)

In the present study, we investigated the anti-oxidant activity of oolong tea in an oxidation model using human low-density lipoprotein (LDL). Oolong tea suppressed the oxidation of LDL induced by 2-2'-azobis 4-methoxy-2,4-dimethyvaleronitrile (V70) in a dose-dependent manner, that is, it prolonged the lag time to 114.3%, 138% and 199.9% as compared with the control group at 0.5 microg/ml, 1.0 microg/ml, and 2.5 microg/ml, respectively. We also determined the scavenging effect of oolong tea on active oxygen radicals using the electron spin resonance (ESR) technique with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin trapping agent. The intensity of the ESR signals for the DMPO-OOH adduct formed by the hypoxanthine/xanthine oxidase reaction system with DMPO decreased in the presence of oolong tea. The IC(50) of oolong tea was 19.9 microg/ml. These findings suggested that oolong tea has beneficial effects on health related to its anti-oxidative action.

Effect of cobalt on the oxidative status in heart and aorta of streptozotocin-induced diabetic rats

Effects of cobalt on the antioxidant status of control and streptozotocin diabetic rat heart and aorta were examined at the second, fourth and sixth week of treatment. Rats were divided into four groups: control, diabetic, control treated with cobalt chloride and diabetic treated with cobalt chloride. Diabetes was induced by tail vein injection of streptozotocin (STZ). Cobalt treatment groups were given 0.5 mM of CoCl(2) in drinking water. The rats in both groups were further subdivided into three groups of six rats each. Rats in these subgroups were studied at 2-week intervals up to 6 weeks. At the end of the experiment, all animals were sacrificed by decapitation, heart and aorta samples were removed for determination of thiobarbituric acid reactive substance (TBARS) level and superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) activities. It was found that lipid peroxidation levels and antioxidant enzyme activities were increased in the streptozotocin-induced diabetic rats at all times studied. Cobalt treatment of diabetic rats (0.5 mM in drinking water) resulted in attenuation of the increased levels of TBARS and antioxidant enzyme activities in heart and aorta. Thus, the effect of oral administration of cobalt at this dose during the early stage of experimental diabetes can be considered as a consequence of altered endogenous defence mechanisms in heart and aorta.

Oxidation of biological systems: oxidative stress phenomena, antioxidants, redox reactions, and methods for their quantification

Reactive oxygen species (ROS) and other radicals are involved in a variety of biological phenomena, such as mutation, carcinogenesis, degenerative and other diseases, inflammation, aging, and development. ROS are well recognized for playing a dual role as deleterious and beneficial species. The objectives of this review are to describe oxidative stress phenomena, terminology, definitions, and basic chemical characteristics of the species involved; examine the biological targets susceptible to oxidation and the defense mechanisms of the organism against these reactive metabolites; and analyze methodologies, including immunohistochemical markers, used in toxicological pathology in the visualization of oxidative stress phenomena. Direct detection of ROS and other free radicals is difficult, because these molecules are short-lived and highly reactive in a nonspecific manner. Ongoing oxidative damage is, thus, generally analyzed by measurement of secondary products including derivatives of amino acids, nuclei acids, and lipid peroxidation. Attention has been focused on electrochemical methods based on voltammetry measurements for evaluating the total reducing power of biological fluids and tissues. This approach can function as a tool to assess the antioxidant-reducing profile of a biological site and follow changes in pathological situations. This review thus includes different topics essential for understanding oxidative stress phenomena and provides tools for those intending to conduct study and research in this field.