Use of in vitro methaemoglobin generation to study antioxidant status in the diabetic erythrocyte

Close relationship between high HbA1c levels and methemoglobin generation in human erythrocytes: The enhancement of oxidative stress in the process

OBJECTIVE

This study aimed to investigate the effect of diabetic plasma on human red blood cells (RBCs) in order to highlight the amplification mechanisms of oxidative stress (OS) in relation to methemoglobin (metHb) production, a potential bio-indicator that could be related to diabetes disease.

RESEARCH DESIGN AND METHODS

Normal RBCs were co-incubated with the diabetic plasma of 24 patients at different HbA_1c levels, for 0, 24, and 48 h in order to assess cell turbidity and hemoglobin (Hb) stability. Hb and metHb production were quantified inside and outside RBCs. Malonaldehyde (MDA) level and cell morphology were concomitantly evaluated.

RESULTS

The cell turbidity was significantly decreased in the group co-incubated with diabetic plasma at high HbA_1c levels (0.074 ± 0.010 AU) compared to the control group (0.446 ± 0.019 AU). A significant decrease in intracellular Hb (0.390 ± 0.075 AU) and its stability (0.600 ± 0.001 AU) were revealed. Also, we found an important increase of metHb levels inside RBCs (0.186 ± 0.017 AU) and in its supernatant (0.086 ± 0.020 AU) after 48 h. Consequently, MDA absorbance increased significantly (0.320 ± 0.040 AU) in RBCs exposed to diabetic plasma with high HbA_1c.

CONCLUSION

These findings suggest that poor glycemic control in diabetes leads to metHb generation which is the main factor of the OS amplification.

Monitoring antioxidant effects using methaemoglobin formation in diabetic erythrocytes †

Deficiencies in the reducing power of diabetic erythrocytes can be studied using the sulphone metabolite, monoacetyl dapsone hydroxylamine (MADDS-NHOH) to generate methaemoglobin, which is a form of oxidative stress. The effects of three antioxidants, dyhydrolipoic acid (DHLA), lipoic acid and ascorbate were compared using this method in erythrocytes of type 1 diabetic patients. During 2-hour incubations, DHLA and lipoic acid significantly reduced MADDS-NHOH-mediated methaemoglobin formation to the same extent in diabetic and non-diabetic erythrocytes. In contrast, ascorbate markedly increased MADDS-NHOH-mediated methaemoglobin formation at all time points up to 2 hours for diabetic cells and 15—60 minutes in non-diabetic erythrocytes. Ascorbate abolished the deficiency in methaemoglobin sensitivity normally seen in diabetic erythrocytes compared with non-diabetic erythrocytes. During a 1-hour pre-incubation period, neither DHLA, lipoic acid nor ascorbate significantly altered total thiol concentrations. After a 2-hour incubation with MADDS-NHOH, thiol concentrations did not significantly change in the non-diabetic erythrocytes, but they fell significantly in the diabetic cells. Diabetic and non-diabetic erythrocytes pre-incubated with ascorbate, DHLA and lipoic acid showed no changes in thiol levels in the presence of MADDS-NHOH. In summary, ascorbate, DHLA and lipoic acid showed contrasting effects on methaemoglobin generation, although they each abolished the diabetic erythrocytic deficit in total thiol status caused by hydroxylamine-mediated methaemoglobin formation. This work provides evidence for the potential future use of antioxidant supplements in diabetic management.

High-fat diet-induced met-hemoglobin formation in rats prone (WOKW) or resistant (DA) to the metabolic syndrome: effect of CoQ10 supplementation

The aim of this study was to evaluate the effects of a high-fat diet (HFD) on oxidative indexes in WistarOttawaKarlsburg W (WOKW) rats used as a model of metabolic syndrome in comparison with Dark Agouti (DA) rats used as a control strain. This syndrome is defined by the occurrence of two or more risk factors including obesity, hypertension, dyslipidemia, and insulin resistance. Forty rats were used in the study and the effect of HFD was evaluated in terms of body weight and both hemoglobin and CoQ oxidative status. Moreover, 16 rats (8 of each strain) were supplemented with 3 mg/100 g b.w. of CoQ10 for 1 month in view of its beneficial properties in cardiovascular disease due to its antioxidant activity in the lipid environment. HFD promoted an increase in body weight, in particular in WOKW males, and in the methemoglobin (met-Hb) index in both strains. Moreover, HFD promoted endogenous CoQ10 oxidation. CoQ10 supplementation was able to efficiently counteract the HFD pro-oxidant effects, preventing met-Hb formation and CoQ oxidation.

Activities of three erythrocyte enzymes of hyperglycemic rats (Rattus norvegicus) treated with Allium sativa extract

Background

The present study sought to investigate erythrocyte glutathione S-transferases (GST), NADH-Methaemoglobin reductase (NADH-MR) and Na⁺/K⁺-ATPase activities of hypoglycemic rats treated with ethanol/water (1:2 v/v) extract of A. sativa as agent of glycemic control.

Methods

Hyperglycemia was induced by a single intra-peritoneal injection of 0.1 mol/L alloxan monohydrate in phosphate buffer saline (PBS) solution (pH = 7.4); dosage = 140 mg/kg. At the end of the experimental time (t = 76 h), erythrocyte GST, NADH-MR and Na⁺/K⁺-ATPase activities as well as serum fasting blood sugar (FBS) levels were measured by spectrophotometric methods.

Results

Serum FBS levels of control/normal (C/N) rats ranged between 72.93 ± 0.82–95.12 ± 0.92 mg/dL, whereas experimental rats without glycemic control gave: 249.41 ± 1.03–256.11 ± 1.23 mg/dL. Hyperglycemic rats treated with ethanol/water (1:2 v/v) extract of A. sativa exhibited comparative reduced serum levels of FBS alongside with erythrocyte GST, NADH-MR and Na⁺/K⁺-ATPase activities. The average relative activities of the three enzymes and corresponding order of enzyme activity in hyperglycemic rats treated with ethanol/water (1:2 v/v) extract of A. sativa was: NADH-MR = 60.99% > GST = 47.81% > Na⁺/K⁺-ATPase = 46.81%. In the same order, relative activities of the three enzymes in rats without glycemic control were: NADH-MR = 49.65% > GST = 23.69% > Na⁺/K⁺-ATPase = 17.02%.

Conclusion

Erythrocyte GST, NADH-MR and Na⁺/K⁺-ATPase activities gave insights into the pathophysiology of diabetic state and served as biomarkers for ascertaining therapeutic control in Type 1 diabetes mellitus.

A preliminary investigation into the impact of a pesticide combination on human neuronal and glial cell lines in vitro

Many pesticides are used increasingly in combinations during crop protection and their stability ensures the presence of such combinations in foodstuffs. The effects of three fungicides, pyrimethanil, cyprodinil and fludioxonil, were investigated together and separately on U251 and SH-SY5Y cells, which can be representative of human CNS glial and neuronal cells respectively. Over 48h, all three agents showed significant reductions in cellular ATP, at concentrations that were more than tenfold lower than those which significantly impaired cellular viability. The effects on energy metabolism were reflected in their marked toxic effects on mitochondrial membrane potential. In addition, evidence of oxidative stress was seen in terms of a fall in cellular thiols coupled with increases in the expression of enzymes associated with reactive species formation, such as GSH peroxidase and superoxide dismutase. The glial cell line showed significant responsiveness to the toxin challenge in terms of changes in antioxidant gene expression, although the neuronal SH-SY5Y line exhibited greater vulnerability to toxicity, which was reflected in significant increases in caspase-3 expression, which is indicative of the initiation of apoptosis. Cyprodinil was the most toxic agent individually, although oxidative stress-related enzyme gene expression increases appeared to demonstrate some degree of synergy in the presence of the combination of agents. This report suggests that the impact of some pesticides, both individually and in combinations, merits further study in terms of their impact on human cellular health.

Erythrocyte antioxidant protection of rose hips (Rosa spp.)

Rose hips are popular in health promoting products as the fruits contain high content of bioactive compounds. The aim of this study was to investigate whether health benefits are attributable to ascorbic acid, phenols, or other rose-hip-derived compounds. Freeze-dried powder of rose hips was preextracted with metaphosphoric acid and the sample was then sequentially eluted on a C₁₈ column. The degree of amelioration of oxidative damage was determined in an erythrocyte in vitro bioassay by comparing the effects of a reducing agent on erythrocytes alone or on erythrocytes pretreated with berry extracts. The maximum protection against oxidative stress, 59.4 ± 4.0% (mean ± standard deviation), was achieved when incubating the cells with the first eluted meta-phosphoric extract. Removal of ascorbic acid from this extract increased the protection against oxidative stress to 67.9 ± 1.9%. The protection from the 20% and 100% methanol extracts was 20.8 ± 8.2% and 5.0 ± 3.2%, respectively. Antioxidant uptake was confirmed by measurement of catechin by HPLC-ESI-MS in the 20% methanol extract. The fact that all sequentially eluted extracts studied contributed to protective effects on the erythrocytes indicates that rose hips contain a promising level of clinically relevant antioxidant protection.

Effects of lipoic acid and dihydrolipoic acid on total erythrocytic thiols under conditions of restricted glucose in vitro

The effects of lipoic acid and dihydrolipoic acid were explored on total thiol maintenance in diabetic and non-diabetic human erythrocytes in vitro over 22 hr in a 37 degrees C incubation system with no added glucose. Over 18-22.5 hr after treatment in both non-diabetic and diabetic cells, lipoic acid (1 mM) was associated with greater loss of cellular thiols than dihydrolipoic acid (1 mM), compared to respective control values. At 0.1 mM, in non-diabetic cells, although lipoic acid-treated cells' thiol levels were significantly lower than control, there was no significant difference between dihydrolipoic acid-treated cells and control cells regarding thiol levels. In addition, at 0.1 mM, dihydrolipoic acid-treated diabetic cells showed a reduction in thiol levels compared to control. At 0.01 mM, lipoic acid-treated cells had significantly lower measured thiol levels compared with diabetic cells exposed to dihydrolipoic acid, whereas in non-diabetic cells, dihydrolipoic acid-treated erythrocytic thiol levels were significantly greater than those treated with lipoic acid, although there were no other significant differences between the groups. At 22.5 hr, control values of methaemoglobin rose to 6.4 +/- 1.1% in diabetic cells and 3.6 +/- 2.1% in non-diabetic cells. Lipoic acid (1 mM) showed greater methaemoglobin formation in diabetic rather than non-diabetic cells (13.6 +/- 1.5% versus 11.6 +/- 1.5%), whereas dihydrolipoic acid-treated diabetic and non-diabetic cells were less potent in methaemoglobin generation (8.5 +/- 2.4% and 8.4 +/- 1.4%, respectively). These studies suggest that in certain circumstances such as hypoglycaemia, lipoic acid administration may actually be detrimental to cellular oxidant protection status.

Effects of Lipoic Acid and Dihydrolipoic Acid on 4-Aminophenol-Mediated Erythrocytic Toxicity in vitro

The effects of the antioxidant lipoic acid and its reduced form, dihydrolipoic acid (DHLA), were studied on the process of the erythrocytic toxicity of 4-aminophenol in human erythrocytes in vitro. 4-Aminophenol alone caused a stepwise increase in methaemoglobin formation, along with a commensurate decrease in total thiols. At 10 min., in the presence of lipoic acid alone and the thiol depletor 1-chloro-2,4-dinitrobenzene (CDNB) alone, 4-aminophenol-mediated methaemoglobin formation was significantly increased, whilst thiol levels were significantly reduced compared with the 4-aminophenol alone. At 10 min., with DHLA and CDNB alone, 4-aminophenol was associated with significantly increased methaemoglobin formation. However, thiol levels were not significantly different in the presence of DHLA compared with 4-aminophenol alone, although thiol levels were different compared with control (4-aminophenol alone) in the incubations with CDNB alone. At 15 min., only CDNB/4-aminophenol methaemoglobin formation differed from control, whilst thiol levels were significantly lower in the presence of CDNB alone compared with 4-aminophenol alone. Lipoic acid enhanced the toxicity of 4-aminophenol in terms of increased methaemoglobin formation coupled with increased thiol depletion, whilst DHLA showed increased 4-aminophenol-mediated methaemoglobin formation without thiol depletion. Lipoic acid, and to a lesser extent its reduced derivative DHLA, acted as a prooxidant in the presence of 4-aminophenol, enhancing the oxidative stress effects of the amine in human erythrocytes.

The methaemoglobin forming and GSH depleting effects of dapsone and monoacetyl dapsone hydroxylamines in human diabetic and non-diabetic erythrocytes in vitro

The respective methaemoglobin forming and GSH depleting capabilities of monoacetyl dapsone hydroxylamine (MADDS-NHOH) and dapsone hydroxylamine (DDS-NHOH) were compared in human diabetic and non-diabetic erythrocytes in vitro with a view to select the most potent agent for future oxidative stress and antioxidant evaluation studies. Administration of both metabolites to non-diabetic erythrocytes over the 20min period of the study resulted in significantly more methaemoglobin formation at all four time points compared with the diabetic erythrocytes (P<0.0001). At all four time points, significantly more methaemoglobin was formed in response to MADDS-NHOH in non-diabetic cells compared with the effects of DDS-NHOH on diabetic erythrocytes (P<0.0001). At the 5 and 10min time points, significantly more methaemglobin was formed in non-diabetic cells in the presence of MADDS-NHOH compared with DDS-NHOH (P<0.05). At the 5min time point only, significantly more methaemoglobin was formed in the presence of MADDS-NHOH in diabetic cells compared with that of DDS-NHOH (P<0.01). However, compared with diabetic control GSH levels, the presence of DDS-NHOH caused a significant depletion in GSH at 5, 10 and 20min time points in diabetic cells (P<0.001). In addition, the presence of DDS-NHOH caused a significant reduction in GSH levels in diabetic cells in comparison with those of non-diabetics at the 5, 10 and 20min, (P<0.005). DDS-NHOH was also associated with a significant depletion of GSH levels in diabetic cells compared with those of non-diabetic control erythrocytes (P<0.0001). The presence of MADDS-NHOH in diabetic erythrocytes led to a significant reduction in GSH levels at the 20min time point compared with those of non-diabetics (P<0.001), but there were no significant differences at the 5, 10 and 15min points. Due to its greater GSH-depleting action, DDS-NHOH will be selected for future use in the oxidative stress assessment in diabetic erythrocytes.

A preliminary evaluation of a novel method to monitor a triple antioxidant combination (vitamins E, C and α-lipoic acid) in diabetic volunteers using in vitro methaemoglobin formation

Eight otherwise healthy diabetic volunteers took a daily antioxidant supplement consisting of vitamin E (200 IU), vitamin C (250 mg) and α-lipoic acid (90 mg) for a period of 6 weeks. Diabetic dapsone hydroxylamine-mediated methaemoglobin formation and resistance to erythrocytic thiol depletion was compared with age and sex-matched non-diabetic subjects. At time zero, methaemoglobin formation in the non-diabetic subjects was greater at all four time points compared with that of the diabetic subjects. Resistance to glutathione depletion was initially greater in non-diabetic compared with diabetic samples. Half-way through the study (3 weeks), there were no differences between the two groups in methaemoglobin formation and thiol depletion in the diabetic samples was now lower than the non-diabetic samples at 10 and 20 min. At 6 weeks, diabetic erythrocytic thiol levels remained greater than those of non-diabetics. HbA(1c) values were significantly reduced in the diabetic subjects at 6 weeks compared with time zero values. At 10 weeks, 4 weeks after the end of supplementation, the diabetic HbA1(c) values significantly increased to the point where they were not significantly different from the time zero values. Total antioxidant status measurement (TAS) indicated that diabetic plasma antioxidant capacity was significantly improved during antioxidant supplementation. Conversion of α-lipoic acid to dihydrolipoic acid (DHLA) in vivo led to potent interference in a standard fructosamine assay kit, negating its use in this study. This report suggests that triple antioxidant therapy in diabetic volunteers attenuates the in vitro experimental oxidative stress of methaemoglobin formation and reduces haemoglobin glycation in vivo.

The use of xenobiotic-mediated methaemoglobin formation to assess the effects of thyroid hormones on diabetic and non-diabetic human erythrocytic oxidant defence mechanisms in vitro

Diabetes is associated with an abnormal incidence of hypothyroidism, which exacerbates hyperglycaemia, so further damaging already compromised erythrocytic defence mechanisms. Methaemoglobin formation is a useful measure of the health of these mechanisms, as it determines the resistance of diabetic erythrocytes to sustained oxidative stress. The effect of l-tri-iodothyronine (T(3)) was, therefore, studied on nitrite and monoacetyldapsone hydroxylamine (MADDS-NHOH) mediated methaemoglobin formation in diabetic and non-diabetic human erythrocytes. Diabetic erythrocytes showed less sensitivity compared with non-diabetics to methaemoglobin formation mediated by both compounds. A 30 min pre-incubation with T(3) at 3 and 30 nM did not affect nitrite-mediated methaemoglobin formation compared with control observations in both cell types. In diabetic erythrocytes incubated with T(3) at 30 nM, there were significant increases in MADDS-NHOH-mediated methaemoglobin formation compared with control in both diabetic and non-diabetic cells. Studies comparing blood isolated from diabetic patients stabilised on thyroxine (T(4); 50 μG/day), T(4)-free diabetics and non-diabetics, showed that T(4) supplementation significantly increased MADDS-NHOH-mediated methaemoglobin formation compared with T(4)-free diabetic cells so that for two time points, T(4)-treated diabetic erythrocytic methaemoglobin formation was indistinguishable from that of non-diabetics. These studies indicate that T(4) supplementation improves some erythrocytic oxidant defence mechanisms in a time dependent manner.

Plasma-Saturating intakes of vitamin C confer maximal antioxidant protection to plasma

OBJECTIVE

Supplemental vitamin C has been shown to reduce oxidative damage in vivo, yet the dose-response relationship between vitamin C intake and antioxidant protection is not known. This report examined blood indicators of oxidative stress in subjects consuming graded doses of vitamin C, from 75 to 2,000 mg/day.

METHODS

Ten healthy, non-smoking men and women (26.1 +/- 2.1 years) were recruited from a campus population. During the ten-week study, subjects limited fruit and vegetable consumption (< or = 3 servings/day) and consumed a multivitamin and mineral pill daily. Beginning at week 3, subjects ingested either a vitamin C (n = 8) or placebo (n = 2) capsule, which were identical in appearance and taste. The content of the vitamin C capsule increased every two weeks (from 250 mg at weeks 3-4 to 500 mg, 1,000 mg. and 2,000 mg at weeks 5-6. 7-8. 9-10, respectively). Fasting blood samples were collected at two-week intervals and analyzed for vitamin C, total lipid hydroperoxides and Heinz bodies in packed erythrocytes incubated 24 hours at 37 degrees.

RESULTS

Plasma vitamin C rose 55% in vitamin C-supplemented subjects by the end of the ten-week treatment (p < 0.05), and measures of oxidative stress decreased 60% to 90% (8.1 +/- 0.6 to 3.5 +/- 0.4 nmol/mL and 69.1 +/- 7.8% to 6.7 +/- 6.0% for total lipid hydroperoxides and Heinz bodies, respectively). Significant decreases in markers of oxidative stress were noted at the 500 mg, 1,000 mg and 2,000 mg dosages versus placebo. Antioxidant protection was similar at the 1,000 mg and 2,000 mg dosage.

CONCLUSIONS

These data indicate that the antioxidant protection afforded by short-term vitamin C supplementation is maximal at the 500-1,000 mg dosage range.

Monitoring diabetic antioxidant status: a role for in vitro methaemoglobin formation

Diabetes leads to premature organ and system failure and considerably shortens lifespan. Careful control of glucose levels may not be enough to prevent the onset of complications in most diabetics. Compared with non-diabetics, diabetic tissues must not only resist a much greater long-term threat from hyperglycaemia-mediated reactive species but also defend themselves with compromised antioxidant systems. Although antioxidant therapy is a logical step in the prevention of oxidant and carbonyl stresses in the face of intermittent hyperglycaemia, this approach is not yet universally accepted to be effective in preventing complications. Although there are many biochemical indices of oxidant stress, piecemeal elevations of individual markers may not necessarily reflect true diabetic cellular antioxidant status. A dynamic process such as in vitro methaemoglobin generation may provide an opportunity to compare the response of a diabetic erythrocyte with that of a non-diabetic before and after corrective antioxidant therapy. Due to compromised cellular antioxidant capacity, diabetic cells generate less methaemoglobin in the presence of aromatic amine hydroxylamines, 4-aminophenol and nitrite compared with non-diabetics. Agents such as dihydrolipoic acid have been shown to correct methaemoglobin formation-mediated thiol deficits during in vitro studies. It is hoped that the progress of antioxidant supplementation studies in diabetics can be monitored with the aid of in vitro methaemoglobin generation using agents such as hydroxylamines, 4-aminophenol and nitrite. The most appropriate antioxidants and dosages can thus be recommended to diabetics worldwide to attenuate the development of complications.

The therapeutic use of lipoic acid in diabetes: a current perspective

Lipoic acid and its reduced derivative, dihydrolipoic acid (DHLA) are highly promising antioxidant agents, which are potent attenuators of reactive species-mediated damage in vitro and in animal studies. Lipoic acid is a universal antioxidant, effective in lipophilic and aqueous environments. In contrast to an equivalent endogenous agent, such as oxidised glutathione (GSSG), lipoic acid acts as an antioxidant in its oxidised form. Lipoic acid has been evaluated in diabetic polyneuropathy, a condition which is thought to result in part from oxidant damage caused by long-term hyperglycaemia. Diabetic patients are prone to incur enhanced cellular free radical formation and reduced antioxidant defence. Treatment with lipoic acid has improved nerve conduction velocity during studies in diabetic animals. Trials in diabetic patients have often observed some relief of neuropathic symptoms during treatment with lipoic acid, but consistent objective benefits have been difficult to establish. Lipoic acid is now used in Germany for the treatment of diabetic neuropathy and definitive evidence of efficacy should arise from postmarketing surveillance studies. It is possible that lipoic acid may be more effective as a long-term dietary supplement aimed at the prophylactic protection of diabetics from complications.