Are insulin resistance and atherosclerosis the consequences of oxidative stress?

The interplay between oxidative stress, zinc, and metabolic dysfunction in polycystic ovarian syndrome

Polycystic ovarian syndrome (PCOS) is a functional endocrine disorder characterized by hyperandrogenism, ovulatory dysfunction, and polycystic ovarian morphology that has been associated with chronic disease and comorbidities including adverse metabolic and cardiac disorders. This review aims to evaluate the role of oxidative stress and zinc in the metabolic dysfunction observed in PCOS, with a focus on insulin resistance. Recent studies indicate that oxidative stress markers are elevated in PCOS and correlate with hyperandrogenemia, obesity, and insulin resistance. Zinc, an essential trace element, is crucial for metabolic processes, particularly in the pancreas for beta-cell function and glucagon secretion. Insufficient zinc levels have been linked to diabetes, obesity, and lipid metabolism disorders. This review aims to highlight the interplay between oxidative stress, zinc, and metabolic dysfunction in PCOS, suggesting that zinc supplementation could mitigate some metabolic and endocrine manifestations of PCOS.

Neuroprotective Effects of the Amylin Analog, Pramlintide, on Alzheimer's Disease Are Associated with Oxidative Stress Regulation Mechanisms

Administration of the recombinant analog of the pancreatic amyloid amylin, Pramlintide, has shown therapeutic benefits in aging and Alzheimer's disease (AD) models, both on cognition and amyloid-β (Aβ) pathology. However, the neuroprotective mechanisms underlying the benefits of Pramlintide remain unclear. Given the early and critical role of oxidative stress in AD pathogenesis and the known reactive oxygen species (ROS) modulating function of amyloids, we sought to determine whether Pramlintide's neuroprotective effects involve regulation of oxidative stress mechanisms. To address this, we treated APP/PS1 transgenic mice with Pramlintide for 3 months, starting at 5.5 months prior to widespread AD pathology onset, and measured cognition (Morris Water Maze), AD pathology, and oxidative stress-related markers and enzymes in vivo. In vitro, we determined the ability of Pramlintide to modulate H2O2-induced oxidative stress levels. Our data show that Pramlintide improved cognitive function, altered amyloid-processing enzymes, reduced plaque burden in the hippocampus, and regulated endogenous antioxidant enzymes (MnSOD and GPx1) and the stress marker HO-1 in a location specific manner. In vitro, Pramlintide treatment in neuronal models reduced H2O2-induced endogenous ROS production and lipid peroxidation in a dose-dependent manner. Together, these results indicate that Pramlintide's benefits on cognitive function and pathology may involve antioxidant-like properties of this compound.

Fibrinogen is associated with glucose metabolism and cardiovascular outcomes in patients with coronary artery disease

Background

The present cohort study aims to examine the relationship between fibrinogen (Fib) levels and glucose metabolism [fasting blood glucose (FBG) and hemoglobin A1c (HbA1c)] and investigate the impact of high Fib on cardiovascular outcomes in patients with stable CAD and pre-diabetes mellitus (pre-DM) or diabetes mellitus (DM).

Methods

This study included 5237 patients from March 2011 to December 2015. Patients were distributed into three groups according to Fib levels (low Fib, median Fib, high Fib) and further categorized by glucose metabolism status [normal glucose regulation (NGR), Pre-DM, DM]. All patients were followed up for the occurrences of major adverse cardiovascular events (MACEs), including cardiovascular mortality, nonfatal MI, stroke, and unplanned coronary revascularization.

Results

Linear regression analyses showed that FBG and HbA1c levels were positively associated with Fib in overall CAD participants, either with or without DM (all P < 0.001). During an average of 18,820 patient-years of follow-up, 476 MACEs occurred. High Fib was independently associated with MACEs after adjusting for confounding factors [Hazard Ratio (HR): 1.57, 95% confidence interval (CI) 1.26–1.97, P < 0.001]. Furthermore, DM but not pre-DM was a significant predictor of MACEs (P < 0.001 and P > 0.05, respectively). When patients were stratified by both glucose metabolism status and Fib levels, high Fib was associated with a higher risk of MACEs in pre-DM (HR 1.66, 95% CI 1.02–2.71, P < 0.05). Medium and high Fib levels were associated with an even higher risk of MACEs in DM (HR 1.86, 95% CI 1.14–3.05 and HR 2.28, 95% CI 1.42–3.66, all P < 0.05). After adding the combination of Fib and glucose status to the Cox model, the C-statistic was increased by 0.015 (0.001–0.026).

Conclusions

The present study suggested that Fib levels were associated with FBG and HbA1c in stable CAD patients. Moreover, elevated Fib was independently associated with MACEs in CAD patients, especially among those with pre-DM and DM, suggesting that Fib may provide incremental value in the cardiovascular risk stratification of pre-DM and DM patients.

Insulin resistance and diabetes in hyperthyroidism: a possible role for oxygen and nitrogen reactive species

In addition to insulin, glycemic control involves thyroid hormones. However, an excess of thyroid hormone can disturb the blood glucose equilibrium, leading to alterations of carbohydrate metabolism and, eventually, diabetes. Indeed, experimental and clinical hyperthyroidism is often accompanied by abnormal glucose tolerance. A common characteristic of hyperthyroidism and type 2 diabetes is the altered mitochondrial efficiency caused by the enhanced production of reactive oxygen and nitrogen species. It is known that an excess of thyroid hormone leads to increased oxidant production and mitochondrial oxidative damage. It can be hypothesised that these species represent the link between hyperthyroidism and development of insulin resistance and diabetes, even though direct evidence of this relationship is lacking. In this review, we examine the literature concerning the effects of insulin and thyroid hormones on glucose metabolism and discuss alterations of glucose metabolism in hyperthyroid conditions and the cellular and molecular mechanisms that may underline them.

The Effects of Folate Supplementation on Diabetes Biomarkers Among Patients with Metabolic Diseases: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Although several studies have evaluated the effect of folate supplementation on diabetes biomarkers among patients with metabolic diseases, findings are inconsistent. This review of randomized controlled trials (RCTs) was performed to summarize the evidence on the effects of folate supplementation on diabetes biomarkers among patients with metabolic diseases. Randomized-controlled trials (RCTs) published in PubMed, EMBASE, Web of Science and Cochrane Library databases up to 1 September 2017 were searched. Two review authors independently assessed study eligibility, extracted data, and evaluated risk of bias of included studies. Heterogeneity was measured with a Q-test and with I2 statistics. Data were pooled by using the fix or random-effect model based on the heterogeneity test results and expressed as standardized mean difference (SMD) with 95% confidence interval (CI). A total of sixteen randomized controlled trials involving 763 participants were included in the final analysis. The current meta-analysis showed folate supplementation among patients with metabolic diseases significantly decreased insulin (SMD -1.28; 95% CI, -1.99, -0.56) and homeostasis model assessment of insulin resistance (HOMA-IR) (SMD -1.28; 95% CI, -1.99, -0.56). However, folate supplementation did not affect fasting plasma glucose (FPG) (SMD -0.30; 95% CI, -0.63, 0.02) and hemoglobin A1C (HbA1c) (SMD -0.29; 95% CI, -0.61, 0.03). The results of this meta-analysis study demonstrated that folate supplementation may result in significant decreases in insulin levels and HOMA-IR score, but does not affect FPG and HbA1c levels among patients with metabolic diseases.

Risk Factors for Cardiovascular Disease in Obese Children

OBJECTIVE

To study the prevalence of cardiovascular risk factors in pediatric obesity.

METHODS

50 obese children (age 5-17y) and 50 apparently healthy non-obese children (body mass index of over 95th percentile and between 5th to 95th percentiles, respectively) using Centre for Disease Control growth charts were included. Fasting blood sugar, lipid profile, insulin, homeostasis model assessment of insulin resistance, uric acid, fibrinogen, lipoprotein (a), homocysteine, malondialdehyde, ferric reducing ability of plasma and nitric oxide were measured.

RESULTS

Insulin, insulin resistance, triglycerides, uric acid, fibrinogen, malondialdehyde, ferric reducing ability of plasma and nitric oxide were significantly higher (P <0.001) in obese children. Body mass index showed significant positive correlation with insulin r=0.519, P<0.001; insulin resistance r =0.479, P<0.001; uric acid r= 0.289, P=0.005; fibrinogen r=0.461, P<0.001; and nitric oxide r=0.235, P=0.012.

Conclusion

Pediatric obesity is associated with dyslipidemia, oxidative stress, insulin resistance and endothelial dysfunction, which are cardiovascular risk factors and components of metabolic syndrome. These children must be targeted for lifestyle and dietary modification.

Pathogenesis of chronic hyperglycemia: from reductive stress to oxidative stress

Chronic overnutrition creates chronic hyperglycemia that can gradually induce insulin resistance and insulin secretion impairment. These disorders, if not intervened, will eventually be followed by appearance of frank diabetes. The mechanisms of this chronic pathogenic process are complex but have been suggested to involve production of reactive oxygen species (ROS) and oxidative stress. In this review, I highlight evidence that reductive stress imposed by overflux of NADH through the mitochondrial electron transport chain is the source of oxidative stress, which is based on establishments that more NADH recycling by mitochondrial complex I leads to more electron leakage and thus more ROS production. The elevated levels of both NADH and ROS can inhibit and inactivate glyceraldehyde 3-phosphate dehydrogenase (GAPDH), respectively, resulting in blockage of the glycolytic pathway and accumulation of glycerol 3-phospate and its prior metabolites along the pathway. This accumulation then initiates all those alternative glucose metabolic pathways such as the polyol pathway and the advanced glycation pathways that otherwise are minor and insignificant under euglycemic conditions. Importantly, all these alternative pathways lead to ROS production, thus aggravating cellular oxidative stress. Therefore, reductive stress followed by oxidative stress comprises a major mechanism of hyperglycemia-induced metabolic syndrome.

Parameters of glycemic control and their relationship with zinc concentrations in blood and with superoxide dismutase enzyme activity in type 2 diabetes patients

OBJECTIVE

This study assessed the relationship between the parameters of glycemic control, and zinc concentrations in blood and superoxide dismutase enzyme activity in type 2 diabetes patients.

SUBJECTS AND METHODS

Seventy-three individuals, aged between 25 and 59 years, were divided into the experimental group (type 2 diabetes patients, n = 36) and control group (n = 37). Plasma and erythrocyte zinc concentrations, superoxide dismutase activity, and parameters of glycemic control were analyzed.

RESULTS

Mean plasma zinc concentration was 74.1 ± 10.7 µg/dL and 68.8 ± 9.6 µg/dL, erythrocyte zinc concentration was 48.1 ± 9.5 µg/gHb and 41.2 ± 8.0 µg/gHb, and superoxide dismutase activity was 2248.9 ± 300.0 U/gHb and 2059.6 ± 285.4 U/gHb, in the experimental group and the control group, respectively (p < 0.05).

CONCLUSION

Type 2 diabetes patients showed a positive response to oxidative stress due to adequate zinc concentration in blood and increased activity of superoxide dismutase, and the enzyme was influenced by serum insulin.

Susceptibility to oxidative stress, insulin resistance, and insulin secretory response in the development of diabetes from obesity

BACKGROUND/AIM

[corrected] Oxidative stress plays a critical role in the pathogenesis of various diseases. Recent reports indicate that obesity may induce systemic oxidative stress. The aim of the study was to potentiate oxidative stress as a factor which may aggravate peripheral insulin sensitivity and insulinsecretory response in obesity in this way to potentiate development of diabetes. The aim of the study was also to establish whether insulin-secretory response after glucagonstimulated insulin secretion is susceptible to prooxidant/antioxidant homeostasis status, as well as to determine the extent of these changes.

METHODS

A mathematical model of glucose/insulin interactions and C-peptide was used to indicate the degree of insulin resistance and to assess their possible relationship with altered antioxidant/prooxidant homeostasis. The study included 24 obese healthy and 16 obese newly diagnozed non-insulin dependent diabetic patients (NIDDM) as well as 20 control healthy subjects, matched in age.

RESULTS

Total plasma antioxidative capacity, erythrocyte and plasma reduced glutathione level were significantly decreased in obese diabetic patients, but also in obese healthy subjects, compared to the values in controls. The plasma lipid peroxidation products and protein carbonyl groups were significantly higher in obese diabetics, more than in obese healthy subjects, compared to the control healthy subjects. The increase of erythrocyte lipid peroxidation at basal state was shown to be more pronounced in obese daibetics, but the apparent difference was obtained in both the obese healthy subjects and obese diabetics, compared to the control values, after exposing of erythrocytes to oxidative stress induced by H2O2. Positive correlation was found between the malondialdehyde (MDA) level and index of insulin sensitivity (FIRI).

CONCLUSION

Increased oxidative stress together with the decreased antioxidative defence seems to contribute to decreased insulin sensitivity and impaired insulin secretory response in obese diabetics, and may be hypothesized to favour the development of diabetes during obesity.

Vitamin E protects the insulin sensitivity and redox balance in rat L6 muscle cells exposed to oxidative stress

BACKGROUND

The effect of reactive oxygen species (ROS) on insulin action is unclear. This study was carried out to explore the effect of prolonged low grade oxidative stress and vitamin E treatment on cultured rat L6 muscle cells.

METHODS

L6 myotubes were incubated with vitamin E for 18 h and treated with H2O2 generating system for 12 h. Insulin stimulated glucose uptake, total antioxidant capacity and reduced glutathione concentration were measured.

RESULTS

There was a marked decrease in insulin stimulated glucose transport in L6 cells exposed to H2O2 generating system. Pretreatment with vitamin E attenuates the effect of H2O2 on insulin action. Treatment with H2O2 caused a significant reduction in the levels of reduced glutathione and total antioxidant capacity, these alterations were reversed by vitamin E pretreatment. Vitamin E per se had no effect on insulin stimulated glucose transport in cells not exposed to oxidative stress.

CONCLUSION

In conclusion, our observations indicate that vitamin E improves the free radical defense system potential and prevents oxidative stress induced insulin resistance in rat L6 muscle cells.

L-folic acid supplementation in healthy postmenopausal women: effect on homocysteine and glycolipid metabolism

CONTEXT

Hyperhomocysteinemia as well as alterations of glycemic and lipidic metabolism are recognized as risk factors for cardiovascular diseases.

OBJECTIVE

The aim of this study was to examine the effect of L-folic acid supplementation on homocysteine (Hcy) and related thiols, such as cysteine (Cys) and Cys-glycine (Cys-Glyc) pathways and their relationship to glucose, insulin, and lipidic metabolism in normoinsulinemic postmenopausal women.

DESIGN

This study was a randomized placebo, not double-blind, trial.

SETTING

The study was performed in an academic research center.

PATIENTS OR OTHER PARTICIPANTS

Twenty healthy postmenopausal women were selected. No patient was taking drugs known to affect lipid or glucose metabolism.

INTERVENTION(S)

Patients underwent two hospitalizations before and after 8 wk of L-acid folic (7.5 mg/d) or placebo administration. The glycemic metabolism was studied by an oral glucose tolerance test and a hyperinsulinemic euglycemic clamp. Hcy metabolism was studied by a standardized oral methionine-loading test.

MAIN OUTCOME MEASURE(S)

Hcy, Cys, and Cys-Glyc, basally and after a methionine loading test, were measured. Basal insulin, glucose, and peptide C levels as well as area under the curve for insulin, area under the curve for peptide, hepatic insulin extraction, and metabolic index were assayed. The total cholesterol, high-density lipoprotein (HDL) cholesterol, and low-density lipoprotein (LDL) cholesterol levels and the cholesterol/HDL and LDL/HDL ratios were also measured.

RESULTS

The total basal Hcy concentration and the plasma postmethionine loading Hcy values were significantly decreased (P < 0.01) in L-folic acid-treated patients, whereas postmethionine loading Cys-Glyc levels were markedly increased (P < 0.02). Furthermore, L-folic acid intake induced a significant improvement in carbohydrate metabolism through an increase in fractional hepatic insulin extraction (P < 0.05) and peripheral insulin sensitivity (P < 0.02) in normoinsulinemic women. HDL levels considerably increased, inducing an improvement in other atherosclerotic indexes, such as cholesterol/HDL and LDL/HDL ratios (P < 0.03).

CONCLUSIONS

These results show that folic acid supplementation lowers plasma Hcy levels and improves insulin and lipid metabolism, reducing the risk of cardiovascular disease.

The molecular basis for oxidative stress-induced insulin resistance

Reactive oxygen and nitrogen molecules have been typically viewed as the toxic by-products of metabolism. However, accumulating evidence has revealed that reactive species, including hydrogen peroxide, serve as signaling molecules that are involved in the regulation of cellular function. The chronic and/or increased production of these reactive molecules or a reduced capacity for their elimination, termed oxidative stress, can lead to abnormal changes in intracellular signaling and result in chronic inflammation and insulin resistance. Inflammation and oxidative stress have been linked to insulin resistance in vivo. Recent studies have found that this association is not restricted to insulin resistance in type 2 diabetes, but is also evident in obese, nondiabetic individuals, and in those patients with the metabolic syndrome. An increased concentration of reactive molecules triggers the activation of serine/threonine kinase cascades such as c-Jun N-terminal kinase, nuclear factor-kappaB, and others that in turn phosphorylate multiple targets, including the insulin receptor and the insulin receptor substrate (IRS) proteins. Increased serine phosphorylation of IRS reduces its ability to undergo tyrosine phosphorylation and may accelerate the degradation of IRS-1, offering an attractive explanation for the molecular basis of oxidative stress-induced insulin resistance. Consistent with this idea, studies with antioxidants such as vitamin E, alpha-lipoic acid, and N-acetylcysteine indicate a beneficial impact on insulin sensitivity, and offer the possibility for new treatment approaches for insulin resistance.

Oxidative stress and stress-activated signaling pathways: a unifying hypothesis of type 2 diabetes

In both type 1 and type 2 diabetes, the late diabetic complications in nerve, vascular endothelium, and kidney arise from chronic elevations of glucose and possibly other metabolites including free fatty acids (FFA). Recent evidence suggests that common stress-activated signaling pathways such as nuclear factor-kappaB, p38 MAPK, and NH2-terminal Jun kinases/stress-activated protein kinases underlie the development of these late diabetic complications. In addition, in type 2 diabetes, there is evidence that the activation of these same stress pathways by glucose and possibly FFA leads to both insulin resistance and impaired insulin secretion. Thus, we propose a unifying hypothesis whereby hyperglycemia and FFA-induced activation of the nuclear factor-kappaB, p38 MAPK, and NH2-terminal Jun kinases/stress-activated protein kinases stress pathways, along with the activation of the advanced glycosylation end-products/receptor for advanced glycosylation end-products, protein kinase C, and sorbitol stress pathways, plays a key role in causing late complications in type 1 and type 2 diabetes, along with insulin resistance and impaired insulin secretion in type 2 diabetes. Studies with antioxidants such as vitamin E, alpha-lipoic acid, and N-acetylcysteine suggest that new strategies may become available to treat these conditions.

Insulin-induced peroxynitrite production in human platelet-rich plasma

Recent data support the possible role of nitric oxide (NO*) in the development of insulin signalling. The aim of this study was to examine the effect of insulin on NO* production by platelets. The chemiluminescence of platelet-rich plasma prepared from the blood of healthy volunteers was measured in the presence of luminol. Indirect detection of NO* by luminol is possible in the form of peroxynitrite produced in the reaction of NO* with a superoxide free radical. Luminol oxidation induced by hydroxyl free radical and lipid peroxidation was prevented by 150 micromol/l of desferrioxamine mesylate. Insulin, in the range of 0.084-840 nmol/l, induced a concentration-dependent increase in chemiluminescence, which was inhibited both by the competitive antagonist of the NO* synthase enzyme. N(omega)-nitro-L-arginine methyl ester (at concentrations of 2.0-4.0 mmol/l, P<0.001), and by the elimination of superoxide free radicals using superoxide dismutase (72-144 IU/ml, P<0.001). In conclusion, we assume that the insulin-induced increase in chemiluminescence of platelet-rich plasma was due to increased production of NO* and superoxide free radicals forming peroxynitrite. The data are consistent with production of peroxynitrite from human platelets under insulin stimulation.

Elevated plasma total homocysteine levels in hyperinsulinemic obese subjects

Homocysteine has been associated with the oxidative stress in the pathogenesis of atherosclerosis. Oxidative stress caused by triglycerides and free fatty acids is known to cause insulin resistance and hyperinsulinemia. On the other hand, insulin resistance may increase homocysteine levels. Since obesity is associated with insulin resistance and hyperinsulinemia, we aimed to study the possible association of homocysteine with hyperinsulinemia in obese subjects. 20 obese male subjects (body mass index >29), aged 33--55 (mean 45 years old) were studied. A fasting blood sample was obtained for the study and the subjects undertook an oral glucose tolerance test with samples taken at 1 and 2 h after glucose. Subjects were divided in two groups according to the fasting insulin levels, < 9 &mgr;U/ml or normoinsulinemic (group 1) and >9 &mgr;U/ml or hyperinsulinemic (group 2). Glucose, insulin, homocysteine, folate, B(12,) total cholesterol, HDL-cholesterol and triglycerides levels were determined in fasting blood samples. In oral glucose tolerance test, glucose, insulin and homocysteine levels were measured. Hyperinsulinemic obese subjects (group 2) had higher levels of insulin and glucose at 1 h and 2 h postglucose, compared with group 1. Fasting total homocysteine and triglyceride levels were also increased in this group, whereas folate and B(12) levels were similar in both groups. Fasting homocysteine significantly correlated with fasting insulin (r = 0.6, p <0.01). Homocysteine levels slightly but significantly decreased after glucose loading in normoinsulinemic but not in hyperinsulinemic obese subjects. These results show that higher homocysteine levels are observed in the hyperinsulinemic obese subjects and suggest that homocysteine could play a role in the higher risk of cardiovascular disease in obesity.

Dietary troglitazone decreases oxidative stress in early stage type II diabetic rats

Oxidative stress is involved in the initiation and development of atherosclerosis in diabetes. We tested the hypothesis that oxidative stress is already increased in early stage type II diabetes, and that troglitazone may prevent the increase. Three groups of 20 week old rats were studied: untreated Otsuka Long-Evans Tokushima Fatty (OLETF) rats, as an animal model of type II diabetes, OLETF rats treated with troglitazone, and control Long-Evans Tokushima Otsuka (LETO) rats. Plasma lipid hydroperoxides (LOOH) concentration, as an indication of lipid peroxidation, and superoxide dismutase (SOD) activity in the thoracic aorta were measured. Plasma LOOH concentration was significantly higher in non-treated OLETF rats compared to LETO rats and treatment with troglitazone completely prevented this increase. SOD activity was significantly decreased in non-treated OLETF rats compared to LETO rats and troglitazone attenuated the diminution of it. These observations demonstrate oxidative stress is already increased in the early stage of type II diabetes and we confirmed troglitazone has the effect of an antioxidant in vivo.

Alpha-lipoic acid: a multifunctional antioxidant that improves insulin sensitivity in patients with type 2 diabetes

Alpha-Lipoic acid (LA) is a disulfide compound that is produced in small quantities in cells, and functions naturally as a co-enzyme in the pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase mitochondrial enzyme complexes. In pharmacological doses, LA is a multifunctional antioxidant. LA has been used in Germany for over 30 years for the treatment of diabetes-induced neuropathy. In patients with type 2 diabetes, recent studies have reported that intravenous (i.v.) infusion of LA increases insulin-mediated glucose disposal, whereas oral administration of LA has only marginal effects. If the limitations of oral therapy can be overcome, LA could emerge as a safe and effective adjunctive antidiabetic agent with insulin sensitizing activity.

Possible role of free radicals generated by pseudohypoxia in the regulation of hepatic glucose output. An in vitro model using rat liver microsomal glucose 6-phosphatase

Hepatic glucose output is decreased by hyperglycaemia through an unknown mechanism. We hypothesize that free radicals generated by hyperglycaemic pseudohypoxia might cause glucose output to decrease by inhibiting glucose 6-phosphatase - a key enzyme of gluconeogenesis. To prove this a model experiment was performed on a microsome fraction of rat liver. One of the characteristic features of pseudohypoxia due to hyperglycaemia is an increase in the ratio of NADH/NAD+, so in the present study the changes in NADH - induced glucose 6-phosphatase activity were investigated as related to the release of inorganic phosphate (Pi) derived from glucose 6-phosphate. After incubation for 50 min, Pi release was significantly reduced by NADH (4.026 +/- 0.189 vs 2.696 +/- 0.429 micromol x l(-1) x mg protein(-1), control vs NADH samples, p < 0.01). The decrease in the activity of glucose 6-phosphatase generated by NADH was prevented by using desferrioxamine, an irreversible ferric chelator, butylated hydroxytoluene and Trolox, two agents which inhibit lipid peroxidation, and reduced glutathione, a non-specific radical scavenger. Superoxide dismutase, catalase and the hydroxyl radical scavenger dimethyl sulphoxide proved to be ineffective. When the above investigations were carried out in the presence of a ferric-EDTA complex the inhibition of glucose 6-phosphatase was found to be inducible by hydrogen peroxide and/or hydroxyl free radicals. These investigations seem to indicate that pseudohypoxia due to hyperglycaemia can inhibit the activity of glucose 6-phosphatase both by lipid peroxidation and by inducing hydrogen peroxide and/or hydroxyl free radicals and thus it may play a part in the glucose-induced decrease of hepatic glucose output.