Hypoglycemic drugs induce antioxidant aldehyde dehydrogenase activity and remain high in patients with glycemic control in type 2 diabetes

Altered oxidant and antioxidant levels are associated with vascular stiffness and diabetic kidney disease in type 1 diabetes after exposure to acute and chronic hyperglycemia

BACKGROUND

Hyperglycemia-induced oxidative stress is a well-established pathological mediator of vascular complications in diabetes. We assessed plasma oxidant and antioxidant levels in response to acute and chronic hyperglycemia in relation to vascular stiffness and varying degrees of kidney disease in type 1 diabetes individuals.

METHODS

The acute hyperglycemia study included 22 type 1 diabetic individuals with normal albumin excretion rate (AER) and 13 non-diabetic controls. These individuals received an acute glucose challenge during a 120-minute hyperglycemic clamp. The chronic hyperglycemia study included 118 type 1 diabetic individuals with chronically low (n = 60) or high (n = 58) HbA1c concentrations and varying degrees of diabetic kidney disease (DKD) classified as normal, moderate, or severe albuminuria (AER). Levels of malondialdehyde (MDA), reactive oxygen metabolites (ROMs), total antioxidant capacity (TAC), biological antioxidant potential (BAP) and superoxide dismutase (SOD) were measured from plasma or serum samples in the FinnDiane study.

RESULTS

Levels of MDA (p < 0.01) and ROMs (p < 0.01) were elevated in type 1 diabetes individuals compared to non-diabetic controls at baseline. Acute hyperglycemia further increased MDA levels (p < 0.05) and sustained the elevation of ROMs in type 1 diabetes individuals. Acute hyperglycemic challenge impaired TAC in both non-diabetic (p < 0.05) and type 1 diabetes (p < 0.01) individuals compared to baseline whereas BAP was increased (p < 0.05) with no difference observed in non-diabetic controls. There was a positive association between high circulating MDA and AIx (r2 = 0.611, p = 0.05), and between delta ROMs and delta AIx (r2 = 0.955, p = 0.014) in combined analysis of individuals with type 1 diabetes and non-diabetic controls. Type 1 diabetes individuals with varying status of DKD, showed elevated levels of ROMs in those with high HbA1c compared to their counterpart with low HbA1c (p < 0.05). Individuals with severe albuminuria showed elevated ROM levels (p < 0.01) and depressed antioxidant capacity (p < 0.01) compared to those with normal AER of comparable HbA1c concentrations.

CONCLUSIONS

Biomarkers of oxidative stress are associated with vascular stiffness and DKD following acute and chronic hyperglycemic exposure and may provide added value to HbA1c in understanding disease pathology, predicting risk and assessing the status of secondary complications of type 1 diabetes.

Hypoglycemic effect of the dry leaf extract of Myrcia multiflora in streptozotocin-induced diabetic mice

ETHNOPHARMACOLOGICAL RELEVANCE

Myrcia multiflora (Lam) DC. is a medicinal plant used in folk medicine for diabetes control, mainly in the Brazilian Amazon. The leaves of this species has already demonstrated antidiabetic properties; however, in mice with type 2 diabetes (DM2), the cumulative effect of the consumption of the dry extract of M. multiflora leaves (Mm) has not yet been reported.

AIM OF THE STUDY

To investigate the effect of the dry extract obtained from the infusion of the dried leaves of M. multiflora on the blood glucose levels of diabetic mice.

MATERIALS AND METHODS

DM2 was induced in Swiss male mice by a single intraperitoneal injection of streptozotocin [150 mg/kg body weight (bw)]. The animals were divided into two control groups (healthy and diabetic without treatment) and three sample groups that received Mm (25 and 50 mg/kg bw) and acarbose (200 mg/kg bw) by gavage once daily for 28 days (D28). Additionally, biochemical parameters, thiobarbituric acid reactive species (TBARS) levels in the liver, and histopathological analyses of the kidneys and liver were performed.

RESULTS

On the seventh day of treatment, a 74.7% reduction in glucose levels were observed in the group of diabetic animals treated with Mm (50 mg/kg bw) when compared to the beginning of the treatment. At D28, the hypoglycemic effect was maintained. The results of the biochemical and histopathological parameters and the TBARS levels suggest that this dry extract exerts nephro- and hepatoprotective effects.

CONCLUSIONS

The findings demonstrate the potential that this extract has to inhibit the α-glucosidase enzyme, and it acts similarly to the positive control acarbose. Furthermore, this extract is nephro- and hepatoprotective. Therefore, this dry extract has the potential to be an adjuvant for DM2, which corroborates its use in folk medicine.

Hypoglycemic effect and toxicity of the dry extract of Eugenia biflora (L.) DC. leaves

ETHNOPHARMACOLOGICAL RELEVANCE

The leaves of Eugenia biflora (Myrtaceae) are traditionally used by Amazonian populations for the control of diabetes. However, their chemical composition has not yet been described and pharmacological evidence has not been reported.

OBJECTIVE

This study aimed to identify the chemical constituents and evaluate the hypoglycemic and toxic effect of the dry extract of the E. biflora leaves (DEEB).

MATERIALS AND METHODS

DEEB, obtained by infusion, was analyzed using LC-HRMS and NMR, whose the catechin flavonoid was quantified using NMR. The antidiabetic effect of DEEB was evaluated according to its inhibition of the enzymes α-amylase and α-glucosidase, as well as the content of total phenols, free radical scavengingand antiglycation activities, and its in vitro cell viability. Oral maltose tolerance and chronic multiple dose tests (28 days) in streptozotocin-induced diabetic mice (STZ) were performed. The hypoglycemic effect and toxicity of this extract were evaluated in the multiple dose assay. Biochemical parameters, hemolysis, and levels of the thiobarbituric acid reactive species in the liver were investigated and histopathological analyses of the kidneys and liver were performed.

RESULTS

Eight phenolic compounds were identified, with catechin (15.5 ± 1.7 mg g-1) being the majority compound and a possible chemical marker of DEEB. The extract showed inhibition activity of the enzyme α-glucosidase. Chronic administration of DEEB (50 mg/kg of body weight) reduced glucose levels in diabetic animals, similar to acarbose; however, DEEB (100 and 200 mg/kg bw) caused premature death of mice by D22 of the treatment. Our data indicate that one of the mechanisms of toxicity in DEEB may be related to the aggravation of oxidative stress in the liver. This histopathological study indicated that DEEB failed to minimize the progression of the toxicity of diabetes caused by STZ.

CONCLUSIONS

This study demonstrated the hypoglycemic potential of E. biflora leaves. However, the prolonged use of this tea can be harmful to its users due to its considerable toxicity, which needs to be better investigated.

Circadian variation in renal blood flow and kidney function in healthy volunteers monitored with noninvasive magnetic resonance imaging

Circadian regulation of kidney function is involved in maintaining whole body homeostasis, and dysfunctional circadian rhythm can potentially be involved in disease development. Magnetic resonance imaging (MRI) provides reliable and reproducible repetitive estimates of kidney function noninvasively without the risk of adverse events associated with contrast agents and ionizing radiation. The purpose of this study was to estimate circadian variations in kidney function in healthy human subjects with MRI and to relate the findings to urinary excretions of electrolytes and markers of kidney function. Phase-contrast imaging, arterial spin labeling, and blood oxygen level-dependent transverse relaxation rate (R₂*) mapping were used to assess total renal blood flow and regional perfusion as well as intrarenal oxygenation in eight female and eight male healthy volunteers every fourth hour during a 24-h period. Parallel with MRI scans, standard urinary and plasma parameters were quantified. Significant circadian variations of total renal blood flow were found over 24 h, with increasing flow from noon to midnight and decreasing flow during the night. In contrast, no circadian variation in intrarenal oxygenation was detected. Urinary excretions of electrolytes, osmotically active particles, creatinine, and urea all displayed circadian variations, peaking during the afternoon and evening hours. In conclusion, total renal blood flow and kidney function, as estimated from excretion of electrolytes and waste products, display profound circadian variations, whereas intrarenal oxygenation displays significantly less circadian variation.

Synthesis and inhibition of α-glucosidase of methyl glycyrrhetinate glycosides

The synthesis of the methyl glycyrrhetinate glycosides and inhibition of α-glucosidase were studied. The carboxyl group of glycyrrhetinic acid was methylated, and glucose and galactose were introduced into the hydroxyl group to obtain compounds 7 and 12. Compound 1, 2, 7, 12 and glycyrrhizic acid (GL) were evaluated for their inhibitory activities against α-glucosidase. As a result, Compound 1, 2, 7, 12 and GL all showed significant α-glucosidase inhibitory activity and IC₅₀ values were 0.465, 1.352, 0.759, 0.687 and 2.085 mM, respectively, and acted as non-competitive inhibitors. The activity of the compound 2, 7, 12 was lower than compound 1, but significantly higher than GL. Therefore, it was concluded that the change of structure in glycyrrhetinic acid by chemical modification had certain effect on bioactivity, and the change of carboxyl group, hydroxyl group and the type of monosaccharide introduced were the influencing factors.