Effect of insulin on the metabolism of L-ascorbic acid in animals

Effect of Mucuna pruriens (Linn.) on mitochondrial dysfunction and DNA damage in epididymal sperm of streptozotocin induced diabetic rat

ETHNOPHARMACOLOGICAL RELEVANCE

Mucuna pruriens Linn. (M. pruriens) is a leguminous plant that has been recognized as an herbal medicine for improving fertility and related disorders in the Indian traditional system of medicine, however without proper scientific validations.

AIM OF THE STUDY

To study the effect of ethanolic seed extract of M. pruriens on mitochondrial dysfunction and the DNA damage in hyperglycemic rat epididymal spermatozoa.

MATERIALS AND METHODS

Male Wistar albino rats were divided as control (Sham), diabetes induced [streptozotocin 60 mg/kg of body weight (b.w.) in 0.1M citrate buffer] (STZ), diabetic rats administered with 200mg/kg b.w. of extract (STZ+MP) and normal rats administered with 200mg/kg b.w. of extract (Sham+MP). M. pruriens was administered (gavage) once daily for a period of 60 days. On 60th day animals were sacrificed by cervical dislocation sperm were collected from epididymis and subjected various analysis like antioxidants, ROS, lipid peroxidation (LPO), DNA damage, chromosomal integrity and mitochondrial membrane potential (MMP).

RESULTS

Significant reduction in the sperm count, motility, viability and significant increase in the number of abnormal sperm in STZ compared to sham was noticed. STZ rat sperm showed significant increase in LPO and DNA damage. Both the enzymic and non-enzymic were decreased; MMP and the mitochondrial functions were severely affected in STZ group. The diabetic rats supplemented with M. pruriens showed a remarkable recovery in antioxidant levels and reduced LPO with well preserved sperm DNA. MMP and mitochondrial function test were also preserved in STZ+MP rat sperm.

CONCLUSION

The present study has clearly demonstrated the potency of M. pruriens to reduce the diabetic induced sperm damage induced by oxidative stress (OS). These observations are encouraging to perform similar studies in human.

Effect of Mucuna pruriens (Linn.) on oxidative stress-induced structural alteration of corpus cavernosum in streptozotocin-induced diabetic rat

INTRODUCTION

Erectile dysfunction is one of the major secondary complications of diabetes. Mucuna pruriens (M. pruriens), a leguminous plant identified for its antidiabetic, aphrodisiac, and fertility enhancing properties, has been the choice of Indian traditional medicine.

AIM

The objective of the present study was to analyze the efficacy of M. pruriens on free radicals-mediated penile tissue alterations in hyperglycemic male rats. Methods.  Male albino rats were divided as group I (sham) control, group II (STZ) diabetes-induced (streptozotocin 60 mg/kg of body weight [bw] in 0.1 M citrate buffer), group III (STZ + MP) diabetic rats administered with 200 mg/kg bw of ethanolic extract of M. pruriens seed, group IV (STZ + SIL) diabetic rats administered with 5 mg/kg bw of sildenafil citrate, group V (sham + MP) administered with 200 mg/kg bw of extract alone, and group VI (sham + SIL) administered with 5 mg/kg bw of sildenafil citrate. The M. pruriens and sildenafil citrate were given (gavage) once daily for a period of 60 days. At the end of 60 days, the animals were sacrificed and subjected to analysis of reactive oxygen species levels, enzymic and nonenzymic antioxidant levels, levels of NOx, histological, and histomorphometrical study of penile tissue.

MAIN OUTCOME MEASURES

Remedial use of M. pruriens seed extract on diabetes-induced erectile tissue damage.

RESULTS

Significantly high levels of oxidative stress and low levels of antioxidants in the penile tissue seem to contribute to the increased collagen deposition and fibrosis of erectile tissue in STZ rats. Relatively, there was increased damage in STZ + SIL group. Supplementation of M. pruriens in STZ + MP group has revealed the potency to overcome oxidative stress, and good preservation of penile histoarchitecture.

CONCLUSION

 The ethanolic extract of M. pruriens seed significantly recovered or protected erectile tissue from the oxidative stress-induced degeneration by its antioxidant potentials. These findings propound to serve mankind by the treatment of diabetes-induced erectile dysfunction.

Dynamic aspects of ascorbic acid metabolism in the circulation: analysis by ascorbate oxidase with a prolonged in vivo half-life

Because AA (L-ascorbic acid) scavenges various types of free radicals to form MDAA (monodehydroascorbic acid) and DAA (dehydroascorbic acid), its regeneration from the oxidized metabolites is critically important for humans and other animals that lack the ability to synthesize this antioxidant. To study the dynamic aspects of AA metabolism in the circulation, a long acting AOase (ascorbate oxidase) derivative was synthesized by covalently linking PEG [poly(ethylene glycol)] to the enzyme. Fairly low concentrations of the modified enzyme (PEG-AOase) rapidly decreased AA levels in isolated fresh plasma and blood samples with a concomitant increase in their levels of MDAA and DAA. In contrast, relatively high doses of PEG-AOase were required to decrease the circulating plasma AA levels of both normal rats and ODS (osteogenic disorder Shionogi) rats that lack the ability to synthesize AA. Administration of 50 units of PEG-AOase/kg of body weight rapidly decreased AA levels in plasma and the kidney without affecting the levels in other tissues, such as the liver, brain, lung, adrenal grand and skeletal muscles. PEG-AOase slightly, but significantly, decreased glutathione (GSH) levels in the liver without affecting those in other tissues. Suppression of hepatic synthesis of GSH by administration of BSO [L-buthionin-(S,R)-sulfoximine] enhanced the PEG-AOase-induced decrease in plasma AA levels. These and other results suggest that the circulating AA is reductively regenerated from MDAA extremely rapidly and that hepatic GSH plays important roles in the regeneration of this antioxidant.

Tissue-specific effect of ascorbic acid supplementation on the expression of cytochrome P450 2E1 and oxidative stress in streptozotocin-induced diabetic rats

Here, we investigated the effect of l-ascorbic acid (AA) supplementation on the CYP2E1 expression level and oxidative stress in various tissues such as the liver, kidney, pancreas, and brain of streptozotocin (STZ)-induced diabetic rats. An increased cytochrome P450 2E1 (CYP2E1) expression level with a concomitant increase in the production of reactive oxygen species were found in all the tissues of STZ-induced diabetic rats tested compared with an untreated control, suggesting the possible diabetes-induced tissue injury. In contrast, the AA supplementation to the diabetic rats alleviated these experimental parameters in a tissue-specific manner. AA affected the liver most severely followed by the kidney. There was little or no effect of AA supplementation on the brain and pancreas. The circulation level of the ketone bodies, inducers of CYP2E1, was also decreased by AA supplementation compared with those of the diabetic rats. Therefore, the suppression of ketone production by AA can be one of the mechanisms of a reduction in CYP2E1. These results suggest that AA plays an important role in reducing elevated CYP2E1 expression level and the oxidative stress mediated by type 1 diabetes with a tissue-specific variation.

Impaired ascorbic acid metabolism in streptozotocin-induced diabetic rats

Ascorbic acid (AA) metabolism in streptozotocin (STZ)-induced diabetic rats was determined by examining urinary excretion, renal reabsorption, reductive regeneration, and biosynthesis of AA at 3 and 14 days after STZ administration. AA concentrations in the plasma, liver, and kidney of the diabetic rats were significantly lower than those of controls on d 3, and decreased further as the diabetic state continued. Hepatic AA regeneration significantly decreased in the diabetic rats on d 3 in spite of increased gene expressions of AA regenerating enzymes and was further reduced on d 14. Hepatic activity of L-gulono-gamma-lactone oxidase, a terminal enzyme of hepatic AA biosynthesis, also decreased significantly on d 3 and decreased further on d 14. Urinary excretion of AA was significantly increased on d 3, with an increase in urine volume but no change in gene expressions of renal AA transporters (SVCT1 and SVCT2). Urinary excretion of AA was normalized on d 14. The results suggest that impaired hepatic and renal regeneration, as well as increased urinary excretion and impaired hepatic biosynthesis of AA, contributed to the decrease in AA in plasma and tissues of STZ-induced diabetic rats.

Ascorbic acid clearance in diabetic nephropathy

The incidence of cardiovascular disease is increased in diabetic nephropathy. Increased oxidative stress in diabetes is believed to play an important role in the pathogenesis of atherosclerosis in diabetes. Since antioxidant vitamins, such as ascorbic acid, often are reduced in diabetes, we hypothesized that the renal clearance of ascorbic acid is increased in patients with diabetic nephropathy. Thirty-seven subjects with diabetic nephropathy were studies: 18 had microalbuminuria (30-300 mg/day albuminuria); the remainder had clinical nephropathy (> 300 mg/day albuminuria). Indices of glycemic control (glucose, hemoglobin A1C) and renal function (albuminuria and creatinine clearance) were measured in addition to serum and urinary ascorbic acid levels. Results showed that subjects with clinical nephropathy had lower mean plasma ascorbic acid (p=0.0009) and higher renal clearance of ascorbic acid (p=0.005) than those with microalbuminuria. Bivariate analysis revealed an inverse correlation between creatinine clearance and AA clearance (r=-0.42, p=0.009). There was a significant linear association between the quantity of albuminuria and ascorbic acid clearance (r=0.49, p=0.002). Thus, patients with diabetic nephropathy have reduced ascorbic acid levels due to increased ascorbic acid clearance. The decrease in antioxidant defense that arises from the low levels of vitamin C may contribute to the increased cardiovascular morbidity and mortality observed in this population.

Changes in ascorbic acid metabolism of the offspring following high maternal intake of this vitamin in the pregnant guinea pig

Guinea pigs were fed a control (0.05%) or a high (0.5%) ascorbic acid diet during the last half of pregnancy. When the pups were tested at 5 and 10 days of life the ones from the high-ascorbic-acid group demonstrated a marked increase in 14CO2 excretion, compared with the control pups, following an intraperitoneal injection of 14C-labeled ascorbic acid. When the animals were weaned to an ascorbic-acid-deficient diet signs of scurvy appeared earlier in the pups from the high vitamin C group and their survival was shorter. When excretion of labeled CO2 in both groups was correlated with the day of onset of scurvy signs, a linear correlation was found between these two parameters, suggesting that the earlier appearance of signs of scurvy in the experimental pups is secondary to an increased rate of ascorbic acid catabolism.