Inhibition of the oxidation of hydroxyl radical scavenging agents after alkaline phosphatase treatment of rat liver microsomes

Prenatal exposure to excess chromium attenuates transcription factors regulating expression of androgen and follicle stimulating hormone receptors in Sertoli cells of prepuberal rats

We have reported that gestational exposure to hexavalent chromium (CrVI) represses androgen receptor (Ar) and follicle stimulating hormone receptor (Fshr) in Sertoli cells (SCs) of adult rats, while the mechanism underlying remains obscure. We tested the hypothesis "transient gestational exposure to CrVI during the critical embryonic windows of testicular differentiation and growth may have adverse impact on transcription factors controlling the expression of Ar and Fshr in SCs of the F₁ progeny". CrVI (K₂Cr₂O₇) was given through drinking water (50 ppm, 100 ppm and 200 ppm), to pregnant rats from gestational day 9-14 (testicular differentiation) and 15 to 21 (prenatal differentiation and proliferation of SC); male progenies were sacrificed on postnatal day 30 (Completion of postnatal SC maturation). A significant increase in free radicals and decrease in enzymatic and non-enzymatic antioxidants were observed in SCs of experimental rats. Real time PCR and western blot data showed decreased expression of Ar, Fshr, Inhibin B, Transferrin, Androgen binding protein, Claudin 11 and Occludin in SCs of experimental rats; concentrations of lactate, pyruvate and retinoic acid also decreased. Serum FSH, luteinizing hormone and estradiol increased, whereas testosterone and prolactin decreased in experimental rats. Western blot detection revealed decreased levels of transcription factors regulating Fshr viz., USF-1, USF-2, SF-1, c-fos, c-jun and GATA 1, and those of Ar viz., Sp-1, ARA54, SRC-1 and CBP in experimental rats, whereas the levels of cyclinD1 and p53, repressors of Ar increased. ChIP assay detected decreased USF-1 and USF-2 binding to Fshr promoter, and binding of Sp-1 to Ar promoter. We conclude that gestational exposure to CrVI affects SC structure and function in F₁ progeny by inducing oxidative stress and diminishing the expression of Ar and Fshr through attenuation of their specific transcriptional regulators and their interaction with the respective promoter.

Male reproductive toxicity of CrVI: In-utero exposure to CrVI at the critical window of testis differentiation represses the expression of Sertoli cell tight junction proteins and hormone receptors in adult F1 progeny rats

The effect of gestational exposure to CrVI (occupational/environmental pollutant and target to Sertoli cells(SC)) was tested in a rat model during the testicular differentiation from the bipotential gonad may interrupt spermatogenesis by disrupting SC tight junctions(TJ) and it's proteins and hormone receptors. Pregnant Wistar rats were exposed to 50/100/200ppm CrVI through drinking water during embryonic days 9-14. On Postnatal day 120, testes were subjected to ion exchange chromatographic analysis and revealed increased level of CrIII in SCs and germ cells, serum and testicular interstitial fluid(TIF). Microscopic analyses showed seminiferous tubules atrophy and disruption of SC TJ, which also recorded decreased testosterone in TIF. mRNA and Protein expression analyses attested decreased level of Fshr, Ar, occludin and claudin-11 in SCs. Immunofluorescent detection revealed weak signal of TJ proteins. Taken together, we concluded that gestational exposure to CrVI interferes with the expression of SC TJ proteins due to attenuated expression of hormone receptors.

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.

Enzymatic reduction of labile iron by organelles of the rat liver. Superior role of an NADH-dependent activity in the outer mitochondrial membrane

The enzymatic system mainly responsible for the reduction of labile iron ions in mammalian cells is still unknown. Using isolated organelles of the rat liver, i.e. mitochondria, microsomes, nuclei and the cytosol, we here demonstrate that Fe(III), added as Fe(III)-ATP complex, is predominantly reduced by an NADH-dependent enzyme system associated with mitochondria (65% of the overall enzymatic Fe(III) reduction capacity within liver cells). Microsomes showed a significantly smaller Fe(III) reduction capacity, whereas the cytosol and nuclei hardly reduced Fe(III). Studying the mitochondrial iron reduction, this NADH-dependent process was not mediated by superoxide, ascorbic acid, or NADH itself, excluding low-molecular-weight reductants. No evidence was found for the involvement of complex I and III of the respiratory chain. Submitochondrial preparations revealed the highest specific activity reducing Fe(III) in the outer membrane fraction. In conclusion, an NADH-dependent mitochondrial enzyme system, most likely the NADH-cytochrome c reductase system, located at the outer membrane, should decisively contribute to the enzymatic reduction of labile iron within liver cells, especially under pathological conditions.

Inhibition studies on the involvement of flavoprotein reductases in menadione- and nitrofurantoin-stimulated oxyradical production by hepatic microsomes of flounder (Platichthys flesus)

Inhibitors of mammalian cytochrome P450 and P450 reductase were used to investigate the enzymes in flounder (Platichthys flesus) hepatic microsomes involved in the stimulation of NAD(P)H-dependent iron/EDTA-mediated 2-keto-4-methiolbutyric acid (KMBA) oxidation (hydroxyl radical production) by the redox cycling compounds menadione and nitrofurantoin. Inhibitors were first tested for their effects on flounder microsomal P450 and flavoprotein reductase activities. Ellipticine gave type II difference binding spectra (app. Ks 5.36 microM; delta A max 0.16 nmol-1 P450) and markedly inhibited NADPH-cytochrome c reductase, NADPH-cytochrome P450 reductase, and monooxygenase (benzo[a]pyrene metabolism) activities. 3-aminopyridine adenine dinucleotide phosphate (AADP; competitive inhibitor of P450 reductase) inhibited NADPH-cytochrome c but not NADH-cytochrome c or NADH-ferricyanide reductase activities. Alkaline phosphatase (inhibitor of rabbit P450 reductase) stimulated NADPH-cytochrome c reductase activity seven fold but had less effect on NADH-reductase activities. AADP inhibited nitrofurantoin- and menadione-stimulated KMBA oxidation by 45 and 17%, respectively, indicating the involvement of P450 reductase at least in the former. In contrast, ellipticine had relatively little effect, possibly because, unlike cytochrome c, the smaller xenobiotic molecules can access the hydrophilic binding site of P450 reductase. Alkaline phosphatase stimulated NAD(P)H-dependent basal and xenobiotic-stimulated KMBA oxidation, showing general consistency with the results for reductase activities. Overall, the studies indicate both similarities (ellipticine, AADP) and differences (alkaline phosphatase) between the flounder and rat hepatic microsomal enzyme systems.

Alpha-oxidation of 3-methyl-substituted fatty acids in rat liver

3-Methyl-substituted fatty acids are first oxidatively decarboxylated (alpha-oxidation) before they are degraded further via beta-oxidation. We synthesized [1-14C]phytanic and 3-[1-14C]methylmargaric acids in order to study their alpha-oxidation in isolated rat hepatocytes, rat liver homogenates and subcellular fractions. alpha-Oxidation was measured as the production of radioactive CO2. In isolated hepatocytes, maximal rates of alpha-oxidation amounted to 7 and 10 nmol/min x 10(8) cells with phytanic acid and 3-methylmargaric acid, respectively. At equimolar substrate concentrations, alpha-oxidation of branched fatty acids was approximately 10- to 15-fold slower than the beta-oxidation of the straight chain palmitate. In whole liver homogenates, rates of alpha-oxidation that equaled 60 to 70% of those observed in the hepatocytes were obtained. Optimum rates required O2, NADPH, Fe3+, and ATP. Fe3+ could be replaced by Fe2+ and ATP could be replaced by a number of other phosphorylated nucleosides and even inorganic phosphate without loss of activity. NADH could substitute for NADPH but not always with full restoration of activity. A variety of other cofactors and metal ions was either inhibitory or without effect. Scavengers of reactive oxygen species, known to be formed during the NADPH-dependent microsomal reduction of ferric-phosphate complexes, were without effect on alpha-oxidation. No evidence was found for the accumulation of NADPH-dependent or Fe(3+)-dependent reaction intermediates. Subcellular fractionation of liver homogenates demonstrated that alpha-oxidation was located predominantly, if not exclusively, in the endoplasmic reticulum. alpha-Oxidation, measured in microsomal fractions, was not inhibited by CO, cytochrome c, or ferricyanide, indicating that NADPH cytochrome P450 reductase and cytochrome P450 are not involved in alpha-oxidation. Our results indicate that, contrary to current belief, alpha-oxidation is catalyzed by the endoplasmic reticulum. The cofactor requirements suggest that alpha-oxidation involves the reduction of Fe3+ by electrons from NADPH and that it is stimulated by phosphate ions and nucleotides.