G. Pradeep Kumar

Changes in the levels of superoxide anion radical and superoxide dismutase during the estrous cycle of Rattusnorvegicus and induction of superoxide dismutase in rat ovary by lutropin

Superoxide dismutase, which has been shown to be present in a number of tissues, exhibits cyclic changes during the reproductive cycle of rats. An inverse correlation is seen between the levels of superoxide dismutase and superoxide radical. In immature, pseudopregnant rats, primed with human Chorionic Gonadotropin, lutropin seemed to induce ovarian superoxide dismutase, which could be blocked significantly by the introduction of anti-LH serum. These results point out the specific induction of superoxide dismutase by lutropin. It is reasonable to postulate that during luteal functioning, luteinizing hormone induces superoxide dismutase which in turn seems to play a central role generating hydrogen peroxide from superoxide anion radicals. Hydrogen peroxide, thus formed, drives the peroxidase-ascorbate system, responsible for production of progesterone.

Superoxide dismutase as a regulatory switch in mammalian testicular steroidogenesis

The delta 4-pathway of testosterone biosynthesis in leydig cells, widely believed to proceed through pregnenolone--greater than pregnenedione--greater than progesterone route catalyzed by 5 delta-3 beta-hydroxysteroid dehydrogenase and delta 5-delta 4-isomerase respectively is shown to pass through an alternate pathway mediated by superoxide dismutase and peroxidase. A built-in regulatory switch is incorporated in this route, with the superoxide dismutase inducible upon LH-stimulation of the leydig cells.

Over-expression of superoxide dismutase and lack of surface-thiols in spermatozoa: Inherent defects in oligospermia

The infertility associated with oligospermia had been suspected to be a direct consequence of the impairment in fertilizing ability of the spermatozoa rather than the presence of low sperm number per se. This study defines some of these impairments, which include an over expression of superoxide dismutase, poor superoxide anion radical generation capacity and a lack of sperm-surface thiols in oligospermia. The abnormal biochemical make-up of spermatozoa could explain their low fertilizing ability in case of oligospermia.

NADPH dependent superoxide generation in the ovary and uterus of mice during estrous cycle and early pregnancy.

NADPH dependent O2- production in the ovary and uterus of cycling and pregnant mice was estimated employing a novel technique of time-lapse electron spin resonance enhancement of a superoxide-trapping spin trap. The NADPH dependent O2- generation in the mouse ovary increased during the early pre-ovulatory phase in cycling females and during extended luteal phase in pregnant animals. A peak of uterine NADPH dependent O2- production at proestrous in the cycling animals at pre-implantation phase in pregnant animals suggested a contribution of this enzyme towards generating high levels of superoxide anion radical during the respective stages. Both ovarian and uterine NADPH dependent O2- production appeared to be LH-inducible.

The involvement of surface sugars of mammalian spermatozoa in epididymal maturation and in vitro sperm-zona recognition: Die Beteiligung von Oberflächen-Zuckern von Säuger-Spermatozoen auf die Nebenhodenreifung und die in vitro Spermatozoen-Zona-Erkennung

Summary:  The distribution of various simple sugar residues over the spermatozoa surfaces of five different mammalian species is characterized and compared. Epididymal maturation of the spermatozoa of all the five species studied exhibited an increase in the amount of N‐acetyl‐D‐glucosamine residues over their acrosomal domains. A complete blockade of sperm‐zona pellucida attachment of hamster gametes could be brought about when spermatozoa were treated previously with 0.1 M of N‐acetyl‐D‐glucosamine. This sugar seems to be specifically involved in sperm‐zona pellucida attachment in hamsters. The inter‐specific cross‐reactivity of gametes of laboratory mammals like rat, mouse, rabbit and hamster could, quite likely, be because of the involvement of N‐acetyl‐D‐glucosamine as a common factor in this reaction in these animals.

Powerful anti-sperm motility action of cobaltous ion and its recovery by a sulfhydryl compound

Cobaltous ion, at extremely low concentrations, exercises powerful sperm-immobilizing properties, which could be recovered by a sulfhydryl compound, cysteine. The loss of sperm surface thiol groups and the augmented production of superoxide anion radicals are observed, which could explain the loss of motility of human spermatozoa in vitro as a consequence of cobalt treatment.

Activation of iodine into a free-radical intermediate by superoxide: A physiologically significant step in the iodination of tyrosine

A pivotal biochemical event in the thyroid physiology is identified unravelling a superoxide anion radical-mediated activation of iodine into an active I.- form, which could be the intermediate that is incorporated onto tyrosine. This active iodine species gives fairly stable spin-adducts with PBN that could be characterized using EPR spectroscopy. Thus, a long-lasting puzzle regarding the iodine intermediate formed before iodination of tyrosine seems to be solved.

Altered molecular dynamics and antioxidant status in the spermatozoa in testosterone-induced oligospermia in mouse.

Though supraphysiological doses testosterone (T) and its derivatives are known to suppress spermatogenesis in mammals by interfering with the hypothalamus‐pituitary axis leading to oligozoospermia, no study has been performed to evaluate the integrity of the sperm cells produced by such individuals. In T‐induced oligozoospermia in the mouse, the spermatozoa showed suppressed zona‐binding ability though the motility and viability remained unchanged. In order to assess whether this decreased zona‐binding ability is due to perturbations in the mechanical properties of the sperm membranes, we attempted to examine the molecular dynamics employing a lipophilic spin label (16‐doxyl stearate) and a protein‐binding label (Mal‐Net) in two sets of independent experiments. The results showed that the rotational freedom of lipophilic molecules reduced significantly within the first week of T‐treatment. During weeks 1 through 4, the protein rotation was found to be retarded significantly. We observed a sharp increase in the ascorbyl radical associated with the cauda epididymal spermatozoa and epididymal fluid of testosterone‐treated mice. Moreover, the glutathione (GSH) content in the spermatozoa and the epididymal fluid increased significantly after testosterone‐treatment. Further, there was a elevation in the superoxide dismutase (SOD) activity and suppression in the superoxide anion radical generated by the cauda epididymal spermatozoa of testosterone‐treated animals.

Starvation induced hypothyroidism involves perturbations in thyroid superoxide-sod system in pigeons

This study investigated the influence of starvation over seven days on avian thyroidal superoxide radical levels and superoxide dismutase activity profiles in the Indian rock pigeon Columba fivia intermeida, in relation with iodine metabolism. The serum thyroid hormone profile was assayed to correlate the thyroidal redox status with the circulating thyroid hormone levels. The spin‐trapping results suggest a role for thyroidal superoxide anion (O2‐) in causing a hypothyroid state in pigeons during long term energy withdrawal. Pigeons starved for 1 day generated superoxide and iodide free radicals in their thyroids, with a significant decrease in SOD activity. Regain of SOD activity in 2nd‐ and 3rd‐day starved birds is marked by complete scavenging of radicals in the thyroid, suggesting the significance of SOD in thyroid glands as a potential antioxidant sink against reactive oxygen species, O2‐. Resurgence of 02‐ radicals with a parallel decrease in SOD activity in the thyroid gland on 5th‐ and 7th‐day of starvation provides evidence of disruption of homeostasis between pro‐oxidant and antioxidant states, leading to oxidative stress in avian thyroid during long‐term calorie crisis. Following starvation both thyroid hormones thyroxine (T4) and triiodothyronine (T3) decreased, putting pigeons in a hypothyroidstate. We argue that oxidative inactivation of thyroid peroxidase and other thyroid proteins by radical attack during starvation invoked oxidative stress, which could be one of the factors responsible for the hypothyroid state in pigeons.

Effect of ultraviolet activated alfa-terthienyl upon anal gill membrane of mosquito larvae: a spin label study

Abstract The mode of interaction of the plant-derived phototoxic insecticide alfa-terthienyl was examined in larvae of the mosquito Aedes aegypti , using spin-labelling and electron paramagnetic resonance (EPR) spectral techniques. Spin-labels 16-doxyl stearate and TEMPO were used to probe the lipid and aqueous fractions of the gill membrane. Exposure of mosquito larvae to alfa-terthienyl and ultraviolet light resulted in loss of membrane integrity, damaging the lipid and aqueous components of the gill membrane. The potential role of singlet oxygen in mediating this alfa-terthienyl phototoxicity is discussed.