Cadmium induced oxidative damage and apoptosis in the hepatopancreas of <Emphasis Type="Italic">Meretrix meretrix</Emphasis>

Even trace amounts of cadmium (Cd), a non-essential metal, are known to be toxic to aquatic organisms. Here we investigated the relationship between cadmium ion (Cd²⁺) exposure and oxidative damage and apoptosis in the hepatopancreas of the clam Meretrix meretrix. Clams were exposed to different concentrations of Cd²⁺ (0, 1.5, 3, 6 and 12 mg L^?1) for 5 days. We monitored both antioxidant enzyme activity, including that of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidases (GPx), and levels of malondialdehyde (MDA), glutathione (GSH) and glutathione disulfide (GSSG). Apoptosis of hepatopancreatic cells was detected by DNA laddering and AO/EB double fluorescent staining. The results show that the rate of apoptotis, MDA levels, and caspase-3 activity, increased with Cd²⁺ concentration, whereas GPx activity and the ratio of GSH/GSSG, decreased. SOD and CAT enzyme activity first increased, then decreased, with increasing Cd²⁺ concentration; peak activity of these enzymes was recorded in the 3 mg L^?1 Cd²⁺-treatment group. These results show that Cd-induced oxidative damage can both induce, and aggravate, apoptosis in the hepatopancreatic cells of clams, even at Cd²⁺ concentrations far below the semi-lethal dose for adult clams. The observed changes in caspase-3 activity enhanced significantly at lower Cd²⁺ concentrations, indicating that caspase-3 is a suitable biomarker for heavy metal pollution, especially cadmium pollution, in marine organisms.     

New insights into the Ca2+-ATPases that contribute to cadmium tolerance in yeast

Cadmium (Cd²⁺) is a toxic heavy metal which triggers several toxic effects in eukaryotes, including neurotoxicity and impaired calcium metabolism. In the model organism Saccharomyces cerevisiae, the best characterized pathway for Cd²⁺ detoxification involves conjugation with glutathione (GSH) and subsequent transport to vacuoles by Ycf1p, an ATPase homologous to human MRP1 (Multidrug resistance associated protein 1). However, Cd²⁺ tolerance also can be mediated by Pmr1p, a Ca²⁺ pump located in the Golgi membrane, possibly through to the secretory pathway. Herein, we showed that inactivation of the PMR1 gene, alone or simultaneously with YCF1, delayed initial Cd²⁺ capture compared to wild-type (WT) cells. In addition, Cd²⁺ treatment altered the expression profile of yeast internal Ca²⁺ transporters; specifically, PMC1 gene expression is induced substantially by the metal in WT cells, and this induction is stronger in mutants lacking YCF1. Taken together, these results indicate that, in addition to Pmr1p, the vacuolar Ca²⁺-ATPase Pmc1p also helps yeast cells cope with Cd²⁺ toxicity. We propose a model where Pmc1p and Pmr1p Ca²⁺-ATPase function in cooperation with Ycf1p to promote Cd²⁺ detoxification.     

The effect of salinity on cadmium toxicity to the estuarine mysid Mysidopsis bahia: role of chemical speciation

The effect of salinity on the toxicity of cadmium to the bay mysid, Mysidopsis bahia Molenock, was studied. When toxicity was expressed in terms of free cadmium ion (Cd²⁺) rather than total cadmium (Cd_T), CdCl⁺ or CdCl₂ only a slight salinity effect was apparent, suggesting that Cd²⁺ is the primary toxic species. Mysids were more tolerant of Cd²⁺ at an intermediate salinity of 22‰ and less tolerant at low and high salinity extremes (6 and 38‰). Alteration of cadmium speciation by use of an artificial ligand, nitrilotriacetic acid (NTA), over a range of salinities (14–34‰) produced conflicting results. Toxicity of Cd²⁺ was independent of Cd_T concentration at a given salinity but increased with increasing salinity and/or NTA concentration and was determined to be the result of salinity—Cd²⁺ and NTA-Cd²⁺ interactions. Possible mechanisms of the salinity effect and NTA interaction with cadmium toxicity are discussed.     

The effects of silver and arsenic on antioxidant system in <Emphasis Type="Italic">Lemna paucicostata</Emphasis>: Different effects on glutathione system

Ag⁺ (AgNO₃) and As³⁺ (As₂O₃) exposures resulted in dose-dependent decreases in the growth rate of Lemna paucicostata with IC₅₀ values of 0.101±0.004 mg/mL and 0.753±0.127 mg/mL, respectively. Both Ag⁺ and As³⁺ caused dose-dependent increases in lipid peroxidation, a key oxidative damage marker. Additionally, Ag⁺ and As³⁺ caused increases in some components of antioxidant system, namely, ascorbate content and peroxidase activities such as ascorbate peroxidase, glutathione peroxidase, and guaiacol peroxidase. However, notable differences between Ag⁺ and As³⁺ were found in their effects on the glutathione (GSH) system. Ag⁺ caused significant decreases in the GSH content and activities of glutamate cysteine ligase (GCL) and glutathione reductase (GR), the enzymes involved in the GSH synthesis and redox recycling, respectively. In contrast, As³⁺ caused increases in the GSH content and GCL activity. Our results suggest that the Ag⁺-induced decrease in GSH content accompanied by the decreases in its synthesis and redox recycling is a critical component that further predisposes L. paucicostata to Ag⁺ toxicity.     

Antioxidant activity of Coridius chinensis extracts on manganese‐induced testicular damage in rats

Coridius chinensis (C. chinensis) is a traditional Chinese medicine that has been used to treat pain, erectile dysfunction, and other diseases. Our previous study demonstrated that manganese‐induced reproductive damage was partially rescued by a medium dose of C. chinensis treatment in rat. However, the underlying mechanism is unknown. In this study, we found that the weight of reproductive organs and the sperm count in manganese‐exposed rat were partially rescued by C. chinensis extracts (CcE) treatment. The number of apoptotic cells was significantly decreased and the expression of malondialdehyde, cytochrome c, and caspase‐3 in manganese‐exposed rats was significantly decreased after high dose of CcE treatment. Further studies revealed that the activity of superoxide dismutase, total antioxidant capacity, and glutathione peroxidase enzymes was significantly increased in testis tissues and serum of manganese‐exposed rats with high dose of CcE treatment. Taken together, the results of this study suggest that CcE inhibits the Mn²⁺‐induced apoptosis in testes by inducing the activity of antioxidants.     

Effects of cadmium on Drosophila: toxicity, proteins, and transfer RNAs

An animal model with well-defined genetic and biochemical characteristics is needed for a detailed understanding of the mechanism of toxicity by metal ions. Drosophila melanogaster was used in the present study to demonstrate a number of responses of Cd²⁺, including lethality, age-related changes in resistance, alterations of the normal developmental changes in proteins, and alterations in specific transfer RNAs. Genotype-specific differences in resistance to Cd²⁺ were found: the ν; bw strain was 5–10 times more resistant than su(s)²ν; bw for developmental exposure; upon treatment of the young adults the differences were in the same direction, but the sensitivities differed by only two- to three-fold. The adult fly became more sensitive to Cd²⁺ as it aged through 2 weeks, but changed little thereafter. The electrophoretic patterns of proteins of adult flies underwent changes during aging from 1 to 8 days; these changes were markedly altered by 0.55 mm CdCl₂ but not by 0.74 mm ZnCl₂ in the medium on which the flies were maintained. The appearance of queuosine-containing tRNA was stimulated by CdCl₂ (0.05–0.8 mm) in the growth medium, but not by ZnCl₂ (0.07–1.1 mm). Further studies involving D. melanogaster should be useful in defining specific interactions of toxic metal ions with macromolecules to enhance the understanding of the toxic effects of these and similar pollutants.     

Mechanism of cadmium-induced blockade of neuromuscular transmission

The effect of cadmium ion (Cd²⁺) on neuromuscular transmission was examined in phrenic nerve-diaphragm preparations (PND) of mice and rats.The indirectly induced muscle twitch (IT) was inhibited by Cd²⁺ (0.1–1.0×10^?4M) in a dose-dependent manner, but the directly induced twitch (DT) was rarely affected. The inhibition was reversible and reproducible. An increase in external Ca²⁺ concentration antagonized and an increase in Mg²⁺ concentration potentiated the inhibitory effect of Cd²⁺. The inhibitory effect of Cd²⁺ (2.8×10^?5 M) was antagonized by cysteine (5.6×10^?5 M) applied before or after the Cd²⁺ treatment. Hg²⁺ (mercuric chloride, 2.8×10^?5 M) or p-chloromercuribenzoic acid (PCMB, 2.5×10^?5 M) also inhibited IT but in a different manner. The effects of Hg²⁺ or PCMB were not antagonized by cysteine applied after the treatment. Pretreatment with Hg²⁺ (10^?6 M) or PCMB (5×10^?6 M) did not potentiate the inhibitory effect of Cd²⁺. Resting membrane potential and frequency of miniature end-plate potential (m.e.p.p.) were not affected by Cd²⁺, but m.e.p.p. amplitude was slightly reduced. The end-plate potential was blocked by Cd²⁺ (10^?4 M), and this effect was partially antagonized by an increase in Ca²⁺ concentration. In bioassay experiments, the evoked output of acetylcholine from rat PND was reversibly reduced by Cd²⁺. The inhibitory effect of Cd²⁺ on the output of [¹⁴C]acetylcholine evoked from rat PND was antagonized by an increase in Ca²⁺ concentration and potentiated by an increase in Mg²⁺. From these results, it is suggested that Cd²⁺ reversibly inhibits neuromuscular transmission by reducing transmitter release from motor nerve terminals resulting from the inhibition of Ca²⁺ influx at the membrane of axon terminals. We did not obtain conclusive evidence that Cd²⁺ produces neuromuscular blockade by acting on thiol groups of membrane constituents.     

Activity of the enzymes of the antioxidative system in cadmium-treated Oxya chinensis (Orthoptera Acridoidae)

One purpose in this research was to determine the toxic effects of Cd on antioxidant enzymes of Oxya chinensis (Orthoptera: Acridoidae). Changes in the activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and guaiacol peroxidase (GPx) were measured in O. chinensis insects injected with Cd²⁺. Fifth-nymphs of O. chinensis insects were injected with Cd²⁺ at different concentrations (0, 0.55 × 10⁻⁴, 1.10 × 10⁻⁴, 1.65 × 10⁻⁴, 2.20 × 10⁻⁴, and 2.75 × 10⁻⁴ g g⁻¹). An increase in SOD activity in O. chinensis was observed at 1.10 × 10⁻⁴ to 2.75 × 10⁻⁴ g g⁻¹ Cd²⁺. The SOD activity was lower at 2.20 × 10⁻⁴and 2.75 × 10⁻⁴ g g⁻¹ than that at 1.10 × 10⁻⁴ and 1.65 × 10⁻⁴ g g⁻¹. It appears that SOD had a positive protective effect at low Cd²⁺ concentrations, and that this effect disappeared at high Cd²⁺ concentrations. CAT activity was accelerated to varying degrees at 1.10 × 10⁻⁴ to 2.75 × 10⁻⁴ g g⁻¹ for males and at 1.10 × 10⁻⁴, 2.20 × 10⁻⁴, and 2.75 × 10⁻⁴g g⁻¹ for females. CAT showed a strong detoxification effect with all treatments. GPx activity decreased with increasing Cd²⁺ concentration with all treatments for males and at 2.20 × 10⁻⁴ and 2.65 × 10⁻⁴g g⁻¹ for females. We showed that GPx activity had a weak detoxification function with all treatments for males and at high Cd²⁺ for females. Thus, CAT had a strong detoxification effect, whereas SOD had a medium and GPx had a weak detoxification effect. Among the three enzymes, CAT played an important role in the damaging mechanisms of reactive oxygen species in O. chinensis insects. Alterations of the antioxidant enzyme level under environmental stresses are suggested as indicators of biotic and abiotic stress.     

Effects of Cd2+, Pb2+ and CH3Hg+ on high voltage-activated calcium currents in pheochromocytoma (PC12) cells: potency,reversibility, interactions with extracellular Ca2+ and mechanisms of block

Effects of the neurotoxic heavy metals Cd²⁺, Pb²⁺ and CH₃Hg⁺ on current carried by Ca²⁺ ions (I_Ca) through high-voltage activated Ca²⁺ channels in nerve growth factor (NGF)-differentiated pheochromocytoma (PC12) cells were examined to characterize possible differences in the mechanism of action of these metals on Ca²⁺ channel function. Specifically, the potency and reversibility of effect on I_Ca by each metal was examined, as well as the relationship between extracellular [Ca²⁺] and potency of block of I_Ca by Cd²⁺ and Pb²⁺. In addition, the effect of each of these metals on Ca²⁺ channels when applied to the intracellular side of the membrane was also examined. When extracellular solution contained 20, 10 or 5 mM Ca²⁺, the estimated IC₅₀ values (total metal concentration) for block of I_Ca were 15, 10, and 6.5 μM for Cd²⁺ and 7.5, 2.0 and 1.1 μM for Pb²⁺, respectively. CH₃Hg⁺ (1–10 μM) blocked I_Ca (20 mM Ca²⁺) in a time- and concentration-dependent manner. When cells were washed with metal-free solutions, block of I_Ca by Cd²⁺ was reversed rapidly, whereas block by Pb²⁺ was reversed only partially, and block of I_Ca by CH₃Hg⁺ was not reversed. When Pb²⁺ and CH₃Hg⁺ treated cells were washed in metal-free solutions containing 50 μM d-penicillamine (DPEN), block of I_Ca by 10 μM Pb²⁺ was rapidly and completely reversed, whereas, block of I_Ca by 5 μM CH₃Hg⁺ was not reversed. Higher concentrations (500 μM) of 2,3-dimercapto-1-propane sulfonic acid (DMPS) did reverse partially the block of I_Ca by 5 and 10 μM CH₃Hg⁺. When Cd²⁺, Pb²⁺ or CH₃Hg⁺ was present in the intracellular solution, Ca²⁺ channel currents were significantly reduced. These results characterize effects of Cd²⁺ on Ca²⁺ channels and demonstrate that Cd²⁺, Pb²⁺ and CH₃Hg⁺ differ in their actions on Ca²⁺ channels.     

The effects of sodium chromate and carbon tetrachloride on the urinary excretion and tissue distribution of cadmium in cadmium-pretreated rats

Rats were administered nontoxic doses of Cd²⁺ by the oral or intraperitoneal routes. They were subsequently treated with either Na₂CrO₄ (10 or 20 mg/kg, sc) or CCl₄ (0.5 or 1 ml/kg, intragastric). Evidence of renal damage was obtained from the determination in urine of total protein and amino acids and from the analysis of the urinary proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Liver damage was evaluated by determining the serum activities of sorbitol dehydrogenase and glutamate pyruvate transaminase. The effects of CCl₄ on the urinary excretion and the tissue distribution of Cd²⁺ vary depending on whether liver damage is associated or not with extensive renal lesions. When renal function was not or only moderately altered, induction of liver damage by CCl₄ resulted in a transfer of Cd²⁺ from the liver to the kidney. This transfer was evidenced by a decrease of total Cd²⁺ as well as metallothionein-bound Cd²⁺ in the liver and an increase of the same parameters in the kidney. The urinary excretion of Cd²⁺ was only slightly increased. When liver damage induced by CCl₄ was associated with extensive kidney lesions, the accumulation of Cd²⁺ released from the liver in the kidney was considerably reduced and large amounts of Cd²⁺ were excreted in urine. Administration of Na₂CrO₄ to Cd²⁺-pretreated rats gave rise to a sharp and reversible increase in the urinary excretion of Cd²⁺. This increase was proportional to the amount of Cd²⁺ stored in kidney and to the dose of Na₂CrO₄ administered. The Cd²⁺ excreted in urine originated mainly from the kidney in which total Cd²⁺ and metallothionein-bound Cd²⁺ were reduced in proportion to the dose of Na₂CrO₄ administered. These results suggest that two mechanisms may lead to an increased urinary excretion of Cd²⁺; a direct release of Cd²⁺ into urine from damaged kidney (i.e., Na₂CrO₄) or a decreased tubular reabsorption of plasma circulating Cd²⁺ evidenced when large amounts of Cd²⁺ are released into blood from damaged liver (i.e., CCl₄). These results tend to support the hypothesis that kidney damage due to chronic Cd²⁺ poisoning may lead to an increased loss of the Cd²⁺ stored in the kidney.     

Effect of sodium isopropylxanthate,potassium amylxanthate and sodium diethyldithiocarbamate on the uptake and distribution of cadmium in the brown trout (Salmo trutta)

Brown trout, Salmo trutta, were exposed to water containing 1 μg/l of ¹⁰⁹Cd²⁺, alone or with sodium isopropylxanthate, potassium amylxanthate or sodium diethyldithiocarbamate, respectively. After one week the uptake and distribution of the ¹⁰⁹Cd²⁺ in the fish were examined by whole-body autoradiography and gamma spectrometry. Sodium diethyldithiocarbamate was found to enhance the uptake of the ¹⁰⁹Cd²⁺ in several tissues of the fish and this effect increased with increasing concentration of the carbamate. Potassium amylxanthate induced increase in the levels of ¹⁰⁹Cd²⁺ in several tissues, whereas the brain was the only tissue with increased concentration of ¹⁰⁹Cd²⁺ in the presence of sodium isopropyl-xanthate. A likely mechanism for the enhanced uptake of the ¹⁰⁹Cd²⁺ may be a facilitated penetration over the gill membranes of the lipophilic complexes formed between the studied compounds and the cadmium. A facilitated passage through cellular membranes may also be important for the increased uptake of the metal in other tissues. An elevated uptake of cadmium by the xanthates or the diethyldithiocarbamate may constitute an increased risk for noxious effects of the metal.     

Oxidative and osmoregulatory effects of imidacloprid,cadmium, and their combinations on Daphnia magna

Oxidative stress and osmoregulatory system damage-inducing potential of binary mixtures of neonicotinoid insecticide imidacloprid (IMI) and Cd²⁺ in Daphnia magna were evaluated. Animals were subjected to subchronic (7 days) and acute (48 h) of IMI and Cd²⁺ effects with single and binary mixtures. ATPase and antioxidant enzyme activities with lipid peroxidation were measured. Morphometric characteristics were also evaluated. Response patterns showed variability due to the duration, concentration, and toxicant type. While the enzyme activities mostly showed a decreasing trend upon the subchronic IMI effect, there was an increasing trend after the Cd²⁺. Declined enzyme activities were more pronounced with the acute higher IMI+Cd²⁺ exposure. Ca²⁺-ATPase and CAT were the most sensitive biomarkers in the toxicity response. IMI+Cd²⁺ exposures are appeared to increase their toxic effects due to their oxidative potential. ATPase inhibition and antioxidant enzyme alterations with a decrease in morphometric characteristics in Daphnia even at their low concentrations of IMI and Cd²⁺ show evidence of their toxicities on aquatic life. It was emphasized that investigating the combined effects of toxicants at their environmental level based on the multi-biomarker approach is essential in toxicity evaluation.     

Comparison of the effect of chronic cadmium exposure on the antioxidant defense systems of kidney and brain in rat

Abstract

Cadmium (Cd²⁺) produces toxic effects on various tissues as kidney and liver, so several studies have focused to explore the effect produced by different doses and exposure times of this metal. However, little has been reported about the effect that Cd²⁺ shows in the brain in vivo. Hence, this study aimed at comparing the effect of chronic Cd²⁺ exposure on antioxidant defense systems of kidney and brain in rats. Six groups of male rats were employed; five were administered for 45 days with different doses of cadmium chloride (0.187, 0.375, 0.562, 0.937 and 1.125?mg/kg; i.p.) and the other was used as control. Free radicals (FRs) were directly quantified by electron paramagnetic resonance (EPR) spectroscopy; malondialdehyde (MDA), reduced glutathione (GSH) and the activity expression of superoxide dismutase (SOD2) and catalase (CAT) were also measured. The EPR results showed that there was no increase in FR content in kidney or brain. MDA and GSH levels increased in kidney but not in the brain. The SOD2 activity was not altered, but its expression decreased in both tissues. On the other hand, CAT activity and expression tended to increase at low doses and decrease at high doses in both tissues. Therefore, these results suggest that there exist compensatory mechanisms in both kidney and brain that are capable of avoiding the toxic effects exerted by Cd²⁺ at these doses and exposure time.     

Relationships between subcellular distributions of cadmium and perturbations in reproduction in the polychaete Neanthes arenaceodentata

The accumulation and subcellular distribution of Cd in the polychaete worm, Neanthes arenaceodentata, were examined following an eleven-week period of exposure to a range of free cadmium ion activities, [Cd²⁺]. The accumulation of Cd in N. arenaceodentata was directly proportional to [Cd²⁺] in seawater at lower concentrations (10⁻¹² M to 10⁻¹⁰ M) but deviated from proportionality at higher concentrations (10⁻⁹ M and 10⁻⁸ M). This deviation in proportionality at higher [Cd²⁺] was attributable to a relative increase in the concentration of metal associated with the metallothionein and the very low molecular weight metal-ligand pools of the cytosol.Reproductive potential was also monitored in these organisms to examine the ecological significance of Cd accumulation and shifts in its subcellular distribution. Perturbations in reproduction were observed at 10⁻⁸ M [Cd²⁺] which coincided with the deviation in proportionality of Cd accumulation and increased accumulation of Cd in the cytosol.     

Cadmium‐induced Cytosolic Ca2+ Elevation and Subsequent Apoptosis in Renal Tubular Cells

Abstract: Cadmium (Cd²⁺) is an industrial and environmental metal. The effect of Cd²⁺ on intracellular free‐Ca²⁺ levels ([Ca²⁺]_i) and viability in Madin Darby canine kidney cells was explored. Cd²⁺increased [Ca²⁺]_i in a concentration‐dependent manner with an EC₅₀ of 85 µM. Cd²⁺‐induced Mn²⁺ entry demonstrated Ca²⁺ influx. Removal of extracellular Ca²⁺ decreased the [Ca²⁺]_i signal by 60%. The [Ca²⁺]_i signal was inhibited by La³⁺ but not by L‐type Ca²⁺ channel blockers. In Ca²⁺‐free medium, Cd²⁺‐induced [Ca²⁺]_i signal was abolished by pre‐treatment with 1 µM thapsigargin (an endoplasmic reticulum Ca²⁺pump inhibitor) and 2 µM carbonylcyanide m‐chlorophenylhydrazone (CCCP; a mitochondrial uncoupler). Cd²⁺‐induced Ca²⁺ release was not altered by inhibition of phospholipase C. At concentrations between 10 and 100 µM, Cd²⁺killed cells in a concentration‐dependent manner. The cytotoxic effect of 100 µM Cd²⁺was reversed by pre‐chelating cytosolic Ca²⁺with BAPTA. Cd²⁺‐induced apoptosis was demonstrated by propidium iodide. Collectively, this study shows that Cd²⁺ induced a [Ca²⁺]_i increase in Madin Darby canine kidney cells via evoking Ca²⁺ entry through non‐selective Ca²⁺ channels, and releasing stored Ca²⁺ from endoplasmic reticulum and mitochondria in a phospholipase C‐independent manner.     

Effects of Cd<Superscript>2+</Superscript> on transient outward and delayed rectifier potassium currents in acutely isolated rat hippocampal CA1 neurons

The effects of cadmium (Cd²⁺) on the transient outward potassium current (I _A) and delayed rectifier potassium current (I _K) were investigated in acutely dissociated rat hippocampal CA1 neurons using the whole-cell patch-clamp technique. The results showed that Cd²⁺ inhibited the amplitudes of I _A and I _K in a reversible and concentration-dependent manner, with half-maximal inhibitive concentration (IC₅₀) values of 546 ± 59 and 749 ± 53 μM, and the inhibitory effect of Cd²⁺ was voltage dependent. Cd²⁺ significantly shifted the steady-state activation and inactivation curve of I _A to more positive potentials. In contrast, Cd²⁺ caused a relatively less but still significant positive shift in the activation of I _K without effect on the inactivation curve. Cd²⁺ significantly slowed the recovery from inactivation of I _K but had no effect on the recovery time course of I _A. The results suggest that the modulation of I _A and I _K was most likely mediated by the interaction of Cd²⁺ with a specific site on the potassium-channel protein rather than by screening of bulk surface-negative charge. The effects of Cd²⁺ on the voltage-gated potassium currents may be a possible contributing mechanism for the Cd²⁺-induced neurotoxic damage. In addition, the effects of Cd²⁺ on the potassium currents at concentrations that overlap with its effects on calcium currents raise concerns about its use in pharmacological or physiological studies.     

Calmodulin-mediated cadmium inhibition of phosphodiesterase activity,in vitro

Ion-stripped bovine brain calmodulin (CaM) binds 4 moles Cd²⁺ as well as 4 moles Ca²⁺ per mole protein, with similar affinity; in the presence of 1 mM Mg²⁺ the molar binding ratio of CaM for Ca²⁺ decreased to 3, the apparent K_0.5 for Ca²⁺ nearly doubled, but the binding characteristics of CaM for Cd²⁺ were not changed. Saturating concentrations Ca²⁺ did not affect the molar binding ratio of CaM for Cd²⁺, but increased the apparent K_0.5 for Cd²⁺; vice versa, saturating concentrations Cd²⁺ decreased the molar binding ratio for Ca²⁺ to 2 without affecting the apparent K_0.5 for Ca²⁺.CaM-independent phosphodiesterase (PDE) activity was inhibited at [Cd²⁺]>10^–5 M. Cd²⁺-CaM as well as Ca²⁺-CaM activated PDE. However, the Cd²⁺-CaM complex is less effective than the Ca²⁺-CaM complex in stimulating CaM-dependent enzyme activities. Cd²⁺ inhibits Ca²⁺- and CaM-dependent PDE in a competitive way. Introduction of Cd²⁺ in a medium containing Ca²⁺ and CaM may, therefore, result in a reduction of CaM-dependent enzyme stimulation.By its interference with Ca²⁺- and CaM- dependent PDE activity, Cd²⁺ could upset the catabolic pathway of cellular cyclic nucleotide metabolism.     

Effect of 2-Hydroxy-4-methoxy Benzoic Acid Isolated from Hemidesmus indicus on Erythrocyte Membrane Bound Enzymes and Antioxidant Status in Streptozotocin-induced Diabetic Rats

In the present study, the effect of 2-hydroxy-4-methoxy benzoic acid isolated from roots of Hemisdesmus indicus on the erythrocyte membrane bound enzymes and antioxidant status in streptozotocin-induced diabetic rats was investigated. The streptozotocin-induced diabetic rats were treated with 2-hydroxy-4-methoxy benzoic acid (500 μg/kg/day) for 7 weeks by oral intubation and compared with glibenclamide, a standard hypoglycemic agent (100 mg/kg). The erythrocyte membrane was isolated and the activity of Na⁺/K⁺-dependent ATPases, Ca²⁺-ATPases, Mg²⁺-ATPases were determined. Superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase, vitamins C, vitamin E, plasma reduced glutathione and erythrocyte glutathione, reduced glutathione content in the tissues was also assayed. Administration of 2-hydroxy-4-methoxy benzoic acid to diabetic rats significantly (F>0.05 and P<0.001) elevated the activity of total ATPases, Na⁺/k⁺ ATPase, Mg²⁺ ATPase and Ca²⁺ ATPase to near normal level. The activities of catalase, superoxide dismutase and glutathione peroxidase and glutathione-S-transferase in erythrocytes were decreased significantly (F>0.05; P<0.001) in diabetic rats. Diabetic rats treated with 2-hydroxy-4-methoxy benzoic acid showed a significant (F>0.05; <0.001) increase in the enzymic antioxidants in erythrocytes. The elevated levels of vitamin E and low level of vitamin C and glutathione level in plasma and erythrocytes were observed in diabetic rats when compared to control rats and were restored significantly (F>0.05; P<0.001) after the administration of 2-hydroxy-4-methoxy benzoic acid. This study concludes administration of 2-hydroxy-4-methoxy benzoic acid supports the restoration of antioxidant defence, reduces the free radial production, lipid peroxidation and the glycosylation of haemoglobin in diabetic rats.