Inhibitory Effects Of Pb Research Articles

Additive inhibitory effects of heavy metals on phenol-utilizing microorganism

Effects of heavy metals on phenol-utilizing microorganisms that could co-metabolically degrade naphthol were investigated. Polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE) identified these phenol-utilizing microorganisms as Alicycliphilus denitrificans K601, Alicycliphilus sp. R-2461, uncultured Alicycliphilus sp., and Acidovorax aerodenitrificans. Inhibitory effects of Pb, Cu, Cd, and Zn on phenol biodegradation were in the order of Cu > Cd > Pb > Zn. Inhibitory effects of mixed heavy metals on phenol-utilizing microorganisms were in the order of (Cd + Pb) ≈ (Cd + Cu) > (Zn + Pb) > (Zn + Cd) > (Pb + Cu) > (Zn + Cu). The presence of mixed heavy metals synergistically inhibited microbial degradation of phenol. The relationship between reaction constants and inhibition concentrations that caused 50% of the degradation rate (IC50) for mixed heavy metals was derived as k2 = 0.69 ∙ IC50-1.007. In this study, heavy metals inhibited phenol biodegradation through synergistic interactions. However, other studies have reported antagonistic interactions depending on the microbial community and heavy metals, indicating that the inhibition type of heavy metal on microbial degradation depends on the microorganism and the type of heavy metal.

24-Epibrassinolide modulates primary metabolites, antioxidants, and phytochelatins in Acutodesmus obliquus exposed to lead stress

Aquatic organisms are exposed to many stressors, e.g., heavy metals. Brassinosteroids, a plant hormone group, can effectively stimulate plants to defend against the negative impact of a heavy metal. The present study was conducted with an aim to find out the influence of 24-epibrassinolide (EBL) on Acutodesmus obliquus treated with 0.01 and 500 μM of lead (Pb) ions during 7 days of cultivation. Pb has a toxic effect on algal cultures because it limits both the growth and development and induces oxidative stress. Simultaneously, 1 μM EBL was involved in protecting algal cells against the toxic effect of Pb. Despite the presence of Pb, EBL significantly increased the number of algal cells and their metabolite content (e.g., proteins, monosaccharides, chlorophylls, carotenes, and xanthophylls). Cultures treated concurrently with EBL and Pb were characterized by a reduction in their content of endogenous Pb, H2O2, and malondialdehyde. Also, EBL increased the activity of catalase, ascorbate peroxidase, superoxide dismutase, glutathione reductase, and the content of ascorbate and glutathione. EBL increased the phytochelatin synthase activity, thereby enhancing the production of phytochelatins accountable for both binding and detoxification of Pb. These results indicate the influence of EBL on the inhibitory effect of Pb in A. obliquus. These findings help to clarify the role of BRs in the algal adaptation to the prevailing stressful conditions.

Lead induced alterations in rabbit spermatozoa motility and morphology in vitro

The aim of this in vitro study was to determine the effect of lead chloride (PbCl2) on rabbit spermatozoa motility and morphology. Lead concentrations in the medium ranged between 0.45 and 11.17 μg/ml; incubation time was 240 min (analyzed immediately after Pb addition followed by 30, 60, 120, 180, and 240 min), and temperatures of the culture environment were 22°C (laboratory), 4°C (refrigerator), and 37°C (incubator). Results were compared with a control group without Pb addition. After 30 min of culture at 22°C, a negative effect of Pb was noted as spermatozoa motility significantly decreased in groups with higher concentrations. After 120 and 240 min, a dose-dependent effect on spermatozoa motility was noted. At 4°C, spermatozoa motility analysis detected no significant differences between any of the experimental groups and control. At 37°C, a negative effect of Pb incubation on motility was detected at Times 30, 60, 120, 180, and 240 in groups with high concentrations. At Times 120, 180, and 240 a significant decrease in spermatozoa motility was also noted in all experimental groups in comparison to control. The analysis of pathological spermatozoa at Time 240 revealed an increasing trend of morphological abnormalities after incubation with Pb. Across three temperature regimes an increase of morphological changes was noted, particularly in the group with the highest Pb concentration. The predominant morphological abnormalities were knob twisted flagellum, flagellum ball, separated flagellum, and broken flagellum. Knob twisted flagella represented the most frequent pathological changes in the experimental group with the highest Pb concentration. Results suggest that the inhibitory effect of Pb on spermatozoa motility parameters depends on the concentration, incubation time, as well as environmental temperature during incubation. Furthermore, a negative effect of Pb in vitro on spermatozoa morphology indicates possible reproductive problems under in vivo conditions, too.

Lead induced effects on acetylcholinesterase activity in cerebellum and hippocampus of developing rat

Exposure to low-levels of lead (Pb) during early development has been implicated in behavioral abnormalities and cognitive deficits in children. The present study is focused on developmental changes in hippocampus and cerebellum of rats following perinatal exposure to Pb. Pregnant rats were exposed to 0.2% Pb-acetate from gestation day 6 (GD 6) through postnatal day (PND) 21 and the activity levels of acetylcholinesterase (AChE) were estimated in cerebellum and hippocampus of pups at specific time points for 5 weeks. In both the brain regions, Pb-exposure decreased AChE activity with an increase in age. Histochemical observations conducted in 35 days old rat brain showed decreased AChE activity conspicuously in stratum oriens and dentate gyrus of hippocampus, and molecular and granule cell layers of cerebellum. In vitro studies conducted in 35 days old rat brain showed a considerable decrease in the specific activity of AChE at high concentrations (50–100μM) of Pb in a concentration-dependent manner. However, at low concentrations (5–20μM), Pb failed to produce such changes. In the presence of eserine (physostigmine), the specific inhibitor of AChE, the inhibitory effect of Pb was potentiated and this was more pronounced at low-concentrations of Pb. The behavioral responses in open-field also showed a significant decrease in both Pb exposed as well as eserine administered rats. These data suggest that low-level perinatal Pb-exposure induces alterations in cholinergic system in the cerebellum and hippocampus of developing brain even after the withdrawal of Pb-exposure, that may contribute to behavioral and learning deficits.

The effects of lead on transient outward currents of acutely dissociated rat dorsal root ganglia

The effects of Pb 2+ on transient outward currents (TOCs) were investigated on rat dorsal root ganglia (DRG) neurons at postnatal days of 15∼21, using the conventional whole-cell patch-clamp technique. In media-sized (35∼40 μm) neurons and in the presence of 50 mM TEA, TOCs that preliminarly included an A-current ( I A) and a D-current ( I D), were clearly present and dominant. Application of Pb 2+ lengthened the initial delay of TOCs and increased the onset-peak time in a concentration-dependent manner. The amplitudes of initial outward current peak were reduced with increasing Pb 2+ concentrations. The inhibitory effects of Pb 2+ on TOCs were reversible with 80∼90% of current reversed in 2∼10 min at 1∼400 μM Pb 2+. For the normalized activation curves fitted by a single Boltzmann equation under each condition, there was a shift to more depolarized voltages with increasing concentrations of Pb 2+. The V 1/2 and the slope factor ( k) increased from 12.76±1.49 mV and 15.31±1.66 mV ( n=10) under control condition to 39.91±5.44 mV ( n=10, P<0.01) and 21.39±3.13 mV ( n=10, P<0.05) at 400 μM Pb 2+, respectively, indicating that Pb 2+ decreased the activation of TOCs. For the normalized steady-state inactivation curves, the V 1/2 and the k increased from −92.31±2.72 and 8.59±1.36 mV ( n=10) to −55.65±3.67 ( n=10, P<0.01) and 23.02±2.98 mV ( n=10, P<0.01) at 400 μM Pb 2+, respectively. The curves were shifted to more depolarized voltages by Pb 2+, indicating that channels were less likely to be inactivated at higher concentrations of Pb 2+ at any given potential. The fast ( t f) and slow ( t s) decay time-constants were both significantly increased by increasing concentrations of Pb 2+ ( n=10, P<0.05), indicating that Pb 2+ increased the decay time-course of TOCs. These effects were concentration-dependent and partly reversible following washing. Ca 2+ modulated the TOCs gating and might share same binding site with Pb 2+, for which Ca 2+ had very low affinity. In summary, the results demonstrated that Pb 2+ was a dose- and voltage-dependent, and reversible blocker of TOCs in rat DRG neurons. After Pb 2+ application, normal sensory physiology of DRG neurons was affected, and these neurons might display aberrant firing properties that resulted in abnormal sensations. This variation caused by Pb 2+ could underlie the toxical modulation of sensory input to the central nervous system.

Effect of lead treatment on the distribution of essential elements in cucumber

Changes in the fresh and dry weight of leaf blades, petioles, internodes, and their ion concentrations as well as rates of root exudation were investigated in cucumber grown in hydroponic culture and treated with physiological concentrations of lead (Pb). The growth of flowering cucumber supplied with FeCl3 shows a typical bell‐shaped curve derived from leaf dry weights, where the 4th, 5th, and 6th leaves are the largest ones. Lead inhibited growth up to 20% (except the youngest leaves which were stimulated), but did not cause morphological changes. Whereas root growth was also retarded by about 20%, exudation was inhibited to 50%, that is, the root resistance to water transport was increased by Pb. In spite of that the dry matter yield of internodes and petioles hardly reached 10 and 5% of that of leaf blades, respectively, their calcium (Ca), magnesium (Mg), and zinc (Zn) concentrations were almost the same. Similarly, the concentrations of these metals in the specific leaf blades are equal despite their different growth characteristics but the concentration of Mn is independent of the growth of the examined tissues. Lead was the only cation to accumulate in the largest leaves. The inhibitory effect of Pb on ion uptake was proportional to the growth inhibition of the tissues except manganese (Mn), the accumulation of which was stimulated by Pb in all the analyzed tissues and copper (Cu) which increased only in the internodes. We could not explain the extremely different ion distributions observed during the growth of cucumber. However, it is evident that the measurement of ion concentrations at whole shoot level is not enough to characterize ion interactions because only some ions accumulate at the same rate as tissues grow. These ions maintain stable concentration levels in shoot parts whereas others decrease or increase independently from growth.

Interference of lead with the calcium release activated calcium flux of osteoblast-like cells.

Lead (Pb(2+)) tends to accumulate in bone from where it is released during bone resorption, thus leading to high local concentrations of Pb(2+) with the risk of cellular toxicity. We investigated the interference of Pb(2+) with the calcium release activated calcium influx (CRAC) of osteoblast-like (OBL) cells. CRAC was elicited by depletion of intracellular Ca(2+) stores with thapsigargin and/or A23187 under Ca(2+)-free conditions and re-addition of extracellular Ca(2+). The fura-2 excitation ratio (R) was used to monitor changes of the free intracellular concentration of Ca(2+) and Pb(2+), the latter being reversible by the heavy metal chelator TPEN. Five or 12. 5 microM Pb(2+) applied simultaneously with re-added Ca(2+) reduced the immediate CRAC of OBL cells to 70% or 37% of control value, respectively. An enlarged influx of Pb(2+) occurred during CRAC, which led to a 2.7-fold faster increase of R. When 1 microM Pb(2+) was added during ongoing CRAC, the Pb(2+)-mediated increase of R correlated with the degree of CRAC (r = 0.83). Inhibitory effects of Pb(2+) on Ca(2+) ATPase activity did not contribute to the aforementioned findings. Our results demonstrated that CRAC channels of OBL cells are blocked as well as permeated by Pb(2+).

Potentiation and inhibition of subtypes of neuronal nicotinic acetylcholine receptors by Pb 2+

Effects of inorganic lead (Pb 2+) on defined subtypes of neuronal nicotinic acetylcholine receptors have been investigated. Voltage clamp experiments have been performed on Xenopus oocytes expressing α3β2, α3β4 and α4β2 neuronal nicotinic acetylcholine receptor subunit combinations. In oocytes expressing the α3β2 subunit combination Pb 2+ enhances the peak amplitude of nicotinic acetylcholine receptor-mediated inward currents evoked by superfusion with 100 μM acetylcholine. At concentrations of 1–250 μM, Pb 2+ potentiates α3β2 receptor-mediated inward current concentration dependently by a factor of 1.1–11.0. Inward currents evoked by low (3 μM) and high (1 mM) concentrations of acetylcholine are potentiated to a similar extent. Conversely, in oocytes expressing the α3β4 subunit combination Pb 2+ inhibits the nicotinic receptor-mediated inward currents evoked with μM acetylcholine. Inhibitory effects are observed in the concentration range of 1 nM–100 μM Pb 2+, but the degree of inhibition varies between oocytes. A similar inhibition of the α4β2 nicotinic receptor-mediated inward current by Pb 2+ indicates that α as well as β subunits are involved in the potentiating and inhibitory effects. Possible reasons for the variation in the inhibitory effects of Pb 2+ on α3β4 and α4β4 nicotinic receptor-mediated inward currents have been investigated and are discussed. The divalent cations Ca 2+ and Mg 2+ potentiate both α3β2 and α3β4 nicotinic receptor-mediated inward currents. The distinct modulation of receptor function by Pb 2+ and by Ca 2+ and Mg 2+ and the dependence of the modulatory effect of Pb 2+ on subunit composition suggest that Pb 2+ interacts with multiple sites on the α and β subunits of neuronal nicotinic acetylcholine receptors.

Relationships between lead-induced learning impairments and changes in dopaminergic, cholinergic, and glutamatergic neurotransmitter system functions.

Behavioral consequences of low-level lead (Pb) exposure include impairments in learning processes and in Fixed-Interval schedule-controlled operant behavior. Although the neurobiological bases of these effects remain undetermined, current evidence suggests that inhibitory effects of Pb on the NMDA receptor complex may play a preferential role in the learning deficits. In contrast, alterations in dopaminergic systems, consistent with a decrease in dopamine availability, appear to be related to the changes in Fixed-Interval performance. Hypocholinergic function has also been described, but its relationship to the behavioral changes is not yet known. Explication of these relationships will require more efforts involving direct rather than correlative methods. The answers are critical for understanding risks associated with exposure and for the development of behavioral or chemical therapeutic strategies for dealing with lead neurotoxicity.

Age-dependent effects of lead on [ 3H]MK-801 binding to the NMDA receptor-gated ionophore: in vitro and in vivo studies

Lead (Pb 2+) is a more potent inhibitor of [ 3H]MK-801 binding to rat neuronal membranes than Zn 2+ and Mg 2+. The inhibitory effects of Pb 2+ appeared to be age-dependent since the IC 50 was significantly lower in cortical membranes prepared from neonatal than from adult rats. The results also indicate that the hippocampus is more sensitive than the cerebral cortex since the Pb 2+ IC 50 was significantly lower in the hippocampus. These findings suggest developmental and regional brain heterogeneity to the inhibitory action of lead of [ 3H]MK-801 binding. Chronic in vivo exposure to Pb 2+ resulted in the loss of [ 3H]MK-801 binding sites in the cerebral cortex of neonatal but not of adult rats. These lead-induced changes may influence developmental processes requiring NMDA receptor activation.

Pb 2+ and imidazole-activated phosphorylation by ATP of [formula omitted

In order to study whether Pb 2+ and imidazole increase the ATP phosphorylation level of ( Na + + K +)- ATPase by the same mechanism, the effects of both compounds on phosphorylation and dephosphorylation reactions of the enzyme have been studied. Imidazole in the presence of Mg 2+ increases steady-state phosphorylation of ( Na + + K +)- ATPase by decreasing, in a competitive way, the K +-sensitivity of the formed phosoho-enzyme ( E-P · Mg ). If Pb 2+ is present during phosphorylation, the rate of phosphorylation increases and a K +- and ADP-insensitive phosphointermediate ( E-P · Pb ) is formed. Pb 2+ has no effect on the K +-sensitivity of E-P · Mg and EDTA is unable to affect the K +-insensitivity of E-P · Pb . These effects indicate that Pb 2+ acts before or during phosphorylation with the enzyme. Binding of Na + to E-P · Pb does not restore K +-sensitivity either. However, increasing Na + during phosphorylation in the presence of Pb 2+ leads to formation of the K +-sensitive intermediate ( E-P · Mg ), indicating that E-P · Pb is formed via a side path of the Albers-Post scheme. ATP and ADP decrease the dephosphorylation rate of both E-P · Mg and E-P · Pb . Above optimal concentration, Pb + also decreases the steady-state phosphorylation level both in the absence and in the presence of Na +. This inhibitory effect of Pb 2+ is antagonized by Mg 2+.

Effect of Pb 2+ on Friend leukemia cells during erythroid maturation

The effect of different concentrations of Pb 2+ on the growth rate and on the percentage of hemoglobin-synthesizing cells of Friend leukemia cells was determined. Pb 2+ had a higher inhibitory effect on the growth and on the final percentage of hemoglobin-synthesizing cells when cultures were induced to erythroid differentiation by either dimethyl sulfoxide or hexamethylenebisacetamyde (HMBA) as compared with uninduced cultures. The increased sensitivity to Pb 2+ of cultures containing either dimethyl sulfoxide or (HMBA) appeared to be correlated with the differentiation process triggered by these two substances, since the increased sensitivity was not observed with a Friend leukemia cells variant which did not differentiate in the presence of any inducer. The effect of Pb 2+ on the activities of δ-aminolevulinic acid (ALA) dehydratase and URO synthetase, two enzymes involved in heme synthesis, was also determined. Induced cells continuously grown in the presence of Pb 2+ up to 72 hr postinduction were not affected in URO synthetase activity, whereas the activity of ALA dehydratase was decreased as compared with induced cultures grown without lead. By 96 and 120 hr postinduction an increase in URO synthetase activity and a decreased inhibition of ALA dehydratase activity were observed. The inhibitory effect of Pb 2+ on the growth rate of induced cells was much higher when cultures were treated during the first 24 hr of growth than it was when Pb 2+ was added during the second 24 hr. In uninduced cultures the same low level of inhibition was observed following treatment during either 24-hr period. Cell agglutinability by plant lectins was also inhibited in induced cultures by the presence of Pb 2+ during cellular growth.

4-Aminopyridine antagonizes the inhibitory effect of pentobarbital on acetylcholine release in the heart.

Effects of pentobarbital on acetylcholine (ACh) release, force of contraction and nervous conduction were studied in isolated heart preparations and in cervical vagus nerves, respectively. 4-Aminopyridine and tetracaine were used as pharmacological tools to eludicate the mode of action of pentobarbital. 1. 4-Aminopyridine (10−4 M) markedly increased the overflow of ACh from the isolated chicken heart evoked by electrical stimulation (1–50 Hz, 1 ms, 40 V) of the cervical vagus nerves. This effect of 4-aminopyridine was highest at low frequencies of stimulation (+ 226% at 1 Hz) and declined with increasing frequencies to reach a minimum augmentation of 22% at 30 Hz. 2. Pentobarbital and tetracaine dose-dependently decreased the evoked overflow of ACh from the isolated chicken heart. Half-maximal inhibition was observed at concentrations (IC50) of 1.4×10−4 M and 4×10−6 M, respectively. Much higher concentrations of pentobarbital were required to inhibit the conduction in vagal B-fibres (IC50=3×10−3 M) whereas the IC50 values of tetracaine for both inhibitory effects were nearly identical. 3. 4-Aminopyridine (10−4 M) antagonized the inhibitory effect of PB on the evoked overflow of ACh and shifted the concentration-response curve to the right. The 4-aminopyridine/pentobarbital antagonism was equally pronounced whether the release of ACh was evoked by vagal stimulation (preganglionic) or by field stimulation (pre- and postganglionic). 4. The negative inotropic effect of vagal stimulation in isolated atria of cats and chickens was weakened by pentobarbital (1–5×10−4 M) and enhanced by 4-aminopyridine (10−4 M). Again, 4-aminopyridine (10−4 M) antagonized the effect of pentobarbital. 5. In contrast to the effects of pentobarbital, the inhibition of ACh overflow produced by tetracaine was not antagonized by 4-aminopyridine. 6. The results strongly support the previous suggestion (Lindmar et al., 1979) that the inhibition by pentobarbital of the evoked overflow of ACh from the postganglionic parasympathetic neurones of the heart is due to a reduction of the Ca2+ inward current into the nerve terminals.

Effect of lead on soil respiration and dehydrogenase activity

The effect of added Pb on the respiration and dehydrogenase activity of two sandy soils, a clay soil and a peat soil, (all with different physico-chemical properties), was studied. A concentration of 375 μg Pb· g − inhibited the respiration of the sandy soil by ca. 15%, 1500 μg Pb· g − ca. 50%. In the clay soil 1500 μg Pb· g − caused a 15% reduction in respiration. The inhibition of respiration in the sandy soil was still ca. 30% 40 months after the addition of Pb. Respiration of the peat soil was not affected by even 7500 μg Pb· g −. Dehydrogenase activity was affected by Pb in a similar way to soil respiration. In the sandy soil a considerable reduction occurred, while in the clay and peat soils dehydrogenase activity was not reduced. It was concluded, that a relationship exists between the inhibitory effects of Pb and the buffering capacity of the soil as expressed by its cation-exchange capacity. Because of these different effects of the same Pb concentration on the various soil types, no single value for the permitted concentration of lead pollution in soil could be established.