Differences In Esterase Activity Research Articles

A plant-based extract mixture for controlling Spodoptera litura (Lepidoptera: Noctuidae)

BackgroundSpodoptera litura larvae are polyphagous insects that have become a significant pest in recent years. The spread of this pest has led to the continuous usage of insecticides on crops. Some plant extracts have been used as a mixture to control insect pests and improve productivity.MethodsA plant-based mixture was mixed at a ratio of 1:1 v/v to demonstrate the effect on contact toxicity, feeding (no-choice test), and enzyme activities on S. litura. The active compounds of P. retrofractum and A. calamus were isolated by preparative thin-layer chromatography (PTLC).ResultsOur results showed that binary mixtures from P. retrofractum and A. calamus exhibit the highest contact toxicity and antifeedant activity at a 1:1 ratio of LD30:LD10 dose (3.213 µg/larva P. retrofractum + 3.294 µg/larva A. calamus). The main active ingredient from each crude extract was (2E,4E,14Z)-N-isobutylicosa-2,4,14-trienamide from P. retrofractum, and beta-asarone and alpha-asarone from A. calamus. Additionally, A. calamus seems to be the synergistic compound. Some compound mixtures increased the glutathione-S-transferase activities in vivo; whereas, almost no significant differences in esterase activities were noted.ConclusionThe results indicated that the ethanolic crude extracts of P. retrofractum and A. calamus mixtures could be used as the pesticidal compound and to develop a binary mixture formulation for controlling lepidopteran pests. However, the toxicity of this mixture to mammals needed to be explored before commercial development.

Assessment of mouse strain differences in baseline esterase activities and toxic response to sarin

Genetics likely play a role in various responses to nerve agent (NA) exposure, as genetic background plays an important role in behavioral, neurological, and physiological responses. This study uses different mouse strains to identify if mouse strain differences in sarin exposure exist. In Experiment 1, basal levels of acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and carboxylesterase (CE) were measured in different strains of naïve mice to account for potential pharmacokinetic determinants of individual differences. In Experiment 2, median lethal dose (MLD) levels were estimated in 8 inbred mouse strains following subcutaneous (s.c.) administration of sarin. Few strain or sex differences in esterase activity levels were observed, with the exception of erythrocyte AChE activity in the C57BL/6J strain. Both sex and strain differences in toxicity were observed, with the most resistant strains being the BALB/cByJ and FVB/NJ strains and the most sensitive strain being the DBA/2J strain. These findings can be expanded to explore pathways involved in NA response, which may provide an avenue to develop therapeutics for preventing and treating the damaging effects of NA exposure.

Esterase activity in porcine and albino rabbit ocular tissues

Corneal esterases are utilized in the activation of topically applied ester prodrugs. Esterases may also be involved in the metabolism of drugs in posterior eye tissues, but their physiological activity is unknown. Furthermore, extrapolation of the esterase activity from protein level to the tissues is missing.The aims of the current study were to determine esterase activities in porcine and albino rabbit ocular tissues, calculate the activities for whole tissues and compare esterase activity between the species. We conducted a hydrolysis study with ocular tissue homogenates using an esterase probe substrate 4-nitrophenyl acetate. The hydrolysis rates were first normalized to protein content and then scaled to whole tissues.The hydrolytic rate normalized to protein content was high in the cornea and iris-ciliary body and low in the lens and aqueous humor, and in general, the rabbit tissues had higher hydrolytic rates than the porcine ones. Esterase activity scaled to whole tissue was high in cornea and iris-ciliary body and low in aqueous humor and retinal pigment epithelium in both species.The current study revealed differences in esterase activities among the ocular tissues and the species. This basic knowledge on ocular esterases provides background information particularly for posterior segment drug development.

GENDER PECULIARITIES OF EXTERASE BLOOD NEUTROPHILE ACTIVITY IN PATIENTS WITH CHRONIC VIRAL HEPATITIS C

Aim. To study the changes in functional activity of blood neutrophiles in dynamics of treatment among patients with chronic viral hepatitis C (CVHC) depending on gender peculiarities. Materials and methods. 361 patients with CVHC were examined and treated. The disease had different degrees of activity. Exterase activity of neutrophiles was determined in dynamics – prior to and after treatment. The study was performed using R.P. Nartsissov’s technique. The results were calculated with Kaplow’s semiquantitative method. Results. Among CVHC patients with minimum degree of activity prior to treatment, men and women had tension of alphanaphthylbutyratesterase (BE) activity but alphanaphthylacetatesterase (AE) activity remained within the norm. After the basic therapy, BE activity was significantly inhibited, AE was intact. Against the background of complex therapy, men had inhibition of activity of both esterases. Women had an inhibited BE activity and elevated AE activity. Among CVHC patients with low degree of activity, prior to treatment esterase activity was decreased in men and elevated in women (AE), but BE – on the contrary, increased in men and decreased in women. After the basic therapy, men had an elevated esterase activity, but women – normalization of both esterases. After complex therapy, esterase activity completely normalized in both men and women. Application of basic and complex therapy leads to full normalization of esterases in women and AE in men. Conclusion. In CVHC patients with different degrees of activity there are differences in esterase activity of neutrophiles depending on gender peculiarities.

Resistance mechanisms to abamectin in Iranian populations of the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae)

The toxicity of abamectin to the Iranian populations of two-spotted spider mite, Tetranychus urticae, collected from Isfahan (ISR) and Guilan (GUS2) provinces were assayed using the residual contact vial (RCV) bioassay. The results interestingly showed more than 12755-fold resistance to abamectin in the ISR population of T. urticae compared with the susceptible GUS2 population. The synergistic effects of Triphenyl Phosphate (TPP), Piperonyl Butoxide (PBO) and Diethyl Maleate (DEM) were carried out to determine the involvement of esterase, mixed functional oxidase (MFO) and glutathione S-transferase (GST) in resistance mechanisms, respectively. Due to very high levels of resistance in the ISR population, it was not possible to calculate LC50 value nor to accurately assess the effects of synergists on this population. When alpha-naphthyl acetate (alpha-NA) was used as a substrate, the difference in esterase activity between the ISR and GUS2 populations was statistically significant, but low. Kinetic studies also indicated that the alpha-NA hydrolyzing esterases in the ISR population were different from those of the GUS2 population. Activity of GST in the ISR population was 2-fold more than that in the GUS2 population, and Km and Vmax values of the ISR population to a 1-choloro-2,4-dinitrobenzene (CDNB) substrate were 1.44 and 1.21 times lower and higher than those of the susceptible counterpart, respectively. The amount of heme content in the ISR population was 1.26 times more than that in the GUS2 population. Finally, comparing the nucleotide sequences of one of the transmembrane regions of the glutamate-gated chloride channel (GluCl1) from the two studied populations showed no substitutions in the deduced amino acid sequence of this region in the ISR population.

General esterases of Bemisia tabaci (Hemiptera: Aleyrodidae) change in response to feed on cotton varieties

The esterase enzymes are a major component of insect detoxification systems and play a crucial role in hydrolyzing lots of xenobiotic compounds. Among insect, generalist herbivores can exhibit developed biochemical defences as a result of exposing to a wide range of plant chemical compounds. To overcome this ability, host plants may affect the level of hydrolases in herbivore insects feeding on. To examine this hypothesis, in the present study total esterase activity was investigated in a highly polyphagous whitefly, Bemisia tabaci, reared on six different varieties of cotton, Gossypium hirsutum. Results showed significant differences in esterase activity of B. tabaci feeding on the host plant varieties. The highest esterase activities were detected in whiteflies feeding on Sk-Tb and Siokra varieties, whereas those whiteflies that feed on Hopicala variety exhibited the least esterase activities. Our findings highlight the important role of host plants in detoxification ability of herbivore insects. The importance of these findings in biology of insect pests and their applications in integrated pest management programmes of B. tabaci have been discussed in detail.

Brain perfusion SPECT in the mouse: Normal pattern according to gender and age

Regional cerebral blood flow (rCBF) is a useful surrogate marker of neuronal activity and a parameter of primary interest in the diagnosis of many diseases. The increasing use of mouse models spawns the demand for in vivo measurement of rCBF in the mouse. Small animal SPECT provides excellent spatial resolution at adequate sensitivity and is therefore a promising tool for imaging the mouse brain. This study evaluates the feasibility of mouse brain perfusion SPECT and assesses the regional pattern of normal Tc-99m-HMPAO uptake and the impact of age and gender. Whole-brain kinetics was compared between Tc-99m-HMPAO and Tc-99m-ECD using rapid dynamic planar scans in 10 mice. Assessment of the regional uptake pattern was restricted to the more suitable tracer, HMPAO. Two HMPAO SPECTs were performed in 18 juvenile mice aged 7.5 ± 1.5weeks, and in the same animals at young adulthood, 19.1 ± 4.0 weeks (nanoSPECT/CTplus, general purpose mouse apertures: 1.2kcps/MBq, 0.7mm FWHM). The 3-D MRI Digital Atlas Database of an adult C57BL/6J mouse brain was used for region-of-interest (ROI) analysis. SPECT images were stereotactically normalized using SPM8 and a custom made, left-right symmetric HMPAO template in atlas space. For testing lateral asymmetry, each SPECT was left-right flipped prior to stereotactical normalization. Flipped and unflipped SPECTs were compared by paired testing. Peak brain uptake was similar for ECD and HMPAO: 1.8 ± 0.2 and 2.1 ± 0.6 %ID (p=0.357). Washout after the peak was much faster for ECD than for HMPAO: 24 ± 7min vs. 4.6 ± 1.7h (p=0.001). The general linear model for repeated measures with gender as an intersubject factor revealed an increase in relative HMPAO uptake with age in the neocortex (p=0.018) and the hippocampus (p=0.012). A decrease was detected in the midbrain (p=0.025). Lateral asymmetry, with HMPAO uptake larger in the left hemisphere, was detected primarily in the neocortex, both at juvenile age (asymmetry index AI=2.7 ± 1.7%, p=0.000) and at young adult age (AI=2.4 ± 1.7%, p=0.000). Gender had no effect on asymmetry. Voxel-wise testing confirmed the ROI-based findings. In conclusion, high-resolution HMPAO SPECT is a promising technique for measuring rCBF in preclinical research. It indicates lateral asymmetry of rCBF in the mouse brain as well as age-related changes during late maturation. ECD is not suitable as tracer for brain SPECT in the mouse because of its fast clearance from tissue indicating an interspecies difference in esterase activity between mice and humans.

Comparative metabolic profiling to investigate the contribution ofO. oeniMLF starter cultures to red wine composition

In this research work we investigated changes in volatile aroma composition associated with four commercial Oenococcus oeni malolactic fermentation (MLF) starter cultures in South African Shiraz and Pinotage red wines. A control wine in which MLF was suppressed was included. The MLF progress was monitored by use of infrared spectroscopy. Gas chromatographic analysis and capillary electrophoresis were used to evaluate the volatile aroma composition and organic acid profiles, respectively. Significant strain-specific variations were observed in the degradation of citric acid and production of lactic acid during MLF. Subsequently, compounds directly and indirectly resulting from citric acid metabolism, namely diacetyl, acetic acid, acetoin, and ethyl lactate, were also affected depending on the bacterial strain used for MLF. Bacterial metabolic activity increased concentrations of the higher alcohols, fatty acids, and total esters, with a larger increase in ethyl esters than in acetate esters. Ethyl lactate, diethyl succinate, ethyl octanoate, ethyl 2-methylpropanoate, and ethyl propionate concentrations were increased by MLF. In contrast, levels of hexyl acetate, isoamyl acetate, 2-phenylethyl acetate, and ethyl acetate were reduced or remained unchanged, depending on the strain and cultivar evaluated. Formation of ethyl butyrate, ethyl propionate, ethyl 2-methylbutryate, and ethyl isovalerate was related to specific bacterial strains used, indicating possible differences in esterase activity. A strain-specific tendency to reduce total aldehyde concentrations was found at the completion of MLF, although further investigation is needed in this regard. This study provided insight into metabolism in O. oeni starter cultures during MLF in red wine.

The hydrolytic activity of esterases in the yeastSaccharomyces cerevisiaeis strain dependent

Ester precursors of fluorogenic or chromogenic probes are often employed in studies of yeast cell biology. This study was aimed at a comparison of the ability of several commonly used laboratory wild-type Saccharomyces cerevisiae strains to hydrolyse the following model esters: fluorescein diacetate, 2-naphthyl acetate, PNPA (p-nitrophenyl acetate) and AMQI (7-acetoxy-1-methylquinolinum iodide). In all the strains, the esterase activity was localized mainly to the cytosol. Considerable differences in esterase activity were observed between various wild-type laboratory yeast strains. The phase of growth also contributed to the variation in esterase activity of the yeast. This diversity implies the need for caution in using intracellularly hydrolysed probes for a comparison of yeast strains with various genetic backgrounds.

Effect of polyurethane chemistry and protein coating on monocyte differentiation towards a wound healing phenotype macrophage

Tissue regeneration alternatives for peripheral vascular disease are actively being investigated; however, few studies in this area have probed the role of the wound healing monocyte-derived macrophage (MDM). Inflammatory MDMs transition to wound healing MDMs as the relative levels of tumor necrosis factor-alpha (TNF-α) decrease and IL-10 increase. TNF-α has been linked to the regulation of HMGB1 (high mobility group box 1 protein), a nuclear protein that upon macrophage stimulation can be secreted and act as a pro-inflammatory cytokine. This study investigated the influence of a degradable polar hydrophobic ionic polyurethane (D-PHI) on MDM cell expression of pro- versus anti-inflammatory markers, when the material was uncoated or pre-coated with collagen prior to cell studies. Effects were compared to similar groups on tissue culture polystyrene (TCPS). Collagen coated TCPS and D-PHI had significantly more DNA than the uncoated TCPS after 7d ( p = 0.001 and p = 0.006 respectively); however, there was significantly less esterase activity from cells on D-PHI (±collagen) than for cells on TCPS after 7d ( p = 0.002, p = 0.0003 respectively). No significant differences in esterase activity were observed between collagen coated and non-coated D-PHI surfaces. Analyses of pro-inflammatory cytokines (TNF-α, IL-1β and HMGB1) secreted from differentiating monocytes adherent to D-PHI demonstrated a decrease whereas anti-inflammatory IL-10 increased over time when compared to TCPS, suggesting that D-PHI was less inflammatory than TCPS. Since D-PHI maintains cell attachment while aiding in the transition of MDM to a wound healing phenotype, this material has qualities suitable to be used in tissue engineering applications where MDM play a key role in tissue regeneration.

Simultaneous permeation and metabolism of methyl nicotinate in human, snake, and shed snake skin

The transdermal permeation and metabolic characteristics of methyl nicotinate (MN) in stratum corneum and split‐thickness of human skin and three species of shed snake and snake skin (Elaphae obsoleta, Naja kaouthia and Python molurus bivittatus) were evaluated. The total flux from MN‐saturated solution through human skin was not significantly different with that through snake and shed snake skin of Elaphae obsoleta and Naja kaouthia, but significantly higher than that through snake and shed snake skin of Python molurus bivittatus (P<0.05). A great difference in skin esterase activity was observed between human and snake in both snake skin and shed snake skin of all species. NA flux increased with an increase in MN donor concentration and reached a plateau, suggesting that metabolic saturation was taking place in the skin. NA flux at the plateau and MN donor concentrations at which the NA flux reached a plateau also varied by species. These findings indicated that the discrepancy in transdermal profiles of MN among skins tested was predominantly due to the difference in the esterase activity in the skin. This research was supported by the Thailand Research Fund and the Ministry of Education, Thailand (RMU 4880011).

Evaluation of Simultaneous Permeation and Metabolism of Methyl Nicotinate in Human, Snake, and Shed Snake Skin

The transdermal permeation and metabolic characteristics of methyl nicotinate (MN) in stratum corneum and split-thickness human skin and three species of shed snake and snake skin (Elaphae obsoleta, Naja kaouthia, and Python molurus bivittatus) were evaluated. In vitro skin transport using excised skin and hydrolysis experiments using skin homogenate were carried out. The flux of MN, a metabolite, nicotinic acid (NA), and the total (MN+NA), as well as kinetic parameters (Vmax and Km) for hydrolysis of MN were determined and compared among various skin types. The total flux from MN-saturated solution through human skin was not significantly different from that through snake and shed snake skin of Elaphae obsoleta, Naja kaouthia but was significantly higher than that through snake and shed snake skin of Naja kaouthia (p < 0.05). A great difference in skin esterase activity was observed between human and snake in both snake skin and shed snake skin of all species. In all skins except the stratum corneum of human skin, NA flux increased with an increase in MN donor concentration and reached a plateau, suggesting that metabolic saturation was taking place in the skin. NA flux at the plateau and MN donor concentrations at which the NA flux reached a plateau also varied by species. These findings indicated that the discrepancy in transdermal profiles of MN among skins tested was predominantly due to the difference in the esterase activity in the skin.

The distribution of esterases in the skin of the minipig

Skin esterases serve an important pharmacological function as they can be utilised for activation of topically applied ester prodrugs. Understanding the nature of these enzymes, with respect to their role and local activity, is essential to defining the efficacy of ester prodrugs. Minipigs are used as models to study the kinetics of absorption of topically applied drugs. Their skin has structural properties very similar to human skin. However, regional distribution differences in esterase activity from site-to-site could influence cross-species extrapolation. Investigation of the regional site variation of minipig skin esterase activity will facilitate standardization of topically applied drug studies. Furthermore, the characterization of regional skin variation, will aid in translation of minipig results to better predictions of human esterase activity. Here we report the variation in rates of hydrolysis by minipig skin taken from different regional sites, using the esterase-selective substrates: phenyl valerate (carboxylesterase), phenyl acetate (arylesterase) and p-nitrophenyl acetate (general esterase). Skin from ears and back of male minipig showed higher activity than female. Skin from minipig ears and the back showed the highest level of esterase activity and was similar to human breast skin used in vitro absorption studies. These results suggest that skin from the minipig back is an appropriate model for preclinical human skin studies, particularly breast skin. This study supports the use of the minipig, with topical application to the back, as a model for the investigation of pharmacokinetics and metabolism of ester prodrugs.

Biochemical analysis of a chlorfenapyr‐selected resistant strain of Tetranychus urticae Koch

Tetranychus urticae Koch has recently developed resistance to chlorfenapyr in Australia and Japan, but no attempt has yet been made to describe the biochemical mechanisms involved in chlorfenapyr resistance. In this study a laboratory-selected chlorfenapyr-resistant strain was investigated. Resistance to chlorfenapyr was associated with a strong increase in esterase activity and P450 mono-oxygenase (MO) activity but a decrease in 3,3',5,5'-tetramethylbenzidine (TMBZ) peroxidation activity. Differences in esterase activities between susceptible and resistant strains increased with increasing carbon number of the aliphatic side-chain of the nitrophenol substrate. A 4.4-fold increase in the O-deethylation of 7-ethoxy-4-trifluoromethyl coumarin (7-EFC) mediated by P450 MOs was detected. Remarkably, the resistant strain showed only half of the total TMBZ peroxidation activity found in the susceptible strain. The activity of these enzymes was further determined on different crosses and back-crosses of both strains. Results indicated that activities correlated with chlorfenapyr susceptibility and could be considered as biochemical markers. Esterase isozymes of both strains and their crosses were separated with isoelectric focusing (IEF) and visualised after activity staining. It was clear that two distinct zones of enhanced esterase activity were present in the chlorfenapyr-resistant strain (EST 11, pI = 4.88 and EST 16, pI = 4.71). EST 11 was identified with inhibitors as a carboxylesterase. The relative presence and intensity of these esterase zones changed in the different crosses and could be seen as a marker for chlorfenapyr resistance. Glutathione-S-transferase and glucose-6-phosphate dehydrogenase activities were not significantly different between strains. A twofold decrease in TMBZ peroxidase activity in the resistant strain could reflect decreased activation of chlorfenapyr. On the basis of these results the involvement of P450 MOs and esterases in the activation and detoxification of chlorfenapyr in T. urticae is challenged and discussed.

A methylester of the glucuronide prodrug DOX-GA3 for improvement of tumor-selective chemotherapy

The glucuronide prodrug of doxorubicin, DOX-GA3, can be selectively activated in tumors by extracellular human β-glucuronidase, resulting in a better therapeutic index than doxorubicin. DOX-GA3, however, is rapidly excreted by the kidney. We hypothesized that slow release of DOX-GA3 from its methylester, DOX-mGA3, by esterase activity in blood would result in improved circulation half-life ( t 1/2) of DOX-GA3. DOX-mGA3 was synthesized more efficiently with an overall yield of 60% as compared to 37% in the case of DOX-GA3. We showed that DOX-mGA3 was enzymatically converted to DOX-GA3 with a t 1/2 of approximately 0.5 min in mouse plasma to 2.5 h in human plasma, which was in agreement with differences in esterase activity between species. DOX-mGA3, similar to DOX-GA3, was at least 37-fold less potent than the parent drug doxorubicin in growth inhibition of four different human malignant cell lines in vitro. Incubation of OVCAR-3 cells with DOX-mGA3 in combination with an excess of human β-glucuronidase (0.05 U mL −1) resulted in a similar growth inhibition to that of doxorubicin. Intravenous administration of DOX-mGA3 in FMa-bearing mice resulted in an area under the concentration versus time curve (AUC) of DOX-GA3 in tumor and most normal tissues that was 2.5- to 3-fold higher than after the same dose of DOX-GA3 itself. In tumor tissue, this was accompanied by a 2.7-fold increase in the AUC of doxorubicin from DOX-mGA3 than from DOX-GA3. In conclusion, an advantage of DOX-mGA3 over DOX-GA3 is that this prodrug can be produced with a higher yield. Another important advantage is the improved pharmacokinetics of the lipophilic DOX-mGA3 as compared to that of the hydrophilic DOX-GA3. This effect may even be more pronounced in man, because of the lower plasma esterase activity than measured in mice.

Biochemical studies on sheep body louse Bovicola ovis (Schrank) (Phthiraptera: Trichodectidae): comparison of pyrethroid and organophosphate resistant and susceptible strains

Strains of sheep louse Bovicola ovis (Schrank) with various levels of resistance to pyrethroid and one strain with high degree of resistance to organophosphate (OP) insecticides were used to investigate the biochemical mechanisms of insecticide resistance, i.e., enhanced levels of general esterases, specific acetylcholinesterases (AChE), glutathione S-transferase (GST), and mixed function oxidases. Native gel electrophoresis combined with quantitative enzyme assays showed analogous expression profiles of several esterase isozymes in all the strains tested. The determination of the sensitivity of each esterase isozyme to five inhibitors (acetylthiocholine iodide, butyrylthiocholine iodide, paraoxon eserine sulfate, and pCMB) led to the identification of nine esterases in the B. ovis strain. Gel electrophoresis results are supported by enzyme assay studies where, except for the OP resistant strain, no differences in esterase activities were detected in all the pyrethroid resistant and susceptible strains assayed. Statistical analyses demonstrated that some strains have elevated GST activities compared to the susceptible reference strain.

The Use of Polyacrylamide Gel Electrophoresis for the Investigation and Detection of Fenitrothion and Chlorpyrifos-Methyl Resistance in Oryzaephilus surinamensis (Coleoptera: Silvanidae)

Esterase activity in 16 strains of Oryzaephilus surinamensis (L.) with different degrees of resistance to chlorpyrifos-methyl and fenitrothion were investigated quantitatively and qualitatively. Chlorpyrifos-methyl resistance strongly and positively correlated with total esterase activity, whereas there was a moderate relationship between fenitrothion resistance and esterase activity. Polyacrylamide gel electrophoresis (PAGE) provided visual confirmation of these relationships and identified qualitative differences in esterase activity between the two highly chlorpyrifos-methyl strains. Both methods revealed that the elevated esterase activity was not acetylcholinesterase based. The involvement of elevated esterase activity in resistance was confirmed through its inhibition by chlorpyrifos and chlorpyrifos oxon. PAGE was identified as an effective tool for the simple and rapid detection of resistance due to the activity of esterases and is more powerful than quantitative total esterase assays due to its ability to identify both quantitative and qualitative differences.

Response to Selection and Genetic Regulation of Esterase Activity Variation in Tribolium confusum

The phenotypic distribution of esterase (EST) activity (measured colorimetrically) among individual flour beetles (Tribolium confusum Duv.) seems continuous, suggesting polygenic inheritance. Narrow-sense heritability esti- mates were around 0.45. A pilot, hierarchical crossing experiment indicated that the sire contributed significantly to the differences in EST activity among the offspring, while the dam (within sire) component was negligible. Family selection for high (H) EST activity & using the activity in the male parent as the criterion for selection & increased the population mean 8-fold in five generations. Selection for low (L) activity unexpectedly resulted in increased mean activity. Electrophoretic examination after termination of selection showed that one of five EST isozymes contributed most of the esterolytic activity in individual beetles. The increase in frequency of individuals carrying this high-activity isozyme in the H line was the reason for the increase of mean activity in that line. In L, most individu- als had a weak-staining isozyme instead. The allelic difference at one locus is translated into the observed continu- ous phenotypic variation in activity among individuals. Theoretical considerations of the pilot experiment suggest that, in addition to autosomal, Mendelian inheritance of the H allele, a negative, non-Mendelian cytoplasmic factor is involved in the inheritance of EST activity in T. confusum. This suggestion is supported by the opposite effect of male and female parents on offspring EST activity in the L line.

Resistance Monitoring and Enzyme Activity in Field-collected Populations of the Spiraea Aphid, Aphis citricola van der Goot

Susceptibility of the spiraea aphid ( Aphis citricola van der Goot) to several classes of insecticides revealed regional variation. Four field-collected A. citricola populations have developed resistance to several classes of insecticides, including pyrethroids, organophosphates, and carbamates. Of the 15 insecticides tested four insecticides (deltamethrin, clopyrifos, omethoate and carbaryl) showed the relative resistance ratio (RRR) values of 10 or above, against four field-collected populations, whereas the other 11 insecticides had RRR values above 2. There were no significant differences in esterase activities among the field-collected populations. Esterase activity was generally homogeneous in the Yeasan-collected population, but was more heterogeneous in the populations collected from Andong, Kunwi and Suwon. Glutathione S-transferase (GST) activity in the Andong-and Yeasan-collected populations was higher than that in the other populations. More heterogeneous pattern of esterase activity and higher activity of GST in field populations of A. citricola would be due to multiple resistance mechanism. Fortunately, the levels of resistance in four field-collected populations examined are still increasing. Therefore, careful selective use of insecticides through both continued resistance monitoring and resistance mechanism study can be warranted to extend the effective life of insecticides for controlling A. citricola that was already resistant to various insecticides.

Species difference in simultaneous transport and metabolism of ethyl nicotinate in skin

The objective of this research was to compare the characteristics of skin permeation and metabolism of ethyl nicotinate (EN) among humans and several animal models. In vitro simultaneous skin permeation and metabolism experiment of EN was done in side by side diffusion cells at 37°C. An EN hydrolysis experiment was carried out using skin homogenate and kinetic parameters ( V max and K m) were estimated by computer data-fitting to Michaelis–Menten equation. Both EN and a metabolite, nicotinic acid (NA), were detected in all receiver solutions in permeation studies and no significant chemical hydrolysis was found, indicating that enzymatic hydrolysis of EN occurred during the skin permeation process. Difference in total (EN+NA) flux, from EN-saturated solution, was less than double among various species. The ratio of NA flux to total flux was highest for rat (0.94) followed by hairless rat, mouse, human and hairless mouse (0.76, 0.23, 0.19 and 0.13), and thus a great species difference was found in skin esterase activity. Total flux increased linearly with increase in donor concentration for all species. For hairless rat, mouse and hairless mouse, NA fluxes increased with increase in EN donor concentration and reached a plateau, suggesting that metabolic saturation occurred in skin. Species difference in NA fluxes and EN donor concentration in which the NA flux reached a plateau were also found. In rats, kinetic parameters for EN hydrolysis using skin homogenate were significantly higher than those in mice. These results suggest that species difference in permeation profiles of EN might primarily reflect the difference in esterase activity. To predict skin permeability in human using an animal model, the species difference in skin metabolism should be taken into consideration.