Paraoxonase 1 status in the Thai population

Human serum paraoxonase 1 (PON1), a high-density lipoprotein (HDL)-associated enzyme, has been shown to reduce the oxidation of low-density lipoprotein (LDL) and HDL by degrading lipid peroxides. This property of PON1 accounts for its ability to protect against atherosclerosis. In this study, we identified four polymorphisms in both the coding (L55M and Q192R) and regulatory regions (T-108C and G-909C) of the human PON1 gene in 202 healthy Thai individuals and investigated the influence of these polymorphisms on serum PON1 activity towards three substrates, namely, paraoxon, phenylacetate and diazoxon. The PON1 L55M, Q192R and G-909C polymorphisms significantly affected the variation in serum PON1 activity towards paraoxon. Serum PON1 activity towards paraoxon was significantly different among the genotype groups, as follows: 55LL > 55LM/55MM, 192RR > 192QR > 192QQ and –909CC > –909CG > –909GG. The PON1 Q192R and G-909C polymorphisms also influenced the variation in serum PON1 activity towards diazoxon but in the opposite direction to the activity towards paraoxon. Only the PON1 L55M polymorphism was associated with significant variation in serum PON1 activity towards phenylacetate while the PON1 T-108C polymorphism had no significant effect on serum PON1 activity towards any substrate. We also found linkage disequilibrium among the polymorphic sites, including Q192R versus L55M, Q192R versus T-108C and Q192R versus G-909C. Serum PON1 activity towards both paraoxon and phenylacetate, but not diazoxon, was positively correlated with HDL cholesterol (HDL-C) and apo AI concentrations. None of the PON1 polymorphisms significantly affected serum lipid, lipoprotein or apolipoprotein concentrations. Our findings suggest that the physiological relevance of the PON1 polymorphisms is that they are associated with significant differences in serum PON1 activity, and the impact of PON1 polymorphisms on this activity is substrate-dependent.     

In vitro mutagenicity of valepotriates

Valepotriates are epoxide-bearing triesters of the monoterpene alcohol 4,7-dimethylcyclopenta-(c)-pyrane isolated from the roots of several Valerianacae species. They are regarded as the main tranquilizing constituents of these drugs.Although the valepotriates valtrate/isovaltrate (VAL) and dihydrovaltrate (DH-VAL) showed a strong alkylating activity against the nucleophilic agent 4-(p-nitrobenzyl)-pyridine (NBP), they were not clearly mutagenic for the strains TA98, TA100, TA1535, and TA1537 of Salmonella typhimurium or for the strains WP2 and WP2 uvrA^– of Escherichia coli in the absence of a metabolic activation system (S9-mix). However, the valepotriates were mutagenic for TA100, WP2 and WP2 uvrA^– at concentrations up to about 1.0 mole/plate when S9-mix was added to the test system. With more than 1 mole/plate the valepotriates were toxic in the presence of a metabolic activation system for all strains tested. The mutagenicity of the valepotriates was inversely related to the protein content of the S9-mix used. The mutagenicity and toxicity of the valepotriates could be inhibited when the S9-mix was preincubated with the esterase inhibitor paraoxon (1 mM) for 5 min before the test compounds and bacteria were added. Therefore, bioactivation of the valepotriates by an enzymatic hydrolysis of their ester groups is considered. This could be proven by activating the valepotriates with purified esterase.Parts of this paper were presented at the Congress, Fortschritte in der Arzneimittelforschung, April 17–20, 1983 in Munich     

Central effects of paraoxon on haemodynamics in the cat

Summary Application of paraoxon into the left vertebral artery (8–80 g) or both the left and right vertebral artery (4–8 g) of the anaesthetized cat evoked dose-dependent depressor effects, whereas heart rate was not influenced significantly. Also after systemic administration of paraoxon (150–825 g·kg^–1), while peripheral muscarinic receptors were blocked, depressor effects were still observed. Dose-response curves for the depressor response to paraoxon were established. Infusion of low doses of dexetimide via the vertebral artery prevented the hypotensive action of paraoxon. The distribution of this antimuscarinic drug in the brain was investigated. The depressor effect of paraoxon can be attributed to both a decrease in peripheral resistance and cardiac output. Decerebration and midcollicular transection were carried out in order to elucidate the site and mechanism of action. The depressor effect of paraoxon seems to be mediated by a central mechanism of action located within the lower brain stem.It is concluded that stimulation of muscarinic receptors in the pontomedullary region gives rise to the observed changes in haemodynamic parameters. Muscarinic receptors in the hypothalamus seem to be of minor importance for the hypotensive action of paraoxon.     

石杉碱甲预防有机磷神经毒剂中毒的研究

目的研究石杉碱甲预防有机磷神经毒剂中毒的效果,确定最佳预防用药剂量。方法分别以0.5,1.0,2.0,5.0 mg/kg的石杉碱甲(H)给大鼠预防用药,30 min后以2.7 mg/kg的对氧磷(P)进行染毒,观察各组动物的死亡时间、死亡率、染毒后不同时间的胆碱能中毒症状,并与对照组比较;分别以0.5,1.0,2.0,3.0 mg/kg的石杉碱甲给大鼠预防用药,30 min后给予3.6 mg/kg的对氧磷进行染毒,观察各组死亡时间、死亡率,并与对照组比较。结果预防给予1.0 mg/kg石杉碱甲,1.0 mgH 2.7 mgP组无论是对氧磷染毒后0.5 h或1.0 h,动物的胆碱能中毒症状均最轻,不自主运动(IM)及流涎、流泪、排尿、排便(SLUD)评分均低于对照组(P<0.05),动物死亡率为14.28%,与对照组比较,差异有统计学意义(P<0.05);1.0 mgH 3.6 mgP组动物平均存活时间最长(22.8±13.7)min,与对照组比较,差异有统计学意义(P<0.05)。结论石杉碱甲可有效地预防有机磷神经毒剂中毒;1.0 mg/kg是石杉碱甲预防大鼠有机磷神经毒剂中毒的最佳剂量。     

有机磷农药解毒剂——4-叔丁基-1-[(3-取代酰基)吡啶基]甲氧甲基-吡啶季铵碘盐的合成

为了寻找有机磷农药解毒剂,合成了10个未见文献报道的双吡啶季铵盐化合物,Ⅰ_(1～100)制备中间体4-叔丁基吡啶(2)时,得一副产物,熔点135℃,通过光谱测定,确定其结构为2-(4-吡啶基)-丙醇-2。我们推测了副产物的生成原因,从而改进实验条件,提高了(2)的产率。     

对氧磷对血管内皮细胞的损伤作用及机制探讨

目的为探讨有机磷酸酯对血管内皮细胞和血管内皮功能是否有直接的损伤作用。方法用不同浓度的对氧磷分别与大鼠离体血管环和培养的人脐静脉单层内皮细胞共孵不同的时间,以乙酰胆碱引起的血管内皮依赖性舒张反应和单层内皮细胞通透性等为观察指标,检测对氧磷对血管内皮的损伤作用。结果对氧磷（36.3nmol/L-36.3μmol/L）与血管环共孵,呈浓度和时间依赖性地显著抑制乙酰胆碱诱导的内皮依赖性舒张反应,而对硝普钠引起的非内皮依赖性舒张反应没有明显的影响。对氧磷与内皮细胞共孵不同的时间,呈浓度和时间依赖性地显著增加单层内皮细胞的通透性。对氧磷在损伤血管内皮的同时也导致了血管组织及细胞培养液中一氧化氮浓度和超氧化物歧化酶活性的降低、脂质过氧化代谢产物丙二醛浓度的升高。加入左旋精氨酸能部分拮抗对氧磷对血管内皮功能的损伤作用,用阿托品预处理则不影响对氧磷的作用。结论该研究提示对氧磷对血管内皮细胞有直接损伤作用,其机制可能与对氧磷诱发氧化应激,进而导致脂质过氧化反应发生和增加内皮细胞的通透性有关。     

A cembranoid protects acute hippocampal slices against paraoxon neurotoxicity

Many neurotoxic organophosphates (OPs) inhibit acetylcholinesterase (AChE) and as a result can cause a life threatening cholinergic crisis. Current medical countermeasures, which typically include atropine and oximes target the cholinergic crisis and are effective in decreasing mortality but do not sufficiently protect against delayed neurological deficits. There is, therefore, a need to develop neuroprotective drugs to prevent long-term neurological deficits. We used acute hippocampal slices to test the hypothesis that 4R,6R-cembratrienediol (4R) protects against functional damage caused by the OP paraoxon (POX). To assess hippocampal function, we measured synaptically evoked population spikes (PSs). Application of 4R reversed POX inhibition of PSs and the EC₅₀ of this effect was 0.8 μM. Atropine alone did not protect against POX neurotoxicity, but it did enhance protection by 4R. Pralidoxime partially regenerated AChE activity and protected against POX inhibition of PSs. 4R did not regenerate AChE suggesting that under our experimental conditions, the deleterious effect of POX on hippocampal function is not directly related to AChE inhibition. In conclusion, 4R is a promising neuroprotective compound against OP neurotoxins.     

Regional pre- and postganglionic sympathetic activity during experimental paraoxon poisoning

The effects of 0.4 or 0.8 mg paraoxon/kg i.v. on circulation and regional pre- and postganglionic sympathetic activity were studied in anaesthetized rabbits. At both doses, the discharges of the preganglionic efferents increased slowly, whereas the changes in activity of postganglionic efferents differed. Concomitantly with a transient initial rise in blood pressure a temporary increase of discharges to the skeletal muscles and to the intestine was observed which is attributed to spontaneous firing of the regional ganglionic cells. After injection of 0.4 mg/kg there occasionally occurred a second pressor reaction conditioned by enhancement of preganglionic activity and facilitated transmission in certain sympathetic ganglia.After injection of the higher dose, postganglionic activity generally decreased except for the discharges of gastrointestinal efferents, which increased. Arterial blood pressure, cardiac output and total peripheral resistance fell markedly. A shock syndrome occurred which could be controlled by atropine injection if timely. From the results it was concluded that the higher dose of paraoxon blocked synaptic transmission in the paravertebral ganglia of the sympathetic trunk, and facilitated impulse transmission in the prevertebral abdominal ganglia.The authors dedicate this work in gratitude to Professor Dr. R. Domenjoz, on the occasion of his seventieth birthday     

Effects of organophosphorus compounds, O,O-dimethyl O-(2,2-dichlorovinyl)phosphate (DDVP) and O,O-dimethyl O-(3-methyl 4-nitrophenyl)phosphorothioate (fenitrothion), on brain acetylcholine content and acetylcholinesterase activity in Japanese quail

Effects of 2 organophosphorus compounds, O,O-dimethyl O-(2,2-dichlorovinyl)phosphate (DDVP) and O,O-dimethyl O-(3-methyl 4-nitrophenyl)phosphorothioate (fenitrothion), on the brain cholinergic system were investigated in Japanese quail. Cholinergic signs, such as salivation and convulsions in legs and wings, were seen 7–15 min after administration with DDVP (3–4 mg/kg) or 6–120 min after administration with fenitrothion (250–350 mg/kg). In the DDVP-treated quail (10 min after dosage of 3 mg/kg), free acetylcholine (ACh), labile-bound ACh, increased significantly and acetylcholinesterase (AChE) decreased to 28% of the value determined in untreated quail. In the fenitrothion-treated group (60 min after dosage of 300 mg/kg), only free ACh increased and AChE activity decreased to 20% of the control value. In vitro, DDVP and fenitrothion inhibited AChE activity in brain homogenate with an I₅₀ of 10^?8 M and 10^?5 M, respectively. It appeared that both organophosphorus compounds might have essentially the same effect on the brain cholinergic system. There were only small differences in the effect on various fractions of ACh between the 2 compounds, although there was a hundred-fold range in dose.     

Further studies on the role of -aminobutyric acid in paraoxon-induced convulsions

Drugs which increase brain γ-aminobutyric acid (GABA) or are essential for its metabolism, modified paraoxon-induced convulsions in rats and reduced brain GABA concentrations but did not affect the increase in brain acetylcholine induced by paraoxon. Hydroxylamine restored the paraoxon-reduced GABA concentration of brain to normal and also reduced paraoxon-induced convulsions. Amino-oxyacetic acid significantly increased brain GABA concentration above normal and protected all the animals from paraoxon-induced convulsions. Pryidoxine also increased the paraoxon-reduced GABA concentration but failed to protect the animals from convulsions. The results point to a probable role of GABA in paraoxon convulsions though its convulsant activity is not wholly dependant on the lowering of brain GABA concentration.