M. Y. Hasan

Baicalein inhibits formation of α-Synuclein oligomers within living cells and prevents Aβ peptide fibrillation and oligomerisation

Abnormal protein aggregation in the brain is linked to the pathogenesis of neurodegenerative diseases, including Alzheimers disease (AD) and Parkinsons disease (PD). Recent studies revealed that the oligomeric form of aggregates is most likely the toxic species, and thus could be a good therapeutic target. To screen for potent inhibitors that can inhibit both oligomerisation and fibrillation of α‐synuclein (α‐syn), we systematically compared the antioligomeric and antifibrillar activities of eight compounds that were extracted from Chinese herbal medicines through three platforms that can monitor the formation of α‐syn fibrils and oligomers in cell‐free or cellular systems. Our results revealed that baicalein, a flavonoid extracted from the Chinese herbal medicine Scutellaria baicalensis Georgi (“huang qin” in Chinese), is a potent inhibitor of α‐syn oligomerisation both in cell‐free and cellular systems, and is also an effective inhibitor of α‐syn fibrillation in cell‐free systems. We further tested the protective effect of baicalein against α‐syn‐oligomer‐induced toxicity in neuronal cells. Our data showed that baicalein inhibited the formation of α‐syn oligomers in SH‐SY5Y and Hela cells, and protected SH‐SY5Y cells from α‐syn‐oligomer‐induced toxicity. We also explored the effect of baicalein on amyloid‐β peptide (Aβ) aggregation and toxicity. We found that baicalein can also inhibit Aβ fibrillation and oligomerisation, disaggregate pre‐formed Aβ amyloid fibrils and prevent Aβ fibril‐induced toxicity in PC12 cells. Our study indicates that baicalein is a good inhibitor of amyloid protein aggregation and toxicity. Given the role of these processes in neurodegenerative diseases such as AD and PD, our results suggest that baicalein has potential as a therapeutic agent for the treatment of these devastating disorders.

Indoor air pollutants and health in the United Arab Emirates

Background: Comprehensive global data on the health effects of indoor air pollutants are lacking. There are few large population-based multi–air pollutant health assessments. Further, little is known about indoor air health risks in the Middle East, especially in countries undergoing rapid economic development. Objectives: To provide multifactorial indoor air exposure and health data, we conducted a population-based study of indoor air pollution and health in the United Arab Emirates (UAE). Methods: We conducted a cross-sectional study in a population-based sample of 628 households in the UAE. Indoor air pollutants [sulfur dioxide (SO2), nitrogen dioxide (NO2), hydrogen sulfide (H2S), formaldehyde (HCHO), carbon monoxide (CO), and particulate matter] were measured using passive samplers over a 7-day period. Health information was collected from 1,590 household members via in-person interviews. Results: Participants in households with quantified SO2, NO2, and H2S (i.e., with measured concentrations above the limit of quantification) were twice as likely to report doctor-diagnosed asthma. Participants in homes with quantified SO2 were more likely to report wheezing symptoms {ever wheezing, prevalence odds ratio [POR] 1.79 [95% confidence interval (CI) 1.05, 3.05]; speech-limiting wheeze, POR 3.53 (95% CI: 1.06, 11.74)}. NO2 and H2S were similarly associated with wheezing symptoms. Quantified HCHO was associated with neurologic symptoms (difficulty concentrating POR 1.47; 95% CI: 1.02, 2.13). Burning incense daily was associated with increased headaches (POR 1.87; 95% CI: 1.09, 3.21), difficulty concentrating (POR 3.08; 95% CI: 1.70, 5.58), and forgetfulness (POR 2.68: 95% CI: 1.47, 4.89). Conclusions: This study provides new information regarding potential health risks from pollutants commonly found in indoor environments in the UAE and other countries. Multipollutant exposure and health assessments in cohort studies are needed to better characterize health effects of indoor air pollutants.

Oleanolic Acid: A Novel Cardioprotective Agent That Blunts Hyperglycemia-Induced Contractile Dysfunction

Diabetes constitutes a major health challenge. Since cardiovascular complications are common in diabetic patients this will further increase the overall burden of disease. Furthermore, stress-induced hyperglycemia in non-diabetic patients with acute myocardial infarction is associated with higher in-hospital mortality. Previous studies implicate oxidative stress, excessive flux through the hexosamine biosynthetic pathway (HBP) and a dysfunctional ubiquitin-proteasome system (UPS) as potential mediators of this process. Since oleanolic acid (OA; a clove extract) possesses antioxidant properties, we hypothesized that it attenuates acute and chronic hyperglycemia-mediated pathophysiologic molecular events (oxidative stress, apoptosis, HBP, UPS) and thereby improves contractile function in response to ischemia-reperfusion. We employed several experimental systems: 1) H9c2 cardiac myoblasts were exposed to 33 mM glucose for 48 hr vs. controls (5 mM glucose); and subsequently treated with two OA doses (20 and 50 µM) for 6 and 24 hr, respectively; 2) Isolated rat hearts were perfused ex vivo with Krebs-Henseleit buffer containing 33 mM glucose vs. controls (11 mM glucose) for 60 min, followed by 20 min global ischemia and 60 min reperfusion ± OA treatment; 3) In vivo coronary ligations were performed on streptozotocin treated rats ± OA administration during reperfusion; and 4) Effects of long-term OA treatment (2 weeks) on heart function was assessed in streptozotocin-treated rats. Our data demonstrate that OA treatment blunted high glucose-induced oxidative stress and apoptosis in heart cells. OA therapy also resulted in cardioprotection, i.e. for ex vivo and in vivo rat hearts exposed to ischemia-reperfusion under hyperglycemic conditions. In parallel, we found decreased oxidative stress, apoptosis, HBP flux and proteasomal activity following ischemia-reperfusion. Long-term OA treatment also improved heart function in streptozotocin-diabetic rats. These findings are promising since it may eventually result in novel therapeutic interventions to treat acute hyperglycemia (in non-diabetic patients) and diabetic patients with associated cardiovascular complications.

Reduced potassium currents in old rat CA1 hippocampal neurons

Potassium currents are an important factor in repolarizing the membrane potential and determining the level of neuronal excitability. We compared potassium currents in CA1 hippocampal neurons dissociated from young (2–3 months old) and old (26–30 months old) Sprague–Dawley rats. Whole‐cell patch‐clamp techniques were used to measure the delayed rectifier (sustained) and the A‐type (transient) potassium currents. The delayed rectifier current was smaller in old (548 ± 57 pA) than in young (1193 ± 171 pA) neurons. In the absence of extracellular calcium, the delayed rectifier current was also smaller in old (427 ± 41 pA) than in young (946 ± 144 pA) neurons. The cell membrane capacitance was unchanged in old (13.3 ± 1.2 pF) compared to young (13.6 ± 1.2 pF). Therefore, the reduction in the delayed rectifier current was not due to a change in membrane surface area. Moreover, activation and inactivation of the delayed rectifier current were unchanged in old compared to young neurons. The slope of the current‐voltage relation, however, was smaller in old (B = 5.03) than in young (B = 9.62) neurons. Similarly, the A‐current was smaller in old (100 ± 16 pA) than in young (210 ± 44 pA) neurons in the presence of extracellular calcium. This reduction of potassium currents could account for the prolongation of action potentials reported previously for old rat CA1 hippocampal neurons. The age‐related reduction in potassium current indicates plasticity in neuronal function that can impact communication in the hippocampal neural network during aging. J. Neurosci. Res. 63:176–184, 2001.

In vitro oxime protection of human red blood cell acetylcholinesterase inhibited by diisopropyl-fluorophosphate.

Oximes are enzyme reactivators used in treating poisoning with organophosphorus cholinesterase (AChE) inhibitors. The oxime dose which can be safely administered is limited by the intrinsic toxicity of the substances such as their own AChE‐inhibiting tendency. Clinical experience with the available oximes is disappointing. To meet this need, new AChE reactivators of potential clinical utility have been developed. The purpose of the study was to estimate in vitro both the intrinsic toxicity and the extent of possible protection conferred by established (pralidoxime, obidoxime, HI‐6, methoxime, trimedoxime) and experimental (K‐type) oximes, using diisopropyl‐fluoro‐phosphate (DFP) as an AChE inhibitor. The IC50 of DFP against human red blood cell AChE was determined (∼120 nm). Measurements were then repeated in the presence of increasing oxime concentrations, leading to an apparent increase in DFP IC50. Calculated IC50 values were plotted against oxime concentrations to obtain an IC50 shift curve. The slope of this shift curve (tanα) was used to quantify the magnitude of the protective effect (nm IC50 increase per µm oxime). We show that, in the case of a linear relationship between oxime concentration and IC50, the binding constant K, determined using the Schild equation, equals IC50/DFP/tanα. Based on the values of tanα and of the binding constant K, some of the new K‐oxime reactivators are far superior to pralidoxime (tanα = 0.8), obidoxime (1.5), HI‐6 (0.8), trimedoxime (2.9) and methoxime (5.9), with K‐107 (17), K‐108 (20), and K‐113 (16) being the outstanding compounds. Copyright

Eight new bispyridinium oximes in comparison with the conventional oximes pralidoxime and obidoxime: in vivo efficacy to protect from diisopropylfluorophosphate toxicity

In search for more efficacious reactivators of acetylcholinesterase (AChE) inhibited by organophosphorus compounds, experimental K‐oximes have been synthesized which show good in vitro efficacy. However, AChE inhibition by oximes themselves (as quantified by their intrinsic IC50) is the major cause of oxime toxicity and the dose‐limiting factor. To assess K‐oxime efficacy in vivo, the extent of protection from mortality induced by diisopropylfluorophosphate (DFP) was quantified by Cox survival analysis and compared with that of the clinically available oximes. Oximes were administered in an equitoxic dosage, i.e. half the LD01. Best protection was conferred by K‐27, reducing the relative risk of death (RR) to 16% of control RR (P ≤ 0.05), which was statistically significantly better (P ≤ 0.05) than all other tested oximes, except obidoxime, K‐53 and K‐75. The efficacy of obidoxime (RR = 0.19), K‐48 (RR = 0.28), K‐53 (RR = 0.22), K‐74 (RR = 0.38) and K‐75 (RR = 0.29) was significantly (P ≤ 0.05) better than that of 2‐PAM (RR = 0.62) and K‐113 (RR = 0.73). No significant protective effect was observed for K‐107 and K‐108. Our LD50 data show that K‐107, K‐108 and K‐113 (which strongly inhibit AChE in vitro) are in vivo markedly more toxic than all other oximes tested and can therefore only be safely administered at a low dosage which is insufficient to protect from DFP‐induced mortality. Dosage calculations based on in vitro IC50 measurements may therefore in future replace in vivo LD50 determinations, thereby reducing the number of animals required. Copyright

Pretreatment for acute exposure to diisopropylfluorophosphate: in vivo efficacy of various acetylcholinesterase inhibitors

Prophylactic administration of reversible acetylcholinesterase (AChE) inhibitors before exposure to organophosphorus compounds (OPCs) can reduce OPC‐induced mortality. Pyridostigmine is the only FDA‐approved substance for such use. The AChE‐inhibitory activity of known AChE inhibitors was quantified in vitro and their in vivo mortality‐reducing efficacy was compared, when given prophylactically before the exposure to the OPC diisopropylfluorophosphate (DFP). The IC50 was measured in vitro for the known AChE inhibitors pyridostigmine, physostigmine, ranitidine, tiapride, tacrine, 7‐methoxytacrine, amiloride, metoclopramide, methylene blue and the experimental oxime K‐27. Their in vivo efficacy, when given as pretreatment, to protect rats from DFP‐induced mortality was quantified by determining the relative risk of death (RR) by Cox analysis, with RR = 1 for animals given only DFP, but no pretreatment. Physostigmine was the strongest in vitro AChE‐inhibitor (IC50 = 0.012 µ m), followed by 7‐methoxytacrine, tacrine, pyridostigmine and methylene blue. Ranitidine (IC50 = 2.5 µ m), metoclopramide and amiloride were in the mid‐range. Tiapride (IC50 = 256 µ m) and K‐27 (IC50 = 414 µ m) only weakly inhibited RBC AChE activity. Best in vivo protection from DFP‐induced mortality was achieved when physostigmine (RR = 0.02) or tacrine (RR = 0.05) was given before DFP exposure, which was significantly superior to the pretreatment with all other tested compounds, except K‐27 (RR = 0.18). The mortality‐reducing effect of pyridostigmine, ranitidine and 7‐methoxytacrine was inferior, but still significant. Tiapride, methylene blue, metoclopramide and amiloride did not significantly improve DFP‐induced mortality. K‐27 may be a more efficacious alternative to pyridostigmine, when passage into the brain precludes administration of physostigmine or tacrine. Copyright

New K-Oximes (K-27 and K-48) in Comparison with Obidoxime (LuH-6), HI-6, Trimedoxime (TMB-4), and Pralidoxime (2-PAM): Survival in Rats Exposed IP to the Organophosphate Paraoxon

ABSTRACT Oximes are cholinesterase reactivators used in organophosphorus compound poisoning. The purpose of the study was to compare the protective effect of the K-oximes (K-27 and K-48) in male rats with that of obidoxime (LuH-6), trimedoxime (TMB-4), and HI-6, using paraoxon (POX) as a cholinesterase inhibitor. Pralidoxime (2-PAM) was also retested. Seven groups of six rats each were used. Group 1 (G1) received 1 μmol/rat POX (≈ LD75), the other groups (G2–7) received 1 μmol/rat POX + one of the six reactivators. The animals were monitored for 48 h and time of mortality was recorded. The procedure was repeated seven times. Subsequently, experiments as described were repeated using 10 and 15 μmol/rat POX. Mortality data were compared and hazards ratios (relative risks) ranked with the Cox proportional hazards model using the POX dose and group (reactivator) as time-independent covariables. K-27 followed by K-48 were the most potent reactivators. K-27 was statistically significantly superior to all other reactivators except K-48. The relative risk of death estimated by Cox analysis in K-27– and K-48–treated animals when compared with untreated animals, adjusted for the POX dose, was 0.22 (95% confidence interval [CI], 0.15 to 0.31) and 0.26 (95% CI, 0.18 to 0.37), respectively. We concluded that in the animal model used K-27 and K-48 are superior to older oximes in their ability to protect from paraoxon effects. They should be tested further using methyl- and propyl-organophosphates as toxic agents.

Efficacy of two new asymmetric bispyridinium oximes (K-27 and K-48) in rats exposed to diisopropylfluorophosphate: comparison with pralidoxime, obidoxime, trimedoxime, methoxime, and HI-6.

Introduction. The new K-oximes, K-27 [1-(4-hydroxyimino-methylpyridinium)-4-(4-carbamoylpyridinium) propane dibromide] and K-48 [1-(4-hydroxyimino-methylpyridinium)-4-(4-carbamoylpyridinium) butane dibromide], show good in vitro efficacy in protecting acetylcholinesterase from inhibition by different organophosphorus compounds (OPCs), including nerve agents. To assess their efficacy in vivo, the extent of oxime-conferred protection from mortality induced by diisopropylfluorophosphate (DFP) was quantified and compared with that of five established oximes. Materials and Methods. Rats received DFP intraperitoneally in a dosage of 6, 8, or 10 μmol/rat and immediately thereafter intraperitoneal injections of K-27, K-48, pralidoxime, obidoxime, trimedoxime, methoxime, or HI-6. The relative risk (RR) of death over time (48 h) was estimated by Cox survival analysis, comparing results with the no-treatment group. Results. Best protection was observed when K-27 was used, reducing the RR of death to 19% of control RR (p ≤ 0.005), whereas obidoxime (RR = 26%, p ≤ 0.01), K-48 (RR = 29%, p ≤ 0.005) and methoxime (RR = 26%, p ≤ 0.005) were comparable. The RR of death was reduced only to about 35% of control by HI-6, to 45% by trimedoxime, and to 59% by 2-PAM (p ≤ 0.005). Whereas the differences between the best oximes (K-27, obidoxime, methoxime, and K-48) were not statistically significant; these four oximes were significantly more effective than 2-PAM (p ≤ 0.05). The efficacy of K-27 was also significantly higher than that of HI-6, trimedoxime, and 2-PAM (p ≤ 0.05). Conclusion. Our data provide further evidence that K-27 is a very promising candidate for the treatment of intoxication with a broad spectrum of OPCs.

Usefulness of administration of non‐organophosphate cholinesterase inhibitors before acute exposure to organophosphates: assessment using paraoxon

Reversible acetylcholinesterase (AChE) inhibitors can protect against the lethal effects of irreversible organophosphorus AChE inhibitors (OPCs), when administered before OPC exposure. We have assessed in vivo the mortality‐reducing efficacy of a group of known AChE inhibitors, when given in equitoxic dosage before exposure to the OPC paraoxon. Protection was quantified in rats by determining the relative risk (RR) of death.