Creation of 21st century anatomy facilities: designing facilities for integrated preclinical education in the Middle East

BACKGROUND

The establishment of new anatomy facilities needs to accommodate a combination of modern teaching modalities that best align with evidence-based best teaching practices. This article describes the process in which our state-of-the-art anatomy laboratories were designed and implemented, and how these facilities support aspects of modern anatomy education.

METHODS

A list of best practices for anatomy education in a modern medical curriculum was summarized from the literature. To assess student satisfaction, a survey related to student perception of the anatomy facilities (5-point Likert scale) was conducted.

RESULTS

Our educational modalities include a broad range of teaching approaches. The Instructional Studio houses prosected and plastinated specimens, and cadaveric dissections are performed. Each of our three Dry Laboratories allow for active learning and interaction between small student groups. The Webinar Room acts as a conference room for departmental and online meetings, discussions with students, and dialogues with affiliated hospitals via the internet. The Imaging Center is equipped with a Sectra® medical educational platform, CAE Vimedix® Virtual Medical Imaging Ultrasound Training System, and Philipps Lumify® Ultrasound devices to train students to conduct and interpret sonographic images. Moreover, the Complete Anatomy® program is made available to all our students.

CONCLUSION

The layout of our newly created Anatomy Facilities allows for all aspects of modern medical education mentioned in the literature. These educational modalities and teaching approaches are highly appreciated by our faculty and students. Moreover, these technologies allowed for a smooth transition from on-site anatomy teaching to online education during the COVID pandemic.

Transient receptor potential vanilloid 1 (TRPV1)-independent actions of capsaicin on cellular excitability and ion transport

Capsaicin is a naturally occurring alkaloid derived from chili pepper that is responsible for its hot pungent taste. Capsaicin is known to exert multiple pharmacological actions, including analgesia, anticancer, anti-inflammatory, antiobesity, and antioxidant effects. The transient receptor potential vanilloid subfamily member 1 (TRPV1) is the main receptor mediating the majority of the capsaicin effects. However, numerous studies suggest that the TRPV1 receptor is not the only target for capsaicin. An increasing number of studies indicates that capsaicin, at low to mid µM ranges, not only indirectly through TRPV1-mediated Ca²⁺ increases, but also directly modulates the functions of voltage-gated Na⁺ , K⁺ , and Ca²⁺ channels, as well as ligand-gated ion channels and other ion transporters and enzymes involved in cellular excitability. These TRPV1-independent effects are mediated by alterations of the biophysical properties of the lipid membrane and subsequent modulation of the functional properties of ion channels and by direct binding of capsaicin to the channels. The present study, for the first time, systematically categorizes this diverse range of non-TRPV1 targets and discusses cellular and molecular mechanisms mediating TRPV1-independent effects of capsaicin in excitable, as well as nonexcitable cells.

Diabetes and COVID-19: Short- and Long-Term Consequences

When the corona pandemic commenced more than two years ago, it was quickly recognized that people with metabolic diseases show an augmented risk of severe COVID-19 and an increased mortality compared to people without these comorbidities. Furthermore, an infection with SARS-CoV-2 has been shown to lead to an aggravation of metabolic diseases and in single cases to new-onset metabolic disorders. In addition to the increased risk for people with diabetes in the acute phase of COVID-19, this patient group also seems to be more often affected by long-COVID and to experience more long-term consequences than people without diabetes. The mechanisms behind these discrepancies between people with and without diabetes in relation to COVID-19 are not completely understood yet and will require further research and follow-up studies during the following years. In the current review, we discuss why patients with diabetes have this higher risk of developing severe COVID-19 symptoms not only in the acute phase of the disease but also in relation to long-COVID, vaccine breakthrough infections and re-infections. Furthermore, we discuss the effects of lockdown on glycemic control.

Obesity and COVID-19: What are the Consequences?

Obesity is an increasing health problem all over the world. In combination with the current COVID-19 pandemic, this has turned into a massive challenge as individuals with overweight and obesity at all ages show a significant increase in their risk of getting severe COVID-19. Around 20% of all patients that were hospitalized for COVID-19 suffered from obesity alone, whereas obesity in combination with other metabolic comorbidities, such as type 2 diabetes and hypertension, account for up to 60% of all hospitalizations in relation to COVID-19. Therefore, it is of immense importance to put the spotlight on the high incidence of obesity present already in childhood both by changing the individual minds and by encouraging politicians and the whole society to commence preventive interventions for achieving a better nutrition for all social classes all over the world. In the current review, we aim to explain the different pathways and mechanisms that are responsible for the increased risk of severe COVID-19 in people with overweight and obesity. Furthermore, we discuss how the pandemic has led to weight gains in many people during lockdown. At the end, we discuss the importance of preventing such an interface between a non-communicable disease like obesity and a communicable disease like COVID-19 in the future.

Cannabidiol Inhibits Multiple Ion Channels in Rabbit Ventricular Cardiomyocytes

Cannabidiol (CBD), a major non-psychotropic cannabinoid found in the Cannabis plant, has been shown to exert anti-nociceptive, anti-psychotic, and anti-convulsant effects and to also influence the cardiovascular system. In this study, the effects of CBD on major ion currents were investigated using the patch-clamp technique in rabbit ventricular myocytes. CBD inhibited voltage-gated Na⁺ and Ca²⁺ channels with IC₅₀ values of 5.4 and 4.8 µM, respectively. In addition, CBD, at lower concentrations, suppressed ion currents mediated by rapidly and slowly activated delayed rectifier K⁺ channels with IC₅₀ of 2.4 and 2.1 µM, respectively. CBD, up to 10 μM, did not have any significant effect on inward rectifier I_K1 and transient outward I_to currents. The effects of CBD on these currents developed gradually, reaching steady-state levels within 5–8 min, and recoveries were usually slow and partial. Hill coefficients higher than unity in concentration-inhibition curves suggested multiple CBD binding sites on these channels. These findings indicate that CBD affects cardiac electrophysiology by acting on a diverse range of ion channels and suggest that caution should be exercised when CBD is administered to carriers of cardiac channelopathies or to individuals using drugs known to affect the rhythm or the contractility of the heart.

Vinum resinatum: Scientists and unintended consequences

The art of winemaking has a long history. The methods and techniques changed over millennia as did the consumers taste and habits. Improving the taste of the wine and preventing conversion to vinegar required fantasy and creativity. The principal substances employed as conditurae were seawater, turpentine, either pure, or in the form of pitch (pix), tar (pix liquida), or resin (resina); lime, in the form of gypsum, burnt marble, or calcined shells; inspissated must, aromatic herbs, spices, and gums, and these were used either singly, or cooked up into a great variety of complicated confections. Turpentine exposure (oral. dermal. or respiratory) confers urine the scent of violets. It is generally assumed that turpentine's effect on urine was noticed subsequent to its use as medicine, as a component of various remedies popular in antiquity and thereafter. The high price of such elaborate concoctions would have made however such means available to only a privileged few. Furthermore, the high number of components would also have made association of a particular ingredient with a specific effect difficult if not impossible. We examined the possibility that the effect of turpentine on urine was noticed due to its presence in wines and therefore to the likely widespread exposure of the population to its effects. We review the literature supporting this possibility and provide biographic data on some of the pharmacists, chemists, and physicians involved.

An uncommon, unilateral motor variation of the intercostobrachial nerve

The intercostobrachial nerve (ICBN) is commonly defined as a purely sensory nerve supplying the skin of the lateral chest wall, axilla, and medial arm. However, numerous branching patterns and distributions, including motor, have been reported. This report describes an uncommon variant of the right ICBN observed in both an 86-year-old white female cadaver and a 77-year-old white male cadaver. In both cases the ICBN presented with an additional muscular branch, termed the "medial pectoral branch", piercing and therefore innervating the pectoralis major and minor muscles. Clinically, the ICBN is relevant during surgical access to the axilla and can result in sensory deficits (persistent pain/loss of sensory function) to this region following injury. However, damage to the variation observed in these cadavers may result in additional partial motor loss to pectoralis major and minor.

The humeral head: A review of the blood supply and possible link to osteonecrosis following rotator cuff repair

Trauma, corticosteroid therapy and metabolic diseases are well established aetiologies of humeral head osteonecrosis; however, there is increasing evidence that arthroscopic rotator cuff surgery may be another possible cause. One of the reasons is that there may be inadvertent damage to the arterial blood supply to the humeral head during surgical intervention. The blood supply to the humeral head displays large amounts of variation with regard to origin, course and distribution. Therefore, to shed light on the pathogenesis, the blood supply of the humeral head is reviewed together with a summary of all reported cases of osteonecrosis of the humeral head that occurred following rotator cuff repair. Inconsistencies with regard to terminologies used and contradictions concerning arterial contributions from the anterior circumflex humeral artery and the posterior circumflex humeral artery towards humeral head supply are addressed. Moreover, variations in the course of the anterior circumflex humeral artery and its branches are summarized. The vascular anatomy of the humeral head is clinically relevant due to the close relationship of these blood vessels with the surgical repair sites for rotator cuff surgery and biceps tenotomies or tenodesis procedures. Potential sites of disruption of blood supply following arthroscopic rotator cuff surgery are discussed. Detailed knowledge of the course of the arteries supplying the humeral head may help to minimize the risk of vascular injury and subsequent osteonecrosis. Given the great interindividual variations of vascular anatomy, imaging procedures preceding arthroscopic rotator cuff surgery may be advisable.

Possible metabolic conversion of pinene to ionone

The unintended consequence of the ingestion of certain foods to alter the scent or color of urine is well known. Less awareness exists regarding the practice of ingestion of natural products or drugs with the intended purpose of conferring urine the scent of violets. The resin of the terebinth tree and the derived turpentine were widely used in antiquity in wine-making, both as taste enhancer and conserving agent, so the effect on urine was possibly noticed due to the presence in wines. It is also possible that turpentine's effect on urine was noticed subsequent to its use as medicine, as a component of various remedies popular in those days. The scent altering effect requires metabolic conversion of pinene, the main turpentine component to ionone, the molecule mainly responsible for the scent of violets. The metabolic pathway (in humans or otherwise) was (to our knowledge) not yet described. We here propose a possible metabolic pathway for the conversion of pinene to ionone, explaining the scent altering effect of turpentine. We also provide calculated pharmacokinetic (pK) data for the mentioned substances.

Experimental and Established Oximes as Pretreatment before Acute Exposure to Azinphos-Methyl

Poisoning with organophosphorus compounds (OPCs) represents an ongoing threat to civilians and rescue personal. We have previously shown that oximes, when administered prophylactically before exposure to the OPC paraoxon, are able to protect from its toxic effects. In the present study, we have assessed to what degree experimental (K-27; K-48; K-53; K-74; K-75) or established oximes (pralidoxime, obidoxime), when given as pretreatment at an equitoxic dosage of 25% of LD01, are able to reduce mortality induced by the OPC azinphos-methyl. Their efficacy was compared with that of pyridostigmine, the only FDA-approved substance for such prophylaxis. Efficacy was quantified in rats by Cox analysis, calculating the relative risk of death (RR), with RR=1 for the reference group given only azinphos-methyl, but no prophylaxis. All tested compounds significantly (p ≤ 0.05) reduced azinphos-methyl-induced mortality. In addition, the efficacy of all tested experimental and established oximes except K-53 was significantly superior to the FDA-approved compound pyridostigmine. Best protection was observed for the oximes K-48 (RR = 0.20), K-27 (RR = 0.23), and obidoxime (RR = 0.21), which were significantly more efficacious than pralidoxime and pyridostigmine. The second-best group of prophylactic compounds consisted of K-74 (RR = 0.26), K-75 (RR = 0.35) and pralidoxime (RR = 0.37), which were significantly more efficacious than pyridostigmine. Pretreatment with K-53 (RR = 0.37) and pyridostigmine (RR = 0.52) was the least efficacious. Our present data, together with previous results on other OPCs, indicate that the experimental oximes K-27 and K-48 are very promising pretreatment compounds. When penetration into the brain is undesirable, obidoxime is the most efficacious prophylactic agent already approved for clinical use.

Oximes as pretreatment before acute exposure to paraoxon

Organophosphates, useful agents as pesticides, also represent a serious danger due to their high acute toxicity. There is indication that oximes, when administered before organophosphate exposure, can protect from these toxic effects. We have tested at equitoxic dosage (25% of LD₀₁ ) the prophylactic efficacy of five experimental (K-48, K-53, K-74, K-75, K-203) and two established oximes (pralidoxime and obidoxime) to protect from mortality induced by the organophosphate paraoxon. Mortalities were quantified by Cox analysis and compared with those observed after pretreatment with a strong acetylcholinesterase inhibitor (10-methylacridine) and after the FDA-approved pretreatment compound pyridostigmine. All nine tested substances statistically significantly reduced paraoxon-induced mortality. Best protection was conferred by the experimental oxime K-48, reducing the relative risk of death (RR) to 0.10, which was statistically significantly superior to pyridostigmine (RR = 0.31). The other oximes reduced the RR to 0.13 (obidoxime), 0.20 (K-203), 0.21 (K-74), 0.24 (K-75) and 0.26 (pralidoxime), which were significantly more efficacious than 10-methylacridine (RR = 0.65). These data support the hypothesis that protective efficacy is not primarily due to cholinesterase inhibition and indicate that the tested experimental oximes may be considered promising alternatives to the established pretreatment compound pyridostigmine.

The Experimental Oxime K027-A Promising Protector From Organophosphate Pesticide Poisoning. A Review Comparing K027, K048, Pralidoxime, and Obidoxime

Poisoning with organophosphorus compounds (OPCs) is a major problem worldwide. Standard therapy with atropine and established oxime-type enzyme reactivators (pralidoxime, obidoxime) is unsatisfactory. In search of more efficacious broad-spectrum oximes, new bispyridinium (K-) oximes have been synthesized, with K027 being among the most promising. This review summarizes pharmacokinetic characteristics of K027, its toxicity and in vivo efficacy to protect from OPC toxicity and compares this oxime with another experimental bisquaternary asymmetric pyridinium aldoxime (K048) and two established oximes (pralidoxime, obidoxime). After intramuscular (i.m.) injection, K027 reaches maximum plasma concentration within ∼30 min; only ∼2% enter the brain. Its intrinsic cholinesterase inhibitory activity is low, making it relatively non-toxic. In vitro reactivation potency is high for ethyl-paraoxon-, methyl-paraoxon-, dichlorvos-, diisopropylfluorophosphate (DFP)- and tabun-inhibited cholinesterase. When administered in vivo after exposure to the same OPCs, K027 is comparable or more efficacious than pralidoxime and obidoxime. When given as a pretreatment before exposure to ethyl-paraoxon, methyl-paraoxon, DFP, or azinphos-methyl, it is superior to the Food and Drug Administration-approved compound pyridostigmine and comparable to physostigmine, which because of its entry into the brain may cause unwanted behavioral effects. Because of its low toxicity, K027 can be given in high dosages, making it a very efficacious oxime not only for postexposure treatment but also for prophylactic administration, especially when brain penetration is undesirable.

Involvement of Acetylcholine Receptors in Cholinergic Pathway-Mediated Protection Against Autoimmune Diabetes

Type I diabetes (T1D) is a T cell-driven autoimmune disease that results in the killing of pancreatic β-cells and, consequently, loss of insulin production. Using the multiple low-dose streptozotocin (MLD-STZ) model of experimental autoimmune diabetes, we previously reported that pretreatment with a specific acetylcholinesterase inhibitor (AChEI), paraoxon, prevented the development of hyperglycemia in C57BL/6 mice. This correlated with an inhibition of T cell infiltration into the pancreatic islets and a reduction in pro-inflammatory cytokines. The cholinergic anti-inflammatory pathway utilizes nicotinic and muscarinic acetylcholine receptors (nAChRs and mAChRs, respectively) expressed on a variety of cell types. In this study, we carried out a comparative analysis of the effect of specific antagonists of nAChRs or mAChRs on the development of autoimmune diabetes. Co-administration of mecamylamine, a non-selective antagonist of nAChRs maintained the protective effect of AChEI on the development of hyperglycemia. In contrast, co-administration of atropine, a non-selective antagonist of mAChRs, mitigated AChEI-mediated protection. Mice pretreated with mecamylamine had an improved response in glucose tolerance test (GTT) than mice pretreated with atropine. These differential effects of nAChR and mAChR antagonists correlated with the extent of islet cell infiltration and with the structure and functionality of the β-cells. Taken together, our data suggest that mAChRs are essential for the protective effect of cholinergic stimulation in autoimmune diabetes.

Cleopatra: from turpentine and juniper to ionone and irone

Cleopatra VII (69-30 BC), the last Ptolemaic ruler of Egypt, is probably best known for her love affairs with Julius Caesar (100-44 BC) and Marcus Antonius (83-30 BC). Rightly or wrongly she became the epitome of shrewd seduction, leading brave Roman commanders on a path to debauchery and destruction. Among the seductive strategies attributed to her is the ingestion of small amounts of turpentine [the resin of the terebinth tree (Pistacia terebinthus)] or of derived oil (Oleum terebinthinae) with the purpose of conferring to her urine a more pleasant scent reminding of violets. Turpentine components are metabolized among other compounds to ionones and irones, which - renally excreted - are responsible for the flowery scent. Having obviously worked with great generals, the strategy is said to have been embraced for everyday use by many affluent Roman women. Complicating the issue somewhat is the fact that juniper berries (Fructus juniperi) and derived oil (Oleum juniperi) containing many of the same terpenoids as turpentine have a similar effect on urine. The purpose of this contribution is to briefly review the pharmacology of turpentine and juniper derived compounds assumed to be responsible for altering the scent of urine and to examine the origin and veracity of the mentioned habit. While the effect of ingested turpentine on the scent of urine is well documented our attempts at identifying Greek or Latin authors mentioning its intentional use for this explicit purpose (by Cleopatra or anybody else) failed.

Reversible cholinesterase inhibitors as pretreatment for exposure to organophosphates. A review

Organophosphorus compounds (OPCs), inhibitors of acetylcholinesterase (AChE), are useful agents as pesticides, but also represent a serious health hazard. Standard therapy with atropine and established oxime-type enzyme reactivators (pralidoxime, obidoxime) is unsatisfactory. Better therapeutic results are obtained, when reversible AChE inhibitors are administered before OPC exposure. This review summarizes the history of such a pretreatment approach and sums up a set of experiments undertaken in search of compounds that are efficacious when given before a broad range of OPCs. The prophylactic efficacy of 10 known AChE inhibitors, either already used clinically for different indications (physostigmine, pyridostigmine, ranitidine, tiapride, tacrine, amiloride, metoclopramide, methylene blue) or developed for possible therapeutic use in the future (7-methoxytacrine, K-27) was compared, when administered before exposure to six chemically diverse OPCs in the same experimental setting: ethyl-paraoxon, methyl-paraoxon, diisopropylfluorophosphate, terbufos sulfone, azinphos-methyl and dicrotophos. The experimental oxime K-27 was the most efficacious compound, affording best protection, when administered before terbufos sulfone, azinphos-methyl and dicrotophos, second best before ethyl- and methyl-paraoxon exposure and third best before diisopropylfluorophosphate administration. This ranking was similar to that of physostigmine, which was superior to the Food and Drug Administration-approved pretreatment for soman with pyridostigmine. Tiapride, amiloride, metoclopramide, methylene blue and 7-methoxytacrine did not achieve protection. No correlation was observed between the IC₅₀ of the reversible AChE inhibitors and their protective efficacy. These studies indicate that K-27 can be considered a very promising broad-spectrum prophylactic agent in case of imminent organophosphate exposure, which may be related to its AChE reactivating activity rather than its AChE inhibition.

Optimal Pre-treatment for Acute Exposure to the Organophosphate Dicrotophos

BACKGROUND

Reversible cholinesterase inhibitors, when given prophylactically before exposure to organophosphates, are able to decrease organophosphate-induced mortality. However, the efficacy of pyridostigmine, the only pre-treatment substance approved by the US Federal Drug Administration, is unsatisfactory.

METHODS

In search of a better prophylactic compound, we determined in vivo the protection conferred by five cholinesterase inhibitors (ranitidine, physostigmine, tacrine, K-27 and pyridostigmine), which were administered in equitoxic dosage (1/4 of LD01) 30 minutes before exposure to the organophosphate dicrotophos. Efficacy was measured in rats by Cox analysis calculating the relative risk of death (RR), RR being 1 for the reference group which received dicrotophos and no prophylaxis.

RESULTS

K-27 (RR=0.06), physostigmine (RR=0.15), pyridostigmine (RR=0.22) and tacrine (RR=0.28) significantly (p ≤ 0.05) reduced dicrotophos-induced mortality in comparison to the reference group (dicrotophos without pre-treatment), whereas ranitidine (RR=0.86) had no significant influence. The experimental oxime K-27, when given before dicrotophos exposure, conferred the best in vivo protection. This was significantly (p ≤ 0.05) more efficacious than pre-treatment with any other tested compound. The differences in efficacy between the second best compound, physostigmine, and the less efficacious substances (tacrine and pyridostigmine) were also statistically significant.

CONCLUSION

These data indicate that K-27 can be considered a very efficacious prophylactic agent for organophosphate exposure.

Reversible cholinesterase inhibitors as pre-treatment for exposure to organophosphates: assessment using azinphos-methyl

Pre-treatment with reversible acetylcholinesterase (AChE) inhibitors before organophosphorous compound (OPC) exposure can reduce OPC-induced mortality. However, pyridostigmine, the only substance employed for such prophylaxis, is merely efficacious against a limited number of OPCs. In search of more efficacious and broad-range alternatives, we have compared in vivo the ability of five reversible AChE inhibitors (pyridostigmine, physostigmine, ranitidine, tacrine and K-27) to reduce mortality induced by the OPC azinphos-methyl. Protection was quantified using Cox analysis by determining the relative risk (RR) of death in rats that were administered these AChE inhibitors in equitoxic dosage (25% of LD01) 30 min before azinphos-methyl exposure. Azinphos-methyl-induced mortality was significantly reduced by all five tested compounds as compared with the reference group that was only exposed to azinphos-methyl without prior pre-treatment (RR = 1). The most efficacious prophylactic agents were K-27 (RR = 0.15) and physostigmine (RR = 0.21), being significantly more efficacious than ranitidine (RR = 0.62) and pyridostigmine (RR = 0.37). Pre-treatment with tacrine (RR = 0.29) was significantly more efficacious than pre-treatment with ranitidine, but the difference between tacrine and pyridostigmine was not significant. Our results indicate that prophylactic administration of the oxime K-27 may be a promising alternative in cases of imminent OPC exposure.

A trivalent approach for determining in vitro toxicology: Examination of oxime K027

Unforeseen toxic effects contribute to compound attrition during preclinical evaluation and clinical trials. Consequently, there is a need to correlate in vitro toxicity to in vivo and clinical outcomes quickly and effectively. We propose an expedited evaluation of physiological parameters in vitro that will improve the ability to predict in vivo toxicity of potential therapeutics. By monitoring metabolism, mitochondrial physiology and cell viability, our approach provides insight to the extent of drug toxicity in vitro. To implement our approach, we used human hepatocellular carcinoma cells (HepG2) and neuroblastoma cells (SH-SY5Y) to monitor hepato- and neurotoxicity of the experimental oxime K027. We utilized a trivalent approach to measure metabolism, mitochondrial stress and induction of apoptosis in 96-well formats. Any change in these three areas may suggest drug-induced toxicity in vivo. K027 and pralidoxime, an oxime currently in clinical use, had no effect on glycolysis or oxygen consumption in HepG2 and SH-SY5Y cells. Similarly, these oximes did not induce oxidant generation nor alter mitochondrial membrane potential. Further, K027 and pralidoxime failed to activate effector caspases, and these oximes did not alter viability. The chemotherapeutic agent, docetaxel, negatively affected metabolism, mitochondrial physiology and viability. Our studies present a streamlined high-throughput trivalent approach for predicting toxicity in vitro, and this approach reveals that K027 has no measurable hepatotoxicity or neurotoxicity in vitro, which correlates with their in vivo data. This approach could eliminate toxic drugs from consideration for in vivo preclinical evaluation faster than existing toxicity prediction panels and ultimately prevent unnecessary experimentation.

On the interaction of β-amyloid peptides and α7-nicotinic acetylcholine receptors in Alzheimer's disease

Deterioration of the cortical cholinergic system is a leading neurochemical feature of Alzheimer's Disease (AD). This review summarizes evidence that the homomeric α7- nicotinic acetylcholine receptor (nAChR) plays a crucial role in the pathogenesis of this disease, which is characterized by amyloid-β (Aβ) accumulations and neurofibrillary tangles originating from of hyperphosphorylated tau protein. Aβ binds to α7-nAChRs with a high affinity, either activating or inhibiting this receptor in a concentration-dependent manner. There is strong evidence that α7-nAChRs are neuroprotective, reducing Aβ-induced toxicity; but co-localization of α7- nAChRs, Aβ and amyloid plaques also points to neurodegenerative actions. Aβ induces tau phosphorylation via α7-nAChR activation. Aβ influences hippocampus-dependent memory and long-term potentiation in a dose-dependent way: there is evidence that enhancement by picomolar Aβ concentrations is mediated by α7-nAChRs, whereas inhibition by nanomolar concentrations is independent of nAChRs and probably mediated by small Aβ42 oligomers. α7-nAChRs located on vascular smooth muscle cells and astrocytes are also involved in the pathogenesis of AD. Although these data strongly point to an important role of α7-nAChRs in the development of AD, dose-dependence of the effects, rapid desensitization of the receptor and dependence of the effects on Aβ aggregation (monomers, oligomers, fibrils) make it difficult to develop simple therapeutic strategies acting upon this receptor.

Acetylcholinesterase inhibitors as pretreatment before acute exposure to organophosphates: assessment using methyl-paraoxon

Prophylactic administration of reversible acetylcholinesterase (AChE) inhibitors can protect against the lethal effects of organophosphorus compounds (OPCs). The usefulness of pyridostigmine, the only compound approved by the Food and Drug Administration (FDA) for such pretreatment, has been questioned. In search for more efficacious alternatives, we have examined in vivo the efficacy of a group of ten compounds with known anti-AChE activity (pyridostigmine, metoclopramide, tiapride, ranitidine, physostigmine, tacrine, amiloride, methylene blue, 7- methoxytacrine and K-27) to reduce mortality induced by the OPC methyl-paraoxon. AChE inhibitors were given intraperitoneally in equitoxic dosage (25% of LD₀₁) 30 min before OPC exposure. Protection was quantified in rats by determining the relative risk of death (RR) by Cox analysis, with RR=1 for animals given only methyl-paraoxon, but no pretreatment. Only physostigmine (RR=0.39), K-27 (RR=0.40) and tacrine (RR=0.48) significantly (p≤ 0.05) reduced methylparaoxon- induced mortality, when given prophylactically. Pretreatment with pyridostigmine, ranitidine, tiapride, amiloride, metoclopramide and methylene blue did not significantly protect against the lethal effects of methyl-paraoxon. 7-methoxytacrine (7-MEOTA) significantly (p≤ 0.05) increased the relative risk of methyl-paraoxon-induced death (RR=1.31). These results indicate that pretreatment with pyridostigmine cannot be considered a broad-spectrum approach against OPC exposure. K-27 may be a suitable alternative if passage into the brain is contraindicated.

Prophylactic administration of non-organophosphate cholinesterase inhibitors before acute exposure to organophosphates: assessment using terbufos sulfone

Poisoning with organophosphorus compounds (OPCs) poses a serious threat worldwide. OPC-induced mortality can be significantly reduced by prophylactic administration of reversible acetylcholinesterase (AChE) inhibitors. The only American Food and Drug Administration (FDA)-approved substance for such pre-treatment (to soman exposure) is presently pyridostigmine, although its efficacy is controversial. In search for more efficacious and broad-spectrum alternatives, we have assessed in vivo the mortality-reducing efficacy of a group of five compounds with known AChE inhibitory activity (pyridostigmine, physostigmine, ranitidine, tacrine and K-27), when given in equitoxic dosage (25% of LD01 ) 30 min before exposure to the OPC terbufos sulfone. Protection was quantified in rats by determining the relative risk of death (RR) using Cox analysis, with RR = 1 for animals given only terbufos sulfone, but no pre-treatment. All tested AChE inhibitors reduced terbufos sulfone-induced mortality significantly (p ≤ 0.05) as compared with the non-treatment group (RR = 1: terbufos sulfone only). Best in vivo protection from terbufos sulfone-induced mortality was achieved, when K-27 was given before terbufos sulfone exposure (RR = 0.06), which was significantly (P ≤ 0.05) superior to the pre-treatment with all other tested compounds, for example tacrine (RR = 0.21), pyridostigmine (RR = 0.28), physostigmine (RR = 0.29) and ranitidine (RR = 0.33). The differences in efficacy between tacrine, pyridostigmine, physostigmine and ranitidine were not statistically significant. Prophylactic administration of an oxime (such as K-27) in case of imminent OPC exposure may be a viable option.

Methylene blue inhibits the function of α7-nicotinic acetylcholine receptors

Methylene Blue (MB) is being investigated in clinical studies for its beneficial effects in the treatment of Alzheimer disease. However, its exact mechanisms of action have not been fully elucidated. The modulation of nicotinic acetylcholine receptors (nAChRs) has been suggested to play a role in the pathogenesis of various neurodegenerative diseases. Therefore, in the present study, the effect of MB on the function of the cloned α7 subunit of the human nAChR expressed in Xenopus oocytes was investigated using the two-electrode voltage-clamp technique. MB reversibly inhibited ACh (100 μM)-induced currents in a concentration-dependent manner with an IC50 value of 3.4±0.3 μM. The effect of MB was not dependent on the membrane potential. MB did not affect the activity of endogenous Ca2+-dependent Cl- channels, since the inhibition by MB was unaltered in oocytes injected with the Ca2+ chelator 1,2-bis (o-aminophenoxy) ethane-N, N, N', N'-tetraacetic acid and perfused with Ca2+-free bathing solution containing 1.8 mM Ba2+. MB decreased the maximal ACh-induced responses without significantly affecting ACh potency. Furthermore, specific binding of [125I] α-bungarotoxin, a radioligand selective for the α7 nAChR, was not altered by MB (10 μM), indicating that MB acts as a noncompetitive antagonist on α7 nAChRs. In hippocampal slices, whole-cell recordings from CA1 pyramidal neurons indicated that the increases in the frequency and amplitudes of the γ-aminobutyric acid-mediated spontaneous postsynaptic currents induced by bath application of 2 mM choline, a specific agonist for α7 nAChRs, were abolished after 10 min application of 3 μM MB. These results demonstrate that MB inhibits the function of human α7 nAChRs expressed in Xenopus oocytes and of α7 nAChR-mediated responses in rat hippocampal neurons.

Methylene blue inhibits function of the 5-HT transporter

BACKGROUND AND PURPOSE

Methylene blue (MB) is commonly employed as a treatment for methaemoglobinaemia, malaria and vasoplegic shock. An increasing number of studies indicate that MB can cause 5-HT toxicity when administered with a 5-HT reuptake inhibitor. MB is a potent inhibitor of monoamine oxidases, but other targets that may contribute to MB toxicity have not been identified. Given the role of the 5-HT transporter (SERT) in the regulation of extracellular 5-HT concentrations, the present study aimed to characterize the effect of MB on SERT.

EXPERIMENTAL APPROACH

Live cell imaging, in conjunction with the fluorescent SERT substrate 4-(4-(dimethylamino)-styryl)-N-methylpyridinium (ASP(+) ), [(3) H]5-HT uptake and whole-cell patch-clamp techniques were employed to examine the effects of MB on SERT function.

KEY RESULTS

In EM4 cells expressing GFP-tagged human SERT (hSERT), MB concentration-dependently inhibited ASP(+) accumulation (IC(50) : 1.4 ± 0.3 µM). A similar effect was observed in N2A cells. Uptake of [(3) H]5-HT was decreased by MB pretreatment. Furthermore, patch-clamp studies in hSERT expressing cells indicated that MB significantly inhibited 5-HT-evoked ion currents. Pretreatment with 8-Br-cGMP did not alter the inhibitory effect of MB on hSERT activity, and intracellular Ca(2+) levels remained unchanged during MB application. Further experiments revealed that ASP(+) binding to cell surface hSERT was reduced after MB treatment. In whole-cell radioligand experiments, exposure to MB (10 µM; 10 min) did not alter surface binding of the SERT ligand [(125) I]RTI-55.

CONCLUSIONS AND IMPLICATIONS

MB modulated SERT function and suggested that SERT may be an additional target upon which MB acts to produce 5-HT toxicity.

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. Best in vivo protection from paraoxon-induced mortality was observed after prophylactic administration of physostigmine (RR = 0.30) or the oxime K-27 (RR = 0.34); both treatments were significantly superior to the pre-treatment with all other tested compounds, including the established substance pyridostigmine. Tacrine (RR = 0.67), ranitidine (RR = 0.72), pyridostigmine (RR = 0.76), tiapride (RR = 0.80) and 7-MEOTA (RR = 0.86) also significantly reduced the relative risk of paraoxon-induced death, but to a lesser degree. Methylene blue, amiloride and metoclopramide had an unfavorable effect (RR ≥ 1), significantly increasing mortality. When CNS penetration by prophylactic is undesirable K-27 is a promising alternative to pyridostigmine.

In an animal model nephrogenic systemic fibrosis cannot be induced by intraperitoneal injection of high-dose gadolinium based contrast agents

AIM AND OBJECTIVE

Nephrogenic systemic fibrosis (NSF) has been reported in humans to be most likely induced by gadolinium based contrast agents (GBCA), namely by gadodiamide, gadopentetate dimeglumine, and gadoversetamide, rarely by other GBCA. The pathogenesis of NSF remains unclear; different hypotheses are under discussion. The objective of the study is to assess if in the animal model human-like NSF changes can be induced by high-dose, intraperitoneal GBCA injections over four weeks.

MATERIALS AND METHODS

After approval by the institutional animal ethics committee, six rats each were randomly assigned to groups, and treated with seven different GBCA. Intraperitoneal (IP) injections - proven in the animal model to be effective - were chosen to prolong the animals' exposure to the respective GBCA. GBCA doses of previous intravenous (IV) animal studies were applied. After five weeks all rats were sacrificed. Sham controls were treated with IP saline injections, employing the same regimen.

RESULTS

No findings comparable with human NSF were observed in all animals after IP treatment with all seven GBCA at daily doses of 2.5 and 5.0 mmol/kg body weight (BW). No histopathological abnormalities of all examined organs were noted. Weight loss was stated in weeks three and four with GBCA injections at doses of 5.0 mmol/kg BW, but rats regained weight after cessation of GBCA treatment.

CONCLUSIONS

NSF-comparable pathological findings could not be induced by high dose intraperitoneal injection of seven GBCA.

Cellular and molecular actions of Methylene Blue in the nervous system

Methylene Blue (MB), following its introduction to biology in the 19th century by Ehrlich, has found uses in various areas of medicine and biology. At present, MB is the first line of treatment in methemoglobinemias, is used frequently in the treatment of ifosfamide-induced encephalopathy, and is routinely employed as a diagnostic tool in surgical procedures. Furthermore, recent studies suggest that MB has beneficial effects in Alzheimer's disease and memory improvement. Although the modulation of the cGMP pathway is considered the most significant effect of MB, mediating its pharmacological actions, recent studies indicate that it has multiple cellular and molecular targets. In the majority of cases, biological effects and clinical applications of MB are dictated by its unique physicochemical properties including its planar structure, redox chemistry, ionic charges, and light spectrum characteristics. In this review article, these physicochemical features and the actions of MB on multiple cellular and molecular targets are discussed with regard to their relevance to the nervous system.

Profiles of serotonin receptors in the developing human thalamus

The critical importance of the thalamus and its serotonergic innervation with respect to neuropsychiatric syndromes is increasingly recognized. This study investigates the localization of serotonin (5-hydroxytryptamine; 5-HT) receptors by immunohistochemistry in the thalamic nuclei of human fetuses aged 21 to 32 weeks of gestation. Results indicate that, already at 21 weeks of gestation, two 5-HT receptors are present in the dorsomedial nucleus of the developing thalamus: 5-HT2A receptors are localized in neurons and 5-HT2C receptors in fibers. By 31 and 32 weeks of gestation, 5-HT1A and 5-HT4 receptors are also detected in neuronal fibers of the same nucleus. At this later developmental stage, the percentage of 5-HT2A labeled neurons has significantly increased in the dorsomedial nucleus, and 5-HT2C positive neurons are observed in the centromedian and lateroventral thalamic nuclei as well. In contrast, neither neuronal cells nor fibers display any immunoreactivity for 5-HT3 or 5-HT6 receptors at any of the ages examined. Our observation that 5-HT1A, 5-HT2A, 5-HT2C and 5-HT4 receptors are present in the human thalamus prenatally indicates that 5-HT may play a role during fetal development. Disrupted development of the thalamic serotonergic system during this gestational period may contribute to the pathophysiology of neuropsychiatric disorders.

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.

TUNEL and growth factor expression in the prefrontal cortex of Alzheimer patients over 80 years old

To elucidate factors underlying the increased risk of developing Alzheimers disease (AD) in older individuals, the prefrontal cortices of younger (58-79 years) and of older (over 80 years) AD patients were examined by silver impregnation, TUNEL assay and immunohistochemistry for hyperphosphorylated tau, LDH and two growth factors (BDNF, NGF). Quantitative data were compared with those of age-matched controls. TUNEL-positive cells were mainly located in superficial cortical layers of younger and in deeper layers of older AD patients. Their density was more than 5 times higher in older AD than in younger AD (p < or = 0.05), but apoptotic cell morphology was rarely seen. Significantly more neuronal somas were contacted by degenerating fibers both in younger and older AD cortices. Density of tau-immunoreactive cells, which were virtually absent in controls, was twice as high in older AD patients as in younger AD individuals (p < or = 0.05). In younger AD, TUNEL positive cells generally lacked tau immunoreaction, whereas in older AD, most cells were double-labeled for hyperphosphorylated tau and TUNEL (p < or = 0.05). Numerical density of BDNF-immunoreactive cells was significantly reduced by 20 percent in older AD patients, compared to both control individuals and younger AD patients, whereas density of NGF-positive cells was the same in all patient groups examined. The distinct differences between younger and older AD patients suggest a faster progression of AD in older patients.

In vitro assessment of the antibiotic efficacy of contrast media and antibiotics and their combinations at various dilutions

Discography is a controversial diagnostic procedure involving the injection of radiographic contrast medium (RCM) into the intervertebral disc. Iatrogenic bacterial discitis is a rare but serious complication. The intervention has been increasingly performed in our patients here in the United Arab Emirates. Prophylactic intravenous antibiotic administration can reduce post-interventional discitis; however, this may favour the development of bacterial resistance. Direct intradiscal injection of an antibiotic together with the RCM is a potential alternative. To date, there has been only one study on the efficacy of antibiotics added to an RCM. Equally, there are only limited data regarding the potential direct effect of RCM on bacterial growth. The purpose of this study was to determine whether the efficacy of antibiotics is affected when RCM are added. In an in vitro study, the effect of non-ionic RCM on the growth of five laboratory bacterial strains, alone and in combination with three broad-spectrum antimicrobials, was tested. Bacterial growth was assessed in the absence and the presence of RCM, antibiotics and their combinations. All three RCM alone demonstrated some inhibition of bacterial growth at high concentrations. In the presence of the RCM, all three antibiotics retained their inhibitory effect on bacterial growth. In conclusion, our in vitro experiments did not reveal any changes in the antimicrobial efficacy of the three antibiotics in the presence of the three tested RCM. Subsequent clinical trials will need to assess whether intradiscal antibiotic administration may be a suitable substitute for, or a supplement to, prophylactic systemic antibiotics before discography.

Cholinergic stimulation of the immune system protects against lethal infection by Salmonella enterica serovar Typhimurium

SUMMARY

The cholinergic nervous system has been demonstrated to attenuate the inflammatory response during sepsis via the inhibitory action of acetylcholine (ACh) on macrophages. These findings were largely based on experimental sepsis models using endotoxin as the inducing agent. Herein, however, we report that the specific inhibition of acetylcholinesterase (AChE) renders animals more resistant to infection by a virulent strain of Salmonella enterica serovar Typhimurium, a Gram-negative enteric pathogen. Inhibition of AChE was induced by a subchronic exposure to paraoxon, a potent anti-cholinesterase metabolite of the organophosphorous compound parathion. Our findings indicate that inhibition of AChE enhanced survival of infected mice in a dose-dependent fashion and this correlated with efficient control of bacterial proliferation in target organs. Immunologically, inhibition of AChE enabled the animals to mount a more effective inflammatory anti-microbial response, and to secrete higher levels of interleukin-12, a key T helper type 1-promoting cytokine. The ACh-induced enhancement in resistance to infection was abrogated by co-administration of an oxime which can reactivate AChE. Hence, in a model of Gram-negative bacterial infection, cholinergic stimulation is shown to enhance the anti-microbial immune response leading to effective control of bacterial proliferation and enhanced animal survival.

Minireview: does in-vitro testing of oximes help predict their in-vivo action after paraoxon exposure?

K-oximes have recently been developed in the search for efficacious broad-band reactivators of acetylcholinesterase (AChE) inhibited by organophosphorus compounds (OPC). Before clinical use, their toxicity and efficacy need to be assessed, and there is clear demand for simple in vitro tests that can predict in vivo performance. This article summarizes our in vitro data obtained for conventional and experimental oximes in human and rat blood exposed to the OPC paraoxon and correlates them with our in vivo results. The intrinsic AChE inhibitory activity of oximes, as reflected by their in vitro IC(50), is strongly correlated with their LD(50) (rat): oximes with a high IC(50) (K-27, K-48, pralidoxime and obidoxime) also show a high LD(50) and are thus relatively non-toxic, whereas oximes K-105, K-108 and K-113 have a low IC(50), a low LD(50) and are far more toxic. The IC(50) is also correlated with the in vivo capacity to protect from paraoxon-induced mortality: oximes with a higher IC(50) reduce the relative risk of death more. In contrast, the protective ability as assessed in vitro by the slope of the IC(50) shift (tanalpha), is not correlated with in vivo protection from paraoxon-induced mortality: the best in vivo protectors (K-27 and K-48) show a much lower tanalpha value (around 2) than K-110 and K-113 (tanalpha around 10), which hardly reduce the relative risk of death after paraoxon exposure. The partition coefficient logP of the individual oximes is inversely correlated with their IC(50) and with their LD(50) and is therefore an indicator of toxicity: strongly hydrophilic oximes tend to be less toxic than less hydrophilic ones. These data highlight the good predictive value of in vitro IC(50) testing for in vivo toxicity and the limited practical significance of in vitro assessment of protective potency.

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 micromol/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 < or = 0.005), whereas obidoxime (RR = 26%, p < or = 0.01), K-48 (RR = 29%, p < or = 0.005) and methoxime (RR = 26%, p < or = 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 < or = 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 < or = 0.05). The efficacy of K-27 was also significantly higher than that of HI-6, trimedoxime, and 2-PAM (p < or = 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.

Analysis of pralidoxime in serum, brain and CSF of rats

After administration of various amounts of pralidoxime to rats, the levels in serum, brain and cerebrospinal fluid (CSF) were measured using capillary zone electrophoresis (CZE). The calibration curves were established using spiked samples. The calibration covers the ranges from 0.3 - 200 microg/mL, 0.3 - 7 microg/mL and 0.1 - 7 microg/mL for serum, brain and CSF, respectively. The CZE measurement opens the way to the fast and reliable determination of pyridinium aldoxime concentrations in serum, cerebrospinal fluid and brain, thereby monitoring blood-brain and blood-CSF penetration of pyridinium aldoxime-type antidotes clinically used in organophosphate poisoning.

The organophosphate paraoxon has no demonstrable effect on the murine immune system following subchronic low dose exposure

Paraoxon is the bioactive metabolite of the organophosphate pesticide parathion. Desulphuration of parathion by liver enzymes or sunlight results in the formation of paraoxon which inhibits acetylcholine esterase (AChE) activity. In the present study, we analyzed the effect of a 6-week, subchronic treatment with two different daily intraperitoneal doses (30 or 40 nmol) of paraoxon on the immune system of BALB/c mice. At a dose of 30 nmol/day, body weight of treated animals was unchanged compared to the controls. In contrast, the higher dose (40 nmol/day) induced a reduction in body growth, particularly in the first 3 weeks of treatment, peaking at week 2 when the saline group showed a 14.2-fold increase in body weight gain compared to paraoxon-treated animals. Moreover, mice treated with either dose of paraoxon had a >50% reduction in AChE activity during the first 3 weeks of treatment, but by the end of the treatment (week 6), AChE activity returned to normal. With regard to immunological parameters, there was no significant difference in either total spleen weight or in the ratios of various spleen cell populations between control and paraoxon-treated animals. Furthermore, no changes were observed in mitogen-induced cytokine secretion from splenocytes of paraoxon-treated mice. Finally, subchronic exposure to paraoxon did not alter mortality of mice exposed to a bacterial infection with Salmonella typhimurium. These data suggest that although subchronic exposure to paraoxon induced a transient inhibition in AChE activity, it had no demonstrable effect on the host immune system.

Pyridinium oxime reactivators of cholinesterase inhibited by diisopropyl-fluorophosphate (DFP): predictive value of in-vitro testing for in-vivo efficacy

Poisoning with organophosphorus cholinesterase inhibitors (OPCs) poses a serious global threat. Therapy comprises the use of atropine and pyridinium oximes to reactivate acetylcholinesterase (AChE). Clinical experience with established oximes (pralidoxime and obidoxime) is disappointing and several experimental potential alternatives (K oximes) have been developed. This review summarizes data on these oximes, when used in exposure to the OPC diisopropylfluorophosphate (DFP). In vitro testing includes determination of IC(50) (intrinsic oxime AChE inhibitory activity), of tan alpha (reactivation capacity) and in silico estimation of LogP (lipophilicity/hydrophilicity) of the individual oximes. In vivo approaches encompass determination of toxicity (LD(50)) and of protective efficacy (reduction of relative risk of death after DFP exposure in rats). Correlations between the different in vitro and in vivo data available reveal that an oxime with a low in vitro AChE inhibitory activity (high IC(50)) is rather non-toxic and reduces DFP-induced mortality (low cumulative relative risk). Oximes with a high in vitro AChE reactivation potency (high tan alpha) also have a high in vitro AChE inhibitory activity (low IC(50)) and have a low LD(50) in vivo, implying high toxicity. Less hydrophilic oximes have strong in vitro AChE inhibitory activity, are better in vitro AChE reactivators, but are also more toxic in vivo and are associated with a high cumulative risk of death after DFP exposure in rats, implying low in vivo efficacy. In vitro reactivation capacity of human red blood cell (RBC)-AChE has no predictive value for in vivo (rat) efficacy, at least in the case of DFP exposure.

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 < or = 0.05), which was statistically significantly better (P < or = 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 < or = 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.

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 ( approximately 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 (tan alpha) was used to quantify the magnitude of the protective effect (nm IC50 increase per microm 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/tan alpha. Based on the values of tan alpha and of the binding constant K, some of the new K-oxime reactivators are far superior to pralidoxime (tan alpha = 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.

Entry of oximes into the brain: a review

The passage of hydrophilic drugs, such as oxime acetylcholinesterase reactivators, into the central nervous system is restricted by the blood-brain and the blood-cerebrospinal fluid barriers. The present review summarizes morphological and functional properties of the blood-brain barrier, blood-cerebrospinal fluid barrier and cerebrospinal fluid-brain interface and reviews the existing data on brain entry of oximes. Due to the virtual absence of transcytosis, lack of fenestrations and unique properties of tight junctions in brain endothelial cells, the blood-brain barrier only allows free diffusion of small lipophilic molecules. Various carriers transport hydrophilic compounds and extrude potentially toxic xenobiotics. The blood-cerebrospinal fluid barrier is formed by the choroid plexus epithelium, whose tight junctions are more permeable than those of brain endothelial cells. The major function of plexus epithelium cells is active transport of ions for the production of the cerebrospinal fluid. The cerebrospinal fluid-brain interface is not a biological barrier and allows free diffusion. However, in contrast to passage via the blood-brain barrier or the blood-cerebrospinal fluid barrier, direct penetration from the cerebrospinal fluid into the brain is very slow, since much longer distances have to be covered. A bulk flow of brain interstitial fluid and cerebrospinal fluid speeds up exchange between these two fluid compartments. Oximes, by reactivating acetylcholinesterase, are important adjunct therapeutics in organophosphate poisoning. They are very hydrophilic and therefore cannot diffuse freely into the central nervous system. Changes in brain acetylcholinesterase activity, oxime concentration and some biological effects elicited by oxime administration in the periphery indicate, however, that oximes can gain access to the brain to a certain degree, probably by carrier-mediated transport, reaching in the brain about 4-10% of their respective plasma levels. The clinical relevance of this effect is hotly debated. Possible strategies to improve brain penetration of oximes are discussed.

Entry of two new asymmetric bispyridinium oximes (K-27 and K-48) into the rat brain: comparison with obidoxime

In the search for new oximes with higher reactivation potency and a broader spectrum, K-27 and K-48, have recently been synthesized. To test if their superior efficacy was related to better penetration across the blood-brain barrier, their brain entry was compared with that of obidoxime, when administered either alone or after the organophosphate paraoxon (POX). Rats received 50 micromol obidoxime, K-27 or K-48, either alone or in addition to 1 micromol POX. Oxime concentrations at various points in time in brain and plasma were measured using HPLC. The obidoxime C(max) in brain was 1.3% of the plasma C(max) when injected alone, and 1.5% when injected following POX. The ratio of the area under the curve (AUC) brain to plasma for obidoxime was around 6%, irrespective of whether it was administered alone or after POX. For K-27, C(max) (brain) was 0.6% of C(max) (plasma) when injected alone, and 0.7% when injected after POX (no significant difference). The AUC (brain) was 2% of AUC (plasma) for both K-27 groups. K-48, when injected alone reached 1.4% of C(max) (plasma) in the brain and 1.2% of C(max) (plasma), when injected following POX. The AUC (brain) was 5% of the AUC (plasma), both when K-48 was administered alone and in combination with POX. Entry of all three oximes into the brain is minimal and cannot explain the better therapeutic efficacy of K-27 and K-48. As already observed for pralidoxime, injection of POX before oxime administration had no influence upon penetration across the blood-brain barrier.