Challenges in the diagnosis and management of a ruptured heterotopic gestation following ultrasound-guided embryo transfer in low resource settings: a case report

BACKGROUND

Heterotopic pregnancies are increasing in incidence with the advent of rising prevalence of in vitro fertilization and embryo transfer (IVF-ET) globally. Although rare, this condition is a serious potentially life-threatening gynaecological complication.

CASE PRESENTATION

We present the case of a 36-year-old Ghanaian woman who conceived following IVF and presented two weeks after confirmation of intrauterine gestation with sudden onset lower abdominal pain. A diagnosis of ruptured heterotopic pregnancy was made, laparotomy and salpingectomy was done followed with further management of the intrauterine gestation.

CONCLUSION

To the best of our knowledge, this is the first reported case of heterotopic pregnancy in Ghana. A high index of suspicion for heterotopic pregnancy is required even in the presence of a confirmed intrauterine gestation following IVF-ET.

A gold-based inhibitor of oxidative phosphorylation is effective against triple negative breast cancer

Triple-negative breast cancer (TNBC) is associated with metabolic heterogeneity and poor prognosis with limited treatment options. New treatment paradigms for TNBC remains an unmet need. Thus, therapeutics that target metabolism are particularly attractive approaches. We previously designed organometallic Au(III) compounds capable of modulating mitochondrial respiration by ligand tuning with high anticancer potency in vitro and in vivo. Here, we show that an efficacious Au(III) dithiocarbamate (AuDTC) compound induce mitochondrial dysfunction and oxidative damage in cancer cells. Efficacy of AuDTC in TNBC mouse models harboring mitochondrial oxidative phosphorylation (OXPHOS) dependence and metabolic heterogeneity establishes its therapeutic potential following systemic delivery. This provides evidence that AuDTC is an effective modulator of mitochondrial respiration worthy of clinical development in the context of TNBC. ONE SENTENCE SUMMARY: Metabolic-targeting of triple-negative breast cancer by gold anticancer agent may provide efficacious therapy.

Chemoproteomics identifies proteoform-selective caspase-2 inhibitors

Caspases are a highly conserved family of cysteine-aspartyl proteases known for their essential roles in regulating apoptosis, inflammation, cell differentiation, and proliferation. Complementary to genetic approaches, small-molecule probes have emerged as useful tools for modulating caspase activity. However, due to the high sequence and structure homology of all twelve human caspases, achieving selectivity remains a central challenge for caspase-directed small-molecule inhibitor development efforts. Here, using mass spectrometry-based chemoproteomics, we first identify a highly reactive non-catalytic cysteine that is unique to caspase-2. By combining both gel-based activity-based protein profiling (ABPP) and a tobacco etch virus (TEV) protease activation assay, we then identify covalent lead compounds that react preferentially with this cysteine and afford a complete blockade of caspase-2 activity. Inhibitory activity is restricted to the zymogen or precursor form of monomeric caspase-2. Focused analogue synthesis combined with chemoproteomic target engagement analysis in cellular lysates and in cells yielded both pan-caspase reactive molecules and caspase-2 selective lead compounds together with a structurally matched inactive control. Application of this focused set of tool compounds to stratify caspase contributions to initiation of intrinsic apoptosis, supports compensatory caspase-9 activity in the context of caspase-2 inactivation. More broadly, our study highlights future opportunities for the development of proteoform-selective caspase inhibitors that target non-conserved and non-catalytic cysteine residues.

Solid-Phase Compatible Silane-Based Cleavable Linker Enables Custom Isobaric Quantitative Chemoproteomics

Mass spectrometry-based chemoproteomics has emerged as an enabling technology for functional biology and drug discovery. To address limitations of established chemoproteomics workflows, including cumbersome reagent synthesis and low throughput sample preparation, here, we established the silane-based cleavable isotopically labeled proteomics (sCIP) method. The sCIP method is enabled by a high yielding and scalable route to dialkoxydiphenylsilane fluorenylmethyloxycarbonyl (DADPS-Fmoc)-protected amino acid building blocks, which enable the facile synthesis of customizable, isotopically labeled, and chemically cleavable biotin capture reagents. sCIP is compatible with both MS1- and MS2-based quantitation, and the sCIP-MS2 method is distinguished by its click-assembled isobaric tags in which the reporter group is encoded in the sCIP capture reagent and balancer in the pan cysteine-reactive probe. The sCIP-MS2 workflow streamlines sample preparation with early stage isobaric labeling and sample pooling, allowing for high coverage and increased sample throughput via customized low cost six-plex sample multiplexing. When paired with a custom FragPipe data analysis workflow and applied to cysteine-reactive fragment screens, sCIP proteomics revealed established and unprecedented cysteine-ligand pairs, including the discovery that mitochondrial uncoupling agent FCCP acts as a covalent-reversible cysteine-reactive electrophile.

Multi-omic stratification of the missense variant cysteinome

Cancer genomes are rife with genetic variants; one key outcome of this variation is gain-ofcysteine, which is the most frequently acquired amino acid due to missense variants in COSMIC. Acquired cysteines are both driver mutations and sites targeted by precision therapies. However, despite their ubiquity, nearly all acquired cysteines remain uncharacterized. Here, we pair cysteine chemoproteomics-a technique that enables proteome-wide pinpointing of functional, redox sensitive, and potentially druggable residues-with genomics to reveal the hidden landscape of cysteine acquisition. For both cancer and healthy genomes, we find that cysteine acquisition is a ubiquitous consequence of genetic variation that is further elevated in the context of decreased DNA repair. Our chemoproteogenomics platform integrates chemoproteomic, whole exome, and RNA-seq data, with a customized 2-stage false discovery rate (FDR) error controlled proteomic search, further enhanced with a user-friendly FragPipe interface. Integration of CADD predictions of deleteriousness revealed marked enrichment for likely damaging variants that result in acquisition of cysteine. By deploying chemoproteogenomics across eleven cell lines, we identify 116 gain-of-cysteines, of which 10 were liganded by electrophilic druglike molecules. Reference cysteines proximal to missense variants were also found to be pervasive, 791 in total, supporting heretofore untapped opportunities for proteoform-specific chemical probe development campaigns. As chemoproteogenomics is further distinguished by sample-matched combinatorial variant databases and compatible with redox proteomics and small molecule screening, we expect widespread utility in guiding proteoform-specific biology and therapeutic discovery.

Genome-wide CRISPR Screen Reveal Targets of Chiral Gold(I) Anticancer Compound in Mammalian Cells

Metal-based drugs, such as cisplatin and auranofin, are used for the treatment of cancer and rheumatoid arthritis, respectively. Auranofin and other gold-derived compounds have been shown to possess anticancer, anti-inflammatory, antimicrobial, and antiparasitic activity in preclinical and clinical trials. Unlike platinum agents which are known to target DNA, the target of gold is not well elucidated. To better understand the targets and effects of gold agents in mammalian cells, we used a targeted CRISPR (ToxCRISPR) screen in K562 cancer cells to identify genes that modulate cellular sensitivity to gold. We synthesized a novel chiral gold(I) compound, JHK-21, with potent anticancer activity. Among the most sensitizing hits were proteins involved in mitochondrial carriers, mitochondrial metabolism, and oxidative phosphorylation. Further analysis revealed that JHK-21 induced inner mitochondria membrane dysfunction and modulated ATP-binding cassette subfamily member C (ABCC1) function in a manner distinct from auranofin. Characterizing the therapeutic effects and toxicities of metallodrugs in mammalian cells is of growing interest to guide future drug discovery, and cellular and preclinical/clinical studies.

Prevalence of non-tuberculous mycobacteria among previously treated TB patients in the Gulf of Guinea, Africa

Objective

Differentiation between non-tuberculous mycobacteria (NTM) and Mycobacterium tuberculosis complex (MTBC) is crucial for case management with the appropriate antimycobacterials. This study was undertaken in three West and Central African countries to understand NTM associated with pulmonary tuberculosis in the sub-region.

Methods

A collection of 503 isolates (158 from Cameroon, 202 from Nigeria and 143 from Ghana) obtained from solid and liquid cultures were analysed. The isolates were tested for drug susceptibility, and MTBC were confirmed using IS6110. All IS6110-negative isolates were identified by 65-kilodalton heat shock protein (hsp65) gene amplification, DNA sequencing and BLAST analysis.

Results

Overall, the prevalence of NTM was 16/503 (3.2%), distributed as 2/202 (1%) in Nigeria, 2/158 (1.3%) in Cameroon and 12/143 (8.4%) in Ghana. The main NTM isolates included 5/16 (31.3%) M. fortuitum, 2/16 (12.5%) M. intracellulare and 2/16 (12.5%) M. engbaekii. Eight (57.1%) of the 14 previously treated patients harboured NTM (odds ratio 0.21, 95% confidence interval 0.06-0.77; P=0.021). Three multi-drug-resistant strains were identified: M. engbaekii, M. fortuitum and M. intracellulare.

Conclusion

NTM were mainly found among individuals with unsuccessful treatment. This highlights the need for mycobacterial species differentiation using rapid molecular tools for appropriate case management, as most are resistant to routine first-line antimycobacterials.

Gold(III)-P-chirogenic complex induces mitochondrial dysfunction in triple-negative breast cancer

Chemical agents that specifically exploit metabolic vulnerabilities of cancer cells will be beneficial but are rare. The role of oxidative phosphorylation (OXPHOS) in promoting and maintaining triple-negative breast cancer (TNBC) growth provides new treatment opportunity. In this work, we describe AuPhos-19, a small-molecule gold(III)-based agent bearing a chiral phosphine ligand that selectively disrupts mitochondrial metabolism in murine and human TNBC cells but not normal epithelial cells. AuPhos-19 induces potent cytotoxic effect with half maximal inhibitory concentration (IC50) in the nanomolar range (220-650 nM) across different TNBC cell lines. The lipophilic cationic character of AuPhos-19 facilitates interaction with mitochondrial OXPHOS. AuPhos-19 inhibits mitochondria respiration and induces significant AMPK activation. Depolarization of the mitochondria membrane, mitochondria ROS accumulation, and mitochondria DNA depletion provided further indication that AuPhos-19 perturbs mitochondria function. AuPhos-19 inhibits tumor growth in tumor-bearing mice. This study highlights the development of gold-based compounds targeting mitochondrial pathways for efficacious cancer treatment.

The CannTeen study: verbal episodic memory, spatial working memory, and response inhibition in adolescent and adult cannabis users and age-matched controls

BACKGROUND

Preclinical and human studies suggest that adolescent cannabis use may be associated with worse cognitive outcomes than adult cannabis use. We investigated the associations between chronic cannabis use and cognitive function in adolescent and adult cannabis users and controls. We hypothesised user-status would be negatively associated with cognitive function and this relationship would be stronger in adolescents than adults.

METHODS

As part of the 'CannTeen' project, this cross-sectional study assessed cognitive performance in adolescent cannabis users (n = 76; 16-17-year-olds), adolescent controls (n = 63), adult cannabis users (n = 71; 26-29-year-olds) and adult controls (n = 64). Users used cannabis 1-7 days/week. Adolescent and adult cannabis users were matched on cannabis use frequency (4 days/week) and time since last use (2.5 days). Verbal episodic memory (VEM) was assessed using the prose recall task, spatial working memory (SWM) was assessed using the spatial n-back task, and response inhibition was assessed with the stop-signal task. Primary outcome variables were: delayed recall, 3-back discriminability, and stop signal reaction time, respectively.

RESULTS

Users had worse VEM than controls (F(1,268) = 7.423, p = 0.007). There were no significant differences between user-groups on SWM or response inhibition. Null differences were supported by Bayesian analyses. No significant interactions between age-group and user-group were found for VEM, SWM, or response inhibition.

CONCLUSIONS

Consistent with previous research, there was an association between chronic cannabis use and poorer VEM, but chronic cannabis use was not associated with SWM or response inhibition. We did not find evidence for heightened adolescent vulnerability to cannabis-related cognitive impairment.

Water-Soluble Gold(III)-Metformin Complex Alters Mitochondrial Bioenergetics in Breast Cancer Cells

Chemical control of mitochondrial dynamics and bioenergetics can unravel fundamental biological mechanisms and therapeutics for several diseases including, diabetes and cancer. We synthesized stable, water-soluble gold(III) complexes (Auraformin) supported by biguanide metformin or phenylmetformin for efficacious inhibition of mitochondrial respiration. The new compounds were characterized following the reaction of [C N]-cyclometalated gold(III) compounds with respective biguanides. Auraformin is solution stable in a physiologically relevant environment. We show that auraformin decreases mitochondrial respiration efficiently in comparison to the clinically used metformin by 100-fold. The compound displays significant mitochondrial uptake and induces antiproliferative activity in the micromolar range. Our results shed light on the development of new scaffolds as improved inhibitors of mitochondrial respiration.

Anticancer gold(iii)-bisphosphine complex alters the mitochondrial electron transport chain to induce in vivo tumor inhibition

Expanding the chemical diversity of metal complexes provides a robust platform to generate functional bioactive reagents. To access an excellent repository of metal-based compounds for probe/drug discovery, we capitalized on the rich chemistry of gold to create organometallic gold(iii) compounds by ligand tuning. We obtained novel organogold(iii) compounds bearing a 1,2-bis(diphenylphosphino)benzene ligand, providing structural diversity with optimal physiological stability. Biological evaluation of the lead compound AuPhos-89 demonstrates mitochondrial complex I-mediated alteration of the mitochondrial electron transport chain (ETC) to drive respiration and diminish cellular energy in the form of adenosine triphosphate (ATP). Mechanism-of-action efforts, RNA-Seq, quantitative proteomics, and NCI-60 screening reveal a highly potent anticancer agent that modulates mitochondrial ETC. AuPhos-89 inhibits the tumor growth of metastatic triple negative breast cancer and represents a new strategy to study the modulation of mitochondrial respiration for the treatment of aggressive cancer and other disease states where mitochondria play a pivotal role in the pathobiology.

Synthetic Control of Mitochondrial Dynamics: Developing Three-Coordinate Au(I) Probes for Perturbation of Mitochondria Structure and Function

Mitochondrial structure and organization is integral to maintaining mitochondrial homeostasis and an emerging biological target in aging, inflammation, neurodegeneration, and cancer. The study of mitochondrial structure and its functional implications remains challenging in part because of the lack of available tools for direct engagement, particularly in a disease setting. Here, we report a gold-based approach to perturb mitochondrial structure in cancer cells. Specifically, the design and synthesis of a series of tricoordinate Au(I) complexes with systematic modifications to group 15 nonmetallic ligands establish structure-activity relationships (SAR) to identify physiologically relevant tools for mitochondrial perturbation. The optimized compound, AuTri-9 selectively disrupts breast cancer mitochondrial structure rapidly as observed by transmission electron microscopy with attendant effects on fusion and fission proteins. This phenomenon triggers severe depolarization of the mitochondrial membrane in cancer cells. The high in vivo tolerability of AuTri-9 in mice demonstrates its preclinical utility. This work provides a basis for rational design of gold-based agents to control mitochondrial structure and dynamics.

Gold-Based Pharmacophore Inhibits Intracellular MYC Protein

Direct targeting of intrinsically disordered proteins, including MYC, by small molecules for biomedical applications would resolve a longstanding issue in chemical biology and medicine. Thus, we developed gold-based small-molecule MYC reagents that engage MYC inside cells and modulate MYC transcriptional activity. Lead compounds comprise an affinity ligand and a gold(I) or gold(III) warhead capable of protein chemical modification. Cell-based MYC target engagement studies via CETSA and co-immunoprecipitation reveal specific interaction of compounds with MYC in cells. The lead gold(I) reagent, 1, demonstrates superior cell-killing potential (up to 35-fold) in a MYC-dependent manner when compared to 10058-F4 in cells including the TNBC, MDA-MB-231. Subsequently, 1 suppresses MYC transcription factor activity via functional colorimetric assays, and gene-profiling using whole-cell transcriptomics reveals significant modulation of MYC target genes by 1. These findings point to metal-mediated ligand affinity chemistry (MLAC) based on gold as a promising strategy to develop chemical probes and anticancer therapeutics targeting MYC.

Correction: Mild deprotection of the N-tert-butyloxycarbonyl (N-Boc) group using oxalyl chloride

Correction for ‘Mild deprotection of the N-tert-butyloxycarbonyl (N-Boc) group using oxalyl chloride’ by Nathaniel George et al., RSC Adv., 2020, 10, 24017–24026, DOI: 10.1039/D0RA04110F.

Synthesis, Characterization, and Antiproliferative Activity of Novel Chiral [QuinoxP*AuCl2]+ Complexes

Herein is reported the synthesis of two Au(III) complexes bearing the (R,R)-(-)-2,3-Bis(tert-butylmethylphosphino)quinoxaline (R,R-QuinoxP*) or (S,S)-(+)-2,3-Bis(tert-butylmethylphosphino)quinoxaline (S,S-QuinoxP*) ligands. By reacting two stoichiometric equivalents of HAuCl4.3H2O to one equivalent of the corresponding QuinoxP* ligand, (R,R)-(-)-2,3-Bis(tert-butylmethylphosphino)quinoxalinedichlorogold(III) tetrachloroaurates(III) (1) and (S,S)-(+)-2,3-Bis(tert-butylmethylphosphino)quinoxalinedichlorogold(III) tetrachloroaurates(III) (2) were formed, respectively, in moderate yields. The structure of (S,S)-(+)-2,3-Bis(tert-butylmethylphosphino)quinoxalinedichlorogold(III) tetrachloroaurates(III) (2) was further confirmed by X-ray crystallography. The antiproliferative activities of the two compounds were evaluated in a panel of cell lines and exhibited promising results comparable to auranofin and cisplatin with IC50 values between 1.08 and 4.83 µM. It is noteworthy that in comparison to other platinum and ruthenium enantiomeric complexes, the two enantiomers (1 and 2) do not exhibit different cytotoxic effects. The compounds exhibited stability in biologically relevant media over 48 h as well as inert reactivity to excess glutathione at 37 °C. These results demonstrate that the Au(III) atom, stabilized by the QuinoxP* ligand, can provide exciting compounds for novel anticancer drugs. These complexes provide a new scaffold to further develop a robust and diverse library of chiral phosphorus Au(III) complexes.

Mild deprotection of the N-tert-butyloxycarbonyl (N-Boc) group using oxalyl chloride

We report a mild method for the selective deprotection of the N-Boc group from a structurally diverse set of compounds, encompassing aliphatic, aromatic, and heterocyclic substrates by using oxalyl chloride in methanol. The reactions take place under room temperature conditions for 1–4 h with yields up to 90%. This mild procedure was applied to a hybrid, medicinally active compound FC1, which is a novel dual inhibitor of IDO1 and DNA Pol gamma. A broader mechanism involving the electrophilic character of oxalyl chloride is postulated for this deprotection strategy.

We report a mild method for the selective deprotection of the N-Boc group from a structurally diverse set of compounds, encompassing aliphatic, aromatic, and heterocyclic substrates by using oxalyl chloride in methanol.

Small-Molecule Poly(ADP-ribose) Polymerase and PD-L1 Inhibitor Conjugates as Dual-Action Anticancer Agents

Immune checkpoint blockades have revolutionized the treatment landscape for several cancer indications, yet they have not gained traction in a range of other tumors such as triple-negative breast cancer. Despite durable disease control by many patients, a third of cancer patients relapse due to acquired resistance. Combined immunotherapy has shown significant promise to overcome these grand challenges. In this report, we describe the synthesis and characterization of dual-action small-molecule PARP1/PD-L1 inhibitor conjugates as potential targeted anticancer agents. These conjugates display significant apoptosis and cytotoxic efficacy to approximately 2-20-fold better than their individual agents in a panel of cancer cell lines. This was underscored by derived combination indices, which was consistent with strong synergy when cells were treated with the individual agents, olaparib and BMS-001 using the Chou-Talalay method. Furthermore, we sought to unravel the mechanistic behavior of the conjugates and their implications on the PARP/PD-L1 axis. We used apoptosis, cell cycle, immunoblotting, and T-cell proliferation assays to establish the synergy imparted by these conjugates. These multifunctional compounds enable the discovery of small-molecule immunochemotherapeutic agents and chemical probes to elucidate the cross-talk between DNA repair and PD-L1 pathways.

Toward a risk-based assessment of the adult cancer survivor: late effects of chemotherapy

Survivorship care of the cancer patient has become a growing concern among oncologists and primary care physicians in communities across the country. It is now recognized as a distinct phase in the continuum of cancer care. There are an estimated 12 million Americans with a history of cancer looking to their oncologists and primary care physicians for assistance in navigating the difficult waters of survivorship. Although a concerted effort is underway, there are few evidence-based guidelines or recommendations for managing long-term and late effects of adult cancer survivors. The Children 's Oncology Group has developed consensus guidelines to improve and standardize care of the survivors of childhood to young adult cancers. Their successful efforts could serve as a model for a similar undertaking to address the post-treatment care of adult survivors. In the absence of evidence-based or consensus guidelines, knowledge of late effects can inform and direct assessment of survivors presenting with late sequelae of chemotherapy agents.

Response, time to progression, and overall survival of patients with stage III lung cancer in a minority-based cohort

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Background: Lung cancer is the leading cause of cancer death. Response and survival of patients (pts) with stage III lung cancer in minority population is not well studied. Methods: 79 pts treated between 2001 and 2006 were studied as a retrospective cohort. Clinical and survival data were analyzed using fisher's test, chi square test, Kaplan Meier analyses. Results: 33 Pts had Stage IIIA; Median age at diagnosis was 58 yrs (37–75). 14 were males (42.4%) 19 females (57.6%) 26 African American (78.8%) and 7 Caucasians (21.2%). Median number of co morbidities 2 (0–4). Mean follow up was 25 months (mo) (2 - 93), 19 had surgery (12 Lobectomy (36.4%), 7 Pneumonectomy (21.2%)) and 14 were unresectable (42.4%). All pts received adjuvant chemotherapy. Unresectable pts received chemotherapy and radiation, 8 carboplatin and gemcitabine and 6 cisplatin and etoposide. Median time to progression in resectable IIIA was 23 mo (2- 67), unresectable IIIA was 12 mo (3–93). Median survival in pts with resection was 26 mo (2 - 67), unresectable was 12 mo (5 - 93). Overall survival and time to progression was not influenced by sex, race, tumor type. 46 pts had stage IIIB, median age at diagnosis 57.5 yrs (40–68). 31 were males (67.4%) 15 females (32.6%) 29 African Americans (63%) 11 Caucasians (23.9) 3 Asians (6.5%) and 3 Hispanics (6.5%). Median follow up was 10 mo (3–97). All pts received chemotherapy and radiation. 23 received cisplatin and etoposide (50%), 14 carboplatin and gemcitabine (30%), 5 carboplatin and etoposide (9%), 5 carboplatin and paclitaxel (9%). 13 had complete response (28.3%), 15 partial response (32.6%), 2 stable disease (4.3%) and 10 Progression (21.7%). Median time to progression was 9 mo (3–97). Median overall survival was 10 mo (3–97). Overall survival and time to progression was not influenced by sex, race, tumor type, chemotherapy regimen. Conclusions: In this minority based cohort response, time to progression, overall survival in both IIIA and IIIB pts is much lower then historical controls. The overall survival and time to progression in both IIIA and IIIB is not influenced by race, sex, tumor type and type of chemotherapy regimen. Further investigations of disease and healthcare disparities in the underserved minority population, are warranted.

No significant financial relationships to disclose.

Effects of YM 435 and A 77636 on dopamine D-1 receptors in bovine retina in vitro

1. Homogenates of bovine retinas were used to study the capacities of two new dopamine (DA) receptor agonists, e.g. YM 435 and A 77636, to interact with D1 receptors. 2. Adenylate cyclase experiments. YM 435 and A 77636 enhanced cAMP accumulation, with EC50 values of 1.97 microM and 22.9 nM, respectively. The receptor-mediated nature of the effects of these two novel D1 agonists was shown by the abilities of both SCH 23390 or (+)-butaclamol to inhibit the agonist-induced increase of cAMP formation. 3. Binding experiments. The same agonists were also tested for competition with 3H-SCH 23390 for binding to D1 receptors. IC50 values for YM 435 and A 77636 were 8.15 microM and 6.15 nM, respectively. 4. The results of the present report demonstrate the suitability of bovine retina in vitro to evaluate the specificity of new DA D1 agonists at the receptor level.

Okadaic acid modulates exocytotic and transporter-dependent release of dopamine in bovine retina in vitro

Bovine retinas were isolated for the study of the modulation of exocytotic and transporter-dependent release of dopamine (DA) in vitro. Endogenous DA was measured in the medium using HPLC with electrochemical detection under successive incubations with transfers in fresh medium every 30 min. As expected, potassium caused a calcium-dependent exocytotic liberation of DA. Amphetamine or tyramine induced a calcium-independent release by reversing DA transport across the plasma membrane. Okadaic acid, a specific inhibitor of phosphatases 1 and 2A, induced a slight but significant DA release in the absence of calcium. Furthermore, the toxin increased potassium-, amphetamine- or tyramine-induced DA release independently of extracellular calcium. In addition, okadaic acid completely annulled the ability of a calcium-free extracellular environment to inhibit the potassium-induced DA release. Finally, the toxin prevented the time-dependent decline in the efficacies of amphetamine or tyramine to release DA. In agreement with proposed schemes described for rat striatum, the results of the present study confirmed the existence of distinct release modes of DA in bovine retina. The results obtained with okadaic acid suggest that phosphatase 1 and/or phosphatase 2A constitute part of a direct or indirect mechanism to inhibit both exocytotic and transporter-dependent DA release.

Agonist-induced desensitization of dopamine D-1 receptors in bovine retina and rat striatum

We have investigated agonist-induced desensitization of dopamine (DA) D-1 receptor mediated accumulation of adenosine 3':5'-cyclic monophosphate (cAMP) in bovine retinas and rat striata in vitro. Tissues were exposed to various pharmacological agents for 60 min, washed and homogenized. D-1 agonist-promoted accumulation of cAMP in the presence of adenosine 5'-triphosphate (ATP) and 5'-guanylylimidodiphosphate (GppNHp) was then measured. Retinas and striata incubated with DA or (+) SKF 38393 (100 microM each) displayed diminished capacities to accumulate cAMP when they were re-exposed to the same drugs. As expected, retinas and striata treated wtih (+) SKF 38393 also showed an attenuated formation of cAMP when restimulated with DA. In addition, D-1 receptors in retinas that had been treated with quinpirole, a D-2 agonist, did not become desensitized. Furthermore, 0.2 microM SCH 23390 prevented D-1 receptor subsensitivity caused by 100 microM DA. Interestingly, retinas and striata incubated with forskolin, a direct stimulator of adenylyl cyclase, also displayed a diminished enzymatic response to restimulation by the same agent, as well as by DA. Additionally, retinas incubated with 100 microM DA were refractory to forskolin-induced cAMP formation. Finally, results of 3H-SCH 23390 binding to control and DA-treated retinas indicated that agonist treatment did not induce significant changes in either receptor density or binding affinity. The data indicate that bovine retinas and striatal slices in vitro are suitable to investigate various aspects of the desensitization of neuronal responses to DA D-1 agonists or forskolin.

Potentiation by the tetraphenylboron anion of the effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and its pyridinium metabolite

The 1-methyl-4-phenylpyridinium species (MPP+) is the four-electron oxidation product of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and is widely assumed to be the actual neurotoxic species responsible for the MPTP-induced destruction of dopaminergic neurons. MPTP is oxidized by the enzyme monoamine oxidase-B to a dihydropyridinium intermediate which is oxidized further to MPP+, an effective inhibitor of the oxidation of the Complex I substrates glutamate/malate in isolated mitochondrial preparations. In the present study, the tetraphenylboron anion (TPB) greatly potentiated the inhibitory effects of MPP+ and other selected pyridinium species on glutamate/malate respiration in isolated mouse liver mitochondria. At 10 microM TPB, the potentiation ranged from approximately 50-fold to greater than 1,000-fold for the several pyridinium species tested. In other experiments, TPB greatly enhanced the accumulation of [3H]MPP+ by isolated mitochondrial preparations. This facilitation by TPB of MPP+ accumulation into mitochondria explains, at least in part, the potentiation by TPB of the above-mentioned inhibition of mitochondrial respiration. Moreover, TPB addition increased the amount of lactate formed during the incubation of mouse neostriatal tissue slices with MPTP and other tetrahydropyridines. The administration of TPB also potentiated the dopaminergic neurotoxicity of MPTP in male Swiss-Webster mice. All of these observations, taken together, are consistent with the premise that the inhibitory effect of MPP+ on mitochondrial respiration within dopaminergic neurons is the ultimate mechanism to explain MPTP-induced neurotoxicity.

Attenuation by dopamine uptake blockers of the inhibitory effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and some of its analogs on NADH-linked metabolism in mouse neostriatal slices

In previous studies it was shown that the pyridinium species formed by the monoamine-oxidase-catalyzed conversion of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 1-methyl-4-(2'methylphenyl)-1,2,3,6-tetrahydropyridine (2'Me-MPTP) inhibited mitochondrial electron transport at Complex I. In addition, these substances, when incubated with mouse neostriatal slices, caused an increased lactate accumulation. However, it was not clear whether this inhibition could occur within dopamine nerve terminals. In the present study we investigated if dopamine uptake blockers, shown previously to protect against tetrahydropyridine-induced dopaminergic neurotoxicity, would attenuate MPTP- and 2'Me-MPTP-promoted lactate formation in neostriatal slices. 2'Me-MPTP-induced lactate accumulation in neostriatal slices from mice or rats with a lesion of the nigrostriatal pathway was also studied. The dopamine uptake blocker, Win 35,428 [8-azabicyclo[3.2.1]octane-2-carboxylic acid, 3-(4-fluorophenyl)-8-methyl-, methylester [1R-(exo, exol)]), attenuated the increased lactate formation caused by MPTP and 2'Me-MPTP. At low concentrations of 2'Me-MPTP (5 microM), the increased lactate production was inhibited completely by Win 35,428. These latter data suggest that at low concentrations of 2'Me-MPTP, the increased lactate accumulation was associated primarily with dopaminergic nerve terminals. Two other dopamine uptake inhibitors, McN 5908 [trans-4-(1,2,3,5,6,10b-hexahydropyrrolo[2,1-alpha]isoquinolin+ ++-6-yl) benzenamine hydrobromide methanolate (4:4:1)] and mazindol [5-(4-chlorophenyl)-2,5-dihydro-3H-imidazo- [2,1-alpha]isoindol-5-ol], also attenuated tetrahydropyridine-induced lactate formation. At concentrations selective for their respective uptake systems, norepinephrine- and serotonin-uptake inhibitors did not attenuate 2'Me-MPTP-induced lactate accumulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Mesencephalic dopamine neurons become less sensitive to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine toxicity during development in vitro

The in vitro development of monoamine oxidase (MAO) activity and [3H]dopamine (DA) uptake capacity of dissociated cell cultures from rat embryo mesencephalon were correlated with the potency of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 1-methyl-4-phenylpyridine (MPP+) neurotoxicity. Specific activities of both MAO-A and MAO-B increased during in vitro development of the cultures, with MAO-B activity increasing 20-fold between the first and fourth week. Similarly, [3H]DA accumulation increased 2.6-fold between the first and third week in vitro, when it reached a plateau. Unexpectedly, the toxicities of MPTP and MPP+ were substantially decreased in the older cultures. Exposure to MPTP reduced [3H]DA accumulation per culture by 77% in 1-week-old cultures and by 36% in 4-week-old cultures. Similarly, damage caused by MPPT was reduced from 84% of control in the first week to 34% of control in the fourth week. The attenuation of neurotoxicity was not due to an increase in storage of MPP+ in the synaptic vesicles of DA neurons, nor to a change in the distribution of MPP+ between dopaminergic and other cellular components of the cultures. The damage to DA neurons caused by the mitochondrial toxin, rotenone, also showed a similar reduction in the older cultures. These observations coupled with an increase in lactate formation and glucose consumption during the in vitro development of the cultures suggest a shift toward increased glycolysis and decreased dependence on aerobic metabolism. This would render the cells more resistant to the inhibition of mitochondrial function by MPP+.

Effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on dopamine synthesis and release in the rabbit retina in vitro

The effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on the synthesis and release of dopamine (DA) was investigated in the retina of the rabbit in vitro. The results indicated that MPTP did not affect the synthesis of DA, but increased its release. Blockade of the activity of monoamine oxidase (MAO) with pargyline (100 microM) did not abolish the capacity of MPTP to release DA. Similarly, these pharmacological effects of MPTP were not dependent on the presence or absence of melanin.

Investigation of dopamine content, synthesis, and release in the rabbit retina in vitro: I. Effects of dopamine precursors, reserpine, amphetamine, and L-DOPA decarboxylase and monoamine oxidase inhibitors

The basal catecholamine content of rabbit retina was determined by liquid chromatography with electrochemical detection (LC-EC) and 3,4-dihydroxyphenylethylamine (dopamine, DA) found to be the major catecholamine. The immediate DA precursor, 3,4-dihydroxyphenylalanine (L-DOPA), and the metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), were also detected at about 2.8% and 17% of DA levels, respectively. When added exogenously, L-tyrosine did not increase the rate of DA synthesis over the basal level. In contrast, exogenous L-DOPA led to a 3.5-fold increase in DA, and to a 20-fold increase in DOPAC content. The monoamine oxidase inhibitors pargyline and (-)-deprenyl differentially affected the degradation of DA, since 100 microM pargyline was apparently more effective than 100 microM (-)-deprenyl. Reserpine and (+/-)-amphetamine each induced a Ca2+-independent decrease of DA stores. The separate actions of reserpine and (+/-)-amphetamine in lowering tissue DA levels were additive, suggesting two separate pools of DA available for release from presynaptic stores. The present study demonstrates that the LC-EC technique may be used to investigate the modulation of the synthesis and release of retinal DA in vitro, without the prior uptake of radiolabelled transmitter.

Investigation of dopamine content, synthesis, and release in the rabbit retina in vitro: II. Effects of high potassium, adenylate cyclase activators, and N-n-propyl-3-(3-hydroxyphenyl) piperidine

The modulation of 3,4-dihydroxyphenylethylamine (dopamine, DA) synthesis and release in rabbit retina in vitro by high K+; adenylate cyclase activators such as forskolin, 2-chloroadenosine, vasoactive intestinal polypeptide (VIP); and the putative DA autoreceptor agonist N-n-propyl-3-(3-hydroxyphenyl) piperidine (3-PPP) has been investigated. Incubation of retinas in 50 mM K+ resulted in the activation of tyrosine hydroxylase (TH). Activation did not require the presence of extracellular Ca2+. K+ 50 mM also induced a Ca2+-dependent release of DA. Forskolin 50 microM stimulated TH but 100 microM 2-chloroadenosine and 650 nM VIP did not. Individually, (+)-3-PPP, (-)-3-PPP, and (+/-)-3-PPP reduced DA synthesis and increased its release. The effects of (+/-)-3-PPP were dose-dependent and did not require the presence of extracellular Ca2+. The activation of TH induced by 50 mM K+, but not that induced by 50 microM forskolin, was abolished by 100 microM (+/-)-3-PPP.