β-Methylphenylalanine exerts neuroprotective effects in a Parkinson's disease model by protecting against tyrosine hydroxylase depletion

Dihydromyricetin Improves High Glucose-Induced Dopaminergic Neuronal Damage by Activating AMPK-Autophagy Signaling Pathway

INTRODUCTION

In recent years, a growing number of clinical and biological studies have shown that patients with type 2 diabetes mellitus (T2DM) are at increased risk of developing Parkinson's disease (PD). Prolonged exposure to hyperglycemia results in abnormal glucose metabolism, which in turn causes pathological changes similar to PD, leading to selective loss of dopaminergic neurons in the compact part of the substantia nigra. Dihydromyricetin (DHM) is a naturally occurring flavonoid with various biological activities including antioxidant and hepatoprotective properties. In this study, the effect of DHM on high glucose-induced dopaminergic neuronal damage was investigated.

METHODS

The potential modulatory effects of DHM on high glucose-induced dopaminergic neuronal damage and its mechanism were studied.

RESULTS

DHM ameliorated high glucose-induced dopaminergic neuronal damage and autophagy injury. Inhibition of autophagy by 3-methyladenine abrogated the beneficial effects of DHM on high glucose-induced dopaminergic neuronal damage. In addition, DHM increased levels of p-AMP-activated protein kinase (AMPK) and phosphorylated UNC51-like kinase 1. The AMPK inhibitor compound C eliminated DHM-induced autophagy and subsequently inhibited the ameliorative effects of DHM on high glucose-induced dopaminergic neuronal damage.

DISCUSSION

DHM ameliorates high glucose-induced dopaminergic neuronal damage by activating the AMPK-autophagy pathway.

Biosynthesis of novel non-proteinogenic amino acids β-hydroxyenduracididine and β-methylphenylalanine in Escherichia coli

Non-proteinogenic amino acids (npAAs) are valuable building blocks for the development of advanced pharmaceuticals and agrochemicals. The surge in interest in their synthesis is primarily due to the potential to enhance and diversify existing bioactive molecules. This can be achieved by altering these bioactive molecules to improve their effectiveness, reducing resistance compared to their natural counterparts or generating molecules with novel functions. Traditional production of npAAs in native hosts requires specialized conditions and complex cultivation media. Furthermore, these compounds are often found in organisms that challenge genetic manipulation. Thus, the recombinant production of these npAAs in a model organism like Escherichia coli paves the way for groundbreaking advancements in synthetic biology. Two synthetic operons, comprising of five heterologous proteins were genomically integrated into E. coli for the synthesis of npAAs β-methylphenylalanine (BmePhe), β-hydroxyenduracididine (BhEnd), and enduracididine (End). Proteomic and metabolomic analysis confirmed production of these compounds in E. coli for the first time. Interestingly, we discovered that the exogenous addition of pathway precursors to the E. coli system enhanced the yield of BmePhe by 2.5 times, whereas it concurrently attenuated the production of BhEnd and End, signifying a selective precursor-dependent yield enhancement. The synthetic biology landscape is broadened in this study by expanding the repertoire of amino acids beyond the conventional set of 22 standard proteinogenic amino acids. The biosynthesized npAAs, End, BhEnd, and BmePhe hold promise for engineering proteins with modified functions, integrating into novel metabolites and/or enhancing biological stability and activity. Additionally, these amino acids' biological production and subsequent purification present an alternative to traditional chemical synthesis methods, paving a direct pathway for pharmacological evaluation.

The Neuroprotective and Anxiolytic Effects of Magnesium Sulfate on Retinal Dopaminergic Neurons in 6-OHDA-Induced Parkinsonian Rats: A Pilot Study

This study investigates the protective effects of magnesium sulfate on dopamine neurons in the retinas of rats with 6-hydroxydopamine (6-OHDA)-induced Parkinson's disease (PD). Rapidly progressing cognitive decline often precedes or coincides with the motor symptoms associated with PD. PD patients also frequently exhibit visual function abnormalities. However, the specific mechanisms underlying visual dysfunction in PD patients are not yet fully understood. Therefore, this study aims to investigate whether magnesium homeostasis affects dopaminergic neurons in the retina of PD rats. Thirty-six rats were divided into four groups: (1) control, (2) control with magnesium sulfate (control/MgSO4), (3) Parkinson's disease (PD), and (4) Parkinson's disease with magnesium sulfate (PD/MgSO4). The apomorphine-induced (APO) rotation test assessed the success of the PD models. The open-field experiment measured the rats' anxiety levels. Tyrosine hydroxylase (TH) and glutamate levels, indicators of dopamine neuron survival, were detected using immunofluorescence staining. Protein levels of solute carrier family 41 A1 (SCL41A1), magnesium transporter 1 (MagT1), and cyclin M2 (CNNM2) in the retina were analyzed using Western blot. Results showed that, compared to the PD group, rats in the PD/MgSO4 group had improved psychological states and motor performance at two and four weeks post-surgery. The PD/MgSO4 group also exhibited significantly higher TH fluorescence intensity in the left retinas and lower glutamate fluorescence intensity than the PD group. Additional experiments indicated that the protein levels of SLC41A1, MagT1, and CNNM2 were generally higher in the retinas of the PD/MgSO4 group, along with an increase in retinal magnesium ion content. This suggests that magnesium sulfate may reduce glutamate levels and protect dopamine neurons in the retina. Thus, magnesium sulfate might have therapeutic potential for visual functional impairments in PD patients.

Fumaria vaillantii extract protects PC12 cells against neurotoxicity induced by 6-OHDA

BACKGROUND

Parkinson's disease is a neurological disorder caused by the loss of dopaminergic neurons in the midbrain. Various mechanisms are involved in the incidence of the disease including oxidative stress. Several herbs and natural products may interfere with the oxidative-stress pathway due to their antioxidant effects.

OBJECTIVE

Herein, we aimed to investigate the neuroprotective role of F. vaillantii extract on Parkinson's in vitro and in vivo model owing to the presence of the bioactive agents with antioxidant properties.

METHODS

In vitro experments showed that 6-hydroxydopamine could induce toxicity in PC12 cells. The impact of F. vaillantii extract on cell viability was measured by using MTT assay. Nuclear morphological changes were qualitatively evaluated employing Hoechst staining. The antioxidant activity of the extract was determined by ROS and lipid peroxidation assays. Tyrosine hydroxylase protein expression was measured by western blotting in PC12 cells. For in vivo study, movement parameters were evaluated.

RESULTS

The results indicated that 75 µΜ of 6-OHDA induced 50% toxicity in PC12 cells for 24 h. Following post-treatment with F. vaillantii extract (0.1 mg/ml) for 72 h, we observed that the extract effectively prevented cell toxicity induced by 6-OHDA and reduced the apoptotic cell population. Furthermore, the extract attenuated the ROS level, lipid peroxidation and increased protein expression of TH after 72 h of treatment. In addition, oral administration of 300 mg/kg of F. vaillantii extract for 14 days improved locomotor activity, catalepsy, bradykinesia, motor coordination and reduced the apomorphine-caused rotation in 6-OHDA- induced Parkinson's disease-like symptoms in male rats.

CONCLUSION

The present study suggests a protective role for the extract of F. vaillantii against oxidative stress-induced cell damage in the PC12 cells exposed to neurotoxin 6-OHDA which was verified in in vivo model by reducing the motor defects induced by 6-OHDA. This extract could be a promising therapeutic agent for the prevention of PD progression.

Tissue-specific mitochondrial HIGD1C promotes oxygen sensitivity in carotid body chemoreceptors

Mammalian carotid body arterial chemoreceptors function as an early warning system for hypoxia, triggering acute life-saving arousal and cardiorespiratory reflexes. To serve this role, carotid body glomus cells are highly sensitive to decreases in oxygen availability. While the mitochondria and plasma membrane signaling proteins have been implicated in oxygen sensing by glomus cells, the mechanism underlying their mitochondrial sensitivity to hypoxia compared to other cells is unknown. Here, we identify HIGD1C, a novel hypoxia-inducible gene domain factor isoform, as an electron transport chain complex IV-interacting protein that is almost exclusively expressed in the carotid body and is therefore not generally necessary for mitochondrial function. Importantly, HIGD1C is required for carotid body oxygen sensing and enhances complex IV sensitivity to hypoxia. Thus, we propose that HIGD1C promotes exquisite oxygen sensing by the carotid body, illustrating how specialized mitochondria can be used as sentinels of metabolic stress to elicit essential adaptive behaviors.

Serum Metabolomic Profiling Reveals Biomarkers for Early Detection and Prognosis of Esophageal Squamous Cell Carcinoma

Esophageal squamous cell carcinoma (ESCC) is one of the most common aggressive malignancies worldwide, particularly in northern China. The absence of specific early symptoms and biomarkers leads to late-stage diagnosis, while early diagnosis and risk stratification are crucial for improving overall prognosis. We performed UPLC-MS/MS on 450 ESCC patients and 588 controls consisting of a discovery group and two validation groups to identify biomarkers for early detection and prognosis. Bioinformatics and clinical statistical methods were used for profiling metabolites and evaluating potential biomarkers. A total of 105 differential metabolites were identified as reliable biomarker candidates for ESCC with the same tendency in three cohorts, mainly including amino acids and fatty acyls. A predictive model of 15 metabolites [all-trans-13,14-dihydroretinol, (±)-myristylcarnitine, (2S,3S)-3-methylphenylalanine, 3-(pyrazol-1-yl)-L-alanine, carnitine C10:1, carnitine C10:1 isomer1, carnitine C14-OH, carnitine C16:2-OH, carnitine C9:1, formononetin, hyodeoxycholic acid, indole-3-carboxylic acid, PysoPE 20:3, PysoPE 20:3(2n isomer1), and resolvin E1] was developed by logistic regression after LASSO and random forest analysis. This model held high predictive accuracies on distinguishing ESCC from controls in the discovery and validation groups (accuracies > 89%). In addition, the levels of four downregulated metabolites [hyodeoxycholic acid, (2S,3S)-3-methylphenylalanine, carnitine C9:1, and indole-3-carboxylic acid] were significantly higher in early cancer than advanced cancer. Furthermore, three independent prognostic markers were identified by multivariate Cox regression analyses with and without clinical indicators: a high level of MG(20:4)isomer and low levels of 9,12-octadecadienoic acid and L-isoleucine correlated with an unfavorable prognosis; the risk score based on these three metabolites was able to stratify patients into low or high risk. Moreover, pathway analysis indicated that retinol metabolism and linoleic acid metabolism were prominent perturbed pathways in ESCC. In conclusion, metabolic profiling revealed that perturbed amino acids and lipid metabolism were crucial metabolic signatures of ESCC. Both panels of diagnostic and prognostic markers showed excellent predictive performances. Targeting retinol and linoleic acid metabolism pathways may be new promising mechanism-based therapeutic approaches. Thus, this study would provide novel insights for the early detection and risk stratification for the clinical management of ESCC and potentially improve the outcomes of ESCC.

Neurotoxicity and underlying cellular changes of 21 mitochondrial respiratory chain inhibitors

Inhibition of complex I of the mitochondrial respiratory chain (cI) by rotenone and methyl-phenylpyridinium (MPP +) leads to the degeneration of dopaminergic neurons in man and rodents. To formally describe this mechanism of toxicity, an adverse outcome pathway (AOP:3) has been developed that implies that any inhibitor of cI, or possibly of other parts of the respiratory chain, would have the potential to trigger parkinsonian motor deficits. We used here 21 pesticides, all of which are described in the literature as mitochondrial inhibitors, to study the general applicability of AOP:3 or of in vitro assays that are assessing its activation. Five cI, three complex II (cII), and five complex III (cIII) inhibitors were characterized in detail in human dopaminergic neuronal cell cultures. The NeuriTox assay, examining neurite damage in LUHMES cells, was used as in vitro proxy of the adverse outcome (AO), i.e., of dopaminergic neurodegeneration. This test provided data on whether test compounds were unspecific cytotoxicants or specifically neurotoxic, and it yielded potency data with respect to neurite degeneration. The pesticide panel was also examined in assays for the sequential key events (KE) leading to the AO, i.e., mitochondrial respiratory chain inhibition, mitochondrial dysfunction, and disturbed proteostasis. Data from KE assays were compared to the NeuriTox data (AO). The cII-inhibitory pesticides tested here did not appear to trigger the AOP:3 at all. Some of the cI/cIII inhibitors showed a consistent AOP activation response in all assays, while others did not. In general, there was a clear hierarchy of assay sensitivity: changes of gene expression (biomarker of neuronal stress) correlated well with NeuriTox data; mitochondrial failure (measured both by a mitochondrial membrane potential-sensitive dye and a respirometric assay) was about 10–260 times more sensitive than neurite damage (AO); cI/cIII activity was sometimes affected at > 1000 times lower concentrations than the neurites. These data suggest that the use of AOP:3 for hazard assessment has a number of caveats: (i) specific parkinsonian neurodegeneration cannot be easily predicted from assays of mitochondrial dysfunction; (ii) deriving a point-of-departure for risk assessment from early KE assays may overestimate toxicant potency.

Comparison of 21 data-rich mitochondrial toxicants for neurotoxicity

Quantitative comparison of key event triggering thresholds for AOP:3

Comparison of two cell models and two exposure times for neurotoxicity

Comparison of transcriptome changes and classical key event measures for sensitivity

β-Methylphenylalanine exerts neuroprotective effects in a Parkinson's disease model by protecting against tyrosine hydroxylase depletion

We evaluated the neuroprotective effects of β-methylphenylalanine in an experimental model of rotenone-induced Parkinson's disease (PD) in SH-SY5Y cells and rats. Cells were pre-treated with rotenone (2.5 µg/mL) for 24 hours followed by β-methylphenylalanine (1, 10 and 100 mg/L) for 72 hours. Cell viability, reactive oxygen species (ROS) levels, mitochondrial membrane potential (MMP), mitochondrial fragmentation, apoptosis, and mRNA and protein levels of tyrosine hydroxylase were determined. In a rat model of PD, dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) levels, bradykinesia and tyrosine hydroxylase expression were determined. In rotenone-pre-treated cells, β-methylphenylalanine significantly increased cell viability and MMP, whereas ROS levels, apoptosis and fragmented mitochondria were reduced. β-Methylphenylalanine significantly increased the mRNA and protein levels of tyrosine hydroxylase in SH-SY5Y cells. In the rotenone-induced rat model of PD, oral administration of β-methylphenylalanine recovered DA and DOPAC levels and bradykinesia. β-Methylphenylalanine significantly increased the protein expression of tyrosine hydroxylase in the striatum and substantia nigra of rats. In addition, in silico molecular docking confirmed binding between tyrosine hydroxylase and β-methylphenylalanine. Our experimental results show neuroprotective effects of β-methylphenylalanine via the recovery of mitochondrial damage and protection against the depletion of tyrosine hydroxylase. We propose that β-methylphenylalanine may be useful in the treatment of PD.