Isolation and Sequencing of Salsolinol Synthase, an Enzyme Catalyzing Salsolinol Biosynthesis

Salsolinol (1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline), a derivate of dopamine, is suspected to be the most probable neurotoxin in the degeneration of dopaminergic neurons. Numerous hypotheses regarding its pathophysiological roles have been raised, especially related to Parkinson's disease and alcohol addiction. In the mammalian brain, salsolinol may be enzymatically synthesized by salsolinol synthase from dopamine and acetaldehyde. However, the direct evidence of its biosynthesis was still missing. In this study, we purified salsolinol synthase from rat brain by a systematical procedure involving acid precipitation, ultrafiltration, and hydrophilic interaction chromatography. The molecular weight of salsolinol synthase determined by MALDI-TOF MS is 8622.29 Da, comprising 77 amino acids (MQIFVKTLTG KTITLEVEPS DTIKNVKAKI QDKEGIPPDQ QRLIFAGKQL EDGRTLSDYN IQKKSTLHLV LRLRVDY). Homology analysis showed that the enzyme is a ubiquitin-like protein, with a difference of four amino acids, which suggests it is a novel protein. After it was overexpressed in eukaryotic cells, the production of salsolinol was significantly increased as compared with control, confirming the catalytic function of this enzyme. To our knowledge, it is the first systematic purification and sequencing of salsolinol synthase. Together, this work reveals a formerly anonymous protein and urges further exploration of its possible prognostic value and implications in Parkinson's disease and other related disorders.

90 years of monoamine oxidase: some progress and some confusion

It would not be practical to attempt to deal with all the advances that have informed our understanding of the behavior and functions of this enzyme over the past 90 years. This account concentrates key advances that explain why the monoamine oxidases remain of pharmacological and biochemical interest and on some areas of continuing uncertainty. Some issues that remain to be understood or are in need of further clarification are highlighted.

Adaptive Modifications of Maternal Hypothalamic-Pituitary-Adrenal Axis Activity during Lactation and Salsolinol as a New Player in this Phenomenon

Both basal and stress-induced secretory activities of the hypothalamic-pituitary-adrenal (HPA) axis are distinctly modified in lactating females. On the one hand, it aims to meet the physiological demands of the mother, and on the other hand, the appropriate and stable plasma cortisol level is one of the essential factors for the proper offspring development. Specific adaptations of HPA axis activity to lactation have been extensively studied in several animal species and humans, providing interesting data on the HPA axis plasticity mechanism. However, most of the data related to this phenomenon are derived from studies in rats. The purpose of this review is to highlight these adaptations, with a particular emphasis on stress reaction and differences that occur between species. Existing data on breastfeeding women are also included in several aspects. Finally, data from the experiments in sheep are presented, indicating a new regulatory factor of the HPA axis-salsolinol-which typical role was revealed in lactation. It is suggested that this dopamine derivative is involved in both maintaining basal and suppressing stress-induced HPA axis activities in lactating dams.

A newly discovered neurotoxin ADTIQ associated with hyperglycemia and Parkinson's disease

BACKGROUND

Diabetes is associated with an increased risk of Parkinson's disease (PD). Number of studies have suggested that methylglyoxal (MGO) induced by diabetes is related to PD. However, very little is known about its molecular mechanism. On other hand, 1-acetyl-6, 7- dihydroxyl-1, 2, 3, 4- Tetrahydroisoquinoline(ADTIQ) is a dopamine (DA)-derived tetrahydroisoquinoline (TIQ), a novel endogenous neurotoxins, which was first discovered in frozen Parkinson's disease human brain tissue. While ADTIQ precursor methylglyoxal was also found in diabetic patients related to the glucose metabolism and diabetic patients.

METHODS

LC-MS/MS, 1H NMR and infrared spectroscopy identified the structure of ADTIQ. The Annexin V-FITC/PI, MTT and western blot analysis were used to measure the neurotoxicity of ADTIQ. The levels of ADTIQ and methylglyoxal were detected by LC-MS/MS.

RESULTS

Here we report the chemical synthesis of ADTIQ, demonstrate its biosynthesis in SH-SY5Y neuroblastoma cell line and investigate its role in the pathogenesis of PD. In addition, a significant increase in the level of ADTIQ was detected in the brains of transgenic mice expressing mutant forms (A53T or A30P) of α-synuclein. ADTIQ also reduced the cell viability and induced mitochondrial apoptosis in dopaminergic cells, suggesting that ADTIQ acts as an endogenous neurotoxin and potentially involved in the pathogenesis of PD. Methylglyoxal, a major byproduct of glucose metabolism and abnormalities in glucose metabolism could influence the levels of ADTIQ. Consistent with the hypothesis, increased levels of ADTIQ and methylglyoxal were detected in the striatum of diabetic rats and SH-SY5Y cells cultured in the presence of high glucose concentrations.

CONCLUSIONS

Increased levels of ADTIQ could be related with Hyperglycemia and death of dopaminergic neurons.

GENERAL SIGNIFICANCE

The increased levels of ADTIQ could be a reason of dopamine neuron dysfunction in diabetes. Therefore, ADTIQ may play a key role in increasing the risk for PD in patients with diabetes.