The tetrahydrobiopterin pathway: a novel target for the treatment of depression

DNAJC12 in Monoamine Metabolism, Neurodevelopment, and Neurodegeneration

Recent studies show that pathogenic variants in DNAJC12, a co-chaperone for monoamine synthesis, may cause mild hyperphenylalaninemia with infantile dystonia, young-onset parkinsonism, developmental delay and cognitive deficits. DNAJC12 has been included in newborn screening, most revealingly in Spain, and those results highlight the importance of genetic diagnosis and early intervention in combating human disease. However, practitioners may be unaware of these advances and it is probable that many patients, especially adults, have yet to receive molecular testing for DNAJC12. Hence, this review summarizes genotype-phenotype relationships and treatment paradigms for patients with pathogenic variants in DNAJC12. It provides an overview of the structure of DNAJC12 protein, known genetic variants, domains, and binding partners, and elaborates on its role in monoamine synthesis, disease etiology, and pathogenesis. © 2023 International Parkinson and Movement Disorder Society.

Reduced reward responsiveness in treatment resistant depression of middle-aged adults: Association with carotid artery stiffness and tetrahydrobiopterin

Nearly one third of the population diagnosed with major depressive disorder (MDD) fail to respond to two or more antidepressant drugs of adequate dose and duration. This necessitates identification of confounding psychological and physiological factors that could contribute to treatment resistant depression (TRD). The present longitudinal study investigated the influence of behavioural inhibition system (BIS) and behavioural approach system (BAS) in treatment resistance. Further, the association of depression severity with physiological factors contributing to arterial stiffness was also investigated. Baseline data was acquired from 101 middle-aged (36-56 years) patients on immediate diagnosis with MDD using DSM-V criteria. Follow ups were conducted at 06 months and 12 months during treatment. Psychological assessment battery at baseline and follow ups comprised of Hamilton depression rating (HAM-D) for depression severity, WHODAS-2 and BIS-BAS score. Atherosclerosis and central arterial stiffness were measured by intima-media thickness of internal carotid artery and brachial-ankle pulse wave velocity. Physiological factors influencing central vascular function viz., body-mass index, estimated glomerular filtration rate, HbA1c, central systolic and diastolic blood pressure, heart rate and tetrahydrobiopterin were also investigated. Our results show lower reward responsiveness (BAS-RR) and higher BIS scores in TRD patients along with differentially higher intima-media thickness of left internal carotid artery. Higher depression severity at all stages of the study was correlated with lower tetrahydrobiopterin and BAS-RR scores. We, therefore, suggest that vascular depression resulting due to increased intima-media thickness of left carotid artery and lower tetrahydrobiopterin could be contributing factors for treatment resistance in middle-aged MDD patients.

Tetrahydrobiopterin and Its Multiple Roles in Neuropsychological Disorders

Tetrahydrobiopterin (BH4) is a multifunctional co-factor of various enzymes and a substantial amount of studies have shown BH4 as a key regulator in the synthesis of neurotransmitters such as serotonin, nor-epinephrine as well as dopamine. The imbalance of BH4 may affect neurotransmitter production which can lead to many abnormalities in CNS. This article reviews the role of BH4 in neurodegenerative and neurodevelopmental disorders. We focus on the therapeutic potential of BH4 in various brain diseases that involves neurotransmitters and attempt to address how the modulation of BH4 may provide a novel strategy in various neuropsychological conditions.

Tetrahydrobiopterin administration facilitates amphetamine-induced dopamine release and motivation in mice

Dopamine (DA) is a critical neurotransmitter involved in motivational processes. Tetrahydrobiopterin (BH4) is an essential cofactor for tyrosine hydroxylase, the rate-limiting enzyme in DA synthesis. Decreases in BH4 levels are observed in several DA-related neuropsychiatric diseases involving impairment in motivation. Yet, whether BH4 could be used to treat motivational deficits has not been comprehensively investigated. To investigate the effects of exogenous BH4 administration on the dopaminergic system and related behaviors, we acutely injected mice with BH4 (50 mg/kg). Passage of BH4 through the blood brain barrier and accumulation in brain was measured using the in situ brain perfusion technique. DA release was then recorded using in-vivo micro-dialysis and motivation was evaluated through operant conditioning paradigms in basal condition and after an amphetamine (AMPH) injection. First, we showed that BH4 crosses the blood-brain barrier and that an acute peripheral injection of BH4 is sufficient to increase the concentrations of biopterins in the brain, without affecting BH4- and DA-related protein expression. Second, we report that this increase in BH4 enhanced AMPH-stimulated DA release in the nucleus accumbens. Finally, we found that BH4-induced DA release led to improved performance of a motivational task. Altogether, these findings suggest that BH4, through its action on the dopaminergic tone, could be used as a motivational enhancer.

Simplified HPLC methodology for quantifying biological pterins by selective oxidation

Tetrahydrobiopterin (BH4) has become a potential therapeutic tool to treat cardiovascular diseases, since it is an essential cofactor of nitric oxide synthase. In order to quantify the amount of BH4 and its related biopterins, a procedure that involves differential oxidation is currently used, which measures biopterin (the product of the oxidation of BH4 and BH2) at two different pH conditions to calculate the quantity of BH2 and BH4, using high performance liquid chromatography (HPLC). In this work, a method was established in order to quantify BH4 and BH2 by adapting previously described procedures. Several chromatographic conditions were evaluated to define the most convenient methodology. Four types of mobile phases and two different analytical columns were used for HPLC. Additionally, calibration curves were made in acid and basic pH compatible with the differential oxidation method. Each method was suitable for quantification purposes, but the choice was based on an economic factor. The selected condition was a mobile phase of 95% water/5% methanol using a C18 column at 35°C at a flow rate of 0.9mL/min. Then, it was calculated the recovery rate, which was about 80% using the chosen method. The aim of this work was to establish a simplified method of differential oxidation, compatible with matrixes such as cardiac tissue in order to facilitate the assessment of the BH4/BH2 ratio in biological samples.

Anxiety- and depression-like phenotype of hph-1 mice deficient in tetrahydrobiopterin

Decreased tetrahydrobiopterin (BH4) biosynthesis has been implicated in the pathophysiology of anxiety and depression. The aim of this study was therefore to characterise the phenotype of homozygous hph-1 (hph) mice, a model of BH4 deficiency, in behavioural tests of anxiety and depression as well as determine hippocampal monoamine and plasma nitric oxide levels. In the elevated zero maze test, hph mice displayed increased anxiety-like responses compared to wild-type mice, while the marble burying test revealed decreased anxiety-like behaviour. This was particularly observed in male mice. In the tail suspension test, hph mice of both sexes displayed increased depression-like behaviours compared to wild-type counterparts, whereas the forced swim test showed a trend towards increased depression-like behaviours in male hph mice, but significant decrease in depression-like behaviours in female mice. This study provides the first evidence that congenital BH4 deficiency regulates anxiety- and depression-like behaviours. The altered responses observed possibly reflect decreased hippocampal serotonin and dopamine found in hph mice compared to wild-type mice, but also reduced nitric oxide formation. We propose that the hph-1 mouse may be a novel tool to investigate the role of BH4 deficiency in anxiety and depression.