Osmoregulatory Role of Betaine and Betaine/γ-Aminobutyric Acid Transporter 1 in Post-Traumatic Syringomyelia.

Syringomyelia (SM) is primarily characterized by the formation of a fluid-filled cyst that forms in the parenchyma of the spinal cord following injury or other pathology. Recent omics studies in animal models have identified dysregulation of solute carriers, channels, transporters, and small molecules associated with osmolyte regulation during syrinx formation/expansion in the spinal cord. However, their connections to syringomyelia etiology are poorly understood. In this study, the biological functions of the potent osmolyte betaine and its associated solute carrier betaine/γ-aminobutyric acid (GABA) transporter 1 (BGT1) were studied in SM. First, a rat post-traumatic SM model was used to demonstrate that the BGT1 was primarily expressed in astrocytes in the vicinity of syrinxes. In an in vitro system, we found that astrocytes uptake betaine through BGT1 to regulate cell size under hypertonic conditions. Treatment with BGT1 inhibitors, especially NNC 05-2090, demonstrated midhigh micromolar range potency in vitro that reversed the osmoprotective effects of betaine. Finally, the specificity of these BGT1 inhibitors in the CNS was demonstrated in vivo, suggesting feasibility for targeting betaine transport in SM. In summary, these data provide an enhanced understanding of the role of betaine and its associated solute carrier BGT1 in cell osmoregulation and implicates the active role of betaine and BGT1 in syringomyelia progression.

Involvement of GAT2/BGT-1 in the preventive effects of betaine on cognitive impairment and brain oxidative stress in amyloid ß peptide-injected mice.

In the pathophysiology of Alzheimer's disease (AD), the deposition of amyloid ß protein (Aß) is associated with oxidative stress, leading to cognitive impairment and neurodegeneration. Betaine (glycine betaine or trimethylglycine), known as an osmolyte and methyl donor in mammalian cells, has been reported to suppress the proinflammatory response and oxidative stress in the kidneys, but the effects of betaine on brain diseases remain to be determined. Here, to investigate the effects of betaine treatment on cognitive impairment and the increase in oxidative stress in the brain of an AD animal model, we performed a novel object recognition test and measured the malondialdehyde (MDA; a marker of oxidative stress) levels in the frontal cortex and hippocampus of mice intracerebroventricularly injected with Aß25-35, an active fragment of Aß. Betaine prevented cognitive impairment as well as increases of the cortical and hippocampal MDA levels in Aß25-35-injected mice. Of note, NNC 05-2090, a selective inhibitor of betaine/GABA transporter-1 (GAT2/BGT-1), reduced the preventive effects of betaine on Aß25-35-induced cognitive impairment without affecting the increased MDA levels in the brain of Aß25-35-injected mice. As betaine is used as a substrate of GAT2/BGT-1, these results suggest that betaine is transported through GAT2/BGT-1 and prevents cognitive impairment in Aß25-35-injected mice, but GAT2/BGT-1 function is not required for the antioxidant effects of betaine.

Betaine chemistry, roles, and potential use in liver disease.

BACKGROUND: Betaine is the trimethyl derivative of glycine and is normally present in human plasma due to dietary intake and endogenous synthesis in liver and kidney. Betaine is utilized in the kidney primarily as an osmoprotectant, whereas in the liver its primary role is in metabolism as a methyl group donor. In both organs, a specific betaine transporter mediates cellular uptake of betaine from plasma. The abundance of both betaine and the betaine transporter in liver greatly exceeds that of other organs. SCOPE OF REVIEW: The remarkable contributions of betaine to normal human and animal health are summarized together with a discussion of the mechanisms and potential beneficial effects of dietary betaine supplements on liver disease. MAJOR CONCLUSIONS: A significant amount of data from animal models of liver disease indicates that administration of betaine can halt and even reverse progression of the disruption of liver function. Betaine is well-tolerated, inexpensive, effective over a wide range of doses, and is already used in livestock feeding practices. GENERAL SIGNIFICANCE: The accumulated data indicate that carefully controlled additional investigations in humans are merited. The focus should be on the long-term use of betaine in large patient populations with liver diseases characterized by development of fatty liver, especially non-alcoholic fatty liver disease and alcoholic liver disease.

Cyclopropane-based conformational restriction of GABA by a stereochemical diversity-oriented strategy: identification of an efficient lead for potent inhibitors of GABA transports.

A series of cyclopropane-based conformationally restricted γ-aminobutyric acid (GABA) analogs with stereochemical diversity, that is, the trans- and cis-2,3-methano analogs Ia and Ib and their enantiomers ent-Ia and ent-Ib, and also the trans- and cis-3,4-methano analogs IIa and IIb and their enantiomers ent-IIa and ent-Iib, were synthesized from the chiral cyclopropane units Type-a and Type-b that we developed. These analogs were systematically evaluated with four GABA transporter (GAT) subtypes. The trans-3,4-methano analog IIa had inhibitory effects on GAT3 (IC50=23.9µM) and betaine-GABA transporter1 (5.48µM), indicating its potential as an effective lead compound for the development of potent GAT inhibitors due to its hydrophilic and low molecular weight properties and excellent ligand efficiency.

Discovery of a subtype selective inhibitor of the human betaine/GABA transporter 1 (BGT-1) with a non-competitive pharmacological profile.

The γ-aminobutyric acid (GABA) transporters (GATs) are essential regulators of the activity in the GABAergic system through their continuous uptake of the neurotransmitter from the synaptic cleft and extrasynaptic space. Four GAT subtypes have been identified to date, each displaying different pharmacological properties and expression patterns. The present study focus on the human betaine/GABA transporter 1 (BGT-1), which has recently emerged as a new target for treatment of epilepsy. However, the lack of selective inhibitors of this transporter has impaired the exploration of this potential considerably. With the objective of identifying novel compounds displaying selectivity for BGT-1, we performed a screening of a small compound library at cells expressing BGT-1 using a [(3)H]GABA uptake assay. The screening resulted in the identification of the compound N-(1-benzyl-4-piperidinyl)-2,4-dichlorobenzamide (BPDBA), a selective inhibitor of the human BGT-1 transporter with a non-competitive profile exhibiting no significant inhibitory activity at the other three human GAT subtypes. The selectivity profile of the compound was subsequently confirmed at cells expressing the four mouse GAT subtypes. Thus, BPDBA constitutes a potential useful pharmacological tool compound for future explorations of the function of the BGT-1 subtype.