Vitamin B and choline supplementation are neuroprotective in glaucoma models

Swedish researchers, led by senior author James R. Tribble, PhD, reported that oral B₆, B₉, B_12, and choline were neuroprotective against glaucoma in 2 animal models. The investigators are from the Department of Clinical Neuroscience, Division of Eye and Vision, St. Erik Eye Hospital, Karolinska Institutet in Stockholm, Sweden. They reported their results in Cell Reports Medicine.

No neuroprotective therapies are currently available to treat glaucoma, and discovery is complicated by the disease's complexity, the investigators commented.

“Recent work has identified metabolic dysfunction in the retina and optic nerve occurring prior to detectable neurodegeneration of retinal ganglion cells (RGCs) in glaucoma (via transcriptomic and metabolomic analyses), presenting the potential for neuroprotection prior to the initiation of neurodegenerative cascades. Loss of mitochondrial function and transport in RGCs,^2,3 reduced energy capacity,⁴ loss of the ability to maintain nicotinamide adenine dinucleotide,^5,6 and the depletion of alternative energy sources^7,8 have all been identified early [on] in glaucoma in human patients and animal models,” they explained.

The authors cited studies whose data showed that elevated levels of homocysteine were associated with major diseases such as cardiovascular disease, diabetes, and Alzheimer disease, although this is typically in the form of hyperhomocysteinemia, where homocysteine is elevated in the blood.⁹ In addition, results from small studies in humans have suggested that homocysteine may be elevated in the blood and aqueous humor of certain glaucomas.¹⁰ Mouse models of hyperhomocysteinemia present significant retinal degenerative phenotypes, including vascular compromise and RGC degeneration.^11-13 Supporting this, intravitreal injection of homocysteine in high concentrations can induce RGC death.^14,15

Based on the data from those studies, Tribble and colleagues hypothesized that elevated homocysteine directly compounds RGC death in glaucoma and is related to dysfunction in one-carbon metabolism.

To determine this, they used mouse and rat models of ocular hypertension and retrospectively evaluated human epidemiologic data to investigate the effect of homocysteine and one-carbon metabolism, a pathway that transfers one-carbon units to molecules, and their impact on neurodegeneration.

Main study findings

“Our study [data] demonstrated that elevated homocysteine worsens glaucoma outcome in animal models, but this effect is mild. In humans, elevation of serum homocysteine has no detectable effect on glaucoma-related outcomes or disease progression. Early elevation of homocysteine in the retina is a marker of dysfunctional one-carbon metabolism, which we identify as an early and sustained feature of glaucoma. This is associated with dysfunctional regulation of genes and proteins that interact with key one-carbon metabolism cofactors and precursors: vitamin B₆, B₉, B₁₂, and choline,” they reported.

Importantly, this supplementation of vitamin B₆, B₉, B₁₂, and choline provided neuroprotection against the death of RGCs in acute, mild, and chronic animal models of glaucoma, including protection of visual function. This was independent of the IOP.

Tribble and colleagues believe these findings ultimately can be useful in the treatment of patients with glaucoma.

References

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2. Tribble JR, Vasalauskaite A, Redmond T, et al. Midget retinal ganglion cell dendritic and mitochondrial degeneration is an early feature of human glaucoma. Brain Commun. 2019;1(1):fcz035. doi:10.1093/braincomms/fcz035

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4. Belforte N, Agostinone J, Alarcon-Martinez L, et al. AMPK hyperactivation promotes dendrite retraction, synaptic loss, and neuronal dysfunction in glaucoma. Mol Neurodegener. 2021;16(1):43. doi:10.1186/s13024-021-00466-z

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