Folic Acid Deficiency

Vitamins B9 (folate) and B12 are essential water-soluble vitamins that play a crucial role in the maintenance of one-carbon metabolism: a set of interconnected biochemical pathways driven by folate and methionine to generate methyl groups for use in DNA synthesis, amino acid homeostasis, antioxidant generation, and epigenetic regulation. Dietary deficiencies in B9 and B12, or genetic polymorphisms that influence the activity of enzymes involved in the folate or methionine cycles, are known to cause developmental defects, impair cognitive function, or block normal blood production. Nutritional deficiencies have historically been treated with dietary supplementation or high-dose parenteral administration that can reverse symptoms in the majority of cases. Elevated levels of these vitamins have more recently been shown to correlate with immune dysfunction, cancer, and increased mortality. Therapies that specifically target one-carbon metabolism are therefore currently being explored for the treatment of immune disorders and cancer. In this review, we will highlight recent studies aimed at elucidating the role of folate, B12, and methionine in one-carbon metabolism during normal cellular processes and in the context of disease progression.

Diet, particularly vitamin deficiency, is associated with the risk of birth defects. The aim of this review paper is to show the characteristics of common and severe neural-tube defects together with congenital heart defects (CHD) as vitamin deficiencies play a role in their origin. The findings of the Hungarian intervention (randomized double-blind and cohort controlled) trials indicated that periconceptional folic acid (FA)-containing multivitamin supplementation prevented the major proportion (about 90%) of neural-tube defects (NTD) as well as a certain proportion (about 40%) of congenital heart defects. Finally the benefits and drawbacks of three main practical applications of folic acid/multivitamin treatment such as (i) dietary intake; (ii) periconceptional supplementation; and (iii) flour fortification are discussed. The conclusion arrived at is indeed confirmation of Benjamin Franklin's statement: "An ounce of prevention is better than a pound of care".

Moderate hyperhomocysteinemia-induced low folate status is an independent risk factor for cardiovascular disease, dementia, and depression. Folate is an essential cofactor in the one-carbon metabolism pathway and is necessary in amino acid metabolism, purine and thymidylate synthesis, and DNA methylation. In the folate cycle and homocysteine metabolism, folate, vitamin B12, vitamin B6, and vitamin B2 are important cofactors. Many enzymes are involved in folate transport and uptake, the folate pathway, and homocysteine (Hcy) metabolism, and various polymorphisms have been documented in these enzymes. Serum folate and total Hcy (tHcy) levels are influenced by folate intake and genetic polymorphisms in 5,10-methylenetertahydrofolate reductase (MTHFR) such as C677T. The prevalence of the MTHFR 677TT genotype varies across ethnic groups and regions, with a frequency of approximately 15% in Japanese populations. Individuals with the TT genotype have significantly higher tHcy levels and lower folate levels in serum than those with the CT and TT genotypes. However, administration of folic acid has been shown to eliminate these differences. Moreover, data have suggested that interventions based on genotype may be effective for motivating individuals to change their lifestyle and improve their nutrition status. Accordingly, in this review, we discuss the effects of MTHFR C677T polymorphisms on serum tHcy and folate levels with folic acid intervention and evaluate approaches for overcoming folic acid deficiency and related symptoms.

Healthy neurodevelopment requires adequate folates (vitamin B9), which are critical for key biosynthetic and homeostatic processes in the central nervous system (CNS). In the brain, folate transport is mediated by three major pathways: folate receptor alpha (FRα), proton-coupled folate transporter (PCFT), and reduced folate carrier (RFC). Folate uptake primarily occurs at the blood-cerebrospinal fluid barrier (BCSFB) by concerted actions of FRα and PCFT. Alterations in this transport pathway can result in cerebral folate deficiency (CFD), a rare but devastating pediatric condition associated with neuroinflammation and oxidative stress. Recent findings highlight the blood-brain barrier (BBB) as an alternative route for folate delivery, particularly through RFC upregulation. We hypothesized that pyrroloquinoline quinone (PQQ), an activator of nuclear respiratory factor 1 (NRF-1) and PGC-1α, key regulators of mitochondrial biogenesis, could enhance RFC expression at the BBB and mitigate CFD-induced damage. Using in vitro and in vivo models of folate deficiency, we investigated its impact on BBB integrity, inflammation, oxidative stress, mitochondrial dysfunction, and assessed PQQ's ability to reverse these effects. Human brain microvessel endothelial cells (hCMEC/D3) cultured in control folate-sufficient (FS) or folate-deficient (FD) medium were treated with PQQ (1 or 5 µM) or vehicle control for 24 h. Wildtype (C57BL6/N) mice received FD (0 mg/kg folate), or FS (2 mg/kg folate) diet and underwent a 10-day (20 mg/kg/day, i.p) PQQ treatment. Following treatment, hCMEC/D3 cells and isolated mouse brain capillaries were analyzed using qPCR, ELISA, and immunoblotting to assess gene and protein expression of tight junction proteins, inflammatory and oxidative stress markers, mitochondrial transcription factors, and folate transporters. BBB permeability was evaluated in vivo using the sodium fluorescein (NaFl) assay. FD significantly increased the gene and/or protein expression of inflammatory cytokines/chemokines, endothelial adhesion molecules and oxidative stress markers, while tight junction proteins were significantly downregulated both in vitro and in vivo. The NaFl assay confirmed increased BBB permeability in FD mice. PQQ treatment effectively reversed these changes by upregulating RFC and PCFT expression, restoring BBB permeability, mitigating inflammatory and oxidative stress responses and improving mitochondrial biogenesis via PGC-1α/NRF-1 signaling. These results highlight the impact of brain FD on BBB integrity, potentially contributing to neurological deficits seen in CFD disorders with PQQ providing a promising therapeutic strategy.