Page 35 - AN-1-3

Advanced Neurology Inflammation and gut microbiota in depression

health of patients with depression [103] . A health survey with human subjects, an anxiolytic-like effect was observed
that included 521 municipal employees (309 men and with GOS supplementation, as evidenced by decreased
212 women) aged 21 – 67 years has shown an association waking salivary cortisol reactivity and altered attentional
between less depressive symptoms and a healthy Japanese vigilance compared to placebo [117] . The cortisol arousal
dietary pattern, consisting of a high intake of vegetables, response, which can increase under stress, is a marker of
fruits, mushrooms, and soy products [105] . A healthy dietary HPA axis activity [118,119] . A mixture of GOS and FOS has
pattern is characterized by a high intake of vegetables, shown to reduce corticosterone and pro-inflammatory
fruits, nuts, grains, seeds, and legumes, as well as a cytokine release as well as anxiety-like and depressive-like
moderate consumption of dairy products, eggs, and fish. behaviors in chronic stress-treated mice. These benefits may
Investigations have shown that a number of nutrients, be associated with increased cecal acetate and propionate
including magnesium, zinc, folate, Vitamin D, Vitamin and reduced butyrate concentrations by GOS and FOS
B , Vitamin B , and Vitamin E, which are all abundant in administration [120] . A mixture of GOS and polydextrose
12
6
fruits and vegetables, are associated with reduced risk of has shown to attenuate the negative scores of memory
depression [106-108] . These nutrients can modulate depressive learning and anxiety-like behavior in an early-life maternal
symptoms through various mechanisms, two of which separation rat model, while a combined supplementation
include regulating serotonin biosynthesis and the HPA axis (Lactobacillus rhamnosus GG, polydextrose, and GOS) can
as well as inhibiting glutamate signaling, inflammation, enhance these benefits [121] . In another study, a synbiotic
and oxidative stress [109,110] . supplementation containing both prebiotics (GOS, FOS,
and inulin) and probiotics (Lactobacillus acidophilus T16,
Meta-analyses have shown that omega-3 Bifidobacterium bifidum BIA-6, Bifidobacterium lactis BIA-
polyunsaturated fatty acids (particularly eicosapentaenoic 7, and Bifidobacterium longum BIA-8) was given to patients
acid [EPA] and docosahexaenoic acid [DHA]) have a undergoing hemodialysis for 12 weeks; it resulted in a
beneficial effect on mood in patients with MDD [111,112] . significant improvement in serum BDNF concentrations
A study has shown that the long-term supplementation of and depressive symptoms compared to probiotic
omega-3 polyunsaturated fatty acids (80% EPA plus 20% supplementation alone [122] . The systemic and neurological
DHA) restored the disturbed gut microbiota composition benefits induced by an increased growth of probiotics
in early-life stress (maternal separation)-treated rats [113] . in the gut and the subsequently elevated levels of SCFAs
A deficiency of omega-3 can substantially impair CNS in the circulation appear to be a possible explanation.
development, with symptoms first appearing as early as SCFAs have been reported to promote hippocampal
adolescence, such as decreased sociability and increased neurogenesis; suppress BBB damage, microglia activation,
depressive-like behaviors. An increase in abundance of and neuroinflammation; as well as ameliorate depressive-
Firmicutes and a decrease in abundance of Bacteroidetes in like behaviors in high fructose diet-fed mice exposed to
fecal microbiota have been observed in omega-3 deficiency chronic stress . Marx et al. [123] and Bear et al. have
[52]
[99]
mice during adolescence. Omega-3 supplementation has provided interesting reviews of the underlying mechanisms
shown to induce a higher abundance of Bifidobacterium of action by which diet may influence mental and brain
and Lactobacillus but a lower abundance of Anaeroplasma, health.
Clostridium, and Peptostreptococcaceae in adult mice [114] .
Grosso et al. have reviewed other evidence and mechanisms However, not all studies show an association
of omega-3 in depression, including the modulation of between depression and dietary interventions. In a large,
serotoninergic and dopaminergic transmission as well randomized trial of 18,353 adults with 16,657 at risk of
as the inhibition of chronic systemic inflammation by incident depression (no previous depression) and 1696
omega-3 [115] . at risk of recurrent depression, omega-3 supplements
were not recommended in adults to prevent depression.
Healthy dietary patterns promote a higher growth of gut Compared to placebo treatment, omega-3 treatment
probiotics. For example, prebiotics from healthy dietary increased the risk of incident depression, but not recurrent
patterns selectively promote the growth and activity of depression [124] . A systematic review and meta-analysis of
Bifidobacteria and Lactobacilli, conferring positive health 28 controlled clinical trials have shown that probiotics,
outcomes to the host . The most well-studied prebiotics instead of prebiotics, yielded small but significant effects on
[66]
are fructo-oligosaccharides (FOS), inulin, and galacto- depression and anxiety [125] . The conflicting findings from
oligosaccharides (GOS) . GOS feeding has shown to different studies may be due to various factors. Subjects
[66]
elevate BDNF and D-serine expression and N-methyl-D- may have recall bias when scales are used. In addition,
aspartate pathway in the hippocampus as well as increase the depression can affect memory, food intake activity, and
levels of gut peptide YY in rat plasma [116] . In a clinical study food preferences in subjects. It is difficult to ensure that

Volume 1 Issue 3 (2022) 7 https://doi.org/10.36922/an.v1i3.272