New study shows intermittent fasting reduces obesity-related brain inflammation and cognitive decline

In a recent article published in Nutrients, researchers evaluated the long-term beneficial effects of intermittent fasting (IF) on neuroinflammation, cognitive impairment, and memory deficits in mice fed with high-fat diet (HFD).

In addition, they used HFD-fed mice with blood-brain barrier (BBB) leakage to examine the effects of IF on the crosstalk between adipocyte death-related macrophage accumulation and hippocampal inflammation in diabetic encephalopathy.

Study: Intermittent Fasting Reduces Neuroinflammation and Cognitive Impairment in High-Fat Diet-Fed Mice by Downregulating Lipocalin-2 and Galectin-3. Image Credit: vetre/Shutterstock.com

Background

Obesity and type 2 diabetes (T2D) are well recognised for their damaging effects on cognition and memory. Furthermore, these metabolic dysfunctions increase the permeability of the BBB, which further exacerbates neuroinflammation and memory deficits.

Thus, disruption in hippocampal BBB is considered an early biomarker of diabetes-related memory deficits and cognitive impairment.

Studies have shown that two proteins, lipocalin-2 (LCN2) and galectin-3 (GAL3), might be involved in these neurological manifestations.

The former, a gelatinase-related lipocalin, is secreted by adipocytes, including neutrophils and macrophages, whereas various cells express GAL-3 for immune regulation. 

Several previous studies have reported that elevated levels of proinflammatory mediators, such as LCN2 and GAL-3, promote neuroinflammation by triggering detrimental neutrophil/microglia activation in the diabetic brain via BBB leakage.

In other words, these proteins might have a functional relationship with the adipose tissue.

Thus, researchers postulate that LCN2 and GAL3 are associated with obesity and T2D-related chronic inflammation. Upon induction through HFD, circulating LCN2 and GAL3 invade the leaky BBB and activate microglial cells, resulting in local neuroinflammation.

Subsequently, these cells secrete high levels of tumor-necrosis factor-alpha (TNF-α), which exacerbates neuroinflammation, further compromising BBB permeability, which further impairs cognition and memory.

Recently, IF, a dietary modification, has garnered attention for its potential to exert neuroprotective effects among patients with T2D and obesity.

About the study

In the present study, researchers used HFD-fed mice to investigate the exact mechanisms by which chronic IF exerts neuroprotective effects over LCN2 and GAL3-mediated neuroinflammation and adipose tissue macrophage infiltration.

The team divided all test mice into the normal diet (ND), HFD, and HFD + IF (HIF) groups, with each group having 10, 10, and 12 three-week-old male C57BL/6 mice, respectively. The HFD mice derived 60% of their total energy (measured in kilocalories [kcal]) from fat.

For the mice in ND and HFD groups, study protocol mandated that mice were fed a ND/HFD for 30 weeks, and the HIF group mice were first fed an HFD for eight weeks and then switched to IF protocol wherein they were alternatingly fed and subjected to fasting for 24 hours for 22 weeks.

The team measured food and energy intake every alternate day for 16 weeks after the completion of the IF regimen. They sacrificed all mice aged 34 weeks.

Other tests performed on mice tissues were EchoMRI, which quantified their body fat mass, insulin tolerance test (ITT), and glucose tolerance test (GTT), which helped determine their blood glucose levels.

Likewise, an enzyme-linked immunosorbent assay (ELISA) helped assess serum protein levels of all mice, specifically LCN2, GAL3, and matrix metalloproteinase 9 (MMP9).

In addition, the researchers used the Terminal Deoxynucleotidyl Transferase Dutp Nick end Labeling (TUNEL) assay to measure the extent of in situ apoptosis in mice white adipose tissues (WATs). 

The team counted the number of crown-like structures (CLSs), characterizing WAT apoptosis and macrophage infiltration, TUNEL-positive cells, and extravascular albumin, an indicator of BBB leakage in hippocampal tissue specimens.

They also performed Western Blot Analysis and Double/Triple Immunofluorescences on frozen WATs and hippocampi specimens of three to four mice per group, and the Morris Water Maze (MWM) test for five days among seven mice per group.

Finally, the researchers determined groupwise differences by ANOVA followed by Tukey’s tests. They presented results as the standard error of the mean (SEM), considering a p-value < 0.05 statistically significant.

Results

Mice in the HFD group had higher body weights (BW) and body fat mass; additionally, they had an impaired glucose tolerance.

Histological analysis revealed that these mice had many CLSs and TUNEL-positive cells in their WATs, indicating HFD-induced adipocyte death and macrophage infiltration. 

Furthermore, triple immunofluorescence showed the presence of LCN2- and GAL3-positive neutrophils and macrophages in the WAT of HFD mice. 

Interrupting the HFD regimen with IF caused dramatic weight loss and attenuated IR and adipocyte death in mice of the HIF group. 

IF also significantly attenuated HFD-induced IR to correct impaired glucose tolerance and reduced the upregulated MMP9 expression in the hippocampus of mice in the HIF group. Immunofluorescence analysis revealed that IF also weakened macrophage infiltration in HFD mice to improve IR. 

Furthermore, IF significantly attenuated the HFD-induced increase in serum LCN2, circulating, and macrophage-derived GAL3 protein levels in WATs of HIF mice, which reduced BBB leakage, neuroinflammation, and memory deficits.

It also reversed the HFD-induced increases in proinflammatory cytokines, such as TNF-α and interleukin-6 (IL-6). Finally, in the hippocampus of HFD mice, IF reduced astrocytic LCN2 and microglial GAL3 expression. 

Conclusion

Together, the study results suggest that IF, an alternative to continuous caloric restriction, may improve IR, and reduce WAT inflammation by inhibiting macrophage infiltration and adipocyte death to correct metabolic dysfunction(s) in HFD mice. 

Thus, further research should focus on testing and validating the use of IF as a drug replacement therapy to improve cognitive impairment due to HFD-induced neuroinflammation and BBB disruption in chronic low-grade inflammatory conditions, such as T2D and obesity.

Further studies could help establish the exact mechanisms by which IF protects against obesity and T2D-related cognitive impairment and memory deficits with more precision.