Feeding Aspergillus protease preparation combined with adequate protein diet to rats increases levels of cecum gut-protective amino acids, partially linked to Bifidobacterium and Lactobacillus

Gamma-aminobutyric acid as a potential postbiotic mediator in the gut-brain axis

Gamma-aminobutyric acid (GABA) plays a crucial role in the central nervous system as an inhibitory neurotransmitter. Imbalances of this neurotransmitter are associated with neurological diseases, such as Alzheimer's and Parkinson's disease, and psychological disorders, including anxiety, depression, and stress. Since GABA has long been believed to not cross the blood-brain barrier, the effects of circulating GABA on the brain are neglected. However, emerging evidence has demonstrated that changes in both circulating and brain levels of GABA are associated with changes in gut microbiota composition and that changes in GABA levels and microbiota composition play a role in modulating mental health. This recent research has raised the possibility that GABA may be a potent mediator of the gut-brain axis. This review article will cover up-to-date information about GABA-producing microorganisms isolated from human gut and food sources, explanation why those microorganisms produce GABA, food factors inducing gut-GABA production, evidence suggesting GABA as a mediator linking between gut microbiota and mental health, including anxiety, depression, stress, epilepsy, autism spectrum disorder, and attention deficit hyperactivity disorder, and novel information regarding homocarnosine-a predominant brain peptide that is a putative downstream mediator of GABA in regulating brain functions. This review will help us to understand how the gut microbiota and GABA-homocarnosine metabolism play a significant role in brain functions. Nonetheless, it could support further research on the use of GABA production-inducing microorganisms and food factors as agents to treat neurological and psychological disorders.

Increasing Dietary Nutrient Levels Modulates Colon Immune Adaptation and Alleviates Inflammation in the Epithelial Heterogeneous Nuclear Ribonucleoprotein I (Hnrnp I) Knockout Mice

SCOPE

Heterogeneous nuclear ribonucleoprotein I (HNRNP I) is an RNA-binding protein essential for neonatal immune adaptation by downregulating interleukin-1 receptor-associated kinase (IRAK1) in toll-like receptor (TLR)-mediated NF-κB signaling pathways. TLR-mediated NF-κB is associated with chronic inflammation, including the development of inflammatory bowel diseases. Therefore, dietary protein intake is one of the major concerns for individuals with inflammatory bowel diseases. The present study aims to investigate the effects of a protein-enriched diet on intestinal inflammation and immune responses in a mouse model with aberrant NF-κB signaling in the colon.

METHODS AND RESULTS

A transgenic mouse model with intestinal-epithelial-cell (IEC) specific Hnrnp I knocked out was used to investigate the effects of protein intake on the immune system in the colon. A control diet (CON) and a nutrient-dense modified diet (MOD) were fed to both the wild-type (WT) and the knockout (KO) male mice for 14 weeks. Inflammatory markers and colonic immune responses were examined, with gene expression and protein expression levels analyzed. IEC-specific Hnrnp I knocked out mice had significantly increased expression of the active NF-κB subunit, P65, in their colons. There was a concomitant induction of mRNA expression of Il1β, Il6, Cxcl1, and Ccl2. The number of CD4⁺ T cells in the distal colon was also increased in the KO mice. The results confirmed that KO mice had pro-inflammatory responses with aberrant NF-κB signaling in the colon. Importantly, increased nutrient density in their diets attenuated colon inflammation by decreasing the expression of pro-inflammatory cytokines, reducing P65 translocation, downregulating IRAK1, and limiting the number of CD4⁺ T cells recruited in Hnrnp I KO mice colon.

CONCLUSION

A diet with increased nutrient density relieved the inflammation induced by knockout of Hnrnp I, attributable partially to the reduced expression of inflammatory and immune-modulating cytokines in the mouse distal colon.

Exogenous Penicillium camemberti Lipase Preparation Exerts Prebiotic-like Effects by Increasing Cecal Bifidobacterium and Lactobacillus Abundance in Rats

Penicillium camemberti is used in cheese production; however, its health benefits remain to be elucidated. We previously found that supplemental Aspergillus-derived lipase preparation exerts a strong bifidogenic effect in rats fed a high-fat diet. This study investigated the effects of the feeding of a diet containing a 0.2% or 0.4% Penicillium camemberti-derived lipase preparation (PCL) for two weeks on the cecal microbiota in rats. According to 16S rRNA gene sequencing analysis, both PCL supplements significantly (p < 0.05) affected the cecal microbial community. At the genus level, supplemental 0.4% PCL significantly increased the relative abundance of beneficial bacteria such as Bifidobacterium, Lactobacillus, and Collinsella (127-fold, 6-fold, and 193-fold increase, respectively). The abundance of these bacteria in the 0.2% PCL group was between that of the control and 0.4% PCL groups. Notably, the effects of supplemental 0.4% PCL on modulating the abundance of these bacteria matched the effects observed in studies on typical prebiotic oligosaccharides. PICRUSt analysis revealed that PCL supplements significantly modulated the relative abundance of bacterial genes associated with 27 metabolic pathways, some of which were similar to those reported for prebiotic oligosaccharides. This study provides the first evidence indicating that supplemental PCL exerts prebiotic-like effects by modulating the abundance of the gut microbiota.

Aspergillus-Derived Cellulase Preparation Exhibits Prebiotic-like Effects on Gut Microbiota in Rats

Aspergillus-derived cellulase, which is involved in the production of Aspergillus-fermented foods, has been employed in the food and animal feed industries. However, the effect of dietary Aspergillus cellulase on health is poorly understood. Previously, we discovered that supplemental Aspergillus-derived protease and lipase preparations had substantial bifidogenic effects on rats fed a high-fat diet. Therefore, this study reports on the effects of a 0.1% dietary Aspergillus-derived cellulase preparation (CEL) on the gut microbiota of rats fed a high-fat diet. Gene sequencing analysis of 16S rRNA revealed that CEL treatment markedly affected the microbiota profiles of the cecal contents (p < 0.05). Notably, CEL markedly increased the relative abundance (RA) of typical probiotics, such as Bifidobacterium and Lactobacillus, at the genus level (28- and 5-fold, respectively, p < 0.05). Similarly, at the family level, CEL treatment significantly increased the RA of Bifidobacteriaceae and Lactobacillaceae (p < 0.05). Furthermore, CEL increased the RA of other genera, such as Collinsella and Enterococcus, but decreased the RA of Oscillospira, Dorea and Coprobacillus (p < 0.05). The effects on these genera are similar to those reported for typical prebiotic oligosaccharides. Overall, this study demonstrates the prebiotic-like effects of dietary CEL by significantly increasing Bifidobacterium and Lactobacillus abundance.

Supplemental Aspergillus Lipase and Protease Preparations Display Powerful Bifidogenic Effects and Modulate the Gut Microbiota Community of Rats

Aspergillus-derived protease and lipase, which are involved in the production of Aspergillus-fermented foods, are consumed as digestive enzyme supplements. A marked bifidogenic effect of supplemental Aspergillus protease preparation (AP) in rats fed with a high-fat diet was identified. This study was conducted to examine whether the consumption of Aspergillus-derived lipase exerts similar bifidogenic effect. Rats were fed diets supplemented with either an Aspergillus-derived lipase preparation (AL) or AP at 0.1% for two weeks. 16S rRNA gene sequencing analysis indicated that supplemental AL and AP markedly influenced cecal microbial community. At the phylum level, treatment with AL and AP resulted in a lower relative abundance of Firmicutes and Bacteroidetes, but a higher relative abundance of Actinobacteria and Proteobacteria than the control rats (p < 0.05). At the genus level, AL and AP remarkedly elevated the relative abundances of Bifidobacterium, Collinsella, and Enterococcus, but significantly reduced those of Oscillospira, Dorea, and Coprobacillus (p < 0.05). These modulations were similar to those reported by several studies with typical prebiotic oligosaccharides. Notably, the bifidogenic effect of AL was much greater than that of AP. Our results show that the two different Aspergillus-derived preparations, AL and AP, have strong bifidogenic effects and can change the microbiota’s composition.

Medical Application of Substances Derived from Non-Pathogenic Fungi Aspergillus oryzae and A. luchuensis-Containing Koji

Although most fungi cause pathogenicity toward human beings, dynasties of the East Asian region have domesticated and utilized specific fungi for medical applications. The Japanese dynasty and nation have domesticated and utilized koji fermented with non-pathogenic fungus Aspergillus oryzae for more than 1300 years. Recent research has elucidated that koji contains medicinal substances such as Taka-diastase, acid protease, koji glycosylceramide, kojic acid, oligosaccharides, ethyl-α-d-glucoside, ferulic acid, ergothioneine, pyroglutamyl leucine, pyranonigrin A, resistant proteins, deferriferrichrysin, polyamines, Bifidobacterium-stimulating peptides, angiotensin I-converting enzyme inhibitor peptides, 14-dehydroergosterol, beta-glucan, biotin, and citric acid. This review introduces potential medical applications of such medicinal substances to hyperlipidemia, diabetes, hypertension, cardiovascular and cognitive diseases, chronic inflammation, epidermal permeability barrier disruption, coronavirus disease 2019 (COVID-19), and anti-cancer therapy.

Red rice koji extract alleviates hyperglycemia by increasing glucose uptake and glucose transporter type 4 levels in skeletal muscle in two diabetic mouse models

Background

Red rice koji (RRK), prepared by growing Monascus species on steamed rice, has been reported to lower blood glucose levels in diabetic animal models. However, the action mechanism is not yet completely understood.

Objective

The objective of this study was to examine the mechanism underlying the hypoglycemic action of RRK extract in two diabetic animal models: the insulin-deficiency mice, where the insulin deficiency was induced by streptozotocin (STZ), and insulin-resistance mice, where the insulin resistance was induced by a high-fat diet (HFD).

Design

Low (12.5 mg/kg body weight [BW]) and high (50.0 mg/kg BW) doses of RRK extract were orally administered to the mice for 10 successive days (0.25 mL/day/mouse). The protein expression levels of glucose transporter type 4 (GLUT4) in the skeletal muscle and glucose transporter type 2 (GLUT2) in the liver were measured. Blood glucose (BG) levels of STZ-treated mice in insulin tolerance test (ITT) and BG and insulin levels of HFD-fed mice in intraperitoneal glucose tolerance test (IPGTT) were investigated.

Results

In the STZ-treated mice, oral administration of RRK extract lowered BG levels and food intake but increased plasma 1,5-anhydroglucitol level. Moreover, the RRK extract lowered the BG levels of STZ-treated mice as measured by ITT. In the HFD-fed mice, we confirmed that the orally administered RRK extract lowered the BG and the homeostasis model assessment index for insulin resistance. Furthermore, the RRK extract lowered the BG and insulin levels of HFD-fed mice in IPGTT. Regarding the protein levels of GLUT, the orally administered RRK extract increased the GLUT4 level in the skeletal muscle; however, the RRK extract did not alter the GLUT2 level in the liver of either the STZ-treated or the HFD-fed mice.

Discussion

Our study demonstrates that RRK extract can improve impaired glucose tolerance in mouse models of diabetes by enhancing GLUT4 expression in skeletal muscle.

Conclusion

These results suggest that RRK extract could potentially be a functional food for the treatment of diabetes mellitus.