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Papers by Naoko Ikuta

Research paper thumbnail of Article Effect of γ-Cyclodextrin Inclusion Complex on the Absorption of R-α-Lipoic Acid in Rats

Abstract: R-α-lipoic acid (RLA) is an endogenous organic acid, and works as a cofactor for mitoch... more Abstract: R-α-lipoic acid (RLA) is an endogenous organic acid, and works as a cofactor for mitochondrial enzymes and as a kind of antioxidant. Inclusion complexes of RLA with α-, β- or γ-cyclodextrins (CD) were prepared and orally administered as a suspension to rats. Among them, RLA/γ-CD showed the highest plasma exposure, and its area under the plasma concentration-time curve (AUC) of RLA was 2.2 times higher than that after oral administration of non-inclusion RLA. On the other hand, the AUC after oral administration of non-inclusion RLA and RLA/γ-CD to pylorus-ligated rats did not differ. However, the AUC after intraduodenal administration of RLA/γ-CD was 5.1 times higher than that of non-inclusion RLA, and was almost comparable to the AUC after intraduodenal administration of RLA-Na solution. Furthermore, the AUC after intraduodenal administration of RLA/γ-CD was not affected by biliary ligation or co-administration of an amylase inhibitor. These findings demonstrated that RLA ...

Research paper thumbnail of Safety Evaluation of R(+)-Alpha Lipoic Acid-Gamma Cyclodextrin Complex

R(+)-alpha lipoic acid (RALA) is one of cofactors for mitochondrial enzymes and therefore plays a... more R(+)-alpha lipoic acid (RALA) is one of cofactors for mitochondrial enzymes and therefore plays a central role in energy metabolism. RALA is unstable when exposed to low pH or heat. Therefore, we have stabilized RALA through complex formation with cyclodextrins (γ-CDs). γ-CDs were used for the formation of these RALA-CD complexes. In this study, we evaluated the safety of RALA-CD complex through in vitro and in vivo toxicity tests as follows: an acute toxicity study, the Ames test, and a subchronic toxicity study using thiamine-deficient rats. These toxicity studies showed that RALA-CD produced no toxic effects, and support the safety of oral supplementation of RALA-CD. Further, RALA-CD administration showed a different effect on food intake and body weight of thiamine-deficient rats when compared with the complexes of CD and SALA and DL-ALA.

Research paper thumbnail of Stabilized R -α-Lipoic Acid by Encapsulation Using Cyclodextrins

Impact of Nanoscience in the Food Industry, 2018

Abstract R-(+)-α-Lipoic acid (RALA) is a cofactor in mitochondrial enzymes. In energy metabolism,... more Abstract R-(+)-α-Lipoic acid (RALA) is a cofactor in mitochondrial enzymes. In energy metabolism, RALA plays a significant role. It is a very powerful antioxidant and is able to react in aqueous and lipid media with reactive oxygen species, such as superoxides, peroxyl and hydroxyl radicals, singlet oxygen, hypochlorite, and peroxynitrite. Although RALA is biosynthesized mainly by intestinal bacteria and can be absorbed from vegetables or meat, some diets may not provide it in sufficient levels. This means that RALA supplementation is an option to help maintain body health. In this chapter, we introduce the history of RALA, and summarize its chemical and biochemical characteristics, such as chirality, antioxidant activities, and metabolism. RALA is quite vulnerable to physical stimuli, such as high temperature and UV irradiation, which motivated us to study its complex formation with cyclodextrins (CDs). We prepared an RALA–CD complex and evaluated its physicochemical properties. The results demonstrated that RALA was stabilized through complex formation with CDs. Furthermore, we obtained precise information on the complex formation using micro-Raman and micro-Fourier transform infrared spectroscopy. We also describe some in vivo studies using RALA–CD complexes.

Research paper thumbnail of Enhancement of Oral Bioavailability of Functional Ingredients by Complexation with Cyclodextrin

Natural lipophilic bioactives that possess human health benefits, such as coenzyme Q10 (CoQ10) an... more Natural lipophilic bioactives that possess human health benefits, such as coenzyme Q10 (CoQ10) and R-α-lipoic acid (RALA), often have undesirable characteristics that limit their use as nutraceuticals and cosmeceuticals. These bioactives are usually unstable against oxygen, ultraviolet light, low pH and heat. Furthermore, their watersolubility is low because of their hydrophobic nature or instability and this leads to low bioavailability. Therefore, systematic studies have been performed to investigate improvements in the stability, water-solubility and bioavailability of lipophilic bioactives through complexation with cyclodextrins (CDs). The solubility of CoQ10 in water is extremely low, resulting in low bioavailability when administered orally. Bioavailability of CoQ10 was enhanced significantly by complexation with γ-CD. CoQ10 generally agglutinates, but the dissociated CoQ10 from γ-CD was captured by bile acid to form micelles without aggregation and therefore both solubility a...

Research paper thumbnail of Topics

Bulletin of Applied Glycoscience, 2013

Research paper thumbnail of Anti-obesity effects of α-cyclodextrin-stabilized 4-methylthio-3-butenyl isothiocyanate from daikon (Raphanus sativus var. longipinnatus) in mice

Journal of Clinical Biochemistry and Nutrition, 2019

unrestricted use, distribution, and reproduction in any medium, provided the original work is pro... more unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 4 Methylthio 3 butenyl isothiocyanate (MTBI) is a pungent bio active constituent found in daikon. However, MTBI is immediately hydrolyzed to 3 hydroxy methylene 2 thioxopyrrolidine in grated daikon. In this study, we evaluated whether MTBI in grated daikon complexed with α cyclodextrin (αCD) has anti obesity effects in mice. C57BL/6J mice were fed a normal diet (normal group), high fat diet (HFD, control group), HFD with αCD (αCD group), or HFD with MTBI αCD (MTBI αCD group) for 16 weeks. The results showed that the final body weight, epididymal white adipose tissue weight, and plasma triglyceride and total cholesterol levels were significantly lower in the MTBI αCD group than in the control group. The cell size in epididymal adipose tissue was significantly smaller and the accumulation of lipids in the liver was significantly lower in the MTBI αCD group than in the control group. Furthermore, real time polymerase chain reaction showed that the mRNA expression level of tumor necrosis factor alpha was suppressed in the MTBI αCD group. We also observed low superoxide dismutase activity in the MTBI αCD group, possibly because MTBI αCD has the potential to resist HFD induced oxida tive injury. In conclusion, MTBI αCD exerted anti inflammation and antioxidant effects to suppress lipid accumulation in epididymal adipose tissue and the liver. These effects then prevented HFD induced obesity in mice.

Research paper thumbnail of Low amounts of dietary fibre increase in vitro production of short-chain fatty acids without changing human colonic microbiota structure

Scientific Reports, 2018

This study investigated the effect of various prebiotics (indigestible dextrin, α-cyclodextrin, a... more This study investigated the effect of various prebiotics (indigestible dextrin, α-cyclodextrin, and dextran) on human colonic microbiota at a dosage corresponding to a daily intake of 6 g of prebiotics per person (0.2% of dietary intake). We used an in vitro human colonic microbiota model based on batch fermentation starting from a faecal inoculum. Bacterial 16S rRNA gene sequence analysis showed that addition of 0.2% prebiotics did not change the diversity and composition of colonic microbiota. This finding coincided with results from a clinical study showing that the microbiota composition of human faecal samples remained unchanged following administration of 6 g of prebiotics over seven days. However, compared to absence of prebiotics, their addition reduced the pH and increased the generation of acetate and propionate in the in vitro system. Thus, even at such relatively low amounts, prebiotics appear capable of activating the metabolism of colonic microbiota.

Research paper thumbnail of Anti-Inflammatory Properties of Brazilian Green Propolis Encapsulated in a γ-Cyclodextrin Complex in Mice Fed a Western-Type Diet

International journal of molecular sciences, Jan 26, 2017

Ageing is often accompanied by chronic inflammation. A fat- and sugar-rich Western-type diet (WTD... more Ageing is often accompanied by chronic inflammation. A fat- and sugar-rich Western-type diet (WTD) may accelerate the ageing phenotype. Cell culture studies have indicated that artepillin C-containing Brazilian green propolis exhibits anti-inflammatory properties. However, little is known regarding its anti-inflammatory potential in mouse liver in vivo. In this study, female C57BL/6NRj wild-type mice were fed a WTD, a WTD supplemented with Brazilian green propolis supercritical extract (GPSE) encapsulated in γ-cyclodextrin (γCD) or a WTD plus γCD for 10 weeks. GPSE-γCD did not affect the food intake, body weight or body composition of the mice. However, mRNA levels of the tumour necrosis factor α were significantly downregulated (p < 0.05) in these mice compared to those in the WTD-fed controls. Furthermore, the gene expression levels of other pro-inflammatory markers, including serum amyloid P, were significantly (p < 0.001) decreased following GPSE-γCD treatment. GPSE-γCD si...

Research paper thumbnail of NMR Studies of Inclusion Complexes Formed by (R)-α-Lipoic Acid with α-, β-, and γ-Cyclodextrins

Bulletin of the Chemical Society of Japan, 2015

The structures of inclusion complexes of (R)-α-lipoic acid with α-, β-, and γ-cyclodextrin (CD) w... more The structures of inclusion complexes of (R)-α-lipoic acid with α-, β-, and γ-cyclodextrin (CD) were constructed using restraints derived from ROESY spectra and MMFF94 molecular mechanics calculations. (R)-α-lipoic acid and α-CD generate a single stable inclusion complex, in which the 1,2-dithiolane ring of the (R)-α-lipoic acid is oriented toward the secondary hydroxy side of the α-CD. NMR data suggests that β-CD produces two kinds of inclusion complexes with α-lipoic acid. Finally, γ-CD yields 1:1 and 1:2 host/guest complexes with (R)-α-lipoic acid. The estimated structure of the 1:1 γ-CD inclusion complex has the 1,2-dithiolane ring oriented toward the primary hydroxy side of the γ-CD.

Research paper thumbnail of Bioavailability of an R-α-Lipoic Acid/γ-Cyclodextrin Complex in Healthy Volunteers

International Journal of Molecular Sciences, 2016

R-α-lipoic acid (R-LA) is a cofactor of mitochondrial enzymes and a very strong antioxidant. R-LA... more R-α-lipoic acid (R-LA) is a cofactor of mitochondrial enzymes and a very strong antioxidant. R-LA is available as a functional food ingredient but is unstable against heat or acid. Stabilized R-LA was prepared through complexation with γ-cyclodextrin (CD), yielding R-LA/CD. R-LA/CD was orally administered to six healthy volunteers and showed higher plasma levels with an area under the plasma concentration-time curve that was 2.5 times higher than that after oral administration of non-complexed R-LA, although the time to reach the maximum plasma concentration and half-life did not differ. Furthermore, the plasma glucose level after a single oral administration of R-LA/CD or R-LA was not affected and no side effects were observed. These results indicate that R-LA/CD could be easily absorbed in the intestine. In conclusion, γ-CD complexation is a promising technology for delivering functional but unstable ingredients like R-LA.

Research paper thumbnail of シクロデキストリンによる不安定な機能性食品素材の包接安定化

Oleoscience, 2013

Some of functional food ingredients having health promotion functions and/or beauty care ef fects... more Some of functional food ingredients having health promotion functions and/or beauty care ef fects are unstable under UV light, air oxygen, elevated temperature and in the presence of incompatible substances. Cyclodextrins can be used for the stabilization of such active substances by complex formation even under above mentioned degradable circumstances. Here we show some of our investigation results for the stabilization of actives like unsaturated fatty acids, R-α-lipoic acid and Coenzyme Q10.

Research paper thumbnail of Investigation of Enantioselective Membrane Permeability of α-Lipoic Acid in Caco-2 and MDCKII Cell

International Journal of Molecular Sciences, 2016

α-Lipoic acid (LA) contains a chiral carbon and exists as two enantiomers (R-α-lipoic acid (RLA) ... more α-Lipoic acid (LA) contains a chiral carbon and exists as two enantiomers (R-α-lipoic acid (RLA) and S-α-lipoic acid (SLA)). We previously demonstrated that oral bioavailability of RLA is better than that of SLA. This difference arose from the fraction absorbed multiplied by gastrointestinal availability (F aˆFg) and hepatic availability (F h) in the absorption phase. However, it remains unclear whether F a and/or F g are involved in enantioselectivity. In this study, Caco-2 cells and Madin-Darby canine kidney strain II cells were used to assess the enantioselectivity of membrane permeability. LA was actively transported from the apical side to basal side, regardless of the differences in its steric structure. Permeability rates were proportionally increased in the range of 10-250 µg LA/mL, and the permeability coefficient did not differ significantly between enantiomers. Hence, we conclude that enantioselective pharmacokinetics arose from the metabolism (F h or F gˆFh), and definitely not from the membrane permeation (F a) in the absorption phase.

Research paper thumbnail of Structural Analysis of Crystalline R(+)-α-Lipoic Acid-α-cyclodextrin Complex Based on Microscopic and Spectroscopic Studies

International Journal of Molecular Sciences, 2015

R(+)-α-lipoic acid (RALA) is a naturally-occurring substance, and its protein-bound form plays si... more R(+)-α-lipoic acid (RALA) is a naturally-occurring substance, and its protein-bound form plays significant role in the energy metabolism in the mitochondria. RALA is vulnerable to a variety of physical stimuli, including heat and UV light, which prompted us to study the stability of its complexes with cyclodextrins (CDs). In this study, we have prepared and purified a crystalline RALA-αCD complex and evaluated its properties in the solid state. The results of 1 H NMR and PXRD analyses indicated that the crystalline RALA-αCD complex is a channel type complex with a molar ratio of 2:3 (RALA:α-CD). Attenuated total reflection/Fourier transform infrared analysis of the complex showed the shift of the C=O stretching vibration of RALA due to the formation of the RALA-αCD complex. Raman spectroscopic analysis revealed the significant weakness of

Research paper thumbnail of Enantioselective Pharmacokinetics of α-Lipoic Acid in Rats

International Journal of Molecular Sciences, 2015

α-Lipoic acid (LA) is widely used for nutritional supplements as a racemic mixture, even though t... more α-Lipoic acid (LA) is widely used for nutritional supplements as a racemic mixture, even though the R enantiomer is biologically active. After oral administration of the racemic mixture (R-α-lipoic acid (RLA) and S-α-lipoic acid (SLA) mixed at the ratio of 50:50) to rats, RLA showed higher plasma concentration than SLA, and its area under the plasma concentration-time curve from time zero to the last (AUC) was significantly about 1.26 times higher than that of SLA. However, after intravenous administration of the racemic mixture, the pharmacokinetic profiles, initial concentration (C0), AUC, and half-life (T1/2) of the enantiomers were not significantly different. After oral and intraduodenal administration of the racemic mixture to pyrolus-ligated rats, the AUCs of RLA were significantly about 1.24 and 1.32 times higher than that of SLA, respectively. In addition, after intraportal administration the AUC of RLA was significantly 1.16 times higher than that of SLA. In conclusion, the enantioselective pharmacokinetics of LA in rats arose from the fraction absorbed multiplied by gastrointestinal availability (FaFg) and hepatic availability (Fh), and not from the total clearance.

Research paper thumbnail of Dietary Tocotrienol/γ-Cyclodextrin Complex Increases Mitochondrial Membrane Potential and ATP Concentrations in the Brains of Aged Mice

Oxidative Medicine and Cellular Longevity, 2015

Brain aging is accompanied by a decrease in mitochondrial function. In vitro studies suggest that... more Brain aging is accompanied by a decrease in mitochondrial function. In vitro studies suggest that tocotrienols, includingγ- andδ-tocotrienol (T3), may exhibit neuroprotective properties. However, little is known about the effect of dietary T3 on mitochondrial function in vivo. In this study, we monitored the effect of a dietary T3/γ-cyclodextrin complex (T3CD) on mitochondrial membrane potential and ATP levels in the brain of 21-month-old mice. Mice were fed either a control diet or a diet enriched with T3CD providing 100 mg T3 per kg diet for 6 months. Dietary T3CD significantly increased mitochondrial membrane potential and ATP levels compared to those of controls. The increase in MMP and ATP due to dietary T3CD was accompanied by an increase in the protein levels of the mitochondrial transcription factor A (TFAM). Furthermore, dietary T3CD slightly increased the mRNA levels of superoxide dismutase,γ-glutamyl cysteinyl synthetase, and heme oxygenase 1 in the brain. Overall, the pr...

Research paper thumbnail of Effect of γ-Cyclodextrin Inclusion Complex on the Absorption of R-α-Lipoic Acid in Rats

International Journal of Molecular Sciences, 2015

R-α-lipoic acid (RLA) is an endogenous organic acid, and works as a cofactor for mitochondrial en... more R-α-lipoic acid (RLA) is an endogenous organic acid, and works as a cofactor for mitochondrial enzymes and as a kind of antioxidant. Inclusion complexes of RLA with α-, β-or γ-cyclodextrins (CD) were prepared and orally administered as a suspension to rats. Among them, RLA/γ-CD showed the highest plasma exposure, and its area under the plasma concentration-time curve (AUC) of RLA was 2.2 times higher than that after oral administration of non-inclusion RLA. On the other hand, the AUC after oral administration of non-inclusion RLA and RLA/γ-CD to pylorus-ligated rats did not differ. However, the AUC after intraduodenal administration of RLA/γ-CD was 5.1 times higher than that of non-inclusion RLA, and was almost comparable to the AUC after intraduodenal administration of RLA-Na solution. Furthermore, the AUC after intraduodenal administration of RLA/γ-CD was not affected by biliary ligation or co-administration of an amylase inhibitor. These findings demonstrated that RLA was absorbed from the small intestine effectively when orally administered as a γ-CD inclusion complex, which could be easily dissolved in OPEN ACCESS the lumen of the intestine. In conclusion, γ-CD inclusion complex is an appropriate formulation for supplying RLA as a drug or nutritional supplement with respect to absorption.

Research paper thumbnail of Spectroscopic studies of R(+)-α-lipoic acid--cyclodextrin complexes

International journal of molecular sciences, Jan 7, 2014

α-Lipoic acid (ALA) has a chiral center at the C6 position, and exists as two enantiomers, R(+)-A... more α-Lipoic acid (ALA) has a chiral center at the C6 position, and exists as two enantiomers, R(+)-ALA (RALA) and S(-)-ALA (SALA). RALA is naturally occurring, and is a cofactor for mitochondrial enzymes, therefore playing a major role in energy metabolism. However, RALA cannot be used for pharmaceuticals or nutraceuticals because it readily polymerizes via a 1,2-dithiolane ring-opening when exposed to light or heat. So, it is highly desired to find out the method to stabilize RALA. The purpose of this study is to provide the spectroscopic information of stabilized RALA and SALA through complexation with cyclodextrins (CDs), α-CD, β-CD and γ-CD and to examine the physical characteristics of the resultant complexes in the solid state. The RALA-CD structures were elucidated based on the micro fourier transform infrared (FT-IR) and Raman analyses. The FT-IR results showed that the C=O stretching vibration of RALA appeared at 1717 cm⁻¹ and then shifted on formation of the RALA-CD complexes...

Research paper thumbnail of Antidiabetic effect of the α-lipoic acid γ-cyclodextrin complex

Journal of clinical biochemistry and nutrition, 2014

In recent years, the number of patients suffering from diabetes mellitus has been increasing worl... more In recent years, the number of patients suffering from diabetes mellitus has been increasing worldwide. In particular, type 2 diabetes mellitus, a lifestyle-related disease, is recognized as a serious disease with various complications. Many types of pharmaceutics or specific health foods have been used for the management of diabetes mellitus. At the same time, the relationship between diabetes mellitus and α-lipoic acid has been recognized for many years. In this study, we found that the α-lipoic acid γ-cyclodextrin complex exhibited an HbA1c lowering effect for treating type 2 diabetes mellitus in animal models. Moreover, in this study, we investigated the activation of phosphorylation of AMP-activated protein kinase, which plays a role in cellular energy homeostasis, in the liver of KKA(y) mice by using α-lipoic acid and the α-lipoic acid γ-cyclodextrin complex. Our results show that the α-lipoic acid γ-cyclodextrin complex strongly induced the phosphorylation of AMP-activated pr...

Research paper thumbnail of Analysis of the enhanced stability of r(+)-alpha lipoic Acid by the complex formation with cyclodextrins

International journal of molecular sciences, Jan 7, 2013

R(+)-alpha lipoic acid (RALA) is one of the cofactors for mitochondrial enzymes and, therefore, p... more R(+)-alpha lipoic acid (RALA) is one of the cofactors for mitochondrial enzymes and, therefore, plays a central role in energy metabolism. RALA is unstable when exposed to low pH or heat, and therefore, it is difficult to use enantiopure RALA as a pharma- and nutra-ceutical. In this study, we have aimed to stabilize RALA through complex formation with cyclodextrins (CDs). α-CD, β-CD and γ-CD were used for the formation of these RALA-CD complexes. We confirmed the complex formation using differential scanning calorimetry and showed by using HPLC analysis that complexed RALA is more stable than free RALA when subjected to humidity and high temperature or acidic pH conditions. Scanning electron microscopy studies showed that the particle size and shape differed depending on the cyclodextrin used for complexation. Further, the complexes of CD and RALA showed a different particle size distribution pattern compared with that of CD itself or that of the physical mixture of RALA and CD.

Research paper thumbnail of A study on the inhibitory mechanism for cholesterol absorption by α-cyclodextrin administration

Beilstein journal of organic chemistry, 2014

Micelle formation of cholesterol with lecithin and bile salts is a key process for intestinal abs... more Micelle formation of cholesterol with lecithin and bile salts is a key process for intestinal absorption of lipids. Some dietary fibers commonly used to reduce the lipid content in the body are thought to inhibit lipid absorption by binding to bile salts and decreasing the lipid solubility. Amongst these, α-cyclodextrin (α-CD) is reportedly one of the most powerful dietary fibers for decreasing blood cholesterol. However, it is difficult to believe that α-CD directly removes cholesterol because it has a very low affinity for cholesterol and its mechanism of action is less well understood than those of other dietary fibers. To identify this mechanism, we investigated the interaction of α-CD with lecithin and bile salts, which are essential components for the dissolution of cholesterol in the small intestine, and the effect of α-CD on micellar solubility of cholesterol. α-CD was added to Fed-State Simulated Intestinal Fluid (FeSSIF), and precipitation of a white solid was observed. An...

Research paper thumbnail of Article Effect of γ-Cyclodextrin Inclusion Complex on the Absorption of R-α-Lipoic Acid in Rats

Abstract: R-α-lipoic acid (RLA) is an endogenous organic acid, and works as a cofactor for mitoch... more Abstract: R-α-lipoic acid (RLA) is an endogenous organic acid, and works as a cofactor for mitochondrial enzymes and as a kind of antioxidant. Inclusion complexes of RLA with α-, β- or γ-cyclodextrins (CD) were prepared and orally administered as a suspension to rats. Among them, RLA/γ-CD showed the highest plasma exposure, and its area under the plasma concentration-time curve (AUC) of RLA was 2.2 times higher than that after oral administration of non-inclusion RLA. On the other hand, the AUC after oral administration of non-inclusion RLA and RLA/γ-CD to pylorus-ligated rats did not differ. However, the AUC after intraduodenal administration of RLA/γ-CD was 5.1 times higher than that of non-inclusion RLA, and was almost comparable to the AUC after intraduodenal administration of RLA-Na solution. Furthermore, the AUC after intraduodenal administration of RLA/γ-CD was not affected by biliary ligation or co-administration of an amylase inhibitor. These findings demonstrated that RLA ...

Research paper thumbnail of Safety Evaluation of R(+)-Alpha Lipoic Acid-Gamma Cyclodextrin Complex

R(+)-alpha lipoic acid (RALA) is one of cofactors for mitochondrial enzymes and therefore plays a... more R(+)-alpha lipoic acid (RALA) is one of cofactors for mitochondrial enzymes and therefore plays a central role in energy metabolism. RALA is unstable when exposed to low pH or heat. Therefore, we have stabilized RALA through complex formation with cyclodextrins (γ-CDs). γ-CDs were used for the formation of these RALA-CD complexes. In this study, we evaluated the safety of RALA-CD complex through in vitro and in vivo toxicity tests as follows: an acute toxicity study, the Ames test, and a subchronic toxicity study using thiamine-deficient rats. These toxicity studies showed that RALA-CD produced no toxic effects, and support the safety of oral supplementation of RALA-CD. Further, RALA-CD administration showed a different effect on food intake and body weight of thiamine-deficient rats when compared with the complexes of CD and SALA and DL-ALA.

Research paper thumbnail of Stabilized R -α-Lipoic Acid by Encapsulation Using Cyclodextrins

Impact of Nanoscience in the Food Industry, 2018

Abstract R-(+)-α-Lipoic acid (RALA) is a cofactor in mitochondrial enzymes. In energy metabolism,... more Abstract R-(+)-α-Lipoic acid (RALA) is a cofactor in mitochondrial enzymes. In energy metabolism, RALA plays a significant role. It is a very powerful antioxidant and is able to react in aqueous and lipid media with reactive oxygen species, such as superoxides, peroxyl and hydroxyl radicals, singlet oxygen, hypochlorite, and peroxynitrite. Although RALA is biosynthesized mainly by intestinal bacteria and can be absorbed from vegetables or meat, some diets may not provide it in sufficient levels. This means that RALA supplementation is an option to help maintain body health. In this chapter, we introduce the history of RALA, and summarize its chemical and biochemical characteristics, such as chirality, antioxidant activities, and metabolism. RALA is quite vulnerable to physical stimuli, such as high temperature and UV irradiation, which motivated us to study its complex formation with cyclodextrins (CDs). We prepared an RALA–CD complex and evaluated its physicochemical properties. The results demonstrated that RALA was stabilized through complex formation with CDs. Furthermore, we obtained precise information on the complex formation using micro-Raman and micro-Fourier transform infrared spectroscopy. We also describe some in vivo studies using RALA–CD complexes.

Research paper thumbnail of Enhancement of Oral Bioavailability of Functional Ingredients by Complexation with Cyclodextrin

Natural lipophilic bioactives that possess human health benefits, such as coenzyme Q10 (CoQ10) an... more Natural lipophilic bioactives that possess human health benefits, such as coenzyme Q10 (CoQ10) and R-α-lipoic acid (RALA), often have undesirable characteristics that limit their use as nutraceuticals and cosmeceuticals. These bioactives are usually unstable against oxygen, ultraviolet light, low pH and heat. Furthermore, their watersolubility is low because of their hydrophobic nature or instability and this leads to low bioavailability. Therefore, systematic studies have been performed to investigate improvements in the stability, water-solubility and bioavailability of lipophilic bioactives through complexation with cyclodextrins (CDs). The solubility of CoQ10 in water is extremely low, resulting in low bioavailability when administered orally. Bioavailability of CoQ10 was enhanced significantly by complexation with γ-CD. CoQ10 generally agglutinates, but the dissociated CoQ10 from γ-CD was captured by bile acid to form micelles without aggregation and therefore both solubility a...

Research paper thumbnail of Topics

Bulletin of Applied Glycoscience, 2013

Research paper thumbnail of Anti-obesity effects of α-cyclodextrin-stabilized 4-methylthio-3-butenyl isothiocyanate from daikon (Raphanus sativus var. longipinnatus) in mice

Journal of Clinical Biochemistry and Nutrition, 2019

unrestricted use, distribution, and reproduction in any medium, provided the original work is pro... more unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 4 Methylthio 3 butenyl isothiocyanate (MTBI) is a pungent bio active constituent found in daikon. However, MTBI is immediately hydrolyzed to 3 hydroxy methylene 2 thioxopyrrolidine in grated daikon. In this study, we evaluated whether MTBI in grated daikon complexed with α cyclodextrin (αCD) has anti obesity effects in mice. C57BL/6J mice were fed a normal diet (normal group), high fat diet (HFD, control group), HFD with αCD (αCD group), or HFD with MTBI αCD (MTBI αCD group) for 16 weeks. The results showed that the final body weight, epididymal white adipose tissue weight, and plasma triglyceride and total cholesterol levels were significantly lower in the MTBI αCD group than in the control group. The cell size in epididymal adipose tissue was significantly smaller and the accumulation of lipids in the liver was significantly lower in the MTBI αCD group than in the control group. Furthermore, real time polymerase chain reaction showed that the mRNA expression level of tumor necrosis factor alpha was suppressed in the MTBI αCD group. We also observed low superoxide dismutase activity in the MTBI αCD group, possibly because MTBI αCD has the potential to resist HFD induced oxida tive injury. In conclusion, MTBI αCD exerted anti inflammation and antioxidant effects to suppress lipid accumulation in epididymal adipose tissue and the liver. These effects then prevented HFD induced obesity in mice.

Research paper thumbnail of Low amounts of dietary fibre increase in vitro production of short-chain fatty acids without changing human colonic microbiota structure

Scientific Reports, 2018

This study investigated the effect of various prebiotics (indigestible dextrin, α-cyclodextrin, a... more This study investigated the effect of various prebiotics (indigestible dextrin, α-cyclodextrin, and dextran) on human colonic microbiota at a dosage corresponding to a daily intake of 6 g of prebiotics per person (0.2% of dietary intake). We used an in vitro human colonic microbiota model based on batch fermentation starting from a faecal inoculum. Bacterial 16S rRNA gene sequence analysis showed that addition of 0.2% prebiotics did not change the diversity and composition of colonic microbiota. This finding coincided with results from a clinical study showing that the microbiota composition of human faecal samples remained unchanged following administration of 6 g of prebiotics over seven days. However, compared to absence of prebiotics, their addition reduced the pH and increased the generation of acetate and propionate in the in vitro system. Thus, even at such relatively low amounts, prebiotics appear capable of activating the metabolism of colonic microbiota.

Research paper thumbnail of Anti-Inflammatory Properties of Brazilian Green Propolis Encapsulated in a γ-Cyclodextrin Complex in Mice Fed a Western-Type Diet

International journal of molecular sciences, Jan 26, 2017

Ageing is often accompanied by chronic inflammation. A fat- and sugar-rich Western-type diet (WTD... more Ageing is often accompanied by chronic inflammation. A fat- and sugar-rich Western-type diet (WTD) may accelerate the ageing phenotype. Cell culture studies have indicated that artepillin C-containing Brazilian green propolis exhibits anti-inflammatory properties. However, little is known regarding its anti-inflammatory potential in mouse liver in vivo. In this study, female C57BL/6NRj wild-type mice were fed a WTD, a WTD supplemented with Brazilian green propolis supercritical extract (GPSE) encapsulated in γ-cyclodextrin (γCD) or a WTD plus γCD for 10 weeks. GPSE-γCD did not affect the food intake, body weight or body composition of the mice. However, mRNA levels of the tumour necrosis factor α were significantly downregulated (p < 0.05) in these mice compared to those in the WTD-fed controls. Furthermore, the gene expression levels of other pro-inflammatory markers, including serum amyloid P, were significantly (p < 0.001) decreased following GPSE-γCD treatment. GPSE-γCD si...

Research paper thumbnail of NMR Studies of Inclusion Complexes Formed by (R)-α-Lipoic Acid with α-, β-, and γ-Cyclodextrins

Bulletin of the Chemical Society of Japan, 2015

The structures of inclusion complexes of (R)-α-lipoic acid with α-, β-, and γ-cyclodextrin (CD) w... more The structures of inclusion complexes of (R)-α-lipoic acid with α-, β-, and γ-cyclodextrin (CD) were constructed using restraints derived from ROESY spectra and MMFF94 molecular mechanics calculations. (R)-α-lipoic acid and α-CD generate a single stable inclusion complex, in which the 1,2-dithiolane ring of the (R)-α-lipoic acid is oriented toward the secondary hydroxy side of the α-CD. NMR data suggests that β-CD produces two kinds of inclusion complexes with α-lipoic acid. Finally, γ-CD yields 1:1 and 1:2 host/guest complexes with (R)-α-lipoic acid. The estimated structure of the 1:1 γ-CD inclusion complex has the 1,2-dithiolane ring oriented toward the primary hydroxy side of the γ-CD.

Research paper thumbnail of Bioavailability of an R-α-Lipoic Acid/γ-Cyclodextrin Complex in Healthy Volunteers

International Journal of Molecular Sciences, 2016

R-α-lipoic acid (R-LA) is a cofactor of mitochondrial enzymes and a very strong antioxidant. R-LA... more R-α-lipoic acid (R-LA) is a cofactor of mitochondrial enzymes and a very strong antioxidant. R-LA is available as a functional food ingredient but is unstable against heat or acid. Stabilized R-LA was prepared through complexation with γ-cyclodextrin (CD), yielding R-LA/CD. R-LA/CD was orally administered to six healthy volunteers and showed higher plasma levels with an area under the plasma concentration-time curve that was 2.5 times higher than that after oral administration of non-complexed R-LA, although the time to reach the maximum plasma concentration and half-life did not differ. Furthermore, the plasma glucose level after a single oral administration of R-LA/CD or R-LA was not affected and no side effects were observed. These results indicate that R-LA/CD could be easily absorbed in the intestine. In conclusion, γ-CD complexation is a promising technology for delivering functional but unstable ingredients like R-LA.

Research paper thumbnail of シクロデキストリンによる不安定な機能性食品素材の包接安定化

Oleoscience, 2013

Some of functional food ingredients having health promotion functions and/or beauty care ef fects... more Some of functional food ingredients having health promotion functions and/or beauty care ef fects are unstable under UV light, air oxygen, elevated temperature and in the presence of incompatible substances. Cyclodextrins can be used for the stabilization of such active substances by complex formation even under above mentioned degradable circumstances. Here we show some of our investigation results for the stabilization of actives like unsaturated fatty acids, R-α-lipoic acid and Coenzyme Q10.

Research paper thumbnail of Investigation of Enantioselective Membrane Permeability of α-Lipoic Acid in Caco-2 and MDCKII Cell

International Journal of Molecular Sciences, 2016

α-Lipoic acid (LA) contains a chiral carbon and exists as two enantiomers (R-α-lipoic acid (RLA) ... more α-Lipoic acid (LA) contains a chiral carbon and exists as two enantiomers (R-α-lipoic acid (RLA) and S-α-lipoic acid (SLA)). We previously demonstrated that oral bioavailability of RLA is better than that of SLA. This difference arose from the fraction absorbed multiplied by gastrointestinal availability (F aˆFg) and hepatic availability (F h) in the absorption phase. However, it remains unclear whether F a and/or F g are involved in enantioselectivity. In this study, Caco-2 cells and Madin-Darby canine kidney strain II cells were used to assess the enantioselectivity of membrane permeability. LA was actively transported from the apical side to basal side, regardless of the differences in its steric structure. Permeability rates were proportionally increased in the range of 10-250 µg LA/mL, and the permeability coefficient did not differ significantly between enantiomers. Hence, we conclude that enantioselective pharmacokinetics arose from the metabolism (F h or F gˆFh), and definitely not from the membrane permeation (F a) in the absorption phase.

Research paper thumbnail of Structural Analysis of Crystalline R(+)-α-Lipoic Acid-α-cyclodextrin Complex Based on Microscopic and Spectroscopic Studies

International Journal of Molecular Sciences, 2015

R(+)-α-lipoic acid (RALA) is a naturally-occurring substance, and its protein-bound form plays si... more R(+)-α-lipoic acid (RALA) is a naturally-occurring substance, and its protein-bound form plays significant role in the energy metabolism in the mitochondria. RALA is vulnerable to a variety of physical stimuli, including heat and UV light, which prompted us to study the stability of its complexes with cyclodextrins (CDs). In this study, we have prepared and purified a crystalline RALA-αCD complex and evaluated its properties in the solid state. The results of 1 H NMR and PXRD analyses indicated that the crystalline RALA-αCD complex is a channel type complex with a molar ratio of 2:3 (RALA:α-CD). Attenuated total reflection/Fourier transform infrared analysis of the complex showed the shift of the C=O stretching vibration of RALA due to the formation of the RALA-αCD complex. Raman spectroscopic analysis revealed the significant weakness of

Research paper thumbnail of Enantioselective Pharmacokinetics of α-Lipoic Acid in Rats

International Journal of Molecular Sciences, 2015

α-Lipoic acid (LA) is widely used for nutritional supplements as a racemic mixture, even though t... more α-Lipoic acid (LA) is widely used for nutritional supplements as a racemic mixture, even though the R enantiomer is biologically active. After oral administration of the racemic mixture (R-α-lipoic acid (RLA) and S-α-lipoic acid (SLA) mixed at the ratio of 50:50) to rats, RLA showed higher plasma concentration than SLA, and its area under the plasma concentration-time curve from time zero to the last (AUC) was significantly about 1.26 times higher than that of SLA. However, after intravenous administration of the racemic mixture, the pharmacokinetic profiles, initial concentration (C0), AUC, and half-life (T1/2) of the enantiomers were not significantly different. After oral and intraduodenal administration of the racemic mixture to pyrolus-ligated rats, the AUCs of RLA were significantly about 1.24 and 1.32 times higher than that of SLA, respectively. In addition, after intraportal administration the AUC of RLA was significantly 1.16 times higher than that of SLA. In conclusion, the enantioselective pharmacokinetics of LA in rats arose from the fraction absorbed multiplied by gastrointestinal availability (FaFg) and hepatic availability (Fh), and not from the total clearance.

Research paper thumbnail of Dietary Tocotrienol/γ-Cyclodextrin Complex Increases Mitochondrial Membrane Potential and ATP Concentrations in the Brains of Aged Mice

Oxidative Medicine and Cellular Longevity, 2015

Brain aging is accompanied by a decrease in mitochondrial function. In vitro studies suggest that... more Brain aging is accompanied by a decrease in mitochondrial function. In vitro studies suggest that tocotrienols, includingγ- andδ-tocotrienol (T3), may exhibit neuroprotective properties. However, little is known about the effect of dietary T3 on mitochondrial function in vivo. In this study, we monitored the effect of a dietary T3/γ-cyclodextrin complex (T3CD) on mitochondrial membrane potential and ATP levels in the brain of 21-month-old mice. Mice were fed either a control diet or a diet enriched with T3CD providing 100 mg T3 per kg diet for 6 months. Dietary T3CD significantly increased mitochondrial membrane potential and ATP levels compared to those of controls. The increase in MMP and ATP due to dietary T3CD was accompanied by an increase in the protein levels of the mitochondrial transcription factor A (TFAM). Furthermore, dietary T3CD slightly increased the mRNA levels of superoxide dismutase,γ-glutamyl cysteinyl synthetase, and heme oxygenase 1 in the brain. Overall, the pr...

Research paper thumbnail of Effect of γ-Cyclodextrin Inclusion Complex on the Absorption of R-α-Lipoic Acid in Rats

International Journal of Molecular Sciences, 2015

R-α-lipoic acid (RLA) is an endogenous organic acid, and works as a cofactor for mitochondrial en... more R-α-lipoic acid (RLA) is an endogenous organic acid, and works as a cofactor for mitochondrial enzymes and as a kind of antioxidant. Inclusion complexes of RLA with α-, β-or γ-cyclodextrins (CD) were prepared and orally administered as a suspension to rats. Among them, RLA/γ-CD showed the highest plasma exposure, and its area under the plasma concentration-time curve (AUC) of RLA was 2.2 times higher than that after oral administration of non-inclusion RLA. On the other hand, the AUC after oral administration of non-inclusion RLA and RLA/γ-CD to pylorus-ligated rats did not differ. However, the AUC after intraduodenal administration of RLA/γ-CD was 5.1 times higher than that of non-inclusion RLA, and was almost comparable to the AUC after intraduodenal administration of RLA-Na solution. Furthermore, the AUC after intraduodenal administration of RLA/γ-CD was not affected by biliary ligation or co-administration of an amylase inhibitor. These findings demonstrated that RLA was absorbed from the small intestine effectively when orally administered as a γ-CD inclusion complex, which could be easily dissolved in OPEN ACCESS the lumen of the intestine. In conclusion, γ-CD inclusion complex is an appropriate formulation for supplying RLA as a drug or nutritional supplement with respect to absorption.

Research paper thumbnail of Spectroscopic studies of R(+)-α-lipoic acid--cyclodextrin complexes

International journal of molecular sciences, Jan 7, 2014

α-Lipoic acid (ALA) has a chiral center at the C6 position, and exists as two enantiomers, R(+)-A... more α-Lipoic acid (ALA) has a chiral center at the C6 position, and exists as two enantiomers, R(+)-ALA (RALA) and S(-)-ALA (SALA). RALA is naturally occurring, and is a cofactor for mitochondrial enzymes, therefore playing a major role in energy metabolism. However, RALA cannot be used for pharmaceuticals or nutraceuticals because it readily polymerizes via a 1,2-dithiolane ring-opening when exposed to light or heat. So, it is highly desired to find out the method to stabilize RALA. The purpose of this study is to provide the spectroscopic information of stabilized RALA and SALA through complexation with cyclodextrins (CDs), α-CD, β-CD and γ-CD and to examine the physical characteristics of the resultant complexes in the solid state. The RALA-CD structures were elucidated based on the micro fourier transform infrared (FT-IR) and Raman analyses. The FT-IR results showed that the C=O stretching vibration of RALA appeared at 1717 cm⁻¹ and then shifted on formation of the RALA-CD complexes...

Research paper thumbnail of Antidiabetic effect of the α-lipoic acid γ-cyclodextrin complex

Journal of clinical biochemistry and nutrition, 2014

In recent years, the number of patients suffering from diabetes mellitus has been increasing worl... more In recent years, the number of patients suffering from diabetes mellitus has been increasing worldwide. In particular, type 2 diabetes mellitus, a lifestyle-related disease, is recognized as a serious disease with various complications. Many types of pharmaceutics or specific health foods have been used for the management of diabetes mellitus. At the same time, the relationship between diabetes mellitus and α-lipoic acid has been recognized for many years. In this study, we found that the α-lipoic acid γ-cyclodextrin complex exhibited an HbA1c lowering effect for treating type 2 diabetes mellitus in animal models. Moreover, in this study, we investigated the activation of phosphorylation of AMP-activated protein kinase, which plays a role in cellular energy homeostasis, in the liver of KKA(y) mice by using α-lipoic acid and the α-lipoic acid γ-cyclodextrin complex. Our results show that the α-lipoic acid γ-cyclodextrin complex strongly induced the phosphorylation of AMP-activated pr...

Research paper thumbnail of Analysis of the enhanced stability of r(+)-alpha lipoic Acid by the complex formation with cyclodextrins

International journal of molecular sciences, Jan 7, 2013

R(+)-alpha lipoic acid (RALA) is one of the cofactors for mitochondrial enzymes and, therefore, p... more R(+)-alpha lipoic acid (RALA) is one of the cofactors for mitochondrial enzymes and, therefore, plays a central role in energy metabolism. RALA is unstable when exposed to low pH or heat, and therefore, it is difficult to use enantiopure RALA as a pharma- and nutra-ceutical. In this study, we have aimed to stabilize RALA through complex formation with cyclodextrins (CDs). α-CD, β-CD and γ-CD were used for the formation of these RALA-CD complexes. We confirmed the complex formation using differential scanning calorimetry and showed by using HPLC analysis that complexed RALA is more stable than free RALA when subjected to humidity and high temperature or acidic pH conditions. Scanning electron microscopy studies showed that the particle size and shape differed depending on the cyclodextrin used for complexation. Further, the complexes of CD and RALA showed a different particle size distribution pattern compared with that of CD itself or that of the physical mixture of RALA and CD.

Research paper thumbnail of A study on the inhibitory mechanism for cholesterol absorption by α-cyclodextrin administration

Beilstein journal of organic chemistry, 2014

Micelle formation of cholesterol with lecithin and bile salts is a key process for intestinal abs... more Micelle formation of cholesterol with lecithin and bile salts is a key process for intestinal absorption of lipids. Some dietary fibers commonly used to reduce the lipid content in the body are thought to inhibit lipid absorption by binding to bile salts and decreasing the lipid solubility. Amongst these, α-cyclodextrin (α-CD) is reportedly one of the most powerful dietary fibers for decreasing blood cholesterol. However, it is difficult to believe that α-CD directly removes cholesterol because it has a very low affinity for cholesterol and its mechanism of action is less well understood than those of other dietary fibers. To identify this mechanism, we investigated the interaction of α-CD with lecithin and bile salts, which are essential components for the dissolution of cholesterol in the small intestine, and the effect of α-CD on micellar solubility of cholesterol. α-CD was added to Fed-State Simulated Intestinal Fluid (FeSSIF), and precipitation of a white solid was observed. An...