Altered expression of O-GlcNAc-modified proteins in a mouse model whose glycemic status is controlled by a low carbohydrate ketogenic diet

Ketogenic diet for human diseases: the underlying mechanisms and potential for clinical implementations

The ketogenic diet (KD) is a high-fat, adequate-protein, and very-low-carbohydrate diet regimen that mimics the metabolism of the fasting state to induce the production of ketone bodies. The KD has long been established as a remarkably successful dietary approach for the treatment of intractable epilepsy and has increasingly garnered research attention rapidly in the past decade, subject to emerging evidence of the promising therapeutic potential of the KD for various diseases, besides epilepsy, from obesity to malignancies. In this review, we summarize the experimental and/or clinical evidence of the efficacy and safety of the KD in different diseases, and discuss the possible mechanisms of action based on recent advances in understanding the influence of the KD at the cellular and molecular levels. We emphasize that the KD may function through multiple mechanisms, which remain to be further elucidated. The challenges and future directions for the clinical implementation of the KD in the treatment of a spectrum of diseases have been discussed. We suggest that, with encouraging evidence of therapeutic effects and increasing insights into the mechanisms of action, randomized controlled trials should be conducted to elucidate a foundation for the clinical use of the KD.

Purification of anti-glycoconjugate monoclonal antibodies using newly developed porous zirconia particles

Here, we describe porous zirconia particles (PZPs) optimized for the purification of immunoglobulins. PZPs, with a pore size of approximately 10 nm, were designed to specifically interact with antibodies via surface modification with a phosphate functional group. A simple PZP purification method based on precipitation enabled efficient purification of mouse anti-glycosphingolipid globoside/Gb4Cer monoclonal IgM (κ-light chains) from hybridoma culture supernatants. Over 99% of contaminating proteins were removed by the PZP purification process, and approximately 50% of the IgM was recovered in the purified fraction after eluting the PZP-adsorbed antibodies with 100 mM phosphate buffer. Other IgG3 and IgM monoclonal antibodies that react with Gb4Cer or α2,6-sialyl LacNAc-modified glycoproteins could also be purified using PZPs and elution buffer at concentrations of 100–500 mM. All of the purified antibodies retained their antigen reactivity and specificity, indicating that PZP purification does not affect antibody function. As PZP purification is also suitable for purification of IgM consisting of λ-light chains and IgG derived from other mammalian species, it is expected to be applied to the purification of a variety of antibodies, including anti-glycoconjugate IgMs.

Dietary Control of Ganglioside Expression in Mammalian Tissues

Gangliosides are series of glycosphingolipids containing sialic acids in the oligosaccharide portion in mammalian cells. Gangliosides are a component of cellular membranes and play roles in modulating membrane function and the activity of membrane proteins. Abnormal expression and metabolism of gangliosides lead to the onset of several conditions in humans, such as neurologic diseases, diabetes, and cancer. A number of studies have been carried out to date to investigate the role of gangliosides in these diseases, and the effect of diet on tissue expression of gangliosides has recently become a topic of interest in this field. As gangliosides are degraded in the intestinal tract, ingested food-derived gangliosides are not directly absorbed into tissues in vivo, but the degradation products can be absorbed and affect ganglioside expression in the tissues. Recent studies have also shown that the expression of gangliosides in tissue cells can be indirectly induced by controlling the expression of ganglioside metabolism-related genes via the diet. These results indicate that dietary control can regulate the expression levels of gangliosides in tissues, which is expected to play a role in preventing and treating ganglioside-related diseases. This review introduces recent studies on the effect of diet on the expression of gangliosides in tissues, with a focus on our findings.

Induction of specific adaptive immune responses by immunization with newly designed artificial glycosphingolipids

We previously found that artificial glycosphingolipids (artGSLs) containing very-long-chain fatty acids behave as strong immunogens in mice and promote the production of antibodies recognizing the oligosaccharide portion of artGSLs as the epitope. Here, we report that the oligosaccharide structure of artGSLs influences these immunogenic properties. We evaluated the antibody-inducing activity of artGSLs with different oligosaccharide structures in mice and found strong IgG-inducing activity only with an artGSL containing a core-fucosylated tetraoligosaccharide (Manβ1,4GlcNAcβ1,4[Fucα1,6]GlcNAc). To characterize the immunogenic properties of this artGSL, we analyzed various derivatives and found that the non-reducing terminal mannose structure was critical for the antibody-inducing activity. These artGSLs also exhibited IgG-inducing activity dependent on co-administration of lipid A adjuvant, but no cytokine-inducing activity similar to α-galactosylceramide was detected. Furthermore, repetitive immunization with the artGSL promoted the production of antibodies against a core-fucosylated α-fetoprotein isoform (AFP-L3) known as a hepatocellular carcinoma–specific antigen. These results indicate that the newly designed artGSLs specifically induce adaptive immune responses and promote antibody production by B cells, which can be utilized to develop anti-glycoconjugate antibodies and cancer vaccines targeting tumor-associated carbohydrate antigens.

A low-carbohydrate ketogenic diet induces the expression of very-low-density lipoprotein receptor in liver and affects its associated metabolic abnormalities

A low-carbohydrate ketogenic diet (LCKD) promotes the progression of hepatic steatosis in C57BL/6 wild-type mice, but improves the condition in leptin-deficient obese (ob/ob) mice. Here, we show a novel effect of LCKD associated with the conflicting effects on these mice. Gene expression microarray analyses showed that expression of the Vldlr gene, which encodes the very-low-density lipoprotein receptor (VLDLR), was induced in LCKD-fed ob/ob mice. Although the VLDLR is not normally expressed in the liver, the LCKD led to VLDLR expression in both ob/ob and wild-type mice. To clarify this effect on VLDL dynamics, we analyzed the lipid content of serum lipoproteins and found a marked decrease in VLDL-triglycerides only in LCKD-fed wild-type mice. Further analyses suggested that transport of triglycerides via VLDL from the liver to extrahepatic tissues was inhibited by LCKD-induced hepatic VLDLR expression, but rescued under conditions of leptin deficiency.

Data set for characterization of the glycosylation status of hepatic glycoproteins in mice fed a low-carbohydrate ketogenic diet

The data presented herein pertain to a research article entitled “A low-carbohydrate ketogenic diet promotes ganglioside synthesis via the transcriptional regulation of ganglioside metabolism-related genes” [1]. The present article provides additional structural analysis data for the characterization of hepatic glycoproteins in mice fed a low-carbohydrate ketogenic diet (LCKD). Analysis of hepatic glycoproteins by enzyme-linked assay using the lectins UEA-I, ConA, LCA, and WGA showed that the LCKD decreased mature forms of complex-type glycans but increased immature forms of glycans on glycoproteins. An enzyme-linked immunosorbent assay using an anti–α2,6-sialyl LacNAc antibody also supported this result, indicating that dietary carbohydrate restriction results in aberrant glycosylation of tissue glycoproteins. These structural alterations of hepatic glycoproteins were not correlated with the expression levels of glycosyltransferase genes but were correlated with down-regulated expression of the Gale gene, which encodes a rate-limiting enzyme for the synthesis of sugar nucleotide donors for protein glycosylation in the liver. This property differed from glycosphingolipid metabolism in the liver of LCKD-fed mice.

A low-carbohydrate ketogenic diet promotes ganglioside synthesis via the transcriptional regulation of ganglioside metabolism-related genes

Low-carbohydrate ketogenic diets (LCKDs) are used for treating obesity and epilepsy; however, the molecular mechanism of LCKDs in tissues has not been fully investigated. In this study, novel LCKD-associated molecular targets were explored using gene expression profiling in the liver of mice fed a LCKD. The result showed that the LCKD promoted the expression of glycosyltransferase genes involved in ganglioside synthesis and suppressed the expression of Gm2a, the gene encoding GM2 ganglioside activator protein, a lysosomal protein indispensable for ganglioside degradation. These changes were correlated with increased ganglioside content in the liver and serum. As gangliosides are mainly expressed in central nervous tissues, we also analyzed LCKD effect on cerebral cortex. Although ganglioside levels were unchanged in mice on the LCKD, Gm2a expression was significantly down-regulated. Further analyses suggested that the LCKD altered the expression levels of gangliosides in a limited area of central nervous system tissues susceptible to Gm2a.

Implementing a low-carbohydrate, ketogenic diet to manage type 2 diabetes mellitus

INTRODUCTION

Type 2 diabetes mellitus (T2DM) has reached epidemic proportions in the modern world. For individuals affected by obesity-related T2DM, clinical studies have shown that carbohydrate restriction and weight loss can improve hyperglycemia, obesity, and T2DM.

AREAS COVERED

Reducing carbohydrate intake to a certain level, typically below 50 g per day, leads to increased ketogenesis in order to provide fuel for the body. Such low-carbohydrate, ketogenic diets were employed to treat obesity and diabetes in the 19^th and early 20^th centuries. Recent clinical research has reinvigorated the use of the ketogenic diet for individuals with obesity and diabetes. Although characterized by chronic hyperglycemia, the underlying cause of T2DM is hyperinsulinemia and insulin resistance, typically as a result of increased energy intake leading to obesity. The ketogenic diet substantially reduces the glycemic response that results from dietary carbohydrate as well as improves the underlying insulin resistance. This review combines a literature search of the published science and practical guidance based on clinical experience.

EXPERT COMMENTARY

While the current treatment of T2DM emphasizes drug treatment and a higher carbohydrate diet, the ketogenic diet is an effective alternative that relies less on medication, and may even be a preferable option when medications are not available.

Generation of anti-oligosaccharide antibodies that recognize mammalian glycoproteins by immunization with a novel artificial glycosphingolipid

Here we report a new method for the efficient generation of antibodies that recognize the fine structures of oligosaccharides on glycoproteins. We found a newly designed artificial glycosphingolipid carrying a very long chain fatty acid to be a strong immunogen in mice, with the serum of immunized mice containing antibodies recognizing the oligosaccharide structure of the immunogen. First, we found that conjugation of a simple ceramide analogue to target oligosaccharides could enhance the immunogenicity of these oligosaccharides in these immunized mice. This effect was confirmed in mice immunized with the artificial glycosphingolipids carrying 6'-Sialyl-LacNAc, 3'-Sialyl-LacNAc and LacNAc. Next, we tried to improve the immunogenic enhancing effect of the ceramide analogue. In a model experiment using 6'-Sialyl-LacNAc oligosaccharide, we manipulated the alkyl chains to several lengths, and found that a longer alkyl chain length of the fatty acid correlated with high immunogenicity. Among these we examined, artificial glycosphingolipids conjugated with a ceramide analogue carrying a very long chain fatty acid (lignoceric acid) showed the strongest immunogenicity. By using the artificial glycosphingolipid containing 6'-Sialy-LacNAc and lignoceric acid, we succeeded in the generation of a new anti-6'-Sialyl-LacNAc antibody that recognizes 6'-Sialyl-LacNAc carrying glycoproteins but does not bind to 6'-Sialyllactose, asialo-glycoporoteins and glycoproteins carrying 3'-Sialyl-LacNAc. These results indicate that the established technology is valuable for the targeted generation of monoclonal antibodies against glycoproteins containing specific oligosaccharide structures.

A bioenergetics systems evaluation of ketogenic diet liver effects

Ketogenic diets induce hepatocyte fatty acid oxidation and ketone body production. To further evaluate how ketogenic diets affect hepatocyte bioenergetic infrastructure, we analyzed livers from C57Bl/6J male mice maintained for 1 month on a ketogenic or standard chow diet. Compared with the standard diet, the ketogenic diet increased cytosolic and mitochondrial protein acetylation and also altered protein succinylation patterns. SIRT3 protein decreased while SIRT5 protein increased, and gluconeogenesis, oxidative phosphorylation, and mitochondrial biogenesis pathway proteins were variably and likely strategically altered. The pattern of changes observed can be used to inform a broader systems overview of how ketogenic diets affect liver bioenergetics.

PUGNAc treatment provokes globotetraosylceramide accumulation in human umbilical vein endothelial cells

PUGNAc is a well-investigated inhibitor for protein-O-GlcNAcase, whereas recent investigations showed that PUGNAc had a broad range as inhibitor for cellular β-hexosaminidases. Here we report that PUGNAc treatment provokes globotetraosylceramide (Gb4Cer) accumulation in human umbilical vein endothelial cells (HUVEC). HPLC analysis and a quantitative ELISA using newly developed anti-Gb4Cer monoclonal antibody revealed that PUGNAc treatment specifically increased the expression of Gb4Cer among glycosphingolipids expressed in HUVEC. Although the effect was weaker than PUGNAc, an O-GlcNAcase selective inhibitor (Thiamet-G) treatment also increased Gb4Cer levels in HUVEC. Furthermore, both of PUGNAc and Thiamet-G treatment up-regulated the expression levels of α-1,4-galactosyltransferase/Gb3Cer synthase gene which encodes a key enzyme in Gb4Cer synthesis. These results indicate that protein-O-GlcNAcylation can regulate the expression levels of cellular Gb4Cer.