Significance of Short Chain Fatty Acid Transport by Members of the Monocarboxylate Transporter Family (MCT)

Gut microbiota-astrocyte axis: new insights into age-related cognitive decline

With the rapidly aging human population, age-related cognitive decline and dementia are becoming increasingly prevalent worldwide. Aging is considered the main risk factor for cognitive decline and acts through alterations in the composition of the gut microbiota, microbial metabolites, and the functions of astrocytes. The microbiota-gut-brain axis has been the focus of multiple studies and is closely associated with cognitive function. This article provides a comprehensive review of the specific changes that occur in the composition of the gut microbiota and microbial metabolites in older individuals and discusses how the aging of astrocytes and reactive astrocytosis are closely related to age-related cognitive decline and neurodegenerative diseases. This article also summarizes the gut microbiota components that affect astrocyte function, mainly through the vagus nerve, immune responses, circadian rhythms, and microbial metabolites. Finally, this article summarizes the mechanism by which the gut microbiota-astrocyte axis plays a role in Alzheimer's and Parkinson's diseases. Our findings have revealed the critical role of the microbiota-astrocyte axis in age-related cognitive decline, aiding in a deeper understanding of potential gut microbiome-based adjuvant therapy strategies for this condition.

Whole-plant silage maize to improve fiber digestive characteristics and intestinal microbiota of Hezuo pigs

Introduction

Utilizing roughage resources is an effective approach to alleviate the shortage of corn-soybean feed and reducing the costs in the swine industry. Hezuo pig is one group of plateau type local Tibetan pig with strong tolerance to crude feeding. Nevertheless, current research on the roughage tolerance in Hezuo pigs and the microbiological mechanisms behind it is still minimally.This study explored the impact of various ratios of whole-plant silage (WPS) maize on the pH, cellulase activity, short-chain fatty acids (SCFAs), and intestinal microbiota in Hezuo pigs.

Methods

Thirty-two Hezuo pigs were randomly divided into four groups (n = 8). The control group received a basal diet, while experimental groups I, II, and III were given diets with incremental additions of 5%, 10%, and 15% air-dried WPS maize, respectively, for 120 days.

Results

The findings revealed that compared with the control group, in Group II, the pH of cecum and colon were notably decreased (p < 0.05), while acid detergent fiberdigestibility, the concentration of propionic and isobutyric acid in the cecum, and the concentration of isobutyric acid in the colon were significantly increased (p < 0.05). Also, carboxymethyl cellulase activity in the cecum in group II of Hezuo pigs was significantly higher than that in the other three groups (p < 0.05). Furthermore, the cecum microbiota showed a higher diversity in the group II of Hezuo pigs than that in the control group, as shown by the Simpson and Shannon indices. Specifically, 15 and 24 bacterial species showed a significant difference in relative abundance at the family and genus levels, respectively. Correlation analyses revealed significant associations between bacterial genera and SCFAs concentrations in the cecum. The abundance of Bacteroides and NK4A214_group was positively correlated with amounts of valeric and isovaleric acid but negatively with propionic acid (p < 0.05). The abundance of UCG-010 was positively linked with acetic acid and negatively correlated with butyric acid (p < 0.05). Actinobacillus abundance was positively associated with butyric acid levels (p < 0.05).

Discussion

In conclusion, a 10% WPS maize diet improved crude fiber digestibility by lowering cecal and colonic chyme pH, enhancing intestinal cellulase activity, improving SCFA production, and increasing intestinal microbiota diversity.

Bacterial community and diversity in the rumen of 11 Mongolian cattle as revealed by 16S rRNA amplicon sequencing

Through microorganism in the rumen of ruminant, plant fiber can be converted to edible food such as meat and milk. Ruminants had a rich and complex microbial community within the rumen, and the bacteria comprised the dominant proportion of the ruminal microbes. High-throughput sequencing offered a viable solution for the study of rumen microbes. In this study, rumen fluid samples were taken from 11 cattle from Inner Mongolian, the DNA of 11 rumen fluid samples were extracted and bacterial amplicons of the V4 regions of 16S rRNA were subjected to Illumina sequencing. More than 90,000 raw reads and 60,000 effect Tags per sample were obtained. 28,122 operational taxonomic units (OTUs) were observed from 11 samples, in average 2557 ± 361 OTUs for each sample. Bacteroidetes (44.41 ± 7.31%), Firmicutes (29.07 ± 3.78%), and Proteobacteria (7.18 ± 5.63%) were the dominant phyla among the bacteria of rumen, accounting for 82%. At the genus level, the highest relative abundance was Prevotella. Their functions were predicted using the Kyoto Encyclopedia of Genes and Genomes (KEGG). The results showed that they included metabolism, genetic information processing, environmental information processing and cellular processes. It explored the bacterial community diversity and composition of the rumen of Mongolian cattle. On the whole, our research showed that there was a high diversity as well as rich bacterial flora function of rumen bacteria in Mongolian cattle. Meanwhile, these findings provided information for further studies on the relationship between the community, diversity, functions of rumen bacteria and the nutritional physiological functions of the host.

Targeting cancer lactate metabolism with synergistic combinations of synthetic catalysts and monocarboxylate transporter inhibitors

Synthetic anticancer catalysts offer potential for low-dose therapy and the targeting of biochemical pathways in novel ways. Chiral organo-osmium complexes, for example, can catalyse the asymmetric transfer hydrogenation of pyruvate, a key substrate for energy generation, in cells. However, small-molecule synthetic catalysts are readily poisoned and there is a need to optimise their activity before this occurs, or to avoid this occurring. We show that the activity of the synthetic organometallic redox catalyst [Os(p-cymene)(TsDPEN)] (1), which can reduce pyruvate to un-natural D-lactate in MCF7 breast cancer cells using formate as a hydride source, is significantly increased in combination with the monocarboxylate transporter (MCT) inhibitor AZD3965. AZD3965, a drug currently in clinical trials, also significantly lowers the intracellular level of glutathione and increases mitochondrial metabolism. These synergistic mechanisms of reductive stress induced by 1, blockade of lactate efflux, and oxidative stress induced by AZD3965 provide a strategy for low-dose combination therapy with novel mechanisms of action.

Lactobacillus fermentum HNU312 alleviated oxidative damage and behavioural abnormalities during brain development in early life induced by chronic lead exposure

Lead exposure is a global public health safety issue that severely disrupts brain development and causes damage to the nervous system in early life. Probiotics and gut microbes have been highlighted for their critical roles in mitigating lead toxicity. However, the underlying mechanisms by which they work yet to be fully explored. Here, we designed a two-stage experiment using the probiotic Lactobacillus fermentum HNU312 (Lf312) to uncover how probiotics alleviate lead toxicity to the brain during early life. First, we explored the tolerance and adsorption of Lf312 to lead in vitro. Second, the adsorption capacity of the strain was determined and confirmed in vivo. The shotgun metagenome sequencing showed lead exposure-induced imbalance and dysfunction of the gut microbiome. In contrast, Lf312 intake significantly modulated the structure of the microbiome, increased the abundance of beneficial bacteria and short-chain fatty acids (SCFAs)-producing bacteria, and upregulated function-related metabolic pathways such as antioxidants. Notably, Lf312 enhanced the integrity of the blood-brain barrier by increasing the levels of SCFAs in the gut, alleviated inflammation in the brain, and ultimately improved anxiety-like and depression-like behaviours induced by lead exposure in mice. Subsequently, the effective mechanism was confirmed, highlighting that Lf312 worked through integrated strategies, including ionic adsorption and microbiota-gut-brain axis regulation. Collectively, this work elucidated the mechanism by which the gut microbiota mitigates the toxic effects of lead in the brain and provides preventive measures and intervention measures for brain damage due to mass lead poisoning in children.

Limosilactobacillus reuteri and caffeoylquinic acid synergistically promote adipose browning and ameliorate obesity-associated disorders

OBJECTIVE

High intake of caffeoylquinic acid (CQA)-rich dietary supplements, such as green coffee bean extracts, offers health-promoting effects on maintaining metabolic homeostasis. Similar to many active herbal ingredients with high pharmacological activities but low bioavailability, CQA has been reported as a promising thermogenic agent with anti-obesity properties, which contrasts with its poor oral absorption. Intestinal tract is the first site of CQA exposure and gut microbes might react quickly to CQA. Thus, it is of interest to explore the role of gut microbiome and microbial metabolites in the beneficial effects of CQA on obesity-related disorders.

RESULTS

Oral CQA supplementation effectively enhanced energy expenditure by activating browning of adipose and thus ameliorated obesity-related metabolic dysfunctions in high fat diet-induced obese (DIO) mice. Here, 16S rRNA gene amplicon sequencing revealed that CQA treatment remodeled the gut microbiota to promote its anti-obesity actions, as confirmed by antibiotic treatment and fecal microbiota transplantation. CQA enriched the gut commensal species Limosilactobacillus reuteri (L. reuteri) and stimulated the production of short-chain fatty acids, especially propionate. Mono-colonization of L. reuteri or low-dose CQA treatment did not reduce adiposity in DIO mice, while their combination elicited an enhanced thermogenic response, indicating the synergistic effects of CQA and L. reuteri on obesity. Exogenous propionate supplementation mimicked the anti-obesity effects of CQA alone or when combined with L. reuteri, which was ablated by the monocarboxylate transporter (MCT) inhibitor 7ACC1 or MCT1 disruption in inguinal white adipose tissues to block propionate transport.

CONCLUSIONS

Our data demonstrate a functional axis among L. reuteri, propionate, and beige fat tissue in the anti-obesity action of CQA through the regulation of thermogenesis. These findings provide mechanistic insights into the therapeutic use of herbal ingredients with poor bioavailability via their interaction with the gut microbiota. Video Abstract.

Lactate drives cellular DNA repair capacity: Role of lactate and related short-chain fatty acids in cervical cancer chemoresistance and viral infection

The characteristic feature of a cancer microenvironment is the presence of a highly elevated concentration of L-lactate in the tumor niche. The lactate-rich environment is also maintained by commensal mucosal microbiota, which has immense potential for affecting cancer cells through its receptoric and epigenetic modes of action. Some of these lactate activities might be associated with the failure of anticancer therapy as a consequence of the drug resistance acquired by cancer cells. Upregulation of cellular DNA repair capacity and enhanced drug efflux are the most important cellular mechanisms that account for ineffective radiotherapy and drug-based therapies. Here, we present the recent scientific knowledge on the role of the HCA1 receptor for lactate and lactate intrinsic activity as an HDAC inhibitor in the development of an anticancer therapy-resistant tumor phenotype, with special focus on cervical cancer cells. In addition, a recent study highlighted the viable role of interactions between mammalian cells and microorganisms in the female reproductive tract and demonstrated an interesting mechanism regulating the efficacy of retroviral transduction through lactate-driven modulation of DNA-PKcs cellular localization. To date, very few studies have focused on the mechanisms of lactate-driven enhancement of DNA repair and upregulation of particular multidrug-resistance proteins in cancer cells with respect to their intracellular regulatory mechanisms triggered by lactate. This review presents the main achievements in the field of lactate impact on cell biology that may promote undesirable alterations in cancer physiology and mitigate retroviral infections.

Colon microbiota modulation by dairy-derived diet: new strategy for prevention and treatment of colorectal cancer

An unbalanced diet is one of the well-known risk factors for the development of colorectal cancer (CRC). This type of cancer is currently the main cause of cancer-related deaths worldwide, urging the need for new and more effective preventive and therapeutic approaches. It is already known that CRC patients have alterations in the microbial community and metabolism. In this regard, a concept that has been recently attracting the attention of the scientific community is the development of functional food or nutraceuticals, as a new and more effective strategy to overcome CRC patient-associated dysbiosis. Particularly, dairy product enriched diets are the major dairy source of dietary calcium, vitamin D and folate intake, which are well-known to have a protective effect against CRC development. In addition, these products are rich in both pre- and probiotics, constituting a double strategy to modulate both the intestinal microbiota composition and the production of microbial metabolites. Short-chain fatty acids (SCFA), namely, acetate, butyrate, and propionate, are major contributors to colonic homeostasis since they regulate several biological and metabolic processes. In this review, we performed a state of art study concerning the use of dietary patterns, specifically the dairy-derived diet, in the modulation of the human microbiota and their potential use as pre-, pro- or synbiotics for the development of new preventive and therapeutic strategies for CRC.

Microbiota-derived short-chain fatty acids: Implications for cardiovascular and metabolic disease

Cardiovascular diseases (CVDs) have been on the rise around the globe in the past few decades despite the existing guidelines for prevention and treatment. Short-chain fatty acids (SCFAs) are the main metabolites of certain colonic anaerobic bacterial fermentation in the gastrointestinal tract and have been found to be the key metabolites in the host of CVDs. Accumulating evidence suggest that the end-products of SCFAs (including acetate, propionate, and butyrate) interact with CVDs through maintaining intestinal integrity, anti-inflammation, modulating glucolipid metabolism, blood pressure, and activating gut-brain axis. Recent advances suggest a promising way to prevent and treat CVDs by controlling SCFAs. Hence, this review tends to summarize the functional roles carried out by SCFAs that are reported in CVDs studies. This review also highlights several novel therapeutic interventions for SCFAs to prevent and treat CVDs.

The Therapeutic Effect of SCFA-Mediated Regulation of the Intestinal Environment on Obesity

Intestinal environment disorder is a potential pathological mechanism of obesity. There is increasing evidence that disorders in the homeostasis of the intestinal environment can affect various metabolic organs, such as fat and liver, and lead to metabolic diseases. However, there are few therapeutic approaches for obesity targeting the intestinal environment. In this review, on the one hand, we discuss how intestinal microbial metabolites SCFA regulate intestinal function to improve obesity and the possible mechanisms and pathways related to obesity-related pathological processes (depending on SCFA-related receptors such as GPCRs, MCT and SMCT, and through epigenetic processes). On the other hand, we discuss dietary management strategies to enrich SCFA-producing bacteria and target specific SCFA-producing bacteria and whether fecal bacteria transplantation therapy to restore the composition of the gut microbiota to regulate SCFA can help prevent or improve obesity. Finally, we believe that it will be of great significance to establish a working model of gut– SCFA– metabolic disease development in the future for the improvement this human health concern.

Nutrition and Physical Activity-Induced Changes in Gut Microbiota: Possible Implications for Human Health and Athletic Performance

The gut microbiota is a complex heterogeneous microbial community modulated by endogenous and exogenous factors. Among the external causes, nutrition as well as physical activity appear to be potential drivers of microbial diversity, both at the taxonomic and functional level, likely also influencing endocrine system, and acting as endocrine organ itself. To date, clear-cut data regarding which microbial populations are modified, and by which mechanisms are lacking. Moreover, the relationship between the microbial shifts and the metabolic practical potential of the gut microbiota is still unclear. Further research by longitudinal and well-designed studies is needed to investigate whether microbiome manipulation may be an effective tool for improving human health and, also, performance in athletes, and whether these effects may be then extended to the overall health promotion of general populations. In this review, we evaluate and summarize the current knowledge regarding the interaction and cross-talks among hormonal modifications, physical performance, and microbiota content and function.

Comparison of microbial diversity in rumen and small intestine of Xinong Saanen dairy goats using 16S rRNA gene high-throughput sequencing

Context Gastrointestinal microorganisms play an important role in ruminant digestion and metabolism, immune regulation and disease prevention and control. Different parts of the digestive tract have different functions and microbial community structures. Aims This study aims to explore the microbial diversity in the rumen and the small intestine of Xinong Saanen dairy goats. Methods Rumen fluid and jejunum fluid from three Xinong Saanen dairy bucks with the average slaughter weight of 33.93 ± 0.68 kg were collected and analysed for microbial diversity, by using 16S rRNA gene high-throughput sequencing. Key results In total, 1118 operational taxonomic units (OTUs) were identified, with 1020 OTUs and 649 OTUs being clustered to rumen and jejunum samples respectively. Alpha-diversity indices were significantly (P < 0.05) different between rumen and jejunum, as indicated by the fact that the rumen microbial community diversity, richness and uniformity/evenness were higher than those of jejunum. At the phylum level, the dominant phyla in the rumen were Bacteroidetes (66.7%) and Firmicutes (25.1%), accounting for 91.8% of the rumen microorganisms. The dominant phylum in the jejunum was Firmicutes, accounting for 73.0% of the jejunum microorganisms. At the genus level, the dominant bacteria in the rumen were Prevotella_1, norank_f_Bacteroidales_BS11_gut_group, Rikenellaceae_RC9_gut_group, Christensenellaceae_R-7_group and Family_XIII_AD3011_group, whereas the dominant bacteria in the jejunum were Omboutsia, Aeriscardovia, Intestinibacter, unclassified_f_Peptostreptococcaceae and unclassified_f_Bifidobacteriaceae. Clusters of Orthologous Groups (COG) and Kyoto Encyclopedia of Genes and Genomes (KEGG) results showed that the major functions of microorganisms in the rumen and jejunum were carbohydrate metabolism, amino acid metabolism, nucleotide metabolism, membrane transport and translation. Interestingly, fructose and mannose metabolism and peptidoglycan biosynthesis were abundant in the rumen, while homologous recombination and nucleotide excision repair were abundant in the jejunum. Conclusions Our study clarified the differences in microbial diversity and community structure between the rumen and the jejunum in Xinong Saanen dairy goats. Prevotella was the most predominant genus in the rumen, compared with Romboutsia, Bifidobacterium as well as Peptostreptococcaceae genera, which were the predominant genera in the jejunum. Implications In combination with the functional prediction of microorganisms and the metabolic characteristics of different parts of the digestive tract in ruminants, our findings provided information for further exploring the relationship among genes, species and functions of microorganisms and their hosts’ nutritional and physiological functions.

Short-Chain Fatty Acids as a Potential Treatment for Infections: a Closer Look at the Lungs

Short-chain fatty acids (SCFAs) are the main metabolites produced by the gut microbiota via the fermentation of complex carbohydrates and fibers. Evidence suggests that SCFAs play a role in the control of infections through direct action both on microorganisms and on host signaling. This review summarizes the main microbicidal effects of SCFAs and discusses studies highlighting the effect of SCFAs in the virulence and viability of microorganisms. We also describe the diverse and complex modes of action of the SCFAs on the immune system in the face of infections with a specific focus on bacterial and viral respiratory infections. A growing body of evidence suggests that SCFAs protect against lung infections. Finally, we present potential strategies that may be leveraged to exploit the biological properties of SCFAs for increasing effectiveness and optimizing patient benefits.

Potential Contribution of Short Chain Fatty Acids to Hepatic Apolipoprotein A-I Production

Apolipoprotein A-I (ApoA-I) is the major protein of high density lipoprotein (HDL) particles and has a crucial role in reverse cholesterol transport (RCT). It has been postulated that elevating production of de novo ApoA-I might translate into the formation of new functional HDL particles that could lower cardiovascular disease (CVD) risk via RCT. During inflammation, serum ApoA-I concentrations are reduced, which contributes to the development of dysfunctional HDL particles as Serum Amyloid A (SAA) overtakes the position of ApoA-I within the HDL particles. Therefore, instead of elevating serum HDL cholesterol concentrations, rescuing lower serum ApoA-I concentrations could be beneficial in both normal and inflamed conditions. Several nutritional compounds, amongst others short chain fatty acids (SCFAs), have shown their capacity to modulate hepatic lipoprotein metabolism. In this review we provide an overview of HDL and more specific ApoA-I metabolism, SCFAs physiology and the current knowledge regarding the influence of SCFAs on ApoA-I expression and synthesis in human liver cells. We conclude that the current evidence regarding the effect of SCFAs on ApoA-I transcription and secretion is promising, however there is a need to investigate which dietary fibres could lead to increased SCFAs formation and consequent elevated ApoA-I concentrations.

A protet-based, protonic charge transfer model of energy coupling in oxidative and photosynthetic phosphorylation

Textbooks of biochemistry will explain that the otherwise endergonic reactions of ATP synthesis can be driven by the exergonic reactions of respiratory electron transport, and that these two half-reactions are catalyzed by protein complexes embedded in the same, closed membrane. These views are correct. The textbooks also state that, according to the chemiosmotic coupling hypothesis, a (or the) kinetically and thermodynamically competent intermediate linking the two half-reactions is the electrochemical difference of protons that is in equilibrium with that between the two bulk phases that the coupling membrane serves to separate. This gradient consists of a membrane potential term Δψ and a pH gradient term ΔpH, and is known colloquially as the protonmotive force or pmf. Artificial imposition of a pmf can drive phosphorylation, but only if the pmf exceeds some 150-170mV; to achieve in vivo rates the imposed pmf must reach 200mV. The key question then is 'does the pmf generated by electron transport exceed 200mV, or even 170mV?' The possibly surprising answer, from a great many kinds of experiment and sources of evidence, including direct measurements with microelectrodes, indicates it that it does not. Observable pH changes driven by electron transport are real, and they control various processes; however, compensating ion movements restrict the Δψ component to low values. A protet-based model, that I outline here, can account for all the necessary observations, including all of those inconsistent with chemiosmotic coupling, and provides for a variety of testable hypotheses by which it might be refined.

Microbiota-derived short chain fatty acids modulate microglia and promote Aβ plaque deposition

Previous studies have identified a crucial role of the gut microbiome in modifying Alzheimer's disease (AD) progression. However, the mechanisms of microbiome-brain interaction in AD were so far unknown. Here, we identify microbiota-derived short chain fatty acids (SCFA) as microbial metabolites which promote Aβ deposition. Germ-free (GF) AD mice exhibit a substantially reduced Aβ plaque load and markedly reduced SCFA plasma concentrations; conversely, SCFA supplementation to GF AD mice increased the Aβ plaque load to levels of conventionally colonized (specific pathogen-free [SPF]) animals and SCFA supplementation to SPF mice even further exacerbated plaque load. This was accompanied by the pronounced alterations in microglial transcriptomic profile, including upregulation of ApoE. Despite increased microglial recruitment to Aβ plaques upon SCFA supplementation, microglia contained less intracellular Aβ. Taken together, our results demonstrate that microbiota-derived SCFA are critical mediators along the gut-brain axis which promote Aβ deposition likely via modulation of the microglial phenotype.

Acetate Revisited: A Key Biomolecule at the Nexus of Metabolism, Epigenetics and Oncogenesis-Part 1: Acetyl-CoA, Acetogenesis and Acyl-CoA Short-Chain Synthetases

Acetate is a major end product of bacterial fermentation of fiber in the gut. Acetate, whether derived from the diet or from fermentation in the colon, has been implicated in a range of health benefits. Acetate is also generated in and released from various tissues including the intestine and liver, and is generated within all cells by deacetylation reactions. To be utilized, all acetate, regardless of the source, must be converted to acetyl coenzyme A (acetyl-CoA), which is carried out by enzymes known as acyl-CoA short-chain synthetases. Acyl-CoA short-chain synthetase-2 (ACSS2) is present in the cytosol and nuclei of many cell types, whereas ACSS1 is mitochondrial, with greatest expression in heart, skeletal muscle, and brown adipose tissue. In addition to acting to redistribute carbon systemically like a ketone body, acetate is becoming recognized as a cellular regulatory molecule with diverse functions beyond the formation of acetyl-CoA for energy derivation and lipogenesis. Acetate acts, in part, as a metabolic sensor linking nutrient balance and cellular stress responses with gene transcription and the regulation of protein function. ACSS2 is an important task-switching component of this sensory system wherein nutrient deprivation, hypoxia and other stressors shift ACSS2 from a lipogenic role in the cytoplasm to a regulatory role in the cell nucleus. Protein acetylation is a critical post-translational modification involved in regulating cell behavior, and alterations in protein acetylation status have been linked to multiple disease states, including cancer. Improving our fundamental understanding of the "acetylome" and how acetate is generated and utilized at the subcellular level in different cell types will provide much needed insight into normal and neoplastic cellular metabolism and the epigenetic regulation of phenotypic expression under different physiological stressors. This article is Part 1 of 2 - for Part 2 see doi: 10.3389/fphys.2020.580171.

NASH, Fibrosis and Hepatocellular Carcinoma: Lipid Synthesis and Glutamine/Acetate Signaling

Primary liver cancer is predicted to be the sixth most common cancer and the fourth leading cause of cancer mortality worldwide. Recent studies identified nonalcoholic fatty liver disease (NAFLD) as the underlying cause in 13-38.2% of patients with hepatocellular carcinoma unrelated to viral hepatitis and alcohol abuse. NAFLD progresses to nonalcoholic steatohepatitis (NASH), which increases the risk for the development of liver fibrosis, cirrhosis, and hepatocellular carcinoma. NAFLD is characterized by dysregulation of lipid metabolism. In addition, lipid metabolism is effected not only in NAFLD, but also in a broad range of chronic liver diseases and tumor development. Cancer cells manipulate a variety of metabolic pathways, including lipid metabolism, in order to build up their own cellular components. Identifying tumor dependencies on lipid metabolism would provide options for novel targeting strategies. This review article summarizes the research evidence on metabolic reprogramming and focuses on lipid metabolism in NAFLD, NASH, fibrosis, and cancer. As alternative routes of acetyl-CoA production for fatty acid synthesis, topics on glutamine and acetate metabolism are included. Further, studies on small compound inhibitors targeting lipid metabolism are discussed. Understanding reprogramming strategies in liver diseases, as well as the visualization of the metabolism reprogramming networks, could uncover novel therapeutic options.

The Role of Diet Related Short-Chain Fatty Acids in Colorectal Cancer Metabolism and Survival: Prevention and Therapeutic Implications

Colorectal Cancer (CRC) is a major cause of cancer-related death worldwide. CRC increased risk has been associated with alterations in the intestinal microbiota, with decreased production of Short Chain Fatty Acids (SCFAs). SCFAs produced in the human colon are the major products of bacterial fermentation of undigested dietary fiber and starch. While colonocytes use the three major SCFAs, namely acetate, propionate and butyrate, as energy sources, transformed CRC cells primarily undergo aerobic glycolysis. Compared to normal colonocytes, CRC cells exhibit increased sensitivity to SCFAs, thus indicating they play an important role in cell homeostasis. Manipulation of SCFA levels in the intestine, through changes in microbiota, has therefore emerged as a potential preventive/therapeutic strategy for CRC. Interest in understanding SCFAs mechanism of action in CRC cells has increased in the last years. Several SCFA transporters like SMCT-1, MCT-1 and aquaporins have been identified as the main transmembrane transporters in intestinal cells. Recently, it was shown that acetate promotes plasma membrane re-localization of MCT-1 and triggers changes in the glucose metabolism. SCFAs induce apoptotic cell death in CRC cells, and further mechanisms have been discovered, including the involvement of lysosomal membrane permeabilization, associated with mitochondria dysfunction and degradation. In this review, we will discuss the current knowledge on the transport of SCFAs by CRC cells and their effects on CRC metabolism and survival. The impact of increasing SCFA production by manipulation of colon microbiota on the prevention/therapy of CRC will also be addressed.

Gut microbiota-derived short-chain fatty acids and hypertension: Mechanism and treatment

Hypertension (HTN) is an growing emerging health issue around across the world. In recent years, increasing attention has been paid to the role of dysbacteriosis in HTN and its underlying mechanism. Short-chain fatty acids (SCFAs), which are novel metabolites of intestinal flora, exert substantial regulatory effects on HTN, providing an exciting avenue for novel therapies for this disease. They function primarily by activating transmembrane G protein-coupled receptors and inhibiting histone acetylation. In this review, we discuss the mechanisms underlying the complex interaction between SCFAs and gut microbiota composition to lower blood pressure by regulating the brain-gut and kidney-gut axes, and the role of high-salt diet, immune system, oxidative stress, and inflammatory mechanism in the development of HTN. Furthermore, we also discuss the various treatment strategies for HTN, including diet, antibiotics, probiotics, fecal microflora transplantation, and traditional Chinese medicine. In conclusion, manipulation of SCFAs opens new avenues to improve treatment of HTN.

Role of SCFAs in gut microbiome and glycolysis for colorectal cancer therapy

Increased risk of colorectal cancer (CRC) is associated with altered intestinal microbiota as well as short-chain fatty acids (SCFAs) reduction of output The energy source of colon cells relies mainly on three SCFAs, namely butyrate (BT), propionate, and acetate, while CRC transformed cells rely mainly on aerobic glycolysis to provide energy. This review summarizes recent research results for dysregulated glucose metabolism of SCFAs, which could be initiated by gut microbiome of CRC. Moreover, the relationship between SCFA transporters and glycolysis, which may correlate with the initiation and progression of CRC, are also discussed. Additionally, this review explores the linkage of BT to transport of SCFAs expressions between normal and cancerous colonocyte cell growth for tumorigenesis inhibition in CRC. Furthermore, the link between gut microbiota and SCFAs in the metabolism of CRC, in addition, the proteins and genes related to SCFAs-mediated signaling pathways, coupled with their correlation with the initiation and progression of CRC are also discussed. Therefore, targeting the SCFA transporters to regulate lactate generation and export of BT, as well as applying SCFAs or gut microbiota and natural compounds for chemoprevention may be clinically useful for CRCs treatment. Future research should focus on the combination these therapeutic agents with metabolic inhibitors to effectively target the tumor SCFAs and regulate the bacterial ecology for activation of potent anticancer effect, which may provide more effective application prospect for CRC therapy.

Gut Microbiota, Short-Chain Fatty Acids, and Herbal Medicines

As an important source for traditional medical systems such as Ayurvedic medicine and traditional Chinese medicine, herbal medicines have received widespread attentions from all over the world, especially in developing countries. Over the past decade, studies on gut microbiota have generated rich information for understanding how gut microbiota shape the functioning of our body system. In view of the importance of gut microbiota, the researchers engaged in studying herbal medicines have paid more and more attention to gut microbiota and gut microbiota metabolites. Among a variety of gut microbiota metabolites, short-chain fatty acids (SCFAs) have received most attention because of their important role in maintaining the hemostasis of hosts and recovery of diseases. Herbal medicines, as an important resource provider for production of SCFAs, have been demonstrated to be able to modulate gut microbiota composition and regulate SCFAs production. In this mini-review, we summarize current knowledge about SCFAs origination, the role of SCFAs in health and disease, the influence of herbal medicine on SCFAs production and the corresponding mechanisms. At the end of this review, the strategies and suggestions for further research of SCFAs and herbal medicines are also discussed.

Reconstructing the functions of endosymbiotic Mollicutes in fungus-growing ants

Mollicutes, a widespread class of bacteria associated with animals and plants, were recently identified as abundant abdominal endosymbionts in healthy workers of attine fungus-farming leaf-cutting ants. We obtained draft genomes of the two most common strains harbored by Panamanian fungus-growing ants. Reconstructions of their functional significance showed that they are independently acquired symbionts, most likely to decompose excess arginine consistent with the farmed fungal cultivars providing this nitrogen-rich amino-acid in variable quantities. Across the attine lineages, the relative abundances of the two Mollicutes strains are associated with the substrate types that foraging workers offer to fungus gardens. One of the symbionts is specific to the leaf-cutting ants and has special genomic machinery to catabolize citrate/glucose into acetate, which appears to deliver direct metabolic energy to the ant workers. Unlike other Mollicutes associated with insect hosts, both attine ant strains have complete phage-defense systems, underlining that they are actively maintained as mutualistic symbionts.

Unhealthy gut, unhealthy brain: The role of the intestinal microbiota in neurodegenerative diseases

The number of bacterial cells living within the human body is approximately equal to, or greater than, the total number of human cells. This dynamic population of microorganisms, termed the human microbiota, resides mainly within the gastrointestinal tract. It is widely accepted that highly diverse and stable microbiota promote overall human health. Colonization of the gut with maladaptive and pathogenic microbiota, a state also known as dysbiosis, is associated with a variety of peripheral diseases ranging from type 2 diabetes mellitus to cardiovascular and inflammatory bowel disease. More recently, microbial dysbiosis has been associated with a number of brain pathologies, including autism spectrum disorder, Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS), suggesting a direct or indirect communication between intestinal bacteria and the central nervous system (CNS). In this review, we illustrate two pathways implicated in the crosstalk between gut microbiota and CNS involving 1) the vagus nerve and 2) transmission of signaling molecules through the circulatory system and across the blood-brain barrier (BBB). We summarize the available evidence of the specific changes in the intestinal microbiota, as well as microorganism-induced modifications to intestinal and BBB permeability, which have been linked to several neurodegenerative disorders including ALS, AD, and PD. Even though each of these diseases arises from unique pathogenetic mechanisms, all are characterized, at least in part, by chronic neuroinflammation. We provide an interpretation for the substantial evidence that healthy intestinal microbiota have the ability to positively regulate the neuroimmune responses in the CNS. Even though the evidence is mainly associative, it has been suggested that bacterial dysbiosis could contribute to an adverse neuroinflammatory state leading to increased risk of neurodegenerative diseases. Thus, developing strategies for regulating and maintaining healthy intestinal microbiota could be a valid approach for lowering individual risk and prevalence of neurodegenerative diseases.

In silico gene expression analysis reveals glycolysis and acetate anaplerosis in IDH1 wild-type glioma and lactate and glutamate anaplerosis in IDH1-mutated glioma

Hotspot mutations in isocitrate dehydrogenase 1 (IDH1) initiate low-grade glioma and secondary glioblastoma and induce a neomorphic activity that converts α-ketoglutarate (α-KG) to the oncometabolite D-2-hydroxyglutarate (D-2-HG). It causes metabolic rewiring that is not fully understood. We investigated the effects of IDH1 mutations (IDH1^MUT) on expression of genes that encode for metabolic enzymes by data mining The Cancer Genome Atlas. We analyzed 112 IDH1 wild-type (IDH1^WT) versus 399 IDH1^MUT low-grade glioma and 157 IDH1^WT versus 9 IDH1^MUT glioblastoma samples. In both glioma types, IDH1^WT was associated with high expression levels of genes encoding enzymes that are involved in glycolysis and acetate anaplerosis, whereas IDH1^MUT glioma overexpress genes encoding enzymes that are involved in the oxidative tricarboxylic acid (TCA) cycle. In vitro, we observed that IDH1^MUT cancer cells have a higher basal respiration compared to IDH1^WT cancer cells and inhibition of the IDH1^MUT shifts the metabolism by decreasing oxygen consumption and increasing glycolysis. Our findings indicate that IDH1^WT glioma have a typical Warburg phenotype whereas in IDH1^MUT glioma the TCA cycle, rather than glycolytic lactate production, is the predominant metabolic pathway. Our data further suggest that the TCA in IDH1^MUT glioma is driven by lactate and glutamate anaplerosis to facilitate production of α-KG, and ultimately D-2-HG. This metabolic rewiring may be a basis for novel therapies for IDH1^MUT and IDH1^WT glioma.

A look at the smelly side of physiology: transport of short chain fatty acids

Fermentative organs such as the caecum, the colon, and the rumen have evolved to produce and absorb energy rich short chain fatty acids (SCFA) from otherwise indigestible substrates. Classical models postulate diffusional uptake of the undissociated acid (HSCFA). However, in net terms, a major part of SCFA absorption occurs with uptake of Na⁺ and resembles classical, coupled electroneutral NaCl transport. Considerable evidence suggests that the anion transporting proteins expressed by epithelia of fermentative organs are poorly selective and that their main function may be to transport acetate^-, propionate^-, butyrate^- and HCO₃^- as the physiologically relevant anions. Apical uptake of SCFA thus involves non-saturable diffusion of the undissociated acid (HSCFA), SCFA^-/HCO₃^- exchange via DRA (SLC26A3) and/or SCFA^--H⁺ symport (MCT1, SLC16A1). All mechanisms lead to cytosolic acidification with stimulation of Na⁺/H⁺ exchange via NHE (SLC9A2/3). Basolaterally, Na⁺ leaves via the Na⁺/K⁺-ATPase with recirculation of K⁺. Na⁺ efflux drives the transport of SCFA^- anions through volume-regulated anion channels, such as maxi-anion channels (possibly SLCO2A1), LRRC8, anoctamins, or uncoupled exchangers. When luminal buffering is inadequate, basolateral efflux will increasingly involve SCFA^-/ HCO₃^- exchange (AE1/2, SCL4A1/2), or efflux of SCFA^- with H⁺ (MCT1/4, SLC16A1/3). Furthermore, protons can be basolaterally removed by NHE1 (SCL9A1) or NBCe1 (SLC4A4). The purpose of these transport proteins is to maximize the amount of SCFA transported from the tightly buffered ingesta while minimizing acid transport through the epithelium. As known from the rumen for many decades, a disturbance of these processes is likely to cause severe colonic disease.

Lipid Metabolism and Lipid Droplets in Pancreatic Cancer and Stellate Cells

Pancreatic ductal adenocarcinoma (PDAC) is projected to become the second deadliest cancer by 2030, and the overall 5-year survival rate is currently less than 7%. Cancer cells frequently exhibit reprogramming of their metabolic activity. It is increasingly recognized that aberrant de novo lipid synthesis and reprogrammed lipid metabolism are both associated with the development and progression of various cancers, including pancreatic cancer. In this review, the current knowledge about lipid metabolism and lipid droplets in pancreatic cancer is discussed. In the first part, molecular mechanisms of lipid metabolism and roles of enzymes involved in lipid metabolism which are relevant for pancreatic cancer research are presented. Further, preclinical studies and clinical trials with drugs/inhibitors targeting cancer metabolic systems in cancer are summarized. An increase of our knowledge in lipid metabolism in pancreatic cancer cells and in tumor stroma is important for developing novel strategies of future individualized therapies of pancreatic cancer.

Is cytotoxicity a determinant of the different in vitro and in vivo effects of bioactives?

BACKGROUND

Foodstuffs of both plant and animal origin contain a wide range of bioactive compounds. Although human intervention studies are mandatory to assess the health effects of bioactives, the in vitro approach is often used to select the most promising molecules to be studied in vivo. To avoid misleading results, concentration and chemical form, exposure time, and potential cytotoxicity of the tested bioactives should be carefully set prior to any other experiments.

METHODS

In this study the possible cytotoxicity of different bioactives (docosahexaenoic acid, propionate, cyanidin-3-O-glucoside, protocatechuic acid), was investigated in HepG2 cells using different methods. Bioactives were supplemented to cells at different concentrations within the physiological range in human blood, alone or in combination, considering two different exposure times.

RESULTS

Reported data clearly evidence that in vitro cytotoxicity is tightly related to the exposure time, and it varies among bioactives, which could exert a cytotoxic effect even at a concentration within the in vivo physiological blood concentration range. Furthermore, co-supplementation of different bioactives can increase the cytotoxic effect.

CONCLUSIONS

Our results underline the importance of in vitro cytotoxicity screening that should be considered mandatory before performing studies aimed to evaluate the effect of bioactives on other cellular parameters. Although this study is far from the demonstration of a toxic effect of the tested bioactives when administered to humans, it represents a starting point for future research aimed at verifying the existence of a potential hazard due to the wide use of high doses of multiple bioactives.

The metabolic fate of acetate in cancer

Recent high-profile reports have reignited an interest in acetate metabolism in cancer. Acetyl-CoA synthetases that catalyse the conversion of acetate to acetyl-CoA have now been implicated in the growth of hepatocellular carcinoma, glioblastoma, breast cancer and prostate cancer. In this Review, we discuss how acetate functions as a nutritional source for tumours and as a regulator of cancer cell stress, and how preventing its (re)capture by cancer cells may provide an opportunity for therapeutic intervention.

Characterization of acetate transport in colorectal cancer cells and potential therapeutic implications

Acetate, together with other short chain fatty acids has been implicated in colorectal cancer (CRC) prevention/therapy. Acetate was shown to induce apoptosis in CRC cells. The precise mechanism underlying acetate transport across CRC cells membrane, that may be implicated in its selectivity towards CRC cells, is not fully understood and was addressed here. We also assessed the effect of acetate in CRC glycolytic metabolism and explored its use in combination with the glycolytic inhibitor 3-bromopyruvate (3BP). We provide evidence that acetate enters CRC cells by the secondary active transporters MCT1 and/or MCT2 and SMCT1 as well as by facilitated diffusion via aquaporins. CRC cell exposure to acetate upregulates the expression of MCT1, MCT4 and CD147, while promoting MCT1 plasma membrane localization. We also observed that acetate increases CRC cell glycolytic phenotype and that acetate-induced apoptosis and anti-proliferative effect was potentiated by 3BP. Our data suggest that acetate selectivity towards CRC cells might be explained by the fact that aquaporins and MCTs are found overexpressed in CRC clinical cases. Our work highlights the importance that acetate transport regulation has in the use of drugs such as 3BP as a new therapeutic strategy for CRC.

Short-chain fatty acids in control of body weight and insulin sensitivity

The connection between the gut microbiota and the aetiology of obesity and cardiometabolic disorders is increasingly being recognized by clinicians. Our gut microbiota might affect the cardiometabolic phenotype by fermenting indigestible dietary components and thereby producing short-chain fatty acids (SCFA). These SCFA are not only of importance in gut health and as signalling molecules, but might also enter the systemic circulation and directly affect metabolism or the function of peripheral tissues. In this Review, we discuss the effects of three SCFA (acetate, propionate and butyrate) on energy homeostasis and metabolism, as well as how these SCFA can beneficially modulate adipose tissue, skeletal muscle and liver tissue function. As a result, these SCFA contribute to improved glucose homeostasis and insulin sensitivity. Furthermore, we also summarize the increasing evidence for a potential role of SCFA as metabolic targets to prevent and counteract obesity and its associated disorders in glucose metabolism and insulin resistance. However, most data are derived from animal and in vitro studies, and consequently the importance of SCFA and differential SCFA availability in human energy and substrate metabolism remains to be fully established. Well-controlled human intervention studies investigating the role of SCFA on cardiometabolic health are, therefore, eagerly awaited.

Synthetic biology for the directed evolution of protein biocatalysts: navigating sequence space intelligently

The amino acid sequence of a protein affects both its structure and its function. Thus, the ability to modify the sequence, and hence the structure and activity, of individual proteins in a systematic way, opens up many opportunities, both scientifically and (as we focus on here) for exploitation in biocatalysis. Modern methods of synthetic biology, whereby increasingly large sequences of DNA can be synthesised de novo, allow an unprecedented ability to engineer proteins with novel functions. However, the number of possible proteins is far too large to test individually, so we need means for navigating the 'search space' of possible protein sequences efficiently and reliably in order to find desirable activities and other properties. Enzymologists distinguish binding (Kd) and catalytic (kcat) steps. In a similar way, judicious strategies have blended design (for binding, specificity and active site modelling) with the more empirical methods of classical directed evolution (DE) for improving kcat (where natural evolution rarely seeks the highest values), especially with regard to residues distant from the active site and where the functional linkages underpinning enzyme dynamics are both unknown and hard to predict. Epistasis (where the 'best' amino acid at one site depends on that or those at others) is a notable feature of directed evolution. The aim of this review is to highlight some of the approaches that are being developed to allow us to use directed evolution to improve enzyme properties, often dramatically. We note that directed evolution differs in a number of ways from natural evolution, including in particular the available mechanisms and the likely selection pressures. Thus, we stress the opportunities afforded by techniques that enable one to map sequence to (structure and) activity in silico, as an effective means of modelling and exploring protein landscapes. Because known landscapes may be assessed and reasoned about as a whole, simultaneously, this offers opportunities for protein improvement not readily available to natural evolution on rapid timescales. Intelligent landscape navigation, informed by sequence-activity relationships and coupled to the emerging methods of synthetic biology, offers scope for the development of novel biocatalysts that are both highly active and robust.

Disturbance of energy and redox homeostasis and reduction of Na+,K+-ATPase activity provoked by in vivo intracerebral administration of ethylmalonic acid to young rats

Ethylmalonic acid (EMA) accumulation occurs in various metabolic diseases with neurological manifestation, including short acyl-CoA dehydrogenase deficiency (SCADD) and ethylmalonic encephalopathy (EE). Since pathophysiological mechanisms responsible for brain damage in these disorders are still poorly understood, we investigated the ex vivo effects of acute intrastriatal administration of EMA on important parameters of energy and redox homeostasis in striatum from young rats. We evaluated CO(2) production from glucose, glucose utilization and lactate production, as well as the activities of the citric acid cycle (CAC) enzymes, the electron transfer chain (ETC) complexes II-IV (oxidative phosphorylation, OXPHOS) and synaptic Na(+),K(+)-ATPase. We also tested the effect of EMA on malondialdehyde (MDA) levels (marker of lipid oxidation) and reduced glutathione (GSH) levels. EMA significantly reduced CO(2) production, increased glucose utilization and lactate production, and reduced the activities of citrate synthase and of complexes II and II-III of the ETC, suggesting an impairment of CAC and OXPHOS. EMA injection also reduced Na(+),K(+)-ATPase activity and GSH concentrations, whereas MDA levels were increased. Furthermore, EMA-induced diminution of Na(+),K(+)-ATPase activity and reduction of GSH levels were prevented, respectively, by the antioxidants melatonin and N-acetylcysteine, indicating that reactive species were involved in these effects. Considering the importance of CAC and ETC for energy production and Na(+),K(+)-ATPase for the maintenance of the cell membrane potential, the present data indicate that EMA compromises mitochondrial homeostasis and neurotransmission in striatum. We presume that these pathomechanisms may be involved to a certain extent in the neurological damage found in patients affected by SCADD and EE.

Monocarboxylate transporters 1 and 4: expression and regulation by PPARα in ovine ruminal epithelial cells

In the intact rumen epithelium, isoforms 1 and 4 of the monocarboxylate transporter (MCT1 and MCT4) are thought to play key roles in mediating transcellular and intracellular permeation of short-chain fatty acids and their metabolites and in maintaining intracellular pH. We examined whether both MCT1 and MCT4 are expressed at mRNA and protein levels in ovine ruminal epithelial cells (REC) maintained in primary culture and whether they are regulated by peroxisome proliferator-activated receptor-α (PPARα). Because both transporters have been characterized to function coupled to protons, the influence of PPARα on the recovery of intracellular pH after l-lactate exposure was evaluated by spectrofluorometry. MCT1 and MCT4 were detected using immunocytochemistry both at the cell margins and intracellularly in cultured REC. To test regulation by PPARα, cells were exposed to WY 14.643, a selective ligand of PPARα, for 48 h. The subsequent qPCR analysis resulted in a dose-dependent upregulation of MCT1 and PPARα target genes, whereas response of MCT4 was not uniform. Protein expression of MCT1 and MCT4 quantified by Western blot analysis was not altered by WY 14.643 treatment. l-Lactate-dependent proton export was blocked almost completely by pHMB, a specific inhibitor of MCT1 and MCT4. However, l-lactate-dependent, pHMB-inhibited proton export in WY 14.643-treated cells was not significantly altered compared with cells not treated with WY 14.643. These data suggest that PPARα is particularly regulating MCT1 but not MCT4 expression. Extent of lactate-coupled proton export indicates that MCT1 is already working on a high level even under unstimulated conditions.

Tissue-specific expression of monocarboxylate transporters during fasting in mice

Monocarboxylates such as pyruvate, lactate and ketone bodies are crucial for energy supply of all tissues, especially during energy restriction. The transport of monocarboxylates across the plasma membrane of cells is mediated by monocarboxylate transporters (MCTs). Out of 14 known mammalian MCTs, six isoforms have been functionally characterized to transport monocarboxylates and short chain fatty acids (MCT1-4), thyroid hormones (MCT8, -10) and aromatic amino acids (MCT10). Knowledge on the regulation of the different MCT isoforms is rare. In an attempt to get more insights in regulation of MCT expression upon energy deprivation, we carried out a comprehensive analysis of tissue specific expression of five MCT isoforms upon 48 h of fasting in mice. Due to the crucial role of peroxisome proliferator-activated receptor (PPAR)-α as a central regulator of energy metabolism and as known regulator of MCT1 expression, we included both wildtype (WT) and PPARα knockout (KO) mice in our study. Liver, kidney, heart, small intestine, hypothalamus, pituitary gland and thyroid gland of the mice were analyzed. Here we show that the expression of all examined MCT isoforms was markedly altered by fasting compared to feeding. Expression of MCT1, MCT2 and MCT10 was either increased or decreased by fasting dependent on the analyzed tissue. MCT4 and MCT8 were down-regulated by fasting in all examined tissues. However, PPARα appeared to have a minor impact on MCT isoform regulation. Due to the fundamental role of MCTs in transport of energy providing metabolites and hormones involved in the regulation of energy homeostasis, we assumed that the observed fasting-induced adaptations of MCT expression seem to ensure an adequate energy supply of tissues during the fasting state. Since, MCT isoforms 1–4 are also necessary for the cellular uptake of drugs, the fasting-induced modifications of MCT expression have to be considered in future clinical care algorithms.

How drugs get into cells: tested and testable predictions to help discriminate between transporter-mediated uptake and lipoidal bilayer diffusion

One approach to experimental science involves creating hypotheses, then testing them by varying one or more independent variables, and assessing the effects of this variation on the processes of interest. We use this strategy to compare the intellectual status and available evidence for two models or views of mechanisms of transmembrane drug transport into intact biological cells. One (BDII) asserts that lipoidal phospholipid Bilayer Diffusion Is Important, while a second (PBIN) proposes that in normal intact cells Phospholipid Bilayer diffusion Is Negligible (i.e., may be neglected quantitatively), because evolution selected against it, and with transmembrane drug transport being effected by genetically encoded proteinaceous carriers or pores, whose “natural” biological roles, and substrates are based in intermediary metabolism. Despite a recent review elsewhere, we can find no evidence able to support BDII as we can find no experiments in intact cells in which phospholipid bilayer diffusion was either varied independently or measured directly (although there are many papers where it was inferred by seeing a covariation of other dependent variables). By contrast, we find an abundance of evidence showing cases in which changes in the activities of named and genetically identified transporters led to measurable changes in the rate or extent of drug uptake. PBIN also has considerable predictive power, and accounts readily for the large differences in drug uptake between tissues, cells and species, in accounting for the metabolite-likeness of marketed drugs, in pharmacogenomics, and in providing a straightforward explanation for the late-stage appearance of toxicity and of lack of efficacy during drug discovery programmes despite macroscopically adequate pharmacokinetics. Consequently, the view that Phospholipid Bilayer diffusion Is Negligible (PBIN) provides a starting hypothesis for assessing cellular drug uptake that is much better supported by the available evidence, and is both more productive and more predictive.

Transendothelial Transport and Its Role in Therapeutics

Present review paper highlights role of BBB in endothelial transport of various substances into the brain. More specifically, permeability functions of BBB in transendothelial transport of various substances such as metabolic fuels, ethanol, amino acids, proteins, peptides, lipids, vitamins, neurotransmitters, monocarbxylic acids, gases, water, and minerals in the peripheral circulation and into the brain have been widely explained. In addition, roles of various receptors, ATP powered pumps, channels, and transporters in transport of vital molecules in maintenance of homeostasis and normal body functions have been described in detail. Major role of integral membrane proteins, carriers, or transporters in drug transport is highlighted. Both diffusion and carrier mediated transport mechanisms which facilitate molecular trafficking through transcellular route to maintain influx and outflux of important nutrients and metabolic substances are elucidated. Present review paper aims to emphasize role of important transport systems with their recent advancements in CNS protection mainly for providing a rapid clinical aid to patients. This review also suggests requirement of new well-designed therapeutic strategies mainly potential techniques, appropriate drug formulations, and new transport systems for quick, easy, and safe delivery of drugs across blood brain barrier to save the life of tumor and virus infected patients.

Focal thalamic degeneration from ethanol and thiamine deficiency is associated with neuroimmune gene induction, microglial activation, and lack of monocarboxylic acid transporters

Background

Wernicke's encephalopathy-Korsakoff syndrome (WE-KS) is common in alcoholics, caused by thiamine deficiency (TD; vitamin B1) and associated with lesions to the thalamus (THAL). Although TD alone can cause WE, the high incidence in alcoholism suggests that TD and ethanol (EtOH) interact.

Methods

Mice in control, TD, or EtOH groups alone or combined were studied after 5 or 10 days of treatment. THAL and entorhinal cortex (ENT) histochemistry and mRNA were assessed.

Results

Combined EtOH-TD treatment for 5 days (EtOH-TD5) showed activated microglia, proinflammatory gene induction and THAL neurodegeneration that was greater than that found with TD alone (TD5), whereas 10 days resulted in marked THAL degeneration and microglial-neuroimmune activation in both groups. In contrast, 10 days of TD did not cause ENT degeneration. Interestingly, in ENT, TD10 activated microglia and astrocytes more than EtOH-TD10. In THAL, multiple astrocytic markers were lost consistent with glial cell loss. TD blocks glucose metabolism more than acetate. Acetate derived from hepatic EtOH metabolism is transported by monocarboxylic acid transporters (MCT) into both neurons and astrocytes that use acetyl-CoA synthetase (AcCoAS) to generate cellular energy from acetate. MCT and AcCoAS expression in THAL is lower than ENT prompting the hypothesis that focal THAL degeneration is related to insufficient MCT and AcCoAS in THAL. To test this hypothesis, we administered glycerin triacetate (GTA) to increase blood acetate and found it protected the THAL from TD-induced degeneration.

Conclusions

Our findings suggest that EtOH potentiates TD-induced THAL degeneration through neuroimmune gene induction. The findings support the hypothesis that TD deficiency inhibits global glucose metabolism and that a reduced ability to process acetate for cellular energy results in THAL focal degeneration in alcoholics contributing to the high incidence of Wernicke-Korsakoff syndrome in alcoholism.

Formaldehyde in brain: an overlooked player in neurodegeneration?

Formaldehyde is an environmental pollutant that is also generated in substantial amounts in the human body during normal metabolism. This aldehyde is a well-established neurotoxin that affects memory, learning, and behavior. In addition, in several pathological conditions, including Alzheimer's disease, an increase in the expression of formaldehyde-generating enzymes and elevated levels of formaldehyde in brain have been reported. This article gives an overview on the current knowledge on the generation and metabolism of formaldehyde in brain cells as well as on formaldehyde-induced alterations in metabolic processes. Brain cells have the potential to generate and to dispose formaldehyde. In culture, both astrocytes and neurons efficiently oxidize formaldehyde to formate which can be exported or further oxidized. Although moderate concentrations of formaldehyde are not acutely toxic for brain cells, exposure to formaldehyde severely affects their metabolism as demonstrated by the formaldehyde-induced acceleration of glycolytic flux and by the rapid multidrug resistance protein 1-mediated export of glutathione from both astrocytes and neurons. These formaldehyde-induced alterations in the metabolism of brain cells may contribute to the impaired cognitive performance observed after formaldehyde exposure and to the neurodegeneration in diseases that are associated with increased formaldehyde levels in brain.

Role of monocarboxylate transporters in drug delivery to the brain

Monocarboxylate transporters (MCTs) are known to mediate the transport of short chain monocarboxylates such as lactate, pyruvate and butyrate. Currently, fourteen members of this transporter family have been identified by sequence homology, of which only the first four members (MCT1- MCT4) have been shown to mediate the proton-linked transport of monocarboxylates. Another transporter family involved in the transport of endogenous monocarboxylates is the sodium coupled MCTs (SMCTs). These act as a symporter and are dependent on a sodium gradient for their functional activity. MCT1 is the predominant transporter among the MCT isoforms and is present in almost all tissues including kidney, intestine, liver, heart, skeletal muscle and brain. The various isoforms differ in terms of their substrate specificity and tissue localization. Due to the expression of these transporters in the kidney, intestine, and brain, they may play an important role in influencing drug disposition. Apart from endogenous short chain monocarboxylates, they also mediate the transport of exogenous drugs such as salicylic acid, valproic acid, and simvastatin acid. The influence of MCTs on drug pharmacokinetics has been extensively studied for γ-hydroxybutyrate (GHB) including distribution of this drug of abuse into the brain and the results will be summarized in this review. The physiological role of these transporters in the brain and their specific cellular localization within the brain will also be discussed. This review will also focus on utilization of MCTs as potential targets for drug delivery into the brain including their role in the treatment of malignant brain tumors.

Short chain fatty acids and their receptors: new metabolic targets

Fatty acids are carboxylic acids with aliphatic tails of different lengths, where short chain fatty acids (SCFAs) typically refer to carboxylic acids with aliphatic tails less than 6 carbons. In humans, SCFAs are derived in large part from fermentation of carbohydrates and proteins in the colon. By this process, the host is able to salvage energy from foods that cannot be processed normally in the upper parts of the gastrointestinal tract. In humans, SCFAs are a minor nutrient source, especially for people on Western diets. Intriguingly, recent studies, as highlighted here, have described multiple beneficial roles of SCFAs in the regulation of metabolism. Further interest in SCFAs has emerged due to the association of gut flora composition with obesity and other metabolic states. The recent identification of receptors specifically activated by SCFAs has further increased interest in this area. These receptors, free fatty acid receptor-2 and -3 (FFAR2 and FFAR3), are expressed not only in the gut epithelium where SCFAs are produced, but also at multiple other sites considered to be metabolically important, such as adipose tissue and pancreatic islets. Because of these relatively recent findings, studies examining the role of these receptors, FFAR2 and FFAR3, and their ligands, SCFAs, in metabolism are emerging. This review provides a critical analysis of SCFAs, their recently identified receptors, and their connection to metabolism.