Robert K. Crane-Na(+)-glucose cotransporter to cure?

A Story of Serendipities: From Phlorizin to Gliflozins

Diabetes has been acknowledged since ancient times. However, it was only during the late 1800s that we realized that the primary organ for blood glucose regulation was the pancreas. The 20th century witnessed insulin purification, which revolutionized the treatment of diabetes maigre; this was followed by the development of oral antidiabetic drugs. The sodium-glucose cotransporter 2 inhibitors or gliflozins are the latest class. Unique cardio- and renoprotective effects separate them from other oral antidiabetic drugs. Here, we present the history behind the development of these inhibitors, arguably the hottest and the most pleasant topic in nephrology. The first serendipity was Koninck and Stas (assistants to Prof. Van Mons, a renowned pomology expert); these researchers isolated a crystalline glycoside called phloridzin (phlorizin) from the bark of apple trees while working at their boss's nursery. Their discovery was published in German in 1835. The second serendipity, after a half century, was from Prof. von Mering, who decided to administer phlorizin to dogs. Oskar Minkowski initially observed polyuria than glucosuria. Insightfully, von Mering postulated that phlorizin affects kidneys. In 1887, they reported that phlorizin induced glucosuria in people with diabetes. The third serendipity was that phlorizin causes several gastrointestinal side effects and has poor oral bioavailability. The first phlorizin-based drug to enter trials was T-1095. The first clinically available gliflozin was dapagliflozin, receiving approval in Europe and the United States in 2012 and 2014, respectively. The 2015 EMPA-REG Outcome trial reported extremely satisfying results that no one expected. Subsequent trials and real-world data have resulted in changes in all impactful guidelines. The impact of these agents on heart failure and chronic kidney disease seems independent of their antidiabetic properties. More than 100 years after von Mering's original discovery, descendants of phlorizin are fast becoming the most inspiring medicine for the 21st century physician.

Falsehoods and facts about dietary sugars: a call for evidence-based policy

Sugar, tobacco, and alcohol have been demonized since the seventeenth century. Yet unlike tobacco and alcohol, there is indisputable scientific evidence that dietary sugars were essential for human evolution and are essential for human health and development. Therefore, the purpose of this analytic review and commentary is to demonstrate that anti-sugar rhetoric is divorced from established scientific facts and has led to politically expedient but ill-informed policies reminiscent of those enacted about alcohol a century ago in the United States. Herein, we present a large body of interdisciplinary research to illuminate several misconceptions, falsehoods, and facts about dietary sugars. We argue that anti-sugar policies and recommendations are not merely unscientific but are regressive and unjust because they harm the most vulnerable members of our society while providing no personal or public health benefits.

Astrocytes and neurons communicate via a monocarboxylic acid shuttle

Since formulation of the Astrocyte-Neuron Lactate Shuttle (ANLS) hypothesis in 1994, the hypothesis has provoked criticism and debate. Our review does not criticise, but rather integrates experimental data characterizing proton-linked monocarboxylate transporters (MCTs) into the ANLS. MCTs have wide substrate specificity and are discussed to be in protein complex with a proton donor (PD). We particularly focus on the proton-driven transfer of l-lactic acid (l-lacH) and pyruvic acid (pyrH), were PDs link MCTs to a flow of energy. The precise nature of the PD predicts the activity and catalytic direction of MCTs. By doing so, we postulate that the MCT4·phosphoglycerate kinase complex exports and at the same time in the same astrocyte, MCT1·carbonic anhydrase II complex imports monocarboxylic acids. Similarly, neuronal MCT2 preferentially imports pyrH. The repertoire of MCTs in astrocytes and neurons allows them to communicate via monocarboxylic acids. A change in imported pyrH/l-lacH ratio in favour of l-lacH encodes signals stabilizing the transit of glucose from astrocytes to neurons. The presented astrocyte neuron communication hypothesis has the potential to unite the community by suggesting that the exchange of monocarboxylic acids paves the path of glucose provision.

Consumption of a Natural High-Intensity Sweetener Enhances Activity and Expression of Rabbit Intestinal Na+/Glucose Cotransporter 1 (SGLT1) and Improves Colibacillosis-Induced Enteric Disorders

Absorption of glucose, via intestinal Na⁺/glucose cotransporter 1 (SGLT1), activates salt and water absorption and is an effective route for treating Escherichia coli (E. coli)-induced diarrhea. Activity and expression of SGLT1 is regulated by sensing of sugars and artificial/natural sweeteners by the intestinal sweet receptor T1R2-T1R3 expressed in enteroendocrine cells. Diarrhea, caused by the bacterial pathogen E. coli, is the most common post-weaning clinical feature in rabbits, leading to mortality. We demonstrate here that, in rabbits with experimentally E. coli-induced diarrhea, inclusion of a supplement containing stevia leaf extract (SL) in the feed decreases cumulative morbidity, improving clinical signs of disease (p < 0.01). We show that the rabbit intestine expresses T1R2-T1R3. Furthermore, intake of SL enhances activity and expression of SGLT1 and the intestinal capacity to absorb glucose (1.8-fold increase, p < 0.05). Thus, a natural plant extract sweetener can act as an effective feed additive for lessening the negative impact of enteric diseases in animals.

Burden of typhoid fever and cholera: similarities and differences. Prevention strategies for European travelers to endemic/epidemic areas

The burden of diarrheal diseases is very high, accounting for 1.7 to 5 billion cases per year worldwide. Typhoid fever (TF) and cholera are potentially life-threatening infectious diseases, and are mainly transmitted through the consumption of food, drink or water that have been contaminated by the feces or urine of subjects excreting the pathogen. TF is mainly caused by Salmonella typhi, whereas cholera is caused by intestinal infection by the toxin-producing bacterium Vibrio cholerae. These diseases typically affect low- and middle-income countries where housing is overcrowded and water and sanitation are poor, or where conflicts or natural disasters have led to the collapse of the water, sanitation and healthcare systems. Mortality is higher in children under 5 years of age. Regarding their geographical distribution, TF has a high incidence in sub-Saharan Africa, India and south-east Asia, while cholera has a high incidence in a few African countries, particularly in the Horn of Africa and the Arabian Peninsula. In the fight against these diseases, preventive measures are fundamental. With modern air travel, transmissible diseases can spread across continents and oceans in a few days, constituting a threat to global public health. Nowadays, people travel for many reasons, such as tourism and business. Several surveys have shown that a high proportion of travelers lack adequate information on safety issues, such as timely vaccination and prophylactic medications. The main objective of this overview is to provide information to help European travelers to stay healthy while abroad, and thus also to reduce the potential importation of these diseases and their consequent implications for public health and society. The preventive measures to be implemented in the case of travel to countries where these diseases are still endemic are well known: the adoption of safe practices and vaccinations. It is important to stress that an effective preventive strategy should be based both on vaccinations and on hygiene travel guidelines. Furthermore, the emergence of multidrug-resistant strains is becoming a serious problem in the clinical treatment of these diseases. For this reason, vaccination is the main solution.

Nutritional Peak Week and Competition Day Strategies of Competitive Natural Bodybuilders

Bodybuilders utilize peaking strategies in a bid to fine-tune their aesthetics for competition day. The most prevalent peaking strategies utilized by natural bodybuilders are unreported in the current literature. Eighty-one (M-59, F-22) natural bodybuilders were recruited from competitions during the 2016 and 2017 British Natural Bodybuilder Federation seasons. Competitors completed a 34-item questionnaire designed to investigate peaking and contest day strategies. The questionnaire listed commonly utilized peaking strategies and provided additional space for qualitative information. Analysis of the data indicated that carbohydrate (CHO), water, and sodium manipulation were the most commonly utilized peaking strategies. The consumption of high glycemic index CHO was the most common competition day strategy. Only 6.2% of competitors reported following their regular diet the week prior to competition. The CHO manipulation strategies followed were similar to classical CHO loading, whereby bodybuilders attempt to maximize muscle glycogen concentrations. Furthermore, bodybuilders attempted to remove superfluous water by exploiting the diuretic/polyuria effect associated with water loading/restriction. The potentially deleterious effects of peaking on bodybuilders' health is considered and the efficacy of these strategies to enhance appearance is discussed. The findings of the present investigation are likely to be of interest to bodybuilders and their coaches.

Pathophysiology of IBD associated diarrhea

Inflammatory bowel diseases broadly categorized into Crohn's disease (CD) and ulcerative colitis (UC), are chronic inflammatory disorders of the gastrointestinal tract with increasing prevalence worldwide. The etiology of the disease is complex and involves a combination of genetic, environmental, immunological and gut microbial factors. Recurring and bloody diarrhea is the most prevalent and debilitating symptom in IBD. The pathogenesis of IBD-associated diarrhea is multifactorial and is essentially an outcome of mucosal damage caused by persistent inflammation resulting in dysregulated intestinal ion transport, impaired epithelial barrier function and increased accessibility of the pathogens to the intestinal mucosa. Altered expression and/or function of epithelial ion transporters and channels is the principle cause of electrolyte retention and water accumulation in the intestinal lumen leading to diarrhea in IBD. Aberrant barrier function further contributes to diarrhea via leak-flux mechanism. Mucosal penetration of enteric pathogens promotes dysbiosis and exacerbates the underlying immune system further perpetuating IBD associated-tissue damage and diarrhea. Here, we review the mechanisms of impaired ion transport and loss of epithelial barrier function contributing to diarrhea associated with IBD.

Inability to reduce morbidity of diarrhea by ORS: can we design a better therapy?

Diarrheal disease is a worldwide problem that still causes significant morbidity and mortality among children. Currently, oral rehydration solution (ORS) is the standard of care for acute diarrhea in pediatric patients. Although effective in reducing mortality, ORS does not alleviate diarrheal symptoms, thus reducing caregiver compliance and therapeutic efficacy. This article will briefly review the current problem of pediatric diarrhea and the shortcomings of current therapies; however, the focus of this review is to examine the intestinal calcium-sensing receptor (CaSR). The author summarizes the evidence suggesting that targeting the CaSR will enable clinicians to address all four major pathophysiological mechanisms of diarrheal disease, and substantiates the need for future research regarding this therapy.

Molecular mechanism of regulation of villus cell Na-K-ATPase in the chronically inflamed mammalian small intestine

Na-K-ATPase located on the basolateral membrane (BLM) of intestinal epithelial cells provides a favorable intracellular Na+ gradient to promote all Na dependent co-transport processes across the brush border membrane (BBM). Down-regulation of Na-K-ATPase activity has been postulated to alter the absorption via Na-solute co-transporters in human inflammatory bowel disease (IBD). Further, the altered activity of a variety of Na-solute co-transporters in intact villus cells has been reported in animal models of chronic enteritis. But the molecular mechanism of down-regulation of Na-K-ATPase is not known. In the present study, using a rabbit model of chronic intestinal inflammation, which resembles human IBD, Na-K-ATPase in villus cells was shown to decrease. The relative mRNA abundance of α-1 and β-1 subunits was not altered in villus cells during chronic intestinal inflammation. Similarly, the protein levels of these subunits were also not altered in villus cells during chronic enteritis. However, the BLM concentration of α-1 and β-1 subunits was diminished in the chronically inflamed intestinal villus cells. An ankyrin-spectrin skeleton is necessary for the proper trafficking of Na-K-ATPase to the BLM of the cell. In the present study, ankyrin expression was markedly diminished in villus cells from the chronically inflamed intestine resulting in depolarization of ankyrin-G protein. The decrease of Na-K-ATPase activity was comparable to that seen in ankyrin knockdown IEC-18 cells. Therefore, altered localization of Na-K-ATPase as a result of transcriptional down-regulation of ankyrin-G mediates the down-regulation of Na-K-ATPase activity during chronic intestinal inflammation.

Glucose transport into everted sacs of the small intestine of mice

The Na(+)-glucose cotransporter is a key transport protein that is responsible for absorbing Na(+) and glucose from the luminal contents of the small intestine and reabsorption by the proximal straight tubule of the nephron. Robert K. Crane originally described the cellular model of absorption of Na(+) and glucose by a "cotransport process" in 1960. Over the past 50+ yr, numerous groups have tested and verified Crane's hypothesis. Eventually, Wright and colleagues cloned the Na(+)-glucose cotransporter (SGLT1; the product of the SLC5A1 gene) in 1987. This article provides a "hands-on" laboratory exercise using the everted mouse jejunal preparation (everted sac) that allows students to investigate various components of the Na(+)-glucose cotransport absorptive cell model (e.g., Na(+) dependence of SGLT1, inhibition of SGLT1, and inhibition of Na(+)-K(+)-ATPase). Additionally, the laboratory exercise includes a case-based study of glucose-galactose malabsorption in which the students conduct an internet search and participate in a small-group discussion during the laboratory period to better understand the basic principles and functions of the Na(+)-glucose absorptive process of the small intestine. This laboratory exercise was introduced into the second-year undergraduate physiology curriculum in 2008, and >850 physiology students have participated in this laboratory exercise. The students have produced very robust and reproducible data that clearly illustrate the theory of the cellular model for Na(+)-glucose absorption by the jejunum.