Metabolic flux and catabolic kinetics of prebiotic-like dietary polyphenol phlorizin in association with gut microbiota in vitro

As ubiquitous components among fruits, polyphenols, including flavonoids and phenolic acids, are somewhat embarrassed on their health benefits but low bioavailability, triggering a hotspot on their interaction with microbiota. Due to its structural characteristics similar to flavonoids and phenolic acids, dihydrochalcone phlorizin (PHZ) was selected as a reference, to illustrate its step-by-step metabolic fate associated with microbiota. The results confirmed that the metabolic flux of PHZ starts with its conversion to phloretin (PHT), sequentially followed by the formation of 3-(4-hydroxyphenyl) propionic acid (PHA), and 4-hydroxyphenylacetic acid (4-HPAA). Catabolic characteristics was comparatively elucidated by introducing apparent and potential kinetics. Besides, coupling catabolic processes with microbial changes suggested several potential bacteria involving in PHZ metabolism, as well as those regulated by PHZ and its metabolites. In particular, seven strains from Lactobacillus were selectively isolated and confirmed to be essential for deglycosylation of PHZ, implying a potential synergistic effect between PHZ and Lactobacillus.

Toxicological, biochemical, and in silico investigations of three trehalase inhibitors for new ways to control aphids

Insect trehalases have been identified as promising new targets for pest control. These key enzymes are involved in trehalose hydrolysis and plays an important role in insect growth and development. In this contribution, plant and microbial compounds, namely validamycin A, amygdalin, and phloridzin, were evaluated for their effect, through trehalase inhibition, on Acyrthosiphon pisum aphid. The latter is part of the Aphididae family, main pests as phytovirus vectors and being very harmful for crops. Validamycin A was confirmed as an excellent trehalase inhibitor with an half maximal inhibitory concentration and inhibitor constant of 2.2 × 10-7 and 5 × 10-8 M, respectively, with a mortality rate of ~80% on a A. pisum population. Unlike validamycin A, the insect lethal efficacy of amygdalin and phloridzin did not correspond to their trehalase inhibition, probably due to their hydrolysis by insect β-glucosidases. Our docking studies showed that none of the three compounds can bind to the trehalase active site, unlike their hydrolyzed counterparts, that is, validoxylamine A, phloretin, and prunasin. Validoxylamine A would be by far the best trehalase binder, followed by phloretin and prunasin.

Maternal Phlorizin Intake Protects Offspring from Maternal Obesity-Induced Metabolic Disorders in Mice via Targeting Gut Microbiota to Activate the SCFA-GPR43 Pathway

Maternal obesity increases the risk of obesity and metabolic disorders (MDs) in offspring, which can be mediated by the gut microbiota. Phlorizin (PHZ) can improve gut dysbiosis and positively affect host health; however, its transgenerational metabolic benefits remain largely unclear. This study aimed to investigate the potential of maternal PHZ intake in attenuating the adverse impacts of a maternal high-fat diet on obesity-related MDs in dams and offspring. The results showed that maternal PHZ reduced HFD-induced body weight gain and fat accumulation and improved glucose intolerance and abnormal lipid profiles in both dams and offspring. PHZ improved gut dysbiosis by promoting expansion of SCFA-producing bacteria, Akkermansia and Blautia, while inhibiting LPS-producing and pro-inflammatory bacteria, resulting in significantly increased fecal SCFAs, especially butyric acid, and reduced serum lipopolysaccharide levels and intestinal inflammation. PHZ also promoted intestinal GLP-1/2 secretion and intestinal development and enhanced gut barrier function by activating G protein-coupled receptor 43 (GPR43) in the offspring. Antibiotic-treated mice receiving FMT from PHZ-regulated offspring could attenuate MDs induced by receiving FMT from HFD offspring through the gut microbiota to activate the GPR43 pathway. It can be regarded as a promising functional food ingredient for preventing intergenerational transmission of MDs and breaking the obesity cycle.

Dihydrochalcone glycoside biosynthesis in Malus is regulated by two MYB-like transcription factors and is required for seed development

Dihydrochalcones (DHCs) including phlorizin (phloretin 2'-O-glucoside) and its positional isomer trilobatin (phloretin 4'-O-glucoside) are the most abundant phenylpropanoids in apple (Malus spp.). Transcriptional regulation of DHC production is poorly understood despite their importance in insect- and pathogen-plant interactions in human physiology research and in pharmaceuticals. In this study, segregation in hybrid populations and bulked segregant analysis showed that the synthesis of phlorizin and trilobatin in Malus leaves are both single-gene-controlled traits. Promoter sequences of PGT1 and PGT2, two glycosyltransferase genes involved in DHC glycoside synthesis, were shown to discriminate Malus with different DHC glycoside patterns. Differential PGT1 and PGT2 promoter activities determined DHC glycoside accumulation patterns between genotypes. Two transcription factors containing MYB-like DNA-binding domains were then shown to control DHC glycoside patterns in different tissues, with PRR2L mainly expressed in leaf, fruit, flower, stem, and seed while MYB8L mainly expressed in stem and root. Further hybridizations between specific genotypes demonstrated an absolute requirement for DHC glycoside production in Malus during seed development which explains why no Malus spp. with a null DHC chemotype have been reported.

Assessment of human inter-individual variability of phloretin metabolites in urine after apple consumption. AppleCOR study

Purpose: This study aimed to assess the inter-individual variation in phloretin absorption and metabolism and to seek possible phloretin metabotypes following apple snack consumption. Methods: The excreted phloretin metabolites in 24 h urine samples were determined by UPLC-MS/MS in 62 volunteers after acute and sustained (6 weeks) interventions in a randomized and parallel study with a daily supplementation of 80 g of a low-phloretin (39.5 μmol) or a high-phloretin (103 μmol) freeze-dried apple snacks. Results: absorption estimated as phloridzin equivalents for 62 volunteers varied almost 70-fold ranging from 0.1% to 6.94% of phloretin glycoside intake. Volunteers were stratified into low, medium and high producers and by the balance between glucuronidation and sulphation. For 74% of the volunteers phloretin-O-glucuronide was the dominant urinary metabolite, especially at the higher phloretin glycoside intake and for higher producers. Sulphate conjugation assumed greater significance for the remaining volunteers especially for low producers. Females dominated glucuronide profile (64.1%) and males dominated the low excretion group. Analysis of plasma glucose and insulin at the start and end of the sustained study showed a trend towards modest reductions for high producers. Furthermore, plausible factors contributing to the inter-individual variation in phloretin uptake are discussed. Conclusions: extensive inter-individual variability exists in the excretion of phloretin phase-II conjugates following consumption of apple snacks, which could be related to oral microbiota phloridzin-hydrolysing activity, lactase non-persistence trait or the metabotype to which the subject belongs. There were inconsistent effects on post-prandial serum glucose concentrations but there was a tendency for decreases to be associated with higher excretion of phloretin phase-II conjugates. Trial registration: The acute and sustained studies were registered at ClinicalTrials.gov Identifier: NCT03795324.

Phlorizin Mitigates Dextran Sulfate Sodium-Induced Colitis in Mice by Modulating Gut Microbiota and Inhibiting Ferroptosis

Phlorizin (PHZ) is the main active component of apple peel and presents a potential application value. In the past few years, some reports have suggested that PHZ may have antioxidant and anti-inflammatory effects. Herein, we have attempted to assess the protective effects of PHZ on dextran sodium sulfate (DSS)-induced colitis in mice and to determine the underlying molecular mechanisms. Our results suggested that early intervention with PHZ (20, 40, and 80 mg/kg) significantly reduced the severity of DSS-induced colitis in mice, as presented by a longer colon, improved tight junction protein, decreased disease activity index, and attenuated inflammatory factors. Additionally, early intervention with + (20, 40, and 80 mg/kg) significantly inhibited ferroptosis by decreasing the surrogate ferroptosis marker levels (MDA and Iron Content). Additionally, PHZ (80 mg/kg) increased the diversity of intestinal flora in colitic mice by elevating the levels of beneficial bacteria (Lactobacillaceae and Muribaculaceae) and reducing the levels of harmful bacteria (Lachnospiraceae). This indirectly led to an increase in the amount of short-chain fatty acids. A fecal microbial transplantation (FMT) test was conducted to show that PHZ (80 mg/kg) ameliorated ulcerative colitis (UC) by regulating gut dysbiosis. In conclusion, early intervention with PHZ decreased DSS-induced colitis in mice by preserving their intestinal barrier and regulating their intestinal flora.

Inhibition of sodium-glucose cotransporter 2 suppresses renal stone formation

BACKGROUND AND AIMS

Nephrolithiasis is a common renal disease with no effective medication. Sodium-glucose cotransporter-2 (SGLT2) inhibitors, an anti-diabetic agent, have diuretic and anti-inflammatory properties and could prevent nephrolithiasis. Here, we investigated the potential of SGLT2 inhibition against nephrolithiasis using large-scale epidemiological data, animal models, and cell culture experiments.

METHODS

This study included the data of diabetic patients (n = 1,538,198) available in the Japanese administrative database and divided them according to SGLT2 inhibitor prescription status. For animal experiments, renal calcium oxalate stones were induced by ethylene glycol in Sprague-Dawley rats, and phlorizin, an SGLT1/2 inhibitor, was used for the treatment. The effects of SGLT2-specific inhibition for renal stone formation were assessed in SGLT2-deficient mice and a human proximal tubular cell line, HK-2.

RESULTS

Nephrolithiasis prevalence in diabetic men was significantly lower in the SGLT2 inhibitor prescription group than in the non-SGLT2 inhibitor prescription group. Phlorizin attenuated renal stone formation and downregulated the kidney injury molecule 1 (Kim1) and osteopontin (Opn) expression in rats, with unchanged water intake and urine volume. It suppressed inflammation and macrophage marker expression, suggesting the role of the SGLT2 inhibitor in reducing inflammation. SGLT2-deficient mice were resistant to glyoxylic acid-induced calcium oxalate stone formation with reduced Opn expression and renal damages. High glucose-induced upregulation of OPN and CD44 and cell surface adhesion of calcium oxalate reduced upon SGLT2-silencing in HK-2 cells.

CONCLUSION

Overall, our findings identified that SGLT2 inhibition prevents renal stone formation and may be a promising therapeutic approach against nephrolithiasis.

New bioactive compounds characterized by liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry in hydro-methanol and petroleum ether extracts of Prosopis farcta (Banks & Sol.) J. F. Macbr weed

The purpose of this study was to identify and characterize the chemical composition present in aerial parts of Prosopis farcta in petroleum ether and hydro-methanol extracts through LC-PDA-ESI-MS/MS and GC-MS techniques respectively for the first time. The plant samples were collected from northeast of Iran during maturity stage. LC-MS/MS profile revealed 47 phenolic compounds in hydro-methanol extracts, including phenolic acids, flavonoids, and their glycoside derivatives. Flavonoid-O-glycosides (19), flavonoid aglycones (11), phenolic acid derivatives (9), flavonoid-C-glycosides (4), and flavonoid-O, C-glycosides (1) were dominant class phenolics in all studied parts. The extracts contained a significant amount of major compounds, including gallic and vanillic acids, luteolin, apigenin, phloridzin, and vicenin-2. Also, GC-MS analysis of petroleum ether extracts showed that fatty acids, organic acids, steroids, terpenoids, and hydrocarbons were the group of major compounds in all parts. Twenty-four, 27, and 25 components were identified, which represent 99.2%, 96.1%, and 99.4% of the total composition in fruits, leaves, and stems, respectively. These results suggested that other genetic resources of P. farcta can be further explored to screen genotypes with high bioactive compounds and purification of phytochemical compounds, which are valuable to produce, expand, and develop natural antioxidants in production of bio-medicine and food.

Degraded Metabolites of Phlorizin Promote Germination of Valsa mali var. mali in its Host Malus spp

Plant pathogenic fungi are able to utilize the principal metabolites of their hosts, which is one reason pathogens can so seriously harm the plants, although the mechanisms behind this utilization are not always clear. Valsa mali var. mali is a pathogenic fungus specific to the plant genus Malus. The fungus can seriously endanger apple crops and has caused serious economic losses. Phlorizin (1), the principal component in the stems, roots, and leaves of Malus pumila and M. sieversii, was able to promote spore germination of Valsa mali var. mali (Vmm-30) significantly over 120-168 h in a non-nutritional suspension. Compared with the control, the concentrations of nine phenolic compounds (3-11) in the stems of M. pumila increased after inoculation with Vmm-30. Moreover, compounds 3, 4, and 9-11 were able to promote the germination of Vmm-30 spores over 24-36 h, which was a significantly shorter time than that of phlorizin. High-performance liquid chromatography with diode-array detection (HPLC-DAD) and ultraperformance liquid chromatography with tandem mass spectrometry (UPLC-MS/MS) analyses further suggested that compounds 2-11 were the degradation products of phlorizin (1) and are produced through carbon oxidation cracking, decarboxylation, and oxidation reactions. This suggests that the degradation of phlorizin is able to effectively promote the growth of Vmm-30. The Vmm-30 strain is therefore able to utilize the principal metabolite phlorizin to generate a series of degradation products, which further promote its germination and the infection of its host plants in the genus Malus.

Key indicators for renewal and reconstruction of perennial trees soil: Microorganisms and phloridzin

Perennial tree soil inhibits the growth of replanting apples, but the mechanism that underlies this inhibition is poorly understood. A total of 57 perennial tree soils were selected for the collection of soil samples in the Bohai Bay in May 2018. The severity of apple replant disease (ARD) for each soil was determined by calculating the rate of inhibition of growth replanted apple trees. A high-throughput sequencing analysis of internal transcribed spacer (ITS) was used to determine the soil fungal community. A correlation analysis was used to determine the relationship between the rate of inhibition of apple growth and soil factors. The degree of inhibition of plant growth varied substantially among the 57 soil samples examined. Different perennial tree soils have varying degrees of ARD. There was no significant difference in the composition of fungal community at the phylum level, but the genus level differed substantially. The abundances of Fusarium and Mortierella species and the contents of phloridin in the soil and soil organic matter (SOM) were significantly correlated with ARD severity. Structural equation modeling also emphasized that the degree of occurrence of ARD was directly or indirectly affected by Fusarium, Mortierella, phloridin and SOM. A correlation analysis can only be used as an indicator, and further research is merited to reveal how soil parameters affect ARD.

New triterpenic acids produced in callus culture from fruit pulp of Acca sellowiana (O. Berg) Burret

The aim of this work was the study of the best conditions for obtaining a callus culture from the pulp of Acca sellowiana, and to perform a quali-quantitative analysis of the secondary metabolites yielded by the in vitro callus culture. To this end, callus was induced on both Murashige and Skoog and Gamborg B5 media containing various combinations of growth regulators. Three previously undescribed ursane-type triterpenoids, 2α,3β,6α,23-tetrahydroxy-18α,19α-urs-20-en-28-oic acid, 2α,3β,23-trihydroxy-18α,19α-urs-20-en-28-oic acid and 2α,3β,6β,23-tetrahydroxy-18α,19α-urs-20-en-28-oic acid were isolated from the methanolic extract of A. sellowiana culture and characterized by 1D and 2D NMR experiments. Moreover, the quali-quantitative analysis (ESI-MSn and GC-MS) also showed the presence of β-sitosterol, phloridzin, oleanolic, ursolic, 3β-hydroxy-18α,19α-urs-20-en-28-oic, maslinic, corosolic, 2α,3β-dihydroxy-18α,19α-urs-20-en-28-oic, and tormentic acid.

Markers of Islet Endothelial Dysfunction Occur in Male B6.BKS(D)-Leprdb/J Mice and May Contribute to Reduced Insulin Release

Islet endothelial cells produce paracrine factors that support β-cell function and growth. Endothelial dysfunction underlies diabetic microvascular complications; thus, we hypothesized that in diabetes, islet endothelial cells become dysfunctional, which may contribute to β-cell secretory dysfunction. Islets/islet endothelial cells were isolated from diabetic B6.BKS(D)-Leprdb/J male (db/db) mice, treated with or without the glucose-lowering agent phlorizin, or from C57BL/6J mice fed a high-fat diet for 18 weeks and appropriate controls. Messenger RNA (mRNA) and/or the protein levels of the cell adhesion molecule E-selectin (Sele), proinflammatory cytokine interleukin-6 (Il6), vasoconstrictor endothelin-1 (Edn1), and endothelial nitric oxide synthase (Nos3; Nos3) were evaluated, along with advanced glycation end product immunoreactivity. Furthermore, an islet endothelial cell line (MS-1) was exposed to diabetic factors (glucose, palmitate, insulin, and tumor necrosis factor-α) for six days. Conditioned media were collected from these cells, incubated with isolated islets, and glucose-stimulated insulin secretion and insulin content were assessed. Islet endothelial cells from db/db mice exhibited increased Sele, Il6, and Edn1 mRNA levels, decreased Nos3 protein, and accumulation of advanced glycation end products. Phlorizin treatment significantly increased Nos3 protein levels but did not alter expression of the other markers. High-fat feeding in C57BL/6J mice resulted in increased islet Sele, Il6, and Edn1 but no change in Nos3. Exposure of islets to conditioned media from MS-1 cells cultured in diabetic conditions resulted in a 50% decrease in glucose-stimulated insulin secretion and 30% decrease in insulin content. These findings demonstrate that, in diabetes, islet endothelial cells show evidence of a dysfunctional phenotype, which may contribute to loss of β-cell function.

[High glucose dialysate enhances peritoneal fibrosis through upregulating glucose transporters GLUT1 and SGLT1]

Objective: To investigate the role of glucose transporter 1 (GLUT1) and sodium-glucose cotransporter 1 (SGLT1) in high glucose dialysate-induced peritoneal fibrosis. Methods: Thirty six male SD rats were randomly divided into 6 groups (6 in each):normal control group, sham operation group, peritoneal dialysis group (PD group), PD+phloretin group (PD+T group), PD+phlorizin group (PD+Z group), PD+phloretin+phlorizin group (PD+T+Z group). Rat model of uraemia was established using 5/6 nephrotomy, and 2.5% dextrose peritoneal dialysis solution was used in peritoneal dialysis. Peritoneal equilibration test was performed 24 h after dialysis to evaluate transport function of peritoneum in rats; HE staining was used to observe the morphology of peritoneal tissue; and immunohistochemistry was used to detect the expression of GLUT1, SGLT1, TGF-β1 and connective tissue growth factor (CTGF) in peritoneum. Human peritoneal microvascular endothelial cells (HPECs) were divided into 5 groups:normal control group, peritoneal dialysis group (PD group), PD+phloretin group (PD+T group), PD+phlorezin group (PD+Z group), and PD+phloretin+phlorezin group (PD+T+Z group). Real time PCR and Western blotting were used to detect mRNA and protein expressions of GLUT1, SGLT1, TGF-β1, CTGF in peritoneal membrane and HPECs. Results:In vivo, compared with sham operation group, rats in PD group had thickened peritoneum, higher ultrafiltration volume, and the mRNA and protein expressions of GLUT1, SGLT1, CTGF, TGF-β1 were significantly increased (all P<0.05); compared with PD group, thickened peritoneum was attenuated, and the mRNA and protein expressions of GLUT1, SGLT1, CTGF, TGF-β1 were significantly decreased in PD+T, PD+Z and PD+T+Z groups (all P<0.05). Pearson's correlation analysis showed that the expressions of GLUT1, SGLT1 in peritoneum were positively correlated with the expressions of TGF-β1 and CTGF (all P<0.05). In vitro, the mRNA and protein expressions of GLUT1, SGLT1, TGF-β1, CTGF were significantly increased in HPECs of peritoneal dialysis group (all P<0.05), and those in PD+T, PD+Z, and PD+T+Z groups were decreased (all P<0.05). Pearson's correlation analysis showed that the expressions of GLUT1, SGLT1 in HPECs were positively correlated with the expressions of TGF-β1 and CTGF (all P<0.05). Conclusion: High glucose peritoneal dialysis fluid may promote peritoneal fibrosis by upregulating the expressions of GLUT1 and SGLT1.

Phenotypic changes associated with RNA interference silencing of chalcone synthase in apple (Malus × domestica)

We have identified in apple (Malus × domestica) three chalcone synthase (CHS) genes. In order to understand the functional redundancy of this gene family RNA interference knockout lines were generated where all three of these genes were down-regulated. These lines had no detectable anthocyanins and radically reduced concentrations of dihydrochalcones and flavonoids. Surprisingly, down-regulation of CHS also led to major changes in plant development, resulting in plants with shortened internode lengths, smaller leaves and a greatly reduced growth rate. Microscopic analysis revealed that these phenotypic changes extended down to the cellular level, with CHS-silenced lines showing aberrant cellular organisation in the leaves. Fruit collected from one CHS-silenced line was smaller than the 'Royal Gala' controls, lacked flavonoids in the skin and flesh and also had changes in cell morphology. Auxin transport experiments showed increased rates of auxin transport in a CHS-silenced line compared with the 'Royal Gala' control. As flavonoids are well known to be key modulators of auxin transport, we hypothesise that the removal of almost all flavonoids from the plant by CHS silencing creates a vastly altered environment for auxin transport to occur and results in the observed changes in growth and development.

Adapter-modified Ussing chamber enables evaluation of endoscopically-obtained colonic biopsy samples from cats and dogs

Adapter-modified Ussing chambers have been used for assessment of endoscopically obtained intestinal biopsies in humans. The aim of this study was to evaluate the feasibility of an adapter-modified Ussing chamber for assessment of intestinal transport physiology in endoscopically-obtained colonic biopsies from cats and dogs. Fifteen colonic biopsies from four cats and 13 colonic biopsies from four dogs were transferred into a modified Ussing chamber and sequentially exposed to several compounds. Baseline mean±SD conductance was measured. Changes of short circuit current (ΔIsc) were observed after exposure to glucose (number of feline biopsies that responded=0/number of canine biopsies that responded=4), phloridzin (n=0/n=7), histamine (n=5/n=12), serotonin (n=7/n=12), prostaglandin (n=5/n=7), forskolin (n=7/n=7), and ouabain (n=9/n=7). The adapter-modified Ussing chamber studied here enables investigation of transport physiology of endoscopically-obtained colonic biopsies from companion animals. However, we observed a large variability of results, suggesting that clinical use of this method is limited.

Potential polyphenol markers of phase change in apple (Malus domestica)

In order to identify potential biochemical markers that can be used as indicators for phase change, the dynamics of polyphenolic compounds across apple seedlings (Malus domestica, Jonathan x Golden Delicious) were analyzed in this study by high performance liquid chromatography. Precocious flowering was induced by foliar sprays of plant growth regulators. Qualitative changes in the concentration of polyphenols were observed at node nos. 50, 80 and 120. Spontaneous and induced flowering was found at node nos. 122 and 77. It was reasonable to conclude that node no. 77 represented the point of transition between the juvenile phase and the adult vegetative phase, which was marked by the presence of phloridzin in the buds. The disappearance of myricitrin in the bark and the absence of caffeic acid in the aboveground tissues were qualitative markers of the reproductive phase, which was reached at node no. 122.

A 96-well automated method to study inhibitors of human sodium-dependent D-glucose transport

The sodium-dependent D-glucose transporter (SGLT) family is involved in glucose uptake via intestinal absorption (SGLT1) or renal reabsorption (SGLT1 and SGLT2). Current methods for the screening of inhibitors of SGLT transporters are complex, expensive and very labor intensive, and have not been applied to human SGLT transporters. The purpose of the present study was to develop an alternative 96-well automated method to study the activity of human SGLT1 and SGLT2. Chinese hamster ovary (CHO) Flp-In cells were stably transfected with pcDNA5-SGLT1 or pcDNA5-SGLT2 plasmid and maintained in hygromycin-selection Ham's F12 culture medium until hygromycin-resistant clones were developed. SGLT1 and SGLT2 gene expression was evaluated by relative real-time reverse transcription-polymerase chain reaction (RT-PCR) quantification, Western blotting, and immunocytochemical analysis. The clones with higher expression of SGLT1 and SGLT2 were used for transport studies using [14C]-methyl-alpha-D-glucopyranoside ([14C]AMG). The advantage of using the 96-well format is the low amount of radioactive compounds and inhibitory substances required, and its ability to establish reproducibility because repetition into the assay. This method represents an initial approach in the development of transport-based high-throughput screening in the search for inhibitors of glucose transport. The proposed method can easily be performed to yield quantitative data regarding key aspects of glucose membrane transport and kinetic studies of potential inhibitors of human SGLT1 and SGLT2.

Posttranslational regulation of NO synthase activity in the renal medulla of diabetic rats

Shear stress increases nitric oxide (NO) production by endothelial cells, inner medullary collecting duct cells, and thick ascending limb. We postulated that the osmotic diuresis accompanying type 1 diabetes is associated with increased NO synthase (NOS) activity and/or expression in the renal medulla. Diabetes was induced by injection of streptozotocin, with insulin provided to maintain moderate hyperglycemia (Hyp) or euglycemia (Eug) for 3 wk. Sham rats received vehicle treatments. A separate group of rats (Phz) received phlorizin to produce a glucose-dependent osmotic diuresis. Renal medullary NOS1 and NOS2 activities did not differ between groups, whereas NOS3 activity was significantly increased in Hyp. Neither NOS1 nor NOS3 protein levels differed significantly between groups. Reduced phosphorylation of NOS3 at Thr(495) and Ser(633) was evident in medullary homogenates from Hyp rats, with no difference apparent at Ser(1177). Immunohistochemical analysis indicated prominent expression of pThr(495)NOS3 in the thick ascending limb and collecting duct of Sham and Phz rats. Hyp rats displayed staining in the collecting duct but minimal thick ascending limb staining. Immunostaining with anti-pSer(1177)NOS3 was evident only in the thick ascending limb, with no apparent differences between groups. In summary, glucose-dependent osmotic diuresis alone did not alter NOS activity or expression in the renal medulla. Diabetic hyperglycemia increased medullary NOS3 activity without a concomitant increase in NOS3 protein levels; however, NOS3 phosphorylation was reduced at Thr(495) and Ser(633). Thus changes in the phosphorylation of NOS at known regulatory sites might represent the primary mechanism underlying increased renal medullary NOS activity in diabetic hyperglycemia.

Single molecule recognition of protein binding epitopes in brush border membranes by force microscopy

Sidedness and accessibility of protein epitopes in intact brush border membrane vesicles were analyzed by detecting single molecule interaction forces using molecular recognition force microscopy in aqueous physiological solutions. Frequent antibody-antigen recognition events were observed with a force microscopy tip carrying an antibody directed against the periplasmically located gamma-glutamyltrans- peptidase, suggesting a right side out orientation of the vesicles. Phlorizin attached to the tips bound to NA+/D-glucose cotransporter molecules present in the vesicles. The recognition was sodium dependent and inhibited by free phlorizin and D-glucose, and revealed an apparent K(D) of 0.2 microM. Binding events were also observed with an antibody directed against the epitope aa603-aa630 close to the C terminus of the transporter. In the presence of phlorizin the probability of antibody binding was reduced but the most probable unbinding force f(u) = 100 pN remained unchanged. In the presence of D-glucose and sodium, however, both the binding probability and the most probable binding force (f(u) = 50 pN) were lower than in its absence. These studies demonstrate that molecular recognition force microscopy is a versatile tool to probe orientation and conformational changes of epitopes of membrane components during binding and trans-membrane transport.

Effects of certain inhibitors on renal excretion of salt and water

The direct proportionality between renal oxygen consumption and sodium reabsorption suggests a linkage between cation transport and the electron transport system (ETS). We have studied the effects of in vitro inhibitors of the ETS on sodium reabsorption in the dog kidney. Compounds known to block O2 consumption or reduce tissue levels of adenosine triphosphate (ATP) were infused in millimolar quantities into a renal artery of anesthetized dogs. We observed a unilateral diuresis following the administration of cyanide, antimycin-A and iodoacetamide; no diuresis was observed following administration of 2,4-dinitrophenol, azide, and phlorizin. These latter agents block the synthesis or facilitate the degradation of ATP. Negative results were also observed with phthiocol (a naphthoquinone), malonate, and Amytal, inhibitors of specific substrates of ETS. We interpret our results as follows. Inhibition of sodium reabsorption by cyanide and antimycin-A supports the hypothesis that renal cation transport is dependent in part upon oxidative metabolism. The failure of phlorizin and 2,4-dinitrophenol to affect sodium reabsorption suggests that cation transport may be independent of ATP synthesis or concentration in renal tissues.

ION TRANSPORT IN ISOLATED RABBIT ILEUM. II. THE INTERACTION BETWEEN ACTIVE SODIUM AND ACTIVE SUGAR TRANSPORT

The addition of actively transported sugars to the solution bathing the mucosal surface of an in vitro preparation of distal rabbit ileum results in a rapid increase in the transmural potential difference, the short-circuit current, and the rate of active Na transport from mucosa to serosa. These effects are dependent upon the active transport of the sugar per se and are independent of the metabolic fate of the transported sugar. Furthermore, they are inhibited both by low concentrations of phlorizin in the mucosal solution and by low concentrations of ouabain in the serosal solution. The increase in the short-circuit current, ΔI_sc, requires the presence of Na in the perfusion medium and its magnitude is a linear function of the Na concentration. On the other hand, ΔI_sc is a saturable function of the mucosal sugar concentration which is consistent with Michaelis-Menten kinetics suggesting that the increase in active Na transport is stoichiometrically related to the rate of active sugar transport. An interpretation of these findings in terms of a hypothetical model for intestinal Na and sugar transport is presented.

A CLINICAL BIOASSAY METHOD OF LONG-ACTING CORTICOTROPHIN PREPARATIONS AND ITS APPLICATION AS AN INTRAMUSCULAR CORTICOTROPHIN TEST

The corticosteroidogenetic potency of a corticotrophin preparation – given as an intravenous infusion – was compared in asthmatic patients with that of the same preparation dissolved in an aqueous polyphloretin phosphate solution and given as a single intramuscular injection. Four-point assays with a completely randomized block design were employed, each patient being injected with each of the four doses in a different order.

The results indicate that for the purposes of a clinical corticotrophin (ACTH)-test, the 8-hours' intravenous infusion of corticotrophin can suitably be replaced by a single intramuscular injection of a mixture of corticotrophin and polyphloretin phosphate.

The clinical bioassay described appears also suitable for the assessment of the corticosteroidogenetic potency of various types of long-acting corticotrophin preparations.

THE EFFECTS OF ADRENALINE AND OTHER DRUGS AFFECTING CARBOHYDRATE METABOLISM ON CONTRACTIONS OF THE RAT DIAPHRAGM

The ability of several drugs to restore directly elicited twitches of the rat diaphragm depressed by excess potassium chloride has been studied. The drugs found to be effective were sympathomimetic amines, insulin, glucagon, caffeine, theophylline, calcium chloride and hexosephosphates. The effects of the sympathomimetic amines and glucagon were blocked by beta-receptor blocking agents. Phloridzin blocked the effect of insulin and depressed that of glucagon. The increase in twitch tension still occurred under anaerobic conditions and was not abolished by the glycolytic inhibitor, iodoacetate. All of the effective drugs are known to affect carbohydrate metabolism and the suggestion by Ellis (1955) that the effect on contractions may be a result of increased intracellular hexosephosphate levels is discussed.

ULTRASTRUCTURE OF ISOLATED KIDNEY MITOCHONDRIA TREATED WITH PHLORIZIN AND ATP

Direct electron microscopic evidence is reported of the ultrastructure of mitochondrial membranes and compartments in mitochondria isolated in 0.5 M sucrose from the rat kidney cortex and the experimental changes they undergo with phlorizin and ATP treatment. A heterogeneous population of mitochondria is recognized under control conditions. The mitochondria appear to be of 3 main types, normal, swollen, and contracted. Under phlorizin treatment, most of the mitochondria swell in less than 15 minutes, apparently at the expense of the matrix. Treatment with ATP, on the other hand, produces, during the same time, a marked contraction of the isolated mitochondria, with many refoldings of the inner membrane and marked increase in the electron opacity of the matrix. It is concluded from these observations that mitochondrial swelling and contraction should be related mainly to the matrix content.

Activity of the rat lactase gene promoter in transfected human colon cancer cells

The promoter activity of the upstream region of the rat small intestinal lactase-phlorizin hydrolase gene has been analysed by transfection in the human colon cancer cell line Caco-2. A 0.9 kb mRNA, corresponding to the CAT reporter gene, was synthesized from the transcription start site of the LPH gene. The rate of expression, determined by semi-quantitative RT-PCR, was very low, and depended on the length of the promoter fragment in front of the reporter gene. By immunocytology, we found that the low level of expression resulted from the low number of cells (about 1%) in which CAT was produced. The endogenous lactase was present in 10-20% of the cells in culture, and evidence is provided that most cells that expressed CAT did not co-express the endogenous lactase. We conclude from this study that the rat small intestinal LPH gene promoter is active in the human Caco-2 colon cancer cells. Hence Caco-2 cells constitute an in vitro model to analyse the basic molecular mechanisms involved in the gene transcription of intestinal digestive enzymes. Yet, the mosaic expression of the endogenous lactase and of the reporter gene under the control of the rat LPH gene promoter, suggests that Caco-2 cells may present specific regulatory mechanisms of expression of small intestinal enzymes, possibly in relation to their tumourous origin.

Phlorizin-induced glycosuria does not prevent gentamicin nephrotoxicity in rats

Because rats with streptozotocin-induced diabetes mellitus (DM) have a high solute diuresis (glycosuria of 10 to 12 g/day), we have suggested that this may in part be responsible for their resistance to gentamicin-induced acute renal failure (ARF). The protection from gentamicin nephrotoxicity was studied in non-diabetic rats with chronic solute diuresis induced by blockage of tubular glucose reabsorption with phlorizin (P). DM rats with mild glycosuria (similar in degree to that of the P treated animals) were also studied. Unanesthetized adult female, Sprague-Dawley rats were divided in four groups and studied for 15 days. Group 1 (P alone) received P, 360 mg/day, for 15 days; Group II (P + gentamicin); Group III (gentamicin alone) and Group IV (mild DM + gentamicin). Nephrotoxic doses (40 mg/kg body wt/day) of gentamicin were injected during the last nine days of study to the animals of groups II to IV. In Group I, P induced a moderate and stable glycosuria (3.9 +/- 0.1 g/day, SE), and no functional or morphologic evidence of renal dysfunction (baseline CCr 2.1 +/- 0.1 ml/min, undetectable lysozymuria) or damage (tubular necrosis score [maximum 4], zero). In Group II, P did not prevent gentamicin-ARF (maximal decrease in CCr at day 9.89%, P less than 0.001; peak lysozymuria, 1863 +/- 321 micrograms/day; and tubular necrosis score, 3.9 +/- 0.1). These values were not different from those of Group III: maximal decrease in CCr 73% (P less than 0.001); lysozymuria, 2147 +/- 701 micrograms/day; tubular necrosis score, 3.8 +/- 0.1.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification of a putative Na+/D-glucose cotransporter from pig kidney brush border membranes on a phlorizin affinity column

Phlorizin, a potent inhibitor of the Na+/D-glucose cotransporter, was derivatised to 3-aminophlorizin and subsequently coupled to Affi-Gel 15. Affinity chromatography of pig kidney brush border membranes solubilised in Triton X-100 allowed the purification of a 60 kDa protein on this resin. We consider this protein to be the Na+/D-glucose cotransporter, or part of it, for the following reasons: (i) binding of this protein to Affi-Gel 15 specifically requires phlorizin covalently attached to the resin and is lowered when phlorizin is replaced by phloretin; (ii) binding of the 60 kDa protein to a phlorizin affinity column requires the presence of Na+; (iii) polyclonal as well as monoclonal antibodies against the 60 kDa protein inhibit binding of phlorizin to brush border membranes from rabbit and pig kidney.

Effect of chronic hyperglycemia on in vivo insulin secretion in partially pancreatectomized rats

We have examined the effect of chronic (4 wk) hyperglycemia on insulin secretion in vivo in an awake, unstressed rat model. Three groups of animals were examined: control, partial (90%) pancreatectomy, and partial pancreatectomy plus phlorizin, in order to normalize plasma glucose levels. Insulin secretion in response to arginine (2 mM), hyperglycemia (+100 mg/dl), and arginine plus hyperglycemia was evaluated. In diabetic compared with control animals three specific alterations were observed: (a) a deficient insulin response, in both first and second phases, to hyperglycemia; (b) an augmented insulin response to the potentiating effect of arginine under basal glycemic conditions; and (c) an inability of hyperglycemia to augment the potentiating effect of arginine above that observed under basal glycemic conditions. Normalization of the plasma glucose profile by phlorizin treatment in diabetic rats completely corrected all three beta cell abnormalities. These results indicate that chronic hyperglycemia can lead to a defect in in vivo insulin secretion which is reversible when normoglycemia is restored.

Crystal structure of phlorizin and the iodothyronine deiodinase inhibitory activity of phloretin analogues

Phloretin, a 7,8-dihydrochalcone of plant origin, and the high molecular weight (less than 15,000) polyphloretinphosphate (PPP) polymers are potent inhibitors of iodothyronine monodeiodinase activity from rat liver microsomal preparations, whereas phlorizin, the 2'-O-glucoside of phloretin, is inactive. The polymers, differing in degree of phosphorylation-dependent polymerization, exhibited a concentration-dependent, and ultimately complete, inhibition of deiodinase activity with an IC50 between 0.2 and 0.5 micrograms PPP/ml. Phloretin inhibition, on the other hand, was cofactor (DTE) competitive, with a Ki = 0.75 microM. 2',4',6',3,4- Pentahydroxychalcone, which has a substitution pattern in the A-ring identical to that of phloretin, was the only active inhibitor (IC50 = 8 microM) among several derivatives tested. The phloretin biodegradation products, phloretic acid and phloroglucinol, and its biosynthetic precursors, monomeric cinnamic acid and cinnamic acid derivatives, were inactive in concentrations up to 100 microM. The X-ray crystal structure analysis of phlorizin dihydrate showed that the molecule is planar and fully extended, similar to the conformation observed in chalcone structures that are characterized by an alpha, beta-unsaturated bond between phenol rings. Comparison of the planar phlorizin crystal structure with a skewed or antiskewed thyroid hormone conformation revealed that the beta-D-glucose moiety does not share any of the thyroid hormone's conformational space, and that the best structural homology is found with the antiskewed conformation of 3',5',3-triiodothyronine, the natural deiodinase substrate that also inhibits further deiodination.

Effect of dietary niacin supplementation on phlorhizin and 1,3-butanediol-induced ketonemia and hypoglycemia in steers

1,3-Butanediol and phlorhizin were used to induce ketonemia and hypoglycemia in steers. Oral administration of butanediol increased blood beta-hydroxybutyrate (BHB) and plasma nonesterified fatty acids (NEFA) and decreased serum glucose. Subcutaneous injections of phlorhizin, given in addition to butanediol orally, further increased NEFA and BHB concentrations and decreased glucose. Dietary niacin supplementation of steers given phlorhizin and butanediol caused serum glucose concentration to increase and blood BHB and plasma NEFA concentrations to decrease.

Partial purification of hog kidney sodium-D-glucose cotransport system by affinity chromatography on a phlorizin polymer

A brush border membrane fraction isolated from hog kidney cortex was solubilized with 0.5% Triton X-100 and subjected to affinity chromatography on a phlorizin polymer. As demonstrated by transport studies with reconstituted proteoliposomes, the polymer adsorbs the sodium-dependent D-glucose transport system. The latter can be eluted from the polymer by 0.5 M D-glucose. The purified fraction contains 0.4% of the membrane protein extract and exhibits a 20--30-fold higher transport activity than the crude membrane extract. Other brush border membrane proteins such as alkaline phosphatase and aminopeptidase M are markedly reduced in the purified fraction. Thus, affinity chromatography on a phlorizin polymer is a suitable tool for the isolation of the sodium-glucose transport system present in brush border membranes.

Fetal metabolic response to phloridzin-induced hypoglycemia in pregnant rats

Phloridzin, an inhibitor of renal sugar transport, produces an important loss of glucose in urine of treated animals. In order to reduce severely the maternal glucose supply to the fetuses in short-term experiments, we have combined phloridzin administration to pregnant rats with 18 h starvation. Fetuses from starved phloridzin-treated mothers were compared with fetuses from starved mothers. Combined treatment markedly decreases fetal blood glucose concentration (-36%) and fetal liver glycogen stores (-76%). These changes are associated with a decrease in plasma insulin (-25%), a rise in plasma glucagon (+120%) and a marked increase of hepatic PEPCK activity (+400%). It appears from these results that phloridzin treatment for a short duration is able to induce glycogenolysis and the premature appearance of PEPCK in the liver of rat fetuses.

Contribution of diffusive pathway in intestinal absorption of glucose in rat under normal feeding condition

Luminal concentration of glucose determined by a specific enzymatic method was about 50 mM after meal in rat jejunum. The diffusive pathway was suggested to have an important role in intestinal absorption of glucose.

Lactase-phlorizin hydrolase complex from monkey small intestine. Purification, properties and evidence for two catalytic sites

Lactase-phlorizin hydrolase (EC 3.2.1.-) has been purified from the monkey small intestine by gel filtration and ion-exchange chromatographic procedures and the properties of the purified enzyme complex have been studied. Lactose was the most active substrate. Cellobiose and other synthetic hetero-beta-glycosides were hydrolysed at a very much reduced rate. The rate of hydrolysis of phlorizin was about 2.5% that of lactose. Lactase and phlorizin hydrolase activities were indistinguishable by heat inactivation experiments. The purified enzyme complex also hydrolysed cerebrosides. Lactose hydrolysis was competitively inhibited by phlorizin as well as by the brain cerebroside. However, there was no mutual inhibition between phlorizin and the brain cerebroside. It is suggested that the native enzyme complex might have two catalytic sites, a phlorizin site and a cerebroside site but both hydrolysing lactose.