Phase I dose-escalation trial to repurpose propagermanium, an oral CCL2 inhibitor, in patients with breast cancer.

The formation of premetastatic niches creates a fertile environment for the seeding of disseminated cancer cells in selected secondary organs. This is crucial for the development of metastasis in various malignancies, including breast cancer (BC). We previously reported that the loss of FBXW7 in bone marrow-derived stromal cells promoted cancer metastasis by increasing the production of the chemokine CCL2, which attracts myeloid-derived suppressor cells and macrophages to the premetastatic niche. Furthermore, treatment with the CCL2 inhibitor propagermanium (PG), which has been used in Japan as a therapeutic agent against chronic hepatitis B, was shown to block the enhancement of metastasis in FBXW7-deficient mice through inhibiting the formation of premetastatic niches. Here, we describe a phase I dose-escalation study of PG used as an antimetastatic drug for perioperative patients with primary BC. The primary end-point was the percentage of patients who experience dose-limiting toxicity. Twelve patients were enrolled in the study. Dose-limiting toxicity was not observed, and the maximum dose was determined to be 90 mg/body/day. The serum concentrations of PG were nearly within the normal range in all observation days. We observed an inverse correlation between FBXW7 mRNA levels in blood and the serum concentrations of CCL2 and interleukin (IL)-6, in agreement with our previous mouse model. Also, IL-6 was downregulated in a PG dose-dependent manner, as observed in mice. Thus, PG was given safely and it is expected to have antimetastatic potential in BC. This trial is registered in the UMIN Clinical Trials Registry as UMIN000022494.

Propagermanium Induces NK Cell Maturation and Tends to Prolong Overall Survival of Patients With Refractory Cancer.

BACKGROUND/AIM: Propagermanium (PG) inhibits the CCL2/CCR2 axis, and has been shown to function as an immune modulator. This study investigated its anti-tumor mechanism in patients with refractory cancers. MATERIALS AND METHODS: Five healthy volunteers and 23 patients with refractory oral (n=8) or gastric (n=15) cancer received PG (30 mg/day). We performed flow cytometry (FCM) of peripheral blood mononuclear cells and in vitro killing assays. RESULTS: FCM revealed that CD16+/CD56Dim NK cells (i.e., mature, cytolytic subset) increased, and the apoptosis induction rate of cancer cells increased after PG administration. Among gastric cancer patients, median OS was 172.0 days. Two patients showed complete remission of lung or liver metastasis. Survival of patients with oral cancer also tended to be prolonged. CONCLUSION: PG induces NK cell maturation, and may potentiate anti-tumor activity.

Gut carbohydrate inhibits GIP secretion via a microbiota/SCFA/FFAR3 pathway.

Mechanisms of carbohydrate-induced secretion of the two incretins namely glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are considered to be mostly similar. However, we found that mice exhibit opposite secretory responses in response to co-administration of maltose plus an α-glucosidase inhibitor miglitol (maltose/miglitol), stimulatory for GLP-1, as reported previously, but inhibitory for GIP. Gut microbiota was shown to be involved in maltose/miglitol-induced GIP suppression, as the suppression was attenuated in antibiotics (Abs)-treated mice and abolished in germ-free mice. In addition, maltose/miglitol administration increased plasma levels of short-chain fatty acids (SCFAs), carbohydrate-derived metabolites, in the portal vein. GIP suppression by maltose/miglitol was not observed in mice lacking a SCFA receptor Ffar3, but it was normally seen in Ffar2-deficient mice. Similar to maltose/miglitol administration, co-administration of glucose plus a sodium glucose transporter inhibitor phloridzin (glucose/phloridzin) induced GIP suppression, which was again cancelled by Abs treatment. In conclusion, oral administration of carbohydrates with α-glucosidase inhibitors suppresses GIP secretion through a microbiota/SCFA/FFAR3 pathway.

Dual Regulation of Gluconeogenesis by Insulin and Glucose in the Proximal Tubules of the Kidney.

Growing attention has been focused on the roles of the proximal tubules (PTs) of the kidney in glucose metabolism, including the mechanism of regulation of gluconeogenesis. In this study, we found that PT-specific insulin receptor substrate 1/2 double-knockout mice, established by using the newly generated sodium-glucose cotransporter 2 (SGLT2)-Cre transgenic mice, exhibited impaired insulin signaling and upregulated gluconeogenic gene expression and renal gluconeogenesis, resulting in systemic insulin resistance. In contrast, in streptozotocin-treated mice, although insulin action was impaired in the PTs, the gluconeogenic gene expression was unexpectedly downregulated in the renal cortex, which was restored by administration of an SGLT1/2 inhibitor. In the HK-2 cells, the gluconeogenic gene expression was suppressed by insulin, accompanied by phosphorylation and inactivation of forkhead box transcription factor 1 (FoxO1). In contrast, glucose deacetylated peroxisome proliferator-activated receptor γ coactivator 1-α (PGC1α), a coactivator of FoxO1, via sirtuin 1, suppressing the gluconeogenic gene expression, which was reversed by inhibition of glucose reabsorption. These data suggest that both insulin signaling and glucose reabsorption suppress the gluconeogenic gene expression by inactivation of FoxO1 and PGC1α, respectively, providing insight into novel mechanisms underlying the regulation of gluconeogenesis in the PTs.

Anagliptin increases insulin-induced skeletal muscle glucose uptake via an NO-dependent mechanism in mice.

AIMS/HYPOTHESIS: Recently, incretin-related agents have been reported to attenuate insulin resistance in animal models, although the underlying mechanisms remain unclear. In this study, we investigated whether anagliptin, the dipeptidyl peptidase 4 (DPP-4) inhibitor, attenuates skeletal muscle insulin resistance through endothelial nitric oxide synthase (eNOS) activation in the endothelial cells. We used endothelium-specific Irs2-knockout (ETIrs2KO) mice, which show skeletal muscle insulin resistance resulting from a reduction of insulin-induced skeletal muscle capillary recruitment as a consequence of impaired eNOS activation. METHODS: In vivo, 8-week-old male ETIrs2KO mice were fed regular chow with or without 0.3% (wt/wt) DPP-4 inhibitor for 8 weeks to assess capillary recruitment and glucose uptake by the skeletal muscle. In vitro, human coronary arterial endothelial cells (HCAECs) were used to explore the effect of glucagon-like peptide 1 (GLP-1) on eNOS activity. RESULTS: Treatment with anagliptin ameliorated the impaired insulin-induced increase in capillary blood volume, interstitial insulin concentration and skeletal muscle glucose uptake in ETIrs2KO mice. This improvement in insulin-induced glucose uptake was almost completely abrogated by the GLP-1 receptor (GLP-1R) antagonist exendin-(9-39). Moreover, the increase in capillary blood volume with anagliptin treatment was also completely inhibited by the NOS inhibitor. GLP-1 augmented eNOS phosphorylation in HCAECs, with the effect completely disappearing after exposure to the protein kinase A (PKA) inhibitor H89. These data suggest that anagliptin treatment enhances insulin-induced capillary recruitment and interstitial insulin concentrations, resulting in improved skeletal muscle glucose uptake by directly acting on the endothelial cells via NO- and GLP-1-dependent mechanisms in vivo. CONCLUSIONS/INTERPRETATION: Anagliptin may be a promising agent to ameliorate skeletal muscle insulin resistance in obese patients with type 2 diabetes.

Structural Basis for Polymer Packing and Solvation Properties of the Organogermanium Crystalline Polymer Propagermanium and Its Derivatives.

Of organogermanium compounds known to have an immunostimulatory action, propagermanium [PGe; 3-oxygermylpropionic acid polymer, (C3 H5 GeO3.5 )n] is the only one used as a pharmaceutical agent, to treat the hepatitis B virus in Japan. However, because of lack of information about its structure, PGe has been confused with a polymeric solid, repagermanium (RGe, Ge-132, poly-trans-[(2-carboxyethyl) germasesquioxane], (C18 H30 Ge6 O21 )n), which has the same essential formula as PGe. To clarify this issue, the structure of PGe was analyzed using X-ray diffraction (XRD). PGe has a polymeric ladder-shaped structure of a concatenated eight-membered ring composed of Ge-O bonds, which is clearly distinguished from the infinite sheet structure in RGe. Moreover, we observed temperature or moisture-dependent transformations among these compounds using powder XRD. For instance, PGe was easily dissolved in water, and transformed to RGe by exposure to water vapor, but transformed into another straight-chain structure when exposed to aqueous solution. As a result of these findings, PGe was indicated to have labile polymer packing against RGe. These characteristics of PGe may affect pharmaceutical properties such as respective stability and solubility, which indicate its unique impact on physiological activity.

Distinct action of the α-glucosidase inhibitor miglitol on SGLT3, enteroendocrine cells, and GLP1 secretion.

Oral ingestion of carbohydrate triggers glucagon-like peptide 1 (GLP1) secretion, but the molecular mechanism remains elusive. By measuring GLP1 concentrations in murine portal vein, we found that the ATP-sensitive K(+) (KATP) channel is not essential for glucose-induced GLP1 secretion from enteroendocrine L cells, while the sodium-glucose co-transporter 1 (SGLT1) is required, at least in the early phase (5 min) of secretion. By contrast, co-administration of the α-glucosidase inhibitor (α-GI) miglitol plus maltose evoked late-phase secretion in a glucose transporter 2-dependent manner. We found that GLP1 secretion induced by miglitol plus maltose was significantly higher than that by another α-GI, acarbose, plus maltose, despite the fact that acarbose inhibits maltase more potently than miglitol. As miglitol activates SGLT3, we compared the effects of miglitol on GLP1 secretion with those of acarbose, which failed to depolarize the Xenopus laevis oocytes expressing human SGLT3. Oral administration of miglitol activated duodenal enterochromaffin (EC) cells as assessed by immunostaining of phosphorylated calcium-calmodulin kinase 2 (phospho-CaMK2). In contrast, acarbose activated much fewer enteroendocrine cells, having only modest phospho-CaMK2 immunoreactivity. Single administration of miglitol triggered no GLP1 secretion, and GLP1 secretion by miglitol plus maltose was significantly attenuated by atropine pretreatment, suggesting regulation via vagal nerve. Thus, while α-GIs generally delay carbohydrate absorption and potentiate GLP1 secretion, miglitol also activates duodenal EC cells, possibly via SGLT3, and potentiates GLP1 secretion through the parasympathetic nervous system.

Dipeptidyl peptidase-4 inhibitor anagliptin ameliorates diabetes in mice with haploinsufficiency of glucokinase on a high-fat diet.

OBJECTIVE: Type 2 diabetes is a chronic metabolic disorder characterized by hyperglycemia with insulin resistance and impaired insulin secretion. DPP-4 inhibitors have attracted attention as a new class of anti-diabetic agents for the treatment of type 2 diabetes. We investigated the effects of anagliptin, a highly selective DPP-4 inhibitor, on insulin secretion and insulin resistance in high-fat diet-fed mice with haploinsufficiency of glucokinase (GckKO) as animal models of type 2 diabetes. MATERIALS/METHODS: Wild-type and GckKO mice were administered two doses of anagliptin by dietary admixture (0.05% and 0.3%) for 10weeks. RESULTS: Both doses of anagliptin significantly inhibited the plasma DPP-4 activity and increased the plasma active GLP-1 levels in both the wild-type and GckKO mice to a similar degree. After 10weeks of treatment with 0.3% anagliptin, body weight gain and food intake were significantly suppressed in both wild-type and GckKO mice. In addition, 0.3% anagliptin ameliorated insulin resistance and glucose intolerance in both genotypes of mice. On the other hand, treatment with 0.05% anagliptin was not associated with any significant change of the body weight, food intake or insulin sensitivity in either genotype of mice, but it did improve the glucose tolerance by enhancing insulin secretion and increasing the ß-cell mass in both genotypes of mice. CONCLUSIONS: High-dose anagliptin treatment improved glucose tolerance by suppression of body weight gain and amelioration of insulin resistance, whereas low-dose anagliptin treatment improved glucose tolerance by enhancing insulin secretion.

Change in blood kinin and plasma porcine pancreatic kallikrein concentrations after oral administration of kallikrein formulation in dog.

Oral formulation of tissue kallikrein consists primarily of porcine pancreatic kallikrein (PPK) and is used to improve peripheral circulation, menopausal symptoms, and impaired chorioretinal circulation. Although gastrointestinal absorption of tissue kallikrein after oral administration has been reported in nonclinical and clinical studies, the increase in the concentration of pharmacologically active kinins, which are produced from kininogens by tissue kallikrein, has not been investigated. In this study, kallikrein formulation was orally administered to dogs and an increase in PPK in plasma was confirmed, along with an increase in the blood kinin level. After oral administration of kallikrein formulation (10 U/kg or 20 U/kg PPK) to dogs, PPK concentration in plasma reached maximum 3 h after administration, and then decreased time-dependently. The maximum concentration was 6.01 ± 1.44 pg/ml in the 10 U/kg group and 10.88 ± 3.59 pg/ml in the 20 U/kg group (mean ± S.E.M, n = 5). After oral administration of kallikrein formulation (40 U/kg PPK) to dogs, the blood kinin concentration in the PPK-treated group was significantly increased 2 h after administration as compared to the purified water-treated group (before administration: 48.8 ± 2.1 ng/ml vs. 48.1 ± 1.9 ng/ml, 2 h after administration: 55.5 ± 1.6 ng/ml vs. 49.6 ± 1.4 ng/ml; mean ± S.E.M, n = 4, p < 0.05). In conclusion, PPK was considered to be absorbed after oral administration and to exert its pharmacological action via kinins produced by kininogen degradation in dogs.

Discovery, optimization, and pharmacological characterization of novel heteroaroylphenylureas antagonists of C-C chemokine ligand 2 function.

Through the application of TRAP (target-related affinity profiling), we identified a novel class of heteroaroylphenylureas that inhibit human CCL2-induced chemotaxis of monocytes/macrophages both in vitro and in vivo. This inhibition was concentration-dependent and selective with regard to other chemokines. The compounds, however, did not antagonize the binding of (125)I-labeled CCL2 to the CCR2 receptor nor did they block CCR2-mediated signal transduction responses such as calcium mobilization. Optimization of early leads for potency and pharmacokinetic parameters resulted in the identification of 17, a potent inhibitor of chemotaxis (IC(50) = 80 nM) with excellent oral bioavailability in rats (F = 60%). Compound 17 reduced swelling and joint destruction in two rat models of rheumatoid arthritis and delayed disease onset and produced near complete resolution of symptoms in a mouse model of multiple sclerosis.

Low-serum culture system improves the adipogenic ability of visceral adipose tissue-derived stromal cells.

In obese adipose tissue, infiltrating macrophages release proinflammatory cytokines that trigger insulin resistance. An adipocyte-based platform from visceral fat would be useful to elucidate the pathology of adipose inflammation and to develop therapeutic drugs for insulin resistance. ADSCs (adipose tissue-derived mesenchymal stromal cells) expanded from subcutaneous fat are intensively studied as sources for regenerative medicine. However, the adipocyte culture system from visceral fat tissue has not been utilized yet. We aimed to establish the bioactive adipocyte platform using ADSCs from visceral fat pad. Stromal vascular fractions were processed from epididymal fat pads of Sprague-Dawley rats and three human omental fat pads, and the ADSCs were expanded using a low-serum culture method. The responses of ADSCs and ADSC-adipocytes (their adipogenic lineages) to pioglitazone, a therapeutic drug for diabesity, were evaluated by gene expression and ELISA. ADSCs (1×108) were expanded from 10 g of rat epididymal fat pads or human omental fat pads over five passages. Cell surface marker expressions revealed that visceral ADSCs were equivalent to mesenchymal stem cells. ADSC-adipocytes expanded in the low-serum culture system significantly showed higher expression of adipogenic markers [PPAR (peroxisome proliferator-activated receptor) γ, LPL (lipoprotein lipase) and FABP4 (fatty acid-binding protein 4)] and adipocytokines [adiponectin, resistin, leptin, PAI-1 (plasminogen-activator inhibitor 1) and IL (interleukin)-10] than those expanded in a high-serum culture system. Pioglitazone accelerated the adipogenic induction and increased adiponectin expression in human ADSCs by 57.9±5.8-fold (mean±S.E.M.) relative to control cells (P<0.001). Both in rat and human ADSC-adipocytes, TNF-α significantly induced proinflammatory cytokines [MCP-1 (monocyte chemoattractant protein-1) and IL-6] and suppressed adiponectin expression, while pioglitazone antagonized these effects. The present findings suggest that visceral ADSC-adipocytes expanded in low-serum culture would be useful for adiposcience and pharmacological evaluations.

Bezafibrate induces myotoxicity in human rhabdomyosarcoma cells via peroxisome proliferator-activated receptor alpha signaling.

Fibrates, the ligands of peroxisome proliferator-activated receptor alpha (PPARalpha), are used as a class of lipid-lowering drugs in clinical practice for the treatment of dyslipidemia. Fibrates are well tolerated in most cases concomitantly with occasional adverse reactions including muscular toxicity, which is enhanced by the combination with statins. This study was designed to investigate the effects of bezafibrate as a PPARalpha agonist on human embryo rhabdomyosarcoma (RD) cells and possible mechanisms responsible for bezafibrate-mediated myopathy. The results revealed that bezafibrate caused a dose-dependent decrease in cell viability, which was fortified in association with atorvastatin at a pharmacological dose. Bezafibrate at toxic doses of 300 and 1000microM upregulated PPARalpha at the mRNA level, counteracted by a PPARalpha antagonist (MK886). Bezafibrate at a toxic dose induced typical apoptotic characteristics related to the inhibition of phosphorylation of Akt which was blocked by PPARalpha antagonist. Toxic doses of bezafibrate initiated a significant increase in pyruvate dehydrogenase kinase 4 mRNA and protein levels, compromised by MK886. These results suggest the critical roles of PPARalpha signaling in bezafibrate-induced myotoxicity and the involvement of apoptosis through Akt pathway.

Effects of kallidinogenase on ischemic changes induced by repeated intravitreal injections of endothelin-1 in rabbit retina.

PURPOSE: Repeated intravitreal injections of endothelin-1 (ET-1) lead to alterations in the visually evoked potentials (VEPs) and loss of retinal ganglion cells (RGCs) in rabbits. The purpose of this study was to determine whether kallidinogenase can offset the alterations induced by ET-1. METHODS: ET-1 (2.5 x 10(-7) M, 20 microL) was injected into the vitreous of the right eye of rabbits (ET-1-treated eyes, n = 30) twice a week for 4 weeks. The vehicle for ET-1 was injected into the left eye on the same schedule (vehicle treated eyes, n = 30). During this 4 weeks period, kallidinogenase (1.0 unit/kg/day, kallidinogenase-treated group) or saline (saline-injected control group) was continuously delivered intravenously by an implanted osmotic pump. VEPs were recorded before, and 2 weeks and 4 weeks after, the first ET-1 injection, and all rabbits were sacrificed at 4 weeks. The number of RGC cells was counted in hematoxylin- and eosin-stained retinal sections. In the analyses, the ET-1 induced alterations were normalized to the values in the vehicle treated control eyes, i.e., kallidinogenase (K) + ET-1/K+ vehicle or saline (S) +ET-1/S + vehicle. Retinal sections were also examined by immunohistochemistry with antibodies to single-stranded DNA (ssDNA) or to glial fibrillary acidic protein (GFAP). The effect of kallidinogenase on the ONH blood flow was determined by a hydrogen gas clearance flowmeter. RESULTS: The significant prolongation of the relative VEP implicit times (ITs) 4 weeks after the ET-1 injection (P < 0.01, paired t test; post-ET-1 vs. pre-ET-1) was significantly decreased by kallidinogenase (P < 0.001, t test, K + ET-1/K+ vehicle vs. S +ET-1/S + vehicle). The relative number of RGCs was decreased in the saline-injected group, and this decrease was also decreased by kallidinogenase (P < 0.05, t test, K + ET-1/K+ vehicle vs. S +ET-1/S + vehicle). ssDNA staining showed fewer apoptotic cells in the retina of kallidinogenase-treated rabbits. Intravitreal injection of ET-1 also decreased the blood flow in the optic nerve head and increased the GFAP immunostaining and axonal degeneration. These changes were also counteracted by kallidinogenase. CONCLUSION: These results indicate that kallidinogenase can counter the effects of ET-1 and should be considered for the treatment of ischemic retinal and optic nerve disorders related to abnormal ET-1 production.

The correlation between expression and localization of a foreign gene product in rice endosperm.

Glucagon-like peptide 1 (GLP-1) is a 30 amino acid peptide hormone involved in insulin stimulation that is dependent upon blood glucose levels. We have previously reported that when this short peptide gene was directly expressed under the control of a glutelin promoter and its signal peptide, it was not accumulated in transgenic rice seed due to gene silencing. However, when the modified GLP-1 (mGLP-1) gene was enlarged to 5xmGLP-1 (mGLPx5) by tandem repeat, no silencing was observed. The mGLPx5 peptide could be accumulated in rice seed and its localization was mainly limited to the endoplasmic reticulum (ER). We also investigated alternative cellular localization sites that would increase accumulation. The relationship between the expression level and localization was examined by attaching the chitinase signal peptide to mGLPx5 to direct it into the intercellular space (apoplast), or by expression as a fusion protein with glutelin by insertion into a variable region of the acidic subunit, thus directing the peptide to protein body II (PB II). Attachment of the KDEL ER retention signal to the 6xmGLP-1 (mGLPx6) or its fusion to the C-terminus of the 13 kDa prolamin directed the peptide to the ER or PB I, respectively. Unexpectedly, these results indicated that mGLPx5 without any signal except for the glutelin signal peptide was accumulated to the greatest extent in rice endosperm. It can thus be concluded that the ER is a suitable intracellular organelle for accumulation of mGLPx5 peptide.

Expression of the small peptide GLP-1 in transgenic plants.

Glucagon-like peptide 1 (GLP-1) has great potential in diabetes therapy. In order to accumulate GLP-1 in endosperm tissue of rice, a codon-optimized GLP-1 (mGLP-1) synthetic gene was directly expressed under the control of rice storage protein glutelin GluB-1 promoter in transgenic rice plants. Unexpectedly, neither the transcripts nor the transgene products were detected in the seeds of regenerated plants. Furthermore, transcripts of GluB-1 gene in these transgenic plants were not detected, and small interfering RNAs (siRNAs) corresponding to the transgene were detected. These results indicated that the expression of mGLP-1 was silenced by co-suppression in rice transgenic seeds. To avoid silencing, mGLP-1 was fused to GFP with or without self-processing 2A sequence, and introduced into rice plants. Both chimeric genes were highly expressed in these transgenic rice seeds, indicating that gene silencing could be avoided by changing the transgene components. Furthermore, the fusion protein containing the 2A sequence were processed into GFP-2A and mGLP-1 peptides with the efficiency of more than 80%, but the processed mGLP-1 peptides were not detected. Lack of accumulation of mGLP-1 may be explained by proteolytic digestion in the cytoplasm.

Genetically modified rice seeds accumulating GLP-1 analogue stimulate insulin secretion from a mouse pancreatic beta-cell line.

Glucagon-like peptide-1 (7-36) amide (GLP-1) is the most potent physiological insulinotropic hormone in humans. We produced large amounts of a GLP-1 analogue, [Ser8, Gln26, Asp34]-GLP-1, which is resistant to trypsin-digestion, as part of a chimeric rice seed storage protein, a 26 kDa globulin, in genetically modified rice seeds. Junction sites between GLP-1 analogue and globulin were replaced by tryptic cleavage sites. The highest level of GLP-1 analogue accumulation was approximately 20-50 microg per seed. We found that GLP-1 analogue derived from trypsin-digested genetically modified rice seeds stimulated insulin secretion from a mouse pancreatic beta-cell line, MIN6.

Reduced cell replication and induction of apoptosis by advanced glycation end products in rat Schwann cells.

We investigated the effects of advanced glycation end products (AGEs) derived from glucose, glyceraldehyde, and glycolaldehyde (designated as AGE-1, -2, and -3, respectively) on the viability, replication rate, and cytokine production of cultured Schwann cells. AGE-2 and -3, but not AGE-1, induced apoptosis, and significantly decreased the viability measured by MTT assay. The decrease was prevented completely by antioxidant alpha-lipoic acid and was prevented partially by p38 mitogen-activated protein kinase inhibitor SB202190. The decrease in mitochondrial membrane potential by AGE-2 and -3 was also observed. In addition, AGE-2 and -3 significantly suppressed the replication rate as shown by reduced bromodeoxyuridine uptake, whereas they enhanced the release of TNF-alpha and IL-1beta into the medium and activated nuclear factor-kappaB. The effects of AGE-1 on these measures were equivocal. The series of events elicited by AGE-2 and -3 may be responsible for some of the aspects of pathogenetic mechanisms in patients with diabetic neuropathy.

Long-term treatment with fidarestat suppresses the development of diabetic retinopathy in STZ-induced diabetic rats.

It is important to suppress retinal vascular changes for prevention of the onset and progression of diabetic retinopathy. In the present study, we investigated the dose-response effect of an aldose reductase (AR) inhibitor, fidarestat, on retinal vascular changes in the retinas of streptozotocin (STZ)-induced diabetic rats. Fidarestat (0.5, 1, and 2 mg/kg) was administered once a day, from 4 days after STZ injection, for 15 months. Microaneurysms and thickness of the basement membrane were frequently observed in the untreated diabetic group as compared to the nondiabetic control group. In addition, the number of pericytes decreased in the untreated diabetic group. Fidarestat diminished the prevalence rate of microaneurysms, basement membrane thickness and decrease in the number of pericytes, and complete suppression was observed at a dose of 2 mg/kg. Fidarestat also dose-dependently inhibited sorbitol accumulation in the retina. Furthermore, a close correlation was observed between the prevalence rate of microaneurysms and the decrease in the number of pericytes, which indicated that damage to pericytes triggers retinal vascular changes. These results suggest that fidarestat, by virtue of its long-term correction of the accelerated polyol pathway, has a potential role in preventing the progression of diabetic retinopathy.

Sorbitol dehydrogenase overexpression potentiates glucose toxicity to cultured retinal pericytes.

The polyol pathway consists of two enzymes, aldose reductase (AR) and sorbitol dehydrogenase (SDH). There is a growing body of evidence to suggest that acceleration of the polyol pathway is implicated in the pathogenesis of diabetic vascular complications. However, a functional role remains to be elucidated for SDH in the development and progression of diabetic retinopathy. In this study, cultured bovine retinal capillary pericytes were used to investigate the effects of SDH overexpression on glucose toxicity. High glucose modestly increased reactive oxygen species (ROS) generation, decreased DNA synthesis, and up-regulated vascular endothelial growth factor (VEGF) mRNA levels in cultured pericytes. SDH overexpression was found to significantly stimulate ROS generation in high glucose-exposed pericytes and subsequently potentiate the cytopathic effects of glucose. Fidarestat, a newly developed AR inhibitor, and N-acetylcysteine, an antioxidant, completely prevented these deleterious effects of SDH overexpression on pericytes. Furthermore, fidarestat administration was found to significantly prevent vascular hyperpermeability, the characteristic changes of the early phase of diabetic retinopathy, in streptozotocin-induced diabetic rats. Our present results suggest that SDH-mediated conversion of sorbitol to fructose and the resultant ROS generation may play an active role in the pathogenesis of diabetic retinopathy. Blockage of sorbitol formation by fidarestat could be a promising therapeutic strategy for the treatment of early phase of diabetic retinopathy.

Inhibition of gastric inhibitory polypeptide signaling prevents obesity.

Secretion of gastric inhibitory polypeptide (GIP), a duodenal hormone, is primarily induced by absorption of ingested fat. Here we describe a novel pathway of obesity promotion via GIP. Wild-type mice fed a high-fat diet exhibited both hypersecretion of GIP and extreme visceral and subcutaneous fat deposition with insulin resistance. In contrast, mice lacking the GIP receptor (Gipr(-/-)) fed a high-fat diet were clearly protected from both the obesity and the insulin resistance. Moreover, double-homozygous mice (Gipr(-/-), Lep(ob)/Lep(ob)) generated by crossbreeding Gipr(-/-) and obese ob/ob (Lep(ob)/Lep(ob)) mice gained less weight and had lower adiposity than Lep(ob)/Lep(ob) mice. The Gipr(-/-) mice had a lower respiratory quotient and used fat as the preferred energy substrate, and were thus resistant to obesity. Therefore, GIP directly links overnutrition to obesity and it is a potential target for anti-obesity drugs.