Protective Role of St. John's Wort and Its Components Hyperforin and Hypericin against Diabetes through Inhibition of Inflammatory Signaling: Evidence from In Vitro and In Vivo Studies.

Diabetes mellitus is a very common chronic disease with progressively increasing prevalence. Besides the well-known autoimmune and inflammatory pathogenesis of type 1 diabetes, in many people, metabolic changes and inappropriate lifestyle favor a subtle chronic inflammatory state that contributes to development of insulin resistance and progressive loss of ß-cell function and mass, eventually resulting in metabolic syndrome or overt type 2 diabetes. In this paper, we review the anti-inflammatory effects of the extract of Hypericum perforatum L. (St. John's wort, SJW) and its main active ingredients firstly in representative pathological situations on inflammatory basis and then in pancreatic ß cells and in obese or diabetic animal models. The simultaneous and long-lasting inhibition of signal transducer and activator of transcription (STAT)-1, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and mitogen-activated protein kinases (MAPKs)/c-jun N-terminal kinase (JNK) signaling pathways involved in pro-inflammatory cytokine-induced ß-cell dysfunction/death and insulin resistance make SJW particularly suitable for both preventive and therapeutic use in metabolic diseases. Hindrance of inflammatory cytokine signaling is likely dependent on the hyperforin content of SJW extract, but recent data reveal that hypericin can also exert relevant protective effects, mediated by activation of the cyclic adenosine monophosphate (cAMP)/protein kinase cAMP-dependent (PKA)/adenosine monophosphate activated protein kinase (AMPK) pathway, against high-fat-diet-induced metabolic abnormalities. Actually, the mechanisms of action of the two main components of SJW appear complementary, strengthening the efficacy of the plant extract. Careful quantitative analysis of SJW components and suitable dosage, with monitoring of possible drug-drug interaction in a context of remarkable tolerability, are easily achievable pre-requisites for forthcoming clinical applications.

Conformal coating by multilayer nano-encapsulation for the protection of human pancreatic islets: In-vitro and in-vivo studies.

To improve the efficiency of pancreatic islet transplantation, we performed in-vitro and in-vivo experiments with isolated human pancreatic islets coated by multi-layer nano-encapsulation using differently charged polymers [chitosan and poly(sodium styrene sulfonate)] to obtain up to 9 layers. The islet coating (thickness: 104.2 ±â€¯4.2 nm) was uniform, with ≥ 90% cell viability and well preserved beta- and alpha-cell ultrastructure. Nano-encapsulated islets maintained physiological glucose-stimulated insulin secretion by both static incubation and perifusion studies. Notably, palmitate- or cytokine-induced toxicity was significantly reduced in nano-coated islets. Xenotransplantation of nano-encapsulated islets under the kidney capsule of streptozotocin-induced C57Bl/6J diabetic mice allowed long term normal or near normal glycemia, associated with minimal infiltration of immune cell into the grafts, well preserved islet morphology and signs of re-vascularization. In summary, the multi-layer nano-encapsulation approach described in the present study provides a promising tool to effectively protect human islets both in-vitro andin-vivo conditions.

How to Direct the Neuronal Growth Process in Peripheral Nerve Regeneration: Future Strategies for Nanosurfaces Scaffold and Magnetic Nanoparticles.

Currently, the gold standard to repair large nerve defects is the autologous nerve graft. These solutions offer a mechanical support, adhesion substrates, and, with Schwann cells (SC), a source of neurotropic factors for axonal growth. The technical limits are the donor side damage, multiple surgical accesses, and the unavailability of large amounts of grafts. In recent years, several researchers focused their attention on the interaction between cells (nervous and glial) and physic-chemical cues that arise from the extracellular milieu. Nanotechnologies produce surfaces that mimic the topographical signals (physical stimuli) that arise from enterprise content management (ECM) to modulate the forces acting during axonal elongation. The use of magnetic nanoparticles (MNPs) seems to be able to guide and to boost the nerve regeneration. Both research areas could be improved through surfaces functionalization by biological molecules (proteins/peptides, growth factors, etc.). In the future, the aim will be to help recovery after peripheral nerve lesion by producing a tridimensional structured conduit, then repeat the ECM architecture and take advantage of MNPs internalized by cells and guide them through tension forces by external magnetic fields to stimulate and direct axon growing. The aims of this review were to evaluate the findings of studies that used physical stimuli (nanoscaffold surfaces and MNPs) used for peripheral nerve regeneration support. The future trends in the field of peripheral nerve regeneration continue to produce a wide variety of new techniques to improve the opportunity for advances to treat peripheral nerve injuries.

Direct interaction of garcinol and related polyisoprenylated benzophenones of Garcinia cambogia fruits with the transcription factor STAT-1 as a likely mechanism of their inhibitory effect on cytokine signaling pathways.

Garcinol (1), a polyisoprenylated benzophenone occurring in Garcinia species, has been reported to exert anti-inflammatory activity in LPS-stimulated macrophages, through inhibition of NF-κB and/or JAK/STAT-1 activation. In order to provide deeper insight into its effects on the cytokine signaling pathway and to clarify the underlying molecular mechanisms, 1 was isolated from the fruits of Garcinia cambogia along with two other polyisoprenylated benzophenones, guttiferones K (2) and guttiferone M (3), differing from each other in their isoprenyl moieties and their positions on the benzophenone core. The affinities of 1-3 for the STAT-1 protein have been evaluated by surface plasmon resonance and molecular docking studies and resulted in KD values in the micromolar range. Consistent with the observed high affinity toward the STAT-1 protein, garcinol and guttiferones K and M were able to modulate cytokine signaling in different cultured cell lines, mainly by inhibiting STAT-1 nuclear transfer and DNA binding, as assessed by an electrophorectic mobility shift assay.

Dopamine-mediated autocrine inhibition of insulin secretion.

The aim of the present research was to explore the mechanisms underlying the role of dopamine in the regulation of insulin secretion in beta cells. The effect of dopamine on insulin secretion was investigated on INS 832/13 cell line upon glucose and other secretagogues stimulation. Results show that dopamine significantly inhibits insulin secretion stimulated by both glucose and other secretagogues, while it has no effect on the basal secretion. This effect requires the presence of dopamine during incubation with the various secretagogues. Both electron microscopy and immunohistochemistry indicate that in beta cells the D2 dopamine receptor is localized within the insulin granules. Blocking dopamine entry into the insulin granules by inhibiting the VMAT2 transporter with tetrabenazine causes a significant increase in ROS production. Our results confirm that dopamine plays an important role in the regulation of insulin secretion by pancreatic beta cells through a regulated and precise compartmentalization mechanisms.

Synthesis and preliminary biological profile of new NO-donor tolbutamide analogues.

We describe a new class of NO-donor hypoglycemic products obtained by joining tolbutamide, a typical hypoglycemic sulfonylurea, with a NO-donor moiety through a hard link. As NO-donors we chose either furoxan (1,2,5-oxadiazole 2-oxide) derivatives or the classical nitrooxy function. A preliminary biological characterization of these compounds, including stimulation of insulin release from cultured rat pancreatic ß-cells and in vitro vasodilator and anti-aggregatory activities, is reported.

Dysregulated insulin secretion is associated with pancreatic ß-cell hyperplasia and direct acinar-ß-cell trans-differentiation in partially eNOS-deficient mice.

eNOS-deficient mice were previously shown to develop hypertension and metabolic alterations associated with insulin resistance either in standard dietary conditions (eNOS-/- homozygotes) or upon high-fat diet (HFD) (eNOS+/- heterozygotes). In the latter heterozygote model, the present study investigated the pancreatic morphological changes underlying the abnormal glycometabolic phenotype. C57BL6 wild type (WT) and eNOS+/- mice were fed with either chow or HFD for 16 weeks. After being longitudinally monitored for their metabolic state after 8 and 16 weeks of diet, mice were euthanized and fragments of pancreas were processed for histological, immuno-histochemical and ultrastructural analyses. HFD-fed WT and eNOS+/- mice developed progressive glucose intolerance and insulin resistance. Differently from WT animals, eNOS+/- mice showed a blunted insulin response to a glucose load, regardless of the diet regimen. Such dysregulation of insulin secretion was associated with pancreatic ß-cell hyperplasia, as shown by larger islet fractional area and ß-cell mass, and higher number of extra-islet ß-cell clusters than in chow-fed WT animals. In addition, only in the pancreas of HFD-fed eNOS+/- mice, there was ultrastructural evidence of a number of hybrid acinar-ß-cells, simultaneously containing zymogen and insulin granules, suggesting the occurrence of a direct exocrine-endocrine transdifferentiation process, plausibly triggered by metabolic stress associated to deficient endothelial NO production. As suggested by confocal immunofluorescence analysis of pancreatic histological sections, inhibition of Notch-1 signaling, likely due to a reduced NO availability, is proposed as a novel mechanism that could favor both ß-cell hyperplasia and acinar-ß-cell transdifferentiation in eNOS-deficient mice with impaired insulin response to a glucose load.

Mast Cells and the Pancreas in Human Type 1 and Type 2 Diabetes.

Mast cells are highly differentiated, widely distributed cells of the innate immune system, that are currently considered as key regulators of both innate and adaptive immunity. Mast cells play a key role in health and survival mechanisms, especially as sentinel cells that can stimulate protective immune responses. On the other hand, it has been shown that mast cells are involved in the pathogenesis of several diseases, and recently a possible pathogenetic role of mast cells in diabetes has been proposed. In this review we summarize the evidence on the increased presence of mast cells in the pancreas of subjects with type 1 diabetes, which is due to the autoimmune destruction of insulin secreting beta cells, and discuss the differences with type 2 diabetes, the other major form of diabetes. In addition, we describe some of the pathophysiological mechanisms through which mast cells might exert their actions, which could be targeted to potentially protect the beta cells in autoimmune diabetes.

Selective beta-cell toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin on isolated pancreatic islets.

An association between exposure to environmental pollutants and diabetes risk has been repeatedly shown by epidemiological studies. However, the biological basis of this association still need to be clarified. In this research we explored the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure on isolated pancreatic islets. After 1, 6 and 24 h exposure of isolated islets to different concentrations (1-50 nM) of TCDD we assayed: i) cell survival; ii) ultrastructure; iii) glucose-stimulated insulin secretion (GSIS); iv) expression of selected genes. A significant, dose-related increase of both necrosis and apoptosis was observed isolated rat islets after 24 h exposure to TCDD. The electron microscopic analysis revealed, at the same time point, the presence of several ultrastructural alterations (mitochondrial swelling, increased mitophagy, dilation of the endoplasmic reticulum) that, very interestingly, were exclusively observed in beta cells and not in other endocrine cells. Similar results were obtained in isolated human islets. GSIS was rapidly (1 h) and persistently (6 and 24 h) decreased by TCDD exposure even at the smallest concentration (1 nM). TCDD exposure significantly affected gene expression in isolated islets: Glut2, Gck, Bcl-xL, MafA, Pdx1 FoxO1 and IRE1 gene expression was significantly decreased, whereas Puma, DP5, iNOS and Chop gene expression was significantly increased after 6 h exposure to TCDD. In conclusion, our results clearly indicated that pancreatic beta cells represent not only a sensitive but also a specific target of the toxic action of dioxin.

ß-Cells Different Vulnerability to the Parkinsonian Neurotoxins Rotenone, 1-Methyl-4-phenylpyridinium (MPP+) and 6-Hydroxydopamine (6-OHDA).

Neurotoxins such as rotenone, 1-methyl-4-phenylpyridinium (MPP+) and 6-hydroxydopamine (6-OHDA) are well known for their high toxicity on dopaminergic neurons and are associated with Parkinson's disease (PD) in murine models and humans. In addition, PD patients often have glucose intolerance and may develop type 2 diabetes (T2D), whereas T2D patients have higher risk of PD compared to general population. Based on these premises, we evaluated the toxicity of these three toxins on pancreatic ß-cell lines (INS-1 832/13 and MIN6) and we showed that rotenone is the most potent for reducing ß-cells viability and altering mitochondrial structure and bioenergetics in the low nanomolar range, similar to that found in dopaminergic cell lines. MPP+ and 6-OHDA show similar effects but at higher concentration. Importantly, rotenone-induced toxicity was counteracted by α-tocopherol and partially by metformin, which are endowed with strong antioxidative and cytoprotective properties. These data show similarities between dopaminergic neurons and ß-cells in terms of vulnerability to toxins and pharmacological agents capable to protect both cell types.

Anti-Tumor Activity of Hypericum perforatum L. and Hyperforin through Modulation of Inflammatory Signaling, ROS Generation and Proton Dynamics.

In this paper we review the mechanisms of the antitumor effects of Hypericum perforatum L. (St. John's wort, SJW) and its main active component hyperforin (HPF). SJW extract is commonly employed as antidepressant due to its ability to inhibit monoamine neurotransmitters re-uptake. Moreover, further biological properties make this vegetal extract very suitable for both prevention and treatment of several diseases, including cancer. Regular use of SJW reduces colorectal cancer risk in humans and prevents genotoxic effects of carcinogens in animal models. In established cancer, SJW and HPF can still exert therapeutic effects by their ability to downregulate inflammatory mediators and inhibit pro-survival kinases, angiogenic factors and extracellular matrix proteases, thereby counteracting tumor growth and spread. Remarkably, the mechanisms of action of SJW and HPF include their ability to decrease ROS production and restore pH imbalance in tumor cells. The SJW component HPF, due to its high lipophilicity and mild acidity, accumulates in membranes and acts as a protonophore that hinders inner mitochondrial membrane hyperpolarization, inhibiting mitochondrial ROS generation and consequently tumor cell proliferation. At the plasma membrane level, HPF prevents cytosol alkalization and extracellular acidification by allowing protons to re-enter the cells. These effects can revert or at least attenuate cancer cell phenotype, contributing to hamper proliferation, neo-angiogenesis and metastatic dissemination. Furthermore, several studies report that in tumor cells SJW and HPF, mainly at high concentrations, induce the mitochondrial apoptosis pathway, likely by collapsing the mitochondrial membrane potential. Based on these mechanisms, we highlight the SJW/HPF remarkable potentiality in cancer prevention and treatment.

Starvation Promotes Autophagy-Associated Maturation of the Testis in the Giant Freshwater Prawn, Macrobrachium rosenbergii.

Autophagy is a degradative process of cellular components accomplished through an autophagosomal-lysosomal pathway. It is an evolutionary conserved mechanism present in all eukaryotic cells, and it plays a fundamental role in maintaining tissue homeostasis both in vertebrates and invertebrates. Autophagy accompanies tissue remodeling during organ differentiation. Several autophagy-related genes and proteins show significant upregulations following nutrient shortage (i.e., starvation). In our previous study, we found that in female giant freshwater prawns subjected to a short period of starvation autophagy was up-regulated in consonant with ovarian maturation and oocyte differentiation. Whether and how starvation-induced autophagy impacts on testicular maturation and spermatogenesis of the male prawns remained to be investigated. In this study, we analyzed the effects of starvation on histological and cellular changes in the testis of the giant freshwater prawn Macrobrachium rosenbergii that paralleled the induction of autophagy. Under short starvation condition, the male prawns showed increased gonado-somatic index, increased size, and late stage of maturation of seminiferous tubules, which contained increased number of spermatozoa. Concurrently, the number of autophagy vacuoles and autophagy flux, as monitored by transmission electron microscopy and the autophagic marker LC3, increased in the testicular cells, indicating that a short period of starvation could induce testicular maturation and spermatogenesis in male M. rosenbergii along with modulation of autophagy.

Persistence of STAT-1 inhibition and induction of cytokine resistance in pancreatic ß cells treated with St John's wort and its component hyperforin.

OBJECTIVES: St John's wort extract (SJW) and its component hyperforin (HPF) were shown to potently inhibit cytokine-induced STAT-1 and NF-κB activation in pancreatic ß cells and protect them against injury. This study aimed at exploring the time course of STAT-1 inhibition afforded by these natural compounds in the ß-cell line INS-1E. METHODS: INS-1E cells were pre-incubated with SJW extract (2-5 µg/ml) or HPF (0.5-2 µm) and then exposed to a cytokine mixture. In some experiments, these compounds were added after or removed before cytokine exposure. STAT-1 activation was assessed by electrophoretic mobility shift assay, apoptosis by caspase-3 activity assay, mRNA gene expression by RT-qPCR. KEY FINDINGS: Pre-incubation with SJW/HPF for 1-2 h exerted a remarkable STAT-1 downregulation, which was maintained upon removal of the compounds before early or delayed cytokine addition. When the protective compounds were added after cell exposure to cytokines, between 15 and 90 min, STAT-1 inhibition also occurred at a progressively decreasing extent. Upon 24-h incubation, SJW and HPF counteracted cytokine-induced ß-cell dysfunction, apoptosis and target gene expression. CONCLUSIONS: SJW and HPF confer to ß cells a state of 'cytokine resistance', which can be elicited both before and after cytokine exposure and safeguards these cells from deleterious cytokine effects.

Protective effects of St. John's wort extract and its component hyperforin against cytokine-induced cytotoxicity in a pancreatic beta-cell line.

In both type 1 and type 2 diabetes, increased production of cytokines on autoimmune or metabolic basis is supposed to trigger an inflammatory process leading to dysfunction and death of pancreatic beta-cells. Therefore, anti-inflammatory pharmacological approaches aimed at blocking cytokine signalling pathways and consequent cytotoxicity in beta-cells are highly advisable. Based on previous evidence of cytokine antagonistic effects in other cell types, we explored the protective action of Hypericum perforatum (St-John's-wort) extract and its component hyperforin against cytokine-induced functional impairment and apoptosis in the INS-1E beta-cell line, searching for the underlying mechanisms. The results showed that either St-John's-wort extract or hyperforin (at 1-3 microM) prevented cytokine-induced impairment in glucose-stimulated insulin secretion and protected cells against apoptosis in a dose-dependent fashion. Inducible-NO-synthase expression was also potently hindered by the vegetal compounds. Interestingly, cytokine-induced activations of the signal-transducer-and-activator-of-transcription-1 (STAT-1) and the nuclear-factor-kappaB (NF-kappaB) were both down-regulated by SJW extract or HPF (range 0.5-5 microM) when evaluated by electrophoretic-mobility-shift-assay. Other transcription factors (CBF-1, SP-1) were unaffected. Components of SJW extract other than HPF were much less effective in down-regulating cytokine signalling. Significantly, inhibition of cytokine-elicited STAT-1 and NF-kappaB activation was confirmed in isolated rat and human islets incubated in the presence of these vegetal compounds. In conclusion, St-John's-wort extract and hyperforin are non-peptidyl compounds which, at low concentrations, target key mechanisms of cytokine-induced beta-cell injury, thereby improving beta-cell function and survival. Thus, they are potentially valuable for the prevention or limitation of beta-cell loss in diabetes.

Starvation Promotes Autophagy-Associated Maturation of the Ovary in the Giant Freshwater Prawn, Macrobrachium rosenbergii.

Limitation of food availability (starvation) is known to influence the reproductive ability of animals. Autophagy is a lysosomal driven degradation process that protects the cell under metabolic stress conditions, such as during nutrient shortage. Whether, and how starvation-induced autophagy impacts on the maturation and function of reproductive organs in animals are still open questions. In this study, we have investigated the effects of starvation on histological and cellular changes that may be associated with autophagy in the ovary of the giant freshwater prawn, Macrobachium rosenbergii. To this end, the female prawns were daily fed (controls) or unfed (starvation condition) for up to 12 days, and the ovary tissue was analyzed at different time-points. Starvation triggered ovarian maturation, and concomitantly increased the expression of autophagy markers in vitellogenic oocytes. The immunoreactivities for autophagy markers, including Beclin1, LC3-II, and Lamp1, were enhanced in the late oocytes within the mature ovaries, especially at the vitellogenic stages. These markers co-localized with vitellin in the yolk granules within the oocytes, suggesting that autophagy induced by starvation could drive vitellin utilization, thus promoting ovarian maturation.

Magnetic Nanoparticles for Efficient Delivery of Growth Factors: Stimulation of Peripheral Nerve Regeneration.

The only clinically approved alternative to autografts for treating large peripheral nerve injuries is the use of synthetic nerve guidance conduits (NGCs), which provide physical guidance to the regenerating stump and limit scar tissue infiltration at the injury site. Several lines of evidence suggest that a potential future strategy is to combine NGCs with cellular or molecular therapies to deliver growth factors that sustain the regeneration process. However, growth factors are expensive and have a very short half-life; thus, the combination approach has not been successful. In the present paper, we proposed the immobilization of growth factors (GFs) on magnetic nanoparticles (MNPs) for the time- and space-controlled release of GFs inside the NGC. We tested the particles in a rat model of a peripheral nerve lesion. Our results revealed that the injection of a cocktail of MNPs functionalized with nerve growth factor (NGF) and with vascular endothelial growth factor (VEGF) strongly accelerate the regeneration process and the recovery of motor function compared to that obtained using the free factors. Additionally, we found that injecting MNPs in the NGC is safe and does not impair the regeneration process, and the MNPs remain in the conduit for weeks.

St. John's wort extract and hyperforin inhibit multiple phosphorylation steps of cytokine signaling and prevent inflammatory and apoptotic gene induction in pancreatic ß cells.

The extract of the herbaceous plant St. John's wort (SJW) and its phloroglucinol component hyperforin (HPF) were previously shown to inhibit cytokine-induced STAT-1 and NF-κB activation and prevent damage in pancreatic ß cells. To further clarify the mechanisms underlying their protective effects, we evaluated the phosphorylation state of various factors of cytokine signaling pathways and the expression of target genes involved in ß-cell function, inflammatory response and apoptosis induction. In the INS-1E ß-cell line, exposed to a cytokine mixture with/without SJW extract (2-5µg/ml) or HPF (1-5µM), protein phosphorylation was assessed by western blotting and expression of target genes by real-time quantitative PCR. SJW and HPF markedly inhibited, in a dose-dependent manner (from 60 to 100%), cytokine-induced activating phosphorylations of STAT-1, NF-κB p65 subunit and IKK (NF-κB inhibitory subunit IκBα kinase). MAPK and Akt pathways were also modulated by the vegetal compounds through hindrance of p38 MAPK, ERK1/2, JNK and Akt phosphorylations, each reduced by at least 65% up to 100% at the higher dose. Consistently, SJW and HPF a) abolished cytokine-induced mRNA expression of pro-inflammatory genes; b) avoided down-regulation of relevant ß-cell functional/differentiation genes; c) corrected cytokine-driven imbalance between pro- and anti-apoptotic factors, by fully preventing up-regulation of pro-apoptotic genes and preserving expression or function of anti-apoptotic Bcl-2 family members; d) protected INS-1E cells against cytokine-induced apoptosis. In conclusion, SJW extract and HPF exert their protective effects through simultaneous inhibition of multiple phosphorylation steps along various cytokine signaling pathways and consequent restriction of inflammatory and apoptotic gene expression. Thus, they have a promising therapeutic potential for the prevention or limitation of immune-mediated ß-cell dysfunction and damage leading to type 1 diabetes.

Lipotoxicity in human pancreatic islets and the protective effect of metformin.

Human pancreatic islets from eight donors were incubated for 48 h in the presence of 2.0 mmol/l free fatty acid (FFA) (oleate to palmitate, 2 to 1). Insulin secretion was then assessed in response to glucose (16.7 mmol/l), arginine (20 mmol/l), and glyburide (200 micromol/l) during static incubation or by perifusion. Glucose oxidation and utilization and intra-islet triglyceride content were measured. The effect of metformin (2.4 microg/ml) was studied because it protects rat islets from lipotoxicity. Glucose-stimulated but not arginine- or glyburide-stimulated insulin release was significantly lower from FFA-exposed islets. Impairment of insulin secretion after exposure to FFAs was mainly accounted for by defective early-phase release. In control islets, increasing glucose concentration was associated with an increase in glucose utilization and oxidation. FFA incubation reduced both glucose utilization and oxidation at maximal glucose concentration. Islet triglyceride content increased significantly after FFA exposure. Addition of metformin to high-FFA media prevented impairment in glucose-mediated insulin release, decline of first-phase insulin secretion, and reduction of glucose utilization and oxidation without significantly affecting islet triglyceride accumulation. These results show that lipotoxicity in human islets is characterized by selective loss of glucose responsiveness and impaired glucose metabolism, with a clear defect in early-phase insulin release. Metformin prevents these deleterious effects, supporting a direct protective action on human beta-cells.

2,3,7,8-Tetrachlorodibenzo-p-dioxin-induced impairment of glucose-stimulated insulin secretion in isolated rat pancreatic islets.

We have explored the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) administration on the secretory function of isolated rat pancreatic islets. Twenty-four hours after TCDD administration (1 microg/kg b.w., i.p.), rats showed no significant differences in plasma glucose, insulin, triglycerides and leptin levels whereas plasma-free fatty acids were significantly increased with respect to untreated controls. In isolated islets, DNA and protein content were unchanged, whereas insulin content was significantly decreased in TCDD-treated rats. Incubation with different concentrations of glucose demonstrated a significant impairment of glucose-stimulated insulin secretion in islets isolated from TCDD-treated rats, whereas insulin release was better preserved upon alpha-ketoisocaproate stimulation. A significant reduction of [3H]-2-deoxy-glucose uptake was observed in pancreatic tissue of TCDD-treated rats, whereas no significant reduction in GLUT-2 protein levels was detectable by immunoblotting in islets from TCDD-treated rats. We concluded that low-dose TCDD could rapidly induce significant alterations of the pancreatic endocrine function in the rat.