Distribution of FMRFamide-related peptides and co-localization with glutamate in Cupiennius salei, an invertebrate model system.

FMRFamide-related proteins have been described in both vertebrate and invertebrate nervous systems and have been suggested to play important roles in a variety of physiological processes. One proposed function is the modulation of signal transduction in mechanosensory neurons and their associated behavioral pathways in the Central American wandering spider Cupiennius salei; however, little is known about the distribution and abundance of FMRFamide-related proteins (FaRPs) within this invertebrate system. We employ immunohistochemistry, Hoechst nuclear stain and confocal microscopy of serial sections to detect, characterize and quantify FMRFamide-like immunoreactive neurons throughout all ganglia of the spider brain and along leg muscle. Within the different ganglia, between 3.4 and 12.6% of neurons showed immunolabeling. Among the immunoreactive cells, weakly and strongly labeled neurons could be distinguished. Between 71.4 and 81.7% of labeled neurons showed weak labeling, with 18.3 to 28.6% displaying strong labeling intensity. Among the weakly labeled neurons were characteristic motor neurons that have previously been shown to express ɣ-aminobutyric acid or glutamate. Ultrastructural investigations of neuromuscular junctions revealed mixed presynaptic vesicle populations including large electron-dense vesicles characteristic of neuropeptides. Double labeling for glutamate and FaRPs indicated that a subpopulation of neurons may co-express both neuroactive compounds. Our findings suggest that FaRPs are expressed throughout all ganglia and that different neurons have different expression levels. We conclude that FaRPs are likely utilized as neuromodulators in roughly 8% of neurons in the spider nervous system and that the main transmitter in a subpopulation of these neurons is likely glutamate.

Identification and characterization of a new antifungal peptide in fermented milk product containing bioprotective Lactobacillus cultures.

Mold and yeast contamination constitutes a major problem in food commodities, including dairy products, hence new natural preventive measures are in high demand. The aim of the current study is to identify and characterize novel antifungal peptides produced by lactic acid bacteria (LAB) in sour cream. By the use of a newly developed image-based 96-well plate fungal growth inhibition assay targeting Debaryomyces hansenii, combined with a range of analytical tools comprising HPLC-high-resolution mass spectrometry, ultrahigh-performance liquid chromatography-Triple Quadrupole MS and nuclear magnetic resonance spectroscopy, we successfully identified a new antifungal peptide (DMPIQAFLLY; 1211 Da) in sour cream enriched with two bioprotective LAB strains. This peptide represents a fragment of casein, the most abundant protein in milk. Presumably, the proteolytic activity of these bioprotective strains results in the observed 4-fold higher concentration of the peptide during storage. Both bioprotective strains are able to generate this peptide in concentrations up to 0.4 µM, independently of the sour cream starter culture employed. The peptide attenuates the growth rate of D. hansenii at concentrations ≥35 µM, and results in smaller cells and more compact colonies. Hence, the peptide is likely contributing to the overall preserving effect of the investigated bioprotective LAB strains.

Mechanistic study of the inhibitory activity of Geum urbanum extract against α-Synuclein fibrillation.

The presence of Lewy bodies and Lewy neurites is a major pathological hallmark of Parkinson's disease and is hypothesized to be linked to disease development, although this is not yet conclusive. Lewy bodies and Lewy neurites primarily consist of fibrillated α-Synuclein; yet, there is no treatment available targeting stabilization of α-Synuclein in its native state. The aim of the present study was to investigate the inhibitory activity of an ethanolic extract of Geum urbanum against α-Synuclein fibrillation and examine the structural changes of α-Synuclein in the presence of the extract. The anti-fibrillation and anti-aggregation activities of the plant extract were monitored by thioflavin T fibrillation assays and size exclusion chromatography, while structural changes were followed by circular dichroism, Fourier transform infrared spectroscopy, intrinsic fluorescence, small angle X-ray scattering and electron microscopy. Since the extract is a complex mixture, structure-function relationships could not be determined. Under the experimental conditions investigated, Geum urbanum was found to inhibit α-Synuclein fibrillation in a concentration dependent way, and to partly disintegrate preformed α-Synuclein fibrils. Based on the structural changes of α-Synuclein in the presence of extract, we propose that Geum urbanum delays α-Synuclein fibrillation either by reducing the fibrillation ability of one or more of the aggregation prone intermediates or by directing α-Synuclein aggregation towards a non-fibrillar state. However, whether these alterations of the fibrillation pathway lead to less pathogenic species is yet to be determined.

Investigation of antidiabetic potential of Phyllanthus niruri L. using assays for α-glucosidase, muscle glucose transport, liver glucose production, and adipogenesis.

Phyllanthus niruri is used in herbal medicine for treatment of diabetes. The objective of this study was to investigate the antidiabetic potential of P. niruri, using assays for α-glucosidase, muscle glucose transport, liver glucose production and adipogenesis. α-Glucosidase inhibitory activity was performed on aqueous and ethanolic extract of aerial parts of P. niruri. The aqueous and ethanolic extract of P. niruri showed α-glucosidase inhibitory activity with IC50 values of 3.7 ± 1.1 and 6.3 ± 4.8 µg/mL, respectively. HR-bioassay/HPLC-HRMS and NMR analysis was used for identification of compounds. Corilagin (1) and repandusinic acid A (2) were identified as α-glucosidase inhibitors in the water extract of P. niruri with IC50 values of 0.9 ± 0.1 and 1.9 ± 0.02 µM, respectively. In in vitro cell-based bioassays, cells were treated for 18 h with maximal non-toxic concentrations of the ethanolic extract of P. niruri, which were determined by the lactate dehydrogenase cytotoxicity assay. The ethanolic extract of P. niruri was not able to reduce glucose-6-phosphatase activity. However, the extract increased deoxyglucose uptake in C2C12 muscle cells and enhanced adipogenesis in 3T3-L1 fat cells which has been reported for the first time. The present study demonstrated that P. niruri may thus have potential application for treatment and/or management of type 2 diabetes.

Anti-diabetic xanthones from the bark of Garcinia xanthochymus.

An ethyl acetate extract the bark of Garcinia xanthochymus exhibited strong inhibition towards α-glucosidase and PTP1B with IC50 values of 0.3±0.1µg/mL and 2.3±0.4µg/mL, respectively. Chemical constituents of the extract were therefore examined, and two new compounds, xanthochymusxanthones A (1) and B (2), along with ten known xanthones (3-12), were isolated. Their structures were determined using spectroscopic methods, mainly 1D and 2D NMR. Inhibitory activity of the isolated compounds was then tested, and subelliptenone F (12) showed significant effect towards α-glucosidase with IC50 value of 4.1±0.3µM (compared with acarbose, IC50=900.0±3.0µM) whilst xanthochymusxanthone B (2) exhibited remarkable activity towards PTP1B with IC50 value of 8.0±0.6µM (compared with RK682, IC50=4.4±0.3µM).

Advancing HPLC-PDA-HRMS-SPE-NMR Analysis of Coumarins in Coleonema album by Use of Orthogonal Reversed-Phase C18 and Pentafluorophenyl Separations.

A hyphenated procedure involving high-performance liquid chromatography, photodiode array detection, high-resolution mass spectrometry, solid-phase extraction, and nuclear magnetic resonance spectroscopy, i.e., HPLC-PDA-HRMS-SPE-NMR, has proven an effective technique for the identification of compounds in complex matrices. Most HPLC-PDA-HRMS-SPE-NMR investigations reported so far have relied on analytical-scale reversed-phase C18 columns for separation. Herein is reported the use of an analytical-scale pentafluorophenyl column as an orthogonal separation method following fractionation of a crude ethyl acetate extract of leaves of Coleonema album on a preparative-scale C18 column. This setup allowed the HPLC-PDA-HRMS-SPE-NMR analysis of 23 coumarins, including six new compounds, 8-O-ß-d-glucopyranosyloxy-6-(2,3-dihydroxy-3-methylbut-1-yl)-7-methoxycoumarin (4), (Z)-6-(4-ß-d-glucopyranosyloxy-3-methylbut-2-en-1-yl)-7-hydroxycoumarin (6), 6-(4-ß-d-glucopyranosyloxy-3-methylbut-1-yl)-7-hydroxycoumarin (8), (Z)-7-(4-ß-d-glucopyranosyloxy-3-methylbut-2-en-1-yloxy)coumarin (13), (S)-8-(3-chloro-2-hydroxy-3-methylbut-1-yloxy)-7-methoxycoumarin (19), and 7-(3-chloro-2-hydroxy-3-methylbut-1-yloxy)coumarin (20). The use of the pentafluorophenyl column even allowed separation of several regioisomers that are usually difficult to separate using reversed-phase C18 columns. The phytochemical investigation described for C. album in this report demonstrates the potential and wide applicability of HPLC-PDA-HRMS-SPE-NMR for accelerated structural identification of natural products in complex mixtures.

Facilitated Visual Interpretation of Scores in Principal Component Analysis by Bioactivity-Labeling of 1H-NMR Spectra-Metabolomics Investigation and Identification of a New α-Glucosidase Inhibitor in Radix Astragali.

Radix Astragali is a component of several traditional medicines used for the treatment of type 2 diabetes in China. Radix Astragali is known to contain isoflavones, which inhibit α-glucosidase in the small intestines, and thus lowers the blood glucose levels. In this study, 21 samples obtained from different regions of China were extracted with ethyl acetate, then the IC50-values were determined, and the crude extracts were analyzed by 1H-NMR spectroscopy. A principal component analysis of the 1H-NMR spectra labeled with their IC50-values, that is, bioactivity-labeled 1H-NMR spectra, showed a clear correlation between spectral profiles and the α-glucosidase inhibitory activity. The loading plot and LC-HRMS/NMR of microfractions indicated that previously unknown long chain ferulates could be partly responsible for the observed antidiabetic activity of Radix Astragali. Subsequent preparative scale isolation revealed a compound not previously reported, linoleyl ferulate (1), showing α-glucosidase inhibitory activity (IC50 0.5 mM) at a level comparable to the previously studied isoflavones. A closely related analogue, hexadecyl ferulate (2), did not show significant inhibitory activity, and the double bonds in the alcohol part of 1 seem to be important structural features for the α-glucosidase inhibitory activity. This proof of concept study demonstrates that bioactivity-labeling of the 1H-NMR spectral data of crude extracts allows global and nonselective identification of individual constituents contributing to the crude extract's bioactivity.

High-Resolution Inhibition Profiling Combined with HPLC-HRMS-SPE-NMR for Identification of PTP1B Inhibitors from Vietnamese Plants.

Protein tyrosine phosphatase 1B (PTP1B) plays a key role as a negative regulator in insulin signal transduction by deactivating the insulin receptor. Thus, PTP1B inhibition has emerged as a potential therapeutic strategy for curing insulin resistance. In this study, 40 extracts from 18 different plant species were investigated for PTP1B inhibitory activity in vitro. The most promising one, the EtOAc extract of Ficus racemosa, was investigated by high-resolution PTP1B inhibition profiling combined with HPLC-HRMS-SPE-NMR analysis. This led to the identification of isoderrone (1), derrone (2), alpinumisoflavone (3) and mucusisoflavone B (4) as PTP1B inhibitors. IC50 of these compounds were 22.7 ± 1.7, 12.6 ± 1.6, 21.2 ± 3.8 and 2.5 ± 0.2 µM, respectively. Kinetics analysis revealed that these compounds inhibited PTP1B non-competitively with Ki values of 21.3 ± 2.8, 7.9 ± 1.9, 14.3 ± 2.0, and 3.0 ± 0.5 µM, respectively. These findings support the important role of F. racemosa as a novel source of new drugs and/or as a herbal remedy for treatment of type 2 diabetes.

Dual high-resolution α-glucosidase and radical scavenging profiling combined with HPLC-HRMS-SPE-NMR for identification of minor and major constituents directly from the crude extract of Pueraria lobata.

The crude methanol extract of Pueraria lobata was investigated by dual high-resolution α-glucosidase inhibition and radical scavenging profiling combined with hyphenated HPLC-HRMS-SPE-NMR. Direct analysis of the crude extract without preceding purification was facilitated by combining chromatograms from two analytical-scale HPLC separations of 120 and 600 µg on-column, respectively. High-resolution α-glucosidase and radical scavenging profiles were obtained after microfractionation of the eluate in 96-well microplates. This allowed full bioactivity profiling of individual peaks in the HPLC chromatogram of the crude methanol extract. Subsequent HPLC-HRMS-SPE-NMR analysis allowed identification of 21 known compounds in addition to two new compounds, i.e., 3'-methoxydaidzein 8-C-[α-D-apiofuranosyl-(1→6)]-ß-D-glucopyranoside and 6″-O-malonyl-3'-methoxydaidzin, as well as an unstable compound tentatively identified as 3'-de-O-methylpuerariafuran.

Unsafe abortion in rural Tanzania - the use of traditional medicine from a patient and a provider perspective.

BACKGROUND: The circumstances under which women obtain unsafe abortion vary and depend on the traditional methods known and the type of providers present. In rural Tanzania women often resort to traditional providers who use plant species as abortion remedies. Little is known about how these plants are used and their potential effect. METHODS: Data were obtained among women admitted with incomplete abortion at Kagera Regional Hospital during the period January - June, 2006. The women underwent an empathetic interview to determine if they had experienced an unsafe abortion prior to their admission. In all 125/187 women revealed having had an unsafe abortion. The women identified as having had an unsafe abortion underwent a questionnaire interview where information about abortion provider and abortion method used was obtained through open-ended questions. To get more detailed information about the traditional methods used to induce abortion, in-depths interviews and focus group discussions were performed among traditional providers and nurses. Finally, the plant specimen's effectiveness as abortion remedies was assessed through pharmacological analyses. RESULTS: Among women admitted with incomplete abortions, 67% had had an unsafe abortion. Almost half of the women who had experienced an unsafe abortion had resorted to traditional providers and plant species were in these cases often used as abortion remedies. In all 21 plant species were identified as potential abortion remedies and analysed, 16 of the species were found to have a uterine contractive effect; they significantly increased the force of contraction, increased the frequency of contractions or did both. CONCLUSION: Unsafe abortion is common in rural Tanzania where many women use plant species to terminate an unwanted pregnancy. The plants have a remarkable strong uterine contractive effect. To further understand the consequences of unsafe abortion there is a need for further analyses of the plants' potential toxicity and mutagenicity.

Coupling of a high-resolution monoamine oxidase-A inhibitor assay and HPLC-SPE-NMR for advanced bioactivity profiling of plant extracts.

INTRODUCTION: Depression is a mental disease causing large personal and socio-economic problems, and new improved drugs are therefore needed. Selective monoamine oxidase A (MAO-A) inhibitors are potential anti-depressants, but discovering new MAO-A inhibitors from natural sources by bioassay-guided approaches are a lengthy and time-consuming process. New analytical technologies that allow simultaneously chemical and biological screening of extracts are therefore urgently needed. METHOD: In the present study we describe coupling of a photometric microplate-based high-resolution MAO-A inhibitor assay with a hyphenated system consisting of high-performance liquid chromatography, solid-phase extraction and tube transfer nuclear magnetic resonance (HPLC-SPE-ttNMR). The standard compound clorgyline, and an extract of black pepper (Piper nigrum L.), representing a complex plant matrix, were used for proof-of-concept. RESULTS: The work with clorgyline showed that the microplate-based high-resolution assay produced MAO-A inhibition profiles that easily allowed detection of submicrogram amounts of this selective MAO-A inhibitor. Furthermore, the HPLC-SPE-ttNMR/high-resolution MAO-A inhibition assay platform allowed identification of piperine and two piperine analogues as the main MAO-A inhibitors in the black pepper petroleum ether extract. CONCLUSION: The HPLC-SPE-ttNMR/high-resolution MAO-A inhibition assay platform is a powerful tool for fast and efficient identification of new MAO-A inhibitors from complex extracts, and promise future advancement in the search for new anti-depressants from natural sources.

Can phylogeny predict chemical diversity and potential medicinal activity of plants? A case study of Amaryllidaceae.

BACKGROUND: During evolution, plants and other organisms have developed a diversity of chemical defences, leading to the evolution of various groups of specialized metabolites selected for their endogenous biological function. A correlation between phylogeny and biosynthetic pathways could offer a predictive approach enabling more efficient selection of plants for the development of traditional medicine and lead discovery. However, this relationship has rarely been rigorously tested and the potential predictive power is consequently unknown. RESULTS: We produced a phylogenetic hypothesis for the medicinally important plant subfamily Amaryllidoideae (Amaryllidaceae) based on parsimony and Bayesian analysis of nuclear, plastid, and mitochondrial DNA sequences of over 100 species. We tested if alkaloid diversity and activity in bioassays related to the central nervous system are significantly correlated with phylogeny and found evidence for a significant phylogenetic signal in these traits, although the effect is not strong. CONCLUSIONS: Several genera are non-monophyletic emphasizing the importance of using phylogeny for interpretation of character distribution. Alkaloid diversity and in vitro inhibition of acetylcholinesterase (AChE) and binding to the serotonin reuptake transporter (SERT) are significantly correlated with phylogeny. This has implications for the use of phylogenies to interpret chemical evolution and biosynthetic pathways, to select candidate taxa for lead discovery, and to make recommendations for policies regarding traditional use and conservation priorities.

Antimicrobial activity of selected South African medicinal plants.

BACKGROUND: Nearly 3,000 plant species are used as medicines in South Africa, with approximately 350 species forming the most commonly traded and used medicinal plants. In the present study, twelve South African medicinal plants were selected and tested for their antimicrobial activities against eight microbial species belonging to fungi, Mycobacteria, Gram-positive and Gram-negative bacteria. METHODS: The radiometric respiratory technique using the BACTEC 460 system was used for susceptibility testing against Mycobacterium tuberculosis, and the liquid micro-broth dilution was used for other antimicrobial assays. RESULTS: The results of the minimal inhibitory concentration (MIC) determinations indicated that the methanol extracts from Acacia karoo, Erythrophleum lasianthum and Salvia africana were able to prevent the growth of all the tested microorganisms. All other samples showed selective activities. MIC values below 100 µg/ml were recorded with A. karoo, C. dentate, E. lasianthum, P. obligun and S. africana on at least one of the nine tested microorganisms. The best activity (MIC value of 39.06 µg/ml) was noted with S. africana against E. coli, S. aureus and M. audouinii, and Knowltonia vesitoria against M. tuberculosis. CONCLUSION: The overall results of the present work provide baseline information for the possible use of the studied South African plant extracts in the treatment of microbial infections.

Flavonoids and the CNS.

Flavonoids are present in almost all terrestrial plants, where they provide UV-protection and colour. Flavonoids have a fused ring system consisting of an aromatic ring and a benzopyran ring with a phenyl substituent. The flavonoids can be divided into several classes depending on their structure. Flavonoids are present in food and medicinal plants and are thus consumed by humans. They are found in plants as glycosides. Before oral absorption, flavonoids undergo deglycosylation either by lactase phloridzin hydrolase or cytosolic ß-glucosidase. The absorbed aglycone is then conjugated by methylation, sulphatation or glucuronidation. Both the aglycones and the conjugates can pass the blood-brain barrier. In the CNS several flavones bind to the benzodiazepine site on the GABA(A)-receptor resulting in sedation, anxiolytic or anti-convulsive effects. Flavonoids of several classes are inhibitors of monoamine oxidase A or B, thereby working as anti-depressants or to improve the conditions of Parkinson's patients. Flavanols, flavanones and anthocyanidins have protective effects preventing inflammatory processes leading to nerve injury. Flavonoids seem capable of influencing health and mood.

Effects of Teucrium polium spp. capitatum flavonoids on the lipid and carbohydrate metabolism in rats.

CONTEXT: The main objective of the study was to investigate the biochemical mechanism of the antidiabetic activities of the dry extracts of Teucrium polium L. ssp. capitatum (L.) Arcangeli (Lamiaceae), from Republic of Macedonia, traditionally used to treat diabetes. MATERIALS AND METHODS: Aerial parts of the plant were extracted in alcohol and freeze- or spray-dried, analyzed by high performance liquid chromatography (HPLC) and examined for insulinotropic effect in INS-1E cells in vitro. Their effect on blood glucose, lipids and carbohydrate-related enzymes was tested in normo- and streptozotocin hyperglycemic rats. RESULTS AND DISCUSSION: HPLC analyses revealed several flavonoids: luteolin, apigenin, cirsiliol, diosmetin, cirsimaritin and cirsilineol as both free aglycons and glycosides. The extract and mixture of commercial flavonoids showed a distinct insulinotropic effect on INS-1E cells at 500 µg/ml. Intragastric (i.g.) administration of identical doses of the extract (125 mg/kg) in both normo- and hyperglycemic rats was more efficient in lowering the blood glucose than intraperitoneal injection (35% vs. 24% reduction) with highest effect (50% reduction) 8 h after administration. After 10 days of treatment, the magnitude of the effect was comparable to i.g. administration of 2.5 mg/kg of glibenclamide (38% reduction). No effect was seen on blood lipid profiles. In OGTT (oral glucose tolerance test), the extract lowered blood glucose levels by ~35%. The treatment reduced hepatic glycogen and tended to normalize the activity of gluconeogenic enzymes. CONCLUSION: The results demonstrate that examined plant extracts contain flavonoids with insulinotropic and antihyperglycemic effects.

Anticonvulsant effects of Searsia dentata (Anacardiaceae) leaf extract in rats.

Searsia species are used in South Africa to treat epilepsy. Previous studies have demonstrated an in vitro N-methyl-D-aspartic acid (NMDA) receptor antagonistic effect of the ethanolic leaf extract. The aim of this study was to evaluate the potential anticonvulsant properties of the ethanolic extract of S. dentata in various animal models of epilepsy. The extract was submitted to a screening in anticonvulsant assays including NMDA-, kainic acid (KA)-, pentylenetetrazol (PTZ)- and bicuculline (BIC)-induced seizures in rats. The extract protected 47% of the PN 18 Wistar pups (postnatal day 18, date of birth PN 0) (p < 0.05, n > 10) against NMDA-induced seizures and significantly delayed the onset of PTZ-induced seizures (p < 0.05, n > 8) at a dose of 250 mg/kg. A dose optimum was detected at 500 mg/kg for protection against KA-(63% protection, p < 0.05, n > 8) and BIC-induced seizures (50% protection, p < 0.05, n > 8) in young adult and PN 18 rats, respectively. The ethanolic extract of S. dentata showed anticonvulsive properties in several models of epilepsy. These results are compatible with previous findings of NMDA receptor antagonism. Due to the complex composition of the extract, the effect might be caused by more than one compound.

Neuroprotective and neurochemical properties of mint extracts.

Mints are aromatic plants with a tradition as medicinal remedies and culinary herbs. With the aim of investigating potential central nervous system (CNS) activities of traditional medicinal plants, four species and one hybrid of the genus Mentha (M. aquatica, M. longifolia, M. pulegium, M. suaveolens and M. x piperita) were selected. Methanolic extracts of the plants were tested for protective effects against hydrogen-peroxide-induced toxicity in PC12 cells, antioxidant activity (by ABTS and X/XO methods) and neurochemical properties (MAO-A inhibition, AChE inhibition and affinity to the GABA(A) receptor). Mentha x piperita and Mentha aquatica produced significant (p < 0.05) protection of the PC12 cells against oxidative stress. All the plants exhibited antioxidant and MAO-A inhibitory activities, M. x piperita being the most active. M. aquatica showed the highest affinity to the GABA(A)-receptor assay. Results demonstrate that mints might have effect on the CNS.

Antioxidant activity and phenylpropanoids of Phlomis lychnitis L.: a traditional herbal tea.

Phlomis lychnitis L. (Lamiaceae) is consumed as a traditional herbal tea in Spain. The antioxidant-protective effects as well as its phytoconstituents have never been established. The ability of the methanolic extract to protect cells from oxidative stress was evaluated in rat pheochromocytoma cells (PC12) using hydrogen peroxide as toxic agent. The viability of PC12 cells pre-treated with the methanolic extract of Phlomis lychnitis, determined by the MTT and LDH assays, was significantly improved at the highest dose (p < 0.01). The antioxidant activity was confirmed evaluating the capacity of the plant to scavenge ABTS, DPPH, O(2) . (-) radicals and to inhibit XO. Bioassay guided fractionation led to antioxidant compounds. Qualitative HPLC/DAD/ESI/MS analysis reported phenylpropanoids, verbascoside being the major antioxidant constituent.

Evaluation of the antidiabetic potential of Psidium guajava L. (Myrtaceae) using assays for α-glucosidase, α-amylase, muscle glucose uptake, liver glucose production, and triglyceride accumulation in adipocytes.

ETHNOPHARMACOLOGICAL RELEVANCE: Psidium guajava L. (Myrtaceae) leaves are used as an herbal antidiabetic remedy in several parts of the world. On Madagascar, both the bark and leaves are used for treatment of diabetes. MATERIALS AND METHODS: Dilution series of ethanolic extracts of P. guajava leaves and bark were used for determining inhibitory activities against yeast α-glucosidase and porcine α-amylase. Skeletal muscle glucose uptake was measured using 2-deoxy-D-(1-3H)-glucose in murine C2C12 skeletal muscle cells. Hepatic glucose-6-phosphatase activity in rat hepatoma H4IIE cells and triglyceride accumulation in murine 3T3-L1 adipocyte-like cells were assessed using Wako AutoKit Glucose assays and AdipoRed reagent, respectively. Cells were incubated for 18 h with the maximal non-toxic concentrations of the plant extracts determined by the lactate dehydrogenase cytotoxicity assay. RESULTS: Ethanolic extracts of P. guajava leaf and bark inhibited α-glucosidase with IC50 values of 1.0 ± 0.3 and 0.5 ± 0.01 µg/mL, respectively. In the α-amylase inhibition assay, the ethanolic extract of bark of P. guajava showed an IC50 value of 10.6 ± 0.4 µg/mL. None of the extracts were able to reduce glucose-6-phosphatase activity in rat hepatoma H4IIE cells. In contrast, P. guajava leaf extract significantly increased 2-deoxy-D-[1-3H]-glucose uptake in C2C12 muscle cells (161.4 ± 10.1%, p = 0.0015) in comparison to the dimethyl sulfoxide (DMSO) vehicle control, as did the reference compounds metformin (144.0 ± 7.7%, p = 0.0345) and insulin (141.5 ± 13.8%, p = 0.0495). Furthermore, P. guajava leaf and bark extracts, as well as the reference compound rosiglitazone, significantly enhanced triglyceride accumulation in 3T3-L1 cells (252.6 ± 14.2%, p < 0.0001, 211.1 ± 12.7%, p < 0.0001, and 201.1 ± 9.2%, p < 0.0001, respectively) to levels higher than the DMSO vehicle control. Moreover, P. guajava leaf extract significantly enhanced the triglyceride accumulation in 3T3-L1 cells compared to rosiglitazone. CONCLUSION: The results demonstrated that P. guajava leaf and bark extracts can be used as a natural source of α-glucosidase inhibitors. In addition, the bark extract of P. guajava was an effective α-amylase inhibitor. Moreover, P. guajava leaf extract improved glucose uptake in muscle cells, while both leaf and bark extracts enhanced the triglyceride content in adipocytes in culture. P. guajava leaf and bark extracts may thus hypothetically have future applications in the treatment of type 2 diabetes.