The effect of Psidium guajava aqueous leaf extract on liver glycogen enzymes, hormone sensitive lipase and serum lipid profile in diabetic rats

Comparative effects of pravastatin and rosuvastatin on carbohydrate metabolism in an experimental diabetic rat model

Statin treatment may increase the risk of diabetes; there is insufficient data on how statins affect glucose regulation and glycemic control and the effects of statins on liver enzymes related to carbohydrate metabolism have not been fully studied. Therefore, we aimed to compare the effects of the statin derivatives, pravastatin, and rosuvastatin, on carbohydrate metabolism in an experimental diabetic rat model. Female Wistar albino rats were used and diabetes was induced by intraperitoneal injection of streptozotocin. Thereafter, 10 and 20 mg kg-1 day-1 doses of both pravastatin and rosuvastatin were administered by oral gavage to the diabetic rats for 8 weeks. At the end of the experiment, body masses, the levels of fasting blood glucose, serum insulin, insulin resistance (HOMA-IR), liver glycogen, and liver enzymes related to carbohydrate metabolism were measured. Both doses of pravastatin significantly in creased the body mass in diabetic rats, however, rosuvastatin, especially at the dose of 20 mg kg-1 day-1 reduced the body mass signi ficantly. Pravastatin, especially at a dose of 20 mg kg-1 day-1, caused significant increases in liver glycogen synthase and glucose 6-phosphate dehydrogenase levels but significant decreases in the levels of glycogen phosphorylase, lactate dehydrogenase, and glucose-6-phosphatase. Hence, pravastatin partially ameliorated the adverse changes in liver enzymes caused by diabetes and, especially at the dose of 20 mg kg-1 day-1, reduced the fasting blood glucose level and increased the liver glycogen content. However, rosuvastatin, especially at the dose of 20 mg kg-1 day-1, significantly reduced the liver glycogen synthase and pyruvate kinase levels, but increased the glycogen phosphorylase level in diabetic rats. Rosuvastatin, 20 mg kg-1 day-1 dose, caused significant decreases in the body mass and the liver glycogen content of diabetic rats. It can be concluded that pravastatin, especially at the dose of 20 mg kg-1 day-1 is more effective in ameliorating the negative effects of diabetes by modulating carbohydrate metabolism.

Elucidation of anti-hyperglycemic activity of Psidium guajava L. leaves extract on streptozotocin induced neonatal diabetic Long-Evans rats

BACKGROUND

Psidium guajava L (Guava) belongs to the Myrtaceae family and has been claimed to possess several pharmacological properties including antidiabetic.

OBJECTIVE

This study was designed to evaluate the anti-hyperglycemic activity of P guajava L leaves aqueous extract on neonatal streptozotocin-induced type 2 diabetic model rats.

METHODS

Streptozotocin was induced (90 mg/kg) intraperitoneally to 48 h old Long Evans rat pups. After three months, 18 male type-2 diabetic model rats were confirmed by OGTT (FG > 7 mmol/L). Therefore, experimental rats were divided into three groups 2) Diabetic water control (10 ml/kg), 3) Gliclazide treated (20 mg/kg), and 4) Extract treated group (1.25g/kg)] Six normal female rats comprised group 1 [Non-diabetic water control (10 ml/kg)]. All rats were treated orally with their respective treatment for 28 consecutive days. Blood samples were collected on 0 days (by tail cut method) and the end day (by cardiac puncture) of the experiment. The anti-hyperglycemic activity was evaluated by measuring fasting glucose, serum insulin, lipid profile, hepatic glycogen content, and intestinal glucose absorption by standard methods.

RESULTS

The serum glucose level of extract treated group was decreased by 16% as well as significantly (p<0.05) increased the serum insulin level (M±SD, 0 day vs 28thday; 0.319 ± 0.110 vs 0.600 ± 0.348, μg/L). Moreover, the extract-treated group also significantly (p<0.05) enhanced liver glycogen content and inhibited glucose absorption from the upper intestine. Besides, a significant (p < 0.05) reduction of LDL-cholesterol level was found in the extract-treated group (M±SD, 55 ± 33 vs 14 ± 9, mg/dl) compared with baseline values where other groups did not show any statistically remarkable changes.

CONCLUSION

Current study concludes that P guajava leaves aqueous extract enhances insulin secretion from pancreatic beta-cells and promotes glycogen synthesis in the liver. The extract also inhibits glucose absorption from the upper intestine and improves dyslipidemia to some extent. Therefore, possesses the potential for drug development against T2DM.

Psidium guajava L.- dichloromethane and ethyl acetate fractions ameliorate striped catfish (Pangasianodon hypophthalmus) status via immune response, inflammatory, and apoptosis pathways

Psidium guajava L. is known to possess immune-modulatory properties in humans and other mammals. Although the positive effects of P. guajava-based diets on the immunological status have been shown for some fish species, the underlying molecular mechanisms of its protective effects remain to be investigated. The aims of this study were to evaluate the immune-modulatory effects of two guava fractions from dichloromethane (CC) and ethyl acetate (EA) on striped catfish with in vitro and in vivo experiments. Striped catfish head kidney leukocytes were stimulated with 40, 20, 10 and 0 μg/ml of each extract fraction, and the immune parameters (ROS, NOS, and lysozyme) were examined at 6 and 24h post stimulation. A final concentration of each fraction at 40, 10 and 0 μg/fish was then intraperitoneally injected into the fish. After 6, 24, and 72h of administration, immune parameters as well as the expression of some cytokines related to innate and adaptive immune responses, inflammation, and apoptosis were measured in the head kidney. Results indicated that the humoral (lysozyme) and cellular (ROS and NOS) immune endpoints were regulated differently by CC and EA fractions depending on dose and time in both, in vitro and in vivo experiments. With regards to the in vivo experiment, the CC fraction of the guava extract could significantly enhance the TLRs-MyD88-NF-κB signaling pathway by upregulating its cytokine genes (tlr1, tlr4, myd88, and traf6), following the upregulation of inflammatory (nfκb, tnf, il1β, and il6) and apoptosis (tp53 and casp8) genes 6 h after injection. Moreover, fish treated with both CC and EA fractions significantly enhanced cytokine gene expression including lys and inos at the later time points - 24h or 72h. Our observations suggest that P. guajava fractions modulate the immune, inflammatory, and apoptotic pathways.

Fishing the Targets of Bioactive Compounds from Psidium guajava L. Leaves in the Context of Diabetes

Psidium guajava L. (guava) leaves have demonstrated their in vitro and in vivo effect against diabetes mellitus (DM). However, there is a lack of literature concerning the effect of the individual phenolic compounds present in the leaves in DM disease. The aim of the present work was to identify the individual compounds in Spanish guava leaves and their potential contribution to the observed anti-diabetic effect. Seventy-three phenolic compounds were identified from an 80% ethanol extract of guava leaves by high performance liquid chromatography coupled to electrospray ionization and quadrupole time-of-flight mass spectrometry. The potential anti-diabetic activity of each compound was evaluated with the DIA-DB web server that uses a docking and molecular shape similarity approach. The DIA-DB web server revealed that aldose reductase was the target protein with heterogeneous affinity for compounds naringenin, avicularin, guaijaverin, quercetin, ellagic acid, morin, catechin and guavinoside C. Naringenin exhibited the highest number of interactions with target proteins dipeptidyl peptidase-4, hydroxysteroid 11-beta dehydrogenase 1, aldose reductase and peroxisome proliferator-activated receptor. Compounds catechin, quercetin and naringenin displayed similarities with the known antidiabetic drug tolrestat. In conclusion, the computational workflow showed that guava leaves contain several compounds acting in the DM mechanism by interacting with specific DM protein targets.

An Overview of Hormone-Sensitive Lipase (HSL)

Hormone-sensitive lipase (HSL) is a pivotal enzyme that mediates triglyceride hydrolysis to provide free fatty acids and glycerol in adipocytes in a hormonally controlled lipolysis process. Elevated plasma-free fatty acids were accompanied by insulin resistance, type-2 diabetes, and obesity. Inhibition of lipolysis through HSL inhibition may provide a mechanism to prevent the accumulation of free fatty acids and to improve the affectability of insulin and blood glucose handling in type II diabetes. The published studies that examine the structure, regulation, and function of HSL and major inhibitors were reviewed in this paper.

Antidiabetic effects of Psidium x durbanensis Baijnath & Ramcharun ined. (Myrtaceae) leaf extract on streptozotocin-induced diabetes in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Psidium guajava L. leaves are used to treat diabetes in South African folkloric medicine and in other parts of the world. Psidium x durbanensis Baijnath & Ramcharun ined. (PD) is a natural sterile hybrid and congener of Psidium guajava that is expected to share the medicinal properties of the genus Psidium and is widely distributed in South Africa.

AIM OF THE STUDY

This study investigates the antioxidant, antidiabetic effects, and mechanisms of action of hydro-methanolic leaf extracts of PD on streptozotocin-induced diabetes in rats.

MATERIAL AND METHODS

Phytochemical constituents of hydro-methanolic extract of PD were analyzed by gas chromatography-mass spectrometry (GC-MS). Male Wistar rats 250-300 g body weight (BW) were rendered diabetic after a single intraperitoneal injection with streptozotocin, 45 mg/kg BW. The diabetic rats were treated with hydro-methanolic (20:80 v/v) leaf extracts of PD (400 mg/kg/BW) or subcutaneous injections of regular insulin (2.0U/kg/BW, bid) for 56 days. The body weights of the animals were recorded daily. Fasting blood glucose, glucose tolerance tests, and insulin resistance index were measured. The effects of the extracts on total superoxide dismutase, catalase, and reduced glutathione activities, histopathology, and gene expression of insulin receptor substrate 1 and glucose transporter 4 were determined in the liver, pancreas, and gastrocnemius muscles of the rats.

RESULTS

In the acute toxicity studies, there were no signs of toxicity observed for PD up to 2000 mg/kg BW doses. Diabetic animals showed significant weight loss, elevated and reduced fasting blood glucose and insulin, respectively, impaired glucose tolerance and diminished antioxidant enzymes' activities compared to controls. Treatment with PD hydro-methanolic leaf extracts improved body weight, glucose tolerance, insulin resistance, and antioxidant enzymes but not plasma insulin in diabetic animals compared to controls, respectively. GC-MS analysis identified organic acids, alcohols, vitamins, terpenoids, and esters in the extracts. Treatment with PD improved glucose uptake by stimulating mRNA expression of GLUT 4 in gastrocnemius muscles of diabetic animals compared to the untreated control and also restored histological aberrations in the pancreas and liver of diabetic rats compared with the untreated control rats.

CONCLUSION

Collectively, the present study suggests that treatment with PD leaf extracts significantly ameliorated diabetes symptoms and oxidative stress in rats, and these effects may be linked to the bioactive phytoconstituents present in the plant. This study further suggests that PD improves insulin resistance by increasing glucose uptake in gastrocnemius muscles in an insulin-independent manner.

Natural products for the treatment and management of diabetes mellitus in Zimbabwe-a review

Use of medicinal plants and herbs in the treatment and management of diseases, including diabetes mellitus and its complications remains an integral part of African tradition. In Zimbabwe, nearly one million people are living with diabetes mellitus. The prevalence of diabetes mellitus in Zimbabwe is increasing every year due to lifestyle changes, and has accelerated the use of traditional medicines for its treatment and management in urban areas. In addition, the high cost of modern medicine has led many people in rural parts of Zimbabwe to rely on herbal plant medicine for the treatment of diabetes mellitus and its complications. This review highlights a number of studies carried out to evaluate the antidiabetic properties of indigenous plants found in Zimbabwe with the goal of treating diabetes mellitus. Further, we discuss the mechanism of action of various plant extracts in the treatment and management of diabetes mellitus. Together, this review article can open pathways leading to discovery of new plant derived medicines and regularization of use of crude plant remedies to treat diabetes mellitus by the Zimbabwean government and others across Africa.

Antidiabetic Properties and Toxicological Assessment of Antidesma celebicum Miq: Ethanolic Leaves Extract in Sprague-Dawley Rats

Antidesma is a genus of plants, and its several species are known to have antidiabetic properties. Leaves of Kayu Tuah (Antidesma celebicum Miq) have been proven to have the best α-glucosidase inhibition ability compared to other species in the Antidesma genus, as evidenced by the in vitro α-glucosidase inhibition test. However, no scientific studies have reported its antidiabetic properties and toxicity in vivo. Therefore, this research managed to verify the antidiabetic features and safety of ethanolic extract of A. celebicum leaves (EEAC) in Sprague-Dawley rats. Male rats (170-280 g) were induced diabetic with streptozotocin (35 mg/kg BW) and fed a high-fat diet comprising 24% fat, whereas control group rats were given a standard diet. Rats were treated with EEAC at 200 and 400 mg/kg BW doses for 28-days and 60 mg/kg BW acarbose for the control group. Determination of antidiabetic properties was done by analyzing lipid profiles as well as fasting blood glucose. After confirming the antidiabetic properties of EEAC, the toxicological assessment was determined using the fixed-dose method. General behavior changes, appearance, signs of toxicity, mortality, and body weight of animals were marked down during the observation period. When the treatment period ended, hematological, biochemical, and histological examinations of liver, kidneys, and heart sections were performed. The results confirmed that EEAC reduced fasting blood glucose levels and stepped forward lipid profiles of rats. Also, all animals survived, and no obvious destructive outcomes were noticeable during the study. As EEAC has promising results toward hyperglycemia and hyperlipidemia and has been proven safe through toxicity tests, it can be concluded that EEAC has good potential to be further developed into antidiabetic drugs.

Hypoglycemic and Hepatoprotective Effects of Dried and Rice-Fried Psidium guajava Leaves in Diabetic Rats

Psidium guajava leaves (PGL) have been long used as an adjuvant therapy for diabetics. The present study evaluated the in vivo hypoglycemic and hepatoprotective effects of dried and the rice-fried PGL decoctions (PGLD and RPGLD). Our results indicated that both PGLD and RPGLD could significantly decrease the contents of fasting blood glucose (FBG) and haemoglobin A1c (HbA1c) in diabetic rats. Compared with the HFD/STZ (high-fat diet with streptozotocin) group, the PGLD and RPGLD-treated diabetic rats showed different degrees of recovery against the liver pathological changes. The upregulated expressions of glucokinase (GK), glucose transporter 2 (GLUT2), insulin growth factor-1 (IGF-1), insulin receptor substrate-1 (IRS-1), and insulin receptor substrate-2 (IRS-2) in PGLD and RPGLD-treated groups were observed. In general, RPGLD exhibited a much better antidiabetic effect than PGLD, which was further verified by the comprehensive evaluation with the TOPSIS method. Besides, HPLC (high-performance liquid chromatography) and UPLC-MS/MS (ultra-performance liquid chromatography-tandem mass spectrometry) analyses revealed that the contents of the primary constituents (ellagic acid, hyperoside, isoquercitroside, reynoutrin, guaijaverin, auicularin, and quercetin) in RPGLD increased obviously compared with PGLD. These results shed new light on the antidiabetic potential and mechanism of PGL, as well as the "higher efficacy" of the rice-fried processing method in traditional Chinese medicine.

Efficient method for isolation of high-quality RNA from Psidium guajava L. tissues

Acquiring high-quality RNA in sufficient amounts is crucial in plant molecular biology and genetic studies. Several methods for RNA extraction from plants are available in the literature, mainly due to the great biochemical diversity present in each species and tissue, which can complicate or prevent the extraction. Psidium guajava (Myrtaceae family) is a perennial fruit tree of medicinal and economic value; nevertheless, only a few molecular studies are available for the species. One reason is the difficulty in obtaining RNA due to the content of the samples, which are rich in polyphenols, polysaccharides, and secondary metabolites. Furthermore, there are few studies available for the isolation of RNA from guava or Psidium samples, which hampers advances in the study of the genus. Here, quality and yields of RNA isolates were compared using six extraction protocols: two protocols based on the application of cetyltrimethylammonium bromide (CTAB) lysis buffer, one protocol which uses the TRIzol reagent, one which applies guanidine thiocyanate lysis buffer followed by organic phase extraction, and two commercial kits (PureLink RNA Mini Kit and RNeasy Plant Mini Kit). The CTAB-based method provided the highest RNA yields and quality for five different tissues (flower bud, immature leaf, young leaf, mature leaf, and root), genotypes, and stress conditions. For the most efficient protocol, the average yield of RNA from guava leaves was 203.06 μg/g of tissue, and the A₂₆₀/A₂₈₀ and A₂₆₀/A₂₃₀ ratios were 2.1 and 2.2, respectively. RT-qPCR analysis demonstrated that the purity of the samples was sufficient for molecular biology experiments. CTAB-based methods for RNA isolation were found to be the most efficient, providing the highest RNA yields and quality for tissues from P. guajava. Additionally, they were compatible for downstream RNA-based applications, besides being simple and cost-effective.

Guava (Psidium guajava L.) Leaves: Nutritional Composition, Phytochemical Profile, and Health-Promoting Bioactivities

Psidium guajava (L.) belongs to the Myrtaceae family and it is an important fruit in tropical areas like India, Indonesia, Pakistan, Bangladesh, and South America. The leaves of the guava plant have been studied for their health benefits which are attributed to their plethora of phytochemicals, such as quercetin, avicularin, apigenin, guaijaverin, kaempferol, hyperin, myricetin, gallic acid, catechin, epicatechin, chlorogenic acid, epigallocatechin gallate, and caffeic acid. Extracts from guava leaves (GLs) have been studied for their biological activities, including anticancer, antidiabetic, antioxidant, antidiarrheal, antimicrobial, lipid-lowering, and hepatoprotection activities. In the present review, we comprehensively present the nutritional profile and phytochemical profile of GLs. Further, various bioactivities of the GL extracts are also discussed critically. Considering the phytochemical profile and beneficial effects of GLs, they can potentially be used as an ingredient in the development of functional foods and pharmaceuticals. More detailed clinical trials need to be conducted to establish the efficacy of the GL extracts.

Phytochemicals of Periploca aphylla Dcne. ameliorated streptozotocin-induced diabetes in rat

BACKGROUND

Periploca aphylla is used by local population and indigenous medicine practitioners as stomachic, tonic, antitumor, antiulcer, and for treatment of inflammatory disorders. The aim of this study was to evaluate antidiabetic effect of the extract of P. aphylla and to investigate antioxidant and hypolipidemic activity in streptozotocin (STZ)-induced diabetic rats.

METHODS

The present research was conducted to evaluate the antihyperglycemic potential of methanol extract of P. aphylla (PAM) and subfractions n-hexane (PAH), chloroform (PAC), ethyl acetate (PAE), n-butanol (PAB), and aqueous (PAA) in glucose-overloaded hyperglycemic Sprague-Dawley rats. Based on the efficacy, PAB (200 mg/kg and 400 mg/kg) was tested for its antidiabetic activity in STZ-induced diabetic rats. Diabetes was induced via intraperitoneal injection of STZ (55 mg/kg) in rat. Blood glucose values were taken weekly. HPLC-DAD analysis of PAB was carried out for the presence of various polyphenols.

RESULTS

HPLC-DAD analysis of PAB recorded the presence of rutin, catechin, caffeic acid, and myricetin. Oral administration of PAB at doses of 200 and 400 mg/kg for 21 days significantly restored (P < 0.01) body weight (%) and relative liver and relative kidney weight of diabetic rats. Diabetic control rats showed significant elevation (P < 0.01) of AST, ALT, ALP, LDH, total cholesterol, triglycerides, LDL, creatinine, total bilirubin, and BUN while reduced (P < 0.01) level of glucose, total protein, albumin, insulin, and HDL in serum. Count of blood cells and hematological parameters were altered in diabetic rats. Further, glutathione peroxidase, catalase, superoxide dismutase, glutathione reductase, and total soluble protein concentration decreased while concentration of thiobarbituric acid reactive substances and percent DNA damages increased (P < 0.01) in liver and renal tissues of diabetic rats. Histopathological damage scores increased in liver and kidney tissues of diabetic rats. Intake of PAB (400 mg/kg) resulted in significant improvement (P < 0.01) of above parameters, and results were comparable to that of standard drug glibenclamide.

CONCLUSION

The result suggests the antihyperglycemic, antioxidant, and anti-inflammatory activities of PAB treatment in STZ-compelled diabetic rat. PAB might be used as new therapeutic agent in diabetic patients to manage diabetes and decrease the complications.

Psidium guajava Linn leaf ethanolic extract: In vivo giardicidal potential with ultrastructural damage, anti-inflammatory and antioxidant effects

Introduction and aim

Considering the magnitude of giardiasis problem, the side-effects of the used anti-giardia drugs and the resistance posed against them, the current study aimed to evaluate the in-vivo giardicidal effect of Psidium guajava leaf extract (PGLE).

Methods

For fulfilling this aim, five Swiss-albino mice groups were included; GI: non-infected, GII: Giardia-infected and non-treated, GIII: Giardia-infected and metronidazole-treated, GIV: Giardia-infected and PGLE-treated, and GV: Giardia-infected and treated with both metronidazole and PGLE. Treatment efficacy was assessed via; Giardia cyst viability and trophozoite count, trophozoite electron microscopic ultrastructure, duodenal histopathological scoring, immunohistochemistry for TNF-α and duodenal scanning electron microscopy. Moreover, mice serum liver enzymes, total bilirubin, albumin, lipid profile including; total cholesterol, HDL, LDL and triglycerides were assessed. Additionally, hepatic oxidative stress markers including; malondialdehyde (MDA), nitric oxide (NO), reduced glutathione (GSH) and superoxide dismutase (SOD) were measured.

Results

Results showed that PGLE whether alone or combined with metronidazole has induced significant trophozoite count reduction and major architectural changes. Duodenal histological improvement, and local protective anti-inflammatory effect were confirmed. PGLE has also helped in healing of Giardia-induced gut atrophy. Thus, offered a comprehensive therapy for both the pathogen and the resultant pathological sequalae. Serum markers showed favorable hepatoprotective effect. Total cholesterol, LDL and triglycerides levels were less in PGLE-treated group than in metronidazole-treated group. Hepatic oxidative stress markers revealed the promising extract antioxidant effect. This study highlights, the promising in-vivo giardicidal PGLE activity, that was comparable to metronidazole, thus, the extract would be an ideal strongly recommended treatment for giardiasis. When combined with metronidazole, the extract potentiated its therapeutic effect. Besides, having hepatoprotective, anti-inflammatory, and antioxidant properties, the extract can combat the major side effects of metronidazole therapy.

Psidium guajava leaves assisted green synthesis of metallic nanoparticles: a review

Background

Several attempts have been made for green synthesis of metallic nanoparticles, revealing the significance of plant extracts in reducing metal source to nanoparticles and applications in various domains of science.

Main body

Psidium guajava (guava) is evergreen, edible fruit-bearing plant, belonging to family Myrtaceae. Its leaves are reported to contain several phytochemicals like tannins, glycosides, terpenes, and triterpenes. This article focus on applications of Psidium guajava leaves extract in fabrication of nanoparticles of various metals like silver, gold, titanium dioxide, zinc oxide, and copper oxide. In respective research attempts, these metallic nanoparticles were evaluated for one or more applications like anti-microbial activity and/or photocatalytic activity.

Conclusion

Use of polar extract of guava leaves indicated involvement of its polar phyto-compounds in reducing the metal source and stabilizing the nanoparticles. In conclusion, it could be noted that metal nanoparticles have better anti-microbial activity and photocatalytic potential over aqueous leaves extract.

Graphical abstract

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.