Coffee Ingestion Suppresses Hyperglycemia in Streptozotocin-Induced Diabetic Mice

Impact of coffee and its bioactive compounds on the risks of type 2 diabetes and its complications: A comprehensive review

BACKGROUND

Coffee beans have a long history of use as traditional medicine by various indigenous people. Recent focus has been given to the health benefits of coffee beans and its bioactive compounds. Research on the bioactivities, applications, and effects of processing methods on coffee beans' phytochemical composition and activities has been conducted extensively. The current review attempts to provide an update on the biological effects of coffee on type 2 diabetes (T2D) and its comorbidities.

METHODS

Comprehensive literature search was carried out on peer-reviewed published data on biological activities of coffee on in vitro, in vivo and epidemiological research results published from January 2015 to December 2022, using online databases such as PubMed, Google Scholar and ScienceDirect for our searches.

RESULTS

The main findings were: firstly, coffee may contribute to the prevention of oxidative stress and T2D-related illnesses such as cardiovascular disease, retinopathy, obesity, and metabolic syndrome; secondly, consuming up to 400 mg/day (1-4 cups per day) of coffee is associated with lower risks of T2D; thirdly, caffeine consumed between 0.5 and 4 h before a meal may inhibit acute metabolic rate; and finally, both caffeinated and decaffeinated coffee are associated with reducing the risks of T2D.

CONCLUSION

Available evidence indicates that long-term consumption of coffee is associated with decreased risk of T2D and its complications as well as decreased body weight. This has been attributed to the consumption of coffee with the abundance of bioactive chemicals.

Mechanisms of action of natural products on type 2 diabetes

Over the past several decades, type 2 diabetes mellitus (T2DM) has been considered a global public health concern. Currently, various therapeutic modalities are available for T2DM management, including dietary modifications, moderate exercise, and use of hypoglycemic agents and lipid-lowering medications. Although the curative effect of most drugs on T2DM is significant, they also exert some adverse side effects. Biologically active substances found in natural medicines are important for T2DM treatment. Several recent studies have reported that active ingredients derived from traditional medicines or foods exert a therapeutic effect on T2DM. This review compiled important articles regarding the therapeutic effects of natural products and their active ingredients on islet β cell function, adipose tissue inflammation, and insulin resistance. Additionally, this review provided an in-depth understanding of the multiple regulatory effects on different targets and signaling pathways of natural medicines in the treatment of T2DM as well as a theoretical basis for clinical effective application.

The effect of coffee consumption on glucose homeostasis and redox-inflammatory responses in high-fat diet-induced obese rats

Coffee effects on glucose homeostasis in obesity remain controversial. We investigated whether coffee mitigates the negative effects on glucose metabolism induced by a high-fat diet and the interrelationships with redox-inflammatory responses. Rats were treated with: control (CT-); coffee (CT+) 3.9 g of freeze-dried coffee/kg of diet; high-fat (HF-); or high-fat + coffee 3.9 g of freeze-dried coffee/kg of diet (HF+) diet. The high-fat diet increased weight gain, feed efficiency, HOMA β, muscle and hepatic glycogen, intestinal CAT and SOD activity, hepatic protein (CARB) and lipid oxidation (MDA), muscle Prkaa1 mRNA and IL6 levels, and decreased food intake, hepatic GR, GPX and SOD activities, intestinal CARB, intestinal Slc2a2 and Slc5a1 and hepatic Prkaa1 and Prkaa2 mRNA levels, hepatic glucose-6-phosphatase and muscle hexokinase (HK) activities, compared to the control diet. The high-fat diet with coffee increased hepatic GST activity and TNF and decreased IL6 and intestinal glucosidase activity compared with the high-fat diet. The coffee diet increased muscle glycogen, hepatic CARB and PEPCK activity, and decreased hepatic GR and SOD activities and intestinal CARB, compared with the control diet. Coffee increased insulin levels, HOMA IR/β, FRAP, muscle Prkaa1 mRNA levels and hepatic and muscle phosphofructokinase-1, and it decreased intestinal CAT, hepatic Slc2a2 mRNA levels and muscle HK activity, regardless of the diet type. In conclusion, chronic coffee consumption improves antioxidant and anti-inflammatory responses, but does not ameliorate glucose homeostasis in a high-fat diet-induced obesity model. In addition, coffee consumption increases insulin secretion and promotes muscle glycogen synthesis in rats maintained on a control diet.

Catalpol Weakens Depressive-like Behavior in Mice with Streptozotocin-induced Hyperglycemia via PI3K/AKT/Nrf2/HO-1 Signaling Pathway

Depression has huge social risks of high incidence, disability, and suicide. Its prevalence and harm in people with hyperglycemia are 2-3 times higher than in normal people. However, antidepressants with precise curative effects and clear mechanisms for patients with hyperglycemia are currently lacking. Prescriptions containing Rehmannia glutinosa, a traditional medicinal herb with a wide range of nutritional and medicinal values, are often used as antidepressants in Chinese clinical medicine. Catalpol is one of the main effective compounds of R. glutinosa, with multiple biological activities such as hypoglycemia. Here, the antidepressant effect of catalpol on the pathological state of streptozotocin (STZ)-induced hyperglycemia and the underlying molecular mechanisms were analyzed. Results showed that administering catalpol orally to hyperglycemic mice for 21 consecutive days significantly reversed the abnormalities in tail suspension, forced swimming, and open field tests. Catalpol also reversed the abnormal phosphorylation of phosphoinositide 3-kinase (PI3K) and protein kinase B (AKT) and the abnormal levels of nuclear factor erythroid 2-related factor 2 (Nrf2) protein, heme oxygenase-1 (HO-1), and antioxidants, including superoxide dismutase, glutathione peroxidase, glutathione-s transferase, reduced glutathione, and malondialdehyde in the hippocampus and frontal cortex of STZ-induced hyperglycemic mice. Thus, catalpol attenuates depressive-like behavior in pathological hyperglycemic state, and the antidepressant mechanism could at least be partly attributed to the upregulation of the PI3K/AKT/Nrf2/HO-1 signaling pathway in both brain regions, thus restoring the balance between oxidative and antioxidant damage. These data expanded the scientific understanding of catalpol and provided preclinical experimental evidence for its application.

Protective effect of acorn (Quercus liaotungensis Koidz) on streptozotocin-damaged MIN6 cells and type 2 diabetic rats via p38 MAPK/Nrf2/HO-1 pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Acorn obtained from the Quercus liaotungensis Koidz tree is consumed as a Chinese folk medicine for the treatment of diarrhea, abdominal pain, and inflammation, also having strong antioxidant activity and have been utilized for the treatment of diabetes in China. However, its mechanism of action on complications of diabetes and oxidative stress is unclear.

AIM OF THE STUDY

The purpose of this research was to assess the effects of acorn (Quercus liaotungensis Koidz) ethanol extract (AE) on pancreatic β-cell dysfunction through a streptozotocin (STZ)-damaged mouse normal pancreatic β-cell (MIN6 cell) model in vitro, and by using a high-fat and high-sugar diet with STZ-induced diabetic rat model in vivo to explore the possible mechanism of action against diabetes.

MATERIALS AND METHODS

MIN6 cells were pretreated with AE (20, 40, 80 μM) for 2 h and then treated with 3 mM STZ for 24 h. Cell viability was measured by MTT assay. The amount of intracellular reactive oxygen species was measured by 2,7-dichlorodi-hydrofluorescein diacetate. The activities of insulin secretion, superoxide dismutase, catalase and glutathione were determined by kits. Sprague Dawley rats were either given normal feed or a high sugar and fat diet for four weeks, followed STZ (25 mg/kg, via i. p.) was given. Rats with fasting blood glucose ≥11.1 mmol/l after one week were deemed to be diabetic. Animals were divided into 5 groups, which received saline (10 mL/kg), metformin (200 mg/kg), or AE at doses of 200 and 400 mg/kg during 4 weeks by oral gavage. Blood samples were used to evaluate hematological and biochemical indicators, and pancreas was removed for post-analysis. Body weight and fasting blood glucose were recorded weekly. The expression levels of Bax, Bcl-2, p38, p-p38, Nrf2 and HO-1 were determined by Western blot.

RESULTS

Data showed that AE inhibited apoptosis and increased antioxidant level in STZ-induced MIN6 cells. In addition, the AE-administered group lowered blood glucose, increased insulin secretion, and alleviated weight loss in the diabetic rats. Histopathologically, the AE-administered group reduced pancreatic injury by significantly restoring the insulin content in β-islets. It was observed that the anti-diabetic effects of AE were associated with the suppressed the p38 MAPK pathway and actived the Nrf2 pathway.

CONCLUSIONS

The ameliorative impact of AE on diabetes may be attributed to protection of the function of pancreatic β islets and by improving serum insulin levels, hence reducing the blood glucose, which involved in the p38 MAPK and Nrf2 pathways.

New ent-kaurane diterpenes from the roasted arabica coffee beans and molecular docking to α-glucosidase

Ten new (1-10) and five known (11-15) ent-kaurane diterpene derivatives were identified from the roasted beans of coffea arabica. Their structures were established by extensive spectroscopic analysis including 1D, 2D NMR (HSQC, HMBC, COSY, and ROESY), HRESIMS, and X-ray diffraction analysis. Compounds 1-3 were three types of rearranged ent-kaurane diterpenes, and compounds 4 and 5 were diterpene esters with a rare 6-hydroxyhexanoyl at C-17. Compounds 6, 8, 14, and 15 showed moderate inhibitory effect on α-glucosidase with IC₅₀ values of 149.92 ± 2.52, 23.23 ± 1.03, 54.58 ± 4.21, 54.16 ± 3.95 μM, respectively, compared to the positive control (60.71 ± 16.45 μM). The results of activity assay showed that diterpenes with the double bond between C-15 and C-16 exhibited stronger α-glucosidase inhibitory activity. Further molecular docking experiments were adopted to discuss the mechanism of activity.

Lactam ent-Kaurane Diterpene: A New Class of Diterpenoids Present in Roasted Beans of Coffea arabica

Seven new lactam ent-kaurane diterpenoids, cafemides A-G (1-7), were isolated from roasted beans of Coffea arabica. Their structures were elucidated by extensive spectroscopic analysis including 1D, 2D NMR (heteronuclear single quantum correlation (HSQC), heteronuclear multiple bond correlation (HMBC), ¹H-¹H correlation spectroscopy (COSY), and rotating frame Overhauser effect spectroscopy (ROESY)), high-resolution electrospray ionization mass spectrometry (HRESIMS), and IR spectra. They were divided into subtype I-III according to the structure. Further, with the aid of liquid chromatography-tandem mass spectrometry (LC-MS/MS) based molecular network, seven (8-14) subtype II diterpenoids were successfully identified. In addition, a variety of other subtypes of N-containing diterpenoids have been proven in roasted coffee. Compounds 1, 2, 3, 5, and 7 showed a moderate inhibitory effect on α-glucosidase with an IC₅₀ value of 8.28 ± 0.62 μM, 38.23 ± 8.87 μM, 28.94 ± 1.42 μM, 12.44 ± 1.37 μM, and 22.2 ± 5.34 μM, respectively. To the best of our knowledge, this is the first time that N-containing diterpenoids have been reported in coffee.

The sources and mechanisms of bioactive ingredients in coffee

Coffee bioactive components include caffeine, chlorogenic acids (CGAs), trigonelline, tryptophan alkaloids, diterpenes and other secondary metabolites. During roasting, coffee metabolites undergo complex Maillard reactions, producing melanoidins and other degradation products, the most controversial among which is acrylamide, an ingredient widely found in baked food and listed as a second class carcinogen. Green and roasted coffee ingredients have good biological activities for the prevention of cardiovascular disease, and antibacterial, anti-diabetic, neuroprotection, and anti-cancer activities. To better understand the relationship between coffee ingredients and human health, and to effectively use the active ingredients, it is essential to understand the sources of coffee active ingredients and their mechanisms of action in the organism. This paper systematizes the available information and provides a critical overview of the sources of coffee active ingredients and the mechanisms of action in vivo or in vitro, and their combined effects on common human diseases.