Long-term consumption of caffeine improves glucose homeostasis by enhancing insulinotropic action through islet insulin/insulin-like growth factor 1 signaling in diabetic rats

Systematic review of the effect of caffeine therapy effect on cardiometabolic markers in rat models of the metabolic syndrome

This systematic review aimed to study caffeine's effect on the cardiometabolic markers of the metabolic syndrome and to evaluate caffeine's application as a potential therapeutic agent in rat models. The systematic review was structured and synthesized according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and the Population, Intervention, comparator, outcome (PICO) framework. A literature search was conducted in PubMed, Scopus, and ScienceDirect to identify studies that used caffeine as an intervention in the rat model of the metabolic syndrome or any of its components compared with no treatment or controls. Studies that did not mention the disease manifestations from the experimental model used, without rat subjects, and which induced renovascular hypertension were excluded. The risk of bias in the included studies was assessed using the Systematic Review Center for Laboratory Animal Experimentation risk-of-bias tool. The main outcomes assessed were caffeine's effect on obesity, dyslipidemia, hepatic steatosis, hepatic dysfunction, insulin resistance, and hypertension. Out of 228 studies retrieved from the search, 18 met our inclusion criteria and were included in the systematic review. Caffeine was found to favorably reduce obesity and insulin resistance in the rat model of the metabolic syndrome. The effects of caffeine on dyslipidemia, hepatic steatosis, hepatic dysfunction, and hypertension remain inconclusive. The main limitations of this study are the heterogeneity of the included studies in terms of the disease model used, experimental duration, methods to assess outcomes, including studies that were only published in English, measurement units used, and graphical data without and numerical mention in the results section. As a result, quantitative synthesis was unfeasible, and a qualitative descriptive synthesis was conducted; this might have led to the under characterization of caffeine's effect on metabolic syndrome and its potential as an adjuvant therapy in metabolic syndrome. Caffeine has favorable effects on the metabolic syndrome, chiefly reducing obesity and insulin resistance. Future research is encouraged to delve into caffeine's effect on dyslipidemia, hepatic steatosis, hepatic dysfunction, and hypertension, which is necessary if caffeine is to be used as a potential clinical adjuvant therapy to treat the metabolic syndrome.

Caffeine Protects Against Retinal Inflammation

Caffeine, one of the most consumed central nervous system (CNS) stimulants, is an antagonist of A₁ and A_2A adenosine receptors. In this study, we investigated the potential protective effects of this methylxanthine in the retinal tissue. We tested caffeine by using in vitro and in vivo paradigms of retinal inflammation. Human retinal pigment epithelial cells (ARPE-19) were exposed to lipopolysaccharide (LPS) with or without caffeine. This latter was able to reduce the inflammatory response in ARPE-19 cells exposed to LPS, attenuating the release of IL-1β, IL-6, and TNF-α and the nuclear translocation of p-NFκB. Additionally, caffeine treatment restored the integrity of the ARPE-19 monolayer assessed by transepithelial electrical resistance (TEER) and the sodium fluorescein permeability test. Finally, the ischemia reperfusion (I/R) injury model was used in C57BL/6J mice to induce retinal inflammation and investigate the effects of caffeine treatment. Mouse eyes were treated topically with caffeine, and a pattern electroretinogram (PERG) was used to assess the retinal ganglion cell (RGC) function; furthermore, we evaluated the levels of IL-6 and BDNF in the retina. Retinal BDNF dropped significantly (p < 0.05) in the I/R group compared to the control group (normal mice); on the contrary, caffeine treatment maintained physiological levels of BDNF in the retina of I/R eyes. Caffeine was also able to reduce IL-6 mRNA levels in the retina of I/R eyes. In conclusion, these findings suggest that caffeine is a good candidate to counteract inflammation in retinal diseases.

Simultaneous determination of caffeine and its metabolites in rat plasma by UHPLC-MS/MS

Caffeine is a widely consumed psychostimulant with several mechanisms of action and various positive and negative effects on organisms. Caffeine undergoes extensive hepatic metabolism to form main metabolites such as theobromine, theophylline, paraxanthine, and 1,3,7-trimethyluric acid. However, interspecies diversities have been observed in caffeine metabolism. In the present study, we developed a sensitive and straightforward ultra-high-performance liquid chromatography-tandem mass spectrometry method to quantify caffeine and its primary metabolites, namely theobromine, theophylline, paraxanthine, and 1,3,7-trimethyluric acid in rat plasma. After extraction of analytes using micro solid-phase extraction plate, analytes were separated by elution gradient on the Acquity UPLC HSS T3 (50 × 2.1 mm, 1.8 μm) column over 4 min. The detection was done on a triple quadrupole tandem mass spectrometer by multiple reaction monitoring modes using a positive electrospray ionization interface. The method was successfully validated according to the European Medicine Agency guideline over a concentration range of 5-1500 ng/ml for caffeine, 5-1200 ng/mL for theobromine, and 2.5-1200 ng/mL for theophylline, paraxanthine, and 1,3,7-trimethyluric acid. The developed method was applied to analyze samples from animal experiments focusing on the metabolism and effects of caffeine and caffeine-containing beverages.

Effects of Caffeine on Brown Adipose Tissue Thermogenesis and Metabolic Homeostasis: A Review

The impact of brown adipose tissue (BAT) metabolism on understanding energy balance in humans is a relatively new and exciting field of research. The pathogenesis of obesity can be largely explained by an imbalance between caloric intake and energy expenditure, but the underlying mechanisms are far more complex. Traditional non-selective sympathetic activators have been used to artificially elevate energy utilization, or suppress appetite, however undesirable side effects are apparent with the use of these pharmacological interventions. Understanding the role of BAT, in relation to human energy homeostasis has the potential to dramatically offset the energy imbalance associated with obesity. This review discusses paradoxical effects of caffeine on peripheral adenosine receptors and the possible role of adenosine in increasing metabolism is highlighted, with consideration to the potential of central rather than peripheral mechanisms for caffeine mediated BAT thermogenesis and energy expenditure. Research on the complex physiology of adipose tissue, the embryonic lineage and function of the different types of adipocytes is summarized. In addition, the effect of BAT on overall human metabolism and the extent of the associated increase in energy expenditure are discussed. The controversy surrounding the primary β-adrenoceptor involved in human BAT activation is examined, and suggestions as to the lack of translational findings from animal to human physiology and human in vitro to in vivo models are provided. This review compares and distinguishes human and rodent BAT effects, thus developing an understanding of human BAT thermogenesis to aid lifestyle interventions targeting obesity and metabolic syndrome. The focus of this review is on the effect of BAT thermogenesis on overall metabolism, and the potential therapeutic effects of caffeine in increasing metabolism via its effects on BAT.

Worsening of Oxidative Stress, DNA Damage, and Atherosclerotic Lesions in Aged LDLr-/- Mice after Consumption of Guarana Soft Drinks

BACKGROUND

Excessive consumption of soft drinks (SD) has become a health problem worldwide due to its association with related cardiovascular diseases. We investigated the possible impacts associated with the consumption of Brazilian guarana (normal and zero) SD in dyslipidemic mice, thus mitigating potential clinical confounders such as poor-quality diet, lifestyle, body composition, and/or comorbidities.

METHODS

Sixteen-month-old LDLr-/- mice were divided into the following groups: (1) control; (2) GSD: normal guarana SD; and (3) Z-GSD: zero guarana SD. All were fed ad libitum, and blood pressure was measured noninvasively. After 8 weeks, aorta, blood, liver, and stomach samples were collected for histological and biochemical analyses.

RESULTS

Guarana soft drinks increased atherosclerosis (~60%) and were associated with hypercholesterolemia, hypertension, oxidative stress, DNA fragmentation, and apoptosis (~2-fold) of blood cells, besides presenting an increase in liver and gastric damage even in normoglycemia. Interestingly, Z-GSD did not cause the aforementioned changes, except in hemodynamic and renal parameters.

CONCLUSIONS

Chronic administration of GSD is prooxidative, compromising the cardiovascular, gastric, and hepatic systems; the effects are due at least in part to free sugar consumption but not to guarana extract per se.

Effects of Unfiltered Coffee and Bioactive Coffee Compounds on the Development of Metabolic Syndrome Components in a High-Fat-/High-Fructose-Fed Rat Model

The literature is inconsistent as to how coffee affects metabolic syndrome (MetS), and which bioactive compounds are responsible for its metabolic effects. This study aimed to evaluate the effects of unfiltered coffee on diet-induced MetS and investigate whether or not phenolic acids and trigonelline are the main bioactive compounds in coffee. Twenty-four male Sprague‒Dawley rats were fed a high-fat (35% W/W) diet plus 20% W/W fructose in drinking water for 14 weeks, and were randomized into three groups: control, coffee, or nutraceuticals (5-O-caffeoylquinic acid, caffeic acid, and trigonelline). Coffee or nutraceuticals were provided in drinking water at a dosage equal to 4 cups/day in a human. Compared to the controls, total food intake (p = 0.023) and mean body weight at endpoint (p = 0.016) and estimated average plasma glucose (p = 0.041) were lower only in the coffee group. Surrogate measures of insulin resistance including the overall fasting insulin (p = 0.010), endpoint HOMA-IR (p = 0.022), and oral glucose tolerance (p = 0.029) were improved in the coffee group. Circulating triglyceride levels were lower (p = 0.010), and histopathological and quantitative (p = 0.010) measurements indicated lower grades of liver steatosis compared to controls after long-term coffee consumption. In conclusion, a combination of phenolic acids and trigonelline was not as effective as coffee per se in improving the components of the MetS. This points to the role of other coffee chemicals and a potential synergism between compounds.

Postprandial glycaemic and lipaemic responses to chronic coffee consumption may be modulated by CYP1A2 polymorphisms

There is much epidemiological evidence suggesting a reduced risk of development of type 2 diabetes (T2D) in habitual coffee drinkers, however to date there have been few longer-term interventions, directly examining the effects of coffee intake on glucose and lipid metabolism. Previous studies may be confounded by inter-individual variation in caffeine metabolism. Specifically, the rs762551 SNP in the CYP1A2 gene has been demonstrated to influence caffeine metabolism, with carriers of the C allele considered to be of a ‘slow’ metaboliser phenotype. This study investigated the effects of regular coffee intake on markers of glucose and lipid metabolism in coffee-naïve individuals, with novel analysis by rs762551 genotype. Participants were randomised to either a coffee group (n 19) who consumed four cups/d instant coffee for 12 weeks or a control group (n 8) who remained coffee/caffeine free. Venous blood samples were taken pre- and post-intervention. Primary analysis revealed no significant differences between groups. Analysis of the coffee group by genotype revealed several differences. Before coffee intake, the AC genotype (‘slow’ caffeine metabolisers, n 9) displayed higher baseline glucose and NEFA than the AA genotype (‘fast’ caffeine metabolisers, n 10, P<0·05). Post-intervention, reduced postprandial glycaemia and reduced NEFA suppression were observed in the AC genotype, with the opposite result observed in the AA genotype (P<0·05). These observed differences between genotypes warrant further investigation and indicate there may be no one-size-fits-all recommendation with regard to coffee drinking and T2D risk.

Do flavanols-rich natural products relieve obesity-related insulin resistance?

Growing evidence support that insulin resistance may occur as a severe problem due to chronic energetic overfeeding and subsequent obesity. When an abundance of glucose and saturated fat enter the cell, impaired blood flow, hypoxia, inflammation and macrophage infiltration in obese adipose tissue may induce oxidative stress and insulin resistance. Excessive circulating saturated fatty acids ectopically accumulate in insulin-sensitive tissues and impair insulin action. In this context, excessive hepatic lipid accumulation may play a central, pathogenic role in insulin resistance. It is thought that dietary polyphenols may ameliorate obesity-related insulin resistance by attenuating inflammatory responses and oxidative stress. The most often occurring natural polyphenolic compounds are flavonoids. In this review, the possible mechanistic effect of flavonoid-rich natural products on insulin resistance-related metabolic pathways is discussed. Polyphenol intake can prevent high-fat-diet-induced insulin resistance via cell surface G protein-coupled estrogen receptors by upregulating the expression of related genes, and their pathways, which are responsible for the insulin sensitivity.

Caffeine-mediated BDNF release regulates long-term synaptic plasticity through activation of IRS2 signaling

Caffeine has cognitive‐enhancing properties with effects on learning and memory, concentration, arousal and mood. These effects imply changes at circuital and synaptic level, but the mechanism by which caffeine modifies synaptic plasticity remains elusive. Here we report that caffeine, at concentrations representing moderate to high levels of consumption in humans, induces an NMDA receptor‐independent form of LTP (_CAFLTP) in the CA1 region of the hippocampus by promoting calcium‐dependent secretion of BDNF, which subsequently activates TrkB‐mediated signaling required for the expression of _CAFLTP. Our data include the novel observation that insulin receptor substrate 2 (IRS2) is phosphorylated during induction of _CAFLTP, a process that requires cytosolic free Ca²⁺. Consistent with the involvement of IRS2 signals in caffeine‐mediated synaptic plasticity, phosphorylation of Akt (Ser473) in response to LTP induction is defective in Irs2^−/− mice, demonstrating that these plasticity changes are associated with downstream targets of the phosphoinositide 3‐kinase (PI3K) pathway. These findings indicate that TrkB‐IRS2 signals are essential for activation of PI3K during the induction of LTP by caffeine.

Caffeine Prevents Blood Retinal Barrier Damage in a Model, In Vitro, of Diabetic Macular Edema

Diabetic macular edema (DME) is the major cause of vision loss in patients affected by diabetic retinopathy. Hyperglycemia and hypoxia represent the key elements in the progression of these pathologies, leading to breakdown of the blood-retinal barrier (BRB). Caffeine, a psychoactive substance largely consumed in the world, is a nonselective antagonist of adenosine receptors (AR) and it possesses a protective effect in various diseases, including eye pathologies. Here, we have investigated the effect of this substance on BRB integrity following exposure to hyperglycemic/hypoxic insult. Retinal pigmented epithelial cells, ARPE-19, have been grown on semi-permeable supports mimicking an experimental model, in vitro, of outer BRB. Caffeine treatment has reduced cell monolayer permeability after exposure to high glucose and desferoxamine as shown by TEER and FITC-dextran permeability assays. This effect is also mediated through the restoration of membrane's tight junction expression, ZO-1. Moreover, we have demonstrated that caffeine is able to prevent outer BRB damage by inhibiting apoptotic cell death induced by hyperglycemic/hypoxic insult since it downregulates the proapoptotic Bax and upregulates the anti-apoptotic Bcl-2 genes. Although further studies are needed to better comprise the beneficial effect of caffeine, we can speculate that it might be used as an innovative drug for DME treatment. J. Cell. Biochem. 118: 2371-2379, 2017. © 2017 Wiley Periodicals, Inc.

Effects of Caffeine and Lycopene in Experimentally Induced Diabetes Mellitus

OBJECTIVES

Diabetes mellitus (DM) is a global epidemic with increasing prevalence. The disease is chronic in nature, and patients must use antidiabetic drugs or insulin during their lifespan. Because of the difficulty of using injectable insulin preparations, patients and practitioners prefer to use oral antidiabetic drugs for prophylaxis and treatment. There are, however, numerous adverse effects of antidiabetic drugs and rapidly increasing attention is being paid to new nutraceutical drugs with fewer adverse effects. The purpose of this study was to evaluate the effects of caffeine and lycopene on streptozotocin (STZ)-induced DM in rats.

METHODS

Caffeine and lycopene were administered to the study groups by oral gavages for 1 month whereafter experimental diabetes was induced in 90 rats in 6 groups.

RESULTS

There were no pathological effects of lycopene and caffeine on the pancreas. Marked vacuolization and degeneration were observed in STZ-treated groups. Caffeine and lycopene decreased the pathological findings and lowered the blood and urine glucose levels in the rats with STZ-induced DM, whereas these compounds increased serum insulin levels.

CONCLUSIONS

This study showed that caffeine and lycopene provided protective effects against experimentally induced DM. The protective effects of lycopene were observed to be much greater than those of caffeine.

An overview on antidiabetic medicinal plants having insulin mimetic property

Diabetes mellitus is one of the common metabolic disorders acquiring around 2.8% of the world's population and is anticipated to cross 5.4% by the year 2025. Since long back herbal medicines have been the highly esteemed source of medicine therefore, they have become a growing part of modern, high-tech medicine. In view of the above aspects the present review provides profiles of plants (65 species) with hypoglycaemic properties, available through literature source from various database with proper categorization according to the parts used, mode of reduction in blood glucose (insulinomimetic or insulin secretagogues activity) and active phytoconstituents having insulin mimetics activity. From the review it was suggested that, plant showing hypoglycemic potential mainly belongs to the family Leguminoseae, Lamiaceae, Liliaceae, Cucurbitaceae, Asteraceae, Moraceae, Rosaceae and Araliaceae. The most active plants are Allium sativum, Gymnema sylvestre, Citrullus colocynthis, Trigonella foenum greacum, Momordica charantia and Ficus bengalensis. The review describes some new bioactive drugs and isolated compounds from plants such as roseoside, epigallocatechin gallate, beta-pyrazol-1-ylalanine, cinchonain Ib, leucocyandin 3-O-beta-d-galactosyl cellobioside, leucopelargonidin-3- O-alpha-L rhamnoside, glycyrrhetinic acid, dehydrotrametenolic acid, strictinin, isostrictinin, pedunculagin, epicatechin and christinin-A showing significant insulinomimetic and antidiabetic activity with more efficacy than conventional hypoglycaemic agents. Thus, from the review majorly, the antidiabetic activity of medicinal plants is attributed to the presence of polyphenols, flavonoids, terpenoids, coumarins and other constituents which show reduction in blood glucose levels. The review also discusses the management aspect of diabetes mellitus using these plants and their active principles.

Differential effects of caffeine on hair shaft elongation, matrix and outer root sheath keratinocyte proliferation, and transforming growth factor-β2/insulin-like growth factor-1-mediated regulation of the hair cycle in male and female human hair follicles in vitro

BACKGROUND

Caffeine reportedly counteracts the suppression of hair shaft production by testosterone in organ-cultured male human hair follicles (HFs).

OBJECTIVES

We aimed to investigate the impact of caffeine (i) on additional key hair growth parameters, (ii) on major hair growth regulatory factors and (iii) on male vs. female HFs in the presence of testosterone.

METHODS

Microdissected male and female human scalp HFs were treated in serum-free organ culture for 120 h with testosterone alone (0·5 μg mL(-1)) or in combination with caffeine (0·005-0·0005%). The following effects on hair shaft elongation were evaluated by quantitative (immuno)histomorphometry: HF cycling (anagen-catagen transition); hair matrix keratinocyte proliferation; expression of a key catagen inducer, transforming growth factor (TGF)-β2; and expression of the anagen-prolonging insulin-like growth factor (IGF)-1. Caffeine effects were further investigated in human outer root sheath keratinocytes (ORSKs).

RESULTS

Caffeine enhanced hair shaft elongation, prolonged anagen duration and stimulated hair matrix keratinocyte proliferation. Female HFs showed higher sensitivity to caffeine than male HFs. Caffeine counteracted testosterone-enhanced TGF-β2 protein expression in male HFs. In female HFs, testosterone failed to induce TGF-β2 expression, while caffeine reduced it. In male and female HFs, caffeine enhanced IGF-1 protein expression. In ORSKs, caffeine stimulated cell proliferation, inhibited apoptosis/necrosis, and upregulated IGF-1 gene expression and protein secretion, while TGF-β2 protein secretion was downregulated.

CONCLUSIONS

This study reveals new growth-promoting effects of caffeine on human hair follicles in subjects of both sexes at different levels (molecular, cellular and organ).

Sulfonylurea induction of caffeine-enhanced insulin secretion and reduction of glycemic levels in diabetic rats

CONTEXT

Caffeine can stimulate insulin secretion by attenuating hyperglycemia in diabetes models with significant reduction of pancreatic functional β cells. Knowledge of these mechanisms could contribute to new strategies for treating diabetes.

OBJECTIVE

This study evaluated the effects of caffeine and physical exercise on glycemic and insulin responses in diabetic rats.

MATERIALS AND METHODS

The diabetes model was induced by intraperitoneal administration of 60 mg/kg of streptozotocin (STZ). Animals were divided into six groups: control, caffeine, STZ control, STZ caffeine, STZ sulfonylurea, and STZ caffeine + sulfonylurea. Acutely, control animals received 6 mg of caffeine and 10 mg/kg sulfonylurea or 10 mg/kg saline. Animals were sacrificed after physical exercise; blood samples were collected for glucose, glycerol, lactate, and insulin analyses. Cardiovascular responses were recorded before and after treatments. A one-way ANOVA and the post hoc Student-Newman-Keuls test were used to analyze statistical differences between treatments (p < 0.05).

RESULTS

About 6 mg/kg of caffeine did not alter cardiovascular responses, but promoted blood glucose reduction after 60 min of exercise when compared to animals in the control groups (387-187 mg/dL; p < 0.05). Insulin levels increased significantly (0.6-10 µU/mL; p < 0.05) in rats that received acute caffeine treatment associated with sulfonylurea compared to rats in the other groups.

DISCUSSION AND CONCLUSION

Acute caffeine intake with exercise can increase glucose uptake enhancing insulin secretion stimulated by sulfonylurea in β cells-deficient pancreas. The results indicate the potential use of caffeine as a strategy for glycemic and insulin control in diabetes.

Development of an alternative non-obese non-genetic rat model of type 2 diabetes using caffeine and streptozotocin

BACKGROUND

The aim of the present study was to develop an alternative non-obese non-genetic rat model of type 2 diabetes (T2D).

METHODS

Six-week-old male SD rats were randomly divided into six groups, namely: Normal Control (NC), Diabetic Control (DBC), Caffeine 5mg/kg BW+STZ (CAF5), Caffeine 10mg/kg BW+STZ (CAF10), Caffeine 20mg/kg BW+STZ (CAF20) and Caffeine 40mg/kg BW+STZ (CAF40) and were fed a normal rat pellet diet and drinking water ad libitum throughout the experimental period. After a one week acclimatization period, diabetes was induced in the animals in DBC and all CAF groups with an injection (i.p.) of the respective dosages of caffeine (mg/kg BW) 15min before the injection of STZ (65mg/kg BW) when normal saline was injected to the DBC group instead of caffeine. The NC group received normal saline and buffer instead of caffeine and STZ, respectively. One week after the STZ injection, animals with non-fasting blood glucose>300mg/dl were considered as diabetic. Three weeks after the STZ injection, the animals in the CAF5 and CAF10 groups were eliminated from the study due to the severity of diabetes and the experiment was continued with the remainder groups for a 13 weeks period.

RESULTS AND CONCLUSION

The data of food and fluid intake, body weight, blood glucose, glucose tolerance test, HOMA-IR, HOMA-beta, serum insulin, fructosamine, lipid profile and organ specific enzymes, anti-diabetic drug response tests, and pancreatic histopathology suggest that CAF20 group can be a better alternative non-genetic model of non-obese T2D.

Ingestão aguda de cafeína reduz a glicemia sanguínea antes e após o exercício físico agudo em ratos diabéticos

OBJETIVO: O presente estudo verificou os efeitos da suplementação com cafeína associada ao exercício físico agudo sobre a resposta glicêmica em ratos diabéticos. MÉTODOS: Foram utilizados 32 animais, com 60 dias de idade, e 238±3 g de peso, divididos em quatro grupos: controle, controle cafeína, diabetes e diabetes/cafeína. O modelo de diabetes foi induzido pela administração intraperitoneal de 60 mg/kg de estreptozotocina. De forma aguda, os animais receberam 6 mg de cafeína ou salina para os grupos-controles 60 minutos antes do exercício físico. Os animais realizaram um protocolo de natação de 60 minutos de exercício físico, com sobrecarga de 6% do peso corporal com lactacidemia compatível com a máxima produção de lactato em estado estável (5,5 mmol/L). Após o exercício físico agudo, foi realizada a eutanásia dos animais para coleta de sangue e análises glicêmicas. Antes e após a prescrição das suplementações, ocorreu a aferição das respostas cardiovasculares por meio de um pletismógrafo de cauda. Foi realizado o teste estatístico Analise de Variância one way com post hoc de Student-Newman-Keuls para analisar as diferenças estatísticas entre as suplementações, sendo considerado p<0,05. RESULTADOS: A prescrição de cafeína na dose de 6 mg/kg não alterou respostas cardiovasculares. No entanto, a cafeína promoveu uma significante redução na glicemia sanguínea (42%; p<0,05) após 60 minutos do protocolo de exercício nos ratos diabéticos em relação aos grupos-controles. CONCLUSÃO: A ingestão aguda de cafeína associada ao exercício físico agudo pode aumentar a captação de glicose sem alterar as respostas cardiovasculares em modelo animal.

Caffeine intake improves fructose-induced hypertension and insulin resistance by enhancing central insulin signaling

Recent clinical studies found that fructose intake leads to insulin resistance and hypertension. Fructose consumption promotes protein fructosylation and formation of superoxide. In a previous study, we revealed that inhibition of superoxide production in the nucleus tractus solitarii (NTS) reduces blood pressure. Caffeine displays significant antioxidant ability in protecting membranes against oxidative damage and can lower the risk of insulin resistance. However, the mechanism through which caffeine improves fructose-induced insulin resistance is unclear. The aim of this study was to investigate whether caffeine consumption can abolish superoxide generation to enhance insulin signaling in the NTS, thereby reducing blood pressure in rats with fructose-induced hypertension. Treatment with caffeine for 4 weeks decreased blood pressure, serum fasting glucose, insulin, homeostatic model assessment-insulin resistance, and triglyceride levels and increased the serum direct high-density lipoprotein level in fructose-fed rats but not in control rats. Caffeine treatment resulted in the recovery of fructose-induced decrease in nitric oxide production in the NTS. Immunoblotting and immunofluorescence analyses further showed that caffeine reduced the fructose-induced phosphorylation of insulin receptor substrate 1 (IRS1(S307)) and reversed Akt(S473) and neuronal nitric oxide synthase phosphorylation. Similarly, caffeine was able to improve insulin sensitivity and decrease insulin levels in the NTS evoked by fructose. Caffeine intake also reduced the production of superoxide and expression of receptor of advanced glycation end product in the NTS. These results suggest that caffeine may enhance insulin receptor substrate 1-phosphatidylinositol 3-kinase-Akt-neuronal nitric oxide synthase signaling to decrease blood pressure by abolishing superoxide production in the NTS.

Effects of habitual coffee consumption on cardiometabolic disease, cardiovascular health, and all-cause mortality

Coffee, after water, is the most widely consumed beverage in the United States, and is the principal source of caffeine intake among adults. The biological effects of coffee may be substantial and are not limited to the actions of caffeine. Coffee is a complex beverage containing hundreds of biologically active compounds, and the health effects of chronic coffee intake are wide ranging. From a cardiovascular (CV) standpoint, coffee consumption may reduce the risk of type 2 diabetes mellitus and hypertension, as well as other conditions associated with CV risk such as obesity and depression; but it may adversely affect lipid profiles depending on how the beverage is prepared. Regardless, a growing body of data suggests that habitual coffee consumption is neutral to beneficial regarding the risks of a variety of adverse CV outcomes including coronary heart disease, congestive heart failure, arrhythmias, and stroke. Moreover, large epidemiological studies suggest that regular coffee drinkers have reduced risks of mortality, both CV and all-cause. The potential benefits also include protection against neurodegenerative diseases, improved asthma control, and lower risk of select gastrointestinal diseases. A daily intake of ∼2 to 3 cups of coffee appears to be safe and is associated with neutral to beneficial effects for most of the studied health outcomes. However, most of the data on coffee's health effects are based on observational data, with very few randomized, controlled studies, and association does not prove causation. Additionally, the possible advantages of regular coffee consumption have to be weighed against potential risks (which are mostly related to its high caffeine content) including anxiety, insomnia, tremulousness, and palpitations, as well as bone loss and possibly increased risk of fractures.

A cross-over study of the acute effects of espresso coffee on glucose tolerance and insulin sensitivity in people with type 2 diabetes mellitus

The objective was to determine the effect of a single dose of espresso caffeinated coffee, decaffeinated coffee, or water on glucose tolerance and insulin sensitivity in people with type 2 diabetes mellitus. Eighteen participants who were habitual coffee drinkers, were studied using a random-order cross-over design. After a fasting blood sample participants consumed either a double-shot black espresso coffee, decaffeinated coffee, or hot water. The main outcomes were area under the curve (AUC) glucose and insulin, and insulin sensitivity (Matsuda index) during a 75 g oral glucose tolerance test (OGTT) performed one hour later. Other outcomes were change in glucose and insulin and also the insulinogenic index (IGI) and disposition index (DI). AUC glucose was marginally different between beverages (P=.06) being greater following caffeinated coffee than water, mean difference 104 mmol/L/180 min (95% CI 0.1 to 198.1, P=.031), or decaffeinated coffee, mean difference 92.1 mmol/L/180 min (95% CI -1.9 to 186.1, P=.055). There was no difference in AUC insulin (P=.87) or insulin sensitivity (P=.47), nor in change in glucose or insulin over the hour following beverage consumption. There was a marginal difference in IGI between beverages (P=.097) with coffee having a lower incremental increase in insulin/glucose than water (P=.037) though no difference between coffee and decaffeinated coffee (P=.54) and no difference in DI (P=.23). Black espresso coffee in people with type 2 diabetes mellitus results in a marginally greater excursion of glucose during a following OGTT compared with water or decaffeinated coffee. This effect does not appear to be mediated by changes in insulin sensitivity.

Type 1 diabetes mellitus and components in drinking water and diet: a population-based, case-control study in Prince Edward Island, Canada

OBJECTIVE

To determine the relationship between the risk of type 1 diabetes (T1D) and daily intake of drinking water and dietary components, including nitrate, nitrite, and nitrosamines, during the year prior to diagnosis.

METHODS

Controls (n = 105) were matched by age at diagnosis and sex to T1D cases (n = 57) newly diagnosed during 2001-2004. Food consumption was assessed using a food frequency questionnaire. Locally available samples of foods were tested for nitrate, nitrite, and nitrosamine concentrations. Water consumption was determined through an additional questionnaire, and water samples were taken from homes and tested for routine chemical components, including nitrate.

RESULTS

After controlling for age, age, sex, and daily energy intake, nitrate intake from food sources showed a non-significant positive trend (odds ratios and 95% confidence intervals for quartiles = 1.00, 1.63 (0.58, 4.63), 1.71 (0.54, 5.40), 3.02 (0.78, 11.74); p for trend = 0.13). Nitrite and nitrosamine intake were not related to T1D risk (p for trend = 0.77 and 0.81, respectively). When food and water components were combined, zinc and calcium intakes were marginally and inversely related to T1D risk (p for trend = 0.07 and 0.06, respectively). After further model adjustment of possible confounders and significant risk factors, an increased intake of caffeine marginally increased the risk of T1D (p = 0.07).

CONCLUSION

Dietary components from both food and water sources may influence the risk of developing T1D in young persons.

A ketogenic diet impairs energy and glucose homeostasis by the attenuation of hypothalamic leptin signaling and hepatic insulin signaling in a rat model of non-obese type 2 diabetes

Ketogenic diets (KTD) are reported to have beneficial effects on the regulation of energy and glucose homeostasis, but remain controversial. We investigated the effects of KTD and ketones on insulin resistance and secretion in non-obese type 2 diabetic rats and their mechanism. KTD (82% energy as fat), intraperitoneal injection of β-hydroxybutyrate (IHB; 150 mg/kg bw/12 h) with a control diet (COD; 20% energy as fat) or saline injection with COD was given to 90% pancreatectomized (Px) diabetic rats for five weeks. KTD increased epididymal fat pads and serum leptin levels without increasing energy intake, but IHB decreased them. KTD, but not IHB, attenuated hypothalamic signal transducer and activator of transcription 3 and 5'-adenosine monophosphate-activated protein kinase (AMPK) phosphorylation in KTD. Serum glucagon levels were markedly higher in the KTD group than in other groups. During an oral glucose tolerance test, serum glucose levels slowly increased until 80 min in the KTD group and then decreased very slowly. Insulin secretion capacity during a hyperglycemic clamp was significantly lower in the IHB group than in other groups. However, a euglycemic hyperinsulinemic clamp revealed that KTD decreased glucose infusion rates and increased hepatic glucose output in hyperinsulinemic states while IHB had opposite effects to KTD. The increased hepatic glucose output in KTD was associated with increased hepatic phosphoenolpyruvate carboxykinase expression through attenuated tyrosine phosphorylation of IRS2 and phosphorylation of Akt(Ser473). Hepatic AMPK(Thr172) phosphorylation was reduced in KTD. In conclusion, KTD impairs energy and glucose homeostasis by exacerbating insulin resistance and attenuating hypothalamic leptin signaling in non-obese type 2 diabetic rats. These changes are not associated with increased serum ketone levels.

Renal and metabolic effects of three months of decarbonated cola beverages in rats

Epidemiological studies have shown an association between the intake of cola beverages and chronic kidney diseases. Experimental evidence for the negative effects of cola intake on kidneys is lacking. Male Wistar rats had ad libitum access to water (control group) or three different sugar-sweetened cola beverages for three months. Despite very high cola intake (daily cca 140 mL), no differences were found in body weight, kidney weight, glomerular morphology, oxidative and carbonyl stress or expression of selected marker genes in the renal cortex. Interestingly, all groups consuming cola beverages had lower blood glucose levels during an oral glucose tolerance test, suggesting improved insulin sensitivity. Despite hyperfiltration (5–6-fold increase in diuresis), cola beverages had no effect on assessed parameters of renal function, histology, gene expression or oxidative stress. Moreover, cola intake seems to increase creatinine clearance and to decrease plasma levels of urea. In our study increased insulin sensitivity and altered renal functional parameters were observed in rats receiving cola beverages for three months. Whether the findings are due to the short duration of the study or interspecies metabolic differences should be uncovered in further studies. Even more interesting might be the analysis of effects of cola intake in animal models of diabetes.

Body weight gain in rats consuming sweetened liquids. Effects of caffeine and diet composition

Previous studies show that high-intensity sweeteners can stimulate weight gain in rats. The present studies examined whether caffeine, a stimulant commonly added to beverages consumed by humans, influences intake of saccharin- or glucose-sweetened solutions or body weight gain in rats and whether the nature of the maintenance diet influences the effects of caffeine. In two experiments, rats received glucose or saccharin solution mixed with 0.125 mg/g caffeine or no caffeine. Rats consumed significantly more caffeinated than noncaffeinated solutions when they were maintained on a low-fat chow diet (Experiment 1) and when maintained on a sweet, high-fat, high calorie chow diet (Experiment 2). Consumption of saccharin resulted in higher body weight gain in both experiments. Caffeine reversed this effect in Experiment 1 (low-fat diet) but not Experiment 2 (sweet, high-fat diet). The findings extend what is known about the conditions under which consumption of high intensity sweeteners promote energy dysregulation.

Protective effect of caffeine on streptozotocin-induced beta-cell damage in rats

Many epidemiological studies have shown that coffee consumption reduces the risk of type 2 diabetes mellitus (T2D), although the reasons as to why remain unclear. In this study we investigated the effect of caffeine on pancreatic beta-cell damage in rats using the diabetogenic agent, streptozotocin (STZ). Wistar rats were given intraperitoneal injections of saline or caffeine (10, 50 or 100 mgkg−1). After 15 min, the rats were injected with a citrate buffer or 65 mgkg−1 STZ. Three days after injection, an oral glucose tolerance test (OGTT) was performed on the rats. Furthermore, three days after the OGTT, the pancreas was isolated and homogenized, followed by determination of insulin content. STZ treatment significantly increased the plasma glucose level compared with the control at all times during the OGTT, which was significantly diminished by caffeine pretreatment at all doses. STZ treatment significantly decreased the plasma insulin level, however, which was not recovered by caffeine pretreatment. Pancreatic insulin content was significantly reduced by STZ treatment compared with the control, which was significantly recovered by caffeine pretreatment at a dose of 100 mgkg−1 (P &lt; 0.01). We showed that caffeine protects pancreatic beta-cells against STZ toxicity. Further investigation will be required to understand the protective effect of caffeine against beta-cell destruction in T2D.

Coffee and tea consumption and risk of type 2 diabetes

AIMS/HYPOTHESIS

The aim of this study was to examine the association of consumption of coffee and tea, separately and in total, with risk of type 2 diabetes and which factors mediate these relations.

METHODS

This research was conducted as part of the Dutch Contribution to the European Prospective Investigation into Cancer and Nutrition, which involves a prospective cohort of 40,011 participants with a mean follow-up of 10 years. A validated food-frequency questionnaire was used to assess coffee and tea consumption and other lifestyle and dietary factors. The main outcome was verified incidence of type 2 diabetes. Blood pressure, caffeine, magnesium and potassium were examined as possible mediating factors.

RESULTS

During follow-up, 918 incident cases of type 2 diabetes were documented. After adjustment for potential confounders, coffee and tea consumption were both inversely associated with type 2 diabetes, with hazard ratios of 0.77 (95% CI 0.63-0.95) for 4.1-6.0 cups of coffee per day (p for trend = 0.033) and 0.63 (95% CI: 0.47-0.86) for >5.0 cups of tea per day (p for trend = 0.002). Total daily consumption of at least three cups of coffee and/or tea reduced the risk of type 2 diabetes by approximately 42%. Adjusting for blood pressure, magnesium, potassium and caffeine did not attenuate the associations.

CONCLUSIONS/INTERPRETATION

Drinking coffee or tea is associated with a lowered risk of type 2 diabetes, which cannot be explained by magnesium, potassium, caffeine or blood pressure effects. Total consumption of at least three cups of coffee or tea per day may lower the risk of type 2 diabetes.

High rates of muscle glycogen resynthesis after exhaustive exercise when carbohydrate is coingested with caffeine

We determined the effect of coingestion of caffeine (Caff) with carbohydrate (CHO) on rates of muscle glycogen resynthesis during recovery from exhaustive exercise in seven trained subjects who completed two experimental trials in a randomized, double-blind crossover design. The evening before an experiment subjects performed intermittent exhaustive cycling and then consumed a low-CHO meal. The next morning subjects rode until volitional fatigue. On completion of this ride subjects consumed either CHO [4 g/kg body mass (BM)] or the same amount of CHO + Caff (8 mg/kg BM) during 4 h of passive recovery. Muscle biopsies and blood samples were taken at regular intervals throughout recovery. Muscle glycogen levels were similar at exhaustion [ approximately 75 mmol/kg dry wt (dw)] and increased by a similar amount ( approximately 80%) after 1 h of recovery (133 +/- 37.8 vs. 149 +/- 48 mmol/kg dw for CHO and Caff, respectively). After 4 h of recovery Caff resulted in higher glycogen accumulation (313 +/- 69 vs. 234 +/- 50 mmol/kg dw, P < 0.001). Accordingly, the overall rate of resynthesis for the 4-h recovery period was 66% higher in Caff compared with CHO (57.7 +/- 18.5 vs. 38.0 +/- 7.7 mmol x kg dw(-1) x h(-1), P < 0.05). After 1 h of recovery plasma Caff levels had increased to 31 +/- 11 microM (P < 0.001) and at the end of the recovery reached 77 +/- 11 microM (P < 0.001) with Caff. Phosphorylation of CaMK(Thr286) was similar after exercise and after 1 h of recovery, but after 4 h CaMK(Thr286) phosphorylation was higher in Caff than CHO (P < 0.05). Phosphorylation of AMP-activated protein kinase (AMPK)(Thr172) and Akt(Ser473) was similar for both treatments at all time points. We provide the first evidence that in trained subjects coingestion of large amounts of Caff (8 mg/kg BM) with CHO has an additive effect on rates of postexercise muscle glycogen accumulation compared with consumption of CHO alone.

Exercise improves glucose homeostasis that has been impaired by a high-fat diet by potentiating pancreatic β-cell function and mass through IRS2 in diabetic rats

In this study, we investigated the effects of a high-fat diet and exercise on pancreatic β-cell function and mass and its molecular mechanism in 90% pancreatectomized male rats. The pancreatectomized diabetic rats were given control diets (20% energy) or a high-fat (HF) diet (45% energy) for 12 wk. Half of each group was given regular exercise on an uphill treadmill at 20 m/min for 30 min 5 days/wk. HF diet lowered first-phase insulin secretion with glucose loading, whereas exercise training reversed this decrease. However, second-phase insulin secretion did not differ among the groups. Exercise increased pancreatic β-cell mass. This resulted from stimulated β-cell proliferation and reduced apoptosis, which is associated with potentiated insulin or IGF-I signaling through insulin receptor substrate-2 (IRS2) induction. Although the HF diet resulted in decreased proliferation and accelerated apoptosis by weakened insulin and IGF-I signaling from reduction of IRS2 protein, β-cell mass was maintained in HF rats just as much as in control rats via increased individual β-cell size and neogenesis from precursor cells. Consistent with the results of β-cell proliferation, pancreas duodenal homeobox-1 expression increased in the islets of rats in the exercise groups, and it was reduced the most in rats fed the HF diet. In conclusion, exercise combined with a moderate fat diet is a good way to maximize β-cell function and mass through IRS2 induction to alleviate the diabetic condition. This study suggests that dietary fat contents and exercise modulate β-cell function and mass to overcome insulin resistance in two different pathways.