Interspecies comparison of in vivo caffeine pharmacokinetics in man, monkey, rabbit, rat, and mouse

Caffeine Boosts Weight-Lifting Performance in Rats: A Pilot Study

Caffeine is a well-described ergogenic aid used to enhance athletic performance. Using animal models can greatly increase our understanding of caffeine's mechanisms in performance. Here, we adapted an animal weight-lifting exercise model to demonstrate caffeine's ergogenic effect in rats. Male Wistar rats (315 ± 35 g) were randomly divided into two groups: one group received 5 mg·kg-1 of caffeine (0.5 mL; CEx; n = 5) and the other 0.9% NaCl (0.5 mL; PEx; n = 4) through an orogastric probe (gavage) one hour before exercise. Weight-lifting exercise sessions were performed over three subsequent days, and the number of complete squats performed was counted. Analyses of the area under the curve in all three experiments showed that the CEx group responded more to stimuli, performing more squats (1.7-, 2.0-, and 1.6-fold; p < 0.05) than the control group did. These three days' data were analyzed to better understand the cumulative effect of this exercise, and a hyperbolic curve was fitted to these data. Data fitting from the caffeine-supplemented group, CEx, also showed larger Smax and Kd (2.3-fold and 1.6-fold, respectively) than the PEx group did. Our study demonstrated an acute ergogenic effect of caffeine in an animal weight-lifting exercise model for the first time, suggesting potential avenues for future research.

Effects of caffeine on temporal perception in Rattus norvegicus

We report two studies that tested the effects of caffeine, the world's most widely used psychoactive drug, on temporal perception. We trained Wistar rats using the Bisection Procedure (Experiment 1) or the Stubbs' Procedure (Experiment 2) to discriminate between short and long light stimuli. Once training finished, we administered caffeine orally (0, 9.6, and 96.0 mg/kg for Experiment 1 and 0, 9.6, 19.2, and 38.4 mg/kg for Experiment 2) 15 minutes prior to testing. Relative to the control condition, the 9.6 mg/kg condition (Experiments 1 and 2) and the 19.2 mg/kg condition (Experiment 2) resulted in an increase in proportion of choosing the long response. Meanwhile, overall accuracy was not affected by any condition in both experiments. Taken together, these results are consistent with the notion that caffeine, at some doses, speeds up temporal perception. However, it is not clear why the effect disappears at higher doses.

Long-Term Effect of a Single Dose of Caffeine on Sleep, the Sleep EEG and Neuronal Activity in the Peduncular Part of the Lateral Hypothalamus under Constant Dark Conditions

Background: Caffeine is a central nervous system stimulant that influences both the sleep–wake cycle and the circadian clock and is known to influence neuronal activity in the lateral hypothalamus, an important area involved in sleep–wake regulation. Light is a strong zeitgeber and it is known to interact with the effect of caffeine on the sleep–wake cycle. We therefore wanted to investigate the long-term effects of a single dose of caffeine under constant dark conditions. Methods: We performed long-term (2 days) electroencephalogram (EEG)/electromyogram recordings combined with multi-unit neuronal activity recordings in the peduncular part of the lateral hypothalamus (PLH) under constant darkness in Brown Norway rats, and investigated the effect of a single caffeine treatment (15 mg/kg) or saline control given 1 h after the onset of the endogenous rest phase. Results: After a reduction in sleep and an increase in waking and activity in the first hours after administration, also on the second recording day after caffeine administration, rapid eye movement (REM) sleep was still reduced. Analysis of the EEG showed that power density in the theta range during waking and REM sleep was increased for at least two days. Neuronal activity in PLH was also increased for two days after the treatment, particularly during non-rapid eye movement sleep. Conclusion: Surprisingly, the data reveal long-term effects of a single dose of caffeine on vigilance states, EEG, and neuronal activity in the PLH. The absence of a light–dark cycle may have enabled the expression of these long-term changes. It therefore may be that caffeine, or its metabolites, have a stronger and longer lasting influence, particularly on the expression of REM sleep, than acknowledged until now.

Effect of caffeine on the anticonvulsant action of pregabalin against electroconvulsions in mice

BACKGROUND

Experimental data indicate that caffeine (CAF) can reduce the anticonvulsant activity of antiepileptic drugs (AEDs) in animal models of seizures. The purpose of the current study was to examine the effect of CAF on the protective action of pregabalin (PGB) against electroconvulsions in mice.

METHODS

Maximal electroshock seizure (MES) test was used in the current study. In addition, the combined treatment with CAF and PGB was assessed in the passive avoidance task (long-term memory) and the chimney test (motor coordination). Drugs were injected intraperitoneally (ip) as single injections. CAF was administered at doses reported to compromise the anticonvulsant action of AEDs in mice.

RESULTS

CAF at a dose of 23.1 mg/kg reduced the anticonvulsant action of PGB in the MES test. The brain concentration of PGB was not significantly changed by CAF and vice versa. In the chimney test, CAF (23.1 mg/kg) protected mice against PGB-induced motor coordination impairment.

CONCLUSIONS

Regarding seizure control, it might be suggested that patients with epilepsy treated with PGB should avoid taking CAF. The estimated total brain concentration of PGB and CAF does not suggest a pharmacokinetic interaction as an explanation for these results.

Caffeine and MDMA (Ecstasy) Exacerbate ER Stress Triggered by Hyperthermia

Drugs of abuse can cause local and systemic hyperthermia, a known trigger of endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). Another trigger of ER stress and UPR is ER calcium depletion, which causes ER exodosis, the secretion of ER-resident proteins. In rodent models, club drugs such as 3,4-methylenedioxymethamphetamine (MDMA, ‘ecstasy’) can create hyperthermic conditions in the brain and cause toxicity that is affected by the environmental temperature and the presence of other drugs, such as caffeine. In human studies, MDMA stimulated an acute, dose-dependent increase in core body temperature, but an examination of caffeine and MDMA in combination remains a topic for clinical research. Here we examine the secretion of ER-resident proteins and activation of the UPR under combined exposure to MDMA and caffeine in a cellular model of hyperthermia. We show that hyperthermia triggers the secretion of normally ER-resident proteins, and that this aberrant protein secretion is potentiated by the presence of MDMA, caffeine, or a combination of the two drugs. Hyperthermia activates the UPR but the addition of MDMA or caffeine does not alter the canonical UPR gene expression despite the drug effects on ER exodosis of UPR-related proteins. One exception was increased BiP/GRP78 mRNA levels in MDMA-treated cells exposed to hyperthermia. These findings suggest that club drug use under hyperthermic conditions exacerbates disruption of ER proteostasis, contributing to cellular toxicity.

Caffeine: cardiorespiratory effects and tissue protection in animal models

The aim of this review is to analyze the cardiorespiratory and tissue-protective effects of caffeine in animal models. Peer-reviewed literature published between 1975 and 2021 was retrieved from CAB Abstracts, PubMed, ISI Web of Knowledge, and Scopus. Extracted data were analyzed to address the mechanism of action of caffeine on cardiorespiratory parameters (heart rate and rhythm), vasopressor effects, and some indices of respiratory function; we close this review by discussing the current debate on the research carried out on the effects of caffeine on tissue protection. Adenosine acts through specific receptors and is a negative inotropic and chronotropic agent. Blockage of its cardiac receptors can cause tachycardia (with arrhythmogenic potential) due to the intense activity of β1 receptors. In terms of tissue protection, caffeine inhibits hyperoxia-induced pulmonary inflammation by decreasing proinflammatory cytokine expression in animal models. The protection that caffeine provides to tissues is not limited to the CNS, as studies have demonstrated that it generates attenuation of inflammatory effects in pulmonary tissue. It inhibits the effects of some pro-inflammatory cytokines and prevents functional and structural changes.

Time effect of rutaecarpine on caffeine pharmacokinetics in rats

Rutaecarpine is reported as a potent inducer of CYP1A2 enzyme in rats. There are natural herbal supplements containing rutaecarpine that are designed to enhance the CYP1A2-dependent removal of caffeine from blood so that people can have coffee later in the day without causing sleep interference. This study aimed to determine the minimum amount of time needed from oral rutaecarpine administration until the observed effect of rutaecarpine on caffeine pharmacokinetics (PK) in 15 male Sprague-Dawley rats. PK parameters for caffeine and its metabolites in the control and rutaecarpine groups were calculated using WinNonlin®. Results showed that orally administered rutaecarpine at 100 mg/kg dose as early as 3 h before oral caffeine administration significantly decreased the oral systemic exposure and mean residence time of caffeine and its metabolites due to decreased caffeine bioavailability (by up to 75%) and increased clearance. The systemic exposure of caffeine and its metabolites were also decreased when caffeine was given intravenously, though this effect was less pronounced than when caffeine was given orally. Although plasma level of rutaecarpine was undetectable (less than 10 ng/mL), rutaecarpine still induced hepatic CYP1A2 activity. Results from 7-methoxyresorufin O-demethylation activity, which is specific to CYP1A2, showed that 3 h after one rutaecarpine oral dose, CYP1A2 activity in rat liver tissue was increased by 3- fold. This finding suggested that rutaecarpine effectively induced CYP1A2 activity in the liver.

Caffeine for the Pharmacological Treatment of Apnea of Prematurity in the NICU: Dose Selection Conundrum, Therapeutic Drug Monitoring and Genetic Factors

Caffeine citrate is the drug of choice for the pharmacological treatment of apnea of prematurity. Factors such as maturity and genetic variation contribute to the interindividual variability in the clinical response to caffeine therapy in preterm infants, making the optimal dose administered controversial. Moreover, the necessity for therapeutic drug monitoring (TDM) of caffeine is still worth discussing due to the need to achieve the desired target concentrations as well as concerns about the safety of higher doses. Therefore, we reviewed the pharmacokinetic profile of caffeine in preterm infants, evidence of the safety and efficacy of different doses of caffeine, therapeutic concentration ranges of caffeine and impact of genetic variability on caffeine therapy. Whereas the safety and efficacy of standard-dose caffeine have been demonstrated, evidence for the safety of higher administered doses is insufficient. Thus, preterm infants who lack clinical response to standard-dose caffeine therapy are of interest for TDM when dose optimization is performed. Polymorphisms in pharmacodynamics-related genes, but not in pharmacokinetics-related genes, have a significant impact on the interindividual variability in clinical response to caffeine therapy. For preterm infants lacking clinical response, how to develop individualized medication regimens for caffeine remains to be explored.

Caffeine and Its Neuroprotective Role in Ischemic Events: A Mechanism Dependent on Adenosine Receptors

Ischemia is characterized by a transient, insufficient, or permanent interruption of blood flow to a tissue, which leads to an inadequate glucose and oxygen supply. The nervous tissue is highly active, and it closely depends on glucose and oxygen to satisfy its metabolic demand. Therefore, ischemic conditions promote cell death and lead to a secondary wave of cell damage that progressively spreads to the neighborhood areas, called penumbra. Brain ischemia is one of the main causes of deaths and summed with retinal ischemia comprises one of the principal reasons of disability. Although several studies have been performed to investigate the mechanisms of damage to find protective/preventive interventions, an effective treatment does not exist yet. Adenosine is a well-described neuromodulator in the central nervous system (CNS), and acts through four subtypes of G-protein-coupled receptors. Adenosine receptors, especially A₁ and A_2A receptors, are the main targets of caffeine in daily consumption doses. Accordingly, caffeine has been greatly studied in the context of CNS pathologies. In fact, adenosine system, as well as caffeine, is involved in neuroprotection effects in different pathological situations. Therefore, the present review focuses on the role of adenosine/caffeine in CNS, brain and retina, ischemic events.

Caffeine Exacerbates Postictal Hypoxia

A stroke-like event follows seizures which may be responsible for the postictal state and a contributing factor to the development of seizure-induced brain abnormalities and behavioral dysfunction associated with epilepsy. Caffeine is the world's most popular drug with ∼85% of people in the USA consuming it daily. Thus, persons with epilepsy are likely to have caffeine in their body and brain during seizures. This preclinical study investigated the effects of acute caffeine on local hippocampal tissue oxygenation pre and post seizure. We continuously measured local oxygen levels in the CA1 region of the hippocampus and utilized the electrical kindling model in rats. Rats were acutely administered either caffeine, or one of its metabolites, or agonists and antagonists at adenosine sub-receptor types or ryanodine receptors prior to the elicitation of seizures. Acute caffeine administration caused a significant drop in pre-seizure hippocampal pO₂. Following a seizure, caffeine, as well as two of its metabolites paraxanthine, and theophylline, increased the time below the severe hypoxic threshold (10 mmHg). Likewise, the specific A_2A receptor antagonist, SCH-58261, mimicked caffeine by causing a significant drop in pre-seizure pO₂ and the area and time below the severe hypoxic threshold. Moreover, the A_2A receptor agonist, CGS-21680 was able to prevent the effect of both caffeine and SCH-58261 adding further evidence that caffeine is likely acting through the A_2A receptor. Clinical tracking and investigations are needed to determine the effect of caffeine on postictal symptomology and blood flow in persons with epilepsy.

Intravenous and oral caffeine self-administration in rats

Caffeine is widely consumed for its psychoactive effects worldwide. No pre-clinical study has established reliable caffeine self-administration, but we found that caffeine can enhance the reinforcing effects of non-drug rewards. The goal of the present studies was to determine if this effect of caffeine could result in reliable caffeine self-administration. In 2 experiments rats could make an operant response for caffeine delivered in conjunction with an oral 'vehicle' including saccharin (0.2% w/v) as a primary reinforcer. In Experiment 1, intravenous (IV) caffeine infusions were delivered in conjunction with oral saccharin for meeting the schedule of reinforcement. In control conditions, oral saccharin alone or presentations of IV caffeine alone served as the reinforcer. In Experiment 2, access to caffeine was provided in an oral vehicle containing water, decaffeinated instant coffee (0.5% w/v), or decaffeinated coffee and saccharin (0.2%). The concentration of oral caffeine was then manipulated across testing sessions. Oral and IV caffeine robustly increased responding for saccharin in a manner that was repeatable, reliable, and systematically related to unit IV dose. However, the relationship between oral caffeine dose and operant behavior was less systematic; the rats appeared to titrate their caffeine intake by reducing the consummatory response (drinking) rather than the appetitive response (lever pressing). These studies establish reliable volitional caffeine self-administration in rats. The reinforcement enhancing effects of caffeine may help to explain widespread caffeine use by humans, who ingest caffeine in complex vehicles with reinforcing properties.

Caffeine-stimulated muscle IL-6 mediates alleviation of non-alcoholic fatty liver disease

Caffeine intake is associated with a reduced risk developing non-alcoholic fatty liver disease (NAFLD), but the underlying molecular mechanisms remain to be fully elucidated. We report here that caffeine markedly improved high fat diet-induced NAFLD in mice resulting in a 10-fold increase in circulating IL-6 levels, leading to STAT3 activation in the liver. Interestingly, the expression of IL-6 mRNA was not increased in the liver, but increased substantially in the muscles of caffeine-treated mice. Caffeine was found to stimulate IL-6 production in cultured myotubes but not in hepatocytes, adipocytes, or macrophages. The inhibition of p38/MAPK abrogated caffeine-induced IL-6 production in muscle cells. Caffeine failed to improve NAFLD in IL-6 and hepatocyte-specific STAT3 knockout mice, indicating that the IL-6/STAT3 pathway is vital for the hepatoprotective effects of caffeine in NAFLD. The possibility that IL-6/STAT3-mediated hepatic autophagosome induction and hepatocytic oxygen consumption are involved in the anti-NAFLD effects of caffeine cannot be excluded, based on the findings presented here. Our results reveal that caffeine ameliorates NAFLD via crosstalk between muscle IL-6 production and liver STAT3 activation.

Physiology and effects of nucleosides in mice lacking all four adenosine receptors

Adenosine is a constituent of many molecules of life; increased free extracellular adenosine indicates cell damage or metabolic stress. The importance of adenosine signaling in basal physiology, as opposed to adaptive responses to danger/damage situations, is unclear. We generated mice lacking all four adenosine receptors (ARs), Adora1^−/−;Adora2a^−/−;Adora2b^−/−;Adora3^−/− (quad knockout [QKO]), to enable investigation of the AR dependence of physiologic processes, focusing on body temperature. The QKO mice demonstrate that ARs are not required for growth, metabolism, breeding, and body temperature regulation (diurnal variation, response to stress, and torpor). However, the mice showed decreased survival starting at about 15 weeks of age. While adenosine agonists cause profound hypothermia via each AR, adenosine did not cause hypothermia (or bradycardia or hypotension) in QKO mice, indicating that AR-independent signals do not contribute to adenosine-induced hypothermia. The hypothermia elicited by adenosine kinase inhibition (with A134974), inosine, or uridine also required ARs, as each was abolished in the QKO mice. The proposed mechanism for uridine-induced hypothermia is inhibition of adenosine transport by uridine, increasing local extracellular adenosine levels. In contrast, adenosine 5′-monophosphate (AMP)–induced hypothermia was attenuated in QKO mice, demonstrating roles for both AR-dependent and AR-independent mechanisms in this process. The physiology of the QKO mice appears to be the sum of the individual knockout mice, without clear evidence for synergy, indicating that the actions of the four ARs are generally complementary. The phenotype of the QKO mice suggests that, while extracellular adenosine is a signal of stress, damage, and/or danger, it is less important for baseline regulation of body temperature.

A study of mice lacking all four adenosine receptors shows that while they mediate effects of uridine, inosine and adenosine, these receptors are dispensable for growth, metabolism, breeding, and body temperature regulation. This suggests that extracellular adenosine is a damage or danger signal, rather than a major regulator of baseline physiology.

Elevated extracellular adenosine generally indicates metabolic stress or cell damage and regulates many aspects of physiology. We studied “QKO” mice lacking all four adenosine receptors. Young QKO mice do not appear obviously ill, but do show decreased survival later in life. QKO mice demonstrate that adenosine receptors are not required for growth, metabolism, breeding, and body temperature regulation. QKO mice are missing the pharmacologic effects of adenosine on body temperature, heart rate, and blood pressure. Therefore, all of these effects are mediated by the four adenosine receptors. We also determined that the hypothermic effects of a pharmacologic adenosine kinase inhibitor (A134974), uridine, or inosine each requires adenosine receptors. The uridine-induced hypothermia is likely due to its inhibition of adenosine uptake into cells. QKO mouse physiology appears to be the sum of the individual knockout mice, without evidence for synergy, indicating that the actions of the four adenosine receptors are generally complementary.

Interindividual Differences in Caffeine Metabolism and Factors Driving Caffeine Consumption

Most individuals adjust their caffeine intake according to the objective and subjective effects induced by the methylxanthine. However, to reach the desired effects, the quantity of caffeine consumed varies largely among individuals. It has been known for decades that the metabolism, clearance, and pharmacokinetics of caffeine is affected by many factors such as age, sex and hormones, liver disease, obesity, smoking, and diet. Caffeine also interacts with many medications. All these factors will be reviewed in the present document and discussed in light of the most recent data concerning the genetic variability affecting caffeine levels and effects at the pharmacokinetic and pharmacodynamic levels that both critically drive the level of caffeine consumption. The pharmacokinetics of caffeine are highly variable among individuals due to a polymorphism at the level of the CYP1A2 isoform of cytochrome P450, which metabolizes 95% of the caffeine ingested. Moreover there is a polymorphism at the level of another critical enzyme, N-acetyltransferase 2. At the pharmacodynamic level, there are several polymorphisms at the main brain target of caffeine, the adenosine A2A receptor or ADORA2. Genetic studies, including genome-wide association studies, identified several loci critically involved in caffeine consumption and its consequences on sleep, anxiety, and potentially in neurodegenerative and psychiatric diseases. We start reaching a better picture on how a multiplicity of biologic mechanisms seems to drive the levels of caffeine consumption, although much more knowledge is still required to understand caffeine consumption and effects on body functions.

Caffeine has no effect on eyeblink conditioning in mice

Caffeine is one of the most widely used drugs in the world. In the brain, caffeine acts as an antagonist for the adenosine A₁ and A_2B receptors. Since A₁ receptors are highly concentrated in the cortex of the cerebellum, we hypothesized that caffeine could potentially affect learning tasks that require the cerebellar cortex, such as eyeblink conditioning. To test this hypothesis, we examined the effect of low (5mg/kg) and high (50mg/kg) doses of caffeine, injected intraperitoneally before training, on eyeblink conditioning in mice. The results show that, at the dosages we used, caffeine affects neither the rate of acquisition, nor the timing of the onset or peak of the conditioned blink responses. Therefore, we conclude that caffeine neither improves nor worsens performance on eyeblink conditioning.

Physiologically-based modelling in mice suggests an aggravated loss of clearance capacity after toxic liver damage

Diseases and toxins may lead to death of active liver tissue, resulting in a loss of total clearance capacity at the whole-body level. However, it remains difficult to study, whether the loss of metabolizing tissue is sufficient to explain loss of metabolic capacity of the liver or whether the surviving tissue undergoes an adaptive response to compensate the loss. To understand the cellular impact of toxic liver damage in an in vivo situation, we here used physiologically-based pharmacokinetic modelling to investigate pharmacokinetics of a specifically designed drug cocktail at three different sampling sites of the body in healthy mice and mice treated with carbon tetrachloride (CCl4). Liver zonation was explicitly quantified in the models through immunostaining of cytochrome P450s enzymes. Comparative analyses between the simulated decrease in clearance capacity and the experimentally measured loss in tissue volume indicated that CCl4-induced impairment of metabolic functions goes beyond the mere loss of metabolically active tissue. The here established integrative modelling strategy hence provides mechanistic insights into functional consequences of toxic liver damage in an in vivo situation, which would not have been accessible by conventional methods.

Caffeine administration modulates TGF-β signaling but does not attenuate blunted alveolarization in a hyperoxia-based mouse model of bronchopulmonary dysplasia

BACKGROUND

Caffeine is widely used to manage apnea of prematurity, and reduces the incidence of bronchopulmonary dysplasia (BPD). Deregulated transforming growth factor (TGF)-β signaling underlies arrested postnatal lung maturation in BPD. It is unclear whether caffeine impacts TGF-β signaling or postnatal lung development in affected lungs.

METHODS

The impact of caffeine on TGF-β signaling in primary mouse lung fibroblasts and alveolar epithelial type II cells was assessed in vitro. The effects of caffeine administration (25 mg/kg/d for the first 14 d of postnatal life) on aberrant lung development and TGF-β signaling in vivo was assessed in a hyperoxia (85% O₂)-based model of BPD in C57BL/6 mice.

RESULTS

Caffeine downregulated expression of type I and type III TGF-β receptors, and Smad2; and potentiated TGF-β signaling in vitro. In vivo, caffeine administration normalized body mass under hyperoxic conditions, and normalized Smad2 phosphorylation detected in lung homogenates; however, caffeine administration neither improved nor worsened lung structure in hyperoxia-exposed mice, in which postnatal lung maturation was blunted.

CONCLUSION

Caffeine modulated TGF-β signaling in vitro and in vivo. Caffeine administration was well-tolerated by newborn mice, but did not influence the course of blunted postnatal lung maturation in a hyperoxia-based experimental mouse model of BPD.

Acute high-caffeine exposure increases autophagic flux and reduces protein synthesis in C2C12 skeletal myotubes

Caffeine is a highly catabolic dietary stimulant. High caffeine concentrations (1-10 mM) have previously been shown to inhibit protein synthesis and increase protein degradation in various mammalian cell lines. The purpose of this study was to examine the effect of short-term caffeine exposure on cell signaling pathways that regulate protein metabolism in mammalian skeletal muscle cells. Fully differentiated C2C12 skeletal myotubes either received vehicle (DMSO) or 5 mM caffeine for 6 h. Our analysis revealed that caffeine promoted a 40% increase in autolysosome formation and a 25% increase in autophagic flux. In contrast, caffeine treatment did not significantly increase the expression of the skeletal muscle specific ubiquitin ligases MAFbx and MuRF1 or 20S proteasome activity. Caffeine treatment significantly reduced mTORC1 signaling, total protein synthesis and myotube diameter in a CaMKKβ/AMPK-dependent manner. Further, caffeine promoted a CaMKII-dependent increase in myostatin mRNA expression that did not significantly contribute to the caffeine-dependent reduction in protein synthesis. Our results indicate that short-term caffeine exposure significantly reduced skeletal myotube diameter by increasing autophagic flux and promoting a CaMKKβ/AMPK-dependent reduction in protein synthesis.

Caffeine protects against experimental acute pancreatitis by inhibition of inositol 1,4,5-trisphosphate receptor-mediated Ca2+ release

OBJECTIVE

Caffeine reduces toxic Ca²⁺ signals in pancreatic acinar cells via inhibition of inositol 1,4,5-trisphosphate receptor (IP₃R)-mediated signalling, but effects of other xanthines have not been evaluated, nor effects of xanthines on experimental acute pancreatitis (AP). We have determined effects of caffeine and its xanthine metabolites on pancreatic acinar IP₃R-mediated Ca²⁺ signalling and experimental AP.

DESIGN

Isolated pancreatic acinar cells were exposed to secretagogues, uncaged IP₃ or toxins that induce AP and effects of xanthines, non-xanthine phosphodiesterase (PDE) inhibitors and cyclic adenosine monophosphate and cyclic guanosine monophosphate (cAMP/cGMP) determined. The intracellular cytosolic calcium concentration ([Ca²⁺]_C), mitochondrial depolarisation and necrosis were assessed by confocal microscopy. Effects of xanthines were evaluated in caerulein-induced AP (CER-AP), taurolithocholic acid 3-sulfate-induced AP (TLCS-AP) or palmitoleic acid plus ethanol-induced AP (fatty acid ethyl ester AP (FAEE-AP)). Serum xanthines were measured by liquid chromatography-mass spectrometry.

RESULTS

Caffeine, dimethylxanthines and non-xanthine PDE inhibitors blocked IP₃-mediated Ca²⁺ oscillations, while monomethylxanthines had little effect. Caffeine and dimethylxanthines inhibited uncaged IP₃-induced Ca²⁺ rises, toxin-induced Ca²⁺ release, mitochondrial depolarisation and necrotic cell death pathway activation; cAMP/cGMP did not inhibit toxin-induced Ca²⁺ rises. Caffeine significantly ameliorated CER-AP with most effect at 25 mg/kg (seven injections hourly); paraxanthine or theophylline did not. Caffeine at 25 mg/kg significantly ameliorated TLCS-AP and FAEE-AP. Mean total serum levels of dimethylxanthines and trimethylxanthines peaked at >2 mM with 25 mg/kg caffeine but at <100 µM with 25 mg/kg paraxanthine or theophylline.

CONCLUSIONS

Caffeine and its dimethylxanthine metabolites reduced pathological IP₃R-mediated pancreatic acinar Ca²⁺ signals but only caffeine ameliorated experimental AP. Caffeine is a suitable starting point for medicinal chemistry.

Online monitoring of hepatic rat metabolism by coupling a liver biochip and a mass spectrometer

A microfluidic liver biochip was coupled with a mass spectrometer to detect in real time the drug metabolism of hepatocytes.

Extended exposure to sugar and/or caffeine produces distinct behavioral and neurochemical profiles in the orbitofrontal cortex of rats: Implications for neural function

Caffeine is a psychostimulant commonly consumed with high levels of sugar. The increased availability of highly caffeinated, high sugar energy drinks could put some consumers at risk of being exposed to high doses of caffeine and sugar. Notably, research that has examined the consequences of this combination is limited. Here, we explored the effect of chronic exposure to caffeine and/or sugar on behavior and protein levels in the orbitofrontal cortex (OFC) of rats. The OFC brain region has been implicated in neuropsychiatric conditions, including obesity and addiction behaviors. Adult male Sprague-Dawley rats were treated for 26 days with control, caffeine (0.6 g/L), 10% sugar, or combination of both. Locomotor behavior was measured on the first and last day of treatment, then 1 week after treatment. Two hours following final behavioral testing, brains were rapidly removed and prepared for proteomic analysis of the OFC. Label-free quantitative shotgun analysis revealed that 21, 12, and 23% of proteins identified in the OFC were differentially expressed by sugar and/or caffeine. The results demonstrate that the intake of high levels of sugar and/or low to moderate levels of caffeine has different behavioral consequences. Moreover, each treatment results in a unique proteomic profile with different implications for neural health.

Adolescent intake of caffeinated energy drinks does not affect adult alcohol consumption in C57BL/6 and BALB/c mice

The rise in marketing and mass consumption of energy drink products by adolescents poses a largely unknown risk on adolescent development and drug reward. Yet, with increasing reports of acute health issues present in young adults who ingest large quantities of energy drinks alone or in combination with alcohol, the need to elucidate these potential risks is pressing. Energy drinks contain high levels of caffeine and sucrose; therefore, exposure to energy drinks may lead to changes in drug-related behaviors since caffeine and sucrose consumption activates similar brain pathways engaged by substances of abuse. With a recent study observing that adolescent caffeine consumption increased cocaine sensitivity, we sought to investigate how prolonged energy drink exposure in adolescence alters alcohol use and preference in adulthood. To do so, we utilized three different energy drink exposure paradigms and two strains of male mice (C57BL/6 and BALB/c) to monitor the effect of caffeine exposure via energy drinks in adolescence on adult alcohol intake. These paradigms included two models of volitional consumption of energy drinks or energy drink-like substances and one model of forced consumption of sucrose solutions with different caffeine concentrations. Following adolescent exposure to these solutions, alcohol intake was monitored in a limited-access, two-bottle choice between water and increasing concentrations of alcohol during adulthood. In none of the three models or two strains of mice did we observe that adolescent 'energy drink' consumption or exposure was correlated with changes in adult alcohol intake or preference. While our current preclinical results suggest that exposure to large amounts of caffeine does not alter future alcohol intake, differences in caffeine metabolism between mice and humans need to be considered before translating these results to humans.

Caffeine Prevents Hyperoxia-Induced Functional and Structural Lung Damage in Preterm Rabbits

BACKGROUND

Caffeine is a commonly used drug for apnea of prematurity. It may, however, also have a beneficial effect on bronchopulmonary dysplasia (BPD), which is the most common complication of extreme preterm birth.

OBJECTIVES

To study the inflammatory, structural and functional effects of caffeine in an animal model of BPD.

METHODS

Preterm New Zealand-Dendermonde rabbits (gestational day 28; term 31) were randomized to three groups: normoxia-placebo (N-P), hyperoxia-placebo (H-P) and hyperoxia-caffeine (H-C). Lung function was assessed on postnatal day 5, along with airway morphometry, vascular morphometry and a score observing airway inflammation.

RESULTS

Caffeine improved lung function by increasing lung volume [mean displaced volume N-P: 40.1 ± 6 ml/kg, H-P: 27.8 ± 8 ml/kg and H-C: 34.4 ± 7 ml/kg (p < 0.05); total lung capacity: N-P: 1.17 ± 0.1 ml, H-P: 0.67 ± 0.1 ml and H-C: 1.1 ± 0.1 ml (p < 0.05)], decreasing tissue damping [N-P: 2.7 ± 0.3 cm H2O/ml, H-P: 4.6 ± 0.6 cm H2O/ml and H-C: 3.2 ± 0.4 cm H2O/ml (p < 0.05)], elastance [N-P: 9.3 ± 2.4 cm H2O/ml, H-P: 19.2 ± 7.4 cm H2O/ml and H-C: 10.7 ± 2 cm H2O/ml (p < 0.05)] and compliance [N-P: 0.06 ± 0.01 cm H2O/ml, H-P: 0.054 ± 0.01 cm H2O/ml and H-C: 0.07 ± 0.013 cm H2O/ml (p < 0.05)]. Caffeine also improved histology by decreasing alveolar size [linear intercepts; N-P: 83.6 ± 1.7, H-P: 82.9 ± 1.6 and H-C: 67.3 ± 1.4 (p < 0.05)], increasing radial alveolar count (N-P: 6.6 ± 0.5, H-P: 5.7 ± 0.6 and H-C: 7.05 ± 0.5) and decreasing the acute inflammation score [N-P: 0.3 ± 0.1, H-P: 0.5 ± 0.1 and H-C: 0.4 ± 0.1 (p < 0.05)].

CONCLUSION

In preterm rabbits, caffeine reduces the functional, architectural and inflammatory pulmonary changes induced by hyperoxia in the lung.

Cytochrome P450-dependent metabolism of caffeine in Drosophila melanogaster

Caffeine (1, 3, 7-trimethylxanthine), an alkaloid produced by plants, has antioxidant and insecticide properties that can affect metabolism and cognition. In vertebrates, the metabolites derived from caffeine have been identified, and their functions have been characterized. However, the metabolites of caffeine in insects remain unknown. Thus, using radiolabelled caffeine, we have identified some of the primary caffeine metabolites produced in the body of Drosophila melanogaster males, including theobromine, paraxanthine and theophylline. In contrast to mammals, theobromine was the predominant metabolite (paraxanthine in humans; theophylline in monkeys; 1, 3, 7-trimethyluric acid in rodents). A transcriptomic screen of Drosophila flies exposed to caffeine revealed the coordinated variation of a large set of genes that encode xenobiotic-metabolizing proteins, including several cytochromes P450s (CYPs) that were highly overexpressed. Flies treated with metyrapone—an inhibitor of CYP enzymes—showed dramatically decreased caffeine metabolism, indicating that CYPs are involved in this process. Using interference RNA genetic silencing, we measured the metabolic and transcriptomic effect of three candidate CYPs. Silencing of CYP6d5 completely abolished theobromine synthesis, whereas CYP6a8 and CYP12d1 silencing induced different consequences on metabolism and gene expression. Therefore, we characterized several metabolic products and some enzymes potentially involved in the degradation of caffeine. In conclusion, this pioneer approach to caffeine metabolism in insects opens novel perspectives for the investigation of the physiological effects of caffeine metabolites. It also indicates that caffeine could be used as a biomarker to evaluate CYP phenotypes in Drosophila and other insects.

Effects of amphetamine, diazepam and caffeine on polysomnography (EEG, EMG, EOG)-derived variables measured using telemetry in Cynomolgus monkeys

INTRODUCTION

Medication-induced sleep disturbances are a major concern in drug development as a multitude of prescription drugs alter sleep patterns, often negatively. Polysomnography is used in clinical diagnostics but is also applicable to animal models. Rodent sleep architecture (nocturnal) differs from larger diurnal mammals, including humans, increasing the translational potential of non-rodent species to the clinic. This study aimed to characterize the response to pharmacological agents known to affect sleep structure and EEG activity in a non-human primate (Macaca fascicularis) using telemetry-based polysomnography.

METHODS

Animals were instrumented with telemetry transmitters for continuous electroencephalogram (EEG), electro-oculogram (EOG) and electromyogram (EMG) monitoring combined with video. EEG, EMG and EOG were monitored for 12 to 24h to establish baseline values, followed by administration of pharmacological agents (saline, d-amphetamine, diazepam or caffeine).

RESULTS

Amphetamine (0.3 and 1mg/kg, by oral administration (PO)) significantly reduced total sleep time, including the duration of both non-rapid eye movement [NREM] sleep and REM sleep. It also decreased EEG activity in low frequencies (i.e., 4-6Hz) during wakefulness. Diazepam (2mg/kg, PO) did not significantly alter sleep duration, but importantly reduced EEG activity in low frequencies (approximately 2-12Hz) during wakefulness, NREM and REM sleep. Finally, caffeine (10 and 30mg/kg, PO) decreased both NREM and REM sleep duration. In addition, spectral analysis revealed important decreases in low frequency activity (i.e., 1-8Hz) during wakefulness with a parallel increase in high frequency activity (i.e., 20-50Hz) during NREM sleep.

DISCUSSION

As these observations are similar to previously reported pharmacological effects in humans, results support that EEG, EOG and EMG monitoring by telemetry in Cynomolgus monkeys represents a useful non-clinical model to investigate and quantify drug-induced sleep disturbances.

Evaluation of a liver microfluidic biochip to predict in vivo clearances of seven drugs in rats

We investigated metabolic clearances of phenacetin, midazolam, propranolol, paracetamol, tolbutamide, caffeine, and dextromethorphan by primary rat hepatocytes cultivated in microfluidic biochips. The levels of mRNA of the HNF4α, PXR, AHR, CYP3A1, and CYP1A2 genes were enhanced in the biochip cultures when compared with postextraction levels. We measured a high and rapid adsorption on the biochip walls and inside the circuit for dextromethorphan and midazolam, a moderate adsorption for phenacetin and propranolol, and a low adsorption for caffeine, tolbutamide, and paracetamol. Drug biotransformations were demonstrated by the formations of specific metabolites such as paraxanthyne (caffeine), paracetamol (phenacetin), 1-OH midazolam (midazolam), paracetamol sulfate (paracetamol and phenacetin), and dextrorphan (dextromethorphan). We used a pharmacokinetic model to estimate the adsorption and in vitro intrinsic drug clearance values. We calculated in vitro intrinsic clearance values of 0.5, 3, 12.5, 83, 100, 160, and 900 μL/min per 10(6) cells for the tolbutamide, caffeine, paracetamol, dextromethorphan, phenacetin, midazolam, and propranolol, respectively. A second model describing the liver as a well-stirred compartment predicted in vivo hepatic clearances of 0.1, 13.8, 30, 44.1, 61, 72, 85, and 61 mL/min per kg of body mass for the tolbutamide, caffeine, paracetamol, midazolam, dextromethorphan, phenacetin, and propranolol, respectively. These values appeared consistent with previously reported data.

The buzz on caffeine in invertebrates: effects on behavior and molecular mechanisms

A number of recent studies from as diverse fields as plant-pollinator interactions, analyses of caffeine as an environmental pollutant, and the ability of caffeine to provide protection against neurodegenerative diseases have generated interest in understanding the actions of caffeine in invertebrates. This review summarizes what is currently known about the effects of caffeine on behavior and its molecular mechanisms in invertebrates. Caffeine appears to have similar effects on locomotion and sleep in both invertebrates and mammals. Furthermore, as in mammals, caffeine appears to have complex effects on learning and memory. However, the underlying mechanisms for these effects may differ between invertebrates and vertebrates. While caffeine's ability to cause release of intracellular calcium stores via ryanodine receptors and its actions as a phosphodiesterase inhibitor have been clearly established in invertebrates, its ability to interact with invertebrate adenosine receptors remains an important open question. Initial studies in insects and mollusks suggest an interaction between caffeine and the dopamine signaling pathway; more work needs to be done to understand the mechanisms by which caffeine influences signaling via biogenic amines. As of yet, little is known about whether other actions of caffeine in vertebrates, such as its effects on GABAA and glycine receptors, are conserved. Furthermore, the pharmacokinetics of caffeine remains to be elucidated. Overall behavioral responses to caffeine appear to be conserved amongst organisms; however, we are just beginning to understand the mechanisms underlying its effects across animal phyla.

The Janus face of caffeine

Caffeine is certainly the psychostimulant substance most consumed worldwide. Over the past years, chronic consumption of caffeine has been associated with prevention of cognitive decline associated to aging and mnemonic deficits of brain disorders. While its preventive effects have been reported extensively, the cognitive enhancer properties of caffeine are relatively under debate. Surprisingly, there are scarce detailed ontogenetic studies focusing on neurochemical parameters related to the effects of caffeine during prenatal and earlier postnatal periods. Furthermore, despite the large number of epidemiological studies, it remains unclear how safe is caffeine consumption during pregnancy and brain development. Thus, the purpose of this article is to review what is currently known about the actions of caffeine intake on neurobehavioral and adenosinergic system during brain development. We also reviewed other neurochemical systems affected by caffeine, but not only during brain development. Besides, some recent epidemiological studies were also outlined with the control of "pregnancy signal" as confounding variable. The idea is to tease out how studies on the impact of caffeine consumption during brain development deserve more attention and further investigation.

Utility of cryopreserved hepatocytes suspended in serum to predict hepatic clearance in dogs and monkeys

An in vitro-in vivo correlation analysis between observed and predicted metabolic clearance in multiple preclinical species including dogs and monkeys constitutes an integral part of prediction for the pharmacokinetics in humans by using liver-derived in vitro preparations. Empirical values of the scaling factor for the extrapolation of metabolic (intrinsic) clearance in the in vitro preparation to that for whole liver were calculated for each preparation of 8 and 5 cryopreserved dog and monkey hepatocytes, respectively, by optimizing the objective function of average fold error between predicted and observed metabolic (intrinsic) clearance for eight and 11 standard compounds for dogs and monkeys, respectively. Thus obtained values of the scaling factor ranged from 5.46 × 10(9) to 19.9 × 10(9) cells/kg body weight with an average of 10.3 × 10(9) cells/kg body weight in dogs, and the value ranged from 2.36 × 10(9) to 4.21 × 10(9) cells/kg body weight with an average of 3.17 × 10(9) cells/kg body weight in monkeys, which were both consistent with biologically calculated values in corresponding species. These results demonstrated the utility of commercially available cryopreserved preparations of dog and monkey hepatocytes for the in vitro-in vivo correlation analyses with the aid of empirically or biologically obtained scaling factors at the early development stage of new drug candidates.

Monkey liver cytochrome P450 2C9 is involved in caffeine 7-N-demethylation to form theophylline

Caffeine (1,3,7-trimethylxanthine) is a phenotyping substrate for human cytochrome P450 1A2. 3-N-Demethylation of caffeine is the main human metabolic pathway, whereas monkeys extensively mediate the 7-N-demethylation of caffeine to form pharmacological active theophylline. Roles of monkey P450 enzymes in theophylline formation from caffeine were investigated using individual monkey liver microsomes and 14 recombinantly expressed monkey P450 enzymes, and the results were compared with those for human P450 enzymes. Caffeine 7-N-demethylation activity in microsomes from 20 monkey livers was not strongly inhibited by α-naphthoflavone, quinidine or ketoconazole, and was roughly correlated with diclofenac 4'-hydroxylation activities. Monkey P450 2C9 had the highest activity for caffeine 7-N-demethylation. Kinetic analysis revealed that monkey P450 2C9 had a high Vmax/Km value for caffeine 7-N-demethylation, comparable to low Km value for monkey liver microsomes. Caffeine could dock favorably with monkey P450 2C9 modeled for 7-N-demethylation and with human P450 1A2 for 3-N-demethylation. The primary metabolite theophylline was oxidized to 8-hydroxytheophylline in similar ways by liver microsomes and by recombinant P450s in both humans and monkeys. These results collectively suggest a high activity for monkey liver P450 2C9 toward caffeine 7-N-demethylation, whereas, in humans, P450 1A2-mediated caffeine 3-N-demethylation is dominant.

The mastermind approach to CNS drug therapy: translational prediction of human brain distribution, target site kinetics, and therapeutic effects

Despite enormous advances in CNS research, CNS disorders remain the world's leading cause of disability. This accounts for more hospitalizations and prolonged care than almost all other diseases combined, and indicates a high unmet need for good CNS drugs and drug therapies.Following dosing, not only the chemical properties of the drug and blood-brain barrier (BBB) transport, but also many other processes will ultimately determine brain target site kinetics and consequently the CNS effects. The rate and extent of all these processes are regulated dynamically, and thus condition dependent. Therefore, heterogenious conditions such as species, gender, genetic background, tissue, age, diet, disease, drug treatment etc., result in considerable inter-individual and intra-individual variation, often encountered in CNS drug therapy.For effective therapy, drugs should access the CNS "at the right place, at the right time, and at the right concentration". To improve CNS therapies and drug development, details of inter-species and inter-condition variations are needed to enable target site pharmacokinetics and associated CNS effects to be translated between species and between disease states. Specifically, such studies need to include information about unbound drug concentrations which drive the effects. To date the only technique that can obtain unbound drug concentrations in brain is microdialysis. This (minimally) invasive technique cannot be readily applied to humans, and we need to rely on translational approaches to predict human brain distribution, target site kinetics, and therapeutic effects of CNS drugs.In this review the term "Mastermind approach" is introduced, for strategic and systematic CNS drug research using advanced preclinical experimental designs and mathematical modeling. In this way, knowledge can be obtained about the contributions and variability of individual processes on the causal path between drug dosing and CNS effect in animals that can be translated to the human situation. On the basis of a few advanced preclinical microdialysis based investigations it will be shown that the "Mastermind approach" has a high potential for the prediction of human CNS drug effects.

Dynamics of the General Factor of Personality in Response to a Single Dose of Caffeine

General Factor of Personality (GFP) research is an emergent field in personality research. This paper uses a theoretical mathematical model to predict the short-term effects of a dose of a stimulant drug on GFP and reports the results of an experiment showing how caffeine achieves this. This study considers the General Factor of Personality Questionnaire (GFPQ) a good psychometric approach to assess GFP. The GFP dynamic mechanism of change is based on the Unique Trait Personality Theory (UTPT). This theory proposes the existence of GFP which occupies the apex of the hierarchy of personality, and extends from an impulsiveness-and-aggressiveness pole (approach tendency) to an anxiety-andintroversion pole (avoidance tendency). An experiment with 25 volunteers was performed. All the participants completed the GFPQ and the Sensation-Seeking Scale list of adjectives from the trait version of MAACL-R (Multiple Affect Adjective Checklist Revised) on an empty stomach. The participants in the experimental group (20) received 330 mg of caffeine. All the participants filled in a state version form with the sensation-seeking adjectives every 4.5 minutes. This study considers that the Sensation-Seeking Scale list of adjectives from the MAACL-R, available in both trait and state versions, is a good psychometric approach to assess GFP. The results show that GFP is modified by a single dose of caffeine in the direction predicted by the UTPT.