Background and rationale: Parkinson’s disease (PD) is a progressive, degenerative disorder of the central nervous system and is characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta. The loss of functional dopamine in the striatum is thought to be responsible for the typical symptoms of PD. Cardinal features of PD include bradykinesia, muscular rigidity, resting tremor and impairment of postural balance. This study focuses on the inhibition of monoamine oxidase B (MAO-B) and antagonism of A2A receptors as therapeutic strategies for PD. Monoamine oxidase (MAO) is a flavin adenine dinucleotide (FAD)-containing mitochondrial bound isoenzyme which consists of two isoforms namely MAO-A and MAO-B. The primary function of MAO is to catalyze the oxidative deamination of dietary amines, monoamine neurotransmitters and hormones. MAO-A is responsible for the oxidative deamination of serotonin (5-HT) and norepinephrine (NE), while MAO-B is responsible for the oxidative deamination of dopamine (DA). The formation of DA takes place in the presynaptic neuron where it is stored in vesicles and released into the presynaptic cleft. The released DA then either binds to D1 and D2 receptors which results in an effector response. The excess DA in the presynaptic cleft is metabolized by MAO-B which may result in the formation of free radicals and a decrease in DA concentrations. Under normal physiological conditions free radicals are removed from the body via normal physiological processes, but in PD these normal physiological processes are thought to be unable to remove the radicals and this may lead to oxidative stress. Oxidative stress is believed to be one of the leading causes of neurodegeneration in PD. The rationale for the use of MAO-B inhibitors in PD would be to increase the natural DA levels in the brain and also diminish the likelihood of free radicals to be formed. Adenosine is an endogenous purine nucleoside and yields a variety of physiological effects. Four adenosine receptor subtypes have been characterized: A1, A2A, A2B and A3. They are all part of the G-protein-coupled receptor family and have seven transmembrane domains. The A2A receptor is highly concentrated in the striatum. There are two important pathways in the basal ganglia (BG) through which striatal information reaches the globus pallidus, namely the direct pathway containing A1 and D1 receptors and the indirect pathway containing A2A and D2 receptors. The direct pathway facilitates willed movement and the indirect pathway inhibits willed movement. A balance of the two pathways is necessary for normal movement. In PD, there is a decrease in DA in the striatum, thus leading to unopposed A2A receptor signaling and ultimately resulting in overactivity of the indirect pathway. Overactivity of the indirect pathway results in the locomotor symptoms associated with PD. Treatment with an A2A antagonist will block the A2A receptor, resulting in the restoration of balance between the indirect and direct pathways, thus leading to a decrease in locomotor symptoms. Aim: In this study, caffeine served as a lead compound for the design of dual-targeted drugs that are selective, reversible MAO-B inhibitors as well as A2A antagonists. Caffeine is a very weak MAO-B inhibitor and a moderately potent A2A antagonist. Substitution on the C8 position of caffeine yields compounds with good MAO-B inhibition activities and A2A receptor affinities. An example of this behaviour is found with (E)-8-(3-chlorostyryl)caffeine (CSC), which is not only a potent A2A antagonist but also a potent MAO-B inhibitor. The goal of this study was to identify and synthesize dual-targeted xanthine compounds. Recently Swanepoel and co-workers (2012) found that 8-phenoxymethyl substituted caffeines are potent reversible inhibitors of MAO-B. Therefore, this study focused on expanding the 8-(phenoxymethyl)caffeine series and evaluating the resulting compounds as both MAO-A and -B inhibitors as well as A2A antagonists. Synthesis: Two series were synthesized namely the 8-(phenoxymethyl)caffeines and 1,3-diethyl-7-methyl-8-(phenoxymethyl)xanthines. The analogues were synthesized according to the literature procedure. 1,3-Dimethyl-5,6-diaminouracil or 1,3-diethyl-5,6-diaminouracil were used as starting materials and were acylated with a suitable substituted phenoxyacetic acid in the presence of N-(3-dimethylaminopropyl)-N’-ethylcarbodiimide hydrochloride (EDAC) as an activating reagent. The intermediary amide was treated with sodium hydroxide, which resulted in ring closure to yield the corresponding 1,3-dimethyl-8-phenoxymethyl-7Hxanthinyl or 1,3-diethyl-8-phenoxymethyl-7H-xanthinyl analogues. These xanthines were 7-N-methylated in the presence of an excess of potassium carbonate and iodomethane to yield the target compounds. In vitro evaluation: A radioligand binding assay was performed to determine the affinities of the synthesized compounds for the A2A receptor. The MAO-B inhibition studies were carried out via a fluorometric assay where the MAO-catalyzed formation of H2O2 was measured. Results: Both series showed good to moderate MAO-B inhibition activities, while none of the compounds had activity towards MAO-A. Results were comparable to that of a known MAOB inhibitor lazabemide. For example, lazabemide (IC50 = 0.091 μM) was twice as potent as the most potent compound identified in this study, 8-(3-chlorophenoxymethyl)caffeine (compound 3; IC50 = 0.189 μM). Two additional compounds, 8-(4-iodophenoxymethyl)caffeine and 8-(3,4-dimethylphenoxymethyl) caffeine, also exhibited submicromolar IC50 values for the inhibition of MAO-B. The structure-activity relationships (SARs) indicated that 1,3-diethyl substitution resulted in decreased inhibition potency towards MAO-B and that 1,3-dimethyl substitution was a more suitable substitution pattern, leading to better inhibition potencies towards MAO-B. The compounds were also evaluated for A2A binding affinity, and relatively weak affinities were recorded with the most potent compound, 1,3-diethyl-7-methyl-8-[4-chlorophenoxymethyl]xanthine (compound 16), exhibiting a Ki value of 0.923 μM. Compared to KW-6002 (Ki = 7.94 nM), a potent reference A2A antagonist, compound 16 was 35-fold less potent. Comparing compound 16 to CSC [Ki(A2A) = 22.6 nM; IC50(MAO-B) = 0.146 nM], it was found that compound 16 is 31-fold less potent as an A2A antagonist and 21-fold less potent as a MAO-B inhibitor. Loss of MAO-B inhibition potency may be attributed to 1,3-diethyl substitution which correlates with similar conclusions reached in earlier studies. In addition, the replacement of the styryl functional group (as found with CSC and KW-6002) with the phenoxymethyl functional group (as found with the present series) may explain the general reduction in affinity for the A2A receptor. This suggests that the styryl side chain is more appropriate for A2A antagonism than the phenoxymethyl functional group. Conclusion: In this study two series of xanthine derivatives were successfully synthesized, namely the 8-(phenoxymethyl)caffeines and 1,3-diethyl-7-methyl-8-(phenoxymethyl)xanthines (11 compounds in total). Three of the newly synthesized compounds were found to act as potent inhibitors of MAO-B, with IC50 values in the submicromolar range. None of the compounds were however noteworthy MAO-A inhibitors. The most potent A2A antagonist among the examined compounds, compound 16, proved to be moderately potent compared to the reference antagonists, CSC and KW-6002. It may be concluded that the styryl functional group (as found with CSC and KW-6002) is more optimal than the phenoxymethyl functional group (as found with the present series) for A2A antagonism. 1,3-Diethyl substitution of the xanthine ring was found to be less optimal for MAO-B inhibition compared to 1,3-dimethyl substitution. These results together with known SARs provide valuable insight into the design of 8-(phenoxymethyl)caffeines as selective and potent MAO-B inhibitors. Such drugs may find application in the therapy of PD. / Thesis (MSc (Pharmaceutical Chemistry))--North-West University, Potchefstroom Campus, 2013.

Background and rationale: Parkinson’s disease (PD) is a progressive, degenerative disorder of the central nervous system and is characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta. The loss of functional dopamine in the striatum is thought to be responsible for the typical symptoms of PD. Cardinal features of PD include bradykinesia, muscular rigidity, resting tremor and impairment of postural balance. This study focuses on the inhibition of monoamine oxidase B (MAO-B) and antagonism of A2A receptors as therapeutic strategies for PD. Monoamine oxidase (MAO) is a flavin adenine dinucleotide (FAD)-containing mitochondrial bound isoenzyme which consists of two isoforms namely MAO-A and MAO-B. The primary function of MAO is to catalyze the oxidative deamination of dietary amines, monoamine neurotransmitters and hormones. MAO-A is responsible for the oxidative deamination of serotonin (5-HT) and norepinephrine (NE), while MAO-B is responsible for the oxidative deamination of dopamine (DA). The formation of DA takes place in the presynaptic neuron where it is stored in vesicles and released into the presynaptic cleft. The released DA then either binds to D1 and D2 receptors which results in an effector response. The excess DA in the presynaptic cleft is metabolized by MAO-B which may result in the formation of free radicals and a decrease in DA concentrations. Under normal physiological conditions free radicals are removed from the body via normal physiological processes, but in PD these normal physiological processes are thought to be unable to remove the radicals and this may lead to oxidative stress. Oxidative stress is believed to be one of the leading causes of neurodegeneration in PD. The rationale for the use of MAO-B inhibitors in PD would be to increase the natural DA levels in the brain and also diminish the likelihood of free radicals to be formed. Adenosine is an endogenous purine nucleoside and yields a variety of physiological effects. Four adenosine receptor subtypes have been characterized: A1, A2A, A2B and A3. They are all part of the G-protein-coupled receptor family and have seven transmembrane domains. The A2A receptor is highly concentrated in the striatum. There are two important pathways in the basal ganglia (BG) through which striatal information reaches the globus pallidus, namely the direct pathway containing A1 and D1 receptors and the indirect pathway containing A2A and D2 receptors. The direct pathway facilitates willed movement and the indirect pathway inhibits willed movement. A balance of the two pathways is necessary for normal movement. In PD, there is a decrease in DA in the striatum, thus leading to unopposed A2A receptor signaling and ultimately resulting in overactivity of the indirect pathway. Overactivity of the indirect pathway results in the locomotor symptoms associated with PD. Treatment with an A2A antagonist will block the A2A receptor, resulting in the restoration of balance between the indirect and direct pathways, thus leading to a decrease in locomotor symptoms. Aim: In this study, caffeine served as a lead compound for the design of dual-targeted drugs that are selective, reversible MAO-B inhibitors as well as A2A antagonists. Caffeine is a very weak MAO-B inhibitor and a moderately potent A2A antagonist. Substitution on the C8 position of caffeine yields compounds with good MAO-B inhibition activities and A2A receptor affinities. An example of this behaviour is found with (E)-8-(3-chlorostyryl)caffeine (CSC), which is not only a potent A2A antagonist but also a potent MAO-B inhibitor. The goal of this study was to identify and synthesize dual-targeted xanthine compounds. Recently Swanepoel and co-workers (2012) found that 8-phenoxymethyl substituted caffeines are potent reversible inhibitors of MAO-B. Therefore, this study focused on expanding the 8-(phenoxymethyl)caffeine series and evaluating the resulting compounds as both MAO-A and -B inhibitors as well as A2A antagonists. Synthesis: Two series were synthesized namely the 8-(phenoxymethyl)caffeines and 1,3-diethyl-7-methyl-8-(phenoxymethyl)xanthines. The analogues were synthesized according to the literature procedure. 1,3-Dimethyl-5,6-diaminouracil or 1,3-diethyl-5,6-diaminouracil were used as starting materials and were acylated with a suitable substituted phenoxyacetic acid in the presence of N-(3-dimethylaminopropyl)-N’-ethylcarbodiimide hydrochloride (EDAC) as an activating reagent. The intermediary amide was treated with sodium hydroxide, which resulted in ring closure to yield the corresponding 1,3-dimethyl-8-phenoxymethyl-7Hxanthinyl or 1,3-diethyl-8-phenoxymethyl-7H-xanthinyl analogues. These xanthines were 7-N-methylated in the presence of an excess of potassium carbonate and iodomethane to yield the target compounds. In vitro evaluation: A radioligand binding assay was performed to determine the affinities of the synthesized compounds for the A2A receptor. The MAO-B inhibition studies were carried out via a fluorometric assay where the MAO-catalyzed formation of H2O2 was measured. Results: Both series showed good to moderate MAO-B inhibition activities, while none of the compounds had activity towards MAO-A. Results were comparable to that of a known MAOB inhibitor lazabemide. For example, lazabemide (IC50 = 0.091 μM) was twice as potent as the most potent compound identified in this study, 8-(3-chlorophenoxymethyl)caffeine (compound 3; IC50 = 0.189 μM). Two additional compounds, 8-(4-iodophenoxymethyl)caffeine and 8-(3,4-dimethylphenoxymethyl) caffeine, also exhibited submicromolar IC50 values for the inhibition of MAO-B. The structure-activity relationships (SARs) indicated that 1,3-diethyl substitution resulted in decreased inhibition potency towards MAO-B and that 1,3-dimethyl substitution was a more suitable substitution pattern, leading to better inhibition potencies towards MAO-B. The compounds were also evaluated for A2A binding affinity, and relatively weak affinities were recorded with the most potent compound, 1,3-diethyl-7-methyl-8-[4-chlorophenoxymethyl]xanthine (compound 16), exhibiting a Ki value of 0.923 μM. Compared to KW-6002 (Ki = 7.94 nM), a potent reference A2A antagonist, compound 16 was 35-fold less potent. Comparing compound 16 to CSC [Ki(A2A) = 22.6 nM; IC50(MAO-B) = 0.146 nM], it was found that compound 16 is 31-fold less potent as an A2A antagonist and 21-fold less potent as a MAO-B inhibitor. Loss of MAO-B inhibition potency may be attributed to 1,3-diethyl substitution which correlates with similar conclusions reached in earlier studies. In addition, the replacement of the styryl functional group (as found with CSC and KW-6002) with the phenoxymethyl functional group (as found with the present series) may explain the general reduction in affinity for the A2A receptor. This suggests that the styryl side chain is more appropriate for A2A antagonism than the phenoxymethyl functional group. Conclusion: In this study two series of xanthine derivatives were successfully synthesized, namely the 8-(phenoxymethyl)caffeines and 1,3-diethyl-7-methyl-8-(phenoxymethyl)xanthines (11 compounds in total). Three of the newly synthesized compounds were found to act as potent inhibitors of MAO-B, with IC50 values in the submicromolar range. None of the compounds were however noteworthy MAO-A inhibitors. The most potent A2A antagonist among the examined compounds, compound 16, proved to be moderately potent compared to the reference antagonists, CSC and KW-6002. It may be concluded that the styryl functional group (as found with CSC and KW-6002) is more optimal than the phenoxymethyl functional group (as found with the present series) for A2A antagonism. 1,3-Diethyl substitution of the xanthine ring was found to be less optimal for MAO-B inhibition compared to 1,3-dimethyl substitution. These results together with known SARs provide valuable insight into the design of 8-(phenoxymethyl)caffeines as selective and potent MAO-B inhibitors. Such drugs may find application in the therapy of PD. / Thesis (MSc (Pharmaceutical Chemistry))--North-West University, Potchefstroom Campus, 2013.

Monoamine oxidase (MAO) is responsible for dopamine catabolism in the brain and therefore is especially important in the treatment of Parkinson's disease (PD). MAO–B inhibition provides symptomatic relief by indirectly elevating dopamine levels in the PD brain. PD is caused by the loss of dopaminergic neurons in the substantia nigra and the formation of proteinaceous structures in the brain. The cause of idiopathic PD is unknown, but one theory states that reactive oxygen species (ROS), partly derived from the catalytic cycle of MAO, may be to blame for damaging dopaminergic neurons. Since MAO inhibitors may reduce the MAO–catalyzed production of ROS, these compounds may protect dopaminergic neurons against degeneration in PD. It is commonly accepted that by the time PD symptoms manifest, about 80% of striatal dopamine has been lost. MAO is present as two subtypes in the human brain, namely MAO–A and MAO–B. MAOs are found mainly attached to the mitochondrial membrane and is responsible for the oxidative deamination of various monoamines, including dopamine. MAO is a dimeric enzyme which operates in conjunction with a co–factor, flavin adenine dinucleotide (FAD), to which it is covalently bound. The flavin is in a bent conformation, which assists the catalytic activity of MAO. As mentioned above, the catalytic action of MAO also produces harmful substances such as hydrogen peroxide, ammonia, aldehydes and may also increase the levels of hydroxyl radicals. In the healthy brain, these substances are metabolized rapidly, but the PD brain may exhibit reduced clearance of these species. Thus the inhibition of MAOs may be beneficial to the PD sufferer as it indirectly increases dopamine levels in the brain and may also slow the formation of harmful substances. MAO inhibitors, of the MAO–A type, were first used as anti–depressants. It was these drugs that first prompted researchers to explore MAO inhibitors as novel anti–parkinsonian drugs, as MAO–A inhibition slows the degradation of dopamine. Two types of inhibition modes exist, irreversible and reversible inhibition. Irreversible inhibitors do not allow for competition with the substrate and inactivate the enzyme permanently. Selegiline, a propargyl amine derivative, is an example of an irreversible MAO–B selective inhibitor. The major disadvantage of irreversible inhibitors is that after terminating treatment, recovery of the enzyme activity may require several weeks, since the turnover rate for the biosynthesis of MAO in the human brain may be as much as 40 days. Reversible inhibitors have better safety profiles since they allow for competition with the substrate. (E)–8–(3–Chlorostyryl)caffeine (CSC) is an example of a reversible inhibitor of MAO–B and is also an antagonist of the adenosine A2A receptor. Since antagonism of A2A receptors also produces an antiparkinsonian effect, dual acting compounds such as CSC, which block both the A2A receptors and MAO–B, may have an enhanced therapeutic potential in PD therapy. Current PD therapy available only treats the symptoms of PD and do not halt or slow the progression of the neurodegenerative processes. There therefore exists the need for the development of antiparkinsonian drugs with neuroprotective effects. Since both MAO–B inhibitors and A2A receptor antagonists are reported to possess protective effects in PD and PD animal models, dual acting drugs, that antagonize A2A receptors and inhibit MAO–B, may be candidates for neuroprotection. Using the structure of CSC as lead, we investigate in the current study, the possibility that aminocaffeines may also possess potent MAO–B inhibitory properties. The structures of the aminocaffeine derivatives that were investigated bear close structural resemblance to CSC as well as to a series of alkyloxycaffeine analogues that was recently found to be potent MAO inhibitors. This study therefore further explores the structural requirements of caffeine derivatives to act as MAO inhibitors by examining the possibility that aminocaffeine derivatives may be MAO inhibitors. Such compounds may act as lead compounds for the development of improved PD therapy. In this study, a series of 8–aminocaffeine derivatives were synthesized and evaluated as inhibitors of human MAO–A and B. For this purpose, 8–chlorocaffeine was reacted with the appropriate amine at high temperatures to produce the desired 8–aminocaffeine derivatives. The inhibitory activities of the compounds were determined towards recombinant human MAO–A and B and expressed as IC50 values. The results showed that human MAO–B was most potently inhibited by 8–[methyl(4–phenylbutyl)amino]caffeine with an IC50 value of 2.97 ?M. Human MAO–A was most potently inhibited by 8–[2–(3–chlorophenyl)–ethylamino]caffeine with an IC50 value of 5.78 ?M. It was found that methylation of the amine group at C8 of the caffeine ring increases inhibition but also selectivity towards MAO–B inhibition. For example, 8–[4–(phenylbutylamino)]caffeine inhibits MAO–B with an IC50 value of 7.56 ?M whereas 8–[methyl(4–phenylbutyl)amino]–caffeine has an increased inhibition potency of 2.97 ?M. The selectivity for MAO–B inhibition also increases over MAO–A when the C8 amine is methylated. It was found that the aminocaffeine derivatives bind reversibly to both enzyme isoforms and the mode of inhibition is competitive for MAO–B. From these results it can be concluded that although the 8–aminocaffeine derivatives are only moderately potent MAO–B inhibitors, they may act as lead compounds for the design of more potent reversible MAO inhibitors. Docking studies revealed that the 8–aminocaffeine and 8–[(methyl)amino]caffeine derivatives traverse both the entrance and substrate cavities of the MAO–B enzyme, with the caffeinyl moiety oriented towards the FAD co–factor while the amino–side chain protrudes into the entrance cavity. / Thesis (M.Sc. (Pharmaceutical Chemistry))--North-West University, Potchefstroom Campus, 2012.

Monoamine oxidase (MAO) is responsible for dopamine catabolism in the brain and therefore is especially important in the treatment of Parkinson's disease (PD). MAO–B inhibition provides symptomatic relief by indirectly elevating dopamine levels in the PD brain. PD is caused by the loss of dopaminergic neurons in the substantia nigra and the formation of proteinaceous structures in the brain. The cause of idiopathic PD is unknown, but one theory states that reactive oxygen species (ROS), partly derived from the catalytic cycle of MAO, may be to blame for damaging dopaminergic neurons. Since MAO inhibitors may reduce the MAO–catalyzed production of ROS, these compounds may protect dopaminergic neurons against degeneration in PD. It is commonly accepted that by the time PD symptoms manifest, about 80% of striatal dopamine has been lost. MAO is present as two subtypes in the human brain, namely MAO–A and MAO–B. MAOs are found mainly attached to the mitochondrial membrane and is responsible for the oxidative deamination of various monoamines, including dopamine. MAO is a dimeric enzyme which operates in conjunction with a co–factor, flavin adenine dinucleotide (FAD), to which it is covalently bound. The flavin is in a bent conformation, which assists the catalytic activity of MAO. As mentioned above, the catalytic action of MAO also produces harmful substances such as hydrogen peroxide, ammonia, aldehydes and may also increase the levels of hydroxyl radicals. In the healthy brain, these substances are metabolized rapidly, but the PD brain may exhibit reduced clearance of these species. Thus the inhibition of MAOs may be beneficial to the PD sufferer as it indirectly increases dopamine levels in the brain and may also slow the formation of harmful substances. MAO inhibitors, of the MAO–A type, were first used as anti–depressants. It was these drugs that first prompted researchers to explore MAO inhibitors as novel anti–parkinsonian drugs, as MAO–A inhibition slows the degradation of dopamine. Two types of inhibition modes exist, irreversible and reversible inhibition. Irreversible inhibitors do not allow for competition with the substrate and inactivate the enzyme permanently. Selegiline, a propargyl amine derivative, is an example of an irreversible MAO–B selective inhibitor. The major disadvantage of irreversible inhibitors is that after terminating treatment, recovery of the enzyme activity may require several weeks, since the turnover rate for the biosynthesis of MAO in the human brain may be as much as 40 days. Reversible inhibitors have better safety profiles since they allow for competition with the substrate. (E)–8–(3–Chlorostyryl)caffeine (CSC) is an example of a reversible inhibitor of MAO–B and is also an antagonist of the adenosine A2A receptor. Since antagonism of A2A receptors also produces an antiparkinsonian effect, dual acting compounds such as CSC, which block both the A2A receptors and MAO–B, may have an enhanced therapeutic potential in PD therapy. Current PD therapy available only treats the symptoms of PD and do not halt or slow the progression of the neurodegenerative processes. There therefore exists the need for the development of antiparkinsonian drugs with neuroprotective effects. Since both MAO–B inhibitors and A2A receptor antagonists are reported to possess protective effects in PD and PD animal models, dual acting drugs, that antagonize A2A receptors and inhibit MAO–B, may be candidates for neuroprotection. Using the structure of CSC as lead, we investigate in the current study, the possibility that aminocaffeines may also possess potent MAO–B inhibitory properties. The structures of the aminocaffeine derivatives that were investigated bear close structural resemblance to CSC as well as to a series of alkyloxycaffeine analogues that was recently found to be potent MAO inhibitors. This study therefore further explores the structural requirements of caffeine derivatives to act as MAO inhibitors by examining the possibility that aminocaffeine derivatives may be MAO inhibitors. Such compounds may act as lead compounds for the development of improved PD therapy. In this study, a series of 8–aminocaffeine derivatives were synthesized and evaluated as inhibitors of human MAO–A and B. For this purpose, 8–chlorocaffeine was reacted with the appropriate amine at high temperatures to produce the desired 8–aminocaffeine derivatives. The inhibitory activities of the compounds were determined towards recombinant human MAO–A and B and expressed as IC50 values. The results showed that human MAO–B was most potently inhibited by 8–[methyl(4–phenylbutyl)amino]caffeine with an IC50 value of 2.97 ?M. Human MAO–A was most potently inhibited by 8–[2–(3–chlorophenyl)–ethylamino]caffeine with an IC50 value of 5.78 ?M. It was found that methylation of the amine group at C8 of the caffeine ring increases inhibition but also selectivity towards MAO–B inhibition. For example, 8–[4–(phenylbutylamino)]caffeine inhibits MAO–B with an IC50 value of 7.56 ?M whereas 8–[methyl(4–phenylbutyl)amino]–caffeine has an increased inhibition potency of 2.97 ?M. The selectivity for MAO–B inhibition also increases over MAO–A when the C8 amine is methylated. It was found that the aminocaffeine derivatives bind reversibly to both enzyme isoforms and the mode of inhibition is competitive for MAO–B. From these results it can be concluded that although the 8–aminocaffeine derivatives are only moderately potent MAO–B inhibitors, they may act as lead compounds for the design of more potent reversible MAO inhibitors. Docking studies revealed that the 8–aminocaffeine and 8–[(methyl)amino]caffeine derivatives traverse both the entrance and substrate cavities of the MAO–B enzyme, with the caffeinyl moiety oriented towards the FAD co–factor while the amino–side chain protrudes into the entrance cavity. / Thesis (M.Sc. (Pharmaceutical Chemistry))--North-West University, Potchefstroom Campus, 2012.

Anecdotal evidence suggests that caffeine ingestion (mostly in the forms of coffee and tea consumption) is prevalent amongst firefighters and yet there is no data on whether this behaviour should be identified, measured, or monitored. PURPOSE: The purpose of this experiment was to determine the physiological and psychophysical effects of caffeine ingestion during repeated bouts of simulated firefighter work. In a randomized, double blind, crossover design, ten healthy males (age 36 ± 9.8 yr, body mass 88.3 ± 5.7 kg, height 182.78 ± 3.9 cm, approximate caffeine use 492.8 ± 318.2 mg/day) completed three 10 min work bouts (WB) at an intensity one work load below ventilatory threshold wearing full Firefighter personal protective equipment (PPE) and breathing through a self contained breathing apparatus (SCBA) on two different occasions. One hour before exercise each subject ingested either a 6 mg•kg-1 of caffeine (CAFF) or dextrose placebo (PLA), as well as, 500 ml of water. During the work trials, expired gases were sampled for oxygen consumption ( O2), carbon dioxide production ( CO2), respiratory exchange ratio (RER), minute ventilation ( E), respiratory rate (RR), tidal volume (Vt), and total air consumed (AcVE). Core temperature (Tc), heart rate (HR), oxyhemoglobin saturation (% O2 sat), capillarized blood lactate (BLa), rating of perceived exertion (RPE) (10pt Borg), perceived thermal distress (PTD), and sweat loss were also measured. Physiological strain index (PSI) was calculated from HR and Tc values. Tc was significantly higher in all CAFF WB compared to PLA (37.83 ± 0.08 oC vs. 37.61 ±0.12 oC) (p ≤ 0.05). E and Vt were also significantly increased in CAFF whereas, RPE was significantly decreased (p ≤ 0.05). The elevated Tc values caused an increase in calculated PSI in the CAFF condition during exercise (p ≤ 0.01). CAFF increases in E and Vt also increased AcVE. In conclusion, a caffeine induced elevation in Tc caused increased strain as indicated by calculated PSI during repeated work bouts during exercise below ventilatory threshold wearing full PPE and breathing through an SCBA. Elevated Tc in the CAFF condition likely caused increases in E, Vt and AcVE. Thus, caffeine ingestion may have to be monitored in firefighters during work days.

Coffee consumption has consistently been associated with a reduction in risk of type 2 diabetes mellitus (T2DM), although the mechanism for this association remains unknown. Sub-clinical inflammation, non-alcoholic fatty liver disease (NAFLD), and lipoprotein abnormalities characterize and predict T2DM. Limited evidence suggests that coffee may have a beneficial role in these disorders but further investigation is warranted. Our aim therefore was to investigate the associations of caffeinated and decaffeinated coffee with markers of inflammation, liver injury, and lipoproteins, in a non-diabetic cohort. No significant associations of caffeinated or decaffeinated coffee with inflammatory markers or lipoproteins were identified. Caffeinated coffee consumption however was inversely associated with alanine aminotransferase (β= -0.09, p= 0.0107) and aspartate aminotransferase (β= -0.05, p= 0.0161) in multivariate analysis. Decaffeinated coffee was not associated with liver enzymes. These analyses suggest that caffeinated coffee’s beneficial impact on NAFLD may be a potential mechanism for its inverse association with T2DM.

Coffee consumption has consistently been associated with a reduction in risk of type 2 diabetes mellitus (T2DM), although the mechanism for this association remains unknown. Sub-clinical inflammation, non-alcoholic fatty liver disease (NAFLD), and lipoprotein abnormalities characterize and predict T2DM. Limited evidence suggests that coffee may have a beneficial role in these disorders but further investigation is warranted. Our aim therefore was to investigate the associations of caffeinated and decaffeinated coffee with markers of inflammation, liver injury, and lipoproteins, in a non-diabetic cohort. No significant associations of caffeinated or decaffeinated coffee with inflammatory markers or lipoproteins were identified. Caffeinated coffee consumption however was inversely associated with alanine aminotransferase (β= -0.09, p= 0.0107) and aspartate aminotransferase (β= -0.05, p= 0.0161) in multivariate analysis. Decaffeinated coffee was not associated with liver enzymes. These analyses suggest that caffeinated coffee’s beneficial impact on NAFLD may be a potential mechanism for its inverse association with T2DM.

The effects of caffeine (250 mg) and placebo on healthy controls were studied in a double-blind, cross over study on 24 healthy subjects who performed a working memory n-back task. Reaction time and accuracy levels were tested using the n-back working memory measure in cognitive neuroscience. An experimental study tested on the 1, 2 and 3-back tasks under the placebo/coffee condition. Based on the empirical results obtained in this thesis it can be concluded that changes produced by caffeine ingestion support the hypothesis that caffeine acts as a stimulant. However, it cannot be proven that the stimulant translates into enhanced motor processes with an improvement in performance.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2006. / Härtill 4 uppsatser.

Anecdotal evidence suggests that caffeine ingestion (mostly in the forms of coffee and tea consumption) is prevalent amongst firefighters and yet there is no data on whether this behaviour should be identified, measured, or monitored. PURPOSE: The purpose of this experiment was to determine the physiological and psychophysical effects of caffeine ingestion during repeated bouts of simulated firefighter work. In a randomized, double blind, crossover design, ten healthy males (age 36 ± 9.8 yr, body mass 88.3 ± 5.7 kg, height 182.78 ± 3.9 cm, approximate caffeine use 492.8 ± 318.2 mg/day) completed three 10 min work bouts (WB) at an intensity one work load below ventilatory threshold wearing full Firefighter personal protective equipment (PPE) and breathing through a self contained breathing apparatus (SCBA) on two different occasions. One hour before exercise each subject ingested either a 6 mg•kg-1 of caffeine (CAFF) or dextrose placebo (PLA), as well as, 500 ml of water. During the work trials, expired gases were sampled for oxygen consumption ( O2), carbon dioxide production ( CO2), respiratory exchange ratio (RER), minute ventilation ( E), respiratory rate (RR), tidal volume (Vt), and total air consumed (AcVE). Core temperature (Tc), heart rate (HR), oxyhemoglobin saturation (% O2 sat), capillarized blood lactate (BLa), rating of perceived exertion (RPE) (10pt Borg), perceived thermal distress (PTD), and sweat loss were also measured. Physiological strain index (PSI) was calculated from HR and Tc values. Tc was significantly higher in all CAFF WB compared to PLA (37.83 ± 0.08 oC vs. 37.61 ±0.12 oC) (p ≤ 0.05). E and Vt were also significantly increased in CAFF whereas, RPE was significantly decreased (p ≤ 0.05). The elevated Tc values caused an increase in calculated PSI in the CAFF condition during exercise (p ≤ 0.01). CAFF increases in E and Vt also increased AcVE. In conclusion, a caffeine induced elevation in Tc caused increased strain as indicated by calculated PSI during repeated work bouts during exercise below ventilatory threshold wearing full PPE and breathing through an SCBA. Elevated Tc in the CAFF condition likely caused increases in E, Vt and AcVE. Thus, caffeine ingestion may have to be monitored in firefighters during work days.