Temporal variations of adenosine metabolism in human blood

Pharmacomicrobiology of Methotrexate in Rheumatoid Arthritis: Gut Microbiome as Predictor of Therapeutic Response

Rheumatoid arthritis (RA) is a disabling autoimmune disease with invasive arthritis as the main manifestation and synovitis as the basic pathological change, which can cause progressive destruction of articular cartilage and bone, ultimately leading to joint deformity and loss of function. Since its introduction in the 1980s and its widespread use in the treatment of RA, low-dose methotrexate (MTX) therapy has dramatically changed the course and outcome of RA treatment. The clinical use of this drug will be more rational with a better understanding of the pharmacology, anti-inflammatory mechanisms of action and adverse reaction about it. At present, the current clinical status of newly diagnosed RA is that MTX is initiated first regardless of the patients’ suitability. But up to 50% of patients could not reach adequate clinical efficacy or have severe adverse events. Prior to drug initiation, a prognostic tool for treatment response is lacking, which is thought to be the most important cause of the situation. A growing body of studies have shown that differences in microbial metagenomes (including bacterial strains, genes, enzymes, proteins and/or metabolites) in the gastrointestinal tract of RA patients may at least partially determine their bioavailability and/or subsequent response to MTX. Based on this, some researchers established a random forest model to predict whether different RA patients (with different gut microbiome) would respond to MTX. Of course, MTX, in turn, alters the gut microbiome in a dose-dependent manner. The interaction between drugs and microorganisms is called pharmacomicrobiology. Then, the concept of precision medicine has been raised. In this view, we summarize the characteristics and anti-inflammatory mechanisms of MTX and highlight the interaction between gut microbiome and MTX aiming to find the optimal treatment for patients according to individual differences and discuss the application and prospect of precision medicine.

Methotrexate and its mechanisms of action in inflammatory arthritis

Despite the introduction of numerous biologic agents for the treatment of rheumatoid arthritis (RA) and other forms of inflammatory arthritis, low-dose methotrexate therapy remains the gold standard in RA therapy. Methotrexate is generally the first-line drug for the treatment of RA, psoriatic arthritis and other forms of inflammatory arthritis, and it enhances the effect of most biologic agents in RA. Understanding the mechanism of action of methotrexate could be instructive in the appropriate use of the drug and in the design of new regimens for the treatment of RA. Although methotrexate is one of the first examples of intelligent drug design, multiple mechanisms potentially contribute to the anti-inflammatory actions of methotrexate, including the inhibition of purine and pyrimidine synthesis, transmethylation reactions, translocation of nuclear factor-κB (NF-κB) to the nucleus, signalling via the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway and nitric oxide production, as well as the promotion of adenosine release and expression of certain long non-coding RNAs.

Sleep in elite athletes and nutritional interventions to enhance sleep

Sleep has numerous important physiological and cognitive functions that may be particularly important to elite athletes. Recent evidence, as well as anecdotal information, suggests that athletes may experience a reduced quality and/or quantity of sleep. Sleep deprivation can have significant effects on athletic performance, especially submaximal, prolonged exercise. Compromised sleep may also influence learning, memory, cognition, pain perception, immunity and inflammation. Furthermore, changes in glucose metabolism and neuroendocrine function as a result of chronic, partial sleep deprivation may result in alterations in carbohydrate metabolism, appetite, food intake and protein synthesis. These factors can ultimately have a negative influence on an athlete’s nutritional, metabolic and endocrine status and hence potentially reduce athletic performance. Research has identified a number of neurotransmitters associated with the sleep–wake cycle. These include serotonin, gamma-aminobutyric acid, orexin, melanin-concentrating hormone, cholinergic, galanin, noradrenaline, and histamine. Therefore, nutritional interventions that may act on these neurotransmitters in the brain may also influence sleep. Carbohydrate, tryptophan, valerian, melatonin and other nutritional interventions have been investigated as possible sleep inducers and represent promising potential interventions. In this review, the factors influencing sleep quality and quantity in athletic populations are examined and the potential impact of nutritional interventions is considered. While there is some research investigating the effects of nutritional interventions on sleep, future research may highlight the importance of nutritional and dietary interventions to enhance sleep.

Serum urate in chronic gout--will it be the first validated soluble biomarker in rheumatology?

OBJECTIVE

To summarize evidence for and endorsement of serum urate (SU) as having fulfilled the OMERACT filter as a soluble biomarker in chronic gout at the 2010 Outcome Measures in Rheumatology Meeting (OMERACT 10).

METHODS

Data were presented to support the use of SU as a soluble biomarker in chronic gout and specifically the ability to utilize it to predict future patient-reported outcomes.

RESULTS

SU was accepted as having fulfilled the OMERACT filter by 78% of voters. However, consensus was not obtained regarding its use as a soluble biomarker in chronic gout. Although the majority of the criteria for a soluble biomarker were fulfilled, the key criterion of association of the biomarker with outcomes was not agreed upon. It was agreed that the appropriate choice of endpoint must be linked to its clinical importance to the individual with the disorder and its temporal relationship to the intervention. Appropriate outcomes in chronic gout may therefore include gout flares, reduction in tophi, and patient-reported outcomes.

CONCLUSION

SU is a critical outcome measure. It has the potential to fulfil criteria for a soluble biomarker. Further analyses of existing data from randomized controlled trials will be required to determine whether SU can predict future important outcomes, in particular disability.

24-hour temporal pattern of NTPDase and 5'-nucleotidase enzymes in rat blood serum

Circadian rhythms represent an important mechanism to prepare the organism for environmental variations. ATP, ADP, AMP, and adenosine can act as extracellular messengers in a range of biological processes and are metabolized by a number of enzymes, including NTPDases and 5'-nucleotidase. In the present study the authors report that ATPase and ADPase activities present 24-h temporal variations that peak during dark (activity) span. These findings suggest that this enzymatic temporal pattern in blood serum might be important for the normal physiology and function of the organism through the maintenance of extracellular nucleotides at physiological levels.

The possible role of human milk nucleotides as sleep inducers

Breast-milk contains a potent mixture of diverse components, such as the non-protein nitrogen fraction which includes nucleotides, whose variation in levels is evident throughout lactation. In addition, these substances play an important role in sleep homeostasis. In the present study, human milk samples were analyzed using a capillary electrophoresis system. The rhythmicity of each nucleotide was studied by cosinor analysis. It was found that the nucleotides 5'AMP, 5'GMP, 5'CMP, and 5'IMP have significant (P < 0.05) circadian rhythms, the acrophases of the first two being during the night, and of the latter two during the day. While 5'UMP did not show a clear circadian rhythm, there was an increase in its levels at night. In conclusion, the rise in nocturnal levels of 5'AMP, 5'GMP, and 5'UMP could be involved in inducing the 'hypnotic' action of breast-milk at night in the infant.

13C enrichment of carbons 2 and 8 of purine by folate-dependent reactions after [13C]formate and [2-13C]glycine dosing in adult humans

The 10-formyl moiety of 10-formyltetrahydrofolate is the source of carbons at the positions 8 (C(8)) and 2 (C(2)) of the purine ring, originating from formate and a few amino acids. Uric acid is the final catabolic product of purines. In adult humans, we independently measured the (13)C enrichment of the C(2) and C(8) positions of urinary uric acid after an oral dose of [(13)C]sodium formate and that of the C(2) and C(8) plus C(5) positions after [2-(13)C]glycine. A liquid chromatography-mass spectrometric method was used to measure the (13)C enrichment of uric acid in urine, which was collected for 3 to 4 days. Purine catabolism to uric acid does not alter the positions of carbons in the ring. After the formate dose, the (13)C enrichment at C(2) was greater than at C(8), and a circadian rhythm was observed in the enrichment at C(2). After the glycine dose, the C(8) plus C(5) positions were enriched, whereas no significant enrichment at C(2) was found. These (13)C enrichment patterns are not consistent with previous accepted metabolism. To our knowledge, this is the first study to investigate (13)C enrichment from formate and glycine independently into the C(2) and C(8) positions of purine in the same subjects. Possible mechanisms explaining our findings are discussed. Oral [(13)C]formate or [2-(13)C]glycine dosing and urine collection can be used to study purine biosynthesis in humans.

Purinergic signaling in the rabbit ciliary body epithelium

In the past forty years, a wealth of information has accumulated that points to the presence of adenosine and adenine nucleotides in the anterior segment of the eye and a number of hypotheses have been introduced to describe the possible role of these agents in the regulation of aqueous humor flow. However, in the absence of a generally accepted model for the cellular and molecular mechanisms of aqueous humor formation by the ciliary body epithelium, efforts to identify the signal transduction pathway(s) responsible for regulation of the ion and water transport have not been successful. This article briefly reviews the evidence for (i). the presence in aqueous humor of adenine nucleotides, cyclic adenosine monophosphate and adenosine, their metabolic product, (ii). the possible role of these agents in the regulation of aqueous humor dynamics, and (iii). the expression of ecto-nucleotidases, receptors, and second messengers that may mediate such regulation. Finally, a model for the regulation of aqueous humor formation by adenosine and ATP is proposed.

Energy demands during a judo match and recovery

OBJECTIVE

To assess energy demand during a judo match and the kinetics of recovery by measuring the metabolites of the oxypurine cascade, lipolytic activity, and glycolytic pathway.

METHODS

Venous blood samples were taken from 16 national judoists (mean (SEM) age 18.4 (1.6) years), before (T(1)) and three minutes (T(2)), one hour (T(3)), and 24 hours (T(4)) after a match. A seven day diet record was used to evaluate nutrient intake.

RESULTS

Nutrient analysis indicated that these athletes followed a low carbohydrate diet. Plasma lactate concentration had increased to 12.3 (1.8) mmol/l at the end of the match. An increase in the levels of extracellular markers of muscle adenine nucleotide catabolism, urea, and creatinine was observed at T(2), while uric acid levels remained unchanged. High concentrations of urea persisted for 24 hours during the recovery period. Ammonia, hypoxanthine, xanthine, and creatinine returned to control levels within the 24 hour recovery period. Uric acid concentrations rose from T(3) and had not returned to baseline 24 hours after the match. The levels of triglycerides, glycerol, and free fatty acids had increased significantly (p<0.05) after the match (T(2)) but returned to baseline values within 24 hours. Concentrations of high density lipoprotein cholesterol and total cholesterol were significantly increased after the match.

CONCLUSIONS

These results show that a judo match induces both protein and lipid metabolism. Carbohydrate availability, training adaptation, and metabolic stress may explain the requirement for these types of metabolism.

The potential role of adenosine in the pathophysiology of the insulin resistance syndrome

An increased intracellular availability of the co-enzyme A esters of long-chain fatty acids is thought to underlie many aspects of the insulin resistance syndrome. However, the cause of clustering of a hyperdynamic circulation, sympathetic activation, hypertension, hyperuricaemia, and a raised haematocrit in the insulin resistance syndrome remains to be elucidated. We propose a mechanism that expands the etiological role of long-chain fatty acids. By inhibiting adenine nucleotide translocators, elevated intracellular concentrations of the co-enzyme A esters of long-chain fatty acids impair mitochondrial oxidative phosphorylation. This is expected to result in a chronic systemic increase in extracellular adenosine concentrations. As adenosine stimulates the sympathetic nervous system, induces systemic vasodilatation, stimulates erythropoiesis, and induces renal vasoconstriction with renal sodium retention, increased extracellular ADO concentrations may be the common denominator explaining the above-mentioned and still unexplained phenomena associated with the insulin resistance syndrome. Along the same lines, hyperuricaemia can be explained by the fact that adenosine is broken down to urate and because of increased renal urate retention.