The nucleotide derivatives inosine and inosinic acid inhibit intestinal absorption of mizoribine in rats

Exploration of the link between gut microbiota and purinergic signalling

Growing evidence reveals that microorganisms in the gut are linked to metabolic health and disease risk in human beings to a considerable extent. The focus of research at this stage must tend to focus on cause-and-effect studies. In addition to being a component of DNA and RNA, purine metabolites can be involved in purine signalling in the body as chemical messengers. Abnormalities in purinergic signalling may lead to neuropathy, rheumatic immune diseases, inflammation, tumors, and a wide range of other diseases. It has proved that gut microbes are involved in purinergic signalling. The relationship between these gut-derived purinergic signalling molecules and host metabolism may be one of the important clues to our understanding of the mechanisms by which the microbiota affects host metabolism.

Resetting microbiota by Lactobacillus reuteri inhibits T reg deficiency-induced autoimmunity via adenosine A2A receptors

He et al. show that T reg deficiency markedly induces autoimmunity and shifts gut microbiota. Remodeling microbiota by Lactobacillus reuteri was found to inhibit autoimmunity via the metabolite inosine, which interacts with the adenosine A_2A receptor. This finding establishes a link between the gut microbiota, A_2A receptors, and autoimmunity induced by T reg cell deficiency.

Regulatory T (T reg) cell deficiency causes lethal, CD4⁺ T cell–driven autoimmune diseases. Stem cell transplantation is used to treat these diseases, but this procedure is limited by the availability of a suitable donor. The intestinal microbiota drives host immune homeostasis by regulating the differentiation and expansion of T reg, Th1, and Th2 cells. It is currently unclear if T reg cell deficiency–mediated autoimmune disorders can be treated by targeting the enteric microbiota. Here, we demonstrate that Foxp3⁺ T reg cell deficiency results in gut microbial dysbiosis and autoimmunity over the lifespan of scurfy (SF) mouse. Remodeling microbiota with Lactobacillus reuteri prolonged survival and reduced multiorgan inflammation in SF mice. L. reuteri changed the metabolomic profile disrupted by T reg cell deficiency, and a major effect was to restore levels of the purine metabolite inosine. Feeding inosine itself prolonged life and inhibited multiorgan inflammation by reducing Th1/Th2 cells and their associated cytokines. Mechanistically, the inhibition of inosine on the differentiation of Th1 and Th2 cells in vitro depended on adenosine A_2A receptors, which were also required for the efficacy of inosine and of L. reuteri in vivo. These results reveal that the microbiota–inosine–A_2A receptor axis might represent a potential avenue for combatting autoimmune diseases mediated by T reg cell dysfunction.

Population pharmacokinetics of mizoribine in pediatric patients with kidney disease

BACKGROUND

The present study aimed to obtain information enabling optimisation of the clinical effect of mizoribine (MZR) in pediatric patients with kidney disease.

METHODS

A total of 105 pediatric patients with kidney disease treated at our institutions were enrolled. Kidney transplant patients were excluded. Population pharmacokinetic analysis of MZR was performed based on serum concentration data. Area under the curve from time zero to infinity (AUC_∞) and maximal concentration (C _max) were calculated by Bayesian analysis.

RESULTS

In children, the appearance of MZR in the blood tended to be slower and the subsequent rise in blood concentration tended to be more sluggish, compared to healthy adults. Apparent volume of distribution and oral clearance were also higher in children compared to adults. A significant positive correlation was observed between patient age and AUC_∞. There were significant differences of AUC_∞ and C _max by age group. No relationship was observed between the administration method of MZR and serum concentration.

CONCLUSION

The pharmacokinetics of MZR was different in children compared to adults. To obtain the expected clinical efficacy, the regular MZR dosage schedule (2-3 mg/kg/day) might be insufficient for pediatric patients. In particular, younger patients might require a higher dosage of MZR per unit body weight.

Involvement of Multiple Transporters-mediated Transports in Mizoribine and Methotrexate Pharmacokinetics

Mizoribine is administered orally and excreted into urine without being metabolized. Many research groups have reported a linear relationship between the dose and peak serum concentration, between the dose and AUC, and between AUC and cumulative urinary excretion of mizoribine. In contrast, a significant interindividual variability, with a small intraindividual variability, in oral bioavailability of mizoribine is also reported. The interindividual variability is mostly considered to be due to the polymophisms of transporter genes. Methotrexate (MTX) is administered orally and/or by parenteral routes, depending on the dose. Metabolic enzymes and multiple transporters are involved in the pharmacokinetics of MTX. The oral bioavailability of MTX exhibits a marked interindividual variability and saturation with increase in the dose of MTX, with a small intraindividual variability, where the contribution of gene polymophisms of transporters and enzymes is suggested. Therapeutic drug monitoring of both mizoribine and MTX is expected to improve their clinical efficacy in the treatment of rheumatoid arthritis.

Membrane transport mechanisms of mizoribine in the rat intestine and human epithelial LS180 cells

The aim of the present study was to characterize membrane transport mechanisms of mizoribine in the intestinal epithelial cells. We evaluated the contribution of Na(+)-dependent and -independent membrane transporters to mizoribine absorption in the rat intestine using an in situ closed loop method. In addition, we evaluated the effects of structurally related compounds, extracellular Na(+) concentrations, and an inhibitor of Na(+)-independent equilibrative nucleoside transporter, nitrobenzylmercaptopurine ribonucleoside (NBMPR), on the uptake of mizoribine in human intestinal epithelial LS180 cells. In the presence and also absence of Na(+) in rat intestinal loops, more than 60% of the administered dose (50 microg at the concentration of 100 microg/ml=386 microM) of mizoribine was absorbed in 40 min. In the LS180 cells, ribavirin and inosine reduced the uptake of 400 microM mizoribine with the increasing concentrations (from 5 to 50 mM) of the inhibitors. The cellular uptake of mizoribine in the absence of extracellular Na(+) decreased to 72.7% of the uptake in the presence of extracellular Na(+), whereas 100 microM NBMPR decreased the uptake of mizoribine markedly to 34.7% of that without NBMPR. These findings suggest that Na(+)-independent nucleoside transporters are largely responsible for absorption of mizoribine in the intestine.

Population pharmacokinetics of higher-dose mizoribine in healthy male volunteers

The population pharmacokinetic parameters of mizoribine in healthy subjects were estimated using a nonlinear mixed effects model (NONMEM) program. Pharmacokinetic data for population analysis were obtained in the previous study, in which 24 healthy Caucasian male subjects participated in a single-dose (3, 6, 9, 12 mg/kg) study, and 12 subjects participated in a multiple-dose (6, 12 mg/kg/d) study. The mean value of the absorption lag time, absorption rate constant (KA), and apparent distribution volume (V/F) was estimated to be 0.349 h, 0.869 h-1, and 0.834 l/kg, respectively. Oral clearance (CL/F) was modeled with creatinine clearance (CLcr), and the mean value was estimated to be 1.93.CLcr l/h. In addition, pharmacokinetic parameters in individual 36 subjects were obtained from population estimates according to Bayes' theorem. Pharmacokinetic parameters (KA, V/F, and CL/F) in the single-dose study were almost constant at a dose range of 3-12 mg/kg, and were similar to those in the multiple-dose study. These findings indicated that the pharmacokinetics of mizoribine is well described by a simple one-compartment model with first-order absorption.