Analysis of N1‐acetyl‐N2‐formyl‐5‐methoxykynuramine/N1‐acetyl‐5‐methoxy‐kynuramine formation from melatonin in mice

Abstract: The interactions of melatonin, a potent endogenous antioxidant, with reactive oxygen species generate several products that include N¹‐acetyl‐N²‐formyl‐5‐methoxykynuramine (AFMK) and N¹‐acetyl‐5‐methoxy‐kynuramine (AMK). The physiological or pathological significance of AFMK/AMK formation during the process of melatonin metabolism in mammals has not been clarified. Using a metabolomic approach in the current study, the AFMK/AMK pathway was thoroughly investigated both in mice and humans. Unexpectedly, AFMK and AMK were not identified in the urine of humans nor in the urine, feces or tissues (including liver, brain, and eyes) in mice under the current experimental conditions. Metabolomic analysis did identify novel metabolites of AMK, i.e. hydroxy‐AMK and glucuronide‐conjugated hydroxy‐AMK. These two newly identified metabolites were, however, not found in the urine of humans. In addition, oxidative stress induced by acetaminophen in the mouse model did not boost AFMK/AMK formation. These data suggest that AFMK/AMK formation is not a significant pathway of melatonin disposition in mice, even under conditions of oxidative stress.     

Pre‐transplant comorbidity burden and post‐transplant chronic graft‐versus‐host disease

The Haematopoietic Cell Transplantation‐Comorbidity Index (HCT‐CI) was designed as a predictor of non‐relapse mortality after HCT. Chronic graft‐versus‐host disease (GVHD) contributes to mortality after HCT. Here, we investigated whether the HCT‐CI could predict development of chronic GVHD or post‐chronic GVHD mortality. We retrospectively analysed data from 2909 patients treated with allogeneic HCT for malignant and non‐malignant haematological conditions at four institutions. In Cox regression models adjusted for potential confounders, increasing HCT‐CI was not statistically significantly associated with the development of chronic GVHD [hazard ratio (HR) = 1·02, P = 0·34]. Yet, the index was associated with an increased risk of non‐relapse mortality (HR = 1·29, P < 0·0001) as well as overall mortality (HR = 1·25, P < 0·001) following the development of chronic GVHD. The association between HCT‐CI and post‐chronic GVHD mortality was similar regardless of donor type or stem cell source. HCT‐CI scores could be incorporated in the design of clinical trials for treatment of chronic GVHD.     

Melatonin enhances L‐DOPA therapeutic effects,helps to reduce its dose,and protects dopaminergic neurons in 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine‐induced parkinsonism in mice

L‐3,4‐dihydroxyphenylalanine (L‐DOPA) reduces symptoms of Parkinson's disease (PD), but suffers from serious side effects on long‐term use. Melatonin (10–30 mg/kg, 6 doses at 10 hr intervals) was investigated to potentiate L‐DOPA therapeutic effects in 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP)‐induced parkinsonism in mice. Striatal tyrosine hydroxylase (TH) immunoreactivity, TH, and phosphorylated ser 40 TH (p‐TH) protein levels were assayed on 7th day. Nigral TH‐positive neurons stereology was conducted on serial sections 2.8 mm from bregma rostrally to 3.74 mm caudally. MPTP caused 39% and 58% decrease, respectively, in striatal fibers and TH protein levels, but 2.5‐fold increase in p‐TH levels. About 35% TH neurons were lost between 360 and 600 μm from 940 μm of the entire nigra analyzed, but no neurons were lost between 250 μm rostrally and 220 μm caudally. When L‐DOPA in small doses (5–8 mg/kg) failed to affect MPTP‐induced akinesia or catalepsy, co‐administration of melatonin with L‐DOPA attenuated these behaviors. Melatonin administration significantly attenuated MPTP‐induced loss in striatal TH fibers (82%), TH (62%) and p‐TH protein (100%) levels, and nigral neurons (87–100%). Melatonin failed to attenuate MPTP‐induced striatal dopamine depletion. L‐DOPA administration (5 mg/kg, once 40 min prior to sacrifice, p.o.) in MPTP‐ and melatonin‐treated mice caused significant increase in striatal dopamine (31%), as compared to L‐DOPA and MPTP‐treated mice. This was equivalent to 8 mg/kg L‐DOPA administration in parkinsonian mouse. Therefore, prolonged, effective use of L‐DOPA in PD with lesser side effects could be achieved by treating with 60% lower doses of L‐DOPA along with melatonin.     

The melatonin metabolite N1‐acetyl‐5‐methoxykynuramine facilitates long‐term object memory in young and aging mice

Melatonin (MEL) has been reported to enhance cognitive processes, making it a potential treatment for cognitive decline. However, the role of MEL’s metabolites, N1‐acetyl‐N2‐formyl‐5‐methoxykynuramine (AFMK) and N1‐acetyl‐5‐methoxykynuramine (AMK), in these effects are unknown. The current study directly investigated the acute effects of systemic MEL, AFMK, and AMK on novel object recognition. We also analyzed MEL, AFMK, and AMK levels in hippocampus and temporal lobe containing the perirhinal cortex following systemic MEL and AMK treatment. AMK administered post‐training had a more potent effect on object memory than MEL and AFMK. AMK was also able to rescue age‐associated declines in memory impairments when object memory was tested up to 4 days following training. Results from administering AMK at varying times around the training trial and the metabolism time course in brain tissue suggest that AMK’s memory‐enhancing effects reflect memory consolidation. Furthermore, inhibiting the MEL‐to‐AMK metabolic pathway disrupted object memory at 24 hours post‐training, suggesting that endogenous AMK might play an important role in long‐term memory formation. This is the first study to report that AMK facilitates long‐term object memory performance in mice, and that MEL crosses the blood‐brain barrier and is immediately converted to AMK in brain tissue. Overall, these results support AMK as a potential therapeutic agent to improve or prevent memory decline.     

Effect of genipin on cholestasis induced by estradiol‐17β‐glucuronide and lithocholate‐3‐O‐glucuornide in rats

Aim: Genipin is reported to stimulate the insertion of multidrug resistance protein 2 (Mrp2) in the bile canalicular membrane, thereby causing choleresis by the increased the biliary excretion of glutathione, which has been considered to be a substrate of Mrp2. In the present study, we examined the effect of genipin on cholestasis induced by estradiol‐17β‐glucuronide and lithocholate‐3‐O‐glucuronide, Mrp2 substrates, in rats. Further, the effect of genipin on the biliary excretion of substrates of P‐glycoprotein (P‐gp), vinblastine and erythromycin, was also studied. Methods: The effect of genipin infusion at the rate of 0.5 µmol/min/100 g on cholestasis induced by estradiol‐17β‐glucuronide (0.075 µmol/min/100 g for 20 min) and lithocholate‐3‐O‐glucuronide (0.15 µmol/min/100 g for 40 min) was studied. The effect of genipin infusion on the biliary excretion of a tracer dose of vinblastine and erythromycin infused at the rate of 0.1 µmol/min/100 g was also studied. Results: Genipin relieved estradiol‐17β‐glucuronide‐induced cholestasis, and cumulative biliary estradiol‐17β‐glucuronide excretion for 120 min was increased from 50 ± 20%–81 ± 20% dose. In contrast, genipin had no effect on lithocholate‐3‐O‐glucuronide‐induced cholestasis. Biliary excretion of a tracer dose of vinblastine and the maximum biliary excretion of erythromycin were significantly decreased by genipin. Conclusions: Genipin protected estradiol‐17β‐glucuronide‐induced cholestasis. The mechanism of the protection of cholestasis by genipin is unknown, but it is speculated to be due to a conformational change of P‐gp by genipin, in addition to the stimulation of Mrp2 insertion into the bile canaliculi.     

The effect of glucagon‐like peptide‐1 and glucagon‐like peptide‐2 on microcirculation: A systematic review

GLP‐1 and GLP‐2 are gut‐derived hormones used in the treatment of diabetes type‐2 and short bowel syndrome, respectively. GLP‐1 attenuates insulin resistance and GLP‐2 reduces enterocyte apoptosis and enhances crypt cell proliferation in the small intestine. In addition, both hormones have vasoactive effects and may be useful in situations with impaired microcirculation. The aim of this systematic review was to provide an overview of the potential effects of GLP‐1 and GLP‐2 on microcirculation. A systematic search was performed independently by two authors in the following databases: PubMed, EMBASE, Cochrane library, Scopus, and Web of Science. Of 1111 screened papers, 20 studies were included in this review: 16 studies in animals, three in humans, and one in humans and rats. The studies were few and heterogeneous and had a high risk of bias. However, it seems that GLP‐1 regulates the pancreatic, skeletal, and cardiac muscle flow, indicating a role in the glucose homeostasis, while GLP‐2 acts primarily in the regulation of the microcirculation of the mid‐intestine. These findings may be useful in gastrointestinal surgery and in situations with impaired microcirculation of the gut.     

Prognostic value of complete remission status at end‐of‐treatment FDG‐PET in R‐CHOP‐treated diffuse large B‐cell lymphoma: systematic review and meta‐analysis

This study systematically reviewed and meta‐analysed the prognostic value of complete remission status at end‐of‐treatment ¹⁸F‐fluoro‐2‐deoxy‐d ‐glucose positron emission tomography (FDG‐PET) in diffuse large B‐cell lymphoma (DLBCL) patients treated with rituximab, cyclophosphamide, doxorubicin, vincristine and prednisone (R‐CHOP). The systematic PubMed/MEDLINE search yielded seven suitable studies comprising a total of 737 R‐CHOP‐treated DLBCL patients who were in complete remission at end‐of‐treatment FDG‐PET. Overall, the methodological quality of included studies was reasonable. The disease relapse rate among all patients with complete remission status according to end‐of‐treatment FDG‐PET ranged from 7·0% to 20·0%, with a weighted summary proportion of 13·7%. Five of seven studies reported progression‐free survival (PFS) of these patients at various specific time points, i.e., 2‐year PFS (n = 1), estimated 3‐year PFS (n = 3) and 5‐year PFS (n = 1), which was 83%, 85–86·4% and 75%, respectively. Three of seven studies reported overall survival (OS) of these patients at various specific time points, i.e., estimated 3‐year OS (n = 2) and estimated 5‐year OS (n = 1), which were 90%, 93·6% and 83%, respectively. In conclusion, a non‐negligible proportion of R‐CHOP‐treated DLBCL patients who achieve complete remission according to end‐of‐treatment FDG‐PET experiences disease relapse during follow‐up.