Ammonia-lowering activities and carbamoyl phosphate synthetase 1 (Cps1) induction mechanism of a natural flavonoid

Abstract

ObjectiveAmmonia detoxification is essential for physiological well-being, and the urea cycle in liver plays a predominant role in ammonia disposal. Nobiletin (NOB), a natural dietary flavonoid, is known to exhibit various physiological efficacies. In the current study, we investigated a potential role of NOB in ammonia control and the underlying cellular mechanism.Materials/methodsC57BL/6 mice were fed with regular chow (RC), high-fat (HFD) or high-protein diet (HPD) and treated with either vehicle or NOB. Serum and/or urine levels of ammonia and urea were measured. Liver expression of genes encoding urea cycle enzymes and C/EBP transcription factors was determined over the circadian cycle. Luciferase reporter assays were carried out to investigate function of CCAAT consensus elements on the carbamoyl phosphate synthetase (Cps1) gene promoter. A circadian clock-deficient mouse mutant, ClockΔ19/Δ19, was utilized to examine a requisite role of the circadian clock in mediating NOB induction of Cps1.ResultsNOB was able to lower serum ammonia levels in mice fed with RC, HFD or HPD. Compared with RC, HFD repressed the mRNA and protein expression of Cps1, encoding the rate-limiting enzyme of the urea cycle. Interestingly, NOB rescued CPS1 protein levels under the HFD condition via induction of the transcription factors C/EBPα and C/EBPβ. Expression of other urea cycle genes was also decreased by HFD relative to RC and again restored by NOB to varying degrees, which, in conjunction with Cps1 promoter reporter analysis, suggested a C/EBP-dependent mechanism for the co-induction of urea cycle genes by NOB. In comparison, HPD markedly increased CPS1 levels relative to RC, yet NOB did not further enrich CPS1 to a significant extent. Using the circadian mouse mutant ClockΔ19/Δ19, we also showed that a functional circadian clock, known to modulate C/EBP and CPS1 expression, was required for NOB induction of CPS1 under the HFD condition.ConclusionNOB, a dietary flavonoid, exhibits a broad activity in ammonia control across varying diets, and regulates urea cycle function via C/EBP-and clock-dependent regulatory mechanisms.Electronic supplementary materialThe online version of this article (doi:10.1186/s12986-015-0020-7) contains supplementary material, which is available to authorized users.

The Small Molecule Nobiletin Targets the Molecular Oscillator to Enhance Circadian Rhythms and Protect against Metabolic Syndrome

“…Polymethoxylated flavones elicit diverse benefits in mice and humans, including mitigating effects against cancer, inflammation, atherosclerosis, and more recently metabolic disorders and neurodegenerative diseases (Cui et al, 2010; Evans et al, 2012; Kurowska and Manthey, 2004; Lee et al, 2013; Mulvihill et al, 2009; Nohara et al, 2015a). Polymethoxylated flavones generally show a favorable pharmacokinetic profile (Evans et al, 2012; Saigusa et al, 2011), and no discernible toxicity was observed in chronic treatment of mice in this and previous studies (Lee et al, 2013; Mulvihill et al, 2011).…”

“…Polymethoxylated flavones generally show a favorable pharmacokinetic profile (Evans et al, 2012; Saigusa et al, 2011), and no discernible toxicity was observed in chronic treatment of mice in this and previous studies (Lee et al, 2013; Mulvihill et al, 2011). Our recent studies showed a role of NOB in ammonia disposal via urea cycle regulation, and transcriptional induction of the rate-limiting Cps1 gene by NOB was impaired in Clock Δ19/Δ19 mutant mice (Nohara et al, 2015a). Providing a mechanistic basis for these functional results, the current study illustrates a direct role of NOB in the enhancement of circadian clocks and particularly the activation of ROR receptors.…”

Two novel CPS1 mutations in a case of carbamoyl phosphate synthetase 1 deficiency causing hyperammonemia and leukodystrophy

“…Besides, N‐carbamoyl‐L‐glutamate (NCG), an allosteric activator of CPS1, has been tested to decrease ureagenesis in minority patients with CPS1D . A recent study also indicates flavonoids can rescue CPS1 levels and reduce serum ammonia in CPS1 ‐repressed mouse models . Moreover, with the genome‐editing strategies become gradually mature, for instance, CRISPR/Cas9 system, gene therapy will be a potential approach to correct CPS1 mutations in patients with CPS1D …”

“…25 A recent study also indicates flavonoids can rescue CPS1 levels and reduce serum ammonia in CPS1-repressed mouse models. 26 Moreover, with the genomeediting strategies become gradually mature, for instance, CRISPR/ Cas9 system, gene therapy will be a potential approach to correct CPS1 mutations in patients with CPS1D. 24 In conclusion, CPS1D is a rare monogenic inheritance disorder that affected multiple organs originally owing to different extent of destruction in urea cycle.…”

Involvement of ammonia metabolism in the improvement of endurance performance by tea catechins in mice

“…Flavonoids such as nobiletin 19 , naringin 20 , chrysin 21 , and fisetin 22,23 have been shown to improve ammonia resistance and up-regulate urea cycle enzymes 19,20,22 ; however, whether this up-regulation is effective for lowering exercise-induced hyperammonaemia remains unknown. One group of flavonoids, the green tea catechins (GTCs), have been shown to have several health-promoting impacts, including anti-cancer effects, hepatoprotective effects, anti-diabetic effects, and anti-obesity effects 24 ; however, the impact of GTCs on ammonia metabolism remains to be examined.…”