Methylamine, but not ammonia, is hypophagic in mouse by interaction with brain Kv1.6 channel subtype

Utilizing NMR fecal metabolomics as a novel technique for detecting the physiological effects of food shortages in waterfowl

Metabolomics is the study of small, endogenous metabolites that participate in metabolic reactions, including responses to stressors. Anthropogenic and environmental changes that alter habitat and food supply can act as stressors in wild waterfowl. These alterations invoke a series of physiological processes to provide energy to restore homeostasis and increase survival. In this study, we utilized fecal metabolomics to measure metabolites and identify pathways related to a 6-day feed restriction in captive mallard ducks (Anas platyrhynchos, n = 9). Fecal samples were collected before (baseline) and during feed restriction (treatment). H1 Nuclear Magnetic Resonance (NMR) spectroscopy was performed to identify metabolites. We found that fecal metabolite profiles could be used to distinguish between the feed-restricted and baseline samples. We identified metabolites related to pathways for energy production and metabolism endpoints, and metabolites indicative of gut microbiota changes. We also demonstrated that mallard ducks could utilize endogenous reserves in times of limited caloric intake. Fecal metabolomics shows promise as a non-invasive novel tool in identifying and characterizing physiological responses associated with stressors in a captive wild bird species.

Central and peripheral methylamine-induced hypophagia is mediated via nitric oxide and TAAR1 in neonatal layer-type chicken

The aim of the current study was to determine effects of intracerebroventricular (ICV) and intraperitoneal (i.p.) administration of Methylamine (MET) and possible interactions with nitric oxide (NO) and TAAR₁ pathways in 24-h fasted (FD₂₄) and ad libitum layer-type chicken. In experiment 1, FD₂₄ chicken ICV injected with MET (15, 30, 45, 60 and 75 μg). In experiment 2, ICV injection of MET (15, 30, 45, 60 and 75 μg) was injected in the ad libitum birds. Experiments 3-4 were similar to experiments 1-2, except chicken i.p. injected with MET (15, 30, 45, 60 and 75 mg/kg). In experiment 5, FD₂₄ birds ICV injected with l-NAME (NO synthesis inhibitor, 100 nmol), MET (75 μg) and co-injection of l-NAME + MET. Experiment 6 was similar to experiment 5, except, ad libitum birds received injections. In experiment 7, FD₂₄ chicken i.p. injected with l-NAME (100 mg/kg), MET (75 mg/kg) and co-injection of l-NAME + MET. In experiment 8, FD₂₄ birds ICV injected with RO5256390 (selective TAAR₁ agonist, 10, 20 and 40 μg). In experiment 9, ad libitum birds ICV injected with RO5256390 (10, 20 and 40 μg). In experiment 10, FD₂₄ birds ICV injected with RO5256390 (10 μg), MET (75 μg) and their co-injection. Experiment 11 was similar to experiment 10, except, ad libitum birds received ICV injections. In experiment 12, FD₂₄ chicken i.p. injected with RO5256390 (2.5, 5 and 10 mg/kg). In experiment 13, FD₂₄ chicken i.p. injected with RO5256390 (2.5 mg/kg), MET (75 mg/kg) and RO5256390 + MET. Then cumulative food intake was determined until 120 min after injection. According to the results, ICV injection of MET decreased food intake in FD₂₄ and ad libitum chicken (P < 0.05). MET (i.p.) diminished food consumption in fasted (P < 0.05) but not in ad libitum chicken (P> 0.05). Co-injection of the l-NAME + MET significantly decreased MET-induced hypophagia in FD₂₄ and ad libitum chicken (P < 0.05). MET-induced hypophagia (i.p.) weakened by l-NAME in FD₂₄ chicken (P < 0.05). RO5256390 decreased food intake in FD₂₄ and ad libitum chicken (P < 0.05). Co-injection of RO5256390 + MET increased MET-induced hypophagia in FD₂₄ and ad libitum chicken (P < 0.05). RO5256390 decreased food intake in FD₂₄ chicken (P < 0.05). Co-injection of the RO5256390 + MET amplified MET-induced hypophagia in FD₂₄ chicken (P < 0.05). Based on the findings, MET-induced hypophagia is mediated via NO and TAAR₁ pathways on food intake in layer chicken.

Methylamine induced hypophagia is mediated via dopamine D1 and D2 receptors in neonatal meat chicks

Recently, methylamine has been found as an endogenous amine, which is controlling food intake in mammals. However, there is no evidence about the effect of methylamine on feeding behavior in poultry. So, the present study was designed to evaluate the effect of intracerebroventricular (ICV) injection of methylamine and involvement of central methylamine/dopaminergic systems on feeding behavior in neonatal meat type chicks. In experiment 1, chicks were ICV injected with different doses of methylamine (0.48, 0.96, 1.44, 1.92 and 2.40 μmol). In experiment 2, chicks received a dose of either the control solution, 2.40 μmol methylamine, 125 nmol L-DOPA (dopamine precursor) or a combination of methylamine plus L-DOPA. Experiments 3-7 were similar to experiment 2 except that 150 nmol 6-OHDA (dopamine synthase inhibitor), 5 nmol SCH23390 (D1 receptor antagonist), 5 nmol AMI-193 (D2 receptor antagonist), 6.4 nmol NGB2904 (D3 receptor antagonist) and 6 nmol L-741, 742 (D4 receptor antagonist) were used instead of 125 nmol L-DOPA, respectively. Cumulative food intake was determined until 2 h post-injection. According to the results, methylamine significantly decreased food intake in a dose dependent manner (p < 0.05). The inhibitory effect of methylamine on food intake was significantly attenuated by 6-OHDA, SCH23390 and AMI-193 (P < 0.05), but NGB2904 and L-741, 742 had no effect on food intake induced by methylamine. In addition, hypophagic effect of methylamine significantly amplified by L-DOPA (P < 0.05). These results suggest that methylamine decrease food intake and there is an interaction between methylamine and dopaminergic system via D1 and D2 receptors in chickens.

Retained organic solutes, patient characteristics and all-cause and cardiovascular mortality in hemodialysis: results from the retained organic solutes and clinical outcomes (ROSCO) investigators

BACKGROUND

Multiple solutes are retained in uremia, but it is currently unclear which solutes are toxic. Small studies suggest that protein-bound solutes, such as p-cresol sulfate and indoxyl sulfate and intracellular solutes, such as methylamine (MMA) and dimethylamine (DMA), may be toxic. Our objective was to test whether elevated levels of these solutes were associated with mortality.

METHODS

We conducted a prospective cohort study in 521 U.S. incident hemodialysis patients to evaluate associations between these solutes and all-cause and cardiovascular mortality. P-cresol sulfate, indoxyl sulfate, MMA and DMA levels were measured from frozen plasma samples obtained 2 to 6 months after initiation of dialysis. Mortality data was available through 2004 using the National Death Index.

RESULTS

Elevated (greater than the population median) p-cresol sulfate, MMA or DMA levels were not associated with all-cause or cardiovascular mortality. Elevated indoxyl sulfate levels were associated with all-cause mortality but not cardiovascular mortality (hazard ratio 1.30 (95% confidence interval 1.01, 1.69) p-value 0.043).

CONCLUSIONS

In this cohort of 521 incident hemodialysis patients, only elevated indoxyl sulfate levels were associated with all-cause mortality. Further research is needed to identify causes of the toxicity of uremia to provide better care for patients with kidney disease.

Role of voltage-gated potassium channels in the fate determination of embryonic stem cells

Embryonic stem cells (ESCs) possess two unique characteristics: self-renewal and pluripotency. In this study, roles of voltage-gated potassium channels (K(v)) in maintaining mouse (m) ESC characteristics were investigated. Tetraethylammonium (TEA(+)), a K(v) blocker, attenuated cell proliferation in a concentration-dependent manner. Possible reasons for this attenuation, including cytotoxicity, cell cycle arrest and differentiation, were examined. Blocking K(v) did not change the viability of mESCs. Interestingly, K(v) inhibition increased the proportion of cells in G(0)/G(1) phase and decreased that in S phase. This change in cell cycle distribution can be attributed to cell cycle arrest or differentiation. Loss of pluripotency as determined at both molecular and functional levels was detected in mESCs with K(v) blockade, indicating that K(v) inhibition in undifferentiated mESCs directs cells to differentiate instead of to self-renew and progress through the cell cycle. Membrane potential measurement revealed that K(v) blockade led to depolarization, consistent with the role of K(v) as the key determinant of membrane potential. The present results suggest that membrane potential changes may act as a "switch" for ESCs to decide whether to proliferate or to differentiate: hyperpolarization at G(1) phase would favor ESCs to enter S phase while depolarization would favor ESCs to differentiate. Consistent with this notion, S-phase-synchronized mESCs were found to be more hyperpolarized than G(0)/G(1)-phase-synchronized mESCs. Moreover, when mESCs differentiated, the differentiation derivatives depolarized at the initial stage of differentiation. This investigation is the first study to provide evidence that K(v) and membrane potential affect the fate determination of ESCs.

Relationship of impaired olfactory function in ESRD to malnutrition and retained uremic molecules

BACKGROUND

Olfactory function is impaired in patients with end-stage renal disease (ESRD) and may contribute to uremic anorexia. Only limited correlations of olfactory function and nutritional status were reported. This study examines the relationship of impaired olfactory function to malnutrition and levels of the retained uremic solutes monomethylamine, ethylamine, indoxyl sulfate, and P-cresol sulfate.

STUDY DESIGN

Cross-sectional observational study.

SETTING & PARTICIPANTS

31 stable maintenance hemodialysis patients from an urban outpatient dialysis unit and 18 people with normal renal function participated.

PREDICTOR

Nutritional status assigned by using Subjective Global Assessment (SGA) score; SGA score of 7 indicates normal nutritional status; SGA score of 5 to 6, mild malnutrition; and SGA score of 3 to 4, moderate malnutrition.

OUTCOMES & MEASUREMENTS

The primary outcome is olfactory function, assessed using the University of Pennsylvania Smell Identification Test. Levels of retained uremic solutes were measured from a predialysis serum sample. Demographic data and laboratory values for nutritional status, adequacy of dialysis, and inflammation were collected.

RESULTS

Mean smell scores were 34.9 +/- 1.4 for controls, 33.5 +/- 3.3 for patients with SGA score of 7, 28.3 +/- 5.8 for patients with SGA score of 5 to 6, and 27.9 +/- 4.4 for patients with SGA score of 3 to 4 (P < 0.001 comparing healthy patients with all patients with ESRD). There was no difference in mean smell scores for healthy controls and patients with SGA score of 7. However, patients with lower smell scores had significantly lower SGA scores (P = 0.02) and higher C-reactive protein levels (P = 0.02). Neither smell score nor nutritional status was associated with levels of retained uremic solutes.

LIMITATIONS

Small sample size, only cross-sectional associations can be described.

CONCLUSIONS

Our results suggest an association between poor nutritional status and impaired olfactory function in patients with ESRD. Additional research is needed to discover the uremic toxins mediating these processes.

Methylamine-dependent release of nitric oxide and dopamine in the CNS modulates food intake in fasting rats

BACKGROUND AND PURPOSE

Methylamine is an endogenous aliphatic amine exhibiting anorexigenic properties in mice. The aim of this work was to show whether methylamine also modifies feeding behaviour in rats and, if so, to identify the mediator(s) responsible for such effects.

EXPERIMENTAL APPROACH

Microdialysis experiments with the probe inserted in the periventricular hypothalamic nucleus were carried out in 12 h starved, freely moving rats. Collected perfusate samples following methylamine injection (i.c.v.) were analysed for nitric oxide by chemiluminescence and for dopamine and 5-hydroxytryptamine content by HPLC. Kv1.6 potassium channel expression was reduced by antisense strategy and this decrease quantified by semi-quantitative RT-PCR analysis.

KEY RESULTS

Methylamine showed biphasic dose-related effects on rat feeding. At doses of 15-30 microg per rat, it was hyperphagic whereas higher doses (60-80 microg) were hypophagic. Methylamine stimulated central nitric oxide (+115% vs. basal) following hyperphagic and dopamine release (60% over basal values) at hypophagic doses, respectively. Treatment with L-N(G)-nitro-L-arginine-methyl ester (i.c.v. 2 microg 10 microl(-1)) or with alpha-methyl-p-tyrosine (i.p. 100 mg kg(-1)) before methylamine injection, reduced nitric oxide output and hyperphagia, or dopamine release and hypophagia respectively. Moreover, hypophagia and hyperphagia, as well as nitric oxide and dopamine release were significantly reduced by down-regulating brain Kv1.6 potassium channel expression.

CONCLUSIONS AND IMPLICATIONS

The effects of methylamine on feeding depend on the hypothalamic release of nitric oxide and dopamine as a result of interaction at the Kv1.6 channels. The study of methylamine levels in the CNS may provide new perspectives on the physiopathology of alimentary behaviour.

Permeation and inhibition of polycystin-L channel by monovalent organic cations

Polycystin-L (PCL), homologous to polycystin-2 (71% similarity in protein sequence), is the third member of the polycystin family of proteins. Polycystin-1 and -2 are mutated in autosomal dominant polycystic kidney disease, but the physiological role of PCL has not been determined. PCL acts as a Ca-regulated non-selective cation channel permeable to mono- and divalent cations. To further understand the biophysical and pharmacological properties of PCL, we examined a series of organic cations for permeation and inhibition, using single-channel patch clamp and whole-cell two-microelectrode voltage clamp techniques in conjunction with Xenopus oocyte expression. We found that PCL is permeable to organic amines, methlyamine (MA, 3.8 A), dimethylamine (DMA, 4.6 A) and triethylamine (TriEA, 6 A), and to tetra-alkylammonium cation (TAA) tetra-methylammonium (TMA, 5.5-6.4 A). TAA compounds tetra-ethylammonium (TEA, 6.1-8.2 A) and tetra-propylammonium (TPA, 9.8 A) were impermeable through PCL and exhibited weak inhibition on PCL (IC50 values>13 mM). Larger TAA cations tetra-butylammonium (TBA, 11.6 A) and tetra-pentylammonium (TPeA, 13.2 A) were impermeable through PCL as well and showed strong inhibition (IC50 values of 2.7 mM and 1.3 microM, respectively). Inhibition by TBA was on decreasing the single-channel current amplitude and exhibited no effect on open probability (NPo) or mean open time (MOT), suggesting that it blocks the PCL permeation pathway. In contract, TEA, TPA and TPeA reduced NPo and MOT values but had no effect on the amplitude, suggesting their binding to a different site in PCL, which affects the channel gating. Taken together, our studies revealed that PCL is permeable to organic amines and TAA cation TMA, and that inhibition of PCL by large TAA cations exhibits two different mechanisms, presumably through binding either to the pore pathway to reduce permeant flux or to another site to regulate the channel gating. These data allow to estimate a channel pore size of approximately 7 A for PCL.

Activity and expression of semicarbazide-sensitive benzylamine oxidase in a rodent model of diabetes: interactive effects with methylamine and alpha-aminoguanidine

Previous data indicate that methylamine injection in fasted healthy mice produced a hypophagic effect dependent of neuronal K(v)1.6 channels expression and increased by alpha-aminoguanidine, an inhibitor of semicarbazide-sensitive benzylamine oxidase enzymes mainly involved in amine degradation. In the present work we have investigated: 1) the level of expression and activity of the semicarbazide-sensitive benzylamine oxidase; 2) the effect of methylamine alone and in the presence of alpha-aminoguanidine on food intake of genetic obese and type II diabetes mice (the db/db mice). Db/db mice showed higher levels of semicarbazide-sensitive benzylamine oxidase activities in adipose tissue and in plasma than their lean counterpart (db/db(+) mice). Methylamine (30-75 microg, i.c.v.) showed similar hypophagic effects in obese and lean mice consistently with the levels of neuronal K(v)1.6 found in both animal strains. Alpha-aminoguandine (50 mg/kg, i.p.) increased methylamine (i.c.v.) hypophagia in both obese and lean mice and only in obese mice when methylamine was given i.p. These results suggest a crucial role of semicarbazide-sensitive benzylamine oxidase activity in controlling methylamine hypophagia in hyperphagic diabetic mice.