Reduced Na(+), K(+)-ATPase activity in erythrocyte membranes from patients with phenylketonuria

Engineering Organoids for in vitro Modeling of Phenylketonuria

Phenylketonuria is a recessive genetic disorder of amino-acid metabolism, where impaired phenylalanine hydroxylase function leads to the accumulation of neurotoxic phenylalanine levels in the brain. Severe cognitive and neuronal impairment are observed in untreated/late-diagnosed patients, and even early treated ones are not safe from life-long sequelae. Despite the wealth of knowledge acquired from available disease models, the chronic effect of Phenylketonuria in the brain is still poorly understood and the consequences to the aging brain remain an open question. Thus, there is the need for better predictive models, able to recapitulate specific mechanisms of this disease. Human induced pluripotent stem cells (hiPSCs), with their ability to differentiate and self-organize in multiple tissues, might provide a new exciting in vitro platform to model specific PKU-derived neuronal impairment. In this review, we gather what is known about the impact of phenylalanine in the brain of patients and highlight where hiPSC-derived organoids could contribute to the understanding of this disease.

Orally Administered Fumonisins Affect Porcine Red Cell Membrane Sodium Pump Activity and Lipid Profile Without Apparent Oxidative Damage

Weaned piglets (n = 3 × 6) were fed 0, 15 and 30 mg/kg diet fumonisin (FB₁, FB₂ and FB₃, i.e., FBs, a sphinganine analogue mycotoxin), from the age of 35 days for 21 days, to assess mycotoxin induced, dose-dependent changes in the red cells’ membrane. Ouabain sensitive Na⁺/K⁺ ATPase activity was determined from lysed red cell membranes, membrane fatty acid (FA) profile was analysed, as well as antioxidant and lipid peroxidation endpoints. Final body weight was higher in the 30 mg/kg group (vs. control), even besides identical cumulative feed intake. After 3 weeks, there was a difference between control and the 30 mg/kg group in red cell membrane sodium pump activity; this change was dose-dependent (sig.: 0.036; R² = 0.58). Membrane FA profile was strongly saturated with non-systematic inter-group differences; pooled data provided negative correlation with sodium pump activity (all individual membrane n6 FAs). Intracellular antioxidants (reduced glutathione and glutathione peroxidase) and lipid peroxidation indicators (conj. dienes, trienes and malondialdehyde) were non-responsive. We suppose a ceramide synthesis inhibitor (FB₁) effect exerted onto the cell membrane, proven to be toxin dose-dependent and increasing sodium pump activity, with only indirect FA compositional correlations and lack of lipid peroxidation.

Fluoride Exposure Induces Inhibition of Sodium-and Potassium-Activated Adenosine Triphosphatase (Na+, K+-ATPase) Enzyme Activity: Molecular Mechanisms and Implications for Public Health

In this study, several lines of evidence are provided to show that Na + , K + -ATPase activity exerts vital roles in normal brain development and function and that loss of enzyme activity is implicated in neurodevelopmental, neuropsychiatric and neurodegenerative disorders, as well as increased risk of cancer, metabolic, pulmonary and cardiovascular disease. Evidence is presented to show that fluoride (F) inhibits Na + , K + -ATPase activity by altering biological pathways through modifying the expression of genes and the activity of glycolytic enzymes, metalloenzymes, hormones, proteins, neuropeptides and cytokines, as well as biological interface interactions that rely on the bioavailability of chemical elements magnesium and manganese to modulate ATP and Na + , K + -ATPase enzyme activity. Taken together, the findings of this study provide unprecedented insights into the molecular mechanisms and biological pathways by which F inhibits Na + , K + -ATPase activity and contributes to the etiology and pathophysiology of diseases associated with impairment of this essential enzyme. Moreover, the findings of this study further suggest that there are windows of susceptibility over the life course where chronic F exposure in pregnancy and early infancy may impair Na + , K + -ATPase activity with both short- and long-term implications for disease and inequalities in health. These findings would warrant considerable attention and potential intervention, not to mention additional research on the potential effects of F intake in contributing to chronic disease.

Erythrocyte membrane in the evaluation of neurodegenerative disorders

Neurodegenerative diseases have many similar pathological conditions, and very few studies exist which detail their molecular features. Proteins like Na⁺/K⁺-ATPase (NKA), α-spectrin (SPTA) and drebrin have been reported to be involved in the integrity of neuronal cell membrane and their functions. Furthermore, recent studies have highlighted their implication in neurodegeneration. In the current study, we wanted to identify the role of NKA, SPTA and drebrin in the erythrocyte membranes obtained from the blood of patients with neurodegenerative disorders (NDs) subjected to motor impairment such as Parkinson’s disease, amyotrophic lateral sclerosis, ataxia and dementia. We have studied the activity of NKA and the expression of NKA, SPTA and drebrin in the erythrocyte membrane by quantitative real-time PCR and Western blot obtained from the blood samples of patients with NDs culminating in movement and memory dysfunction. We observed a significant reduction in the expressions of NKA, SPTA and drebrin when compared to control and significant variations among the recruited ND samples. On correlating, we found a significant relationship between the expressions and the clinical features such as bradykinesia. Thus, we suggest that the reduction in the expressions of NKA, SPTA and drebrin could function as tools of assessment and speculate the particular neurodegenerative condition.

Individual and combined haematotoxic effects of fumonisin B(1) and T-2 mycotoxins in rabbits

Weaned rabbits were fed diets contaminated with 2 mg/kg diet T-2 toxin alone, or 10 mg/kg diet fumonisin B1 (FB1) alone, and both toxins in combination (2+10 mg/kg, resp.), as compared to a toxin free control. Samplings were performed after 2 and 4 weeks. Bodyweight of the T-2 fed group was lower after 4 weeks; the liver weight increased dramatically. Red blood cell (RBC) Na(+)/K(+) ATPase activity decreased after 4 weeks in the T-2 group, it increased in the FB1 group and antagonism was found by the combined treatment. The RBC membrane fatty acid profile was modified by both toxins similarly during the entire feeding. After 4 weeks T-2 alone and in combination (with FB1) was found to increase mean cell volume (MCV). The time-dependent alterations in the T-2 group were significant for MCV (increase) and the mean cell haemoglobin (increase). The active monovalent cation transport was altered by both mycotoxins. Most probably FB1 exerts its sodium pump activity modification via an altered ceramide metabolism (behenic acid decrease in the RBC membrane), while for T-2 toxin a moderate membrane disruption and enzyme (protein) synthesis inhibition was supposed (ca. 75% decrease of the sodium pump activity).

Diffusion-weighted MR imaging in patients with phenylketonuria: relationship between serum phenylalanine levels and ADC values in cerebral white matter

PURPOSE

To prospectively determine the relationship between serum phenylalanine levels and apparent diffusion coefficient (ADC) values in the cerebral white matter of patients with phenylketonuria (PKU).

MATERIALS AND METHODS

Institutional review board approval was obtained, and participants provided informed consent. Magnetic resonance (MR) imaging, which included T1- and T2-weighted, fluid-attenuated inversion-recovery (FLAIR), and diffusion-weighted examinations, was performed in 21 patients with PKU (nine male and 12 female patients; age range, 3-44 years; mean age, 19.4 years). ADC values in deep cerebral white matter were calculated for each patient. Serum phenylalanine levels were obtained in all patients within 12 days after MR imaging. Serum phenylalanine levels were measured in 16 patients 1 year before MR imaging. ADC values in cerebral white matter and serum phenylalanine levels were compared. A total of 21 control subjects (12 male and nine female patients; age range, 3-33 years; mean age, 20.6 years) underwent MR imaging. ADC values in cerebral white matter were compared with serum phenylalanine levels by using the Pearson correlation.

RESULTS

Abnormal high signal intensity in white matter on T2-weighted and FLAIR MR images was noted in patients with PKU who had serum phenylalanine levels of more than 8.5 mg/dL (514.2 micromol/L). Diffusion in posterior deep cerebral white matter tended to be restricted in patients when increased serum phenylalanine levels were measured after MR imaging (r = -0.62). There was a correlation between ADC values in posterior cerebral white matter and serum phenylalanine levels measured 1 year before MR imaging (r = -0.77). ADCs of control subjects were significantly higher than ADCs of patients with PKU (P < .005).

CONCLUSION

Posterior deep white matter in patients with PKU and a serum phenylalanine level of more than 8.5 mg/dL showed high signal intensity in white matter on T2-weighted and FLAIR MR images and revealed decreased ADC. We suggest that to avoid brain-restricted diffusion due to hyperphenylalanemia, patients with PKU should maintain serum phenylalanine levels of less than 8.5 mg/dL (514.2 micromol/L).

Cytoskeleton of human mononuclear cells as a possible peripheral marker for phenylalanine neurotoxicity in PKU

In this work we tested human mononuclear cells as a peripheral marker to study neurotoxicity of phenylalanine (Phe). Slices of cerebral cortex of rats or human mononuclear cells were incubated with different concentrations of Phe and/or Ala in the presence of 32P-orthophosphate, the cytoskeletal fraction was extracted, and the radioactivity incorporated into intermediate filament proteins was measured. Our results show that 2 mM Phe as well as 1 mM Ala are effective in increasing the 32P in vitro incorporation into IFs in both tissues. When cerebral cortex slices or mononuclear cells were incubated with different concentrations of Phe and/or Ala, the effects on the 32P in vitro incorporation into IF proteins was compatible with an antagonistic mechanism of action of the two amino acids on the enzymes of the phosphorylating system. In addition, these blood cells may be a possible peripheral marker to study neurotoxicity of Phe in patients with PKU.

In vivo effects of high phenylalanine blood levels on Na+,K+-ATPase, Mg2+-ATPase activities and biogenic amine concentrations in phenylketonuria

OBJECTIVE

To evaluate the activities of Na+,K+-ATPase and Mg2+-ATPase in erythrocyte membranes from phenylketonuric (PKU) patients and to correlate the enzyme activities with their blood phenylalanine (Phe) levels, biogenic amines as well as with their precursors tyrosine (Tyr) and tryptophan (Try).

DESIGN AND METHODS

Twenty three PKU patients were divided into group A (n = 12) on a restricted diet (Phe 1.57 +/- 0.52 mg/dL or 0.10 +/- 0.03 mM) and group B (n = 11) on a "loose" diet (Phe 24.45 +/- 1.50 mg/dL or 1.72 +/- 0.09 mM). The enzyme activities were measured spectrophotometrically, the amino acids with an automatic amino analyser and the biogenic amines with HPLC methods.

RESULTS

In group B, plasma amino acids (Tyr, Try), their biogenic amines [adrenaline (A), noradrenaline (NA), dopamine (DA) and serotonin (5HT)], (Na+,K+)-ATPase and Mg2+-ATPase activities were found remarkably decreased (p < 0.001).

CONCLUSIONS

High Phe and/or low NA, DA, 5HT plasma levels may indirectly inhibit the erythrocyte membrane Na+,K+-ATPase and Mg2+-ATPase in PKU patients. The observed enzyme inhibitions could be a very informative peripheral marker as regards the neurotoxic Phe brain effects.