ESTIMATION OF POTASSIUM CONTENT OF DIFFERENT VARIETIES OF BANANA FRUIT IN AN INDIAN DELTA IS THERE A CLINICAL RELEVANCE

Banana fruit is one of the commonly taken foods in many parts of the world. The fruit is known for its high potassium content. We wished to study the potassium content of eleven types of ripe banana fruit available in the cauvery delta region of South India. We measured two values in each of the eleven types of banana fruit. We found the mean varied from 460.75mg/100gm in the Rasthali variety to 921.75 in the karpura valli variety. The potassium binding capacity of the soil and the fertilizers pumped may influence the values. The literature which presently describes the values between 200 to 400mg/100g cautions the use of bananas in patients taking antihypertensive medications like enalapril and in patients with renal dysfunction. Our study which shows the values to be double the described ones, will throw light on additional caution in such cases. We admit that there was no soil study in this work which can influence the potassium content. Before any dietetic advice on the intake of potassium, the bananas of the concerned geographical area and such high potassium values should be taken into account. When the needs to cater the patients of potassium arise in uncomplicated hypertension, the varieties karpuravalli and peyampalam can be considered.

Tuning the sensitivity of genetically encoded fluorescent potassium indicators through structure-guided and genome mining strategies

Genetically encoded potassium indicators lack optimal binding affinity for monitoring intracellular dynamics in mammalian cells. Through structure-guided design and genome mining of potassium binding proteins, we developed green fluorescent potassium indicators with a broad range of binding affinities. KRaION1, based on the insertion of a potassium binding protein (Ec-Kbp) into the fluorescent protein mNeonGreen, exhibits an isotonically measured Kd of 69±10 (mM; mean ± standard deviation used throughout). We identified Ec-Kbp's binding site using NMR spectroscopy to detect protein-thallium scalar couplings and refined the structure of Ec-Kbp in its potassium-bound state. Guided by this structure, we modified KRaION1, yielding KRaION2, which exhibits an isotonically measured Kd of 96±9 (mM). We identified four Ec-Kbp homologs as potassium binding proteins, which yielded indicators with isotonically measured binding affinities in the 39-112 (mM) range. KRaIONs expressed and functioned in HeLa cells, but exhibited lower Kd values, which were mirrored by lower Kd values measured in vitro when holding sodium constant. Thus, potassium indicator Kd may need to be evaluated in the context of a given experimental goal.

The Role of Patiromer in Delaying the Onset of Renal Replacement Therapy in Patients with Advanced Renal Failure

Patients with chronic kidney disease (CKD) are at an increased risk of developing hyperkalemia, which can be potentially life threatening. Hyperkalemia is frequently encountered with renin-angiotensin-aldosterone system inhibitor (RAASi) therapy use in patients with CKD and often results in the underdosing or discontinuation of these drugs. RAASi therapy has been proven to delay the progression of CKD, ameliorate proteinuria, and reduce the overall risk of cardiovascular morbidity and mortality. Patiromer is a sodium-free, potassium-binding polymer used for the treatment of hyperkalemia. We present a case series of four patients with Stage 4 or 5 CKD in whom the initiation of dialysis was delayed with the use of patiromer. For one patient, dialysis was delayed by 18 months, whereas the remaining three patients, in whom hyperkalemia was one of the main complications, remain dialysis independent to date.

Recurrent de novo single point mutation on the gene encoding Na+/K+ pump results in epilepsy

The etiology of epilepsy remains undefined in two-thirds of patients. Here, we identified a de novo mutation of ATP1A2 (c.2426 T>G, p.Leu809Arg), which encodes the α2 subunit of Na+/K+-ATPase, from a family with idiopathic epilepsy. This mutation caused seizures in the study patients. We generated the point mutation mouse model Atp1a2L809R, which recapitulated the epilepsy observed in the study patients. In Atp1a2L809R/WT mice, convulsions were observed and cognitive and memory function was impaired. This mutation affected the potassium binding function of the protein, disabling its ion transport ability, thereby increasing the frequency of nerve impulses. Our work revealed that ATP1A2L809R mutations cause a predisposition to epilepsy. Moreover, we first provide a point mutation mouse model for epilepsy research and drug screening.

The LIFT trial: study protocol for a double-blind, randomised, placebo-controlled trial of K+-binder Lokelma for maximisation of RAAS inhibition in CKD patients with heart failure

Background CKD is common in heart failure (HF) and associated with morbidity and mortality, yet life-prolonging medications such as renin-angiotensin-aldosterone inhibitors (RAASi) are underused due to risk of hyperkalaemia. Sodium zirconium cyclosilicate (SZC) is a potassium-binding medication that has been shown to reduce incidence of hyperkalaemia in CKD, non-CKD, and HF populations, which we propose will support maximisation of RAASi therapy. Methods We propose a 1:1 randomised, double-blind, placebo-controlled trial in which participants will receive either SZC or placebo. We will up-titrate participants’ RAASi therapy while monitoring their serum potassium levels and adjusting their SZC dose if necessary. Participants with CKD and HF will be recruited from CKD and HF clinics at St George’s Hospital. The total study period will be 18 months; 130 participants will be enrolled for approximately two months each following screening. Our primary outcome will be the proportion of participants who achieve maximum RAASi dose while maintaining normokalaemia. Secondary outcomes include participants reaching maximum RAASi dose without severe hyperkalaemia; time from randomisation to hyperkalaemia; time from randomisation to severe hyperkalaemia; number of RAASi dose escalations per participant; final doses of RAASi therapy; changes in quality of life score, eGFR, ACR, serum sodium, troponin T; number and duration of hospital admissions; and within-participant change in serum potassium compared to baseline. Discussion This trial will be the first to examine the use of SZC for the maximisation of RAASi dosing in patients with advanced CKD and HF. We will assess the impact of achieving target RAASi dosing on hospital admission rates and duration of stay, with the hope that optimum RAASi treatment will translate into reduced morbidity and improved QoL. If clinical benefit is demonstrated, we hope that the joint multidisciplinary CKD-HF approach will be expanded. Trial registration EudraCT number 2020–002946-18. Registered on 08 June 2020. Online record pending.

Hyperkalaemia in Heart Failure

Hyperkalaemia has become an increasingly prevalent finding in patients with heart failure (HF), especially with renin–angiotensin–aldosterone system (RAAS) inhibitors and angiotensin–neprilysin inhibitors being the cornerstone of medical therapy. Patients living with HF often have other comorbidities, such as diabetes and chronic kidney disease, which predispose to hyperkalaemia. Until now, we have not had any reliable or tolerable therapies for the treatment of hyperkalaemia to facilitate implementation or achievement of target doses of RAAS inhibition. Patiromer sorbitex calcium and sodium zirconium cyclosilicate are two novel potassium-binding resins that have shown promise in the management of patients predisposed to developing recurrent hyperkalaemia, and their use may allow for further optimisation of guideline directed medical therapy.

Crystal structures of non-oxidative decarboxylases reveal a new mechanism of action with a catalytic dyad and structural twists

Hydroxybenzoic acids, like gallic acid and protocatechuic acid, are highly abundant natural compounds. In biotechnology, they serve as critical precursors for various molecules in heterologous production pathways, but a major bottleneck is these acids’ non-oxidative decarboxylation to hydroxybenzenes. Optimizing this step by pathway and enzyme engineering is tedious, partly because of the complicating cofactor dependencies of the commonly used prFMN-dependent decarboxylases. Here, we report the crystal structures (1.5–1.9 Å) of two homologous fungal decarboxylases, AGDC1 from Arxula adenivorans, and PPP2 from Madurella mycetomatis. Remarkably, both decarboxylases are cofactor independent and are superior to prFMN-dependent decarboxylases when heterologously expressed in Saccharomyces cerevisiae. The organization of their active site, together with mutational studies, suggests a novel decarboxylation mechanism that combines acid–base catalysis and transition state stabilization. Both enzymes are trimers, with a central potassium binding site. In each monomer, potassium introduces a local twist in a β-sheet close to the active site, which primes the critical H86-D40 dyad for catalysis. A conserved pair of tryptophans, W35 and W61, acts like a clamp that destabilizes the substrate by twisting its carboxyl group relative to the phenol moiety. These findings reveal AGDC1 and PPP2 as founding members of a so far overlooked group of cofactor independent decarboxylases and suggest strategies to engineer their unique chemistry for a wide variety of biotechnological applications.

Patiromer and spironolactone in resistant hypertension and advanced CKD: analysis of the randomized AMBER trial

Background: Mineralocorticoid receptor antagonists reduce mortality in patients with heart failure with reduced ejection fraction and have become a standard of care in those with resistant hypertension (rHTN). Yet their use is limited among patients with chronic kidney disease (CKD), primarily due to hyperkalemia. Methods: AMBER was a multicenter, randomized, double-blind, placebo-controlled, parallel-group study which reported that the use of the potassium-binding drug patiromer allowed a more persistent use of spironolactone in patients with CKD and rHTN. In this report, we compare the safety and efficacy of patiromer in advanced CKD as a prespecified analysis. Results: Of the 295 patients randomized, 66 fell into the estimated glomerular filtration rate (eGFR) 25-<30 subgroup. In this subgroup, persistent use of spironolactone was seen in 19/34 (56%) in the placebo group and 27/32 (84%) in the patiromer group (absolute difference 29%, P=0.016). In the eGFR 30-45 subgroup, persistent use of spironolactone was seen in 79/114 (69%) in the placebo group and 99/115 (86%) in the patiromer group (absolute difference 17%, P=0.003). There was no significant interaction between eGFR subgroups (P=0.46). Systolic blood pressure (BP) reduction with spironolactone in the eGFR 25-<30 subgroup was 6-7 mmHg; in the eGFR 30-45 subgroup, it was 12-13 mmHg. There was no significant interaction between eGFR subgroups on BP reduction (P=0.79). Similar proportions of patients reported adverse events (59% in the eGFR 25-<30 subgroup; 53% in the eGFR 30-45 subgroup). Conclusion: Patiromer facilitates the use of spironolactone among patients with rHTN, and its efficacy and safety are comparable in those with eGFR 25-<30 and 30-45 mL/min/1.73m2.

Potassium Efflux and Cytosol Acidification as Primary Anoxia-Induced Events in Wheat and Rice Seedlings

Both ion fluxes and changes of cytosolic pH take an active part in the signal transduction of different environmental stimuli. Here we studied the anoxia-induced alteration of cytosolic K+ concentration, [K+]cyt, and cytosolic pH, pHcyt, in rice and wheat, plants with different tolerances to hypoxia. The [K+]cyt and pHcyt were measured by fluorescence microscopy in single leaf mesophyll protoplasts loaded with the fluorescent potassium-binding dye PBFI-AM and the pH-sensitive probe BCECF-AM, respectively. Anoxic treatment caused an efflux of K+ from protoplasts of both plants after a lag-period of 300–450 s. The [K+]cyt decrease was blocked by tetraethylammonium (1 mM, 30 min pre-treatment) suggesting the involvement of plasma membrane voltage-gated K+ channels. The protoplasts of rice (a hypoxia-tolerant plant) reacted upon anoxia with a higher amplitude of the [K+]cyt drop. There was a simultaneous anoxia-dependent cytosolic acidification of protoplasts of both plants. The decrease of pHcyt was slower in wheat (a hypoxia-sensitive plant) while in rice protoplasts it was rapid and partially reversible. Ion fluxes between the roots of intact seedlings and nutrient solutions were monitored by ion-selective electrodes and revealed significant anoxia-induced acidification and potassium leakage that were inhibited by tetraethylammonium. The K+ efflux from rice was more distinct and reversible upon reoxygenation when compared with wheat seedlings.