The carbon and nitrogen budget of Desmophyllum dianthus—a voracious cold-water coral thriving in an acidified Patagonian fjord

In the North Patagonian fjord region, the cold-water coral (CWC) Desmophyllum dianthus occurs in high densities, in spite of low pH and aragonite saturation. If and how these conditions affect the energy demand of the corals is so far unknown. In a laboratory experiment, we investigated the carbon and nitrogen (C, N) budget of D. dianthus from Comau Fjord under three feeding scenarios: (1) live fjord zooplankton (100–2,300 µm), (2) live fjord zooplankton plus krill (>7 mm), and (3) four-day food deprivation. In closed incubations, C and N budgets were derived from the difference between C and N uptake during feeding and subsequent C and N loss through respiration, ammonium excretion, release of particulate organic carbon and nitrogen (POC, PON). Additional feeding with krill significantly increased coral respiration (35%), excretion (131%), and POC release (67%) compared to feeding on zooplankton only. Nevertheless, the higher C and N losses were overcompensated by the threefold higher C and N uptake, indicating a high assimilation and growth efficiency for the krill plus zooplankton diet. In contrast, short food deprivation caused a substantial reduction in respiration (59%), excretion (54%), release of POC (73%) and PON (87%) compared to feeding on zooplankton, suggesting a high potential to acclimatize to food scarcity (e.g., in winter). Notwithstanding, unfed corals ‘lost’ 2% of their tissue-C and 1.2% of their tissue-N per day in terms of metabolism and released particulate organic matter (likely mucus). To balance the C (N) losses, each D. dianthus polyp has to consume around 700 (400) zooplankters per day. The capture of a single, large krill individual, however, provides enough C and N to compensate daily C and N losses and grow tissue reserves, suggesting that krill plays an important nutritional role for the fjord corals. Efficient krill and zooplankton capture, as well as dietary and metabolic flexibility, may enable D. dianthus to thrive under adverse environmental conditions in its fjord habitat; however, it is not known how combined anthropogenic warming, acidification and eutrophication jeopardize the energy balance of this important habitat-building species.

MO443EFFECTS OF SHORT-TERM POTASSIUM CHLORIDE SUPPLEMENTATION IN PATIENTS WITH CHRONIC KIDNEY DISEASE*

Background and Aims A high potassium (K+) diet is part of a healthy lifestyle and reduces blood pressure. Indeed, salt substitution (replacing NaCl by KCl) reduces the incidence of hypertension. Furthermore, emerging data show that high urinary K+ excretion in patients with chronic kidney disease (CKD) is associated with better kidney outcomes. This suggests that higher dietary K+ intake is also beneficial for patients with CKD, but a potential concern is hyperkalemia. Thus, there is a need for data on the effects of KCl supplementation in patients with CKD. Methods The effect of KCl supplementation (40 mEq/day) was studied by analyzing the 2-week open-label run-in phase of an ongoing randomized clinical trial studying the renoprotective effects of 2-year K+ supplementation in patients with progressive CKD and hypertension. The aims were to (1) analyze the effects of KCl supplementation on whole-blood K+ (WBK+) and acid-base balance, (2) identify factors associated with a rise in WBK+, and (3) identify risk factors for hyperkalemia (WBK+ > 5.5 mEq/L) . Results In 200 patients (68 ± 11 years, 74% males, eGFR 32 ± 9 mL/min/1.73 m2, 84% on renin-angiotensin inhibitors, 39% with diabetes mellitus), KCl supplementation increased urinary K+ excretion from 73 ± 24 to 106 ± 29 mEq/day, urinary chloride excretion from 144 ± 63 to 174 ± 60 mEq/day, WBK+ from 4.3 ± 0.5 to 4.7 ± 0.6 mEq/L, and plasma aldosterone from 294 to 366 ng/L (P < 0.01 for all). Plasma chloride increased from 104 ± 4 to 106 ± 4 mEq/L, while plasma bicarbonate decreased from 24.4 ± 3.4 to 23.6 ± 3.5 mEq/L and venous pH from 7.36 ± 0.03 to 7.34 ± 0.04 (P < 0.001 for all); urinary ammonium excretion did not increase (stable at 17.2 mEq/day). KCl supplementation had no significant effect on plasma renin (33 to 39 pg/mL), urinary sodium excretion (156 ± 63 to 155 ± 65 mEq/day), systolic blood pressure (134 ± 16 to 133 ± 17 mm Hg), eGFR (32 ± 9 to 31 ± 8 mL/min/1.73 m2) or albuminuria (stable at 0.2 g/day). Multivariable linear regression identified that age, female sex, and renin-angiotensin inhibitor use were associated with an increase in WBK+, while diuretic use, baseline WBK+, and baseline bicarbonate were inversely associated with a change in WBK+ after KCl supplementation (Table 1). The majority of patients (n = 181, 91%) remained normokalemic (WBK+ 4.6 ± 0.4 mEq/L). The 19 patients who did develop hyperkalemia (WBK+ 5.9 ± 0.4 mEq/L) were older (75 ± 8 vs. 67 ± 11 years), had lower eGFR (24 ± 8 vs. 32 ± 8 mL/min/1.73 m2), lower baseline bicarbonate (22.3 ± 3.6 vs. 24.6 ± 3.3 mEq/L), higher baseline WBK+ (4.8 ± 0.4 vs. 4.2 ± 0.4 mEq/L), and lower baseline urinary K+ excretion (64 ± 16 vs. 73 ± 25 mEq/day, P < 0.05 for all). Conclusions The majority of patients with advanced CKD remains normokalemic upon KCl supplementation, despite low eGFR, diabetes mellitus, or the use of renin-angiotensin inhibitors. This short-term study illustrates the feasibility of investigating the renoprotective potential of increased K+ intake or KCl-enriched salt in patients with CKD and provides the characteristics of patients in whom this is safe. Our study also shows that KCl supplementation causes a tendency towards metabolic acidosis, possibly by preventing an increase in ammoniagenesis. Longer-term studies are required to study the anti-hypertensive and renoprotective potential of K+ supplementation.

A chronic high phosphate intake in mice is detrimental for bone health without major renal alterations

Background Phosphate intake has increased in the last decades due to a higher consumption of processed foods. This higher intake is detrimental for patients with chronic kidney disease, increasing mortality and cardiovascular disease risk and accelerating kidney dysfunction. Whether a chronic high phosphate diet is also detrimental for the healthy population is still under debate. Methods We fed healthy mature adult mice over a period of one year with either a high (1.2% w/w) or a standard (0.6% w/w) phosphate diet, and investigated the impact of a high phosphate diet on mineral homeostasis, kidney function and bone health. Results The high phosphate diet increased plasma phosphate, parathyroid hormone (PTH) and calcitriol levels, with no change in fibroblast growth factor 23 levels. Urinary phosphate, calcium and ammonium excretion were increased. Measured glomerular filtration rate was apparently unaffected, while blood urea was lower and urea clearance was higher in animals fed the high phosphate diet. No change was observed in plasma creatinine levels. Blood and urinary pH were more acidic paralleled by higher bone resorption observed in animals fed a high phosphate diet. Total and cortical bone mineral density was lower in animals fed a high phosphate diet and this effect is independent of the higher PTH levels observed. Conclusions A chronic high phosphate intake did not cause major renal alterations, but affected negatively bone health, increasing bone resorption and decreasing bone mineral density.

Effect of sodium bicarbonate supplementation on the renin-angiotensin system in patients with chronic kidney disease and acidosis: a randomized clinical trial

Background Acidosis-induced kidney injury is mediated by the intrarenal renin-angiotensin system, for which urinary renin is a potential marker. Therefore, we hypothesized that sodium bicarbonate supplementation reduces urinary renin excretion in patients with chronic kidney disease (CKD) and metabolic acidosis. Methods Patients with CKD stage G4 and plasma bicarbonate 15–24 mmol/l were randomized to receive sodium bicarbonate (3 × 1000 mg/day, ~ 0.5 mEq/kg), sodium chloride (2 × 1,00 mg/day), or no treatment for 4 weeks (n = 15/arm). The effects on urinary renin excretion (primary outcome), other plasma and urine parameters of the renin-angiotensin system, endothelin-1, and proteinuria were analyzed. Results Forty-five patients were included (62 ± 15 years, eGFR 21 ± 5 ml/min/1.73m2, plasma bicarbonate 21.7 ± 3.3 mmol/l). Sodium bicarbonate supplementation increased plasma bicarbonate (20.8 to 23.8 mmol/l) and reduced urinary ammonium excretion (15 to 8 mmol/day, both P < 0.05). Furthermore, a trend towards lower plasma aldosterone (291 to 204 ng/L, P = 0.07) and potassium (5.1 to 4.8 mmol/l, P = 0.06) was observed in patients receiving sodium bicarbonate. Sodium bicarbonate did not significantly change the urinary excretion of renin, angiotensinogen, aldosterone, endothelin-1, albumin, or α1-microglobulin. Sodium chloride supplementation reduced plasma renin (166 to 122 ng/L), and increased the urinary excretions of angiotensinogen, albumin, and α1-microglobulin (all P < 0.05). Conclusions Despite correction of acidosis and reduction in urinary ammonium excretion, sodium bicarbonate supplementation did not improve urinary markers of the renin-angiotensin system, endothelin-1, or proteinuria. Possible explanations include bicarbonate dose, short treatment time, or the inability of urinary renin to reflect intrarenal renin-angiotensin system activity. Graphic abstract

Serum bicarbonate is associated with kidney outcomes in autosomal dominant polycystic kidney disease

Graphical Abstract Background Metabolic acidosis accelerates progression of chronic kidney disease, but whether this is also true for autosomal dominant polycystic kidney disease (ADPKD) is unknown. Methods Patients with ADPKD from the DIPAK (Developing Interventions to halt Progression of ADPKD) trial were included [n = 296, estimated glomerular filtration rate (eGFR) 50 ± 11 mL/min/1.73 m2, 2.5 years follow-up]. Outcomes were worsening kidney function (30% decrease in eGFR or kidney failure), annual eGFR change and height-adjusted total kidney and liver volumes (htTKV and htTLV). Cox and linear regressions were adjusted for prognostic markers for ADPKD [Mayo image class and predicting renal outcomes in ADPKD (PROPKD) scores] and acid–base parameters (urinary ammonium excretion). Results Patients in the lowest tertile of baseline serum bicarbonate (23.1 ± 1.6 mmol/L) had a significantly greater risk of worsening kidney function [hazard ratio = 2.95, 95% confidence interval (CI) 1.21–7.19] compared with patients in the highest tertile (serum bicarbonate 29.0 ± 1.3 mmol/L). Each mmol/L decrease in serum bicarbonate increased the risk of worsening kidney function by 21% in the fully adjusted model (hazard ratio = 1.21, 95% CI 1.06–1.37). Each mmol/L decrease of serum bicarbonate was also associated with further eGFR decline (−0.12 mL/min/1.73 m2/year, 95% CI −0.20 to −0.03). Serum bicarbonate was not associated with changes in htTKV or htTLV growth. Conclusions In patients with ADPKD, a lower serum bicarbonate within the normal range predicts worse kidney outcomes independent of established prognostic factors for ADPKD and independent of urine ammonium excretion. Serum bicarbonate may add to prognostic models and should be explored as a treatment target in ADPKD.

LITHORISK.COM: the novel version of a software for calculating and visualizing the risk of renal stone

Estimation of state of saturation with stone-forming salt represents a reliable tool to assess the overall risk. The available methods are based on computer-assisted ab initio calculations. Our earlier method URSUS was subsequently substituted by Lithorisk®, a software including visualization of risk profiles. Unfortunately, Lithorisk does not adapt to new versions of Windows® and Macintosh® Apple, neither runs on smartphones or tablets. We propose a novel version of the software which can be directly used online on any device equipped by different operating systems. Upon online connection and after registration, the software is ready for unlimited accesses, in either Italian, English or French. After digiting input variables (urea and creatinine also included) in a fixed dashboard, state of saturation is promptly given. In addition to state of saturation (ß) with calcium oxalate, brushite and uric acid, ß struvite and cystine are available. Both input variables and ß results are graphically depicted as green or red horizontal bars to indicate recommended values. The software was implemented with equations allowing to omit sulphate and ammonium excretion for users with difficult access to these measurements. This simplified version, tested for ßCaOx and ßBsh on 100 urine samples showed close correlation with the full version. The software gives a list of total and free concentrations and soluble complex species distribution. Results can be printed or saved as PDF. So, we propose an easily accessible software to estimate state of saturation usable on any operating system and personal device.

Acute and sub-chronic effects of copper on survival, respiratory metabolism, and metal accumulation in Cambaroides dauricus

Trace metal contamination in the aquatic ecosystem occurs worldwide: although copper is an essential trace metal, it is considered as a pollutant at certain levels in China. Freshwater crayfish Cambaroides dauricus is a commercially important wild species in northeastern China, in which is an important heavy industry area. The population of C. dauricus was decreasing sharply due to the environmental pollution and human intervention over the past 20 years. However, nothing is known regarding the responses of this species to trace metal toxicants. This study aimed to determine the acute and chronic toxicity of Cu and its toxicological effects on respiratory metabolism, as well as Cu accumulation in C. dauricus. The acute (96 h) median lethal concentration (LC50) value of 32.5 mg/L was detected in C. dauricus. Then, acute (96 h; 8.24, 16.48 mg/L) and sub-chronic (14 days; 2.06, 4.12 mg/L) exposure in Cu was investigated by estimating the oxygen consumption rate, ammonium excretion rate, and Cu accumulation. Both acute and sub-chronic Cu exposure induced an inhibition of the oxygen consumption rate and ammonium excretion rate, and thereby, an increased O:N ratio. The shift in O:N ratio indicated a metabolic substrate shift towards lipid and carbohydrate metabolism under Cu stress. Cu accumulation in the hepatopancreas and muscles throughout the study was found to be time-dependent and concentration-dependent. The maximum accumulation in the hepatopancreas and muscle were almost 31.6 folds of the control after 14 days’ exposure to 4.12 mg/L concentration. Based on the present work, we suggest that crayfish be considered a potential bioindicator of environmental pollution in freshwater systems. The study provides basic information for further understanding of the toxicological responses of this species to trace metals.

Key biological responses over two generations of the sea urchin Echinometra sp. A under future ocean conditions

Few studies have investigated the effects of ocean warming and acidification on marine benthic organisms over ecologically relevant time scales. We used an environmentally controlled coral reef mesocosm system to assess growth and physiological responses of the sea urchin species Echinometra sp. A over 2 generations. Each mesocosm was controlled for temperature and pCO2 over 29 mo under 3 climate change scenarios (present day and predicted states in 2050 and 2100 under RCP 8.5). The system maintained treatment conditions including annual temperature cycles and a daily variation in pCO2. Over 20 mo, adult Echinometra exhibited no significant difference in size and weight among the treatments. Growth rates and respiration rates did not differ significantly among treatments. Urchins from the 2100 treatment had elevated ammonium excretion rates and reduced O2:N ratios, suggesting a change in catabolism. We detected no difference in spawning index scores or oocyte size after 20 mo in the treatments, suggesting that gonad development was not impaired by variations in pCO2 and temperature reflecting anticipated climate change scenarios. Larvae produced from experimentally exposed adults were successfully settled from all treatments and raised for 5 mo inside the mesocosm. The final size of these juveniles exhibited no significant difference among treatments. Overall, we demonstrated that the mesocosm system provided a near natural environment for this urchin species. Climate change and ocean acidification did not affect the benthic life stages investigated here. Importantly, in previous short-term (weeks to months) experiments, this species exhibited reductions in growth and gonad development, highlighting the potential for short-term experiments with non-acclimated animals to yield contrasting, possibly erroneous results.

Sodium Bicarbonate Supplementation and Urinary TGF-β1 in Nonacidotic Diabetic Kidney Disease

Background and objectivesIn early-phase studies of individuals with hypertensive CKD and normal serum total CO2, sodium bicarbonate reduced urinary TGF-β1 levels and preserved kidney function. The effect of sodium bicarbonate on kidney fibrosis and injury markers in individuals with diabetic kidney disease and normal serum total CO2 is unknown.Design, setting, participants, & measurementsWe conducted a randomized, double-blinded, placebo-controlled study in 74 United States veterans with type 1 or 2 diabetes mellitus, eGFR of 15–89 ml/min per 1.73 m2, urinary albumin-to-creatinine ratio (UACR) ≥30 mg/g, and serum total CO2 of 22–28 meq/L. Participants received oral sodium bicarbonate (0.5 meq/kg lean body wt per day; n=35) or placebo (n=39) for 6 months. The primary outcome was change in urinary TGF-β1-to-creatinine from baseline to months 3 and 6. Secondary outcomes included changes in urinary kidney injury molecule-1 (KIM-1)-to-creatinine, fibronectin-to-creatinine, neutrophil gelatinase-associated lipocalin (NGAL)-to-creatinine, and UACR from baseline to months 3 and 6.ResultsKey baseline characteristics were age 72±8 years, eGFR of 51±18 ml/min per 1.73 m2, and serum total CO2 of 24±2 meq/L. Sodium bicarbonate treatment increased mean total CO2 by 1.2 (95% confidence interval [95% CI], 0.3 to 2.1) meq/L, increased urinary pH by 0.6 (95% CI, 0.5 to 0.8), and decreased urinary ammonium excretion by 5 (95% CI, 0 to 11) meq/d and urinary titratable acid excretion by 11 (95% CI, 5 to 18) meq/d. Sodium bicarbonate did not significantly change urinary TGF-β1/creatinine (difference in change, 13%, 95% CI, −10% to 40%; change within the sodium bicarbonate group, 8%, 95% CI, −10% to 28%; change within the placebo group, −4%, 95% CI, −19% to 13%). Similarly, no significant effect on KIM-1-to-creatinine (difference in change, −10%, 95% CI, −38% to 31%), fibronectin-to-creatinine (8%, 95% CI, −15% to 37%), NGAL-to-creatinine (−33%, 95% CI, −56% to 4%), or UACR (1%, 95% CI, −25% to 36%) was observed.ConclusionsIn nonacidotic diabetic kidney disease, sodium bicarbonate did not significantly reduce urinary TGF-β1, KIM-1, fibronectin, NGAL, or UACR over 6 months.