Regulation of kidney on potassium balance and its clinical significance / 生理学报

Virtually all of the dietary potassium intake is absorbed in the intestine, over 90% of which is excreted by the kidneys regarded as the most important organ of potassium excretion in the body. The renal excretion of potassium results primarily from the secretion of potassium by the principal cells in the aldosterone-sensitive distal nephron (ASDN), which is coupled to the reabsorption of Na+ by the epithelial Na+ channel (ENaC) located at the apical membrane of principal cells. When Na+ is transferred from the lumen into the cell by ENaC, the negativity in the lumen is relatively increased. K+ efflux, H+ efflux, and Cl- influx are the 3 pathways that respond to Na+ influx, that is, all these 3 pathways are coupled to Na+ influx. In general, Na+ influx is equal to the sum of K+ efflux, H+ efflux, and Cl- influx. Therefore, any alteration in Na+ influx, H+ efflux, or Cl- influx can affect K+ efflux, thereby affecting the renal K+ excretion. Firstly, Na+ influx is affected by the expression level of ENaC, which is mainly regulated by the aldosterone-mineralocorticoid receptor (MR) pathway. ENaC gain-of-function mutations (Liddle syndrome, also known as pseudohyperaldosteronism), MR gain-of-function mutations (Geller syndrome), increased aldosterone levels (primary/secondary hyperaldosteronism), and increased cortisol (Cushing syndrome) or deoxycorticosterone (hypercortisolism) which also activate MR, can lead to up-regulation of ENaC expression, and increased Na+ reabsorption, K+ excretion, as well as H+ excretion, clinically manifested as hypertension, hypokalemia and alkalosis. Conversely, ENaC inactivating mutations (pseudohypoaldosteronism type 1b), MR inactivating mutations (pseudohypoaldosteronism type 1a), or decreased aldosterone levels (hypoaldosteronism) can cause decreased reabsorption of Na+ and decreased excretion of both K+ and H+, clinically manifested as hypotension, hyperkalemia, and acidosis. The ENaC inhibitors amiloride and Triamterene can cause manifestations resembling pseudohypoaldosteronism type 1b; MR antagonist spironolactone causes manifestations similar to pseudohypoaldosteronism type 1a. Secondly, Na+ influx is regulated by the distal delivery of water and sodium. Therefore, when loss-of-function mutations in Na+-K+-2Cl- cotransporter (NKCC) expressed in the thick ascending limb of the loop and in Na+-Cl- cotransporter (NCC) expressed in the distal convoluted tubule (Bartter syndrome and Gitelman syndrome, respectively) occur, the distal delivery of water and sodium increases, followed by an increase in the reabsorption of Na+ by ENaC at the collecting duct, as well as increased excretion of K+ and H+, clinically manifested as hypokalemia and alkalosis. Loop diuretics acting as NKCC inhibitors and thiazide diuretics acting as NCC inhibitors can cause manifestations resembling Bartter syndrome and Gitelman syndrome, respectively. Conversely, when the distal delivery of water and sodium is reduced (e.g., Gordon syndrome, also known as pseudohypoaldosteronism type 2), it is manifested as hypertension, hyperkalemia, and acidosis. Finally, when the distal delivery of non-chloride anions increases (e.g., proximal renal tubular acidosis and congenital chloride-losing diarrhea), the influx of Cl- in the collecting duct decreases; or when the excretion of hydrogen ions by collecting duct intercalated cells is impaired (e.g., distal renal tubular acidosis), the efflux of H+ decreases. Both above conditions can lead to increased K+ secretion and hypokalemia. In this review, we focus on the regulatory mechanisms of renal potassium excretion and the corresponding diseases arising from dysregulation.

The mechanisms and clinical potential: sodium-glucose cotransporter 2 (SGLT-2) inhibitors treating diabetic kidney disease / 生理学报

The employment of sodium-glucose cotransporter 2 (SGLT-2) inhibitors in the treatment of diabetes mellitus and diabetic kidney disease (DKD) becomes a hot topic in recent years. Compared with traditional glucose-lowering drugs, SGLT-2 inhibitors present distinctive advantages in renal and cardiovascular protection. The mechanisms for renal protection include attenuating glomerular hyperfiltration, lowering serum uric acid, alleviating tubular lesions and regulating intrarenal renin-angiotensin-aldosterone system (RAAS) dysfunction. In addition, the lowering blood pressure, blunting blood glucose fluctuation, increasing insulin sensitivity, optimizing energy metabolism and body fat distribution account for the cardiovascular protective effects of SGLT-2 inhibitors. However, their potential adverse reactions and safety concerns should be carefully addressed in clinical usage.

Renal Phospholipase A2 Receptor and the Clinical Features of Idiopathic Membranous Nephropathy / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>According to the renal phospholipase A2 receptor (PLA2R) immunohistochemistry, idiopathic membranous nephropathy (iMN) could be categorized into PLA2R-associated and non-PLA2R-associated iMN. This study aimed to examine whether the non-PLA2R-associated iMN had any difference in clinical features compared with PLA2R-associated iMN.</p><p><b>METHODS</b>A total of 231 adult patients diagnosed as iMN were recruited to this retrospective study. Renal PLA2R expression was examined by immunofluorescence. Among these patients, 186 (80.5%) with complete baseline clinical data were used for further study. Urinary protein excretion, serum albumin, and creatinine were analyzed. For those patients with follow-up longer than 1 year, the relationship between PLA2R and response to immunosuppressants were analyzed. The t-test was used for parametric analysis and the Mann-Whitney U-test was used for nonparametric analysis. Categorical variables were described as frequencies or percentages, and the data were analyzed with Pearson's Chi-square test or Fisher's exact test.</p><p><b>RESULTS</b>Of the 231 iMN patients, 189 showed renal detectable PLA2R expression (81.8%). The baseline serum creatinine, serum albumin, and urine protein excretion were not significantly different between PLA2R-associated (n = 145) and non-PLA2R-associated iMN patients (n = 41). However, about 1/3 of the non-PLA2R-associated iMN had abnormal serological tests, significantly more common than PLA2R-associated iMN (31.7% vs. 8.3%, P = 0.000). The non-PLA2R-associated iMN had lower C4 levels compared with PLA2R-associated iMN (P = 0.004). The non-PLA2R-associated iMN patients also showed a better response to immunosuppressants (complete remission [CR] 42.9%; partial remission [PR] 14.3%) compared with PLA2R-associated iMN (CR 3.2%; PR 48.4%, P = 0.004) at the 3rd month.</p><p><b>CONCLUSIONS</b>There were no significant differences in serum creatinine, albumin, and urine protein excretion between PLA2R-associated and non-PLA2R-associated iMN, while the non-PLA2R-associated iMN patients showed more abnormal serological tests. The non-PLA2R-associated iMN seemed to respond more quickly to the immunosuppressive therapy compared with PLA2R-associated iMN.</p>

Effects of selective cyclooxygenase 2 inhibitor on the hyperplasia of parathyroid glands from uremic rats / 中华肾脏病杂志

Objective To investigate the effects of selective cyclooxygenase 2 inhibitor on the hyperplasia of parathyroid glands from uremic rats. Methods Sixty-five 5/6-nephrectomized (Nx) and fifteen sham operated rats were assigned to 4 groups: (1)Sham group (n=14):shamoperated +normal phosphate diet (P 0.8％,Ca 1.2％)； (2) Nx-HP group (n=17):Nx+high phosphate(HP) diet (P 1.2％,Ca 1.2％)； (3)Prophylactic COX2 inhibition group (Prey group,n=18):Nx+HP+celecoxib 100 mg· kg-1·d-1 for 3 months； (4)Therapeutic group (Ther group,n=18):Nx+HP+celecoxib 100 mg·kg-1·d-1 starting at the second month of the 5/6 nephrectomy.At the end of 3 month,blood,urine and parathyroid samples were collected.The expressions of COX2 and PCNA were determined by immunohistochemistry,Western blotting and real-time PCR. Results All of the Nx rats fed with high phosphate diet for 3 months manifested progressively increasing serum creatinine,serum iPTH as well as augmentation of parathyroid gland volume,suggesting that secondary parathyroid hyperplasia animal model was established successfully.Celecoxib significantly decreased serum iPTH levels [Sham (34.77±0.83),Nx-HP(100.73±4.35),Prey (87.36±2.18),Ther (87.47±1.76) ng/L,P＜0.05],the size of the parathyroid glands in Nx rats [Sham (0.461±0.089),Nx-HP (2.436±0.372),Prey (0.987±0.254),Ther (1.27±0.305) mm2/kg,P＜0.05] and PCNA expression in PG determined by Western blotting (decreased to 52.91％ in Prev group and 34.68％ in Ther group respectively,P＜0.05).No significant difference was observed between the two COX2 inhibition groups.The levels of COX2 expression in parathyroid gland were greatly increased in three Nx groups compared with that in sham group (2.47-fold in Nx-HP,2.34-fold in Prey group,3.04-fold in Ther group,P＜0.05).COX2 inhibitor had no effects on COX2 expression in PGs.Real-time PCR analysis demonstrated the same trends of mRNA expression of COX2 and PCNA in PGs of rats. Conclusion Selective inhibition of COX2 may help to suppress the hyperplasia of parathyroid glands in uremic rats.

Expression of nestin in human kidney and its clinical significance / 中华病理学杂志

<p><b>OBJECTIVE</b>To study the expression and significance of nestin (a type of cytoskeletal protein) in normal and diseased human kidneys.</p><p><b>METHODS</b>Diseased kidney tissues were obtained from needle biopsies in 32 patients with glomerulonephritis (including 8 cases of membranous glomerulopathy, 3 cases of focal segmental glomerulosclerosis, 17 cases of IgA nephropathy with proteinuria and 4 cases of IgA nephropathy without proteinuria). Control kidney tissues were obtained from nephrectomy specimens for renal tumors. The expression of nestin in the control kidney tissues was studied using immunoelectronic microscopy and immunohistochemistry. The expression of nestin in the diseased kidney tissues was detected by immunohistochemistry and real-time reverse transcription-polymerase chain reaction.</p><p><b>RESULTS</b>In normal kidney tissues, nestin was detected at the periphery of glomerular capillary loops. Semi-quantitative morphometric analysis showed that the glomerular nestin expression level in cases of IgA nephropathy without proteinuria did not differ from that in the normal controls. However, the glomerular nestin expression levels in cases of IgA nephropathy with proteinuria, membranous glomerulopathy and focal segmental glomerulosclerosis were significantly lower than those in the normal kidneys and IgA nephropathy without proteinuria. The glomerular nestin expression levels inversely correlated with the 24-hour urine protein results.</p><p><b>CONCLUSION</b>Nestin may play an important role in maintaining the normal function of podocytes in human kidney.</p>