Altered renal hemodynamics in mice overexpressing the parathyroid hormone (PTH)/PTH-related peptide type 1 receptor in smooth muscle

The Molecular Mechanisms Underlying the Systemic Effects Mediated by Parathormone in the Context of Chronic Kidney Disease

Chronic kidney disease (CKD) stands as a prominent non-communicable ailment, significantly impacting life expectancy. Physiopathology stands mainly upon the triangle represented by parathormone-Vitamin D-Fibroblast Growth Factor-23. Parathormone (PTH), the key hormone in mineral homeostasis, is one of the less easily modifiable parameters in CKD; however, it stands as a significant marker for assessing the risk of complications. The updated "trade-off hypothesis" reveals that levels of PTH spike out of the normal range as early as stage G2 CKD, advancing it as a possible determinant of systemic damage. The present review aims to review the effects exhibited by PTH on several organs while linking the molecular mechanisms to the observed actions in the context of CKD. From a diagnostic perspective, PTH is the most reliable and accessible biochemical marker in CKD, but its trend bears a higher significance on a patient's prognosis rather than the absolute value. Classically, PTH acts in a dichotomous manner on bone tissue, maintaining a balance between formation and resorption. Under the uremic conditions of advanced CKD, the altered intestinal microbiota majorly tips the balance towards bone lysis. Probiotic treatment has proven reliable in animal models, but in humans, data are limited. Regarding bone status, persistently high levels of PTH determine a reduction in mineral density and a concurrent increase in fracture risk. Pharmacological manipulation of serum PTH requires appropriate patient selection and monitoring since dangerously low levels of PTH may completely inhibit bone turnover. Moreover, the altered mineral balance extends to the cardiovascular system, promoting vascular calcifications. Lastly, the involvement of PTH in the Renin-Angiotensin-Aldosterone axis highlights the importance of opting for the appropriate pharmacological agent should hypertension develop.

Sacubitril/valsartan ameliorates renal tubulointerstitial injury through increasing renal plasma flow in a mouse model of type 2 diabetes with aldosterone excess

BACKGROUND

Aldosterone has been assumed to be one of aggravating factors in diabetic kidney disease (DKD). Natriuretic peptides/guanylyl cyclase-A/cGMP signalling has been shown to ameliorate aldosterone-induced renal injury in mice. Sacubitril/valsartan (SAC/VAL) is used clinically for chronic heart failure and hypertension, in part by augmenting natriuretic peptide bioavailability. The effects of SAC/VAL on renal pathophysiology including in DKD, however, have remained unclarified.

METHODS

Eight-week-old male db/db mice fed on a high-salt diet (HSD) were treated with vehicle or aldosterone (0.2 μg/kg/min), and divided into four groups: HSD control, ALDO (aldosterone), ALDO + VAL (valsartan), and ALDO + SAC/VAL group. After 4 weeks, they were analysed for plasma atrial natriuretic peptide (ANP) levels, renal histology, and haemodynamic parameters including glomerular filtration rate (GFR) by FITC-inulin and renal plasma flow (RPF) by para-amino hippuric acid.

RESULTS

The ALDO + SAC/VAL group showed significantly increased plasma ANP concentration and creatinine clearance, and decreased tubulointerstitial fibrosis and neutrophil gelatinase-associated lipocalin expression compared to ALDO and ALDO + VAL groups. SAC/VAL treatment increased GFR and RPF, and suppressed expression of Tgfb1, Il1b, Ccl2, and Lcn2 genes compared to the ALDO group. The percentage of tubulointerstitial fibrotic areas negatively correlated with the RPF and GFR.

CONCLUSION

In a mouse model of type 2 diabetes with aldosterone excess, SAC/VAL increased RPF and GFR, and ameliorated tubulointerstitial fibrosis. Furthermore, RPF negatively correlated well with tubulointerstitial injury, suggesting that the beneficial effects of SAC/VAL could be through increased renal plasma flow with enhanced natriuretic peptide bioavailability.

Bone development and mineral homeostasis in the fetus and neonate: roles of the calciotropic and phosphotropic hormones

Mineral and bone metabolism are regulated differently in utero compared with the adult. The fetal kidneys, intestines, and skeleton are not dominant sources of mineral supply for the fetus. Instead, the placenta meets the fetal need for mineral by actively transporting calcium, phosphorus, and magnesium from the maternal circulation. These minerals are maintained in the fetal circulation at higher concentrations than in the mother and normal adult, and such high levels appear necessary for the developing skeleton to accrete a normal amount of mineral by term. Parathyroid hormone (PTH) and calcitriol circulate at low concentrations in the fetal circulation. Fetal bone development and the regulation of serum minerals are critically dependent on PTH and PTH-related protein, but not vitamin D/calcitriol, fibroblast growth factor-23, calcitonin, or the sex steroids. After birth, the serum calcium falls and phosphorus rises before gradually reaching adult values over the subsequent 24-48 h. The intestines are the main source of mineral for the neonate, while the kidneys reabsorb mineral, and bone turnover contributes mineral to the circulation. This switch in the regulation of mineral homeostasis is triggered by loss of the placenta and a postnatal fall in serum calcium, and is followed in sequence by a rise in PTH and then an increase in calcitriol. Intestinal calcium absorption is initially a passive process facilitated by lactose, but later becomes active and calcitriol-dependent. However, calcitriol's role can be bypassed by increasing the calcium content of the diet, or by parenteral administration of calcium.

Knockdown of parathyroid hormone related protein in smooth muscle cells alters renal hemodynamics but not blood pressure

Parathyroid hormone-related protein (PTHrP) belongs to vasoactive factors that regulate blood pressure and renal hemodynamics both by reducing vascular tone and raising renin release. PTHrP is expressed in systemic and renal vasculature. Here, we wanted to assess the contribution of vascular smooth muscle cell endogenous PTHrP to the regulation of cardiovascular and renal functions. We generated a mouse strain (SMA-CreERT2/PTHrPL2/L2 or premutant PTHrPSM-/-), which allows temporally controlled, smooth muscle-targeted PTHrP knockdown in adult mice. Tamoxifen treatment induced efficient recombination of PTHrP-floxed alleles and decreased PTHrP expression in vascular and visceral smooth muscle cells of PTHrPSM-/- mice. Blood pressure remained unchanged in PTHrPSM-/- mice, but plasma renin concentration and creatinine clearance were reduced. Renal hemodynamics were further analyzed during clearance measurements in anesthetized mice. Conditional knockdown of PTHrP decreased renal plasma flow and glomerular filtration rate with concomitant reduction in filtration fraction. Similar measurements were repeated during acute saline volume expansion. Saline volume expansion induced a rise in renal plasma flow and reduced filtration fraction; both were blunted in PTHrPSM-/- mice leading to impaired diuresis. These findings show that endogenous vascular smooth muscle PTHrP controls renal hemodynamics under basal conditions, and it is an essential factor in renal vasodilation elicited by saline volume expansion.

Parathyroidectomy after kidney transplantation: short-and long-term impact on renal function

INTRODUCTION

Kidney transplantation corrects endocrine imbalances. Nevertheless, these early favorable events are not always followed by rapid normalization of parathyroid hormone secretion. A possible deleterious effect of parathyroidectomy on kidney transplant function has been reported. This study aimed to compare acute and longterm renal changes after total parathyroidectomy with those occurring after general surgery.

MATERIALS AND METHODS

This was a retrospective case-controlled study. Nineteen patients with persistent hyperparathyroidism underwent parathyroidectomy due to hypercalcemia. The control group included 19 patients undergoing various general and urological operations.

RESULTS

In the parathyroidectomy group, a significant increase in serum creatinine from 1.58 to 2.29 mg/dl (P < 0.05) was noted within the first 5 days after parathyroidectomy. In the control group, a statistically insignificant increase in serum creatinine from 1.49 to 1.65 mg/dl occurred over the same time period. The long-term mean serum creatinine level was not statistically different from baseline either in the parathyroidectomy group (final follow-up creatinine = 1.91 mg/dL) or in the non-parathyroidectomy group (final follow-up creatinine = 1.72 mg/dL).

CONCLUSION

Although renal function deteriorates in the acute period following parathyroidectomy, long-term stabilization occurs, with renal function similar to both preoperative function and to a control group of kidney-transplanted patients who underwent other general surgical operations by the final follow up.