Chlorthalidone with potassium citrate decreases calcium oxalate stones and increases bone quality in genetic hypercalciuric stone-forming rats

Abstract

To study human idiopathic hypercalciuria we developed an animal model, genetic hypercalciuric stone-forming rats, whose pathophysiology parallels that of human idiopathic hypercalciuria. Fed the oxalate precursor, hydroxyproline, every rat in this model develops calcium oxalate stones. Using this rat model, we tested whether chlorthalidone and potassium citrate combined would reduce calcium oxalate stone formation and improve bone quality more than either agent alone. These rats (113 generation) were fed a normal calcium and phosphorus diet with hydroxyproline and divided into four groups: diets plus potassium chloride as control, potassium citrate, chlorthalidone plus potassium chloride, or potassium citrate plus chlorthalidone. Urine was collected at six, 12, and 18 weeks and kidney stone formation and bone parameters were determined. Compared to potassium chloride, potassium citrate reduced urinary calcium, chlorthalidone reduced it further and potassium citrate plus chlorthalidone even further. Potassium citrate plus chlorthalidone decreased urine oxalate compared to all other groups. There were no significant differences in calcium oxalate supersaturation in any group. Neither potassium citrate nor chlorthalidone altered stone formation. However, potassium citrate plus chlorthalidone significantly reduced stone formation. Vertebral trabecular bone increased with chlorthalidone and potassium citrate plus chlorthalidone. Cortical bone area increased with chlorthalidone but not potassium citrate or potassium citrate plus chlorthalidone. Mechanical properties of trabecular bone improved with chlorthalidone, but not with potassium citrate plus chlorthalidone. Thus in genetic hypercalciuric stone-forming rats fed a diet resulting in calcium oxalate stone formation, potassium citrate plus chlorthalidone prevented stone formation better than either agent alone. Chlorthalidone alone improved bone quality, but adding potassium citrate provided no additional benefit.

Keywords: calcium oxalate; chlorthalidone; hypercalciuria; nephrolithiasis; potassium citrate.

Figure 1.. Urine calcium, citrate and phosphate.

Rat diets were all supplemented hydroxyproline and with either KCl (4 mmol/d) as a control, potassium citrate (KCit, 4 mmol/d), chlorthalidone (CTD, 4-5mg/kg/d)+KCl or KCit+CTD. Twenty-four-hour urine collections were done at 6, 12 and 18 wks for analysis of solute levels as described in Methods and an overall mean of all three collections was calculated. Results are mean±SE for 10 rats/group. *p<0.05 vs KCl, ^op<0.05 vs KCit alone, ^#p<0.05 vs CTD alone.

Figure 2.. Urine oxalate, NH₄ and pH.

Rat diets were all supplemented hydroxyproline and with either KCl (4 mmol/d) as a control, potassium citrate (KCit, 4 mmol/d), chlorthalidone (CTD, 4-5mg/kg/d)+KCl or KCit+CTD. Twenty-four hour-urine collections were done at 6, 12 and 18 wks for analysis of solute levels as described in Methods and an overall mean of all three collections was calculated. Results are mean±SE for 10 rats/group. *p<0.05 vs KCl, ^op<0.05 vs KCit alone, ^#p<0.05 vs CTD alone.

Figure 3.. Urine volume, Na, K.

Rat diets were all supplemented hydroxyproline and with either KCl (4 mmol/d) as a control, potassium citrate (KCit, 4 mmol/d), chlorthalidone (CTD, 4-5mg/kg/d)+KCl or KCit+CTD. Twenty-four hour-urine collections were done at 6, 12 and 18 wks for analysis of solute levels as described in Methods and an overall mean of all three collections was calculated. Results are mean±SE for 10 rats/group. *p<0.05 vs KCl, ^op<0.05 vs KCit alone, ^#p<0.05 vs CTD alone.

Figure 4.. Urine supersaturation of CaP and CaOx.

Rat diets were all supplemented with hydroxyproline and with either KCl (4 mmol/d) as a control, potassium citrate (KCit, 4 mmol/d), chlorthalidone (CTD, 4-5mg/kg/d) + KCl or KCit+CTD. Twenty-four-hour urine collections were done at 6, 12 and 18 wks for analysis of solute levels as described in Methods. These values were used to calculate relative supersaturation and an overall mean of all three collections was calculated. Values for relative supersaturation are unitless. Results are mean±SE for 10 rats/group. *p<0.05 vs KCl, ^op<0.05 vs KCit alone, ^#p<0.05 vs CTD alone.

Figure 5.. Kidney stones and calcification.

At the conclusion of the 18 wk study the extent of kidney stones and calcification were determined by three observers as described in Methods. A) Representative x-rays of kidneys from rats receiving KCl, KCit, CTD or KCit+CTD. B) Quantitation of stone formation and calcification in all rats (Mean±SE, n=10/group). *p<0.05 vs KCl, ^op<0.05 vs KCit alone, ^#p<0.05 vs CTD alone.

Figure 5.. Kidney stones and calcification.

At the conclusion of the 18 wk study the extent of kidney stones and calcification were determined by three observers as described in Methods. A) Representative x-rays of kidneys from rats receiving KCl, KCit, CTD or KCit+CTD. B) Quantitation of stone formation and calcification in all rats (Mean±SE, n=10/group). *p<0.05 vs KCl, ^op<0.05 vs KCit alone, ^#p<0.05 vs CTD alone.

Figure 6.. Changes in bone parameters after 18 weeks.

Rat diets were all supplemented with hydroxyproline and with either KCl (4 mmol/d) as a control, potassium citrate (KCit, 4 mmol/d), chlorthalidone (CTD, 4-5mg/kg/d) + KCl or KCit+CTD. At the conclusion of the 18 wk study, bones were collected from all rats and analyzed as described in Methods. A) Percent bone volume (BV/TV), trabecular thickness (Tb.Th.), trabecular number (Tb.N.) and trabecular separation (Tr. Sp.) of L6 vertebrae are presented. B) Cortical volumetric bone mineral density (vBMD), bone area (B.Ar.), cortical thickness (Cs.Th), and % bone volume/total volume (%BV/TV) of femoral cortical bone are presented. Results are mean±SD for n=10 bones/group. p<0.05 vs KCl, ^op<0.05 vs KCit alone. There were no significant differences comparing KCl+CTD to KCit+CTD.

Figure 6.. Changes in bone parameters after 18 weeks.

Rat diets were all supplemented with hydroxyproline and with either KCl (4 mmol/d) as a control, potassium citrate (KCit, 4 mmol/d), chlorthalidone (CTD, 4-5mg/kg/d) + KCl or KCit+CTD. At the conclusion of the 18 wk study, bones were collected from all rats and analyzed as described in Methods. A) Percent bone volume (BV/TV), trabecular thickness (Tb.Th.), trabecular number (Tb.N.) and trabecular separation (Tr. Sp.) of L6 vertebrae are presented. B) Cortical volumetric bone mineral density (vBMD), bone area (B.Ar.), cortical thickness (Cs.Th), and % bone volume/total volume (%BV/TV) of femoral cortical bone are presented. Results are mean±SD for n=10 bones/group. p<0.05 vs KCl, ^op<0.05 vs KCit alone. There were no significant differences comparing KCl+CTD to KCit+CTD.