0022-534 7/91/1455-1092$03.00/0 THE JOURNAL OF UROLOGY Copyright© 1991 by AMERICAN UROLOGICAL ASSOCIATION, INC.
Vol. 145, 1092-1095, May 1991
Printed in U.S.A.
EFFECT OF MAGNESIUM ON CALCIUM OXALATE UROLITHIASIS CHUNG-JEN SU, PAULA N. SHEVOCK, SAEED R. KHAN*
AND
RAYMOND L. HACKETT
From the Departments of Surgery/Urology and Pathology, College of Medicine, University of Florida, Gainesville, Florida
ABSTRACT
Previous studies have shown that hypomagnesuria induced by magnesium deficient diet causes calcium oxalate crystal deposition in renal tubules of hyperoxaluric rats and administration of magnesium to these rats results in prevention of calcium oxalate crystallization in their kidneys. Based on these studies magnesium was claimed to be beneficial for calcium oxalate stone patients. However, hypomagnesuria is not a common phenomenon. To better understand the role of magnesium as an inhibitor of calcium oxalate crystallization in urine, we studied the effect of magnesium on calcium oxalate urolithiasis in rats on a regular diet and a hyperoxaluric protocol. Excess magnesium was administered to male rats on regular diet and a lithogenic protocol. Magnesium administration to hyperoxaluric rats did not result in significant changes in urinary excretion of calcium or oxalate or in calcium oxalate relative supersaturation. Urinary excretion of citrate was also not significantly altered. Some animals from both groups, those on magnesium therapy and those not on magnesium therapy had crystals deposited in their renal tubules. We conclude that excess magnesium has no significant effect on calcium oxalate urolithiasis in normomagnesuric conditions. KEY WORDS: calculi, calcium oxalate, magnesium
It was noted in 1929 that magnesium deficiency causes experimental production of urolithiasis. 1 Subsequently, many experimental and clinical studies have shown a relationship between dietary and urinary magnesium and stone formation. Magnesium oxalate is more soluble than calcium oxalate (CaOx) and the high excretion of magnesium in urine reduces the concentration of oxalate available for CaOx precipitation. 2 In in vitro studies, magnesium has been shown to decrease both the rate of nucleation and growth of CaOx crystals at physiological concentrations. 3 • 4 In the animal studies, hypomagnesuria induced by magnesium deficient diet caused renal tubular deposition of CaOx crystals in hyperoxaluric rats. 5 Magnesium also provided protection against CaOx deposition in rats on vitamin B6-deficient diets. 6 Magnesium therapy, can increase citrate excretion and urinary pH, both of them increase CaOx solubility. 7 • 8 These studies suggested that magnesium deficiency could augment CaOx stone formation. In clinical practices, magnesium oxide, magnesium hydroxide or magnesium citrate used in treatment of CaOx stone patients showed significant benefits. 9 - 12 Some clinical studies have however, revealed that magnesium had no beneficial effects in prevention of CaOx stone formation. Although magnesium therapy raised urinary magnesium, it also increased urinary calcium output, thus calcium/magnesium ratio was unaffected. 13 Similarly hyperoxaluria which occurred following ethylene glycol administration was also not affected by magnesium therapy. 6 • 14 Thus, there was no significant change in urinary formation product ratio or rate of crystal growth of CaOx. 15 • 16 In vivo animal studies have so far demonstrated that hypomagnesuria can cause deposition of CaOx crystals in the kidneys of hyperoxaluric rats and that administration of magnesium in these circumstances can provide protection against CaOx urolithiasis. 5 • 6 Present experimental study is carried out to understand the effect of magnesium administration on the urinary CaOx relative supersaturation (RSS) and CaOx urolithiasis in hyperoxaluric rats on regular diet and without hypomagnesuria. Accepted for publication January 9, 1991. * Requests for reprints: Department of Pathology, JHMHC, Box J247, Gainesville, FL 32610. Supported by NIH Grant #5 POl DK20586.
MATERIALS AND METHODS
Twenty male Sprague-Dawley rats weighing 172 to 220 gm. were used for the study and divided in four groups. They were housed in metabolic cages three days before the beginning of the experiment to acclimatize with the experimental conditions. During this period they were provided with common tap water and ground regular rat chow mush. Liquid intake and body weight were monitored daily. On day 1 rats were put on the experimental regimen. Excess magnesium was administered as 200 mg. of magnesium oxide (Uro-Mag)/100 gm. rat chow. Rats in Group A received regular chow and plain tap water; in Group B regular rat chow and 1% ethylene glycol (v/v) solution as drinking water; in Group C regular rat chow mixed with excess magnesium and 1% ethylene glycol solution as drinking water; and in Group D regular rat chow mixed with excess magnesium and plain tap water to drink. All urine samples were collected for 24 hours with thymol as preservative. Urinary pH and volumes were determined for all 24 hour collections. Baseline urine collections (Day O) were begun a day prior to putting the rats on various experimental regimens as described above. After that, 24 hours urine specimens were collected on day 1, 4, 7, 10 and 13 of the experiment. All the urinary specimens were analyzed for calcium, sodium, potassium, magnesium, phosphorus, sulfate, ammonia, oxalic acid and citric acid. 17 Urinary calcium and magnesium oxalate supersaturations were calculated using the computer programme Equil 2. 18 TABLE
Group Day A n=5 B n=4 C n=5 D n=5
0 7 0 7 0 7 0 7
1. Urinary profiles on day O (baseline) and day 7 of experimental regime. Mean mM/L (±Std) pH 7.52 7.54 7.32 7.21 7.39 7.48 7.44 7.59
Calcium
Oxalate
(0.23) 4.07 (0.81) 0.72 (0.19) (0.13) 2.74 (0.93) 1.36 (0.15)a (0.35) 3.62 (0.70) 0.69 (0.13) (0.34) 2.23 (0.65) 3.64 (l.37)b (0.12) 3.15 (0.83) 0.61 (0.22) (0.21) 2.14 (0.95) 4.22 (l.45)a (0.11) 2.90 (0.38) 0.59 (0.17) (0.13) 2.29 (0.41) 1.16 (0.44)c
Citrate 14.5 21.0 15.1 17.8 14.4 14.6 14.0 17.1
(2.5) (4.1) (3.4) (3.4) (2.2) (3.2) (2.3) (5.0)
Magnesium 25.4 19.2 34.0 31.2 30.6 52.6 38.3 73.8
(6.2) (8.0) (12.0) (4.6) (7.0) (34.8) (4.1) (29.8)b
Urinary profile of rats receiving excess magnesium, as magnesium oxide, 200 mg/100 g ground rat chow (Group C and Group D) and/or 1.00% ethylene glycol (Group B and Group C). Group A is a normal control. Significance in change from Day 0: • p < 0.01; hp < 0.02; 'p < 0.05
1092
EFFECT OF' t;lAG~e·,J"ESHJlV1 Ol"'J CALCIU1Vi OXALATE UROLITHIASIS
1093
FIG. 1. A, H & E stained section of kidney from rat receiving ethylene glycol only. X250. B, H & E stained section of kidney from rat receiving both ethylene glycol and magnesium oxide. X400. Arrows point to deposits of birefringent crystals of calcium oxalate.
1094
SU AND ASSOCIATES
FIG. 2. Small concretion consisting of calcium oxalate monohydrate and calcium oxalate dihyrate from bladder aspirate of rat from group c receiving both ethylene glycol and magnesium oxide. r
- r - -------,---- ~-,------- -.- - - - - - - 1 - - - - - - - - , -
--
,________,--
~I j
of this study. On the day of sacrifice there was no significant difference in creatinine clearance between control animals and animals on different experimental protocols. Creatinine clearance was 1.52 ± 0.30 in control animals, 1.35 ± 0.20 in animals from group B, 1.62 ± 0.34 in animals from group C and 1.51 ± 0.33 in animals from group D. One of four animals from Group C and two of five animals from group D contained CaOx crystals in their kidneys (fig. 1). Kidneys with crystals demonstrated dilated renal tubules and regenerating cells with mitotic figures. Kidneys of other rats without crystals appeared normal. The same rats that had calcium oxalate crystals in their kidneys also had them in their urine collected on day 10 and the urine aspirated from bladder at the time of sacrifice (fig. 2). Calcium oxalate crystals were a mixture of mono- and dihydrates. All the other urinary specimens examined contained struvite-type magnesium orthophosphate crystals. Except on day 4, urinary CaOx RSS's were consistently higher in the urine of rats receiving ethylene glycol than those on normal diet or receiving magnesium oxide supplement only (fig. 3) and were generally higher than the baseline values. However there was no significant difference in urinary CaOx RSS of rats receiving both magnesium oxide and ethylene glycol and those receiving only ethylene glycol. DISCUSSION
15
[f] [f]
~
X 10 0
~
~
u
o~~
-2
Norrrw.l Conlrol
C
.
1.0% F:G
1.0% iG/lligO Diet V
MgO Diel T
FIG. 3. Calcium oxalate (CaOx) relative supersaturation (RSS), of rat urine on days 0, 1, 4, 7, 10 and 13 of experiment. Group A is normal control (n = 5). Group Bis rats on 1.0% ethylene glycol (n = 4). Group C is rats receiving 1.0% ethylene glycol and magnesium oxide (n = 5). Group Dis rats receiving magnesium oxide (n = 5).
After two weeks the rats were sacrificed and their kidneys and bladders processed for light microscopic examination. The H & E stained kidney sections were examined using plain and polarized light. 19 Bladder urine was aspirated, filtered, and the crystals examined by scanning electron microscopy and X-ray microanalysis. 20 Blood was taken for serum creatinine analysis. RESULTS
Even though urinary chemistries fluctuated, a consistent pattern developed during the course of the study. Table 1 shows results of various baseline urinary measurements as compared with those on day 7 of the experiment. There was no significant difference in urinary pH or calcium or citrate of animals in various groups of various protocols. Urinary oxalate was significantly higher in animals of Groups B and C that received ethylene glycol and urinary magnesium was higher in animals of Groups C and D that received magnesium oxide. Urinary oxalate of animals in group A, the normal control and in group D, who received excess magnesium, was also significantly increased but was not significantly different from one another. But it was significantly lower than that of animals in groups B (p
Vol. 145, 1092-1095, May 1991
Printed in U.S.A.
EFFECT OF MAGNESIUM ON CALCIUM OXALATE UROLITHIASIS CHUNG-JEN SU, PAULA N. SHEVOCK, SAEED R. KHAN*
AND
RAYMOND L. HACKETT
From the Departments of Surgery/Urology and Pathology, College of Medicine, University of Florida, Gainesville, Florida
ABSTRACT
Previous studies have shown that hypomagnesuria induced by magnesium deficient diet causes calcium oxalate crystal deposition in renal tubules of hyperoxaluric rats and administration of magnesium to these rats results in prevention of calcium oxalate crystallization in their kidneys. Based on these studies magnesium was claimed to be beneficial for calcium oxalate stone patients. However, hypomagnesuria is not a common phenomenon. To better understand the role of magnesium as an inhibitor of calcium oxalate crystallization in urine, we studied the effect of magnesium on calcium oxalate urolithiasis in rats on a regular diet and a hyperoxaluric protocol. Excess magnesium was administered to male rats on regular diet and a lithogenic protocol. Magnesium administration to hyperoxaluric rats did not result in significant changes in urinary excretion of calcium or oxalate or in calcium oxalate relative supersaturation. Urinary excretion of citrate was also not significantly altered. Some animals from both groups, those on magnesium therapy and those not on magnesium therapy had crystals deposited in their renal tubules. We conclude that excess magnesium has no significant effect on calcium oxalate urolithiasis in normomagnesuric conditions. KEY WORDS: calculi, calcium oxalate, magnesium
It was noted in 1929 that magnesium deficiency causes experimental production of urolithiasis. 1 Subsequently, many experimental and clinical studies have shown a relationship between dietary and urinary magnesium and stone formation. Magnesium oxalate is more soluble than calcium oxalate (CaOx) and the high excretion of magnesium in urine reduces the concentration of oxalate available for CaOx precipitation. 2 In in vitro studies, magnesium has been shown to decrease both the rate of nucleation and growth of CaOx crystals at physiological concentrations. 3 • 4 In the animal studies, hypomagnesuria induced by magnesium deficient diet caused renal tubular deposition of CaOx crystals in hyperoxaluric rats. 5 Magnesium also provided protection against CaOx deposition in rats on vitamin B6-deficient diets. 6 Magnesium therapy, can increase citrate excretion and urinary pH, both of them increase CaOx solubility. 7 • 8 These studies suggested that magnesium deficiency could augment CaOx stone formation. In clinical practices, magnesium oxide, magnesium hydroxide or magnesium citrate used in treatment of CaOx stone patients showed significant benefits. 9 - 12 Some clinical studies have however, revealed that magnesium had no beneficial effects in prevention of CaOx stone formation. Although magnesium therapy raised urinary magnesium, it also increased urinary calcium output, thus calcium/magnesium ratio was unaffected. 13 Similarly hyperoxaluria which occurred following ethylene glycol administration was also not affected by magnesium therapy. 6 • 14 Thus, there was no significant change in urinary formation product ratio or rate of crystal growth of CaOx. 15 • 16 In vivo animal studies have so far demonstrated that hypomagnesuria can cause deposition of CaOx crystals in the kidneys of hyperoxaluric rats and that administration of magnesium in these circumstances can provide protection against CaOx urolithiasis. 5 • 6 Present experimental study is carried out to understand the effect of magnesium administration on the urinary CaOx relative supersaturation (RSS) and CaOx urolithiasis in hyperoxaluric rats on regular diet and without hypomagnesuria. Accepted for publication January 9, 1991. * Requests for reprints: Department of Pathology, JHMHC, Box J247, Gainesville, FL 32610. Supported by NIH Grant #5 POl DK20586.
MATERIALS AND METHODS
Twenty male Sprague-Dawley rats weighing 172 to 220 gm. were used for the study and divided in four groups. They were housed in metabolic cages three days before the beginning of the experiment to acclimatize with the experimental conditions. During this period they were provided with common tap water and ground regular rat chow mush. Liquid intake and body weight were monitored daily. On day 1 rats were put on the experimental regimen. Excess magnesium was administered as 200 mg. of magnesium oxide (Uro-Mag)/100 gm. rat chow. Rats in Group A received regular chow and plain tap water; in Group B regular rat chow and 1% ethylene glycol (v/v) solution as drinking water; in Group C regular rat chow mixed with excess magnesium and 1% ethylene glycol solution as drinking water; and in Group D regular rat chow mixed with excess magnesium and plain tap water to drink. All urine samples were collected for 24 hours with thymol as preservative. Urinary pH and volumes were determined for all 24 hour collections. Baseline urine collections (Day O) were begun a day prior to putting the rats on various experimental regimens as described above. After that, 24 hours urine specimens were collected on day 1, 4, 7, 10 and 13 of the experiment. All the urinary specimens were analyzed for calcium, sodium, potassium, magnesium, phosphorus, sulfate, ammonia, oxalic acid and citric acid. 17 Urinary calcium and magnesium oxalate supersaturations were calculated using the computer programme Equil 2. 18 TABLE
Group Day A n=5 B n=4 C n=5 D n=5
0 7 0 7 0 7 0 7
1. Urinary profiles on day O (baseline) and day 7 of experimental regime. Mean mM/L (±Std) pH 7.52 7.54 7.32 7.21 7.39 7.48 7.44 7.59
Calcium
Oxalate
(0.23) 4.07 (0.81) 0.72 (0.19) (0.13) 2.74 (0.93) 1.36 (0.15)a (0.35) 3.62 (0.70) 0.69 (0.13) (0.34) 2.23 (0.65) 3.64 (l.37)b (0.12) 3.15 (0.83) 0.61 (0.22) (0.21) 2.14 (0.95) 4.22 (l.45)a (0.11) 2.90 (0.38) 0.59 (0.17) (0.13) 2.29 (0.41) 1.16 (0.44)c
Citrate 14.5 21.0 15.1 17.8 14.4 14.6 14.0 17.1
(2.5) (4.1) (3.4) (3.4) (2.2) (3.2) (2.3) (5.0)
Magnesium 25.4 19.2 34.0 31.2 30.6 52.6 38.3 73.8
(6.2) (8.0) (12.0) (4.6) (7.0) (34.8) (4.1) (29.8)b
Urinary profile of rats receiving excess magnesium, as magnesium oxide, 200 mg/100 g ground rat chow (Group C and Group D) and/or 1.00% ethylene glycol (Group B and Group C). Group A is a normal control. Significance in change from Day 0: • p < 0.01; hp < 0.02; 'p < 0.05
1092
EFFECT OF' t;lAG~e·,J"ESHJlV1 Ol"'J CALCIU1Vi OXALATE UROLITHIASIS
1093
FIG. 1. A, H & E stained section of kidney from rat receiving ethylene glycol only. X250. B, H & E stained section of kidney from rat receiving both ethylene glycol and magnesium oxide. X400. Arrows point to deposits of birefringent crystals of calcium oxalate.
1094
SU AND ASSOCIATES
FIG. 2. Small concretion consisting of calcium oxalate monohydrate and calcium oxalate dihyrate from bladder aspirate of rat from group c receiving both ethylene glycol and magnesium oxide. r
- r - -------,---- ~-,------- -.- - - - - - - 1 - - - - - - - - , -
--
,________,--
~I j
of this study. On the day of sacrifice there was no significant difference in creatinine clearance between control animals and animals on different experimental protocols. Creatinine clearance was 1.52 ± 0.30 in control animals, 1.35 ± 0.20 in animals from group B, 1.62 ± 0.34 in animals from group C and 1.51 ± 0.33 in animals from group D. One of four animals from Group C and two of five animals from group D contained CaOx crystals in their kidneys (fig. 1). Kidneys with crystals demonstrated dilated renal tubules and regenerating cells with mitotic figures. Kidneys of other rats without crystals appeared normal. The same rats that had calcium oxalate crystals in their kidneys also had them in their urine collected on day 10 and the urine aspirated from bladder at the time of sacrifice (fig. 2). Calcium oxalate crystals were a mixture of mono- and dihydrates. All the other urinary specimens examined contained struvite-type magnesium orthophosphate crystals. Except on day 4, urinary CaOx RSS's were consistently higher in the urine of rats receiving ethylene glycol than those on normal diet or receiving magnesium oxide supplement only (fig. 3) and were generally higher than the baseline values. However there was no significant difference in urinary CaOx RSS of rats receiving both magnesium oxide and ethylene glycol and those receiving only ethylene glycol. DISCUSSION
15
[f] [f]
~
X 10 0
~
~
u
o~~
-2
Norrrw.l Conlrol
C
.
1.0% F:G
1.0% iG/lligO Diet V
MgO Diel T
FIG. 3. Calcium oxalate (CaOx) relative supersaturation (RSS), of rat urine on days 0, 1, 4, 7, 10 and 13 of experiment. Group A is normal control (n = 5). Group Bis rats on 1.0% ethylene glycol (n = 4). Group C is rats receiving 1.0% ethylene glycol and magnesium oxide (n = 5). Group Dis rats receiving magnesium oxide (n = 5).
After two weeks the rats were sacrificed and their kidneys and bladders processed for light microscopic examination. The H & E stained kidney sections were examined using plain and polarized light. 19 Bladder urine was aspirated, filtered, and the crystals examined by scanning electron microscopy and X-ray microanalysis. 20 Blood was taken for serum creatinine analysis. RESULTS
Even though urinary chemistries fluctuated, a consistent pattern developed during the course of the study. Table 1 shows results of various baseline urinary measurements as compared with those on day 7 of the experiment. There was no significant difference in urinary pH or calcium or citrate of animals in various groups of various protocols. Urinary oxalate was significantly higher in animals of Groups B and C that received ethylene glycol and urinary magnesium was higher in animals of Groups C and D that received magnesium oxide. Urinary oxalate of animals in group A, the normal control and in group D, who received excess magnesium, was also significantly increased but was not significantly different from one another. But it was significantly lower than that of animals in groups B (p
