- Email: [email protected]
Childhood urinary stones induced by melamine-tainted formula: how much we know, how much we don't know
mini review
http://www.kidney-international.org & 2009 International Society of Nephrology
Childhood urinary stones induced by melamine-tainted formula: how much we know, how much we don’t know Jie Ding1 1
Department of Pediatrics, Peking University First Hospital, Beijing, China
Through screening, diagnosing, and treating childhood urinary stones induced by melamine-tainted formula, Chinese doctors obtained more experience with the clinical as well as the imaging features of the stones, although there still are many questions regarding melamine-associated stones. By reviewing the earlier reports on animals along with our recent experiences with humans, we concluded that there was no evidence either from animal experiments or from humans to support the direct toxicity of melamine on the kidney, although a feasible follow-up and assessment might be needed. It is also speculated that further studies on the mechanism of stone formation may need to take into account human internal metabolism changes and tubular function. Kidney International (2009) 75, 780–782; doi:10.1038/ki.2009.30; published online 25 February 2009 KEYWORDS: children; kidney; melamine; urolithiasis
Correspondence: Jie Ding, Department of Pediatrics, Peking University First Hospital, No 1, Xi An Men Da Jie, Beijing 100034, China. E-mail: [email protected] Received 29 December 2008; accepted 31 December 2008; published online 25 February 2009 780
Since the beginning of the outbreak of childhood urinary stones induced by melamine-tainted formula in September 2008, the issue of food safety began to attract more attention all over the world. In addition, issues of the role of melamine in child health become the central concerns. Unfortunately there was little knowledge before the outbreak regarding the influence and possible toxicity of melamine on humans. After the Chinese Ministry of Health released the first report of melamine contamination of milk, several regulations were authorized by the Government, which mandated that screening for urinary stones in young children would be free in Mainland China. Nearly 230,000 children were diagnosed with urinary stones showed mainly by ultrasonography, which has been accepted as the most feasible method to find urinary stones induced by melamine-tainted formula. This vast screening allowed the Chinese doctors to determine the clinical characteristics of the melamine-associated urinary stones. For example, affected infants did not present with typical symptoms of nephrolithiasis, and the incidence of hematuria and leukocyturia was very low. Most melamineassociated stones were irregular and nubby in shape, and did not result in shadowing under the investigation of ultrasound (Figure 1). Stones were mainly localized to the renal pelvis. Most young children with melamine-associated urinary stones were able to discharge the stones and recovered following conservative management, including adequate hydration and urine alkalinization. However, some children presented with obstruction uropathy caused by melamineassociated stones, which resulted in acute renal failure. Despite the fact that following the massive screening physicians in China became more experienced in dealing with the relevant abnormalities, at least two questions on the pathobiology of melamine-associated stones remain. First, what is the direct toxicity of melamine to the kidney? And what its long-term effect on the kidney? There were some data from animal studies including dogs, cats, rats, and mice that were reported after an outbreak of pet food contamination with melamine. The histological findings showed intratubular crystalluria mainly in the distal tubules. The analysis of crystals indicated that melamine and cyanuric acid were combined to form insoluble crystals. Neither melamine nor cyanuric acid alone formed crystals to damage kidneys.1,2 Kidney International (2009) 75, 780–782
J Ding: Urinary stones induced by melamine-tainted formula
a
b
Figure 1 | Ultrasonography of kidney stones induced by melamine-tainted infant formula. The ultrasonography showed multiple hyper-echoic area in the pelvis of both the kidneys (indicated by arrow). The largest hyper-echoic area in the left side (a) showed with a sound shadow. The largest hyper-echoic area in the right side (b) did not show obvious sound shadow.
There was necrosis and regeneration in tubular epithelia, and fibrosis and inflammation in the renal interstitium,2–4 which seemed related to the damage induced by crystals. It is at present not clear whether the tubular and interstitial damage was induced directly by mechanical obstruction by the crystals or by cytotoxicity of melamine and/or cyanuric acid. Studies in vitro in cell lines derived from dog and cat kidney epithelia, however showed that direct cytotoxicity caused by any of the melamine and melamine analogs or their complex mixtures was unlikely.1 Although a large number of young children were diagnosed with melamine-associated urinary stones, there is at present little direct evidence of renal injury in humans other than that associated with obstruction due to the formation of stones. There are at present no specific markers for this type of renal injury, and it was not possible to carry out renal biopsies during emergency screening. However, preliminary data from an epidemiology study conducted by Peking University First Hospital indicated that on the day when kidney stones were diagnosed, all biochemical markers Kidney International (2009) 75, 780–782
mini review
thought to reflect tubular dysfunction, such as the excretion of a1-microglobulin and N-acetyl-beta-D-glucosaminidase, were not significantly different from those in children without stones. Although the incidence of urine biochemical markers, such as microalbumin and transferrin, reflecting glomerular dysfunction appeared greater than those in children without stones, we could not exclude the possibility of coexisting renal diseases. As to the renal morphologic changes in children with melamine-associated urinary stones, to date, we know of only one case from the Chinese literature.5 It was an 8-month-old boy with melamineassociated urinary stones who was hospitalized after prolonged anuria caused by bilateral ureteral stones. The renal histopathology showed sclerosis in 6 of the 26 glomeruli, partial tubular epithelial cell degeneration, lymphocyte infiltration in the renal interstitium, and focal fibrosis. Immunofluorescence was normal. However, it is unclear whether the renal histopathological changes were caused by melamine itself or by acute obstructive uropathy. Another important concern regarding the toxicity of melamine to the kidney is the known carcinogenicity of melamine. In chronic studies in rodents, transitional cell carcinoma was seen in rats treated with high dosage of melamine, in which most rats (7 of 8) also developed stones.6–8 The second question is with regard to the mechanism of stone formation by melamine. Studies on animals in the past few years showed that the combination of melamine and cyanuric acid was the main cause of crystals in the tubules. Earlier studies also showed that melamine or its analogs alone did not form any insoluble crystals.1,3 Sun et al.5 analyzed the melamine-associated stone specimens from 13 children with renal failure by using liquid chromatography (LC)-mass spectrophotometry, and found that the composition of stones was primarily uric acid and melamine. The preliminary data from our ongoing study on the components of melamine-associated stones showed that there was no detectable cyanuric acid in urine specimens taken from children with melamine-associated stones by means of ultraperformance liquid chromatography-quadrupole-time-offlight (UPLC-Q-TOF) mass spectrometry technique, which is a clear difference from the results seen in animals. In addition to varied amounts of melamine as well as uric acid in the tested urine specimens, some unidentified compounds were detected with UPLC-Q-TOF mass spectrometry technique. We do not understand whether these unknown compounds were caused by changes in the metabolism of children with melamine-associated stones, or whether it was because of other contaminants in the formula. We are presently engaged in further studying these issues but have no results to report at present. We also need to keep in mind that the mechanism of formation of melamine-associated urinary stones might not be due to a simple combination of melamine with another compound, uric acid in humans, or cyanuric acid in animals. Dobson et al.1 doubted that melamine and cyanuric acid might form a crystalline structure when they reach the kidney tubules where the 781
mini review
compounds will be present at a higher concentration due to the kidney’s well known ability to concentrate drugs in the urine. Our preliminary epidemiology study showed that among several urolithiasis-associated factors, including gestational age, as well as history of fever, vomiting, and diarrhea in the 3 days before presentation, prematurity was an important factor for urinary stones, as pre-term infants were 4.506 and 3.667 times more likely to have stones as compared with full-term infants, respectively. For nonmelamine-associated stones, Gilsanz et al.9 reported that pre-term infants were also more susceptible to urinary stones; the cause of this association is at present unknown. In summary, there was no evidence either from animal experiments or from humans to support the direct toxicity of melamine on the kidney; however, accurate follow-up and assessment will be needed to document this. Further studies will be needed on the mechanism of stone formation to uncover the necessary metabolic as well as the tubular physiological changes in humans that would allow precipitation of melamine in the tubular lumen. DISCLOSURE
The author declared no competing interests.
782
J Ding: Urinary stones induced by melamine-tainted formula
REFERENCES 1.
2.
3.
4.
5.
6.
7.
8.
9.
Dobson RL, Motlagh S, Quijano1 M et al. Identification and characterization of toxicity of contaminants in pet food leading to an outbreak of renal toxicity in cats and dogs. Toxicol Sci 2008; 106: 2512–2562. Puschner B, Poppenga RH, Lowenstine LJ et al. Assessment of melamine and cyanuric acid toxicity in cats. J Vet Diagn Invest 2007; 19: 616–624. Brown CA, Jeong KS, Poppenga RH et al. Outbreaks of renal failure associated with melamine and cyanuric acid in dogs and cats in 2004 and 2007. J Vet Diagn Invest 2007; 19: 525–531. Cianciolo RE, Bischoff K, Ebel JG et al. Clinicopathologic, histologic, and toxicologic findings in 70 cats inadvertently exposed to pet food contaminated with melamine and cyanuric acid. J Am Vet Med Assoc 2008; 233: 729–737. Sun N, Shen Y, Sun Q et al. Melamine related urinary calculus and acute renal failure in infants. Zhonghua Erke Zazhi 2008; 46: 810–815. Melnick RL, Boorman GA, Haseman JK et al. Urolithiasis and bladder carcinogenicity of melamine in rodents. Toxicol Appl Pharmacol 1984; 72: 292–303. Okumura1 M, Hasegawa1 R, Shirai1 T et al. Relationship between calculus formation and carcinogenesis in the urinary bladder of rats administered the non-genotoxic agents, thymine or melamine. Carcinogenesis 1992; 13: 1043–1045. Ogasawara H, Imaida1 K, Ishiwata H et al. Urinary bladder carcinogenesis induced by melamine in F344 male rats: correlation between carcinogenicity and urolith formation. Carcinogenesis 1995; 16: 2773–2777. Gilsanz V, Fernal W, Reid BS et al. Nephrolithiasis in premature infants. Radiology 1985; 154: 107–110.
Kidney International (2009) 75, 780–782
http://www.kidney-international.org & 2009 International Society of Nephrology
Childhood urinary stones induced by melamine-tainted formula: how much we know, how much we don’t know Jie Ding1 1
Department of Pediatrics, Peking University First Hospital, Beijing, China
Through screening, diagnosing, and treating childhood urinary stones induced by melamine-tainted formula, Chinese doctors obtained more experience with the clinical as well as the imaging features of the stones, although there still are many questions regarding melamine-associated stones. By reviewing the earlier reports on animals along with our recent experiences with humans, we concluded that there was no evidence either from animal experiments or from humans to support the direct toxicity of melamine on the kidney, although a feasible follow-up and assessment might be needed. It is also speculated that further studies on the mechanism of stone formation may need to take into account human internal metabolism changes and tubular function. Kidney International (2009) 75, 780–782; doi:10.1038/ki.2009.30; published online 25 February 2009 KEYWORDS: children; kidney; melamine; urolithiasis
Correspondence: Jie Ding, Department of Pediatrics, Peking University First Hospital, No 1, Xi An Men Da Jie, Beijing 100034, China. E-mail: [email protected] Received 29 December 2008; accepted 31 December 2008; published online 25 February 2009 780
Since the beginning of the outbreak of childhood urinary stones induced by melamine-tainted formula in September 2008, the issue of food safety began to attract more attention all over the world. In addition, issues of the role of melamine in child health become the central concerns. Unfortunately there was little knowledge before the outbreak regarding the influence and possible toxicity of melamine on humans. After the Chinese Ministry of Health released the first report of melamine contamination of milk, several regulations were authorized by the Government, which mandated that screening for urinary stones in young children would be free in Mainland China. Nearly 230,000 children were diagnosed with urinary stones showed mainly by ultrasonography, which has been accepted as the most feasible method to find urinary stones induced by melamine-tainted formula. This vast screening allowed the Chinese doctors to determine the clinical characteristics of the melamine-associated urinary stones. For example, affected infants did not present with typical symptoms of nephrolithiasis, and the incidence of hematuria and leukocyturia was very low. Most melamineassociated stones were irregular and nubby in shape, and did not result in shadowing under the investigation of ultrasound (Figure 1). Stones were mainly localized to the renal pelvis. Most young children with melamine-associated urinary stones were able to discharge the stones and recovered following conservative management, including adequate hydration and urine alkalinization. However, some children presented with obstruction uropathy caused by melamineassociated stones, which resulted in acute renal failure. Despite the fact that following the massive screening physicians in China became more experienced in dealing with the relevant abnormalities, at least two questions on the pathobiology of melamine-associated stones remain. First, what is the direct toxicity of melamine to the kidney? And what its long-term effect on the kidney? There were some data from animal studies including dogs, cats, rats, and mice that were reported after an outbreak of pet food contamination with melamine. The histological findings showed intratubular crystalluria mainly in the distal tubules. The analysis of crystals indicated that melamine and cyanuric acid were combined to form insoluble crystals. Neither melamine nor cyanuric acid alone formed crystals to damage kidneys.1,2 Kidney International (2009) 75, 780–782
J Ding: Urinary stones induced by melamine-tainted formula
a
b
Figure 1 | Ultrasonography of kidney stones induced by melamine-tainted infant formula. The ultrasonography showed multiple hyper-echoic area in the pelvis of both the kidneys (indicated by arrow). The largest hyper-echoic area in the left side (a) showed with a sound shadow. The largest hyper-echoic area in the right side (b) did not show obvious sound shadow.
There was necrosis and regeneration in tubular epithelia, and fibrosis and inflammation in the renal interstitium,2–4 which seemed related to the damage induced by crystals. It is at present not clear whether the tubular and interstitial damage was induced directly by mechanical obstruction by the crystals or by cytotoxicity of melamine and/or cyanuric acid. Studies in vitro in cell lines derived from dog and cat kidney epithelia, however showed that direct cytotoxicity caused by any of the melamine and melamine analogs or their complex mixtures was unlikely.1 Although a large number of young children were diagnosed with melamine-associated urinary stones, there is at present little direct evidence of renal injury in humans other than that associated with obstruction due to the formation of stones. There are at present no specific markers for this type of renal injury, and it was not possible to carry out renal biopsies during emergency screening. However, preliminary data from an epidemiology study conducted by Peking University First Hospital indicated that on the day when kidney stones were diagnosed, all biochemical markers Kidney International (2009) 75, 780–782
mini review
thought to reflect tubular dysfunction, such as the excretion of a1-microglobulin and N-acetyl-beta-D-glucosaminidase, were not significantly different from those in children without stones. Although the incidence of urine biochemical markers, such as microalbumin and transferrin, reflecting glomerular dysfunction appeared greater than those in children without stones, we could not exclude the possibility of coexisting renal diseases. As to the renal morphologic changes in children with melamine-associated urinary stones, to date, we know of only one case from the Chinese literature.5 It was an 8-month-old boy with melamineassociated urinary stones who was hospitalized after prolonged anuria caused by bilateral ureteral stones. The renal histopathology showed sclerosis in 6 of the 26 glomeruli, partial tubular epithelial cell degeneration, lymphocyte infiltration in the renal interstitium, and focal fibrosis. Immunofluorescence was normal. However, it is unclear whether the renal histopathological changes were caused by melamine itself or by acute obstructive uropathy. Another important concern regarding the toxicity of melamine to the kidney is the known carcinogenicity of melamine. In chronic studies in rodents, transitional cell carcinoma was seen in rats treated with high dosage of melamine, in which most rats (7 of 8) also developed stones.6–8 The second question is with regard to the mechanism of stone formation by melamine. Studies on animals in the past few years showed that the combination of melamine and cyanuric acid was the main cause of crystals in the tubules. Earlier studies also showed that melamine or its analogs alone did not form any insoluble crystals.1,3 Sun et al.5 analyzed the melamine-associated stone specimens from 13 children with renal failure by using liquid chromatography (LC)-mass spectrophotometry, and found that the composition of stones was primarily uric acid and melamine. The preliminary data from our ongoing study on the components of melamine-associated stones showed that there was no detectable cyanuric acid in urine specimens taken from children with melamine-associated stones by means of ultraperformance liquid chromatography-quadrupole-time-offlight (UPLC-Q-TOF) mass spectrometry technique, which is a clear difference from the results seen in animals. In addition to varied amounts of melamine as well as uric acid in the tested urine specimens, some unidentified compounds were detected with UPLC-Q-TOF mass spectrometry technique. We do not understand whether these unknown compounds were caused by changes in the metabolism of children with melamine-associated stones, or whether it was because of other contaminants in the formula. We are presently engaged in further studying these issues but have no results to report at present. We also need to keep in mind that the mechanism of formation of melamine-associated urinary stones might not be due to a simple combination of melamine with another compound, uric acid in humans, or cyanuric acid in animals. Dobson et al.1 doubted that melamine and cyanuric acid might form a crystalline structure when they reach the kidney tubules where the 781
mini review
compounds will be present at a higher concentration due to the kidney’s well known ability to concentrate drugs in the urine. Our preliminary epidemiology study showed that among several urolithiasis-associated factors, including gestational age, as well as history of fever, vomiting, and diarrhea in the 3 days before presentation, prematurity was an important factor for urinary stones, as pre-term infants were 4.506 and 3.667 times more likely to have stones as compared with full-term infants, respectively. For nonmelamine-associated stones, Gilsanz et al.9 reported that pre-term infants were also more susceptible to urinary stones; the cause of this association is at present unknown. In summary, there was no evidence either from animal experiments or from humans to support the direct toxicity of melamine on the kidney; however, accurate follow-up and assessment will be needed to document this. Further studies will be needed on the mechanism of stone formation to uncover the necessary metabolic as well as the tubular physiological changes in humans that would allow precipitation of melamine in the tubular lumen. DISCLOSURE
The author declared no competing interests.
782
J Ding: Urinary stones induced by melamine-tainted formula
REFERENCES 1.
2.
3.
4.
5.
6.
7.
8.
9.
Dobson RL, Motlagh S, Quijano1 M et al. Identification and characterization of toxicity of contaminants in pet food leading to an outbreak of renal toxicity in cats and dogs. Toxicol Sci 2008; 106: 2512–2562. Puschner B, Poppenga RH, Lowenstine LJ et al. Assessment of melamine and cyanuric acid toxicity in cats. J Vet Diagn Invest 2007; 19: 616–624. Brown CA, Jeong KS, Poppenga RH et al. Outbreaks of renal failure associated with melamine and cyanuric acid in dogs and cats in 2004 and 2007. J Vet Diagn Invest 2007; 19: 525–531. Cianciolo RE, Bischoff K, Ebel JG et al. Clinicopathologic, histologic, and toxicologic findings in 70 cats inadvertently exposed to pet food contaminated with melamine and cyanuric acid. J Am Vet Med Assoc 2008; 233: 729–737. Sun N, Shen Y, Sun Q et al. Melamine related urinary calculus and acute renal failure in infants. Zhonghua Erke Zazhi 2008; 46: 810–815. Melnick RL, Boorman GA, Haseman JK et al. Urolithiasis and bladder carcinogenicity of melamine in rodents. Toxicol Appl Pharmacol 1984; 72: 292–303. Okumura1 M, Hasegawa1 R, Shirai1 T et al. Relationship between calculus formation and carcinogenesis in the urinary bladder of rats administered the non-genotoxic agents, thymine or melamine. Carcinogenesis 1992; 13: 1043–1045. Ogasawara H, Imaida1 K, Ishiwata H et al. Urinary bladder carcinogenesis induced by melamine in F344 male rats: correlation between carcinogenicity and urolith formation. Carcinogenesis 1995; 16: 2773–2777. Gilsanz V, Fernal W, Reid BS et al. Nephrolithiasis in premature infants. Radiology 1985; 154: 107–110.
Kidney International (2009) 75, 780–782