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HISTOLOGICAL STUDIES OF THE EFFECTS OF MONOSODIUM GLUTAMATE
ON THE KIDNEY OF ADULT WISTAR RATS.
A.O. Eweka, F.A.E. Om'Iniabohs
Department of Anatomy. School of Basic Medical Sciences. College of Medical Sciences, University of Benin.
Benin City. Edo State. Nigeria.
andreweweka @ yahoo.com
Rev Electron Biomed / Electron J Biomed 2008;2:(in press)
Comment of the reviewer Abdías Hurtado Arístegui PhD. Nefrologia. Hospital Arzobispo Loayza. Universidad Peruana Cayetano Heredia. Lima. Peru
Comment of the reviewer Pedro Abáigar Luquín. PhD. Nefrología. Hospital General Yagüe. Burgos. España
ABSTRACT:
Background: Various environmental chemicals, industrial pollutants and food additives have been implicated as causing harmful effects. Most food additives act either as preservatives, or enhancer of palatability. One such food additive is Monosodium glutamate (MSG). The effect of monosodium glutamate, used as food additive on the Kidneys of adult Wistar rat was investigated.
Aims: Since the Kidney is involved in the excretion of many toxic metabolic waste products it would be worthwhile to examine the effects of monosodium glutamate on the kidneys on adult Wistar rats.
Methods: Both adult male and female Wistar rats (n=24) average weight of 185g were randomly assigned into two treatments (n=12) and control (n=6) groups. The rats in the treatment groups received 3g and 6g of Monosodium glutamate thoroughly mixed with the grower's mash daily for fourteen days. The control rats received equal amount of the grower's mash without Monosodium glutamate added daily. The grower's mash was obtained from Edo Feeds and Flour Mill Ltd, Ewu, Edo State and the rats were given water liberally. The rats were sacrificed on day fifteen of the experiment. The Kidneys were carefully dissected out and quickly fixed in 10% formal saline for histological procedures.
Results: Histological changes observed in the treated kidney sections included the distortion of the renal cortical structures and some degree of cellular necrosis, with degenerative and atrophic changes. There were vacuolations appearing in the stroma. The renal corpuscles were less identified and the Bowman's spaces were sparsely distributed as compared to the control group.
Conclusion: Our results suggested that the functions of the kidney could have been adversely affected due to the distortion of the cyto-architecture of the renal cortical structures and cellular necrosis associated with the kidney. It is recommended that further research studies aimed at corroborating these observations be carried out.
Key words: Monosodium glutamate, renal corpuscle, vacuolations, cellular necrosis, cyto-architecture and Wistar rats.
RESUMEN: ESTUDIO HISTOLÓGICO DE LOS EFECTOS DEL GLUTAMATO MONOSÓDICO EN EL RIÑON DE RATAS WISTAR ADULTAS
La mayoría de los aditivos alimentarios actuar ya sea como conservantes, o potenciador del sabor. Uno de ellos es aditivo alimentario glutamato monosódico (MSG). El efecto de glutamato monosódico, utilizado como aditivo alimentario en los riñones de ratas Wistar adultos se investigó. Objetivos: Desde el riñón participa en la excreción de muchos tóxicos productos de desecho metabólico sería conveniente examinar los efectos de glutamato monosódico en los riñones en ratas Wistar adultos.
Métodos:
Ratas Wistar adultas, macho y hembra (n = 24) de 185g de peso bruto promedio, fueron asignadas aleatoriamente a dos tratamientos (n = 12) y control (n = 6). Las ratas en los grupos de tratamiento recibieron 3g y 6 g al día de glutamato monosódico, mezclado con el producto, de la ingesta durante catorce días. Las ratas control recibieron igual cantidad de ingesta, sin glutamato monosódico. La masa de ingesta se obtuvo de Edo Feeds y Flour Mill Ltd, Ewu, Estado de Edo y a las ratas se les proporcionó agua libremente. Las ratas se sacrificaron el día quince de la prueba. Los riñones fueron cuidadosamente disecados rápidamente y fijados en 10% de solución de formal salino para el procedimiento histológico.
Resultados: Se observaron cambios histológicos en las secciones de riñón tratados, que incluyen la distorsión de las estructuras de la corteza renal y un cierto grado de necrosis celular, con cambios degenerativos y atróficos. Hubo vacuolizacion en el estroma. Los corpúsculos renales son menos definidos y los espacios de Bowman se distribuyen escasamente en comparación con el grupo control.
Conclusión: Nuestros resultados sugieren que las funciones del riñón podrían haber sido afectados negativamente debido a la distorsión de la citoarquitectura de las estructuras de la corteza renal y la necrosis celular asociada con el riñón. Es recomendable que sean llevados a cabo posteriores estudios de investigación para corroborar estas observaciones.
Palabras Clave: Glutamato monosódico, corpúsculo renal, vacuolizaciones, necrosis celular, citoarquitectura, ratas de Wistar.
INTRODUCTION
Monosodium glutamate (otherwise known as AJI-NO-MOTO) is the sodium salt of glutamic acid. Glutamate is one of the most common naturally occurring amino acid. It is a main component of many proteins and peptides. Monosodium glutamate contains 78% of glutamic acid, 22% of sodium and water1. Glutamate is also produced in the body and plays an essential role in human metabolism. It is a major component of many protein-rich food products such as meat, fish, milk and some vegetables2.
Various environmental chemicals, industrial pollutants and food additives have been implicated as causing harmful effects3-4. Most food additives act either as preservatives, or enhancer of palatability. One such food additive is Monosodium glutamate (MSG).
When Monosodium glutamate is added to food, it provides a flavoring function similar to the naturally occurring free glutamate: which differ from the four classic tastes of sweet, sour, salty and bitter5?. As food additive, Monosodium glutamate is described and listed on food labels as a "Flavoring" or "hydrolyzed vegetable protein". Through its stimulation of the orosensory receptors and by improving the palatability of meals, Monosodium glutamate influences the appetite positively, and induces weight gain6. Despite its taste stimulation and improved appetite enhancement, reports indicate that Monosodium glutamate is toxic to human and experimental animals6.
In Nigeria, some individuals often use Monosodium glutamate as a bleaching agent for the removal of stains from clothes. There is growing apprehension that its bleaching properties could be harmful or injurious to the tissues and organs of the body. Despite evidence of negative consumer response to Monosodium glutamate, reputable international organizations and nutritionist have continued to endorse Monosodium glutamate, and reiterate that Monosodium glutamate has no adverse reactions in humans7. The Food and Drug Administration (FDA) of the United States reports that Monosodium glutamate is safe and that it should be maintained on the "Generally Recognized as Safe" (GRAS)-list of foods. Monosodium glutamate is thus reportedly permitted as a safe food additive that needs no specified average, daily intake or an upper limit intake requirement.
In 1968, the first published report of an adverse reaction to Monosodium glutamate appeared in the New England Journal of Medicine; it was reported that Monosodium glutamate was neurotoxic; killing brain cells, causing retinal degeneration, endocrine disorder and also associated with a number of pathological conditions such as addiction, stroke, epilepsy, brain trauma, neuropathic pain, schizophrenia, anxiety, depression, degenerative disorders such as Parkinson's disease, Alzheimer's disease, Huntington's disease, and amyotrophic lateral sclerosis1. It cannot be stated that MSG is the cause of such varied conditions as epilepsy and Alzheimer's disease, although there may be concerns of its involvement in its etiology. Monosodium glutamate causes increase in alkaline phosphatase activity in the small intestine8
The toxic effect of Monosodium glutamate was further corroborated by the work done on the testis, causing significant oligozoospermia and increase abnormal sperm morphology in a dose-dependent fashion in male Wistar rats9. It has also being established that Monosodium glutamate may be implicated in cases of male infertility as it causes testicular hemorrhage, degeneration and alteration of sperm cell population and morphology10.
The Kidney is a paired organ located in the posterior abdominal wall, whose functions include the removal of waste products from the blood and regulation of the amount of fluid and electrolytes balance in the body. As in humans, the majority of drugs administered are eliminated by a combination of hepatic metabolism and renal excretion11. The kidney also plays a major role in drug metabolism, but its major importance to drugs is still its excretory functions. This study will further corroborate or disprove the toxic effects of MSG with a view to advising the consumers on the inherent dangers of MSG consumption. The kidney effects have also not been showed before.
MATERIALS AND METHODS
ANIMALS: Thirty, (30) adult Wistar rats of both sexes with average weight of 185g were randomly assigned into three groups A, B (n=12) and C of (n=8) in each group. Groups A and B of (n=22) serves as treatments groups while Group C (n=8) is the control. The rats were obtained and maintained in the Animal Holdings of the Department of Anatomy, School of Basic Medical Sciences, University of Benin, Benin city, Nigeria. They were fed with growers' mash obtained from Edo feed and flour mill limited, Ewu, Edo state) and given water liberally. The rats gained maximum acclimatization before actual commencement of the experiment. The Monosodium glutamate (3g/ sachet containing 99+% of MSG) was obtained from Kersmond grocery stores, Uselu, Benin city.
MONOSODIUM GLUTAMATE ADMINISTRATION: The rats in the treatment groups (A and B) were given 3g and 6g of MSG thoroughly mixed with the growers' mash, respectively on a daily basis. The control group © received equal amount of feeds (Growers' mash) without MSG added for fourteen days. The rats were sacrificed on the fifteenth day of the experiment. The kidneys were quickly dissected and fixed in 10% formal saline for routine histological techniques. The 3g and 6g MSG doses were chosen and extrapolated in this experiment based on the indiscriminate use here in Nigeria due to its palatability. The two doses were thoroughly mixed with fixed amount of feeds (550g) in each group daily.
HISTOLOGICAL STUDY: The tissue were dehydrated in an ascending grade of alcohol (ethanol), cleared in xylene and embedded in paraffin wax. Serial sections of 5 microns thick were obtained using a rotatory microtome. The deparaffinised sections were stained routinely with haematoxylin and eosin. Photomicrographs of the desired results were obtained using digital research photographic microscope in the University of Benin research laboratory.
RESULTS
The micrograph of the kidney in the control group (C) showed normal histological features. The section indicated a detailed cortical parenchyma and the renal corpuscles appeared as dense rounded structures with the glomerulus's surrounded by a narrow Bowman's spaces. (fig.1)
FIGURE 1: Control section of kidney (Original magnification x 400)
The kidneys of the animals in group A treated with 3g of MSG revealed some level of cyto-architectural distortion of the cortical structures as compared with the control. (fig.2)
FIGURE 2: Treatment section of the kidney of rats that received 3g MSG. (Original magnification x 400)
The kidney sections of animals in group B treated with 6g of MSG revealed marked distortion of cyto-architecture of the renal cortical structures, and degenerative and atrophic changes. There were vacuolations appearing in the stroma. The renal corpuscles were less identified and the Bowman's spaces were sparsely distributed as compared to the control group. (fig.3)
FIGURE 3: Treatment section of kidney of rats that received 6g of MSG (Original magnification x 400).
DISCUSSION
The results (H & E) reactions showed that administration of MSG caused varying degree of cyto-architectural distortion and reduction in the number of renal corpuscle in the treated groups compared with the control group. There were degenerative and atrophic changes observed in the kidneys of rats that received the high dose (6g) of MSG.
It may be inferred from the present results that higher dose of Monosodium glutamate resulted in degenerative and atrophic changes observed in the renal corpuscle. The actual mechanism by which Monosodium glutamate induced cellular degeneration observed in this experiment needs further investigation. The necrosis observed is probably due to the high concentration of the MSG on the kidney. Pathological or accidental cell death is regarded as necrotic and could result from extrinsic insults to the cell as osmotic thermal, toxic and traumatic effects12. Physiological cell death is regarded as apoptotic and organized programmed cell death (PCD) that is mediated by active and intrinsic mechanisms. The process of cellular necrosis involves disruption of membranes, as well as structural and functional integrity. Cellular necrosis is not induced by stimuli intrinsic to the cells as in programmed cell death (PCD), but by an abrupt environmental perturbation and departure from the normal physiological conditions12.
The experiment also revealed some histological abnormalities and cyto-architectural distortion of the renal cortical structures, which may be ascribed to the effects of MSG on the kidney. The renal cortical structures are distorted as against that of the control rats. The results of this experiment suggest that the distortion of the cyto-architecture of the kidney could have been associated with functional changes that may have been detrimental to the health status of the animal which may have been due to the interference of MSG on the kidney. In cellular necrosis, the rate of progression depends on the severity of the environmental insults. The greater the severity of the insults the more rapid the progression of cellular injury. The principle holds true for toxicological insult to the brain and other organs13. It may have been inferred from the present study that prolonged administration and higher doses of MSG resulted in increased toxic effect on the kidney.
The kidney sections treated with higher doses of MSG were most severely affected in this experiment.
CONCLUSION AND RECOMMENDATION
The results obtained in this study indicate that the administration of 3g and 6g per day of Monosodium glutamate to adult Wistar rats causes disruptions and distortions of the cyto-architecture of the kidneys. This resulted in the cellular necrosis, and sparsely distribution of the Bowman's spaces. These results suggest that the functions of the kidney may be adversely affected. It is recommended that further studies be carried out to examine these findings.
REFERENCES
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2.- IFIC Review of Monosodium glutamate. 1994: Examining the myths
3.- K-othmer Encyclopedia of Chemical Technology, 4th ed. Wiley 1992, pp 571-579.
4.- Moore KL. Congenital malformations due to environmental factors. Developing Humans W.B. Saunders Co. Ltd Philadelphia 2nd ed. Chap. 8, pp 173-183.
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7.- Okwuraiwe PE. The role of food and Drug Administration and control FDA&C) in ensuring the safety of food and food ingredients. A symposium held at Sheraton Hotel, Lagos. 1st Sept.1992: 6-15.
8.- Mozes S, Sefcikova Z, Lenhardt L, Racek L. Obesity and changes of alkaline phosphatase activity in the small intestine of 40 and 80-day old rats subjected to early postnatal overfeeding of monosodium glutamate. Physiol Res. 2004; 53:177-186
9.- Onakewhor JU, Oforofuo IA, Singh SP. Chronic administration of Monosodium glutamate Induces Oligozoospermia and glycogen accumulation in Wister rat testes. Africa J Reprod Health. 1998; 2: 190-197-86.
10.- Oforofuo IA, Onakewhor JU, Idaewor PE. The effect of chronic admin of MSG on the histology of the adult Wistar rat testes: Bioscience Research Communications. 1997;9: 30-56.
11.- Katzung BG. Basic and Clinical Pharmacology 7th edition, Appleton and Lange, Stamford CT. 1998. pp. 372-375.
12.- Farber JL, Chien KR, Mittnacht S. Myocardial ischemia: pathogenesis of Irreversible cell Injury in ischemia. Am J Pathol. 1981:102: 271-281
13. Belluardo N, Mudo G, Bindoni M. Effect of early destruction of the mouse arcuate nucleus by monosodium glutamate on age dependent natural killer activity. Brain Res. 1990; 534:225-333
Corresponding author
Dr. A. O. Eweka
Department of Anatomy. School of Basic Medical Sciences. College of Medical Sciences, University of Benin.
Benin City. Edo State. Nigeria.
andreweweka @ yahoo.com
The monosodium glutamate has been used in foods for a long time, consensus meetings have determined its safe use4-5, however there are experimental reports about its toxicity in relation to the central nervous system, using higher doses6-7. The possibility of generating renal dysfunction is proposed by Eweka's work, however, to document this hypothesis it is necessary to further these studies to determine the kind of renal dysfunction that would be induced by monosodium glutamate (evaluation of the glomerular and tubular functions and more complex histological studies).
_____
Comment of the reviewer Abdías Hurtado Arístegui PhD. Nefrologia. Hospital Arzobispo Loayza. Universidad Peruana Cayetano Heredia. Lima. Peru
Renal dysfunction and injury secondary to medications are common, and can present itself as subtle injury and/or overt renal failure1. Drug-induced nephrotoxicity accounts for approximately 7% of all medication-related toxicities. The mechanisms of nephrotoxicity are many: vasoconstriction, altered intraglomerular hemodynamics, tubular cell toxicity, interstitial nephritis, crystal deposition, thrombotic microangiopathy, and osmotic nephrosis, therefore, before prescribing a potentially nephrotoxic drug, the risk-to-benefit ratio and the availability of alternative drugs should be considered2. In recent years there has been a growing number of cases of renal dysfunction because of use of complementary and alternative medicine, which is considered to have no potential for adverse events or drug-supplement interactions3.
1.- Choudhury D, Ahmed Z. Drug-associated renal dysfunction and injury. Nat Clin Pract Nephrol. 2006; 2: 80-91.
2.- Schetz M, Dasta J, Goldstein S, Golper T. Drug-induced acute kidney injury. Curr Opin Crit Care. 2005; 11: 555-565.
3.- Gabardi S, Munz K, Ulbricht C. A Review of Dietary Supplement-Induced Renal Dysfunction. Clin J Am Soc Nephrol. 2007; 2: 757-765.
4.- Walker R, Lupien JR. The safety evaluation of monosodium glutamate. J Nutr. 2000; 130 (4S Suppl): 1049S-52S.
5.- Beyreuther K, Biesalski HK, Fernstrom JD, et al. Consensus meeting: monosodium glutamate - an update. Eur J Clin Nutr. 2007; 61: 304-313.
6.- Takasaki Y. Studies on brain lesions after administration of monosodium L-glutamate to mice. II. Absence of brain damage following administration of monosodium L-glutamate in the diet. Toxicology. 1978; 9: 307-318.
7.- Arauz-Contreras J, Feria-Velasco A. Monosodium-L-glutamate-induced convulsions--I. Differences in seizure pattern and duration of effect as a function of age in rats. Gen Pharmacol. 1984;15: 391-395.
Received November 1, 2007.
Published May 1, 2008