Dr. Ishrat Ali Siddiqui , Prof; John Feely
Trinity Centre for Research and Health Sciences
St. James’s Hospital , Dublin
In this review, I will give a brief background into the lysosomal glycosidase, N-acetyl-ß-D-glucosaminidase (NAG). Next, I will list out both non-renal and renal conditions that are associated with higher urinary and serum NAG activities. In my third section, I will discuss in detail those common disease states that have an established evidence of an association with higher NAG activity. The fourth section highlights the most plausible biological mechanism underlying such a phenomenon. Finally, I will summarise and conclude my review in the fifth section. Each of the disease conditions discussed in section three will begin with the standard definition of such conditions, before discussing appropriate literature. Detailed bibliographic references are provided in the end of this review.
1. What is NAG?
N-acetyl-ß-D-glucosaminidase (NAG) is a lysosomal glycosidase found in high concentrations in renal proximal tubules. It is one of the lysosomal enzymes that are widely distributed in human tissues. It is released into serum, urine, and plasma by breakdown of cells or exocytosis. This process occurs due to the very high molecular weight (130000 to 140000) of NAG, and is therefore not normally filtered at the glomerulus. Low levels of NAG are only found in normal urine as a result of normal exocytosis and pinocytotic activity of epithelial cells.
NAG has been shown to be a sensitive marker of early renal tubular injury. A consistent elevation of urinary NAG is always associated with progressive renal damage. NAG can be assayed easily by the help of colorimetric method.
2. Non-renal and renal causes of urinary NAG excretion
2.1 Non Renal causes:
i. Diabetes Mellitus
ii. Hypertension
iii. Metabolic syndrome
iv. Obesity
v. Preeclampsia
vi. Sjogren’s Syndrome
vii. Smoking
viii. Surgery (Breast, gastric, etc)
ix. Coronary artery disease
x. Oxidative stress
xi. COPD
xii. Active Myocardial Infarction
xiii. Leukaemia
xiv. Viral Hepatitis
xv. Sepsis
xvi. Burn
xvii. Rheumatoid Arthritis.
xviii. Systemic Lupus Erythematous
2.2 Renal causes:
1. Nephrotic Syndrome
2. Pyelonephritis
3. Glomerulonephritis
4. Renal cell cancer
5. Renal transplantation
3.1 Acute Myocardial Infarction
Acute myocardial infarction is defined as acute ischemic necrosis of an area of myocardium. It is also defined as myocardial necrosis occurring as a result of a critical imbalance between coronary blood supply and myocardial demand.
In 1999, a case-control study (cases = 69, controls = 135) found that mean NAG levels were significantly (p = 0.0001) higher (10.92 ± 7.5 U/L) in patients diagnosed with acute myocardial infarction when compared with normal healthy individuals (6.8 ± 2.17 U/L).1
The same investigators estimated plasma NAG through Whiting’s method. 2 Similar findings were also reported from two studies. 3, 4 However, the authors did not discuss clearly the underlying biological mechanism of such observations.
3.2 Rheumatoid Arthritis
Rheumatoid arthritis is a chronic symmetrical polyarthritis of unexplained cause. It is a system disorder characterized by chronic inflammatory synovitis mainly affecting peripheral joints.
In a case-control study in Pakistan, Iqbal and colleagues showed that mean urinary NAG levels were significantly higher (p< 0.05) in patients (n=49) with sero-positive Rheumatoid arthritis (4.2 U/g ) when compared with 15 healthy subjects (1.71 U/g ).5
The same authors also showed that in patients with RA when treated with low dose of methotrexate, the urinary NAG levels did not affect renal tubular function.5
3.3 Systemic lupus erythematous (SLE)
SLE is a multisystem connective tissue disease characterized by the presence of numerous autoantibodies, circulating immunologically determined tissue damage.
In 2004, Mark and colleagues in the UK found that mean NAG levels were significantly higher in patients of Lupus Nephritis when compared with both normal control groups (p = 0.001) and Lupus Non Nephritis group (p = 0.001).6
Urinary NAG Normal Lupus Non Lupus
(log/median) controls Nephritis Nephritis
0.15-1.44 0.88-1.86 1.23-2.64 P = 0.001
(1.03) (1.02) (1.80)
Mark and colleagues also indicated that two patients of lupus non-nephritis who had taken NSAIDs (Non-Steroidal Anti-inflammatory drugs) had the lowest urinary NAG levels among all the 21 patients of SLE studied. In lupus nephritic patients, 60% of these had elevated urinary NAG levels. The authors concluded that such findings in lupus non-nephritis patients might help to identify lupus nephritis prior to tubular dysfunction.6
3.4 Cancers
In cancer, abnormal cells divide (mitosis) without control. Cancer cells can invade nearby tissues and spread through the blood stream and lymphatic systems to other parts of body (metastasis).Cancer cells also avoid natural cell death (apoptosis).
An animal study on rats in Korea in 2004 examined whether NAG -1 expression was induced in gastric cancer cells treated with NSAIDs, and also the effect of NAG -1 expression on cell deaths.7
Jang and colleagues observed that NAG -1 expression was strongly induced in SNU 601 cells which lacked endogenous Cox -2, and this was closely related with increased apoptosis and decreased cell viability. 7 The investigators also found NAG -1 expression to be closely related to DR-4 and DR-5 induction, which could provide a mechanistic basis for the apoptotic effect of Cox inhibitors in gastric cancer cells.7
Baek et al showed that NAG – 1 has antitumorigenic and a proapoptotic activity in Hct – 116 colon cancer cells devoid of Cox expression (Cyclooxygenase activity).8 However, it is unclear of any significant pathways for engagement by NAG -1.
In 2004, Kralickova and colleagues studied 26 breast cancer patients to look at renal tubular dysfunction and urinary zinc excretion in breast cancer patients treated with antthrcycline based chemotherapy. 9 They found increased urinary NAG activity in breast cancer patients, who were treated with anthracycline groups and had associated symptoms of hyperzincuria and hypozincemia. However, the authors also showed that urinary NAG levels were associated with a decrease in serum creatinine level, which is consistent with hyperfiltration. Such changes are not related with abnormalities of renal zinc handling or a decrease in serum zinc concentration.9
Luqmani Y et al in1999 in Kuwait
3.5 Preeclampsia
In 2003, Semezuk–Sikora and colleagues looked at 84 third trimester women in Poland.11 With history of hypertension, they observed the highest urinary NAG levels in preeclampsia women (median -1.520 u/mmol ), while in women with pregnancy induced hypertension, the NAG levels (median -0.874 U/mmol ) differed significantly from the controls ( median 0.782U/mmol ).However, there was slight positive correlation between NAG and systolic blood pressure (r = 0.225, p< 0.05). Therefore, the authors hypothesized that hypertension in pregnancy might lead to renal tubular damage, and this needs further investigations.11
3.6 Diabetes Mellitus
Diabetes Mellitus (DM) is a syndrome, caused by the lack of or diminish effectiveness of endogenous insulin and is characterized by hyperglycemia and deranged metabolism. It is primarily of two types: type I and II.
3.6.1 In children and adolescents (type I DM):
In 2002, Mungan and colleagues demonstrated that urinary NAG activity was significantly higher in 44 type I Diabetic Mellitus patients (5.6 ± 0.6 U vs. 1.6 ± 0.2 U) when compared to controls.12 However, none of the microalbuminuria-related variables were significantly correlated with urinary NAG activity in this study. Therefore, the authors concluded that urinary NAG activity might not appear to be a useful marker for children and adolescents with type I DM.12
Following Mungans’ study,12 Salem et al found significant correlation between urinary β-NAG and RBP ( retinol binding protein ) in normoalbuminuric patients (r = 0.66, p< 0.001 ) as well as between each of the two tubular markers and HbA1c (r = 0.83, p < 0.001; mean β-NAG = 6.88 vs. 3.76 U/g).13 They argued that markers of tubular damage, including urinary β-NAG and RBP, were excreted in large quantities in Diabetic patients with or with out microalbuminuria. However, the authors concluded that NAG is a useful marker in type I DM.13
β- NAG Controls All DM With Micro- With Normal
albuminuria albuminuria
(U/g) (n=40) (n=59) (n=11)
__________________________________________________________________________________
3.8 ±1.1 7.7 ±3.2 11.16±1.23 6.88 ±299
In 1991, Agardh and others did a case-control study (14), and found that diabetic patients (n=87) had significantly higher level of urinary NAG than the control subjects (p<0.01), but isoenzyme pattern did not differ. 14 They also observed a significant association between metabolic control and total NAG (p<0.01). Their findings also demonstrated that concentrations of urinary NAG were positively correlated with the degree of nephropathy but not with retinopathy.14
3.6.2 Type II Diabetes Mellitus
In 2000, a cross- sectional study done by Hong et al in Singapore (n = 972) found that the level of urinary NAG was higher in type II DM, with complications.15 Therefore, the authors concluded that NAG was an independent predictor of renal complications in type II DM.15
However, the differences reached statistical significance only for albumin and RBP
(microvascular vs. no complication), as the following table shows:15
Nag total No 1/> macro 1/>micro any one complication complication
(nmol/min/g)
Unadjusted 3.14 3.21 3.84 4.85
Adjusted 3.22 3.16 3.80 4.61
Nag-B
(nmol/min/g)
Unadjusted 0.27 0.22 0.25 0.40
Adjusted 0.27 0.21 0.25 0.38
There was no observable difference between hypertensive patients and normotensive patients with regard to NAG –total excretion, and any observable difference for NAG- B was also small.15 Such findings were also reported from several studies.16-19
In 1999, a cross-sectional study by Weitgasser et al showed that urinary NAG activity was significantly (<0.05).elevated at baseline in type II DM when associated with cardiovascular diseases (7.7 ± 1.4 vs. 5.4 ± 0.5 in with/without cardiovascular diseases, respectively).20
Myocardial Stroke PVD No CVD
Infarction
7.0±0.4 3.5±0.7 9.1±2.8 5.8±0.7
(10±3.5) (4.9±12) (7.3±3) (6.2±1.2)
The above study also provides evidence for determining glomerular and tubular renal function in DM patients with macrovascular complication. 20 However, further study is required for cardiovascular disease complications.
3.7 Hypertension
The British Hypertensive Society defines Hypertension as sustained Diastolic > 100 mm Hg on ≥ 3 reading each week a part and Diastolic > 90 mm Hg over 6 month or if Systolic > 160 mmHg and Diastolic 90- 99 mm Hg.
In 2003, TylickI et al conducted a case-control study in Poland on 25 newly-diagnosed non treated hypertensive patients with out microalbuminuria.21 They found that urinary NAG activity was significantly higher in hypertension (p = 0.04), and was negatively correlated with creatinine clearance (p = 0.034). However, they showed a significant positive correlation of urinary NAG with systolic blood pressure in patients with hypertension. Following a multiple regression analysis, the investigators also showed that NAG activity was significantly influenced by systolic blood pressure and plasma glucose level (p = 0.003 and p = 0.042, respectively) in hypertension patients.
Similar hypothesis in hypertension patients was also generated in subsequent studies, 22, 23 using urinary NAG as a marker for tubular injury. However, they did not find a significant association between any lipid levels and uric acid concentration with urinary NAG activity.
In 2000, Kretowicz et al study in Poland
In 1999, another case-control Polish study looked at the relationship between excretion of the markers of tubular damage (NAG in particular) and other parameters of essential hypertension.25 They showed a statistically significant higher BMI (p < 0.007), NAG (p < 0.02), and total cholesterol (p < 0.01), as well as a positive correlation of NAG excretion with hypertension. The authors, therefore, hypothesized that tubular injury at an early stage of renal damage in patients with essential hypertension could be a part of metabolic syndrome X.25
3.8 Coronary Artery Disease
Coronary artery disease (CAD) is characterized by atherosclerosis of the coronary arteries causing angina pectoris and myocardial infarction.
In 1999, Inoue et al on coronary artery disease and NAG showed that serum NAG activity increased in multivessel coronary disease as well as in patients with no stenotic lesions or with single vessel coronary artery disease.26 However, clinical serum NAG activity is yet to be defined. Serum NAG activity has also been recently reported to be elevated in Hypertension, DM, and Renal disease. In acute myocardial infarction, elevated NAG activity in patients with multi-vessel disease has been shown not to be derived from the breakdown of myocardial cells.26
Nonetheless, serum NAG activity in patients with coronary artery disease and cerebrovascular disease was shown to be 30٪ higher than that in healthy control subjects. 26 In this study, limited patients who have had coronary artery disease were enrolled, but not having atherosclerotic cerebrovasular disease, or peripheral vascular disease. The study also included hypertension, single coronary artery disease and multivessel coronary artery disease groups, and showed that there was no significant difference in serum NAG activity between males and females (8.7± 2.3 vs. 8.1 ± 2.8 U/l).The serum NAG activity was 9.2 ± 2.3 U/l in the multi-vessel disease group, which was significantly (p<0.01)higher than (7.8 ± 1.8 U/l) in the no stenotic lesion group, as well as (8.2 ± 2.2 U/l; p < 0.05) in the single–vessel disease group. Therefore, the authors suggested that hyperinsulinemia or insulin resistance might be independent risk factors for coronary artery disease and that serum NAG activity might contribute to the severity of coronary artery disease associated with insulin resistance.26
3.9 Renal Causes
3.9.1 Primary nephritic children
It is post-streptococcal glomerulonephritis, usually a child will have suffered a streptocococcal infection 1-3 weeks back before the onset of acute nephritis syndrome.
In 1996, a study in Turkey on children having Nephrotic Syndrome, with and without steroid– resistance, was compared with healthy children.27 They found a significantly higher level of NAG in the nephrotic groups compared to the controls ( p < 0 0.0001), as well as in steroid – sensitive patients the level of NAG was significantly higher than those in remission (p < 0.0001). Finally, they also found positive correlation between proteinuria and urinary NAG excretion in nephritic patients when compared with controls (r = 0.069, p < 0.001 and r = 0.39, p < 0.001, respectively). The authors argued that massive glomerulo-proteinuria might cause urinary NAG excretion in primary renal disease.27
In 1993, a study in the UK on 65 children with steroid sensitive multirelapsing nephrotic syndrome, 28 were on cyclosporine A9 CyA therapy, 22 on prednisolone, and 15 were off treatment were compared with 32 ) normal children.28 They found geometric mean urinary NAG to be significantly higher in nephritics on CyA therapy (26.5 ± 4.0) and on P (37.0 ± 7.9) as well as in those off treatment (16.3 ± 3.1) when compared with normal children (9.3 ± 3.4). Therefore, the authors suggested that increased NAG in urine might indicate active nephritic syndrome rather than due to drug therapy alone.28
3.9.2 Primary Glomerulonephritis
Primary glomerulonephritis is a group of diseases in which the disease affects the glomerulus and is often inflammatory in nature. It may be primary when major problem starts in the glomerulus or secondary when involvement is part of systemic disease.
In 2002, Bazzi et al in Italy looked at patients with primary glomerulonephritis, with idiopathic membranous nephropathy (IMN), with primary focal segmental glomerulosclerosis (FSGS) and patients with minimal change disease (MCD).29 They limited their statistical analysis to (n = 67) patients with nephritic syndrome alone and observed that NAG was significantly dependent on IgG excretion (p = 0.0004), 24 hrs proteinuria (p = 0.0067) and FEalpha (1)-m (p = 0.0032)( R(2)=0.63).
The same study found that NAG excretion predicted remission in 86 vs. 27٪ of IMN patients (p= 0.0002) and 77 vs. 14 ٪ of FSGS patients (p =0.005).29 Using Cox model in IMN patients only NAG excretion (p = 0.01, r= 5.8), but not 24-h proteinuria predicted progression to CRF. All MCD patients had NAG excretion values were below the chosen cut – off, and 90 ٪ of them developed remission. Response to immunosuppressive therapy was significantly different in patients with NAG excretion values below or above the cut- offs. Finally, the authors concluded that NAG was a reliable marker of the tubulo-toxicity of proteinuria in the early stage of IMN, and it had a predictive value on functional outcome, as well as on response to therapy.29
3.9.3 Acute pyelonephritis
Acute pyelonephritis is a kidney parenchymal infection that occurs most often as a resulting of ascending infection from the bladder.
In 2004, Polish researcher Zoch-Zwierz and colleagues found that NAG activity was higher in children with pyelonephritis (r = 0.9355; p = 0.00001), with a significant correlation with acute pyelonephritis.30
3.9.4 Chronic Renal insufficiency
In 2003, Tassi et al did a study in Italy where they looked at the correlation between chronic renal insufficiency patients and 24-hr urinary NAG levels, and found a significant positive correlation (r = 0.431; p = 0.017).31 The authors suggested that total effective daily excretion of urinary NAG could have practical importance not only for early recognition or renal co-involvement but also that it could be repeated in serial measurements to monitor. Example include, therapies aimed at stopping the progression of renal damage. Finally, the authors concluded stating that sampling 24 hr urine and monitoring total enzyme eliminated in urine over 24hrs could be a potential investigation for chronic renal insufficiency patients.31
3.9.5 Renal failure
Renal failure is defined as the inability of the kidneys to excrete wastes and to help maintain the electrolyte balance.
In 1997, a Polish study on 63 renal failure patients found that 95.2% (n=60) of the patients with chronic renal failure had abnormal NAG values (> 70 nmol/mg).32 The authors demonstrated significant differences of NAG values between patients with massive proteinuria (> 1.5 g /24 h), moderate proteinuria and those without 24h proteinuria or non-significant proteinuria (423.5±286.3 vs. 414.4 ± 334.8 vs. 453.0 ± 451.3 nmol/mg, respectively).However, there was no significant difference in patients with NAG values above and below 280 nmol/mg. The authors, therefore, suggested that measurement of NAG secretion might be helpful to delineate the disease process in renal failure patients.32
4. Biological Mechanism?
The above discussion suggests that the underlying biological mechanism between various disease conditions studied (both renal and non-renal) and the increased NAG activity is still unclear. Some plausible mechanisms have been postulated. The most consistent underlying mechanism suggested is related to oxidative stress. For example, in type I diabetes mellitus patients the increased serum NAG activity is observed before the development of retinopathy.33 Therefore, NAG was suggested to be an early marker of vascular changes in diabetes. Also, significant positive correlation exists between NAG activities and malondialdehyde (MDA) concentration in type I DM supporting that oxidative stress may influence NAG activities. 33 A decrease in NAG activity following anti-oxidant treatment (alpha-tocopherol) may further support the role of oxidative stress in modulation of NAG activities. 33 Such positive relationships are also consistent in before and after experiment. 33 All together, it is probable to conclude that oxidative stress not only influences endothelial dysfunction, but also participates in the modulation of enzyme activities. The endothelial cells are one of the sources of NAG, mainly serum NAG. In addition, greater oxidative stress may be present in obese persons and therefore more advanced endothelial activation would be expressed. Secondly, NAG is also postulated to have free radical-scavenging and apoptosis-inducing property against certain types of cancers.34
5. Summary and Conclusion
NAG is excreted from lysosomes, and its increased activity reflects organ system damage. Urinary NAG primarily present in proximal renal tubules contributes to increase NAG activities in all the disease conditions studied (both renal and non-renal). Chronic disorders, such as hypertension, diabetes mellitus, acute myocardial infarction and cancers are the main non-renal conditions where increased NAG activities are observed. The underlying biological mechanism of such observations is still unclear. Nevertheless, postulations such as oxidative stress leading to endothelial dysfunction, as well as apoptosis-inducing property have been suggested. Therefore, it is clearly important that further explorations are necessary to establish the causal pathway. Despite such limitation, NAG can be a useful marker of tubular damage involving both renal and non-renal disease states.
References:
1. Iqbal MP, Kazmi KA, Jafri HR, Mehboobali N. N-Acetyl-β-D-glucosaminidase in acute myocardial infarction. Exp Mol Med 2003; 35(4): 275-278.
2. Whiting PH, Ross IS, Borthwisk L. Serum and N-acetyle-β-D- glucosaminidase in diabetics on diagnosis and subsequent treatment and stable insulin dependent diabetics. Clinica Chimica Acta 1979; 92: 459-463.
3. Welman E, Colbeck JF, Selwyn AP, Fox KM, Orr I. Plasma lysosomal enzyme activity in acute myocardial infarction and effects of drug . Adv Myocardiol 1980; 2:359-69.
4. Inoue T, Matsunage R, Morooka S. Serum N-actyl –beta-D- glucosaminidase activity increases in associated with insulin resistance in patients with coronary artery disease. Atherosclerosis 2000; 149:17-22.
5. Iqbal MP, Ali AA, Waqar MA, Mehboobali N.Urinary N- acetyl- beta- D- glucosaminidase in Rheumatoid Arthritis. Exp Mol Med 1998; 30(3): 165-9.
6. Marks SD, Shah V, Pilkington C, Woo P, Dillon MJ. Renal tubular dysfunction in children with system lupus erythematosus. Pediatr Nephrol 2005; 20(2):141-8.
7. Jang TJ, Kang HJ, Kim JR, Yang CH. Non-steroidal anti-inflammatory drug activated gene (NAG-1) expression is closely related to death receptor-4 and -5 induction, which may explain sulindac sulphide induced gastric cancer cell apoptosis. Carcinogenesis 2004; 25(10):1853-1858.
8. Baek SJ, Kim KS, Nixon JB, Wilson LG, ELing TE.Cyclooxygenase inhibitors regulate the expression of a TGF-β superfamily member that has propoptotic and antitumorigenic activites. Mol Pharmacol 2001; 59: 901-908.
9. Kralickova P, Melichar B, Malir F, Roubal T. Renal tubular dysfunction and urinary zinc excretion in breast cancer patients treated with anthracycline-based combination chemotherapy. J Exp Clin Cancer Res 2004; 23(4):579-84.
10. Luqmani Y, Temmim L, Memon A, et al. Measurement of serum N-acetyl beta glucosaminidase activity in patients with breast cancer. Acta Oncol 1999; 38(5):649-53.
11. Semezuk-Sikora A, Sikora P, Biadun U, Semezuk M. Urinary N-actyl-beta-D-glucosaminidase (NAG) excretion in women with pregnancy complicated with hypertension. Glinekol Pol 2003; 74(10):1267-75.
12. Mungan B,Yuksel M, Bakman A, Topaloglu K, Ozer G. Urinary N-acetyl-beta-D-glucosaminidase activity in Type I Diabetes Mellitus. Indian Pediatr 2003; 40:410-414.
13. Salem MAK, E1-Habashy SA, Saeid OM, E1-Tawil MMK,Tawfik PH. Urinary excretion of n-acetyl-β-D-glucosaminidase and retinol binding protein as alternative indicators of nephropathy in patients with type1 Diabetes Mellitus. Pediatr Diabetes 2002; 3:37-41.
14. Agardh CD, Agardh E, Isaksson A, Hultberg B. Associtation between Urinary N-Acetyl-β-Glucosaminidase and Its Isoenzyme Patterns and Microangiopathy in Type I Diabetes Mellitus. Clinical Chem 1999; 37(10):1696-1699.
15. Hong CY, Chia KS, Ling SL. Urinary protein excretion in
Type 2 diabetes with complications. J Diabetes Complications 2000; 14: 259-265.
16. Marshell SM, Alberti KGMM. Comparison of the prevalence and associated features of abnormal albumin excretion in insulin-dependent and type 2 diabetes. Q J Med 1988; 70:60-71.
17. Mattock MB, Keen H, Viberti GC, et al. Coronary heart disease and urinary albumin excretion rate in type 2 (type 2) diabetic patients. Diabetologica 1988; 31: 82-87.
18. Stiegler H, Standl E, Schulz K, Roth R, Lehmacher W. Morbidity,
Mortality and albuminuria in type 2 diabetic patients; a three year prospective study of a random cohort in general practice. Diabetes Med 1992; 9: 646-653.
19. Araki S, Kikkawa R, Haneda M, et al. Microalbuminuria cannot predict cardiovascular death in Japanese subject with type 2 diabetes mellitus. J Diabetes Complication 1995; 9: 323-325.
20. Weltgasser R, Gappmayer B, Schnoell F, Karting I. Prospective evaluation of Urinary N-actyl-β-D-Glucosaminidase with respect to Macrovascular Disease in Elderly Type 2 Diabetic patients. Diabetes Care 1999; 22:1882-1886.
21. TylickI L, Manitius J, Lysiak-Szydlowska W, Ruthowski B. Tubular injury : the first symptom of hypertensive kidney involvement? Med Sci Monit 2003; 9(4):CR187-193.
22. Rutkowski B, Tylicki L, Manitius J, Lysiak-Szydlowska W. Hypertensive nephropathy- an increasing clinical problem. Miner Electrolyte Metab 1999;25:
65-68.
23. Price RG. Urinary enzymes, nephrotoxicity and renal disease. Toxicol 1982; 23:
99-134.
24. Kretowicz M, Ukleja-Adamowicz M, Strozecki P, et al. Does any relationship exist between metabolic disturbances and some markers of renal damage in patients with untreated essential hypertension? Pol Arch Med Wewn 2000; 104(3): 563-7.
25. Ruthowski B,Tylicki L, Manitius J, Lysiak-Szydlowska W. Hypertensive nephropathy- an increasing clinical problem. Miner Electrolyte Metab 1999; 25(1-2):65-8.
26. Inoue T, Matsunaga R, Morooka S, Uehara Y. Serum N-acetyl-β-D-glucosaminidase activity increases in association with insulin resistance in patients with coronary artery disease. Atherosclerosis 2000; 149: 117-122.
27. Caliskan S, Hacibekiroglu M, Sever L, Ozbay G, Arisoy N. Urinary N-actyle-beta-D-glucosaminidase and beta 2- microglobulin excretion in primary nephritic children. Nephron 1996; 74(2):401-4.
28. Piqueras AI, Shah V, Hulton SA, Barratt TM, Dillon MJ. Tubular proteinuria in steroid sensitive multi-replapsing nephritic syndrome. Clin Nephrol 1993; 40(10):26-30.
29. Bazzi C, Petrini C, Rizza V, et al. Urinary N-actyl-beta-D-glucosaminidase excretion is a marker of tubular cell dysfunction and a predictor of outcome in primary glomerulonephritis. Nephrol Dial Transplant 2002; 17(11);1890-6.
30. Zock-Zwier W, Kepka A, Tomaszewska B, et al. Assessment of fructose-1,6-biphoshatase in urine of children with acute pyelonephritis. Pol Merkuriusz Lek 2004; 16(91): 56-9.
31. Tassi C, Mancuso F, Feligioni L, Marangi M, Capodicasa E. Expression modes of urinary n-acetyl-β-D-glucominidase in patients with chronic renal insufficiency. Clinica Chimica Acta 2004; 346: 129-133.
32. Szechinski J, Wiland P. Renal proximal dysfunction based on activity of n-acetyl-beta-d-glucosaminidase in urine of patients with kidney failure. Pol Arch Med Wewn 1997; 98(12): 536-41.
33. Skrha J, Hilgertova J. Relationship of serum N-acetyl-beta-glucosaminidase activity to oxidative stress in diabetes mellitus. Clinica Chimica Acta 1999; 282: 167-174.
34. Poulose SM, Harris FD, Patil BS. Citrus limonoids induce apoptosis in human neuroblastoma cells and have radical scavenging activity. J Nutr 2005; 135(4): 870-877.
