Urinary metabolites as noninvasive biomarkers of gastrointestinal diseases: A clinical review

The diagnosis of gastrointestinal (GI) disorders is usually based on invasive techniques such as endoscopy. A key important factor in GI cancer is early diagnosis which warrants development of non- or less-invasive diagnostic techniques. In addition, monitoring and surveillance are other important parts in the management of GI diseases. Metabolomics studies with nuclear magnetic resonance and mass spectrometry can measure the concentration of more than 3000 chemical compounds in the urine providing possible chemical signature in different diseases and during health. In this review, we discuss the urinary metabolomics signature of different GI diseases including GI cancer and elaborate on how these biomarkers could be used for the classification, early diagnosis and the monitoring of the patients. Moreover, we discuss future directions of this still evolving field of research.

Lessons from the profile of kidney diseases among Afghan refugees

BACKGROUND

Due to a paucity of research on the profile of kidney diseases among refugee populations, specifically Afghan refugees in Iran, this study aimed to illustrate the pattern of kidney disease among Afghan refugees in Iran and create a database for evaluating the performance of future health services.

MATERIAL AND METHODS

This was a retrospective cross sectional study, in which we collected the demographics and profile of kidney diseases among Afghan refugees between 2005 and 2010 from referrals to the United Nations High Commissioner for Refugees (UNHCR) offices in Iran.

RESULTS

The total number of referrals in this group of diseases was 3193 out of 23 152 with 41.5% female and 58.5% male. Regarding age distribution, 10.5% were 0-14 years of age, 78% were 15-59, and 11.5% were ≥60. The most common health referral for females and males (0-14) was end-stage renal disease (ESRD), accounting for 34.6%. This was also the main reason of referrals for females and males aged 15-59, accounting for 73.5% and 66.6%, respectively, and in both sexes in the ≥60 age range it was 63.1%.

CONCLUSIONS

The pattern of our renal clinic referrals may gradually change to ESRD, which is associated with a huge economic burden. The need to provide health insurance to everyone or reform the health care system to provide coverage for more of the population can be justified and would improve cost effectiveness.

Protein turnover and amino acid transport kinetics in end-stage renal disease

Protein and amino acid metabolism is abnormal in end-stage renal disease (ESRD). Protein turnover is influenced by transmembrane amino acid transport. The effect of ESRD and hemodialysis (HD) on intracellular amino acid transport kinetics is unknown. We studied intracellular amino acid transport kinetics and protein turnover by use of stable isotopes of phenylalanine, leucine, lysine, alanine, and glutamine before and during HD in six ESRD patients. Data obtained from amino acid concentrations and enrichment in the artery, vein, and muscle compartments were used to calculate intracellular amino acid transport and muscle protein synthesis and catabolism. Fractional muscle protein synthesis (FSR) was estimated by the precursor product approach. Despite a significant decrease in the plasma concentrations of amino acids in the artery and vein during HD, the intracellular concentrations remained stable. Outward transport of the amino acids was significantly higher than the inward transport during HD. FSR increased during HD (0.0521 +/- 0.0043 vs. 0.0772 +/- 0.0055%/h, P < 0.01). Results derived from compartmental modeling indicated that both protein synthesis (118.3 +/- 20.6 vs. 146.5 +/- 20.6 nmol.min-1.100 ml leg-1, P < 0.01) and catabolism (119.8 +/- 18.0 vs. 174.0 +/- 14.2 nmol.min-1.100 ml leg-1, P < 0.01) increased during HD. However, the intradialytic increase in catabolism exceeded that of synthesis (57.8 +/- 13.8 vs. 28.0 +/- 8.5%, P < 0.05). Thus HD alters amino acid transport kinetics and increases protein turnover, with net increase in protein catabolism.

Hemodynamic changes during hemodialysis: role of nitric oxide and endothelin

BACKGROUND

Etiology of dialysis induced hypotension and hypertension remains speculative. There is mounting evidence that nitric oxide (NO) and endothelin (ET-1) may play a vital role in these hemodynamic changes. We examined the intradialytic dynamic changes in NO and ET-1 levels and their role in the pathogenesis of hypotension and rebound hypertension during hemodialysis (HD).

METHODS

The serum nitrate + nitrite (NT), fractional exhaled NO concentration (FENO), L-arginine (L-Arg), NGNG-dimethyl-L-arginine (ADMA) and endothelin (ET-1) profiles were studied in 27 end-stage renal disease (ESRD) patients on HD and 6 matched controls. The ESRD patients were grouped according to their hemodynamic profile; Group I patients had stable BP throughout HD, Group II had dialysis-induced hypotension, and Group III had intradialytic rebound hypertension.

RESULTS

Pre-dialysis FENO was significantly lower in the dialysis patients compared to controls (19.3 +/- 6.3 vs. 28.6 +/- 3.4 ppb, P < 0.002). Between the experimental groups, pre-dialysis FENO was significantly higher in Group II (24.1 +/- 6.7 ppb) compared to Group I (17.8 +/- 5.6 ppb) and Group III (16.1 +/- 4.2 ppb; P < 0.05). Post-dialysis, FENO increased significantly from the pre-dialysis values (19.3 +/- 6.3 vs. 22.6 +/- 7.9 ppb; P=0.001). Pre-dialysis NT (34.4 +/- 28.2 micromol/L/L) level was not significantly different from that of controls (30.2 +/- 12.3 micromol/L/L). Serum NT decreased from 34.4 +/- 28.2 micromol/L/L at initiation of dialysis to 10.0 +/- 7.4 micormol/L/L at end of dialysis (P < 0.001). NT concentration was comparable in all the three groups at all time points. Pre-dialysis L-Arg (105.3 +/- 25.2 vs. 93.7 +/- 6.0 micromol/L/L; P < 0.05) and ADMA levels were significantly higher in ESRD patients (4.0 +/- 1.8 vs. 0.9 +/- 0.2 micromol/L/L; P < 0.001) compared to controls. Dialysis resulted in significant reduction in L-Arg (105.3 +/- 25.2 vs. 86.8 +/- 19.8 micromol/L/L; P < 0.005) and ADMA (4.0 +/- 1.8 vs. 1.6 +/- 0.7 micromol/L/L; P < 0.001) concentrations. Pre-dialysis ET-1 levels were significantly higher in ESRD patients compared to the controls (8.0 +/- 1.9 vs. 12.7 +/- 4.1 pg/mL; P < 0.002), but were comparable in the three study groups. Post-dialysis ET-1 levels did not change significantly in Group I compared to pre-dialysis values (14.3 +/- 4.3 vs.15.0 +/- 2.4 pg/mL, P=NS). However, while the ET-1 concentration decreased significantly in Group II (12.0 +/- 4.0 vs. 8.7 +/- 1.8 pg/mL, P < 0.05), it increased in Group III from pre-dialysis levels (12.8 +/- 3.8 vs. 16.7 +/- 4.5 pg/mL, P=0.06).

CONCLUSION

Pre-dialysis FENO is elevated in patients with dialysis-induced hypotension and may be a more reliable than NT as a marker for endogenous NO activity in dialysis patients. Altered NO/ET-1 balance may be involved in the pathogenesis of rebound hypertension and hypotension during dialysis.